1974 Volume 2 Issue 2 Pages 47-52
The change of the gelation state of PVC particles during mixing with a Brabender plastograph was observed by eye and with an electron microscope. At the same time mixtures with different degrees of gelation were prepared with reference to the torque curve, and the effect of the degree of gelation on the capillary flow properties was examined by means of a Koka flow tester.
At the peak position of the torque curve, gelation was incomplete and some particle structure still remained.At a position a little past the peak, a honogeneous structure was attained and gelation was complete.
With increasing gelation, the viscosity increased and also the Barus effect and melt fracture distortions, which are due to melt elasticity, became more noticeable. Moreover, these properties were more pronounced in a material prepared by a tin formulation than in one preparcd by a lead formulation; the former is easier to gelate than the latter.
These experimental results support Berens's hypothesis namely, that an increase of gelation couses the particle flow mechanism to shift to a homogeneous flow mechanism, with a resulting increase ih the viscosity and elasticity.
However, the end correction coefficient, which is another measure of elasticity in capillary flow, decreased with an increase of gelation and was larger in the lead formulation that in the tin formulation. Consequently, it may be assumed that the end correction coeffcient is an inadequate measure of elasticity, at least in materials such as PVC compounds which have inhomogeneous structure and exhibit dilatant flow behavior.