Supercritical CO2 is a promising solvent for application in polymer blending and foaming. The addition of small amounts of compressed gases to polymer phases results in substantial and sometimes dramatic changes in the physical properties that dictate processing. Interfacial tension is a key parameter in determining the bubble nucleation and growth rates, as well as droplet break up in blending. However very limited data on this property is available in the literature for CO2-polymer systems. A novel technique is presented to determine the interfacial tension for the polymer melts and high pressure CO2 systems by analysis on the axisymmetric pendant drop shape profile, which can simultaneously yield the density, swelling and interfacial tension results. The method avoids the “capillary effect” and the “necking effect” and provides good axisymmetry of the pendant drop, which makes it a suitable method for measuring the interfacial tension for polymer melts under high pressure CO2 conditions. The interfacial tension between polymer melt (PS, PP, PLGA, PMMA) and high pressure CO2, and the interfacial tension between polymer melt pairs (PS/PP) saturated with high pressure CO 2 were studied using the pendant drop method in a high pressure, temperature view cell. CO 2 was found to significantly depress the interfacial tension in the pressure range studied. The linear gradient theory combining with the Sanchez-Lacombe Equation of State was applied in predicting the surface tension or interfacial tensions for polymer melts under high pressure CO2 conditions, which correctly predicts the depression of interfacial tension by high pressure CO2 and yields reasonable agreement with experimental data. The role of CO2 in enhancing the polymer blending process was carried out based on the Capillary Number, which is the most important parameter governing the drop breakage and coalescence in the blending process and thus the morphology of the blends. A highly simplified population balance model was applied to calculate the morphology evolution by only considering the droplet breakup during the mixing. The calculated results agree with the experimental data relatively well. Based on the model, the effect of CO2 on the morphology evolution was also discussed.
|School:||The Ohio State University|
|School Location:||United States -- Ohio|
|Source:||DAI-B 79/09(E), Dissertation Abstracts International|
|Keywords:||Capillary number, Co2, Gradient theory, Interfacial tension, Pendant drop, Polymer processing|
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