Elasticity-Enhanced and Aligned Structure Nanocellulose Foam-like Aerogel Assembled with Cooperation of Chemical Art and Gradient Freezing

Cellulose nanofibril (CNF) aerogels are renewable and biocompatible materials with high porosity and tunable surface chemistry. However, ultralight and ultraporous aerogels remain a great challenge to obtain high elasticity. This work focused on a scalable strategy to create large-scale lamellar-aligned CNF foam-like aerogels and the relationship between structure and mechanical properties. The morphology and mechanical properties of aerogels assembled by original TEMPO-mediated oxidation CNF cross-linking with 1,2,3,4-butanetetracarboxylic acid were investigated for homogeneous freezer freezing and unidirectional gradient freeze-casting. This study successfully fabricated ultralight foam-like aerogels with centimeter-sized and aligned lamellar/porous structure via cooperation of tunable chemical reaction and unidirectional gradient freezing. The resulting aerogels exhibited flyweight densities of 3–4 mg/cm3, enhanced recovery from 70% strain, water adsorption 82.5 times over self-weight at 20 °C and 52.0 times over self-weight at high temperature (100 °C) for 20 cycles. Moreover, the aligned aerogel followed by carbonization showed a differential and anisotropic electrical resistivity.