Aliphatic Polyesters Biodegradation

Aliphatic polyesters are degraded by microorganisms present in the environment. A list of microorganisms capable of degrading PCL [2], PHB [43], PLA [44] and PBS [45] can be found elsewhere. 

The biodegradation of polyesters is also affected by the chemical structure, hydrophilic/hydrophobic balance within the main chain, MW and crystallinity, which acts as a hindrance to biodegradability. In fact, biodegradation first takes place in the amorphous region of the polymer, where the erosion rate is much higher than in 

Rizzarelli and co-workers [50] studied a set of polyalkylene dicarboxylates derived from 1,4-butandiol and methyl esters of succinic (PBS), adipic and sebacic acids. The soil burial degradation test was performed at 30 0.1 °C, under moisture controlled conditions, using a mixture of milled perlite and soil. The incorporation of butylene adipate units and butylene sebacate units in the polymer chain gave rise to an enhancement of biodegradation. 

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Keywords Aliphatic polyester Biodegradable polymer Functionalized polymer Lactone Living polymerization Macromolecular engineering Ring-opening... 

Discarded conventional plastics remain in the environment for decades. They block sewers and drains, disfigure the streets, beaches and countryside, and kill wildlife on land, in rivers and oceans. To overcome these problems increasing attention has been paid to the development of degradable plastics (1) starch-based, biodegradable, (2) aliphatic polyesters, biodegradable, (3) photodegradable, and (4) oxo-biodegradable. 

Why are many aliphatic polyesters biodegradable and which parameters control the differences in the degradation rate ... 

Biodegradation of the aliphatic polyesters occurs by bulk erosion. 

Ethoxylation of the carboxylic acid end groups of aliphatic polyesters significantly changes the biodegradation rate as well as the crystallinity of these materials (41). 

Pitt, C. G., Marks, T. A., and Schindler, A., Biodegradable drug delivery systems based on aliphatic polyesters application to contraceptives and narcotic antagonists, in Controlled Release of Bioactive Materials (R. Baker, ed.). Academic Press, New York, 1980, pp. 19-43. 

If the homopolymer decomposes at the fabrication temperature another approach is to make a copolymer that can be melt processed at a lower temperature. For example, polyhydroxybutyrate decomposes at the processing temperature (190°C), whereas the copolymer with valeric acid can be processed at 160°C without decomposition. These aliphatic polyesters are biodegradable and most importantly, the decomposition products are not toxic, hence their use in medical applications (e.g., sutures). 

Common biodegradable polymers for medical devices are constructed from synthetic linear aliphatic polyesters. One material commonly used for internal sutures is poly(glycolic acid) (PGA). PGA is synthesized from the dimer of glycolic acid (Fig. 13.1.l). 1... 

Syntheses of aliphatic polyesters by fermentation and chemical processes have been extensively studied from the viewpoint of biodegradable materials science. Recently, another approach to their production has been made by using an isolated lipase or esterase as catalyst via non-biosynthetic pathways under mild reaction conditions. Lipase and esterase are enzymes which catalyze hydrolysis of esters in an aqueous environment in living systems. Some of them can act as catalyst for the reverse reactions, esterifications and transesterifications, in organic media [1-5]. These catalytic actions have been expanded to... 

In 2002, Lee et al. [51] reported the biodegradation of aliphatic polyester-based nanocomposites under compost. Figure 9.13(A, B) represent the clay content dependence of biodegradation of APES-based nanocomposites prepared with two different types of MMT clays. They assumed that the retardation of biodegradation was due to the improvement of the barrier properties of the aliphatic APSE after nanocomposite preparation with clay. However, there are no data about permeability. 

Biodegradation of the aliphatic polyesters occurs by bulk erosion. The lactide/gly-colide polymer chains are cleaved by random nonenzymatic hydrolysis to the monomeric lactic and glycolic acids and are eliminated from the body through the Krebs cycle, primarily as carbon dioxide and in urine. 

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