Sulfonated cellulose nanofibrils obtained from wood pulp through regioselective oxidative bisulfite pre-treatment

The consecutive pre-treatment of cellulose with periodate and bisulfite was used as a new potential method to promote nanofibrillation of hardwood pulp and to obtain nanofibrils with sulfonated functionality. Nanofibrils having typical widths of 10–60 nm were obtained from sulfonated celluloses having low anionic charge densities (0.18–0.51 mmol/g) by direct high-pressure homogenization without the use of any mechanical pre-treatments. The aqueous nanofibrils existed as highly viscous and transparent gels and possessed cellulose I crystalline structures with crystallinity indexes of approximately 40 %. A transparent film was obtained from sulfonated nanofibrils having tensile strength of 164 ± 4 MPa and Young’s modulus of 13.5 ± 0.4 MPa. Oxidative sulfonation was shown to be a potential green method to promote nanofibrillation of cellulose, as it avoids the production of halogenated wastes, because the periodate used can be efficiently regenerated and recycled as shown in the preliminary experiments.