抄録
The effects of pre-elongation ratio, stress relaxation time and recovery time on the hysteresis behavior of the stress-strain curve are discussed for segmented Poly(urethane-urea).
The loss of stress and extension energy was found to be much larger than unrecovered strain with pre-elongation. In the range of low extension ratio of α<2, the large loss in shear modulus was shown for unloading and re-elongation curves. However the breaking energy of the linkages was lower than 0.75kJ/mol. As for the range of 2<α<3.5, the linkage having the bond energy of 20 kJ/mol were broken by pre-elongation. The pre-elongation of α>4 led to break the linkages having the strong bond energy of 75kJ/mol. This energy corresponds to the break down of intermolecular hydrogen bond of hard segment. The molecular weight between cross-link points(Mc) estimated by shear modulus of unloading or re-elongation curves was almost the same as that of the prepolymer. The strong hydrogen bond of 75kJ/mol between hard segments re-bonded and recovered faster than other weaker linkages.
The Moony-Rivlin plots of unloading and re-elongation curves had much smaller values of C2 than those of the pre-elongation curves. This suggests that the strain softening effect decreased by preelongation. It is especially interesting that the unloading curve for elongation of α>4 had the value of C2_??_0 and showed ideal rubber elasticity.
