No abstract

Herein, an innovative method to improve the dewatering of micro-and nanofibrillated cellulose (MNFC) containing furnishes is proposed. This method is based on fiber flotation in which cationic bubbles are injected into the furnish to separate fibers from liquid medium and accumulate them on the surface of the furnish. These cationic bubbles are generated by pressurizing a solution of Hexadecyltrimethylammonium chloride in deionized water in a dissolved air flotation (DAF) tank. The drainage properties of the furnishes with MNFC content from 0% to 25% were studied. With the help of the cationic bubbles, drainage rate of 0% and 15% MNFC furnish increased from 183 ml/s to 210 ml/s and 38 ml/s to 113 ml/s, respectively. The final couch solids content of these furnishes also increased from 16 wt% to 23 wt% and from 21 wt% to 24 wt%, respectively. Cationic bubbles flocculate MNFC fibers and increase retention. Sheets characteristics including morphology, permeability, mass distribution and surface profilometry were investigated. Cationic bubbles help structure fiber elements and improve the sheet formation.

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.

In this study, two different sample preparation methods to synthesize activated carbon from pine wood were compared. The pine wood activated carbon was prepared by mixing ZnCl2 by physical mixing, i.e., “dry mixing” and impregnation, i.e., “wet mixing” before high temperature carbonization. The influence of these methods on the physicochemical properties of activated carbons was examined. The activated carbon was analyzed using nitrogen sorption (surface area, pore volume and pore size distribution), XPS, density, Raman spectroscopy, and electrochemistry. Physical mixing led to a slightly higher density carbon (1.83 g/cm3) than wet impregnation (1.78 g/cm3). Raman spectroscopy analysis also showed that impregnation led to activated carbon with a much higher degree of defects than physical mixing, i.e., ID/IG = 0.86 and 0.89, respectively. The wet impregnated samples also had better overall textural properties. For example, for samples activated with 1:1 ratio, the total pore volume was 0.664 vs. 0.637 cm3/g and the surface area was 1191 vs. 1263 m2/g for dry and wet mixed samples, respectively. In the electrochemical application, specifically in supercapacitors, impregnated samples showed a much better capacitance at low current densities, i.e., 247 vs. 146 F/g at the current density of 0.1 A/g. However, the physically mixed samples were more stable after 5000 cycles: 97.8% versus 94.4% capacitance retention for the wet impregnated samples.

Micro-nano fibrillated cellulose (MNFC) films have the potential for applications in, e.g., packaging and printed electronics. However, the production paradigm for these types of products has still not been established. This study uses twin-rollers to form films from high consistency (15% w/w) micro fibrillated cellulose furnishes. MFC furnishes were produced at 20% wt dry matter content with enzymatic hydrolysis and PFI refining. We used the twin-roller method to spread the material over a supporting substrate by repeatedly passing between two parallel rollers with decreasing nip. Rheological behavior and physical properties of furnishes were analyzed. We found that only some furnishes with relatively short fiber lengths were formable. Refining improved the formation of the sheets. Roll-formed sheets showed comparable strength and formation to conventional wet-laid hand sheets.