Flame retardant modification of thermoplastic polyurethane elastomers with quinolinyl phthalocyanine

Metal phthalocyanines, owing to their unique and stable chemical structures, have significant potential for enhancing the flame retardancy of polymers. In this study, 2(3), 9(10), 16(17), 23(24)-tetra-(8-oxyquinolinyl) zinc phthalocyanine (ZnQPc) was synthesized and evaluated for its effectiveness in improving the flame retardancy of thermoplastic polyurethane (TPU). The synergistic flame-retardant effect of ammonium polyphosphate (APP) and ZnQPc was further evaluated for TPU. ZnQPc exhibited flame-retardant properties for TPU, achieving a limiting oxygen index (LOI) value of 23.6% at a loading of 3wt%, while also reducing total smoke release (TSR) by 20.5%, thereby effectively suppressing smoke and CO generation. The combination of APP and ZnQPc demonstrated enhanced flame retardancy compared to APP alone. Specifically, the 9%APP&1%ZnQPc/TPU composite resulted in a 54.3% reduction in peak heat release rate (pHRR), a 25.2% reduction in total heat release (THR), a 37.1% reduction in peak smoke production rate (pSPR), and a 15.1% reduction in TSR. Mechanistic studies indicated that ZnQPc promotes early TPU decomposition and catalyzes char formation at elevated temperatures. When combined with APP, ZnQPc facilitates the formation of a dense char layer, further enhancing flame retardancy. This study offers a noval perspective on the application of metal phthalocyanines in improving the flame retardancy of TPU.