Studies of time effects in the flow of polymer melts using a biconical viscometer

摘要

AbstractThe variation of viscosity of various polymer melts under constant shear rate conditions has been investigated using a biconical viscometer, a cone‐plate viscometer, and a 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 occuring 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 i