Oils, multiviscosity

The purpose of a multiviscosity motor oil is to offer good engine protection over the operating range of the engine from a cold start to the normal operation temperature. Addition of a low Tg polymer allows for a wider range where viscosity is approximately constant. 

Addition of about 1% of an EPM is used today to achieve most of our multiviscosity oils. These copolymers were developed as part of Exxon s program that Ed Kresge and fellow researchers were involved with that also produced the miscible blends used to make automotive bumpers and panels (Section 7.8). 

It is important to note that the Tg values of component polymers may be unaffected when they are present in multiphase blends (separate phases at the microlevel), and this is the basis for many multiviscosity oils. This is also true for block and graft copolymers, which have characteristic Tg values corresponding to the polymers of each of the comonomers. 

The viscosities usually recommended are SAE 20W-20 or 30 for temperatures down to about 18°C, and SAE 20W-20 or 10W for lower temperatures. For extreme low temperatures, SAE 5W, 5W-20, or 5 W-30 oils may be recommended. Multiviscosity SAE 10W-30 or 5W-30 oils are often recommended for year-round use, and are now the primary recommendation of several U.S. engine manufacturers. European engine manufacturers often recommend higher viscosities, particularly multiviscosity oils where SAE 20W-40 and 20W-50 oils are frequently preferred. 

Multiviscosity or Mineral oil to which a viscosity index improver has been added... 

MV EG MVMA different viscosities at 100°C. Fluids with very high natural viscosity indexes, such as some synthetic fluids, are also classified as multiviscosity. Motor Vehicle Emission Group (Europe). Motor Vehicle Manufacturers Association (U.S. passengers cars). A North American OEM association. As part of ILSAC, it participates in promoting the ILSAC engine oil standards. 

VOC/VOF (Example Taking an oil in the SAE 10 range, adding a VI improver, would give us some oil like SAE 20W-40. Adding the VI improver to an SAE 30 would yield an SAE 40). See multiviscosity the definition of SAE 10 and SAE 40 oils. Volatile organic compound/or volatile organic fraction. 

Mueller, H.G. and Leidigkeit, G. (1979) Thermal and oxidative degradation of polymers in multiviscosity oils (in German). Schmiertech. Tribal. 26 (6) 201-204. 

A polymer may be internally plasticized by random copolymerization with a monomer whose homopolymer is very soft (has a low Tg, see Chapter 6). There are obviously never any permanence problems when this is done. The composition of the copolymer can be adjusted to give the desired properties at a particular temperature. Above this temperature, the copolymer will be softer than intended and below this temperature, it wUl be harder. With external plasticizers, the same sort of temperature compensation as in the multiviscosity motor oils is obtained, giving materials that maintain the desired flexibility over a broader temperature range. 

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