Improvement of Condensed Structure and Mechanical Properties of Ultra‐High Molecular Weight Polyethylene Fibers Under Multi‐Factor Coupling

ABSTRACT The exceptional properties of ultra‐high molecular weight polyethylene (UHMWPE) fibers stem from their condensed state structure, which consists of crystalline regions, amorphous regions, and the transition zones between them. The formation of this structure is a non‐equilibrium process, resulting from the combined effects of various factors such as temperature and tensile stress. Initially, UHMWPE fiber hot stretching devices have been designed and built to efficiently carry out multi‐stage and multi‐fold stretching tests on as‐spun fibers under the coupled influence of stress and temperature. These experiments allowed us to investigate the influence laws of multiple factors, including temperature, tensile stress, and stretching speed, on the condensed state structure and mechanical properties of the fibers. The experimental results revealed that temperature not only promotes the movement and disentanglement of molecular chains but also facilitates the perfection of the crystal structure. Appropriate temperature and specific tensile stress can increase the crystallinity of the fibers. Lower stretching speeds and tensile stress can significantly improve the maximum stretching ratio of the as‐spun fibers. The increase in tensile stress contributes to enhancing the orientation of molecular chains spanning both crystalline and amorphous regions within the fibers. Notably, through three‐stage thermal stretching and optimizing the conditions at each stretching stage, UHMWPE fibers can undergo a transition from folded‐chain lamellar crystals to extended‐chain lamellar and fibrillar crystal structures, thereby enhancing the regularity and density of their condensed state structure. This process is highly beneficial for improving the mechanical properties of the fibers.