Abstract
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 °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.Graphic abstract
Highlights
Porous materials, such as foams and aerogels, have low densities and high porosities
Because the viscosity of the carboxymethylated CNF (CMCNF) suspension was low (96 cPs), bubbles were greatly generated at low surfactant dosages by vigorous stirring, but there may have been a limit to the foamability
In the case of the 0.5 wt% suspension, the foamability was less than 125% at 0.01 wt% octylamine content, which was likely owing to the increased viscosity of the Cellulose nanofibril (CNF) suspension (960 cPs) compared with the 0.25 wt% CNF consistency
Summary
Porous materials, such as foams and aerogels, have low densities and high porosities. Depending on the structure and size distribution of the pores, foams and aerogels can be applied to many fields including packaging (Chen et al 2020; Manzocco et al 2021), thermal insulation (Hasan et al 2017; Illera et al 2018), adsorbents (Hong et al 2018; Singh et al 2018; Bolisetty et al 2019), and energy storage (Liu and Chen 2014; Huang et al 2019) Most of these materials are manufactured from petroleum chemicals or silica, which exhibit poor sustainability and biodegradability or high brittleness (Demilecamps et al 2015; Feng et al 2015; Gupta et al 2018). CNF can be either processed into various forms (including hydrogels, sheets, and porous materials) or used as a reinforcing element for composites (Dufresne 2013, 2017; Kim et al 2015b; Abitbol et al 2016)
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