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Water-induced crystallization and nano-scale spinodal decomposition of cellulose in NMMO and ionic liquid dope

Nishiyama, Yoshiharu, Asaadi, Shirin, Ahvenainen, Patrik, Sixta, Herbert
Cellulose 2019 v.26 no.1 pp. 281-289
acetates, cellulose, coagulation, crystallization, diffusivity, ionic liquids, nanofibers, water content
We followed the cellulose structure formation induced by water diffusion into Lyocell dopes based on both N-Methylmorpholine N-oxide (NMMO) and 1,5-diazabicyclo[4.3.0]non-5-ene acetate ([DBNH][OAc], by using scanning simultaneous small- and wide-angle scattering (SAXS-WAXS) experiment along the diffusion gradient. The water content at each point was estimated from the wide-angle scattering profile, giving a binary diffusion constant of the order of 5 × 10⁻¹⁰ m²/sec. In the case of the cellulose solution in NMMO monohydrate, diffraction peaks corresponding to cellulose II appeared concomitantly with the increase in small angle scattering features indicative of nanofibril formation. In the cellulose solution in the ionic liquid, an increase in small angle scattering intensity with the progression of water content appeared at scattering vector q = 0.015 Å⁻¹ corresponding to a correlation length of about 40 nm, indicative of nanometric spinodal decomposition preceding the coagulation process, though no crystalline peak appeared in the wide-angle scattering.