Carbon-fiber-filled polymers made from ethylene propylene diene monomer (EPDM) have been found to be useful as ablative thermal-insulation materials. Like the silica-filled EPDM polymers described in the preceding article, these polymers have been investigated as candidates to replace some previously developed polymeric ablative rocket-engine insulating materials that will soon become commercially unavailable.

Several formulations of carbon-fiber-filled EPDM polymers have been investigated. As in the case of the silica-filled polymers described in the preceding article, improvements are incorporated where possible and examples of improvements include the use of a tackifier or the choice of one or more accelerator(s) to obtain a longer scorching time as well as desired curing properties. For each formulation, the ingredients are mixed in the following procedure:

First, the ingredients are mixed according to ordinary rubber-processing techniques in a two-pass mixing procedure implemented in an internal mixer. All the ingredients except the accelerator(s) and sulfur (if used) are added during the first pass, and the accelerators and sulfur (if used) are added during the second pass. The resulting mixture is dissolved in a suitable solvent such as hexane. The solution is then mixed with carbon fibers, using a minimum of mixing to disperse the fibers and distribute them uniformly without breaking them excessively. The solution/fiber mixture is then spread thin on a flat sheet so that the solvent can evaporate (if desired, evaporation can be done in an oven). The resulting uncured insulating material is then cured in the required shape.

In ablative tests, some of the formulations investigated performed a little better than others did, probably because of differences in mixing.

This work was done by David G. Guillot of Thiokol Corp. for Marshall Space Flight Center. For further information, please contact the company at This email address is being protected from spambots. You need JavaScript enabled to view it..

Title to this invention has been waived under the provisions of the National Aeronautics and Space Act {42 U.S.C. 2457(f)} to Thiokol Corporation. Inquiries concerning licenses for its commercial development should be addressed to

Thiokol Propulsion
Intellectual Property Department
PO Box 707
M/S A11
Brigham City, UT 84302-0707

Refer to MFS-31405, volume and number of this NASA Tech Briefs issue, and the page number.