Strong ultralight foams based on nanocrystalline cellulose for high-performance insulation

Environmentally friendly, sustainable, and high-performance thermal insulators are in high demand. Petroleum-based insulator foams usually have high thermal conductivity and pose health hazards. Here, we report ultralight composite foams that are highly strong, elastic, and super-insulating. The foams are composed of nanocrystalline cellulose (NCC) (74 wt%), polyvinyl alcohol (7.5 wt%), and a crosslinking agent (18.5 wt%). The fabrication process is simple and uses only water. The composite foams exhibit an elastic strain of ˜13% at a modulus of 250 K Pa and a stress of 73 K Pa at 50% strain (100+ and 18 times, respectively, higher than those of pure NCC foam); both exceed the values of reported nanocellulose-based foams with no reinforcement. The foams exhibit a thermal conductivity of 0.027 Wm^-1 K^-1, which is superior to those of traditional insulating materials. The structural integrity is also preserved after burning. Our results show that NCC-based materials can be engineered towards high-performance insulation applications.