ULTIMATE TENSILE PROPERTIES OF ACRYLONITRILE-METHYLACRYLATE COPOLYMERIC FIBERS: IV. EFFECTS OF MOLECULAR WEIGHT ON ULTIMATE TENSILE PROPERTIES

The variation of creep and creep recovery with temperature, and the ultimate properties under a condition of constant load have been measured for acrylonitrile-methylacrylate copolymeric fibers composed of different molecular weights. In the experiments of creep and creep recovery, the response against external force becomes sensitive with decreasing molecular weight. It is assumed that the response against external force is determined in the relatively low ordered region formed around the end points of molecular chains. In the creep rupture experiments, the following results are obtained. The effects of the molecular weight are clearly observed at the rubbery or leathery zone of the compliance at break and the increase of molecular weight makes the leathery zone shift towards longer times if a reference temperature is fixed at a constant value. In the temperature region approximately from 80 to 130°C; the temperature dependence of the shift factor aT along the logarithmic axis of the time to break is unaltered and independent of the molecular weight. The composite curves of the logarithmic tensile strength plotted against the logarithmic time to break exhibit an identical shape, where the composite curves are obtained from the measurements in the same temperature region stated above. In contrast, the temperature dependence of aT approximately above 130°C and the composite curves of the tensile strength obtained at the corresponding temperature region show different behaviours in accordance with the values of the molecular weight. The maximum value of the ultimate elongation decreases with increased molecular weight. These effects of molecular weight may be explained in terms of “doubly bonded structure” discussed by Andrews and Kimmel.