Rheological and Tribological Properties of Hydroxypropyl Methylcellulose-Fucoidan Mixtures: Effect of Fucoidan Concentration and Salt

Abstract

Our study sought to investigate the effect of fucoidan concentration (0-2.0%) on rheological and tribological properties of hydroxypropyl methylcellulose (HPMC) at 2.0%. Additionally, to examine the effect of salts (NaCl, KCl, and CaCl2) on the tribo-rheological properties of HPMC-fucoidan mixtures, a mixture containing equal concentrations of each biopolymer (2.0%) was used. A mixture with 0.5% fucoidan exhibited a lower flow behavior index value (n, 0.62) than HPMC alone but the n value increased with increasing fucoidan concentration. The apparent viscosity at 10 s-1 (eta a,10) for the mixture at 0.5% fucoidan was higher than HPMC alone but decreased at a higher fucoidan concentration (0.5-2.0%). Conversely, the eta a,100 value increased as fucoidan concentration increased. In contrast, regardless of salt type, apparent viscosity decreased with salt addition. All mixtures exhibited tan delta values greater than 1, indicating liquid-like properties. With increasing fucoidan concentration, elastic (G') and viscous (G") moduli increased and the tan delta value decreased. The mixtures with monovalent salts exhibited lower viscoelastic moduli values than that without salt, whereas the mixture with CaCl2 presented a higher G' value and lower G'' and tan delta values. The mixtures exhibited a lower maximum friction coefficient (mu 1) value with a higher fucoidan concentration, in addition to a shortening of the mixed regime. Conversely, the mixed regime was extended with salt addition, and the monovalent salt induced an increase in the mu 1 value. Our findings indicated that there was viscoelastic and lubrication synergism between the polymers, which was influenced by salt addition.