Preparation, processing and properties of lignosulfonate-flax composite boards.

Hemp, hay, straw for animal litters, raffia and sisal stems, abaca and jute bleached pulp fibres, miscanthus stems and flax fibres were mixed to lignosulfonate at 70% filler concentration and compressed in the form of 5 cm-thick boards. Flax was found to give the best mechanical properties measured in bending mode and used for all tests. Several methods able to improve adhesion between matrix and flax fibres were studied. A treatment of flax fibres with NaOH-water was found to decrease the mechanical properties of composites. Ethanol or dichloromethane solvents that are known to dewax flax fibre surfaces improve the mechanical properties of final board. The addition of pectin to the lignosulfonate matrix was found to improve the mechanical properties in the same order of magnitude as with the ethanol treatment. Both methods improve the flexural strength by 60% while keeping the elastic modulus constant. Mechanical improvement shows that these two methods are increasing the lignosulfonate/flax fibre interfacial adhesion. The best compositions have mechanical properties above the normalized minimum required for wood-based boards.