Self-sustained webs of polyvinylidene fluoride electrospun nanofibers at different electrospinning times: 1. Desalination by direct contact membrane distillation

Abstract

Self-sustained electrospun nanofibrous membranes (ENMs) were prepared using the polymer polyvinylidene fluoride (PVDF) and applied for desalination by direct contact membrane distillation (DCMD). Different electrospinning times were considered to prepare the PVDF ENMs of different thicknesses ranging from 144.4 to 1529.3 mu m. A systematic experimental study on the effects of membrane thickness on the DCMD performance is carried out for the first time. The surface and cross-section of the ENMs were studied by scanning electron microscopy and the mean size of the fibers together with its distribution was determined. The water contact angle, the inter-fiber space, the void volume fraction and the liquid entry pressure of water inside the inter-fiber space were determined by different characterization techniques. It was observed an enhancement of the thickness and the liquid entry pressure of water with the increase of electrospinning time, a decrease of the mean size of the inter-fiber space, whereas no significant changes were observed for the diameter of the electrospun fibers (1.0-1.3 mu m), the void volume fraction (0.85-0.93) and the water contact angle (137.4-141.1 degrees). The size of the inter-fiber space is not uniform throughout the thickness of the ENMs. The effects of the ENMs thickness on the DCMD performance was studied for different feed temperatures and sodium chloride feed aqueous solutions with concentrations up to 60 g/L, which is about two times greater than a typical seawater concentration. The permeate flux of the ENMs is lower for longer electrospinning time and the obtained permeate fluxes in this study are higher than those reported so far for PVDF ENMs.