Eco-friendly Lubricants Research Articles

Mucus-inspired biomass-derived carbon dots-based solvent-free nanofluid with polyelectrolytes networks toward excellent green lubrication

Mechanical friction and wear account for 23 % of global energy, highlighting a need for eco-friendly lubricants. Drawing inspiration from marine organisms' adsorption proteins, we have developed carbon dots-based solvent-free nanofluid. Incorporating hydrophilic polyelectrolytes, the nanofluid forms three-dimensional adsorption-lubrication networks, leveraging carbon dots' strong chelating affinity, synergistically enhancing lubrication. Using the UMT-3 TriboLab and a 3D optical profilometer, we assessed the tribological performance of nanofluid and remarkably reduced the friction coefficient by 47.3 % and wear rate by 90.8 % compared to PEG 200 (Polyethylene Glycol with an average molecular weight of 200). Additionally, the infrared camera detected that nanofluid as water additives, significantly reduce wear and heat generation, decreasing temperature rise by 4.7 times. This biomimetic approach paves the way for green, oil-free, and high-performance water-based lubrication technologies.

Unravelling molecular origins of improved tribological properties of amino acid ionic liquid water-based lubricants

In the quest for sustainable lubrication, this study explores the potential of water-based lubricants (WBLs) with amino acid ionic liquid (AAIL) additives. The research combines experimental and reactive molecular dynamics (MD) simulations to assess the tribological and rheological enhancements provided by AAILs. Specifically, tetrabutylphosphonium (P4444) cations paired with Serine (Ser) and Tryptophan (Trp) anions were mixed into water to create AAIL WBLs. The introduction of AAILs significantly improved the lubricants’ rheological properties and reduced the coefficient of friction by up to 34 %. This reduction is attributed to the formation of hydration shells around the amino acid anions, which create a chemically adsorbed tribofilm on iron oxide surfaces, and P4444 cations that establish a load-bearing layer in the middle regions of the lubricant. This dual-layer structure, supported by hydration lubrication, effectively maintains lubricant fluidity while bearing substantial loads. Among the AAIL WBLs tested, those with a thicker, more stable, hydrated amino acid tribofilm demonstrated more significant friction reduction. These insights into the molecular mechanisms behind AAIL WBLs’ tribological behaviour underscore their promise as eco-friendly lubricants, contributing to advancing a circular economy in industries reliant on lubrication.

Environmentally Acceptable Lubricants for Stern Tube Application: Shear Stability and Friction Factor

Stern tube lubricants are essential in maritime operations, safeguarding ship propeller shafts from wear and corrosion while ensuring efficient propulsion. Their role in reducing friction and maintaining system integrity is critical. With growing environmental concerns, the adoption of environmentally acceptable lubricants (EALs) for stern tubes has gained importance, balancing operational performance with environmental protection. This study investigates the rheological and tribological properties of EALs formulated for ship propeller stern tube applications. The primary focus is on comparing these EALs with conventional mineral oils to assess their suitability in marine environments. EALs are increasingly favored due to their biodegradability and reduced environmental impact. Key parameters such as shear stability, friction factor, and temperature dependency were evaluated using a range of experimental methods including rotational viscometry and tribological analysis. The results indicate that the newly formulated EALs based on synthetic esters exhibit the highest viscosity index, a higher range of shear stability, and lower friction factors, compared to commercially available mineral oils, especially under varying operational conditions. These findings contribute to the ongoing efforts to promote eco-friendly lubricants in maritime industries, aligning with global environmental protection initiatives.

Wormlike Micellar Glycerol Solutions Formed from a Double-Tailed Surfactant with Two Quaternary Ammonium Head Groups.

Herein, a quaternary ammonium surfactant with dual heads and tails, N1,N1,N1,N3,N3-pentamethyl-N3-(3-(2-tetradecylhexadecanamido)propyl)propane-1,3-diaminium dibromide, abbreviated as Di-C14-N2, was synthesized. For the first time, clear observation of aggregate structures formed by surfactants in pure glycerol systems was achieved using cryogenic transmission electron microscopy (cryo-TEM). The system's rheological properties were analyzed using both steady-state shear and oscillatory rheological measurements. The lubricating efficiency of the Di-C14-N2 glycerol solution was assessed for its tribological properties using a tribological wear tester, white light interferometer, and scanning electron microscope. In glycerol, Di-C14-N2 formed long wormlike micelles, which resulted in a glycerol solution with the zero-shear viscosity of 1013 Pa·s at 90 mM, which is the most viscous glycerol system up to now. The system displayed distinct rheological properties from the aqueous system, as evidenced by two intersections in the loss and storage moduli. The formed wormlike micelles in glycerol lead to a significant alteration in the viscoelasticity of the system, thus endowing the Di-C14-N2 glycerol solution with potential as an eco-friendly lubricant. The friction coefficient of the system was found to be 23% lower and the wear rate was 83% lower than that of pure glycerol after the addition of Di-C14-N2. This demonstrates that the addition of Di-C14-N2 greatly improves the frictional properties of pure glycerol. This study offers the possibility of directly observing the aggregate structures formed by surfactants in pure glycerol systems. It contributes to the exploration of the self-assembly behavior of surfactants in nonaqueous polar media, thereby aiding in a deeper understanding of the correlation between molecular structure, mesoscale structure, and macroscopic properties.

Tribological and Chemical–Physical Behavior of a Novel Palm Grease Blended with Zinc Oxide and Reduced Graphene Oxide Nano-Additives

The role of industrial lubricants in machinery is to reduce friction and wear between moving components. Due to the United Nations’ tendency to reduce dependency on fossil fuel, a general awareness is strongly driven towards developing more eco-friendly lubricants. Palm oil possesses promising properties, which promote it to be a competitive alternative to the hostile mineral oils. Still, marginal oxidation stability, viscosity, and tribological properties remain critical issues for performance improvement. This paper presents an improved palm grease using reduced graphene oxide (rGO) and zinc oxide (ZnO) nano-additives at different concentrations. Oil and grease samples were tested for viscosity, oxidation stability, pour point, penetration, roll stability, dropping point, churned grease-oil release, copper corrosion, friction, and wear. ZnO additives enhanced the oxidation stability by 60% and shifted the pour point to 6 °C. Adding ZnO and rGO to the palm grease increased the load-carrying capacity between 30% and 60%, respectively, and reduced the friction coefficient by up to 60%. From the wear scar morphologies, it is believed that graphene 2D nanoparticles formed absorption layers which contributed to the increase in load-carrying capacity, while ZnO chemically reacted with the metallic surface layer, forming zinc compounds that resulted in a protective boundary lubricating film.

Feasibility Study of Developing an Eco-Friendly Bio Lubricant from Flaxseed Oil

The increasing global demand for sustainable and environmentally friendly lubricants has led to the exploration of bio-based alternatives. This study focuses on the production of a bio- lubricant using Flax Seed oil as the feedstock through an epoxidation process followed by acid testing. The first step involves the epoxidation of Flax Seed, where the unsaturated fatty acids present in the oil are converted into epoxides. This process is carried out using a catalyst and a peroxide source. The reaction conditions, such as temperature, time, and reactant ratios, are optimized to achieve the highest conversion and selectivity of epoxidized Flax Seed oil. The epoxidized Flax Seed is then subjected to acid testing to evaluate its suitability as a bio- lubricant. The acid value, which measures the amount of acidic compounds present, is determined. A low acid value indicates good stability and resistance to oxidation. Additionally, the viscosity, flash point and other relevant properties are assessed to ensure that the bio- lubricant meets industry standards. The results of the acid testing provide valuable insights into the quality and performance of the produced bio-lubricant. By analyzing the acid value and other properties, the effectiveness of the epoxidation process and the feasibility of using Flax Seed oil as a sustainable feedstock for bio-lubricant production can be determined. This research contributes to the development of eco-friendly lubricants by utilizing Flax Seed oil as a renewable resource. The epoxidation process and subsequent acid testing serve as crucial steps in the production and evaluation of bio-lubricants, highlighting their potential as a viable alternative to conventional petroleum-based lubricants

Improving physicochemical and tribological characteristics of bio-lubricants using carbon-based hybrid nanomaterials modified by tertiary-butyl-hydroquinone

Vegetable oils are being increasingly studied in tribology due to their environmental benefits. This study investigates the physicochemical and tribological properties of carbon black/silver (CB/Ag) hybrid nanomaterials modified by tertiary-butylhydroquinone (TBHQ) as lubricant additives. The composition of the tribolayer formed were characterized using an FE-SEM, 3D surface profilometer, and XPS analysis. The results reveal a substantial decrease in the coefficient of friction (COF) value for the hybrid nanolubricant, with an approximate 31% reduction compared to the baseline oil. Finally, the characterization of worn surfaces strongly supports the noteworthy improvement in friction performance, primarily ascribed to the synergistic effects of CB, Ag nanoparticles, and TBHQ antioxidant surfactants. This study affirms that TBHQ-modified CB/Ag hybrid nanoparticles serve as eco-friendly lubricant additives.

Investigations on Ways to Improve the Scuffing and Wear Behavior of Oil-Free Water-Based Lubricants for Gear Applications

Abstract Today, mineral or synthetic oils that are made out of fossil raw materials are the most common lubricants in gear drive applications. Most of them are nonbiodegradable and may pose a risk to the environment. An important step to minimize the risk and the ecological footprint is the use of biodegradable and eco-friendly lubricants. Former research shows the potential of water-based lubricants in gear applications. Therefore, an oil-free, water-based lubricant was developed for this study. The base lubricant contains plant-based thickeners to generate an appropriate viscosity for a sufficient lubricant film thickness in the tooth contact. In experimental investigations, the sliding wear and scuffing performance has been examined under variation of the added polymers and additives. The scuffing tests A/8.3/RT are performed according to DIN ISO 14635-1. The wear test procedure is based on DGMK 377-01. In both scuffing tests with the sample, the failure load stage = 8 was achieved. For case-carburized gears, a “medium” to “high” amount of wear can be detected. Additional tests with nitrided gears show a “low” amount of wear. This article aims to show the great potential of water-based oils for gear lubrication and suggests operating conditions for maximum wear and scuffing carrying capacity.

A novel 2D/2D MoS2/CeO2 nanohybrid and its lubricating mechanism in green rapeseed oil

The incomplete stacking of two distinct types of two-dimensional (2D) layered materials to form a 2D/2D nanohybrid, accompanied by the generation of ultra-low friction at the interface, offers a novel solution for designing lubricants with superior tribological performance. This work utilized a facile and gentle method to synthesize MoS2 and CeO2 nanosheets with varying sizes, which were then stacked to form 2D/2D nanohybrid. This nanohybrid was employed as dispersant additives in eco-friendly lubricant to effectively reduce friction. The tribological testing results revealed that this nanohybrid exhibited remarkable reductions in the average coefficient of friction (COF) and wear rate of rapeseed oil, compared to single MoS2 or CeO2. At a 1.5 wt% addition of MoS2/CeO2, the average COF and wear rate decreased to the lowest value, respectively. Moreover, the frictional behaviors of the rapeseed oil containing MoS2/CeO2 nanohybrid under various sliding conditions were explored as well. By analyzing the microstructure and composition of the counterparts’ surfaces, a lubrication mechanism for 2D/2D nanohybrid of MoS2/CeO2 was proposed. This research might promote the application of MoS2/CeO2 nanohybrid as additive for ecologically friendly lubricants.

Eco-friendly lubricants for improving performance and environmental impact in cold rolling

Cold rolling of strips is a well-known metal forming process, carried out below the material recrystallization temperature to improve the surface finish and the geometrical tolerance of the rolled strip. Friction plays a fundamental role in the rolling process and, even in case of a favorable roll bite condition, a non-optimal lubrication causes the rapid wear of the work rolls and high energy consumptions. Most of the currently used lubricants are based on synthetic or semi-synthetic formulations. However, the increase in the cost of petroleum-based products and the tightening of the environmental regulations is pushing the scientific and industrial community to search for more sustainable alternatives. Recently, the demand for green lubricants capable of matching non-toxicity, high biodegradability while keeping good lubricating performance is becoming of outmost importance. In the present work, the environmental impact and the lubricating performance of two innovative natural-based lubricants have been assessed using laboratory tests. An animal-based (AB) and a vegetable-based (VB) formulation were investigated and the results compared with a commercial mineral-based (MB) one. As concerns the environmental impact, emulsions at 2% oil concentration were chemically treated using a powder composed of bentonite and activated carbons and the Chemical Oxygen Demand (COD) and total Surfactants in the aqueous phase were evaluated. The lubricating performance of the emulsions at 2% oil concentration was assessed by conducting tribological tests using the Falex tribometer in accordance with the Standard. The experimental comparison revealed that it is not only feasible but also convenient in terms of both environmental impact and performance to replace the mineral-based lubricant.

Development of nano biochar as a lubricating oil additive for tribological applications

Nano-materials, given their excellent anti-friction and anti-wear characteristics, have attracted significant attention in tribological applications. However, conventional nano-materials have difficulty meeting the development requirements of the eco-friendly lubricants. In this study, nano biochar derived from sesame stalk was synthesized and used as a lubricant additive in poly-alpha olefin-6 (PAO6). The tribological properties were evaluated by four ball tribological tests with steel and ceramic balls as the friction pair. Following the friction experiment, the worn surface on the steel ball was analyzed by X-ray photoelectron spectrometry. The steel ball friction results showed that the lubricants containing 0.2 wt% nano biochar achieved a maximum wear volume reduction of 46% compared to PAO6, and the friction coefficient decreased by 34.6% for the ceramic balls. Analysis indicated that the enhanced wettability of nano biochar lubricant contributed to improving the anti-wear properties. Characterization of the worn surface revealed that the addition of nano biochar facilitated the formation of strong Fe3O4 tribofilms. This study demonstrated that nano biochar could serve as an environmentally friendly additive in the liquid lubricant industry.

Biolubricants as an industrial sustainable product: source, emissions impact, physiochemical and tribological properties—An overview

Bio lubricants are known for their biodegradable and non-toxic to humans and the environment. In contrast to mineral oils, bio-lubricant usage is still quite limited despite this trend in research and innovation. The development in demand for eco-friendly lubricants is linked to the evolution of environmental regulation, which is growing more stringent to limit improper disposal's environmental impact. Bio lubricants are classified as synthetic or natural oils based on their chemical composition. Natural oils of animal or vegetable origin are rarely considered due to their unstable propensity at high pressures and temperatures. This work gives an overview of the green potential of bio-lubricants, sources, emission impact, and physiochemical and tribological properties. Lignocellulosic biomass has a substantial ability to reduce greenhouse gas emissions and global warming through the use of biofuel products. The various bio-lubricants from vegetable oils and other biomaterials are obtained from different routes, primarily through yielding branched-chain or straight monoesters, polyol esters, triesters, or diesters. One or more reactions may be accompanied or preceded by the conversion of triglycerides to esters to boost reactions like hydrogenation and epoxidation.

A Comparative Analysis of the Lubricating Performance of an Eco-Friendly Lubricant vs Mineral Oil in a Metallic System

Eco-friendly lubricant research continues to increase since it has a comparative performance to commercial mineral lubricants to overcome the effects of environmental impact. However, the efficiency of these green lubricants depends on specific applications. In this study, we analyzed the friction and wear performance of a castor/sesame oil mixture as an eco-friendly lubricant and its comparison to a commercial mineral lubricant tested in a metallic system employed in bearing elements. For this purpose, AISI 8620 steel against ISO 100Cr6 was used as tribological pair. The friction and wear tests were carried out through a Tribometer of ball-on-disk configuration under boundary lubricating conditions, whereas the worn surfaces were investigated by using optical and electron microscopy. The physical properties and the rheological properties of the lubricants were also determined. The friction and wear performance between the eco-friendly lubricant and mineral oil were similar so that the CLE were comparable. The CLE values in terms of friction and wear ranged from 86% to 99.4%, respectively.

Hexagonal boron nitride nanosheets eco-friendly dispersed in pure water for lubrication in fretting contacts between steel pairs

The lubricating effect of h-BN nanosheets, dispersed in pure water without the use of any chemicals, was investigated under fretting contacts. The resistance against oxidation of sliding pairs was also considered using AISI 52100 and AISI 304 steel pairs separately, given that oxidation is inevitable on steel surfaces. In the partial slip regime, effects of the type of lubricant and oxidation on wear and friction were insignificant. In the mixed slip regime, the mending effect of h-BN counteracted the oxidation of sliding surfaces, resulting in mild wear. In the gross slip regime, the mending effect collapsed due to oxide debris, resulting in severe wear. Moreover, the results showed that the presence of h-BN nanosheets influenced the transition of fretting regimes. These findings suggest that aqueous-dispersed h-BN nanosheets can be an effective eco-friendly lubricant additive, particularly when fretting conditions enable a stable mending effect and sliding surfaces exhibit high corrosion resistance.

Research on the Rice Bran Oil – Flammability Tests on a High Temperature Surface

In this work rice oil was tested when it is dripped onto a high temperature surface. The tests conducted determined the lowest temperature at which rice oil ignited and the highest temperature at which rice oil did not ignite in three tests conducted at the same temperature. The results of this study show that the values of the evaluated temperatures are of major importance regarding the use of rice oil as an eco-friendly lubricant. Thus, the highest temperature at which rice oil did not ignites is 465 °C, while the lowest temperature at which rice oil ignited is 470 °C. Moreover, at the end of the 8 tests performed, part of the oils collected in the tray of the installations used in the present study were subjected to spectrophotometric tests. Based on the obtained data, the transmittance spectra were plotted and the trichromatic components and coordinates were calculated, as well as the colour differences of the tested oils.

Tribological Performance Evaluation of Blended Lubricants Incorporated with Organic Polymer

Eco-friendly lubricants have drawn a lot of interest in the lubrication industry as a way of promoting global sustainability in response to the growing environmental pollution danger posed by the use of petroleum-based lubricants. As a result of these, developing lubricants with organic additives stands as a promising technique in solving the environmental challenges caused by non-degradable materials. This research investigates the effect of bio-based water hyacinth (Eichhornia crassipes) (EC) carboxylmethyl cellulose (CMC) polymer in different base lubricants as well as under different volumetric blend to determine their compatibility effect on lowering friction and wear using base rapeseed oil (BRO) and mineral oil (MO) as a base lubricant sample. High frequency reciprocating rig tribo-tester machine was used in the experiment, followed by substrate surface analysis via energy dispersive x-ray spectroscopy. The additives were evaluated for their potential to improve tribology in terms of friction, surface roughness and wear reduction, load-carrying capacity, and mechanism of repair. Testing the additive concentrations, produced recommendable result at 0.8 mass% EC-CMC. The best performance was obtained when BRO70/MO30 was blended with 0.8 mass% EC-CMC. When compared to base BRO and MO lubricants under 80 N, 0.8 mass% BRO70/MO30 reduced the coefficient of friction and wear scar diameter by 44%, 32%, and 33%, 21% respectively. However, it was shown that nanoparticles had greater tribological performance at higher working capacities owing to the rapid and active tribo-film formation.

Layered Magnesium Phosphate as an Environmentally Friendly Solid Lubrication Additive: Morphology Control and Tribological Properties

To develop a new type of environmentally friendly solid lubricant and expand the high-value utilization of salt lake resources, we prepared a layered magnesium phosphate (MgHPO4·1.2H2O) eco-friendly lubricant using an improved green hydrothermal synthesis route in which particle size and morphology were controlled. The tribological properties of the layered magnesium phosphate samples as additives in PAO8 calcium-based grease were evaluated using an Optimol SRV-V oscillating reciprocating tester (hereafter referred to as SRV tester). Products exhibited excellent friction behavior when added to grease. When added at 3.0 wt %, the tribological properties of the grease were improved significantly; the highest operating load was raised from 400 to 600 N, the wear volume was decreased from 44.98 to 7.50 (10–4 mm3), and friction curves became more stable and smooth. A possible lubricating mechanism was proposed. Macro to micro analysis of rubbing surfaces showed that the MgP materials had a protective effect on the PAO8 calcium-based grease matrix, and lubricating films were clearly formed on the friction pair surface.

Lubricant mechanisms of eco-friendly lubricant blended with mineral oil for steel-steel contact

This study intends to explore the lubrication mechanism of eco-friendly lubricant formulated from non-edible vegetable oils and mineral oil. The efficacy of the lubricant as friction and wear-reduction additive is determined to have a mixed lubrication regime with the optimum concentration of 80 % S100, 10 % C100, and 10 % J100 (S80C10J10). A protective film and mending effect have been suggested as lubricating mechanisms. The lubrication regime is changed from mixed to hydrodynamic by increasing the volume percent of C100 and J100, which improves the COF because fluid drags cause friction to be produced by the fluid on the moving surface. The inability of the additive to form a protective layer led to the worst COF and WSD.

Tuning the interfacial behavior of extreme pressure lubrication by stearic acid-modified TiO2 nanoparticles

The development of high-performance lubricants under extreme pressure (EP) is of great significance for reducing energy waste and protecting ecology in heavy industries such as aerospace, large machinery, and so on. Sulfurized isobutylene (SIB) has been explored as one of the most effective EP additives for oil-based lubricants and delivered promising friction-reducing performance. However, the excessive corrosion caused by SIB on the metal surface seriously reduces the instrument’s lifetime and hinders its extensive practical application. Herein, we develop stearic acid-modified TiO2 nanoparticles (SA-TiO2) as a lubricant additive to improve the EP lubrication performance of obtained composite lubricant (CL). During EP friction, the SA-TiO2 can tune the interfacial structure of tribopair and form a high-strength nano-ceramic film to improve tribological performance. Meanwhile, the SA-TiO2 can also compensate for the high wear caused by SIB, thus significantly enhancing the antiwear, friction reduction, and EP properties by 27%, 20%, and 25%, respectively, when compared with the traditional lubricant (TL) obtained by only SIB. Benefiting from the above synergistic effects, the CL can significantly lower the SIB contents while maintaining high EP performance (4900 N weld load). These findings demonstrate a promising eco-friendly lubricant and provide new insights into the mechanism study for EP lubrication.

A Review on the Effect of Minimum Quantity Lubrication on Different Machining Parameters Emphasizing Vegetable Oil-Based Lubricants for Sustainable Manufacturing

The cutting fluid plays a significant role in minimizing heat generation and chip removal process during the machining of materials, hence improving tool life and surface finish of the workpiece. Many researchers have focused on minimum quantity lubrication (MQL) among the existing methods on the application of the coolant as it reduces the usage of coolant by spurting a mixture of compressed air and cutting fluid in an improved way instead of flood cooling. The MQL method has demonstrated to be appropriate as it fulfills the necessities of ‘green’ machining. Additionally, considering current environmental issues and provisions for safe healthy working conditions at the workplace, it is important to divert machining processes towards an eco-friendly path. Hence, the focus of research has been shifted to MQL using eco-friendly lubricants for green and sustainable manufacturing processes. In this review paper, the effect of different vegetable oil-based biodegradable coolants like castor oil, coconut oil, palm oil, etc. for different machining process parameters like cutting force, cutting temperature, surface finish, tool wear, etc. has been reviewed. It is observed that proper selection of cutting parameters along with lubricant through MQL can provide enhanced machinability to get desired outputs.