Abstract: The stress relaxation modulus of PTFE(polytetrafluorethylene) was studied by using fractional Maxwell model. The asymptotic solutions of fractional Maxwell model were assumed to be the starting point to decide the parameters(β, α, τ, E), but the relaxation time τ fitted by experimental data is in contradiction with the conditions of the asymptotic solutions. The principles for choosing the parameters were discussed. The relaxation exponent β and α (the order of the fractional derivatives) can be decided according to the relaxation behavior of the initial and terminal time respectively. Choosing the relaxation time τ properly, the modulus E can be determined by using the experimental data of the initial time. By optimiz
ing the parameters τ and α, the fractional Maxwell model can describe viscoelastic relaxation process very well. The relative error of the relaxation modulus of PTFE fitted by fractional Maxwell model is 0.64%.

Key words: PTFE, Viscoelasticity, Stress relaxation modulus, Fractional Maxwell model