Starch/clay aerogel reinforced by cellulose nanofibrils for thermal insulation

Characterized by low cost, flame resistance and mild processing procedure, freeze-dried clay aerogel is an ideal alternative for thermal insulation in building sector. However, the negatively charged surface of clay platelet and high freezing rate require the addition of a high amount of polymer to ensure the integrity of aerogel during freezing stage, which inevitably increases the density as well as the thermal conductivity of aerogel. Herein, we reported a green and versatile strategy to fabricate crack-free yet thermal insulative aerogel by introducing cellulose nanofibrils (CNFs) into starch/clay system. Owing to the abundant hydroxyl groups, high aspect ratio and excellent mechanical strength of CNFs, the CNF/starch/clay aerogels prepared exhibit enhanced crack resistance and compressive strength, enabling the reduction of starch content from 4 to 2% while maintaining the integrity of aerogel in the process of freezing. As a result, the density and thermal conductivity of aerogel significantly decrease from 0.12 to 0.05 g/cm 3 and 48.3 to 41.5 mW/mK respectively. Further crosslinked by glutaraldehyde, the CNF/starch/clay aerogels display improved moisture resistance, shape recovery and thermal stability. Being versatile and cost-effective, the present approach is thought-provoking for the up-scale production of freeze-dried clay aerogel for thermal insulation. Graphical abstract