Fabrication of durable hydrophobic porous polyurethane membrane via water droplet induced phase separation for protective textiles

The demand for functional membranes with balanced waterproofness and with good water vapor transmission in wearable applications is increasing by the day. However, their low wear resistance, low moisture tolerance, complicated fabrication procedures, and high health risk limit their outdoor use. In this study, we fabricated a waterproof and breathable polyurethane porous membrane for a membrane outside/fabric inside wearable fabric through an effective and facile dry process called evaporation induced phase separation. The matrix of the polyurethane membrane was mainly modified by water droplets and diisocyanate crosslinking agents, which allow the resultant membrane to be porous and durable. The water vapor transmission of the polyurethane water in oil emulsion was efficiently enhanced by introducing a porous network incorporated with tiny water droplets in the polyurethane emulsion. The optimization method for the emulsion allowed the waterproof, breathable porous membrane to sustain a tensile load of 35 MPa with an abrasion resistance of 15,000 cycles. Notably, the optimized porous membrane tended to exhibit a high hydrostatic pressure of 3500 mmH ₂ O, good breathability of 3000 g/m ² day, and excellent porosity of 65%, which suggests that evaporation induced phase separation is a facile method for designing the membrane. These promising results show that the waterproof and breathable porous membrane can compete with commercially available protective membranes and coatings because of its porosity, facile synthesis, low cost, non-swelling behavior, high stability, and commercial scale production.