Dilute solvent welding: A quick and scalable approach for enhancing the mechanical properties and narrowing the pore size distribution of electrospun nanofibrous membrane

Abstract

Major limitations to the practical use of nanofibrous membranes in water filtration are their weak mechanical properties and wide pore size distribution. This study describes a quick and scalable method to improve the mechanical properties and narrow the pore size distribution of nanofibrous membranes by welding the nanofibers at their junction points. The welding process involves a simple dilute solvent spraying step followed by heating, requiring only a few minutes. The polymer's solvent was diluted with a non-solvent to avoid excessive dissolution of the nanofibers. With that, the degree of welding can be controlled by the volume fraction of solvent, the heating temperature and heating temperature. Dilute solvent welding enhanced the mechanical properties of the nanofibrous membrane while slightly changed the fiber crystallinity and fiber size distribution. Furthermore, the membrane pore size distribution narrowed with welding while high porosity (~80%) was retained. In membrane distillation (MD) experiments, the welded nanofibrous membrane exhibited more robust MD performance than the pristine nanofibrous membrane with only slight decreases of vapor flux. This technique can be applied universally to treat both nanofibrous flat sheet and tubular membranes made from soluble polymers with their corresponding diluted solvents.