Continuous bundles of aligned electrospun polyacrylonitrile (PAN) precursor nanofibers of different stages in electrospinning process were prepared with a flowing water bath collector.Then the as-electrospun nanofiber bundles were stretched in hot water at 97℃ into 2 and 3 times of the original lengths.Subsequently

characterizations and evaluations were carried out to understand their morphology

diameter

density

crystalline structure and orientation using SEM

WAXD etc.The study revealed that:(1) the polymer solution jet was stretched/elongated during electrospinning process

which formed and improved the crystalline structure and orientation; during the electrospinning process

the diameter of as-electrospun nanofiber bundles was decreased from 664 nm to 353 nm

while the crystallinity and the orientation increased from 42.55% to 47.76% and 37.48% to 43.93%

respectively

which led to the density increased from 1.1917 g/cm3 to 1.1943 g/cm3; and (2) the improvement of the crystalline structure and orientation was limited when most solvent was removed during the electrospinning process

and post-spinning stretching could substantially improve the crystalline structure and orientation.Meanwhile

the improvement of the crystalline structure and orientation of as-electrospun nanofiber bundles could enhance the post-spinning stretching process.