Miscellaneous ethers

Only one other cellulose ether has been marketed for moulding and extrusion applications, benzyl cellulose. This material provides a rare example of a polymer which although available in the past is no longer commercially marketed. The material had a low softening point and was unstable to both heat and light and has thus been unable to compete with the many alternative materials now available. 

A number of water-soluble cellulose ethers are marketed. Methyl cellulose is prepared by a method similar to that used for ethyl cellulose. A degree of substitution of 1.6-1.8 is usual since the resultant ether is soluble in cold water but not in hot. It is used as a thickening agent and emulsifier in cosmetics, as a paper size, in pharmaceuticals, in ceramics and in leather tanning operations. 

Hydroxyethyl cellulose, produced by reacting alkali cellulose with ethylene oxide, is employed for similar purposes. 

Hydroxypropyl cellulose, like methyl cellulose, is soluble in cold water but not in hot, precipitating above 38°C. It was introduced by Hercules in 1968 (Klucel) for such uses as adhesive thickeners, binders, cosmetics and as protective colloids for suspension polymerisation. The Dow company market the related hydroxypropylmethyl cellulose (Methocel) and also produce in small quantities a hydroxyethylmethyl cellulose. 

Schematic equations for the production of fully substituted varieties of the above three ethers are given below (R represents the eellulose skeleton). 

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