Photodegradation of plastics

Despite many similarities between thermooxidation and photooxidation of plastics, on one hand, and WPCs, on the other, there are some important differences. Photodegradation of plastics typically occurs in oxygen starvation conditions, while photodegradation of WPC, which are always porous, occurs in the presence of plenty of oxygen in the... 

Some definitions and technical terms used in descriptions of photodegradation of plastics and WPCs (from Atlas Weathering Testing Guidebook, with some modifications) ... 

Figure 15. Photodegradation of plastics modified by including carbon monoxide in polymer chain (Bunce, 1994).

The wide application of plastics in agriculture has a decisive influence on cultivation practices. Plastic films used as a growing aid in the form of mulch and tunnel covers have increased yields. The debris of these films left behind after the harvest poses a serious disposal problem. The controlled photodegradation of plastics affords a workable solution not only to this problem but opens new possibilities of the programmed removal of the films even during the growing period of the crops when this is desirable. 

Photodegradation of plastic contamination in the marine environment (cf section 8.4). 

This article highlights the growing problem of plastics waste disposal and then investigates modes of polymer degradation - thermal, chemical, mechanical, photodegradation, bio-degradation, solvolysis andglycerolysis. 4 refs. 

This type of degradation can also be referred to as photodegradation or ultraviolet (UV) degradation. It includes photo-oxidation. It produces some of the more familiar signs of degradation of plastics embrittlement, discoloration and loss of transparency. 

F. Photodegradation of polymers-. Photodegradation of polymers assumes importance in two different contexts (i) ultraviolet and visible radiations are harmful to biopolymers like DNA, polysaccharides, proteins, etc. and an understanding of their mode of photolysis is important in life processes and (ii) more and more use of plastic materials in everyday life has created a problem of disposal. 

There are many different types of glasses made that can have an impact of the photodegradation of pharmaceuticals and their testing results. Among these types are fused quartz, soda-lime, borosilicate (e.g., Pyrex) and a variety of colored glasses. These glasses come in a variety of different shapes such as float, sheet, plate, and cylinder blown glass. They may be chemically treated, coated or laminated with plastic, clear or tinted. 

Walker et al. (26) reported that doxorubicin, 2mg/mL in glass vials or plastic syringes and also 1 mg/mL in plastic syringes, is stable for 124 days when stored at 23°C without photoprotection. However, the photodegradation of anthracycline drug solutions (daunorubicin, doxorubicin, epirubicin) maybe substantial at concentrations below O.lmg/mL, if the solutions are exposed to UV-VIS radiation for longer periods (28,29). Above concentrations of 0.1 mg/mL, little or no photodegradation was observed. 

Furthermore, resistance to photodegradation has also been demonstrated over a wide range of conditions, for periods up to two months. No changes in the photodegradation of 5-FU solutions were found when various diluents or different containers (plastic bags or glass bottles) were studied. Exposure to fluorescent radiation, 24 hours a day, under ambient temperatures had no significant effect on 5-FU stability (53). 

The photolysis of copolymers containing ketone groups has both academic and practical interest since the way in which the polymeric environment affects the photochemical pathways leads to an understanding of the photodegradation of polymers in which the ketone group is present as an adventitious or intended impurity. Copolymers with vinyl ketones also provide a practical means for preparing plastics with controlled lifetimes as a means of combatting litter problems (1.-3). 

Many authors have the opinion that photodegradation of colourless plastic is mainly due to long-lived triplet states of the dissolved colorant. Such triplet states may be... 

Upper layers as well as in the bulk of the material. Hence, different kinetics and sometimes different chemistry of photodegradation of WPC compared with those of neat plastics. 

This practice is technically eqnivalent to ASTM D 2565 (see above) that covers xenon-arc exposnres of plastics intended for long-term use in ontdoor applications. This proce-dnre covers testing of photodegradable plashes intended to deteriorate rapidly when exposed to solar radiation, heat, moistnre, and other degrading elements of the weather. 

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