ODC-free solvent implementation issues for vulcanized rubber and bond systems

Thiokol Propulsion has worked extensively to replace 1,1,1-trichloroethane (TCA) with ODC-free solvents for use in the manufacture of the Reusable Solid Rocket Motor (RSRM) for the Space Shuttle Program. As Thiokol has transitioned from sub-scale to full-soale testing and implementation of these new solvents, issues have been discovered which have required special attention. The original intent of Thiokors solvent replacement strategy was to replace TCA with a single drop-in solvent for all equivalent applications. We have learned that a single candidate does not exist for replacing TCA. Solvent incompatibility with process materials has caused us to seek for niche solvents and/or processing changes that provide an ODC-free solution for special applications. This paper addresses some of the solvent incompatibilities, which have lead to processes changes and possible niche solvent usage. These incompatibilities were discovered during full-scale testing of ODC-free solvents and relate to vulcanized rubber and bond systems in the RSRM. Specifically, the following items are presented: Cure effects of d-limonene based solvents on Silica Filled Ethylene Propylene Diene Monomer (SF-EPDM) rubber. During fullscale test operations, Thiokol discovered that d-limonene (terpene) based solvents inhibit the cure of EPDM rubber. Subsequent testing showed the same issue with Nitrile Butadiene Rubber (NBR). Also discussed are efforts to minimize uncured rubber exposure to solvents. Copyright © 2001 ATK Thiokol Propulsion Corp. Published by The American Institute of Aeronautics and Astronautics Inc. with permission. Cured bond system sensitivity to ODCfree solvents. During full scale testing it was discovered that a natural rubber to steel vulcanized bond could degrade after prolonged exposure to ODC-free solvents. Follow on testing showed that low vapor pressure and residence time seemed to be most likely cause for failure.