Process development of chitosan–dextran sulfate fibers via polyelectrolyte complexation

Fibrous materials have attracted considerable interest due to their high surface-area-to-volume ratio, tunable morphology and versatility for a wide range of applications. In recent years, increasing attention has been devoted to the fabrication of sustainable alternatives based on aqueous processing routes and natural polymers. Among these, chitosan (CS) and dextran sulfate sodium (DSS) are particularly attractive candidates due to their biocompatibility and biodegradability. Owing to their opposite charges, these polysaccharides can spontaneously interact through electrostatic forces to form polyelectrolyte complexes (PECs). Under controlled conditions, the interfacial complex can be continuously drawn into filaments, providing a sustainable route for bio-based fiber production. For natural polymers, fiber production often relies on coagulation baths or inorganic crosslinkers, limiting sustainability and material versatility. Although PEC-based approaches enable fiber formation without additional crosslinkers, they often suffer from limited scalability and discontinuous processing. Moreover, while CS and DSS have been widely investigated individually and as polyelectrolyte complexes, their combined use for fiber production remains largely unexplored and the relationships between processing conditions and fiber properties are still poorly understood. This thesis investigates the production of CS-DSS fibers through polyelectrolyte complexation by evaluating and optimizing different wet spinning strategies to enhance fiber formation and process continuity. Particular attention is devoted to the influence of key processing parameters, such as polymer concentration, spinning and complexation conditions and air-gap distance, as the simultaneous processing of two interacting polyelectrolytes introduces additional challenges compared with single-polymer spinning, requiring the simultaneous control of complexation kinetics, solution rheology and filament stability. The results highlight the critical role of processing conditions in governing fiber formation. Among the investigated strategies, interfacial polyelectrolyte complexation emerged as the most promising approach, enabling the formation of CS-DSS filaments under optimized conditions, whereas wet spinning showed limited suitability for the investigated system. These findings provide new insights into the processing–structure relationships of CS-DSS polyelectrolyte fibers and establish a basis for future development of scalable, environmentally friendly bio-based fibers.