## 1 Introduction  
The wear resistance of polymers is a problem because their properties usually lead to severe and quick wear while in service. This fact has led to research regarding the possibility of improving this property by the addition of different discontinuous reinforcements such as short fibres and particles. Two different approaches are usually explored to reach this objective. On one hand, the improvement of the mechanical properties may allow an enhancement of the wear resistance, reducing some of the non-adhesive mechanisms of wear. For example, the addition of short glass/carbon fibres was proved as a good alternative under certain wear conditions [1, 2]. On the other hand, the use of particles that may act as solid lubricants may also be a good approach to improve the wear behaviour by creating films between the two counterparts during the test. For example, graphite can be used for this purpose [3, 4]. The lubricating properties of graphite have been extensively studied and scientifically demonstrated [5, 6, 7]. The reason for this behaviour may be a structure of C-C covalent bond sheets, which are joined together by weak Van der Waals forces. Carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) are also constituted by one or more of these C-C sheets and should have a lubricating effect. For this reason, graphene may be an emerging solid lubricant that reduces friction between contact surfaces. Furthermore, the tribological behaviour of graphene is better than graphite due to the intercalation of water molecules between carbon sheets, which facilitates movement and reduces friction. Previous studies have shown that the deposition of a layer from a solution of ethanol with a small amount of graphene on a steel surface reduces both friction and wear in humid air and dry nitrogen [8; 9]. The use of graphene and its derivatives as a reinforcement for polymer matrices has attracted a great interest because of their outstanding properties--not only mechanical but also electrical and thermal characteristics of the final nanocomposites--which have led to extensive research in electronic industry, protective coatings and electromechanical sensors, among others [10; 11; 12; 13; 14; 15]. Taking the good results of graphite reinforcement as the basis [16], the addition of graphene should lead to an improvement of the wear properties at lower concentrations. As the number of particles per mass unit is higher due to the extremely low thickness of these nanoparticles, its addition could allow the creation of a lubricant film at the beginning of the material wear, thus reducing the following abrasion. This effect is extended to other graphene related nanoparticles, such as graphene oxide sheets, functionalized graphene sheets and so on. Although the presence of experimental studies based on epoxy/graphene are scarce, some studies have already demonstrated the potential use of this material family (polymer-/graphene-based nanoparticles). The addition of graphene nanoplatelets to polytetrafluoroethylene (PTFE), one of the most widely used solid lubricants, reduces the steady state wear rate four orders of magnitude [17]. The addition of graphene oxide nanosheets in a concentration of 0.1 wt.% to 3 wt.% results in a large decrease in the wear rate of ultra-high molecular weight polyethylene (UHMWPE), which is a material used for implants for the hip and knee [18; 19]. Moreover, the addition of graphene to polymer matrices has an effect on two additional parameters commonly affecting the wear behaviour of polymers: Mechanical properties and temperature. The increase of the mechanical properties, mainly hardness and stiffness, due to the addition of graphene is not always achieved due to the formation of aggregates, weak interface interaction and poorer quality of the final material due to the increased difficulty of their processing conditions. Nevertheless, authors have reported increments in these properties when they totally or partially overcome these inconveniences [19; 20; 21; 22; 23].