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288 Carraher’s Polymer Chemistry

9.5 ESTERS AND ETHERS OF CELLULOSE

It must be remembered that the three hydroxyl groups on the individual cellulose rings are not
equivalent. The two ring hydroxyls are acidic with pKas similar to hydroquinone while the third
nonring hydroxyl is similar to an aliphatic hydroxyl in acidity. Thus, in an aqueous sodium hydrox-
ide solution the two ring hydroxyls will be deprotonated at high pHs. In theory, all three hydroxyls
can undergo reaction, but in actuality less than three undergo reaction either because of reactivity
restrictions and/or because of steric limitations. With many of the electrophilic/nucleophilic reac-
tions it is the ring hydroxyls that are favored to react initially. The average number of hydroxyl
groups that are reacted are often given as the degree of substitution or DS.

9.5.1 INORGANIC ESTERS
The most widely used so-called inorganic ester of cellulose is cellulose nitrate (CN), also called
nitrocellulose and gun cotton. Celluloid is produced from a mixture of cellulose nitrate and cam-
phor. Cellulose nitrate was first made in about 1833 when cellulose-containing linen, paper, or

sawdust was reacted with concentrated nitric acid. It was the first “synthetic” cellulose recognized

product. Initially, CN was used as a military explosive and improvements allowed the manufacture
of smokeless powder. A representation of CN is given below:

O – O O – O – O –
O O O
N + N + N + N +

O O O O
H O O H O O H O O O O
H H H
O H O H O H H O H H
R H H H H R (9.7)
+ + N +
N H O N + H O N H O H O
O – O O – O O – O O –
O +
N + N + N + N –
O O – O O – O O – O O
Cellulose nitrate

The development of solvents and plasticizing agents for cellulose nitrate led to the production of
many new and useful nonexplosive products. Celluloid was produced in 1870 from a mixture of CN
and camphor. Films were cast from solution and served as the basis for the original still and motion
pictures. After World War I, the development of stable CN solutions allowed the production of fast-
drying lacquer coatings.
While CN played an important role in the development of technology, its importance today is
greatly diminished. It is still used as a protective and decorative lacquer coating, in gravure inks, in
water-based emulsions as coatings, and to a lesser extent in plastics and fi lms.
Cellulose phosphate esters are produced from reaction with phosphoric acid and urea. The prod-
ucts are used to treat hypercalciuria because of its ability to bind calcium. It has also been used for
the treatment of kidney stones.

9.5.2 ORGANIC ESTERS
The most important cellulose ester is cellulose acetate because of its use in fibers and plastics. They

were first made in 1865 by heating cotton with acetic anhydride. During World War I, a cellulose
acetate replaced the highly flammable CN coating on airplane wings and fuselage fabrics.

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