Modification of the chemical structure of an environmentally‐friendly castor oil lubricant

Widely used mineral‐oil based lubricants are often released into the environment and cause pollution. Therefore importance is attached to developing environmentally‐friendly lubricants. Vegetable oils have been used as lubricants since ancient times. These materials, similar to synthetic esters, have better biodegradability than mineral oils. They are also renewable. Vegetable oils have some shortcomings, such as a higher pour point and a lower viscosity index than synthetic esters. They have a limited viscosity range and lower oxidative stability due to the presence of unsaturated bonds. Therefore vegetable oils as such cannot satisfy all the requirements of modern machine lubrication. In this paper, the chemical structure of natural castor oil is modified by an isomerisation reaction and by extending the carbon chain, so as to lower the pour point and improve the viscosity index. The results show that structurally modified castor oil has very good lubrication characteristics. Its viscosity at 40°C is 150 mm²/s, its pour point is −40°C, and its viscosity index is improved. The antiwear and friction characteristics are better than those of mineral oil of the same viscosity and comparable to pentaerythritol esters and diisocapryl sebacate.     

Tribological degradation of two vegetable‐based lubricants at elevated temperatures

Renewable‐based lubricants are being considered as potential alternatives to petroleum‐based lubricants for various reasons, mainly increased environmental sensitivity. However, understanding the tribological performance of such vegetable‐based lubricants under elevated temperatures is critical for their industrial implementation. This study focuses on the friction and abrasion rate characteristics of soybean and sunflower base oils in comparison to a base mineral oil under sliding wear at elevated temperatures. It was found that the abrasion rate and friction were less severe for the vegetable‐based lubricants up to temperatures around 100°C. The observed performance of the vegetable‐based lubricants was verified using a kinetic reaction mechanism model of lubricant degradation. Copyright © 2007 John Wiley & Sons, Ltd.     

Influence of fatty acid composition on the tribological performance of two vegetable‐based lubricants

In light of diminishing natural resources, global climatic change and increased environmental sensitivity, renewable‐based lubricants are being considered potential alternatives to petroleum‐based lubricants. Understanding the tribological performance of vegetable‐based lubricants in relation to their chemical composition is essential for their industrial implementation. This study focuses on the friction and abrasion rate characteristics of soybean and sunflower oils in comparison to a base mineral oil under sliding wear at ambient conditions for various applied loads. It was found that the abrasion rate and friction were the least severe for the soybean, followed by the sunflower oil. The observed trends were attributed to differences in their fatty acid compositions, in particular, a lower percentage of linoleic and oleic acids within the soybean oil. Copyright © 2007 John Wiley & Sons, Ltd.     

Mixture of safflower oil and synthetic ester as a base stock for biodegradable lubricants

Biodegradable industrial lubricant applications are gaining popularity with growing environmental concern and stringent government regulations. Plant oils are major base stocks for eco‐friendly green lubricants. However, because of their poor oxidation stability, their applications are restricted to limited usages. Improvements of these plant oils can be made either by addition of functional additives or by chemical/genetic modifications. This paper evaluates the synergistic approach of phenolic and aminic antioxidants in safflower oil. Further, to enhance the oxidation properties of the plant oil, we incorporated and studied synthetic esters (SEs) for thermo‐oxidative stability by using rotating pressure vessel oxidation test and differential scanning calorimeter. The combination of phenolic and aminic antioxidants at a 2 : 1 ratio exhibited the best synergistic effect, when incorporated into a combination of plant oil and SE. In addition to thermo‐oxidative properties, the tribological properties of neat base stocks were also studied. A substitute of mineral oil‐based lubricants can be formulated cost effectively by using an appropriate mixture of plant oil and SE. Copyright © 2013 John Wiley & Sons, Ltd.     

Vegetable oil derivatives: environment‐friendly lubricants and fuels

A critical appraisal is made of the applications of vegetable oils, the fatty esters complex and synthetic esters as rapidly biodegradable and non‐toxic lubricants and fuels in the developed countries of America, Europe and Asia. The criteria employed for assessing the toxicity and biodegradability of the various fluids and limits set by various state and regional organizations are reviewed. The properties of vegetable oils, fatty esters, chemically modified esters and synthetic esters relevant for performance as lubricants in various applications such as hydraulic oils, refrigeration oils, chainsaw lubricants, metalworking fluids, engine oils, two‐stroke oils, mould release lubricants, greases, gear and transmission oils vis‐à‐vis conventional mineral oils and greases for corresponding applications are compared. The advantages, such as high lubricity, viscosity–temperature relationship, low lubricant consumption, energy efficiency combined with public health, safety and environmental contamination, more than offset the disadvantages of initial costs in most of these applications. It has been suggested that modified and stabilized oils of wasteland and forest origin and other non‐edible oils and their chemically modified derivatives can be produced at relatively cheaper cost than similar oils marketed in the developed world and can be introduced in India with immense environmental and performance benefits, particularly in applications involving high environmental contamination safety and public health. When blended with highly refined diesel fuels, methyl esters can work as highly efficient environment‐friendly fuels particularly for applications in passenger transport, light commercial vehicles and generators. Copyright © 2006 John Wiley & Sons, Ltd.     

Influence of thermo‐oxidative degradation on the biodegradability of lubricant base oils

The paper addresses the problem of how the thermo‐oxidative changes in the chemical structure influence the biodegradability of lubricating base oils. The tests were conducted using synthetic polyolesters, polyalphaolefins (PAO 4) and blended polyolesters with 30 wt % of PAO 4. Oil biodegradability was evaluated in accordance with the International Standards Organization (ISO) 14593 test. The thermo‐oxidative degradation consisted of a 24‐hour exposure of the oil samples to the temperature of 150°C in a universal test apparatus at an air flow rate of 15 L/hour. The results have revealed that the thermo‐oxidative degradation of the chemical structure produces changes in the physico‐chemical properties of the base oils and improves biodegradability. The polyolester oils tested were found to be readily biodegradable both before and after thermo‐oxidative tests. PAO 4 oil and its blends with polyolester oils could not be classified as readily biodegradable. The thermo‐oxidative changes in their chemical structures can exert a positive effect on their biodegradability. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of oil type on the performance characteristics of a two‐axial groove journal bearing

The use of environmentally adapted lubricants (EALs) is a subject of growing interest to industry as legislation increasingly demands the replacement of mineral oil lubricants. Vegetable‐based fluids are widely seen as providing lubricants from a renewable source, as well as meeting demands for improved biodegradability. However, at present, utilization of such fluids is limited due to their rapid oxidation. EALs produced from other base stocks (i.e. synthetic esters) have been shown to provide performance benefits in hydrodynamic thrust bearings. In the present study, a hydrodynamic journal bearing test rig has been employed to compare the performance of three EALs (a VG32 saturated ester, rapeseed base fluid and a propylene glycol dioleate) relative to three mineral turbine oils (ISOVG32, ISOVG46 and ISOVG68) in the hydrodynamic regime. Results are given in terms of temperature, power loss and minimum film thickness. The impact of oil viscosity index is also discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Miscibility and stability of synthetic lubricants with HFC refrigerants

The phase-out of CFC production and further regulations on HCFC are required because of their association with the depletion of stratospheric ozone. HFCs and their mixtures have evolved as long-term replacements for CFCs and HCFCs. For air conditioning and refrigeration systems, new synthetic lubricants having miscibility with HFC refrigerants, similar to that of mineral oils with CFCs, have been developed. Data on the miscibility ofR-32/125 and R-125/143a with polyol ester lubricants are presented in this paper. In the temperature range of interest (−40°C to 60°C), we observed the upper immiscible region, lower immiscible region, as well as the coalescence of the two regions, for polyol ester lubricants with these HFC refrigerant mixtures. HFC-143a is least miscible among the three pure HFC refrigerants. The stability of R-32/125 and R-125/143a with dry polyol ester lubricants is very good at 204° C. With high moisture content, hydrolysis of the lubricant occurs at high temperatures. The onset of significant hydrolysis of lubricant (B) takes place between 175°C and 200°C. Care must be exercised to maintain the dryness of polyol ester lubricants and refrigeration systems to prevent this occurring.     

Assessing friction characteristics of liquid lubricants

A reduction in friction in tribological contacts will lead to reduced energy requirements. It is therefore important to be able to measure the frictional characteristics of various liquid lubricants. Current laboratory tests measure friction, but the test rigs invariably induce wear between the mating contacts. A new test rig, the wire‐on‐capstan rig, is presented which measures friction without inducing wear between the wire and the rotating capstan. All seven lubricants tested (three without additives and four proprietary hydraulic oils) exhibit a reducing coefficient of friction with increasing temperature. Temperatures ranged from 25°C to 100°C. The mineral‐based oil showed the lowest friction coefficient and the three synthetic ester based oils produced the highest friction coefficient over the complete temperature range. Future testing will extend the range of operating conditions and product types. Copyright © 2006 John Wiley & Sons, Ltd.     

Lubricity characteristics of ethyl hexyl esters of mono‐, Di‐, and triethenoic acids

Ethyl hexyl esters of oleic, linoleic, and linolenic acids were synthesised and thermally polymerised to obtain products with viscosities in the range of hydrocarbon lubricants at 100°C (11–22 cSt). Molecular weight, elemental analysis, IR, ¹³C NMR, and intrinsic viscosity data showed that most of these derivatives are mixtures of monomers, dimers, and trimers and have linear and cyclic products with predominantly trans characteristics. The lubricity characteristics were determined on a friction and wear tester under conditions of thick‐film lubrication. A comparison was made with hydrocracked hydrocarbon lubricants of comparable viscosities at 100°C and comparable viscosity indices. It is inferred that all the esters maintained relatively thicker surface films and much lower friction coefficients than the hydrocarbon oils. The wear‐scar data show that the antiwear characteristics of polymerised ethyl hexyl oleate and linoleate are only slightly inferior to those of the hydrocarbon oils, but at higher temperatures their antiwear characteristics rapidly deteriorate while the friction coefficients markedly increase and become comparable to those of hydrocarbon oils. These studies are being undertaken with a view to selecting and modifying vegetable oils containing mixtures of fatty acids for obtaining esters of outstanding friction, wear, and film‐forming characteristics.     

Recent trends in environmentally friendly lubricants

Many of the lubricants used in the world today cause environmental pollution through total‐loss applications, spillage, evaporation, and in other ways. To reduce this environmental damage, new lubricants that are rapidly biodegradable and ecologically non‐toxic have started to be developed and marketed. This paper discusses the introduction of environmentally friendly lubricants and their constituents, with particular emphasis on their environmental benefits, applications, the limits to their use, their technical performance characteristics, and relative cost aspects; many of these lubricants are based on vegetable oils and esters. Comparisons are also made in the paper with conventional mineral‐oil based materials.     

The influence of lubricating fluid type on the properties of biodegradable greases

The lubricating ability of a grease depends on both the base oil and the thickener. As a result of their intrinsic properties and/or because of their com‐patibility with thickeners and specific additives, base fluids have different influences upon the properties of grease formulations. It is well known that mineral oils are the most widely used lubricant bases due to their inherent lubricity and lower cost, but recent environmental concern has led to consideration of the use of vegetable oils and readily biodegradable synthetic fluids as raw materials in lubricating grease formulations. As well as the base materials, the additives for biodegradable greases should also be biodegradable. This requirement limits the kind of products that may be used in environmentally friendly greases. This paper presents comparative data concerning the tribological and physico‐chemical properties of biodegradable greases formulated with certain vegetable oils, such as rape seed oil, castor oil, and soybean oil or their mixtures, and synthetic esters. The improvement of the load‐carrying properties of biodegradable greases and the antioxidative effect of some suitable additives have also been studied, and the results are presented here.     

Lubricant components from vegetable oils of indian origin

A number of transesterified and alkarylated derivatives have been synthesised from available vegetable oils of Indian origin. The viscosity, viscosity index, freezing points, load-carrying characteristics, friction coefficient, and thermo-oxidative stability of these derivatives as compared to highly refined hydrorefined hydrocarbon oils have been studied. It has been found that several esters of fatty acids of these vegetable oils have a high natural viscosity index, low pour points, and high thermooxidative stability, and can meet the requirements as base fluid components for energy-efficient, eco-friendly, long-drain interval, multigrade oils. These oils have markedly lower viscosities at 40°C, higher load-carrying characteristics, and lower friction coefficients than the base fluids of currently marketed multigrade oils. A 50% blend with hydrorefined hydrocarbon oils could prove highly viable. The above results clearly establish the potential for utilising these esters, either alone, or in combination with mineral oils, for formulating cost-effective high-performance, energy-efficient, and environmentally friendly lubricants. Performance characteristics of these oils as engine oils, automotive gear oils, and 2 stroke oil with conventional additives and with alternative additives are under investigation in comparison to the most advanced hydrocarbon based multigrade oil formulations of long-drain interval.     

Lubricating properties of rapeseed‐based oils

Three commercially available hydraulic/transmission lubricants based on rapeseed oil have been investigated for their lubricating properties. The coefficient of friction, scuffing‐load capacity, and pitting resistance were evaluated, and the results compared with a corresponding commercial mineral‐based oil. The results showed in general a substantially lower coefficient of friction and better pitting resistance for rapeseed‐based oils than for the mineral oil. Scuffing load capacity was, with one exception, the same for all oils. As a result of lower shear stresses during contact, and a higher viscosity index, the temperatures in the gearbox were lower for the rapeseed oils tested than for the mineral oil. Insufficient antiwear behaviour at high loads was found to be a major drawback of these vegetable oils.     

Metalworking emulsions from industrial vegetable oils

In the present work, an attempt has been made to develop the indigenous formulation for metalworking lubricants by replacing mineral oils partially with non‐edible industrial oils like rapeseed and karanja oil. Metalworking formulations consist of vegetable oil, mineral oil, an emulsifier and commercial additives for better performance. Non‐edible vegetable oils such as karanja and rapeseeds are renewable, biodegradable and cheaper than synthetic fluids. The constituent vegetable oils and mineral oils were evaluated for physico‐chemical characteristics and blended as per the saponification value and viscosity requirements of the reference oils. The so formulated oils are taken as 5% oil‐in‐water emulsion and tested for lubricity, load bearing capacity, particle size distribution, wear test, weld load test and plate‐out test. Performance of all formulated oils was compared with that of the reference oils, and optimized to meet the market requirements. Copyright © 2008 John Wiley & Sons, Ltd.     

Eco‐friendly base fluids for lubricant oil formulations

There is an increasing move towards the use of environmentally safe lubricants. However, the development of a common biodegradable base stock that could replace conventional ones is a big challenge. Synthetic lubricants, whether synthetic hydrocarbons, organic esters, or others, all have problems associated with their use. However, in general terms synthetic lubricants protect better, last longer, and outperform their conventional mineral‐based counterparts in certain applications. Future lubricant specifications in view of the demand for improved performance to meet stringent environmental regulations are the main drivers for new technological developments. As part of a study to produce polyol ester lubricant base stocks from C₅ polyols and C₆‐C₁₄ carboxylic acids in the presence of eco‐friendly catalysts, a series of products has been synthesised. A biodegradable lubricant formulation for automotive transmission fluids has been developed based on a synthesised product as a base fluid. This paper reports on the physico‐chemical characteristics and performance evaluation results of this formulation, which is a promising base stock for automotive transmission fluids.     

A potential biodegradable lubricant from castor biodiesel esters

Worldwide, 12 million tonnes per year of lubricants are disposed of in the environment through leakages, exhausted gas, incorrect disposal, water–oil emulsions and so on. Some are resistant to biodegradation, representing an environmental threat. One solution to modify this situation is the replacement of mineral oils by biodegradable synthetic lubricants. Esters, whose chemical structures are similar to natural triglycerides, are excellent substitutes for mineral oils. Castor oil contains around 90% ricinoleic acid, and as a result, castor oil has a higher viscosity and a lower viscosity index, compared with other vegetable oils. This work was based on the production of biodegradable lubricant base fluids from castor biodiesel esters, using various chemical catalysts to yield products with interesting properties, such as high viscosity index and good oxidation stability, compared with mineral oils. This route to lubricants is safer, more economical and more efficient. Copyright © 2012 John Wiley & Sons, Ltd.     

Improvement of thermooxidative stability of non‐edible vegetable oils of Indian origin for biodegradable lubricant application

For environmental reasons, as well as the dwindling source of petroleum, a new class of environmentally acceptable and renewable lubricants based on vegetable oils is available. Even though vegetable oils possess excellent lubricant‐related properties, there are some concerns about using it as lubricant base oil. Still, unmodified and modified varieties of soybean, rapeseed, sunflower and canola oils have been in use in the USA and Europe. In India, with the shortage of edible oil, alternate sources of vegetable oils stocks are being explored. With this aim, a comprehensive study has been conducted earlier in the authors' laboratory. In this study, numerous options of non‐edible vegetable oil sources were explored, and a few potential vegetable oils were studied in the laboratory. It was found that even though the oils performed much better in comparison with other vegetable oils, it still required improvement in thermooxidative stability. Therefore, in the later part of the study, different options were explored to improve thermooxidative stability. With a background on the initial studies of the authors as described above, the present paper deals with the studies on improvement of these non‐edible candidate vegetable oils of Indian origin for lubricant by treating with selected antioxidants for applying them in lubricants. Copyright © 2010 John Wiley & Sons, Ltd.     

Study of some non-edible vegetable oils of Indian origin for lubricant application

Due to growing environmental concerns, eco-friendly processes and materials have become one of the key interests of research and in the area of tribology, natural esters are gaining popularity as lubricants. Natural esters are being used in many applications as eco-friendly lubricant base. In Europe, canola/rapeseed oil and sunflower oil are mainly used, whereas in the USA, soybean oil is in use for formulating environmentally friendly lubricants. Native and genetically modified high oleic varieties of these oils are being widely used. In the Indian scenario, since the above-mentioned oils are scarcely available for industrial applications, there is a need to look for other viable alternatives. Some candidate non-edible vegetable oils of Indian origin were selected which were unexplored or less explored in the field of lubricant application, and their suitability in lubricant application focusing mainly on physico-chemical characteristics, thermo-oxidative stability and lubrication characteristics was studied. These oils were found to be promising candidates for application in lubricants in view of their physico-chemical characteristics and better thermo-oxidative and hydrolytic stability. Copyright © 2007 John Wiley & Sons, Ltd.     

Suitable additives for vegetable oil‐based automotive shock absorber fluids: an overview

Formulation of a cost‐effective, high‐performance and eco‐friendly lubricant, largely depends on the base oil quality, then the selection of suitable additives and their proportions. Vegetable oils, identified to be eco‐friendly, renewable, future‐available and cost‐effective treasures for lubricant formulation, apart from processing, will rely much on suitable additives to meet the performance requirements for automotive shock absorber (ASA) fluids. Additives that will guarantee performance, longevity and eco‐friendliness of formulated vegetable‐based functional fluids have to be uncommonly effective, resistant to depletion, non‐toxic and highly biodegradable. Their selection in these regards will require skills and experience, which will harness the various arms of synergism as effective tools to succour the known weaknesses of the base oil. This is a review on additives that could be used in formulation of vegetable oil‐based (ASA) fluids. The outcome shows that there are customary and novel additives that are suitable for formulating vegetable oil‐based ASA fluids. Copyright © 2016 John Wiley & Sons, Ltd.