Weight loss abstract
This invention relates to an improvement to a process for synthesizing
cellulose aminomethanate wherein cellulose is steeped in an aqueous
urea containing solution, dried to form an intimate mixture of cellulose
and urea of known composition, and heated to form the cellulose
aminomethanate; the improvement comprising, heating the mixture
to a temperature above about 125 degrees centigrade, measuring the
weight loss of the mixture during heating, comparing the measured
weight loss of the mixture during heating to the weight of an equivalent
amount of ammonia released in accord with the reaction path: continuing
heating until the total measured weight loss corresponds to the
total weight of an amount of ammonia released in the reaction when
from about 30 to about 100% of the total weight of urea present
in the mixture reacts with cellulose. Cellulose aminomethanate manufactured
in accord with this process, can be made having a uniform distributioon
of substituent throughout the cellulose at the molecular level and
comprises a consistently reproducable product for manufacturing
Weight loss claims
What is claimed is:
1. In a process for synthesizing cellulose aminomethanate, wherein
cellulose is steeped in a urea containing solution, dried to form
an intimate mixture of cellulose and urea of known composition,
and heated to form the cellulose aminomethanate; the improvement
comprising, heating the dried intimate mixture to a temperature
above about 125 degrees centigrade, measuring the weight loss of
the mixture as a result of heating, comparing the measured weight
loss of the mixture to the known weight of an equivalent amount
of ammonia released in accord with the reaction path:
continuing heating until the measured weight loss corresponds to
the weight of an amount of ammonia released in the reaction when
from about 30 to about 100% of the total weight of urea present
in the mixture reacts with cellulose.
2. The process of claim 1 wherein the steep solution comprises
aqueous caustic, the caustic is neutralized with an acidic neutralizing
solution, and a neutral liquor containing urea and a salt of the
neutralizing solution is removed prior to heating.
3. The process of claim 2 wherein the neutral liquor is regenerated,
after removal, and recycled.
4. The process of claim 1 wherein the cellulose is steeped in liquid
ammonia in the presence of urea.
5. The process of claim 3 wherein the acid of the neutral liquor
is regenerated and recycled.
6. The process of claim 4 wherein at least one of urea and liquid
ammonia is regenerated and recycled.
7. The process of claim 2 wherein the intimate mixture is neutralized,
before forming the cellulose aminomethanate, by the addition of
an organic acid.
8. The process of claim 2 wherein the intimate mixture is neutralized,
before forming the cellulose aminomethanate, by the addition of
an inorganic acid.
9. The process of claim 1 wherein the mixture is washed, before
forming the cellulose aminomethanate, with aqueous urea.
10. The process of claim 7 wherein the acid solution is regenerated
11. The process of claim 8 wherein the acid solution is regenerated
12. The process of claim 9 wherein the aqueous urea is separated
from the mixture and recycled.
13. The process of claim 10 wherein the acid is regenerated by
passing through an ion-exchanger.
14. The process of claim 11 wherein the acid is regenerated by
passing through an ion-exchanger.
15. The process of claim 1 wherein the comparison comprises quantification
of percentage urea decomposition.
16. The process of claim 1 wherein the comparison comprises quantification
of percentage reaction completion.
17. The process of claim 1 wherein cellulose is slurried with an
aqueous solution comprising from about 2 to about 10% by weight
caustic and about 12 to about 35% by weight urea, in a cellulose:aqueous
solution weight ratio of from about 1:6 to about 1:15, steeped at
a temperature from about 0 degrees centigrade to about -10 degrees
centigrade for a time sufficient to form a mixture of swelled cellulose
intermingled with urea, neutralized by the addition of an aqueous
acidic solution and thereafter heated to form the cellulose aminomethanate.
18. The process of claim 17 wherein the aqueous acidic solution
also comprises urea.
19. The process of claim 17 wherein the aqueous acidic solution
comprises an inorganic acid.
20. The process of claim 17 wherein the mixture is filtered before
21. Cellulose aminomethanate, produced by a process wherein cellulose
is slurried, in a weight ratio of from about 1:6 to about 1:15,
with an aqueous solution comprising from about 2 to about 10% by
weight caustic and from about 12 to about 35% by weight urea, steeped
at a temperature from about 0 degrees centigrade to about -10 degrees
centigrade for a time sufficient to permit swelling of the cellulose
and distribution of the urea to available hydroxy units within the
swelled cellulose structure, neutralized by the addition of an acidic
solution, and heated to a temperature sufficient to cause reaction
of the urea with the cellulose structure.
22. The cellulose aminomethanate of claim 21 wherein from 0.5 to
30 numerical percent of the cellulose hydroxy groups have been substituted
with aminomethanate groups.
23. A tubular sausage casing comprising the cellulose aminomethanate
of claim 21.
Weight loss description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for monitoring the synthesis
of cellulose aminomethanate which has utility in the manufacture
of cellulose film, such as sausage casing and cellulose films.
2. History of the Prior Art
The replacement of viscose dissolved, modified cellulose film with
the use of ammonia derivatives, such as urea, reacted with cellulose
to form a soluble product is a technology which has been gaining
acceptance in the sausage casing industry. The use of such materials,
in replacement of the traditional viscose regenerated cellulose
process, is preferable as by-products are easily managed and do
not appear to represent significant environmental impact. U.S. Pat.
Nos. 1,771,461; 2,134,825; and 2,129,708 comprise some of the early
work in this technology and demonstrate that film products are obtainable.
Though the final products formed showed potential for use as a film,
it wasn't until U.S. Pat. No. 4,789,006 that film products were
produced using urea and cellulose for use as sausage casings.
Various different terminology has been used to describe the products
of cellulose and urea, such as cellulose aminoformates, cellulose
carbamates, cellulose aminomethanoate and cellulose aminomethanates
as adopted in U.S. Pat. No. 4,789,006. To deter further confusion,
the products formed with cellulose and urea as presented in the
above patents and hereinafter will be referred to as cellulose aminomethanates.
With recent improvements in cellulose aminomethanate technology,
such as those described in U.S. patent applications Nos. 365,272
and 365,267 filed on even date herewith, entitled Cellulose Aminomethanate
By Acid Neutralization (M. Rahman), Preparation of Cellulose Aminomethanate
(M. Rahman and D. Bridgeford) and Cellulose Aminomethanate by Ion
Exchange Extraction (D. Bridgeford), each herewith incorporated
by reference, the manufacture of cellulose aminomethanate product
has become more convenient and suitable for use in the large volumes
required for the sausage casing industry. Problems still exist however,
in the manufacturing process, occasioned by the difficulty of controlling
the extent of reaction that takes place between the urea and the
cellulose structure in forming the cellulose aminomethanate. Thus
there is a need for a method of monitoring the urea/cellulose reaction
which will allow increased control over the reaction to improve
consistency and product quality in the manufacturing process.
It is an object of this invention to improve the process for the
formation of cellulose aminomethanate by providing means for monitoring
the urea/cellulose reaction.
It is another object of this invention to provide a cellulose aminomethanate
material having improved processibility.
It is a further object of this invention to provide a convenient
means for processing urea intermingled cellulose which is being
treated by heating.
BRIEF DESCRIPTION OF THE INVENTION
The aforementioned objects and more are achieved by an improvement
in the process for synthesizing cellulose aminomethanate, wherein
cellulose is steeped in a urea containing solution, dried to form
an intimate mixture of cellulose and urea of known composition,
and heated to form the cellulose aminomethanate. The improvement
comprises, heating the dried intimate mixture to a temperature above
about 125 degrees centigrade, measuring the weight loss of the mixture
during heating, comparing the measured weight loss of the mixture
to the weight of an equivalent amount of ammonia released in accord
with the reaction path:
continuing heating until the weight loss corresponds to the weight
of an amount of ammonia released in the reaction when from about
30 to about 100% of the total weight of urea present in the mixture
decomposes for reaction with cellulose.
It has been found that when cellulose aminomethanate is manufactured
in accord with this process, a higher consistency in quality is
obtained and the soluble product formed has clarity and filterability
suitable for manufacturing a strong film.
DETAILED DESCRIPTION OF THE INVENTION
The synthesis of cellulose aminomethanate suitable for use in the
manufacture of sausage casings involves at least two controlling
elements. First, the cellulose structure of the material used must
be impregnated with urea in a uniformly distributed manner to assure
uniformity of reaction throughout the reaction mass. Second, the
thus impregnated cellulose structure must then be thermally treated
for a sufficient time and temperature to efficiently decompose the
distributed urea and form the cellulose aminomethanate derivative
without causing significant undesirable degradation to the cellulose
In order to achieve uniform distribution, it has been found that
the hydrogen bonded networks and associated crystalline structure
of cellulose need be broken to make the cellulose sufficiently accessible
to the urea. In the process of U.S. Pat. No. 4,404,369 this accessibility
is accomplished by steeping cellulose in a solution of urea in liquid
ammonia, the liquid ammonia apparently acting to cause the cellulose
to swell, which makes the cellulose more accessible to the urea.
In U.S. Pat. Nos. 2,129,708 and 2,134,825, as well as European patent
Office Application 85890246.3, the method of achieving distribution
of the urea is by steeping cellulose in a solution of urea in aqueous
sodium hydroxide at room temperature such that swelling of the cellulose
structure is achieved and urea can theoretically be distributed
The previously described co-pending applications, filed of even
date herewith, address the discovery that low concentration caustic
solutions, of minimum volume and low temperature, can be utilized
in steeping, without multiple washings of the slurry with dilute
aqueous urea as required by the prior art and without the concurrent
material, energy and waste-product disposal costs associated therewith.
These applications also disclose the use of acidic neutralizing
solutions and the application of ion-exchange techniques to resolve
sodium hydroxide effects.
It is apparent that though many of the problems associated with
reactant uniformity and processing contaminants have been overcome,
little has been done to monitor and control the reaction responsible
for the formation of the cellulose aminomethanate and thus the quality
of the soluble cellulose product remains inconsistent.
In the prior art, the conventional technique for achieving the
urea/cellulose reaction is typically a batch processing technique
wherein the intimate mixture is heated to a temperature of above
about 130 degrees centigrade for a length of time seen as sufficient
for the reaction to go to completion. Typically determining the
end point of the process comprises taking multiple sequential samples
which are tested to determine if an adequately soluble product has
been attained which can be utilized to form a film. Thus, through
the technique of trial and error the appropriate time and temperature
for heating a batch is determined. As should be apparent, optimization
of such time temperature technique is difficult due to the inherent
variables of mass, pad geometry, heating uniformity, heat transfer
uniformity and other associated problems. With such technique it
was not unusual that product quality, particularly solubility, clarity
or filterability varied significantly from batch to batch and even
within samples from a single batch.
Control of the reaction between the urea and the cellulose is a
significant element in the production of a suitable film product,
particularly sausage casing. It has been found that once the minimal
reaction temperature necessary to form the cellulose aminomethanate
is attained, degradation of the cellulose structure begins and the
obtaining of suitable film material involves a balancing of appropriate
reaction completion with the prevention of significant degradation.
Thus, a key element to quality of product has involved the determination
of when an adequate quantity of urea has been reacted with the cellulose.
Interestingly, it has also been found that the method utilized
to uniformly distribute the urea reactant within the cellulose structure,
particularly the method used to remove the excess base, has a significant
effect upon the degree of completion necessary in the reaction between
the urea and cellulose to produce a suitable film product. For example
it has been found that when the distribution method involves low
concentration aqueous caustic steeping, and the excess caustic is
partially removed, or neutralized, the theoretical percentage of
urea which must be reacted to form a suitable commercial product
is greater than when the product has been steeped in high concentration
aqueous caustic solutions and the excess caustic is completely removed.
A convenient and accurate determination of the progress of the
reaction can be attained by measuring the weight loss of the dry
reaction mixture, theoretically due to the loss of ammonia according
to the reaction path:
Thus, regardless of the process used to attain the intimate urea/cellulose
dry mixture, when the weight loss of the dried reaction mixture
is factored as the weight of ammonia generated during the heating
process, in accord with the above reaction path, a reliable measure
predictive of the quality of the reaction product is provided. Such
measure can be conveniently quantified by comparison to urea decomposition.
One particularly convenient quantified scale comprises the measure
based upon direct comparison to urea decomposition, e.g. % urea
decomposed. A less convenient quantified scale comprises a measure
indirectly based upon urea decomposition and involves comparison
to the cellulose being reacted, e.g. % completion of reaction.
In the process of this invention, a measure of percent urea decomposition
can thus be attained using the relationship: ##EQU1## The measure
of the % cellulose reacted can be similarly attained by using the
relationship: ##EQU2## Where the process utilizes a low concentration
caustic urea steeping solution (2%-12%) which is incompletely removed
prior to heating, a weight of ammonia generated theoretically equivalent
to about 95%-100% calculated urea decomposition (also representing
95-100% urea add-on to the available cellulose) provides consistently
good quality soluble cellulose aminomethanate for use in manufacturing
films such as sausage casings.
When the process utilizes caustic concentrations which were neutralized
with an acidic solution, or treated with an ion exchanger, a weight
of ammonia generated theoretically equivalent to about 30%-70% calculated
urea decomposition provides consistently good quality soluble cellulose
aminomethanate for manufacturing films such as sausage casing. The
same 30-70% equivalency of ammonia generation applies to a liquid
ammonia steeping process. It is stressed, however, that it is essential
that the ammonia generated from volatilization of the liquid ammonia
be distinguished from the ammonia generated from the decomposition
of urea. Thus, there is variation in the theoretical equivalent
amount of urea decomposition which is appropriate to achieve good
quality films. Depending upon the residual caustic from the various
steeping processes used in obtaining the uniform intimate mixture
of reactants, consistency of the final product is directly measurable
from the theoretical generation of ammonia.
Generally, when using an indirect comparison scale comprising percentage
reaction quantification, the preferred products are attained in
the above various processes when between about 110% and about 140%
extent of reaction is calculated.
As can be seen, the above monitoring and control process can utilize
the intimate urea/cellulose dry mixture attained from multiple of
the prior art processes including the liquid ammonia and various
high, medium and low concentration caustic treatments described
in various of the prior art patents and the applications previously
In the practice of this process, the intimate cellulose/urea reactant
mixture typically comprises a pressed cake which may have a water
content well above 50% or more. Thus, the initial heating of the
pressed cake typically constitutes a drying of the cake with concomitant
evaporation of water therefrom which must be taken into consideration
when measuring the weight loss of the reactant mixture for purposes
of this invention. Generally, the cake itself will not reach the
minimum temperatures of this invention until essentially all of
the water has been evaporated therefrom. In addition, no significant
reaction appears to occur between the cellulose and the urea until
most of the water (95% or greater) has been removed from the pressed
cake through drying. Knowing the dry weight of the starting cellulose
pulp and the concentrations of the initial and depleted treating
solutions, the composition of the pressed cake can be easily calculated
by means known in the chemical arts. The known composition of the
pressed cake allows for ready determination of the calculated dry
weight of the urea/cellulose components and, by weight loss, of
the extent of water removal. From a practical experience, weight-loss/time,
due to drying of a pressed cake progresses rapidly until only trace
amounts of water are present, then weight-loss/time slows appreciably
beginning with the reaction of the cellulose with the urea, with
concomitant release of gaseous ammonia.
For purposes of this invention the change in weight of the dry
reactant mixture itself and/or the weight of the gaseous products
removed may be measured. The weight loss can be directly measured
or may be derived through, for example, the concentration of ammonia
released. Multiple different means can be utilized to determine
the weight loss and each is meant to be incorporated herein.
The process of this invention is particularly useful when cellulose
is treated with urea in caustic solutions and most useful when low
caustic concentrations (2-10%) are used in accord with the aforedescribed
applications. Generally, when using low concentrations of caustic
it is also desirable to use the lower steeping temperatures disclosed
in the foregoing identified applications, from about -15.degree.
to about +10.degree. C.
The concentration of urea necessary in an aqueous alkaline steep
solution to provide adequate reactant for the formation of cellulose
aminomethanate generally ranges from about 12 to about 35% urea
by weight and preferably from about 15 to about 30% by weight. A
preferred aqueous solution would contain from about 4 to about 8%
caustic and from about 15 to about 30% urea by weight.
The volume of aqueous solution used in the steeping process is
generally preferred to be minimized to reduce waste products. The
volume of aqueous component must be sufficient to assure wetting
of the cellulose while containing adequate quantities of caustic
to swell the cellulose and urea to react therewith. Thus, the greater
the concentration of caustic, the less volume may be utilized. Generally,
when using low caustic concentrations, a ratio of combined caustic
and urea containing aqueous solution to cellulose should be less
than about 15:1 and preferably less than about 10:1.
Generally, in processing of a cellulose pulp slurry, steeping at
an appropriate temperature for from about 15 minutes to an hour
is adequate. The slurry should be steeped for an amount of time
sufficient to swell the cellulose and allow migration of the urea
into the cellulose structure, however, steeping can be continued
for longer times as long as no significant adverse effect is imposed
upon the cellulose structure.
Removal of the caustic or neutralization of the steeped slurry
is typically the next step in the steeping process and either may
be accomplished as a part of the steeping process or as a separate
step if desired.
Removal of the caustic can be achieved by multiple washings and/or
pressings of the pulp using water containing dissolved urea or by
ion exchange extraction. The pressing step acts to both rid the
slurry of its aqueous component while embedding the urea in the
swelled cellulose. The washing step, with dilute urea, acts to disperse
remaining salts and assure an excess of urea. The washed slurry
is then filtered and/or centrifuged to a desired pressed weight
ratio(PWR), which is calculated by dividing the wet weight of the
pad by the weight of the dry cellulose starting material.
Another method of caustic removal is to suspend the steeped cellulose/caustic/urea
in an aqueous urea solution, mix the solution thoroughly, pump the
mixed solution through a filter into an ion-exchanger and re-circulate
back into the original suspension. Such process can produce a salt-free,
cellulose/urea product suitable for forming the cellulose aminomethanate.
However, since the original alkaline suspension typically contains
soluble cellulose fractions which can precipitate inside the ion-exchange
resin, such process should be carefully filtered.
Neutralization can be achieved by simply adding an appropriate
amount of an acidic neutralizing solution to the steeping solution.
Neutralization can be carried out with any acid neutralizing agent
such as sulfuric, acetic or any suitable inorganic acid, organic
acid, or anhydride of an acid, such as carbon dioxide. The acid
solution can be of varying strengths and may or may not contain
additional amounts of urea. Urea is typically added when the urea
concentration of the initial steep solution was low.
The direct neutralization technique can be applied to low caustic
low temperature steeping, high caustic room temperature steeping
and any combination of conditions. It can also be applied to separately
mercerized, alkali cellulose crumb as produced in commercial viscose
processes, by subsequent steeping in aqueous urea before neutralization.
Separation of the cellulose-urea from the neutralized or caustic
free and/or reduced caustic steeping liquor is typically the next
step in the treatment process. Removal of the liquor can be attained
by filtration, pressing, centrifugation or other methods of the
After caustic removal or neutralization, and separation of the
cellulose/urea mixture, the recovered liquor contains urea and may
also contain the salt of the neutralizing acid with few, if any,
dissolved cellulose fragments. Thus the liquor can be simply and
conveniently regenerated through an ion-exchanger and be re-used
after appropriate adjustment of concentrations. Surprisingly, the
sodium sulfate left in the cellulose/urea mixture when using sulfuric
acid neutralizing solution does not appear to adversely affect the
subsequent thermal reaction to form the cellulose aminomethanate.
Interestingly sodium salts of any nature appear not to affect the
The resulting impregnated cellulose can then be cured in accord
with the process of the invention and frequently results in little
discoloration or significant degradation.
The following examples are provided to exemplify the invention
and are not meant to be a limitation thereof.
Ten (10) grams of cellulose (510-550 DP.sub.v Buckeye V-65 pulp)
was added to 200 g of 20% urea in 0.5% sodium hydroxide and macerated
in a Waring blender. The mixture was allowed to stand 30 minutes
at room temperature followed by 1 hour at 0.degree. C. The mixture
was then brought back to approximately room temperature and filtered
on a Buchner funnel, using a polypropylene filter mat, under suction
to form a 31.2 g. pressed cellulose-urea cake. The pressed cake
was directly placed in a 150.degree. C. forced air oven and heated
until the weight became 12.7 g (approx. 75 minutes).
A portion of the product, representing 8.4 g of cellulose, was
washed with water, filtered, placed in a tared beaker and mixed
with a solution containing 37 g of 4.8% ZnO in 24% aqueous NaOH
(the water was ice-cold). The final composition was in the ratio
of 7:1.5:7.4:84.1 of Cellulose:ZnO:NaOH:Water.
On cooling the above mixture to -5.degree. C., a clear viscous
solution was obtained. The solution was aged two days, alternately
at 0.degree. C. and room temperature, centrifuged and converted
into handcast films using a 30 mil drawbar. On coagulation-neutralization,
washing and drying the clear transparent films showed rewet Mullen
burst strengths of 14.3-17 psi.
Twenty (20) grams of cellulose (510-550 DP.sub.v Buckeye V-65 sheet
pulp) was added to 200 grams of a steeping solution consisting of
5% (W/W) sodium hydroxide and 30% (W/W) urea at about room temperature.
The sheet structure was broken to make a uniform slurry with the
help of a spatula and the slurry was cooled overnight in a -16.degree.
C. freezer. The next day, the slurry was neutralized with 100 g
of 12.25% aqueous sulfuric acid to a final pH of 9.3. The cellulose-urea-sodium
sulfate mixture was collected on Whatman 541 filter paper over a
Buchner funnel under suction. Excess liquid was squeezed out of
the pad and into the filtrate using a rubber dam. The pressed weight
of the resulting cellulose urea pad was 83.2 g and had a pressed
weight ratio (PWR) of 4.16, The filtrate did not show any significant
amount of precipitated cellulose on further acidification and standing
overnight. The composition of the pressed cake was calculated from
the PWR and concentrations of starting and spent solutions to have
a 63% urea add-on, 19% sodium sulfate add-on, and a calculated dry
weight of 36.4 g.
The pressed cake was placed in a 150.degree. C. forced air oven
for initial drying and maintained there for thermal decomposition.
The progress of the reaction was monitored by weighing the material
at various times and/or decomposition intervals. When the sample
reached a calculated dry weight of about 36.4 g, further weight
loss was considered as comprising ammonia loss. Samples representing
5 g of starting cellulose were taken out as shown in Table 1.
TABLE I ______________________________________ Extent of Time Weight
Reaction (min) (grams) (% urea dec.) Sampling ______________________________________
0 83.2 -- 20 66.3 Drying 42 53.2 Drying 70 41.5 Drying 87 37.25
Drying 100 35.45 27 110 35.05 38 Sample 1, 8.76 g taken 125 25.86
54 Sample 2, 8.62 g taken 140 17.02 67 Sample 3, 8.51 g taken 155
8.30 89 Sample 4, 8.30 g taken ______________________________________
A plot of weight versus time showed an early curvature typical
of a drying curve and a later linear representation. On an expanded
scale, the linear representation appeared as a zero order kinetic
plot as expected from the solid phase reaction.
The solubility of each of the four samples (TABLE I) in 9% aqueous
NaOH/1% ZnO was tested. Two-fifths of each sample, representing
2 g of cellulose, was washed three times with lukewarm water, filtering
each time through a Whatman 541 filter on a Buchner funnel under
suction. The water content of the washed product was then adjusted
to 20 g and 10 g of a solvent concentrate, made as 27% NaOH and
3% ZnO, was added. The mixture was stirred at room temperature,
all small lumps were broken, and a uniform slurry was produced within
a short time. The mixture was then cooled by dipping into a methanol-filled
cryobath maintained at -16.degree. C. Within 5-10 minutes, clear,
fiber-free solutions were obtained from samples 2 and 3, but not
from samples 1 and 4. Even after prolonged cooling of samples 1
and 4, undissolved fibers could be seen under polarized light. This
demonstrates that the most readily soluble products were obtained
when the extents of reaction corresponded to 50-70% urea decomposition
at 50-70% urea loading.
Sample 2 visually appeared to have the lowest viscosity, at 22.degree.-23.degree.
C., of the samples. When the solution became bubble-free on standing
for 0.5-1 hour, a hand-cast film was made on a glass plate using
a 30 mil drawbar. The film was coagulated and neutralized in a conventional
acid-salt bath used for viscose coagulation-regeneration. Excess
acid and salt were then washed off and the neutral film was mildly
plasticized with 2% aqueous propylene glycol and dried on a plastic
hoop overnight at room temperature. The next day, the rewet Mullen
Burst Strength of the 38-40 g/m.sup.2 film was found to be 12.5
The remaining 3 g cellulose derivative samples of each part were
washed, dried and analyzed for nitrogen and average degree of polymerization
(DP.sub.V). Each sample's degree of aminomethanate substitution
(DS) was calculated directly from its nitrogen content. The results
are presented in TABLE II.
TABLE II ______________________________________ Sample % N Calc.
DS DP.sub.V average ______________________________________ 1 0.50
0.06 502 2 0.90 0.11 494 3 1.10 0.13 495 4 1.54 0.19 509 ______________________________________
Twenty (20) grams of cellulose (Buckeye V-60 pulp, average DP.sub.V
670), was treated in the same way as in Example II, to a PWR of
3.82. Calculations from PWR, starting and final solution concentrations
gave a urea add-on of 56.3%, a sodium sulfate add-on of 16.7% and
a calculated dry weight of 34.6 g. TABLE III contains the thermal
TABLE III ______________________________________ Extent of Time
Weight Reaction (min) (grams) (% urea dec.) Sampling ______________________________________
0 76.3 Start 20 58.3 Drying 42 44.9 Drying 70 35.0 almost dry 87
33.35 39 Sample 1, 8.34 g taken 100 24.73 52 110 24.36 67 Sample
2, 8.12 g taken 125 16.05 78 Sample 3, 8.03 g taken 140 7.88 97
Sample 4, 7.88 g taken ______________________________________
A plot of weight versus time was found to be similar to that of
Example II. Solubility in caustic/zincate solvent, nitrogen content,
DS and DP.sub.v of the four samples are shown in TABLE IV.
TABLE IV ______________________________________ Sample Solubility
% N DS DP.sub.V ______________________________________ Sample 1
Poor 0.66 .08 534 Sample 2 Excellent 1.26 .15 565 Sample 3 Fair
1.28 .15 559 Sample 4 Poor 1.27 .15 550 ______________________________________
By visual comparison, the solution from sample 4 was most viscous
and that from sample 2 was least viscous.
Two hundred (200) grams of cellulose (Buckeye V-65, 510-550 DP.sub.v
sheet pulp) was added to 2000 g of steeping liquor made up of 8%
sodium hydroxide and 20% urea. The sheet structure was broken to
a uniform slurry with a mechanical stirrer and the mixture was cooled
overnight in a freezer at -16.degree. C.
The next day, the mixture was neutralized with 1000 g of an acidic
urea solution containing 19.6% sulfuric acid and 20% urea, mixed
thoroughly, and filtered to obtain a wet pressed weight of 927 g.
The PWR was calculated to be 4.635. The filtered cake was then broken
by hand into smaller fragments, placed in a wire basket lined with
a porous paper, dried initially at 102.degree. C., then at 125.degree.
C., 130.degree. C. and finally maintained at 150.degree. C.
The composition, determined from the PWR, starting and final solution
concentrations, was calculated to have a urea add-on of 72.7%, a
sodium sulfate add-on of 20.7% and a calculated dry weight of 387
g. The data relative to thermal reaction is presented in TABLE V.
TABLE V ______________________________________ Extent of Time Weight
Reaction (min) (grams) (% urea dec.) Comments ______________________________________
0 927 Initial wt. Left overnight @ room temp. 0 869 Start 30 805
Drying 60 738 Drying Oven temp. raised to 125.degree. C. 90 665
Drying 120 597 Drying 150 536 Drying 180 478 Drying Oven temp. raised
to 130.degree. C. 210 446 Drying 240 408 Drying Oven temp. raised
to 150.degree. C. 280 381 14 NH.sub.3 odor 300 374 31 Strong NH.sub.3
odor 315 371 38 Strong NH.sub.3 odor 325 368 48 Sample 1, 18.4 g
taken 345 346 57 Sample 2, 310 g taken 360 34.2 100 Sample 3, 34.2
g taken ______________________________________
The calculated amounts of cellulose in each of the three samples
were: Sample 1, 10 g; Sample 2, 170 g; Sample 3, 20 g.
Portions of each sample were tested for solubility in 9% NaOH with
and without ZnO. Other portions were washed, dried and analyzed
for nitrogen and DP.sub.v. DS was calculated from the nitrogen and
cellulose content. The results are presented in TABLE VI.
TABLE VI ______________________________________ Solubility Calc.
Sample with ZnO w/o ZnO % N DS DP ______________________________________
1 Good Poor 1.02 .12 448 2 Excellent Good 1.46 .18 440 3 Good Good
2.11 .26 490 ______________________________________
On freezing and thawing, the solutions without ZnO gelled much
earlier than the ones with ZnO.
Another solution of Sample 2 was made at 7.7% cellulose concentration
and a film was cast using a 22 mil drawbar. Processing and drying
the film as in Example II gave a rewet Mullen burst strength of
11 psi at 37.5 g/m.sup.2 basis weight.
Fifteen (15) kilograms of cellulose (Buckeye V-65, 530 DP.sub.v
pulp) was slurried into 300 kg of an aqueous solution of 6% sodium
hydroxide and 25% urea, in a 200-gallon mixer. The slurry was passed
through an attrition mill to insure comminution and thorough mixing.
The slurry was then cooled to -8.degree. C. through a scraped surface
heat exchanger, warmed to 17.degree. C., and neutralized with 65
kg of an aqueous acid solution containing 34% sulfuric acid and
The neutral slurry was filtered through a flat-bed suction filter
device to produce eight approximately equal cellulose-urea pads.
Each pad was placed in a tared wire frame, dried to a constant weight,
sampled for analysis of its composition, and then heated at 150.degree.
C. while monitoring the weight at various intervals. The extent
of reaction was calculated as mole percent of ammonia lost, based
on moles of anhydroglucose unit in the cellulose, instead of % of
urea decomposed that was used in the previous examples. The results
are shown in Table VII.
TABLE VII ______________________________________ Extent of Dry
Pad Cellulose Cured Pad Reaction Reaction Pad# wt (kg) wt (kg) wt
(kg) (%) Time (min) ______________________________________ 1 3.20
1.48 3.02 118 175 2 3.32 1.50 3.12 128 113 3 3.49 1.56 3.29 128
85 4 3.22 1.49 3.02 122 112 5 3.21 1.55 3.00 133 114 6 3.10 1.57
2.91 119 160 7 3.46 1.64 3.12 198 85 8 3.08 1.52 2.90 110 115 ______________________________________
The variation of reaction time from 85 minutes to 175 minutes to
achieve a desired 110-140% reaction, that is, loss of 1.10 to 1.40
moles of ammonia per mole of anhydroglucose unit in the cellulose,
indicates that the heating environment could not heat all the pads
uniformly. In fact, each pad was turned around at approximately
midpoint of their target weight-loss in order to minimize any large
variation of the extent of reaction within the various parts of
the pad. Sample #7 was inadvertently placed in an oven hot spot
and unexpectedly went to 198% reaction in a very short time. This
result was thrown out as not representative because the product
was obviously over reacted and would be of poor quality based on
previous findings of inferior solubility of over reacted materials.
Pads 1-6 and 8 were combined and slurried in ambient water then
comminuted by passing through an attrition mill. Excess water was
partially removed and the wet material was reslurried in aqueous
sodium hydroxide solution to a final composition of cellulose to
NaOH to water of 7.0: 7.5: 85.5 respectively.
Cooling the slurry to -7.degree. C. through a scraped surface heat
exchanger provided a clear, fiber-free, viscous solution of light
tan color. The solution was filtered, de-aerated and then treated
by a conventional viscose coagulation/regeneration process to produce
approximately 700 feet of fiber reinforced sausage casing, commonly
known in the trade as fibrous casing. The resulting casing appeared
to have slightly less strength than typical commercial viscose-reinforced
Semi-dry sausages were made with this casing without encountering
any unusual breakage or other problems. Analysis of the casing under
a scanning electron microscope showed a somewhat higher population
of voids at the fiber-matrix interface than the viscose derived
product. This might explain the slightly lower strength property