APPLICATION OF A COMMERCIAL LIPASE ENZYME ON BIOBLEACHING OF KRAFT BAGASSE PULP

A study on TCF (totally chlorine-free) bleachability of kraft pulps from bagasse was carried out by treating them with a commercial lipase from the Aspergillus niger fungus, followed by a sequence of oxygen and peroxide bleaching stages. The effect of the enzymatic stage on bleachability has been studied and compared with that of xylanase (produced from Trichoderma reesei) and control Pulps (processed Without enzyme addition). A final brightness of 71-72% ISO was achieved after complete bleaching. Direct bleaching affects both pulp brightness (by 2.5-1.9% ISO) and delignification (by 0.28 and 0.20%, on oven-dry pulp) immediately after the enzymatic stage. The bleachability of these Pulps was superior to that of the control during all peroxide stages, under peroxide charges between 3 and 9%. Bleaching selectivity was determined by changes in intrinsic viscosity. Generally, higher bleachability and higher bleaching selectivity of the xylanase-treated Pulps caused a maximal gain in pulp brightness (or bleach boosting, as the main objective of xylanase application), which could be achieved only after the first and second peroxide bleaching stages, followed by a substantial diminishing by the end of the sequence.