The functions of cellulose ether in mortar are: water retention, increasing cohesion, thickening, affecting setting time, and air-entraining properties. Because of these characteristics, it has a wide application space in building material mortar.
1. The water retention of cellulose ether is the most important characteristic in the application of mortar.
The main factors affecting the water retention of cellulose ether: viscosity, particle size, dosage, active ingredient, dissolution rate, water retention mechanism: the water retention of cellulose ether itself comes from the solubility and dehydration of cellulose ether itself. Although the cellulose molecular chain contains a large number of hydroxyl groups with strong hydration properties, it is not soluble in water. This is because the cellulose structure has a high degree of crystallinity, and the hydration ability of hydroxyl groups alone is not enough to destroy the strong intermolecular bonds. Hydrogen bonds and van der Waals forces, so it only swells but does not dissolve in water. When a substituent is introduced into the molecular chain, not only the substituent breaks the hydrogen bond, but also the interchain hydrogen bond is broken due to the wedging of the substituent between adjacent chains. The larger the substituent, the greater the distance between the molecules is, which destroys the hydrogen bond effect. The larger the cellulose lattice, the solution enters after the cellulose lattice expands, and the cellulose ether becomes water-soluble, forming a high-viscosity solution. When the temperature rises, the hydration of the polymer weakens, and the water between the chains is driven out. When the dehydration is sufficient, the molecules begin to aggregate, forming a three-dimensional network structure and gel precipitation.
(1) Effect of particle size and mixing time of cellulose ether on water retention
With the same amount of cellulose ether, the water retention of mortar increases with the increase of viscosity; the increase of the amount of cellulose ether and the increase of viscosity increases the water retention of mortar. When the content of cellulose ether exceeds 0.3%, the change of mortar water retention tends to be balanced. The water retention capacity of mortar is largely controlled by the dissolution time, and the finer cellulose ether dissolves faster, and the water retention capacity develops faster.
(2) Effect of degree of etherification of cellulose ether and temperature on water retention
As the temperature rises, the water retention decreases, and the higher the degree of etherification of cellulose ether, the better the high temperature water retention of cellulose ether. During use, the temperature of the freshly mixed mortar is usually lower than 35°C, and under special climate conditions, the temperature may reach or even exceed 40°C. In this case, the formula must be adjusted and the product with a higher degree of etherification should be selected. That is, consider choosing a suitable cellulose ether.
2. Effect of cellulose ether on air content of mortar
In dry-mixed mortar products, due to the addition of cellulose ether, a certain amount of tiny, uniformly distributed and stable air bubbles are introduced into the freshly mixed mortar. Due to the ball effect of the air bubbles, the mortar has good workability and reduces the torsion of the mortar. Crack and shrinkage, and increase the output rate of mortar.
3. Effect of cellulose ether on cement hydration
Cellulose ether has retardation to the hydration of cement-based mortar, and the retardation effect is enhanced with the increase of cellulose ether content. The influencing factors of cellulose ether on cement hydration are: dosage, degree of etherification, type of cement.
Post time: Feb-02-2023