Effect of citric acid crosslinking on the physicochemical and permeation properties of chitosan membranes for diclofenac separation

We have carried out the formation of chitosan membranes as flat films by solvent evaporation method to determine the aqueous diclofenac (DCF) permeation. Chitosan was extracted from shrimp skeletons, with molecular weight of 560 kDa determined by viscometry and deacetylation degree of 85% determined by FTIR. Membranes were crosslinked with citric acid at different weight fractions and characterized using techniques such as FTIR, SEM, TGA and DSC. The FTIR demonstrated the link formation because of the crosslinking reaction. The vibration at 1620 cm ⁻¹ associated with the primary amines (NH ₂ ) in chitosan loses its intensity in membrane crosslinked samples indicating the crosslink of the polymer. The thermal stability of the membranes increases by crosslinking reaction, as thermal characterizations by TGA reveal. Moreover, the energy absorption quantified by DSC increased as citric acid concentration increases, evidencing the formation of crosslinked points. In this context, the swelling factor S f in water varies inversely to citric acid weight fraction, and S f is between 1.41 and 1.17, which can be considered as a low ratio. Membranes were evaluated in the liquid phase permeation of NaCl, used as a probe molecule where permeability decreases as the inlet pressure increases. Then, membranes were evaluated in the aqueous diclofenac permeation, where increasing the DCF concentration, the permeability decreases. Rejection factor evaluated for both NaCl and DCF permeation was higher to 90% demonstrating that membranes can separate diclofenac from water. SEM images exhibit diclofenac crystals retained in the upper side of the membrane. Characterizations carried out in samples after permeation tests show that diclofenac interacts with the membrane by slightly shifting of the characteristic vibrations of functional groups associated with DCF in FTIR, by an endothermic broad absorption from 165 to 180 °C in DSC and degradation temperature of the sample in TGA. Crosslinked membranes can retain diclofenac, so the permeated water has a high purity.