Enhancing Flame Retardancy of Thermoplastic Vulcanizate Based on a Phenylsilane/Tri-Piperazine Phosphate Cross-Linking Microaggregate

Abstract

The structural and compositional design of flame retardants plays a pivotal role in determining their effectiveness. In this study, a phenylsilane/tri-piperazine phosphate-based cross-linked aggregate (MPNSI) was employed as a char-forming flame retardant for thermoplastic vulcanizate (TPV). Compared to the conventional linear piperazine pyrophosphate (PAPP), the aggregate MPNSI with the integration of phosphorus, nitrogen, and silicon-based groups significantly had a higher flame retardant performance in the elastomer. Specifically, a 20 wt % loading of the MPNSI/melamine polyphosphate (MPP) blend enabled TPV to achieve a UL-94 V-0 rating at 3.2 mm thickness, compared to 23 wt % required for the PAPP/MPP system. Furthermore, 23 wt % MPNSI/MPP endowed TPV with a UL-94 V-0 rating in the test of a 1.6 mm thickness sample, whereas the PAPP-based formulation failed to pass. The limiting oxygen index was also significantly increased through the MPNSI system. In the cone calorimeter test, MPNSI/MPP with a 23 wt % dosage achieved a 78.0% reduction in the peak heat release rate and a 66.5% reduction in the peak smoke production rate. Beyond flame retardancy, the incorporation of the MPNSI-based system had minimal impact on the mechanical properties of TPV. Notably, the 23 wt % MPNSI/MPP formulation retained a 89.5% level of elongation at break of neat TPV, thus preserving the essential elastomeric characteristics required for functional applications. These findings demonstrate the promise of phenylsilane/tri-piperazine phosphate-based aggregates as an effective strategy for achieving high-performance flame retardancy while maintaining mechanical integrity in elastomers.