Synthesis and Tribology Properties of Self-Lubricating Polyformaldehyde with Oil-Loaded Mesoporous Silica

The design and development of self-lubricating materials can reduce friction and wear in industrial activities to satisfy higher demands for environmental sustainability. Silica nanoparticles, as a representative of inorganic nanomaterials, have the advantages of low thermal expansion coefficient, large specific surface area and pore volume, adjustable particle size, and easy functionalization. When used to modify single-component polymer materials, silica materials can effectively improve the wear resistance performance of polymer substrates by enhancing their mechanical properties. However, the enhancement of self-lubricating properties of polymers by silica materials is less effective than that achieved by liquid lubricants. In this paper, liquid lubricants such as dimethyl silicone oil (DSO) and perfluoropolyether lubricating oil (PFPE) were loaded using mesoporous silica nanoparticles (MSNs), and the oil content was about 24 and 48 wt %, respectively. The oil-loaded MSNs (MSNs-DSO or MSNs-PFPE) were filled into a polyoxymethylene (POM) matrix, and a POM-based composite with self-lubricating properties was prepared by a hot pressing process. The materials were tested and analyzed by a thermogravimetric analyzer, a Fourier infrared analyzer, a scanning electron microscope, a three-dimensional profile analyzer, a multifunctional friction and wear tester, a universal material testing machine, and an X-ray photoelectron spectroscopy analyzer. Compared to pure POM, the coefficient of friction and wear rate of POM-based composites containing 5 wt % MSNs-DSO were reduced by 75.3% and 69.2%, respectively. During the friction process, the lubricant components in the composite are released from the POM matrix under load and friction heat to migrate toward the friction interface, forming a corresponding transfer tribofilm that avoids direct contact between the POM matrix and the friction counterpart so that the material has excellent self-lubricating properties.