The role of cellulose ether in dry mixed mortar!

Hydroxypropyl methyl cellulose is a synthetic polymer made from natural cellulose through chemical modification. Cellulose ether is a derivative of natural cellulose. The production of cellulose ether is different from synthetic polymers. Its most basic material is cellulose, a natural polymer compound. Due to the special structure of natural cellulose, cellulose itself has no ability to react with etherifying agents. However, after treatment with the swelling agent, the strong hydrogen bonds between and within the molecular chains are destroyed, and the active release of the hydroxyl group becomes alkali cellulose with the ability to react. After the reaction of the etherifying agent, the -OH group is converted into the -OR group. Cellulose ether is obtained.

The properties of cellulose ethers depend on the type, number and distribution of substituents. The classification of cellulose ethers is also based on the type of substituents, degree of etherification, solubility properties and related application capabilities. According to the type of substituents on the molecular chain, it can be divided into monoether and mixed ether. MC we usually use is monoether, and HPMC is mixed ether. Methylcellulose ether MC is a product in which the hydroxyl group on the glucose unit of natural cellulose is replaced by a methoxy group; hydroxypropyl methylcellulose ether HPMC is a product in which part of the hydroxyl group on the unit is replaced by a methoxy group and the other part is replaced by a hydroxypropyl group. The products obtained by radical substitution, and hydroxyethyl methylcellulose ether HEMC, are the main varieties widely used and sold in the market.

From the perspective of solubility properties, it can be divided into ionic and non-ionic. Water-soluble nonionic cellulose ethers are mainly composed of two series: alkyl ethers and hydroxyalkyl ethers. Ionic CMC is mainly used in synthetic detergents, textile printing, dyeing, food and oil extraction. Non-ionic MC, HPMC, HEMC, etc. are mainly used in building materials, latex coatings, medicine, daily chemicals, etc. Used as thickener, water retaining agent, stabilizer, dispersant and film-forming agent.

In the production of building materials, especially dry-mixed mortar, cellulose ether plays an irreplaceable role, especially in the production of special mortar (modified mortar), it is an indispensable and important component.

The important role of water-soluble cellulose ether in mortar mainly lies in three aspects. One is excellent water retention capacity, the other is its influence on mortar consistency and thixotropy, and the third is interaction with cement.

The water-retaining 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 cellulose ether itself comes from the solubility and dehydration of cellulose ether itself. As we all know, although the cellulose molecular chain contains a large number of highly hydratable OH groups, it itself is not soluble in water. This is because the cellulose structure 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 but does not dissolve in water. When a substituent is introduced into the molecular chain, not only the substituent destroys the hydrogen chain, but also the interchain hydrogen bonds are destroyed due to the wedge of substituents between adjacent chains. The larger the substituent, the wider the intermolecular space. The greater the distance. The greater the hydrogen bond effect is destroyed, the cellulose lattice swells, the solution enters, and the cellulose ether becomes water-soluble, forming a high-viscosity solution. As the temperature increases, the hydration of the polymer weakens and the interchain water is driven out. When the dehydration effect is sufficient, the molecules begin to aggregate, forming a three-dimensional network structure and the gel folds out. Factors that affect the water retention of mortar include cellulose ether viscosity, addition amount, particle fineness and use temperature.

7. Plaster: as a paste instead of natural substances, it can improve the water retention and improve the glue relay with the substrate.

8. Coating: as a plasticizer of latex coating, it plays a role in improving the operability and fluidity of coating and putty powder.

9. Spraying coating: it has a good effect on preventing the sinking of cement or latex spraying filler and improving the fluidity and spray pattern.

10. Secondary products of cement and gypsum: used as the press out molding binder of hydraulic substances such as cement asbestos system to improve the fluidity and obtain uniform molded products.

11. Fiber wall: due to the anti enzyme and anti-bacterial effect, it is effective as the adhesive of sand wall.

12. Others: it can be used as bubble retention agent (PC version) for thin mortar, sand mortar and mud hydraulic operator.

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