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Hemp hits its stride

Claire Cockcroft, The Guardian, May 10, 2001

The cousin of cannabis is perfect for an industry looking for greener resources, says Claire Cockcroft

It is green, high in fibre, improves strength and reduces weight. This is not the perfect diet but an ingredient for the car industry. Hemp, once an outcast in agricultural circles, is making a comeback and cropping up in unconventional places.

It has been heralded as the environmentally friendly raw material for many consumer needs, including composites for the automotive industry, in a move towards the widespread production of greener, recyclable car parts. Cannabis sativa, to use hemp's official name, has been harvested for millennia for the strong and extremely long coarse fibres in the stem, and its valuable seed oil. It has been used to make ropes, textiles and paper, and fragments of hemp fabric dating from 8,000 BC have been unearthed.

Hemp production prospered during both world wars but was then rejected in favour of cheaper synthetic fibres. Although often confused with marijuana, hemp is a distinct variety within the species: over the years, plant breeders have cultivated hemp varieties with increased stem fibre content and very low levels of delta 9-tetrahydro-cannabinol (THC), the psychoactive ingredient of its controversial cousin. Several countries have legalised hemp farming, some even using it to manufacture currency paper. Plants in Poland are used to make hemp particle board, private plots in Japan provide material for the Emperor's religious robes.

Hemp produces more pulp per acre than timber and is a sustainable alternative for the paper industry. Since it is low in lignin, a natural strengthening agent in plant cells, and is naturally a creamy colour, it requires fewer environmentally damaging chemical treatments, like bleaching, during paper production. Plant-based composites have been widely used in construction: the ancient Egyptians used straw to reinforce clay walls and wattle and daub was used in medieval times. With the rise of more durable construction materials, plant fibres were left in the lurch.

Now, they are being recognised as a valuable alternative for the composites industry. About four billion tons of hemp, flax, jute or kenaf are grown globally, representing a vast sustainable and renewable raw resource that has a lower impact on the environment than fibreglass and plastic. These "bast" fibres have a better stiffness per unit weight and outstanding intrinsic mechanical properties, consisting of about 85% cellulose and hemicellulose, which gives enormous tensile strength, and 15% lignin and pectin. They have excellent heat, sound and insulating properties, good chemical reactivity for processing and even anti-microbial and anti-mildew properties - a built-in pesticide system.

Last year, the ministry of agriculture commissioned a report on natural fibres in the automotive industry. At a meeting of the alternative crops technology interactive network (Actin) Joe Ellison, of the Textile Consultancy, reported that of the 50 million vehicles made globally, up to 20kg of natural fibres could be used to make parts including dashboards, door panels and parcel shelves per vehicle. Germany is the driving force, responsible for more than two-thirds of European production of natural fibre composites with the car manufacturers Mercedes (Daimler/Chrysler), BMW and Audi/Volkswagen leading the way.

Following the introduction of jute-based door panels in the Mercedes E class five years ago, fibre usage in the German car industry has soared from 4,000 tons in 1996 to 15,500 tons in 1999 and consumption is predicted to double over the next five years. The door trim panels for the Daimler/Chrysler Sebring convertible are made from Eco-Cor, a biocomposite plastic made of 25% hemp, 25% kenaf and 50% polypropylene. The blend is formulated for fire-resistance and is "self-extinguishing".

Not only are plant-based fibres usually cheaper to process and more environmentally friendly than glass-fibre and plastic alternatives, which are tricky to dispose of, they often have superior technical properties. They are less prone to splintering and save weight by as much as 30%, improving fuel consumption. With market prices of 30-35p/kg, compared to 85-90p/kg for plastics or 5.50/kg for fibreglass, natural fibre composites present a cheaper alternative that can also be recycled. EC legislation now demands that manufacturers reduce the environmental impacts of vehicles. Ian Bartle, the chief executive of Actin, says:

"With the new 'end of life' vehicle (ELV) regulations, car manufacturers can no longer be complacent about the life cycle of their product, since they are now responsible for the envi ronmentally sound disposal of their creation." Hemcore Ltd was founded in 1993 when grain mountains were getting higher and farmers were on the look-out for alternative land uses. With the volatility in the wheat market, finding a viable alternative crop was critical.

Based in Essex, Hemcore is the only hemp producer in the UK. According to its managing director, Ian Low, hemp provides an excellent break in cereal rotation as it can be grown organically. It also cleans the ground: its quick growth suppresses weed competition, its deep roots improve soil structure and fewer pests and diseases afflict the following wheat crops because of its anti-fungal and anti-microbial properties.

• Dr Claire Cockcroft is at the Institute of Biotechnology in Cambridge

 
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