Synergistic effect of ammonium polyphosphate and α-zirconium phosphate in flame-retardant poly(vinyl alcohol) aerogels

To overcome the flammability and melt dripping issues of poly(vinyl alcohol) (PVA) aerogel , a combination of ammonium polyphosphate (APP) and α-zirconium phosphate (α-ZrP) was used to enhance the flame retardancy of PVA aerogels, which were fabricated using a simple mixing and freeze-drying approach. Results obtained from transmission electron microscopy (TEM) and atomic force microscopy (AFM) confirm that α-ZrP was successfully exfoliated by ultrasonic stripping. The effects of the exfoliated α-ZrP nano-plates on the microstructure, composition , flame retardancy, fire behavior of the aerogels was investigated using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), limiting oxygen index (LOI), UL-94 vertical burning, and cone calorimetry test. It was found that the incorporation of α-ZrP improved the 3D network structure of the PVA aerogel. The results showed that a sample with 2 wt% α-ZrP and 13 wt% APP could reach the maximal LOI value of 43.1%, achieved the UL-94 V-0 rating, and the peak heat release rate (PHRR) and total heat release (THR) of the sample reduced by 82.6% and 76.3%, respectively. Thermogravimetric analysis (TGA) revealed that α-ZrP improved the thermal stability of PVA-APP system. The residues analysis revealed that α-ZrP accelerated the formation of a compact and graphitization structure of residues and catalyzed the charring of PVA during burning.