Effective parameters on fabrication and performance of superhydrophobic/superoleophilic polyurethane sponge: Design of experiment approach

Abstract

Referring to importance of the oil/water separation as one of the main challenges in the environmental conditions, numerous researches in the superhydrophobic/superoleophilic materials especially in the industrial oily wastewater treatment have been focused. In this study, the commercial polyurethane (PU) sponge was dip-coated by zinc stearate (Zn(St)2) particles and a novel adhesive of hexamethylenetetramine (HMTA) cured phenol-formaldehyde resin (PFR). For this purpose, a design of experiment (DOE) was applied to statistically specify the effect of important process variables on the final product properties. The second-order central composite design (CCD) approach based on the response surface methodology (RSM) analysis was conducted by changing namely the Zn(St)2 suspension concentration (2–4 wt%), PFR concentration (10–30 wt%), HMTA/PFR weight ratio (10–20 wt%), and sponge density (12, 15 and 17 kg∙m−3) on the key response output variables including oil and water absorption capacity of the Zn(St)2/HMTA cured PFR-coated PU. The optimal predicted results were experimentally verified and matched well to achieve the modified superhydrophobic PU sponge for the oil/water separation. The characterizations of the modified PU sponge by SEM, EDX mapping, FTIR, XRD, UV-Vis, BET, and TGA results confirmed that the Zn(St)2 uniformly covered the entire PU sponge. In addition, it showed a high demulsification capacity, the absorption capacity of various oil and solvents, and a water contact angle as high as 165° which was further approved to be oil wet in less than <10 millisecond. More importantly, the prepared modified superhydrophobic PU sponge presented an excellent reusability performance and chemical, thermal and mechanical stability in harsh conditions. This stable superhydrophobic PU sponge with the aforementioned outstanding properties is expected to be widely used for the practical oil/water separation.