A dual-nucleophilic ester-induced supramacromolecular fire-proof hydrogel coating for protecting polymers

Polymer materials are highly vulnerable to fire disaster. However, current research focuses on flame retardancy rather than protection. In this work, two natural extracts of phytic acid (PA) and tannic acid (TA), were successfully compounded via dual-nucleophilic esterification, which facilitated the formation supramolecular hydrogel (T-P₅-PAA). This hydrogel was highly remold-able, self-healable, mechanically adaptable, and environmentally durable, which could form a thin (600 μm) protective coating on multiple polymer materials. Multiple aromatic rings and rich phosphorus elements endowed T-P₅ with excellent physical/chemical synergistic flame retardancy. The dense nanoscale pore structure within the hydrogel network not only effectively impeded heat conduction and gas transmission but also reinforced the material's framework, stabilized its structure, and slowed down thermal decomposition and combustion reactions. Resultantly, the time to ignition (TTI) value of the protected substrates was greater than 1280 s, which was increased by more than 2800 %. The limiting oxygen index (LOI) value exceeded 60 vol%. Remarkably, the protected polymer materials could maintain their original structures and mechanical properties even after being contact with flames directly. These phenomena were significantly distinctive from the previously reported flame retardant strategies that structure and performance degradation were often inevitable upon fire. In brief, we believe that our work not only proposes an effective flame protection strategy, but also offers new enlightenment for future design of high-performance supramolecular soft matters.