Synergistically enhanced tracking resistance and flame retardancy of silicone rubber via promoting surface ceramization and free-radical scavenging

Flux-free T-FPN enables ceramifiable silicone rubber at low filler loading. • ALSR/T-FPN4 achieves UL-94 V-0, 34.7% LOI, and lower heat release. • The composite passes 4.5 kV tracking with only 0.26% erosion after 6 h. • Hindered amine groups quench radicals and suppress backbone degradation. • Confined cross-linking forms a dense SiOC barrier against heat and arcs. Ceramifiable silicone rubber (SR) is promising for electrical insulation and fire-safety applications, but conventional low-melting-point fluxes often compromise flame retardancy and mechanical performance. Herein, a flux-free strategy (without conventional low-melting-point fluxes) is proposed for addition-cure liquid silicone rubber (ALSR) composites by surface-modifying fluorophlogopite nanosheets with a hindered amine-functionalized silane (T-FPN). Incorporating 4 phr T-FPN simultaneously improved the fire safety, tracking resistance, and mechanical properties of ALSR. Among the T-FPN loadings from 1 to 5 phr, ALSR/T-FPN4 exhibited the best overall performance. It achieved a limiting oxygen index (LOI) of 34.7% and a UL-94 V-0 rating, with peak heat release rate and total heat release reduced by 37.6% and 22.2%, respectively. It passed the 4.5 kV inclined-plane test with an erosion rate of 0.26% after 6 h. The improvement arises from a synergistic mechanism: well-dispersed FPN nanosheets restricted heat and mass transfer, while the hindered amine functionality provided oxygen-centered radical-scavenging capability and helped suppress oxidative degradation of the SR backbone. Meanwhile, confined interlaminar spaces favored Pt-assisted in situ cross-linking of preserved siloxane chains, forming a compact SiOC ceramic layer that shielded the matrix from heat and high-voltage arc erosion. This work offers an efficient route to fire-safe and tracking-resistant silicone rubber. Download: Download high-res image (177KB) Download: Download full-size image