Abstract
AbstractOzawa macrokinetic model is applied to describe the nonisothermal melt crystallization process of polypropylene (PP), in natural rubber/polypropylene (NR/PP) thermoplastic elastomers (TPEs) as a function of blend ratio and dynamic vulcanization of the rubber phase. It was found that as cooling rate increases, the crystallization temperature Tc and half time for crystallization t1/2 get diminished. Dynamic vulcanizates show a similar trend in crystallization as that of neat PP. Crystallization rate constant and Ozawa exponent were found out for different temperatures by linear regression method using Ozawa analysis. Ozawa exponent, nO, showed variation in values when the conversion proceeded. For neat PP, the value of nO changes from 1.4 (102°C) to 3 (112°C). The nO values for NR/PP 50/50 blend were higher (e.g. 4.1 at 116°C). Crystallization rate constant KO shows a maximum at 0.5 relative crystallinity. The highest crystallization rate constants were found for NR/PP 50/50 TPEs. The activation energy for the melt crystallization was found to vary with the degree of conversion, as well as with the concentration of NR in the TPEs. Finally, attempts have been made to correlate the crystallization process with morphology of the blend. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
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