Dynamic moduli for short fiber‐CR composites

The dynamic moduli, E′ and E″, and tan δ for nylon–CR and PET–CR composites with unidirectional short fibers were studied as a function of temperature by using a Rheovibron. The temperature dependence of tan δ showed two dispersion peaks for nylon–CR composite. The peak at −28°C corresponded to the main dispersion of CR and the peak at 100°C to the α‐dispersion of nylon 6. For a PET‐CR composite, in addition to the individual dispersion of CR and PET, a small and broad peak was observed at about 90°C. The angular dependence of E′ indicated that the short fibers assumed good orientation. The storage modulus for the composites was given by the parallel model as E ′ = V f ′ E f + V m E ′ m ., where E ′ c , E ′ f and E ′ m were the storage modulus for the composite, fiber, and matrix and V f and V m were the volume fraction of fiber and matrix, respectively. In the transverse direction of fiber, the peak values of tan δ at −28°C were given by the following equation; tan δ c = tan δ m − δ V f , where tan δ c and tan δ m are the loss tangent for the composite and matrix, respectively, and α is coefficient depending on fiber type. The results indicated that a region with strong interaction was formed between fibers and CR matrix.