Experimental study on flame spread over PMMA composites with addition of carbon nanotubes

Abstract

Experiments on flame spread over cantilevered polymethyl methacrylate (PMMA) composites with addition carbon nanotubes (CNTs) were conducted and flame spread behaviors was analyzed. Results show that the two flame regions, surface flame and dripping flame, are distinguished because of the enhanced viscosity of the molten materials with the addition of CNTs. The combustion-supporting effect from the dripping flame promotes flame spread, the flame height and the flame spread rate are increased with CNTs. There is a power-law relationship between the whole flame height and the dripping flame height, H∝H20.682. The heat transfer analysis is also conducted based on the divisions of flame region. As the content of CNTs increases, the heat flux from surface flame is almost constant, but for dripping flame, it is twice as much as pure PMMA at 2.5% CNTs and the contribution in heat flux of dripping flame reaches 40%. The heat flux from dripping flame has important effects on sustaining flame spread and the increasing flame spread rate is mainly attributed to the enhancement of the heat feedback of dripping flame. These results are contrary to the effects of the flame retardancy by CNTs, which means the application of CNTs as flame retardants in polymers needs to consider the fire scenarios.