Bioderivable “Latent” Noncombustive CO ₂ -Generating Polymers: A New Class of High-Performing Fire-Resistant Materials

Polymeric materials are indispensable in fire safety applications within various engineering sectors. Notably, polybenzoxazines (PBZs) present potential as high-performance thermosets for fire-retardant materials. However, modern fire retardants rely on fillers to improve their fire retardancy via thermal decomposition, producing incombustible gases to hinder further combustion. Furthermore, PBZs suffer from reliance on petroleum-derived synthesis precursors. We report a novel bio-based PBZ formulation that interestingly exhibits innate CO2 generation during thermal curing in a latent and non-combustive manner, while being free of any fillers towards this effect. This demonstrates a novel possibility of utilizing the mechanism of innate CO2-based self-extinguishment in PBZ fire retardants. The PBZ, synthesized from lignin-derivable vanillyl alcohol, features a dual-cure system via acrylate functionalization of its monomer. Formulation with a diacrylate cross-linker simultaneously achieves suppression of thermally-induced uncontrolled foaming of the PBZ and lowered viscosity from 1.2 to 0.06 Pa s, proving its suitability for solventless coating applications. Using a partial thermal curing protocol to enable both self-production of CO2 and the formation of a fire-resistant PBZ network, the PBZ formulation demonstrated applications as a wood-compatible coating with notable fire-protection performance and thermal stability with near-instantaneous self-extinguishment from a flame, a char yield of ∼30%, and a UL-94 V-0 rating.