The high temperature secondary crystallisation of aged isotactic polypropylene

Abstract

The secondary crystallization of aged isotactic polypropylene (iPP) of different morphologies, which occurs during annealing in the vicinity of the melting temperature (140 degreesC), was studied using differential scanning calorimetry (DSC) and density measurements. The results of calorimetric and density measurements were correlated. Kinetics of the high temperature secondary crystallization (HTSC) was studied by using Avrami relations. Avrami exponents, obtained according to the increase in crystallinity after annealing at 140 degreesC, were considered as the measure of the ability of iPP to crystallize secondarily. Depending on the initial morphology of the samples, accelerated ageing influences in different ways the ability of iPP to subsequently crystallize upon annealing. The aged samples with larger amorphous content show a reduced secondary crystallization at high temperature compared with the unaged samples. On the other hand, aging of medium crystalline samples leads to more pronounced HTSC. (C) 2004 Elsevier Ltd. All rights reserved.