Article No : a05_419

Cellulose Esters
KLAUS BALSER, Wolff Walsrode AG, Walsrode, Federal Republic of Germany
LUTZ HOPPE, Wolff Walsrode AG, Walsrode, Federal Republic of Germany
THEO EICHER, Stuttgart, Federal Republic of Germany
MARTIN WANDEL, Bayer AG, Leverkusen, Federal Republic of Germany
HANS-JOACHIM ASTHEIMER, Rhodia AG, Freiburg, Federal Republic of Germany
HANS STEINMEIER, Rhodia Acetow AG, Freiburg, Federal Republic of Germany
JOHN M. ALLEN, Eastman Chemical Company, Kingsport, TN 37662, USA

1. Inorganic Cellulose Esters . . . . . . . . . . . 333 2.1.3.3. Hydrolysis. . . . . . . . . . . . . . . . . . . . . . . . 358

1.2. Esterification . . . . . . . . . . . . . . . . . . . . . 335 2.1.3.4. Precipitation and Processing. . . . . . . . . . . 359
1.3. Cellulose Nitrate . . . . . . . . . . . . . . . . . . 336 2.1.4. Recovery of Reactants . . . . . . . . . . . . . . . 360
1.3.1. Physical Properties . . . . . . . . . . . . . . . . . 336 2.1.5. Properties . . . . . . . . . . . . . . . . . . . . . . . . 360
1.3.2. Chemical Properties. . . . . . . . . . . . . . . . . 337 2.1.6. Analysis and Quality Control . . . . . . . . . . 361
1.3.3. Raw Materials . . . . . . . . . . . . . . . . . . . . . 339 2.1.7. Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362
1.3.4. Production. . . . . . . . . . . . . . . . . . . . . . . . 340 2.2. Cellulose Mixed Esters. . . . . . . . . . . . . . 362
1.3.4.1. Cellulose Preparation. . . . . . . . . . . . . . . . 341 2.2.1. Production. . . . . . . . . . . . . . . . . . . . . . . . 363
1.3.4.2. Nitration . . . . . . . . . . . . . . . . . . . . . . . . . 342 2.2.2. Composition . . . . . . . . . . . . . . . . . . . . . . 363
1.3.4.3. Stabilization and Viscosity Adjustment . . . . 343 2.2.3. Properties . . . . . . . . . . . . . . . . . . . . . . . . 363
1.3.4.4. Displacement and Gelatinization . . . . . . . 344 2.2.4. Other Organic Mixed Esters. . . . . . . . . . . 364
1.3.4.5. Acid Disposal and Environmental Problems 344 2.2.5. Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364
1.3.4.6. Other Nitrating Systems. . . . . . . . . . . . . . 344 2.3. Cellulose Acetate Fibers. . . . . . . . . . . . . 365
1.3.5. Commercial Types and Grades. . . . . . . . . 346 2.3.1. Properties . . . . . . . . . . . . . . . . . . . . . . . . 365
1.3.6. Analysis and Quality Control . . . . . . . . . . 346 2.3.2. Raw Materials . . . . . . . . . . . . . . . . . . . . . 366
1.3.7. Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348 2.3.3. Production. . . . . . . . . . . . . . . . . . . . . . . . 366
1.3.8. Legal Provisions . . . . . . . . . . . . . . . . . . . 350 2.3.4. Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
1.4. Other Inorganic Cellulose Esters . . . . . . 350 2.3.5. Economic Aspects . . . . . . . . . . . . . . . . . . 367
1.4.1. Cellulose Sulfates . . . . . . . . . . . . . . . . . . 350 2.4. Cellulose Ester Molding Compounds . . . 367
1.4.2. Cellulose Phosphate and Cellulose Phosphite 351 2.4.1. Physical Properties of Cellulose Ester
1.4.3. Cellulose Halogenides . . . . . . . . . . . . . . . 352 Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . 368
1.4.4. Cellulose Borates. . . . . . . . . . . . . . . . . . . 352 2.4.2. Polymer Modified Cellulose Mixed Esters 370
1.4.5. Cellulose Titanate . . . . . . . . . . . . . . . . . . 352 2.4.3. Chemical Properties. . . . . . . . . . . . . . . . . 371
1.4.6. Cellulose Nitrite . . . . . . . . . . . . . . . . . . . 352 2.4.4. Raw Materials . . . . . . . . . . . . . . . . . . . . . 371
1.4.7. Cellulose Xanthate . . . . . . . . . . . . . . . . . 353 2.4.5. Production. . . . . . . . . . . . . . . . . . . . . . . . 373
2. Organic Esters . . . . . . . . . . . . . . . . . . . . 353 2.4.6. Trade Names. . . . . . . . . . . . . . . . . . . . . . 374
2.1. Cellulose Acetate . . . . . . . . . . . . . . . . . . 354 2.4.7. Quality Requirements and Quality Testing 374
2.1.1. Chemistry . . . . . . . . . . . . . . . . . . . . . . . . 354 2.4.8. Storage and Transportation . . . . . . . . . . . 374
2.1.2. Raw Materials . . . . . . . . . . . . . . . . . . . . . 355 2.4.9. Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . 374
2.1.3. Industrial Processes . . . . . . . . . . . . . . . . . 355 2.4.10. Toxicology and Occupational Health . . . . 376
2.1.3.1. Pretreatment . . . . . . . . . . . . . . . . . . . . . . 356 References . . . . . . . . . . . . . . . . . . . . . . . 376
2.1.3.2. Esterification . . . . . . . . . . . . . . . . . . . . . . 357

1. Inorganic Cellulose Esters lent polymeric alcohol. Esterification can be

carried out by using mineral acids as well as
Definition. Cellulose esters are cellulose de- organic acids or their anhydrides with the aid of
rivatives which result by the esterification of the dehydrating substances. Cellulose nitrate [9004-
free hydroxyl groups of the cellulose with one or 70-0] is the most important and only industrially
more acids, whereby cellulose reacts as a triva- produced inorganic cellulose ester (abbreviation

2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI: 10.1002/14356007.a05_419.pub2
334 Cellulose Esters Vol. 7

CN, according to DIN 7728, T 1, 1978). A The discovery that fibrous products could be
comprehensive bibliography on inorganic cellu- modified by, for example, dissolution in an
lose esters may be found in [12–19]. alcohol/ether mixture (film for wound protec-
Historical Aspects [20]. The nitric acid ester tion) or by gelatinization with softeners brought
of cellulose is the oldest known cellulose deriva- additional uses. Films made from camphor and
tive and is still the most important inorganic castor oil were used in collodium photography
cellulose ester. The term ‘‘nitrocellulose’’ is still as carriers for light-sensitive materials (ARCHER,
used, but it is not the precise scientific term for 1851). Nitrofilms found increasing use in pho-
cellulose nitrate. Cellulose esters were first de- tography and cinematography until they were
scribed and industrially used at a time when the replaced by nonflammable cellulose acetate
structure of esters was unknown and information films.
on the polymeric primary material cellulose was The year 1869 is considered to be the begin-
not yet available. ning of the age of plastics. J. W. HYATT discov-
The nitration of polysaccharides with concen- ered celluloid, the first thermoplastic synthetic
trated nitric acid had already been described in material. It was originally used as a substitute for
1832. H. BRACONNOT obtained a white and easily ivory in the production of billiard balls.
inflammable powder when he transformed starch The practical use of cellulose nitrate as a raw
with nitric acid. The product obtained was material for lacquers began in 1882, when STEVENS
xyloidine. TH.-J. PELOUZE treated paper with nitric suggested amyl acetate as a highly volatile solvent
acid and obtained an insoluble product containing (Zaponlack). The nitro lacquers achieved impor-
ca. 6 % nitrogen which he called pyroxiline and tance at first after World War I (FLAHERTY, 1921),
which he provided for military use. when new applications were being sought as a
C. F. SCHÖNBEIN and R. BÖTTGER are consid- result of the sharply declining demand for gun-
ered to be the inventors of so-called gun cotton powder. Only after the possibility of depolymeri-
(1845). They transformed cotton with a mixture zation of cellulose nitrate by pressure boiling
of nitric and sulfuric acid into a highly nitrated during production had become known during the
product that could serve as a substitute for black 1930s it was possible to use cellulose nitrate in
powder. Production on an industrial scale was protective and pigmented lacquers. Thus, it be-
stopped in 1847 because its extremely rapid came possible to use nitro lacquers for painting
catalytic decomposition was the cause of numer- automobiles on the assembly line.
ous plant explosions. Production was legally Cellulose xanthate [9032-37-5] is a cellulose
prohibited in 1865. ester obtained with the inorganic acid dithiocar-
The use of cellulose nitrate as an explosive bonic acid. CH. F. CROSS discovered this impor-
brought new momentum to its further industrial tant alkali-soluble cellulose ester in 1891 while
and scientific development, as well as to its he was reacting cellulose with alkali and carbon
economic significance. F. ABEL made a basic disulfide. It represents the base of the viscose
breakthrough in 1865 when he succeeded in process introduced in 1894 by BEVAN and BEADLE
developing a safe method of handling. He was for producing man-made cellulosic fibers (rayon,
able to achieve a better washing of the adhering rayon staple) and cellophane.
nitrating acid and a hydrolytic decomposition of Other cellulose esters with inorganic acids are
the unstable sulfuric acid ester by grinding the presently only of theoretical interest and have not
nitrated fibers in water. This process allowed this attained any industrial or economic importance.
product to attain military importance for its use as
gunpowder. Present Significance. Cellulose nitrate is
In 1875, A. NOBEL phlegmatized nitroglycer- still important, 150 years after its discovery. It
ine by mixing with cellulose nitrate and discov- is industrially produced in large quantities for
ered blasting gelatin. In the 1880s, smokeless diversified applications. The reasons for this are
gunpowders were developed. VIEILLE developed the relatively simple production process with
Poudre B (blanche) and NOBEL developed Bal- high yields, its solubility in organic solvent sys-
listit, the first dibasic gunpowder from cellulose tems and its excellent film-forming properties
nitrate and nitrogycerol. ABEL and DEWAR devel- from such solutions (collodion cotton as a
oped a similar gunpowder called Cordit. raw material for lacquers), compatibility and
Vol. 7 Cellulose Esters 335

gelatinability with softeners and other polymers Course of Reaction. The three functional
(thermoplastics), as well as inflammability (gun hydroxyl groups on each anhydroglucose unit of
cotton for explosives). Cellulose nitrate has cellulose are blocked by intermolecular and
maintained its importance as a raw material for intramolecular hydrogen bonds and, therefore,
the manufacture of protective and coating lac- are not freely accessible for the reaction partners.
quers as well as blasting agents and explosives. The supermolecular arrangement and micro-
Densified products, colored or pigmented structure within the cellulose fiber, whose inten-
chips kneaded with softeners, as well as aqueous sity depends on the origin and previous history of
dispersion systems with a low solvent content, the cellulose material, is determined by these
are available today. They facilitate transport and hydrogen bonds. The accessibility to the reaction
processing, secure existing application forms, partners and the reactivity of the alcohol groups
open up new ones, and are becoming increasingly also depend on this structure.
nonpolluting. Due to the fact that cellulose is insoluble in all
The viscose process (see ! Cellulose) with its common solvents, reactions to form derivatives
essential intermediate cellulose xanthate will are usually carried out in heterogeneous systems.
remain, because of the availability of a constantly As the reaction proceeds, new reactive centers
regrowing raw material supply, an important are created so that ultimately almost all parts of
source of textile fibers for years to come. Alter- the cellulose fibers are included and in special
native processes are intensively being sought to cases yield soluble derivatives which react to
reduce pollution by sulfurous decomposition completion in a homogeneous phase.
gases resulting during manufacturing. Cellulose Little information is available on the esterifi-
nitrite, the cellulose ester of nitrous acid, is the cation process. The following two reaction types
most prominent example. are under discussion:
Cellulose esters with other inorganic acids
have been frequently described and investigat- . An intermicellar reaction, which initially con-
ed. Cellulose sulfate [9032-43-3] was of some sists of the penetration of the reaction partner
interest because of its solubility in water, but into the so-called amorphous regions between
never achieved any practical importance. Cel- the highly organized cellulose micelles and
lulose phosphate [9015-14-9], borate, and tita- proceeds during the course of esterification
nate show interesting properties such as fire from the surface to the innermost regions of
retardation, but are not yet of any industrial the micelles. The reaction speed is determined
significance. by diffusion.
. An intramicellar or permutoid reaction, in
which the reagent penetrates all regions includ-
1.2. Esterification ing the micelles so that practically all cellulose
molecules react almost simultaneously. The
Mechanism. The alcoholic hydroxyl groups reaction speed is specified by adjustment of
of cellulose are polar and can be substituted by the esterification equilibrium.
nucleophilic groups in strongly acid solutions.
The mechanism of esterification assumes the Arguments for both mechanisms are based on
formation of a cellulose oxonium ion followed X-ray analyses. The possibility exists that both
by the nucleophilic substitution of an acid residue reaction types occur and ultimately merge. This
and the splitting off of water. Esterification is in depends on the reaction conditions, especially
equilibrium with the reverse reaction; saponifi- the esterification mixture and the temperature.
cation can be inhibited largely by binding the The hydrogen bonds between the cellulose
resulting water. molecules are almost completely broken down
during esterification. The introduction of ester
groups separates the cellulose chains so
completely that the fiber structure is either altered
or completely destroyed. Whether the cellulose
ester is soluble in a solvent or in water depends on
the types of substituents added.
336 Cellulose Esters Vol. 7

Substitution. The esterification reactions Table 2. Thermodynamic properties of some cellulose nitrates
do not necessarily proceed stoichiometrically Heat of formation trinitrate  2.19 kJ/g
because of equilibrium adjustment. The maximal dinitrate  2.99 kJ/g
attainable substitution with a mean degree of cellulose  5.95 kJ/g
substitution (DS) of 3 is generally not reached.
Heat of combustion trinitrate  9.13 kJ/g
A triester can only be obtained under carefully dinitrate  10.91 kJ/g
controlled conditions. The primary hydroxyl cellulose  17.43 kJ/g
group on the C-6 atom reacts most readily, while
the neighboring hydroxyl groups on the C-2 and Specific heat celluloid film 1.26 – 1.76 J g1 K1
(70 % CN and
C-3 atoms of the anhydroglucose ring react 30 % camphor)
considerably slower due to steric hindrance.
Basically, esterification is possible with all Thermal conductivity celluloid film 0.84 kJ m1 h1 K1
inorganic acids. Limiting factors are the type and (70 % CN and
30 % camphor)
the size of the acid residue as well as the varying
degree of acid-catalyzed hydrolysis, which can Heat of solution CN with 11.5 %  73.25 J/g
lead to a complete cleavage of the cellulose in acetone N content
molecule as the result of statistical chain splitting. CN with 14.0 %  81.64 J/g
N content

1.3. Cellulose Nitrate Specific Surface The laboratory apparatus

described by S. ROSSIN [23] is best suited for the
Summary monographs on cellulose nitrate in determination of the specific surface of cellulose
addition to those in the Reference list can be nitrate, which is 1 850 – 4 700 cm2/g, depending
found in [21] and [22]. on the fineness of the cellulose nitrate.
The determination of the inner surface accord-
ing to the BET method showed dependence
1.3.1. Physical Properties on the molar mass (i.e., an inner surface area of
1.44 m2/g would correspond to a molar mass of
Cellulose nitrate (CN) is a white, odorless, and 180 000 g and a surface area of 2.41 m2/g would
tasteless substance. Its characteristics are depen- correspond to a molar mass of 400 000 g).
dent on the degree of substitution. It must, however, be noted that the degassing
temperature was lowered from the usual 200
C
Density The density of cellulose nitrate is to 60
C due to the fact that cellulose nitrate
dependent on its nitrogen content and, therefore, deflagrates at 180
C. It is possible that complete
on the degree of substitution (Table 1). desorption did not take place under these
The bulk density of commercially available conditions.
CN types is between 0.25 and 0.60 kg/L for
moistened CN cotton, 0.15 – 0.40 kg/L when Thermodynamic Properties see [24, pp.
converted to dry mass. 137 – 154]. The most important thermodynamic
Cellulose nitrate chips, which contain at least properties are listed in Table 2.
18 % dibutyl phthalate in addition to cellulose
nitrate, have a density of 1.45 g/cm3 (measured at Electrical Properties [24, p. 136]. The follow-
20
C in an air-comparison pycnometer). The ing electrical properties were measured on cellulose
bulk density is 0.3 – 0.65 kg/L. nitrate containing 30 wt % camphor (celluloid):
Table 1. The density of cellulose nitrate in relation to its nitrogen
content (degree of substitution) Dielectric constant
at 50 – 60 Hz 7.0 – 7.5
Degree of Density at 106 Hz 6.0 – 6.5
Nitrogen content, % substitution (DS) 20
C, g/cm3 Dissipation factor (tan d)
at 50 – 60 Hz 0.09 – 0.12
11.5 2.1 1.54
106 Hz 0.06 – 0.09
12.6 2.45 1.65
Specific resistance 1011 – 1012 W  cm
13.3 2.7 1.71
Vol. 7 Cellulose Esters 337

Table 3. Mechanical properties of CN lacquer films acid. The varying degrees of nitration can be
Elongation, Tensile strength,
related to the following theoretical nitrogen
Typea % N/mm2 contents:
Cellulose mononitrate, C6H7O2(OH)2(ONO2)
E 4 24 – 30 98 – 103
E 6 23 – 28 98 – 103
6.75 % N
E 9 23 – 28 88 – 98 Cellulose dinitrate, C6H7O2(OH)(ONO2)2
E 13 20 – 25 88 – 98 11.11 % N
E 15 18 – 23 78 – 98 Cellulose trinitrate, C6H7O2(ONO2)3 14.14 % N
E 21 12 – 18 78 – 88
E 22 10 – 15 74 – 84
E 24 8 – 12 69 – 78 Cellulose nitrate with a nitrogen content between
E 27 5 – 10 59 – 69 10.8 and 12.6 % is a suitable raw material for
E 32 <5 39 – 49 lacquers, and CN with > 12.3 % N is suitable for
E 34 <3 29 – 49
a
explosives exclusively.
According to DIN 53179: The E-type designation specifies the
CN concentration (% in dry condition) in acetone which gives a
viscosity of 400  25 mPa  s.
Degree of Substitution – Nitrogen Content –
Solubility The degree of substitution can be
calculated from the nitrogen content of the vari-
Mechanical Properties [25]. The stress – ous CN types (Fig. 1). The degree of substitution
strain diagram of cellulose nitrate films shows determines the solubility of cellulose nitrate in
the elongation and tensile strength to be depen- organic solvents. CN for lacquers can be classi-
dent on the size of the molecule (expressed as a fied according to its solubility in organic solvents
term of viscosity). as follows:
The higher the molecular mass of a CN, the
more elastic is the film made from it. Films alcohol-soluble CN (A types)
become more brittle and their tensile strength nitrogen content: approx. 10.9 – 11.3 %
declines with decreasing molecular mass (see readily soluble in alcohols, esters, and ketones
Table 3).
moderately soluble CN (AM types)
Optical Properties Cellulose nitrate films nitrogen content: approx. 11.4 – 11.7 %
are optically anisotropic because of their micro- soluble in esters, ketones, and glycol ethers
crystalline structure. The colors change in polar- with excellent blendability or compatibili-
ized light in relation to the nitrogen content of the ty with alcohol
CN: CN soluble in esters (E types)
11.4 % N weakly red nitrogen content: 11.8 – 12.2 % for lacquer
11.5 – 11.8 % N yellow cotton, up to 13.7 % for guncotton
12.0 – 12. 6 % N blue to green
The index of refraction is 1.51, and the maxi-
mal light transmission is achieved at 313 nm.

Light Stability Exposure to sunlight, and

especially to ultraviolet light, has a detrimental
effect on cellulose nitrate film by causing it to
become yellowish and brittle. Solvents, soft-
eners, and resins can either promote or hinder
yellowing.

1.3.2. Chemical Properties

The three hydroxyl groups of cellulose can be Figure 1. Variation of the degree of substitution with the
completely or partially esterified by nitrating nitrogen content of cellulose nitrate
338 Cellulose Esters Vol. 7

readily soluble in esters, ketones, and glycol catalysis, are responsible for its physicochemi-
ethers cal instability. This substance-specific property
is dependent on the temperature, the specimen,
Intrinsic Viscosity – Degree of Polymeriza- and whether catalytically active decomposition
tion [24, pp. 85 – 121] The mean number of products remain or are removed from the
anhydroglucose units in cellulose nitrate mole- sample.
cules is designated as the mean degree of poly- Another basic instability of cellulose nitrate is
merization (DP). The viscosity of the solution (at observed during the production process. Mixed
the same concentration in the same solvent) is sulfuric acid esters transmit a chemical instabili-
generally considered to be a relative measure of ty to the nitrocellulose molecule. These mixed
the molecular mass. The molecular mass can be esters are destroyed in weakly acid water during
mathematically expressed as a function of the the stabilization phase of production. The long
intrinsic viscosity (Staudinger – Mark – Hou- reaction time required by this procedure can be
wink equation). For further information ! Plas- considerably shortened by increasing the reac-
tics, Analysis. tion temperature. The time required can be
reduced to only a few hours by raising the
Distribution of the Molecular Mass The temperature to 60 – 110
C. Under these condi-
starting material of cellulose nitrate is natural tions the nitrate ester remains stable; the gluco-
cellulose, the quality of which is subjected to sidic bond of cellulose nitrate, on the other hand,
annual growth cycles. It is, therefore, of great is attacked. This property is used to advantage to
importance to have polymolecular data, such specifically reduce the degree of polymerization
as the mean degree of polymerization and the of the cellulose nitrate.
distribution of the molecular mass, available in Thermogravimetry, IR spectroscopy, and
addition to viscosity, solubility behavior, and electron spectroscopy (ESCA) [26], [27] have
nitrogen values. These values are important, been used to determine the extent of thermally
for example, in assessing the mechanical induced and light-induced decomposition of cel-
properties and aging processes of polymer lulose nitrate. The reaction proceeds as follows:
products.
CellONO2 !CellOþNO2
The isolation of the polymers according to
their molecular mass can be achieved elegantly It is proceeded by a series of extremely exo-
by gel permeation chromatography (GPC). thermic oxidation reactions triggered by the NO2
radical, which often leads to spontaneous def-
Chemical Compatibility An everyday use of lagration. NO2 is reduced to NO and in the
cellulose nitrate is in nitro lacquers, where it is presence of air NO2 is reformed, thus initiating
dissolved in organic solvents. In this solution, an autocatalytic chain reaction, at the end of
cellulose nitrate is extremely compatible with which the gaseous reaction products COx, NOx,
essential substances in the lacquer formulation N2, H2O, and HCHO are found.
such as alkyd resins, maleic resins, ketone resins, By adding stabilizers such as weak organic
urea resins, and polyacrylates. A large number of bases (diphenylamine) or acids (phosphoric acid,
softeners, such as adipates, phthalates, phos- citric acid, or tartaric acid), intermediary nitric
phates, and raw and saturated vegetable oils are oxides can be bound and the autocatalytic de-
compatible with cellulose nitrate. composition prevented.
Thermal decomposition does not occur at
Chemical and Thermal Stability Cellulose temperatures below 100
C. The temperature
nitrate, as a solid or in solution, should not be (according to [28]) at which cellulose nitrate
brought into contact with strong acids (degrada- spontaneously deflagrates is used as a measure
tion), bases (denitration), or organic amines (de- of its thermal stability. A well-stabilized lacquer
composition) since they all induce a destruction of cotton has a deflagration temperature of
cellulose nitrate. This may proceed very rapidly  180
C. The deflagration temperature of plas-
and lead to deflagration of the cellulose nitrate. ticized cellulose nitrate chips with at least 18
The ester bonds of cellulose nitrate, which wt % softener (i.e., dibutyl or dioctyl phthalate) is
can be broken by saponifying agents or by  170
C.
Vol. 7 Cellulose Esters 339

The Bergmann – Junk test [29] and the warm quantity, and topographic distribution of the
storage test are additional methods for determin- accompanying hemicelluloses and lignin to be
ing the stability of cellulose nitrate. responsible for the nitrating capability of cellu-
loses. These factors determine the swelling
properties and thereby the uniformity of nitra-
1.3.3. Raw Materials tion, as well as the compressibility and the
relaxation capacity of the fibers, which in turn
Cellulose. Until the beginning of World influence the retention capacity of the fiber
War I, the only raw material available for nitra- mass. Linters with a lower acid retention capac-
tion was cellulose obtained from cotton in the ity of 110 – 130 % are definitely superior to
form of bleached linters (as flakes or crape). This wood pulp (acid retention capacity of prehydro-
was due to the high degree of purity (a-cellulose lyzed sulfate pulps up to 230 %, of sulfite pulps
> 98 %), which allowed a high yield and pro- up to 300 %) in this respect. The suitability of a
ducts with good clarity and little yellowing. raw material for nitration can be tested by a
Especially in times when linters were scarce, specially developed machine that measures the
it was possible to produce gunpowder from wood compression and relaxation characteristics of a
celluloses, even unbleached, other cellulose cellulose fiber pile.
fibers (annual plants), and even from wood if Approximately 150 000 t (3.4 %) of the annual
attention was given to the adequate disintegration worldwide production of 4.4  106 t of chemical-
of the raw materials. Lacquer types obtained grade pulps are used for the production of cellu-
from wood celluloses, especially from hard- lose nitrate.
wood, gave dull and mat films and lacquers with
inferior mechanical properties. This is due to the Industrial Nitrating Agents. The so-called
high content of pentosans, which is also nitrated nitrating acid as developed by SCH€oNBEIN, the
but is easily split by hydrolysis in conventional nitric acid/sulfuric acid/water system, is still
nitrating acid systems and thus becomes the nitrating agent of choice for industrial
insoluble. purposes. The highest attainable degree of
The development of highly purified chemi- substitution using this system is at DS 2.7
cal-grade wood pulp by refinement with hot = 13.4 % N. This is achieved only when the
and cold alkali having R18 values of 92 – 95 % nitric acid used is not hydrated and the molar
(see Table 16) allows this type of raw material ratio of nitric acid to sulfuric acid monohy-
to be used in the same manner as were linters, drate is 1 : 2. The optimal nitrating mixture is
which currently are used only for the produc- as follows:
tion of special and highly viscous CN types.
The highly refined prehydrolyzed sulfate pulps
with R18 values of above 96 % are especially HNO3 H2SO4 H2O

well-suited for nitration. The viscosity range molar ratio 1 2 2

of CN products can be adjusted in advance by wt % 21.36 66.44 12.20
choosing an initial cellulose with an adequate
DP. A low ash content, and above all a low Water plays a special role as far as the attain-
calcium content, of the cellulose is important able degree of nitration is concerned. Below 12 %
in preventing calcium sulfate precipitation water there is no increase in substitution, but a
during industrial nitration. higher water content results in a drastic decline in
A comparative study on the nitrating behav- the degree of nitration (Fig. 2).
ior of linters and wood pulps [30] shows the It is assumed that increasingly hydrated nitric
morphological factors of the fibers (fiber length acid causes increased swelling and gelatinization
and distribution, cross-section form and thick- of the cellulose so that the nitrating acid is no
ness of the secondary wall, and fine structure longer able to penetrate into the inner structures
including packing density, degree of crystalli- of the micelles.
zation, and lateral arrangement of the fibrils), The desired degrees of esterification can be
the chemical composition of the cellulose (DP adjusted by varying the nitrating acid mixture
and polydispersibility) as well as the type, according to the CN types (Table 4), whereby in
340 Cellulose Esters Vol. 7

2. Area of solution:
nitric acid 0 – 10 %
sulfuric acid 60 – 100 %
water 0 – 40 %
Little or no nitration takes place in this range.
Cellulose is degraded to the point of complete
dissolution in concentrated sulfuric acid.

3. Area of swelling: Nitric acid is increasingly

hydrated in this range of increasing water
content. Nitration decreases rapidly.

A process developed in the United States, but

Figure 2. Dependence of the degree of esterification (DS) on less important, uses magnesium nitrate instead of
the water content of the optimal nitrating mixture (HNO3 :
H2SO4 ¼ 1 : 2) sulfuric acid as a dehydrating agent [31]. Mag-
nesium nitrate can bind water as its hexahydrate.
industrial processes the nitric acid content is kept The nitrating mixture consists of 45 – 94% nitric
nearly constant at 25 – 26 %. acid, 3.3 – 34% magnesium nitrate, and 2.7 –
The ternary system HNO3/H2SO4/H2O has 21% water; the ratio of magnesium nitrate : water
been extensively investigated. The results are is 1.2 – 2.2 : 1. A cellulose nitrate with an N
summarized in Figure 3. content of 11.9% was obtained, for example,
The curves of the same degrees of substitution with 64.5% HNO3, 19.5% Mg(NO3)2, and 16%
(% N) in relation to the nitrating acid composi- H2O. This nitrating system is appropriate for a
tion are presented here. The cross-hatched band continuous process, in which waste and washing
identifies those areas in which the cellulose acid are reprocessed in ion exchangers and the
material is extremely swollen and gelatinized. magnesium nitrate is recycled. Thus, acid and
Three zones can therefore be differentiated in the sulfate no longer pose a waste disposal problem.
phase diagram:

1. Area of technical nitration: 1.3.4. Production

nitric acid 15 – 100 % The flow diagram (Fig. 4) shows the industrial
sulfuric acid 0 – 80 % production of CN according to the mixed acid
water 0 – 20 % process. The viscosity of the end product is
In this range, nitric acid is present in a non- determined by the choice of the initial cellulose,
hydrated form and induces true nitration (N and the degree of nitration is determined by the
content 10 %). The industrially used range composition of the mixing acid. The final vis-
with 20 – 30 % HNO3, 55 – 65 % H2SO4, and cosity adjustment follows during the pressure
8 – 20 % water is also included in this area. boiling step (see Section 1.3.4.21.3.4.2).

Table 4. Industrially used nitrating acid solutions

Nitrating acid

CN type % HNO3 % H2SO4 % H2O N content,% DS

Lacquer cotton A 25 55.7 19.3 10.75 1.90

Celluloid cotton 25 55.8 19.2 10.90 1.95
Lacquer cotton AM 25 56.6 18.4 11.30 2.05
Dynamite cotton 25 59.0 16.0 12.10 2.30
Lacquer cotton E 25 59.5 15.5 12.30 2.35
Powder cotton 25 59.8 15.2 12.60 2.45
Gun cotton 25 66.5 8.5 13.40 2.70
Vol. 7 Cellulose Esters 341

Figure 3. Composition of the nitrating mixtures and attainable N contents of cellulose nitrates

1.3.4.1. Cellulose Preparation Pressed pulp sheets must be appropriately shred-

ded to obtain rapid and uniform nitration. Spruce
Cotton linters with a moisture content of up to 7% or beech celluloses, preactivated with 20% sodi-
are mechanically disintegrated homogeneously. um hydroxide (mercerization), were formerly

Figure 4. Flow diagram of cellulose nitrate production

342 Cellulose Esters Vol. 7

used for this purpose in the form of crape papers cellulose to oxalic acid by way of oligo- and
with a mass per unit area of ca. 25 g/m3. To avoid monosaccharides, whereby the nitric acid is
the costly transformation of the cellulose to reduced to nitrogen oxides, NOx. In addition,
paper sheets, a process was attempted to obtain mechanical losses during the subsequent sepa-
a loose product resembling linters by direct ration process, due particularly to short fibers
disintegration of pulps to fibers. A moisture (cellulose from hard wood), must also be taken
content of 50 % proved to be optimal for nitra- into consideration.
tion and washing out the acid. The required The reaction mixture is drained from the
drying of the cellulose flakes before nitration reactor into the centrifuge, where the excess acid
proved to be disadvantageous. is separated and removed at high speed and
The Stern shredder [32], in which the pulp reprocessed for recycling. The mixture must
sheets are torn rather than being cut into small remain moist so that it does not ignite and
elongated shreds to avoid compression at the deflagrate.
edges, was a definite improvement. Currently, The degree with which the product retains
cellulose for nitration is used in the form of fluff, acid after separation is of economic importance
shreds, or chips. The packing density and com- because of the acid loss and the expense of the
pression behavior of the cellulose fibers in the ensuing washings. Linters with an acid retention
fiber pile are decisive factors for the swelling and of 100 – 130 % clearly surpass wood celluloses
nitration kinetics, as well as the acid retention in this respect which, depending on the wood and
capability [30]. cellulose type as well as its processing, can retain
up to 3 times more adhering acid relative to CN
1.3.4.2. Nitration [30].
The still acid-moist product is immediately
Nitration on an industrial scale is still frequently placed into a great excess of water (consistency
carried out according to a batch process that was 1 %) so that the adhering acid is displaced as
developed from a process described by DuPont in rapidly as possible and the saponification of the
1922. The equipment is constructed of stainless CN is prevented.
steel. The adjusted and preheated nitrating acid Continuous nitrating processes, which are
reaches the stirring reactor that is charged with more economical, were developed in the 1960s
cellulose by means of a measuring system; a [33], [34]; they ensure a more uniform product
large excess of acid (1 : 20 to 1 : 50) is added to quality and are safer to handle. The nitrating
retain the ability of the reaction mixture to be system consists of two or more consecutively
stirred and to ensure that heat is carried off. The arranged straight-run vats or tube systems con-
nitrating temperature is between 10
C (dynamite taining conveyers (screw conveyer or turbulence
type) and 36
C (celluloid type). The total heat of stirring apparatus) which forward the reaction
reaction is estimated to be over 200 kJ per kg of mixture. The prepared cellulose is directed into
CN, of which the enthalpy of formation of CN is this cascading equipment from storage bunkers
about one-third. over automatic weighing scales and continuously
Even though the reaction is nearly complete mixed with the added nitrating acid. It is impor-
after ca. 5 min, the mixture remains in the reactor tant that the cellulose is rapidly added and
for about 30 min. The temperature must remain immediately covered with acid. There it remains
constant (cooling), since hydrolytic degradation for 30 – 55 min. A newer process using a
processes that lead to considerable losses in yield continuous loop-formed pressure reactor [35]
begin at temperatures as low as 40
C. requires the cellulose to remain only for 6 –
The theoretical yield of commonly used in- 12 min. The reactant is then sent into a continu-
dustrial types with a DS of 1.8 – 2.7 (= 10.4 – ously operating special centrifuge, where the
13.4 % N) is between 150 and 176 % with re- excess acid is separated and simultaneously tak-
spect to cellulose. The practical yield, however, en up with water. The fact that the reactant
is up to 15 % lower and depends on the type and remains only a few seconds reduces the risk of
purity of the cellulose, as well as on the temper- spontaneous deflagration and saponification.
ature and duration of nitration. Losses arise Figure 5 shows schematically the continuous
from the inevitable complete decomposition of process according to Hercules [31].
Vol. 7 Cellulose Esters 343

Figure 5. Continuous cellulose nitrate production according to Hercules a) Preconditioning; b) Auto-matic scale; c) Reactor;
d) Washing zone; e) Centrifuge

The broken-up and preconditioned cellulose found in weakly nitrated CN, of which 70 – 85 %
(a) is brought by way of the automatic scales (b) to is in the form of the acidic sulfuric acid semiester,
the continuous reactor (c). The reaction product is while highly nitrated CN contains only 0.2 –
centrifuged in a washing zone (d) and simulta- 0.5 % total sulfate, of which 15 – 40 % is thought
neously washed by zones with water in a coun- to exist as an ester. Semiesters can be easily
tercurrent. The product leaves the centrifuge al- saponified and washed out by boiling with water.
most free of acid, and the washed out acid can be It is not yet certain whether the so-called resistant
recycled and reused almost without loss [36]. sulfate content exists in the form of the neutral
sulfuric acid ester or the physically adsorbed
1.3.4.3. Stabilization and Viscosity Adjustment sulfuric acid.
The desired final viscosity of the CN is
The prestabilization step following the prewash- adjusted in the following process step, which is
ing further purifies the product by means of pressure boiling (digestion under pressure) in a
repeated washing and boiling with water that consistency of 6 – 8 % at 130 – 150
C, by
contains 0.5 – 1 % acid residue. The batch meth- means of specific degradation of the degree of
od requires large amounts of space, water, and polymerization. The remaining extremely low
energy; the required boiling time varies between sulfuric acid content induces hydrolytic decom-
6 (celluloid type) and 40 h (guncotton). Auto- position at this temperature and under pressure.
matic continuous processes have been developed The viscosity can, for example, be reduced to
in this case as well [37]. 1/10 of the initial viscosity within 3 h at 132
C
Most of the remaining sulfuric acid is re- by using this process. This process made the
moved during prestabilization, since it would development of high solid coating and protective
promote the catalytic self-decomposition of CN. nitro lacquers possible. The stabilization process
The sulfuric acid is bound by adsorption and of guncottons is accelerated by pressure boiling;
esterified. A total sulfate content of 1 – 3 % was dynamite wools are usually not pressure boiled.
344 Cellulose Esters Vol. 7

Further product losses are due to chain degra- 1.3.4.5. Acid Disposal and Environmental
dation ranging from soluble cleavage products to Problems
oxalic acid. Nitrous gases (NOx) are released by
the reduction of nitric acid, which must be con- The nitrous gases formed during the nitrating and
tinuously drawn off to avoid decomposition of stabilizing side reactions are drawn off and
CN. washed out in trickling towers. The lower nitro-
Pressure boiling can be achieved batchwise in gen oxides are regained after oxidation as 50 –
autoclaves, as well as continuously in a tube 60 % nitric acid.
reactor of 1 500 m in length and 100 mm in The waste acids resulting from the first sepa-
diameter, e.g., with direct steam. A one-pot ration contain 2 – 3 % more water and 3 – 4 %
process in which prestabilization, pressure boil- less nitric acid than the initial mixture. They are
ing, and poststabilization are carried out in one circulated in a closed system and constantly
operation is described in [38]. regenerated with nitric acid and oleum. The acid
During the stabilization process, the remain- that adheres to the product must also be replaced.
ing sulfuric acid is almost completely removed The proportion of adhering acid depends on
by additional washing and boiling. While cellu- the initial cellulose and the CN type. It ranges
loid and lacquer types are finished in flaky, between 80 % (guncotton) and up to 200 – 300 %
fibrous form, guncotton must be ground. This is (lacquer types) with regard to CN and is removed
done in grinding hollander engines at 12 – 15 % with the water used for washing and boiling.
consistency or continuously in a series of cone Aside from the economic aspects of acid loss
refiners, whereby the material is gradually con- in wastewater, environmental considerations are
centrated from 3 to 10 % between the various beginning to play an increasingly important role.
grinding steps. Sorting steps are inserted by While older manufacturing facilities using simple
hydrocyclones during the final washing process- centrifuging to remove waste acid produced
es. The last acid remnants in the fiber capillaries 300 m3 of water per ton of CN, containing 0.5 %
are removed during the grinding process by acid and with a pH of 1, it was possible to reduce the
means of diffusion against water. Weak bases, volume of wastewaters to a fraction of its previous
sodium carbonate, or chalk are used to maintain a volume by almost completely closing the cycles.
pH of 7. Stabilizers (organic acids) may be added Before proceeding into the draining ditch, the
during this step. wastewater must be separated from the hardly
decomposable sludge consisting of cellulose and
1.3.4.4. Displacement and Gelatinization CN, and then be neutralized. The sulfate propor-
tion can be reduced by calcium sulfate precipita-
A water-wet CN cotton with a water content of tion, while the nitrate proportion remains
25 – 35 % remains in the centrifuge after the completely in the wastewater. Organic matter of
final separation and is then packed into drums communal sewage, for example, can be biologi-
or PE sacks. cally decomposed without additional oxygen,
Water contained in celluloid and lacquer types whereby nitrates disappear almost completely as
is displaced by alcohols specified by the proces- a result of biological denitrification.
sors (ethanol, 2-propanol, n-butanol) in displace- The salt/acid process with magnesium nitrate
ment presses or displacement centrifuges. Con- (see Section 1.3.4.1) is more favorable with regard
tinuous processes prevail here also [39]. The to the wastewater problem. Sulfates are completely
resulting aqueous alcohols must be distilled to absent, and magnesium nitrate is recycled and,
remove the water. therefore, causes no water pollution problems. The
The water-wet CN cotton can be gelatinized amount of wastewater can be reduced by 80 % and
with softeners such as phthalates in kneading the nitric acid requirement by 83 % in comparison
aggregates and dried on drum or band driers for to the formerly used discontinuous processes.
the production of CN chips [40], [41]. Colored
chips are obtained by adding carbon black or 1.3.4.6. Other Nitrating Systems
pigments from which colored enamels can be
produced without the use of ball mills or roller Numerous attempts have been made to improve
mills. nitration by the introduction of other nitrating
Vol. 7 Cellulose Esters 345

Table 5. Nitrating systems

Max. N
Nitrating system content, % Comments

HNO3/H2SO4/H2O 13.4 Industrial nitration

HNO3 < 75 % ‘‘Knecht compound,’’ unstable

78 – 85 % 8 Dissolution in the nitrating acid
85 – 89 % 10 Gelatinization
90 – 100 % 13.3 No swelling
HNO3 þ nitrates, sulfates, phosphates 13.9
HNO3 vapor 13.75 Slow reaction, stable nitrate
HNO3 vapor þ nitrogen oxides 13.8
N2O5 14.12
N2O5 in CCl4 14.14 Trinitrate
HNO3 in CH2Cl2 14.0
HNO3 in nitromethane 14.0 Homogeneous reaction
HNO3 þ H3PO4/P2O5 14.04 Rapid reaction without decomposition (polymer analogue)
14.12 After extraction with methanol
HNO3 þ acetic acid/acetic anhydride 14.08 Great stability
14.14 After extraction with ethanol
HNO3 þ propionic acid/butyric acid 14.0

systems, or at least to increase the degree of nitrated and highly stable products in which
substitution. Further details may be obtained the fiber structure remains intact largely. After
from [12], [14], [17], and [21]. Table 5 gives a extraction of these nitrates with water or alcohol,
summary of alternative nitrating systems, none the theoretical degree of substitution of the trini-
of which was able to displace the ternary system trate may be attained.
HNO3/H2SO4/H2O for industrial nitration. Nitrating systems which achieve a high
Nitration with pure nitric acid is possible in degree of nitration without degradation of the
principle. Esterification is not possible with acid cellulose chain are of special scientific interest.
concentrations below 75 %. Acid concentrations This process is known as polymer analogous
less than 75 % cause the formation of the unstable nitration. After a critical examination of all
so-called Knecht compound, which has been known nitrating mixtures, the nitric acid/acetic
described as either a molecular complex or an acid/acetic anhydride system in a ratio of
oxonium salt of the nitric acid. Cellulose nitrates 43 : 32 : 25 at 0
C [42] was recommended for
with 5 – 8 % N, which dissolve in excess acid, determining the molecular mass of native cellu-
are formed at acid concentrations of 78 – 85 %. loses of such solutions by using absolute methods
Nitrogen contents of 8 – 10 % are attained at and the intrinsic viscosity number [43]. The sys-
concentrations between 85 and 90 % HNO3; tem anhydrous nitric acid in dichloromethane also
these products have a strong tendency to gelati- allows the application of such polymer analogous
nize. Heterogeneous nitration without apparent reactions at temperatures between 0 and 30
C
swelling takes place at a HNO3 concentration [44]. Other authors [45] prefer the system nitric
above 89 %, and 13.3 % N can be achieved with acid/phosphoric acid/phosphorus pentoxide.
100% HNO3. Nitration can be increased to Nitration in the Laboratory. Preparative
13.9 % N with 100 % HNO3 by addition of cellulose nitration with HNO3/H2SO4 nitrating
inorganic salts such as sulfates, acid phosphates, acid to products with whatever N content up to
and particularly nitrates, preferably in a 15 % 13.65 % is desired, stabilization and stabilization
concentration. tests, nitration with the nitric acid/phosphoric acid
The nitric acid/phosphoric acid system is of (< 13.9 % N) and nitric acid acetic anhydride
special interest in a 1 : 1 ratio with 2.5 % phos- systems up to the trinitrate, denitration with hy-
phorus pentoxide added, with which an almost drogen sulfide to cellulose II, the analytic deter-
completely nitrated product of great stability was mination of the N and sulfate content, and the
achieved. The nitric acid/acetic acid/acetic an- solution of the CN and the viscosity determination
hydride system in a ratio of 2 : 1 : 1 gives highly of the solution are extensively described in [46].
346 Cellulose Esters Vol. 7

1.3.5. Commercial Types and Grades Table 6. Cellulose nitrate types

Degree of
Cellulose nitrates receive, because of their fluffy Type N content, % substitution (DS)
structure and cottonlike appearance, the addi-
Celluloid cotton 10.5 – 11.0 1.82 – 1.97
tional designation ‘‘cotton.’’ Alcohol-soluble > 10.9 – 11.3 1.94 – 2.06
Two parameters are decisive for the industrial lacquer cotton
use of cellulose nitrate: Lacquer cotton 11.4 – 11.7 2.08 – 2.17
moderately
soluble in alcohol
Nitrogen content (including the resulting solu- Ester-soluble > 11.8 – 12.2 2.20 – 2.32
bility properties) lacquer cotton
Viscosity Powder cotton 12.3 – 12.9 2.55 – 2.57
Gun cotton 13.0 – 13.6 2.58 – 2.76

As seen in Table 6, cellulose nitrates with

differing nitrogen contents have various appli-
cations. Cellulose nitrates for lacquers are avail- facilities. The total world capacity may be esti-
able in numerous viscosities. It is possible to mated to 150 000 t/a of dry cellulose nitrate.
categorize all stages of viscosity according to
the European norm (DIN 53179), but the vis- Other Commercial Types. Also available,
cosity of cellulose nitrates is primarily catego- in addition to cellulose nitrate cotton types, are
rized by using the Cochius method and the so-called cellulose nitrate chips, made from cel-
British or American ball drop method (ASTM lulose nitrate plasticized by gelatinizing soft-
D 1343 – 69). eners. For safety reasons, the softener content
In addition to the so-called cotton types den- has been established at a minimum of 18 wt %.
sified CN types are available. These may be Chips are preferred in processes where alcohols
obtained by either nitrating compressed cellulose interfere in the formulation of lacquers.
or by subsequently compressing the fluffy cellu- The dispersions of cellulose nitrate with soft-
lose nitrate. It is possible to almost double the eners or resins in water manufactured by the
bulk density by compression. Wolff Walsrode AG are other available forms.
For safety reasons, the commercially avail- The solvent-free or low-solvent dispersions are
able CN cotton types must be wetted with at least not polluting and may be used in all areas in which
25 wt % water or aliphatic alcohols. In addition to cellulose nitrate lacquers also are used [55].
water, ethanol, n-butanol, and 2-propanol may
also be used as wetting agent.
The largest manufacturers of cellulose nitrates 1.3.6. Analysis and Quality Control
are the following:
The most important analytical characteristics
Hercules Inc. USA
relate to the determination of the N content and,
Wolff Walsrode AG FR Germany thereby, the average degree of substitution (DS),
Hagedorn FR Germany as well as the viscosity of the solution as a
WNC Nitrochemie GmbH FR Germany measure of the average molecular mass or
Soci
et
e Nationale des Poudres
et Explosifs (SNPE) France
chain-length.
Imperial Chemical Industries Great Britain
(ICI) Analytic Tests. The most commonly used
S.I.P.E. Nobel S.p.A. Italy analytic procedures are summarized in [25], [46],
Unión de Explosivos R
ıo [47], and [48].
Tinto S.A. Spain
Bofors Sweden Dry content is determined by careful drying of
Asahi Japan a small, thinly layered alcohol or water-wet
Daicel Chemical Industries, Ltd. Japan sample at room temperature for 12 – 16 h, in a
weighing glass at 100 – 105
C for 1 h, or with
compressed warm air at 60 – 65
C for 0.5 – 1 h.
Many countries in South America, Asia, and Ash content is determined by decomposing a
Eastern Europe maintain small CN production dried sample with HNO3 and incinerating the
Vol. 7 Cellulose Esters 347

Table 7. Characterization of cellulose nitrates according to DIN 53179

CN concentration, CN concentration, CN concentration,

A types % absol. dry) AM types % (absol. dry) E types % (absol. dry)

E 1440 4
E 1160 7
E 950 9
E 840 12
AM 760 14
AM 750 15
E 730 15
AM 700 17
E 620 21
E 560 22
E 510 24
A 500 27 AM 500 27
A 400 30 E 400 27
E 375 32
AM 330 36 E 330 34

residue. Specifications require that the ash con- this requirement show a apparent dynamic vis-
tent should not be above 0.3 %. cosity of 400  25 mPa  s in the ball drop
N-content is determined by reducing nitrates viscometer according to H€oppler (ball no. 4) at
according to the following reaction (Schulze- 20
C (Table 7).
Thiemann): Cochius Viscosity [25]: The viscosity of the
various cellulose types is measured in commonly
NO 
3 þ3FeCl2 þ4HCl!3FeCl3 þCl þ2H2 OþNO used solvent mixtures:
or by the following reaction: A and AM types: butanol/ethylene glycol/
toluene/ethanol in the following proportions
2NO 2
3 þ4H2 SO4 þ3Hg!3HgSO4 þSO4 þ4H2 Oþ2NO 1:2:3:4
The resulting NO is collected in a Du Pont E types: butanol/butyl acetate/toluene in the
nitrometer. following proportions 3 : 4 : 5
Dried CN is dissolved in varying concentra-
Stability Tests. [25]. Deflagration Tem- tions depending on the type and the time which an
peratures: Well-stabilized CN deflagrates at air bubble requires to rise 500 mm between two
temperatures above 180
C. calibrations in a 7 mm Cochius tube at 18
C is
Bergmann – Junk Test [29]: A quantity of 2 g measured in seconds. The Cochius seconds are
of dried CN is kept at a temperature of 32
C for 2 converted to absolute viscosity units mPa  s by
h in a special apparatus for the elimination reac- multiplying with the factor 3.64 mPa.
tion, after which time the amount of the developed Ball drop method according to ASTM [49]:
nitrous gases (after reduction to NO) is deter- Dried CN is dissolved according to its viscosity
mined. CN is stable according to this test if no stage in 12.5, 20.0, or 25.0 % ethanol/toluene/
more than 2.5 cm3 of NO per gram is measured. ethyl acetate according to [48]. The drop time of
Warm Storage Test: A quantity of 5 g of dried the balls with a diameter between 1/4 and 1/16 in.
CN is stored in a glass-stoppered tube at 75
C. at 25
C is given in seconds or converted into
Note is then made when the first nitric oxide (red- Pa  s. Figure 6 shows the relationship between
brown gas) becomes visible. Well-stabilized CN the degree of polymerization and the technical
can be stored at 75
C for at least 10 days. viscosity (fall velocity of the balls in a 17.2 % CN
ASTM Stability Test [48]: After storage at solution in acetone).
134.5  0.5
C the time is noted in which the Comparative viscosity charts for converting
nitrous gases discolor methyl violet test paper. the various viscosities and comparing the various
types are found in [25].
Viscosity. Viscosity according to DIN
53179: If CN is dissolved in acetone in the Solubility and Color. The color and cloud-
appropriate concentration, CN solutions meeting iness of solutions produced according to [48] are
348 Cellulose Esters Vol. 7

distinctions can be made: monobasic powder,

which is based solely on cellulose nitrate; dibasic
powder, which contains further energy carriers
such as, for example, nitroglycerin or diglycol
dinitrate in addition to cellulose nitrate; tribasic
powder, which contains in addition to the com-
ponents of the dibasic powder a third agent such
as nitroguanidine.
The selection of the cellulose nitrate is of
special importance. The types of cellulose ni-
trates that differ in the degree of nitration were
standardized as follows:
CP I (Collodium powder) also known as gun-
cotton, nitrogen content: 13.3 – 13.5 %
CP II (Collodium) nitrogen content: 12.0 –
12.7 %, mostly 12.6 %
PE (Powder standard) nitrogen content:
11.5 – 12.0%, mostly 11.5%
Figure 6. Degree of polymerization (DP) and technical Aromatic amines, such as diphenylamine, are
viscosity (‘‘ball drop’’ in seconds of a 12.2 % CN solution added to gunpowder as stabilizers. They are
with 12 % N in acetone). DP ¼ 170  viscosity capable of binding the nitrous gases generated
during the decomposition of the nitric acid ester.
A mixture of ca. 80 % highly nitrated gunpowder
tested visually. Consistency, appearance, and
(13.4 % N) and ca. 20 % less-nitrated collodium
depth of color can be controlled according to [50].
cotton (12.5 % N) is used for the production of the
Dilution with Toluene. Toluene is added to a
monobasic propellant powder. Since cellulose
12.2% CN solution in butyl acetate at 25
C until
nitrate granules are easy to charge electrostati-
CN continuously precipitates. The dilution factor
cally, they are made conductive with a fine
is noted. The dilution ratio of CN solutions with
graphite coating.
other solvents and blending agents is determined
The multibasic powders usually contain cel-
according to [51].
lulose nitrate CP II. Mixtures of 40 % PE cotton
and 60 % CP I are also used because they have the
Film Test. The solutions made according to
same energy content as CP II with 12.6 % N.
[48] are diluted with an equal volume of butyl
The introduction of a third component to
acetate and poured as a film onto a glass plate. The
tribasic powder results in a lower heat of com-
dried films are examined for undissolved parti-
bustion in comparison to dibasic powder, thereby
cles, surface structure, transparency, and gloss.
lengthening the life of the gun barrel.
Gunpowder is used in small-arms ammunition
1.3.7. Uses as well as large-caliber guns and tanks. (For
further details ! Explosives, Section 7.2.)
Explosives. Explosives may be categorized
according to their use: Lacquers. Cellulose nitrate lacquers are
characterized by the outstanding film-forming
blasting agents properties of the physically drying cellulose ni-
propellants and shooting agents trate. Moreover, cellulose nitrate is compatible
detonating agents with many other raw materials used in lacquers
igniting agents and can be used advantageously in combination
pyrotechnical agents with resins, softeners, pigments, and additives.
In addition to the nonvolatile lacquer compo-
Cellulose nitrates are used primarily as pro- nents, the composition of the solvent mixture is
pellants and gun powder, whereby the following decisive for the formation of a film.
Vol. 7 Cellulose Esters 349

The most important uses for nitro lacquers are For further information on the formulation of
as follows: wood lacquers (especially furniture cellulose nitrate lacquers, see [52], [53], and also
lacquers), metal lacquers, paper lacquers, foil ! Paints and Coatings, 1. Introduction.
lacquers (also as hot sealing lacquers, e.g., cello-
phane, plastic, and metal foils), leather lacquers, Dispersions. Conventional cellulose nitrate
adhesive cements, putties, and printing ink (for lacquers contain between 60 and 90 % organic
flexo and gravure printing). solvents, which are released during drying. For
The processes used for applying cellulose economic and environmental reasons, it is desir-
nitrate lacquers to substrates are as follows: able to substitute organic solvents by water.
spraying (compressed-air, airless, and electro- Aqueous cellulose nitrate/softener dispersions
static spraying), casting (for example, with a (e.g., Isoderm, Bayer AG; Coreal, BASF;
curtain coater), rolling (especially for the appli- Waloran N, Wolff Walsrode AG) are available
cation of small amounts of lacquer), doctor knife for such absorbing substrates as leather [54].
coating, and dipping. Other aqueous cellulose nitrate dispersions for
The casting and rolling processes are used use on wood, foil, and metal have also been
for lacquering large, even areas. Irregularly developed (Waloran N, special-types, Wolff
shaped objects are sprayed. The choice of a Walsrode AG) [55]. The film forming process
suitable type of cellulose nitrate (e.g., of water-insoluble cellulose nitrate requires a
completely or moderately soluble in alcohol, small amount of coalescents in the dispersion
soluble in esters, degree of viscosity) is de- systems.
pendent on the lacquer type. A highly viscous
cellulose nitrate type is used if elastic and thin Celluloid. A special use of cellulose nitrate
applications are desired (e.g., leather). How- is in the production of celluloid [56]. Cellulose
ever, if hard and thick layers are desired, low- nitrate with a nitrogen content of 10.5 – 11.0 %
viscosity types are preferred. is mixed in a kneader with softeners, particularly
The concentration or the degree of viscosity of camphor, and solvents (alcohols).
the cellulose nitrate determine the viscosity of the Normal celluloid contains ca. 25 – 30 % cam-
lacquer solution. However, the formulation of the phor and 70 – 75 % cellulose nitrate. Celluloid
lacquer must be taken into consideration when that contains 10 – 15 % solvent can be formed
the mode of application is chosen. For example, a into the desired articles in heated piston or screw
highly viscous dipping lacquer cannot be sprayed presses (e.g., tubes and round and profile rods).
or casted. In the past decades, celluloid has been widely
Furthermore, the striking differences between replaced by synthetic materials and thermoplas-
ester-soluble and alcohol-soluble types should be tics. Celluloid is still of economic importance in
taken into consideration when nitro lacquers are the following areas: combs and hair ornaments,
formulated (Table 8). toilet articles, office supplies (drafting and

Table 8. CN lacquer cottons

Ester-soluble type Alcohol-soluble type

Possible use of alcohol in the lacquer formulation Use of alcohol, especially ethanol, in any desired amount as a solvent
Good dilutability with aliphatic and aromatic hydrocarbons Good dilutability with aromatic hydrocarbons
Very rapid solvent release Rapid solvent release
Formation of hard films Formation of films with thermoplastic properties
Attainment of good mechanical properties as far as the cold-check Attainment of good mechanical properties; some special problems of
test, stretch, hardness, and tensile strength are concerned lacquer production may be solved such as:
Lacquers which can be diluted with ethanol in any desired manner
(wood polishes)
Odorless lacquers (printing inks)
Gel dipping lacquers
Hot sealing waxes (cellophane lacquers and aluminum foil lacquers)
350 Cellulose Esters Vol. 7

measuring instruments), ping-pong balls, and butanol belongs to category II d, but is not con-
various special uses. sidered to be hazardous to health in a damped
mixture of a maximum 35 % concentration.

1.3.8. Legal Provisions Storage and Shipping. Cellulose nitrate,

especially guncotton, burns in air with a yellow
Toxicology and Industrial Safety. Con- flame and deflagrates if present in larger quan-
centrated sulfuric acid, nitric acid, and nitrous tities, especially after rapid heating. An explo-
gases formed during the production of cellulose sion can be caused by friction or a sharp impact.
nitrate are considered hazardous chemical pro- Dry CN has electrostatic charge. Friction, par-
ducts [57]: ticularly on metals but also on plastics, can
cause sparks which lead to a deflagration.
1. Sulfuric acid Therefore, cellulose nitrate should be stored in
5 – 15 % EC-No. 016 – 020 – 01 – 5 a moist and cool place [60], [61]. Rooms in
above 15 % EC-No. 016 – 020 – 00 – 8 which cellulose nitrate is processed must be
adequately protected according to the guide-
2. Nitric acid lines for protection from explosions.
20 – 70 % EC-No. 007 – 004 – 01 – 9 Cellulose nitrate is subjected to the regula-
above 70 % EC-No. 007 – 004 – 00 – 1 tions governing explosives [62]. The transporta-
3. Nitrous gases tion of phlegmatized cellulose nitrates proceeds
EC-No. 007 – 002 – 00 – 0 according to the most recent versions of the
hazardous materials regulation; see [25]. Wetted
They are subjected to the Arbeitsstoffverord- cellulose nitrate is shipped in thick-walled, gal-
nung (working substance regulation) [58] and vanized, tightly closing iron or fiber drums which
must, therefore, be adequately labeled. are adequately labeled.
Concentrated nitric acid and mixed nitrating Dried cellulose nitrate may not be shipped
acids are oxidizing when brought into contact under any circumstances.
with organic materials [59]. The MAK values For further information on the properties,
(maximum working place concentration) are as handling, storage, and transportation of hazard-
follows: ous goods, see also [63].
nitric acid vapors 10 mL/m3 (ppm); = 25
mg/m3 1.4. Other Inorganic Cellulose Esters
nitrogen oxides (NO2) 5 mL/m3 (ppm); = 9 mg/
m3 Summaries on the esterification products of cel-
Employees should be examined regularly for lulose with other inorganic acids may be found in
obstructive respiratory tract illnesses. [12–19]. For publications on the modification of
cellulose, including esterification, see [64].
Cellulose nitrate is neither toxic nor hazard-
ous to health [60]. Damping agents in CN and
nitrous gases which may be formed during com- 1.4.1. Cellulose Sulfates
bustion and smoldering processes are potentially
hazardous to health if inhaled. Cellulose sulfates [9032-43-3] are the most fre-
Commercially available phlegmatized cellu- quently investigated of all other inorganic cellu-
lose nitrate for the production of lacquer with less lose esters. The ability of concentrated sulfuric
than 12.6 % N contains at least 18 % of a gela- acid to dissolve cellulose, particularly in concen-
tinizing softener. According to the first paragraph trations between 70 and 75 %, has been known
in [58], cellulose nitrate is a hazardous substance since 1819. After precipitation immediately fol-
and must be packaged and labeled accordingly. lowing dissolution, the cellulose contains little or
EEC regulations (1982) are similar. no bound sulfate. An almost homogeneous ester-
Damping agents such as ethanol and 2-pro- ification takes place only if the cellulose is left in a
panol are not subjected to these regulations; sulfuric acid solution over a longer period of time.
Vol. 7 Cellulose Esters 351

However, the ester yield is very poor. The major SO3/DMF complex. Uniformly substituted cel-
portions of the reaction products consist of hy- lulose sulfate with a range of DS values between
drolytically split decomposition products with a 0.3 and 2.0 and solution viscosities up to 7 000
maximum degree of substitution of 1.5. mPa  s (in 1 % solution) can be obtained by
In their free acidic form, cellulose sulfates are using this process [68]. Such transesterified
fairly unstable and easily saponified. A semiester products can be cross-linked by metal ions to
was developed in 1953 in the United States [65] form highly effective thickening agents for
in an esterification mixture consisting of 1 mol of aqueous media [69].
cellulose with 20 – 30 % water, 3.5 – 15 mol of Such processes have been further developed
sulfuric acid, 0.3 – 1.0 mol of a primary or [66] and make interesting novel fields of appli-
secondary C3 – C5 alcohol, and an inert volatile cation accessible as a result of the rheological and
organic solvent such as toluene or carbon tetra- gel-forming properties of the Na cellulose sulfate
chloride (reaction temperatures between  5 and semiester.
 10
C). The product was soluble in hot or cold Mixed esters such as cellulose acetate sul-
water, yielded relatively stable, clear, and highly fates, cellulose acetate butyrate sulfates [70],
viscous solutions, and was recommended for use cellulose acetate propionate sulfate [71], and
as a thickener for aqueous systems (emulsion ethyl cellulose sulfates [70], [72] are described
paints and printing inks, printing pastes for tex- in the patent literature.
tiles, and food products), as well as for fat- and Being polyelectrolytes, cellulose sulfates
oil-proof finish, and as paper glue. This product, form salts and have ion-exchanging properties;
however, is of no economic importance. thus, they have been recommended for use as
Numerous attempts have been made to find cation exchangers [64, p. 65], [73], [74].
improved preparation methods for water-soluble
cellulose sulfates stable to saponification. Known
reaction systems are summarized in a tabular 1.4.2. Cellulose Phosphate and Cellulose
overview [65]. The reaction of cellulose with Phosphite
sulfuric acid in organic solvents, especially in
lower-mass aliphatic alcohols, gives by way of a Reaction of cellulose with aqueous phosphoric
heterogeneous reaction fibrous and water-soluble acid gives the following unstable addition com-
cellulose sulfates with a maximum DS value of 1. pound: 3 C6H10O5  H3PO4, from which the
More highly substituted products are obtained by cellulose can be regenerated unchanged by
reaction with sulfuric acid/acetic acid anhydride reaction with water. Cellulose phosphates
(up to a DS value of 2.8) or esterification with [9015-14-9] with a low phosphorus content are
chlorosulfuric acid in pyridine or formamide. The obtained by reacting cellulose or linters with
reaction with SO3 only or in various organic phosphoric acid in an urea melt [75]. Higher
systems yields trisubstituted products. The reac- phosphorus contents and a lower degradation
tion mechanism may be described as the addition rate of the cellulose may be obtained with excess
of the strongly electrophilic SO3 to the hydroxyl urea at reduced reaction time (ca. 15 min) and at
groups with the succeeding disintegration of the high temperature (ca. 140
C). Water-soluble
intermediately formed oxonium ion. cellulose phosphate with a high degree of sub-
stitution may be obtained from a mixture of
phosphoric acid and phosphorus pentoxide in
an alcoholic medium [76].
Phosphorylated cellulose fibers show in-
creased swelling after partial hydrolytic degrada-
Completely water-soluble, highly viscous tion and transfer into the alkali salt form and were,
sodium cellulose sulfate semiesters are obtained therefore, suggested for use as adsorbents [77].
in homogeneous systems by the reaction of Cellulose phosphates with a 17 % phosphorus
cellulose nitrite [67]. The intermediate that is content (this represents about 3/4 of the maximal
formed and dissolved, cellulose nitrite, is ob- possible substitution of triphosphate with 23 %
tained in the N2O4/dimethylformamide system phosphorus) were already produced in 1933 by
and is at the same time transesterified by the reacting cellulose with a mixture consisting of
352 Cellulose Esters Vol. 7

concentrated sulfuric acid and phosphoric acid in Ti(OH)4 [81]. Ethyl trichlorotitanate has been
the presence of a weakly acidic catalyst [78]. shown to be the most reactive. Esters with 16 %
Cellulose phosphites [37264-91-8] and cellu- titanium content are possible.
lose phosphonates may be prepared by transes- Cellulose esters with a titanium content
terification with alkyl phosphites. All cellulose between 3 and 5 % do not burn or smolder.
esters containing phosphorus have fire-retarding They possess considerable hydrolytic stability
properties [78] and have attracted some interest in neutral and weakly alkaline media, but are
due to their ion-exchanging effect [74], [79], but easily hydrolyzed at a low pH.
are not yet industrially used.

1.4.6. Cellulose Nitrite

1.4.3. Cellulose Halogenides
The nitrite of cellulose came of scientific and
Various preparative methods are suitable for the possibly practical interest as a cellulose deriva-
synthesis of halogenated cellulose derivatives tive in 1974 [67]. It is obtained by reacting
[64, p. 64]. Halogenation can be carried out by cellulose with nitrosyl compounds such as dini-
transesterification of such cellulose esters as trogen tetroxide, N2O4 (corresponding to nitrosyl
tosylate, nitrate, and sulfate with hydrohalic nitrate), or nitrosyl chloride, NOCl, in dimethyl-
acids [80]. Nucleophilic substitution proceeds formamide or dimethylacetamide as a proton
considerably faster in homogeneous systems acceptor and solvent for the resulting ester. The
than in heterogeneous aqueous systems. reaction proceeds in a homogeneous phase to the
The Finkelstein transesterification process of trinitrite.
cellulose nitrate with sodium iodide in anhydrous
acetone leads to deoxyiodo cellulose. The reac-
tion of cellulose with thionyl chloride, SOCl2, in
the presence of pyridine produced a monosub-
stituted, but strongly decomposed and unstable,
hydrogen chloride ester.
Halogenation of cellulose improves its water- Cellulose nitrite is extremely sensitive to hy-
resistant and flame-resistant properties. Slight drolysis. Chain degradation to a DP of 200 (level-
fluorination increases oil resistancy and lowers off DP) was observed to take place within 3 h in
the soiling potential of cellulose textiles [64]. the presence of water. The scientific and prepar-
Commercial applications are not yet known. ative importance of cellulose nitrite is based on
its high reactivity, which may be used to produce
many other cellulose esters, also mixed esters, by
1.4.4. Cellulose Borates transesterification in a homogeneous phase [82].
Transesterification to stable cellulose sulfates
The preparation of cellulose borate succeeded by has already been mentioned [67]. In this manner,
means of transesterification of methyl and n- water-soluble cellulose nitrates with a DS value
propyl borate with cellulose [64, p. 7]. The of 0.5 – 0.6 may also be obtained [83].
products with a maximum DS value of 2.88 are, Cellulose solutions produced under cold con-
however, extremely sensitive to hydrolysis and ditions (up to ca. 5
C) in a N2O4/DMF system are
alcoholysis. relatively stable to degradation and can be pro-
duced, depending on the DP of the cellulose, up
to a concentration of 14 %. The cellulose can be
1.4.5. Cellulose Titanate regenerated in an unaltered form to cellulose II,
with the result that this process has already been
Cellulose can be reacted to cellulose titanates in a considered as an alternative to the environmen-
heterogeneous reaction system by reacting it with tally detrimental viscose process [84]. Not only
titanium tetrachloride in DMF or with chlorinat- an attempt was made to achieve good mechanical
ed anhydrides, chlorinated ester anhydrides, textile properties from the regenerated fibers,
and esters of the hypothetical orthotitanic acid but also to recycle the expensive solvent. An
Vol. 7 Cellulose Esters 353

economic solution to the competition with the acetate butyrate [9004-36-8] have been manu-
viscose process has not yet been found. factured for over 70 years and continue to be
commercially viable products. Because of their
instability, formic acid esters are of no industrial
1.4.7. Cellulose Xanthate importance.
The only other commercial organic ester of
Cellulose xanthate [9032-37-5], an important in- cellulose, cellulose acetate phthalate [9004-38-
termediary molecule for the production of regen- 0], has found use as an enteric coating in phar-
erated cellulose according to the viscose process maceutical applications. A recently developed
(see Cellulose Section 3.2.1), must also be con- commercial cellulose ether-ester, carboxymethyl
sidered as an ester of an inorganic acid, namely cellulose acetate butyrate [160047-24-5], has
the nonexistent thiol – thion carbonic acid. found utility in water-based coating systems.
None of the other cellulose esters of organic
acids, such as cellulose palmitate, cellulose stea-
rate, esters of unsaturated acids such as crotonic
acid, or esters of dicarboxylic acids, are industri-
ally manufactured.
The O ester of this compound with organic
Historical Aspects. Cellulose acetate was
residues is the xanthic acid and the appropriate
first synthesized by P. SCHUTZENBERGER in 1865
salts. Sodium cellulose xanthate is obtained by
by heating cellulose and acetic acid under pres-
reacting alkali cellulose with carbon disulfide,
sure, whereby a product of very low molecularity
which dissolves in dilute sodium hydroxide to an
was obtained. In 1879, A. P. N. FRANCHIMONT
orange-yellowish, highly viscous solution, the
added sulfuric acid to the esterification process,
so-called viscose.
which remains to this day the most frequently
used catalyst. The limited solubility of cellulose
acetate in less-expensive solvents and poor com-
patibility with the then-known softeners was a
considerable obstacle for its industrial use. The
The regenerated cellulose is precipitated in problem was solved in 1904 when F. D. MILES
the form of fibers (rayon, cord, and rayon staple), and A. EICHENGR€uN simultaneously succeeded in
foils (cellophane), or tubes in precipitation baths synthesizing an acetone-soluble secondary ace-
containing sulfuric acid and salts (see ! Cellu- tate by partially hydrolyzing a primary triacetate.
lose, Section 3.1.3.). About 4  106 t of regen- During World War I, the less-flammable air-
erated cellulose is presently produced worldwide plane paints based on cellulose secondary acetate
by using the viscose process. reached considerable importance as a replace-
For further information, see ! Cellulose, ment for nitrocellulose. At almost the same time,
Chap. 3.. the manufacture of foils, films, synthetic silk, and
plastic masses developed.
An especially high number of publications
2. Organic Esters and patents were achieved between 1920 and
1935. Ultimately, only a few processes proved
Theoretically, cellulose can be chemically con- to be industrially useful, most of which are still
verted into an unlimited number of organic acid used today.
esters because each of its anhydroglucose units The technology of cellulose ester manufacture
possesses three reactive hydroxyl groups. Indus- has been well established for quite some time.
trial possibilities however, are drastically limited Research continues with respect to rationalization
by the complex nature of the cellulose polymer. and improvement of production methods to pro-
Highly esterified organic esters therefore are vide products at greater efficiencies and with
normally produced from a few aliphatic fatty greater uniformity and improved properties. De-
acids with up to four carbon atoms. velopment of new applications for cellulose esters
Cellulose acetate [9004-35-7], cellulose ac- continues into the modern era as societal innova-
etate propionate [9004-39-1], and cellulose tions generate uses for their unique properties.
354 Cellulose Esters Vol. 7

2.1. Cellulose Acetate

2.1.1. Chemistry

The chemistry of cellulose acetate includes two

discreet chemical transformations that convert
the fibrous cellulose polymer into a commer-
cially functional thermoplastic. The first step
involves acetylation of all primary and second-
ary hydroxyl groups to give a fully esterified
cellulose triacetate species that can be isolated
or processed further. The relative reactivities of
primary versus secondary hydroxyl groups have A number of acetylation catalysts have been
little consequence in industrial acetylations identified [93], however, sulfuric acid is the
[83], [86]. The second chemical step involves predominant catalyst of commercial impor-
hydrolysis of a portion of the acetyl groups to tance. Perchloric acid can be used commercial-
regenerate hydroxyl groups and provide a prod- ly, however, it presents equipment corrosion
uct with the desired level of acetyl substitution issues and safety concerns with respect to the
per anhydroglucose unit on the cellulose back- potential instability of its neutralized salts. Oth-
bone. The level of acetyl substitution is noted as er mineral acids are not acidic enough in the
degree of esterification (degree of substitution, acetic acid-acetic anhydride esterification me-
DS), where the maximum theoretical DS is dia to be effective. Zinc chloride is no longer
three. Other important chemical transforma- used commercially due to the high dosage re-
tions during the preparation of cellulose acetate quired (0.5 – 1.0 parts per part cellulose) and
include sulfation and desulfation of hydroxyl recovery costs.
groups, and molecular weight reduction all as a One major advantage of sulfuric acid is that it
result of the catalytic effect of the predominant immediately absorbs onto the cellulose fiber
acetylation catalyst, sulfuric acid [87]. surface during the cellulose pre-swelling stage
Potential cellulose acetylation reagents in- (pretreatment) prior to acetic anhydride addition.
clude acetic acid, acetyl chloride, ketene, and This pretreatment serves to swell the fiber and
acetic anhydride. Acetic acid reacts very slug- allows for a more uniform catalyst distribution,
gishly with cellulose yielding esters with very which enhances the subsequent reactivity of the
low acetyl content [88], [89]. Use of acetyl cellulose mass. The presence of sulfuric acid
chloride has been investigated in combination during the pretreatment stage also provides a
with catalyst, however, no practical commercial desired level of reduction in chain length through
process has evolved. Ketene, which would pro- catalyzed hydrolysis of the glycosidic linkages of
duce no byproduct, has not been demonstrated the cellulose backbone [94], [95].
commercially as an effective acetylation reagent Upon addition of acetic anhydride (in stoi-
[90]. Only acetic anhydride has achieved com- chiometric excess) to the pretreated cellulose
mercial significance, where three molecules of mass, the sulfuric acid species immediately
acetic anhydride react with three hydroxyl bonds to the cellulose hydroxyl groups to form
groups in each anhydroglucose unit, yielding a cellulose sulfate ester acid intermediate [96],
three molecules of acetic acid byproduct. The [97]. It is further known that sulfuric acid reacts
use of acetic anhydride was first demonstrated in with acetic anhydride to form acetyl sulfuric
1869 by direct reaction with cellulose in a sealed acid, and therefore both sulfuric acid and acetyl
tube at 180
C [91]. This elevated temperature sulfuric acid are believed to play important roles
most probably would have produced a severely during the esterification reaction [98]. The cellu-
degraded product. The discovery of the potential lose sulfate ester acid intermediate reacts with the
benefits of catalyst by FRANCHIMONT in 1879 acetic acid-acetic anhydride medium replacing
eventually led to opportunities to prepare cellu- the sulfate ester group with acetyl. This exother-
lose ester derivatives at lower temperatures with- mic esterification must be balanced with the rate
out excessive degradation [92]. of cellulose chain length reduction, via catalyzed
Vol. 7 Cellulose Esters 355

acetolysis, in order to meet product molecular Table 9. Analytical values obtained from bleached linters according to
[99]
weight requirements.
The acetyl hydrolysis reaction is catalyzed by a-Cellulose 99.7 %
sulfuric acid. It is initiated after the esterification b-Cellulose 0.2 %
reaction has completed by the addition of water g-Cellulose 0.1 %
Carboxyl groups <0.02 %
in excess of the amount needed to react with the Total ash 0.02 %
remaining anhydride. The catalyst and water Degree of polymerization 1000 – 7000
concentrations are usually adjusted to control
the acetyl hydrolysis rate and the level of hydro-
lytic chain length reduction. Upon hydrolysis to siderably. Table 9 shows analytical values of
the desired degree of acetyl substitution, the good linters [99].
catalyst is neutralized with an acetate salt of Wood pulp has become the most used raw
calcium, magnesium, or sodium. material for cellulose acetate manufacture. Both
As a consequence of the catalytic action of softwood (conifer) and hardwood (deciduous)
sulfuric acid, a significant amount of the sulfate pulps can be purified for this purpose. In early
remains chemically bonded to the hydroxyl days of cellulose acetate manufacture, wood pulp
groups on the polymer backbone in the form of could only be used for the manufacture of lower-
combined sulfate ester after the acetylation reac- quality products because of the 90–95 % a-cel-
tion has completed. The major portion of this lulose content. Improvements in sulfite and Kraft
sulfate ester is hydrolytically cleaved during the pulping techniques have allowed for more effi-
water addition. The subsequent hydrolysis reac- cient lignin and hemicellulose removal, provid-
tion also serves to remove additional combined ing pulps with greater than 95 % a-cellulose
sulfate ester groups [96]. content. Typical pulp properties are provided in
Table 16. Higher purity wood pulps have been
available since the 1950s and have steadily re-
2.1.2. Raw Materials placed cotton linters due to cost advantages.
Wood pulp-based cellulose acetates are compa-
Cellulose. Post-process performance require- rable to those produced from linters with respect
ments dictate the use of high purity celluloses for to tensile strength, color, clarity of the solutions,
acetate manufacture. The two major naturally oc- and light and thermal stability.
curring cellulose raw material sources for cellulose
acetate are cotton and wood. Acetic Anhydride. Most manufacturers of
Cotton linters provide an exceptionally high cellulose acetate convert the byproduct acetic
purity raw material with an a-cellulose content of acid to anhydride directly on the premises and
greater than 99 %. After the long layered spin- adjust the concentrations as required for their
nable cotton has been freed of the cotton seed by process, generally between 90 and 95 %.
ginning, the remaining shorter fibers on the seed
pod are usually removed with two cuts before the
seeds go to the oil presses for further processing. 2.1.3. Industrial Processes
The first cut gives about 4 % longer linters rela-
tive to the entire cotton flower, which are pref- Only a few of the proposed industrial processes
erentially processed to medicinal cotton, felt, for the manufacture of cellulose esters have
paper, etc. The second cut gives about 8 % shorter attained industrial significance. Despite the fact
layered linters, which are best suited for further that no two manufacturers use identical process-
chemical processing. es, the following categories can be distinguished:
The raw linters undergo mechanical cleaning
by means of screening, pressure boiling in a 3 – 1. Acetylation in a homogeneous system (solu-
5 % sodium hydroxide solution, and finally ac- tion acetate process)
id–alkaline bleaching. Special care should be Use of glacial acetic acid as a solvent (glacial
taken during drying, since local over-drying of acetic acid process)
cellulose (the water content of which should lie Use of methylene chloride as a solvent (meth-
between 3 and 8 %) impairs the reactivity con- ylene chloride process)
356 Cellulose Esters Vol. 7

2. Acetylation in a heterogeneous system (fiber lose fibers to allow for efficient diffusion of the
acetate process) acetylation chemicals during the subsequent
esterification reaction. A range of swelling
In the solution acetate process, the reaction agents can theoretically be used, including water,
begins heterogeneous in nature with cellulose aliphatic acids, alcohols, amines and 10 % aque-
fibers dispersed in the reactants and solvents. ous sodium hydroxide solution, however, acetic
Upon acetylation to the cellulose triacetate spe- acid is the most commonly used pretreat reagent
cies, the fibers dissolve in the reaction medium to for manufacture of cellulose acetate [94]. Non-
form a homogeneous viscous solution. The dis- acetic acid swelling agents need to be removed
solved cellulose triester can subsequently be by exchange with acetic acid prior to acetylation.
solution hydrolyzed to give the desired level of The cellulose is generally used with a mois-
acetyl and hydroxyl groups in a uniform manner. ture content between 4 and 7 %. The actual
Direct esterification of cellulose to an acetyl level moisture content is heavily dependent on the
lower than the triester has not proven feasible. drying history at the cellulose producer and level
In the fiber acetate process, a cellulose triace- of humidity prior to use. With respect to activa-
tate fiber is formed in the presence of nonsol- tion, the presence of pulp moisture is beneficial,
vents, similar to the nitration of cellulose. This however it reacts with anhydride during the
method does not permit uniform hydrolysis of the esterification reaction, driving up the cost of
acetyl groups. production. Low pulp moistures tend to reduce
A flow diagram of the entire glacial acetic acid the activation effectiveness leading to a sluggish
solution process is shown in Figure 7. esterification reaction.
The ratio of acetic acid to cellulose, activation
2.1.3.1. Pretreatment times, and temperatures are varied based on the
manufacturer’s process. The activation medium
From a traditional chemical perspective, hydrox- can also contain a small portion of sulfuric acid to
yl group esterification and ester hydrolysis ap- further improve the effectiveness of the fiber
pear relatively straightforward, however the un- swelling and to provide time for even distribution
ique morphology of the cellulose fiber presents of the catalyst prior to acetylation. The catalyst
challenges that require unique chemical proces- also imparts a desired degree of cellulose chain
sing techniques. One such step is pretreatment (or length reduction through hydrolysis of the gly-
activation), which involves swelling the cellu- cosidic linkages. The amount of chain length

Figure 7. Flow chart for the production of cellulose esters according to [103] a) Acid reconditioning; b) Acidanhydride;
c) Esterification; d) Hydrolysis; e) Precipitation; f) Washing; g) Centrifuge; h) Drier; i) Evaporator; k) Azeotropic distillation;
l) Cooler; m) Decanter
Vol. 7 Cellulose Esters 357

reduction depends on the temperature, uniformi- the polymer chain actually continues to de-
ty of the catalyst distribution, and amount of crease during this phase. False viscosity is also
water present during this stage. Higher inherent caused by the presence, type, and quantity of
pulp moisture levels retard the rate of chain hemicelluloses in the starting cellulose, which
length reduction via solvation of the strong acid become esterified during acetylation [102]. Un-
catalyst [95]. derstanding the ramifications of false viscosity
during the esterification reaction is important to
2.1.3.2. Esterification providing a final product with the desired mo-
lecular weight.
Acetic Acid Process. The heterogeneous After the reaction solution is free of fibers, the
acetylation mixture consists of glacial acetic reaction is quenched by adding water or dilute
acid, an excess of 10 – 40 % acetic acid anhy- water in acetic acid, which reacts with the excess
dride, the activated cellulose mass, and 2 – 15 % anhydride and provides water for the subsequent
sulfuric acid catalyst based on the cellulose hydrolysis reaction.
weight. The quantities of each component de- Cooled kneaders are suitable reaction vessels
pend on the manufacturer’s acetylation process. in that they allow a rapid and uniform mixture
Upon addition of acetic anhydride and cata- and catalyst distribution through intensive mix-
lyst to the activated cellulose mass, the esterifi- ing, which is important for controlling the reac-
cation reaction initiates with a rapid exothermic tion (Fig. 8).
reaction between water contained in the activated
cellulose and a portion of the acetic anhydride. Methylene Chloride Process. Using meth-
The exothermic esterification reaction then pro- ylene chloride (bp 41
C) as a solvent presents
ceeds in a heterogeneous fashion whereby the several advantages over acetic acid. Because
unesterified and partially esterified cellulose methylene chloride is an excellent solvent for
fibers are dispersed in a semiliquid mass. The cellulose triacetate, lower catalyst concentra-
reaction temperature is controlled by reaction tions (1 % sulfuric acid) are required at higher
vessel cooling and the use of pre-cooled anhy- esterification temperatures. Furthermore, due to
dride and acid. Typical reaction temperatures can its low boiling point, the heat of reaction can be
be up to 50
C. As the fibers esterify to the removed by means of vaporization and return of
cellulose triacetate species, they begin to dis- the cooled methylene chloride. The reaction of
solve in the reaction medium. Upon complete highly viscous solutions can, thus, be better
esterification and dissolution of the fibers, a controlled. Finally, only a half to a third as much
smooth highly viscous solution is formed. A dilute acetic acid must be recycled compared
controlled amount of chain length reduction is with the glacial acetic acid process.
desirable for purposes of solubility in the reaction Table 10 shows typical acetylation recipes for
medium and final product properties. The the glacial acetic acid and methylene chloride
amount of chain length reduction is determined processes. Figure 9 shows a sceme for the pro-
by catalyst level, reaction temperature, reaction duction of cellulose acetate according to the
time, and acid : anhydride ratio [100], [101]. methylene chloride process.
The acetic acid : acetic anhydride reaction Acetylation according to the methylene chlo-
medium is actually a poor solvent for the fully ride process is carried out largely in rotating
substituted triacetylated species. Therefore, the drums (roll vats) or in horizontal containers with
solubilized triacetate species must contain a shovel-like stirrers on both sides. The problem of
small portion of chemically combined sulfate corrosion, which arises during esterification and
ester, which is a reaction intermediate in the especially during hydrolysis, has only been par-
sulfuric acid catalyzed esterification. If the reac- tially solved by using equipment constructed of
tion is allowed to proceed to the fully substituted bronze, high-alloy steels, or plates containing
cellulose triacetate via replacement of the re- metals such as silver, titanium, or tantalum.
maining sulfate ester groups with acetyl groups,
the solution viscosity will increase dramatically Fiber Acetate. Cellulose can be esterified
until the reaction mass becomes gelled. This is maintaining its fiber structure by adding suffi-
known as false viscosity as the molecular mass of cient amounts of nonsolvents during acetylation.
358 Cellulose Esters Vol. 7

Figure 8. Cellulose acetate production by the kneader method according to [104] a) Weighing scale; b) Sprinkling vat;
c) Kneader; d) Mill; e) Rinsing vat; f) Stabilizing vat; g) Bleaching vat; h) Floater; i) Stock pan; k) Centrifuge; l) Dust chamber;
m) Drier

Carbon tetrachloride, benzene, or toluene can be As shown in Figure 10, fiber acetate is pro-
used as nonsolvents [106], [107]. duced by rotation in various directions and at
Temperature and catalyst concentrations are various speeds in a perforated drum enclosed in a
similar to those required for the solution process. metal casing. The shaft of the drum is hollow so
A large amount of nonsolvent is required to keep that liquid may be added during rotation [108].
the loose voluminous cellulose in suspension.
Perchloric acid is preferred over sulfuric acid as 2.1.3.3. Hydrolysis
a catalyst because of the great difficulty in re-
moving the resulting combined sulfuric acid ester The solution esterification process provides a
in this process. solubilized cellulose triacetate species, which
A uniform hydrolysis of the fibrous acetate to can be isolated for commercial use. This cellu-
an acetone-soluble material is not possible in a lose triacetate is also known as primary acetate
heterogeneous system. Therefore, the use of the and has an approximate acetyl DS of 2.9. Com-
fiber acetate process is limited to special applica- mercially, the most common hydrolyzed cellu-
tions, such as the manufacture of foils and films lose acetate product is cellulose diacetate, also
from triacetate. known as secondary acetate. Cellulose diacetate
has an approximate acetyl DS of 2.5.
Table 10. Acetylating preparations according to the glacial acetic acid After the addition of water at the end of
process and the methylene chloride process [104] esterification, the water content is adjusted to the
desired level, generally 5–10%, the concentration
Methylene chloride
Acetic acid process process of which controls the amount of primary versus
secondary hydroxyl groups in the final product
Cellulose 700 kg 3 500 kg
Pretreatment 700 kg glacial 1 200 kg glacial
[109]. Depending on the manufacturer’s process,
acetic acid acetic acid typical hydrolysis temperatures range between 40
Acetylation 1 900 kg anhydride 10 500 kg anhydride and 80
C. The acetyl hydrolysis rate is mostly
4800 kg glacial 14000 kg methylene determined by catalyst concentration and temper-
acetic acid chloride
50 kg sulfuric acid 35 kg sulfuric acid
ature. Higher water concentrations can serve to
prevent excessive chain length reduction [110].
Vol. 7 Cellulose Esters 359

Figure 9. Cellulose acetate production according to the methylene chloride process [105] a) Weighing scale; b) Bale opener;
c) Sprinkling vat; d) Acetylator; e) Precipitating vat; f) Prebreaker; g) Vacuum vessel; h) Pipe cooler; i) Pump for viscous
substances; k) Filter bath; l) Mill; m) Floater; n) Sprinkling line; o) Centrifuge; p) Vacuum shovel drier; q) To reprocessing of
methylene chloride

The course of hydrolysis is constantly moni- former procedure provides flake particles,
tored by checking the solubility of the secondary whereas the latter procedure provides a powder.
acetate. Upon completion of hydrolysis, the sulfu- The morphology of the precipitate is carefully
ric acid catalyst is neutralized with magnesium, controlled by the precipitation conditions, which
sodium, or calcium acetate, which also serves to include the acetic acid concentration, degree of
neutralize the remaining small portion of bonded agitation, and temperature. Proper control of
sulfate on the polymer backbone for stability pur- precipitation conditions provides a particle with
poses during isolation and post-processing steps. an open pore structure, allowing for efficient
removal of the acids and salts in the subsequent
2.1.3.4. Precipitation and Processing water washing operation. The methylene chlo-
ride process requires that the methylene chloride
Isolation of the cellulose acetate from the viscous be completely removed by distillation prior to
hydrolysis solution involves precipitation of the precipitation. The precipitate can be broken
polymer by either pouring the viscous solution down and thoroughly washed, and the resulting
into water, which can also contain a portion of dilute acetic acid can be fed back into the
acetic acid, or by adding a dilute solution of manufacturing cycle.
acetic acid in water to the stirred solution. The Water washing is primarily conducted using
continuous methods based on the countercurrent
principle (Fig. 9). High-quality products for
plastic applications are stabilized and bleached.
The remaining residual combined sulfate can be
removed by either boiling under pressure or
heating in 1% mineral acids during stabilization.
After further rinsing and removal of excess
water by suctioning, centrifugation, pressing, or
by thrust extraction, the product is carefully dried,
preferably in a vacuum shovel drier, to less than 1–
3 % water content. From an efficient process, the
cellulose acetate yield is at least 9 5% of
theoretical.
Manufacturers of cellulose acetate include:
Eastman Chemical Company, United States; Rho-
Figure 10. Acetylation equipment for cellulose triacetate
fibers [104] a) Perforated drum; b) Reaction solution; dia Acetow, Germany; Celanese AG, United
c) Cellulose fibers; d) Cooler for acetylating liquid; e) Acety- States; Acordis, United Kingdom; Daicel Chemi-
lating liquid circulation cal Industries, Ltd., Japan; and Acetati SPA, Italy.
360 Cellulose Esters Vol. 7

2.1.4. Recovery of Reactants

The recovery of the large amount of acetic acid

remaining after product isolation is a critical
factor in minimizing costs, which is crucial for
the profitability of a cellulose acetate process.

Recovery of Acetic Acid. Depending on the

process, 2 – 6 parts of 15 – 25 % dilute acetic
acid per part of cellulose remain after isolation of
the cellulose ester. This acetic acid is recovered
and reprocessed to glacial acetic acid and acetic
acid anhydride. For acetic acid recovery, only
continuous processes consisting of a combina-
tion of extraction and azeotropic distillation are
of practical importance. The dilute acid is ex-
tracted with ethyl acetate in a countercurrent
fashion. This extract is subsequently distilled to
remove azeotropic ethyl acetate-water from the
top of the column, while yielding 99.8 % glacial Figure 11. Solubility of cellulose acetate in various solvents
(abridged according to [116]) * Technical grade
acetic acid from the bottom of the column.

Recovery of Acetic Anhydride. Since only degree of acetyl substitution primarily determines
a portion of the accumulated glacial acetic acid is the solubility and compatibility with solvents,
required for the acetylation process, the remain- plasticizers, softeners, resins, varnishes, etc., and
der must be converted to acetic anhydride. ultimately also influences the mechanical proper-
The ketene process developed by the Wacker ties. With decreasing acetyl content, compatibili-
Co. (! Acetic Anhydride and Mixed Fatty Acid ty with plasticizers and solubility in polar solvents
Anhydrides, Section 1.3.1.1.) can be used [111]. increases, while solubility in nonpolar solvents
Pure, almost anhydrous glacial acetic acid is decreases. Figure 11 shows solvent solubility
continuously vaporized under a vacuum and ranges of acetyl substituted celluloses of industri-
converted to ketene in the presence of small al interest. Also, the span of solubility properties
amounts of the catalyst, triethyl phosphate. Ke- of the full theroretical range of hydrolyzed cellu-
tene proceeds to react with glacial acetic acid to lose acetates is provided in Table 12. This table
form the anhydride (! Acetic Anhydride and also provides the relationship between degree of
Mixed Fatty Acid Anhydrides, Section 1.3.1.2.). esterification (DS), acetyl content, and bound
acetic acid content, which are used interchange-
Recovery of Methylene Chloride. Methy- ably to describe the degree of acetyl substitution
lene chloride can be recovered inexpensively on the polymer backbone.
because its insolubility in water allows for isola- As described previously, the two commercial-
tion in almost pure form from the raw solution ly produced cellulose acetates are cellulose tri-
without further processing steps. acetate (approximate acetyl content of 43.6 %)
and cellulose diacetate (approximate acetyl con-
tent of 39.5 %). Both cellulose acetates are white,
2.1.5. Properties nontoxic, odorless, and tasteless materials, which
are commercially available as a powder or flake.
Properties of cellulose acetates are generally de- They are less flammable than nitrocellulose,
termined by their molecular weight and degree of resistant to weak acids and largely stable to
acetyl substitution. Solution viscosity is used as mineral and fatty oils as well as petroleum.
an indicator for molecular weight, which also Some physical characteristics of cellulose tri-
correlates to the mechanical properties of the acetate and cellulose diacetate are given in
resulting fibers, films, coatings, or plastics. The Table 11.
Vol. 7 Cellulose Esters 361

Table 11. Physical characteristics of cellulose acetate [99], [104], properties. Plasticizers also impart desired
[115]
physical properties in the final product, e.g.
Secondary they increase the flexibility and toughness of
Characteristic Triacetate acetate an otherwise brittle polymer. Common com-
Density, g/cm3 1.27 – 1.29 1.28 – 1.32 patible cellulose diacetate plasticizers include
Thermal stability,
C >240 ca. 230 triacetin, triethyl citrate, diethyl phthalate, and
Tensile strength of fibers, 14 – 25 16 – 18 triphenyl phosphate. Careful plasticizer choice
kg/mm2 is important with respect to permanence in
Tensile strength of foils
longitudinal, kg/mm2 12 – 14 8.5 – 10 long-term applications [112]. Detailed infor-
transverse, kg/mm2 10 – 12 8.5 – 10 mation on solvent solubility and plasticizer
Refractive index of fibers selection can be found in the literature and
toward the fiber axis the manufacturer’s informational brochures
longitudinal 1.469 1.478
transverse 1.472 1.473 [112][113][114].
Double refraction 0.003 þ0.005
Dielectric constant e
50 – 60 Hz 3.0 – 4.5 4.5 – 6.5 2.1.6. Analysis and Quality Control
106 Hz 4.0 – 5.5
Dielectric loss factor tan d
50 – 60 Hz 0.01 – 0.02 0.007 Standard test methods for cellulose acetate can
106 Hz 0.026 be found under ASTM D871–96. The viscosity is
Specific resistance, W  cm 1013 – 1015 1011 – 1013 determined in practice by usual methods. Along
Specific heat, J g1 K1 1.46 – 1.88
Thermal conduction, J m1h1K1 0.63 – 1.25
with the relative viscosity, the measurement of
15 – 20 % solutions according to the ball drop
method corresponding to ASTM D1343–95
Cellulose triacetate is a crystalline polymer (2000) has been generally accepted.
that melts with significant decomposition at tem- The acetyl content is generally determined by
peratures close to 300
C. It has very limited saponification of the ester with 0.5 N-potassium
compatibility with plasticizers, making it im- hydroxide and back-titration of the excess. His-
practical for melt processing, and is soluble in torically, free acids from mixed esters (see Sec-
a very limited number of solvents, the most tion 2.2) are separated from the residue after
commercially important being methylene chlo- saponification by means of distillation or extrac-
ride, which is used for film casting applications. tion and by extraction or azeotropic distillation
Cellulose diacetate is significantly less crys- followed by titration. A comprehensive presen-
talline than cellulose triacetate, is soluble in a tation can be found in [117], [118]. Gas chro-
wider range of solvents, and compatible with a matographic methods are routinely used in the
number of commercially useful plasticizers. The modern era for free acid analysis after saponifi-
most important industrial solvent for cellulose cation and acidification.
diacetate is acetone, which serves as the basis for Determination of the free hydroxyl groups in
the long-standing cellulose acetate fiber business pure cellulose acetate is not necessary, since a
(see Section 2.3). Melt processing applications precise analysis of bound acetic acid is possible.
require use of plasticizers to provide a greater Hydroxyl content can be determined by complete
separation between decomposition and melting esterification with acetic acid anhydride in pyridine
temperatures and to improve thermoplastic flow and back-titration of the excess [119]. The value is

Table 12. Solubility of cellulose acetate at various degrees of esterification [103]

Degree of Bound acetic

esterification Acetyl content, % acid, % Chloroform Acetone 2-Methoxyethanol Water

2.8 – 3.0 43 – 44.8 % 60 – 62.5 % soluble

2.2 – 2.7 37 – 42 % 51 – 59 % soluble
1.2 – 1.8 24 – 32 % 31 – 45 % soluble
0.6 – 0.9 14 – 19 % 1.8 – 2.6 % soluble
<0.6 14 <18 %
362 Cellulose Esters Vol. 7

mostly given as a percentage of the hydroxyl or as and coating applications. In the film area, it has
the hydroxyl value (mg of KOH/g). found utility as a pressure sensitive tape, where
Additional quality control methods for unpro- its transparency, resistance to ‘‘neck-in’’, and
cessed cellulose esters include: determination of ease of tear properties are valued. Other film
temperature stability by heating to 220 – 240
C applications include clear packaging windows,
and evaluation of discoloration and melting be- print protective laminations, and labels. Cellu-
havior, determination of free acid as an indicator lose acetate can be used in reverse osmosis
for the efficacy of the washing process, and applications, where it is film cast to achieve
determination of the ash content as well as clari- desired porosity characteristics for water purifi-
ty, color, and filterability of the solution. cation [123].
Cellulose acetate has been used in coating
applications since the First World War, where
2.1.7. Uses it replaced the more flammable nitrocellulose in
airplane coatings. Acetone is a common coating
Cellulose acetates are used in a broad range of solvent for cellulose acetate and is known for its
commercial applications including the general fast evaporation rate. Other solvents such as
areas of films, fibers, plastics, and coatings. Fiber ethanol and slower evaporating retarder solvents
applications of cellulose triacetate and cellulose are commonly incorporated into the formulation
diacetate are covered in Section 2.3. Plastic to achieve the desired rheological and coated film
applications for cellulose diacetate are described properties [121]. Plasticizers are often added to
in Section 2.4. For commercial purposes, cellu- the coating formulation to control and generate
lose diacetate is simply referred to as cellulose desired film properties including flexibility, elec-
acetate, which will be used when discussing trical characteristics, flammability, moisture re-
applications and uses during the remainder of sistance, and weather resistance. Coating appli-
this text. cations for cellulose acetate include lacquers for
electric insulators, glass, paper/paperboard, re-
Cellulose Triacetate. Cellulose triacetate lease paper, food packaging, plastic, wire, and
has been used as a photographic film base since wood [121].
the 1950s. Cellulose triacetate is solution cast Cellulose acetate manufactured using cGMP
from methylene chloride to provide a clear (current Good Manufacturing Practices) techni-
smooth film that is subsequently coated with ques is utilized in the pharmaceutical area where
photographic film emulsions. Important film it is formulated with the active drug ingredient in
properties of the solvent cast cellulose triacetate osmotic drug and sustained-release systems
include optical isotropy, high clarity, toughness, [122].
scratch and moisture resistance, dimensional In certain environments, cellulose acetate is
stability, and slowness to burn. biodegradable. The biodegradability is strongly
A more recent commercial development for influenced by the degree of acetyl substitution,
cellulose triacetate film has been in the field of morphology, and choice of plasticizer [123].
liquid crystal displays (LCD) for flat panel tele-
visions, computer monitors, laptops, personal
digital assistants, games, automobile navigation 2.2. Cellulose Mixed Esters
screens, view screens on cameras and camcor-
ders, and mobile phones. In this market, cellulose Apart from the cellulose acetate, cellulose mixed
triacetate serves to protect the polarizing films in esters of acetic and propionic acid, cellulose
the display, while maintaining permeability be- acetate propionate [9004-39-1], or acetic and
cause of its inherent high moisture vapor trans- butyric acid, cellulose acetate butyrate [9004-
mission rate [120]. 36-8], are the only other cellulose esters that have
attained any notable importance. Pure cellulose
Cellulose Diacetate. Cellulose acetate’s in- propionates [9004-48-2] and cellulose butyrates
creased compatibility with common solvents and [9015-12-7] can also be prepared.
plasticizers versus cellulose triacetate allows it to Cellulose esters of higher acids such as
be utilized in a wider range of commercial film isobutyrates, valerates, caprolates, laureates,
Vol. 7 Cellulose Esters 363

palmitates, etc., have been prepared, although cation medium as well as in the subsequent
they are difficult to produce and generally require hydrolysis reaction.
unique commercially nonviable techniques Whereas pure cellulose acetates are charac-
[124], [125]. The anhydrides of these acids react terized by their viscosity and acetyl content,
sluggishly with activated cellulose due to their mixed esters require data on the individual acids
high degree of steric hindrance. Esters of unsat- and possibly free hydroxyl groups. Standard test
urated acids and dicarboxylic acids have attained methods for cellulose butyrates and propionates
no industrial importance [4]. can be found in ASTM D817–96.
Cellulose acetate propionates and cellulose
acetate butyrates are manufactured by Eastman
2.2.1. Production Chemical Company in the United States.

With respect to the chemistry and processing, the

basic description given in Section 2.1) for cellu- 2.2.3. Properties
lose acetate is also applicable to mixed cellulose
esters, which similarly uses cotton linters and The properties of mixed esters are determined by
highly purified wood pulp as the cellulose raw their molecular weight, molecular weight distri-
material. Mixed ester manufacture uses the bution, degree of substitution of acetyl, butyryl
homogeneous solution process exclusively (see (or propionyl), and hydroxyl content [126]. A
Section 2.1.3). The esterification chemicals con- wide range of properties is achievable based on
sist of a mixture of anhydrides of acetic acid and the composition of the polymer.
propionic acid or of acetic acid and butyric acid As the degree of substitution changes, the
with sulfuric acid used as the catalyst. properties of cellulose mixed esters vary over
In comparison to preparation of cellulose a wide range from pure acetates to pure butyrates,
acetate, more effective pre-swelling of the cellu- with the propionates occupying a property-pro-
lose fiber is desirable for the production of cellu- file position between the cellulose mixed esters
lose mixed esters as propionic and butyric acids and pure acetates. For example, if one considers
and their anhydrides are slower to penetrate the the mixing range from pure cellulose acetate
fiber during the esterification reaction, and the through the various mixing ratios to pure cellu-
catalyst is less readily absorbed. The reactivity of lose butyrate for cellulose acetate butyrates (the
aliphatic fatty anhydrides decreases very rapidly degree of esterification is adjusted in such a way
as the chain length increases. Therefore, the that the esters in pure cellulose acetate contain
reaction temperature strategies for mixed esters 44.8 % acetyl and those in pure cellulose butyrate
are somewhat different than in the case of cellu- contain 57.3 % butyryl groups), then the density
lose acetate, especially to avoid excessive cellu- varies from ca. 1.32 (cellulose acetate) to 1.16
lose chain length reduction during esterification. (cellulose butyrate). Similarly, the melting
Mixed esters consisting of propionic acid and point ranges from ca. 300
C (cellulose acetate)
butyric acid or acetic acid, propionic acid and to 160
C (cellulose butyrate), while the water
butyric acid are not produced on an industrial absorption at 90 % relative humidity varies be-
scale. tween ca.12 % (cellulose acetate) and 1.5 % (cel-
lulose butyrate). Tensile strength, hardness, and
stiffness increase with higher acetyl contents,
2.2.2. Composition while flexibility increases with higher butyryl
content. In general, the glass transition tempera-
Cellulose acetate butyrates and propionates can ture decreases with increased butyryl content.
be produced in a wide range of butyryl (or Solubility in ketones, esters, alcohols, glycol
propionyl), acetyl, and hydroxyl contents, as well ethers, and glycol ether-esters solvents varies over
as a broad range of molecular weights. The ester a wide range with the range of usable solvents
composition is carefully controlled in the generally increasing with higher butyryl content
manufacturing process by the ratio of butyryl (or [128], [114]. The range of usable plasticizers also
propionyl) to acetyl components in the esterifi- increases with higher butyryl content.
364 Cellulose Esters Vol. 7

Table 13. Characteristic data of Eastman cellulose acetate propionate [114]

CAP-482-20 CAP-482-0.5 CAP-504-0.2

Acetyl content, % 2.5 2.5 0.6

Propionyl content, % 46 45.0 42.5
Hydroxyl content, % 1.8 2.6 5.0
Viscosity-ASTM D817 formula A and D1343, (s/poise) 20/76 0.40/1.52 0.20/0.76
Melting range,
C 188 – 210 188 – 210 188 – 210
Glass transition temperature,
C 147 142 159

Commercial cellulose acetate butyrates have 2.2.5. Uses

acetyl contents from 2.0 to 29.5 % and butyryl
contents from 17 % to 55 %. For commercial Mixed cellulose esters are compatible with a
cellulose acetate propionates, the acetyl content wider range of plasticizers, soluble in a wider
varies from 0.6 % to 2.5 %, and the propionyl range of solvents, and compatible with a wider
content from 42.5 to 46.0 %. There are many range of resins than cellulose acetate. The ability
more grades of cellulose acetate butyrate avail- to modify and control polymer structure includ-
able than cellulose acetate propionate [114]. ing acyl content (butyryl, propionyl, or acetyl),
Examples of cellulose acetate propionate and hydroxyl content, molecular weight and molec-
cellulose acetate butyrate grades are given in ular weight distribution allows one to ‘‘dial-in’’
Tables 13 and 14 respectively. specific properties to meet unique requirements
in a broad range of applications. Many commer-
cial uses have required the development of a
2.2.4. Other Organic Mixed Esters special grade to meet the unique performance
requirements of a particular application.
Cellulose acetate phthalates [9004-38-0] are cellu- Mixed esters based on cellulose acetate buty-
lose mixed esters prepared from hydrolyzed cellu- rate and cellulose acetate propionate are used in
lose acetate and phthalic anhydride providing a the production of molding plastics covered in
carboxy-functionalized cellulosic [130], [131]. Section 2.4.
Cellulose acetate phthalate (C–A–P) is utilized in
the controlled release market as an enteric coating Films. Cellulose acetate butyrate and cellu-
for delivery of pharmaceutic. It is applied as a thin lose acetate propionate can be solvent-cast into
film to a tablet formulation, which allows for a clear smooth films. The range of useable solvents
slow rate of disintegration in the stomach and a fast is much greater for mixed esters than for cellu-
rate of disintegration in the small intestine, where lose acetates [114]. Cellulose acetate propionate
the active is released for absorption into the blood and cellulose acetate butyrate can be cast from
stream. Plasticizers are often incorporated to im- many common ketone, ether, and ester ester
prove the toughness of the coating to protect the solvents. Both cellulose esters have been histori-
tablet during the manufacturing process and time cally used as a base for photographic films. More
prior to use [123]. This product can also be used as recent applications of cellulose acetate butyrate
a water- or alkali-soluble textile auxiliary and an film include polarizing films in sunglasses and
antistatic agent in film coating. privacy films for computer screens, which limits

Table 14. Characteristic data of selected Eastman cellulose acetate butyrate [114]

CAB-171-15 CAB-381-20 CAB-381-0.5 CAB-500-5 CAB-551-0.2

Acetyl content, % 29.5 13.5 13.5 4.0 2.0

Butyryl content, % 17.0 37 38.0 51.0 52.0
Hydroxyl content, % 1.1 1.8 1.3 1.0 1.8
Viscosity-ASTM D817 formula A and D1343, (s/poise) 15/57 20/76 0.50/1.90 5/19 0.20/0.76
Melting range,
C 230 – 240 195 – 205 155 – 165 165 – 175 130 – 140
Glass transition temperature,
C 161 141 130 96 101
Vol. 7 Cellulose Esters 365

the viewing angle of the automatic teller bank specific heat and thermal conductivity), dimen-
machines. Like cellulose acetates, cellulose ace- sional stability, low temperature impact strength,
tate butryate can be used as an electrical insulat- and color stability upon exposure to UV light are
ing film. important features provided by mixed esters
[114].
Surface Coatings. Mixed cellulose ester Cellulose acetate butyrates are used in con-
lacquers, with their excellent lightfastness, gloss, junction with other coating resins such as ther-
low combustibility, and good thermal stability, moplastic or thermosetting acrylics, polyesters,
coupled with their indifference to hydrocarbons, phenolic, melamine, alkyd, crosslinking urea-
oils, and greases, quickly became established in formaldehyde, and polyisocyanates imparting
numerous coating applications upon their devel- many of their desired performance benefits
opment in the 1930’s. Mixed cellulose esters are described above.
particularly characterized by lower water absorp- Like cellulose acetate (Section 2.1.7), cellu-
tion, good compatibility with extenders, and in lose acetate butyrate can be manufactured using
the case of the low-viscosity grades, also allow ‘‘cGMP’’ practices for use in sustained release of
the production of high-solid lacquers. pharmaceutical actives in tablet formulations
Of the two categories of mixed esters, cellu- [122].
lose acetate butyrates are predominant in com- Carboxymethyl cellulose acetate butyrate
mercial coating applications. A wide range of (CMCAB) is relatively new mixed ether-ester,
cellulose acetate butyrate compositions are man- which is produced by the esterification of car-
ufactured ranging from a very high to a low boxymethyl cellulose [132]. It has found utility in
butyryl : acetyl ratio, from low to high molecular the water-borne coatings area. This new cellulose
weights, and a broad range of hydroxyl content ester imparts several of the beneficial features of
[114]. Cellulose acetate butyrate with lower bu- cellulose acetate butyrate to water-based coating
tyryl content provides coatings with increased systems [133].
hardness and toughness compared to coatings
with higher butyryl content. Higher butyryl esters
provide softer and more flexible coatings. In- 2.3. Cellulose Acetate Fibers
creasing the hydroxyl content provides increased
solubility in alcohols, hardness, and reactivity Cellulose acetate is the most important cellulose
with cross-linking agents. Higher molecular ester. It is primarily used for textile yarn and
weight esters provide greater toughness and cigarette filter tow. The cellulose acetate is usu-
better mechanical properties in the final coated ally dissolved in a suitable organic solvent and
film, while lower molecular weight esters allow spun by dry spinning (! Fibers, 3. General
for higher solids concentration of the coating Production Technology). Secondary (2.5) ace-
formulation. tate with an acetic acid content of 54 – 56 % is
Mixed esters can be used as the major film normally used, whereas only a small amount of
former, as a modifying resin, or as an additive in a cellulose triacetate is normally produced.
range of coating applications. Mixed esters are
utilized in a wide variety of applications includ-
ing protective and decorative coating systems for 2.3.1. Properties
wood, plastic, metal, glass, leather, cloth, and
paper/paperboard. They are also used in printing The viscosity and the filterability of the spinning
inks, nail care, hot melts, and adhesives. Benefits solution (spinning dope) are particularly impor-
of cellulose esters include reduced drying time, tant in the production of cellulose acetate fibers.
improved flow and leveling, reduced cratering, The spinning dope has a high viscosity, which
sag control, color control, improved sprayability, depends on the degree of polymerization. The
viscosity control, redissolve resistance, metal strength and stretch properties of the fibers also
flake control, pigment dispersibility, reduced depend on the concentration and the degree of
blocking, solvent craze resistance, polishability, polymerization as well as on the distribution of
and gloss control. Other desirable properties such the acetate groups along the cellulose chain.
as weatherability, good feel (due to their low Because the fibers are produced by extruding the
366 Cellulose Esters Vol. 7

Table 15. Physical properties of acetate fibers and tow [134] Table 16. Typical properties of acetate wood pulps

Secondary Triacetate Sulfite softwood Sulfate hard-wood

acetate Characteristica pulp (conifer) pulp (deciduous)

Strength, cN/dtex 1.0 – 1.5 1.0 – 1.5 R10, % 95 96

Stretch, % 25 – 30 25 – 30 R18, % 97 98
Density, g/cm3 1.33 1.30 Ash, % 0.08 0.08
Moisture uptake, % (65 % Silica, % 0.001 0.003
relative humidity, 20
C) 6 – 6.5 4 – 4.5 Calcium, % 0.006 0.008
Water retention capability, % 25 – 28 16 – 17 Pentosans, % 1.2 1.2
Melting point,
C 225 – 250 decom- Moisture content, % 6.5 6.5
position Apparent density, g/cm3 0.45 0.5
at 310 – 315 DP 2300 1700
DP 300 300 a
R10 and R18 are residues in 10 or 18 % sodium hydroxide at 20
C
[135]

spinning dope through minute spinneret holes, the sulfite pulping process with hot alkali extrac-
insoluble particles must first be removed from the tion or by the prehydrolyzed sulfate (Kraft)
spinning dope by filtration. These particles are process with cold caustic extraction (! Pulp).
primarily composed of very small, incompletely The lignins and hemicelluloses are removed from
acetylated cellulose fibers or gels, which can the wood to give wood pulps with an a-cellulose
obstruct the spinneret holes. content of over 96 % (Table 16). High-purity
Secondary acetate and triacetate fibers have cotton linters are no longer used in the production
similar physical properties (Table 15). Their of cellulose acetate fibers for economic reasons.
densities are lower than that of viscose rayon For the production of high-quality cellulose
fibers and equal to that of wool. For textile yarns, acetate fibers the wood pulp must have good
the fibers should be as free of color as possible. swelling properties for uniform accessibility of
The chemical reactions of cellulose acetate the cellulose to the catalyst and the acetylation
are similar to those of organic esters. Cellulose agent and a uniform reactivity. In addition, it
acetate is hydrolyzed by strong acids and alkali; it must produce a spinning solution without fibers
is sensitive to strong oxidizing agents but not and gels which can easily be filtered.
affected by hypochlorite or peroxide solutions.
Acetate fibers cannot be dyed under the same
conditions as viscose rayon fibers because their 2.3.3. Production
swelling properties are different. Acetate fibers
can only be dyed with water-disperse dyes at the The general points discussed in Section 2.2.5 for
boiling point of the medium usually in the pres- the production of cellulose acetate also apply
ence of carriers (! Textile Auxiliaries, 5. Dye- here. The sulfuric acid catalyst initially forms the
ing Auxiliaries). The carriers promote fiber cellulose sulfate ester. The sulfate groups are then
swelling and enhance dye uptake by the fibers. replaced by acetyl groups as the acetylation pro-
The dyeing process coupled with the textile ceeds. The sulfate ester contents is further reduced
spinning operation assures color fastness. Triac- in the hydrolysis stage. However, any sulfate ester
etate fibers have better wash-and-wear properties groups remaining at the end of the hydrolysis
than secondary acetate because of better dimen- stage must be neutralized with an appropriate
sional stability and higher crease resistance. stabilizer, e.g., magnesium salts [136], [137]. Any
‘‘free’’ sulfate ester groups will affect the stability
of the acetate because under the influence of heat
2.3.2. Raw Materials and humidity they splitt off as sulfuric acid and
degrade the fiber [138].
Wood pulp produced from various softwood For secondary acetate spinning, acetone is
(conifer) or hardwood (deciduous) species is the used as the solvent. For triacetate, the solvent is
cellulose source for the production of cellulose 90 % dichloromethane and 10 % methanol or
acetate fibers. The wood pulps are produced by acetic acid (wet-spinning process). The viscosity
Vol. 7 Cellulose Esters 367

of the spinning solution with a cellulose acetate polymer, it is expected to find application for
concentration of 20 – 30 % is between 300 and other uses in the future.
500 Pa s at 45 – 55
C. The spinning dope is
filtered in one or more steps and is then deaerated
in large vessels. 2.3.5. Economic Aspects
Dry spinning is used almost exclusively;
wet spinning is occasionally used for triacetate Secondary acetate and triacetate fibers for tex-
only. The spinnerets for textile filament have tiles and filter cigarette tow accout for 80 % of all
between 20 and 100 holes and those for tow up cellulose ester production. The balance is used
to 1000. The fibers are formed by evaporating for plastics and film. Secondary acetate and
the solvent with a countercurrent of air at triacetate textile fibers have a small share (about
80 – 100
C in a 4- to 6-m spinning column. 1 %) of all textile fiber production.
The fibers are then stretched while still plastic In the late 1990s synthetic fiber production
to increase their strength. Melt spinning of continued to expand (Table 17), whereas the
cellulose acetate or triacetate has no commer- acetate production was stable at about 850 000
cial importance due to the limited heat stabili- t/a. The acetate fiber production decreased slight-
ty at the melting point. ly compensated by a slight increase in filter tow
A core-skin structure is formed in triacetate production. The five largest manufactures of
fibers. The acetyl groups are distributed very filter tow are Hoechst-Celanese and Eastman
regularly in cellulose triacetate compared to Chemicals in the United States, Rhodia Acetow
secondary acetate; therefore, crystallization in Germany, Daicel in Japan, and Acordis in the
occurs when triacetate fibers are heated at United Kingdom.
180 – 200
C (heat setting) [134], [138], [139].
This heat treatment, which enhances the wash-
and-wear properties of triacetate textiles, re- 2.4. Cellulose Ester Molding
quires several minutes at 180
C or several sec- Compounds
onds at 220
C. Heating for shorter periods is not
effective and longer heating periods lead to Cellulose esters represent a category of plastics
deterioration of the mechanical properties of the that are derived from a natural, renewable, and
textile. Heat-setting reduces water retention to sustainable resource, cellulose. In the category
10 % and water absorption to 2.5 %. ‘‘plastics made from natural materials’’, thermo-
plastics based on cellulose acetate or cellulose
mixed esters remain an important category of
2.3.4. Uses commercial plastics [142], [143]. As early as
1920, A. EICHENGR€uN developed thermoplastic
By blending and twisting of cellulose acetate or cellulose ester molding compounds as a spraying
triacetate fibers with nylon or polyester a combi- and molding powder. Cellulose acetate and
nation of properties is achieved that make them mixed esters are used in injection molding
suitable for different end uses in linings. In this and extrusion; mixed esters are also used for
way the weaker physical properties of acetate fluidized-bed dip coating and rotational molding.
fibers can be compensated for while maintaining
the positive characteristics, for instance, the high
moisture absorption and the silk-like softness. Table 17. Worldwide production of textile fibers (1000 t) [141]
Due to the unique hydrophobic – hydrophil-
Fiber 1993 1995
ic properties, semipermeable membranes made
from cellulose acetate fibers have a remarkable Man-made fibers a
19781 21741
potential in desalination (reverse osmosis) of Synthetics 16652 18471
Cellulosics 3129 3270
water. Cotton 18494 18602
Cellulose acetate hollow fibers are also suit- Wool 1687 1767
able for gas separation and hemodialysis [140]. Silk 68 92
For cellulose acetate is non-toxic, biodegrad- a
Excl. polyolefin fibers, textile glass fibers, and acetate cigarette
able and the raw material is a renewable natural filter tow.
368 Cellulose Esters Vol. 7

The use of inorganic cellulose esters (see

Section 1.3.7) is continually decreasing in the
plastics sector because of high flammability
properties.

2.4.1. Physical Properties of Cellulose

Ester Plastics

By themselves, cellulose esters have melting

points close to their thermal decomposition tem- Figure 12. Density of cellulose acetate (CA), cellulose ace-
perature and therefore undergo excessive degra- tate propionate (CP), and cellulose acetate butyrate (CAB) as
dation upon melt processing. Addition of a com- a function of the plasticizer content (determined in accor-
patible plasticizer reduces the melting range of dance with DIN 53479 or ISO/R 1183)
the cellulose ester, resulting in an easily melt
processable polymer. The plasticizer not only The indices (e.g. CAB10) give the plasticizer
significantly improves the melt processability, it content in percent by weight.
also modifies the properties of the polymer to
give a softer, tougher, and more flexible plastic Table 18 shows the electrical properties of
when compared to the cellulose ester itself. medium-hardness cellulose ester molding com-
Common plasticizers for cellulose esters are pounds; their shear moduli and damping proper-
listed in Section 2.4.4. ties are given in Figure 23. Figure 24 shows the
The individual cellulose esters generally differ position of the damping maxima as a function of
in their mechanical properties and compatibility the plasticizer content.
with plasticizers. Mixed esters are compatible Long-term properties derived from the tensile
with a wider range of plasticizers than cellulose creep test are shown in Figures 25–29. Time-to-
acetate. As a rule, mixed ester molding com- failure curves, modulus of creep curves and
pounds have plasticizer loadings ranging from isochronous stress – strain curves of slightly and
3 – 25 %, whereas cellulose acetate molding highly plasticized grades of cellulose acetates,
compounds generally contain 15 – 35 % plasti- cellulose acetate propionates, and cellulose ace-
cizer. Cellulosic plastic properties vary with ester tate butyrates are given here.
composition as well as choice and level of plasti- Figure 30 shows results of the dynamic fatigue
cizer, resulting in a broad range of conceivable test in the tensile pulsating range on a medium-
physical properties. Lower plasticizer levels pro- plasticity cellulose acetate, a slightly plasticized
vide a harder surface, greater rigidity, higher heat cellulose acetate propionate, and a medium-
distortion temperature, higher tensile strength, plasticity cellulose acetate butyrate.
and better dimensional stability. Impact strength,
extensibility, and softness are increased at higher
plasticizer levels. Figures 12,13, 14, 15, 16, 17,
18, 19, 20, 21, 22 show the physical properties as a
function of the plasticizer content; the property
levels may vary by as much as 15 – 20 % in either
direction, depending on the type of plasticizer and
the relative viscosity of the cellulose ester. In all
of the diagrams and tables featured here, the
abbreviations used are as follows:
CA ¼ Cellulose acetate molding compound
(acetic acid content approximately 39 %)
CP ¼ (CAP) Cellulose acetate propionate Figure 13. Tensile strength at yield ss and elongation es of
cellulose acetate, cellulose acetate propionate, and cellulose
molding compound acetate butyrate as a function of the plasticizer content
CAB ¼ Cellulose acetate butyrate molding (determined in accordance with DIN 53455 or ISO/R 527;
compound specimen no. 3, rate of deformation 25 mm/min)
Vol. 7 Cellulose Esters 369

Figure 14. Tensile strength at break sR and elongation eR of

cellulose acetate, cellulose acetate propionate, and cellulose
acetate butyrate as a function of the plasticizer content
(determined in accordance with DIN 53455 or ISO/R 527;
specimen no. 3, rate of deformation 25 mm/min) Figure 16. Flexural stress at a given strain sbG of cellulose
acetate, cellulose acetate propionate, and cellulose acetate
butyrate as a function of the plasticizer content (determined in
Figure 31 shows results of the alternating bend- accordance with DIN 53452 or ISO/R 178; test specimen
ing test on slightly and highly plasticized cellulose 4  10  80 mm, rate of deformation 2 mm/min)
acetate, cellulose acetate propionate, and cellulose
acetate butyrate molding compounds. ‘‘repolishing’’ effect to the material, which
Thermoplastic cellulose ester plastics are means that scratches disappear as the object is
generally characterized by optical clarity, high used. The relatively low modulus of elasticity
mechanical strength, chemical resistance, and gives excellent damping of vibrations, so that
toughness. One particularly noteworthy feature the acoustical behavior is not affected by an-
is that the material reacts to mechanical stresses noying resonance or ambient noise.
by exhibiting cold flow, which helps to elimi- Mixed esters absorb considerably less water
nate problems with insert molding of metal parts than cellulose acetates, allowing parts produced
(e.g., stress cracking). Light-stable material is from mixed esters to retain their dimensional
available in a wide range of transparent, trans- stability even in humid climates. Cellulose ace-
lucent, and opaque colors and shades. High tate butyrates and (with certain restrictions)
surface gloss coupled with antistatic properties cellulose acetate propionates can also be treated
(i.e., electrical charges disperse rapidly, not with UV inhibitors to ensure serviceability of
allowing annoying dust patterns to form) en- the moldings during years of outdoor exposure
sures that moldings retain their attractive [144]. In principle, cellulose ester molding
appearance for years. High surface elasticity compounds can be reinforced with glass fibers
ensures a good ‘‘natural feel’’ and imparts a [146].

Figure 15. Tensile modulus of cellulose acetate, cellulose Figure 17. Notched impact strength ak of cellulose acetate,
acetate propionate, and cellulose acetate butyrate as a func- cellulose acetate propionate, and cellulose acetate butyrate as
tion of the plasticizer content (determined in accordance with a function of the plasticizer content (determined in accor-
DIN 53455 or ISO/R 527) dance with DIN 53453 or ISO/R 179; specimen no. 2)
370 Cellulose Esters Vol. 7

Figure 20. Vicat softening temperature VST/B50 of cellulose

acetate, cellulose acetate propionate, and cellulose acetate
butyrate as a function of the plasticizer content (determined
in accordance with DIN 53460/B or ISO/R 306; sheet 10  10
Figure 18. Izod notched impact strength of cellulose acetate,  4 mm)
cellulose acetate propionate, and cellulose acetate butyrate as
a function of the plasticizer content (determined in accor-
dance with ASTM D 256, Method A, or ISO/R 180; test
specimen 63.5  12.7  3.2 mm)

2.4.2. Polymer Modified Cellulose Mixed

Esters

Historically, cellulose acetate butyrates and cel-

lulose acetate propionates have been formulated
with polymeric modifiers such as ethylene-vinyl
acetate, which provided advantages in heat dis-
tortion temperature, creep behavior, stiffness,
delayed crazing from long-term outdoor expo- Figure 21. Heat distortion temperature FISO of cellulose
sure and freedom from potential plasticizer mi- acetate, cellulose acetate propionate, and cellulose acetate
gration [150], [151], [152]. These formulations butyrate as a function of the plasticizer content (determined in
are no longer commercial available upon Bayer accordance with ASTM D 648, ISO/R 75, or DIN 53461; test
specimen 12.7  12.7  120 mm)
exiting the mixed ester business in the 1980s.

Figure 19. Rockwell hardness (R scale) of cellulose acetate, Figure 22. Melt flow index of cellulose acetate, cellulose
cellulose acetate propionate, and cellulose acetate butyrate as acetate propionate, and cellulose acetate butyrate as a func-
a function of the plasticizer content (determined in accor- tion of the plasticizer content (determined in accordance with
dance with ASTM D 785) DIN 53735 or ISO/R 1133)
Vol. 7 Cellulose Esters 371

Table 18. Electrical properties of organic cellulose ester molding compounds

Cellulose Cellulose acetate Cellulose acetate

Type of test Unit Test specification Specimen acetate [164] propionate [151] butyrate [151]

Dielectric strength Ed
(50 Hz, 0.5 kV/s)
dry VDE 0303 Circular 315 355 350
4 days at 80 % rel. humidity kV/cm Pt. 2, discs 95 mm Ø 290 330 330
24 h water immersion DIN 53481  1 mm 280 330 330
Surface resistance R0
dry VDE 0303 8  1013 2  1014 9  1013
4 days at 80 % rel. humidity W Pt. 3, 150  15  4 mm 3  1012 1  1013 9  1012
24 h water immersion DIN 53482 4  1011 5  1012 9  1012
Insulation resistance Ra
dry VDE 0303 5  1015 5  1015 5  1015
4 days at 80 % rel. humidity W Pt. 3, 150  5  4 mm 1  1013 6  1013 5  1013
24 h water immersion DIN 53482 7  1011 2  1013 2  1013
Volume resistivity rD
dry W/cm VDE 0303 Circular 2  1015 1  1016 4  1015
4 days at 80 % rel. humidity Pt. 3, discs 95 mm Ø 2  1012 5  1013 6  1013
24 h water immersion DIN 53482  1 mm 2  1011 1  1013 2  1013

Relative permittivity er, dry

at 50 Hz VDE 0303 Circular 5.1 4.1 4.0
at 800 Hz Pt. 4, discs 95 and 4.0 3.9 3.8
at 1 MHz DIN 53483 80 mm Ø  1 mm 4.1 3.6 3.4

Dissipation factor tan d, dry

at 50 Hz VDE 0303 Circular 0.009 0.005 0.006
at 800 Hz Pt. 4 discs 95 and 0.019 0.011 0.012
at 1 MHz DIN 53483 80 mm Ø  1 mm 0.050 0.026 0.028

Tracking resistance VDE 030

KB method Pt. 1/9.64
Test solution A DIN 53480/6 20  15 mm >600 >600 >600

2.4.3. Chemical Properties Cellulose acetate propionate molding compounds,

45 % propionyl acid content
Thermoplastic cellulosic plastics have good 2.5 % acetyl content
resistance to chemically induced stress cracking
Cellulose acetate butyrate molding compounds,
by typical household, industrial, and medical
37 % butyryl content
chemicals. They show good resistance to com-
13.5 % acetyl content
mon everyday chemicals including toothpaste
flavorants, aliphatic hydrocarbons, grease, oil, Cellulose acetate molding compounds,
bleach/soaps, ethylene glycol, salt solutions, approximately 39.5 % acetyl content
vegetable and mineral oils, and alcohols [147], approximately 37.0 – 38.4 % acetyl (for
[148]. Table 19 provides guide values for resis- block acetate only [149])
tance to a range of substances, but thorough
practical tests are recommended in each case. Of the large number of plasticizers that are
compatible with cellulose esters [6], the follow-
ing have acquired industrial significance, either
2.4.4. Raw Materials alone or in combination:

Typical cellulose ester compositions with respect For cellulose acetate propionates and cellulose
to acetyl, propionyl and butyryl content for pro- acetate butyrates:
duction of cellulose ester molding compounds di-2-ethylhexyl phthalate, dibutyl adipate, di-2-
are as follows: ethylhexyl adipate, dibutyl azelate and dibutyl
372 Cellulose Esters Vol. 7

Figure 23. Shear modulus G0 and damping tan s of cellulose

acetate22, cellulose acetate propionate10, and cellulose ace-
tate butyrate10 (determined in accordance with DIN 53445 or
ISO/R 537)

sebacate, dioctyl azelate, dioctyl sebacate,

palmitates, stearates, etc.
For cellulose acetates: Figure 25. Tensile creep strength sB/t of cellulose acetate,
dimethyl, diethyl, dibutyl, di-2-ethylhexyl, and cellulose acetate propionate, and cellulose acetate butyrate
(determined in accordance with DIN 53444 or ISO/R 899; test
di-2-methoxyethyl phthalate; triphenyl and specimen no. 3)
trichloroethyl phosphate, triacetin, and triethyl
citrates.
Processing auxiliaries for cellulose ester
The stabilizers and antioxidants used for cellu- molding compounds include zinc stearate, butyl
lose ester molding compounds include: alkali salts stearate, and paraffin oil.
and alkaline-earth salts of sulfuric, acetic, and Numerous combinations of dyes can be used
carbonic acid, tartaric acid, oxalic acid, citric acid, for coloring cellulose ester molding compounds
higher molecular mass epoxides, and phenolic [155]. The following groups of dyes have proven
antioxidants. In special cases these stabilizers and successful in practice: alkaline, acid, and sub-
antioxidants can be complemented by others [153]. stantive dyes (provided they are sufficiently sol-
From the range of ultraviolet absorbers avail- uble in the solvent); Zapon, Sudan, and Ceres
able, various benzophenones, benzotriazoles,
salicylates, and benzoates are recommended for
organic cellulose ester molding compounds
[154].

Figure 26. Creep rupture strength sB103 of cellulose acetate

Figure 24. Temperature of the damping maxima of cellulose butyrate at 23
C, 80
C, and 100
C as a function of the
acetate, cellulose acetate propionate, and cellulose acetate plasticizer content (determined in accordance with DIN
butyrate as a function of the plasticizer content 53444 or ISO/R 899)
Vol. 7 Cellulose Esters 373

Figure 29. Isochronous stress – strain curves of cellulose

acetate, cellulose acetate propionate, and cellulose acetate
butyrate for 1000 h (determined in accordance with DIN
53444 or ISO/R 899)

2.4.5. Production

Cellulose acetates, cellulose acetate propionates,

and cellulose acetate butyrates are formulated
with plasticizers, stabilizers, antioxidants, dyes,
and sometimes ultraviolet absorbers and proces-
Figure 27. Creep modulus Ec/t of cellulose acetate, cellulose
sing aids, utilizing thorough mixing at room
acetate propionate, and cellulose acetate butyrate (determined temperature. Plastification and homogenization
in accordance with DIN 53444 or ISO/R 899) are carried out at higher temperatures (between
150 and 210
C, depending on the type and the
dyes (provided they are sufficiently resistant to degree of plasticization) in single- or twin-screw
sublimation); and organic and inorganic kneaders or roll mills. Depending on the type of
pigments. equipment used, this results in granules in the
form of pellets (bulk density 500 – 620 g/L) or
cubes (bulk density 400 – 470 g/L).
No wastewater or waste gas problems are
associated with the production of thermoplastic

Figure 30. Dynamic fatigue test in the range of pulsating

Figure 28. Isochronous stress – strain curves of cellulose tensile stresses (number of load cycles) of cellulose acetate22,
acetate, cellulose acetate propionate, and cellulose acetate cellulose acetate propionate5, and cellulose acetate butyrate10
butyrate for 1 h (determined in accordance with DIN 53444 or (determined in accordance with DIN 50100; stress amplitude
ISO/R 899)  sa (N ¼ 1) means stress amplitude under initial loading)
374 Cellulose Esters Vol. 7

compounds are dependent on the molecular

weight properties of the cellulosic polymer as
well as the plasticizer selection and content. With
respect to cellulose acetate the following tests are
all standardized: determination of the viscosity
and viscosity ratio in a dilute solution [156],
determination of the insoluble constituents
[157], viscosity loss during molding [158], light
absorption before and after heating [159], and
determination of constituents extractable with
ethyl ether [160]. The methods described for
cellulose acetate are similarly applicable to cel-
lulose mixed esters.
The manufacturers also carry out numerous
Figure 31. Dynamic fatigue test in the range of alternating in-house tests during the course of their quality
flexural stresses (number of load cycles) of cellulose acetate, control programs. These tests include determi-
cellulose acetate propionate, and cellulose acetate butyrate nation of mechanical data, testing of purity,
(determined in accordance with DIN 50100; stress amplitude checking thermal stability, colorimetry, determi-
 sa (N ¼ 1) means stress amplitude under initial loading)
nation of flow properties (melt index, Brabender,
extrusiometer), etc.
cellulose ester molding compounds. The inevitable In Germany, cellulose ester molding com-
plasticizer vapors that occur during processing pounds are standardized in accordance with DIN
should be removed by exhaust ventilation. 7742, Parts 1 and 2. In the United States, stan-
dardization is in accordance with ASTM D 706–
98 (cellulose acetate), D 707–98 (cellulose ace-
2.4.6. Trade Names tate butyrate), and D 1562–98 (cellulose acetate
propionate).
Trade names of thermoplastic cellulose ester
molding compounds are as follows:
2.4.8. Storage and Transportation
Cellulose Acetate Propionates: Tenite Pro-
pionate (Eastman Chemical Company, United Storage of thermoplastic cellulose ester molding
States), Cellidor CP and Albis (Albis Plastics compounds presents no problems. Even after 10
GmbH, Germany). years in storage, no changes in composition have
been detected. It is, however, recommended that
Cellulose Acetate Butyrates: Tenite Buty- thermoplastic cellulose ester molding com-
rate (Eastman Chemical Company, Kingsport, pounds are pre-dried in accordance with the
TN, United States), Cellidor B and Albis (Albis particular manufacturer’s guidelines before pro-
Plastics GmbH, Germany). cessing [161].
Transportation of thermoplastic cellulose es-
Cellulose Acetate: Tenite Acetate (Eastman ters as a class are not regulated by the DOT
Chemical Company, United States), Rotuba Ac- (USA), ICAO, and IMDG. They are also not
etate (Rotuba Plastics, United States), Setlithe governed by the GGVS/ADR, GGVE/RID,
and Plastiloid (Mazzucchelli, Italy), and Acety GGVSee/IMDG code or DGR/ICAO regulations
(Daicel, Japan). for the transportation of hazardous goods.

2.4.7. Quality Requirements and Quality 2.4.9. Uses [162], [143]

Testing
Cellulose ester plastics have excellent injection
As has already been stated, the mechanical prop- molding, extrusion, and fabrication characteris-
erties of thermoplastic cellulose ester molding tics. They are known for having a wide processing
Vol. 7 Cellulose Esters 375

Table 19. Typical valuesa for the chemical resistance of organic cellulose ester molding compounds

Cellulose acetate Cellulose acetate Cellulose acetate Cellulose acetate

Solvent (< 55 % acetic acid) (> 55 % acetic acid) propionate butyrate

Water þ þ þ þ
Alcohols    
Ethyl acetate  0 0 0
Methylene chloride  0 0 0
Acetone 0 0 0 0
Carbon tetrachloride þ þ þ þ
Trichloroethylene þ þ  
Perchloroethylene þ þ þ þ
Benzene þ þ  
Xylene þ þ  
Petroleum spirit þ þ þ þ
Motor fuel mixture (high octane) þ þ þ þ
Mineral oil (paraffin) þ þ þ þ
Linseed oil þ þ þ þ
Turpentine oil þ þ þ þ
Lavender oil þ þ  
Ether þ þ þ þ
Formalin   þ þ
2-Chlorophenol 0 0 0 0
Sulfuric acid, conc.    
Sulfuric acid, 10 % þ þ þ þ
Hydrochloric acid, conc.    
Hydrochloric acid, 10 %    
Nitric acid, conc.    
Nitric acid, 10 %    
Caustic potash solution, 50 %    
Caustic potash solution, 10 %   þ þ
a
Key to symbols: þ ¼ resistant; þ  ¼ resistant, but swells;  ¼ not resistant;   ¼ not resistant, swells; 0 ¼ soluble.

window and excellent processing in secondary propionate is also used for visor glazings for skiers,
operations such as solvent polishing, cutting, drivers, and workers in industry. These applica-
cementing, drilling, painting, and decorating tions have been made possible by the surface
[163]. Scrap material generated during processing saponification of the plastic, which ensures perma-
operations is often easily reprocessed. nent antifogging properties (the surface has very
In the ophthalmic area, both cellulose acetate good wetting properties and excellent water
and cellulose acetate propionate are used because absorption) [164]. Cellulose acetate propionates
of their excellent clarity, pleasant feel, color- with special infrared/ultraviolet-absorbing charac-
ability, machinability, and chemical resistance. teristics can be utilized for welding goggles and
They are also solvent polishable, which imparts a certain types of sunglasses [164].
very high gloss finish. Cellulose acetate propio- Cellulose acetate is utilized as a sheet material
nate is more commonly utilized for injection- for making high-end ophthalmic frames because
molded applications, while cellulose acetate is of the ease of producing unique color effects. For
more commonly utilized in extruded sheet this purpose, uni- or multicolored plates are
applications. either cast or made by extrusion.
Cellulose acetate propionate has excellent Cellulose acetate and cellulose acetate buty-
stiffness, good dimensional stability under heat, rate are easily extruded into transparent profiles
and low moisture absorptivity, making it an for production of tool handles. Benefits in this
excellent choice for eyeglass frames, high quality application include toughness, clarity, ease of
frames for sunglasses, protective goggles for post-extrusion machinability, and scuff resis-
industry, and sports goggles [164]]. Due to its tance. Particularly important features include
high transparency, good impact resistance, and solvent polishability, impact resistance, good
low level of light scattering, cellulose acetate feel, and absence of stress cracking. Metal tool
376 Cellulose Esters Vol. 7

parts can easily be insertion molded without Extruded cellulose acetate sheet is utilized for
stress cracking (the blades can even be driven high-end playing cards, because of its toughness,
‘‘cold’’ into the handles), which brings obvious durability, dimensional stability, excellent warm
economic advantages. feel, and longer lasting life than cards made from
Colorability, toughness, and chemical resis- other materials.
tant properties make cellulose acetate and cellu- Other applications of cellulose ester molding
lose acetate propionate excellent materials for compounds include pen barrels, automotive and
hairbrushes, combs, and toothbrushes. Resis- furniture trim, sporting goods such as fishing
tance to stress cracking make cellulose acetate lures, health care supplies, medical tubing, ap-
propionate particularly suited for toothbrushes, pliances for durable goods, and electrical insula-
which requires close spacing of the drill holes and tion. Further applications include lamp covers,
a high bristle density. Cellulose acetate propio- high-quality toys, shoe-string tip films, shoe
nate also satisfies the requirement for high tuft heels, umbrella handles, curtain rings, toilet
pull-out strength. seats, tap handles, transparent mouthwash spray
Cellulose acetate butyrate sheet is used for attachments, instrument panel covers (glazing),
backlighted sign faces and panels for illuminated and knife handle grips.
advertising signs. Cellulosic sheeting has also
been used for machine hoods, lamp covers, out- Economic Facts.. With an apparently
door shelters, and dome lights. High light trans- guaranteed supply of raw materials and a tremen-
mission, practically unrestricted choice of colors, dous scope for variation of cellulose ester mold-
antistatic characteristics, easy of processing, ease ing compounds and of their property combina-
of joining (by simply gluing), good printing and tions, this class of plastics should maintain its
coating properties, the absence of stress cracking, market significance in special areas of applica-
and finally, excellent mechanical strength are the tion for years to come.
main factors influencing the choice of this mate-
rial in this area.
Cellulose esters are used in tubular packag- 2.4.10. Toxicology and Occupational
ing applications for their clarity, rigidity, scuff Health
resistance, and impact strength properties. Ex-
truded and injection molded cellulose acetate In general, components of cellulose ester
propionate is used in cosmetic packaging be- plastic formulations are listed on the TSCA,
cause of its post-extrusion machinability, trans- EINECS and other worldwide regulatory lists.
parency, chemical resistance, and appropriate Components should be reviewed for compli-
FDA regulatory status. With their minimal plas- ance with a region’s appropriate regulatory
ticizer migration, cellulose mixed esters are law.
preferred over cellulose acetate for the packag- Cellulose acetate and cellulose propionate
ing of toiletries. Other reasons for their use in molding compounds comply with Recommenda-
this sector include the brilliance and depth of tion XXVI of the Federal Health Authorities of
color, as well as the ability to produce special Germany [169].
color effects. There are also various cellulose esters and
Decorative trim made of cellulose acetate cellulose ester plasticizers that satisfy requirements
butyrate combined with aluminum foil [165] has of the U. S. Food and Drug Administration. Each
been firmly established in industry for years. An should be reviewed for lawful usage prior to use.
aluminum foil is coated with the cellulose mixed
ester and shaped in the crosshead die of an
extruder [166]. With its practically unlimited References
scope for metal and wood effects, elasticity,
resistance to detergents, and simple fixing, this 1 V. Stannet: Cellulose Acetate Plastics, Temple Press
combination of materials has been used with Ltd., London 1950.
great success in the automotive industry [167], 2 K. Thinius: Analytische Chemie der Plaste, Springer
as well as in the electrical, audio, and domestic Verlag, Berlin-G€ottingen-Heidelberg 1952.
appliance sectors [168]. 3 Kirk-Othmer, vol. 3, pp. 357 ff.
Vol. 7 Cellulose Esters 377

4 E. Ott, H. M. Spurlin, M. W. Grafflin: Cellulose and Wedlock, P. A. Williams (eds.): Cellulose and its Deri-
Cellulose Derivatives, 2nd ed., vol. V, part II, Inter- vatives, Ellis Horwood, Chichester 1985, pp. 329–336.
science Publ., New York-London 1954. 27 A. H. K. Fowler, H. S. Munro: ‘‘Some Surface Aspects of
5 R. Houwink, A. J. Staverman: Chemie und Technologie the Thermal and X-Ray Induced Degradation of Cellu-
der Kunststoffe, 4th ed., vol. II/2, Akademische Ver- lose Nitrates as Studied by ESCA, ’’ in [26] pp. 245–253.
lagsgesellschaft Geest & Porting KG, Leipzig 1963. 28 Enclosure I of the International Rail Transport Regula-
6 K. Thinius: Chemie, Physik und Technologie der tions (RID), Appendix 1.
Weichmacher, VEB Deutscher Verlag f€ur Grundstoffin- 29 E. Berl, Angew. Chem. 1904, 982, 1018, 1074. E. Berl-
dustrie, Leipzig 1963. Lunge: Chemisch-technische Untersuchungsmetho-
7 V. E. Yarsley, W. Flarell, P. S. Adamson, N. G. Perkins: den, 8th ed., vol. III, Julius Springer, Berlin 1932,
Cellulose Plastics, Iliffe Book Ltd., London 1964. p. 1294.
8 Encyclopedia of Polymer Science and Technology, vol. 30 P. Kassenbeck: ‘‘Faktoren, die das Nitrierverhalten von
3, J. Wiley & Sons, New York 1965. Baumwoll-Linters und Holzzellstoffen beeinflussen, ’’
9 R. Vieweg, E. Becker: Kunstoff-Handbuch, vol. III: report 3/83, ICT-Fraunhofer-Institut f€ur Treib- und Ex-
‘‘Abgewandelte Naturstoffe,’’ Hanser Verlag, M€unchen plosivstoffe, Pfinztal-Berghausen 1983.
1965. 31 Hercules Powder, US 2776965, 1957; US 3063981,
10 P. B. Koslov, G. I. Braginski: Chemistry and Technology 1962.
of Polymers, Iskustvo, Moscow 1965 (Russ.). 32 Hercules Powder, US 2028080, 1936.
11 H. Temming, H. Grunert: Temming-Linters, 2nd ed., P. 33 Hercules Powder, US 2950278, 1960.
Temming, Gl€uckstadt 1972. 34 Soci
et
e Nationale des Poudres et Explosifs, FR 1394779,
12 J. Barsha: ‘‘Inorganic Esters,’’ in E. Ott, H. M. Spurlin, 1964; DE-OS 1246487, 1965; FR 1566688, 1968; DE-
M. W. Grafflin (eds.): Cellulose and Cellulose Deriva- OS 1914673, 1969.
tives, 2nd ed., part II, Interscience Publ., New York- 35 Soci
et
e Nationale des Poudres et Explosifs, DE-OS
London 1954, pp. 713–762. 2813730, 1977.
13 E. D. Klug: ‘‘Cellulose Derivatives,’’ in Kirk-Othmer, 36 Hercules Powder, US 2776944, 1957; US 2776964,
2nd ed., vol. 4, J. Wiley & Sons, New York-London- 1957.
Sydney-Toronto 1964, pp. 616–652. 37 Wolff Walsrode, DE-OS 2727553, 1977; DE-OS
14 G. D. Hiatt, W. J. Rebell: ‘‘Esters,’’ in N. M. Bikales, L. 2727554, 1977.
Segal (eds.): Cellulose and Cellulose Derivatives, part 38 Wasag Chemie, DE-OS 1771006, 1968.
V, Wiley-Interscience, New York-London-Sydney-Tor- 39 Wolff & Co. Walsrode, DE-OS 1153663, 1961.
onto 1971, pp. 741–777. 40 Wolff & Co. Walsrode, DE-OS 1203652, 1964.
15 J. Honeyman: Recent Advances in the Chemistry of 41 Soci
et
e Nationale des Poudres et Explosifs, DE-OS
Cellulose and Starch, Heywood & Comp., London 1959. 2338852, 1973.
16 E. Sj€ostr€
om: Wood Chemistry, Fundamentals and Ap- 42 C. F. Bennett, T. E. Timell, Sven. Papperstidn. 58 (1955)
plications, Academic Press, New York-London 1981. 281–286.
17 D. Fengel, G. Wegener: Wood–Chemistry, Ultrastruc- 43 D. A. J. Goring, T. E. Timell, Tappi 45 (1962) 454–460.
ture, Reactions, De Gruyter, Berlin-New York 1983. 44 K. Thinius, W. Th€ummler, Makromol. Chem. 99 (1966)
18 K. Balser: ‘‘Derivate der Cellulose,’’ in W. Burchard 117–125.
(ed.): Polysaccharide, Springer Verlag, Berlin-Heidel- 45 M. Marx-Figini, Makromol. Chem. 50 (1961) 196–219.
berg-New York-Tokyo 1985, pp. 84–110. 46 J. W. Green in R. L. Whistler, J. W. Green, J. N. BeMiller
19 L. C. Wadsworth, D. Daponte: ‘‘Cellulose Esters,’’ in T. (eds.): ‘‘Cellulose,’’ Methods in Carbohydrate Chemis-
P. Nevell, S. H. Zeronian (eds.): Cellulose Chemistry try, vol. III, Academic Press, New York-London 1963,
and its Applications, Ellis Horwood Ltd., Chichester pp. 213–237.
1985, pp. 344–362. A. Revely: ‘‘A Review of Cellulose 47 W. J. Alexander, G. C. Gaul: ‘‘Cellulose Derivatives,’’ in
Derivatives and their Industrial Applications,’’ in Cellu- Encyclopedia of Industrial Chemical Analysis, vol. 9, J.
lose Chemistry and its Applications, pp. 211–225. Wiley & Sons, New York-London-Sydney-Toronto
20 Company Publication of Wolff Walsrode AG: 100 Jahre 1970, pp. 59–94.
Collodiumwolle (1979) . 48 ASTM D 301–72 (1983) : Soluble Cellulose Nitrate.
21 K. Fabel: Nitrocellulose, Enke Verlag, Stuttgart 1950. 49 ASTM D 1343–69 (1979) : Viscosity of Cellulose
22 F. D. Miles: Cellulose Nitrate, Oliver & Boyd, London Derivatives by Ball-Drop Method.
1955. 50 ASTM D 365–79: Soluble Nitrocellulose Base
23 S. Rossin, M
emorial des Poudres 40 (1958) 457–471. Solutions.
24 H. Temming, H. Grunert: Temming-Linters, 2nd ed. 51 ASTM D 1720–79: Dilution Ratio in Cellulose Nitrate
(engl.), Peter Temming AG, Gl€uckstadt 1973. Solutions for Active Solvents, Hydrocarbons, Diluents
25 Company Publication of Wolff Walsrode AG: Walsro- and Cellulose Nitrates.
der Nitrocellulose, no. 500/203/007 (1984) . 52 A. Kraus: Handbuch der Nitrocelluloselacke, Westliche
26 J. Isler, D. Flegier: ‘‘The Self-Ignition Mechanism in Berliner Verlagsgesellschaft Heenemann KG, Berlin,
Nitrocellulose,’’ in J. F. Kennedy, G. O. Phillips, D. J. vol. 1: 1955, vol. 2: 1963, vol. 3: 1961, vol. 4: 1966.
378 Cellulose Esters Vol. 7

53 H. Kittel: Lehrbuch der Lacke und Beschichtungen, 81 D. A. Predvoditelev, M. S. Bakseeva; Zh. Prikl. Khim.
vols. 1– 8 Heenemann GmbH, Stuttgart-Berlin 1971– (Leningrad) 45 (1972) 857; Faserforsch. Textiltech. 9
1980. (1972) 361.
54 Bayer, DE-OS 2853578, 1978. 82 D. C. Johnson: ‘‘Solvents for Cellulose,’’ in Cellulose
55 Wolff Walsrode, DE-OS 3139840, 1981; DE-OS Chemistry and its Applications, Ellis Horwood, Chi-
3407932, 1984. chester 1985, pp. 181–201.
56 Ullmann, 4th ed., 9, (1975) 179–183. 83 L. P. Clermont, F. Bender, J. Polym. Sci. Part A-1 10
57 Leaflet M 051 by the German Employers’ Liability (1972) 1669.
Insurance Association of the Chemical Industry: Dan- 84 R. B. Hammer, A. F. Turbak, ACS Symp. Ser. 58 (1977)
gerous Chemical Substances, Jedermann-Verlag 40. H. L. Hergert, Tappi 61 (1978) 63. ITT Rayonier, US
Dr. Otto Pfeffer, Heidelberg 1984. 4056675, 1977.
58 Verordnung u€ber gef€ ahrliche Arbeitsstoffe 11 Feb. 82 85 C. J. Malm, L. J. Tanghe, B. C. Laird, J. Am. Chem. Soc.
BGBl I, Carl Heymanns, K€oln 1982, p. 144. 72 (1950) 2674.
59 Leaflet M 014 by the German Employers’ Liability 86 C. J. Malm, L. J. Tanghe, B. C. Laird, G. D. Smith, J. Am.
Insurance Association of the Chemical Industry: Nitric Chem. Soc. 75 (1953) 80.
Acid, Nitrogen Oxides, Nitrous Gases, Jedermann-Ver- 87 C. J. Malm, L. J. Tanghe, Ind. Eng. Chem. 47 (1955) 995.
lag Dr. Otto Pfeffer, Heidelberg 1985. 88 Cross, Bevan, Tranquair, Chem. -Ztg. 29 (1905) 528.
60 Leaflet M 037 by the German Employers’ Liability 89 C. J. Malm, H. T. Clarke, J. Am. Chem. Soc. 51 (1929)
Insurance Association of the Chemical Industry: Nitro- 274.
cellulose, Jedermann-Verlag Dr. Otto Pfeffer, Heidel- 90 Du Pont, US 1990483, 1935.
berg 1984. 91 Schutzenberger, Naudin, Z. Chem., 1869, 264.
61 E. v. Schwartz: Handbuch der Feuer- und Explosions- 92 Franchimont, Comp. Rend. 89 (1879) 711.
gefahr, 5th ed., Feuerschutz-Verlag P. L. Jung, 93 C. J. Malm, L. J. Tanghe, J. T. Schmitt, Ind. Eng. Chem.
M€ unchen 1958, p. 303. 53 (1961) 363.
62 German Explosives Law, publ. 13 Sept. 1976, BGBl I, p. 94 C. J. Malm, K. T. Barkey, D. C. May, E. A. Lefferts, Ind.
2737; amended 10 Apr. 1981, BGBl I, Carl Heymanns, Eng. Chem. 44 (1952) 2904.
K€ oln 1981, p. 388. 95 C. J. Malm, K. T. Barkey, E. B. Lefferts, R. T. Gielow,
63 H. Dorias: Gef€ ahrliche G€ uter, Springer Verlag, Berlin- Ind. Eng. Chem. 50 (1958) 103.
Heidelberg-New York-Tokyo 1984. 96 C. J. Malm, L. J. Tanghe, B. C. Laird, Ind. Eng. Chem. 38
64 Z. A. Rogovin, L. S. Galbraich, W. Albrecht (eds.): Die (1946) 77.
chemische Behandlung und Modifizierung der Cellu- 97 A. J. Rosenthal, Pure Appl. Chem. 14 (1967) 535.
lose, Thieme Verlag, Stuttgart-New York 1983. 98 L. J. Tanghe, R. J. Brewer, Anal. Chem. 40 (1968) 350.
65 Hercules Powder Comp., US 2753337, 1953. 99 H. Temming, H. Grunert: Temming Linters, 2nd ed.,
66 B. Philipp, W. Wagenknecht: Cellul. Chem. Technol. 17 P. Temming, Gl€uckstadt 1972.
(1983) 443. 100 C. J. Malm, R. E. Glegg, J. Thompson, L. J. Tanghe,
67 R. G. Schweiger, Tappi 57 (1974) 86; ACS Symp. Ser. 77 TAPPI 47 (1964) 533.
(1978) 163; US 4138535, 1977. 101 C. J. Malm, L. J. Tanghe, TAPPI 46 (1963) 629.
68 R. G. Schweiger, Carbohydr. Res. 70 (1979) 185. 102 F. L. Wells, W. C. Schattner, A. Walker, TAPPI 46
69 R. G. Schweiger, DE-OS 3025094, 1980. (1963) 581.
70 Eastman Kodak, US 3075962, 1963; US 3075963, 1963; 103 B. P. Rousse, Encycl. Polym. Sci. Technol. 1964–1977, 3.
US 3075964, 1963. 104 Ullmann, 3rd ed., 5, 187 ff.
71 Eastman Kodak, US 3068007, 1963. 105 Bios Final Report No. 1600, Item No. 22, H. M. Station-
72 W. D. Slowig, M. E. Rowley, Text. Res. J. 38 (1968) 879. ary Office, London 1948.
73 J. Pastyr, L. Kuniak, Cellul. Chem. Technol. 6 (1972) 249. 106 L. Ledderer, DE 200916, 1905.
74 J. B. Lawton, G. O. Phillips, Text. Res. J. 45 (1975) 4. 107 Boehringer, GB 363700, 1930.
75 K. Katsuura, T. Fujinami, Kogyo Kagaku Zasshi 71 108 Bios Final Report No. 1850, Item No. 21, H. M. Station-
(1968) 771. ary Office, London 1948.
76 Eastman Kodak, US 2759924, 1956. 109 C. J. Malm, L. J. Tanghe, B. C. Laird, J. Am. Chem. Soc.
77 Kimberly-Clark, US 3658790, 1970. 72 (1950) 2674.
78 National Chemical & Manufacturing, US 1896725, 110 C. J. Malm, R. E. Glegg, J. T. Salzer, D. F. Ingerick, L. J.
1933. Tanghe, I&EC Process Design and Development 5
79 R. A. A. Muzzarelli, G. Marcotrigiano, C.-S. Liu, A. (1966) 81.
Fr^eche, Anal. Chem. 39 (1967) 1792.ensp; 111 Cons. f. Elektrochem. Ind., DE 687065, 1933; US
80 L. S. Sletkina, A. J. Poljakov, Z. A. Rogovin, Vysokomol. 2108829, 1934.
Soedin 7 (1965) 199; Faserforsch. Textiltech. 2 (1965) 112 C. R. Fordyce, L. W. Meyer, Ind. Eng. Chem. 32 (1940)
299. 1053.
Vol. 7 Cellulose Esters 379

113 Arthur K. Doolittle: The Technology of Solvents and 140 W. Pusch: ‘‘Membranes from Cellulose and Cellulose
Plasticizers, John Wiley & Sons Inc., New York 1954, Derivatives,’’ in Wood and Cellulosics, Ellis Horwood
pp. 203 – 206. Limited, Chichester 1985, pp. 475–482.
114 Eastman Chemical Company: ‘‘Eastman Cellulose Es- 141 Man-Made Fiber Yearbook, Fiber Organon, Washing-
ters’’ Publication E-325, 2003. ton D.C. 1996, p. 12.
115 Company Publication of Bayer AG, Leverkusen. 142 W. Fischer, Kunststoffe 62 (1972) 653.
116 Company Publication of Hercules Powder Comp., Wil- 143 Eastman Chemical Company: ‘‘From Trees to Plastics’’
mington, USA. Publication PPC-100D, 1999.
117 E. Yarsley, W. Flavell, P. S. Adamson, N. G. Perkins: 144 Eastman Chemical Company: ‘‘Weathering of Tenite
Cellulosic Plastics, Iliffe Book Ltd., London 1964. Butyrate’’ Publication PP-104B, 1999.
118 K. Thinius: Analytische Chemie der Plaste, Springer 145 Eastman Chem. Prod.: Specifications, T 58–3289, King-
Verlag, Berlin-G€ottingen-Heidelberg 1952. sport, Tennessee 1958.
119 C. J. Malm, L. B. Genung, R. F. Williams, Ind. Eng. 146 W. Fischer, Kunststoffe 63 (1973) 292.
Chem. Anal. Act. 14 (1942) 935. 147 Eastman Chemical Company: ‘‘Tenite Acetate Chemi-
120 J. F. Tremblay, Chem. Eng. News, 1999, July 10, 21. cal Resistance’’ Publication PP-101, 1996
121 Eastman Chemical Company: ‘‘Eastman Cellulose 148 Eastman Chemical Company: ‘‘Tenite Butryate Chemi-
Acetate for Coatings’’ Publication E-305A, January cal Resistance’’ Publication PP-102, 2002.
1996. 149 Paist: Cellulosics, Reinhold Plastics Application Series,
122 Eastman Chemical Company: ‘‘A Feasibility Study Reinhold Publishing Corporation, New York 1958, pp.
Using Cellulose Acetate and Cellulose Acetate Buty- 45 – 46.
rate’’, Publication EFC-234, October 2000. 150 W. Fischer, C. Leuschke, H. P. Baasch, Kunststoffe 67
123 K. J. Edgar et al., Prog. Polym. Sci. 26 (2001) 1605. (1977) no. 6, 348–252.
124 C. J. Malm, J. W. Mench, D. L. Kendall, G. D. Hiatt, Ind. 151 C. Leuschke, M. Wandel, Plastverarbeiter 33 (1982) no.
Eng. Chem. 43 (1951) 684. 9, 1095–1098.
125 J. W. Mench, B. Fulkerson, G. D. Hiatt, I&EC Product 152 Bayer, DE-OS 2951800, 1979; DE-OS 2951747, 1979;
Research and Development 5 (1966) June, 110. DE-OS 2951748, 1979. K. Thinius: Chemie, Physik und
126 C. J. Malm, Svensk Kemisk Tidskrift 73 (1961) no. 10, Technologie der Weichmacher, VEB Deutscher Verlag
523. f€ur Grundstoffindustrie, Leipzig 1963.
127 H. Saechtling, W. Zebrowski: Kunststoff-Taschenbuch, 153 Mod. Plast. Encycl. 1970, 1971 840, 870.
18th ed., C. Hanser, M€unchen 1971. 154 Mod. Plast. Encycl. 1970, 1971, 876.
128 C. J. Malm, C. R. Pordyce, H. A. Tanner, Ind. Eng. 155 Mod. Plast. Encycl. 1970, 1971, 850.
Chem. 34 (1942) 430. E. Ott, H. M. Spurlin, M. W. 156 ISO/R 1157–1990.
Grafflin: Cellulose and Cellulose Derivatives, vol. V, 157 ISO/R 1598–1990.
Part II, 2nd edn., Interscience Publ. Inc., New York- 158 ISO/R 1599–1990.
London 1954. W. Ballas, Internal communication, 159 ISO/R 1600–1990.
Bayer AG, Leverkusen. 160 ISO/R 1875–1982.
129 Bayer AG: Cellit, Cellit BP and PR, Brochures nos. KL 161 Eastman Chemical Company: ‘‘Drying Tenite Cellulos-
44172 and KL 44170, Leverkusen 1982. ic Plastics’’ Publication PP-105B, 2000.
130 Eastman Chemical Company: ‘‘C–A–P Enteric Coating 162 M. Wandel, C. Leuschke, Kunststoffe 74 (1984) no. 10,
Material for Pharmaceutical Drug Delivery’’ Publication 589 – 592.
EFC-205, 1998. 163 Eastman Chemical Company: ‘‘Secondary Fabrication
131 C. J. Malm, et al. Ind. Eng. Chem. 49 (1957) 84. Techiques for Tenite Cellulosic Plastics’’ Publication
132 Eastman Chemical Company., US 5668273, 1997 (J. M. PP-110D, 2000.
Allen, A. K. Wilson, P. L. Lucas, L. G. Curtis). 164 Bayer AG: Cellidor f€ ur die optische Industrie, Company
133 Eastman Chemical Company., US 5994530, 1999 (J. D. Publication KU 40029, Leverkusen 1984.
Posey-Dowty, A. K. Wilson, L. G. Curtis, P. M. Swan, K. 165 J. G€oller, H. Peters, W. Fischer, Kunststoffe 65 (1975)
S. Seo). no. 6, 326–332.
134 J. Corbiere, Faserforsch. Textiltech. 22 (1971) 71. 166 Glas Lab, DE-AS 1226291, 1955 (A. Shanok, V. Sha-
135 Technical Association of Paper and Pulp Industry (TAP- nok, J. Shanok).
PI), DIN or ISO-standards. 167 Bayer AG: Zierleisten und Profile in der Autoindustrie,
136 Celanese Corp. of America, US 2597156, 1952 (M. E. Company Publication KL 40025, Leverkusen 1979.
Martin, L. G. Reed). 168 Bayer AG: Zierleisten in der Elektro- und
137 Eastman Kodak Co., US 2652340, 1953 (G. D. Hiatt, R. M€ obelindustrie, Company Publication KL 40011, Le-
F. Willmans). verkusen 1975.
138 E. Heim, Chemiefasern 16 (1966) 618. 169 Bundesgesundheitsblatt, 19th ed., 1976, No. 6, Carl Hey-
139 Ullmann, 4th ed., 9, 213. manns Verlag, K€oln-Berlin-Bonnhyphen;Muuml;nchen.
380 Cellulose Esters Vol. 7

Further Reading online: DOI: 10.1002/0471238961.1518070107050415.

a01.
J. P. Agrawal: High Energy Materials, Wiley-VCH, Wein- J. M€ussig (ed.): Industrial Applications of Natural Fibres,
heim 2010. Wiley, Chichester 2010.
L. Bottenbruch, S. Anders (eds.): Engineering Thermoplas- M. C. Shelton: Cellulose Esters, Inorganic, ‘‘Kirk Othmer
tics - Polycarbonates, Polyacetals, Polyesters, Cellulose Encyclopedia of Chemical Technology’’, 5th edition, vol.
Esters, Hanser/Gardner, Cincinnati 1996. 5, p. 394–412, John Wiley & Sons, Hoboken, NJ, 2004,
S. Gedon, R. Fengi: Cellulose Esters, Organic, ‘‘Kirk Othmer online: DOI: 10.1002/0471238961.0914151806051407.
Encyclopedia of Chemical Technology’’, 5th edition, vol. a01.pub2.
5, p. 412–439, John Wiley & Sons, Hoboken, NJ, 2004,