(670d) Tuning the “Drawability” of Ultra-High Molecular Weight Polyethylene Fibers

Ultra-high molecular weight polyethylene (UHMWPE) fibers have been extensively studied because of their remarkable tensile modulus and strength. Most researchers agree these properties are induced during post drawing, or heated stretching, of the fiber. To achieve properties that are industrially useful draw ratios (a measure of the applied deformation) greater than 100 are required. Typical PE melts can not be drawn to this extent. Gel-spinning is necessary to produce materials with sufficient “drawability”. Gels made from dilute polymer solutions generate a system with lower entanglement density which allows for greater extensibility before failure. Further works have reported other methods and techniques to increase the ultimate draw ratio but are largely empirical observations. To continue to improve PE fibers a more detailed understanding of the factors that control “drawability” is needed. In this study we use a modified extensional rheometer (VADER 1000) to analyze the post-draw processing of UHMWPE fibers. With this instrument we can monitor true stress and strain at failure as a function of various draw parameters such as rate and temperature. Small angle x-ray scattering is used to correlate crystalline structure to the failure characteristics. With this information a fundamental understanding of how to control post-drawing will be developed.