Effects of chemical-physical pre-treatment processes on hemp fibres for reinforcement of composites and textiles

Retted hemp fibres were treated using chemical-physical pre-treatments and the material was characterised chemically in order to evaluate the effect of the pre-treatments, respectively, wet oxidation (WO), hydrothermal treatment (HT) and steam explosion (STEX). Process variables were addition of base and oxidant. These treatments were performed to make fibres that are useful as reinforcement in composite materials and for textiles. All pre-treatments tested increased the content of cellulose in the fibres by degrading and dissolving non-cell wall material (NCWM, e.g., pectin and waxes), lignin and to some degree hemicellulose. A high loss of dry matter in the process was connected with a high loss of cellulose since cellulose is the main component. Generally losses were bigger for steam explosion than for wet oxidation and hydrothermal treatment. All the pre-treatments with base gave cellulose degradation probably due to the effect of Na2CO3 in opening the structure of the molecules making them more accessible for degradation. The processes where least dry matter was degraded (15-17%) were WO, HT and STEX without base addition. In these processes, no cellulose was lost. Originally being grey, the pre-treatments gave fibre colours ranging from white to dark brown. Alkaline wet oxidation produced the brightest fibres with potential for use in textiles. Use of retted fibres in the pre-treatment resulted in fibres with high cellulose content (86-90%) of potential as reinforcement in composite materials. (C) 2006 Published by Elsevier B.V.