Effect of shear flow on spherulitic growth and nucleation rates of polypropylene

Abstract

The effect of flow on the crystallization kinetics of polymers is well known, at least from a qualitative point of view. Quantitative determinations are difficult to obtain, due to the experimental difficulties of obtaining direct measurements of nucleation and growth rates during flow. In this work, step shear tests were conducted in the Linkam device adopting a new protocol in which the flow is applied when the crystalline structures have already reached dimensions easily detectable by an optical microscope. This delayed protocol allowed to achieve a more accurate experimental analysis of the effect of flow on spherulite growth rate with respect to what already reported in the literature. The new results obtained for the growth rate were interpreted, with the equilibrium melting temperature function of the shear rate. Also the nucleation rate could be assessed and the existence of a correlation between nucleation rate and growth rate was confirmed.