Biodegradation of biaxially stretched polyethylene-starch composite films

The biodegradation of biaxially stretched composite films were investigated by using ultra-high molecular weight polyethylene (UHMWPE) with viscosity average molecular weight of 6x10 super(6) and starch. The films were prepared by gelation/crystallization from dilute solutions of polyethylene (PE), in which starch particles were dispersed. The UHMWPE-starch compositions chosen were 1/1, and 1/5. After stretching, most of starch particles were remained within the composite films. Biodegradative behavior of the composite films was examined by using the samples buried in two kinds of soils, paddy soil and red clay, for 16 months. The weight decrease after the degradation was evaluated and found to be dependent on the starch content, draw ratio of films and kinds of soil. The weight loss of the samples buried in paddy soil was larger than that of the sample buried in red clay. However, the decreases in the storage modulus of the film sample buried in red clay were larger than that buried in paddy soil. This result is of interest since the order of weight decreasing rate for these samples is opposite. Significant morphological changes were observed by scanning electron microscopy (SEM) for the samples buried in red clay. The photograph of the samples buried in red clay revealed that drastic morphological changes occurred not only in the starch domain but also in the PE domain. This phenomenon is in good agreement with the decrease of melting point of polyethylene measured by differential scanning calorimetry (DSC). However, no degradation was observed for the stretched PE sample (1/0) buried in red clay. This indicates that the biodegradation of PE in the composite films buried in red clay is induced by the dispersed starch component.