Tribological evaluation of PEG-based nanolubricants modified with graphene and copper oxide

Abstract

Nanolubricants are dispersions of nanomaterials in a lubricating base. In this work, polyethylene glycol (PEG) was modified with graphene (G) and copper oxide (CuO) to obtain a nanolubricant (NL). The nanolubricants were prepared and their physicochemical and tribological properties were evaluated. The base and the nanomaterials were evaluated using Fourier-transform infrared spectrometry (FTIR), field-emission scanning electron microscopy coupled with energy dispersive spectroscopy (FE-SEM-EDS), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Raman spectroscopy (Raman). Rheology and Tribology tests were also performed using a four-ball tester according to ASTM 2783. The results showed that nanolubricants have a Newtonian behavior and the viscosity was not significantly modified with the additives. The weld point obtained for the nanolubricants was 160 kgf. In addition, when compared to the PEG, the size of the wear scars was reduced by 9.6% (PEG with 0.01% w/w of CuO) and 35.3% (PEG with 0.05% w/w of CuO and G). The wear protection provided by G is higher than the protection provided by CuO. When the two additives were added, the wear protection increased, and a synergistic effect was observed. Two protection mechanisms were observed in the SEM: rolling bearing/ball effect (CuO) and deposition of G at valleys and peaks of the surface roughness. This article shows novel results related to a laboratory evaluation of nanolubricants in a typical tribological test (four-ball). A novel result was observed in the synergistic effect between the two additives (graphene and CuO) determined by the wear mechanism observed in the tests.

Graphical Abstract

Keywords:

• Nanolubricants
• graphene
• copper oxide
• wear mechanism
• dispersion stability

Disclosure statement

All authors declare that they have no conflicts of interest.

Additional information

Funding

The authors are grateful to the Instituto Tecnológico Metropolitano for financial support through project P20210.