High-performance, electrical-grade polysulfide (MIL-S-8516F) is used extensively throughout the Department of Defense (DoD) as a fuel-resistant sealant for electrical components in aircraft. It is also used by the Department of Energy (DOE) to protect warhead arming, fusing, and firing sections. Because of the increasingly restrictive requirements being placed on hazardous waste minimization, there is a strong likelihood that lead-containing (8516 type) polysulfides will be difficult or impossible to acquire within the next few years. Vendors are finding it difficult to obtain the proper grade of the required lead peroxide curative.
The beginning of the program consisted of applied research to develop a nonhazardous material substitute. This will be followed by technology transfer to both aerospace and DOE-integrated suppliers, contractors, and repair depots.
Initially, a viscosity envelope for evaluating the flow of both the lead-containing polysulfide and alternative materials, such as lead-free polysulfides and thioethers, was developed. The project investigated the feasibility of using non-polysulfide formulations and evaluated polysulfide formulations with non-lead additives. Finally, research was conducted into the use of encapsulants that do not rely on toluene solvents.
Research was conducted into the use of heavy metal peroxides, such as manganese dioxide, and thioethers. A range of heavy metal peroxides varying in particle size, purity, surface area, and reactivity were tested and found unsuitable, as were the thioethers, which demonstrated poor low-temperature properties. A number of organic curing agents also were tested. Results indicated that the urethanes demonstrated good low-temperature properties. Epoxies, however, demonstrated poor low temperature properties and poor high-temperature electrical resistance. This research led to a revision of MIL-S-8516F. This project was completed in FY 1997.
This project will cooperate with the interested government agencies and vendors in order to develop an environmentally friendly, drop-in replacement material.