Surface modification of electrospun poly(vinyl chloride) membrane for oil-water separation

Abstract

Oil pollution is a critical problem that is caused by the activity of several industries and oil spills. It causes damage to the environment and human life. Thus, an effective and versatile technique is needed to treat the oily wastewater. The objectives of this thesis were to make (a) a hydrophobic porous membrane for separation of oil from water, and (b) a hydrophilic porous membrane by surface modification to remove water from oily wastewater by gravity. A series of polyvinyl chloride (PVC) electrospun membranes with various pore sizes (2.5 – 0.8 µm) was fabricated. The electrospinning process parameters such as voltage, tip-to-collector distance, and polymer-solvent ratio were optimized by Response Surface methodology to obtain a desired fiber diameter. The optimum conditions were found to be [polymer] = 16 wtpercent, the solvent ratio DMF:THF = 62.5:37.5, polymer feed rate = 1 ml-h, voltage = 11 kV, tip to collector distance = 14 cm, and drum speed = 500 rpm. The porosity, pore size distribution, hydrostatic pressure head, and membrane thickness were controlled by adjusting the electrospinning time. The pore size decreased with the increase of electrospinning time while the membrane thickness and hydrostatic pressure head increased. The resulting electrospun PVC membranes were superhydrophobic-superoleophilic with water contact angle above 140°. The chemical stability of the membrane against different conditions of pH and salinity was studied. Moreover, the oil filtration efficiency of the hydrophobic porous PVC membrane was investigated as a function of pore size for two membranes with the average fiber diameter of around 118 and 470 nm. The diesel oil recovery values after 45 minutes for the membranes with the average pore size of 2.5 µm and 0.8 µm were 95percent and 80percent, respectively. Hydrophilization of the PVC porous membranes was achieved by surface modification using two different approaches: (1) The membrane was first aminated with triethylenetetraamine (TETA) and then cationiz