抄録
Stress relaxation measurements under various strain from 1 to 5%, have been carried out for polyethylene films having different degree of crystallinity at various temperatures from -20°C to near melting point.
Stress relaxation modulus can be described approximately by a power series polynomial in strain. Validity of time-temperature superposition for the coefficients Fn(t) of polynomial have been examined (n=1, 2 for low density and n=1, 2, 3 for high density polyethylene). The stress relaxation master curves of Fn (t) were obtained by a digital computer by means of the mini-max method in a temperature range of -20°C to 60°C for low density and to 110°C for high density sample. Temperature dependence of shift factor aT gave two straight lines, when plotted in log aT vs 1/T, intersecting at about 40°C for low density and 70°C for high density sample. The master curves of the first coefficient F1 (t) were compared with the results of the linear viscoelastic region obtained by Fujino and others. It was found that there were good agreement between both curves. These facts suggest that the relaxation mechanism observed for the nonlinear region seemes to be same as that of the linear region.
