Cellulose Ether Thickening and Thixotropy

 Cellulose Ether Thickening and Thixotropy

Cellulose ether gives the wet mortar excellent viscosity, can significantly increase the bonding ability of the wet mortar and the base layer, and improve the sag resistance of the mortar. It is widely used in plastering mortar, brick mortar and external insulation system. The thickening effect of cellulose ether can also increase the anti-dispersion ability and homogeneity of freshly mixed materials, prevent materials from delamination, segregation and bleeding, and can be used in fiber concrete, underwater concrete and self-compacting concrete.

The thickening effect of cellulose ether on cement-based materials comes from the viscosity of the cellulose ether solution. Under the same conditions, the higher the viscosity of cellulose ether, the better the viscosity of the modified cement-based material, but if the viscosity is too large, it will affect the fluidity and operability of the material (such as sticking plastering knife). Self-leveling mortar and self-compacting concrete, which require high fluidity, require low viscosity of cellulose ether. In addition, the thickening effect of cellulose ether will also increase the water demand of cement-based materials and increase the output of mortar.

High viscosity cellulose ether aqueous solution has high thixotropy, which is also a major characteristic of cellulose ether. Aqueous solutions of methyl cellulose generally have pseudoplasticity and non-thixotropic fluidity below their gel temperature, but exhibit Newtonian flow properties at low shear rates. Pseudoplasticity increases with the molecular weight or concentration of cellulose ether, regardless of the type and degree of substitution. Therefore, cellulose ethers of the same viscosity grade, whether MC, HPMC, HEMC, as long as the concentration and temperature are kept constant, always show the same rheological properties. When the temperature is increased, a structural gel is formed and high thixotropic flow occurs.

High-concentration and low-viscosity cellulose ethers exhibit thixotropy even below the gel temperature. This property is of great benefit for adjusting the leveling and sagging properties of construction mortar. It should be noted here that the higher the viscosity of the cellulose ether, the better the water retention, but the higher the viscosity, the higher the relative molecular weight of the cellulose ether, and the lower its solubility, which has a negative impact on the mortar concentration and construction performance.