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Abstract
The development of phenolic hydroxyl and carbonyl groups and the changes in the molecular weight of lignin during the autocatalyzed ethanol-water pulping of Eucalyptus globulus wood was modeled. The models were developed using a response surface method and were employed to study the influence of cooking temperature, cooking time and ethanol concentration on lignin characteristics. The functional groups content was found to increase as the cooking time was risen and the concentration of ethanol in the pulping liquor was reduced. These cooking conditions lead to a more extensive cleavage of the bonds between lignin units due to the longer treatment, higher temperature and increased acidity of the pulping liquor. The cleavage of lignin bonds resulted in the occurrence of new functional groups and a reduction in lignin molecular weight. The steady decrease in molecular weight with the intensity of cooking conditions indicates that lignin condensation does not play an important role under the conditions studied.
ACKNOWLEDGEMENTS
The authors are grateful to the Comisión Interministerial de Ciencia y Tecnología for financial support (project AMB94–0012–C02–01).