Hemp processing starts after cultivation of hemp, a bast fibre plant, “bast” being a German word for “bark” or the outer portion of the stem. The inner or core of the stem is known as “hurd”. There are many markets for the fibre and the hurd separately but only very few which can utilise the whole stem or whole chopped or crushed stem. Therefore primary hemp processing involves separation of bast and hurd fractions of the stem, approximately about 20% and 70% respectively (about 10% is lost as dust in processing).
Traditional methods for separating the fibre components of the stem include mechanical and hand systems in hemp processing. The hemp stem is usually “retted” in the field for 4-6 weeks after harvesting, a process involving naturally occurring fungal and bacterial organisms which break down the bonds between the stem fibres, making separation easier. In some regions, retting and separation is traditionally conducted in water baths, a labour intensive process that results in a very fine bast fibre product.
Primary Hemp Processing
Primary hemp processing in Europe is generally conducted by mechanical means, although advanced technologies for sonar and chemical separation are being researched. The stalk enters the processing line as round bales or large square bales, goes through an extensive chopping and hammermilling system and the fibre fractions are then screened and separated. At this stage, bast fibres are grey, 30-50 mm long and contain up to 20% of hurd as impurities.
Bast fibre markets require various grades of fibre. Some markets, such as paper pulp and building products can take this fibre with higher levels of hurd. Other markets, such as polycomposites and plastics, require cleaner bast fibre. The fibre therefore goes through further screening process for removal of hurd, to less than 2% of the final fibre.
Hurd product is collected as a result of these several screening processes. For animal bedding, the dust is extracted and it is packaged into bags ready for use.
Ecofibre Industries on Hemp Processing
In Australia, Ecofibre Industries is planning a pilot hemp processing plant in New South Wales in conjunction with local partners, a “proof of concept” mill which tests our Australian designed system for processing Australian grown fibre for early stage markets. This mill will overcome the core hurdle for the Australian hemp industry for many years: local processing. Once local processing is in place, then we can process Australian grown hemp stalk for products to local markets. Then the supply chain is in place. Larger scale hemp processing will follow once the supply chain has proven its ability at all three levels: we can grow it, we can process it and we can sell it.