Abstract
The low shear rate viscosity behavior of SBR random copolymers is investigated in steady and transient shear flow. The polymers studied have high enough molecular weights to make them of commercial interest. The measurements were performed on an apparatus specially designed but readily available and easy to operate. The results showed that even at very low shear rates, the polymers exhibit non-Newtonian steady shear viscosities. A log-log plot of zero shear rate viscosity vs weight-average molecular weight yields a straight line of slope 3.5. The transient shear data show no stress overshoot at shear rates when the viscosity is non-Newtonian. A theoretical discussion of the independence of these two nonlinear effects is provided. The discussion is based on some popular single-integral constitutive equations. It is shown that a recent modification by Carreau to the Lodge elastic liquid model is very realistic. That is, Carreau's model allows one to obtain separately transient shear stress overshoot and non-Newtonian steady shear viscosity.
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