关键词: 超高分子量聚乙烯（UHMWPE）, 凝聚态结构, 蠕变行为, 力学性能, 热拉伸

Abstract: Ultrahigh molecular weight polyethylene (UHMWPE) fibers have a highly oriented crystalline chain structure. This special structure contributes them with excellent physical and mechanical properties. UHMWPE fibers are considered to be the material with the highest specific strength and specific modulus in the world. Additionally, they exhibit low density, excellent moisture absorption, exceptional chemical resistance, high impact strength, and remarkable wear resistance. These outstanding characteristics make them indispensable in various industrial sectors such as aerospace, automotive engineering, national defense, textile manufacturing, chemical engineering, and medical technology. With so many excellent properties, the UHMWPE fiber has its shortcomings, for instance, poor temperature resistance, bad composite adhesion and creep resistance. The creep behavior makes UHMWPE fibers unstable in product size and shape, which greatly limits their application in composite materials, ropes and other fields. Therefore, improving the creep resistance of UHMWPE fibers has been the focus of researchers. By exploring the evolution of condensed matter structure of UHMWPE fibers during multistage thermal stretching, the creep rule of fibers under different conditions and the change rule of fiber properties after creep behavior, the article can provide theoretical support for improving the creep resistance of fibers. In order to study the creep properties of ultrahigh strength UHMWPE fibers during multistage thermal drawing, fiber samples with different thermal stretching rates were collected in different sections on actual industrial production lines. The condensed matter structure, mechanical properties and creep properties of chemical fibers during thermal stretching were studied by means of two-dimensional wide-angle X-ray diffractometer, universal testing machine and creep property tester. The variation of fiber creep rates under different temperatures and stresses, as well as the correlation between creep size and fiber structure and mechanical properties, were analyzed. The results showed that with tiered thermal stretching grading, the rate of crystallization and orientation of the fibers could reach 88.97% and 0.973 respectively, which indicated that not only the mechanical properties of the fibers but the creep resistance were improved. When the test temperature was less than 70 ℃, the creep behavior of the fiber was not obvious. It demonstrated two distinct stages of rapid and gradual increase with increasing applied stress, while the transition time between these stages decreased as both temperature and applied stress rose. The creep behavior of the fiber, however, exhibited a continuous acceleration when the temperature reached 90 ℃. Furthermore, it was observed that the magnitude of stress directly influenced the extent of creep acceleration during later stages. When the fiber creeped by 10%, its breaking strength showed an increasing trend, and when it creeped by more than 20%, its mechanical properties became worse.

Key words: UHMWPE, condensed matter structure, creep behavior, mechanical properties, thermal tensile