Enhanced energy savings in enzymatic refining of hardwood and softwood pulp

Abstract

Background: Pulp refining is an energy consuming, but integral part of paper production with the aim to increase tensile strength and smoothness of paper sheets. Commercial enzyme formulations are used to lower the energy requirements by pre-treatment of pulp before refining. However, a high number of different commercial enzyme products are available on the market containing enzymes of varying origin and composition, which complicates the prediction of their behavior, especially using different pulp types. Results: Endoglucanase-rich enzyme formulations were characterized regarding enzyme activity at different temperatures, resulting in a significant decrease of activity above 70 °C. Some enzyme preparations additionally contained arabinosidase, xylanase and β-glucosidase activity consequently resulting in a release of xylose and glucose from pulp as determined by high-performance liquid chromatography. Interestingly, one enzyme formulation even showed lytic polysaccharide monooxygenase (LPMO) activity of 3.05 nkat mg−1. A correlation between enzyme activity using the endoglucanase specific derivatized cellopentaose (CellG5) substrate and enzyme performance in laboratory PFI (Papirindustriens forskningsinstitut) refining trials was observed on softwood pulp resulting in a maximum increase in the degree of refining values from 27.7°SR to 32.7°SR. When added to a purified endoglucanase enzyme (31.6°SR), synergistic effects were found for cellobiohydrolase II (34.7°SR) or β-glucosidase enzymes (35.7°SR) in laboratory refining. Comparison with previously obtained laboratory refining results on hardwood pulp allowed differences in enzyme performance based on varying pulp types to be elucidated. Conclusions: Interestingly, the individual enzymes indeed showed different refining effects on softwood and hardwood pulp. This difference could be predicted after development of an adapted enzyme activity assay by combination of the derivatized cellopentaose CellG5 substrate with either softwood or hardwood sulfate pulp.