Abstract
Application of a laccase mediator system (an L stage) to TCF and ECF bleached pulp from Eucalyptus globulus with low residual lignin content (KN lig ⩽ 1.0) provides useful information about its effects on hexenuronic acids, functional groups (carboxyl and carbonyl) and electrokinetic properties such as ζ potential and surface charge. The use of laccase from Trametes villosa in combination with the mediator 1-hydroxybenzotriazole (HBT) was found to oxidize cellulose to carbonyl groups and reduce the amount of carboxyl groups present in TCF pulp by effect of its partially removing hexenuronic acids from it. This result may open up new prospects for improving brightness stability in pulp. In addition, the laccase mediator system modifies the surface charge and ζ potential in the fibre suspension for the removal of ionizables groups in TCF pulp. This result has no adverse effect on the pulp refining efficiency. L treatment requires less mechanical energy than conventionally refined pulp to obtain an optimal tensile and tear index in handsheets. This behavior may be attributable to the modification of the electrokinetic properties.
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