The objective of this project is to demonstrate and validate novel single- (1K) and two-component (2K) siloxane-based topcoats that are environmentally friendly alternatives to the isocyanate-based two-component polyurethanes currently used on Department of Defense (DoD) aircraft (fixed and rotary wing) and aerospace ground support equipment. Isocyanates are considered toxic, which can result in environmental and health issues for both coating applicators and those in proximity during touch-up and full painting applications. The project team will scale-up topcoats with camouflage and gloss finishes, verify performance in a laboratory setting in accordance with current Navy and Air Force specification requirements (e.g., MIL-PRF-85285E, Type IV), and conduct field demonstrations on active aircraft and support equipment platforms to validate performance compared to qualified topcoats. Demonstration locations on aircraft will include removable parts, areas requiring touch-up, wheel wells, interior, and the outer mold line (exterior). A cost-benefit analysis will demonstrate environmental savings based on the elimination of isocyanates, volatile organic compound (VOC) reductions, and other factors.
The siloxane-based topcoats are free of toxic isocyanates and hazardous air pollutants (HAPs), possess lower VOCs and reduced flammability compared to polyurethanes, exhibit high flexibility and solvent resistance, and are exterior durable (e.g., color retentive) due to the presence of a silicon-oxygen bond network. The single-component topcoat is based on a novel polymer with a flexible aliphatic backbone and terminal alkoxysilane groups. The system reacts with atmospheric moisture at room temperature and will cure over a wide range of conditions. As a single-component system, all materials are pre-mixed in a can and do not require the addition of components or a catalyst before application, thereby providing a user friendly system for painters. The two-component topcoat is based on a unique combination of amino-functional polysiloxane polymers, epoxy-functional oligomers, and flexible aliphatic polymers. This system will also cure under ambient conditions. The siloxane-based topcoats are applied using standard high volume, low pressure (HVLP) spray equipment, thus unfamiliar and/or expensive equipment is not required. When tested in the laboratory, these topcoats have demonstrated the ability to meet or exceed the performance of most, if not all, Navy aircraft topcoat requirements. Success in the field will be based on the topcoats demonstrating equivalent or greater performance on active platforms when compared to qualified topcoats.
Implementation of the siloxane-based topcoats will enable DoD to minimize, if not eliminate, the environmental hazards and health risks associated with toxic isocyanate-based polyurethanes, in addition to reducing the costs attributed to industrial hygiene monitoring. These novel topcoats will also allow for increased productivity and logistics at facilities by allowing concurrent maintenance in nearby areas during painting applications, will provide an environmental benefit by reducing the emission of VOCs and HAPs, as well as providing depots and bases with greater flexibility in managing their overall VOC limits, and will eliminate the need for storage in separate flammable lockers on ships. The enhanced exterior durability of the topcoats will eliminate the need for inferior touch-up topcoats, will reduce life-cycle costs by extending painting cycles, and will reduce the emission of VOCs and HAPs due to the depainting process. The single-component system will reduce errors and application costs due to the improper mixing of components, in addition to reducing the generation of hazardous waste from unused mixed materials. The costs of the topcoats are expected to be competitive with qualified polyurethanes. A completely non-hazardous coating system for platforms could be realized by using the siloxane-based topcoats over a non-chromate primer and pretreatment. (Anticipated Project Completion - 2018)