477697 Gradient Foaming of Polymers in Supercritical Carbon Dioxide

Monday, November 14, 2016
Grand Ballroom B (Hilton San Francisco Union Square)
Joseph Sarver, Jenna Sumey and Erdogan Kiran, Chemical Engineering, Virginia Tech, Blacksburg, VA

Polymeric foams find use in many applications ranging from heat or sound insulation to scaffolds for tissue engineering. Foaming with supercritical carbon dioxide is an attractive technique which is environmentally benign. The process often involves exposing the polymer to carbon dioxide at high pressure which is then followed by rapid depressurization to cause bubble nucleation and pore formation. Pore formation is not only a function of the amount of carbon dioxide that dissolves in the system, but also is influenced by changes in thermophysical properties of the polymer such as the viscosity or the glass transition or the crystallization temperature. Determining the effect of pressure and temperature is a time-intensive process which can be more effectively explored using a temperature-gradient field where a constant pressure is employed. This method allows for the combinatorial evaluation of the polymer behavior under carbon dioxide across a range of temperatures at a given pressure. In this study, temperature gradients are generated by heating one end of a 25-cm long high-pressure foaming cell while cooling the other end with ice-water. Temperatures in the gradient field are measured using dedicated thermocouples. After foaming, the sections of the foam from different temperature zones are freeze-fractured and analyzed for their pore morphology and size/distributions. In this poster, the unique experimental system, and the recent results of foaming a semi-crystalline polymer, poly(ethylene-co-vinyl acetate) are described.

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