Thermal Insulation of Flame Retardant Silica Aerogel Composites from Rice Husk Ash and Plastic Waste Fibers

Amidst the global concerns in sustainable development and climate change mitigation, the demand for heat-insulating materials has been increasing in which the research objects mostly attracting attention are those from agricultural and industrial wastes due to their abundance. Aerogels have been studied for practical applications in construction because of their lightweight and super-porous properties as well as remarkable thermal insulation. An attempt has been made to create novel silica aerogel composites via in situ synthesis of rice husk ash-derived silica aerogels on the recycled polyethylene terephthalate (rPET) fiber framework and cost-effective ambient drying. Replacing expensive and toxic organosiloxane precursors with low-cost waste materials to synthesize the aerogel composites is a more economical, feasible, and user-friendly approach compared with the previous works. The fabricated aerogel composites exhibit characteristic features of aerogels, the low thermal conductivity of 0.040–0.056 W/(m·K), and a flame propagation speed of approx. 0.27 mm/s due to the adhesion of silica aerogels on the rPET fibers. The durability of the silica aerogel composites is enhanced with a structure of 4 layers of rPET fibers stacked on top of each other and alternating layers of silica aerogels, thus the as-fabricated aerogel composites show a high Young’s modulus of 84.099 kPa and can withstand 695 times their weight. The as-fabricated silica aerogel composites having both thermal insulation and flame retardancy exhibit great potential in eco-friendly and energy-efficient design for construction purposes.