Comprehensive Analysis of Thickening and Thixotropy of Cellulose Ether(1)
Consistency can also be adjusted by choosing particle size and choosing cellulose ethers with different degrees of modification. The so-called modification is to introduce a certain degree of substitution of hydroxyalkyl groups on the skeleton structure of MC. By changing the relative substitution values of the two substituents, that is, the DS and MS relative substitution values of the methoxy and hydroxyalkyl groups that we often say. Various performance requirements of cellulose ether can be obtained by changing the relative substitution values of the two substituents.
High-viscosity cellulose ether aqueous solution has high thixotropy, which is also a major characteristic of cellulose ether. Aqueous solutions of MC polymers usually have pseudoplastic and non-thixotropic fluidity below their gel temperature. However, it exhibits Newtonian flow properties at low shear rates. Pseudoplasticity increases with the molecular weight or concentration of cellulose ether, regardless of the type of substituent and the degree of substitution.
Therefore, cellulose ethers of the same viscosity grade, no matter MC, HPMC, HEMC. As long as the concentration and temperature are kept constant, they always exhibit the same rheological properties. Structural gels are formed when the temperature is raised, and highly thixotropic flows occur.
High concentration and low viscosity cellulose ethers show thixotropy even below the gel temperature. This property is of great benefit to the adjustment of leveling and sagging in the construction of building mortar.
It needs to be explained here that the higher the viscosity of cellulose ether, the better the water retention. However, the higher the viscosity, the higher the relative molecular weight of cellulose ether, and the corresponding decrease in its solubility. This negatively affects mortar consistency and workability.
The higher the viscosity, the more obvious the thickening effect on the mortar, but it is not completely proportional. Some medium and low viscosity, but the modified cellulose ether has better performance in improving the structural strength of wet mortar. With the increase of viscosity, the water retention of cellulose ether improves.
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