Preparation of thin film composite membranes with polyamide film on hydrophilic supports

The interest in osmotically driven processes such as pressure retarded osmosis (PRO) has increased during the past decade. The synthesis of new membranes specifically designed for the process is essential for the development of these technologies. Conventional TFC have a relatively hydrophobic support layer e.g., polysulfone. However, a more hydrophilic support layer is desirable in osmotically driven processes as such supports would give better water flux, less internal concentration polarization (ICP) and less fouling. In the current project it was demonstrated that it is possible to coat a hydrophilic support membrane given there are enough functional/reactive groups on the surface of the support membrane. This is achieved by reacting the support with polyfunctional acid chlorides in a reaction step prior to interfacial polymerization (IP). In this way, covalent bonds between the support and the active layer are formed and the composite will be stabilized. Hydrolysed cellulose acetate CA membranes have been coated with a polyamide (PA) layer by this modified IP method. These membranes displayed a salt rejection up to 97%, and water fluxes from 7.6×10−7 to 4.7×10−6 m3/m2/s at 1.3×106 Pa differential pressures.

Graphical AbstractA comparison of a conventional TFC membrane (a) where the active layer stays on the support by adhesion forces, and the modified IP method (b) with a covalent bond between the active layer and the support layer. In the current project it was demonstrated that it is possible to coat a hydrophilic support membrane given there are enough functional/reactive groups on the surface of the support membrane.Figure optionsDownload full-size imageDownload high-quality image (184 K)Download as PowerPoint slideHighlights► PA coating on hydrophilic CA support. ► Modified IP method successfully developed. ► PA layer covalently bonded to CA.