No abstract

The effect of friction on the wear of engineering polymers is a complex and intricate consequence of the micro-and macroscopic interactions of surfaces moving against one another. Friction and the resulting wear are not material properties of plastics; therefore, they cannot be reduced to tabular data of material characteristics that can be found in relevant manuals. Determining friction and the resulting wear involves more complex examination because they are characteristics of a frictional contact system where the effects of the entire system are manifest. Precise knowledge of system conditions is essential to evaluate the friction and resulting wear [1]. These materials have system-dependent tribological behaviour; thus, trends can be defined at a given condition, and the materials can be compared. The system approach is well-known from the literature [2, 199 An engineering approach to dry friction behaviour of numerous engineering plastics with respect to the mechanical properties G. Kalácska Abstract. Twenty-one different commercial-grade engineering polymers, including virgin and composite types, were selected for testing, based on mechanical engineering practices. Three groups were formed according to typical applications: 1) Sliding machine element materials; 2) Mechanically load-carrying machine element materials that are often subjected to friction and wear effects; and 3) Additional two amorphous materials used as chemically resistant materials that have rare sliding load properties. The friction running-in state was tested using a dynamic pin-on-plate test rig. During steady-state friction tests, two pv regimes (0.8 and 2 MPa"ms -1 ) were analysed by a pin-on-disc test system. Based on the measured forces on ground structural steel, surface friction coefficients were calculated and analysed with respect to the mechanical effects of friction. The friction results were evaluated by the measured mechanical properties: yield stress, Shore D hardness, Young's modulus and elongation at the break. The three material groups exhibited different trends in friction with respect to changing mechanical properties. Linear (with varying positive and negative slopes), logarithmic and exponential relationships were observed, and occasionally there were no effects observed. At steady-state friction, the elongation at the break had less effect on the friction coefficients. The dynamic sliding model, which correlates better to real machine element applications, showed that increasing hardness and yield stress decreases friction. During steady-state friction, an increase in pv regime often changed the sign of the linear relationship between the material property and the friction, which agrees with the frictional theory of polymer/steel sliding pairs.

A study is presented on cold plasma treatment of the surfaces of two engineering polymers, polyamide 6 (PA6) and polyoxymethylene (POM-C), by diffuse coplanar surface barrier discharges under atmospheric air conditions. We found that plasma treatment improved the adhesion of both polymers for either polymer/polymer or polymer/steel joints. However, the improved adhesion was selective for the investigated adhesive agents that were dissimilar for the two studied polymers. In addition, improvement was significantly higher for PA6 as compared to POM-C. The observed variation of the adhesion was discussed in terms of the changes in surface chemistry, wettability and topography of the polymer surface.

The surfaces of two engineering polymers including polyamide 66 (PA66) and polytetrafluoroethylene (PTFE) were treated by diffuse coplanar surface barrier discharges in atmospheric air. We found that plasma treatment improved the adhesion of PA66 for either polymer/polymer or polymer/steel joints, however, it was selective for the investigated adhesive agents. For PTFE the adhesion was unaltered for plasma treatment regardless the type of used adhesive. Tribological properties were slightly improved for PA66, too. Both the friction coefficient and wear decreased. Significant changes, again, could not be detected for PTFE. The occurred variation in the adhesion and tribology was discussed on the basis of the occurred changes in surface chemistry, wettability and topography of the polymer surface.

No abstract

No abstract

No abstract

After cold plasma treatment of poly(ethylene terephthalate) and poly(ether‐ether ketone) surfaces by dielectric barrier discharge (DBD) under atmospheric (air) conditions, variations in surface chemistry, and morphology were investigated in relation with adhesion and tribological properties. According to XPS measurements, surface oxidation caused the formation of low molecular weight moieties of carboxylic acids. The latter resulted in more hydrophilic surfaces according to water contact angle measurements, with mainly a higher polar surface energy component. In parallel, the surface roughness of originally polished surfaces reduced due to flattening of local surface asperities after DBD. The DBD significantly improved the adhesive shear strength for different glue types in polymer/polymer and polymer/steel joints, while the best adhesion was observed for a two‐component epoxy type adhesive. Under dry sliding conditions, the coefficients of friction were lower after DBD compared to pristine samples only under mild sliding conditions (v = 0.05 m/s; p < 1 MPa.m/s), while the higher normal loads caused an increase in coefficients of friction likely due to the higher contributions of surface deformation. Most interestingly, the lower coefficients of friction after DBD were observed under oil lubrication and after cleaning the sliding track (“run‐out” condition), due to the better retention of oil at the sliding surface for plasma‐treated polymers. POLYM. ENG. SCI., 58:E93–E103, 2018. © 2017 Society of Plastics Engineers