Isothermal crystallization of isotactic poly(propylene) studied by superfast calorimetry

摘要

The isothermal crystallization behavior and the structure and morphology of isotactic poly(propylene) (iPP) and iPP/hydrogenated hydrocarbon resin (HR) 90/10 blend were analyzed. To cover the entire temperature range, isothermal crystallizations were studied using superfast calorimetry at a high cooling rate in the range 0 to 110 degrees C, and by conventional DSC at a low cooling rate in the range 120 to 140 degrees C. Structural and morphological changes due to the different thermal treatments were also analyzed. The complete crystallization curve ranging from T-g to T-m showed bimodal crystallization behaviors for both iPP and iPP/HR 90/10 blend. This result is explained by taking into consideration the polymorph properties of iPP. It is in fact assumed that the curve from T-g to 60 degrees C referred mainly to the : crystallization kinetics of the iPP mesomorphic form by homogeneous nucleation, whereas the curve from 60 degrees C to Tm mainly represented the crystallization kinetic curve for the monoclinic alpha form by heterogeneous nucleation. This hypothesis is confirmed by the analysis of the structures obtained using wide angle X-ray experiments. Moreover, the addition of HR to iPP causes a drastic reduction in the crystallization rate of iPP in both regions due to the diluent effect of the miscible resin.