1 research outputs found
Solution-Electrospun Poly(ethylene terephthalate) Fibers: Processing and Characterization
Electrospun polyÂ(ethylene terephthalate) (PET) fibers
were prepared
from a trifluoroacetic acid (TFA)-based solvent. Rheological studies
revealed the concentration (Ï•) dependence of the specific viscosity
(η<sub>sp</sub>) to be η<sub>sp</sub> ∼ ϕ<sup>3.7</sup> for PET/TFA solutions in the entangled regime. The determined
entanglement concentration (Ï•<sub>e</sub>) was higher using
a lower-molecular-weight PET. To obtain bead-free fibers, the minimum
concentration for the electrospinning
was 0.8–1.0ϕ<sub>e</sub> owing to the high volatility
of TFA solvent, which significantly enhanced the chain network strength
during jet whipping. The double-logarithmic plots of the jet (<i>d</i><sub>j</sub>) and fiber (<i>d</i><sub>f</sub>) diameters versus the zero-shear viscosity (η<sub>0</sub>)
revealed that two scaling laws existed for the present solutions,
i.e., <i>d</i><sub>j</sub> ∼ η<sub>0</sub><sup>0.06</sup> and <i>d</i><sub>f</sub> ∼ η<sub>0</sub><sup>0.77</sup>. The microstructural evolution of the electrospun
PET fibers from stepwise annealing to crystal melting was investigated
by simultaneous small-angle X-ray scattering (SAXS)/wide-angle X-ray
diffraction (WAXD) measurements using synchrotron radiation sources.
The conformer transformation from gauche to trans was monitored by
in-situ Fourier transform infrared spectral measurement. In the absence
of any WAXD reflection, the as-spun PET fibers possessed a SAXS scattering
peak, indicating the presence of a mesomorphic phase with an interdomain
distance of 6.8 nm. At annealing temperatures (<i>T</i><sub>a</sub>) higher than 100 °C, the mesomorphic phase gradually
transformed into imperfect triclinic crystals and reached its saturation
at 130 °C. Further increased <i>T</i><sub>a</sub> perfected
the triclinic structure without altering fiber crystallinity until
the initial crystal melting at 218 °C, at which a significantly
increased long period was detected. When the electrospun PET fibers
were embedded in an isotactic polypropylene (iPP) matrix, surface-induced
crystallization occurred to develop a transcrsytalline layer of iPP
monoclinic crystals at the interface