Characterization and Application of Calotropis Procera Fiber as a Sustainable Filter for Oil Removal from Aqueous Emulsion

Fibers extracted from Calotropis procera (CP) fruits were successfully used to filter engine oil from a synthetic oil-in-water effluent. Fiber morphology was examined by scanning electron (SEM) and optical (OM) microscopies, while their structural, vibrational and chemical properties were systematically studied by thermogravimetric analysis (TG), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. It was first demonstrated that the fibers are tubular with strong anisotropy and that when placed in oil, most oil adsorption occurs at their internal surfaces, a region with higher hemicellulose concentration. Contact angle experiments and standard gravimetric measurements confirmed that the fibers are hydrophobic, while FTIR results have suggested a small amount of water retained within the fiber walls after forced submersion. Using a cylindrical filter in continuous mode and a semispherical filter in batch mode, the percentile of oil removal (OR %) was 67% for 200 mg of fiber mass (FM) and a flow rate (Q) of 172 mL min^-1 and higher than 95% when the effluent is under agitation at 140 rpm and FM of 30 mg. The OR % variation data with FM in the cylindrical filter was consistent with a constant removal ratio as a function of penetration depth, whereas the results for the semispherical geometry have indicated an increase in OR % with effluent speed. The fibers retained their effectiveness throughout three reuse cycles, consistently adsorbing more than 50% of the emulsified oil. Thus, this study represents the first report on the application of CP fibers as an oil filter for oil-in-water emulsions and provides the most detailed chemical composition analysis of these fibers to date.