Summary

In order to analyse the fundamentals of alkaline chemi-mechanical pulping of hardwoods, the chemical state of the wood was related to both the swelling level of fibres and the papermaking properties of pulp. Wafers of poplar wood were alkali treated following a factorial experimental design for two variables: temperature and alkali concentration. Treated wafers were hot defibrated in a 300-mm disk mill at 15% consistency, and then refined in PFI mill at 20% consistency. Results show how fibre swelling gradually increases as alkaline action is increased. The significant improvement in tensile and tear strength of the pulp can, in great part, be ascribed to the development of fibre bonding capacity. A limited effect of ion content on cell wall swelling was found. Swelling correlates well with deacetylation level, and is a major factor in determining the tensile strength and scattering ability of the pulp.