The manufacture and mechanical testing of thermosetting natural fibre composites

High volume fraction hemp and flax fibre composites were manufactured using low viscosity epoxy and phenolic resins. Using 80% volume fraction of flax fibres in epoxy resin, composites with a mean stiffness of 26 GPa and a me an strength of 378 MPa were produced. By reducing processing damage of the plant fibres mechanical properties could be increased by 40%. Strips of ret ted fibre tissue were found to be just as effective for reinforcement as fi bre bundles and individual fibres. Phenolic resin and decorticated flax fib res produced very poor composites. Using 40% volume fraction of fibres the mean stiffness was 3.7 GPa and the mean strength was 27 MPa. Two fibre pre- treatments were devised to improve adhesion with resins. The first, 6 M ure a was used only in natural fibre-epoxy composites where it increased the st iffness but not the strength. The second pre-treatment was a 50% PVA soluti on, which was cured prior to the addition of space filling resin. The PVA t reatment improved the stiffness and strength of both natural fibre-epoxy co mposites and natural fibre-phenolic composites. (C) 2000 Kluwer Academic Pu blishers.