Mass Transfer of Near Critical Carbon Dioxide in Poly(Methyl Methacrylate)
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Publisher:The Ohio State University
Series/Report no.:The Ohio State University. Department of Chemical and Biomolecular Engineering Honors Theses; 2007
Supercritical carbon dioxide has gained popularity in recent decades in a wide variety of fields. From Supercritical Fluid Extraction (SFE) to ‘Green Chemistry’, supercritical carbon dioxide has been shown to be a non-toxic, non-flammable, and inexpensive alternative to traditional hazardous or undesirable chemicals. One of the most promising applications of supercritical carbon dioxide is in polymer processing. Although there has been much research on carbon dioxide polymer processing, one commonly overlooked characteristic has been the effect carbon dioxide at its critical temperature (30.98oC) and pressure (7.38 MPa) on polymer matrixes. This tends to be hard to characterize because of the inherent high variability at the critical point. However, recent research has shown that polymers display ‘anomalous’ behavior at this point that may be useful for polymer processing. This study helps to try to characterize this ‘anomalous’ behavior by measuring the carbon dioxide solubility and diffusivity near its critical point. Samples of Poly(methyl methacrylate) (PMMA) were exposed to carbon dioxide at various conditions between 30oC to 70oC and 548 psia to 1520 psia. The solubility was extrapolated from sample desorption using the Gravimetric Mass Balance method. The diffusivity coefficient was calculated from a time-dependent sorption curve. Solubility and diffusivity measurements matched well with data from the literature. Although no ‘anomalous’ behavior was observed around the critical point, solubility information suggested that there was a distinct change in carbon dioxide and PMMA interactions. Furthermore, setting polymer processing conditions at the critical temperature and pressure of carbon dioxide appears to give an optimum amount of dissolved carbon dioxide for the lowest temperature and pressure. Additional research should be conducted to see whether this ‘anomalous’ behavior is distinguishable for a wider range of diffusivities or for thinner polymer films.
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