Thermal Transitions of Polypropylene in Blends and Composites with Polypyrrole and Polypyrrole/Montmorillonite

Abstract

Thermal transitions of the semi-crystalline isotactic polypropylene, in polypropylene/polypyrrole blends and polypropylene/polypyrrole/montmorillonite composites, processed by two different ways, were investigated by differential scanning calorimetry. Glass transition temperature of polypropylene was found to remain unchanged at 269 K, whereas the crystallization rate was found to be higher in the blends and composites, which is explained in terms of increased concentration of extrinsic crystallization nuclei. The effect is larger in the materials processed by mixing and subsequent compression molding as compared to the materials prepared directly by compression molding. The degree of crystallinity of polypropylene did not show any systematic variation with composition, whereas it is slightly higher for the samples prepared by direct compression molding, being in the range of 50–59%. The polypropylene in the blends and the composites crystallizes in the stable α form, whereas metastable crystallites of the β form were observed as a minor component, depending on the thermal history of the samples. The results are discussed on the basis of the picture emerging from morphological studies.