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BACKGROUND OF THE INVENTION
This invention relates to a high amylose starch-based, water resistant,
alkaline corrugating adhesive with improved runnability or tack. More
particularly, this invention is directed to chemically treated high
amylose raw starch which is useful in alkaline corrugating adhesives and
provides high levels of water resistance while being operable at high
corrugator running speeds.
The term "corrugated paperboard" as used herein refers to a fluted medium
and a facing adhesively joined to the tips on one or both sides of the
fluted medium. The procedures employed in the production of corrugated
paperboard usually involve a continuous process whereby a strip of
paperboard is first corrugated by means of heated, fluted rolls. The
protruding tips on one side of this fluted paperboard strip are then
coated with an adhesive, and a flat sheet of paperboard, commonly known in
the trade as a facing, is thereafter applied to these tips. By applying
heat and pressure to the two paperboard strips thus brought together, an
adhesive bond is formed therebetween. The above-described procedure
produces what is known to those skilled in the art as a single-faced board
in that the facing is applied to only one surface thereof. If a
double-faced paperboard in which an inner fluted layer sandwiched between
two facings is desired, a second operation is performed wherein the
adhesive is applied to the exposed tips of the single-faced board and the
adhesive-coated tips are then pressed against a second facing in the
combining section of the corrugator under the influence of pressure and
heat. The typical corrugating process and the operation and use of
corrugators in general are described in U.S. Pat. Nos. 2,051,025 and
2,102,937 issued on Aug. 18, 1936 and Dec. 21, 1937 respectively to Bauer.
A major concern in such processes is the selection of the appropriate
adhesive, as its properties will affect not only the strength and
stability of the final corrugated product, but also the parameters, such
as corrugator speed, within which the process can be operated. Thus, such
adhesives are chosen in light of the specific requirements of the process
and the properties desired in the ultimate corrugated paperboard. The
adhesives most commonly used in corrugating are starch-based adhesives
which are popular because of their desirable adhesive properties, low cost
and ease of preparation.
The most fundamental of starch corrugating adhesives is an alkaline
adhesive which is comprised of ungelatinized raw starch suspended in an
aqueous dispersion of cooked starch (carrier). The adhesive is produced by
gelatinizing starch in water with sodium hydroxide (caustic soda) to yield
a primary mix of gelatinized or cooked carrier, which is then slowly added
to a secondary mix of raw (ungelatinized) starch, borax and water to
produce the fully formulated adhesive. In the corrugating process, the
adhesive is applied (usually at between 25.degree. and 55.degree. C.) to
the tips of the fluted paper medium or single-faced board, whereupon the
application of heat causes the raw starch to gelatinize, resulting in an
instantaneous increase in viscosity and tack and formation of the adhesive
bond.
It is often desired or necessary in the manufacture of corrugated
paperboard that the adhesive yield water resistant bonds which can
withstand extended exposure to high humidity, water, melting ice and the
like. A number of approaches have been devised to produce water resistant
corrugating adhesives. One method involves preparation of an acidic,
starch-based adhesive wherein urea-formaldehyde together with an acidic
catalyst is added to the composition to produce water resistant bonds in
corrugated board. Another more commonly followed method involves the use
of alkaline curing starch-based adhesive wherein thermosetting resin such
as urea-formaldehyde, ketone-formaldehyde or resorcinol-formaldehyde are
added as crosslinking additives to produce water resistant bonds.
In recent years, due to the uncertainty of the safety of formaldehyde,
efforts have been made to reduce the levels of exposure to formaldehyde or
even better, to provide a formaldehyde-free alkaline starch-based adhesive
composition which is useful in the manufacture of corrugated paperboard.
While water resistance is an important factor to be considered in
formulating a corrugating adhesive, another property which must be
considered and is directly related to the utility of the formulation is
its ability to rapidly form an initial bond, termed "tack" or "green bond
strength". This rate of tack development is directly related to the speed
at which the corrugator can be run, i.e., runnability, and consequently
there exists a need for corrugating adhesives possessing high green bond
strengths and rapid development of tack.
While there are different theories regarding the respective roles of the
raw starch and the carrier in the development of adhesive properties, some
research has centered on the view that the carrier contributes to the bond
strength and setting speed of the adhesive. Indeed, it has been suggested
that good tack in the carrier leads to good tack (and therefore improved
runnability) in the adhesive (see e.g., R. Williams, C. Leake and M.
Silano, TAPPI, Vol. 60, No. 4, Apr. 1977, pp. 86-89). Further, it has been
known for many years that a corrugating adhesive whose carrier portion is
prepared from a high amylose starch exhibits superior tack to one prepared
from pearl starch, which contains about 27% amylose, because the high
amylose carrier will have improved rheological and film-forming
properties, and also increased moisture resistance particularly when used
with chemical crosslinkers. Consequently, there are many different
carriers available for use in starch-based adhesives.
To date, however, relatively little experimentation has been done with the
raw (uncooked or ungelatinized) starch portion of the adhesive, other than
varying the species of starch source utilized. While high amylose starch,
as noted above, has been used in the carrier portion of the adhesive to
provide improved water resistance and tack, it has not been found to be
useful in the raw starch because of its added expense and more
significantly, because it does not provide the level of tack or
runnability desired. This is noted in U.S. Pat. No. 3,532,648 issued on
Oct. 6, 1970 where it is disclosed that by varying the secondary
(unpasted) starch (i.e., ungelatinized or raw starch) employed, the
properties of the adhesive can advantageously be tailored to the
particular corrugated-based production requirements. The patent then
discloses that when an amylose component (at least 35% by weight) is added
to a given formulation to provide at least a portion of the secondary
starch (raw starch), the waterproofness of the adhesive is improved but
such improvement is accompanied by a decrease in the machine speed of the
adhesive, depending on how much amylose component is used.
Accordingly, the need still exists for a formaldehyde-free alkaline
starch-based adhesive that has good water resistance properties and also
has an improved and satisfactory degree of tack or runnability that will
make it particularly useful in corrugating paperboard manufacturing
operations.
SUMMARY OF THE INVENTION
It has now been found that a starch-based, water resistant alkaline
corrugating adhesive free of formaldehyde and other crosslinking additives
and having improved tack or green bond strength is obtained when a
chemically treated or modified high amylose starch is used as the
ungelatinized raw starch component. This high amylose containing adhesive
has high levels of water resistance and improved runnability making it
especially useful in high speed corrugator operations.
More particularly, this invention is directed to a starch-based alkaline
corrugating adhesive comprising an aqueous dispersion of a cooked or
gelatinized starch and a raw starch which is a chemically treated or
modified high amylose starch, i.e., at least 40% by weight amylose
content. This corrugating adhesive, which has good water resistance and
improved runnability or tack as evidenced by its green bond strength,
results from the use of high amylose raw starch which has been mildly
treated or modified by oxidation, hydrolysis, esterification,
etherification, crosslinking, and alkali or solvent treatment.
DETAILED DESCRIPTION OF THE INVENTION
The alkaline corrugating adhesive composition of this invention comprises
an ungelatinized raw starch, a cooked carrier starch, an alkali base
material and water.
The ungelatinized raw starch component utilized in this invention is
comprised in whole or in part by a chemically treated or modified high
amylose starch containing at least 40% and preferably at least 50% by
weight of amylose content.
As previously noted, the use of high amylose starch as the raw component of
corrugating adhesives has not provided the level of tack or runnability
desired. While not wishing to be bound by theory, it is believed that
chemical treatment or modification of high amylose starch as described
herein, has in some way weakened or disrupted the granular structure of
the starch and/or increased the ability of the granule to swell and absorb
water. This in turn results in an adhesive having an increased rate of
tack development and green bond strength and provides improved runnability
and the ability to operate at higher corrugator speeds with no reduction
in water resistance.
The chemical treatment or modification of the higher amylose starch to
weaken or disrupt the granular structure involves one or more operations
including oxidation, hydrolysis, esterification, etherification,
crosslinking, and alkali or solvent treatment. While each of these steps
have been utilized in the treatment of various starches, it is important
that the chemical treatment or modification of high amylose starch as used
herein only involves a mild or low treatment level or degree of
application. This allows the high amylose starch to satisfactorily perform
as the raw starch component in a corrugating adhesive while providing good
water resistance and improved tack or runnability properties. Furthermore,
and significantly, it eliminates the use of formaldehyde or other chemical
additives needed to provide water resistance.
Oxidation using alkaline hypochlorite and more particularly sodium
hypochlorite is a preferred treatment for the high amylose starch. This is
carried out using a light oxidation of 0.1 to 1.5, more preferably 0.2 to
1.2% by weight available chlorine under alkaline conditions, pH of 7.5 to
12. While hypochlorite is a preferred and well known oxidizing agent,
other known oxidants such as hydrogen peroxide, persulfate, peracetic acid
and permanganate as well as combinations of permanganate and hydrogen
peroxide as disclosed in U.S. Pat. No. 4,838,944 issued on Jun. 13, 1988
to L. Kruger may be used.
Hydrolysis by acid treatment with e.g. concentrated HCl at 0.1 to 1% by
weight is also useful in the chemical treatment or modification of high
amylose starch. Besides hydrochloric acid, other acids and particularly
mineral acids such as sulfuric acid and phosphoric acid may also be used.
Treatment of starch under alkaline conditions is also useful in the
chemical treatment and modification of high amylose starch. Sodium
hydroxide, at 2 to 4% by weight treatment, is a preferred alkaline
material but alkali metal hydroxides such as potassium hydroxide, alkaline
earth hydroxides such as calcium hydroxide, alkaline earth oxides such as
barium oxide, alkali metal carbonates such as sodium carbonate, and alkali
metal silicates such as sodium silicate may also be used.
Another treatment technique for disrupting the amylose granular structure
involves the use of solvents such as dimethyl sulfoxide and other polar,
aprotic solvents, e.g. N-methyl pyrrolidone and dimethyl formamide, and
aliphatic alcohols. Particularly useful is dimethyl sulfoxide diluted with
other solvents such as aliphatic alcohols or halogenated hydrocarbons such
as chloroform. The solvent is typically added in a sufficient amount, e.g.
1.5 to 15 parts per part by weight of starch and then the mixture is
refluxed.
Besides the treatments noted above, chemical modification of the high
amylose starch can be made by esterification, etherification or
crosslinking using known procedures but at low treatment levels.
Esterification, for example, may involve acetylation with acetic anhydride
or formation of the half-esters of dicarboxylic acids/anhydrides at 0.5 to
3% by weight treatment levels. Etherification may involve modification
with alkylene oxides such as ethylene oxide and propylene oxide or
carboxymethylation with e.g., sodium chloroacetate, at treatment levels of
0.5 to 3% by weight. Crosslinking may involve modification, for example,
with multifunctional reagents such as epichlorohydrin, phosphorus
oxychloride, trimetaphosphates, and dicarboxylic acid anhydrides at
treatment levels of 0.005 to 0.1% by weight. The various treatments and
modifications as disclosed herein are further described in
Starch:Chemistry and Technology, edited by R. L. Whistler, et al.,
Chapters X and XVII, 1984 and Modified Starches:Properties and Uses,
edited by O. B. Wurzburg, Chapters 2-6, 9 and 11, 1986.
While the various treatments of high amylose as described above can be used
alone, they may also be combined, such as treatment with dimethyl
sulfoxide in combination with hypochlorination in order to obtain
desirable properties.
The high amylose starch material used in this invention as the raw starch
component and optionally as the carrier component is one containing at
least 40% by weight of amylose. It is well known that starch is composed
of two fractions, the molecular arrangement of one being linear and the
other being branched. The linear fraction is known as amylose and the
branched fraction amylopectin. Starches from different sources, e.g.
potato, corn, tapioca, and rice, etc., are characterized by different
relative proportions of amylose and amylopectin components. Some plant
species have been generally developed which are characterized by a large
preponderance of one fraction over the other. For instance, certain
varieties of corn which normally contain about 22-28% amylose have been
developed which yield starch composed of over 40% amylose. These hybrid
varieties have been referred to as high amylose or amylomaize.
High amylose corn hybrids were developed in order to naturally provide
starches of high amylose content and have been available commercially
since about 1963. Suitable high amylose starches useful herein are any
starches with an amylose content of at least 40% and preferably at least
50% by weight. While high amylose corn starch has been especially
suitable, other starches which are useful include those derived from any
plant species which produces or can be made to produce a high amylose
content starch, e.g., corn, peas, barley and rice. Additionally, high
amylose starch can be obtained by separation or isolation such as the
fractionation of a native starch material or by blending isolated amylose
with a native starch.
The high amylose starch used in the raw starch component as described
herein, may comprise the entire starch portion of that component or it may
comprise a blend of 10% or more, preferably 25% or more and more
preferably 50% or more by weight of chemically treated or modified high
amylose starch with other starches suitable for use in corrugating
adhesives. These other starches as well as the starch in the carrier
component may be selected from the several starches, native or converted,
heretofore employed in starch corrugating adhesive compositions. Suitable
starches include, for example, those starches derived from corn, potato,
waxy maize, sorghum, wheat and the carrier may also include high amylose
starches i.e. having 40% or more by weight of amylose. Modified starches
and various derivatives such as ethers, esters, thin-boiling types
prepared by known processes such as mild acid treatments, oxidation, etc.,
and other starches typically employed in corrugating may be used. Other
starches which may be used as the carrier starch include the high amylose
starches having greater than 60% by weight amylose as disclosed in
application docket no. 1458, filed on the same date as this application
and entitled "All Natural, Starch-Based, Water Resistant Corrugating
Adhesive", which is incorporated herein by reference.
The ratio of raw starch to carrier will vary depending on properties
desired and generally will range from about 2:1 to 16:1 by weight
depending on the nature of the starch and the viscosity desired. The total
amount of starch employed including the gelatinized or cooked carrier and
the ungelatinized raw starch will typically be in the range of about 10 to
50% by weight, based on the weight of the composition
While the corrugating adhesive composition as described herein is primarily
directed to the particularly preferred embodiment of a composition
comprising a carrier starch and a raw starch, it may also include a no
carrier composition having just a single starch component comprising an
ungelatinized starch which upon subsequent treatment with alkali becomes
partially swollen. This single starch composition will comprise the
chemically treated or modified high amylose starch of this invention,
optionally with blends of other starches as described herein. The total
amount of starch employed in the single starch component composition (no
carrier) will range from about 10 to 50% by weight, based on the weight of
the composition. Other components including the alkali, boron-containing
salt and water will be used in amounts as otherwise described herein.
The adhesive composition also includes an alkali which is used in amounts
sufficient to provide the adhesive with a pH greater than 7, more
particularly from about 7.5 to 13 and preferably from 10 to 13. Typically
this represents an amount of from about 0.3 to 5% and preferably from
about 1 to 4% by weight based on the weight of starch.
The alkali (base) employed herein is preferably sodium hydroxide; however,
other bases may be used in partial or full replacement of the sodium
hydroxide and include, for example, alkali metal hydroxides such as
potassium hydroxide, alkaline earth hydroxides such as calcium hydroxide,
alkaline earth oxides such as barium oxides, alkali metal carbonates such
as sodium carbonate, and alkali metal silicates such as sodium silicate.
The alkali may be employed in aqueous or solid form.
Another common ingredient of corrugating adhesives is a boron-containing
salt, e.g., borax which is useful as a tackifier and which is optionally
used in amounts of up to about 5% by weight, based on the total weight of
starch. Additionally, any conventional non-chemically functional additives
may be incorporated into the adhesive in minor amounts, if desired. Such
additives include, for example, preservatives; defoamers; wetting agents;
plasticizers; solubilizing agents; rheology modifiers; water conditioners;
penetration control agents; peptizers such as urea; gelatinization
temperature modifiers; inert fillers such as clay and finely ground
polymers; thickeners such as inorganic colloidal clays, guar, hydroxethyl
cellulose, alginates, polyvinyl alcohol, polymers of ethylene oxide and
the like; colorants; and emulsions such as polyvinyl acetate.
The remainder or balance of the adhesive composition will be water in an
amount of from about 40 to 90% and preferably about 50 to 80% by weight,
based on the total weight of the adhesives.
In the preparation of the corrugating adhesives herein, the method used by
the practitioner can vary without serious consequences. Ordinarily,
however, the carrier starch is first gelatinized (cooked) in a portion of
the water with the alkali (caustic soda) to provide the carrier component
of the adhesive. In a separate vessel, a mixture or slurry is made of the
raw starch, borax (optional) and remaining water. The carrier and raw
starch mixture are combined to form the final adhesive. Optional
ingredients, if desired, can be added at any convenient point during the
preparation of either component but are usually added to the finished
adhesive.
The adhesives herein can be used to bond single- or double-faced boards
using any equipment which is presently employed for the preparation of
corrugated board. Thus, the adhesive is usually maintained at a
temperature of between 20 and 55.degree. C. before its application to the
protruding tips of the fluted paper strip. The actual application may be
accomplished by the use of glue rolls which are ordinarily employed in
most corrugating machines, or one may, if desired, utilize other
application methods which may be able to achieve a different distribution
of adhesive. Following the application of the adhesive to the fluted paper
strip, the latter is then brought into immediate contact with the facing
board under the influence of heat and pressure, as is well know in the
art. A double-faced board may be subsequently prepared by bringing a
second facing in contact with the open fluted surface of the single-faced
board by the usual procedures.
Any of the various paperboard substrates may be utilized in combination
with the adhesive composition of the present invention in order to provide
corrugated paperboard. As the corrugating adhesive of the present
invention provides water resistant properties, it is usually desirable to
utilize a water resistant paperboard in combination with the adhesive in
order to provide a water resistant corrugated paperboard product. One
preferred paperboard product is a wax impregnated paperboard, however, any
of the various water resistant paperboard products such as, e.g., resin
impregnated paperboard, may be utilized in combination with the water
resistant adhesive of the present invention.
In the following examples, which are merely illustrative of the various
embodiments of this invention, all parts and percentages are given by
weight and all temperatures are in degrees Celsius unless otherwise noted.
The following test procedures were used to evaluate the various adhesives
and starches herein used in preparing corrugated board.
BRABENDER PEAK VISCOSITY
A Brabender alkaline solution containing 0.86% sodium hydroxide and 0.74%
10 mole borax was used to slurry the starch sample. A 350 cmg sensitivity
cartridge was used. To a 32 g anhydrous sample of starch was added the
caustic/borax Brabender solution to a total charge weight of 460 g. The
mixture was slurried and placed in a Brabender cup and the sample heated
to 30.degree. C. and held for five minutes, then heated at 1.5.degree.
C./minute to 90.degree. C. The peak viscosity in Brabender units (B.U.)
was observed for each sample.
TACK TEST
Samples of adhesive were examined for tack development and green bond
strength in the joining of a 62 lb/MSF (1000 square fee) wet strength
corrugating liner to a 33 lb/MSF wet strength corrugating medium.
The adhesive was applied to the corrugating liner using a 10 mil Bird
applicator. Subsequently, a sheet of corrugating medium was placed atop a
hot plate at 350.degree. F. (177.degree. C.) under a 5 g/cm.sup.2 weight
for 30 seconds. Immediately thereafter, one end of the liner was attached
to a dial-type spring scale. The medium was then manually separated from
the liner in a continuous fashion and the force required to achieve such
separation was periodically recorded. This force is a measure of the green
bond strength and the rate of tack development with time and is related to
the speed at which a corrugator can be run, i.e., the higher the green
bond strength and the faster tack is developed, the faster the corrugator
can be run.
WATER RESISTANT PROPERTIES
Sample adhesives were evaluated for the water resistant properties of bonds
formed on double-faced corrugated paperboard using the following method
which simulates conditions of the double-back section of a corrugator.
The adhesive sample was applied at 3 mil thickness with a Bird applicator
to a glass plate and was transferred to sheets of a single-face web of 62
lb/1000 ft .sup.2 (0.302 kg/m.sup.2) wet strength liner and 33 lb/1000 ft
.sup.2 (0.147 kg/m.sup.2) wet strength medium by means of direct hand
pressure. The single-face samples were then placed on top of another
sample of the wet strength liner and the resultant double-faced board was
bonded at 0.25 psi on a hot plate at 177.degree. C. for 5 seconds. The
bonded boards were then placed in a conditioning atmosphere of 22.degree.
C., 50% relative humidity for 24 hours, after which dry 2.times.4 inch
samples and additional 2.times.4 inch samples of the boards placed in
water at 22.degree. C. for 24 hours were tested as described below.
The sample boards were evaluated for dry pin adhesion and wet pin adhesion
using the tests described in TAPPI Standard T 821 OM-87 using a Hinde and
Dauch Crush Tester obtainable from Testing Machines Inc., Mineola, N.Y.
The test results were recorded in pounds (per 8 square inches) required to
separate completely the double-face liner from the single face web. The
results are the average of six replicate trials.
STEIN-HALL VISCOSITY
Viscosities were determined using a conventional Stein-Hall cup and
measuring the time in seconds, required for 100 ml of the adhesive
composition to pass through an orifice having a diameter of 3/32 inch.
BROOKFIELD VISCOSITY
Viscosities were determined using a Brookfield Viscometer (model RVT) at 20
rpm and 100.degree. F.
EXAMPLE 1
Preparation of Adhesive
All samples of corrugating adhesive were prepared in essentially the same
manner, differing only in the precise starches employed and the ratios of
components. A representative preparation is presented below.
A carrier component was prepared by cooking at 60.degree. C. (140.degree.
F.) 65.3 g of high amylose corn starch (70% amylose) in 132 g of water. A
total of 5.1 g of sodium hydroxide (dissolved in 13.2 g of water) was then
added and the system was agitated for 10 to 20 minutes. Then, 132.0 g of
water was added to cool the system and quench the reaction.
The raw starch component was prepared in a separate vessel by combining
221.6 g of selected treated or other starch with 429.1 g of water at about
30.degree. C. (90.degree. F.) and adding 3.8 g of borax (pentahydrate) to
provide a slurry which was agitated for five minutes. The carrier
component was then slowly added and additional water added, if desired, to
adjust viscosity. The prepared adhesive was subsequently used in the
different test procedures.
EXAMPLE 2
To a slurry of 1 kg of a high amylose corn starch material, (-50% amylose)
in 1.5 l of water at 30.degree. C., enough 3% NaOH was added to raise the
pH to 10.8. Sufficient sodium hypochlorite (NaOCl) at 4.84% available
Cl.sub.2 was added to provide solutions at treatment levels of 0.2, 0.4,
0.6, 0.82 and 1.2% available Cl.sub.2 respectively. Each solution slurry
was stirred for 18 hours while the pH was maintained above 10.8 by
addition of 3% NaOH. Excess sodium hypochlorite was neutralized with 10%
sodium bisulfite. The pH was adjusted to 6.0 with HCl, the slurry filtered
and washed three times with 1.5 l of water. The alkaline Brabender peak
viscosity for each solution was determined and the results noted as
follows:
______________________________________
NaOCl treatment level
Alkaline Brabender
(% available/Cl.sub.2)
Peak Viscosity
______________________________________
0.0 1500 B.U.
0.2 2710 B.U.
0.4 2900 B.U.
0.6 2590 B.U.
0.82 2000 B.U.
1.2 1545 B.U.
______________________________________
Samples of each treated solution were then used as the treated high amylose
raw starch component in a corrugating adhesive prepared in accordance with
Example 1.
TABLE 1
__________________________________________________________________________
RAW STARCH WITH TACK DEVELOPMENT
NaOCl TREATED
% STEIN BROOKFIELD
GEL measured
HIGH AMYLOSE
STARCH
HALL VISCOSITY
TEMPER-
DRY WET in grams over time
(50% AMYLOSE)
IN VISCOSITY
20 rpm ATURE PIN PIN 5 10 15 20 25
(% AVAILABLE Cl.sub.2)
WATER (sec.) @ 100.degree. F.
(.degree.F.)
(lb)
(lb)
sec
sec
sec
sec
sec
__________________________________________________________________________
Untreated 28.5% 81 4050 154 118 17.1
175
200
200
225
250
0.2% 27.8% 137 3700 155 129 16.3
300
350
400
700
900
0.4% 28.1% 81 3500 154 116 15.8
250
375
375
650
975
0.6% 27.8% 75 2920 154 123 18.8
200
250
350
625
850
0.82% 28.5% 93 3550 156 133 18.9
275
325
475
650
925
1.2% 27.8% 130 3720 152 120 17.7
300
325
500
625
800
__________________________________________________________________________
The adhesive samples were then tested for various properties which are
shown in Table 1 along with a comparative sample which used untreated high
amylose starch (50% amylose) as the raw component. The results illustrate
the improvement in runnability as shown by the tack development test of
corrugating adhesives containing the NaOCl treated raw starch over the
untreated raw starch.
Additional corrugating test adhesives containing other treated high-amylose
raw starch components are shown below.
EXAMPLE 3
Alkaline Treatment of High Amylose Raw Starch
To a slurry of 1 kg of high amylose corn starch (50% amylose) in 1.5 l of
water, enough 3% NaOH was added to raise the pH to 11.5. The slurry was
stirred for 18 hours at 45.degree. C. and then filtered and washed twice
with 1.5 l of pH 11.5 water. The alkaline Brabender peak viscosity was
determined to be 1860 Brabender units (B.U.). The solution was then used
as the treated high amylose raw starch component in a corrugating adhesive
prepared in accordance with Example 1 and the adhesive tested for various
properties as shown in Table 2.
EXAMPLE 4
Acid Treatment of High Amylose Raw Starch
To a stirred slurry of 1 kg of high amylose corn starch (50% amylose) in
1.5 l of water at 52.degree. C., 5.0 g of concentrated hydrochloric acid
(0.5% treatment) was added and the slurry stirred for 18 hours. The slurry
was then neutralized by slowly adding sodium carbonate to raise the pH to
4.5 and then 3% NaOH was added to bring the pH up to 5.5. The slurry was
filtered and washed with 1.5 l of water. The alkaline Brabender viscosity
was determined to be 1260 Brabender units The treated solution was then
used as the raw starch component in a corrugating adhesive prepared in
accordance with Example 1 and the adhesive tested for various properties
as shown in Table 2.
EXAMPLE 5
Hydroxypropylation of High Amylose Raw Starch
To a stirred slurry of 15 g NaOH, 90 g of sodium sulfate and 1 kg of high
amylose corn starch (50% amylose) in 1.5 l of water, 5.0 g of propylene
oxide (0.5% treatment) was added. The slurry was sealed and placed in a
tumbler at 40.degree. C. for 18 hours. The pH was adjusted to 5.5 with
17.5% nitric acid and the slurry filtered and washed three times with 1.5
l of water. The alkaline Brabender peak viscosity was determined to be
1800 B.U. The solution was used as the treated high amylose raw starch
component in a corrugating adhesive prepared as in Example 1 and then
tested for various properties as shown in Table 2.
EXAMPLE 6
Acetylation of High Amylose Raw Starch
To a stirred slurry of 1 kg of high amylose corn starch (50% amylose) in
1.5 l water at pH 8 and room temperature, 20.g of acetic anhydride (2%
treatment) was added dropwise. The pH was controlled at 8 by addition of
3.0% NaOH and the slurry was then stirred for an additional 30 minutes at
room temperature. The pH was adjusted to 5.5 with 9.25% HCl and the slurry
was filtered and washed three times with water. The alkaline Brabender
peak viscosity was 1800 B.U. This treated starch was used as the raw
starch component in a corrugating adhesive prepared as in Example 1 and
tested for various properties with results shown in Table 2.
EXAMPLE 7
Carboxymethylation of High Amylose Raw Starch
To a stirred slurry of 1 kg of high amylose corn starch (50% amylose) and
3.95 g of NaOH in 2 l of 95% isopropanol/water, 10 g of sodium
chloroacetate (1% treatment) was added. The slurry was stirred at
50.degree. C. for 18 hours, then neutralized by addition of 5.93 g of
acetic acid. The slurry was filtered and washed three times with 1.5 l of
water. Alkaline Brabender peak viscosity was 2020 B.U. The treated starch
was used as the raw starch component of a corrugating adhesive as in
Example 1 and the adhesive tested for various properties shown in Table 2.
EXAMPLE 8
DMSO Treatment of High Amylose Raw Starch
A mixture of 1 kg of high amylose corn starch (50% amylose) and 2.5 1 of
60:40 methanol/dimethyl sulfoxide (DMSO) was refluxed for 0.5 hours. The
mixture was filtered hot and washed twice with 2 l of methanol followed by
1 l of ethanol. The starch had a fat content reduced from 0.85% to 0.06%
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