Carbon Nanotube/Epoxy Composites for Improved Fire Safety

Pristine carbon nanotubes (CNTs) were treated to make them rich in carbon-centered free radicals. CNTs with various contents of carbon-centered free radicals were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electron paramagnetic resonance (EPR). The CNTs were used to reinforce epoxy resins, and the fire safety (limited oxygen index (LOI), vertical burning test (UL-94), and cone calorimeter test) and mechanical performances (tensile properties, impact strength, and dynamic mechanical analysis (DMA)) of the obtained composites were tested. It was found that the carbon-centered free radical-rich CNTs increased the LOI value of the epoxy matrix dramatically and exhibited obvious advantages over the other CNTs. In addition, the carbon-centered free radical-rich CNTs also had the best reinforcing effect on the mechanical properties. Based on comparison experiments and attempts at correlating the fire performance of the composite with the free radical content and edge content of the CNTs, the improved fire safety was attributed to the free radical scavenging effect of the numerous dangling bonds on the carbon-centered free radical-rich CNTs. In situ EPR experiments revealed the evolution of the free radical scavenging effect during the thermal decomposition of the composite. Carbon-centered free radical-rich CNTs were found to retard the development of fire in the initial period.