Rapid in situ quantification of rheo-optic evolution for cellulose spinning in ionic solvents.

It is critical to monitor the structural evolution of complex fluids for optimal manufacturing performance, including textile spinning. However, in situ measurements in a textile-spinning process suffer from the paucity of non-destructive instruments and interpretations of the measured data. In this work, kinetic and rheo-optic properties of a cellulose/ionic liquid solution are measured simultaneously while fibers are regenerated in aqueous media from a model wet-spinning process via a customized polarized microscope. This system enables to capture key geometrical and structural information of the fiber under spinning at varying draw ratios and residence time, including the flow kinematics extracted from feature tracking, and the flow-induced morphology and birefringent responses. A physics-oriented rheological model is applied to connect the kinematic and structural measurements in a wet-spinning process incorporating both shear and extensional flows. The birefringent responses of fibers under coagulation are compared with an orientation factor incorporated in the constitutive model, from which a superposed structure-optic relationship under varying spinning conditions is identified. Such structural characterizations inferred from the flow dynamics of spinning dopes exhibit strong connections with the mechanical properties of the fully-regenerated fibers, thus enabling to predict the spinning performance in a non-destructive protocol.