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20. February 2020

Methods for simultaneous dynamic-mechanical and dielectric analysis – Part 1: Dielectric investigation of elastomer composites under static deformation

Electrically conductive fillers can be used as “markers” for condition monitoring of elastomer components, provided the exact correlation between the mechanical and dielectric properties of the material is known. Part 1 of a series of three articles on simultaneous dynamic-mechanical and dielectric analysis, deals with the influence of a defined static mechanical deformation on the dielectric spectra of a carbon black-filled HNBR.

Sample and appropriate sample holders for dielectric measurements. (Source: Netzsch)

Sample and appropriate sample holders for dielectric measurements. (Source: Netzsch)

S. Aloui, W. Wurpts, H. Deckmann

Elastomeric materials are used in technical applications, among other things, as seals or vibration dampers. The desired property profile can be realized by a variety of design options. In addition to the selection of suitable polymers and additives required for processing, the filler used plays a crucial role in determining the desired properties. In practice, the finished end product has different application-related requirements for the stiffness, compressive strength, thermal and chemical resistance of the material. Depending on the installation and/or environmental conditions, creep and relaxation processes lead to premature mechanical and/or chemical aging and premature wear of the technical elastomers. Thus, a general reliable statement about aging processes is not possible.

Elastomeric materials are usually reinforced with electrically conductive fillers such as carbon black. The carbon black structures present in the “virgin” rubber matrix change under mechanical deformation. Due to mechanical damage of the carbon black network, the dielectric conductivity changes accordingly. It becomes deformation-dependent. In this context a so called “marker”, which continuously monitors and “reports” the mechanical state of the assembled elements would be ideal. In carbon black-filled elastomeric materials, the carbon black could be used as a “marker” for a characteristic “snapshot”. What is missing so far is a measuring method that uses the “voluntarily marker” provided by the material system to read its mechanical state. Dielectric analysis is a measuring method suitable for this state detection. In order to use it for this purpose, knowledge of the exact correlation between the mechanical and dielectric properties of the final product is necessary. When the relationship between the mechanical state and the “snapshot” dielectric spectrum of the material is known, inexpensive and long-lived dielectric sensors can be used.

It is the simultaneous analysis of the dynamic- mechanical and dielectric properties that ensures the required information. The key to understanding the correlation is thus the use of a simultaneous dynamic-mechanical and dielectric analysis. The work presented in this article deals with the defined mechanical deformation of elastomeric materials based on carbon black-filled hydrogenated acrylonitrile-butadiene rubber (HNBR) and the affected dielectric spectra. For these investigations, a Diplexor 500 N from Netzsch was used.

S. Aloui, W. Wurpts, H. Deckmann, RFP Rubber Fibres Plastics, 01 2020, 26-31.


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