Conventional Greases Research Articles

Enhancement of polyurea grease performance through graphene oxide-functionalized polyurea thickeners: A novel hydrogen-bond network approach

In conventional grease formulations, thickeners and additives are added as distinct components. This study introduces a method that integrates graphene oxide (GO) functionalized polyurea thickeners, creating a unified structure of polyurea and GO. The impact of GO functionalized polyurea on the rheological and lubrication performance of polyurea grease was investigated. Results showed that the polyurea modifies GO by covalent bonds and forms a hydrogen bond network. The GO modified polyurea reduced the yield stress and improved the flowability of the polyurea grease. The GO modified polyurea enhanced the tribological performance of polyurea grease because of the collaboration effect of tribo-chemical film and graphene boundary film. This study emerges as a viable strategy to improve the performance of polyurea grease.

Tribological Performance Evaluation of Greases on a Four-Ball Tester with Graphene Oxide Nanoparticles.

Conventional greases have an exceptional place in the field of lubrication. They are unique in the sense of their areas of application and are very difficult to replace with other lubricating substances for the same reason. The advancements in the field of nanoparticles and the results they provide as an additive in greases have great scientific interest as they improve the tribological properties of greases to a great extent. The current work's aim is to synthesize a nanogripe using graphene oxide (GO) nanoparticles to lithium grease (Li grease), which will increase the tribological properties of the plain Li grease. Steps were taken to investigate the impact of variation of load on the frictional and wear characteristics of nanogrease. Synthesis of nanogrease and tribological evaluation were performed with a magnetic stirrer with a hot plate and a four-ball tester. Results indicated that nanogrease exhibits better tribological properties. It is also found that the antiwear and frictional properties of grease are not proportional to the wt % of GO nanoparticles. It is also detected that with the increase in load, the tribological properties of nanogrease increase.

A novel layered double hydroxides oleogel lubricant: Inspired by conventional greases

Grease lubricants serve as a simple, effective and convenient source of lubrication for saving energy. However, the most applicable lithium greases meet contradictory pressures of high performance and low pricing demands because of the substantial development of the global electric vehicles industry and the ubiquity of lithium batteries. In order to alleviate the dependence on lithium resources and develop resource-widespread and economical lubricating grease, herein, a class of thickener and oleogel system based on organic acid intercalated layered double hydroxides (LDHs) inspired by traditional grease has been reported. LDHs materials can be regarded as a preassembled “salt-like” compound, comparable to the self-assembled traditional metal soap salt thickener. LDHs oleogels exhibit viscoelastic properties and tribological performance similar to those of lithium greases. This study presents ideas for future development through layered materials regarding as "salt-like" compounds as a replacement for traditional grease thickeners.

Production and Performance Evaluation of Shea Butter-Based Lubricating Grease

The overwhelming cost of conventional lubricants has instigated the need for alternatives in the engineering industry. This study identified the physicochemical properties of Shea butter made from the shea nut and their application as a bio-grease in the food processing and industrial sectors. Some preliminary tests were conducted to ascertain the combination of materials that will produce grease with the right consistency as the commercial product. Results on its physicochemical properties showed that shea butter was suitable for use as lube base oil. Best bio-grease was obtained with mass combinations of 80.0 g of Shea butter, 0.5 g of resin, 1.0 g of P.K.O, 1.5 g of calcium hydroxide, 8 g of stearic acid, 1.5 g of silicate, 1.5 g of sodium carbonate, 4 g of biochar, and 2 g of cellulose. The physicochemical properties observed were evaporation loss (1.2%), ash content (4%), moisture content (0%), flash point (146.5℃), fire point (155℃), pour point (25.9℃), and density (0.97 g/cm3). Most of the properties of the bio-grease were found to be comparable with conventional grease. In addition, since the bio-grease was produced from majorly edible sources and based on its properties, it could be classified as H3 food-grade grease.

Lubricity and mechanical stability of bio-grease formulated from non-edible vegetable oil

This study proposes the formulation of a novel grease material using biological resources, which displayed satisfactory mechanical and lubrication properties. This bio-grease material was formulated using non-edible vegetable oils (such as castor, neem and jatropha oils), with a beeswax thickener and hexagonal Boron Nitride (hBN) as the nano additive. Thereafter, the optimal formulation of the bio-grease material was conducted using the Taguchi-based Grey Relational Analysis technique. The lubricity and mechanical stability of the formulated bio-grease material was tested with the help of a 4-ball tribometer based on the modified sliding frictional wear test, described in the ASTM D2266 standard. The fundamental wear mechanism occurring between the contact surfaces was also determined by investigating the surface morphology using Scanning Electron Microscopy embedded with Energy Dispersive X-Ray Analysis (SEM-EDX). The results of the study indicated that base oil was the most significant factor that affected the Coefficient of Friction (COF) and the mechanical stability loss of the formulated bio-grease. Furthermore, the optimised bio-grease material contained 5 wt.% of thickener in castor oil and showed the lowest COF value of 0.04 and the highest delay in the mechanical stability loss (13,200 s). The acquired results were compared with those of the conventional grease material and observed that the SEM images of conventional grease material showed higher adhesive wear and rougher surface compared to the micrographs of the samples that were lubricated using the optimally-formulated bio-grease material.

Tribological Behavior of Novel CNTs-Based Lubricant Grease in Steady-State and Fretting Sliding Conditions

The tribological behavior of novel 7.5 wt% carbon nanotube-based lubricant greases in PAO (polyalphaolefin) oil with and without 1.0 wt% MoS2, together with several other commercial greases such as calcium, lithium, were studied. The test results showed a marked reduction of frictional coefficient achieved by the CNTs based grease samples with an average benefit of around 30% compared to conventional greases. The steady state test under 1.00 GPa average contact pressure in a mixed lubrication regime and the fretting test showed the best results in terms of friction reduction obtained by CNTs greases. Steady state tests at higher average contact pressure of 1.67 GPa proved to have a lower friction coefficient for CNTs grease containing MoS2; otherwise CNTs grease without MoS2 showed an average value of CoF comparable to calcium and lithium greases, both in a boundary and a mixed regime. The protection against wear, a considerable decrease (−60%) of reference parameter was measured with CNTs grease with MoS2 (NLGI 2) in comparison with the worst conventional grease and −22% in comparison with the best conventional grease. The data indicated that our novel carbon nanotube greases show superior tribological properties and will have promising applications in the corresponding industry.

Synergistic effect of binary systems of nanostructured MoS2/SiO2 and GO/SiO2 as additives to coconut oil‐derived grease: Enhancement of physicochemical and lubrication properties

AbstractThe present work addresses the use of synergistic blends of two different types of nanomaterials (spherical particles and lamellar sheets) as additives for coconut oil‐based grease formulation to provide the energy‐efficient and sustainable alternative to conventional grease. The spherical SiO2 nanoparticles are separately blended with 2D lamellar sheets of MoS2 and graphene oxide (GO) in variable ratio and probed their synergistic effects for enhancement of physicochemical and lubrication properties. The SiO2 nanoparticles, MoS2, and GO nanosheets are prepared by modified sol–gel, hydrothermal reduction, and Hummer's methods, respectively. The 0.05 wt% nanomaterials blends of MoS2/SiO2 (30:70) and GO/SiO2 (50:50) as optimised doses furnished the maximum reduction in the friction and wear. The combination of rolling friction and low shear properties using the synergistic blend of the spherical nanoparticles (SiO2) and nanosheets (MoS2 and GO) showed significant improvement in tribological properties. The optimised blends of nanoadditives, that is, MoS2/SiO2 and GO/SiO2 conserved the energy by 20% and 19%, respectively. These findings suggest that the use of synergistic blends of variable nanomaterials to vegetable oil‐based lubricants can pave a direction for new generation lubricant formulation, where environmental sustainability and energy conservation are on prime importance.

Preparation and Characterization of Grease using Used Cooking Oil and Used Engine Oil

Used engine oil (UEO) and used cooking oil (UCO) are treated as hazard to human health and the environment. A proper management of them are necessary to prevent its adverse impacts. This study is to examine the potential of UEO and UCO used as raw material in preparing grease. UEO and UCO has the potential in replacing the base fluid (mineral oil) and thickener precursor, respectively in conventional grease making. The thickener has been prepared by using calcium hydroxide and sodium hydroxide to react with UCO with the ratio of 1:2 (hydroxide: UCO) and denoted as calcium and sodium thickener, respectively. In grease making, different concentration of thickener (20, 30 and 40%) was used to react with UEO for 180 min at 160 – 180 °C. The formation of grease is confirmed by FTIR analysis, where a new peak was form in 1377 cm−1 – 1423 cm−1. Apart from that it was found that, 20% calcium thickener with 80% UEO grease and 40% sodium thickener with 60% UEO grease were comparable with commercial grease in term of dropping point and water resistance properties.

Viscosity-adjustable grease matrices for serial nanocrystallography

Serial femtosecond crystallography (SFX) has enabled determination of room temperature structures of proteins with minimum radiation damage. A highly viscous grease matrix acting as a crystal carrier for serial sample loading at a low flow rate of ~0.5 μl min−1 was introduced into the beam path of X-ray free-electron laser. This matrix makes it possible to determine the protein structure with a sample consumption of less than 1 mg of the protein. The viscosity of the matrix is an important factor in maintaining a continuous and stable sample column from a nozzle of a high viscosity micro-extrusion injector for serial sample loading. Using conventional commercial grease (an oil-based, viscous agent) with insufficient control of viscosity in a matrix often gives an unexpectedly low viscosity, providing an unstable sample stream, with effects such as curling of the stream. Adjustment of the grease viscosity is extremely difficult since the commercial grease contains unknown compounds, which may act as unexpected inhibitors of proteins. This study introduces two novel grease matrix carriers comprising known compounds with a viscosity higher than that of conventional greases, to determine the proteinase K structure from nano-/microcrystals.

Characterisation of food service establishment wastewater and its implication for treatment

Essential for the selection of a reliable treatment system is the characterisation of the effluent to treat. Kitchen wastewater (KWW) from food service establishments (FSEs) is a strong organic and fat-rich effluent whose characterisation has not been sufficiently addressed. KWW composition is highly variable and linked to the FSE's size, the type of meals prepared and the amount of water used during the cleaning. COD, TSS and fat content (FOG) are the most common parameters found in literature. However, other physical and chemical parameters (e.g. temperature, pH, oil droplets characteristics and trace elements), correlated to commercial kitchen cleaning practices rather than the specific effluent, but equally influential on the treatment efficiencies of both physical and biological methods, have hardly been investigated. A comprehensive characterisation of wastewaters from three food service establishments was used to generate data to support the selection of appropriate FOG mitigation methods. Two novel analytical methods were used to quantify the proportion of emulsified FOG and associated droplet size from different kitchen washing effluents. The results showed that more than 90% of the FOG from the dishwasher effluent and around 35% of sink one was emulsified, with droplet sizes less than 100 μm, well below the removal capabilities of conventional grease interceptors, but easily removed using biological means. From the WW composition results, a formula for predictive modelling was derived to represent average organic matter composition for kitchen wastewater as C20H38O10N, applicable in remediation processes. These results offer a good starting point for the design, operation, and optimisation of wastewater treatment systems of oil-rich KWW.

A Master Curve for the Shear Degradation of Lubricating Greases with a Fibrous Structure

In this article, the mechanical aging behavior of lubricating greases with a fibrous structure is studied by aging fresh samples at controlled shear rates and temperatures in an in-house-made Couette aging machine. The rheological properties of fresh and aged samples were evaluated in a plate–plate rheometer. In the absence of oxygen, no chemical reactions occurred. The results showed that shear degradation is accelerated by increasing the temperature. This thermal effect can be described by an Arrhenius law. A grease aging master curve was created to describe the influence of shear and temperature on the mechanical aging of fibrous structured grease. Next, the model was validated using a conventional grease worker test. Finally, the model was applied to full ball bearings using an R0F + bearing test rig. The master curve forms an important contribution to the development of grease life models.

EVALUATION OF LUBRICATION EFFICIENCY BASED ON WEAR DURING VARIABLE LOADS AND SLIDING VELOCITIES

The results of the tribological studies on the lubrication efficiency of greases evaluated based on tribological tests performed at varying pressure p and rubbing speed v are presented. For the efficiency criterion, the volume of wear VF(d) obtained from the regression equations of wear was adopted (wear F (d) = f (F, v)). Six different lubricants were tested; two of them were commercial greases, and four of them were compositions based on them, including conventional solid greases (PTFE, tin, copper, and boron nitride). The experiment was carried out on a four-ball extreme pressure tester according to a rotatable design on five levels. For each of the selected lubricants, a regression function was developed that defined wear as a function of rubbing speed and load. The volume of the obtained wear VF(d) was calculated and relevant conclusions were drawn.

Renewable Resource‐Based Lubricating Greases from Natural and Synthetic Sources: Insights and Future Challenges

AbstractGreases enhance most mechanical equipment in terms of joint performance and operation age by reducing friction and wear. However, they are also considered a dangerous source of soil and water pollution because of their synthetic nature. Renewable resource‐based materials are a safe and environmentally friendly solution. In the present work, a comprehensive study is conducted to evaluate the performance of existing synthetic and biodegradable greases. This work also provides insights into existing literature and presents ideas for future development through general recommendations regarding the use of renewable resource‐based ingredients as a replacement for traditional synthetic materials in conventional greases.

Rheological and Tribological Characterization of a New Acylated Chitosan–Based Biodegradable Lubricating Grease: A Comparative Study with Traditional Lithium and Calcium Greases

This work compares the thermal, rheological, and tribological properties of a new gel-like biodegradable formulation, prepared using an acylated chitosan thickener and castor oil, with properties exhibited by two conventional greases thickened with lithium and calcium soaps, respectively, taken as benchmarks. Thermogravimetric (TGA), rheological (small-amplitude oscillatory shear [SAOS], rheodestruction, and viscous flow) and tribological (friction and wear analysis) tests, as well as roll-stability measurements were carried out to characterize the three grease samples. In addition, infrared spectroscopy and differential scanning calorimetry (DSC) were used to chemically characterize the acylated chitosan thickener agent. From a thermogravimetric point of view, the new formulation displayed better thermal resistance than the calcium and lithium lubricating greases. The evolution of the linear viscoelasticity functions with frequency and viscosity values in the shear rate and temperature ranges studied were similar to those obtained with the commercial lubricating greases. However, the linear viscoelasticity functions of the biodegradable formulation were slightly more affected by temperature. The mechanical stability behavior and recovery of the rheological functions found in the biodegradable formulation were also better than that exhibited by the calcium-based grease. However, the friction coefficient measured at low rotational speed is slightly higher than that obtained with the benchmarks, with similar or lower values obtained at a high rotational speed. Resulting wear marks obtained after the frictional tests using the acylated chitosan–based grease were larger than those obtained with the commercial greases.

Tribological Properties of Thermo-Reversible Gel-Lubricants Containing Solid Lubricants

Previously, we have reported tribological characteristics of a new unique Thermo-Reversible Gel-Lubricants (TR Gel-Lube), which consists of base fluids and gel agent. TR Gel-Lube has low friction property compared with conventional greases under mild lubricating conditions. However, under severe lubricating condition, extreme pressure (EP) property must be improved by some EP additives. In this study, addition of solid lubricants was investigated. Tribological properties were examined by some tribometers and various enhancements by Molybdenum disulfide, Melamine Cyanuric Acid and Boron Nitrides were observed. Mechanisms of the lubricity improvements were proposed by results of some chemical/physical analyses.

Tribological Properties and Film Formation Behavior of Thermoreversible Gel Lubricants

The tribological properties of a new and unique thermoreversible gel lubricant (TR gel lube) were investigated. TR gel lube, which includes 10–40% of amide-type gelling agent in base fluid, is able to repeatedly alter or convert phase from gel state to liquid state at the melting point of the gelling agent. High-pressure rheological tests were performed in order to characterize the behavior of base oil and TR gel lube as a function of pressure and temperature. The effect of TR gel lube on ball bearing fatigue life was carried out by systematic tests using thrust ball bearings. The results of L 10 life tests of TR gel lube showed a longer life than the conventional greases. This result was investigated from the oil film formation. It was found that the gelling agent played a key role in the lubricating properties. Some mechanisms such as adsorbed film formation and solid-like formation are proposed.

Performance of Grease Abatement Devices for Removal of Fat, Oil, and Grease

This study assessed the performance of a conventional grease abatement device and the impact of internal geometry modifications on fat, oil, and grease (FOG) removal efficiency. Analysis was performed using experimental results and computational fluid dynamics (CFD) on alternative inlet, outlet, and baffle wall designs. Numerical and experimental results indicated that the conventional two-compartment design leads to substantial FOG short circuiting when operated at a 20-min hydraulic retention time (HRT). Alterations to the inlet configuration and baffle wall arrangement yielded FOG removal enhancements with the 20-min HRT that approached removal performance levels obtained with the standard configurations at the 1-h HRT. CFD simulations effectively reproduced performance trends observed on the lab-scale with the exception of simulations using a distributive inlet tee, where CFD over predicted the removal performance.

EHL Oil Film Behavior of Thermo-Reversible Gel-Lubricants

This study investigates about the characteristic of the thermo-reversible gel-lubricant (TR Gel-Lube) under elastohydrodynamic lubrication (EHL) conditions. TR Gel-Lube is the lubricant, which consists of base fluid and a gel agent. TR Gel-Lube is repeatedly able to change gel-state to liquid-state at the melting point of its gel agent. Moreover, TR Gel-Lube has good tribological properties, anti-evaporability and so on. This paper describes about investigation of the EHL oil film thickness characteristic, the oil starvation at EHL inlet region and the EHL traction characteristic. It was observed that TR Gel-Lube had low EHL traction, thick EHL film thickness and good stability of EHL oil film formation compared with conventional greases.

Direct Observation of Thermo-Reversible Gel-Lubricants in EHL by FT-IR Micro-Spectroscopy

The tribological properties of a new unique thermo-reversible Gel-Lubricant (TR Gel-Lube) were investigated. TR Gel-Lube which includes 10-40% of amide type gel agent in base fluid, is repeatedly able to change from gel-state to liquid-state at the melting point of its gel agent. TR Gel-Lube can be used as an impregnant for porous-material due to its physical state change. TR Gel-Lube indicated lower frictional and better lubricating properties than that of conventional greases. In particular, when TR Gel-Lube was sintered in a copper-type sintered bearing, a lower friction coefficient compared with oils was observed. In this study, to clarify the mechanisms of TR Gel-Lube, the behavior of gel agent on the EHL region was investigated by ball-on-disk tribometer. It was found that gel agent played a key role in the lubricating properties. Some mechanisms such as adsorbed film formation, smooth surface formation and solid like film formation are proposed.

Total vegetable oil greases

AbstractA grease has two major constituents, namely, a lubricant, that performs the function of lubrication; and a gellant, that provides a solid continuous phase, occludes the lubricant, and gives apparent physical structure to the grease. Generally, the gellant is 5–30% and the lubricant 65–90%, additives and fillers making up the rest. In conventional greases, the gellant is a vegetable oil soap, and the lubricant is a liquid oil of petroleum origin or is a synthetic. Such greases have limited biodegradability, because the major constituent, i.e., the lubricant, is normally not biodegradable.In total vegetable oil grease, both the gellant and the lubricant are derived from vegetable oils, giving a grease of potentially high eco‐compatibility. Esters, dibasic acid esters, and alkylated esters of vegetable oil are known to be high‐quality lubricants. These can be used with soap stocks prepared from vegetable oils to give a grease of total vegetable oil origin.The vegetable‐oil based lubricants and soaps are prepared separately and combined in appropriate proportions to give a grease of the required specifications. Alternatively, esterification and saponification can be carried out simultaneously to give a grease of the desired specifications, where an alkali will be the catalyst for esterification, and reactant for saponification. In this paper, the process parameters, and kinetics of these simultaneous reactions are discussed. The results of experimental evaluation of some of these greases are also presented.