Views:0 Author:Site Editor Publish Time: 2020-05-14 Origin:Site
Cellulose Ethers HPMC in Construction Mortar Materials
The functions of cellulose ether HPMC in mortar are: water retention, increased adhesion, thickening, affecting the setting time, and air entrainment. Because of these characteristics, it has a wide application space in mortar building material .
Cellulose ether HPMC water retention is the most important characteristic in mortar applications.
The main factors affecting the water retention of cellulose ether HPMC: viscosity, particle size, dosage, active ingredient, dissolution rate.
The water retention mechanism: the water retention of cellulose ether HPMC 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 the hydroxyl group alone is not enough to destroy the strong molecular Hydrogen bond and van der Waals force, so it only swells in water and does not dissolve. When a substituent is introduced into the molecular chain, not only the substituent breaks the hydrogen bond, but also the hydrogen bond between the chains due to the wedging of the substituent between adjacent chains. The larger the substituent, the greater the distance between the molecules and the hydrogen bond effect is destroyed. The larger the expansion of the cellulose lattice, the solution enters, and the cellulose ether becomes water-soluble, forming a highly viscous solution. When the temperature increases, the polymer hydration weakens, and the water between the chains is expelled. When the dehydration is sufficient, the molecules begin to aggregate and form a three-dimensional network structure gel to precipitate out.
Effect of cellulose ether particle size and mixing time on water retention
With the increase in viscosity of the same amount of cellulose ether HPMC, the water retention of the mortar increases; the increase in the amount of cellulose ether and the increase in viscosity increase the water retention of the mortar. When the content of cellulose ether exceeds 0.3%, the change of mortar water retention tends to balance. The water retention capacity of mortar is largely controlled by the dissolution time. The finer cellulose ether HPMC dissolves faster and the water retention performance develops faster.
Effect of degree and temperature of cellulose ether etherification on water retention
As the temperature increases, the water retention decreases, and the higher the degree of etherification of cellulose ether HPMC, the better the high temperature water retention of cellulose ether. During use, the temperature of the freshly mixed mortar is usually lower than 35 ℃. Under special climatic conditions, the temperature may reach or even exceed 40 ℃. In this case, the formulation must be adjusted to select products with a higher degree of etherification. That is to consider the selection of suitable cellulose ether.
Effect of cellulose ether HPMC on mortar gas content
In the dry-mixed mortar products, due to the addition of cellulose ether HPMC, 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 turtle of the mortar. Crack and shrink, and increase the yield of mortar.
Effect of cellulose ether HPMC on cement hydration
Cellulose ether HPMC has a delay to the hydration of cement-based mortar, and the delay effect is enhanced with the increase of the amount of cellulose ether HPMC. The influencing factors of cellulose ether on cement hydration are: dosage, degree of etherification, and type of cement.
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