Abstract
Relationships between stress-strain curves and the linear viscoelastic properties and also the dependence of viscosity on a shear rate were investigated using synthetic cis-1, 4-polyisoprene and natural rubber of which Mooney viscosities were from 28 to 70. In the comparison of the zero shear viscosities of both samples in the same Mooney viscosity region, natural rubber showed a higher value than synthetic cis-1, 4-polyisoprene, Stress-strain curves at -10°C to 70°C and under the strain rate, ε, between 1/9 and 1/900 sec-1 were expressed bp the following equations for both samples;
S(t, ε)=(T/T0)f(t)g(ε) and f(t)=(1/t)_??_t0E(ti)dti
where S(t, ε) is stress, E(t) stress relaxation modulus, T absolute temperature, T0 reference temperature and t=ε/ε. g(ε) of synthetic cis-1, 4-polyisoprene well coincided with that of natural rubber. It follows from this that synthetic cis-1, 4-polyisoprene has a lower weight-average molecular weight than natural rubber in the same Moonep viscositp region so that synthetic cis-1, 4-polyisoprene is apt to cold flow and shows a lower green strength than natural rubber.
