Carboxymethyl cellulose：
Ionic cellulose ether is made from natural fibers (cotton, etc.) after alkali treatment, using sodium monochloroacetate as etherification agent, and undergoing a series of reaction treatments. 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, and it will contain more water when stored under general conditions.
(2) Carboxymethyl cellulose aqueous solution does not produce gel, and the viscosity decreases with the increase of temperature. When the temperature exceeds 50°C, the viscosity is irreversible.
(3) Its stability is greatly affected by PH. Generally, it can be used in gypsum-based mortar, but not in cement-based mortar. When highly alkaline, it will lose viscosity.
(4) Its water retention is much lower than that of methyl cellulose. It has a retarding effect on gypsum-based mortar and reduces its strength. However, the price of carboxymethyl cellulose is significantly lower than that of methyl cellulose.
Cellulose alkyl ether：
Representative ones are methyl cellulose and ethyl cellulose. In industrial production, methyl chloride or ethyl chloride is generally used as etherification agent, and the reaction is as follows:
In the formula, R represents CH3 or C2H5. Alkali concentration not only affects the degree of etherification, but also affects the consumption of alkyl halides. The lower the alkali concentration, the stronger the hydrolysis of the alkyl halide. In order to reduce the consumption of etherifying agent, the alkali concentration must be increased. However, when the alkali concentration is too high, the swelling effect of cellulose is reduced, which is not conducive to the etherification reaction, and the degree of etherification is therefore reduced. For this purpose, concentrated lye or solid lye can be added during the reaction. The reactor should have a good stirring and tearing device so that the alkali can be evenly distributed.
Methyl cellulose is widely used as thickener, adhesive and protective colloid etc. It can also be used as a dispersant for emulsion polymerization, a bonding dispersant for seeds, a textile slurry, an additive for food and cosmetics, a medical adhesive, a drug coating material, and for latex paint, printing ink, ceramic production, and mixed into cement Used to control the setting time and increase the initial strength, etc.
Ethyl cellulose products have high mechanical strength, flexibility, heat resistance and cold resistance. Low-substituted ethyl cellulose is soluble in water and dilute alkaline solutions, and high-substituted products are soluble in most organic solvents. It has good compatibility with various resins and plasticizers. It can be used to make plastics, films, varnishes, adhesives, latex and coating materials for drugs, etc.
The introduction of hydroxyalkyl groups into cellulose alkyl ethers can improve its solubility, reduce its sensitivity to salting out, increase the gelation temperature and improve hot melt properties, etc. The degree of change in the above properties varies with the nature of the substituents and the ratio of alkyl to hydroxyalkyl groups.
Cellulose hydroxyalkyl ether：
Representative ones are hydroxyethyl cellulose and hydroxypropyl cellulose. Etherifying agents are epoxides such as ethylene oxide and propylene oxide. Use acid or base as catalyst. Industrial production is to react alkali cellulose with etherification agent: hydroxyethyl cellulose with high substitution value is soluble in both cold water and hot water. Hydroxypropyl cellulose with high substitution value is only soluble in cold water but not in hot water. Hydroxyethyl cellulose can be used as a thickener for latex coatings, textile printing and dyeing pastes, paper sizing materials, adhesives and protective colloids. The use of hydroxypropyl cellulose is similar to that of hydroxyethyl cellulose. Hydroxypropyl cellulose with low substitution value can be used as a pharmaceutical excipient, which can have both binding and disintegrating properties.
Carboxymethylcellulose, abbreviated as CMC, generally exists in the form of sodium salt. The etherifying agent is monochloroacetic acid, and the reaction is as follows:
Carboxymethyl cellulose is the most widely used water-soluble cellulose ether. In the past, it was mainly used as drilling mud, but now it has been extended to be used as an additive of detergent, clothing slurry, latex paint, coating of cardboard and paper, etc. Pure carboxymethyl cellulose can be used in food, medicine, cosmetics, and also as an adhesive for ceramics and molds.
Polyanionic cellulose (PAC) is an ionic cellulose ether and is a high-end substitute product for carboxymethyl cellulose (CMC). It is a white, off-white or slightly yellow powder or granule, non-toxic, tasteless, easily soluble in water, forming a transparent solution with a certain viscosity, has better heat resistance stability and salt resistance, and strong antibacterial properties. No mildew and deterioration. It has the characteristics of high purity, high degree of substitution, and uniform distribution of substituents. It can be used as binder, thickener, rheology modifier, fluid loss reducer, suspension stabilizer, etc. Polyanionic cellulose (PAC) is widely used in all industries where CMC can be applied, which can greatly reduce the dosage, facilitate use, provide better stability and meet higher process requirements.
Cyanoethyl cellulose is the reaction product of cellulose and acrylonitrile under the catalysis of alkali:
Cyanoethyl cellulose has a high dielectric constant and low loss coefficient and can be used as a resin matrix for phosphor and electroluminescent lamps. Low-substituted cyanoethyl cellulose can be used as insulating paper for transformers.
Higher fatty alcohol ethers, alkenyl ethers, and aromatic alcohol ethers of cellulose have been prepared, but have not been used in practice.
The preparation methods of cellulose ether can be divided into water medium method, solvent method, kneading method, slurry method, gas-solid method, liquid phase method and the combination of the above methods.
Post time: Feb-20-2023