Abstract

Hemicelluloses comprise roughly approximate one-fourth of the weight of wood, thus ranking second in abundance after cellulose. During kraft pulping hemicelluloses are degraded into low molecular weight isosaccharinic acids and end up in the black liquor together with degraded lignin. However, it is possible to extract the hemicelluloses from wood prior to pulping by chemical disassembly and use the carbohydrates from soluble streams for biofuels and high added value biomaterials production. In this work, hemicelluloses disassembling from Pinus radiata wood chips were performed using different extraction conditions (120 to 170°C temperature, 30 to 120 min extraction time and pH 2 to 12). Both solid material and extracts were characterized for their chemical composition and molar mass distribution. The wood chips of the extraction process were submitted to kraft pulping and the effect of hemicellulose extraction prior pulping was evaluated in pulp yield and strength properties of pulps. Results showed that hemicelluloses in P. radiata represent 26% of wood dry weight and, from this amount; hexoses are responsible for 64% of its composition. The maximal amount of hemicelluloses extracted was between 12-16% (on wood basis) according to the extraction conditions. Kraft pulps with kappa number 30 were prepared from wood chips with different content of residual hemicelluloses (26 g/100g for control and 19 g/100g wood for extracted wood chips). The average screened pulp yield was 48% and 44% for control and extracted wood chips, respectively. When pulps where refined to 30°SR, pulps from extracted wood needed 6% more revolutions in PFI mill to achieve the same beating degree than control pulps. Strength properties (tensile, tear and burst indexes) were slightly higher or similar in control pulps as compared with extracted wood pulps.