The catalytic pyrolysis of titanium in the highly charring metal-coordinated flame retardant synthesized for use in polyamide 66

The existing research has revealed the positive effects of titanium compounds, while the flame-retardant mechanism of titanium remains to be explored and clarified. Herein, we have synthesized an organic titanium-based flame retardant, designated as TiPPDS. The synthesized TiPPDS exhibits high thermal stability, with an initial degradation temperature of 303 °C and a high char yield of 64.3 % at 800 °C, meeting the high-temperature processing requirements of polyamide 66 (PA66). Flammability tests demonstrate that TiPPDS exhibits efficient flame retardancy in PA66. Incorporating 15 wt% TiPPDS into PA66 elevated the limiting oxygen index value to 28.5 %. Compared to neat PA66, the peak heat release rate and total heat release of PA66–15TiPPDS were reduced by 31 % and 41 %, respectively. To investigate the underlying mechanism, a specialized apparatus was designed for pyrolytic gas analysis. Unsaturated hydrocarbons and hydrogen were detected in the pyrolysis products of PA66–15TiPPDS.The unsaturated hydrocarbons exhibit lower combustion heat and a strong tendency toward incomplete combustion, consequently reducing heat release during combustion. Further analysis revealed that TiPPDS decomposes to generate a titanium phosphate semiconductor with band gap of about 3.4 eV, and the residue has a structure defect of Ti³⁺ accompanied with oxygen vacancies. These results indicated the catalytic dehydrogenation of PA66 to thermal excitation of titanium semiconductor during combustion. This work contributes to a thorough understanding of the catalytic mechanism of titanium compounds during combustion, thereby providing theoretical guidance for the development of high-performance titanium-based flame retardants.