CHARACTERIZATION OF LIGNIN IN WOOD AND PULPS FROM EUCALYPTUS GLOBULUS HEARTWOOD AND SAPWOOD Ana Lourenço 1* , Jorge Gominho 1 , António Velez Marques 2 and Helena Pereira 1 1 Forest Research Center, School of Agriculture, Technical University of Lisbon, Tapada da Ajuda 1349-017 Lisbon, Portugal. 2 Research Center for Chemical Engineering and Biotechnology, Superior Institute of Engineering of Lisbon, Rua Conselheiro Emídio Navarro, 1, 1959-007 Lisbon, Portugal. * E-mail: analourenco@isa.utl.pt ABSTRACT Heartwood and sapwood were separated from a 18-yr-old tree of Eucalyptus globulus, and characterized by Py-GC/MS and GC/FID in respect to composition and content of lignin. Heartwood and sapwood presented similar lignin content in an extractive-free basis (23.7% and 23.0% respectively), with no differences in lignin composition in respect to S-units (76.0% vs. 76.3%), G-units (22.0% vs. 21.0%) and H-units (1.9% vs. 2.7%), and S/G ratio (3.5 vs. 3.6). The lignin-derived pyrolysis compounds were clustered by groups as: in S-units “syringol”, “S- aldehydes”, “S-ketones”, “S-alcohols” and “C 11 H 12 O 3 ”; in G-units “guaiacol”, “eugenol”, “G- aldehydes”, “G-ketones”, “G-alcohols” and “others”; and in H-units “phenol” and “H-aldehydes”. The wood samples were kraft pulped at isothermal conditions at 130ºC, 150ºC and 170ºC and several cooking times (0 to 180 min, with 5 min heating time to temperature). The effect of temperature upon delignification was evident. At 130 ºC the delignification was slow with no significant selectivity in respect to the composition of lignin and similar S/G ratio of 2.65 and 2.83, respectively in sapwood and heartwood pulps. This contrasts with the wood behavior at higher temperatures, where S/G ratio decreased to 0.59 (150ºC) and 0.55 (170ºC), due to the removal of the S-units of lignin in the last pulping phase. At the end of delignification at 170ºC, the residual lignin was characterized by an increased content of “guaiacol”, “eugenol” groups from the G-units, and “phenol” group (H-units), but with less “syringol” and “S-aldehydes”. There were no differences in the content and composition of the residual lignin in the pulps obtained from heartwood and sapwood. The lower pulp yields and difficulty on pulping of heartwood should therefore be ascribed to extractives presence. I. INTRODUCTION Eucalyptus globulus wood is prized for the production of high yield kraft pulps (del Rio et al., 2005). The lignin content and composition, in particular the S/G ratio is an important characteristic in the selection of wood for pulping (del Rio et al., 2005; Pinto et al., 2005; Rodrigues et al., 2001). since S-lignin degrades more easily during pulping (González et al., 1999), leading to low alkali consumption and high pulp yield (del Rio et al., 2005; Collins et al., 1990). The accurate determination of the S/G is difficult, as discussed by Bose et al. (2009). In this context Py-GC/MS has been used for wood and pulps characterization (Lourenço et al., 201_) with the advantage of requiring small amounts of sample with no pre-treatment except extraction and grinding (Meier and Faix, 1992). The lignin degradation during pyrolysis involves dehydration, producing phenolic compounds with unsaturated side chains and low molecular mass products and gases (Yang et al., 2007; Meier and Faix, 1999), but the major products are lignin marker derivatives: guaiacol and syringol (Meier and Faix, 1992; 1999). To our knowledge, no studies were performed using Py- GC/MS for lignin characterization of sapwood and heartwood from E. globulus. The objective of this work was to contribute for the improvement of eucalypt wood pulping, by evaluating the lignin degradation during isothermal kraft pulping, at 130 ºC, 150 ºC and 170 ºC, and several cooking times (ranging from 0 to 180 min), using heartwood and sapwood of E. globulus and Py- CG/MS(FID) as analytical tool.