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A novel and facile strategy, combining anisotropic micellization of amphiphilic crystalline-coil copolymer in water and reassembly during single spinneret electrospinning, was developed for preparing nanofibers with very fine core-shell structure. Polyvinyl alcohol (PVA) and polyethylene glycol-block-poly(p-dioxanone) (PEG-b-PPDO) were used as the shell and the crystallizable core layer, respectively. The core-shell structure could be controllably produced by altering concentration of PEG-b-PPDO, and the chain length of the PPDO block. The morphology of the nanofibers was investigated by Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM). X-ray rocking curve measurements were performed to investigate the degree of ordered alignment of the PPDO crystalline lamellae in the nanofiber. The results suggested that the morphology of nanoparticles in spinning solution plays very important role in determining the phase separation of nanofibers. The amphiphilic PEG-b-PPDO copolymer self-assembled into star anise nanoaggregates in water solution induced by the crystallization of PPDO blocks. When incorporated with PVA, the interaction between PVA and PEG-b-PPDO caused a morphological transition of the nanoaggregates from star anise to small flake. For flake-like particles, their flat surface is in favor of compact stacking of PPDO crystalline lamellae and interfusion of amorphous PPDO in the core of nanofibers, leading to a relatively ordered alignment of PPDO crystalline lamellae and well-defined core-shell phase separation. However, for star anise-like nanoaggregates, their multibranched morphology may inevitably prohibit the compact interfusion of PPDO phase, resulting in a random microphase separation.

Nanofibers of poly(vinyl alcohol) (PVA)/ layered double hydroxide (Mg-Al LDH) composites are prepared by the electrostatic fiber spinning using water as the solvent at a high voltage of 21 kV. Either inorganic LDH carbonate (LDH-CO 3 ) or L-lactic acid-modified LDH (Lact-LDH) is used for incorporating with PVA. Scanning electron microscopy SEM investigations on the nanofibers suggest that the average diameters of PVA/LDH composite fibers are smaller than that of neat PVA. Transmission electron microscopy (TEM) investigations indicate that the dispersity of the LDH in PVA matrix is much improved after modification with L-lactic acid. The mechanical prop-erties of the PVA/LDH fibers are obviously enhanced compared to that of neat PVA. For example, the tensile stress and elongation at break of the PVA/Lact-LDH electrospun fibrous mat with 5 wt % Lact-LDH are 31.7 MPa and 36.7%, respectively, which are significantly higher than those of neat PVA, and also higher than those of PVA/LDH-CO 3 owing to the better dispersity of Lact-LDH nanoparticles.

Phosphorus-containing poly(ethylene terephthalate-co-diethylene terephthalate) (PEDT) with a low melting temperature was synthesized through esterification and copolycondensation of terephthalic acid, ethylene glycol, diethylene glycol (DEG), and 3-(hydroxyphenylphosphinyl)propionic acid (HPPPA). DSC results showed that PEDTs still were crystallizable and that the lowest melting temperature of the PEDTs was reduced to 118.0 °C although the chain regularity was destroyed by the incorporation of comonomers. It was found that the addition of HPPPA can improve the thermal oxidative stability of copolyesters. The results of the limiting oxygen index (LOI) test, the UL-94 vertical test, and the cone calorimeter test indicated that HPPPA endowed PEDT with good flame-retardant properties. The LOI values of the PEDTs were increased to 30.5−34.8, the UL-94 ratings of vertical burning were improved to V-0, and both the peak heat release rate (pHRR) and the total heat release (THR) obviously decreased.

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