Optimization of cellulose nanofibril production under enzymatic pretreatment and evaluation of dislocations in plant fibers

Abstract

Dislocations are weak and discontinuous areas of plant cell walls. This study aims to evaluate the cellulase-mediated enzymatic pretreatment as a mechanical-chemical initiator of dislocations in unbleached and bleached fibers of commercial Eucalyptus kraft pulp, comparing both before and after the formation of micro/nanofibers in the mechanical process, in addition to evaluating the dislocations themselves. Four enzyme complexes were evaluated, of which three were endoglucanase (A, B and C) and one was a mixture of endoglucanase and exoglucanase (D), in addition to a control pretreatment. During the mechanical treatment of the fibers pretreated with enzyme B, samples were collected at pass/cycles 0, 5, 10, 15, 20, 25 and 30 in the mechanical fibrillator. The dislocations were evaluated using a polarized light microscope to analyze the index of dislocations (ID), dislocation angle and curvature index, while the crystallinity was analyzed by Raman spectroscopy. For bleached fibers, a reduction in the ID occurred with enzyme C and an increase with enzyme B, while for unbleached fibers, the ID did not change significantly. During the mechanical treatment, the enzyme did not cause a reduction in the fiber length (FL) but allowed a significant increase in the ID up to 20 passages for all pretreated fibers, with and without enzymes. The dislocation angle decreased with the enzymatic action and with the curvature index. The results show that the enzymatic pretreatment can affect the integrity of the fibers, increasing the number of dislocations and amorphous regions and decreasing the length of the cellulose chain.