Combustion Properties Of Flame Retardant RTV Silicone Rubber Composites Based On Aluminum Hypophosphite

Silicone rubber (SR), one of the fastest growing synthetic materials, is widely used in various areas, especially in electronic and electric products aspects, because of its excellent thermal stability, low-temperature toughness, and electrical-insulting properties. However, the flammable characteristics of SR when it is ignited restricted its application in some fields. So the flame retardancy of SR still needs to be improved. To increase the flame retardant property of the material, flame retardants (FRs) are often added to SR. Aluminum hypophosphite (AHP) has been used as an effective halogen-free flame retardant through the formation of the compact and protective char layer, which protected the inner material from further burning.In this paper, Aluminum hypophosphite (AHP), expandable graphite (EG), hollow glass microspheres (HGM), ferrite red (Fe2O3), ferrite yellow (FeOOH) and ferrocene (Fer) were used to prepare flame retardant SR composites by mixing method. And, the flammability, thermal stability and volatile products of SR composites were studied using cone calorimeter test (CCT), thermogravimetric analysis (TGA) and fourier transform infrared spectroscopy (FT-IR). The main content includes the following in this paper.(1) The synergistic effect of EG and AHP on the flame retardancy of SR. The synergistic effects of EG with AHP in halogen-free flame retardant SR composites have been studied by CCT, TGA and FT-IR. The CCT results showed that AHP and EG can effectively reduce the flammable properties including PHRR, THR, SPR, TSR and SF. An improvement of thermal stability of SR/AHP/EG was also observed. The experimental observations from digital photo graphs give positive evidence that the synergistic effects between AHP with EG. The TGA results reveal that SR/AHP/EG samples show slower thermal degradation rate and higher thermal stability at high temperature than SR sample. The FT-IR results showed that the addition of AHP and EG significantly decreased the combustible gaseous products such as hydrocarbons. These attractive features of SR/AHP/EG suggest that the method proposed herein is a good approach to prepare very effective flame retardants and corresponding super flame retarding SR.(2) The synergistic effect of AHP and HGM on the flame retardancy of SR. The synergistic effects of HGM with AHP in flame retardant SR composites have been studied by CCT, TGA and FT-IR. The CCT results showed that AHP and HGM can effectively reduce the flammable properties including PHRR, THR, SPR, TSR and SF. The experimental observations from digital photo graphs give positive evidence that the synergistic effects between AHP with HGM. The TGA results reveal that SR/AHP/HGM samples show slower thermal degradation rate and higher thermal stability at high temperature than SR sample. The FT-IR results showed that the addition of AHP and HGM significantly decreased the combustible gaseous products such as hydrocarbons. These attractive features of SR/AHP/HGM suggest that the method proposed herein is a good approach to prepare very effective flame retardants and corresponding super flame retarding SR.(3) The synergistic flame retardant effects between AHP and Fe2O3, FeOOH and Fer in SR composites were evaluated using CCT, TGA and FT-IR. The CCT results showed that AHP and Fe2O3, FeOOH and Fer can effectively reduce the flammable properties and thermal stability. The experimental observations from digital photo graphs give positive evidence that the synergistic effects between AHP with Fe2O3 (FeOOH, Fer). The TGA results reveal that SR/AHP/Fe2O3 (FeOOH, Fer) samples show slower thermal degradation rate and higher thermal stability at high temperature than SR sample. The FT-IR results showed that the addition of AHP and Fe2O3, FeOOH, Fer significantly decreased the combustible gaseous products such as hydrocarbons. These attractive features suggest that the method proposed herein is a good approach to prepare very effective flame retardants and corresponding super flame retarding SR.