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The electrospinning of polyacrylonitrile (PAN) fibers from strain-hardening PAN solutions was studied. The strain-hardening PAN electrospinning solutions were prepared by adding ultrahigh-molecular-weight PAN (UHMWPAN) into medium-molecular-weight PAN (MMWPAN) solutions. The strain-hardening behavior of the solutions was evidenced by the CaBER extensional rheological tests. In electrospinning of PAN nanofibers, the solutions containing UHMWPAN were found to be stable when large electric field intensity was applied at a constant source-target distance, different from the case that a solution without UHMWPAN was used. PAN nanofibers with smaller diameter (270 nm compared with 496 nm for the nanofibers containing no UHMWPAN) could be electrospun from the strain-hardening solutions at larger electric field intensity and no beaded fibers were observed. The results of X-ray diffraction (XRD) and mechanical tests showed that the crystallinity, crystal orientation and mechanical performance of electrospun PAN nanofibers were improved with the increase of electric field intensity.

The spinnability in pre-gelled gel spinning of polyacrylonitrile (PAN) precursor fibers was investigated. The spinning solutions were aged at 25 °C for different times prior to fiber spinning. The pre-gelled spinning solution aged for 2.5 h was much more strain hardening than the ungelled one, which can increase the spinnability of the solution. The maximum take-up velocity of the first winding roller V 1m, which reflects the spinnability of the spinning solutions, was found to be largest when the aging time was 1.5 h. The spinnability increased with the increase of the air gap length and the lengthdiameter ratio L/D of the spinnerette. Once the L/D increased beyond 15, the spinnability hardly changed. The fibers spun from the spinning solution aged for 1.5 h had the best mechanical properties and favorable structure, showing that good spinnability favors the performance increase of resultant PAN precursor fibers.

The homogeneity of PAN/DMSO/H2O spinning dopes with conventional PAN molecular weight and comparative high PAN concentration have been investigated using rheology method. The rheological results show that G′ and G″ of these solutions increase with increasing oscillation frequency. At lower temperature and higher H2O content, higher viscous modulus and elastic modulus are observed, too. The homogeneity of PAN/DMSO/H2O systems is reflected through the logG′-logG″ plots as well as gel point temperatures. The theoretical analysis indicates PAN/DMSO/H2O spinning solutions with conventional PAN molecular weight are close to homogeneous systems, which are very suitable for gel spinning.