Studies on structure of cuprammonium cellulose .3. Structure of regenerated cellulose treated by cuprammonium solution

An attempt was made to clarify the supermolecular structure of regenerated celluloses recovered from the copper-absorbing celluloses, which were prepared by treating solid cellulose with aqueous (ag) cuprammonium hydroxide (CAH) solutions having different hydroxyl ion content (C-OH). X-Ray diffraction and CP/MAS C-13 NMR analyses carried out on the regenerated cellulose samples revealed that the samples had a wide variation of supermolecular structures depending on the C-OH: (1) The CAH solutions with C-OH<0.174 mol l(-1) brought about the increase in crystallinity, crystalline size and intramolecular hydrogen bond formation, and (2) the CAH solutions with C-OH>0.479 mol l(-1) tend to give the reverse results. Circular dichroism (CD) spectra for the cellulose films treated by two kinds cuprammonium solutions with C-OH<0.174 and C-OH>0.479 revealed that cuprammonium ions orderly coordinate to C-2 and C-3 hydroxyl groups of glucopyranose units of cellulose in only amorphous region in the case of C-OH<0.174 and the CAH with C-OH>0.479 penetrates into even a part of crystalline region of cellulose and causes a ligand exchange from ammonia to hydroxyl groups to give a non-dissociated complex form of cellulose having certain random cross-linking by copper atom. Thus, we concluded that the difference in the complex form of the copper-absorbing cellulose influences considerably the super-molecular structure of the regenerated celluloses.