Dynamic mechanical analysis and water sorption of some experimental elastomeric soft lining materials

Abstract

This research was undertaken to develop a better understanding of the relationships among the compositions, structures and properties of denture soft liners. Five butadiene-styrene-acrylic elastomers were prepared. They were prepared using 50% of powdered prepolymerized butadiene-styrene polymer combined with 50% of a methacrylate monomer (HMA or EHMA) plus varying amounts of initiator and crosslinker. The mixtures were gelled and processed conventionally. Specimens were then committed to dynamic mechanical analysis and water sorption. Dynamic mechanical analysis was performed over the temperature range 5–95°C at the rate of 2.5°C/min using a Perkin Elmer DMA-7 with 3 mm flat tip probe at 1 Hz. Wet and dry values for storage modulus (E') and damping factor (tan δ) were determined at 37°C. Water sorption of these butadiene styrene elastomer-acrylic systems from solutions of varying concentrations was measured in order to establish the role 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 and glucose may be interpreted as related to reduced water sorption from these solutions. Increasing crosslinking increased the modulus and decreased 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 experimental materials, water uptake from saline and glucose solutions confirmed that the diffusion process is osmotically driven.