On tracking and erosion resistance of high temperature vulcanizing silicone rubber

High temperature vulcanizing silicone rubber is highly filled with aluminium trihydrate (ATH, Al₂O₃·3H₂O) to assure UL-94 VO rating (insulation is self-extinguishing). Different simultaneous mechanisms, including the release of chemically bound water are responsible for the efficient flame retarding and smoke suppressing effect of ATH. In ATH containing silicone rubber samples occasionally tracking occurs, often accompanied by deep erosion patterns. In this study the effect of different halogen free flame retardant additives on tracking and erosion behaviour was studied. Amongst these, melamine cyanurate led to UL-94 VO in combination with a significantly improved tracking and erosion resistance. Measurements of dielectric loss and permittivity indicated that melamine cyanurate does not alter the electrical properties of silicone rubber considerably.