32〜37年間土壌埋没LDPEの生分解性の検討,劣化分解のメカニズム

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Degradation of low density polyethylene (LDPE) concealed in soil for 32-37 years was examined. A large weight loss which is due to the oxidative degradation was observed. The degradation was particularly noteworthy for the whitened parts which were directly in contact with the soil. Several metal ions were concentrated in these regions. These ions were considered to participate the redox type decomposition of hydroperoxides formed along the polymer chain. ESCA analysis has revealed that the oxidation is most remarkable on the extreme surface of the LDPE film.The surface FT-IR spectrum of the whitened parts compared with that of the clear parts of the film which were not in contact with soil. The distinct difference between two parts was observed. 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 biodegradation of LDPE under a well controlled environments, we concluded that the degradation of the clear parts proceeds by the normal oxidative process, while the degradation of the whitened parts was explained by the complex mechanism of the oxidative degradation and biodegradation. Under the biotic conditions, it has been suggested that the scission of alkoxy radicals may preceed via γ-scission mechanism to form vinyl groups and volatile products in addition to the normal β-scission mechanism.Our results showed that even the high molecular weight LDPE is degradable to form low molecular weight products by a biotic oxidation process, if they were concealed under bioactive soil for several ten years. It was also shown that the formation of active oxidation sites is essential for the acceleration of the biodegradation of LDPE.
日本ゴム協会の論文

32〜37年間土壌埋没LDPEの生分解性の検討,劣化分解のメカニズム

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