Application of Cellulose Nanofibrils to PVA Impregnation for the Improvement of Durability of Papers

Abstract

High durable papers are required to the specific area where their shape or properties have to be conserved for a long time. Banknote, poster, and passport are representative papers which need durability. In order to develop the durability of papers, long service life, high mechanical strength and anti-soiling property should be considered. Anti-soiling property means resistance against moisture and contaminants. The conventional method of manufacturing durable papers is the impregnation of polyvinyl alcohol (PVA). However, the durability of papers should be improved for a long circulation use. This study focuses on the use of another additive in PVA solution, cellulose nanofibrils (CNF).

The application of CNF to PVA impregnation was analyzed in terms of mechanical strength and anti-soiling property. The addition level of CNF was controlled when prepared CNF-PVA suspension and the miscibility of the suspension was good enough to apply PVA-CNF suspension to the impregnation. 5% CNF content improved tensile strength and folding endurance despite of lower pickup weight of impregnated papers. It points out the impregnated papers by PVA-CNF suspension could be made use of lightweight papers with good mechanical strength. However, the anti-soiling properties under dry and wet condition were not improved, which PAE was introduced as another additive of impregnating agent. . As PVA-CNF suspension including PAE showed high low shear viscosity, impregnated papers by the suspension presented lower pickup weight and folding endurance than impregnated papers by PVA solution. However, anti-soiling property of impregnated papers dramatically increased. While the paper impregnated by PVA-CNF(5%) suspension was destroyed after 20 min-soiling, the paper by PVA-CNF(5%)+PAE suspension was well preserved. Lastly, silylated CNF suspension (SCNF) was applied as an additive of PVA solution instead of CNF. SCNF suspension was obtained by the silylation of CNF suspension using methyltrimethoxysilane (MTMS) under an aqueous system. The miscibility of PVA-SCNF suspension was good but anti-soiling of this part did not show any significant increase. The water contact angle of impregnated papers by PVA-SCNF suspension was higher than PVA-CNF suspension, which can have the possibility to increase the anti-soiling by using other silane agents instead of using MTMS.