Characterization of Cellulose Aerogel Composites

The morphologies of aerogels were observed by SEM (JSM 6700F, JEOL, Tokyo, Japan) at 3 kV accelerating voltage. Compressive tests were performed on an Instron high-capability 5900 series press (Instron Co., Norwood, MA, USA)) with a 500 N cell at a constant rate of 2 mm/min in triplicate. The CpA aerogels were compressed along the thickness direction up to 80% strain. Zeta potentials of pure CNF, pDA, CNF-g-pDA, AF and CpA at pH of 2.5, 7.0 and 8.5 were measured by ZEN 3600 zetasizer (Malvern Instruments, Worcestershire, UK) with a 4 mW laser (wavelength of 632.8 nm). The number of measurements per scan were determined automatically by the instrument. The FT-IR analysis was conducted by Bruker Tensor 27 IR Spectrometer (Bruker Optic GmbH, Ettlingen, Germany). The porosity of the aerogels was determined by calculation using Equation (1) [35 (link)]: $$Porosity \left(\%\right) = \left(1-\frac{{\rho }_{aerogel}}{f_{Cellulose} {\rho }_{Cellulose}+f_{Amyloids} {\rho }_{Amyloids}}\right)\times 100$$
where $${\rho }_{aerogel}$$ is the aerogel density, which is calculated by taking the mass of the aerogel (measured by a balance) and dividing it by the determined volume of the aerogel (determined by optical microscopy images taken using Leica MZ12). The $${\rho }_{Cellulose}$$ and $${\rho }_{Amyloids}$$ are the densities of CNF and AF, respectively, $$f_{Cellulose}$$ and $$f_{Amyloids}$$ are the weight fractions of the CNF and AF fibrils.