Improved self-supporting property of ceramifying silicone rubber composites by forming crystalline phase at high temperatures

Abstract

Abstract Ceramic-like residues were obtained by firing silicone rubber (SiR)/ammonium polyphosphate (APP) composites both with and without magnesium hydroxide (MH) composites at different temperatures. To evaluate the self-supporting property, the bending angles of the residues were tested. The effect of MH and firing temperatures on the self-supporting property was investigated. Results show that the addition of MH reduces the bending angles of the residues and improves their densification. Furthermore, as temperature increases, the bending angles of the residues containing magnesium decrease and their flexural strength is improved. Infrared spectroscopy (IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analyses demonstrate that formation of crystalline magnesium pyrophosphate within the residues is due to interaction between MH and APP, and the relative content of the crystalline phase increases with increasing temperatures. Solid-state nuclear magnetic resonance (SNMR) further confirms the phosphates, but the above crystalline phase also amorphous magnesium orthophosphate and magnesium metaphosphate. Moreover, as temperatures increase, the relative content of the crystalline phase is improved, which agrees well with the XRD analysis. Therefore, the crystalline phase formed at high temperatures plays a main role in the improvement of the self-supporting property.