Potential of lignin and cellulose as renewable materials for the synthesis of flame-retardant aerogel composites

Aerogels are ultraporous solid materials characterized by numerous distinctive characteristics, such as an ultrahigh specific surface area, ultralow bulk density, ultralow modulus, extremely low thermal conductivity, extremely low sonic velocity or sound speed, extremely low refractive index, and extremely low dielectric constant. Due to these tunable properties, aerogels are regarded as versatile functional materials that have the potential to be used in various industries as flame retardants, including in oil and gas, building and construction, transportation, and electronics. At present, the dominant component used to synthesize flame-retardant aerogels is silica, the abundance and extraction of which are unsustainable. On the other hand, lignocellulosic biomass is the most plentiful renewable resource on the planet (making it comparable to the abundance of silica), can be obtained at low cost (i.e., derived from agricultural and forestry residue), and can be used to create aerogel frameworks. In addition, lignin can serve as a relatively nontoxic fire-retardant agent. The aim of this research work was to describe the present and anticipated market landscape of flame-retardant aerogel composites (FRACs), summarize the recent progress in the development of lignin- and cellulose-based FRAC systems, and identify the existing challenges to their wider industrial manufacturing and application.