Oriented Crystallization Induced by Uniaxial Drawing from Poly(tetrafluoroethylene) Melt

The melt-drawing behavior of poly(tetrafluoroethylene) (PTFE) with ultrahigh molecular weight (UHMW) was analyzed using in situ measurements composed of stress−strain curves and wide-angle X-ray diffraction with synchrotron radiation. The stress−strain behavior of the melt-drawing of UHMW−PTFE was quite different from that of the solid drawing. In particular, the former exhibited a plateau stress region, followed by a rapid increase in stress with strain. No crystalline reflection appeared in the plateau stress region. However, oriented crystallization was observed in the later strain-hardening region. Correspondingly, the resultant mechanical properties and transparency of the melt-drawn films are much better than those of the solid-drawn films. Optimizing the melt-drawing conditions elongated the plateau stress region, which successfully achieved further property development. The effects of sample MW on melt-drawing behavior and resultant properties were also discussed. The lower MW film produced a long...