Chemimechanical Pulping of Poplar Wood. Alkaline Wood Pretreatment at Low Temperature

The low temperature alkaline treatment of Cottonwood (Populus deltoides) was studied by applying a factorial experimental design. The effects of treatment time and alkali concentration on alkali consumption, as well as treatment yield, carboxyl groups and acetyl groups contents were investigated. Relationships between these contents and wood swelling measured by the water retention value (WRV) were also analyzed. In the whole alkali-concentration range under study, the deacetylation process was responsible for a great part of the alkali consumption. Fitted curves show that the swelling obtained is always increasing despite the fact that the carboxyl groups content attains its higher levels at intermediate times. The unique relationship found for the WRV of the wood and its acetyl groups content indicates that the deacetylation, rather than the acid group content, is the process determining the wood swelling brought about by the alkaline treatment.