NEW INSIGHTS INTO EUCALYPTUS LIGNIN & PULPING CHEMISTRY Anderson Guerra, Ilari Filpponen, Lucian A. Lucia and Dimitris S. Argyropoulos* Organic Chemistry of Wood Components Laboratory, Department of Forest Biomaterials Science & Engineering, North Carolina State University, Raleigh, North Carolina 27695-8005. e-mail: dsargyro@ncsu.edu ABSTRACT Despite the growing importance of Eucalyptus wood as pulp and paper raw material, there is a lack of knowledge on the specific chemistry of the macromolecular components of Eucalyptus species. The present paper addresses this issue by combining the recently developed protocol for isolating enzymatic mild acidolysis lignins (EMAL) with the novel combination of derivatization followed by reductive cleavage (DFRC) and quantitative 31 P NMR. More specifically, EMALs were isolated from E. globulus, E. grandis, redwood and White fir, milled under different ball milling conditions. Overall, the yields and purities of EMALs isolated from Eucalyptus were found to be higher than those from the examined softwoods. Comparison of lignins isolated from E. globulus and E. grandis by 31 P NMR showed significant differences in their chemical structure. Lignin from E. globulus was found to contain higher contents of arylglycerol-β-aryl ether structures, free phenolic hydroxyl groups and syringyl- type units than lignin from E. grandis. New insights provided by the combination of DFRC and 31 P NMR revealed that up to 62.2% of arylglycerol-β-aryl ether structures in E. globulus are uncondensed, while in E. grandis the amount of this uncondensed structures were found to be lower than 48%. Syringyl to guaiacyl ratio determined by 31 P NMR before and after DFRC indicated that syringyl-type units in both Eucalyptus woods are predominantly non-phenolic. Size-exclusion chromatography (SEC) analyses performed on these EMALs showed that lignins from E. grandis and softwoods associate in greater extension than lignin isolated from E. globulus. Furthermore, green liquor (GL)-modified pulping was confirmed to be a feasible technology for producing Eucalyptus and softwood pulps. GL pretreatment of Eucalyptus wood chips offered significant savings in the total amount of active alkali, besides reducing the amount of rejects and the residual lignin retained on the fibers. Kinetic studies performed on isolated lignin from E. grandis, E. globulus and a mixture of softwoods revealed that the higher the amount of free phenolic hydroxyl contents within the lignin, the faster the degradation of arylglycerol-β-aryl ether structures under GL impregnation conditions. INTRODUCTION Hardwoods are important raw materials used in the production of pulp and paper. For example, Betula Pendula (birch) is the dominant hardwood species for such applications in Northern Europe, whereas Eucalyptus species represent the main fiber sources for the pulp and paper industry in the Iberian Peninsula and South America (1). Despite the growing importance of Eucalyptus wood as pulp and paper raw material, there is a lack of knowledge on the specific chemistry of the macromolecular components of Eucalyptus wood (1,2). As far as lignin is concerned, few efforts have been made to better understand its isolation process from this hardwood (2,3). Milled wood lignin (MWL) from Eucalyptus is always obtained in poor yields (2,4) and with high proportion of attached hemicelluloses and tannins, which hinder the quantitative analysis of the lignin structural elements (2). As such, a study aimed at understanding how to isolate lignin from Eucalyptus wood in high yield and purity is warranted. Recent reports that deal with the isolation of the lignin from wood have shown that a novel procedure, using the combination of enzymatic and mild acidolysis (EMAL), isolates lignin that may be more representative of the total lignin present in milled- wood (5). Because a mild acid hydrolysis can liberate lignin from lignin-carbohydrate complexes (known to preclude lignin isolation in high yields), it can be combined with low severity of milling, facilitating the isolation of less modified lignin in high yields and purities from milled-wood (5). We have recently shown that the yields of EMAL are from 2 to 5 times greater than the corresponding MWL and cellulolytic enzyme lignin (CEL) isolated from the same batch of milled-wood, depending upon the wood species from which they were isolated (6). Comparison of the chemical structure of EMAL, MWL and CEL has revealed only subtle differences, evidencing that EMAL is released by cleaving lignin-carbohydrate bonds rather than other linkages within lignin macromolecule (5,6). Consequently, the aforementioned protocol presents a real opportunity to improve yield and purity of lignin from Eucalyptus, since such lignin is always obtained in low yields and purities due to the high proportion of attached hemicelluloses (2). A novel approach for the quantification of different lignin structures using the combination of Derivatization Followed by Reductive Cleavage (DFRC) and quantitative 31 P NMR was recently described (5,6,7). Since quantitative 31 P NMR determines the amounts of the various hydroxyl groups, such spectra “before DFRC” provide quantitative information about the aliphatic hydroxyls, carboxylic groups and condensed and uncondensed units bearing phenolic hydroxyl groups within lignin. Such hydroxyl groups are revealed and quantified by 31 P NMR after phosphitylating lignin with 2-chloro-