Rheological properties of carboxymethyl cellulose–fucoidan mixture: effect of fucoidan concentration and salt

Abstract

In this study, we investigated the effect of fucoidan concentration and salts (NaCl, KCl, and CaCl₂) on the rheological properties of carboxymethyl cellulose (CMC)–fucoidan mixtures. All mixtures exhibited shear-thinning behavior, with the apparent viscosity (η_a) of CMC–fucoidan mixtures at shear rates < 3.0 s⁻¹ being higher than that of CMC alone. However, as the shear rate increased to ≤ 30 s⁻¹, a more significant decrease in η_a was observed in CMC–fucoidan mixtures than in CMC alone. Consequently, the η_a,100 value of the mixtures decreased in a fucoidan concentration-dependent manner. In contrast, viscoelastic moduli increased with a higher fucoidan concentration, with a more pronounced increase observed in the elastic modulus than in the viscous modulus. Upon the addition of monovalent salts, the η_a value of CMC–fucoidan mixtures decreased due to the charge screening effect of cations. Conversely, the opposite result was observed with CaCl₂ addition due to Ca²⁺-induced crosslinking between both anionic polymers. Moreover, regardless of the salt type, CMC–fucoidan mixtures with salt showed higher viscoelastic moduli than those without salt, with a noticeable increase observed when CaCl₂ was added. This was likely due to the indirect/direct crosslinking effect of mono- and divalent cations. Our findings demonstrate that fucoidan and CMC exhibit a viscoelastic synergistic interaction, which is sensitive to shearing and influenced by the type of salt.

Graphical abstract

The effect of fucoidan concentration and salt addition on the rheological properties of carboxymethyl cellulose–fucoidan mixtures was investigated. Rheological synergism between the two anionic polymers occurred due to the formation of an entangled network with hydrophobic junction zones. The addition of salt enhanced this synergism through the indirect/direct crosslinking effects of mono- and di-valent cations.