Title: UV Cross-Linked Semi-Interpenetrating Polymer Networks (SIPNs) as Membranes for SRNF Applications
Other Titles: UV vernette semi-interpenetrerende polymeernetwerken (SIPN) als membranen voor SRNF toepassingen
Authors: Struzynska-Piron, Izabela; S0222204
Issue Date: 20-Mar-2014
Abstract: The growing market of liquid and gas separation (GS) demands for improvements of existing membranes and/or development of new membranes. In the case of GS, crucial are the anti-plasticization properties of the membrane polymer, while for e.g. solvent resistant nanofiltration (SRNF), solvent stability is important, including stability in a wide range of pH (1-14) and at high temperature. When preparing thin film composite membranes for any kind of membrane applications, the support layer is preferably highly chemically stable to allow coating of the selective layer from any kind of solvent or to allow any kind of chemical or thermal post-treatment. All these very diverse aspects require implementation of cross-linking in membrane synthesis. The most typical method is via chemical cross-linking, realized through a chemical reaction between the membrane polymer (e.g. polyimide) and a cross-linker (e.g. a diamine). Such cross-linking methods have some disadvantages. Firstly, they cannot be used to all polymers, such as polysulfones (PSUs) or poly(ether ether ketones) (PEEKs), because of the lack of reactive groups in the backbone of such polymer chains. In addition, chemical cross-linking also generates waste streams, often very environmentally unfriendly. A new generic way to prepare highly chemical and thermal resistant SRNF membranes is presented in this PhD thesis. The concept is based on the preparation via nonsolvent induced phase separation (NIPS) of an asymmetric membrane consisting of a semi-interpenetrating polymer network (SIPN). As base polymer for the membranes, polysulfone (PSU) was proposed because of its good chemical, thermal, and mechanical properties, as well as its intrinsic photosensitivity and lack of reactive groups. The latter is of importance in e.g. SRNF, where membrane polarity is often undesired. When combined with the appropriate acrylate cross-linkers, SIPN structure was obtained by employing simple UV cross-linking, hence not generating any waste streams. Moreover, this method is quick, easy to use and upscale. In the first part, the photochemical aspects of the synthesis of SRNF membranes via NIPS/UV were studied. Additives suitable for UV cross-linking reaction were chosen, including cross-linkers with a varying functionality, as well as initiators from the group of free-radical photoinitiators type I and type II. The photoinitiators were applied in different concentrations. The influence of the additives, of the UV dose, and of the membrane thickness on the UV curing efficiency was investigated. The resulting membranes were analysed by ATR-FTIR, HPLC, DSC, and screened for solvent resistance. The SIPN network structure was characterized by DSC and TGA analysis. The best type and concentration of photoinitiator were selected for the further studies.In the second part, the morphological aspects and the performance of the resulting membranes in SRNF were explored. Asymmetric membranes consisting of 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (TPO) as photoinitiator and acrylate cross-linkers with different functionality were synthesized via NIPS/UV. The effects of various cross-linker types and of the membrane synthesis sequence on morphology, SRNF, and solvent resistant properties of the membrane were examined. Based on the obtained results, various poly(aryl sulfones) (PASUs) were screened in the last part. The influence of PASU type and concentration in the casting solution on UV curing efficiency, membrane morphology, SRNF performance, and solvent resistance was investigated. Polysulfone (with high and low molecular weight), poly(ether sulfone), and poly(phenyl sulfone) membranes were prepared using 3 wt% of TPO and 5 wt% of penta-acrylate cross-linker. The membranes were synthesized by NIPS/UV and characterized by SEM, ATR-FTIR, and SRNF. As a result, SIPN based membranes consisting of linear PSU and cross-linked polyacrylate (PAc) were developed by a very easy, versatile, and environmentally benign method. The optimized asymmetric membranes based on such SIPN, showed good SRNF performance and superior chemical resistance in comparison to conventional PSU membranes.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Centre for Surface Chemistry and Catalysis

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