BENZYL ALCOHOL PAINT STRIPPING
alcohol and benzyl alcohol blends have been identified as paint strippers
that do not contain Hazardous Air Pollutants (HAPs) that can be substituted
for methylene chloride paint strippers. Specifically, benzyl alcohol has
been found to be effective on typical aircraft coatings (e.g., epoxy primer
and polyurethane topcoat). Benzyl alcohol strippers also can be used in
conjunction with conventional strippers to strip hard-to-remove coatings.
Benzyl alcohol is a colorless liquid with a mild aromatic odor and sharp burning taste. It has a flash point of 201°F. Benzyl alcohol solutions can generally be divided into acidic and basic formulations. Alkaline benzyl alcohol strippers contain approximately 30 to 50 percent benzyl alcohol, 5 to 10 percent amine or ammonia compounds and has a pH of 11.0. Acid benzyl alcohol strippers contain approximately 25 to 35 percent benzyl alcohol, 10 to 15 percent formic acid and have a pH of 2.5. A neutral benzyl alcohol stripper also has been identified.
The acid formulations, which use formic acid as an accelerator, have been found to react faster than the alkaline strippers. The acid strippers are generally safe for all metals, except high strength steel or magnesium. Acid-based benzyl alcohol strippers have the potential to embrittle high strength steel. As a result, some manufacturers, owners, and the Navy prohibit the use of acid strippers. Nonmetallic surfaces, such as fiber reinforced composites and rubber boots and seals, must be masked or removed as when stripping with methylene chloride solutions.
Benzyl alcohol solutions have excellent adherence to vertical surfaces and remain active for approximately four hours. Acidic benzyl alcohol solutions typically take slightly longer to delaminate the paint compared to methylene chloride. Alkaline benzyl alcohol solutions take longer.
Benzyl alcohol solutions rinse easily and may not generate a hazardous wastewater, depending on the paint removed and the final pH of the solution. The cost difference between benzyl alcohol and methylene chloride strippers can be significant ($6.00/gal for methylene chloride vs. $10.00 - $25.00/gal for benzyl alcohol).
The Naval Aviation Depot in Jacksonville, FL has used the alkaline solution stripper on military aircraft. The process required using the same amount of an alkaline benzyl alcohol stripper as methylene chloride solution. They found benzyl alcohol solutions effective on certain paint systems. They have found them more effective on polyurethane with solvent-based primers than on polyurethane with water-based primers. They reported that Turco 6813 and T6813E are some of the best benzyl alcohol strippers currently available for their applications. They also have reported success removing polysulfide sealants effectively using CB 1058 and Turco 6744.
Among the reported limitations are: 1) very slow reaction rate below 65 deg. F; 2) additional time required to strip very thick coatings (over 0.009 in) and water borne applied primers as opposed to solvent primers, and 3) additional time required to strip coatings with very aggressive conversion coating below the primer.
They found that using benzyl alcohol solutions increases the time required to strip equipment by approximately 25 percent. In addition it is more labor intensive than methylene chloride. They have begun testing other benzyl alcohol strippers that seem to work more quickly but have not yet completed testing. NADEP Jacksonville has begun to use a new Turco product, T6881. T6881 is a single component hydrogen peroxide product that does not cause corrosion or smutting on the aircraft skin. Caution should be used when drumming the waste product as the reaction can continue and cause gassing out.
Tinker Air Force Base has used a two-part stripping system with benzyl alcohol as a component of the stripper. They use the solutions to strip several aircraft including the KC-135 with Koroflex primer and surfaces with polyurethane paint and epoxy primers. The facility used an alkaline benzyl alcohol solution with a hydrogen peroxide based stripper. The facility used El Dorado PR3140 or P3170 (an alkaline benzyl alcohol solution) with El Dorado PR5000 (a hydrogen peroxide solution). The facility found that the mixed paint stripper worked approximately 25 percent faster than methylene chloride on the Koroflex primer and needed approximately half as much stripper to complete the job. For the polyurethane/epoxy primer systems, the benzyl alcohol solution took 50% longer to complete the job and used the same amount of solution as with a methylene chloride stripping system. Tinker personnel also stated that the benzyl alcohol stripper waste should be rinsed thoroughly with water prior to drumming to prevent ammonia vapor generation.
Because the permissible exposure limit (PEL) for methylene chloride will be reduced from 500 ppm to 25 ppm in the near future, facilities that use methylene chloride strippers will be required to use supplied air for workers or perform costly upgrades to facility ventilation systems. As a result alkaline benzyl alcohol strippers may be an alternative that provides satisfactory stripping performance without the health and safety concerns of methylene chloride.
Switching from methylene
chloride to benzyl alcohol paint stripping will decrease a facility’s
HAPs emissions which will decrease the possibility that a facility will
meet the HAP emission threshold for an air permit under 40 CFR 70
and 71. Unfortunately, the use of benzyl alcohol will not decrease
the facility’s VOC emissions and may increase permitting needs in ozone
non-attainment areas. In addition, a decrease in chemical usage has been
observed for using benzyl alcohol as a component of a stripper. Decreasing
the amount of chemical usage decreases the possibility that a facility
will meet reporting thresholds of SARA Title III (40 CFR 302 and 370;
and EO 12856).
Alkaline benzyl alcohol is generally safe for all metal magnesium. Paint removers that qualify to TT-R-2918 will be safe on aircraft metals. Acidic benzyl alcohol blends have the potential to embrittle high strength steel and should not be used on those components. Nonmetallic surfaces, such as fiber reinforced composites and rubber boots and seals must be masked or removed in a similar fashion to that required when stripping with methylene chloride solutions.
|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 implementing the use benzyl alcohol. Normal good practices
for handling all chemicals to avoid any unnecessary exposure should be
followed. This includes wearing of safety glasses and washing off any
material that accidentally contacts the skin and, in particular, the eyes,
with plenty of water.
economics of using benzyl alcohol versus other paint removal methods will
depend on the application. A comparison between benzyl alcohol and methylene
chloride was not developed because of methylene chloride’s use restriction.
Therefore, this analysis is made between two environmentally friendly alternatives,
benzyl alcohol and traditional abrasive sandblasting. According to Air Force
PRO-ACT, an estimated capital cost for a sandblasting unit for F-4 aircraft
from 1987 was $1,400,000. The P-3 (which is used for this analysis) is a
much larger aircraft and costs have escalated. For the following analysis,
a conservative estimate for installation for traditional sandblasting equipment
would be $2,500,000.
Annual Operating Cost Comparison for Benzyl Alcohol versus Traditional Sandblasting
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.
Technical Order 1-1-8 provides authority for use of specific environmentally acceptable paint removers, which are primarily benzyl alcohol based, and a list of approved manufacturers and products is provided. T.O. 1-1-8 does not approve the use of any benzyl alcohol based strippers with acid components or the two-component benzyl alcohol paint removers. The weapon system manager must approve use of the acid-based or two component strippers on an individual basis.
|Points of Contact:||
Empire Abrasive Equipment
This is not meant to be a complete list, as there may be other suppliers of this type of equipment.
Mr. Brad Baum, Baum & Associates, Inc., May 1996