Views:1 Author:Site Editor Publish Time: 2021-11-09 Origin:Site
Following the previous article, we continue to introduce HEC and CMC in the classification of cellulose ethers.
1.1.3 Hydroxyethyl cellulose (HEC)
It is made from refined cotton treated with alkali and reacted with ethylene oxide as etherizing agent in the presence of acetone. Its substitution degree is generally 1.5~2.0. It has strong hydrophilicity and is easy to absorb moisture.
(1) hydroxyethyl cellulose can be dissolved in cold water, hot water dissolution is more difficult. Its solution is stable at high temperature and does not have gel. It can be used for a longer time under high temperature in mortar, but the water retention is lower than that of methyl cellulose.
(2) hydroxyethyl cellulose has stability to general acid and alkali, alkali can accelerate its dissolution, and slightly improve the viscosity, its dispersibility in water is slightly worse than methyl cellulose and hydroxypropyl methyl cellulose.
(3) hydroxyethyl cellulose has good performance on mortar anti-draping, but the slow setting time of cement is longer.
1.1.4 Carboxymethyl cellulose (CMC)\[C6H7O2(OH)2och2COONa\]n
Made from natural fibers (cotton, etc.) after alkali treatment, with sodium monochloroacetate as etherizing agent, after a series of reaction processing and made of ionic cellulose ether. The degree of substitution is generally 0.4~1.4, and its performance is greatly affected by the degree of substitution.
(1) Carboxymethyl cellulose is more hygroscopic, general conditions of storage will contain large water.
(2) Carboxymethyl cellulose aqueous solution does not produce gel, with the temperature and viscosity decreases. When the temperature exceeds 50℃, the viscosity is irreversible.
(3) Its stability is greatly affected by pH. Generally it can be used in gypsum-based mortar, not in cement-based mortar. At high alkalinity, it will lose viscosity.
(4) Its water retention is much lower than that of methyl cellulose. It has retarding effect on gypsum-based mortar and reduces its strength. However, the price of carboxymethyl cellulose is significantly lower than that of methyl cellulose. Landcel has many years of experience in developing and producing HEC and CMC, and the CMC produced and developed are used in various applications such as construction and food.
Hydroxypropyl methylcellulose has an important role in mortars, and that is water retention. Mortars with poor water retention are prone to segregation and water loss during transport. When laid on the surface of porous materials, most of the water is easily absorbed and the properties of the mortar
As the main admixture in construction dry-mix mortar products, hydroxypropyl methyl cellulose plays a key role in the performance and cost of dry-mix mortars. Currently, the majority of cellulose ether products are used in construction materials worldwide. An important property of cellulose ethers i