Controlled retention and drainage of microfibrillated cellulose in continuous paper production

Abstract

In the current study, an attempt has been made to scale up microfibrillated cellulose (MFC) reinforced paper using a pilot scale Experimental Paper Machine (XPM) in continuous mode. Complete retention of MFC (≈2 nm–10 μm in diameter) on the XPM (using 150 wire mesh, 100 μm pore size) was not possible. Consequently, a “mixed/hybrid” approach was followed using pulp fibers (≈25 μm diameter) as the supportive phase. The produced dense network (≈3 μm pore size) of long pine fibers on wire mesh (100 μm pore size) might be responsible for holding MFC by introducing hydrogen bonds in the continuous production of paper on the XPM. Thereafter, an increase in MFC retention was further observed using additives (cationic starch and anionic silica microparticles) and a maximum 23.4 wt% of MFC in the final paper was calculated. The highest retention (73%), adequate water drainage time (<1 min) and improved formation were recorded using a mixture of 65 wt% long pine fibers, 35 wt% MFC, 1.2 wt% cationic starch and 0.3 wt% silica microparticles at a machine speed of 1.4 m min⁻¹. The produced paper showed aligned fibers towards the machine direction (supported by SEM images and tensile strength). Furthermore, a compacted micro/nano morphology after addition of MFC and a decrease in average pore size after addition of additives were recorded. An 11% and 17% increase in density was recorded after introduction of MFC and additives, respectively. The improved tensile strength of the paper (≈3 fold) compared to that of the reference paper was recorded. The β-radiogram analysis confirms improved network formation in the paper after addition of MFC and additives. Therefore, machine trials confirm the possibility of producing tons of MFC reinforced paper using a roll-to-roll approach in continuous mode with high retention of MFC and improved properties.