polymers in oil

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Jan 28, 2003
Given this statement, do the polymers adhere to the oil molecules, or just mix in with the oil? On the same line, what happens when you mix a 10w oil with a 90w oil? Polymers are added to a light base (5W, 10W, 20W), which prevent the oil from thinning as much as it warms up. At cold temperatures the polymers are coiled up and allow the oil to flow as their low numbers indicate. As the oil warms up the polymers begin to unwind into long chains that prevent the oil from thinning as much as it normally would.
There is no 90w oil...the W signifies "Winter" or cold testing. There is 75W-90, 80W-90, etc. Anyway, all SAE oil viscosities from 75 and up are gear oils, not motor oils. An SAE 90 gear oil is about the same viscosity as a 40 or 50 wt. motor oil. Ken
Ok, 50W then. Do they just blend together? Why would the two not separate? I don't think they will, but can't explain or prove they won't. I'm in the middle of a debate and my reputation is on the line.
They will blend together. This used to be common making the heavier oils, 20-40 WT if the normal blend stocks were not available. It is not as good, we called it a "dumbbell" blend. Remember that most of these thicker oils are a blend of different feedstocks;light, medium, or heavy neutral or/and bright stock. Oh, and I am talking about dino oils. richard
I believe you may be referring specifically to those long chain molekules for VII additves, such as polymethacrylates, styrenes, etc. Polymers are simply macromolecules chained together. The process of joing these molecules of thousands of atoms is called, "Polymerization," in which many small molecules, called monomers, form very large molecules. Various VII polymers are created in the lab to mix with both synthetic and petroleum oils. Some VII polymers will mix with both. How well they mix depends on the solubility of the base oil and the polymers' molecular structure. If they didn't mix, we would be in a heap of trouble. Polymerization is the keyword for creating synthetic hydrocarbons, such as PAO's, and esters used in full synthetic motor oils. This is why Group III oils do not meet the criteria or definition of full synthetic oils.
I don't know if I'm answering the question that was asked, but I'll give it a try. The viscosity properties of a solution of polymers is largely determined by the longest (or largest) molecules in the mixture. So if you mix a 10 weight oil with a 30 weight, you don't end up with a 20 weigth oil, but rather a mixture with closer to 30 weight viscosity characteristics. The largest molecules affect the viscosity at both 40 degrees C and 100 degrees C. This holds for straight weight oils, which exhibit Newtonian viscometric properties, which are determined just by polymer length. One way to look at this is that longer polymers have larger surface areas that can form a greater number of weak chemical interactions with other molecules than shorter polymers. That doesn't really explain the whole viscosity thing, but it is a start. When VI improvers are added to a base oil, they "dissolve" in the base oil since they are themselves hydrocarbons that can form the same types of weak interactions with the hydrocarbons in the base oil as the base oil components do with themselves. Heat is just molecular motion. As the amount of heat in a system increases, the interactive forces between molecules will decrease and viscosity of a solution goes down. VI improvers increase in size as the temperature goes up either by uncoiling or expanding (depending on the type of additive) as the temperature increases. Thus, thus with increasing temperature, a certain percentage of the molecules in a multi grade oil get larger and expose more surface area for interactions with other molecules. This tends to counteract the effect of heat on the base oil molecules and has the effect of minimizing the effect of temperature on viscosity. This is an oversimplification, since the shapes and chemical properties of the interacting molecules themselves also influence viscosity, especially when shear forces are acting on the solution. But I hope this helps.
I think this explains it: "The viscosity properties of a solution of polymers is largely determined by the longest (or largest) molecules in the mixture." So then it looks like the same applies to different weight oils. A light wieght oil has short molecules, and a heavy wietht oil has long molecules. If you mix the two together you end up with a mixture of both long and short molecules. This dumbbell blend is not as good as an oil with the right length molecules that would match the viscosity fo the blend. Do I understand correctly?
greencrew, Yes, the two extremely different oils can be blended together to form an intermediate product, which we would call a dumbbell blend. Realize that most of the products, as I stated before, are blends of two or more basestocks. This probably is not true so much for the lighter base oils. richard
Greencrew - Yes, that was the point re viscosity. But whether a "dumbell blend" is better or worse than what a manufacturer provides would require an uninformed opinion. I am both impressed and amazed by the things some of the folks on this board are doing with their own engines. We are sure to learn a lot.
Drstressor, This dumbbell blend was made by a major oil company. It did not happen very often, but if problems arose meeting schedule or demand, they were made. richard
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