Diffusion Barriers

PTFE-laminated rubber diaphragms are increasingly being used for applications in the chemical, pharmaceutical and food industries. In most cases, the film coating is intended to protect the elastomer from chemical influences, but the physiological harmlessness of the fluoroplastic is also appreciated, especially in the food industry.
Despite the PTFE coating, aggressive media such as chlorine dioxide or solvents such as ethyl or butyl acetate can attack the elastomer back during pumping. The reason for this lies in the diffusion of the substances through the PTFE film, which is thin due to its flexibility. This occurs increasingly with small molecules that can easily migrate through the polymer matrix. As a result, the PTFE lamination separates from the elastomer backing, which drastically reduces the service life of the composite diaphragms and ultimately leads to diaphragm failure. However, the stress on the elastomer membrane caused by aggressive chemicals or chemical components diffused into the diaphragm harbours equally great risks with regard to the mechanical properties of the diaphragm and in particular the loss of resistance to bending cycles, which results in shorter service lives and higher failure probabilities.
In order to increase the service life of the diaphragms with an almost constant film thickness, the permeability of the PTFE film must be significantly reduced with regard to aggressive materials, especially for molecules with small diameters. The mechanical properties of the membranes must be preserved. Therefore, the construction of a diffusion barrier in the form of a coating or a surface modification of the PTFE membranes is considered, which at the same time, however, does not entail any restrictions of the mechanical component properties (flexibility, elasticity) as well as physiology (PTFE properties).