Effect of heat-press conditions on electrospun membranes for desalination by direct contact membrane distillation

Membrane distillation (MD) is considered as a promising next-generation technology for desalination. However, there is no specific membrane designed and engineered for this application yet. Recently, electrospun polymeric membranes have been widely investigated due to their relatively high porosity, high hydrophobicity and controllable pore size. However, the robustness of such membranes is not guaranteed as they are susceptible to wetting in long-term operation. Heat-press treatment is a simple and effective procedure to improve both morphological and mechanical characteristics of the electrospun membrane. Nevertheless, the heat-press technique is not fully investigated although some conditions are applied to the electrospun membrane in previous researches. In this paper, a comprehensive investigation of the effect of heat-press temperature, pressure and duration on the morphological and mechanical characteristics of electrospun membrane is accomplished. Impressive improvement of mechanical strength and liquid entry pressure (LEP) can be achieved after heat-press treatment on the electrospun membranes. It is also found that temperature and duration play more important roles than pressure in heat-press treatment. In addition, it is ascertained that optimal treatment conditions for heat-press includes temperature at 150 degrees C, pressure at 6.5 kPa, and duration for 8 h for the present electrospun polyvinylidene fluoride-co-hexafluoropropylene membrane. A decent DCMD permeation flux of 29 LMH and salt rejection of 99.99% can be achieved with the optimally heat-pressed electrospun membranes for desalination at feed and permeate temperatures of 60 and 20 degrees C, respectively. (C) 2015 Elsevier B.V. All rights reserved.