Application technology of cellulose HPMC in mortar

The functions of cellulose in mortar are: water retention, increasing cohesiveness, thickening, influencing setting time and air entraining. Because of these characteristics, it has a wide application space in building materials 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 are viscosity, particle size, dosage, active components, dissolution rate and water retention mechanism. The water retention of cellulose ether itself comes from the solubility and dehydration of cellulose ether itself. Although the molecular chain of cellulose contains a large number of hydroxyl groups with strong hydration properties, it is insoluble in water. This is because the structure of cellulose is highly crystalline, and the hydration ability of hydroxyl groups alone is not enough to destroy the strong hydrogen bond and Van der Waals force between molecules, so it only swells but does not dissolve in water. When a substituent is introduced into a molecular chain, not only the substituent destroys the hydrogen bond, but also the intermolecular hydrogen bond is destroyed due to the wedging of substituents between adjacent chains. The larger the substituent is, the larger the intermolecular distance is, and the greater the hydrogen bond destruction effect is. After the cellulose lattice is expanded, the solution enters, and the cellulose ether becomes water-soluble to form a high viscosity solution. When the temperature rises, the hydration of polymer weakens, and the water between chains is expelled. When the dehydration is sufficient, the molecules begin to aggregate, forming a three-dimensional network structure and gel precipitation. (a) the influence of particle size and mixing time of cellulose ether on water retention With the increase of viscosity, the water retention of mortar increases with the same amount of cellulose ether. With the increase of cellulose content and viscosity, the water retention rate of mortar increases. When the content of cellulose ether exceeds 0.3%, the change of water retention rate of mortar tends to balance. The water-holding capacity of mortar is largely controlled by the dissolution time. The finer cellulose ether dissolves faster, and the water-holding capacity develops faster. (2) The influence of etherification degree and temperature of cellulose ether on water retention The higher the temperature, the lower the water retention, the higher the etherification degree of cellulose ether, and the better the water retention of cellulose ether at high temperature. In use, the temperature of fresh mortar is usually lower than 35℃, and it may reach or even exceed 40℃ under special climatic conditions. In this case, it is necessary to adjust the formula and choose the product with higher etherification degree, that is, consider choosing appropriate cellulose ether. Second, the influence of cellulose ether on the air content of mortar In dry-mixed mortar products, due to the addition of cellulose ether, a certain amount of tiny, evenly distributed and stable bubbles are introduced into fresh mortar. Because of the ball effect of bubbles, mortar has good workability, reduces the cracking and shrinkage of mortar, and improves the output rate of mortar. Third, the influence of cellulose ether on cement hydration Cellulose has a delay effect on the hydration of cement-based mortar, and the delay effect increases with the increase of cellulose ether content. The influencing factors of cellulose on cement hydration are: dosage, degree of etherification and type of cement.

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