Keywords: straight chain crystal, fiber spinning, crystalline morphology
Summary:There has been extensive study of ultra-high molecular weight polyethylene (UHMWPE) fibers owing to their remarkable tensile modulus and strength. It is generally understood that these properties develop during the post drawing process. However, many questions remain regarding the importance of crystalline morphology and structure on the observed mechanical properties. Furthermore, basic relationships between starting as-spun fiber crystalline structure, drawing rate, temperature and the evolution of crystalline structure during drawing are unaddressed. Such relationships are fundamental in understanding the importance of crystalline structure and morphology on mechanical properties. In this study we use a modified extensional rheometer to perform controlled drawing experiments on a series of as-spun UHMWPE fibers. We measure true stress and strain throughout the drawing process, and relate mechanical properties to processing parameters such as rate of drawing, temperature, and fiber diameter. Furthermore, the crystalline structure is measured as a function of draw ratio via small angle x-ray scattering to correlate structure, processing, and performance. Ultimately, a model is presented to explain the observed evolution of mechanical properties in UHMWPE fibers.