The effect of eucalypt tree overaging on pulping and paper properties

Overaged trees of Eucalyptus globulus were evaluated to determine their aptitude for pulping with industrial chips as reference. The overaged wood was separated into sapwood and heartwood. Compared with industrial chips, the overaged E. globulus heartwood and sapwood contained approximately 1.5 times more extractives (3.8 vs. 5.2 and 5.9 %), similar amounts of lignin (21.4 vs. 23.3 and 19.9 %) and the holocellulose ranged from 69.5 % (heartwood) to 74.5 % (industrial chips). Overaged heartwood and sapwood produced kraft pulps with 44.6 % yields (48.4 % from industrial chips). The unbeaten pulps from overaged heartwood and sapwood compared with industrial chips have wider cells (19.5–20.7 vs. 17.7 µm), and higher coarseness (0.066–0.097 vs. 0.060 mg m⁻¹) and more primary fines (27.4–27.5 vs. 16.6 %). Overaged wood produced handsheets with lower bulk density and higher water retention value (2.25–2.93 vs. 1.12 g/g). The refining behavior was similar as well as the tensile and tear strength development. The results show that overaged E. globulus trees with large diameters may be introduced into the pulp feedstock without extensive impacts on the pulp characteristics.