A crystalline low-melting polyester fiber and a method for producing the same

Abstract

This invention discloses a crystalline low-melting-point polyester fiber and its preparation method, relating to the field of polyester fiber technology. The fiber consists of a sheath and a core layer, employing an integrated sheath-core crystalline design. The sheath is a 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 terephthalic acid, 12-15 parts 2,5-furandicarboxylic acid, 28-32 parts 1,4-cyclohexanediethanol, 8-10 parts polycaprolactone, 1.0-1.5 parts crystallization coordinator, 0.5-1.0 parts antioxidant, and 0.3-0.5 parts hindered amine light stabilizer. The crystallization coordinator is a compound of hydroxylated graphene and maleic anhydride-grafted polyolefin elastomer in a mass ratio of (2-3):1. This fiber exhibits good high-temperature resistance and durability, a low melting point, excellent dimensional stability, and a long service life.

Description

Technical Field

[0001] This invention relates to the field of polyester fiber technology, and in particular to a crystalline low-melting-point polyester fiber and its preparation method. Background Technology

[0002] Polyester fibers are widely used due to their excellent mechanical properties and chemical stability. However, the high melting point of traditional polyester fibers (usually 250-260℃) limits their application in fields such as hot melt bonding and composite materials. It is under these circumstances that low-melting-point polyester fibers have emerged, and their appearance has attracted widespread attention in the industry.

[0003] Existing low-melting-point polyester fibers suffer from problems such as high oligomer content and high release of odorous substances (such as acetaldehyde and acrolein), affecting product safety and user experience. Furthermore, commercially available low-melting-point polyester fiber products also exhibit varying degrees of insufficient high-temperature resistance, poor melt uniformity, and require further improvement in durability. During processing, the significant difference in crystallization properties between the sheath and core materials leads to large shrinkage rates in the finished product, resulting in technical defects such as product deformation and demolding.

[0004] To address the aforementioned issues, Chinese invention patent CN106811829B discloses a crystalline low-melting-point polyester fiber and its preparation method. The crystalline low-melting-point polyester fiber has a core-sheath structure, with the sheath being low-melting-point polyester and the core being PET. The low-melting-point polyester is composed of terephthalic acid segments, isophthalic acid segments, 1,3-propylene glycol segments, dipropylene glycol segments, and a molecular weight regulator. The molecular weight regulator segments specifically correspond to 1,8-naphthalenedicarboxylic acid, phthalic acid, 1,2-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, or their corresponding dimethyl or diethyl esters. The preparation method includes low-melting-point polyester polymerization and core-sheath composite spinning steps. The subsequent spinning employs a drawing-washing process, with drawing using an oil bath containing sodium sulfite. The crystalline low-melting-point polyester fiber is obtained after crimping, cutting, and drying. The crystalline low-melting-point polyester fiber produced by this invention has a low melting point and a low total content of acetaldehyde and acrolein. However, its durability still needs further improvement.

[0005] It is evident that it is necessary to seek more effective methods to prepare crystalline low-melting-point polyester fibers with good high-temperature resistance and durability, low melting point, good dimensional stability, and long service life. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a crystalline low-melting-point polyester fiber with good high-temperature resistance and durability, low melting point, good dimensional stability and long service life, and a method for preparing the same.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A crystalline low-melting-point polyester fiber, comprising a sheath and a core layer, employing an integrated sheath-core crystalline design; the sheath is a 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 terephthalic acid, 12-15 parts 2,5-furandicarboxylic acid, 28-32 parts 1,4-cyclohexanediethanol, 8-10 parts polycaprolactone, 1.0-1.5 parts crystallization coordinator, 0.5-1.0 parts antioxidant, and 0.3-0.5 parts hindered amine light stabilizer; the crystallization coordinator is a compound of hydroxylated graphene and maleic anhydride-grafted polyolefin elastomer in a mass ratio of (2-3):1.

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

[0010] Preferably, the comonomer is a mixture of 2,5-furandicarboxylic acid and 1,4-cyclohexanediethanol in a mass ratio of 1:1; and the average particle size of the nano-silicon carbide is 20-50 nm.

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

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

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

[0014] Preferably, the antioxidant is antioxidant 1010; 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 invention is to provide a method for preparing the crystalline low-melting-point polyester fiber, comprising the following steps:

[0017] Step S1, Synthesis of Skin-Modified Copolyester: Terephthalic acid, 2,5-furandicarboxylic acid, and 1,4-cyclohexanediethanol were added to a reactor, along with a composite catalyst. The mixture was heated to 220-230℃ under a nitrogen atmosphere and esterified until the water content reached the theoretical value of 95%. Then, polycaprolactone and a crystallization coordinator were added, and the temperature was raised to 250-260℃. The reaction was continued for 50-70 minutes under a vacuum of 30-70 Pa. Finally, an antioxidant and a hindered amine light stabilizer were added, and the mixture was stirred at this temperature for 15-25 minutes to obtain the skin-modified copolyester.

[0018] Step S2, Preparation of core-layer modified PET: Vacuum dry PET chips at 115-125℃ for 3-5 hours; add the dried PET chips, comonomer and nano silicon carbide into a twin-screw extruder, mix them thoroughly in the molten state, and then extrude and pelletize to obtain core-layer modified PET;

[0019] Step S3, Core-Sheath Composite Spinning: Core-sheath composite spinning process is adopted, and spinning is carried out through concentric core-sheath spinnerets;

[0020] Step S4, Post-crystallization treatment: Three-stage hot roller stretching is used, with temperatures of 70℃, 90℃ and 110℃ respectively, and a total stretching ratio of 3.2 times; then it is treated in a saturated steam environment of 0.12MPa and 135℃ for 35-45 minutes to achieve co-crystallization of the core and sheath layers, and obtain crystalline low-melting-point polyester fiber.

[0021] Preferably, the composite catalyst in step S1 is a mixture of tetrabutyl titanate and antimony glycol 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-furandicarboxylic acid and 1,4-cyclohexanediethanol.

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

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

[0025] Preferably, in step S3, the spinning temperature of the outer layer is 230-240℃, the spinning temperature of the core layer is 265-275℃, and the spinning speed is 1300-1500m / min; the cooling adopts an isothermal wind field design with a wind temperature of 43-48℃ and a wind speed of 2-2.4m / s.

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

[0027] (1) The crystalline low-melting-point polyester fiber provided by this invention incorporates 2,5-furandicarboxylic acid and 1,4-cyclohexanediethanol in the sheath layer and adds the same comonomer to the core layer, so that the molecular chains of the sheath and core 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 sheath-core interface, promotes the transmission of crystallization information, reduces the crystallization temperature difference between the sheath and core layers, and forms a single crystallization peak. This synergistic crystallization mechanism endows the fiber with a more uniform and perfect crystal structure, which significantly improves its mechanical properties such as strength and modulus, while also improving dimensional stability.

[0028] (2) The crystalline low-melting-point polyester fiber provided by the present invention is composed of a sheath and a core layer, and adopts an integrated sheath and core crystallization design; the sheath 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: 38-42 parts of terephthalic acid, 12-15 parts of 2,5-furandicarboxylic acid, 28-32 parts of 1,4-cyclohexanediethanol, 8-10 parts of polycaprolactone, 1.0-1.5 parts of crystallization coordinator, 0.5-1.0 parts of antioxidant, and 0.3-0.5 parts of hindered amine light stabilizer; the crystallization coordinator is composed of hydroxylated graphene and maleic anhydride grafted polyolefin elastomer in a mass ratio of (2-3):1; the modified PET is composed of the following raw materials in weight percentage: 2-3 wt% of comonomer, 0.2-0.4 wt% of nano-silicon carbide, 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 advantages such as good high temperature resistance and durability, low melting point, good dimensional stability and long service life.

[0029] (3) The crystalline low-melting-point polyester fiber provided by this invention achieves precise control of the raw material ratio of the modified copolyester in the sheath layer. For example, 38-42 parts of terephthalic acid are used to provide a rigid skeleton, and 12-15 parts of 2,5-furandicarboxylic acid are used to moderately disrupt the molecular chain regularity to reduce the melting point. Combined with the flexible adjustment of polycaprolactone, the melting point of the sheath layer is precisely controlled to meet the requirements of low-melting-point applications. At the same time, 0.2-0.4 wt% of nano-silicon carbide particles are added to the core layer. Their high thermal conductivity effectively constructs a heat conduction network, reducing local overheating. Combined with the high melting point of the PET core layer itself, the fiber as a whole can maintain stable performance at a high temperature of 200℃.

[0030] (4) The crystalline low-melting-point polyester fiber provided by this invention has 0.5-1.0 parts of antioxidant and 0.3-0.5 parts of hindered amine light stabilizer added to the sheath formulation. The antioxidant can capture free radicals and prevent thermal oxidation chain reaction; the hindered amine light stabilizer delays photo-oxidative aging by capturing free radicals and decomposing hydrogen peroxide. At the same time, the nano-silicon carbide particles in the core layer can inhibit ester bond hydrolysis and reduce molecular chain breakage, thereby greatly improving the durability of the crystalline low-melting-point polyester fiber product.

[0031] (5) The crystalline low-melting-point polyester fiber provided by this invention features a unique crystallization coordinator composed of hydroxylated graphene and maleic anhydride-grafted polyolefin elastomer in a mass ratio of (2-3):1. The hydroxylated graphene forms a "molecular bridge" at the core-sheath interface, promoting the transmission of crystallization information, reducing the temperature difference between the core-sheath layers, and greatly enhancing the interaction and crystallization synchronization between the core-sheath layers. The maleic anhydride-grafted polyolefin elastomer further improves interfacial compatibility, making the crystallization process of the entire fiber system smoother, thereby achieving superior overall performance, such as higher crystallinity and better mechanical properties. Detailed Implementation

[0032] To enable those skilled in the art to better understand the technical solutions of the present invention and to make the above-mentioned features, objectives, and advantages of the present invention clearer and easier to understand, the present invention will be further described below with reference to embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0033] Example 1

[0034] A crystalline low-melting-point polyester fiber is composed of a sheath layer and a core layer, employing an integrated sheath-core crystalline design. The sheath layer is a modified copolyester, and the core layer is modified PET. The modified copolyester is composed of the following raw materials in parts by weight: 38 parts terephthalic acid, 12 parts 2,5-furandicarboxylic acid, 28 parts 1,4-cyclohexanediethanol, 8 parts polycaprolactone, 1.0 part crystallization coordinator, 0.5 parts antioxidant, and 0.3 parts hindered amine light stabilizer. The crystallization coordinator is a compound of hydroxylated graphene and maleic anhydride-grafted polyolefin elastomer in a mass ratio of 2:1.

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

[0036] The polycaprolactone has a number-average molecular weight of 8000; the hydroxylated graphene has a sheet diameter of 1-3 μm, a thickness of 1-5 nm, and a hydroxyl content of 2 wt%; 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; the PET chips are WK-631 PET chips.

[0037] A method for preparing the crystalline low-melting-point polyester fiber includes the following steps:

[0038] Step S1, Synthesis of Skin-Modified Copolyester: Terephthalic acid, 2,5-furandicarboxylic acid, and 1,4-cyclohexanediethanol were added to a reactor, along with a composite catalyst. The mixture was heated to 220°C under a nitrogen atmosphere and esterified until the water content reached the theoretical value of 95%. Then, polycaprolactone and a crystallization coordinator were added, and the mixture was heated to 250°C and reacted for 50 minutes under a vacuum of 30 Pa. Finally, an antioxidant and a hindered amine light stabilizer were added, and the mixture was kept warm and stirred for 15 minutes to obtain the skin-modified copolyester.

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

[0040] Step S3, Core-Sheath Composite Spinning: Core-sheath composite spinning process is adopted, and spinning is carried out through concentric core-sheath spinnerets;

[0041] Step S4, Post-crystallization treatment: Three-stage hot roller stretching is used, with temperatures of 70℃, 90℃ and 110℃ respectively, and a total stretching ratio of 3.2 times; then it is treated in a saturated steam environment of 0.12MPa and 135℃ for 35 minutes to achieve co-crystallization of the core and sheath layers, and obtain crystalline low-melting-point polyester fiber.

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

[0043] In step S3, the concentric sheath-core spinneret, through its flow channel design, enables the sheath melt and core melt to form a concentric cylindrical structure during extrusion molding. 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%. In step S3, the sheath spinning temperature is 230℃, the core spinning temperature is 265℃, and the spinning speed is 1300m / min. Cooling is achieved using an isothermal air field design with an air temperature of 43℃ and an air speed of 2m / s.

[0044] Example 2

[0045] A crystalline low-melting-point polyester fiber is composed of a sheath and a core layer, employing an integrated sheath-core crystalline design. The sheath is a modified copolyester, and the core layer is modified PET. The modified copolyester is composed of the following raw materials in parts by weight: 39 parts terephthalic acid, 13 parts 2,5-furandicarboxylic acid, 29 parts 1,4-cyclohexanediethanol, 8.5 parts polycaprolactone, 1.2 parts crystallization coordinator, 0.6 parts antioxidant, and 0.35 parts hindered amine light stabilizer. The crystallization coordinator is a compound of hydroxylated graphene and maleic anhydride-grafted polyolefin elastomer in a mass ratio of 2.2:1.

[0046] The modified PET is composed of the following raw materials by weight percentage: 2.3 wt% comonomer, 0.25 wt% nano-silicon carbide, and the balance being PET chips; the comonomer is a mixture of 2,5-furandicarboxylic acid and 1,4-cyclohexanediethanol in a mass ratio of 1:1; the average particle size of the nano-silicon carbide is 30 nm; the number average molecular weight of the polycaprolactone is 9000; the hydroxylated graphene has a sheet diameter of 1-3 μm, a thickness of 1-5 nm, and a hydroxyl content of 2 wt%; 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; the PET chips are WK-631 PET chips.

[0047] A method for preparing the crystalline low-melting-point polyester fiber includes the following steps:

[0048] Step S1, Synthesis of Skin-Modified Copolyester: Terephthalic acid, 2,5-furandicarboxylic acid, and 1,4-cyclohexanediethanol were added to a reactor, along with a composite catalyst. The mixture was heated to 223°C under a nitrogen atmosphere and esterified until the water content reached the theoretical value of 95%. Then, polycaprolactone and a crystallization coordinator were added, and the mixture was heated to 253°C and reacted for 55 minutes under a vacuum of 40 Pa. Finally, an antioxidant and a hindered amine light stabilizer were added, and the mixture was kept at this temperature and stirred for 17 minutes to obtain the skin-modified copolyester.

[0049] Step S2, Preparation of core-layer modified PET: PET chips are vacuum dried at 117°C for 3.5 hours; the dried PET chips, comonomers and nano-silicon carbide are added to a twin-screw extruder and fully mixed in the molten state, and then extruded and pelletized to obtain core-layer modified PET;

[0050] Step S3, Core-Sheath Composite Spinning: Core-sheath composite spinning process is adopted, and spinning is carried out through concentric core-sheath spinnerets;

[0051] Step S4, Post-crystallization treatment: Three-stage hot roller stretching is used, with temperatures of 70℃, 90℃ and 110℃ respectively, and a total stretching ratio of 3.2 times; then it is treated in a saturated steam environment of 0.12MPa and 135℃ for 37 minutes to achieve co-crystallization of the core and sheath layers, and obtain crystalline low-melting-point polyester fiber.

[0052] The composite catalyst mentioned in step S1 is a mixture of tetrabutyl titanate and antimony glycol in a mass ratio of 2.3:1; the amount of composite catalyst added in step S1 is 0.023% of the total mass of terephthalic acid, 2,5-furandicarboxylic acid and 1,4-cyclohexanediethanol; the temperature of each section of the twin-screw extruder in step S2 is: zone 1 259℃, zone 2 269℃, zone 3 274℃, zone 4 269℃, and the screw speed is 200 r / min.

[0053] In step S3, the concentric sheath-core spinneret, through its flow channel design, enables the sheath melt and core melt to form a concentric cylindrical structure during extrusion molding. The cross-sectional area of ​​the sheath accounts for 40% of the total cross-sectional area of ​​the fiber, and the core layer accounts for 60%. In step S3, the sheath spinning temperature is 233℃, the core spinning temperature is 268℃, and the spinning speed is 1350m / min. Cooling is achieved using an isothermal air field design with an air temperature of 44℃ and an air velocity of 2.2m / s.

[0054] Example 3

[0055] A crystalline low-melting-point polyester fiber is composed of a sheath layer and a core layer, employing an integrated sheath-core crystalline design. The sheath layer is a modified copolyester, and the core layer is modified PET. The modified copolyester is composed of the following raw materials in parts by weight: 40 parts terephthalic acid, 13.5 parts 2,5-furandicarboxylic acid, 30 parts 1,4-cyclohexanediethanol, 9 parts polycaprolactone, 1.3 parts crystallization coordinator, 0.8 parts antioxidant, and 0.4 parts hindered amine light stabilizer. The crystallization coordinator is a compound of hydroxylated graphene and maleic anhydride-grafted polyolefin elastomer in a mass ratio of 2.5:1.

[0056] The modified PET is composed of the following raw materials by weight percentage: 2.5 wt% comonomer, 0.3 wt% nano-silicon carbide, and the balance being PET chips; the comonomer is a mixture of 2,5-furandicarboxylic acid and 1,4-cyclohexanediethanol in 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 10,000; the hydroxylated graphene has a sheet diameter of 1-3 μm, a thickness of 1-5 nm, and a hydroxyl content of 2 wt%; 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; the PET chips are WK-631 PET chips.

[0057] A method for preparing the crystalline low-melting-point polyester fiber includes the following steps:

[0058] Step S1, Synthesis of Skin-Modified Copolyester: Terephthalic acid, 2,5-furandicarboxylic acid, and 1,4-cyclohexanediethanol were added to a reactor, along with a composite catalyst. The mixture was heated to 225°C under a nitrogen atmosphere and esterified until the water content reached the theoretical value of 95%. Then, polycaprolactone and a crystallization coordinator were added, and the mixture was heated to 255°C and reacted for 60 minutes under a vacuum of 50 Pa. Finally, an antioxidant and a hindered amine light stabilizer were added, and the mixture was kept warm and stirred for 20 minutes to obtain the skin-modified copolyester.

[0059] Step S2, Preparation of core-layer modified PET: PET chips are vacuum dried at 120℃ for 4 hours; the dried PET chips, comonomers and nano-silicon carbide are added to a twin-screw extruder and fully mixed in the molten state, and then extruded and pelletized to obtain core-layer modified PET;

[0060] Step S3, Core-Sheath Composite Spinning: Core-sheath composite spinning process is adopted, and spinning is carried out through concentric core-sheath spinnerets;

[0061] Step S4, Post-crystallization treatment: Three-stage hot roller stretching is used, with temperatures of 70℃, 90℃ and 110℃ respectively, and a total stretching ratio of 3.2 times; then it is treated in a saturated steam environment of 0.12MPa and 135℃ for 40 minutes to achieve co-crystallization of the core and sheath layers, and obtain crystalline low-melting-point polyester fiber.

[0062] The composite catalyst mentioned in step S1 is a mixture of tetrabutyl titanate and antimony glycol in a mass ratio of 2.5:1; the amount of composite catalyst added in step S1 is 0.025% of the total mass of terephthalic acid, 2,5-furandicarboxylic acid and 1,4-cyclohexanediethanol; the temperature of each section of the twin-screw extruder in step S2 is: zone 1 260℃, zone 2 270℃, zone 3 275℃, zone 4 270℃, and the screw speed is 210 r / min.

[0063] In step S3, the concentric sheath-core spinneret, through its flow channel design, enables the sheath melt and core melt to form a concentric cylindrical structure during extrusion molding. 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%. In step S3, the sheath spinning temperature is 235℃, the core spinning temperature is 270℃, and the spinning speed is 1400m / min. Cooling is achieved using an isothermal airflow design with an air temperature of 45℃ and an air velocity of 2.2m / s.

[0064] Example 4

[0065] A crystalline low-melting-point polyester fiber, comprising a sheath and a core layer, employing an integrated sheath-core crystalline design; the sheath is a modified copolyester, and the core layer is modified PET; the modified copolyester is composed of the following raw materials in parts by weight: 41 parts terephthalic acid, 14 parts 2,5-furandicarboxylic acid, 31 parts 1,4-cyclohexanediethanol, 9.5 parts polycaprolactone, 1.4 parts crystallization coordinator, 0.9 parts antioxidant, and 0.45 parts hindered amine light stabilizer; the crystallization coordinator is a compound of hydroxylated graphene and maleic anhydride-grafted polyolefin elastomer in a mass ratio of 2.9:1.

[0066] The modified PET is composed of the following raw materials by weight percentage: 2.8 wt% comonomer, 0.35 wt% nano-silicon carbide, and the balance being PET chips; the comonomer is a mixture of 2,5-furandicarboxylic acid and 1,4-cyclohexanediethanol in a mass ratio of 1:1; the average particle size of the nano-silicon carbide is 45 nm; the number average molecular weight of the polycaprolactone is 11,000; the hydroxylated graphene has a sheet diameter of 1-3 μm, a thickness of 1-5 nm, and a hydroxyl content of 2 wt%; 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; the PET chips are WK-631 PET chips.

[0067] A method for preparing the crystalline low-melting-point polyester fiber includes the following steps:

[0068] Step S1, Synthesis of Skin-Modified Copolyester: Terephthalic acid, 2,5-furandicarboxylic acid, and 1,4-cyclohexanediethanol were added to a reactor, along with a composite catalyst. The mixture was heated to 228°C under a nitrogen atmosphere and esterified until the water content reached the theoretical value of 95%. Then, polycaprolactone and a crystallization coordinator were added, and the mixture was heated to 258°C and reacted for 65 minutes under a vacuum of 60 Pa. Finally, an antioxidant and a hindered amine light stabilizer were added, and the mixture was kept warm and stirred for 23 minutes to obtain the skin-modified copolyester.

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

[0070] Step S3, Core-Sheath Composite Spinning: Core-sheath composite spinning process is adopted, and spinning is carried out through concentric core-sheath spinnerets;

[0071] Step S4, Post-crystallization treatment: Three-stage hot roller stretching is used, with temperatures of 70℃, 90℃ and 110℃ respectively, and a total stretching ratio of 3.2 times; then it is treated in a saturated steam environment of 0.12MPa and 135℃ for 43 minutes to achieve co-crystallization of the core and sheath layers, and obtain crystalline low-melting-point polyester fiber.

[0072] The composite catalyst mentioned in step S1 is a mixture of tetrabutyl titanate and antimony glycol in a mass ratio of 2.8:1; the amount of composite catalyst added in step S1 is 0.028% of the total mass of terephthalic acid, 2,5-furandicarboxylic acid and 1,4-cyclohexanediethanol; the temperature of each section of the twin-screw extruder in step S2 is: zone 1 261℃, zone 2 271℃, zone 3 277℃, zone 4 271℃, and the screw speed is 220 r / min.

[0073] In step S3, the concentric sheath-core spinneret, through its flow channel design, enables the sheath melt and core melt to form a concentric cylindrical structure during extrusion molding. 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%. In step S3, the sheath spinning temperature is 238℃, the core spinning temperature is 273℃, and the spinning speed is 1450m / min. Cooling is achieved using an isothermal air field design with an air temperature of 47℃ and an air velocity of 2.3m / s.

[0074] Example 5

[0075] A crystalline low-melting-point polyester fiber, comprising a sheath and a core layer, employing an integrated sheath-core crystalline design; the sheath is a modified copolyester, and the core layer is modified PET; the modified copolyester is composed of the following raw materials in parts by weight: 42 parts terephthalic acid, 15 parts 2,5-furandicarboxylic acid, 32 parts 1,4-cyclohexanediethanol, 10 parts polycaprolactone, 1.5 parts crystallization coordinator, 1.0 part antioxidant, and 0.5 parts hindered amine light stabilizer; the crystallization coordinator is a compound of 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 by weight percentage: 3 wt% comonomer, 0.4 wt% nano-silicon carbide, and the balance being PET chips; the comonomer is a mixture of 2,5-furandicarboxylic acid and 1,4-cyclohexanediethanol 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 12,000; the hydroxylated graphene has a sheet diameter of 1-3 μm, a thickness of 1-5 nm, and a hydroxyl content of 2 wt%; 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; the PET chips are WK-631 PET chips.

[0077] A method for preparing the crystalline low-melting-point polyester fiber includes the following steps:

[0078] Step S1, Synthesis of Skin-Modified Copolyester: Terephthalic acid, 2,5-furandicarboxylic acid, and 1,4-cyclohexanediethanol were added to a reactor, along with a composite catalyst. The mixture was heated to 230°C under a nitrogen atmosphere and esterified until the water content reached the theoretical value of 95%. Then, polycaprolactone and a crystallization coordinator were added, and the mixture was heated to 260°C and reacted for 70 minutes under a vacuum of 70 Pa. Finally, an antioxidant and a hindered amine light stabilizer were added, and the mixture was kept warm and stirred for 25 minutes to obtain the skin-modified copolyester.

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

[0080] Step S3, Core-Sheath Composite Spinning: Core-sheath composite spinning process is adopted, and spinning is carried out through concentric core-sheath spinnerets;

[0081] Step S4, Post-crystallization treatment: Three-stage hot roller stretching is used at temperatures of 70℃, 90℃, and 110℃, with a total stretching ratio of 3.2 times; then, it is treated in a saturated steam environment at 0.12MPa and 135℃ for 45 minutes to achieve co-crystallization of the core and sheath layers, resulting in crystalline low-melting-point polyester fiber.

[0082] The composite catalyst mentioned in step S1 is a mixture of tetrabutyl titanate and antimony glycol in a mass ratio of 3:1; the amount of composite catalyst added in step S1 is 0.03% of the total mass of terephthalic acid, 2,5-furandicarboxylic acid and 1,4-cyclohexanediethanol; the temperature of each section of the twin-screw extruder in step S2 is: zone 1 262℃, zone 2 272℃, zone 3 278℃, zone 4 272℃, and the screw speed is 230 r / min.

[0083] In step S3, the concentric sheath-core spinneret, through its flow channel design, enables the sheath melt and core melt to form a concentric cylindrical structure during extrusion molding. The cross-sectional area of ​​the sheath accounts for 40% of the total cross-sectional area of ​​the fiber, and the core layer accounts for 60%. In step S3, the sheath spinning temperature is 240℃, the core spinning temperature is 275℃, and the spinning speed is 1500m / min. Cooling is achieved using an isothermal air field design with an air temperature of 48℃ and an air velocity of 2.4m / s.

[0084] Comparative Example 1

[0085] A crystalline low-melting-point polyester fiber and its preparation method are basically 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 its preparation method are basically the same as those in Example 1, except that no crystallization coordinator is added.

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

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

[0090] Core-modified PET nuclear magnetic resonance spectroscopy (1H) - NMR: Core-modified PET was tested using deuterated chloroform (CDCl3) as solvent on a 600 MHz nuclear magnetic resonance spectrometer. A peak at chemical shift δ, at 7.8–8.2 ppm, was observed attributable to the proton signal of the benzene ring in the terephthalic acid unit; at 4.0–4.2 ppm, a peak attributable to the methylene proton in 1,4-cyclohexanediethanol; and at 2.5–2.7 ppm, a peak attributable to the proton signal on the furan ring of the comonomer 2,5-furandicarboxylic acid. Calculations based on peak area integration indicated that the actual molar percentage of the comonomer in the core layer was 2.2%.

[0091] Fourier transform infrared (FT-IR) spectroscopy of core-modified PET: Attenuated total reflectance (ATR) mode, scanning range 400-4000 cm⁻¹ -1 The core-layer modified PET was tested. At 1710 cm⁻¹ -1 A strong absorption peak appears at 1610 cm⁻¹, corresponding to the stretching vibration of the ester carbonyl group (C=O) in the PET molecular chain; -1 1500cm -1 A skeletal vibrational peak corresponding to the benzene ring appears at 1250 cm⁻¹. After adding the comonomer, a peak appears at 1250 cm⁻¹. -1 A new peak appears at 1080 cm⁻¹, attributed to the stretching vibration of COC in 1,4-cyclohexanediethanol; -1 The characteristic absorption peak of the 2,5-furandicarboxylic acid furan ring appears at [location].

[0092] Gel permeation chromatography (GPC) of the cortex-modified copolyester: Tetrahydrofuran (THF) was used as the mobile phase at a flow rate of 1.0 mL / min at 35 °C. The results showed that the number-average molecular weight (Mn) was 36,500 g / mol, the weight-average molecular weight (Mw) was 42,000 g / mol, and the molecular weight distribution index (PDI = Mw / Mn) was 1.15.

[0093] Fourier transform infrared (FT-IR) of the cortex was performed on modified copolyester using attenuated total reflectance (ATR) mode, with a scanning range of 400-4000 cm⁻¹. -1 The result showed: 1720cm -1 A stretching vibration peak of the ester carbonyl group (C=O) appears at 1260 cm⁻¹. -1 The stretching vibration peak of COC appears at 750 cm⁻¹. -1 The characteristic bending vibration peak of the furan ring of 2,5-furandicarboxylic acid appears at 1050 cm⁻¹. -1 The presence of saturated CH bending vibration peaks of 1,4-cyclohexanediethanol directly confirms the chemical structural integrity of each monomer unit in the cortex copolyester.

[0094] (2) Taking the product of Example 1 as an example, crystallization performance and melting point tests were conducted. Crystallization performance was tested according to ASTM D3418-21, with a heating rate of 10℃ / min. The product of Example 1 showed a single crystallization peak at 125-135℃, with a crystallization enthalpy of 37.23 J / g. Crystallinity was tested according to ISO 11357-7:2022, and the crystallinity of the product of Example 1 was 26.59%. Melting point was tested according to GB / T19466.3-2004, and the melting point of the outer layer of the product of Example 1 was 150-160℃, while the melting point of the core layer was 258℃.

[0095] (3) The fracture strength of each product was tested in accordance with GB / T 14337-2008. Each product was placed at 120℃ for 24 hours, cooled to room temperature and the fracture strength was tested again. The retention rate of fracture strength was calculated. The higher the value, the better the high temperature resistance. Each product was placed at 85℃ and 85% relative humidity for 1000 hours, cooled to room temperature and the fracture strength was tested again. The retention rate of fracture strength was calculated. The higher the value, the better the durability. The test results are shown in Table 1.

[0096] Table 1. Test results of properties of crystalline low-melting-point polyester fibers

[0097] project Average fracture strength (cN / dtex) High temperature resistance (%) 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 can be seen from Table 1, the crystalline low-melting-point polyester fibers disclosed in the embodiments of the present invention have better mechanical properties, high-temperature resistance and durability than the comparative products. The combined use of 2,5-furandicarboxylic acid and crystallization coordinator is beneficial to improving the above properties.

[0099] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A crystalline low-melting-point polyester fiber, characterized in that, It consists of a skin layer and a core layer, and adopts an integrated skin-core crystalline 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: 38-42 parts terephthalic acid, 12-15 parts 2,5-furandicarboxylic acid, 28-32 parts 1,4-cyclohexanediethanol, 8-10 parts polycaprolactone, 1.0-1.5 parts crystallization coordinator, 0.5-1.0 parts antioxidant, and 0.3-0.5 parts hindered amine light stabilizer; the crystallization coordinator is a compound of hydroxylated graphene and maleic anhydride-grafted polyolefin elastomer in a mass ratio of (2-3):1; the modified PET is composed of the following raw materials in weight percentage: 2-3 wt% comonomer, 0.2-0.4 wt% nano-silicon carbide, and the balance being PET chips; the comonomer is a mixture of 2,5-furandicarboxylic acid and 1,4-cyclohexanediethanol in a mass ratio of 1:

1.

2. The crystalline low-melting polyester fiber according to claim 1, characterized by The average particle size of the nano-silicon carbide is 20-50 nm; the PET slices are WK-631 PET slices.

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

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

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

6. A process for producing the crystalline low-melting polyester fiber according to any one of claims 1 to 5, characterized by, Includes the following steps: Step S1, Synthesis of Skin-Modified Copolyester: Terephthalic acid, 2,5-furandicarboxylic acid, and 1,4-cyclohexanediethanol were added to a reactor, along with a composite catalyst. The mixture was heated to 220-230℃ under a nitrogen atmosphere and esterified until the water content reached the theoretical value of 95%. Then, polycaprolactone and a crystallization coordinator were added, and the temperature was raised to 250-260℃. The reaction was continued for 50-70 minutes under a vacuum of 30-70 Pa. Finally, an antioxidant and a hindered amine light stabilizer were added, and the mixture was kept warm and stirred for 15-25 minutes to obtain the skin-modified copolyester. Step S2, Preparation of core-layer modified PET: Vacuum dry PET chips at 115-125℃ for 3-5 hours; add the dried PET chips, comonomer and nano silicon carbide into a twin-screw extruder, mix them thoroughly in the molten state, and then extrude and pelletize to obtain core-layer modified PET; Step S3, Core-Sheath Composite Spinning: Core-sheath composite spinning process is adopted, and spinning is carried out through concentric core-sheath spinnerets; Step S4, Post-crystallization treatment: Three-stage hot roller stretching is used, with temperatures of 70℃, 90℃ and 110℃ respectively, and a total stretching ratio of 3.2 times; then it is treated in a saturated steam environment of 0.12MPa and 135℃ for 35-45 minutes to achieve co-crystallization of the core and sheath layers, and obtain crystalline low-melting-point polyester fiber.

7. The method of producing a crystalline low-melting polyester fiber according to claim 6, characterized by, The composite catalyst mentioned in step S1 is a mixture of tetrabutyl titanate and antimony 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-cyclohexanediethanol.

8. The method for preparing crystalline low-melting-point polyester fiber according to claim 6, characterized in that, The temperatures of each section of the twin-screw extruder in step S2 are: Zone 1 258-262℃, Zone 2 268-272℃, Zone 3 273-278℃, Zone 4 268-272℃, and the screw speed is 190-230 r / min.

9. The method of producing a crystalline low-melting polyester fiber according to claim 6, characterized by, In step S3, the concentric sheath-core spinneret, through its flow channel design, enables the sheath melt and core melt to form a concentric cylindrical structure during extrusion molding. 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%. In step S3, the sheath spinning temperature is 230-240℃, the core spinning temperature is 265-275℃, and the spinning speed is 1300-1500m / min. Cooling adopts an isothermal air field design with an air temperature of 43-48℃ and an air speed of 2-2.4m / s.