Impact modification of wood flour reinforced PP composites: Problems, analysis, solution

Polypropylene (PP)/elastomer/wood flour composites were prepared from two PP reactor blends. The detailed analysis of the deformation and failure of the composites has shown that several local deformation processes take place during loading which differ considerably in terms of energy consumption. These processes may even interact with each other, sometimes resulting in an antagonistic effect on impact resistance. The shear yielding of the matrix consumes energy the most efficiently. The presence of wood decreases shear yielding by hindering overall deformation and initiating other local processes like debonding. The role of debonding is controversial; it may increase, but also decrease plastic deformation and impact resistance. The fracture of wood does not consume much energy and thus does not contribute to impact resistance. PP cannot be reinforced with wood flour, if impact resistance is an important aspect. Other methods are more suitable in such cases, like the addition of synthetic fibers.