Affiliation:
1. Institute for Thermal Separation Processes Hamburg University of Technology Eißendorfer Straße 38 21073 Hamburg Germany
2. aerogel‐it GmbH Albert‐Einstein‐Str. 1 49076 Osnabrück Germany
3. Laboratory for Development and Modelling of Novel Nanoporous Materials Hamburg University of Technology Eißendorfer Straße 38 21073 Hamburg Germany
Abstract
AbstractIn this work, nanostructured and transparent cellulose aerogels are synthesized via a purely salt induced approach from non‐modified microcrystalline cellulose type II. The production process requires in contrast to state of the art methods no pretreatment of cellulose or use of expensive cellulose‐solvents: it consists of hydrogel formation via cross‐linking of cellulose with calcium ions, a solvent exchange and a supercritical drying step. A systematic multiparameter study reveals that a high level of structural control is achievable: ratios of macro‐ to mesoporosity and the size of mesopores can be tailored by adjustment of the calcium ion content, while keeping a high overall porosity in the range of 92% – 96 %. The build‐up of homogeneous, fine pore structures results in a significant increase of the specific surface area as compared to conventional calcium‐free aerogels (684 vs. 300 m2 g−1). Remarkably, the Ca2+‐cross‐linking renders aerogels transparent, with Rayleigh scattering being the dominant scattering mechanism. Additional ion exchange to Ca2+ in the hydrogel‐state leads to further reduction of the pore size and to products with optimized optical properties, e.g., light transmission of 91% at an incidents light wavelength of 800 nm and a substrate thickness of 1.5 mm.