Fouling-resistant membranes surface modification

Changes in cross-flow velocity or transmembrane pressure cannot always alleviate fouling. Membranes made from hydrophilic polymers like cellulose acetate are generally less prone to fouling than the hydrophobic polymers. However, cellulose acetate is limited in its tolerance to high or low pH, organic solvents and elevated temperature. In some cases, surface modification of the more chemically-resistant polymers has rendered them less susceptible to fouling. 

Zhou, Y., Yu, S., Gao, C. and Feng, X. 2009. Surface modification of thin composite polyamide membranes by electrostatic self-deposition of polycations for improved fouling resistance. Sep. Purif. Technol. 66 287-294. 

Reddy, A.V.R., Mohan, D.J., Bhattacharya, A., Shah, V.J. and Ghosh, P.K. 2003. Surface modification of ultrafiltration membranes by preadsorption of a negatively charged polymer 1. Permeation of water soluble polymers and inorganic salt solutions and fouling resistance properties. 214 211-221. 

It is well documented that the surface chemistry and morphology of the membranes play an important role in the transmembrane transport of permeates (Khayet and Matsuura 2003a,b). To enhance the overall performance of a membrane, it is often necessary to modify the membrane material or its structure. Generally, the objective of modification is not only to increase the flux and/or selectivity, but also to control the pore size, eliminate defects, and improve the chemical resistance, for example, the solvent resistance, swelling, or fouling resistance. 

Modification of the membranes affects the properties. Cross-linking improves mechanical properties and chemical resistivity. Fixed-charge membranes are formed by incorporating polyelectrolytes into polymer solution and cross-linking after the membrane is precipitated (6), or by substituting ionic species onto the polymer chain (eg, sulfonation). Polymer grafting alters surface properties (7). Enzymes are added to react with permeable species (8—11) and reduce fouling (12,13). 

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