Types of Cellulose Ethers
Release Time:
2021-11-26
Source:
Types of Cellulose Ethers
In ready-mixed mortars, the dosage of cellulose ethers is relatively low; nevertheless, they can significantly enhance the performance of wet mortar and are a key additive that influences workability. Appropriately selecting cellulose ethers of different grades, viscosities, particle sizes, degrees of viscosity, and dosages exerts a positive and substantial impact on improving the performance of dry-mix mortars. Currently, many masonry and plastering mortars exhibit poor water retention, with slurry separation occurring after only a few minutes of standing. Water retention is an important property of methyl cellulose ethers and is a critical performance parameter of concern for many domestic dry-mix mortar manufacturers, particularly those operating in southern regions with higher ambient temperatures. Factors influencing the water-retention performance of dry-mix mortars include the dosage of cellulose ether, its viscosity, particle fineness, and the temperature of the application environment.
Cellulose ethers are synthetic polymeric materials obtained by chemically modifying natural cellulose. As derivatives of natural cellulose, the production of cellulose ethers differs from that of synthetic polymers in that their primary raw material is cellulose—a naturally occurring macromolecule. Due to the unique structure of natural cellulose, cellulose itself lacks the ability to react directly with etherification agents. However, after treatment with a swelling agent, the strong hydrogen bonds both between and within the polymer chains are disrupted, thereby exposing the hydroxyl groups and converting the cellulose into alkali cellulose, which is now reactive. Subsequent reaction with an etherification agent then converts the hydroxyl groups (–OH) into alkoxy groups (–OR), yielding the final cellulose ether product.
The properties of cellulose ethers depend on the type, number, and distribution of substituent groups. Accordingly, cellulose ethers are classified based on the nature of the substituents, the degree of etherification, their solubility characteristics, and their performance in specific applications. According to the type of substituent groups along the polymer chain, they can be divided into monoethers and mixed ethers; the cellulose commonly used is typically a monoether, whereas HP cellulose is a mixed ether. Methyl cellulose ether is produced when the hydroxyl groups on the glucose units of natural cellulose are partially replaced by methoxy groups, with the structural formula [COH7O2(OH)3–h(OCH3)h]x. Hydroxypropyl methyl cellulose ether (HP cellulose) is obtained by replacing part of the hydroxyl groups with methoxy groups and another part with hydroxypropyl groups, resulting in the structural formula [C6H7O2(OH)3–m–n(OCH3)m[OCH2CH(OH)CH3]n]x. There is also hydroxyethyl methyl cellulose ether (HE cellulose). These three types are currently the main varieties widely used and marketed.
Based on their solubility characteristics, cellulose ethers can be further classified into ionic and nonionic types. Water-soluble nonionic cellulose ethers mainly comprise two major series: alkyl ethers and hydroxyalkyl ethers. Ionic cellulose ethers are primarily used in synthetic detergents, textile printing and dyeing, food processing, and oil extraction. In contrast, nonionic cellulose ethers such as HP cellulose and HE cellulose are mainly employed in building materials, latex coatings, pharmaceuticals, and daily chemical products, where they serve as thickeners, water-retaining agents, stabilizers, dispersants, and film-forming agents.
