Introduction
draw PTFE extrudates above their static T m , draw was not attainable, since they fractured on heating above the T m or at a low strain on tensile draw in an air oven, Nascent poly(tetrafluoroethylene) (PTFE) reactor due to the melting combined with shrinkage force. powder has been shown to be highly crystalline and
In this Communication, we report a new two-stage has a more-or-less chain-extended conformation, [1][2][3] draw process for the preparation of high modulus and suggesting a low entanglement state. Consistent with strength PTFE films, by applying a pin draw above the this, the compacted powder billets and films of PTFE, static T m on a coextrusion-drawn powder film, comwhich have never been heated above the melting tempacted below the T m . By this pin draw technique, a perature ( T m ), exhibited high ductility in the solid state minimum exposure of the extrudate to high temperaon drawing by solid-state extrusion, 4 by coextrusion, 5 tures is achieved, and an effective and high draw was and by a two-stage draw. 6 The two-stage draw consists attained. This technique is similar to the zone drawing of the first-stage solid-state coextrusion followed by a method, extensively developed by Kunugi and his cotensile draw. The ductility increases with draw temperworkers. 11 ature for both the extrusion 4 and coextrusion. 5 How-
The maximum DR t of 140, and the corresponding ever, it was found that the extrudates with an extrusion tensile modulus and strength along the fiber axis at draw ratio (EDR) of 6-20 exhibited the highest draw-24ะC of 82 { 5 and 1.2 { 0.2 GPa, respectively, were ability at 60-100ะC for the second-stage tensile draw. 6 achieved by this new draw process. This modulus corre-These temperatures are remarkably low, 235-290ะC, sponds to ร 55% of the crystal modulus of 158 GPa 12 below the T m (335ะC) of the PTFE powder. This is in at room temperature, determined from an X-ray measharp contrast to other crystalline polymers that genersurement of the actual strains in the crystal in chain ally show the highest ductility near their T m . The highdirection. The modulus developed here is significantly est tensile modulus and strength at room temperature, higher than those previously reported. 6,10 The strength 62.5 GPa and 392 MPa, respectively, were obtained at corresponds to 3.5 times that previously achieved by the maximum achieved total draw ratio (DR t ) of 50 by our two-stage draw 6 but is remarkably lower than that the two-stage draw. 6 (2.31 GPa) reported by Shimizu et al. 10 The similarities It was shown that films of UHMW-PE reactor powand differences in our process and those of Shimizu et der, 7 compacted below the T m and coextrusion drawn al. 10 and Kunugi et al. 11 are discussed. to an EDR of 6, and those of UHMW-PE 8,9 and PTFE 10 crystallized from the melt are ultradrawable above their static T m , producing high modulus and strength films and fibers. However, in our previous attempt 6 to EXPERIMENTAL