## 1 Introduction  
Carbon textiles consist of thousands of bundled carbon fibres. Before carbon fibres are combined into bundles, their surface needs to be electrochemically activated (by anodic oxidation in an electrolytic solution). Each fibre is then coated by a mixture of various chemicals (sizing) to protect it from mechanical damage during production handling and improve its wetting performance [1; 2; 3]. Furthermore sizing leads to an increased chemical reactive site as well as enhanced adhesion between carbon and impregnation material [4; 5]. After single carbon fibres are bundled together, the so-called carbon roving is again impregnated to improve adhesion and handling for further application. Usually, epoxy resin or styrene-butadiene rubber (SBR) based polymers are used for impregnation. The thesis of Wetjen [6] gives an overview of the production and processing of carbon. The following statements are based on this source, unless otherwise indicated. The carbon rovings usually consist of thousands of individual combined carbon fibres, which are also called filaments and have an average thickness of 5-7 microns. Carbon fibres consist of 92% by weight of carbon. They can be produced chemically from different polymers, the most common being the production from polyacrylonitrile (PAN), since the highest strengths with high carbon yield can be achieved at comparatively low price. Graphite consists of hexagonal layers in which each carbon atom is connected to three other carbon atoms with a strong covalent bond. The individual layers are connected only by relatively weak London forces, whereby the distance of the layers in relation to the distance of the carbon atoms in the hexagons is large and the direction-dependent conductivity of graphite can be explained [6]. Compared to graphite, carbon fibres have a turbostratic structure that results from random spinning, folding, splitting, canting, branching and concatenation of the lattice structure in the manufacturing process. This inhomogeneity explains both the increased strength between the basal planes and the increased reactivity of the carbon fibre surface in comparison. In addition, the structural inhomogeneity increases the spacing between the lattice planes. After production of the carbon fibre, surface activation of the carbon fibre follows, typically by electrochemical anodic oxidation in an electrolyte. The amount and type of functional groups formed on the surface depends inter alia on the duration of polarization, the electrolyte and the electrical potential. The surface activation is done to obtain a good wettability of the carbon fibre over a later applied sizing or other impregnating materials by a higher proportion of polar functional groups [6]. Poltavtseva et al. [7] have described the formation of surface oxides in carbons by summarizing relevant literature. The formation of surface oxides is complex because it is not possible to separate the different reactions from each other. It depends on the pH, electrode potential, pressure, temperature and humidity as well as the physical and chemical properties of the carbon compounds. Thus, a different dissolution process results for different carbon-based materials, since materials such as carbon black, graphite and carbon fibres differ in the size and orientation of the graphitic crystalline layers. Pure graphite consists of hexagonal layers as described above. While graphite has many surface defects, carbon fibres without activation have a high degree of longitudinal orientation with fewer defects. Without these lattice defects, the graphitic crystalline layers behave inertly. The existing lattice defects, pores and edges provide for free valences, which are already functionalized under normal conditions to form surface oxides. Anodic polarization causes the dissolution of water and the generation of further oxygen-containing functional groups on the surface. First, hydroxyl ions are discharged to hydroxyl radicals by the electrolysis of water according to Equations (1) and (2).