The gloss topcoats used on the exterior, interior, and components of Department of Defense (DoD) aircraft and support equipment are two-component (2K) solvent borne polyurethanes that are qualified to MIL-PRF-85285 performance requirements. These topcoats contain hazardous isocyanate-functional molecules and carcinogenic airborne solvents that can cause serious health issues to individuals exposed both during and immediately after painting operations. Furthermore, these topcoats contain large quantities of volatile organic solvents, and several topcoats contain fluorinated alkyls, in the form of fluorinated polymers, which are persistent environmental pollutants. For this project, single-component (1K) gloss white and gloss orange polysiloxane topcoats, which are an environmentally friendly alternative to the legacy polyurethanes, will be tested to MIL-PRF-85285, Type IV and extended performance requirements in the laboratory, then validated by demonstrating they provide equivalent, or better, performance on active DoD aircraft and components compared to qualified gloss polyurethane topcoats. The project also aims to prove that the organosilane polymer in the 1K gloss polysiloxane topcoats has reduced toxicity compared to aliphatic isocyanates, as well as showing that the 1K gloss topcoats are applicator friendly, will reduce paint preparation times, and will reduce the generation of hazardous paint waste and associated disposal costs.

The gloss polysiloxane topcoat is a single-component (i.e., all-in-one-can) coating that is free of isocyanates, fluorinated alkyls, and carcinogenic chemicals, while also possessing reduced volatile organic solvents compared to qualified polyurethane topcoats. The binder for the polysiloxane topcoat is a novel organosilane polymer with flexible aliphatic segments, N-substituted urea linkages, and terminal alkoxysilane groups. Upon application of the 1K polysiloxane topcoat these alkoxysilane groups hydrolyze with atmospheric moisture and form a cross-linked network of Si—O—Si linkages that engender the topcoat with enhanced thermal stability and weatherability. For this project, the 1K gloss polysiloxane topcoats will be applied over chromate and non-chromate epoxy primers, and success in the laboratory and field will be based on the 1K topcoats demonstrating equivalent, or better, performance compared to Type IV qualified gloss polyurethane topcoats.

Single-component gloss polysiloxane topcoats will enable the DoD to eliminate health issues associated with worker exposure to hazardous isocyanates and hazardous air pollutants, in addition to reducing air polluting solvent emissions that result in climate change. These topcoats will also enable greater scheduling flexibility at depots during maintenance intervals by allowing non-paint operations to occur in the vicinity of painting, as opposed to evacuating the area for fear of isocyanate exposure from airborne mists. Additionally, the gloss polysiloxane topcoats will enable painters to save time during preparation because no components are mixed when using a single-component system, and costs attributed to paint reworks, which can result from improperly metered and mixed 2K polyurethane topcoats, will be eliminated. Cost savings will also result from the elimination of airborne isocyanate sampling during polyurethane paint operations, including a reduction in hazardous waste and disposal costs due to the minimal amount of waste generated with a 1K topcoat.