When used in applications other than benchtop cleaning, VMS fluids require equip- ment and systems designed to accommodate their flash points. One such process employs a pneumatically controlled machine that requires no electrical components. Air-driven pumps are used to circulate the cleaning fluid, with the compressed gas supply directed to the final stage to speed drying. Multitank systems are also in successful operation with methylsiloxane fluids.
SUMMARY
When manufactured to ultralow NVR levels, VMS fluids and VMS-based azeotropes have been proved to be effective cleaning agents for precision and industrial applications, and for removal of cured silicone coatings. Although the low KB value of straight VMS lim- its its cleaning performance to nonpolar contaminants such as greases, oils, and silicones, the inherent low surface tension helps undercut and lift many soils. Since VMS fluids are miscible in most solvents, they can be used in conjunction with more polar fluids, provid- ing a solution with greater versatility than either type alone. Often the combination results in a formulation that cleans a broad range of contaminants, yet reduces the content of the more aggressive solvents.
These ozone-safe materials demonstrate a favorable health and environmental profile, and their use is not likely to be restricted by foreseeable legislation. VMS fluids can usually be reprocessed using established technology, depending on the specific contaminants. Spent fluid is currently being fuel blended in cement manufacturing, used for its silica con- tent and BTU value.
Equipment designed to handle flammable liquids safely can typically be used for cleaning with VMS. Developed as an alternative to conventional solvent technology, these fluids help contribute to greater worker comfort and safety. While no drop-in replacement has yet been found to equal the cleaning performance and cost of ODCs, VMS fluids offer an exceptional balance of performance and ecological properties.
REFERENCES
1. Atkinson, R., Kinetics of the gas-phase reactions of a series of organosilicon compounds with OH and NO3radicals and O3at 297# 2 K, Environ. Sci. Technol., 25, 863, 1991.
2. Sommerlade, R., Parlar, H., Wrobel, D., and Kochs, P., Product analysis and kinetics of the gas- phase reactions of selected organosilicon compounds with OH radicals using a smog chamber- mass spectrometer system, Environ. Sci. Technol., 27, 2435, 1993.
3. Battelle Lab Report to Newark Air Force Base, Experimental Evaluation of the Adhesive Degradation and Corrosion Potential of Silicone Fluids, Contract F09603-90-D-2217-Q805, January, 1995.
4. U.S. EPA, Fed. Regist., 192, 50693–50696, 1994.
5. Iwata, T., Motavassel, F. and Perryman P., Ozone Depleting Compounds Replacement Guidelines, California South Coast Air Quality Management District, Office of Stationary Source Compliance, January, 1996.
6. Carter, W.P.L., Pierce, J.A., Malkina, L.L., and Duo, D., Investigation of the Ozone Formation Potential of Selected Volatile Silicone Compounds, final report from the University of California to Dow Corning Corporation, November 20, 1992.
7. Jenkin, M.E., and Johnson, C.E., Photochemical Ozone Creation Potentials of Volatile Siloxanes, AEA Technology Consulting Services (AEA/CS/16411030/001 Issue 1), August, 1993.
8. Carter, W.P.L., Luo, D., Malkina, I., and Venkataraman, C., Screening Experiments to Evaluate the Aerosol Forming Potential of Selected Volatile Silicone Compounds, final report from the University of California, Riverside to Dow Corning Corporation, June 16, 1994.
9. U.S. EPA, Testing Consent Order for Octamethylcyclotetrasiloxane, Fed Regist., 54, 818–821, 1989. 10. Sousa, J.V., McNamara, P.C., Putt, A.E., Machado, M.W., Surprenant, D.C., Hamelink, J., Kent, D.J., Silberhorn, E.R., and Hobson, J.F., Effects of octamethylcyclotetrasiloxane (OMCTS) on freshwater and marine organisms, Environ. Toxicol. Chem., 14, 1639, 1995.
11. Mueller, J.A., DiTorio, D.M., and Maiello, J.A., Fate of octamethylcyclotetrasiloxane (OMCTS) in the atmosphere and in sewage treatment plants as an estimation of aquatic exposure, Environ.
Toxicol. Chem.,14, 1657, 1995.
12. Hobson, J.F., and Silberhorn, E.M., Octamethylcyclotetrasiloxane (OMCTS), a case study: sum- mary and aquatic risk assessment, Environ. Toxicol. Chem., 14, 1667, 1995.
13. Kent, D.J., McNamara, P.C., Putt, A.E., Hobson, J.F., and Silberhorn, E.M., Octamethylcyclote- trasiloxane in aquatic sediment toxicity and risk assessment, Ecotoxicol. Environ. Saf., 29, 372, 1994.
14. Dow Corning OS Fluids Product Stewardship Summary, Dow Corning form 10-678-96.
15. Ambati, R.R. and Kaiser, R., Silicone Particle Removal Study for Gyro Components, Entropic Systems, report prepared for Defense Construction Supply Center, June, 1994.
16. Witucki, B.A. and Cull, R.A., Evaluation of volatile methylsiloxane fluids as potential replace- ments for ozone depleting solvents, presented at the 213th ACS National Meeting, San Francisco, paper TECH-06, April 13–17, 1997.
17. Swanson, S., Cull, R., Bryant, D., and Moore, J., Cleaning Performance and New Technologies Based on Volatile Methyl Siloxanes, Dow Corning Corporation paper, presented at SAMPE Seattle, November, 1996.
CHAPTER 1.10
Benzotrifluorides
P. Daniel SkellyCONTENTS
Overview
Properties of the Benzotrifluorides Solvent Toxicity
Worker Protection
Cleaning Systems for Benzotrifluorides General Considerations
Size and Shape of Parts Materials of Construction
Volume of Parts to Be Cleaned and Amount of Soil They Contain Soil Loading Cold Cleaning Mechanical Agitation Heated Cleaning Solvent Blends Compatibility
Compatibility with Metals
Compatibility with Polymers and Elastomers Approved Military and Aerospace Applications Reclamation and Disposal
References
[Editor’s note: Many factors impact the cleaning options available to components manufac- turers. The situation with the benzotrifluorides illustrates the impact of overall business plans of chemical producers. Recently, as this book was going to press, Occidental Chemical, the U.S. producer of benzotrifluorides, announced its intention to exit the mar- ket, ceasing production of parachlorobenzotrifluoride (PCBTF) and offering the business for sale. At this point, the future of PCBTF and related compounds as cleaning agents is not known, although some imported PCBTF may be available.]
Despite the uncertainty, this chapter has been included for two reasons. For one thing, PCBTF has been found to be a valid option for some components manufacturers. In addi- tion, Mr. Skelly has written a thoughtful approach to cleaning options. PCBTF has been introduced as a substitute for mineral spirits, and it is particularly valuable in areas of poor air quality. In Southern California, some local regulations explicitly depend on PCBTF for cold cleaning. In addition, because it is neither a VOC or a HAP, PCBTF has been used along with acetone in the reformulation of coatings to meet regulatory constraints. This is perhaps an object lesson to all of us, including end users, formulators, equipment manu- facturers, and regulators that depending on a single or primary chemical to resolve major problems may not be prudent. PCBTF is produced throughout the world, but it is prima- rily a chemical intermediate, not a cleaning agent. In the interest of assuring options, it is hoped that the material will continue to be made available with the appropriate technical support and product stewardship.—B.K.]
OVERVIEW
Three commercially available benzotrifluorides, benzotrifluoride (BTF), parachloroben- zotrifluoride (PCBTF) and 3,4-dichlorobenzotrifluoride (DCBTF), have potential as replace- ments for ozone-depleting compounds and other organic solvents. Because it is exempt as a volatile organic compound (VOC), PCBTF is used in cleaning applications, particularly in areas with high regulatory constraints.
“Likes dissolves like.” This is why, over the years, people have used organic solvents to clean oils, greases, and other organic contaminants off their parts and assemblies. However, most organic solvents used in cleaning operations are VOCs, which contribute to ground- level ozone or smog formation. As a result, restrictions have become burdensome and per- mits difficult to obtain, especially in metropolitan areas where air pollution is a significant problem. Although the three benzotrifluorides have been commercially produced in the United States since the 1960s, until the mid-1990s, their use was limited to chemical inter- mediates for the agricultural and pharmaceutical industries. Interest in their use as clean- ing agents developed when it was discovered that the atmospheric lifetimes of the benzotrifluorides are short enough to avoid ozone depletion. The compounds are not listed as hazardous air pollutants (HAPs). The low tropospheric reactivity of PCBTF led to VOC exemption by the U.S. EPA.