The use of unretted hemp fibre in composite manufacture

The usefulness of unretted hemp as a source of fibre for composite manufacture is investigated. A decortication machine was used to remove fibre from retted and unretted stems using two different decortication procedures, defined as ‘normal’ and ‘pinning’. The later caused less fibre breakage. Composites manufactured with fibre from the different treatments, and epoxy resin, were subjected to tensile tests and the Young's Modulus and strength recorded. The pinning-decortication treatment resulted in stronger, stiffer, composites. Lack of retting did not significantly change the reinforcing capabilities 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 strength of 90 MPa (S.D. 22). However in unretted fibre more Cuticle and epidermal tissue remained attached to the fibre tissue and it was shown that the interface between these two tissues is susceptible to breakdown over time. This 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.