Extraction of xylans from hardwood chips prior to kraft cooking

The aim of this work is to define an extraction process of hemicelluloses from hardwood chips, prior to their transformation into paper pulp by the kraft process. Eucalyptus wood chips were submitted to autohydrolysis and acid hydrolysis treatments. Autohydrolysis means that no extra acid is added during the heating of the wood suspension, whereas sulphuric acid is added for the acid hydrolysis treatment. The liquor to wood ratio was 4, and temperature and time were varied so as to optimise the hemicelluloses extraction. Quantities of xylans varying between 12 and 38 g/l of hydrolysate (or between 9 and 15% on wood) could be extracted. Kraft cooking process was applied to the pre-hydrolysed wood chips. It was shown that they were easier to delignify than untreated wood chips, and the resulting pulp was also easier to bleach. The resulting cellulosic fibres were characterised for their papermaking properties: the higher the pentosan removal, the lower the strength properties of the pulps produced. (C) 2012 Elsevier Ltd. All rights reserved.