Note: Descriptions are shown in the official language in which they were submitted.
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Process for producin~ cellulose derivatives
The invention relates to a process for producing cellulose derivatives, with which
the cellulose is impregnated with an aLIcali solution, the impregnated cellulose is
optionally pressed and the cellulose is subjected to a substitution or addition
reaction, wherein a cellulose derivative witll a substitution degree DS is obtained.
Most substitution reactions of cellulose take place via alkali cellulose as
intermediate stage. Here a distinction is made bet~,veen reactions with alkali
consumption, e.g. the production of methyl or ethyl cellulose by reaction with the
corresponding aL~;yl halogenides, the production of carboxy-methyl cellulose by
reaction with chloracetic acid or its sodium salt, or the production of cell~llose
xanthogenate by reaction with carbon disulphide, and reactions without alkali
consumptiQn, e g= the produç~ion of hydrsxy-ethyl ~nd hydroxy-prQpyl cellulose
by reaction of the alkali cellulose with ethylene o~ide or propylene oxide, or the
production of cyano-ethyl cellulose by reaction with acrylonitrile.
Cleaned cellulose is converted to alkali cellulose by treating it ~ith alkali, in the
industry practically e~clusively soda lye (alkalisation). It is assumed that in the
aLkali cellulose part of the cellulose is present in the form of a hydrated alcoholate
Cell-O~a+ ... H~ O~. The soda lye furtherrnore serves to s~,vell the cellulose and
make it accessible to the reaction partners of the subsequent derivation reactions.
In the amorphous part of the cellulose the cellulose alcoholate is formed relatively
easily. So that this will also occur for the crystalline part of the cellulose, certain
conditions must be maintained with regard to the temperature and concentration of
the soda lye. Only when the concentration of soda lye is sufficiently high, will the
lattice of soda cellulose I be forrned, which durin~ the washing (regeneratin~)
changes over to the lattice of cellulose II (regenerated cellulose). During the
conversion of cellulose I to soda cellulose I, the distances of the 101-lattice planes
of about 7 are widened to appro~imately 12 A. This change can also be noted by
looking at the apparent density. Cellulose material with a high crystallinity has a
k~6
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high resistance to ~lk~ tion. In practice only a narrow NaOH-concentration
range produces alkali celluloses suitable for industrial use. With the known
industrial processes the pre-comminuted cellulose is immersed in 18-20% aqueous
soda Iye (Iye ratio at least 10:1). A large part of tl~e soda Iye is subsequently
removed again by pressing. However, when doing so normally a composition of
approximately 34% by mass cellulose and 66% by mass aqueous NaOH (steeping
and pressing) is obtained or of only 25% by mass cellulose and 75% by mass
NaOH (slurry and roller press).
A large part of the soda lye rem~ining behind in this cellulose is, however, notused for the subsequent derivation reactions, but adheres as loose associate to the
cellulose and is not removed during the pressing. A w:~hin~ out with water is not
possible, as this dilutes the soda lye and the initial modification would again
occur.
The amount of soda lye which is excess for the production of the cellulose
derivatives causes during the derivation reactions a high reagent consumption,
which generally is associated with a salt formation and the formation of by-
products. During the xanthogenation the excess soda lye reacts with carbon
disulphide to, for example, the undesirable trithio-carbonate. The salts as well as
the by-products must be separated, to some extent at high expense and must be
disposed of or processed. For the cellulose ethers, the costs for this already
amo~mt to 70% of the production costs. For the production of viscose via
cellulose xanthogenate, because of the strict of~cial environmental protection
requirements, considerable costs are also required for cleaning the waste water.
Notwithstanding the high excess of soda lye used with the known process, it is
found that in the derivatives produced via alkali cellulose as intermediate stage,
inhomogeneous substituent distributions are present. In cellulose ethers these can
be noted, for example, by a too low solubility, a to<) great turbidity and a too low
flocculation temperature.
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It has already been reported that with activated cellulose compared to untreatedcellulose, the lattice conversion from cellulose I to soda cellulose I takes place
already at a considerably lower NaOH concentration. In this connection ~ve referto Schleicher, Daniels and Philipp, in "Faserforschung ~md Textiltechnik" 24
(1973) p. 371 to 376 and WO 96/30411. However, these publications do not
suggest that with a view to the subsequent derivation reactions the absolute quan-
tity of alkali, i.e. the molar NaO~/AHG ratio (AHG = anhydroglucose unit), couldplay a role.
It was, therefore, the object of the invention to make available a process
mentioned at the outset, which does not have the indicated disadvantages of the
state of the art. It ~as a particular object of the invention to make available a
process of the type mentioned at the outset, with ~,vhich at the beginning of the
derivation reaction only a small e~cess or a stoichiometric or even a sub-
stoichiometric quantity of alkali is present.
According to the invention this object is achieved by a process for producing
cellulose derivatives with which a) cellulose is impregnated with an alkali
solution, b) the impregnated cellulose is optionally pressed and c) the cellulose is
subjected to a substitution or addition reaction, ~ herein a cellulose derivati~e ~ith
a substitution degree DS is obtained, which is characterised in that the cellulose
used is an ammonia-activated cellulose and the molar ratio of aLkali to AHG in the
cellulose at the beginning of step c) does not e~ceed ~ times the DS.
To be understood under "alkali solution" are aqueous or alcoholic solutions of
aL~cali metal or ~lk~line earth metal hydro~cides, o~ides andlor carbonates.
Preferably, the aLkali solution is aqueous or alcoholic soda lye or potassium lye.
The alcoholic solutions preferably contain methanol, ethanol and/or isopropanol as
solvent.
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., ~
With processes according to the invention, alkali solutions with a low concen-
tration are already effective since for the successful further conversion a
transformation by alkali to the cellulose II-lattice is not necessary, seeing that as a
result of the activation a new cellulose modification ~ith widened lattice has
already occurred. Generally, concentrations of approximately 12% by mass or
less are suitable. Preferably, the alkali solution has a concentration of less than
approximately 10, in particular less than approximately 8% by mass. Concen-
trations of approximately 1 to 6% by mass are particularly suitable.
The molar aL~;ali/AHG ratio at the beginning of step c) does not e~ceed 2 times,preferably 1.5 times, in particular 1.1 times the desired substitution degree. In
particular, in the case of aL~ali-consuming reactions a stoichiometric aL~ali/AHG
ratio can be used. To be understood under stoichiometric is a molar aL~alilAHG
ratio which lies close to the desired substitution degree of the end product.
With reactions which are only catalysed by alkali, it is even possible to use a sub-
stoichiometric ratio with respect to the desired substitution degree.
The substitution or addition reaction can preferably be brought about by reaction
with carbon disulphide, acyl-group transferring reagents, such as carbo~ylic acid
anhydrides, e.g. acetic anhydride, isopropenyl acetate, dicarboxylic acid
anhydrides, e.g. phthalic anhydride, succinic anhydride, glutaric anhydride, maleic
anhydride, carboxylic acid chlorides, e.g. propionic chloride, stearylic chloride,
carbo~ylic acids, e.g. formic acid; aL~yl-group transferring reagents such as methyl
chloride, ethyl chloride, ben~zyl chloride; aL~ene oxides, such as ethylene oxide,
propylene o~ide, styrene o~cide; a-halocarboxylic acids, such as chloracetic acid,
or their salts, cc"~-unsaturated carbonyl compounds or acrylonitrile. In addition,
sometimes a catalyst such as, for example, benzyl trimethyl ammonium chloride,
tetrabut l ammonium chloride, -hydroxide, hydrogen sulphate, Ti(OR)~,
imidazole, N-methyl imidazole, Li-, Na- and Mg-acetate is advantageous. The
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reaction can take place in an aqueous medium or an organic solvent, such as NMP,DMAc, DMSO, DMF, dioxan, THF, iso-propanol, tert-butanol or mi~;tures
thereof.
With the process according to the invention ammonia-activated cellulose must be
used. "Ammonia activation" means that the cellulose has been treated under high
pressure with liquid arnmonia and subsequently the pressure of the system has
been released. Native cellulose is a polysaccharide which, because of the
formation of intermolecular hydrogen bridge bonds, comprises crystalline parts.
The ammonia molecule, because of its nucleophilic properties, is able to push
itself between the cellulosic OH-groups. This ensures a swelling and widening ofthe lattice. D~lring the subsequent pressure release the ammonia evaporates for the
greater part. When doing so, the degree of swelling or the widening of the lattice
decreases again and assumes a value between the complete swelling and tlle
untreated cellulose. The known processes for the ammonia activation of cellulosecan be divided into the simple ammonia e~pansion and the so-called ammonia
explosion. With both the cellulose is treated with liquid ammonia in a pressure
vessel. With the ammonia expansion technology, by opening a valve with a small
bore on the pressure reactor, it is ensured that under a reduction of the pressure
part of the liquid ammonia escapes from the pressure vessel in the gaseous form.The cellulose rem~ining behind in the pressure reactor does not release all the
liquid ammonia, but approximately 50~iO of the ammonia used remains behind in
the cellulose. Such a process is described, for example, in the DE 43 29 937 Cl.With the ammonia explosion technology, the volume available to the system
cellulose/liquid ammonia is increased in an e~plosion-like manner whilst reducing
the pressure. For the practical implementation thereof, on the pressure reactor a
valve with a large bore can be opened, when the cellulose and ammonia are flung
in sudden bursts out of the pressure tank into an e~plosion or collecting charnber.
With this the greater part of the ammonia evaporates from the cellulose; only a
small residual ammonia content remains behind, the amount of which depends on
the process parameters.
E
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.. . .
.
For the purposes of the invention the activated cellulose preferably has a LODP-value ~"Limiting Degree of Polymerisation" or "Levelling-off Degree of Polymer-
isation" (LODP-value); see Hans A. Krassig "Polymer Monographs", Vol. 11,
Gordon and Breach Science Publishers, in particular p. 191 et seq.) of between
approximately 100 and 160 and in particular between approximately 120 and 145.
Preferably, the activated cellulose is in the form of fluff and is characterised by a
low density of less tllan approximately 0.2 g/cm3, in particular less than appro-
ximately 0.1 g/cm3. Activated cellulose had a widened space-reticular structure as
well as a high specific surface with high accessibility.
Preferably, the activated cellulose is obtained by a process with which the
cellulose is brought into contact with liquid ammonia at an initial pressure higher
than atmospheric pressure and at a temperature of at least approximately 25~C,
whereir. the quar~tity of the liquid ammonia suffices at least to wet the sl~..ce of
the cellulose and the volume available to the system cellulose/liquid ammonia isincreased in an explosion-like manner ~,vhilst reducing the pressure by at least S
bar.
When the term "explosion-like" is used here, this must be seen in the narrow
sense. Preferably, the e~cplosion-like increase in volume takes place within less
than one second, in particular less than 0.5 seconds. A continuous process is based
on an incremental celluloselliquid ammonia quantity. The cellulose preferably isbrought into contact with the liquid ammonia in a pressure device, and the
pressure of the system cellulose/liquid arnmonia is reduced by transferring it into
an explosion chamber with a volume that is larger than that of the pressure device.
Preferably, the starting pressure lies between appro~imately S and 46 bar, in par-
ticular between appro~imately ~5 and 30 bar. The minimum drop in pressure of S
bar is critical. Below this no adequate activation of the cellulose will be obtained.
E~ceeding the upper limit value of appro~irnately 46 bar will not result in further
advantages. The obtaining of such a value requires a relatively great amount of
apparatus, so that from a practical point of view a further increase does not make
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sense. The temperature of approximately 25 to 85~C or 55 to 65~C correlates withthe indicated pressure frame. Preferably, the starting pressure in the system
cellulose/liquid ammonia is reduced in an explosion-like manner by at least
approximately 10 bar and, in particular, approximately 30 bar. Preferably, the
explosion takes place in an explosion chamber which is kept under vacuum. This
explosion chamber must be chosen sufficiently large so as to obtain in the largevolume the desired separation into fibres or defibrillation. Preferably, the
ammonia is drawn off from the explosion chamber, condensed again and fed back
into the process.
A sufficient quantity of ammonia must be pressed into the pressure device, so that
under the pressure and temperature conditions required according to the invention
liquid arnmonia will be present and at least the surface of the cellulose is wetted.
Preferably per 1 part by mass of cellulose at least approximately 1 part by mass, in
particular approximately S to 10 parts by mass of liquid ammonia are used. As a
result of the ammonia an at least partial swelling of the cellulose takes place.
The preferred activation process can be carried out discontinuously or continuous-
ly. With the discontinuous process the apparatus essentially comprises a pressure
tank which can be filled with the material to be treated, and a collecting or e~pan-
sion tank connected to same by way of a valve. Here it must be ensured that the
valve, when open, has a large opening so that during the explosion the cellulosematerial will not dam up and not only ammonia will escape. The expansion tank
has a much larger volume than the pressure tank, e.g. the volume of the pressuretank is 1 1 and the volume of the e~;pansion tank 30 1. The pressure tank is
provided with a feed pipe for ammonia, optionally with the interposition of a
pressure-increasing device. To ensure a further increase in pressure, in addition a
feed pipe for inert gases, e.g. nitrogen, may be provided.
The process can be carried out in a continuous manner, using a tubular or cylinder
shaped, pressure-resistant reactor, with which the bringing into contact of the
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cellulose and liquid ammonia takes place in the cylinder of the reactor and the
impregnated material is transported through the reactor with the aid of a conveyor
screw in the form of a wad and is discharged intermittently through a valve or asuitable system of pressure locks into a collecting chamber. Suitable components,
which the expert can easily adapt for carrying out the process according to the
invention, are described inthe EP-A-329 173 andthe US-4 211 163 respectively.
Thç cellulose should have a low moisture content, preferably less than 9% by
mass, in particular less than 7% by mass. Preferably it is chemically pure, i.e.~refer~bly it contains less than approximately 12, in particular less than
approximately 8% by mass of foreign substances. The contact time between the
liquid ammonia and the cellulose is not critical. As an expedient minimum
contact time appro~imately 4 minutes can be indicated; as a rule it amounts to
approximately 8 minutes.
An activated cellulose produced by ammonia explosion has a special X-ray
diffraction spectrum with peaks at the following diffraction angles 2 ~ and withthe relative intensities:
Peak 1 1,25 + 1 of the relative intensity of appro~imately 15 to 25,
Peak 17 + 1 of the relative intensity of appro~imately 25 to 40 and
Peak 20,5 + 1 of the relative intensity 100 (reference value).
This cellulose modification is also called cellulose III~. It was found that during
the treatment of this cellulose modification with 4 to 12% by mass soda lye, a
mixture of cellulose II and amorphous cellulose is obtained, wherein the portion of
the amorphous cellulose increases with the concentration of the used soda lye.
During the conventional mercerisation, i.e. the treatment of native cellulose with
18 to 20% by mass soda lye, from the cellulose I first alkali cellulose and fromthis cellulose II, but never amorphous cellulose, is obtained. During the treatrnent
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of cellulose III* with soda lye of a concentration of less than 4% by mass, in
particular less than 2% by mass, probably an addition compound of cellulose III*and NaOH is formed.
The following explanations are given with special reference to the ammonia
explosion and aqueous soda Iye, but apply correspondingly to other activation
processes, alkalis and solvents.
For the treatment witll aqueous soda Iye, the residual ammonia content of the
cellulose after the NH3-explosion is not critical. After the NH,-explosion the
ammonia-activated cellulose is brought into contact with diluted soda lye in a
suitable manner. To this end, the cellulose can be fed into a solution of the lye in
~vater or can be sprayed with the solution, or the solution can be passed through
the cellulose in counter-current. All technological embodiments of the bringing
into contact of a solid substance with a liquid component, which lead to a
thorough mixing or penetration, are conceivable and possible here.
The high accessibility of the NH3-exploded cellulose as well as its high specific
surface (low density) perrnit the quick diffusion of the NaOH-solution into the
inside of the cellulose, resulting in a homogeneous distribution of the NaOH
through the entire cellulose. The NH3-exploded cellulose is included by the diluted
NaOH-solution.
In doing so the NaOH-molecules displace the NH3-molecules that are still present,
forming the known polar structure with the celiulosic OH-groups, since due to the
higher basicity of the NaOH the ammonia is expelled from the cellulose.
Accordingly there exists the following "task distribution": the arnmonia explosion
produces a high accessibility of the cellulose, and the NaOH forms dipoles with
the cellulosic OH-groups.
A~ ~E
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The advantages of the splitting up of the activation or the increase in t~e
accessibility on the one side and of the formation of aL~ali cellulose on the other
side, are obvious. The activation, preferably by ammonia explosion, constitutes an
essential prerequisite for the production of stoichiometric alkali cellulose. The
advantages of the formation of stoichiometric aL~cali cellulose and of the cellulose
derivatives produced from same can be sl-mm~rised as follows:
In contrast to the conventional mercerisation or ~lk~ tion, less or no a&ering,
i.e. e~cess Iye occurs. Aceordingly, the process step of pressing out the Iye can
optionally be dispensed with. The consumption of NaOH can, therefore, be
drastically reduced (up to 75%). Closely associated therewith are a lower con-
sumption of reagents, an increased yield and a lower salt and by-product
formation.
The reactions, although still carried out hetero~eneously, approach a homogeneous
pattern. As a result, also a higher product quality and performance is obtained for
the end products, which can be attributed to a more homogeneous substituent
distribution. This in turn is the result of a homogeneous distribution of the
cellulose-o~onium-NaOH-complexes .
In the following the advantages will be e~plained with reference to the production
of viscose:
For the ammonia explosion the cellulose need only be pre-comminuted relatively
coarsely ~torn up). As a result of the NH3-e~plosion the cellulose is then to a far
reaching e~tent separated into ~lbres, so that a filrther mechanical comminuting(shredding) can be dispensed with, which means a considerable saving of energy.
When using cellulose with a polymerisation degree close to that which is to be
obtained for the end product, also the so-called ripeness is not required. With
regard to the production of viscose this is a relati~ ely tricky process step, since
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during same the risk of a drying out of the cellulose crurnbs e~ists, which
inevitably results in inhomogeneous reactivities.
During the production of xanthogenate by the process according to the invention,the for example ammonia-exploded cellulose is fed into 5-6% NaOH, the lye ratio
being chosen in such a way that after the complete dissolving an 8-9% viscose isobtained. This corresponds to the cellulose xanthogenate concentration customaryduring spinning. The formation of the xanthogenate takes plays whilst stirring or
shearing and slowly adding CS2, when during the course of the reaction in-
creasingly larger portions of cellulose are dissolved. The monitoring of the
dissolving process by suitable technical means (optical sensors, viscosity, torque
etc) permits the use of only as much carbon disulphide as is required. The reaction
takes place more quickly than with the conventional process. As a result, with
existing plants an up to 30% higher production capacity can be obtained.
Alternatively, the for example ammonia-e~ploded cellulose can be brought into
contact with only 1-2% NaOH, after which carbon disulphide is added and parallelto the adding of the carbon disulphide or after completing the adding of the carbon
disulphide, the spinning concentration of the viscose can be adjusted with concen-
trated ~aOH.
In the following e~amples all percentage data are % by mass, unless otherwise
indicated.
E~ample 1: Production of ammonia-e~ploded cellulose
200 g commercial cellulose (Cuo~am - DP 480) with an a-cellulose content of
appro~imately 96%, in sheet form (water eontent appro~imately 8%) was cut Up
into approximately 1.3 x 1.3 cm pieces and p~lt into an autoclave of 1 1 with a
double wall for steam heating. Subsequently 400 g liquid ammonia were pressed
into the autoclave throu~h a valve. The mass ratio ammonia/cellulose was 2:1. Bythe stearn heating of the autocla~,e the temperature was increased to 60~C. Thisresulted in a pressure inside the autoclave of appro~cimately 20 bar. The reaction
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12
mixture was kept under these conditions for 60 s. Subsequently, by opening the
valve (inside diameter 4 cm), the mixture was suddenly and completely released
into an explosion tank with a volume of 30 1. An optimum defibrillation took
place. The ~tr,monia corter.t of the product occ~rn:ng jn the explosion chamber
amounted to approximately 1% by mass, related to the de~lbrillated cellulose.
Example 2: Production of benzvl cellulose
This NH3-activated cellulose with a residual ammonia content of 3% is dispersed
in soda lye (400 ml to 10 g cellulose). This suspension is kept for 1 hour at 20-
25~C. The modified cellulose is washed with ethanol after the aqueous soda lye
has ~Irst been drawn off. The content of remaining NaOH was 2.5% (related to thecellulose). The washed cellulose is fed into a N-methyl-pyrrolidone ~), which
contains 3.9% benzyl-trimethyl ammonium chloride. The suspension is placed
under a slight vacuum (20 mbar) at 40~C so as to completely remove the ethanol.
Subsequently, under norrnal pressure, whilst stirring vigorously, a solution of
benzyl chloride in NlvIP is added, the molar ratio benzyl chloride/AHG amountingto 2:1. After a reaction time of 1 hour at 40~C, the obtained benzyl cellulose is
filtered off and washed with water until a pH value of close on 7 is obtained in the
washing water. Subsequently, the benzyl cellulose is dried at a temperature of
80~C under a vacuum of 1 mm Hg. The substitution degree according to infrared
spectroscopy was 0.15.
Example 3: Production of benzo~l cellulose
10 g ammonia-exploded cellulose with a residual ammonia content of 7.7% is
mixed into 120 ml of a 1~,/o aqueous NaOH-solution for 1 hour at 20-25~C. After
drawing off the soda lye (residual soda lye: 2.4%, related to cellulose), the
cellulose is mixed with 200 ml N-methyl pyrrolidone and then left to stand for 12
hours to permit an exchange of the NMP by water. Subsequently, the cellulose is
largely freed from the water containing NMP by pressing out and is then taken upin pure NMP. Af'cer cooling to 15~C, 3.3% by mass benzyl trimethyl ammonium
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chloride, related to the cellulose, is added. Subsequently so much benzoyl
chloride, dissolved in NMP, is added that the molar ratio to the cellulose amounts
to 1:1. The reaction mixture is heated for 3 hours to 50~C, then cooled again and
left to stand for 12 hours. The obtained benzoyl cellulose is filtered off and
washed with water and then with alcohol. Subsequently a drying takes place ~mdervacuum at 80~C.
Example 4: Production of cyano-ethvl cellulose
NH3-activated cellulose with a residual arnmonia content of 3% is dispersed in an
aqueous 0.5% soda Iye. This mixture is kept for 1 hour at 5~C, then stirred for 15-
30 minutes. Then acrylonitrile is added in a quantity so as to obtain a molar ratio
acrylonitrile/AHG of 2:1. After stirring, the reaction rnixture is kept for 1.5 to 3
hours at 45~C, then for approximately 2 hours at 0~C. The mixture is neutralisedwith acetic acid. The cyano-ethyl cellulose is filtered off and washed ~,vith water,
then with alcohol. Subsequently the cyano-ethyl cellulose is dried at 80~C undervacuum. The obtained cyano-ethyl cellulose has a substitution degree of 0.28.
Example 5: P~oduction of h~,dro~v-eth-,l cellulose
60 g cellulose (type Modo, DP ~Cuo~an) ~ 570) after the ammonium e~plosion are
taken up in 750 ml 2% NaOH and degassed in the rotation evaporator for 30
minutes at a temperature of 25~C under a vacuum of 40 mbar. Then the swollen
cellulose is pressed to appro~imately 150 g, mixed with 400 g tert-butanol in a 2 1
round flask on the rotation evaporator and evacuated to approximately 50 mbar.
Subsequently 9 g ~aseous ethylene oxide are added at 25~C within 30 minutes,
during which the pressure does not exceed 600 mbar. After 1 h the pressure dropsto approximately 220 mbar. A pressure compensation with respect to atmospheric
pressure is carried out with nitrogen, followed by heating to 60~C and stirring for 1
hour. After cooling to 20~C, the reaction mixture is neutralised with acetic acid.
The reaction mixture is poured into 2 1 acetone, filtered off and washed with anacetone/water solution (90%/10%). After drying in the vacuum drying cabinet at
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90~C/10 mbar up to constant mass, 63 g of hydroxy-ethyl cellulose (DS ~ 0.4) areobtained. The product is completely soluble in water.
E~ample 6: Production of hvdro~v-ethvl cellulose
20 g cellulose (type Modo, DP (Cuoxan) ~ 570) after the ammonium explosion are
taken up in 120 ml 2% NaOH and degassed in the rotation evaporator for 30
minutes at a temperature of 25~C under a vacuum of 40 mbar. Then the swollen
cellulose is pressed to approximately 60 g, mixed thoroughly with 140 g tert-
butanol in a 1 1 stirring autoclave and scavenged with nitrogen. Subsequently 18 g
ethylene oxide are added at 25~C, heated ~,vithin 30 minutes to 60~C and stirred for
1 hour. After cooling the autoclave to 20~C the reaction mixture is neutralised with
acetic acid. The reaction mixture is poured into 500 ml of a tert-butanol/water
solution (80%/20%), filtered off and washed with tert-butanoV~,vater (80%/20%).
After drying in the vacuum drying cabinet at 90~C/10 mbar up to constant mass,
28 g of hydroxy-ethyl cellulose (DS ~ 2.6) are obtained. The product is com-
pletely soluble in water.
Example 7: Viscosin~
20 g cellulose (type Viscokraft LV 4, DP (Cuoxan) ~ 400) after the ammonium
explosion are taken up in 120 ml 4~/o NaOH and de assed in the rotation
evaporator in a 1 1 round flask for 30 minutes at a temperature of 25~C under
vacuum (40 mbar). Subsequently 5 g carbon disulphide are metered into the
rotating flask at 25-30~C ~,-ithin 5 minutes, during which the pressure increases to
approximately 500 mbar. After 2 h the pressure drops to approximately 180 mbar.
Then the flask is cooled by means of an ice bath. After cooling to below 10~C,
80 ml of 8% NaOH are added and stirred for 12 h until a light yellow, clear
viscose solution is obtained.
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