Static Electrification of Plastics under Friction: The Position of Engineering-Grade Polyethylene Terephthalate in the Triboelectric Series

There is an emerging trend to replace moving metallic parts, such as bearings or bushes, with plastic components. The electrostatic hazard associated with plastic components subject to mechanical friction is well documented, but the magnitude as well as physical–chemical origin of this phenomenon remains debated. Using atomic force microscopy and Faraday pail measurements, the triboelectrification of Ertalyte®, a commonly used bearing-grade formulation of polyethylene terephthalate, when rubbed against other polymers and metals, is studied. The sign and magnitude of the net charge that Ertalyte® gains in relation to the chemical nature—electron affinity and ionization energy—of the contacting material are analyzed, concluding that this material should be located toward the negative end of the triboelectric series. It is also shown that large charge densities and fast charge decays result from contact of Ertalyte® with polymers of a small Derjaguin–Muller–Toporov (DMT) modulus and unstable ions, suggesting that ion transfer leads to the electrification of a dynamic insulator/insulator contact. These findings have immediate implications in the choice of the material used to manufacture plastic parts subject to friction and wear and to help address ongoing fundamental questions over the nature of the charge carriers that leads to static electricity.