Nonisothermal crystallization of isotactic polypropylene blended with poly(alpha-pinene). I. Bulk crystallization

The influence of a natural terpene resin, poly(alpha -pinene) (P alphaP), o n the nonisothermal crystallization process of isotactic polypropylene (iPP ) was investigated. The solidification process strongly depends on cooling rate, composition, and miscibility of the system. For the blends containing P alphaP up to 30 wt %, the overall nonisothermal crystallization rate is depressed with respect to plain iPP. This is probably the result of the dil uting effect of the polyterpene because the two components are miscible. Th e 50/50 blend presents, instead, two amorphous phases: an iPP-rich phase an d a P alphaP-rich phase. For this composition, solidification starts at tem peratures higher than those for plain iPP and blends with lower P alphaP co ntent, given that the diluting effect of P alphaP in the iPP-rich phase is counterweighted by an increased number of nuclei that originate from the po lyterpene-rich phase domains. P alphaP also influences the morphology of iP P spherulites, which are spherical in plain iPP and become more irregular w ith increasing P alphaP content. The number and dimension of iPP spherulite s depend on blend composition and miscibility of the components. Moreover, the nonisothermal crystallization kinetics of iPP/P alphaP blends was analy zed with the Ozawa equation. (C) 2001 John Wiley & Sons, Inc.