Study of thermal and flame behavior of phosphorus-based silica for epoxy composites

Phosphorous-containing silica was prepared by acid hydrolysis of sodium silicate via a cost-effective sol–gel method. Phosphorus was incorporated during synthesis of silica by adding three different phosphorus compounds namely di-sodium hydrogen orthophosphate, orthophosphoric acid, and hypophosphorous acid. The silica powder was analyzed by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and dynamic light scattering (DLS). FTIR spectrum shows the presence of phosphorous in the samples. SEM picture of phosphorous containing silica is globular whereas pure silica is fluffier. The EDX results indicate the phosphorous incorporation up to 5 wt% atomic weight. TGA analysis shows approximately 15 wt% loss up to 150 °C for oven dried samples and the residue at 700 °C is higher for phosphorous containing samples. DLS results show the particle size for all the samples near 1000 nm. Limiting oxygen index (LOI) and smoke density of the epoxy composite samples was evaluated. The LOI value of the phosphorous containing silica composite material has been slightly improved. But the burning behavior of the samples indicates the sufficient formation of protective char layer and the char analysis of the composite samples shows more bubble structure. This type of foam structure of the char protects the surface from fire propagation.