Eucalyptus wood quality and its impact on kraft pulp production and use

This paper summarizes the authors’ research findings over the last five years on eucalyptus wood properties and their impact on process efficiency and pulp use, addressing the influence of species and harvesting age. Efficient production of kraft pulp is achieved with eucalyptus wood having reasonably high density, low extractives and lignin contents, high lignin S/G ratio, and high xylan and uronic acid contents. Woods containing large amounts of lignin tend to possess lignin with low S/G ratios and are hard to process. Age significantly affects the chemistry and morphology of wood and its behavior in kraft pulping and pulp use. Wood density, extractives content, and fiber coarseness increase with age. Eucalyptus hemicelluloses are composed mainly of a xylan unusually rich in uronic acids, which is reasonably stable in kraft pulping. The xylans retained in the kraft pulp substantially improve its refinability. The increase in wood age and density increases fiber coarseness, which negatively affects pulp refinability, but increases pulp drainability.