The Effect of Molecular Weight and Molecular Weight Distribution on the Non-Newtonian Behavior of Ethylene-Propylene-Diene Polymers

The non‐Newtonian melt viscosity‐shear rate relationships of a number of fractions and blends of fractions of ethylene‐propylene‐diene polymers was determined using the Instron Capillary Rheometer. The effect of molecular weight, molecular weight distribution, and temperature of measurements was examined in view of the theoretical derivations by Bueche, and Middleman. The present results could not be correlated by Bueche's expression. The effect of polymer molecular weight distribution given by Middleman was modified by the introduction of chain entanglement. The non‐Newtonian behavior of polymer blends was calculated using the modified equation from the behaviors of individual components. Reasonable agreements were obtained on comparison with experimental results. Empirical relationships for the shear dependence of melt viscosity were derived for the ethylene‐propylene‐diene polymer system. The non‐Newtonian melt viscosity (η)‐shear stress ${\mathrm{(\tau }}_w)$ relationship was correlated by the equation: $\mathrm{Log}\hspace{0.17em}\frac{\eta }{{\eta }_0}{\mathrm{=-K\tau }}_w$ over the range of shear stress from ${10}^6$ to ${\text{2.5×10}}^6\hspace{0.17em}{\mathrm{dynes/cm}}^2.$ The parameter, ${\eta }_0,$ increased with molecular weight and decreased with temperature; whereas the parameter, K, increased with the breadth of the molecular weight distribution over the range of $M_w{\mathrm{/M}}_n\text{=1–20.}$ Samples of very broad molecular weight distributions gave anomolous results. The viscosity at a given shear stress of the polymer fractions is proportional to ${\mathrm{M̄}}_v^b$ with the exponent b essentially constant $\text{(b=3.6)}$ over the range of shear stress studied.