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

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

Modeling of Hexavalent Chromium Removal with Hydrophobically Modified Cellulose Nanofibers

“…where V ads is the volume of adsorbent and the consistency is the dried mass of adsorbent at 60 • C [42]. These compiled data were subsequently analyzed through different kinetic models.…”

Fundamentals of Hybrid Cellulose Nanofibril Foam Production by Microwave-Assisted Thawing/Drying Mechanism

“…First, there is no external foaming agent such as octylamine (OA) or pluronic P123 used for this foam-forming process; such reagents have been used extensively by previous studies, especially while replacing freeze-drying or supercritical CO 2 drying with oven/ convection drying. 19,20,55,56 Second, in this study, the wet stability of the foams is achieved with an in situ crosslinking reaction compared to the more complex steps reported in previous studies. 19,36,57 Overall, this study reports a simple approach to produce wet stable CNF-based foams with significant time and energy efficiency.…”

“…Additionally, chemical modifications are oftentimes needed to overcome the inherent hydrophilicity of cellulosic materials. Other researchers have attempted to produce CNF-based foams using oven drying and foaming agents. , A recent study reported the application of freeze–thawing–drying cycles in the presence of urea to produce low-density structures from microfibrillated cellulose (MFC)another term often used in lieu of CNF, using a combination of oven and air drying. An MFC to urea ratio of 1:1 was needed for producing the MFC foams with the least shrinkage and deformation.…”

Nanocellulose-based composite phase change materials for thermal energy storage: status and challenges

“…It was reported that by adjusting the charge density of the CNF, nanocellulosic foams with different densities could be obtained, and the chemical crosslinking with aldehydes and physical adsorption of octylamine on the CNF successfully tuned the strength and water resistance of the resulting foams, respectively. The effect of wet foaming conditions of a Pickering emulsion on the structural properties of CNF foam was investigated by Park et al , 81 and it was concluded that the consistency of CNF dispersion and the usage of a surfactant affect the wet foam stability and the shrinkage of dry foams, which in turn determine the pore size, porosity and mechanical strength of the dried foam. Qiao et al fabricated ultralight CNC aerogels with hierarchical porous structures from a stabilized Pickering emulsion, where aminated CNCs acted as both stabilizers of Pickering emulsions and building blocks of the nanocellulose aerogels.…”