Properties and mechanism of high-performance flame retardant thermoplastic vulcanizate with silicon-based alkenyl-crosslinking molecule

A novel flame retardant was synthesized by introducing tetramethyl tetravinyl cyclotetrasiloxane (MVC) into the alkenyl-crosslinking structure formed by anhydrous piperazine and vinyl phosphoric acid, resulting in a silicon-based alkenyl-crosslinking molecule GMA-nMVC. The GMA-15 %MVC, with an optimal component ratio, enhanced the flame retardancy and mechanical properties of thermoplastic vulcanizate (TPV) composites. At 20 wt.% loading, the limiting oxygen index of the GMA-15 %MVC/MPP/TPV system reached 30.2 %, and both 3.2 mm and 1.6 mm samples passed UL 94 V-0. Compared to GMA/MPP/TPV and pure TPV, GMA-15 %MVC significantly reduced the peak heat release rate, total heat release, smoke release, and effective combustion heat, while increasing residual char yield and promoting a denser char layer. The tensile strength of GMA-15 %MVC/MPP/TPV system reached 17.2 MPa, with an increase of 48.3 % and 23.7 % compared to GMA/MPP/TPV and pure TPV, respectively. The corresponding elongation at break reached 987.7 %, surpassing GMA/MPP/TPV and pure TPV. Siloxane’s flexible chain segments and strong char-forming ability led to excellent synergistic effects, offering a new approach for developing TPV materials with high flame retardancy and superior mechanical properties.