Diffusion barrier layers

Diaphragms are often used as hermetic seals for media separation in moving systems. The fields of application are manifold and include pumps, compensators, valves, pressure transmitters, pressure accumulators, drives and more. The research project aims to evaluate new approaches for the generation of such diffusion barrier layers and, as a result, to provide evidence for a significantly reduced permeability of PTFE membranes or effective diffusion barrier especially for small molecules.

Today, PTFE-laminated rubber membranes are increasingly being used in the chemical, pharmaceutical and food industries. The film layer is usually intended to protect the elastomer from chemical influences, but the food industry in particular also appreciates the physiological safety of the fluoroplastic.
Despite the PTFE coating, the elastomer back can be attacked when aggressive media such as chlorine dioxide or solvents such as ethyl or butyl acetate are pumped. The reason for this is 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 detaches from the elastomer backing, drastically limiting the service life of the composite diaphragms and ultimately leading to diaphragm failure. However, exposure of elastomeric diaphragms to diffused, aggressive chemicals or chemical components poses equally high risks with regard to mechanical diaphragm properties and, in particular, loss of flexural fatigue resistance, resulting in shortened service lives and higher probabilities of failure.In order to increase the service life of the membranes with almost constant film thickness, the permeability of the PTFE film with respect to aggressive materials, especially for molecules with small diameters, must be significantly reduced. The mechanical properties of the membranes must be maintained at the same time. Therefore, the construction of a diffusion barrier in the form of a coating or a surface modification of the PTFE membranes is being considered, which, however, at the same time does not entail any restrictions of the mechanical component properties (flexibility, elasticity) as well as physiology (PTFE properties).