Anisotropic nanocellulose aerogels with ordered structures fabricated by directional freeze-drying for fast liquid transport

Directional freeze-drying is considered to regulate the structure of nanocellulose aerogels with special performances. In this work, TEMPO-oxidized cellulose nanofiber aerogels with high porosity (>99.5%) and low density (similar to 7mg/cm(3)) were produced by different freeze-drying methods. The effects of temperature, freezing reagents and freezing methods on the structure and properties of aerogels were investigated. Among them, an anisotropic cellulose aerogel was obtained using a simple and flexible directional freezing in ethanol of -30 degrees C by a self-made directional freezer. Our results demonstrated that it could present honeycomb-like pores in the transverse direction and regular directional tunnels in the longitudinal direction, and some attractive features, such as high water adsorption (120g/g) and stability in water. Compared with other aerogels, this anisotropic structure also provided the aerogel with excellent compressive property (15.2kPa) and faster liquid transport (4.95mm/s) in the longitudinal direction than in other directions. The distinctive aerogels based on nanocellulose by directional freeze-drying are also expected to be combined with multifunctional materials to achieve directional applications to meet the requirements of different fields. [GRAPHICS] .