Viscoelastic Properties of κ-Carrageenan in Saline Solution

Viscoelastic properties of .kappa.-carrageenan in saline soln. at various concns. and pH were investigated by dynamic rheol. techniques, viscosity, elasticity measurements, and IR spectrometry. The viscosity and elasticity at low concns. of .kappa.-carrageenan do not depend on pH, confirming that .kappa.-carrageenan is in a disordered conformation. At 0.7% .kappa.-carrageenan, the disordered conformation transforms into an ordered helical conformation with the possibility of weak-type gel formation. The transformation is also confirmed by dynamic measurements of loss and storage moduli. Furthermore, at this concn., the viscosity and elasticity are highly dependent on pH. At higher concns. of NaCl (0.5 M) at some pHs, we obsd. that storage modulus is greater than loss modulus for the entire frequency region. Hence, there is a possibility of structure transformation from weak-type gel to a somewhat intermediate gel. The lowest viscosity and elasticity were obtained at extreme pH, confirming that there are structural changes occurring at these pHs due to hydrolysis. This is confirmed by IR data.