Synthesis and Characterization of Crosslinked Polysaccharide Derivative (O-Pul/Pei) Coatings for the Development of Modified Polyvinylidene Fluoride Membranes

Abstract

This study investigated the synthesis, characterization, and performance evaluation of crosslinked oxidized pullulan/polyethyleneimine (O-Pul/PEI) coatings for the modification of polyvinylidene fluoride (PVDF) membranes. The research was conducted under controlled laboratory conditions simulating real-world water treatment challenges typical of the Suzhou region, using model foulants such as bovine serum albumin (BSA), humic acid, oil emulsions, and bacteria. A two-step dip-coating method was employed to fabricate modified membranes with varying PEI concentrations (0.2 - 0.5 wt.%). Oxidized pullulan was synthesized via sodium periodate oxidation to introduce reactive aldehyde groups, enabling covalent crosslinking with PEI through Schiff-base and Michael-type reactions. Membrane characterization was performed using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and water contact angle (WCA) measurements to assess morphology, chemical structure, and hydrophilicity. The results confirmed the successful formation of a stable crosslinked coating, evidenced by the appearance of characteristic functional groups (C=N, C-N) and the emergence of O1s and N1s peaks in XPS spectra. SEM analysis revealed that an optimal PEI concentration (0.4 wt.%) produced a thin, uniform, and well-adhered coating layer, effectively modifying the membrane surface without compromising its structural integrity. This optimized membrane exhibited enhanced hydrophilicity, improved surface smoothness, and superior antifouling performance. In contrast, lower PEI concentrations resulted in insufficient coating coverage, while excessive concentrations led to poor adhesion due to bulk crosslinking in solution. The study concludes that the O-Pul/PEI crosslinking system provides an effective, reproducible, and environmentally sustainable approach for enhancing PVDF membrane performance. The incorporation of hydrophilic functional groups significantly improves wettability and fouling resistance, making the modified membranes suitable for advanced water treatment applications. It is recommended that future studies focus on long-term performance evaluation, scale-up potential, and application under real industrial wastewater conditions. Additionally, further optimization of coating parameters and exploration of other biopolymer combinations could enhance multifunctional membrane properties for sustainable water purification technologies.