Abstract: Hydrogenated styrene isoprene styrene （SEPS）/polypropylene （PP） masterbatch was prepared through melt blending and underwater wire drawing. The resultant SEPS/PP bead foams with a uniform cell structure were then prepared through autoclave foaming with CO2 as a foaming agent. The effect of foaming process on the cell size， foaming ratio， bulk density， and cell density of the bead foams were investigated. The crystallization behavior of SEPS/PP masterbatch and the change of cell size during foaming was studied by differential scanning calorimetry and scanning electron microscopy. The results indicated that the bead foams obtained a cell size of 61~190 μm， an expansion ratio of 3~10， and a cell density of 7.9×105~3.9×107 cells/cm3. This type of SEPS/PP bead foams could be prepared at a foaming temperature of 116~124 ℃ and a saturation time of 0~60 min with a saturation pressure of 2.5~4.0 MPa. The effect of steam chest pressure on the mechanical properties and cyclic compression of the SEPS/PP foam boards with different densities were investigated by selecting the SEPS/PP foam boards with expansion ratios of 5， 7， and 10 through steam chest molding. The results indicated that the foam boards exhibited the highest tensile strength of 715 kPa and the largest elongation at break of 63 % when prepared at an expansion ratio of 10. A highest recovery rate of up to 88 % was achieved for the foam boards at a foam ratio of 7. This foaming material exhibited great application potential to replace the thermoplastic polyurethane （TPU） and ethylene vinyl acetate （EVA） foaming materials.

Key words: hydrogenated styrene isoprene styrene, polypropylene, blend, foaming process, cell size, mechanical property