Nanopolysaccharide coatings for functional surfaces in water-treatment materials : From mechanisms to process scalability

Sammanfattning: In this thesis, materials from renewable resources were used to develop functionalized surfaces for water treatment. The work is thus inspired by, and contributes to, the United Nations sustainable goals of: (i) clean water and sanitation, (ii) climate action, (iii) responsible consumption and production, (iv) life below water, and (v) partnerships for the goals.Nanopolysaccharides, most specifically nanocellulose and nanochitin, are great candidates for functional and renewable materials for multiple applications, including the treatment of water and wastewater. This thesis focused on the formulation of different types of nanopolysaccharide-based coatings to enhance the performance of commercially available membranes and cellulose fabrics. We developed a simple waterborne layer-by-layer cellulose nanocrystals (CNC) and TEMPO-oxidized cellulose nanofibrils (T-CNF) coating for commercially available membranes. By changing the surface and pore structure of the membrane, the coating tuned which substrates could pass through the membrane, improved antifouling performanced, and when derived from T-CNF, it was harmful to bacterial colonization. Considering the observed T-CNF’s effect on bacteria, we developed a chemically crosslinked T-CNF/Poly(vinyl) alcohol (PVA) coating with outstanding antibiofouling performance, ion adsorption/rejection combined with size exclusion, and with dimensional and pH stability. Furthermore, we used a surface-impregnation approach based on bio-based nanotechnology which resulted in highly efficient, with improved mechanical properties, and fully bio-based high-flux water filtration membranes using commercially available nonwoven fabrics. Membranes with coatings prepared from CNC, chitin nanocrystals (ChNC) and T-CNF separated particles in the size range of bacteria and viruses, and those prepared from also T-CNF showed high microplastic filtration efficiency. Moreover, membrane coating based on ChNC and T-CNF had outstanding antibacterial properties.Overall, we demonstrated that nanopolysaccharide coatings on membranes could provide a significant reduction in organic fouling and biofilm formation while enabling the adsorption of ions and separation of microplastics. In the case of biofilm formation, the functional group and surface charge of the different nanopolysaccharides determined the effect over bacteria, indicating that surfaces could be tailored against microbes. In addition, we directly compared the effect of the different nanopolysaccharides of interest (CNC, T-CNF, ligno-celullose nanocrystals (L-CNC), and ChNC) on bacterial viability and biofilm formation, and found a great difference between the different types of nanocellulose and a different mechanism for nanochitin. Thorough, none of the nanopolysaccharides displayed cytotoxic effects while in indirect contact with the bacterial cells. Nevertheless, T-CNF, ChNC and L-CNC showed a cytostatic effect on bacterial proliferation. Furthermore, the nanomechanical properties of the bacterial cells and interacting forces between the nanopolysaccharides and Escherichia coli (E. coli) were affected when in direct contact with the nanopolysaccharide surfaces.Lastly, we upscaled one of our coating processes, demonstrating that the method could be easily implemented at an industrial level. The impact of this thesis relies on the effectiveness of the coatings, the different types of functionalities observed, the demonstrated fast implementation at an industrial scale, and the potential to extrapolate this technology to other applications.