Mechanical and physical properties of industrial hemp-based insulation materials

In recent years, research in the field of insulation materials in buildings has been focusing increasingly more upon ecological properties of these materials. Hemp is an annual bast fibre plant, which delivers fibres, shives, and seeds. Bast fibres are used as a raw material for thermal insulations while shives have been mainly used in animal bedding and construction. The aim of this research was to evaluate the mechanical and physical properties of the industrial hemp fibre-and bast-based insulation materials and compare them with wood-based materials. For producing hemp fibreboards, the hemp shives were ground with separative milling by a semi-industrial disintegrator to the average particle size of 0.136 mm. Urea-formaldehyde (UF) resin was used as the adhesive for hemp particleboards and fibreboards made by the dry method. Fibreboards made by the wet method were bonded without using any binders. Some fibreboards made by the dry method were covered with kraft paper on both sides using UF resin and PVA glue. Properties of particleboards and fibreboards were tested with the determination of density, swelling, resistance to axial withdrawal of screws, tensile strength perpendicular to the plane of the board, bending strength, and air permeability. The results showed that fibreboards made by the dry method were stronger and tougher than fibreboards made by the wet method. The only shortcoming of the former was their low water resistance as samples dissolved in water. Hemp particleboards were lighter and less dense than wood particleboards. However, the mechanical properties of the hemp particleboards were inferior to those of wood particleboards. In addition, the levels of water absorption and swelling of the hemp particleboards were higher than those of the wood particleboards.