Green recycling of fly ash into heat and sound insulation composite aerogels reinforced by recycled polyethylene terephthalate fibers

Fly ash is waste from thermal power plants that not only has a serious impact on soil and water but also accumulates in landfills and must be treated properly. In addition, plastic waste, especially polyethylene terephthalate bottles, deteriorates for a long time, so there is an urgent need to recycle them into valuable products. To solve the environmental pollution mentioned above, a feasible zero-waste method has been developed that converts 100% of fly ash into a lightweight composite aerogel reinforced with recycled polyethylene terephthalate fiber. In this study, raw fly ash is bound to the skeleton of the fibers by a non-toxic, biodegradable xanthan gum solution as a binder, which is then lyophilized, leaving a hollow porous structure. The obtained composite aerogels display extremely low density of 0.026–0.062 g/cm3, high porosity of 96.59–98.42%, low thermal conductivity of 34–39 mW/(m·K), flexibility with Young's modulus of 3.98–20.61 kPa, and noise reduction coefficient of 0.18–0.31. Adding fly ash to the fiber framework results in a lightweight composite aerogel with higher porosity, heat, and acoustic insulation, as well as impressive compressive modulus, compared to the fly ash-free aerogels. This study provides a safe, environmentally friendly, and cost-effective solution for recycling fly ash into high-value engineering materials. [Display omitted] •Zero waste procedures have been developed to completely recycle FA into composite aerogels.•The combination of FA and rPET fibers increases the flexibility of the aerogel.•The fabricated composite aerogel is lightweight and has a porosity of over 96%.•The compressive strength of composite aerogel is 20 times higher than that of FA-free aerogel.•Composite aerogels exhibit both excellent thermal and acoustic insulation without any required modification.