Recrystallization behavior of β-phase isotactic polypropylene by heating

Recrystallization behavior of beta -phase iPP by heating was studied using DSC, WAXD and photomicrograph measurements. The heating rate dependence of the melting temperature was obtained at rates of 1.25-80 k/min. When the sample is heated at a slow rate, the melting and the crystallization processes occur at about the same temperature. And the recrystallization process is the beta - > alpha transition. The melting temperature of the resultant does not depend on the heating rate. Annealing procedures used were a combination of slow heating (5K/min) to T sub a (T sub a = 382-444K) and subsequent rapid cooling (40K/min) to room temperature. The resultant structure was measured by rescanning with the constant heating rate of 40K/min. By heating to 402-416K with a heating rate of 5K/min, beta -phase iPP slightly recrystallized to alpha -phase. The melting temperature of beta -phase (T sub m ( beta )) increased with T sub a in the range of T sub a = 416K to T sub a = 422K and it became 429.1K for the sample annealed at T sub a = 422K. But the sample annealed at higher temperatures (T sub a > 428K) could not find the existence of beta -phase. , . 8 ref.--AA