Abstract
Differential scanning calorimetry (DSC) measurements and scanning electron microscopy (SEM) imaging showed a new high temperature crystal phase in powder-pressed and stretched films of ultra high molecular weight polytetrafluoroethylene (PTFE). Whereas a melting peak was observed at 345°C in the DSC curve of the pristine powder of PTFE, a new endothermic peak appeared at 380°C for the films pressed at 320°C and stretched at 180°C or for the films with a thickness of less than 10 μm that were pressed at 320°C between aluminum plates. Rigid rods with a diameter of 0.2 μm indicated the formation of crystals with a structure different from that of the pristine powder. Additional experiments were carried out to elucidate the properties of the new crystal structure.
