Tailored Pore Size and Hydrophilicity: Advancing Poly(vinyl formal) Sponges for Efficient Emulsion Separation

In the field of emulsion separation, the application of porous hydrophilic sponge materials is of paramount importance; however, the conventional preparation process of hydrophilic poly(vinyl formal) (PVF) restricts the simultaneous enhancement of separation efficiency and water flux. In this work, by introducing two poly(vinyl alcohol) (PVA) and aldehyde feedstocks with different molecular weights and functional group contents into the reaction system, the differences in the mobility and reactivity of the feedstocks were exploited to successfully achieve tailoring of the pore size and hydrophilicity. The PVF sponge prepared by using this method exhibited high separation efficiency and water flux in emulsion separation. This preparation method not only avoided the requirement for pore-forming agents in traditional preparations but also significantly reduced the amount of formaldehyde by adding trace amounts of glutaraldehyde, ensuring the hydrophilicity of the sponge and markedly reducing the pore size. The experimental results showed that the addition of 1.5 × 10^–3 mol/L glutaraldehyde could effectively reduce the average pore size of the PVF sponge from 26.5 to 7.2 μm while maintaining excellent hydrophilicity. The preparation mechanism of PVF sponges was thoroughly explored, and the effects of different concentrations of formaldehyde and glutaraldehyde on the sponge properties were extensively investigated. Experimental results demonstrated that the prepared PVF sponge achieved a separation efficiency of up to 98.5% for the OP-10-stabilized oil-in-water emulsion and exhibited outstanding recyclability. This cost-effective and easily scalable method for PVF sponge preparation could be employed to produce a range of highly efficient filtration materials, effectively separating target oil-in-water emulsions.