Investigation of the structure and performance of antibacterial ultrafiltration membranes fabricated via 3D printing platform

Although ultrafiltration membrane technology holds critical importance in a wide range of fields from water treatment to biotechnology, it is limited by the lack of standardization in production processes and biofouling problems that reduce operational efficiency. This doctoral thesis encompasses the development of a methodologically precise laboratory-scale production platform and the synthesis of membranes with renewable antibacterial properties utilizing a material science approach, in order to offer a holistic solution to these two fundamental problems. In the first phase of the study, a commercial 3D printer was converted into a precise film casting platform without requiring any hardware modifications to overcome the reproducibility problem in laboratory-scale membrane production. Using this platform, casting temperature, casting speed, coagulation bath temperature, and film thickness parameters, which affect the morphology and performance of polyethersulfone membranes, were optimized using the systematic one-variable-at-a-time (OVAT) method. As a result of the analyses, it was determined that 60 oC casting temperature, 65 mm s-1 casting speed, 30 oC coagulation bath temperature, and 50 μm applicator gap were the optimum conditions providing the balance of high flux (271 L m-2 h-1) and high selectivity (over %95 BSA rejection). In the second phase of the study, a functional homopolymer containing hydantoin rings was synthesized and integrated into the PES matrix under optimum conditions to develop a sustainable solution against biofouling. N-halamine additive membranes, activated by the chlorination process, gained a strong oxidative potential with a 0.31% active chlorine loading. In antibacterial tests, these membranes served as an active biocidal barrier by providing 100% complete inactivation against both Staphylococcus aureus and Escherichia coli bacteria in just a 15-minute contact time. The most original finding of the study is the renewable fouling resistance property of the developed membranes. The chemical cleaning process performed with commercial sodium hypochlorite not only cleaned the membrane surface but also activated the N-halamine structures. Thanks to the increased surface hydrophilicity and oxidative effect, the irreversible fouling ratio of the membranes was reduced to the level of 1.4%, and a high flux recovery ratio of 98.6% was achieved during repeated fouling cycles. In conclusion, this thesis has put forward a pioneering approach in the development of long-lasting, high-performance, and self-renewing new-generation membranes by combining 3D printer technology with smart material chemistry.