Flame-retardant effect and mechanism of melamine phosphate on silicone thermoplastic elastomer

Different from the traditional silicone materials, which are not easily ignited, silicone thermoplastic elastomer (Si-TPE) has poor flame retardant properties due to the existence of the hard segments in its molecular chains. In this paper, melamine phosphate (MP), a kind of halogen free flame retardant, was adopted to improve the flame retardancy of Si-TPE. The results showed that MP played the role of flame retardant in both gas and condensed phases due to its nitrogen-phosphorus-containing structure. Inert gases, including nitrogen, steam and ammonia which were released by the degradation of melamine during burning, could take away the heat and dilute the oxygen in the gas phase, and further working with the phosphoric acid, which was generated in the condensed phase, to form a denser and firmer char layer. In this way, Si-TPE/MP composite with good flame retardancy was obtained. Interestingly, MP had little influence on the thermal processability of Si-TPE, even at 28 wt% content, ascribing to its two opposite effects on Si-TPE, but enhanced the comprehensive mechanical properties of Si-TPE with suitable loadings, e.g. when the MP content was 28 wt%, the composite reached UL94-V0 rating, and its tensile strength and Young's modulus were 3.5 MPa and 37.7 MPa, respectively.