Short-chain amino acids functionalized cellulose nanofibers composite ultrafiltration membrane with enhanced properties

TEMPO-oxidized cellulose nanofibers (TOCNs) were blended with cellulose acetate (CA) to fabricate a high water flux ultrafiltration membrane. In order to further reduce the fouling behavior of the membrane, short-chain amino acids were selected as modifiers to graft onto the membrane surface. Some properties of modified membranes had been changed such as penetrability, contact angle, zeta potential, anti-fouling and mechanical properties. It was observed that the water flux of the TOCNs composite membrane was raised from 11.8 l m^-2 h^-1 to 123.4 l m^-2 h^-1, an over 10 times increment compared with unmodified CA membrane. As reinforcing nanofibers, TOCNs also have a positive impact for the modified membrane on mechanical properties. The tensile strength and elongation at break of the composite membrane were increased by 23.9% and 40.4%, respectively. After short-chain amino acids modification, little or even no variation had been found in the cross-section morphology and pore structure of the membrane. The flux recovery ratio (FRR) of lysine modified membrane was increased from 80.0% to 95.9%, while irreversible fouling loss (R_ir) decreased from 20% to 4.1%. Grafting lysine onto the membrane effectively improved the resistance to protein fouling of the membrane, without sacrificing water flux and mechanical properties.