Preparation of high-performance polyimide fibers via a partial pre-imidizationprocess

Abstract: In this work, a series of polyimide fibers (PI) based on 3,30 ,4,40-biphenyltetracarboxylic anhydride (BPDA)/p-phenylenediamine (PDA)were prepared through a partial pre-imidization process, and theproperties of these fibers were investigated in detail. Thepre-imidization degree (pre-ID) was successfully controlled byadjusting the amount of dehydration reagents, which was confirmed byFourier Transform Infrared. The scanning electron microscope imagesshow that the addition of dehydration reagents in the poly(amic acid)spinning dope improves the shaping of the precursor fibers, which isrelated to the thermodynamic phase separation in the coagulationbath. The WAXD patterns indicate that the formed partial rigid-rodand oriented PI chains in the preimidization process are beneficialfor forming a more ordered and regular crystalline structure in thepost-heat-drawing process, thus improving their mechanicalproperties, which exhibit an optimum tensile strength and modulus of1.7 GPa and 95.0 GPa, respectively. Meanwhile, the prepared PI fibersexhibit excellent thermal stabilities with the 5 wt% (T5%) weightloss temperature ranging from 530 to 568 C depending on thepre-imidization degree. This work provides a simple and facileapproach to preparing high-performance PI fibers through the partialpre-imidization process.