Properties of Cellulose Nanofibril Foam Depending on Wet Foaming Conditions

Cellulose nanofibril (CNF) foam, which has advantages of sustainability and biodegradability, has a potential to apply to diverse fields including packaging, thermal insulation, and absorbent. In recent days, the oven drying of Pickering-stabilized CNF wet foam was proposed as an alternate approach to manufacture CNF-based porous foams. To produce CNF foam with uniform structure, the properties of wet foam are very important. In this study, carboxymethylated cellulose nanofibril (CMCNF) was used to prepare CNF foam. The effects of wet foaming conditions such as CMCNF consistency, surfactant amount, and shear rate on the properties of the wet and dry foams were investigated. A low addition level of surfactant led to insufficient generation of bubbles, whereas high levels of surfactant generated unstable wet foam. A proper amount of the surfactant and CMCNF consistency yielded wet foams with excellent stability. CNF wet foam with high stability resulted in CNF foam with uniform pore structure and high compressive strength. The shear rate during wet foam generation also had a significant impact on the foamability of wet foam, which determined the density and the pore size of the oven-dried CNF foam.