Fluorine-free waterproof breathable polyurethane fibrous membranes enabled by in situ polyurea cross-linking

Fluorine-free waterproof breathable fibrous membranes are attractive for protective textiles and related applications, yet balancing waterproofness, breathability, and mechanical robustness remains difficult in highly porous structures. Here, a sequential impregnation strategy was developed for polyurethane fibrous membranes using amino-functional polysiloxane and a waterborne blocked isocyanate in a water/ethanol medium. The polysiloxane established a low-surface-energy hydrophobic interface, while the blocked isocyanate served as a latent cross-linking agent that was thermally activated to stabilize the deposited modifier and reinforce inter-fiber junctions. This coupling of interfacial hydrophobization and BI-assisted latent cross-linking regulated the pore architecture without collapsing the fibrous framework. The resulting membrane delivered a hydrostatic pressure of 48.3 kPa while maintaining a water vapor transmission rate of 3.4 kg m −2 d −1 and an air permeability of 6.7 mm/s; the tensile strength increased from 6.1 to 10.28 MPa. This work provides a practical fluorine-free post-modification route for mitigating the trade-off among waterproofness, breathability, and mechanical integrity in fibrous membranes through a water/ethanol-based and process-controllable treatment strategy.