A novel PAN-based fiber with accelerated alkaline hydrolysis efficiency: co-polymerization, spinning, and modification

This study reported a simple two-step process for improving the efficiency of surface alkaline hydrolysis of Polyacrylonitrile (PAN)-based fibers. In the first step, poly(acrylonitrile-co-acrylic acid) (P(AN-co-AA)) was synthesized by aqueous-phase suspension polymerization with the introduction of an appropriate amount of acrylic acid (AA) comonomers, and P(AN-co-AA) fibers were prepared using wet spinning. However, the absence of neutral comonomers in the copolymer led to suboptimal spinnability of the P(AN-co-AA) solutions. The solvent was difficult to remove during the washing process, thereby hindering the fibers from being drawn at high multiplicity. Therefore, to address this issue, the pH of the washing bath was reduced to disrupt the deprotonation of the carboxyl (COOH) groups. This adjustment successfully realized the preparation of P(AN-co-AA) fibers with a high draw ratio by wet spinning. In the second step, the P(AN-co-AA) fibers were immersed in 12 % NaOH solution at 60 °C for 20 min for surface alkaline hydrolysis modification. The alterations in the structure and properties of the P(AN-co-AA) fibers before and after hydrolysis were analyzed using SEM, FTIR, backward reflection experiments, and XRD. In addition, the improvement of surface alkaline hydrolysis efficiency by introducing COOH groups during the polymerization stage, followed by hydrolysis, was confirmed by comparison with PAN fibers under the same surface alkaline hydrolysis conditions using FTIR and XPS. This is significant for the large-scale preparation of highly hydrophilic PAN fibers, as well as for the further functionalization of the active sites on the fiber surface.