Isocyanate-Free Organosilane Polymers for Specialty Aircraft Coatings

Dr. Erick Iezzi | U.S. Naval Research Laboratory (NRL)

WP20-1107

Objective

Specialty coatings used on the exterior of Department of Defense (DoD) aircraft are elastomeric polyurethanes that contain hazardous isocyanate-functional molecules and emit large quantities of volatile organic compounds (VOCs) and hazardous air pollutants (HAPs) in the form of organic solvents. Isocyanate exposure to applicators can lead to numerous health issues, such as symptoms of asthma and sensitization, whereas HAPs are carcinogenic and VOCs reduce air quality. To address these issues, the research team aims to develop novel organosilane polymers with linear and highly flexible backbones, then demonstrate, as a proof-of-concept, that these polymers can be used to create isocyanate-free elastomeric polysiloxane coatings with similar properties as the polyurethanes used for specialty aircraft coatings.

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Technical Approach

The organosilane polymers will be alkoxysilane-terminated N-substituted polyureas or polyureaurethanes. These polymers will be synthesized using traditional routes, which include the use of isocyanatefunctional molecules, in addition to green synthetic pathways, which do not require the use of isocyanates. The structure of these organosilane polymers will be characterized using various analytical techniques, such as nuclear magnetic resonance and infrared spectroscopy. All polymers will utilize renewable raw materials to the maximum extent possible, and all solvents will the HAP-free. The organosilane polymers will be formulated as clear and filled single-component (1K) systems with reduced VOCs, then cast or spray-applied to form cross-linked polysiloxane coatings at various thicknesses. Characterization of the cross-linked coatings will include surface and bulk chemical analysis, thermal and mechanical properties, resistance to elevated temperature and humidity, and resistance to accelerated weathering. A sustainability analysis of the organosilane polymers and 1K polysiloxane coatings thereof will be conducted to determine human health, environmental impacts, and associated life-cycle costs of these new materials.

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Benefits

New polymers and isocyanate-free coatings thereof that demonstrate similar, or improved, properties compared to isocyanate-containing polyurethane elastomers would advance science in the area of polymeric materials and cross-linked networks. For the DoD, the use of isocyanate-free specialty coatings would enable a reduction, and potential elimination, of health and environmental issues associated with isocyanate exposures to the end-user, thereby reducing costs associated with medical claims and isocyanate monitoring. Removal of HAPs would eliminate the risk of exposure to carcinogenic molecules. Reducing the amount of VOCs released from specialty coatings would improve air quality and enable depots to apply greater quantities of these coatings while remaining within permissible emission limits, thus improving operational readiness for aircraft. Furthermore, improved performance properties, such as increased weatherability and thermal stability, would extend the service-life of specialty coatings and reduce the frequency of applications, thereby reducing maintenance costs. Finally, specialty coatings with enhanced performance properties would provide greater protection for the warfighter, which is vital when operating aircraft in enemy territory.

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Points of Contact

Principal Investigator

Dr. Erick Iezzi

Naval Research Laboratory

Phone: 202-404-2889

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