Factors Affecting Biodegradability

The accessibility of the polymer to water-borne enzyme systems is vitally important because the first step in the biodegradation of plastics usually involves the action of extracellular enzymes which break down the polymer into products small enough to be assimilated. Therefore, the physical state of the plastic and the surface offered for attack, are important factors. Biodegradability is usually also affected by the hydrophilic nature (wettability) and the crystallinity of the polymer. A semicrystalline nature tends to limit the accessibility, effectively confining the degradation to the amorphous regions of the polymer. However, contradictory results have been reported. For example, highly crystalline starch materials and bacterial polyesters are rapidly hydrolysed. 

The molecular weight distribution of the polymer can have a dramatic effect on rates of depolymerisation. This effect has been demonstrated for a number of polymers, where a critical lower limit must be present before the process will start. The molecular origin for this effect is still subject to speculation, and has been attributed to a range of canses such as changes in enzyme accessibility, chain flexibility, fits with active sites, crystallinity, or other aspects of morphology. 

Albertsson and S. Karlsson in Degradable Materials Perspectives, Issues and Opportunities, Eds., S.A. Barenberg, J.L. Brash, R. Narayan and A.E. Redpath, CRC Press, Boca Raton, FL, USA, 1990, 263. 

Albertsson and B. Ranby, Journal of Applied Polymer Science Applied Polymer Symposia, 1979, 35, 423. 

Austin in Degradable Materials Perspectives, Issues and Opportunities, 

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This section focuses on (1) a discussion of the overall process of biodegradation, (2) a review of the different types, aspects and phases of biodegradation of several classes of organic pollutants, (3) an examination of the environmental factors affecting biodegradation and biotransformation mechanisms, and (4) a description of the different biodegradation and biotransformation pathways. 

The data presented illustrate the need of further studies on the factors affecting biodegradation of environmental persistent chemicals sorbed on sludge and soil nnder both aerobic and anaerobic conditions. 

Chu, C.C., 1995a. Biodegradable suture materials intrinsic and extrinsic factors affecting biodegradation phenomena. In Handbook of Biomaterials and Applications, D.L. Wise, D.E. Altobelli, E.R. Schwartz, M. Yszemski, J.D. Gresser, and D.J. Trantolo, Eds., Marcel Dekker, New York. 

This volume in the series deals in a timely and comprehensive manner with the crucial topic of biodegradable polymers of natural synthetic or semi-synthetic origin. All the key classes of absorbable polymers used in the fabrication of microspheres and nanospheres, membranes, reservoirs and other components ofinjected or implanted delivery systems are covered. A better understanding of the chemical and physical factors affecting biodegradability will allow more precise prediction of the lifetime of systems in vivo and the more informed choice of polymeric vehicle. 

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