Degradable composite fiber and preparation method and application thereof

Abstract

The invention provides a degradable composite fiber as well as a preparation method and application thereof. The preparation raw materials of the composite fiber comprise a polymer and an antioxidant, the polymer comprises a cellulose grafted polylactic acid copolymer and poly (terephthalic acid-butanediol adipate) copolyester (PBAT); wherein in the polymer, the mass content of the cellulose grafted polylactic acid copolymer is 1%-80%; in the polymer, the mass content of the poly (terephthalic acid-adipic acid-butanediol) copolyester is 20%-90%; and the antioxidant accounts for 0.1%-0.3% of the mass of the polymer. According to the invention, the hard and brittle cellulose grafted polylactic acid material and the soft and tough PBAT material are blended to prepare the composite fiber, and the composite fiber has the advantages of excellent processability, excellent mechanical properties and degradability.

Description

Technical Field

[0001] The present invention belongs to the field of degradable fibers. Specifically, it relates to a degradable composite fiber, a preparation method thereof, and an application thereof. Background Art

[0002] Among numerous bio-based materials, cellulose is the largest natural renewable bio-based polymer material in nature, widely existing in natural raw materials such as wood, cotton, and reed. The cellulose fiber prepared therefrom has advantages such as moisture absorption, purity, softness, excellent biocompatibility, and excellent degradation performance. However, most of the existing cellulose fibers use solution spinning technology, which requires the use of specific solvents and production on specific equipment, resulting in low production efficiency and a relatively cumbersome post-treatment process. The emergence of cellulose grafted polymer materials such as cellulose esters and cellulose ethers breaks the hydrogen bonds between cellulose molecular chains, reduces the glass transition temperature and melt flow temperature of cellulose-based polymers, and enables them to have the conditions for melt processing. Among a series of cellulose-based copolymers, cellulose grafted polylactic acid materials are a new type of material with great application potential in the fields of degradable fibers and non-woven fabrics because they have both thermoplastic processing properties and excellent degradability. However, cellulose grafted polylactic acid materials have the problem of insufficient toughness, which limits their application.

[0003] Poly(butylene adipate-co-terephthalate) (PBAT) is one of the recognized chemically synthesized degradable materials. The flexible aliphatic chain segments in the PBAT molecule endow the PBAT material with excellent flexibility and film-forming properties, and by adjusting the relative content of aromatic and aliphatic chain segments in the molecule, the properties of PBAT can be regulated within a large range to meet different usage requirements. As a fiber material, PBAT fibers have the advantages of softness, elasticity, and degradability. However, PBAT also has problems such as slow crystallization rate and easy adhesion of the melt during the spinning process. At the same time, PBAT fibers have the problem of relatively low fiber strength. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides the following technical solutions:

[0005] A composite fiber, the raw materials for preparing the composite fiber include a polymer and an antioxidant; the polymer includes a cellulose grafted polylactic acid copolymer and poly(butylene adipate-co-terephthalate) (PBAT); wherein,

[0006] In the polymer, the mass content of the cellulose grafted polylactic acid copolymer is 1% - 80%, for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%;

[0007] In the polymer, the mass content of the poly(butylene adipate terephthalate) copolyester is 20% - 90%, such as 30%, 40%, 50%, 60%, 70%, 80%.

[0008] The antioxidant accounts for 0.1% - 0.3% of the mass of the polymer.

[0009] According to an embodiment of the present invention, the poly(butylene adipate terephthalate) copolyester is selected from at least one of PBAT-1, PBAT-2, PBAT-3, PBAT-4, PBAT-5, PBAT-6, PBAT-7. The poly(butylene adipate terephthalate) copolyester in the present invention is commercially available, for example, purchased from Xinjiang Tunhe Co., Ltd.

[0010] According to an embodiment of the present invention, the molecular weight of the poly(butylene adipate terephthalate) copolyester is 50,000 - 150,000, such as 100,000.

[0011] According to an embodiment of the present invention, the glass transition temperature of the poly(butylene adipate terephthalate) copolyester is -40°C to -20°C, such as -30°C.

[0012] According to an embodiment of the present invention, the melting point of the poly(butylene adipate terephthalate) copolyester is 110 - 120°C, such as 115°C.

[0013] According to an embodiment of the present invention, the melt index of the poly(butylene adipate terephthalate) copolyester is 0.7 - 14 g / 10 min (2.16 kg, 120 - 150°C).

[0014] According to an embodiment of the present invention, the cellulose-grafted polylactic acid copolymer is obtained by graft copolymerization of cellulose and lactide in an ionic liquid. Preferably, the cellulose-grafted polylactic acid copolymer is prepared according to the method disclosed in the patent document CN103193964B, and its synthesis process is as Figure 1 shown.

[0015] According to an embodiment of the present invention, the cellulose is selected from those with a degree of polymerization DP of DP100 - DP1000, such as DP200, DP300, DP400, DP500, DP600, DP700, DP800, DP900.

[0016] According to an embodiment of the present invention, the cellulose is selected from at least one of microcrystalline cellulose, cotton pulp, and cotton linter.

[0017] Exemplarily, the cellulose is selected from at least one of microcrystalline cellulose (e.g., DP220), cotton pulp (e.g., DP650), and cotton pulp (e.g., DP434).

[0018] According to an embodiment of the present invention, the ionic liquid is selected from one, two, or more of 1-allyl-3-methylimidazolium chloride (AmimCl) ionic liquid, 1-butyl-3-methylimidazolium acetate (BmimAc) ionic liquid, 1-ethyl-3-methylimidazolium acetate (EmimAc) ionic liquid, 1-butyl-3-methylimidazolium chloride (BmimCl) ionic liquid, 1-butyl-3-methylimidazolium benzoate (BmimPhCOO) ionic liquid, 1-ethyl-3-methylimidazolium propionate (EmimP) ionic liquid, and 1-ethyl-3-methylimidazolium methyl phosphate ionic liquid.

[0019] According to an embodiment of the present invention, the catalyst is selected from at least one of 4-dimethylaminopyridine (DMAP), tetrabutyl titanate, methanesulfonic acid, stannous octoate, 1,8-diazabicyclo-bicyclo(5,4,0)-7-undecene, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene.

[0020] According to an embodiment of the present invention, the molar ratio of the catalyst to the hydroxyl group in the cellulose is 0.1:1 to 2:1 (mol / mol).

[0021] According to an embodiment of the present invention, the molar ratio of the cellulose to lactide is 1:1 - 1:9, for example, 1:4, 1:5, 1:6.

[0022] According to an embodiment of the present invention, in the cellulose-grafted polylactic acid copolymer, the mass fraction of the polylactic acid component is 30% - 90%, for example, 70%, 80%. In the present invention, the polylactic acid component refers to the lactide unit in the cellulose-grafted polylactic acid copolymer.

[0023] According to an embodiment of the present invention, the glass transition temperature of the cellulose-grafted polylactic acid copolymer is 50°C - 120°C, for example, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C.

[0024] According to an embodiment of the present invention, the heat flow temperature of the cellulose-grafted polylactic acid copolymer is 130°C - 200°C, for example, 150°C.

[0025] According to an embodiment of the present invention, the Mn(D) of the cellulose-grafted polylactic acid copolymer is 50,000 - 100,000 (for example, 60,000, 70,000, 80,000, 90,000), and the Mw(D) of the cellulose-grafted polylactic acid copolymer is 130,000 - 190,000 (for example, 140,000, 150,000, 160,000, 170,000, 180,000).

[0026] According to an embodiment of the present invention, the melt index of the cellulose-grafted polylactic acid copolymer is 0.25 - 20 g / 10 min (2.16 kg), for example, 0.5 g / 10 min, 1 g / 10 min, 5 g / 10 min, 10 g / 10 min.

[0027] According to an embodiment of the present invention, the antioxidant is selected from at least one of antioxidant B215 and antioxidant 1010.

[0028] According to an embodiment of the present invention, the antioxidant accounts for 0.1%, 0.2%, 0.3% of the cellulose-grafted polylactic acid copolymer and poly(butylene adipate-co-terephthalate).

[0029] According to an embodiment of the present invention, the composite fiber has degradability.

[0030] According to an embodiment of the present invention, the composite fiber has at least one of the following properties:

[0031] (1) The tensile strength is 10 MPa - 600 MPa, for example, 20 MPa, 50 MPa, 100 MPa, 150 MPa, 300 MPa;

[0032] (2) The elongation at break is 5% - 500%, for example, 10%, 50%, 100%, 150%, 200%, 250%, 400%;

[0033] (3) The elastic modulus is 400 MPa - 30,000 MPa, for example, 500 MPa, 1000 MPa, 3000 MPa, 5000 MPa, 7000 MPa, 15000 MPa, 25000 MPa, 30000 MPa;

[0034] (4) The fiber diameter is 1 - 200 μm, for example, 2 μm, 5 μm, 8 μm, 15 μm, 50 μm, 100 μm, 150 μm, 200 μm.

[0035] The present invention also provides a method for preparing the above composite fiber. The method for preparing the composite fiber includes: blending the preparation raw materials to obtain a composite material; and melting and spinning the composite material to prepare the composite fiber.

[0036] According to an embodiment of the present invention, the blending method of the preparation raw materials is selected from Method 1 or Method 2, wherein,

[0037] Method 1 includes the following steps:

[0038] (A1) Prepare a blending solution: dissolve the cellulose-grafted polylactic acid copolymer in a good solvent, add the poly(butylene terephthalate-co-adipate) copolyester and an antioxidant and mix evenly to obtain a blending solution;

[0039] (A2) Dry the blending solution prepared in step (A1) to obtain the composite material;

[0040] Method 2 includes the following steps:

[0041] (B1) Mix the cellulose-grafted polylactic acid copolymer, the poly(butylene terephthalate-co-adipate) copolyester and an antioxidant to prepare a blend;

[0042] (B2) Carry out internal mixing blending on the blend in step (B1) to obtain the composite material.

[0043] According to an embodiment of the present invention, in step (A1), the good solvent is selected from at least one of dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF).

[0044] According to an embodiment of the present invention, in step (A2), the drying means removing the good solvent at a certain temperature.

[0045] According to an embodiment of the present invention, in step (A2), the drying is carried out at a temperature above 100°C, for example, at 100 - 120°C.

[0046] According to an embodiment of the present invention, in step (B1), the blend can be prepared in a device known in the art, such as a twin-screw extruder or a minilab (micro mixing rheometer).

[0047] According to an embodiment of the present invention, in step (B2), the conditions for internal mixing blending are as follows: the blending temperature is 120 - 190°C; the screw speed is 10 - 30 r / min.

[0048] According to an embodiment of the present invention, the melting can be carried out using a device known in the art, such as a non-woven fabric machine.

[0049] According to an embodiment of the present invention, the temperature of the melting is the spinning temperature. Preferably, the spinning temperature is 120 - 250°C, for example, 150°C, 180°C, 210°C.

[0050] According to an embodiment of the present invention, the melting time can be selected from the times known in the art, for example, 10 minutes.

[0051] According to an embodiment of the present invention, the spinning conditions are as follows: under a certain pressure condition, the composite fiber is obtained by winding. Preferably, the spinning pressure is 1.0 kg to 5.0 kg, for example, 2.16 kg.

[0052] According to an embodiment of the present invention, the winding can be carried out on a winding device known in the art, and no specific limitation is made in the present invention.

[0053] According to an embodiment of the present invention, the spinning equipment can be selected from the spinning equipment known in the art, and no specific limitation is made in the present invention.

[0054] According to an embodiment of the present invention, the spinning speed is 5 - 100 m / min, for example, 10 m / min, 15 m / min, 90 m / min.

[0055] The present invention also provides the application of the above composite fiber in the field of degradable materials. For example, the degradable composite fiber can be applied to industrial textiles such as degradable non-woven fabrics, personal protection, medical protection, medical dressings and other fields.

[0056] The beneficial effects of the present invention are as follows:

[0057] The present invention solves the problems of insufficient toughness of the cellulose grafted polylactic acid material, slow melt crystallization rate and easy adhesion of PBAT. By blending the hard and brittle cellulose grafted polylactic acid material with the soft and tough PBAT material, a series of degradable composite fibers are obtained. It can not only improve the thermoplastic processing performance and flexibility of the cellulose grafted polylactic acid material, but also improve the strength of PBAT, which is an effective way to obtain fiber materials with excellent comprehensive performance of processing performance, mechanical performance and degradation performance.

[0058] The elongation at break of the composite fiber of the present invention is improved compared with the cellulose grafted polylactic acid material, and the tensile strength and modulus are also improved compared with PBAT. At the same time, it has the characteristics of excellent processing performance, excellent mechanical performance and degradability. Description of the Drawings

[0059] Figure 1 It is the synthesis process of the cellulose grafted polylactic acid copolymer.

[0060] Figure 2 It is a physical diagram, in which the left figure is Example 2; the right figure is Example 3.

[0061] Figure 3 It is a physical diagram of the fiber prepared in Comparative Example 1.

[0062] Figure 4 SEM images of the degradable composite fiber of the present invention; among them, the left figure is the surface magnified 5000 times; the right figure is the cross-section magnified 10000 times. Detailed implementation manners

[0063] The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to illustrate and explain the present invention exemplarily, and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0064] Unless otherwise specified, the raw materials and reagents used in the following embodiments are all commercially available products, or can be prepared by known methods.

[0065] Example 1:

[0066] Preparation of degradable composite fiber:

[0067] At 80 °C, 8 g of microcrystalline cellulose (degree of polymerization is 220) was dissolved in 152 g of ionic solvent 1-allyl-3-methylimidazolium chloride (AmimCl). After dissolving for 1.5 h, 28.5 g of lactide and 9.12 g of catalyst 4-dimethylaminopyridine were added. After reacting for 10 h, it was washed with deionized water and precipitated, and then dried in a blast drying oven at 50 °C to obtain cellulose-grafted polylactic acid copolymer, denoted as cellulose-g-PLA 1:4. The glass transition temperature of cellulose-g-PLA 1:4 is 95.5 °C, the number average molecular weight is 58722 D, the weight average molecular weight is 133368 D, and the melt index is 0.25 g / 10 min (190 °C). 8 g of cellulose-g-PLA 1:4, 2 g of PBAT-1 (Xinjiang Tunhe), and 0.01 g of antioxidant 1010 were dissolved in 20 g of DMF, and magnetically stirred and mixed evenly at 60 °C. After drying the solvent on a hot table with a ventilation system at 100 °C, a composite material was obtained. The above composite material was added into the barrel of the melt indexer, melted at 190 °C for 10 min, and under the pressure of 2.16 kg weight, the melt was extruded from the micro-discharge port at the bottom of the melt indexer; one end of the melt was clamped with tweezers, bypassed the winding pulley, and the filament was wound on a winding device rotating at 20 m / min to obtain degradable composite fiber #1, and its performance is listed in Table 1.

[0068] Example 2:

[0069] Preparation of degradable composite fiber:

[0070] At 80 °C, 8 g of microcrystalline cellulose DP220 was dissolved in 152 g of the ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl). After 1.5 h of dissolution, 28.5 g of lactide and 9.12 g of the catalyst 4-dimethylaminopyridine were added. After reacting for 10 h, it was washed with deionized water and precipitated, and then dried in a blast drying oven at 50 °C to obtain cellulose-g-PLA 1:4. The glass transition temperature of cellulose-g-PLA 1:4 was 95.5 °C, the number average molecular weight was 58722 D, the weight average molecular weight was 133368 D, and the melt index was 0.25 g / 10 min (190 °C). 5 g of cellulose-g-PLA 1:4, 5 g of PBAT-2 (Xinjiang Tunhe), and 0.01 g of antioxidant 1010 were dissolved in 20 g of DMF, and magnetically stirred and mixed evenly at 60 °C. After drying the solvent on a hot stage with a ventilation system at 100 °C, a composite material was obtained. The above composite material was added into the barrel of the melt indexer, melted at 150 °C for 10 min, and under the pressure of a 2.16 kg weight, the melt was extruded from the micro-discharge port at the bottom of the melt indexer; one end of the melt was clamped with tweezers, bypassed the winding pulley, and the filament was wound on a winding device rotating at 20 m / min to obtain the degradable composite fiber #2, and its properties are listed in Table 1.

[0071] Example 3:

[0072] Preparation of degradable composite fiber:

[0073] At 80 °C, 8 g of microcrystalline cellulose DP220 was dissolved in 152 g of the ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl). After 1.5 h of dissolution, 28.5 g of lactide and 9.12 g of the catalyst 4-dimethylaminopyridine were added. After reacting for 10 h, it was washed with deionized water and precipitated, and then dried in a blast drying oven at 50 °C to obtain cellulose-g-PLA 1:4. The glass transition temperature of cellulose-g-PLA 1:4 was 95.5 °C, the number average molecular weight was 58722 D, the weight average molecular weight was 133368 D, and the melt index was 0.25 g / 10 min (190 °C). 8 g of cellulose-g-PLA 1:4, 2 g of PBAT-2 (Xinjiang Tunhe), and 0.01 g of antioxidant 1010 were dissolved in 20 g of DMF, and magnetically stirred and mixed evenly at 60 °C. After drying the solvent on a hot stage with a ventilation system at 100 °C, a composite material was obtained. The above composite material was added into the barrel of the melt indexer, melted at 180 °C for 10 min, and under the pressure of a 2.16 kg weight, the melt was extruded from the micro-discharge port at the bottom of the melt indexer; one end of the melt was clamped with tweezers, bypassed the winding pulley, and the filament was wound on a winding device rotating at 20 m / min to obtain the degradable composite fiber #3, and its properties are listed in Table 1.

[0074] Example 4:

[0075] Preparation of degradable composite fiber:

[0076] At 80 °C, 8 g of microcrystalline cellulose DP220 was dissolved in 152 g of ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl). After dissolving for 1.5 h, 28.5 g of lactide and 9.12 g of catalyst 4-dimethylaminopyridine were added. After reacting for 10 h, it was washed with deionized water and precipitated, and then dried in a blast drying oven at 50 °C to obtain cellulose-g-PLA 1:4. The glass transition temperature of cellulose-g-PLA 1:4 was 95.5 °C, the number average molecular weight was 58722 D, the weight average molecular weight was 133368 D, and the melt index was 0.25 g / 10 min (190 °C). 8 g of cellulose-g-PLA 1:4, 2 g of PBAT-7 (Xinjiang Tunhe Blue Mountains), and 0.01 g of antioxidant 1010 were dissolved in 20 g of DMF, and magnetically stirred and mixed evenly at 60 °C. After drying the solvent on a hot table with a ventilation system at 100 °C, a composite material was obtained. The above composite material was added into the barrel of the melt indexer, melted at 180 °C for 10 min, and under the pressure of a 2.16 kg weight, the melt was extruded from the micro-discharge port at the bottom of the melt indexer;

[0077] One end of the melt was clamped with tweezers, bypassed the winding pulley, and the filament was wound around a winding device rotating at 20 m / min to obtain degradable composite fiber #4, and its properties are listed in Table 1.

[0078] Comparative Example 1:

[0079] Preparation of PBAT fiber: 5 g of PBAT-2 was added into the barrel of the melt indexer, melted at 130 °C for 10 min, and under the pressure of a 2.16 kg weight, the melt was extruded from the micro-discharge port at the bottom of the melt indexer; One end of the melt was clamped with tweezers, bypassed the winding pulley, and the filament was wound around a winding device rotating at 20 m / min to obtain PBAT fiber, as Figure 3 shown; its properties are listed in Table 1.

[0080] As Figure 3 can be seen, it can be seen from the left figure that the PBAT fiber obtained by using pure PBAT-2 is sticky, which is caused by the slow crystallization of the pure PBAT-2 melt; moreover, it can be seen from the figure that the fiber prepared from the pure PBAT-2 melt cannot be continuously spun, which is because the melt strength of the pure PBAT-2 fiber is low.

[0081] Examples 5 - 9

[0082] The preparation and spinning process of the degradable composite fibers in Examples 5-9 are the same as those in Example 1, except that: in Example 5, the feed of the blend is 2 g of cellulose-g-PLA and 8 g of PBAT-2;

[0083] In Example 6, the feed of PBAT-3 in the blend is 2 g;

[0084] In Example 7, the feed of PBAT-4 in the blend is 2 g;

[0085] In Example 8, the feed of PBAT-5 in the blend is 2 g;

[0086] In Example 9, the feed of PBAT-6 in the blend is 2 g;

[0087] The degradable composite fibers #5-#9 are prepared respectively, and their properties are listed in Table 1.

[0088] Table 1 Performance parameters of degradable fibers

[0089]

[0090] By comparing the data in Table 1, it can be seen that the degradable composite fibers prepared by blending cellulose-g-PLA and PBAT prepared by the present invention have finer fiber fineness, higher tensile strength and elastic modulus than PBAT, and there is no situation of mutual adhesion between fibers during the spinning process, and they have better processing performance.

[0091] The above describes the exemplary embodiments of the present invention. However, the protection scope of this application is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A composite fiber, characterized in that, The raw materials for preparing the composite fiber include a polymer and an antioxidant; the polymer includes a cellulose-grafted polylactic acid copolymer and poly(butylene adipate terephthalate) (PBAT); wherein, In the polymer, the mass content of the cellulose-grafted polylactic acid copolymer is 1%-80%; In the polymer, the mass content of the poly(butylene adipate terephthalate) is 20%-90%; The antioxidant accounts for 0.1%-0.3% of the mass of the polymer.

2. The composite fiber according to claim 1, characterized in that, The poly(butylene adipate terephthalate) is selected from at least one of PBAT-1, PBAT-2, PBAT-3, PBAT-4, PBAT-5, PBAT-6, PBAT-7. Preferably, the molecular weight of the poly(butylene adipate terephthalate) is 50,000-150,000. Preferably, the glass transition temperature of the poly(butylene adipate terephthalate) is -40°C to -20°C. Preferably, the melting point of the poly(butylene adipate terephthalate) is 110-120°C. Preferably, the melt index of the poly(butylene adipate terephthalate) is 0.7-14 g / 10 min. Preferably, the cellulose-grafted polylactic acid copolymer is obtained by graft copolymerization of cellulose and lactide in an ionic liquid.

3. The composite fiber according to claim 1 or 2, characterized in that, The cellulose is selected from those with a degree of polymerization DP of DP100 to DP1000. Preferably, the cellulose is selected from at least one of microcrystalline cellulose, cotton pulp, and cotton pulp. Preferably, the ionic liquid is selected from one, two, or more of 1-allyl-3-methylimidazolium chloride ionic liquid, 1-butyl-3-methylimidazolium acetate ionic liquid, 1-ethyl-3-methylimidazolium acetate ionic liquid, 1-butyl-3-methylimidazolium chloride ionic liquid, 1-butyl-3-methylimidazolium benzoate ionic liquid, 1-ethyl-3-methylimidazolium propionate ionic liquid, and 1-ethyl-3-methylimidazolium methyl phosphate ionic liquid. Preferably, the catalyst is selected from at least one of 4-dimethylaminopyridine, tetrabutyl titanate, methanesulfonic acid, stannous octoate, 1,8-diazabicyclo-bicyclo(5,4,0)-7-undecene, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene.

4. The composite fiber according to any one of claims 1 to 3, characterized in that, The molar ratio of the catalyst to the hydroxyl group in cellulose is 0.1:1 to 2:1 (mol / mol). Preferably, the molar ratio of cellulose to lactide is 1:1-1:

9. Preferably, in the cellulose-grafted polylactic acid copolymer, the mass fraction of the polylactic acid component is 30%-90%. Preferably, the glass transition temperature of the cellulose-grafted polylactic acid copolymer is 50°C-120°C. Preferably, the thermal flow temperature of the cellulose-grafted polylactic acid copolymer is 130°C-200°C. Preferably, the Mn(D) of the cellulose-grafted polylactic acid copolymer is 50,000-100,000, and the Mw(D) of the cellulose-grafted polylactic acid copolymer is 130,000-190,000. Preferably, the melt index of the cellulose-grafted polylactic acid copolymer is 0.25 - 20 g / 10 min (2.16 kg).

5. The composite fiber according to any one of claims 1-4, characterized in that The antioxidant is selected from at least one of antioxidant B215 and antioxidant 1010. Preferably, the composite fiber has degradability. Preferably, the composite fiber has at least one of the following properties: (1) The tensile strength is 10 MPa - 600 MPa; (2) The elongation at break is 5% - 500%; (3) The elastic modulus is 400 MPa - 30000 MPa; (4) The fiber diameter is 1 - 200 μm.

6. The preparation method of the composite fiber according to any one of claims 1-5, characterized in that, The method for preparing the composite fiber includes: blending the preparation raw materials to obtain a composite material; and preparing the composite fiber by melting and spinning the composite material.

7. The preparation method according to claim 6, characterized in that, The blending method of the preparation raw materials is selected from Method 1 or Method 2, where Method 1 includes the following steps: (A1) Prepare a blended solution: dissolve the cellulose-grafted polylactic acid copolymer in a good solvent, add the poly(butylene terephthalate-co-adipate) copolymer and the antioxidant, and mix evenly to obtain a blended solution; (A2) Dry the blended solution prepared in step (A1) to obtain the composite material; Method 2 includes the following steps: (B1) Mix the cellulose-grafted polylactic acid copolymer, the poly(butylene terephthalate-co-adipate) copolymer and the antioxidant to prepare a blend; (B2) Conduct melt blending of the blend in step (B1) to obtain the composite material.

8. The preparation method according to claim 6 or 7, characterized in that, In step (A1), the good solvent is selected from at least one of dimethyl sulfoxide and N,N-dimethylformamide (DMF). Preferably, in step (A2), the drying means removing the good solvent at a certain temperature. Preferably, in step (A2), the drying is carried out at a temperature above 100°C. Preferably, in step (B2), the conditions for melt blending are: the blending temperature is 120 - 190°C; the screw speed is 10 - 30 r / min.

9. The preparation method according to any one of claims 6-8, characterized in that, The temperature of melting is the spinning temperature. Preferably, the spinning temperature is 120 - 250°C. Preferably, the conditions for spinning are: winding under a certain pressure condition to obtain the composite fiber. Preferably, the spinning pressure is 1.0 kg - 5.0 kg. Preferably, the spinning speed is 5 - 100 m / min.

10. Use of the composite fiber according to any one of claims 1 - 5 in the field of degradable materials.

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