In situ crosslinkable anti-fouling hydrogel coatings for filtration membranes

In situ crosslinkable anti-fouling hydrogel coatings for filtration membranes

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Although membrane-based separations became tailor-made for several applications in recent years, they still suffer from limited separation performance, i.e. the relation between permeability and selectivity, and are also highly affected by fouling processes. Fouling can be generally divided into three categories, namely biofouling, colloidal fouling (especially by natural organic matter) and inorganic fouling (scaling). Besides operational conditions as well as feed water and foulant characteristics, membrane properties are a crucial factor for fouling mechanisms. Despite that many membrane functionalizations show improved anti-fouling behavior, their application is still limited to lab-scale or implementation during membrane fabrication.

This project is focusing on surface-selective, reactive anti-fouling hydrogel coatings which can be applied on demand in situ to filtration membranes in modules [1,2]. To obtain such protective layer systems, it is promising to establish zwitterionic copolymers as building blocks which can be crosslinked to hydrogels on surfaces by using a second functionality. Zwitterionic segments, e.g. carboxy- or sulfobetaines, can inhibit nonspecific adsorption, what is attributed to a strongly bound hydration water shell. The second functionality of the building blocks should, in combination with an added crosslinker or initiator system having complementary reactivity, enable chemical crosslinking [3]. Such a system will only form a polyzwitterionic hydrogel above a critical concentration and thus concentration polarization can be utilized to form the hydrogel only on the membrane surface. According to the film model, filtration through a membrane will lead to a concentration gradient of retained substances, resulting from a balance of convective and diffusive mass transport. Thus applying a filtration with crosslinkable building blocks which are rejected by the membrane will increase their concentration at the membrane surface. For a controlled modification feed concentration as well as flux can be adjusted to obtain the necessary gelation conditions. Additionally, to guarantee tight grafting of these hydrogel layers, one can take advantage of the chemical properties of the membrane to be coated. For example, polyamide nanofiltration membranes often offer a negatively charged surface, which can be covered with a cationic and cross-linkable macromolecular surface linker. Various building polymeric blocks and surface linkers for coating systems are synthesized, coating preparation conditions are established, and the coating-protected membranes are evaluated with respect to permeability, solute rejection and resistance to fouling.

References

  1. J. Lei, M. Ulbricht, J. Membr. Sci. 2014, 455, 207
  2. M. Quilitzsch, R. Osmond, M. Krug, M. Heijnen, M. Ulbricht, J. Membr. Sci. 2016, 518, 328
  3. K. Daumann, P. May, J. Brückerhoff, M. Ulbricht, React. Funct. Polym. 2018, 131, 251

Contact:
Patrick May