Wood and Fibre Mechanics Related to the Thermomechanical Pulping Process

The main objective of this thesis was to improve the understanding of some aspects on wood and fibre mechanics related to conditions in the thermomechanical pulping process. Another objective was to measure the power distribution between the rotating plates in a refiner. The thesis comprises the following parts: – A literature review aimed at describing fracture in wood and fibres as related to the thermomechanical pulping process – An experimental study of fracture in wood under compression, at conditions similar to those in feeding of chips into preheaters and chip refiners – An experimental study of the effect of impact velocity on the fracture of wood, related to conditions of fibre separation in the breaker bar zone in a chip refiner – A micromechanical model of the deterioration of wood fibres, related to the development of fibre properties during the intense treatment in the small gap in the refining zone – Measurements of the power distribution in a refiner. The fracture in wood under compression was investigated by use of acoustic emission monitoring. The wood was compressed in both lateral and longitudinal directions to predict preferred modes of deformation in order to achieve desired irreversible changes in the wood structure. It was concluded that the most efficient compression direction in this respect is longitudinal. Preferable temperature at which the compression should be carried out and specific energy input needed in order to achieve substantial changes in the wood structure were also given.