Monday, 1 March 2021

Design Properties for Engineers – Tribological Properties of High Performance Polymers

 In this blog post, we discuss the tribological properties of high performance polymers and what to consider when selecting materials for sliding applications.

In tribology, the friction coefficient µ plays an important role. It is the resistance of two different surfaces to each other. Also, wearing of the surfaces is of interest. It is measured in µm/km. Tribological properties of plastics are described with the friction coefficient (µ) and wear (µm/km).

Friction properties of high performance polymers

In Figure 1, the friction properties of selected high performance polymers are shown. PTFE has a very low dynamic coefficient of friction compared to other high performance polymers. If you consider the wear too (Figure 2), it can be seen that PTFE has a high wear factor due to its low mechanical strength.

Figure 1: Coefficient of friction of different high performance polymers

Figure 2: Wear of different high performance polymers


Polyimides (PI, PAI, PBI) have low wear properties, combined with a low coefficient of friction of 0.4. It is beneficial to select materials in sliding applications which have a low wear rate together with a low coefficient of friction.

Optimization of tribological properties is done by using additives such as graphite, carbon fibers, molybdenum sulfide, and carbon nanotubes. However, certain additives can reduce the mechanical strength of the base resin (up to 50% reduction).

Conclusion

Friction and wear properties should be evaluated as good as possible on the life part. Among the high performance polymers, polyimides (PI, PAI, PBI) have overall good tribological properties due to their high resistance molecular structure. Using additives can help to reduce the wear of the material and improvement of friction coefficient is limited. 

Thank you for reading and #findoutaboutplastics

Best regards,

Herwig Juster

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Literature

[1] Saechtling Kunststoff Taschenbuch 

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