The viscoelastic properties of oriented nylon 66 fibers. Part III: Stress relaxation and dynamic mechanical properties

Abstract

Abstract To test the applicability of the phenomenological theory of linear viscoelasticity, stress relaxation and dynamic mechanical properties are measured on oriented nylon 66 fibers and compared with previously reported creep data. Although the three types of viscoelastic experiments are performed on slightly different samples, the agreement is excellent. The values of log aτ employed for time-temperature superposition of the stress relaxation data agree quantitatively with those previously used to superpose creep data. Assuming these values are valid for the complex dynamic modulus, values of E as a function of temperature are converted into values of E as a function of reduced time. The values of E obtained experimentally and calculated from both creep and dynamic modulus experiments are in excellent agreement. The time dependence of E is slight, decreasing by a factor of 5 in 13 decades of time scale. There are no similarities between the viscoelasticity of this oriented nylon 66 and typical amorphous polymers above Tg. However, there is almost quantitative agreement with the viscoelasticity of glassy amorphous poly(methy1 methacrylate). For both materials, log aτ is a linear function of temperature with a slope of −0.09. It is suggested that the units responsible for molecular motion in both cases are small segments of the polymer chain.