alpha and beta interfacial structures of the iPP/PET matrix/fiber systems

The interfacial structures of the iPP/PET matrix/fiber composite systems prepared by introducing the PET fiber into the iPP melt or supercooled melt were studied via optical and scanning electron microscopies. We found that unlike the iPP matrix/fiber single polymer composites prepared in the same way, where homoepitaxy induced by solid α-iPP fiber dominates the crystallization process of the iPP matrix, the iPP in iPP/PET composites displays the feature of crystallization in temperature gradient. Optical microscopy observations show that the interfacial structures of the iPP/PET composites depend strongly on the fiber introduction temperature. At higher fiber introduction temperature, e.g., over 170 °C, the crystallization of iPP takes place in its α-phase. At lower fiber introduction temperature, e.g., below 145 °C, the iPP crystallizes in its β-phase. This is different from the crystallization of iPP in iPP/PET composite under quiescent conditions, where the PET exerts only a moderate α nucleating effe...