An effective mono-component intumescent flame retardant for the enhancement of water resistance and fire safety of thermoplastic polyurethane composites

Flame-retardant thermoplastic polyurethane (TPU) composites are usually used in the wire and cable areas, but the water resistance of composites seriously restrains its further application. Herein, a mono-component intumescent flame retardant dimelamine pyrophosphate (DMPY) was successfully synthesized and incorporated into TPU matrix. The fire safety, mechanical performance, water resistance and flame retarded mechanisms of TPU/DMPY composites were systematically investigated. When 15 wt% DMPY was incorporated, the samples of TPU/DMPY fulfilled UL-94 V-0 grade during vertical burning tests with the limiting oxygen index of 27.3%. The blowing-out effect appeared during vertical burning tests and it improved the flame retardant performance of composites. The integrated, dense and partially graphitized char layer was produced on TPU/DMPY composites surface during combustion. Moreover, the release of noncombustible gases exerted diluted effect in gas phase. As a results, the production of heat, toxicity and smoke were significantly suppressed and led to good fire safety performance of TPU composites. Furthermore, the TPU/DMPY remained satisfied flame retardancy and mechanical performance after the samples were soaked into 70 °C for 168 h and dried to a constant weight. The TPU/DMPY composites with good comprehensive performance as well as fire safety, water resistance and mechanical performance were prepared in this investigation, which would bring more chance for wider application of TPU composites in key fields.