Mixing: VIIs, PPDs, Waxes

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Warning: the following is a little long, but the question is interesting to me. I have been looking at some of the literature on viscosity index improvers, pour point depressants, and base oil waxes. From what I can gather, some VIIs can interact with waxes and PPDs (and solvent for that matter) such that the VIIs would crystallize at very different temperatures in different base oils (waxes and solvent) or in the presence of different PPDs. So, it seems that you could mix two fully formulated oils and get a very different viscosity than you would predict from measurement of the two oils separately. From what I can tell, this differences could sometimes be seen at temperatures as high as 40 C. As a general observation, it seems that for these types of interactions, the resulting viscosity would be higher than predicted. In addition, it could take several days of the oil being undisturbed for the co-crystals to form (from patent discussion, US 5460739 A). On the other hand, when VIIs are mixed within otherwise identical oils, the resulting cold temperature performance is reduced viscosity (eg. Journal of Polymer Science 2013, 3(3):35-45). This phenomenon appears to be due to VIIs interacting with each other (as opposed to interacting with waxes, PPDs, or solvent). So the question is, has anyone seen commercial formulations of PCMO that act differently when mixed than would predicted from viscosity measures of each separately? It seems as though the likely combinations would be fairly polar (RedLine maybe) with some of the less polar (heavy PAO). Alternatively, when a high-quality synthetic with very low wax content is mixed with a lower quality mineral with heavy wax content, there could be problem. The high quality synthetic could be formulated with the assumption that the selected VIIs would not encounter waxes. Similarly, are any of the blenders willing to share examples of where they have stumbled upon combinations that act unexpectedly?
 

GMorg

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Well, I found an example on my own. It's a 20 year old paper and all that I can get from here is the abstract. In any case, it seems that at least some of the cold-related engine failure was due to mixing incompatible, multigrade oils. Specifically, the waxes in one oil were not compatible with the VIIs in another oil at extreme cold temps. Citation: Rhodes, R., "Low-Temperature Compatibility of Engine Lubricants and the Risk of Engine Pumpability Failure," SAE Technical Paper 932831, 1993, doi:10.4271/932831. Abstract: An investigation of an engine field-failure found low-temperature incompatibility to be the root-cause of an engine pumping failure. This was established from an examination of the rheology of the new and used oils. It was later discovered that some SAE multigrade oils that contain higher-cloud-point basestocks are incompatible with other same-W-grade oils that contain VI improvers that have a propensity to interact with wax precursors. The latter oils, which failed the Scanning Brookfield test, but not the TP1 mini-rotary viscometer test, were found to be incompatible with a number of commercial multigrade oils at low-temperature.
 

GMorg

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Same author. Citation: Rhodes, R., "Assessment of the Low-Temperature Incompatibility Risk of Commercial Engine Oils," SAE Technical Paper 941976, 1994, doi:10.4271/941976. Abstract: A portion of the Institute of Materials database which contained data on more than 650 multigrade oils was searched to obtain an estimate of the percentage of oils that meet SAE J300 low-temperature pumpability requirements but exhibit properties which make the low-temperature properties suspect. The suspect oils studied either failed the Scanning Brookfield test (SBT) or produced significantly different viscosities in the one-day mini-rotary viscometer (MRV) test and the two-day MRV test, which uses the slow-cool, TP1 cooling cycle. Several of these commercial multigrade oils were obtained from the Institute of Materials (IOM). The oils were then blended with off-the-shelf commercial (CO-numbered) oils having the same SAE W-grade designation and evaluated in the two-day MRV test (TP1-MRV), which has been a reliable predictor of engine lubricant pumpability characteristics. A number of failures were recorded and some of the off-the-shelf oils were found to be more likely to fail than others. The low-temperature rheology of the IOM-supplied oils identified them as being suspect formulations. In this report they are referred to as rheospecific formulations. Conversely, the rheology was not suspect for the majority of CO-numbered oils that were incompatible in the TP1-MRV with the IOM-supplied oils. Such oils are identified herein as rheolatent formulations; they have good low-temperature performance in themselves, but are victimized when combined with the rheospecific blends.
 

GMorg

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The abstract above is not about incompatible oils. It is about incompatible measurements. I read it too fast the first time through.
 
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GMorg, the latter wasn't exactly measuring error from my reading, but the fact that the oils behaved differently on different cooling rates. Slower cooling gives the waxes time to grow into a gel that's not possible with snap cooling...so a snap test at X degrees (like a cold carpark for a work shift) isn't the same as a test at the same temp if the cooling rate is slower...the latter can be worse. I think it was Tom NJ in another thread mentioned an oil that had issues in the North of the US because it did exactly that...got bad at slow cooling rates... edit...yep, here, standard tests, and a specific cooling profile that made problems. http://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3503628/Re:_The_oft_quoted_ASTM_D6922#Post3503628
 
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Originally Posted By: GMorg
So the question is, has anyone seen commercial formulations of PCMO that act differently when mixed than would predicted from viscosity measures of each separately? It seems as though the likely combinations would be fairly polar (RedLine maybe) with some of the less polar (heavy PAO). Alternatively, when a high-quality synthetic with very low wax content is mixed with a lower quality mineral with heavy wax content, there could be problem. The high quality synthetic could be formulated with the assumption that the selected VIIs would not encounter waxes. Similarly, are any of the blenders willing to share examples of where they have stumbled upon combinations that act unexpectedly?
Bump, member KCJeep calculated out a blend, and the results weren't as expected. http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2948797 even within the same family group.
 
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