Polymer-counterface bonding

C. J. Schwartz, S. Bahadur (2001) The role of filler deformability, filler-polymer bonding, and counterface material on the tribological behavior of polyphenylene sulfide (PPS), Near 751,1532. 

In the case of 30% CuS, 70% HOPE sliding against an abraded steel surface, a thin film of the filled polymer is formed on the counterface. Electron diffraction analyses of the wear debris provided evidence of the presence of the compounds of Fe, S and Cu which implies that the transfer film is being bonded chemically to the steel surface. 

This device, then, permits the transfer of extremely thin polymer films and allows for the identification of the onset of adhesion and transfer, providing the opportunity to identify when bonding occurs and some indication of bond strength. If the polymer is seen to transfer to a counterface surface, then it is reasonable to assume that the interfacial adhesive bond strength is greater than the cohesive strength of the polymer itself. This observation will only hold where the counterface surface is atomically smooth. 

Polymer to Counterface Bonding. Of extreme interest to the tribolo-gist is the nature and structure of interfacial adhesion of polymers to substrate surfaces because it contributes heavily to the adhesive wear of polymers. A very useful tool for the study of this subject is quantitative absorption - reflection thickness infrared spectroscopy (QUARTIR). This device is uniquely suited for the study of preferential orientation of large molecules at interfaces. Thus, insight into the structural interfacial bonding of molecules can be had, adhesion and accordingly adhesive wear better understood. 

In order to explain the influence of the way sulfur is bonding in polymer materials on modification of the surface layer of iron, the metal counterface was subjected to sliding friction against ... 

From the specific spectra of secondary ions (Fig. 14.2) and comparison between normalized counts for particular cases (Fig. 14.3) it follows, that the highest amount of sulfur, in a form of SH- ions, was transferred to the surface layer of iron counterface by ebonite. In the case of polysulphone, due to strong sulfur bonding to macromolecular backbone (Fig. 14.4) and different from other polymers studied mechanisms of mechano-degrada-tion, the expected effect of sulfur transfer is practically absent. 

There does not seem to be any means of actually predicting the rate of interfacial wear processes, be they arising from transfer wear processes or through chemical degradation. This is not surprising in view of the uncertainty as to what is involved in the transfer process. However, what is not known is that if certain polymers are filled with hard or chemically active fillers then a securely bonded transfer film will attach to metal counterfaces and then the rates of wear will be reduced by several orders of... 

The transfer film essentially modifies the initial surface topography of the counterface (smoothening effect) and depending upon the shear properties of the film, the frictional work could also be reduced. The shear properties of the transfer film are determined by the mechanical interlocking between the asperities and the polymer molecules and the possibility of the formation of physical or chemical bonding between the transferred polymer molecules and the substrate. The oxides such as CuO and PbO, which are present on the metal surfaces, play a major role in the formation of transfer films of polymers (17,18). The presence of copper (from CuS and CuO), for example, in PTFE has also been found to enhance transfer film bonding to the steel counterface (17). Thus, a reduction in the... 

The interfacial term of friction is the main cause of adhesive wear and may involve processes such as stick-slip motion, transfer film formation with or without chemical bonding, chemical wear, fatigue wear, and thermal softening of the interface (2,24). The adhesive wear is promoted only when the roughness of the counterface is very low, a value where cohesive wear or ploughing due to counterface asperity interaction may be safely neglected, and the adhesive interaction between the polymer and the counterface as a result of junction growth becomes an important factor. 

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