Synthesis of light weight, high strength biomass-derived composite aerogels with low thermal conductivities

Aerogels that are very porous, mechanically tough, and have low thermal conductivities have attracted significant research interest due to their potential use in engineering applications. Herein, we describe the preparation of biomass-derived composite aerogels containing agar, chitosan (CS), esterified cellulose nanocrystals (ECNCs), and graphene using an environmentally friendly ice-templating method. The prepared composite aerogels have high porosities (> 97%) and low densities (3.1–4.3 kg/m3). FESEM images of these aerogels reveal interconnected honeycomb-like structures several micrometers in size. The thermal conductivity of the ECNCs/CS/agar aerogel was found to be 21 mW/m K, which is close to the thermal conductivity of air under ambient conditions (25.4 mW/m K). The ECNCs/CS/agar aerogel exhibited a stress of 210 kPa, which is about 500% higher than that of the CS/agar aerogel. The compressive strength of the graphene/ECNCs/CS/agar aerogel increased from 210 to 580 kPa (a factor of 2.8) as the graphene content was increased from 0 to 1.3%. Furthermore, the composite aerogels are flexible and compressible, and are candidates for practical applications such as insulating materials.