Crystallization of isotactic polypropylene containing carbon black as a filler

Abstract

Studies on the effect of carbon black on the properties and kinetics of crystallization of isotactic polypropylene are presented in this paper. Polypropylene samples containing 2–30% weight fraction of carbon black were prepared by mixing the initial sample containing 40% carbon black. The samples were produced using a screw injection moulding press. The analysis of melting, crystallization and kinetics of crystallization was carried out using the difference scanning calorimetry at seven stages whose aim was to melt and heat isothermally the filled samples of polypropylene. The analysis covered the dependence of melting and crystallization temperatures on the content of carbon black in the polypropylene. Two stages of crystallization were observed. They were described by means of the Avrami equation. It was found that both the nature of nucleation and growth mechanism of crystalline polypropylene changed depending on the crystallization temperature and black content. Half time of crystallization and induction period of crystallization enabled an in-depth analysis of the crystallization process which led to the conclusion that the rates of nucleation and crystallization increased significantly particularly in the case of samples with a small content of carbon black.