CN114127345A

CN114127345A - Bicomponent thermoplastic polyurethane fibers and fabrics made therefrom

Info

Publication number: CN114127345A
Application number: CN202080052026.4A
Authority: CN
Inventors: L·B·苏拉加尼韦努; J·J·小翁托西克
Original assignee: Lubrizol Advanced Materials Inc
Current assignee: Lubrizol Advanced Materials Inc
Priority date: 2019-07-03
Filing date: 2020-07-01
Publication date: 2022-03-01
Anticipated expiration: 2040-07-01
Also published as: TW202111175A; US20220411970A1; JP2022538459A; WO2021003236A1; KR20220027161A; CN114127345B; EP3994299A1

Abstract

The present invention relates to a bicomponent fiber wherein the fiber has a core and sheath structure. The bicomponent fibers are made from two different polyester thermoplastic polyurethanes to provide fibers with enhanced clarity and low shrinkage.

Description

Bicomponent thermoplastic polyurethane fibers and fabrics made therefrom

Technical Field

The present technology relates to bicomponent fibers and fabrics made therefrom, particularly core-sheath fibers made from two different thermoplastic polyurethanes, to provide fibers with unique properties.

Disclosure of Invention

The present invention relates to a bicomponent fiber wherein the bicomponent fiber has a core and sheath structure wherein the bicomponent fiber comprises (a) a core comprising a first polyester thermoplastic polyurethane having a melt enthalpy of at least 50J/g measured according to ASTM D3418 and (b) a sheath comprising a second polyester thermoplastic polyurethane having a melt enthalpy of 5J/g or less measured according to ASTM D3418.

The invention also relates to fabrics made from the bicomponent fibers of the invention.

Detailed Description

As used herein, the term "bicomponent fiber" refers to the conjugate product of at least two melt-spinnable components, wherein the conjugate product has at least two distinct longitudinally coextensive polymer segments. In one embodiment, the bicomponent fibers of the present invention comprise two different polymeric materials that are intimately adhered to each other along the length of the fiber such that the cross-section of the fiber is, for example, a core-sheath configuration.

The bicomponent fibers of the present invention are made from two different polyester thermoplastic polyurethanes. Thermoplastic polyurethanes are typically prepared by reacting a polyisocyanate with a polyol intermediate and optionally a chain extender, all of which are well known to those skilled in the art.

The bicomponent fibers of the present invention use two different thermoplastic polyurethane materials, each based on a different polyester polyol intermediate. The hydroxyl terminated polyester intermediate is typically a linear polyester having a number average molecular weight (Mn) of from about 500 to about 10,000, desirably from about 700 to about 5,000, and preferably from about 700 to about 4,000, and an acid number generally less than 1.3 and preferably less than 0.8. The molecular weight is determined by measuring the terminal functional groups and is related to the number average molecular weight. These polyester polyols are prepared by (1) esterification of one or more diols with one or more dicarboxylic acids or anhydrides or (2) by transesterification, i.e., the reaction of one or more diols with esters of dicarboxylic acids. To obtain a predominantly linear chain of terminal hydroxyl groups, it is generally preferred that the molar ratio of diol to acid exceeds one mole. Suitable polyester intermediates also include various lactones such as polycaprolactone typically made from epsilon-caprolactone and a difunctional initiator such as diethylene glycol. The dicarboxylic acids of the desired polyester may be aliphatic, cycloaliphatic, aromatic, or combinations thereof. Suitable dicarboxylic acids, which may be used alone or in mixtures, typically have a total of from 4 to 15 carbon atoms and include: succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, and the like. Anhydrides of the above dicarboxylic acids, such as phthalic anhydride, tetrahydrophthalic anhydride, and the like, may also be used. The diols reacted to form the desired polyester intermediate may be aliphatic, aromatic, or combinations thereof, and have a total of from 2 to 12 carbon atoms, and include ethylene glycol, 1, 2-propylene glycol, 1, 3-butylene glycol, 1, 4-butylene glycol, 1, 5-pentanediol, 1, 6-hexanediol, 2-dimethyl-1, 3-propanediol, 1, 4-cyclohexanedimethanol, decanediol, dodecanediol, and the like.

In one embodiment, the fiber of the present invention comprises a first thermoplastic polyurethane based on butanediol succinate and a second thermoplastic polyurethane based on butanediol adipate.

The thermoplastic polyurethane used in the present invention is prepared using a polyisocyanate component. In some embodiments, the polyisocyanate component includes one or more diisocyanates. Useful polyisocyanates may be selected from aromatic polyisocyanates or aliphatic polyisocyanates or combinations thereof. Examples of useful polyisocyanates include, but are not limited to: aromatic diisocyanates, such as 4,4' -methylenebis (phenyl isocyanate) (MDI), m-Xylylene Diisocyanate (XDI), phenylene-1, 4-diisocyanate, 3' -dimethyl-4, 4' -biphenyl diisocyanate (TODI), 1, 5-Naphthalene Diisocyanate (NDI) and Toluene Diisocyanate (TDI), and aliphatic diisocyanates such as isophorone diisocyanate (IPDI), 1, 6-Hexamethylene Diisocyanate (HDI), 1, 4-cyclohexyl diisocyanate (CHDI), decane-1, 10-diisocyanate, Lysine Diisocyanate (LDI), 1, 4-Butane Diisocyanate (BDI) and dicyclohexylmethane-4, 4' -diisocyanate (H12 MDI). In some embodiments, a mixture of two or more polyisocyanates may be used.

In some embodiments, the polyisocyanate component comprises or consists of one or more aromatic diisocyanates. In some embodiments, the polyisocyanate component is substantially free, or even completely free, of aliphatic diisocyanates.

The thermoplastic polyurethane compositions described herein are optionally prepared using a chain extender component. The chain extender may include diols, diamines, and combinations thereof.

Suitable chain extenders include relatively small polyols, such as low carbon number aliphatic or short chain diols having 2 to 20 or 2 to 12 or 2 to 10 carbon atoms. Suitable examples include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1, 4-Butanediol (BDO), 1, 6-Hexanediol (HDO), 1, 3-butanediol, 1, 5-pentanediol, neopentyl glycol, 1, 4-Cyclohexanedimethanol (CHDM), 2-bis [4- (2-hydroxyethoxy) phenyl ] propane (HEPP), hexamethylene glycol, heptanediol, nonanediol, dodecanediol, 3-methyl-1, 5-pentanediol, ethylenediamine, butanediamine, hexamethylenediamine, and Hydroxyethylresorcinol (HER), and the like, and mixtures thereof.

The above three essential ingredients (hydroxyl terminated intermediate, polyisocyanate and chain extender) are preferably reacted in the presence of a catalyst.

In general, any conventional catalyst can be used to react the diisocyanate with the hydroxyl terminated intermediate or chain extender, and such catalysts are well known in the art and in the literature. Examples of suitable catalysts include various alkyl ethers or alkyl thiol ethers of bismuth or tin wherein the alkyl portion has from 1 to about 20 carbon atoms, specific examples including bismuth octoate, bismuth laurate, and the like. Preferred catalysts include various tin catalysts such as stannous octoate, dibutyltin dioctoate, dibutyltin dilaurate, and the like. The amount of such catalysts is typically small, for example, from about 20 to about 200 parts per million, based on the total weight of the polyurethane-forming monomers.

The thermoplastic polyurethanes of the present invention may be prepared by any conventional polymerization process well known in the art and literature.

The thermoplastic polyurethanes of the present invention are preferably prepared by the "one shot" process, wherein all of the components are added simultaneously or substantially simultaneously together to a heated extruder and reacted to form the polyurethane. The equivalent ratio of the diisocyanate to the total equivalents of the hydroxyl terminated intermediate and the glycol chain extender is generally from about 0.95 to about 1.10, desirably from about 0.97 to about 1.03, and preferably from about 0.97 to about 1.00. The molecular weight (Mw) of the thermoplastic polyurethanes useful in the present invention can be from about 50,000 daltons to about 300,000 daltons, for example from 50,000 daltons to about 100,000 daltons, as measured by GPC versus polystyrene standards. In one embodiment, the thermoplastic polyurethane used for the sheath in the bicomponent fiber of the present invention has a molecular weight of about 50,000 daltons to 75,000 daltons. In one embodiment, the thermoplastic polyurethane used for the core in the bicomponent fiber of the present invention has a molecular weight of about 80,000 daltons to about 100,000 daltons.

Thermoplastic polyurethanes can also be prepared using a prepolymer process. In the prepolymer route, the hydroxyl-terminated intermediate is reacted with a generally equivalent excess of one or more polyisocyanates to form a prepolymer solution having free or unreacted polyisocyanate therein. Subsequently, a selective type of chain extender as described above is added in an equivalent amount generally equal to the isocyanate end groups and equal to any free or unreacted diisocyanate compounds. Thus, the total equivalent ratio of total diisocyanate to the total equivalents of hydroxyl terminated intermediate and chain extender is from about 0.95 to about 1.10, desirably from about 0.98 to about 1.05, and preferably from about 0.99 to about 1.03. In general, the prepolymer route can be carried out in any conventional apparatus, preferably an extruder. Thus, the hydroxyl terminated intermediate is reacted with an equivalent excess of diisocyanate in a first section of the extruder to form a prepolymer solution, followed by addition of a chain extender and reaction with the prepolymer solution at a downstream section. Any conventional extruder may be used, wherein the extruder is equipped with a barrier screw having a length to diameter ratio of at least 20 and preferably at least 25.

Useful additives may be used in suitable amounts and include opacifying pigments, colorants, mineral fillers, stabilizers, lubricants, UV absorbers, processing aids, and other desired additives. Useful opacifying pigments include titanium dioxide, zinc oxide and titanate yellow (titanate yellow), while useful tinting pigments include carbon black, yellow oxides, brown oxides, raw and fired loess or umber, chromium oxide green, cadmium pigments, chromium pigments and other mixed metal oxides and organic pigments. Useful fillers include diatomaceous earth (superfloss) clay, silica, talc, mica, wollastonite, barium sulfate, and calcium carbonate. Useful stabilizers, such as antioxidants, including phenolic antioxidants, can also be used if desired, while useful light stabilizers include organophosphates and organotin mercaptides (mercaptides). Useful lubricants include metal stearates, paraffin oils and amide waxes. Useful UV absorbers include 2- (2' -hydroxyphenol) benzotriazole and 2-hydroxybenzophenone.

Plasticizer additives can also be advantageously used to reduce hardness without affecting performance.

The bicomponent continuous filaments of the present invention can be made using a melt spinning process. Figure 1 illustrates a typical bicomponent melt spinning technique using a pair of extruders. The step of preparing the bicomponent fiber comprises: drying at 80 ℃ for 12 hours in batches under vacuum; feeding the dried thermoplastic polyurethane polymer from a hopper to an extruder; melting the first and second thermoplastic polyurethane compositions in respective extruders having a 1.24 inch single screw and an L/D of 24; and the melt is extruded through a melt pump using two feed systems/conduits and then to a spinneret or die. The back pressure at the extruder outlet was kept constant by loop control. The extruder has four heating zones, which are maintained at a temperature between 180 ℃ and 220 ℃. The basic system consists of two feed systems, two polymers for the spin pack and a distribution system to meter the two polymers to the die. It will be appreciated by those skilled in the art that spinnerets for producing bicomponent or multicomponent filaments are known in the industry. Such a process is described in U.S. Pat. No. 5,162,074, which is incorporated herein by reference. Typically, spinnerets comprise a casting containing a spin pack and a plurality of plates to form a pattern for flowing the polymer. The bicomponent continuous filament spinneret can also be configured for the extrudate to have a desired cross-section, such as symmetrical (concentric) core/sheath, asymmetrical core/sheath, side-by-side, crescent-shaped, and the like. In addition, multiple extruders may be added to increase the number of parts.

Once the fiber exits the spinneret, the fiber is cooled and then wound onto a spool. The fiber passes through one set of godets, is coated with finish, and then enters the other set of godets.

In some embodiments, the thermoplastic polyurethane described above may be crosslinked with a crosslinking agent in a melt spinning process. The crosslinking agent is typically a prepolymer of a hydroxyl terminated intermediate which is a polyether, polyester, polycarbonate, polycaprolactone, or mixture thereof reacted with a polyisocyanate. The crosslinking agent (also referred to as a prepolymer in some cases) generally has an isocyanate functionality of greater than about 1.0, preferably from about 1.0 to about 3.0, more preferably from about 1.8 to about 2.2.

In one embodiment of the invention, the bicomponent fiber is formed without the use of a crosslinking agent. In this embodiment, both the core thermoplastic polyurethane and the sheath thermoplastic polyurethane are not crosslinked.

The bicomponent fibers of the present invention can be made in a variety of deniers. Denier is a term in the art that refers to fiber size. Denier is the weight in grams of 9000 meters of fiber length. The bicomponent fibers of the present invention are typically made in sizes in the range of 20 to 2500 denier, such as 20 to 600 denier, further such as 40 to 400 denier.

When bicomponent fibers are prepared by the process of the present invention, an anti-tack additive (e.g., an oil, one example of which is silicone oil) is typically added to the surface of the fiber after or during cooling and immediately prior to winding into a spool.

The bicomponent fiber according to the present invention has a core and sheath structure, wherein the bicomponent fiber has a core comprising a first polyester thermoplastic polyurethane having a melting enthalpy of at least about 50J/g, such as about 60J/g, measured according to ASTM D3418(DSC, second thermal cycle), and a sheath comprising a second polyester thermoplastic polyurethane having a melting enthalpy of about 5J/g or less, measured according to ASTM D3418(DSC, second thermal cycle). In one embodiment of the bicomponent fiber, the first polyester thermoplastic polyurethane has a contact transparency of 4% or less as measured according to ASTM D1003. In another embodiment of the bicomponent fiber, the second polyester thermoplastic polyurethane has a contact clarity of at least 12% as measured according to ASTM D1003.

The bicomponent fibers of the present invention comprise a core thermoplastic polyurethane and a sheath thermoplastic polyurethane, wherein the thermoplastic polyurethane materials of the core and sheath are different from each other. In one embodiment, the core thermoplastic polyurethane comprises the reaction product of butanediol succinate and an aromatic diisocyanate, and the sheath thermoplastic polyurethane comprises the reaction product of butanediol adipate, an aromatic diisocyanate, and at least one chain extender glycol.

In the present invention, the bicomponent fiber comprises from about 10% to about 35% by weight of the core thermoplastic polyurethane composition, and from about 65% to about 90% by weight of the second thermoplastic polyurethane.

In one embodiment of the invention, the final bicomponent fiber has low shrinkage and good clarity. For some applications, bicomponent fibers having a shrinkage after 90 seconds exposure at 70 ℃ of less than about 20% and a contact clarity of greater than about 13% as measured according to ASTM D1003 are desired. The present invention surprisingly provides these properties by combining two different thermoplastic polyurethane materials having different shrinkage and transparency properties. In one embodiment, the core comprises a thermoplastic polyurethane composition having a melting enthalpy of at least 50J/g measured according to ASTM D3418 and a contact transparency of about 4% or less measured according to ASTM D1003, and the sheath comprises a thermoplastic polyurethane composition having a melting enthalpy of about 5J/g or less measured according to ASTM D3418(DSC, second heat cycle) and a contact transparency of at least 12% measured according to ASTM D1003. In another embodiment, the core thermoplastic polyurethane has a shrinkage of less than about 10% after 90 seconds of exposure at 70 ℃, and the sheath thermoplastic polyurethane has a shrinkage of about 40% to about 60% after 90 seconds of exposure at 70 ℃. Shrinkage was measured by using one meter long of fiber and measuring the length before and after exposure to elevated temperature. The difference between the two measurements is the shrinkage.

The invention also includes a fabric comprising the bicomponent fiber of the invention. In one embodiment, the fabric comprises bicomponent fibers, wherein the bicomponent fibers have a core and sheath structure, wherein the core comprises a thermoplastic polyurethane composition having a melting enthalpy of at least about 50J/g, e.g., about 60J/g, as measured by ASTM D3418(DSC, second thermal cycle) and a contact transparency of 4% or less as measured by ASTM D1003, and the sheath comprises a thermoplastic polyurethane composition having a melting enthalpy of about 5J/g or less as measured by ASTM D3418(DSC, second thermal cycle) and a contact transparency of at least about 12% as measured by ASTM D1003. In one embodiment, the core thermoplastic polyurethane composition has a shrinkage of less than about 10% after 90 seconds of exposure at 70 ℃ and the sheath thermoplastic polyurethane composition has a shrinkage of about 40% to about 60% after 90 seconds of exposure at 70 ℃. In the fabric according to the invention, the bicomponent fibres have a core to sheath ratio of 10:90 to 35: 65.

In another embodiment, the fabric of the present invention comprises bicomponent fibers having a shrinkage after 90 seconds exposure at 70 ℃ of less than about 20% and a contact clarity of greater than about 13% as measured according to ASTM D1003. The bicomponent fibers used in the fabric may also have a melting range of 100 ℃ to 120 ℃ as measured by DSC.

Fabrics made using the fibers of the present invention can be made by knitting or weaving. In some embodiments, fabrics may be made by using the bicomponent fibers of the present invention with other fibers such as nylon and/or polyester. The fabrics of the present invention may be used in the manufacture of garments, for example for sports apparel applications. The increased clarity of the fibers of the present invention also provides benefits for applications in which graphics are applied to fabrics.

The invention will be better understood by reference to the following examples.

Filaments were prepared based on the thermoplastic polyurethanes listed in table 1. TPU 1 is a polyester thermoplastic polyurethane comprising the reaction product of butanediol succinate and an aromatic diisocyanate having a melting enthalpy of 60J/g as measured by DSC (second thermal cycle). TPU 2 is a polyester thermoplastic polyurethane comprising the reaction product of butanediol adipate, aromatic diisocyanate, and chain extender glycol having a melting enthalpy of 5J/g as measured by DSC (second thermal cycle). Comparative examples C1-C9 were made from 100% of a TPU material or a particulate blend of TPU 1 and TPU 2 to form monocomponent filaments. Inventive examples 1-4 are bicomponent fibers having a core-sheath cross section. When a fiber could be successfully made, it was tested for shrinkage using a one meter length of fiber, measured before and after exposure to a temperature of 70 ℃ for 90 seconds.

TABLE 1

¹The filaments are spun and knitted into a fabric. Heating fuses the fibers in the fabric. The fabric shrinks and deforms such that a transparency measurement cannot be obtained.

²Continuous filaments cannot be made with these blends. Incompatibility between the two TPU materials (immiscibility ) results in insufficient melt strength of the blend to make continuous filaments.

As shown by the above data, blends of two incompatible thermoplastic polyurethanes cannot form continuous filaments with acceptable both shrinkage and clarity. However, bicomponent fibers of the same two thermoplastic polyurethane compositions unexpectedly provide both high clarity and low shrinkage.

Except in the examples, or where otherwise explicitly indicated, all numbers in this description specifying amounts of materials, reaction conditions, molecular weights, numbers of carbon atoms, and the like, are to be understood as modified by the word "about". It is understood that the upper and lower limits of the amounts, ranges and ratios set forth herein may be independently combined. Similarly, the ranges and amounts for each element of the invention can be used with ranges or amounts for any of the other elements.

As used herein, the transitional term "comprising" synonymous with "including," "containing," or "characterized by," is inclusive or open-ended and does not exclude additional unrecited elements or method steps. However, in each recitation of "comprising" herein, the term is intended to encompass the phrases "consisting essentially of … …" and "consisting of … …" as alternative embodiments, wherein "consisting of … …" excludes any elements or steps not specified, and "consisting essentially of … …" allows for the inclusion of other unrecited elements or steps that do not materially affect the essential or essential and novel characteristics of the contemplated composition or method.

While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. In this regard, the scope of the invention is limited only by the following claims.

Claims

1. A fabric, comprising:

a bicomponent fiber, wherein the bicomponent fiber has a core and sheath structure, wherein the core comprises a thermoplastic polyurethane composition having a melt enthalpy of at least about 50J/g measured according to ASTM D3418 and a contact transparency of 4% or less measured according to ASTM D1003, and the sheath comprises a thermoplastic polyurethane composition having a melt enthalpy of about 5J/g or less measured according to ASTM D3418 and a contact transparency of at least 12% measured according to ASTM D1003.

2. The fabric of claim 1 wherein the shrinkage of the core thermoplastic polyurethane composition after 90 seconds exposure at 70 ℃ is less than 10%.

3. The fabric of claim 1 or 2, wherein the shrinkage of the sheath thermoplastic polyurethane composition after 90 seconds of exposure at 70 ℃ is from 40% to 60%.

4. The fabric of any of claims 1-3, wherein the bicomponent fiber has a core to sheath ratio of 10:90 to 35: 65.

5. The fabric of any one of claims 1 to 4, wherein the bicomponent fiber has a shrinkage after 90 seconds exposure at 70 ℃ of less than 20% and a contact clarity of greater than 13% measured according to ASTM D1003.

6. The fabric of any one of claims 1 to 5, wherein the bicomponent fiber has a melting range of 100 ℃ to 120 ℃ as measured by DSC.

7. The fabric of any of claims 1 to 6, wherein the core comprises a polyester thermoplastic polyurethane.

8. The fabric of any of claims 1 to 7, wherein the sheath comprises a polyester thermoplastic polyurethane that is different from the core thermoplastic polyurethane.

9. The fabric of any of claims 1 to 8, wherein the core comprises a thermoplastic polyurethane comprising the reaction product of a butanediol succinate and an aromatic diisocyanate.

10. The fabric of claim 9, wherein the core comprises a thermoplastic polyurethane consisting of the reaction product of butanediol succinate and an aromatic diisocyanate.

11. The fabric of any of claims 1 to 10, wherein the sheath comprises a thermoplastic polyurethane comprising the reaction product of butanediol adipate, aromatic diisocyanate, and a chain extender.

12. The fabric of claim 11, wherein the sheath comprises a thermoplastic polyurethane consisting of the reaction product of butanediol adipate, aromatic diisocyanate, and chain extender.

13. The fabric of any of claims 1 to 11, wherein both the core thermoplastic polyurethane and the sheath thermoplastic polyurethane are not crosslinked.

14. The fabric of any one of claims 1 to 13, wherein the core comprises a thermoplastic polyurethane having a melting enthalpy of about 60J/g.

15. The fabric according to any one of claims 1 to 14, wherein the sheath comprises a thermoplastic polyurethane having a melting enthalpy of 5J/g.

16. A bicomponent fiber having a core and sheath structure, wherein said bicomponent fiber comprises:

(a) a core comprising a first polyester thermoplastic polyurethane, wherein the first polyester thermoplastic polyurethane has a melt enthalpy of at least 50J/g measured according to astm d 3418;

(b) a sheath comprising a second polyester thermoplastic polyurethane, wherein the second polyester thermoplastic polyurethane has a melt enthalpy of 5J/g or less measured according to astm d 3418.

17. The bicomponent fiber of claim 16, wherein the first polyester thermoplastic polyurethane has a contact transparency of 4% or less as measured according to astm d 1003.

18. The bicomponent fiber of claim 16 or 17, wherein the second polyester thermoplastic polyurethane has a contact transparency of at least 12% as measured according to ASTM D1003.

19. The bicomponent fiber of any one of claims 16 to 18, wherein the first polyester thermoplastic polyurethane comprises the reaction product of butanediol succinate and an aromatic diisocyanate.

20. The bicomponent fiber of any one of claims 16 to 19, wherein the second polyester thermoplastic polyurethane comprises the reaction product of butanediol adipate, aromatic diisocyanate, and chain extender.

21. The bicomponent fiber of any one of claims 16 to 20, wherein the bicomponent fiber comprises from 65% to 90% by weight of the second thermoplastic polyurethane.

22. The bicomponent fiber of any one of claims 16 to 21, wherein the bicomponent fiber comprises from 10% to 35% by weight of the core thermoplastic polyurethane composition.

23. The bicomponent fiber of any one of claims 16 to 22, wherein the first thermoplastic polyurethane has a shrinkage of less than 10% after 90 seconds exposure at 70 ℃.

24. The bicomponent fiber of any one of claims 16 to 23, wherein the shrinkage of the second thermoplastic polyurethane after 90 seconds exposure at 70 ℃ is from 40% to 60%.

25. The bicomponent fiber of any one of claims 16 to 24, wherein the first polyester thermoplastic polyurethane has a melt enthalpy of 60J/g measured according to ASTM D3418.

26. The bicomponent fiber of any one of claims 16 to 25, wherein the second polyester thermoplastic polyurethane has a melt enthalpy of 5J/g measured according to ASTM D3418.

27. The bicomponent fiber of any one of claims 16 to 26, wherein both the first thermoplastic polyurethane and the second thermoplastic polyurethane are not crosslinked.

28. A fabric, comprising:

a bicomponent fiber, wherein the bicomponent fiber has a core and sheath structure, wherein the core comprises a polyester thermoplastic polyurethane comprising the reaction product of butanediol succinate and an aromatic diisocyanate and having a melt enthalpy of at least 50J/g measured according to ASTM D3418 and a contact transparency of 4% or less measured according to ASTM D1003, and the sheath comprises a polyester thermoplastic polyurethane comprising the reaction product of butanediol adipate, an aromatic diisocyanate and a chain extender and having a melt enthalpy of 5J/g or less measured according to ASTM D3418 and a contact transparency of at least 12% measured according to ASTM D1003, wherein neither the core thermoplastic polyurethane nor the sheath thermoplastic polyurethane is crosslinked.

29. The fabric of claim 28, wherein the fabric is a knitted fabric.

30. The fabric of claim 28, wherein the fabric is a woven fabric.

31. The fabric of claim 28, wherein the fabric is a nonwoven fabric.