STRESS-STRAIN AND STRESS-RELAXATION IN OXIDATED SHORT CARBON FIBER-THERMOPLASTIC ELASTOMER COMPOSITES

Stress-strain and stress relaxation properties are studied in composit es consisting of a thermoplastic elastomer butadiene styrene copolymer (SBS) matrix and oxidated carbon fiber. The results obtained from sam ples at different degrees of oxidation are contrasted with those obtai ned from SBS filled with commercial carbon fiber. Carbon fiber oxidati on with nitric acid gives rise to an increase in functional surface gr oups, which in turn enhance the capacity in the fiber to interact with the matrix. In the experimental composites, the increase in fiber-mat rix interactions translates into proportionally greater strain necessa ry to reach the yield point, as well as into an increase in stress at the yield point. In addition, at initial strain below the strain at yi eld point, a slower stress relaxation rate is observed in oxidated fib er composites, as compared with those recorded for the matrix filled w ith commercial fiber. In the oxidated fiber composites, stress relaxat ion occurs in three stages, the first two of which may be associated t o the fiber-matrix interface. (C) 1996 John Wiley & Sons, Inc.