Structural engineering and liquid filtration performance regulation of micro-/nanofibrous nonwovens

To develop micro-/nanofibrous nonwoven filtration media with high particle-retention efficiency, favorable liquid transport, and mechanical stability, PA6/LDPE sea–island fibers were employed. The nonwovens, comprising three-dimensionally intermingled PA6 microfibers and nanofibers, were fabricated by bicomponent melt spinning, hydroentanglement, selective dissolution-based fiber opening, and hot calendering. The effects of the mass ratio of neat PA6 to the PA6/LDPE sea–island component and hot-calendering pressure on fiber morphology, mechanical properties, pore structure, and liquid filtration performance were investigated. Changing the component ratio from 7:3 to 3:7 produced bimodal fiber-diameter distributions: the microfiber diameter decreased from 8.2 to 5.7 μm, while the nanofiber diameter remained at 710–750 nm and the average pore size decreased from 7.09 to 2.80 μm. Increasing the hot-calendering pressure from 0.1 to 3 MPa reduced the average pore size from 3.38 to 1.71 μm and increased the machine-direction breaking force from 380.36 to 419.86 N, whereas the cross-direction tearing force decreased from 33.34 to 25.68 N. At 50 °C, 2 MPa, and 1.4 m/min, filtration efficiencies for 800 nm, 3 μm, and 5 μm SiO 2 particles were 38.6%, 86.4%, and 98.7%, respectively, at 0 kPa, with a water flux of 523.4 L m −2 h −1 . At 5 kPa, the corresponding efficiencies were 33.5%, 83.2%, and 97.6%, with a water flux of 4325.8 L m −2 h −1 . For YH-15 aviation hydraulic oil at 5 kPa, the material hot-calendered at 3 MPa achieved efficiencies of 97.5%, 99.6%, and 99.7% for 4, 6, and 14 μm A3 test dust particles, respectively, with an oil flux of 1106.2 L m −2 h −1 . These findings guide the fabrication of PA6-based micro-/nanofibrous nonwovens with controllable pore structures for precision water and aviation hydraulic oil filtration.