Biodegradation of high-strength and high-modulus PE–starch composite films buried in several kinds of soils

Abstract

The biodegradative behaviors of composite films of ultrahigh molecular weight polyethylene (UHMWPE) (6×106) and starch (ST) particles were investigated. The films were prepared by gelation–crystallization from dilute solutions of PE, in which ST particles were dispersed. The PE–ST compositions chosen were 3/1, 1/1, 1/3, and 1/5. The elongation was done up to 80 times in a hot oven at 135°C under nitrogen. Using the undrawn and drawn specimens, biodegradation of PE was examined by burying the blend materials for 16 months in three kinds of soils, namely, paddy soil, farmyard manure, and red clay. The weight decrease after the degradation was found to be dependent on ST content, draw ratio of original films, type of soils, and burying period. The weight loss was the highest for the specimen buried in paddy soil and lowest for that in red clay. Nevertheless, the changes in the tensile strength and Young's modulus after degradation were most prominent in the specimen buried in the red clay. This result is of interest since the weight decrease in this specimen was lowest. Drastic morphological changes were observed by scanning electron microscopy for the specimens buried in red clay. Significant chain scission of ultra UHMWPE could be observed. The specimen showed the largest decrease in storage modulus. No degradation, however, was observed for the ultradrawn UHMWPE specimen (1/0) buried in red clay. Thus it turned out that the degradation of PE in the composite materials buried in red clay is induced by the dispersed ST particles.