Viscosity and water retention properties of cellulose ethers

Viscosity and water retention properties of cellulose ethers

Cellulose ether is often an indispensable component in dry-mixed mortars. Because it is an important water retention agent with excellent water retention properties. This water retention property can prevent the water in the wet mortar from evaporating prematurely or being absorbed by the substrate, prolong the operable time of the wet mortar, ensure the cement is fully hydrated, and thus ultimately ensure the mechanical properties of the mortar, which is especially beneficial to the construction of thin mortars (such as plastering mortars) and mortars in highly absorbent substrates (such as aerated concrete blocks), high temperature and dry conditions.

The water retention property of cellulose is highly related to its viscosity. The higher the viscosity of cellulose ether, the better the water retention performance. Viscosity is an important parameter of MC performance. At present, different MC manufacturers use different methods and instruments to test the viscosity of MC, and the main methods are Haake Rotovisko, Hoppler, Ubbelohde and Brookfield. For the same product, the viscosity results measured by different methods vary greatly, and some are even exponentially different. Therefore, when comparing viscosities, it is important to do so between the same test methods, including temperature, rotor, etc.

Generally speaking, the higher the viscosity, the better the water retention effect. However, the higher the viscosity, the higher the molecular weight of MC and the corresponding decrease in its solubility, which has a negative effect on the strength and construction performance of the mortar. The higher the viscosity, the more obvious the thickening effect on the mortar. The higher the viscosity, the stickier the wet mortar will be, both in construction, as shown by the sticky scraper and the high adhesion to the substrate. However, it does not help much to increase the structural strength of the wet mortar itself. When both construction, it shows the anti-sagging performance is not obvious. On the contrary, some low to medium viscosity but modified methyl cellulose ethers have excellent performance in improving the structural strength of wet mortar.