Wood flour filled polypropylene composites: Interfacial adhesion and micromechanical deformations

Polypropylene/wood flour composites were prepared in a wide composition range from 0 to 80 wt% filler content. The adhesion of the components was modified by two maleic anhydride functionalized polypropylenes (MAPP) with different maleic anhydride content and molecular weight. The components were homogenized in an internal mixer and then compression molded to 4 mm thick plates. Tensile properties were measured and micromechanical deformation processes were followed by acoustic emission as well as volume strain measurements. The detailed analysis of the results identified four micromechanical deformation processes in the matrix and the composites, respectively. The matrix polymer deforms mainly by shear yielding, which basically does not emit sound. The presence of wood flour initiates particle related processes in the composites. Debonding dominates in the absence of coupling agent. Pull‐out of fibers may follow the debonding of large particles at an intermediate stress level. The introduction of functionalized polymer increases interfacial adhesion considerably and completely changes the deformation mechanism; the fracture of wood particles becomes the dominating process in this case. Further improvement of composite strength is possible only by the increase of the inherent strength of the wood. POLYM. ENG. SCI., 47:1246–1255, 2007. © 2007 Society of Plastics Engineers