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Holding Back Hydrolysis


Holding Back Hydrolysis

With a few exceptions, water is not a welcome companion of lubricating oils or greases. Not only can it displace lubricants at critical points, potentially damaging components, it can also chemically degrade them through a process known as hydrolysis.

Standard approaches for dealing with water have mostly focused on keeping the water out in the first place or finding ways to extract it from lubricants once they become contaminated. Recently, Dow Chemical brought an additional solution: an additive, compatible with many lubricants, that aims to absorb the water.

According to the Midland, Michigan-based chemical company, its Ucon WaterGuard stabilizers come in two different formulations, WG-1 and WG-2, meant for use with different types of ester base stocks. The polyalkylene glycol based additives act like a sponge, soaking up water that has accumulated within a lubricant, including greases.

Both variations are readily biodegradable, Dow says. This is important, as esters are typically used to formulate products that meet regulatory and other standards for biodegradability. While ester based lubricants have made great strides, they are still prone to hydrolysis to varying degrees. This is a particular problem because many applications that require biodegradable lubricants, such as marine and forestry, frequently result in exposure to water.

WG-1 is meant for use with most natural and synthetic esters, including saturated and unsaturated varieties. WG-2, a triblock copolymer, is targeted for saturated synthetic esters. Dow says it has demonstrated improvements in hydrolytic stability at concentrations as low as 5 percent with fully saturated trimethylolpropane ester. Stability improvements were smaller when applied with polyol esters, which are more resistant to hydrolysis on their own.

Both products have a high viscosity index, and WG-1 is considered to have good low-temperature performance, according to the company.

Martin Greaves, research leader at Dow, told LubesnGreases that WG-1 is based on Dows butylene oxide chemistry. WG-2 is based on ethylene oxide and propylene oxide chemistry, with the polymer designed to have three blocks of these oxides. We call this a triblock. Some triblocks have unique water absorbing characteristics, explained Greaves. We believe they can trap water like a polymeric sponge in which the blocks of oxyethylene swell by forming inter-polymer hydrogen bridges. In the presence of an ester, water is held by the polymeric sponge, reducing its ability to hydrolyze the ester. This results in a slower kinetic rate of hydrolysis.

The mechanism of WG-1 is less clear. It is not quite as efficient in its ability to reduce hydrolysis of esters, but it is more compatible with a wider range of esters, said Greaves.

WG-1 has a typical kinematic viscosity at 40 degrees Celsius of 32 square millimeters per second, which means it meets the ISO 32 industry specification, one of the most common viscosity grades for formulating finished Environmentally Acceptable Lubricants, such as biobased hydraulic fluids. A common base oil for these fluids is a synthetic diester such as an adipate ester. Since WG-1 is also an ISO 32 grade, formulators do not need to adjust the viscometrics of their formulation in this example, he explained. And it can also be applied with lubricants of other viscosities.

Typically, Greaves noted, WG-1 and WG-2 are used as an additive or co-base fluid in a lubricant formulation. He said Dow is working with finished lubricant producers that are using the product, but declined to share names or details.

Greaves said Dow references the Organization for Economic Co-operation and Development (OECD) test number 301F, which is an aerobic biodegradation test that gauges oxygen consumption over a 28-day period. Under that test, both products are readily biodegradable, said Greaves. Based in part on that certification, both WG-1 and WG-2 can be used to formulate EALs as defined by the United States Environmental Protection Agencys Vessel General Permit, as well as other countries regulatory definitions.

Formulators have used polyalkylene glycols for many years as components of EALs, Greaves said, and natural and synthetic esters are perhaps the most popular choice of base fluid for these lubes. However, under certain conditions hydrolysis can shorten the life of esters, he said. WG-1 and WG-2 are intended to minimize this weakness and hopefully extend the life of the ester based EAL, Greaves explained. Formulators now have an additional building block in their toolbox when designing EALs for formulations to meet the Vessel General Permit and EU Ecolabel requirements.

But those are not the only possible uses for the new additives. In addition to esters, WG-1 is compatible with conventional API Group I through Group III hydrocarbon oils, as well as polyalphaolefins. Most lubricants use a hydrocarbon oil as a primary base oil; some include esters to impart unique properties such as friction control, detergency, seal swell behavior and so on, said Greaves. The inclusion of WG-1 in such formulations may help with improving the hydrolytic stability of the added esters, especially where water contamination may be an issue, he explained. Examples include wind turbine oils or rotary screw air compressor fluids.

For food processing applications, according to Greaves, WG-1 is registered with NSF International as an HX-1 additive for formulating H1 lubricants. The finished products can be used where incidental food contact may occur. It is specifically designed to conform to US FDA 21 CFR178.3570.

Dow is also pitching the product for marine applications, including lubricants protecting the operation of critical machinery like deck equipment, where the company says WaterGuard can extend the life of lubricants and help to control deposit and varnish formation as the lubricant ages.

The marine environment is certainly the right area to be promoting this, said Tyler Housel, vice president of the Lexolube division at Zschimmer & Schwarz, a U.S.-based supplier of synthetic esters. Housel said he had some exposure to samples of the Dow product, and it does seem to be as advertised. I didnt see any downside in terms of what it claims to do, and I have recommended it to some customers that face those issues, he said.

Housel noted that hydrolytic stability can be a weak point for esters in many markets, though not where he does most of his work. Most of the lubricant work we do is in the higher temperatures, above 200 C, and at those temperatures, water really isnt an issue.

From his reading of Dows literature, K. Anand, Ph.D., a lubrication expert for a large power generation company in India, said the product itself seems fairly stable as a standalone compound and in the presence of oils.

Given its potential use for marine applications and environments where lubricating oils are in contact with combusted gases in an engine, Anand said, the potential for reaction with gases that contain sulfur oxide needs to be assessed. Also, he noted that much of the additives performance depends on whether mechanical entrainment of separated water is possible in the oil pumping circuit. My opinion is that using hydrophobic additives in oil that are stable and compatible, with the right pressure, velocity and viscosity characteristics, is a good idea, he said. However, he noted, the efficacy should be assessed for robustness at a system-wide level before making a decision.

John Sander, vice president of research and development at Wichita, Kansas-based Lubrication Engineers, a company that provides lubrication reliability services, has often focused on the problem of water contamination. Everyone has said oil and water dont mix. Dow is saying they can if formulated properly, said Sander. However, he noted, as long as the water is still in the lubricant, it can potentially cause problems. It can transfer heat better, but it is not a good lubricant, he noted.

Lubricant molecules are mostly carbon and hydrogen and are very non-polar, he explained. Thats the scientific reason they dont mix well with water. When they do combine, water-which is very polar-will tend to settle out.

Dows efforts to handle water, lubricate and offer biodegradability is ambitious, Sander believes. Something that degrades quickly is typically not something with good hydrolytic stability, he noted. This makes for a tough conversation, because you are trying to make a good lubricant that will last [in use] but not persist in the environment-so those tend to be contradictory goals.

Sander said WaterGuard seems like a useful product, but Im still on the fence because there are situations where I think it could still be problematic, he added. For example, he expressed concern that the product could end up increasing the amount of water a lubricant can carry. This could be helpful from an antiwear standpoint, but Im not as confident about the hydrolytic stability or foaming properties, he said. Furthermore, since the ultimate goal should be removal of water, a sponge product could complicate the task.

At higher temperatures, which can be inevitable in many applications, what does the water do? How does this work with water filtration equipment, desiccants or vacuum dehydration? he asked.

Ultimately, the key is to keep water out. Thats simply good lubrication practice, said Sander. However, if you are at a point where you have done everything and you find you cant keep it out, maybe [WaterGuard] makes sense, he added.

Alan Earls is a business and technology writer based in Franklin, Massachusetts. Contact him at

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