Photo-biodegradable polymers

Four main types of polymer are currently accepted as being environmentally degradable. They are the photolytic polymers, peroxidisable polymers, photo-biodegradable polymers and hydro-biodegradable polymers. Commercial products may be composite materials in which hydrolysable and peroxidisable polymers are combined (e.g. starch-polyethylene composites containing prooxidants). The application, advantages and limitations of each group will be briefly discussed. 

Scott, G. 1995. Photo-biodegradable plastics. In Degradable polymers Principles and applications, eds. G. Scott and D. Gilead, 170. New York, NY Chapman and Hall. 

Photo-biodegradation Degradation of the polymer is triggered by UV light and assisted by the presence of UV sensitisers. In this process the polymer is converted to low molecular weight material and in a second step converted to carbon dioxide and water by bacterial action. 

Figure 3.2 Mechanical property change of photo-biodegradable polyethylene carrier bags during outdoor exposure in England (Reproduced with permission from D. Gilead and G. Scott, in Developments in Polymer Stabilisation - 5, ed. G. Scott, Applied Science Publications, 1982, p. 103)...

Farmers are notoriously conservative and do not take kindly to innovations in agricultural practice, particularly if it is likely to cost more. The key question then in considering the viability of photo-biodegradable plastics is do they improve profitability Nowhere is cost more important than in China and yet a much higher proportion of the annual output of the polymer industries is used in agriculture in China than anywhere else in the world (Table 5.1) and this usage increased almost 2000 times between 1980 and 1991 (Table 5.2). 

S-G photo-biodegradable polyethylene is now being used in a different way to reduce the pollution of water courses by fertilisers. By encapsulating the fertiliser in porous photo-biodegradable capsules fertiliser release times can be achieved from 40 days to one year. Nitrogenous fertiliser based on this principle are manufactured by Chisso-Asahi Fertilizer Company of Japan and scientific studies by Kawai of Okayama University have shown (personal communication) that the empty polymer capsules biodegrade rapidly in soil. 

G. Scott, Photo-biodegradable plastics their role in the protection of the environment, Polym. Degrad. Stabil, 1990, 29,135-154. 

Torikai A, Kato H, Fueki K, Suzuki Y, Okizaki A, Nagata M (1993) J AppI Polym Sci 50 2185 Andrady AL, Accelerated environmental exposure. Laboratory testing, and recyclability study of photo/biodegradable plastics . Final Report to USEPA under Contact 68-02-4544 Task 11-60. January 1991. 

SYNTHESIS OF BIODEGRADABLE WATER-SOLUBLE POLYMERS 505 Table 12.2 Photodegradation of Photo/Biodegradable Carboxylates... 

Figure 9.1 Ideal behaviour of a photo-biodegradable LDPE film for use as a protective mulch ( indicates that the polymer is brittle).

Scott, G., 1995, Photo-Biodegradable Plastics. In Degradable Polymers Principles and Applications (Chapman Hall, eds.), London, 9 169-185. 

Commercial polyolefins show no significant reduction in molar mass in typical ambient biometric tests over many months or even years. The resistance of hydrocarbon polymers to biodegradation during use is one of their major advantages in agricultural application over bio-based plastics. The useful life of photo-biodegradable polyolefins is controlled commercially by appropriate transition metal complexes in which the ligands are... 

Scott G (1995) Photo-biodegradable plastics in Scott G and Gilead D, eds. Degradable Polymers Principles and Applications, 1st edn. Chapman Hall (Kluwer Acad. Pub.), Chapter 9. 

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