|Title||Enzyme-catalyzed modification of poly(ethersulfone) membranes|
|Source||Wageningen University. Promotor(en): Remko Boom; Han Zuilhof, co-promotor(en): Karin Schroen; Maurice Franssen. - S.l. : s.n. - ISBN 9789461731456 - 172|
Food Process Engineering
|Publication type||Dissertation, internally prepared|
|Keyword(s)||membranen - oppervlakteverandering - laccase - enzymen - kunststoffen - membranes - surface modification - laccase - enzymes - plastics|
The robustness of a membrane is determined by the properties of the base polymer and the functionality of its surface. One of the most popular polymers used for membrane preparation is polyethersulfone (PES), which has excellent thermo-physical properties, but the surface properties are in need of improvement to reduce membrane fouling by adsorption of e.g. protein and live cells, which cause sever flux decline during filtration. Therefore, it is not strange that a wide range of modification methods has been published to reduce surface hydrophobicity of PES membranes. However, the methods that are currently suggested are all rather offer random control over the resulting surface structure and may be environmentally adverse
This study presents enzyme-initiated grafting of PES membranes as the first successful example of an environmentally friendly modification of PES membranes. Various phenolic acids, such as 4-hydroxybenzoic acid and gallic acid (3,4,5-trihydroxybenzoic acid), were coupled to the membrane in aqueous medium at room temperature using laccase from Trametes versicolor as catalyst. This enzyme is able to oxidize phenolic compounds to their corresponding free radicals that are subsequently grafted onto PES membranes, introducing polar groups (OH, COOH) on the membrane surface by formation of a covalent C-O linkage as was proven by spin density calculations and IRRAS.
We succeed in altering the surface properties of PES membranes using laccase-catalyzed modification method. It was found that the surface structure or shape that can be tuned through both the modification conditions and the modifier structure, has a significant role in prevention of adsorption rather than surface hydrophilicity as is often assumed. Membrane flux is hardly influenced (10% reduction), and foulant (e.g., bovine serum albumin, dextrin, tannin, and pathogenic bacterium Listeriamonocytogenes) repellence is greatly increased.
In conclusion, the enzyme-catalyzed modification method shows a remarkable flexibility, and allows careful tuning of the membrane properties in such a way that membrane fouling can be suppressed. Besides, the modification method does not influence the bulk properties of the membrane adversely, the modification layer is resistant to a wide range of pH, and the costs of this modification on industrial scale are reasonable, which makes this modification method an interesting eco-friendly alternative to currently used methods.