Polymer Concentration-Driven Morphological and Mechanical Variations in Flash-Spun High-Density Polyethylene Fibers

Flash-spun filaments (FSFs) made from high-density polyethylene (HDPE) are widely used in industrial nonwovens due to their unique morphology and mechanical robustness. In this study, we investigated the effect of polymer concentration (5-15 wt%) on FSF formation using a laboratory-scale flash-spinning system operating under supercritical conditions. Morphological, mechanical, and crystallographic analyses were conducted to understand the underlying mechanisms. As polymer concentration increased, filament thickness, crystallinity, and strength improved, with optimal performance observed at 12 wt%, where the modulus peaked at 270.77 cN/tex and elongation was minimized. At 15 wt%, mechanical properties declined due to hindered solvent evaporation, which disrupted polymer alignment and reduced filament orientation. X-ray diffraction analysis revealed small crystal sizes (6.4-6.9 nm) across all samples, suggesting that rapid phase separation limited crystal growth. This indicates that polymer concentration mainly affects the number of crystalline domains rather than their size. The results demonstrate that solvent evaporation dynamics and phase separation behavior play critical roles in determining FSF structure and performance. Precise control of polymer concentration is therefore essential to optimize fiber morphology, orientation, and mechanical stability, providing valuable insights for the design of high-performance flash-spun nonwovens in industrial applications.