Can additive carbon nanotubes reduce the PMMA fire risk?

The flammability and melt dripping illustrate polymer's fire risk. The high-efficiency thermal shielding effect of carbon nanotubes has been widely concerned to improve polymer's flame retardancy. However, the high thermal conductivity and wick effect of carbon nanotubes may enhance heat and mass transfer to promote fire development. A series of experiments about ignition, heat release, horizontal flame spread and dripping behaviors were carried out to comprehensively analyze the fire risk of polymer composite including polymethyl methacrylate (PMMA) and multi-walled carbon nanotubes (MWCNTs). The results showed after the addition of MWCNTs, the limiting oxygen index (LOI) increased from 18% to 20%, the peak of heat release rate (PHRR) decreased from 548 kW/m 2 to 372 kW/m 2 , and the flame spread rate (FSR) increased from 0.28 mm/s to 1.1 mm/s, respectively. These results indicate that MWCNTs decreased the ignition risk of PMMA and its heat generation, however, the fire growth rate increased sharply. That was due to the thermal shielding effect and the heat and mass transfer effect of the char layer, respectively. Therefore, the effects of MWCNTs addition on the fire risk of polymer composites need a comprehensive assessment of multiple factors including the fire growth risk.