Microcellular wood fibre reinforced PP composites - A comparative study between extrusion, injection moulding and compression moulding

Microcellular wood fibre reinforced polymers have practical significance given the possibility of reducing the density of automotive components due to their microcellular structure, as well as processing and performance advantages. A microcellular foaming process with a chemical foaming agent was applied at an experimental stage to injection moulding, extrusion and compression moulding of wood fibre reinforced polypropylene composites. The focus of the research was to investigate these processes using a chemical foaming agent and to perform comparative studies of the physico-mechanical properties of microcellular materials. The effects of the presence of the chemical foaming agent (exothermic) and variation of its content on density, microvoid content, mechanical properties (tensile and flexural), odour concentration and cell morphology of microcellular polypropylene-wood fibre composites were studied. The morphology, cell size, shape and distribution of the microcells were investigated using scanning electron micrographs. Injection moulding process produced finer microcellular structures in comparison with the other processes. As compared to the non foamed composites, the density reduced maximum 30 % (0.741 g/cm(3)), 20 % (0.837 g/cm(3)) and 22 % (0.830 g/cm(3)) for the injection moulding, extrusion and compression moulding process respectively. The chemical foaming agent reduced the odour concentration in relation to the same non foamed composites. Injection moulding showed better performance in comparison with extrusion and compression moulding in terms of cell morphology, density reduction, odour concentration and mechanical properties.