Cross‐Scale Correlation of Aging Behavior of <scp>PET</scp> Industrial Fiber Under Marine Service Conditions: From Molecular Chain Reconstruction to Macro‐Mechanical Property Evolution

ABSTRACT This study investigates the seawater aging behavior of high‐tenacity PET industrial fibers. Additionally, the varying length scales of structural changes were studied to reveal the seawater aging mechanisms. The fibers exhibit excellent long‐term stability after 127 days of immersion at 30°C, exhibiting negligible changes. In contrast, accelerated aging at 90°C reveals a three‐stage degradation process. In the pre‐aging stage ( t ≤ 1 day), elevated temperature induces molecular chain relaxation and disorientation in the amorphous regions, leading to an increase in elongation at break. During the steady‐aging stage (1 day &lt; t ≤ 37 days), a competition occurs between hydrolytic degradation in the amorphous regions and thermally‐induced recrystallization, manifesting as a gradual molecular weight decrease and a concurrent increase in crystallinity. In the rapid degradation stage ( t &gt; 37 days), intensive hydrolysis causes extensive chain scission, resulting in a sharp decline in both tenacity and elongation at break. Collectively, this work establishes a cross‐scale correlation from molecular chain reconstruction to macroscopic embrittlement, providing a mechanistic framework for predicting the service life of PET industrial fibers in marine environments.