Aging study of neoprene FB uncured rubber in support of an obsolescence issue for EPDM rubber insulation used in the Reusable Solid Rocket Motor of the Space Shuttle

摘要

Thioliol/Wasatch (TC/W) in Utah is the manufacturer of the Reusable Solid Rocket Motor (RSRM) for the Space Shuttle, and filled EPDM and NBR rubber insulators are used on RSRM for erosion resistance. Since DuPont/Dow is closing production lines for Neoprene FB and two Nordel EPDM polymers used in three EPDM insulators for RSRM, TC/W will stockpile 6-7 years of Neoprene FB and Nordel to support RSRM production until reformulated EPDMs can be developed and recertified. NASA/MSFC used several thermal analysis techniques to study the effect of aging on a lot of uncured Neoprene FB kept in cold storage at 40 degrees F (4.4 degrees C) for more than 11 years ('old'). A lot of uncured Neoprene FB kept in cold storage for 8 months ('new') was used for comparison in the study. In processing of uncured calendered sheets by the Shuttle vendor that are later cured near 150 degrees C as RSRM insulation by TC/W, Neoprene FB is mixed into the EPDM formulation at 105"C. Uncured Neoprene FB is a solid at room temperature with a texture similar to that of cheese, but was shown by DSC to have a peak melting endotherm at 50 degrees C, becoming a low viscosity liquid until it begins to cross-link at higher temperatures. From a DMA study on the uncured 'old' and 'new' lots of Neoprene FB at cure temperatures of 95, 105 and 115 degrees C, a linear Arrhenius relationship of the logarithm of the time to gelation versus reciprocal absolute temperature yielded activation energies for the two lots of rubber When this: linear relationship was extrapolated down to the cold storage temperature of 4.4 degrees C, gel times of the 'old' and 'new' rubber lots were predicted to be 12.7 and 72.6 years, respectively. This data shows that the 'old' lot of Neoprene FB still has a considerably useful shelf life in cold storage. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 6]