Hydrophobic-Oleophilic Composite Membranes of Poly(L-lactic Acid)/ Polycaprolactone/ Modified Eggshell Particles for Oil-Water Separation

Oily wastewater from industrial activities demands separation technologies that are both efficient and environmentally sustainable. In this study, hydrophobic – oleophilic composite membranes based on biodegradable poly(L-lactic acid)/polycaprolactone (PLLA/PCL) blends reinforced with stearic-acid-modified eggshell microparticles (MESP) were fabricated via non-solvent-induced phase separation. The stearic-acid treatment converts hydrophilic calcite-rich eggshell powder into a low-surface-energy filler, enabling improved dispersion, hierarchical micro – nano roughness, and strong interfacial compatibility with the PLLA/PCL matrix. Comprehensive physicochemical characterization (FTIR, XRD, FESEM, AFM) confirmed successful surface modification, filler incorporation, and morphology control. MESP loadings of 20–25 wt% provided an optimal balance between stiffness (Young’s modulus ≈370–430 MPa), acceptable ductility, and enhanced hydrophobicity (water contact angle up to ~125°), while glacial acetic acid post-treatment of 30 wt% MESP membranes further sharpened hierarchical roughness, yielding a water contact angle of ~132° and nearly zero oil contact angle. Under stirred-cell filtration of surfactant-stabilized petrol-in-water emulsions at 20 psi, the optimized membranes achieved quasi-steady fluxes of up to ~2,900 L m−2 h−1, with oil rejection approaching 90%, alongside a marked reduction and narrowing of droplet-size distributions. These results demonstrate that eggshell biowaste can be valorized into a functional hydrophobic filler for fully biodegradable membranes, offering a promising route toward sustainable oil – water remediation technologies.