Chemo-enzymatic treatment of mechanical pulping: An efficient method for energy reduction and pulp strengthening

Conventional mechanical pulping faces critical challenges of high energy intensity (1200–2000 kWh/t) and compromised fiber quality, driving demand for innovative solutions to balance energy efficiency with performance. This study established a chemo-enzyme synergistic pretreatment system and elucidated its effects on refining energy consumption and pulp properties in eucalyptus mechanical pulping through multiscale characterization (SEM, XRD, XPS, HSQC NMR). By optimizing the synergistic pretreatment with NaOH (6 %) and cellulase (10 FPU/g), refining energy consumption was significantly reduced to 765.11 kWh/t, achieving energy savings of 40.99 % and 33.99 % compared to conventional mechanical pulp (MP) and chemical-mechanical pulp (C-MP), respectively. Alkaline pretreatment dissolved 20.33 % of hemicellulose and 7.02 % of lignin, cleaving ester bonds in lignin-carbohydrate complexes (LCC) and breaking β-O-4 lignin linkages (9.7 % reduction quantified by NMR), while increasing the syringyl/guaiacyl (S/G) ratio from 2.02 to 3.05, thereby enhancing cellulose accessibility for enzyme pretreatment. Subsequent enzyme pretreatment hydrolyzed 25.59 % of cellulose and 22.07 % of hemicellulose, promoting S1-S2 layer delamination of cellulose fiber wall during refining. Enzyme pretreatment shortened fiber length and increased fiber fines content, but it results in significant increases in tensile strength and burst index for the bio-chemical-mechanical pulp (B-MP) compared to MP, respectively. The synergistic "softening-enzymolysis" mechanism enabled the targeted deconstruction of dense fiber structures, establishing a theoretical foundation for low-energy dissociation of lignocellulosic feedstocks. • Alkali pretreatment enhances the accessibility of cellulase. • Enzymes liberate cellulose and hemicellulose, separating the wood S1-S2 layers. • Alkali-enzyme synergy shows major energy savings. • Multi-scale characterization reveals alkali-enzyme synergy.