Vegetable‐based biodegradable lubricating oil additives

M.A. Maleque; H.H. Masjuki; S.M. Sapuan

Vegetable-based biodegradable lubricating oil additives

Masjuki Haji Hassan

2003, Industrial Lubrication and Tribology

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5 pages

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Recently, much effort has been focused on research and development of new types of lubricating oil additives to reduce wear and friction in the tribological systems. It has been noted that the use of additives to improve the lubricating capacity and durability of oil plays an important role in the wear and friction process of materials, Due to the environmental problems, many researchers are embarking on the viability of the vegetable-based lubricants, In this article a critical review has been made on vegetable-based lubricant additives with specific properties and application. This article explains the advantages and manufacturing processes of vegetable-based oils, which will give a better understanding of using biodegradable lubricating oil additives. A case study on palm oil methyl ester as an additive has been presented in this paper. http://www.emeraldinsight.com/journals.htm?issn=0036-8792&volume=55&issue=3&articleid=874623&show=pdf

Vegetable-based biodegradable lubricating oil additives M.A. Maleque and H.H. Masjuki are at the Department of Mechanical Engineering, University of Malaya, Kuala Lumpur, Malaysia. S.M. Sapuan is based at the Department of Mechanical Engineering, University Putra Malaysia, Serdang, Malaysia. A lubricant performs a variety of functions in engines and machines, such as, it protects metal surfaces against corrosion, acts as a heat transfer agent, flushes out contaminants, absorbs shocks and seals foam (Khoorramian et al., 1993). Lubricants are commonly used to reduce the friction and wear between two sliding solid bodies. In some applications, the solid surfaces are so close together that some asperities come into contact and others are mitigated by a thin film of lubricant. Most lubricants are introduced into a sliding system with the aim of reducing the amount of interaction between the contacting surfaces, often under a variety of equipment speed and loads. Thus, a lubricant may be used to reduce the frictional force, the amount of wear, or the degree of surface adhesion. Sometimes, however, the prime task of the lubricant is to reduce the interfacial temperature, which otherwise might produce a harmful change, such as melting, in one of the contacting materials. Some of the most important properties necessary for a satisfactory lubricant performance are the following. . Low volatility under operating conditions. Volatility characteristics are essentially inherent in the choice of base stock oil for a particular type of service. Viscosity gives an indication of the volatility of a lubricant: in general, the lower its viscosity the higher its volatility. . Satisfactory viscosity characteristics in the temperature range of use. Viscosity of engine oil is one of its most important and most evident properties. Chemical additives, fuel dilution, contaminants from within and outside of the engine, wax in the oil, oil oxidation, volatilization, and many other materials found in or added to the oil affect the viscosity in advantageous or disadvantageous ways. For engine oil, a small change in viscosity with temperature (high viscosity index) is desirable to provide a wide range of operating temperatures over which a given oil will provide satisfactory lubrication. . Superior stability or ability to maintain desirable characteristics for a reasonable period of use. The factors, which affect the lubricant stability are temperature, oxygen, and contamination with water, unburned fuel fragments, and corrosive acids, which limit the useful life of a lubricant. All lubricating oils react with oxygen in the air, eventually forming acid or sludge products. These products could cause surface corrosion or blocking of oil lines. There are numerous laboratory tests for oxidation stability (Robertson, 1984). All tests depend on artificially accelerated oxidation, by heating the oil and by blowing air or oxygen through it, in some cases in the presence of a catalyst. This is the area where additives have made a major contribution in improving the performance characteristics and extending the useful life of lubricants. . Compatibility with material pairs in the system. Compatibility of lubricants with bearings, seals, clutch plates, etc. may also be partially associated with the base oil. However, additive chemistry can have a major influence on such characteristics. Lubricating oils find applications in engines, industrial uses, greases and automotive transmissions. The major uses of these oils are in engines (55 per cent), industry (27 per cent), processes (9 per cent), greases (5 per cent), and automotive transmissions (4 per cent) (Gergel, 1984). The aim of this article is to provide information about vegetable-based lubricant additives and to offer a case presentation on palm oil methyl ester (POME) as a vegetable-based lubricant additive. Vegetable-based oils: their advantages, limitations and properties Vegetable-based oils are liquid agricultural products and are produced from plants and cash crops. The advantages of vegetablebased oils over mineral-based oils are given below: . Vegetable oils are biodegradable – vegetable oils are non-toxic and derived from foods whereas mineral oils are derived from chemicals; renewable – the source of vegetable oil is a crop and they promote self-reliance as ample production capacity exists but the source of mineral oil is a finite mineral deposit. Vegetable oils present higher flash point than mineral oils, which is always a concern with flammable liquids; they are also generally safer to humans. It is worth remembering that while fatty acid-based products from vegetable and animal origins used to be the main source of lubricants up to and beyond the late 19th century (Wilson, 1998), when mineral oils became available in large volumes at increasingly competitive prices. For some time, blends of mineral oil and natural fatty acid products, referred to as fatty oils, were widely used. Vegetable fats and oils (known by the generic term lipids) comprise, primarily, triglycerides, that is, tri-esters of long chain carboxylic acids (fatty acids) combined with glycerol. Most of these oils contain at least four and sometimes as many as 12 different fatty acids. The proportions of each fatty acid depend not only on the type of plant, but also on the climate, the weather and the food available. Table I shows the sources of main types of natural oils and their world production, and the chief fatty acids they contain (Wilson, 1998). Vegetable oils are usually good boundary lubricants but the major limitations are their high cost, thermal and oxidation instability. Oxidation stability of vegetable oils depends on the level of unsaturated products present. The lower the unsaturation the better the oxidative stability but the higher melting point. In general, vegetable oils can be used up to a maximum temperature of 1208C. However, the use of appropriate anti-oxidants can solve this problem (Bowman and Stachowiak, 1999). It must also be noted that vegetable-based oils are hydrolytically stable, foam more, and have lower filterability compared to mineral oils. These oils, when reacting with an alcohol in the presence of fatty acids, can make synthetic esters. To do this, branched alcohol with more favourable properties are chosen and reacted with pure acid (such as oleic acid) to produce a synthetic ester with better performance characteristics. But not all types of vegetable oils are suitable for a lubricant. For good performance, special lubricant requirements must be fulfilled, i.e. good lubricity, good corrosion protection, compatibility with other materials, fair oxidative and hydrolytic stability and low temperature behaviour associated with the triglyceride (Arnsek and Vizintin, 1999). Rapeseed and castor oils are the most common base stocks for vegetable-based lubricants. Full text is available at : http://www.emeraldinsight.com/journals.htm?issn=0036-8792&volume=55&issue=3&articleid=874623&show=pdf

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