Dissolution and fibre spinning of cellulose from an ionic liquid

Abstract: Regenerated cellulose fibres can become a sustainable alternative to cotton and polyester in textile applications. One method of producing such is dissolution of cellulose in an ionic liquid (IL) and regeneration through air-gap spinning. In this master thesis, the dissolution state of cellulose in the ionic liquid 1-ethyl-3-methylimidazolium acetate (EmimAc) together with dimethyl sulfoxide (DMSO) has been studied through concentration series and diffusion nuclear magnetic resonance (NMR). It was shown that a stoichiometric relation of 3 or higher between the IL and anhydroglucose unit (AGU) is needed for complete dissolution and that one acetate ion bind to each AGU. In pure EmimAc, a structure of anions and cations is proposed to form around the polymer chain. The structure of the cellulose chains in solution was studied through small-angle x-ray scattering (SAXS) showing stiff cylinders with repulsive interactions. Rheological measurements were performed to evaluate spinnability of the solutions. Fibres were produced using air-gap spinning and the titer, tenacity, elongation at break and birefringence obtained at two different draw ratios (DR=4 and 6) and using two different coagulation mediums (water and isopropanol) were investigated. The level of crystallinity and internal fibre structure was evaluated using wide-angle x-ray scattering (WAXS) and SAXS. Fibres coagulated in water showed higher tenacity and a higher level of crystallinity but little dependence on the DR could be shown. An internal structure of 20 nm thick crystalline lamella in an amorphous matrix is proposed.