Evaluation of dislocations in cellulose pulps submitted to pre-treatments

Abstract

Dislocations are designations given to the permanent deformations of cell wall cellulosic fiber. Wood fibers may have its resistance compromised with dislocations on the cell wall. The application of chemical and enzymatic treatments and mechanical defibrillation can contribute to the reduction of fiber resistance, acting in the increase of dislocations and as a facilitator for the deconstruction of the cellular wall of the vegetal fiber. In this sense the work evaluated the effect of chemical and enzymatic pre-treatments on bleached and unbleached cellulosic fibers in the formation of dislocations in the cell wall of the fibers, besides evaluating the dislocations in fibers after enzymatic pre-treatment and mechanically defibrillated. The pulp was subjected to chemical pre-treatment with sodium hydroxide at concentrations of 5% for 2 h and 10% for 1 h and 2 h and with hydrogen peroxide with alkaline solution. For the enzymatic pre-treatment, the enzymes A, B and C of the endoglucanase type and the enzyme D corresponding to the mixture of endoglucanase with exoglucanase were used. For fibers that were mechanically defibrillated, a pre-treatment with enzyme B was used and the dislocations were analyzed before (0 passages) and after mechanical defibrillation (5, 10, 15, 20, 25 and 30 passages). Characterization analyzes of the dislocations on the cell walls of the fibers were carried out by optical microscopy with polarized light, analyzing the index of dislocations, angle of dislocations and the curvature of the fibers. The results showed an increase on the dislocations index for bleached and unbleached fibers after chemical pre-treatments, as well as a reduction in the angle of dislocations. The straightness of the fibers after the pretreatments was altered in relation to the control treatment, generating more curved fibers. For the enzymatic pre-treatment in bleached fibers, the index of dislocations presented variation as a function of the enzyme used, generating reduction of dislocations for enzyme C and an increase of dislocations for the enzyme B, whereas for the unbleached fibers the enzymatic action on the wall cellular fibers generated a low index of dislocations, as well as, little difference in the angle of observed dislocations. For bleached fibers pre-treated with enzyme and without pre-treatment mechanically processed , enzyme B did not cause reduction in fiber length but allowed a significant increase in dislocations with an increase in the defibrillator passages. The increase of the dislocations occurred up to 20 passages in the mechanical defibrillator, when the fiber reached the maximum index of dislocations in relation to all conditions and passages. The angle of the dislocations was reduced with the enzymatic action (B), being statistically different from the control for all passages analyzed, as well as the fiber curvature index, which, due to the fiber breaking during the passages, reduced to the point of not observing curvature . The results show that the application of chemical, enzymatic and mechanical pre-treatments in the fibers can affect the integrity of the fiber, creating dislocations, besides generating modifications in the angles of the dislocations.