COMPARISON OF PREMELTING AND RECRYSTALLIZATION BEHAVIOR OF BETA-PHASE ISOTACTIC POLYPROPYLENE BY HEATING AND COOLING AT DIFFERENT RATES

Different heat treatments (heating and subsequent cooling with quick or slow rates but up to the same temperature in the melting range) were made on beta -polypropylene ( beta -PP), and premelting and recrystallization behavior were compared using d. s. c. and WAXS measurements. The results suggest that, under our experimental conditions, lamellar growth during heating and cooling takes place chiefly at the expense of, or under the existence of, a melt neighboring to the lamella, and that the growth in the solid state by molecular refolding plays a minor role. The influence of the recrystallized alpha -phase, yielded during heating, on the growth of beta -form is also discussed.