Poly-phenylene terephthalamide (PPTA-pulp)-reinforced ethylene propylene diene elastomer (EPDM)composites were prepared in an open mixer. The effects of fiber content on medium-resistance performance and heat aging resistance of the composites were investigated. With swelling behavior of the composites studied by the weighing method

the experimental curves were fitted by computer. The swelling dynamic rate equations were established. Experimental results showed that medium-resistance performance

and heat aging resistance of the composites increased greatly by adding PPTA-pulp. When the content of the fiber was up to 25% (mass)

the composites showed the best performance. The swelling behavior of EPDM/PPTA-pulp composite could be described by the Voigt parallel dashpot-spring model.Basic equation was not changed

but equilibrium swelling ratio and relaxation time of chain movement were changed on the addition of fiber. Both swelling ratio and relaxation time decreased with increasing fiber content.