Production of cellulose nanofibrils via an eco-friendly approach

Swelling of cellulose fibers facilitates the fibrillation process by mechanical treatment. In this study, potassium hydroxide (KOH)-urea (KUr) solution was investigated to swell fibers for the production of cellulose filaments. The properties of cellulose fibers following KUr swelling process were evaluated by determining the viscosity, morphology, degree of polymerization, crystallinity, and chemical structure. The results demonstrated that the KUr solution could substantially swell the fiber (e.g. increasing average width from 29.4 to 44.7 µm) while preserving the degree of polymerization (DP) of cellulose (91% or higher). Moreover, after treatment with KUr solution, a great amount of ridges on the fiber was formed. Following mechanical grinding of the swollen fibers, the swollen fibers were more likely to undergo mechanical exfoliation to release cellulose nanofibrils (CNFs). Besides, the generated CNFs were demonstrated to have excellent mechanical properties such as the high tensile stress, tensile strain, and toughness. Overall, this study highlights the potential for the efficient preparation of CNFs by using alkaline urea swollen of cellulose. Graphical abstract KUr-CNFs was prepared by homogeneous refining of cellulose fibers after swelling in alkaline urea solution