Fabrication of laminated composite filter with nonwoven fabrics for oil/water separation

Various materials have been prepared and applied for the oil-water mixture separation, but there are some problems such as high cost, complicated formulation process and inferior durability. Nonwoven fabrics are widely used in industrial fields because of their low production cost and high economic benefit. In this study, a sandwich-structure filter was prepared for oil/water separation based on laminated nonwovens. Spunbond-meltblown-spunbond (SMS) nonwoven treated with silica and fluorine resin was selected for the hydrophobic top layer. The spunlaced viscose (VS) impregnated with citrate was used for the hygroscopic core layer while spunbond polypropylene (PP) prepared for the bottom substrate. These three layers were reinforced on an ultrasonic-bonding machine and tested for oil-water separation. Surface morphology and chemical group changes of treated fiber were recorded by scanning electron microscope (SEM), atomic force microscope (AFM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR). The effect of surface hydrophobicity and core hydrophilicity on separation efficiency was analyzed. The durability after recycles was evaluated and discussed. The possible separation mechanism was proposed. The results demonstrated that coating and spraying methods achieved uniform distribution of silica and fluorine resin onto the fiber surface. The suitable conditions for the preparation of composite filter were obtained as follows: the surface SMS layer was coated with silica, then sprayed with fluorine resin for a 6.0%weight gain to get a hydrophobic layer. The core layer viscose fiber impregnated with 3.0% citrate to enhance its hygroscopicity. The three layers were laminated and reinforced for the composite filter. Improving the hydrophobicity of top layer and the hydrophilicity of core layer both contributed to the enhance of separation efficiency and stability. The pore size of composite filter was mainly in the range of 9-11 mu m with a 35% distribution. After 15 times recycles, the water recovery ratio remains over 95% while water contact angle decreased from 150 degrees to 135 degrees. After layers laminated and bonding, the hydrophobic surface trapped oil and water in the mixture, hygroscopicity layer enabled a connection with the water in mixture through SMS layer and formed a capillary water channel. The water transferred to the sublayer by gravity and capillary action to actualize oil-water separation. These results provided new insights for the application of nonwoven fabrics on oil-water separation.