Optimizing Hemp Fiber Production for High Performance Composite Applications

Hemp is a sustainable and environmental friendly crop that can provide valuable raw\r\nmaterials to a large number of industrial applications. Traditionally harvested at full\r\nflowering for textile destinations, nowadays hemp is mainly harvested at seed maturity\r\nfor dual-purpose applications and has a great potential as multipurpose crop. However,\r\nthe European hemp fiber market is stagnating if compared to the growing market of\r\nhemp seeds and phytocannabinoids. To support a sustainable growth of the hemp\r\nfiber market, agronomic techniques as well as genotypes and post-harvest processing\r\nshould be optimized to preserve fiber quality during grain ripening, enabling industrial\r\nprocessing and maintaining, or even increasing, actual fiber applications and improving\r\nhigh-added value applications. In this paper, the effect of genotypes, harvest times,\r\nretting methods and processing on the yield and quality of long hemp for wet spun yarns\r\nwas investigated. Conventional green-stem varieties were compared with yellow-stem\r\nones on two harvesting times: at full flower and seed maturity. Scutching was performed\r\non un-retted stems and dew-retted stems, the un-retted scutched fiber bundles were\r\nthen bio-degummed before hackling. Both scutching and hackling was performed on\r\nflax machines. Quality of hackled hemp, with particular reference to its suitability for\r\nhigh performance composites production, was assessed. The results of fiber extraction\r\nindicate that yellow-stem varieties are characterized by higher scutching efficiency than\r\ngreen-stem varieties. Composites strength at breaking point, measured on specimens\r\nproduced with the Impregnated Fiber Bundle Test, was lower with hemp obtained from\r\nstems harvested at seed maturity than at full flowering. On average, back-calculated\r\nfiber properties, from hackled hemp-epoxy composites, proved the suitability of long\r\nhemp fiber bundles for high performance composites applications, having properties\r\ncomparable to those of high quality long flax.