Mechanical Relaxations and Transitions in Polytetrafluoroethylene

Thermal expansion, ultrasonic and creep behavior of polytetrafluoroethylene are studied in temperatures from -100° to 180°C. The glass transition and primary dispersion of this polymer observed. The assignments of relaxations and transitions described in what follows are found to be quite compatible with experimental data in existing literatures as well as new information in the present study. The γ peak is ascribed to local mode motion in amorphous and paracrystalline phases. The glass transition in amorphous phase is found from -65° to -35°C. The β' peak just above these temperatures is associated with segmental motion in amorphous phase. The β peak above two crystalline transitions at 19° and 30°C is attributed to crystalline relaxation. The transition at 130°C ( T α ) and the α peak near above T α are associated with two-dimensional brownian motion in paracrystalline phase. The behavior above the melting point ( T m ) and the relation between T m and T α are interpreted assuming the melting to be the phase transition from crystal to paracrystal.