Multiscale Evolution of Chain Orientation and Crystal Structure under the Dual Action of Temperature and Stress

A comprehensive understanding of the multiscale structural evolution that governs fiber properties during polyamide formation is essential for the theoretical development of high-strength fibers. This study systematically investigates the hierarchical structural transformations in high-strength polyamide 66 fibers (H-PA66F) at key stages during high-speed spinning, with a focus on molecular chain conformations, hydrogen bonding networks, crystalline organization, orientation dynamics, and long-period structural features. By constructing a three-phase structural model, the study elucidates the progressive structural-property relationships during fiber processing. The mechanical enhancement observed throughout the formation process is attributed to synchronized structural optimizations: hot drawing enhances fiber strength through crystal perfection and increases the alignment of rigid segments, while subsequent heat setting stabilizes the structure by reducing defects. These findings establish a robust structure-performance framework, providing theoretical insights for the targeted multiscale structural engineering of high-performance polyamide fibers.