Development of Dewatering Concentration Method for Cellulose-Nanofibers Slurry by Using Multi Wires

Abstract

Cellulose nanofibers (CNFs) which are extremely small fibers with a width of several nm comprising mainly crystalline cellulose. They are a promising material with many superior characteristics in a wide range of industrial fields, and have been developed by domestic and foreign paper mill companies. CNF slurry with a high water content (> 98%) is usually supplied because CNFs are generally produced through pulp nanofibrillation in a relatively large volume water. Dewatering of CNF slurry is an important issue because this process affects various processes such as shipping, drying, and product developments. To dehydrate and concentrate CNF with a high-water retention efficiently, the original dewatering CNF method with multiple wires was used in this study. First, the CNFs obtained by mechanical nanofibrillation were prepared using a grinder from Laubholz bleached kraft pulp (LBKP). The fibers with a nano-scale width and a micro-scale fiber network were observed in the prepared CNF slurry. Furthermore, flocculation and dispersion in CNF slurry occurred. Second, the initial solid concentration of CNF slurry, wire opening, and number of wire stacks affected the CNF dewatering in the static and batch tests. In this test, a recovery yield (retention) of 87.7% and concentration to 9.5% were achieved using three stacked wires from CNF slurry of 1.7%. Third, the laboratory-scale apparatus for dynamic CNF dewatering was constructed assuming the practical continuous manufacturing machine, and applied. The gradual suction; combining weaker suction (5 kPa) with multiple wires in the early stage and stronger suction with a single wire in the later stage, was the most effective for dewatering CNF using metal wires. However, multiple wires and the combination of weaker suction in the early stage and stronger suction in the later stage were suitable for dewatering CNF using plastic wires. Ultimately, 98% retention a solid concentration of 9.9% were achieved in the dynamic tests using multiple plastic wires.