6.1 Separation of bast fibres and core material (shives)

In the first processing stage, the hemp bast fibres are separated from the core material. The core material obtained after separation is called 'shives' or ‘hurds’.

This process is to some extent identical for all technical applications. The main parameter is the degree to which the bast fibres are separated from the shives.

Bale opening
The bales of retted hemp straw are taken from the storage and fed into the processing line, starting from the bale opener (Image below). The bale opener also removes possible contamination of materials from the land; such as sand and stones.

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Bale opener. Photo HempFlax.

Separation of the bast fibre from the woody core
A hammer mill is used to separate the bast fibres from the core material (shives or hurds). Hempflax uses a patented proprietary design hammer mill.

Subsequently, the fibres and shives are separated by means of a rotating sieve drum through which the fibres and shives are pushed; the shives fall through the sieve, the bast fibres stay in the sieve drum and leave the drum at the end of the line. After this, the bast fibres are reasonably clean, but they still contain a small amount of shives.

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Duvex sieve drum for separating bast fibres and shives. Photo Cretes.

Further cleaning and refining
The quality of the fibres coming from the previous separation step is already suitable for paper making. However, further cleaning is needed if the fibres are intended for composites and textiles. To this end, several additional refining and cleaning steps are available (Figure below). Depending on the settings of the processing line and the input quality of the straw, different output quality can be obtained. The finest and longest fibres are suitable for textiles. Within the range of fibres suitable for textiles, there are again different qualities (Chapter 7).

For textile applications, the fibres go through a scanner which – based on colour – detects and removes undesired parts such as knots from twines which were used for baling.

Many of the machines used by Hempflax were originally developed for processing other kind of fibres, and over the years have been modified by Hempflax for optimal processing of hemp.

With the addition of a bio-enzymatic treatment, the fibres can be made even finer, making it suitable for use in nappies, sanitary towels and cleaning wipes.