Dynamic crystallization of polypropylene and wood-based composites

Abstract

Thermoplastic composites made of an isotactic polypropylene (iPP) matrix and woodflour (WF) were prepared by melt-blending, using twin-screw extrusion and injection molding. Up to 20 wt % of the composite was composed of WF. The incorporation of an interfacial agent made of an ethylene/methacrylic acid copolymer to iPP and WF, PP /WF, binary blends causes a compatibilization effect that becomes evident due to a reduction in the crystallization temperature of PP. In both the binary composites and the compatibilized or ternary composites, the PP adopts an a or monoclinic structure when crystallization occurs from the melt under dynamic conditions at cooling rates between 1 and 20°C min -1. On the other hand, X-ray diffraction analysis using synchrotron radiation of the injection-molded samples demonstrates the existence of a βor trigonal form in the binary as well as the ternary PP/WF composites. They reach kβ levels between 0.18 and 0.25, which can be interpreted as the co-operation between a reduction of the crystallization rate and the shear effect induced during the injection. © 2006 Wiley Periodicals, Inc.