Carbon chain polymers, abiotic

Scott G (1995) Introduction to the abiotic degradation of carbon chain polymers. In Scott G, Gilead D (eds) Degradable polymers principles and applications. Chapman 8c... 

In the case of PVA, which is one of the few carbon-chain polymers that does not need to be abiotically peroxidised before biological attack, polyketones are the initial products and these are catabolysed to carboxylic acids and bioassimilated by bacteria e.g. Pseudomonas). Kawai has shown (personal communication) that the PEGs behave rather similarly and are bioassimilated by Sphingomonas. The active enzymes are believed to be PEG dehydrogenase coupled with cytochrome c, the oxidase enzyme of the baeterial respiratory system. Since the polyethers are also very peroxidisable abiotically, abiotic peroxidation may also play a part in the overall process. 

Introduction to the abiotic degradation of carbon chain polymers... 

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 above discussion allows us to conclude that the bioassimilation of synthetic carbon-chain polymers has much in common with that of their natural analogues (notably natural rubber, resins and lignin). In all cases, nature uses abiotic oxidation chemistry together with biotic chemistry, very often together. The degradation products formed by oxo-biodegradation are of benefit to the agricultural environment as biomass and ultimately in the form of humus. 

The term antioxidant is used to describe the inhibition of polymer peroxidation in both abiotic and biotic systems [6,8,11]. It embraces more specific technological terms such as antidegradants (thermoantioxidants), antifatigue agents (mechanooxidation inhibitors) and light stabilisers (photoantioxidants). It was seen above that peroxidation of carbon-chain polymers occurs by a free radical chain mechanism (reactions 1 and 2) and that the hydroperoxide products that are the intrinsic initiators for peroxidation dissociate to oxyl radicals under the influence of heat and light. Both hydroperoxide formation and hydroperoxide decompostion are thus catalysed by transition metal ions. 

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