Lamellae break induced formation of shish-kebab during hot stretching of ultra-high molecular weight polyethylene precursor fibers investigated by in situ small angle X-ray scattering

The extracted low-oriented ultra-high molecular weight polyethylene precursor fibers were stretched at the temperature of 80 °C. In situ small-angle X-ray scattering (SAXS) measurement using synchrotron radiation was applied to study the microstructure evolutions of fibers including the deformation and break of lamellae, the diminishing of microvoids, and the formation of shish-kebab. It was found that hot stretching could induce different kinds of SAXS patterns: two-point pattern indicating the stacking lamellae, X-shaped pattern indicating the tilted state of lamellae, the changing of streak pattern indicating the evolution of microvoids and shish structures respectively. During later stage of stretching, the shish structures along the fiber axis became remarkable to develop the final shish-kebab structures accompanied by the break-reorganization of original lamellae. The results also reveal the close relationship between macroscopic deformation and microstructural evolution that the macroscopic external stress loaded on internal microstructures can effectively promote the transformation from chain-folded lamellae to chain-extended crystals.