Deformation and failure of PP composites reinforced with lignocellulosic fibers: Effect of inherent strength of the particles

PP/wood composites were prepared from two lignocellulosic fibers with different particle size and aspect ratio in order to determine the effect of these factors on the deformation and failure mechanism as well as on the properties of the composites. Wood content was changed from 0 to 80 wt%. Maleinated polypropylene (MAPP) was added to improve interfacial adhesion. The MAPP/wood ratio was kept constant at 0.1. Mechanical properties were determined by tensile testing. Micromechanical deformation processes were followed by acoustic emission (AE) and volume strain (VOLS) measurements, and by the study of fracture surfaces. The results proved that micromechanical deformations change drastically both with decreasing particle size and changing interfacial adhesion. Less debonding, fiber pull out and fiber fracture occur in composites containing small particles. Hardly any change was observed in the mechanical properties of the composites with decreasing particle size, in spite of the drastic modification of the deformation mechanism. The apparently slight influence of particle size on composite strength results from the smaller aspect ratio of the small particles, which indicates that orientation and orientation distribution must have a strong effect on reinforcement. Further improvement in composite strength is possible only through the optimization of particle size, aspect ratio and the inherent strength of wood.