Recent Advances in the Chemistry of Eucalyptus Wood

The chemical characteristics of the woods from several eucalypt hybrids from the Brazilian Genolyptus program were studied. The analyses of the lipophilic extractives indicated a similar composition in all eucalypt hybrids, which were dominated by sitosterol, sitosterol esters and sitosteryl 3β-Dglucopyranoside that are responsible for pitch deposition during kraft pulping. The analysis indicated that the wood from U1xU2 presents the lowest amounts of these pitch-forming compounds. The composition and structure of the lignins were analyzed by 2D-NMR that indicated a predominance of syringyl (S) over guaiacyl (G) units and only traces of p-hydroxyphenyl (H) units in all woods, with the highest S/G ratio for G1xUGL. All the lignins showed a predominance of β-O-4' ether linkages (75-79% of total side-chains), followed by resinols (9-11%) and lower amounts of phenylcoumarans and spirodienones. The lignin from the hybrid G1xUGL also presented the highest proportion of β-O-4' linkages, and therefore, it is foreseen that the wood from this hybrid will be more easily delignifiable than the other selected Brazilian eucalypt hybrids.