Polycarbonate foams with tailor-made cellular structures by controlling the dissolution temperature in a two-step supercritical carbon dioxide foaming process

• PC foams with expansion ratios up to 14 were prepared by two-step scCO2 foaming.
• At a CO2 dissolution temperature of 80 °C PC foams showed a microcellular structure.
• At 100 °C PC foams presented bigger and highly elongated cells.
• PC foams obtained by dissolving CO2 at 100 °C showed a more marked physical aging.
• Physical aging of PC could be reduced with increasing the heating foaming time.

Closed-cell polycarbonate foams were prepared using a two-step foaming process, which consisted of the initial dissolution of supercritical CO2 (scCO2) into PC foaming precursors and their later expansion by heating using a double contact restriction method. The effects of the parameters of both CO2 dissolution and heating stages on the cellular structure characteristics as well as on the physical aging of PC in the obtained foams were investigated. A higher amount of CO2 was dissolved in PC with increasing the dissolution temperature from 80 to 100 °C, with similar CO2 desorption trends and diffusion coefficients being found for both conditions. PC foams displayed an isotropic-like microcellular structure at a dissolution temperature of 80 °C. It was shown that it is possible to reduce their density while keeping their microcellular structure with increasing the heating time. On contrary, when dissolving CO2 at 100 °C and later expanding, PC foams presented a cellular morphology with bigger cells and with an increasingly higher cell elongation in the vertical growth direction with increasing the heating time. Comparatively, PC foams obtained by dissolving CO2 at 100 °C presented a more marked physical aging after CO2 dissolution and foaming, although this effect could be reduced and ultimately suppressed with increasing the heating time.

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