WO2009024837A1 - Method for forming polylactic acid fibers - Google Patents

Abstract

A method of forming a polylactic acid fiber that involves the use of a macrocyclic ester oligomer to improve the crystallization properties of polylactic acid is provided. Without intending to be limited by theory, it is believed that the macrocyclic ester oligomer undergoes a ring-opening reaction during melt processing and thus converts to a low molecular weight linear crystal structure. These linear crystals may act as a nucleating 'seed' for increasing the degree and rate of crystallization of polylactic acid, which improves its ability to be formed into fibers and webs. That is, polymers having a higher degree of melt and crystallization enthalpy are more readily able to bond at higher speeds and also have a lower degree of shrinkage, thereby improving web stability, tensile strength, and web aesthetics.

Description

METHOD FOR FORMING POLYLACTIC ACID 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 relatively slow crystallization rate often leads to processing difficulties, such as heat shrinkage. As such, a need currently exists for a 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 fiber is disclosed. The method comprises forming a thermoplastic composition that comprises at least one polylactic acid in an amount from about 60 wt.% to about 99.9 wt.% and at least one macrocyclic ester oligomer in an amount from about 0.1 wt.% to about 25 wt.%. The method further comprises melt extruding the thermoplastic composition.

In accordance with another embodiment of the present invention, a fiber is disclosed that is formed from a thermoplastic composition. The thermoplastic composition includes at least one polylactic acid in an amount from about 60 wt.% to about 99.9 wt.% and at least one macrocyclic ester oligomer in an amount from about 0.1 wt.% to about 25 wt.%. The thermoplastic composition has a crystallization temperature of from about 100°C to about 130°C.

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 schematic illustration of a process that may be used in one embodiment of the present invention to form a nonwoven web;

Fig. 2 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. 3 is the first cooling cycle of the DSC curve of Example 2, which graphically illustrates the change in enthalpy versus temperature for the samples.

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 ah and U.S. Patent No. 5,336,552 to Strack et a!.. 5,108,820 to Kaneko, et a!.. 4,795,668 to Krueqe, et a!.. 5,382,400 to Pike, et a!.. 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 HiNs, 5,466,410 to H]IIs, 5,069,970 to Larqman, et al.. and 5,057,368 to Largman, 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 Kinney, 3,341 ,394 to Kinnev, 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 "carded web" refers to a web made from staple fibers that are sent through a combing or carding unit, which separates or breaks apart and aligns the staple fibers in the machine direction to form a generally machine direction-oriented fibrous nonwoven web. Such fibers are usually obtained in bales and placed in an opener/blender or picker, which separates the fibers prior to the carding unit. Once formed, the web may then be bonded by one or more known methods.

As used herein, the term "airlaid web" refers to a web made from bundles of fibers having typical lengths ranging from about 3 to about 19 millimeters (mm). The fibers are separated, entrained in an air supply, and then deposited onto a forming surface, usually with the assistance of a vacuum supply. Once formed, the web is then bonded by one or more known methods.

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

Generally speaking, the present invention is directed to a method of forming a polylactic acid fiber that involves the use of a macrocyclic ester oligomer to improve the crystallization properties of polylactic acid. Without intending to be limited by theory, it is believed that the macrocyclic ester oligomer undergoes a ring-opening reaction during melt processing and thus converts to a low molecular weight linear crystal structure. These linear crystals may act as a nucleating "seed" for increasing the degree and rate of crystallization of polylactic acid, which improves its ability to be formed into fibers and webs. That is, polymers having a higher degree of melt and crystallization enthalpy are more readily able to bond at higher speeds and also have a lower degree of shrinkage, thereby improving web stability, tensile strength, and web aesthetics.

Various embodiments of the present invention will now be described in more detail. I. Thermoplastic Composition 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 melting point of from about 100⁰C to about 240°C, in some embodiments from about 120⁰C to about 220⁰C, and in some embodiments, from about 140⁰C to about 200⁰C. Such polylactic acids are useful in that they biodegrade at a fast rate. The glass transition temperature ("T₉") of the polylactic acid may be relatively high, such as from about 10°C to about 80⁰C, in some embodiments from about 2O⁰C to about 70⁰C, and in some embodiments, from about 25⁰C to about 65⁰C. 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. 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.e., 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 19O⁰C 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., 190⁰C), measured in accordance with ASTM Test Method D1238-E. B. Macrocyclic Ester Oligomers

The term "macrocyclic ester oligomer" 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 Il I! wherein,

R¹ 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. Macrocyclic ester oligomers typically have a low apparent viscosity that provides greater processing flexibility and also allows them to be more easily formed into fibers. The apparent viscosity of the oligomers may, for example, be about 300 milliPascals^*seconds (mPa-s) or less, in some embodiments about 250 mPa-s or less, and in some embodiments, about 200 rnPa-s or less, as determined at a temperature of 180°C. Other properties of the macrocyclic ester oligomers make them advantageous for use in resins used to form fibers. For instance, macrocyclic ester oligomers are typically dimensionally stable and resistant to heat and chemical attack. Fibers thus composed of macrocyclic ester oligomers generally have improved ductility, impact resistance, tensile strength, and other properties. Additionally, a material advantage of some macrocyclic ester oligomers is that they are biodegradable.

The amount of macrocyclic ester oligomers may be selectively controlled to achieve the desired properties for the fibers. For example, too low an amount of the oligomers may result in heat shrinkage, while too high of an amount may result in a loss of tensile fiber. Thus, the oligomers are typically 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 thermoplastic composition. Likewise, polylactic acid typically constitutes from about 60 wt.% to about 99.9 wt.%, in some embodiments from about 70 wt.% to about 99.8 wt.%, in some embodiments from about 90 wt.% to about 99.5 wt.%, and in some embodiments, from about 95 wt.% to about 99 wt.% of the thermoplastic composition. C. Other Components Other components may of course be utilized for a variety of different reasons. For instance, a plasticizer may be employed to help lower the viscosity of the polylactic acid and improve its flexibility. When utilized, such plasticizers may constitute from about 1 wt.% to about 30 wt.%, in some embodiments from about 2 wt.% to about 25 wt.%, and in some embodiments, from about 5 wt.% to about 20 wt.%, of the thermoplastic composition. Any plasticizer that is compatible with 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, poly-1 ,3- propanediol, 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 hydroxy! groups that can attack the ester linkages of the polylactic acid and result in chain scission, thus improving the flexibility of the polylactic acid. Such hydroxyl-group containing plasticizers may also attack the ring of the macrocyclic oligomer and bind to the oligomer. Polyethylene glycol ("PEG"), for instance, is an example of a plasticizer that is particularly effective in decreasing the constraints on mobility and as a result helps provide a higher crystallization rate within a broader thermal window. 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.

Water, is another component that may be employed in the present invention. Under appropriate conditions, water is also capable of hydrolytically degrading the starting polylactic acid and thus reducing its molecular weight. The hydroxy! groups of water are believed to attack the ester linkages of the polylactic acid, thereby causing 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 0 to about 5000 parts per million ("ppm"), in some embodiments from about 20 to about 4000 ppm, and in some embodiments, from about 100 to about 3000, and in some embodiments, from about 1000 to about 2500 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.

Still other materials that may be used include, without limitation, wetting agents, melt stabilizers, processing stabilizers, heat stabilizers, light stabilizers, antioxidants, pigments, surfactants, waxes, flow promoters, particulates, and other materials added to enhance processability. II. Melt Processing

The melt processing of the polylactic acid, macrocyclic ester oligomer, and any optional additional components may be performed using any of a variety of known techniques. In one embodiment, for example, the raw materials (e.g., polylactic acid, macrocyclic ester oligomer, etc.) may be supplied separately or in combination. For instance, the raw materials may first be dry mixed together to form an essentially homogeneous dry mixture. The raw materials may likewise be supplied either simultaneously or in sequence to a melt processing device that dispersively blends the materials. Batch and/or continuous melt processing techniques may be employed. For example, a mixer/kneader, Banbury mixer, Farrel continuous mixer, single-screw extruder, twin-screw extruder, roll mill, etc., may be utilized to blend and melt process the materials. One particularly suitable melt processing device is a co-rotating, twin-screw extruder (e.g., ZSK-30 twin- screw extruder available from Werner & Pfleiderer Corporation of Ramsey, New Jersey). Such extruders may include feeding and venting ports and provide high intensity distributive and dispersive mixing. For example, the polylactic acid and macrocyclic ester oligomer may be fed to a feeding port of the twin-screw extruder and melt blended to form a substantially homogeneous melted mixture. If desired, water or other additives (e.g., organic chemicals) may be thereafter injected into the polymer melt and/or separately fed into the extruder at a different point along its length. Alternatively, the polylactic acid may simply be supplied in a pre- humidified state.

Regardless of the particular melt processing technique chosen, the raw materials may be blended under high shear/pressure and heat to ensure sufficient dispersion. For example, melt processing may occur at a temperature of from about 50°C to about 500⁰C, in some embodiments, from about 100⁰C to about 350⁰C, and in some embodiments, from about 150⁰C to about 300⁰C. Likewise, the apparent shear rate during melt processing may 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. The apparent shear rate is equal to 4Q/πR³, where Q is the volumetric flow rate ("m³/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 homogeneity.

Under appropriate conditions, it is believed that the macrocyclic ester oligomer undergoes a ring-opening reaction during melt processing and thus converts to a low molecular weight linear structure that may readily act as a "nucleating" agent for improving the crystallization properties of the polylactic acid. That is, the thermoplastic composition may crystallize at a higher temperature and at a faster crystallization rate than the starting polylactic acid, which may allow the thermoplastic composition to more readily processed. The crystallization temperature may, for instance, be increased so that the ratio of the thermoplastic composition crystallization temperature to the starting polylactic acid crystallization temperature is greater than 1 , in some embodiments at about 1.2 or more, and in some embodiments, about 1.5 or more. For example, the crystallization temperature of the thermoplastic composition may range from about 60⁰C to about 130°C, in some embodiments from about 80°C to about 130°C, and in some embodiments, from about 100⁰C to about 130⁰C. Likewise, the ratio of the crystallization rate during the first cooling cycle (expressed in terms of the latent heat of crystallization, ΔH_C) of the thermoplastic composition to the crystallization rate of the starting polylactic acid is greater than 1 , in some embodiments about 2 or more, and in some embodiments, about 3 or more. For example, the thermoplastic composition may possess a latent heat of crystallization (ΔH_C) during the first cooling cycle of about 10 J/g or more, in some embodiments about 20 J/g or more, and in some embodiments, about 30 J/g or more. The thermoplastic composition may also have a latent heat of fusion (ΔH_f) of about 15 Joules per gram ("J/g") or more, in some embodiments about 20 J/g or more, and in some embodiments about 30 J/g or more, and in some embodiments, about 40 J/g or more. Furthermore, the composition may also exhibit a width (ΔW1/2) at the half height of the crystallization peak of about 2O⁰C or less, in some embodiments about 10⁰C or less, and in some embodiments, about 5°C or less. The latent heat of fusion (ΔH_f), latent heat of crystallization (ΔH_C), crystallization temperature, and width at the half height of the crystallization peak may all be determined as is well known in the art using differential scanning calorimetry ("DSC") in accordance with ASTM D-3417.

Due to the increase in the crystallization temperature, the temperature window between the glass transition temperature and crystallization temperature is also increased, which provides for greater processing flexibility by increasing the residence time for the material to crystallize. For example, the temperature window between the crystallization temperature and glass transition temperature of the thermoplastic composition may be about 20°C apart, in some embodiments about 4O⁰C apart, and in some embodiments greater than about 60⁰C apart. In addition to possessing a higher crystallization temperature and broader temperature window, the thermoplastic composition may also exhibit improved processability due to a lower apparent viscosity and higher melt flow rate than the starting polylactic acid. Thus, when processed in equipment lower power settings can be utilized, such as using less torque to turn the screw of the extruder. The apparent viscosity may for instance, be reduced so that the ratio of the starting polylactic acid viscosity to the thermoplastic composition 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 thermoplastic composition 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 thermoplastic composition may have a melt flow rate (dry basis) of from about 1 to about 500 grams per 10 minutes, in some embodiments from about 2 to about 100 grams per 10 minutes, and in some embodiments, from about 5 to about 50 grams per 10 minutes (190°C, 2.16 kg). Of course, the extent to which the apparent viscosity, melt flow rate, etc. are altered (if at all) by the addition of the macrocyclic ester oligomer may vary depending on the intended application. III. Fiber Formation Fibers formed from the thermoplastic composition 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 thermoplastic composition 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 biodegradable, 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 biodegradable, such as aliphatic polyesters, such as polyesteramides, modified polyethylene terephthalate, polylactic acid (PLA) and its copolymers, terpolymers based on polylactic acid, 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. 1 , 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 thermoplastic composition having the desirable combination of low apparent viscosity and high melt flow rate.

In Fig. 1 , for instance, the raw materials (e.g., polylactic acid, macrocyclic ester oligomer, etc.) are fed into an extruder 12 from a hopper 10. The raw materials may be provided to the hopper 10 using any conventional technique and in any state. The extruder 12 is driven by a motor 11 and heated to a temperature sufficient to extrude the melted polymer. For example, the extruder 12 may employ one or multiple zones operating at a temperature of from about 50⁰C to about 500°C, in some embodiments, from about 100°C to about 400°C, and in some embodiments, from about 150°C to about 250⁰C. 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 thermoplastic composition may be subsequently fed to another extruder in a fiber formation line (e.g., extruder 12 of a meltblown spinning line). Alternatively, the thermoplastic composition 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. 1 , 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. 1 , 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 Levy et al., U.S. Patent No. 5,962,112 to Havnes et a!.. U.S. Patent 6,093,665 to Savovitz et al., 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 thermoplastic composition 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 thermoplastic composition 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 thermoplastic composition 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 thermoplastic composition 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.% thermoplastic composition 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 Georqer, et al.: which are incorporated herein in their entirety by reference thereto for all purposes.

Referring to Fig. 2, 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 thermoplastic composition. For example, the nonwoven web of one layer may be a meltblown or coform web that contains the thermoplastic composition, while the nonwoven web of another layer contains thermoplastic composition, 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 thermoplastic composition. The spunbond layer may be formed from the thermoplastic composition, 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 Bornslaeger; 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. III. Articles

The nonwoven web 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., outer cover), a liquid-permeable layer (e.g., bodyside liner, surge layer, etc.), and an absorbent core. In one embodiment, for example, a nonwoven web formed according to the present invention may be used to form an outer cover of an absorbent article. If desired, the nonwoven web may be laminated to a liquid-impermeable film that is either vapor-permeable or vapor-impermeable.

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

Test Methods 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°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. 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 190⁰C or 23O⁰C. 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.

Thermal Properties: The melting temperature, glass transition temperature and degree of crystallinity of a material was determined by differential scanning calorimetry (DSC). The differential scanning calorimeter was a DSC Q100 Differential Scanning Calorimeter, which was outfitted with a liquid nitrogen cooling accessory and with a UNIVERSAL ANALYSIS 2000 (version 4.6.6) analysis software program, both of which are available from T.A. Instruments Inc. of New Castle, Delaware. To avoid directly handling the samples, tweezers or other tools were used. The samples were placed into an aluminum pan and weighed to an accuracy of 0.01 milligram on an analytical balance. A lid was crimped over the material sample onto the pan. Typically, the resin pellets were placed directly in the weighing pan, and the fibers were cut to accommodate placement on the weighing pan and covering by the lid.

The differential scanning calorimeter was calibrated using an indium metal standard and a baseline correction was performed, as described in the operating manual for the differential scanning calorimeter. A material sample was placed into the test chamber of the differential scanning calorimeter for testing, and an empty pan is used as a reference. All testing was run with a 55-cubic centimeter per minute nitrogen (industrial grade) purge on the test chamber. For resin pellet samples, the heating and cooling program was a 2-cycle test that began with an equilibration of the chamber to -25°C, followed by a first heating period at a heating rate of 10°C per minute to a temperature of 200°C, followed by equilibration of the sample at 200°C for 3 minutes, followed by a first cooling period at a cooling rate of 10°C per minute to a temperature of -25°C, followed by equilibration of the sample at -25°C for 3 minutes, and then a second heating period at a heating rate of 10°C per minute to a temperature of 200°C. For fiber samples, the heating and cooling program was a 1 -cycle test that began with an equilibration of the chamber to -25°C, followed by a heating period at a heating rate of 10°C per minute to a temperature of 200⁰C, followed by equilibration of the sample at 200°C for 3 minutes, and then a cooling period at a cooling rate of 10°C per minute to a temperature of -25°C. All testing was run with a 55-cubic centimeter per minute nitrogen (industrial grade) purge on the test chamber.

The results were then evaluated using the UNIVERSAL ANALYSIS 2000 analysis software program, which identified and quantified the glass transition temperature (T₉) of inflection, the endothermic and exothermic peaks, and the areas under the peaks on the DSC plots. The glass transition temperature was identified as the region on the plot-line where a distinct change in slope occurred, and the melting temperature was determined using an automatic inflection calculation. The areas under the peaks on the DSC plots were determined in terms of joules per gram of sample (J/g). For example, the heat of fusion of a resin or fiber sample was determined by integrating the area of the endothermic peak. The area values were determined by converting the areas under the DSC plots (e.g. the area of the endotherm) into the units of joules per gram (J/g) using computer software. The exothermic heat of crystallization (ΔH_C) was determined during the first cooling cycle. In certain cases, the exothermic heat of crystallization was also determined during the first heating cycle (ΔH_ci) and the second cycle (ΔH_C2)-

If desired, the % crystallinity may also be calculated as follows:

% crystallinity = 100 * (A - B)IC wherein,

A is the sum of endothermic peak areas during the heating cycle (J/g); B is the sum of exothermic peak areas during the heating cycle (J/g); and C is the heat of fusion for the selected polymer where such polymer has 100% crystallinity (J/g). For polylactic acid, C is 93.7 J/g (Cooper-White, J. J., and Mackay, M. E., Journal of Polymer Science, Polymer Physics Edition, p.1806, Vol. 37, (1999)). The areas under any exothermic peaks encountered in the DSC scan due to insufficient crystallinity may also be subtracted from the area under the endothermic peak to appropriately represent the degree of crystallinity. 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 25.4 millimeters (width) x 152.4 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%.

Three samples were tested by applying the test load along the machine- direction ("MD") and three 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), and "energy to peak" were measured.

EXAMPLE 1

A polylactic acid (PLA) polymer resin was obtained from Biomer Inc. (Germany) under the designation BIOMER™ L-9000. Macrocyclic poly(1 ,4- butylene terephthalate) was obtained from Cyclics Corporation under the name CBT® 100 Thermoplastic Resin. The polylactic acid polymer resin and CBT® 100 resin were combined in various amounts and conditions as described below in Table 1 and melt processed using a Wernerer Phleiderer Model ZSK-30 co- rotating, twin screw extruder. The length of the screw was 1328 millimeters, and the screw speed was from about 150 revolutions per minute to about 500 revolutions per minute. The extruder had 7 temperature zones and consisted of 14 barrels numbered consecutively from the feed hopper to the die. The first barrel received the BIOMER™ L-9000 resin and CBT® 100 via two volumetric feeders at a total throughput of 20 pounds per hour. The die used to extrude the resin had 3 die openings (6 millimeters in diameter) that were separated by 4 millimeters. After extrusion, the modified polymer strands were cooled on a conveyor belt and palletized using a Conair pelletizer. Reactive extrusion parameters were monitored during the reactive extrusion process. The conditions are set forth below in Table 1.

Table 1 : Compounding Conditions for Samples 1 -9

Compundlng conditions for PLA L-9000 and CBT100

PLA L-9000 Moisture CBT100 Throughput Speed Zoπe i Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Zone 7 Tmelt Pmelt Torque

Samples (%) (ppm) (%) (IWh) (rpm) CC) (°C) ("C) CC) ("C) CC) CC) ("C) (Psi) (%)

No 1 95 20 20 160 190 220 220 220 220 220 160 174 215 58

No 2 90 20 10 20 160 190 220 220 220 220 220 160 176 190 54

No 3 85 20 15 20 160 190 220 220 220 220 220 160 176 170 50

No 4 95 20 5 20 500 190 220 220 220 220 220 160 177 160 59

No 5 90 20 10 20 500 190 220 220 220 220 220 160 179 145 56

No 6 85 20 15 20 500 190 220 220 220 220 220 160 178 140 50

No 7 95 1300 5 20 500 190 220 220 220 220 220 160 177 145 55

No S 90 1380 10 20 500 190 220 220 220 220 220 160 180 140 53

No 9 85 1380 15 20 500 190 220 220 220 220 220 160 178 140 50

As indicated, the torque and die pressure of the extruder were moderately reduced as the amount of CBT® 100 increased. For instance, the torque decreased from about 59% (Sample 4) to about 50% (Sample 6). The melt flow index of each sample was determined using method ASTM D-1239 with a Tinius Olsen Extrusion Plastometer at 190⁰C and 2.16 kilograms. The results are illustrated in Table 2 and show that increased amounts of CBT® 100 can moderately reduce the melt viscosity of PLA. Thus, the processability of the thermoplastic composition improved with the addition of CBT® 100.

Table 2: Melt Flow Index Data

MFI for PLA and CBT 100 blends

Samples No 1 No 2 No 3 No 4 No 5 No 6 No 7 No 8 No 9

MFI at 190 ⁰C and 2.16Kg 12.3 15.8 19.2 14.4 17.8 20.6 27.8 28.7 29.6

The compounded PLA and CBT® 100 Samples 1-9 were also subjected to DSC analysis. Thermogram of the blends showed that addition of CBT® 100 significantly increased the crystallization rate of PLA. During the first cool cycle, there was no apparent crystallization observed for PLA L-9000 alone. However, with a 5% addition of CBT® 100 (Sample 4), PLA crystallized with a temperature peak at 92.5⁰C and a width at the half height of the crystallization peak of 15.6⁰C. A 10% addition of CBT® 100 (Sample 5) increased the crystallization peak temperature to 110.4⁰C and decreased the width to 4.9°C. Therefore, the CBT®

100 significantly increased the crystallization temperature, the latent heat of crystallization during the firs cool cycle, and crystallization rate of PLA, as illustrated in Table 3.

Table 3: Thermal Properties

Thermal properties of PLA, CBT100 and their blends

2nd Heat 1st Cool

Sample Tg (⁰C) Tm (⁰C) ΔHc2 (J/g) ΔHf (J/g) ΔHc(J/g) Tc (⁰C) ΔW1/2 (⁰C)

PLA L-9000 61.5 167.6 3.9 0 n/a n/a

CBT100 23.5 126.5 24.4 5.8 74 19.7

No 4 59.7 165.8 5.6 29.7 13.2 92.5 15.6

No 5 56.9 166.3 26.5 24.1 110.4 4.9

No 6 55.2 165.1 27.2 25.1 110.9 6.4 EXAMPLE 2

A polylactic acid resin was obtained from NatureWorks LLC (Minnetonka, Minnesota) under the designation of PLA 6200D. The polylactic acid resin was pre-conditioned at open ambient condition to give a final moisture level of 1380 parts per million. Sample 10 was then formed from the moisturized PLA resin melt blended with 17.5% polyethylene glycol (PEG) 8000 from Dow under the trademark of Carbowax 8000 with a ZSK-30 twin screw extruder as described above. The extruded PLA blend was dried overnight at 13O⁰F to give a moisture level of 700 parts per million. The dried PLA blend (Sample 10) was compounded with 5% of CBT® 100 with a total throughput of 30 pounds per hour to result in Sample 11. The compounding conditions for Samples 10 and 11 are illustrated in Table 4.

Table 4: Compounding Conditions for Samples 10 and 11

Samples Compuπdlπg conditions for PLA 6200D, PEG 8000 and CBT100

PLA 6200D Moisture PEG 8000 Throughput Speed Zone 1 Zone 2 Zone 3 Zone 7 Tmelt p_me[_t Torque Samples I (%) (ppm) (%) (Ib/h) (rpm) ("C) l°C) ("C) ("C) ("C) (PsI) (%)

No 10 825 1370 17 5 25 450 100 235 120 14B

PLA/PEG 150 (low

No 11 (95%) 800 CBT (5%) 30 shear) 150 170

DSC analysis, shown in Table 5, for Sample 10 showed a broad crystallization peak during the first cool cycle with the crystallization peak at 85.8°C and the width at the half height of the crystallization peak at 13.7°C. However, with the addition of 5% CBT® 100 into sample 10 through melt blending, Sample 11 gave a sharp crystallization peak at 109⁰C and a width at the half height of the crystallization peak at 3.4°C. The heat of fusion of Sample 10 and Sample 11 were 14.2 and 30 Joules per gram, respectively. Table 5: Thermal Properties for Samples 10 and 11

Thermal properties of PLA blends

2nd Heat 1 st Cool

Sample Tg (⁰C) Tm (⁰C) ΔHf (J/g) ΔHc(J/g) Tc (⁰C) ΔW1/2

No 10 No CBTIOO N/A 164.5 28.9 14.2 85.8 13.7 No 1 1 5% CBT 100 N/A 164.3 31 30 109 3.4

DSC curves of the first cool cycles for the samples are also shown in Fig. 3. The first peak shown for Sample 11 in Fig. 3, for instance, is the crystallization peak during the first cooling cycle.

EXAMPLE 3

Sample 10, Sample 11 , and a dry blend consisting of 20 pounds of Sample 10 with 5% CBT® 100 were used to form a meltblown web. 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-inch spray and an orifice size of 0.0145 inch. The modified resin was fed via gravity into the extruder and then transferred into the hose connected with the meltblown die. Table 6 shows the process conditions used during spinning. Melt blown Samples 12, 13, and 14 were made from resin samples, Sample 10, Sample 10 dry blended with 5% CBT® 100, and Sample 11 , respectively. The meltblown webs were analyzed by DSC, and the results are shown in Table 7. Thermo analysis by DSC demonstrated that the meltblown web from CBT® 100 containing resin gave a higher crystallization temperature and a much faster crystallization rate. For instance, Sample 12 containing no CBT® 100 had a width at the half height of the crystallization peak of 12⁰C compared to Sample 14, which had a width at the half height of the crystallization peak of 4°C.

Table 6: Meltblown Web Processing Conditions

Extruder profile FrimaryAir

Samples Zone temp from 1-4 (F) Speed (rpm) Ftessure (FSi) Hose (F) De(F) Temp (F) Fressure (FSi)

No 10 280 375 380 375 25 83 350 370 420 55

No 10 dry bend with

5%CBΠOO 280 375 380 375 25 81 350 370 420 55

No 11 280 375 380 375 25 80 350 370 420 55

Table 7: Meltblown Web Thermal Properties

The tensile properties of melt blown Samples 12-14 were tested. The results are illustrated in Table 8. Although there was little change in the tensile strength ("peak load") and percentage strain at break among Samples 12-14, the elongation (i.e., % strain at peak load) of Sample 13 and Sample 14 were much higher than those of Sample 12. Additionally, the energy to peak of Samples 13 and 14 were also increased compared to Sample 12.

Table 8: Meltblown Web Thermal Properties

MB Samples measured with 1" X6" strips on a Sintech 1/D

Samples Base weight Peak Load (gf) Strain at Peak (%) % Strain at Break Energy to Peak (in*lbf)

MD 21 750 ± 60 29 ± 34 425 ± 26 1 8 ± 24

CD 222 438 ± 34 33 7 ± 18 5 40 + 20 6 1 18 + 0 75

MD 20 735 ± 44 48 + 15 50 5 ± 123 286 ± 0 9

CD 21 425 ± 38 68 9 ± 144 71 4 ± 166 236 + 0 65

MD 20 2 797 ± 22 80 6 ± 18 7 87 + 18 7 52 ± 1 21

CD 21 471 ± 18 854 ± 224 91 ± 237 3 22 ± 0 88

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.

Claims

WHAT IS CLAIMED IS:

1. A method for forming a fiber, the method comprising: forming a thermoplastic composition that comprises at least one polylactic acid in an amount from about 60 wt.% to about 99.9 wt.% and at least one macrocyclic ester oligomer in an amount from about 0.1 wt.% to about 25 wt.%; extruding the thermoplastic composition.

2. The method of claim 1 , wherein the macrocyclic ester oligomer contains a cyclic molecule having 8 or more atoms covalently connected to form a ring.

3. The method of claim 1 , wherein the macrocyclic ester oligomer has a structural repeat unit of the formula: o o

H Ii

wherein,

R¹ is an alkylene, cycloalkylene, or a mono- or polyoxyalkylene group; and

A is a divalent aromatic or alicyclic group.

4. The method of claim 3, wherein the macrocyclic ester oligomer is 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, or a co-ester oligomer thereof.

5. The method of claim 1 , wherein the macrocyclic ester oligomer has an apparent viscosity of about 200 Pa-s or less, as determined at a temperature of about 180⁰C.

6. The method of claim 1 , wherein the macrocyclic ester oligomer constitutes from about 0.5 wt.% to about 10 wt.% of the thermoplastic composition.

7. The method of claim 1 , wherein the ratio of the thermoplastic composition crystallization temperature to the polylactic acid crystallization temperature is greater than 1.

8. The method of claim 1 , wherein the thermoplastic composition has a crystallization temperature of from about 60⁰C to about 130⁰C.

9. The method of claim 1 , wherein the thermoplastic composition has a crystallization temperature of from about 100⁰C to about 130⁰C.

10. The method of claim 1 , wherein the ratio of the latent heat of crystallization of the thermoplastic composition during the first cooling cycle to the latent heat of crystallization of the polylactic acid during the first cooling cycle is greater than 1 , as determined using differential scanning calorimetry in accordance with ASTM D-3417.

11. The method of claim 1 , wherein the latent heat of crystallization of the thermoplastic composition during the first cooling cycle is about 10 J/g or more, as determined using differential scanning calorimetry in accordance with ASTM D- 3417.

12. The method of claim 1 , wherein the latent heat of crystallization of the thermoplastic composition during the first cooling cycle is about 20 J/g or more, as determined using differential scanning calorimetry in accordance with ASTM D- 3417.

13. The method of claim 1 , wherein the thermoplastic composition exhibits a width at the half height of the crystallization peak of about 20°C or less, as determined using differential scanning calorimetry in accordance with ASTM D- 3417.

14. The method of claim 1 , wherein the thermoplastic composition exhibits a width at the half height of the crystallization peak of about 10⁰C or less, as determined using differential scanning calorimetry in accordance with ASTM D- 3417.

15. The method of claim 1 , wherein the thermoplastic composition further comprises a plasticizer.

16. The method of claim 15, wherein the plasticizer is an alkylene glycol, alkane diol, alkylene oxide, or a combination thereof.

17. The method of claim 1 , wherein the polylactic acid contains monomer units derived from L-lactic acid, D-lactic acid, meso-lactic acid, or mixtures thereof.

18. The method of claim 1 , wherein the polylactic acid is a copolymer that contains monomer units derived from L-lactic acid and monomer units derived from D-lactic acid.

19. The method of claim 1 , wherein the polylactic acid constitutes from about 90 wt.% to about 99.5 wt.% of the thermoplastic composition.

20. The method of claim 1 , wherein the thermoplastic composition is extruded through a meltblowing die.

21. A fiber formed from a thermoplastic composition that comprises at least one polylactic acid in an amount from about 60 wt.% to about 99.9 wt.% and at least one macrocyclic ester oligomer in an amount from about 0.1 wt.% to about 25 wt.%, wherein the thermoplastic composition has a crystallization temperature of from about 100⁰C to about 130°C.

22. The fiber of claim 21 , wherein the macrocyclic ester oligomer has a structural repeat unit of the formula: o o Il I! wherein,

R¹ is an alkylene, cycloalkylene, or a mono- or polyoxyalkylene group; and

A is a divalent aromatic or alicyclic group.

23. The fiber of claim 22, wherein the macrocyclic ester oligomer is 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, or a co-ester oligomer thereof.

24. The fiber of claim 21 , wherein the oligomer constitutes from about 0.5 wt.% to about 10 wt.% of the thermoplastic composition.

25. The fiber of claim 21 wherein the latent heat of crystallization of the thermoplastic composition during the first cooling cycle is about 10 J/g or more, as determined using differential scanning calorimetry in accordance with ASTM D- 3417.

26. The fiber of claim 21 , wherein the latent heat of crystallization of the thermoplastic composition during the first cooling cycle is about 20 J/g or more, as determined using differential scanning calorimetry in accordance with ASTM D- 3417.

27. The fiber of claim 21 , wherein the thermoplastic composition exhibits a width at the half height of the crystallization peak of about 20⁰C or less, as determined using differential scanning calorimetry in accordance with ASTM D-

3417.

28. The fiber of claim 21 , wherein the thermoplastic composition exhibits a width at the half height of the crystallization peak of about 1O⁰C or less, as determined using differential scanning calorimetry in accordance with ASTM D- 3417.

29. The fiber of claim 21 , wherein the polylactic acid contains monomer units derived from L-lactic acid, D-lactic acid, meso-lactic acid, or mixtures thereof.

30. The fiber of claim 21 , wherein the thermoplastic composition further comprises a plasticizer.

31. The fiber of claim 30, wherein the plasticizer is an alkylene glycol, alkane diol, alkylene oxide, or a combination thereof.

32. The fiber of claim 21 , wherein the polylactic acid constitutes from about 90 wt.% to about 99.5 wt.% of the thermoplastic composition.

33. A nonwoven web comprising the fiber of claim 21.

34. The nonwoven web of claim 33, wherein the web is a meltblown web.

35. The nonwoven web of claim 34, wherein the web is a composite that further comprises an absorbent material.

36. The nonwoven web of claim 33, wherein the web is a spunbond web.

37. An absorbent article comprising an absorbent core positioned between a liquid-permeable layer and a generally liquid-impermeable layer, the absorbent article comprising the nonwoven web of claim 33.

38. A wipe comprising the nonwoven web of claim 33.