Characterization of the filter cake drainage resistance coefficient for cellulose nanofibril suspensions

The dewatering of cellulose nanofibril (CNF) suspensions is important in several processes such as concentrating the material before transportation, producing dry CNFs for composite structures, and applying the material to the surface of a paper web. Dewatering of a CNF suspension onto paper is one possible way to form a CNF layer on paper to produce excellent grease and oil-resistant packaging materials. Even though this property of the CNF suspension is important, little work has been reported in the literature to model and characterize this process. Refiner produced CNF suspensions were filtered on cellulose acetate membranes, filter paper, and paperboard in a standard Büchner funnel with a known vacuum pressure. The volume filtered as a function of time was recorded and the equation for constant pressure filtration was used to fit the results for various initial concentrations and different qualities of CNFs. The specific cake resistance coefficient (α) was obtained from the results. The results revealed the dewatering of CNFs follows the filtration theory well with an R² value greater than 0.98. Increasing the quality or degree of fibrillation of the CNFs gave a small increase in the specific cake resistance. The specific cake resistance obtained was able to predict the dewatering of a CNF suspension on a paperboard in a bench scale sheet former. Significant clogging of the base membrane or paper was found to occur, especially for the cellulose acetate membranes. These results provide insights regarding CNF dewatering and the basis for the design of filtration-based dewatering equipment as well as the operation of wet end processes that deposit CNFs onto the web.

Graphical abstract