Polyhydroxyalkanoate fiber

Abstract

Disclosed is a synthetic fiber formed from a composition made from about 1 to about 98 weight percent of at least one polyhydroxyalkanoate; about 1 to about 10 weight percent of at least one nucleating agent selected from the group consisting of polyester wax, behenamide, crodamide, stearamide, erucamide, pentaerythritol, dipentaerythritol, boron nitride, and mixtures thereof; and about 0.1 to about 5 weight percent of at least one melt flow modifier selected from the group consisting of calcium stearate, zinc stearate, starch, diamide oligomers, organic peroxides, and mixtures thereof.

Description

[Technical Field]

[0001] The present disclosure relates generally to synthetic fibers. More particularly, the present disclosure relates to synthetic fibers made from polyhydroxyalkanoates combined with a second biopolymer. [Background technology]

[0002] Synthetic fibers are traditionally made from petroleum-based polymers such as polypropylene or polyethylene terephthalate. Despite the good mechanical properties of these polymers, there is a growing demand for fibers made from more environmentally friendly materials such as polyhydroxyalkanoates (PHAs). However, PHA fibers have been found to be difficult to process due to poor mechanical strength and / or thermal decomposition compared to petroleum-based polymers.

[0003] Therefore, it is desirable, and an object of the present disclosure, to provide synthetic fibers formed from PHA-based compositions that have improved mechanical properties and resistance to thermal degradation. Preferably, fibers formed from these PHA-based compositions have mechanical properties comparable to those of fibers formed from petroleum-based polymers.

[0004] It is also desirable, and an object of the present disclosure, to provide a method for forming synthetic fibers from PHA-based compositions that preserves the molecular weight and mechanical properties of the PHA-based compositions. Summary of the Invention

[0005] These and other needs are met by synthetic fibers formed from PHA-based compositions in accordance with the present disclosure.

[0006] In one aspect, the present disclosure provides synthetic fibers. According to certain embodiments, the synthetic fibers are formed from a composition made from about 1 to about 98 weight percent of at least one polyhydroxyalkanoate. The composition also comprises about 1 to about 10 weight percent of at least one nucleating agent selected from the group consisting of polyester wax, behenamide, crodamide, stearamide, erucamide, pentaerythritol, dipentaerythritol, boron nitride, and mixtures thereof; and about 0.1 to about 5 weight percent of at least one melt flow modifier selected from the group consisting of calcium stearate, zinc stearate, starch, diamide oligomers, organic peroxides, and mixtures thereof.

[0007] Preferably, the composition is made from about 30 to about 70 weight percent of at least one polyhydroxyalkanoate, about 1 to about 5 weight percent of at least one nucleating agent, and about 0.1 to about 3 weight percent of at least one melt flow modifier. Even more preferably, the composition is made from about 40 to about 60 weight percent of at least one polyhydroxyalkanoate, about 1.5 to about 3 weight percent of at least one nucleating agent, and about 0.2 to about 3 weight percent of at least one melt flow modifier.

[0008] In some embodiments, the composition can include a mixture of different polyhydroxyalkanoates. In some embodiments, for example, the composition can be comprised of from about 1 to about 97 weight percent of at least one polyhydroxyalkanoate copolymer or terpolymer and from 1 to about 20 weight percent of polyhydroxybutyrate.

[0009] Preferably, the composition comprises from about 30 to about 70 of at least one polyhydroxyalkanoate copolymer or terpolymer and from 5 to about 15 weight percent of polyhydroxybutyrate. Even more preferably, the composition comprises from about 40 to about 60 of at least one polyhydroxyalkanoate copolymer or terpolymer and from 7 to about 12 weight percent of polyhydroxybutyrate.

[0010] In certain embodiments, other biodegradable polymers can be included along with the polyhydroxyalkanoate. For example, the composition can include about 30 to about 65 weight percent of at least one polyhydroxyalkanoate and about 30 to about 60 weight percent of at least one biopolymer selected from the group consisting of polylactic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, phenylbenzimidazole sulfonic acid, and mixtures thereof.

[0011] Preferably, the composition may comprise from about 35 to about 60 weight percent of at least one polyhydroxyalkanoate and from about 30 to about 50 weight percent of at least one biopolymer. Even more preferably, the composition may comprise from about 40 to about 56 weight percent of at least one polyhydroxyalkanoate and from about 30 to about 40 weight percent of at least one biopolymer.

[0012] In some embodiments, the at least one polyhydroxyalkanoate comprises a polyhydroxyalkanoate copolymer.

[0013] According to certain embodiments, at least one poly(hydroxyalkanoate) is made from about 5 to about 20 mole percent of monomer repeat units selected from the group consisting of 3-hydroxyhexanoate, 3-hydroxyoctanoate, 3-hydroxydecanoate, and mixtures thereof. Even more preferably, at least one poly(hydroxyalkanoate) is made from about 10 to about 15 mole percent of monomer repeat units.

[0014] In some cases, the at least one polyhydroxyalkanoate is comprised of poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (P3HB-co-P3HHx), which contains from about 2 to about 8 mole percent 3-hydroxyhexanoate monomer repeat units.

[0015] In certain embodiments, at least one polyhydroxyalkanoate is comprised of a polyhydroxyalkanoate terpolymer, which in turn is comprised of from about 75 to about 99.8 mole percent monomeric repeat units of 3-hydroxybutyrate, from about 0.1 to about 24.9 mole percent monomeric repeat units of 3-hydroxyhexanoate, and from about 0.1 to about 24.9 mole percent monomeric repeat units of a third 3-hydroxyalkanoate selected from the group consisting of 3-hydroxyhexanoate, 3-hydroxyoctanoate, and 3-hydroxydecanoate.

[0016] Preferably, the terpolymer is composed of from about 80 to about 95 mole percent 3-hydroxybutyrate monomer repeat units, from about 0.9 to about 19.9 mole percent 3-hydroxyhexanoate monomer repeat units, and from about 0.1 to about 19.1 mole percent of a third 3-hydroxyalkanoate monomer repeat unit.

[0017] More preferably, the terpolymer is composed of from about 85 to about 90 mole percent 3-hydroxybutyrate monomer repeat units, from about 1.9 to about 11.1 mole percent 3-hydroxyhexanoate monomer repeat units, and from about 3.9 to about 13.1 mole percent third 3-hydroxyalkanoate monomer repeat units.

[0018] In some embodiments, the composition preferably comprises from about 30 to about 50 weight percent of at least one polyhydroxyalkanoate and further comprises from about 5 to about 20 weight percent of at least one filler selected from the group consisting of calcium carbonate, talc, polysaccharides, starch, clay, diatomaceous earth, kaolinite, montmorillonite, bentonite, silica, chitin, titanium dioxide, nanoclay, mica, hemp, nanocellulose, and mixtures thereof.

[0019] Preferably, the composition comprises from about 32 to about 45 weight percent of at least one polyhydroxyalkanoate and from about 7 to about 18 weight percent of at least one filler, more preferably from about 37 to about 43 weight percent of at least one polyhydroxyalkanoate and from about 10 to about 15 weight percent of at least one filler.

[0020] In certain cases, the at least one biopolymer preferably comprises polylactic acid.

[0021] In certain embodiments, the at least one polyhydroxyalkanoate preferably has a weight average molecular weight of about 50,000 to about 1,500,000 daltons as determined by ASTM D5296-05, preferably about 200,000 to about 1,000,000 daltons, more preferably about 300,000 to about 600,000 daltons.

[0022] According to some embodiments, the at least one polyhydroxyalkanoate preferably has a bimodal molecular weight distribution, as determined by ASTM D5296-05, with a first molecular weight peak centered between about 100,000 and about 175,000 daltons and a second molecular weight peak centered between about 200,000 and about 300,000 daltons.

[0023] In some cases, the at least one polyhydroxyalkanoate preferably has a polydispersity index, as determined by ASTM D5296-05, of about 1.5 to about 5. Preferably, the polydispersity index is about 1.75 to about 4, more preferably about 2 to 3.

[0024] In certain embodiments, the at least one polyhydroxyalkanoate has a weight average molecular weight of from about 100,000 to about 400,000 daltons, as determined by ASTM D5296-05, and a polydispersity index of from about 2 to about 3, as determined by ASTM D5296-05.

[0025] According to certain embodiments, the composition preferably has a melting temperature, as determined by ASTM D3418, of from about 110°C to about 165°C, more preferably from about 135°C to about 155°C, and even more preferably from about 140°C to about 150°C.

[0026] Additionally, in some embodiments, the composition preferably has a melt flow index of from about 5 to about 1500 grams / 10 minutes when measured according to ASTM D1238 at a temperature of 175° C. and a load of 2.16 kg.

[0027] According to certain embodiments, the composition also preferably comprises from about 0.1 to about 4.0 weight percent of at least one melt strength enhancer selected from the group consisting of carbodiimides, epoxides, and mixtures thereof. Preferably, the composition comprises from about 0.5 to about 3 weight percent of the at least one melt strength enhancer. More preferably, the composition comprises from about 0.75 to about 1.5 weight percent of the at least one melt strength enhancer.

[0028] More specifically, the melt flow index of the composition is preferably selected to allow for spinning of fibers at temperatures that do not result in degradation of the polyhydroxyalkanoate polymer and loss of weight average molecular weight.

[0029] Thus, according to some embodiments, the fibers are filament spun and the composition has a melt flow index of from about 5 to about 30 grams / 10 minutes, preferably from about 10 to about 25 grams / 10 minutes, and more preferably from about 12 to about 18 grams / 10 minutes, when measured according to ASTM D1238 at a temperature of 175° C. and a load of 2.16 kg.

[0030] According to another embodiment, the nonwoven fabric is formed from synthetic fibers and the composition has a melt flow index of about 50 to about 100 grams / 10 minutes, preferably about 65 to about 90 grams / 10 minutes, and more preferably about 75 to about 85 grams / 10 minutes, when measured according to ASTM D1238 at a temperature of 175°C and a load of 2.16 kg.

[0031] In still other embodiments, the nonwoven fabric is formed from synthetic fibers and the composition has a melt flow index of from about 500 to about 1500 grams / 10 minutes, preferably from about 750 to about 1300 grams / 10 minutes, and more preferably from about 900 to about 1100 grams / 10 minutes, when measured in accordance with ASTM D1238 at a temperature of 175° C. and a load of 2.16 kg.

[0032] In some cases, the fibers are preferably oriented.

[0033] Additionally, in certain embodiments, the fibers are post-treated with a fiber lubricant composition, preferably comprising at least one lubricant selected from the group consisting of hydrophobic esters, mineral oils, silicon compositions, and mixtures thereof.

[0034] In another aspect, the present disclosure also provides a nonwoven fabric comprised of a plurality of the aforementioned synthetic fibers. In certain embodiments, the present disclosure also provides an article formed from the nonwoven fabric, the article being selected from the group consisting of medical protective equipment, personal hygiene wipes, cleaning wipes, filtration systems, diapers, feminine hygiene products, coffee / tea bags, and laundry sheets.

[0035] In a further aspect, the present disclosure provides a method for forming a plurality of synthetic fibers. According to one embodiment, the method includes blending at least one polyhydroxyalkanoate, at least one nucleating agent, and at least one melt flow modifier in a first extruder to form a resin composition. The resin composition comprises from about 1 to about 98 weight percent of the at least one polyhydroxyalkanoate, from about 1 to about 10 weight percent of at least one nucleating agent selected from the group consisting of polyester wax, behenamide, crodamide, stearamide, erucamide, pentaerythritol, dipentaerythritol, boron nitride, and mixtures thereof, and from about 0.1 to about 5 weight percent of at least one melt flow modifier selected from the group consisting of calcium stearate, zinc stearate, starch, diamide oligomers, organic peroxides, and mixtures thereof.

[0036] The method also includes melt processing the resin composition at a temperature of about 165 to about 185° C. and extruding the composition through a plurality of spinnerets to produce a plurality of fibers.

[0037] Advantageously, extruding and spinning fibers within this temperature range has been found to minimize polymer degradation and loss of polymer weight average molecular weight. To extrude and spin fibers within this relatively low temperature range, melt flow modifiers are selected to provide a composition viscosity appropriate for fiber spinning.

[0038] According to certain embodiments of this method, the plurality of fibers comprises fiber filaments having a length of at least 300 mm. In such embodiments, the resin composition preferably has a melt flow index of about 5 to about 30 grams per 10 minutes when measured according to ASTM D1238 at a temperature of 175°C and a load of 2.16 kg.

[0039] In some embodiments, the method includes the further step of collecting a plurality of fibers on a flat conveyor belt and bonding the fibers together to form a spunbond nonwoven web. In such embodiments, the resin composition preferably has a melt flow index of about 50 to about 100 grams per 10 minutes when measured according to ASTM D1238 at a temperature of 175°C and a load of 2.16 kg.

[0040] In other embodiments, the method includes the further step of collecting a plurality of fibers on a rotating carousel and bonding the fibers together to form a meltblown nonwoven web. In such embodiments, the resin composition preferably has a melt flow index of about 500 to about 1500 grams / 10 minutes when measured according to ASTM D1238 at a temperature of 175°C and a load of 2.16 kg. DETAILED DESCRIPTION OF THE INVENTION

[0041] The present disclosure provides, for the first time, synthetic fibers formed from PHA-based compositions that have improved mechanical properties and resistance to thermal degradation.

[0042] In general, the present disclosure provides synthetic fibers formed from a composition that includes at least one polyhydroxyalkanoate and, optionally, at least one additional biopolymer.

[0043] According to the present disclosure, synthetic fibers may include staple fibers, nonwoven fibers, yarn fibers, and filaments.

[0044] For example, fibers may be melt spun by melting a composition of the present disclosure and spinning the molten composition through a spinneret to form filaments. In some cases, a monofilament may be collected, while in other cases, multiple fibers may be collected together as a single strand.

[0045] The filaments so produced may be very long or may be cut into relatively short staple fibers. For staple fibers, the length of the staple fibers is typically from about 10 mm to about 150 mm. Filaments that are not cut into staple fibers typically have a length of from about 300 mm to about 5 meters.

[0046] In various embodiments, the fibers of the present disclosure can have a solid cross-section or a hollow cross-section structure. In some embodiments, the fibers of the present disclosure can have a bicomponent structure, such as a side-by-side structure, a core and sheath structure, etc.

[0047] The average cross-sectional diameter of the fibers is typically from about 2 to about 50 microns.

[0048] According to certain embodiments of the present disclosure, the fibers are preferably oriented by drawing the fibers.

[0049] In some embodiments, the fibers are also post-treated with a fiber lubricant composition, preferably comprising at least one lubricant selected from the group consisting of hydrophobic esters, mineral oils, silicon compositions, and mixtures thereof. A suitable example of such a fiber lubricant is Lurol PL, available from Goulston Technologies, Inc.

[0050] In some embodiments, fibers made from the compositions of the present disclosure may be used to form nonwoven fabrics. For example, nonwoven fabrics may be formed by a spunbond process in which multiple fibers are simultaneously extruded onto a flat conveyor belt and then bonded together (such as by thermal bonding or hydroentangling) to form a nonwoven material. Alternatively, nonwoven fabrics may be formed by a meltblown process in which a molten composition is sprayed from a thin capillary to form fine fibers that are collected on a rotating carousel and bonded together to form a nonwoven material.

[0051] A variety of articles can be formed from nonwoven fabrics according to the present disclosure, such as medical protective equipment, personal hygiene wipes, cleaning wipes, filtration systems, diapers, feminine hygiene products, coffee / tea bags, and laundry sheets.

[0052] As described above, the fibers are prepared from a composition comprising at least one polyhydroxyalkanoate. In some embodiments, the composition also comprises at least one additional biopolymer selected from the group consisting of polylactic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, phenylbenzimidazole sulfonic acid, and mixtures thereof.

[0053] Generally, the composition comprises from about 1 to about 98 weight percent of at least one polyhydroxyalkanoate, more preferably from about 30 to about 70, and even more preferably from 40 to about 60 weight percent of at least one polyhydroxyalkanoate.

[0054] In various embodiments, the at least one polyhydroxyalkanoate can comprise a homopolymer, copolymer, terpolymer, or mixtures thereof. In some cases, the composition can comprise a polyhydroxyalkanoate homopolymer, such as polyhydroxybutyrate. In other cases, the composition can comprise a polyhydroxyalkanoate copolymer.

[0055] In some embodiments, at least one poly(hydroxyalkanoate) is composed of from about 1 to about 25 mole percent, preferably from about 5 to about 20 mole percent, and more preferably from about 10 to about 15 mole percent of monomer repeat units selected from the group consisting of 3-hydroxyhexanoate, 3-hydroxyoctanoate, 3-hydroxydecanoate, and mixtures thereof.

[0056] In another embodiment, the at least one polyhydroxyalkanoate is preferably poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (P3HB-co-P3HHx), which contains from about 2 to about 8 weight percent 3-hydroxyhexanoate monomers.

[0057] In some embodiments, the at least one polyhydroxyalkanoate preferably comprises a polyhydroxyalkanoate terpolymer, the terpolymer being composed of from about 75 to about 99.8 mole percent monomeric repeat units of 3-hydroxybutyrate, from about 0.1 to about 24.9 mole percent monomeric repeat units of 3-hydroxyhexanoate, and from about 0.1 to about 24.9 mole percent monomeric repeat units of a third 3-hydroxyalkanoate selected from the group consisting of 3-hydroxyhexanoate, 3-hydroxyoctanoate, and 3-hydroxydecanoate.

[0058] More preferably, the terpolymer is composed of from about 80 to about 95 mole percent 3-hydroxybutyrate monomer repeat units, from about 0.9 to about 19.9 mole percent 3-hydroxyhexanoate monomer repeat units, and from about 0.1 to about 19.1 mole percent of a third 3-hydroxyalkanoate monomer repeat unit.

[0059] Even more preferably, the terpolymer is composed of from about 85 to about 90 mole percent 3-hydroxybutyrate monomer repeat units, from about 1.9 to about 11.1 mole percent 3-hydroxyhexanoate monomer repeat units, and from about 3.9 to about 13.1 mole percent third 3-hydroxyalkanoate monomer repeat units.

[0060] The composition may also include a mixture of polyhydroxyalkanoate homopolymers, copolymers, and / or terpolymers.

[0061] In some cases, the composition comprises from about 1 to about 97 weight percent of at least one polyhydroxyalkanoate copolymer or terpolymer, and from 1 to about 20 weight percent of polyhydroxybutyrate.

[0062] More preferably, the composition comprises about 30 to about 70 weight percent of at least one polyhydroxyalkanoate copolymer or terpolymer and about 6 to 15 weight percent of polyhydroxybutyrate. Even more preferably, the composition comprises about 40 to about 60 weight percent of at least one polyhydroxyalkanoate copolymer or terpolymer and about 7 to 12 weight percent of polyhydroxybutyrate.

[0063] In certain embodiments, the at least one polyhydroxyalkanoate preferably has a weight average molecular weight of about 50,000 to about 1,500,000 daltons as determined by ASTM D5296-05, preferably about 200,000 to about 1,000,000 daltons, more preferably about 300,000 to about 600,000 daltons.

[0064] In other embodiments, the at least one polyhydroxyalkanoate more preferably has a weight average molecular weight of from about 100,000 to about 400,000 daltons as determined by ASTM D5296-05.

[0065] In some embodiments, the at least one polyhydroxyalkanoate may have a unimodal molecular weight distribution, having one distinct peak in the molecular weight distribution.

[0066] However, in other embodiments, it is preferred that the at least one polyhydroxyalkanoate typically has a bimodal molecular weight distribution, as determined by ASTM D5296-05, having a first molecular weight peak centered between about 100,000 and about 175,000 daltons and a second molecular weight peak centered between about 200,000 and about 300,000 daltons.

[0067] In some cases, the at least one polyhydroxyalkanoate preferably has a polydispersity index, as determined by ASTM D5296-05, of about 1.5 to about 5. Preferably, the polydispersity index is about 1.75 to about 4, more preferably about 2 to 3. More preferably, the at least one polyhydroxyalkanoate has a weight average molecular weight, as determined by ASTM D5296-05, of about 100,000 to about 400,000 daltons, and a polydispersity index, as determined by ASTM D5296-05, of about 2 to about 3.

[0068] In addition to the polyhydroxyalkanoate, the composition may also contain at least one additional biopolymer. This biopolymer is typically selected from the group consisting of polylactic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, phenylbenzimidazole sulfonic acid, and mixtures thereof. In some embodiments, the biopolymer is more preferably polylactic acid. The additional biopolymer is present in the composition in an amount of about 30 to about 60 weight percent, preferably about 30 to about 50 weight percent, and more preferably about 30 to about 40 weight percent.

[0069] The composition also contains at least one nucleating agent to improve the crystallization rate of the polymer. Typically, the nucleating agent is selected from the group consisting of polyester wax, behenamide, crodamide, stearamide, erucamide, pentaerythritol, dipentaerythritol, boron nitride, and mixtures thereof. More preferably, the nucleating agent is pentaerythritol. The amount of nucleating agent in the composition is typically about 1 to about 10 weight percent, preferably about 1 to about 5 weight percent, and more preferably about 1.5 to about 3 weight percent.

[0070] The composition further comprises at least one melt flow modifier to improve the melt flow index of the composition. Typically, the at least one melt flow modifier is selected from the group consisting of calcium stearate, zinc stearate, starch, diamide oligomers, organic peroxides, and mixtures thereof. The amount of melt flow modifier is generally about 0.1 to about 5 weight percent, preferably about 0.1 to about 3 weight percent, and more preferably about 0.2 to about 3 weight percent.

[0071] The melt flow modifier typically causes the composition to have a melt flow index of from about 5 to about 1500 grams per 10 minutes when measured at a temperature of 175°C and a load of 2.16 kg according to ASTM D1238.

[0072] More specifically, the melt flow index of the composition can be more closely optimized depending on the properties of the fiber to be formed therefrom. For example, when fibers are to be filament-spun from the composition, the composition generally has a melt flow index of about 5 to about 30 grams / 10 minutes, preferably about 10 to about 25 grams / 10 minutes, and more preferably about 12 to about 18 grams / 10 minutes, when measured according to ASTM D1238 at a temperature of 175°C and a load of 2.16 kg.

[0073] In embodiments in which the fibers are formed from spunbond, the composition generally has a melt flow index of from about 50 to about 100 grams / 10 minutes, preferably from about 65 to about 90 grams / 10 minutes, and more preferably from about 75 to about 85 grams / 10 minutes, when measured according to ASTM D1238 at a temperature of 175° C. and a load of 2.16 kg.

[0074] In yet another embodiment, the fibers are preferably formed from meltblown compositions having a melt flow index of from about 500 to about 1500 grams / 10 minutes, preferably from about 750 to about 1300 grams / 10 minutes, and more preferably from about 900 to about 1100 grams / 10 minutes, when measured in accordance with ASTM D1238 at a temperature of 175° C. and a load of 2.16 kg.

[0075] In some cases, the composition also includes at least one filler material. For example, the filler may be selected from the group consisting of calcium carbonate, talc, polysaccharides, starch, clay, diatomaceous earth, kaolinite, montmorillonite, bentonite, silica, chitin, titanium dioxide, nanoclay, mica, hemp, nanocellulose, and mixtures thereof. When a filler is present, the composition preferably includes from about 5 to about 20 weight percent of at least one filler and from about 30 to about 50 weight percent of at least one polyhydroxyalkanoate.

[0076] According to certain embodiments, the composition also preferably comprises from about 0.1 to about 4.0 weight percent of at least one melt strength enhancer selected from the group consisting of carbodiimides, epoxides, and mixtures thereof. More preferably, the composition comprises from about 0.5 to about 3 weight percent of the at least one melt strength enhancer. Even more preferably, the composition comprises from about 0.75 to about 1.5 weight percent of the at least one melt strength enhancer.

[0077] Without being bound by theory, it is believed that in certain embodiments, the addition of melt strength enhancers allows the fiber to be stretched while still maintaining a desired melt flow index for processing. Furthermore, it is believed that these melt strength enhancers also prevent degradation of the fiber during processing due to hydrolysis of the polymer and / or exposure to shear and heat.

[0078] Additionally, in certain embodiments, the composition may also include one or more additional additives selected from the group consisting of dodecenyl succinic anhydride, succinic anhydride, and mixtures thereof.

[0079] In some cases, the composition preferably has a melt temperature of about 140° C. to about 150° C. as determined by ASTM D3418.

[0080] In a further aspect, the present disclosure also provides a nonwoven fabric comprised of a plurality of the aforementioned synthetic fibers. The nonwoven fabric may be formed using processes such as spunbond and meltblown.

[0081] In addition to nonwovens, the fibers of the present disclosure may also be used in staple, airlaid, and spunlaid processes.

[0082] The present disclosure also provides a method for forming the above-described plurality of synthetic fibers, in which the components for the fiber composition are first blended together in a first extruder to form a resin composition, which includes at least one polyhydroxyalkanoate, at least one nucleating agent, and at least one melt flow modifier, as well as any other biopolymers or other additives.

[0083] The resulting resin composition is then typically melt processed in a second extruder, typically at a temperature of about 165 to about 185°C, and the composition is extruded through multiple spinnerets to produce multiple fibers.

[0084] These melt processing temperatures are significantly lower than conventional processing temperatures for spinning PHA-based synthetic fibers, especially fibers intended for use in nonwoven fabrics. Synthetic fibers for spunbond nonwoven fabrics typically have diameters on the order of about 10 microns (μm), while fibers for meltblown nonwoven fabrics typically have even smaller diameters, on the order of about 1-2 microns (μm).

[0085] To spin such small diameter fibers, the viscosity of the polymer composition must be fairly low. Typically, this is achieved by heating the polymer composition to very high temperatures, at least about 190-210°C, before spinning. However, heating a PHA-based composition to such temperatures results in decomposition of the PHA molecules, resulting in a significant loss of weight-average molecular weight for the PHA molecules.

[0086] However, according to the present disclosure, the viscosity of the polymer composition is reduced by the addition of a melt flow modifier, rather than by excessively heating the polymer composition prior to spinning.

[0087] Thus, depending on the intended use of the fiber, the fiber composition may have significantly different melt flow properties when the fiber is first formed.

[0088] In some embodiments, the plurality of fibers is comprised of fiber filaments having a length of at least 300 mm. In such embodiments, the resin composition preferably has a melt flow index of about 5 to about 30 grams per 10 minutes when measured according to ASTM D1238 at a temperature of 175°C and a load of 2.16 kg.

[0089] In other embodiments, the fibers may be used to form spunbond nonwoven webs, which are formed by collecting a plurality of fibers on a flat conveyor belt and bonding the fibers together to form a nonwoven web. In such embodiments, the resin composition preferably has a melt flow index of about 50 to about 100 grams per 10 minutes when measured according to ASTM D1238 at a temperature of 175°C and a load of 2.16 kg.

[0090] In other embodiments, the fibers may be used to form a meltblown nonwoven web, formed by collecting a plurality of fibers on a rotating carousel and bonding the fibers together to form the meltblown nonwoven web. In such embodiments, the resin composition preferably has a melt flow index of about 500 to about 1500 grams per 10 minutes when measured according to ASTM D1238 at a temperature of 175°C and a load of 2.16 kg.

[0091] Embodiment The present disclosure is also further illustrated by the following embodiments.

[0092] Embodiment 1. A synthetic fiber formed from a composition, the composition comprising: from about 1 to about 98 weight percent, preferably from about 30 to about 70 weight percent, and more preferably from about 40 to about 60 weight percent of at least one polyhydroxyalkanoate; about 1 to about 10 weight percent, preferably about 1 to about 5 weight percent, and more preferably about 1.5 to about 3 weight percent of at least one nucleating agent selected from the group consisting of polyester wax, behenamide, crodamide, stearamide, erucamide, pentaerythritol, dipentaerythritol, boron nitride, and mixtures thereof; and about 0.1 to about 5 weight percent, preferably about 0.1 to about 3 weight percent, and more preferably about 0.2 to about 3 weight percent of at least one melt flow modifier selected from the group consisting of calcium stearate, zinc stearate, starch, diamide oligomers, organic peroxides, and mixtures thereof.

[0093] Embodiment 2. The synthetic fiber of embodiment 1, wherein the composition comprises from about 1 to about 97 weight percent, preferably from about 30 to about 70 weight percent, more preferably from about 40 to about 60 weight percent of at least one polyhydroxyalkanoate copolymer or terpolymer, and from 1 to about 20 weight percent, preferably from about 5 to about 15 weight percent, more preferably from about 7 to about 12 weight percent of polyhydroxybutyrate.

[0094] Embodiment 3. The composition comprises: about 30 to about 65 weight percent, preferably about 35 to about 60 weight percent, and more preferably about 40 to about 56 weight percent of at least one polyhydroxyalkanoate; 3. The synthetic fiber of embodiment 1 or 2, comprising about 30 to about 60 weight percent, preferably about 30 to about 50 weight percent, and more preferably about 30 to about 40 weight percent of at least one biopolymer selected from the group consisting of polylactic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, phenylbenzimidazole sulfonic acid, and mixtures thereof. Preferably, the at least one biopolymer comprises polylactic acid.

[0095] Embodiment 4. The synthetic fiber of any preceding embodiment, wherein the at least one polyhydroxyalkanoate comprises a polyhydroxyalkanoate copolymer.

[0096] Embodiment 5. The synthetic fiber of any preceding embodiment, wherein the at least one poly(hydroxyalkanoate) comprises from about 1 to about 25 mole percent, preferably from about 5 to about 20 mole percent, or from about 10 to about 15 mole percent, of monomer repeat units selected from the group consisting of 3-hydroxyhexanoate, 3-hydroxyoctanoate, 3-hydroxydecanoate, and mixtures thereof.

[0097] Embodiment 6. The synthetic fiber of any preceding embodiment, wherein the at least one polyhydroxyalkanoate comprises poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (P3HB-co-P3HHx), comprising from about 2 to about 8 mole percent of 3-hydroxyhexanoate monomer repeat units.

[0098] Embodiment 7. The at least one polyhydroxyalkanoate comprises a polyhydroxyalkanoate terpolymer, the terpolymer comprising: from about 75 to about 99.8 mole percent, preferably from about 80 to about 95 mole percent, and more preferably from about 85 to about 90 mole percent, of 3-hydroxybutyrate monomer repeat units; from about 0.1 to about 24.9 mole percent, preferably from about 0.9 to about 19.9 mole percent, and more preferably from about 1.9 to about 11.1 mole percent of 3-hydroxyhexanoate monomer repeat units; and about 0.1 to about 24.9 mole percent of the monomer, preferably about 0.1 to about 19.1 mole percent, and more preferably about 3.9 to about 13.1 mole percent of a third 3-hydroxyalkanoate repeat unit selected from the group consisting of 3-hydroxyhexanoate, 3-hydroxyoctanoate, and 3-hydroxydecanoate.

[0099] Embodiment 8. The synthetic fiber of any preceding embodiment, wherein the composition comprises about 30 to about 50 weight percent, preferably about 32 to about 45 weight percent, and more preferably about 37 to about 43 weight percent of at least one polyhydroxyalkanoate, and further comprises about 5 to about 20 weight percent, preferably about 7 to about 18 weight percent, and more preferably about 10 to about 15 weight percent of at least one filler selected from the group consisting of calcium carbonate, talc, polysaccharides, starch, clay, diatomaceous earth, kaolinite, montmorillonite, bentonite, silica, chitin, titanium dioxide, nanoclay, mica, hemp, nanocellulose, and mixtures thereof.

[0100] Embodiment 9. The synthetic fiber of any preceding embodiment, wherein the at least one polyhydroxyalkanoate has a weight average molecular weight, as determined by ASTM D5296-05, of about 50,000 to about 1,500,000 daltons, preferably about 200,000 to about 1,000,000 daltons, and more preferably about 300,000 to about 600,000 daltons.

[0101] Embodiment 10. The synthetic fiber of any preceding embodiment, wherein the at least one polyhydroxyalkanoate has a bimodal molecular weight distribution, as determined by ASTM D5296-05, having a first molecular weight peak centered between about 100,000 and about 175,000 daltons and a second molecular weight peak centered between about 200,000 and about 300,000 daltons.

[0102] Embodiment 11. The synthetic fiber of any preceding embodiment, wherein the at least one polyhydroxyalkanoate has a polydispersity index, as determined by ASTM D5296-05, of from about 1.5 to about 5, preferably from about 1.75 to about 4, and more preferably from about 2 to about 3.

[0103] Embodiment 12. The synthetic fiber of any preceding embodiment, wherein the at least one polyhydroxyalkanoate has a weight average molecular weight, as determined by ASTM D5296-05, of about 100,000 to about 400,000 daltons, and a polydispersity index, as determined by ASTM D5296-05, of about 2 to about 3.

[0104] Embodiment 13. The synthetic fiber of any preceding embodiment, wherein the composition has a melt temperature of about 140°C to about 150°C, as determined by ASTM D3418.

[0105] Embodiment 14. The synthetic fiber of any preceding embodiment, wherein the composition has a melt flow index of from about 5 to about 1500 grams per 10 minutes when measured in accordance with ASTM D1238 at a temperature of 175°C and a load of 2.16 kg.

[0106] Embodiment 15. The synthetic fiber of any preceding embodiment, wherein the composition further comprises from about 0.1 to about 4.0 weight percent, preferably from about 0.5 to about 3 weight percent, and more preferably from about 0.75 to about 1.5 weight percent of at least one melt strength enhancer selected from the group consisting of carbodiimides, epoxides, and mixtures thereof.

[0107] Embodiment 16. The synthetic fiber of any preceding embodiment, wherein the fiber is filament spun and the composition has a melt flow index of from about 5 to about 30 grams / 10 minutes, preferably from about 10 to about 25 grams / 10 minutes, and more preferably from about 12 to about 18 grams / 10 minutes, when measured in accordance with ASTM D1238 at a temperature of 175°C and a load of 2.16 kg.

[0108] Embodiment 17. The synthetic fiber of any preceding embodiment, wherein the fiber is oriented.

[0109] Embodiment 18. The synthetic fiber of any preceding embodiment, wherein the fiber has been post-treated with a fiber lubricant composition comprising at least one lubricant selected from the group consisting of hydrophobic esters, mineral oils, silicon compositions, and mixtures thereof.

[0110] Embodiment 19. A nonwoven fabric comprising a plurality of synthetic fibers according to any of the preceding embodiments.

[0111] Embodiment 20. A spunbond nonwoven fabric formed from the synthetic fibers of any one of embodiments 1 to 18, wherein the composition has a melt flow index of about 50 to about 100 grams / 10 minutes, preferably about 65 to about 90 grams / 10 minutes, and more preferably about 75 to about 85 grams / 10 minutes, when measured in accordance with ASTM D1238 at 175°C and a load of 2.16 kg.

[0112] Embodiment 21. A meltblown nonwoven fabric formed from the synthetic fibers of any one of embodiments 1 to 18, wherein the composition has a melt flow index of about 500 to about 1500 grams / 10 minutes, preferably about 750 to about 1300 grams / 10 minutes, and more preferably about 900 to about 1100 grams / 10 minutes, when measured in accordance with ASTM D1238 at a temperature of 175°C and a load of 2.16 kg.

[0113] Embodiment 22. An article comprising the nonwoven fabric of any one of embodiments 19-22, wherein the article is selected from the group consisting of medical protective equipment, personal hygiene wipes, cleaning wipes, filtration systems, diapers, feminine hygiene products, coffee / tea bags, and laundry sheets.

[0114] Embodiment 23. A method for forming a plurality of synthetic fibers, comprising: At least one polyhydroxyalkanoate, at least one nucleating agent, and at least one melt flow modifier are blended in a first extruder to produce a resin composition, from about 1 to about 98 weight percent of at least one polyhydroxyalkanoate; about 1 to about 10 weight percent of at least one nucleating agent selected from the group consisting of polyester wax, behenamide, crodamide, stearamide, erucamide, pentaerythritol, dipentaerythritol, boron nitride, and mixtures thereof; forming a resin composition comprising: about 0.1 to about 5 weight percent of at least one melt flow modifier selected from the group consisting of calcium stearate, zinc stearate, starch, diamide oligomers, organic peroxides, and mixtures thereof; melt processing the resin composition at a temperature of about 165 to about 185°C and extruding the composition through a plurality of spinnerets to produce a plurality of fibers.

[0115] Embodiment 24. The method of embodiment 23, wherein the plurality of fibers comprises fiber filaments having a length of at least 300 mm.

[0116] Embodiment 25. The method of embodiment 24, wherein the resin composition has a melt flow index of about 5 to about 30 grams per 10 minutes when measured according to ASTM D1238 at a temperature of 175°C and a load of 2.16 kg.

[0117] Embodiment 26. The method of embodiment 23, further comprising collecting a plurality of fibers on a flat conveyor belt and bonding the fibers together to form a spunbond nonwoven web.

[0118] Embodiment 27. The method of embodiment 26, wherein the resin composition has a melt flow index of about 50 to about 100 grams per 10 minutes when measured according to ASTM D1238 at a temperature of 175°C and a load of 2.16 kg.

[0119] Embodiment 28. The method of embodiment 23, further comprising collecting a plurality of fibers on a rotating carousel and bonding the fibers together to form a meltblown nonwoven web.

[0120] Embodiment 29. The method of embodiment 28, wherein the composition has a melt flow index of about 500 to about 1500 grams per 10 minutes when measured in accordance with ASTM D1238 at a temperature of 175°C and a load of 2.16 kg. [Example]

[0121] The following non-limiting examples illustrate various additional aspects of the present invention. Unless otherwise indicated, temperatures are in degrees Celsius and percentages are by weight based on the dry weight of the formulation.

[0122] Example 1.6: A fiber composition consisting of 5.25% 6 mol% hexanoate and 94% butyrate polyhydroxyalkanoate copolymer, 31.25% PLA, 1.50% pentaerythritol, and 2.00% calcium stearate was compounded in a twin-screw extruder with a melt flow index of 15 grams / 10 minutes at a compounding temperature of 175-180°C. The compounded material was converted into filaments at a process temperature of 170-175°C, a pump setting of 20 RPM, and a 30% post-conversion finishing treatment. The filaments were collected at a feed roll speed of 300 meters per minute (mpm) at a temperature of 50°C, a draw roll at a temperature of 400 mpm and 50°C, and a relax roll at a temperature of 500 mpm and 30°C.

[0123] Example 2.4: A fiber composition consisting of 5.25% 6 mol% hexanoate and 94% butyrate polyhydroxyalkanoate copolymer, 51.25% PLA, 1.5% pentaerythritol, and 2.00% N,N'-ethylenebis-12-hydroxystearamide was compounded in a twin-screw extruder with a melt flow index of 13 grams / 10 min at a compounding temperature of 175-180°C. The compounded material was converted into filaments at a process temperature of 170-175°C, a pump setting of 20 RPM, and a 30% post-conversion finishing treatment. The filaments were collected at a feed roll speed of 300 mpm at 50°C, a draw roll at 400 mpm and 50°C, and a relax roll at 500 mpm and 50°C.

[0124] Example 3.5: A fiber composition consisting of 6.75% 6 mol% hexanoate and 94% butyrate polyhydroxyalkanoate copolymer, 41.25% PLA, 1.5% pentaerythritol, and 0.5% calcium stearate was compounded in a twin-screw extruder with a melt flow index of 91 grams / 10 minutes. The compounded material was converted into filaments at a process temperature of 165-172°C, a die temperature of 165°C, a feeder speed of 20-30 rpm, and an air pressure of 20-40 PSI. The filaments were then converted into a spunbond material using thermal bonding at a calender temperature of 100°C.

[0125] Example 4.4 A fiber composition consisting of 6.75% 6 mol% hexanoate and 94% butyrate polyhydroxyalkanoate copolymer, 36.25% PLA, 1.50% pentaerythritol, 10.00% calcium carbonate, 5.00% talc, and 0.50% calcium stearate was compounded in a twin-screw extruder with a melt flow index of 111 grams / 10 min at a compounding temperature of 175-180°C. The compounded material was converted into filaments at a process temperature of 165-172°C, a die temperature of 165°C, a feeder speed of 20-30 rpm, and an air pressure of 20-40 PSI. The filaments were then converted into a spunbond material using thermal bonding at a calender temperature of 100°C.

[0126] Example 5.5: A fiber composition consisting of 6.75% 6 mol% hexanoate and 94% butyrate polyhydroxyalkanoate copolymer, 31.25% PLA, 1.50% pentaerythritol, 10.00% calcium carbonate, and 0.50% calcium stearate was compounded in a twin-screw extruder with a melt flow index of 149 grams / 10 min at a compounding temperature of 175-180°C. The compounded material was converted into filaments at a process temperature of 165-172°C, a die temperature of 165°C, a feeder speed of 20-30 rpm, and an air pressure of 20-40 PSI. The filaments were then converted into a spunbond material using thermal bonding at a calender temperature of 100°C.

[0127] Example 6.4 A fiber composition consisting of 6.75% 6 mol% hexanoate and 94% butyrate polyhydroxyalkanoate copolymer, 36.25% PLA, 1.5% pentaerythritol, 0.5% calcium stearate, and 15% calcium carbonate was compounded in a twin-screw extruder with a melt flow index of 241 grams / 10 minutes at a compounding temperature of 175-180°C. The compounded material was converted into filaments at a process temperature of 165-172°C, a die temperature of 165°C, a feeder speed of 20-30 rpm, and an air pressure of 20-40 PSI. The filaments were then chopped into smaller pieces and converted into staple fibers.

[0128] Example 7.5 A fiber composition consisting of 4.25% polyhydroxyalkanoate copolymer, 30.75% PLA, 1.5% pentaerythritol, 2% N,N'-ethylenebis-12-hydroxystearamide, 1.5% calcium stearate, 5% calcium carbonate, and 5% talc was compounded in a twin-screw extruder with a melt flow index of 580 grams per 10 minutes at a compounding temperature of 175-180°C. The compounded material was converted to a meltblown material at a process temperature of 175-185°C using a line with 368 capillaries and a diameter of 0.009 inches. The die temperature was 185°C, the feeder speed was 20-25 rpm, and the blow air temperature was 185°C. Samples were collected at thicknesses of 20, 50, and 100 grams per square meter (gsm).

[0129] Example 8.6 A fiber composition consisting of 4.25% 6 mol% hexanoate and 94% butyrate polyhydroxyalkanoate copolymer, 30.75% PLA, 1.5% pentaerythritol, 2% N,N'-ethylenebis-12-hydroxystearamide, and 1.5% calcium stearate was compounded in a twin-screw extruder with a melt flow index of 487 grams / 10 minutes at a compounding temperature of 175-180°C. The compounded material was converted to a meltblown material at a process temperature of 175-185°C using a line with 368 capillaries and a diameter of 0.009 inches. The die temperature was 185°C, the feeder speed was 20-25 rpm, and the blow air temperature was 185°C. Samples were collected at thicknesses of 20, 50, and 100 gsm.

[0130] Example 9.5: A fiber composition consisting of 4.25% 6 mol% hexanoate and 94% butyrate polyhydroxyalkanoate copolymer, 40.25% PLA, 1.50% pentaerythritol, 2.00% N,N'-ethylenebis-12-hydroxystearamide, and 2.00% calcium stearate was compounded in a twin-screw extruder with a melt flow index of 455 grams / 10 minutes at a compounding temperature of 175-180°C. The compounded material was converted to a meltblown material at a process temperature of 175-185°C using a line with 368 capillaries and a diameter of 0.009 inches. The die temperature was 185°C, the feeder speed was 20-25 rpm, and the blow air temperature was 185°C. Samples were collected at thicknesses of 20, 50, and 100 gsm.

[0131] Example 10.6 A fiber composition consisting of 4.25% 6 mol% hexanoate and 94% butyrate polyhydroxyalkanoate copolymer, 30.25% PLA, 1.50% pentaerythritol, 2.00% N,N'-ethylenebis-12-hydroxystearamide, and 2.00% calcium stearate was compounded in a twin-screw extruder with a melt flow index of 455 grams / 10 minutes at a compounding temperature of 175-180°C. The compounded material was converted to a meltblown material at a process temperature of 175-185°C using a line with 368 capillaries and a diameter of 0.009 inches. The die temperature was 185°C, the feeder speed was 20-25 rpm, and the blow air temperature was 185°C. Samples were collected at 20, 50, and 100 gsm thicknesses.

[0132] The foregoing description of preferred embodiments of the present disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. These embodiments have been chosen and described in an effort to provide the best illustration of the principles of the present disclosure and its practical application, thereby enabling those skilled in the art to utilize the present disclosure in various embodiments and with various modifications as suited to the particular uses contemplated.

Claims

1. 1. A synthetic fiber formed from a composition, the composition comprising: 1 to 98 weight percent of at least one polyhydroxyalkanoate; 1 to 10 weight percent of at least one nucleating agent selected from the group consisting of polyester wax, behenamide, crodamide, stearamide, erucamide, pentaerythritol, dipentaerythritol, boron nitride, and mixtures thereof; 0.1 to 5 weight percent of at least one melt flow modifier selected from the group consisting of calcium stearate, zinc stearate, starch, diamide oligomers, organic peroxides, and mixtures thereof.

2. 10. The synthetic fiber of claim 1, wherein the composition comprises 1 to 97 weight percent of at least one polyhydroxyalkanoate copolymer or terpolymer and 1 to 20 weight percent of polyhydroxybutyrate.

3. The composition comprises:

10. The synthetic fiber of claim 1, comprising 30 to 65 weight percent of at least one polyhydroxyalkanoate and further comprising 30 to 60 weight percent of at least one biopolymer selected from the group consisting of polylactic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, phenylbenzimidazole sulfonic acid, and mixtures thereof.

4. The synthetic fiber of claim 1 , wherein the at least one polyhydroxyalkanoate comprises a polyhydroxyalkanoate copolymer.

5. 10. The synthetic fiber of claim 1, wherein the at least one poly(hydroxyalkanoate) comprises 1 to 25 mole percent of monomer repeat units selected from the group consisting of 3-hydroxyhexanoate, 3-hydroxyoctanoate, 3-hydroxydecanoate, and mixtures thereof.

6. 10. The synthetic fiber of claim 1, wherein the at least one polyhydroxyalkanoate comprises poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (P3HB-co-P3HHx), which comprises 2 to 8 mole percent of 3-hydroxyhexanoate monomer repeat units.

7. 10. The synthetic fiber of claim 1, wherein the at least one polyhydroxyalkanoate comprises a polyhydroxyalkanoate terpolymer, the terpolymer comprising 75 to 99.8 mole percent monomeric repeat units of 3-hydroxybutyrate, 0.1 to 24.9 mole percent monomeric repeat units of 3-hydroxyhexanoate, and 0.1 to 24.9 mole percent monomeric repeat units of a third 3-hydroxyalkanoate selected from the group consisting of 3-hydroxyhexanoate, 3-hydroxyoctanoate, and 3-hydroxydecanoate.

8. 10. The synthetic fiber of claim 1, wherein the at least one polyhydroxyalkanoate has a weight average molecular weight of 50,000 to 1,500,000 Daltons as determined by ASTM D5296-05.

9. 10. The synthetic fiber of claim 1, wherein the at least one polyhydroxyalkanoate has a bimodal molecular weight distribution, as determined by ASTM D5296-05, with a first molecular weight peak centered between 100,000 and 175,000 daltons and a second molecular weight peak centered between 200,000 and 300,000 daltons.

10. 10. The synthetic fiber of claim 1, wherein the at least one polyhydroxyalkanoate has a polydispersity index of 1.5 to 5 as determined by ASTM D5296-05.

11. 10. The synthetic fiber of claim 1, wherein the composition has a melting temperature of 140°C to 150°C as determined by ASTM D3418.

12. 10. The synthetic fiber of claim 1, wherein the composition further comprises 0.1 to 4.0 weight percent of at least one melt strength enhancer selected from the group consisting of carbodiimides, epoxides, and mixtures thereof.

13. 10. The synthetic fiber of claim 1, wherein the fiber is filament spun and the composition has a melt flow index of 5 to 30 grams / 10 minutes when measured according to ASTM D1238 at a temperature of 175°C and a load of 2.16 kg.

14. 10. The synthetic fiber of claim 1, wherein the fiber is post-treated with a fiber lubricant composition comprising at least one lubricant selected from the group consisting of hydrophobic esters, mineral oils, silicon compositions, and mixtures thereof.

15. 10. A spunbond nonwoven fabric formed from the synthetic fibers of claim 1, wherein the composition has a melt flow index of 50 to 100 grams per 10 minutes when measured in accordance with ASTM D1238 at a temperature of 175°C and a load of 2.16 kg.

16. 10. A meltblown nonwoven fabric formed from the synthetic fibers of claim 1, wherein the composition has a melt flow index of 500 to 1500 grams / 10 minutes when measured in accordance with ASTM D1238 at a temperature of 175°C and a load of 2.16 kg.

17. 1. A method for forming a plurality of synthetic fibers, comprising: At least one polyhydroxyalkanoate, at least one nucleating agent, and at least one melt flow modifier are blended in a first extruder to produce a resin composition comprising: 1 to 98 weight percent of at least one polyhydroxyalkanoate; 1 to 10 weight percent of at least one nucleating agent selected from the group consisting of polyester wax, behenamide, crodamide, stearamide, erucamide, pentaerythritol, dipentaerythritol, boron nitride, and mixtures thereof; forming a resin composition comprising: 0.1 to 5 weight percent of at least one melt flow modifier selected from the group consisting of calcium stearate, zinc stearate, starch, diamide oligomers, organic peroxides, and mixtures thereof; melt processing the resin composition at a temperature of 165-185°C and extruding the composition through a plurality of spinnerets to produce a plurality of fibers.

18. 18. The method of claim 17, wherein the plurality of fibers comprises fiber filaments having a length of at least 300 mm.

19. 19. The method of claim 18, wherein the resin composition has a melt flow index of 5 to 30 grams per 10 minutes when measured according to ASTM D1238 at a temperature of 175°C and a load of 2.16 kg.

20. 20. The method of claim 17, further comprising collecting the plurality of fibers on a flat conveyor belt and bonding the fibers together to form a spunbond nonwoven web.

21. 21. The method of claim 20, wherein the resin composition has a melt flow index of 50 to 100 grams per 10 minutes when measured according to ASTM D1238 at a temperature of 175°C and a load of 2.16 kg.

22. 20. The method of claim 17, further comprising collecting the plurality of fibers on a rotating carousel and bonding the fibers together to form a meltblown nonwoven web.

23. 23. The method of claim 22, wherein the composition has a melt flow index of 500 to 1500 grams per 10 minutes when measured according to ASTM D1238 at a temperature of 175°C and a load of 2.16 kg.

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