Preparation of MoS₂/ZnS Nano-Powder and Tribological Behavior of MoS₂/ZnS nano-powder Reinforced Polyimide Composites

Friction and wear are one of the main causes of material failure and waste of resources. Therefore, it is particularly urgent to develop new high-performance lubricating materials to reduce the friction and wear of moving parts. Polyimide (PI) has increasingly become an important engineering material in industrial production and life due to its excellent thermal stability, mechanical properties and excellent anti-solvent and anti-radiation properties, which is widely used in automotive, aerospace, transportation and other fields. However, single component PI material is difficult to meet the requirements of engineering materials for friction and wear properties. Molybdenum disulfide (MoS₂) is a two-dimensional layered material. Its layers are connected by weak van der Waals forces. When subjected to external shear, it is easy to produce relative motion and slip. Based on this feature, MoS₂ become an extremely important solid lubricating additive. However, MoS₂ will spontaneously oxidize and absorb moisture in the air during the friction process, resulting in a significant reduction in lubrication and wear resistance life. Meanwhile, Zinc sulfide (ZnS), as a metal sulfide with a wide range of uses, has also gained certain applications in the field of anti-friction and anti-wear. In summary, MoS₂ and ZnS nanomaterials are widely used in the field of anti-friction and anti-wear, either alone or in combination with other materials. However, there is no report on the synergistic enhancement of the tribological properties by MoS₂ and ZnS. Therefore, in this paper, the MoS₂/ZnS hybrid was synthesized by a one-step hydrothermal method to study the friction and wear properties of the PI resin matrix composites, and the synergistic enhancement effects of MoS₂ and ZnS nanoparticles on the PI composites were further explored by the friction measurements. The molybdenum disulfide/zinc sulphide (MoS₂/ZnS) nano-hybrid was synthesized by one-step hydrothermal method, and then polyimide/molybdenum disulfide/zinc sulphide (PI/MoS₂/ZnS) composites were obtained by hot-pressing technology. The morphology and chemical composition of the prepared MoS₂/ZnS nano-hybrid were characterized by SEM (Scanning electron microscope), TEM (Transmission electron microscope), XRD (X-ray diffraction) and XPS (X-ray photoelectron spectroscopy) to prove the formation of MoS₂/ZnS nano-hybrid. The results of thermogravimetric analysis and differential scanning calorimetry showed that the introduction of MoS₂/ZnS nano-hybrid significantly improved the thermal stability of PI matrix. The friction and wear test results showed that all the three fillers (MoS₂, ZnS, MoS₂/ZnS) could effectively improve the tribological properties of polyimide matrix, while the MoS₂/ZnS nano-hybrid presented the optimal enhancement effect. When the mass fraction of MoS₂/ZnS nano-hybrid was 1.5%, the tribological properties of PI/MoS₂/ZnS composites were the optimal. Compared with pure polyimide, the friction coefficient and wear rate of PI/MoS₂/ZnS composites were reduced by 15.9% and 34.3%, respectively. This was mainly due to the synergistic enhancement effect of the MoS₂/ZnS hybrid on PI composites. During the friction process of PI/MoS₂/ZnS composites, MoS₂ nanosheets promote the formation of friction transfer films, while ZnS nanoparticles enhance the load-bearing capacity of the composites. In addition, the friction transfer film formed on the counterpart surface of the PI/MoS₂/ZnS composite material was also more uniform and dense, further confirming that the PI/MoS₂/ZnS composite material present the most excellent tribological properties.