High-performance polymer fibers have broad applications in composites due to high strength and excellent toughness. However, the enhancement in tensile strength often results in a decrease in elongation at break, and simultaneous increase of strength and toughness is still challenging for aramid fiber. Herein, an effective method based on relaxation time theory is proposed to simultaneously enhance the tensile strength and elongation at break for heterocyclic aramid fiber. Ultra-high molecular weight heterocyclic aramid (HMPBIA) was added in the heterocyclic aramid (PBIA) spinning dope to prepare fibers. The structure evolution of fiber is studied in detail combining with experiment and simulation. Results of Molecular Dynamics simulations prove that HMPBIA acts as a role of mainstay by maintaining straight chain conformation in highly oriented fibers. This unique mainstay-body structure weaken slippage between molecular chains when the fiber is subject to tension. Further characterizations by small angle X-ray scattering (SAXS) and scanning electron microscope (SEM) confirm the formation of mainstay-body structure in the fiber, which improves tensile strength and elongation at break by 17.7% and 16.7%, respectively.

高性能聚合物纤维由于具有高强度和出色的韧性而在复合材料中具有广泛的应用。然而，拉伸强度的提高通常导致断裂伸长率的降低，并且强度和韧性的同时提高对于芳族聚酰胺纤维仍然是挑战。在此，提出了一种基于松弛时间理论的有效方法来同时提高杂环芳纶纤维的拉伸强度和断裂伸长率。将超高分子量杂环芳族聚酰胺（HMPBIA）添加到杂环芳族聚酰胺（PBIA）纺丝原液中以制备纤维。结合实验和仿真，详细研究了纤维的结构演变。分子动力学模拟的结果证明，HMPBIA通过在高度取向的纤维中保持直链构象而起到了主体作用。当纤维受到张力时，这种独特的主体结构会削弱分子链之间的滑动。通过小角X射线散射（SAXS）和扫描电子显微镜（SEM）进行的进一步表征证实了纤维中形成了主体结构，从而分别将拉伸强度和断裂伸长率提高了17.7％和16.7％。