Enzymatic hydrolysis as a strategy for fibre modification and energy reduction in mechanical pulping

This thesis investigates the potential of enzymatic hydrolysis to reduce energy consumption in refining mechanical pulps, specifically bleached chemi-thermomechanical pulp. Mechanical pulping, although advantageous for high yield and sustainability, remains energy-intensive, with significant energy consumption during fibre separation and development. This research explores how enzymatic treatments, particularly cellulases, can enhance refining efficiency by modifying fibre structures, thus reducing the energy required for refining without compromising fibre quality. This study evaluates the effects of enzyme incubation conditions – such as pH, temperature, duration, and enzyme dosage – on fibre morphology and refining energy through a series of laboratory and pilot-scale experiments. Results show that enzymatic hydrolysis can facilitate fibre shortening and fines generation during refining compared to unhydrolyzed BCTMP. These findings suggest that enzymatic treatments increase fibres’ susceptibility to mechanical action by weakening their structure, promoting greater fibrillation, and improving water drainage. Softwood BCTMP exhibited significant energy savings, while hardwood BCTMP, particularly aspen, showed more limited effects, with enzymatic hydrolysis modifying the fibres’ response to repulping. Thus, enzyme treatments should be tailored for different wood species. Moreover, the study indicates that alkaline incubation conditions improve enzyme diffusion and fibre modification, potentially reducing the need for buffer solutions in industrial-scale applications. However, the research also highlights challenges, such as the need for further investigation into enzyme combinations and the impacts of different wood species and pulping processes on enzyme efficiency. The findings contribute to a better understanding of enzymatic hydrolysis as an energy-efficient strategy in pulp refining, presenting a sustainable approach to improving pulp and paper production efficiency. Enzymatic hydrolysis presents a promising approach for reducing energy consumption in mechanical pulping. By modifying fibre structure to enhance refining efficiency, enzymatic treatments can contribute to sustainability in the pulp and paper industry. Future research should investigate multi-enzyme systems and broaden the application to other pulping processes and wood species to further optimize and scale this technology.