Injection moulded microcellular wood fibre-polypropylene composites

The polymer-wood fibre composites utilize wood fibres as a reinforcing filler in the polymer matrix and are known to be advantageous over the neat polymers in terms of the materials cost and some mechanical properties such as stiffness and strength. These wood fibre composites are microcellular processed to create a new class of materials with unique properties. Recent studies have demonstrated the feasibility of developing microcellular structures in polymer-wood fibre composites. An experimental investigation was conducted to research the microcellular behaviour in the injection moulding foam processing of polypropylene-wood fibre composites using chemical foaming agents. The effects of fibre type (hard and soft wood fibre) and different chemical foaming agents (endothermic, exothermic and endo/exothermic) on the density, physico-mechanical properties, surface roughness and cell morphology of foamed PP-wood fibre composites are studied. A compatibiliser maleic anhydride polypropylene copolymer (MAH-PP) was used with the intension of improving the mechanical properties of foamed composites. The structures of the foamed composites were examined using scanning electron microscopy and optical microscopy to determine the cell size, shape and distribution of cells to account for this behaviour. The density of microfoarned hard wood fibre-PP composites reduced around 30% and decreased up to 0.741 g/cm(3) with the using of exothermic chemical foaming agent. Optical microscopy showed that the cells are round and cell sizes are affected by chemical foaming agents. Tensile and flexural tests are performed on the foamed composites to investigate the dependence of these properties on the density (specific properties) of foamed specimens and compared with non-foamed composites and MAH-PP has improved the physico-mechanical properties up to 80%. Chemical foaming agents have also an effect on surface roughness of the composites which decreased surface roughness of the foamed composites compared to the non-foamed composites. Water absorption and thickness swelling of the composites investigated also. (c) 2005 Elsevier Ltd. All rights reserved.