High resin content natural matrix–natural fibre biocomposites

Composites of good performance formed from non-woven mats of flax and hemp fibres and natural resin matrices have been prepared. Both higher density thin composites as well as lower density thicker composites have been prepared. Two natural matrices types were used: (i) commercial mimosa flavonoid tannin extract with 5% hexamine added as hardener and (ii) a mix of mimosa tannin + hexamine with glyoxalated organosolv lignin of low molecular weight, these two resins mixed 50/50 by solids content weight. The composites prepared were tested for MOE in bending and in tension and for maximum breaking strength in tension. Some of the mats were corona treated and the optimum length of corona treatment determined to improve the composites MOEs and breaking strength. These were related to the morphology of the treated fibre. Thermomechanical analysis (TMA), Brinell surface hardness and contact angle tests were also carried out with good results. The composites made with the mix of tannin and lignin resins as a matrix remained thermoplastic after a first pressing. The flat sheets prepared after the first pressing were then thermoformed into the shape wanted.