U.S. patent application number 16/467516 was filed with the patent office on 2019-10-31 for wet-laid microfibers including polyolefin and thermoplastic starch.
This patent application is currently assigned to KIMBERLY-CLARK WORLDWIDE, INC.. The applicant listed for this patent is KIMBERLY-CLARK WORLDWIDE, INC.. Invention is credited to Mark M. Mleziva, Thomas G. Shannon, Bo Shi, Gregory J. Wideman.
Application Number | 20190330770 16/467516 |
Document ID | / |
Family ID | 62558965 |
Filed Date | 2019-10-31 |
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United States Patent
Application |
20190330770 |
Kind Code |
A1 |
Shi; Bo ; et al. |
October 31, 2019 |
WET-LAID MICROFIBERS INCLUDING POLYOLEFIN AND THERMOPLASTIC
STARCH
Abstract
Spun microfibers include a blend of 70 wt. % to 90 wt. %
meltblown-grade polyolefin and 10 wt. % to 30 wt. % thermoplastic
starch, wherein the microfibers are suitable for use in a wet-laid
process. A method for producing an absorbent product includes
producing a blend of 70 wt. %-90 wt. % meltblown-grade polyolefin
with 10 wt. % to 30 wt. % thermoplastic modified starch (TPMS),
wherein the blend prior to spinning has a melt flow index greater
than 150; spinning the blend into microfibers in a fiber spinning
process; cutting the microfibers into staple fibers; and
incorporating the staple fibers into a wet-laid process for making
a nonwoven web.
Inventors: |
Shi; Bo; (Neenah, WI)
; Wideman; Gregory J.; (Menasha, WI) ; Shannon;
Thomas G.; (Neenah, WI) ; Mleziva; Mark M.;
(Appleton, WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KIMBERLY-CLARK WORLDWIDE, INC. |
Neenah |
WI |
US |
|
|
Assignee: |
KIMBERLY-CLARK WORLDWIDE,
INC.
Neenah
WI
|
Family ID: |
62558965 |
Appl. No.: |
16/467516 |
Filed: |
December 16, 2016 |
PCT Filed: |
December 16, 2016 |
PCT NO: |
PCT/US16/67131 |
371 Date: |
June 7, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D04H 1/4291 20130101;
D01D 5/0985 20130101; D01F 8/06 20130101; D01F 6/46 20130101; D10B
2321/02 20130101 |
International
Class: |
D01F 8/06 20060101
D01F008/06; D01D 5/098 20060101 D01D005/098; D04H 1/4291 20060101
D04H001/4291 |
Claims
1. Spun microfibers comprising a blend of 70 wt. % to 90 wt. %
meltblown-grade polyolefin and 10 wt. % to 30 wt. % thermoplastic
starch, wherein the microfibers are suitable for use in a wet-laid
process.
2. The spun microfibers of claim 1, wherein the blend prior to
spinning has a melt flow index greater than 150.
3. The spun microfibers of claim 1, wherein the microfibers are
staple fibers.
4. The spun microfibers of claim 1, further comprising a surfactant
treatment.
5. The spun microfibers of claim 1, the blend further comprising a
compatibilizer.
6. The spun microfibers of claim 1, wherein the meltblown-grade
polyolefin is polypropylene.
7. The spun microfibers of claim 1, wherein the meltblown-grade
polyolefin is polyethylene.
8. The spun microfibers of claim 1, wherein the starch is a native
starch derived from cereal grains such as corn, waxy corn, wheat,
sorghum, rice, and waxy rice; tubers such as potatoes; roots such
as tapioca, sweet potato, and arrowroot; or the pith of the sago
palm.
9. The spun microfibers of claim 8, wherein native starch has been
modified to become thermoplastic modified starch (TPMS).
10. A method for producing spun microfibers comprising: producing a
blend of 70 wt. %-90 wt. % meltblown-grade polyolefin with 10 wt. %
to 30 wt. % thermoplastic modified starch (TPMS) derived from
native starch; and spinning the blend into microfibers in a fiber
spinning process, wherein the microfibers are suitable for use in a
wet-laid process.
11. The method of claim 10, wherein the blend prior to spinning has
a melt flow index greater than 150.
12. The method of claim 10, further comprising cutting the
microfibers into staple fibers.
13. The method of claim 10, further comprising applying a
surfactant treatment to the microfibers.
14. The method of claim 10, wherein the blend further comprises a
compatibilizer.
15. The method of claim 10, wherein the meltblown-grade polyolefin
is polypropylene.
16. The method of claim 10, wherein the meltblown-grade polyolefin
is polyethylene.
17. The method of claim 10, wherein the native starch is derived
from cereal grains such as corn, waxy corn, wheat, sorghum, rice,
and waxy rice; tubers such as potatoes; roots such as tapioca,
sweet potato, and arrowroot; or the pith of the sago palm.
18. A method for producing an absorbent product, the method
comprising: producing a blend of 70 wt. %-90 wt. % meltblown-grade
polyolefin with 10 wt. % to 30 wt. % thermoplastic modified starch
(TPMS), wherein the blend prior to spinning has a melt flow index
greater than 150; spinning the blend into microfibers in a fiber
spinning process; cutting the microfibers into staple fibers; and
incorporating the staple fibers into a wet-laid process for making
a nonwoven web.
19. The method of claim 18, further comprising converting the
nonwoven web into an absorbent product.
20. The method of claim 18, wherein the absorbent product is a
tissue product.
Description
BACKGROUND
[0001] Current wet-laid microfibers are produced with a limited
number of fiber-grade synthetic polymers such as PE, PP, PET, and
PLA. The limited number of options for fiber-grade polymers is due
to a set of stringent requirements for fiber melt spinning. There
are no wet-laid microfibers containing biopolymers such as starch,
although thermoplastic starch is widely used in blends of
polyolefin or PLA for breathable, stretchable, or packaging film
applications.
[0002] In an attempt to increase sustainability, thermoplastic
modified starch (TPMS) can be added to fiber-grade polyolefins. The
resulting fibers, however, such as those in U.S. Pat. No. 6,623,854
to Bond, cannot be spun without the fibers breaking, except at very
low speeds, which is inefficient, costly, and inappropriate for
commercial production. Using TPMS with standard fiber spinning
grades of polyolefins does not allow commercial scale speeds.
Further, TPMS and meltblown-grade polyolefins cannot be spun into
fiber individually using staple fiber spinning equipment because
their melt-flow indexes (MFIs) are insufficient. TPMS has an MFI
that is too low, whereas meltblown-grade polyolefins have an MFI
that is too high.
[0003] U.S. Pat. No. 8,470,222 B2 to Shi et al. describes a
biodegradable fiber spun from blends of modified aliphatic-aromatic
polyester and TPMS. The reason to modify aliphatic-aromatic
polyester via alcoholysis is because thermoplastic starch alone
cannot be spun into fibers due to its unfavorable rheological
characteristics. The modified aliphatic-aromatic polyester can
alter rheological profile of thermoplastic starch suitable for
fiber melt spinning. However, polyester resins are expensive
relative to polyolefins and alcoholysis through reactive extrusion
can involve the use of undesirable chemical reagents. The
disclosure described herein directly blends meltblown-grade
polyolefins and thermoplastic modified starch for wet-laid
microfiber spinning. The results demonstrate an unexpected success
to spin fibers from blends of meltblown-grade polyolefin and
thermoplastic starch. Conversely, as described above, conventional
fiber-grade polyolefin containing TPMS cannot be realistically spun
into fibers.
[0004] It is well known that few renewable materials by themselves
are suitable for fiber spinning. Attempts to date have dealt with
improving processability for renewable materials such as starch in
their respective blends for fiber spinning. Different processing
aids were added into fiber blends. However, there is no direct use
of meltblown synthetic polymers in their blends.
SUMMARY
[0005] The present disclosure describes novel fiber compositions
using meltblown polyolefins and thermoplastic modified starch to
create miscible blends for wet-laid microfiber spinning via
conventional polymer processing equipment.
[0006] This disclosure addresses the use of a low-cost starch
biopolymer together with a commodity meltblown-grade polyolefin for
wet-laid microfiber production. Successful inclusion of
thermoplastic starch in meltblown-grade polyethylene or
polypropylene for wet-laid microfiber spinning creates
opportunities in 1) cost reduction when it is used in bath/facial
tissue or towel manufacturing, and in 2) increased use of bio-based
renewable material content, all of which is consistent with
sustainability objectives.
[0007] More specifically, synthetic microfibers are made in a
conventional fiber spinning process (not a meltblown process) from
a blend of meltblown-grade polyolefin(s) and thermoplastic modified
starch (TPMS). These blends can be made with or without a
compatibilizer, such as maleic anhydride grafted polymers or
polar-group grafted polymeric additives or coupling agents. The
wet-laid microfiber can be in any cross-sectional configurations
such as monofilament, side-by side, island-in-the sea, or
sheath-core structures. The fibers can be cut into staple fibers or
used as a continuous fiber without cutting. For tissue
applications, the fibers are cut into lengths less than 5 mm, with
a normal range of 1 to 3 mm long.
[0008] In one aspect, spun microfibers include a blend of 70 wt. %
to 90 wt. % meltblown-grade polyolefin and 10 wt. % to 30 wt. %
thermoplastic starch, wherein the microfibers are suitable for use
in a wet-laid process.
[0009] In another aspect, a method for producing spun microfibers
includes producing a blend of 70 wt. %-90 wt. % meltblown-grade
polyolefin with 10 wt. % to 30 wt. % thermoplastic modified starch
(TPMS) derived from native starch; and spinning the blend into
microfibers in a fiber spinning process, wherein the microfibers
are suitable for use in a wet-laid process.
[0010] In still another aspect, a method for producing an absorbent
product includes producing a blend of 70 wt. %-90 wt. %
meltblown-grade polyolefin with 10 wt. % to 30 wt. % thermoplastic
modified starch (TPMS), wherein the blend prior to spinning has a
melt flow index greater than 150; spinning the blend into
microfibers in a fiber spinning process; cutting the microfibers
into staple fibers; and incorporating the staple fibers into a
wet-laid process for making a nonwoven web.
BRIEF DESCRIPTION OF THE FIGURES
[0011] The foregoing and other features and aspects of the present
disclosure and the manner of attaining them will become more
apparent, and the disclosure itself will be better understood by
reference to the following description, appended claims and
accompanying drawings, where:
[0012] FIG. 1 graphically illustrates Differential Scanning
calorimeter (DSC) thermograms (2nd heat) of PP/TPMS blend
samples;
[0013] FIG. 2 graphically illustrates the effect of composition (Wt
% TPMS) on melt temperature of PP/TPMS blends; and
[0014] FIG. 3 graphically illustrates the effect of composition (Wt
% TPMS) on melt enthalpy of PP/TPMS blends.
[0015] Repeat use of reference characters in the present
specification and drawings is intended to represent the same or
analogous features or elements of the present disclosure. The
drawings are representational and are not necessarily drawn to
scale. Certain proportions thereof might be exaggerated, while
others might be minimized.
DETAILED DESCRIPTION
[0016] The terms "absorbent article" and "absorbent product" refer
herein to an article that can be placed against or in proximity to
the body (i.e., contiguous with the body) of the wearer to absorb
and contain various liquid, solid, and semi-solid exudates
discharged from the body. Such absorbent articles, as described
herein, are intended to be discarded after a limited period of use
instead of being laundered or otherwise restored for reuse. It is
to be understood that the present disclosure is applicable to
various disposable absorbent articles, including, but not limited
to, diapers, training pants, youth pants, swim pants, feminine
hygiene products, including, but not limited to, menstrual pads,
incontinence products, medical garments, surgical pads and
bandages, other personal care or health care garments, and the like
without departing from the scope of the present disclosure. The
term can also include bath tissue, facial tissue, toweling, and the
like.
[0017] The term "carded web" refers herein to a web containing
natural or synthetic staple fibers typically having fiber lengths
less than about 100 mm. Bales of staple fibers can undergo an
opening process to separate the fibers that are then sent to a
carding process that separates and combs the fibers to align them
in the machine direction after which the fibers are deposited onto
a moving wire for further processing. Such webs are usually
subjected to some type of bonding process such as thermal bonding
using heat and/or pressure. In addition to or in lieu thereof, the
fibers can be subject to adhesive processes to bind the fibers
together such as by the use of powder adhesives. The carded web can
be subjected to fluid entangling, such as hydroentangling, to
further intertwine the fibers and thereby improve the integrity of
the carded web. Carded webs, due to the fiber alignment in the
machine direction, once bonded, will typically have more machine
direction strength than cross machine direction strength.
[0018] The term "hydrophilic" refers herein to fibers or the
surfaces of fibers that are wetted by aqueous liquids in contact
with the fibers. The degree of wetting of the materials can, in
turn, be described in terms of the contact angles and the surface
tensions of the liquids and materials involved. Equipment and
techniques suitable for measuring the wettability of particular
fiber materials or blends of fiber materials can be provided by
Cahn SFA-222 Surface Force Analyzer System, or a substantially
equivalent system. When measured with this system, fibers having
contact angles less than 90 degrees are designated "wettable" or
hydrophilic, and fibers having contact angles greater than 90
degrees are designated "nonwettable" or hydrophobic.
[0019] The term "meltblown" refers herein to fibers formed by
extruding a molten thermoplastic material through a plurality of
fine, usually circular, die capillaries as molten threads or
filaments into converging high velocity heated gas (e.g., air)
streams that attenuate the filaments of molten thermoplastic
material to reduce their diameter, which can be a microfiber
diameter. Thereafter, the meltblown fibers are carried by the high
velocity gas stream and are deposited on a collecting surface to
form a web of randomly dispersed meltblown fibers. Such a process
is disclosed, for example, in U.S. Pat. No. 3,849,241 to Butin et
al., which is incorporated herein by reference. Meltblown fibers
are microfibers that can be continuous or discontinuous, are
generally smaller than about 0.6 denier, and can be tacky and
self-bonding when deposited onto a collecting surface.
[0020] The term "nonwoven" refers herein to materials and webs of
material that are formed without the aid of a textile weaving or
knitting process. The materials and webs of materials can have a
structure of individual fibers, filaments, or threads (collectively
referred to as "fibers") that can be interlaid, but not in an
identifiable manner as in a knitted fabric. Nonwoven materials or
webs can be formed from many processes such as, but not limited to,
meltblowing processes, spunbonding processes, carded web processes,
etc.
[0021] The term "pliable" refers herein to materials that are
compliant and that will readily conform to the general shape and
contours of the wearer's body.
[0022] The term "spunbond" refers herein to small diameter fibers
that are formed by extruding molten thermoplastic material as
filaments from a plurality of fine capillaries of a spinnerette
having a circular or other configuration, with the diameter of the
extruded filaments then being rapidly reduced by a conventional
process such as, for example, eductive drawing, and processes that
described in U.S. Pat. No. 4,340,563 to Appel et al., U.S. Pat. No.
3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki
et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat.
No. 3,502,763 to Hartmann, U.S. Pat. No. 3,502,538 to Peterson, and
U.S. Pat. No. 3,542,615 to Dobo et al., each of which is
incorporated herein in its entirety by reference. Spunbond fibers
are generally continuous and often have average deniers larger than
about 0.3, and in an aspect, between about 0.6, 5 and 10 and about
15, 20 and 40. Spunbond fibers are generally not tacky when they
are deposited on a collecting surface.
[0023] The term "thermoplastic" refers herein to a polymeric
material that becomes pliable or moldable above a specific
temperature and returns to a solid state upon cooling.
[0024] The term "meltblown-grade polyolefin" refers to a polyolefin
characterized by an extremely high melt flow rate homopolymer
resin. The melt flow rate of a meltblown-grade polyolefin can range
from 200 to 1550 g/10 min under standard testing conditions (ISO
1133-1). Meltblown-grade polyolefins can also have a narrow
molecular weight distribution.
[0025] The term "microfiber" refers to a fiber (including staple
fibers and filaments) with a linear mass density less than 1 dtex,
where dtex is an abbreviation of decitex, the mass in grams per
10,000 meters.
[0026] Generally, a method of producing wet-laid microfibers using
spunbond TPMS and meltblown-grade polymers is disclosed herein.
This disclosure addresses the use of a low-cost starch biopolymer
together with a low-cost commodity meltblown-grade polyolefin for
wet-laid microfiber production. Successful inclusion of
thermoplastic starch in meltblown-grade polyethylene or
polypropylene for wet-laid microfiber spinning creates
opportunities for cost reduction when used in bath/facial tissue or
towel manufacturing, and in increased use of bio-based renewable
material content, all of which are consistent with sustainability
objectives.
[0027] Many companies wish to reduce their forest fiber footprints.
A key component in achieving this goal can be to transfer a
significant portion of wood fiber sourced from natural forests to
alternative, renewable sources. In certain cases, this goal calls
for a reduction in northern bleached softwood Kraft (NBSK) pulp.
Products such as tissue, towels, and industrial wipers are
responsible for a significant portion of virgin NBSK consumption.
NBSK can be the most expensive fiber among a company's spend on
commodity pulps annually. There are also uncertainties with respect
to long softwood fiber supply and fluctuations in NBSK prices. The
initiative described herein, generally NBSK replacement using a
low-cost wet-laid microfiber, is a timely initiative to support
corporate sustainability. The fibers described herein can also be
used in any other suitable nonwoven process including the
production of bonded carded webs.
[0028] The present disclosure employs a thermoplastic starch.
Starch is a natural polymer composed of amylose and amylopectin.
Amylose is essentially a linear polymer having a molecular weight
in the range of 100,000-500,000, whereas amylopectin is a highly
branched polymer having a molecular weight of up to several
million. Although starch is produced in many plants, typical
sources includes seeds of cereal grains, such as corn, waxy corn,
wheat, sorghum, rice, and waxy rice; tubers, such as potatoes;
roots, such as tapioca (i.e., cassava and manioc), sweet potato,
and arrowroot; and the pith of the sago palm. Broadly speaking, any
natural (unmodified) and/or modified starch may be employed in the
present invention. Modified starches, for instance, are often
employed that have been chemically modified by typical processes
known in the art (e.g., esterification, etherification, oxidation,
acid hydrolysis, enzymatic hydrolysis, etc.). Starch ethers and/or
esters may be particularly desirable, such as hydroxyalkyl
starches, carboxymethyl starches, etc. The hydroxyalkyl group of
hydroxylalkyl starches may contain, for instance, 2 to 10 carbon
atoms, in some embodiments from 2 to 6 carbon atoms, and in some
embodiments, from 2 to 4 carbon atoms. Representative hydroxyalkyl
starches such as hydroxyethyl starch, hydroxypropyl starch,
hydroxybutyl starch, and derivatives thereof. Starch esters, for
instance, may be prepared using a wide variety of anhydrides (e.g.,
acetic, propionic, butyric, and so forth), organic acids, acid
chlorides, or other esterification reagents. The degree of
esterification may vary as desired, such as from 1 to 3 ester
groups per glucosidic unit of the starch.
[0029] Regardless of whether it is in a native or modified form,
the starch may contain different percentages of amylose and
amylopectin, different size starch granules and different polymeric
weights for amylose and amylopectin. High amylose starches contain
greater than about 50% by weight amylose and low amylose starches
contain less than about 50% by weight amylose. Although not
required, low amylose starches having an amylose content of from
about 10% to about 40% by weight, and in some embodiments, from
about 15% to about 35% by weight, are particularly suitable for use
in the present invention. Examples of such low amylose starches
include corn starch and potato starch, both of which have an
amylose content of approximately 20% by weight. Such low amylose
starches typically have a number average molecular weight ("Mn")
ranging from about 50,000 to about 1,000,000 grams per mole, in
some embodiments from about 75,000 to about 800,000 grams per mole,
and in some embodiments, from about 100,000 to about 600,000 grams
per mole, as well as a weight average molecular weight ("Mw")
ranging from about 5,000,000 to about 25,000,000 grams per mole, in
some embodiments from about 5,500,000 to about 15,000,000 grams per
mole, and in some embodiments, from about 6,000,000 to about
12,000,000 grams per mole. The ratio of the weight average
molecular weight to the number average molecular weight ("Mw/Mn"),
i.e., the "polydispersity index", is also relatively high. For
example, the polydispersity index may range from about 20 to about
100.
[0030] A plasticizer is also employed in the thermoplastic starch
to help render the starch melt-processible. Starches, for instance,
normally exist in the form of granules that have a coating or outer
membrane that encapsulates the more water-soluble amylose and
amylopectin chains within the interior of the granule. When heated,
plasticizers may soften and penetrate the outer membrane and cause
the inner starch chains to absorb water and swell. This swelling
will, at some point, cause the outer shell to rupture and result in
an irreversible destructurization of the starch granule. Once
destructurized, the starch polymer chains containing amylose and
amylopectin polymers, which are initially compressed within the
granules, will stretch out and form a generally disordered
intermingling of polymer chains. Upon resolidification, however,
the chains may reorient themselves to form crystalline or amorphous
solids having varying strengths depending on the orientation of the
starch polymer chains. Because the starch is thus capable of
melting and resolidifying at certain temperatures, it is generally
considered a "thermoplastic starch."
[0031] Suitable plasticizers may include, for instance, polyhydric
alcohol plasticizers, such as sugars (e.g., glucose, sucrose,
fructose, raffinose, maltodextrose, galactose, xylose, maltose,
lactose, mannose, and erythrose), sugar alcohols (e.g., erythritol,
xylitol, malitol, mannitol, and sorbitol), polyols (e.g., ethylene
glycol, glycerol, propylene glycol, dipropylene glycol, butylene
glycol, and hexane triol), etc. Also suitable are hydrogen bond
forming organic compounds which do not have hydroxyl group,
including urea and urea derivatives; anhydrides of sugar alcohols
such as sorbitan; animal proteins such as gelatin; vegetable
proteins such as sunflower protein, soybean proteins, cotton seed
proteins; and mixtures thereof. Other suitable plasticizers may
include phthalate esters, dimethyl and diethylsuccinate and related
esters, glycerol triacetate, glycerol mono and diacetates, glycerol
mono, di, and tripropionates, butanoates, stearates, lactic acid
esters, citric acid esters, adipic acid esters, stearic acid
esters, oleic acid esters, and other acid esters. Aliphatic acids
may also be used, such as copolymers of ethylene and acrylic acid,
polyethylene grafted with maleic acid, polybutadiene-co-acrylic
acid, polybutadiene-co-maleic acid, polypropylene-co-acrylic acid,
polypropylene-co-maleic acid, and other hydrocarbon based acids. A
low molecular weight plasticizer is preferred, such as less than
about 20,000 g/mol, preferably less than about 5,000 g/mol and more
preferably less than about 1,000 g/mol.
[0032] The relative amount of starches and plasticizers employed in
the thermoplastic starch may vary depending on a variety of
factors, such as the desired molecular weight, the type of starch,
the affinity of the plasticizer for the starch, etc. Typically,
however, starches constitute from about 30 wt. % to about 95 wt. %,
in some embodiments from about 40 wt. % to about 90 wt. %, and in
some embodiments, from about 50 wt. % to about 85 wt. % of the
thermoplastic starch. Likewise, plasticizers typically constitute
from about 5 wt. % to about 55 wt. %, in some embodiments from
about 10 wt. % to about 45 wt. %, and in some embodiments, from
about 15 wt. % to about 35 wt. % of the thermoplastic composition.
It should be understood that the weight of starch referenced herein
includes any bound water that naturally occurs in the starch before
mixing it with other components to form the thermoplastic starch.
Starches, for instance, typically have a bound water content of
about 5% to 16% by weight of the starch.
[0033] Additional information with respect to the processing and
use of thermoplastic starch can be found in U.S. Pat. No. 8,470,222
to Shi et al., which is incorporated herein by reference to the
extent it does not conflict herewith.
[0034] Conventional synthetic microfibers are made in a
conventional fiber spinning process (not a meltblown process) from
conventional fiber-grade polymer. The process described herein
substitutes a blend of less expensive meltblown-grade polyolefin(s)
and a low-cost thermoplastic modified starch (TPMS). These blends
can be made with or without a compatibilizer, such as maleic
anhydride grafted polymers or polar-group grafted polymeric
additives or coupling agents. The wet-laid microfiber described
herein can be in any cross-sectional configurations such as
monofilament, side-by side, island-in-the sea, or sheath-core
structures. The fibers can be cut into staple fibers or used as a
continuous fiber without cutting. For tissue applications, the
fibers are cut into lengths less than 5 mm, with a normal range of
1 mm to 3 mm long.
[0035] If TPMS is added to fiber-grade polyolefins in a
conventional fiber-spinning process, fibers cannot be spun without
the fibers breaking except at very low speeds. Further, TPMS and
meltblown-grade polyolefins are not able to be spun into fiber on
their own because their MFIs are either too low (TPMS) or too high
(meltblown-grade polyolefins) to produce fibers.
[0036] The microfibers produced herein can be optionally surface
treated with a surfactant for use in a wet-laid process. These
microfibers, with or without surfactant treatment, can be used in
tissue/towel substrates, absorbent articles, and in any other
suitable application.
[0037] The present disclosure relates to microfiber material
compositions and methods for thermoplastic starch extrusion
converting, compounding, and wet-laid microfiber fabrication for
tissue and towel applications. Examples containing meltblown-grade
polyolefin and TPMS can be blended with or without any
compatibilizer, including but not limited to, maleic anhydride
grafted polymers or polar-group grafted polymeric additives or
coupling agents for successful fiber spinning. Experimental data
indicates these blends can be spun into a fiber, which is then
surface treated using a selected surfactant to create a wet-laid
fiber for papermaking.
[0038] To be hydrophilic or wettable for tissue or towel
applications, the microfiber surface can be treated by surfactants
such as SF-19 during microfiber spinning or a surfactant could be
compounded into the fiber blends outlined in U.S. Pat. No.
5,759,926 to Pike et al.
EXAMPLES
[0039] The following is provided for exemplary purposes to
facilitate understanding of the disclosure and should not be
construed to limit the disclosure to the examples. Other
formulations and substrates can be used within this disclosure and
the claims presented below.
[0040] Materials
[0041] Hydroxypropylated corn starch, GLUCOSOL 800, was purchased
from Chemstar (Minneapolis, Minn.) with a weight-averaged molecular
weight, determined by GPC, of 2,900,000 and a polydispersity
estimated at 28. The modified starch has a bulk density of 0.64
g/cm.sup.3, its particle sizes pass 98% min through 140 Mesh, and
it is supplied as off-white powders.
[0042] METOCENE MF650X metallocene polypropylene homopolymer,
purchased from Lyondellbasell (Carrollton, Tex.), has a specific
density of 0.91 g/cm.sup.3 and a melt flow index (230.degree.
C./2.16 kg) of 1200 g/10 min.
[0043] DNDA-1082 linear low density polyethylene, purchased from
the Dow Chemical Company (Midland, Mich.), has a specific density
is 0.94 g/cm.sup.3 and a melt flow index (190.degree. C./2.16 kg)
of 160 g/10 min.
[0044] PPH 3762 polypropylene homopolymer and PPH M3766 metallocene
isostatic polypropylene were purchased from Total Petrochemicals
(Houston, Tex.). The specific density and melt flow index for PPH
3762 are 0.91 g/cm.sup.3 and 18 g/10 min (190.degree. C./2.16 kg)
and those for PPH M3766 are 0.90 g/cm.sup.3 and 23 g/10 min
(190.degree. C./2.16 kg).
[0045] PLA 6201 D fiber-grade polylactic acid was purchased from
NatureWorks (Minnetonka, Minn.), with a specific density of 1.24
g/cm.sup.3 and a melt flow index (190.degree. C./2.16 kg) of 15 to
30 g/10 min.
[0046] FUSABOND E528 anhydride-modified polyethylene and FUSABOND
353 chemically-modified polypropylene copolymer are used as
compatibilizers, purchased from DuPont (Wilmington, Del.).
[0047] INFUSE 9807 high-performance olefin block copolymer is
purchased from the Dow Chemical Company (Midland, Mich.). It has a
density of 0.87 g/cm.sup.3 and a melt flow index of 15 g/10 min
(190.degree. C. and 2.16 kg).
[0048] Masil SF-19 is a surfactant used to make a fiber surface
hydrophilic. It was purchased from Lubrizol Inc. (Spartanburg,
S.C.).
[0049] Material Processing
Example 1: Making Thermoplastic Modified Starch (TPMS) Using
GLUCOSOL 800 Biopolymer
[0050] A K-TRON feeder (K-Tron America, Pitman, N.J.) was used to
feed the starch material into a ZSK-30 extruder (Werner and
Pfleidere Corporation, Ramsey, N.J.). The ZSK-30 extruder is a
co-rotating, twin screw extruder. The extruder diameter is 30 mm
with the length of the screws up to 1328 mm. The extruder has 14
barrels, numbered consecutively 1-14 from the feed hopper to the
die. The first barrel (#1) received the modified starch at 15
lbs./hr. when the extruder was heated to the temperature profile as
shown in Table 1 and the screw was set to rotate at 170 rpm.
Glycerin as a plasticizer was pumped into barrel #2 using an Eldex
pump from Eldex Laboratories, Inc. (Napa, Calif.). The vent was
opened at the end of the extruder to release moisture. The die used
to convert starch to thermoplastic starch has 3 openings of 5 mm in
diameter that were separated by 3 mm. The thermoplastic starch
strands were cooled on a conveyer belt and then pelletized.
TABLE-US-00001 TABLE 1 Processing Conditions for Making TPMS on
ZSK-30 Material Feeding Extruder Sample Rate Modified Glycerin
Speed Extruder Temperature Profile (.degree. C.) P.sub.melt Torque
No. (lb/hr) Starch (%) (rpm) T.sub.1 T.sub.2 T.sub.3 T.sub.4
T.sub.5 T.sub.6 T.sub.7 T.sub.melt (psi) (%) Example 1 15 75 25 170
80 105 137 150 145 142 140 155 60-70 50-60
[0051] The following examples were made similarly to those of
Example 1 with the exception that no glycerin was needed. All
processing conditions such as temperatures, screw speed, etc. from
Example 2 to Example 10 are listed in Table 2 below.
TABLE-US-00002 TABLE 2 Processing Conditions for Compounding TPMS
with Polyolef ins on ZSK-30 Resin Non- Feeding DNDA MF650X
Meltblown Extruder Rate TPMS 1082 PE PP PPH Speed Extruder
Temperature Profile (.degree. C.) P.sub.melt Torque Sample No.
(lb/hr) (%) (%) (%) (%) (rpm) T.sub.1 T.sub.2 T.sub.3 T.sub.4
T.sub.5 T.sub.6 T.sub.7 T.sub.melt (psi) (%) Example 2 20 10 90*
160 99 118 141 155 161 145 144 167 20-25 46-51 Example 3 20 20 80*
160 99 118 141 155 161 145 144 167 20-25 63-68 Example 4 20 30 70*
160 99 118 141 155 161 145 144 167 20-25 61-70 Example 5 20 25 75*
160 100 121 140 155 160 145 145 164 20-25 58-64 Example 6 20 10 90
160 100 120 140 155 160 147 145 162 10-20 61-66 Example 7 20 20 80
160 100 120 140 155 160 147 145 162 18-20 71-78 Example 8 20 30
70** 160 100 120 140 155 160 147 145 162 18-22 60-65 Example 9 20
Example 8 @ 50% 50* 160 100 120 140 155 160 147 145 162 20-23 40-43
Example 10 20 10 (M3766) 90* 160 140 150 160 160 160 160 164 191
120-125 64-66 *FUSABOND 353 chemically-modified polypropylene
copolymer used at about 1%. **FUSABOND E528 anhydride-modified
polyethylene used at about 1%.
[0052] Examples 2 to 5 were blends created using TPMS made from
Example 1 and meltblown-grade polypropylene with a
compatibilizer.
[0053] Examples 6 to 7 were blends created using TPMS made from
Example 1 and meltblown-grade polypropylene without any
compatibilizer.
[0054] Example 8 was a blend created using TPMS made from Example 1
and meltblown-grade polyethylene with a compatibilizer.
[0055] Example 9 was a blend created by compounding Example 8 and
the meltblown-grade PP using 5% INFUSE 9807 high-performance olefin
block copolymer as a compatibilizer for polyolefin resins.
[0056] Examples 10 is a blend created using non-meltblown-grade
polypropylene (PPH M3766) and TPMS with a compatibilizer.
[0057] Thermal Properties
[0058] The melt flow rate (MFR) is the weight of a polymer (in
grams) forced through an extrusion rheometer orifice (0.0825-inch
diameter) when subjected to a load of 2160 grams in 10 minutes,
typically at 190.degree. C. or 230.degree. C. Unless otherwise
indicated, the melt flow rate was measured in accordance with ASTM
Test Method D1239 with a melt indexer (Tinius Olsen, Willow Grove,
Pa.). The melt flow indexes for all 10 examples were measured and
are listed in Table 3. The melt flow index value for TPMS is close
to be negligible. In comparison to the neat meltblown-grade
polypropylene, the melt flow index values for the blends containing
TPMS are significantly lower. Example 8 is the blend using
meltblown-grade polyethylene and TPMS (70/30); its melt flow index
value is also significantly lower relative to the neat
meltblown-grade polyethylene.
TABLE-US-00003 TABLE 3 Fiber Blend Melt Flow Index (in g/10 min)
Example 1 2 3 4 5 6 7 8 9 10 MFI <0.5 646 499 375 412 609 478 60
200 13
[0059] A Differential Scanning calorimeter (DSC) analysis was
carried out to understand the thermal properties of the resin
samples. Pellet samples were analyzed using a TA Instruments Q200
Differential Scanning calorimeter. A DSC thermogram for a sample
(approximately 5 mg) in a sealed aluminum pan was recorded in the
temperature range of 50.degree. C. to 200 QC under a dynamic
nitrogen atmosphere using a heating/cooling rate of 10.degree.
C./min. Universal analysis NT software provided by TA Instruments
was used for analyzing data.
[0060] DSC thermograms (2nd heat) for blends of PP with TPMS
amounts ranging from 10% to 20% to 30% (resin samples made from
Examples 2, 3, and 4) are compared in FIG. 1. As shown in FIG. 2,
the melting temperatures for all blends are around 154.degree. C.,
which is the melting temperature of neat meltblown-grade
polypropylene. The results show that the melt temperature does not
vary significantly with increasing TPMS content. The melt enthalpy,
however, which is displayed in FIG. 3, decreased from 99 J/g (the
neat meltblown-grade polypropylene) to about 75 J/g for the PP/TPMS
(70/30) blend, indicating a decrease in crystallinity.
[0061] Fiber Spinning
[0062] A fiber spinning line (Davis Standard Corporation,
Pawcatuck, Conn.), which consists of two extruders, a quench
chamber, and a godet with a maximal speed of 3000 meters per minute
was used for melt fiber spinning. The spinning line had the
capacity to make monofilament, side-by-side, and sheath core
fibers. The spinning die plate used for the monofilament fiber
samples presented in this disclosure was a 16-hole plate with each
hole having a diameter of 0.4 mm. Only one extruder was used. Table
4 outlines the fiber spinning processing conditions and
corresponding sample codes.
TABLE-US-00004 TABLE 4 Fiber Spinning Parameters Extruders for
Sample 11 Sample No. Examples 2 to 4 Examples 6 to 7 Example 10
Sheath Core Extruder Zone 7 (.degree. C.) 175 160 210 200 180 Zone
6 (.degree. C.) 175 160 210 200 180 Zone 5 (.degree. C.) 165 160
174 200 180 Zone 4 (.degree. C.) 170 160 210 200 180 Zone 3
(.degree. C.) 170 150 210 195 180 Zone 2 (.degree. C.) 170 150 200
195 175 Zone 1 (.degree. C.) 153 140 165 195 175 Ext 1 Melt 90 65
1145 650 790 Outlet Pressure (psi) Spinning Spin Beam 180 160 190
195 Temp and (.degree. C.) Speed Godet Speed 700, 500, 300 700,
500, 300 300 700, 500, 300 (m/min) Misc. Ext 1 Melt 6.6 9 14.6 2 18
Pump (rpm) Pack Type Monofilament Monofilament Monofilament
Sheath/Core
[0063] Example 11 was a sheath core fiber, where the core material
was from Example 9 and the sheath material is PLA 6201 D
fiber-grade polylactic acid at a ratio of (90/10).
[0064] Fiber Properties
[0065] Individual fiber specimens were shortened (i.e., cut with
scissors) to 38 mm in length and placed separately on a black
velvet cloth. 10 to 15 fiber specimens were collected in this
manner. The fiber specimens were then mounted in a substantially
straight condition on a rectangular paper frame having external
dimensions of 51 mm.times.51 mm and internal dimensions of 25
mm.times.25 mm. The ends of each fiber specimen were operatively
attached to the frame by carefully securing the fiber ends to the
sides of the frame with adhesive tape. Each fiber specimen was then
measured for its external, cross-fiber dimension employing a
conventional laboratory microscope that was properly calibrated and
set at 40.times. magnification. This cross-fiber dimension was
recorded as the diameter of the individual fiber specimen. The
frame helped to mount the ends of the sample fiber specimens in the
upper and lower grips of a constant rate of extension type tensile
tester, MTS SYNERGY 200 tensile tester from MTS Systems Corporation
(Eden Prairie, Mich.).
[0066] Tenacity values were expressed in terms of gram-force per
denier. The denier is the mass in grams per 9000 meters of fiber.
Peak elongation (% strain at break), peak stress, and peak load
were also measured.
[0067] Fiber mechanical properties were determined for the blends
at 300 and 500 meters per minute drawing speeds. The properties of
fibers spun at 700 m/min were not tested. The results are tabulated
in Table 5.
TABLE-US-00005 TABLE 5 Fiber Mechanical Properties Fiber Drawing
Peak Peak Speed Load Stress Elongation Denier Example No. Blend
Ratio (m/min) (gf) (MPa) (%) Tenacity (gf) Example 2 PP/TPMS
(90/10) 300 3.6 30.7 132 0.37 9.3 500 2.5 37.0 277 0.47 5.4 Example
3 PP/TPMS (80/20) 300 3.8 33.4 693 0.42 8.9 500 2.5 39.6 655 0.50
5.2 Example 4 PP/TPMS (70/30) 300 3.4 27.1 581 0.34 10.2 500 2.0
41.6 472 0.52 3.9 Example 6 PP/TPMS (90/10) 300 2.0 27.6 188 0.35
6.0 500 2.1 44.1 235 0.56 4.0 Example 7 PP/TPMS (80/20) 300 1.9
27.2 164 0.34 6.9 500 1.8 35.8 199 0.46 5.1 Example 10 PP3766/TPMS
(90/10) 300 11.9 102 667 1.28 9.3 500 N/A N/A N/A N/A N/A Example
12 PLA/Example 9 (10/90) 300 8.7 37.5 233 0.47 21.3 500 5.4 48.8
197 0.61 9.9
[0068] As indicated, fiber elongation improved with an increasing
amount of the modified thermoplastic starch in Examples 3 and 4
relative to Example 2. The blends containing no FUSABOND
compatibilizer shown in Examples 6 and 7 can be spun into fibers
but fiber elongation is relatively low. Example 10 can be spun into
fiber only at 300 m/min; at 500 m/min the fiber could not be spun
for tenacity testing. The fiber diameters varied but were mostly
about 30 to 40 microns, depending on fiber drawing speed. The fiber
peak stress improved as fiber drawing speed is increased.
[0069] Meltblown-grade polyolefins are commonly used to make
meltblown webs for nonwoven applications. The prior art does not
teach how to compound meltblown-grade polyolefin with thermoplastic
modified starch for short-cut wet-laid microfibers in tissue or
towel applications. Fibers were surprisingly able to be spun from
the novel blends described herein. These new wet-laid microfiber
compositions and fabrication processes produced results not
previously thought possible.
[0070] In a first particular aspect, spun microfibers include a
blend of 70 wt. % to 90 wt. % meltblown-grade polyolefin and 10 wt.
% to 30 wt. % thermoplastic starch, wherein the microfibers are
suitable for use in a wet-laid process.
[0071] A second particular aspect includes the first particular
aspect, wherein the blend prior to spinning has a melt flow index
greater than 150.
[0072] A third particular aspect includes the first and/or second
aspect, wherein the microfibers are staple fibers.
[0073] A fourth particular aspect includes one or more of aspects
1-3, further including a surfactant treatment.
[0074] A fifth particular aspect includes one or more of aspects
1-4, the blend further including a compatibilizer.
[0075] A sixth particular aspect includes one or more of aspects
1-5, wherein the meltblown-grade polyolefin is polypropylene.
[0076] A seventh particular aspect includes one or more of aspects
1-6, wherein the meltblown-grade polyolefin is polyethylene.
[0077] An eighth particular aspect includes one or more of aspects
1-7, wherein the starch is a native starch derived from cereal
grains such as corn, waxy corn, wheat, sorghum, rice, and waxy
rice; tubers such as potatoes; roots such as tapioca, sweet potato,
and arrowroot; or the pith of the sago palm.
[0078] A ninth particular aspect includes one or more of aspects
1-8, wherein native starch has been modified to become
thermoplastic modified starch (TPMS).
[0079] In a tenth aspect, a method for producing spun microfibers
includes producing a blend of 70 wt. %-90 wt. % meltblown-grade
polyolefin with 10 wt. % to 30 wt. % thermoplastic modified starch
(TPMS) derived from native starch; and spinning the blend into
microfibers in a fiber spinning process, wherein the microfibers
are suitable for use in a wet-laid process.
[0080] An eleventh particular aspect includes the tenth particular
aspect, wherein the blend prior to spinning has a melt flow index
greater than 150.
[0081] A twelfth particular aspect includes the eleventh and/or
tenth aspect, further including cutting the microfibers into staple
fibers.
[0082] A thirteenth particular aspect includes one or more of
aspects 10-12, further including applying a surfactant treatment to
the microfibers.
[0083] A fourteenth particular aspect includes one or more of
aspects 10-13, wherein the blend further includes a
compatibilizer.
[0084] A fifteenth particular aspect includes one or more of
aspects 10-14, wherein the meltblown-grade polyolefin is
polypropylene.
[0085] A sixteenth particular aspect includes one or more of
aspects 10-15, wherein the meltblown-grade polyolefin is
polyethylene.
[0086] A seventeenth particular aspect includes one or more of
aspects 10-16, wherein the native starch is derived from cereal
grains such as corn, waxy corn, wheat, sorghum, rice, and waxy
rice; tubers such as potatoes; roots such as tapioca, sweet potato,
and arrowroot; or the pith of the sago palm.
[0087] In an eighteenth particular aspect, a method for producing
an absorbent product includes producing a blend of 70 wt. %-90 wt.
% meltblown-grade polyolefin with 10 wt. % to 30 wt. %
thermoplastic modified starch (TPMS), wherein the blend prior to
spinning has a melt flow index greater than 150; spinning the blend
into microfibers in a fiber spinning process; cutting the
microfibers into staple fibers; and incorporating the staple fibers
into a wet-laid process for making a nonwoven web.
[0088] A nineteenth particular aspect includes the eighteenth
particular aspect, further including converting the nonwoven web
into an absorbent product.
[0089] A twentieth particular aspect includes the eighteenth and/or
nineteenth aspects, wherein the absorbent product is a tissue
product.
[0090] In the interests of brevity and conciseness, any ranges of
values set forth in this disclosure contemplate all values within
the range and are to be construed as support for claims reciting
any sub-ranges having endpoints that are whole number values within
the specified range in question. By way of hypothetical example, a
disclosure of a range of from 1 to 5 shall be considered to support
claims to any of the following ranges: 1 to 5; 1 to 4; 1 to 3; 1 to
2; 2 to 5; 2 to 4; 2 to 3; 3 to 5; 3 to 4; and 4 to 5.
[0091] The dimensions and values disclosed herein are not to be
understood as being strictly limited to the exact numerical values
recited. Instead, unless otherwise specified, each such dimension
is intended to mean both the recited value and a functionally
equivalent range surrounding that value. For example, a dimension
disclosed as "40 mm" is intended to mean "about 40 mm."
[0092] All documents cited in the Detailed Description are, in
relevant part, incorporated herein by reference; the citation of
any document is not to be construed as an admission that it is
prior art with respect to the present disclosure. To the extent
that any meaning or definition of a term in this written document
conflicts with any meaning or definition of the term in a document
incorporated by references, the meaning or definition assigned to
the term in this written document shall govern.
[0093] While particular aspects of the present disclosure have been
illustrated and described, it would be obvious to those skilled in
the art that various other changes and modifications can be made
without departing from the spirit and scope of the disclosure. It
is therefore intended to cover in the appended claims all such
changes and modifications that are within the scope of this
disclosure.
* * * * *