Foamed TPU (thermoplastic polyurethane) fiber as well as preparation method and application thereof

Abstract

The invention provides a foamed TPU (thermoplastic polyurethane) fiber as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) adding TPU resin, a chain extender and a cross-linking agent into a first-stage double-screw extruder, injecting a physical foaming agent into the screw extruder at the same time, and then extruding; and (2) feeding the material extruded from the first-stage twin-screw extruder into a second-stage single-screw extruder, and spraying and drawing through a foaming machine head and a spinning die head to obtain the foamed TPU fiber. The foamed TPU fiber provided by the invention is light in weight, air-permeable and moisture-permeable, can keep a cool feeling, and is good in flexibility.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of foamed materials, and particularly relates to a foamed TPU fiber and a preparation method and application thereof. BACKGROUND

[0002] TPU (thermoplastic polyurethane elastomer) foamed material is a foamed thermoplastic polyurethane, which has the advantages of light weight, high elasticity, compression resistance, low temperature resistance, etc., and is widely used in the shoe material industry, especially for making insoles and soles. Traditional foaming technology usually uses environmentally unfriendly blowing agents or involves the use of a large amount of solvent, which is difficult to meet the development goal of carbon peak and carbon neutralization.

[0003] As a kind of physical foaming, supercritical fluid foaming is gradually widely used due to its clean and environmentally friendly characteristics. However, the supercritical fluid saturation time of the polymer is long in the supercritical fluid molding foaming preparation process, and the production efficiency is low. Moreover, there are few studies on introducing supercritical fluid foaming into the field of fibers.

[0004] The existing technology discloses a method for preparing a plastic porous fiber by using micro-extrusion foaming technology. The preparation can be divided into three steps, including (1) gas saturation of TPU filaments, (2) micro-extrusion of gas-saturated TPU filaments, and (3) collection of porous TPU fibers under stretching. The prepared fiber has excellent air permeability, moisture permeability, radiation cooling capacity and lower density than seawater, etc. Unfortunately, the foamed fiber is brittle and cannot meet the flexibility of existing shoe and clothing fiber materials, which limits its further industrial application.

[0005] Therefore, it is necessary to provide a foamed TPU fiber with excellent mechanical properties. SUMMARY

[0006] In view of the deficiencies of the prior art, the purpose of the present application is to provide a foamed TPU fiber and a preparation method and application thereof.

[0007] To achieve the purpose of the present application, the following technical solutions are adopted:

[0008] In a first aspect, the present application provides a preparation method of a foamed TPU fiber, which comprises:

[0009] (1) adding TPU resin, chain extender and crosslinking agent into a first-stage double-screw extruder, and simultaneously injecting a physical foaming agent into the screw extruder, and then extruding;

[0010] (2) sending the material extruded from the first-stage double-screw extruder into a second-stage single-screw extruder, and spraying and drawing through a foaming die head and a spinneret to obtain the foamed TPU fiber.

[0011] In the present application, the TPU resin is first chain-extended and cross-linked in a supercritical double-stage (double screw + single screw) extrusion device using a chain extender and a cross-linking agent to increase the melt strength of the TPU resin. The modified TPU resin with high melt strength has excellent processing performance and mechanical properties. In the subsequent foaming, extrusion and drawing using a physical foaming agent, the problem of melt rupture and size instability can be reduced. At the same time, the foaming bubbles do not collapse and rupture during the foaming process, and a uniform and delicate foaming structure can be obtained. Therefore, the foamed TPU fiber obtained by the present application is light in quality, breathable and moisture permeable, and has good flexibility and is not easy to break.

[0012] Preferably, the TPU resin is 100 parts by weight, the chain extender is 5-8 parts by weight, for example 5 parts by weight, 5.2 parts by weight, 5.5 parts by weight, 5.8 parts by weight, 6 parts by weight, 6.2 parts by weight, 6.5 parts by weight, 6.8 parts by weight, 7 parts by weight, 7.2 parts by weight, 7.5 parts by weight, 7.8 parts by weight, 8 parts by weight, etc., and the cross-linking agent is 0.1-1 parts by weight, for example 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.7 parts by weight, 0.8 parts by weight, 0.9 parts by weight, 1 parts by weight, etc.

[0013] The TPU of the present application undergoes chain extension and cross-linking reaction with the chain extender and the cross-linking agent, which can increase the melt strength of the modified TPU resin. Although the melt strength of the modified TPU resin increases with the increase of the content of the chain extender and the cross-linking agent, excessive addition of the cross-linking agent and / or the chain extender will lead to a decrease in the cross-linking degree and the melt strength of the modified TPU resin. Therefore, the addition amount of the three components is preferably within the above range, so that the finally obtained modified TPU resin has a relatively high melt strength.

[0014] At the same time, the content of the TPU resin is limited in the present application. If the content of the TPU resin is too low, it means that the addition amount of the chain extender and the cross-linking agent is too high. If the content of the TPU resin is too high, the addition amount of the chain extender and the cross-linking agent is too low, which will still affect the melt strength of the finally obtained modified TPU resin and the subsequent foaming performance.

[0015] Preferably, the TPU resin includes aromatic TPU resin and / or aliphatic TPU resin, preferably aliphatic TPU resin.

[0016] Preferably, the aliphatic TPU resin includes aliphatic polyester type TPU resin, aliphatic polyether type TPU resin or aliphatic polycarbonate type TPU resin, preferably aliphatic polyester type TPU resin.

[0017] The present invention preferably uses an aliphatic polyester TPU resin, which has high crystallinity and melt strength, and can make the final modified TPU resin have high melt strength.

[0018] Preferably, the chain extender comprises at least two functional groups, and the functional groups are selected from hydroxyl groups and / or amino groups.

[0019] Although there are many types of chain extenders that can react with TPU resin, the present invention preferably introduces hydroxyl and / or amino groups into the chain extender. Chain extenders with hydroxyl and / or amino groups have high reaction efficiency with both TPU and crosslinking agents, and can make the final modified TPU resin have higher melt strength and better foaming performance.

[0020] Preferably, the chain extender includes any one of an alcohol chain extender, an amine chain extender, an alcoholamine chain extender or a triazine chain extender, or a combination of at least two thereof, preferably an alcohol chain extender.

[0021] Preferably, the alcohol chain extender includes diols and / or polyols.

[0022] Preferably, the diol includes any one of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,10-decanediol or diethylene glycol, or a combination of at least two thereof, preferably diethylene glycol and / or 1,6-hexanediol.

[0023] Preferably, the polyol includes any one of alkyl polyol, polyether polyol or polyester polyol, or a combination of at least two of them.

[0024] Preferably, the alkyl polyol comprises trimethylolpropane and / or glycerol.

[0025] Preferably, the polyether polyol includes any one of polyethylene glycol, poly-1,2-propylene ether glycol and poly-1,3-propylene ether glycol, polytetramethylene ether glycol or polyhexamethylene ether glycol, or a combination of at least two thereof.

[0026] Preferably, the polyester polyol includes any one of polyethylene adipate, poly(1,4-butylene adipate) or polyethylene adipate-1,4-butylene adipate diol, or a combination of at least two thereof.

[0027] Preferably, the amine chain extender includes aliphatic diamine and / or aromatic diamine.

[0028] Preferably, the cross-linking agent comprises an isocyanate cross-linking agent, further preferably comprises any one or a combination of at least two of aliphatic diisocyanate, aromatic diisocyanate or other diisocyanate, most preferably comprises aliphatic diisocyanate.

[0029] Preferably, the aliphatic diisocyanate comprises any one or a combination of at least two of hexamethylene diisocyanate, isophorone diisocyanate or dicyclohexyl methane-4,4-diisocyanate.

[0030] Preferably, the aromatic diisocyanate comprises any one or a combination of at least two of diphenyl methane diisocyanate, toluene diisocyanate or polymethylene polyphenyl polyisocyanate.

[0031] In the present application, the compound containing amino and / or hydroxyl (functional degree ≥ 2) is used as a chain extender, and the isocyanate with a functional degree ≥ 2 is used as a cross-linking agent, both of which can react with TPU, that is, the present application synergistically improves the chain extension reaction and the cross-linking reaction, which can not only increase the molecular weight and the molecular chain length of TPU, but also endow it with a three-dimensional network structure, so that the obtained modified TPU resin has high melt strength.

[0032] The modified TPU resin with high melt strength has excellent processing performance and mechanical properties, which can better maintain the shape during extrusion molding, and has less melt fracture and size instability problems, and can effectively prevent bubble collapse and rupture during foaming, and obtain a uniform and delicate cell structure, so that the present application can obtain a foaming TPU fiber with excellent performance for shoe and clothing fibers.

[0033] Preferably, in the preparation method, the preparation raw material further comprises an additive.

[0034] Preferably, the additive is selected from an antioxidant and / or an anti-UV agent, preferably the antioxidant is added in an amount of 0.1-1 parts by weight, for example 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.7 parts by weight, 0.8 parts by weight, 0.9 parts by weight, 1 parts by weight, etc., and preferably the anti-UV agent is added in an amount of 0.1-1 parts by weight, for example 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.7 parts by weight, 0.8 parts by weight, 0.9 parts by weight, 1 parts by weight, etc.

[0035] The antioxidant and anti-UV agent described in the present application are conventional additives in the art, and the present application does not limit specific antioxidants and anti-UV agents, and any antioxidant and / or anti-UV agent that can be applied to the present application can be used.

[0036] In the present application, the addition of the anti-UV agent can enable the finally obtained foamed TPU fiber to have excellent anti-UV performance, if the addition amount is low, the finally obtained fiber is prone to yellowing, and if the addition amount is high, the melt strength and the foaming performance of the modified TPU will be affected.

[0037] Preferably, in the preparation method, the preparation raw material further comprises a POE elastomer.

[0038] Preferably, the addition amount of the POE elastomer is 5-20 parts by weight, for example, 5 parts by weight, 6 parts by weight, 8 parts by weight, 10 parts by weight, 12 parts by weight, 15 parts by weight, 16 parts by weight, 18 parts by weight, 20 parts by weight, etc.

[0039] The present application can increase the compatibility between the incompletely reacted raw materials by introducing the POE elastomer (polyolefin elastomer), and can also reduce the cost of raw materials.

[0040] Preferably, in the preparation method, the screw rotation speed of the first-stage double-screw extruder is 300-350 r / min, for example, 300 r / min, 305 r / min, 310 r / min, 315 r / min, 320 r / min, 325 r / min, 330 r / min, 335 r / min, 340 r / min, 345 r / min, 350 r / min, etc., and the extrusion temperature is 190-210℃, for example, 190℃, 195℃, 200℃, 205℃, 210℃, etc.

[0041] Preferably, the physical foaming agent comprises any one or a combination of at least two of carbon dioxide, nitrogen, propane, n-butane or isobutane, and preferably carbon dioxide and / or nitrogen.

[0042] The preparation method provided by the present application has low use amount of the selected physical foaming agent, and is safe and environmentally friendly.

[0043] Preferably, the addition amount of the physical foaming agent is 1-1.3% of the mass of the TPU resin, for example, 1%, 1.05%, 1.1%, 1.15%, 1.2%, 1.25%, 1.3%, etc.

[0044] Preferably, the injection pressure of the physical foaming agent is 15-20 MPa, for example, 15 MPa, 16 MPa, 17 MPa, 18 MPa, 19 MPa, 20 MPa, etc.

[0045] Preferably, the residence time of the material in the first-stage double-screw extruder is 90-100 s, for example, 90 s, 91 s, 92 s, 93 s, 94 s, 95 s, 96 s, 97 s, 98 s, 99 s, 100 s, etc.

[0046] Preferably, in the preparation method, the temperature of the second-stage single-screw extruder is 205-215℃, such as 205℃, 208℃, 210℃, 212℃, 215℃, etc.

[0047] Preferably, the residence time of the material in the second-stage single-screw extruder is 120-150s, such as 120s, 122s, 125s, 128s, 130s, 132s, 135s, 138s, 140s, 142s, 145s, 148s, 150s, etc.

[0048] Preferably, the temperature of the foaming die head and the spinneret head is each independently selected from 205-215℃, such as 205℃, 208℃, 210℃, 212℃, 215℃, etc.

[0049] Preferably, the rate of the pulling is 5-35m / mim, such as 5m / mim, 8m / mim, 10m / mim, 15m / mim, 20m / mim, 25m / mim, 30m / mim, 35m / mim, etc.

[0050] The pulling of the present application can be provided with multiple pullings, and the rate of each pulling can be the same or different.

[0051] In the second aspect, the present application provides a foamed TPU fiber prepared by the preparation method of the first aspect.

[0052] Preferably, the diameter of the foamed TPU fiber is 0.15-2.0mm, such as 0.15mm, 0.2mm, 0.3mm, 0.5mm, 0.6mm, 0.8mm, 1mm, 1.2mm, 1.5mm, 1.8mm, 2.0mm, etc.

[0053] Preferably, the density of the foamed TPU fiber is 0.2-0.5g / cm 3 , such as 0.2g / cm 3 , 0.25g / cm 3 , 0.3g / cm 3 , 0.35g / cm 3 , 0.4g / cm 3 , 0.45g / cm 3 , 0.5g / cm 3 , etc.

[0054] The diameter of the foamed TPU fiber of the present application is determined by the diameter of the spinneret head and the pulling rate, and the present application preferably the diameter of the foamed TPU fiber is in the range of 0.15-2.0mm, and the fiber in this range is not easy to break during preparation and has higher application prospect.

[0055] The foamed TPU fiber provided by the application has high foaming ratio, light quality, air permeability, moisture permeability and other characteristics.

[0056] In a third aspect, the application provides application of the foamed TPU fiber of the second aspect in shoe and clothing fibers.

[0057] The foamed TPU fiber obtained by the application has light quality, air permeability, moisture permeability, can maintain cool feeling, has good flexibility, and can be widely applied in the field of shoes and clothes.

[0058] Compared with the prior art, the application has the following beneficial effects:

[0059] (1) The chain extension reaction and crosslinking reaction are synergistic in the application, which can not only increase the molecular weight and molecular chain length of the TPU, but also give the TPU a three-dimensional network structure, so that the modified TPU resin obtained has high melt strength;

[0060] (2) The modified TPU resin with high melt strength has excellent processing performance and mechanical properties, which can better maintain the shape during extrusion molding, reduce melt rupture and size instability, and effectively prevent bubble collapse and rupture during foaming, so that a uniform and delicate bubble structure is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0061] Fig. 1 FIG. 1 is a cross-sectional microstructure diagram of the cross section of the foamed TPU fiber obtained in Example 1 of the application;

[0062] Fig. 2 FIG. 1 is a cross-sectional microstructure diagram of the cross section of the foamed TPU fiber obtained in Example 1 of the application; DETAILED DESCRIPTION

[0063] The technical solutions of the application will be further described through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the application and should not be regarded as specific limitations on the application.

[0064] Unless otherwise specified, the raw materials involved in the following specific embodiments of the application are all conventional materials in the art and can be purchased through commercially available products. Some raw material information is shown in Table 1:

[0065] Table 1

[0066]

[0067] Examples 1-6 and Comparative Examples 1-8

[0068] The present embodiment provides a preparation method of foamed TPU fiber and the foamed TPU fiber obtained therefrom, wherein the preparation raw materials used are shown in Table 2.

[0069] Table 2

[0070]

[0071]

[0072] Note: the chain extender is PEG-2000, the crosslinking agent is 2-aminoethyl-2,3-dihydroxypropyl-hydroxyphosphate, the antioxidant is BASF 1010, and the anti-UV agent is BASF 234.

[0073] The preparation method is as follows:

[0074] (1) The TPU resin, chain extender, crosslinking agent, antioxidant, and anti-UV agent are added into a first-stage double-screw extruder, and a physical foaming agent is injected into the screw extruder, and then extruded, wherein:

[0075] The screw rotation speed is 350 r / min, the extrusion temperature is 200℃, the physical foaming agent is carbon dioxide, the amount of the physical foaming agent is 1.2% of the mass of the TPU resin, the injection pressure is 18 MPa, and the residence time of the raw materials in the double-screw extruder is 100 s;

[0076] (2) The material extruded from the first-stage double-screw extruder is sent into a second-stage single-screw extruder, and is extruded and drawn through a foaming die head and a spinning die head to obtain a foamed TPU fiber, wherein:

[0077] The temperature of the second-stage single-screw extruder is 210℃, the residence time of the raw materials in the single-screw extruder is 120 s, the temperatures of the foaming die head and the spinning die head are both 210℃, two drawing devices are arranged, the speed of the first drawing device is 5 m / min, the speed of the second drawing device is 15 m / min, and the diameter of the finally obtained foamed TPU fiber is 1.5 mm.

[0078] Example 7

[0079] The present embodiment provides a preparation method of a foamed TPU fiber and a foamed TPU fiber obtained therefrom.

[0080] The difference from Example 1 is that in the present embodiment, the aliphatic polyester type TPU (TPU resin 1) is replaced by an equal mass of aliphatic polyether type TPU (TPU resin 2).

[0081] Example 8

[0082] The present embodiment provides a preparation method of a foamed TPU fiber and a foamed TPU fiber obtained therefrom, and the preparation method is as follows:

[0083] (1) 100 parts of TPU resin 1, 7 parts of chain extender PPG-1000, 0.1 part of hexamethylene diisocyanate, 0.1 part of antioxidant BASF-168 and 1 part of anti-UV agent BASF-234 are added into a first-stage double screw extruder, and a physical foaming agent is injected into the screw extruder, and then extruded, wherein:

[0084] The screw rotation speed is 300 r / min, the extrusion temperature is 190°C, the physical foaming agent is nitrogen, the amount of the physical foaming agent is 1.3% of the mass of the TPU resin, the injection pressure is 20 MPa, and the residence time of the raw material in the double screw extruder is 90 s;

[0085] (2) The material extruded from the first-stage double screw extruder is sent into a second-stage single screw extruder, and is sprayed and pulled through a foaming die head and a spinning die head to obtain a foamed TPU fiber, wherein:

[0086] The temperature of the second-stage single screw extruder is 215°C, the residence time of the raw material in the single screw extruder is 150 s, the temperature of the foaming die head and the spinning die head is both 215°C, two pulling devices are set, and the speed of each pulling device is 5 m / min, and finally the diameter of the foamed TPU fiber is 2 mm.

[0087] Example 9

[0088] The present embodiment provides a preparation method of a foamed TPU fiber and a foamed TPU fiber obtained therefrom, and the preparation method is as follows:

[0089] (1) 100 parts of TPU resin 1, 8 parts of chain extender 1,8-octanediol, 1 part of isophorone diisocyanate, 0.5 parts of antioxidant BASF-168 and 1 part of anti-UV agent BASF-234 are added into a first-stage double screw extruder, and a physical foaming agent is injected into the screw extruder, and then extruded, wherein:

[0090] The screw rotation speed is 320 r / min, the extrusion temperature is 210°C, the physical foaming agent is nitrogen, the amount of the physical foaming agent is 1% of the mass of the TPU resin, the injection pressure is 15 MPa, and the residence time of the raw material in the double screw extruder is 95 s;

[0091] (2) The material extruded from the first-stage double screw extruder is sent into a second-stage single screw extruder, and is sprayed and pulled through a foaming die head and a spinning die head to obtain a foamed TPU fiber, wherein:

[0092] The temperature of the second-order single-screw extruder was 205°C, the residence time of the raw material in the single-screw extruder was 140 s, the temperature of the foaming head and the spinneret head was 205°C, two traction devices were set, the speed of the first traction device was 5 m / min, and the speed of the second traction device was 35 m / min, and finally the diameter of the foamed TPU fiber was 0.15 mm.

[0093] Comparative Example 9

[0094] The present comparative example provides a method for preparing a foamed TPU fiber and a foamed TPU fiber obtained therefrom.

[0095] The difference from Example 1 is that in the present comparative example, the chain extender is 1,8-octanedioic acid.

[0096] Performance test

[0097] The foamed TPU fibers provided by the examples and comparative examples were subjected to performance tests, wherein the melt strength and the tensile strength and elongation at break were tested for unfoamed samples, and the method was as follows:

[0098] (1) Melt strength: tested according to ISO 16790:2015 as the test standard;

[0099] (2) Tensile strength and elongation at break: tested according to GB / T 14344-2022 as the test standard;

[0100] (3) Density: tested according to ASTM D792 as the test standard;

[0101] (4) UV resistance: tested according to GB / T 16422.3 as the test standard, 340 nm, irradiance 0.89 w / m 2 , 24 h, and the color difference change ΔE was recorded;

[0102] (5) Foaming ratio:

[0103] Take a sample of mass m1 and measure its volume V1 by the drainage method to obtain the apparent density of the sample to be tested ρ1 = m1 / V1;

[0104] Take the sample to be tested and process it according to the method of the reference example (without adding a physical foaming agent) to test the density of the obtained unfoamed sample ρ2;

[0105] The foaming ratio R = ρ2 / ρ1 is calculated to obtain the foaming ratio, and 5 parallel tests are performed for each group of samples and the average value is taken.

[0106] The test results are as follows:

[0107] Figs. 1-2This is a SEM photograph of the cross section of the foamed TPU fiber prepared in Example 1. As can be seen from the figure, the foamed TPU fiber obtained in the present invention has a uniform and fine pore structure.

[0108] The test results are shown in Table 3:

[0109] Table 3

[0110]

[0111]

[0112] Note: The foamed TPU fiber obtained in Comparative Example 1 is unevenly foamed, brittle, and easily broken.

[0113] It can be seen from the examples and performance tests that the TPU obtained by the preparation method provided by the present invention has a high melt strength, and the foamed TPU fiber has a uniform and fine pore structure.

[0114] It can be seen from Examples 1 and 5 that when the contents of TPU resin and chain extender are the same, a higher content of cross-linking agent can enhance the cross-linking effect of the system, form a more stable network structure, and the prepared TPU will have higher melt strength; at the same time, the increase in the content of antioxidant and anti-UV agent will not have a substantial effect on the fiber, but can increase the antioxidant and UV resistance of the fiber.

[0115] It can be seen from Examples 2-4 that when the contents of TPU resin and chain extender are the same, an appropriate increase in the crosslinking agent can increase the crosslinking strength of the system, while a larger amount of crosslinking agent will lead to a decrease in the crosslinking degree of the system and a decrease in the melt strength.

[0116] From the comparison between Example 4 and Example 5, it can be seen that the introduction of POE resin can increase the compatibility between materials and improve material performance.

[0117] From the comparison between Example 1 and Example 7, it can be seen that the use of aliphatic polyester TPU as a raw material has a higher crystallinity, which can make the final modified TPU resin have a higher melt strength, which is conducive to processing to obtain foamed TPU fibers with excellent performance.

[0118] From the comparison between Example 1 and Comparative Examples 1-3, it can be seen that in the present invention, by simultaneously introducing a chain extender and a cross-linking agent to carry out chain extension and cross-linking modification of the TPU resin, a modified TPU resin with higher melt strength can be obtained for foaming processing. The foamed TPU fiber finally obtained has excellent performance and is uniform and fine in foaming.

[0119] From the comparison of Example 5 and Comparative Examples 4, 6, Example 1 and Comparative Example 5, Example 6 and Comparative Examples 7-8, it can be seen that the TPU resin, the chain extender and the anti-UV agent defined in the present application have the best effect when the addition amount of the chain extender and the anti-UV agent is within the range defined in the present application. From the comparison of Example 1 and Comparative Example 9, it can be seen that the chain extender with hydroxyl and / or amino is preferred in the present application.

[0120] The applicant declares that the process of the present application is illustrated by the above examples, but the present application is not limited to the above process steps, i.e. it does not mean that the present application must rely on the above process steps to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of the raw materials selected by the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for preparing foamed TPU fiber, characterized in that: The preparation method comprises: (1) Add TPU resin, chain extender and cross-linking agent into the first-stage twin-screw extruder, and inject physical foaming agent into the screw extruder at the same time, and then extrude; (2) The material extruded from the first-stage twin-screw extruder is fed into a second-stage single-screw extruder, and is ejected and pulled through a foaming head and a spinneret to obtain the foamed TPU fiber.

2. The preparation method according to claim 1, characterized in that In parts by weight, the TPU resin comprises 100 parts by weight, the chain extender comprises 5-8 parts by weight, and the cross-linking agent comprises 0.1-1 parts by weight.

3. The preparation method according to claim 1 or 2, characterized in that The TPU resin includes aromatic TPU resin and / or aliphatic TPU resin, preferably aliphatic TPU resin; Preferably, the aliphatic TPU resin includes an aliphatic polyester TPU resin, an aliphatic polyether TPU resin or an aliphatic polycarbonate TPU resin, and is preferably an aliphatic polyester TPU resin.

4. The preparation method according to any one of claims 1 to 3, characterized in that The chain extender comprises at least two functional groups, wherein the functional groups are selected from hydroxyl groups and / or amino groups; Preferably, the chain extender comprises any one of an alcohol chain extender, an amine chain extender, an alcoholamine chain extender or a triazine chain extender, or a combination of at least two thereof, preferably an alcohol chain extender; Preferably, the alcohol chain extender comprises diols and / or polyols; Preferably, the diol includes any one of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,10-decanediol or diethylene glycol, or a combination of at least two thereof, preferably diethylene glycol and / or 1,6-hexanediol; Preferably, the polyol comprises any one or a combination of at least two of alkyl polyol, polyether polyol or polyester polyol; Preferably, the alkyl polyol comprises trimethylolpropane and / or glycerol; Preferably, the polyether polyol comprises any one or a combination of at least two of polyethylene glycol, poly-1,2-propylene ether glycol and poly-1,3-propylene ether glycol, polytetramethylene ether glycol or polyhexamethylene ether glycol; Preferably, the polyester polyol comprises any one or a combination of at least two of polyethylene adipate, polybutylene adipate-1,4-diol or polyethylene adipate-1,4-diol diol; Preferably, the amine chain extender includes aliphatic diamine and / or aromatic diamine.

5. The preparation method according to any one of claims 1 to 4, characterized in that The cross-linking agent includes an isocyanate cross-linking agent, and further preferably includes any one or a combination of at least two of an aliphatic diisocyanate, an aromatic diisocyanate or other diisocyanates, and most preferably includes an aliphatic diisocyanate; Preferably, the aliphatic diisocyanate includes any one or a combination of at least two of hexamethylene diisocyanate, isophorone diisocyanate or dicyclohexylmethane-4,4-diisocyanate; Preferably, the aromatic diisocyanate includes any one of diphenylmethane diisocyanate, toluene diisocyanate or polymethylene polyphenyl polyisocyanate, or a combination of at least two thereof.

6. The preparation method according to any one of claims 1 to 5, characterized in that In the preparation method, preparing the raw materials further comprises adding auxiliary agents; Preferably, the additive is selected from an antioxidant and / or an anti-UV agent, preferably the antioxidant is added in an amount of 0.1-1 parts by weight, and preferably the anti-UV agent is added in an amount of 0.1-1 parts by weight; Preferably, in the preparation method, the preparation raw materials further include POE elastomer; Preferably, the added amount of the POE elastomer is 5-20 parts by weight.

7. The preparation method according to any one of claims 1 to 6, characterized in that In the preparation method, the screw speed of the first-stage twin-screw extruder is 300-350 r / min, and the extrusion temperature is 190-210° C.; Preferably, the physical foaming agent comprises any one or a combination of at least two of carbon dioxide, nitrogen, propane, n-butane or isobutane; Preferably, the amount of the physical foaming agent added is 1-1.3% of the mass of the TPU resin; Preferably, the injection pressure of the physical foaming agent is 15-20 MPa; Preferably, the residence time of the material in the first-stage twin-screw extruder is 90-100 s.

8. The preparation method according to any one of claims 1 to 6, characterized in that In the preparation method, the temperature of the second-stage single-screw extruder is 205-215°C; Preferably, the residence time of the material in the second-stage single-screw extruder is 120-150s; Preferably, the temperature of the foaming die and the spinneret are independently selected from 205-215°C; Preferably, the pulling speed is 5-35 m / min.

9. A foamed TPU fiber prepared by the preparation method according to any one of claims 1 to 8; Preferably, the diameter of the foamed TPU fiber is 0.15-2.0 mm; Preferably, the density of the foamed TPU fiber is 0.2-0.5 g / cm 3 .

10. Use of the foamed TPU fiber according to claim 9 in footwear and clothing fibers.

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