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

The influence of a natural terpene resin, poly(a-pinene) (PaP), on 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 PaP up to 30 wt %, the overall nonisothermal crystallization rate is depressed with respect to plain iPP. This is probably the result of the diluting effect of the polyterpene because the two components are miscible. The 50/50 blend presents, instead, two amorphous phases: an iPP-rich phase and a PaP-rich phase. For this composition, solidification starts at temperatures higher than those for plain iPP and blends with lower PaP content, given that the diluting effect of PaP in the iPP-rich phase is counterweighted by an increased number of nuclei that originate from the polyterpene-rich phase domains. PaP also influences the morphology of iPP spherulites, which are spherical in plain iPP and become more irregular with increasing PaP content. The number and dimension of iPP spherulites depend on blend composition and miscibility of the components. Moreover, the nonisothermal crystallization kinetics of iPP/PaP blends was analyzed with the Ozawa equation.