Blends of poly[ethylene(vinyl acetate)] and polychloroprene: Studies on capillary and dynamic flows

Rheological properties of the blends of poly[ethylene(vinylacetate)] (EVAc; vinylacetate content 28%) and polychloroprene (CR) have been measured through capillary and dynamic uniaxial elongational flows. Capillary flow indicates their shear thinning behavior. The decrease in the out of phase viscosities with increasing frequency is in accordance with the power law equation, whereas dynamic elongational viscosities follow nonlinear relationship in log-log plot with an initial increase at 11 Hz, followed by a very sharp drop. With an increase in temperature, the viscosity for capillary flow of all blends goes down due to their positive activation energy of flow but for dynamic elongational flow of EVAc blended with CR, viscosity increases, except for 30/70 blend and pure CR, in which case the dynamic elongational viscosity decreases with an increase in temperature. This abnormal behavior in dynamic elongational viscosity is due to the process of melting and recrystallization of EVAc at low heating rate (1 degrees C/min) beyond the melting temperature. Capillary viscosities of all blends show positive deviation from the log additive values of pure polymers. But in the case of dynamic elongational flow, all blends show positive deviation at frequencies of 3.5 and 35 Hz and at higher temperatures (80-120 degrees C). (C) 1997 John Wiley & Sons, Inc.