Fabrication of chitosan/PDMCHEA blend positively charged membranes with improved mechanical properties and high nanofiltration performances

Chitosan (CS) was blended with copolymer PDMCHEA made from 2-methacryloyloxy ethyl trimethylammonium chloride (DMC) and 2-hydroxyethyl acrylate (HEA), and the blend positively charged nanofiltration membranes (BPCNFMs) were prepared via chemical cross-linking method. Chemical compositions and structures of BPCNFMs were characterized by attenuated total reflectance fourier transform infrared spectroscopy, wide angle X-ray diffraction, differential scanning calorimetry and field emission scanning electron microscope, respectively. Mechanical properties of the BPCNFM25 loaded with 25 wt.% PDMCHEA were greatly improved, showing 2.4 times higher breaking elongation and 2.0 times higher tensile strength as compared with that of the pristine CS membrane. The surface hydrophilicity and separation performances of BPCNFMs were examined by water contact angle and nanofiltration tests. BPCNFMs were subjected to the nanofiltration, and the effects of PDMCHEA content and feed concentration on nanofiltration performances were investigated. It is found that a high water permeability and salt selectivity, e.g., JH2O = 20.6 L·m− 2·h− 1, RZnCl2 = 97.5%, RNaCl = 57.1% was obtained for the BPCNFM50 containing 50% PDMCHEA (testing with aqueous 1 g·L− 1 inorganic salts solutions at 25 °C and 0.6 MPa). Moreover, the stability and anti-fouling properties of BPCNFMs were significantly improved in the long-term nanofiltration process.