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

Abstract

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 longer plateau region. Subsequent oriented crystallization in the strain-hardening region also exhibited a rapid increase of the crystalline reflection intensity, compared to that for the higher MW film. However, the resultant properties were lower than those for the higher MW film, due to the higher content of the chain ends, even if a higher resultant crystallinity was achieved.

Reinforcing polyamide 1212 with graphene oxide via a two-step melt compounding process

“…During tensile loading, only the polymer chains oriented along the loading direction experienced the stretching force [17]. The slight improvement in crystal orientation degree enhanced the mechanical performance [19]; however, it is not the major factor.…”

“…For melt compounding method, nanofiller alignment in composites is achieved through stretching or drawing after molding [17,18]. This method is often used to improve the composites' mechanical properties [19,20]. Nanofiller alignment in composites causes high reinforcement efficiency; this process enables composites to bear load along the orientation direction during drawing [20,21].…”

“…Strong interfacial adhesion and good dispersion increase the nanofiller-orientation degree because of great shear force during drawing [20]. During deformation, the number of polymer chains that experience force along load direction increases with increasing polymer 4 chain-orientation degree [17,19]. Polymer chain-orientation degree is influenced by adding aligned nanofillers.…”

Effects of surface modification of carbon nanofibers on the mechanical properties of polyamide 1212 composites

“…With the addition of 0.3 wt % CNFs, the crystallization onset temperature (T c,o ) and peak temperature (T c,p ) increase by 7 C and 4 C, respectively. 24 However, for drawn composites, crystallinities decrease slightly with the addition of CNFs, possibly because of the hindering phenomena from carbon nanofibers. In addition, a double-melting behavior is observed in the composites.…”

“…13,20 Further, the surface modification of nanofillers will enhance polymer chains orientation effectively due to the improved interfacial adhesion and dispersion in polymer matrix. 11,24 Then improving degree of polymer chain orientation is another way of reinforcing the composites. 11,24 Then improving degree of polymer chain orientation is another way of reinforcing the composites.…”