DYNAMIC-MECHANICAL ANALYSIS AND WATER SORPTION OF SOME EXPERIMENTAL ELASTOMERIC SOFT LINING MATERIALS

This research was undertaken to develop a better understanding of the relationships among the compositions, structures and properties of den ture soft liners. Five butadiene-styrene-acrylic elastomers were prepa red. They were prepared using 50% of powdered prepolymerized butadiene -styrene polymer combined with 50% of a methacrylate monomer (HMA or E HMA) plus varying amounts of initiator and crosslinker. The mixtures w ere gelled a nd precessed conventionally. Specimens were then committe d to dynamic mechanical analysis and water sorption. Dynamic mechanica l analysis was performed over the temperature range 5-95 degrees C at the rate of 2.5 degrees C/min using a Perkin Elmer DMA-7 with 3 mm fla t tip probe at 1 Hz. Wet and dry values for storage modulus (E') and d amping factor (tan delta) were determined at 37 degrees C. Water sorpt ion of these butadiene styrene elastomer-acrylic systems from solution s of varying concentrations was measured in order to establish the rol e of osmotic pressure. Diffusion coefficient (D-d) was determined from the desorption values. The relatively lower values of D-d observed in most highly concentrated solutions particularly 1 M sodium chloride a nd glucose may be interpreted as related to reduced water sorption fro m these solutions. Increasing crosslinking increased the modulus and d ecreased water sorption. Using hydrophobic EHMA instead of HMA reduced water uptake, reduced dry modulus and reduced the decrease in modulus caused by water sorption. Dynamic moduli and water sorption generally exceeded those of the commercial materials studied. For all experimen tal materials, water uptake from saline and glucose solutions confirme d that the diffusion process is osmotically driven.