Rheology of polytetrafluoroethylene

The rheology of polytetrafluoroethylene above its melting point was studied by the technique of stress relaxation. The temperature shift for the maximum relaxation time at various temperatures fits the WLF equation, if the value of T g is taken to be 110°C. Degradation of the polymer becomes appreciable above 380°C. Master stress relaxation curves were constructed from the data between 336 and 380°C. The continuous distribution of relaxation times was obtained, and also the discrete distribution of relaxation times by procedure X. The contribution of the maximum relaxation time to the total flow viscosity indicates that the molecular weight distribution of the sample used was narrow.