Properties of antimony oxide-coated clay/polypropylene composites

Brominated flame retardant polypropylene composites were prepared by melt blending polypropylene, tetrabromobisphenol A, antimony oxide and organically-modified montmorillonite clay. The synergy between antimony oxide, clay and the brominated fire retardant was studied by thermogravimetric analysis under oxygen and UL-94 testing. Thermal, structural and tensile properties were studied using differential scanning calorimetry, X-ray diffraction and a universal testing machine respectively. Tetrabromobisphenol A and/or antimony oxide with clay is more efficient than clay alone in improving the flame retardancy of the materials and promoting carbonization in the polypropylene matrix. Thermogravimetric analysis showed significant improvements in the degradation temperature for all composites compared with the neat one. This can be ascribed to the physico-chemical adsorption of the volatile degradation products on the silicates. In the presence of montmorillonite, the melting and cooling points and degree of crystallization shift to higher values. These observations are compatible with the assumption that montmorillonite and other additives behave as nucleating agents, as a result of their large relative surface area. Moreover, the structure of the composites was characterized by scanning electron microscopy, which revealed good dispersion of the fillers in the polymer matrix. The experimental results of tensile tests indicated that the incorporation of clay and other additives improved the Young's modulus, but decreased the tensile strength.