ポリエチレンフィルムの非線型応力緩和挙動の温度依存性

抄録

Relaxation modulus E_r(t, ε) of polyethylene films measured at various temperatures from -20°C to near melting point under strain of 1_??_5% are expressed by following equations:
(1) Time-strain factorized model;
(2) Time-strain reduced model; In the above equations, the nonlinearized functions f(ε) and a_ε (ε) are approximated by where ε₀ is the reduced strain. The α_f; and α_a represent the nonlinearity in the respective models. The nonlinearities of high density polyethylene are greater than those of low density polyethylene at any temperature. The α_f and α_a decrease with increasing temperature in the low temperature range, while they depend less on temperature in the high temperature range.
The α_f and α_a are analyzed by a composite model of crystalline and noncrystalline phase and a free volume theory, respectively. If the various assumptions are introduced in the analyses on the basis of molecular aspects, the above experimental results are interpreted qualitatively.
Master curves of the time-temperature superposition reduced to 20°C at each strain are obtained by the horizontal shift alone. The shift factor a_T(T) is found to be independent on strain at each temperature. The evaluated apparent activation energies, however, are larger than those in references. Since this result can not be explained resonably, it would be still premature to conclude that the time-temperature superposition might hold in the nonlinear stress relaxation process.