Highly porous fibre structures and biocomposites made of mixtures of wood, biopolymers and hemp

Highly porous structures made by foam forming technique from natural fibres have several possible future applications. Among these are acoustic materials or cushioning elements in packages. Certain compression strength level is needed in both applications. We investigated the effect of fibre length distribution on the compression strength using hemp bast fibres as long fibres, softwood cellulose as medium length fibres and lignin-rich fines made from spruce wood as the micro fibre component. In addition wooden-like hemp shives were used. The fibre mixtures were foamed with two different types of surfactants: an anionic sodium dodecyl sulphate (SDS) surfactant that has a neutral effect on material bonding and a non-ionic polyvinyl alcohol (PVA) surfactant that enhances bonding. Lignin-rich fines improved the compression strength in all fibre mixtures when SDS was used as the foaming surfactant. The significance of fines addition was minor with materials foamed with PVA. Long hemp bast fibres decreased the compression strength with both surfactants. Addition of stiff hemp shives with bonding enhancing surfactant resulted in good compression strength. Overall, surfactant selection between a bonding and non-bonding one had a larger effect on the compression strength compared to the selected fibre types and fibre mixtures. Hemp is one of the annual crops, which use has increased in different applications in recent years. The traditional use of hemp fibre is in textiles, but the use in different composites, nonwovens and even medical applications has increased. Hemp fibre in plant is located in stem and it's mechanical performance is comparable to glass fibre properties making it good choice for reinforcement in biocomposites. We studied hemp fibre and shive in different potential applications from composites to non-woven structures and hemp based nanocelluloses in order to find potential novel uses for hemp. According to the preliminary results hemp fibre and shives are potential raw materials in natural-fibre plastic composites. In strength point of view it competes with other cellulose based composites and gives new visual design aspects for the material. Nanocellulose made of hemp fibres formed highly viscous hydrogel, which is attractive as a reinforcing component, rheology modifier and film forming material. Their characteristics can be further improved by chemical pre-treatments. Hemp based nanocelluloses have similar or even better characteristics compared to the commercial and wood-based nanocelluloses