Structure development in the condensed state of cellulose fiber regenerated from alkali complex solution

Regenerated cellulose fibers were successfully wet-spun from a cellulose/NaOH/thiourea/urea aqueous solution by an efficient extrusion dissolution method. The structure changes of these regenerated cellulose fibers that occurred during wet spinning process had been investigated by field-emission scanning electron microscope, carbon nuclear magnetic resonance spectroscopy (¹³C-NMR), attenuated total reflection infrared spectroscopy and the corresponding two-dimensional spectroscopy, wide-angle-X-ray-diffraction, small-angle-X-ray scattering (SAXS), tensile testing, and thermogravimetric analysis. Results revealed that higher crystallinity and orientation were obtained because of the improved post-processing, while the annealed fiber exhibited lower crystallinity and orientation, owing to a disruption of some oriented crystallites and heat shrinkage during hot air drawing process. SAXS results indicated that the microvoid in the cellulose fibers were smaller with the spinning process, and the pore structure had a more significant impact on the mechanical properties of the regenerated cellulose fibers. Moreover, an increased tensile strength (2.40 cN/dtex) and elongation at break (8.20%) in dry state were obtained in regenerated cellulose fibers due to heat treatment process. Therefore, the structure development contributed toward the improvement of the tensile strength, modulus and thermal stability of the regenerated cellulose fibers during spinning process. On the other hand, a simple, environmentally friendly pathway was proposed for cellulose regeneration, which could significantly affect the cellulose regeneration in current industries.