A Single Fiber Peel Test to Measure Fibrillar Interactions in Ultra High Molecular Weight Polyethylene Fibers

Abstract

This paper examines the effects of meso/nanostructure in ultra high molecular weight polyethylene (UHMWPE) fibers on their macroscopic mechanical properties. Tensile strength and stiffness in UHMWPE fibers is achieved through a drawing process that results in the extension and alignment of the polymer chains. However, the drawing process also yields a complex fibrillar hierarchy at the meso/nanoscale. Nanoscale fibrils, the fundamental structural feature of the fibers, are consolidated through the drawing process with physical branches connecting adjacent fibrils, creating a 3-dimensional network. The interaction of fibrils through consolidation and network junctions has implications for the way load is transferred through the fiber in applications involving tensile and transverse compressive loads. A single fiber peel test has been designed to quantify fibril interaction for fibers of different levels of draw and subsequently different mechanical properties. A miniature peel test apparatus, along with high speed cameras, is used to measure and observe the peeling of the fiber and separation of the fibrillar network. Results indicate an increase in adhesive fracture energy for fiber having undergone a higher draw ratio. Images acquired during the peel test indicate that higher fracture energy is directly related to consolidation of fibrils into larger bundles influencing the deformation of the fibril network. These results are explored and the implications for the relationship between processing, structure, and properties are discussed.