The use of unretted hemp fibre in composite manufacture

The usefulness of unretted hemp as a source of fibre for composite manufact ure is investigated. A decortication machine was used to remove fibre from retted and unretted stems using two different decortication procedures, def ined as 'normal' and 'pinning'. The later caused less fibre breakage. Compo sites manufactured with fibre from the different treatments, and epoxy resi n, were subjected to tensile tests and the Young's Modulus and strength rec orded. The pinning-decortication treatment resulted in stronger, stiffer, c omposites. Lack of retting did not significantly change the reinforcing cap abilities of hemp fibre. Composites made with unretted, pinned, fibre at a volume fraction of 0.2 had a Young's Modulus of 8 GPa (S.D. 1.9) and streng th of 90 MPa (S.D. 22). However in unretted fibre more Cuticle and epiderma l tissue remained attached to the fibre tissue and it was shown that the in terface between these two tissues is susceptible to breakdown over time. Th is could Limit the useful life of the composites. It would therefore be an advantage if the processing of unretted hemp could be improved so that more epidermal tissue is removed. (C) 2000 Elsevier Science Ltd. All rights res erved.