Lupin hull cellulose nanofiber aerogel preparation by supercritical CO2 and freeze drying

In this study, aerogels were prepared from cellulose nanofiber hydrogels obtained via ultrasonication of subcritical water-assisted treated lupin hull. The SCCO2 drying and freeze drying were evaluated for aerogel formation with initial hydrogel concentrations in the range of 1-2 wt%. The effects of concentration and drying method on resultant aerogel properties (density, porosity, specific surface area, pore size and pore volume), crystallinity, thermal behavior and morphology were investigated. The SCCO2 drying was more advantageous in aerogel formation, allowing the production of aerogels with lower density (0.009-0.05 g/cm(3)), and higher surface area (72-115 m(2)/g) compared to freeze-dried aerogels at each concentration level investigated. The aerogel prepared from 1 wt% hydrogel concentration using SCCO2 drying provided the lowest density of 0.009 g/cm(3), the highest porosity of 99% and the highest specific surface area of 115 m(2)/g with high crystallinity index (72%) and thermal stability with degradation temperature of 310 degrees C.