Sheet sealing in single and multilayer nanopapers

This study addresses one of the limiting factors for producing micro and nanofibrillated cellulose (MNFC)-containing papers: poor water removal properties. We focus on the sheet sealing phenomenon during dewatering. A modified dynamic drainage analyzer (DDA) is used to examine both multilayer and single layer forming of MNFC and pulp mixtures. It was found that a thin layer of pulp fibers on the exit layer with the grammage as low as 5 gsm was enough to significantly improve the dewatering of MNFC. For example, the dewatering rate of a furnish with 50% MNFC increased from 0.6 mL/s for a mixed system to 2 mL/s for multilayer system. However, the sheet sealing behavior was completely different when a lower proportion of MNFC was used. For the furnishes with less than 20% MNFC content, the mixed furnishes dewatered faster because the high amount of pulp fibers were able to prevent MNFC from enriching on the exit layer. Surprisingly, we found that very high final solids content (couch solids) could sometimes be achieved when MNFC was used. The highest solids contents achieved were 34 and 29% for the mixed systems. This compares to the 15–20% range typical of standard papermaking furnishes without MNFC. Overall, the results show that contrary to current thinking MNFC containing papers may lead, under some circumstances, to enhanced wire section dewatering.