(163al) Absorption and Diffusion in Bio-Based Polymer Films

Interest in polymers derived from biological sources has increased due to recent shocks to the supply and price of petroleum. Thin bio-based polymer films have been shown to have potential uses in a variety of applications, such as medical coatings, food packaging, and textile fibers. Interest has increased in such materials due to recent shocks to the supply and price of petroleum. In order to optimize their use, it is essential to understand how these films interact with their environment and how these interactions effect changes in the properties of these films. This study will present experimental measurements of moisture transport in two semi-crystalline bio-based polymers, polylactide (PLA) and poly (ethylene glycol) (PEG), obtained using a combined Quartz Crystal Microbalance and Heat Conduction Calorimeter (QCM/HCC) and Dynamic Vapor Sorption (DVS). The QCM measures changes in the frequency of an oscillating quartz crystal coated with a polymer film in order to calculate the amount of moisture absorbed into the film over time. The HCC uses the inverse Peltier effect to generate a measurable voltage correlated to the amount of heat flow in the film as a result of the absorption. Measurements of moisture sorption in PLA, a moderately hydrophobic polymer, versus relative humidity and temperature show that moisture sorption increases with degradation but is only weakly dependent on crystallinity. Experiments varying the composition of the end groups in PLA have shown that the moisture sorption is normally independent of whether the end groups are hydrophilic or hydrophobic. The QCM/HCC technique will be used to study moisture sorption in PEG, a hydrophilic polymer, and results will be shown comparing absorption enthalpies both above and below the melting temperature of the polymer. These measurements show the effect of changes in crystallinity during sorption/desorption on measured sorption enthalpies.