Sandwich-structured composite fibrous membranes with tunable porous structure for waterproof, breathable, and oil-water separation applications.

HYPOTHESIS: In general, microporous membranes with waterproofness, breathability, and oil-water separation performance are prepared from hydrophobic raw materials and demonstrated to exhibit an interconnected porous structure. Hence, constructing porous and gradient-structured composite membranes by integrating robust hydrophobic/lipophilic polyvinylidene fluoride (PVDF) and breathable polyurethane (PU) microporous membranes could help realize a selective separation process.

EXPERIMENT: Here, novel polyvinylidene fluoride-carbon nanotube/polyurethane/polyvinylidene fluoride-carbon nanotube (PVDF-CNT/PU/PVDF-CNT) sandwich-structured microporous membranes were fabricated by sequential electrospinning. The influence of the thickness ratios of PVDF/PU/PVDF and carbon nanotube (CNT) content on the fibrous construction, porous structure, and wettability of the composite membranes was systematically studied by scanning electron microscopy (SEM), pore size, porosity and contact angle. Significantly, the effect of the fibrous construction, porous structure, and wettability on the waterproofness, breathability, and oil-water separation ability of the composite membranes was investigated.

FINDINGS: The novel separation system proved the 'complementary effect' between the PVDF and PU membranes. Further, because of the elaborate gradient construction, superior porous structure, and robust hydrophobicity-oleophilicity, the resultant membranes exhibited moderate waterproofness (38 kPa) and excellent breathability (8.63 kg m-2  d-1 ), and oil-water separation, confirming that they could be promising alternatives for numerous practical applications, such as protective clothing, treatment of oil-contaminated water, and membrane distillation.