Experimental Characterization of the Tensile Behavior of Microcellular Polycarbonate Foams

Novel polycarbonate (PC) foams with bubbles on the order of 10 μm and cell nucleation densities between 1 and 10 billion cells per cubic centimeter of foam have been produced using carbon dioxide as the blowing agent. The size and number of bubbles can be controlled to produce a wide range of foam densities. This paper presents the results of an experimental study of the tensile behavior of these unique microcellular foams. It was found that the tensile strength of microcellular PC foams is proportional to the foam density. The strength is less than that predicted by the rule of mixtures, suggesting that the microcellular structure is inefficient in carrying the tensile load. The saturation of PC by CO₂ was found to reduce the tensile strength of the virgin material by approximately 20 percent. This showed that the sorption of a very high concentration of gas molecules by the polymer must be considered when characterizing and modelling the microcellular foam mechanical properties. The relative tensile modulus of microcellular foam was found to increase as the square of the foam’s relative density over the range of densities explored.