An efficient strategy for simultaneously improving tracking resistance and flame retardancy of addition-cure liquid silicone rubber

How to effectively improve tracking resistance and flame retardancy of silicone rubber is one of the key problems needed to be resolved in the development of high performance silicone rubber insulating materials. In this work, a novel functional silane containing hindered amine and urethane groups, named PPAS, was synthesized by using 1,2,2,6,6-pentamethyl-4-piperidinol, (3-isocyanatopropyl) triethoxysilane and allyl acohol via the nucleophilic substitution and trans-etherification. The effects of PPAS on the tracking resistance, flame retardancy and thermal stability of addition-cure liquid silicone rubber (ALSR) were investigated. It was found that PPAS could effectively enhance the tracking resistance and flame retardancy of ALSR simultaneously. When the content of PPAS was only 3.0 phr, ALSR/PPAS could pass the 1A4.5 kV level in the inclined plane (IP) test and had outstanding electrical erosion resistance, which showed great potential in exterior insulator. In particular, the limiting oxygen index (LOI) of the ALSR/PPAS was 30.0%, and it had a good self-extinguishing capability. Meanwhile, the risk of fire measured by cone calorimeter was also significantly reduced. The mechanism for these phenomena were further studied and revealed: PPAS could effectively quench the peroxyl radicals and suppress the oxidation degradation of Si-CH3 groups, eliminate the Si-OH groups and promote the cross-linked reaction during the thermal degradation of ALSR.