Process Impacts on Mechanical Pulp Fibre and Sheet Dimensions, 1999 International Mechanical Pulping Conference Proceedings

Stuart R. Corson

PAPRO, Forest Research

Variations in mechanical pulp fibre dimensions and sheet structures are examined in this paper as a function of the principal process stages and variables. Fibre dimensions examined are length and those associated with their cross-sections, ie. fibre wall area, fibre wall thickness, and fibre and lumen perimeters. Sheet dimensions examined are fibre wall and inter- and intra-fibre pore area. Trends identified provide an overview of the mechanisms of mechanical pulp fibre quality behaviour and development.

Pulp fibre length is determined initially by the length of the fibre (tracheid) in the wood, refining intensity and fibre cross-sectional dimensions. Fibres of larger diameter lose more of their length and wall thickness and are more likely to split with refining than those of smaller diameter. It is the thicker-walled fibres that preferentially retain intact cross-sections. Fibres can be efficiently fractionated into different lengths classes by pressure screening. Hydrocyclones (centri-cleaners) allow the separation of fibre on the basis of their specific surface area. Small diameter hydrocyclones can separate fibres of contrasting width and wall thickness, but differences between accept and reject streams are not large.