Optimizing the Ablation Performance of Silicone Rubber Composites by Controlling the Vinyl Content

The influence of cross-linking density on the mechanical properties of silicone rubber (SR) is well-established, but its role in ablation and thermal protection under thermomechanical coupling remains unclear. Herein, vinyl methyl silicone rubber (VMQ) composites with different vinyl contents were prepared to regulate the cross-linked network. Results indicated that the low vinyl content reduced cross-linking density, enhanced segmental mobility and stress relaxation, and achieved a tensile strength of 7.12 MPa and an elongation at break of 923%. During stress ablation, the low-cross-link-density network relieved stress concentrations caused by tensile loading, thermal stress, and pyrolysis shrinkage, thereby suppressing microcrack propagation in the ceramicized protective layer and maintaining a continuous thermal-insulation barrier. Consequently, burn-through was delayed: a 3 mm thick specimen under 10% strain and a heat flux of 1 MW/m2 reached 82 s. These findings provide molecular design guidance for flexible SR composites combining mechanical robustness and ablation resistance.