Synergistic effect of intumescent flame retardant system consisting of hexophenoxy cyclotriphosphazene and ammonium polyphosphate on methyl ethyl silicone rubber

In order to improve the flame retardancy of methyl ethyl silicone rubber (VMQ), the synergistic effect of an intumescent flame retardant (IFR) system consisting of hexophenoxy cyclotriphosphazene (HPCP) and ammonium polyphosphate (APP) was investigated. The results showed that with a total loading of 30 wt% IFR, the flame-retarded VMQ composite got the highest limiting oxygen index (LOI) of 30.6% and UL-94V-0 rating at mass ratio of HPCP and APP of 1:1. Meanwhile, the flame retardancy index (14.88) indicated that the synergistic effect of the system was excellent. Then digital photographs, SEM images and FTIR spectra of residue chars obtained from the CC test demonstrated the flame retarding mechanism in the condensed phase. In addition, mechanisms were also discussed based on TG and Py-GCMS results.