Cellulose nanofibril (CNF) based aerogels prepared by a facile process and the investigation of thermal insulation performance

Herein, a facile method on fabricating aerogels with hierarchical porous structures was created by freeze-drying the cellulose nanofibril (CNF)/methyltrimethoxysilan (MTMS)/fumed silica (FS) suspension. FS was introduced for its porous structure, which could improve the thermal insulation performance of freeze-dried aerogels. The as-prepared aerogels were hydrophobic with improved mechanical properties (elastic recovery rate was up to 99.7%) and reduced thermal conductivity (0.027 Wm(-1) K-1 at 25 degrees C). Most importantly, the addition of FS was proved to improve the thermal insulation stability of cellulose aerogels efficiently in different values of relative humidity (RH) and temperatures. The thermal conductivity of pure CNF aerogel conditioned at 25 degrees C and 95% RH was 196% higher than that of the fully-dried one, while the increase was 56% for the composite aerogel. Besides, at 30% RH, the thermal conductivity increased by 24% for the pure CNF aerogel when tested from 20 to 60 degrees C while only a 2% increase for the composite aerogel. Moreover, when tert-butanol was used as the solvent to optimize the distribution of the pores of freeze-dried aerogels, their thermal insulation performance was further improved. Our work provides easily available CNF/MTMS/FS ternary aerogels, which are stable in thermal conductivity in the changing environment.