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Viscosity Modifiers II

Posted By: Gokhan

Viscosity Modifiers II - 06/17/19 03:38 AM

Originally Posted by MolaKule
There are three (3) key features of polymer viscosity modifiers, specifically VII VM's:

VII and VM are the same thing.

Originally Posted by MolaKule
They do modify the rate of change in viscosity verses temperature.

No, this is the most common misconception about VIIs. They do not modify the rate of change of the viscosity vs. the temperature.

Most VIIs boost the viscosity by roughly the same factor at all temperatures. (PMA is an exception but it's not commonly used in motor oil.)

The way the viscosity index VI is defined is such that even if you multiply KV40 and KV100 by the same number (which is what a typical VII does), VI increases. Hence, it's called a VII. They do not selectively boost the viscosity at high temperatures as most people incorrectly believe. This is why there is no difference between a VM and a VII.

The advantage of using a VII comes at cold cranking. Cold-cranking simulator (CCS) is a high-shear test and the VII shears and the oil passes the test by measuring below the maximum CCS viscosity limit.
Posted By: Gokhan

Re: Viscosity Modifiers II - 06/17/19 08:47 AM

Here is more on the widespread misconception that viscosity-index improvers work by thickening the oil more at higher temperatures.

On the contrary most VIIs (VII = VM) thicken the oil somewhat less at higher temperatures than at lower temperatures:

[Linked Image]

Shear thinning and hydrodynamic fri...g oils. Part I: Shear-thinning behaviour
Shear thinning and hydrodynamic friction of viscosity-modifier-containing oils. Part I: Shear-thinning behaviour
Nigel Marx (1), Luis Fernández (2), Francisco Barceló (2), and Hugh Spikes (1)
(1) Imperial College, London, UK
(2) Repsol Technology Centre, Madrid, Spain
June 21, 2018
(Image posted under Creative Commons license)


Take Oil #1 for example. The thickening power of the VII is 2.0 vs. 1.7 for 40 °C and 100 °C, respectively. KV40/KV100 for the base-oil and finished oil are 35.89/6.05 cSt and 107.26/16.19 cSt, respectively. Base-oil viscosity index VI for Oil #1 is 114 and the finished-oil VI for Oil #1 is 162. So, despite the VII thickening the oil more at lower temperatures than at higher temperatures, the VI is still improved by a large amount.

This is because of the definition of the VI. Thicker oils have a higher VI by definition even if their viscosity varies the same or somewhat faster. Try this calculator, for example with KV40/KV100 40/6 cSt vs. 80/12 cSt, which gives 91 vs. 145, respectively, despite the viscosity varying the same:

https://www.widman.biz/English/Calculators/calc-visc-index.html

The main exception is the PMA VII, which is in Oil #10. As you see in the figure, it thickens the oil a lot more at higher temperatures. However, it requires three to six times the polymer content of the other VII types, and therefore, it is not commonly used in engine oil, as this would lead to increased engine and turbocharger deposits and sludge.

The reason behind the misconception is that people don't realize the real trick of the VII, which is allowing the oil to pass the cold-cranking simulator (CCS) test to pass while thickening the oil not only at high temperatures but at all temperatures (usually somewhat more or about the same at low temperatures). This is accomplished because the VII temporarily shears during the CCS test, which is a high-shear test.

So, MolaKule, you should perhaps add this fourth key feature of the VII, which is the CCS performance.
Posted By: MolaKule

Re: Viscosity Modifiers II - 06/17/19 07:19 PM

Originally Posted by Gokhan
Originally Posted by MolaKule
There are three (3) key features of polymer viscosity modifiers, specifically VII VM's:

VII and VM are the same thing.


According to "Review of Viscosity of Modifier Lubricant Additives," Martini, et. al., there is a hierarchy in describing Viscosity Modifiers and that is:

Viscosity Modifiers:

Thickeners such as highly viscous BrightStock, PIB's, etc.

Viscosity Index Improvers such as OCP's, PAMA's, etc.

Thickeners and VII's need to be differentiated as to types of Viscosity Modifiers.



Originally Posted by Gokhan
Originally Posted by MolaKule
They do modify the rate of change in viscosity verses temperature.

No, this is the most common misconception about VIIs. They do not modify the rate of change of the viscosity vs. the temperature.

Most VIIs boost the viscosity by roughly the same factor at all temperatures. (PMA is an exception but it's not commonly used in motor oil.)


So most VII's boost viscosity as the base oil temp changes; seems like a rate-of-change vs temp situation to me, or are you using some other definition of dx/dy?
Posted By: MolaKule

Re: Viscosity Modifiers II - 06/17/19 07:31 PM

Originally Posted by Gokhan
Here is more on the widespread misconception that viscosity-index improvers work by thickening the oil more at higher temperatures.


No need to repeat yourself as in the other post.



Originally Posted by Gokhan
So, MolaKule, you should perhaps add this fourth key feature of the VII, which is the CCS performance.


According to "Review of Viscosity of Modifier Lubricant Additives," Martini, et. al., the three key feature were:

Quote
Thickening efficiency, the viscosity-temperature relationship, and shear stability are all Key features of Viscosity Index Improvers.



I think I explained the QOTD's purposes here:

Quote
As to the QOTD, it was conceived to be a purely educational thread where a basic Tribology question was asked and answers could be given by anyone if the original post said "Open to All."

The QOTD was not conceived as a forum for protracted discussion, which is why the suggestion was made to Write up a White Paper to address any further technical material one would wish to contribute on any topic, including those in QOTD. The White Paper section is open to any BITOG member to submit technical material at any time.


and here:

Quote
under the Major Forum heading of:

Science and Technology of Oils and Lubricant Additives


The three SubForums are:

Interesting Articles - People find pertinent articles from Professional Sources or the Web and post them there,

Question of the Day - As already Explained above,

Technicial and White Papers - Where BITOG members do their OWN research on a topic and speak to the topic In their own words, and where ALL members can see the information and provide feedback and discussion.



Question of the Day
Posted By: MolaKule

Re: Viscosity Modifiers II - 06/17/19 07:50 PM

Originally Posted by Gokhan


Most VIIs boost the viscosity by roughly the same factor at all temperatures. (PMA is an exception but it's not commonly used in motor oil.)



Are you aware of the PAMA-OCP grafted co-polymers?

Grafted polymers may possibly be the reason why some of the graphical relationships shown in the various papers by Marx, et. al., do not always follow predicted patterns and raise specific questions.

Lastly, we cannot know the exact VII chemistry unless Infineum or Lubrizol, or Afton or others gives us the exact molecular formula of the VII's. While I deal mostly with Lubrizol and Oronite, and am quite close to these guys, not even they will tell me, so you cannot be certain of the VII chemistry incorporated into any of these products. So being outside the internal additive company loop is a guessing game.

I don't know what your specific research interests are but mine is in the molecular structure of Friction Modifiers in ATF's for fluid shear in non-contact "unit" regions of wet clutches, and the role of different acid chain lengths at the shear-strength interface.

So our interests seem to have a common thread. smile

Posted By: Gokhan

Re: Viscosity Modifiers II - 06/17/19 11:17 PM

Regarding the so-called bright stocks, since they are nothing but thick (KV100 = 30+ cSt) Group I base stocks, I would consider them as part of the base oil but not as any sort of a VM.

Apparently they are getting rare and expensive. This company has some data on them:

Ergon bright stocks

I don't have much data on the PIB polymers but are they any different than other VIIs? High-molecular-weight PIBs increase the VI just like any other VII, don't they? They seem to be unpopular as VIIs today as better-performing VIIs are now available.

The reason I brought up the temperature dependence is because most people think that they increase the viscosity more at higher temperatures than at lower temperatures and that's the reason behind the VI improvement. In reality, the thickening effect is not necessarily strongly temperature dependent and actually thickening is more at lower temperatures than at higher temperatures for most VIIs. (See the figure above.) The reason they improve the VI is because the way VI is defined, it's based on actual base oils -- Group I to be exact -- and their viscosities change more rapidly with temperature as the base oils get thicker. So, if a VII multiplies the viscosity by the same number at all temperatures or even a slightly smaller number at higher temperatures, that's still an improvement in VI over how an actual base oil (such as Group I) would behave. PMA is an exception, as it thickens much more at higher temperatures, which could be used to make ultrahigh-VI oils (VI well over 200) but it requires 3 - 6 times the polymer content of other VIIs.

It's a very interesting subject and I'm glad it's a research interest of yours.

Nevertheless, I've also noticed that newer oils are trying to avoid VIIs as much as possible. For example, the recently introduced ACEA C5 0W-20 oils (Mobil 1 ESP x2 and Castrol LL IV) with Euro OEM specs seem to have very little VII. As ZeeOSix and I have been discussing, it looks like the best way to make an oil with high fuel economy, low wear, and low deposits is to start from a base oil as thick as possible with a VI as high as possible and use the least amount of VII possible. Large temporary shear of the VII at 10^6 1/s is not necessarily a bad thing, which improves the fuel economy, as they all fully shear at high-enough shear rates anyway. Likewise, high thickening power is not necessarily a good thing, which makes the fuel economy worse, as the viscosity at lower shear rates gets higher. Again, apart from picking an oxidatively stable polymer (such as an OCP), the key to making a good motor oil seems to start from a base oil that is as thick as possible and has a VI as high as possible so that the VII content could be reduced as much as possible. In practice the availability of the base oils and economics determines what one can make.
Posted By: Gokhan

Re: Viscosity Modifiers II - 06/18/19 04:54 AM

Correction: The increasing VII content usually improves the fuel economy. This is because the HTHS viscosity decreases with respect to the low-shear viscosity, decreasing the minimum-oil film thickness (MOFT) and friction in the bearings. Also, the viscosity index (VI) increases, which increases the fuel economy at lower oil temperatures by keeping the oil thinner when colder.

The fuel economy and wear usually conflict each other. As I mentioned in my previous pots, ACEA C5 and Euro OEM 0W-20 oils (Mobil 1 ESP x2 and Castrol LL IV) favor low VII content, which helps lower the deposits and wear, whereas Japanese 0W-20 oils (such as TGMO and Eneos Sustina) favor high VII content, which helps improve the fuel economy.

This is the summary of how key viscosity quantities relate to the VII content:

L = low-shear (HTLS) viscosity
H = high-shear (HTHS) viscosity
F = full-shear (HTFS) viscosity (base oil and sheared additives)
V = VII content
A = A_Harman index
b = VII viscosity-boost rate ~ 10.5 (typical value but varies)
s = VII temporary-shear rate ~ 2 (typical value but varies)
c = b/s ~ 5.25 (typical value but varies)

A = H/L

V = (1/s) * (1 - A) = (1/s) * (1 - H/L)

(L/F) - 1 = c * (1 - A) = (b/s) * (1 - A) = (b/s) * (1 - H/L) = b * V

(L/F) - 1 represents how pronounced the non-Newtonian (S-shaped region) is. When it gets higher (the S-shaped region in the curve gets deeper), the fuel economy may improve but the wear may increase.

[Linked Image]

Also:

1 - A = 1 - H/L = s * V

1 - A represents how much the oil shears at 10^6 1/s, which is the shear rate at which the HTHS viscosity is measured. When it gets higher, the high-shear (HTHS) viscosity gets lower with respect to the low-shear (HTLS) viscosity. It is directly related to the VII content and how much the VII temporarily shears at the 10^6 1/s shear rate. Note that part of the additive package temporarily shears as well, appearing as a VII even if the oil is a monograde with no VII but only an additive (detergent inhibitor [DI]) package.
Posted By: MolaKule

Re: Viscosity Modifiers II - 06/19/19 01:50 AM

Originally Posted by Gokhan
Regarding the so-called bright stocks, since they are nothing but thick (KV100 = 30+ cSt) Group I base stocks, I would consider them as part of the base oil but not as any sort of a VM.

Apparently they are getting rare and expensive....


You are welcome to your opinion but highly viscous BrightStocks have been considered as a thickener additive since about 1923 in both gear oils and engine oils. They are no longer used in engine oils because of their poor deposit characteristics.

Originally Posted by Gokhan
I don't have much data on the PIB polymers but are they any different than other VIIs? High-molecular-weight PIBs increase the VI just like any other VII, don't they? They seem to be unpopular as VIIs today as better-performing VIIs are now available.



Yes they are different. Many PIBS only thicken and don't have any VII characteristics.
Posted By: Shannow

Re: Viscosity Modifiers II - 06/19/19 04:59 AM

Molakule,
we had some issues a few years ago with ISO460 gear oils rapidly becoming 200(ish) in service.

The manufacturer denied having Viscosity Modifiers in their ISO grades, pointing to the 98 VI...but within 3 months, no changes at our end on multiple pieces of equipment, the oil stopped breaking...three years later, it was back again...evidence of PIB (or similar thickeners)
Posted By: userfriendly

Re: Viscosity Modifiers II - 06/19/19 08:10 PM

Group I from Singapore?
Posted By: MolaKule

Re: Viscosity Modifiers II - 06/19/19 10:00 PM

Originally Posted by Shannow
Molakule,
we had some issues a few years ago with ISO460 gear oils rapidly becoming 200(ish) in service.

The manufacturer denied having Viscosity Modifiers in their ISO grades, pointing to the 98 VI...but within 3 months, no changes at our end on multiple pieces of equipment, the oil stopped breaking[breaking down?...losing viscosity?]...three years later, it was back again...evidence of PIB (or similar thickeners)


When you asked about VM's they may have interpreted it as asking about VII's, not thickeners.

Assuming no contaminants such as moisture (steam) or solvent intrusion, they may have used PIB's as thickeners and tackifiers, but PIB's are usually shear resistant and hydrophobic (tending to repel or fail to mix with water).

The one problem with PIBs is they are only solvent in Group I, naphthenic oils, or other solvents.

It could have been they used highly shearable base oils or BrightStock as a thickener.

I have seen cheap and inferior OCP's degrade and allow the bulk oil to lose viscosity.

Did you ever have that oil analyzed?
Posted By: Shannow

Re: Viscosity Modifiers II - 06/20/19 02:25 AM

Yep,
viscosity in the mid 200s...no moisture or wear metal abnormality...we never had the oil "pulled apart" to work out what chemically went wrong with it...but it was very clean looking, just broken.

We even confirmed that controlled drums, sampled before and after being in service were the right viscosity before use, and broken after.
Posted By: MolaKule

(NA) Re: Viscosity Modifiers II - 06/20/19 03:46 AM

Originally Posted by Shannow
Yep,
viscosity in the mid 200s...no moisture or wear metal abnormality...we never had the oil "pulled apart" to work out what chemically went wrong with it...but it was very clean looking, just broken.

We even confirmed that controlled drums, sampled before and after being in service were the right viscosity before use, and broken after.


So basic (viscosity) analysis showed the used oil went from ISO 460 down to ISO 220 or thereabouts?
Posted By: Gokhan

(NA) Re: Viscosity Modifiers II - 06/20/19 07:42 AM

Don't forget that the DI pack (additive pack) shears as well per the Hugh Spikes et al. paper on shear-thinning I posted here.

In addition the DI pack serves as a thickener. 50+% increase in the viscosity by the DI pack is possible. It's quite possible that they used a very high-shear DI pack and you witnessed it shear.
Posted By: Gokhan

(NA) Re: Viscosity Modifiers II - 06/20/19 09:00 AM

However, it turns out that the additive package in gear oils is only about 1 - 2% of the total composition; so, that's not what shears.

According to Exxon Mobil Advanced synthetic base stocks brochure (not the blending guide), monograde gear oils seem to use all sorts of VIIs (PMA, PIB, EPC, ultra-high-viscosity PAO, etc.) and they permanently shear substantially. See the bottom of Page 7:

https://www.exxonmobilchemical.com/en/library/Asset/99EA9EECD9E640CCB78B1C8B443DC067

It looks like they did use a VII that undergoes a lot of permanent shear.
Posted By: MolaKule

Re: Viscosity Modifiers II - 06/20/19 06:38 PM

Indopol seems to think that PIB polymers are shear resistant:

Quote
BENEFITS

Excellent thickeners and shear stable polymers.
Good lubricity, high film strength and viscosity indices.
Low pour points, volatility and toxicity.
Good tack and anti-throw properties.
Hydrophobic, non-corrosive, non-drying, non-staining.
Burns cleanly, leaving no residue at elevated temperatures.
Wide molecular weight and viscosity range.


They also have this chart to show thickening efficiency verses BrightStock:




Attached picture PIB verses Brightstock.jpeg
Posted By: MolaKule

Re: Viscosity Modifiers II - 06/20/19 06:54 PM

Originally Posted by Gokhan
However, it turns out that the additive package in gear oils is only about 1 - 2% of the total composition; so, that's not what shears.


It's more like 3.5% to 10% by weight:

Typical Gear Oil Formulations

Originally Posted by Gokhan
According to Exxon Mobil Advanced synthetic base stocks brochure (not the blending guide), monograde gear oils seem to use all sorts of VIIs (PMA, PIB, EPC, ultra-high-viscosity PAO, etc.) and they permanently shear substantially. See the bottom of Page 7:


Under the Metallocene category of PAO's it says:

Quote
Performance benefits
include:
• High viscosity index (VI)
• Excellent low temperature properties
• Good shear stability for
enhanced durability


Originally Posted by Gokhan
https://www.exxonmobilchemical.com/en/library/Asset/99EA9EECD9E640CCB78B1C8B443DC067

It looks like they did use a VII that undergoes a lot of permanent shear.


We can't know that since the oil did not go through extensive analytical assessments.

Posted By: Gokhan

Re: Viscosity Modifiers II - 06/20/19 10:06 PM

Originally Posted by MolaKule
Indopol seems to think that PIB polymers are shear resistant:

Hmm, not according to Ergon (see Page 12):

Advancements in bright-stock refining technology by Ergon (PDF)

Or NACO (see the paragraph named bright-stock replacement):

NACO synthetic base oils with emphasis on the 20.5 cSt (23 cSt nominal) alkylated naphthalene (AN)
Posted By: MolaKule

Re: Viscosity Modifiers II - 06/21/19 06:55 PM

Originally Posted by Gokhan
Originally Posted by MolaKule
Indopol seems to think that PIB polymers are shear resistant:

Hmm, not according to Ergon (see Page 12):

Advancements in bright-stock refining technology by Ergon (PDF)


I sent an email to Tom requesting to see if they had ever done an SSI test between their new naphthenic derived BS and PIBS, and what pibs were tested.

Originally Posted by Gokhan


The NACO oils are simply blends of AN's and high viscosity PAO's but I thought you said PAO's had poor shear stability?

Janex also disagrees with your assessment of PIB's Shear Stability:

Quote
POLYISOBUTYLENE (PIB)
Polyisobutylene (PIB) and Polybutylene are liquid polymers produced by the cationic polymerisation of isobutylene and raffinate-1 respectively. We offer a comprehensive product range with molecular weight from 450 to 90,000 MW.

Polyisobutene CAS 9003-27-4 / EC 204-066-3 - Polybutene CAS 9003-29-6 / EC 203-452-9


Properties:

Low gas or moisture permeability
Low / non-toxicity & colourless / transparent
Water white colour and odourless
High thickening efficiency
Good shear stability
Clean burning / low deposit
Good electrical insulation
Oxidation stability to light/UV and air
Tackifier/adhesive properties
Low temperature properties


https://www.janex.ch/en/products/polyisobutylene-pib?qs=products/polyisobutylene-pib
Posted By: Gokhan

Re: Viscosity Modifiers II - 06/21/19 07:20 PM

Originally Posted by MolaKule
The NACO oils are simply blends of AN's and high viscosity PAO's but I thought you said PAO's had poor shear stability?

Janex also disagrees with your assessment of PIB's Shear Stability:

High-viscosity PAO can have poor shear stability, and the permanent shear-stability index (SSI) is inversely proportional to the viscosity of the PAO. Although, there is the m-PAO that is a lot more shear-stable.

It's not my assessment really. Different companies are making different claims. The permanent SSI will depend on the viscosity of the PIB and perhaps the manufacturer as well. If some are saying the PIB has poor permanent SSI, at least in some cases it must be true.
Posted By: MolaKule

(NA) Re: Viscosity Modifiers II - 06/21/19 07:34 PM

Here are some interesting conclusions from an older paper on base oil viscosity and VII's:


Base Oil Viscoitiy and VII by Lubrizol India - HTHS and SSI
Posted By: Gokhan

(NA) Re: Viscosity Modifiers II - 06/21/19 08:22 PM

Originally Posted by MolaKule
Here are some interesting conclusions from an older paper on base oil viscosity and VII's:


Base Oil Viscoitiy and VII by Lubrizol India - HTHS and SSI

I'm sorry to say this but this is very poor-quality research. The authors are all over the place and there is no systematic scientific approach. I would entirely ignore their conclusions.

HTHS viscosity doesn't depend on the VII content? Really? One of the main uses of the VII is to adjust and tune the HTHS viscosity.
Posted By: Gokhan

(NA) Re: Viscosity Modifiers II - 06/22/19 01:29 AM

Looking at the Lubrizol India paper more carefully, I see that they are not claiming that the HTHS viscosity does not increase with the VII content, which I thought what they were claiming and called it absurd. So, it is fine.

However, looking at Table 5, I see some unusual behavior.

First, the KV and HTHS viscosity columns are mislabeled and they should be switched -- actually KV (cSt) is on the left and HTHS viscosity (cP) is on the right.

The rather unusual behavior I see is the collosal increase in the viscosity (colossal thickening power) -- 341.6% for OCP and 1860.7% for SIP. You don't see that in commercial oils. For example that would turn a KV100 = 6 cSt base oil into a KV100 = 118 cSt oil in the case of SIP. As a comparison SAE 60 KV100 < 26.1 cSt. Then, they see some variation of the thickening power with the base-oil viscosity as well as the VII content. I am not sure if this would be seen in practical applications of VIIs, where the thickening power is below about 140% in the extreme commercial cases -- 5W-50 and 10W-60 oils. Therefore, the nonlinear results (nonlinear in the VII content and base-oil viscosity) may be because of the unusually high VII content.
Posted By: MolaKule

(NA) Re: Viscosity Modifiers II - 06/22/19 03:06 AM

Originally Posted by Gokhan
Originally Posted by MolaKule
Here are some interesting conclusions from an older paper on base oil viscosity and VII's:


Base Oil Viscoitiy and VII by Lubrizol India - HTHS and SSI

I'm sorry to say this but this is very poor-quality research. The authors are all over the place and there is no systematic scientific approach. I would entirely ignore their conclusions.

HTHS viscosity doesn't depend on the VII content? Really? One of the main uses of the VII is to adjust and tune the HTHS viscosity.


The paper does have a section in which they show the Experimental Procedure they used and the basis for their data tables.

I agree editing of Figure 5's Text could have been better but again, they are stating the results dervived from their Experimental Procedure whether you agree with those results or not.
Posted By: Gokhan

(NA) Re: Viscosity Modifiers II - 06/22/19 04:29 AM

As I said in my previous post, they are not claiming that HTHS doesn't vary with VII content as I first thought, so, it's fine. Instead they are making some claims about the HTHS thickening rate (increase per VII content) and permanent shear.

The data is probably OK and the results are somewhat interesting. As I also said in my previous post, the problem is that the thickening is so large (as large as a factor of 20) that the results don't really apply to commercial oils, in which the thickening is usually a factor of 2 or less (100% or less thickening) and virtually always under a factor of 2.5 (150% thickening). Nonlinear (in VII content and base-oil viscosity) behavior they observe, while interesting, probably doesn't appear for the range of the VII content used in commercial motor oils.
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