Study of the crystallization behaviors of polypropylene and maleic anhydride grafted polypropylene

Abstract

The crystallization kinetics of isotactic polypropylene (iPP) and maleic anhydride grafted polypropylene (MA-PP) and their blends, crystallized both nonisothermally and isothermally, were investigated by differential scanning calorimetry, During isothermal crystallization, relative crystallinity developed with the time dependence described by the Avrami equation with exponents n approximate to 2.7 for neat iPP and n approximate to 3.8 for MA-PP. The half crystallization time for MA-PP was much smaller than that for iPP. The half crystallization time of iPP depended more strongly on the crystallization temperature than that of MA-PP did. A kinetic equation for nonisothermal crystallization was employed to analyze the crystallization characteristics of iPP and MA-PP. The nonisothermal crystallization kinetic analysis for MA-PP at different cooling rates was possible, assuming that the spherulitic growth was initiated by heterogeneous nucleation alone while that for iPP at high cooling rates was successfully done by assuming both homogeneous and heterogeneous nucleations. The diffusional activation energy was smaller for MA-PP than for iPP. The number of heterogeneous nuclei for MA-PP was larger than that for iPP. The presence of MA-PP in iPP affects the crystallization of iPP by acting as a nucleating agent. (C) 1999 Elsevier Science Ltd. All rights reserved.