Hemp – an alternative
Hemp bast or long fibre and hurds or inner short fibre can be processed and used with existing technology in construction. The hemp stalk can be incorporated into building materials straight from the field. Hemp fibre added to concrete increases tensile and compressive strengths, reduces shrinkage and cracking.
The demand for renewable raw materials is increasing. Currently many companies produce non-woven products like mats for insulation and car/vehicle composites based mainly on flax but increasingly now on hemp fibres. Hemp fibres have excellent potential – they can reinforce plastics, substitute mineral fibres, be recycled, can be grown ecologically, and have no waste disposal problems. A range of products can be derived from non-woven mats for a range of uses: insulation, filters, geotextile, growth media, reinforced plastics and composites.
Processing Hemp Stalk
Natural fibre composites (NFCs) are formulated from a blend of natural fibres such as kenaf, hemp, flax, jute and sisal, and thermoplastic polymers. NFCs are approximately 25 percent stronger than wood fibre reinforced thermoplastics and have none of the negative handling or environmental issues associated with glass fibre.
The Suffolk Housing Society in UK undertook a project to build homes out of hemp and to compare their performance to brick and block built houses. This project has since gained international attention. It all started when Ralph Carpenter, a local architect, took a trip to France and saw, in Rene, a collection of houses made of hemp. The construction material was developed by Madame France Perier.
There is an interesting story behind the development of the hemp construction material. France Perier was a conventional chemist. She developed skin cancer and searched for a cure. She found that hemp oil was effective and cured her skin cancer. She then set out to research the amazing properties of hemp. Coincidentally she saw a bridge that was constructed in the Metrovingian period (Roman period) and that used hemp in the mortar between the rocks. France Perier investigated the uses of hemp in construction and developed a product she called Isochanvre (Chanvre means hemp).
Isochanvre is flame-proof, non-toxic, 1/9 the weight of cement concrete, has excellent insulation properties, unpalatable to rats, termites or insects, and is flexible and strong. Because of its strength and flexibility it is an ideal building material in areas prone to cyclone and earthwakes.
Ralph Carpenter brought the idea back to St Edmundsbury Borough Council and Suffolk Housing and convinced them to seriously consider hemp housing. The project was funded by the society with grants from the Housing Corporation and St Edmundsbury Council. The project commenced to build and test four houses – two hemp houses and two traditional brick and block houses. Two houses (one hemp and one brick) were occupied when they were completed and two were left unoccupied for three months to monitor their environmental performance.
Structure & durability
The qualities of hemp homes were found to be at least equal to those of traditional construction.
Heating fuel consumed by the hemp homes is no greater than that used in the traditionally constructed houses. It was discovered from an examination of the composite images of the front and rear elevations of both houses that there was significant heat loss through external walls and windows from the traditionally build masonry house in comparison with the hemp house.
Both forms of construction appear to give complete protection against water penetration. However, the hemp homes generate less condensation.
The advantages that the hemp homes display are:
- The use of renewable materials, particularly the hemp
- Low use of energy in producing the principal materials
- Reduced excavation of subsoil for foundations
- The materials are recyclable
- Minimal amounts of energy will be required to demolish the buildings compared to brickwork and concrete.
Textiles – Moulded or Pressed
Moulded or pressed hemp textiles are currently used by car manufacturers such as Mercedes, BMW, Audi, Cadillac to make a wide range of parts and accessories such as headliners, rear window shelving, dashboards, door panels, trunk/boot liners and air bag parts. With the European Commission criteria for 70 percent of a car’s parts to be made from recyclable material there is more pressure on car manufacturers to use hemp and other plant fibre (composites) in their manufacturing process, for not only smaller parts of the car but for all exterior bodywork and interior trim.
There are three different way that hemp can be used to manufacture plastic products.
- The hurds can be processed into cellophane – hemp based cellophane was common from 1880s to 1930s.
- The hurds can be blended – 50 percent hemp/ 50 percent recycled plastic mixture for manufacturing injection-moulded products.
- Hemp seed oil can be converted into a valuable plastic resin.