Ultralow friction polymer composites incorporated with monodispersed oil microcapsules

Ultralow friction polymer composites were prepared by adding oil-loaded microcapsules into epoxy (EP) resin. Mono-dispersed polystyrene (PS)/poly alpha olefin (PAO) microcapsules with a diameter of ~2 μm and a shell thickness of ~ 30 nm were prepared by solvent evaporation method in an oil-in-water emulsion. The lubrication behaviors of the EP resin composites with oil-loaded microcapsules have been investigated under different loads and sliding speeds. As compared with the pure EP resin, the friction coefficient of the composite could be reduced to 4% (from 0.71 to 0.028) and the wear rate could be decreased up to two orders of magnitude. It was demonstrated that the released PAO oil from the microcapsules during the friction process produced a boundary lubricating film, which could prevent the direct contact of two rubbing surfaces, and thus leading to an extremely low friction coefficient and wear rate. Moreover, the composites with microcapsules could achieve comparable lubrication properties to the case under the external lubrication condition, while the former case could effectively minimize the lubricant leakage and improve the lubrication efficiency.

Core–shell nanospheres to achieve ultralow friction polymer nanocomposites with superior mechanical properties

The mechanical and lubrication properties of the core–shell nanocomposite show great advantages over those of conventional composites prepared by mechanical mixing.

THE INFLUENCE OF A CONSTANT STATE OF DEFORMATION ON THE FRICTION COEFFICIENT IN SELECTED THERMOPLASTICS (POLYMER–STEEL PAIR)

The effect of tensile deformation on polymer structures and their mechanical properties is described in various papers. However, the majority of articles are focused on high deformation (a few hundred percentiles) at increased temperature. It causes changes in orientation and the crystallinity ratio. The authors of this paper asses the influence of strain (max. 50%) on hardness and the coefficient of friction (polymer–steel A1 couple) for selected polymers. The deformation was conducted at room temperature and maintained during tests. There was a significant reduction (up to 50%) of hardness after deformation, in the case of all examined polymers. In the case of PE-HD, the coefficient of kinetic friction almost doubled its value (89% increase). The reduction of the coefficient of static friction for sliding pairs that include PTFE and PA6 was about 26% (in comparison with non-deformed polymer). For all investigated polymers, hardness increased over time (up to 40% after 24 hours). Coefficients of static and kinetic friction decreased in 24 hours (up to 29% coefficient of static friction and 19% coefficient of kinetic friction). The research shows that a small deformation causes changes in polymer properties. Moreover, these changes appear at room temperature directly after deformation.

Chemical Understanding of Friction Polymer Based Tribo-Chemical Films Derived From Nanolubricant

MoS2 multi-component nanolubrication system showed significant friction and wear reduction (more than 30% in friction reduction and 50% in wear reduction) in sliding steel surfaces, especially under mixed and boundary lubrication conditions [1–3]. It is believed that the formation of tribofilms in MoS2 multi-component nanolubrication system under different lubrication regimes is the primary reason for reduced friction and wear. To investigate the in-depth science of the tribo-chemical interface formed by MoS2 multicomponent nanolubrication system, it is necessary to study the chemical states of tribofilm during its evolution (generation ↔ regeneration) process at tribo-interfaces. Tribofilms from various lubrication regimes were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), Raman microscope, and X-ray photoelectron spectroscopy (XPS) techniques to study the morphology, chemical composition, elemental distribution, and chemical bonding of tribo-chemical surface, respectively. Besides the evolution process, the characterization of tribofilms also reveals the possibility of forming new meta-stable phases (chemical compounds) after tribological testing. Patchy tribofilms and progressive tribofilms have been observed from the SEM analysis and the EDX results showed existence of Mo-S-P as the composition of tribo-chemical films. The Raman spectroscopy analysis of tribofilms showed significant difference (such as formation of poly-molybdates) in chemical information of nanolubricants and tribofilms, which is an indication of the formation of friction polymer [4–5]. Additionally, phosphates and oxides, acting as components of surface protecting layer of tribofilms, have been found on surface by XPS technique. Moreover, MoS2 nanoparticles are found to navigate into surface asperities to protect the contacting surfaces. The results (information about the chemical states of the tribofilm) obtained from different characterization techniques can be used to explain the mechanism of friction and wear reduction associated with MoS2 multi-component nanolubrication system that has been reported in the literature.