Abstract
The variation of viscosity of various polymer melts under constant shear rate conditions has been investigated using a biconical viscometer, cone-plate viscometer and capillary rheometer. The validity of the biconical viscometer edge zone correction was investigated. Comparisons between the three types of viscometer showed that sample fracture at the material boundary contributed to the decrease of viscosity with time of shearing occurring in the cone-plate viscometer. Polymer melts are subjected to hydrostatic pressure within the biconical viscometer and fracture appears to be prevented. Shear stress - shear rate - time relationships were obtained for the materials studied with the biconical viscometer at shear rates up to a few reciprocal seconds. There was good agreement with capillary data at high shear rates and cone-plate data at low shear rates. A recoverable decrease of viscosity with time of shearing was found to occur. Both the fractional decrease in viscosity and the time taken to recover the original viscosity become smaller as the temperature is increased. Shear stress - shear rate - time relationships were also obtained for volume concentrations of up to 0. 085 of rigid spheres of diameter 75-90 um and 25-4-5 um dispersed in polymer melts. For the suspensions studied, the ratio viscosity of the suspension/ viscosity of the melt evaluated under comparable conditions of shear rate and pretreatment was independent of the time of shearing, up to ninety minutes, and of the shear rate, 0.24-1.42 s[-1]. Control experiments were also carried out with suspensions in a Newtonian fluid. No significant difference in the dependence of n[r] on C[v] was noted from comparisons made either between the various suspensions in the polymer melts studied or between the aforementioned suspensions and those in Newtonian fluids. A description is also given of particle migration effects which were apparent in suspensions which had been sheared for long times in the Biconical Viscometer.