Nanofibrillation of pulp fibers by twin-screw extrusion

The effect of the fibrillation process through a twin-screw extruder (TSE) on properties of pulp fibers was studied, considering the degree of both fibrillation and degradation of the fibers. Never-dried refined bleached kraft pulp (NBKP) was passed through a TSE several times at a high concentration of 28 wt%. The output of fibrillated fibers had a solid content up to ca. 50 wt%, and the material was in powder form. Characterizations of the morphology, dewatering speed, sedimentation, laser light scattering, scanning electron microscopy of cellulose suspensions, and light transmittance of resin-impregnated films showed that the fibrillation degree of the pulp was enhanced with a higher number of passes. However, the results from thermogravimetry, intrinsic viscosity, and X-ray diffraction analyses indicated that some degradation occurred during the fibrillation process in the TSE. In addition, the mechanical properties of the fibrillated pulp sheets reflected the effects of treatment on the fibrillation and degradation of the cellulose. For never-dried refined NBKP pulp, the best compromise in terms of fibrillation and degradation degree is between 3 and 14 passes, depending on the envisaged properties and applications. The possibility of nanocellulose production at the reported high solid contents is of great interest for industry.