In this study, clay and/or graphite particles have been added in various quantities to polypropylene matrix by melt blending. The morphology and more particularly the dispersion of particles in these composites have been compared by transmission electron microscopy (TEM). Their thermal stability has also been studied by thermogravimetric analysis (TGA). The experimental results reveal that the addition of 5 wt % of graphite particles or clay improves the thermal stability in air of the matrix by about 50 and 90 degrees C, respectively. In a second step, these blends have been melt-spun to produce multifilament yarns. The experiments have shown that the addition of graphite particles up to 5 wt % do not reduce the spinnability of the polypropylene, while the incorporation of more than 1 wt % of clay was causing difficulties for the spinning and more particularly for the drawing step. However, a slight improvement of the Young's modulus of the filaments reinforced with 1 wt % of Cloisite(R)15A is observed when the filaments are drawn up. The flammability of the different blends used as knitted fabrics has finally been evaluated with a mass loss calorimeter at 35 kW/m(2). An atypical behavior has been highlighted for all blends and will be discussed. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1185-1195, 2010