Robust Nanofibrillated Cellulose Hydro/Aerogels from Benign Solution/Solvent Exchange Treatment

To fabricate robust nanofibrillated cellulose (NFC) hydro/aerogels, benign solution/solvent exchange treatment was developed by adding five different water miscible solutions/solvents into a NFC aqueous suspension. The NFC self-aggregated and formed self-standing gels during the solution/solvent exchange treatment. After a further exchange of solution/solvent inside the gels with water by a thorough water washing followed by freeze-drying, NFC hydrogels and aerogels were obtained. The NaOH-hydrogel demonstrated a decent rheology with a storage modulus of 36.4 kPa and a satisfactory mechanical property with a compressive modulus of 37.6 kPa. On the contrary, the acetone-hydrogel was weak due to disaggregation. The NFC aerogels were lightweight and had a characteristic porous structure. The packing density and structure varied among aerogels with different solution/solvent treatments. The NaOH-aerogel had a 2D sheet-like structure with densely packed micrometer-sized pores uniformly distributed within the aerogel network, which demonstrated a high compressive strength. However, the structures of other aerogels were loose, leading to a low compressive strength. These NFC aerogels demonstrated high thermal stability and superior performance for efficient thermal insulation. We believe our work can stimulate interest in the development of NFC hydro/aerogels with multiple structures, properties, and functions for a variety of applications.