Advanced Fabrication of Lightweight Aerogels from Fly Ash for Thermal Insulation

Abstract

For the first time, an environmentally friendly and effective procedure to produce high-value engineering aerogels from fly ash (FA) has been developed by dispersing FA particles into a mixture of biodegradable polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC), followed by freezedrying. The effect of FA content on the physical properties, morphology, mechanical strength, and thermal conductivity of FA aerogels is also studied comprehensively. The lightweight FA aerogels show a low density of 0.072 – 0.093 g/cm3 with high porosity of 94.94 – 95.78%. The morphology of aerogels shows the uniform distribution of FA particles in PVA-CMC matrixes that creates a porous structure with a pore size of 2-5 mm. Therefore, the FA aerogels exhibit good heat insulation with extremely low thermal conductivity of 0.040 – 0.047 W/m.K at ambient temperature and pressure that is comparable to some commercial insulation materials such as mineral wool, fiberglass, expanded polystyrene, and other silica-based aerogels from waste. Moreover, the compressive modulus of FA aerogels is about 67.73 – 254.75 kPa indicating their excellent mechanical properties under 1 kN vertical compression. The experimental results indicate the significant better durability of FA aerogels than that of previous aerogels from other wastes such as sugarcane bagasse (88 kPa), pineapple leaf fibers (1.64 – 5.34 kPa), recycled polyethylene terephthalate (1.16 – 2.87 kPa), spent coffee grounds (5.41 – 15.62 kPa), and silica – cellulose (86 – 169 kPa). It is concluded that FA aerogels are a promising candidate as a lightweight thermal insulating material.

Recent Progresses in Eco-Friendly Fabrication and Applications of Sustainable Aerogels from Various Waste Materials

“…The addition of rPET fibers is found to enhance the compressive strength of the aerogels. Compared to the previous fly ash-based aerogels [105,106], the developed composite aerogels are 5 times lighter and 1.5 times better in heat insulation at ambient condition. Overall, these works represent green methods to utilize 100% of fly ash without any chemical treatment, increasing the atom efficiency of the process and thus reducing the amount of waste generated.…”

“…Another approach by Do et al [106] was carried out by using a combination of industrial PVA with low viscosity and CMC as an anti-settlement agent to bind fly ash into a monolithic gel, followed by sublimation to obtain lightweight aerogels with porosity of 94.94-95.78%. Both fabricated fly ash aerogels exhibited heat insulation with poor thermal conductivity (40-50 mW/mK).…”