Numerous sealants are required on aircraft systems to prevent moisture entry, provide corrosion protection and electrical insulation, and seal fuel tanks. Hexavalent chromium, in the form of chromates, is the primary corrosion-inhibiting component in currently used sealants. It is also a known carcinogen and is highly regulated by the Environmental Protection Agency and the Occupational Health and Safety Administration. Most of these sealants also contain relatively high levels of volatile organic compounds (VOC).
The objective of this project was to develop environmentally compatible, non-chromated, drop-in replacement sealants for military use. In addition to hexavalent chromium elimination, the VOC content of the sealants was significantly reduced. These environmental goals were further enhanced by rapid cure times and longer shelf life of the replacement sealants.
A new rapid curing polythioether polymer was used as the base. Several epoxy and urethane curing agents were tried and combinations of non-chromated salts were investigated. After a number of prototype formulations were developed and tested, the best formulation was tested and qualified to both military and industry standards. In the final phase of the project, other classes of sealants for a wide range of uses were developed.
New non-chromated corrosion-inhibiting sealants have been developed and are currently available for use. Transition from the old chromated sealants to the new non-chromated sealants is in progress. Most of the aircraft produced today are using the non-chromated sealants, and many Department of Defense aircraft depots are switching to the new non-chromated materials.
The benefit of non-chromated, low-VOC sealants is a significant reduction in material disposal costs for aircraft maintenance, the elimination of a major source of waste material that contains a hazardous material, a significant reduction in VOC emissions when these new sealants are used, and increased safety for personnel involved in the application and removal of these materials. (Project Completed – 2005)