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13. June 2019

Gas permeation behavior of thermoplastic vulcanizates (TPV) and ethylene-propylene-diene rubber (EPDM) under consideration of processing influences

For sealing materials in contact with gases such as hydrogen, a consideration of gas permeability is of elementary importance for the assessment of safety, functionality and reliability. The aim of the presented study is to give an overview of the permeation behavior of thermoplastic vulcanizates (TPV) and ethylene-propylenediene rubber (EPDM) towards hydrogen under consideration of processing influences. A comparison of TPV and EPDM shows a differentiated permeation behavior.

Permeation process

Permeation process

Gas permeation behavior of thermoplastic vulcanizates (TPV) and ethylene-propylene-diene rubber (EPDM) under consideration of processing influences
Hopmann, M. Drach, N. Yesildag, S. Gharbi, S. Sitz
RFP Rubber Fibres Plastics 02|2019

With the increasing development of new drive technologies, new demands on sealing materials come forward. In addition to changing temperature profiles and requirements for chemical resistance to new media, the focus has shifted to the behaviour towards gaseous media. An obvious requirement is the material behaviour in contact with hydrogen. From the point of view of sealing technology, this is relevant for various reasons, e.g. safety aspects. The development of fuel cell technology has repeatedly attracted the attention of industry in recent years. Thus, the following investigations are focusing on the permeation behaviour of hydrogen in various polymer-based sealing materials as well. In addition, permeation behaviour plays a major role for other drive technologies. For example, an understanding of the fundamental correlations is also relevant for battery media, gas-powered engines or drive technologies using e-fuels. A substantial need for further research can be identified here.

EPDM as a classic sealing material is frequently used in vehicles in various parts. The main areas of application are seals, bellows, cooling water hoses and automotive sealing profiles, and windshield wiper blades. Due to the combination of media resistance, temperature and ageing resistance and, last but not least, a favourable price, EPDM was selected as the material for the following investigations.

The thermoplastic elastomers selected as comparison material are multi-phase systems consisting of a thermoplastic hard phase and an elastomer soft phase. Depending on their structure, TPE materials are divided into block copolymers and blends. The hard and soft phases are present in the same molecule in the form of molecular segments (block copolymers) or a heterogeneous phase distribution of elastomers and thermoplastics (polymer blends).

The investigations show that EPDM has a lower gas permeability than TPV. Depending on their material composition, TPV materials show a different permeation behaviour towards hydrogen. Further investigations are necessary at this point: For example, it would be interesting to see how elevated temperatures influence gas permeation of TPEs in general or TPV specifically. Other material classes, in particular TPU, are also interesting with regard to their permeation behaviour, even if these materials may have disadvantageous properties concerning media and temperature resistance.

With regard to processing, no significant influence was found in the tests carried out. Weak points that have been introduced deliberately, such as weld lines, can obviously be compensated in the injection molding process in such a way that the gas permeability does not change in a detectable way. In the case of elastomers, a low infl uence of processing can be detected. The gas permeation behaviour is very strongly dependent on the base polymer, while the material composition, meaning fillers and other components, can influence the permeation only to a limited extent. Processing probably only plays a minor role, but this is still to be confirmed.

Citation:
Hopmann, M. Drach, N. Yesildag, S. Gharbi, S. Sitz, RFP Rubber Fibres Plastics, 02|2019, 104-109

https://www.gupta-verlag.com/magazines/rfp-rubber-fibres-plastics-international/02-2019

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