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Hanson et al.: Removing Hydraulic Fluid From Composites

The traditional method of removing hydraulic fluid con-tamination from composite materials involves packing the contaminated area with breather cloth and heating it to an el-evated temperature under vacuum [3]; however, this method is costly and time consuming. A more cost-effective method of removing hydraulic fluid contamination uses methyl iso-butyl ketone (MIBK) [4, 5]. However, MIBK is not very ef-fective at removing hydraulic fluid from composite materials; it is used only because it does not pose a threat to workers. Hexane, on the other hand, has been found to be very effec-tive at removing hydraulic fluid. The problem with using it, though, is that it is a hazardous chemical and must be used in a controlled environment to prevent prolonged exposure to workers. When aircraft are deployed, there is a limited number of controlled environments where this process can be performed.

To solve this problem, a previous NAVAIR effort investi-gated several solvents and recommended further research [6]. As a result of the effort, though, Hypersolve (n-propyl bro-mide) was approved for use as an alternative to the hazard-ous air pollutant (HAP)-based products traditionally used. n-propyl bromide is an effective cleaner, but it has strong odor and safety concerns. To validate the use of n-propyl bromide for cleaning application, the Environmental Protection Agency is currently investigating the toxicity of n-propyl bromide to ensure worker safety and cleaner environment. Further work yielded no fruitful alternatives as replacements for the current materials and processes in use [7, 8].

This study focused on optimizing/blending aliphatic and aromatic solvents, which are HAP free, to form effective cleaners that are capable of removing hydraulic fluid from composite materials effectively and safely. This effort will lead to increased understanding of the physical and chemical properties of cleaning solvents that are capable of decontami-nating composite materials safely and effectively. The results of this effort will benefit the Naval Aviation Enterprise by providing a more efficient, cost-effective, and environmen-tally acceptable means to clean hydraulic fluid from critical composite weapons system components. The cost savings will be realized through reduced maintenance costs, compli-ance with environmental regulations, and enhanced mission readiness.

Experiment

Solvent SelectionAlthough other operational fluids intrude into composite

skin and honeycomb-based structures on aircraft, hydrau-lic fluid was deemed to be the most significant in affecting the bond line in bonded repairs and the most persistent in the maintenance environment. Specifically, usage of MIL-PRF-83282 [9] hydraulic fluid was identified as more wide-spread than other products according to specifications. To address the removal of hydraulic fluid from a polarity and solvency standpoint, a consideration of the constituents of the fluid was made. Table 1 lists the composition of a

TABLE 1. Description of the components of MIL-PRF-83282 [9] hydraulic fluid.

Component Description/Polarity

Poly-alpha-olefin Synthetic hydrocarbon/NPDiisooctyl adipate Synthetic ester/PTricresyl phosphate Phosphate ester antiwear additive/PEthanox 4702 Phenolic antioxidant/PBenzotriazole Corrosion inhibitor/POil Red 235 Oil-soluble red dye

Note. NP = nonpolar, P = polar.

representative hydraulic fluid qualified to MIL-PRF-83282 and includes a description and polarity of the components. Because the hydraulic fluid to be removed consists of both polar and nonpolar compounds, a single solvent system is un-likely to effectively remove all of the components in the hy-draulic fluid. For that reason, a mixture of solvents, or a sol-vent blend, will be used to complete the decontamination. As a measure of solvency, the Kauri-butanol (Kb) values of the pure solvents were first considered before the down-select.

To formulate an effective and environmentally friend-ly cleaner, the properties of the optimized cleaner must be defined. The formulated cleaner must have the following properties: HAP-free and low odor; low vapor pressure; free of ozone-depleting substances (ODS); flash point >140°F (60°C); compatible with metals and nonmetals; high cleaning efficiency; and safe to use. Based on these criteria, the initial candidates for use in the solvent blend were identified. Table 2 lists the control materials; the initial materials considered for this study; and the final, optimum formulation (4.2), along with the properties considered. It should be noted that all of the solvents considered are HAP-free and ODS-free, and the last five are exempt from volatile organic compounds (VOC exempt).

Cleaning EfficiencyThe neat and formulated solvents were screened to be

able to meet several initial criteria before being subjected to the more intensive material compatibility testing. These ini-tial criteria were prioritized because they pertain to ensuring the suitability of the cleaner and its ability to effectively and efficiently decontaminate the surface. The selected solvents and formulations for testing and evaluation, which include control solvents (hexane and MIBK), solvent ingredients (base series), and formulation blends (form series), are listed in Table 3.

The IM7/977-3 structural composite system was chosen for this study because it is the main aerospace-grade compos-ite material that is used in both primary and secondary struc-tures on several naval aircraft such as the F/A-18 and F-35. IM7/977-3 is composed of graphite fiber reinforcements (IM7) in a toughened epoxy-based polymer matrix (977-3). Composite laminates were fabricated by hand lay-up from IM7/977-3 unidirectional prepreg material supplied by Cytec

NAVAIR Journal for Scientists and Engineers 2 Vol. 1 Issue 1


TABLE 2. List of the base solvent candidates and their physical properties.

Flash point Vapor pressure Material Description Kb value (°F) (at 68°F, mm Hg) Odor

Hexane (control) NH 31 –15 132 StrongMIBK (control) POH * 57 15 SweetIsopar Ga NH 27 111 1 LightIsopar Ha NH 26 129 0.5 LightIsopar Ka NH 27 133 0.5 LightIsopar La NH 27 144 0.3 Very lightIsopar Ma NH 27 203 0.1 Very lightExxsol D40a NH 32 104 2.03 Mild solventExxsol D60a NH 31 143 0.45 Mild solventExxsol D80a NH 26 171 0.17 Mild solventExxsol D95a NH 26 205 0.07 Mild solventExxsol D110a NH 26 221 0.02 Mild solventd-Limonene NH 63 118 3 CitrusMethyl lactate POH * 124 2.7 ModerateEthylhexyl lactate POH * 235 * *Dibasic ester POH * 212 0.2 *Methyl soyate POH 58 218 2 MildDipropylene glycol n-Butyl ether POH * 212 0.06 *Propylene glycol n-Butyl ether POH * 145 0.85 *HFE-7100b FH 10 None 202 SlightHFE-7200b FH 10 None 109 FaintVertrel XFc FH 10 None 186 SlightDC-245d MS * 171 0.11 OdorlessDC-246d MS * 199 * OdorlessFormulation 4.2 Blend 27e 141f 0.4g *

Note. NH = nonpolar hydrocarbon, POH = polar oxygenated hydrocarbon, FH = fluorinated hydrocarbon, MS = methyl siloxane. aExxonMobil, b3M Novec, cDuPont, dDow Corning, eVerified by American Society for Testing and Materials (ASTM) D1133, fVeri-fied by ASTM D93, gCalculated from components. *Data unavailable.

Engineered Materials, Inc. The panels were fabricated with a 16-ply quasi-isotropic (0, ±45, 90, 90, ±45, 0)s lay-up. The autoclave cure cycle recommended by the manufacturer was used to process the panels. After autoclave cure, the panels were ultrasonically inspected to ensure their quality. Ultra-sonic testing was performed using a TechTrend International laboratory scanner and Arius II software. Scanning of the samples was performed using a 10db gain level and a 5MHz concave transducer with a 2in. focal length. Index and scan increments were 0.05in. at a rate of 6in./s.

To measure the effectiveness of the developed formula-tions, three cleaning techniques were used for removing hy-draulic fluid from composite materials, as described in the following sections.

Method 1: Gravimetric immersion cleaning. Previous experience investigating a test method to measure the cleaning efficiency of low-VOC and VOC-exempt solvents to remove soils from stainless steel panels led to the inclusion of a sol-vent immersion test method in the MIL-PRF-32295A speci-fication [10]. Using this method, polished stainless steel cou-pons (1in. wide × 2in. long × 0.05in. thick) are weighed, are coated on one side with 20–25mg of soil, and are reweighed. Stained coupons are cyclically immersed and withdrawn from a 150ml beaker containing 100ml of the solvent at a rate of 20 cycles per min for 5min. To prevent excess soil from be-

ing removed by gravity, the coupons are flash-dried at 140°F (60°C) for 5min. The coupons are then cooled to room tem-perature and are reweighed. Cleaning efficiency is determined gravimetrically as an average of three coupons in the same soil. The soil was simulated by mixing 10% by weight carbon black into MIL-PRF-83282 hydraulic fluid. This method is preferred because it produces reproducible results and allows a number of samples to be averaged to determine cleaning efficiency. Method 1 cleaning efficiency results are presented in Table 4.

Method 2: Wipe (swab) cleaning. The wipe (swab) cleaning procedure for removing hydraulic fluid from com-posite materials was developed by Tillman and Boswell in a previous study [6]. Cleaning efficiency was evaluated based on the number of cotton swab wipe cycles needed to remove the entirety of the fluid contamination from the composite surface. In this method, 6in. wide × 2in. long × 0.037in. thick panels of IM7/977-3 are immersed in a beaker contain-ing MIL-PRF-83282 hydraulic fluid for 2 weeks. Panels are removed, are lightly wiped with Tech Wipe tissues, and are hang-dried to the perpendicular for 24hr at ambient tempera-ture. Upon verification of hydraulic fluid presence by visual inspection, the panels are cleaned by depositing 0.3ml of sol-vent onto a cotton swab, cleaning a 1in. × 1in. area of the contaminated composite by wiping six times in one direction, and wringing the swab out into a glass vial. The surface is



TABLE 3. Selected solvents and blended formulations that were tested and evaluated.

Solvent Flash Point (°F)

Hydraulic fluid 401 Hexane –15 MIBK 57 Base 2 N/A Form 2.1 N/A Base 3 N/A Form 3.1 N/A Form 4.1 N/A Form 4.2 141

wiped, and the residue is deposited into the vial twice more. Three wipes with the same swab constitute one wash cycle. The solvent that is wrung-out from the swab is deposited onto a potassium bromide salt plate and is dried at 104°F (40°C) at 2psi for 15min. The salt disc is analyzed via infrared spec-troscopy to indicate the presence of the hydraulic fluid resi-due on the surface. Additional cleaning cycles are performed until the infrared spectra show no hydraulic fluid presence.

Fourier Transform Infrared Spectroscopy (FT-IR) is the analytical tool of choice to detect trace residual hydraulic fluid. A Nicolet model 550 Magna FT-IR spectrometer was used with data collection by transmission through the sample that was deposited on the potassium bromide disc. All FT-IR background and sample spectra were collected using 32 scans with a spectral resolution of 2 cm–1. Figure 1 shows the spec-tra for the contaminant hydraulic fluid (top) and a representa-tive hydrocarbon solvent. The absorption at 1710–1740 cm–1 range was identified as a differentiator between contaminant and solvent; this peak corresponds to the carbonyl-stretching vibration from the dibasic ester in the MIL-PRF-83282 hy-draulic fluid. Figure 2 shows the decrease in peak height for successive cleaning cycles. This cleaning method is preferred because it is a better representation of the actual decontami-nation scenario, being fluid removal from composite material as opposed to stainless steel. Method 2 cleaning efficiency results are presented in Table 5.

Method 3: Composite immersion cleaning. In order to incorporate the benefits of the two existing test methods, the MIL-PRF-32295A cleaning efficiency procedure was modi-fied to use IM7/977-3 composite panels. Other than the panel material, the only difference between this procedure and the MIL-PRF-32295A procedure is that the panels were dried at 248°F (120°C) and were cooled to ambient immediately before using to ensure that all adsorbed moisture had been driven off. Method 3 cleaning efficiency results are presented in Table 6.

Flash PointTo give indication that the flash points of developed

solvents exceeded the National Fire Protection Agency (NFPA) 30 Class III lower limit of 140°F (60 °C), testing was completed using American Society for Testing and Ma-terials (ASTM) D93 [11] using Procedure B and a manual

TABLE 4. Results of Method 1 gravimetric immersion clean-ing using the various solvents.

Solvent CE (%) SD

Hexane 92.2 1.8 MIBK 98.7 0.4 Base 1 97.5 0.4 Base 2 94.4 0.8 Form 2.1 94.2 0.8 Form 2.2 93.4 0.6 Base 3 95.9 0.3 Form 3.1 98.1 0.4 Form 3.2 95.8 0.7 Form 4.1 96.7 0.5 Form 4.2 96.2 0.5 Form 4.3 95.3 0.5

Note. CE = cleaning efficiency.

apparatus. The flash point for the optimized cleaner (formula-tion 4.2) was measured in accordance with the ASTM D93 method and was found to be 141°F.

Drying TimeDrying times for selected solvents were measured in ac-

cordance with the MIL-PRF-32295A specification. One gram of solvent was placed in an aluminum weighing dish of 2in. (5cm) diameter and 0.6in. (1.5cm) depth and was heated in an oven at 120°F (49°C) in 10min increments. After each increment, the dish was removed from the oven, cooled to ambient, weighed, and re-placed in the oven. This procedure continued until the weight of the dish returned to its original weight, indicating that the solvent had dried off completely. Results for the drying time study are presented in Table 7.

Residual Surface ContaminantsTape peel adhesion testing. Tape peel adhesion tests were

performed in accordance with ASTM D3330M-02 Method A [12] to determine if the new solvent formulations deposited any residual surface contaminates on the composite laminates after cleaning, which might degrade bond strength. The per-formances of the new solvent formulations were compared to several currently used solvents (see Table 3). Both unexposed and hydraulic fluid-saturated composite specimens were also tested as baseline controls. IM7/977-3 composite specimens were immersed in the cleaning fluids under test for 1 week at room temperature, removed, and dry-wiped once. Coastline Flash breaker 5R tape, consisting of polyester carrier with a 0.007in. thick rubber-based adhesive, was applied to the sur-face and was pressure-adhered by five back-and-forth passes using a 5lb roller. This tape was chosen because it does not stretch or rip during removal. An alternate peel region width of 2in. was chosen to survey a larger peel area to decrease edge effects while increasing the probability of recording ad-hesion fluctuations caused by surface contamination. The tape was gripped on one side with a 100lb load cell having a cross-head travel of 0.001in. and frame resolution of ~0.05–0.1%



FIGURE 1. Infrared spectra for MIL-PRF-83282 hydraulic fluid (top, in red) and standard hydrocarbon solvent (bottom, in pink) showing the spectral differences in the 1710–1740 cm–1 carbonyl stretch vibration region.

of the load cell. To improve confidence in the results, five specimens were tested per condition. Test parameters were maintained along with data/channel acquisition (20Hz) by us-ing MTS TestWorks 4 control software. The average results of these studies for each solvent are provided in Table 8.

Compression lap shear (CLS) testing. The preliminary peel adhesion evaluations that were performed used adhe-sive-backed tape that was applied at room temperature. For many aircraft in-service composite bonded repairs, though, an elevated temperature adhesive cure step is required. To evaluate if any solvent residual might potentially degrade the bond line between the adhesive and composite surface dur-ing the elevated temperature cure step, CLS tests were per-formed on adhesively bonded composite laminate specimens. For the CLS evaluations, only the Form 4.2 solvent formula-tion was used. All IM7/977-3 laminates used to fabricate the CLS specimens were first dried per ASTM D5229 Procedure D [13]. To prepare the test specimens, one set of IM7/977-3 composite panels (4in. × 4in., 16-ply, quasi-isotropic lay-up) was first soaked (i.e., cleaned) in Form 4.2 solvent for 1hr followed by air drying. One surface of two of the soaked pan-els and two baseline, uncleaned panels were lightly sanded using 200-grit sandpaper. This sanded set of CLS-bonded composite test specimens was prepared following standard

Navy procedure to lightly sand a composite surface before applying an adhesive to ensure removal of any residual con-tamination. Past in-service bonded repair experience has traced the residual contamination to a specific solvent wipe step and, for certain solvent residuals, a portion can still re-main even after the sanding step.

A pair of panels from the complete set of IM7/977-3 composite panels (i.e., cleaned/sanded, cleaned/unsanded, no cleaning/sanded, no cleaning/unsanded) next were bonded together with Henkel EA 9394 adhesive. EA 9394 is a Navy- qualified adhesive system that is used in composite-bonded repair. Scrim cloth (Reemay polyester scrim, 0.005in. thick) was used to produce a uniform bond thickness between the laminates. The bonded laminates were vacuum bag cured at 135°F for 60min followed by a post cure at 200°F for 60min. CLS specimens were next machined from the bonded panels in accordance with ASTM D3846 [14]. The specimen dimen-sion was 3in. long × 0.5in. wide, with a lap width of 0.25in. CLS tests were performed following ASTM D3846. Five specimens were tested per test condition.

Material CompatibilityPreliminary flexural strength and short beam shear (SBS)

tests were performed on IM7/977-3 specimens that were



FIGURE 2. Infrared spectra for the residue remaining after the first (top, in red), second (middle, in pink), and third (bottom, in blue) cleaning cycles for one of the solvents (swab method).

TABLE 5. Results of Method 2 wipe cleaning testing.

Solvent Trials

Hexane 3 MIBK 5 Base 2 3 Form 2.1 3 Base 3 3 Form 3.1 3 Form 4.1 2 Form 4.2 2

exposed to the new solvent formulations to demonstrate that the mixtures do not degrade the mechanical properties of this specific composite material system. The flexural strength test was chosen because it is sensitive to surface ply degradation. The 3-point bending moment during the test induces large in-plane compressive and tensile loads in the outer surfaces of the specimen. As such, the test is sensitive to any surface-localized mechanical property knockdowns that are induced by the composite’s exposure to hydraulic fluid or cleaners. The SBS test was chosen because it is a simple method for evaluating resin-dominated, bulk property knockdowns in a composite laminate.

Flexural strength testing. The flexural strength properties of IM7/977-3 composite after exposure to the new solvent for-mulations were determined in accordance with ASTM D790 [15]. The solvent formulations evaluated are listed in Table 3. The composite test specimens were first conditioned by soak-ing them in MIL-PRF-83282 hydraulic fluid for 1-week and 3-week periods, followed by exposure to the test solvents for 1hr. A solvent soak of 1hr was chosen as the maximum ex-posure time the composite would encounter in the field. This

TABLE 6. Results of Method 3 composite immersion testing.

Solvent CE (%) SD

Hexane 94.8 0.3 MIBK 97.1 0.3 Base 2 96.9 0.2 Form 2.1 97.1 0.3 Base 3 99.1 0.1 Form 3.1 99.1 0.3 Form 4.1 98.9 0.1 Form 4.2 99.5 0.3

time was chosen because the next step in the cleaning step is vacuum bagging and application of heat, which will remove any residual solvent that is trapped in the composite. Five specimens at each condition were run for ASTM D790.

SBS strength testing. The SBS properties of IM7/977-3 composite after exposure to the new solvent formulations were determined in accordance with ASTM D2344 [16]. The composite test specimens were conditioned the same as de-scribed in the previous paragraph. Ten SBS specimens were tested for each exposure condition.

Results and Discussion

Cleaning EfficiencyMethod 1: Gravimetric immersion cleaning. The results

of the gravimetric immersion cleaning method for the selected solvents and developed formulations are listed in Table 4. The data show the disparity between the two control solvents, as hexane underperformed all of the tested materials and MIBK outperformed all of them. The strong performances of several



TABLE 7. Results of drying time testing.

Solvent # of dry cyclesa

Hexane 1 MIBK 1 Base 2 3 Form 2.1 4 Base 3 5 Form 3.1 5 Form 4.1 4 Form 4.2 4aA dry cycle is defined as the number of 10min heating cycles at 120°F (49°C) required to evaporate all solvent from the tray.

base and formulated solvents were noted, particularly Bases 1, 2, and 3 and Formulations 2.1, 3.1, 4.1, and 4.2. All of the formulated solvents were verified to have flash points >140°F (60°C).

Method 2: Wipe cleaning (swab). After completion of Method 1, the high cleaning efficiencies of six base solvents and formulations were evaluated along with the controls us-ing the wipe (swab) cleaning method. The Base 1 solution was excluded due to its low flash point. The results of Meth-od 2 cleaning are shown in Table 5. Surprisingly, the results for the two controls are inverted relative to Cleaning Method 1, as hexane displayed strong solvency for the fluid on the composite surface. All formulated solvents showed equal or better efficiency than the controls, with two particular formu-lations, Form 4.1 and 4.2, performing the best, requiring only two trials to see complete removal of the contaminant.

Method 3: Composite immersion cleaning. The results of the third test method, incorporating the benefits of the first two methods by measuring soil removed from a composite panel gravimetrically, are shown in Table 6. The data indicate less differentiation between the solvents using this method, with the overall results clustered around full removal of the applied soil. As seen with Cleaning Methods 1 and 2, several formulations outperformed the controls, specifically Base 3 and Forms 3.1, 4.1, and 4.2.

Drying TimeThe results for the drying time study are presented in

Table 7. None of the base solvents or formulations was able to dry nearly as fast as the two controls. This is not surpris-ing given the vapor pressure differences between the controls (15mmHg for MIBK, 132mmHg for hexane) and the solvents under consideration, which were generally <3mmHg for the solvents with the greater solvency (Kauri-butanol value).

Residual Surface ContaminantsTape peel adhesion tests results. The results for the peel

tests are presented in Table 8. As expected, the peel strength of the sample that was exposed to hydraulic fluid had the lowest value compared to the other test conditions. An average value of only 2.50lb ft/in. was measured for the hydraulic fluid sam-ple versus 9.74 to 10.68lb ft/in. for specimens that were wiped

TABLE 8. Results of peel strength testing after condition exposure.

Condition Peel strength (lb ft/in.) SD

No Exposure 10.62 0.77 Hydraulic Fluid 2.50 0.42 Hexane 10.01 0.78 MIBK 11.38 0.19 Base 2 9.74 0.61 Form 2.1 10.04 0.68 Base 3 10.19 0.40 Form 3.1 9.89 0.49 Form 4.1 10.68 0.33 Form 4.2 10.48 0.42

with the solvents. Based on the encouraging peel strength esult, the most promising solvent formulations were down-elected for further testing to Form 3.1, 4.1, and 4.2. Although orm 2.1 had a greater peel strength measured than Form 3.1,

he former had a lower cleaning efficiency than the latter. CLS results. The preliminary CLS test results are shown

n Table 9. Compared to the baseline IM7/977-3 panels which were not cleaned with Form 4.2), the cleaned pan-ls showed significantly higher shear strengths. This was the ase even for the unsanded sample compared to the baseline anded specimen. The results indicate that Form 4.2 not only eft no contamination residuals that would degrade the bond ine, but it also increased the bond strength and decreased the easurement scatter compared to the controls. Further CLS

valuations are planned for the second phase of the project hen the specific bonded patch repair materials and process ill be evaluated.

aterial CompatibilityFlexural strength testing. The results for the flexural

trength tests are shown in Table 10. Based on the variance n the test data, the overall results indicate no reduction in the exural strength properties of the IM7/977-3 specimen that as soaked in hydraulic fluid, followed by the solvent soak. lthough several conditions show higher flexural strengths

or samples that were exposed to hydraulic fluid for 1 week compared to no exposures and 2-week exposures), the stan-ard deviations are high. Given the small statistical sample et (i.e., five specimens per test condition), the statistical ignificance of both sets of numbers is most likely near iden-ical, meaning that if two bell curves were generated for the ets of data, the curves would overlap.

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TABLE 9. Results of compression lap shear testing.

Condition Bond strength (psi) SD

Unsanded Sanded Unsanded, cleaned Sanded, cleaned

6580 6980 7467 7515

300370

8373



TABLE 10. Results of flexural strength testing.

Soak time

No solvent Hexane MIBK Form 3.1 Form 4.1 Form 4.2

ksi SD ksi SD ksi SD ksi SD ksi SD ksi SD

None 1 week 3 weeks

132.4 142.2 135.2

9.1 5.6 6.5

136.7 143.4 136.5

7.9 7.4 6.7

137.6 142.6 139.7

9.3 4.0 5.8

137.1 138.1 133.0

5.3 11.7 7.0

138.4 141.7 138.9

6.5 3.9 3.8

138.2 137.4 136.8

6.15.18.4

Note. ksi = thousands of pounds per square inch.

SBS strength testing. The results for the SBS tests are shown in Table 11. As for the previous flexural tests, based on the variance in the data, the overall results indicate no reduction in the SBS strength properties of the IM7/977-3 specimen that was soaked in hydraulic fluid, followed by the solvent soak. This result is not surprising as the test measures the bulk resin properties (not surface) of the laminate with the failure mode in the mid-plane of the specimen. As such, it is unlikely that any surface degradation of the composite caused by the solvent formulation would be detected.

ConclusionThis effort was focused on developing an effective, safe,

and environmentally friendly nonaqueous solvent cleaner to remove hydraulic fluid from composite materials. Sev-eral formulations were developed from selected aliphatic, aromatic, oxygenated, fluorinated, and silanated solvents to meet the established properties and usage requirements of a “green” cleaning solution. These properties include the fol-lowing: HAP-free, ODS-free, noncarcinogenic, high solven-cy, high flash point, low vapor pressure, and compatibility with metals and nonmetals. Using multiple techniques, the cleaning efficiency of the optimized formulation (Form 4.2) was measured and was found to be more effective than the control solvents (hexane and MIBK) that are currently autho-rized for use in the Navy maintenance depots.

The effects of nonvolatile residue on both room and el-evated temperature composite-adhesive bonding were evalu-ated by the adhesive peel and CLS tests. These preliminary results on the IM7/977-3 composite system indicate that the lab formulations leave no contamination residue on the com-posite surface to degrade peel and lap shear strengths. This indicates that, although the formulated solvent dries slower than the two solvents currently in use, it does not present a contamination issue at the bond line.

The fluid sensitivity of the down-selected Form 4.2 on M7/977-3 mechanical properties was also evaluated. Pre-iminary flexural strength and SBS tests on IM7/977-3 speci-ens exposed to Form 4.2 found no knockdown in these

roperties. Further studies are underway to show that the ew formulation causes no degradation to the bond lines in onded composite skin/honeycomb structures using flat-wise ension and CLS measurements. These skin/honeycomb ele-ents are more representative of the final composite struc-

ures found on Naval aircraft. Future use of the optimized cleaner will permit com-

liance with current environmental regulations on cleaning olvents and will provide a user-friendly and more efficient leaning solution for removal of hydraulic fluid contamina-ion from composites. In addition, as the cost to replace a omposite part is 10 times the cost to repair a composite part, he ability to more efficiently remove hydraulic fluid from hese components and thus lower the bonded repair scrap rate ould have a significant impact on Navy sustainment costs.

AcknowledgmentThe authors wish to acknowledge with appreciation the

financial support of the Naval Innovative Science and Engi-neering Program/Section 219 to this effort.

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[2] National Transportation Safety Board, “NTSB urges inspec-tions of certain Airbus A300 rudders,” NTSB, Washington, DC, Safety Recommendation Letters, A-06-27, A-06-28, Mar. 24, 2006.

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TABLE 11. Results of short beam shear strength testing.

Soak time

No solvent Hexane MIBK Form 3.1 Form 4.1 Form 4.2

ksi SD ksi SD ksi SD ksi SD ksi SD ksi SD

None 1 week 3 weeks

7.7 7.3 7.8

0.9 0.7 0.8

8.3 7.6 7.3

1.1 0.6 0.5

7.3 7.8 7.6

0.5 0.7 0.5

7.4 7.1 7.2

0.4 0.3 0.4

7.6 7.8 7.5

0.3 0.7 0.5

7.7 7.5 7.2

0.80.40.3



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[14] ASTM International, “Standard test method for in-plane shear strength of reinforced plastics,” ASTM International, West Conshohocken, PA, ASTM D3846, 2008.

[14] ASTM International, “Standard test methods for flexural prop-erties of unreinforced and reinforced plastics and electrical in-sulating materials,” ASTM International, West Conshohocken, PA, ASTM D790, 2010.

[15] ASTM International, “Standard test method for short-beam strength of polymer matrix composite materials and their lami-nates,” ASTM International, West Conshohocken, PA, ASTM D2344, 2006.

Dane Hanson is a chemist in the Industrial and Operational Chemicals Branch (AIR-4.3.4.2) of the Materials Engineering Di-vision at the Naval Air Warfare Center Aircraft Division (NAW-CAD), Patuxent River, MD. He holds a BS in chemistry from the University of Maryland, Baltimore County, and is currently pursuing an MS in systems engineering from Johns Hopkins University. He has authored and presented

papers at several technical conferences. His main focus is on identifying safe, effective alternatives to highly volatile organic compound cleaners, hazardous air pollutant paint removers, and chromated bond primers for use on Navy aircraft. E-mail: dane.hanson @navy.mil

Dr. El Sayed Arafat is a chemist in the Industrial and Operational Chemicals Branch (AIR-4.3.4.2) of the Materials Engineering Divi-sion at NAWCAD, Patuxent River, MD. He holds a PhD in chemistry from the University of Mississippi. He has published more than 25 articles in professional journals and has six patents. He has a broad background in several re-search areas, such as solvents, cleaners, and corrosion-preven-

tive compounds. Dr. Arafat has received several national awards. E-mail: [email protected]

Dr. Raymond Meilunas is a senior engineer in the Polymers and Components Branch (AIR-4.3.4.2) of the Materials Engi-neering Division at NAWCAD, Patuxent River, MD. He holds a PhD and BS in materials science and engineering from Northwest-ern University and the Massa-chusetts Institute of Technology (MIT), respectively. Research in-terests include polymer and com-posites materials and processes,

nanocomposites, carbon nanotubes, high-performance computing-based computational materials and process analysis, composite repair, and long-term composite dura-bility prediction. E-mail: [email protected]

Zachary Olshenske is an aerospace engineer supporting the Polymers and Components Branch (AIR-4.3.4.2) of the Ma-terials Engineering Division at NAWCAD, Patuxent River, MD. He holds a BS in aerospace engi-neering from Pennsylvania State University. His areas of technical focus include composite struc-tural repair, materials processing, prototyping, composite materi-als testing, development of ad-

vanced nondestructive inspection techniques, and support of various aircraft sustainment programs. E-mail: [email protected]


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