MODIFYING AGENTS
Various modifying agents are used
with polymers to obtain certain specific properties. These modifiers are known
to be microbial nutrients. This includes some lubricants and plasticizers. With
the large number of destructive agents and the adaptability of each, it is highly
probable that there are no plasticizers that are completely free from fungal or
bacterial attack. Some are readily used by the microorganism as the source of
carbon. As the microorganisms grow, they secrete digestive enzymes which
accelerate the degradation process of the film by advancing the mycelial
growth. The destruction of polymer by plasticizer results in tack and
exudation, embrittlement, weight loss and discoloration.
Polyolefins in
their unmodified form exhibit excellent resistance to biological destruction.
When these polymers are compounded with additives or plasticizers the biological
decomposition varies in degree and also is of various types. Plasticizers are
substances that are added to plastic compounds to improve their flexibility,
extensibility and processibility. Deterioration of the polymer by
microorganisms is chemical, involving changes in composition and breaking of
chemical bonds. It is the result of enzymes produced by the microorganisms. Various
plasticizers that exhibit higher susceptibility towards microbial attack are: acetals,
butyrates, laurates, oleates, sebacates, epoxidized oil, epoxidized tallate
esters, polyester, glycolates, stearates, abiotic acid derivatives, aliphatic
acid derivatives, aliphatic alcohols, n-phthalic acid derivatives, rcinoleates,
succinic acid derivatives. Vegetable oils like tung oil, linseed oil, soy bean
oil, cottonseed oil, castor oil, dehydrated castor oil, ground nut oil, etc,
also exhibit higher susceptibility towards microbial attack.
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