Impact of nanofibrillation degree of eucalyptus and Amazonian hardwood sawdust on physical properties of cellulose nanofibril films

The production of cellulose nanofibrils (CNFs) from Amazonian wood wastes could reduce pollution and raw material costs for cellulose industry. Further studies are required to analyze the feasibility of using hardwood sawdust for the production of high-quality CNF films. Therefore, the objective of this study was to evaluate the impact of various nanofibrillation degrees of waste sawdust generated from the primary processing of different hardwood species on the physical properties of CNF films. Raw sawdust was submitted to alkaline and bleaching pre-treatments. The chemical composition of the bleached fibers was determined. The CNFs were obtained by mechanical shearing of the bleached fibers using a grinder Super MassColloider after 10, 20, 30 and 40 passages. CNFs were evaluated by transmission electron microscopy. The CNF films were formed by the casting method. Residual lignin and hemicelluloses content greatly varied among species after bleaching. No clear influence of the number of passages on apparent density was observed. None of the films was degraded in significant amounts after water immersion. Water vapor absorption (WVA) consistently decreased with more passages through the Super MassColloider for Amazonian species until 30 passages. Residual hemicelluloses of the bleached fibers adversely affected WVA. Bleached fibers made of highly purified cellulose or containing residual lignin showed lower WVA after 30 and 40 passages. Water vapor permeability showed consistent relation with the apparent density of the films. For hardwood wastes, 10-30 passages through the grinder are recommended.