Morphological and structural formation of the regenerated cellulose membranes recovered from its cuprammonium solution using aqueous sulfuric acid

Morphological and structural formation of the regenerated cellulose membranes from its cuprammonium hydroxide solution by acid coagulation was investigated. Scanning electron microscopic observation revealed that the morphology of the membranes changed drastically as functions of both the cellulose concentration in the original cellulose solution C_Cell and the concentration of sulfuric acid as a coagulant C_H2SO4. It was found that at a constant polymer concentration (8 wt %) the membrane prepared by using 5 wt % aqueous sulfuric acid exhibits higher water flux, far smaller swelling anisotropy parameter L_t, and larger porosity P_r with a thinner skin structure, and these parameters were proven to be associated with lower (11 0) crystal plane orientation coefficient f_{∥(11 0)} compared with those for the membranes obtained by aqueous sulfuric acid with more than 10 wt %. On the other hand, at constant coagulant concentration (10 wt %) the membrane prepared by using the polymer solution with 5 wt % shows far greater P_r with practically no distinct skin structure; hence, a higher flux. The drastic changes in the morphology and structural parameters as functions of C_Cell and C_H2SO4 were found to be well correlated with abrupt changes in material transportation (copper ion, ammonium ion, and water) from the polymer solution to aqueous coagulants as a function of C_Cell and C_H2SO4. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1669–1678, 1999