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8 DesIGnInG WItH PoLYMeRs elements35 Issue 2|2011 Innovative engine oil additives reduce fuel consumption and CO 2 emissions Perfectly lubricated Lubricants for engines and drives are all-stars: they function as well in heat as in ice cold, despite mechanical stresses, and remain stable for years. They owe these advantages mainly to high-performance additives. Specialists at <strong>Evonik</strong> in Darmstadt have developed comb polymers, which not only meet all the demands of advanced drives but also noticeably reduce consumption and emissions. [ text Boris Eisenberg, Dr. Torsten Stöhr, Dr. Michael Müller ] To ensure the engine runs smoothly: Engine oils should work reliably for about 30,000 kilometers. Gear oils, which are more complicated to change, should retain their lubricating action for roughly 20 years
no MACHIne, PLAnt, engine would be any use with out lubricant. Wherever moving metal surfaces come in contact with each other, a lubricant is vital. They reduce friction, muffle noise, prevent premature wear and tear. Lubricants work best when their viscosity is aligned to the application: if the oil is too thick, it prevents the parts from moving. If it is too thin, the metal surfaces can engage without any protection—machines and engines then break down very quickly. The effectiveness of lubricants depends on their viscosity, and the viscosity, in turn, depends on the temperature. The colder the temperature, the higher the viscosity, and the thicker the fluid. At high temperatures, viscosity decreases, and the liquid becomes thinner and more free-flowing. This is based on a simple molecular mechanism: particles of thick liquids are strongly bound to each other by mole cular interactive forces and, therefore, relatively immobile. This inner friction resembles the movement of two layers of molecules lying interlocked, one above the other. Force must be used to overcome the inter - l ocking. When the temperature rises, the interactive forces weaken, and the molecules glide across each other easier. The viscosity decreases as a result, and the liquid becomes thinner. The effect of temperature on polymer solubility. Because polymers swell with rising temperatures, they ensure that the viscosity of the solution stays as constant as possible compared to pure oil Poor Low Solubility in oil Temperature This principle applies to all fluids—whether honey, water or oils. The viscosity index (VI) is key to the evaluation of lubricants. It describes the temperature dependency of the kinematic viscosity of the oil—the force necessary to loosen the molecular interlocking and get the oil to flow. Oils with a low VI change their viscosity with the temperature more easily than oils with a high VI. As a rule, engines require oils that work reliably both summer and winter, which means oils with a high viscosity index. These kinds of oils provide adequate lubrication in summer, and are sufficiently free-flowing in winter. High standards for mineral oils Pure mineral oils are suitable to only a limited extent in applications with changing temperature ranges. At 15 degrees Celsius, they are already as thick as butter and behave less like lubricants and more like brakes on the moving parts. Today, a conventional engine oil has to work reliably and efficiently between minus 40 and plus 150 degrees Celsius. This is why existing engine oils normally consist of a low-viscosity base oil selectively thickened with additives. <strong>Evonik</strong> has long produced polymer-based additives that increase and optimize the viscosity index. 333 DesIGnInG WItH PoLYMeRs 9 Good High elements35 Issue 2|2011
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