Novel elastic nanofibers of syndiotactic polypropylene obtained from electrospinning

Uniform nanofibers of syndiotactic polypropylene (sPP) with diameters between 140 and 350 nm were successfully obtained from high-temperature solution electrospinning. Effects of sPP concentration and fiber-collecting method, either by a stationary plate or by a rotating disc, were investigated. The internal structure of the as-spun nanofibers was characterized via wide-angle X-ray diffraction (WAXD), small-angle scattering (SAXS), Fourier transform-infrared (FT-IR) spectroscopy, and differential scanning calorimetric (DSC) analysis. Based on the WAXD results, the as-spun nanofibers exhibited both all-trans mesophases and helical form I crystallites. Mesophase was the dominant phase of the sPP nanofibers obtained from the 5 wt% solution, whereas form I was the dominant phase of those obtained from the 8 wt% solution. For the more viscous solution, the enhancement of form I was attributed to the less effective stretching during processing, which induced oriented but amorphous chains in the sPP nanofibers deposited on the collector. Post crystallization of the un-crystallizing chains at ambient temperature that yielded more form I was evidenced by the in situ FT-IR probes. For the aligned nanofibers collected by a rotating disc, the amount of mesophase increased due to additional stretching force on the solidifying nanofibers. Under cyclic tensile deformation, the aligned sPP nanofibers exhibited low permanent set and intermediate hysteresis with a mechanical behavior similar to particle-filled elastomers.