Synthesis of Cobalt Borate Compound to Confer Fire-proof Properties to Epoxy-Based Composites by Achieving Synergistic Effect with Red Phosphorus

This study investigated the synergistic effect of a cobalt borate (CoB) compound synthesized by molten-salt-assisted borothermal reduction on epoxy resins, both alone and in combination with red phosphorus (RP) flame-retardant additives, on flame-retardancy. In the first stage of the research, the CoB compound was synthesized using a molten salt-assisted borothermal method, yielding Co3B2O6 at 750°C. X-ray diffraction (XRD), scanning electron microscopy equipped with energy dispersive x-ray spectroscopy (SEM-EDX), thermogravimetric analysis (TGA), and fourier transform infrared (FTIR) spectroscopy were used to characterize the synthesized compound. The synthesized CoB compound was first tested alone at varying weight ratios to investigate its flammability. Subsequently, it was used in combination with a RP-containing flammability additive, and its synergistic interactions were evaluated using UL- 94, limiting oxygen index (LOI), and cone calorimeter tests. The flammability tests showed that the combination containing 1% CoB and 9% RP demonstrated the highest resistance to combustion. In this sample, a V0 rating was achieved in the UL-94 vertical test; LOI increased by 1.5-2.0 units compared to the additive-free epoxy, and the heat release rate (HRR) was approximately 30% lower in the calorimeter test compared to the additive-free epoxy resin.