Thermoplastic polyurethane/polytetrafluoroethylene/bridged dopo derivative composites: Flammability, thermal stability, and mechanical properties

A phenethyl-bridged DOPO derivative (DiDOPO) is combined with polytetrafluoroethylene (PTFE) in thermoplastic polyurethane (TPU). The flame retardancy and thermal stability of TPU/PTFE/DiDOPO composites with different weight percentages of DiDOPO are investigated by using limiting oxygen index (LOI), UL-94 test, cone calorimetry test (CCT), scanning electronic microscopy (SEM), energy-dispersive spectrometry, and thermogravimetric analysis (TGA). With the incorporation of 8 wt% DiDOPO, the LOI value of TPU/PTFE/DiDOPO composites increases to 34.0% from 25.4% of TPU, and the V-0 rating level is achieved. The CCT results indicate that the peak heat release rate and total heat release of TPU/PTFE/DiDOPO composites decrease due to the addition of DiDOPO and PTFE. The thermal decomposition process of TPU is changed due to the present of DiDOPO and PTFE. Based on this, the Flynn-Wall-Ozawa method for the determination of characteristic degradation kinetics parameters is evaluated. SEM results and residues from TGA curves show that the addition of DiDOPO promotes the increase in the char layer and a crosslinked char coating exists after burning. The flame-retardant mechanism is flame inhibition. Overall, these findings indicate that the combination of DiDOPO with PTFE in TPU is an effective way in developing high-performance resins with attractive flame retardancy. POLYM. ENG. SCI., 59:1593-1602 2019. (c) 2019 Society of Plastics Engineers