The physical foaming technology of supercritical fluid foaming and chemical foaming technology were combined to fabricate porous structure for polymers. Sodium bicarbonate was used as a chemical foaming agent. Poly(ε-caprolactone) (PCL) was first blended with sodium bicarbonate by a twin screw extruder and pelletized. The different foaming processes were conducted on a conventional injection molding machine and a microcellular injection molding machine separately. The foaming results were investigated by comparing the two methods of injection molding and microcellular injection molding. The results revealed that it was feasible by combining physical foaming and chemical foaming to fabricate porous structure for PCL

whose foaming quality was better than that of only chemical foaming method. The introduction of chemical foaming agent not only improved general foaming

but also served as nucleating agent of the gas bubbles of physical foaming. The interconnectivity of the pores was investigated

as well as the "web" structure on the cell walls. When the bubbles were growing

the cell walls were stretched in different directions

and the mutual wall of neighbored pores was stretched by the pores

therefore the "web" structure was obtained.