Synergistic expansion-ceramization in silicone rubber composites for rapid fire sealing and structure stability in building openings

Ventilation ducts, cable trenches, and other openings serve as essential structural components in buildings. During fires, flames rapidly propagate through these structures, exacerbating fire spread. In this work, a novel ceramifiable, rapid-expansion, and highly efficient fire-resistant sealing system was developed, based on silicone rubber composites (CSR) incorporated with sodium silicate (SS) and low-melting-point glass powder frits (GF) as fillers. The effect of the SS and SR matrix on the expansion behavior of CSR and the structure of the obtained ceramic was investigated. The synergistic mechanism of SS and GF for improving the fireproofing and plugging of silicone rubber was also intensively discussed. It was found that CSR expanded by 4.49 times in volume at 500 °C for 5 min and transformed into a rigid ceramic foam with a compressive strength of 16.1 MPa after treating at 700 °C. CSR exhibited prolonged resistance to 1300 °C flame ablation with the backside temperature of only 128.5 °C after 10 min. During fire exposure, the morphology and crystal structure of CSR were transformed, forming a multi-level structure from exterior to interior, including the cristobalite protective layer, porous ceramic layer, expanded insulation layer, and internal matrix. In addition, the composites can reach the 3 h level of the fire sealing test for cracks, with backside temperatures only 70.8 °C and no flame penetration. This work provides novel insights into the design of ceramifiable silicone rubber systems and expands their potential applications in real fire scenarios.