High performance cellulose acetate/polyamide (CA/PA) thin film composite forward osmotic (TFC‐FO) membranes from dual solvent modification processes

Abstract

Polyamide (PA) based thin film composite forward osmotic (TFC‐FO) membranes were prepared through inter‐facial polymerization (IP) processes on porous cellulose acetate (CA) substrates. A dual solvent modification process of adding DMF in the aqueous phase followed by activation with methanol was found to be able to simultaneously improve the permselectivity and anti‐fouling capability of the modified membranes. On top of the acidic CA substrates, DMF could not only absorb the HCl formed in the IP processes, but also chemically bind with the PA matrix by reaction with MPD monomers, leading to formation of homogeneous thin and flat PA layers, while methanol activation further swelled the PA matrix, repaired defects and optimized water permeating channels. Using 1 M NaCl solution as the draw solution, the water flux of the CA/PA‐DMF4‐ME1 membrane was twice that of the pristine membrane, and 24% increase in Jw/Js value from 182 to 225 L·mol−1. Its Jw/Js value could be further increased 10 times to 2000 L·mol−1 using 1 M Na2SO4 solution as draw solution. RO tests for the CA/PA‐DMF4‐ME1 membranes showed 6‐fold increase in water permeance, from 1.16 to 7.02 L·m−2·h−1·bar−1, as well as increase in NaCl rejection from 94.8% to 97.7% from pristine membrane.