Thermocleavable friction modifiers for controlled release in lubricants

Abstract

Abstract Organic friction modifiers (FMs) are commonly utilized in lubricants. FM molecules possess a polar head group that interacts with metallic surfaces and aliphatic chains that cohesively interact with neighboring molecules. Under boundary lubrication conditions, as experienced in engine valve trains and cylinders, fluid films are unable to form between metallic surfaces. This results in metal-metal contact. Thus, organic friction modifiers are commonly utilized to reduce friction under these conditions. While efficacious, these molecules are consumed over time owing to engine environments, reducing their effectiveness. To replenish organic friction modifier stocks in base oil lubricants, tertiary ester derivatives of fatty acid-containing dicarboxylic acids were investigated. A series of fatty acid-containing dicarboxylic acids were first developed based on a tartaric acid backbone and their friction modifying capabilities assessed. Coefficient of friction studies illustrated that friction-modifying capabilities were heavily influenced by polar head group type (i.e., carboxylic acid, ester) and chemical bond to tartaric acid (i.e., ester, ether). Thermogravimetric analysis coupled gas-phase Fourier transform infrared spectroscopy revealed that fatty acid-containing dicarboxylic acids degraded into their respective fatty acids at elevated temperatures. Controlled release studies were conducted on a compound modified with thermocleavable esters, and showed sustained friction modifying activity through the course of the entire study. These systems are ideal candidates for the controlled delivery of friction modifiers, which can increase engine efficiency and reduce fuel consumption, effectively reducing vehicle emissions.