Many Faces of Methylcellulose-Based Nanocomposites - From Responsive Hydrogels to Optical Fibers

This thesis covers the development of methylcellulose-based nanocomposite optical fibers starting from the preparation of a hydrogel spinning dope followed by the establishment of a fiber spinning process and, finally, the characterization of optical fiber capabilities and additional functionalities. Additionally, interfacial polyelectrolyte complexation (IPC) is explored as an alternative method to prepare nanocellulosic composite fibers. Cellulose-derived functional nanocomposite materials form the overall theme of the thesis. Publication I presents thermoresponsive methylcellulose-cellulose nanocrystal (MC-CNC) nanocomposite hydrogels with tunable mechanical and optical properties. The effects of both temperature and gel composition on the respective properties were screened and the interactions between MC matrix and CNC nanorods were analyzed. The hydrogels were further utilized in Publication II to prepare solid, fully cellulose-derived fibers. In Publications II and III, two different methods, wet-spinning and IPC spinning, respectively, were used to produce cellulose-based nanocomposite fibers with straightforward and environmentally benign processes without the need for chemical crosslinkers. Through the optimization of the MC-CNC composition in Publication II, exceptionally ductile, smooth, and transparent fibers were achieved. In Publication III, coated and compartmentalized cellulose nanofibril (CNF) -based fibers were feasibly achieved via IPC spinning. Humidity sensitive reversible shape change, i.e., crimping, of the compartmentalized fibers inspired by the natural wool fibers was demonstrated. The ductile fibers from Publication II were further modified and examined as potential biopolymeric optical fibers in Publication IV. Signal propagation comparable to the state-of-the-art biopolymeric optical fibers and good mechanical performances were achieved. In addition to CNCs, atomically precise gold nanoclusters (GNCs) and CNC-GNC hybrids were used in the nanocomposite fibers to enable additional photoluminescent and sensory functionalities. Overall, multifunctional and advanced cellulose-based materials were feasibly prepared from relatively simple raw materials. The thesis contributes to the development of advanced functional cellulosic materials and provides a relatively rare approach to the preparation of high-performance cellulosic fibers from the point of view of optical fibers. The results encourage more deeply to explore the potential of cellulosic nanocomposites as optical fibers and waveguides.