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 membran es from its cuprammonium hydroxide solution by acid coagulation was investi gated. Scanning electron microscopic observation revealed that the morpholo gy of the membranes changed drastically as functions of both the cellulose concentration in the original cellulose solution C-Cell and the concentrati on 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 % aqueo us sulfuric acid exhibits higher water flux, far smaller swelling anisotrop y parameter L-t, and larger porosity P-r with a thinner skin structure, and these parameters were proven to be associated with lower (<1(1)over bar>0) crystal plane orientation coefficient f(parallel to(<1(1)over bar>0)) comp ared with those for the membranes obtained by aqueous sulfuric acid with mo re than 10 wt %. On the other hand, at constant coagulant concentration (10 wt %) the membrane prepared by using the polymer solution with 5 wt % show s far greater P-r with practically no distinct skin structure; hence, a hig her flux. The drastic changes in the morphology and structural parameters a s functions of C-Cell and C-H2SO4 were found to be well correlated with abr upt changes in material transportation (copper ion, ammonium ion, and water ) from the polymer solution to aqueous coagulants as a function of C-Cell a nd C-H2SO4. (C) 1999 John Wiley & Sons, Inc.