DEVELOPMENT OF WOOD GRINDING 2. EFFECTS OF WOOD MOISTURE ON FIBRE PROPERTIES

Abstract

"The wood grinding model recently published was based on an energy balance of the active grinding zone, i.e. the limited volumes of wood and grindstone that were heated by the grindstone generated compression and tension strains in the wood surface. Generally speaking, the data obtained in well controlled laboratory grindings complied with the derived model meaning that compression–tension power ratios presented as a function of the specific pulp production resulted in linears. However, the wood moisture contents varying from water-saturated to air-dried wood needed further elaboration for better understanding. Accordingly, the aim of this presentation was to find reasonable explanations for the grinding effects on the wood fibres by considering groundwood pulp and paper sheet properties, for example shives and fines contents, as well as tensile strength and light scattering of the paper sheet. The compression–tension power ratios provided by the model reflect simultaneously both compression and tension strain in wood, and accordingly, the resulting fibre properties would be dependent on both brittle and tough fractures. Evidently, the water contents played a role in this context, both as a stiffener of the water-saturated wood, and as a wood and fibre coolant. "