Isotactic polypropylene (iPP) fibers with diameters between 0.3 and 1.2 μm were successfully produced from high-temperature electrospinning solutions using a jacket-type heat exchanger to maintain the solution temperature, an infrared emitter to control the environmental temperature, and a laser heating device to heat locally the needle spinneret to a desired temperature (100-120 °C). The iPP/o-dichlorobenzene solutions with concentrations lower than the entanglement concentration were feasibly electrospun to produce bead-free iPP fibers, suggesting that fast solvent evaporation takes place to assist the formation of sufficiently strong chain networks prior to the jet whipping process to resist the breakup of electrified jets. Through Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, small-angle X-ray scattering, and differential scanning calorimeter (DSC) analyses, the internal structure of as-spun fibers was characterized, and the annealing effect on the structure evolution was investigated. For comparison, stepwise annealing of the melt-quenched film was also carried out. For the as-spun fibers, a major mesophase with minor α-form crystal modification was found. During stepwise annealing to high temperatures, the amorphous phase remained unchanged, and the mesophase gradually transformed into stable α-form crystals prior to crystal melting. DSC results showed that both the reorganization temperature and meso → α transformation temperature in the fibers were higher than those in the melt-quenched film. On the basis of our results, a plausible mechanism for the meso → α transformation in the electrospun fibers is proposed: the initial helix reorganization takes place at the interfacial region of the mesomorphic domains, where noncrystalline chains with a preferred orientation are developed due to the elongation flow during electrospinning. After forming stable α-form nuclei, the progressive transformation of meso → α crystals toward the core of mesomorphic domain is expected.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry