Montmorillonite (MMT)/polystyrene (PS) composites were prepared by melt-compounding PS resin and different kinds of MMT. The structures of the composites were investigated by XRD and high resolution TEM. The pyrolytic charring behavior and fire performance of the composites were studied by means of SEM, X- ray energy dispersive spectrometry (EDX), XRD, oxygen index and cone calorimetry experiments. It is shown that the NaMMT/PS composite is a simple physical blend of PS and virgin MMT (NaMMT), while the organic montmorillonite(OMMT)/PS composite is an intercalated- partially exfoliated nanocomposite. When the mass ratio of MMT to PS is 6 : 100, the peak heat release rate(PHRR) and average heat release rate(AHRR) of the OMMT/ PS composite are only 70.7~/6o and 67.4~ that of its NaMMT/PS counterpart, respectively. Meanwhile, the fire performance index (FPI) of the OMMT/PS composite is 1.2 times that of the NaMMT/PS composite, and the oxygen index value of the former is 1.0% higher than that of the latter. The content of carbon element in the residue surface of OMMT/PS composite is 2.5 times that of NaMMT/PS composite. A thick, compact and continuous carbon-containing silicate residue layer is formed on the surface of the OMMT/PS composite, which can effectively inhibit burning. The NaMMT/PS composite hardly has any charring ability. The residue of this composite derives from the pyrolysis of NaMMT completely and it exhibits very poor flame retardancy.%将聚苯乙烯（PS）树脂与不同种类蒙脱土（MMT）进行熔融复合制备MMT／PS复合材料，通过X射线衍射（XRD）和高分辨透射电镜（HRTEM）对复合材料的微观结构进行了研究。采用SEM、EDX、XRD、氧指数法和锥形量热法研究了复合材料的热分解成炭行为和燃烧性能。结果表明：用蒙脱土原土（NaMMT）制备的NaMMT／PS复合材料是一种简单物理混合物，用有机蒙脱土（OMMT）制备的OMMT／PS复合材料是一种插层-部分剥离型纳米复合材料。MMT与PS质量比为6：100时，OMMT／PS复合材料的热释放速率峰值和平均值分别只有NaMMT／PS复合材料相应值的70．7％和67．4％，火灾性能指数（FPI）是后者的1．2倍，氧指数比后者增加1．0％，热分解残余物表面碳元素含量是后者的2．5倍。OMMT／PS复合材料热分解后在材料表面生成一层厚厚的致密、连续的含碳硅酸盐残余物层，起到良好的阻燃作用，而NaMMT／PS复合材料几乎没有成炭能力，其热分解产物全部来自NaMMT本身的热分解，阻燃性能很差。
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