Abstract
The gas permeability of a porous material is a key property determining the impact of the material in an application such as filter/separation techniques. In the present study, aerogels of cellulose scaffolds were designed with a dual pore space system consisting of macropores with cell walls composing of mesopores and a nanofibrillar network. The gas permeability properties of these dual porous materials were compared with classical cellulose aerogels. Emulsifying the oil droplets in the hot salt–hydrate melt with a fixed amount of cellulose was performed in the presence of surfactants. The surfactants varied in physical, chemical and structural properties and a range of hydrophilic–lipophilic balance (HLB) values, 13.5 to 18. A wide range of hierarchical dual pore space systems were produced and analysed using nitrogen adsorption–desorption analysis and scanning electron microscopy. The microstructures of the dual pore system of aerogels were quantitatively characterized using image analysis methods. The gas permeability was measured and discussed with respect to the well-known model of Carman–Kozeny for open porous materials. The gas permeability values implied that the kind of the macropore channel’s size, shape, their connectivity through the neck parts and the mesoporous structures on the cell walls are significantly controlling the flow resistance of air. Adaption of this new design route for cellulose-based aerogels can be suitable for advanced filters/membranes production and also biological or catalytic supporting materials since the emulsion template method allows the tailoring of the gas permeability while the nanopores of the cell walls can act simultaneously as absorbers.
Highlights
Aerogels of cellulose (AC) are one of the bio-based lightweight open porous materials
10–15 equidistant lines were superimposed over the resulting binary image and the linear intercept in the macropores determined in the cell walls and the macroporosity was determined from the ratio of the line length in the pores in relation to the total line length on the image
Using higher the hydrophilic–lipophilic balance (HLB) values of surfactants, the finely organized macropores could be produced with compact arrangement of cellulose chains in the cell walls which resulted in high cell wall density, low specific surface area and large macropore volume fraction
Summary
Aerogels of cellulose (AC) are one of the bio-based lightweight open porous materials. They have randomly interconnected nanofibrillar networks and a wide range of pore sizes composed of meso- and macropores [1,2,3]. After modifying chemically or physically, the research development on cellulose aerogels has gained much interest in many research fields including the preparation of biocomposites [4,5], template or supporting materials [6], separation techniques [7,8,9], tissue engineering and medicine [10,11]. The physical modifications of cellulose aerogels can produce useful structural properties which can enhance the mechanical properties and improve the permeability of gases and fluids. Bringing in hierarchical dual pore structures, combining interconnected macro- and mesoporous, improves the elastic modulus of the aerogels of cellulose scaffolds in comparison with the cellulose aerogels which have the same density and porosity [16,17]
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