Effect of accelerated aging on the viscoelastic properties of a medical grade silicone

Abstract

The viscoelastic properties of cylinders (diameter 5 mm, height 2.2 ± 0.2 mm) of Nagor silicone elastomer of medium hardness, were investigated before and after the specimens had undergone accelerated aging in saline solution at 70°C for 38, 76 and 114 days (to simulate aging at 37°C, for 1, 2 and 3 years, respectively). All sets of specimens were immersed in physiological saline solution at 37°C during testing and the properties were measured using dynamic mechanical analysis (DMA). A sinusoidal cyclic compression of 40 N ± 5 N was applied over a frequency range, f, of 0.02–25 Hz. Values of the storage, $E^{'}$ , and loss, $E^{″}$ , moduli were found to depend on f; the dependence of $E^{'}$ or $E^{″}$ on the logarithm (base 10) of f was represented by a second-order polynomial. After accelerated aging, the $E^{'}$ and $E^{″}$ values did not increase significantly ( $p < 0.05$ ). Furthermore, scanning electron microscopy (SEM) showed that accelerated aging did not affect the surface morphology of silicone. Attenuated total reflectance Fourier transform infra-red spectroscopy (ATR-FTIR) showed that accelerated aging had a negligible effect on the surface chemical structures of the material. Differential scanning calorimetry (DSC) showed no changes to the bulk properties of silicone, following accelerated aging.

Keywords

Accelerated aging compression dynamic mechanical analysis (DMA)silicone viscoelasticity

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