Formation of strong ceramified ash from silicone-based compositions

Compared with many other polymers, polysiloxanes have shown some desirable properties on fire. These include a slow burning rate without a flaming drip and low emissions of non-toxic smoke. However, the residue formed by firing silicones in air is powdery and has little strength for structural use. Addition of certain inorganic fillers into silicone base polymers can improve the ceramic strength, leading to ceramics with good integrity and shape retention after firing. In this work, compositions based on silicate filled silicone polymers were made and their properties were explored. An insight into the mechanism of the ceramic formation after firing at temperatures up to 1050°C was obtained. Techniques including field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) were used to observe microstructure and phase development. Thermal stability was studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). A mechanism for formation of a strong and coherent ceramic is proposed.