In-situ Observation of Non-solvent-induced Phase Separation of Cellulose Cuprammonium Solution by Small-Angle X-ray Scattering.

Phase separation caused by permeation of non-solvents into polymer solution is called non-solvent-induced phase separation (NIPS). NIPS are often applied to fabrication processes of polymer materials such as wet-spinning of fibers and porous membranes. For example, NIPS of cellulose cuprammonium solution in water has been utilized to manufacture regenerated cellulose fibers. Hence, understanding the mechanism of NIPS has crucial importance in chemical industries. However, study of NIPS is challenging because it is complicated process which includes time-dependent variation of composition of polymer, solvent, and non-solvent molecules. To understand the structure formation mechanism, we performed in-situ structural analysis on NIPS process of cellulose in cuprammonium solution by means of small-angle X-ray scattering (SAXS). From time-development of SAXS profiles of the cellulose solution, we characterized phase separation structure and the dynamics of structural growth. Eventually, we clarified that network structure having ~ 10 nm characteristic length is formed by desorption of ammonia from cellulose solution into water.