A comparison of compounding processes and wood type for wood fibre—PP composites

The structure–properties relationship of wood fibre (WF)–polypropylene (PP) composites was studied in relation to WF types (hardwood and softwood) and compounding techniques, namely two-roll mill, high-speed mixer (agglomerator) and twin-screw extruder. It was shown that twin-screw extruder compounded composites had higher mechanical properties than those compounded in a two-roll mill or a high-speed mixer. The use of compatibilisers (maleated PP of different maleic anhydride content) in the compounding step improved the mechanical properties of the composites in dry conditions regardless of the compounding process, however, in wet conditions a decrease in tensile and flexural strength was observed for all composites. It was shown that the use of a compatibilisers significantly improved the hydrophobicity of WF surface. However, the bulk of WF remains unmodified and accessible to water. The dependence of the moisture uptake of WF was evaluated with respect to WF and compatibiliser type. The effect of the size and shape of the composite samples used in the experiments on the equilibrium water content was also tested.