Synergistic flame retardancy of poly(cyclotriphosphazene-co-piperazine) particle with aluminum diethylphosphinate in epoxy resin

Hexachlorocyclotriphosphazene (HCCP) was reacted with piperazine to obtain poly(cyclotriphosphazene-co-piperazine) particle (PCPS), which was used as the flame retardant for epoxy resin (EP). The structure of PCPS was determined by various methods. When PCPS was used alone and the addition amount of PCPS in the prepared flame-retardant EP (FR-EP) reached 4%, the obtained FR-EP cannot even pass the V-1 level in the Vertical burning (UL-94) test. However, PCPS showed a synergistic flame retardancy with aluminum diethylphosphinate (ADP). When the mixture of ADP and PCPS in EP was 4% and the weight ratio of ADP and PCPS was 3:1, the prepared FR-EP, EP-ADP/PCPS3:1, reached the V-0 level in the UL-94 test. The limiting oxygen index (LOI) value of EP-ADP/PCPS3:1 was 29.7%. Compared with pure EP, the peak heat release rate of EP-ADP/PCPS3:1 obtained by the micro-combustion calorimetry (MCC) test was reduced by 20.6%. Thermogravimetric analysis (TGA) result showed that, with the addition of ADP and PCPS, the char residual of EP-ADP/PCPS3:1 increased about 5.1% compared with EP. The combination of ADP and PCPS showed significant advantage in promoting the flame retardancy of EP. Compared with pure EP, the mechanical properties of EP-ADP/PCPS3:1 was hardly decreased with the addition of ADP and PCPS.