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Modifications of Polymers through the Addition of Ultraviolet Absorbers to Reduce the Aging Effect of Accelerated and Natural Irradiation

Modifications of Polymers through the Addition of Ultraviolet Absorbers to Reduce the Aging... polymers Review Modifications of Polymers through the Addition of Ultraviolet Absorbers to Reduce the Aging Effect of Accelerated and Natural Irradiation 1 , 2 3 4 3 Gamal A. El-Hiti * , Dina S. Ahmed , Emad Yousif , Omar S. A. Al-Khazrajy , Mustafa Abdallh and Saud A. Alanazi Cornea Research Chair, Department of Optometry, College of Applied Medical Sciences, King Saud University, P.O. Box 10219, Riyadh 11433, Saudi Arabia; saaalanazi@ksu.edu.sa Department of Medical Instrumentation Engineering, Al-Mansour University College, Baghdad 64021, Iraq; dina.saadi@muc.edu.iq Department of Chemistry, College of Science, Al-Nahrain University, Baghdad 64021, Iraq; emad.yousif@nahrainuniv.edu.iq (E.Y.); mustafa.abdallh@nahrainuive.edu.iq (M.A.) Department of Chemistry, College of Education for Pure Science (Ibn Al-Haytham), University of Baghdad, Baghdad 64021, Iraq; omar.s.a@ihcoedu.uobaghdad.edu.iq * Correspondence: gelhiti@ksu.edu.sa; Tel.: +966-11469-3778; Fax: +966-11469-3536 Abstract: The photooxidative degradation process of plastics caused by ultraviolet irradiation leads to bond breaking, crosslinking, the elimination of volatiles, formation of free radicals, and decreases in weight and molecular weight. Photodegradation deteriorates both the mechanical and physi- cal properties of plastics and affects their predicted life use, in particular for applications in harsh environments. Plastics have many benefits, while on the other hand, they have numerous disad- vantages, such as photodegradation and photooxidation in harsh environments and the release of Citation: El-Hiti, G.A.; Ahmed, D.S.; Yousif, E.; Al-Khazrajy, O.S.A.; toxic substances due to the leaching of some components, which have a negative effect on living Abdallh, M.; Alanazi, S.A. organisms. Therefore, attention is paid to the design and use of safe, plastic, ultraviolet stabilizers Modifications of Polymers through that do not pose a danger to the environment if released. Plastic ultraviolet photostabilizers act as the Addition of Ultraviolet Absorbers efficient light screeners (absorbers or pigments), excited-state deactivators (quenchers), hydroperox- to Reduce the Aging Effect of ide decomposers, and radical scavengers. Ultraviolet absorbers are cheap to produce, can be used Accelerated and Natural Irradiation. in low concentrations, mix well with polymers to produce a homogenous matrix, and do not alter Polymers 2022, 14, 20. https:// the color of polymers. Recently, polyphosphates, Schiff bases, and organometallic complexes were doi.org/10.3390/polym14010020 synthesized and used as potential ultraviolet absorbers for polymeric materials. They reduced the Academic Editors: Andrea damage caused by accelerated and natural ultraviolet aging, which was confirmed by inspecting the Antonino Scamporrino and Chiara surface morphology of irradiated polymeric films. For example, atomic force microscopy revealed Maria Antonietta Gangemi that the roughness factor of polymers’ irradiated surfaces was improved significantly in the presence of ultraviolet absorbers. In addition, the investigation of the surface of irradiated polymers using Received: 5 December 2021 scanning electron microscopy showed a high degree of homogeneity and the appearance of pores Accepted: 20 December 2021 Published: 22 December 2021 that were different in size and shape. The current work surveys for the first time the use of newly synthesized, ultraviolet absorbers as additives to enhance the photostability of polymeric materials Publisher’s Note: MDPI stays neutral and, in particular, polyvinyl chloride and polystyrene, based mainly on our own recent work in with regard to jurisdictional claims in the field. published maps and institutional affil- iations. Keywords: plastics; polyvinyl chloride; photostabilizers; plastic photodegradation and photooxida- tion; recycling of plastics; photoirradiation Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article 1. Introduction distributed under the terms and Ultraviolet (UV) light has harmful effects on materials used in outdoor applications. conditions of the Creative Commons Plastics suffer photooxidation when exposed to harsh conditions (high temperature, sun- Attribution (CC BY) license (https:// light for long duration, and humidity) in the presence of oxygen. Plastic degradation, as creativecommons.org/licenses/by/ a result of UV light absorption, leads to discoloration, cracks, and loss of mechanical and 4.0/). Polymers 2022, 14, 20. https://doi.org/10.3390/polym14010020 https://www.mdpi.com/journal/polymers Polymers 2022, 14, x FOR PEER REVIEW 2 of 18 Polymers 2022, 14, x FOR PEER REVIEW 2 of 18 Polymers 2022, 14, x FOR PEER REVIEW 2 of 18 Polymers 2022, 14, x FOR PEER REVIEW 2 of 18 Polymers 2022, 14, x FOR PEER REVIEW 2 of 18 Polymers 2022, 14, x FOR PEER REVIEW 2 of 18 sunlight for long duration, and humidity) in the presence of oxygen. Plastic degradation, sunlight for long duration, and humidity) in the presence of oxygen. Plastic degradation, Polymers 2022, 14, 20 2 of 16 sunlight for long duration, and humidity) in the presence of oxygen. Plastic degradation, sunlight for long duration, and humidity) in the presence of oxygen. Plastic degradation, sunlight for long duration, and humidity) in the presence of oxygen. Plastic degradation, sunlight for long duration, and humidity) in the presence of oxygen. Plastic degradation, as a result of UV light absorption, leads to discoloration, cracks, and loss of mechanical as a result of UV light absorption, leads to discoloration, cracks, and loss of mechanical as a result of UV light absorption, leads to discoloration, cracks, and loss of mechanical as as a a res res ul ul t t of of UV UV light light abs abs orp orp tion tion , le , le ad ad s s to to di di scolor scolor atat ion, ion, crcr acks, acks, an an d d los los s s of of me me chanic chanic al al as a result of UV light absorption, leads to discoloration, cracks, and loss of mechanical and physical properties [1,2]. Photooxidation resembles autooxidation due to long-term and physical properties [1,2]. Photooxidation resembles autooxidation due to long-term and physical properties [1,2]. Photooxidation resembles autooxidation due to long-term and and ph ph ysi ysi cal cal pro pro pert pert ies ies [1, [1, 2]. 2]. Phot Phot oox oox id id ation ation re re semb semb les les au au to to oxi oxi dd atat ion ion dd ue ue to to l olng ong -ter -ter m m and physical properties [1,2]. Photooxidation resembles autooxidation due to long-term physical properties [1,2]. Photooxidation resembles autooxidation due to long-term heat heat aging, except that the driving force is UV light and not heat [3]. Therefore, during heat aging, except that the driving force is UV light and not heat [3]. Therefore, during heat aging, except that the driving force is UV light and not heat [3]. Therefore, during heat heat ag ag in in g, g, excep excep t t th th at at th th e e driv driv ing ing for for ce ce is is UU V V ligh ligh t t and and not not h eat heat [3]. [3]. Th Th erefo erefo re, re, dd uri uri ng ng heat aging, except that the driving force is UV light and not heat [3]. Therefore, during plasti aging, c manufactu except ring that, the medriving asures sho force uld isbe UV taken light to and ens not ure heat that [3 ]. thTher e mater efor ials e, during will last plastic plastic manufacturing, measures should be taken to ensure that the materials will last plastic manufacturing, measures should be taken to ensure that the materials will last plastic manufacturing, measures should be taken to ensure that the materials will last plastic manufacturing, measures should be taken to ensure that the materials will last plastic manufacturing, measures should be taken to ensure that the materials will last longer manufacturing, and to inhibit pho measur tooxida es should tion an bed pho taken to to degr ensur adati e that on pro thecmaterials esses. will last longer and longer and to inhibit photooxidation and photodegradation processes. longer and to inhibit photooxidation and photodegradation processes. longer and to inhibit photooxidation and photodegradation processes. longer and to inhibit photooxidation and photodegradation processes. longer and to inhibit photooxidation and photodegradation processes. to inhibit photooxidation and photodegradation processes. The polymerization technique was developed over the years to allow the production The polymerization technique was developed over the years to allow the production The polymerization technique was developed over the years to allow the production Th Th e e po po lyly mer mer iza iza tion tion tec tec hni hni qu qu e e wa wa s s d d eve eve loped loped ov ov er er th th e e ye ye ar ar s s to to allo allo w w th th e e pro pro duc duc tion tion The polymerization technique was developed over the years to allow the production The polymerization technique was developed over the years to allow the production of plastics on an industrial scale. There has been a massive increase in the production of of plastics on an industrial scale. There has been a massive increase in the production of of plastics on an industrial scale. There has been a massive increase in the production of of of pl pl as as tic tic s s on on an an in in dustr dustr ial ial scale. scale. Th Th ere ere has has been been a a m m as as sive sive incre incre ase ase in in th th e e pro pro dd uction uction of of of plastics on an industrial scale. There has been a massive increase in the production of of plastics on an industrial scale. There has been a massive increase in the production of plastics in recent years [4]. The scale of polyvinyl chloride (PVC) production has increased plastics in recent years [4]. The scale of polyvinyl chloride (PVC) production has increased plastics in recent years [4]. The scale of polyvinyl chloride (PVC) production has increased pla pla sti sti cs cs in in rec rec ent ent ye ye ar ar s s [4]. [4]. Th Th e e sc sc alal e e o f op f olyviny polyviny l chlo l chlo ride ride (PV (PV CC ) p ) p roduct roduct ion ion ha ha s s incre incre as as ed ed plastics in recent years [4]. The scale of polyvinyl chloride (PVC) production has increased plastics in recent years [4]. The scale of polyvinyl chloride (PVC) production has increased over the years from 3 million tons in 1965 to over 40 million tons in 2018 and is expected over the years from 3 million tons in 1965 to over 40 million tons in 2018 and is expected over the years from 3 million tons in 1965 to over 40 million tons in 2018 and is expected ov ov er er th th e e yea yea rs rs from from 3 3 mi mi lli lli on on to to ns ns in in 19 19 65 65 to to ov ov er er 40 40 million million to to ns ns in in 2018 2018 an an d d is is exp exp ect ect ed ed over the years from 3 million tons in 1965 to over 40 million tons in 2018 and is expected over the years from 3 million tons in 1965 to over 40 million tons in 2018 and is expected to grow further to 60 million tons in 2025 [5]. PVC can be produced in different forms and to grow further to 60 million tons in 2025 [5]. PVC can be produced in different forms and to grow further to 60 million tons in 2025 [5]. PVC can be produced in different forms and to grow further to 60 million tons in 2025 [5]. PVC can be produced in different forms and to grow further to 60 million tons in 2025 [5]. PVC can be produced in different forms and to grow further to 60 million tons in 2025 [5]. PVC can be produced in different forms and to grow further to 60 million tons in 2025 [5]. PVC can be produced in different forms shapes, using both suspension and emulsion polymerization [6]. Plastic waste is a chal- shapes, using both suspension and emulsion polymerization [6]. Plastic waste is a chal- shapes, using both suspension and emulsion polymerization [6]. Plastic waste is a chal- shapes, using both suspension and emulsion polymerization [6]. Plastic waste is a chal- shapes, using both suspension and emulsion polymerization [6]. Plastic waste is a chal- shapes, using both suspension and emulsion polymerization [6]. Plastic waste is a chal- and shapes, using both suspension and emulsion polymerization [6]. Plastic waste is a lenge, and there is a need for not only effective recycling but cutting the waste at the lenge, and there is a need for not only effective recycling but cutting the waste at the lenge, and there is a need for not only effective recycling but cutting the waste at the lenge, lenge, and and th th ere ere is is a a need need for for not not on on ly ly efef fective fective rec rec ycli ycli ng ng but but cu cu tttt ing ing th th e e ww ast ast e e at at th th e e lenge, and there is a need for not only effective recycling but cutting the waste at the challenge, and there is a need for not only effective recycling but cutting the waste at the source. Therefore, further developments in plastic are still needed to keep the environ- source. Therefore, further developments in plastic are still needed to keep the environ- source. Therefore, further developments in plastic are still needed to keep the environ- source source . Th . Th ere ere fore, fore, furt furt her her develop develop men men ts ts in in plastic plastic are are still still ne ne eded eded to to keep keep th th e e env env iron- iron- source. Therefore, further developments in plastic are still needed to keep the environ- source. Therefore, further developments in plastic are still needed to keep the environment ment clean and to elongate the lifetime of plastic [7,8]. ment clean and to elongate the lifetime of plastic [7,8]. ment clean and to elongate the lifetime of plastic [7,8]. men men t clea t clea n and t n and t o elon o elon ga ga te the l te the l ifif etime etime of p of p las las tic tic [7, [7, 8]. 8]. ment clean and to elongate the lifetime of plastic [7,8]. clean and to elongate the lifetime of plastic [7,8]. Plastic contains polymeric chains that are based on carbon, hydrogen, and heteroa- Plastic contains polymeric chains that are based on carbon, hydrogen, and heteroa- Plastic contains polymeric chains that are based on carbon, hydrogen, and heteroa- Plastic contains polymeric chains that are based on carbon, hydrogen, and heteroa- Plastic contains polymeric chains that are based on carbon, hydrogen, and heteroa- Plastic contains polymeric chains that are based on carbon, hydrogen, and heteroa- Plastic contains polymeric chains that are based on carbon, hydrogen, and heteroatoms toms (e.g., sulfur, oxygen, or nitrogen). Polystyrene (PS), polypropylene (PP), polyeth- toms (e.g., sulfur, oxygen, or nitrogen). Polystyrene (PS), polypropylene (PP), polyeth- toms (e.g., sulfur, oxygen, or nitrogen). Polystyrene (PS), polypropylene (PP), polyeth- toms (e.g., sulfur, oxygen, or nitrogen). Polystyrene (PS), polypropylene (PP), polyeth- toms (e.g., sulfur, oxygen, or nitrogen). Polystyrene (PS), polypropylene (PP), polyeth- toms (e.g., (e.g., sulfur sulfu,r,oxygen, oxygen, or or nitr nitrog ogen). en). Polystyr Polystyrene ene (PS), (PS), polypr polypro opylene pylene (PP), (PP), polyethylene polyeth- ylene (PE), PVC, polyethylene terephthalate (PET), and polyurethane (PU) represent 75– ylene (PE), PVC, polyethylene terephthalate (PET), and polyurethane (PU) represent 75– ylene (PE), PVC, polyethylene terephthalate (PET), and polyurethane (PU) represent 75– ylyl ene ene (P (P EE ), ), P VC, PVC, po po lyet lyet hylene hylene terep terep ht ht halate halate (PE (PE T), T), an an d d po po lyly ur ur eth eth ane ane (PU) (PU) r epr repr esent esent 75 75 – – ylene (PE), PVC, polyethylene terephthalate (PET), and polyurethane (PU) represent 75– (PE), PVC, polyethylene terephthalate (PET), and polyurethane (PU) represent 75–80% 80% of Europe’s plastic consumption (Table 1) [9,10]. These polymers have either C–C or 80% of Europe’s plastic consumption (Table 1) [9,10]. These polymers have either C–C or 80% of Europe’s plastic consumption (Table 1) [9,10]. These polymers have either C–C or 80 80 %% o f oEurop f Europ e’s e’s pl pl as as titi c c co co nsump nsump tion tion (T (T abl abl e e 1) 1) [9,1 [9,1 0]0] . Th . Th ese ese po po lyly m m ers ers have have e ither either CC –C –C or or 80% of of Europ Europe’s e’s pl plastic astic co consumption nsumption (T (T abl able e 1) 1[ )9,1 [90] ,10 . ]. These These poly polymers mers have have either either C–CC–C or or C–heteroatom backbones, and their properties are highly dependent on the repeating C–heteroatom backbones, and their properties are highly dependent on the repeating C–heteroatom backbones, and their properties are highly dependent on the repeating CC –het –het eroato eroato m m backbon backbon es es , , an an d d th th eir eir pro pro pert pert ies ies ar ar e ehighly highly depen depen dent dent on on th th e e repeating repeating C–het C–heter eroatom oatom backbon backbones, es, and and theirtheir propert properties ies are highly are high depen ly dependent dent on th on e repeating the repeating units [11]. units [11]. units [11]. uni uni ts ts [11]. [11]. units [11]. units [11]. Table 1. The most common plastics and their European demand [10]. Table 1. The most common plastics and their European demand [10]. Table 1. The most common plastics and their European demand [10]. Table 1. The most common plastics and their European demand [10]. Table 1. The most common plastics and their European demand [10]. Table 1. The most common plastics and their European demand [10]. Table 1. The most common plastics and their European demand [10]. European Demand European Demand European Demand European Demand European Demand Plastic (Repeating Unit) Name Plastic (Repeating Unit) Name Plastic (Repeating Unit) Name Europ European ean Dem Demand and (%) Plastic (Repeating Unit) Name Plastic (Repeating Unit) Name Plastic (Repeating Unit) Name (%) (%) Plastic (Repeating Unit) Name (%) (%) (%) (%) PE 29.6 PE 29.6 PE 29.6 PE 29.6 PE PE 29.6 29.6 PE 29.6 C–C Backbone PP 19.9 PP PP 19.919.9 PP 19.9 PP 19.9 PP 19.9 PP 19.9 C–C Backbone C–C Backbone C–C Backbone PS 7.1 C–C Backbone PS 7.1 C–C Backbone PS PS 7.1 7.1 C–C Backbone PS 7.1 PS 7.1 PS 7.1 PVC 10.4 PVC 10.4 PVC 10.4 PV PVC C 10.4 10.4 PVC 10.4 PVC 10.4 PET 6.9 PET 6.9 PET 6.9 PET 6.9 Heteroatoms in PET PET 6.96.9 Heteroatoms in back- Heteroatoms in back- PET 6.9 Heteroatoms in back- Hetero Hetero atom atom s s in ba in ba ck- ck- Heteroatoms in back- backbone bone bone bone bone bone bone PU 7.4 PU 7.4 PU 7.4 PU 7.4 PU 7.4 PU PU 7.4 7.4 Plastics are highly involved in our daily lives, from household items to very complex Plastics are highly involved in our daily lives, from household items to very complex Plastics are highly involved in our daily lives, from household items to very complex Plastics Plastics ar ar e e hi h ghly ighly involved involved in in our our dd aily aily li ves lives , from , from ho ho usehold usehold items items to to very very com com pl pl ex e x Plastics are highly involved in our daily lives, from household items to very complex medical equipment. They are used in construction materials (e.g., windows, panels, glaz- medical equipment. They are used in construction materials (e.g., windows, panels, glaz- Plastics are highly involved in our daily lives, from household items to very complex medical equipment. They are used in construction materials (e.g., windows, panels, glaz- medica medica l e l q euip quip men men t. Th t. Th ey ey ar ar e e use use d i d i n co n co nstruct nstruct ion m ion m aterial aterial s s (e. (e. g., w g., w indows, indows, pa pa nels, g nels, g laz- laz- medical equipment. They are used in construction materials (e.g., windows, panels, glaz- ing, coatings, siding, roofing, flooring, fencing, and decoration), furniture, offices, agricul- ing, co medical atings, equipment. siding, roofi They ng, fl ar oo e ring used , fe inncing, constr and uction dematerials coration), (e.g., furniture, windows, offices panels, , agricul- glazing, ing, coatings, siding, roofing, flooring, fencing, and decoration), furniture, offices, agricul- ing, coatings, siding, roofing, flooring, fencing, and decoration), furniture, offices, agricul- ing, coatings, siding, roofing, flooring, fencing, and decoration), furniture, offices, agricul- ing, coatings, siding, roofing, flooring, fencing, and decoration), furniture, offices, agricul- ture (e.g., mulch film, materials for greenhouses, and production of sacks), transportation ture (e.g., mulch film, materials for greenhouses, and production of sacks), transportation coatings, siding, roofing, flooring, fencing, and decoration), furniture, offices, agriculture ture (e.g., mulch film, materials for greenhouses, and production of sacks), transportation ture (e.g., mulch film, materials for greenhouses, and production of sacks), transportation ture (e.g., mulch film, materials for greenhouses, and production of sacks), transportation ture (e.g., mulch film, materials for greenhouses, and production of sacks), transportation (e.g., bodywork and production of protective coatings), flame and smoke retardants (high (e.g., bodywork and production of protective coatings), flame and smoke retardants (high (e.g., mulch film, materials for greenhouses, and production of sacks), transportation (e.g., (e.g., bodywork and production of protective coatings), flame and smoke retardants (high (e. (e. g., g., bo bo dywo dywo rk rk and and pro pro du du ctct ion ion of of pro pro tete ctct ive ive coat coat ings), ings), flame flame an an d d smo smo ke ke ret ret ar ar dd an an ts ts (h (h igig h h (e.g., bodywork and production of protective coatings), flame and smoke retardants (high content of chlorine; 57% by weight), insulators, and others [6]. Polycarbonate plastic has conten bodywork t of chlorine; and pr 57 oduction % by weight), of protective insulato coatings), rs, and ot flame hers and [6]. smoke Polycarbonate retardants plast (high ic has content content of chlorine; 57% by weight), insulators, and others [6]. Polycarbonate plastic has con con ten ten t t of of chlorine; chlorine; 57 57 % % by by weight), weight), ins ins ula ula to to rsrs , and , and ot ot hers hers [6]. [6]. Pol Pol ycarbonate ycarbonate pl pl ast ast ic ic has has content of chlorine; 57% by weight), insulators, and others [6]. Polycarbonate plastic has a low thermal conductivity (k) and, therefore, is better than conventional glazing agents a low of th chlorine; ermal con 57% duct by ivit weight), y (k) and insulators, , thereforeand , is bet others ter th [6 an ]. con Polycarbon ventionaate l gla plastic zing agen has ts a low a low thermal conductivity (k) and, therefore, is better than conventional glazing agents a a low low th th erma erma l con l con dd uu ctct ivit ivit y y (k) (k) and and , th , th erefore erefore , i,s is bet bet ter ter th th an an con con ve ve nt nt iona iona l gla l gla zizi ng ng agen agen tsts a low thermal conductivity (k) and, therefore, is better than conventional glazing agents [12]. The demand for plastic has extensively increased due to its unique mechanical and thermal conductivity (k) and, therefore, is better than conventional glazing agents [12]. The [12]. The demand for plastic has extensively increased due to its unique mechanical and [12]. The demand for plastic has extensively increased due to its unique mechanical and [12]. [12]. Th Th e e de de mand mand for for pl pl ast ast ic ic has has ext ext en en sisi vel vel y y incre incre ased ased dd ue ue to to its its unique unique mec mec hani hani cal cal and and [12]. The demand for plastic has extensively increased due to its unique mechanical and physical properties (e.g., light weight, strength, resistance to corrosion and chemicals) and physi demand cal propert fories plastic (e.g.,has lighextensively t weight, strengt increased h, residue stanto ce to its corros unique ion mechanical and chemicals) and physical and physical properties (e.g., light weight, strength, resistance to corrosion and chemicals) and physical properties (e.g., light weight, strength, resistance to corrosion and chemicals) and physical properties (e.g., light weight, strength, resistance to corrosion and chemicals) and physical properties (e.g., light weight, strength, resistance to corrosion and chemicals) and low m pranuf operties acturi (e.g., ng co light st. Inweight, addition, str th ength, e shape resistance and prop to erties corr osion of plas and tics c chemicals) an be manipu and - low low manufacturing cost. In addition, the shape and properties of plastics can be manipu- low manufacturing cost. In addition, the shape and properties of plastics can be manipu- low manufacturing cost. In addition, the shape and properties of plastics can be manipu- low manufacturing cost. In addition, the shape and properties of plastics can be manipu- low manufacturing cost. In addition, the shape and properties of plastics can be manipu- lated manufacturing based on the appli cost. c In ation. addition, Howev the er, shape UV rand adiati pron operties has a of neg plative asticsecan ffect be on manipulated plastic lated based on the application. However, UV radiation has a negative effect on plastic lated based on the application. However, UV radiation has a negative effect on plastic lala ted ted bas bas ed ed o n on th th e e appli appli cat cat ion. ion. Howev Howev er, er, UU V V radiati radiati on on has has a a neg neg ative ative eff eff ect ect o n on pla pla stst ic ic lated based on the application. However, UV radiation has a negative effect on plastic based on the application. However, UV radiation has a negative effect on plastic (e.g., rigid PVC) lifetime and leads to the loss of its strength. The solar irradiation of PVC causes discoloration and the emission of toxic volatiles, which hinders its use in outdoor Polymers 2022, 14, x FOR PEER REVIEW 3 of 18 Polymers 2022, 14, 20 3 of 16 (e.g., rigid PVC) lifetime and leads to the loss of its strength. The solar irradiation of PVC causes discoloration and the emission of toxic volatiles, which hinders its use in outdoor applications [13]. PVC is still used as a construction material, but it can be replaced by applications [13]. PVC is still used as a construction material, but it can be replaced by polyolefins, which are less harmful but cost more. polyolefins, which are less harmful but cost more. The degradation of plastics is of major concern from an environmental perspective The degradation of plastics is of major concern from an environmental perspective in terms of potential hazards to living organisms. The degradation of plastics takes place in terms of potential hazards to living organisms. The degradation of plastics takes place under either abiotic or biotic (e.g., biodegradation) conditions [14]. Biodegradation is under either abiotic or biotic (e.g., biodegradation) conditions [14]. Biodegradation is highly dependent on environmental factors, which vary based on the type of polymer. highly dependent on environmental factors, which vary based on the type of polymer. Color changes and the crazing of plastic are early signs of degradation, followed by sur- Color changes and the crazing of plastic are early signs of degradation, followed by surface face cracking and the formation of small fragments [15]. Floating plastics in seas and cracking and the formation of small fragments [15]. Floating plastics in seas and oceans are oceans are moderately affected by temperatures, solar radiation, and oxygen through pho- moderately affected by temperatures, solar radiation, and oxygen through photoinitiated toinitiated oxidative degradation. For abiotic degradation, the contributing factors are oxidative degradation. For abiotic degradation, the contributing factors are sunlight and sunlight and oxygen, and they affect the plastic through a hydrolysis process [16]. oxygen, and they affect the plastic through a hydrolysis process [16]. Three steps (initiation, propagation, and termination) are involved in plastic degra- Three steps (initiation, propagation, and termination) are involved in plastic degra- dation [17]. The first step is initiated through solar or thermal initiators and leads to the dation [17]. The first step is initiated through solar or thermal initiators and leads to the formation of free radicals. Photoinitiation is not likely for both PE and PP, since they do formation of free radicals. Photoinitiation is not likely for both PE and PP, since they do not not have unsaturated chromophores in their skeletons that are responsible for the absorp- have unsaturated chromophores in their skeletons that are responsible for the absorption tion of light [18]. Impurities or abnormalities within plastics allow for the production of of light [18]. Impurities or abnormalities within plastics allow for the production of free free radicals leading to C–H bonds cleavage in the backbone of polymers [19,20]. In the radicals leading to C–H bonds cleavage in the backbone of polymers [19,20]. In the pres- presence of oxygen, free radicals produce peroxy reactive moieties in the propagation ence of oxygen, free radicals produce peroxy reactive moieties in the propagation step. In step. In addition, hydroperoxides can be produced, leading to the autoxidation of poly- addition, hydroperoxides can be produced, leading to the autoxidation of polymers [21]. In mers [21]. In the propagation step, crosslinking or chain scission takes place [22]. The de- the propagation step, crosslinking or chain scission takes place [22]. The deactivation of activation of free radicals occurs in the termination step, leading to stable products. In the free radicals occurs in the termination step, leading to stable products. In the presence of presence oxygen, the of o formation xygen, the offor oxygen-containing mation of oxygen moieties -containi is ng expected, moietieswhich is expect leads ed, to whic a photoini- h leads to a photoinitiated degradation process. The chain scission and crosslinking (termination) tiated degradation process. The chain scission and crosslinking (termination) of oxygenated of species oxygen leads ated to specie the formation s leads toof tholefins e formation (unsaturated of olefins polymeric (unsaturated chains), poly aldehydes, meric chains and ), al ketones dehyde (Figur s, and ketones e 1) [23]. (Figure 1) [23]. Figure 1. Abiotic degradation pathways for PE (R = H), PP (R = Me), and PS (R = Ph). Figure 1. Abiotic degradation pathways for PE (R = H), PP (R = Me), and PS (R = Ph). Plastic natural degradation is initiated through photodegradation followed by Plastic natural degradation is initiated through photodegradation followed by thermo- thermo-oxidative degradation [24]. Sun UV light provides the energy needed to initiate oxidative degradation [24]. Sun UV light provides the energy needed to initiate the incor- the incorporation of oxygen into the polymeric chains [25]. Plastics are degraded to small poration of oxygen into the polymeric chains [25]. Plastics are degraded to small polymeric po fragments, lymeric fra and gment then s, metabolized and then metby abolized microor by ganisms microorga in n the isms in surrounding the surroun envir ding onment. envi- ronm Microor entganisms . Microorgan tendis to ms convent tend to the con polymeric vent the po chain lymeric carbons chain to ceither arbons carbon to eithe dioxide r carbo or n biomolecules [26,27]. However, such a process is very slow (taking up to 50 years) for the dioxide or biomolecules [26,27]. However, such a process is very slow (taking up to 50 complete degradation of plastics [28]. Chromophores present within the skeleton of poly- mers absorb visible or UV light, and therefore initiate the photodegradation process [29,30]. Polymers 2022, 14, x FOR PEER REVIEW 4 of 18 years) for the complete degradation of plastics [28]. Chromophores present within the Polymers 2022, 14, 20 4 of 16 skeleton of polymers absorb visible or UV light, and therefore initiate the photodegrada- tion process [29,30]. Photodegradation takes place either in the presence of oxygen (e.g., photooxidation) or in its absence (e.g., chain crosslinking or bond breaking). When poly- Photodegradation takes place either in the presence of oxygen (e.g., photooxidation) or in mers (e.g., polyolefins) are exposed to heat, UV light, or mechanical stress in the presence its absence (e.g., chain crosslinking or bond breaking). When polymers (e.g., polyolefins) of oxygen, they produce free radicals that initiate the oxidation process. Therefore, plastics are exposed to heat, UV light, or mechanical stress in the presence of oxygen, they produce should be stabilized to inhibit the oxidative processes to increase the half-life time of ma- free radicals that initiate the oxidation process. Therefore, plastics should be stabilized to terials [31]. inhibit the oxidative processes to increase the half-life time of materials [31]. Plastic weathering involves changes in the physical, mechanical, and chemical prop- Plastic weathering involves changes in the physical, mechanical, and chemical proper- erties of polymers, particularly at the surface [32]. Solar energy, moisture (e.g., rain, snow, ties of polymers, particularly at the surface [32]. Solar energy, moisture (e.g., rain, snow, or or humidity), oxidants (e.g., ozone or atomic or singlet oxygen), and air pollutants (e.g., humidity), oxidants (e.g., ozone or atomic or singlet oxygen), and air pollutants (e.g., sulfur sulfur dioxide, nitrogen oxides, or polycyclic hydrocarbons) are responsible for these dioxide, nitrogen oxides, or polycyclic hydrocarbons) are responsible for these changes [33]. changes [33]. Uneven discoloration, surface cracks, or loss of strength are the most com- Uneven discoloration, surface cracks, or loss of strength are the most common changes mon changes within plastics due to degradation [34]. Climate change and the rise in global within plastics due to degradation [34]. Climate change and the rise in global temperatures temperatures accelerate polymers’ weathering, and impurities (e.g., traces of metals or accelerate polymers’ weathering, and impurities (e.g., traces of metals or oxidants) present oxidants) present in additives increase the rate of photodegradation [35]. in additives increase the rate of photodegradation [35]. PVC is a synthetic plastic that is similar to PP, but the backbone carbons are attached PVC is a synthetic plastic that is similar to PP, but the backbone carbons are attached to chlorine atoms instead of hydrogens. PVC is one of the most common manufactured to chlorine atoms instead of hydrogens. PVC is one of the most common manufactured plastics [36]. Due to the high content of chlorine, PVC is hard and stiff. In addition, PVC plastics [36]. Due to the high content of chlorine, PVC is hard and stiff. In addition, PVC is is polar due to the presence of C–Cl bonds and is soluble in many solvents, particularly polar due to the presence of C–Cl bonds and is soluble in many solvents, particularly those those containing polar atoms such as ethers (e.g., dioxane, tetrahydrofuran, ketones, or containing polar atoms such as ethers (e.g., dioxane, tetrahydrofuran, ketones, or nitroben- nitrobenzene). It has a low cost, is durable, has excellent performance, is easily molded, zene). It has a low cost, is durable, has excellent performance, is easily molded, and can be and can be obtained in different shapes that are suitable for many applications. PVC is obtained in different shapes that are suitable for many applications. PVC is commonly used commonly used in packaging, health care devices, toys, construction materials, electrical in packaging, health care devices, toys, construction materials, electrical wire insulation, wire insulation, clothes, and furnishing [5,6]. For outdoor applications, PVC photostabil- clothes, and furnishing [5,6]. For outdoor applications, PVC photostability should be ity should be enhanced through the addition of suitable additives to inhibit its photodeg- enhanced through the addition of suitable additives to inhibit its photodegradation. The radation. The dechlorination of PVC is autocatalytic, which leads to the formation of – dechlorination of PVC is autocatalytic, which leads to the formation of –C=C–. The forma- C=C–. The formation of unsaturated double bonds within the backbone of PVC leads to tion of unsaturated double bonds within the backbone of PVC leads to its photodegradation, its photodegradation, in which small fragments and polyene residues are produced (Fig- in which small fragments and polyene residues are produced (Figure 2) [37]. ure 2) [37]. Figure 2. Dechlorination of PVC and formation of polyene polymeric chains. Figure 2. Dechlorination of PVC and formation of polyene polymeric chains. Plastic recycling has received attention recently due to the large volume of waste that Plastic recycling has received attention recently due to the large volume of waste it generates [38]. Pyrolysis and incineration of PVC are not recommended due to the high that it generates [38]. Pyrolysis and incineration of PVC are not recommended due to level of hydrogen chloride (HCl) and other toxic volatiles produced [39]. The most com- the high level of hydrogen chloride (HCl) and other toxic volatiles produced [39]. The mon methods for PVC recycling include chemical and mechanical techniques. Mechanical most common methods for PVC recycling include chemical and mechanical techniques. recycling is preferred when the PVC waste composition is known [40]. On the other hand, Mechanical recycling is preferred when the PVC waste composition is known [40]. On the the chemical recycling of PVC converts plastics back to chemicals that can be reused in other hand, the chemical recycling of PVC converts plastics back to chemicals that can be the polymerization process. The development of techniques and instrumentation for the reused in the polymerization process. The development of techniques and instrumentation separation of PVC from the waste stream is still important to allow for the recovery of for the separation of PVC from the waste stream is still important to allow for the recovery most wasted PVC. of most wasted PVC. Recently, our research was directed towards investigating the use of newly synthe- Recently, our research was directed towards investigating the use of newly synthesized sized aromatic compounds and those that include organometallics as potential UV ab- aromatic compounds and those that include organometallics as potential UV absorbers. We sorbers. We made some progress in this field, which is reported in the current work. made some progress in this field, which is reported in the current work. 2. Photostabilization of Polymers 2. Photostabilization of Polymers The photostabilization of polymers has received much attention recently, in order to The photostabilization of polymers has received much attention recently, in order to find efficient methods to inhibit their photochemical degradation. Additives are added to find efficient methods to inhibit their photochemical degradation. Additives are added polymers to improve their performance and mechanical and thermal properties [41]. The to polymers to improve their performance and mechanical and thermal properties [41]. The additives act as stabilizers, fillers, plasticizers, softeners, lubricants, colorants, flame retardants, blowing agents, crosslinking agents, and UV absorbers. UV stabilizers are capable of reducing the rate of photooxidation of polymeric materials [42]. Various pa- rameters such as color, stability, compatibility, volatility, and cost should be taken into Polymers 2022, 14, x FOR PEER REVIEW 5 of 18 Polymers 2022, 14, 20 5 of 16 additives act as stabilizers, fillers, plasticizers, softeners, lubricants, colorants, flame re- tardants, blowing agents, crosslinking agents, and UV absorbers. UV stabilizers are capa- consideration in the ble of selection reducinof g th additives. e rate of pThe hotoox additives idation of should polymer be i capable c materiof als absorbing [42]. Various theparameters such as color, stability, compatibility, volatility, and cost should be taken into considera- harmful UV radiation and dissipating the energy as heat over time at a harmless rate to the tion in the selection of additives. The additives should be capable of absorbing the harmful polymers. Some polymers, such as polymethyl methacrylate and polytetrafluoroethylene UV radiation and dissipating the energy as heat over time at a harmless rate to the poly- are highly stable and do not require the addition of photostabilizers for outdoor applica- mers. Some polymers, such as polymethyl methacrylate and polytetrafluoroethylene are tions. Moderately photostable polymers, such as polyvinyl fluoride and polyvinylidene highly stable and do not require the addition of photostabilizers for outdoor applications. fluoride have a lifetime of a few years in outdoor applications and can be used without the Moderately photostable polymers, such as polyvinyl fluoride and polyvinylidene fluoride addition of photostabilizers. On the other hand, poorly stable polymers such as PVC, PS, have a lifetime of a few years in outdoor applications and can be used without the addition and polyamides have a short lifetime (less than a year), and therefore require the use of UV of photostabilizers. On the other hand, poorly stable polymers such as PVC, PS, and pol- stabilizers for outdoor use [43,44]. The polymer additives act as UV screeners, excited state yamides have a short lifetime (less than a year), and therefore require the use of UV sta- deactivators, hydroperoxide decomposers, and radical scavengers [45]. bilizers for outdoor use [43,44]. The polymer additives act as UV screeners, excited state In the case of PVC, the dipoles along the polymer chain, due to the presence of chlorine deactivators, hydroperoxide decomposers, and radical scavengers [45]. atoms, lead to a high level of secondary valency forces, and therefore reduce chain flexibility. In the case of PVC, the dipoles along the polymer chain, due to the presence of chlo- The van der Waals force within PVC chains is insignificant in cohesion due to the relative rine atoms, lead to a high level of secondary valency forces, and therefore reduce chain bulkiness of the chlorine atoms. The polarized groups within plasticizers bound to polymer flexibility. The van der Waals force within PVC chains is insignificant in cohesion due to dipoles and the non-polar moiety act as shields between polymer dipoles. Therefore, a the relative bulkiness of the chlorine atoms. The polarized groups within plasticizers reduction in dipole bonding between polymer chains, less overall cohesion, and an increase bound to polymer dipoles and the non-polar moiety act as shields between polymer di- in the flexibility of movement are observed [46]. The incorporation of a low concentration poles. Therefore, a reduction in dipole bonding between polymer chains, less overall co- of plasticizers can hesion, lead and to flexible an increase products in the flexi butbility increases of movem the ent stif ar fness e observed at the [46]. same Th time. e incorporation The addition of plasticizers of a low conin cen atration low concentration of plasticizers leads can leto adan to incr flexib ease le pro ind the ucts crystallinity but increases the stiff- ness at the same time. The addition of plasticizers in a low concentration leads to an in- level of the polymers [47]. Therefore, it appears that plasticized PVC has a degree of crease in the crystallinity level of the polymers [47]. Therefore, it appears that plasticized microcrystalline structure. PVC shows solvated regions, which are flexible due to the PVC has a degree of microcrystalline structure. PVC shows solvated regions, which are presence of a plasticizer and non-solvated crystalline areas. The PVC crystallite network flexible due to the presence of a plasticizer and non-solvated crystalline areas. The PVC structure has an impact on the toughness and strength and is responsible for the variation crystallite network structure has an impact on the toughness and strength and is respon- of PVC properties [48,49]. sible for the variation of PVC properties [48,49]. 3. Photostabilization of Polymers Using UV Absorbers 3. Photostabilization of Polymers Using UV Absorbers UV absorbers play an important role in absorbing harmful radiation from light and UV absorbers play an important role in absorbing harmful radiation from light and dissipating it as harmless thermal energy [50–52]. In addition, they block the formation dissipating it as harmless thermal energy [50–52]. In addition, they block the formation of of free radicals that are produced at the early stages of degradation. The most common free radicals that are produced at the early stages of degradation. The most common in- industrial UV absorbers are titanium oxide, carbon black, benzophenones, and triazoles dustrial UV absorbers are titanium oxide, carbon black, benzophenones, and triazoles (e.g., hydroxylbenzophenone and hydroxyphenylbenzotriazole), while the most common (e.g., hydroxylbenzophenone and hydroxyphenylbenzotriazole), while the most common additives used recently for research include Schiff bases and organometallic complexes additives used recently for research include Schiff bases and organometallic complexes (Figure 3). (Figure 3). Figure 3. Structures of some common UV absorbers. Figure 3. Structures of some common UV absorbers. These additives have unique UV absorbance characteristics. For example, benzophe- These additives have unique UV absorbance characteristics. For example, benzophenone none-containing additives absorb UV strongly in the short-wavelength region through a -containing additives absorb UV strongly in the short-wavelength region through a proton proton transfer or tautomeric structure equilibrium (Figure 4). They are more efficient transfer or tautomeric structure equilibrium (Figure 4). They are more efficient compared compared with the additives containing benzotriazole. Benzophenone-based UV absorb- Polymers 2022, 14, x FOR PEER REVIEW wit h the additives containing benzotriazole. Benzophenone-based UV absorbers ha 6v of e u 18 n ique ers have unique properties such as a low cost, low toxicity, and good resistance to water properties such as a low cost, low toxicity, and good resistance to water and acids [53]. and acids [53]. Figure 4. Hydroxybenzophenones energy dissipation through a proton transfer. Figure 4. Hydroxybenzophenones energy dissipation through a proton transfer. −1 –1 Triazoles have high molar extinction coefficients (5 × 106 cm M ) and absorb the most destructive wavelength of light (280–370 nm), which is highly involved in polymer degradation. The excitation of benzotriazoles takes place once the UV light is absorbed; the benzotriazoles then dissipate the energy through either heat release, involving a hy- drogen transfer, or fluorescence emission [54]. In addition, UV absorbers act as quenchers (Q) for the triplet excited state of the polymer chromophoric group (P *), followed by the release of energy as harmless heat (Figure 5) [55]. Similarly, metal complexes act as effec- tive UV quenchers due to their low excitation coefficients and quench the triplet state of the carbonyl groups in polyolefins [56–58]. Figure 5. UV absorbers act as quenchers for the excited state energy of polymers. * Represents the excited state. Recently, we synthesized a range of UV stabilizers (e.g., aromatics, heterocycles, Schiff bases, organometallic complexes, and polyphosphates) and tested their efficiency for the stabilization of polymers [59–94]. These additives, at a low concentration of 0.5% by weight, led to a significant improvement in the photostability of polymers. The stabi- lization effect that the UV absorbers induced in polymers was examined using infrared spectroscopy, the determination of weight and molecular weight, and inspection of the surface of polymers. 4. Morphological Study of the Surface of Irradiated Polymers in the Presence of Additives An investigation of the surface morphology of polymers can provide important in- formation about the damage that takes place due to weathering and the changes in parti- cles’ size and shape. Scanning electron microscopy (SEM) and field-emission scanning electron microscopy (FESEM) are used to provide information about distortion, variation on the surface, the shape and size of particles, and homogeneity [95–99]. The irradiated polymers show the presence of cracks, holes, lumps, spots, and amorphous and irregular surfaces. These changes are mainly due to dehydrochlorination, chain scission, and cross- linking. However, the damage on the surface of polymers was limited in the presence of UV absorbers compared with the blank polymers. In some cases, the irradiated films con- taining additives showed the interesting changes that took place on the surface [100–104]. For example, the SEM image of the surface of the irradiated PVC film blended with a polyphosphate containing benzidine at 25 °C, showing the formation of hexagonal pores (Figure 6) with a honeycomb-like structure, which do not appear within the blank irradi- ated material [74]. Increasing the irradiation time by up to 300 h led to an increase in the number of hexagonal pores. The reasons for the formation of such a structure are not clear, but it could be a result of the elimination of HCl at a low rate and its scavenging by the Sn complex. Crosslinked materials could produce honeycomb-like structures as a result of water stabilization [105–110]. For example, the irradiation of a thin film of crosslinked polystyrene, at 25 °C for 6 h, produced a honeycomb-like structure [106]. The irradiation of polyacrylic glycidyl ether for a short duration led to the formation of a honeycomb film Polymers 2022, 14, x FOR PEER REVIEW 6 of 18 Figure 4. Hydroxybenzophenones energy dissipation through a proton transfer. −1 –1 Triazoles have high molar extinction coefficients (5 × 106 cm M ) and absorb the most destructive wavelength of light (280–370 nm), which is highly involved in polymer Polymers 2022, 14, 20 6 of 16 degradation. The excitation of benzotriazoles takes place once the UV light is absorbed; the benzotriazoles then dissipate the energy through either heat release, involving a hy- 6 1 1 Triazoles have high molar extinction coefficients (5  10 cm M ) and absorb the most destructive wavelength of light (280–370 nm), which is highly involved in polymer drogen transfer, or fluorescence emission [54]. In addition, UV absorbers act as quenchers degradation. The excitation of benzotriazoles takes place once the UV light is absorbed; the (Q) for the triplet excited state of the polymer chromophoric group (P *), followed by the benzotriazoles then dissipate the energy through either heat release, involving a hydrogen transfer, or fluorescence emission [54]. In addition, UV absorbers act as quenchers (Q) release of energy as harmless heat (Figure 5) [55]. Similarly, metal complexes act as effec- for the triplet excited state of the polymer chromophoric group (P *), followed by the tive UV quenchers due to their low excitation coefficients and quench the triplet state of release of energy as harmless heat (Figure 5) [55]. Similarly, metal complexes act as effective UV quenchers due to their low excitation coefficients and quench the triplet state of the the carbonyl groups in polyolefins [56–58]. carbonyl groups in polyolefins [56–58]. Figure 5. UV absorbers act as quenchers for the excited state energy of polymers. * Represents the Figure 5. UV absorbers act as quenchers for the excited state energy of polymers. * Represents the excited state. excited state. Recently, we synthesized a range of UV stabilizers (e.g., aromatics, heterocycles, Schiff bases, organometallic complexes, and polyphosphates) and tested their efficiency for the stabilization of polymers [59–94]. These additives, at a low concentration of Recently, we synthesized a range of UV stabilizers (e.g., aromatics, heterocycles, 0.5% by weight, led to a significant improvement in the photostability of polymers. The Schiff bases, organometallic complexes, and polyphosphates) and tested their efficiency stabilization effect that the UV absorbers induced in polymers was examined using infrared spectroscopy, the determination of weight and molecular weight, and inspection for the stabilization of polymers [59–94]. These additives, at a low concentration of 0.5% of the surface of polymers. by weight, led to a significant improvement in the photostability of polymers. The stabi- 4. Morphological Study of the Surface of Irradiated Polymers in the Presence lization effect that the UV absorbers induced in polymers was examined using infrared of Additives An investigation of the surface morphology of polymers can provide important spectroscopy, the determination of weight and molecular weight, and inspection of the information about the damage that takes place due to weathering and the changes surface of polymers. in particles’ size and shape. Scanning electron microscopy (SEM) and field-emission scanning electron microscopy (FESEM) are used to provide information about distortion, variation on the surface, the shape and size of particles, and homogeneity [95–99]. The 4. Morphological Study of the Surface of Irradiated Polymers in the Presence of irradiated polymers show the presence of cracks, holes, lumps, spots, and amorphous and irregular surfaces. These changes are mainly due to dehydrochlorination, chain Additives scission, and crosslinking. However, the damage on the surface of polymers was limited in the presence of UV absorbers compared with the blank polymers. In some cases, the An investigation of the surface morphology of polymers can provide important in- irradiated films containing additives showed the interesting changes that took place formation about the damage that takes place due to weathering and the changes in parti- on the surface [100–104]. For example, the SEM image of the surface of the irradiated PVC film blended with a polyphosphate containing benzidine at 25 C, showing the cles’ size and shape. Scanning electron microscopy (SEM) and field-emission scanning formation of hexagonal pores (Figure 6) with a honeycomb-like structure, which do not appear within the blank irradiated material [74]. Increasing the irradiation time by up to electron microscopy (FESEM) are used to provide information about distortion, variation 300 h led to an increase in the number of hexagonal pores. The reasons for the formation on the surface, the shape and size of particles, and homogeneity [95–99]. The irradiated of such a structure are not clear, but it could be a result of the elimination of HCl at a low rate and its scavenging by the Sn complex. Crosslinked materials could produce polymers show the presence of cracks, holes, lumps, spots, and amorphous and irregular honeycomb-like structures as a result of water stabilization [105–110]. For example, surfaces. These changes are mainly due to dehydrochlorination, chain scission, and cross- the irradiation of a thin film of crosslinked polystyrene, at 25 C for 6 h, produced a honeycomb-like structure [106]. The irradiation of polyacrylic glycidyl ether for a short linking. However, the damage on the surface of polymers was limited in the presence of duration led to the formation of a honeycomb film [107]. Similarly, the SEM image o UV f the absorbers irradiated PVC com film cpared ontainingwi a 4th -me th thoe xybla benznk oic apo cid-ly Snmers comple. xIn shos w om ed ae cases, the irradiated films con- honeycomb-like structure (Figure 7) [95]. taining additives showed the interesting changes that took place on the surface [100–104]. For example, the SEM image of the surface of the irradiated PVC film blended with a polyphosphate containing benzidine at 25 °C, showing the formation of hexagonal pores (Figure 6) with a honeycomb-like structure, which do not appear within the blank irradi- ated material [74]. Increasing the irradiation time by up to 300 h led to an increase in the number of hexagonal pores. The reasons for the formation of such a structure are not clear, but it could be a result of the elimination of HCl at a low rate and its scavenging by the Sn complex. Crosslinked materials could produce honeycomb-like structures as a result of water stabilization [105–110]. For example, the irradiation of a thin film of crosslinked polystyrene, at 25 °C for 6 h, produced a honeycomb-like structure [106]. The irradiation of polyacrylic glycidyl ether for a short duration led to the formation of a honeycomb film Polymers 2022, 14, x FOR PEER REVIEW 7 of 18 Polymers 2022, 14, 20 7 of 16 [107]. Similarly, the SEM image of the irradiated PVC film containing a 4-methoxybenzoic acid-Sn complex showed a honeycomb-like structure (Figure 7) [95]. Figure 6. SEM image of the surface of an irradiated PVC film blended with a polyphosphate con- Polymers 2022, 14, x FOR PEER REVIEW 8 of 18 Figure 6. SEM image of the surface of an irradiated PVC film blended with a polyphosphate taining a benzidine moiety. containing a benzidine moiety. Figure 7. SEM image of the surface of an irradiated PVC film blended with a 4-methoxybenzoic Figure 7. SEM image of the surface of an irradiated PVC film blended with a 4-methoxybenzoic acid-Sn complex. acid-Sn complex. The irradiated PVC film, blended with a Schiff base and containing a thiadiazole moi- ety in the presence of nickel chloride, showed the presence of hexagonal pores on the sur- face (Figure 8) [72]. The presence of nickel ions is necessary to produce the honeycomb- like structure and to enhance the photostability of the polymeric materials [111]. The struc- ture of the irradiated film was highly porous with a large surface area, possibly due to the incorporation of nickel ions within the polymer. The formation of a honeycomb structure depends on the type of solvent used during the fabrication process of the film, the length of the side-chain within the polymer, and the concentration of the polymer [112]. Polymers 2022, 14, 20 8 of 16 The irradiated PVC film, blended with a Schiff base and containing a thiadiazole moiety in the presence of nickel chloride, showed the presence of hexagonal pores on the surface (Figure 8) [72]. The presence of nickel ions is necessary to produce the honeycomb- like structure and to enhance the photostability of the polymeric materials [111]. The structure of the irradiated film was highly porous with a large surface area, possibly due to the incorporation of nickel ions within the polymer. The formation of a honeycomb Polymers 2022, 14, x FOR PEER REVIEW 9 of 18 structure depends on the type of solvent used during the fabrication process of the film, the length of the side-chain within the polymer, and the concentration of the polymer [112]. Figure 8. SEM image of the surface of an irradiated PVC film blended with a Schiff base containing Figure 8. SEM image of the surface of an irradiated PVC film blended with a Schiff base containing a a thiadiazole moiety in the presence of nickel chloride. thiadiazole moiety in the presence of nickel chloride. The SEM image of the surface of an irradiated PVC film, blended with a melamine- The SEM image of the surface of an irradiated PVC film, blended with a melamine- Schiff base (Figure 9), showed ice-cube-like particles [75]. Meanwhile, the FESEM image Schiff base (Figure 9), showed ice-cube-like particles [75]. Meanwhile, the FESEM image of the of surface the surfac of e anof irradiated an irradPVC iated film, PVC blended film, blended with a trimethoprim-Sn with a trimethop complex, rim-Sn cshowed omplex, rshowed od-like parti rod-lcles ike pa (Figur rticle es 10 (Fi ) g [93 ure ]. 10) It is [93]. believed It is bel that ieve the d th cr at osslinking the crosslink and ing elimination and elimin of a- tion of volatiles and hydrogen chloride at a slow rate are the reasons for the formation of volatiles and hydrogen chloride at a slow rate are the reasons for the formation of the particles the particl that es t have hat have such sshapes uch sha [pe 113 s ,[11 1143,1 ]. 14]. 0 0 The The PS PS film film blended blended with witha a Schif Schiff f base base of of biphenyl-3,3 biphenyl-3,3′,4,4 ,4,4′-tetraamine -tetraamine showed showed spher spher-- ical and embedded ellipsoid pores that have a diameter from 3.4 to 4.3 m (Figure 11) ical and embedded ellipsoid pores that have a diameter from 3.4 to 4.3 µ m (Figure 11) after irradiation [73]. The formation of ball-like pores may be a result of the effective light after irradiation [73]. The formation of ball-like pores may be a result of the effective light absorption and porous structure of UV absorbers. absorption and porous structure of UV absorbers. For comparison, Figures 12 and 13 show the SEM images of the blank PVC and PS For comparison, Figures 12 and 13 show the SEM images of the blank PVC and PS films, respectively, in the absence of any additives after irradiation. films, respectively, in the absence of any additives after irradiation. Polymers 2022, 14, x FOR PEER REVIEW 10 of 18 Polymers Polymers 2022 202 , 214 , 1 , 4 20 , x FOR PEER REVIEW 10 of 18 9 of 16 Figure 9. SEM image of the surface of an irradiated PVC film blended with a Schiff base of melamine. Figure Figure 9. 9. SE SEM M iimage mage of ofthe the surface surface ofof an an irradiated irradiated PVC PVC film film bleblended nded with with a Sca hiff Schif base f base of mof elam melamine. ine. Figure 10. FESEM image of the surface of an irradiated PVC film blended with a trimethoprim-Sn Figure 10. FESEM image of the surface of an irradiated PVC film blended with a trimethoprim-Sn Figure 10. FESEM image of the surface of an irradiated PVC film blended with a trimethoprim- complex. complex. Sn complex. Polymers 2022, 14, x FOR PEER REVIEW 11 of 18 Polymers 2022, 14, 20 10 of 16 Polymers 2022, 14, x FOR PEER REVIEW 11 of 18 Figure 11. SEM image of the surface of an irradiated PS film blended with a Schiff base of biphenyl- Figure 11. SEM image of the surface of an irradiated PS film blended with a Schiff base of biphenyl- Figure 11. SEM image of the surface of an irradiated PS film blended with a Schiff base of biphenyl- 3,3′,4,4′-tetraamine. 0 0 3,3 ,4,4 -tetraamine. 3,3′,4,4′-tetraamine. Figure 12. SEM image of the surface of an irradiated PVC film in the absence of any additive. Figure 12. SEM image of the surface of an irradiated PVC film in the absence of any additive. Figure 12. SEM image of the surface of an irradiated PVC film in the absence of any additive. Polymers 2022, 14, x FOR PEER REVIEW 12 of 18 Polymers 2022, 14, 20 11 of 16 Figure 13. SEM image of the surface of an irradiated PS film in the absence of any additive. Figure 13. SEM image of the surface of an irradiated PS film in the absence of any additive. Atomic force microscopy (AFM) was used as a tool to measure the effectiveness of Atomic force microscopy (AFM) was used as a tool to measure the effectiveness of UV UV absorbers towards the stabilization of polymers [115–117]. The roughness factor (Rq) absorbers towards the stabilization of polymers [115–117]. The roughness factor (Rq) for the surface for the of surfac the blank, e of thirradiated e blank, irr polymers adiated po was lymers always was high alwcompar ays high ed com with pare those d with obtained those for obtained the films forblended the films with blended additives. with Such additives an obse . Survation ch an ob is se evidence rvation is for evide the nce important for the rimpo ole played rtant rol bye additives played by inad stabilizing ditives in polymers stabilizing uppo onlym irradiation. ers upon Highly irradiaar tion omatic . Highly (due ar to o- the matic resonance (due to ef thfect) e reson UVance additives effect) UV that contain additives heter that c oatoms ontai( n het due to ero coor atom dination s (due to coo with the rdi- polymeric chain of PVC, for example) showed the most desirable stabilizing effect (Table 2). nation with the polymeric chain of PVC, for example) showed the most desirable stabiliz- ing effect (Table 2). Table 2. Reduction in the roughness factor Rq (by fold) of polymers in the presence of UV absorbers. Table 2. Reduction in the roughness factor Rq (by fold) of polymers in the presence of UV absorbers. Polymer UV Absorber Organic Moiety Rq Reference Polymer UV Absorber Organic Moiety Rq Reference PS Schiff base Cephalexin 27.1 [92] PS Schiff base Cephalexin0 0 27.1 [92] PS Schiff base Biphenyl-3,3 ,4,4 -tetraamine 8.3 [73] PS Schiff base Biphenyl-3,3′,4,4′-tetraamine 8.3 [73] PS Schiff base 1,2,3,4-Triazole-3-thiol 3.3 [64] PVC Polyphosphates Benzidine 16.8 [68] PS Schiff base 1,2,3,4-Triazole-3-thiol 3.3 [64] 0 0 PVC Schiff base Biphenyl-3,3 ,4,4 -tetraamine 3.6 [66] PVC Polyphosphates Benzidine 16.8 [68] PVC Schiff base Melamine 6.0 [75] PVC Schiff base Biphenyl-3,3′,4,4′-tetraamine 3.6 [66] PVC Ni complex 2-(4-Isobutylphenyl) propanoate 6.3 [65] PVC Schiff base Melamine 6.0 [75] PVC Sn complex 4-Methoxybenzoic acid 21.2 [94] PVC Sn complex 4-(Benzylideneamino) benzenesulfonamide 18.4 [91] PVC Ni complex 2-(4-Isobutylphenyl) propanoate 6.3 [65] PVC Sn complex Ciprofloxacin 16.6 [70] PVC Sn complex 4-Methoxybenzoic acid 21.2 [94] PVC Sn complex Trimethoprim 11.3 [93] PVC Sn complex 4-(Benzylideneamino) benzenesulfonamide 18.4 [91] PVC Sn complex Telmisartan 9.4 [78] PVC Sn complex Ciprofloxacin 16.6 [70] PVC Sn complex Valsartan 7.4 [81] PVCPVC Sn complex Sn complex Trimethop Fur ri osemide m 11.3 6.6 [93] [63 ] PVC Sn complex Carvedilol 6.4 [88] PVC Sn complex Telmisartan 9.4 [78] PVC Sn complex Naproxen 5.2 [77] PVC Sn complex Valsartan 7.4 [81] PVC Sn complex Furosemide 6.6 [63] PVC Sn complex Carvedilol 6.4 [88] Polymers 2022, 14, 20 12 of 16 5. Conclusions and Future Perspectives Polymer stabilization is one of the most important processes that is used to elongate the lifetimes of plastic products. Plastics used in outdoor applications suffer in harsh environments and quickly lose their mechanical and physical properties. The proper solution for inhibiting the photooxidation of plastics due to the inevitable exposure to light and oxygen is through the addition of efficient ultraviolet absorbers that are capable of acting as efficient scavengers for light and blocking the formation of free radicals within the polymeric chains. The additives should absorb irradiation light directly and decompose peroxide species. In addition, they should be very compatible with the polymers, not alter the color, be used at a very low concentration, and be safe for the environment if released. Progress was made with the design and use of safe additives to enhance plastic stability and, in particular, polystyrene and polyvinyl chloride. Polyphosphates, Schiff bases, and organometallic complexes containing aromatic moieties showed the potential to be used as ultraviolet absorbers for plastics. The damage on the surface of irradiated plastics in the presence of ultraviolet absorbers is low compared with the blank films. Since the additives are not linked to plastic through covalent bonds, they can be leached to the surrounding environments. The leakage of these chemicals followed by their degradation poses a danger to both animals and humans. Therefore, future research should be attention to the design, synthesis, and use of safe, non-toxic, and highly stable polymeric additives to suppress the degradation of plastic. Some progress was made, but there is still room for further improvements and modifications. Author Contributions: Conceptualization: G.A.E.-H., D.S.A. and E.Y.; literature review: G.A.E.-H., D.S.A., E.Y., O.S.A.A.-K. and M.A.; writing—original draft preparation: G.A.E.-H., D.S.A., E.Y., O.S.A.A.-K., M.A. and S.A.A.; writing—review and editing: G.A.E.-H., D.S.A., E.Y., O.S.A.A.-K., M.A. and S.A.A. All authors have read and agreed to the published version of the manuscript. Funding: The authors are grateful to the Deanship of Scientific Research, King Saud University for funding through Vice Deanship of Scientific Research Chairs. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Data are contained within the article. Acknowledgments: We thank Al-Nahrain University for support. Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results. References 1. Yousif, E.; Haddad, R. Photodegradation and photostabilization of polymers, especially polystyrene: Review. SpringerPlus 2013, 2, 398. [CrossRef] [PubMed] 2. Chamas, A.; Moon, H.; Zheng, J.; Qiu, Y.; Tabassum, T.; Jang, J.H.; Abu-Omar, M.; Scott, S.L.; Suh, S. Degradation rates of plastics in the environment. ACS Sustain. Chem. Eng. 2020, 8, 3494–3511. [CrossRef] 3. Yaqoob, A.A.; Noor, N.H.M.; Serrà, A.; Mohamad Ibrahim, M.N. Advances and challenges in developing efficient graphene oxide-based ZnO photocatalysts for dye photo-oxidation. Nanomaterials 2020, 10, 932. [CrossRef] [PubMed] 4. The State of Plastics: World Environment Day Outlook 2018. Available online: https://www.unep.org/resources/report/state- plastics-world-environment-day-outlook-2018 (accessed on 5 November 2021). 5. Plastics—The Facts 2020. An Analysis of European Plastics Production, Demand and Waste Data. Available online: https: //issuu.com/plasticseuropeebook/docs/plastics_the_facts-web-dec2020 (accessed on 2 November 2021). 6. Wheeler, R.N., Jr. Poly (vinyl chloride) processes and products. Environ. Health Perspect. 1981, 41, 123–128. [CrossRef] [PubMed] 7. Schyns, Z.O.G.; Shaver, M.M. Mechanical recycling of packaging plastics: A review. Macromol. Rapid Commun. 2021, 42, 2000415. [CrossRef] 8. Singh, N.; Hui, D.; Singh, R.; Ahuja, I.P.S.; Feo, L.; Fraternali, F. Recycling of plastic solid waste: A state of art review and future applications. Compos. B. Eng. 2017, 115, 409–422. [CrossRef] 9. Gewert, B.; Plassmann, M.M.; MacLeod, M. Pathways for degradation of plastic polymers floating in the marine environment. Environ. Sci. Process. Impacts 2015, 17, 1513–1521. [CrossRef] Polymers 2022, 14, 20 13 of 16 10. Matthews, C.; Moran, F.; Jaiswal, A.K. A review on European Union’s strategy for plastics in a circular economy and its impact on food safety. J. Clean. Prod. 2021, 283, 125263. [CrossRef] 11. Potaufeux, J.-E.; Odent, J.; Notta-Cuvier, D.; Lauro, F.; Raquez, J.-M. A comprehensive review of the structures and properties of ionic polymeric materials. Polym. Chem. 2020, 11, 5914–5936. [CrossRef] 12. Moretti, E.; Zinzi, M.; Belloni, E. Polycarbonate panels for buildings: Experimental investigation of thermal and optical performance. Energy Build. 2014, 70, 23–35. [CrossRef] 13. Turner, A.; Filella, M. Polyvinyl chloride in consumer and environmental plastics, with a particular focus on metal-based additives. Environ. Sci. Process. Impacts 2021, 23, 1376–1384. [CrossRef] 14. Shah, A.A.; Hasan, F.; Hameed, A.; Ahmed, S. Biological degradation of plastics: A comprehensive review. Biotechnol. Adv. 2008, 26, 246–265. [CrossRef] [PubMed] 15. Hahladakis, J.N.; Velis, C.A.; Weber, R.; Iacovidou, E.; Purnell, P. An overview of chemical additives present in plastics: Migration, release, fate and environmental impact during their use, disposal and recycling. J. Hazard. Mater. 2018, 344, 179–199. [CrossRef] [PubMed] 16. Umar, K.; Yaqoob, A.A.; Ibrahim, M.N.M.; Parveen, T.; Safian, M.T. Environmental applications of smart polymer composites. Smart Polym. Nanocompos. Biomed. Environ. Appl. 2020, 15, 295–320. [CrossRef] 17. Albertsson, A.-C.; Karlsson, S. The three stages in degradation of polymers—Polyethylene as a model substance. J. Appl. Polym. Sci. 1988, 35, 1289–1302. [CrossRef] 18. Chatge, S.; Yang, Y.; Ahn, J.-H.; Hur, H.-G. Biodegradation of polyethylene: A brief review. Appl. Biol. Chem. 2020, 63, 27. [CrossRef] 19. Singh, B.; Sharma, N. Mechanistic implications of plastic degradation. Polym. Degrad. Stab. 2008, 93, 561–584. [CrossRef] 20. Vohlídal, J. Polymer degradation: A short review. Chem. Teach. Int. 2020, 3, 213–220. [CrossRef] 21. Gryn’ova, G.; Hodgson, J.L.; Coote, M.L. Revising the mechanism of polymer autooxidation. Org. Biomol. Chem. 2011, 9, 480–490. [CrossRef] [PubMed] 22. Webb, H.K.; Arnott, J.; Crawford, R.J.; Ivanova, E.P. Plastic degradation and its environmental implications with special reference to poly (ethylene terephthalate). Polymers 2013, 5, 1–18. [CrossRef] 23. Raquez, J.M.; Bourgeois, A.; Jacobs, H.; Degée, P.; Alexandre, M.; Dubois, P. Oxidative degradations of oxodegradable LDPE enhanced with thermoplastic pea starch: Thermo mechanical properties, morphology, and UV-ageing studies. J. Appl. Polym. Sci. 2011, 122, 489–496. [CrossRef] 24. Zheng, Y.; Yanful, E.K.; Bassi, A.S. A review of plastic waste biodegradation. Crit. Rev. Biotechnol. 2005, 25, 243–250. [CrossRef] 25. Müller, R.-J.; Kleeberg, I.; Deckwer, W.-D. Biodegradation of polyesters containing aromatic constituents. J. Biotechnol. 2001, 86, 87–95. [CrossRef] 26. Andrady, A.L. Microplastics in the marine environment. Mar. Pollut. Bull. 2011, 62, 1596–1605. [CrossRef] [PubMed] 27. Coyle, R.; Hardiman, G.; O’Driscoll, K. Microplastics in the marine environment: A review of their sources, distribution processes, uptake and exchange in ecosystems. Case Stud. Therm. Environ. Eng. 2020, 2, 100010. [CrossRef] 28. Paulsson, M.; Parkås, J. Review: Light-induced yellowing of lignocellulosic pulps–mechanism and penetrative methods. BioRe- sources 2012, 7, 5995–6040. [CrossRef] 29. Jin, C.; Christensen, P.A.; Egerton, T.A.; Lawson, E.J.; White, J.R. Rapid measurement of polymer photo-degradation by FTIR spectrometry of evolved carbon dioxide. Polym. Deg. Stab. 2006, 91, 1086–1096. [CrossRef] 30. Mu, Z.; Chen, Q.; Zhang, L.; Guan, D.; Li, H. Photodegradation of atmospheric chromophores: Changes in oxidation state and photochemical reactivity. Atmos. Chem. Phys. 2021, 21, 11581–11591. [CrossRef] 31. Wang, C.-N.; Torng, J.-H. Experimental study of the absorption characteristics of some porous fibrous materials. Appl. Acoust. 2001, 62, 447–459. [CrossRef] 32. Ojeda, T.; Freitas, A.; Birck, K.; Dalmolin, E.; Jacques, R.; Bento, F.; Camargo, F. Degradability of linear polyolefins under natural weathering. Polym. Degrad. Stab. 2011, 96, 703–707. [CrossRef] 33. Sharratt, V.; Hill, C.A.S.; Kint, D.P.R. A study of early colour change due to simulated accelerated sunlight exposure in Scots pine (Pinus sylvestris). Polym. Degrad. Stab. 2009, 94, 1589–1594. [CrossRef] 34. Bais, A.F.; Mckenzie, R.L.; Aucamp, P.J.; Ilyas, M.; Madronich, S.; Tourpali, K. Ozone depletion and climate change: Impacts on UV radiation. Photochem. Photobiol. Sci. 2015, 14, 19–52. [CrossRef] [PubMed] 35. Vitt, R.; Laschewski, G.; Bais, A.F.; Diémoz, H.; Fountoulakis, I.; Siani, A.-M.; Matzarakis, A. UV-Index climatology for Europe based on satellite data. Atmosphere 2020, 11, 727. [CrossRef] 36. Martins, J.N.; Freire, E.; Hemadipou, H. Applications and market of PVC for piping industry. Polímeros 2009, 19, 58–62. [CrossRef] 37. Kumagai, H.; Tashiro, T.; Kobayashi, T. Formation of conjugated carbon bonds on poly (vinyl chloride) films by microwave- discharge oxygen-plasma treatments. J. Appl. Polym. Sci. 2005, 96, 589–594. [CrossRef] 38. Yu, J.; Sun, L.; Ma, C.; Qiao, Y.; Yao, H. Thermal degradation of PVC: A review. Waste Manag. 2016, 48, 300–314. [CrossRef] 39. Miskolczi, N.; Bartha, L.; Angyal, A. Pyrolysis of polyvinyl chloride (PVC)-containing mixed plastic wastes for recovery of hydrocarbons. Energy Fuels 2009, 23, 2743–2749. [CrossRef] 40. Braun, D. Recycling of PVC. Prog. Polym. Sci. 2002, 27, 2171–2195. [CrossRef] 41. Marturano, V.; Cerruti, P.; Ambrogi, V. Polymer additives. Phys. Sci. Rev. 2017, 2, 20160130. [CrossRef] Polymers 2022, 14, 20 14 of 16 42. Brostow, W.; Lu, X.; Gencel, O.; Osmanson, A.T. Effects of UV stabilizers on polypropylene outdoors. Materials 2020, 13, 1626. [CrossRef] 43. Noukakis, D.; Suppan, P. Mechanism of protection of polymers by photostabilizers. J. Photochem. Photobiol. A 1991, 58, 393–396. [CrossRef] 44. Sabaa, M.W.; Sanad, M.A.; Abd El-Ghaffar, M.A.; Abdelwahab, N.A.; Sayed, S.M.A.; Soliman, S.M.A. Synthesis, characterization, and application of polyanisidines as efficient photostabilizers for poly (vinyl chloride) films. J. Elastomers Plast. 2020, 52, 537–547. [CrossRef] 45. Karimi, S.; Helal, E.; Gutierrez, G.; Moghimian, N.; Madinehei, M.; David, E.; Samara, M.; Demarquette, N. A review on graphene’s light stabilizing effects for reduced photodegradation of polymers. Crystals 2021, 11, 3. [CrossRef] 46. Marcilla, A.; García, S.; García-Quesada, J.C. Study of the migration of PVC plasticizers. J. Anal. Appl. Pyrolysis 2004, 71, 457–463. [CrossRef] 47. Szarka, G.; Iván, B. Degradative Transformation of Poly (vinyl chloride) Under Mild Oxidative Conditions. In Polymer Degradation and Performance; Celina, M.C., Wiggins, J.S., Billingham, N.C., Eds.; ACS: Washington, DC, USA, 2009; Volume 1004, Chapter 19; pp. 219–226. [CrossRef] 48. Wang, T.; Li, X.; Xiong, Y.; Guo, S.Y. Super-tough PVC/CPE composites: An efficient CPE network by an MGA copolymer prepared through a vibro-milling process. RSC Adv. 2020, 10, 44584–44592. [CrossRef] 49. Marshall, R.A. Effect of crystallinity on PVC physical properties. J. Vinyl Addit. Technol. 1994, 16, 35–38. [CrossRef] 50. Larché, J.-F.; Bussière, P.-O.; Thérias, S.; Gardette, J.-L. Photooxidation of polymers: Relating material properties to chemical changes. Polym. Degrad. Stab. 2012, 97, 25–35. [CrossRef] 51. Geuskens, G.; Baeyens-Volant, D.; Delaunois, G.; Lu Vinh, Q.; Piret, W.; David, C. Photo-oxidation of polymers–II. The sensitized decomposition of hydroperoxides as the main path for initiation of the photo-oxidation of polystyrene irradiated at 253.7 nm. Eur. Polym. J. 1978, 14, 299–303. [CrossRef] 52. Yaqoob, A.A.; Noor, N.H.M.; Umar, K.; Adnan, R.; Ibrahim, M.N.M.; Rashid, M. Graphene oxide–ZnO nanocomposite: An efficient visible light photocatalyst for degradation of rhodamine B. Appl. Nanosci. 2021, 11, 1291–1302. [CrossRef] 53. Huang, Z.; Ding, A.; Guo, H.; Lu, G.; Huang, X. Construction of nontoxic polymeric UV-absorber with great resistance to UV-photoaging. Sci. Rep. 2016, 6, 25508. [CrossRef] 54. Sonnenschein, M.F.; Guillaudeu, S.J.; Landes, B.G.; Wendt, B.L. Comparison of adipate and succinate polymers in thermoplastic polyurethanes. Polymer 2010, 51, 3685–3692. [CrossRef] 55. Lu, T.; Solis-Ramos, E.; Yi, Y.; Kumosa, M. UV degradation model for polymers and polymer matrix composites. Polym. Degrad. Stab. 2018, 154, 203–210. [CrossRef] 56. Rabek, J. Polymer Photodegradation: Mechanisms and Experimental Methods; Champan & Hall: London, UK, 1995; pp. 383–391. 57. George, G.A. The mechanism of photoprotection of polystyrene film by some ultraviolet absorbers. J. Appl. Polym. Sci. 1974, 18, 117–124. [CrossRef] 58. Liu, X.; Gao, C.; Sangwan, P.; Yu, L.; Tong, Z. Accelerating the degradation of polyolefins through additives and blending. J. Appl. Polym. Sci. 2014, 131, 40750. [CrossRef] 59. Balakit, A.A.; Ahmed, A.; El-Hiti, G.A.; Smith, K.; Yousif, E. Synthesis of new thiophene derivatives and their use as photostabi- lizers for rigid poly (vinyl chloride). Int. J. Polym. Sci. 2015, 2015, 510390. [CrossRef] 60. Yousif, E.; El-Hiti, G.A.; Haddad, R.; Balakit, A.A. Photochemical stability and photostabilizng efficiency of poly (methyl methacrylate) based on 2-(6-methoxynaphthalen-2-yl) propanoate metal ions complexes. Polymers 2015, 7, 1005–1019. [CrossRef] 61. Yousif, E.; El-Hiti, G.A.; Hussain, Z.; Altaie, A. Viscoelastic, spectroscopic and microscopic study of the photo irradiation effect on the stability of PVC in presence of sulfamethoxazole Schiff’s bases. Polymers 2015, 7, 2190–2204. [CrossRef] 62. Yousif, E.; Hasan, A.; El-Hiti, G.A. Spectroscopic, physical and topography of photochemical process of PVC films in the presence of Schiff base metal complexes. Polymers 2016, 8, 204. [CrossRef] [PubMed] 63. Ali, M.M.; El-Hiti, G.A.; Yousif, E. Photostabilizing efficiency of poly (vinyl chloride) in the presence of organotin (IV) complexes as photostabilizers. Molecules 2016, 21, 1151. [CrossRef] 64. Ali, G.Q.; El-Hiti, G.A.; Tomi, I.H.R.; Haddad, R.; Al-Qaisi, A.J.; Yousif, E. Photostability and performance of polystyrene films containing 1,2,4-triazole-3-thiol ring system Schiff bases. Molecules 2016, 21, 1699. [CrossRef] 65. Mohammed, R.; El-Hiti, G.A.; Ahmed, A.; Yousif, E. Poly (vinyl chloride) doped by 2-(4-isobutylphenyl) propanoate metal complexes: Enhanced resistance to UV irradiation. Arab. J. Sci. Eng. 2017, 42, 4307–4315. [CrossRef] 66. Ahmed, D.S.; El-Hiti, G.A.; Hameed, A.S.; Yousif, E.; Ahmed, A. New tetra-Schiff bases as efficient photostabilizers for poly (vinyl chloride). Molecules 2017, 22, 1506. [CrossRef] 67. Ali, M.M.; El-Hiti, G.A.; Yousif, E. Investigation of the photodecomposition rate constant of poly (vinyl chloride) films containing organotin (IV) complexes. Al-Nahrain J. Sci. 2017, 20, 18–23. [CrossRef] 68. Ahmed, D.S.; El-Hiti, G.A.; Yousif, E.; Hameed, A.S. Polyphosphates as inhibitors for poly (vinyl chloride) photodegradation. Molecules 2017, 22, 1849. [CrossRef] 69. Yousif, E.; Haddad, R.; El-Hiti, G.A.; Yusop, R.M. Spectroscopic and photochemical stability of polystyrene films in the presence of metal complexes. J. Taibah Univ. Sci. 2017, 11, 997–1007. [CrossRef] Polymers 2022, 14, 20 15 of 16 70. Ghazi, D.; El-Hiti, G.A.; Yousif, E.; Ahmed, D.S.; Alotaibi, M.H. The effect of ultraviolet irradiation on the physicochemical properties of poly (vinyl chloride) films containing organotin (IV) complexes as photostabilizers. Molecules 2018, 23, 254. [CrossRef] [PubMed] 71. Shaalan, N.; Laftah, N.; El-Hiti, G.A.; Alotaibi, M.H.; Muslih, R.; Ahmed, D.S.; Yousif, E. Poly (vinyl chloride) photostabilization in the presence of Schiff bases containing a thiadiazole moiety. Molecules 2018, 23, 913. [CrossRef] [PubMed] 72. Hashim, H.; El-Hiti, G.A.; Alotaibi, M.H.; Ahmed, D.S.; Yousif, E. Fabrication of ordered honeycomb porous poly (vinyl chloride) thin film doped with a Schiff base and nickel (II) chloride. Heliyon 2018, 4, e00743. [CrossRef] 73. Yousif, E.; Ahmed, D.S.; El-Hiti, G.A.; Alotaibi, M.H.; Hashim, H.; Hameed, A.S.; Ahmed, A. Fabrication of novel ball-like polystyrene films containing Schiff bases microspheres as photostabilizers. Polymers 2018, 10, 1185. [CrossRef] [PubMed] 74. Alotaibi, M.H.; El-Hiti, G.A.; Hashim, H.; Hameed, A.S.; Ahmed, D.S.; Yousif, E. SEM analysis of the tunable honeycomb structure of irradiated poly (vinyl chloride) films doped with polyphosphate. Heliyon 2018, 4, e01013. [CrossRef] 75. El-Hiti, G.A.; Alotaibi, M.H.; Ahmed, A.A.; Hamad, B.A.; Ahmed, D.S.; Ahmed, A.; Hashim, H.; Yousif, E. The morphology and performance of poly (vinyl chloride) containing melamine Schiff bases against ultraviolet light. Molecules 2019, 24, 803. [CrossRef] [PubMed] 76. Alotaibi, M.H.; El-Hiti, G.A.; Yousif, E.; Ahmed, D.S.; Hashim, H.; Hameed, A.S.; Ahmed, A. Evaluation of the use of polyphos- phates as photostabilizers and in the formation of ball-like polystyrene materials. J. Polym. Res. 2019, 26, 161. [CrossRef] 77. Hadi, A.G.; Yousif, E.; El-Hiti, G.A.; Ahmed, D.S.; Jawad, K.; Alotaibi, M.H.; Hashim, H. Long-term effect of ultraviolet irradiation on poly (vinyl chloride) films containing naproxen diorganotin (IV) complexes. Molecules 2019, 24, 2396. [CrossRef] 78. Hadi, A.G.; Jawad, K.; El-Hiti, G.A.; Alotaibi, M.H.; Ahmed, A.A.; Ahmed, D.S.; Yousif, E. Photostabilization of poly (vinyl chloride) by organotin (IV) compounds against photodegradation. Molecules 2019, 24, 3557. [CrossRef] 79. Ahmed, A.A.; Ahmed, D.S.; El-Hiti, G.A.; Alotaibi, M.H.; Hashim, H.; Yousif, E. SEM morphological analysis of irradiated polystyrene film doped by a Schiff base containing a 1,2,4-triazole ring system. Appl. Petrochem. Res. 2019, 9, 169–177. [CrossRef] 80. El-Hiti, G.A.; Ahmed, D.S.; Yousif, E.; Alotaibi, M.H.; Star, H.A.; Ahmed, A.A. Influence of polyphosphates on the physicochemical properties of poly (vinyl chloride) after irradiation with ultraviolet light. Polymers 2020, 12, 193. [CrossRef] 81. Mohammed, A.; El-Hiti, G.A.; Yousif, E.; Ahmed, A.A.; Ahmed, D.S.; Alotaibi, M.H. Protection of poly (vinyl chloride) films against photodegradation using various valsartan tin complexes. Polymers 2020, 12, 969. [CrossRef] 82. Ahmed, D.S.; El-Hiti, G.A.; Ibraheem, H.; Alotaibi, M.H.; Abdallh, M.; Ahmed, A.A.; Ismael, M.; Yousif, E. Enhancement of photostabilization of poly (vinyl chloride) doped with sulfadiazine tin complexes. J. Vinyl Addit. Technol. 2020, 26, 370–379. [CrossRef] 83. Mahmood, Z.N.; Yousif, E.; Alias, M.; El-Hiti, G.A.; Ahmed, D.S. Synthesis, characterization, properties, and use of new fusidate organotin complexes as additives to inhibit poly (vinyl chloride) photodegradation. J. Polym. Res. 2020, 27, 267. [CrossRef] 84. Majeed, A.; Yousif, E.; El-Hiti, G.A.; Alotaibi, M.H.; Ahmed, D.S.; Ahmed, A.A. Stabilization of PVC containing captopril tin complexes against degradation upon exposure to ultraviolet light. J. Vinyl Addit. Technol. 2020, 26, 601–612. [CrossRef] 85. Salam, B.; El-Hiti, G.A.; Bufaroosha, M.; Ahmed, D.S.; Ahmed, A.; Alotaibi, M.H.; Yousif, E. Tin complexes containing an atenolol moiety as photostabilizers for poly (vinyl chloride). Polymers 2020, 12, 2923. [CrossRef] [PubMed] 86. Omer, R.M.; Al-Tikrity, E.T.B.; Yousif, E.; El-Hiti, G.A.; Ahmed, D.S.; Ahmed, A.A. Spectroscopic and morphological study of irradiated PVC films doped with polyphosphates containing 4,4 -methylenedianiline. Russ. J. Appl. Chem. 2020, 93, 1888–1898. [CrossRef] 87. Mohamed, S.H.; Hameed, A.S.; El-Hiti, G.A.; Ahmed, D.S.; Kadhom, M.; Baashen, M.A.; Bufaroosha, M.; Ahmed, A.A.; Yousif, E. A process for the synthesis and use of highly aromatic organosilanes as additives for poly (vinyl chloride) films. Processes 2021, 9, 91. [CrossRef] 88. Mousa, O.G.; El-Hiti, G.A.; Baashen, M.A.; Bufaroosha, M.; Ahmed, A.; Ahmed, A.A.; Ahmed, D.S.; Yousif, E. Synthesis of carvedilol-organotin complexes and their effects on reducing photodegradation of poly (vinyl chloride). Polymers 2021, 13, 500. [CrossRef] 89. Ahmed, A.; El-Hiti, G.A.; Hadi, A.G.; Ahmed, D.S.; Baashen, M.A.; Hashim, H.; Yousif, E. Photostabilization of poly (vinyl chloride) films blended with organotin complexes of mefenamic acid for outdoor applications. Appl. Sci. 2021, 11, 2853. [CrossRef] 90. Jasem, H.; Hadi, A.G.; El-Hiti, G.A.; Baashen, M.A.; Hashim, H.; Ahmed, A.A.; Ahmed, D.S.; Yousif, E. Tin-naphthalene sulfonic acid complexes as photostabilizers for poly (vinyl chloride). Molecules 2021, 26, 3629. [CrossRef] [PubMed] 91. Ghani, H.; Yousif, E.; Ahmed, D.S.; Kariuki, B.M.; El-Hiti, G.A. Tin Complexes of 4-(Benzylideneamino) benzenesulfonamide: Synthesis, structure elucidation and their efficiency as PVC photostabilizers. Polymers 2021, 13, 2434. [CrossRef] 92. Yaseen, A.A.; Al-Tikrity, E.T.B.; Yousif, E.; Ahmed, D.S.; Kariuki, B.M.; El-Hiti, G.A. Effect of ultraviolet irradiation on polystyrene containing cephalexin Schiff bases. Polymers 2021, 13, 2982. [CrossRef] 93. Yaseen, A.A.; Yousif, E.; Al-Tikrity, E.T.B.; El-Hiti, G.A.; Kariuki, B.M.; Ahmed, D.S.; Bufaroosha, M. FTIR, weight, and surface morphology of poly (vinyl chloride) doped with tin complexes containing aromatic and heterocyclic moieties. Polymers 2021, 13, 3264. [CrossRef] 94. Hadi, A.G.; Baqir, S.J.; Ahmed, D.S.; El-Hiti, G.A.; Hashim, H.; Ahmed, A.; Kariuki, B.M.; Yousif, E. Substituted organotin complexes of 4-methoxybenzoic acid for reduction of poly (vinyl chloride) photodegradation. Polymers 2021, 13, 3946. [CrossRef] Polymers 2022, 14, 20 16 of 16 95. Nikafshar, S.; Zabihi, O.; Ahmadi, M.; Mirmohseni, A.; Taseidifar, M.; Naebe, M. The effects of UV light on the chemical and mechanical properties of a transparent epoxy-diamine system in the presence of an organic UV absorber. Materials 2017, 10, 180. [CrossRef] 96. Venkateshaiah, A.; Padil, V.V.T.; Nagalakshmaiah, M.; Waclawek, S.; Cerník, M.; Varma, R.S. Microscopic techniques for the analysis of micro and nanostructures of biopolymers and their derivatives. Polymers 2020, 12, 512. [CrossRef] 97. Sawyer, L.C.; Grubb, D.T.; Meyers, G.F. Polymer Microscopy, 3rd ed.; Springer: New York, NY, USA, 2008; Chapter 5. 98. Valko, L.; Klein, E.; Kovar ˇík, P.; Bleha, T.; Šimon, P. Kinetic study of thermal dehydrochlorination of poly (vinyl chloride) in the presence of oxygen: III. Statistical thermodynamic interpretation of the oxygen catalytic activity. Eur. Polym. J. 2001, 37, 1123–1132. [CrossRef] 99. Shi, W.; Zhang, J.; Shi, X.-M.; Jiang, G.-D. Different photo-degradation processes of PVC with different average degrees of polymerization. J. Appl. Polym. Sci. 2008, 107, 528–540. [CrossRef] 100. Pospíšil, J.; Nešpurek, S. Photostabilization of coatings. Mechanisms and performance. Prog. Polym. Sci. 2000, 25, 1261–1335. [CrossRef] 101. Jafari, A.J.; Donaldson, J.D. Determination of HCl and VOC emission from thermal degradation of PVC in the absence and presence of copper, copper (II) oxide and copper (II) chloride. J. Chem. 2009, 6, 685–692. [CrossRef] 102. Pi, H.; Xiong, Y.; Guo, S. The kinetic studies of elimination of HCl during thermal decomposition of PVC in the presence of transition metal oxides. Polym. Plast. Technol. Eng. 2005, 44, 275–288. [CrossRef] 103. Nief, O.A. Photostabilization of polyvinyl chloride by some new thiadiazole derivatives. Eur. J. Chem. 2015, 6, 242–247. [CrossRef] 104. Chaochanchaikul, K.; Rosarpitak, V.; Sombatsompop, N. Photodegradation profiles of PVC compound and wood/PVC composites under UV weathering. Express Polym. Lett. 2013, 7, 146–160. [CrossRef] 105. Zhang, A.; Bai, H.; Li, L. Breath figure: A nature-inspired preparation method for ordered porous films. Chem. Rev. 2015, 115, 9801–9868. [CrossRef] 106. Bui, V.-T.; Lee, H.S.; Choi, J.-H. Data from crosslinked PS honeycomb thin film by deep UV irradiation. Data Brief 2015, 5, 990–994. [CrossRef] 107. Zheng, K.; Hu, D.; Deng, Y.; Maitloa, I.; Nie, J.; Zhu, X. Crosslinking poly (acrylic glycidyl ether) honeycomb film by cationic photopolymerization and its converting to inorganic SiO film. Appl. Surf. Sci. 2008, 428, 485–491. [CrossRef] 108. Kayyarapu, B.; Kumar, M.; Mohommad, H.B.; Neeruganti, G.; Chekuria, R. Structural, thermal and optical properties of pure and 2+ Mn doped poly (vinyl chloride) films. Mater. Res. 2016, 19, 1167–1175. [CrossRef] 109. Dou, Y.; Jin, M.; Zhou, G.; Shui, L. Breath figure method for construction of honeycomb films. Membranes 2015, 5, 399–424. [CrossRef] 110. Cheng, C.X.; Tian, Y.; Shi, Y.Q.; Tang, R.P.; Xi, F. Porous polymer films and honeycomb structures based on amphiphilic dendronized block copolymers. Langmuir 2005, 21, 6576–6581. [CrossRef] 111. Rahman, M.Y.A.; Ahmad, A.; Lee, T.K.; Farina, Y.; Dahlan, H.D. Effect of ethylene carbonate (EC) plasticizer on poly (vinyl chloride)-liquid 50% epoxidised natural rubber (LENR50) based polymer electrolyte. Mater. Sci. Appl. 2011, 2, 817–825. [CrossRef] 112. Huh, M.; Gauthier, M.; Yun, S. Honeycomb structured porous films prepared from arborescent graft polystyrenes via the breath figures method. Polymer 2016, 107, 273–281. [CrossRef] 113. Wang, Z.M.; Wagner, J.; Ghosal, S.; Bedi, G.; Wall, S. SEM/EDS and optical microscopy analyses of microplastics in ocean trawl and fish guts. Sci. Total Environ. 2017, 603–604, 616–626. [CrossRef] 114. Devi, M.R.; Saranya, A.; Pandiarajan, J.; Dharmaraja, J.; Prithivikumaran, N.; Jeyakumaran, N. Fabrication, spectral characteriza- tion, XRD and SEM studies on some organic acids doped polyaniline thin films on glass substrate. JKSUS 2019, 31, 1290–1296. [CrossRef] 115. Kara, F.; Aksoy, E.A.; Yuksekdag, Z.; Hasirci, N.; Aksoy, S. Synthesis and surface modification of polyurethanes with chitosan for antibacterial properties. Carbohydr. Polym. 2014, 112, 39–47. [CrossRef] 116. Shinato, K.W.; Huang, F.; Jin, Y. Principle and application of atomic force microscopy (AFM) for nanoscale investigation of metal corrosion. Corros. Rev. 2020, 38, 423–432. [CrossRef] 117. See, C.H.; O’Haver, J. Atomic force microscopy characterization of ultrathin polystyrene films formed by admicellar polymeriza- tion on silica disks. J. Appl. Polym. Sci. 2003, 89, 36–46. [CrossRef] http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Polymers Multidisciplinary Digital Publishing Institute

Modifications of Polymers through the Addition of Ultraviolet Absorbers to Reduce the Aging Effect of Accelerated and Natural Irradiation

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polymers Review Modifications of Polymers through the Addition of Ultraviolet Absorbers to Reduce the Aging Effect of Accelerated and Natural Irradiation 1 , 2 3 4 3 Gamal A. El-Hiti * , Dina S. Ahmed , Emad Yousif , Omar S. A. Al-Khazrajy , Mustafa Abdallh and Saud A. Alanazi Cornea Research Chair, Department of Optometry, College of Applied Medical Sciences, King Saud University, P.O. Box 10219, Riyadh 11433, Saudi Arabia; saaalanazi@ksu.edu.sa Department of Medical Instrumentation Engineering, Al-Mansour University College, Baghdad 64021, Iraq; dina.saadi@muc.edu.iq Department of Chemistry, College of Science, Al-Nahrain University, Baghdad 64021, Iraq; emad.yousif@nahrainuniv.edu.iq (E.Y.); mustafa.abdallh@nahrainuive.edu.iq (M.A.) Department of Chemistry, College of Education for Pure Science (Ibn Al-Haytham), University of Baghdad, Baghdad 64021, Iraq; omar.s.a@ihcoedu.uobaghdad.edu.iq * Correspondence: gelhiti@ksu.edu.sa; Tel.: +966-11469-3778; Fax: +966-11469-3536 Abstract: The photooxidative degradation process of plastics caused by ultraviolet irradiation leads to bond breaking, crosslinking, the elimination of volatiles, formation of free radicals, and decreases in weight and molecular weight. Photodegradation deteriorates both the mechanical and physi- cal properties of plastics and affects their predicted life use, in particular for applications in harsh environments. Plastics have many benefits, while on the other hand, they have numerous disad- vantages, such as photodegradation and photooxidation in harsh environments and the release of Citation: El-Hiti, G.A.; Ahmed, D.S.; Yousif, E.; Al-Khazrajy, O.S.A.; toxic substances due to the leaching of some components, which have a negative effect on living Abdallh, M.; Alanazi, S.A. organisms. Therefore, attention is paid to the design and use of safe, plastic, ultraviolet stabilizers Modifications of Polymers through that do not pose a danger to the environment if released. Plastic ultraviolet photostabilizers act as the Addition of Ultraviolet Absorbers efficient light screeners (absorbers or pigments), excited-state deactivators (quenchers), hydroperox- to Reduce the Aging Effect of ide decomposers, and radical scavengers. Ultraviolet absorbers are cheap to produce, can be used Accelerated and Natural Irradiation. in low concentrations, mix well with polymers to produce a homogenous matrix, and do not alter Polymers 2022, 14, 20. https:// the color of polymers. Recently, polyphosphates, Schiff bases, and organometallic complexes were doi.org/10.3390/polym14010020 synthesized and used as potential ultraviolet absorbers for polymeric materials. They reduced the Academic Editors: Andrea damage caused by accelerated and natural ultraviolet aging, which was confirmed by inspecting the Antonino Scamporrino and Chiara surface morphology of irradiated polymeric films. For example, atomic force microscopy revealed Maria Antonietta Gangemi that the roughness factor of polymers’ irradiated surfaces was improved significantly in the presence of ultraviolet absorbers. In addition, the investigation of the surface of irradiated polymers using Received: 5 December 2021 scanning electron microscopy showed a high degree of homogeneity and the appearance of pores Accepted: 20 December 2021 Published: 22 December 2021 that were different in size and shape. The current work surveys for the first time the use of newly synthesized, ultraviolet absorbers as additives to enhance the photostability of polymeric materials Publisher’s Note: MDPI stays neutral and, in particular, polyvinyl chloride and polystyrene, based mainly on our own recent work in with regard to jurisdictional claims in the field. published maps and institutional affil- iations. Keywords: plastics; polyvinyl chloride; photostabilizers; plastic photodegradation and photooxida- tion; recycling of plastics; photoirradiation Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article 1. Introduction distributed under the terms and Ultraviolet (UV) light has harmful effects on materials used in outdoor applications. conditions of the Creative Commons Plastics suffer photooxidation when exposed to harsh conditions (high temperature, sun- Attribution (CC BY) license (https:// light for long duration, and humidity) in the presence of oxygen. Plastic degradation, as creativecommons.org/licenses/by/ a result of UV light absorption, leads to discoloration, cracks, and loss of mechanical and 4.0/). Polymers 2022, 14, 20. https://doi.org/10.3390/polym14010020 https://www.mdpi.com/journal/polymers Polymers 2022, 14, x FOR PEER REVIEW 2 of 18 Polymers 2022, 14, x FOR PEER REVIEW 2 of 18 Polymers 2022, 14, x FOR PEER REVIEW 2 of 18 Polymers 2022, 14, x FOR PEER REVIEW 2 of 18 Polymers 2022, 14, x FOR PEER REVIEW 2 of 18 Polymers 2022, 14, x FOR PEER REVIEW 2 of 18 sunlight for long duration, and humidity) in the presence of oxygen. Plastic degradation, sunlight for long duration, and humidity) in the presence of oxygen. Plastic degradation, Polymers 2022, 14, 20 2 of 16 sunlight for long duration, and humidity) in the presence of oxygen. Plastic degradation, sunlight for long duration, and humidity) in the presence of oxygen. Plastic degradation, sunlight for long duration, and humidity) in the presence of oxygen. Plastic degradation, sunlight for long duration, and humidity) in the presence of oxygen. Plastic degradation, as a result of UV light absorption, leads to discoloration, cracks, and loss of mechanical as a result of UV light absorption, leads to discoloration, cracks, and loss of mechanical as a result of UV light absorption, leads to discoloration, cracks, and loss of mechanical as as a a res res ul ul t t of of UV UV light light abs abs orp orp tion tion , le , le ad ad s s to to di di scolor scolor atat ion, ion, crcr acks, acks, an an d d los los s s of of me me chanic chanic al al as a result of UV light absorption, leads to discoloration, cracks, and loss of mechanical and physical properties [1,2]. Photooxidation resembles autooxidation due to long-term and physical properties [1,2]. Photooxidation resembles autooxidation due to long-term and physical properties [1,2]. Photooxidation resembles autooxidation due to long-term and and ph ph ysi ysi cal cal pro pro pert pert ies ies [1, [1, 2]. 2]. Phot Phot oox oox id id ation ation re re semb semb les les au au to to oxi oxi dd atat ion ion dd ue ue to to l olng ong -ter -ter m m and physical properties [1,2]. Photooxidation resembles autooxidation due to long-term physical properties [1,2]. Photooxidation resembles autooxidation due to long-term heat heat aging, except that the driving force is UV light and not heat [3]. Therefore, during heat aging, except that the driving force is UV light and not heat [3]. Therefore, during heat aging, except that the driving force is UV light and not heat [3]. Therefore, during heat heat ag ag in in g, g, excep excep t t th th at at th th e e driv driv ing ing for for ce ce is is UU V V ligh ligh t t and and not not h eat heat [3]. [3]. Th Th erefo erefo re, re, dd uri uri ng ng heat aging, except that the driving force is UV light and not heat [3]. Therefore, during plasti aging, c manufactu except ring that, the medriving asures sho force uld isbe UV taken light to and ens not ure heat that [3 ]. thTher e mater efor ials e, during will last plastic plastic manufacturing, measures should be taken to ensure that the materials will last plastic manufacturing, measures should be taken to ensure that the materials will last plastic manufacturing, measures should be taken to ensure that the materials will last plastic manufacturing, measures should be taken to ensure that the materials will last plastic manufacturing, measures should be taken to ensure that the materials will last longer manufacturing, and to inhibit pho measur tooxida es should tion an bed pho taken to to degr ensur adati e that on pro thecmaterials esses. will last longer and longer and to inhibit photooxidation and photodegradation processes. longer and to inhibit photooxidation and photodegradation processes. longer and to inhibit photooxidation and photodegradation processes. longer and to inhibit photooxidation and photodegradation processes. longer and to inhibit photooxidation and photodegradation processes. to inhibit photooxidation and photodegradation processes. The polymerization technique was developed over the years to allow the production The polymerization technique was developed over the years to allow the production The polymerization technique was developed over the years to allow the production Th Th e e po po lyly mer mer iza iza tion tion tec tec hni hni qu qu e e wa wa s s d d eve eve loped loped ov ov er er th th e e ye ye ar ar s s to to allo allo w w th th e e pro pro duc duc tion tion The polymerization technique was developed over the years to allow the production The polymerization technique was developed over the years to allow the production of plastics on an industrial scale. There has been a massive increase in the production of of plastics on an industrial scale. There has been a massive increase in the production of of plastics on an industrial scale. There has been a massive increase in the production of of of pl pl as as tic tic s s on on an an in in dustr dustr ial ial scale. scale. Th Th ere ere has has been been a a m m as as sive sive incre incre ase ase in in th th e e pro pro dd uction uction of of of plastics on an industrial scale. There has been a massive increase in the production of of plastics on an industrial scale. There has been a massive increase in the production of plastics in recent years [4]. The scale of polyvinyl chloride (PVC) production has increased plastics in recent years [4]. The scale of polyvinyl chloride (PVC) production has increased plastics in recent years [4]. The scale of polyvinyl chloride (PVC) production has increased pla pla sti sti cs cs in in rec rec ent ent ye ye ar ar s s [4]. [4]. Th Th e e sc sc alal e e o f op f olyviny polyviny l chlo l chlo ride ride (PV (PV CC ) p ) p roduct roduct ion ion ha ha s s incre incre as as ed ed plastics in recent years [4]. The scale of polyvinyl chloride (PVC) production has increased plastics in recent years [4]. The scale of polyvinyl chloride (PVC) production has increased over the years from 3 million tons in 1965 to over 40 million tons in 2018 and is expected over the years from 3 million tons in 1965 to over 40 million tons in 2018 and is expected over the years from 3 million tons in 1965 to over 40 million tons in 2018 and is expected ov ov er er th th e e yea yea rs rs from from 3 3 mi mi lli lli on on to to ns ns in in 19 19 65 65 to to ov ov er er 40 40 million million to to ns ns in in 2018 2018 an an d d is is exp exp ect ect ed ed over the years from 3 million tons in 1965 to over 40 million tons in 2018 and is expected over the years from 3 million tons in 1965 to over 40 million tons in 2018 and is expected to grow further to 60 million tons in 2025 [5]. PVC can be produced in different forms and to grow further to 60 million tons in 2025 [5]. PVC can be produced in different forms and to grow further to 60 million tons in 2025 [5]. PVC can be produced in different forms and to grow further to 60 million tons in 2025 [5]. PVC can be produced in different forms and to grow further to 60 million tons in 2025 [5]. PVC can be produced in different forms and to grow further to 60 million tons in 2025 [5]. PVC can be produced in different forms and to grow further to 60 million tons in 2025 [5]. PVC can be produced in different forms shapes, using both suspension and emulsion polymerization [6]. Plastic waste is a chal- shapes, using both suspension and emulsion polymerization [6]. Plastic waste is a chal- shapes, using both suspension and emulsion polymerization [6]. Plastic waste is a chal- shapes, using both suspension and emulsion polymerization [6]. Plastic waste is a chal- shapes, using both suspension and emulsion polymerization [6]. Plastic waste is a chal- shapes, using both suspension and emulsion polymerization [6]. Plastic waste is a chal- and shapes, using both suspension and emulsion polymerization [6]. Plastic waste is a lenge, and there is a need for not only effective recycling but cutting the waste at the lenge, and there is a need for not only effective recycling but cutting the waste at the lenge, and there is a need for not only effective recycling but cutting the waste at the lenge, lenge, and and th th ere ere is is a a need need for for not not on on ly ly efef fective fective rec rec ycli ycli ng ng but but cu cu tttt ing ing th th e e ww ast ast e e at at th th e e lenge, and there is a need for not only effective recycling but cutting the waste at the challenge, and there is a need for not only effective recycling but cutting the waste at the source. Therefore, further developments in plastic are still needed to keep the environ- source. Therefore, further developments in plastic are still needed to keep the environ- source. Therefore, further developments in plastic are still needed to keep the environ- source source . Th . Th ere ere fore, fore, furt furt her her develop develop men men ts ts in in plastic plastic are are still still ne ne eded eded to to keep keep th th e e env env iron- iron- source. Therefore, further developments in plastic are still needed to keep the environ- source. Therefore, further developments in plastic are still needed to keep the environment ment clean and to elongate the lifetime of plastic [7,8]. ment clean and to elongate the lifetime of plastic [7,8]. ment clean and to elongate the lifetime of plastic [7,8]. men men t clea t clea n and t n and t o elon o elon ga ga te the l te the l ifif etime etime of p of p las las tic tic [7, [7, 8]. 8]. ment clean and to elongate the lifetime of plastic [7,8]. clean and to elongate the lifetime of plastic [7,8]. Plastic contains polymeric chains that are based on carbon, hydrogen, and heteroa- Plastic contains polymeric chains that are based on carbon, hydrogen, and heteroa- Plastic contains polymeric chains that are based on carbon, hydrogen, and heteroa- Plastic contains polymeric chains that are based on carbon, hydrogen, and heteroa- Plastic contains polymeric chains that are based on carbon, hydrogen, and heteroa- Plastic contains polymeric chains that are based on carbon, hydrogen, and heteroa- Plastic contains polymeric chains that are based on carbon, hydrogen, and heteroatoms toms (e.g., sulfur, oxygen, or nitrogen). Polystyrene (PS), polypropylene (PP), polyeth- toms (e.g., sulfur, oxygen, or nitrogen). Polystyrene (PS), polypropylene (PP), polyeth- toms (e.g., sulfur, oxygen, or nitrogen). Polystyrene (PS), polypropylene (PP), polyeth- toms (e.g., sulfur, oxygen, or nitrogen). Polystyrene (PS), polypropylene (PP), polyeth- toms (e.g., sulfur, oxygen, or nitrogen). Polystyrene (PS), polypropylene (PP), polyeth- toms (e.g., (e.g., sulfur sulfu,r,oxygen, oxygen, or or nitr nitrog ogen). en). Polystyr Polystyrene ene (PS), (PS), polypr polypro opylene pylene (PP), (PP), polyethylene polyeth- ylene (PE), PVC, polyethylene terephthalate (PET), and polyurethane (PU) represent 75– ylene (PE), PVC, polyethylene terephthalate (PET), and polyurethane (PU) represent 75– ylene (PE), PVC, polyethylene terephthalate (PET), and polyurethane (PU) represent 75– ylyl ene ene (P (P EE ), ), P VC, PVC, po po lyet lyet hylene hylene terep terep ht ht halate halate (PE (PE T), T), an an d d po po lyly ur ur eth eth ane ane (PU) (PU) r epr repr esent esent 75 75 – – ylene (PE), PVC, polyethylene terephthalate (PET), and polyurethane (PU) represent 75– (PE), PVC, polyethylene terephthalate (PET), and polyurethane (PU) represent 75–80% 80% of Europe’s plastic consumption (Table 1) [9,10]. These polymers have either C–C or 80% of Europe’s plastic consumption (Table 1) [9,10]. These polymers have either C–C or 80% of Europe’s plastic consumption (Table 1) [9,10]. These polymers have either C–C or 80 80 %% o f oEurop f Europ e’s e’s pl pl as as titi c c co co nsump nsump tion tion (T (T abl abl e e 1) 1) [9,1 [9,1 0]0] . Th . Th ese ese po po lyly m m ers ers have have e ither either CC –C –C or or 80% of of Europ Europe’s e’s pl plastic astic co consumption nsumption (T (T abl able e 1) 1[ )9,1 [90] ,10 . ]. These These poly polymers mers have have either either C–CC–C or or C–heteroatom backbones, and their properties are highly dependent on the repeating C–heteroatom backbones, and their properties are highly dependent on the repeating C–heteroatom backbones, and their properties are highly dependent on the repeating CC –het –het eroato eroato m m backbon backbon es es , , an an d d th th eir eir pro pro pert pert ies ies ar ar e ehighly highly depen depen dent dent on on th th e e repeating repeating C–het C–heter eroatom oatom backbon backbones, es, and and theirtheir propert properties ies are highly are high depen ly dependent dent on th on e repeating the repeating units [11]. units [11]. units [11]. uni uni ts ts [11]. [11]. units [11]. units [11]. Table 1. The most common plastics and their European demand [10]. Table 1. The most common plastics and their European demand [10]. Table 1. The most common plastics and their European demand [10]. Table 1. The most common plastics and their European demand [10]. Table 1. The most common plastics and their European demand [10]. Table 1. The most common plastics and their European demand [10]. Table 1. The most common plastics and their European demand [10]. European Demand European Demand European Demand European Demand European Demand Plastic (Repeating Unit) Name Plastic (Repeating Unit) Name Plastic (Repeating Unit) Name Europ European ean Dem Demand and (%) Plastic (Repeating Unit) Name Plastic (Repeating Unit) Name Plastic (Repeating Unit) Name (%) (%) Plastic (Repeating Unit) Name (%) (%) (%) (%) PE 29.6 PE 29.6 PE 29.6 PE 29.6 PE PE 29.6 29.6 PE 29.6 C–C Backbone PP 19.9 PP PP 19.919.9 PP 19.9 PP 19.9 PP 19.9 PP 19.9 C–C Backbone C–C Backbone C–C Backbone PS 7.1 C–C Backbone PS 7.1 C–C Backbone PS PS 7.1 7.1 C–C Backbone PS 7.1 PS 7.1 PS 7.1 PVC 10.4 PVC 10.4 PVC 10.4 PV PVC C 10.4 10.4 PVC 10.4 PVC 10.4 PET 6.9 PET 6.9 PET 6.9 PET 6.9 Heteroatoms in PET PET 6.96.9 Heteroatoms in back- Heteroatoms in back- PET 6.9 Heteroatoms in back- Hetero Hetero atom atom s s in ba in ba ck- ck- Heteroatoms in back- backbone bone bone bone bone bone bone PU 7.4 PU 7.4 PU 7.4 PU 7.4 PU 7.4 PU PU 7.4 7.4 Plastics are highly involved in our daily lives, from household items to very complex Plastics are highly involved in our daily lives, from household items to very complex Plastics are highly involved in our daily lives, from household items to very complex Plastics Plastics ar ar e e hi h ghly ighly involved involved in in our our dd aily aily li ves lives , from , from ho ho usehold usehold items items to to very very com com pl pl ex e x Plastics are highly involved in our daily lives, from household items to very complex medical equipment. They are used in construction materials (e.g., windows, panels, glaz- medical equipment. They are used in construction materials (e.g., windows, panels, glaz- Plastics are highly involved in our daily lives, from household items to very complex medical equipment. They are used in construction materials (e.g., windows, panels, glaz- medica medica l e l q euip quip men men t. Th t. Th ey ey ar ar e e use use d i d i n co n co nstruct nstruct ion m ion m aterial aterial s s (e. (e. g., w g., w indows, indows, pa pa nels, g nels, g laz- laz- medical equipment. They are used in construction materials (e.g., windows, panels, glaz- ing, coatings, siding, roofing, flooring, fencing, and decoration), furniture, offices, agricul- ing, co medical atings, equipment. siding, roofi They ng, fl ar oo e ring used , fe inncing, constr and uction dematerials coration), (e.g., furniture, windows, offices panels, , agricul- glazing, ing, coatings, siding, roofing, flooring, fencing, and decoration), furniture, offices, agricul- ing, coatings, siding, roofing, flooring, fencing, and decoration), furniture, offices, agricul- ing, coatings, siding, roofing, flooring, fencing, and decoration), furniture, offices, agricul- ing, coatings, siding, roofing, flooring, fencing, and decoration), furniture, offices, agricul- ture (e.g., mulch film, materials for greenhouses, and production of sacks), transportation ture (e.g., mulch film, materials for greenhouses, and production of sacks), transportation coatings, siding, roofing, flooring, fencing, and decoration), furniture, offices, agriculture ture (e.g., mulch film, materials for greenhouses, and production of sacks), transportation ture (e.g., mulch film, materials for greenhouses, and production of sacks), transportation ture (e.g., mulch film, materials for greenhouses, and production of sacks), transportation ture (e.g., mulch film, materials for greenhouses, and production of sacks), transportation (e.g., bodywork and production of protective coatings), flame and smoke retardants (high (e.g., bodywork and production of protective coatings), flame and smoke retardants (high (e.g., mulch film, materials for greenhouses, and production of sacks), transportation (e.g., (e.g., bodywork and production of protective coatings), flame and smoke retardants (high (e. (e. g., g., bo bo dywo dywo rk rk and and pro pro du du ctct ion ion of of pro pro tete ctct ive ive coat coat ings), ings), flame flame an an d d smo smo ke ke ret ret ar ar dd an an ts ts (h (h igig h h (e.g., bodywork and production of protective coatings), flame and smoke retardants (high content of chlorine; 57% by weight), insulators, and others [6]. Polycarbonate plastic has conten bodywork t of chlorine; and pr 57 oduction % by weight), of protective insulato coatings), rs, and ot flame hers and [6]. smoke Polycarbonate retardants plast (high ic has content content of chlorine; 57% by weight), insulators, and others [6]. Polycarbonate plastic has con con ten ten t t of of chlorine; chlorine; 57 57 % % by by weight), weight), ins ins ula ula to to rsrs , and , and ot ot hers hers [6]. [6]. Pol Pol ycarbonate ycarbonate pl pl ast ast ic ic has has content of chlorine; 57% by weight), insulators, and others [6]. Polycarbonate plastic has a low thermal conductivity (k) and, therefore, is better than conventional glazing agents a low of th chlorine; ermal con 57% duct by ivit weight), y (k) and insulators, , thereforeand , is bet others ter th [6 an ]. con Polycarbon ventionaate l gla plastic zing agen has ts a low a low thermal conductivity (k) and, therefore, is better than conventional glazing agents a a low low th th erma erma l con l con dd uu ctct ivit ivit y y (k) (k) and and , th , th erefore erefore , i,s is bet bet ter ter th th an an con con ve ve nt nt iona iona l gla l gla zizi ng ng agen agen tsts a low thermal conductivity (k) and, therefore, is better than conventional glazing agents [12]. The demand for plastic has extensively increased due to its unique mechanical and thermal conductivity (k) and, therefore, is better than conventional glazing agents [12]. The [12]. The demand for plastic has extensively increased due to its unique mechanical and [12]. The demand for plastic has extensively increased due to its unique mechanical and [12]. [12]. Th Th e e de de mand mand for for pl pl ast ast ic ic has has ext ext en en sisi vel vel y y incre incre ased ased dd ue ue to to its its unique unique mec mec hani hani cal cal and and [12]. The demand for plastic has extensively increased due to its unique mechanical and physical properties (e.g., light weight, strength, resistance to corrosion and chemicals) and physi demand cal propert fories plastic (e.g.,has lighextensively t weight, strengt increased h, residue stanto ce to its corros unique ion mechanical and chemicals) and physical and physical properties (e.g., light weight, strength, resistance to corrosion and chemicals) and physical properties (e.g., light weight, strength, resistance to corrosion and chemicals) and physical properties (e.g., light weight, strength, resistance to corrosion and chemicals) and physical properties (e.g., light weight, strength, resistance to corrosion and chemicals) and low m pranuf operties acturi (e.g., ng co light st. Inweight, addition, str th ength, e shape resistance and prop to erties corr osion of plas and tics c chemicals) an be manipu and - low low manufacturing cost. In addition, the shape and properties of plastics can be manipu- low manufacturing cost. In addition, the shape and properties of plastics can be manipu- low manufacturing cost. In addition, the shape and properties of plastics can be manipu- low manufacturing cost. In addition, the shape and properties of plastics can be manipu- low manufacturing cost. In addition, the shape and properties of plastics can be manipu- lated manufacturing based on the appli cost. c In ation. addition, Howev the er, shape UV rand adiati pron operties has a of neg plative asticsecan ffect be on manipulated plastic lated based on the application. However, UV radiation has a negative effect on plastic lated based on the application. However, UV radiation has a negative effect on plastic lala ted ted bas bas ed ed o n on th th e e appli appli cat cat ion. ion. Howev Howev er, er, UU V V radiati radiati on on has has a a neg neg ative ative eff eff ect ect o n on pla pla stst ic ic lated based on the application. However, UV radiation has a negative effect on plastic based on the application. However, UV radiation has a negative effect on plastic (e.g., rigid PVC) lifetime and leads to the loss of its strength. The solar irradiation of PVC causes discoloration and the emission of toxic volatiles, which hinders its use in outdoor Polymers 2022, 14, x FOR PEER REVIEW 3 of 18 Polymers 2022, 14, 20 3 of 16 (e.g., rigid PVC) lifetime and leads to the loss of its strength. The solar irradiation of PVC causes discoloration and the emission of toxic volatiles, which hinders its use in outdoor applications [13]. PVC is still used as a construction material, but it can be replaced by applications [13]. PVC is still used as a construction material, but it can be replaced by polyolefins, which are less harmful but cost more. polyolefins, which are less harmful but cost more. The degradation of plastics is of major concern from an environmental perspective The degradation of plastics is of major concern from an environmental perspective in terms of potential hazards to living organisms. The degradation of plastics takes place in terms of potential hazards to living organisms. The degradation of plastics takes place under either abiotic or biotic (e.g., biodegradation) conditions [14]. Biodegradation is under either abiotic or biotic (e.g., biodegradation) conditions [14]. Biodegradation is highly dependent on environmental factors, which vary based on the type of polymer. highly dependent on environmental factors, which vary based on the type of polymer. Color changes and the crazing of plastic are early signs of degradation, followed by sur- Color changes and the crazing of plastic are early signs of degradation, followed by surface face cracking and the formation of small fragments [15]. Floating plastics in seas and cracking and the formation of small fragments [15]. Floating plastics in seas and oceans are oceans are moderately affected by temperatures, solar radiation, and oxygen through pho- moderately affected by temperatures, solar radiation, and oxygen through photoinitiated toinitiated oxidative degradation. For abiotic degradation, the contributing factors are oxidative degradation. For abiotic degradation, the contributing factors are sunlight and sunlight and oxygen, and they affect the plastic through a hydrolysis process [16]. oxygen, and they affect the plastic through a hydrolysis process [16]. Three steps (initiation, propagation, and termination) are involved in plastic degra- Three steps (initiation, propagation, and termination) are involved in plastic degra- dation [17]. The first step is initiated through solar or thermal initiators and leads to the dation [17]. The first step is initiated through solar or thermal initiators and leads to the formation of free radicals. Photoinitiation is not likely for both PE and PP, since they do formation of free radicals. Photoinitiation is not likely for both PE and PP, since they do not not have unsaturated chromophores in their skeletons that are responsible for the absorp- have unsaturated chromophores in their skeletons that are responsible for the absorption tion of light [18]. Impurities or abnormalities within plastics allow for the production of of light [18]. Impurities or abnormalities within plastics allow for the production of free free radicals leading to C–H bonds cleavage in the backbone of polymers [19,20]. In the radicals leading to C–H bonds cleavage in the backbone of polymers [19,20]. In the pres- presence of oxygen, free radicals produce peroxy reactive moieties in the propagation ence of oxygen, free radicals produce peroxy reactive moieties in the propagation step. In step. In addition, hydroperoxides can be produced, leading to the autoxidation of poly- addition, hydroperoxides can be produced, leading to the autoxidation of polymers [21]. In mers [21]. In the propagation step, crosslinking or chain scission takes place [22]. The de- the propagation step, crosslinking or chain scission takes place [22]. The deactivation of activation of free radicals occurs in the termination step, leading to stable products. In the free radicals occurs in the termination step, leading to stable products. In the presence of presence oxygen, the of o formation xygen, the offor oxygen-containing mation of oxygen moieties -containi is ng expected, moietieswhich is expect leads ed, to whic a photoini- h leads to a photoinitiated degradation process. The chain scission and crosslinking (termination) tiated degradation process. The chain scission and crosslinking (termination) of oxygenated of species oxygen leads ated to specie the formation s leads toof tholefins e formation (unsaturated of olefins polymeric (unsaturated chains), poly aldehydes, meric chains and ), al ketones dehyde (Figur s, and ketones e 1) [23]. (Figure 1) [23]. Figure 1. Abiotic degradation pathways for PE (R = H), PP (R = Me), and PS (R = Ph). Figure 1. Abiotic degradation pathways for PE (R = H), PP (R = Me), and PS (R = Ph). Plastic natural degradation is initiated through photodegradation followed by Plastic natural degradation is initiated through photodegradation followed by thermo- thermo-oxidative degradation [24]. Sun UV light provides the energy needed to initiate oxidative degradation [24]. Sun UV light provides the energy needed to initiate the incor- the incorporation of oxygen into the polymeric chains [25]. Plastics are degraded to small poration of oxygen into the polymeric chains [25]. Plastics are degraded to small polymeric po fragments, lymeric fra and gment then s, metabolized and then metby abolized microor by ganisms microorga in n the isms in surrounding the surroun envir ding onment. envi- ronm Microor entganisms . Microorgan tendis to ms convent tend to the con polymeric vent the po chain lymeric carbons chain to ceither arbons carbon to eithe dioxide r carbo or n biomolecules [26,27]. However, such a process is very slow (taking up to 50 years) for the dioxide or biomolecules [26,27]. However, such a process is very slow (taking up to 50 complete degradation of plastics [28]. Chromophores present within the skeleton of poly- mers absorb visible or UV light, and therefore initiate the photodegradation process [29,30]. Polymers 2022, 14, x FOR PEER REVIEW 4 of 18 years) for the complete degradation of plastics [28]. Chromophores present within the Polymers 2022, 14, 20 4 of 16 skeleton of polymers absorb visible or UV light, and therefore initiate the photodegrada- tion process [29,30]. Photodegradation takes place either in the presence of oxygen (e.g., photooxidation) or in its absence (e.g., chain crosslinking or bond breaking). When poly- Photodegradation takes place either in the presence of oxygen (e.g., photooxidation) or in mers (e.g., polyolefins) are exposed to heat, UV light, or mechanical stress in the presence its absence (e.g., chain crosslinking or bond breaking). When polymers (e.g., polyolefins) of oxygen, they produce free radicals that initiate the oxidation process. Therefore, plastics are exposed to heat, UV light, or mechanical stress in the presence of oxygen, they produce should be stabilized to inhibit the oxidative processes to increase the half-life time of ma- free radicals that initiate the oxidation process. Therefore, plastics should be stabilized to terials [31]. inhibit the oxidative processes to increase the half-life time of materials [31]. Plastic weathering involves changes in the physical, mechanical, and chemical prop- Plastic weathering involves changes in the physical, mechanical, and chemical proper- erties of polymers, particularly at the surface [32]. Solar energy, moisture (e.g., rain, snow, ties of polymers, particularly at the surface [32]. Solar energy, moisture (e.g., rain, snow, or or humidity), oxidants (e.g., ozone or atomic or singlet oxygen), and air pollutants (e.g., humidity), oxidants (e.g., ozone or atomic or singlet oxygen), and air pollutants (e.g., sulfur sulfur dioxide, nitrogen oxides, or polycyclic hydrocarbons) are responsible for these dioxide, nitrogen oxides, or polycyclic hydrocarbons) are responsible for these changes [33]. changes [33]. Uneven discoloration, surface cracks, or loss of strength are the most com- Uneven discoloration, surface cracks, or loss of strength are the most common changes mon changes within plastics due to degradation [34]. Climate change and the rise in global within plastics due to degradation [34]. Climate change and the rise in global temperatures temperatures accelerate polymers’ weathering, and impurities (e.g., traces of metals or accelerate polymers’ weathering, and impurities (e.g., traces of metals or oxidants) present oxidants) present in additives increase the rate of photodegradation [35]. in additives increase the rate of photodegradation [35]. PVC is a synthetic plastic that is similar to PP, but the backbone carbons are attached PVC is a synthetic plastic that is similar to PP, but the backbone carbons are attached to chlorine atoms instead of hydrogens. PVC is one of the most common manufactured to chlorine atoms instead of hydrogens. PVC is one of the most common manufactured plastics [36]. Due to the high content of chlorine, PVC is hard and stiff. In addition, PVC plastics [36]. Due to the high content of chlorine, PVC is hard and stiff. In addition, PVC is is polar due to the presence of C–Cl bonds and is soluble in many solvents, particularly polar due to the presence of C–Cl bonds and is soluble in many solvents, particularly those those containing polar atoms such as ethers (e.g., dioxane, tetrahydrofuran, ketones, or containing polar atoms such as ethers (e.g., dioxane, tetrahydrofuran, ketones, or nitroben- nitrobenzene). It has a low cost, is durable, has excellent performance, is easily molded, zene). It has a low cost, is durable, has excellent performance, is easily molded, and can be and can be obtained in different shapes that are suitable for many applications. PVC is obtained in different shapes that are suitable for many applications. PVC is commonly used commonly used in packaging, health care devices, toys, construction materials, electrical in packaging, health care devices, toys, construction materials, electrical wire insulation, wire insulation, clothes, and furnishing [5,6]. For outdoor applications, PVC photostabil- clothes, and furnishing [5,6]. For outdoor applications, PVC photostability should be ity should be enhanced through the addition of suitable additives to inhibit its photodeg- enhanced through the addition of suitable additives to inhibit its photodegradation. The radation. The dechlorination of PVC is autocatalytic, which leads to the formation of – dechlorination of PVC is autocatalytic, which leads to the formation of –C=C–. The forma- C=C–. The formation of unsaturated double bonds within the backbone of PVC leads to tion of unsaturated double bonds within the backbone of PVC leads to its photodegradation, its photodegradation, in which small fragments and polyene residues are produced (Fig- in which small fragments and polyene residues are produced (Figure 2) [37]. ure 2) [37]. Figure 2. Dechlorination of PVC and formation of polyene polymeric chains. Figure 2. Dechlorination of PVC and formation of polyene polymeric chains. Plastic recycling has received attention recently due to the large volume of waste that Plastic recycling has received attention recently due to the large volume of waste it generates [38]. Pyrolysis and incineration of PVC are not recommended due to the high that it generates [38]. Pyrolysis and incineration of PVC are not recommended due to level of hydrogen chloride (HCl) and other toxic volatiles produced [39]. The most com- the high level of hydrogen chloride (HCl) and other toxic volatiles produced [39]. The mon methods for PVC recycling include chemical and mechanical techniques. Mechanical most common methods for PVC recycling include chemical and mechanical techniques. recycling is preferred when the PVC waste composition is known [40]. On the other hand, Mechanical recycling is preferred when the PVC waste composition is known [40]. On the the chemical recycling of PVC converts plastics back to chemicals that can be reused in other hand, the chemical recycling of PVC converts plastics back to chemicals that can be the polymerization process. The development of techniques and instrumentation for the reused in the polymerization process. The development of techniques and instrumentation separation of PVC from the waste stream is still important to allow for the recovery of for the separation of PVC from the waste stream is still important to allow for the recovery most wasted PVC. of most wasted PVC. Recently, our research was directed towards investigating the use of newly synthe- Recently, our research was directed towards investigating the use of newly synthesized sized aromatic compounds and those that include organometallics as potential UV ab- aromatic compounds and those that include organometallics as potential UV absorbers. We sorbers. We made some progress in this field, which is reported in the current work. made some progress in this field, which is reported in the current work. 2. Photostabilization of Polymers 2. Photostabilization of Polymers The photostabilization of polymers has received much attention recently, in order to The photostabilization of polymers has received much attention recently, in order to find efficient methods to inhibit their photochemical degradation. Additives are added to find efficient methods to inhibit their photochemical degradation. Additives are added polymers to improve their performance and mechanical and thermal properties [41]. The to polymers to improve their performance and mechanical and thermal properties [41]. The additives act as stabilizers, fillers, plasticizers, softeners, lubricants, colorants, flame retardants, blowing agents, crosslinking agents, and UV absorbers. UV stabilizers are capable of reducing the rate of photooxidation of polymeric materials [42]. Various pa- rameters such as color, stability, compatibility, volatility, and cost should be taken into Polymers 2022, 14, x FOR PEER REVIEW 5 of 18 Polymers 2022, 14, 20 5 of 16 additives act as stabilizers, fillers, plasticizers, softeners, lubricants, colorants, flame re- tardants, blowing agents, crosslinking agents, and UV absorbers. UV stabilizers are capa- consideration in the ble of selection reducinof g th additives. e rate of pThe hotoox additives idation of should polymer be i capable c materiof als absorbing [42]. Various theparameters such as color, stability, compatibility, volatility, and cost should be taken into considera- harmful UV radiation and dissipating the energy as heat over time at a harmless rate to the tion in the selection of additives. The additives should be capable of absorbing the harmful polymers. Some polymers, such as polymethyl methacrylate and polytetrafluoroethylene UV radiation and dissipating the energy as heat over time at a harmless rate to the poly- are highly stable and do not require the addition of photostabilizers for outdoor applica- mers. Some polymers, such as polymethyl methacrylate and polytetrafluoroethylene are tions. Moderately photostable polymers, such as polyvinyl fluoride and polyvinylidene highly stable and do not require the addition of photostabilizers for outdoor applications. fluoride have a lifetime of a few years in outdoor applications and can be used without the Moderately photostable polymers, such as polyvinyl fluoride and polyvinylidene fluoride addition of photostabilizers. On the other hand, poorly stable polymers such as PVC, PS, have a lifetime of a few years in outdoor applications and can be used without the addition and polyamides have a short lifetime (less than a year), and therefore require the use of UV of photostabilizers. On the other hand, poorly stable polymers such as PVC, PS, and pol- stabilizers for outdoor use [43,44]. The polymer additives act as UV screeners, excited state yamides have a short lifetime (less than a year), and therefore require the use of UV sta- deactivators, hydroperoxide decomposers, and radical scavengers [45]. bilizers for outdoor use [43,44]. The polymer additives act as UV screeners, excited state In the case of PVC, the dipoles along the polymer chain, due to the presence of chlorine deactivators, hydroperoxide decomposers, and radical scavengers [45]. atoms, lead to a high level of secondary valency forces, and therefore reduce chain flexibility. In the case of PVC, the dipoles along the polymer chain, due to the presence of chlo- The van der Waals force within PVC chains is insignificant in cohesion due to the relative rine atoms, lead to a high level of secondary valency forces, and therefore reduce chain bulkiness of the chlorine atoms. The polarized groups within plasticizers bound to polymer flexibility. The van der Waals force within PVC chains is insignificant in cohesion due to dipoles and the non-polar moiety act as shields between polymer dipoles. Therefore, a the relative bulkiness of the chlorine atoms. The polarized groups within plasticizers reduction in dipole bonding between polymer chains, less overall cohesion, and an increase bound to polymer dipoles and the non-polar moiety act as shields between polymer di- in the flexibility of movement are observed [46]. The incorporation of a low concentration poles. Therefore, a reduction in dipole bonding between polymer chains, less overall co- of plasticizers can hesion, lead and to flexible an increase products in the flexi butbility increases of movem the ent stif ar fness e observed at the [46]. same Th time. e incorporation The addition of plasticizers of a low conin cen atration low concentration of plasticizers leads can leto adan to incr flexib ease le pro ind the ucts crystallinity but increases the stiff- ness at the same time. The addition of plasticizers in a low concentration leads to an in- level of the polymers [47]. Therefore, it appears that plasticized PVC has a degree of crease in the crystallinity level of the polymers [47]. Therefore, it appears that plasticized microcrystalline structure. PVC shows solvated regions, which are flexible due to the PVC has a degree of microcrystalline structure. PVC shows solvated regions, which are presence of a plasticizer and non-solvated crystalline areas. The PVC crystallite network flexible due to the presence of a plasticizer and non-solvated crystalline areas. The PVC structure has an impact on the toughness and strength and is responsible for the variation crystallite network structure has an impact on the toughness and strength and is respon- of PVC properties [48,49]. sible for the variation of PVC properties [48,49]. 3. Photostabilization of Polymers Using UV Absorbers 3. Photostabilization of Polymers Using UV Absorbers UV absorbers play an important role in absorbing harmful radiation from light and UV absorbers play an important role in absorbing harmful radiation from light and dissipating it as harmless thermal energy [50–52]. In addition, they block the formation dissipating it as harmless thermal energy [50–52]. In addition, they block the formation of of free radicals that are produced at the early stages of degradation. The most common free radicals that are produced at the early stages of degradation. The most common in- industrial UV absorbers are titanium oxide, carbon black, benzophenones, and triazoles dustrial UV absorbers are titanium oxide, carbon black, benzophenones, and triazoles (e.g., hydroxylbenzophenone and hydroxyphenylbenzotriazole), while the most common (e.g., hydroxylbenzophenone and hydroxyphenylbenzotriazole), while the most common additives used recently for research include Schiff bases and organometallic complexes additives used recently for research include Schiff bases and organometallic complexes (Figure 3). (Figure 3). Figure 3. Structures of some common UV absorbers. Figure 3. Structures of some common UV absorbers. These additives have unique UV absorbance characteristics. For example, benzophe- These additives have unique UV absorbance characteristics. For example, benzophenone none-containing additives absorb UV strongly in the short-wavelength region through a -containing additives absorb UV strongly in the short-wavelength region through a proton proton transfer or tautomeric structure equilibrium (Figure 4). They are more efficient transfer or tautomeric structure equilibrium (Figure 4). They are more efficient compared compared with the additives containing benzotriazole. Benzophenone-based UV absorb- Polymers 2022, 14, x FOR PEER REVIEW wit h the additives containing benzotriazole. Benzophenone-based UV absorbers ha 6v of e u 18 n ique ers have unique properties such as a low cost, low toxicity, and good resistance to water properties such as a low cost, low toxicity, and good resistance to water and acids [53]. and acids [53]. Figure 4. Hydroxybenzophenones energy dissipation through a proton transfer. Figure 4. Hydroxybenzophenones energy dissipation through a proton transfer. −1 –1 Triazoles have high molar extinction coefficients (5 × 106 cm M ) and absorb the most destructive wavelength of light (280–370 nm), which is highly involved in polymer degradation. The excitation of benzotriazoles takes place once the UV light is absorbed; the benzotriazoles then dissipate the energy through either heat release, involving a hy- drogen transfer, or fluorescence emission [54]. In addition, UV absorbers act as quenchers (Q) for the triplet excited state of the polymer chromophoric group (P *), followed by the release of energy as harmless heat (Figure 5) [55]. Similarly, metal complexes act as effec- tive UV quenchers due to their low excitation coefficients and quench the triplet state of the carbonyl groups in polyolefins [56–58]. Figure 5. UV absorbers act as quenchers for the excited state energy of polymers. * Represents the excited state. Recently, we synthesized a range of UV stabilizers (e.g., aromatics, heterocycles, Schiff bases, organometallic complexes, and polyphosphates) and tested their efficiency for the stabilization of polymers [59–94]. These additives, at a low concentration of 0.5% by weight, led to a significant improvement in the photostability of polymers. The stabi- lization effect that the UV absorbers induced in polymers was examined using infrared spectroscopy, the determination of weight and molecular weight, and inspection of the surface of polymers. 4. Morphological Study of the Surface of Irradiated Polymers in the Presence of Additives An investigation of the surface morphology of polymers can provide important in- formation about the damage that takes place due to weathering and the changes in parti- cles’ size and shape. Scanning electron microscopy (SEM) and field-emission scanning electron microscopy (FESEM) are used to provide information about distortion, variation on the surface, the shape and size of particles, and homogeneity [95–99]. The irradiated polymers show the presence of cracks, holes, lumps, spots, and amorphous and irregular surfaces. These changes are mainly due to dehydrochlorination, chain scission, and cross- linking. However, the damage on the surface of polymers was limited in the presence of UV absorbers compared with the blank polymers. In some cases, the irradiated films con- taining additives showed the interesting changes that took place on the surface [100–104]. For example, the SEM image of the surface of the irradiated PVC film blended with a polyphosphate containing benzidine at 25 °C, showing the formation of hexagonal pores (Figure 6) with a honeycomb-like structure, which do not appear within the blank irradi- ated material [74]. Increasing the irradiation time by up to 300 h led to an increase in the number of hexagonal pores. The reasons for the formation of such a structure are not clear, but it could be a result of the elimination of HCl at a low rate and its scavenging by the Sn complex. Crosslinked materials could produce honeycomb-like structures as a result of water stabilization [105–110]. For example, the irradiation of a thin film of crosslinked polystyrene, at 25 °C for 6 h, produced a honeycomb-like structure [106]. The irradiation of polyacrylic glycidyl ether for a short duration led to the formation of a honeycomb film Polymers 2022, 14, x FOR PEER REVIEW 6 of 18 Figure 4. Hydroxybenzophenones energy dissipation through a proton transfer. −1 –1 Triazoles have high molar extinction coefficients (5 × 106 cm M ) and absorb the most destructive wavelength of light (280–370 nm), which is highly involved in polymer Polymers 2022, 14, 20 6 of 16 degradation. The excitation of benzotriazoles takes place once the UV light is absorbed; the benzotriazoles then dissipate the energy through either heat release, involving a hy- 6 1 1 Triazoles have high molar extinction coefficients (5  10 cm M ) and absorb the most destructive wavelength of light (280–370 nm), which is highly involved in polymer drogen transfer, or fluorescence emission [54]. In addition, UV absorbers act as quenchers degradation. The excitation of benzotriazoles takes place once the UV light is absorbed; the (Q) for the triplet excited state of the polymer chromophoric group (P *), followed by the benzotriazoles then dissipate the energy through either heat release, involving a hydrogen transfer, or fluorescence emission [54]. In addition, UV absorbers act as quenchers (Q) release of energy as harmless heat (Figure 5) [55]. Similarly, metal complexes act as effec- for the triplet excited state of the polymer chromophoric group (P *), followed by the tive UV quenchers due to their low excitation coefficients and quench the triplet state of release of energy as harmless heat (Figure 5) [55]. Similarly, metal complexes act as effective UV quenchers due to their low excitation coefficients and quench the triplet state of the the carbonyl groups in polyolefins [56–58]. carbonyl groups in polyolefins [56–58]. Figure 5. UV absorbers act as quenchers for the excited state energy of polymers. * Represents the Figure 5. UV absorbers act as quenchers for the excited state energy of polymers. * Represents the excited state. excited state. Recently, we synthesized a range of UV stabilizers (e.g., aromatics, heterocycles, Schiff bases, organometallic complexes, and polyphosphates) and tested their efficiency for the stabilization of polymers [59–94]. These additives, at a low concentration of Recently, we synthesized a range of UV stabilizers (e.g., aromatics, heterocycles, 0.5% by weight, led to a significant improvement in the photostability of polymers. The Schiff bases, organometallic complexes, and polyphosphates) and tested their efficiency stabilization effect that the UV absorbers induced in polymers was examined using infrared spectroscopy, the determination of weight and molecular weight, and inspection for the stabilization of polymers [59–94]. These additives, at a low concentration of 0.5% of the surface of polymers. by weight, led to a significant improvement in the photostability of polymers. The stabi- 4. Morphological Study of the Surface of Irradiated Polymers in the Presence lization effect that the UV absorbers induced in polymers was examined using infrared of Additives An investigation of the surface morphology of polymers can provide important spectroscopy, the determination of weight and molecular weight, and inspection of the information about the damage that takes place due to weathering and the changes surface of polymers. in particles’ size and shape. Scanning electron microscopy (SEM) and field-emission scanning electron microscopy (FESEM) are used to provide information about distortion, variation on the surface, the shape and size of particles, and homogeneity [95–99]. The 4. Morphological Study of the Surface of Irradiated Polymers in the Presence of irradiated polymers show the presence of cracks, holes, lumps, spots, and amorphous and irregular surfaces. These changes are mainly due to dehydrochlorination, chain Additives scission, and crosslinking. However, the damage on the surface of polymers was limited in the presence of UV absorbers compared with the blank polymers. In some cases, the An investigation of the surface morphology of polymers can provide important in- irradiated films containing additives showed the interesting changes that took place formation about the damage that takes place due to weathering and the changes in parti- on the surface [100–104]. For example, the SEM image of the surface of the irradiated PVC film blended with a polyphosphate containing benzidine at 25 C, showing the cles’ size and shape. Scanning electron microscopy (SEM) and field-emission scanning formation of hexagonal pores (Figure 6) with a honeycomb-like structure, which do not appear within the blank irradiated material [74]. Increasing the irradiation time by up to electron microscopy (FESEM) are used to provide information about distortion, variation 300 h led to an increase in the number of hexagonal pores. The reasons for the formation on the surface, the shape and size of particles, and homogeneity [95–99]. The irradiated of such a structure are not clear, but it could be a result of the elimination of HCl at a low rate and its scavenging by the Sn complex. Crosslinked materials could produce polymers show the presence of cracks, holes, lumps, spots, and amorphous and irregular honeycomb-like structures as a result of water stabilization [105–110]. For example, surfaces. These changes are mainly due to dehydrochlorination, chain scission, and cross- the irradiation of a thin film of crosslinked polystyrene, at 25 C for 6 h, produced a honeycomb-like structure [106]. The irradiation of polyacrylic glycidyl ether for a short linking. However, the damage on the surface of polymers was limited in the presence of duration led to the formation of a honeycomb film [107]. Similarly, the SEM image o UV f the absorbers irradiated PVC com film cpared ontainingwi a 4th -me th thoe xybla benznk oic apo cid-ly Snmers comple. xIn shos w om ed ae cases, the irradiated films con- honeycomb-like structure (Figure 7) [95]. taining additives showed the interesting changes that took place on the surface [100–104]. For example, the SEM image of the surface of the irradiated PVC film blended with a polyphosphate containing benzidine at 25 °C, showing the formation of hexagonal pores (Figure 6) with a honeycomb-like structure, which do not appear within the blank irradi- ated material [74]. Increasing the irradiation time by up to 300 h led to an increase in the number of hexagonal pores. The reasons for the formation of such a structure are not clear, but it could be a result of the elimination of HCl at a low rate and its scavenging by the Sn complex. Crosslinked materials could produce honeycomb-like structures as a result of water stabilization [105–110]. For example, the irradiation of a thin film of crosslinked polystyrene, at 25 °C for 6 h, produced a honeycomb-like structure [106]. The irradiation of polyacrylic glycidyl ether for a short duration led to the formation of a honeycomb film Polymers 2022, 14, x FOR PEER REVIEW 7 of 18 Polymers 2022, 14, 20 7 of 16 [107]. Similarly, the SEM image of the irradiated PVC film containing a 4-methoxybenzoic acid-Sn complex showed a honeycomb-like structure (Figure 7) [95]. Figure 6. SEM image of the surface of an irradiated PVC film blended with a polyphosphate con- Polymers 2022, 14, x FOR PEER REVIEW 8 of 18 Figure 6. SEM image of the surface of an irradiated PVC film blended with a polyphosphate taining a benzidine moiety. containing a benzidine moiety. Figure 7. SEM image of the surface of an irradiated PVC film blended with a 4-methoxybenzoic Figure 7. SEM image of the surface of an irradiated PVC film blended with a 4-methoxybenzoic acid-Sn complex. acid-Sn complex. The irradiated PVC film, blended with a Schiff base and containing a thiadiazole moi- ety in the presence of nickel chloride, showed the presence of hexagonal pores on the sur- face (Figure 8) [72]. The presence of nickel ions is necessary to produce the honeycomb- like structure and to enhance the photostability of the polymeric materials [111]. The struc- ture of the irradiated film was highly porous with a large surface area, possibly due to the incorporation of nickel ions within the polymer. The formation of a honeycomb structure depends on the type of solvent used during the fabrication process of the film, the length of the side-chain within the polymer, and the concentration of the polymer [112]. Polymers 2022, 14, 20 8 of 16 The irradiated PVC film, blended with a Schiff base and containing a thiadiazole moiety in the presence of nickel chloride, showed the presence of hexagonal pores on the surface (Figure 8) [72]. The presence of nickel ions is necessary to produce the honeycomb- like structure and to enhance the photostability of the polymeric materials [111]. The structure of the irradiated film was highly porous with a large surface area, possibly due to the incorporation of nickel ions within the polymer. The formation of a honeycomb Polymers 2022, 14, x FOR PEER REVIEW 9 of 18 structure depends on the type of solvent used during the fabrication process of the film, the length of the side-chain within the polymer, and the concentration of the polymer [112]. Figure 8. SEM image of the surface of an irradiated PVC film blended with a Schiff base containing Figure 8. SEM image of the surface of an irradiated PVC film blended with a Schiff base containing a a thiadiazole moiety in the presence of nickel chloride. thiadiazole moiety in the presence of nickel chloride. The SEM image of the surface of an irradiated PVC film, blended with a melamine- The SEM image of the surface of an irradiated PVC film, blended with a melamine- Schiff base (Figure 9), showed ice-cube-like particles [75]. Meanwhile, the FESEM image Schiff base (Figure 9), showed ice-cube-like particles [75]. Meanwhile, the FESEM image of the of surface the surfac of e anof irradiated an irradPVC iated film, PVC blended film, blended with a trimethoprim-Sn with a trimethop complex, rim-Sn cshowed omplex, rshowed od-like parti rod-lcles ike pa (Figur rticle es 10 (Fi ) g [93 ure ]. 10) It is [93]. believed It is bel that ieve the d th cr at osslinking the crosslink and ing elimination and elimin of a- tion of volatiles and hydrogen chloride at a slow rate are the reasons for the formation of volatiles and hydrogen chloride at a slow rate are the reasons for the formation of the particles the particl that es t have hat have such sshapes uch sha [pe 113 s ,[11 1143,1 ]. 14]. 0 0 The The PS PS film film blended blended with witha a Schif Schiff f base base of of biphenyl-3,3 biphenyl-3,3′,4,4 ,4,4′-tetraamine -tetraamine showed showed spher spher-- ical and embedded ellipsoid pores that have a diameter from 3.4 to 4.3 m (Figure 11) ical and embedded ellipsoid pores that have a diameter from 3.4 to 4.3 µ m (Figure 11) after irradiation [73]. The formation of ball-like pores may be a result of the effective light after irradiation [73]. The formation of ball-like pores may be a result of the effective light absorption and porous structure of UV absorbers. absorption and porous structure of UV absorbers. For comparison, Figures 12 and 13 show the SEM images of the blank PVC and PS For comparison, Figures 12 and 13 show the SEM images of the blank PVC and PS films, respectively, in the absence of any additives after irradiation. films, respectively, in the absence of any additives after irradiation. Polymers 2022, 14, x FOR PEER REVIEW 10 of 18 Polymers Polymers 2022 202 , 214 , 1 , 4 20 , x FOR PEER REVIEW 10 of 18 9 of 16 Figure 9. SEM image of the surface of an irradiated PVC film blended with a Schiff base of melamine. Figure Figure 9. 9. SE SEM M iimage mage of ofthe the surface surface ofof an an irradiated irradiated PVC PVC film film bleblended nded with with a Sca hiff Schif base f base of mof elam melamine. ine. Figure 10. FESEM image of the surface of an irradiated PVC film blended with a trimethoprim-Sn Figure 10. FESEM image of the surface of an irradiated PVC film blended with a trimethoprim-Sn Figure 10. FESEM image of the surface of an irradiated PVC film blended with a trimethoprim- complex. complex. Sn complex. Polymers 2022, 14, x FOR PEER REVIEW 11 of 18 Polymers 2022, 14, 20 10 of 16 Polymers 2022, 14, x FOR PEER REVIEW 11 of 18 Figure 11. SEM image of the surface of an irradiated PS film blended with a Schiff base of biphenyl- Figure 11. SEM image of the surface of an irradiated PS film blended with a Schiff base of biphenyl- Figure 11. SEM image of the surface of an irradiated PS film blended with a Schiff base of biphenyl- 3,3′,4,4′-tetraamine. 0 0 3,3 ,4,4 -tetraamine. 3,3′,4,4′-tetraamine. Figure 12. SEM image of the surface of an irradiated PVC film in the absence of any additive. Figure 12. SEM image of the surface of an irradiated PVC film in the absence of any additive. Figure 12. SEM image of the surface of an irradiated PVC film in the absence of any additive. Polymers 2022, 14, x FOR PEER REVIEW 12 of 18 Polymers 2022, 14, 20 11 of 16 Figure 13. SEM image of the surface of an irradiated PS film in the absence of any additive. Figure 13. SEM image of the surface of an irradiated PS film in the absence of any additive. Atomic force microscopy (AFM) was used as a tool to measure the effectiveness of Atomic force microscopy (AFM) was used as a tool to measure the effectiveness of UV UV absorbers towards the stabilization of polymers [115–117]. The roughness factor (Rq) absorbers towards the stabilization of polymers [115–117]. The roughness factor (Rq) for the surface for the of surfac the blank, e of thirradiated e blank, irr polymers adiated po was lymers always was high alwcompar ays high ed com with pare those d with obtained those for obtained the films forblended the films with blended additives. with Such additives an obse . Survation ch an ob is se evidence rvation is for evide the nce important for the rimpo ole played rtant rol bye additives played by inad stabilizing ditives in polymers stabilizing uppo onlym irradiation. ers upon Highly irradiaar tion omatic . Highly (due ar to o- the matic resonance (due to ef thfect) e reson UVance additives effect) UV that contain additives heter that c oatoms ontai( n het due to ero coor atom dination s (due to coo with the rdi- polymeric chain of PVC, for example) showed the most desirable stabilizing effect (Table 2). nation with the polymeric chain of PVC, for example) showed the most desirable stabiliz- ing effect (Table 2). Table 2. Reduction in the roughness factor Rq (by fold) of polymers in the presence of UV absorbers. Table 2. Reduction in the roughness factor Rq (by fold) of polymers in the presence of UV absorbers. Polymer UV Absorber Organic Moiety Rq Reference Polymer UV Absorber Organic Moiety Rq Reference PS Schiff base Cephalexin 27.1 [92] PS Schiff base Cephalexin0 0 27.1 [92] PS Schiff base Biphenyl-3,3 ,4,4 -tetraamine 8.3 [73] PS Schiff base Biphenyl-3,3′,4,4′-tetraamine 8.3 [73] PS Schiff base 1,2,3,4-Triazole-3-thiol 3.3 [64] PVC Polyphosphates Benzidine 16.8 [68] PS Schiff base 1,2,3,4-Triazole-3-thiol 3.3 [64] 0 0 PVC Schiff base Biphenyl-3,3 ,4,4 -tetraamine 3.6 [66] PVC Polyphosphates Benzidine 16.8 [68] PVC Schiff base Melamine 6.0 [75] PVC Schiff base Biphenyl-3,3′,4,4′-tetraamine 3.6 [66] PVC Ni complex 2-(4-Isobutylphenyl) propanoate 6.3 [65] PVC Schiff base Melamine 6.0 [75] PVC Sn complex 4-Methoxybenzoic acid 21.2 [94] PVC Sn complex 4-(Benzylideneamino) benzenesulfonamide 18.4 [91] PVC Ni complex 2-(4-Isobutylphenyl) propanoate 6.3 [65] PVC Sn complex Ciprofloxacin 16.6 [70] PVC Sn complex 4-Methoxybenzoic acid 21.2 [94] PVC Sn complex Trimethoprim 11.3 [93] PVC Sn complex 4-(Benzylideneamino) benzenesulfonamide 18.4 [91] PVC Sn complex Telmisartan 9.4 [78] PVC Sn complex Ciprofloxacin 16.6 [70] PVC Sn complex Valsartan 7.4 [81] PVCPVC Sn complex Sn complex Trimethop Fur ri osemide m 11.3 6.6 [93] [63 ] PVC Sn complex Carvedilol 6.4 [88] PVC Sn complex Telmisartan 9.4 [78] PVC Sn complex Naproxen 5.2 [77] PVC Sn complex Valsartan 7.4 [81] PVC Sn complex Furosemide 6.6 [63] PVC Sn complex Carvedilol 6.4 [88] Polymers 2022, 14, 20 12 of 16 5. Conclusions and Future Perspectives Polymer stabilization is one of the most important processes that is used to elongate the lifetimes of plastic products. Plastics used in outdoor applications suffer in harsh environments and quickly lose their mechanical and physical properties. The proper solution for inhibiting the photooxidation of plastics due to the inevitable exposure to light and oxygen is through the addition of efficient ultraviolet absorbers that are capable of acting as efficient scavengers for light and blocking the formation of free radicals within the polymeric chains. The additives should absorb irradiation light directly and decompose peroxide species. In addition, they should be very compatible with the polymers, not alter the color, be used at a very low concentration, and be safe for the environment if released. Progress was made with the design and use of safe additives to enhance plastic stability and, in particular, polystyrene and polyvinyl chloride. Polyphosphates, Schiff bases, and organometallic complexes containing aromatic moieties showed the potential to be used as ultraviolet absorbers for plastics. The damage on the surface of irradiated plastics in the presence of ultraviolet absorbers is low compared with the blank films. Since the additives are not linked to plastic through covalent bonds, they can be leached to the surrounding environments. The leakage of these chemicals followed by their degradation poses a danger to both animals and humans. Therefore, future research should be attention to the design, synthesis, and use of safe, non-toxic, and highly stable polymeric additives to suppress the degradation of plastic. Some progress was made, but there is still room for further improvements and modifications. Author Contributions: Conceptualization: G.A.E.-H., D.S.A. and E.Y.; literature review: G.A.E.-H., D.S.A., E.Y., O.S.A.A.-K. and M.A.; writing—original draft preparation: G.A.E.-H., D.S.A., E.Y., O.S.A.A.-K., M.A. and S.A.A.; writing—review and editing: G.A.E.-H., D.S.A., E.Y., O.S.A.A.-K., M.A. and S.A.A. All authors have read and agreed to the published version of the manuscript. Funding: The authors are grateful to the Deanship of Scientific Research, King Saud University for funding through Vice Deanship of Scientific Research Chairs. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Data are contained within the article. Acknowledgments: We thank Al-Nahrain University for support. Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results. References 1. Yousif, E.; Haddad, R. Photodegradation and photostabilization of polymers, especially polystyrene: Review. SpringerPlus 2013, 2, 398. [CrossRef] [PubMed] 2. Chamas, A.; Moon, H.; Zheng, J.; Qiu, Y.; Tabassum, T.; Jang, J.H.; Abu-Omar, M.; Scott, S.L.; Suh, S. Degradation rates of plastics in the environment. ACS Sustain. Chem. Eng. 2020, 8, 3494–3511. [CrossRef] 3. Yaqoob, A.A.; Noor, N.H.M.; Serrà, A.; Mohamad Ibrahim, M.N. Advances and challenges in developing efficient graphene oxide-based ZnO photocatalysts for dye photo-oxidation. Nanomaterials 2020, 10, 932. [CrossRef] [PubMed] 4. The State of Plastics: World Environment Day Outlook 2018. Available online: https://www.unep.org/resources/report/state- plastics-world-environment-day-outlook-2018 (accessed on 5 November 2021). 5. Plastics—The Facts 2020. An Analysis of European Plastics Production, Demand and Waste Data. Available online: https: //issuu.com/plasticseuropeebook/docs/plastics_the_facts-web-dec2020 (accessed on 2 November 2021). 6. Wheeler, R.N., Jr. Poly (vinyl chloride) processes and products. Environ. Health Perspect. 1981, 41, 123–128. [CrossRef] [PubMed] 7. Schyns, Z.O.G.; Shaver, M.M. Mechanical recycling of packaging plastics: A review. Macromol. Rapid Commun. 2021, 42, 2000415. [CrossRef] 8. Singh, N.; Hui, D.; Singh, R.; Ahuja, I.P.S.; Feo, L.; Fraternali, F. Recycling of plastic solid waste: A state of art review and future applications. Compos. B. Eng. 2017, 115, 409–422. [CrossRef] 9. Gewert, B.; Plassmann, M.M.; MacLeod, M. Pathways for degradation of plastic polymers floating in the marine environment. Environ. Sci. Process. Impacts 2015, 17, 1513–1521. [CrossRef] Polymers 2022, 14, 20 13 of 16 10. Matthews, C.; Moran, F.; Jaiswal, A.K. A review on European Union’s strategy for plastics in a circular economy and its impact on food safety. J. Clean. Prod. 2021, 283, 125263. [CrossRef] 11. Potaufeux, J.-E.; Odent, J.; Notta-Cuvier, D.; Lauro, F.; Raquez, J.-M. A comprehensive review of the structures and properties of ionic polymeric materials. Polym. Chem. 2020, 11, 5914–5936. [CrossRef] 12. Moretti, E.; Zinzi, M.; Belloni, E. Polycarbonate panels for buildings: Experimental investigation of thermal and optical performance. Energy Build. 2014, 70, 23–35. [CrossRef] 13. Turner, A.; Filella, M. Polyvinyl chloride in consumer and environmental plastics, with a particular focus on metal-based additives. Environ. Sci. Process. Impacts 2021, 23, 1376–1384. [CrossRef] 14. Shah, A.A.; Hasan, F.; Hameed, A.; Ahmed, S. Biological degradation of plastics: A comprehensive review. Biotechnol. Adv. 2008, 26, 246–265. [CrossRef] [PubMed] 15. Hahladakis, J.N.; Velis, C.A.; Weber, R.; Iacovidou, E.; Purnell, P. An overview of chemical additives present in plastics: Migration, release, fate and environmental impact during their use, disposal and recycling. J. Hazard. Mater. 2018, 344, 179–199. [CrossRef] [PubMed] 16. Umar, K.; Yaqoob, A.A.; Ibrahim, M.N.M.; Parveen, T.; Safian, M.T. Environmental applications of smart polymer composites. Smart Polym. Nanocompos. Biomed. Environ. Appl. 2020, 15, 295–320. [CrossRef] 17. Albertsson, A.-C.; Karlsson, S. The three stages in degradation of polymers—Polyethylene as a model substance. J. Appl. Polym. Sci. 1988, 35, 1289–1302. [CrossRef] 18. Chatge, S.; Yang, Y.; Ahn, J.-H.; Hur, H.-G. Biodegradation of polyethylene: A brief review. Appl. Biol. Chem. 2020, 63, 27. [CrossRef] 19. Singh, B.; Sharma, N. Mechanistic implications of plastic degradation. Polym. Degrad. Stab. 2008, 93, 561–584. [CrossRef] 20. Vohlídal, J. Polymer degradation: A short review. Chem. Teach. Int. 2020, 3, 213–220. [CrossRef] 21. Gryn’ova, G.; Hodgson, J.L.; Coote, M.L. Revising the mechanism of polymer autooxidation. Org. Biomol. Chem. 2011, 9, 480–490. [CrossRef] [PubMed] 22. Webb, H.K.; Arnott, J.; Crawford, R.J.; Ivanova, E.P. Plastic degradation and its environmental implications with special reference to poly (ethylene terephthalate). Polymers 2013, 5, 1–18. [CrossRef] 23. Raquez, J.M.; Bourgeois, A.; Jacobs, H.; Degée, P.; Alexandre, M.; Dubois, P. Oxidative degradations of oxodegradable LDPE enhanced with thermoplastic pea starch: Thermo mechanical properties, morphology, and UV-ageing studies. J. Appl. Polym. Sci. 2011, 122, 489–496. [CrossRef] 24. Zheng, Y.; Yanful, E.K.; Bassi, A.S. A review of plastic waste biodegradation. Crit. Rev. Biotechnol. 2005, 25, 243–250. [CrossRef] 25. Müller, R.-J.; Kleeberg, I.; Deckwer, W.-D. Biodegradation of polyesters containing aromatic constituents. J. Biotechnol. 2001, 86, 87–95. [CrossRef] 26. Andrady, A.L. Microplastics in the marine environment. Mar. Pollut. Bull. 2011, 62, 1596–1605. [CrossRef] [PubMed] 27. Coyle, R.; Hardiman, G.; O’Driscoll, K. Microplastics in the marine environment: A review of their sources, distribution processes, uptake and exchange in ecosystems. Case Stud. Therm. Environ. Eng. 2020, 2, 100010. [CrossRef] 28. Paulsson, M.; Parkås, J. Review: Light-induced yellowing of lignocellulosic pulps–mechanism and penetrative methods. BioRe- sources 2012, 7, 5995–6040. [CrossRef] 29. Jin, C.; Christensen, P.A.; Egerton, T.A.; Lawson, E.J.; White, J.R. Rapid measurement of polymer photo-degradation by FTIR spectrometry of evolved carbon dioxide. Polym. Deg. Stab. 2006, 91, 1086–1096. [CrossRef] 30. Mu, Z.; Chen, Q.; Zhang, L.; Guan, D.; Li, H. Photodegradation of atmospheric chromophores: Changes in oxidation state and photochemical reactivity. Atmos. Chem. Phys. 2021, 21, 11581–11591. [CrossRef] 31. Wang, C.-N.; Torng, J.-H. Experimental study of the absorption characteristics of some porous fibrous materials. Appl. Acoust. 2001, 62, 447–459. [CrossRef] 32. Ojeda, T.; Freitas, A.; Birck, K.; Dalmolin, E.; Jacques, R.; Bento, F.; Camargo, F. Degradability of linear polyolefins under natural weathering. Polym. Degrad. Stab. 2011, 96, 703–707. [CrossRef] 33. Sharratt, V.; Hill, C.A.S.; Kint, D.P.R. A study of early colour change due to simulated accelerated sunlight exposure in Scots pine (Pinus sylvestris). Polym. Degrad. Stab. 2009, 94, 1589–1594. [CrossRef] 34. Bais, A.F.; Mckenzie, R.L.; Aucamp, P.J.; Ilyas, M.; Madronich, S.; Tourpali, K. Ozone depletion and climate change: Impacts on UV radiation. Photochem. Photobiol. Sci. 2015, 14, 19–52. [CrossRef] [PubMed] 35. Vitt, R.; Laschewski, G.; Bais, A.F.; Diémoz, H.; Fountoulakis, I.; Siani, A.-M.; Matzarakis, A. UV-Index climatology for Europe based on satellite data. Atmosphere 2020, 11, 727. [CrossRef] 36. Martins, J.N.; Freire, E.; Hemadipou, H. Applications and market of PVC for piping industry. Polímeros 2009, 19, 58–62. [CrossRef] 37. Kumagai, H.; Tashiro, T.; Kobayashi, T. Formation of conjugated carbon bonds on poly (vinyl chloride) films by microwave- discharge oxygen-plasma treatments. J. Appl. Polym. Sci. 2005, 96, 589–594. [CrossRef] 38. Yu, J.; Sun, L.; Ma, C.; Qiao, Y.; Yao, H. Thermal degradation of PVC: A review. Waste Manag. 2016, 48, 300–314. [CrossRef] 39. Miskolczi, N.; Bartha, L.; Angyal, A. Pyrolysis of polyvinyl chloride (PVC)-containing mixed plastic wastes for recovery of hydrocarbons. Energy Fuels 2009, 23, 2743–2749. [CrossRef] 40. Braun, D. Recycling of PVC. Prog. Polym. Sci. 2002, 27, 2171–2195. [CrossRef] 41. Marturano, V.; Cerruti, P.; Ambrogi, V. Polymer additives. Phys. Sci. Rev. 2017, 2, 20160130. [CrossRef] Polymers 2022, 14, 20 14 of 16 42. Brostow, W.; Lu, X.; Gencel, O.; Osmanson, A.T. Effects of UV stabilizers on polypropylene outdoors. Materials 2020, 13, 1626. [CrossRef] 43. Noukakis, D.; Suppan, P. Mechanism of protection of polymers by photostabilizers. J. Photochem. Photobiol. A 1991, 58, 393–396. [CrossRef] 44. Sabaa, M.W.; Sanad, M.A.; Abd El-Ghaffar, M.A.; Abdelwahab, N.A.; Sayed, S.M.A.; Soliman, S.M.A. Synthesis, characterization, and application of polyanisidines as efficient photostabilizers for poly (vinyl chloride) films. J. Elastomers Plast. 2020, 52, 537–547. [CrossRef] 45. Karimi, S.; Helal, E.; Gutierrez, G.; Moghimian, N.; Madinehei, M.; David, E.; Samara, M.; Demarquette, N. A review on graphene’s light stabilizing effects for reduced photodegradation of polymers. Crystals 2021, 11, 3. [CrossRef] 46. Marcilla, A.; García, S.; García-Quesada, J.C. Study of the migration of PVC plasticizers. J. Anal. Appl. Pyrolysis 2004, 71, 457–463. [CrossRef] 47. Szarka, G.; Iván, B. Degradative Transformation of Poly (vinyl chloride) Under Mild Oxidative Conditions. In Polymer Degradation and Performance; Celina, M.C., Wiggins, J.S., Billingham, N.C., Eds.; ACS: Washington, DC, USA, 2009; Volume 1004, Chapter 19; pp. 219–226. [CrossRef] 48. Wang, T.; Li, X.; Xiong, Y.; Guo, S.Y. Super-tough PVC/CPE composites: An efficient CPE network by an MGA copolymer prepared through a vibro-milling process. RSC Adv. 2020, 10, 44584–44592. [CrossRef] 49. Marshall, R.A. Effect of crystallinity on PVC physical properties. J. Vinyl Addit. Technol. 1994, 16, 35–38. [CrossRef] 50. Larché, J.-F.; Bussière, P.-O.; Thérias, S.; Gardette, J.-L. Photooxidation of polymers: Relating material properties to chemical changes. Polym. Degrad. Stab. 2012, 97, 25–35. [CrossRef] 51. Geuskens, G.; Baeyens-Volant, D.; Delaunois, G.; Lu Vinh, Q.; Piret, W.; David, C. Photo-oxidation of polymers–II. The sensitized decomposition of hydroperoxides as the main path for initiation of the photo-oxidation of polystyrene irradiated at 253.7 nm. Eur. Polym. J. 1978, 14, 299–303. [CrossRef] 52. Yaqoob, A.A.; Noor, N.H.M.; Umar, K.; Adnan, R.; Ibrahim, M.N.M.; Rashid, M. Graphene oxide–ZnO nanocomposite: An efficient visible light photocatalyst for degradation of rhodamine B. Appl. Nanosci. 2021, 11, 1291–1302. [CrossRef] 53. Huang, Z.; Ding, A.; Guo, H.; Lu, G.; Huang, X. Construction of nontoxic polymeric UV-absorber with great resistance to UV-photoaging. Sci. Rep. 2016, 6, 25508. [CrossRef] 54. Sonnenschein, M.F.; Guillaudeu, S.J.; Landes, B.G.; Wendt, B.L. Comparison of adipate and succinate polymers in thermoplastic polyurethanes. Polymer 2010, 51, 3685–3692. [CrossRef] 55. Lu, T.; Solis-Ramos, E.; Yi, Y.; Kumosa, M. UV degradation model for polymers and polymer matrix composites. Polym. Degrad. Stab. 2018, 154, 203–210. [CrossRef] 56. Rabek, J. Polymer Photodegradation: Mechanisms and Experimental Methods; Champan & Hall: London, UK, 1995; pp. 383–391. 57. George, G.A. The mechanism of photoprotection of polystyrene film by some ultraviolet absorbers. J. Appl. Polym. Sci. 1974, 18, 117–124. [CrossRef] 58. Liu, X.; Gao, C.; Sangwan, P.; Yu, L.; Tong, Z. Accelerating the degradation of polyolefins through additives and blending. J. Appl. Polym. Sci. 2014, 131, 40750. [CrossRef] 59. Balakit, A.A.; Ahmed, A.; El-Hiti, G.A.; Smith, K.; Yousif, E. Synthesis of new thiophene derivatives and their use as photostabi- lizers for rigid poly (vinyl chloride). Int. J. Polym. Sci. 2015, 2015, 510390. [CrossRef] 60. Yousif, E.; El-Hiti, G.A.; Haddad, R.; Balakit, A.A. Photochemical stability and photostabilizng efficiency of poly (methyl methacrylate) based on 2-(6-methoxynaphthalen-2-yl) propanoate metal ions complexes. Polymers 2015, 7, 1005–1019. [CrossRef] 61. Yousif, E.; El-Hiti, G.A.; Hussain, Z.; Altaie, A. Viscoelastic, spectroscopic and microscopic study of the photo irradiation effect on the stability of PVC in presence of sulfamethoxazole Schiff’s bases. Polymers 2015, 7, 2190–2204. [CrossRef] 62. Yousif, E.; Hasan, A.; El-Hiti, G.A. Spectroscopic, physical and topography of photochemical process of PVC films in the presence of Schiff base metal complexes. Polymers 2016, 8, 204. [CrossRef] [PubMed] 63. Ali, M.M.; El-Hiti, G.A.; Yousif, E. Photostabilizing efficiency of poly (vinyl chloride) in the presence of organotin (IV) complexes as photostabilizers. Molecules 2016, 21, 1151. [CrossRef] 64. Ali, G.Q.; El-Hiti, G.A.; Tomi, I.H.R.; Haddad, R.; Al-Qaisi, A.J.; Yousif, E. Photostability and performance of polystyrene films containing 1,2,4-triazole-3-thiol ring system Schiff bases. Molecules 2016, 21, 1699. [CrossRef] 65. Mohammed, R.; El-Hiti, G.A.; Ahmed, A.; Yousif, E. Poly (vinyl chloride) doped by 2-(4-isobutylphenyl) propanoate metal complexes: Enhanced resistance to UV irradiation. Arab. J. Sci. Eng. 2017, 42, 4307–4315. [CrossRef] 66. Ahmed, D.S.; El-Hiti, G.A.; Hameed, A.S.; Yousif, E.; Ahmed, A. New tetra-Schiff bases as efficient photostabilizers for poly (vinyl chloride). Molecules 2017, 22, 1506. [CrossRef] 67. Ali, M.M.; El-Hiti, G.A.; Yousif, E. Investigation of the photodecomposition rate constant of poly (vinyl chloride) films containing organotin (IV) complexes. Al-Nahrain J. Sci. 2017, 20, 18–23. [CrossRef] 68. Ahmed, D.S.; El-Hiti, G.A.; Yousif, E.; Hameed, A.S. Polyphosphates as inhibitors for poly (vinyl chloride) photodegradation. Molecules 2017, 22, 1849. [CrossRef] 69. Yousif, E.; Haddad, R.; El-Hiti, G.A.; Yusop, R.M. Spectroscopic and photochemical stability of polystyrene films in the presence of metal complexes. J. Taibah Univ. Sci. 2017, 11, 997–1007. [CrossRef] Polymers 2022, 14, 20 15 of 16 70. Ghazi, D.; El-Hiti, G.A.; Yousif, E.; Ahmed, D.S.; Alotaibi, M.H. The effect of ultraviolet irradiation on the physicochemical properties of poly (vinyl chloride) films containing organotin (IV) complexes as photostabilizers. Molecules 2018, 23, 254. [CrossRef] [PubMed] 71. Shaalan, N.; Laftah, N.; El-Hiti, G.A.; Alotaibi, M.H.; Muslih, R.; Ahmed, D.S.; Yousif, E. Poly (vinyl chloride) photostabilization in the presence of Schiff bases containing a thiadiazole moiety. Molecules 2018, 23, 913. [CrossRef] [PubMed] 72. Hashim, H.; El-Hiti, G.A.; Alotaibi, M.H.; Ahmed, D.S.; Yousif, E. Fabrication of ordered honeycomb porous poly (vinyl chloride) thin film doped with a Schiff base and nickel (II) chloride. Heliyon 2018, 4, e00743. [CrossRef] 73. Yousif, E.; Ahmed, D.S.; El-Hiti, G.A.; Alotaibi, M.H.; Hashim, H.; Hameed, A.S.; Ahmed, A. Fabrication of novel ball-like polystyrene films containing Schiff bases microspheres as photostabilizers. Polymers 2018, 10, 1185. [CrossRef] [PubMed] 74. Alotaibi, M.H.; El-Hiti, G.A.; Hashim, H.; Hameed, A.S.; Ahmed, D.S.; Yousif, E. SEM analysis of the tunable honeycomb structure of irradiated poly (vinyl chloride) films doped with polyphosphate. Heliyon 2018, 4, e01013. [CrossRef] 75. El-Hiti, G.A.; Alotaibi, M.H.; Ahmed, A.A.; Hamad, B.A.; Ahmed, D.S.; Ahmed, A.; Hashim, H.; Yousif, E. The morphology and performance of poly (vinyl chloride) containing melamine Schiff bases against ultraviolet light. Molecules 2019, 24, 803. [CrossRef] [PubMed] 76. Alotaibi, M.H.; El-Hiti, G.A.; Yousif, E.; Ahmed, D.S.; Hashim, H.; Hameed, A.S.; Ahmed, A. Evaluation of the use of polyphos- phates as photostabilizers and in the formation of ball-like polystyrene materials. J. Polym. Res. 2019, 26, 161. [CrossRef] 77. Hadi, A.G.; Yousif, E.; El-Hiti, G.A.; Ahmed, D.S.; Jawad, K.; Alotaibi, M.H.; Hashim, H. Long-term effect of ultraviolet irradiation on poly (vinyl chloride) films containing naproxen diorganotin (IV) complexes. Molecules 2019, 24, 2396. [CrossRef] 78. Hadi, A.G.; Jawad, K.; El-Hiti, G.A.; Alotaibi, M.H.; Ahmed, A.A.; Ahmed, D.S.; Yousif, E. Photostabilization of poly (vinyl chloride) by organotin (IV) compounds against photodegradation. Molecules 2019, 24, 3557. [CrossRef] 79. Ahmed, A.A.; Ahmed, D.S.; El-Hiti, G.A.; Alotaibi, M.H.; Hashim, H.; Yousif, E. SEM morphological analysis of irradiated polystyrene film doped by a Schiff base containing a 1,2,4-triazole ring system. Appl. Petrochem. Res. 2019, 9, 169–177. [CrossRef] 80. El-Hiti, G.A.; Ahmed, D.S.; Yousif, E.; Alotaibi, M.H.; Star, H.A.; Ahmed, A.A. Influence of polyphosphates on the physicochemical properties of poly (vinyl chloride) after irradiation with ultraviolet light. Polymers 2020, 12, 193. [CrossRef] 81. Mohammed, A.; El-Hiti, G.A.; Yousif, E.; Ahmed, A.A.; Ahmed, D.S.; Alotaibi, M.H. Protection of poly (vinyl chloride) films against photodegradation using various valsartan tin complexes. Polymers 2020, 12, 969. [CrossRef] 82. Ahmed, D.S.; El-Hiti, G.A.; Ibraheem, H.; Alotaibi, M.H.; Abdallh, M.; Ahmed, A.A.; Ismael, M.; Yousif, E. Enhancement of photostabilization of poly (vinyl chloride) doped with sulfadiazine tin complexes. J. Vinyl Addit. Technol. 2020, 26, 370–379. [CrossRef] 83. Mahmood, Z.N.; Yousif, E.; Alias, M.; El-Hiti, G.A.; Ahmed, D.S. Synthesis, characterization, properties, and use of new fusidate organotin complexes as additives to inhibit poly (vinyl chloride) photodegradation. J. Polym. Res. 2020, 27, 267. [CrossRef] 84. Majeed, A.; Yousif, E.; El-Hiti, G.A.; Alotaibi, M.H.; Ahmed, D.S.; Ahmed, A.A. Stabilization of PVC containing captopril tin complexes against degradation upon exposure to ultraviolet light. J. Vinyl Addit. Technol. 2020, 26, 601–612. [CrossRef] 85. Salam, B.; El-Hiti, G.A.; Bufaroosha, M.; Ahmed, D.S.; Ahmed, A.; Alotaibi, M.H.; Yousif, E. Tin complexes containing an atenolol moiety as photostabilizers for poly (vinyl chloride). Polymers 2020, 12, 2923. [CrossRef] [PubMed] 86. Omer, R.M.; Al-Tikrity, E.T.B.; Yousif, E.; El-Hiti, G.A.; Ahmed, D.S.; Ahmed, A.A. Spectroscopic and morphological study of irradiated PVC films doped with polyphosphates containing 4,4 -methylenedianiline. Russ. J. Appl. Chem. 2020, 93, 1888–1898. [CrossRef] 87. Mohamed, S.H.; Hameed, A.S.; El-Hiti, G.A.; Ahmed, D.S.; Kadhom, M.; Baashen, M.A.; Bufaroosha, M.; Ahmed, A.A.; Yousif, E. A process for the synthesis and use of highly aromatic organosilanes as additives for poly (vinyl chloride) films. Processes 2021, 9, 91. [CrossRef] 88. Mousa, O.G.; El-Hiti, G.A.; Baashen, M.A.; Bufaroosha, M.; Ahmed, A.; Ahmed, A.A.; Ahmed, D.S.; Yousif, E. Synthesis of carvedilol-organotin complexes and their effects on reducing photodegradation of poly (vinyl chloride). Polymers 2021, 13, 500. [CrossRef] 89. Ahmed, A.; El-Hiti, G.A.; Hadi, A.G.; Ahmed, D.S.; Baashen, M.A.; Hashim, H.; Yousif, E. Photostabilization of poly (vinyl chloride) films blended with organotin complexes of mefenamic acid for outdoor applications. Appl. Sci. 2021, 11, 2853. [CrossRef] 90. Jasem, H.; Hadi, A.G.; El-Hiti, G.A.; Baashen, M.A.; Hashim, H.; Ahmed, A.A.; Ahmed, D.S.; Yousif, E. Tin-naphthalene sulfonic acid complexes as photostabilizers for poly (vinyl chloride). Molecules 2021, 26, 3629. [CrossRef] [PubMed] 91. Ghani, H.; Yousif, E.; Ahmed, D.S.; Kariuki, B.M.; El-Hiti, G.A. Tin Complexes of 4-(Benzylideneamino) benzenesulfonamide: Synthesis, structure elucidation and their efficiency as PVC photostabilizers. Polymers 2021, 13, 2434. [CrossRef] 92. Yaseen, A.A.; Al-Tikrity, E.T.B.; Yousif, E.; Ahmed, D.S.; Kariuki, B.M.; El-Hiti, G.A. Effect of ultraviolet irradiation on polystyrene containing cephalexin Schiff bases. Polymers 2021, 13, 2982. [CrossRef] 93. Yaseen, A.A.; Yousif, E.; Al-Tikrity, E.T.B.; El-Hiti, G.A.; Kariuki, B.M.; Ahmed, D.S.; Bufaroosha, M. FTIR, weight, and surface morphology of poly (vinyl chloride) doped with tin complexes containing aromatic and heterocyclic moieties. Polymers 2021, 13, 3264. [CrossRef] 94. Hadi, A.G.; Baqir, S.J.; Ahmed, D.S.; El-Hiti, G.A.; Hashim, H.; Ahmed, A.; Kariuki, B.M.; Yousif, E. Substituted organotin complexes of 4-methoxybenzoic acid for reduction of poly (vinyl chloride) photodegradation. Polymers 2021, 13, 3946. [CrossRef] Polymers 2022, 14, 20 16 of 16 95. Nikafshar, S.; Zabihi, O.; Ahmadi, M.; Mirmohseni, A.; Taseidifar, M.; Naebe, M. The effects of UV light on the chemical and mechanical properties of a transparent epoxy-diamine system in the presence of an organic UV absorber. Materials 2017, 10, 180. [CrossRef] 96. Venkateshaiah, A.; Padil, V.V.T.; Nagalakshmaiah, M.; Waclawek, S.; Cerník, M.; Varma, R.S. Microscopic techniques for the analysis of micro and nanostructures of biopolymers and their derivatives. Polymers 2020, 12, 512. [CrossRef] 97. Sawyer, L.C.; Grubb, D.T.; Meyers, G.F. Polymer Microscopy, 3rd ed.; Springer: New York, NY, USA, 2008; Chapter 5. 98. Valko, L.; Klein, E.; Kovar ˇík, P.; Bleha, T.; Šimon, P. Kinetic study of thermal dehydrochlorination of poly (vinyl chloride) in the presence of oxygen: III. Statistical thermodynamic interpretation of the oxygen catalytic activity. Eur. Polym. J. 2001, 37, 1123–1132. [CrossRef] 99. Shi, W.; Zhang, J.; Shi, X.-M.; Jiang, G.-D. Different photo-degradation processes of PVC with different average degrees of polymerization. J. Appl. Polym. Sci. 2008, 107, 528–540. [CrossRef] 100. Pospíšil, J.; Nešpurek, S. Photostabilization of coatings. Mechanisms and performance. Prog. Polym. Sci. 2000, 25, 1261–1335. [CrossRef] 101. Jafari, A.J.; Donaldson, J.D. Determination of HCl and VOC emission from thermal degradation of PVC in the absence and presence of copper, copper (II) oxide and copper (II) chloride. J. Chem. 2009, 6, 685–692. [CrossRef] 102. Pi, H.; Xiong, Y.; Guo, S. The kinetic studies of elimination of HCl during thermal decomposition of PVC in the presence of transition metal oxides. Polym. Plast. Technol. Eng. 2005, 44, 275–288. [CrossRef] 103. Nief, O.A. Photostabilization of polyvinyl chloride by some new thiadiazole derivatives. Eur. J. Chem. 2015, 6, 242–247. [CrossRef] 104. Chaochanchaikul, K.; Rosarpitak, V.; Sombatsompop, N. Photodegradation profiles of PVC compound and wood/PVC composites under UV weathering. Express Polym. Lett. 2013, 7, 146–160. [CrossRef] 105. Zhang, A.; Bai, H.; Li, L. Breath figure: A nature-inspired preparation method for ordered porous films. Chem. Rev. 2015, 115, 9801–9868. [CrossRef] 106. Bui, V.-T.; Lee, H.S.; Choi, J.-H. Data from crosslinked PS honeycomb thin film by deep UV irradiation. Data Brief 2015, 5, 990–994. [CrossRef] 107. Zheng, K.; Hu, D.; Deng, Y.; Maitloa, I.; Nie, J.; Zhu, X. Crosslinking poly (acrylic glycidyl ether) honeycomb film by cationic photopolymerization and its converting to inorganic SiO film. Appl. Surf. Sci. 2008, 428, 485–491. [CrossRef] 108. Kayyarapu, B.; Kumar, M.; Mohommad, H.B.; Neeruganti, G.; Chekuria, R. Structural, thermal and optical properties of pure and 2+ Mn doped poly (vinyl chloride) films. Mater. Res. 2016, 19, 1167–1175. [CrossRef] 109. Dou, Y.; Jin, M.; Zhou, G.; Shui, L. Breath figure method for construction of honeycomb films. Membranes 2015, 5, 399–424. [CrossRef] 110. Cheng, C.X.; Tian, Y.; Shi, Y.Q.; Tang, R.P.; Xi, F. Porous polymer films and honeycomb structures based on amphiphilic dendronized block copolymers. Langmuir 2005, 21, 6576–6581. [CrossRef] 111. Rahman, M.Y.A.; Ahmad, A.; Lee, T.K.; Farina, Y.; Dahlan, H.D. Effect of ethylene carbonate (EC) plasticizer on poly (vinyl chloride)-liquid 50% epoxidised natural rubber (LENR50) based polymer electrolyte. Mater. Sci. Appl. 2011, 2, 817–825. [CrossRef] 112. Huh, M.; Gauthier, M.; Yun, S. Honeycomb structured porous films prepared from arborescent graft polystyrenes via the breath figures method. Polymer 2016, 107, 273–281. [CrossRef] 113. Wang, Z.M.; Wagner, J.; Ghosal, S.; Bedi, G.; Wall, S. SEM/EDS and optical microscopy analyses of microplastics in ocean trawl and fish guts. Sci. Total Environ. 2017, 603–604, 616–626. [CrossRef] 114. Devi, M.R.; Saranya, A.; Pandiarajan, J.; Dharmaraja, J.; Prithivikumaran, N.; Jeyakumaran, N. Fabrication, spectral characteriza- tion, XRD and SEM studies on some organic acids doped polyaniline thin films on glass substrate. JKSUS 2019, 31, 1290–1296. [CrossRef] 115. Kara, F.; Aksoy, E.A.; Yuksekdag, Z.; Hasirci, N.; Aksoy, S. Synthesis and surface modification of polyurethanes with chitosan for antibacterial properties. Carbohydr. Polym. 2014, 112, 39–47. [CrossRef] 116. Shinato, K.W.; Huang, F.; Jin, Y. Principle and application of atomic force microscopy (AFM) for nanoscale investigation of metal corrosion. Corros. Rev. 2020, 38, 423–432. [CrossRef] 117. See, C.H.; O’Haver, J. Atomic force microscopy characterization of ultrathin polystyrene films formed by admicellar polymeriza- tion on silica disks. J. Appl. Polym. Sci. 2003, 89, 36–46. [CrossRef]

Journal

PolymersMultidisciplinary Digital Publishing Institute

Published: Dec 22, 2021

Keywords: plastics; polyvinyl chloride; photostabilizers; plastic photodegradation and photooxidation; recycling of plastics; photoirradiation

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