Note: Descriptions are shown in the official language in which they were submitted.
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ELECTRO-SPINNING PROCESS FOR MAKING STARCH
s FILAMENTS FOR FLEXIBLE STRUCTURE
io
FIELD OF THE INVENTION
The present invention relates to flexible structures comprising starch
filaments, and more specifically, to flexible structures having differential
regions.
is BACKGROUND OF THE INVENTION
Cellulosic fibrous webs such as paper are well known in the art. Low
density fibrous webs are in common use today for paper towels, toilet tissue,
facial tissue, napkins, wet wipes, and the like. The large demand for such
paper
products has created a demand for improved versions of the products and the
2o methods of their manufacture. In order to meet such demands, papermaking
manufacturers must balance the costs of machinery and resources with the total
cost of delivering the products to the consumer.
For conventional papermaking operations, wood cellulosic fibers are re-
pulped, beaten or refined to achieve a level of fiber hydration in order to
form an
2s aqueous pulp slurry. Processes for the making of paper products for use in
tissue, toweling, and sanitary products generally involve the preparation of
the
aqueous slurry and then subsequently removing the water from the slurry while
contemporaneously rearranging the fibers therein to form a paper web.
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r
Subsequent to dewatering, the web is processed into a dry roll or sheet form
and
eventually converted into a consumer package. Various types of machinery must
be employed to assist in the dewatering process and converting operations
requiring a significant investment in capital.
s Another aspect of the conventional papermaking operation involves the
incorporation of additives into the pulp in order to achieve specific end
properties.
For instance, additives such as strength resins, debonding surfactants,
softening
agents, pigments, ' lattices, synthetic micro-spheres, fire-retardants, dyes,
perfumes, etc., are often employed in the manufacture of paper. The efficient
io retention of these additives at the wet end of a papermaking process
presents
difficulty to the manufacturer since that portion which is not retained
creates not
only an economic loss but also significant pollution problems if it becomes
part of
a plant effluent. Additives can also be added to the paper web subsequent to
dewatering via coating or saturation processes commonly known in the art.
is These processes usually require that excess heating energy be consumed to
re-
dry the paper after coating. Moreover, in some instances, the coating systems
are required to be solvent based which increases capital costs and requires
recovery of volatile materials to meet regulatory requirements.
Various natural fibers other than cellulose as well as a variety of synthetic
2o fibers have been employed in making paper, however, all these replacements
have failed to provide a commercially acceptable substitute for cellulose due
to
their high cost, poor bonding properties, chemical incompatibilities, and
handling
difficulties in manufacturing systems. Starch filaments have been suggested as
a
substitute for cellulose in various aspects of the papermaking process,
however,
2s commercial attempts to use such starch filaments have been unsuccessful. As
a
result, paper products are still being manufactured almost exclusively from
wood-based cellulosic ingredients.
Accordingly, the present invention provides a flexible structure comprising
long starch filaments and a process for making same. Particularly, the present
so invention provides a flexible structure comprising a plurality of starch
filaments,
2
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T 6
wherein the structure comprises two or more regions having distinct intensive
properties for improved strength, absorbency, and softness.
The present invention also provides methods of making starch filaments.
Particularly, the present invention provides an electro-spinning process of
s producing a plurality of starch filaments.
SUMMARY OF THE INVENTION
a
A flexible structure comprises a plurality of starch filaments. At least some
of the plurality of starch filaments have a size from about 0.001 dtex to 135
dtex,
and more specifically from 0,01 dtex to 5 dtex. An aspect ratio of a length of
a
io major axis of at least some starch filaments to an equivalent diameter of a
cross-
section perpendicular to the major axis of the starch filaments is greater
than
10011, more specifically greater than 50011, and still more specifically
greater
than 100011, and even more specifically, greater than 5000/1.
The structure comprises at least a first region and a second region, each
is of the first and second regions having at least one common intensive
property
selected from the group consisting of density, basis weight, elevation,
opacity,
crepe frequency, and any combination thereof. At least one common intensive
property of the first region differs in value from the at least one common
intensive
property of the second region.
2o In one embodiment, one of the first and second regions comprises a
substantially continuous network, and the other of the first and second
regions
comprises a plurality of discrete areas dispersed throughout the substantially
continuous network. In another embodiment, at least one of the first region
and
the second region comprises a semi-continuous network.
2s The flexible structure can further comprise at least a third region having
at
least one intensive property that is common with and differs in value from the
intensive property of the first region and the intensive property of the
second
region. In one embodiment, at least one of the first, second, and third
regions
can comprise a substantially continuous network. In another embodiment, at
3
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least one of the first, second, and third regions can comprise discrete, or
discontinuous, areas. In still another embodiment, at least one of the first,
second, and third regions can comprise substantially semi-continuous areas. In
yet anoi:her embodiment, at least one of the first, second, and third regions
can
s comprise a plurality of discrete areas dispersed throughout the
substantially
continuous network.
In the embodiment wherein the flexible structure comprises a substantially
continuous network region and a plurality of discrete areas dispersed
throughout
the substantially continuous network region, the substantially continuous
network
io region c:an have a relatively high density relative to a relatively low
density of the
plurality of discrete areas. When the structure is disposed on a horizontal
reference plane, the first region defines a first elevation, and the second
region
outwardly extends from the first region to define a second elevation greater
(relative to the horizontal reference plane) than the first elevation.
ns In the embodiment comprising at least three regions, the first region can
define a first elevation, the second region can define a second elevation, and
the
third region can define a third elevation when the structure is disposed on a
horizoni:al reference plane. At least one of the first, second, and third
elevations
can be different from at least one of the other elevations, for example, the
second
2o elevation can be intermediate the first elevation and the third elevation.
In one embodiment, the second region comprises a plurality of starch
pillows, wherein an individual pillow can comprise a dome portion extending
from
the first elevation to the second elevation and a cantilever portion laterally
extending from the dome portion at the second elevation. A density of the
starch
2s cantilever portion can be equal to or different from at least one of a
density of the
first region and a density of the dome portion, or be intermediate the density
of
the first region and the density of the dome portion. The cantilever portions
are
typically elevated from the first plane to form substantially void spaces
between
the first region and the cantilever portions.
4
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The flexible structure can be made by producing the plurality of starch
filaments by melt-spinning, dry-spinning, wet-spinning, electro-spinning or
any
combination thereof; providing a molding member having a three-dimensional
filament-receiving side structured to receive the plurality of starch
filaments
s thereon, depositing the plurality of starch filaments to the filament-
receiving side
of the molding member, wherein the plurality of starch filaments at least
partially
conform to the pattern thereof; and separating the plurality of the starch
filaments
from the molding mea~nber.
The step of depositing the plurality of starch filaments to the filament-
io receiving side of the molding member may include causing the plurality of
starch
filaments to at least partially conform to the three-dimensional pattern of
the
molding member. That can be accomplished by for example, applying a fluid
pressure differential to the plurality of starch filaments.
In one embodiment, the step of depositing the plurality of starch filaments
Is to the molding member comprises depositing the starch filaments at an acute
angle relative to the filament-receiving side of the molding member, wherein
the
acute angle is from about 5 degrees to about 85 degrees.
The molding member comprises, in one embodiment, a resinous
framework joined to a reinforcing element. The molding member can be fluid-
2o permeable, fluid-impermeable, or partially fluid-permeable. The reinforcing
element can be positioned between the filament-receiving side and at least a
portion of the backside of the framework. The filament-receiving side can
comprise a substantially continuous pattern, a substantially semi-continuous
pattern, a discontinuous pattern, or any combination thereon. The framework
can
2s comprise a plurality of apertures therethrough that can be continuous,
discrete, or
semi-continuous, analogously and conversely to the pattern of the framework.
In one embodiment, the molding member is formed by a reinforcing
element disposed at a first elevation, and a resinous framework joined to the
reinforcing element in a face-to-face relationship and outwardly extending
from
s
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the reinforcing element to form a second elevation. The molding member can
comprise a plurality of interwoven yarns, a felt, or any combination thereof.
When the plurality of the starch filaments is deposited to the filament-
receiving side of the molding member, they tend, due to their flexibility
and/or as
s a result of application of fluid pressure differential; to at least
partially conform to
the three-dimensional pattern of the molding member, thereby forming the first
regions of the plurality of starch filaments supported by the patterned
framework,
and the second regions of the plurality of starch filaments deflected into the
aperture or apertures thereof and supported by the reinforcing element.
to In one embodiment, the molding member comprises suspended portions.
The resinous framework of such a molding member comprises a plurality of
bases outwardly extending from the reinforcing element and a plurality of
cantilever portions laterally extending from the bases at the second elevation
to
form void spaces between the cantilever portions and the reinforcing element,
is wherein the plurality of bases and the plurality of cantilever portions
form, in
combination, the three-dimensional filament-receiving side of the molding
member. Such a molding member can be formed by at least two layers joined
together in a face-to-face relationship such that portions of the framework of
one
of the layers correspond to apertures in the other layer. The molding member
2o comprising suspended portions can also be formed by differential curing of
the
photosensitive resinous layer through a mask having a pattern comprising areas
of differential opacity.
The process of making the flexible structure of the present invention may
further comprise a step of densifying selected portions of the plurality of
starch
2s filaments, for example, by applying a mechanical pressure to the plurality
of
starch filaments.
The process may further include a step of foreshortening the plurality of
starch filaments. The foreshortening may be accomplished by creping,
microcontraction, or a combination thereof.
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An electro-spinning process for making starch filaments comprises steps
of providing a starch composition having an extensional viscosity from about
50
pascal~second to about 20,000 pascal~second; and electro-spinning the starch
composition, thereby producing starch filaments having a size from about 0.001
s dtex to about 135 dtex. The step of electro-spinning the starch composition
typically comprises electro-spinning the starch composition through a die.
The starch in the starch composition has a weight-average molecular
weight from about 1',000 to about 2,000,000; and the starch composition has a
capillary number of at least 0.05, and more specifically at least 1.00. In one
io embodiment, the starch composition comprises from about 20% to about 99% by
weight is amylopectin. The starch in the starch composition may have a weight-
average molecular weight from about 1,000 to about 2,000,000. The starch
composition may comprise a high polymer having a weight-average molecular
weight of at least 500,000.
is The starch composition may comprise from about 10% to about 80% by
weight of the starch and from about 20% to about 90% by weight of additives.
Such a starch composition may have an extensional viscosity from about 100
Pascal~seconds to about 15,000 Pascal~seconds at a temperature from about 20
°C to about 180°C.
zo The starch composition may comprise from about 20% to about 70% by
weight of the starch and from about 30% to about 80% by weight of additives.
Such a starch composition may have the extensional viscosity from about 200
Pascal~seconds to about 10,000 Pascal~seconds at a temperature from about 20
°C to about 100°C.
Zs The starch composition have the extensional viscosity from about 200
Pascal~seconds to about 10,000 Pascal~seconds may have a capillary number
from about 3 to about 50. More specifically, the starch composition having the
extensional viscosity from about 300 pascal~seconds to about 5,000 pascal~
seconds may have a capillary number from about 5 to about 30.
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CA 02329289 2000-12-20
In one embodiment, the starch composition comprises from about
0.0005% to about 5% by weight of a high polymer substantially compatible with
the starch and having an average molecular weight of at least 500,000.
The starch composition can comprise an additive selected from the group
s consisting of plasticizers and diluents. Such a starch composition may
further
comprise from about 5% to about 95% by weight of a protein, wherein the
protein ,
comprises a corn-derived protein, a soybean-derived protein, a wheat derived
protein, or any combination thereof.
The process for making the starch filaments may further comprise a step
to of attenuating the starch filaments with streams of air.
In one embodiment, a process for making a flexible structure comprising
starch filaments includes steps of providing a starch composition having an
extensional viscosity from about 100 pascal~second to about 10,000 pascal~
second; providing a molding member having a three-dimensional filament-
ls receiving side and a backside opposite thereto, the filament-receiving side
comprising a substantially continuous pattern, a substantially semi-continuous
pattern, a discrete pattern, or any combination thereof; electro-spinning the
starch composition, thereby producing a plurality of starch filaments; and
depositing the plurality of starch filaments to the filament-receiving side of
the
2o molding member, wherein the starch filaments conform to the three-
dimensional
pattern of the filament-receiving side.
In an industrial process, the molding member continuously travels in a
machine direction.
BRIEF DESCRIPTION OF THE DRAWINGS
2s Fig. 1 is a schematic plan view of an embodiment of the flexible structure
of
the present invention.
Fig. 1A is a schematic cross-sectional view taken along line 1A-1A of Fig. 1.
s
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Fig.2 is a schematic plan view of another embodiment of the flexible
structure of the present invention.
Fig. 3 is a schematic cross-sectional view of another embodiment of the
flexible structure of the present invention.
s Fig. 4 is a schematic plan view of an embodiment of a molding member that
can be used to form the flexible structure of the present invention.
Fig. 4A is a scher~aatic cross-sectional view taken along line 4A-4A of Fig.
4.
Fig.5 is a schematic plan view of another embodiment of the molding
member that can be used to form the flexible structure of the present
to invention.
Fig. 5A is a schematic cross-sectional view taken along line 5A-5A of Fig. 5.
Fig. 6 is a schematic cross-sectional view of a still another embodiment of
the
molding member that can be used to form the flexible structure of the
present invention.
is Fig. 7 is a schematic partial side-elevational and cross-sectional view of
an
embodiment of an electro-spinning process and apparatus of making
flexible structure comprising starch filaments.
Fig. 7A is a schematic view taken along line 7A-7A of Fig. 7.
Fig. 8 is a schematic side-elevational view of an embodiment of a process of
20 the present invention.
Fig.9 is a schematic side-elevational view of another embodiment of a
process of the present invention.
Fig. 9A is a schematic side-elevational and partial view of another embodiment
of a process of the present invention.
2s Fig. 10 is a schematic view of a fragment of an embodiment of a starch
filament having differential cross-sectional areas perpendicular to the
filament's major (longitudinal) axis.
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Fig. 10A is a schematic view of several exemplary, non-exclusive, embodiments
of a cross-sectional area of a starch filament.
Fig. 11 is a schematic view of a fragment of a starch filament having a
plurality
of notches along at least a portion of the filament's length.
s DETAILED DESCRIPTION OF THE INVENTION
As used herein, the following terms have the following meanings.
'
"Flexible structure comprising starch filaments," or simply "flexible
structure," is an arrangement comprising a plurality of starch filaments that
are
mechanically inter-entangled to form a sheet-like product having certain pre-
lo determined microscopic geometric, physical, and aesthetic properties.
"Starch filament" is a slender, thin, and highly flexible object comprising
starch and having a major axis which is very long, compared to the fiber's two
mutually-orthogonal axes that are perpendicular to the major axis. An aspect
ratio of the major's axis length to an equivalent diameter of the filament's
cross-
is section perpendicular to the major axis is greater than 10011, more
specifically
greater than 500/1, and still more specifically greater than 100011, and even
more
specifically, greater than 500011. The starch filaments may comprise other
matter, such as, for example water, plasticizers, and other optional
additives.
"Equivalent diameter" is used herein to define a cross-sectional area and a
ao surface area of an individual starch filament, without regard to the shape
of the
cross-sectional area. The equivalent diameter is a parameter that satisfies
the
equation S=114~D2, where S is the starch filament's, cross-sectional area
(without
regard to its geometrical shape), ~ = 3.14159, and D is the equivalent
diameter.
For example, the cross-section having a rectangular shape formed by two
2s mutually opposite sides "A" and two mutually opposite sides "B" can be
expressed as: S = A x B. At the same time, this cross-sectional area can be
expressed as a circular area having the equivalent diameter D. Then, the
equivalent diameter D can be calculated from the formula: S=114~D2, where S is
to
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the known area of the rectangle. (Of course, the equivalent diameter of a
circle is
the circle's real diameter.) An equivalent radius is'/2 of the equivalent
diameter.
"Pseudo-thermoplastic" in conjunction with "materials" or "compositions" is
intended to denote materials and compositions that by the influence of
elevated
s temperatures, dissolution in an appropriate solvent, or otherwise can be
softened
to such a degree that they can be brought into a flowable state, in which
condition
they can be shaped as desired, and more specifically, processed to form starch
filaments suitable for forming a flexible structure. Pseudo-thermoplastic
materials
may be formed, for example, under combined influence of heat and pressure.
io Pseudo-thermoplastic materials differ from thermoplastic materials in that
the
softening or liquefying of the pseudo-thermoplastics is caused by softeners or
solvents present, without which it would be impossible to bring them by any
temperature or pressure into a soft or flowable condition necessary for
shaping,
since pseudo thermoplastics do not "melt" as such. The influence of water
Is content on the glass transition temperature and melting temperature of
starch can
be measured by differential scanning calorimetery as described by Zeleznak and
Hoseny in "Cereal Chemistry", Vol. 64, No. 2, pp. 121-124, 1987. Pseudo-
thermoplastic melt is a pseudo-thermoplastic material in a flowable state.
"Micro-geometry" and permutations thereof refers to relatively small (i. e.,
Zo "microscopical") details of the flexible structure, such as, for example,
surface
texture, without regard to the structure's overall configuration, as opposed
to its
overall (i. e., "macroscopical") geometry. Terms containing "macroscopical" or
"macroscopically" refer to an overall geometry of a structure, or a portion
thereof,
under consideration when it is placed in a two-dimensional configuration, such
as
2s the X-Y plane. For example, on a macroscopical level, the flexible
structure,
when it is disposed on a flat surface, comprises a relatively thin and flat
sheet.
On a microscopical level, however, the structure can comprise a plurality of
first
regions that form a first plane having a first elevation, and a plurality of
domes or
"pillows" dispersed throughout and outwardly extending from the framework
3o region to form a second elevation.
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"Intensive properties" are properties which do not have a value dependent
upon an aggregation of values within the plane of the flexible structure . A
common intensive property is an intensive property possessed by more than one
region. Such intensive properties of the flexible structure of the present
invention
s include, without limitation, density, basis weight, elevation, opacity, and
crepe
frequency (if the structure is to be foreshortened). For example, if a density
is a
common intensive property of two differential regions, a value of the density
in
one region can differ from a value of the density in the other region. Regions
(such as, for example, a first region and a second region) are identifiable
areas
to distinguishable from one another by distinct intensive properties.
"Basis weight" is the weight (measured in grams force) of a unit area of the
starch flexible structure , which unit area is taken in the plane of the
starch
filament structure. The size and shape of the unit area from which the basis
weight is measured is dependent upon the relative and absolute sizes and
is shapes of the regions having differential basis weights.
"Density" is the ratio of the basis weight to a thickness (taken normal to the
plane of the flexible structure) of a region. Apparent density is the basis
weight of
the sample divided by the caliper with appropriate unit conversions
incorporated
therein. Apparent density used herein has the units of grams / centimeters
cubed
20 (glcm3)
"Caliper" is a macroscopic thickness of a sample measured as described
below. Caliper should be distinguished from the elevation of differential
regions,
which is microscopical characteristic of the regions.
"Glass transition temperature," T9, is the temperature at which the material
2s changes from a viscous or rubbery condition to a hard and relatively
brittle
condition.
"Machine direction" (or MD) is the direction parallel to the flow of the
flexible structure being made through the manufacturing equipment. "Cross
machine direction" (or CD) is the direction perpendicular to the machine
direction
3o and parallel to the general plane of the flexible structure being made.
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Y t
"X," "Y," and "Z" designate a conventional system of Cartesian
coordinates, wherein mutually perpendicular coordinates "X" and "Y" define a
reference X-Y plane, and "Z" defines an orthogonal to the X-Y plane. "Z-
direction" designates any direction perpendicular to the X-Y plane.
Analogously,
s the term "Z-dimension" means a dimension, distance, or parameter measured
parallel to the Z-direction. When an element, such as, for example, a molding
member curves or otherwise deplanes, the X-Y plane follows the configuration
of
the element. t
"Substantially continuous" region (area I network I framework) refers to an
io area within which one can connect any two points by an uninterrupted line
running entirely within that area throughout the line's length. That is, the
substantially continuous region has a substantial "continuity" in all
directions
parallel to the first plane and is terminated only at edges of that region.
The term
"substantially," in conjunction with continuous, is intended to indicate that
while an
is absolute continuity is preferred, minor deviations from the absolute-
continuity
may be tolerable as long as those deviations do not appreciably affect the
performance of the flexible structure (or a molding member) as designed and
intended.
"Substantially semi-continuous" region (area I network I framework) refers
2o an area which has "continuity" in all, but at least one, directions
parallel to the first
plane, and in which area one cannot connect any two points by an uninterrupted
line running entirely within that area throughout the line's length. The semi-
continuous framework may have continuity only in one direction parallel to the
first plane. By analogy with the continuous region, described above, while an
2s absolute continuity in all, but at least one, directions is preferred,
minor deviations
from such a continuity may be tolerable as long as those deviations do not
appreciably affect the performance of the structure (or the deflection
member).
"Discontinuous" regions refer to discrete, and separated from one another
areas that are discontinuous in all directions parallel to the first plane.
13
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',
"Absorbency" is the ability of a material to take up fluids by various means
including capillary, osmotic, solvent, or chemical action and retain such
fluids:
Absorbency can be measured according to the test described herein.
"Flexibility" is the ability of a material or structure to deform under a
given
s load without being broken, regardless of the ability or inability of the
material or
structure to return itself to its pre-deformation shape.
"Molding member" is a structural element that can be used as a support for
.
the starch filaments that can be deposited thereon during a process of making
the flexible structure of the present invention, and as a forming unit to form
(or
to "mold") a desired microscopical geometry of the flexible structure of the
present
invention. The molding member may comprise any element that has the ability to
impart a three-dimensional pattern to the structure being produced thereon,
and
includes, without limitation, a stationary plate, a belt, a woven fabric, and
a band.
"Reinforcing element" is a desirable, but not necessary, element in some
is embodiments of the molding member, serving primarily to provide or
facilitate
integrity, stability, and durability of the molding member comprising, for
example,
a resinous material. The reinforcing element can be fluid-permeable, fluid-
impermeable, or partially fluid-permeable, and may comprise a plurality of
interwoven yarns, a felt, a plastic, other suitable synthetic material, or any
2o combination thereof.
"Press-surface" is a surface that can be pressed against the fillament-
receiving side of the molding member having a plurality of starch filaments
thereon, to deflect, at least partially; the starch filaments into the molding
member
having a three-dimensional pattern of depressions/protrusions therein.
2s "Decitex," or "dtex," is a unit of measure for a starch filament expressed
in
grams per 10,000 meters, grams
10,000 meters
"Melt-spinning" is a process by which a thermoplastic or pseudo-
thermoplastic material is turned into fibrous material through the use of an
14
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attenuation force. Melt-spinning can include mechanical elongation, melt-
blowing, spun-bonding, and electro-spinning.
"Mechanical elongation" is the process inducing a force on a fiber thread
by having it come into contact which a driven surface, such as a roll, to
apply a
s force to the melt thereby making fibers.
"Melt-blowing" is a process for producing fibrous webs or articles directly
from polymers or resins using high-velocity air or another appropriate force
to
4
attenuate the filaments. In a melt-blowing process the attenuation force is
applied in the form of high speed air as the material exits the die or
spinnerette.
to "Spun-bonding" comprises the process of allowing the fiber to drop a
predetermined distance under the forces of flow and gravity and then applying
a
force via high velocity air or another appropriate source.
"Electro-spinning" is a process that uses electric potential as the force to
attenuate the fibers.
is "Dry-spinning," also commonly known as "solution-spinning," involves the
use of solvent drying to stabilize fiber formation. A material is dissolved in
an
appropriate solvent and is attenuated via mechanical elongation, melt-blowing,
spun-bonding, and/or electro-spinning. The fiber becomes stable as the solvent
is evaporated.
20 "Wet-spinning" comprises dissolving a material in a suitable solvent and
forming small fibers via mechanical elongation, melt-blowing, spun-bonding,
andlor electro-spinning. As the fiber is formed it is run into a coagulation
system
normally comprising a bath filled with an appropriate solution that solidifies
the
desired material, thereby producing stable fibers.
2s High Polymer "substantially compatible with starch" means that the high
polymer is capable of forming a substantially homogeneous mixture composition
with the starch (i.e., the composition that appears transparent or translucent
to
the naked eye) when the composition is heated to a temperature above the
softening andlor its melting temperature.
is
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"Melting temperature" means the temperature or the range of temperature
at or above which the starch composition melts or softens sufficiently to be
capable of being processed into starch filaments in accordance with the
present
invention. It is to be understood that some starch compositions are pseudo-
s thermoplastic compositions and as such may not exhibit pure "melting"
behavior.
"Processing temperature" means the temperature of the starch
composition, at which temperature the starch filaments of the present
invention
can be formed, for e~Cample, by attenuation.
Flexible Structure
to Referring to Figs. 1-3, a flexible structure 100 comprising pseudo-
thermoplastic starch filaments comprises at least a first region 110 and a
second
region 120. Each of the first and second regions has at least one common
intensive property, such as, for example, a basis weight or density. The
common
intensive property of the first region 110 differs in value from the common
is intensive property of the second region 120. For example, the density of
the first
region 110 can be higher than the density of the second region 120.
The first and second regions 110 and 120 of the flexible structure 100 of
the present invention can also differentiate in their respective micro-
geometry. In
Fig. 1, for example, the first region 110 comprises a substantially continuous
2o network forming a first plane at a first elevation when the structure 100
is
disposed on a flat surface; and the second region 120 can comprise a plurality
of
discrete areas dispersed throughout the substantially continuous network.
These
discrete areas may, in some embodiments, comprise discrete protuberances, or
"pillows," outwardly extending from the network region to form a second
elevation
2s greater than the first elevation, relative to the first plane. It is to be
understood
that pillows can also comprise a substantially continuous pattern and a
substantially semi-continuous pattern.
In one embodiment, the substantially continuous network region can have
a relatively high density, and the pillows have a relatively low density. In
another
16
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n
embodiment, the substantially continuous network region can have a relatively
low basis weight, and the pillows have a relatively high basis weight: In
still other
embodiments, the substantially continuous network region can have a relatively
low density, and the pillows can have a relatively high density. An embodiment
is
s contemplated, in which the substantially continuous network region can have
a
relatively high basis weight, and the pillows have a relatively low basis
weight.
In other embodiments, the second region 120 can comprise a semi-
continuous network. In Fig. 2, the second region 120 comprises discrete areas
122, similar to those shown in Fig. 1; and semi-continuous areas 121,
extending
io in at least one direction as seen in the X-Y plane (i. e., a plane formed
by the first
region 110 of the structure 100 disposed on a flat surface).
In the embodiment shown in Fig. 2, the flexible structure 100 comprises a
third region 130 having at least one intensive property that is common with
and
differs in value from the intensive property of the first region 110 and the
intensive
is property of the second region 120. For example; the first region 110 can
have
the common intensive property having a first value, the second region 120 can
have the common intensive property having a second value, and the third region
130 can have the common intensive property having a third value, wherein the
first value can be different from the second value, and the third value can be
2o different from the second value and the first value.
When the structure 100 comprising at least three differential regions 110,
120, 130, as described herein above, is disposed on a horizontal reference
plane
(e. g., the X-Y plane), the first region 110 defines the plane having the
first
elevation, and the second region 120 extends therefrom to define the second
Zs elevation. An embodiment is contemplated, in which the third region 130
defines
a third elevation, wherein at least one of the first, second, and third
elevations is
different from at least one of the other elevations. For example, the third
elevation can be intermediate the first and second elevations.
t~
CA 02329289 2000-12-20
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The following table shows, without limitation, some possible combinations
of embodiments of the structure 100 comprising at least three regions having
differential (i. e., high, medium, or low) intensive properties. All of these
embodiments are included in the scope of the present invention.
s
INTENSIVE PROPERTIES
HIGH MEDIUM LOW
Continuous Discontinuous Discontinuous
Continuous Discontinuous ----
Continuous ---- Discontinuous
Semi-continuous Semi-continuous Semi-continuous
Semi-continuous Semi-continuous Discontinuous
Semi-continuous Semi-continuous ----
Semi-continuous Discontinuous Semi-continuous
Semi-continuous Discontinuous Discontinuous
Semi-continuous ---- Semi-continuous
Discontinuous Continuous Discontinuous
Discontinuous Continuous ----
Discontinuous Semi-continuous Semi-continuous
Discontinuous Semi-continuous Discontinuous
Discontinuous Discontinuous Continuous
Discontinuous Discontinuous Semi-continuous
Discontinuous Discontinuous Discontinuous
Discontinuous ---- Continuous
---- Continuous Discontinuous
---- Semi-continuous Semi-continuous
- - [ Discontinuous I Continuous
Fig. 3 shows yet another embodiment of the flexible structure 100 of the
present invention, in which embodiment the second region 120 comprises a
is
CA 02329289 2000-12-20
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plurality of starch pillows, wherein at least some of the pillows comprises a
starch
dome portion 128 and a starch cantilever portion 129 extending from the starch
dome portion 128. The starch cantilever portion 129 is elevated from the X-Y
plane and extends, at an angle, from the dome portion 128, to form
substantially
s void spaces, or "pockets," 115 between the first region 110, the starch
domes
128 extending therefrom, and the starch cantilever portions 129.
In large part due to the existence of these substantially void pockets 115
4
capable of receiving and retaining significant amount of fluid, the flexible
structure
100 schematically shown in Fig. 3 is believed to exhibit very high, for a
given
to basis weight, absorbency characteristics. The pockets 115 are characterized
by
having none or very little amount of starch filaments therein.
One skilled in the art will appreciate that due to a process of making the
flexible structure 100, as discussed below, and because of a highly flexible
nature
of the starch filaments and the flexible structure 100 as a whole, some amount
of
is individual starch filaments present in the pockets 115 may be tolerable as
long as
those starch filaments do not interfere with the designed pattern of the
structure
100 and its intended properties. In this context, the term "substantially"
void
pockets 115 is intended to recognize that due to a highly flexible nature of
the
structure 100 and individual starch filaments comprising the structure 100,
some
2o insignificant amount of starch filaments or their portions may be found in
the
pockets 115. A density of the pockets 115 is not greater than 0.005 gram per
cubic centimeter (glcc), more specifically, not greater than 0.004 glcc, and
still
more specifically not greater than 0.003 glcc.
In another aspect, the flexible structure 100 comprising the cantilever
2s portions 129 is characterized by an enhanced overall surface area, relative
to that
of the comparable structure not having the cantilever portions 129. One
skilled in
the art will appreciate that the greater the number of the individual
cantilever
portions 129 and their respective microscopic surface areas, the greater a
resulting microscopic specific surface area (i. e., the resulting microscopic
3o surface area per unit of the overall macroscopic area of the structure
disposed on
19
CA 02329289 2000-12-20
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a flat surface). As one skilled in the art will also recognize, the greater
the
absorption surface area of a structure, the greater the absorption capacity
thereof, all other parameters being equal.
In embodiments of the structure 100 comprising cantilever portions 129,
s the cantilever portions 129 may comprise third regions of the structure 100.
For
example, an embodiment is contemplated in which a density of the starch
cantilever portions 129 is intermediate a density of the first region 110 and
a
density of the second region 120 comprising the dome portion(s). In another
embodiment, the density of the dome portion 128 can be intermediate a
relatively
to high density of the first region 110 and a relatively low density of the
cantilever
portion 129. By analogy, the basis weight of the cantilever portion 129 can be
equal to, intermediate, or greater than one or both of the first region 110
and the
dome portion 128.
Process For Making Flexible Structure
is Figs. 8 and 9 schematically show two embodiments of a process for making
a flexible structure 100 comprising starch filaments.
First, a plurality of starch filaments is provided. The production of starch
filaments for the flexible structure 100 according to the present invention
can be
made by a variety of techniques known in the art. For example, the starch
2o filaments can be produced from the pseudo-thermoplastic melt starch
compositions by various melt-spinning processes. Sizes of the starch filaments
may vary, from about 0.001 dtex to about 135 dtex, more specifically from
about
0.005 dtex to about 50 dtex, and even more specifically from about 0.01 dtex
to
about 5.0 dtex.
2s Some references, including U.S. Patent No. 4,139,699 issued to
Hernandez et al, on February 13, 1979; U.S. Patent No. 4,853,168 issued to
Eden
et al. on August 1, 1989; and U.S. Patent No. 4,234,480 issued to Hernandez et
al. on January 6, 1981. U.S. Patent Nos. 5,516,815 and 5,316,578 to Buehler et
a1., relate to starch compositions for making starch filament using a melt-
spinning
~ CA 02329289 2003-10-07
Case 8335
process. The melt starch composition can be extruded through a spinnerette to
produce filaments having diameters slightly enlarged relative to the diameter
of
the die orifices of the spinnerette (i.e., due to a die swell effect). The
filaments are
subsequently drawn down mechanically or thermomechanically by a drawing unit
s to reduce the fiber diameter.
Several devices for producing non-woven thermoplastic fabric structures
from extruded polymers are known in the art and can be suitable for making
long
flexible starch filaments. For example, an extruded starch composition can be
forced through a spinneret (not shown) forming a vertically oriented curtain
of
to downwardly-advancing starch filaments. The starch filaments can be quenched
with air in conjunction with a suction-type drawing or attenuating air slot.
U.S.
Pat. No. 5,292,239 issued to Zeldin, et al., on March 8, 1994 discloses a
device
that reduces significant turbulence in the air flow in order to uniformly and
consistently apply a drawing force to the starch filaments.
~s
For the present invention, starch filaments can be produced from a mixture
comprising starch, water, plasticizers, and other optional additives. For
example,
the suitable starch mixture can be converted to a pseudo-thermoplastic melt in
an
extruder and conveyed through a spinneret to a drawing unit forming a
vertically
oriented curtain of downward advancing starch filaments. The spinneret can
comprise an assembly which is known in the art. The spinneret can include a
plurality of nozzle bores with holes having cross-sectional areas suitable for
starch filament production. The spinneret can be adapted to the fluidity of
the
starch composition so that every nozzle bore has the same rate of flow, if so
desired. Alternatively, the rates of flow of differential nozzles can vary.
2s
A drawing unit (not shown), can be located downstream of the extruder,
and may comprise an open upper end, an open lower end opposite thereto, and
an air supply manifold supplying compressed air to internal nozzles oriented
in a
21
CA 02329289 2003-10-07
Case 8335
downward direction. As compressed air flows through the internal nozzles, air
is
drawn into the open upper end of the drawing unit forming a rapidly moving
stream of air flowing in the downward direction. The air stream produces a
drawing force on the starch filaments causing them to be attenuated or
stretched
s before exiting the open lower end of the drawing unit.
It has now been found that the starch filaments suitable for the flexible
structure 100 can be produced by an electro-spinning process, wherein an
electric field is applied to a starch solution to form charged starch jet. The
electro-spinning process is known in the art. The dissertation entitled "The
lo Electro-Spinning Process and Applications of Electro-Spun Fibers" by Doshi,
Jayesh, Natwarlal,. Ph.D., 1994, (Published by UMI Dissertation Services, Ann
Arbor, 1997), pages 7 to 20, describes an electro-spinning process and
conducts
a study of the forces involved in the process. This dissertation also explores
some commercial applications of the electro-spun filaments.
is
United States Patent Nos. 1,975,504 (Oct. 2, 1934); 2,123,992 (July 19,
1938); 2,116,942 (May 10, 1938); 2,109,333 (Feb. 22, 1938); 2,160,962 (June 6,
1939); 2,187,306 (Jan. 16, 1940); and 2,158,416 (May 16, 1939), all issued to
Formhals, describe electro-spinning processes and equipment therefor. Other
2o references describing electro-spinning processes include: U.S. Patent Nos.
3,280,229 (Oct. 18, 1966) issued to Simons; 4,044,404 (Aug. 30, 1977) issued
to
Martin et al.; 4,069,026 (Jan. 17, 1978) issued to Simm et al.; 4,143,196
(March
6, 1979) issued to Simm; 4,223,101 (Sept. 16, 1980) issued to Fine et al.;
4,230,650 (Oct. 28, 1980) issued to Guignard; 4,232,525 (Nov. 11, 1980) issued
2s to Enjo et al.; 4,287,139 (Sept. 1, 1981) issued to Guignard; 4,323,525
(April 6,
1982) issued to Bornat; 4,552,707 (Nov. 12, 1985) issued to How; 4,689,186
(Aug. 25, 1987) issued to Bornat; 4,798,607 (Jan. 17, 1989) issued to
Middleton
et al.; 4,904,272 (Feb. 27, 1990) issued to Middleton et al.; 4,968,238 (Nov.
6,
1990) issued to Satterfield et al.; 5,024,789 (Jan. 18, 1991 ) issued to
Barry;
30 6,106,913 (Aug. 22, 2000) issued to Scardino et al.; and, 6,110,590 (Aug.
29,
2000) issued to Zarkoob et al.
22
CA 02329289 2003-10-07
Case 8335
While the foregoing references teach a variety of electro-spinning
processes and equipment therefor, they fail to teach that a starch composition
can
s be successfully processed and extruded into thin, substantially continuous
starch
filaments suitable for forming the flexible structure 100 of the present
invention.
Naturally occurring starch is not processible by an electro-spinning process,
because natural starch generally has a granular structure. Now it has been
discovered that a modified, "destructurized," starch composition can be
io successfully processed by using an electro-spinning process.
Commonly assigned patent application titled "Melt Processible Starch
Composition" (Larry Neil Mackey et al., Attorney Docket #7967R), filed on the
filing date of the present application, discloses a starch composition
suitable for
production of the starch filaments used in the flexible structure 100 of the
present
is invention. That starch composition comprises starch having a weight-average
molecular weight ranging from about 1,000 to about 2,000,000, and can contain
a
high polymer that is substantially compatible with starch and has a weight-
average molecular weight of at least 500,000. In one embodiment, that starch
composition can have from about 20% to about 99% by weight of amylopectin.
2o The disclosure of this commonly-assigned application is incorporated herein
by
reference.
According to the present invention, a starch polymer can be mixed with
water, plasticizers, and other additives, and a resulting melt can be
processed
(for example, extruded) and configured to produce starch filaments suitable
for
2s the flexible structure of the present invention. The starch filaments may
have
from a trace amount to one hundred percent of starch, or be a blend of starch
and other suitable materials, such as, for example, cellulose, synthetic
materials,
proteins, and any combination thereof.
Starch polymers can include any naturally occurring starch, physically
3o modified starch or chemically modified starch. Suitable naturally occurring
23
CA 02329289 2000-12-20
Case 8335
starches can include, without limitation, corn starch, potato starch, sweet
potato
starch, wheat starch, sago palm starch, tapioca starch, rice starch, soybean
starch, arrow root starch, bracken starch, lotus starch, waxy maize starch,
high
amylose corn starch, and commercial amylose powder. Naturally occurring
s starches, particularly corn starch, potato starch, and wheat starch, are the
starch
polymers of choice due to their availability.
Physically modified starch is formed by changing its dimensional structure.
Physically modified starch can include a.-starch, fractionated starch,
moisture and
heat treated starch and mechanically treated starch.
to Chemically modified starch may be formed by reaction of its OH groups
with alkylene oxides, and other ether-, ester-, urethane-, carbamate-, or
isocyanate-forming substances. Hydroxyalkyl, acetyl, or carbamate starches or
mixtures thereof are among embodiments of chemically modified starches. The
degree of substitution of the chemically modified starch is from 0.05 to 3.0,
and
Is more specifically from 0.05 to 0.2.
A native water content can be from about 5% to about 16% by weight, and
more specifically, from about 8% to about 12%. The amylose content of the
starch is from 0% to about 80%, and more specifically, from about 20% to about
30%.
20 A plasticizer can be added to the starch polymer to lower the glass
transition temperature of the starch filaments being made, thereby enhancing
their flexibility. In addition, the presence of the plasticizer can lower the
melt
viscosity which in turn facilitates the melt extrusion process. The
plasticizer is an
organic compound having at least one hydroxyl group, such as, for example, a
2s polyol. Sorbitol, mannitol, D-glucose, polyvinyl alcohol, ethylene glycol,
polyethylene glycol, propylene glycol, polypropylene glycol, sucrose,
fructose,
glycerol and mixtures thereof have been found suitable. The examples of
plasticizers include sorbitol, sucrose, and fructose in quantities ranging
from
about 0.1 % by weight to about 70% by weight, more specifically from about
0.2%
24
CA 02329289 2000-12-20
Case 8335
by weight to about 30% by weight, and still more specifically from about 0.5%
by
weight to about 10% by weight.
Other additives can be typically included with the starch polymer as a
processing aid and to modify physical properties, such as, for example,
elasticity,
s dry tensile strength, and wet strength, of the extruded starch filaments.
Additives
are typically present in quantities ranging from 0.1 % to 70% by weight on a
non-
volatiles basis (meaning that the quantity is calculated by excluding
volatiles
such as water). The examples of additives include, without limitation, urea,
urea
derivatives, cross-linking agents, emulsifiers, surfactants, lubricants,
proteins and
io their alkali salts, biodegradable synthetic polymers, waxes, low melting
synthetic
thermoplastic polymers, tackifying resins, extenders, and mixtures thereof.
Examples of biodegradable synthetic polymers include, without limitation,
polycaprolactone, polyhydroxybutyrates, polyhydroxyvalerates, polylactides,
and
mixtures thereof. Other additives include optical brighteners, antioxidants,
flame
is retardants, dyes, pigments, and fillers. For the present invention, an
additive
comprising urea in quantities ranging from 0.5% to 60% by weight can
beneficially be included in the starch composition.
Suitable extenders for use herein include gelatin; vegetable proteins, such
as corn protein, sunflower protein, soybean proteins, cotton seed proteins;
and
2o water soluble polysaccharides, such as alginates, carrageenans, guar gum,
agar,
gum arabic and related gums, and pectin; and water soluble derivatives of
cellulose, such as alkylcelluloses, hydroxyalkylcelluloses,
carboxymethylcellulose, etc. Also, water soluble synthetic polymers such as
polyacrylic acids, polyacrylic acid esters, polyvinylacetates,
polyvinylalcohols,
2s polyvinylpyrrolidone, etc., may be used.
Lubricant compounds may further be added to improve flow properties of
the starch material during the process of the present invention. The lubricant
compounds can include animal or vegetable fats, preferably in their
hydrogenated form, especially those which are solid at room temperature.
so Additional lubricant materials include mono-glycerides and di-glycerides
and
2s
CA 02329289 2003-10-07
Case 8335
phosphatides, especially lecithin. For the present invention, a lubricant
compound that includes mono-glyceride, glycerol mono-stearate is believed to
be
beneficial.
Further additives, including inorganic fillers, such as the oxides of
s magnesium, aluminum, silicon, and titanium, may be added as inexpensive
fillers
or processing aides. Additionally, inorganic salts, including alkali metal
salts,
alkaline earth metal salts, phosphate salts, etc., may be used as processing
aides. '
Other additives may be desirable depending upon the particular end use of
io the product contemplated. For example, in products such as toilet tissue,
disposable towels, facial tissues and other similar products, wet strength is
a
desirable attribute. Thus, it is often desirable to add to the starch polymer
cross-
linking agents known in the art as "wet-strength" resins.
A general dissertation on the types of wet strength resins utilized in the
is paper art can be found in TAPPI monograph series No. 29, Wet Strength in
Paper
and Paperboard, Technical Association of the Pulp and Paper Industry (New
York,
1965. The most useful wet strength resins have generally been cationic in
character. Polyamide-epichlorohydrin resins are cationicpolyamide amine-
epichlorohydrin wet strength resins which have been found to be of particular
2o utility. Suitable types of such resins are described in U.S. Patent Nos.
3,700,623, issued on October 24, 1972, and 3,772,076, issued on November 13,
1973, both issued to Keim. One commercial source of a useful polyamide-
epichlorohydrin resin is Hercules, Inc. of Wilmington, Delaware, which markets
such resins under the mark Kymene TM
Glyoxylated polyacrylamide resins have also been found to be of utility as
wet strength resins. These resins are described in U.S. Patent Nos. 3,556,932,
issued on January 19, 1971, to Coscia, et al. and 3,556,933, issued on January
19,
1971, to Williams et al. One commercial source of glyoxylated polyacrylamide
resins is Cytec
26
CA 02329289 2000-12-20
Case 8335
Co. of Stanford, Connecticut, which markets one such resin under the mark
ParezTM 631 NC.
Still other water-soluble cationic resins that can be used in this invention
are
urea formaldehyde and melamine formaldehyde resins. The more common
s functional groups of these polyfunctional resins are nitrogen containing
groups
such as amino groups and methylol groups attached to nitrogen.
Polyethylenimine
type resins may also find utility in the present invention. In addition,
temporary wet
strength resins such as Caldas 10 (manufactured by Japan Carlit) and CoBond
1000 (manufactured by National Starch and Chemical Company) may be used in
io the present invention.
For the present invention, one cross-linking agent is the wet strength resin
KymeneTM, in quantities ranging from about 0.1 % by weight to about 10% by
weight, and more specifically from about 0.1 % by weight to about 3% by
weight.
In order to produce suitable starch filaments for the flexible structure 100
is of the present invention, the starch compostion should exhibit certain
rheological
behavior during processing, such as a certain extensional viscosity and a
certain
capillary number. Of course, the type of processing (e. g., melt-blowing,
electro-
spinning, etc.), can dictate the required rheological qualities of the starch
composition.
2o Extensional, or elongational, viscosity (rle) relates to melt extensibility
of
the starch composition, and is particularly important for extensional
processes
such as starch filament making. The extensional viscosity includes three
types,
depending on the type of deformation of the composition: uniaxial or simple
extensional viscosity, biaxial extensional viscosity, and pure shear
extensional
2s viscosity. The uniaxial extensional viscosity is especially importanf for
uniaxial
extensional processes such as mechanical elongation, melt-blowing, spun-
bonding, and electro-spinning. The other two extensional viscosities are
important for the biaxial extension or forming processes for making films,
foams,
sheets or parts.
27
CA 02329289 2000-12-20
Case 8335
For conventional fiber spinning thermoplastics such as polyolefins,
polyamides and polyesters, there is a strong correlation between extensional
viscosity and shear viscosity of these conventional thermoplastic materials
and
blends thereof. That is, the spinnability of the material can be determined
simply
s by the melt shear viscosity, even though the spinnablity is a property
controlled
primarily by melt extensional viscosity. The correlation is quite robust such
that
the fiber industry has relied on the melt shear viscosity in selecting and
formulating melt spi~nable materials. The melt extensional viscosity has
rarely
been used as an industrial screening tool.
io It is therefore surprising to find that the starch compositions of the
present
invention do not necessarily exhibit such a correlation between shear and
extensional viscosities. The starch compositions herein exhibit melt flow
behavior
typical of a non-Newtonian fluid and as such may exhibit a strain hardening
behavior, that is, the extensional viscosity increases as the strain or
deformation
is increases.
For example, when a high polymer selected according to the present
invention is added to a starch composition, the shear viscosity of the
composition
remains relatively unchanged, or even decreases slightly. Based on
conventional
wisdom, such a starch composition would be expected to exhibit decreased melt
2o processability and would not be expected to be suitable for melt-
extensional
processes. However, it was surprisingly found that the starch composition
herein
shows a significant increase in extensional viscosity when even a small amount
of high polymer is added. Consequently, the starch composition herein is found
to have enhanced melt extensibility and is suitable for melt extensional
2s processes, especially those including melt-blowing, spun-bonding, and
electro-
spinning.
A starch composition having a shear viscosity, measured according to the
Test Method disclosed hereinafter, of less than about 30 Pascal~second (Pa~s),
more specifically from about 0.1 Pa~s to about 10 Pa~s, and even more
3o specifically from about 1 to about 8 Pa~s, is useful in the melt
attenuation
28
CA 02329289 2000-12-20
Case 8335
processes herein. Some starch compositions herein may have low melt viscosity
such that they may be mixed, conveyed, or otherwise processed in traditional
polymer processing equipment typically used for viscous fluids, such as a
stationary mixer equipped with metering pump and spinneret. The shear
s viscosity of the starch composition may be effectively modified by the
molecular
weight and molecular weight distribution of the starch, the molecular weight
of the
high polymer, and the amount of plasticizers and/or solvents used. It is
believed
that reducing the average molecular weight of the starch is an effective way
to
lower the shear viscosity of the composition.
io In one embodiment of the present invention, the melt-processable starch
compositions have an extensional viscosity in the range of from about 50 Pa~s
to
about 20,000 Pa~s, more specifically from about 100 Pa~s to about 15,000 Pa~s,
more specifically from about 200 Pa~s to about 10,000 Pa~s, and even more
specifically from about 300 Pa~s to about 5,000 Pa~s and yet more specifically
Is from about 500 Pa~s to about 3,500 Pa~s at a certain temperature. The
extensional viscosity is calculated according to the method set forth
hereinafter in
the Analytical Methods section.
Many factors can affect the rheological (including the extensional viscosity)
behavior of the starch composition. Such factors include, without limitation:
the
2o amount and the type of polymeric components used, the molecular weight and
molecular weight distribution of the components, including the starch and the
high
polymers, the amylose content of the starch, the amount and type of additives
(e.g., plasticizers, diluents, processing aids), the type of processing (e.
g., melt-
blowing or electro-spinning) and the processing conditions, such as
temperature,
2s pressure, rate of deformation; and relative humidity, and in the case of
non-
Newtonian materials, the deformation history (i.e., a time or strain history
dependence). Some materials can strain-harden, i. e., their extensional
viscosity
increases as the strain increases. This is believed to be due to stretching of
an
entangled polymer network. If stress is removed from the material, the
stretched
3o entangled polymer network relaxes to a lower level of strain, depending on
the
29
CA 02329289 2000-12-20
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relaxation time constant, which is a function of temperature, polymer
molecular
weight, solvent or plasticizer concentration, and other factors.
The presence and properties of high polymers can have a significant effect
on the extensional viscosity of the starch composition. The high polymers
useful
s for enhancing the melt extensibility of the starch composition used in the
present
invention are typically high molecular weight, substantially linear polymers.
Moreover, high polymers that are substantially compatible with starch are most
effective in enhancin°g the melt extensibility of the starch
composition.
It has been found that starch compositions useful for melt extensional
io processes typically have their extensional viscosity increased by a factor
of at
least 10 when a selected high polymer is added to the composition. Typically,
the
starch compositions of present invention show an increase in the extensional
viscosity of a factor of about 10 to about 500; more specifically of about 20
to
about 300, still more specifically from about 30 to about 100, when a selected
is high polymer is added. The higher the level of the high polymer, the
greater the
increase in extensional viscosity. High polymer can be added to adjust the
extensional viscosity to a value of 200 to 2000 Pa~sec at a Hencky strain of
6.
For example, polyacrylamide having molecular weight (MW) from 1 million to 15
million at a level of 0.001 % to 0.1 % can be added to comprise the starch
2o composition.
The type and level of starch that is employed can also have an impact on
the extensional viscosity of the starch composition. In general, as the
amylose
content of the starch decreases, the extensional viscosity increases. Also, in
general, as the molecular weight of the starch within the prescribed range
as increases, the extensional viscosity increases. Lastly, in general, as the
level of
starch in the compositions increases, the extensional viscosity increases.
(Conversely, in general, as the level of additive in the compositions
increases, the
extensional viscosity decreases).
Temperature of the starch composition can significantly affect the
3o extensional viscosity of the starch composition. For the purposes of the
present
CA 02329289 2000-12-20
Case 8335
invention, all conventional means of controlling the temperature of the starch
composition can be utilized, if suitable for a particular process employed.
For
example, in the embodiments wherein the starch filaments are produced by
extrusion through a die, the die temperature can have a significant impact on
the
s extensional viscosity of the starch compositions being extruded
therethrough. In
general, as the temperature of the starch composition increases, the
extensional
viscosity of the starch composition decreases. The temperature of the starch
composition can range form about 20°C to about 180°C, more
specifically from
about 20°C to about 90°C, and even more specifically from about
50°C to about
l0 80°C. It is to be understood that the presence or absence of solids
in the starch
composition can affect the required temperature thereof.
The Trouton ratio (Tr) can be used to express the extensional flow
behavior. The Trouton ratio is defined as the ratio between the extensional
viscosity (rle) and the shear viscosity (ris),
Tr = ~1e(~~~ t) ~ its .
wherein the extensional viscosity rye is dependent on the deformation rate
(g') and time (t). For a Newtonian fluid, the uniaxial extension Trouton ratio
has a
2o constant value of 3. For a non-Newtonian fluid, such as the starch
compositions
herein, the extensional viscosity is dependent on the deformation rate (s')
and
time (t). It has also been found that melt processable compositions of the
present
invention typically have a Trouton ratio of at least about 3. Typically, the
Trouton
ratio ranges from about 10 to about 5,000, specifically from about 20 to about
2s 1,000, and more specifically from about 30 to about 500, when measured at a
processing temperature and an extension rate of 700s' at a Hencky strain of 6.
Applicants have also found that in the embodiments in which the starch
filaments are produced by extrusion, the capillary number (Ca) of the starch
composition, as it passes through the extrusion die, is important for melt
31
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processability. The capillary number is a number representing the ratio of the
viscous fluid forces to surface tension forces. Near the exit of a capillary
die, if
the viscous forces are not significantly larger than the surface tension
forces, the
fluid filament will break into droplets, which is commonly termed
"atomization."
s The Capillary Number is calculated according to the following equation:
Ca = (~1s ~ Q)l(~ ~ ~ ~a)
where rls is the shear viscosity in Pascal~seconds measured at a shear
a
rate of 3000 s-'; Q is the volumetric fluid flow rate through capillary die in
mils; r
is the radius of the capillary die in meters (for non-circular orifices, the
equivalent
io diameter/radius can be used); and 6 is the surface tension of the fluid in
Newtons per meter.
Because the capillary number is related to shear viscosity as described
above, it is influenced by the same factors that affect shear viscosity and in
a
similar way. As used herein, the term "inherent" in conjunction with capillary
is number or surface tension indicates properties of a starch composition not
influenced by outside factors, such for example, as presence of an electric
field.
The term "effective" indicates the properties of the starch composition that
has
been influenced by outside factors, such for example, as presence of an
electric
field.
2o In one embodiment of the present invention, the melt-processable starch
compositions have an inherent capillary number as they pass through the die of
at least 0.01 and an effective capillary number of at least 1Ø Without
electrostatics, the capillary number needs to be greater than 1 for stability,
and
preferably greater than 5 for robust stability of the filament being formed.
With
2s electrostatics, charge repulsion counteracts the effect of surface tension
so the
inherent capillary number, measured without an electrical charge present, can
be
less than 1. When an electric potential is applied to the filament being
formed the
effective surface tension is decreased and the effective capillary number is
increased based on the following equations:
32
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While capillary number may be expressed in varying forms, a
representative equation, that can be used to determine the inherent capillary
number of a material, is:
Cainherent - ~s ~V~~~
s where: Ca~nherent is an inherent capillary number
rls is a shear viscosity of the fluid
v is a.the linear velocity of the fluid
a is a surface tension of the fluid
As it pertains to the current invention, a representative sample had the
io following composition and properties.
Formula
TM
Purity Gum 59 from National Starch Inc. 40.00%
Deionize~ Water 59.99%
Superfloc MN-300 LMW from Cytec (high 0.01
molecular weight polyacrylamide)
Run Temperature 120 F
Shear Viscosity at 3000S-10.1 Pa.s
nozzle diameter .0254 cm
Linear Velocity .236 m/sec
Inherent Surface Tension 72 dynes/cm
Experimentally, without an electrostatic charge on the fluid, this material
will flow
through the nozzle tip, form small droplets and then drop under the force of
gravity in discreet drops. As an electric potential on the system is increased
the
~ s drops become smaller in size and begin to accelerate towards the grounding
mechanism. When the electric potential, (25 Kilovolts for this sample) reaches
a
critical value the drop no longer forms at the tip of the nozzle and a small
continuous fiber is expelled from the nozzle tip. Thus the applied electric
potential
has now overcome the surface tension forces eliminating the capillary failure
2o mode. The effective capillary number is now greater than 1. Laboratory
experiments, with the described solution and experimental setup, produced
essentially continuous fibers. The fibers were collected on a vacuum screen in
33
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the form of a fiber mat. Analysis via optical microscopy showed the resulting
fibers were continuous and had diameters ranging from 3 to 5 microns.
In some embodiments, the inherent capillary number can be at least 1,
more specifically, from 1 to 100, still more specifically from about 3 to
about 50,
s and yet still more specifically from about 5 to about 30.
The starch composition herein is processed in a flowable state, which
typically occurs at a temperature at least equal to or higher than its
"melting
temperature." Therefore, the processing temperature range is controlled by the
"melting temperature" of the starch composition, which is measured according
to
io the Test Method described in detail herein. The melting temperature of the
starch composition herein ranges from about 20°C to about 180°C,
more
specifically from about 30°C to about 130°C, and still more
specifically from about
50°C to about 90°C. The melting temperature of the starch
composition is a
function of the amylose content of the starch (higher amylose content requires
is higher melting temperature), the water content, the plasticizer content and
the
type of plasticizer.
Exemplary uniaxial extensional processes suitable for the starch
compositions include melt spinning, melt blowing, and spun bonding. These
processes are described in detail in U. S. Patent No. 4,064,605, issued on
2o December 27, 1977 to Akiyama et al.; U.S. Patent No. 4,418,026, issued on
November 29, 1983 to Blackie et al.; U. S Patent No. 4,855,179, issued on
August 8, 1989 to Bourland et al.; U. S. Patent No. 4,909,976, issued on March
20, 1990 to Cuculo et al.; U. S. Patent No. 5,145,631, issued on September 8,
1992 to Jezic; U.S. Patent No. 5,516,815, issued on May 14, 1996 to Buehler et
2s al.; and U.S. Patent No. 5,342,335, issued on August 30, 1994 to Rhim et
al.
Schematically shown in Figs. 7, 8 and 9, is an apparatus 10 fbr producing
starch filaments suitable for the flexible structure 100 of the present
invention.
The apparatus 10 may comprise, for example, a single-screw or twin-screw
3o extruder, positive displacement pump, or a combination thereof, as is known
in
34
CA 02329289 2000-12-20
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the art. The starch solution can have a total water content, i.e. water of
hydration
plus added water, in the range of from about 5% to about 80%, and more
specifically in the range of from about 10% to about 60% relative to a total
weight
of ,the starch material. The starch material is heated to elevated
temperatures
s sufficient to form a pseudo-thermoplastic melt. Such temperature is
typically
higher than the glass transition andlor melting temperature of the formed
material. The pseudo-thermoplastic melts of the invention are polymeric fluids
having a shear rate dependent viscosity, as known in the art. The viscosity
decreases with increasing shear rate as well as with increasing temperature.
io The starch material can be heated in a closed volume in the presence of a
low concentration of water, to convert the starch material to a pseudo-
thermoplastic melt. The closed volume can be a closed vessel or the volume
created by the sealing action of the feed material as happens in the screw of
extrusion equipment. Pressures created in the closed vessel will include
is pressures due to the vapor pressure of water as well as pressures generated
due
to compression of materials in the screw-barrel of the extruder.
A chain scission catalyst, which reduces the molecular weight by splitting
the glycosidic bonds in the starch macromolecules resulting in a reduction of
the
average molecular weight of the starch, may be used to reduce the viscosity of
2o the pseudo-thermoplastic melt. Suitable catalysts include inorganic and
organic
acids. Suitable inorganic acids include hydrochloric acid, sulfuric acid,
nitric acid,
phosphoric acid, and boric acid as well as the partial salts of polybasic
acids, e.g.
NaHS04 or NaH2 P04 etc. Suitable organic acids include formic acid, acetic
acid,
propionic acid, butyric acid, lactic acid, glycolic acid, oxalic acid, citric
acid,
Zs tartaric acid, itaconic acid, succinic acid, and other organic acids known
in the art,
including partial salts of the polybasic acids. Hydrochloric acid, sulfuric
acid, and
citric acid, including mixtures thereof can be beneficially ' used in the
present
invention.
The reduction of the molecular weight of the non-modified starch used can
3o be by a factor of from 2 to 5000, and more specifically by a factor of from
4 to
CA 02329289 2003-10-07
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4000. The concentration of catalysts is in the range of 10'~ to 10'2 mole of
catalyst
per mole of anhydro-glucose unit, and more specifically between 0.1x10'3 to
5x10'
3 mole of catalyst per mole of anhydro-glucose unit of starch.
In Fig. 7, the starch composition is supplied into the apparatus 10 for
s electro-spinning production of starch filaments used in making the flexible
structure 100 of the present invention. The apparatus 10 comprises a housing
11
structured and configured to receive (arrow A) the starch composition 17 that
can
be maintained therein and extruded (arrow D) into starch filaments 17a through
a
jet 14 of a die head 13. An annular cavity 12 can be provided to circulate
(arrows
io B and C) a heating fluid that heats the starch composition to a desired
temperature. Other means for heating well known in the art, such as, those
using
electro-heating, pulse combustion, water- and steam-heating, etc., can be used
to
heat the starch composition.
The electric field can be applied directly to the starch solution, for
example,
is through a electrically-charged probe, or to the housing 11 and/or extrusion
die 13.
If desired, the molding member 200 can be electrically charged with the
electric
charge opposite to the charge of the starch filaments being extruded.
Alternatively, the molding member can be grounded. The electric differential
can
be from 5kV to 60kV, and more specifically from 20kV to 40kV.
2o The plurality of extruded starch filaments can then be deposited to the
molding member 200 travelling in a closed loop over rollers 200a, 200b, 200c
and 200d in a machine direction MD, at a certain distance from the apparatus
10.
This distance should be sufficient to allow the starch filaments to elongate
and
then dry, and at the same time maintain a differential charge between the
starch
2s filaments exiting the jet nozzle 14 and the molding member 200. For that
purpose, a stream of drying air can be applied to the plurality of starch
filaments
to cause the plurality of starch filaments to turn at an angle. This would
allow
one to maintain a minimal distance between the jet nozzle 14 and the molding
member 200 - for the purposes of maintaining a differential charge
3o therebetween, and at the same time, to maximize the length of a portion of
the
filaments between the nozzle and the molding member 200 - for
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the purposes of effectively drying the filaments. In such an arrangement, the
molding member 200 can be disposed at an angle relative to a direction of the
fiber filaments when they exit the jet nozzle 14 (arrow D in Fig. 7).
Optionally, attenuating air can be used in combination with an electrostatic
s force to provide the drawing force causing the starch filaments to be
attenuated,
or stretched, prior to being deposited to the molding member 200. Fig. 7A
schematically shows an exemplary embodiment of the die head provided with
one annular orifice 1'5 encompassing the jet nozzle 14, and three other
orifices 16
equally spaced at 120° around the jet nozzle 14, for attenuating air.
Of course,
to other arrangements of the attenuating air, as known in the art, are
contemplated
in the present invention
According to the present invention, the starch filaments can have a size
ranging from about 0.01 decitex to about 135 decitex, more specifically from
about 0.02 decitex to about 30 decitex, and even more specifically from about
is 0.02 decitex to about 5 decitex. Starch filaments can have various cross-
sectional shapes, including, but not limited to, circular, oval, rectangular,
triangular, hexagonal, cross-like, star-like, irregular, and any combinations
thereof. One skilled in the art will understand that such a variety of shapes
can
be formed by differential shapes of die nozzles used to produce the starch
2o filaments.
Fig. 10A schematically shows, without limitation, some possible cross-
sectional areas of the starch filaments. The starch filament's cross-sectional
area
is an area perpendicular to the starch filament's major axis and outlined by a
perimeter formed by the starch filament's outside surface in a plane of the
cross-
2s section. It is believed that the greater the surface area of the starch
filament (per
a unit of length or weight thereof) the greater the opacity of the flexible
structure
comprising the starch filaments. Therefore, it is believed that maximizing the
surface area of the starch filaments by increasing the starch filaments'
equivalent
diameter can be beneficial to increase the opacity of the resulting flexible
3o structure 100 of the present invention. One way of increasing the starch
37
CA 02329289 2000-12-20
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filaments' equivalent diameter comprises forming starch filaments having non-
circular, multi-surface, cross-sectional shapes.
Furthermore; starch filaments need not have a uniform thickness and/or
cross-sectional area throughout the filament's length or a portion thereof.
Fig. 10,
s for example, schematically shows a fragment of the starch filament having a
differential cross-sectional area along its length. Such differential cross-
sectional
areas can be formed by, for example, varying pressure within a die, or by
changing at least one of the characteristics (such as, velocity, direction,
etc.) of
attenuating air or drying air in a melt-blowing process, or a combination
io meltblowing and electro-spinning process.
Some starch filaments may have "notches" distributed at certain intervals
along the filament's length or a portion thereof. Such variations in the
starch
filaments' cross-sectional area along the filaments' length are believed to
encourage flexibility of the filaments, facilitate the filaments' ability to
mutually
is entangle in the flexible structure 100 being made, and positively influence
the
softness and flexibility of the resulting flexible structure 100 being made.
The
notches, or other beneficial irregularities in the starch filaments can be
formed by
contacting the starch filaments with a surface having sharp edges or
protrusions,
as described below.
2o The next step of the process comprises providing a molding member 200.
The molding member 200 can comprise a patterned cylinder (not shown) or other
pattern-forming member, such as a belt or a band. The molding member 200
comprises a filament-contacting side 201 and a backside side 202 opposite to
the
filament-contacting side 201. A fluid pressure differential (for example, a
vacuum
Zs pressure, that can be present beneath the belt or within the drum) can
force the
starch filaments into the pattern of the molding member to form the
distinguishable
regions within the flexible structure being made.
In the course of a process of making the structure 100 of the present
invention, the starch filaments are deposited onto the filament-contacting
side 201.
3o The second side 202 typically contacts the equipment, such as support
rolls,
38
CA 02329289 2003-10-07
Case 8335
guiding rolls, a vacuum apparatus, etc., as required by a specific process.
The
filament-contacting side 201 comprises a three-dimensional pattern of
protrusions
and/or depressions. Typically (although not necessarily), that pattern is non-
random and repeating. The three-dimensional pattern of the filament contacting
s side 201 can comprise a substantially continuous pattern (Fig. 4), a
substantially
semi-continuous pattern (Fig. 5), a pattern comprising a plurality of discrete
protuberances (Fig. 5), or any combination thereof. When the plurality of
starch
filaments is deposited onto the filament contacting side 201 of the molding
member 200, the plurality of flexible starch filaments at least partially
conforms to
io the molding pattern of the molding member 200.
The molding member 200 can comprise a belt or band that is
macroscopically monoplanar when it lies in a reference X-Y plane, wherein a Z-
direction is perpendicular to the X-Y plane. Likewise, the flexible flexible
structure
100 can be thought of as macroscopically monoplanar and lying in a plane
~s parallel to the X-Y plane. Perpendicular to the X-Y plane is the Z-
direction along
which extends a caliper, or thickness, of the flexible structure 100, or
elevations
of the differential regions of the molding member 200 or of the flexible
structure
100.
If desired, the molding member 200 comprising a belt may be executed as
2o a press felt. A suitable press felt for use according to the present
invention may
be made according to the teachings of U.S. Patent Nos. 5,549,790, issued Aug.
27, 1996 to Phan; 5,556,509, issued Sept. 17, 1996 to Trokhan et al.;
5,580,423,
issued Dec. 3, 1996 to Ampulski et al.; 5,609,725, issued Mar. 11, 1997 to
Phan;
5,629,052 issued May 13, 1997 to Trokhan et al.; 5,637,194, issued June 10,
2s 1997 to Ampulski et al.; 5,674,663, issued Oct. 7, 1997 to McFarland et
al.;
5,693,187 issued Dec. 2, 1997 to Ampulski et al.; 5,709,775 issued Jan. 20,
1998
to Trokhan et al.; 5,776,307 issued Jul. 7, 1998 to Ampulski et al.; 5,795,440
issued Aug. 18, 1998 to Ampulski et al.; 5,814,190 issued Sept. 29, 1998 to
Phan; 5,817,377 issued October 6, 1998 to Trokhan et al.; 5,846,379 issued
Dec.
30 8, 1998 to Ampulski et al.; 5,855,739 issued Jan. 5, 1999 to Ampulski et
al.; and
5,861,082 issued Jan. 19, 1999 to Ampulski et al.
39
CA 02329289 2003-10-07
Case 8335
In an alternative embodiment, the molding member 200 may be executed
as a press felt according to the teachings of U.S. Pat. No. 5,569,358 issued
Oct.
29, 1996 to Cameron.
One principal embodiment of the molding member 200 comprises a
s resinous framework 210 joined to a reinforcing element 250. The resinous
framework 210 can have a certain pre-selected pattern. For example, Fig. 4
shows the substantially continuous framework 210 having a plurality of
apertures
220 therethrough. in some embodiments, the reinforcing element 250 can be
substantially fluid-permeable. The fluid-permeable reinforcing element 250 may
io comprise a woven screen, or an apertured element, a felt, or any
combination
thereof. The portions of the reinforcing element 250 registered with apertures
220
in the molding member 200 prevent starch filaments from passing through the
molding member 200, and thereby reduce the occurrences of pinholes in the
resulting flexible structure 100. If one does not wish to use a woven fabric
for the
Is reinforcing element 250, a nonwoven element, screen, net, press felt or a
plate or
film having a plurality of holes therethrough may provide adequate support and
strength for the framework 210. Suitable reinforcing element 250 may be made
according to U.S. Pat. Nos. 5,496,624, issued March 5, 1996 to Stelljes; et
al.,
5,500,277 issued March 19, 1996 to Trokhan et al., and 5,566,724 issued
Zo October 22, 1996 to Trokhan et al.
Various types of the fluid-permeable reinforcing element 250 are described
in several US Patents, for example, 5,275,700 and 5,954,097. The reinforcing
element 250 may comprise a felt, also referred to as a "press felt" as is used
in convetional
2s papermaking. The framework 210 may be applied to the reinforcing element
250,
as taught by U.S. Patents 5,549,790, issued Aug. 27, 1996 to Phan; 5,556,509,
issued Sept. 17, 1996 to Trokhan et al.; 5,580,423, issued Dec. 3, 1996 to
Ampulski et al.; 5,609,725, issued Mar. 11, 1997 to Phan; 5,629,052 issued May
13, 1997 to Trokhan et al.; 5,637,194, issued June 10, 1997 to Ampulski et
al.;
30 5,674,663, issued Oct. 7, 1997 to McFarland et al.; 5,693,187 issued Dec.
2,
CA 02329289 2003-10-07
Case 8335
1997 to Ampulski et al.: 5,709,775 issued Jan. 20, 1998 to Trokhan et al.,
5,795,440 issued Aug. 18, 1998 to Ampulski et al., 5,814,190 issued Sept. 29,
1998 to Phan; 5,817,377 issued October 6, 1998 to Trokhan et al.; and
5,846,379
issued Dec. 8, 1998 to Ampulski et al. ,
Alternatively, the reinforcing element 250 may be fluid-impermeable. The
fluid-impermeable reinforcing element 250 can comprise, for example, a
polymeric
resinous material, identical to, or different from, the material used for
making a
framework 210 of the molding member 200 of the present invention; a plastic
to material; a metal; any other suitable natural or synthetic material; or any
combination thereof. One skilled in the art will appreciate that the fluid-
impermeable reinforcing element 250 will cause the molding member 10, as a
whole, to be also fluid-impermeable. It is to be understood that the
reinforcing
element 250 may be partially fluid-permeable and partially fluid-impermeable.
is That is, some portion of the reinforcing element 250 may be fluid-
permeable, while
another portion of the reinforcing element 250 may be fluid-impermeable. The
molding member 200, as a whole, can be fluid-permeable, fluid-impermeable, or
partially fluid-permeable. In a partially fluid-permeable molding member 200,
only
a portion or portions of a macroscopical area or areas of the molding member
200
2o is fluid-permeable.
If desired, the reinforcing element 250 comprising a Jacquard weave can
be utilized. Illustrative belts having the Jacquard weave can be found in U.S.
Pat.
Nos. 5,429,686 issued 7/4/95 to Chiu, et al.; 5,672,248 issued 9/30/97 to
Wendt,
et al.; 5,746,887 issued 5/5/98 to Wendt, et al.; and 6,017,417 issued 1125/00
to
2s Wendt, et al.
The present inverition contemplates the molding member 200 comprising the
filament-contacting side 201 having a Jacquard-weave pattern. Such a
Jacquard-weave pattern may be utilized as a forming member 500, a molding
member 200, a pressing surface, etc. A jacquard weave is reported in the
41
CA 02329289 2003-10-07
Case 8335
literature to be particularly useful where one does not wish to compress or
imprint
a structure in a nip, such as typically occurs upon transfer to a Yankee
drying
drum.
In accordance with the present invention, one, several, or all of the
s apertures 220 of the molding member 200 may be "blind," or "closed," as
described in US Patent 5,972,813, issued to Polat et al. on Oct. 26, 1999. As
the patent cited immediately above describes, polyurethane foams, rubber, and
silicone can be used to render the aperatures 220 fluid-impermeable.
~o An embodiment of the molding member 200 shown in Fig. 6 comprises a
plurality of suspended portions 219 extending (typically laterally) from a
plurality of
base portions 211. The suspended portions 219 are elevated from the
reinforcing
element 250 to form void spaces 215 into which the starch filaments of the
present
invention can be deflected to form cantilever portions 129, as described above
is with reference to Fig. 3. The molding member 200 comprising suspended
portions 219 may comprise a multi-layer structure formed by at least two
layers
(211, 212) joined together in a face-to-face relationship (Fig. 6). Each of
the
layers can comprise a structure similar to one of the several patents
described
above and incorporated herein by reference. Each of the layers (211, 212) can
2o have at least one aperture (220, Figs. 4, 4A) extending between the top
surface
and the bottom surface. The joined layers are positioned such that the at
least
one aperture of one layer is superimposed (in the direction perpendicular to
the
general plane of the molding member 200) with a portion of the framework of
the
other layer, which portion forms the suspended portion 219 described herein
2s above.
Another embodiment of the molding member comprising a plurality of
suspended portions can be made by a process of differential curing of a layer
of a
photosensitive resin, or other curable material, through a mask comprising
transparent regions and opaque regions. The opaque regions comprise regions
3o having differential opacity, for example, regions having a relatively high
opacity
42
CA 02329289 2000-12-20
Case 8335
(non-transparent, such as black) and regions having a relatively low, partial,
opacity (i. e, having some transparency).
When the curable layer having a filament-receiving side and an opposite
second side is exposed to curing radiation through the mask adjacent to the
s filament-receiving side of the coating, the non-transparent regions of the
mask
shield first areas of the coating from the curing radiation to preclude curing
of the
first areas of the coating through the entire thickness of the coating. The
partial
4
opacity regions of the mask only partially shield second areas of the coating
to
allow the curing radiation to cure the second areas to a predetermined
thickness
to less than the thickness of the coating (beginning from the filament-
receiving side
of the coating towards the second side thereof). The transparent regions of
the
mask leave third areas of the coating unshielded to allow the curing radiation
to
cure the third areas through the entire thickness of the coating.
Consequently, the uncured material can be removed from a partially-
is formed molding member. The resulting hardened framework has a filament-
contacting side 201 formed from the filament-receiving side of the coating and
a
backside 202 formed from the second side of the coating. The resulting
framework has a plurality of bases 211 comprising the backside 202 and formed
from the third areas of the coating and a plurality of suspended portions 219
2o comprising the web-contacting side 201 and formed from the second areas of
the
coating. The plurality of bases may comprise a substantially continuous
pattern, a
substantially semi-continuous pattern, a discontinuous pattern, or any
combination
thereof, as discussed above. The suspended portions 219 extend, at an angle
(typically, but not necessarily, at about 90°) from the plurality of
bases and are
2s spaced from the backside 202 of the resulting framework to form void spaces
between the suspended portions and the backside 201. Typically, when the
molding member 200 comprising a reinforcing element 250 is used, the void
spaces 215 are formed between the suspended portions 219 and the reinforcing
element 250, as best shown in Fig. 6. .
43
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The next step comprises depositing the plurality of pseudo-thermoplastic
starch filaments on the filament contacting side 201 of the molding member
200,
as schematically shown in Figs. 7-9, and causing the plurality of starch
filaments
to at least partially conform to the three-dimensional pattern of the molding
s member 200. Referring to an embodiment schematically shown in Fig. 7, upon
exiting the drawing unit, the starch filaments 17a are deposited on the three-
dimensional filament contacting side 201 of a molding member 200. In an
industrial continuous.process, the molding member 200 comprises an endless
belt
continuously traveling in a machine direction MD, as schematically shown in
Figs.
~0 7-9. The starch filaments can then be joined to one another and mutually
entangled through a variety of conventional techniques. The disclosure of U.S.
Pat. No. 5,688,468 issued to Lu on November 18, 1997 teaches a process and
apparatus for producing a spunbond, non-woven web composed of filaments of
reduced diameter.
is In some embodiments, the plurality of starch filaments may first be
deposited not to the molding member 10, but to a forming member 500, as
schematically shown in Fig. 9. This step is optional and can be utilized to
facilitate uniformity in the basis weight of the plurality of starch filaments
throughout a width of the structure 10 being made. The forming member 500
2o comprising a wire is contemplated by the present invention. In an exemplary
embodiment of Fig. 9, the forming member 500 travels in the machine direction
about rolls 500a and 500b. The forming member is fluid permeable, and a
vacuum apparatus 550 located under the forming member 500 and applying fluid
pressure differential to the plurality of starch filaments disposed thereon
2s encourages a more-or-less even distribution of the starch filaments
throughout
the receiving surface of the forming member 500.
If desired, the forming member 500 can also be used to form various
irregularities in the starch filaments, particularly on the surface of the
filaments.
For example, a filament-receiving surface of the forming member can comprise a
3o variety of sharp edges (not shown) structured to imprint still relatively
soft starch
44
CA 02329289 2003-10-07
Case 8335
filaments deposited thereto, to create notches (schematically shown in Fig. 11
) or
other irregularities in the starch filaments, that can be beneficial to the
flexible
structure 100 being made, as described above.
In the embodiment of Fig. 9, the plurality of filaments can be transferred
s from the forming member 500 to the molding member 200 by any conventional
means known in the art, for example, by a vacuum shoe 600 that applies a
vacuum pressure which is sufficient to cause the plurality of starch filaments
disposed on the forming member 500 to separate therefrom and adhere to the
molding member 200.
~o It is contemplated that in the continuous process of making the flexible
structure 100, the molding member 200 may have a linear velocity that is less
that that of the forming member 500. The use of such a velocity differential
at the
transfer point is commonly known in the papermaking arts and can be used for
so
called "microcontraction" that is typically believed to be efficient when
applied to
is low-consitency, wet webs. U.S. Patent 4,440,597 describes in detail "wet-
microcontraction."
Briefly, wet-microcontraction involves transferring the web having a low fiber-
consistency from a first member (such as a foraminous member) to a second
member (such as a loop of open-weave fabric) moving slower than the first
~ member. Now, it is believed that if the starch filaments can be formed and
the
plurality of starch filaments can be maintained in a sufficiently flexible
condition by
the time of transferal from a relatively slower moving support (such, for
example,
as the forming member 500) to a relatively faster moving support (such as, for
example, the molding member 200), it may be possible to effectively subject
the
2s plurality of starch filaments to microcontraction, thereby foreshortening
the
flexible structure 100 being made. The velocity of the molding member 200 can
be from about 1 % to about 25% greater than that of the forming member 500.
Fig. 9A shows an embodiment of the process according to the present
invention, wherein the starch filaments can be deposited to the molding member
45
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1
200 at an angle A that can be from 1 ° to 89°, and more
specifically; from about 5°
to about 85°. This embodiment is believed to be especially beneficial
when the
molding member 200 having suspended portions 219 is used. Such an "angled"
deposition of the starch filaments 17a to the molding member 200 makes the
void
s spaces 215 formed between the suspended portions 219 and the reinforcing
element 250 more accessible to long and flexible starch filaments 17a, and
encourages the starch filaments to more easily fill the void spaces 215. In
Fig. 9A,
the starch filaments °17a are deposited to the molding member 200 in
two steps,
so that both kinds of the void spaces 219 -- upstream void spaces 215a and
io downstream void spaces 215b -- can benefit from the angled deposition of
the
filaments to the molding member 200. Depending on a specific geometry of the
molding member 200, particularly the geometry and/or orientation of its
suspended portions 219, a downstream angle A may be equal or different from an
upstream angle B.
is As soon as the plurality of starch filaments is disposed on the filament
contacting side 201 of the molding member 200, the plurality of filaments at
least
partially conforms to its three-dimensional pattern. In addition, various
means
can be utilized to cause or encourage the starch filaments to conform to the
three-dimensional pattern of the molding member 200. One method comprises
2o applying a fluid pressure differential to the plurality of starch
filaments. This
method can be especially beneficial when the molding member 200 is fluid-
permeable. For example, a vacuum apparatus 550 disposed at the backside 202
of the fluid-permeable molding member 200 can be arranged to apply a vacuum
pressure to the molding member 200 and thus to the plurality of starch
filaments
2s disposed thereon, Fig. 8. Under the influence of the vacuum pressure, some
of
the starch filaments can be deflected into the apertures 220 andlor the void
spaces 215 of the molding member 200 and otherwise conform to the three-
dimensional pattern thereof.
It is believed that all three regions of the flexible structure 100 may have
3o generally equivalent basis weights. By deflecting a portion of starch
filaments into
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the apertures 220, one can decrease the density of the resulting pillows 120
relative to the density of the first, imprinted, regions 110. The regions 110
that are
not deflected in the apertures 220 may be imprinted by compressing flexible
structure in a compression nip. If imprinted, the density of the imprinted
regions
s 110 is increased relative to the density of the pillows 120 and the density
of the
third region 130. The densities of the regions 110 not deflected into the
apertures
220 and the density of the third region 130 are higher than the density of the
pillows
120. The third region 130 will likely have a density intermediate those of the
imprinted regions 110 and the pillows 120.
to Referring still to Fig. 1A, the flexible structure 100 according to the
present
invention may be thought of as having three different densities. The highest
density region will be the high density imprinted region 110. The imprinted
region
110 corresponds in position and geometry to the framework 210 of the molding
member 200. The lowest density region of the flexible structure 100 will be
that of
is the pillows 120, corresponding in position and geometry to the apertures
220 of the
molding member 200. The third region 130, corresponding to the synclines 230
in
the molding member 200, will have a density intermediate those of the pillows
120
and the imprinted region 110. The "synclines" 230 are surfaces of the
framework
210 having a Z-direction vector component extending from the filament-
receiving
2o side 201 of the molding member 200 towards the backside 202 thereof. The
synclines 230 do not extend completely through the framework 210, as do the
apertures 220. Thus, the difference between a syncline 230 and the apertures
220
may be thought of as the aperture 220 represents a through hole in the
framework
210, whereas a syncline 230 represents a blind hole, fissure, chasm, or notch
in the
Zs framework 210.
The three regions of the structure 100, according to the present invention,
may be thought of as being disposed at three different elevations. As used
herein,
the elevation of a region refers to its distance from a reference plane (i.
e., X-Y
plane). For convenience, the reference plane can be visualized as horizontal,
3o wherein the elevational distance from the reference plane is vertical. The
elevation
47
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of a particular region of the starch filament structure 100 may be measured
using
any non-contacting measurement device suitable for such purpose as is well
known
in the art. A particularly suitable measuring device is a non-contacting Laser
Displacement Sensor having a beam size of 0.3 X 1.2 millimeters at a range of
50
s millimeters. Suitable non-contacting Laser Displacement Sensors are sold by
the
Idec Company as models MX1A/B. Alternatively, a contacting stylis gauge, as is
knov~in in the art, may be utilized to measure the different elevations. Such
a stylis
gauge is described jn U.S. Patent 4,300,981 issued to Carstens. The structure
100 according to the present invention is placed on the reference plane with
the
to imprinted region 11- in contact with the reference plane. The pillows 120
and the
third region 130 extend vertically from the reference plane. Differential
elevations of the regions 110, 120, and 130 can also be formed using the
molding member 200 having differential depths or elevations of its three-
dimensional pattern, as schematically shown in Fig. 5A. Such three-dimensional
S patterns having differential depthslelevations can be made by sanding pre-
selected portions of the molding member 200 to reduce their elevation. Also,
the
molding member 200 comprising a curable material can be made by using a
three-dimensional mask. By using a three-dimensional mask comprising
differential depthslelevations of its depressions/protrusions, one can form a
2° corresponding framework 210 also having differential elevations.
Other
conventional techniques of forming surfaces with differential elevation can be
used for the foregoing purposes.
To ameliorate possible negative effect of a sudden application of a fluid
pressure differential by a vacuum apparatus 550 (Figs. 8 and 9) or a vacuum
2s pick-up shoe 600 (Fig. 9), that could force some of the filaments or
portions
thereof all the way through the molding member 200 and thus lead to forming so-
called pin-holes in the resultant flexible structure, the backside of the
molding
member can be "textured" to form microscopical surface irregularities. Those
surface irregularities can be beneficial in some embodiments of the molding
3o member 200, because they prevent formation of a vacuum seal between the
backside 202 of the molding member 200 and a surface of the papermaking
48
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equipment (such as, for example, a surtace of the vacuum apparatus}, thereby
creating a "leakage" therebetween and thus mitigating undesirable consequences
of an application of a vacuum pressure in a through-air-drying process of
making
the flexible structure 100 of the present invention. Other methods of creating
s such a leakage are disclosed in U.S. Patents 5,718,806; 5,741,402;
5,744,007;
5,776,311; and 5,885,421.
The leakage can also be created using so-called "differential fight
transmission techniques" as described in U.S. patents 5,624,790; 5,554,467;
0 5,529,664; 5,514,523; and 5,334,289. The molding member can be made by
applying a coating of photosensitive resin to a reinforcing element that has
opaque portions, and then exposing the coating to light of an activating
wavelength through a mask having transparent and opaque regions, and also
through the reinforcing element.
is Another way of creating backside surface irregularities comprises the use
of a textured forming surface, or a textured barrier film, as described in
U.S.
patents 5,364,504; 5,260,171; and 5,098,522. The molding member can be
made by casting a~photosensitive resin over and through the reinforcing
element
while the reinforcing element travels over a textured surface, and then
exposing
2o the coating to light of an activating wavelength through a mask which has
transparent and opaque regions.
Such means as a vacuum apparatus 550 applying a vacuum (i. e., negative,
less than atmospheric) pressure to the plurality of filaments through the
fluid-
2s permeable molding member 200, or a fan (not shown) applying a positive
pressure to the plurality of filaments can be used to facilitate deflection of
the
plurality of filaments into the three-dimensional pattern of the molding
member.
Furthermore, Fig. 9 schematically shows an optional step of the process of
the present invention, wherein the plurality of starch filaments is overlaid
with a
3o flexible sheet of material 800 comprising an endless band traveling around
rolls
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800a and 800b and contacting the plurality of filaments. That is, the
plurality of
filaments is sandwiched, for a certain period of time, between the molding
member 200 and the flexible sheet of material 800. The flexible sheet of
material
800 can have air-permeability less than that of the molding member 200, and in
s some embodiments can be air-impermeable. An application of a fluid pressure
differential P to the flexible sheet 800 causes deflection of at feast a
portion of the
flexible sheet towards, and in some instances into, the three-dimensional
pattern
of the molding member 200, thereby forcing the plurality of starch filaments
to
closely conform to the three-dimensional pattern of the molding member 200. US
'o patent 5,893,965 describes a principle arrangement of an equipment and a
process utilizing the flexible sheet of material.
Additionally or alternatively to the fluid pressure differential, mechanical
pressure can also be used to facilitate formation of the three-dimensional
~s microscopical pattern of the flexible structure 100 of the present
invention. Such
a mechanical pressure can be created by any suitable press surface,
comprising,
for example a surface of a roll or a surface of a band. Fig. 8 shows two
exemplary embodiments of pressing surface. A pair or several pairs of press
roll
900a and 900b, and 900c and 900d can be used to force the starch filaments
2o disposed on the molding member 200 to more fully conform to the three-
dimensional pattern thereof. The pressure exerted by the press rolls can be
phased, if desired, for example, the pressure created between the rolls 900c
and
900d can be greater than that between the rolls 900 a and 900b. Alternatively
or
additionally, an endless press band 950 traveling about rolls 950a and 950b,
can
2s be pressed against a portion of the filament side 201 of the molding member
200,
to impress the flexible structure 100 therebetween.
The press surface can be smooth or have a three-dimensional pattern of its
own. In the latter instance, the press surface can be used as an embossing
device, to form a distinctive micro-pattern of protrusions and/or depressions
in the
3o flexible structure 100, in cooperation with or independently from the three-
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CA 02329289 2003-10-07
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dimensional pattern of the molding member 200. Furthermore, the press surface
can be used to deposit a variety of additives, such for example, as softeners,
and
ink, to the flexible structure 200 being made. Conventional techniques, such
as,
for example, ink roll 910, or spraying device (or shower) 920 may be used to
s directly or indirectly deposit a variety of additives to the flexible
structure~100
being made.
The structure 100 may optionally be foreshortened, as is known in the art.
Foreshortening can' be accomplished by creping the structure 100 from a rigid
surface, and more specifically from a cylinder, such as, for example, a
cylinder
to 290 schematically shown in Fig. 9. Creping is accomplished with a doctor
blade
292, as is well known in the art. Creping may be accomplished according to
U.S.
Patent 4,919,756, issued April 24, 1992 to Sawdi. Alternatively or
additionally,
foreshortening may be accomplished via microcontraction, as described above.
is The flexible structure 100 that is foreshortened is typically more
extensible
in the machine direction than in the cross machine direction and is readily
bendable about hinge lines formed by the foreshortening process, which hinge
lines extend generally in the cross-machine direction, i. e., along the width
of the
flexible structure 100. The flexible structure 100 which is not creped and/or
20 otherwise foreshortened, is contemplated to be within the scope of the
present
invention.
A variety of products can be made using the flexible structure 100 of the
present invention. The resultant products may find use in filters for air, oil
and
water; vacuum cleaner filters; furnace filters; face masks; coffee filters,
tea or
2s coffee bags; thermal insulation materials and sound insulation materials;
nonwovens for one-time use sanitary products such as diapers, feminine pads,
and incontinence articles; biodegradable textile fabrics for improved moisture
absorption and softness of wear such as microfiber or breathable fabrics; an
electrostatically charged, structured web for collecting and removing dust;
so reinforcements and webs for hard grades of paper, such as wrapping paper,
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CA 02329289 2000-12-20
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writing paper, newsprint, corrugated paper board, and webs for tissue grades
of
paper such as toilet paper, paper towel, napkins and facial tissue; medical
uses
such as surgical drapes, wound dressing, bandages, dermal patches and self
dissolving sutures; and dental uses such as dental floss and toothbrush
bristles.
s The flexible structure may also include odor absorbants, termite repellents,
insecticides, rodenticides, and the like, for specific uses. The resultant
product
absorbs water and oil and may find use in oil or water spill clean-up, or
controlled
water retention and. release for agricultural or horticultural applications.
The
resultant starch filaments or fiber webs may also be incorporated into other
Io materials such as saw dust, wood pulp, plastics, and concrete, to form
composite
materials, which can be used as building materials such as walls, support
beams,
pressed boards, dry walls and backings, and ceiling tiles; other medical uses
such as casts, splints, and tongue depressors; and in fireplace logs for
decorative andlor burning purpose.
Is TEST METHODS
A. Shear Viscosity
The shear viscosity of the composition is measured using a capillary
rheometer (Model Rheograph 2003, manufactured by Goettfert). The
measurements are conducted using a capillary die having a diameter D of 1.0
2o mm and a length L of 30 mm (i.e., LID = 30). The die is attached to the
lower end
of a barrel, which is held at a test temperature (t) ranging from 25 °C
to 90 °C. A
sample composition which has been preheated to the test temperature is loaded
into the barrel section of the rheometer, and substantially fills the barrel
section
(about 60 grams of sample is used). The barrel is held at the specified test
2s temperature (t). If after the loading, air bubbles to the surface,
compaction prior
to running the test is used to rid the sample of entrapped air. A piston is
programmed to push the sample from the barrel through the capillary die at a
set
of chosen rates. As the sample goes from the barrel through the capillary die,
the
sample experiences a pressure drop. An apparent shear viscosity is calculated
3o from the pressure drop and the flow rate of the sample through the
capillary die.
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Then log (apparent shear viscosity) is plotted against log (shear rate) and
the plot
is fitted by the power law r1 = K yn-1, wherein K is a material constant, y is
the
shear rate. The reported shear viscosity of the composition herein is an
extrapolation to a shear rate of 3000 s-' using the power law relation.
s B. Extensional Viscosity
The extensional viscosity is measured using a capillary rheometer (Model
Rheograph 2003, mpnufactured by Goettfert). The measurements are conducted
using a semi-hyperbolic die design with an initial diameter(D;~;t~a~) of 15mm,
a final
diameter(Df~ay of 0.75mm and a length(L) of 7.5mm. '
to The semi-hyperbolic shape of the die is defined by two equations. Where Z
= the axial distance from the initial diameter, and where D(z) is the diameter
of
the die at distance z from D;~,t,a~;
(n-t)
Z p ( L ~- I ) ° total - I
is
( 2
D(Z n)= 1D initial
z
I + Z n D initial - I
L . D final
The die is attached to the lower end of a barrel, which is held at a fixed
test temperature (t) which corresponds to the temperature at which the starch
composition is to be processed. The test temperature (processing temperature)
is a temperature above the melting point of a sample starch composition. The
2s sample starch composition is preheated to the die temperature is loaded
into the
barrel section of the rheometer, and substantially fills the barrel section.
If after
the loading, air bubbles to the surface, compaction prior to running the test
is
used to rid the molten sample of entrapped air. A piston is programmed to push
s3
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the sample from the barrel through the hyperbolic die at a chosen rate. As the
sample goes from the barrel through the orifice die, the sample experiences a
pressure drop. An apparent extensional viscosity is calculated from the
pressure
drop and the flow rate of the sample through the die according to the
following
s equation:
Extensional Viscosity = (delta P/extension rate/Eh) ~ 10+s),
where Extensional Viscosity is in Pascal-Seconds, delta P is the pressure
io drop in bars, extension rate is the flow rate of the sample through the die
in sec',
and Eh is dimensionless Hencky strain. Hencky strain is the time or history
dependent strain. The strain experienced by a fluid element in a non-Newtonian
fluid is dependent on its kinematic history, that is
is t
~ = J ~~(t,) a t~
0
The Hencky Strain (Eh) for this design is 5.99 defined by the equation:
Eh = In~(D;nitia~ /Dfi~a~) 2~
The apparent extensional viscosity is reported as a function of extension
rate of 250-' using the power law relation. Detailed disclosure of extensional
viscosity measurements using a semi-hyperbolic die is found in U.S. Patent No.
5,357,784, issued October 25, 1994 to Collier, the disclosure of which is
2s incorporated herein by reference.
C. Molecular Weight and Molecular Weight Distribution
The weight-average molecular weight (Mw) and molecular weight
distribution (MWD) of starch are determined by Gel Permeation Chromatography
(GPC) using a mixed bed column. Parts of the instrument are as follows:
Pump: Waters Model 600E
s4
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System controller: Waters Model 600E
Autosampler: Waters Model 717 Plus
Column: PL gel 20 ~m Mixed A column (gel molecular weight
ranges from 1,000 to 40,000,000) having a length of
s 600 mm and an internal diameter of 7.5 mm.
Detector: Waters Model 410 Differential Refractometer GPC
software Waters Millennium~ software
The column is calibrated with Dextran standards having molecular weights
to of 245,000; 350,000; 480,000; 805,000; and 2,285,000. These Dextran
calibration standards are available from American Polymer Standards Cor-p.,
Mentor, OH. The calibration standards are prepared by dissolving the standards
in the mobile phase to make a solution of about 2 mglml. The solution sits
undisturbed overnight. Then it is gently swirled and ~Itered through a syringe
is filter (5 ~m Nylon membrane, Spartan-25, available from VWR) using a
syringe (5
ml, Norm-Ject, available from VWR).
The starch sample is prepared by first making a mixture of 40wt% starch in
tap water, with heat applied until the mixture gelatinizes. Then 1.55 grams of
the
gelatinized mixture is added to 22 grams of mobile phase to make a 3 mglml
Zo solution which is prepared by stirring for 5 minutes, placing the mixture
in an oven
at 105°C for one hour, removing the mixture from the oven, and cooling
to room
temperature. The solution is filtered using the syringe and syringe filter as
described above.
The filtered standard or sample solution is taken up by the autosampler to
as flush out previous test materials in a 100 ~I injection loop and inject the
present
test material into the column. The column is held at 70°C. The sample
eluded
from the column is measured against the mobile phase background by a
differential refractive index detector held at 50°C and with the
sensitivity range set
at 64. The mobile phase is DMSO with 0.1 % wlv Liar dissolved therein. The
3o flow rate is set at 1.Oml/min and in the isocratic mode (i.e., the mobile
phase is
constant during the run). Each standard or sample is run through the GPC three
times and the results are averaged._
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The molecular weight distribution (MWD) is calculated as follows:
MWD = weight average molecular weight/number average molecular weight
s D. Thermal Properties'
Thermal properties of the present starch compositions are determined
using a TA Instruments DSC-2910 which has been calibrated with an indium
metal standard, which has an melting temperature (onset) of 156.6°C and
a heat
of melting of 6.80 calories per gram, as reported in the chemical literature.
lo Standard DSC operating procedure per manufacturer's Operating Manual is
used. Due to the volatile evolution (e.g., water vapor) from the starch
composition during a DSC measurement, a high volume pan equipped with an o-
ring seal is used to prevent the escape of volatiles from the sample pan. The
sample and an inert reference (typically an empty pan) are heated at the same
Is rate in a controlled environment. When an actual or pseudo phase change
occurs in the sample, the DSC instrument measures the heat flow to or from the
sample versus that of the inert reference. The instrument is interfaced with a
computer for controlling the test parameters (e.g., the heating/cooling rate),
and
for collecting, calculating and reporting the data.
2o The sample is weighed into a pan and enclosed with an o-ring and a cap.
A typical sample size is 25-65 milligrams. The enclosed pan is placed in the
instrument and the computer is programmed for the thermal measurement as
follows:
1. equilibrate at 0°C;
2s 2. hold for 2 minutes at 0°C;
3. heat at 10°Clmin to 120°C;
4. hold for 2 minutes at 120°C;
5. cool at 10°C/min to 30°C;
6. equilibrate at ambient temperature for 24 hours, the sample
3o pan may be removed from the DSC instrument and placed in a
controlled environment at 30°C in this duration;
s6
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7. return sample pan to the DSC instrument and equilibrate at 0°C;
8. hold for 2 minutes;
9. heat at 10°C/min to 120°C;
10. hold for 2 minutes at 120°C;
s 11. cool at 10°Clmin to 30°C and equilibrate; and
12. remove the used sample.
The computer calculates and reports the thermal analysis result as
differential heat flov~i (~H) versus temperature or time. Typically the
differential
heat flow is normalized and reported on per weight basis (i.e, callmg). Where
the
io sample exhibits a pseudo phase transition, such as a glass transition, a
differential of the DH v. time/temperature plot may be employed to more easily
determine a glass transition temperature.
E. Water Solubility
is A sample composition is made by mixing the components with heat and
stirring until a substantially homogeneous mixture is formed. The melt
composition is cast into a thin film by spreading it over a Teflon~ sheet and
cooling at ambient temperature. The film is then dried completely (i.e., no
water
in the film/composition) in an oven at 100°C. The dried film is then
equilibrated to
20 room temperature. The equilibrated film is ground into small pellets.
To determine the % solids in the sample, 2 to 4 grams of the ground
sample is placed in a pre-weighed metal pan and the total weight of pan and
sample is recorded. The weighed pan and sample is placed in a 100°C
oven for
2 hours., and then taken out and weighed immediately. The % solids is
2s calculated as follows:
Solids = (dried weight o fground sample & pan - wei hg t of pan) ~ 100
(first weight of ground sample & pan - weight of pan)
so To determine the solubility of the sample composition, weigh 10 grams of
ground sample in a 250mL beaker. Add deionized water to make a total weight of
s~
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100 grams. Mix the sample and water on a stir plate for 5 minutes. After
stirring,
pour at least 2mL of stirred sample into a centrifuge tube. Centrifuge 1 hour
at
20,OOOg at 10°C. Take the supernatant of the centrifuged sample and
read the
refractive index. The % solubility of the sample is calculated as follows:.
s
Soluble Solids - (Refractive Index #~~ 1000
Solids
to
F. Caliper
Prior to testing, the film sample is conditioned at a relative humidity of 48%
- 50% and at a temperature of 22°C to 24°C until a moisture
content of about 5%
to about 16% is achieved. The moisture content is determined by TGA (Thermo
is Gravimetric Analysis). For Thermal Gravimetric Analysis, a high resolution
TGA2950 Termogravimetric analyzer from TA Instruments is used.
Approximately 20 mg of sample is weighed into a TGA pan. Following the
manufacturer's instructions, the sample and pan are inserted into the unit and
the
temperature is increased at a rate of 10°Clminute to 250°C. The
% moisture in
2o the sample is determined using the weight lost and the initial weight as
follows:
Start Weight - Weight @ 250° C
Moisture = * 100%
Start Weight
Preconditioned samples are cut to a size greater than the size of the foot
2s used to measure the caliper. The foot to be used is a circle with an area
of 3.14
square inches.
The sample is placed on a horizontal flat surface and confined between
the flat surface and a load foot having a horizontal loading surface, where
the
load foot loading surface has a circular surface area of about 3.14 square
inches
3o and applies a confining pressure of about 15 glsquare cm (0.21 psi) to the
sample. The caliper is the resulting gap between the flat surface and the load
foot
58
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loading surface. Such measurements can be obtained on a VIR Electronic
Thickness Tester Model II available from Thwing-Albert, Philadelphia, Pa. The
caliper measurement is repeated and recorded at least five times. The result
is
reported in mils.
s The sum of the readings recorded from the caliper tests is divided by the
number of readings recorded. The result is reported in mils.
59
