Shear-governed microstructural variation and evolution of PPTA in dry-jet-wet spinning process

• Flow-induced shearing dominates microstructural evolution of PPTA fibers. • Shearing rate mediates chain alignment during the manufacturing process. • Larger aspect ratios of spinnerets improve the quality of PPTA fiber products. A kind of aramid fiber with excellent mechanical properties, PPTA often shows process-induced, position-dependent molecular chain alignment that greatly impacts its mechanical performance. Direct observation of the chain reorientation along with other microstructural variation and evolution characteristics during fiber spinning has been a challenge for experiments. This study develops a coarse-grained molecular dynamics (CG-MD) model to investigate the shear-governed microstructural evolution of PPTA during dry-jet-wet spinning considering various shear deformation and rates. By using MD-based X-ray scattering, the shearing effects on microstructures are revealed systematically for PPTA both in the solution and after drying. The MD results are further coupled with a macroscopic analysis assuming Poiseuille flow to demonstrate how PPTA chain alignment varies in the cross section of a fiber, and how geometry of the fine orifice of a spinneret governs the shear deformation and chain alignment. These insights are expected to guide future process design to improve the quality and properties of PPTA fibers made via dry-jet-wet spinning.