The United States Environmental Protection Agency made a landmark decision in 2008 regarding HHT – hexahydro-1,3,5-tris(2-hydroxyethyl)-s-triazine – a representative of a class of biocides known as formaldehyde condensate, or FC, microbicides. The effects of this decision have been dramatic, according to Fred Passman of Biodeterioration Control Associates, Inc., a specialist microbiology consultancy based in New Jersey. 

“The U.S. EPA assumed that because FC microbicides function through the release of formaldehyde, they dissociate in solution. Consequently, exposure risks were calculated as though FCs dissociated 100 percent in solution, i.e., in an MWF,” Passman explained to Lubes’n’Greases.

Despite the industry presenting data showing that FCs do not dissociate in metalworking fluids, “the EPA set the maximum permissible concentration in end-use diluted MWFs to 500 parts per million,” said Passman. This is about half the concentration at which these materials are effective as microbicides, and as a result three of the four suppliers of this class of material withdrew from the market with resultant loss of breadth to the portfolio.

The loss of FC products on both sides of the Atlantic “provided the impetus for increased use of BIT [1,2-Benzisothiazolin-3-one],” he said. 

“However, in early 2019, the Chinese producer of ortho-nitrochlorobenzene – the sole source of this chemistry – was first shut down by China’s EPA and then experienced a fire.” BIT is still in short supply in early 2020.

Enhancing a Smaller Palette

Against this background, workshop customers are looking for better surface finishes and longer tool life. Replacing the metalworking fluid more frequently is a non-starter due to the additional cost of fresh fluids, disposal of old fluids and lost production time. What options are therefore available to a formulator? 

“With the decreasing portfolio of chemistries available to formulators, there is a higher focus on being creative with how to utilize the current chemistry toolbox,” said Nicole Clarkson, global segment lead of metalworking fluids for Illinois-based Angus Chemical Company.

Angus has undertaken numerous studies that demonstrate a potential synergistic effect between amino alcohols and a broad range of commonly used biocides in metalworking fluids, Clarkson said. 

“This synergistic effect is highly dependent on the individual formulation and can help significantly improve bacterial and fungal control to deliver long-life metalworking fluids with a more favorable environmental health and safety profile, while helping formulators reduce secondary amine content in their formulations.”

Clarkson went on to explain that secondary amines have been a hot topic in the metalworking fluid industry due to their potential to form hazardous n-nitrosamines.

“In certain geographies, regulatory restrictions are in place limiting the use of secondary amines in metalworking fluid formulations, such as TRGS 611 in Germany,” she said.

Angus’ amino alcohols make it easier for formulators to optimize the use of approved biocides. However, the approved biocides are mostly restricted to very low concentrations. Are there other strategies?

Playing Various Tunes

John Neale Ltd, a fluid and corrosion protection company based in the United Kingdom, has made a variety of changes to its formulations because of the impact of BPR. These cover fungicides and bactericides, as well as a move away from formaldehyde and formaldehyde-donating chemistries, founder John Neale told Lubes’n’Greases.

“We have always tried to keep clear of sensitizing fungicides in our fluids. This steered us towards sodium pyrithione and OPP [orthophenyl phenol, a common agricultural fungicide] as potential fungicides,” Neale said.

The labelling of sodium pyrithione has become stricter in terms of it being an environmental hazard. This places a limit on the amount that can be formulated into products whilst avoiding hazard labelling and United Nations hazard classifications for transport, Neale explained. While OPP can be a suitable alternative fungicide, it is not a universal solution.

While Neale believes there are sufficient fungicides available for metalworking fluids, “the BPR has significantly reduced the palette of bactericides, and none of those available fully meet the market expectations,” he said. 

The market has moved significantly toward water-mix metalworking fluids that are free of formaldehyde and formaldehyde donors. These fluids are based on bio-stable amine technology. 

According to Neale, the most common amine for bio-stability is dicyclohexylamine, but other amines have now become available from a number of suppliers. These are primarily used for corrosion inhibition and buffering, in other words controlling the acidity or basicity of a solution. But they also have a useful secondary characteristic of controlling the level of bacteria and inhibiting bacteria in coolants. 

“We have a particular amine we use which gives excellent corrosion protection and buffering and has excellent bio-stability controlling the level of bacteria to near zero in coolants working even in difficult applications,” Neale said.

John Neale Ltd has also developed coolants that do not support bacterial growth and can remain near sterile for years in sumps without the use of traditional bactericides. They also avoid biodegradable emulsifiers, oils and esters, giving the bacteria little to feed on.

Cleaning Up the Fluid

Perhaps the most technologically revolutionary approach uses ultraviolet light to kill the biologically active species. Process fluid company Quaker Houghton developed equipment in partnership with Swedish clean tech company Wallenius Water Innovation based on the latter’s ballast water purification systems. These remove invasive microorganisms in ballast water with UV radiation, a technology that also is used in municipal and industrial water applications.

Despite conventional wisdom that this could not work because mineral oils absorb UV light, Quaker Houghton claims its equipment, when coupled with a specifically formulated metalworking fluid, can kill 99.9 percent of bacteria.

The fluid flows along an annular channel with a light source in the center (see figure 1) while a translucent quartz sleeve offers protection to the lamp. Even though UV light can only penetrate a short distance through these process fluids, bacteria are deactivated by high UV intensity and turbulent flow in the reactor, which brings a significant volume of the fluid close to the lamp on every pass. Recirculation helps to keep bacteria levels low.

Using UV eliminates exposure of workers to both the bacteria and biocide, which have been variously linked to eczema, allergies, respiratory problems, sterility and even cancer.

“In real-life applications bacterial populations can be reduced by 99.9 percent, without the use of a biocide,” said Lee Bowditch, business development director of the Europe, Middle East and Africa region at Quaker Houghton’s fluid intelligence solutions division. 

There are also financial benefits to using UV light, such as saving on the costs of expensive biocides, process fluids and waste disposal.

Options, Options

With formulators having access to molecules that work synergistically with allowed biocides, others finding chemicals that have shown benefits in non-lubricants applications and new pieces of kit that do what was previously thought to be impossible, there are some glimmers of hope for workshop managers and their suppliers of fluids. With many metalworking workshops experiencing shutdowns due to coronavirus and several downstream customers likely to experience reduced demand when they return to work, workshop managers need all the good news they can get.

Trevor Gauntlett has more than 25 years’ experience in blue chip chemicals and oil companies, including 18 years as the technical expert on Shell’s Lubricants Additives procurement team. He can be contacted at trevor@gauntlettconsulting.co.uk