Microbial and oxidative effects in degradation of polyethene

Biodegradative conversion of 14 C present in high‐density (linear) polyethene (HDPE) film to respiratory 14 CO 2 during a two‐year aerated cultivation with soil or with Fusarium redolens dropped from 0.36% by weight to less than 0.16% by weight when the HDPE film was deprived from most of its low molecular components by extraction with cyclohexane. Decrease of 14 CO 2 production after extraction could be observed in different abiotic aging cultures. This is direct evidence for a primary utilization of the short‐chain oligomeric fraction of the main crystalline materials. The extractable oligomeric fraction of HDPE was analyzed by gel permeation chromatography (GPC), and M n 1049, 1088, and 1297 were found in untreated, aged, and biodegraded materials, respectively, indicating that microbes can oxidize somewhat longer polyolefin chains than aboitic forces do during aging. The limited degradation of HDPE confined to extractable material is comparable to the degradation of straight‐chain n ‐alkanes and presumably proceeds according to similar mechanism. Such material ( n ‐alkanes) can exit in the interstitial spaces between the crystalline lamellae as fringed micelles which infiltrate these cavities as amorphous clusters but are also produced to some extent during aging and weathering. Protection of HDPE by antioxidant (a sterically hindered phenol) resulted in an inhibition of microbiological catabolism of 14 C to 14 CO 2 . Aging was also suppressed in this way, indicating that although remnants of the supported CrCO 3 polymerization catalyst are responsible for a slight but cumulative abiotic oxidation of the unprotected polymer, this effect will be counteracted too by the antioxidative additive. As biological degradation is superimposed on the chemistry of aging, a mutual synergism between the two effects is feasible.