United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-95/079
June 1995
vvEPA Project Summary
Radome Depainting
Evaluation at Tinker Air
Force Base
Methyl ethyl ketone (MEK), a hazard-
ous chemical, is used in chemical
depainting of aircraft radomes at Tinker
Air Force Base (TAFB). This report sum-
marizes a laboratory scale screening
study which evaluated ten solvent so-
lutions as a potential replacement for
MEK in TAFB depainting operations.
A test program was developed by
Pacific Environmental Services, Inc.
(PES) to determine the feasibility of us-
ing alternative solvents, less hazard-
ous to the environment and public
health than MEK. PES prepared a test
protocol for conducting the evaluation,
which specified the stripping solutions
to be evaluated, all necessary equip-
ment, test procedures, and method of
evaluating each test.
A qualitative approach was used to
determine the removal efficiency of
each solvent. The testing involved im-
mersing a 2" x 2" square of an aircraft
radome (a fiberglass and epoxy or poly-
ester composite material, in a honey-
comb structure) in a beaker of the
selected solvent. The parameters evalu-
ated included a visual assessment of
the degree of attack (% removal) on
the coating in 0.5-, 1-, 2-, 4-, 8-, and 24-
hr increments. MEK was tested to es-
tablish a baseline. Ten potential
solvents were then evaluated to deter-
mine which chemical, if any, would be
a suitable substitute for MEK.
Test results indicated that several of
the solvents stripped the paint quicker
and more efficiently than MEK (EZE
540, EZE 542, Turco 6776 Lo, Turco
6776 Thin, and Turco 6813). Although
visual examination showed no damage
to the substrate, there was some con-
cern over potential substrate damage
due to the complete and aggressive
removal of all three coats (primer, poly-
urethane rain-erosion coating, and poly-
urethane anti-static topcoat).
Three of the Huntsman solvents
(7210-60-1, 7210-60-2, and 7210-60-5)
completely removed the top two coats
while leaving the primer untouched.
This concept of leaving the primer layer
intact is being considered by the USAF
as a suitable alternative to complete
removal. Leaving the primer layer in-
tact would ensure that the substrate is
not damaged during the depainting op-
eration. Additionally, there may be
some economic advantages in material
and manpower savings. Further test-
ing of the Huntsman solvents at TAFB
is anticipated later this year.
This Project Summary was developed
by EPA's National Risk Management
Research Laboratory, Cincinnati, OH,
to announce key findings of the re-
search project that is fully documented
in a separate report of the same title
(see Project Report ordering informa-
tion at back).
Introduction
The U.S. EPA is encouraging the de-
velopment of programs to reduce the gen-
eration or emissions of hazardous wastes.
The Waste Reduction at Federal Sites
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(WREAFS) program is part of this effort.
This Project Summary covers radome
depainting, a single phase of efforts to
prevent pollution at Tinker Air Force Base
where heavy aircraft such as the B-52,
KC-135, etc. are overhauled. When an
aircraft is overhauled, paint and soils are
first removed so that the underlying struc-
ture can be carefully inspected and re-
paired if necessary. The radome, which is
a large ellipsoid structure made of an ep-
oxy impregnated glass over a honeycomb,
is coated with three layers of paint: primer,
rain erosion layer, and the topcoat. The
two outercoats are usually urethanes, and
the primer is an epoxy. In the present
depainting process, the radome is placed
on end in a large ventilated booth, and
the outer coats are scored so that the
solvent will penetrate to the primer. Me-
thyl ethyl ketone (MEK) is sprayed over
the surface for a period of up to 3 hours
during which the primer dissolves, and
the topcoat chips slough off and are col-
lected in a sump. The MEK in the sump is
recycled; evaporative losses in 1993 were
about 50,000 Ib, while about 700 Ib of
paint chips were sent to disposal.
Air Force personnel wanted to replace
MEK for several reasons: It is flammable
(flash point 26°F), and has a high vapor
pressure, so that it evaporated easily,
causing high air emissions as well as sol-
vent loss. MEK vapors cannot be cap-
tured on activated carbon, as there are
instances of it causing fires in the carbon
bed. A previous study at TAFB had dem-
onstrated that low volatility solvent blends
could replace MEK, but the best one con-
tained NMP, whose toxicity had become
suspect. EPA decided that other propy-
lene carbonate blends might be effective
paint strippers, while retaining the desired
low toxicity, high flash point, and low vola-
tility. Huntsman again made and supplied
five blends, two containing lowered con-
centrations of NMP, and three having
none. These were then evaluated and
compared to five commercial strippers and
MEK in laboratory tests on 2"x 2" pieces
cut from a discarded radome. The compo-
sitions of the ten strippers are given be-
low.
• Huntsman Formulation C
#7210-60-1
40 - 60% Propylene carbonate
10 - 30% Methyl-2-pyrrolidinone
15 - 35% Dibasic ester (DuPont)*
4 - 10% Methyl-2-hexanone
(methylisoamyl ketone)
* A mixture of dibasic esters comprising 24% dimethyl
succinate, 60% dimethyl glutarate, 15% dimethyl
adipate, plus 1% water and methanol.
• Huntsman Formulation D
#7210-60-2
20 - 40% Propylene carbonate
10 - 30% Methyl-2-pyrrolidinone
25 - 45% Dibasic ester
10 - 20% Ethylene glycol diacetate
• Huntsman Formulation E
#7210-60-3
15 - 35% Propylene carbonate
40 - 60% Dibasic ester
20 - 40% Butyrolactone (gamma)
• Huntsman Formulation F
#7210-60-4
35 - 55% Propylene carbonate
30 - 50% Dibasic ester
5 - 15% Triethylene glycol
• Huntsman Formulation G
#7210-60-5
30 - 50% Propylene carbonate
30 - 50% Dibasic ester
10 - 30% Diethylene glycol
monobutyl ether
• EZE 540
28 - 35% Benzyl Alcohol
10 - 15% Formic Acid
1 - 5% Petroleum Hydrocarbon
• EZE 542
30 - 40% Benzyl Alcohol
5 - 10% Ethanolamine
1- 5% 2-Ethylhexyl Mercaptoacetate
1 - 5% Petroleum Hydrocarbon
• Turco 6776 Lo
15% Proprietary Ingredient No. 1
5% Formic Acid
<5% High Boiling Aromatic Solvent
10% Proprietary Ingredient No. 2
Also contains:
Unk.% Water
• Turco 6776 Thin
10% Proprietary Ingredient No. 1
10% Formic Acid
10% Solvent Refined Hydrotreated
Middle Distillate
10% Proprietary Ingredient No. 2
Also contains:
Unk.% Water
Unk.% Sodium Xylene Sulfonate
• Turco 6813
40% Proprietary Ingredient
<5% High Boiling Aromatic Solvent
Also contains:
Unk.% Water
Unk.% Hexynol
Unk.% Ammonium Hydroxide
(Ammonia)
Test Procedure
A test program was developed by Pa-
cific Environmental Services, Inc. (PES)
to determine the feasibility of using these
alternative solvents, comparing them to
MEK. PES prepared a test protocol for
conducting the evaluation, which speci-
fied the stripping solutions to be evalu-
ated, all necessary equipment, test
procedures, and method of evaluating each
test.
A qualitative approach was used to de-
termine the removal efficiency of each sol-
vent. The testing involved immersing a 2"
x 2" square of an aircraft radome (a fiber-
glass and epoxy or polyester composite
material, in a honeycomb structure) in a
beaker of the selected solvent. The pa-
rameters evaluated included a visual as-
sessment of the degree of attack (%
removal) on the coating at 0.5-, 1-, 2-, 4-,
8-, and 24-hr intervals. MEK was included
in the test to establish a baseline. The
potential depainting compositions were
then evaluated to determine which were
suitable substitutes for MEK.
Test results indicated that several of
the commercially available compositions
stripped the paint quicker and more effi-
ciently than MEK. These were EZE 540,
EZE 542, Turco 6776 Lo, Turco 6776
Thin, and Turco 6813. While these were
effective strippers, there is some concern
over ingredients such as formic acid (toxic,
as well as corrosive) and ammonia. Al-
though visual examination showed that
these caused no damage to the substrate,
conversations with TAFB engineers indi-
cated some concern over potential sub-
strate damage due to the complete and
aggressive removal of all three coats
(primer, polyurethane rain-erosion coating,
and polyurethane anti-static topcoat). The
visual identification of the three separate
coats was easily accomplished due to the
distinctive color of each coat. (The top
coat was a dark grey, the second or middle
coat was white, while the primer coat was
red). In addition, the substrate was a dis-
tinct yellow-brown.
Three of the Huntsman solvents (7210-
60-1, 7210-60-2, and 7210-60-5) com-
pletely removed the top two coats while
leaving the primer untouched. This con-
cept of leaving the primer layer intact is
being considered by the USAF as a suit-
able alternative to complete removal. Leav-
ing the primer layer intact would ensure
that the substrate is not damaged during
the depainting operation. Additionally there
may be some economic advantages in
relation to material and manpower sav-
ings. Further testing of the Huntsman sol-
vents at TAFB is anticipated later this
year where it is planned to strip a com-
plete radome, and, if time allows, test the
adhesion of new topcoats to the primer.
Test Results
The removal effectiveness of the sol-
vents varied greatly. Some of the solvents
aggressively removed all three coats of
paint, while others selectively removed only
the top two, leaving the primer coat intact.
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Even though visual inspection of the ra-
dome test sections indicated no physical
signs of damage or deterioration to the
substrate upon complete removal of all
coats of paint, it may be desirable, when
the primer coat is in good condition, to
leave it intact, thus ensuring the integrity
of the substrate.
For complete removal of the first two
coats while leaving the primer coat intact,
the following solvents exhibited the best
results:
• Huntsman Corporation, Formulation E,
7210-60-3
• Huntsman Corporation, Formulation F,
7210-60-4
• Huntsman Corporation, Formulation
G, 7210-60-5
For complete removal of all three coats
the following solvents exhibited the best
results:
EZE Products, Inc., EZE 540**
EZE Products, Inc., EZE 542
Turco Products, Inc., Turco
6776 Thin**
Turco Products, Inc., Turco 6776 Lo*
"Required a final waterwash to completely remove the
primer coat.
Costs
Purchase costs for each of the solvents
used in this test program are presented in
Table 1. The costs for the commercially
available strippers are as quoted, while
those of the Huntsman formulations are
calculated from the cost of the individual
components multiplied by their percent-
age in the final blend; no cost of blending
the mixtures or a profit margin for the
supplier of the blends are included.
Cost effectiveness of each solvent must
also consider solvent loss, waste disposal,
depainting time, degree of paint removal,
subsequent surface treatment and related
factors. Such an evaluation was beyond
the scope of this study.
Conclusions
These screening tests indicate that there
are viable replacements for MEK which
effectively remove the two topcoats while
leaving the primer relatively intact. Further
testing must be done to evaluate new top
coat adhesion to primer which has been
exposed to the stripper in a full scale
depainting test; two radomes and solvent
blends have been procured for trials
planned for late 1994. The results of these
full scale trials will then be evaluated by
TAFB engineers to determine if installa-
tion on a test aircraft is justified.
The full report was submitted in fulfill-
ment of Contract No. 68-D2-0062 by PES,
Research Triangle Park, NC, under the
sponsorship of the U.S. Environmental Pro-
tection Agency.
Table 1. Purchase Cost Comparison of Selected Solvents
Solvent/Blend
Approximate Cost $/gallon
MEK
EZE 540
EZE 542
Turco 6776 Lo
Turco 6776 Thin
Turco 6813
Huntsman No. 1
Huntsman No. 2
Huntsman No. 3
Huntsman No. 4
Huntsman No. 5
5.00
14.00
18.00
17.00
17.00
17.00
12.00
12.00
9.00
9.00
9.00
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This Summary was authored by the staff of Southern Research Institute,
Birmingham, AL 35205; Pacific Environmental Services, Inc., Research
Triangle Park, NC 27709; and EPA author, S. Garry Howell, National Risk
Management Research Laboratory, Cincinnati, OH 45268.
James S. Bridges is the EPA Project Officer (see below).
The complete report, entitled "Radome Depainting Evaluation at Tinker Air
Force Base," (Order No. PB95-230835; Cost: $17.50, subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
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EPA/600/SR-95/079
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