Structural properties of cellulose nanofibril foam depending on wet foaming conditions in Pickering stabilization

Porous cellulose nanofibril (CNF) foam was prepared by stabilizing bubbles with CNF and a surfactant and then drying the stabilized wet foam in a convection oven. The consistency of carboxymethylated CNF (CMCNF) and the addition amount of the surfactant were controlled and the effects of these factors on the CNF wet foam and dry foam properties were investigated. An adequate amount of the surfactant (0.02-0.04 wt%) with CMCNF consistency higher than 0.5 wt% yielded wet foams with excellent stability. When the wet foam was dried at 60 degrees C in an oven, dry CNF foam with over 97% porosity was generated. The stable wet foams resulted in dry CNF foam with a sphere-like pore structure and low levels of shrinkage during drying. In contrast, unstable wet foams generated dry foam with severe shrinkage and large cavities. The pore size and the porosity of the dried foam were determined by the shape of bubbles in the wet foam and the degree of shrinkage during drying, which, in turn, affected the mechanical strength. In addition, the compressive strength of the oven-dried foam was 83% higher than that of the freeze-dried foam. Therefore, the preparation of a stable wet porous CMCNF foam by controlling the CMCNF consistency and the amount of surfactant was essential for obtaining a porous CMCNF foam with a uniform pore structure and good mechanical strength by oven drying.

Automated summary

Porous cellulose nanofibril foam can be prepared by stabilizing wet foam with a surfactant and drying it in an oven. The properties of the wet and dry foam are affected by the consistency of carboxymethylated CNF and the amount of surfactant used. Stable wet foams result in dry foam with spherical pores and low levels of shrinkage, while unstable wet foams lead to foam with severe shrinkage and large cavities. The pore structure and mechanical strength of the dry foam are determined by the shape of bubbles in the wet foam and the degree of shrinkage during drying.