Facile and scalable preparation of poly(vinyl alcohol) hydrogels: Insights into thermal kinetics, combustion behavior, and flame retardancy

A flame-retardant (FR) hydrogel with controllable size and shape was synthesized using only poly(vinyl alcohol) (PVA) and ammonium polyphosphate (APP). The self-assembled PVA-APP (PA) hydrogel was formed via hydrogen bonding , enabling customizable shapes and sizes by simply shaking and stacking. Its dimensions were up to 250 × 400 × 2 mm 3 . In PA-n ( n = APP/PVA mass ratio; n = 4, 6, and 8), PA-6 exhibited a compressive strength of 16.17 kPa and fracture elongation of 238 %. The hydrogel can be rolled for portability and retains its structure and performance after unfolding, ensuring its suitability for long-term storage. Moreover, PA-6 achieved a limited oxygen index of 39.22 % and peak heat-release rate of 157.97 kW/m 2 , demonstrating excellent FR properties. Organic and structural analyses before and after combustion revealed that the FR mechanism involved air pathways, phosphate radical chelation, char formation, and gas dilution. In addition, the PA hydrogel exhibited excellent thermal protection performance when applied to various substrates, including pig skin, paper, and polyurethane foam, and was effectively used as a fire blanket to suppress flames in a model car. These findings highlight the potential of PA hydrogels for broad applications in various industrial fields.