Studies on Elongational Viscosity of Polymer Melts

Abstract

This paper summarizes an experimental study on an elongational rheometer and elongational viscosity measurements of polymer melt developed by the present author and his coworkers. The elongational viscosity increases with time by two steps: One is a gradual viscosity increase at small strain and the other is a rapid viscosity increase at large strain. The rapid viscosity increase behavior does not depend on strain rate, temperature, and average molecular weight, but does depend on molecular weight distribution and chain branching. These experimental results were explained by introduction of small amount of extremely long relaxation time mode into the normal relaxation spectrum which is estimated from linear viscoelastic data. The elongational rheometer can quickly detect the extremely long relaxation time mode.