Design of bio-based P-N synergistic aerogels: Integrating phosphorylated chitosan into sodium alginate for fire-safe thermal insulation

In response to the growing demand for sustainable thermal management solutions, this study developed an eco-friendly flame-retardant aerogel through a green manufacturing process that incorporates bio-derived phosphorylated chitosan (PCS) into a sodium alginate (SA) matrix. The strategic incorporation of PCS, synthesized from renewable chitin resources, significantly enhanced the interfacial compatibility and thermal stability of the composite material while introducing a phosphorus-nitrogen synergistic flame-retardant mechanism. Systematic characterization revealed that the sodium alginate mixed with 30% that mass of phosphorylated chitosan (SA-30 PCS) exhibits exceptional fire safety performance, achieving a limiting oxygen index (LOI) of 33.7% and a V-0 rating in the vertical burning test (Underwriters Laboratories Standard 94), which indicates the highest level of flame resistance. Additionally, this formulation shows a 45% reduction in total heat release compared to pristine SA aerogels. The composite maintains low thermal conductivity (0.035 0 W/(m·K)), fulfilling dual requirements for high-temperature insulation and fire protection. A sustainable hydrophobic modification strategy employing methyltrichlorosilane vapor deposition further endowed the aerogel with moisture resistance. As a wholly biomass-derived system (SA/PCS), the aerogel eliminates persistent toxic residues associated with halogenated flame retardants, while its phosphorus components are covalently bonded in polymeric chains, significantly reducing environmental mobility compared to inorganic phosphates. The inherent biopolymer composition enables potential end-of-life management via enzymatic digestion (e.g., chitinase/alginate lyase), positioning it as an eco-design alternative for sustainable insulation.