The effects of temperatures and volumetric expansion on the diffusion of fluids through solid polymers

Abstract

This study examines moisture sorption behaviors of two glassy polymers, epoxy and vinylester, immersed in different fluids at two temperatures below the glass transition temperatures of the polymers. The main purpose of this study is to understand the effect of volume‐dependent temperatures and deformations on the diffusion process of solid polymers. Diffusivity coefficients are first determined by assuming the diffusion to follow the classical Fickian diffusion. In some cases, moisture sorption led to quite significant changes of volume, and the diffusion process cannot be well described by the Fickian diffusion. In such situation, the coupled deformation–diffusion model for linear elastic isotropic materials presented by Gurtin is adopted, as a first approximation. This coupled deformation‐diffusion model reduces to a Fickian diffusion model when the coupling parameters are absent and the volume changes in the solid polymers during diffusion are negligible. A finite difference method is used in order to solve for the coupled deformation‐diffusion model. The model is used to predict the one‐dimensional moisture diffusion in thin plates and the multiaxial three‐dimensional moisture diffusion in dogbone specimens. The multiaxial diffusion in the dogbone specimens is used to validate the calibrated material parameters from the standard thin plate diffusion characterization. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45151.

Diffusion of water in glass fiber reinforced polymer composites at different temperatures

“…However, it is also noticed that the maximum percent mass change (at saturation or at the end of the tests) is insensitive to temperature, which agrees with previous studies. 10,17 The maximum percent mass change is around 1.0% for both temperatures, and it can be seen that the maximum percent mass change in GFRP is less than that of neat epoxy squares (with the same resin/hardener and curing cycle) immersed in deionized water at the same conditioning temperatures and for the same time periods, as observed in the literature (the maximum mass changes for epoxy are $2.8% at room temperature and $2.1% at 50 C, as discussed by Fan et al 21 ).…”

“…With respect to results in the literature, the authors are not aware of similar studies on these materials in these particular conditions. For the Springer transverse diffusivity (equations (6a) and (6b)), the matrix diffusivity was obtained from immersion of the epoxy samples, as discussed in Fan et al 21 It should be noted that the present study is not on determining the temperaturedependent diffusivity of FRP composites. In fact, testing at two temperatures is not sufficient to address the temperature-dependent diffusion behaviors.…”

“…In order to improve the simulation results, the coupled deformationdiffusion model with a concentration-dependent diffusivity (D ¼ D 0 À C) is considered. 21 There are five material parameters that need to be obtained: the elastic modulus E, diffusivity D, coupling parameters , , and .…”

“…The next step is to determine the parameters D, a, and in order to capture the diffusion response. In this case, as the lateral diffusion is governed by the matrix diffusion, the resin diffusivity discussed in Fan et al 21 and the following material parameters are considered: D 0 ¼ 4:5 Â 10 À4 mm 2 h ¼ 1:25 Â 10 À7 mm 2 s , ¼ 3 Â 10 À4 mm 2 h ¼ 8:33 Â 10 À7 mm 2 s , ¼ 3 Â 10 À4 mm 2 h ¼ 8:33 Â 10 À7 mm 2 s . Figure 7 shows the response from the coupled deformation-diffusion model with concentration-dependent diffusivity.…”

“…The finite difference method was used to solve the coupled differential equations, which is discussed in Fan et al 21 The mass of the GFRP specimens was recorded during the experiments, allowing to extrapolate the concentration, defined as…”