The flame retardancy of ionic liquid functionalized graphene oxide in unsaturated polyester resins

Graphene oxide (GO) was prepared from graphite powder by the classic Hummers method, and modified by 1-N-butyl-3-methylimidazolium hexafluorophosphate (IL) and 3-aminopropyltriethoxysilane (KH550) to obtain ionic liquid functionalized graphene oxide (ILGO). ILGO, compounded with traditional flame retardants (ammonium polyphosphate and expandable graphite), was used in unsaturated polyester resin (UPR) to enhance the flame retardancy. The flame retardant property and thermal degradation of the UPR composites were analyzed by limiting oxygen index (LOI), UL-94, cone calorimeter test (CCT), and thermogravimetric analysis (TGA). The results show that there is an obvious synergism between ILGO and the traditional flame retardants. The LOI value of UPR-4 containing ILGO reaches 28.2% and passes V-0 of UL-94, and UPR-4's the initial temperature (T_i), maximum degradation temperature (T_max), and residual carbon greatly increase. The experimental data shows that ILGO can promote UPR to form more residual carbon during combustion, enhance thermal stability, and make the material not easy to decompose. The morphology of carbon layer measured after CCT was observed by scanning electron microscope (SEM). SEM images show that the surface of char layer of UPR-4 containing ILGO becomes smoother, flatter and denser, compared with UPR containing only flame retardants. The cohesiveness and compact structure residual carbon can effectively prevent the oxygen, combustible gas, and heat transfer between the flame zone and the base material to reduce flammability.