Activation of softwood Kraft pulp at high solids content by endoglucanase and lytic polysaccharide monooxygenase

The manufacturing of man-made cellulose fibers starts with the dissolution of wood pulp fibers. Pulps can dissolve at different rates and leave different amounts of undissolved particles. Thus, their properties can be modified to achieve better dissolution. Enzymatic treatments are an effective means of enhancing pulp dissolution, and this study compares the effect of endoglucanase (TrCel45A) and lytic polysaccharide monooxygenase (LPMO, TrAA9A) on bleached softwood Kraft pulp at 20 % solids content. The enzymes were applied individually and in combination. Both enzymes increased fibrillation, fines content, porosity, water retention value, crystallinity index and crystallite size, but the largest changes were achieved with the enzyme mixture. For example, fiber saturation point and water retention value increased by 64 and 37 % with TrCel45A, by 27 and 25 % with TrAA9A, and by 73 and 52 % with both TrCel45A and TrAA9A. Pulp reactivity was indirectly assessed by measuring the dissolution time in cupriethylenediamine. The average dissolution time of the reference pulp measured 642 s, while those of the pulps treated with TrCel45A, TrAA9A and their mixture were 399, 473 and 298 s, respectively. The decrease in dissolution time correlated with the increase in fines, fibrillation, porosity, and water retention value.