N-METHYL PYRROLIDONE
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| Overview: | N-Methyl
Pyrrolidone (NMP) is an alternate cleaner for several applications including
electronics cleaning, paint stripping, fiberglass fabrication, printing,
and urethane foam production. NMP-based products have proven to be effective
solvents, which when used in proper equipment and in well designed formulations,
will meet metal cleaning requirements. NMP is also used as a solvent for
surface coatings, including acrylates, epoxies, polyurethanes, polyvinyl
chlorides, polyamidimide-based wire enamels, water-based coatings, and printing
inks. It also works on varnishes, lacquers, and burnt-on carbon deposits.
NMP's low evaporation rate contributes to even, smooth surfaces. Many plastics,
including polystyrene, polyesters, and polyvinyl chloride are soluble in
NMP. According to PRO-ACT, NMP is best used in a tank type process. It would require testing and engineering approval for it to be used as a general wipe solvent and paint remover. NMP has been commercially produced in the United States since the mid 1960s. The typical pH of NMP is 8.0 to 9.5. It is a highly polar colorless liquid with a mild amine odor. NMP has a high flash point (196 °F [91 °C]), low vapor pressure (0.24 mm Hg/68 °F [20 °C]), is very stable, water-soluble and is biodegradable with a minimal potential for bioaccumulation. A typical cleaning process may involve a heated immersion/ultrasonic-cleaning tank with NMP, followed by a heated rinse tank, filled with clean water or NMP. Because the rinsing agents do not evaporate rapidly, a subsequent drying step may be required. NMP is commonly used in the pure state but can be used in a blend with various surfactants and thickeners. It is completely miscible in water and in most organic solvents, including alcohols, ethers, ketones, aromatics, and chlorinated hydrocarbons. After a cleaning process, NMP can be separated and sent back to the wash tank. Many oils become miscible in NMP only at temperatures above 17 to 20 °C (63 - 68 °F). This makes it easy to separate contaminated NMP in a settling tank. In the electronics industry, NMP has been used for cleaning and degreasing single-crystal silicon wafers for integrated circuits. NMP is also an active ingredient in a commercially available product that is a water-miscible, semiaqueous cleaner used to deflux printed wiring boards (PWBs) after wave solder or vapor phase reflow. The product dissolves various contaminants ranging from flux and pyrolized flux to inorganic contaminants and fingerprints. The product is designed to clean through immersion at ambient temperatures but cleaning can be enhanced through either ultrasonics, spraying, spraying under immersion, or agitation. NMP is used in some commercial processes to strip paint. NMP removes paint more slowly than methylene chloride, but NMP dissolves multiple layers rather than lifting each coat. While NMP paint removers work slower, they have lower vapor pressures, a factor that reduces the potential for solvent inhalation. NMP blends tend to cost more than conventional solvents but typically require up to 40 percent less usage than these solvents. NMP-based formulas will effectively strip acrylic latex gloss, epoxy spray paint, polyurethane gloss enamel, high gloss polyurethanes and tallow oil alkyd spray paints. NMP has been used as a replacement for MEK in immersion engine cleaning applications. One alternate immersion product, Fine Organics (FO) 606, which is based on n-methyl pyrrolidone (NMP), is being used at Tinker AFB in the Tank and Cooler Processing Shop as an immersion bath for the removal of carbon and other difficult to remove soils. The Tinker AFB requirement involves a 30-minute to 6-hour residence time in a 120 to 160 °F (49 to 71 °C) bath. FO 606 is a powerful stripping and cleaning agent for the removal of heavy greases, oils, and paints from metal surfaces and is considered a suitable replacement for 1,1,1-TCA in vapor degreasing applications. At present, FO 606 is used in heated tank applications at OC-ALC, WR-ALC, and SM-ALC. Personnel at Kelly Air Force Base have tested N-methyl pyrrolidone as a wipe cleaner in place of MEK. The facility performed a study to evaluate the performance of NMP in cleaning uncured and partially cured epoxy and polysulfide sealants and adhesives. They reported that NMP was effective but slower than MEK in removing these sealants and adhesives. NMP was not shown to be effective on cured epoxy and polysulfide adhesives. The facility is waiting on the completion of a toxicological evaluation prior to implementing the use of NMP. Discussions with Army personnel revealed that except for small applications in well-ventilated areas, the Army is not currently using NMP as a cleaning solvent, owing to concerns over the odor and potential reproductive toxicological effects of NMP. Safety concerns related to the use of NMP-based products, include potential effects on the human reproductive system. Several studies have been conducted to determine the toxicity of NMP. A multigenerational reproduction study in rats, initiated in 1989, concluded that NMP administered in the diet at a dose of 500 mg/kg/day significantly affected reproduction indices in both male and female rats during the second generation. |
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| Compliance Benefit: |
Switching from conventional
solvents to NMP for paint stripping can reduce solvent usage. Decreasing
the amount of chemical usage decreases the possibility that a facility
will meet the reporting thresholds for MSDS submission and Tier I/Tier
II information under 40 CFR 370 and EO 12856. Additionally, less
hazardous waste may be generated from NMP stripping operations since less
solvent is used. The reduction of hazardous waste helps facilities meet
the requirements of waste reduction under RCRA, 40 CFR 262, Appendix,
and may also help facilities reduce their generator status and lessen
their regulatory burden (i.e., recordkeeping, reporting, inspections,
transportation, accumulation time, emergency prevention and preparedness,
emergency response) under RCRA, 40 CFR 262.
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| Materials Compatibility: |
NMP dissolves polyamides,
polyimides, polyesters, polystyrenes, polyacrylonitriles, polyvinyl chlorides,
polyvinyl acetates, polyurethanes, polycarbonates, polysulfones, polymethylmethacrylate,
and many copolymers. Assemblies containing these materials should be tested
before using NMP. NMP will dissolve or swell Buna-N rubber, natural rubber,
neoprene, and Viton. Assemblies containing these materials should be tested
before using NMP.
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| Safety and Health: |
The safety and health issues must be evaluated on a case-by-case basis. Consult your local industrial health specialist, your local health and safety personnel, and the appropriate MSDS prior to using these materials. NMP is resisted by polyethylene, polypropylene, polytetrafluorethyene (Teflon), and butyl rubber. Teflon is recommended for wetted seals and gaskets. Butyl rubber is recommended for personal protective equipment. Potential reproductive toxicological effects have been cited as reasons for not implementing the use of NMP in the services. Repeated or prolonged skin contact with NMP should be avoided. NMP does not appear to be a sensitizing agent but it is a severe eye irritant. The vapor pressure or volatility of this product at room temperature is very low, thus minimizing the chance of exposure by inhalation. Normal practices for handling all chemicals to avoid any unnecessary exposure should be followed.
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| Benefits: |
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| Disadvantages: |
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| Economic Analysis: | The
economics of using NMP versus other solvents will depend on the application.
NMP blends tend to be more expensive than standard solvents but according
to manufacturers the amount NMP required to perform the task may be 30 to
40 percent less. While NMP strippers may be more expensive per gallon than
traditional products, less product will be required to achieve similar results.
Assumptions:
Annual Operating Cost Comparison for NMP versus Methylene Chloride
Economic Analysis Summary
Click here to View an Active Spreadsheet for this Economic Analysis and Enter Your Own Values. To return from the Active Spreadsheet, click the reverse arrow in the Tool Bar.
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| Approving Authority: |
Approval is controlled locally and should be implemented only after engineering approval has been granted. Major claimant approval is not required. For Air Force applications, N-Methyl Pyrrolidone must not be used on any aircraft or weapon systems without the knowledge and approval of the appropriate systems manager, office(s) having engineering authority on the specific airframe(s) and the Air Force Corrosion Prevention and Control Office. For Army applications, N-Methyl Pyrrolidone must not be used on any aircraft or weapon systems without the knowledge and approval of the appropriate systems Program Manager office(s) having engineering authority on the specific airframe(s) or weapon system.
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| NSN/MSDS: |
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| Points of Contact: |
Air Force:
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| Vendors: |
This is not meant
to be a complete list, as there may be other suppliers of this type of
equipment.
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| Sources: |
Mr. Brad Baum, Baum & Associates,
Inc., May 1996 |