US20190330770A1

US20190330770A1 - Wet-laid microfibers including polyolefin and thermoplastic starch

Info

Publication number: US20190330770A1
Application number: US16/467,516
Authority: US
Inventors: Bo Shi; Gregory J. Wideman; Thomas G. Shannon; Mark M. Mleziva
Original assignee: Kimberly Clark Worldwide Inc
Current assignee: Kimberly Clark Worldwide Inc
Priority date: 2016-12-16
Filing date: 2016-12-16
Publication date: 2019-10-31
Also published as: WO2018111299A1

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.

Description

BACKGROUND

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.
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.
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.
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

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.
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.
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.
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.
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.
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

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:

FIG. 1 graphically illustrates Differential Scanning calorimeter (DSC) thermograms (2nd heat) of PP/TPMS blend samples;

FIG. 2 graphically illustrates the effect of composition (Wt % TPMS) on melt temperature of PP/TPMS blends; and

FIG. 3 graphically illustrates the effect of composition (Wt % TPMS) on melt enthalpy of PP/TPMS blends.

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

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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.”
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.
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.
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.
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.
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.
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.
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.
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

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.
Materials
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/cm³, its particle sizes pass 98% min through 140 Mesh, and it is supplied as off-white powders.
METOCENE MF650X metallocene polypropylene homopolymer, purchased from Lyondellbasell (Carrollton, Tex.), has a specific density of 0.91 g/cm³and a melt flow index (230° C./2.16 kg) of 1200 g/10 min.
DNDA-1082 linear low density polyethylene, purchased from the Dow Chemical Company (Midland, Mich.), has a specific density is 0.94 g/cm³and a melt flow index (190° C./2.16 kg) of 160 g/10 min.
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/cm³and 18 g/10 min (190° C./2.16 kg) and those for PPH M3766 are 0.90 g/cm³and 23 g/10 min (190° C./2.16 kg).
PLA 6201 D fiber-grade polylactic acid was purchased from NatureWorks (Minnetonka, Minn.), with a specific density of 1.24 g/cm³and a melt flow index (190° C./2.16 kg) of 15 to 30 g/10 min.
FUSABOND E528 anhydride-modified polyethylene and FUSABOND 353 chemically-modified polypropylene copolymer are used as compatibilizers, purchased from DuPont (Wilmington, Del.).
INFUSE 9807 high-performance olefin block copolymer is purchased from the Dow Chemical Company (Midland, Mich.). It has a density of 0.87 g/cm³and a melt flow index of 15 g/10 min (190° C. and 2.16 kg).
Masil SF-19 is a surfactant used to make a fiber surface hydrophilic. It was purchased from Lubrizol Inc. (Spartanburg, S.C.).
Material Processing

Example 1: Making Thermoplastic Modified Starch (TPMS) Using GLUCOSOL 800 Biopolymer

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 1

Processing Conditions for Making TPMS on ZSK-30

Material

Feeding

Extruder

Sample

Rate

Modified

Glycerin

Speed

Extruder Temperature Profile (° C.)

P_melt

Torque

No.	(lb/hr)	Starch	(%)	(rpm)	T₁	T₂	T₃	T₄	T₅	T₆	T₇	T_melt	(psi)	(%)

Example 1	15	75	25	170	80	105	137	150	145	142	140	155	60-70	50-60

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 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 (° C.)

P_melt

Torque

Sample No.

(lb/hr)

(%)

(rpm)

T₁

T₂

T₃

T₄

T₅

T₆

T₇

T_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%.

Examples 2 to 5 were blends created using TPMS made from Example 1 and meltblown-grade polypropylene with a compatibilizer.
Examples 6 to 7 were blends created using TPMS made from Example 1 and meltblown-grade polypropylene without any compatibilizer.
Example 8 was a blend created using TPMS made from Example 1 and meltblown-grade polyethylene with a compatibilizer.
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.
Examples 10 is a blend created using non-meltblown-grade polypropylene (PPH M3766) and TPMS with a compatibilizer.
Thermal Properties
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° C. or 230° 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 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

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° C. to 200 QC under a dynamic nitrogen atmosphere using a heating/cooling rate of 10° C./min. Universal analysis NT software provided by TA Instruments was used for analyzing data.
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° 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.
Fiber Spinning
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 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 (° C.)	175	160	210	200	180
	Zone 6 (° C.)	175	160	210	200	180
	Zone 5 (° C.)	165	160	174	200	180
	Zone 4 (° C.)	170	160	210	200	180
	Zone 3 (° C.)	170	150	210	195	180
	Zone 2 (° C.)	170	150	200	195	175
	Zone 1 (° 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

(° C.)

Speed

Godet Speed

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

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).
Fiber Properties
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×51 mm and internal dimensions of 25 mm×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× 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.).
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.
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 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

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.
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.
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.
A second particular aspect includes the first particular aspect, wherein the blend prior to spinning has a melt flow index greater than 150.
A third particular aspect includes the first and/or second aspect, wherein the microfibers are staple fibers.
A fourth particular aspect includes one or more of aspects 1-3, further including a surfactant treatment.
A fifth particular aspect includes one or more of aspects 1-4, the blend further including a compatibilizer.
A sixth particular aspect includes one or more of aspects 1-5, wherein the meltblown-grade polyolefin is polypropylene.
A seventh particular aspect includes one or more of aspects 1-6, wherein the meltblown-grade polyolefin is polyethylene.
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.
A ninth particular aspect includes one or more of aspects 1-8, wherein native starch has been modified to become thermoplastic modified starch (TPMS).
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.
An eleventh particular aspect includes the tenth particular aspect, wherein the blend prior to spinning has a melt flow index greater than 150.
A twelfth particular aspect includes the eleventh and/or tenth aspect, further including cutting the microfibers into staple fibers.
A thirteenth particular aspect includes one or more of aspects 10-12, further including applying a surfactant treatment to the microfibers.
A fourteenth particular aspect includes one or more of aspects 10-13, wherein the blend further includes a compatibilizer.
A fifteenth particular aspect includes one or more of aspects 10-14, wherein the meltblown-grade polyolefin is polypropylene.
A sixteenth particular aspect includes one or more of aspects 10-15, wherein the meltblown-grade polyolefin is polyethylene.
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.
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.
A nineteenth particular aspect includes the eighteenth particular aspect, further including converting the nonwoven web into an absorbent product.
A twentieth particular aspect includes the eighteenth and/or nineteenth aspects, wherein the absorbent product is a tissue product.
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.
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.”
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.
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.

Claims

We claim:

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.