Biodegradable Packaging for Corrosion Inhibition Via Supercritical Fluid
Supercritical carbon dioxide has been used in a wide variety of material processing applications, such as low-temperature blending, polymer grafting, reaction medium for polymerization, and diffusive drying, in addition to the most broadly used supercritical fluid extraction. The popularity of carbon dioxide as a supercritical fluid of choice mainly stems from its low critical temperature (31.4°C), moderate critical pressure (7.38 MPa), nontoxicity, low-cost availability, and good compatibility with a variety of other fluids and macromolecular substances. The unique properties of supercritical carbon dioxide (SC-CO2) make it an ideal medium to perform a number of applications. Supercritical fluid has a liquid-like density yet maintains gas-like properties for viscosity, diffusivity, and surface tension. Furthermore, supercritical carbon dioxide has high solvent strength and is capable of softening and swelling polymeric materials by effectively lowering the material's softening point. Therefore, supercritical carbon dioxide can be ideally used to infuse a volatile or temperature-sensitive material into a polymeric matrix without going through high-temperature melt processing. In this study, supercritical carbon dioxide is used to infuse Ecoflex® resin, a biodegradable aliphatic-aromatic copolyester, with sodium nitrite (NaNO2), which is a common volatile corrosion inhibitor (VCI). The effects of temperature, pressure, amount of VCI, and, time in the reactor were first studied. Next, the effects of fluid density on the infusion depth were investigated. Finally, the corrosion protection ability of VCI-infused biodegradable polymer was compared to VCI-infused low-density polyethylene (LDPE). Infusion using supercritical fluid is an attractive alternative to traditional melt blending methods which are often used to manufacture VCI-infused polymeric products. Melt processing methods often result in decreased polymer molecular weight, particle agglomeration, and excess moisture retention. A 2^4-1 partial factorial design of experiments was designed as a guide for the set of infusion experiments. The infusion penetration depth and color change were used as a basis to determine degree of infusion. These experiments indicate that the most significant variable was the processing temperature. The results also indicate that reactor pressure and duration play a significant role; however the amount of NaNO2 was not found to be a significant factor. After the samples were infused, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were performed to determine if any changes in the melting temperature and degradation temperature occurred. The melting temperature of the infused samples changed by 4°C, while there was little change in the onset of the degradation temperature. The findings indicate that the effects of fluid density are minimal and overshadowed by the effects of temperature. The scanning electron microscopy (SEM) results also indicate that the average particle size of the infused crystalline salts is by an order of magnitude smaller than that of the original powder. The ability of the VCI-infused packages to protect the samples was demonstrated in both the biodegradable packaging as well as the nonbiodegradable samples. These findings not only demonstrate the infusion capability of a supercritical carbon dioxide system, but also help elucidate the effects of processing conditions on the final products and infusion quality. Additionally, the corrosion protection ability of the infused films was verified. This study further validates potential development of specialty films with multiple functionalities that are, in most typical situations, mutually exclusive, i.e. biodegradability and corrosion prevention.
L. A. Leavitt and S. Lee, "Biodegradable Packaging for Corrosion Inhibition Via Supercritical Fluid," Proceedings of the AIChE Annual Meeting, American Institute of Chemical Engineers (AIChE), Nov 2007.
AIChE Annual Meeting
Chemical and Biochemical Engineering
Article - Conference proceedings
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