Single-Step Fiber Pretreatment with Monocomponent Endoglucanase: Defibrillation Energy and Cellulose Nanofibril Quality

The combination of enzymatic pretreatment of cellulose fibers followed by mechanical defibrillation has become a green and low-energy route to obtain cellulose nanofibrils (CNF). However, the variability in the properties of the as-produced CNF remains a major challenge that needs to be addressed for any application to be realized. Herein, we study the effect of monocomponent endoglucanase (EG) on the energy consumed in defibrillation as well as the physical properties of the obtained CNF. This single-step enzymatic pretreatment (0.5-25 EGU/g cellulose fibers for 1-3 h) reduces the defibrillation energy (by up to 50%) at nearly 100% yield to obtain CNF of a similar morphology, size, and crystallinity compared to CNF obtained in the absence of pretreatment. Under mild conditions (5.6 EGU/g for 1 h), aiming to minimize energy consumption while preserving rheological properties, EG pretreatment increased the water retention value, reduced the molecular weight, and promoted structural surface modification (amorphogenesis), without significant cellulose solubilization. In addition, the carbohydrate binding module of the EG was found to improve the interaction of the catalytic core with the substrate. The combination of the factors considered here boosts the effect of the enzyme even if used at low loadings, facilitating high-yield, more sustainable production of CNF.