Final Report: Clean Water Based Self-Priming Aircraft Coatings Technology

EPA Contract Number: 68D00202
Title: Clean Water Based Self-Priming Aircraft Coatings Technology
Investigators: Usmani, Arthur M.
Small Business: ALTEC USA
EPA Contact: Richards, April
Phase: I
Project Period: September 1, 2000 through March 1, 2001
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2000) RFA Text |  Recipients Lists
Research Category: SBIR - Pollution Prevention , Pollution Prevention/Sustainable Development , Small Business Innovation Research (SBIR)

Description:

ALTEC USA has developed a single-layered aircraft coating to replace the currently used three-layered coating system that consists of toxic chromate conversion coating (CCC), the primer, and the topcoat. Currently, used primer also is loaded with chromate inhibitor pigment. Functions of all three layers were combined in the unicoat system. The coating consists of new pigment type, nontoxic, corrosion inhibitors to replace toxic chromate. Topcoat pigments and extenders also are included and dispersed in recently developed aqueous polymer dispersions. Selection of inhibitors and aqueous dispersions were described in the earlier reports. Coating design and preparation as well as electrochemical corrosion testing results are described in this report. For completeness, discussion on aircraft coatings, nontoxic pigments, aqueous polymer dispersions, and recommendations for future work have been included in this report.

Summary/Accomplishments (Outputs/Outcomes):

A combination of Halox SZP391 and Shieldex AC-3 gave adequate protection as determined by electrochemical impedance spectroscopy (EIS). Thin coatings (1 mil) yielded impedance of 800 K. Currently used aircraft coatings are in the 2.0?2.5 mil ranges. Thicker coatings yielded impedance of more than 1,000 K, which is quite satisfactory. The coatings also passed 2,000 hr of salt spray testing.

EIS generates many corrosion parameters. Two of the most useful plots used in corrosion analysis are NYQIST and BODE. Extended exposure in both plots analyzes the degradation behavior of the coatings. In two coatings based on SZP391 and AC-3, no degradation took place during 30 days of exposure to 3.5 percent NaCl. These coatings resulted in a barrier resistance of more than 106 ohms that was maintained throughout the exposure. More importantly, there were no changes in any corrosion reactions. Another coating based on Moly-White MZAP and AC-3 yielded the second-best result. In this coating, a barrier resistance of 105 ohms was maintained throughout the exposure.

Salt spray has been used for decades to predict corrosion protection, but the results are not reliable. However, electrochemical methods, specifically EIS, is highly reliable and provides several parameters. It has been adopted by the U.S. Air Force to determine the corrosion prevention behavior of aircraft coatings. Hybridur 580 and Cytec 5035 dispersions produced good coatings. The barrier properties of the coatings are good enough to provide more than 12 years of durability. EMMAQUA exposure testing and lifetime prediction using Usmani- developed Gauss and Weibull models must be conducted to assure coating durability. ALTEC USA can further improve the barrier properties and durability by slight-to-medium crosslinking with a water-based polyaziridine.

Conclusions:

Coatings developed through this project offer better corrosion protection than the currently used three-layered toxic aircraft coatings. After the coating compositions are optimized in Phase II, the new unicoat will no doubt outperform the currently used three-layered coating system. It will be safe to the environment and protect personnel who paint military and civilian aircraft. Water pollution due to toxic chromates also will be eliminated in communities with large aircraft production facilities. In addition to EPA, the U.S Air Force and U.S. Navy will be most interested in this work. Currently, aircraft coatings use CCC-containing Cr6+, which does not interact with human DNA. However, it becomes Cr5+ by a known reductive pathway and damages human DNA, causing many ailments, notably lung cancer. EPA is hoping that the aerospace industry can eliminate or substantially reduce the use of Cr6+.

Supplemental Keywords:

pollution prevention, coatings, emissions, engineering, chemistry, aircraft., RFA, Scientific Discipline, Toxics, Waste, Sustainable Industry/Business, National Recommended Water Quality, Sustainable Environment, cleaner production/pollution prevention, Environmental Chemistry, Chemistry, Technology for Sustainable Environment, Hazardous Waste, New/Innovative technologies, Chemistry and Materials Science, 33/50, Hazardous, Engineering, Environmental Engineering, waste reduction, solvent replacement, benzene, alternative materials, polymers, solvent substitute, alternative aircraft coatings, solvent replacements, polymer design, pollution prevention, source reduction, air emissions