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What Role Does Cellulose Ether Play in Dry Mixed Mortar?

March 1, 2022by admin0

Cellulose ether is a synthetic polymer made from natural cellulose by chemical modification. It is a derivative of natural cellulose. Its production is different from synthetic polymers. Its most basic material is cellulose, a natural polymer compound. Because of its special structure, cellulose itself has no ability to react with etherifying agent. The hydroxyl group of cellulose is broken by the reaction between cellulose and OH group in the chain, but it is converted into hydroxyl ether by alkali reaction.

Its nature depends on the type, quantity and distribution of substituents. Its classification is also based on the type of substituents, etherification degree, solubility and related application types. According to the type of substituents in the molecular chain, it can be divided into single ether and mixed ether. MC we usually use is single ether and HPMC is mixed ether. MC is the product after the hydroxyl group on the glucose unit of natural cellulose is replaced by methoxy group, and the structural formula is [c o h7o2 (OH) 3-h (OCH3) H] X. HPMC is the product obtained by replacing one part of the hydroxyl group on the unit with methoxy group and the other part with hydroxypropyl group, and the structural formula is [c6h7o2 (OH) 3-m-n (OCH3) m [och2ch (OH) CH3] n] X. In addition, HEMC, These are the main varieties widely used and sold in the market.

In terms of solubility, it can be divided into ionic type and non-ionic type. Water soluble nonionic cellulose ether is mainly composed of alkyl ether and hydroxyalkyl ether. Ionic CMC is mainly used in synthetic detergent, textile printing and dyeing, food and oil exploitation. Non ionic MC, HPMC and HEMC are mainly used in building materials, latex coatings, medicine, daily chemistry and so on. It is used as thickener, water retaining agent, stabilizer, dispersant and film-forming agent.

It plays an irreplaceable role in the production of building materials, especially dry mixed mortar, especially in the production of special mortar (modified mortar).

The important role of water-soluble cellulose ether in mortar mainly has three aspects: first, excellent water holding capacity, second, the influence on mortar consistency and thixotropy, and third, the interaction with cement.

Its water holding effect depends on the water absorption of the base, the composition of mortar, the layer thickness of mortar, the water demand of mortar and the setting time of setting materials. Its own water retention comes from its own solubility and dehydration. As we all know, although cellulose molecular chain contains a large number of OH groups with strong hydration, it is not soluble in water because cellulose structure is highly crystalline. The hydration ability of hydroxyl group alone is not enough to pay for the strong intermolecular hydrogen bond and van der Waals force. Therefore, it only swells and 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 hydrogen bond between chains is destroyed due to the wedging of adjacent substituents. The larger the substituent, the greater the distance between molecules. The greater the hydrogen bond breaking effect, the solution enters after the cellulose lattice is expanded, and the cellulose ether becomes water-soluble to form a high viscosity solution. When the temperature increases, the hydration of polymer decreases, and the water between chains is expelled. When the water is fully used, the molecules begin to aggregate and form a three-dimensional network structure. The factors affecting the water retention of mortar include its viscosity, addition amount, particle fineness and service temperature.

The higher its viscosity, the better its water retention performance, and the viscosity of polymer solution. Depending on the molecular weight (degree of polymerization) of the polymer, it is also determined by the molecular structure, chain length and chain morphology. The type and quantity distribution of substituents also directly affects its viscosity range[ η]= Km α

[ η] Intrinsic viscosity of polymer solution

M polymer molecular weight

α Polymer characteristic constant

K viscosity solution coefficient

The viscosity of polymer solution depends on the molecular weight of polymer. The viscosity and concentration of its solution are related to its application in various fields. Therefore, each cellulose ether has many different viscosity specifications, and the adjustment of viscosity is mainly realized through the degradation of alkali cellulose, that is, the fracture of cellulose molecular chain.

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