Abstract
This work aims to prepare new types of grafted and crosslinked cellulose acetate (CA) reverse osmosis (RO) membranes by phase inversion technique. The grafting and/or crosslinking processes of the pristine CA-RO membrane were conducted using N-isopropylacrylamide (N-IPAAm) and N,N-methylene bisacrylamide (MBAAm), respectively. The grafting/crosslinking mechanism onto the CA-RO membrane surface was proposed. Atomic force microscope (AFM) images of the pure CA-RO and 0.1 wt% N-IPAAm-grafted CA-RO membranes revealed that the surface roughness was 42.99 nm and 11.6 nm, respectively. Scanning electron microscopy (SEM) images of the 0.1 wt% grafted/crosslinked membrane indicated the finger-like macrovoids structure. It was observed that the contact angle of the pristine CA-RO membrane was 66.28° and declined to 49.7° for 0.1 wt % N-IPAAm-grafted CA-RO membrane. The salt rejection of the pristine CA-RO membrane was 93.7% and increased to 98.9% for the grafted 0.1 wt % N-IPAAm/CA-RO membrane. The optimum grafted/crosslinked composition was 0.1 wt %/ 0.013 wt % which produced the salt rejection and water flux of 94% and 3.2 L/m2h at low pressure, respectively. It was concluded that both the grafting and crosslinking processes enhanced the performance of the CA-RO membranes.
Highlights
Surface modification techniques such as grafting by hydrophilic molecules have been made to improve the membrane performance[9,10]
The grafting process could be influence the performance of the cellulose acetate (CA)-reverse osmosis (RO) membrane by enhancing the salt rejection and water flux because it forms a new hydrophilic layer with good coverage to the surface to enhance the dense layer properties and treat any defects on the membrane surface
To avoid the probability of the monomer penetration or blocking of the pores which decreases the flux of the membrane by grafting, the crosslinker was inserted to increase the interchain between polymer chain and formed a net structure[28]
Summary
Surface modification techniques such as grafting by hydrophilic molecules have been made to improve the membrane performance[9,10]. In the grafting-to method end-functionalized polymer molecules bind with complementary functional groups located on the surface to produce tethered chains. A redox system composed of potassium persulfate was used to generate initiating radicals for graft polymerization of acrylic acid, N-isopropylacrylamide, and other hydrophilic monomers at the surface of CA membranes. The disadvantages of this method and these monomers are the blocking of the pores of support CA membrane due to the taking place of the polymerization inside these pores, for high degrees of grafting and the flux will be decreased[26]. The surface morphology is investigated and studied by SEM and AFM
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