Electrospun polyurethane microporous membranes for waterproof and breathable application: the effects of solvent properties on membrane performance

Electrospun polyurethane (PU) based nanofibrous mats were fabricated from the solutions prepared with different volume ratios of N,N-dimethylformamide (DMF), methanol (MeOH), and dichloromethane (DCM). The membrane structures such as the nanofiber diameter, the pore size distribution, and the porosity were investigated in detail. And the morphological, mechanical, waterproof, and breathable properties of the membranes were used to estimate the characteristics of the membranes. Various solutions were compared to obtain porous nanofibrous membranes without beads or curls, which revealed that morphologies of PU fibrous membranes could be finely regulated by tuning the solvent volume ratios and the solution concentrations. The results showed that the nanofibrous membranes with the DMF/DCM solvents exhibited the high fiber diameter (500–700 nm) and the wide pore size distribution (0.6–1.2 µm). Besides, the water contact angle (WCA) of the PU nanofibrous film using the 100% DMF was 133°, but it could not persist for a long time. And the resultant membranes presented high hydrostatic pressure to 2.1 kPa, modest water vapor transmission rate of 10.1 kg/m2/day, as well as robust mechanical properties with tensile strength of 6.6 MPa, which are desirable in many important applications including protective clothing.