Enhanced transport and antifouling properties of polyethersulfone membranes modified with α-amylase incorporated in chitosan-based polymeric micelles

The objective of this study is related to the modification of polyethersulfone membranes with alpha-amylase incorporated into chitosan-based polymeric micelles in order to reduce the membrane fouling. Amphiphilic chitosan derivatives have been synthesized through grafting of palmitic (PA) and stearic (SA) acids onto low-molecular weight chitosan. CMC values of palmitoyl and stearoyl derivatives of chitosan are equal to 5.7.10(-2) mg/mL and 3.9.10(-2) mg/mL, respectively. Whereas, the size of polymeric micelles amounted to 707 +/- 64 nm and 609 +/- 57 nm for Chit-g-PA and Chit-g-SA, accordingly. The obtained micelles with enzyme have been adsorbed onto the surface of polyethersulfonic membranes. Modified membranes are characterized by high stability of the coating over time, thanks to the surface-active properties of chitosan derivatives and electrostatic interactions. The antifouling biocatalytic properties of modified membranes were studied in the process of starch filtration. The unmodified membrane showed the lowest permeability with an increase in the concentration of starch solutions due to dramatically increased cake formation. The permeability of modified membranes has been improved remarkably compared to the pristine one during starch ultrafiltration. The cake resistance of modified membranes decreases 6-fold, compared to the unmodified PES one. Furthermore, the effect of concentration polarization is attenuated owing to starch hydrolysis by alpha-amylase incorporated into polymeric micelles. The maximum activity of alpha-amylase immobilized on PES membrane is observed in the pH range of 6.5-7.5 and the higher resistance of enzyme to acidic media compared to the native one has been shown. High stability and reusability of immobilized alpha-amylase has been demonstrated. The degree of starch conversion reduces by 35% and 30% after 10 cycles for a membrane modified with Chit-g-PA and Chit-g-SA, respectively.