High‐Density Polyethylene Janus Fibrous Membrane with Enhanced Breathability and Moisture Permeability via PDA Assisted Hydrophilic Modification

Abstract Functional fibrous membranes with high mechanical properties are intensively developed for different application fields. In this study, to enhance moisture and air permeability without compromising mechanical strength, a facile float‐surface modification strategy is employed to fabricate Janus fibrous membranes with distinct hydrophobicity/hydrophilicity using the high‐density polyethylene (HDPE) fibrous membranes. By coating one side of the HDPE fibrous membranes with polydopamine (PDA) and a superhydrophilic polyelectrolyte, the obtained Janus HDPE fibrous membranes demonstrate an excellent water transmission rate (577.61 ± 72.66 g m − 2 h −1 ), water vapor transmission rate (WVTR, 131.62 ± 24.34 g m − 2 h −1 ) and gas permeability (17,496 ± 235 m 3 m − 2 h −1 bar −1 ), which are much better than those commercial membranes (Tyvek with water transmission rate 518.93 ± 23.20 g m − 2 h −1 , WVTR 53.09 ± 6.19 g m − 2 h −1 , and gas permeability 2,871 ± 145 m 3 m − 2 h −1 bar −1 ). Further, the Janus HDPE fibrous membranes keep outstanding mechanical strength (17.00 ± 4.26 MPa of tensile strength, 45.49 ± 8.75% of strain at break), and exhibit an asymmetric wettability on each side which is demonstrated by the separation experiments with various oil‐water mixtures. This simple modification approach not only improves the serviceability of HDPE fibrous membranes but also offers scalable potential for apparel applications and other industrial applications.