Crystalline low-melting-point polyester fiber and preparation method thereof

Abstract

The invention discloses a crystallinity low-melting-point polyester fiber and a preparation method thereof, and relates to the technical field of polyester fibers, the crystallinity low-melting-point polyester fiber is composed of a skin layer and a core layer, and a skin-core integrated crystallization design is adopted; the skin layer is modified copolyester, and the core layer is modified PET; the modified copolyester is prepared from the following raw materials in parts by weight: 38 to 42 parts of terephthalic acid, 12 to 15 parts of 2, 5-furandicarboxylic acid, 28 to 32 parts of 1, 4-cyclohexanedimethanol, 8 to 10 parts of polycaprolactone, 1.0 to 1.5 parts of a crystallization coordinating agent, 0.5 to 1.0 part of an antioxidant and 0.3 to 0.5 part of a hindered amine light stabilizer. The crystallization coordinating agent is prepared by compounding hydroxylated graphene and maleic anhydride grafted polyolefin elastomer according to a mass ratio of (2 to 3): 1. The fiber is good in high temperature resistance and durability, low in melting point, good in size stability and long in service life.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polyester fibers, in particular to a crystalline low-melting polyester fiber and a preparation method thereof. BACKGROUND

[0002] Polyester fibers are widely used due to their excellent mechanical properties and chemical stability, but the high melting point (usually 250-260℃) of traditional polyester fibers limits their application in hot melt adhesion, composite materials and other fields. In this situation, low-melting polyester fibers have emerged, which have attracted widespread attention in the industry.

[0003] The existing low-melting polyester fibers have high oligomer content and large release amount of odor substances (such as acetaldehyde and propyl aldehyde), which affect the safety and use experience of the products. In addition, the low-melting polyester fiber products on the market also have more or less the problems of insufficient high-temperature resistance, poor melting uniformity, and durability that needs to be further improved. Due to the large difference in crystallization performance between the skin layer material and the core layer material, the skin-core structure causes large shrinkage of the finished product, product deformation, demolding and other technical defects.

[0004] In order to solve the above problems, a crystalline low-melting polyester fiber and a preparation method thereof are disclosed in a Chinese patent with the publication number CN106811829B. The crystalline low-melting polyester fiber has a skin-core structure, the skin layer is a low-melting polyester, and the core layer is PET. The low-melting polyester is composed of terephthalic acid segments, isophthalic acid segments, 1,3-propanediol segments, dipropylene glycol segments, and a molecular weight regulator. The molecular weight regulator segment corresponds to a molecular weight regulator, which is specifically 1,8-naphthalene dicarboxylic acid, phthalic acid, 1,2-cyclopentane dicarboxylic acid, 1,2-cyclohexane dicarboxylic acid, or their corresponding dimethyl or diethyl esters. The preparation method includes low-melting polyester polymerization and skin-core composite spinning steps. The post-spinning adopts a drawing-water washing process, the drawing uses oil bath drawing with the addition of sodium sulfite, and the crystalline low-melting polyester fiber is obtained through crimping, cutting and drying. The crystalline low-melting polyester fiber prepared by the invention has a low melting point and a low total content of acetaldehyde and propyl aldehyde. However, its durability still needs to be further improved.

[0005] It can be seen that it is necessary to seek a more effective method to prepare a crystalline low-melting polyester fiber with good high-temperature resistance and durability, low melting point, good dimensional stability, and long service life. SUMMARY

[0006] Therefore, the present application aims to provide a crystalline low-melting polyester fiber with good high-temperature resistance and durability, low melting point, good dimensional stability, and long service life, and a preparation method thereof.

[0007] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0008] A crystalline low-melting polyester fiber, which is composed of a skin layer and a core layer, adopts a skin-core integrated crystallization design; the skin layer is a modified copolyester, and the core layer is a modified PET; the modified copolyester is composed of the following raw materials in parts by weight: terephthalic acid 38-42 parts, 2,5-furan dicarboxylic acid 12-15 parts, 1,4-cyclohexane dimethanol 28-32 parts, polycaprolactone 8-10 parts, crystallization regulator 1.0-1.5 parts, antioxidant 0.5-1.0 parts, and hindered amine light stabilizer 0.3-0.5 parts; the crystallization regulator is compounded by hydroxylated graphene and maleic anhydride grafted polyolefin elastomer at a mass ratio of (2-3):1.

[0009] Preferably, the modified PET is composed of the following raw materials in percentage by weight: 2-3wt% of a comonomer, 0.2-0.4wt% of nano silicon carbide, and the balance of PET chips.

[0010] Preferably, the comonomer is a mixture of 2,5-furan dicarboxylic acid and 1,4-cyclohexane dimethanol mixed at a mass ratio of 1:1; the average particle size of the nano silicon carbide is 20-50nm.

[0011] Preferably, the number average molecular weight of the polycaprolactone is 8000-12000.

[0012] Preferably, the flake diameter of the hydroxylated graphene is 1-3μm, the thickness is 1-5nm, and the hydroxyl content is 2wt%.

[0013] Preferably, the maleic anhydride grafted polyolefin elastomer is FB521A POE-g-MAH.

[0014] Preferably, the antioxidant is antioxidant 1010; and the hindered amine light stabilizer is light stabilizer UV-3346.

[0015] Preferably, the PET chips are WK-631 PET chips.

[0016] Another object of the present application is to provide a preparation method of the crystalline low-melting polyester fiber, which comprises the following steps:

[0017] Step S1, synthesis of skin layer modified copolyester: terephthalic acid, 2,5-furan dicarboxylic acid and 1,4-cyclohexane dimethanol are added into a reaction kettle, a composite catalyst is added, and the temperature is raised to 220-230℃ under nitrogen atmosphere; esterification is carried out until the water output reaches 95% of the theoretical value; then polycaprolactone and crystallization regulator are added, the temperature is raised to 250-260℃, and the reaction is continued for 50-70 minutes under a vacuum of 30-70Pa; then antioxidant and hindered amine light stabilizer are added, and the mixture is stirred for 15-25 minutes to obtain the skin layer copolyester;

[0018] Step S2, preparation of the core layer modified PET: PET chips are vacuum dried at 115-125℃ for 3-5 hours; the dried PET chips, comonomer and nano silicon carbide are added into a twin-screw extruder, mixed thoroughly in a molten state, extruded, and granulated to obtain the core layer modified PET;

[0019] Step S3, skin-core composite spinning: using a skin-core composite spinning process, spinning is performed through a concentric skin-core spinneret;

[0020] Step S4, synergistic crystallization post-treatment: using three-stage heat rollers for drafting, the temperatures are 70℃, 90℃ and 110℃ respectively, and the total drafting multiple is 3.2 times; then, the fiber is treated in a saturated steam environment at 0.12MPa and 135℃ for 35-45 minutes to realize the synergistic crystallization of the skin and core layers, and a crystalline low-melting point polyester fiber is obtained.

[0021] Preferably, the composite catalyst in step S1 is a mixture of tetrabutyl titanate and ethylene glycol antimony in a mass ratio of (2-3):1.

[0022] Preferably, the amount of the composite catalyst added in step S1 is 0.02-0.03% of the total mass of terephthalic acid, 2,5-furan dicarboxylic acid and 1,4-cyclohexane dimethanol.

[0023] Preferably, the temperature of each section of the twin-screw extruder in step S2 is: zone 1 258-262℃, zone 2 268-272℃, zone 3 273-278℃, and zone 4 268-272℃, and the screw rotation speed is 190-230r / min.

[0024] Preferably, the concentric skin-core spinneret in step S3 is designed through a flow channel to form a concentric cylindrical structure of the skin layer melt and the core layer melt during extrusion molding, wherein the cross-sectional area of the skin layer accounts for 40% of the total cross-sectional area of the fiber, and the core layer accounts for 60%.

[0025] Preferably, the spinning temperature of the skin layer in step S3 is 230-240℃, the spinning temperature of the core layer is 265-275℃, and the spinning speed is 1300-1500m / min; the cooling is designed by using an isothermal air field, the air temperature is 43-48℃, and the air speed is 2-2.4m / s.

[0026] The beneficial effects of the above technical solution are:

[0027] (1) The crystalline low-melting polyester fiber provided by the present application introduces 2,5-furan dicarboxylic acid and 1,4-cyclohexane dimethanol into the skin layer, and adds the same comonomer to the core layer, so that the skin and core molecular chains have similar chemical structural units, and the crystallization behavior is synchronized through intermolecular forces. The hydroxylated graphene in the crystallization coordinator forms a "molecular bridge" at the skin-core interface, promotes the transmission of crystallization information, reduces the crystallization temperature difference between the skin and core layers, and forms a single crystallization peak. This synergistic crystallization mechanism gives the fiber a more uniform and perfect crystal structure, significantly improves its mechanical properties such as strength and modulus, and improves its dimensional stability.

[0028] (2) The crystalline low-melting polyester fiber provided by the present application is composed of a skin layer and a core layer, and adopts a skin-core integrated crystallization design; the skin layer is a modified copolyester, and the core layer is a modified PET; the modified copolyester is composed of the following raw materials in parts by weight: terephthalic acid 38-42 parts, 2,5-furan dicarboxylic acid 12-15 parts, 1,4-cyclohexane dimethanol 28-32 parts, polycaprolactone 8-10 parts, crystallization coordinator 1.0-1.5 parts, antioxidant 0.5-1.0 parts, and hindered amine light stabilizer 0.3-0.5 parts; the crystallization coordinator is compounded from hydroxylated graphene and maleic anhydride grafted polyolefin elastomer at a mass ratio of (2-3):1; the modified PET is composed of the following raw materials in percentage by weight: comonomer 2-3wt%, nano silicon carbide 0.2-0.4wt%, and the balance being PET chips. Through the rational design of the above structure and composition formula, they can cooperate with each other and work together to give the product good high-temperature resistance and durability, low melting point, good dimensional stability, long service life and other advantages.

[0029] (3) The crystalline low-melting polyester fiber provided by the present application precisely regulates the raw material ratio of the skin layer modified copolyester, such as using 38-42 parts of terephthalic acid to provide a rigid skeleton, 12-15 parts of 2,5-furan dicarboxylic acid to moderately destroy the molecular chain regularity to reduce the melting point, and combining the flexibility adjustment of polycaprolactone to precisely control the melting point of the skin layer to meet the application requirements of low melting point. At the same time, 0.2-0.4wt% of nano silicon carbide particles are added to the core layer, which effectively constructs a heat conduction network due to its high thermal conductivity, reduces local overheating, and cooperates with the relatively high melting point of the core layer PET to make the overall fiber stable in performance at a high temperature of 200℃.

[0030] (4) The crystalline low-melting polyester fiber provided by the present application adds 0.5-1.0 parts of antioxidant and 0.3-0.5 parts of hindered amine light stabilizer to the skin layer formula, the antioxidant can capture free radicals and prevent thermal oxidative chain reactions; the hindered amine light stabilizer delays photo-oxidative aging by capturing free radicals and decomposing hydroperoxides. At the same time, the nano silicon carbide particles in the core layer can inhibit ester bond hydrolysis and reduce molecular chain rupture, so that the durability of the prepared crystalline low-melting polyester fiber product is greatly improved.

[0031] (5) The crystalline low-melting polyester fiber provided by the present application, the crystallization coordinator of the present application is compounded by hydroxylated graphene and maleic anhydride grafted polyolefin elastomer at a mass ratio of (2-3):1. Among them, the hydroxylated graphene can form a "molecular bridge" at the skin-core interface, promote the transmission of crystallization information, reduce the crystallization temperature difference between the skin and core layers, and greatly enhance the interaction and crystallization synchronization between the skin and core layers. The maleic anhydride grafted polyolefin elastomer further improves the interfacial compatibility, making the crystallization process of the whole fiber system more smooth, thereby obtaining more excellent comprehensive performance, such as higher crystallinity and better mechanical properties. DETAILED DESCRIPTION

[0032] In order for those skilled in the art to better understand the technical solutions of the present application, and to make the above-mentioned features, objects and advantages of the present application more clear and easy to understand, the present application will be further described below in conjunction with examples. The examples are only used to illustrate the present application and not to limit the scope of the present application.

[0033] Example 1

[0034] A crystalline low-melting polyester fiber, composed of a skin layer and a core layer, adopts a skin-core integrated crystallization design; the skin layer is a modified copolyester, and the core layer is a modified PET; the modified copolyester is composed of the following raw materials in parts by weight: terephthalic acid 38 parts, 2,5-furan dicarboxylic acid 12 parts, 1,4-cyclohexane dimethanol 28 parts, polycaprolactone 8 parts, crystallization coordinator 1.0 parts, antioxidant 0.5 parts, hindered amine light stabilizer 0.3 parts; the crystallization coordinator is compounded by hydroxylated graphene and maleic anhydride grafted polyolefin elastomer at a mass ratio of 2:1.

[0035] The modified PET is composed of the following raw materials in percentage by weight: 2wt% of a comonomer, 0.2wt% of nano silicon carbide, and the balance of PET chips; the comonomer is a mixture of 2,5-furan dicarboxylic acid and 1,4-cyclohexane dimethanol at a mass ratio of 1:1; the average particle size of the nano silicon carbide is 20nm.

[0036] The number average molecular weight of the polycaprolactone is 8000; the flake diameter of the hydroxylated graphene is 1-3μm, the thickness is 1-5nm, and the hydroxyl content is 2wt%; the maleic anhydride grafted polyolefin elastomer is FB521A POE-g-MAH; the antioxidant is antioxidant 1010; the hindered amine light stabilizer is light stabilizer UV-3346; and the PET chips are WK-631 PET chips.

[0037] A preparation method of the crystalline low-melting polyester fiber, comprising the following steps: ​

[0038] Step S1, synthesis of skin layer modified copolyester: terephthalic acid, 2,5-furan dicarboxylic acid, 1,4-cyclohexane dimethanol are added into a reaction kettle, a composite catalyst is added, and the temperature is raised to 220°C under nitrogen atmosphere, and esterification is carried out until the water output reaches 95% of the theoretical value; then polycaprolactone and a crystallization regulator are added, and the temperature is raised to 250°C, and the reaction is continued under a vacuum of 30 Pa for 50 minutes; then an antioxidant and a hindered amine light stabilizer are added, and the mixture is stirred for 15 minutes, to obtain a skin layer copolyester;

[0039] Step S2, preparation of core layer modified PET: PET chips are vacuum dried at 115°C for 3 hours; the dried PET chips, a comonomer and nano silicon carbide are added into a twin-screw extruder, and are fully mixed in a molten state, and are extruded and pelletized to obtain a core layer modified PET;

[0040] Step S3, skin-core composite spinning: a skin-core composite spinning process is adopted, and spinning is carried out through a concentric skin-core spinneret;

[0041] Step S4, post-treatment by synergistic crystallization: three-stage hot roller drafting is adopted, and the temperatures are 70°C, 90°C and 110°C respectively, and the total drafting multiple is 3.2 times; then treatment is carried out in a saturated steam environment at 0.12 MPa and 135°C for 35 minutes, to realize synergistic crystallization of the skin and core layers, and to obtain a crystalline low-melting-point polyester fiber.

[0042] The composite catalyst in step S1 is a mixture of tetrabutyl titanate and antimony glycol in a mass ratio of 2:1; the addition amount of the composite catalyst in step S1 is 0.02% of the total mass of terephthalic acid, 2,5-furan dicarboxylic acid and 1,4-cyclohexane dimethanol; the temperature of each section of the twin-screw extruder in step S2 is: zone 1, 258°C; zone 2, 268°C; zone 3, 273°C; zone 4, 268°C, and the screw rotation speed is 190 r / min.

[0043] The concentric skin-core spinneret in step S3 is designed through a flow channel, so that the skin layer melt and the core layer melt form a concentric cylindrical structure when extruded and formed, wherein the cross-sectional area of the skin layer accounts for 40% of the total cross-sectional area of the fiber, and the core layer accounts for 60%; the spinning temperature of the skin layer in step S3 is 230°C, the spinning temperature of the core layer is 265°C, and the spinning speed is 1300 m / min; the cooling is designed by using an isothermal air field, and the air temperature is 43°C and the air speed is 2 m / s.

[0044] Example 2

[0045] A crystalline low-melting polyester fiber is composed of a sheath layer and a core layer, and adopts a sheath-core integrated crystallization design; the sheath layer is a modified copolyester, and the core layer is a modified PET; the modified copolyester is composed of the following raw materials in parts by weight: terephthalic acid 39 parts, 2,5-furan dicarboxylic acid 13 parts, 1,4-cyclohexane dimethanol 29 parts, polycaprolactone 8.5 parts, crystallization regulator 1.2 parts, antioxidant 0.6 parts, and hindered amine light stabilizer 0.35 parts; the crystallization regulator is compounded from hydroxylated graphene and maleic anhydride grafted polyolefin elastomer at a mass ratio of 2.2:1.

[0046] The modified PET is composed of the following raw materials in percentage by weight: 2.3wt% of a comonomer, 0.25wt% of nano silicon carbide, and the balance of PET chips; the comonomer is a mixture of 2,5-furan dicarboxylic acid and 1,4-cyclohexane dimethanol at a mass ratio of 1:1; the average particle size of the nano silicon carbide is 30nm; the number average molecular weight of the polycaprolactone is 9000; the flake diameter of the hydroxylated graphene is 1-3μm, the thickness is 1-5nm, and the hydroxyl content is 2wt%; the maleic anhydride grafted polyolefin elastomer is FB521A POE-g-MAH; the antioxidant is antioxidant 1010; the hindered amine light stabilizer is light stabilizer UV-3346; and the PET chips are WK-631 PET chips.

[0047] A preparation method of the crystalline low-melting polyester fiber, comprising the following steps:

[0048] Step S1, synthesis of the sheath layer modified copolyester: terephthalic acid, 2,5-furan dicarboxylic acid, and 1,4-cyclohexane dimethanol are added into a reaction kettle, a composite catalyst is added, and the temperature is raised to 223℃ under a nitrogen atmosphere; esterification is carried out until the water output reaches 95% of the theoretical value; then polycaprolactone and a crystallization regulator are added, the temperature is raised to 253℃, and the reaction is continued for 55 minutes under a vacuum of 40Pa; then an antioxidant and a hindered amine light stabilizer are added, and the mixture is stirred for 17 minutes to obtain the sheath layer copolyester;

[0049] Step S2, preparation of the core layer modified PET: PET chips are vacuum dried at 117℃ for 3.5 hours; the dried PET chips, a comonomer, and nano silicon carbide are added into a twin-screw extruder, and are fully mixed in a molten state; then the mixture is extruded and cut into particles to obtain the core layer modified PET;

[0050] Step S3, sheath-core composite spinning: a sheath-core composite spinning process is adopted, and spinning is carried out through a concentric sheath-core spinneret;

[0051] Step S4, post-treatment of synergic crystallization: three-stage hot roller drawing with temperatures of 70℃, 90℃ and 110℃ respectively, and total draw ratio of 3.2; then treatment in saturated steam environment at 0.12 MPa and 135℃ for 37 minutes to realize synergic crystallization of the skin and core layers, and obtain the crystalline low-melting polyester fiber.

[0052] The composite catalyst in step S1 is prepared by mixing tetrabutyl titanate and ethylene glycol antimony at a mass ratio of 2.3:1; the amount of the composite catalyst added in step S1 is 0.023% of the total mass of terephthalic acid, 2,5-furan dicarboxylic acid and 1,4-cyclohexane dimethanol; the temperature of each section of the twin-screw extruder in step S2 is: 259℃ for the first section, 269℃ for the second section, 274℃ for the third section and 269℃ for the fourth section, and the screw rotation speed is 200 r / min.

[0053] The concentric skin-core spinneret in step S3 is designed by flow channel to make the skin layer melt and the core layer melt form a concentric cylindrical structure during extrusion molding, wherein the cross-sectional area of the skin layer accounts for 40% of the total cross-sectional area of the fiber, and the core layer accounts for 60%; the spinning temperature of the skin layer in step S3 is 233℃, the spinning temperature of the core layer is 268℃, and the spinning speed is 1350 m / min; the cooling is designed by isothermal air field with air temperature of 44℃ and air speed of 2.2 m / s.

[0054] Example 3

[0055] A crystalline low-melting polyester fiber composed of a skin layer and a core layer, designed by skin-core integrated crystallization; the skin layer is a modified copolyester, and the core layer is a modified PET; the modified copolyester is composed of the following raw materials in parts by weight: terephthalic acid 40 parts, 2,5-furan dicarboxylic acid 13.5 parts, 1,4-cyclohexane dimethanol 30 parts, polycaprolactone 9 parts, crystallization regulator 1.3 parts, antioxidant 0.8 parts, and hindered amine light stabilizer 0.4 parts; the crystallization regulator is compounded by hydroxylated graphene and maleic anhydride grafted polyolefin elastomer at a mass ratio of 2.5:1.

[0056] The modified PET is composed of the following raw materials in percentage by weight: 2.5wt% of comonomer, 0.3wt% of nano silicon carbide, and the balance of PET chips; the comonomer is a mixture of 2,5-furan dicarboxylic acid and 1,4-cyclohexane dimethanol at a mass ratio of 1:1; the average particle size of the nano silicon carbide is 35 nm; the number average molecular weight of the polycaprolactone is 10000; the flake diameter of the hydroxylated graphene is 1-3 μm, the thickness is 1-5 nm, and the hydroxyl content is 2wt%; the maleic anhydride grafted polyolefin elastomer is FB521A POE-g-MAH; the antioxidant is antioxidant 1010; the hindered amine light stabilizer is light stabilizer UV-3346; and the PET chip is WK-631 PET chip.

[0057] A preparation method of the crystalline low-melting-point polyester fiber, comprising the following steps:

[0058] Step S1, synthesis of the skin layer modified copolyester: terephthalic acid, 2,5-furan dicarboxylic acid, and 1,4-cyclohexane dimethanol are added into a reaction kettle, a composite catalyst is added, and the temperature is raised to 225°C under a nitrogen atmosphere, and esterification is performed until the water output reaches 95% of the theoretical value; then polycaprolactone and a crystallization regulator are added, the temperature is raised to 255°C, and the reaction is continued for 60 minutes under a vacuum of 50 Pa; then an antioxidant and a hindered amine light stabilizer are added, and the mixture is stirred for 20 minutes to obtain the skin layer copolyester;

[0059] Step S2, preparation of the core layer modified PET: the PET chip is vacuum dried at 120°C for 4 hours; the dried PET chip, a comonomer, and nano silicon carbide are added into a twin-screw extruder, and are fully mixed in a molten state, and then are extruded and pelletized to obtain the core layer modified PET;

[0060] Step S3, skin-core composite spinning: the skin-core composite spinning process is adopted, and spinning is performed through a concentric skin-core spinneret;

[0061] Step S4, post-treatment of synergistic crystallization: three-stage heat rollers are adopted for drafting, and the temperatures are 70°C, 90°C, and 110°C respectively, and the total drafting multiple is 3.2 times; then the fiber is treated in a saturated steam environment at 0.12 MPa and 135°C for 40 minutes to realize synergistic crystallization of the skin and core layers, and a crystalline low-melting-point polyester fiber is obtained.

[0062] The composite catalyst in step S1 is prepared by mixing tetrabutyl titanate and antimony glycol in a mass ratio of 2.5:1; the amount of the composite catalyst added in step S1 is 0.025% of the total mass of terephthalic acid, 2,5-furan dicarboxylic acid, and 1,4-cyclohexane dimethanol; and the temperature of each section of the twin-screw extruder in step S2 is as follows: 260°C for the first section, 270°C for the second section, 275°C for the third section, and 270°C for the fourth section, and the screw rotation speed is 210 r / min.

[0063] The concentric skin-core spinneret in step S3 is designed through a flow channel, so that the skin layer melt and the core layer melt form a concentric cylindrical structure during extrusion molding, wherein the cross-sectional area of the skin layer accounts for 40% of the total cross-sectional area of the fiber, and the core layer accounts for 60%; the spinning temperature of the skin layer in step S3 is 235°C, the spinning temperature of the core layer is 270°C, and the spinning speed is 1400 m / min; and the cooling is designed by using an isothermal air field, and the air temperature is 45°C and the air speed is 2.2 m / s.

[0064] Embodiment 4

[0065] A crystalline low-melting polyester fiber is composed of a sheath layer and a core layer, adopting a sheath-core integrated crystallization design; the sheath layer is a modified copolyester, and the core layer is a modified PET; the modified copolyester is composed of the following raw materials in parts by weight: terephthalic acid 41 parts, 2,5-furan dicarboxylic acid 14 parts, 1,4-cyclohexane dimethanol 31 parts, polycaprolactone 9.5 parts, crystallization regulator 1.4 parts, antioxidant 0.9 parts, and hindered amine light stabilizer 0.45 parts; the crystallization regulator is compounded from hydroxylated graphene and maleic anhydride grafted polyolefin elastomer at a mass ratio of 2.9:1.

[0066] The modified PET is composed of the following raw materials in percentage by weight: 2.8wt% of a comonomer, 0.35wt% of nano silicon carbide, and the balance of PET chips; the comonomer is a mixture of 2,5-furan dicarboxylic acid and 1,4-cyclohexane dimethanol at a mass ratio of 1:1; the average particle size of the nano silicon carbide is 45nm; the number average molecular weight of the polycaprolactone is 11000; the flake diameter of the hydroxylated graphene is 1-3μm, the thickness is 1-5nm, and the hydroxyl content is 2wt%; the maleic anhydride grafted polyolefin elastomer is FB521A POE-g-MAH; the antioxidant is antioxidant 1010; the hindered amine light stabilizer is light stabilizer UV-3346; and the PET chips are WK-631 PET chips.

[0067] A preparation method of the crystalline low-melting polyester fiber, comprising the following steps:

[0068] Step S1, synthesis of the sheath layer modified copolyester: terephthalic acid, 2,5-furan dicarboxylic acid, and 1,4-cyclohexane dimethanol are added to a reaction kettle, a composite catalyst is added, and the temperature is raised to 228℃ under a nitrogen atmosphere; esterification is carried out until the water output reaches 95% of the theoretical value; then polycaprolactone and a crystallization regulator are added, the temperature is raised to 258℃, and the reaction is continued under a vacuum of 60Pa for 65 minutes; then an antioxidant and a hindered amine light stabilizer are added, and the mixture is stirred for 23 minutes to obtain the sheath layer copolyester;

[0069] Step S2, preparation of the core layer modified PET: PET chips are vacuum dried at 123℃ for 4.5 hours; the dried PET chips, a comonomer, and nano silicon carbide are added to a twin-screw extruder, and are fully mixed in a molten state; then the mixture is extruded and cut into particles to obtain the core layer modified PET;

[0070] Step S3, sheath-core composite spinning: a sheath-core composite spinning process is adopted, and spinning is carried out through a concentric sheath-core spinneret;

[0071] ​Step S4, post-treatment of synergic crystallization: three-stage hot roller drawing with temperatures of 70℃, 90℃ and 110℃ respectively, and total draw ratio of 3.2; then treatment in saturated steam environment at 0.12 MPa and 135℃ for 43 minutes to realize synergic crystallization of the skin and core layers, and obtain the crystalline low-melting polyester fiber.

[0072] The composite catalyst in step S1 is prepared by mixing tetrabutyl titanate and antimony ethylene glycol in a mass ratio of 2.8:1; the amount of the composite catalyst added in step S1 is 0.028% of the total mass of terephthalic acid, 2,5-furan dicarboxylic acid and 1,4-cyclohexane dimethanol; the temperature of each section of the twin-screw extruder in step S2 is: 261℃ for the first section, 271℃ for the second section, 277℃ for the third section and 271℃ for the fourth section, and the screw rotation speed is 220 r / min.

[0073] The concentric skin-core spinneret in step S3 is designed by flow channel to make the skin layer melt and the core layer melt form a concentric cylindrical structure during extrusion molding, wherein the cross-sectional area of the skin layer accounts for 40% of the total cross-sectional area of the fiber, and the core layer accounts for 60%; the spinning temperature of the skin layer in step S3 is 238℃, the spinning temperature of the core layer is 273℃, and the spinning speed is 1450 m / min; the cooling is designed by isothermal air field, with air temperature of 47℃ and air speed of 2.3 m / s.

[0074] Example 5

[0075] A crystalline low-melting polyester fiber composed of a skin layer and a core layer, designed by skin-core integrated crystallization; the skin layer is a modified copolyester, and the core layer is a modified PET; the modified copolyester is composed of the following raw materials in parts by weight: terephthalic acid 42 parts, 2,5-furan dicarboxylic acid 15 parts, 1,4-cyclohexane dimethanol 32 parts, polycaprolactone 10 parts, crystallization regulator 1.5 parts, antioxidant 1.0 part, and hindered amine light stabilizer 0.5 part; the crystallization regulator is compounded by hydroxylated graphene and maleic anhydride grafted polyolefin elastomer in a mass ratio of 3:1.

[0076] The modified PET is composed of the following raw materials in weight percentage: 3wt% of comonomer, 0.4wt% of nano silicon carbide, and the balance of PET chips; the comonomer is a mixture of 2,5-furan dicarboxylic acid and 1,4-cyclohexane dimethanol in a mass ratio of 1:1; the average particle size of the nano silicon carbide is 50 nm; the number average molecular weight of the polycaprolactone is 12000; the flake diameter of the hydroxylated graphene is 1-3 μm, the thickness is 1-5 nm, and the hydroxyl content is 2wt%; the maleic anhydride grafted polyolefin elastomer is FB521A POE-g-MAH; the antioxidant is antioxidant 1010; the hindered amine light stabilizer is light stabilizer UV-3346; and the PET chips are WK-631 PET chips.

[0077] A preparation method of the crystalline low-melting polyester fiber, comprising the following steps:

[0078] Step S1, synthesis of the skin layer modified copolyester: terephthalic acid, 2,5-furan dicarboxylic acid, 1,4-cyclohexane dimethanol are added into a reaction kettle, a composite catalyst is added, and the temperature is raised to 230°C under a nitrogen atmosphere, and esterification is carried out until the water output reaches 95% of the theoretical value; then polycaprolactone and a crystallization regulator are added, and the temperature is raised to 260°C, and the reaction is continued for 70 minutes under a vacuum of 70 Pa; then an antioxidant and a hindered amine light stabilizer are added, and the mixture is stirred for 25 minutes, to obtain the skin layer copolyester;

[0079] Step S2, preparation of the core layer modified PET: PET chips are vacuum dried at 125°C for 5 hours; the dried PET chips, a comonomer and nano silicon carbide are added into a twin-screw extruder, and are fully mixed in a molten state, and are extruded and pelletized, to obtain the core layer modified PET;

[0080] Step S3, skin-core composite spinning: the skin-core composite spinning process is adopted, and spinning is performed through a concentric skin-core spinneret;

[0081] Step S4, post-treatment of synergistic crystallization: three-stage heat rollers are adopted for drafting, and the temperatures are 70°C, 90°C and 110°C respectively, and the total drafting multiple is 3.2 times; then treatment is performed in a saturated steam environment at 0.12 MPa and 135°C for 45 minutes, to realize synergistic crystallization of the skin and core layers, and to obtain the crystalline low-melting polyester fiber.

[0082] The composite catalyst in step S1 is prepared by mixing tetrabutyl titanate and antimony glycol in a mass ratio of 3:1; the amount of the composite catalyst added in step S1 is 0.03% of the total mass of terephthalic acid, 2,5-furan dicarboxylic acid and 1,4-cyclohexane dimethanol; and the temperature of each section of the twin-screw extruder in step S2 is as follows: 262°C for the first section, 272°C for the second section, 278°C for the third section and 272°C for the fourth section, and the screw rotation speed is 230 r / min.

[0083] The concentric skin-core spinneret in step S3 is designed through a flow channel, so that the skin layer melt and the core layer melt form a concentric cylindrical structure when being extruded and formed, wherein the cross-sectional area of the skin layer accounts for 40% of the total cross-sectional area of the fiber, and the core layer accounts for 60%; the spinning temperature of the skin layer in step S3 is 240°C, the spinning temperature of the core layer is 275°C, and the spinning speed is 1500 m / min; and isothermal air field design is adopted for cooling, and the air temperature is 48°C and the air speed is 2.4 m / s.

[0084] Comparative Example 1

[0085] A crystalline low-melting-point polyester fiber and a preparation method thereof are substantially the same as those in Example 1, except that an equal amount of terephthalic acid is used instead of 2,5-furandicarboxylic acid.

[0086] Comparative Example 2

[0087] A crystalline low-melting-point polyester fiber and a preparation method thereof are substantially the same as those in Example 1, except that no crystallization coordinator is added.

[0088] In order to further illustrate the unexpected positive technical effects achieved by the crystalline low-melting-point polyester fiber products of each embodiment of the present invention, relevant performance tests were conducted on the crystalline low-melting-point polyester fibers prepared in each embodiment. The test methods are as follows:

[0089] (1) Molecular structure characterization: Taking Example 1 as an example,

[0090] Core modified PET NMR spectrum (1H - NMR: The core-modified PET was analyzed using a 600 MHz NMR spectrometer in deuterated chloroform (CDCl3). The chemical shifts (δ) at 7.8-8.2 ppm indicated a peak attributable to the benzene ring protons of the terephthalic acid units; a peak at 4.0-4.2 ppm indicated a peak attributable to the methylene protons of 1,4-cyclohexanedimethanol; and a peak at 2.5-2.7 ppm indicated a peak attributable to the furan ring protons of the comonomer 2,5-furandicarboxylic acid. Calculated by peak area integration, the actual molar proportion of the comonomer in the core layer was 2.2%.

[0091] Fourier transform infrared spectroscopy (FT-IR) of core modified PET: attenuated total reflectance (ATR) mode was used with a scanning range of 400-4000 cm -1 The core modified PET was tested. -1 A strong absorption peak appears at 1610 cm, corresponding to the stretching vibration of the ester carbonyl (C=O) in the PET molecular chain; -1 , 1500cm -1 After adding the comonomer, the peak at 1250cm -1 A new peak appears at 1080 cm, which is attributed to the stretching vibration of COC in 1,4-cyclohexanedimethanol; -1 The characteristic absorption peak of the furan ring of 2,5-furandicarboxylic acid appears at .

[0092] Skin-modified copolyester gel permeation chromatography (GPC): The skin copolyester was tested at a flow rate of 1.0 mL / min at 35°C with tetrahydrofuran (THF) as the mobile phase. The results showed that the number average molecular weight (Mn) was 36500 g / mol, the weight average molecular weight (Mw) was 42000 g / mol, and the molecular weight distribution index (PDI = Mw / Mn) was 1.15.

[0093] Skin-modified copolyester Fourier transform infrared spectroscopy (FT-IR): The attenuated total reflection (ATR) mode was used, and the scanning range was 400-4000 cm -1 . The results showed that: the stretching vibration peak of ester carbonyl (C=O) appeared at 1720 cm -1 , the stretching vibration peak of C-O-C appeared at 1260 cm -1 , the characteristic bending vibration peak of 2,5-furan dicarboxylic acid furan ring appeared at 750 cm -1 , and the saturated C-H bending vibration peak of 1,4-cyclohexane dimethanol appeared at 1050 cm -1 . The presence of these characteristic peaks directly confirmed the chemical structure integrity of each monomer unit in the skin copolyester.

[0094] (2) The crystallization performance and melting point of the product of Example 1 were tested. The crystallization performance test was carried out according to ASTM D3418-21, the heating rate was 10°C / min, the product of Example 1 appeared a single crystallization peak at 125-135°C, and the crystallization enthalpy was 37.23 J / g. The crystallinity test was carried out according to ISO 11357-7:2022, and the crystallinity of the product of Example 1 was 26.59%. The melting point test was carried out according to GB / T19466.3-2004, and the melting point of the skin layer of the product of Example 1 was 150-160°C, and the melting point of the core layer was 258°C.

[0095] (3) The breaking strength of each product was tested according to GB / T 14337-2008. Each product was placed at 120°C for 24h, cooled to room temperature and then tested for breaking strength again, and the retention rate of breaking strength was calculated. The larger the value, the better the high temperature resistance performance. Each product was placed at 85°C and 85% relative humidity for 1000h, cooled to room temperature and then tested for breaking strength again, and the retention rate of breaking strength was calculated. The larger the value, the better the durability performance. The test results are shown in Table 1.

[0096] Table 1 Performance test results of crystalline low melting point polyester fiber

[0097] Item Average breaking strength (cN / dtex) Resistance to high temperature (%) Durability (%) Example 1 3.8 92.1 86.8 Example 2 4.0 95.0 90.0 Example 3 4.5 95.6 93.3 Example 4 4.6 97.8 95.7 Example 5 4.8 97.9 95.8 Comparative Example 1 3.1 80.6 74.2 Comparative Example 2 2.8 71.4 60.7

[0098] As shown in Table 1, the crystalline low-melting polyester fiber disclosed in each embodiment of the present application has better mechanical properties, high-temperature resistance and durability than the comparative product, and the combination use of 2,5-furandicarboxylic acid and the crystallization regulator is beneficial to improving the above properties.

[0099] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above embodiments, and the above embodiments and descriptions in the specification are only the principles of the present application. Various changes and improvements can be made without departing from the spirit and scope of the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A crystalline low-melting-point polyester fiber, characterized in that: It consists of a skin layer and a core layer, and adopts a skin-core integrated crystallization design; the skin layer is modified copolyester, and the core layer is modified PET; The modified copolyester is composed of the following raw materials in parts by weight: 38-42 parts of terephthalic acid, 12-15 parts of 2,5-furandicarboxylic acid, 28-32 parts of 1,4-cyclohexanedimethanol, 8-10 parts of polycaprolactone, 1.0-1.5 parts of a crystallization coordinator, 0.5-1.0 parts of an antioxidant, and 0.3-0.5 parts of a hindered amine light stabilizer; the crystallization coordinator is prepared by compounding hydroxylated graphene and maleic anhydride grafted polyolefin elastomer in a mass ratio of (2-3):

1.

2. The crystalline low-melting polyester fiber according to claim 1, characterized in that The modified PET is composed of the following raw materials in percentage by weight: 2-3 wt% of comonomer, 0.2-0.4 wt% of nano-silicon carbide, and the remainder being PET chips.

3. The crystalline low-melting polyester fiber according to claim 2, characterized in that The comonomer is a mixture of 2,5-furandicarboxylic acid and 1,4-cyclohexanedimethanol in a mass ratio of 1:1; the average particle size of the nano-silicon carbide is 20-50 nm; and the PET slice is WK-631PET slice.

4. The crystalline low-melting polyester fiber according to claim 1, characterized in that The number average molecular weight of the polycaprolactone is 8000-12000.

5. The crystalline low-melting polyester fiber according to claim 1, characterized in that The hydroxylated graphene has a sheet diameter of 1-3 μm, a thickness of 1-5 nm, and a hydroxyl content of 2 wt%.

6. The crystalline low-melting polyester fiber according to claim 1, characterized in that The maleic anhydride grafted polyolefin elastomer is FB521A POE-g-MAH; the antioxidant is antioxidant 1010; and the hindered amine light stabilizer is light stabilizer UV-3346.

7. A method for preparing the crystalline low-melting-point polyester fiber according to any one of claims 1 to 6, characterized in that: The steps include: Step S1, synthesis of a skin-modified copolyester: terephthalic acid, 2,5-furandicarboxylic acid, and 1,4-cyclohexanedimethanol are added to a reactor, a composite catalyst is added, and the temperature is raised to 220-230° C. under a nitrogen atmosphere, and an esterification reaction is carried out until the water output reaches 95% of the theoretical value; polycaprolactone and a crystallization coordinator are then added, the temperature is raised to 250-260° C., and the reaction is continued under a vacuum of 30-70 Pa for 50-70 minutes; an antioxidant and a hindered amine light stabilizer are then added, and the mixture is stirred at this temperature for 15-25 minutes to obtain a skin-modified copolyester; Step S2, preparation of core layer modified PET: vacuum drying PET slices at 115-125° C. for 3-5 hours; adding the dried PET slices, comonomer and nano-silicon carbide into a twin-screw extruder, fully mixing in a molten state, extruding and pelletizing to obtain core layer modified PET; Step S3, sheath-core composite spinning: using a sheath-core composite spinning process, spinning through a concentric sheath-core spinneret; Step S4, post-processing of coordinated crystallization: adopting three-stage hot roller drawing at temperatures of 70°C, 90°C, and 110°C, with a total drawing ratio of 3.2 times; then treating in a saturated steam environment of 0.12 MPa and 135°C for 35-45 minutes to achieve coordinated crystallization of the core and skin layers, thereby obtaining a crystalline low-melting-point polyester fiber.

8. The method for preparing crystalline low-melting-point polyester fiber according to claim 7, characterized in that: The composite catalyst in step S1 is prepared by mixing tetrabutyl titanate and antimony ethylene glycol in a mass ratio of (2-3):1; the amount of the composite catalyst added in step S1 is 0.02-0.03% of the total mass of terephthalic acid, 2,5-furandicarboxylic acid and 1,4-cyclohexanedimethanol.

9. The method for preparing crystalline low-melting-point polyester fiber according to claim 7, characterized in that: The temperature of each section of the twin-screw extruder in step S2 is: zone 1 258-262°C, zone 2 268-272°C, zone 3 273-278°C, zone 4 268-272°C, and the screw speed is 190-230r / min.

10. The method for preparing crystalline low-melting-point polyester fiber according to claim 7, characterized in that: The concentric sheath-core spinneret described in step S3 is designed with a flow channel so that the sheath melt and the core layer melt form a concentric cylindrical structure during extrusion molding, wherein the cross-sectional area of ​​the sheath layer accounts for 40% of the total cross-sectional area of ​​the fiber, and the core layer accounts for 60%; the sheath layer spinning temperature of the spinning described in step S3 is 230-240°C, the core layer spinning temperature is 265-275°C, and the spinning speed is 1300-1500m / min; the cooling adopts an isothermal wind field design with a wind temperature of 43-48°C and a wind speed of 2-2.4m / s.