Volume 39, Issue 4 (July 2011)
Comparative Evaluation of the Moisture Permeation of Polyurethane, Polyethylene, and Fluoropolymer Tubing
Polymer tubing is used for a variety of applications such as the transport of dry nitrogen and other gases in order to purge systems of moisture and other contaminants. While some polymer tubing are marketed for low-moisture applications, permeation data are often not reported to aid in material selection. Tests were performed to compare moisture permeation for a variety of tubing materials that could be used in dry gas purged systems. The results demonstrated that polyethylene and fluoropolymer tubing exhibited practically no moisture permeation, while polyurethane tubing exhibited a noticeable amount of moisture permeation. The results were compared with the moisture permeation of thin films. The permeation was found to be influenced by many factors as dictated by the various results derived from different brands and different durometers within the same brand. The effect of external relative humidity on permeation was also measured. Approximations can also be made on the internal relative humidity based on the external relative humidity. These approximations can be used as well to determine the maximum possible moisture exposure level outside the tubing or the purge time required for a specific application. The results could assist in material selection based on the desired application.