Compatibility of LDPE/PA6 and the Preparation and Performance of Its Sea–Island Ultrafine Fibers

The compatibility of low-density polyethylene (LDPE) and polyamide 6 (PA6) during melt-blending spinning plays a crucial role in ensuring good spinnability, while the drawing and fiber-splitting processes are key to forming ultrafine fibers. This study systematically investigates the Flory–Huggins interaction parameters between LDPE and PA6, as well as the fiber-splitting and drawing behaviors of unfigured sea–island composite fibers, with a focus on compatibility and fabrication techniques. The results reveal that the Flory–Huggins interaction parameters for LDPE and PA6 at different blend ratios are 0.0517 ± 0.0014, significantly exceeding the critical interaction threshold of 0.0091, indicating complete incompatibility between the two polymers. Through an in-depth analysis of the drawing process, it was found that after the drawing ratio of 4, the fiber fineness reached 3.7 dtex, with a fiber orientation of 78%, a breaking strength of 5.56 cN/dtex, and a breaking elongation of 41%. During the fiber-splitting process of LDPE/PA6 sea–island composite fibers, the optimal conditions were determined to be a splitting temperature of 90 °C, a splitting time of 60 min, and a degradation rate of 43%. Under these conditions, the composite fiber diameter significantly decreased from 27.04 μm to 0.85 μm. These findings provide valuable insights into optimizing the manufacturing process and enhancing the performance of LDPE/PA6 composite fibers.