Construction of phenolated nano-lignin-multinuclear hydroxy aluminum double-network aerogel for flame retardants with high smoke suppression performance

Lignin exhibits inherent flame-retardant potential due to its high char yield and unique aromatic structure. However, its application has been limited by factors such as molecular weight heterogeneity and low chemical reactivity. In this research, phenolic modification of alkali lignin yielded highly uniform and reactive lignin nanoparticles, which were subsequently employed to fabricate flame-retardant gels. The phenolized nano-lignin was first reacted with polyethyleneimine (PEI) and ammonium polyphosphate (APP) to synthesize the APPL polymer. Subsequently, a dual-network structure (APPL-MHA) was formed via hydrogen bonding with multinuclear hydroxy aluminum (MHA). Finally, this composite was integrated with sodium alginate (SA) to fabricate an APPL-MHA@SA aerogel, which exhibits excellent flame-retardant properties. A stable hydrogen bond interaction is formed between the rigid network structure of multinuclear hydroxy aluminum and the uniformly dispersed lignin particles of nano-lignin. The incorporation of APPL-MHA significantly enhanced the mechanical strength and compressive modulus of the APPL-MHA@SA aerogels. Moreover, the synergistic effects of phosphorus and aluminum promoted carbonization during combustion, improving thermal stability, fire resistance, and smoke suppression. The limiting oxygen index (LOI) of the APPL-MHA@SA aerogels reached 35.5%, while conical calorimetry demonstrated a 50.8 kW·m −2 reduction in peak heat release rate, a 7.4 MJ·m −2 decrease in total heat release, and a total smoke production of 0.3 m 2 , significantly lower than the 1.0 m 2 observed for pristine SA aerogels. This study presents a novel approach for the high-value utilization of lignin, expanding the potential applications of aerogels in flame-retardant and smoke-suppression technologies.