Structure and properties of helical fibers spun from cellulose solutions in [B_mim]Cl

Man-made fibers were spun from solutions of cotton and wood cellulose in ionic liquid (1-butyl-3-methyl-imidazolium chloride, [B_mim]Cl). Depending on the concentration, cellulose dissolved in [B_mim]Cl down to macromolecules or nanofibrils. The artificial fibers had a diameter of about 100 nm, were uniform, transparent, helical, and optically active. The fibers were composed of the core and shell (∼20% of the radius). The core was composed of the dense helical pseudofibrils of about 30 nm in thick occupying of about 40% of the area of the fiber core cross-section. The tensile strength of the whole fiber was, on average, 250 MPa, while that of the individual pseudofibrils was ∼1.1 GPa. The tensile-strength dependencies were two-stage with drastically different Young's modules. We explain the shape of the loading curves as well as the strength of the fibers by the friction between the twisted pseudofibrils in the core.