ROLE OF INTERFACIAL POTENTIAL IN COAGULATION OF CUPRAMMONIUM CELLULOSE SOLUTION

The electric potential, copper ion Aux, and ammonia flux across the in terface of cuprammonium cellulose solution (CCS) and various 1.0 equiv /L electrolyte solutions (ES) at 25 degrees C were measured. The inter facial potentials were strongly negative (-10 to -35 mV) with H2SO4, H Cl, and (NH4)(2)SO4 as ES, weakly positive (6 to 8 mV) with NaCl, KCl, LICl, CsCL, and RbCl as ES, and strongly positive (19 to 34 mV) with KOH and NaOH as ES, generally showing values similar to the diffusion potentials for electrolyte solutions comprising ions of the same absol ute charge. The ammonia flux (about 1 X 10(-4) mol/cm(2)/s) was relati vely unaffected by the interfacial potential, but the copper ion flux was clearly dependent on it. These results, together with the observed rates of CCS coagulation, indicate that the mechanism of the coagulat ion was largely determined by the interfacial potential, with strongly negative potential gradients accelerating the CU2+ flux into the ES a nd CCS coagulation proceeding rapidly by CU2+ removal, strongly positi ve potential gradients accelerating the Na+ flux into the CCS and coag ulation proceeding rapidly via the formation of cellulose-Na+ complex, and the absence of a strong potential gradient capable of acceleratin g the ion flux resulting in slow coagulation by ammonia removal. It ma y therefore be possible to control the interfacial potential and the i on Aux by the ES composition, and thus to influence the structure of r egenerated cellulosic fibers and membranes. (C) 1996 John Wiley & Sons , Inc.