Last year, the U.S. Environmental Protection Agency declared that production and import of medium- and long-chain chlorinated paraffins could be banned in the U.S. as soon as mid-2017. Ever since, metalworking fluid formulators and additive suppliers have been scrambling on two fronts.
On one side, they are working to convince EPA to rescind or delay the ban on these chemicals, which have been used effectively for more than 80 years in machining fluids.
At the same time, fluid suppliers are pondering what life will look like if these prized extreme pressure agents vanish from their toolbox. The obvious answer is to substitute other additives, including very long-chain chlorinated paraffins (vLCCP), which have secured EPA approval. These can be made to work, as a recent conference heard – but may involve a steep learning curve.
On Sept. 29, Maria J. Doa, Ph.D., director of EPAs Chemical Control Division, spoke in Chicago to the 5th International Conference on Metal Removal Fluids, organized by the Independent Lubricant Manufacturers Association. The proposed ban, she said, will not affect downstream users, who will be permitted to draw upon their CP inventories after the ban until they are used up. But in EPAs view, she said, medium-chain (C14 to C17) and long-chain (C18 to C20) chlorinated paraffins present persistent, bioaccumulative and toxic risk to the environment.
Used in metalworking fluids, MCCPs and LCCPs protect surfaces of tools and parts from friction, wear and overheating at high tool speeds and pressures. Many view them as critical for high-performance metal drawing, forming and removal of titanium alloys and stainless steels used in the aviation, weapons and medical industries.
Short-chain chlorinated paraffins, ranging from C10 to C13, are not likely to replace MCCPs and LCCPs, as they also face global scrutiny of their health and environmental effects. U.S. metalworking fluid formulators largely moved away from short-chain CPs in the 1990s for such reasons.
That leaves very long-chain chlorinated paraffins (vLCCPs), with carbon chain lengths of C21 and higher, as the more feasible alternative for metalworking applications. EPA ruled these may be manufactured in the U.S. because their environmental risks (persistence, bioaccumulation, toxicity) are acceptable.
Dover Chemical, in Dover, Ohio, is the largest U.S. manufacturer of medium- and long-chain CPs, and naturally has been deeply active in trying to counter EPAs ban. As well, Thomas Kelley, global business director for chlorinated products, said vLCCPs have been available from Dover for some time, and his company recently expanded this product offering. Dovers vLCCPs, he told LubesnGreases, are based on alpha olefins and are very light in color: typically 1 on the Gardner scale. One such product has approximately 47 percent chlorine by weight, he said, and none contains more than 15 ppm free hydrochloric acid from the chlorination process.
How do formulators and blenders view the vLCCP option? At Septembers conference, Ed Jones of Hangsterfers Laboratories offered some insights. Based in Mantua, N.J., Hangsterfers has used long-chain CPs since 1937 in its metalforming compounds to improve surface quality of parts and tool life. In certain fluids the company also has been using vLCCPs, with carbon chain lengths greater than C21 and chlorine content below 54 percent. But Jones said he does not consider vLCCPs to be universal drop-in replacements for MCCPs.
Hangsterfers formulates vLCCPs into straight oil and emulsifiable oil products, he said. It has found vLCCPs to be less soluble than medium-chain CPs in semi-synthetic and synthetic metalworking fluid concentrates. Because the concentrates contain water, they are less stable when formulated with vLCCPs, Jones said. He added that it is possible to formulate certain stable synthetic and semi-synthetic concentrates with vLCCPs – but it can be difficult and costly.
Jones, who is Hangsterfers chief operating officer and technical director, recommended the use of vLCCP formulations to machine stainless steels, which are highly resistant to corrosion. For machining mild steels, he advised formulating with vLCCPs plus corrosion inhibitors. Processed parts should be cleaned carefully with hydrocarbons or esters to remove residues, he urged, because chlorine can initiate corrosion during storage.
He also warned against using vLCCPs to process parts for hot downstream applications where temperatures may exceed 500 degrees F, such as jet engine turbine blades. Service temperatures in jet engines often reach 1,000 F, and chlorine-containing residues can cause corrosion that shortens service life.
Jones concluded that blenders need to develop deeper knowledge of how to formulate vLCCPs in metalworking fluids: We need to pay much more attention to both base oils and additive interactions to use vLCCPs.
The Chicago meeting also heard from Jim MacNeil, product manager at Qualice LLC in Hamlet, N.C. Several years ago, Qualice applied to EPA for permission to manufacture certain vLCCPs, and in 2013, the agency allowed it to obtain two CAS numbers for its vLCCPs. These have chain lengths of C21 or longer and chlorine content ranging from 40 percent to 70 percent by weight. The vLCCPs can be manufactured in the U.S., and will not be affected by the proposed ban on MCCPs and LCCPs.
MacNeil noted that Qualices products have consistent physical properties and are useful as extreme pressure additives. He called them viable, cost-effective alternatives to MCCPs and LCCPs, and went on to describe how they stack up in performance tests.
Two vLCCPs were prepared from paraffin hydrocarbons, and two were based on alpha olefin hydrocarbons. All four vLCCPs contain 40 to 50 percent chlorine by weight. Blends of 10/90 and 20/80 vLCCP/naphthenic oil appeared stable (clear) after 24 hours.
To compare fluid efficiency in cutting, forming and machining operations, Qualice used a Microtap Tapping Torque Test. The test machine has a motor that drives (rotates) a spindle at 600 rpm and inserts a lubricated, spiral-point cutting tap tool into a series of pre-drilled holes in a metal bar. Applied torque, temperature, buildup of metal flash on tool edges, and tool wear can be measured. MacNeil showed comparable torque profiles (torque versus depth) for two semi-synthetic metalworking fluids formulated using MCCP or vLCCP at approximately 40 percent chlorine (Cl) by weight. (See Figure 1.)
Figure 1. Tapping Torque Test results for semi-synthetic metalworking fluids
MCCP vLCCP
Average torque (Ncm) 356.4 353.2
Maximum torque (Ncm) 388.0 384.0
Source: Qualice LLC
Qualice also used the independent laboratory TribSys LLC (now part of Sea-Land Chemical) to put vLCCP fluids through twist compression tests. This test simulates lubrication in sliding contacts. A motor rotates a hollow metal cylinder, perpendicular on a flat metal plate, at 10 rpm under 20,000 psi applied pressure, and the coefficient of friction is calculated from transmitted torque and applied pressure.
In this test, two vLCCPs (one paraffinic and one alpha olefinic, both approximately 50 percent chlorine by weight) were compared to an MCCP. Each CP was diluted to 10 percent chlorine content in naphthenic base stock. Average friction and average time to lubricant failure were comparable for all three lubes.
MacNeil ended by saying viscosity is the most significant difference between vLCCPs and MCCPs. For vLCCPs, viscosity increases strongly with percent chlorine. In manufacturing scenarios, handling and blending procedures for vLCCPs can differ from those used for lighter (lower viscosity) MCCPs and LCCPs.
Consultant Jerry Byers, formerly manager of R&D at Cimcool, also spoke in Chicago, and shared his perspective on the challenges of formulating vLCCPs into metalworking fluids. He noted that vLCCPs have longer carbon backbones and generally lower chlorine contents than MCCPs. These differences have several consequences:
First, vLCCPS are inherently more difficult to make stable blends in straight oils and to emulsify in products designed to be diluted with water (soluble oils and semi-synthetic concentrates), versus MCCPs.
Second, different emulsifiers typically are needed for vLCCPs versus MCCPs.
Third, Byers continued, it may be necessary to use higher levels of vLCCPs to match the extreme pressure performance of MCCPs with higher chlorine content.
Fourth, both chlorine content and carbon chain length increase the viscosity of vLCCPs (and products formulated with vLCCPs) versus MCCPs.
As a result, he stated, replacing MCCPs with vLCCPs involves significant reformulation work, higher raw material costs, and production modifications to blend and handle higher viscosity products.
While vLCCPs show some promise in certain formulas, Byers concluded, significant challenges remain before vLCCPs can be adopted widely as MCCP replacements. He observed that other options for EP additives include chlorinated esters and fatty acids as well as sulfur, phosphorus and overbased calcium sulfonate compounds, and more.
Metalworking fluid formulators eventually may benefit from new additive chemistries. (See next months issue for more about some of these alternatives.) But first, the heat is on to replace MCCPs and LCCPs before the anticipated ban goes into effect in mid-2017.
Mary Moon, Ph.D., is a physical chemist with hands-on R&D, management and problem-solving experience in the lubricating oil, grease and specialty chemicals industries. Contact her at marymoonphd@gmail.com or (267) 567-7234.