Note: Descriptions are shown in the official language in which they were submitted.
7033
Background of the Invention
As ~tated in the Encyclopedia of Polymer Science
and Technology, volume 3, page 325 (1972), "Cellulose i~ a
polyhydroxy compound and is therefore capable of reacting
with such reagents as organic acids, anhydrides, and acid
chlorides to form organic e~ters. Theoretically, (cellulose)
esters of almost any organic acicl can be prepared, ..."
For example, cellulose acetate, the most important commercial
cellulose e~ter, has been conventionally prepared by treat-
ment of cellulose pulps in batch-wise operations with acetic
acid and acetic anhydride, catalyzed by a mineral acid such
as sulfuric acid.
A detailed history of organic cellulose esters is
provided on pages 325-354 of the above identified Polymer
Encyclopedia volume.
~ urthermore, volume 4 of Kirk Obhmer Encyclopedia
of Chemical Technology, pages 632 to 637 (1970), sets forth
additional background material on cellulose acetate, cellu-
lose acetate propionate, and cellulose acetate butyrate,
respectively.
The respective cellulose and cellulose triacetate
molecules are pictured on page 329 of the previously described
Polymer Encyclopedia article. In ordex to prepare a cellu-
lose acetate for use in its main application, i.e., fibers
for the textile industry, a product having an acetyl content
of from about 37% to about 41% must be prepared. Another way
of characterizing the cellulose acetate product is by using
the term "degree of substitution" (DS). The degree of sub- -
stitution (DS) is defined as the average number of hydroxyl
groups substituted, of the three hydroxyl groups available
for substitutlon in the anhydro glucose units. For ex~mple,
~0~7~3
so-called cellulose triacetate has an acetyl content of
43.5% and a degree of substitution of about 2.8-3Ø
Two types of acetylation reactions have been
suggested for preparing cellulose esters. The first is
homogeneous or fibrous esterification. In the homogeneous
process, which is by far the major means by which cellulose
acetate is produced commercially, an excess of acetic acid
and acetic anhydride are employed to form cellulose tri-
acetate having a DS of at least 2.8~ The cellulose tri-
aceta~e produced is in solution in the form of a dope, i.e.,a viscous, usually clear, cellulose acetate solution, pre-
ferably ree of fibers. In order to prepare the desired
cellulose ester product having the requisite lower degree of
substitution, the cellulose triacetate dope is hydrolyzed by
increasing the water content by about 5% to 10%.
As described on pages 337-341 of the ~ncyclopedia
of Polymer Science and Technology articla cited above, the
major commercial process for the preparation o cellulose
acetate is the solution or homogeneous acetylation process.
me most commonly used catalyst in this process is, of course~
sulfuric acid. The Encyclopedia article goes on to state
the esterification reaction to produce the triester contem-
plate~ adding cellulose and acetic acid to an acetylation
mixture where, after the cellulose has been ~wollen and acti-
vated, a small portion of the sulfuric acid catalyst is
added to initiate cleavage of the cellulose chain. At this
point, the mixture is cooled and cold acetic anhydride is
added thereto, thus causing any water in the system to be
reacted by the acetylation mechanism. The mixture is then
further cooled and the acetylation reaction initiated by
adding the remainder of the sulfuric acid catalyst. The
reaction temperature i8 regulated to gradually increa~e to
7~33
90 -95 F. during an interval of about 1.5 to 2 hours to
produce the aforementioned cellulose triester dope. A
60% to 75% mixture of acetic acid and water is then added
to t~rminate the acetylation reaction at the requisite vis-
cosity by destroying the excess anhydride present in the
system. This termination step may require about an hour
to complete. If the triester is a desired product, the
catalyst i5 then neutralized and removed. If, however, the
hydrolyzed lower D.S. product is desired, such as secondary
cellulose acetate, the sulfuric acid concenkration is gener-
ally reduced to the desired level for conducting the reaction,
the temperature is adjusted, and the batch is transferred to
an hydrolysis vessel where the cellulose solution is all~wed
to hydrolyze at constant temperature until desired acetyl
value, as previously discussed, is reached. The cellulose
acetate is then re~overed by various known techniques.
On page 340 of the Encyclopedia of Polymer Science
and Technology description, a more detailed di~cussion of
the intricacies of acetylation is provided. More specifically,
in the previously described conventional cellulose acetate
process, the acetic acid is employed as a ~olvent for the
cellulose triester during the reaction, the acetic anhydride
being the esterifying agent and, at the same time, reacting
with any water formed during the est0rifica~ion process.
Critical to the formation of a uni~orm cellulose acetate
product i`Q a uniform distribution of the sulfuric acid
catalyst with respect to the cellulose molecule. H~Wever,
since the sulfation reaction between the cellulose and the
sulfuric acid is much faster than the acetylation reaction,
the sulfuric acid combines completely, but not necessarily
uniformly, with the cellulose immediately after the addition
of the acetic anhydride. Therefore, control of the kinetics
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6333
of both the sulfation and subsequent acetylation reactions,
respectively, to produce a uniform cellulose triester produck
is difficalt, at best. Accordingly, the prior art has pro-
vided means for chemically driving and controling the sul-
fation and acetylation reaction kinetics. In the aforemen-
tioned conventional cellulose acetate formation process,
for example, acetic anhydride ac~s as the driving force for
chemically controling the ~inetics of the respective sulfa-
tion and acetylation reactions. This i9 accomplished by
the use of an excessive amount of expensive acetic anhydride
to form the cellulose triacetate product while meticulously
controling the reaction parameters over an inordinately long
time period. By employing this tedious, step-wise method,
i.e., activation of the cellulose molecule with sulfuric
acid followed by acetylation employing acetic anh~dride, the
requisite uniform cellulose triester dope will, hopefully,
be produced. as stated on lines 14-16 of page 340, of the
Polymer ~ncyclopedia article, "Proper correlation o the
initial speed of reaction, maximum temperature, and total
time of esterification are important in pxoduction control
and in obtaining a fiber-free clear solution of cellulose
triacetate in acetic acid."
The above peculiarities of the cellulose acetyla~
tion reaction are said to be due to several factors. First,
all of the cellulose hydroxyl groups may not be available
for reaction because crystallinity or insolubility of the
cellulose hinders acces~ of the reagent to the hydroxyl
groups. Second, excessive amounts of degradive side reactions
mu~t cause cleavage of the cellulose chains resulting in
undesirable, nonuniform products having un~atisfactory physi-
cal and chemical pxoperties. In the past, the degradation
reactions have been controled by lowering the temperature
16J1~7~)33
and allowing the acetylation reaction to continue for long
periods of time. Third, the rates of esterification of the
primary hydroxyl groups of the cellulose molecule, as com-
pared with the secondary hydroxyl groups, are di~erent. As
shown by C. J. Malm et alO in the Journal of the American
Chemical Society, Volume 75, pages 80-84 (1953), the
uncatalyzed reactions of cellulose with acetic anhydride
indicate that primary hydroxyl groups reacted ten times as
; fast as the secondary. Furthermore, when the reactions were
catalyzed with sulfuric acid, the primary hydroxyl groups
reacted two and one-half times as fast. This is a further
important reason as to why the cellulose ace~ate ~ormation
reaction cannot be~readily controled~
The proposed heterogeneous formation of cellulose
acetate is accomplished topichemically without dissolving
the cellulose fibers. Furthermore, a product having an ~
optimum degree of substitution for acetone solubility (2~2-2.6) ~ 7~ ' `
can theoretiaally be produced by this proce~s in a direct
manner, without going to the cellulose triester, thereby
further reducing the need for employment of large, excess
amounts of acetic acid and acetic anhydride. Until now, how-
ever, an economical process for producing uniformly substituted,
heterogeneous cellulose esters, preferably in a direct manner,
has not been commercially success~ul.
Thus, cellulose acetate, as well as other higher
acid esters, are still, for the most part, produced in batch-
wise operations requiring considerable time, u~ing relativaly
large ~mounts of exce~s anhydride. Thus, the above standard
conventional procedure, ag well as requiring a high capital
investment owing to the need for extensive equipment to main-
tain the cellulose and reactants during the tedious formation
process, also requires a high material cost owing to the
, . . . . .
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: , . . . .
. . . .
~7~33
necessity for using exce~sive amount of expensive organic
anhydrides.
Various patents describe complex processes for
making organic acid esters of cellulo~e~ For Example,
U. S. 2,966,485 to Laughlin et al. relates to th~ production
of cellulose esters employing a eries of at least four
successive reaction æones in an attempt to form uniform
homogenaous prod-~ct. In British Patents 740,171 and 802,863
to Societe Rhodiaceta, tubular esterification zones are pro-
vided for conducting the requisite ~sterification reaction.
In U. S. 2,778,820 to Clevy et al. and U~ S. 2,854,446 to
Robin et al., cellulose fibers, which have been previously
beaten at low consistency, are employed as the cellulose
feed stream for subsequent cellulose ester formation. Other
patents, such as U. S. 3,525,734 to Rajon, d scribe complex
processes for acetylation and/or hydrolysis in producing
cellulose acetate including modifie~ catalyst systems, the
addition of stabilizers, or by providing other addi~ional
steps to an already lengthy formation procedure. Other sys-
20 tems, such as described in U. S. 3,273,807 to Wright, provide
a process for premixing conditioning fluid, such as acetic
acid, with cellulose fiber solids to facilitate the produc-
tion of fluffed pulp, the respective fibers being individually
coated with conditioning fluid. In this case, a refiner is
used to perform the premixing function.
Summary of the Invention
The present invention relates to an esterification
process employed in the rapid and efficient production of
organic acid esters of cellulose, which includes employing a
confrication step as the predominant means for providing
penetration of the esterification chemicals throughout the
cellulose in a uniformly distributed and controled manner,
,
~ L~47~)33
without unwanted de~radation of the confricated product
formed.
"Confrication" is defined, for purposes of this
invention, as high energy, frictional interaction of a
cellulose-containing reaction ~ystem, including cellulose
fibers and all or part of the chemicals required for esteri-
fication, the cellulose fibers and esterification chemicals
being maintained in intimate contact with each other. More
specifically, the chemicals which are employed with the
cellulose for con~rication in a high energy reactor include
an organic reagent and an esterification catalyst. ~he con-
frication step can be conducted in the absence o~ an organic
acid anhydride reactant. Moreover, all or part of the
anhydride reaction can be provided during the confrication
step and/or at a subsequent point in the reaction sequence.
By employing the above confrication step, the
esterification chemicals, and, if present, the organic acid
anhydride, rapidly and substantially completely penetrate i~
.: .
and are uniformly distributed throuyhout, the cellulose fiber ~ -
20 ~tructure without unwanted deyradation thereof. In contra- -~
distinction, the prior art processes provide for topichemical
treatment of the cellulose by mixing, wetting, or condition-
ing. In ~hese topichemical treatment~, esteri~ication i8 ~ ;~
~lowly advanced chemically ~rom layer-to-layer throughout ;~
the cellulose structure as opposed to the rapid, uniform
penetration which occurs when the confrication step of the
present invention i5 employed. Thus, prior art proce~se~,
by their nature, are inefficient, cumbersome, and difficult
to control. Purthermore, in order to attain the requisite
uniformity commexcially required of the subject cellulose
esters, such as cellulose acetate, cellulose diacetate, and
cellulose triacetate, the prior art esterification reactions
.,
,
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1~7~33
must be closely monitored with respect to temperature during
the entire formation procedure, excessive amounts of anhyd-
ride and extensively long periods of time being a prerequis-
ite to forming the desired product.
Quite unexpectedly, when the process of the present
invention is employed, the requisite organic acid esters of
cellulose can be rapidly and continuously formed, the need
to harness the subject exothermic esterification in order
to maintain uniformity and control degradation and molecular
weight of the reaction product being substantially diminished
by employing the subject controled esterification. More
specifically, when the process of this invention is employed,
the above described confrication step can be conducted either
at atmospheric or super-atmospheric reaction conditions,
respectively, and at ambient or elevated temperatures. In ~;
any case, this is totally contrary to the prior art teach-
ings, wherein meticulous regulation o the entire esterifica-
~, ~
tion reaction is mandatory if commercial cellulose esters
are to be produced.
Thus, while the aforementioned conventional prior
art process requires temperature to be maintained at less
than about 95 F., during the course of the entire reaction,
in order to produce a cellulose ester product having the
required physical and chemical properties, temperatures up
to about the boiling point of the organic reagent, at a$mos-
p heric pressure, and above the boiling point of the organic
reagent at corresponding super-atmospheric pressures, can be
employed in the subject proces~. It is further provided
herein t'nat the ~ubjsct controled esterification can be com-
pletPd in a period of at least about 0.5 hour, and preferably
in at least about 0.25 hour, and more preferably in a period
of at least about 0.1 hour, each of the above ime periods
-- 8 --
10~7~33
being measured Erom the point at which the cellulose-
containing reaction system, ln the absence or in the eresence
of an organic acid anhydride, is subjPct to the subject con-
frication.
A reduction in the D.S. of the cellulose ester
product is required, after completion of the subject esteri-
fication, the esterified cellulosic product formed is then
subjected to hydrolysis, using conventional techniques known
in the prior art, thereby producing the requisite organic
acid esters of cellulose by removing some of the acyl groups
formed during the above esteriication formation.
In any event, the overall amount of organic acid
anhydride reactant can in many instances be significantly
~ ~ .
reduced to a level well below that which is required for ~ ~
.
conventional cellulose ester formation. Alternatively, the
anhydride can be substantially eliminated from the reaction
scheme. However, in this latter case, the cellulose esters
produced have a much broader D.S. range as compared to the
above conventional materials, significantly lower D.S. values
being encompassed thereby.
Brie-f-DescriPtion of the Draw ng
,
Figure 1 is a schematic view in hlock form of a
process flow diagram illustrating the formation of organic
acid esters of cellulose according to the present invention.
Det~iled DescriPtion_of the Invention
Referring now to Figure 1, a cellulose feed system 2
is employed, at high consistency, and is comprised of cellu-
lose fibers and water. Suitable materials from which the
cellulose can be derived for use herein include the usual
species of coniferous pulp wood such as spruce, hemlock, fir,
pinQ, and the like; deciduous pulp wood such as poplar, birch,
~: ', ' ' ' . '
7~
cottonwood, alder, etc.; and fibrous plants used in paper-
making exemplified ~y cereal straws, corn stalks, bagasse,
grasses, and the like.
Individual fibers are separated from the lignin
lamella, i.e., the adhesive-like substa~ce which hinds the
Eibers together and surrounds the multi~b layers of the cellu-
lose in its natural state, by conventional means, such as
chemical pulping. The above feed should preferably be
cellulosic pulp of a~ least 90 G~ brightness points, having
a preferred alpha~cellulose content of at least 85%, and
more prefer~bly of at least 90%. Conventional processes
require a 92~-96% alpha-cellulose range.
"Consistency", as used herein, refers to the percent
by weight on a dry basis of the fibers in the feed. Cellu-
lose feed, which is normally prepared as an aqueous mixture,
is dewatered and reduced to a high consistency so that the
respective fibar surfaces are in intimate contact. Con-
sistencies ranging from about 10% to 60%, and preferably from
about 15% to 35%, are advantageously employedO
Since high consistency cellulosic fibers, in the
usual instance, are in a semifluid state, they are generally
considered nonpumpable. Therefore, a device capable of
transporting a relatively immobile mixture, such as a screw
conveyor, or other like means, can be used to charge the
high consistency cellulose to high energy reactor 10.
Reactor 10 can be any device capable of confricating -
cellulose feed system 2 and esterification chemicals 3 to
produce a confricated, organic acid ester of cellulose 7.
As previously discussed, this ~tep urnishes the predominant
means for producing chemical penetration of the esterifica-
tion chemicals 3, and, if present, organic acid anhydride
reactant 6, throughout the cellulose feed fibers in a
: -- 10 --
,
:
substantially complete, uniformly distributed and controled
manner, without unwanted degradation of the confricated
product formed. For example, cellulose feed system 2 can
be introduced into an area formed within high energy reactor
10, the area including means for confricating feed ~ystem 2
and esterification chemicals 3, respectively. More spe
cifically, the confricating means can, for example, compri e
a pair of opposed surfaces forming a work space therebe~ween, ;~
the opposed surfaces being capable of providing the requi~
ite amount of confricating energy to the cellulose feed
system 2 and esterification chemicals 3 passing within the
work space. This provides substantial penetr~tion and ~ ;
uniform distribution of the esterification chemical~ through- ;
out the cellulose fibexs. Typically, a single- or double-
revolving disc refiner is employed as a high energy reactor ~ ;~
10. A double-disc refiner, for instance, can be the same
refiner, in principle, as the one disclosed in U. S. Patents
2,214,704 and 2,568,783, respectively. Operation of a
refiner such as the Bauer 415, in the mechanical sense, is
more specifically described in the aforementioned patents
; and in Example 1 of this application. In a similar manner,
confricated product 7, or the product from ~econdary
reactor 8, can be provided to high energy reactor 9 ~or fur-
ther confrication. This latter confrication step can be
conducted in the absence or presence of additional amounts
of esterification chemicals.
Confricated product 7 can be directly recovered or
hydrolyzed employing ~onventional techniques or, as will be
hereinafter described, can be ~urther reacted with an organic
acid anhydride in secondary reactor 8, or can be further con-
fricated in high energy reactor 9.
.. . .
The amount of energy imparted to the high con-
sistency cellulose ~ystem 2 must be of sufficient magnitude
to provide confrication. The power input and feed rate~ of
the cellulose can therefore be controled, depending on the
type and quality of the cellulose fibers, so that a given
amount of energy can be imparted to the fibers. For
instance, about 8 horsepower days per ton of air-dried pulp
(HPD/T~, the daily horsepower re~uired to produce one ton -~
of pulp per pass through the high energy reactor~s), and
pxeferably about 15 HPD/~, and an upper energy level of
about 40 NPD/~, and preferably 25 HPD/T, can be exPmplarily
employed.
In producing the subject organic acid ester,
esterification chemicals 3 are added ~o high energy reactor
10 along with the cellulose feed system 2. Typically,
esterification chemicals 3 comprise an organic acid reagent
4 and esterification catalyst 5. Regarding the organic
acid reagent 4, lower alkyl organic acids, either individually
or combinations thereof, such as propionic acid, butyric
acid, and acetic acid~ are most often employed since higher
alkyl organic acid reagents generally react too 510wly.
Acetic acid is preferred, however, for use herein. Esteri-
fication catalyst 5 can also be added to high energy reactor
lO as a component of esterification chemicals 3. Although
other cataly~ts have been proposed, a mineral acid catalyst,
and more particularly sul~uric acid, has attained the most
widespread u~e in catalyzing cellulose e terification
reactions.
A~ previously ~tated, the con~rication step can be
conducted in the presence or absence of organic acid anhyd-
ride reactant 6 employing only the aforementioned feed system
2 and esterification chemicals 3, respectively, in forming
- ~2 -
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~47~33
a confricated organic acid ester of cellulose 7O There-
after, in a particular emhodiment of this invention,
organic acid anhydride 6 can be chemically combined with
the previou~ly formed confricated cellulose ester product
7 to produce a substantially complete and esterified
organic acid ester of cellulose. The amount of anhydride
6 employed, in any case, is dependent for the mo~t part
on reaction conditions, the amount of water present, and
the degree of substitution desired. However, since the
anhydride reactant is quite costly with respect to the ;~
other material~ employed, a minimum amount should be
added in order to maintain the commercial feasibility of
the esterification process.
In a further alternative embodiment, varying
amounts of organic acid anhydride 6 can be added along
; with the cellulose feed 3ystem 2, to high energy reactor
10. Further amounts of organic acid anhydride 6, if
desired, may be also added to secondary reactor 8 fox
reaction with confricated cellulose ester product 7, as
previously described.
As in the case of esterification chemicals 3, the
anhydride reactant 6 on reaction in the high energy
reactor 10, substantially penetrates, and is uniformly
di~tributed throughout, the confricated cellulosic product.
~ower alkyl organic acid anhydride, individually or com-
binations thereof, such as propionic anhydride, butyric
anhydride, and acetic anhydride, are, again, typically
ernployed since higher organic acid anhydride generally
; reacts too slowly.
~he conditions of temperature and/or pressure at
which the con~rication step is conducted does not require
the degree sf meticulous regulation present in conventional
- 13 -
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~(~47~333
esterifica-tion processes. Therefore, confrication can be
carried O-lt at a temperature up to the boiling point of
organic acid reagent 4, at atmospheric pressure, and above
the boiling point of organic acid reagent 4, at correspond- ;
ing super-atmospheric pressure. For example, if the organic
acid reagen-t employed is acetic acid, under atmospheric
conditions, the confrication energy in the high energy
reactor 10 can be up to about 118 C. (the boiling point o~
acetic acid).
In the subject controlled esterification process,
an organic acid ester of cellulose, which is substituted in
a substantially uniformly distributed manner, is efficiently
and rapidly producedO The time required to complete the
above esterification, as previously stated, is measured
from the point at which the cellulose reaction system 2, -~
in the absence or in the presence of an organic acid anhyd-
~ ride, is subjected to confrication in high energy reactor
-~ 10. Specifically, the time required to complete the con-
trolled esterification, as previously set forth, is at least
about 0.5 hour, and preferably in at least about 0.25 hour,
and more preferably in at least about 0.1 hour.
Exam~le 1
As an illustration of the process of the present
invention for forming organic acid esters of cellulose, in an
efficient and rapid manner, including the subject controlled
esterification reaction, the following experiments were con-
ducted.
(A) 10.0 pounds of a high alpha, acetate grade,
cellulose pulp and 0.7 pound of water were premixed with 20
pounds of acetic acid, and fed into a Bauer 415 refiner
where they were confricated for a period of 2 minutes, at
a power input of 12 HPD/T. A solution of 20 pounds of
- 14 -
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~47~3
acetic acid ~nd 0.3 pound of sulfuric acid were metered,
over the course of the above 2 minute~' confrication period,
to the center duct or eye of a 24-inch double-disc Bauer 415
high consistency refiner into a working space for~ed between
a pair of rotatable discs. Each of the discs carried a ~ '!
movably mounted, roughened surface, refining plate section. ;~
The nominal consistency of the cellulose-containing reaction
system formed, measured at the exit of the refiner, was
about 19.6%. The discs, in this case, are rotatable in
opposite directions, about a fixed, common axis by suitable
power means. The roughened surfaces were in r~latively
high motion with respect to each other and were operated at ~ ;
a predetermined power input level of about 12 ~PD/~ so that
the desired degree of confrication was maintained therein.
To produce the energy required for confrication,
the relative movement between the two surfaces will vary
depending upon the type of apparatus employed. In general,
if the discs operate in opposed directions, the surfaces will
operate at a relative tangential velocity of no less than
about 1000 ft/minute, and the rotation will be about a fixed
axis to obvia~e relative gyratory movement which causes ball-
ing of the fibers. When one of the surfaces is stationary,
however, the relative tangential velocity of the surface~
will preferably be at least 5000 ft/minute. Wher2 both sur-
~aces are moving in opposite directions, a relative tangential
velocity of at least 15,000 ft/minute is preferred. Under
all conditions, the velocity between the refiner surfaces
should be sufficiently great so as to impart sufficient
energy to the fibers to effect confrication and, at the same
time, provide sufficient energy to move the fiber~ through
the refiner. The two surfaces bet~een which the pulp is
txeated should preferably be roughened by providing
- 15 -
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1~47q~
projections of such character as to engage the high
consistency pulp.
Although the average operating pressure imparted
by the refiner s~rfaces on the cellulosic fibers may vary,
an average pressure of between 5 to 20 pounds/in will be
sufficient to produce a pulp of desired physical and chemical
properties.
The pulp then is moved rapidly and continuously in
a single pass through the work space, in a direction away
O from the point of introduction, toward the point of dis~
charge, the cellulose acetate product being rapidly
formed therein.
From the confricated product formed, six 765-gram -
samples, each containing about 150 grams of cellulose, 600
grams of acetic acid, 5.4 grams of sulfuric acid, and 10.2
grams of water, were added to a cooled solution (at a
temperature of about 0 - 5 C.) of 445.5 grams of acetic
anhydride, 300 grams of acetic acid, and 5.4 grams of sulfuric
acid. The mixtures were stirred and the cellulose quickly
went into solution in a time of about 15 minutes. The product
formed was cellulose triacetate.
(B) The process described in (A) of this example
was repeated, except that in addition to the cellulose, water
and acetic acid, a solution of 0.48 pound of sulfuric acid
and 20 pounds of acetic anhydride was also pumped into the
eye of the refiner over the course of the 2-minute confrica-
tion period. The consistency in the refiner during this run
was about 19.5%. Three samples of 512 grams each were added
to cold solutions of 400 grams of acetic acid, 97 grams of
acetic anhydride, and 2.4 grams of sulfuric acid. The cellu-
lose triacetate formation reaction began so rapidly that the
- 16 -
~ 7~33;~ ~
confricated product was beginning to turn to acetate dope
as it exited the refiner, in a period o~ time o~ at least
0.1 hour.
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