Stress‐Strain and stress relaxation in oxidated short carbon fiber‐thermoplastic elastomer composites

Abstract

Stress-strain and stress relaxation properties are studied in composites consisting of a thermoplastic elastomer butadiene styrene copolymer (SBS) matrix and oxidated carbon fiber. The results obtained from samples at different degrees of oxidation are contrasted with those obtained from SBS filled with commercial carbon fiber. Carbon fiber oxidation with nitric acid gives rise to an increase in functional surface groups, which in turn enhance the capacity in the fiber to interact with the matrix. In the experimental composites, the increase in fiber-matrix interactions translates into proportionally greater strain necessary 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 yield point, a slower stress relaxation rate is observed in oxidated fiber composites, as compared with those recorded for the matrix filled with commercial fiber. In the oxidated fiber composites, stress relaxation occurs in three stages, the first two of which may be associated to the fiber-matrix interface. © 1996 John Wiley & Sons, Inc.