Hindrance to nanofibrillation of undried pulp produced by the kraft cooking process

Kraft pulp is the most common and economically advantageous raw material for making cellulose nanofibers (CNFs). However, when kraft pulp is subjected to mechanical fibrillation, unfibrillated pulp always remains, even though the pulp is undried. In this study, the effect of the kraft pulping process on the fibrillation of undried pulp was studied. The fibrillation ability was compared with that of undried pulp prepared using Wise method and alkaline treatment. Suspensions of undried pulps were mechanically fibrillated with a high-speed blender for different durations. The degree of fibrillation of pulps was evaluated using sedimentation, morphologies from field emission scanning electron microscopy, specific surface area, and water retention values. Every analysis showed that undried, kraft-based pulp was less fibrillated than undried, wise-based pulp. These results suggested that the kraft cooking process at high temperature hindered the fibrillation of pulp. This might be related to the aggregation occur in cellulose.