Mechanical Properties and Biodegradation Characteristics of Biaxially Stretched Ultra-High Molecular Weight Polyethylene and Starch Composite Films

publisher[Synopsis] Simultaneously biaxial-stretching measurement was carried out using ultra-high molecular weight polyethylene (UHMWPE) dry gel films which were prepared by crystallization from solutions at the UHMWPE concentration of 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 g/100m1. The maximum draw ratio was dependent upon the concentration of UHMWPE during preparing. The greatest significant draw ability could be realized at 0.9 g/100m1 which was much higher than the optimum concentration of 0.45 g/100ml assuring the draw ratio＞ 300-fold for uniaxial stretching. Young's modulus of the biaxially stretched film was much lower than that of uniaxial films with the same draw ratio (70-fold), although the Young's modulus of the film with the maximum draw ratio was much higher than that of commercial films. The biodegradation of biaxially stretched composite films by using UHMWPE, with viscosity average molecular weight of 6×10＾6, and starch at the ration of 1/1 and 1/5 were investigated. Most of starch particles were remained within the composite films after stretching. Biodegradable behavior of the composite films was examined by burying the samples in two kinds of soils, paddy soil and red clay, for 16 month. The weight decrease after the degradation was evaluated and found to be dependent on the starch content, draw ratio and soil kind. The weight loss of the samples buried 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 UHMWPE domain. This phenomenon is in good agreement with the decrease of melting point of UHMWPE measured by differential scanning calorimetry (DSC). However, no degradation was observed for the stretched ultra-drawn UHMWPE sample (1/0) buried in red soil. This indicates that the biodegradation of UHMWPE in the composite films buried in red clay is induced by the dispersed starch component