SPHERULITIC GROWTH-RATES AND COALESCENCE PHENOMENA IN POLYPROPYLENE POLYETHYLENE-BASED IONOMER BLENDS

The isothermal radial growth rates of spherulites of polypropylene in blends with an essentially noncrystallizable ionomer have been determined by photomicroscopy. Blends containing 5 and 10 wt % ionomer, crystallized from the melt, have a grainy appearance due to ionomer entrapment and show an increased nucleation density as compared to pure polypropylene. At large supercooling, these blends also show depressed radial growth rates, which are attributed to a significant dissipation of energy by the crystallizing front to affect the rejection of the ionomer domains. Upon repeated crystallization of a given sample, an increase in the radial growth rate with melt time is observed initially giving rise to a maximum, with general behavior that is dependent upon the blend composition and the crystallization temperature. Beyond this maximum the spherulitic growth rate decreases upon further crystallization. The observed effects on the spherulitic radial growth rates with respect to repeated crystallization are attributed to the coalescence of the ionomer dispersed phase. This is consistent with a concomitant increase in the average domain size.Spherulitic Growth Rates and Coalescence Phenomena in Polypropylene/Polyethylene-Based Ionomer Blends. © 1990, American Chemical Society. All rights reserved.