Tribological performance of ionised vegetable oils as lubricity and fatty oiliness additives in lubricants and fuels

Lubricity and fatty oiliness additives, also known as friction modifiers in the tribological vocabulary, are steadily gaining acceptance from lubrication engineers and lubricant formulators. The present communication describes how such additives function in various tribosystems and which parameters control lubricity of finished formulations. Extensive experimental data are presented to demonstrate the outstanding tribological performance of bio‐based lubricity and fatty oiliness additives produced by Elektrionization^TM of vegetable feedstocks. Featuring a unique combination of viscosity and polarity, ionised vegetable oils form sufficiently thick and resilient protective layers by adsorption to rubbing surfaces. It is shown that, unlike extreme pressure additives, which act when a direct asperity–asperity contact occurs in the boundary lubrication regime, ionised vegetable oils function by postponing the onset of the boundary lubrication regime. Copyright © 2009 John Wiley & Sons, Ltd.     

Sulphurised vegetable oils as EP additives for industrial gear oil formulations

Renewable sources can provide, besides fuel, a wide range of feed stocks for the organic chemicals industry. Utilisation of non-edible vegetable oils and speciality chemicals has, therefore, become relevant in recent times. Sulphurisation of three triglyceride oils (karanja, rapeseed, and castor oils) and liquid wax (jojoba) has been investigated in detail in order to examine the potential of sulphurised vegetable oils for use as extreme-pressure (EP) additives for developing formulations for industrial gear oils. The capacity of these oils with respect to the uptake of sulphur, the limitations of some of the sulphurised products for use as EP additives, and the problems in developing such formulations for industrial gear oils, are discussed.     

Synergistic effect of antiwear additives and antioxidants in vegetable oil

Certain vegetable oils have been recognised as promising candidates for environmentally friendly lubricants. Their lubricity can be optimised using antiwear additives. However, decomposition of the additives, accompanied by auto‐oxidation of the vegetable oils, has been found to occur. In other words, the antiwear additives may degrade in vegetable oils, and give less oxidative stability. In order to understand the mechanism, oxidation testing of a vegetable oil was performed by monitoring the peroxide value (POV). It was observed that POV increases as soon as oxidation starts. The value reached 1400–1500 ppm within 50 h of reaction time. Then it decreased to an equilibrium value of 400–500 ppm within 200 h. Antioxidants to prevent peroxide generation were examined. Phenolic antioxidants and zinc dialkyldithiocar‐bamate exhibited good results with regard to preventing peroxide generation, whereas aromatic amines gave poor results. A synergistic effect that prevents the decomposition of the antiwear additives was found.     

Tribological behaviour of three phosphate esters containing the benzotriazole group as additives in rapeseed oil

Since the 1970s more attention has been paid to biodegradable lubricants as a way of reducing the pollution caused by lubricants with a mineral oil base. This concern has promoted the use of vegetable oils as alternative base oils. This paper reports on a study of the effect of phosphate esters containing the benzotriazole group as additives in rapeseed oil (RSO), tests being carried out using a standard four‐ball tester. The results show that these additives produce good antiwear performance and load‐carrying capacity compared with RSO alone. Surface analysis of the worn halls was carried out using X‐ray photoelectron spectroscopy. The tribological mechanism is discussed on the basis of the experimental results.     

Evaluation of ball and disc wear scar data in the HFRR lubricity test

The high‐frequency reciprocating rig (HFRR) lubricity tester has become a widespread method for determining the lubricity of diesel fuels. The test is a ball‐on‐disc method, in which a steel ball scrapes over a steel disc immersed in the liquid to be tested. According to standards, the wear scar generated on the ball, in the form of the average of the x‐ and y‐axes, is used for evaluating the lubricity of the sample. Generally, the smaller the wear scar, the greater the lubricity of the sample. However, a wear scar is also generated on the disc. The size of the wear scar on the disc also depends on the lubricity of the sample. In this work, the wear scar data of the balls and discs of 230 samples related to the testing of biodiesel and related compounds with petrodiesel were evaluated. Data comparisons for all wear scar combinations correlated well by linear regression. Although correlations are slightly better when using only ball wear scar data (r² > 0.99), other wear scar data, including those generated on the disc, appear just as useable (r² ≈ 0.97–0.99) for evaluating lubricity by the HFRR test. The wear scars on the disc have the advantage of being more easily measurable and recognisable under the microscope, especially if the wear scars are small. Limits for all wear scar values corresponding to current limits for average ball wear scar data in standards are presented. Published in 2007 by John Wiley & Sons, Ltd.     

Biodegradable hydraulic fluids: Rheological behaviour at low temperatures of several oleochemically derived synthetic esters

One of the most important aspects of a hydraulic fluid used in mobile systems (e.g., excavators, wheel loaders) is the viscometric behaviour of the fluid at low temperatures. It has been found that the pour point of the base fluid does not predict this behaviour satisfactorily, and, as a result, the Swedish standard for these products (SS155434) requires that the kinematic viscosity of a hydraulic fluid remains stable at low temperatures (−20 or −30°C) during a period of 72 h. However, in rheological studies under dynamic conditions, it has now been found that certain oleochemically derived esters do not show Newtonian flow behaviour at these low temperatures. The authors have found not only a shear‐dependent behaviour of these esters but also a time‐dependent behaviour, especially after (high) energy input from an external source to simulate pumping of the fluid. Given the non‐Newtonian behaviour of these esters, the kinematic viscosity test method with an Ubbelohde tube was found to be inappropriate for the determination of the low‐temperature viscosity because this method assumes Newtonian behaviour. Dynamic viscosity measurements at higher shear rates (e.g., cold cranking simulator) resulted in much better reproducibility and may offer the best method of assessment.     

Phosphate esters with a complex alkyl‐aryl structure considered as tribological fluids

This paper presents results of reserch carried out to produce synthetic ester oils with adequate tribological properties, which could also act as antiwear additives. By varying the molar relationship between aliphatic alcohols of variable chain length and a special alcohol with complex alkyl‐aryl structure, namely 2‐[(o‐sec‐butyl)phenoxy]ethanol, two series of new phosphate esters have been synthesised. The influence of the aryl content and the effect of the length of the aliphatic chain on the characteristics of these esters as base oils, and on their qualities as antiwear additives, have been investigated.     

Preparation and tribological properties of the N‐containing heterocyclic borate esters and Cu microparticles as lubricant additives in base oil

In this paper, four kinds of N‐containing heterocyclic borate esters and polyvinyl pyrrolidone‐protected Cu microparticles were synthesised and characterised. Their tribological properties as lubricant additives in industrial white oil were evaluated using a four‐ball tribometer, and their lubrication mechanisms were investigated by X‐ray photoelectron spectroscopy. The results showed that the anti‐friction and anti‐wear performance of the base oil can be significantly improved by the addition of N‐containing borate esters and Cu microparticles, and they present synergistic tribological effect. Moreover, X‐ray photoelectron spectroscopy results showed a lubricating tribochemical reaction film containing B₂O₃, FeB, FeO, Fe₂O₃ and so on is formed on the worn surface. In addition, Cu microparticles as rolling bearings, which transform sliding friction to rolling sliding and the formation of the Cu microparticles deposited film, are probably responsible for the improvement of tribological performance. Copyright © 2017 John Wiley & Sons, Ltd.     

The identification and evaluation of natural and synthetic esters in mineral oils

The use of mineral-based lubricating oils blended with vegetable oils or their derivatives has raised the question of the detection, identification, and quantitative evaluation of these substances in formulated products. This paper addresses the problem in a systematic way, and suggests some possible solutions by means of analytical pathways using column chromatography, GLC, and HPLC techniques. The methods suggested allow the identification and evaluation of fatty acid esters with mono- and polyalcohols.     

Investigation of wear mechanism by organic sulphides in vegetable oils

Tribological properties of organic sulphides in esters were examined under boundary conditions. Magnification of wear by sulphides was observed in unsaturated esters. A dumb‐bell‐shaped wear scar, composed of a ‘central area’ and a ‘border area’, was found as an intermediate of wear growth. The ‘border area’ then expanded, resulting in a large wear scar. An induction period was observed before the generation of the ‘border area’. Influences of additive concentration on the induction period were also observed. Surface analyses of worn surfaces revealed that organic oxides, sulphides (unreacted additive) and sulphoxides are present in the boundary film. Influence of auto‐oxidation of the base oil on wear mechanism was proposed. Copyright © 2007 John Wiley & Sons, Ltd.     

Tribological properties of phosphate esters as additives in rape seed oil

With the growing concern about environmental pollution, vegetable oils have begun to be applied as base oils for environmentally friendly lubricants. Additives containing phosphorus can be used for their excellent antiwear properties and low toxicity. In view of this, a study of a series of phosphate esters as additives in rape seed oil (RSO) was carried out using a four‐ball tester. The results indicate that phosphate esters possess very good load‐carrying capacity and good antiwear and friction‐reducing properties compared with RSO by itself. Surface analysis of the worn balls was carried out using X‐ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The tribological mechanism of the additives is discussed on the basis of the experimental results.     

The origins of synthetic lubricants: The work of Hermann Zorn in Germany part 2 esters and additives for synthetic lubricants

The second part of this survey of the work of Hermann Zorn¹ covers his research work on esters, and their introduction as lubricants into aviation and other applications. The additives developed for these applications are also described.     

Functional fluids and additives based on vegetable oils and natural products: A review of the potential

Functional fluids and additives normally have an ‘R — P’ type of linear chemical structure, where ‘R’ is a linear or isoalkyl chain, and ‘P’ is a mild-to-strong polar group. For functional fluids ‘P’ is non-polar to mildly polar, and for additive molecules it is mild to highly polar. The additive activity depends upon the degree of polarity. Some natural products also have predominantly linear structures in their constituents. Many of these are available in commercial quantities and some even occur as waste. These could be used for the synthesis of functional fluids and additives. This paper covers three groups of such natural products. These are non-edible vegetable oils, terpenes, and cashew nut shell liquid. The synthesis and characteristics of functional fluids and a variety of possible additives are described. Besides being an alternative non-petroleum resource, such products have a high degree of biodegradability, as they are derivatives of natural products.     

光谱技术在植物油脂掺伪和地沟油检测上的应用

综述了红外光谱、近红外光谱、紫外吸收光谱等光谱技术在植物油脂掺伪以及地沟油检测中的应用。介绍了红外光谱技术、近红外光谱技术等检测油脂的原理和检测方法的优缺点。展望了光谱技术特别是红外光谱技术和近红外光谱在地沟油检测中的应用前景。提出多种方法联合运用的检测掺伪油脂和地沟油的新思路。     

A study of the tribological behaviour of dialkyldithiophosphate esters as additives in rape seed oil

Zinc dialkyldithiophosphates (ZDDP) cannot be used as additives in biodegradable lubricants because of their zinc content. In investigating substitutes for ZDDP, dialkyldithiophosphate esters have been synthesised, and their tribological behaviour as additives in rape seed oil has been evaluated using a four‐ball friction and wear tester and compared with that of ZDDP. The results show that these additives have better antiwear properties and load‐carrying capacity than rape seed oil alone. The morphologies and the elemental chemical states on the worn surfaces of the lubricated steel balls of the tester were examined using X‐ray photoelectron spectroscopy and scanning electron microscopy. The tribological mechanism is discussed on the basis of the experimental results.     

Pyromellitic esters with enhanced aromatic content and a mixed structure considered as tribological fluids

The paper presents results concerning research carried out in order to produce synthetic ester oils with superior thermal resistance and adequate tribological properties. Three series of new tetraesters with mixed structure have been synthesized with pyromellitic dianhydride as the basic acid structure; as for the alcoholic part, large normal or branched aliphatic alcohols have been used along with a special alcohol of aliphatic-aromatic structure, namely 2-phenoxyethanol. By varying the molar relationship between the two alcohols as well as by modifying the structure and the length of the aliphatic alcohol, it has been possible to obtain products with variable properties. Testing has shown this system to be highly flexible and a wide range of values was observed. The synthetic oils created in this way are especially remarkable with respect both to their viscosities, which offer an extended range of values, and to their particularly high thermal stability. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cram be abyssinica oil and its derivatives as renewable lubricants: Synthesis and characterisation of different esters based on crambe fatty acids

The authors have studied the possibility of using Crambe abyssinica oil as a starting material for synthetic lubricants, and in this paper the procedures for the preparation of monoesters from methyl, ethyl, isopropyl, and 2-ethylhexyl alcohol, as well as diesters from neopentylglycol, triesters from trimethylolpropane and tetraesters from pentaerythritol, are described. The different reactions were set up using free fatty acids, methyl esters, and Crambe oil as starting materials. All reactions were carried out in a solvent-free medium, using normally available catalysts and under experimental conditions which could easily be scaled up to industrial level. All the products obtained, along with the refined Crambe abyssinica oil used as a reference, were analysed for viscosity, viscosity index, low-temperature behaviour and oxidative and hydrolytic stability. Results of tests, such as four-ball machine and Noack, are reported. The results show that several products covering a wide range of different applications can be obtained from the basic Crambe abyssinica oil, and, furthermore, the chemical modification of the Crambe abyssinica oil can, in some cases, improve thermal and hydrolytic sensitivity and even the tribological properties.     

Influence of fatty acid additives on the tribological performance of sunflower oil

Vegetable oils are potential substitutes for petroleum‐based lubricants because they are environmentally friendly, renewable, less toxic and readily biodegradable. The addition of free fatty acids has been shown to increase the lubrication performance of vegetable oils at elevated temperatures. The purpose of this study was to evaluate the relationship between the length of the carbon chain in the fatty acid and its effectiveness as an additive for a range of elevated temperatures. Stearic, arachidic and behenic fatty acid additives were added to commercial sunflower oil. All fatty acid additives were shown to be effective in lowering the wear rate and coefficient of friction in ball‐on‐disc tribological tests. The overall carbon chain length was not observed to have a consistent influence on the effectiveness of the additive. All additives were less effective at temperatures above 100°C. Copyright © 2010 John Wiley & Sons, Ltd.     

Polyolefin and poly(alkyl methacrylate) mixed additives as mineral lubricating oil rheology modifiers

Some rheological properties of mineral lubricating oils containing polyolefin (OCP) (ethylene/propylene copolymer) and poly(alkyl methacrylate) (PAMA) mixed additives over a wide composition range have been examined. Increasing the OCP content significantly increases the viscosity and shear stability of solutions, whereas the viscosity index is directly proportional to the PAMA content. The pour point values of the additive solutions investigated are lower than −30°C even for the smallest concentration of PAMA in the polymer mixture of 15 wt.% (at a total polymer mixture concentration in oil of 2 wt.%). The viscosities of dilute mixed additive solutions obey the typical Krigbaum‐Wall equation and, due to the negative viscometric interaction parameter values (Δb₁₂ < 0), the OCP/PAMA mixture is found to be immiscible. The immiscibility becomes more pronounced on increasing the overall polymer concentrations. The viscosities of concentrated mixed additive solutions decrease significantly with an increase of OCP content, showing a minimum of half the initial value at a polymer ratio of about 50/50. On decreasing the polymer concentration to practical levels as well as increasing the temperature, the viscosity values approach the ideal additivity law. Based on the ratio of specific viscosities at 40 and 100°C (Q), the OCP additive solution shows a better thickening effect at lower temperatures (Q < 1). On the other hand, the PAMA additive solution shows a better effect at higher temperatures (Q > 1) with more coherent thickening with temperature change. The mixed polymer additive, containing ∼10 wt.% OCP and ∼90 wt.% PAMA, is a nearly optimal viscosity‐index improver showing the same thickening effect at different temperatures. The results obtained are promising as regards the design of lubricant formulations with mixed polymeric additives.