Synthesis of cellulose based self-sterilizing materials via solid-state reactions

According to the World Health Organization, antimicrobial resistance has become a major threat to global health, food security and social development in the past decades. Among the recently developed strategies to combat antimicrobial resistance, photodynamic inactivation shows a high potential due to its multi-organism efficiency, and ubiquitous activation via visible light. Single-use antimicrobial materials are particularly valuable in situations such as natural disasters, where power sources can be impossible to access. However, such materials rely on the sustainable synthesis of photosensitizers and their immobilization on suitable polymer matrices. Mechanochemistry, a method where solvent use is drastically reduced, offers environmentally friendly synthesis approaches to achieve these goals.  Light-mediated self-sterilizing hybrid materials were developed in publication I. In two different synthesis approaches, toluidine blue was either covalently conjugated or physically adsorbed on (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-oxidized cellulose nanofibers. The results demonstrated that the covalent linked version outperforms the physically adsorbed one within the first 15 minutes under simulated sun irradiation. Next, an environmentally friendly method for chemical modification of cellulose nanocrystals (CNC) was developed in publication II. A mechanochemical approach allowed for the fast tosylation of both uncharged and charged CNCs, yielding a reactive cellulose intermediate that could be substituted with a nucleophile in a solid-state reaction, resulting in amine and ester derivates of CNCs. Incorporating both tosylation and nucleophilic substitution into a one-step mechanochemical method was beneficial for the esterification of cellulose, allowing to reduce the synthesis time to one hour and reduce the solvent usage by at least 10-fold. In publication III, a new method for synthesis of phthalocyanines, which are commonly used as photosensitizers, was developed. The method is based on solid-state synthesis, in which the crucial parameters were investigated systematically. This allows efficient upscaling and to reduce the amount of the high-boiling point organic solvents up to 100- fold.  Overall, this thesis explored different aspects of developing a photoactive hybrid material and a production process of its components, with subsequent projects building upon one another. The results provide a comparison of cellulosic hybrid materials prepared via covalent linkage and physical adsorption, which can be used against multi resistant organisms. By using solid-state reactions and mechanochemistry, a new modification method for cellulose and a synthesis pathway for phthalocyanines were developed.