Demonstration/Validation of Hazardous Air Pollutant-Free 

Torque Seal Inspection Lacquer 

by Faye R. Toulan, Felicia Levine, John J. La Scala, 

Leslie Hasenbein, Genie Jones, and Ivan Davis 

ARL-TR-4863 July 2009 

Approved for public release; distribution is unlimited.
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Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5069 

ARL-TR-4863 July 2009 

Demonstration/Validation of Hazardous Air Pollutant-Free 

Torque Seal Inspection Lacquer 

Faye R. Toulan and Felicia Levine 

Data Matrix Solutions, Inc. 

John J. La Scala 

Weapons and Materials Research Directorate, ARL 

Leslie Hasenbein 

Stanley Associates, Inc.

Genie Jones and Ivan Davis 

U.S. Army Aviation and Missile Command G-4 

Approved for public release; distribution is unlimited. 
ii 

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1. REPORT DATE (DD-MM-YYYY)

July 2009 

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Final 

3. DATES COVERED (From - To) 

1 March 2008–1 December 2008 

4. TITLE AND SUBTITLE 

Demonstration/Validation of Hazardous Air Pollutant-Free Torque Seal Inspection 

Lacquer 

5a. CONTRACT NUMBER 

5b. GRANT NUMBER 

5c. PROGRAM ELEMENT NUMBER 

6. AUTHOR(S) 

Faye R. Toulan,* Felicia Levine,* John J. La Scala, Leslie Hasenbein,† 

Genie Jones,‡ and Ivan Davis‡

5d. PROJECT NUMBER 

SPOTA K42 

5e. TASK NUMBER 

5f. WORK UNIT NUMBER 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 

U.S. Army Research Laboratory 

ATTN: RDRL-WMM-C 

Aberdeen Proving Ground, MD 21005-5069 

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 REPORT NUMBER 

ARL-TR-4863 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 

U.S. Army Research, Development, and Engineering Command 

Environmental Acquisition and Logistics Sustainment Program 

Aberdeen Proving Ground, MD 21010 

10. SPONSOR/MONITOR’S ACRONYM(S) 

RDECOM EALSP 

11. SPONSOR/MONITOR'S REPORT 

 NUMBER(S) 

12. DISTRIBUTION/AVAILABILITY STATEMENT 

Approved for public release; distribution is unlimited. 

13. SUPPLEMENTARY NOTES 

*

Data Matrix Solutions, Inc., 107 Carpenter Dr., Ste. 110, Sterling, VA 20164 

†

Stanley Associates, Inc., 3101 Wilson Blvd., Ste. 700, Arlington, VA 22201 

‡

U.S. Army Aviation and Missile Command G4, Redstone Arsenal, AL 35898 

14. ABSTRACT 

The U.S. Army uses numerous adhesives and sealants among other coating materials that contain significant amounts of 

hazardous air pollutants (HAP). The U.S. Army has determined that it is much more cost effective to reduce or eliminate HAP 

emissions from coatings operations rather than using emissions control devices. 

This work examines laboratory and field demonstration/validation of one highly used sealant, Torque Seal. The adhesives and 

sealants thrust area of the Sustainable Painting Operations for the Total Army program has identified a HAP-free alternative to

Torque Seal containing ethanol as the carrier solvent. Laboratory testing including adhesion, resistance to fluids, resistance to 

humidity, and drying time has validated that the HAP-free sealant performs very similarly to the baseline Torque Seal 

containing methanol (HAP). Furthermore, a demonstration/validation study at Fort Rucker, AL, using a UH-1 helicopter rotor 

shows that the HAP-free sealant has performed as well as the Torque Seal. 

15. SUBJECT TERMS

sealant, HAP-free, adhesion, TGA, humidity, field trial, DSC 

16. SECURITY CLASSIFICATION OF: 

17. LIMITATION 

OF ABSTRACT 

UU 

18. NUMBER 

OF PAGES 

28 

19a. NAME OF RESPONSIBLE PERSON

John J. La Scala 

a. REPORT 

Unclassified 

b. ABSTRACT 

Unclassified 

c. THIS PAGE 

Unclassified 

19b. TELEPHONE NUMBER (Include area code) 

410-306-0768 

Standard Form 298 (Rev. 8/98) 

Prescribed by ANSI Std. Z39.18 
iii 

Contents 

List of Figures v

List of Tables v

Acknowledgments vi

1. Introduction 1

2. Experimental Method 2

2.1 Rheology .........................................................................................................................2

2.2 Nonvolatile Content (Solids) ...........................................................................................3

2.3 Thermogravimetric Analysis (TGA) ...............................................................................3

2.4 Drying Time ASTM D 1640 ...........................................................................................3

2.5 Adhesion Testing ASTM D 3359 ....................................................................................4

2.6 Resistance to Fluid Immersion Section 4.6.8 of MIL-PRF-85285D ...............................4

2.7 Adhesion Testing Conducted on Fluid Immersion Samples ...........................................4

2.8 Differential Scanning Calorimetry (DSC) .......................................................................4

2.9 Flexibility Testing ...........................................................................................................5

2.10 Humidity Testing ASTM D 2247 ....................................................................................5

2.11 Accelerated Weathering ASTM C 732 ...........................................................................5

2.12 Demonstration/Validation Plan .......................................................................................5

3. Results and Discussion 7

3.1 Rheology .........................................................................................................................7

3.2 Nonvolatile Content (Solids) ...........................................................................................7

3.3 Thermogravimetric Analysis (TGA) ...............................................................................8

3.4 Drying Time ASTM D 1640 .........................................................................................10

3.5 Adhesion Testing ASTM D 3359 ..................................................................................10

3.6 Resistance to Fluid Immersion MIL-PRF-85285D .......................................................10

3.7 Adhesion Testing Conducted on Fluid Immersion Samples .........................................11

3.8 Differential Scanning Calorimetry (DSC) .....................................................................12
iv

3.9 Flexibility Testing .........................................................................................................13

3.10 Humidity Testing ASTM D 2247 ..................................................................................13

3.11 Accelerated Weathering ASTM C 732 .........................................................................14

4. Field Trial on UH-1 Helicopter at Fort Rucker 15

5. Conclusions 16

6. References 17

List of Symbols, Abbreviations, and Acronyms 18

Distribution List 19 
v 

List of Figures 

Figure 1. UH-1 helicopter rotor system diagram. ...........................................................................6

Figure 2. Torque Seal applied to UH-1 helicopter. .........................................................................6

Figure 3. Torque Seal rheology. .....................................................................................................8

Figure 4. Torque Seal TGA of dry solids. ......................................................................................9

Figure 5. Torque Seal TGA of dry derivative weight. ....................................................................9

Figure 6. Cross-cut adhesion tape test at –11 °F. ..........................................................................11

Figure 7. Immersion in lubricating oil at 121 °C for 24 h. ...........................................................11

Figure 8. Adhesion after 7-day immersion in JP-8 fuel at room temperature. .............................12

Figure 9. Torque Seal DSC. ..........................................................................................................12

Figure 10. Torque Seal mandrel bend test at 140 °F. ...................................................................13

Figure 11. Color change after exposure to 100% humidity and 40 °C. ........................................14

Figure 12. Torque Seal QUV results after 500 h of exposure. .....................................................14

Figure 13. Torque Seal 60 days after application to a UH-1 helicopter. ......................................16

List of Tables 

Table 1. Quantity of Torque Seal used by Fort Rucker in 2003 (1). ..............................................2

Table 2. Rheology data for Torque Seal. ........................................................................................7

Table 3. TGA (dry) calculated results. ............................................................................................8

Table 4. Drying time results for Torque Seal. ..............................................................................10

Table 5. Fort Rucker summary of field trial results. .....................................................................16
vi 

Acknowledgments 

The authors would like to thank Chris E. Miller of the U.S. Army Research Laboratory for help 

with test preparation and execution, Patrick Taylor of Hughes Associates, Inc. for his assistance, 

and the Sustainable Painting Operations for the Total Army program for support and funding. 
1

1. Introduction 

The U.S. Environmental Protection Agency (EPA) is planning to propose National Emission 

Standards for Hazardous Air Pollutants (NESHAP) for the surface coating of Defense Land 

Systems and Miscellaneous Equipment. The NESHAP is expected to require significant 

reductions in hazardous air pollutant (HAP) emissions from U.S. Army surface coating 

operations. Army installations are establishing environmental sustainability goals to exceed such 

regulatory requirements. The Sustainable Painting Operations for the Total Army (SPOTA) 

program has been established to manage the effort to reduce HAP emissions generated by Army 

coating operations. Adhesives and sealants are a small but significant portion of Army coatings 

HAP emissions. 

Torque Seal, made by Organic Products Co. in Irving, TX, is a HAP-emitting sealant used in 

several Army applications. Torque Seal is used primarily to detect tampering or loosening of 

mechanical fasteners on military aircraft. Applied after bolts or fittings are in proper torque or 

position, this product gives inspectors visual evidence of any movement or tampering. Torque 

Seal dries to form a very brittle film that will crack, flake, or crumble when minimal force is 

applied. Other key product attributes include excellent adhesion to most surfaces and fast 

drying. The manufacturer refers to this product as an inspection seal lacquer or antisabotage 

lacquer. The fast-drying characteristic of Torque Seal is achieved by using low boiling point 

solvents as carriers, specifically ethanol and methanol. While both solvents are volatile organic 

compounds, only methanol is classified by the EPA as a HAP. The reported HAP content of this 

material is 20% by weight. 

Torque Seal comes in a variety of colors (table 1), and all have the same essential properties. 

Although the total HAP emissions from Torque Seal are less than the emissions from many other 

surface coating operations, the product is used at more than 20 Army installations and accounts 

for ~5% of all Army sealant HAP emissions (1). Therefore, the SPOTA program focused on 

replacing Torque Seal with a similar product that contains no HAPs. After a thorough 

investigation, it was found that there was no similar product commercially available and no 

inspection lacquers of any kind that were HAP-free. As a result, a HAP-free version of the 

material was developed by the U.S. Army Research Laboratory (ARL) with Organic Products 

Co. containing only ethanol as the solvent. A single production batch of HAP-free Torque Seal 

was manufactured and used for both the lab testing and field trial. The vapor pressure of 

methanol and ethanol are 16.9 KPa and 7.87 KPa, respectively, at 25 oC, and the vapor pressure 

is higher for methanol at all temperatures (2). The higher vapor pressure of the baseline sealant 

indicates higher volatility and will likely result in a faster drying time and, in this case, a higher 

tendency to crack. 
2

Table 1. Quantity of Torque Seal used by Fort Rucker in 2003 (1).

National Stock 

Number (NSN) Color 

Number of 

0.5-oz Tubes 

Pounds of 

Material 

Pounds of 

HAP 

8030011432702 Red 1638 51.19 10.24 

8030011250055 Orange 847 26.47 5.29 

8030004081137 Green 42 1.31 0.26 

8030011633483 Yellow 0 0.00 0.00 

8030010777674 White 0 0.00 0.00 

8030010668156 Blue 0 0.00 0.00 

All NSNs All 2527 78.97 15.79 

This report summarizes both laboratory and field trial results for the new HAP-free formulation 

of Torque Seal containing only ethanol vs. the current product containing ethanol and methanol. 

The key properties discussed are rheology, nonvolatile content, thermogravimetric analysis 

(TGA), drying time (ASTM D 1640 [3]), adhesion (ASTM D 3359 [4]), resistance to fluid 

immersion (section 4.6.8 of MIL-PRF-85285D [5, 6]), adhesion testing after fluid immersion, 

differential scanning calorimetry (DSC), flexibility, resistance to humidity (ASTM D 2247 [7]), 

and accelerated weathering (ASTM C 732 [8]). A field trial was conducted using a UH-1 

helicopter at Cairns Army Air Field, Fort Rucker, AL, from May to November of 2008. Both 

formulations used in the field trial were supplied by the manufacturer Organic Products Co. in 

standard commercial packaging (0.5-oz plastic crimp tubes). 

2. Experimental Method 

2.1 Rheology 

The viscosities of the wet sealants were measured using a TA Instruments (New Castle, DE) 

AR2000 Rheometer in steady shear flow experiments using a 40-mm, cross-hatched parallel 

plate geometry with a peltier and a solvent trap containing ethanol, at 20 °C. The purpose of the 

solvent trap was to keep samples from volatilizing during the experiment and skinning at the 

edges of the plate, resulting in drag or uneven flow. The shear rate was increased logarithmically 

from 10–5 s

–1 to 1 s–1 and then decreased back to 10–5 s–1, and 10 measurements were taken per 

decade. At a given shear rate, the shear stress was measured every 2 s. The shear rate and 

viscosity were recorded when the shear rate stabilized to within 5% tolerance for three 

consecutive intervals. 
3

2.2 Nonvolatile Content (Solids) 

Wet Torque Seal samples were completely evaporated to determine the solid and volatile content 

in the sealant. An aluminum weighing pan was tared, and ~5 g of thoroughly mixed sealant was 

poured into the tared container, covered, and weighed. After removing the cover, the container 

was placed in an oven at 70 °C  1.1 °C (158 °F  2 °F) until the sample reached a constant 

weight. The covered container with the sample was cooled to 23 C° ± 1.1 °C (73.5 °F ± 2 °F) 

before weighing. Each sample was run in duplicate. The percentage of total solids was 

calculated as follows: 

 Total solids (%) = (weight of residue/original weight of sample) × 100. (1) 

2.3 Thermogravimetric Analysis (TGA) 

TGA was run on the samples of dried formulation solids using a TA Instruments TGA 2950. 

Wet formulation samples were dried in an oven until the sample weight remained constant. This 

dried material was pulverized in a coffee bean grinder to allow the release of any trapped 

solvent. Oven drying of the pulverized sample continued until the sample weight was again 

constant. A 5- to 10-mg sample of dried, pulverized resin and pigment was placed on a tared 

platinum sample holder suspended on a weight-sensing wire hook. The samples were run in air 

up to 800 °C at 10 °C/min. The TGA instrument measures the sample mass as a function of 

temperature throughout the experiment. The percent mass remaining at the end of the run is the 

residual inorganic ash content. Knowing the percentage of ash in the nonvolatile portion of the 

formulation can allow an estimation of the pigment to binder ratio (P/B). The organic resin, 

which acts as the binder, will be burned off in TGA analysis, and the remaining ash will be 

comprised of the pigments, extenders, and other fillers in the formula. P/B can be a useful 

parameter for formula comparison. Three samples of each formulation were run to get a good 

measure of percent error. 

2.4 Drying Time ASTM D 1640 

Beads of the sealants were applied on a glass plate and evaluated for skin time at room 

temperature. Skin time (also known as open time) is the formation of a cohesive film that can 

withstand a light touch with a wooden dowel (9). The product was applied to a uniform 

thickness of 6.5 mil. The tack-free time of the samples was measured periodically with a 

common qualitative industry “touch-test” until the samples were no longer tacky and resisted 

transfer. Lastly, tack-free time of the samples was evaluated using cotton fibers. Testing tackfree time with cotton fibers is a more sensitive touch-test that determines the ability of the 

sample to resist adhesion to the fibers. When the fibers do not transfer to the sealant and the film 

does not deform, the product is dry or tack-free. The time required for the sample to become 

tack-free was recorded as a range rather than a single data point. Drying time studies were 

performed at –11, 75, and 140 oF as outlined in the demonstration/validation plan for Torque 

Seal. A typical average temperature for application of the sealant at a depot is 75 oF, whereas 
4

–11 oF and 140 oF encompass the lower and higher ends of the reasonable temperature 

application spectrum. 

2.5 Adhesion Testing ASTM D 3359 

The baseline and HAP-free sealants were applied to a uniform thickness of 6.5 mil on steel 

substrates that measured 4 × 6 in. Conditioning parameters for adhesion testing were –11, 75, 

and 140 oF. The sealants were allowed to dry for 24 h at room temperature and conditioned for 

2 h before adhesion testing using Test Method B cross-cut tape test. Tape was applied to the 

cross-hatched area and then removed. The amount of sealant remaining in the cross-hatched area 

was rated according to ASTM D 3359 to assess the adhesion performance of the sealants (10). 

2.6 Resistance to Fluid Immersion Section 4.6.8 of MIL-PRF-85285D 

The baseline and HAP-free sealants were applied to a uniform thickness of 6.5 mil on steel 

substrates that measured 4 × 6 in and allowed to dry 24 h at room temperature. Dried films were 

challenged by standing the panels vertically in a container of fluid so that about half of the film 

area was immersed. The following liquids and test conditions were used: 

• MIL-L-23699 (5) lubricating oil at 121 °C for 24 h. 

• MIL-PRF-83282 (5) hydraulic fluid at 66 °C for 24 h. 

• JP-8 fuel at room temperature for 7 days. 

The films were examined 1 h after removal from the fluid for blistering, delamination, and 

discoloration. 

2.7 Adhesion Testing Conducted on Fluid Immersion Samples 

Approximately 2 weeks following the completion of the fluid immersion evaluation (as 

described in section 2.6), adhesion testing at 75 °F was conducted (section 2.5) on the portion of 

sealant submerged in the specified fluids (4, 5). 

2.8 Differential Scanning Calorimetry (DSC) 

DSC calculates the heat flow into or out of a material by measuring the temperature difference 

between a sample pan and an empty reference pan being heated under identical conditions. The 

glass transition (Tg) of a polymer from a rigid to a rubbery material can be seen as an inflection 

point on the ascending temperature DSC curve. Samples of the baseline and HAP-free material 

were dried and pulverized before analysis. A small sample (5–10 mg) was crimped in a pan and 

placed on one sensor in the sample chamber while an empty reference pan was placed on the 

other sensor. The chamber was sealed and heated under nitrogen, and temperature differences 

between the sample and the reference were measured. The samples were exposed to two heat 

cycles, from –10 to 200 °C and back to –10 °C at a rate of 10 °C/min. 
5

2.9 Flexibility Testing 

Flexibility testing was performed using the mandrel bend test. The sealants were applied to a 

uniform thickness of 6.5 mil on tin-coated steel Q-panel substrates that measured 3 × 6 in. The 

samples were allowed to dry for 24 h (at room temperature) then conditioned at one of three 

temperatures (–11, 75, and 140 oF) for 2 h prior to flexibility testing on a 1/8-in mandrel. The 

conditioning time at the specified temperatures was increased until cracking occurred at all three 

temperatures. The Q-panels were bent along the sides of a cylindrical mandrel, with the sealant 

on the opposite side of the mandrel to provide a flexure stress. Because Torque Seal is designed 

to crack when tampered with, this sealant breaks at low flexural stresses. The baseline and HAPfree sealants were characterized for “crack time” occurring at each of these temperatures. 

2.10 Humidity Testing ASTM D 2247 

The baseline and HAP-free sealants were applied to a uniform thickness of 6.5 mil on steel 

substrates that measured 4 × 6 in. The sealants were allowed to dry for 3 days. Prior to humidity 

exposure, the bare steel portion of the panels was covered with a clear packing tape to prevent 

corrosion. The specimens were then subjected to constant conditions of 40 °C and 100% relative 

humidity. Samples were evaluated after 1, 3, 7, 14, and 30 days of exposure for discoloration, 

blistering, and delamination. 

2.11 Accelerated Weathering ASTM C 732 

The baseline and HAP-free sealants were applied to a uniform thickness of 6.5 mil on steel 

substrates that measured 3 × 6 in. The sealants were allowed to dry for 3 days before starting 

accelerated UV exposure in a QUV* accelerated weathering tester cabinet. Torque Seal samples 

were exposed to a 340-nm UVA light source at a radiance level of 0.77 W/m2

 for 8 h at 60 oC 

followed by 4 h of condensation at 50 oC without light exposure. Samples were examined at 100 

and 500 h of exposure for discoloration, blistering, and delamination. 

2.12 Demonstration/Validation Plan 

ARL and Fort Rucker conducted a field trial on 6 May 2008 at Cairns Army Air Field, Fort 

Rucker, AL. Both the baseline and HAP-free Torque Seal products were applied to the UH-1 

helicopter rotor system (figure 1) on approximately 40 assemblies of nuts, bolts, and studs. On 

the day of application, a decision was made to place a bead of each sealant on every fastener, as 

seen in figure 2, for a more accurate side-by-side evaluation. In addition, the operator was 

required to photograph the sealant on each fastener to document any degradation of the sealant as 

a function of time. Photos were also taken at 7, 14, 30, 60, 90, and 120 days after application. 

Inspections were conducted at these same time intervals for delamination (peeling away from 

surface), deterioration, and operation-induced cracking (11). The UH-1 helicopter participated in 

regular training operations under representative flight conditions. This ensured that the HAP-

 *

QUV is a registered trademark of Q-Panel Lab Products, Cleveland, OH. 
6

Figure 1. UH-1 helicopter rotor system diagram. 

Figure 2. Torque Seal applied to UH-1 helicopter. 

Green- Baseline 

Red-HAP free 
7

free and baseline Torque Seal formulations were subjected to vibrations and stresses sufficient to 

demonstrate their performance. This test is important to prevent the occurrence of false 

tampering incidents. 

3. Results and Discussion 

3.1 Rheology 

Both of the sealants tested are non-Newtonian shear thinning fluids, thus their viscosities change 

with shear rate. Typically, there is a Newtonian plateau at very low shear rates where viscosity 

is independent of shear rate before the commencement of shear thinning behavior. The power 

law region of the shear thinning curve has a viscosity as follows: 

 =  n–1, (2) 

where  is the viscosity,  is the flow consistency index,  is the shear rate, and n is the flow 

behavior index. The values of  and  were calculated and used to characterize each product 

formulation (table 2). The baseline product was more viscous than the HAP-free product, as 

seen in figure 3. Despite using a solvent trap to minimize skinning of the product at the edges of 

the rotating plate, this higher Newtonian viscosity may be a result of the higher volatility of 

methanol. However, the shear thinning behavior of both products was similar. 

Table 2. Rheology data for Torque Seal.

Torque Seal 

Product 

Newtonian 

Viscosity 

(Pa*s) 

Standard 

Deviation 

“” 

Flow 

Consistency 

Index 

“n” 

Flow 

Behavior 

Index R2 

Baseline 25,800 878 235 0.4687 0.9944 

HAP-free 11,587 208 37 0.3275 0.9989 

3.2 Nonvolatile Content (Solids) 

The average calculated solids by weight of the baseline (51%  0.53) and HAP-free Torque Seal 

(54%  0.46) were similar. The slight difference between the two products is attributed to the 

higher evaporation rate of methanol as compared to ethanol. It is possible that the HAP-free 

formula trapped some slower evaporating ethanol in the dried samples. According to the 

manufacturer of Torque Seal, the theoretical solids of this product are 50% by weight with the 

other 50% by weight composed of volatiles. These results are not unusual for commercial 

products where there are normal variations in manufacturing (including weighing errors) and 

packing operations. 
8

Figure 3. Torque Seal rheology. 

3.3 Thermogravimetric Analysis (TGA) 

The solids remaining after volatile evaporation (dry solids) were tested by TGA. The 

percentages of organic polymer binder and inorganic ash content represent the solid phase of the 

Torque Seal. Both sealants were relatively similar in organic and inorganic content (±3%). This 

is an acceptable variance and can be attributed to inconsistency of the manufacturing process of 

the product and experimental error in the laboratory analysis (table 3). 

Table 3. TGA (dry) calculated results.

Torque Seal 

Product 

Solids in 

Wet 

Product 

(%) 

Organic 

Binder in 

Solids 

(%) 

Inorganic 

Ash in 

Solids 

(%) 

Baseline 51 73 27 

HAP-free 54 76 24 

The temperatures at which thermal degradation occurs (indicated by sharp sample weight loss) 

can give some insight to the types of chemical bonds within those materials. Figure 4 illustrates 

the thermal degradation of the organic binder. The remaining weight fraction above 600 °C is 

inorganic ash, which is not subject to oxidative degradation at these temperatures. Materials that 

comprise the ash portion of a formulation potentially include inorganic pigments, clay 

thickeners, mica, and other mineral ingredients act as fillers and rheology modifiers.

100

1000

10000

100000

1.00E-04 1.00E-03 1.00E-02 1.00E-01

Shear Rate (1/s)

Viscosity (Pa*s)

Torque Seal Baseline 

Torque Seal HAP- Free 
9

Figure 4. Torque Seal TGA of dry solids.

The TGA derivative curve (figure 5) gives a better indication of decomposition temperatures. 

The peaks correspond to degradation temperatures of particular chemical bonds. Without 

running a more probative test to discern exact chemical composition, it is likely that the large 

peak above 500 °C is representative of the C-H bond degradation, the narrower peak between 

400 and 500 °C is most likely the C-C bond cleavage, and the broader peaks below 400 °C are 

most likely from the C-O bonds. The more important point is the baseline and HAP-free 

products have similar degradation profiles. This result was expected since the carrier solvent 

was the only different ingredient and the solid formula ingredients were presumed to be the 

same. 

Figure 5. Torque Seal TGA of dry derivative weight.

0

20

40

60

80

100

120

0 100 200 300 400 500 600 700 800

Temp (°C)

Weight (%)

Baseline

HAP free

0.00E+00

5.00E-02

1.00E-01

1.50E-01

2.00E-01

2.50E-01

3.00E-01

3.50E-01

0 100 200 300 400 500 600 700 800

Temp (°C)

Derivative wt. (%/°C)

Baseline

HAP free
10

3.4 Drying Time ASTM D 1640 

All the values in table 4 were recorded as a range of time as these tests are qualitative in nature. 

Drying time studies were performed at –11, 75, and 140 oF. In every leg of this test method, the 

drying time was slightly longer for the HAP-free sealant relative to the baseline. This result was 

expected because ethanol has a lower volatility than methanol. The difference in drying time 

was not noticeable by the user during application. 

Table 4. Drying time results for Torque Seal.

Test 

Temperature 

(°F) 

Baseline HAP-Free 

Skin on 

Bead 

(min) 

Tack-Free 

by Touch 

(min) 

Tack-Free 

by Cotton 

(min) 

Skin on 

Bead 

(min) 

Tack-Free 

by Touch 

(min) 

Tack-Free 

by Cotton 

(min) 

–11 27–29 37–39 38–40 33–35 70–72 71–73 

75 10–12 19–21 20–22 13–15 23–25 24–26 

140 5–7 6–8 8–10 7–9 9–11 10–12 

3.5 Adhesion Testing ASTM D 3359 

The green sample is the baseline Torque Seal containing HAPs, while the red sample is HAPfree (figure 6). Adhesion testing was conducted at three different temperatures to simulate 

various service conditions the sealant may encounter during use (–11, 75, and 140 °F). The 

HAP-free product performed similarly to the baseline product at all three temperature settings. 

Results for adhesion at –11 °F (figure 6) and 140 °F (not shown) had a rating of 4B, meaning 

small flakes of the coating are detached at intersections and less than 5% of the area is affected 

(4). Adhesion performance at 75 °F (not shown) had a rating of 5B, meaning the edges of the 

cuts are completely smooth and none of the squares of the lattice is detached. A rating of 5B is 

the best that could be given by ASTM D 3359. According to the test method, both 4B and 5B 

ratings are considered passing results. 

3.6 Resistance to Fluid Immersion MIL-PRF-85285D 

The films were examined 1 h after removal from the fluid for blistering, delamination, and 

discoloration. Both the baseline sealant (green) and the HAP-free sealant (red) showed a 

darkening of color after immersion for 24 h in lubricating oil at 121 °C (figure 7), while no 

blistering or delamination occurred. The darkened color observed below the immersion line was 

likely due to oil absorption into the film. Maximum color change appeared to occur in the first 

24 h of immersion and remained somewhat constant after that. However, both the baseline 

sealant and the HAP-free sealant showed no change after immersion for 24 h in hydraulic fluid at 

66 °C (not shown). Similarly, both the baseline sealant and the HAP-free sealant showed no 

change after immersion in JP-8 fuel at room temperature for 7 days (not shown). 
11

Figure 6. Cross-cut adhesion tape test at –11 °F. 

Figure 7. Immersion in lubricating oil at 121 °C for 24 h.

3.7 Adhesion Testing Conducted on Fluid Immersion Samples 

The HAP-free sealant (red) performed similarly to the baseline sealant (green) and had good 

ratings across the board. The adhesion rating after 24-h immersion in lubricating oil at 121 °C 

was 5B (not shown). Chemical or physical alterations from fluid immersion (oil absorption, 

component leaching, film softening, etc.) had no effect on adhesion of the sealants to the 

substrate. The adhesion rating after 24-h immersion in hydraulic fluid at 66 °C (not shown) and 

after 7 days in JP-8 fuel at room temperature was 4B (figure 8). Therefore, although immersion 

in these fluids caused no visible effects, it is apparent that immersion reduced adhesion to the 

substrate slightly vs. the portion of the film not immersed in fluid. 

Baseline 

Rating =4B 

HAP- Free 

Rating =4B 

Baseline 

Before Immersion 

Baseline 

After Immersion 

HAP Free 

Before Immersion 

HAP Free 

After Immersion 
12

Figure 8. Adhesion after 7-day immersion in JP-8 fuel at 

room temperature.

3.8 Differential Scanning Calorimetry (DSC) 

Torque Seal is designed to be brittle. A reduction in Tg would likely reduce the brittleness of this 

material, making it less susceptible to cracking and therefore a less effective inspection lacquer. 

A graph of heat flow (milliwatts) vs. temperature was obtained and an approximate Tg

temperature of 73 °F (figure 9) was determined for both the baseline and HAP-free product. 

Therefore, we can conclude that the replacement of methanol with ethanol had no effect on the 

ultimate Tg of this sealant. 

Figure 9. Torque Seal DSC.

-250

-200

-150

-100

0 20 40 60 80 100 120 140 160

Temperature (°C)

Heat Flow (mW/g)

Baseline

HAP-Free 

Midpoint of DSC glass 

transition range (Tg) 

72.2 - 73.8°C

Baseline- Adhesion 

Rating =4B 

HAP-free Adhesion 

Rating =4B 
13

3.9 Flexibility Testing 

Since Torque Seal is designed to crack when tampered with, this sealant breaks at low flexural 

stresses. Flexibility was tested at –11 °F, room temperature, and 140 °F. The conditioning 

temperature is an important factor in determining the time it takes for the sealants to cure. After 

44 days of conditioning at –11 °F, neither the baseline nor the HAP-free sealants showed any 

stress fractures on the mandrel bend test (not shown). This is likely due to incomplete 

evaporation of the solvents in the sealant at this low temperature. The solvent remaining in the 

applied film acts as a plasticizer and keeps the sealant flexible. Both room temperature samples 

showed stress fractures after 12 days of conditioning (not shown). Additionally, both the 

baseline and HAP-free samples showed stress fractures at the site of the bend after conditioning 

at 140 °F for 4 h (figure 10). The baseline and HAP-free products performed similarly to each 

other for all three temperature parameters. 

Figure 10. Torque Seal mandrel bend test at 140 °F.

3.10 Humidity Testing ASTM D 2247 

No delamination (the failure of the adhesive, either in the adhesive itself or at the interface 

between the adhesive and the adherend) or blistering (9) occurred on any of the panels. 

However, fading in color to a similar extent for both the baseline and HAP-free sealants was 

visible. The samples exposed for 1 day experienced a dramatic color fade. Continuing exposure 

for up to 4 weeks did not show a greater degree of color fading than the 1-day exposure 

(figure 11). Any uneven fading can be attributed to the position of the moisture spray nozzle 

inside the humidity cabinet. This phenomenon was verified by repositioning the various sample 

panels to duplicate the effect. It is apparent that the pigments used in both the baseline and 

HAP-free sealants were extracted by the condensate on the sealant surface. Note that the 

baseline and HAP-free formulations behaved the same under humidity testing. 
14

Figure 11. Color change after exposure to 100% humidity and 40 °C.

3.11 Accelerated Weathering ASTM C 732 

After 100 h of exposure, both the baseline and HAP-free samples faded considerably; thus, gloss 

was reduced from ~40 units to ~2 units at an observation angle of 60°. In addition to a reduction 

in gloss, figure 12 shows extensive chalking. Chalking is defined as the formation of powder, 

usually white in color, on the surface of a sealant caused by the disintegration of the polymer or 

binding medium due to weathering (9). After 500 h of exposure, the gloss and color remained 

the same as after 100 h; however, the samples cracked and delaminated from the substrate (figure 

12). Again, the HAP-free sample performed comparably to the baseline sample. 

Figure 12. Torque Seal QUV results after 500 h of 

exposure. 

HAP free 

After 1day of exposure 

Baseline 

After 2 weeks 

HAP free 

After 4 weeks 

Baseline HAP-Free
15

4. Field Trial on UH-1 Helicopter at Fort Rucker 

The HAP-free Torque Seal formulation and the commercially available (baseline) Torque Seal 

were applied side-by-side to a UH-1 helicopter (ID no. 0-16394) rotor system. The operator 

commented that there was no perceptible difference in ease of application (spreadability, 

viscosity, runniness, etc.) or drying time between the two sealants. The sealants were examined 

for delamination (peeling away from surface) and operation-induced cracking after 7, 14, 30, 60, 

and 90 days. Checklists (found in tables 3–11 of the demonstration/validation plan [11]) were 

used during these examination periods of the field trial to document and consistently 

communicate observations. Originally, the test duration was scheduled for 120 days, but the 

Fort Rucker team ended the demonstration at 90 days, maintaining that the HAP-free sealant was 

comparable to the baseline. The team at Fort Rucker made the following conclusions 

/recommendations upon completion of the field trial: 

In our opinion, the performance of the HAP-free formulations and current Torque 

Sealant are similar with respect to delaminating and cracking. Both sealants 

adhere to clean nongreasy surfaces longer than on greasy surfaces. As for 

cracking, both brands of sealants displayed similar characteristics, cracking 

slightly within 60 days then more over time as they aged, eventually maturing to a 

state of no additional cracks. In conclusion, when focusing on cracking and 

delamination, both the traditional and HAP-free torque sealant performed equally 

well with neither brand performing better than the other. We would recommend 

substitution of the HAP-free formulation, which contains 50% ethanol and 50% 

solids (eliminating methanol), as a viable alternative to assist in meeting 

NESHAP requirements while continuing to meet mission expectations. 

Table 5 shows a summary of the field test data as recorded by the UH-1 service technicians. If a 

bead was recorded as cracked or delaminated at the 30-day check, it was not counted again in the 

90- and 120-day checks. In other words, each check only recorded the new cracks or 

delamination since the previous inspection. However, if a bead was cracked at the 30-day check 

and delaminated (in part or whole) at the 90-day check, it would be recorded once for each 

occurrence. Figure 13 illustrates a partial delamination of the baseline sealant (green) located at 

the base of the nut/bolt assembly. Similar but more subtle is a partial delamination of the HAPfree sealant (red) also located at the base of the nut/bolt assembly. The higher number of cracked 

and delaminated sealant beads for the baseline sealant relative to the HAP-free sealant was likely 

due to the higher volatility of methanol, resulting in lower remaining solvent content within the 

solid bead. Although the total number of cracked and delaminated baseline beads was slightly 

higher than the number of HAP-free beads, the overall performance characteristics of the two 

sealants were qualitatively similar. The majority of the cracking and delamination occurred at 

the 60-day interval, at which point the sealants appeared to perform comparably.
16

Table 5. Fort Rucker summary of field trial results.

Inspection Time 

After Application 

Number of Cracked 

Sealant Beads 

Number of Delaminated 

Sealant Beads 

Baseline HAP-Free Baseline HAP-Free 

7 days 3 1 0 0 

14 days 2 2 0 0 

30 days 3 2 1 0 

60 days 24 13 16 13 

90 days 4 9 16 11 

Totals 36 27 33 24 

Figure 13. Torque Seal 60 days after application to a UH-1 helicopter.

5. Conclusions 

Laboratory testing indicated that the HAP-free Torque Seal using ethanol as the lone solvent 

performed similarly to the baseline product containing both methanol (HAP) and ethanol. 

Results were consistent across the complete test series. Testing showed little to no difference in 

rheology, drying time, adhesion, and weathering/exposure for the HAP-free sealant relative to 

the baseline product. Furthermore, a demonstration/validation study at Fort Rucker, AL, on a 

UH-1 helicopter showed that the HAP-free sealant performed suitably as a substitute material. 

Replacing the baseline Torque Seal with the HAP-free version will reduce HAP emissions at 

more than 20 installations across the Army. ARL and Fort Rucker recommended the 

replacement of the commercial baseline Torque Seal with the HAP-free version to assist in 

meeting NESHAP requirements and sustainability goals. 
17

6. References 

1. Yallaly, B.; Baughn, J. Final Performance Requirements Document Report; Concurrent 

Technologies Corp., Johnstown, PA, May 2007. 

2. Lide, D. R., Ed. CRC Handbook of Chemistry and Physics; 75th ed.; CRC Press: Boca 

Raton, FL, 1994. 

3. ASTM D 1640. Standard Test Methods for Drying, Curing, or Film Formation of Organic 

Coatings. Annu. Book ASTM Stand. 2003. 

4. ASTM D 3359. Standard Test Methods for Measuring Adhesion by Tape Test. Annu. Book 

ASTM Stand. 2002. 

5. MIL-PRF-85285D. Coating: Polyurethane, Aircraft and Support Equipment; Section 4.6.8, 

Resistance to Fluid Immersion; 2007. 

6. ASTM D 1308. Standard Test Method for Effect of Household Chemicals on Clear and 

Pigmented Organic Finishes. Annu. Book ASTM Stand. 2002. 

7. ASTM D 2247. Standard Practice for Testing Water Resistance of Coatings in 100% 

Relative Humidity. Annu. Book ASTM Stand. 2002. 

8. ASTM C 732. Standard Test Method for Aging Effects of Artificial Weathering on Latex 

Sealants. Annu. Book ASTM Stand. 2006. 

9. ASTM D 907. Standard Terminology of Adhesives. Annu. Book ASTM Stand. 2005. 

10. ASTM C 717. Standard Terminology of Building Seals and Sealants. Annu. Book ASTM 

Stand. 2007. 

11. La Scala, J. J. Torque Seal Demonstration/Validation Plan for the SPOTA Program; U.S. 

Army Research Laboratory: Aberdeen Proving Ground, MD, 2008. 
18

List of Symbols, Abbreviations, and Acronyms 

ARL U.S. Army Research Laboratory 

ASTM American Society for Testing and Materials 

EPA Environmental Protection Agency 

Eta ()-viscosity 

Gamma ()-shear rate 

HAP Hazardous air pollutant 

Kappa ()-flow consistency index 

mW Milliwatt 

n Flow behavior index 

NDCEE National Defense Center for Energy and Environment 

NESHAP National Emission Standard for Hazardous Air Pollutants 

Pa*s Pascal second 

R2

 Coefficient of determination 

SPOTA Sustainable Painting Operations for the Total Army 

Tg Glass transition temperature 
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