Aerogels, porous materials with fine skeletal structures, are known to exhibit excellent thermal insulation properties owing to their dense and homogeneous porous structures. Some aerogels are highly transparent and are expected to serve as transparent thermal insulators for windows in houses and cars toward a more sustainable society. However, aerogels in general are too brittle, making them difficult for practical use. To achieve tougher and more transparent aerogels, we chose the chitin gel obtained by the N-acetylation of dissolved chitosan, which is known to have a homogeneous and continuous nano-fibrous network structure. The nanofibrous structure suppresses the light scattering and continuous network structure bears the load upon the deformation, leading to the transparent and tough nature, respectively.
In this study, chitosan was dissolved in aqueous acetic acid solution and diluted with methanol. Subsequently, acetic anhydride as an N-acetylating reagent was added to the solution in low temperature. After sufficient mixing, the solution was poured into molds and kept at room temperature to complete N-acetylation and gelation. Thus obtained chitin alcogels were subjected to solvent exchange to ethanol and subsequent supercritical drying, and chitin aerogels were obtained. It was revealed that the obtained chitin aerogels were composed of thin fibril structure with ~10 nm in diameter, and the average pore size was 20–30 nm. The chitin aerogels exhibited high transparency, low thermal conductivity, and excellent mechanical properties, especially toughness. While general aerogels are fragile and are easily broken, the transparent chitin aerogels in this study were tough enough to even perform tensile tests. In addition, it was demonstrated that the aerogels developed in this study were moldable by choosing the shape of the mold used for gelation.

Dr. Noriyuki Isobe

Researcher, Japan Agency for Marine-Earth Science and Technology

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