Note: Descriptions are shown in the official language in which they were submitted.
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DOCRET NO. P-493
Process for Derivatizing Polygalactomannans Using
Glyoxal in the Process
Backqround of the Invention
the field of art to which this invention pertains is
polygalactomannans and derivatives thereof.
Derivatives of polygalactomannans, such as the hydroxyalkyl
ether, alkyl ether, carboxyalkyl ethers, aminoalkyl ether and
quaternary ammonium alkyl ether derivatives, are well known
compounds and various methods of preparing the derivatives have
been described.
The hydroxyalkyl ethers of polygalactomannans are prepared
by reacting the polygalactomannans with alkylene oxides under
basic conditions. In U.S. Pat. Nos. 3,723,408 and 3,723,409,
guar flour is reacted with alkylene oxides in the presence of
water and sodium hydroxide. The reaction product is then
neutralized with acid, washed with an alcohol-water mixture, and
is then dried and ground. In U.S. Patent No. 3,483,121, the
polygalactomannans and the alkylene oxides are reacted under
basic conditions with small amounts of water and larger amounts
of water miscible or water immiscible organic solvents.
Carboxyalkyl ethers and mixed carboxyhydroxyalkyl ethers of
polygalactomannans are described in U.S. Patent Nos. 3,740,388
and 3,723,409, respectively. These derivatives are made by
reacting the polygalactomannan with the derivatizing agents
(halofatty acid and alkylene oxide) in a water-alcohol mixture
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followed by washing with water-alcohol mixtures.
~ ther derivatives of polygalactomannans are described in
such patents as U.S. Patent No. 2,461,502 (cyanoethyl ethers),
~dS. Patent No. 4,094,795 (dialkylacrylamide ethers) and U.S.
Patent No. 3,498,912 (quaternary ammonium alkyl ethers~. In the
described processes, the reactions are conducted in water-organic
solvent mixtures and the reaction products are washed with
solvents or water solvent mixtures.
In order to avoid the use of volatile flammable organic
liquids and to eliminate the need to recover such organic liquids
when the reactions are completed, commercial processes have been
developed which use only water as the reaction medium. In such
processes, the gum endosperm of the polygalactomannan is reacted
with the derivatizing agent under alkaline catalysis using
sufficient water to swell the endosperm. The resulting products
are then washed to remove unreacted derivatizing agent, caustic,
salt and by-products. During the washing step, care must be
exercised to avoid forming gels which are extremely difficult to
handle and to avoid washing away product.
The water washing problems have been minimized to a great
extent by adding borax at the end of the reaction or in the wash
water. Borax, under basic pH conditions, will complex with
polygalactomannans to form crosslinked gels. Small amounts o~
borax in the derivati~ing reaction will complex and crosslink the
surface of the swollen endosperm particles so that absorption
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of water and solubilization of the particles is inhibited. The
use of borax increases the efficiency of the process. However,
the disadvantage of the process is that the resulting
polygalactomannan products have a slow hydration rate under high
pH conditions.
In U.S~ Patent No. 4,959,464, a process is described for
derivatizing polygalactomannans gums using aluminum salts to
crosslink the gum surface. Derivatized products made by this
process hydrate under alkaline pH more readily than those in
which borax is used. Even so, there is a need for
polygalactomannan gum derivatives which hydrolyze more readily
under basic conditions.
Summary of the Invention
This invention is directed to a process for derivatizing
polygalactomannans. In one aspect, this invention pertains to a
process for derivatizing polygalactomannans under aqueous
conditions. In another aspect, this invention relates to
derivatives of polygalactomannans which are readily hydratable
under both acidic and alkaline conditions.
By the process of this invention, derivatives of
polygalactomannans are prepared by reacting the gum endosperm of
the polygalactomannan with a derivatizing agent under aqueous
alkaline conditions, treating the derivatized product with
glyoxal at acidic pH, washing the treated produce with water, and
either prior to or after centrifuging and milling the product,
treating it with a base to break the glyoxal crosslinking bonds
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and to oxidize and reduce the aldehyde groups by the Cannizzaro
reaction.
DescriPtion of the Invention
The proc~ss of this invention is particularly applicable to
polygalactomannan gums, which gums are polysaccharides composed
principally of galactose and mannose units. The
polygalactomannans are usually found in the endosperm of
leguminous seeds, such as guar, locust bean, honey locust, flame
tree, Kentucky coffee tree, and the like. The particularly
preferred polygalactomannan for use in the process of this
invention is obtained from guar beans.
The basic unit of the galactomannan polymer in guar gum
contains two mannose units with a glycosidic linkage and a
galactose unit attached to one of the hydroxyls of the mannose
unit. On average, each of the sugar units has three available
hydroxyl sites, all of which can react. The extent of reaction
or derivatization of the hydroxyl ~roups is referred to either as
molar substitution (M.S.) which is the number of units (moles of
derivatizing agent) which has reacted per sugar unit of the
polygalactomannan, or degree of substitution (D.S.) which is the
average number of hydroxy groups of the sugar units that has been
reacted with the derivatizing agent.
The guar endosperm as used in this invention is commonly
referred to as "purified splits~, or ~double purified splits"
depending upon the degree of purification. ~Purified splits" are
obtained by mechanical separation of the endosperm from the hull
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and germ of the guar seed in as pure and intact a form as
possible with ~o other processing steps. These purified splits
contain, as impurities, about 6-12 percent moisture, 2-7 percent
protein and 2-7 percent acid insoluble residue. They have a
particle size range of about 4 to about 20 mesh (U.S. Standard
Sieve Series).
The guar particles are reacted with the various derivatizing
agents under aqueous alkaline conditions. Any of the alkali
metal hydroxides can be used, but the preferred one is sodium
hydroxide. Water is the only reaction medium with no organic
solvents being used in the process.
The derivatizing agents used in the process of this
invention are the well known alkylating or etherifying agents
which contain groups which can react with the hydroxyl groups of
the polygalactomannans to form ether groups, such reactive groups
being vicinal epoxide groups, halogen atoms, or ethylenically
unsaturated groups. Examples of such agents are alkylating
agents, hydroxyalkylating agents, carboxyalkylating agents,
aminoalkylating agents, quaternary ammonium alkylating agents,
cyanoalkylating agents, amidoalkylating agents and the like.
Alkylating agents include methyl chloride, me~hyl bromide, ethyl
chloride, ethyl io~ide and isopropyl chloride. Hydroxyalkylating
agents include ethylene oxide, propylene oxide-1,2, butylene
oxide-1,2, hexylene oxide-1,2, ethylene chlorohydrin, propylene
chlorohydrin, and epichlorohydrin. Examples of carboxyalkylating
agents are chloroacetic acid, chloropropionic acid, and acrylic
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acid. Aminoalkylating agents include aminoethyl chloride,
aminopropyl bromide, N,N-dimethyl-aminopropyl chloride and the
like. Quaternary ammonium alkylating agents are such agents as
2,3-epoxypropyl trimethylammonium chloride,
3-chloro-2-hydroxypropyl trimethylammonium chloride and the like.
Ethylenically unsaturated group containing agents which react
through Michael addition with hydroxyl groups are acrylamide,
methacrylamide, acrylonitrile, methacrylonitrile, acrylic acid,
sodium acrylate and any of the polymerizable monomers which
contain one ethylenically unsaturated polymerizable group.
The derivatizing reaction is conducted in a reactor capable
of withstanding vacuum and moderate pressures and is equipped
with means for agitating the reactants. Air is excluded from the
reactor in order to prevent oxidation of the galactomannan
polymer to lower molecular weight species so as to preserve the
viscosity properties of the final product. The reaction is
conducted under an inert gas, e.g., nitrogen, atmosphere. The
polygalactomannan particles, alkali and derivatizing agent are
added to the reactor with sufficient water to swell the
polygalactomannan particles but not to solubilize ~hem.
Generally, the amounts of reactants, on a weight basis, used for
each 100 parts of polygalactomannan gum (on a dry basis) will
range from about 7.5 to about 300 parts of water (including water
in the gum), about 5 to about 300 parts of derivatizing agent and
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alkali, either in catalytic amounts, or in a slight excess over
stoichiometric amounts if the derivatizing agent contains active
halogen atoms or acid groups.
The derivatizing reactions are generally conducted at
ambient temperatures up to about 250F for a time sufficient to
complete the reaction, about 0.5 to about 24 hours. The reaction
is conducted under gentle mixing or tumbling agitation so as to
continually expose the surfaces of the gum particles to the
derivatizing agent and to keep a uniform temperature throughout
the reactor without exerting shearing forces on the particles
that would grind or smear them.
The product after the derivatizing stage contains, in
addition to the derivat~zed polygalactomannan, unreacted alkali,
alkali salts, unreacted derivatizing agent, hydrolyzed
derivatizing agent and water. The derivatized polygalactomannan
is contacted with water to extract~and wash out the undesirable
by-products. The washing stage is conducted by well known
processes such as slurry and decantation, counter current
washing, and centrifuging. During the washing stage, the
polygalactomannan particles absorb water and if the washing is
not properly controlled, the particles will become jelly like and
will actually dissolve in the water. In order to be handleable
: and processable, the water content of the particles, as measured
~fter centrifugation, should not exceed about 80 weight percent.
If the polygalactomannan derivatives are treated with a small
amount of borax before or during the washing step, the surface of
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the polygalactomannan is crosslinked, thereby decreasinq the
ability of the particle to absorb more water and also helping to
retain the integrity of the particle. As described in U.S.
Patent No. 3,808,19~, when borax and polygalactomannan particles
are added to water, the borax retards the development of
stickiness on the particles' surfaces ~y forming a thin film of
crosslinked polymer on the surface. Although the use of borax is
helpful in the processing of polygalactomannan derivatives, its
presence in the polymer results in slow hydration rate of the
derivatives at alkaline p~.
A similar process is described in U.S. Patent No. 4,959,464
wherein aluminum salts are used in place of borax to crosslink
the surface of the polygalactomannan. Although the hydration
rate of the products under alkaline pH is much improved over
that of the borax treated products, the hydration rate is still
too slow for some processes.
According to the process of this invention, glyoxal is mixed
with the products and by-products of the derivatizing stage
before the washing step. The pH is then adjusted to the acid
side, whereby the glyoxal crosslinks the surface of the
polygalactomannan particles, thereby inhibiting the absorption of
water into the particles and reducing the stickiness of the
surface of particles in a manner similar to borax and aluminum
salts. The derivatized polygalactomannans are then washed with
water to remove by-products and are centrifuged to remove the
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excess water leaving particles having a moisture content
(post-centrifuge moisture) of about 60 to about 80 weight
percent. The particles are then flash ground, i.e., ground to
reduce particle size and at the same time moisture is evaporated
under heat. Flash grinding can be conducted in a hammer ~ill
through which heated air is passed. In the flash grinding
operation, the particle size is reduced to about 100 to about 200
mesh (US Standard Sieve) and the moisture content is reduced to
about 10 percent by weight.
The resulting polygalactomannan derivative dried powder,
which is partially crosslinked with glyoxal and hydrates slowly,
is then treated with a base to break the glyoxal crosslinking
bonds and to convert the aldehyde groups to alcohol and acid
groups (Cannizzaro reaction).
Sufficient base is added to raise the pH of the derivatized
polygalactomannan to at least 10 and preferably to about 10.5 to
about 11.5. The base can be added to the powder as an aqueous
solution which is thoroughly mixed with the powder. However in
order to obtain uniform mixing and a uniform product, the base is
preferably mixed with a lower alcohol and this mixture is added
to the powder. The alcohol is then removed from the powder by
air drying or with the application of heat up to about 40C.
In an alternate and preferred process, the base is added to
the derivatized polygalactomannan after the centrifuging step but
prior to the milling step.
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The amount of glyoxal used in the process of this invention
is about 0.2 to about 2 weight percent based on the weight of
polygalactomannan originally present. The glyoxal crosslin~ing
reaction is conducted under acidic pH conditions, generally at a
pH of about 1 to about 6.5. The acid used for acidification can
be any of the well known mineral or water soluble organic acids.
Preferably the acid is acetic acid.
Any of the well known water soluble bases can be used to
raise the pH to 10 or higher. Such bases include alkali metal
hydroxides, amines, and ammonia. The preferred bases are sodium
and potassium hydroxide and the lower alkyl tertiary amines,
i.e., tertiary amines which contain 3 to about 9 carbon atoms in
their alkyl groups. ~he most preferred base is sodium hydroxide
which is usually adde~ as an aqueous solution, about 15 to about
50 percent sodium hydroxide in water.
In using the bases, they are preferably added mixed with a
lower alcohol, i.e., methanol, ethanol or isopropanol, preferably
methanol, wherein the amount of alcohol used is at least about 25
percent of the weight of the dried powder. Theoretically, there
is no upper limit to the amount of alcohol that can be used.
However, for reasons of economy and practicality, the upper limit
is tha~ amount which is equal in weight to the weisht of the
powder.
When the base reacting step is conducted on the post
centrifuge gel before drying, the base can be added as an aqueous
solution wherein the amount of water is about equal to the total
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water and alcohol used in the powder process.
The derivatized polygalactomannans obtained by the process
of this invention hydrate rapidly under both acidic and basic
conditions and find utility in many processes wherein low
hydration rate has been a problem.
The following examples describe the invention in more
detail. Paxts and percentages are by weight unless otherwise
designated.
ExamPle 1
To a suitable reactor are added 1750 parts of water and 162
parts of 50 percent aqueous sodium hydroxide. Agitation is begun
and the temperature is raised to 155F. Double purified guar
splits, 2000 parts, are added, the reactor is sealed, is purged
with nitrogen and is evacuated three times. Propylene oxide, 460
parts, is added while controlling the pressure rise to about 10
psig. After about 30 minutes, the pressure drops to 0 indicating
complete reaction of the propylene oxide. The temperature is
lowered to 80F, followed by the addition of 13 parts by volume
of 40 percent aqueous glyoxal solution and 180 parts by volume of
glacial acetic acid. The mixture is agitated for 20 minutes.
Thirty minutes after the glyoxal addition, the product is
washed 3 times with water, followed by decanting the water after
each washing step. The product is then centrifuged and the
moisture content is determined to be 74.0 percent. The product
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is then milled and dried to a moisture content of about 10
percent.
Twenty parts of the hydroxypropyl guar product is thoroughly
mixed with 0.2 part of triethylamine and 10 parts by volume of
methanol. The mixture is heated in an oven at 100-110F to dry
the product.
The pH of a 1 percent aqueous solution of the dried product
is 7.5. (Ex lA).
Another 20 part portion of the hydroxypropyl guar product is
treated with 2.0 parts of triethylamine and 10 parts by volume of
methanol. ~fter heating in an oven at 100-110F, the dried
product as a 1 percent aqueous solution has a p~ of 10.0 ~Ex lB).
A one percent aqueous solution of the hydroxypropyl guar
product with no base treatment has a pH of 5.5. (Ex lC).
Each of the above products is added to water containing 2
percent potassium chloride and buffered to a pH of 8.0 with
monosodium dihydrogen phosphate and sodium hydroxide. Each
product is added at a concentration of 1.92 grams in 400 mls of
aqueous solution. The rate of hydration is determined by
measuring the viscosity, expressed in centipose, with a Fann 35A
Viscometer. The pH of each solution is measured after 10 minutes
hydration. The hydration rates, initial pH and 10 minute pH are
shown in Table 1.
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TABLE
Ex. pH Minutes pH Minutes
2 3 4 5 10 30 _60
lA 8.0 104 131 147 154 161 7.99 162 163
lB 8.0 124 140 14~ 152 158 8.09 159 160
lC 8.0 80 116 136 146 156 7.93 158 157
Using the same procedure described in Example 1,
carboxymethyl-hydroxypropyl guar is prepared by reacting the
following components:
100 parts o double purified guar splits,
15.74 parts of sodium monochloroacetate,
16.4 parts of 50 percent aqueous sodium hydroxide,
23.0 parts of propylene oxide.
When the reaction is completed, the reaction mass is cooled
to 100F and 3.5 parts of glyoxal (40 percent in water) and 10
parts of glacial acetic acid are added. The reaction mass is
mixed for 30 minutes. The mass is then washed twice with 60-70F
water for 3 minutes and is then centrifuged. The post centrifuge
moisture content is measured as 73-75.8 percent. The gel i5 not
sticky and is easily ground and dried to a powder. The inherent
pH, the pH of a 1 percent aquec>us solution, is 6.5.
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Twenty parts of the carboxymethyl hydroxypropyl guar powder
is mixed with 20 parts by volume of methanol and 0.2 part of 50
percent aqueous caustic. After thorough mixing, the methanol is
removed by heating in an oven at 100~110F.
The caustic treatment is repeated as described above except
the amount of aqueous caustic used is increased to 0.3, 0.45, 0.6
and 0.75 part. The caustic treated products are identified in
Table 2.
Each of the caustic treated products is added to water
containing 2 percent potassium chloride buffered to a pH of 8
with monosodium dihydrogen phosphate and sodium hydroxide. Each
product is added at a concentration of 1.92 grams in 400 mls of
aqueous solution. The hydration rate is determined by measuring
the viscosity, expressed in centipose, with a Fann 35A
Viscometer. The pH of each solution is measured after 10 minutes
hydration.
Measurements of hydration rate are also made with solutions
buffered at pH 7.0 and at 5Ø
The hydration rate, initial buffered pH, and pH after 10
minutes hydration are shown in Table 3.
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TABLE 2
Example Added Caustic ~ 50 % aqueous )
2A
2B 0.2
2 C
2 D
2E 0.6
2 F
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TABLE 3
Example pH Minutes pH Minutes
_ 2 3 5 10 30 60
2A 8.018 45 110135 8.01 140 140
2B 8.031 66 109133 8.07 138 140
2D 8.083 90 103115 8.08 127 130
2E 8.0110115 122126 8.10 130 132
2F 8.0120125 129131 8.10 132 133
2A 7.0 6 7 8 32 7.08 130 131
2B 7.0 6 9 11 53 7.11 130 133
2C 7.0 7 9 12 44 7.13 130 135
2D 7.053 59 73 93 7.06 llS 120
2E 7.092 97 104116 7.07 128 130
2F 7.0118121 123128 7.05 130 130
2D 5.031 34 37 45 5.3 70 90
2E S .082 85 90 90 5.4 104 115
2F 5.0112114 117120 5.5 120 122
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The principles, preferred embodiments and modes of operation
of the present invention have been described in the foregoing
specification. The invention which is intended to be protected
herein, however, is not to be construed as limited to the
particular forms disclosed, since these are to be regarded as
illustrative rather than restrictive. Variations and changes may
be made by those skilled in the art without departing from the
spirit of the invention.
