Viscoelastic and nuclear magnetic resonance studies on molecular mobility of carboxymethylcellulose–calcium complex in concentrated aqueous systems

Abstract

The influence on molecular mobility of complex formation between carboxymethylcellulose (CMC) and calcium ions has been studied through viscoelasticity and NMR measurements. Dynamic viscoelastic properties have been measured by means of a cone-plate type rheometer for aqueous solutions of CMC in the presence of various alkali- and alkaline-earth-metal salts. The dynamic modulus shifts to a longer timescale region on addition of the salts and the frequency-dependence curves of the modulus, which are measured at various salt concentrations, can be superposed to a master curve by horizontal shift only. That is, the addition of salt lengthens the relaxation times for the main chain of the CMC molecule. The shift of the relaxation time occurs most markedly with the addition of calcium salt.That the site of the complex formation is a carboxyl group of the CMC was revealed by the measurements of the spin–lattice relaxation time of each carbon atom.