Note: Descriptions are shown in the official language in which they were submitted.
1
METHOD OF PREPARING PREGELATINIZED, PARTIALLY HYDROLYZED
STARCH AND RELATED METHODS AND PRODUCTS
BACKGROUND OF THE INVENTION
[0002] Starches generally contain two types of polysaccharides (amylose
and
amylopectin) and are classified as carbohydrates. Some starches are
pregelatinized, typically
through thermal means. Generally, pregelatinized starches can form
dispersions, pastes, or
gels with cold water. Pregelatinized starches are generally digestible and
have been used in a
number of ways, including as an additive to a variety of food products (e.g.,
in baking,
snacks, beverages, confections, dairy, gravies, prepared foods, sauces, and
meats) and in
pharmaceuticals.
[0003] Another use for pregelatinized starches is in the preparation of
gypsum wallboard.
In this regard, during manufacture of the board, stucco (i.e., calcined gypsum
in the form of
calcium sulfate hemihydrate and/or calcium sulfate anhydrite), water, starch,
and other
ingredients as appropriate are mixed, typically in a pin mixer as the term is
used in the art. A
slurry is formed and discharged from the mixer onto a moving conveyor carrying
a cover
sheet with one of the skim coats (if present) already applied (often upstream
of the mixer).
The slurry is spread over the paper (with skim coat optionally included on the
paper).
Another cover sheet, with or without skim coat, is applied onto the slurry to
form the
sandwich structure of desired thickness with the aid of, e.g., a forming plate
or the like.
[0004] The mixture is cast and allowed to harden to form set (i.e.,
rehydrated) gypsum by
reaction of the calcined gypsum with water to form a matrix of crystalline
hydrated gypsum
(i.e., calcium sulfate dihydrate). It is the desired hydration of the calcined
gypsum that
enables the formation of the interlocking matrix of set gypsum crystals,
thereby imparting
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strength to the gypsum structure in the product. Heat is required (e.g., in a
kiln) to drive off
the remaining free (i.e., unreacted) water to yield a dry product.
[00051 Often, pregelatinized starches add water demand to the process. To
compensate
for the water demand and allow for sufficient fluidity during manufacture,
water content must
be added into the stucco slurry. This excess water creates inefficiencies in
the manufacture,
including increased drying time, slower manufacturing line speeds, and higher
energy costs.
The inventors have found that pregelatinized and partially hydrolyzed starch
demands less
water.
[00061 The inventors have also found that techniques for preparing
pregelatinized,
partially hydrolyzed starches have not been fully satisfactory. Conventional
methods for
preparing such pregelatinized, partially hydrolyzed starches have not been
efficient, with low
output and slow production, as well as high energy costs. Thus, there is a
need in the art for
an improved method of preparing pregelatinized, partially hydrolyzed starch,
particularly
exhibiting low water demand.
[00071 It will be appreciated that this background description has been
created by the
inventors to aid the reader, and is not to be taken as a reference to prior
art nor as an
indication that any of the indicated problems were themselves appreciated in
the art. While
the described principles can, in some regards and embodiments, alleviate the
problems
inherent in other systems, it will be appreciated that the scope of the
protected innovation is
defined by the attached claims, and not by the ability of the claimed
invention to solve any
specific problem noted herein.
BRIEF SUMMARY OF THE INVENTION
[0008] In one aspect, the invention provides a method of making a
pregelatinized,
partially hydrolyzed starch comprising: (a) mixing at least water, non-
pregelatinized starch,
and a weak acid that substantially avoids chelating calcium ions to make a wet
starch
precursor having a moisture content of from about 8 wt.% to about 25 wt.%; (b)
feeding the
wet starch precursor into an extruder; and (c) pregelatinizing and acid-
modifying the wet
starch precursor in the extruder at a die temperature of about 150 C (about
300 F) to about
210 C (about 410 F). The invention also provides a starch produced according
to this
method.
3
[0009] In another aspect, the invention provides a method of making a
pregelatinized,
partially hydrolyzed starch comprising: (a) mixing at least water, non-
pregelatinized starch,
and a strong acid to make a wet starch precursor having a moisture content of
from about
8 wt.% to about 25 wt.%, wherein the strong acid is in an amount of about 0.05
wt.% or less
by weight of the starch; (b) feeding the wet starch into an extruder; and (c)
pregelatinizing
and acid-modifying the wet starch precursor in the extruder at a die
temperature of about
150 C (about 300 F) to about 210 C (about 410 F). The invention also provides
a starch
produced according to this method.
[0010] In another aspect, the invention provides a method of making board
comprising:
(a) forming a pregelatinized, partially hydrolyzed starch by (i) mixing at
least water,
non-pregelatinized starch, and an acid to form a wet starch precursor having a
moisture
content of from about 8 wt.% to about 25 wt.%, the acid selected from the
group consisting
of: (1) a weak acid that substantially avoids chelating calcium ions, (2) a
strong acid in an
amount of about 0.05 wt.% or less by weight of the starch, or (3) any
combination thereof;
(ii) feeding the wet starch precursor into an extruder; and (iii)
pregelatinizing and acid-
modifying the wet starch in the extruder having a die at a temperature of
about 150 C (about
300 F) to about 210 C (about 410 F); (b) mixing the pregelatinized and
partially hydrolyzed
starch with at least water and stucco to form a slurry; (c) disposing the
slurry between a first
cover sheet and a second cover sheet to form a wet assembly; (d) cutting the
wet assembly
into a board; and (e) drying the board. In some embodiments, the set gypsum
core has a
compressive strength greater than a set gypsum core made with a starch
prepared under a
different method. In another aspect, the invention provides a board produced
according to
this method.
[0010a] In a broad aspect, moreover, the present invention provides a method
of making a
pregelatinized, partially hydrolyzed starch comprising: (a) mixing at least
water, non-
pregelatinized starch, and an acid having a pKa value from 3 to 6 wherein at
least 90% of the
available calcium ions are not chelated to the acid to make a wet starch
precursor having a
moisture content of from about 8 wt.% to about 25 wt.%; (b) feeding the wet
starch precursor
into an extruder; and (c) pregelatinizing and acid-modifying the wet starch in
the extruder at a
die temperature of about 150 C (about 300 F) to about 210 C (about 410 F),
wherein the pregelatinized, partially hydrolyzed starch is at least about 70%
gelatinized, and
wherein the pregelatinized, partially hydrolyzed starch has a cold water
viscosity of from
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3a
about 10 Brabender Unit (BU) to about 120 BU, wherein the cold water viscosity
is
determined for a 10% by weight solution of the starch at 25 C.
[0010b] In another broad aspect, the present invention provides a method of
making board
comprising: (a) forming a pregelatinized, partially hydrolyzed starch by (i)
mixing at least
water, non-pregelatinized starch, and an acid to form a wet starch precursor
having a moisture
content of from about 8 wt. % to about 25 wt. %, the acid being an acid having
a pKa value
from 3 to 6 wherein at least 90% of the available calcium ions are not
chelated to the acid; (b)
feeding the wet starch precursor into an extruder; and (iii) pregelatinizing
and acid-modifying
the wet starch precursor in the extruder having a die at a temperature of
about 150 C. to
about 210 C., wherein the pregelatinized, partially hydrolyzed starch is at
least about 70%
gelatinized and wherein the pregelatinized, partially hydrolyzed starch has a
cold water
viscosity of from about 10 Brabender Unit (BU) to about 120 BU, wherein the
cold water
viscosity is determined for a 10% by weight solution of the starch at 25 C.;
(c) mixing the
pregelatinized and partially hydrolyzed starch with at least water and stucco
to form a slurry;
(d) disposing the slurry between a first cover sheet and a second cover sheet
to form a wet
assembly; (e) cutting the wet assembly into a board; and (f) drying the board.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0011] FIG. 1 is an amylogram plotting viscosity (left y-axis) and
temperature (right
y-axis) versus time (x-axis) that shows pasting profiles of starches extruded
at a moisture
content of 16 wt.% with the solid content of testing slurry being 10 wt.% as
set forth in
Example 2.
[0012] FIG. 2 is an amylogram plotting viscosity (left y-axis) and
temperature (right
y-axis) versus time (x-axis) that shows pasting profiles of starches extruded
at a moisture
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content of 13 wt.% with the solid content of testing slurry being 10 wt.% as
set forth in
Example 2.
[00131 FIG. 3 is a graph plotting temperature versus time showing the
temperature rise
set (TRS) hydration rate of two slurries containing pregelatinized, partially
hydrolyzed
starches treated with alum in an amount of 3 wt.% and retarder in amounts of
0.05 wt.% and
0.0625 wt.%, respectively, and a third slurry containing a conventional
pregelatinized corn
starch having a viscosity of 773 centipoise and retarder in an amount of 0.05
wt.% as set forth
in Example 3.
DETAILED DESCRIPTION OF THE INVENTION
[0014] Embodiments of the invention provide methods of making
pregelatinized,
partially hydrolyzed starches. In one aspect, the invention provides a method
of preparing
board (e.g., gypsum wallboard). Pregelatinized, partially hydrolyzed starches
produced
according to the method of the invention can be used in a variety of other
ways, such as in
foodstuffs (e.g., in baked goods, beverages, confections, dairy, instant
puddings, gravies,
soup mixes, prepared foods, pie fillings, sauces, and meats), pharmaceuticals,
feeds,
adhesives, and colorings. Such starches prepared in accordance with some
embodiments of
the invention are generally digestible and can provide food products with
desired viscosity,
and can retain most of the functional properties of the original base
material.
[0015] Embodiments of the invention are premised, at least in part, on the
surprising and
unexpected discovery of pregelatinizing and acid-modifying starch in a single
step in an
extruder. Surprisingly and unexpectedly, pregelatinizing and acid-modifying
starch in a
single step in an extruder has considerable advantages in comparison to
pregelatinizing and
acid-modifying starch in separate steps. For example, the inventive method of
making
pregelatinized, partially hydrolyzed starch allows for a higher output, faster
production, and
lower energy costs without sacrificing desired properties (e.g., viscosity,
fluidity, cold water
solubility, etc.) as described herein.
[0016] In addition, it has been found that the extrusion conditions (e.g.,
high temperature
and high pressure) can significantly increase the acid hydrolysis rate of
starch. Surprisingly
and unexpectedly, this single step process makes possible using a weak acid,
such as alum,
and/or smaller amounts of strong acid, for starch acid-modification. Either
acid form
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provides a mechanism where protons from acids catalyze the hydrolysis of
starch.
Conventional acid-modification processes include purification and
neutralization steps. The
use of a weak acid (e.g., alum) and/or a small amount of a strong acid avoids
the need for any
neutralization step and the subsequent purification step typically required in
conventional
systems to purify the starch of salts resulting from the neutralization step,
in accordance with
some embodiments of the invention.
[0017] The extrusion process, in accordance with embodiments of the
invention, not only
pregelatinizes the starch, but also partially hydrolyzes (i.e., via acid-
modification) starch
molecules. Thus, the extrusion process in one step provides both physical
modification
(pregelatinization) and chemical modification (acid-modification, partially
acid hydrolysis).
The pregelatinization provides the ability for the starch to impart strength
(e.g., on a final
product such as gypsum board). Acid-modification beneficially partially
hydrolyzes the
starch to provide the starch with the ability to impart strength on a final
product, such as
gypsum board, and low water demand in product manufacture, such as in the case
of gypsum
board manufacturing processes. Thus, the product of methods of preparing
starch in
accordance with embodiments of the invention is pregelatinized and partially
hydrolyzed
starch.
[0018] In accordance with some embodiments, the invention provides a highly
efficient
acid-modification reaction. The pregelatinization and acid-modification in the
extruder
occurs at elevated temperatures and/or pressures as described herein and can
result in an acid
hydrolysis rate that can be, e.g., approximately 30,000 times or greater
faster than
conventional acid hydrolysis rates at lower temperatures (e.g., 50 C) and/or
pressures. The
rate of acid hydrolysis is further increased through the use of low moisture
(about 8 wt.% to
about 25 wt.%) levels in the starch precursor and hence through an increased
concentration of
reactants. Because of this high efficiency of acid-modification, the inventors
have found that,
surprisingly and unexpectedly, a weak acid or a very low level of strong acid
can be used in
the starch precursor to achieve optimal acid-modification and avoid the need
for
neutralization and purification which are costly, time consuming, and
inefficient requirements
of conventional systems.
[00191 In accordance with some embodiments, the hydrolysis is designed to
convert the
starch into smaller molecules within an optimum size range, which is defined
herein by the
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desired viscosity of the pregelatinized, partially hydrolyzed starch. If the
starch is over
hydrolyzed, it can be converted into unduly small molecules (e.g.,
oligosaccharides or
sugars), which, in the case of gypsum board, can result in less board strength
than that
provided by the pregelatinized, partially hydrolyzed starch of desired
viscosity.
[0020] The pregelatinized, partially hydrolyzed starch can be prepared by
(i) mixing at
least water, non-pregelatinized starch, and an acid to form a wet starch
precursor having a
moisture content of from about 8 wt.% to about 25 wt.%. The acid can be: (1) a
weak acid
that substantially avoids chelating calcium ions, (2) a strong acid in an
amount of about
0.05 wt.% or less by weight of the starch, or (3) any combination thereof The
wet starch
precursor is pregelatinized and acid-modified in one step in an extruder at an
elevated die
temperature and/or pressure as described herein. The starch is hydrolyzed to a
degree that
results in a desired viscosity, e.g., as described herein.
[0021] Thus, in some embodiments, a pregelatinized, partially hydrolyzed
starch can be
made by mixing at least water, non-pregelatinized starch, and a weak acid that
substantially
avoids chelating calcium ions to make a wet starch precursor having a moisture
content of
from about 8 wt.% to about 25 wt.%. The wet starch is then fed into an
extruder. While in
the extruder at a die temperature of about 150 C (about 300 F) to about 210 C
(about 410 F),
the wet starch is pregelatinized and acid-modified, such that it is at least
partially hydrolyzed.
[0022] In further embodiments, a pregelatinized, partially hydrolyzed
starch can be made
by mixing at least water, non-pregelatinized starch, and a strong acid to make
a wet starch
precursor having a moisture content of from about 8 wt.% to about 25 wt%,
wherein the
strong acid is in an amount of about 0.05 wt.% or less by weight of the
starch. The wet starch
is then fed into an extruder. While in the extruder at a die temperature of
about 150 C (about
300 F) to about 210 C (about 410'F), the wet starch is pregelatinized and acid-
modified, such
that it is at least partially hydrolyzed.
[0023] Desirably, the resulting pregelatinized, partially hydrolyzed starch
has low water
demand when included in a stucco slurry and can be useful in the manufacture
of board (e.g.,
gypsum board) with good strength, in some embodiments. Thus, in another
aspect, the
invention provides a method of making gypsum board using starch prepared with
the
inventive methods of pregelatinizing and acid-modifying in a single step in an
extruder. In
some embodiments, the pregelatinized, partially hydrolyzed starches prepared
in accordance
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with embodiments of the invention have low water demand relative to other
pregelatinized
starches known in the art.
[0024] As a result, pregelatinized, partially hydrolyzed starches prepared
in accordance
with embodiments of the invention can be included in a stucco slurry (e.g., by
a feed line into
a pin mixer) with good fluidity. In some embodiments, higher amounts of the
pregelatinized,
partially hydrolyzed starches prepared in accordance with embodiments of the
invention can
be included since excess water is not needed to be added to the system, such
that even higher
strengths and lower board densities can be achieved. The resulting board
exhibits good
strength properties (e.g., having good core hardness, nail pull resistance,
compressive
strength, etc., or any relationship therebetween, based on any combination of
values for each
provided herein). Advantageously, inclusion of starch prepared according to
the method of
the invention during the manufacture of gypsum board enables the production of
ultra low
density product because of the strength enhancements. The gypsum board can be
in the form
of, e.g., gypsum wallboard (often referred to as drywall), which can encompass
such board
used not only for walls but also for ceilings and other locations as
understood in the art.
However, starch prepared according to the method can have other applications,
such as in
food products.
Pregelatinization and Acid-Modification
[0025] Starches are classified as carbohydrates and contain two types of
polysaccharides,
namely linear amylose, and branched amylopectin. Starch granules are semi-
crystalline, e.g.,
as seen under polarized light, and are insoluble at room temperatures.
Gelatinization is the
process by which the starch is placed in water and heated ("cooked"), such
that the crystalline
structure of the starch granules is melted, and the starch molecules are
dissolved in water,
resulting in good dispersion. It has been found that, when transforming a
starch granule to
gelatinized form, initially, the starch granule provides little viscosity in
water because starch
granules are water insoluble. As the temperature increases, the starch granule
swells and the
crystalline structure melts at the gelatinization temperature. Peak viscosity
is achieved when
the starch granule has maximum swelling. Further heating will break the starch
granules and
dissolve the starch molecules in water, with a precipitous drop-off in
viscosity. After
cooling, the starch molecule will re-associate to form a 3-D gel structure,
with the viscosity
increasing due to the gel structure. Some commercial starches are sold in a
pregelatinized
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form, while others are sold in the granular form. In accordance with some
embodiments of
the present invention, in relation to gypsum board, the granular form
undergoes at least some
degree of gelatinization. To illustrate, in relation to gypsum board, the
starch is
pregelatinized prior to its addition to gypsum slurry, also referred to herein
as stucco slurry
(typically in a mixer, e.g., a pin mixer).
[0026] Thus, as used herein, "pregelatinized" means that the starch has any
degree of
gelatinization, e.g., before it is included in the gypsum slurry or for use in
other applications.
In some embodiments relating to gypsum board, the pregelatinized starch can be
partially
gelatinized when included in the slurry, but becomes fully gelatinized when
exposed to
elevated temperature, e.g., in the kiln during the drying step to remove
excess water. In some
embodiments relating to gypsum board, the pregelatinized starch is not fully
gelatinized, even
upon exiting the kiln so long as the starch meets the mid-range viscosity
characteristic of
some embodiments when under the conditions according to the Viscosity
Modifying
Admixture (VMA) method.
[0027] When viscosity is referred to herein, it is in accordance with the
VMA method,
unless otherwise indicated. According to this method, viscosity is measured
using a
Discovery HR-2 Hybrid Rheometer (TA Instruments Ltd) with a concentric
cylinder, a
standard cup (diameter of 30 mm) with vane geometry (diameter of 28 mm and
length of
42.05 mm).
[0028] When the starch is obtained, differential scanning calorimetry (DSC)
techniques
are used to determine whether the starch is fully gelatinized. The DSC step
can be utilized to
observe whether starch is fully gelatinized, e.g., to confirm that no
retrogradation has
occurred. One of two procedures is adopted, depending on the temperature
required to fully
gelatinize the starch, which can also be determined by DSC as one of ordinary
skill in the art
will appreciate.
[0029] Procedure 1 is utilized where the DSC reveals that the starch is
fully gelatinized or
has a gelatinization temperature at or below 90 C. Procedure 2 is utilized
where the
gelatinization temperature is above 90 C. Since the viscosity is measured
while the starch is
in water, procedure 2 uses pressure cooking in a sealed vessel to allow for
superheating to
temperatures above 100 C without causing the water to appreciably evaporate.
Procedure 1
is reserved for starches already fully gelatinized or for starches having
gelatinization
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temperature up to 90 C, because, as discussed below, the gelatinization takes
place in the
rheometer which is an open system and cannot create pressurized conditions for
gelatinization. Thus procedure 2 is followed for starches having higher
gelatinization
temperatures. Either way, starch (7.5 g, dry basis) is added into water for a
total weight of 50
g when the viscosity is measured.
[0030] In procedure 1, the starch is dispersed in the water (15% starch of
the total weight
of starch and water) and the sample is immediately transferred to a cylinder
cell. The cell is
covered with aluminum foil. The sample is heated from 25 C to 90 C at 5 C/min
and a shear
rate of 200 s-1. The sample is held at 90 C for 10 min at a shear rate of 200
s-1. The sample
is cooled from 90 C to 80 C at 5 C/min and a shear rate of 200 s-1. The sample
is held at
80 C for 10 min at a shear rate of 0 s-1. The viscosity of the sample is
measured at 80 C and a
shear rate of 100 s-1 for 2 min. The viscosity is the average of the
measurement from 30
seconds to 60 seconds.
[0031] Procedure 2 is used for starches having gelatinization temperature
greater than
90 C. The starch is gelatinized according to the methods well-known in the
starch industry
(e.g., by pressure cooking). The gelatinized starch water solution (15% of
total weight) is
immediately transferred into the rheometer measuring cup and equilibrated at
80 C for 10
minutes. The viscosity of the sample is measured at 80 C and a shear rate of
100 s-1 for 2
minutes. The viscosity is the average of the measurement from 30 seconds to 60
seconds.
[0032] Viscograph and DSC are two different methods to describe starch
gelatinization.
Degree of starch gelatinization can be determined by, for example, thermogram
from DSC,
e.g., using peak area (melting of crystal) for calculation. A viscogram (from
viscograph) is
less desirable to determine degree of partial gelatinization but is a good
tool to obtain data
such as the viscosity change of starch, gelatinization maximum, gelatinization
temperature,
retrogradation, viscosity during holding, viscosity at the end of cooling,
etc. For degree of
gelatinization, the DSC measurements are done in the presence of excess water,
particularly
at or above 67% by weight. If water content of starch/water mixture is less
than 67%,
gelatinization temperature will increase as water content decreases. It is
difficult to melt
starch crystals when available water is limited. When water content of
starch/water mixture
reaches 67%, gelatinization temperature will keep constant no matter how much
more water
is added into the starch/water mixture. Gelatinization onset temperature
indicates the starting
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temperature of gelatinization. Gelatinization end temperature indicates the
end temperature
of gelatinization. Enthalpy of gelatinization represents the amount of
crystalline structure
melted during gelatinization. By using the enthalpy from a starch DSC
thermogram, the
degree of gelatinization can be indicated.
100331 Different starches have different gelatinization onset temperatures,
end
temperatures, and gelatinization enthalpies. Therefore, different starches may
become fully
gelatinized at different temperatures. It will be understood that a starch is
fully gelatinized
when the starch is heated beyond the end temperature of gelatinization in
excess water. In
addition, for any particular starch, if the starch is heated below the end
temperature of
gelatinization, the starch will be partially gelatinized. Thus, partial and
not full gelatinization
will occur when starch in the presence of excess water is heated below
gelatinization end
temperature, e.g., as determined by DSC. Full gelatinization will occur when
starch in the
presence of excess water is heated above gelatinization end temperature, e.g.,
as determined
by DSC. The degree of gelatinization can be adjusted in different ways, such
as, for example,
by heating the starch below the gelatinization end temperature to form partial
gelatinization.
For example, if the enthalpy for fully gelatinizing a starch is 4 J/g, when
the DSC shows the
gelatinization enthalpy of the starch as being only 2 J/g, this means 50% of
the starch has
been gelatinized. Fully gelatinized starch would not have the DSC thermogram
gelatinization
peak (enthalpy = 0 J/g) when it is measured by DSC.
[0034] As noted, the degree of gelatinization can be any suitable amount,
such as about
70% or more, etc. However, smaller degrees of gelatinization will more closely
approximate
granular starch and may not take full advantage of the strength enhancement,
better (more
complete) dispersion, and/or water demand reduction of some embodiments of the
invention.
Thus, in some embodiments, it is preferred that there is a higher degree of
gelatinization, e.g.,
at least about 75%, at least about 80%, at least about 85%, at least about
90%, at least about
95%, at least about 97%, at least about 99%, or full (100%) gelatinization.
Starch with lower
degree of gelatinization can be added to slurry with additional gelatinization
(e.g., to 100%)
taking place in the kiln in the case of gypsum board. For purposes of addition
to slurry, by
"fully gelatinized," it will be understood that the starch is sufficiently
cooked at or above its
gelatinization temperature or to otherwise achieve full gelatinization as can
be seen from
DSC techniques. Although some small degree of retrogradation upon cooling may
be
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expected, the starch will still be understood as "fully gelatinized" for
addition to gypsum
slurry, or for use in other applications, in some embodiments as one of
ordinary skill in the
art will recognize. In contrast, for purposes of the VMA method discussed
herein, such
retrogradation is not accepted in making the viscosity measurement.
[0035] The starch molecule can be acid-modified, e.g., to hydrolyze
glycosidic bonds
between glucose units to achieve desired molecular weight. One benefit of acid-
modifying
starch such that a reduction in molecular weight is achieved is that the water
demand will
decrease. Conventional pregelatinized starches that were not also acid-
modified had a very
high water demand, which is associated with higher energy costs. It has been
conventionally
believed that it is generally preferred that the modification take place
before gelatinization
because it tends to be more efficient and less cost intensive. Surprisingly
and unexpectedly,
however, the inventors have found that pregelatinization and acid-modification
can be
incorporated into a single step, such that they can occur simultaneously
rather than in series.
Method of Preparing Starch
[0036] In accordance with some embodiments of the invention, prior to entry
into the
extruder, a wet starch precursor is prepared. The wet starch precursor can be
prepared by any
suitable method. For example, in some embodiments, the wet starch precursor is
prepared by
adding to a starch raw material water and an acid that is (a) a weak acid that
substantially
avoids chelating calcium ions, and/or (b) a strong acid in a small amount.
[0037] Any suitable starch raw material can be selected to prepare the wet
starch
precursor so long as it can be used to make pregelatinized, partially
hydrolyzed starch, such
as one meeting the mid-range viscosity characteristic of some embodiments of
the invention.
As used herein, "starch" refers to a composition that includes a starch
component. As such,
the starch can be 100% pure starch or may have other components such as those
commonly
found in flours such as protein and fiber, so long as the starch component
makes up at least
about 75% by weight of the starch composition. The starch can be in the form
of a flour
(e.g., corn flour) containing starch, such as flour having at least about 75%
starch by weight
of the flour, e.g., at least about 80%, at least about 85%, at least about
90%, at least about
95%, etc.). Any suitable unmodified starch or flour can be used to prepare the
precursor of
the pregelatinized, partially hydrolyzed starches of the invention. For
example, the starch can
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be CCM260 yellow corn meal, CCF600 yellow corn flour (Bunge North America),
Clinton
106 (ADM), and/or Midsol 50 (MGP Ingredients).
[0038] The wet
starch precursor can be prepared to have any suitable moisture content,
such that desired levels of pre gelatinization and acid-modification are
achieved in an
extruder. In some embodiments, for example, it is desirable that the wet
starch precursor
have a moisture content of from about 8 wt.% to about 25 wt.% by weight of the
total starch
precursor, such as from about 8 wt.% to about 23 wt.%, e.g., from about 8 wt.%
to about
21 wt.%, from about 8 wt.% to about 20 wt.%, from about 8 wt.% to about 19
wt.%, from
about 8 wt.% to about 18 wt.%, from about 8 wt.% to about 17 wt.%, from about
8 wt.% to
about 16 wt.%, from about 8 wt.% to about 15 wt.%, from about 9 wt.% to about
25 wt.%,
from about 9 wt.% to about 23 wt.%, from about 9 wt.% to about 21 wt.%, from
about
9 wt.% to about 20 wt.%, from about 9 wt.% to about 19 wt.%, from about 9 wt.%
to about
18 wt.%, from about 9 wt.% to about 17 wt.%, from about 9 wt.% to about 16
wt.%, from
about 9 wt.% to about 15 wt.%, from about 10 wt.% to about 25 wt.%, from about
10 wt.% to
about 23 wt.%, from about 10 wt% to about 21 wt.%, from about 10 wt.% to about
20 wt.%,
from about 10 wt.% to about 19 wt.%, from about 10 wt.% to about 18 wt.%, from
about
wt.% to about 17 wt.%, from about 10 wt.% to about 16 wt.%, from about 10 wt.%
to
about 15 wt.%, from about 11 wt.% to about 25 wt.%, from about 11 wt.% to
about 23 wt.%,
from about 11 wt.% to about 21 wt%, from about 11 wt.% to about 20 wt.%, from
about
11 wt.% to about 19 wt.%, from about 11 wt.% to about 18 wt.%, from about 11
wt.% to
about 17 wt.%, from about 11 wt.% to about 16 wt.%, from about 11 wt.% to
about 15 wt.%,
from about 12 wt.% to about 25 wt.%, from about 12 wt.% to about 23 wt.%, from
about
12 wt.% to about 21 wt.%, from about 12 wt.% to about 20 wt.%, from about 12
wt.% to
about 19 wt.%, from about 12 wt.% to about 18 wt.%, from about 12 wt.% to
about 17 wt.%,
from about 12 wt.% to about 16 wt.%, from about 12 wt.% to about 15 wt.%, from
about
13 wt.% to about 25 wt.%, from about 13 wt.% to about 23 wt.%, from about 13
wt.% to
about 21 wt.%, from about 13 wt% to about 20 wt.%, from about 13 wt.% to about
19 wt.%,
from about 13 wt.% to about 18 wt.%, from about 13 wt.% to about 17 wt.%, from
about
13 wt.% to about 16 wt.%, from about 13 wt.% to about 15 wt.%, from about 14
wt.% to
about 25 wt.%, from about 14 wt.% to about 23 wt.%, from about 14 wt.% to
about 21 wt.%,
from about 14 wt.% to about 20 wt.%, from about 14 wt.% to about 19 wt.%, from
about
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14 wt.% to about 18 wt.%, from about 14 wt.% to about 17 wt.%, from about 14
wt.% to
about 16 wt.%, or from about 14 wt.% to about 15 wt.% all based on the total
weight of the
wet starch precursor. It will be understood that when preparing the wet
starch, the moisture
contents described herein include ambient moisture as well as water added.
[0039] While not wishing to be bound by any particular theory, it is
believed that a lower
moisture content leads to greater friction in the extruder. In some
embodiments, the wet
starch can be prepared to have a moisture content that allows for sufficient
mechanical energy
input when the wet starch is fed through the extruder, such that friction
prevents the wet
starch from moving through the extruder too easily. The increased friction can
increase the
disruption of hydrogen bonding in the starch.
[0040] Any suitable weak acid that substantially avoids chelating calcium
ions may be
mixed into the wet starch. Without wishing to be bound by any particular
theory, chelation
includes the weak acid, for example, forming a coordination complex with
calcium or
otherwise interfering with the formation of gypsum crystals within the gypsum
slurry. Such
interference may be the reduction in number of gypsum crystals formed,
retardation
(decreased rate) of formation of the crystals, decreasing interactions among
the gypsum
crystals, etc. The term "substantially" with respect to not chelating calcium
ions generally
means that at least 90% (e.g., at least 92%, at least 95%, at least 96%, at
least 97%, at least
98%, or at least 99%) of the available calcium ions are not chelated to the
acid.
[0041] Weak acids in accordance with embodiments of the invention can be
defined as
those having a pKa value from about 1 to about 6, e.g., from about 1 to about
5, from about 1
to 4, from about 1 to 3, from about 1 to 2, from about 1.2 to about 6, from
about 1.2 to about
5, from about 1.2 to about 4, from about 1.2 to about 3, from about 1.2 to
about 2, from about
2 to about 6, from about 2 to about 5, from about 2 to about 4, from about 2
to about 3, from
about 3 to about 6, from about 3 to about 5, from about 3 to about 4, from
about 4 to about 6,
or from about 4 to about 5. As is understood in the art, the pKa value is a
measure of the
strength of an acid; the lower the pKa value, the stronger the acid.
[0042] Weak acids that substantially avoid chelating calcium ions are
characterized, for
example, by a lack of multi-binding sites, such as multiple carboxyl
functional groups
(C00-), which tend to bind calcium ions. In some embodiments, the weak acid
has a
minimal amount of multi-binding sites, such as multi-COO- groups, or is
substantially free of
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multi-binding sites, such as multi-COO- groups, such that, for example,
chelation is minimal
(i.e., substantially avoided) or gypsum crystal formation is not substantially
impacted relative
to the crystal formation in the absence of the weak acid. In some embodiments,
for example,
aluminum sulfate (alum) is an appropriate weak acid to use in preparing the
wet starch since
it substantially avoids chelating calcium ions. Alum does not have multi-
binding sites.
[0043] In some embodiments, alum is added into the wet starch precursor in
any suitable
form, such as in liquid containing alum of desired solids content. For
example, the liquid
alum can be included in an aqueous solution where the alum is present in any
suitable
amount. Other weak acids can be added similarly.
[0044] The wet starch can be mixed to include any suitable amount of a weak
acid that
substantially avoids chelating calcium ions, such that the pregelatinized,
partially hydrolyzed
starch is prepared with desired viscosity and low water demand and is not over
hydrolyzed
into sugar. For example, in some embodiments, such weak acid is included in an
amount of
from about 0.5 wt.% to about 5 wt.% based on the weight of the starch, such as
from about
0.5 wt.% to about 4.5 wt.%, e.g., from about 0.5 wt.% to about 4 wt.%, from
about 0.5 wt.%
to about 3.5 wt.%, from about 0.5 wt.% to about 3 wt.%, from about 1 wt.% to
about 5 wt.%,
from about 1 wt.% to about 4.5 wt.%, from about 1 wt.% to about 4 wt.%, from
about 1 wt.%
to about 3.5 wt.%, from about 1 wt.% to about 3 wt.%, from about 1.5 wt% to
about 5 wt.%,
from about 1.5 wt.% to about 4.5 wt.%, from about 1.5 wt.% to about 4 wt.%,
from about
1.5 wt.% to about 3.5 wt.%, from about 1.5 wt.% to about 3 wt.%, from about 2
wt.% to
about 5 wt.%, from about 2 wt.% to about 4.5 wt.%, from about 2 wt.% to about
4 wt.%,
from about 2 wt.% to about 3.5 wt.%, from about 2 wt% to about 3 wt.%, from
about
2.5 wt.% to about 5 wt.%, from about 2.5 wt.% to about 4.5 wt.%, from about
2.5 wt.% to
about 4 wt.%, from about 2.5 wt.% to about 3.5 wt.%, or from about 2.5 wt.% to
about
3 wt.%. It will be understood that these amounts encompass the weak acid
component, and,
when the weak acid is in a solution, excludes the water or other components of
the solution.
[0045] The wet starch precursor can be prepared to optionally further
comprise secondary
acids that can chelate calcium ion, such as tartaric acid. Thus, in some
embodiments, a
secondary acid, such as tartaric acid, can be combined with any suitable weak
acid that does
not chelate calcium ions. Tartaric acid is known to retard gypsum
crystallization. However,
in combination with the non-chelating weak acid, tartaric acid avoids
substantial retarding of
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gypsum crystallization, such that the hydrolysis reaction via acid-
modification is optimized.
Besides tartaric acid, other secondary acids, such as succinic acid or malic
acid, may be
beneficial so long as they do not surpass the accelerating effect of alum. In
some
embodiments, the wet starch precursor includes both alum and tartaric acid.
[0046] If included, secondary acids (e.g., tartaric acid) can be present in
any suitable
amount. For example, tartaric acid can be present in an amount of from about
0.1 wt.% to
about 0.6 wt.% based on the weight of the starch, e.g., from about 0.1 wt.% to
about
0.4 wt.%, from about 0.2 wt.% to about 0.3 wt.%.
[0047] In some embodiments, oil can optionally be added to the wet starch
to improve the
conveyability of starch inside the extruder. Possible oils include canola oil,
vegetable oil,
corn oil, soybean oil, or any combination thereof, in some embodiments. For
example, in
some embodiments, canola oil or one of the aforementioned substitutes can
optionally be
added in an amount of from about 0 wt.% to about 0.25 wt.% by weight of the
starch, e.g.,
from about 0.1 wt.% to about 0.2 wt.%, from about 0.1 wt.% to about 0.15 wt.%,
from about
0.15 wt.% to about 0.25 wt.%, from about 0.15 wt.% to about 0.2 wt.%, or from
about
0.2 wt.% to about 0.25 wt.%.
[0048] In accordance with some embodiments, the wet starch precursor is
prepared by
mixing water, non-pregelatinized starch, and a small amount of a strong acid.
In some
embodiments, the strong acid has a pKa of about -1.7 or less. Any such strong
acid can be
used and, in some embodiments, the strong acid comprises sulfuric acid, nitric
acid,
hydrochloric acid, or any combination thereof. Sulfuric acid, alone or in
combination with
other acids, is preferred in some embodiments because sulfate ion can
accelerate gypsum
crystallization in gypsum board embodiments.
[0049] The amount of strong acid is relatively small, such as about 0.05
wt.% or less by
weight of the starch, e.g., about 0.045 wt.% or less, about 0.04 wt.% or less,
about
0.035 wt.% or less, about 0.03 wt.% or less, about 0.025 wt.% or less, about
0.02 wt.% or
less, about 0.015 wt.% or less, about 0.01 wt.% or less, about 0.005 wt.% or
less, about
0.001 wt.% or less, about 0.0005 wt.% or less, such as from about 0.0001 wt.%
to about
0.05 wt.%, from about 0.0001 wt.% to about 0.045 wt.%, from about 0.0001 wt.%
to about
0.04 wt.%, from about 0.0001 wt.% to about 0.035 wt.%, from about 0.0001 wt.%
to about
0.03 wt.%, from about 0.0001 wt.% to about 0.025 wt.%, from about from about
0.0001 wt.%
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to about 0.02 wt.%, from about 0.0001 wt.% to about 0.015 wt.%, from about
0.0001 wt.% to
about 0.01 wt.%, from about 0.0001 wt.% to about 0.005 wt.%, from about 0.0001
wt.% to
about 0.001 wt.%, from about 0.0001 wt.% to about 0.0005 wt.% by weight of the
starch. It
will be understood that these amounts encompass the strong acid component,
and, when the
strong acid is in a solution, excludes the water or other components of the
solution. For
example, conventional strong acid-modification uses 2% sulfuric acid solution,
with starch
solid of ¨35% (2 g sulfuric acid for 35 g starch). The percent is based on
pure sulfuric acid
components. It is calculated as the weight of sulfuric acid component divided
by the weight
of the wet starch. For example, if the sulfuric acid is 50% pure (which means
that half the
weight of the solution is pure sulfuric acid), then the weight of the sulfuric
acid solution is
doubled. To illustrate, for 100 g starch, 0.1 g pure sulfuric acid is added to
achieve 0.1 wt.%.
If the concentration of sulfuric solution is 50%, 0.2 g of the 50% sulfuric
acid solution is
added to achieve 0.1 wt%.
[0050] It will be understood that there are different grades of acids
(>95%, 98%,
99.99%). These differences are encompassed by the term "about" in relation to
the amount
of strong acid in the starch precursor. One of ordinary skill in the art will
readily be able to
determine the wt.% described herein to include the different grades. The
amounts of strong
acid used in accordance with some embodiments of the invention are
considerably smaller
than what were included in conventional systems which used, e.g., at least
about 2 g of
sulfuric acid for 35 g of starch. In some embodiments, the strong acid in
small amounts as
described above can be used in combination with a weak acid that does not
chelate calcium
ions, such as alum, as described herein.
[0051] Embodiments of the invention provide feeding the wet starch
precursor through an
extruder, such that the wet starch precursor is pregelatinized and acid-
modified in a single
step in the extruder. It will be appreciated that an extruder is a machine
generally used to
melt and process polymers into a desired shape by melting the polymer and
pumping it
through a die. The extruder can also mix the polymer with other ingredients,
such as color,
reinforcing fibers, mineral fillers, etc. The purpose of the extruder is to
disperse and
distribute all of the ingredients fed into it and to melt the ingredients with
a constant
temperature and pressure.
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[0052] Configurations and arrangements for extruders are known in the art.
In general,
an extruder comprises a feed hopper to deliver the feed material, a
preconditioner comprising
heat jackets for conditioning polymer with plasticizer (e.g., water), an
extruder modular head
comprising heating zones, and a die assembly. Extruders generally include a
feed auger, a
knife, and screw(s). The feed auger is present to help convey the wet starch
precursor into
the extruder. The knife is present to cut the string-like pregelatinized,
partially hydrolyzed
starch into small pellets, such that they can be ground. The screw(s) help mix
the wet starch
precursor, convey the wet starch precursor through the extruder, and provide
mechanical
shearing. An extruder can be of the single-screw or twin-screw varieties as
will be
understood by one of ordinary skill in the art. See, e.g., Leszek Moscicki,
Extrusion-Cooking
Techniques, WILEY-VCH Verlag & Co. KGaA, 2011.
[00531 In single-screw extruders, the screw generally comprises a feed
section with deep
channels for transporting the solids from the throat of the feeder and
compressing them, a
compression section at which point the screw's channels become progressively
less deep and
the polymer is melted, and a metering section with shallow channels that
conveys the melted
polymer to the die. Some screws are designed to include mixing devices (e.g.,
pins extending
from the screw).
[0054] Twin-screw extruders generally have two screws that rotate either in
the same
direction (i.e., co-rotating) or in opposite directions (i.e., counter-
rotating). The two screws
may rotate with non-intermeshing or fully intermeshing flights. Whereas in the
case of
single-screw extruders, the material being fed fills the entire screw channel,
in the case of
twin-screw extruders, only part of the screw channel is filled, such that
downstream feedports
or vents can be utilized for the addition of certain ingredients.
[00551 The die assembly generally comprises a plate, spacer, and die head.
When
extruding materials, the process can be either continuous, such that the
material is extruded in
an indefinite length, or semi-continuous, such that the material is extruded
in pieces.
Materials being extruded may be hot or cold.
[0056] The invention provides a method of preparing pregelatinized,
partially hydrolyzed
starch in an extruder. Any suitable extruder can be used, such as a single-
screw extruder
(e.g., the Advantage 50 available from American Extrusion International,
located in South
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Beloit, IL) or a twin-screw extruder (e.g., the Wenger TX52 available from
Wenger located
in Sabetha, KS).
[0057] As described herein, non-pregelatinized starch, an acid in the form
of a weak acid
that substantially avoids chelating calcium ions and/or a strong acid in a
small amount, and
water are mixed and fed into the extruder. In some embodiments, additional
water may be
added to the extruder. While in the extruder, a combination of heating
elements and
mechanical shearing melts and pregelatinizes the starch, the weak acid
partially hydrolyzes
the starch to a desired molecular weight indicated by viscosity as desirable
as described
herein. The conditions in the extruder, because of the mechanical energy, will
also cause the
starch molecules to degrade, which partially produces the same effect of acid-
modification.
It is believed that because the conditions in an extruder (e.g., high reaction
temperature and
high pressure) in accordance with some embodiments facilitate this chemical
reaction, a weak
acid and/or low amounts of a strong acid can be used. The inventive method,
thus, improves
the efficiency of starch acid-modification.
[0058] The main screw(s) can be operated at any suitable speed, such that
desired mixing
and mechanical shearing are achieved. For example, in some embodiments the
main screw
can be operated at a speed of about 350 RPM ( about 100 RPM). The feed auger
can be
operated at any suitable speed to achieve desired feeding rate. For example,
in some
embodiments the feed auger can be operated at a speed of about 14 RPM (+ about
5 RPM).
[0059] The knife can be operated at any suitable speed. For example, in
various
embodiments the knife can be operated at a speed of from about 400 RPM to
about 1,000
RPM, e.g., from about 400 RPM to about 900 RPM, from about 400 RPM to about
800 RPM,
from about 400 RPM to about 700 RPM, from about 400 RPM to about 600 RPM, from
about 400 RPM to about 500 RPM, from about 500 RPM to about 1,000 RPM, from
about
500 RPM to about 900 RPM, from about 500 RPM to about 800 RPM, from about 500
RPM
to about 700 RPM, from about 500 RPM to about 600 RPM, from about 600 RPM to
about
1,000 RPM, from about 600 RPM to about 900 RPM, from about 600 RPM to about
800
RPM, from about 600 RPM to about 700 RPM, from about 700 RPM to about 1,000
RPM,
from about 700 RPM to about 900 RPM, from about 700 RPM to about 800 RPM, from
about 800 RPM to about 1.000 RPM, from about 800 RPM to about 900 RPM, or from
about
900 RPM to about 1,000 RPM.
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[0060] The wet starch can be pregelatinized and acid-modified in an
extruder having a
die at any suitable temperature, such that the wet starch becomes sufficiently
pregelatinized
without burning the materials. For example, the wet starch can be
pregelatinized and acid-
modified the wet starch in an extruder having a die at a temperature of from
about 150 C
(about 300 F) to about 210 C (about 410 F), e.g., in various embodiments, from
about 150 C
to about 205 C (about 400'F), from about 150 C to about 199 C (about 390 F),
from about
150 C to about 193 C (about 380 F), from about 150 C to about 188 C (about 370
F), from
about 150 C to about 182 C (about 360 F), from about 154 C (about 310 F) to
about 210 C,
from about 154 C to about 205 C (about 400 F), from about 154 C to about 199
C, from
about 154 C to about 193 C, from about 154 C to about 188 C, from about 154 C
to about
182 C, from about 160 C (about 320 F) to about 210 C, from about 160 C to
about 205 C
(about 400 F), from about 160 C to about 199 C, from about 160 C to about 193
C, from
about 160 C to about 188 C, from about 160 C to about 182 C, from about 166 C
(about
330 F) to about 210 C, from about 166 C to about 205 C, from about 166 C to
about 199 C,
from about 166 C to about 193 C, from about 166 C to about 188 C, from about
166 C to
about 182 C, from about 171 C (about 340 F) to about 210 C, from about 171 C
to about
205 C, from about 171 C to about 199 C, from about 171 C to about 193 C, from
about
171 C to about 188 C, from about 171 C to about 182 C, from about 177 C (about
350 F) to
about 210 C, from about 177 C to about 205 C, from about 177 C to about 199 C,
from about
177 C to about 193 C, from about 177 C to about 188 C, or from about 177 C to
about
182 C. While the die of the extruder can be any sufficient temperature as
described herein,
the die temperature generally exceeds the melting temperature of the starch
crystals.
[0061] The degree of gelatinization can be any suitable amount, such as at
least about
70% or more, e.g., at least about 75%, at least about 80%, at least about 85%,
at least about
90%, at least about 95%, at least about 97%, at least about 99%, or full
(100%)
gelatinization. In the case of making wallboard as described below, starch
with such lower
degrees of gelatinization can be added to stucco slurry, e.g., with additional
gelatinization
(for example. to 100%) taking place in the kiln.
[0062] The pressure in the extruder can be at any suitable level, such that
appropriate
conditions for pregelatinization and acid-modification are achieved. Pressure
inside the
extruder is determined by the raw material being extruded, moisture content,
die temperature,
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and screw speed, which will be recognized by one of ordinary skill in the art.
For example,
the pressure in the extruder can be at least about 2,000 psi (about 13,800
kPa), such as at least
about 2,250 psi (about 15,500 kPa), at least about 2,500 psi (about 17,200
kPa), at least about
2,750 psi (about 19,000 kPa), at least about 3,000 psi (about 20,650 kPa), at
least about
3,500 psi (about 24,100 kPa), at least about 4,000 psi (about 27,600 kPa), or
at least about
4,500 psi (about 31,000 kPa). In some embodiments, the pressure can be from
about
2,000 psi to about 5,000 psi (34,500 kPa), e.g., from about 2,000 psi to about
4,500 psi, from
about 2,000 psi to about 4,000 psi, from about 2,000 psi to about 3,500 psi,
from about
2,000 psi to about 3,000 psi, from about 2,000 psi to about 2,500 psi, from
about 2,500 psi to
about 5,000 psi, from about 2,500 psi to about 4,500 psi, from about 2,500 psi
to about
4,000 psi, from about 2,500 psi to about 3,500 psi, from about 2,500 psi to
about 3,000 psi,
from about 3,000 psi to about 5,000 psi, from about 3,000 psi to about 4,500
psi, from about
3,000 psi to about 4,000 psi, from about 3,000 psi to about 3,500 psi, from
about 3,500 psi to
about 5,000 psi, from about 4,000 psi to about 5,000 psi, from about 4,000 psi
to about
4,500 psi, or from about 4,500 psi to about 5,000 psi.
[0063] Surprisingly and unexpectedly, it has been found that the inventive
method of
preparing pregelatinized, partially hydrolyzed starch in a single step in an
extruder is
considerably faster than pregelatinizing and acid-modifying starch in two
steps in series.
Significantly greater amounts of pregelatinized, partially hydrolyzed starch
can be prepared
with the inventive method than starch prepared with any other method. The
higher
production amount and faster output rate are because of high reaction rate at
high temperature
and/or high pressure. In some embodiments, pregelatinization and acid-
modification occur in
less than about 5 minutes, such as less than about 4 minutes, e.g., less than
about 3 minutes,
less than about 2 minutes, less than about 90 seconds, less than about 75
seconds, less than
about 1 minute, less than about 45 seconds, less than about 30 seconds, less
than about 25
seconds, less than about 20 seconds, less than about 15 seconds, or less than
about 10
seconds. In addition, in some embodiments, the pregelatinization and acid-
modification
occur at a rate in the extruder bound by any two of the foregoing points. For
example, the
pregelatinization and acid-modification rate can be between about 10 seconds
and 5 minutes,
e.g., between about 10 seconds and about 4 minutes, between about 10 seconds
and about 3
minutes, between about 10 seconds and about 2 minutes, between about 10
seconds and about
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90 seconds, between about 10 seconds and about 75 seconds, between about 10
seconds and
about 1 minute, between about 10 seconds and about 45 seconds, between about
10 seconds
and about 30 seconds, between about 10 seconds and about 25 seconds, between
about 10
seconds and about 20 seconds, or between about 10 seconds and about 15
seconds.
[0064] The inventive method of preparing pregelatinized, partially
hydrolyzed starch can
be a continuous process occurring at any sufficient rate. In some embodiments,
starch is
pregelatinized and acid-modified at a production output rate in an extruder of
at least about
100 kg/hr, such as at least about 150 kg/hr, at least about 200 kg/hr, at
least about 250 kg/hr,
at least about 300 kg/hr, at least about 350 kg/hr, at least about 400 kg/hr,
at least about
450 kg/hr, 500 kg/hr, at least about 550 kg/hr, e.g., at least about 600
kg/hr, at least about
650 kg/hr, at least about 700 kg/hr, at least about 750 kg/hr, at least about
800 kg/hr, at least
about 850 kg/hr, at least about 900 kg/hr, at least about 950 kg/hr, at least
about 1,000 kg/hr,
at least about 1,050 kg/hr, at least about 1,100 kg/hr, at least about 1,150
kg/hr, at least about
1,200 kg/hr, at least about 1,250 kg/hr, at least about 1,300 kg/hr, at least
about 1,350 kg/hr,
at least about 1,400 kg/hr, at least about 1,450 kg/hr, or at least about
1,500 kg/hr. In
addition, in some embodiments, the production output rate in an extruder can
be bound by
any two of the foregoing points. For example, the production output rate can
be between
about 100 kg/hr and about 1,500 kg/hr (e.g., between about 100 kg/hr and about
1,500 kg/hr,
between about 100 kg/hr and 1,000 kg/hr, between about 250 kg/hr and about
1,500 kg/hr,
between about 250 kg/hr and about 1,000 kg/hr, between about 600 kg/hr and
about
1,250 kg/hr, between about 650 kg/hr and about 1,200 kg/hr, between about 700
kg/hr and
about 1,100 kg/hr, between about 750 kg/hr and about 1,000 kg/hr, etc.).
[0065] It has been found by the inventors that in some embodiments the
conditions in an
extruder (e.g., high temperature and high pressure) are particularly conducive
to efficiently
and sufficiently pregelatinizing and acid-modifying starch in a single step.
When the
extruder mixes the wet starch, it creates very high friction, thereby
generating heat. The
shear force is created by the screw in the extruder because the space between
the screw and
chamber in the extruder is very small. Specific mechanical energy (SME)
describes
mechanical energy of an object per unit of mass. SME will depend on the
moisture content.
Higher moisture content (e.g., for purposes of fluidity) will result in low
viscosity and low
friction and, thus, a smaller SME. If more moisture is present, a smaller SME
will result
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because of low viscosity and low friction. The moisture contents in the wet
starch precursor
of the invention as described herein provide effective SME.
[0066] In the extruder, because of the conditions provided by embodiments
of the
invention as described herein, the starch is pregelatinized highly
efficiently. While not
wishing to be bound by any particular theory, it is believed that the good
mixing in the
extruder in accordance with some embodiments of the invention requires less
water for
reaction in an extruder. Very low moisture content facilitates a high
concentration of
reactant, which can accelerate the chemical reaction rate. The high
temperature of the
extruder also significantly accelerates the reaction rate. When the starch
leaves the extruder,
the reaction has occurred, such that it is pregelatinized and partially
hydrolyzed.
[0067] In conventional acid-modification, starch is added into a strong
acid solution.
This conventional method uses significantly more water and acid than the
surprising and
unexpected method of simultaneously pregelatinizing and acid-modifying starch
in one step
in an extruder as described herein rather than in series. Conventional acid-
modification takes
several hours. After the reaction has taken place, the acid needs to be
neutralized, purified,
and washed away. The neutralization and purification steps are time consuming
and costly.
[0068] Until the inventors' surprising and unexpected discovery, it was
thought
undesirable to use a weak acid that substantially avoids chelating calcium
ions or a strong
acid in a small amount in conventional acid-modification. This is because, in
the
conventional method, the weaker the acid is or the smaller the amount of a
strong acid is, the
longer acid-modification takes. Thus, a strong acid (e.g., having a pKa of
below about -1.7)
in high amounts was desired in conventional acid-modification. Surprisingly
and
unexpectedly, when pregelatinized, partially hydrolyzed starch is prepared in
an extruder
according to embodiments of the invention using a weak acid or a strong acid
in a small
amount as described herein, there is no need for neutralization and
purification steps, due to
the mild acidic condition and less interference with gypsum crystallization,
respectively. In
some embodiments, there can still be acid present in the pregelatinized,
partially hydrolyzed
starch.
Properties of Starch and Advantages of Using the Starch in Gypsum Board
[00691 The starch prepared in an extruder in accordance with embodiments of
the
invention can be any pregelatinized, partially hydrolyzed starch. In some
embodiments, the
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starch can be prepared to have various properties as desired (e.g., mid-range
viscosity, cold
water solubility, cold water viscosity, etc.) as described herein.
[00701 Pregelatinized, partially hydrolyzed starches prepared in an
extruder in accordance
with embodiments of the invention can be suitable for use in gypsum board. For
application
in gypsum board, for instance, pregelatinization and acid-modification are
beneficial, e.g., for
strength purposes by achieving a desired viscosity (and, hence, molecular
weight range) in
accordance with embodiments of the invention as described herein. In the
method of making
wallboard discussed herein, the starch that is introduced into the stucco
slurry can be at least
about 70% gelatinized, e.g., at least about 75% gelatinized, at least about
80% gelatinized, at
least about 85% gelatinized, at least about 90% gelatinized, at least about
95% gelatinized, at
least about 97% gelatinized, or 100% gelatinized (i.e., fully gelatinized).
[0071] Furthermore, feeding a wet starch comprising a weak acid that
substantially
avoids chelating calcium ions as described herein into an extruder, in
accordance with
embodiments of the invention, hydrolyzes the starch, such that a desired
viscosity is
achieved, thus indicating a desired molecular weight range is achieved.
Viscosity thereby
indicates the molecular weight of the pregelatinized, partially hydrolyzed
starch, as will be
appreciated by one of ordinary skill in the art.
[0072] In some embodiments, pregelatinized, partially hydrolyzed starch
prepared in
accordance with embodiments of the invention can be prepared to have any
suitable viscosity.
In some embodiments, the viscosity is characterized as having a -mid-range"
viscosity (i.e.,
having a viscosity from about 20 centipoise to about 700 centipoise) when the
pregelatinized,
partially hydrolyzed starch is subjected to conditions according to the VMA
method with the
pregelatinized, partially hydrolyzed starch in water in an amount of 15% by
weight of the
total weight of the pregelatinized, partially hydrolyzed starch and water.
Thus, the VMA
method is used to determine whether the pregelatinized, partially hydrolyzed
starch exhibits
the mid-range viscosity characteristic when subjected to the conditions of the
VMA method.
This does not mean that the pregelatinized, partially hydrolyzed starch must
be added to the
gypsum slurry under these conditions. Rather, when adding the pregelatinized,
partially
hydrolyzed starch to slurry, it can be in wet (in various concentrations of
starch in the water)
or dry forms, and it need not be fully gelatinized as described herein or
otherwise under the
conditions set forth in the VMA method.
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[0073] In some embodiments, the mid-range viscosity of the pregelatinized
starch can be
from about 20 centipoise to about 700 centipoise, such as from about 20
centipoise to about
500 centipoise, from about 30 centipoise to about 200 centipoise, or from
about 100
centipoise to about 700 centipoise. In embodiments of the invention, the
viscosity of the
pregelatinized starch when tested under the VMA method can be, e.g., as listed
in Tables 1A,
1B and 1C below. In the tables, an "X" represents the range "from about
[corresponding
value in top row] to about [corresponding value in left-most column]." The
indicated values
represent viscosity of the pregelatinized starch in centipoise. For ease of
presentation, it will
be understood that each value represents "about" that value. For example, the
first "X" in
Table lA is the range "about 20 centipoise to about 25 centipoise."
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Table lA
Starting Point for Viscosity Range (centipoise)
20 25 30 35 40 45 50 55 60 65 70 75
25 X
X X
X X X
X X X X
X X X X X
X X X X X X
X X X X X X X
X X X X X X X X
X X X X X X X X X
X X X X X X X X X X
0 75 X X X X X X X X X X X
c.)
a) 100 X X X X X X X X X X X X
125 X X X X X X X X X X X X
=7=7 150 X X X X X X X X X X X X
-4 175 X X X X X X X X X X X X
200 X X X X X X X X X X X X
1 225 X X X X X X X X X X X X
250 X X X X X X X X X X X X
275 X X X X X X X X X X X X
300 X X X X X X X X X X X X
325 X X X X X X X X X X X X
350 X X X X X X X X X X X X
375 X X X X X X X X X X X X
400 X X X X X X X X X X X X
425 X X X X X X X X X X X X
450 X X X X X X X X X X X X
475 X X X X X X X X X X X X
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500 X X X X X X X X X X X X
525 X X X X X X X X X X X X
550 X X X X X X X X X X X X
575 X X X X X X X X X X X X
600 X X X X X X X X X X X X
625 X X X X X X X X X X X X
650 X X X X X X X X X X X X
675 X X X X X X X X X X X X
700 X X X X X X X X X X X X
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Table 1B
Starting Point for Viscosity Range (centipoise)
100 125 150 175 200 225 250 275 300 325 350 375
125 X
150 X X
175 X X X
200 X X X X
225 X X X X X
250 X X X X X X
275 X X X X X X X
.r4 300 X X X X X X X X
325 X X X X X X X X X
350 X X X X X X X X X X
375 X X X X X X X X X X X
400 X X X X X X X X X X X X
0
c.) 425 X X X X X X X X X X X X
450 X X X X X X X X X X X X
475 X X X X X X X X X X X X
500 X X X X X X X X X X X X
-o
W 525 X X X X X X X X X X X X
550 X X X X X X X X X X X X
575 X X X X X X X X X X X X
600 X X X X X X X X X X X X
625 X X X X X X X X X X X X
650 X X X X X X X X X X X X
675 X X X X X X X X X X X X
700 X X X X X X X X X X X X
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Table 1C
Starting Point for Viscosity Range (centipoise)
400 425 450 475 500 525 550 575 600 625 650 675
425 X
ell
= 04 450 X X
475 X X X
500 X X X X
525 X X X X X
550X X X X X X
575 X X X X X X X
CID
=
600 X X X X X X X X
625 X X X X X X X X X
'a' 650 X X X X X X X X X X
675 X X X X X X X X X X X
700 X X X X X X X X X X X X
[0074] Thus, the
viscosity of the pregelatinized, partially hydrolyzed starch prepared in
accordance with embodiments of the invention can have a range between and
including any
of the aforementioned endpoints set forth in Tables 1A, 1B or 1C.
Alternatively, in some
embodiments, the pregelatinized, partially hydrolyzed starch has a viscosity
(10% solids,
93 C) of from about 5 Brabender Units (BU) to about 33 BU, measured according
to the
Brabender method described herein, e.g., from about 10 BU to about 30 BU, from
about 12
BU to about 25 BU, or from about 15 BU to about 20 BU.
[0075] In some
embodiments, pregelatinized, partially hydrolyzed starches prepared in
accordance with embodiments of the invention can provide significant benefits
to the strength
of the product (e.g., wallboard) to which they are applied. Since starch
contains glucose
monomers containing three hydroxyl groups, starch provides many sites for
hydrogen
bonding to gypsum crystals. While not wishing to be bound by any particular
theory, it is
believed that the molecular size of pregelatinized, partially hydrolyzed
starch prepared in
accordance with embodiments of the invention allows for optimal mobility of
starch
molecules to align starch molecules with the gypsum crystals to facilitate
good binding of
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starch to gypsum crystals to strengthen the resulting crystalline gypsum
matrix, e.g., via
hydrogen bonding.
[0076] Conventional pregelatinized starches prepared according to another
method than
that which is described herein, e.g., having viscosities outside the mid-
range, which would
have either longer chain lengths and higher molecular weight (viscosity that
is too high) and
shorter chain lengths and lower molecular weights (viscosity that is too low),
respectively, do
not provide the same combination of benefits. It is also believed that, with
respect to starch
efficiency, when the starch molecules sufficiently bind to the gypsum
crystals, additional
starch does not add significant benefit because the crystals are already bound
such that there
is no further gypsum crystal sites for which the starch to adhere or bind.
Accordingly,
because of the optimal binding between gypsum crystals and the molecules of
pregelatinized,
partially hydrolyzed starch prepared in accordance with embodiments of the
invention, the
strength of the crystalline gypsum matrix is enhanced, and less starch is
required to promote
that strength compared with conventional starches. The inventors have found
dissolved
starch molecules with, for example, mid-range viscosity (representing mid
range molecular
weight of starch) allows for optimal mobility of starch molecules to align
starch molecules
with gypsum crystals to facilitate good starch and gypsum hydrogen-bonding and
core
strength in some embodiments.
[0077] Pregelatinized, partially hydrolyzed starch prepared in accordance
with some
embodiments of the invention also provides advantages with respect to water
demand, in
some embodiments. Adding conventional pregelatinized starch to gypsum slurry
requires
that additional water be added to the gypsum slurry in order to maintain a
desired degree of
slurry fluidity. This is because conventional pregelatinized starch increases
the viscosity and
reduces the fluidity of the gypsum slurry. Thus, the use of pregelatinized
starch in
conventional systems has resulted in an increase in water demand such that
even more excess
water would be required in the gypsum slurry.
[0078] Surprisingly and unexpectedly, pregelatinized, partially hydrolyzed
starch
prepared in accordance with embodiments of the invention, particularly with
the desired
mid-range viscosity, demands less water so that the effect on water demand in
the gypsum
slurry is reduced, especially in comparison to conventional starches.
Furthermore, because of
the efficiency of the pregelatinized, partially hydrolyzed starch prepared in
accordance with
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embodiments of the invention, such that less starch can be used, the positive
impact on water
demand can be even more significant in accordance with some embodiments of the
invention.
This lower water demand provides considerable efficiencies during manufacture.
For
example, excess water requires energy input for drying. The speed of the line
must be slowed
to accommodate the drying. Thus, by reducing the water load in the gypsum
slurry, less
energy resources and cost can be seen, as well as faster production rates. In
some
embodiments, the increase in water demand in a gypsum slurry is less than the
increase in
water demand required by other starches such as pregelatinized starches having
viscosity
above 700 centipoise (e.g., about 773 centipoise), e.g., prepared by a
different method.
[0079] Any suitable non-pregelatinized starch can be selected in preparing
a
pregelatinized, partially hydrolyzed starch so long as it is sufficient to be
pregelatinized and
acid-modified in an extruder. As used herein, "starch" refers to a composition
that includes a
starch component. As such, the starch can be 100% pure starch or may have
other
components such as those commonly found in flours such as protein and fiber,
so long as the
starch component makes up at least about 75% by weight of the starch
composition. The
starch can be in the form of a flour (e.g., corn flour) containing starch,
such as flour having at
least about 75% starch by weight of the flour, e.g., at least about 80%, at
least about 85%, at
least about 90%, at least about 95%, etc.). By way of example, and not in any
limitation, the
starch can be in the form of a corn flour containing starch.
[0080] In some embodiments, the pregelatinized, partially hydrolyzed starch
prepared in
accordance with embodiments of the invention can be prepared to have desired
cold water
solubility. Conventional pregelatinization techniques involve making starch
cold water
soluble and generally require cooking starch in an excess amount of water.
However, these
conventional techniques are not efficient. Extrusion, in accordance with
embodiments of the
invention, which allows for a combination of heating and mechanical shearing,
is surprisingly
and unexpectedly an energy efficient method that can be used to produce
pregelatinized,
partially hydrolyzed starch in a one step process having a low moisture
content with cold
water solubility. Cold water solubility is defined as having any amount of
solubility in water
at room temperature (about 25 C). It was discovered that starches exhibiting
solubility in
cold water can provide significant benefits to the strength of gypsum products
(e.g.,
wallboard). Cold water soluble starches of the present invention have a cold
water solubility
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greater than about 30% and, when added to a set gypsum core, can increase the
strength of
the gypsum core. The solubility of the pregelatinized starch in water is
defined as the amount
of starch that dissolves in room temperature water divided by the total amount
of starch.
[0081] In some embodiments, the cold water solubility of the
pregelatinized, partially
hydrolyzed starch prepared in accordance with embodiments of the invention is
from about
30% to about 100%. In other embodiments, the cold water solubility of the
extruded
pregelatinized, partially hydrolyzed starch is from about 50% to about 100%.
In
embodiments of the invention, the cold water solubility of the extruded
pregelatinized,
partially hydrolyzed starch can be, e.g., as listed in Table 2. In the table,
an "X" represents
the range "from about [corresponding value in top row] to about [corresponding
value in left-
most column]." The indicated values represent the cold water solubility of a
extruded
pregelatinized, partially hydrolyzed starch prepared in accordance with
embodiments of the
invention (Table 2). For ease of presentation, it will be understood that each
value represents
"about" that value. For example, the first "X" in Table 2 is the range "from
about 30% to
about 35%." The ranges of the table are between and including the starting and
endpoints.
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Table 2
Starting Point for Cold Water Solubility Range (%)
30 35 40 45 50 55 60 65 70 75 80 85 90 95
35 X
40 XX
rll 45 XXX
czt
50XXXX
55 X XX X X
=-
60 X XX X X X
ct)
65 X XX X X X X
a.)
70 X XX X X X XX
75 X XX X X X XX X
t,L) 80X XX X X X XX XX
85 X XX X X X XX XXX
-to 90X XX X X X XX XXXX
95 X XX X X X XX XXXXX
100X XX X X X XX XXXXXX
[00821 While not wishing to be bound by any particular theory, it is
believed that a
combination of mechanical and thermal energy during extrusion is responsible
for the cold
water solubility of the pregelatinized, partially hydrolyzed starch prepared
in accordance with
embodiments of the invention. It is believed that when the starch undergoes
extrusion, the
hydrogen bonds between the starch molecules are broken. When the extruded
starch is
dissolved in water, the starch forms hydrogen bonds with the water molecules.
After the
pregelatinization process, the extruded pregelatinized, partially hydrolyzed
starch molecules
are free to hydrogen-bond with the gypsum crystals, thus imparting higher
strength to the
gypsum product. Accordingly, because starches exhibiting solubility in cold
water improve
the strength of gypsum wallboard, less starch is required compared with
conventional
starches.
[00831 In some embodiments, the pregelatinized, partially hydrolyzed starch
has a cold
water viscosity (10% solids, 25 C) of from about 10 BU to about 120 BU,
measured
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according to the Brabender method described herein, e.g., from about 20 BU to
about 110
BU, from about 30 BU to about 100 BU, from about 40 BU to about 90 BU, from
about 50
BU to about 80 BU, or from about 60 BU to about 70 BU.
Use of Starch. Prepared According to the Method in Making Board
[0084] In some embodiments, a board (e.g., gypsum wallboard) can be made by
forming
a pregelatinized, partially hydrolyzed starch by) mixing at least water, non-
pregelatinized
starch, and an acid to form a wet starch precursor having a moisture content
of from about
8 wt.% to about 25 wt.%, the acid selected from: a weak acid that
substantially avoids
chelating calcium ions, a strong acid in an amount of about 0.01 wt.% or less
by weight of the
starch, or any combination thereof.
[0085] The wet starch precursor is then fed into an extruder in which the
temperature of
the die of about 150 C (about 300 F) to about 210 C (about 410 F) where the
wet starch is
pregelatinized and acid-modified, such that it is at least partially
hydrolyzed. The
preglelatinized, partially hydrolyzed starch can then be mixed with at least
water and stucco
to form a slurry, which can then be disposed between a first cover sheet and a
second cover
sheet to form a wet assembly. The wet assembly can then be cut into a board,
which is then
dried. Preferably, the set gypsum core of the board has a compressive strength
greater than a
set gypsum core made with a starch prepared under a different method.
[0086] The pregelatinized, partially hydrolyzed starch prepared in
accordance with
embodiments of the invention surprisingly and unexpectedly can be included in
the slurry in a
relatively low amount (solids/solids basis) and still achieve significant
strength enhancement
in the board. Accordingly, the pregelatinized, partially hydrolyzed starch
prepared in
accordance with embodiments of the invention can be included in the gypsum
slurry in an
amount that is from about 0.1% to about 10% by weight based on the weight of
the stucco,
e.g., from about 0.5% to about 10%.
[00871 It has been found that increasing the amount of the pregelatinized,
partially
hydrolyzed starch prepared in accordance with embodiments of the invention in
the slurry
beyond these ranges does not improve strength as efficiently since strength
levels can
somewhat plateau upon addition of even more starch in some embodiments.
However,
higher starch quantities can be utilized if desired especially where the
diminishing return on
strength is accepted.
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[0088] In
embodiments of the invention, pregelatinized, partially hydrolyzed starch can
be added to the gypsum slurry in an amount, for example, as listed in Tables
3A and 3B
below. In the table, an "X" represents the range "from about [corresponding
value in top
row] to about [corresponding value in left-most column]." The indicated values
represent the
amount of starch as a percentage by weight of the stucco. For ease of
presentation, it will be
understood that each value represents "about" that value. For example, the
first "X" is the
range "from about 0.1% of the starch by weight of the stucco, to about 0.25%
of the starch by
weight of the stucco."
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Table 3A
0.1 0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0 2.25 2.5 2.75 3.0 3.5
0.25 X
0.5 X X
0.75 X X X
1.0 X X X X
1.25 X X X X X
1.5 X X X X X X
1.75 X X X X X X X
2.0 X X X X X X X X
2.25 X X X X X X X X X
2.5 X X X X X X X X X X
2.75 X X X X X X X X X X X
3.0 X X X X X X X X X X X X
3.5 X X X X X X X X X X X X X
4.0 X X X X X X X X X X X X XX
4.5 X X X X X X X X X X X X XX
5.0 X X X X X X X X X X X X XX
5.5 X X X X X X X X X X X X XX
6.0 X X X X X X X X X X X X XX
6.5 X X X X X X X X X X X X XX
7.0 X X X X X X X X X X X X XX'
7.5 X X X X X X X X X X X X XX
8.0 X X X X X X X X X X X X XX
8.5 X X X X X X X X X X X X XX
9.0 X X X X X X X X X X X X XX
9.5 X X X X X X X X X X X X XX
10.0 X X X X X X X X X X X X XX
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Table 3B
4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5
9.0 9.5
4.5 X
5.0 X X
5.5 X X X
_
6.0 X X X X
6.5 X X X X X
7.0 X X X X X X
7.5 X X X X X X X
8.0 X X X X X X X X
8.5 X X X X X X X X X
9.0 X X X X X X X X X X
9.5 X X X X X X X X X X X
10.0 X X X X X X X X X X X X
[0089] Thus, the amount of the pregelatinized, partially hydrolyzed starch
prepared in
accordance with embodiments of the invention added to the slurry can have a
range between
and including any of the aforementioned endpoints set forth in Tables 3A or
3B.
[0090] Pregelatinized, partially hydrolyzed starch prepared in accordance
with
embodiments of the invention can be added to the slurry in combination with
other starches,
in some embodiments for various applications. For example, in the case of
gypsum
wallboard as described below, pregelatinized, partially hydrolyzed starch
prepared in
accordance with embodiments of the invention can be combined with other
starches to
enhance both core strength and paper-core bond, particularly if some increase
in water
demand is accepted.
[0091] Thus, in some embodiments of the invention, gypsum slurry may
include one or
more pregelatinized, partially hydrolyzed starch prepared in accordance with
embodiments of
the invention, as well as one or more other types of starches. Other starches
can include, for
example, pregelatinized starches having viscosity below 20 centipoise and/or
above 700
centipoise. One example is pregelatinized corn starch (e.g., having a
viscosity over 700
centipoise such as about 773 centipoise). The other starches may also be in
the form of, e.g.,
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non-pregelatinized starches, such as acid-modified starches, as well as
alkylated starches,
e.g., ethylated starches, that are not gelatinized, etc. The combination of
starches may be pre-
mixed (e.g, in a dry mix, optionally with other components such as stucco,
etc., or in a wet
mix with other wet ingredients) before addition to the gypsum slurry, or they
can be included
in the gypsum slurry one at a time, or any variation thereof Any suitable
proportion of
pregelatinized, partially hydrolyzed starch prepared in accordance with
embodiments of the
invention and other starch may be included.
[0092] For example, the starch content of pregelatinized, partially
hydrolyzed starch
prepared in accordance with embodiments of the invention as a percentage of
total starch
content to be added to gypsum slurry can be, e.g., at least about 10% by
weight, such as at
least about 20%, at least about 30%, at least about 40%, at least about 50%,
at least about
60%, at least about 70%, at least about 80%, at least about 90%, at least
about 95%, at least
about 99%, at least about 100%, or any range in between). In some embodiments,
the ratio of
pregelatinized, partially hydrolyzed starch prepared in accordance with
embodiments of the
invention to other starch can be about 25:75, about 30:70, about 35:65, about
50:50, about
65:35, about 70:30, about 75:25, etc.
[0093] In addition to the starch component, the slurry is formulated to
include water,
stucco, foaming agent (sometimes referred to simply as "foam"), and other
additives as
desired, in some embodiments. Surprisingly and unexpectedly, in accordance
with some
embodiments, particularly those exhibiting a mid-range viscosity, it has been
found that the
amount of water needed to be added to maintain the slurry fluidity at the same
level it would
be without the pregelatinized, partially hydrolyzed starch prepared in an
extruder in
accordance with embodiments of the invention, is less than the increase in the
amount of
water needed when using a starch prepared according to a different method. The
stucco can
be in the form of calcium sulfate alpha hemihydrate, calcium sulfate beta
hemihydrate, and/or
calcium sulfate anhydrite. The stucco can be fibrous or non-fibrous. Foaming
agent can be
included to form an air void distribution within the continuous crystalline
matrix of set
gypsum. In some embodiments, the foaming agent comprises a major weight
portion of
unstable component, and a minor weight portion of stable component (e.g.,
where unstable
and blend of stable/unstable are combined). The weight ratio of unstable
component to stable
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38
component is effective to form an air void distribution within the set gypsum
core. See, e.g.,
U.S. Patents 5,643,510; 6,342,284; and 6,632,550.
[0094] It has been found that suitable void distribution and wall thickness
(independently) can be effective to enhance strength, especially in lower
density board (e.g.,
below about 35 pcf). See, e.g., US 2007/0048490 and US 2008/0090068.
Evaporative water
voids, generally having voids of about 5 pm or less in diameter, also
contribute to the total
void distribution along with the aforementioned air (foam) voids. In some
embodiments, the
volume ratio of voids with a pore size greater than about 5 microns to the
voids with a pore
size of about 5 microns or less, is from about 0.5:1 to about 9:1, such as,
for example, from
about 0.7:1 to about 9:1, from about 0.8:1 to about 9:1, from about 1.4:1 to
about 9:1, from
about 1.8:1 to about 9:1, from about 2.3:1 to about 9:1, from about 0.7:1 to
about 6:1, from
about 1.4:1 to about 6:1, from about 1.8:1 to about 6:1, from about 0.7:1 to
about 4:1, from
about 1.4:1 to about 4:1, from about 1.8:1 to about 4:1, from about 0.5:1 to
about 2.3:1, from
about 0.7:1 to about 2.3:1, from about 0.8:1 to about 2.3:1, from about 1.4:1
to about 2.3:1,
from about 1.8:1 to about 2.3:1, etc. In some embodiments, the foaming agent
is present in
the slurry, e.g., in an amount of less than about 0.5% by weight of the stucco
such as about
0.01% to about 0.5%, about 0.01% to about 0.4%, about 0.01% to about 0.3%,
about 0.01%
to about 0.2 A, about 0.01% to about 0.1%, about 0.02% to about 0.4%, about
0.02% to about
0.3%, about 0.02% to about 0.2%, etc., all by weight of the stucco.
[0095] Additives such as accelerator (e.g., wet gypsum accelerator, heat
resistant
accelerator, climate stabilized accelerator) and retarder are well known and
can be included,
in some embodiments. See, e.g., U.S. Patents 3,573,947 and 6,409,825. In some
embodiments where accelerator and/or retarder are included, the accelerator
and/or retarder
each can be in the gypsum slurry in an amount on a solid basis of, e.g, from
about 0% to
about 10% by weight of the stucco (e.g., about 0.1% to about 10%), such as,
for example,
from about 0% to about 5% by weight of the stucco (e.g., about 0.1% to about
5%). Other
additives as desired may be included, e.g., to impart strength to enable lower
weight product
with sufficient strength, to avoid permanent deformation, to promote green
strength, for
example, as the product is setting on the conveyor traveling down a
manufacturing line, to
promote fire resistance, to promote water resistance, etc.
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[0096] For example, the slurry can optionally include at least one
dispersant to enhance
fluidity in some embodiments. Like the pregelatinized, partially hydrolyzed
starch prepared
in accordance with embodiments of the invention and other ingredients, the
dispersants may
be included in a dry form with other dry ingredients and/or in a liquid form
with other liquid
ingredients in the core slurry. Examples of dispersants include
naphthalenesulfonates, such
as polynaphthalenesulfonic acid and its salts (polynaphthalenesulfonates) and
derivatives,
which are condensation products of naphthalenesulfonic acids and formaldehyde;
as well as
polycarboxylate dispersants, such as polycarboxylic ethers, for example,
PCE211, PCEI II,
1641, 1641F, or PCE 2641-Type Dispersants, e.g., MELFLUX 2641F, MELFLUX 2651E,
MELFLUX 1641F, MELFLUX 2500L dispersants (BASF), and COATEX Ethacryl M,
available from Coatex, Inc.; and/or lignosulfonates or sulfonated lignin.
Lignosulfonates are
water-soluble anionic polyelectrolyte polymers, byproducts from the production
of wood
pulp using sulfite pulping. One example of a lignin useful in the practice of
principles of
embodiments of the present invention is Marasperse C-21 available from Reed
Lignin Inc.
[0097] Lower molecular weight dispersants are generally preferred. Lower
molecular
weight naphthalenesulfonate dispersants are favored because they trend to a
lower water
demand than the higher viscosity, higher molecular weight dispersants. Thus,
molecular
weights from about 3,000 to about 10,000 (e.g., about 8,000 to about 10,000)
are preferred.
As another illustration, for PCE211 type dispersants, in some embodiments, the
molecular
weight can be from about 20,000 to about 60,000, which exhibit less
retardation than
dispersants having molecular weight above 60,000.
[0098] One example of a naphthalenesulfonate is DILOFLO, available from GEO
Specialty Chemicals. DILOFLO is a 45% naphthalenesulfonate solution in water,
although
other aqueous solutions, for example, in the range of about 35% to about 55%
by weight
solids content, are also readily available. Naphthalenesulfonates can be used
in dry solid or
powder form, such as LOMAR D, available from GEO Specialty Chemicals, for
example.
Another exemplary naphthalenesulfonate is DAXAD, available from Hampshire
Chemical
Corp.
[0099] If included, the dispersant can be included in any suitable
(solids/solids) amount,
such as, for example, from about 0.1% to about 5% by weight based on the
weight of the
stucco, e.g., from about 0.1% to about 4%, from about 0.1% to about 3%, from
about 0.2% to
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about 3%, from about 0.5% to about 3%, from about 0.5% to about 2.5%, from
about 0.5% to
about 2%, from about 0.5 A to about 1.5%, etc.
[01001 In some embodiments, one or more phosphate-containing compounds can
also be
optionally included in the slurry, if desired. For example, phosphate-
containing components
useful in some embodiments include water-soluble components and can be in the
form of an
ion, a salt, or an acid, namely, condensed phosphoric acids, each of which
comprises two or
more phosphoric acid units; salts or ions of condensed phosphates, each of
which comprises
two or more phosphate units; and monobasic salts or monovalent ions of
orthophosphates as
well as water-soluble acyclic polyphosphate salt. See, e.g., U.S. Patents
6,342,284;
6,632,550; 6,815,049; and 6,822,033.
[01011 Phosphate compositions if added in some embodiments can enhance
green
strength, resistance to permanent deformation (e.g., sag), dimensional
stability, etc.
Trimetaphosphate compounds can be used, including, for example, sodium
trimetaphosphate,
potassium trimetaphosphate, lithium trimetaphosphate, and ammonium
trimetaphosphate.
Sodium trimetaphosphate (STMP) is preferred, although other phosphates may be
suitable,
including for example sodium tetrametaphosphate, sodium hexametaphosphate
having from
about 6 to about 27 repeating phosphate units and having the molecular formula
Nan+2P11O311+1
wherein n-6-27, tetrapotassium pyrophosphate having the molecular formula
K4P207,
trisodium dipotassium tripolyphosphatc having the molecular formula
Na31(21)301o, sodium
tripolyphosphate having the molecular formula Na5P3010, tctrasodium
pyrophosphate having
the molecular formula Na4P207, aluminum trimetaphosphate having the molecular
formula
Al(P03)3, sodium acid pyrophosphate having the molecular formula Na2H2P207,
ammonium
polyphosphate having 1,000-3,000 repeating phosphate units and having the
molecular
formula (NH4)11+21'.03.+1 wherein n=1,000-3,000, or polyphosphoric acid having
two or more
repeating phosphoric acid units and having the molecular formula Hii+2P.0311+1
wherein n is
two or more.
[0102] The phosphate can be included in some embodiments in a dry form or
in a form in
water (e.g., a phosphate solution from about 5% to about 20%, such as about a
10% solution).
If included, the phosphate can be in any suitable amount (solids/solids
basis), such as from
about 0.01% to about 0.5% by weight based on the weight of stucco, e.g., from
about 0.03%
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to about 0.4%, from about 0.1% to about 0.3%, or from about 0.12% to about
0.4% by weight
based on the weight of stucco.
[0103] Suitable additives for fire-rated and/or water resistant product can
also optionally
be included, including e.g., siloxanes (water resistance); fiber; heat sink
additives such as
aluminum trihydrite (ATH), magnesium hydroxide or the like; and/or high
expansion
particles (e.g., expandable to about 300% or more of original volume when
heated for about
one hour at 1560 F). See, e.g., co-pending, commonly assigned U.S. Application
No.
13/400,010 (filed February 17, 2012) for description of these and other
ingredients. In some
embodiments, high expansion vermiculite is included, although other fire
resistant materials
can be included. The board of some fire-related product according to the
invention can have
a Thermal Insulation Index (TI) of about 17 minutes or greater, e.g., about 20
minutes or
greater, about 30 minutes or greater, about 45 minutes or greater, about 60
minutes or greater,
etc.; and/or a High Temperature Shrinkage (at temperatures of about 1560 F
(850 C)) of less
than about 10% in the x-y directions and expansion in the z-direction of
greater than about
20%. The fire or water resistance additives can be included in any suitable
amount as desired
depending, e.g., on fire rating, etc. For example, if included, the fire or
water resistance
additives can be in an amount from about 0.5% to about 10% by weight of the
stucco, such as
from about 1% to about 10%, about 1% to about 8%, about 2% to about 10%, about
2% to
about 8% by weight of the stucco, etc.
[0104] If included, in some embodiments, the siloxane preferably is added
in the form of
an emulsion. The slurry is then shaped and dried under conditions which
promote the
polymerization of the siloxane to form a highly cross-linked silicone resin. A
catalyst which
promotes the polymerization of the siloxane to form a highly cross-linked
silicone resin can
be added to the gypsum slurry. In some embodiments, solventless methyl
hydrogen siloxane
fluid sold under the name SILRES BS 94 by Wacker-Chemie GmbH (Munich, Germany)
can
be used as the siloxane. This product is a siloxane fluid containing no water
or solvents. It is
contemplated that about 0.3% to about 1.0% of the BS 94 siloxane may be used
in some
embodiments, based on the weight of the dry ingredients. For example, in some
embodiments, it is preferred to use from about 0.4% to about 0.8% of the
siloxane based on
the dry stucco weight.
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[0105] The slurry formulation can be made with any suitable water/stucco
ratio, e.g.,
from about 0.4 to about 1.3. However, because the pregelatinized, partially
hydrolyzed
starches prepared in accordance with embodiments of the invention reduce the
amount of
water required to be added to the slurry to accommodate them, as compared with
other
starches (e.g., conventional pregelatinized starch prepared according to a
different method),
the slurry can be formulated with a water/stucco ratio input that is lower in
some
embodiments than what is conventional for other starch-containing gypsum
slurries,
especially at low weight/density. For example, in some embodiments, the
water/stucco ratio
can be from about 0.4 to about 1.1, from about 0.4 to about 0.9, from about
0.4 to about 0.85,
from about 0.45 to about 0.85, from about 0.55 to about 0.85, from about 0.55
to about 0.8,
from about 0.6 to about 0.9, from about 0.6 to about 0.85, from about 0.6 to
about 0.8, etc.
[0106] The cover sheets can be formed of any suitable material and basis
weight.
Advantageously, board core formed from slurry comprising pregelatinized,
partially
hydrolyzed starch prepared in accordance with embodiments of the invention
provides
sufficient strength in board even with lower basis weight cover sheets such
as, for example,
less than 45 lbs/MSF (e.g., about 33 lbs/MSF to 45 lbs/MSF) even for lower
weight board
(e.g., having a density of about 35 pcf or below) in some embodiments.
However, if desired,
in some embodiments, heavier basis weights can be used, e.g., to further
enhance nail pull
resistance or to enhance handling, e.g., to facilitate desirable "feel"
characteristics for end-
users.
[0107] In some embodiments, to enhance strength (e.g., nail pull strength),
especially for
lower density board, one or both of the cover sheets can be formed from paper
and have a
basis weight of, for example, at least about 45 lbs/MSF (e.g., from about 45
lbs/MSF to about
65 lbs/MSF, from about 45 lbs/MSF to about 60 lbs/MSF, from about 45 lbs/MSF
to about
55 lbs/MSF, from about 50 lbs/MSF to about 65 lbs/MSF, from about 50 lbs/MSF
to about
60 lbs/MSF, etc.). If desired, in some embodiments, one cover sheet (e.g., the
"face" paper
side when installed) can have aforementioned higher basis weight, e.g., to
enhance nail pull
resistance and handling, while the other cover sheet (e.g., the "back" sheet
when the board is
installed) can have somewhat lower weight basis if desired (e.g., weight basis
of less than
about 45 lbs/MSF, e.g., from about 33 lbs/MSF to about 45 lbs/MSF or from
about
33 lbs/MSF to about 40 lbs/MSF).
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[0108] Board weight is a function of thickness. Since boards are commonly
made at
varying thicknesses, board density is used herein as a measure of board
weight. The
advantages of the pregelatinized, partially hydrolyzed starch prepared in
accordance with
embodiments of the invention can be seen across various board densities, e.g.,
about 40 pcf or
less, such as from about 20 pcf to about 40 pcf, from about 24 pcf to about 37
pcf, etc.
However, preferred embodiments of the invention have particular utility at
lower densities
where the enhanced strength provided by the pregelatinized, partially
hydrolyzed starch
prepared in accordance with embodiments of the invention advantageously
enables the use of
lower weight board with good strength and lower water demand than board made
from other
starches prepared according to a different method.
[0109] For example, in some embodiments, board density can be from about 20
pcf to
about 35 pcf, e.g., from about 20 pcf to about 34 pcf, from about 20 pcf to
about 33 pcf, from
about 20 pcf to about 32 pcf, from about 20 pcf to about 31 pcf, from about 20
pcf to about
30 pcf, from about 20 pcf to about 29 pcf, from about 21 pcf to about 35 pcf,
from about
21 pcf to about 34 pcf, from about 21 pcf to about 33 pcf, from about 21 pcf
to about 32 pcf,
from about 21 pcf to about 31 pcf, from about 21 pcf to about 30 pcf, from
about 21 pcf to
about 29 pcf, from about 24 pcf to about 35 pcf, from about 24 pcf to about 34
pcf, from
about 24 pcf to about 33 pcf, from about 24 pcf to about 32 pcf, from about 24
pcf to about
31 pcf, from about 24 pcf to about 30 pcf, or from about 24 pcf to about 29
pcf.
[0110] The pregelatinized, partially hydrolyzed starches prepared in
accordance with
embodiments of the invention can be added to slurry to provide strength
enhancement to
product according to the invention, which can be especially beneficial at
lower
weight/density. For example, in some embodiments, the board made according to
embodiments of the invention has a compressive strength of at least about 400
psi
(2,750 kPa) at a density of 29 pcf as tested according to the method set forth
in Example 4.
Advantageously, in various embodiments at various board densities as described
herein, the
board produced by the inventive method can be prepared to have a compressive
strength of at
least about 400 psi, e.g., at least about 450 psi (3,100 kPa), at least about
500 psi (3,450 kPa),
at least about 550 psi (3,800 kPa), at least about 600 psi (4,100 kPa), at
least about 650 psi
(4,500 kPa), at least about 700 psi (4,800 kPa), at least about 750 psi (5,200
kPa), at least
about 800 psi (5,500 kPa), at least about 850 psi (5,850 kPa), at least about
900 psi
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(6,200 kPa), at least about 950 psi (6,550 kPa), or at least about 1,000 psi
(6,900 kPa). In
addition, in some embodiments, the compressive strength can be bound by any
two of the
foregoing points. For example, the compressive strength can be between about
450 psi and
about 1,000 psi (e.g., between about 500 psi and about 900 psi, between about
600 psi and
about 800 psi, etc.).
[0111] In some embodiments, board made according to the invention meets
test protocols
according to ASTM Standard C473-10. For example, in some embodiments, when the
board
is cast at a thickness of 1/2 inch, the board has a nail pull resistance of at
least about 65 lb as
determined according to ASTM C473-10, e.g., at least about 68 lb, at least
about 70 lb, at
least about 72 lb, at least about 75 lb, at least about 77 lb, etc. In various
embodiments, the
nail pull resistance can be from about 68 lb to about 100 lb, e.g., from about
68 lb to about
95 lb, from about 68 lb to about 90 lb, from about 68 lb to about 85 lb, from
about 68 lb to
about 80 lb, from about 68 lb to about 77 lb, from about 68 lb to about 75 lb,
from about
68 lb to about 72 lb, from about 68 lb to about 70 lb, from about 70 lb to
about 100 lb, from
about 70 lb to about 95 lb, from about 70 lb to about 90 lb, from about 70 lb
to about 85 lb,
from about 70 lb to about 80 lb, from about 70 lb to about 77 lb, from about
70 lb to about
75 lb, from about 70 lb to about 72 lb, from about 72 lb to about 100 lb, from
about 72 lb to
about 95 lb, from about 72 lb to about 90 lb, from about 72 lb to about 85 lb,
from about
72 lb to about 80 lb, from about 72 lb to about 77 lb, from about 72 lb to
about 75 lb, from
about 75 lb to about 100 lb, from about 75 lb to about 95 lb, from about 75 lb
to about 90 lb,
from about 75 lb to about 85 lb, from about 75 lb to about 80 lb, from about
75 lb to about
77 lb, from about 77 lb to about 100 lb, from about 77 lb to about 95 lb, from
about 77 lb to
about 90 lb, from about 77 lb to about 85 lb, or from about 77 lb to about 80
lb.
[0112] With respect to flexural strength, in some embodiments, when cast in
a board of 1/2
inch thickness, the board has a flexural strength of at least about 36 lb in a
machine direction
(e.g., at least about 38 lb, at least about 40 lb, etc) and/or at least about
107 lb (e.g., at least
about 110 lb, at least about 112 lb, etc) in a cross-machine direction as
determined according
to the ASTM standard C473. In various embodiments, the board can have a
flexural strength
in a machine direction of from about 36 lb to about 60 lb, e.g., from about 36
lb to about
55 lb, from about 36 lb to about 50 lb, from about 36 lb to about 45 lb, from
about 36 lb to
about 40 lb, from about 36 lb to about 38 lb, from about 38 lb to about 60 lb,
from about
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38 lb to about 55 lb, from about 38 lb to about 50 lb, from about 38 lb to
about 45 lb, from
about 38 lb to about 40 lb, from about 40 lb to about 60 lb, from about 40 lb
to about 55 lb,
from about 40 lb to about 50 lb, or from about 40 lb to about 45 lb. In
various embodiments,
the board can have a flexural strength in a cross-machine direction of from
about 107 lb to
about 130 lb, e.g., from about 107 lb to about 125 lb, from about 107 lb to
about 120 lb, from
about 107 lb to about 115 lb, from about 107 lb to about 112 lb, from about
107 lb to about
110 lb, from about 110 lb to about 130 lb, from about 110 lb to about 125 lb,
from about
110 lb to about 120 lb, from about 110 lb to about 115 lb, from about 110 lb
to about 112 lb,
from about 112 lb to about 130 lb, from about 112 lb to about 125 lb, from
about 112 lb to
about 120 lb, or from about 112 lb to about 115 lb.
[0113] In addition, in some embodiments, board can have an average core
hardness of at
least about 11 lb, e.g., at least about 12 lb, at least about 13 lb, at least
about 14 lb, at least
about 15 lb, at least about 16 lb, at least about 17 lb, at least about 18 lb,
at least about 19 lb,
at least about 20 lb, at least about 21 lb, or at least about 22 lb, as
determined according to
ASTM C473-10. In some embodiments, board can have a core hardness of from
about 11 lb
to about 25 lb, e.g., from about 11 lb to about 22 lb, from about 11 lb to
about 21 lb, from
about 11 lb to about 20 lb, from about 11 lb to about 19 lb, from about 11 lb
to about 18 lb,
from about 11 lb to about 17 lb, from about 11 lb to about 16 lb, from about
11 lb to about
15 lb, from about 11 lb to about 14 lb, from about 11 lb to about 13 lb, from
about 11 lb to
about 12 lb, from about 12 lb to about 25 lb, from about 12 lb to about 22 lb,
from about
12 lb to about 21 lb, from about 12 lb to about 20 lb, from about 12 lb to
about 19 lb, from
about 12 lb to about 18 lb, from about 12 lb to about 17 lb, from about 12 lb
to about 16 lb,
from about 12 lb to about 15 lb, from about 12 lb to about 14 lb, from about
12 lb to about
13 lb, from about 13 lb to about 25 lb, from about 13 lb to about 22 lb, from
about 13 lb to
about 21 lb, from about 13 lb to about 20 lb, from about 13 lb to about 19 lb,
from about
13 lb to about 18 lb, from about 13 lb to about 17 lb, from about 13 lb to
about 16 lb, from
about 13 lb to about 15 lb, from about 13 lb to about 14 lb, from about 14 lb
to about 25 lb,
from about 14 lb to about 22 lb, from about 14 lb to about 21 lb, from about
14 lb to about
20 lb, from about 14 lb to about 19 lb, from about 14 lb to about 18 lb, from
about 14 lb to
about 17 lb, from about 14 lb to about 16 lb, from about 14 lb to about 15 lb,
from about
15 lb to about 25 lb, from about 15 lb to about 22 lb, from about 15 lb to
about 21 lb, from
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about 15 lb to about 20 lb, from about 15 lb to about 19 lb, from about 15 lb
to about 18 lb,
from about 15 lb to about 17 lb, from about 15 lb to about 16 lb, from about
16 lb to about
25 lb, from about 16 lb to about 22 lb, from about 16 lb to about 21 lb, from
about 16 lb to
about 20 lb, from about 16 lb to about 19 lb, from about 16 lb to about 18 lb,
from about
16 lb to about 17 lb, from about 17 lb to about 25 lb, from about 17 lb to
about 22 lb, from
about 17 lb to about 21 lb, from about 17 lb to about 20 lb, from about 17 lb
to about 19 lb,
from about 17 lb to about 18 lb, from about 18 lb to about 25 lb, from about
18 lb to about
22 lb, from about 18 lb to about 21 lb, from about 18 lb to about 20 lb, from
about 18 lb to
about 19 lb, from about 19 lb to about 25 lb, from about 19 lb to about 22 lb,
from about
19 lb to about 21 lb, from about 19 lb to about 20 lb, from about 21 lb to
about 25 lb, from
about 21 lb to about 22 lb, or from about 22 lb to about 25 lb.
[0114] Due at least in part to the mid-range viscosity characteristic that
results in some
embodiments of the invention, these standards (e.g., nail pull resistance,
flexural strength, and
core hardness) can be met even with respect to ultra light density board
(e.g., about 31 pcf or
less) as described herein.
[0115] It has also been found by the inventors that pregelatinized,
partially hydrolyzed
starches prepared in accordance with embodiments of the invention demonstrate
temperature
rise set (TRS) hydration rates that are comparable to or surpass those of
conventional
pregelatinized starches prepared according to a different method. The desired
setting time
may depend on the formulation, and the desired setting time can be determined
by one of
ordinary skill in the art depending on plant conditions and available raw
materials.
[0116] Product according to embodiments of the invention can be made on
typical
manufacturing lines. For example, board manufacturing techniques are described
in, for
example, U.S. Patent 7,364,676 and U.S. Patent Application Publication
2010/0247937.
Briefly, in the case of gypsum board, the process typically involves
discharging a cover sheet
onto a moving conveyor. Since gypsum board is normally formed "face down,"
this cover
sheet is the "face" cover sheet in such embodiments.
[0117] Dry and/or wet components of the gypsum slurry are fed to a mixer
(e.g., pin
mixer), where they are agitated to form the gypsum slurry. The mixer comprises
a main body
and a discharge conduit (e.g., a gate-canister-boot arrangement as known in
the art, or an
arrangement as described in U.S. Patents 6,494,609 and 6,874,930). In some
embodiments,
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the discharge conduit can include a slurry distributor with either a single
feed inlet or
multiple feed inlets, such as those described in U.S. Patent Application
Publication
2012/0168527 Al (Application No. 13/341,016) and U.S. Patent Application
Publication
2012/0170403 Al (Application No. 13/341,209), for example. In those
embodiments, using
a slurry distributor with multiple feed inlets, the discharge conduit can
include a suitable flow
splitter, such as those described in U.S. Patent Application Publication
2012/0170403 Al.
Foaming agent can be added in the discharge conduit of the mixer (e.g., in the
gate as
described, for example, in U.S. Patents 5,683,635 and 6,494,609) or in the
main body if
desired. Slurry discharged from the discharge conduit after all ingredients
have been added,
including foaming agent, is the primary gypsum slurry and will form the board
core. This
board core shiny is discharged onto the moving face cover sheet.
[0118] The face cover sheet may bear a thin skim coat in the form of a
relatively dense
layer of slurry. Also, hard edges, as known in the art, can be formed, e.g.,
from the same
slurry stream forming the face skim coat. In embodiments where foam is
inserted into the
discharge conduit, a stream of secondary gypsum slurry can be removed from the
mixer body
to form the dense skim coat slurry, which can then be used to form the face
skim coat and
hard edges as known in the art. If included, normally the face skim coat and
hard edges are
deposited onto the moving face cover sheet before the core slurry is
deposited, usually
upstream of the mixer. After being discharged from the discharge conduit, the
core slurry is
spread, as necessary, over the face cover sheet (optionally bearing skim coat)
and covered
with a second cover sheet (typically the "back" cover sheet) to form a wet
assembly in the
form of a sandwich structure that is a board precursor to the final product.
The second cover
sheet may optionally bear a second skim coat, which can be formed from the
same or
different secondary (dense) gypsum slurry as for the face skim coat, if
present. The cover
sheets may be formed from paper, fibrous mat or other type of material (e.g.,
foil, plastic,
glass mat, non-woven material such as blend of cellulosic and inorganic
filler, etc.).
[0119] The wet assembly thereby provided is conveyed to a forming station
where the
product is sized to a desired thickness (e.g., via forming plate), and to one
or more knife
sections where it is cut to a desired length. The wet assembly is allowed to
harden to form
the interlocking crystalline matrix of set gypsum, and excess water is removed
using a drying
process (e.g., by transporting the assembly through a kiln). Surprisingly and
unexpectedly, it
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has been found that board prepared according to the invention with
pregelatinized, partially
hydrolyzed starch prepared in accordance with embodiments of the invention
requires
significantly less time in a drying process because of the low water demand
characteristic of
the starch. This is advantageous because it reduces energy costs.
[0120] It also is common in the manufacture of gypsum board to use
vibration in order to
eliminate large voids or air pockets from the deposited slurry. Each of the
above steps, as
well as processes and equipment for performing such steps, are known in the
art.
[0121] The pregelatinized, partially hydrolyzed starch prepared in
accordance with
embodiments of the invention can be used in formulating various products, such
as, for
example, gypsum wallboard, acoustical (e.g., ceiling) tile, joint compound,
gypsum-cellulosic
fiber products, such as gypsum-wood fiber wallboard, and the like. In some
embodiments,
such product can be formed from slurry according to embodiments of the
invention.
[0122] As such, pregelatinized, partially hydrolyzed starch prepared in an
extruder in
accordance with embodiments of the invention can have beneficial effect, as
described
herein, in product besides paper-faced gypsum board in embodiments of the
invention. For
example, pregelatinized, partially hydrolyzed starch prepared in accordance
with
embodiments of the invention can be used in mat-faced products (e.g., woven)
where board
cover sheets are in the form of fibrous mats. The mats can optionally bear a
finish to reduce
water permeability. Other ingredients that can be included in making such mat-
faced
product, as well as materials for the fibrous mats and methods of manufacture,
are discussed
in, e.g., U.S. Patent 8,070,895, as well as U.S. Patent Application
Publication 2009/0247937.
[0123] In addition, gypsum-cellulosic product can be in the form of
cellulosic host
particles (e.g., wood fibers), gypsum, pregelatinized, partially hydrolyzed
starch prepared in
accordance with embodiments of the invention, and other ingredients (e.g.,
water resistant
additives such as siloxanes) as desired. Other ingredients and methods of
manufacture are
discussed in, e.g., U.S. Patents 4,328,178; 4,239,716; 4,392,896; 4,645,548;
5,320,677;
5,817,262; and 7,413,603.
Illustrative Examples of Embodiments
[0124] In one embodiment, a method of making a pregelatinized, partially
hydrolyzed
starch comprises: (a) mixing at least water, non-pregelatinized starch, and a
weak acid that
substantially avoids chelating calcium ions to make a wet starch precursor
having a moisture
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content of from about 8 wt.% to about 25 wt.%; (b) feeding the wet starch
precursor into an
extruder; and (c) pregelatinizing and acid-modifying the wet starch precursor
in the extruder
at a die temperature of about 150 C (about 300 F) to about 210 C (about 410
F).
[0125] In another embodiment, the pressure inside the extruder is at least
about 2,000 psi.
[0126] In another embodiment, the pregelatinized, partially hydrolyzed
starch has a cold
water solubility greater than about 50%.
[0127] In another embodiment, the pregelatinized, partially hydrolyzed
starch has a cold
water viscosity (10% solids, 25 C) of from about 10 Brabender Unit (BU) to
about 120 BU.
[0128] In another embodiment, the pregelatinized, partially hydrolyzed
starch has a
viscosity characteristic of from about 20 centipoise to about 700 centipoise
when the
viscosity is measured while the starch is subjected to the conditions
according to the VMA
method.
[0129] In another embodiment, the pregelatinized, partially hydrolyzed
starch has a
viscosity (10% solids, 93 C) of from about 5 BU to about 33 BU.
[0130] In another embodiment, the weak acid that substantially avoids
chelating calcium
ions comprises alum.
[0131] In another embodiment, tartaric acid is included in the mixing to
form the wet
starch precursor.
[0132] In another embodiments, the weak acid that substantially avoids
chelating calcium
ions is in an amount of from about 0.5 wt.% to about 5 wt.% by weight of the
starch.
[0133] In another embodiment, the wet starch has a moisture content of from
about
wt.% to about 20 wt.% by weight of the starch precursor.
[0134] In another embodiment, the pregelatinizing and acid-modifying occurs
at a die
temperature of from at least about 175 C (about 350 F) to about 205 C (about
400 F) in the
extruder.
[0135] In another embodiment, the output of the pregelatinized, partially
hydrolyzed
starch is at least about 100 kg/hr in the extruder.
[0136] In another embodiment, the pregelatinizing and acid-modifying occurs
in less than
about 5 minutes.
[0137] In another embodiment, the pregelatinizing and acid-modifying occurs
in less than
about 1 minute.
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[0138] In another embodiment, the method is free of a purification step for
the
pregelatinized, partially hydrolyzed starch.
[0139] In another embodiment, the method is free of a neutralization step
for the
pregelatinized, partially hydrolyzed starch.
[0140] In another embodiment, the pregelatinized, partially hydrolyzed
starch is at least
about 70% gelatinized.
[0141] In another embodiment, a pregelatinized, partially hydrolyzed starch
is prepared
according to embodiments of the invention.
[0142] In another embodiment, a method of making a pregelatinized,
partially hydrolyzed
starch comprises: (a) mixing at least water, non-pregelatinized starch, and a
strong acid to
make a wet starch precursor having a moisture content of from about 8 wt.% to
about
25 wt.%, wherein the strong acid is in an amount of about 0.05 wt.% or less by
weight of the
starch; (b) feeding the wet starch precursor into an extruder; and (c)
pregelatinizing and acid-
modifying the wet starch in the extruder at a die temperature of about 150 C
(about 300 F) to
about 210 C (about 410 F).
[0143] In another embodiment, a method of making a pregelatinized,
partially hydrolyzed
starch comprises: (a) mixing at least water, non-pregelatinized starch, and a
strong acid to
make a wet starch precursor having a moisture content of from about 8 wt.% to
about
25 wt.%, wherein the strong acid is in an amount of about 0.01 wt.% or less by
weight of the
starch; (b) feeding the wet starch precursor into an extruder; and (c)
pregelatinizing and acid-
modifying the wet starch in the extruder at a die temperature of about 150 C
(about 300 F) to
about 210 C (about 410'F).
[0144] In another embodiment, the strong acid has a pKa of about -1.7 or
less.
[0145] In another embodiment, the strong acid is sulfuric acid, nitric
acid, hydrochloric
acid, or any combination thereof
[0146] In another embodiment, the method of making board comprises: (a)
forming a
pregelatinized, partially hydrolyzed starch by (i) mixing at least water, non-
pregelatinized
starch, and an acid to form a wet starch precursor having a moisture content
of from about
8 wt.% to about 25 wt.%, the acid selected from the group consisting of: (1) a
weak acid that
substantially avoids chelating calcium ions, (2) a strong acid in an amount of
about 0.05 wt.%
or less by weight of the starch, or (3) any combination thereof; (ii) feeding
the wet starch
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precursor into an extruder; and (iii) pregelatinizing and acid-modifying the
wet starch in the
extruder having a die at a temperature of about 150 C (about 300 F) to about
210 C (about
410 F); (b) mixing the pregelatinized and partially hydrolyzed starch with at
least water and
stucco to form a slurry; (c) disposing the slurry between a first cover sheet
and a second
cover sheet to form a wet assembly; (d) cutting the wet assembly into a board;
and (e) drying
the board.
[0147] In another embodiment, the strong acid is in an amount of about 0.01
wt.% or less
by weight of the starch.
[0148] In another embodiment, a method of making board comprises (a)
forming a
pregelatinized, partially hydrolyzed starch by (i) mixing at least water, non-
pregelatinized
starch, and a weak acid that substantially avoids chelating calcium ions to
make a wet starch
precursor having a moisture content of from about 8 wt.% to about 25 wt.%;
(ii) feeding the
wet starch into an extruder; and (iii) pregelatinizing and acid-modifying the
wet starch in an
extruder having a die at a temperature of about 150 C (about 300 F) to about
210 C (about
410 F); (b) mixing the pregelatinized and partially hydrolyzed starch with at
least water and
stucco to form a slurry; (c) disposing the slurry between a first cover sheet
and a second
cover sheet to form a wet assembly; (d) cutting the wet assembly into a board;
and (e) drying
the board.
[0149] In another embodiment, the method of making board comprises: (a)
mixing at
least water, non-pregelatinized starch, and a strong acid to make a wet starch
precursor
having a moisture content of from about 8 wt.% to about 25 wt.%, wherein the
strong acid is
in an amount of about 0.05 wt.% or less by weight of the starch; (ii) feeding
the wet starch
precursor into an extruder; and (iii) pregelatinizing and acid-modifying the
wet starch in the
extruder having a die at a temperature of about 150 C (about 300 F) to about
210 C (about
410 F); (b) mixing the pregelatinized and partially hydrolyzed starch with at
least water and
stucco to form a slurry; (c) disposing the slurry between a first cover sheet
and a second
cover sheet to form a wet assembly; (d) cutting the wet assembly into a board;
and (e) drying
the board.
[0150] In another embodiment, the strong acid is in an amount of about 0.01
wt.% or less
by weight of the starch.
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[0151] In another embodiment, the set gypsum core has a compressive
strength greater
than a set gypsum core made with a starch prepared under a different method.
[0152] In another embodiment, the pregelatinized, partially hydrolyzed
starch is at least
about 70% gelatinized when added to the slurry, with additional gelatinization
taking place in
the drying step.
[0153] In another embodiment, the pregelatinized, partially hydrolyzed
starch is fully
gelatinized when added to the slurry.
[0154] In another embodiment, the board has a compressive strength of at
least about
400 psi (2,800 kPa) at a density of 29 pcf.
[0155] In another embodiment, the board has a core hardness of at least
about 11, as
determined according to ASTM C473-10.
[0156] In another embodiment, the board has a density of from about 21 pcf
to about
35 pcf.
[0157] In another embodiment, the slurry further comprises sodium
trimetaphosphate.
[0158] In another embodiment, the amount of water needed to be added to
maintain the
slurry fluidity at the same level it would be without the pregelatinized,
partially hydrolyzed
starch, is less than the increase in the amount of water needed when using a
pregelatinized,
partially hydrolyzed starch prepared according to a different method.
[0159] In another embodiment, the starch is in an amount of from about 0.5%
to about
10% by weight based on the weight of the stucco.
[0160] In another embodiment, a wallboard is prepared according to
embodiments of the
invention.
[0161] It shall be noted that the preceding are merely examples of
embodiments. Other
exemplary embodiments are apparent from the entirety of the description
herein. It will also
be understood by one of ordinary skill in the art that each of these
embodiments may be used
in various combinations with the other embodiments provided herein.
[0162] The following examples further illustrate the invention but, of
course, should not
be construed as in any way limiting its scope.
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EXAMPLE 1
[0163] This Example illustrates the preparation of pregelatinized,
partially hydrolyzed
starches in accordance with embodiments of the invention.
[0164] Nine pregelatinized, partially hydrolyzed starches prepared in
accordance with
embodiments of the invention were prepared for various tests of specific
properties (e.g.,
viscosity, fluidity, strength). These nine inventive starches were tested
alongside three
commercially available starches.
[0165] In accordance with the inventive method of preparing pregelatinized,
partially
hydrolyzed starch, wet starch precursors were prepared by mixing a
degerminated corn flour
commercially available as CCM 260 Yellow Corn Meal from Bunge North America
(St.
Louis, MO) in an amount of 100 kg, varying amounts of aluminum sulfate (alum),
a weak
acid that substantially avoids chclating with calcium ions, and/or tartaric
acid (less than
20 wt.% of the total of weak acids), and varying amounts of water. The wet
starch precursors
were fed into a single screw extruder commercially available as Advantage 50
from
American Extrusion International (South Beloit, IL). In the extruder, the wet
starch
precursors were pregelatinized and acid-modified in a single step, such that
they occurred
simultaneously.
[0166] Table 4 below describes the parameters of the extrusion of the corn
flour in the
presence of acid. The residence time of extrusion (i.e., the time for
pregelatinization and
acid-modification) was less than 30 seconds. All percents are based on the
total weight of the
starch, except moisture, which is based on the total wet weight, expressed as
the sum of
water, starch, and other additives.
[0167] The resulting pregelatinized, partially hydrolyzed starches were
evaluated against
a conventional pregelatinized corn starch having a viscosity of 773 centipoise
designated
Composition lA (comparative), as well as two low water-demand starches
prepared by
extrusion of acid-modified corn starches, commercially available as Clinton
277 (ADM,
Chicago, IL) and Caliber 159 (Cargill, Wayzata, MN), designated Composition 1B
(comparative) and Composition 1C (comparative), respectively.
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Table 4
Substrate Corn Flour
Canola oil 0.25 wt.%
Liquid alum 1 wt.% -4 wt.%
Tartaric acid 0 wt.% - 0.3 wt.%
Moisture of starch during extrusion 10 wt.% -20 wt.%
Main screw (RPM) 350
Feed auger speed (RPM) 14
Die temperature ( F) 350-370
Knife speed (RPM) 400-1,000
[0168] Pregelatinized, partially hydrolyzed starches, designated
Compositions 1D-1L,
were produced in the extrusion process.
[0169] Table 5 below details the various moisture contents for extrusion
and acid
contents during extrusion for Compositions 1D-1L. Compositions 1D-1H and 1L
were
prepared with a moisture content of 16 wt.%, while Compositions 11-1K were
prepared with
a moisture content of 13 wt.%. Compositions 1D-1G and Compositions 11-1L were
prepared
with liquid alum in an amount of ranging from 1 wt.% to 4 wt. %, while
Composition 1H
included liquid alum and tartaric acid. Compositions 1F and 1L were prepared
using the
same moisture content and amount of acid, but in Example 3 had different
amounts of
retarder.
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Table 5
Composition Moisture Acid
Composition lA 16 wt.% NA
Composition 1B 19 wt.% NA
Composition 1C 19 wt.% NA
Composition 1D 16 wt.% 1 wt.% alum
Composition lE 16 wt.% 2 wt.% alum
Composition 1F 16 wt.% 3 wt.% alum
Composition 1G 16 wt.% 4 wt.% alum
Composition 1H 16 wt.% 2 wt.% alum;
0.3 wt.% tartaric acid
Composition LI 13 wt.% 1 wt.% alum
Composition 1J 13 wt.% 2 wt.%
Composition 1K 13 wt.% 3 wt.% alum
Composition 1L 16 wt.% 3 wt.% alum
[01701 Examples 2-4 below test the Compositions described in Table 5 for
various
properties. in Example 2, Compositions 1B-1L were evaluated with regards to
viscosity in
amylograph tests. Example 3 tested slurries prepared with one of Compositions
IA, 1D-ii,
and 1K-1L for fluidity, which was evaluated by means of a slump test. This
data was then
further corroborated by measuring the time to 50% hydration for the slurries.
This illustrated
how much time it took for the slurries to set. Example 4 tested slurries
prepared with
Compositions 1A, 1D-11, and 1K for strength, which was evaluated by means of a
compressive strength test described herein.
EXAMPLE 2
[01711 This example illustrates the viscosity of pregelatinized, partially
hydrolyzed
starches prepared in an extruder in accordance with embodiments of the
invention.
Compositions 1D-1K were tested in comparison to extruded commercially
available acid-
modified starches (Compositions 1B-1C), specifically with regards to how
viscosity changes
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based on the amount of acid (e.g., alum) and moisture content, defined by the
level of
moisture of the wet starch that is fed through the extruder.
[0172] In preparation for testing, the Compositions were mixed with water
into a starch
slurry, such that the starch slurries contained the Compositions in an amount
of 10 wt.%. It
will be noted that the term "solution" is used when the starch is fully
gelatinized and
completely dissolved and the term "slurry" is used when the starch is not
completely
dissolved. Each Composition was then tested for viscosity at different
temperatures by the
Amylograph technique described herein. The results of the tests were plotted
in FIGS. 1 and
2, which are amylograms evaluating the viscosity of pregelatinized, partially
hydrolyzed
starches at different temperatures by plotting viscosity (left y-axis) and
temperature (right y-
axis) versus time (x-axis). The temperature curve is overlaid against each
sample. The same
temperature profile was used for each sample. The other curves show the
viscosity of the
starches.
[0173] The initial viscosity at 25 C was an indicator of the fluidity of a
slurry system
containing any one of Compositions 1B-1K. 25 C is the temperature at which the
starch will
be mixed with stucco and other ingredients to make board. At this temperature,
furthermore,
the viscosity of the starch is negatively correlated with the fluidity of the
stucco slurry.
[0174] The viscosity at trough (93 C) was an indicator of the molecular
weight of any
one of Compositions 1B-1K. At a temperature of 93 C, the starch molecules are
completely
dissolved in water. The viscosity of the starch solutions at 93 C is
positively correlated with
the molecular weight of the starch, which results from partial hydrolysis.
[0175] FIG. l is an amylogram plotting viscosity (left y-axis) and
temperature (right
y-axis) over a fifty minute period (x-axis). Comparative Compositions 1B and
1C and
inventive Compositions 1D-1H, as described herein, were mixed into starch
solutions in an
amount of 10% by weight based on the weight of the solution. To avoid forming
lumps,
starch was added into the water in a mixing cup of a Waring blender while
mixed at low
speed for 20 seconds. The starch solutions were then evaluated using a
Viscograph-E (C.W.
Brabender Instruments, Inc., South Hackensack, NJ). According to the
Brabender viscosity
measurement procedure as referred to herein, viscosity is measured using a
C.W. Brabender
Viscograph, e.g., a Viscograph-E that uses reaction torque for dynamic
measurement. It is to
be noted that, as defined herein, the Brabender units are measured using a
sample cup size of
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16 fl. oz (about 500 cc), with a 700 cmg cartridge at an RPM of 75. One of
ordinary skill in
the art also will readily recognize that the Brabender units can be converted
to other viscosity
measurements, such as centipoises (e.g., cP = BU X 2.1, when the measuring
cartridge is 700
cmg) or Krebs units, as described therein. The pasting profiles of
Compositions 1D-1H
extruded at 16 wt.% moisture content are shown in FIG. 1 along with
comparative
Compositions 1B and 1C.
[0176] Considering inventive Compositions 1D-1H, as alum increased from 1
wt.% to
4 wt.%, the initial viscosity decreased from 70 Brabender Unit (BU) to 10 BU,
while the
molecular weight decreased as well. The initial viscosities and viscosities at
93 C of
Compositions 1D-1H were reduced as low as those of Compositions 1B and 1C.
Compositions 1B and 1C represent conventional viscosity limits of low water
demand
starches.
[0177] The results of Compositions 1D-1H shown in FIG. 1 demonstrate that
optimal
acid-modification can be achieved during extrusion. These results further
suggest that the
inventive method of preparing pregelatinized, partially hydrolyzed starch
successfully
reduced the viscosity (molecular weight) of the starch. No viscosity peak was
observed
between 70 C to 90 C, indicating that Compositions 1D-1H were fully
gelatinized. Had
Compositions 1D-1H not been fully gelatinized, there would have been an
increase in
viscosity. The full gelatinization of the starch Compositions were confirmed
by differential
scanning calorimetry (DSC).
[0178] FIG. 2 is a second amylogram plotting viscosity (left y-axis) and
temperature
(right y-axis) over a fifty minute period (x-axis). Comparative Compositions
1B and IC and
inventive Compositions II-1K, all as described herein, were mixed into starch
solutions in an
amount of 10% by weight based on the weight of the solution. To avoid forming
lumps,
starch was added into the water in a mixing cup of a Waring blender while
mixed at low
speed for 20 seconds. The starch solutions were then evaluated using a
Viscograph-E. The
pasting profiles of Compositions 1I-1K extruded at 13 wt.% moisture content
are shown in
FIG. 2 along with comparative Compositions 1B and 1C.
[01791 Similar trends observed with Compositions 1D-1H were observed with
Compositions 1I-1K. In particular, the method of preparing pregelatinized,
partially
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hydrolyzed starch in an extruder as described herein successfully reduced the
viscosity of
Compositions 1I-1K.
[0180] As alum increased from 1 wt.% to 3 wt.%, the initial viscosity
decreased from 75
BU to 14 BU, while the molecular weight also decreased. The initial
viscosities and the
viscosity at 93 C of Compositions 11 - 1K were reduced as low as those of
Compositions 1B
and 1C.
[0181] In addition, the results of Compositions 11-1K shown in FIG. 2
demonstrate that
optimal acid-modification can be achieved during extrusion. No viscosity peak
was observed
between 70 C to 90 C, indicating that Compositions 1I-1K were fully
gelatinized.
[0182] Furthermore, these results show that at a lower moisture content,
more starch
hydrolysis can be achieved at a given acid level than at a higher moisture
content because at a
low moisture content there is more mechanical energy and, thus, more starch
degradation,
such that the starch will become smaller using the same acid level.
EXAMPLE 3
[0183] This Example illustrates the fluidity of gypsum slurries containing
Compositions
lA (comparative), 1D-1I, and 1K-1L. The Compositions were evaluated with
regards to
fluidity using a slump test that will be appreciated by one of ordinary skill
in the art.
[0184] In preparation for testing, slurries were prepared with each of
Compositions lA
(comparative), 1D-11, and 1K-1L in an amount of 2 wt.% and the parameters
outlined in
Table 6 below, using a water stucco ratio (WSR) of 100.
Table 6
Ingredient Weight (g)
Stucco 400
Heat resistance accelerator 4
Starch 8
Sodium trimetaphosphate 10%
solution 8
Dispersant 2
Retarder 1% solution 20
Gauging water 357
PFM-33 foam (0.5% solution) 25
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[01851 The starch was weighed into a dry mix comprising stucco having over
95% purity
and heat resistance accelerator. Water, sodium trimetaphosphate (10 wt.%
solution),
dispersant, and retarder were weighed into the mixing bowl of a Hobart Mixer.
The dry mix
was poured into the mixing bowl of a mixer available as N50 5-Quart Mixer from
Hobart
(Troy, OH), soaked for 10 seconds, and mixed at speed II for 30 seconds. For
foam
preparation, a 0.5% solution of Hyonic PFM-33 soap (available from GEO
Specialty
Chemicals, Ambler, PA) was formed, and then mixed with air to make the air
foam. The air
foam was added to the slurry using a foam generator.
[0186] Each slurry was then put into a cylinder, having a diameter of 4.92
cm (1.95 in)
and a height of 10 cm (3.94 in). The cylinder was then lifted, allowing the
slurry to freely
flow. The diameters of the slumps that formed were then measured to illustrate
fluidity of the
slurries and are recorded in Table 7 below. Table 8 also includes the results
of a time to 50%
hydration test explained in further detail below.
Table 7
Composition Retarder Slump (cm) Time to 50%
Hydration (minutes)
Composition lA 0.05 wt.% 13.7 cm (5 3/8 in) 4
Composition 1D 0.05 wt.% 16.5 cm (6 1/2 in) 3.8
Composition lE 0.05 wt.% 15.2 cm (6 in) 3.6
Composition 1F 0.05 wt.% 16.2 cm (6 3/8 in) 3.7
Composition 1G 0.05 wt.% 16.2 cm (63/8 in) 3.3
Composition 1H 0.05 wt.% 17.8 cm (7 in) 3.7
Composition 11 0.05 wt.% 15.9 cm (6 1/4 in) 3.6
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Composition 1K 0.05 wt.% 18.4 cm (7 1/4 in) 3.4
Composition 1L 0.0625 wt.% 18.4 cm (7 1/4 in) 4
[0187] As can be observed from Table 7, slurries prepared with Compositions
1D-11 and
1K showed larger slump sizes than the slurry prepared with Composition lA
(comparative).
They also set faster than Composition lA (comparative), indicating slurries
containing
Compositions 1D-1I and 1K had better fluidity than the slurry containing
Composition 1A.
[0188] In addition, the time to 50% hydration was measured for the slurries
for purposes
of comparing the slump size when the slurries set at the same rate. The
temperature profiles
of the slurries were measured using software as one of ordinary skill in the
art will appreciate.
[0189] This additional test was conducted to confirm that the slump tests
were correct,
specifically to illustrate that the large slumps observed with slurries
including pregelatinized,
partially hydrolyzed starches prepared in accordance with embodiments of the
invention
resulted from improved fluidity in comparison to Composition IA (comparative),
not slow
hydration.
[0190] Composition 1H, prepared with 2 wt.% alum and 0.3 wt.% tartaric
acid,
effectively hydrolyzed starch to a low viscosity and had less impact on the
hydration rate,
because tartaric acid and alum had opposite effect on hydration rate.
[0191] FIG. 3 is a graph plotting temperature versus time, showing the
temperature rise
set (TRS) hydration rate. Compositions 1F with 0.05% and 0.0625% of retarder,
respectively, hydrate faster or at the same rate as Composition lA
(comparative).
[0192] As seen in FIG. 3, Composition 1L, with 0.0625 wt.% of retarder, had
the same
hydration rate as Composition lA (comparative). The slump size of Composition
1L with
0.065 wt.% retarder was 18.415 cm (7 1/4 in), was significantly larger than
Composite 1A.
[0193] This result suggests that the larger slump sizes observed with
slurries including
pregelatinized, partially hydrolyzed starches prepared in accordance with
embodiments of the
invention were due to high fluidity and not to slower setting. Furthermore,
pregelatinized,
partially hydrolyzed starches prepared in accordance with embodiments of the
invention will
allow for wallboards using less water without sacrificing fluidity.
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EXAMPLE 4
[0194] This Example illustrates the strength of gypsum disks prepared with
slurries
containing Compositions lA (comparative), 1D-1I, and 1K. Strength was
evaluated using a
compressive strength test described herein.
[0195] To prepare for testing, slurries were prepared with each of
Compositions lA
(comparative), 1D-11, and 1K-1L in an amount of 2 wt.% and the parameters
outlined in
Table 4 above.
[0196] A water stucco ratio (WSR) of 100 and air foam were used to make
gypsum disks
with a final density of 29 pd. The starch was weighed into a dry mix
comprising stucco and
heat resistance accelerator. Water, sodium trimetaphosphate 10% solution,
dispersant, and
retarder were weighed into the mixing bowl of a Hobart Mixer. The dry mix was
poured into
the mixing bowl of a mixer available as N50 5-Quart Mixer from Hobart (Troy,
OH), soaked
for 10 seconds, and mixed at speed II for 30 seconds. For foam preparation, a
0.5% solution
of Hyonic(R) PFM-33 soap (available from GEO(?) Specialty Chemicals, Ambler,
PA) was
formed, and then mixed with air to make the air foam The air foam was added to
the slurry
using a foam generator. The foam generator was run at a rate sufficient to
obtain the desired
board density of 29 pcf. After foam addition, the slurry was immediately
poured to a point
slightly above the tops of the molds. The excess was scraped as soon as the
plaster set. The
molds had been sprayed with mold release (WD-40Tm). The disks had a diameter
of 10.16
cm (4 in) and a thickness of 1.27 cm (0.5 in).
[0197] After the disks had hardened, the disks were removed from the mold,
and then
dried at 110 F (43 C) for 48 hours. After removing from the oven, the disks
were allowed to
cool at room temperature for 1 hour. The compressive strength was measured
using a
materials testing system commercially available as SATECim E/M Systems from
MTS
Systems Corporation (Eden Prairie, Minnesota). The load was applied
continuously and
without a shock at speed of 0.04 inch/min (with a constant rate between 15 to
40 psi/s). The
results are shown in Table 8 below.
Table 8
Composition Compressive Strength
(PSI@j29pcf)
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Composition lA 396
Composition 1D 439
Composition lE 388
Composition 1F 476
Composition 1G 419
Composition 1H 417
Composition 11 455
Composition 1K 426
[0198] As seen in Table 8, the foam disks containing Compositions 1D-1I and
1K had
compressive strengths comparable to that which contained Composition lA
(comparative),
indicating pregelatinized, partially hydrolyzed starches could reduce water
demand without
sacrificing their strength enhancing property. The desirable compressive
strength of the disk
samples is approximate 400 psi. The strength is required so that the board can
be properly
handled without falling apart.
[01991 The use of the terms "a" and "an" and "the" and "at least one" and
similar
referents in the context of describing the invention (especially in the
context of the following
claims) (e.g., in relation to acids, raw material starches, or other
components or items) are to
be construed to cover both the singular and the plural, unless otherwise
indicated herein or
clearly contradicted by context. The use of the term "at least one" followed
by a list of one or
more items (for example, "at least one of A and B") is to be construed to mean
one item
selected from the listed items (A or B) or any combination of two or more of
the listed items
(A and B), unless otherwise indicated herein or clearly contradicted by
context. The terms
"comprising," "having," "including," and "containing" are to be construed as
open-ended
terms (i.e., meaning "including, but not limited to,") unless otherwise noted.
Recitation of
ranges of values herein are merely intended to serve as a shorthand method of
referring
individually to each separate value falling within the range, unless otherwise
indicated herein,
and each separate value is incorporated into the specification as if it were
individually recited
herein. All methods described herein can be performed in any suitable order
unless otherwise
indicated herein or otherwise clearly contradicted by context. The use of any
and all
examples, or exemplary language (e.g., "such as") provided herein, is intended
merely to
better illuminate the invention and does not pose a limitation on the scope of
the invention
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unless otherwise claimed. No language in the specification should be construed
as indicating
any non-claimed element as essential to the practice of the invention.
[0200] Preferred
embodiments of this invention are described herein, including the best
mode known to the inventors for carrying out the invention. Variations of
those preferred
embodiments may become apparent to those of ordinary skill in the art upon
reading the
foregoing description. The inventors expect skilled artisans to employ such
variations as
appropriate, and the inventors intend for the invention to be practiced
otherwise than as
specifically described herein. Accordingly, this invention includes all
modifications and
equivalents of the subject matter recited in the claims appended hereto as
permitted by
applicable law. Moreover, any combination of the above-described elements in
all possible
variations thereof is encompassed by the invention unless otherwise indicated
herein or
otherwise clearly contradicted by context.
