METHOD FOR FORMING BIODEGRADABLE POLYLACTIC ACIDS FOR USE

IN FORMING FIBERS Background of the Invention

Biodegradable nonwoven webs are useful in a wide range of applications, such as in the formation of disposable absorbent products (e.g., diapers, training pants, sanitary wipes, feminine pads and liners, adult incontinence pads, guards, garments, etc.). To facilitate formation of the nonwoven web, a biodegradable polymer should be selected that is melt processable, yet also has good mechanical and physical properties. Polylactic acid ("PLA") is a common biodegradable and sustainable (renewable) polymer. Although various attempts have been made to use polylactic acid in the formation of nonwoven webs, its high molecular weight and viscosity have generally restricted its use to only certain types of fiber forming processes. For example, conventional polylactic acids are not typically suitable for meltblowing processes, which require a low polymer viscosity for successful microfiber formation. As such, a need currently exists for a biodegradable polylactic acid that exhibits good mechanical and physical properties, but which may be readily formed into a nonwoven web using a variety of techniques (e.g., meltblowing).

Summary of the Invention In accordance with one embodiment of the present invention, a method for forming a biodegradable polymer for use in fiber formation is disclosed. The method comprises supplying a first polylactic acid to a single screw extruder. The first polylactic acid has a water content of from about 500 ppm to about 5000 ppm, based on the dry weight of the first polylactic acid. The single screw extruder contains a screw that is rotatably mounted and received within a barrel, the screw having a length to diameter ratio of from about 15 to about 50. The method further comprises melt processing the first polylactic acid within the extruder so that the polylactic acid undergoes a hydrolysis reaction that results in a second, hydrolytically degraded polylactic acid having a melt flow rate that is greater than the melt flow rate of the first polylactic acid.

Other features and aspects of the present invention are discussed in greater detail below.

Brief Description of the Drawings

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, which makes reference to the appended figures in which:

Fig. 1 is a cross-sectional view of one embodiment of a single screw extruder that may be used in the present invention;

Fig. 2 is an exploded cross-sectional view of one embodiment of a barrier screw that may be used in the present invention; Fig. 3 is a schematic illustration of a process that may be used in one embodiment of the present invention to form a nonwoven web;

Fig. 4 is a schematic illustration of a process that may be used in one embodiment of the present invention to form a coform web; and

Fig. 5 is a perspective view of one embodiment of an absorbent article that may be formed according to the present invention.

Repeat use of references characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention.

Detailed Description of Representative Embodiments Reference now will be made in detail to various embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. Definitions

As used herein, the term "biodegradable" or "biodegradable polymer" generally refers to a material that degrades from the action of naturally occurring microorganisms, such as bacteria, fungi, and algae; environmental heat; moisture;

or other environmental factors. The biodegradability of a material may be determined using ASTM Test Method 5338.92.

As used herein, the term "fibers" refer to elongated extrudates formed by passing a polymer through a forming orifice such as a die. Unless noted otherwise, the term "fibers" includes discontinuous fibers having a definite length and substantially continuous filaments. Substantially filaments may, for instance, have a length much greater than their diameter, such as a length to diameter ratio ("aspect ratio") greater than about 15,000 to 1 , and in some cases, greater than about 50,000 to 1. As used herein, the term "monocomponent" refers to fibers formed from one polymer. Of course, this does not exclude fibers to which additives have been added for color, anti-static properties, lubrication, hydrophilicity, liquid repellency, etc.

As used herein, the term "multicomponent" refers to fibers formed from at least two polymers (e.g., bicomponent fibers) that are extruded from separate extruders. The polymers are arranged in substantially constantly positioned distinct zones across the cross-section of the fibers. The components may be arranged in any desired configuration, such as sheath-core, side-by-side, segmented pie, island-in-the-sea, and so forth. Various methods for forming multicomponent fibers are described in U.S. Patent Nos. 4,789,592 to Taniguchi et aL. and U.S. Patent No. 5,336,552 to Strack et al., 5,108,820 to Kaneko, et al.. 4,795,668 to Krueqe, et a!.. 5,382,400 to Pike, et al., 5,336,552 to Strack, et aL and 6,200,669 to Marmon, et al., which are incorporated herein in their entirety by reference thereto for all purposes. Multicomponent fibers having various irregular shapes may also be formed, such as described in U.S. Patent Nos. 5,277,976 to Hoqle, et al., 5,162,074 to HiTJs, 5,466,410 to HJIs, 5,069,970 to Larqman, et al., and 5,057,368 to Larqman, et al., which are incorporated herein in their entirety by reference thereto for all purposes.

As used herein, the term "multiconstituent" refers to fibers formed from at least two polymers (e.g., biconstituent fibers) that are extruded as a blend. The polymers are not arranged in substantially constantly positioned distinct zones across the cross-section of the fibers. Various multiconstituent fibers are described in U.S. Patent No. 5,108,827 to Gessner, which is incorporated herein in

its entirety by reference thereto for all purposes.

As used herein, the term "nonwoven web" refers to a web having a structure of individual fibers that are randomly interlaid, not in an identifiable manner as in a knitted fabric. Nonwoven webs include, for example, meltblown webs, spunbond webs, carded webs, wet-laid webs, airlaid webs, coform webs, hydraulically entangled webs, etc. The basis weight of the nonwoven web may generally vary, but is typically from about 5 grams per square meter ("gsm") to 200 gsm, in some embodiments from about 10 gsm to about 150 gsm, and in some embodiments, from about 15 gsm to about 100 gsm. As used herein, the term "meltblown" web or layer generally refers to a nonwoven web that is formed by a process in which a molten thermoplastic material is extruded through a plurality of fine, usually circular, die capillaries as molten fibers into converging high velocity gas (e.g. air) streams that attenuate the fibers of molten thermoplastic material to reduce their diameter, which may be to 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. Patent Nos. 3,849,241 to Butin, et al.; 4,307,143 to Meitner, et al.; and 4,707,398 to Wisneski, et al., which are incorporated herein in their entirety by reference thereto for all purposes. Meltblown fibers may be substantially continuous or discontinuous, and are generally tacky when deposited onto a collecting surface.

As used herein, the term "spunbond" web or layer generally refers to a nonwoven web containing small diameter substantially continuous filaments. The filaments are formed by extruding a molten thermoplastic material from a plurality of fine, usually circular, capillaries of a spinnerette with the diameter of the extruded filaments then being rapidly reduced as by, for example, eductive drawing and/or other well-known spunbonding mechanisms. The production of spunbond webs is described and illustrated, for example, in U.S. Patent Nos. 4,340,563 to Appel, et al., 3,692,618 to Dorschner, et al., 3,802,817 to Matsuki, et aL, 3,338,992 to Kinnev, 3,341 ,394 to Kinney, 3,502,763 to Hartman, 3,502,538 to Lew, 3,542,615 to Dobo, et al., and 5,382,400 to Pike, et al.. which are incorporated herein in their entirety by reference thereto for all purposes.

Spunbond filaments are generally not tacky when they are deposited onto a collecting surface. Spunbond filaments may sometimes have diameters less than about 40 micrometers, and are often between about 5 to about 20 micrometers.

As used herein, the term "coform web" generally refers to a composite material containing a mixture or stabilized matrix of thermoplastic fibers and a second non-thermoplastic material. As an example, coform materials may be made by a process in which at least one meltblown die head is arranged near a chute through which other materials are added to the web while it is forming. Such other materials may include, but are not limited to, fibrous organic materials such as woody or non-woody pulp such as cotton, rayon, recycled paper, pulp fluff and also superabsorbent particles, inorganic and/or organic absorbent materials, treated polymeric staple fibers and so forth. Some examples of such coform materials are disclosed in U.S. Patent Nos. 4,100,324 to Anderson, et al.; 5,284,703 to Everhart, et al.; and 5,350,624 to Georqer, et al.; which are incorporated herein in their entirety by reference thereto for all purposes.

Detailed Description

The present invention is directed to a method for forming a biodegradable polylactic acid suitable for use in fibers. Specifically, a polylactic acid is melt processed in an extruder at a controlled water content to initiate a hydrolysis reaction. Without intending to be limited by theory, it is believed that the hydroxyl groups present in water are capable of attacking the ester linkage of polylactic acid, thereby leading to chain scission or "depolymerization" of the polylactic acid molecule into one or more shorter ester chains. The extruder within which the polylactic acid is melt processed in a single screw extruder and contains a screw rotatably mounted and received within a barrel. The screw has a length-to- diameter ("UO") ratio of from about 15 to about 50. With such a single screw extruder, the present inventors have discovered that the reaction components may be effectively mixed together in a highly efficient and cost-effective manner. Further, by selectively controlling the extrusion conditions (e.g., water content, temperature, shear rate, etc.), a hydrolytically degraded polylactic acid may be achieved that has a molecular weight lower than the starting polymer. Such lower molecular weight polymers have a higher melt flow rate and lower apparent viscosity, which are useful in a wide variety of fiber forming applications, such as in

the meltblowing of nonwoven webs. I. Reaction Components A. Polylactic Acid

Polylactic acid may generally be derived from monomer units of any isomer of lactic acid, such as levorotory-lactic acid ("L-lactic acid"), dextrorotatory-lactic acid ("D-lactic acid"), meso-lactic acid, or mixtures thereof. Monomer units may also be formed from anhydrides of any isomer of lactic acid, including L-lactide, D- lactide, meso-lactide, or mixtures thereof. Cyclic dimers of such lactic acids and/or lactides may also be employed. Any known polymerization method, such as polycondensation or ring-opening polymerization, may be used to polymerize lactic acid. A small amount of a chain-extending agent (e.g., a diisocyanate compound, an epoxy compound or an acid anhydride) may also be employed. The polylactic acid may be a homopolymer or a copolymer, such as one that contains monomer units derived from L-lactic acid and monomer units derived from D-lactic acid. Although not required, the rate of content of one of the monomer unit derived from L-lactic acid and the monomer unit derived from D-lactic acid is preferably about 85 mole% or more, in some embodiments about 90 mole% or more, and in some embodiments, about 95 mole% or more. Multiple polylactic acids, each having a different ratio between the monomer unit derived from L-lactic acid and the monomer unit derived from D-lactic acid, may be blended at an arbitrary percentage. Of course, polylactic acid may also be blended with other types of polymers (e.g., polyolefins, polyesters, etc.) to provided a variety of different of benefits, such as processing, fiber formation, etc.

In one particular embodiment, the polylactic acid has the following general structure:

One specific example of a suitable polylactic acid polymer that may be used in the present invention is commercially available from Biomer, Inc. of Krailling, Germany) under the name BIOMER™ L9000. Other suitable polylactic acid polymers are commercially available from Natureworks LLC of Minnetonka,

Minnesota (NATUREWORKS®) or Mitsui Chemical (LACEA™). Still other suitable polylactic acids may be described in U.S. Patent Nos. 4,797,468; 5,470,944; 5,770,682; 5,821 ,327; 5,880,254; and 6,326,458, which are incorporated herein in their entirety by reference thereto for all purposes. The polylactic acid typically has a number average molecular weight ("M _n ") ranging from about 40,000 to about 160,000 grams per mole, in some embodiments from about 50,000 to about 140,000 grams per mole, and in some embodiments, from about 80,000 to about 120,000 grams per mole. Likewise, the polymer also typically has a weight average molecular weight ("M _w ") ranging from about 80,000 to about 200,000 grams per mole, in some embodiments from about 100,000 to about 180,000 grams per mole, and in some embodiments, from about 110,000 to about 160,000 grams per mole. The ratio of the weight average molecular weight to the number average molecular weight ("M _w /M _n ") _> i-β-, the "polydispersity index", is also relatively low. For example, the polydispersity index typically ranges from about 1.0 to about 3.0, in some embodiments from about 1.1 to about 2.0, and in some embodiments, from about 1.2 to about 1.8. The weight and number average molecular weights may be determined by methods known to those skilled in the art.

The polylactic acid may also have an apparent viscosity of from about 50 to about 600 Pascal seconds (Pa-s), in some embodiments from about 100 to about 500 Pa-s, and in some embodiments, from about 200 to about 400 Pa-s, as determined at a temperature of 190 ⁰ C and a shear rate of 1000 sec ^"1 . The melt flow rate of the polylactic acid (on a dry basis) may also range from about 0.1 to about 40 grams per 10 minutes, in some embodiments from about 0.5 to about 20 grams per 10 minutes, and in some embodiments, from about 5 to about 15 grams per 10 minutes. The melt flow rate is the weight of a polymer (in grams) that may be forced through an extrusion rheometer orifice (0.0825-inch diameter) when subjected to a load of 2160 grams in 10 minutes at a certain temperature (e.g., 190 ⁰ C), measured in accordance with ASTM Test Method D1238-E. The polylactic acid also typically has a melting point of from about 100 ⁰ C to about 240 ⁰ C, in some embodiments from about 120 ⁰ C to about 220 ⁰ C, and in some embodiments, from about 140 ⁰ C to about 200 ⁰ C. Such polylactic acids are useful in that they biodegrade at a fast rate. The glass transition temperature

("T _g ") of the polylactic acid may be relatively high, such as from about 10 ⁰ C to about 80 ⁰ C, in some embodiments from about 20 ⁰ C to about 70 ⁰ C, and in some embodiments, from about 25 ⁰ C to about 65°C. As discussed in more detail below, the melting temperature and glass transition temperature may all be determined using differential scanning calorimetry ("DSC") in accordance with ASTM D-3417. B. Water

Under appropriate conditions, water is capable of hydrolytically degrading the starting polylactic acid and thus reducing its molecular weight. More specifically, it is believed that the hydroxyl groups of water can attack the ester linkages of the polylactic acid, thereby leading to chain scission or

"depolymerization" of the polylactic acid molecule into one or more shorter ester chains. The shorter chains may include polylactic acids, as well as minor portions of lactic acid monomers or oligomers, and combinations of any of the foregoing. The amount of water employed relative to the polylactic acid affects the extent to which the hydrolysis reaction is able to proceed. However, if the water content is too great, the natural saturation level of the polymer may be exceeded, which may adversely affect resin melt properties and the physical properties of the resulting fibers. Thus, in most embodiments of the present invention, the water content is from about 500 to about 5000 parts per million ("ppm"), in some embodiments from about 1000 to about 4500 ppm, in some embodiments from about 2000 to about 3500 ppm, and in some embodiments, from about 2200 to about 3000 ppm, based on the dry weight of the starting polylactic acid. The water content may be determined in a variety of ways as is known in the art, such as in accordance with ASTM D 7191-05, such as described in more detail below. The technique employed to achieve the desired water content is not critical to the present invention. In fact, any of a variety of well known techniques for controlling water content may be employed, such as described in U.S. Patent Application Publication Nos. 2005/0004341 to Culbert, et al. and 2001/0003874 to Gillette, et al., which are incorporated herein in their entirety by reference thereto for all purposes. For example, the water content of the starting polymer may be controlled by selecting certain storage conditions, drying conditions, the conditions of humidification, etc. In one embodiment, for example, the polylactic acid may be humidified to the desired water content by contacting pellets of the polymer with an

aqueous medium (e.g., liquid or gas) at a specific temperature and for a specific period of time. This enables a targeted water diffusion into the polymer structure (moistening). For example, the polymer may be stored in a package or vessel containing humidified air. Further, the extent of drying of the polymer during manufacture of the polymer may also be controlled so that the starting polylactic acid has the desired water content. In still other embodiments, water may be added during melt processing of the polylactic acid as described herein. Thus, the term "water content" is meant to include the combination of any residual moisture (e.g., the amount of water present due to conditioning, drying, storage, etc.) and also any water specifically added during melt processing. C. Plasticizer

Although not required, a plasticizer may be used in certain embodiments of the present invention to help lower the viscosity of the polylactic acid and improve its flexibility. Plasticizers are liquid, semi-solid, or solid compounds having a relatively low molecular weight, such as from about 200 to about 10,000, in some embodiments, from about 300 to about 9,000, and in some embodiments, from about 500 to about 8,500. Any plasticizer that is compatible with the selected polylactic acid may generally be employed in the present invention, such as phthalates; esters (e.g., phosphate esters, ether diesters, carboxylic esters, epoxidized esters, aliphatic diesters, polyesters, copolyesters, etc.); alkylene glycols (e.g., ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol, etc.); alkane diols (e.g., 1 ,3-propanediol, 2,2-dimethyl-1 ,3-propanediol, 1 ,3- butanediol, 1 ,4-butanediol, 1 ,5-pentanediol, 1 ,6-hexanediol, 2,2,4-trimethyl-1 ,6- hexanediol, 1 ,3-cyclohexanedimethanol, 1 ,4-cyclohexanedimethanol, 2,2,4,4- tetramethyl-1 ,3-cyclobutanediol, etc.); alkylene oxides (e.g., polyethylene oxide, polypropylene oxide, etc.); and so forth. Certain plasticizers, such as alkylene glycols, alkane diols, alkylene oxides, etc., may possess one or more hydroxyl groups that can also attack the ester linkages of the polylactic acid and result in chain scission. In this manner, such plasticizers may not only improve the flexibility of the polylactic acid, but they may also facilitate the hydrolysis reaction described above. Polyethylene glycol ("PEG"), for instance, is an example of a plasticizer that is particularly effective in facilitating the hydrolytic degradation of

the polylactic acid. The polyethylene glycol employed as a modifier additive can have different molecular weights ranging from number average molecular weight of about 300 to a number average molecular weight of about 10,000 or higher. Suitable PEGs are commercially available from a variety of sources under designations such as PEG 600, PEG 8000, etc. Examples of such PEGs include Carbowax™, which is available from Dow Chemical Co. of Midland, Michigan.

Another suitable plasticizer that may be employed in the present invention is a polyether copolymer contains a repeating unit (A) having the following formula:

C ₂ H ₄ O

(A) wherein, x is an integer from 1 to 250, in some embodiments from 2 to 200, and in some embodiments, from 4 to 150, and also a repeating unit (B) having the following formula:

(B) wherein, n is an integer from 3 to 20, in some embodiments from 3 to 10, and in some embodiments, from 3 to 5; and y is an integer from 1 to 150, in some embodiments from 2 to 125, and in some embodiments, from 4 to 100. Specific examples of monomers for use in forming the repeating unit (B) may include, for instance, 1 ,2-propanediol ("propylene glycol"); 1 ,3-propanediol ("trimethylene glycol"); 1 ,4-butanediol ("tetramethylene glycol"); 2,3-butanediol ("dimethylene glycol"); 1 ,5-pentanediol; 1 ,6-hexanediol; 1 ,9-nonanediol; 2-methyl-1 ,3-propanediol; neopentyl glycol; 2- methyl-1 ,4-butanediol; 3-methyl-1 ,5-pentanediol; 3-oxa-1 ,5-pentanediol ("diethylene glycol"); spiro-glycols, such as 3,9-bis(1 ,1-dimethyl-2-hydroxyethyl)- 2,4,8,10-tetraoxa-spiro [5,5] undecane and 3,9-diethanol-2,4,8,10-tetraoxa-spiro [5,5] undecane; and so forth. Among these polyols, propylene glycol, dimethylene glycol, trimethylene glycol, and tetramethylene glycol are particularly suitable for

use in the present invention. In one particular embodiment, for example, the polyether copolymer may have the following general structure: wherein, x is an integer from 1 to 250, in some embodiments from 2 to 200, and in some embodiments, from 4 to 150; y is an integer from 1 to 150, in some embodiments from 2 to 125, and in some embodiments, from 4 to 100; z is an integer from 0 to 200, in some embodiments from 2 to 125, and in some embodiments from 4 to 100; n is an integer from 3 to 20, in some embodiments from 3 to 10, and in some embodiments, from 3 to 6;

A is hydrogen, an alkyl group, an acyl group, or an aryl group of 1 to 10 carbon atoms, and B is hydrogen, an alkyl group, an acyl group, or an aryl group of 1 to 10 carbon atoms. When "z" is greater than 0, for example, the copolymer has an "ABA" configuration and may include, for instance, polyoxyethylene / polyoxypropylene / polyoxyethylene copolymers (EO/PO/EO) such as described in U.S. Patent Application Publication No. 2003/0204180 to Huang, et al., which is incorporated herein in its entirety by reference thereto for all purposes. Suitable EO/PO/EO polymers for use in the present invention are commercially available under the trade name PLURONIC® (e.g., F-68, F-127 L-122, L-92, L-81 , and L-61 ) from BASF Corporation, Mount Olive, New Jersey.

When employed, plasticizer(s) may be present in an amount of about 0.1 wt.% to about 20 wt.%, in some embodiments from about 0.2 wt.% to about 10 wt.%, and in some embodiments, from about 0.5 wt.% to about 5 wt.%, based on the dry weight of the starting polylactic acid. It should be understood, however, that a plasticizer is not required. In fact, in some embodiments of the present invention, the reactive composition is substantially free of any plasticizers, e.g., less than about 0.5 wt.% based on the dry weight of the starting polylactic acid.

D. Other Components

Other components may of course be utilized for a variety of different reasons. For instance, a wetting agent may be employed in some embodiments of the present invention to improve hydrophilicity. Wetting agents suitable for use in the present invention are generally compatible with polylactic acids. Examples of suitable wetting agents may include surfactants, such as UNITHOX® 480 and UNITHOX® 750 ethoxylated alcohols, or UNICID™ acid amide ethoxylates, all available from Petrolite Corporation of Tulsa, OkIa. Other suitable wetting agents are described in U.S. Patent No. 6,177,193 to Tsai, et al., which is incorporated herein in its entirety by reference thereto for all relevant purposes. Still other materials that may be used include, without limitation, melt stabilizers, processing stabilizers, heat stabilizers, light stabilizers, antioxidants, pigments, surfactants, waxes, flow promoters, particulates, and other materials added to enhance processability. When utilized, such additional ingredients are each typically present in an amount of less than about 5 wt.%, in some embodiments less than about 1 wt.%, and in some embodiments, less than about 0.5 wt.%, based on the dry weight of the starting polylactic acid.

A nucleating agent may be employed if desired to improve processing and to facilitate crystallization during quenching. Suitable nucleating agents for use in the present invention may include, for instance, inorganic acids, carbonates (e.g., calcium carbonate or magnesium carbonate), oxides (e.g., titanium oxide, silica, or alumina), nitrides (e.g., boron nitride), sulfates (e.g., barium sulfate), silicates (e.g., calcium silicate), stearates, benzoates, carbon black, graphite, and so forth. Still another suitable nucleating agent that may be employed is a "macrocyclic ester oligomer", which generally refers to a molecule with one or more identifiable structural repeat units having an ester functionality and a cyclic molecule of 5 or more atoms, and in some cases, 8 or more atoms covalently connected to form a ring. The ester oligomer generally contains 2 or more identifiable ester functional repeat units of the same or different formula. The oligomer may include multiple molecules of different formulae having varying numbers of the same or different structural repeat units, and may be a co-ester oligomer or multi-ester oligomer ( i.e., an oligomer having two or more different structural repeat units having an ester functionality within one cyclic molecule). Particularly suitable macrocyclic

ester oligomers for use in the present invention are macrocyclic poly(alkylene dicarboxylate) oligomers having a structural repeat unit of the formula: o o H H

— O— R ¹ — O C— A— C wherein, R ¹ is an alkylene, cycloalkylene, or a mono- or polyoxyalkylene group, such as those containing a straight chain of about 2-8 atoms; and A is a divalent aromatic or alicyclic group.

Specific examples of such ester oligomers may include macrocyclic poly(1 ,4-butylene terephthalate), macrocyclic poly(ethylene terephthalate), macrocyclic poly(1 ,3-propylene terephthalate), macrocyclic poly(1 ,4-butylene isophthalate), macrocyclic poly(1 ,4-cyclohexylenedimethylene terephthalate), macrocyclic poly(1 ,2-ethylene 2,6-naphthalenedicarboxylate) oligomers, co-ester oligomers comprising two or more of the above monomer repeat units, and so forth. Macrocyclic ester oligomers may be prepared by known methods, such as described in U.S. Patent Nos. 5,039,783; 5,231 ,161 ; 5,407,984; 5,527,976;

5,668,186; 6,420,048; 6,525,164; and 6,787,632. Alternatively, macrocyclic ester oligomers that may be used in the present invention are commercially available. One specific example of a suitable macrocyclic ester oligomer is macrocyclic poly(1 ,4-butylene terephthalate), which is commercially available from Cyclics Corporation under the designation CBT® 100.

The amount of nucleating agents may be selectively controlled to achieve the desired properties for the fibers. For example, nucleating agents may be present in an amount of about 0.1 wt.% to about 25 wt.%, in some embodiments from about 0.2 wt.% to about 15 wt.%, in some embodiments from about 0.5 wt.% to about 10 wt.%, and in some embodiments, from about 1 wt.% to about 5 wt.%, based on the dry weight of the starting polylactic acid. II. Reaction Technique

The reaction is conducted while the starting polymer is in the melt phase ("melt processing") to minimize the need for additional solvents and/or solvent removal processes. More specifically, the reaction components (e.g., biodegradable polymer, water, plasticizer, etc.) are supplied separately or in combination (e.g., in a solution) to a single screw extruder that includes a screw

rotatably mounted and received within a barrel (e.g., cylindrical barrel), which may be heated. The reaction components are moved downstream from a feed end to a discharge end by forces exerted by rotation of the screw. Such single screw extruders are typically divided into three sections along the length of the screw. The first section is a feed section where the solid material is introduced to the screw. The second section is a melting section where a majority of the melting of the solid occurs. Within this section, the screw generally possesses a tapered diameter to enhance melting of the polymer. The third section is the mixing section, which delivers the molten material in a constant amount for extrusion. Referring to Fig. 1 , for example, one embodiment of a single screw extruder

12 is shown that includes a hopper 10 for loading the raw materials and a single screw 2 rotatably mounted and received within a barrel 3. In this embodiment, the extruder 12 defines at least one feed section 4, melting section 6, and mixing section 8. According to the present invention, the ratio of the length to diameter ("UD") of the screw may be selected to achieve an optimum balance between throughput and polylactic acid degradation. For example, too large of an L/D value may increase the retention time to such an extent that the polylactic acid degrades beyond the desired level. On other hand, too low of an L/D value may not result in the desired hydrolysis reaction. Thus, the L/D value is typically from about 15 to about 50, in some embodiments from about 20 to about 45, and in some embodiments from about 25 to about 40. Such L/D ratios may be readily achieved in a single screw extruder by using mixing section(s) that constitute only a small portion of the length of the screw.

The configuration of the screw is not particularly critical to the present invention and it may contain any number and/or orientation of threads and channels as is known in the art. As shown in Fig. 1 , for example, the screw 2 contains a thread 7 that forms a generally helical channel radially extending around a core of the screw 2. The axial distance of one turn of the thread 7 is called "pitch". Referring to Fig. 2, another embodiment of a screw 41 that may be employed in the present invention is shown. The screw 41 of this embodiment includes threads 42 and 43 that extend helically around a core 40. The thread 43 separates the threads 42 into two distinctly sized channels 49 and 48. In this regard, the thread 43 may act as a barrier to prevent unmelted solid particles from

passing between the channels and through the extruder until it is melted. Such "barrier screws" may thus provide improved product quality and stability, and may also ensure that the polylactic acid undergoes the desired degradation during melt processing. In addition to the L/D ratio and screw design, other aspects of the single screw extruder may also be selected to achieve the desired degradation of the polylactic acid. For example, before exiting the extruder through a die, the molten plastic may first travel through one or more screens ("screen pack") within the barrel that are optionally reinforced by a breaker plate. In addition to removing contaminants and unmelted solids, the screen pack/breaker plate assembly also helps create back pressure in the barrel to enhance the melt uniformity and mixing of the polymer. The amount of head pressure can be controlled by varying the configuration of the screen pack (the number of screens, hole size of the screens, etc.). The screen pack may include, for instance, from 2 to 15 screens, in some embodiments from 3 to 10 screens, and in some embodiments, from 4 to 8 screens. When multiple screens are employed, the upstream screens are generally of a size to collect only large particles while subsequent downstream screens are of a size to collect increasingly smaller particles. Although screens of various sizes may be employed, it is typically desired that the pack employ at least one screen having openings of a relatively small size to create a high enough back pressure in the barrel. For example, the screen may contain openings having an average width (or diameter) of about 100 micrometers or less, in some embodiments about 75 micrometers or less, and in some embodiments, from about 1 to about 50 micrometers. Preferably, the pack employs multiple screens (e.g., 3 or more) having openings of this size.

The speed of the screw may also be selected to achieve the desired residence time, shear rate, melt processing temperature, etc. Generally, an increase in product temperature is observed with increasing screw speed due to the additional mechanical energy input into the system. The frictional energy results from the shear exerted by the turning screw on the materials within the extruder and results in the fracturing of large molecules. The degree of such fracturing will depend on the moisture content. This molecular degradation results in lowering the apparent viscosity and increasing the melt flow rate of the finished

material. For example, the screw speed may range from about 50 to about 200 revolutions per minute ("rpm"), in some embodiments from about 70 to about 150 rpm, and in some embodiments, from about 80 to about 120 rpm. As a result, melt processing may occur at a temperature of from about 100°C to about 500°C, in some embodiments, from about 150°C to about 35O ⁰ C, and in some embodiments, from about 150°C to about 300 ⁰ C.

The melt shear rate, and in turn the degree to which they hydrolytic degradation is initiated, may also be increased through the use of one or more distributive and/or dispersive mixing elements within the mixing section of the extruder. Suitable distributive mixers for single screw extruders may include, for instance, Saxon, Dulmage, Cavity Transfer mixers, etc. Likewise, suitable dispersive mixers may include Blister ring, Leroy/Maddock, CRD mixers, etc. As is well known in the art, the mixing may be further improved by using pins in the barrel that create a folding and reorientation of the polymer melt, such as those used in Buss Kneader extruders, Cavity Transfer mixers, and Vortex lntermeshing Pin (VIP) mixers. Regardless of the particular elements selected, the present inventors have discovered that the use of one more mixing elements may create intensive melt shear rates that help initiate the desired hydrolysis reaction. Typically, the apparent shear rate during melt processing may range from about 300 seconds ^"1 to about 10,000 seconds ^"1 , in some embodiments from about 500 seconds ^"1 to about 5000 seconds ^"1 , and in some embodiments, from about 800 seconds ^"1 to about 1200 seconds ^"1 . The apparent shear rate is equal to 4Q/πR ³ , where Q is the volumetric flow rate ("m ³ /s") of the polymer melt and R is the radius ("m") of the capillary (e.g., extruder die) through which the melted polymer flows. Of course, other variables, such as the residence time during melt processing, which is inversely proportional to throughput rate, may also be controlled to achieve the desired degree of hydrolysis.

Under appropriate temperature and shear conditions, as describe above, a hydrolytically degraded polymer species is formed that has a molecular weight lower than that of the starting polylactic acid. The weight average and/or number average molecular weights may, for instance, each be reduced so that the ratio of the starting polylactic acid molecular weight to the hydrolytically degraded polylactic acid molecular weight is at least about 1.1 , in some embodiments at

least about 1.4, and in some embodiments, at least about 2.0. For example, the hydrolytically degraded polylactic acid may have a number average molecular weight ("M _n ") ranging from about 10,000 to about 105,000 grams per mole, in some embodiments from about 20,000 to about 100,000 grams per mole, and in some embodiments, from about 30,000 to about 90,000 grams per mole. Likewise, the hydrolytically degraded polylactic acid may also have a weight average molecular weight ("M _w ") of from about 20,000 to about 140,000 grams per mole, in some embodiments from about 30,000 to about 120,000 grams per mole, and in some embodiments, from about 50,000 to about 100,000 grams per mole. In addition to possessing a lower molecular weight, the hydrolytically degraded polylactic acid may also have a lower apparent viscosity and higher melt flow rate than the starting polymer. The apparent viscosity may for instance, be reduced so that the ratio of the starting polylactic acid viscosity to the hydrolytically degraded polylactic acid viscosity is at least about 1.1 , in some embodiments at least about 2, and in some embodiments, from about 15 to about 100. Likewise, the melt flow rate may be increased so that the ratio of the hydrolytically degraded polylactic acid melt flow rate to the starting polylactic acid melt flow rate (on a dry basis) is at least about 1.5, in some embodiments at least about 5, in some embodiments at least about 10, and in some embodiments, from about 30 to about 100. In one particular embodiment, the hydrolytically degraded polylactic acid may have an apparent viscosity of from about 5 to about 250 Pascal seconds (Pa-s), in some embodiments from about 8 to about 150 Pa-s, and in some embodiments, from about 10 to about 100 Pa-s, as determined at a temperature of 190°C and a shear rate of 1000 sec ^"1 . The melt flow rate of the hydrolytically degraded polylactic acid (dry basis) may range from about 10 to about 1000 grams per 10 minutes, in some embodiments from about 20 to about 900 grams per 10 minutes, and in some embodiments, from about 100 to about 800 grams per 10 minutes (190 ⁰ C, 2.16 kg). Of course, the extent to which the molecular weight, apparent viscosity, and/or melt flow rate are altered by the hydrolysis reaction may vary depending on the intended application.

Although differing from the starting polymer in certain properties, the hydrolytically degraded polylactic acid may nevertheless retain other properties of the starting polymer. For example, the thermal characteristics (e.g., T ₉ , T _m , and

latent heat of fusion) typically remain substantially the same as the starting polymer, such as within the ranges noted above. Further, even though the actual molecular weights may differ, the polydispersity index of the hydrolytically degraded polylactic acid may remain substantially the same as the starting polymer, such as within the range of about 1.0 to about 3.5, in some embodiments from about 1.1 to about 2.5, and in some embodiments, from about 1.2 to about 2.0. III. Fiber Formation

Fibers formed from the hydrolytically degraded polylactic acid may generally have any desired configuration, including monocomponent, multicomponent (e.g., sheath-core configuration, side-by-side configuration, segmented pie configuration, island-in-the-sea configuration, and so forth), and/or multiconstituent (e.g., polymer blend). In some embodiments, the fibers may contain one or more additional polymers as a component (e.g., bicomponent) or constituent (e.g., biconstituent) to further enhance strength and other mechanical properties. For instance, the hydrolytically degraded polylactic acid may form a sheath component of a sheath/core bicomponent fiber, while an additional polymer may form the core component, or vice versa. The additional polymer may be a thermoplastic polymer that is not generally considered biodegredable, such as polyolefins, e.g., polyethylene, polypropylene, polybutylene, and so forth; polytetrafluoroethylene; polyesters, e.g., polyethylene terephthalate, and so forth; polyvinyl acetate; polyvinyl chloride acetate; polyvinyl butyral; acrylic resins, e.g., polyacrylate, polymethylacrylate, polymethylmethacrylate, and so forth; polyamides, e.g., nylon; polyvinyl chloride; polyvinylidene chloride; polystyrene; polyvinyl alcohol; and polyurethanes. More desirably, however, the additional polymer is biodegredable, such as aliphatic polyesters, such as polyesteramides, modified polyethylene terephthalate, polyglycolic acid, polyalkylene carbonates (such as polyethylene carbonate), polyhydroxyalkanoates (PHA), polyhydroxybutyrates (PHB), polyhydroxyvalerates (PHV), polyhydroxybutyrate-hydroxyvalerate copolymers (PHBV), and polycaprolactone, and succinate-based aliphatic polymers (e.g., polybutylene succinate, polybutylene succinate adipate, and polyethylene succinate); aromatic polyesters; or other aliphatic-aromatic copolyesters.

Any of a variety of processes may be used to form fibers in accordance with

the present invention. Referring to Fig. 3, for example, one embodiment of a method for forming meltblown fibers is shown. Meltblown fibers form a structure having a small average pore size, which may be used to inhibit the passage of liquids and particles, while allowing gases (e.g., air and water vapor) to pass therethrough. To achieve the desired pore size, the meltblown fibers are typically "microfibers" in that they have an average size of 10 micrometers or less, in some embodiments about 7 micrometers or less, and in some embodiments, about 5 micrometers or less. The ability to produce such fine fibers may be facilitated in the present invention through the use of a hydrolytically degraded polylactic acid having the desirable combination of low apparent viscosity and high melt flow rate. In Fig. 3, for instance, the raw materials (e.g., polymer, piasticizer, etc.) are fed into an extruder 12 from a hopper 10 (such as shown in Fig. 1 ). The raw materials may be provided to the hopper 10 using any conventional technique and in any state. Alternatively, the polylactic acid may be fed to the hopper 10, and the glycol may be injected into the polylactic acid melt in the extruder 12 downstream from the hopper 10. The extruder 12 is driven by a motor 11 and heated to a temperature sufficient to extrude the polymer and to initiate the hydrolysis reaction. For example, the extruder 12 may employ one or multiple zones operating at a temperature of from about 100°C to about 600°C, in some embodiments, from about 150°C to about 350 ⁰ C, and in some embodiments, from about 175°C to about 300°C. Typical shear rates range from about 100 seconds ^"1 to about 10,000 seconds ^"1 , in some embodiments from about 500 seconds ^"1 to about 5000 seconds ^"1 , and in some embodiments, from about 800 seconds ^"1 to about 1200 seconds ^"1 . If desired, the extruder may also possess one or more zones that remove excess moisture from the polymer, such as vacuum zones, etc. The extruder may also be vented to allow volatile gases to escape.

Once formed, the hydrolytically degraded polylactic acid may be subsequently fed to another extruder in a fiber formation line. Alternatively, the hydrolytically degraded polymer may be directly formed into a fiber through supply to a die 14, which may be heated by a heater 16. It should be understood that other meltblown die tips may also be employed. As the polymer exits the die 14 at an orifice 19, high pressure fluid (e.g., heated air) supplied by conduits 13 attenuates and spreads the polymer stream into microfibers 18. Although not

shown in Fig. 3, the die 14 may also be arranged adjacent to or near a chute through which other materials (e.g., cellulosic fibers, particles, etc.) traverse to intermix with the extruded polymer and form a "coform" web.

The microfibers 18 are randomly deposited onto a foraminous surface 20 (driven by rolls 21 and 23) with the aid of an optional suction box 15 to form a meltblown web 22. The distance between the die tip and the foraminous surface 20 is generally small to improve the uniformity of the fiber laydown. For example, the distance may be from about 1 to about 35 centimeters, and in some embodiments, from about 2.5 to about 15 centimeters. In Fig. 3, the direction of the arrow 28 shows the direction in which the web is formed (i.e., "machine direction") and arrow 30 shows a direction perpendicular to the machine direction (i.e., "cross-machine direction"). Optionally, the meltblown web 22 may then be compressed by rolls 24 and 26. The desired denier of the fibers may vary depending on the desired application. Typically, the fibers are formed to have a denier per filament (i.e., the unit of linear density equal to the mass in grams per 9000 meters of fiber) of less than about 6, in some embodiments less than about 3, and in some embodiments, from about 0.5 to about 3. In addition, the fibers generally have an average diameter of from about 0.1 to about 20 micrometers, in some embodiments from about 0.5 to about 15 micrometers, and in some embodiments, from about 1 to about 10 micrometers.

Once formed, the nonwoven web may then be bonded using any conventional technique, such as with an adhesive or autogenously (e.g., fusion and/or self-adhesion of the fibers without an applied external adhesive). Autogenous bonding, for instance, may be achieved through contact of the fibers while they are semi-molten or tacky, or simply by blending a tackifying resin and/or solvent with the polylactic acid(s) used to form the fibers. Suitable autogenous bonding techniques may include ultrasonic bonding, thermal bonding, through-air bonding, calendar bonding, and so forth. For example, the web may be further bonded or embossed with a pattern by a thermo-mechanical process in which the web is passed between a heated smooth anvil roll and a heated pattern roll. The pattern roll may have any raised pattern which provides the desired web properties or appearance. Desirably, the pattern roll defines a raised pattern which defines a plurality of bond locations which define a bond area between about 2% and 30% of

the total area of the roll. Exemplary bond patterns include, for instance, those described in U.S. Patent 3,855,046 to Hansen et al., U.S. Patent No. 5,620,779 to Lew et al.. U.S. Patent No. 5.962.112 to Havnes et al., U.S. Patent 6,093,665 to Sayovitz et a!., as well as U.S. Design Patent Nos. 428,267 to Romano et al.; 390,708 to Brown; 418,305 to Zander, et al.; 384,508 to Zander, et al.; 384,819 to Zander, et al.; 358,035 to Zander, et al.; and 315,990 to Blenke. et al.. all of which are incorporated herein in their entirety by reference thereto for all purposes. The pressure between the rolls may be from about 5 to about 2000 pounds per lineal inch. The pressure between the rolls and the temperature of the rolls is balanced to obtain desired web properties or appearance while maintaining cloth like properties. As is well known to those skilled in the art, the temperature and pressure required may vary depending upon many factors including but not limited to, pattern bond area, polymer properties, fiber properties and nonwoven properties. In addition to meltblown webs, a variety of other nonwoven webs may also be formed from the hydrolytically degraded polylactic acid in accordance with the present invention, such as spunbond webs, bonded carded webs, wet-laid webs, airlaid webs, coform webs, hydraulically entangled webs, etc. For example, the polymer may be extruded through a spinnerette, quenched and drawn into substantially continuous filaments, and randomly deposited onto a forming surface. Alternatively, the polymer may be formed into a carded web by placing bales of fibers formed from the blend into a picker that separates the fibers. Next, the fibers are sent through a combing or carding unit that further breaks apart and aligns the fibers in the machine direction so as to form a machine direction- oriented fibrous nonwoven web. Once formed, the nonwoven web is typically stabilized by one or more known bonding techniques.

If desired, the nonwoven web may also be a composite that contains a combination of the hydrolytically degraded polylactic acid fibers and other types of fibers (e.g., staple fibers, filaments, etc). For example, additional synthetic fibers may be utilized, such as those formed from polyolefins, e.g., polyethylene, polypropylene, polybutylene, and so forth; polytetrafluoroethylene; polyesters, e.g., polyethylene terephthalate and so forth; polyvinyl acetate; polyvinyl chloride acetate; polyvinyl butyral; acrylic resins, e.g., polyacrylate, polymethylacrylate,

polymethylmethacrylate, and so forth; polyamides, e.g., nylon; polyvinyl chloride; polyvinylidene chloride; polystyrene; polyvinyl alcohol; polyurethanes; polylactic acid; etc. If desired, biodegradable polymers, such as poly(glycolic acid) (PGA), poly(lactic acid) (PLA), poly(β-malic acid) (PMLA), poly(ε-caprolactone) (PCL), poly(p-dioxanone) (PDS), poly(butylene succinate) (PBS), and poly(3- hydroxybutyrate) (PHB), may also be employed. Some examples of known synthetic fibers include sheath-core bicomponent fibers available from KoSa Inc. of Charlotte, North Carolina under the designations T-255 and T-256, both of which use a polyolefin sheath, or T-254, which has a low melt co-polyester sheath. Still other known bicomponent fibers that may be used include those available from the Chisso Corporation of Moriyama, Japan or Fibervisions LLC of Wilmington, Delaware. Polylactic acid staple fibers may also be employed, such as those commercially available from Far Eastern Textile, Ltd. of Taiwan.

The composite may also contain pulp fibers, such as high-average fiber length pulp, low-average fiber length pulp, or mixtures thereof. One example of suitable high-average length fluff pulp fibers includes softwood kraft pulp fibers. Softwood kraft pulp fibers are derived from coniferous trees and include pulp fibers such as, but not limited to, northern, western, and southern softwood species, including redwood, red cedar, hemlock, Douglas fir, true firs, pine (e.g., southern pines), spruce (e.g., black spruce), combinations thereof, and so forth. Northern softwood kraft pulp fibers may be used in the present invention. An example of commercially available southern softwood kraft pulp fibers suitable for use in the present invention include those available from Weyerhaeuser Company with offices in Federal Way, Washington under the trade designation of "NF-405." Another suitable pulp for use in the present invention is a bleached, sulfate wood pulp containing primarily softwood fibers that is available from Bowater Corp. with offices in Greenville, South Carolina under the trade name CoosAbsorb S pulp. Low-average length fibers may also be used in the present invention. An example of suitable low-average length pulp fibers is hardwood kraft pulp fibers. Hardwood kraft pulp fibers are derived from deciduous trees and include pulp fibers such as, but not limited to, eucalyptus, maple, birch, aspen, etc. Eucalyptus kraft pulp fibers may be particularly desired to increase softness, enhance brightness, increase opacity, and change the pore structure of the sheet to increase its wicking ability.

Nonwoven composites may be formed using a variety of known techniques. For example, the nonwoven composite may be a "coform material" that contains a mixture or stabilized matrix of the hydrolytically degraded polylactic fibers and an absorbent material. As an example, coform materials may be made by a process in which at least one meltblown die head is arranged near a chute through which the absorbent materials are added to the web while it is forming. Such absorbent materials may include, but are not limited to, pulp fibers, superabsorbent particles, inorganic and/or organic absorbent materials, treated polymeric staple fibers, and so forth. The relative percentages of the absorbent material may vary over a wide range depending on the desired characteristics of the nonwoven composite. For example, the nonwoven composite may contain from about 1 wt.% to about 60 wt.%, in some embodiments from 5 wt.% to about 50 wt.%, and in some embodiments, from about 10 wt.% to about 40 wt.% hydrolytically degraded polylactic acid fibers. The nonwoven composite may likewise contain from about 40 wt.% to about 99 wt.%, in some embodiments from 50 wt.% to about 95 wt.%, and in some embodiments, from about 60 wt.% to about 90 wt.% absorbent material. Some examples of such coform materials are disclosed in U.S. Patent Nos. 4,100,324 to Anderson, et al.; 5,284,703 to Everhart, et al.; and 5,350,624 to Georger, et al.; which are incorporated herein in their entirety by reference thereto for all purposes.

Referring to Fig. 4, for example, one embodiment of an apparatus for forming a nonwoven coform composite structure is generally represented by reference numeral 110. Initially, the raw materials (e.g., polylactic acid, etc.) are supplied to a hopper 112 of an extruder 114, and then extruded toward two meltblowing dies 116 and 118 corresponding to a stream of gas 126 and 128, respectively, which are aligned to converge at an impingement zone 130. One or more types of a secondary material 132 (fibers and/or particulates) are also supplied by a nozzle 144 and added to the two streams 126 and 128 at the impingement zone 130 to produce a graduated distribution of the material within the combined streams 126 and 128. The secondary material may be supplied using any known technique in the art, such as with a picker roll arrangement (not shown) or a particulate injection system (not shown). The secondary stream 132 merges with the two streams 126 and 128 to form a composite stream 156. An

endless belt 158 driven by rollers 160 receives the stream 156 and form a composite structure 154. If desired, vacuum boxes (not shown) may be employed to assist in retention of the matrix on the surface of the belt 158.

Nonwoven laminates may also be formed in the present invention in which one or more layers are formed from the hydrolytically degraded polylactic acid. For example, the nonwoven web of one layer may be a meltblown or coform web that contains the hydrolytically degraded polylactic acid, while the nonwoven web of another layer contains hydrolytically degraded polylactic acid, other biodegradable polymer(s), and/or any other polymer (e.g., polyolefins). In one embodiment, the nonwoven laminate contains a meltblown layer positioned between two spunbond layers to form a spunbond / meltblown / spunbond ("SMS") laminate. If desired, the meltblown layer may be formed from the hydrolytically degraded polylactic acid. The spunbond layer may be formed from the hydrolytically degraded polylactic acid, other biodegradable polymer(s), and/or any other polymer (e.g., polyolefins). Various techniques for forming SMS laminates are described in U.S. Patent Nos. 4,041 ,203 to Brock et al.; 5,213,881 to Timmons, et al.; 5,464,688 to Timmons, et al.; 4,374,888 to Bomslaeger; 5,169,706 to Collier, et al.; and 4,766,029 to Brock et al., as well as U.S. Patent Application Publication No. 2004/0002273 to Fitting, et al., all of which are incorporated herein in their entirety by reference thereto for all purposes. Of course, the nonwoven laminate may have other configuration and possess any desired number of meltblown and spunbond layers, such as spunbond / meltblown / meltblown / spunbond laminates ("SMMS"), spunbond / meltblown laminates ("SM"), etc. Although the basis weight of the nonwoven laminate may be tailored to the desired application, it generally ranges from about 10 to about 300 grams per square meter ("gsm"), in some embodiments from about 25 to about 200 gsm, and in some embodiments, from about 40 to about 150 gsm.

If desired, the nonwoven web or laminate may be applied with various treatments to impart desirable characteristics. For example, the web may be treated with liquid-repellency additives, antistatic agents, surfactants, colorants, antifogging agents, fluorochemical blood or alcohol repellents, lubricants, and/or antimicrobial agents. In addition, the web may be subjected to an electret treatment that imparts an electrostatic charge to improve filtration efficiency. The

charge may include layers of positive or negative charges trapped at or near the surface of the polymer, or charge clouds stored in the bulk of the polymer. The charge may also include polarization charges that are frozen in alignment of the dipoles of the molecules. Techniques for subjecting a fabric to an electret treatment are well known by those skilled in the art. Examples of such techniques include, but are not limited to, thermal, liquid-contact, electron beam and corona discharge techniques. In one particular embodiment, the electret treatment is a corona discharge technique, which involves subjecting the laminate to a pair of electrical fields that have opposite polarities. Other methods for forming an electret material are described in U.S. Patent Nos. 4,215,682 to Kubik, et al.; 4,375,718 to Wadsworth; 4,592,815 to Nakao; 4,874,659 to Ando; 5,401 ,446 to Tsai, et al.; 5,883,026 to Reader, et al.; 5,908,598 to Rousseau, et al.; 6,365,088 to Knight, et al., which are incorporated herein in their entirety by reference thereto for all purposes. IV. Articles

The nonwoven web of the present invention may be used in a wide variety of applications. For example, the web may be incorporated into a "medical product", such as gowns, surgical drapes, facemasks, head coverings, surgical caps, shoe coverings, sterilization wraps, warming blankets, heating pads, and so forth. Of course, the nonwoven web may also be used in various other articles. For example, the nonwoven web may be incorporated into an "absorbent article" that is capable of absorbing water or other fluids. Examples of some absorbent articles include, but are not limited to, personal care absorbent articles, such as diapers, training pants, absorbent underpants, incontinence articles, feminine hygiene products (e.g., sanitary napkins), swim wear, baby wipes, mitt wipe, and so forth; medical absorbent articles, such as garments, fenestration materials, underpads, bedpads, bandages, absorbent drapes, and medical wipes; food service wipers; clothing articles; pouches, and so forth.

Materials and processes suitable for forming such articles are well known to those skilled in the art. Absorbent articles, for instance, typically include a substantially liquid-impermeable layer (e.g., backsheet), a liquid-permeable layer (e.g., top sheet, surge management layer, ventilation layer, wrap, etc.), and an absorbent core.

Referring to Fig. 5, for instance, one embodiment of an absorbent article 201 is shown in the form of a diaper. However, as noted above, the invention may be embodied in other types of absorbent articles, such as incontinence articles, sanitary napkins, diaper pants, feminine napkins, children's training pants, and so forth. In the illustrated embodiment, the diaper 201 is shown as having an hourglass shape in an unfastened configuration. However, other shapes may of course be utilized, such as a generally rectangular shape, T-shape, or l-shape. As shown, the diaper 201 includes a chassis 202 formed by various components, including an outer cover 217, bodyside liner 205, absorbent core 203, and surge layer 207. It should be understood, however, that other layers may also be used in the present invention. Likewise, one or more of the layers referred to in Fig. 5 may also be eliminated in certain embodiments of the present invention.

The outer cover 217 is typically formed from a material that is substantially impermeable to liquids. For example, the outer cover 217 may be formed from a thin plastic film or other flexible liquid-impermeable material. In one embodiment, the outer cover 217 is formed from a polyethylene film having a thickness of from about 0.01 millimeter to about 0.05 millimeter. The film may be impermeable to liquids, but permeable to gases and water vapor (i.e., "breathable"). This permits vapors to escape from the absorbent core 203, but still prevents liquid exudates from passing through the outer cover 217. If a more cloth-like feeling is desired, the outer cover 217 may be formed from a polyolefin film laminated to a nonwoven web. For example, a stretch-thinned polypropylene film having a thickness of about 0.015 millimeter may be thermally laminated to a spunbond web of polypropylene fibers. If desired, the nonwoven web may contain the fibers of the present invention.

The diaper 201 also includes a bodyside liner 205. The bodyside liner 205 is generally employed to help isolate the wearer's skin from liquids held in the absorbent core 203. For example, the liner 205 presents a bodyfacing surface that is typically compliant, soft feeling, and non-irritating to the wearer's skin. Typically, the liner 205 is also less hydrophilic than the absorbent core 203 so that its surface remains relatively dry to the wearer. The liner 205 may be liquid-permeable to permit liquid to readily penetrate through its thickness. In one particular embodiment, the liner includes a nonwoven web (e.g., spunbond web, meltblown

web, or bonded carded web) containing the multicomponent fibers of the present invention. Exemplary liner constructions that contain a nonwoven web are described in U.S. Patent Nos. 5,192,606; 5,702,377; 5,931 ,823; 6,060,638; and 6,150,002, as well as U.S. Patent Application Publication Nos. 2004/0102750, 2005/0054255, and 2005/0059941 , all of which are incorporated herein in their entirety by reference thereto for all purposes.

As illustrated in Fig. 5, the diaper 201 may also include a surge layer 207 that helps to decelerate and diffuse surges or gushes of liquid that may be rapidly introduced into the absorbent core 203. Desirably, the surge layer 207 rapidly accepts and temporarily holds the liquid prior to releasing it into the storage or retention portions of the absorbent core 203. In the illustrated embodiment, for example, the surge layer 207 is interposed between an inwardly facing surface 216 of the bodyside liner 205 and the absorbent core 203. Alternatively, the surge layer 207 may be located on an outwardly facing surface 218 of the bodyside liner 205. The surge layer 207 is typically constructed from highly liquid-permeable materials. Suitable materials may include porous woven materials, porous nonwoven materials, and apertured films. In one particular embodiment, the surge layer 207 includes a nonwoven web containing the fibers of the present invention. Other examples of suitable surge layers are described in U.S. Patent No. 5,486, 166 to Ellis, et al. and 5,490,846 to Ellis, et al., which are incorporated herein in their entirety by reference thereto for all purposes.

Besides the above-mentioned components, the diaper 201 may also contain various other components as is known in the art. For example, the diaper 201 may also contain a substantially hydrophilic wrapsheet (not illustrated) that helps maintain the integrity of the fibrous structure of the absorbent core 203. The wrapsheet is typically placed about the absorbent core 203 over at least the two major facing surfaces thereof, and composed of an absorbent cellulosic material, such as creped wadding or a high wet-strength tissue. The wrapsheet may be configured to provide a wicking layer that helps to rapidly distribute liquid over the mass of absorbent fibers of the absorbent core 203. The wrapsheet material on one side of the absorbent fibrous mass may be bonded to the wrapsheet located on the opposite side of the fibrous mass to effectively entrap the absorbent core

203. If desired, the wrapsheet may be formed from a nonwoven web that includes the fibers of the present invention.

Furthermore, the diaper 201 may also include a ventilation layer (not shown) that is positioned between the absorbent core 203 and the outer cover 217. When utilized, the ventilation layer may help insulate the outer cover 217 from the absorbent core 203, thereby reducing dampness in the outer cover 217. Examples of such ventilation layers may include a nonwoven web laminated to a breathable film, such as described in U.S. Patent No. 6,663,611 to Blanev, et al., which is incorporated herein in its entirety by reference thereto for all purpose. Such nonwoven webs may be formed from a nonwoven web that includes the fibers of the present invention.

In some embodiments, the diaper 201 may also include a pair of ears (not shown) that extend from the side edges 232 of the diaper 201 into one of the waist regions. The ears may be integrally formed with a selected diaper component. For example, the ears may be integrally formed with the outer cover 217 or from the material employed to provide the top surface. In alternative configurations, the ears may be provided by members connected and assembled to the outer cover 217, the top surface, between the outer cover 217 and top surface, or in various other configurations. As representatively illustrated in Fig. 5, the diaper 201 may also include a pair of containment flaps 212 that are configured to provide a barrier and to contain the lateral flow of body exudates. The containment flaps 212 may be located along the laterally opposed side edges 232 of the bodyside liner 205 adjacent the side edges of the absorbent core 203. The containment flaps 212 may extend longitudinally along the entire length of the absorbent core 203, or may only extend partially along the length of the absorbent core 203. When the containment flaps 212 are shorter in length than the absorbent core 203, they may be selectively positioned anywhere along the side edges 232 of diaper 201 in a crotch region 210. In one embodiment, the containment flaps 212 extend along the entire length of the absorbent core 203 to better contain the body exudates. Such containment flaps 212 are generally well known to those skilled in the art. For example, suitable constructions and arrangements for the containment flaps 212 are described in U.S. Patent No. 4,704,116 to Enloe, which is incorporated herein in its

entirety by reference thereto for all purposes. If desired, one or more of the containment flaps 212 may be formed from a nonwoven web that includes the fibers of the present invention.

The diaper 201 may include various elastic or stretchable materials, such as a pair of leg elastic members 206 affixed to the side edges 232 to further prevent leakage of body exudates and to support the absorbent core 203. In addition, a pair of waist elastic members 208 may be affixed to longitudinally opposed waist edges 215 of the diaper 201. The leg elastic members 206 and the waist elastic members 208 are generally adapted to closely fit about the legs and waist of the wearer in use to maintain a positive, contacting relationship with the wearer and to effectively reduce or eliminate the leakage of body exudates from the diaper 201. As used herein, the terms "elastic" and "stretchable" include any material that may be stretched and return to its original shape when relaxed. Suitable polymers for forming such materials include, but are not limited to, block copolymers of polystyrene, polyisoprene and polybutadiene; copolymers of ethylene, natural rubbers and urethanes; etc. Particularly suitable are styrene-butadiene block copolymers sold by Kraton Polymers of Houston, Texas under the trade name Kraton®. Other suitable polymers include copolymers of ethylene, including without limitation ethylene vinyl acetate, ethylene methyl acrylate, ethylene ethyl acrylate, ethylene acrylic acid, stretchable ethylene-propylene copolymers, and combinations thereof. Also suitable are coextruded composites of the foregoing, and elastomeric staple integrated composites where staple fibers of polypropylene, polyester, cotton and other materials are integrated into an elastomeric meltblown web. Certain elastomeric single-site or metallocene-catalyzed olefin polymers and copolymers are also suitable for the side panels.

The diaper 201 may also include one or more fasteners 230. For example, two flexible fasteners 130 are illustrated in Fig. 5 on opposite side edges of waist regions to create a waist opening and a pair of leg openings about the wearer. The shape of the fasteners 230 may generally vary, but may include, for instance, generally rectangular shapes, square shapes, circular shapes, triangular shapes, oval shapes, linear shapes, and so forth. The fasteners may include, for instance, a hook material. In one particular embodiment, each fastener 230 includes a separate piece of hook material affixed to the inside surface of a flexible backing.

The various regions and/or components of the diaper 201 may be assembled together using any known attachment mechanism, such as adhesive, ultrasonic, thermal bonds, etc. Suitable adhesives may include, for instance, hot melt adhesives, pressure-sensitive adhesives, and so forth. When utilized, the adhesive may be applied as a uniform layer, a patterned layer, a sprayed pattern, or any of separate lines, swirls or dots. In the illustrated embodiment, for example, the outer cover 217 and bodyside liner 205 are assembled to each other and to the absorbent core 203 using an adhesive. Alternatively, the absorbent core 203 may be connected to the outer cover 217 using conventional fasteners, such as buttons, hook and loop type fasteners, adhesive tape fasteners, and so forth. Similarly, other diaper components, such as the leg elastic members 206, waist elastic members 208 and fasteners 230, may also be assembled into the diaper 201 using any attachment mechanism.

Although various configurations of a diaper have been described above, it should be understood that other diaper and absorbent article configurations are also included within the scope of the present invention. In addition, the present invention is by no means limited to diapers. In fact, any other absorbent article may be formed in accordance with the present invention, including, but not limited to, other personal care absorbent articles, such as training pants, absorbent underpants, adult incontinence products, feminine hygiene products (e.g., sanitary napkins), swim wear, baby wipes, and so forth; medical absorbent articles, such as garments, fenestration materials, underpads, bandages, absorbent drapes, and medical wipes; food service wipers; clothing articles; and so forth.

In one embodiment, for example, the nonwoven web of the present invention may be used to form a wipe configured for use on skin, such as a baby wipe, adult wipe, hand wipe, face wipe, cosmetic wipe, household wipe, industrial wipe, personal cleansing wipe, cotton ball, cotton-tipped swab, and so forth. The wipe may assume a variety of shapes, including but not limited to, generally circular, oval, square, rectangular, or irregularly shaped. Each individual wipe may be arranged in a folded configuration and stacked one on top of the other to provide a stack of wet wipes. Such folded configurations are well known to those skilled in the art and include c-folded, z-folded, quarter-folded configurations and so forth. For example, the wipe may have an unfolded length of from about 2.0 to

about 80.0 centimeters, and in some embodiments, from about 10.0 to about 25.0 centimeters. The wipes may likewise have an unfolded width of from about 2.0 to about 80.0 centimeters, and in some embodiments, from about 10.0 to about 25.0 centimeters. The stack of folded wipes may be placed in the interior of a container, such as a plastic tub, to provide a package of wipes for eventual sale to the consumer. Alternatively, the wipes may include a continuous strip of material which has perforations between each wipe and which may be arranged in a stack or wound into a roll for dispensing. Various suitable dispensers, containers, and systems for delivering wipes are described in U.S. Patent Nos. 5,785,179 to Buczwinski, et al.; 5,964,351 to Zander; 6,030,331 to Zander; 6,158,614 to Havnes, et al.: 6,269,969 to Huang, et al.; 6,269,970 to Huang, et al.; and 6,273,359 to Newman, et al., which are incorporated herein in their entirety by reference thereto for all purposes.

In certain embodiments of the present invention, the wipe is a "wet wipe" in that it contains a solution for cleaning, disinfecting, sanitizing, etc. The particular wet wipe solutions are not critical to the present invention and are described in more detail in U.S. Patent Nos. 6,440,437 to Krzvsik, et al.; 6,028,018 to Amundson, et al.; 5,888,524 to Cole; 5,667,635 to Win, et al.; 5,540,332 to Kopacz, et al.; and 4,741 ,944 to Jackson, et al., which are incorporated herein in their entirety by reference thereto for all purposes. The amount of the wet wipe solution employed may depending upon the type of wipe material utilized, the type of container used to store the wipes, the nature of the cleaning formulation, and the desired end use of the wipes. Generally, each wipe contains from about 150 to about 600 wt.% and desirably from about 300 to about 500 wt.% of a wet wipe solution based on the dry weight of the wipe.

The present invention may be better understood with reference to the following examples.

Test Methods Melt Flow Rate: 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 ⁰ C or 230 ⁰ C. Unless otherwise indicated, the melt flow rate was measured in accordance with ASTM Test Method

D1238-E. The melt flow rate may be measured before or after drying. Polymers measured after drying (dry basis) generally have a water content of less than 500 parts per million.

Tensile Properties: The strip tensile strength values were determined in substantial accordance with ASTM Standard D-5034. Specifically, a nonwoven web sample was cut or otherwise provided with size dimensions that measured 25 millimeters (width) x 127 millimeters (length). A constant-rate-of-extension type of tensile tester was employed. The tensile testing system was a Sintech Tensile Tester, which is available from Sintech Corp. of Cary, North Carolina. The tensile tester was equipped with TESTWORKS 4.08B software from MTS Corporation to support the testing. An appropriate load cell was selected so that the tested value fell within the range of 10-90% of the full scale load. The sample was held between grips having a front and back face measuring 25.4 millimeters x 76 millimeters. The grip faces were rubberized, and the longer dimension of the grip was perpendicular to the direction of pull. The grip pressure was pneumatically maintained at a pressure of 40 pounds per square inch. The tensile test was run at a 300- millimeter per minute rate with a gauge length of 10.16 centimeters and a break sensitivity of 40%. Five samples were tested by applying the test load along the machine- direction ("MD") and five samples were tested by applying the test load along the cross direction ("CD"). In addition to tensile strength ("peak load"), peak elongation (i.e., % strain at peak load), the strength at break, and the % strain at break were measured. Water Content:

Water content was determined using an Arizona Instruments Computrac Vapor Pro moisture analyzer (Model No. 3100) in substantial accordance with ASTM D 7191-05, which is incorporated herein in its entirety by reference thereto for all purposes. The test temperature (§ X2.1.2) was 130 ⁰ C, the sample size (§ X2.1.1 ) was 2 to 4 grams, and the vial purge time (§ X2.1.4) was 30 seconds. Further, the ending criteria (§ X2.1.3) was defined as a "prediction" mode, which means that the test is ended when the built-in programmed criteria (which mathematically calculates the end point moisture content) is satisfied.

EXAMPLES

For Examples 1-5, two grades of polylactic acid (PLA) polymer resins were employed, i.e., 6350 and 6250 supplied by Natureworks LLC (Minnetonka, Minnesota). As received, the PLA resins had a low moisture content. To facilitate hydrolytic degradation, however, the resins were subjected to a humid environment at 40 ⁰ C and 75% relative humidity to a moisture content of 4109 ppm for the PLA 6350 resin and 1083 ppm for the PLA 6250 resin. At these moisture levels, the PLA 6350 resin had a melt flow rate of 37 grams per 10 minutes (190 ⁰ C, 2.16 kg) and the PLA 6250 resin had a melt flow rate of 37 grams per 10 minutes (190 ⁰ C, 2.16 kg).

The extruder utilized in the examples was a Davis-Standard (Davis- Standard, LLC, Pawcatuck, CT) 2.5" single screw extruder with 4 barrel zones, 1 transfer zone, and a 6 hole strand die. The L/D ratio of the extruder was approximately 30. A two stage barrier screw with a Maddock mixer and a 5 cavity Cavity Transfer Mixing (CTM) extension was used. PLA was fed into the extruder throat utilizing a Colortronics pellet and powder feeder supplied by Colortronics (Flint, Michigan). Polyethylene Glycol (PEG) 3350 supplied by Dow Chemical (Midland, Michigan) was pre-melted in a Nordson melt tank supplied by Nordson (Westlake, Ohio) and then pumped to an injector placed after the barrier section of the screw. The PEG was added in at a rate to maintain a 13-14% PEG concentration. A vacuum pump was used during the second stage of the extruder to remove some residual moisture.

EXAMPLE 1

The extruder temperature was set to 464°F and the screw speed was set to 75 rpm. A screen pack of 14:40:60 mesh was incorporated just prior to the extrusion die. PEG was added to the extruder at a rate of approximately 22 Ibs/hr. The extruder temperature profile conditions are set forth below in Table 1 :

Table 1 : Extruder Temperature Profile A melt flow rate of 104 g/10 min (190 ⁰ C ₁ 2.16 kg) was observed, however, the extruder exhibited unstable conditions.

EXAMPLE 2

The temperature of the extruder from Example 1 was lowered from 464°F to 455°F and the screen pack was replaced with a 20:60:100:200:300:14 mesh screen pack. All other conditions remained the same. The increased filtration caused increased pressure and shear causing further PLA degradation. A melt flow rate of 100 g/10 min (19O ⁰ C ₁ 2.16 kg) with a moisture content of 1700 ppm was observed. The extruder exhibited stable conditions.

EXAMPLE 3

Since the pressures were still low with the screen pack utilized in Example 2, the 100 and 200 mesh screens were replaced with 300 mesh screens to increase filtration and pressure. All other conditions were the same as Example 2. A melt flow rate of 103 g/10 min (190 ⁰ C, 2.16 kg) was observed.

EXAMPLE 4

The temperature of the extruder was raised from 455°F to 464°F. All other conditions were the same as Example 3. A melt flow rate of 106 g/10 min (190 ⁰ C, 2.16 kg) was observed.

EXAMPLE 5

The conditions of Example 4 were repeated, except that the screw speed was increased from 75 to 100 rpm. At this speed, the PEG addition was increased to 23 Ibs/hr to maintain the 13-14% PEG concentration. A melt flow rate of 127 g/10 min (190°C, 2.16 kg) was observed. The operating conditions and results of Examples 1-5 are summarized in Table 2.

Table 2: Examples 1-5 Operating Conditions

EXAMPLE 6

Meltblown webs were formed from the product of the five examples described above. 20 lbs of the modified PLA from each example was utilized. The meltblown spinning was conducted with a pilot line that included a Killion extruder (Verona, NY), a 10-foot hose from Dekoron/Unitherm (Riviera Beach, FL), and a 14-inch meltblown die with an 11.5 in. spray pattern and an orifice size of 0.0145 in. The modified resin was fed via gravity into the extruder and then transferred into the hose connected with the meltblown die. The conditions for forming the meltblown webs are set forth below in Table 3. Further, various mechanical properties of the webs were tested at dry conditions a 2-week period at room temperature and at 55°C, and also at wet conditions after being soaked in a wiping solution. The results are set forth below in Table 4.

Table 3: Extruder Profile

Table 4: Meltblown Web Properties

While the invention has been described in detail with respect to the specific embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to,

variations of, and equivalents to these embodiments. Accordingly, the scope of the present invention should be assessed as that of the appended claims and any equivalents thereto.