1996 Volume 1996 Issue 4 Pages 325-333
We examined the effect of microbes on several polymer samples which were buried under bio-active soil for over 32 years. We found that low density polyethylene (LDPE) films degraded considerably un, der biotic action, while no evidence was obtained for the degradation of urea formaldehyde resin (UF), polystyrene (PS), and poly (vinyl chloride) (PVC). The part of LDPE which was in directly contact with soil was severely degraded and characterized by whitening. On the other hand, the part which was not in contact with soil was transparent. A distinct difference was observed in surface FT-IR spectra of the whitened and transparent parts. The main oxidation products observed for the clear parts are carboxylic acids and ketones, while for the whitened parts the carbonyl absorption bands considerably decreased and was supplemented by the increase of the absorption by the carbon-carbon double bonds. By comparing with the results of the bio-degradation of LDPE under a well controlled environments, we concluded that the degradation of the clear parts proceeds by the normal oxidative process, while the d egradation of the whitened parts was explained by the complex mechanism of the oxidative degradation and bio-degradation. Under the biotic conditions, it has been suggested that the scission of alkoxyl radicals may proceed via γ-scission mechanism to form vinyl groups and volatile products in addition to the normal β-scission mechanism.
Our results showed t hat even the high molecular weight LDPE is degradable to form low molecular weight products by a biotic oxidation process, if they were concealed under bio-active soil for several ten years. It was also shown that the formation of active oxidation sites is essential for the acceleration of the bio-degradation of LDPE.
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