Synthesis of Heterocyclic Aramid Fiber Based on Solid‐Phase Cross‐Linking of Oligomers with Reactive End Group

Low compressive strength of aramid fiber is one of the major obstacles for its application in advanced composite materials. In this study, poly‐(benzimidazole‐terephthalamide) (PABI) fibers are fabricated by solid‐phase cross‐linking of corresponding oligomers end‐capped with norbornene anhydride (NA). Concentration of the spinning solution increases and apparent viscosity is reduced significantly through this method, which improves its processability. Reactivity and thermal stability of the NA group are measured by in situ Fourier transform infrared (FTIR) and thermogravimetric analysis and it shows high reactivity at 360 °C and adequate thermal stability under 400 °C. Results of solubility test and dynamic mechanical analysis indicate cross‐linking degree increases with decrease of molecular weight of the corresponding oligomer. Results of both 2D wide angle X‐ray diffraction and polarized FTIR illustrate orientation will be affected by cross‐linking and it decreases with the increase of cross‐linking degree. PABI fibers fabricated through this method can maintain outstanding mechanical properties and compressive strength is improved by 67% at most. Interestingly, interfacial shear strength of PABI fibers is improved by nearly 20% and damage between skin–core layers after debonding of fiber and resin is not observed.