Synthesis and Tribology\nProperties of Self-Lubricating\nPolyformaldehyde with Oil-Loaded Mesoporous Silica

The design and development of self-lubricating materials\ncan reduce\nfriction and wear in industrial activities to satisfy higher demands\nfor environmental sustainability. Silica nanoparticles, as a representative\nof inorganic nanomaterials, have the advantages of low thermal expansion\ncoefficient, large specific surface area and pore volume, adjustable\nparticle size, and easy functionalization. When used to modify single-component\npolymer materials, silica materials can effectively improve the wear\nresistance performance of polymer substrates by enhancing their mechanical\nproperties. However, the enhancement of self-lubricating properties\nof polymers by silica materials is less effective than that achieved\nby liquid lubricants. In this paper, liquid lubricants such as dimethyl\nsilicone oil (DSO) and perfluoropolyether lubricating oil (PFPE) were\nloaded using mesoporous silica nanoparticles (MSNs), and the oil content\nwas about 24 and 48 wt %, respectively. The oil-loaded MSNs (MSNs-DSO\nor MSNs-PFPE) were filled into a polyoxymethylene (POM) matrix, and\na POM-based composite with self-lubricating properties was prepared\nby a hot pressing process. The materials were tested and analyzed\nby a thermogravimetric analyzer, a Fourier infrared analyzer, a scanning\nelectron microscope, a three-dimensional profile analyzer, a multifunctional\nfriction and wear tester, a universal material testing machine, and\nan X-ray photoelectron spectroscopy analyzer. Compared to pure POM,\nthe coefficient of friction and wear rate of POM-based composites\ncontaining 5 wt % MSNs-DSO were reduced by 75.3% and 69.2%, respectively.\nDuring the friction process, the lubricant components in the composite\nare released from the POM matrix under load and friction heat to migrate\ntoward the friction interface, forming a corresponding transfer tribofilm\nthat avoids direct contact between the POM matrix and the friction\ncounterpart so that the material has excellent self-lubricating properties.