Eucalyptus wood decay: effects on productivity and quality of cellulose

Summary We evaluated the effect of wood decay, caused by fungi Hypoxylon spp., on pulp productivity and quality. Wood samples with different proportions of contamination (0, 25, 50, 75, and 100%) were used to produce Kraft pulp under the same pulping conditions. In the second step, cookings were performed to achieve the same Kappa number (Kn = 17 ± 1), varying only the alkali charge. Wood and pulp were also analysed by scanning electron microscope (SEM). The risk of occurrence of wood decay reached its maximum between September and October, under inappropriate storage conditions and juvenile wood without bark. It was observed that the increase in the decayed content (DC) of wood chips affected the Kappa number (Kn), according to the model Kn = 1/(0.0595−0.00324*DC0.34102). An increase of 38.7% of alkali charge was necessary to reach the same Kappa number with decayed wood. The yield for the contaminated wood was lower (48%) when compared to non‐contaminated wood (53%). Once contaminated, the wood chips demand more severe cooking conditions because of the difficulty of impregnation. This condition affected the pulp quality, reducing its viscosity by 30% and hemicelluloses content by 5%. In addition, losses of resistance were also observed in the final pulp, where the zero span and tensile indexes were reduced by 5 and 16%, respectively. The SEM observations showed that the ascostroma fungi tissue was not totally degraded during the Kraft process, resulting in the deposition of pitch on fibres. Considering the results achieved, it was possible to conclude that the eucalyptus wood decay, caused by the fungi Hypoxylon spp., significantly affects the pulp process and quality.