Nanocomposites of syndiotactic polypropylene: Phase behavior and morphology

Through differential scanning calorimetry, the crystallization kinetics of syndiotactic polypropylene (sPP) nanocomposites with organically modified layered silicates has been investigated in both nonisothermal and isothermal conditions. A strong influence on the thermal behavior is exerted by the compatibilizer agent (low molecular weight isotactic polypropylene-g-maleic anydrhyde, iPP-g-MA), which increases the crystallization rate of sPP. A further strong increase in the crystallization rate is observed upon increasing the OLS content in the sample. The kinetics data have been analyzed through the Ozawa, Avrami, and Tobin methods, the first of them resulted ineffective in describing our data. Morphological analyses have been performed by polarized optical microscopy and atomic force microscopy. Spherulitic morphology is observed for neat sPP; for the sample containing only the compatibilizer the spherulites grow around the iPP-g-MA particles, revealing their nucleating effect on sPP crystallization; for the nanocomposites the spherulitic morphology is lost: the texture appears globular, compact; inside the globules la-mellae are present, parallel one to the other.