Amines and amino alcohols perform vital functions in todays demanding metalworking fluid systems. Their primary functions are neutralization of acid-functional ingredients, as well as development and maintenance of alkaline pH. Additionally, the neutralization products function as corrosion inhibitors, emulsifiers and lubricants.
However, a secondary function of certain amines is becoming equally important: improvement of fluid microbial resistance through positive interactions with biocides. This is becoming more and more valuable as many metalworking fluid end users desire reduced levels of microbes, fewer additions of biocide and longer fluid life.
Amines contain nitrogen atoms bonded to one, two, or three carbon atoms. If bonded to one carbon, you have a primary amine, two carbons a secondary amine, and three carbons a tertiary amine. All three types are commercially available and currently used in MWFs. However, certain regulatory limits have been placed on secondary amines due to their potential to form stable N-nitrosamines.
Some N-nitrosamines have been shown to cause cancer in laboratory animals, therefore certain fluid producers, including some outside of the European Union, have chosen to eliminate their use. Consequently, globally compliant metalworking fluid formulations – containing only low levels of secondary amines – are increasing. In turn, metalworking fluid producers are becoming more vigilant in demanding disclosure from their suppliers of the secondary amine content of the amines themselves, as well as amine-based additives.
Most affected by the current regulatory limits are the EU countries. To minimize or eliminate the risks associated with N-nitrosamines, German legislators enacted regulations that, in 2008, will affect roughly 178,000 metric tons of water-miscible metalworking fluids. Thats the estimated consumption of water-miscible fluids in the European Union, according to Kline & Companys Metalworking Fluids 2008 Global Series report. Although the Kline study does not report global consumption of water-miscible fluids, it does estimate total worldwide consumption of all metalworking fluids to be 2,055,000 metric tons. The EU water-dilutable share of the global market is therefore approximately 8 percent (Figure 1).
Secondary amine alternatives are available – yet some products do contain secondary amine impurities. However, there are companies, including ANGUS Chemical Company of Buffalo Grove, Ill., that offer products containing low levels of secondary amine impurities.
Why the Concern for Secondary Amines?
When secondary amines come into contact with nitrosating agents such as sodium nitrite, they can form stable N-nitrosamines (also called N-nitrosoamines), which are thought to be harmful to the health of humans and animals. As a result, legislators in Germany enacted Technical Rules for Dangerous Substances 611 in 1993. TRGS 611 concerns the use of water-miscible cooling lubricants, and provides information for the formulation and use of these materials, to minimize or eliminate the risk of N-nitrosamine exposure.
To achieve this, a series of application limitations are declared, based on avoiding nitrosating agents and replacing secondary amines with suitable substitutes – or more specifically, with primary amines.
TRGS 611 states, The content of secondary amines in water-miscible cooling lubricants which results from impurities or by-products may not exceed 0.2 mass percent, based on the cooling lubricant concentrate. This limit also applies to capped secondary amines, such as those liberated under use conditions by hydrolysis. One example cited is bismorpholinomethane, which presumably can generate morpholine – a secondary amine – and lead to the formation of N-nitrosomorpholine (NMOR).
Figure 2 shows the reactions of primary and secondary amines with a typical nitrosating agent, sodium nitrite. The secondary amine forms a stable N-nitrosamine, which means the material exists as an N-nitrosamine for an extended period of time. By contrast, primary amines do not form stable N-nitrosamines, as indicated in the second reaction scheme in Figure 2. As soon as the primary N-nitrosamine is formed, it is destroyed. This illustrates why secondary amine content must be watched so carefully.
Will You be Affected Next?
Though action until now has been focused primarily in European countries, due to the German legislation, there are other factors which could have a global effect. For example, some multinational metalworking fluid producers are moving toward globally compliant formulations, due to the requirements of certain automobile manufacturers.
To start, the BMW Group has developed a standard that incorporates provisions from other publications, including TRGS 611, with the goal of prevention and avoidance of health risks to employees and customers. BMWs standard also includes a listing of prohibited and declarable substances which states, with respect to declarable substances, that a search for a chemical substitute and its documentation is mandatory according to the Gefahrstoffverordnung [dangerous materials ordinance].
N,N-diethanolamine (known as DEA) and triethanolamine (TEA) are included as declarable substances in this standard. The concern with TEA apparently is related to metal complexation, rather than nitrosamine formation. Nevertheless, the Global Automotive Declarable Substance List (GADSL), developed by the Global Automotive Stakeholder Group, lists TEA as declarable because of the possible formation of N-nitroso compound in coolant admixtures. (See www.gadsl.org for details.)
In addition to the BMW Group, General Motors has also enacted restrictions. This is, presumably, because the Global Automotive Stakeholder Group represents the interests of automotive supply chain stakeholders in all major global economies. Accordingly, it is expected that other automobile manufacturers have also adopted the groups Declarable Substance List, or will in the future.
It is important to clarify that the GADSL document states that it only covers substances that are expected to be present in a material or part that remains in the vehicle or part at point of sale. It is unclear what impact this list will have on metalworking fluid sourcing decisions. However, it is probably safe to assume that lower secondary amine content will be preferred – possibly required – in the automotive supply chain.
The percentage of the global water-miscible metalworking fluids market affected by secondary amine concerns could therefore be larger than the 8 percent estimate reported previously (EU market only), and the percentage will likely grow in the future.
Do You Have Alternatives?
Metalworking fluid formulators supplying products to Germany and other EU-member countries have largely moved away from DEA and other secondary amines. In other regions, it all depends upon the end-use customer requirements, as well as the philosophy and business strategy of the fluid supplier.
With respect to secondary amine alternatives, it is common knowledge that there are many commercial products available from the primary and tertiary amine families. However, what may not always be appreciated is that even these materials can contain measurable levels of secondary amine impurities – in some cases as much as 10 to 15 percent.
This means that where secondary amine levels in finished metalworking fluid concentrates are limited, it is critical to know the secondary amine content of the alternatives. This is especially true in semi-synthetic and synthetic fluids, where higher amine levels are generally used.
And it doesnt stop with the amines themselves. There are also amine reaction products to consider, such as alkanolamides and pre-neutralized components (i.e. certain emulsifier bases, amine carboxylate corrosion inhibitors, etc.).
Additionally, some alkanolamides are based on secondary amines and may be overbased; overbased means they may contain unreacted amine. In these cases, it is important to understand the percentage of unreacted amine so an accurate secondary amine level can be calculated for the finished formulation.
The good news is that many commercial amines containing less than 1 percent secondary amines are available. Primary amines are also useful for preparing alkanolamides, and products based on these amines are available. It is important to consult supplier literature, material safety data sheets (MSDS) and sales specifications. In some cases, secondary amine content is limited by specification; in other cases it is not.
To summarize, reduction in the use of secondary amines is increasing due to regulatory limits in European countries, as well as global automotive standards. This may in part be sparking the trend toward globally compliant metalworking fluid formulations. Fluid producers must be vigilant in demanding disclosure of secondary amine content from suppliers of amines as well as amine-based additives. Many secondary amine alternatives exist, some of which are low in secondary amine impurities. The same is true for amine-based additives and packages.
One of several companies supplying primary amine alternatives and low secondary amine products is ANGUS Chemical Company. As regulatory requirements become increasingly strict and multinational, ANGUS is able to continue offering metalworking fluid formulators products and services that help solve difficult formulating challenges.