Biocompatible and Biodegradable Emulsion Gel Lubricants

Due to inclusion of toxic and nondegradable base oils and additives, most of the commercially available semisolid lubricants easily cause severe environmental burdens and health risks. This therefore leads to the use of these lubricant products contrary to the principles of sustainable chemistry and engineering. To solve this crucial issue, in this work, we create a new type of eco-friendly emulsion-based gel lubricant that is able to combine the characteristics of traditional gel lubricants and oil-in-water emulsions. The advantages of employing the emulsion gel lubricants include (1) facile preparation using lost-cost, commercially available pentaerythritol oleate, chitosan, and water in the compositions; (2) high colloidal stability against droplet coalescence and phase separation; (3) good anticreeping and thixotropic performances that allow effective semisolid lubrication; and (4) excellent biocompatibility and biodegradability that can strongly reduce their potential adverse health and environment impacts. It was found that the emulsion gels can provide favorable friction and wear reductions for hard steel surfaces even under very high load-bearing conditions owing to the formation of high-strength mixed lubrication films. Our study may provide new insights into design and production of functional green semisolid materials for engineering applications.