Outgassing rates of PEEK, Kapton® and Vespel® foils

The outgassing rates of PEEK, Vespel® and Kapton® foils as a function of time and thickness have been studied through a series of pump-down tests. Samples of at least five different thicknesses for each material, exposed to normal levels of moisture in the air (30-65% R.H.), were pumped in a dedicated setup. The pump down curves were fitted with a Fickian diffusion model. A discrepancy between the model and the experimental results was observed for extended pump down time. A new empirical model was proposed and applied with excellent results. The discrepancy could be due to micro-voids in the vitreous parts of the polymers as described by the dual model.