Incorporation of bark and tops in Eucalyptus globulus wood pulping

Bark and the tops of E. globulus trees were considered for kraft pulping under industrial conditions. Pulping experiments included wood, bark, tops, and composite samples. Top wood had an average chemical composition most similar to that of wood but with somewhat lower cellulose content (52.8% vs. 56.9%) and higher lignin content (18.8% vs. 17.8%). There was also a small difference between tops and wood for non-polar extractives, which were higher for tops (2.0% vs. 1.4%). Bark had a less favorable chemical composition with more extractives, especially polar extractives (5.3% vs. 1.6%) and 1% NaOH solubility (19.9% vs. 12.2%), pentosans (23.7% vs. 21.3%), and ash (2.9% vs. 1.0%), although the fiber length was higher (1.12 mm vs. 0.98 mm). The kraft pulps obtained using bark showed significantly lower yield, delignification degree, and strength properties but had a quicker response to refining. The incorporation of tops and bark in the wood pulping in levels below or similar to a corresponding whole-stem, however, had a limited effect on pulp yield, kappa number, refining, and pulp strength properties. These additional raw-materials, which were estimated to be 26% of the commercial stem wood (14% bark and 12% tops), may therefore be considered in enlarging the eucalypt fiber feedstock in kraft pulping.