Use of hemp and flax in composite manufacture: a search for new production methods

Abstract

A new cost effective method of fabricating strong plywood-type composites from strips of hemp fibres is reported, which takes advantage of the first frosts in autumn. The extracellular ice formed in the plants detaches the fibre layers from the woody material. In a three-point bending test 20×20×100 mm3 fibre/epoxy test beams with a similar structure to that of plywood were found to be of comparable strength, the highest flexural strength being 65 MPa. A two-component epoxy resin (Araldite®) was used as an adhesive. The mass fraction of the strips was 50–80%. The compressive stress during the manufacturing process was 0.1 or 8 MPa. The good appearance, manufacturing properties and workability of the biofibre composites make them suitable especially for floor and furniture manufacture. By pressing together 48 layers of hemp or flax mats which were originally intended for insulation purposes composites were produced that were even stronger than those made from strips. Hemp was spring harvested, which somewhat reduced the strength of fibre bundles. The great advantage of spring harvesting hemp fibre is that no artificial retting or drying is needed which makes the industrial raw materials, and therefore the final products, economically attractive. The highest flexural strengths of the test beams were around 140 MPa and stiffness 6 GPa with a fibre mass fraction of 50–60%. A 6 MPa compressive stress was applied during the manufacturing process.