Ionic Liquids for Cleaning Operations at Air Force Air Logistics Centers: Part II
Appears in Print as: 'Testing Ionic Liquids for Cleaning Operations at Air Force Air Logistics Centers: Part II'
Researchers evaluate cleaners for potential use in wiping applications.
Many industrial solvents used in cleaning operations have been designated by the United States Environmental Protection Agency (U.S. EPA) as producing greenhouse gases (GHGs) or containing volatile organic compounds (VOCs), hazardous air pollutants (HAPs), and/or ozone-depleting substances (ODSs). Because these chemicals lead to worker health and safety concerns, alternatives have been sought. In Part I of this paper published in Products Finishing on April 1, 2012, it was noted that ionic liquids (ILs) have been considered for cleaning applications because of their negligible vapor pressure (VP), high thermal and electrochemical stability, and low melting points (less than 212 degrees Fahrenheit (°F)) . Cation/anion pairs in ILs can be chosen to ensure an innocuous toxicology, and appropriate mass transport properties and reactivity with water of the IL can also be tailored by the choice of cation/anion pair , .
Because published work showed that 2-ethylhexyl lactate (2ehl) displayed similar performance to hydrofluorinated ether (HFE) 7100, which is currently used in vapor degreasing operations at Air Logistics Centers (ALCs), 2ehl was chosen for investigation as cleaning agent. . Although 2ehl is an organic solvent with low vapor pressure rather than a traditional IL, it has a considerably lower melting point in the mixed form than in each individual component, similar to traditional ILs. Based on chemistry and toxicology information, 1-ethyl-3-methylimidazolium (EMIM) acetate and EMIM ethylsulfate were also selected as being potentially good cleaning agents . Promising results were obtained for cleaning efficiency and materials compatibility testing1; therefore, chemical properties evaluations and hydrogen re-embrittlement testing of these cleaning agents were conducted on 4130 substrates.
EMIM acetate, EMIM ethylsulfate, and 2ehl were procured from Government Scientific Source, Expotech USA, Inc., and Purac America, Inc., respectively. Testing was derived from performance requirements for cleaning operations, which were extracted from technical orders and military specifications that had been supplied by ALCs paint/depaint and plating facilities -15. Testing followed industry and federal standards, including ASTM, U.S. EPA standard, and ALC military specification test methods as shown in Table 1.
Chemical properties evaluations (Table 1) included workmanship, unacceptable materials contained within the cleaners, flashpoint, neutral acidity, pH, VP, cold stability, emulsion characteristics, presence of mercaptan sulfur (doctor test), and non-volatile matter (NVM) and insoluble matter content.
Workmanship was visually examined through a clear, glass 250 mL beaker containing approximately 250 mL of concentrated cleaner (see Figure 1). Each cleaner passed because it was free of turbidity and foreign matter and was homogeneous (no visible separation of undisturbed solutions).