engleski

The influence of structure and chemical functionalization on efficiency of methacrylate pour point depressants

Requirements regarding the less harmful emissions and increasing fuel efficiency of ICE govern the development of modern lubricating oils towards lower viscosity grade and multi-functional, highly efficient additives. Here, two additives, namely viscosity index improvers (VII) and friction modifiers play the most important role. Among the polymeric additives commonly used as VII, poly(alkyl methacrylates) (PAMA) provide the easiest way of changing the composition and structure that are necessary to comply with the new engine oil specifications. PAMA additives are manufactured by the free radical copolymerization of corresponding methacrylate monomers in solution of base oil. Therefore, they can relatively simply be chemically modified by the addition of different functional methacrylate comonomers because of similar copolymerization reactivity. Also, PAMA additives are unique regarding mechanism by which they improve the viscosity and its temperature dependence. Unlike other polymeric VII the hydrodynamic coil of PAMA polymer molecule in the oil solution increases with the temperature increase. The increase is a function of copolymer composition ; it is more pronounced for copolymers that contain methyl methacrylate (MMA). At the same time, MMA can reduce the solubility of the PAMA in oil at lower temperatures causing a certain degree of self-association between polymer molecules. The incorporation of styrene in PAMA enhances the thermal stability and solubility of the polymer in oil, especially at low temperatures. Furthermore, by incorporation of the specific polar comonomers (usually with the amino group) the necessary dispersant properties of the lubricating oil are achieved. Also, dispersant PAMA are able to adsorb onto metal surfaces from oil solution. These thick, viscous boundary films enhance lubricant film formation in conditions of slow-speed and high temperature and thus produce a significant reduction in friction. Apart from excellent dispersing properties, the incorporation of amino methacrylate into PAMA structure enhances its molecular interactions with the base oil solvent, which consequently increases the viscosity of the solution. Recently, it was shown that with the PAMA additives the lubrication properties of the API group II and III base oils can compete with those of synthetic base oils (PAO), especially for some applications, e.g. in wind turbines. Therefore, there is a constant interest in application and improving of the properties of PAMA additives. In addition to the viscosity index improving, the additives based on PAMA are well known and widely used pour point depressants of lubricating oils. They prevent gelation of the oil and deposition of n-paraffins from the base oil at low temperatures due to the crystallization of long alkyl side chains. In this way, they enable oil to flow at much lower temperatures. Accordingly, the share of methacrylates with long chain alkyl ester groups such as octadecyl methacrylate and dodecyl methacrylate is a key for the effective lowering of the pour point of oil. Generally, in order to reach an optimum, it is necessary to adjust the share of polymeric additive and the ratio of constitutive methacrylates to the composition and characteristics of the particular base oil. The aim of this study was to determine the effect of introduction of the dispersant component, namely, dimethyl-aminoethyl methacrylate (DMA) into the PAMA and poly(styrene-co-alkyl methacrylate) viscosity index improver on the pour point and low temperature properties of its solutions in the base oil. The share of DMA in synthesized copolymers has been varied from 0 to 10 mol. %, as well as the molar mass of a copolymer sample that displayed the best pour point. In adition, the effect of composition and molar mass of pure PAMA on pour point were also investigated.

methacrylate ; pour point depressants ; oil

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