ORIGINAL The effect of eucalypt tree overaging on pulping and paper properties Jorge Gominho 1 • Ana Lourenc¸o 1 • Duarte Neiva 1 • Luı ´s Fernandes 2 • Maria Amaral 2 • Ana Paula Duarte 3 • Roge´rio Simo˜es 2 • Helena Pereira 1 Received: 15 December 2014 Ó Springer-Verlag Berlin Heidelberg 2015 Abstract 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 extrac- tives (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 lm), 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. 1 Introduction The pulp industry based on Eucalyptus globulus feedstock has optimized processing to a supply of trees with stem diameters up to about 40 cm which in European temperate regions corresponds to 9–13 years of age (Tome´ et al. 2007). The pulping quality of such raw material has been extensively studied in relation to fiber morphology, wood chemical composition, pulp properties and all their factors of variation, as reviewed in Pereira et al. (2010). However shortage of wood has led the industry to import wood or to consider other less conventional fiber sources such as stumpwood (Gominho et al. 2014). Another raw material source may arise from trees that are above the usual commercial age of harvest for pulping i.e. overaged trees, and which consequently will have stem sizes quite above the current diameters. These overaged trees result from small scale plantations that became unmanaged, from scattered trees in agro-for- estry systems or from road lining; although there are no accurate statistics on availability, the industry considers them as a potential valuable fiber source once concerns over a detrimental effect on the pulp may be overcome. Some differences are expected with such overaged trees given the age trends of some wood features. In eucalypts, the fiber length and wall thickness increase with age, and within the tree they increase from pith to bark (Zobel and van Buijteenen 1989; Wilkes 1988). Wimmer et al. (2002) found for E. globulus that longer fibers have more cellulose and less lignin that promote positively pulp yield, tear index, bending stiffness and pulp freeness, while shorter fibers increase active alkali consumption. The presence of heartwood is another subject to take into account when the pulping industries deal with over- aged trees. Since heartwood diameter increases with tree & Jorge Gominho jgominho@isa.utl.pt; jgominho@isa.ulisboa.pt 1 Centro de Estudos Florestais, Instituto Superior de Agronomia, Universidade de Lisboa, Tapada da Ajuda, 1349-017 Lisbon, Portugal 2 Research Unit of Textile and Paper Materials, Universidade da Beira Interior, 6201-001 Covilha˜, Portugal 3 Centro de Investigac¸a˜o em Cieˆncias da Sau´de, Universidade da Beira Interior, 6200 Covilha˜, Portugal 123 Eur. J. Wood Prod. DOI 10.1007/s00107-015-0965-2