Dry-jet wet spinning of aromatic polyamic acid fiber using chemical imidization

A solution of about 15% polyamic acid (PAA) prepared from 4,4′-oxydianiline and pyromellitic dianhyride in N,N-dimethyl acetamide (DMAc) was used for fiber spinning. To obtain a high draw ratio of the PAA fiber during spinning, acetic anhydride or acetic anhydride and pyridine were added to the PAA solution to make it slightly gelled; such gelling contributed to high drawing of the PAA fibers during spinning. Before spinning the properties of the solution after acetic anhydride or acetic anhydride and pyridine were added, and the diffusion property of DMAc into various coagulants were examined. Even though acetic anhydride was only added to the spinning solution, the diffusion rate became slower and the solution viscosity increased, because PAA was converted to the corresponding polyimide (PI). Pyridine affected the rate dramatically. The mechanical properties of the PAA fibers obtained in this system were examined. Solid PI fibers were also obtained by annealing of the PAA fibers. The ultimate stress and initial modulus of the PAA fiber were around 268 MPa and 4.1 GPa, respectively. After the fiber was annealed at 350°C without tension for 30 min under nitrogen, these values increased to around 399 MPa and 5.2 GPa, respectively.