Super-molecular structures controlling the swelling behavior of regenerated cellulose membranes

Swelling behavior of the regenerated cellulose membranes prepared from cellulose solutions dissolved in aqueous cuprammonium hydroxide and in dimethylacetamide/lithium chloride by various coagulation systems was discussed with special emphasis on crystal plane orientation and amorphous structures characterized by mechanical relaxations. Swelling anisotropy L(t) to thickness direction of the membrane was observed without exception and was found to be categorized into three groups due to coagulation systems (acid, alkaline, and organic systems). Acid coagulation system was omitted from discussion because of discussion elsewhere. L(t) was well correlated with crystallinity chi(c) and its (1(1) over bar0$) plane orientation parameter f(parallel to(1(1) over bar0$)), showing that larger those values give larger L(t). Larger L(t) (hence, larger chi(c), or larger f(parallel to(1(1) over bar0$)) in turn was confirmed to be related with higher T-max for alpha(2) and lower alpha(H2O), beta, and gamma relaxations, and with larger tan delta(max) for all relaxations. These results lead to a conclusion that higher order molecular packing (stronger intermolecular hydrogen bonding) including crystalline part might accompany with the amorphous structure having more mobile local segmental motions during membrane formation studied here. Of these relaxations, beta relaxation was confirmed to be composed of two mechanical relaxation mechanisms, one associated with out-of-phase local motion against (1(1) over bar0$) plane-like structure and the other associated with in-phase segmental motion. The swelling anisotropy was tentatively concluded as a phenomenon that arises from water penetration to more mobile parts, plasticizing molecular chains and integrating some of them along originally existed elementary crystals to the plane orientation direction according to f(parallel to(1(1) over bar0$)), Or simply rearranging the elementary crystals to the thickness direction, and of course water is retained between them.