THE ROLE OF CELLULOSE BINDING DOMAINS IN THE ADSORPTION OF CELLULASES ONTO FIBERS AND ITS EFFECT ON THE ENZYMATIC BEATING OF BLEACHED KRAFT PULP

The adsorption of cellulases onto fibers may be one of the most important factors affecting the enzymatic reaction between cellulases and fibers. This study investigated the adsorption kinetics involved, using isothermal adsorption equations. Cellulose binding domains (CBDs) were isolated from a commercial cellulase, and their role in the adsorption and enzymatic reaction was evaluated. Approximately 13% to 24% of the refining energy was saved after northern bleached softwood kraft pulp samples were pretreated with full cellulase, CBDs, or cellulase lacking CBDs under optimal conditions. The absence of CBDs in cellulase resulted in less effective enzyme adsorption and hydrolysis of the fibers. These data suggest that pretreatment of northern bleached softwood kraft pulp with CBDs may not only improve the beating degree of the pulp and reduce refining energy consumption but also improve the tensile index of the handsheet. Analysis of the degree of cellulose crystallinity and fiber surface morphology by X-ray diffraction and scanning electron microscopy revealed that the CBDs in cellulase help modify the crystalline area and facilitate the enzymatic degradation of cellulose. The adsorption parameters of the cellulases calculated from isothermal adsorption experiments confirmed the role of CBDs in the adsorption of cellulases onto fibers.