The cellulose ether is a polymer compound having an ether structure made of cellulose.
Each glucosyl group in the cellulose macromolecule contains three hydroxyl groups, a primary hydroxyl group on the sixth carbon atom, a secondary hydroxyl group on the second and third carbon atoms, and a hydrogen in the hydroxyl group is substituted by a hydrocarbon group to form a cellulose ether derivative. Object.
According to the chemical structure classification of the substituents, they can be classified into anionic, cationic and nonionic ethers.
Depending on the etherifying agent used, there are methyl cellulose, carboxymethyl cellulose, ethyl cellulose, benzyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, cyanoethyl cellulose, Benzyl cyanoethyl cellulose, carboxymethyl hydroxyethyl cellulose, phenyl cellulose, and the like. Methylcellulose and ethylcellulose are more practical.
The solubility of cellulose after etherification changes significantly, and it can be dissolved in water, dilute acid, dilute alkali or organic solvent. The solubility depends mainly on three factors: (1) the characteristics of the groups introduced during the etherification process, introduced The larger the group, the lower the solubility, the stronger the polarity of the introduced group, the more soluble the cellulose ether is in water, and (2) the degree of substitution and the distribution of the etherified group in the macromolecule. Most cellulose ethers can only be dissolved in water under a certain degree of substitution, and the degree of substitution is between 0 and 3. (3) The degree of polymerization of cellulose ether, the higher the degree of polymerization, the more difficult to dissolve; the higher the degree of polymerization Low, the wider the range of substitutions that are soluble in water. Cellulose ethers are widely used in construction, cement, petroleum, food, textile, detergent, paint, pharmaceutical, paper and electronic components industries.
It is a product in which a hydrogen of a hydroxyl group in a cellulose polymer is substituted with a hydrocarbon group. Cellulose is a polyhydroxy polymer compound which neither dissolves nor melts. The cellulose is soluble in water, a dilute alkali solution and an organic solvent after etherification, and has thermoplasticity.
The high α-cellulose pulp is immersed in an alkali solution to swell to destroy a large number of hydrogen bonds, to facilitate diffusion of the reagent and to form alkali cellulose, and then reacted with an etherifying agent to prepare a cellulose ether. The etherifying agent is a hydrocarbon group halide (or sulfate), an epoxide, and an α, β unsaturated compound having an electron acceptor.
Cellulose alkyl ethers are typically methylcellulose and ethylcellulose. Industrial production generally uses methyl chloride or ethyl chloride as an etherifying agent. The alkali concentration not only affects the degree of etherification, but also affects the consumption of alkyl halides. The lower the alkali concentration, the more the alkyl halide is hydrolyzed. In order to reduce the consumption of the etherifying agent, it is necessary to increase the alkali concentration. However, when the alkali concentration is too high, the swelling effect of cellulose is lowered, which is disadvantageous for the etherification reaction, and the degree of etherification is lowered. For this purpose, a concentrated lye or a solid base can be added during the reaction. The reactor should have a good agitation and tearing device to distribute the alkali evenly.
Methylcellulose is widely used as a thickener, an adhesive, a protective colloid, and the like. It can also be used as a dispersing agent for emulsion polymerization, a binder dispersant for seeds, a textile slurry, an additive for foods and cosmetics, a pharmaceutical adhesive, a drug coating material, and used in latex paints, printing inks, ceramics production, and in cement. Used to control the setting time and increase the initial strength.
Ethyl cellulose products have high mechanical strength, flexibility, heat resistance and cold resistance. Low-substituted ethyl cellulose is soluble in water and dilute alkali solutions, and highly substituted products are soluble in most organic solvents. It has good compatibility with various resins and plasticizers. It can be used to make coating materials for plastics, films, varnishes, adhesives, latexes and pharmaceuticals.
The introduction of a hydroxyalkyl group into a cellulose alkyl ether improves its solubility, reduces its sensitivity to salting out, increases gelation temperature, and improves hot meltability and the like. The degree of change in the above properties varies depending on the nature of the substituent and the ratio of the alkyl group to the hydroxyalkyl group.
Cellulose hydroxyalkyl ethers are typically hydroxyethyl cellulose and hydroxypropyl cellulose. The etherifying agent is an epoxide such as ethylene oxide and propylene oxide. Use an acid or a base as a catalyst. Industrial production is the reaction of alkali cellulose with an etherifying agent:
Highly substituted hydroxyethyl cellulose is soluble in both cold and hot water. Highly substituted hydroxypropyl cellulose is only soluble in cold water and insoluble in hot water. Hydroxyethyl cellulose can be used as a thickener for latex coatings, textile printing pastes, papermaking compounds, adhesives and protective colloids. The use of hydroxypropyl cellulose is similar to that of hydroxyethyl cellulose, and low-substituted hydroxypropyl cellulose can be used as a pharmaceutical excipient, which can have both adhesive and disintegration properties.
Carboxymethylcellulose The English abbreviation CMC is generally present in the form of a sodium salt, and the etherifying agent is monochloroacetic acid.
Carboxymethylcellulose is one of the most widely used water-soluble cellulose ethers. Used primarily as drilling mud, it has now expanded to include detergent additives, laundry syrups, latex paints, paperboard and paper coatings. Pure carboxymethyl cellulose can be used in food, medicine, cosmetics, and as an adhesive for ceramics and molds.
Cyanoethyl cellulose is a product of the reaction of cellulose with acrylonitrile under the catalysis of a base.
Cyanoethyl cellulose has a high dielectric constant and a low loss factor, and can be used as a resin matrix for phosphorus 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 practically applied.
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