Phytic Acid/ADP Interfacial Assembly for Flame Retardancy and Self-Extinguishment in Cellulose Paper

ADP-P@Mn and ADP-P@Ni composites were prepared by the interfacial assembly of ammonium dihydrogen phosphate (ADP) with transition metal-phytic acid (PA) complexes. These composites were then mixed with cellulose fibers in an aqueous solution to produce flame-retardant paper. Morphological analysis revealed that the original ADP particles exhibited a smooth, cubic morphology; however, after functionalization with phytic acid, the particles became rougher. The presence of P-O-Mn and P-O-Ni bonds confirmed the bridging effect between phytic acid and ADP, which led to reduced crystallinity and promoted synergistic flame-retardant effects during combustion. Within all concentration ranges tested, both ADP-P@Mn and ADP-P@Ni exhibited significantly improved flame retardancy compared with pristine ADP and reduced the flame spread rate by up to 50%, showing remarkably enhanced flame-retardant efficiency. Notably, even at low concentrations, these two novel flame retardants endowed cellulose paper with self-extinguishing properties. Additionally, increased carbon and oxygen contents in residual char, along with cross-linking via P-C, P-O, and PO bonds, indicated the formation of a dense carbonaceous layer. Consequently, ADP-P@Mn and ADP-P@Ni significantly enhanced the flame resistance of cellulose paper while maintaining its excellent writing performance, moisture resistance, and mechanical properties.