Rotational moulding and powder processing of natural fibre reinforced thermoplastics

The present paper describes the development of a new processing technology: rotational moulding of natural fibre reinforced thermoplastics. Different polymer-natural fibre and polymer-flour systems have been characterised. A rotomoulding grade of high density polyethylene has been used as the polymer matrix for the experiments. Fibres, including jute, sisal and cabuya, as well as wood, pecan and rice shell flour of different types have been used as reinforcements. The rotomoulding process for those composite systems has been studied using an in-house built two-axis rotomoulding rig with variable speed. The final products have been characterised with special emphasis on estimating the level of dispersion of the fibres and their degree of orientation, as well as the consolidation, sintering and bubble formation processes during the different stages. Comparisons have been made with other powder processing routes, involving the sintering of fibre (or flour) reinforced polymer particles including compression moulding. Morphological characterisation techniques have been adapted to determine the structure-property relationships in these materials at different processing stages. Important improvements in the compression strength of the natural fibre reinforced rotomoulded products compared to the unreinforced materials, accompanied of a good dispersion level of the reinforcing fibres have been reported.