Ionic liquids as plasticizers: Material properties, thermodynamic parameters, cytotoxicity and mammalian toxicological studies

Ionic Liquids (ILs) were tested as plasticizers for polyvinyl chloride) or PVC. Thermodynamic parameters including the solubility parameter, the components of Hansen solubility parameters (HSPs) and the Flory-Huggins interaction parameter in polymer-plasticizer systems were investigated as predictors of compatibility. ILs were particularly difficult to analyze because experimental data (such as vapor pressure, heat of vaporization) could not be obtained. The ionic nature of ILs, in combination with several less common elements and functional groups that constitute ILs, made theoretical calculation challenging. Comparison between traditional plasticizers and ILs were used to evaluate the validity of the thermodynamic analysis. The HSPs were found to be the most accurate method in predicting compatibility between polymers and plasticizers. The predicted compatibility compared favorably to experimental observations on plasticized PVC and few other polymers.; Challenges in developing new plasticizers include improving high temperature stability and minimizing leaching of plasticizers into aqueous solutions, particularly from plasticized polymers used in children's chewable toys and medical plastics. Using FT/IR analysis, the thermal degradation of two IL-plasticized PVC samples was attributed to the chloride-based impurities present in those ILs. Leaching of ILs from plasticized PVC samples in saline solution was found to depend on the hydrophilicity of their components. Apart from some of the commonly observed leaching phenomena, disproportionate leaching of anions and cations was observed, which led to segregation and therefore phase separation of the ILs. However, further analysis is required to confirm the observed trend.; Toxicological effects of the ILs were determined using Drosophila melanogaster S2 cell culture and mice. Cytotoxicity of ILs was found to depend on their anions, cations, alkyl chain lengths in cations, aqueous solubilities, concentrations and exposure times to the cell culture. Dietary feeding of a phosphonium-based bis(trifluoromethane) sulfonylimide IL to mice at up to 50,000 mg/kg concentration was found not to cause any adverse, long term effect as part of mammalian toxicological studies. Based on these observations and the thermodynamic model developed for IL-polymer systems, novel ILs can be designed for diverse polymeric applications including the much needed benign plasticizing actions in medical plastics, children's chewable toys and food-packaging applications.