Influence of aldol condensation processes on the formation of surface films during friction in ester lubricants

The boundary lubrication mode is usually implemented in conditions of low sliding speeds and high loads. The formation of strong boundary lubricating films under this friction mode determines the operability and durability of the friction units. It is believed that the formation of surface boundary films during friction includes the stages of the lubricant oxidation, and the aldol condensation reaction of oxidized molecules. As a result, high-molecular substances called “friction polymers” are formed. The paper studies the formation of surface films in the presence of substances with different reactivity in the aldol condensation and Claisen condensation reactions. Sunflower oil, bis (2-ethylhexyl) sebacate (DEHS), triisodecyl benzene-1,2,4-tricarboxylate (TC) were used as lubricants. It is shown by ATR IR-spectroscopy of that the common thing for the studied oils is that the C=O and C-O groups participate in the formation of boundary films in these oils. The addition of substances, active in aldol condensation reactions, into lubricants does not accelerate the formation of boundary films. Additives that can chemically interact with iron contribute to the dissolution of the surface oxide film and accelerate the formation of boundary layers. The formation of “friction polymers” occurs when the lubricant molecules interact with the metal surface.

Adhesive Wear of Polymers

Adhesive wear is a characteristic but inadequately studied type of wear of polymer materials. In local regions of real contact an intensive molecular (adhesive) interaction is observed under rubbing conditions, which is stronger than the bonds between individual elements in the supermolecular formations or in polymer molecules, leading to cohesive failure of the material. Wear products can escape from the contact region as gases or as solid substances, or they can form a “third body”, i.e., a transferred layer of one material is deposited on the surface of the other. The direction, mechanism, and character of the occurring processes are determined, first of all, by the structures of the interacting materials. To know the mechanism of adhesive wear enables one to predict dangerous failures of the surfaces under rubbing due to seizure, on the one hand, and to find ways of governing the frictional interaction and create efficient self-lubricated polymer-based materials on the other hand. One of the efficient ways of providing minimum wear in metal-polymer friction pairs is to govern the process of developing “friction polymers” and to use mixtures of polymers having different thermophysical properties as antifrictional materials.