Preprocessing considerations for floc reduction in cellulose nanofibril suspensions

Abstract Cellulose nanomaterials provide a promising avenue for combining composite materials with natural polymers or bio-based plastics, however, current studies on rheological characterization at high shear rates is limited. In this study, a capillary rheometer was employed to investigate the rheological characteristics of aqueous nanofibrillated cellulose suspensions (NFCs) at room temperature and shear rates above 1000 s-1. The shear rate-dependent viscosity of NFCs was characterized and monitored for viscosity-related indicators of fibril decomposition or entanglement due to the stresses induced by the high shear-rate flow. Traditional capillary rheology corrections for entrance pressure loss and irregular flow profiles were attempted to compare apparent and true rheological behaviors. Large entanglements of fibrils made the characterization of the suspensions difficult due to their ability to clog the capillary. However, appropriate preprocessing steps enabled better measurement resolution and enhanced dispersion of cellulose nanofibers, as verified by atomic force microscopy. The suspensions display shear thinning behavior and demonstrate higher entrance pressures for lower shear rates. Similar preprocessing techniques could be implemented on a large scale to enhance fibril distribution in NFC suspensions.