Halloysite-based aerogels by bidirectional freezing with mechanical properties, thermal insulation and flame retardancy

Halloysite (Hal) is a natural nanotubular clay mineral with the characteristics of low price and easy availability. The aerogels prepared by Hal are low thermal conductivities, good thermal stabilities and low flammability, which have great application prospects in the field of thermal insulation with flame retardancy. However, they typically suffer from inferior mechanical property and difficulty of mechanically resilient or flexible. Herein, aerogels with anisotropic mechanical properties were prepared by bidirectionally freezing aqueous suspensions of Hal with a small proportion of chitosan (CS). The directionally aligned porous structure gave the aerogels prominent strength in the direction of lamellar orientation, and superelasticity in the vertical direction. The Halbased aerogels showed good performance in the combination of thermal insulation and flame retardancy. The thermal equilibrium temperatures of Hal/CS aerogels at 50 degrees C and 100 degrees C are 27.5 degrees C and 35.2 degrees C, respectively. They also remained unscathed after 180 s of burning in a candle flame. The present study provided a versatile method for design and fabrication aerogels for high-performance thermal insulation materials and had significance in the high-value utilization of Hal mineral resources.

Automated summary

Hal-based aerogels with anisotropic mechanical properties were successfully prepared, showing low thermal conductivities, good thermal stabilities, and flame retardancy. The study provides a versatile method for designing and fabricating high-performance thermal insulation materials aerogels, and has significance in the high-value utilization of Hal mineral resources.