Influence of lamellar MoS₂ size on the crystallization process, surface mechanical properties, and friction behavior of POM self‐lubricating composites

Abstract In order to enhance the self‐lubricating properties of polymers, various types of solid lubricants have been incorporated, with lamellar molybdenum disulfide (MoS₂) being the most widely used. However, impact of the MoS₂ particle size on the molecular chain conformation and properties has been neglected. In this work, different sizes of MoS₂ were incorporated into polyformaldehyde (POM), focusing on the crystallization process, surface mechanical properties and friction behaviors were analyzed. The results indicate that the MoS₂ promotes the POM crystallization process, and the crystallinity is increased both before and after eliminating the thermal history. This leads to an increase in surface microhardness and modulus. As the particle size decreases, the composites show a decrease in the friction coefficient and wear rate when paired with both metal and POM friction balls. The greatest improvement in the friction coefficient was achieved at the particle size of 500 nm, which was 0.154 (POM ball) and 0.124 (metal ball), respectively. Meanwhile, the wear rates were 50.62%(POM ball) and 66.90%(metal ball) lower than those of pure POM, respectively. Interestingly, the friction coefficient decreases with increasing load under the action of POM friction balls, while the opposite trend is observed with metal friction balls. Highlights The crystallinity of all POM/MoS₂ composite samples was increased. The modulus and hardness of POM composites were higher than those of pure POM. The best tribological properties of composites were obtained at MoS₂ of 500 nm.