Experimental scrutiny for the constitutive equation of mesophase pitch

Abstract

Results are presented for the detailed rheological study of four samples of mesophase pitch (MP) in steady and oscillatory shear flows. The linear viscoelasticity of MP placed between a set of parallel plates is characterized in a small-amplitude oscillatory shearing flow and the nonlinear behavior is examined by means of a steady shear flow. The discrete viscoelastic spectrum of the MP is determined from oscillatory experiments. Three differential nonlinear constitutive equations—the three-constant Oldroyd, the nonlinear Spriggs and the Meister models are tested for fitting the experimental data, and their ability of describing the viscoelastic response of MP is evaluated. The Spriggs and the Meister models are reasonably fit to the nonlinear viscoelastic behavior of MP. The discrete viscoelastic spectrum { η p, λ p} is also appropriate for describing the linear viscoelasticity of MP. In addition, the temperature–time equivalence is applicable to the MPs.