Fibres from agricultural hemp waste

Sammanfattning: There is an increasing demand for natural fibres in the textile industry as a consequence of the negative impact of the industry on the environment. Svensk Hampaindustri (SHI) is currently growing hemp in Sweden for its seeds. This leaves residue in the form of hemp stems that could be processed for textile products. Today this residue material is not used for anything, however there is a desire that it could be used for added value. This study investigates the possibility of extracting fibres from the hemp residue mechanically and using them in applications. Hemp, a variety of Cannabis sativa L., is a multipurpose low-input crop cultivated for its seeds, fibres and hurds. Hemp fibre is a bast fibre, derived from the plant’s outer stem tissues. To extract hemp fibres from hemp stems, the first step is to separate the fibre bundles from the other, non-fibrous parts of the stem. This process is done using various mechanical methods. In order to ease the separation, hemp stems are retted. Retting is a biological process that uses enzymatic activities to degrade the pectins and thus making the separation easier. Retting is one of the most considerable challenges towards a wider use of hemp fibres. Water retting offers high fibre-quality but consumes high amounts of water and causes effluents in the wastewater. Dew retting offers a high fibre yield and low labour costs but will result in a lower fibre-quality. Alternative methods that can contribute with a more consistent fibre yield and quality are available, but with an economic uncertainty for the farmers that limits the competitiveness of the hemp fibre. The hemp material provided by SHI was unretted and needed to be broken down by means of mechanical processing in order to extract the fibres. This was done using a domestic blender. The crushed material was then carded using a hand carding machine to achieve oriented and clean fibres. The obtained fibres were then evaluated for their length and fineness. Three different types of nonwoven were made using the hemp fibres: NW1, NW2 and NW3. NW1 consists of 100% hemp, whereas NW2 and NW3 are 80/20 blends of hemp and PLA. NW1 was needle punched, NW2 was thermally bonded and NW3 was manufactured by both thermal bonding and needle punching. The produced nonwovens were evaluated by their air permeability, thermal conductivity, sound absorption, drapability and tensile strength. The results from the study showed that it is possible to extract unretted fibres using mechanical methods. The fibres are quite coarse and therefore more suitable for industrial applications. The different production methods for the nonwovens gave different results which supports the diversity of hemp applications. This study suggests that the residue should be used rather than be disposed of.