Method for preparing melt direct-spun high-viscosity PBAT / low-viscosity pet bicomponent fiber, and polymerization reactor for high-viscosity pbat

Abstract

A method for preparing a melt direct-spun high-viscosity PBAT / low-viscosity PET bicomponent fiber, and a polymerization reactor for high-viscosity PBAT. The method comprises: using two production lines for respectively producing a high-viscosity PBAT melt and a low-viscosity PET melt, and then carrying out spinning. A high-viscosity PBAT production line comprises a first esterification reactor (10), a second esterification reactor (11), a first pre-polymerization reactor (12), a second pre-polymerization reactor (13), and a high-viscosity PBAT polymerization reactor (14). A low-viscosity PET production line comprises a first esterification reactor (10), a second esterification reactor (11), a first pre-polymerization reactor (12), a second pre-polymerization reactor (13), and a low-viscosity PET final polymerization reactor (15). The polymerization reactor (14) comprises disc (9) reaction units in a parallel double-shaft (8) arrangement; and the two shafts (8) rotate in opposite directions, thereby improving the devolatilization effect, achieving self-cleaning, and significantly increasing the viscosity. By using the method, the cost is low, the productivity is high, the process flow is shortened, and the fiber can reach a strength of 2.55-2.85 cN / dtex, a crimp contraction ratio of 25%-60% and a crimp stability of 58%-70%.

Description

Method for preparing melt-spun high-viscosity PBAT / low-viscosity PET bicomponent fiber and polymerization kettle for high-viscosity PBAT Technical Field

[0001] The invention relates to a method for preparing melt-spun high-viscosity PBAT / low-viscosity PET bicomponent elastic fiber and a polymerization kettle for high-viscosity PBAT. Background Art

[0002] The application scope of elastic fibers in the modern chemical fiber industry is becoming wider and wider. Especially in recent years, with the rapid development of the theory of bicomponent elastic fibers, we have a deeper understanding of the forming mechanism and elasticity generation mechanism of parallel bicomponent elastic fibers, and the varieties of elastic fibers and original technologies have also made great progress. Starting in the 1970s, DuPont first launched single-component spandex elastic fiber, which quickly became popular in the market for its unique style and characteristics. In the late 1970s, it launched the two-component parallel elastic fiber T800, which uses PBT / PET parallel composite to produce good elastic effect. However, due to the low glass transition temperature (26-42°C) of the PBT component of PBT / PET elastic fiber, the fiber undergoes rapid crystallization under stress, and the elastic recovery rate and shape retention of T800 fiber are poor. In the 21st century, with the successful industrialization of PDO by chemical and biological fermentation methods, PTT polyester has a unique molecular structure and excellent elastic recovery properties. DuPont's T400, PTT / PET two-component elastic fiber, was launched. The PTT / PET two-component parallel composite fiber has excellent elastic recovery rate and shape retention. The fabric will not deform after repeated stretching. Its elastic sustained-release effect overcomes the restraining feeling of spandex elastic fiber. With its excellent resistance to chlorine bleaching and light exposure, it has become the best elastic fiber variety in the fabric industry.

[0003] The development of bicomponent elastic fibers has been a key area of ​​industry development over the past decade. The latest advances utilize the differing orientation and crystallization behaviors of PET polyester components of varying viscosity. During the spinning process, the high-viscosity and low-viscosity components undergo elastic curling due to the varying speeds and percentages of transition from the oriented state to the crystallized state, forming a spring-like structure that exhibits excellent elastic properties on the fabric. Patents such as CN111101237A, CN101126180A, CN106337212A, CN107964690A, CN101851812A, and CN115613159A disclose a series of PET / PET, PBT / PET, and PTT / PET composite elastic fibers and their preparation methods, as well as methods for preparing easily or deeply dyed elastic fibers using modified PET fibers with retained elasticity, such as high-viscosity ECDP, high-viscosity high-shrinkage polyester, high-viscosity disperse dye-friendly polyester, and high-viscosity CDP cationic polyester, with low-viscosity PET polyester.

[0004] The preparation methods of the above-mentioned elastic fibers are all based on a chip spinning production process in which high-viscosity chips and low-viscosity chips are pre-crystallized and melted by a drying screw, and then formed into a composite spinning box and a composite parallel spinneret. Although this process solves the basic technical problems of parallel composite spinning, the chip spinning technology has obvious defects such as a long process, high cost, low production capacity, and poor product quality stability.

[0005] PBT / PET two-component composite elastic fiber has the characteristics of moderate elasticity, low price and good clothing comfort. Its cost is only half of that of PBT / PET two-component fiber, and its curl shrinkage rate is significantly higher than that of composite elastic fibers such as PET / PET. Combined with its stress relief effect, it has good market application space.

[0006] PBAT is a thermoplastic biodegradable material, a copolymer of butylene adipate and butylene terephthalate. It combines the properties of PBA and PBT, offering excellent ductility and elongation at break, as well as good heat resistance and impact resistance. PBAT / PET two-component composite elastic fibers exhibit greater elasticity than PBT / PET, and their superior softness is well-suited to the characteristics of women's clothing. Their cost is roughly comparable to that of PBT / PET elastic fibers, and significantly lower than PTT / PET elastic fibers and spandex. Therefore, PBAT / PET two-component composite elastic fibers have excellent application scenarios and excellent results.

[0007] However, the curl shrinkage, curl stability, and quality stability of existing PBAT / PET bicomponent fibers are still insufficient, leaving significant room for improvement. Furthermore, during the synthesis of PBAT, the dehydration and cyclization of the 1,4-butanediol raw material in the polymerization system produces a large amount of tetrahydrofuran as a byproduct. This byproduct significantly affects both the polymerization system and the resulting PBAT product. Controlling the content of this byproduct is a major challenge in the PBAT synthesis process.

[0008] Summary of the Invention

[0009] The present invention aims to provide a high-viscosity PBAT polymerization kettle for preparing a high-viscosity PBAT melt. The high-viscosity PBAT melt prepared by the polymerization kettle has a very high viscosity. When used to prepare melt-spun high-viscosity PBAT / low-viscosity PET bicomponent elastic fibers, the fiber performance can be significantly improved.

[0010] The purpose of the present invention is to provide a melt-spun high-viscosity PBAT / low-viscosity PET bicomponent elastic fiber, which has significantly improved curl shrinkage, curl stability and quality stability.

[0011] Another object of the present invention is to provide a method for preparing a melt-spun high-viscosity PBAT / low-viscosity PET bicomponent elastic fiber, which has significantly reduced costs, high production capacity, and a significantly shortened process flow. The curl shrinkage rate, curl stability, and quality stability of the prepared elastic fiber are significantly improved.

[0012] In order to achieve the above object, the technical solution adopted by the present invention is:

[0013] A high-viscosity PBAT polymerizer is used to prepare a high-viscosity PBAT melt, which is used to prepare a high-viscosity PBAT / low-viscosity PET bicomponent elastic fiber. The high-viscosity PBAT polymerizer is a horizontal polymerizer and includes a main body containing a chamber. The main body includes a low-viscosity zone, a medium-high-viscosity zone, and a high-viscosity zone arranged in sequence along the axis of the high-viscosity PBAT polymerizer. The viscosity of the PBAT melt in the low-viscosity zone, the medium-high-viscosity zone, and the high-viscosity zone increases in sequence. The high-viscosity PBAT polymerizer also includes two stirring shafts arranged parallel to the axis thereof, passing through the low-viscosity zone, the medium-high-viscosity zone, and the high-viscosity zone. The two stirring shafts rotate in opposite directions, and each stirring shaft is provided with a plurality of disks. The outer circumference of the disks is circular, and the distance between the two stirring shafts is 1.05-1.10 times the radius of the disks. The disks on the two stirring shafts partially overlap.

[0014] In the present invention, the polymerized materials are mainly polymerized on the disc.

[0015] In the present invention, the distance between the two stirring shafts refers to the distance between the axis lines of the two stirring shafts. In the present invention, the partial overlap of the discs on the two stirring shafts means that the discs on the two stirring shafts overlap and intersect in space. Setting the distance between the two stirring shafts to 1.05-1.10 times the radius of the discs ensures that the discs on the two parallel stirring shafts intersect with each other at the maximum area, forming efficient shear mixing.

[0016] In some embodiments, the discs in the low-viscosity zone are single-disc designs, the discs in the medium-to-high-viscosity zone are single-disc designs, and the discs in the high-viscosity zone are dual-disc designs. Each dual-disc set has 8 to 12 spokes. These spokes serve as a reinforcement structure to accommodate the high dynamic viscosity requirements of melt film drawing in the high-viscosity zone.

[0017] In the present invention, the double disc design refers to a design in which two adjacent disc reactors are fixedly connected and rotated together with the stirring shaft. In the present invention, the spokes refer to the radial strips extending from the stirring shaft to the outer circumference of the disc.

[0018] In some embodiments, the distance between two adjacent discs increases successively from the low viscosity zone to the medium-high viscosity zone to the high viscosity zone; the distance between two adjacent discs in the high viscosity zone is 60-100 mm.

[0019] In some embodiments, along the axial direction of the high-viscosity PBAT polymerization reactor from front to back, the spacing between the disk groups of the double disks in the high-viscosity zone increases successively and is controlled to be 120-200 mm.

[0020] In some embodiments, the number of discs in the low-viscosity area and the medium-high-viscosity area is 35-55, and the total number of discs in the high-viscosity area is 20-30.

[0021] In some embodiments, the lengths of the low viscosity zone, the medium-high viscosity zone, and the high viscosity zone are all one-third of the length of the high viscosity PBAT polymerization kettle.

[0022] In the present invention, one third does not mean an exact value of one third, but refers to approximately one third or thereabouts, and is approximately equal to one third.

[0023] In some embodiments, the high-viscosity PBAT polymerization kettle further includes a prepolymer inlet located at the bottom of the front end of the low-viscosity zone and a high-viscosity PBAT melt outlet located at the bottom of the rear end of the high-viscosity zone, and the high-viscosity PBAT melt outlet is in a bell-mouth shape.

[0024] In some embodiments, composite scrapers are further provided on both sides of the double-plate disc group in the high-viscosity zone. The composite scrapers include an axial scraper for scraping the melt on the stirring shaft, a wall scraper for scraping the melt on the inner wall of the high-viscosity PBAT polymerization kettle, a disc scraper for scraping the melt on the disc, and a bottom scraper for scraping the bottom of the polymerization kettle. The distance between the disc scraper and the disc is 55-75 mm. The use of this composite scraper can ensure that the high-viscosity melt has a good material flow effect under the condition of efficient devolatilization.

[0025] The high-viscosity PBAT polymerization reactor of the present invention is different from the conventional parallel twin-shaft disc reactor design. Although the parallel twin-shaft stirring has an efficient shear effect, for PBAT, a highly viscoelastic melt, when the intrinsic viscosity is higher than 1.15, it is still easy to cause melt climbing. Therefore, the PBAT final polymerization reactor is designed with a low stirring speed and a composite scraper is designed between the discs in the high-viscosity area. The disc scraper can control the thickness of the disc melt film, the wall scraper can timely update the reactor wall material, the axial scraper cleans the stirring shaft, and the bottom scraper controls the melt thickness at the bottom of the polymerization reactor.

[0026] The high-viscosity PBAT polymerization reactor of the present invention is designed with a special disc structure and parallel double-axis discs, which has high material mass transfer efficiency. The two counter-rotating discs form an efficient shearing effect on each other, producing a good self-cleaning effect. The discs in the front half of the reactor are low-pitch single discs, which are suitable for the requirement of rapid viscosity increase of low-viscosity melt with large devolatilization area. The rear high-viscosity area is designed with multiple sets of double discs and a reinforced disc structure to meet the need of significantly increasing the torque of high-viscosity melt. At the same time, the spacing between the rear double discs is controlled between 60 and 100 mm, and the spacing between the discs is gradually increased as the viscosity increases. At the same time, the spacing between the double disc groups is controlled between 120 and 200 mm, and the spacing between the disc groups is gradually increased along the axial direction from low to high viscosity. For the rear double disc group, the spokes of the two disc groups are designed with an angle of 1.0 to 3.0 degrees along the axial rotation direction, and the angle misalignment is used to produce a material propulsion effect.

[0027] The present invention adopts a double-axis disc design in parallel up and down, which has higher devolatilization efficiency and greatly shortens the polymerization reaction time compared with the conventional front-to-back double-axis disc reactor. The residence time of the high-viscosity final polymerization reactor is 40-55% (80-120 minutes) of the conventional front-to-back double-axis disc reactor design. The reaction speed is improved and the residence time is greatly reduced, which effectively suppresses the level of side reactions and improves the quality of the high-viscosity PBAT polyester melt.

[0028] The present invention also provides a method for preparing a high-viscosity PBAT / low-viscosity PET bicomponent elastic fiber using the aforementioned high-viscosity PBAT polymerization reactor, wherein the bicomponent elastic fiber contains a high-viscosity PBAT component and a low-viscosity PET component, wherein the viscosity of the high-viscosity PBAT component is greater than the viscosity of the low-viscosity PET component, and the preparation method comprises the steps of separately preparing a high-viscosity PBAT melt and a low-viscosity PET melt, and spinning the high-viscosity PBAT melt and the low-viscosity PET melt through the same parallel composite spinning assembly to obtain the bicomponent elastic fiber; the viscosity of the high-viscosity PBAT melt is greater than the viscosity of the low-viscosity PET melt; the step of preparing the high-viscosity PBAT melt comprises: reacting terephthalic acid and 1,4-butanediol through a first esterification reactor for a first esterification reaction; The method further comprises the steps of: performing a second esterification reaction in a second esterification kettle, performing a prepolymerization reaction in a first prepolymerization kettle and a second prepolymerization kettle to obtain a PBAT prepolymer; and adding 1,4-butylene adipate prepolymer to the second esterification kettle during the second esterification reaction; and polymerizing the PBAT prepolymer in the high-viscosity PBAT polymerization kettle to obtain the high-viscosity PBAT melt; and preparing a low-viscosity PET melt comprising the steps of sequentially performing an esterification reaction on terephthalic acid and ethylene glycol in the first esterification kettle and the second esterification kettle, performing a prepolymerization reaction in the first prepolymerization kettle and the second prepolymerization kettle to obtain a PET prepolymer; and polymerizing the PET prepolymer in a low-viscosity PET final polymerization kettle to obtain the low-viscosity PET melt.

[0029] In the present invention, PBAT refers to a copolymer of butylene adipate and butylene terephthalate, and PET refers to polyethylene terephthalate.

[0030] In some embodiments, the bicomponent elastic fiber contains, by weight, 30%-70% of a high-viscosity PBAT component and 70%-30% of a low-viscosity PET component.

[0031] In some embodiments, the high-viscosity PBAT melt has an intrinsic viscosity of 1.05 to 1.30 at 25°C, and a dynamic viscosity of 315 to 905 Pa.s at 252°C (measured at 252°C); the low-viscosity PET melt has an intrinsic viscosity of 0.45 to 0.55 at 25°C, and a dynamic viscosity of 90 to 240 Pa.s at 275°C (measured at 275°C).

[0032] In some embodiments, the high-viscosity PBAT melt has an intrinsic viscosity of 0.95 to 1.10 at 25° C. and a dynamic viscosity of 430 to 900 Pa.s at 252° C.

[0033] In some embodiments, the high-viscosity PBAT melt has an intrinsic viscosity of 0.97 to 1.05 at 25° C. and a dynamic viscosity of 500 to 750 Pa.s at 252° C.

[0034] In the present invention, the intrinsic viscosity is the result of measurement in a mixed solvent of phenol and tetrachloroethane at a volume ratio of 3:2.

[0035] In some embodiments, in the same parallel composite spinning assembly, the high-viscosity PBAT melt has a dynamic viscosity of 270 to 650 Pa.s at 252° C., and the low-viscosity PET melt has a dynamic viscosity of 70 to 220 Pa.s at 275° C.

[0036] In some embodiments, the number average molecular weight of the 1,4-butylene adipate prepolymer is 1600-2500.

[0037] In some embodiments, the 1,4-butanediol adipate prepolymer is prepared by esterification and prepolymerization of adipic acid and 1,4-butanediol.

[0038] In some embodiments, the ratio of the molar amount of the adipic acid monomer unit to the molar amount of terephthalic acid in the 1,4-butylene adipate prepolymer is 45-55:45-55.

[0039] In some embodiments, the esterification and prepolymerization of adipic acid and 1,4-butanediol are performed in the presence of a protonic acid catalyst.

[0040] In some embodiments, the esterification reaction in the first esterification kettle for preparing the high-viscosity PBAT melt is carried out at an absolute pressure of 40 to 60 kPa.

[0041] In some embodiments, the esterification reaction in the second esterification kettle for preparing the high-viscosity PBAT melt is carried out under normal pressure.

[0042] In some embodiments, the second esterification kettle for preparing the high-viscosity PBAT melt is a horizontal reactor and includes three compartments arranged in sequence.

[0043] In some embodiments, when preparing a high-viscosity PBAT melt, the preparation method further includes the step of adding a side reaction inhibitor to the first sub-chamber from the front to the rear of the second esterification kettle, wherein the side reaction inhibitor is a Lewis base.

[0044] In some embodiments, the Lewis base is selected from a combination of one or more of triethanolamine, quaternary ammonium salts, ethylenediaminetetraacetic acid, sodium acetate, sodium benzoate, sodium formate, potassium succinate, lithium acetate, and zinc acetate.

[0045] In some embodiments, the mass of the Lewis base is 50 to 500 ppm of the mass of the high-viscosity PBAT melt.

[0046] In some embodiments, the mass of the Lewis base is 100 to 400 ppm of the mass of the high-viscosity PBAT melt.

[0047] In some embodiments, the mass of the Lewis base is 150 to 200 ppm of the mass of the high-viscosity PBAT melt.

[0048] In the present invention, the side reaction inhibitor is a Lewis base, which functions to improve the pH environment of the second esterification kettle under weakly acidic conditions and inhibit the degree of etherification reaction of the 1,4-butanediol raw material to produce tetrahydrofuran. The comprehensive effect can effectively reduce the amount of tetrahydrofuran produced by 15% to 20%.

[0049] In some embodiments, when preparing a high-viscosity PBAT melt, the preparation method further includes the step of adding an esterification catalyst to the first esterification kettle before the first esterification reaction. The esterification catalyst is selected from tetrabutyl titanate, tetraisopropyl titanate, or tetrakis(2-ethylhexyloxy) titanate. Tetrakis(2-ethylhexyloxy) titanate is preferred, and TOT catalyst from Japan Soda Co., Ltd. is more preferred, as it is not easily hydrolyzed, is more stable, and is conducive to the stable polymerization of PBAT.

[0050] In some embodiments, when preparing a high-viscosity PBAT melt, the preparation method further includes the step of introducing a polymerization catalyst into the first prepolymerization kettle before performing the prepolymerization reaction.

[0051] In some embodiments, the polymerization catalyst is prepared by reacting a titanate with a protonic acid under anhydrous conditions, removing alcohol by-products, and dissolving the resultant in 1,4-butanediol.

[0052] In some embodiments, the titanate is selected from tetrabutyl titanate, tetraisopropyl titanate, or tetra(2-ethylhexyloxy) titanate.

[0053] In some embodiments, the protonic acid is selected from a combination of one or more of formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, citric acid, tripolyphosphoric acid, and polyphosphoric acid.

[0054] In some embodiments, the mass ratio of the titanate to the protonic acid is 1:0.5-2.0.

[0055] In some embodiments, the mass percentage of titanium element in the polymerization catalyst is 1.0%-3.0%.

[0056] In some embodiments, the mass of the titanium element in the esterification catalyst accounts for 30 to 40 ppm of the mass of the high-viscosity PBAT melt.

[0057] In some embodiments, the mass of the titanium element in the polymerization catalyst accounts for 50 to 70 ppm of the mass of the high-viscosity PBAT melt.

[0058] In some embodiments, the preparation method controls the residence time of the material in the high-viscosity PBAT polymerization reactor to be 75 to 120 minutes.

[0059] The high-viscosity PBAT polymerization reactor of the present invention achieves a controlled material residence time of 75 to 120 minutes, significantly superior to the 180 to 300 minutes of conventional front-to-back dual-shaft high-viscosity disc reactors. The present high-viscosity PBAT polymerization reactor has a total volume of approximately half that of conventional disc reactors and significantly reduces side reactions. This suppresses the formation of tetrahydrofuran (THF) during the production of high-viscosity PBAT melts. The high-viscosity reactor can achieve an annual capacity of 20,000 to 80,000 tons, depending on production requirements. It can achieve intrinsic viscosities of 1.05 to 1.30 (3:2) and dynamic viscosities of 315 to 905 Pa.s (252°C) for high-viscosity PBAT thickening.

[0060] In some embodiments, the intrinsic viscosity of the PBAT prepolymer fed into the high-viscosity PBAT polymerization reactor is 0.300 to 0.360. After the melt in this range enters the high-viscosity PBAT polymerization reactor (parallel biaxial final polymerization reactor), it can more effectively meet the requirements of the disc design, reduce the overall polymerizer disc material load, obtain the optimal material residence time, significantly reduce the level of polymerization side reactions, and minimize the generation of non-condensable gas.

[0061] In some embodiments, the intrinsic viscosity of the PBAT prepolymer fed into the high-viscosity PBAT polymerization kettle is 0.315 to 0.345.

[0062] In some embodiments, the intrinsic viscosity of the PBAT prepolymer introduced into the high-viscosity PBAT polymerization kettle is 0.325 to 0.330.

[0063] In some embodiments, when preparing a high-viscosity PBAT melt, the 1,4-butylene adipate prepolymer is added to the second esterification kettle from the third sub-chamber from the front to the back of the second esterification kettle.

[0064] In some embodiments, the first esterification kettle and the second esterification kettle for preparing a high-viscosity PBAT melt are both provided with a distillation tower at the top, and the preparation method further includes the steps of extracting a mixture of water and tetrahydrofuran from the top of the two distillation towers and extracting 1,4-butanediol from the bottom of the tower.

[0065] In some embodiments, the preparation method further comprises the step of separating the mixture of water and tetrahydrofuran through a distillation tower to obtain tetrahydrofuran.

[0066] In some embodiments, the preparation method further comprises the step of recovering the extracted 1,4-butanediol.

[0067] In the present invention, when preparing high-viscosity PBAT, the distillation tower of the first esterification kettle adopts a reduced pressure design. The first esterification kettle is a reduced pressure esterification kettle, and its operating pressure is controlled at 40 to 60 kPa (absolute pressure). The top of the tower is equipped with a by-product reflux system and a production system (esterified water + tetrahydrofuran) and a liquid ring vacuum pump. The second esterification kettle is a multi-chamber atmospheric pressure design, and the second esterification kettle distillation tower is designed separately. The independently developed side reaction inhibitor Lewis base is injected into the first subchamber of the second esterification kettle, and the molecular weight of the second esterification kettle is injected into the third subchamber of the second esterification kettle. 1,4-butylene adipate has a strong acidity. Therefore, the second esterification kettle body and all the internals of the kettle are preferably made of SUS316L material. The distillation tower of the second esterification kettle is long-term resistant to the strong acid corrosion of adipic acid, including the tower body and the internals are made of titanium, atmospheric pressure design, and the top reflux system is made of 316L material.

[0068] Recycling can be done using a dedicated recycling device. After recycling, the impurities in the 1,4-butanediol are removed and refined. The refined 1,4-butanediol can be added back to the raw material beating system for subsequent esterification and polymerization reactions.

[0069] Preferably, the distillation tower at the upper end of the second esterification kettle is arranged in the third sub-chamber from the front to the back of the second esterification kettle.

[0070] In some embodiments, the high-viscosity PBAT polymerization kettle further includes steam inlets for introducing superheated 1,4-butanediol vapor, located at the top of the main body at the rear end of the low-viscosity zone, the rear end of the medium-high viscosity zone, and the rear end of the high-viscosity zone. The preparation method further includes the step of metering the superheated 1,4-butanediol vapor using a metering system and introducing it into the high-viscosity PBAT polymerization kettle. This serves to form a gel-crosslinked carbonization in the upper portion of the rear reactor after the high-viscosity melt reactor has operated for a period of time. The 1,4-butanediol vapor inlet facilitates regular cleaning without stopping the reactor, maintaining the long-term operation capability of the device.

[0071] In some embodiments, the high-viscosity PBAT polymerization reactor is connected to a vacuum pump with a maximum vacuum of 60-75 Pa. The preparation method controls the vacuum pump's extraction rate to 85-230 kg / h, and the vacuum level during operation of the high-viscosity PBAT polymerization reactor is controlled to 90-150 Pa. This configuration can meet the production capacity requirements of 30,000 to 100,000 tons / year of high-viscosity PBAT polyester. According to experimental research data, the volatile matter generation rate of a high-viscosity (intrinsic viscosity of 1.05-1.16) PBAT final polymerization reactor is 1.5-2.2 times that of a conventional 0.92 viscosity PBAT polyester plant. The higher the high-viscosity outlet viscosity, the higher the non-condensable gas generation rate. Therefore, the vacuum pump extraction rate is designed to be 1.5-2.5 times that of a conventional polyester plant of the same production capacity. The vacuum pump extraction capacity is selected based on the production capacity of 30,000 to 100,000 tons / year, ranging from 70 to 220 kg / h. The design of the vacuum system of the device takes into account the harmfulness of tetrahydrofuran and adopts a fully enclosed design. A wastewater and waste gas neutralization device is also designed, and the wastewater and waste gas are sent to the stripping tower for treatment to meet emission standards.

[0072] In some embodiments, when used to prepare a high-viscosity PBAT melt, the preparation method further includes the step of introducing a heat stabilizer, an antioxidant, or a colorant into the second esterification kettle before the second esterification reaction; the heat stabilizer is selected from a combination of one or more of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, triphenyl phosphite, and triglyceride phosphate; the antioxidant is selected from a combination of one or more of antioxidant 168, antioxidant 1076, antioxidant 1010, antioxidant 1222, and benzothiazole antioxidants.

[0073] In some embodiments, the amount of the heat stabilizer or antioxidant is 500 to 1200 ppm based on the total mass of the high-viscosity PBT melt.

[0074] To ensure the high-viscosity PBT melt's excellent resistance to heat and thermal-oxidative degradation during esterification and polymerization melt transport, a thermal stabilizer and antioxidant are compounded. To enhance the stability of the high-viscosity PBT melt, these additives can be added to improve the melt's thermal stability and oxidation resistance, respectively. These thermal stabilizers and antioxidants are added to control the level of polymerization side reactions under high-temperature conditions. The antioxidant further reduces the risk of thermal degradation during melt transport caused by trace oxygen.

[0075] Thermal stabilizers and antioxidants are beneficial to reducing the viscosity drop level during the melt conveying process. For high-viscosity PBT melt conveying process, the pipeline residence time is 30 to 40 minutes, and the viscosity drop of high-viscosity PBT melt is effectively controlled between 0.050 and 0.105. The more optimized viscosity drop level is 0.075 to 0.095. Combined with the short-process melt conveying design, the optimal viscosity drop is 0.085 to 0.090. Compared with the existing viscosity drop of 0.150 to 0.235 of thickened high-viscosity PBT polyester, it can greatly reduce the original intrinsic viscosity of the melt and effectively improve product quality.

[0076] In some embodiments, a melt pump is used to transport the high-viscosity PBAT melt and the low-viscosity PET melt, and a melt cooler is provided at the outlet of the melt pump; the preparation method controls the temperature of the high-viscosity PBAT melt to 252-253° C. after cooling by the melt cooler; a filter and a booster pump are provided between the melt pump and the parallel composite spinning assembly; the preparation method controls the transport time of the high-viscosity PBAT melt to 40-50 minutes.

[0077] In some embodiments, the preparation method further includes the step of providing a screw propulsion pump between the high-viscosity PBAT melt outlet and the melt pump to propel the high-viscosity PBAT melt.

[0078] In some embodiments, the low-viscosity PET final polymerization kettle is a horizontal polymerization kettle, and its aspect ratio is 2.2-2.8:1.0.

[0079] In some embodiments, the aspect ratio of the high-viscosity PBAT polymerization kettle is 3.0 to 3.6:1.0. The high aspect ratio is conducive to distributing more disc reactors to increase the effective devolatilization area and improve the vacuum degree of the reactor, thereby increasing the viscosity of the PBAT melt and reducing the level of side reactions. It can also be combined with a high vacuum design to quickly increase the viscosity of the high-viscosity PBAT melt.

[0080] In some embodiments, the preparation method further includes the step of introducing a viscosity reducer into the high-viscosity PBAT melt before the high-viscosity PBAT melt passes through the filter; the viscosity reducer is selected from a combination of one or more of polyethylene terephthalate-1,4-cyclohexanedimethanol PETG, cationic dyeable polyester CDP, cationic dye-easy polyester ECDP, atmospheric pressure boiling dyeable polyester EDDP, polybutylene terephthalate PBAT, and polypropylene terephthalate-1,3-propylene glycol terephthalate PBAT.

[0081] In some embodiments, the amount of the viscosity reducer is 0.2% to 3.0% of the total mass of the melt, preferably 0.5 to 2.0%, and more preferably 0.8 to 1.5%. Adding the viscosity reducer can significantly reduce the kinematic viscosity of the high-viscosity melt, improve the melt conveying efficiency, and reduce process degradation.

[0082] In some embodiments, the molar ratio of terephthalic acid to 1,4-butanediol is 1:1.05-1.65.

[0083] In some embodiments, when used to prepare a high-viscosity PBAT melt, the first esterification reaction is carried out at 245° C. to 247° C.

[0084] In some embodiments, when used to prepare a high-viscosity PBAT melt, the second esterification reaction is carried out at 248° C. to 252° C.

[0085] In some embodiments, the prepolymerization reaction in the first prepolymerization kettle for preparing the high-viscosity PBAT melt is carried out at 250°C to 252°C.

[0086] In some embodiments, the prepolymerization reaction in the first prepolymerization kettle for preparing the high-viscosity PBAT melt is carried out at a pressure of 7 to 10 kPa.

[0087] In some embodiments, the prepolymerization reaction in the second prepolymerization kettle for preparing the high-viscosity PBAT melt is carried out at 251° C. to 252° C.

[0088] In some embodiments, the prepolymerization reaction in the second prepolymerization kettle for preparing the high-viscosity PBAT melt is carried out at a pressure of 0.5 to 1.5 kPa.

[0089] In some embodiments, the same spinning assembly is a composite spinning beam.

[0090] In some embodiments, the composite spinning beam includes a composite spinneret.

[0091] The present invention also provides a high-viscosity PBAT / low-viscosity PET two-component elastic fiber prepared by the above-mentioned preparation method.

[0092] In some embodiments, the bicomponent elastic fiber has a strength of 2.55 to 2.85 cN / dtex, a crimp shrinkage of 25% to 60%, and a crimp stability of 58% to 70%.

[0093] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0094] The present invention takes into account that the polymerization temperature of PBAT is low (generally: 248-255°C), the polymerization process generates adipic acid-1,4-butanediol copolymer block components, the melt polymerization atmosphere is highly acidic, and under the action of acidic catalysis, 1,4-butanediol is more likely to generate a by-product of tetrahydrofuran and its amount is large, the PBAT melt has good fluidity in the low viscosity area and low hanging efficiency, and high viscoelasticity in the high viscosity area, and is easy to stay on the disk for a long time. Therefore, for the design of the final polymerization reactor for melt direct spinning of high-viscosity PBAT melt, a parallel twin-axis disc design is adopted. Compared with the conventional front and back twin-axis disc reactor, it has higher devolatilization efficiency and greatly shortens the polymerization reaction time. The residence time of the high-viscosity polymerization reactor is 40% to 55% (80 to 120 minutes) of the conventional front and back twin-axis disc reactor design, the reaction speed is improved, the residence time is greatly reduced, the side reaction level is effectively suppressed, and the quality of the high-viscosity PBAT polyester melt is improved.

[0095] The high-viscosity PBAT final polymerization reactor of the present invention features a unique disc structure with parallel dual-axis discs. These discs are characterized by high mass transfer efficiency, with the two counter-rotating discs creating a highly efficient shearing effect, resulting in excellent self-cleaning. In the high-viscosity PBAT polymerization reactor, the discs in the front half of the reactor (the low-viscosity zone and the medium-high viscosity zone) are single discs with low spacing, suitable for rapidly increasing the viscosity of low-viscosity melts in the devolatilization area. The rear high-viscosity zone is designed with multiple sets of dual discs, employing a reinforced disc structure, to meet the need for significantly increased torque for high-viscosity melts.

[0096] The present invention utilizes two different polyester production lines to produce high-viscosity PBAT polyester and low-viscosity PET polyester respectively, and then transports the two melts with different viscosities to the same parallel composite spinning assembly through melt conveying. After composite spinning, high-viscosity PBAT / low-viscosity PET two-component elastic fibers are prepared, thereby realizing the preparation of melt-direct spinning high-viscosity PBAT / low-viscosity PET parallel elastic fibers.

[0097] In the present invention, a special polymerization catalyst is used. The polymerization catalyst is prepared by reacting a titanate with a protonic acid under anhydrous conditions, removing alcohol by-products, and dissolving the catalyst in 1,4-butanediol. The polymerization catalyst does not contain a Ti-OH group. The catalyst can significantly inhibit the hydrolysis of ordinary titanium-based catalysts in the polymerization stage, and thus significantly inhibit the occurrence of side reactions in the polymerization stage, which is beneficial to improving the high-viscosity PBAT melt performance and the final two-component elastic fiber performance.

[0098] In the present invention, the intrinsic viscosity of the high-viscosity PBAT melt can reach 1.05 to 1.30, and the intrinsic viscosity of the low-viscosity PET melt is 0.45 to 0.55. The viscosity of the high-viscosity PBAT melt is much higher than that of the prior art.

[0099] The bicomponent elastic fiber of the present invention has a strength of 2.5 to 2.85 cN / dtex, a crimp shrinkage of 25 to 60 percent, and a crimp stability of 58 to 70 percent, far exceeding the performance of existing bicomponent elastic fibers. The bicomponent elastic fiber of the present invention can be in various varieties, including FDY, POY, and DTY.

[0100] The preparation method of the present invention is used for industrial production of two-component elastic fibers, which can achieve a low-viscosity PET melt production capacity of 30,000 to 80,000 tons / year and a high-viscosity PBAT melt production capacity of 30,000 to 80,000 tons / year. When the product is melt-spun high-viscosity PBAT / low-viscosity PET two-component elastic fiber, the comprehensive device production capacity is 60,000 to 160,000 tons / year. BRIEF DESCRIPTION OF THE DRAWINGS

[0101] FIG1 is a schematic diagram of a two-line polymerization system used in the embodiment;

[0102] FIG2 is a schematic structural diagram of a high-viscosity PBAT polymerization kettle used in the embodiment;

[0103] FIG3 is a schematic structural diagram of a composite scraper in a high-viscosity PBAT polymerization reactor used in an embodiment;

[0104] Among them, 1-low viscosity zone, 2-medium and high viscosity zone, 3-high viscosity zone, 4-composite scraper, 5-disc scraper, 6-axial scraper, 7-wall scraper, 8-stirring shaft, 9-disc, 10-first esterification kettle, 11-second esterification kettle, 12-first prepolymerization kettle, 13-second prepolymerization kettle, 14-high viscosity PBAT polymerization kettle, 15-low viscosity PET final polymerization kettle, 16-melt pump. DETAILED DESCRIPTION

[0105] The above scheme is further described below with reference to specific examples. It should be understood that these examples are intended to illustrate the basic principles, main features, and advantages of the present invention, and the present invention is not limited in scope by the following examples. The implementation conditions used in the examples can be further adjusted according to specific requirements. The implementation conditions not specified are generally those used in routine experiments. Unless otherwise specified in the following examples, all raw materials were purchased commercially or prepared by conventional methods in the art.

[0106] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

[0107] The present invention will be further described below in conjunction with the accompanying drawings and preferred embodiments of the present invention. In the following embodiments, it should be noted that the "front" and "rear" directions in the terms are based on the flow direction of the material, and the direction in which the material flows first is the front, and the direction in which the material flows later is the rear. For example, in Figure 1, the "front" in the term refers to the left side in Figure 1, and the "rear" in the term refers to the right side in Figure 1. For example, in Figure 2, the "front" in the term refers to the left side in Figure 1, and the "rear" in the term refers to the right side in Figure 1. Therefore, the directions and positional relationships described in the present invention are only for the convenience of describing the invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific direction, only have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation to the present invention.

[0108] As shown in Figure 1, two production lines were used to prepare high-viscosity PBAT / low-viscosity PET bicomponent elastic fibers in the embodiment. The first production line produces a high-viscosity PBAT melt. As shown in the first row of Figure 1, this production line includes a five-reactor system consisting of a first esterification reactor 10, a second esterification reactor 11, a first prepolymerization reactor 12, a second prepolymerization reactor 13, and a high-viscosity PBAT polymerization reactor 14. The five reactors are connected by necessary pipelines and are connected to the necessary vacuum systems. A melt pump 16 and filters A and B are provided between the second prepolymerization reactor 13 and the high-viscosity PBAT polymerization reactor 14. In actual production processes, filters A and B are not activated at the same time. For example, filter A can be activated first, and after the system has been running for a period of time, filter B can be switched to use, at which time filter A can be cleaned.

[0109] The second production line produces low-viscosity PET melt, as shown in the second row of Figure 1. This line comprises a five-vessel system: a first esterification vessel 10, a second esterification vessel 11, a first prepolymerization vessel 12, a second prepolymerization vessel 13, and a low-viscosity PET final polymerization vessel 15. The five vessels are interconnected by necessary piping and are connected to the necessary vacuum systems. A melt pump 16 and filters A and B are located between the second prepolymerization vessel 13 and the low-viscosity PET final polymerization vessel 15. In actual production, filters A and B are not operated simultaneously. For example, filter A can be activated first, and after a period of operation, filter B can be switched to the system, allowing filter A to be cleaned.

[0110] As shown in FIG2 , the high-viscosity PBAT polymerization kettle 14 is a horizontal polymerization kettle comprising a main body containing a chamber. The main body comprises a low-viscosity zone 1, a medium-high-viscosity zone 2, and a high-viscosity zone 3, arranged in sequence along the axis of the high-viscosity PBAT polymerization kettle. The viscosity of the PBAT melt in these zones increases in sequence. The high-viscosity PBAT polymerization kettle 14 also comprises two stirring shafts 8 arranged parallel to the axis thereof, passing through the low-viscosity zone 1, the medium-high-viscosity zone 2, and the high-viscosity zone 3. The two stirring shafts 8 rotate in opposite directions and are each provided with a plurality of circular disks 9. The disks 9 are spaced 1.05-1.10 times the radius of the disks 9. The disks 9 on the two stirring shafts 8 partially overlap, ensuring that the disks on the two parallel shafts intersect with each other over a maximum area, resulting in efficient shear mixing.

[0111] The disc 9 in the low-viscosity zone 1 is a single-disc design (i.e., each disc 9 is not fixed to the adjacent disc 9 and is set separately), the disc 9 in the medium-high viscosity zone 2 is a single-disc design, and the disc 9 in the high-viscosity zone 3 is a double-disc design. Each double-disc group includes 8 to 12 spokes, which can meet the melt film drawing requirements under the high dynamic viscosity conditions of the high-viscosity zone. From the low-viscosity zone 1 to the medium-high viscosity zone 2 to the high-viscosity zone 3, the spacing between adjacent discs 9 increases successively; the spacing between adjacent discs 9 in the high-viscosity zone 3 is 60-100mm. Along the axial direction of the high-viscosity PBAT polymerization kettle 14 from front to back, the spacing between the disc groups of the double-discs in the high-viscosity zone 3 increases successively and is controlled at 120-200mm.

[0112] The total number of discs 9 in the low-viscosity zone 1 and the medium-high-viscosity zone 2 is 35-55, and the total number of discs 9 in the high-viscosity zone 3 is 20-30. The lengths of the low-viscosity zone 1, the medium-high-viscosity zone 2, and the high-viscosity zone 3 are each one-third the length of the high-viscosity PBAT polymerization kettle 14. The high-viscosity PBAT polymerization kettle 14 also includes a prepolymer inlet located at the front bottom of the low-viscosity zone 1 and a high-viscosity PBAT melt outlet located at the rear bottom of the high-viscosity zone 3. The high-viscosity PBAT melt outlet is bell-shaped.

[0113] As shown in Figure 3, the high viscosity area 1 is also provided with a composite scraper 4, which includes an axial scraper 6 for scraping the melt on the stirring shaft, a wall scraper 7 for scraping the melt on the inner wall of the high viscosity final polymerization kettle 14, a disk scraper 5 for scraping the melt on the disc, and a bottom scraper (not shown) for scraping the bottom of the polymerization kettle. The distance between the disk scraper 5 and the disc 9 is 55-75mm, which can ensure that the high viscosity melt has a good material flow effect under the condition of efficient devolatilization.

[0114] The first and second esterification reactors 10, 11, used to prepare the high-viscosity PBAT melt, are each equipped with a distillation column at their upper ends. The high-viscosity PBAT polymerization reactor 14 also includes steam inlets for superheated 1,4-butanediol vapor, located at the top of the main body in the middle of the medium-high viscosity zone 2, at the rear end of the medium-high viscosity zone 2, and at the rear end of the high viscosity zone 3.

[0115] The high-viscosity PBAT polymerization kettle 14 is connected to a vacuum pump, which is a liquid ring pump with a chilled water device at its inlet for cooling the gas. A melt pump transports the high-viscosity PBAT melt and the low-viscosity PET melt, and a melt cooler is provided at the melt pump outlet.

[0116] After the high-viscosity PBAT polymerization reactor 14 and before the same spinning assembly, a dynamic mixer and a filter are set; before the dynamic mixer, a viscosity reducer injection system is set.

[0117] Necessary melt pumps, vacuum pumps, conveying pipelines, etc. can be installed on the pipeline that serves as a connection between the five kettles on the two production lines.

[0118] The same spinning assembly is a composite spinning manifold, and the high-viscosity PBAT polymerization reactor 14 is set on the top of the composite spinning manifold to shorten the conveying distance of the melt, especially the high-viscosity PBAT melt. The composite spinning manifold contains a spinneret.

[0119] Example 1

[0120] This embodiment provides a method for preparing a high-viscosity PBAT / low-viscosity PET bicomponent elastic fiber, and the specific steps are as follows:

[0121] The preparation method of the polymerization catalyst used in this embodiment is as follows:

[0122] Tetrabutyl titanate and acetic acid are mixed and subjected to an exothermic reaction in a mass ratio of 1:1. After the reaction, a titanium tetraacetate complex and a large amount of n-butanol by-product are generated. The reaction system is vacuum-purified at 50° C. for 2.0 hours to remove the generated n-butanol. The system is cooled to room temperature, and 1,4-butanediol is injected into the reaction system with stirring to prepare a 1,4-butanediol solution of a polymerization catalyst. The injection amount of 1,4-butanediol is controlled so that the titanium content in the polymerization catalyst solution is 1.0%.

[0123] The polymerization devices of the above two production lines are used to synthesize high-viscosity PBAT melt and low-viscosity PET melt respectively.

[0124] For the high-viscosity PBAT melt production line, the device includes a beating kettle, a first esterification kettle (with a distillation tower at the top), a second esterification kettle (three-chamber structure, with a distillation tower at the top), a first prepolymerization kettle, a second prepolymerization kettle, a high-viscosity PBAT polymerization kettle and a supporting vacuum system and melt conveying system, as well as an esterification-prepolymerization system for synthesizing 1,4-butylene adipate prepolymer (PBA) not shown in Figure 1, which can be a batch reactor, including an esterification stage and a prepolymerization stage.

[0125] For the low-viscosity PET melt production line, the equipment includes a beating kettle, a first esterification kettle, a second esterification kettle, a first prepolymerization kettle, a second prepolymerization kettle, a low-viscosity PET final polymerization kettle, and a matching vacuum system and melt conveying system.

[0126] Synthetic high-viscosity PBAT melt:

[0127] Purified terephthalic acid and 1,4-butanediol were sequentially subjected to a first esterification reaction in a first esterification reactor and a second esterification reaction in a second esterification reactor. Prior to the second esterification reaction, PBA with a number-average molecular weight of 1800 was added to the third chamber of the second esterification reactor. This PBA and the product of the first esterification reaction continued to undergo a second esterification reaction, followed by prepolymerization and polymerization. The reaction system then underwent prepolymerization in both the first and second prepolymerization reactors to produce a PBAT prepolymer. The PBAT prepolymer was then polymerized in a high-viscosity PBAT polymerization reactor to produce a high-viscosity PBAT melt. The molar ratio of purified terephthalic acid to 1,4-butanediol was 1:1.25. The molar ratio of adipic acid monomer units to terephthalic acid in the 1,4-butanediol adipate prepolymer was 45:55. The esterification temperature in the first esterification kettle was 245°C to 247°C, and esterification was carried out at a pressure of 40 to 60 kPa (this pressure refers to the actual pressure in the first esterification kettle, which is lower than atmospheric pressure, meaning that the first esterification kettle is actually a reduced-pressure reaction). The esterification temperature in the second esterification kettle was 248°C to 252°C, and esterification was carried out at atmospheric pressure. An esterification catalyst, TOT (tetrakis(2-ethylhexyloxy)titanate) produced by Nippon Soda Co., Ltd., was added to the first esterification kettle in an amount such that the mass of the titanium element in it reached 30 ppm based on the mass of the melt. The polymerization catalyst prepared above was introduced into the bottom of the first prepolymerization kettle in an amount such that the mass of the titanium element in it reached 70 ppm based on the mass of the melt. The reaction temperature in the first prepolymerization reactor was 250-252°C, with a vacuum of 9.9 kPa; the reaction temperature in the second prepolymerization reactor was 251-252°C, with a vacuum of 1.05 kPa. The melt outlet temperature of the high-viscosity PBAT reactor was 252.0°C, and the vacuum in the reactor was 135 Pa. Superheated 1,4-butanediol was injected into the steam feed port of the high-viscosity PBAT reactor via a steam jet pump. To precisely separate the large amount of tetrahydrofuran produced during the polymerization process, a large-capacity chilled water exchanger was placed upstream of the vacuum liquid ring pump. The high-viscosity PBAT melt discharged from the reactor outlet had an intrinsic viscosity of 1.198 and a dynamic viscosity of 615 Pa·s. These intrinsic viscosities were measured at 25°C in a 3:2 volume ratio mixture of phenol and tetrachloroethane. The dynamic viscosity was measured at 252°C.

[0128] Synthetic low-viscosity PET melt:

[0129] Purified terephthalic acid and ethylene glycol are sequentially subjected to an esterification reaction in a first and second esterification reactors, followed by a prepolymerization reaction in a first and second prepolymerization reactors to produce a PET prepolymer. The PET prepolymer is then polymerized in a low-viscosity PET final polymerization reactor to produce a low-viscosity PET melt. The catalysts for both esterification and polymerization are ethylene glycol antimony, used in an amount such that the antimony content is 210 ppm relative to the total mass of the PET melt. This catalyst is added to the reaction system in the first esterification reactor. The first esterification reactor performs pressure esterification, while the second esterification reactor performs atmospheric pressure esterification. By adjusting the reaction conditions (including the vacuum level, stirring rate, and polymerization temperature of the low-viscosity PET final polymerization vessel, controlling the vacuum level to 160-200 Pa, stirring rate to 3.5-5.5 rpm in the low-viscosity zone (front chamber), 2.0-3.5 rpm in the medium-high viscosity and high-viscosity zones (back chamber), and polymerization temperature to 272-275°C), a low-viscosity PET melt with an intrinsic viscosity of 0.452 and a dynamic viscosity of 90 Pa.s was obtained. This intrinsic viscosity was measured at 25°C in a 3:2 volume ratio mixture of phenol and tetrachloroethane. The dynamic viscosity was measured at 275°C.

[0130] Spinning:

[0131] Finally, the high-viscosity PBAT melt and the low-viscosity PET melt are transported to the composite spinning manifold at a mass ratio of 5:5, and spun through the composite spinning spinneret to obtain a high-viscosity PBAT / low-viscosity PET two-component elastic fiber.

[0132] The reaction conditions, parameters of high-viscosity PBAT melt, and low-viscosity PET melt are shown in Tables 1-5, where "-" indicates none.

[0133] Example 2-13

[0134] Example 2-13 provides a method for preparing a high-viscosity PBAT / low-viscosity PET bicomponent elastic fiber. The specific steps are essentially the same as those in Example 1, with the following differences: when synthesizing the high-viscosity PBAT melt, the parameters of the high-viscosity PBAT melt are adjusted by adjusting the reaction conditions (including the vacuum level of the high-viscosity PBAT polymerization reactor, the stirring rate in the low-viscosity zone, the stirring rates in the medium-high-viscosity zone and the high-viscosity zone, the inlet temperature of the PBAT prepolymer melt (PBAT low-viscosity melt), and the residence time of the material in the final polymerization reactor). When synthesizing the low-viscosity PET melt, the parameters of the low-viscosity PET melt are adjusted by adjusting the reaction conditions (including the vacuum level of the low-viscosity PET final polymerization reactor, the stirring rate of the low-viscosity PET final polymerization reactor, and the polymerization temperature of the low-viscosity PET final polymerization reactor). Furthermore, during polymerization, triethanolamine, a Lewis base and side reaction inhibitor, is introduced into the first chamber from the front to the rear of the second esterification reactor, with the mass of triethanolamine accounting for 160 ppm of the mass of the high-viscosity PBAT melt. The reaction conditions, parameters of the high-viscosity PBAT melt, and parameters of the low-viscosity PET melt are shown in Tables 1-5.

[0135] Example 14

[0136] Example 14 provides a method for preparing a high-viscosity PBAT / low-viscosity PET bicomponent elastic fiber. The specific steps are basically the same as those in Example 1, except that: when synthesizing the high-viscosity PBAT melt, the parameters of the high-viscosity PBAT melt are adjusted by adjusting the reaction conditions (including the vacuum degree of the high-viscosity PBAT polymerization kettle, the stirring rate of the low-viscosity zone, the stirring rate of the medium-high viscosity zone and the high-viscosity zone, the inlet temperature of the PBAT prepolymer melt (PBAT low-viscosity melt), the residence time of the final polymerization kettle material, etc.); when synthesizing the low-viscosity PET melt, the reaction conditions (including the vacuum degree of the low-viscosity PET final polymerization kettle, the stirring rate of the low-viscosity PET final polymerization kettle, ... The parameters of the low-viscosity PET melt were adjusted by adjusting the polymerization temperature of the final PET reactor. During polymerization, a Lewis base (triethanolamine) was introduced into the first chamber of the second esterification reactor (from front to back) to suppress side reactions. The amount of triethanolamine, representing 160 ppm of the high-viscosity PBAT melt, was added from the viscosity reducer injection system. The specific viscosity reducer was an amorphous polyester with an intrinsic viscosity of 0.55 (measured at 25°C using a 3:2 volume ratio of phenol:tetrachloroethane) at a dosage of 0.5% relative to the total melt mass. The reaction conditions, parameters for the high-viscosity PBAT melt, and the low-viscosity PET melt are shown in Tables 1-5.

[0137] Example 15

[0138] Example 15 provides a method for preparing a high-viscosity PBAT / low-viscosity PET bicomponent elastic fiber. The specific steps are basically the same as those in Example 1, except that: when synthesizing the high-viscosity PBAT melt, the parameters of the high-viscosity PBAT melt are adjusted by adjusting the reaction conditions (including the vacuum degree of the high-viscosity PBAT polymerization kettle, the stirring rate of the low-viscosity zone, the stirring rate of the medium-high viscosity zone and the high-viscosity zone, the inlet temperature of the PBAT prepolymer melt (PBAT low-viscosity melt), the residence time of the final polymerization kettle material, etc.); when synthesizing the low-viscosity PET melt, the reaction conditions (including the vacuum degree of the low-viscosity PET final polymerization kettle, the stirring rate of the low-viscosity PET final polymerization kettle, ... The parameters of the low-viscosity PET melt were adjusted by adjusting the polymerization temperature of the final PET reactor. During polymerization, a Lewis base (triethanolamine) was introduced into the first chamber of the second esterification reactor (from front to back) to suppress side reactions. The amount of triethanolamine, representing 160 ppm of the high-viscosity PBAT melt, was added from the viscosity reducer injection system. The specific viscosity reducer was an amorphous polyester with an intrinsic viscosity of 0.58 (measured at 25°C using a 3:2 volume ratio of phenol to tetrachloroethane). The dosage was 0.8% of the total melt mass. The reaction conditions, parameters of the high-viscosity PBAT melt, and the low-viscosity PET melt are shown in Tables 1-5.

[0139] Comparative Example 1

[0140] Comparative Example 1 provides a method for preparing a melt-spun high-viscosity PET / low-viscosity PET bicomponent elastic fiber. This method utilizes a six-reactor polymerization apparatus comprising a first esterification reactor, a second esterification reactor, a first prepolymerization reactor, a second prepolymerization reactor, and a high-viscosity final polymerization reactor and a low-viscosity final polymerization reactor, each connected to the second prepolymerization reactor. The high-viscosity PET melt obtained in the high-viscosity final polymerization reactor and the low-viscosity PET melt obtained in the low-viscosity final polymerization reactor are simultaneously melt-fed to the same spinning assembly for parallel spinning. The second esterification reactor is provided with three compartments.

[0141] Specifically, terephthalic acid, ethylene glycol, and an antimony ethylene glycol catalyst are sequentially subjected to an esterification reaction in a first esterification kettle and a second esterification kettle, followed by a prepolymerization reaction in a first prepolymerization kettle and a second prepolymerization kettle to produce an ethylene terephthalate prepolymer. Prior to the second esterification reaction in the second esterification kettle, a conventional titanium dioxide matting agent paste (prepared by grinding and dispersing titanium dioxide and ethylene glycol, with titanium dioxide accounting for 10% by weight and ethylene glycol accounting for 90% by weight) is added to a chamber of the second esterification kettle via a corresponding pipeline. The molar ratio of terephthalic acid to ethylene glycol is 1:1.25, the catalyst is used in an amount such that the antimony element accounts for 210 ppm of the total mass of the melt, and the matting agent is used in an amount such that the titanium dioxide accounts for 0.3% of the total mass of the melt. The ethylene terephthalate prepolymer was then passed through a high-viscosity final polymerization reactor and a low-viscosity final polymerization reactor for polymerization, respectively, to produce high-viscosity PET melt and low-viscosity PET melt. Finally, the high-viscosity PET melt and the low-viscosity PET melt were directly passed through the same parallel composite spinning beam at a mass ratio of 5:5 for spinning to produce PET bicomponent elastic fiber. The parameters of the high-viscosity PET melt and the low-viscosity PET melt are shown in Table 3-5.

[0142] Comparative Example 2

[0143] Comparative Example 2 provides a method for preparing a chip-spun high-viscosity PTT / low-viscosity PET bicomponent elastic fiber. Specifically, high-viscosity PTT and low-viscosity PET melt chips are pre-crystallized and then melted using a dry screw. The two melts are then directly introduced into a parallel composite spinning manifold at a mass ratio of 5:5 for spinning to produce a chip-spun bicomponent elastic fiber. The properties of the corresponding chips are shown in Tables 3-5. Both the high-viscosity PTT and low-viscosity PET chips were commercially available and did not contain a matting agent.

[0144] Comparative Example 3

[0145] Comparative Example 3 provides a method for preparing a chip-spun bicomponent elastic fiber composed of high-viscosity EDDP (disperse dye atmospherically metadyed polyester) and low-viscosity PET. Specifically, high-viscosity EDDP and low-viscosity PET melt chips are pre-crystallized and melted using a dry screw. The two melts are then directly introduced into a parallel composite spinning manifold at a mass ratio of 5:5 for spinning, yielding the chip-spun bicomponent elastic fiber. The properties of the resulting chips are shown in Tables 3-5.

[0146] Table 1 Test indicators of high-viscosity PBAT polyester ester materials

[0147] Table 2 Test indicators of high-viscosity PBAT prepolymer second reactor materials

[0148] Table 3 Test indicators of high viscosity PBAT polyester chips

[0149] Table 4 Physical and chemical indicators of low-viscosity PET polyester chips

[0150] Table 5 High-viscosity PBAT polymerization reactor control data and related indicators of high-viscosity PBAT and low-viscosity PET

[0151] The properties of the composite elastic fibers obtained by spinning the high-viscosity melt and low-viscosity PET melt corresponding to Examples 1-15 and Comparative Examples 1-3 are shown in Table 6, wherein the fiber type is FDY and the specification is 83dtex / 36f.

[0152] Table 6 Physical and chemical indicators of PBAT / PET two-component composite elastic fibers

[0153] It can be seen that the present invention utilizes two different polyester production lines to produce high-viscosity PBAT polyester and low-viscosity PET polyester respectively, and then transports the two melts with different viscosities to the same parallel composite spinning assembly through melt conveying. After composite spinning, high-viscosity PBAT / low-viscosity PET two-component elastic fibers are prepared, thereby realizing the preparation of melt-spinning high-viscosity PBAT / low-viscosity PET parallel elastic fibers, and the obtained fibers have excellent performance.

[0154] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the present invention and implement it accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent variations or modifications based on the spirit and essence of the present invention are intended to be encompassed by the scope of protection of the present invention.

Claims

1. A high-viscosity PBAT polymerization kettle, which is used to prepare a high-viscosity PBAT melt, and the high-viscosity PBAT melt is used to prepare high-viscosity PBAT / low-viscosity PET bicomponent elastic fibers, and is characterized in that: The high-viscosity PBAT polymerization kettle is a horizontal polymerization kettle, and includes a main body with a chamber inside. The main body includes a low-viscosity zone, a medium-high-viscosity zone, and a high-viscosity zone arranged in sequence along the axis of the high-viscosity PBAT polymerization kettle. The viscosities of the PBAT melt in the low-viscosity zone, the medium-high-viscosity zone, and the high-viscosity zone increase in sequence; the high-viscosity PBAT polymerization kettle also includes two stirring shafts arranged parallel to its axis and passing through the low-viscosity zone, the medium-high-viscosity zone, and the high-viscosity zone. The rotation directions of the two stirring shafts are opposite, and multiple discs are arranged on both stirring shafts. The outer periphery of the disc is circular. The distance between the two stirring shafts is 1.05-1.10 times the radius of the disc, and the discs on the two stirring shafts partially overlap.

2. The high-viscosity PBAT polymerization kettle according to claim 1, wherein: The discs in the low-viscosity zone are of single-disc design, the discs in the medium-high-viscosity zone are of single-disc design, and the discs in the high-viscosity zone are of double-disc design. Each group of double-disc group design includes 8-12 spokes.

3. The high-viscosity PBAT polymerization kettle according to claim 1, wherein: From the low-viscosity zone to the medium-high-viscosity zone to the high-viscosity zone, the spacing between two adjacent discs increases in sequence; the spacing between two adjacent discs in the high-viscosity zone is 60-100 mm; and / or, along the axis of the high-viscosity PBAT polymerization kettle from front to back, the spacing between the disc groups of the double-discs in the high-viscosity zone increases in sequence and is controlled within 120-200 mm.

4. The high-viscosity PBAT polymerization kettle according to claim 1, characterized in that: The total number of discs in the low-viscosity zone and the medium-high-viscosity zone is 35-55, and the total number of discs in the high-viscosity zone is 20-30; and / or, the lengths of the low-viscosity zone, the medium-high-viscosity zone, and the high-viscosity zone are all one-third of the length of the high-viscosity PBAT polymerization kettle; and / or, the high-viscosity PBAT polymerization kettle also includes a prepolymer inlet at the bottom of the front end of the low-viscosity zone and a high-viscosity PBAT melt outlet at the bottom of the rear end of the high-viscosity zone. The high-viscosity PBAT melt outlet is in the shape of a flared mouth.

5. The high-viscosity PBAT polymerization kettle according to claim 1, wherein: Composite scrapers are also arranged on both sides between the double-disc groups in the high-viscosity zone. The composite scraper includes an axial scraper for scraping the melt on the stirring shaft, a wall scraper for scraping the melt on the inner wall of the high-viscosity PBAT polymerization kettle, a disc scraper for scraping the melt on the disc, and a bottom scraper for scraping the bottom of the polymerization kettle. The distance between the disc scraper and the disc is 55-75 mm.

6. A preparation method of a high-viscosity PBAT / low-viscosity PET bicomponent elastic fiber, the bicomponent elastic fiber containing a high-viscosity PBAT component and a low-viscosity PET component, the viscosity of the high-viscosity PBAT component being greater than the viscosity of the low-viscosity PET component, characterized in that: The preparation method includes the steps of separately preparing a high-viscosity PBAT melt and a low-viscosity PET melt, and spinning the high-viscosity PBAT melt and the low-viscosity PET melt through the same coaxial composite spinning assembly to obtain the bicomponent elastic fiber; the viscosity of the high-viscosity PBAT melt is greater than that of the low-viscosity PET melt; the step of preparing the high-viscosity PBAT melt includes subjecting terephthalic acid and 1,4-butanediol to a first esterification reaction in a first esterification kettle, a second esterification reaction in a second esterification kettle, and prepolymerization reactions in a first prepolymerization kettle and a second prepolymerization kettle to obtain a PBAT prepolymer, and during the second esterification reaction, adding an adipic acid-1,4-butanediol ester prepolymer to the second esterification kettle, and subjecting the PBAT prepolymer to a polymerization reaction in a high-viscosity PBAT polymerization kettle to obtain the high-viscosity PBAT melt, where the high-viscosity PBAT polymerization kettle is the high-viscosity PBAT polymerization kettle according to any one of claims 1-5; the step of preparing the low-viscosity PET melt includes subjecting terephthalic acid and ethylene glycol to esterification reactions in a first esterification kettle and a second esterification kettle in sequence, and prepolymerization reactions in a first prepolymerization kettle and a second prepolymerization kettle to obtain a PET prepolymer, and subjecting the PET prepolymer to a polymerization reaction in a low-viscosity PET final polymerization kettle to obtain the low-viscosity PET melt.

7. The preparation method according to claim 6, characterized in that: By mass percentage, the bicomponent elastic fiber contains 30%-70% of a high-viscosity PBAT component and 70%-30% of a low-viscosity PET component; and / or, the intrinsic viscosity of the high-viscosity PBAT melt at 25°C is 1.05-1.30, and the dynamic viscosity at 252°C is 315-905 Pa·s; the intrinsic viscosity of the low-viscosity PET melt at 25°C is 0.45-0.55, and the dynamic viscosity at 275°C is 90-240 Pa·s.

8. The preparation method according to claim 6, characterized in that: In the same coaxial composite spinning assembly, the dynamic viscosity of the high-viscosity PBAT melt at 252°C is 270-650 Pa·s, and the dynamic viscosity of the low-viscosity PET melt at 274°C is 70-220 Pa·s.

9. The preparation method according to claim 6, characterized in that: The number-average molecular weight of the adipic acid-1,4-butanediol ester prepolymer is 1600-2500; and / or, the adipic acid-1,4-butanediol ester prepolymer is prepared by esterification and prepolymerization of adipic acid and 1,4-butanediol; and / or, the molar ratio of the adipic acid monomer unit in the adipic acid-1,4-butanediol ester prepolymer to the molar amount of terephthalic acid is 45-55:45-55.

10. The preparation method according to claim 9, characterized in that: The esterification and prepolymerization of adipic acid and 1,4-butanediol are carried out in the presence of a protonic acid catalyst.

11. The preparation method according to claim 6, characterized in that: The esterification reaction in the first esterification kettle for preparing high-viscosity PBAT melt is carried out under an absolute pressure of 40-60 kPa; and / or, the esterification reaction in the second esterification kettle for preparing high-viscosity PBAT melt is carried out under normal pressure; and / or, the second esterification kettle for preparing high-viscosity PBAT melt is a horizontal reaction kettle and includes three compartments arranged in sequence from front to back. Preferably, when preparing high-viscosity PBAT melt, the preparation method further includes the step of adding a side reaction inhibitor to the first compartment from front to back of the second esterification kettle, and the side reaction inhibitor is a Lewis base.

12. The preparation method according to claim 11, characterized in that: The Lewis base is selected from one or a combination of triethanolamine, quaternary ammonium salt, ethylenediaminetetraacetic acid, sodium acetate, sodium benzoate, sodium formate, potassium succinate, lithium acetate and zinc acetate; and / or, the mass of the Lewis base is 50-500 ppm of the mass of the high-viscosity PBAT melt.

13. The preparation method according to claim 6, characterized in that: When preparing high-viscosity PBAT melt, the preparation method further includes the step of adding an esterification catalyst to the first esterification kettle before carrying out the first esterification reaction, and the esterification catalyst is selected from tetrabutyl titanate, tetraisopropyl titanate or tetra(2-ethylhexoxy) titanate.

14. The preparation method according to claim 6, characterized in that: When preparing high-viscosity PBAT melt, the preparation method further includes the step of introducing a polymerization catalyst into the first prepolymerization kettle before carrying out the prepolymerization reaction.

15. The preparation method according to claim 14, characterized in that: The polymerization catalyst is prepared by reacting a titanate with a protonic acid under anhydrous conditions, removing alcohol by-products, and dissolving in 1,4-butanediol.

16. The preparation method according to claim 14, characterized in that: The titanate is selected from tetrabutyl titanate, tetraisopropyl titanate or tetra(2-ethylhexoxy) titanate; and / or, the protonic acid is selected from one or a combination of formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, citric acid, tripolyphosphoric acid and polyphosphoric acid; and / or, the mass ratio of the titanate to the protonic acid is 1:0.5-2.0; and / or, in the polymerization catalyst, the mass percentage of titanium element is 1.0%-3.0%.

17. The preparation method according to claim 13 or 14, characterized in that: The mass of titanium element in the esterification catalyst accounts for 30-40 ppm of the mass of the high-viscosity PBAT melt; and / or, the mass of titanium element in the polymerization catalyst accounts for 50-70 ppm of the mass of the high-viscosity PBAT melt.

18. The preparation method according to claim 6, characterized in that: The intrinsic viscosity of the PBAT prepolymer introduced into the high-viscosity PBAT polymerization kettle is 0.300-0.360; and / or, the residence time of the material in the high-viscosity PBAT polymerization kettle is 75-120 min.

19. The preparation method according to claim 11, characterized in that: When preparing high-viscosity PBAT melt, the adipic acid-1,4-butanediol ester prepolymer is added to the second esterification kettle from the third compartment from front to back of the second esterification kettle.

20. The preparation method according to claim 6, characterized in that: Rectifying towers are arranged at the upper ends of the first esterification kettle and the second esterification kettle for preparing high-viscosity PBAT melt. The preparation method further includes the steps of taking out a mixture of water and tetrahydrofuran from the top of the two rectifying towers and taking out 1,4-butanediol from the bottom of the tower; preferably, the preparation method further includes the step of separating the mixture of water and tetrahydrofuran through a rectifying tower to obtain tetrahydrofuran; preferably, the preparation method further includes the step of recovering the taken-out 1,4-butanediol.

21. The preparation method according to claim 6, characterized in that: The high-viscosity PBAT polymerization kettle further includes a steam inlet for introducing superheated 1,4-butanediol steam at the rear ends of the low-viscosity zone, the medium-high viscosity zone, and the high-viscosity zone at the top of the main body. The preparation method further includes a step of metering the superheated 1,4-butanediol steam by a metering system and introducing it into the high-viscosity PBAT polymerization kettle.

22. The preparation method according to claim 6, characterized in that: The high-viscosity PBAT polymerization kettle is connected to a vacuum pump. The ultimate vacuum degree of the vacuum pump is 60-75 Pa. The preparation method controls the air extraction volume of the vacuum pump to be 85-230 kg / h, and controls the vacuum degree during the operation of the high-viscosity PBAT polymerization kettle to be 90-150 Pa.

23. The preparation method according to claim 6, characterized in that: A melt pump is used to transport the high-viscosity PBAT melt and the low-viscosity PET melt, and a melt cooler is arranged at the outlet of the melt pump; the preparation method controls the temperature of the high-viscosity PBAT melt after being cooled by the melt cooler to be 252-253 °C; a filter and a booster pump are arranged between the melt pump and the co-extrusion spinning assembly; the preparation method controls the transportation time of the high-viscosity PBAT melt to be 40-50 min.

24. The preparation method according to claim 23, characterized in that: The preparation method further includes a step of arranging a screw booster pump between the outlet of the high-viscosity PBAT melt and the melt pump to boost the high-viscosity PBAT melt.

25. The preparation method according to claim 6, characterized in that: The low-viscosity PET final polymerization kettle is a horizontal polymerization kettle, and its aspect ratio is 2.2-2.8:1.

0.

26. The preparation method according to claim 6, characterized in that: The preparation method further includes a step of introducing a viscosity reducer into the high-viscosity PBAT melt before the high-viscosity PBAT melt passes through the filter; the viscosity reducer is selected from one or a combination of polyethylene terephthalate-1,4-cyclohexanedimethanol ester PETG, cationic dyeable polyester CDP, cationic dye easily dyeable polyester ECDP, atmospheric boiling dyeable polyester EDDP, polybutylene terephthalate PBAT, and poly(trimethylene terephthalate) PBAT.

27. The preparation method according to claim 6, characterized in that: The molar ratio of terephthalic acid to 1,4-butanediol is 1:1.05-1.65; and / or, when preparing the high-viscosity PBAT melt, the first esterification reaction is carried out at 245 °C-247 °C.

28. The preparation method according to claim 6, characterized in that: When preparing the high-viscosity PBAT melt, the second esterification reaction is carried out at 248 °C-252 °C; and / or, the prepolymerization reaction in the first prepolymerization kettle for preparing the high-viscosity PBAT melt is carried out at 250 °C-252 °C; and / or, the prepolymerization reaction in the first prepolymerization kettle for preparing the high-viscosity PBAT melt is carried out under a pressure of 7-10 kPa; and / or, the prepolymerization reaction in the second prepolymerization kettle for preparing the high-viscosity PBAT melt is carried out at 251 °C-252 °C; and / or, the prepolymerization reaction in the second prepolymerization kettle for preparing the high-viscosity PBAT melt is carried out under a pressure of 0.5-1.5 kPa.

29. A high-viscosity PBAT / low-viscosity PET bicomponent elastic fiber prepared by the preparation method according to any one of claims 6 to 28.

30. The high-viscosity PBAT / low-viscosity PET two-component elastic fiber according to claim 29, wherein: The strength of the bicomponent elastic fiber is 2.55-2.85 cN / dtex, the crimp shrinkage rate is 25%-60%, and the crimp stability is 58%-70%.

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