Cellulose ethers

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Cellulose ether molecule section (with R = organic residue) with the degree of substitution increasing from top to bottom.
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low degree of substitution
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medium degree of substitution
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high degree of substitution

Cellulose ethers are derivatives of cellulose that are formed by partial or complete substitution of the hydrogen atoms of the hydroxyl groups in the cellulose. This reaction is known as etherification .

properties

The properties of the cellulose ethers depend on the type of substituent, the number of substituted hydroxyl groups and their distribution. Cellulose ethers are thus soluble in water and / or organic solvents, depending on the type and number of ether groups introduced. Some cellulose ethers (e.g. methyl and hydroxypropyl celluloses) show reverse solubility in water, i.e. that is, they can be flocculated from their aqueous solutions by heating. Representatives of the group of cellulose ethers are z. B.

Cellulose ethers obtained by reacting cellulose with more than one etherifying agent are called mixed cellulose ethers z. B.

Different qualities with different property profiles are produced for the individual application areas.

Manufacturing

Cellulose ethers have been produced industrially since 1925, with water-soluble products becoming established. The aim of etherification is to incorporate hydrophilic substituents into the network of hydrogen bonds. The individual cellulose ethers are offered in a wide range of types, which result from the variables degree of substitution, degree of polymerization and solution viscosity. The manufacturing processes are optimized for the different properties of the cellulose ethers, but have the following common features in the basic steps:

All etherification reactions carried out industrially on cellulose are carried out in a heterogeneous reaction, i. That is, there is no dissolution of the cellulose before or during the reaction. The cellulose is usually obtained from tree wood, whereby the lignin contained in the tree wood, initially z. B. must be separated from the cellulose structure as lignosulfonate . High quality celluloses can be obtained from cotton .

application

Wallpaper paste

The market for cellulose derivatives (cellulose ethers and cellulose esters ) is estimated at over 100,000 t in Germany. The most important manufacturers are the groups DOW, Henkel and Shin-Etsu . In terms of quantity, the most important cellulose ether is carboxymethyl cellulose, followed by methyl cellulose and hydroxyethyl cellulose. The most important areas of application for cellulose ethers are building auxiliaries for the targeted adjustment of processing properties for gypsum, plaster, mortar and tile adhesive. Since cellulose ethers are products made from renewable raw materials, they are gaining in importance for environmentally friendly processes, e.g. B. as a textile auxiliary in the textile industry. Cellulose ethers are u. a. used as

They are used in a wide variety of areas such as

supporting documents

  1. ^ Wissenschaft-Online Lexika: Entry on cellulose ethers in the Lexikon der Chemie, accessed on March 17, 2010.
  2. ↑ H.-P. Fink and S. Fischer: Cellulose processing - environmentally friendly technologies on the advance. (PDF, 2MB) Fraunhofer Institute for Applied Polymer Research. In: Practical Science - Chemistry in School , Vol. 54 (2005), No. 7, pp. 18-25.
  3. ^ FNR [specialist agency for renewable raw materials] (2006): Market analysis of renewable raw materials; Gülzow.

literature