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.

PPTA 是一种具有优异机械性能的芳纶纤维，通常表现出工艺诱导的位置依赖性分子链排列，这极大地影响了其机械性能。直接观察链重新定向以及纤维纺丝过程中的其他微观结构变化和演变特征一直是实验的挑战。本研究开发了一个粗粒度分子动力学 (CG-MD) 模型，以研究在考虑各种剪切变形和速率的干喷湿纺过程中 PPTA 的剪切控制微观结构演变。通过使用基于 MD 的 X 射线散射，系统地揭示了 PPTA 在溶液中和干燥后对微观结构的剪切效应。MD 结果进一步与假设泊肃叶流的宏观分析相结合，以证明 PPTA 链排列在纤维横截面中如何变化，以及喷丝头细孔的几何形状如何控制剪切变形和链排列。这些见解有望指导未来的工艺设计，以提高通过干喷湿纺制成的 PPTA 纤维的质量和性能。