Abstract
Polytetrafluoroethylene (PTFE) powder is used as a solid lubricant in commercial antifriction coatings. However, most of the matrix polymers are usually not compatible with virgin PTFE resulting in low dispersion and mechanical film stability and adhesion. In our research PTFE TF 2025 was irradiated by g-beam generating PTFE micropowder with persistant radicals and functional groups. These functional groups are able to perform a chemical grafting (cg) of polyamideimide (PAI) and modified PTFE-micropowder by reactive extrusion in melt. Based on grinded extrudates PAI-PTFE-cg dispersions were formulated followed by characterizing dispersion as well as film properties. It was found, that PAI-PTFE-cg dispersion comprises very small PTFE-particles at higher g-irradiation doses in homogeneous dispersions. In addition, all samples showed outstanding film flexibility. Basic tribological properties under mixed lubrication were studied by using a ring-on-disk tribometer. Finally, diluted dispersions were applied to a multi-surface sliding bearing (four segments) for testing in a hydrodynamic plain test bench.
Highlights
It is well known that polytetrafluoroethylene (PTFE) and polyamideimide (PAI) exhibit outstanding properties
Polytetrafluoroethylene (PTFE) powder is used as a solid lubricant in commercial antifriction coatings
In our research PTFE TF 2025 was irradiated by γ-beam generating PTFE micropowder with persistant radicals and functional groups
Summary
It is well known that polytetrafluoroethylene (PTFE) and polyamideimide (PAI) exhibit outstanding properties. The high temperature stability of both polymers makes them interesting for high performance applications in several areas. Because of its very low coefficient of friction PTFE, depending on the used amounts, acts as a solid lubricant and is able to enhance the antifriction properties of the PAI film on top of a substrate. Without adding any dispersion stabilizer the PTFE particles tend to agglomerate during the storage of the dispersion or during the curing procedure very fast. Bigger PTFE-particles or agglomerates so can result in “breaking points” under mechanical load reducing the total film flexibility and wear resistivity at the end. Subject of the paper is the use of chemically grafted (cg) PAI-PTFE for the formulation of sliding lacquer dispersions, their application to steel blanks followed by a characterization of coating properties and their tribological behavior
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