Polytetrafluoroethylene (PTFE) is characterized by outstanding non-stick properties and very low friction coefficients under tribological load. However, PTFE is incompatible with almost all other polymers exhibits cold flow and a low wear resistivity. However, PTFE can be modified e.g. in the presence of air by using high-energy radiation to achieve carboxylic acid fluorid- (-COF), carboxyl- (-COOH) functional groups and persistent perfluoroalkyl (peroxy) radicals. The hydrophilic functional groups of radiation-modified PTFE can be used to generate a chemically covalent coupling with other monomers/polymers (e.g. polyamides) via addition reactions. Another approach to get a chemical bonding of modified PTFE is the use of radicals for the covalent attachment of olefinic groups (e.g. in oils) through radical reactions. It is already known that the dispersion of modified PTFE in synthetic oils at elevated temperatures results in very stable PTFE-oil dispersions, which have improved tribological properties and are compatible with metals.The aim of this study is the development of novel tribologically effective materials based on radiation-modified PTFE, oil and polyamide 66 (PA66). In the first synthesis step, a chemical coupling between selected oils and various types of PTFE was performed. The bonding was proved by fourier-transform infrared spectroscopy (FTIR) after removing oil excess and further extraction of insoluble residue. Additional electron spin resonance measurements (ESR) showed that the linkages mainly resulted from radical reactions. The second processing step was the chemical coupling of PA66 and oil-modified PTFE by reactive extrusion. In order to get an idea about the influence of the chemical bonding of both lubricants with the polymer matrix on the mechanical material properties compared to origin PA66, multipurpose test specimens according to ISO 3167 were prepared by injection molding. It was found, that even bigger amounts of bonded lubricants did not deteriorate the mechanical characteristics in a significant manner. Finally, initial tribological testing of the novel materials was carried out by using a block on ring tribometer test set up. The antifriction and wear behaviour, as well as the transfer film thickness, were analyzed subsequently.
In this research, the novel materials based on polyamide (PA), polytetrafluoroethylene (PTFE), and olefinic oil molecules are produced as a solid lubricant in metal‐plastic sliding contacts or sacrificial elements in metal–metal sliding contacts. For these applications, high durability of the compound material combined with low wear is required for long‐term use under high friction and mechanical loads. Earlier studies of IPF have shown that chemical bonding between the polymer matrix and the solid lubricant is mandatory to meet these requirements. For this purpose, the compounds are fabricated by a novel two‐step reactive processing procedure based on radiation‐modified PTFE, which exhibits reactive‐functional groups (COOH) and persistent perfluoroalkyl‐(peroxy)‐radicals (COO·). The PA‐PTFE‐oil‐cb compound materials (cb: chemically bonded) are analyzed by differential scanning calorimetry (DSC) concerning breaking down behavior and Fourier‐transform infrared spectroscopy with regards to the chemical covalent bonding state between the three components. Results of scanning electron microscopy investigations in correlation with DSC show that chemical bonding between PA and PTFE‐oil‐cb leads to a homogeneous distribution of solid lubricant particles in the three various PA matrices. Due to the chemical coupling, the compounds offer almost comparable or improved mechanical properties in the case of toughness compared to non‐modified PA.
Polyamide (PA), polytetrafluoroethylene (PTFE), and olefinic oils are incompatible. High‐energy radiation in the presence of oxygen can break the PTFE chain, generating hydrophilic functional groups (COF, COOH) and peroxy‐radicals. Based on the functional groups and radicals, it is possible to establish a chemical bond between PA and PTFE as well as between PTFE and olefinic oil molecules. This study prepared PA‐PTFE‐oil‐cb compounds (cb: chemically bonded) by reactive extrusion. The compounds wetting behavior are analyzed by contact angle measurement. Additionally, the sliding properties of the compound are investigated by micro friction testing against stainless steel. Due to good fragmentation and dispersion of PTFE in PA12 matrix, the PA12‐MP1100‐cb and PA12‐MP1100‐MO‐cb compounds show a slight change in wetting behavior compared to virgin PA12. In contrast, the wetting behavior of compounds based on PA46 increases dramatically compared to virgin PA46. Moreover, due to the chemical bonding, the PA‐PTFE‐cb compound surface is significantly smoother than a physical blend used as a model compound. Similarly, the compounds based on PA12 and PA66‐matrix show improved tribological properties compared to PA46‐based compounds. COF values for PA66 and PA12‐Z7321 are 0.69 and 0.55, respectively. In comparison, PA66‐MP1100‐MO‐cb and PA12‐MP1100‐MO‐cb (Z7321) have COF value of 0.34 and 0.38, respectively.
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