PVC and Tygon Tubing – An Unlikely Introduction to Fick's Second Law of Diffusion

Monday, November 8, 2010: 8:40 AM
Grand Ballroom E (Salt Palace Convention Center)
Asima Chakravorty, Chemical and Life Science Engineering, Virginia Commonwealth University, Richmond, VA and Kenneth J. Wynne, Chemical and Life Science Engineering Department, Virginia Commonwealth University, Richmond, VA

Polymer or “soft” surface science offers rich and diverse opportunities for education, but often experiments may be quite complex or irrelevant to education in chemical engineering. Herein, we describe a laboratory experiment using a commonplace material, Tygon tubing, which is [poly(vinylchloride), PVC] plasticized with dioctylphthalate (DOP). A novel measurement of DOP diffusion coefficient has been developed using Attenuated Total Reflectance Infrared (ATR-IR) spectroscopy. The procedure involves quickly exposing sections of tubing to solvent for various time intervals. The area of the DOP carbonyl peak, which occurs in a PVC “IR window” is monitored vs. time. The peak areas are analyzed using Fick's second law of diffusion. The experiment can also offer an introduction to Differential Scanning Calorimetry (DSC), providing opportunities to study the concept of glass transition temperature and the role of plasticizers in polymers. The instructor may go cover related topics such as PVC production and processing and current concerns about human exposure to DOP. In terms of the minimal amount of materials utilized and the ready availability of ATR-IR spectroscopy and DSC, the experiment qualifies as “green chemical engineering education”.

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