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 degrees C min. On the other hand, X-ray diffraction analysis using synchrotron radiation of the injection-molded samples demonstrates the existence of a P or trigonal form in the binary as well as the ternary PP/WF composites. They reach k(beta) 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. (c) 2006 Wiley Periodicals, Inc.