Transdisciplinary top-down review of hemp fibre composites: From an advanced product design to crop variety selection

Given the vast amount of available research in the area of natural fibre composites, a significant step forward in the development of next-generation plant fibre-based products would be to devise a framework for rational design. The authors use a top-down approach, starting with an example final product to define the product specifications for high-performance hemp fibre-reinforced composites. Thereafter, all process steps are critically analysed: from textile preform and reinforcement yarn production, to fibre extraction and the agricultural process chain, to the microbiology of field retting, to cultivation and selection of crop variety. The aim of the analysis is to determine how far the current state of knowledge and process technologies are in order to use hemp fibres in high- performance composites. Based on this critical evaluation of the state-of-the-art, it can be stated that hemp will be found in high-performance composites in the short-to-medium term. There is, however, a need for performance optimisation especially through the selection of crop variety, best practices in retting, and effective fibre extraction methods to obtain more consistent fibre qualities suitable for reinforcement spinning and composite preform manufacturing processes

Scanner based image analysis to characterise the influence of agronomic factors on hemp (Cannabis sativa L.) fibre width

The potential of industrial hemp to satisfy the increasing demand for natural products is limited by the lack of accurate information on how to measure and control bast fibre quality. A number of research projects have been carried out to study how hemp fibre yield is affected by genotype X environment X management (GXEXM) interaction, however the possibility to study how GXEXM affects fibre quality is hampered by the lack of standard analytical methods that can relate fibre traits, relevant to specific end use applications, to cultivation factors. In this paper an innovative methodology to analyse bast fibre quality (i.e. fibre finessess) is presented and discussed. In particular, fibre is chemically extracted (following the Bredemann method), then mechanically opened with a coarse separator and finally fibres and fibre bundle width is determined with an automated image analysis system (Fibershape). Evaluation of fibre width with this system provided results in agreement with fibre cell diameter measurements carried out on fresh stem cross section. Being fast and cost efficient this method provides researchers with a powerful system to measure the effect of agronomic techniques (i.e. sowing density and harvesting time), plant portion, genotype and potentially retting or other post-harvest managements of the stem on fibre width, which is considered one of the most important quality traits in bast fibre

Optimizing Hemp Fiber Production for High Performance Composite Applications

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

Assessment system to characterise and compare different hemp varieties based on a developed lab-scaled decortication system

With superior quality, hemp fibres are being more and more widely used for a large number of traditional and innovative industrial applications. The quality of the final products is strongly influenced and determined by the quality of the fibres, which in turn is subjected to agronomic factors, such as genotypes (hemp accessions), growing conditions, harvesting and processing. To improve hemp productivity and raw material quality for end-user requirements and advance scientific understanding of gene-to-trait relationships in this crop, characterisation and comparison of hemp samples of different varieties are important research tasks, which are normally carried out on small samples and require accurate and reproducible measurements. Decortication, the mechanical processing of stems to separate bast fibres from shives, plays a very central role in the whole natural fibre production chain. In the frame of the MultiHemp project (http://multihemp.eu/) a partially automated lab-scaled decortication process was designed and developed. The energy consumption during decortication was investigated to characterise and compare different hemp varieties. In order to calibrate the breaking unit a method was developed, and the process stability was analysed. Furthermore a new characterisation value, a so-called \uce\uba-number was introduced and a model of an assessment system was established for a more objective and reproducible evaluation of hemp varieties. Finally the assessment system was tested on three hemp varieties (F\uc3\ua9dora 17, Futura 75 and Tygra) cultivated in the frame of a large Multihemp trial