Viscoelastic behaviour during the crystallisation of isotactic polypropylene

Abstract

Morphology and viscoelastic behaviour during the initial stages of crystallisation of isotactic polypropylene were explored as a function of time and angular frequency by light microscopy and dynamic oscillatory rheology. Results were evaluated according to the Krieger-Dougherty and Palierne models for viscoelastic suspensions of spheres. The data obtained from light microscopy were introduced in the rheological models reproducing quite well the viscoelastic response during crystallisation. The Palierne model was able to describe the behaviour of the system, though it was not possible to observe all the model’s features due to a limited angular frequency range. Further, at high filler contents, an ‘equilibrium’ modulus needs to be introduced for the model to fit the experimental data. The exponent required to model the changes occurring in the ‘equilibrium’ modulus over time resembles that of chemical gelation more than physical gelation.