Adsorption of cellulases on pulp fibers during pretreatment for microfibrillated cellulose film preparation

Differences in the composition of cellulases would lead to different adsorption characteristic which is a key factor in the process of enzymatic hydrolysis treatment of microfibrillated cellulose (MFC) and MFC film preparation. The main purpose of this research was to study how complex cellulase (D cellulase) and endocellulase (R cellulase) with different composition and dosages (Cellulase dosage per gram of pulp, U/g) affect the performances of MFC and MFC film properties. Herein, D cellulase and R cellulase with different dosages were compared to treat bleached eucalyptus kraft pulp (BHKP) for MFC preparation. Enzyme activity and adsorption properties of the two cellulases were comprehensively studied. Meanwhile, the performances of MFC and MFC film were investigated. As a result, D cellulase possessed higher adsorption ratio than R cellulase, but R cellulase demonstrated higher adsorption rate than D cellulase. The crystallinity index (CrI), specific surface area (SSA) and morphology of MFC were tuned by the combination of two cellulases at different dosages. Among them, the CrI of MFC treated by two cellulases increased, respectively, and both reached the maximum when the enzyme dosage was 10 U/g. Elongation at break (E) and tensile strength (TS) of MFC film treated by R cellulase decreased continuously which maintained excellent physical strength at low cellulase dosage compared with D cellulase. According to their respective minimum oxygen permeability coefficients, the MFC film obtained by R cellulase pretreatment possessed the better barrier property compared with MFC film pretreated by D cellulase. In general, this work shows that low-cost R cellulase, which allows MFC film to have good performances at low enzyme dosages, is more suitable than D cellulase for BHKP pretreatment to prepare MFC film.