A STUDY ON THE MECHANISM OF DISSOLUTION OF THE CELLULOSE NH3/NH4SCN SYSTEM .1/

Ammonia/ammonium thiocyanate (NH3/NH4SCN) is an excellent swelling age nt and solvent for cellulose, even at a high degree of polymerization. Because polymorphic conversion in cellulose has been a long-standing, perplexing, troublesome problem, we have undertaken to study that mec hanism. Solid state CP/MAS C-13-NMR and X-ray analysis proved to be ve ry useful analytical techniques for the task. It appears that during t emperature cycling, specific cellulosic inter- and intramolecular hydr ogen-bonds are broken as polymorphic conversion proceeds sequentially from the polymorph I to II to III, and finally at total solvation to a morphous. This proceeds correspondingly via transformation of the poly morph conformations of CH2OH from trans-gauche, ''tg,'' to gauche-tran s, ''gt,'' to gauche-gauche, ''gg.'' (C) 1994 John Wiley & Sons, Inc.