8.2 Viscose

The most elegant route for making textiles from hemp is using the long fibre, which may be shortened for spinning in combination with wool or cotton. An alternative route is to process the hemp plant in a way that viscose can be made from it. Viscose is the common name, and together with acetate, rayon, modal, supra and lyocell belongs to the family of artificial silks or man-made cellulose fibres.

Viscose is made from cellulose, so far mainly obtained from wood. Hemp has a high cellulose content, which also makes it a suitable raw material for making viscose.

The cellulose is extracted from the plant by pulping, a process somewhat similar to making pulp for paper. In that process, lignin, hemicellulose and pectin are chemically separated from the cellulose and removed from the pulp. The cellulose fibre is then cleaned and bleached (e.g. with enzymes) prior to synthetically spinning into viscose from an acid bath. The viscose fibre can then be processed as a continuous filament or as a short staple fibre (shortened to the length of cotton or wool) into yarn and then textiles. The properties of viscose are well known and widely accepted by consumers in, for example, women's clothing and furnishing fabrics.

The price of viscose is about half that of yarn based on long hemp fibre. That price ratio also applies to the price of pulp relative to hemp fibre. Nevertheless, the route to viscose could potentially be interesting in combination with flower and seed production; with plants that are less suitable for extracting good quality fibres; and when the plants are harvested early or very late. In fact, fibre production is then a by-product of flower/seed production. An advantage is that, unlike for fibre production, the entire stem is pulped to obtain cellulose for viscose. A further advantage of early harvest (for flowers) is that the percentage of lignin is still low, which facilitates pulping.

If hemp fibres have become too short or weak after use and mechanical recycling, the fibre can be a good feedstock for viscose; this is then called 'chemical recycling'.

This route has hardly been developed yet for raw materials other than wood. This is because of the high production volumes in pulping; a pulp mill or a viscose mill has a production volume of at least 100,000 tonnes per year, a multiple of a usual fibre hemp processing plant. Currently, there are only a handful of viscose production mills; a few more plants are expected to be built in the coming years.

Where previously used solvent systems were not very sustainable, a process with solvent reuse in a closed system has been developed and is in use now for several years (Lenzing).