Nanofibrillation of Tempo-Oxidized Bleached Hardwood Kraft Cellulose at High Solids Content

AbstractCellulose nanofibrils (NF) are usually produced by disintegration processes at low solids content (<5%). However, the high water content reduces the capacity of production, increases the transportation costs of NF suspensions and narrows the possible applications of NF. The goal of the present study was to test a grinding technique based on oscillatory ball milling. Bleached kraft pulp cellulose was nanofibrillated at high solids contents (≥50%), which was obtained from 2,2,6,6-tetramethylpiperidine-1-oxyl radical-oxidized pulp. The grinding method was only successful when the charge density was at least 0.5 mmol g-1. NFs and cellulose nanocrystals were identified at a charge density of 1.1 mmol g-1and a solids content of 50%. The size reduction of the formed particles was observed by means of flow fractionation and imaging and viscosity measurements after increasing the charge density from 0.3 to 1.1 mmol g-1. A solids content increment and a charge density decrement resulted in particles with low aspect ratio rather than in nanofibrils. Wide angle X-ray diffraction measurements showed the transformation of crystalline cellulose into amorphous material in the case of grounding at 93% solids content.