Preparation and Study on the Flame-Retardant Properties of CNTs/PMMA Microspheres

In this paper, carbon nanotubes (CNTs)/poly(methyl methacrylate) (PMMA) composites with excellent thermal stability and flame retardancy were prepared by in situ polymerization. The morphology, structure, transmittance, thermal stability, flame retardancy, and mechanical properties of the materials were characterized with scanning electron microscopy (SEM), thermogravimetric analysis (TGA), cone calorimetry, etc. According to the results, the initial decomposition temperature of CNTs/PMMA prepared using carbon nanotubes with a concentration of 2 mg/mL increases from 175 to 187 °C when compared with pure PMMA, and the weight loss ratio decreases significantly at the same time. In addition, the maximum limiting oxygen index (LOI) value of CNTs/PMMA composites is 22.17, which is 26.9% higher than that of PMMA. SEM images of residues after LOI tests demonstrate that when CNTs/PMMA is heated, a dense and stable interconnected network structure (i.e., carbon layer) is formed, which can effectively inhibit the combustion of pyrolysis products, prevent the transfer of heat and combustible gas, and finally interrupt the combustion of composite materials. However, a 25% decrease in the transmittance of CNTs/PMMA composites is observed in the Ultraviolet-visible (UV-vis) spectra. Although the addition of CNTs reduces the transparency of PMMA, its tensile and impact strength are all improved, which illustrates that CNT is a competitive flame retardant for PMMA.