Comparing homogeneous and heterogeneous routes for ionic crosslinking of chitosan membranes

H2SO4 - ionically crosslinked chitosan membranes were prepared via homogeneous and heterogeneous routes. The control variable in homogeneous crosslinking was the SO42 −/NH3+ molar ratio (1:4 e 1:6) while for heterogeneous crosslinking it was the immersion time of pure chitosan membrane in H2SO4 0.5 M aqueous solution (5 and 30 min). FTIR-ATR suggested lower crosslinking degree for homogeneous crosslinking, corroborated by XRD analysis that indicated the maintenance of the crystalline structure for such membranes. Thermal analysis showed very similar degradation processes for homogeneous and pure chitosan but quite different for heterogeneous: not only in terms of degradation temperature but also in amount and signal of heat involved. Swelling index results were very dependent on pH of medium. Particularly in acidic medium, homogeneous crosslinked membranes, presented a higher swelling capacity than the heterogeneous ones. Mechanical properties revealed that both methodologies render membranes with lower tensile strength and elongation but with Young modulus about four times higher, due to the interactions of SO42 − groups of H2SO4 with NH3+ of chitosan. Finally, AFM images showed dramatic changes on surface topology, with reduction of roughness for heterogeneous and an increase for the homogeneous one.