Evaluation of Intrinsic-Type and Hydrophobic Three-Dimensional Melamine/Polyvinyl-Alcohol Formaldehyde Sponges Containing a Hierarchical Porous Structure for Emulsion Separation

Abstract

Emulsion separation of emulsified oil wastewater has been an urgent problem from both environmental and economic perspectives to be dealt with. Here, to overcome the emulsion separation material-prepared process involving expensive equipment and consuming large energy and the composite component-functionalized running off problem during application, a series of intrinsic-type and hydrophobically functionalized three-dimensional (3D) melamine/polyvinyl-alcohol formaldehyde (MF/PVF-Cn-x) sponges containing interpenetrating polymer networks (IPNs) and a hierarchical porous structure were synthesized by introducing a PVF network into a commercial melamine (MF) sponge by co-acetalation crosslinking reaction first and further acylating chlorination chemical grafting reactions. Water contact angles of as-prepared sponges were higher than 114.7°. Cross-sectional SEM morphological observation and pore size distribution curves demonstrated that interpenetrating polymer networks (IPN) and a hierarchical porous structure were constructed successfully. Their pore size scope was from 1 to 100 μm, and the average pore size was around 20 μm (15.7 and 25.1 μm), which was similar to a stable emulsion droplet size of 20 μm, which satisfied the size sieving requirement for emulsion separation. Compared with the separation performance of 2D membrane materials, MF/PVF-Cn-x 3D hierarchical porous materials exhibited excellent separation performance and antifouling property. Among them, the MF/PVF-C16-46.8% sponge had the most prominent emulsion separation performance with a flux of 9.55 × 104 L m–2 h–1 bar–1 and an efficiency of nearly 100%. Furthermore, the separation flux of MF/PVF-Cn-x was still higher than 2.22 × 104 L m–2 h–1 bar–1 and the efficiency was nearly 100% after seven cycles. On the other hand, the mechanical properties of MF/PVF-Cn-x sponges were strengthened by the introduced PVF network, and their compress stress was higher than 3.2 MPa. All the comprehensive performances made MF/PVF-Cn-x sponges become a suitable candidate as a highly effective emulsion separation material.