Kinetic crystallization of polypropylene in ternary composites based on fiber-reinforced PP-EPDM blends

The crystallization of isotactic polypropylene (iPP) in its blends with eth ylene-propylene-diene terpolymer (EPDM), reinforced with different fibers, is described in this work. In particular, the effects of both the fibers an d the EPDM on the crystallization kinetics and morphology of IPP are analyz ed. The study was performed using differential scanning calorimetry (DSC) i n dynamic and isothermal conditions and optical microscopy. It was found th at all the fibers act as effective nucleant agents on iPP crystallization i ndependently of the blend composition. The results obtained highlight the a ccelerating effect of the fibers and of the EPDM on the PP crystallization up to a certain EPDM percentage. The halftime of crystallization, tau (1/2) , and the overall crystallization rate, K,, increase in the presence of all the fibers analyzed, showed the aramidic ones the most effective. The isot hermal crystallization kinetics of ternary composites based on PP-EPDM blen d matrices reinforced with different types of fibers can be modeled using t he Avrami equation. On the other hand, the kinetic curves obtained under no nisothermal conditions provide a further confirmation of the nucleating act ion of the fibers on the PP crystallization. Optical polarizing microscopy was also used to investigate the effect of EPDM on the spherulite growth an d the transcrystallinity phenomenon on the surface of the fibers. The resul ts of such analysis showed that the transcrystallinity phenomenon is hinder ed at high rubber percentages. As in the case of the rate of crystallizatio n, the highest proportion of transcrystallinity was observed in the presenc e of the aramidic fibers. (C) 2001 John Wiley & Sons, Inc.