The Effect of Morphology on the Flame-Retardant Behaviors of Melamine Cyanurate in PA6 Composites

Three types of melamine cyanurate (MCA) with micrometer-size sphere-like, micrometer-scale rod-like, and nanometer-scale flake-like morphologies were synthesized by changing the chemical circumstances of the reactions. The microcosmic morphologies of MCA were characterized via scanning electron microscopy and X-ray diffraction. After the MCAs with different morphologies were incorporated into polyamide 6 (PA6), the flame-retardant properties of the MCA/PA6 composites were investigated using the limited oxygen index (LOI), UL94, and cone calorimeter tests. The MCA/PA6 composites with nanometer-scale flake-like MCA obtained an LOI value of 29.5% and a UL94 V-0 rating, which were higher than those with micrometer-size sphere-like and rod-like MCAs. However, the different morphologies did not affect the heat release rate, total smoke release, average carbon monoxide yield, and average carbon dioxide yield based on the cone calorimeter. The flame-retardant mechanism of MCAs with different morphologies was investigated via thermal gravimetric analysis (TGA) and TGA-Fourier transform infrared spectra. The results show that the different morphologies of MCA resulted in different dispersed evenness of MCA. Further, the nanometer-scale flake-like morphology of MCA brought more interactions of hydrogen bond between MCA and PA6, which resulted in the delay of MCA decomposition and the enhancement of MCA flame-retardant effect. The nanometer-scale flake-like MCA had a better performance compared with the other samples because of the delaying and even release of flame-retardant effect by the decomposition of evenly dispersed MCA. (c) 2014 Wiley Periodicals, Inc.