Rejuvenated fly ash in poly(vinyl alcohol)-based composite aerogels with high fire safety and smoke suppression

- A waste of fly ash is used for flame retardant lightweight aerogel.
- The ratio of the utilized waste fly ash is as high as 76.5 wt%.
- Oxides in the fly ash particles remarkably suppress heat release and smoke release in fire.

As a by-product of thermal power plants, a large amount of fly ash (FA) was produced every year. The comprehensive utilization of fly ash has been receiving increasing attention around the world. In this paper, FA simply modified with NaOH was used to enhance the flame retardancy of poly(vinyl alcohol) (PVA)/Laponite (Lap) aerogels via an environmentally friendly freeze-drying method. From the cone calorimetry test, it was obvious that the heat release rate, total heat release, smoke produce rate and total smoke production of the composite aerogels were decreased significantly with the addition of FA. When the content of fly ash exceeded 63.6 wt%, the limiting oxygen index exceeded 60.0%. All the PVA/Lap/FA aerogels reached V-0 ratings in vertical burning test. The thermal stabilities of the PVA/Lap/FA aerogels improved compared with PVA/Lap aerogels by thermogravimetric analysis. The addition of FA can effectively reduce the calorific value of aerogels, and achieved 2.50 MJ/kg when the FA content reached 76.5 wt%. After disposed with ultrasonic cell crusher, the PVA/Lap/FA mixtures became more homogeneous and form the more regular microstructures after freeze-drying, meanwhile, the pore size became smaller with the increase of FA. The PVA/Lap/FA aerogels exhibited stronger mechanical properties, which compression modulus and strength enhanced a lot than PVA/Lap aerogels. The introduction of FA into PVA/Lap aerogels improved their flame retardant properties successfully, demonstrating it a fire safety product. The content of FA has been achieved more than 50 wt% which provided a new method for efficient utilization of FA.