Multiscale Structural Regulation and Environmental Adaptability of Polyamide-Imide Fibers

Polyamide-imide (PAI) molecules, in which amide bonds and imide rings are alternately linked, exhibit high molecular flexibility and improved solubility, thereby overcoming the processing limitations of polyimide (PI) in solvent systems. However, the structural evolution of PAI fibers during wet spinning remains unclear, and studies on their environmental adaptability are limited. In this study, we investigated the wet spinning process of PAI fibers, focusing on three key stages: fiber coagulation, wet-heat drawing, and thermal drawing. By integrating double diffusion theory with the molecular chain mobility mechanism, we systematically analyzed the correlations between process parameters and the multilevel structures of PAI fibers. Furthermore, pilot-scale PAI fibers were used to characterize performance degradation under different aging conditions. The results revealed that appropriate temperature promoted molecular chain orientation, producing fibers with a tensile strength of 3.3 cN/dtex at 340 °C. In addition, PAI fibers exhibited excellent stability under acidic and ultraviolet aging conditions.