(461g) Controlled-Chain Pegma-Enhanced Cellulose Acetate Ultrafiltration Membranes for Fouling Control

Fouling of membranes is controlled by the composition of the feed water and the physical/chemical properties of membranes. In addition, the interaction among the feed water components, including bacteria, and interaction between components and properties of membranes also contribute to the variation of performance [1] and fouling of membranes [2]. Fouling due to organic matter has been previously observed to strongly correlate with membrane hydrophobicity and charge [1.2]. Based on hydrophobic interactions between the membrane surface and organic matter and/or microorganisms, it would be expected that the use of hydrophilic membranes would decrease fouling [3,4,5]. However, commercially available purely hydrophilic (known as low-fouling or non-fouling) membranes suffer limitations such as low chemical resistance [6] and faster flux decline [2] than hydrophobic membranes. Thus, ideal membranes would combine the high chemical resistance of hydrophobic membranes with the excellent fouling resistance of hydrophilic membranes, which is best achieved through modifications of hydrophobic membranes to be rendered hydrophilic. A common surface modification technique is graft polymerization, in which a monomer is grafted on a polymeric membrane support.

We focused on the development and optimization of a technique to graft a hydrophilic monomer onto the surface of a hydrophobic membrane using oxidizing and chain-transfer agents, which lead to increased hydrophilicity. This is expected to decrease fouling tendency while enhancing the permeability and selectivity properties of the modified membrane.

We have modified commercially-available cellulose acetate ultrafiltration membranes using graft polymerization with (1) an oxidant for dehydrogenation of end functional groups, (2) a hydrophilic polymer, and (3) a chain transfer agent to control grafted chain length and density. Modification led to no significant differences in membrane roughness with the virgin and modified membranes displaying roughness values of 4.784 and 4.237 nm, respectively. After fouling, the virgin membrane roughness had increased to 23.002 nm, while that of the modified membrane to 12.613 nm; that is, a significant decrease in fouled membrane roughness induced by fouling due to the modification. Further, in comparing membrane permeability between the virgin and modified membranes, it was determined that modification did not affect membrane permeability. Finally and consistently throughout the study, the selectivity of the modified membrane was on average 15% higher than the selectivity of the virgin membrane when the same feed water was filtered through both.

References:

[1] Peng W., and I. Escobar (2003). Environmental Science and Technology, 37 (19): 4435-4441. [2] Peng W., I. Escobar, and D. White (2004). Journal of Membrane Science, 238 (1-2): 33-46. [3] Mourot, P., & Oliver, M. (1989). Separation Science and Technology, 24: (5/6) 353-367. [4] Ko, M., & Pellegrino, J. (1992). Journal of Membrane Science, 74: 141-157. [5] Dal-Cin, M., Striez, C., Tweddle, T., Capes, C., McLellan, F., & Buisson, H. (1995). Desalination, 101: 155-167. [6] Jönsson, A., & Jönsson, B. (1991). Journal of Membrane Science, 56: 49-76.