(149g) Characterization of the Spinnability of Cellulose/Ionic Liquid Spinning Dopes during a Dry-Jet Wet-Spinning Process through in-Situ Rheo-Optic Techniques

Cellulose-based fabrics, such as cotton, make up 37% of all textile fabrics in the global market. The expansion of production is increasingly limited by the demand of arable land for foods. This has motivated efforts to investigate recycling of these textiles by dissolution of previously-produced fabrics and fibers. However, this is hampered by the paucity of solvents that are capable of dissolving cellulose without destroying the constituent polysaccharide chains. In the past few decades, ionic liquids have demonstrated advantageous solubility and chemical stability for the spinning of cellulose in the dry-jet wet-spinning process. Previous studies have attempted to optimize the spinning parameters by analyzing the mechanical properties of the spun and coagulated fibers. However, the thermomechanical properties of the ultimate fibers convolve all of the contributions from each individual step in the complex spinning process. Process optimization thus typically requires a large number of empirical tests to optimize spin-line geometries, processing conditions and environmental control. It remains unclear if the resulting process parameters are robust with varying material sources or spinning configurations.

In this work, we address these limitations through the implementation of an in-situ rheo-optical technique that monitors the temporal and spatial structural evolution of cellulose fibers during a dry-jet wet-spinning process. The experimental results obtained using a number of ionic solvents (e.g., [EMIM][OAc] and [DBNH][OAc]) demonstrate distinct evolution of the optical retardation in the thinning and solidifying fiber with varying coagulation times and draw ratios. By comparison of the computed birefringence with the stress-optical relationship, we separate the contributions to the flow-induced cellulose reorientation from the dry-jet process and the subsequent coagulation process. Following the evolution of the optical signature at several spatial locations along the spin-line reveals the saturation of birefringence when the fibers are sufficiently drawn, which provides a measure of the maximal alignment of the cellulosic chains that can be achieved at a given draw ratio. We subsequently connect the in-situ characterization of birefringence with ex-situ measurements of the non-linear shear and extensional rheology of the spinning dopes, as well as the mechanical properties of the ultimate fibers through the application of appropriate constitutive models and structural characterization. This information is used to develop a bottom-up mechanical framework for understanding the complex deformation history experienced by the cellulose/IL spinning dopes during the dry-jet wet spinning process, and to provide further insights in the spin-line optimization.