Auxiliated cellulase pretreatment for optimization of cellulose nanofibrils obtention

Abstract

Materials at nanometric scale have gained prominence in the scientific and technological environment because they have their physical and chemical properties enhanced. Among these are nanostructured celluloses, such as nanofibrils and nanocrystals, which have the potential to reduce environmental impacts because they are formed from a renewable source and due to the possibility to replace polymeric materials derived from petroleum. However, the production of cellulose nanofibrils by the mechanical process consumes a lot of electrical energy. The action of cellulase enzymes may facilitate the defibrillation of pulps due to the cleavage they cause in the cellulosic chain, thus reducing energy consumption. The aim of this work was to study the effect of enzymatic pretreatment to facilitate the production of nanofibrils from bleached and unbleached commercial pulps of Eucalyptus sp. and Pinus sp. at low energy consumption. In order to carry out the enzymatic hydrolysis, cellulolytic complexes with endoglucanase activity were used (enzyme A and enzyme B), with a concentration of 3% pulp in suspension, 50 ° C and 2 h of reaction time. Cellulose nanofibrils were obtained by mechanical process using a defibrillator mill, with 5 cycles and 2% concentration, evaluating the energy consumption of each pretreatment. The morphology of cellulose nanofibrils was analyzed by light microscopy (LM) and transmission electron microscopy (TEM). It was analyzed the turbidity, stability in water and zeta potential of cellulose nanofibrils suspensions as well as the preparation of nanostructured films in order to obtain mechanical resistance values of cellulose nanofibrils. Enzymatic pretreatment decreased the energetic consumption of bleached pulps by 58%, whereas for unbleached pulps the decrease was 55%. Even with cellulase application, difficulty in defibrillation of chemithermomechanical pulp (CTMP) was observed. The suspensions of nanofibrils presented greater stability in water with the application of the enzymatic pretreatment, as well as there was an increase in the mechanical resistance of the films formed. Enzyme A showed better performance for bleached pulps, in addition to reducing consumption by 58%, generated nanofibrils with a median diameter of 24 with range between 12 nm and 79 nm. The enzyme B showed more significant results for unbleached pulp, in which it generated median nanofibrils diameter of 22 with range between 13 nm and 66 nm , and complete stability of the suspension in water in the gel formation cycle by the defibrillator. In view of the foregoing, it is expected to improve the procurement and quality of nanostructured cellulosic products for application in various products on the market.