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Hemp for Europe - manufacturing and production systems

Contract nr: FAIR-CT95-0396
Project nr: 396
Project type: SC
Starting date: 01/02/1996
Duration: 36 months
Total cost: 2,054,000 EUR
EC Contribution: 1,400,000 EUR
Scientific Officer: Michel VAN DEN BOSSCHE
Research topic: Biomass prodution (food, feed, non-food and energy uses)
Acronym: HEMP

Hemp (Cannabis sativa) is an environmentally friendly annual fibre crop, grown historically throughout Europe, for which yield and climate adaptation are better than flax or kenaf. Its main use is high quality paper pulps but new high volume and medium value end-products are needed to stimulate the demand (e.g. Composite materials).

The main objectives are to stimulate the expansion of the hemp crop in the EU by overcoming the major limitations (agronomical aspects: plant health, harvesting; breeding: cultivars with other characteristics; new processing systems: extraction; utilisation: new innovative products). This project deals with the entire production chain.

Cannabis sativa has been grown for its fibre for industrial applications for millennia. Recent relaxation of cropping rules within the EU have seen increased interest in the crop. Very little has been done to optimise any aspect of the hemp production chain from breeding through husbandry and agronomy, harvesting and post-harvest treatment. Equally, the fibre characteristics required for different end uses have not previously been well quantified nor indeed has the feasibility of many end products been properly assessed. In 1996 an EU-funded project `Hemp for Europe - Manufacturing and Production Systems' was initiated [PL95-0396]. The principal objective of the project was to stimulate the expansion of the hemp crop in the EU. A number of factors limiting the crops development were identified at each phase of the production chain and were addressed experimentally.

Current situation/results:
The industrial uses of hemp fibre (Cannabis sativa L.) have been recognised for thousands of years, and Europe has a long history of its production (Cromack, 1998). The principal objective of the project was to stimulate the expansion of the hemp crop in the EU. A number of factors limiting the crops development were identified at each phase of the production chain and were addressed experimentally.

Current cultivars and cultivation techniques have mostly been developed in central France, based on the production of dual-purpose crops for seed and fibre. Whilst a number of varieties are grown commercially across Europe and broad guidelines are in place for their production (e.g. Low, 1995), the relationship between husbandry, resource capture and yield productivity are poorly understood throughout Europe. An experimental programme in the UK, the Netherlands and Italy was initiated to provide guidelines for the management of hemp crops grown specifically for fibre in different regions.

The quality of fibre may be as important as its quantity, therefore the crops produced in the crop growth and agronomy studies were examined for key characteristics such as tenacity, decortication resistance and fineness in order to provide management guidelines for the production of fibre of high quality.

Most hemp is allowed to lie in a swathe in the field for a period of 1-6 weeks in order to allow microbe mediated separation of long fibres from short fibres in the stem. This `retting' process is very imprecise, and subject to the vagaries of the climate. The tall rough hemp plant poses considerable mechanisation problems but there has been little development of specialised machinery. Retting is desirable to release long fibres prior to extraction, but scientific predictive information for this biological process is limited. Current decortication processes are slow and costly; a novel device developed for flax has potential to improve efficiency. Techniques to further refine fibre quality, which have been developed for flax shows promise for hemp fibre.

Hemp fibre may be suitable for a number of other applications, in particular for a variety of non-woven materials, which could be used as reinforcements in composite materials, or in textile applications (e.g. geotextiles). Hemp fibres were evaluated for the production of wood-based panel products (particle board and MDF), thermoplastic products and geotextiles. Test products were manufactured, and standard measurements of their characteristics made, and their commercial viability determined.

Crop selection and breeding activities were undertaken with three component objectives. Currently, only cultivars with less than 0.3% _-9 tetra-hydro cannabinol (THC), the narcotic component of cannabis, may be grown in the EC. From 2001/02 this will be further reduced to 0.2%. The development of zero THC lines, with linked genetic markers, would be a distinct advantage and allow the genetic base of the crop to be broadened. Secondly, hemp has been noted to be susceptible to root knot nematode, and this can severely limit yield potential. A selection programme for the development of genotypes with increased nematode resistance was undertaken. Finally, the development of a `yellow line' of hemp with high fibre yield and quality was begun.

Fibre hemp may yield up to 25 t above ground dry matter per hectare (20 t stem dry matter ha-1) which may contain as much as 12 t ha-1 cellulose, depending on environmental conditions and agronomy. Its performance is affected by the onset of flowering and seed development. Effects of cultivar and management on yield and quality were tested at three contrasting sites in Italy, the Netherlands and the UK in three years, making use of standardised protocols for experimental design and research methodology. Highest yields (up to 22.5 tg dry matter ha-1) were obtained in Italy when later cultivars were used. Attainable yields proved slightly lower in the Netherlands and much lower in the UK. The quality of the cellulose was relatively stable over the growing season, but lignification may proceed rapidly some time after flowering.

Results suggest that hemp can yield large quantities of useful cellulose when ecologically adapted cultivars are sown in proper plant densities. The cultivation is environmentally friendly with little harmful accumulation or emission of chemical inputs. More research on ideotyping is required and breeding efforts should be broadened.

If hemp is harvested late in the season, as for bast fibre production, drying conditions are often poor. It would be an advantage to be able to increase the drying rate so that retting would start earlier. If leaves and heads, not of value in hemp harvested for fibre, could be removed at cutting, the stems may dry faster and nutrients would be returned to the soil. The work described here studied the stripping and subsequent drying of hemp. Exposed stems of hemp that had been stripped dried significantly faster than unstripped. Retted hemp dried much faster than unretted. These results suggest that once retted hemp is exposed when a swath is turned, drying of the exposed retted stems will be rapid, and this was confirmed experimentally.

The hemp samples produced by the partners in the agro - industrial trials were tested for fibre quality. The results of the three-year trials showed various effects of agricultural parameters like site, harvest date, variety, N-levels and plant density on the process-ability of the straw and on the resulting hemp fibre quality. They also demonstrated the very high level of heterogeneity within samples for any test criteria. The samples were tested on technological and morphological criteria, as well as on chemical composition. The most significant factor on the fibre quality was location; the country where the hemp is grown.

A breeding programme was carried out in order to combine root knot nematode resistance with good fibre production characteristics and low THC contents into one hemp variety. The breeding and selection scheme resulted in several selected hemp families having the aimed property combination.

Hemp fibre extracted from stems using relatively conventional retting and decortication techniques tends to be relatively coarse compared with other competing fibre types e.g. flax. Accordingly, in order to make it better suited for added value uses such as plastic reinforcement, spinning etc., there is a need to apply treatments which will improve the quality of the fibre, in particular with respect to fibre fineness (total fibre surface area) and surface cleanliness. In this work, two types of treatment were considered, namely steam explosion (STEX) and ultrasonics; both these have the potential to break down fibre bundles and remove natural binding constituents from fibre surfaces.

Although wood is by far the most common raw material used for the manufacture of wood-based panels, a number of non-wood materials e.g. straw, bagasse, bamboo, flax shiv etc. are used in some parts of the world for the manufacture of composition panels. This work investigated the potential for using hemp, either in the form of whole stem material or shiv separated from the long fibre component, as a raw material for chipboard and medium density fibreboard (MDF). For both products a range of process variables were investigated, including resin type, resin catalyst level, wax addition level, particle size, panel density, time of harvest of the hemp crop and the degree of retting of the material.
Conventional thermoplastics are typically characterised by having high toughness and impact resistance properties, but they lack strength and stiffness and are also not easily biodegradable. However, such materials can be strengthened and stiffened by including fibres in them and there are also a range of biodegradable thermoplastics now available which could be used in their place.

This work investigated the potential for using untreated, STEX and ultrasonically treated hemp bast fibres as reinforcements for a range of biodegradable plastics and the potential for using chemically modified (acetylated) / surface treated (silanes, MAPP) normally retted fibre as reinforcements for polypropylene.

Geotextile materials are used predominantly in mulching applications in the horticulture and forest industries. Their purpose is primarily to suppress weed growth around plants and trees and to help retain moisture. The most common materials which have been used in the past are polythene sheeting and spun / woven polypropylene. These materials have the advantage of being relatively cheap, are easy to put down and are durable. However, this latter property can be undesirable, since the materials can last for much longer periods than actually required; consequently, their removal and disposal can be costly.

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