Phosphorus and nitrogen supramolecule for fabricating flame-retardant, transparent and robust polyvinyl alcohol film

Supramolecular flame retardants have attracted increasing attention recently due to their simple and eco-friendly preparation process. In this study, a novel flame retardant HEPFR was prepared using supramolecular self-assembly technology between piperazine and 1-hydroxy ethylidene-1,1-diphosphonic acid (HEDP). It was introduced into polyvinyl alcohol (PVA) matrix to form PVA/HEPFR composite film. Subsequently, the transparency, mechanical properties, thermal stability, and flame retardancy of PVA/HEPFR films were studied. Due to the hydrogen bonded cross-linked network structure between PVA and HEPFR, the mechanical properties of PVA/HEPFR films have been improved, while maintaining good transparency. With 10 wt% addition of HEPFR, PVA films can reach the VTM-0 level in UL-94 testing. And the limiting oxygen index can be increased from 18.5% of pure PVA to 26.5%. The peak heat release rate was reduced by 61.5%. The flame retardancy and thermal stability of PVA/HEPFR films have been greatly improved. This study provides a "one stone, three birds" strategy for preparing flame-retardant, transparent, and robust PVA film.