Effect of incubation conditions of cellulase hydrolysis on mechanical pulp fibre morphology

Abstract

The mechanical pulp industry is diversifying through the manufacture of high-value paper products, such as microfibrillated cellulose. However, the development of fibre quality is still energy-intensive. Enzymatic hydrolysis is hypothesized to promote fibre cutting, greater fibrillation, and reduce refining energy costs. Despite potential benefits, there is little understanding of the mechanisms behind fibre development during enzymatic hydrolysis of mechanical pulp. This work investigates how incubation pH and temperature during enzymatic hydrolysis impact the refining of mechanical pulp short fibres. Incubation with endoglucanase at pH 5 and 60 °C increased fibre cutting by approximately 20 %. Fibrillation was negatively affected at this condition, resulting in increased slim fines formation with refining. Incubation at pH 8 and 80 °C promoted >15 % reduction in fibre length, despite such conditions being associated with low enzyme activity. The pH variation modified the sedimentation height of the fibres and the conductivity of suspensions, indicating a change in fibre surface charge. Fibre morphology changes were induced by enzyme hydrolysis conducted at conditions representative of the full range of pH and temperature observed in mechanical pulp mills.