Ester-based Oils Research Articles

Experimental investigation of the tribological behavior of lubricants with additive containing copper nanoparticles

Abstract This study investigates the tribological behavior of mineral and synthetic ester base oils additivated with copper nanoparticles. The additive was dispersed at 0.3% and 3.0%wt. in each base oil. The friction and wear tests were performed using a tribometer with pin-on-disk and four-ball configuration. Tests with the formulations with and without the nano-additive were carried under different conditions of contact pressures, sliding speeds and oil bath temperatures. The results indicate that the additive, at both concentrations, is not suitable for the application as friction modifier nor as antiwear agent in synthetic polar oil. Furthermore, the results show that the nano-additive in mineral oil reduced the friction coefficient and improved antiwear characteristics at both concentrations tested, especially at 0.3%wt.

Oxidation Products of Ester-Based Oils with and without Antioxidants Identified by Stable Isotope Labelling and Mass Spectrometry

As lubricants with a high thermo-oxidative stability such as synthetic esters are gaining more importance in the lubricant market, a detailed knowledge regarding their oxidative degradation behaviour is of high importance. In order to reveal their degradation products and processes, a novel approach combining artificial alteration, isotope labelling based on oxidation with 16O2 and 18O2, and mass spectrometry (MS), was applied to a bis(2-ethylhexyl) adipate base oil. The degradation products such as 2-ethylhexanol and its monoesters with short-chain fatty acids pinpointed the C–O ester bond as the site prone to oxidative attack, allowing the collection of information about the oxidation mechanisms. Furthermore, the influence of the antioxidant (AO) 4,4′-methylene-bis(2,6-di-tert-butylphenol) as an additive on the oxidation behaviour and resulting products was studied: blends containing AO showed a remarkably higher resistance against oxidation. However, similar degradation products were obtained after AO depletion and without AO. AO cleavage occurred at the carbon atom that bridges the phenols to give 2,6-di-tert-butyl-p-benzoquinone and 3,5-di-tert-butyl-4-hydroxybenzoic acid. By applying the isotope labelling approach, sites of preferential oxidative cleavage and hence differentiation of the origin of oxygen atoms—either from the atmosphere or from base oil components—can be unambiguously related in oxygen-containing base oils, as well as in blends with additives.

Thermal-oxidation mechanism of dioctyl adipate base oil

Abstract The ester base oil of dioctyl adipate (DOA) was oxidized in an oven at 200 °C for 30 h, and variations in the physicochemical and tribological properties were studied. To investigate the thermal-oxidation mechanism, the thermal-oxidation products were analyzed by gas chromatography–mass spectrometry (GC−MS), and the thermal-oxidation process was simulated using visual reactive force field molecular dynamics (ReaxFF MD). The results indicated that the total acid number (TAN) increased significantly because of the presence of 14% carboxylic acids and low molecular weight monoesters. The tribological properties were improved by the formation of the strongly polar carboxylic acids. Additionally, the increase in kinematic viscosity was limited due to the formation of high molecular weight polymerization products and low molecular weight degradation products. Thermal-oxidative degradation and polymerization mechanisms were proposed by combining ReaxFF MD simulations and GC−MS results.

Ultralow Friction of a Tetrahedral Amorphous Carbon Film Lubricated with an Environmentally Friendly Ester-Based Oil

The tribological properties of diamond-like carbon (DLC) films that were lubricated with an environmentally friendly ester-based oil were investigated. Sliding tests were performed on two types of DLC films, hydrogenated amorphous carbon (a-C:H) and tetrahedral amorphous carbon (ta-C) films, using a steel cylinder that was in contact with a steel disk coated with either a-C:H or ta-C under boundary lubrication. To compare the tribological properties of ester-based oils and other based oils, Trimethylolpropane (TMP) ester, polypropylene glycol (PPG), and poly-alpha olefin (PAO) were used as the test lubricants. The ta-C film that was lubricated with TMP ester exhibited the ultralow friction coefficient of 0.015; however, the a-C:H film that was lubricated with TMP ester did not exhibit the ultralow friction. On the other hand, results obtained by a quartz-crystal microbalance with dissipation indicated that the adsorption properties of based oils depended on the type of sensor material (carbon or iron) and the type of based oil used in the measurements. Moreover, the frequency change of based oils increased with decreases in the average frictional coefficients of the steel-steel tribopair and the DLC-steel tribopair. Results of surface analysis indicated that TMP ester formed tribofilms on the ta-C surfaces, which exhibited high viscosity and low friction. All these results suggest that the combination of the ta-C film and TMP ester is the new ultra-low-friction and environmentally friendly sliding system.

Homogeneous Modification of Sugarcane Bagasse by Graft Copolymerization in Ionic Liquid for Oil Absorption Application

Sugarcane bagasse, lignocellulosic residue from the sugar industry, is an abundant and renewable bioresource on the earth. The application of ionic liquids in sugarcane bagasse biorefinery is gaining increasing interest. The homogeneous modification of sugarcane bagasse by free radical initiated graft copolymerization of acrylate monomers using 1-allyl-3-methylimidazolium chloride as solvent was performed. A variety of sugarcane bagasse graft copolymers with different weight percent gain were prepared via adjusting the monomer dosage. FT-IR studies confirmed the success in attaching the poly(acrylate) side chains onto sugarcane bagasse. Oil absorbency studies suggested that the sugarcane bagasse graft copolymers were potential biobased materials for effective treatment of ester-based oils. SEM studies showed that the sugarcane bagasse graft copolymers displayed a dense morphology structure. Thermogravimetric analysis demonstrated that the thermal stability of sugarcane bagasse decreased after the homogeneous modification by the graft copolymerization. The present study provides an alternative strategy to convert sugarcane bagasse into a value-added functional biobased material.

Fourier Transform Infrared (FTIR) Spectroscopy as a Utilitarian Tool for the Routine Determination of Acidity in Ester-Based Oils.

A primary Fourier transform infrared (FTIR) method capable of determining acidity in ester-based oils is described and evaluated. Absolute free fatty acid (%FFA) and acid value (AV) calibrations were devised by spiking oleic acid into a refined, acid-free oil and measuring ν COO(-) at ∼ 1569 and ν phenolate(-) at ∼ 1588 cm(-1), respectively, in the second-derivative differential spectra. The FTIR acidity predictions were compared to the AOCS titrimetric method using acid mixtures as well as acid containing used vendor oils of undefined makeup and provenance, using two spectroscopically divergent reference oils as AC0. Relative to the AOCS reference method, the FTIR procedure was found to be both more accurate (± 0.107 vs ± 0.122) and reproducible (± 0.025 vs ± 0.077) in determining %FFA and similar in predicting AV. The FTIR phenolate method overcomes a variety of limitations of earlier FTIR-based methods, being particularly simple and well suited to routine, semiautomated acidity analysis of ester-based oils using a basic FTIR spectrometer.

In Situ Formed Ionic Liquids in Polyol Esters as High Performance Lubricants for Steel/Steel Contacts at 300 °C

In situ formed ionic liquids (ILs) as high temperature lubricants can be obtained by mixing polyol esters (pentaerythritol oleate or trihydroxymethylpropyl trioleate) with lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) in molar ratios of 1/0.5, 1/1 and 1/1.5. Thermal and rheological analysis indicate that the in situ formed ILs, [Li(polyol ester)]TFSI, with various molar ratios are more resistant to high temperatures and substantially stronger than the polyol ester base oils. Tribological results revealed that these in situ forming ILs with molar ratios of 1/1 and 1/1.5 possessed excellent friction reduction and antiwear performance for steel/steel contact at 300 °C. Moreover, their tribological properties were significantly better than the pure polyol ester base oils and perfluoroalkyl polyether (PFPE, as a reference lubricant) under the same conditions. The results of SEM-EDS show that tribo-films formed on the worn steel discs surface lubricated by [Li(polyol ester)]TFSI. The XPS analytical results...

Computational simulation of palm kernel oil-based esters nano-emulsions aggregation as a potential parenteral drug delivery system

The self-assembled structure of palm kernel oil-based esters (PKOEs) nano-emulsions has shown a great potential used for parenteral drug delivery applications. Here, all-atom level molecular dynamics (MD) was applied to investigate the aggregation process of PKOEs nano-emulsion system. The system consisted of palm kernel oil-based esters (PKOEs) and dipalmitoylphosphatidylcholine (DPPC) in water. The ratio of all constituents was taken from the homogenous region of a ternary phase diagram determined experimentally. The molecules started to aggregate very rapidly from random configurations. A doughnut-like toroidal assembled structure formed at 50ns with PKOEs surrounded by DPPC molecules. The structural and dynamical properties of the self-assembled doughnut-like toroidal aggregate were analyzed using the principle moment of inertia, eccentricity and radius of gyration. The aggregation structures were compact with the average radius of gyration of 4.10 (±0.02) nm over the last 5ns. Additionally, both hydrophobic and hydrophilic interactions were involved in aggregation process with a total solvent accessible surface area of 551.72 (±5.88) nm2.

A novel benztriazole derivative for enhancing the anti-oxidation properties of synthetic ester-based oils

Purpose – The purpose of this paper is to study a novel Mannich adduct of benztriazole-containing diphenylamine (coded as BD) and its anti-oxidation properties as an additive in two typical synthetic ester-based oils. Design/methodology/approach – The anti-oxidation properties in two typical synthetic ester-based oils were evaluated in detail, using rotating pressure vessel oxidation test. The tribological properties of BD in synthetic ester-based oil (A51) were also tested with Optimal SRV-I oscillating friction and wear tester at atmosphere. Findings – The results of tests demonstrated that the novel BD compound is, indeed, a high-performance anti-oxidation additive that was able to remarkably improve the oxidation stability of synthetic ester-based oils, when it was added at only 0.5 per cent concentration and compared with the base oils containing 0.5 per cent of the commercial available antioxidant additives such as 2, 6-di-tert-butyl-4-methylphenol and octyl-butyl diphenylamine. A plausible mechanism of exceptional synergistic anti-oxidation was proposed. Originality/value – This paper first investigated the anti-oxidation properties and mechanisms of the compound with the structure of BD, which can be very useful and would promote the application of BD antioxidant in the lubricant industry.

10.5937/zeint24-6824 = Experimental investigations of mineral and ester-based oils at low temperature

The aim of this study is to create references to mineral oil and recommendations for design rules for ester oil applications. Interest in the application of natural and synthetic ester-based fluids in different types of high voltage power equipment has increased over the last years. Most of the parameters relevant to insulation and cooling of high voltage equipment are studied at room or normal operating temperatures. Nevertheless, this equipment has to keep its functionality over the range of various uncommon conditions. For regions with cold climates, an important issue is the behaviour at low temperature. The objective of this work was to determine the insulation strength of mineral- and ester-based oil under a homogenous field at low temperatures for different oil states (moisture content between 5 and 25%). At low temperature (-25°C), the tested ester-based oil is not solidified but in a very thick aggregate state. At this temperature its insulation strength is still very high, even higher than at room temperature. As soon as the ester-based oil becomes solidified (-35°C), its insulation strength drops dramatically. The insulation strength of the tested ester-based oil at a low temperature, when the oil changes its aggregate state, is not dependent on water content.

Transesterification Reaction for Synthesis of Palm^|^ndash;based Ethylhexyl Ester and Formulation as Base Oil for Synthetic Drilling Fluid

The use of vegetable oil-based ester as a base fluid in synthetic drilling fluid has become a trend in drilling operations due to its environmental advantages. The transesterification reaction of palm oil methyl ester (POME) with 2-ethylhexanol (2EH) produced 98% of palm oil-based ethylhexyl ester in less than 30 minutes. Since the transesterification reaction of POME with 2EH is a reversible reaction, its kinetics was studied in the presence of excess EH and under vacuum. The POME-to-EH molar ratio and vacuum pressure were held constant at 1:2 and 1.5 mbar respectively and the effects of temperature (70 to 110°C) were investigated. Using excess of EH and continual withdrawal of methanol via vacuum promoted the reaction to complete in less than 10 minutes. The rate constant of the reaction (k) obtained from the kinetics study was in the range of 0.44 to 0.66 s⁻¹ and the activation energy was 15.6 kJ.mol⁻¹. The preliminary investigations on the lubrication properties of drilling mud formulated with palm oil-based 2EH ester indicated that the base oil has a great potential to substitute the synthetic ester-based oil for drilling fluid. Its high kinematic viscosity provides better lubrication to the drilling fluid compared to other ester-based oils. The pour point (-15°C) and flash point (204°C) values are superior for the drilling fluid formulation. The plastic viscosity, HPHT filtrate loss and emulsion stability of the drilling fluid had given acceptable values, while gel strength and yield point could be improved by blending it with proper additives.

Short alkyl chain imidazolium ionic liquid additives in lubrication of three aluminium alloys with synthetic ester oil

In this study the authors have compared the tribological behaviour of three aluminium alloys (ASTM 2011 T3, ASTM 6061 T6 and ASTM 7075 T6) lubricated with two room temperature ionic liquids (ILs) with the same short alkyl chain imidazolium cation, 1-ethyl-3-methylimidazolium, and two different anions, tetrafluoroborate (BF4) (L102) and bis(trifluoromethylsulfonyl)imide {[(CF3SO2)2N]; NTf} (LNTf102). The ILs were used as 1 wt-% additives of the synthetic ester base oil propylene glycol dioleate (PGDO) in reciprocating sliding tests. The results are discussed in terms of the properties of the lubricants and the hardness of the aluminium alloys. Plastic deformation, wear mechanisms and surface interactions have been studied by electron microscopy (SEM), energy dispersive (EDS) spectroscopy and three-dimensional profilometry. The tribological performance of both ionic liquids is similar, and depends on hardness values and on the degree of plastic deformation of each alloy. Reductions of more than 40% in the wear rate and surface roughness with respect to the base oil are achieved for both additives only for the hardest alloy Al7075. The performance of the additives is independent of the contribution of the different anions due to the absence of extensive tribocorrosion processes.

Molecular dynamics simulation of palmitate ester self-assembly with diclofenac.

Palm oil-based esters (POEs) are unsaturated and non-ionic esters with a great potential to act as chemical penetration enhancers and drug carriers for transdermal drug nano-delivery. A ratio of palmitate ester and nonionic Tween80 with and without diclofenac acid was chosen from an experimentally determined phase diagram. Molecular dynamics simulations were performed for selected compositions over a period of 15 ns. Both micelles showed a prolate-like shape, while adding the drug produced a more compact micellar structure. Our results proposed that the drug could behave as a co-surfactant in our simulated model.

Synthesis of N-benzylarylamine derivatives and diphenyl esters of α-aminomethanephosphonic acids and examination of their antioxidant properties

A number of new derivatives of N-benzylarylamines and diphenyl α-aminomethanephosphonates have been synthesized, and their structure has been established by IR and 1H NMR spectroscopy. It has been shown that these compounds can be used as effective additives enhancing the thermooxidative stability of ester-based oils.

Study of pentaerythritol tetraoleate ester as industrial gear oil

Attention has been paid to biodegradable lubricating oils in the field of lubricant application because of environmental pollution control measures. In Europe and in some part of Asia, the use of environmentally acceptable lubricant is supported by environmental labels. Synthetic and vegetable oil-based esters offer the best choice in formulating environment-friendly lubricants. Pentaerythritol tetraoleate ester has been synthesised using polyol such as pentaerythritol and oleic acid with indigenous ion exchange resin (Indion-130) catalyst. The product was characterised for its physicochemical properties and was evaluated for lubrication performance. This was then compared with extreme pressure type of industrial gear oil VG-68 (IS 8406:1993). The product was found to have good potential for use as a base stock for formulation as extreme pressure type of industrial gear oil VG-68 (IS 8406:1993). Copyright © 2011 John Wiley & Sons, Ltd.

Influence of oil formulation on gear micropitting and power loss performance

This study presents a study of the influence of oil formulation on the protection against gear micropitting and also its influence on gear efficiency. The study had both components because a well-balanced product is necessary and its behaviour must be demonstrated in dedicated tests. The industrial gear oils studied combined polyalphaolefin with ester base oils and had different additive packages. FZG gear power loss tests were performed using 20MnCr5 carburized gears under a wide range of operating conditions. During the tests, the oil and gearbox temperature were continuously recorded and gear oil samples were collected. After the tests, the gear mass loss was measured and oil samples were analyzed by ferrography. Using an energetic model of the FZG test gearbox, it was possible to quantify the influence of lubricant formulation on the average friction coefficient between gear teeth, which will provide a quantitative comparison of lubricants. The gear micropitting protection provided by the oxidized lubricant samples was evaluated in a FZG test rig according to DGMK short micropitting test procedure. During the tests, lubricant analysis, mass loss measurements, surface observation, and topography measurements were performed to evaluate the micropitting evolution along the tests as well as severity of micropitting. The results obtained show that the base oil, the additive package, as well as their combination can have a very significant influence on the efficiency and micropitting performance of industrial gear oil.

Traction curves and rheological parameters of fully formulated gear oils

The rheological behaviour of several fully formulated gear oils is characterized: two mineral-based oils, one poly-α-olefin, and three ester-based oils. Experimental traction curves were obtained on a mini-traction machine, where the selected gear oils were submitted to numerous traction tests combining several temperatures, contact loads, and rolling speeds. Having obtained the experimental data from the traction tests, it was least-squares fitted to a rheological model (elasto-viscoplastic rheological model) in order to obtain the model’s governing parameters: elastic modulus and limiting shear stress and their dependence on pressure and temperature. This study presents both the traction tests results and the fitted rheological parameters, and discusses the similarities and differences between the oils, as well as the influence of the operating conditions on the behaviour of the oil.

Micropitting of carburized gears lubricated with biodegradable low-toxicity oils

Environmental issues are leading to a growing interest in bio-lubricants, which can have similar or even better performance than mineral and synthetic oils. In this work, the biodegradability and toxicity characteristics of ester-based gear oils are presented and their physical, chemical, and wear properties are compared with those of a commercial mineral oil. In an earlier work, power loss tests were performed on the FZG test rig, using carburized gears and several different lubricants. The operating temperatures of the oil and of the FZG gearbox wall were measured for different values of the input torque and speed. An energetic model of the FZG test gearbox was developed, taking into account the power loss mechanisms inside the gearbox and the heat flow mechanisms from the gearbox to the surrounding environment. Using this model it was possible to quantify the influence of lubricant formulation on the average friction coefficient between gear teeth. Gear micropitting tests were performed on the FZG test rig, using carburized gears and different oils. Post-test analysis included the mass loss measurement of the gear, the ferrometric analysis of lubricant samples collected during the tests, and the visual inspection of the gears. The tooth flanks were inspected using surface topography measurements to assess the number and depth of micropits. In comparison with the gear lubricated with mineral oil, the gears lubricated with ester-based oil showed significantly higher mass loss (3—4 times higher), smaller number of micropits, and less deep micropits. If carefully formulated, biodegradable low-toxicity ester-based gear oils, beside their environmental advantages, enhance gear performance when compared with the mineral lubricant providing (a) lower friction coefficients and lower operating temperatures of gearboxes and (b) lower number of micro-pits (with depths greater than 4 μm). One of the ester-based gear oils passed the FVA gear micropitting criterion.

Statistical Analysis of Impedance Data for Jet Turbine Oil Additives

A gold, parallel-plate capacitor test cell was used to make electrochemical impedance spectroscopy (EIS) measurements on high resistivity gas turbine engine oil as a function of the oil additive type.The additive effects on the EIS response were determined by analyzing ester-based basestock oil mixed with a single additive.This work was performed for four different additives:antioxidant, metal deactivator, anti-wear, and extreme pressure.Multiple measurements were made for each basestock-single additive mixture.To determine whether the EIS response of each additive showed a significant difference, statistical analysis was performed on the data using a student’s t-test.Low-frequency data showed the largest difference in additive responses.Statistical analysis showed that the extreme pressure additive has the greatest effect on oil impedance.Mixtures of antioxidant and metal deactivator additives did not show interaction.

Gear power loss performance of biodegradable low-toxicity ester-based oils

Environmental issues are leading to a growing interest in bio-lubricants, which can have similar or even better performance than mineral and synthetic oils. In this work, the power loss performance of two biodegradable, low toxicity, ester-based gear oils was evaluated and compared with a commercial mineral oil and an ester-based fluid containing zinc dialkyl dithio phosphate (ZDDP) additives. Power loss tests were performed on the FZG test rig, using type C carburized gears and the different lubricants under evaluation. The operating temperatures of the oil and of the FZG gearbox wall were measured for different values of the input torque and speed and lubricant samples were periodically collected and analysed by direct reading ferrography. At the end of the tests, the gear mass loss and the oil viscosity were measured, the teeth flanks were inspected, looking for typical surface failure mechanisms, and the tooth flank surface roughness was measured. An energetic model of the FZG test gearbox, which took into account the power loss mech-anisms inside the gearbox and the heat flow mechanisms from the gearbox to the surrounding environment, was used to calculate the friction losses between the gear teeth, knowing the oil, gearbox wall, and room temperatures, in steady-state conditions. Using this model, it was poss-ible to analyse the influence of lubricant formulation on the average friction coefficient between gear teeth. The results obtained showed that one of the biodegradable, low-toxicity, ester-based gear oils generated significantly lower mass loss than all the other lubricants, presenting almost no degradation, even when operating at very high temperature for long periods. These bio-lubricants generated friction coefficients between gear teeth up to 27 per cent smaller than the commercial mineral oil, promoted significant reductions of the power loss inside the FZG gearbox, increasing the overall efficiency up to 0.25 per cent.