This method permits manufacturing EPDM rocket motor insulation in which carbon
fibers are dispersed and immobilized in the EPDM polymeric matrix but are not excessively
fractured or fragmentized, i.e., broken into smaller fragments, when encountering
degrees of shear necessary to homogeneously or otherwise distribute or disperse
the carbon fibers in the EPDM polymeric matrix. The method is substantially solvent
free and is performed via distributive/reduced shear mixing to distribute the fragile
carbon fibers into a rubber matrix without excessive damage. According to one embodiment,
at least about 50% of the elastomer composition introduced into the mixing apparatus
is liquid EPDM terpolymer having sufficiently low molecular weight and high diene
content to permit dispersion of the carbon fibers in the EPDM without substantial
fragmentation of the fibers. According to another embodiment, mixing takes place
in a kneader capable of rotating a screw having a discontinuous screw thread about
the screw axis while superimposing an axially reciprocating stroke to the screw.
The kneader imparts low shear distributive mixing of the carbon fibers in the EPDM terpolymer.
