Effect of chloride salts on tribological and rheological properties of guar gum-fucoidan mixture

This study sought to investigate the effects of inorganic chloride salts on the rheological and tribological properties of a guar gum (GG)-fucoidan mixture. All of the examined mixtures exhibited shear thinning behavior. With higher salt concentrations, the consistency index and apparent viscosity at 100 s⁻¹ values decreased, whereas the tan δ value increased. Particularly, a pronounced change was observed with calcium chloride. In addition, the mixtures with calcium chloride violated the Cox-Merz rule. In contrast to the mixture without salts, the large fucoidan lumps were observed in confocal laser scanning microscopic images for the mixtures with salts. Moreover, a longer relaxation time was observed as the salt concentration increased. The changes in friction as a function of sliding speed in the mixture without salt exhibited a typical Stribeck curve, consisting of boundary, mixed, and hydrodynamic lubrication regimes. However, a different pattern with five lubrication regimes was observed in mixtures containing salts. This was likely due to the formation of fucoidan lumps caused by salts. The lubricant properties of the mixture were improved by salt addition. Collectively, our findings provide insights into the interactions between fucoidan and other polymers.