Effect of drying method on the microstructures and mechanical strength of polyacrylonitrile nascent fibers

Polyacrylonitrile (PAN) nascent fiber plays an important role in the structural formation and development of the precursor fibers and carbon fibers. This work is used to evaluate the effect of drying methods (water-drying, ethanol-drying, acetone-drying and freeze-drying) on the microstructures and mechanical strength of PAN nascent fibers. The appearance, surface morphologies and chemical groups of nascent fibers were not affected by the different drying methods. However, the pore size distribution, the morphologies of the microfibrillar network, crystal structures and mechanical strength of nascent fibers were significantly influenced by the different drying methods. Water-drying resulted in the decrease in pore size and volume and the shrinkage of nascent fibers. Meanwhile, the pore/void size, pore volume, crystal size and crystallinity of nascent fibers were relatively large after ethanol-drying and acetone-drying. As for freeze-drying technique, the nascent fibers had smaller values of crystal size, crystallinity, tensile strength and tensile modulus. Based on these results, it was suggested that the freeze-drying was suitable method to retain intrinsic structures of nascent fibers.