Enhanced Flame Retardancy and Mechanical Properties of Thermoplastic Vulcanizate by a Multi‐Piperazine/Melamine Vinylphosphonate System

ABSTRACT To meet the dual demands for flame retardancy and mechanical performance of thermoplastic vulcanizate (TPV), two vinylphosphonate‐containing flame‐retardant products, designated as tris(vinylphosphonate salt) of phenylsilane tris(piperazine) (NV) and melamine vinylphosphonate (MV), were prepared and combined to construct an intumescent flame‐retardant system. NV and MV were compounded at different mass ratios, and the 6NV/4MV ratio showed the most favorable overall flame‐retardant performance. At a loading of 24 wt.% (6NV/4MV), the modified TPV exhibited an LOI value of 26.5% and achieved UL‐94 V‐0 ratings at both 3.2 and 1.6 mm thicknesses. Cone calorimeter tests showed substantial reductions in peak heat release rate, peak smoke production rate, total heat release, and total smoke production, together with an increased char residue. SEM‐EDS analysis indicated enhanced retention of phosphorus‐containing species in the condensed phase and the formation of a relatively compact char layer for the 6NV/4MV formulation. At 20 wt.% loading, the tensile strength and elongation at break of 6NV/4MV/TPV increased by 27.5% and 8.3%, respectively, compared with neat TPV. FTIR analysis revealed that the C = C‐related absorption band nearly disappeared after thermal processing, indicating thermally induced changes in the unsaturated groups. This change may have contributed to partial crosslinking among the components. Overall, compositional regulation of the binary NV/MV system provided a favorable balance among flame retardancy, mechanical‐property retention, and durability under water exposure.