Friction of polymer films. I. Lubrication

Abstract

The behavior of several long chain fatty lubricants in thin films of vinylidene chloride-acrylonitrile copolymer and the nature of the lubricated polymer surfaces were studied by means of frictional measurements, critical surface tension of wetting, and light microscopy. The surfaces of the bulk lubricants were also characterized by wetting studies. The critical surface tension of wetting parameter was found to be both a means of characterizing the configuration of the lubricant layer and a measure of the extent to which the polymer surface was covered by the lubricant. There was no evidence of orientation of the lubricant layer on the polymer surface and no evidence of plasticization of the polymer by the lubricant. All lubricants studied appeared in the bulk state at the polymer surface in quantities related to the chain length and chemical constitution of the lubricant. Correlations were observed between the coefficient of static friction of the polymer film and its critical surface tension of wetting. Solid fatty amides having chain lengths of eighteen carbon atoms or greater were found to be effective lubricants for the polymer studied. The lubricating action of these fatty materials was explained in terms of their low surface energies and high structural strengths when in the bulk crystalline state.