Production and Characterization of High Solid Content Cellulose Nanofibrils from Pretreated Fluff Pulp

The increasing demand for cellulose nanofibrils (CNF) necessitates the development of novel processes to produce high-solid content and consistent quality nanofibrils. In this study, we investigated the combination of mechanical and chemical pretreatment methods (carboxymethylcellulose, CMC dispersion, and sodium hydroxide, NaOH swelling with ball milling) for cellulose fibers followed by high-pressure homogenization to evaluate the CNF characteristics. The carboxymethylcellulose (CMC) dispersion with 75 min ball milling and NaOH swelling with 15, 45, and 75 min ball milling of cellulose slurry reduced the fiber dimensions by up to 90% that eased the fibrillation to produce about 6% solid content CNF during high-pressure homogenization. The characterization of CNF hydrogels produced from pretreated samples revealed that they had an average fibril width of less than 30 nm with good dispersion stability. The CMC dispersion and NaOH swelling with ball milling of cellulose slurry did not significantly affect the chemical structure and the crystallinity of CNF hydrogels. On the other hand, the tensile strength of all the pretreated CNF samples was increased up to 105±14 MPa when compared with that of the control sample (58±6 MPa). NaOH treatment has slightly increased the thermal stability of CNF samples over CMC treated and control samples. In conclusion, short fibers generated by mild alkaline pretreatment with ball milling followed by high-pressure homogenization of cellulose fibers can produce the consistent quality CNF with high solid content and tensile strengths for various industrial applications.