Flow Curves of Mixtures of Acrylonitrile-Styrene Copolymers with Different Molecular Weights at Extremely High Shear Rates

The flow curves of mixtures of acrylonitrile—styrene copolymers with the same S/AN ratio (70/30) and different molecular weights (SAN-1; M_w= 1.88 X 10⁵, SAN-2; M_w = 6.5 X 10⁴) were measured up to the shear rate of 10⁷ s ~ ^l. The second Newtonian and the second non-Newtonian region were observed for SAN-1, SAN-2, and their mixtures (< 10⁶s^-1) following the first non-Newtonian region. The viscosity decreased with decrease of molecular weight (increase of SAN-2 content) and the gradient of the flow curve (log viscosity vs log shear rate) of the mixture became smaller with decrease of molecular weight in the first non-Newtonian region. Flow behavior of the mixture was quite different from that of the immiscible polymer blends. The flow curves of SAN with different molecular weights (> 1.28 x 10^s) united into one curve at the shear rates higher than 5 x 10^ss ^{_ l}.