Fatty acids and antioxidant effects on grease microstructures

The search for biobased material as industrial and automotive lubricants has accelerated in recent years. This trend is primarily due to the nontoxic and biodegradable characteristics of seed oils that can substitute mineral oil as base fluid in grease making. The paper discusses the preparation of lithium soap-based soy greases using different fatty acids and the determination of crystallite structure of soap using transmission electron microscopy (TEM). Lithium soaps with palmitic, stearic, oleic, and linoleic acids were synthesized and mixed with soybean oil (SBO) and additives to obtain different grease compositions. TEM measurements have revealed that the soap crystallite structure impact grease consistency. Soap fiber length and their cross-linking mechanism in the matrix control grease consistency (National Lubricating Grease Institute (NLGI) hardness, ASTM D-217 method). Lithium stearate-based soy grease has a relatively more compact fiber structure than Li palmitate. Linoleic acid (C18,  ) with two sites of CC unsaturation in the chain has a much thinner and more compact fiber network than oleic acid (C18, ). The presence of additive in grease produces a soap with looser network and larger fiber structure than similar grease containing no additive. A close analysis of grease microstructure will help in the development of better performing grease for industrial applications.