Electrospun poly(ethylene terephthalate) (PET) fibers were prepared from a trifluoroacetic acid (TFA)-based solvent. Rheological studies revealed the concentration (ϕ) dependence of the specific viscosity (ηsp) to be ηsp ∼ ϕ3.7 for PET/TFA solutions in the entangled regime. The determined entanglement concentration (ϕe) was higher using a lower-molecular-weight PET. To obtain bead-free fibers, the minimum concentration for the electrospinning was 0.8–1.0ϕe 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 (d j) and fiber (d f) diameters versus the zero-shear viscosity (η0) revealed that two scaling laws existed for the present solutions, i.e., d j ∼ η0 0.06 and d f ∼ η0 0.77. 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 (T a) higher than 100 °C, the mesomorphic phase gradually transformed into imperfect triclinic crystals and reached its saturation at 130 °C. Further increased T a 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.

No abstract

No abstract