Fabrication of porous structure of poly(ε-caprolactone) via microcellular injection molding combined with chemical foaming

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.