Aramid fibers are more and more used as reinforcing material in both tires and mechanical rubber goods, such as hoses, belts, etc. In these dynamic rubber applications, optimal adhesion between fiber and rubber is essential. This can be achieved by activating the aramid chemically with an epoxy formulation, followed by RFL (Resorcinol-Formaldehyde Latex) treatment. In the current study fundamental knowledge about the chemical adhesion activation process of aramid has been used to investigate a potential alternative for the epoxy treatment: plasma treatment. It is shown that plasma treatment introduces oxygen-containing functional groups at the surface of aramid yarn, but not to such an extent as epoxy treatment. Moreover, only a limited portion of the oxygen-containing groups can be attributed to hydroxyl groups, which are the key in the adhesion mechanism to, e.g., RFL/rubber. This explains the lower adhesion of plasma-treated yarn in comparison to epoxy-treated yarn. In addition, plasma treatment leads to surface roughening. However, this does not lead to higher adhesion, since the adhesion (Fibre-RFL-Rubber) is dominated by chemical interactions. So based on this experiment, plasma treatment cannot yet replace chemical treatment. Further investigation of ways to increase the number of reactive groups on the surface by plasma treatment is worthwhile since the chemical modification of the aramid surface turns out to be rather persistent in time, which is one of the prerequisites for future industrial application of plasma technology. (C) Koninklijke Brill NV, Leiden, 2012