Turning waste into useful products is a very promising approach for the production of sustainable materials. Cellulose nanocrystals (CNC) are a waste material stemming from biomass, and red mud is an inorganic waste material produced in the Bayer process for alumina production.

Ning Lin, Wuhan University of Technology, China, and colleagues have developed a process which converts these two waste materials to an aerogel with properties that could make it a useful building material. The team extracted CNC from sea pineapple and silylated the nanocrystals’ surface using methyltrimethoxysilane. The red mud was obtained from industry and subjected to ball-milling. The desired aerogels were then prepared from aqueous suspensions of the two waste materials by freeze-drying. The aerogels were crosslinked using diisocyanates to improve their mechanical properties.

The aerogels are highly porous, absorb sound, have a low thermal conductivity, and are flame-retardant. The material self-extinguishes within two seconds. According to the researchers, these properties make the material promising for application as a construction material.

• High-Adsorption, Self-Extinguishing, Thermal, and Acoustic-Resistance Aerogels Based on Organic and Inorganic Waste Valorization from Cellulose Nanocrystals and Red Mud,
  Ge Zhu, Hui Xu, Alain Dufresne, Ning Lin,
  ACS Sust. Chem. Eng. 2018.
  https://doi.org/10.1021/acssuschemeng.8b01244