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BACKGROUND OF THE INVENTION
The invention relates to starch-graft copolymer compositions which absorb
and retain under pressure large quantities of aqueous fluids and to their
method of preparation. The invention further relates to various
compositions and articles of manufacture which utilize the instant
composition.
Crosslinked polymeric substances which possess the ability to absorb large
quantities of fluids are known in the prior art. For example, U.S. Pat.
No. 3,669,103 discloses that a variety of monomers may be polymerized to
give copolymers and terpolymers which must be crosslinked in manners known
in the polymer arts. One such copolymer contains carboxamide and
carboxylate groups and is crosslinked by including a difunctional monomer
such as N,N-methylenebisacrylamide into the polymerization solution. The
crosslinking reaction is of critical importance. When the copolymers and
terpolymers are not crosslinked, they are water soluble and have limited
utility as absorbents.
U.S. Pat. No. 3,670,731 discloses the utility of particulate,
water-insoluble, crosslinked polymeric compositions as absorbents in
fabricated articles such as diapers, sanitary napkins, and the like.
It is an object of this invention to provide polymeric absorbent
compositions which have the preparative ease and economic advantages
inherent in starch graft copolymers and which will absorb aqueous fluids
in quantities many times their own weight.
It is a further object of the invention to provide polymeric absorbent
compositions which have not been subjected to normally used crosslinking
compositions or procedures and yet are water-insoluble solids.
In accordance with the objects of the invention, we prepared aqueous
fluid-absorbing compositions comprising water-insoluble alkali salts of
saponified gelatinized-starch-polyacrylonitrile graft polymers containing
gelatinized starch (GS) and saponified polyacrylonitrile (HPAN) in molar
ratios of from about 1:1.5 to 1:9 GS:HPAN. The water-insoluble alkali
salts of saponified gelatinized-starch-polyacrylonitrile graft polymers
are further characterized as water-insoluble solids capable of absorbing
in excess of 300 parts of water by weight per part of the water-insoluble
solids.
Compositions comprising water-insoluble organic amine salts of the
compositions described above were found to absorb aqueous fluids which
contain organic components in major proportions.
Also in accordance with the objects of the invention, we discovered a
method of preparing water-insoluble aqueous fluid-absorbing compositions
comprising the following steps:
a. saponifying a gelatinized starch-polyacrylonitrile graft polymer
(GS-PAN) in an aqueous slurry with an alkali in amounts such that the
molar ratio of alkali to the acrylonitrile repeating unit of said GS-PAN
is from about 0.1:1 to 7:1 to form a water-soluble saponified GS-PAN
(water-soluble GS-HPAN); and
b. optionally adjusting the pH of said water-soluble GS-HPAN to about 3
followed by isolating the resulting water-insoluble acid form of GS-HPAN,
and readjusting the pH of said water-insoluble acid form of GS-HPAN to
from about 4 to 12 to reform said water-soluble GS-HPAN; and
c. drying said water-soluble GS-HPAN to a moisture level of from about 1 to
15% water by weight.
Incorporation of the instant compositions in disposable soft goods such as
diapers, hospital bed pads, surgical pads and sheets, catamenial devices,
and the like would greatly increase the fluid-absorbing capacity of the
articles. Such increased absorbency of the disposable soft goods is
important from both an economic and an ecological standpoint, since the
higher absorbency permits the use of a smaller quantity of material to be
disposed of by incineration or by discharge into sewage systems. The use
of smaller quantities of GS-HPAN also decreases the amount of the
synthetic polymers used in the application of the invention. Acrylonitrile
is a petrochemical, and its decreased consumption increases the amount of
petroleum that can be diverted to more urgently needed products. The
instant compositions are also useful in agricultural applications for
increasing water-holding capacity of soils which promotes more efficient
germination of seeds and plant growth.
When the instant compositions were applied as coatings onto substrates such
as seeds, clay, starch, fibers, paper, or the like, a large increase in
the water-holding capacity of the substrate was realized.
The organic amine salts of the invention, which absorb large amounts of
aqueous-organic fluids, are useful in the formulation of jellied fuels,
paint removers, and other formulations where it is desirable to have an
organic solvent, containing a minimum amount of water, in an essentially
solid form.
DETAILED DESCRIPTION OF THE INVENTION
In prior art methods of producing water-absorbing compositions, it was
assumed that water-soluble products had to be rendered insoluble by
crosslinking the polymers, by saponifying in an aqueous-alcoholic medium,
or by adjusting the pH so that the product was in an insoluble acid form.
We were surprised, therefore, when we discovered a water-insoluble
composition was formed by simply drying water-soluble saponified
starch-polyacrylonitrile graft polymer containing starch that had been
gelatinized prior to graft polymerization. We were further surprised when
we found that the instant products had water absorptive capabilities which
were from three to over 10 times greater than the best prior art starch
graft compositions. The term "water-soluble composition" is herein defined
to include apparently soluble or highly dispersed compositions.
Water-absorbing alkali salts of saponified starch-polyacrylonitrile graft
polymers are disclosed in U.S. Patent No. 3,661,815. Both the method of
preparation and the resulting products disclosed therein differ from the
method and compositions of the instant invention in several critical
areas. It is specifically stated, for instance, in U.S. Pat. No. 3,661,815
that "carrying out the saponification in an alcohol-containing medium is
an essential feature of (the) invention." Absorptive values in Table VII
of U.S. Pat. No. 3,661,815 show that saponification in an alcohol-free
medium results in a product having water-absorptive properties which are
inferior to the product saponified in an alcohol-containing medium. It is
also disclosed in U.S. Pat. No. 3,661,815 that pretreating starch in an
aqueous slurry at 60.degree. C. before grafting was beneficial to the
product while pretreatment of starch at 65.degree. C. was detrimental, and
that "tapioca and potato starch required lower pretreatment temperatures,
because of their lower gelatinization temperatures."
In contrast to the teachings disclosed in U.S. Pat. No. 3,661,815, we have
found that in the instant method the presence of alcohol in the
saponification medium is not only unnecessary, its use results in final
products having significantly lower absorptive capabilities. Two portions
of GS-PAN were saponified in the presence of alcohol and in the absence of
alcohol in accordance with Examples 24-26 of U.S. Pat. No. 3,661,815, and
the products, which were dried in vacuo at 110.degree. C. for 16 hr., were
tested for water and synthetic urine absorptivity. Aqueous-alcohol-KOH
saponification resulted in a product which absorbed 31 g./g. (i.e., grams
substance absorbed per gram absorbent composition) synthetic urine and 220
g./g. water. The aqueous-KOH saponification product absorbed 53 g./g.
synthetic urine and 800 g./g. water. The reason that the
aqueous-alcohol-KOH saponified product prepared in accordance with
Examples 24-26, U.S. Pat. No. 3,661,815 (supra), had a higher absorptive
value than is shown in Table VII, U.S. Pat. No. 3,661,815, for similar
products is believed to lie in the fact that our starting material was
GS-PAN (i.e., a starch-polyacrylonitrile graft polymer prepared from
starch which had been pretreated in aqueous slurry at temperatures above
the gelatinization temperature of the starch).
It is well known that starch in the granule state is insoluble in water at
ambient temperatures. It is also known that when a water suspension of
unmodified starch granules is heated the granules first slowly and
reversibly take up water with limited swelling and then, at a definite
temperature, typically about 70.degree. C., the granules undergo
irreversibly a sudden rapid swelling. As the temperature is increased
beyond about 70.degree. C., more starch molecules diffuse from the
granules until, at a temperature range of about 80.degree. to 100.degree.
C., the starch appears to become soluble. It is an essential and critical
feature of the present invention that the graft copolymerization of
acrylonitrile be carried out on starch that has been pretreated by methods
known to those skilled in the art so as to render it soluble. We prefer to
solubilize the starch by heating an aqueous suspension of starch to about
70.degree. to 100.degree. C. and holding the suspension at such
temperatures for about 15 min. or longer.
We are aware, also, that U.S. Pat. No. 3,425,971 (cited as a reference in
U.S. Pat. No. 3,661,815) discloses water-soluble alkali salts of
(nongelatinized) starch-polyacrylonitrile graft polymers and the insoluble
acid form thereof which is resolubilized by adjusting the pH with alkali.
The alkali salt products are used as thickeners and as such must be water
soluble or completely water dispersible. In U.S. Pat. No. 3,425,971
(supra) as in U.S. Pat. No. 3,661,815 (supra), there is no teaching that
simply gelatinizing the starch before graft polymerizing and drying the
alkali salt graft polymer after saponification would give an insoluble
product with such surprisingly different properties.
Starch-polyacrylonitrile graft copolymers are well known. Fanta, Block and
Graft Copolymerization, R. J. Ceresa, ed., John Wiley and Sons, 1973,
Chapter 1, has recently reviewed the various methods for making starch
graft copolymers and the influence of such variables as type of initiator
used, type of pretreatment of starch, kinds of polymerization media
employed, amounts of monomer used, and the like on starch copolymer
composition. The preferred monomer used to prepare the instant
compositions is acrylonitrile (AN), but it is herein understood that
methacrylonitrile (MAN) is equivalent to the acrylonitrile monomer
specified in the claims. It is contemplated that, with a minimum of
experimentation, those skilled in the art will find other monomers
suitable for use in accordance with the invention and that monomers so
found are also considered herein to be equivalent to acrylonitrile and
methacrylonitrile. Preferred molar ratios of gelatinized starch to monomer
range from about 1:1.5 to 1:9.
The preferred polymerization initiator is the ceric ammonium nitrate-nitric
acid system used in the examples. However, other suitable initiator
systems will be known to those skilled in the art (cf. Fanta, supra).
Saponification of GS-PAN is accomplished with an alkali defined herein as
being the hydroxide of an alkali metal, preferably Li.sup.+, Na.sup.+, or
K.sup.+, or of NH.sub.4 .sup.+ . It is an essential feature of the instant
invention that the saponification step be carried out in a manner such
that a water-soluble product be obtained. Preferably, GS-PAN is contacted
with an aqueous solution of alkali for from 1 to 3 hr. at a temperature of
about 90.degree.. Saponification apparently takes place only on the -PAN
moiety of GS-PAN, converting nitrile groups to carboxamide and carboxylate
groups to form the -HPAN moiety. During saponification, GS-PAN dissolves
and forms a highly viscous solution or dispersion of GS-HPAN.
Water-soluble GS-HPAN compositions were obtained from saponifications in
which the molar ratio of alkali to the polyacrylonitrile repeating unit
(i.e., alkali:AN) ranged from 0.1:1 to 7.2:1. Alkali:AN molar ratios of
from 0.6:1 to 7.2:1 are preferred.
Compositions in accordance with the invention are prepared directly from
the saponification reaction mixture without previous isolation of
water-soluble GS-HPAN. However, higher absorptivities are obtained from
GS-HPAN compositions which are purified before drying.
Isolation of water-soluble GS-HPAN is readily accomplished after completion
of the saponification step by adjusting the pH of the reaction mixture by
any suitable means to about 3, thereby precipitating the water-insoluble
acid form of GS-HPAN. The water-insoluble precipitate is then isolated,
washed, suspended in water, and the pH readjusted by any suitable means to
a pH of from about 4 to 12, thereby reforming water-soluble GS-HPAN.
Alternatively, the water-insoluble absorbent form of GS-HPAN can be
prepared by packing a column with the acid form of GS-HPAN and allowing
gaseous NH.sub.3 to pass up the column for a period of time sufficient to
form the ammonium salt.
The absorbent form of the polymer is prepared by simply drying the solution
or dispersion obtained from the saponification step. Surprisingly, when a
solution or dispersion containing the water-soluble GS-HPAN is cast into a
film and subsequently dried by known routine methods including over
drying, drum drying, and air drying, the resulting dry films are insoluble
and absorb up to about 300 times their weight in water forming clear,
cohesive, self-supporting gel sheets. The dried films, which preferably
contain from 1 to 15% moisture, can be ground or milled to give flakes or
powders which have greatly increased surface areas over the films. The
water-insoluble character of the product is retained by the flakes and the
powders, and both forms display highly rapid uptake of fluids. The amount
of fluid uptake by the flakes or powders is generally similar to amount of
fluid uptake observed for the parent films. The absorbent polymer can be
in the form of a mat or pad. Such forms result when the soluble form of
the polymer is freeze or foam dried.
As an alternative to the drying procedures described above, the viscous
mixture obtained after addition of alkali is diluted with a water-miscible
organic solvent such as alcohol or acetone and the precipitated product
isolated in powder form by filtration and drying.
Of particular importance is the fact that the dried GS-HPAN films are
insoluble in all solvents despite the fact that no crosslinking reagents
were added. Treatment with boiling water, boiling 1N potassium hydroxide,
and boiling 1N hydrochloric acid failed to dissolve the instant films. The
exact nature by which the polymer forms the insoluble films is not clearly
understood. The insolubilization apparently takes place by some unknown
mechanism when water solutions are dried at temperatures as low as room
temperature or lower. The extremely mild conditions under which this
insolubilization takes place are unique and unexpected. The insoluble and
water-swollen graft copolymer was redispersed in water by subjecting it to
high mechanical shear or to sonification. Mechanical shear was
accomplished in a Waring blendor and a colloid mill. Surprisingly, if
shearing has not been too extensive, this dispersion yields on drying, an
absorbent, insoluble film which has properties similar to the original
insoluble polymer. Even dispersions which have been subjected to the
highest mechanical shear will form insoluble films if they are dried at
room temperature and the dried films are then allowed to stand for from
about 7 to 100 days at room temperature and high humidity, or if they are
dried at 160.degree. for from about 15 to 120 min. Insolubilization of
these sheared polymers is accelerated by heat and gamma irradiation.
The absorbency of a film prepared in accordance with the invention was
reduced from 600 to 100 g. water per gram of polymer by 3 megarads of
gamma irradiation. Such control of film swellability can be utilized in
the gel entrapment of enzymes, where a large initial swelling is desirable
to allow the enzyme to penetrate into the film, but subsequent use of the
film requires a lower degree of swelling to keep the enzyme trapped.
The commercial value of immobilized enzymes has been the subject of many
reports in recent years. One of the more frequently used immobilization
techniques has been physical entrapment. Hicks et al. [Anal. Chem. 38(6):
726-730 (1966)] describe a method of entrapping enzymes such as glucose
oxidase in a polyacrylamide gel. As in most procedures which entrap
enzymes within synthetic polymer matrices, it was necessary for the enzyme
to be present during the polymerization of the acrylamide.
Enzymes have also been entrapped in starch gels [Bouman et al., Anal. Chem
37: 1378 (1965)]. Enzymes were dissolved into a solution of starch and the
mixture worked into a slab of polyurethane foam. Water-insoluble GS-HPAN
film was treated with an aqueous solution of glucoamylase, then treated
with a solution of calcium chloride. The calcium chloride shrunk the
fluid-swollen film sufficiently to entrap the enzyme, which remained
active through five separate and consecutive reactions with starch. The
amounts of enzyme, GS-HPAN, and calcium chloride would be different for
each different enzyme, depending upon the enzyme's molecular size and
desired activity. Therefore, the inventive method should not be limited to
any particular enzyme or to any specific ratios of enzyme to
water-absorbent GS-HPAN. Since the method simply involves the absorption
of a solution of the desired enzyme by the water-absorbent film, it would
be easy for one skilled in the art to perform a few experiments to
determine the necessary amount of all components.
Any soluble mineral salt is suitable for shrinking the gel after it has
absorbed the enzyme solution.
Immobilized amylase enzymes were prepared by two methods. One, an
.alpha.-amylase, was covalently bonded to the instant water-absorbent
compositions, and the other, a glucoamylase, was absorbed according to the
method described above. It was supprising when we discovered that in
neither immobilizing enzyme composition did the amylase degrade the starch
moiety of the GS-HPAN, even though these enzymes are well-known degraders
of starch.
The absorbent polymers of the present invention may be extended by mixing
dispersions of water-soluble GS-HPAN with dispersions of inexpensive
natural polymers, or their derivatives, and then drying the resulting
mixtures. Examples of such natural polymers are flour, guar, gelatin,
starch, or dextrin.
An important application of dried water-insoluble GS-HPAN is the reduction
of the water content of emulsions, suspensions, and dispersions. Milk
containing 27.4% milk solids was treated with the water-absorbent
composition in amounts such that the ratio of absorbent to water was about
1:100. The resulting filtrate, which was still a milk emulsion, contained
39.4% milk solids. It will be understood that milk solids include
minerals, protein, and butterfat. Linseed oil-in-water emulsions
containing 9.5 and 52.3% oil were concentrated to emulsions containing
12.3 and 57.9% oil, respectively, when treated with dried films of the
absorbent compositions in amounts such that the ratios of absorbent to
water were about 0.1:90 and 1:100, respectively. The numerous emulsions
known to those skilled in the art will require varying amounts of the
water-absorbent compositions of the instant invention to accomplish the
desired amounts of concentration. However, optimum amounts of absorbent
for each emulsion can be easily determined by a few simple trial
experiments. Preferably, amounts of the instant absorbent composition to
water contained in emulsions was from 0.1 to 1 part of absorbent to 100
parts of water (by weight).
Aqueous dispersions or suspensions such as sewage sludge can be
beneficially treated by addition of the instant water-absorbent
composition so that the use of settling ponds can be reduced or
eliminated. Sewage sludge containing 3.9% solids was dewatered to the
extent that the solids content was increased by 25% by the addition of 0.5
g. of absorbent to 100 ml. of sludge. When the same sewage sludge was
treated with 1 part of absorbent to 100 ml. of sludge, the resulting fluid
mass was too thick to pass through the 40-mesh sieve used to separate the
gelled water-absorbing composition from concentrated sludge.
Although the fluid mass could be separated by other means, it is preferred
that the instant compositions be added to the sludge at a rate of about
0.1 to 0.5 part absorbent per 100 ml. of water (by weight).
It was found that adding the water-absorbent composition to the sewage
sludge at a rate of at least 2 parts absorbent per 100 parts water
provided a crumbly-solid material which cannot be pumped but can be
handled by mechanical means including shovels, scoops, end loaders, and
conveyors. It can be carried in wheelbarrows and trucks, and can be
dispersed on field by means of manure spreaders and the like.
Theoretically, there is no upper limit to the amount of absorbent which
can be combined with sewage sludge. However, for economic reasons, the
preferred range of addition is from 2 to 10 parts absorbent per 100 parts
water.
Thin films of water-insoluble GS-HPAN greatly increase the water-holding
capacity of many substrates. Since prior art absorbent compositions
require crosslinking reactions or saponifications in the presence of
alcohol to make them insoluble, it would be very difficult to coat
substrates with them in order to increase the water-absorptive abilities
of the substrates. The instant absorptive compositions, on the other hand,
can be easily obtained as coatings on any water-insoluble substrate by
merely drying solutions of water-soluble GS-HPAN while the solutions are
in contact with the desired substrate. Examples of such substrates include
silica, clay, animal litter or bedding, granular starch, cellulose fibers,
cloth, and paper. The preferred amount of dry saponified
starch-polyacrylonitrile is 0.5 to 3%, based on the dry weight of
substrate.
Starch granules coated with water-absorbent GS-HPAN show a viscosity rise
at a lower temperature than untreated starch when heated in water. Also,
final viscosities after heating at 90.degree. C. are higher than that
shown by untreated starch. In the manufacture op paper or mineral board,
coated starches are retained better than untreated starch when added at
the wet end along with a cationic retention aid.
Seeds may be coated with saponified starch-polyacrylonitrile and
subsequently dried. Water content in the vicinity of the seed during
germination would thus be maximized. Also, dry GS-HPAN, in powder or flake
form, may be blended with soil. In an arid climate, such a blend will hold
a higher percentage of water for longer periods than untreated soil. The
instant compositions are also useful as soil conditioners. Silt-type soils
are composed of fine particles which pack together to form almost
impenetrable surfaces, increasing water runoff and greatly adding to
erosion and pollution problems. Many polyelectrolyte materials have been
used to aggregate soil particles so that the soil would allow water to
penetrate, thereby minimizing water runoff.
Dispersions of water-soluble GS-HPAN were added to silt-loam soils in
amounts of from 0.3 to 0.9 part GS-HPAN to 100 parts soil and the
resulting soil allowed to dry, leaving a coating of water-absorbent
compositions on the soil particles. These coated soils and uncoated
control soils were then evaluated according to the soil conditioner
testing method of R. M. Hendric [J. Agr. Food Chem. 2(4): 182-185 (1954)].
Up to 96% of the soils coated with the instant compositions formed
aggregates which would not pass a 20-mesh screen while 100 % of untreated
soil passed through 60-mesh screens.
By adding seeds to a dispersion or solution of saponified
starch-polyacrylonitrile, casting and drying a film from the resulting
mixture, the seeds are immobilized in a water-swellable film for use in
gardening or farming.
Nutrients such as nitrates, lime, etc. can be added to the water-soluble
GS-HPAN solution before casting the film, or they can be added as a
solution to the seed containing water-absorbent film. Seeds thus
immobilized can be planted in strips, or the film can be broken up and the
seeds planted in a more conventional manner. Ground or powdered materials
such as iron can be added to the slurry of seeds and water-soluble GS-HPAN
before casting the seed-ladened film in order to give the immobilized seed
sufficient weight to minimize its being washed away. The use of iron in
the film allows handling by means of magnets.
The form of the polymer, which will absorb large quantities of
aqueous-organic fluids where the organic material is the principle
component, is prepared by first isolating the acid form from the
saponification reaction mixture as described above and reacting it with a
suitable organic amine in quantities such that the reaction mixture has a
pH of from 5 to 11. The resulting thick solutions or dispersions of the
organic-amine salts of GS-HPAN are then dried to yield insoluble film
which will absorb organic fluids containing minimal amounts of water.
Examples of suitable organic amines include primary amines such as
methyl-, ethyl-, hexyl-, dodecyl-, benzyl-, chlorobenzyl-, and
ethanolamines; secondary and tertiary analogs of the same; aniline;
cyclohexylamine and pyridine. Other suitable amines will be known to those
skilled in the art.
The following examples are intended only to further illustrate the
invention which is defined by the claims.
All percentages mentioned herein are by weight unless otherwise specified.
EXAMPLES 1- 8
A. Preparation of GS-PAN
Stirred slurries consisting of 5 to 10% by weight starch in water were
heated for 30 min. at the designated temperature, Table 1, and cooled
under a nitrogen atmosphere to 27.degree. C. To each stirred mixture was
added 0.1 molar ceric ammonium nitrate solution in 1N nitric acid (see
Table 1). After 10 min., acrylonitrile was added and the mixture stirred
for 3 hr. at 35.degree. C. The starch-polyacrylonitrile graft copolymer
was isolated by filtration and dried, Table 1.
B. Preparation of water-insoluble acid form of GS-HPAN
The GS-PAN compositions from Examples 1A-8A were slurried in water and
varying amounts of sodium or potassium hydroxide added, Table 2. The
mixtures were stirred at 90.degree. C. until the orange-red color, which
formed on initial heating with alkali, had disappeared. The smooth, light
yellow dispersions were diluted to 5% solids, cooled to room temperature,
and sulfuric acid added to give a pH of 3.2. The water-insoluble acid
form, which precipitated on acidification, was isolated by centrifugation
and washed successively with water, 5:1 methanol:acetone, and acetone. The
product was finally isolated by filtration and dried at 25.degree. C.,
Table 2.
Table 1
__________________________________________________________________________
Starch
Reaction
Starch H.sub.2 O,
Ce.sup.+.sup.4,
pretreat
time,
Yield,
GS:PAN
Example
variety
GS, g.
AN, g.
ml. mmoles
temp., .degree.C.
hr. g. mole ratio
__________________________________________________________________________
1A Corn 25.0 15.0 400 1.5 95 3 38.3
1:1.6
2A Corn 37.4 40.0 600 1.9 55 3 60.0
1:2.4
3A Corn 27.0 31.8 480 1.5 88 17 57.0
1:3.3
4A Waxy sorghum
27.0 31.8 480 1.5 88 17 57.0
1:3.3
5A Wheat 42.4 61.6 400 1.5 85 3 71.0
1:3.5
6A Waxy corn
42.0 61.5 400 1.5 90 3 87.0
1:3.8
7A Wheat 28.8 75.5 400 1.4 85 3 90.0
1:5.7
8A Corn 25.5 75.0 400 1.5 95 3 97.0
1:8.6
__________________________________________________________________________
Table 2
__________________________________________________________________________
GS-HPAN
water-insol.,
GS-PAN (from Part A) acid form
Amount, Conc. in H.sub.2 O,
Alkali:PAN
Reaction Yield,
Example
g. wt. % Alkali
molar ratio
Temp., .degree.C.
time, hr.
g. % N
__________________________________________________________________________
1B 15 6.12 NaOH 1.3:1 92 3.0 -- --
2B 60 3.0 NaOH 1.3:1 90 3.0 -- --
3B 50 6.25 NaOH 1.3:1 95 3.0 37 4.2
4B 50 6.25 NaOH 1.3:1 95 1.5 41 4.3
5B 32 3.2 KOH 2.7:1 100 1.5 -- 5.5
6B 33 4.4 KOH 1:1 100 2.5 32 --
7B 10 4.0 KOH 7.2:1 80 2.0 -- 6.5
8B 12 4.6 NaOH 1.3:1 92 3.0 -- --
__________________________________________________________________________
C. Preparation of water-insoluble GS-HPAN absorbent compositions
To prepare the absorbent polymer, 5 g. of the water-insoluble acid form of
GS-HPAN selected from Example 1B-8B were sifted into 500 ml. of rapidly
stirred water, and high-speed stirring was continued for 30 sec. The pH of
the dispersion was adjusted to 6-9 by addition of 1N potassium, sodium, or
ammonium hydroxide. Some of the resulting viscous solutions were then
spread on trays and dried at 25.degree.-35.degree. C. to yield a
continuous film of absorbent polymer; other, after tray drying, were
coarsely ground to a flake-like material. Still other solutions of the
water-soluble GS-HPAN compositions were drum dried using a drum
temperature of about 132.degree. C. This product was also coarsely ground.
To rapidly evaluate water absorbency of the dry, particulate products, 0.25
g. of the now water-insoluble GS-HPAN absorbent polymer was sifted into
500 ml. of distilled water and allowed to soak for 30 min. The mixture,
containing swollen polymer and excess water, was then poured onto a
40-mesh sieve held in a funnel leading to a graduated cylinder. The
unabsorbed water was collected and measured, and the grams of fluid
absorbed per gram of dry polymer were calculated.
A similar procedure was followed to determine the absorption of an
electrolyte solution simulating urine (simulated urine: 97.09% distilled
water, 1.94% urea, 0.80% NaCl, 0.11% MgSO.sub.4.sup.. 7H.sub.2 O, 0.06%
CaCl.sub.2). One gram of absorber is soaked for 30 min. in 100 ml. of
simulated urine, poured through a 60-mesh sieve, and the excess urine
collected and measured.
The procedure used with 0.9% sodium chloride solution was identical to that
used with synthetic urine.
See Table 3.
Table 3
__________________________________________________________________________
Absorbency of insol. GS-HPAN
Method of
Water,
Synthetic urine,
0.9% NaCl solu-
Example
Alkali.sup. 1
drying
g./g..sup.2
g./g..sup.2
tion, g./g..sup.2
__________________________________________________________________________
1C NaOH tray 320 34 --
2C NaOH tray 160 30 --
2C NaOH drum 189 34 --
3C-1 KOH drum 896 -- 60
3C-2 KOH tray 648 54 --
3C-3 NH.sub.4 OH
tray 725 53 --
3C-4 NaOH tray 711 61 --
4C KOH drum 1000 60 --
5C KOH tray 1150 -- 115
7C KOH tray 1040 -- 140
8C NaOH tray 973 74 --
Cellulose
(control)
-- -- 43 34 --
__________________________________________________________________________
.sup.1 Alkali used to adjust pH of GS-HPAN.
.sup.2 g./g. = grams of absorbed substance per gram absorbent composition
EXAMPLE 9
Absorbents for aqueous-organic fluids are prepared by reacting saponified
starch-polyacrylonitrile in the acid form with an organic amine.
Ten grams of the acid form of GS-HPAN of Example 3B were sifted into 1
liter of water, and 4 ml. of triethylamine were added to the stirred
mixture. The resulting thick dispersion was spread onto a tray and allowed
to dry at 25.degree.-35.degree. C. The resulting continuous film was then
coarsely ground and tested for absorbency as described in Examples 1-8.
One gram of this polymer absorbed 48 g. of simulated urine, 80 g. of 80:20
(by volume) ethanol:water, and 87 g. of 40:40:20 (by volume)
acetone:methanol:water.
EXAMPLE 10
A stirred slurry of 135 g. of wheat starch in 2400 ml. of water was heated
for 30 min. at 85.degree.-90.degree. C. and then cooled under a nitrogen
atmosphere to 25.degree. C. To the stirred mixture were added 75 g. of 0.1
molar ceric ammonium nitrate solution in 1N nitric acid. After 10 min.,
159 g. of flash-distilled acrylonitrile were added and the mixture stirred
for 3 hr. at 35.degree. C.
The mixture was diluted with water, sodium hydroxide was added in varied
amounts, and the mixture was heated to temperatures of
95.degree.-150.degree. C., Table 4. An autoclave was used for temperatures
over 100.degree. C. The resulting water-soluble GS-HPAN compositions were
shown by infrared analysis to be substantially the same as the composition
prepared in accordance with Examples 1-8.
Table 4
______________________________________
Conc. of Reaction Reaction
GS-PAN in NaOH:PAN temp., time,
water, % mole ratio .degree.C. hr.
______________________________________
4.7 0.85:1 95 3.0
2.4 0.85:1 95 3.0
2.4 0.6:1 95 3.0
2.4 0.4:1 95 3.0
2.4 0.4:1 125 3.0
4.7 0.2:1 150 1.5
6.0 0.4:1 150 --
4.7 0.1:1 150 --
______________________________________
EXAMPLE 11
A particularly convenient method of obtaining the absorbent polymer in
particulate form is to loosely pack a column with the acid form of GS-HPAN
and then pass gaseous ammonia up through the column for 15 min. Infrared
analysis shows conversion from the carboxyl to the carboxylate form. See
Table 5.
EXAMPLE 12
The wide pH range which may be used to prepare the absorbent polymer is
shown in Table 6. The water-insoluble acidic polymer of Example 3B was
neutralized with potassium hydroxide to the pH's given in the table and
the dispersions then dried and ground as in Example 1C.
EXAMPLE 13
The following procedure illustrates prior isolation of the
starch-polyacrylonitrile graft copolymer is unnecessary.
Table 5
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Absorbency
Acid form
Water per Synthetic urine
0.9% NaCl
of GS-HPAN
polymer, per polymer, solution per
(Example)
g./g. g./g. polymer, g./g.
______________________________________
3B 1300 80 --
4B 960 52 50
______________________________________
Table 6
______________________________________
Absorbency
Water per 0.9% NaCl solution
pH Before polymer, per polymer,
drying g./g. g./g.
______________________________________
4.0 450 --
4.8 820 60
6.45 960 80
7.85 920 100
11.3 580 80
12.0 340 60
______________________________________
A slurry of 33.2 g. of waxy corn starch in 600 ml. of distilled water was
stirred and heated at 90.degree. C. for 30 min. and then cooled to
25.degree. C. under nitrogen. To the stirred mixture were added 18.7 g. of
0.1 molar ceric ammonium nitrate in 1N nitric acid. After the mixture was
stirred for 10 min., 40 g. of acrylonitrile were added. The reaction
mixture was stirred for 3 hr. at 35.degree. C. and then heated to
90.degree. C. A solution of 25 g. of sodium hydroxide in 600 ml. of water
was added, and stirring at 90.degree. C. was continued for 3 hr. The
thick, clear dispersion was diluted to 5% solids and cooled to room
temperature. The pH was adjusted to 3.2 by addition of 28 g. of sulfuric
acid. The acid form of GS-HPAN was separated by centrifugation, washed
with 1 liter of water, and finally dewatered with 5:1 methanol:acetone and
dried. The yield was 64 g.
The absorbent form of the copolymer (i.e., water-insoluble GS-HPAN) was
prepared by neutralizing with potassium hydroxide, tray drying, and coarse
grinding as in Examples 1-8. This composition absorbed 795 times its
weight of water at 25.degree. C. and 59 times its weight of synthetic
urine.
The procedure was repeated with the exception that 37.4 g. of waxy corn
starch, 80 g. of acrylonitrile, and 44 g. of NaOH (i.e., 0.75 mole NaOH
per mole PAN) were used. The absorbent form, prepared as above, absorbed
1480 times its weight of water and 87 times its weight of synthetic urine.
EXAMPLE 14
The following procedure illustrates the preparation of water-insoluble
GS-HPAN with no intermediate isolation steps.
Preparation of the starch-polyacrylonitrile graft copolymer and its
reaction with sodium hydroxide were carried out as in .times. 13 with 37.4
g. waxy corn starch, 40 g. acrylonitrile, and 25 g. NaOH. The thick, clear
dispersion was diluted to 5% solids and drum dried directly without
acidification using a drum temperature of 132.degree. C. The yield was 96
g. The dry product was crushed and passed through a coarse screen. This
polymer absorbed 280 times its weight of water at 25.degree. C. and 56
times its weight of synthetic urine.
The above procedure was repeated except that the thick, clear dispersion
was drum dried at 13% solids and gave a comparable product.
The above procedure was again repeated with the exception that 37.4 g. waxy
corn starch, 80 g. acrylonitrile, and 36 g. NaOH (i.e., 0.6 mole NaOH per
mole PAN) were used. The absorbent form, prepared as above, absorbed 425
times its own weight of water and 50 times its weight synthetic urine.
EXAMPLE 15
The rapidity with which these polymer will absorb aqueous fluids is shown
in Table 7 for the absorbent composition of Example 3C-2 which was tray
dried.
EXAMPLE 16
As an estimate of the absorbency of these polymers under pressure, the
compositions of Example 15 containing 648 g./g. water and 54 g./g. urine
were centrifuged at 45 and 180 X gravity. It is apparent from Table 8 that
this polymer loses only a small percentage of its absorbed fluid under
pressure, as compared with cellulose.
EXAMPLE 17
The useful absorptive properties of these polymers are not confined only to
synthetic electrolyte solutions or to water.
The composition of Example 3C-2 absorbed 40 times its weight of pork liver
blood, 100 times its weight of human urine, more than 300 times its weight
of water at 75.degree. C., and more than 300 times its weight of water at
0.degree. C.
EXAMPLE 18
A 2-cm. square of absorbent polymer film, prepared from the tray-dried
product of Example 3C-2 weighed 0.03 g. and had a thickness of 0.009 cm.
When placed in a tray of distilled water, the film imbibed water
immediately, and after 10 min. had swelled to an 11.5-cm. square weighing
9.2 g., which is an absorbence of 300 g./g. When the pH was adjusted to
2.3 with hydrochloric acid, the film shrank back to a 2-cm. square and
showed rubberlike elasticity. When the surrounding liquid was replaced
first with potassium hydroxide solution (pH 11), then with distilled
water, and finally with hydrochloric acid solution (pH 2.3), the
respective dimensions of the squares were 7.5, 12, and 2 cm. This cycling
of expansion and shrinkage with pH adjustment was repeated three times.
Each time the dimensional changes were the same, and apparently the film
will undergo extensions and contractions repeatedly.
Table 7
______________________________________
Absorbency
Water per Synthetic urine
Time, polymer, per polymer,
sec. g./g. g./g.
______________________________________
30 365 --
60 410 39
180 538 --
300 570 46
600 616 49
1800 648 54
3600 -- 54
______________________________________
Table 8
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