Relationship between Water-holding Capacity and Viscosity of Cellulose Ether

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Water retention of cellulose ether: In the production of building materials, especially dry mortar, cellulose ether plays an irreplaceable role, especially in the production of special mortar (modified mortar), it is an indispensable and important part. The important role of water-soluble cellulose ether in mortar mainly has three aspects, one is excellent water retention capacity, the second is the effect on mortar consistency and thixotropy, and the third is the interaction with cement. The water retention effect of cellulose ether depends on the water absorption of the base layer, the composition of the mortar, the thickness of the mortar layer, the water demand of the mortar, and the setting time of the setting material. The water retention of the cellulose ether itself results from the solubility and dehydration of the cellulose ether itself. It is well known that although the molecular chain of cellulose contains a large number of OH groups with strong hydration ability, it is not soluble in water because the structure of cellulose is highly crystalline. The hydration ability of hydroxyl groups alone is not enough to pay for the strong hydrogen bonds and van der Waals forces between molecules. Therefore, it only swells and does not dissolve in water. When a substituent is introduced into the molecular chain, the substituent not only destroys the hydrogen chain, but also destroys the hydrogen bond between the chains due to the wedging of the substituent between the adjacent chains. The larger the substituent, the greater the distance between the molecules. The greater the destruction of the hydrogen bond effect, the cellulose lattice puffed, the solution enters, the cellulose ether becomes water-soluble, forming a high viscosity solution. When the temperature increases, the hydration of the polymer is weakened, and the water between the chains is driven out. When the dewatering effect is sufficient, the molecules begin to aggregate, forming a three-dimensional network structure gel folded out.

The factors that affect the water retention of mortar include cellulose ether viscosity, addition amount, particle fineness and use temperature.
The greater the viscosity of the cellulose ether, the better the water retention properties. Viscosity is an important parameter of cellulose properties, different cellulose manufacturers use different methods and instruments to determine the viscosity of cellulose, 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 multiplied. Therefore, when comparing viscosity, it must be carried out 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 cellulose, its solubility will be correspondingly reduced, which has a negative impact on the strength and construction performance of mortar. The higher the viscosity, the more obvious the thickening effect of mortar, but it is not proportional to the relationship. The higher the viscosity, the wet mortar will be more sticky, both during construction, the performance of the sticky scraper and the high adhesion to the substrate. But the increase in the structural strength of the wet mortar itself is of little help. Both construction, the performance of anti-sagging performance is not obvious. On the contrary, some low viscosity but modified methyl cellulose ether has excellent performance in improving the structural strength of wet mortar.

Key words:

Mortar additive