Characterization and Tribological Behaviour of Siloxane-based Plasma Coatings on HNBR Rubber

A cold atmospheric pressure plasma jet (PlasmaSpot) was developed in our department and was successfully used to deposit siloxane‐based coatings on elastomer materials for tribological improvement. This paper reports on the deposition of a low‐friction atmospheric plasma coating on an HNBR sample using (3‐aminopropyl)triethoxysilane (APEO) as precursor. The chemical structure of the coating was examined with XPS and FTIR spectroscopy. Monitoring the top surface of the coating by optical microscopy showed 2–3 µm wide cracks appearing in the coating some days after deposition. Furthermore, a migration of waxes was seen from the bulk rubber through the cracks. The chemical nature of these products was revealed by FTIR analysis. Although these waxes act as lubricant and are added to the rubber for better processability, a tribological evaluation in a ball‐on‐disc test rig revealed that they did not contribute to the lower friction coefficient. A significant decrease of the friction coefficient was measured for the plasma coated HNBR sample compared to the untreated HNBR sample. The PlasmaSpot is used to deposit siloxane‐based plasma coatings on HNBR to improve the tribological behaviour of the rubber. Cracks are noticed in the coating through which waxes from the rubber recipe migrated to the surface. Although these can act as lubricants, the tribological improvement is attributed only to the siloxane plasma coating.