Water sorption of plasticized denture acrylic lining materials

The objective was to characterize water sorption of plasticized denture acrylic lining materials, with determination both of uptake and diffusion coefficient (D). Feasibility was investigated first for simple binary mixtures of poly(methyl methacrylate), PMMA, and various phthalate plasticizers prepared by radiation polymerization of methyl methacrylate/plasticizer solutions. These were shown to be tractable when samples were saturated with water and then characterized in desorption measurements. Plasticizers were found to decrease the uptake of water. This decrease was attributed to the hydrophobic nature of the plasticizers and also to their ability to fill microvoids in PMMA which, in their absence, would be available to water. Values of D increased monotonically with increasing volume fractions of plasticizer. It appeared that values of D increased more rapidly in cases where large proportions of plasticizer resulted in samples which were above their glass transition temperature, Tg, at the temperature of testing water sorption. Desorption measurements were extended satisfactorily to a model system made from poly(ethyl methacrylate) powder, methyl methacrylate, and dibutyl phthalate, which was polymerized with a conventional redox initiator. Water desorption results were compared with various proprietary materials which were also characterized with respect to Tg and, cursorily, to composition.