Bioassimilation by microorganisms

Hydroperoxides and their breakdown products are of fundamental importance to polymer biodegradation. Not only are they the cause of the free radical chain reaction by rapid dissociation caused by thermal (A) and UV (hv) energy to give initiating radicals (reaction but PO is also the source of the ultimate low molar mass degradation products that are readily bioassimilated by microorganisms. 

Water-swellable or -soluble polsrmers maybe biodegraded by microorganisms if they contain functional groups that are susceptible to enzymatic cleavage. There is considerable evidence that biodegradation is ssmergistic with hydrolysis, which may be chemical or enzymatic and is required to reduce the molecular weight to the point where bioassimilation is possible. 

Natural rubber was one of the earliest industrial polymers to be developed commercially and it was recognised even before it reached the industrialised countries that it very rapidly lost its initial useful properties in the environment. Furthermore, rubber latex products were rapidly attacked by microorganisms, leading to more general loss of mechanical properties and to eventual bioassimilation in the soil environment . 

The evaluations indicated in the side-branches of Fig. 5 have a different purpose. They are intended to show from a scientific standpoint that the oxidation products formed from degradable polyolefins in the natural environment are bioassimilated by soil microorganisms. It would be ideal to take samples of plastics from compost at intervals to carry out biometric (carbon dioxide formation) tests and to measure mass-loss due to bioerosion of the plastic. However, this is a difficult procedure since CO2 formation is concomitant with mass loss during composting and it is difficult to achieve even an approximate mass balance. 

The limited bioassimilation observed in the case of the aPHB2 sample can be explained by considering that very likely PVA-degrading microorganisms are able to use only the low molecular weight finctions of atactic PHB. 

David and co-workers [57] confirmed the bioerosion of polyethylene films, peroxidised in the presence of cobalt acetylacetonate (Coacac) at 40°-70 °C both in compost and in a liquid medium by respirometry in the presence of an extract of microorganisms obtained from compost. The latter provides a method of measuring bioassimilation complementary to that described above. Table 5 shows PE degradation as... 

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