Hemp cultivation still ranks as an exotic status in Switzerland in spite of government promotion. For example the Swiss farming web site’s comment on the subject is that: “On the other hand the slightly more exotic crops such as zebra grass, ambary, hemp and flax have again lost importance.” (1) This inadequate importance of hemp is attributable to the fact that agriculturally produced hemp straw cannot be processed industrially at a profit without new preparation and finishing steps.

However that could soon change. The reason is that through many years of development work Marianne Leupin, ETH researcher at Professor Urs Meyer’s Institute for Manufacturing Automation (2), has succeeded in turning industrial hemp into high-quality fibres(3) that can be spun into pure hemp yarn on an open-end spinning frame in the cotton supply chain (4).

Marianne Leupin chose industrial hemp as the basis for high-quality textile materials for the following reasons: the plant can be cultivated in Switzerland and it has a higher fibre yield per hectare than cotton or flax, for example. Hemp needs no agricultural control chemicals and consequently it can be grown biologically. Textiles made from it also have the same beneficial characteristic features as linen, namely good temperature regulation and moisture absorption.

Decortication using a combine harvester

The industrial hemp that Marianne Leupin needed for her research work was grown at the Agroscope agricultural research station in Tänikon or by the farmer Andreas Maag in Zweidlen. During this period the ETH researcher studied the cultivation conditions and harvesting time that yield fibres suitable for use in textiles.

Decortication with the conveyor belt and combine harvester: agricultural machines with a new function in the production of hemp bast. large

ETH scientist Marianne Leupin researched an improved method for producing hemp textiles from field to yarn. (Photos: ETH Zurich, ART Agroscope) large

Regarding decortication, Marianne Leupin now suggests that the hemp should not be retted first of all in the field and then dry-decorticated as is customary in Europe, but that this step should be carried out immediately while the crop is still in the freshly-harvested state. The reason is that this enables the unavoidable fibre damage caused by field retting and the fibre shortening resulting from dry-decortication to be eliminated. The start of male flowering proved to be the ideal harvesting point for the proposed fresh decortication.

Based on a suggestion by Andreas Maag, the studies of fresh decortication in Tänikon were carried out using an ordinary combine harvester. According to the ETH scientist, a future harvesting method should comprise the following operating steps: cutting off the stem tips, cutting the stems into pieces 30 centimetres long, crushing the stem pieces, decorticating using a single or multi-drum threshing unit and finally separating the bast from the remaining parts of the plant by the combine harvester’s vibrator unit. Ideally the bast can thereafter be dried in the field.

Finer than jeans thread

The scientist used a chemical method to extract the fibres from the bast. This yielded fibres suitable for further processing into textiles. Next the conversion into what is known as a drawframe sliver took place at the SLG Textil AG Company in Zweidlen. The subsequent yarn manufacture was in turn carried out on the ETH Institute’s open-end spinning frame. In this way Marianne Leupin succeeded in producing yarns with a thread count of 50 tex. This means that one kilometre of the yard weighs 50 grams. Normal jeans need 100 tex yarns, and are thus woven from coarser threads.

Hemp as a replacement for tobacco and sugar production?

Based on her work, which has elucidated the whole production chain from seed to hemp yarn, the researcher is altogether convinced that industrial hemp has good opportunities as a branded product in the textile sector in Switzerland. She has also laid the foundation for further research studies. Marianne Leupin’s next aim is to develop a sustainable fibre separation process to enable hemp fibre to push forward into the cotton price range. According to the researcher, if this is successful the old cultivated plant hemp will offer Switzerland an opportunity to withdraw – without job losses – from the heavily subsidised growing of tobacco and from sugar beet farming, which is endangered by the WTO negotiations.