Double-layer microencapsulated piperazine pyrophosphate towards fire-safe styrenic thermoplastic elastomer composites with remarkably improved mechanical properties

The flammable nature of thermoplastic elastomer (TPE) leads to poor fire safety performance. It is difficult to be flame-retardant. A large amount of flame retardant (30–46 wt%) is usually added, weakening their mechanical properties heavily. To address these issues, this study prepared a novel core–shell flame retardant, PAPP@MF@TA, by encapsulating melamine formaldehyde resin (MF) and tannic acid (TA) on the surface of piperazine pyrophosphate (PAPP). Benefiting by the bridging effect of the core–shell structure, the compatibility between TPE and PAPP@MF@TA was improved, and the tensile strength of TPE/PAPP@MF@TA increased by 25.6% compared to TPE/PAPP. The flame-retardant performance was also enhanced. Compared to pure TPE, the peak heat release rate, total heat release and total smoke production of TPE/PAPP@MF@TA decreased by 73.7%, 37.9% and 35.5%, respectively. Besides, the flame-retardant mechanism was studied. This study provides a new approach for designing of TPE composites with comprehensively enhanced flame retardancy and mechanical properties.