Influence of shear on polypropylene crystallization kinetics

Isothermal crystallization kinetics under shear in the melt of iPP was investigated by optical microscopy. It appears that shearing from 200 to the crystallization temperatures enhanced the kinetics, but the shear effect was not obvious if the melt of iPP was sheared only at 200. The experiment results show that relaxation plays an important role during crystallization, and that spherulite growth rates increased with shear rates and were governed by relaxation. The effect of flow on the crystallization kinetics can be understood by considering that the increase of the degree of order due to flow results is an effective change of the melt free energy. The Laurizen-Hoffman theory and the DE-IAA model were used to describe the shear-induced crystallization kinetics of iPP excellently.