Influence of shear rate on gelation of biopolymers solution
The gelation process of mixed biopolymer solution under the shear rate was investigated. To this aim 3% solution of gelatin and sodium carboxymethylcellulose (NaCMC), with the gelation/NaCMC ratio 4/1 was prepared. Rheological measurements were performed using rotational viscometer with coaxial cylinders (“Haake”, Germany) at the temperature of 20°C. Continuous loop hysteresis method was applied. Flow curves of the gels of different ages were obtained after shearing up to D max, 10 min shearing at D max, and down shearing. The gels were also subjected to steady shear at constant shear rate in order to get shear stress-time dependence.
The fresh gel shows rheopexy, i.e., antithixotropy, shear stress increases under steady shearing. During the gel aging structural links are establishing in time, and the gels show thixotropy and then rheopexy. When the gel is subjected to a continuous shearing two processes are taking place simultaneously, link disruption, leading to a shear stress decrease and link setting up, leading to a shear stress increase. The whole effect, depending on which one of the processes prevails during steady shearing, is either rheopexy or thixotropy. A balance between disruption and growth of gel structure is established at a particular gel age.
Key wordsGelatin sodium carboxymethylcellulose gelation thixotropy rheopexy
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