Cellulose ether 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 particularity of the natural cellulose structure, the cellulose itself has no ability to react with etherification agents. However, after the treatment of the swelling agent, the strong hydrogen bonds between the molecular chains and the chains are destroyed, and the active release of the hydroxyl group becomes a reactive alkali cellulose. Obtain cellulose ether.
In ready mix mortar, the addition amount of cellulose ether is very low, but it can significantly improve the performance of wet mortar, and it is a main additive that affects the construction performance of mortar. Reasonable selection of cellulose ethers of different varieties, different viscosities, different particle sizes, different degrees of viscosity and added amounts will have a positive impact on the improvement of the performance of dry powder mortar. At present, many masonry and plastering mortars have poor water retention performance, and the water slurry will separate after a few minutes of standing.
Water retention is an important performance of methyl cellulose ether, and it is also a performance that many domestic dry-mix mortar manufacturers, especially those in southern regions with high temperatures, pay attention to. Factors affecting the water retention effect of dry mix mortar include the amount of MC added, the viscosity of MC, the fineness of particles and the temperature of the use environment.
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 and related application properties. According to the type of substituents on the molecular chain, it can be divided into monoether and mixed ether. The MC we usually use is monoether, and the HPMC is mixed ether. Methyl cellulose ether MC is the product after the hydroxyl group on the glucose unit of natural cellulose is substituted by methoxy. The structural formula is [COH7O2(OH)3-h(OCH3)h ]x. A part of the hydroxyl group on the unit is substituted by methoxy group, and the other part is replaced by hydroxypropyl group, the structural formula is [C6H7O2(OH)3-m-n(OCH3)m[OCH2CH(OH)CH3] n]x Ethyl methyl cellulose ether HEMC, these are the main varieties widely used and sold in the market.
In terms of solubility, it can be divided into ionic and non-ionic. Water-soluble non-ionic cellulose ethers are mainly composed of two series of alkyl ethers and hydroxyalkyl ethers. Ionic CMC is mainly used in synthetic detergents, textile printing and dyeing, food and oil exploration. 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.
Water retention of cellulose ether: In the production of building materials, especially dry powder 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 has three aspects:
1. Excellent water retention capacity
2. Effect on mortar consistency and thixotropy
3. Interaction with cement.
The water retention 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 is not soluble in water, because the cellulose structure has a high degree of crystallinity. The hydration ability of hydroxyl groups alone is not enough to cover 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 bond is destroyed due to the wedging of the substituent between adjacent chains. The larger the substituent, the greater the distance between the molecules. The greater the distance. The greater the effect of destroying hydrogen bonds, the cellulose ether becomes water-soluble after the cellulose lattice expands and the solution enters, 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 effect is sufficient, the molecules begin to aggregate, forming a three-dimensional network structure gel and folded out.
Post time: Dec-06-2022