The STLE Compass, Released September 13, 2011
“Metalworking Fluid Additives: Amines & Microbicides”
with Jerry Byers, Cimcool

KARA: Hello and welcome to the STLE Compass, brought to you by the Society of Tribologists and Lubrication Engineers. The STLE Compass is your convenient and reliable resource for the latest developments in the tribology community. I’m Kara Lemar, Education Manager at STLE and in today’s episode, we’ll take a look at metalworking fluids specifically addressing about additives, amines and microbicides and the tie between these three. Our interviewee has extensive knowledge and expertise with today’s topic. Jerry Byers is the Manager of Product Research & Development at Cimcool Fluid Technologies LLC in Cincinnati, Ohio. He oversees the laboratory development of synthetic, semi-synthetic, soluble oil, and straight oil products for use in the processing of metals, glass, plastics, ceramics, and other materials. He has a bachelors and masters in Chemistry, and is a Certified Metalworking Fluid Specialist (CMFS). Jerry holds a patent for a chlorine-free metalworking lubricant package, has authored several journal articles, and was contributing editor for two books: Metalworking Fluids and Metalworking Fluids, Second Edition. Jerry is currently Vice-President of STLE and has been active in the organization for many years. He has served on the Board of Directors for six years, as an associate editor for Tribology Transactions, and as a member of the STLE Metalworking Fluids Education and Training Subcommittee. He held several offices in the Cincinnati section of STLE, including Chairman. And today, we’ll get to pick his brain and get informed about metalworking fluid additives, amines, and microbicides.
KARA: Jerry, welcome to STLE Compass.
JERRY: Thank you, Kara.
KARA: We’re glad to have you. You’ve been in the field for almost 40 years and have had extensive experience with amines and MWFs. Given this experience, is there anything you’d like to open the interview with?
JERRY: Yes. During my time in this industry, there have been many changes, and the fluids are quite different now than 40 years ago, but there has always been a great interest in the chemistry of metalworking fluids and the additives that are used. Sometimes the interest stems from fear. However, most of the ingredients used in metalworking fluids are found in our own homes and in the products we use every day, so really it isn’t anything to be afraid of, that’s strange and unusual stuff.
KARA: Is that the typical fear – is that it’s just unknown?
JERRY: Yes, I think so. The reason I was thinking about this was because in May, at our Annual Meeting, we had a Hot Topics course that was held in Atlanta and several of the subjects in that hot topics course related to metalworking fluid chemistry. So I thought, well maybe the folks that listen in to STLE Compass might be interested in some conversation around that subject and the amines and microbicides seemed to be an area that might be especially interesting.
KARA: When we did a podcast with Fred Passman as well, he mentioned the impact of the EPA on microbicides and so it’s certainly something that I’ve been hearing a lot about, and I know that the Hot Topics was very popular.
JERRY: Yes, it seemed to be very well attended.
KARA: Given that setup, can you explain the title of today’s talk: MWF additives – amines and microbicides? What’s the link between the three?
JERRY: Well, first it might be useful to mention what an amine is. An amine is an organic compound containing nitrogen; a derivative of ammonia. Microbicides (also called Biocides or anti-microbial pesticides) are used in metalworking fluids to control the growth of bacteria or mold, and many of these contain nitrogen in their structure, so a lot of biocides could be grouped into the amine family, as well. It is important to note that not all amines act as biocides, and many amines can actually be food sources for microbes.
KARA: Which is not a good thing.
JERRY: No, we try to avoid it.
KARA: I understand the purpose for using a microbicide, but why are amines used in metalworking?
JERRY: Most often when amines are used in metalworking fluids, they are present to perform critical functions such as solublizing otherwise water-insoluble materials, neutralizing acids (such as fatty acids or boric acid), buffering the pH of the fluid to a desired level (usually between 8.5 and 9.5), and providing ferrous corrosion control. The most common amines used in MWF are a family called the “Ethanolamines”. The first amine in this group is monoethanolamine (a so called primary amine where, in ammonia, that’s a molecule with nitrogen in the middle and three hydrogens around the outside, well in a primary amine, one of those hydrogens is replaced by an organic group, in this case an ethanol group, so monoethanolamine is the simplest of the ethanolamine family). Then there is triethanolamine (a tertiary amine where all three hydrogens around the ammonia nitrogen have been substituted). There are also secondary amines such as diethanolamine, but it’s not too desirable. In 1977, it was determined that a reaction could occur between sodium nitrite (a corrosion inhibitor used at that time) and diethanolamine to form a potent carcinogen called diethanolnitrosamine. Consequently, nitrites have not been used in metalworking since the mid 1980s, and diethanolamine has not been used since the early 1990s. But there are many more amines that are available to the formulator to help achieve the desired combination of performance properties. A similar family is the Isopropanolamine group, with mono-, di-, and tri-isopropanolamines available. Amino-methyl-propanol is also available, and companies are now offering various butyl amine derivatives. Each amine offers a unique set of benefits.
KARA: Can you go into what those benefits are?
JERRY: Yes. Amines can be used to neutralize longer chain fatty acids to form fatty acid soaps that are used to emulsify oil and can be a lubricant. By varying the amine that’s on there, you get different emulsification, different lubricating properties, different foam levels, so you can make the soap more or less foamy depending on what you make it with. The soaps that are made with amines are usually soft or liquid soaps. You may be familiar with the old fashioned lye soaps, a fatty acid combined with sodium hydroxide or caustic – that makes a hard, solid soap, one that you might use in a shower or bath. Now, if we use these amines to neutralize short chain fatty acids, we call them amine carboxylates, they are good rust inhibitors. If we use the amine to neutralize boric acide, we call them amine borates, which are also good rust inhibitors. If an amine and fatty acid go through a condensation reaction, where another smaller molecule (water) splits off and we take it out, that makes something called a fatty amide which is a good emulsifier and corrosion inhibitor, and is sometimes used as a lubricant. There are also fatty amines, such as tallow amines, that are used as emulsion couplers and can be used as lubricants. Amine oxides act as surfactants or cleaning agents. Certain cyclic amines, fatty amine salts, and other alcohol amines can be used as vapor phase rust inhibitors – protecting metal not actually in contact with the metalworking fluid.
KARA: You mentioned that amines are important for neutralizing acids and raising pH, but can’t other chemicals be used for that purpose?
JERRY: Yes, we could use sodium hydroxide (caustic) for making soaps and raising the mix pH, but sodium hydroxide doesn’t have much reserve alkalinity. Once the fluid begins to be pumped around and sprayed through the air at whirling grinding wheels, it picks up carbon dioxide out of the air. Carbon dioxide acts as a weak acid, which causes the pH to drop back down from where you raised it up to with the caustic. When the mix pH is established with amines, we say the mixture has better pH buffering action or better reserve alkalinity, and the effect is longer lasting; the pH tends to stay near the desired level despite picking up carbon dioxide. However, even though amines are very beneficial in MWF and in consumer home products, from time to time some end users will ask for amine-free formulations. They don’t understand all the benefits of this important group of chemicals. Corrosion control really suffers when you try to take amines out of the product!
KARA: So why do they want to take amines out of the formulation? Replace it with sodium hydroxide?
JERRY: Yes, this gets back into the chemical fear category. People have heard about amines and they’re afraid of them. They’ve heard about the diethanolamine, that formed a carcinogen and we just don’t want amines in our products.
KARA: One bad one ruined it for the whole group?
JERRY: That’s right. They don’t seem to realize that we got rid of that one problem one and the corrosion inhibitor that it reacted with. Amines in general are used in many things that we use every day. They are quite nice chemicals that make life easy.
KARA: Well that’s good. We want to continue to use them. So, what are some new developments in the area of amines and microbicides?
JERRY: Several companies are offering some new amine structures which are quite interesting and finding a niche in the industry. But the major development is that the U.S. EPA is going through a re-registration process with microbicides, including the work-horse for metalworking fluids, Hexahydro-1,3,5-tris(2-hydroxyethyl)-s-triazine or HHT for short. It is sold under several commercial names and is very effective at a low treatment cost. Additionally, HHT can be used both as a tankside additive to treat the fluid in the manufacturing plant and formulated into the metalworking fluid concentrate. Many microbicides are chemically unstable in the as sold concentrates and cannot be used there, like the HHT. Currently the EPA is considering reducing the recommended use dose for HHT from the standard 1500 ppm down to a maximum dose of only 500 ppm. This level simply is not enough to be beneficial. The other thing the EPA has started doing recently when registering new microbicides is to require the statement “may only be used in enclosed metalworking fluid systems with local exhaust ventilation”. They further define an enclosed system as having the “machine or process enclosed by a box or housing”. That sounds good, but no fluid supplier can guarantee that all end users of their products will be using the fluid in a totally enclosed system.
KARA: And it doesn’t make sense to follow up with every single person to make sure it’s being used properly.
JERRY: Yes. Exactly. And so, the EPA is putting these restrictions on microbicides that are currently widely used in Europe. Therefore, that microbicide, when it’s introduced here from Europe, effectively cannot be used in this industry in the U.S.! Faced with such restrictions, some metalworking fluid suppliers have taken the approach of just not using EPA registered microbicides and labeling their products “free of biocides”. What they don’t tell you is that the microbial control of the product is being achieved through the use of unregistered toxic materials. Often these materials are very harsh amines. The end user thinks he is using a much safer product because the product is free of those terrible microbicides, and the fluid just magically doesn’t grow any bugs anymore!
KARA: Talking about harsh amines – what are some things to avoid when you’re using those with MWFs?
JERRY: Well, the EPA simply doesn’t allow anything to be used to kill pests that they have not specifically approved for that purpose and for a particular application, such as metalworking. So, I’d say the thing to avoid is to avoid breaking the law. To do that, we should avoid materials that are doing the jobs of antimicrobial pesticides but aren’t registered. An amine called DCHA, a secondary amine, is sometimes used for microbial control, but it is not a registered biocide. DCHA is a very harsh amine with a 3 health rating (on a scale of 0-4), and has a very low LD50 for acute dermal toxicity (meaning it is absorbed through the skin and is toxic at very low levels). Therefore, I prefer to avoid this material.
KARA: As would I and probably a lot of other people. What, then, are a couple examples of a worst practice that you’ve seen? Using DCHA is probably a good one, but other examples?
JERRY: One thing that’s important about metalworking fluids is to keep the system clean. One of the worst practices that I saw is failing to do a good cleaning of the fluid system (tanks, pipes, etc.) when dumping out the old dirty fluid. Once I was in a plant that was dumping and recharging a large central filtration system. The foreman thought he was doing a good clean-out by opening a drain valve at one end of the tank to let out the old, dirty fluid while at the same time he was adding fresh clean fluid at the other end! That’s really bizarre! Obviously the dirty and clean fluid were getting mixed together in the process, so when he was all done, he had a mixture of old dirty fluid plus fresh fluid, and all the grunge and biofilms that were on the tank walls and in the pipes were still right where they were before. All he had accomplished was to give fresh food to the organisms that were in the tank. Systems really need a good clean-out from time to time to get rid of accumulated metal chips, oils, and biofilms that can quickly re-establish growth of bacteria and mold organisms in the new fluid. These biofilms are little housing communities, if you will, for the bacteria and so forth that’s in the fluid. They need to be cleaned out periodically or they will quickly reestablish the bacteria and mold organisms in the fresh fluid. Another very bad practice is treating the metalworking fluid sump as if it were a sewer, garbage disposal, spittoon, or toilet. Janitors use it for dumping mop water; operators use it to dispose food scraps and worse! Such practices only encourage microbial growth and reduce overall performance. In general, we should keep the fluid as clean as possible, including keeping out leaked machine oil.
KARA: Certainly. On that note, what are some of your best practices?
JERRY: First and foremost, we talked about keeping the system as clean as possible, but then we have to maintain the fluid at the right concentration, the concentration that is was designed to be used at and we should monitor the concentration frequently, because otherwise, the water can evaporate and the fluid can get quite strong, or sometimes people will forget to add concentrate and just add water, so it gets weak and in doing so, we get way away from what the fluid is intended to do. Using dilutions that are too strong can cause problems such as foam, heavy residues and skin irritation, but if it gets too lean or weak, that can cause rust, poor overall cutting performance and unstable emulsions or split mixes. Another best practice is to use good quality water. After all, water makes up 95 percent of the volume of most in-use fluids and so if you start with good quality water…
KARA: You’re 95 percent of the way there.
JERRY: That’s right.
KARA: With that in mind, what would you say those working in the field should take away from today’s discussion?
JERRY: That amines are a very interesting and beneficial group of chemicals that serve multiple important functions in a metalworking fluid. They help with everything from holding the product together to providing rust control. A special group of nitrogen-containing chemicals even helps control the growth of bacteria and mold – organisms that tend to show up wherever there is water. To a chemist, chemicals are like the letters in an alphabet. If someone takes away several of the alphabet letters, fewer words are possible. I am concerned about the current direction of the EPA as they go about re-registering microbicides. The EPA is making it increasingly difficult or impossible to use microbicides that have proved to be both safe and effective in more than fifty years of usage within this industry.
KARA: And you want to use something that you’re used to using and something that works – you don’t change horses midstream.
JERRY: Right.
KARA: Thank you Jerry for joining us today and for your insight. We appreciate it.
JERRY: Thank you, Kara.
KARA: I’m Kara Lemar. For more news, information and research on metalworking fluids, amines, and microbicides, you can visit our website. Thanks for joining us today. This has been another episode of The STLE Compass, pointing you in the right direction.

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