Nano-fibrillation of pulp fibers for the processing of transparent nanocomposites

Pulp fibers were fibrillated uniformly into nano-sized fibers using a grinder with a specially designed set of grinding disks. To investigate the effect of the fibrillation through the grinder on the physical properties of the composites, dissolved pulp fibers were subjected to various passes through the grinder, and the resulting fibrillated pulp fibers were used to make fibrillated pulp fibers/acrylic resin composites. Scanning electron microscopy observations showed that at above five passes, the structure of the fibrillated pulp fibers did not change significantly. The light transmittances of the composites were increased to 80% up to five passes through the grinder, and did not change after further passes. However, the tensile test and thermal expansion analysis indicated that a degradation of the fibrillated pulp occurred during the grinding treatment. To evaluate the fiber degradation, the degree of crystallinity and degree of polymerization of cellulose were measured. Both decreased as the number of passes through the grinder increased. In addition, to reduce the thermal expansion of composites, the fibrillated pulp fibers were additionally treated by sulfuric acid. The thermal expansion of composites was decreased, because the amorphous region of cellulose was removed.