Cellulose Ethers and Esters

Cellulose Ethers and Esters

 

the products obtained from the replacement of the hydrogen atoms in the hydroxyl groups of the cellulose macromolecule by alkyl (cellulose ethers) or acid residues (cellulose esters). The general formula for these products is [C6H7O2(OH)3 – k(OR)k]n, where R represents such groups as —CH3, —C2H5, —C(O)CH3, or —NO2, and k is the number of substituted OH groups in one monomer unit (degree of substitution). Cellulose ethers and esters are prepared in order to impart a new set of properties to cellulose, in particular, solubility and thermoplasticity.

Cellulose ethers are prepared by O-alkylation, that is, the reaction of alkali cellulose with, mainly, alkyl halides (methyl chloride, ethyl chloride). Ethylene oxide and its derivatives and acrylonitrile are also used as alkylating agents. Cellulose esters are obtained through the esterification and acylation resulting from the reaction of cellulose with organic or inorganic acids, the anhydrides of these acids, and acid chlorides. Of the cellulose esters derived from inorganic acids, the greatest practical value has been found for cellulose xanthates, which are used in the production of viscose fibers and cellophane, and cellulose nitrates, used for the production of smokeless powder, celluloid, films, and lacquers. Of the cellulose esters derived from organic acids, cellulose acetates, which occupy first place in terms of volume of production, are used in the production of artificial fibers, films, and plastics. There are also mixed cellulose ethers and esters, which contain various alkyl and acyl substituents, for example, methylhydroxypropylcellulose and cellulose acetobutyrate.

The properties of cellulose ethers and esters depend on the degree of substitution, nature of the radical, and degree Of polymerization. The degree of substitution (k) ranges from 0.5 to 1.0 for slightly substituted cellulose ethers (methyl cellulose, ethyl cellulose, carboxylmethyl cellulose, hydroxyethylcellulose) and from 2.2 to 3.0 for highly substituted cellulose ethers and esters (ethyl cellulose, cyanoethylcellulose, cellulose acetates, cellulose nitrates). Slightly substituted ethers are soluble in water and in aqueous solutions of alkalies, which permits their use as thickening agents and stabilizers of emulsions and suspensions in the textile, paper, petroleum, pharmaceutical, and food-processing industries. Highly substituted cellulose ethers and esters dissolve in common organic solvents and are highly compatible with plasticizers; they are used in producing lacquers and plastics (etrols).

L. S. GALBRAIKH

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