Gas Diffusion in Closed-Cell Foams

Abstract

The objective of this paper is to present an engineering model based on fundamentally sound but simplified treatment of mass diffusion phenomena for practical predictions of the effective diffusion coefficient of gases through closed-cell foams. A special attention was paid to stating all assumptions and simplifications that define the range of applicability of the proposed model. The model developed is based on the electrical circuit analogy, and on the first principles. The analysis suggests that the effective diffusion coefficient through the foam can be expressed as a product of the geometric factor and the gas diffusion coefficient through the foam membrane. Validation against experimental data available in the literature gives satisfactory results. Discrepancies between the model predictions and experimental data have been observed for gases with high solubility in the condensed phase for which Henry's law does not apply. Finally, further experimental data concerning both the foam morphology and the diffusion coefficient in the membrane are needed to fully validate the model.

Sample size effect on the effective diffusion coefficients for the gas contained in closed‐cell polyethylene‐based foam subjected to compressive creep tests

“…1,6,7 However an additional parameter, which might influence the gas diffusion, is sample size. Moreover, as far as we know, no set of data is available in the literature, but only marginal comments about the effect of sample size on the degassing behavior of closed-cell foams subjected to compressive static loading.…”

“…5,6 Hence, understanding and modeling the gas diffusion process in closed-cell foams is of great importance from both fundamental and practical viewpoints. 1 In the previous investigations, the prediction of gas diffusion through closed-cell foams is accomplished via two different types of models that use either discrete or continuous approaches. The continuous diffusion models consider the foams as an homogeneous and isotropic medium through which a gas species "i" diffuses with an effective diffusion coefficient D eff,i .…”

“…4,6 In addition, temperature has a significant influence on the diffusion. Gas diffusion through the solid phase is considered to be a thermally activated process 1 in which the temperature dependence is given by…”

“…The continuous diffusion models consider the foams as an homogeneous and isotropic medium through which a gas species "i" diffuses with an effective diffusion coefficient D eff,i . 1 The composition of each species in the foam is found from the analytical solution of the diffusion equation:…”

“…[1][2][3] In several applications, like structural or packaging, foams are frequently loaded for long periods of time, resulting in a time-dependent sample deformation that can seriously affect its properties. When closed-cell foams are compressed, the continuous deformation is caused by the polymer matrix creep and by the slowly outward diffusion of the gas contained in the cells.…”