The role of dilute concentrations (1 wt %) of a photoinitiator, 4,4 0 -bis(diethylamino)benzophenone, on the processability and properties of the resulting wet-spun polyacrylonitrile (PAN) fibers are reported. Rheology measurements show no adverse effect on the viscosities of solutions by the addition of the photoinitiator. Fibers containing photoinitiator were successfully wet-spun from PAN-DMSO solution. FTIR results prove that 4,4 0 -bis(diethylamino)benzophenone was retained in the fibers after coagulation and poststretching. SEM micrographs show no deterioration of the post-stretched fiber microstructure due to the presence of photoinitiator. Tensile testing results show a small reduction in the strain-at-break of post-stretched fibers containing photoinitiator when compared with pure (control) PAN fibers. After UV treatment, fibers with 4,4 0 -bis(diethylamino)benzophenone display a higher tensile modulus compared with the other sets. Wide-angle X-ray diffraction results show no significant decrease in interplanar spacing and size of the crystals within the fibers containing photoinitiator, but such fibers retain a higher extent of molecular orientation after being UV treated. Conversion indices were measured from the WAXD spectra and compared with conventional thermal stabilized fibers. This correlation confirms that the addition of 1 wt % photoinitiator to PAN followed by 5 min of UV treatment leads to a conversion index that is observed in control fibers after more than an hour, which could reduce the conventional thermo-oxidative stabilization time significantly. These results indicate the potential of the dual stabilization route in generating precursor fibers with higher molecular orientation, and possibly reducing the thermo-oxidation time during carbon fiber processing.

An alternative, rapid stabilization route for polyacrylonitrile (PAN) precursors is reported based on UV-induced crosslinking and cyclization reactions. Two mechanisms of photoinitiation were investigated: homolytic cleavage and hydrogen abstraction. Solution-cast PAN copolymer samples were irradiated for different durations (100, 300, and 600 s) and temperatures ($65 and 100 C, below and above glass transition temperature respectively). FTIR spectra show the formation of carbon-oxygen, carbon-nitrogen, and carbon-carbon double bonds (1450-1700 cm À1 region) attributed to the development of cyclized structure. Conversion indices estimated from the FTIR spectra indicate samples containing hydrogen abstraction photoinitiator show higher extents of cyclization among the three main set of samples. This observation was also confirmed by higher gel percentages measured on the same set of samples. FTIR conversion indices of samples UV-treated above glass transition temperature were higher compared with that for the same specimens UV-treated below glass transition temperature. DSC results show that samples containing hydrogen abstraction photoinitiator enable a higher extent of post-UV thermal cyclization. FTIR spectra of the UV treated samples were compared with conventional thermal stabilized specimens. This comparison confirms that the addition of 1 wt % photoinitiator to PAN followed by 5 min of UV treatment increases the rate of the cyclization reaction and reduces the thermal oxidation time by over an hour, which could significantly reduce the conventional stabilization time by half. These results indicate the potential for an energy-efficient, costeffective route for producing carbon fibers.

A rapid, dual‐stabilization route for the production of carbon fibers from polyacrylonitrile (PAN) precursor fibers is reported. A photoinitiator, 4,4′‐bis(diethylamino)benzophenone, was added to PAN solution before the fiber wet‐spinning step. After a short UV treatment that induced cyclization and crosslinking at a lower temperature, precursor fibers could be rapidly thermo‐oxidatively stabilized and successfully carbonized. Scanning electron microscopy micrographs show no deterioration of the microstructure or hollow‐core formation in the fibers due to UV treatment or presence of photoinitiator. Fast‐thermally stabilized pure PAN‐based carbon fibers show hollow‐core fiber defects due to inadequate thermal stabilization, but such defects were not observed in carbon fibers derived from fast‐thermally stabilized fibers that contained photoinitiator and were UV treated. Tensile testing results confirm that fibers containing 1 wt % photoinitiator and UV treated for 5 min display higher tensile modulus than all other sets of thermally stabilized and carbonized fibers. Wide‐angle X‐ray diffraction results show a higher development of the aromatic structure and molecular orientation in thermally stabilized fibers. No significant increase in interplanar spacing or decrease in crystals size were observed within the UV‐stabilized carbon fibers containing photoinitiator, but such fibers retain a higher extent of molecular orientation when compared with control fibers. These results establish for the first time, the positive effect of the external addition of photoinitiator and UV treatment on the properties of the PAN‐based fibers, and may be used to reduce the precursor stabilization time for faster carbon fiber production rate. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40623.

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