Patent Application
20060280808
This invention relates to compositions and to a process for using said compositions for removing and preventing mildew, mold and fungal growth on various surfaces. In many geographical regions, the unwanted growth of mold and mildew is a serious problem. The rapid growth of mold and mildew on metal surface is a serious problem in humid geographical areas. Mildew growth on the interior of aircraft surfaces, and particularly aircraft operated in humid climates is even more of a serious problem. The buildup of mildew causes corrosion and operational damage to the aircraft in addition to creating potential health hazards to flight crews and maintenance personnel. Present methods of removing mold and mildew are time consuming and inadequate and have caused corrosion when applied to metal substrates such as aircraft interior surfaces and the like.
This invention relates to compositions and to the process of using the compositions for removing and preventing mold, mildew and fungal growth on various surfaces. The composition comprises an aqueous solution having a pH ranging from 7.0 to 10 and contains from about 0.1 to 3.0 percent by weight of at least one alkali metal perborate, from about 0.05 to 5.0 percent by weight of one or more inhibiting compound selected from the group consisting of alkali metal silicates, triazoles such as benzotriazole and mixtures of said silicates and triazoles in any ratio. In addition, the aqueous solutions contain from about 0.0 to 3.0 percent by weight of at least one water soluble corrosion inhibitor selected from the group consisting of benzimidazoles, benzazoles and benzoxazoles, and from about 0.0 to 5.0 percent by weight of at least one water soluble surfactant.
Therefore, it is an object of this invention to provide an effective, noncorrosive mildew inhibitor and remover for aircraft application.
It is another object of this invention to provide an effective noncorrosive mildew inhibitor and remover having performance characteristics required by standard tests in military specifications.
It is another object of this invention to provide an effective noncorrosive mildew inhibitor and remover capable of passing the sandwich corrosion and the immersion corrosion test.
These and other objects of this invention will become apparent by reference to the detailed description when considered in conjunction with the accompanying
More specifically, maintenance procedures to remove mold, mildew growth and mildew staining from aircraft parts have historically required many man-hours. In addition, previously approved materials were often inadequate. The use of unauthorized cleaning solutions, such as household chlorine bleach (sodium hypochlorite), can induce corrosion damage to critical metallic surfaces. In addition, chlorine bleach causes environmental concerns. Results of fungal degradation studies of polymeric materials used in Navy aircraft showed that the approved military cleaning procedure, based on isopropyl alcohol, was ineffective; see: B. Little, R. Ray and J. Lee, “An Overview of Microbiologically Influenced Corrosion In Aircraft”, Naval Research Laboratory, Stennis Space Center, Technical Report No. A709314, (1997), and D. Lavoie, B. Little, R. Ray, K. Hart, P. Wagner, “Microfungal degradation of Polyurethane Paint and Corrosion of Aluminum Alloys in Military Helicopters,” in the Corrosion Proceeding, of the National Association of Corrosion Engineers, International Corrosion/97, paper No. 218, Houston, Tex., (1997). Environmental Scanning Electron Microscopy (ESEM) micrographs indicated that surface cleaning only removes spores from the ends of the mildew hyphae, but fragments of the hyphae remained and re-grow as soon as conditions are favorable. Even through interior surfaces appear clean, they are still contaminated with fungi. In addition, fungi appear to be able to use certain operational fluids, such as hydraulic fluid (MIL-PRF-83282) and corrosion preventive compounds (CPCs) as nutrients.
A study of fungal contamination on the interior surface of H-46 and H-53 rotary-wing aircraft at Naval Air Depot, Cherry Point, N.C., isolated eight genera of microfungi; see: Lavoie, M. D., Little, B. J., “Fungal Contamination of H-53 Aircraft”, Naval Research Laboratory, Stennis Space Center, Technical Report NRL/1MRI/7333-96-7725, (1996). The study indicated that some corrosion on unprotected aluminum surface can be attributed to bacterial and fungal growth. One of the isolated fungi (Aureobasidium) from the H-53 is known to cause superficial discoloration on latex paint; see Zabel, R. A. and Terracina, F., “The role of Aureobasidium Pullulans in the disfigurement of latex paints”, Development in Industrial Microbiology, vol. 21, pages 179-190, (1980). Another report indicated that one microfungus (Cladosporium) similar to the one found on H-53, is capable of corroding 2024 aluminum alloy panels by producing acidic metabolic products; see Videla, H., “The action of Cladosporium resinae growth on the electrochemical behavior of aluminum”, Biologically Induced Corrosion, Proceedings of the International Conference on Biologically induced Corrosion, Dexter, S. C. (ed). National Association of Corrosion Engineers (NACE), Houston, Tex. Pages 215-222, (1986). An additional study by Salvarezza and Videla has shown that fungi are known to thrive at the oil-water interface to produce acids that can corrode metals; see Salvarezza, R. C., and Videla, H. A., “Microbiological corrosion in fuel storage tanks, Part 1: anodic behavior”, Acta Cientifica Venezulan, vol.35, pages 244-247, (1984).
To mitigate these problems, a novel mildew composition was developed by National Air Depot Cherry Point personnel. The original mildew remover formula comprises an aqueous solution consisting of sodium perborate and nonionic detergents; see U.S. Pat. Nos. 6,235,124 (Method and Solution for Removal of Mildew, May 22, 2001, Lynn Rubin) and 6,655,527 (Kit for Removing Mildew, Dec. 2, 2003, Lynn Rubin), the disclosures of which are hereby incorporated by reference. However, the ingredients must be mixed immediately prior to use, as the solution becomes ineffective after about twenty-four hours. The product is applied with clean cheesecloth or a soft bristle brush to mildew growth and allowed to remain for about 5 to 15 minutes. The surface is then cleaned thoroughly with fresh water to rinse away residue.
The patented mildew remover was evaluated to determine the effects on aircraft materials using selected tests from MIL-PRF-85570D and ADS-61A-PRF-2002 (aircraft cleaning) specifications, the disclosures of which are hereby incorporated by reference. The mildew remover was tested in diluted concentrations to simulate rinse residues. Testing was initiated after aging the mixed product for up to about 96 hours to determine the composition's activity period. After completing the initial tests, the above-identified patented mildew remover caused some corrosion in both the sandwich corrosion and the total immersion corrosion tests on titanium alloy (Ti 6Al 4V). As a result of the test, the mildew remover was modified, by incorporating various corrosion inhibitors to mitigate corrosion while maintaining composition performance. Inhibited formulations were subjected to selected tests in Navy MIL-PRF-85570D and Army ADS-61A-PRF-2002 cleaner specifications, and adjusted as necessary. The best formulation was tested to the requirements of the two specifications stated above and then field-tested to validate mildew removing performance. The test methods were taken from the MIL-PRF-85570D and ADS-61A-PRF-2002 specifications as follows:
1. pH Value (ASTM E70-02)
2. Hydrogen Embrittlement as per ASTM F519-97
3. Sandwich Corrosion Test (ASTM F110-02)
4. Cadmium Corrosion Test (ASTM F1111-98)
5. Total Immersion Corrosion (ASTM F483-02)
6. Effect on Polyimide Wire
7. Effect on Painted Surfaces (ASTM F502-02)
8. Effect on Plastics (ASTM F484-02)
9. Stress Corrosion on Titanium (ASTM F945-01)
10. Sealant Adhesions, Paint Adhesion, and Adhesive Bonding (ADS-61-PRF-2002)
11. Field Test for the inhibited mildew remover formulations
In addition to testing the full strength mildew remover to the listed tests, dilutions of 50%, 25% and 10% were tested for sandwich corrosion to simulate the consequences of incomplete rinsing. Aged samples of the mixed product were evaluated in the sandwich corrosion test to determine the window of activity of the mixed product. The sandwich corrosion test was performed in accordance with ASTM F 1110 using deionized/distilled water as a control. The test was performed on four aluminum alloy coupons: anodized aluminum 2024-T3 (SAE-AMS-QQ-A-250/4), Alclad 2024-T3 (SAE-AMS-QQ-A-250/5), anodized aluminum 7075-T6 (SAE-AMS-QQ-A-250/12) and Alclad 7075-T6 (SAE-AMS-QQ-A-250/13). Aluminum coupons were sandwiched together with filter paper saturated with mildew remover between the coupons. The sandwiched coupons were cycled between warm dry air (38° C.) and warm humid air (relative humidity 100%) for 7 days. Sandwich corrosion testing was performed using diluted chlorine bleach solution, Reagent Water (ASTM D1193), a 1.5% Sodium Perborate solution, and a series of perborate and surfactant solutions with various corrosion inhibitors in several concentrations. Inhibitors tested include Zinc Borate, Sodium Dichromate, Monacor 4000, Benzotriazole, Sodium Silicate “N”, Sodium Benzoate, Sodium Orthosilicate, Sodium Metasilicate, Cobratec TT-50-S, Sodium Nitrite, 2-Mercaptobenzimidazole, and 2-Mercaptobenzoxaxole.
Table 3 details the combination of inhibitors investigated and the subsequent sandwich corrosion test results. The test results are shown in Tables 1 and 2 and in
The original mildew remover formulation (Example 1) failed the sandwich corrosion test, as required by the MIL-PRF-85570D and ADS 61A-PRF-2002 specifications as follows:
a. Dilutions of the original mildew remover (50%, 25% and 10% concentration) proved corrosive beyond the specification limits and pitting was observed.
b. Samples made using 24-hour-old solution (uninhibited formula) were found to fail sandwich corrosion testing.
c. Samples made using 96-hour-old solution (uninhibited formula) were found to be comparable to the control.
d. Samples tested at the prescribed temperature of 100° F. showed more pitting than those tested at 72° F.
e. Samples made using tap water in place of reagent water failed with ratings of #4 for corrosion pitting.
The mildew remover formulation (Example 2) passed the sandwich corrosion test, in accordance with the MIL-PRF-85570D and ADS-61A-PRF-2002 specification requirements.
The following examples illustrate the aqueous solutions of this invention, and the method of using the basic solutions for removing and inhibiting the growth of mold and mildew on various surfaces and particularly metal surfaces.
The original Mildew Remover (M.R.) Formulation (uninhibited) consists of the following compounds in an aqueous solutions:
Sodium Perborate Monohydrate, 1.5% by weight
Triton X-100 surfactant, 0.39% by weight
Reagent Water (ASTM D1193)
Inhibited Mildew Remover (M.R.)consists of the following compounds in an aqueous solution:
Sodium Perborate Monohydrate, 1.5% by weight
Triton X-100 surfactant, 0.39% by weight (octylphenoxypolyethoxyethanol)
Sodium Silicate N, 0.5% by weight
Benzotriazole, 0.25% by weight
Reagent Water (ASTM D1193)
Inhibited Mildew Remover consists of the following compounds in solution:
Sodiun Perborate Monohydrate, 1.5% by weight
Triton X-100 surfactant, 0.39% by weight (octylphenoxypolyethoxyethanol)
Sodium Silicate N, 0.5% by weight
2-Mercaptobenzimidazole, 0.25% by weight
Reagent Water (ASTM D1193)
Total Immersion Corrosion Test: The total immersion corrosion test was performed in accordance with ASTM F483. The selected metal alloys were immersed in the mildew remover solution for seven days at 100° F. The weight change of each specimen was calculated, and the specimen was examined for visual evidence of corrosion. The weight changes for the selected metal alloys are listed in Table 1. The selected metal alloys met the test requirements except the Ti 6Al 4V alloy which showed a dark purple color as shown in
The alkali metal perborates of this invention and preferably the sodium and potassium perborates are added to the aqueous solutions in amounts ranging from about 0.1 to 3.0 percent by weight and preferably in amounts ranging from about 1.0 to 2.0 percent by weight of the solutions. To obtain maximum performance in preventing and removing mold and mildew growth on metal surfaces such as aluminum, the inhibiting compounds i.e. the alkali metal silicates such as sodium and potassium silicates and the triazoles are added to the aqueous solution in amounts ranging from about 0.05 to 5.0 percent and preferably in amounts ranging from about 0.1 to 2.0 percent by weight of the solution. These inhibiting compounds are selected from the group consisting of alkali metal silicates and triazoles such as benzotriazole or tolyltriazol and various mixtures of said silicates and triazoles in any ratio.
In preparing the anti-mildew or inhibiting solutions of this invention, known water soluble surfactants are added to the solutions in amounts ranging from about 0.0 to 5.0 percent by weight and preferably from 0.1 to 2.0 or from about 0.1 to 1.0 percent by weight. The surfactants are added to the aqueous solution to provide better wetting properties by lowering the surface tension thereby insuring complete coverage and a more uniform film on the metal substrates. The surfactants include at least one water soluble compound selected from the group consisting of non-ionic, anionic, and cationic surfactants. Some of the water soluble surfactants include monocarboxylimidoazoline, alkylsulfate sodium salts (DUPONOL®), salts of alkylbenzene sulfonates, ethoxylated or propoxylated alkylphenols (IGEPAL®), alkylsulfonamides, alkaryl sulfonates, palmiticalkanol amides (CENTROL®), the alkylarylpolyether alcohols such as octylphenylpolyethoxy ethanol or polyoxyethylene nonylphenyl ether, (TRITON®), sorbitan monopalmitate (SPAN®), dodecylphenyl polyethyleneglycol ether (TERGITOL®), alkyl pyrrolidones, polyalkoxylated fatty acid esters, lower alkylbenzene sulfonates and various mixtures of these surfactants.
The preferred corrosion inhibitors added to the solutions of this invention are water-soluble compounds selected from the group consisting of benzimidazoles, benzazoles, benzoxazoles and mixtures of these corrosion inhibitors in any ratio. The corrosion inhibitors are dissolved in the aqueous solutions, having a pH ranging from 7.0 to 10, in amounts ranging from about 0.0 to 3.0 percent by weight and preferably in amounts ranging from about 0.1 to 2.0 percent by weight of the solution. The preferred inhibitor compounds in addition to the silicates include triazoles containing up to 12 carbon atoms. The preferred aryl triazoles contain from 6-10 carbon atoms, including compounds such as benzotriazole and tolyltriazole. The aryl triazoles are commercially available under the trade name “COBRATEC”.
As shown, a combination of inhibitors e.g. silicates and triazoles was developed to eliminate the corrosion problems associated with the original (Example 1) mildew remover formula The inhibited mildew remover formula eliminates the corrosion problem associated with aluminum alloys in the sandwich corrosion test as seen in
Table 1 is an evaluation of the uninhibited and inhibited mildew remover in accordance with MIL-PRF-85570D (Cleaning Compounds, Aircraft Exterior).
Table 2 shows the evaluation of uninhibited and inhibited mildew remover in accordance with ADS-61A-PRF-2002 (Army Aircraft Cleaner).
* NR: Not Run
0 - No Visible Corrosion
1 - Very Slight Corrosion or Discoloration (up to 5% of surface area)
2 - Slight Corrosion (5 to 10%)
3 - Moderate Corrosion or Pitting (10 to 25%)
4 - Extensive Corrosion or Pitting (25% or more)
While this invention has been described by a number of specific examples, it is obvious that there are other variations and modifications which can be made without departing from the spirit and scope of the invention as particularly set forth in the appended claims.
The invention described herein was made by employee(s) of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.
