Steric Factors Affecting Friction and Wear of Polyalkenes

The sliding performance of polyalkenes in rubbing contact with a metal (oxide) surface is controlled by structural order and molecular symmetry. High density polyethylene surpasses in its overall sliding performance the substituted crystalline polyalkenes. The ability of the conventional (branched) polyethylene to function as a low friction contact when water is the lubricant is attributed to the presence of amorphous regions also present in the linear type. The erratic sliding of isotactic polybutene (and other homologs) is explained by internal friction in the rubbing interface resulting from polymorphic transitions. Crosslinking with a peroxide increases friction of polyethylene but it reduces the abrasive wear of the composites containing carbon black. The use of highly reactive channel blacks requires no free radical source and a further reduction in abrasive wear can be achieved by auxiliary crosslinking agents such as ethylene imine which reacts exothermally with the acidic surface of the carbon black present in the composite structure. The ratio of crystalline and amorphous conformations governs the overall sliding performance of polyalkenes. Frictional effects due to different mating surfaces are explained by material transfer and interfacial shape elastic phenomena. Presented at the 25th ASLE Annual Meeting in Chicago, May 4–8, 1970