Polylactic acid, biodegradable polymeric materials

Polylactic acid (PLA) has been produced for many years as a high-value material for use in medical applications such as dissolvable stitches and controlled release devices, because of the high production costs. The very low toxicity and biodegradability within the body made PLA the polymer of choice for such applications. In theory PLA should be relatively simple to produce by simple condensation polymerization of lactic acid. Unfortunately, in practice, a competing depolymerization process takes place to produce the cyclic lactide (Scheme 6.10). As the degree of polymerization increases the rate slows down until the rates of depolymerization and polymerization are the same. This equilibrium is achieved before commercially useful molecular weights of PLA have been formed. 

They are made of polymeric, waxy, or other protective materials, that is, biodegradable synthetic polymers and modified natural products such as starches, gums, proteins, fats, and waxes. The natural polymers include albumin and gelatin " the synthetic polymers include polylactic acid and polyglycolic acid. ... 

U.S. Pat. No. 6,274,652 [127] discloses a biodegradable composite material comprising bacterial cellulose in a powdery state and a polymeric material such as poly-hydroxybutyrate, polyhydroxyvalerate, polycaprolactone, polybutylenesuccinate, polyethylenesuccinate, polylactic acid, polyvinylalcohol, cellulose acetate, starch, and other biodegradable polymers. 

Interest in polymeric materials prepared from renewable natural resources, such as soybean oil, has grown over the past decade. The advantages of these polymeric materials are their low cost, availability, and possible biodegradability (Kaplan, 1998). Among agricultural resources (starch, cellulose, fibers, polylactic acid, cashew nut... 

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