Permeation of water vapor through high performance laminates for VIPs and physical characterization of sorption and diffusion phenomena

Abstract

Maintaining the long term performance of vacuum insulation panels (VIPs) remains the focus of many technical and scientific investigations. The performance of the barrier laminate is decisive to hold the vacuum level and to resist the permeation of water vapor. This barrier property against water vapor is characterized by the permeance of the laminate. The permeance of several commercially available products was determined by different methods and a good correlation was obtained between the manometric method on laminates and the current reference method on VIPs (weight gain in climatic chambers).Even if the permeance is appropriate to evaluate the performance of VIPs under stationary conditions, the solubility and diffusion coefficients are required for a fine-tuned service life prediction under real climatic loading conditions. Whereas for the PET the absorption isotherm is linear up to high humidity levels, this is not the case for the sealing layers, nor for the laminates. But this deviation from Henry's law does not impact the modeling of the behavior of current laminates because only the external PET layer is exposed to high humidity. The activation energies of sorption and diffusion have been evaluated. The experimental results on metalized and non metalized PET films confirm that the temperature dependence of the diffusion and of the permeance is driven by the behavior of the polymer.