Synergistic Flame Retardant Effect between Ionic Liquid Functionalized Imogolite Nanotubes and Ammonium Polyphosphate in Epoxy Resin

Ionic liquid functionalized imogolite nanotubes (INTs-PF(6)-ILs) were introduced into the epoxy resin (EP)/ammonium polyphosphate (APP) system to investigate the flame retardant performance and thermal properties using the limiting oxygen index (LOI) test, the UL-94 test, and the cone calorimeter test (CCT). The results suggested that a synergistic effect exists between INTs-PF(6)-ILs and APP on the char formation and anti-dripping behavior of EP composites. For the EP/APP, an UL-94 V-1 rating was obtained for the loading of 4 wt% APP. However, the composites containing 3.7 wt% APP and 0.3 wt% INTs-PF(6)-ILs could pass the UL-94 V-0 rating without dripping behavior. In addition, compared with the EP/APP composite, the fire performance index (FPI) value and fire spread index (FSI) value of EP/APP/INTs-PF(6)-ILs composites were remarkably reduced by 11.4% and 21.1%, respectively. Moreover, the char formed by EP/APP composites was intumescent, but of poor quality. In contrast, the char for EP/APP/INTs-PF(6)-ILs was strong and compact. Therefore, it can resist the erosion due to heat and gas formation and protect the inside of the matrix. This was the main reason for the good flame retardant property of EP/APP/INTs-PF(6)-ILs composites.