Effects of laccase/HBT treatment on pulp and lignin structures

A significant increase in delignification was obtained for both a pine kraf t pulp and ail oxygen-delignified pine kraft pulp by means of HBT-mediated (1-hydroxybenzotriazole) laccase treatment compared with the reference trea tments. Residual lignins from the pulps before and after the different trea tments were isolated and characterized. Laccase,without mediator did nor de lignify the pulp, nor did it depolymerize or polymerize the lignin in the f ibres. However some minor chemical modifications occurred in the fibre lign in. On the other hand laccase together with HBT was able to degrade the lig nin in the pulp fibres. HBT-mediated laccase treatment also caused an incre ase in the carbonyl and carboxyl group contents, and a decrease in the free phenolic hydroxyl and methoxyl group contents of the residual lignins.