Water sorption, surface structure and surface energy characteristics of wood composite fibres refined at different pressures

During fibre processing, wood fibres are subjected to a range of physical and chemical conditions sufficient to slightly alter their chemical composition and hence their ultimate performance when used in the manufacture of wood fibre-based composites. In order to better understand the effects of refiner conditions on material performance, wood fibres were subjected to processing at different refiner pressures (4, 6, 8 and 10 bar) and subsequently dried in a flash drier. The fibres were analysed for changes in surface area, surface energy, surface structure and water vapour sorption characteristics. The methods applied were nitrogen adsorption utilising the Brunauer–Emmett–Teller theory, inverse gas chromatography, scanning electron microscopy and dynamic vapour sorption. It was found that increasing refiner pressure resulted in fibres of lower surface area, accompanied by increasing dispersive surface energies up to operating refiner pressures of 8 bar. It was found with fibres refined at different pressures that as the refiner pressure increased the equilibrium moisture content of the fibre decreased at the set relative humidities. However, it was also noted that the hysteresis was not significantly different between each of the refiner pressures. The results suggest that different refiner pressures can be used to tune the surface characteristics which may be beneficial to product development and the improvement of the environmental profile of the wood fibre composites.