Kinetic changes in cellulose properties during defibrillation into microfibrillated cellulose and cellulose nanofibrils by ultra-refining.

Defibrillation of cellulose fibers can lead to the isolation of microfibrillated cellulose (MFC) or cellulose nanofibrils (CNF) with intrinsic properties suitable for various applications. However, to what extent these properties are preserved, enhanced, gained or lowered during defibrillation and how they are related remains unclear. In this study, a kinetic study of the ultra-refining of bleached eucalyptus Kraft pulp (BEKP) in a disc ultra-refiner was performed and characterized in terms of physical-structural, morphological and thermal properties and their interactions and compromises. Defibrillation of BEKP to MFC substantially decreased the fiber diameter and increased viscosity, surface area and morphological heterogeneity. It also led to a remarkable increase in transparency and essentially did not alter the thermostability but significantly degraded the crystallinity. A higher degree of defibrillation to isolate CNF led to fibers with smaller diameter and increased diameter uniformity but required a substantial amount of energy to only marginally increase viscosity and transparency. Crystallinity and thermostability were not altered, comparing with CMF. In conclusion, most changes occurred during the defibrillation of BEKP to CMF. Further defibrillation to CNFs with smaller diameters and better uniformity did not significantly reflect on other important structural cellulose physical properties, despite the much higher energy consumption and degree of defibrillation.