EUREKA JANUARY 2002 FEATURE ARTICLE

Growing a green approach to materials

Biotechnology is the key to new, low-cost methods of making advanced materials from plants. Tom Shelley reports

Natural fibres of high strength and great stiffness can now be separated from agricultural plants at half the cost of mechanical methods.
The first application is in a high-technology wallpaper, but the fibres can also be used as reinforcement in plastics, or used as they are, in a new process to make engineering constructions.
The extraction process is biologically based, consumes no energy and produces no pollution, pointing the way to radically new methods of materials processing. No longer will it be necessary to mechanically tear stems of plants apart, whether by machine based decortication, or by hand beating as in the ancient process to recover linen fibres from flax.
Instead, ordinary fibre hemp plants are harvested and put into 100-tonne capacity plastic biobags. This is followed by the addition of a culture of naturally occurring bacteria which produce enzymes to break down the stalks into their constituent parts. The process takes six weeks, after which 97% of the raw hemp crop is turned into a fibrous pulp. The remaining 3% is a non toxic residue containing solids and liquids which can be put back on the fields as a joint nitrogen fertiliser and general soil improver. Production cost of the separated hemp is about half that of using mechanical methods.
The process is the invention of Scottish Farmer, Henry Aykroyd, who has set up a company, Biofibres, to exploit the technology. The process has been developed with assistance from Napier University, Edinburgh; the Scottish Agricultural Colleges; and Creando Fibretech, based at the Swedish National School of papermaking.
The first commercial product to be announced is a superior quality wallpaper, available via mail order at around 20 per roll (goto www.thehemppapercompany.com). Very large potential markets also exist for use as an engineering material, because of its ready availability, biodegradability and low cost.
The fibrous stalk of the hemp plant has been used industrially since the invention of modern paper in about 105 AD. US readers will be interested to known that the Declaration of Independence was drafted on hemp paper in 1776. Hemp is one of the world's most widely distributed plants. It occurs in most of the temperate and tropic regions of the world. It grows in the Himalaya Mountains, tropical Africa, East and South Africa, United States and Canada and all over Europe. The varieties, which are used as the source of the fibre, grow 3m tall with tough stems and yield only microscopic amounts of cannabis. Hemp ropes have been used in ships for centuries, and although less strong than some synthetic polymer fibres (see table), are much stiffer and, with the invention of the new production process, are potentially much cheaper. In the UK, one of the last commercial makers of hemp ropes is to be found in Chatham Historic Dockyard (www-master-ropemakers.co.uk).
Hemp clothing typically lasts 10 years, compared with five for cotton. Hemp paper can be recycled 10 times, as opposed to three times for most pulp-based paper. Fewer caustic and toxic chemicals are used to make paper from hemp than are used to make paper from trees. An acre of industrial hemp produces four times more paper than an acre of trees.

Fabricating in fibre
Hemp fibre is already being used as replacement for glass fibre in European and US car internal panels.
Nicholas Williamson, as part of a post graduate course at the Royal College of Art in London, investigated making items out of formed felt instead of plastic. His experiments were with wool felt and epoxy resin, but he told Eureka it was possible to make almost any fibre into a felt, including hemp.

His manufacturing technique is bag pressing, in which the felt/resin layers are formed over a tool by a press equipped with a large rubber sheet. His first designs demonstrated both a furry look and feel and great strength. He added the fact that such fabrications are of great usefulness as insulators of heat, vibration and shock and that NASA has developed carbon/aramid fibre felts for space work. A briefcase and headphones, made as demonstrators, are both quite waterproof, despite their appearance. He has now set up his own company, MG Marga Design, which is developing other products. Fire retardents may be included where required.


Jute and hemp fibre boards have also been studied extensively by the Institute of New Materials in Saarbrucken, Germany ( www.inm-gmbh.de )

Structures of straw
The Institute has also been looking at using wheat straw as a source of natural fibre.
As a source material, it is even more abundant-the UK producing 13 million tonnes per year.
Past attempts to chemically digest straw produced large quantities of silica liquor and the Biofibres process does not work with it. We are told that a 40 million UK Government project discovered that, in some years, wheat straw would cost nothing, and in other years it could cost 50 per tonne plus 50 a tonne for transport. In 1968, there were 23 paper mills in the UK making straw paper. Most no longer exist, due to the cost of investment needed to meet the requirements of environmental legislation.
Nonetheless, research continues in many countries.
Several papers were presented on the subject of processing wheat straw and other normally waste natural fibres at a conference organised by Pira International (www.piranet.com) held in Amsterdam in October.
Dr A. Kalleder, at the Institute for New Materials, has been looking at looking at using straw as it is, to replace honeycomb-type cores in composite sandwich construction.
Binders are inorganic, based on silica and developed by the sol-gel route. The only snag is that the straw stems have to be parallel for maximum strength. If the stems are in 'Ideal parallel order' compressive strength is 3.5MPa, falling to 3.0MPa for 'Parallel order' and 1MPa if the stems are in random 'disorder'. Board density is 0.13g/cm3 and can be made both flame resistant and water repellent. The Institute said it would be very interested to hear if anyone could devise a simple method of lining up the straw to form part of a low cost manufacturing process. For more information contact: henry.aykroyd@biofibres.com , sales@master-ropemakers.co.uk , nick@mgmarga.com , kalleder@inm-gmbh.de

Material Strength (MPa) Young's Modulus (GPa) Density (kg/cu m)
Bulk Polyester 50 2.9 1300
Bulk Nylon 63 2.5 1090
Cottom 225 7.9 1540
Hemp 300 32 1490
Nylon Fibre 616 3.9 1140
Polyester Fibre 784 13.2 1390
Alloy Steel 1330 210 7800
Carbon fibre 3430 300 1770
Aramid Fibre 3930 124 1450

Figures from University of Cambridge Department of Engineering Materials

Back to list of stories