Jojoba is the Simmondsia chinensis – commonly known as jojoba – shrub. Native to the Southwestern United States and northern Mexico, jojoba is grown commercially to manufacture jojoba oil, a liquid wax ester extracted from its seed.

In the paper, the researchers noted that from reviewing literature, jojoba oil is unique in structure and different from other vegetable oils. “It is characterized by a high viscosity index and high thermal oxidate stability due to its long-chain monounsaturated fatty ester structure,” they said. “It is also obtained from a sustainable plant that is drought-resistant. Due to its distinctive properties, much more investigation should be conducted on jojoba oil as a futuristic base oil in industrial lubricants.”

The researchers presented in their paper a novel eco-friendly grease made from unmodified jojoba oil as a base oil and lithium stearate as a thickener. To enhance its physicochemical and tribological performance for machinery lubrication, activated carbon nanoparticles – referred to as ACNPs – were fabricated in the work and applied at different concentrations in the biobased grease samples developed by the researchers. The functional groups in such nanoparticles are specific chemical moieties – defined as part of the chemical structure of a molecule or compound that could include a substructure, such as a functional group – attached to the surface of the nanoparticles, which can interact with the metal surface and the corrosive environment. These interactions enhance the corrosion inhibition properties of the activated carbon nanoparticles, they noted.

Jojoba grease samples were prepared in their plant state and with blends of different weights. The researchers then examined the samples for copper corrosion tendency, dropping point, coefficient of friction, wear scar diameter and load carrying capacity, and the results were compared with commercial lithium grease. Wear scar and length is measured using an optical microscope, with smaller wear scare indicating the lubricant has helped prevent wear.

According to the paper, the dynamic performance of jojoba grease samples was also evaluated using ball bearings running at different loads by measuring vibration levels and power consumption. The addition of activated carbon nanoparticles caused a noticeable reduction in the measured bearing vibration values and power consumption levels in comparison with lithium grease, the researchers concluded. “This proves the generation of a stable minimum oil film thickness that ensures the bearing operation in [elasto-hydrodynamic lubrication] full film lubrication zone,” they said.

The jojoba grease without activated carbon nanoparticles additives resulted in a lower level of corrosion resistance due to the presence of stearic acid in the lithium soap and the absence of a corrosion inhibitor. The addition of activated carbon nanoparticles in the samples enhanced the corrosion resistance rating without degrading the stability of jojoba grease, according to the paper.

The researchers said that the grease made with jojoba oil proved to be a competent lubricant with adequate tribological behavior, when compared to some other bio-based greases from review of literature. “For example, jojoba grease with and without activated carbon nanoparticles showed coefficient of friction values similar to findings of bio-grease samples from castor oil with calcium soap, castor oil with methylcellulose, and castor oil with chitin, and cellulosic pulp,” they said.

All four researchers are with the Chemical and Petrochemicals Engineering Department of Egypt-Japan University of Science and Technology in New Borg El-Arab City, Egypt. One is also with a department at the Advanced Technology and New Materials and Research Institute of the City of Scientific Research and Technological Applications in Alexandria, Egypt. Another is also with Aswan University and another is also with Alexandria University, both of which are in Egypt. The open access research paper, “Developing a sustainable grease from jojoba oil with plant waste nanoadditives for enhancement of rolling bearing performance,” with detailed test findings and results, may be viewed at the Scientific Reports website.