A facile method to prepare superhydrophobic nanocellulose- based aerogel with high thermal insulation performance via a two-step impregnation process

Nanocellulose aerogel is the third generation aerogel, and its highly interconnected porous network structure makes it an extraordinary thermal insulation material. However, there are abundant hydroxyl groups on the surface of cellulose nanofibrils, which causes the nanocellulose aeogels to absorb moisture in the air and the environment easily, thereby destroying their porous network structure and damaging their original thermal insulation performance. Herein, cellulose nanofibril (CNF) aerogels were prepared by freeze-drying and then modified by a facile two-step impregnation process. Firstly, the pure CNF aerogels were impregnated in the hydrolyzed sol with methyltriethoxysilane (MTES) as the silicon source; and then the silanol polycondensed in an alkaline environment to form polysiloxane particles. The silanization modification made the CNF aerogels superhydrophobic (water contact angle up to 155.2 degrees) while retaining their original excellent thermal insulation performance (thermal conductivity of 0.03249 Wm(-1) K-1) after being exposed to water, and the thermal conductivity increased (0.03249-0.04561 Wm(-1) K-1) with the increase of cellulose nanofibril concentration (2.5-4.5 wt%). Compared with previous similar studies, the method is simpler and has the advantages of low cost and low risk.