N-METHYL PYRROLIDONE BASED CLEANERS AND STRIPPERS

Revision Date: 8/03
Process Code: Navy/Marines: IND-002-00, IND-002-07, IND-002-14; Air Force: CL-02, MT03; Army: CLD, DPT
Usage List: Navy: Low; Marines: Low; Army: Low; Air Force: Low
Alternative For: Certain paint stripping and cleaning and degreasing processes
Compliance Impact: Medium
Applicable EPCRA Targeted Constituents and CAS Numbers: Methyl ethyl ketone (CAS: 78-93-3), and Dichloromethane (CAS:75-09-2)
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, and when used in well-designed formulations with the proper equipment , can 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 is a very stable, water-soluble cleaner, with a high flashpoint (196 °F [91 °C]) and low vapor pressure (0.24 mm Hg/68 °F [20 °C]). It 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), making 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.


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 SARA Title III (40 CFR 300, 355, 370, and 372) and Executive Order (EO) 13148. 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; the Pollution Prevention Act (42 USC 13101-13109); and EO 13148; 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. Moreover, since solvents may be reduced, VOCs associated with the process would also be reduced, a factor that may decrease the likelihood that a facility will require an air permit under 40 CFR 70 and 71. Reducing VOC emissions may also help a facility to comply with the requirements of the National Emission Standards for Hazardous Air Pollutants (NESHAPs) (40 CFR 63).

The compliance benefits listed here are only meant to be used as general guidelines and are not meant to be strictly interpreted. Actual compliance benefits will vary depending on the factors involved, e.g., the amount of workload involved.


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.

NMP does not react with most metals, including steels, aluminum, nickel, silver, gold, chromium and chromates, copper, tin, and silicon. However, it should not be used with bronze or brass valves in process piping.


Safety and Health: As with all chemicals, care must be taken to avoid unnecessary exposure to NMP. In particular, repeated or prolonged skin contact with NMP should be avoided. Potential reproductive toxicological effects have been cited as reasons for not implementing the use of NMP. Although NMP does not appear to be a sensitizing agent, 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.

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.

Consult your local industrial health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing this technology.


Benefits:
  • Releases fewer organic emissions to the atmosphere. 
  • Miscible in water. 
  • Chemically stable.


Disadvantages:
  • NMP is listed in SARA Title III, Section 313, and is subject to reporting in the Toxics Release Inventory. 
  • Works slower than conventional solvents. 
  • An unpleasant odor has been reported by users. 
  • Potential toxicological concerns have been reported and must be evaluated and compared with standard solvents. 
  • The Air Force does not consider N-Methyl Pyrrolidone as a promising alternative to MEK or methylene chloride due to concerns relating to health and performance. A number of other materials are proving effective for replacing MEK on an individual application basis that are environmentally acceptable, cheaper, and have lower health risks to the workers. This also applies to the potential for N-Methyl Pyrrolidone as a replacement for methylene chloride.


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:

  • Both methylene chloride and NMP stripping wastes are managed as hazardous waste. 
    NMP requires 25 percent less solvent to perform the task. 
  • A stripping operation strips approximately 1,000 square feet of area using 300 gallons of methylene chloride or 225 gallons of NMP, generating corresponding quantities of waste. 
  • Tests have concluded that the use of NMP requires 3 to 10 times longer than the use of conventional products depending on the substrate and the coating. Analysis assumes that employees will perform other tasks during the interval. Therefore, the labor costs are assumed equal. 
  • Cost of equipment downtime is not included in the estimate. 
  • Methylene chloride solution costs $9.00 per gallon. 
  • NMP solution costs $35.00 per gallon. 
  • All solvent is disposed as waste at $3/gallon.

Annual Operating Cost Comparison for NMP versus Methylene Chloride

 

NMP

Methylene Chloride

Operational Costs:    
Solvent costs: $7,875 $2,700
Waste Disposal: $675 $900
Total Costs: $8,550 $3600
Total Recovered Income: $0 $0
Annual Benefit: -$8550 -$3600

Economic Analysis Summary:

Given the high cost of the NMP solvent, it may be better to use NMP for small applications or on applications where performance warrants. 

Click here to View an Active Spreadsheet for this Economic Analysis and Enter Your Own Values. To return from the Active Spreadsheet, click the Back arrow in the Tool Bar.


NSN/MSDS:
Product NSN Unit Size Cost MSDS*
N-Methyl Pyrrolidone 6810-01-200-8003 ea. (4 liter) $93.92 Click me

*There are multiple MSDSs for most NSNs. The MSDS (if shown above) is only meant to serve as an example. To return from the MSDS, click the Back arrow on the Tool Bar.


Approving Authority: Appropriate authority for making process changes should always be sought and obtained prior to procuring or implementing any of the technologies identified herein.

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.


Points of Contact: For more information

Vendors: This is not meant to be a complete list, as there may be other suppliers of this type of equipment.

Fisher Scientific Co.
2000 Park Lane
Pittsburg, PA 15275
Phone: (412) 490-8586
URL: www.fishersci.com

Empire Abrasive Equipment Company
2101 West Cabot Blvd.
Langhorne, PA 19047-1893
Phone: (215) 752-8800
FAX: (215) 752-9373


Sources: Mr. Brad Baum, Baum & Associates, Inc., May 1996
Ms. Chris Mahendra, Naval Air Warfare Center, Lakehurst, NJ, May 1996
Ms. Penny Sue Jones, Puget Sound Naval Shipyard, February 2000.