Peroxidation biodegradation mechanisms

Poly(butylene succinate) is often used in blends with other biodegradable polymers like starch [109], PLA [110-114] and PHAs [115,116]. In many cases PBS is added to other biopolymers to improve properties like heat stability (heat distortion temperature) and impact resistance, and to improve processing behaviour. Although PBS and PLA are immiscible, compatibility is sufficient to allow preparation of blends with good mechanical properties [92, 105]. Peroxides can be used to improve the compatibility of the blend leading to improved impact strength [117]. 

Chitosan (CS) is a partially acetylated glucosamine obtained by deacetylation of chitin, one of the most abundant natural polymers. As a polysaccharide of natural origin, chitosan has many useful features such as nontoxicity, biocompatibility, biodegradability, good mechanical strength and antimicrobial properties. Blends of chitosan (CS) and NR obtained by solvent casting improved the thermal resistance of chitosan. Johns and Rao have also developed chitosan and NR blends vulcanized with dicumyl peroxide (DCP) and... 

Nocardia and P. aeruginosa were shown to break the cw-PI chain by an oxidative mechanism since aldehyde groups were found to accumulate during microbial degradation. This is always the first product formed during the abiotic peroxidation of cw-PI and the evidence suggests that the bacteria initiate a radical-chain peroxidation. This will be discussed further in the context of polyolefin biodegradation. 

A good deal is now known about the kinetics of abiotic peroxidation and stabilisation of carbon-chain polymers and it is possible in principle to extrapolate to the time for ultimate oxidation from laboratory experiments. As already indicated, the key determinant of the time to bioassimilation is the antioxidant and if this is chosen to optimize the service life, bioassimilation can also be achieved as in the case of wood, straw, twigs, etc. It seems that straw is a particularly appropriate model for the biodegradation of the polyolefins since, like the polyolefins, it fully bioassimilated in biologically active soil over a period of about ten years. The most important conclusion from recent work is that nature does not depend on just one degradation mechanism. Abiotically initiated peroxidation is just as important, at least initially as biooxidation. 

The rapid biodegradation of the polyketone obtained by the chemical oxidation of poly(vinyl alcohol) [47,48,49] shown in Scheme 2 supports the proposed mechanism of Suzuki. The byproduct is hydrogen peroxide. 

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