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Drop-in Alternatives to Trichloroethylene
Process Cleaning, Jason Marshall and Heidi Wilcox
Solvents have been used for many years in all fields of cleaning. Many of these solvents, even though they work well, pose health risks to workers and are regulated by state and federal agencies. Efforts have been made to reduce worker exposure. More often than not, these changes arise as a result of a company trying to adhere to the various legal structures that exist, especially liability issues, and account for how most societies approach environmental decision making for cleaning applications.
Therefore, as one tries to follow the myriad list of regulations and restrictions, identifying a substitute for solvents in cleaning applications is not an easy task. There are literally thousands of formulations to choose from. The variability of literature for these products changes from vendor to vendor as well as from product to product, making the search for an applicable substitute nearly impossible. Even after selecting a potential product, there is no guarantee that it will work.
Part of the Toxics Use Reduction Institute Surface Solutions Laboratory’s (SSL) mission is to test and evaluate the effectiveness of different cleaning chemistries and equipment on a variety of substrates and soils. Located at the University of Massachusetts Lowell, the Institute was created to promote reduction in the use of toxic chemicals and the generation of toxic by-products in industry and commerce in the state of Massachusetts. The objective of the lab is to promote and sometimes develop environmentally-friendlier, safer alternatives to hazardous solvents that perform as well, or better, than existing hazardous solvents. SSL has been aiding companies in the search for safer products for more than 10 years and has evaluated more than 500 cleaning formulations and performed more than 1,300 cleaning trials.1 This article discusses SSL’s effort to find alternatives to one hazardous solvent in particular, trichloroethylene (TCE).
In every instance, at least one safer and effective alternative to TCE was found for each of the three end users applications evaluated. Yet, there is no one size fits all for replacing TCE. Specific criteria need to be considered and tested on a caseby- case basis. All of the results of the testing can be found in the TURI Cleaner Solutions Database at www.cleanersolutions.org.
Why Replace TCE?In Massachusetts, TCE has been identified as a high priority substance by the Toxics Use Reduction Act. TCE made the list because it was determined to be especially toxic; it was used in sufficient quantity in Massachusetts and viable alternatives exist for most applications, cleaning being one of them.
Toxic to HealthTCE is a man-made chlorinated solvent (C2HCl3) and is a potentially dangerous health hazard. Some of the health effects target the brain—headache, depression, coma; the heart—irritability, sudden death; the liver—acute chemical hepatitis cirrhosis; the kidney—tubular injury; and the skin—dermatitis.
TCE is volatile and evaporates quickly into the air during cleaning operations. The solvent can break down into phosgene, a known lung irritant. Precipitation carries TCE to groundwater. When in the soil, TCE may filter downward into ground and drinking water supplies, resulting in contamination. Persistence in soil and ground water is long, having a half life up to 10 months. Because of its persistence and prevalence, the solvent is listed as the number one contaminant of groundwater. 2 Table 1 summarizes some of the more important health effects associated with TCE.
Usage of TCEMassachusetts TURA filer statistics for TCE found that there were still 17 facilities that reported that they were using 1,393,981 pounds of TCE in releasing 94,856 pounds. Around 80 percent of the companies were using TCE for vapor degreasing fabricated metal parts and some textiles.3
Existing AlternativesThere are thousands of alternative cleaning chemicals that could be used for replacing TCE. The lab has worked with nearly two dozen companies from Massachusetts and other states in an effort to find less hazardous products. Often, the companies are able to switch to an immersion cleaning process using an aqueous based product.
SSL has conducted more than 100 experiments on 11 contaminant types: abrasives, buffing compounds, coatings, cutting fluids, fluxes, greases, inks, lubricants, oils, paints and waxes. The lab found 44 alternative products from 21 vendors in 11 classes of products. A majority of these (52) were alkaline aqueous products.4 Despite the success of finding aqueous-based alternatives for TCE, these products cannot be used in vapor degreasing situations due to the physical limitations of the alternatives. Likewise, these products cannot be used in those cases where water would pose compatibility issues with certain processing applications, usually related to drying issues or electrical incompatibility.
Drop-in Alternative Solvents for TCEIn keeping with the SSL’s objectives for identifying and testing alternatives to hazardous cleaning solvents, the lab has investigated several solvents for replacing trichloroethylene in vapor degreasing applications. The laboratory focused its testing on product performance for six chemical classes on a variety of soils and substrates. Evaluations were divided into two types of testing protocols. The first set of trials focused on directly comparing the solvent alternatives using immersion cleaning. Next, the same products and soils were tested using vapor degreasing cleaning.
What are the Drop-Ins Tested at SSL?As mentioned, the laboratory identified six classifications for vapor degreasing drop-in solvents. Physical properties of each of the six classifications are provided in Table 2. The health effects of each class are summarized in Table 3 and compared with TCE and two other chlorinated solvents widely used in vapor degreasing applications. The following are the six classifications.
HCFC, HydrochlorofluorocarbonHydrochlorofluorocarbons, commonly known as HCFCs, are a group of man-made compounds containing hydrogen, chlorine, fluorine and carbon. Most HCFCs are broken down in the lowest part of the atmosphere and pose a much smaller risk to the ozone layer. Unfortunately, HCFCs are also very potent greenhouse gases, despite their very low atmospheric concentrations, measured in parts per trillion (million million). 5
HFC, HydrofluorocarbonHydrofluorocarbons (HFCs) are compounds containing carbon, hydrogen and fluorine. Certain chemicals within this class of compounds are viewed by the industry and scientific community as acceptable alternatives to chlorofluorocarbons and hydrochlorofluorocarbons on a long-term basis. Because the HFCs contain no chlorine, they do not directly affect stratospheric ozone. Furthermore, mechanisms for ozone destruction involving fragments produced as HFCs are decomposed within the atmosphere (CF3 radicals) and have been shown to be insignificant. Although it is believed HFCs will not deplete ozone within the stratosphere, this class of compounds has other adverse environmental effects. Concern over these effects may make it necessary to regulate production and use of these compounds at some point in the future. Such restrictions have been proposed in the Kyoto Protocol.6
HFE, Hydrofluo0retherHydrofluoroethers (HFEs) are a class of solvent. In these products, all of the hydrogen atoms reside on carbons with no fluorine substitution and are separated from the fluorinated carbons by the ether oxygen. HFEs offer safety and performance properties similar to CFCs, but offer a superior environmental profile.7
nPB, N-Propyl BromideN-propyl bromide (nPB), or bromopropane, is a non-flammable, organic solvent with a strong odor. It is used to remove solder flux, wax, oil and grease from electronics parts, metals and other materials. In addition, nPB is used as a solvent in adhesive formulation. The U.S. Environmental Protection Agency (EPA) is proposing to allow the use of nPB as a chemical alternative to ozone-depleting substances (ODS) with certain conditions. The SNAP Program thoroughly studies alternatives, such as nPB, to ensure that the use of replacement chemicals will not pose significant risk to human health and to the environment.8
VMS, Volatile Methyl Siloxanes VMS are mild solvents, have a flash point and possess a moderate level of toxicity with a recommended exposure level of 200 ppm. Since the cost for this solvent is high, it is generally used for defluxing and/or degreasing high value parts and PWAs, and is suited primarily for cleaning silicone and other light, nonpolar residues. In many instances, this solvent is used for cold cleaning and wiping. Vapor degreasing machines using this solvent need secondary cooling along with an extended freeboard in order to minimize solvent losses. Open top vapor degreasers are not suitable and would require retrofitting.9
Dichloroethylene1-2 Dichloroethylene is a highly flammable, colorless liquid with a sharp, harsh odor. It is used to produce solvents and in chemical mixtures. The solvent evaporates rapidly into air and takes about five to 12 days for half of it to break down. Most 1,2-dichloroethene in the soil surface or bodies of water will evaporate into air. In addition, 1,2-dichloroethene can travel through soil or dissolve in water in the soil. It is possible that it can contaminate groundwater. When in groundwater, it takes about 13 to 48 weeks to break down. More importantly, there is a slight chance that 1,2-dichloroethene will break down into vinyl chloride, a different chemical, which is believed to be more toxic than 1,2-dichloroethene.10
Table 3 lists the six solvent classes investigated as well as two additional chlorinated solvents. The table lists information on environmental and worker safety information.
Product Testing at SSLSince 1994, the Surface Solutions Laboratory has conducted more than 1,200 cleaning trials for more than 240 companies evaluating nearly 450 cleaning formulations. Specifically for these fields of cleaning products, SSL has run in excess of 30 trials that have investigated the effectiveness of 16 products from multiple vendors. These products have been evaluated for removing 11 specific contaminants. Table 4 lists the contaminants used in evaluating the alternative drop-in solvents. These contaminants were supplied by three companies working with the lab to replace TCE in vapor degreasing operations. One company was also using PERC. Soils 1 – 4 were supplied by a company that manufactured various size capacitors made out of aluminum. Soils 5 – 7 were being used by a tool manufacturer working with steel. The remaining soils, 8 – 11, were for a jewelry manufacturer working with gold and silver materials. One of the goals of testing was to identify products that could be used on all soils in each of the three groups.
Testing ProceduresUsing the vendor supplied information about specific product usage, SSL ran 22 trials for 20 products to determine how effective the drop-in solvents would be. Each trial was run using products at full strength in 250 milliliter Pyrex beakers heated to on a Syborn Corporation Thermolyne Type 2200 Hot Plate. A range of aluminum, steel and silver plated substrates were used for the experimentations. These coupons, also known as panels, were rectangular (approx. 2" x 2") flat sheets matched to a particular part’s materials of construction. Coupons are number-etched for identification. Coupon testing is performed to determine optimal cleaning conditions without wasting parts. This testing is conducted in triplicate (minimally) and consists of:
Step 1: Initial weighing of pre-cleaned coupons by means of an analytical balance (gram weight)
Step 2: Applying the appropriate contaminant (oil, grease, wax, etc.) to the surface of the coupons with a hand-held swab as consistently as possible
Step 3: Re-weighing the artificially-contaminated coupons under the same conditions as Step 1
Step 4: Performing the cleaning trial
Step 5: Final and third weighing of cleaned coupons under the same conditions as Step 1
The information in Table 5 is used to calculate the efficiency of a chemical cleaner. The overall efficiency was obtained by averaging the three coupons cleaned. A Denver Instruments Company Model A250 balance was used for weighing the coupons. When efficiency exceeds 100 percent, two issues may be responsible. The first possible cause may be that the solvent has caused damage to the substrate, reducing the final weight below the initial weight. The second explanation may be that the substrates were not completely cleaned prior to the initial weighing. In addition, some of the efficiencies may be less than 0 percent. Many times, this result is due to the solvent leaving a residue on the substrate or the solvent may have soaked into the contaminant, thus, increasing the remaining weight to a value greater than the initial contaminated weight.
ImmersionThree coupons of the same substrate were cleaned for five minutes in a product heated to 96°F using a Syborn Corporation Thermolyne Type 1000 Stir Plate and a VWR Spin-bar magnetic stirring bar. Coupons were not rinsed. Following cleaning, the coupons were allowed to air dry for two minutes.
Vapor DegreasingThe same breakdown of soils to substrates was maintained for the vapor degreasing evaluations. In this testing, a small scale vapor degreaser was designed to use 250 ml of solvent heated to boiling. Cleaning lasted for five minutes at each product’s boiling point.
Soil Set 1The first four contaminants were supplied by a capacitor manufacturer and applied to aluminum coupons. Cleaning took place for all but one of the products. Efficiencies were calculated and listed in Table 6. Products with efficiencies over 85 percent were considered to be effective and are highlighted in green. Eight of the products were effective on the four soils in this grouping for immersion cleaning and 13 were effective on all four when using vapor degreasing.
Soil Set 2The second set of contaminants was for the tool manufacturer. Steel coupons were coated with the three soils. Again, all but one product were evaluated. All of the products tested were effective in removing Soils 5 and 6 for immersion cleaning. The limiting soil was Soil 7, which was a paint/varnish mix. Eight products were found to be effective on the three soils in this grouping for both immersion and vapor degreasing. Results are in Table 7.
Soil Set 3The final set of contaminants was for the jewelry manufacturer. Silver plated coupons were coated with the four soils. Nineteen products were evaluated. Two soils, 9 and 11, were removed by all of the alternative drop-in solvents in immersion cleaning. Soils 8, 9 and 11 were removed by all in vapor degreasing. Eleven products were effective in removing all four of the soils for immersion cleaning. Eighteen products were found to remove all four soils. The results are listed in Table 8.
Summary and Comparison of Bio-Based Testing to Traditional Cleaning AgentsA majority of the products tested were found to be more effective in vapor degreasing application than when used in immersion cleaning. Average cleaning efficiencies were calculated for five of the six classes of chemicals. (The sixth class of product is usually not used by itself due to its low flash point; instead it is typically mixed with one of the other six to improve efficiency).
The product class was then put into one of three groups based on effectiveness. The first group consisted of products that had an average that was greater than 90 percent effective, and are designated with a “Yes” highlighted in blue. The second group had an average that was less than 90 percent, but greater than 70 percent, and was marked with a “Yes/No” in orange. The remaining group contained efficiencies that were less than 70 percent and contained a non-highlighted “No.” Immersion results are represented in Table
9 and the vapor degreasing results are in Table 10.
Trichloroethylene: Do You Really Need It?TCE does clean and is sometimes needed for specific cleaning applications. Is your cleaning system one of them? Chances are that the answer to this question will be “No.” Reevaluate your process to determine if a “Safer” cleaning system will work for you. Acleaning product that worked in one situation may not work as well in another. Yet, SSL’s testing of the alternatives indicate that safer solutions that perform as well as TCE do exist so companies should not settle for the status quo. The SSL recommends process specific testing on potential replacement cleaning chemicals. If more information is needed on a particular product, or you are interested in conducting cleaning trials, please contact the lab.
Jason Marshall is manager of Laboratory Testing for the Massachusetts Toxics Use Reduction Institute located at the University of Massachusetts Lowell. The lab helps Massachusetts companies evaluate the performance of cleaning chemistries and equipment. He holds a bachelor’s of science in chemical engineering and a master’s of science in environmental studies from the University of Massachusetts Lowell. He is currently enrolled in the UMass Lowell Doctorate of Science, Work Environment Industrial Hygiene program. Jason can be reached at (978) 934-3133.
Heidi Wilcox has worked at the TURI Laboratory as a technician and research associate. She earned a bachelor’s of science degree in microbiology from UMass Amherst and a master’s of science in environmental studies and atmospheric studies from UMass Lowell. Currently, she is a doctoral student in the Department of Work Environment in Cleaner Production. Heidi can be reached at (978) 934- 3133.
*For a list of the drop-in products that were evaluated at SSL for cleaning performance contact Jason or Heidi at the above contact information.
1. Marshall, J. Surface Solutions Laboratory Simple Solutions Database, Toxics Use Reduction Institute, 2003.
2. U.S Environmental Protection Agency. March 9, 2006. Trichloroethylene Hazard Summary [http://www.epa.gov/ttn/atw/hlthef/tri-ethy.html]. June 2, 2006
3. Toxic Use Reduction Institute (TURI) 2005, “Toxics Use Reduction Act data release for reporting year 2003”.
4. Toxic Use Reduction Institute (TURI), “TCE Alternatives Fact Sheet”.
5. Encyclopedia of Atmospheric Environment, http://www.informationsphere.com/html/201.htm accessed 5/27/04
6. Climate Monitoring Diagnostics Laboratory; Hydrofluorocarbon measurements in the Chlorofluorocarbon Alternatives Measurement Project, http://www.cmdl.noaa.gov/noah/flask/hfc.html 5/27/04
7. A Comparison of Hydrofluoroether and Other Alternative Solvent Cleaning Systems, Jason Kehren, 3M Company, St Paul, MN, USA, www.semiconductorfabtech.com/datatech/journals/edition6/downloads/dt6_53_56.pdf , 5/27/04
8. US Environmental Protection Agency: EPA’s Proposed Regulation of n-Propyl Bromide fact sheet EPA-430-F-01-039, June 2003
9. A. D. Little Report, Copyright ©1999 The Alliance for Responsible Atmospheric Policy
10. Agency for Toxic Substances and Disease Registry, http://www.atsdr.cdc.gov/tfacts87.html September 1997 ToxFAQs™ for 1,2- Dichloroethene , accessed 5/27/04