A method for preparing PA6 / PBT composite fibers by melt direct spinning

Abstract

This invention discloses a method for preparing PA6 / PBT composite fibers through melt spinning, comprising the steps of: devolatilizing PA6 condensate to obtain PA6 melt; subjecting PBT condensate to liquid-phase thickening and segmented temperature control to obtain PBT melt; separately feeding the PA6 melt and PBT melt into a composite spinning assembly for melt spinning; and cooling, oiling, drawing, and winding the fibers to obtain the PA6 / PBT composite fibers. This invention combines amine end-capping agents, the devolatilization process of PA6 condensate, and solid-phase thickening of PBT to reduce the extractable content of PA6 melt while controlling the content of terminal amino groups, thereby improving the bonding ability with PBT melt under the action of a compatibilizer. The resulting composite fiber possesses the advantages of both PA6 and PBT, exhibiting a soft hand feel, excellent dyeing performance, strong bonding, good abrasion resistance, and excellent elasticity, making it widely applicable in the textile and other industrial fields.

Description

Technical Field

[0001] This invention relates to the field of spinning technology, specifically to a method for preparing PA6 / PBT composite fibers by melt direct spinning. Background Technology

[0002] Composite fibers are fibers containing two or more immiscible polymer fibers on the same cross-section. They can be used in fillers, fabrics, nonwovens, medical and hygiene products, and other fields. Composite fiber manufacturing technology can be used to obtain bicomponent or multicomponent composite fibers that combine the properties of two or more polymers.

[0003] Polyamide 6 (PA6) fiber is widely used in the textile industry due to its high strength and excellent dyeability and processability. However, PA6 lacks elasticity, so it is generally blended with spandex to increase elasticity. But spandex is not only expensive but also has poor chlorine and heat resistance during production, and its elasticity is lost during dyeing and at high temperatures. Polybutylene terephthalate (PBT) fiber is soft, easy to dye, and possesses good durability, dimensional stability, and elasticity. Its elastic recovery rate is superior to polyester, making it particularly suitable for making high-elasticity textiles such as swimwear, bodysuits, and tights. Replacing spandex with PBT in combination with PA6 creates a functional composite that achieves complementary advantages, improving the fiber's mechanical properties and elasticity. This results in a composite fiber that is soft to the touch, has good abrasion resistance, and excellent elasticity, meeting or even exceeding the requirements of the textile industry.

[0004] Due to limitations in production technology and other factors, the production of PA6 / PBT composite fibers is generally carried out using a chip intermittent spinning process both domestically and internationally. This involves first producing PA6 chips with a relative viscosity of 2.4-2.8 and PBT chips with an intrinsic viscosity of 0.7-1.15 dl / g. The PA6 chips are then extracted, dried, conveyed, and melted by screw extrusion. The PBT chips are conveyed, crystallized, dried, and melted by screw extrusion. After being metered and conveyed by different metering pumps through their respective pipelines, they enter the same composite spinning assembly for spinning and forming.

[0005] For example, Chinese patent application CN117512793A discloses a "PBT / PA6 core-sheath bicomponent composite spun monofilament and its preparation method," which uses two types of chips, respectively, through screw extrusion melting and spinning, to finally obtain PBT / PA6 composite fibers. The PBT material forms the sheath, while the binder and PA6, after being melted by the screw, form the core. The binder provides cohesive and adhesive forces, ensuring good compatibility between the PBT sheath and the PA6 core, reducing the risk of delamination between the sheath and core. However, this process for producing PA6 / PBT composite fibers involves high equipment investment costs, complex processes, long raw material turnover cycles, high energy consumption, and small production scale. Furthermore, adding the binder after remelting the chips can easily disrupt the polymer molecular structure and entanglement, potentially leading to uneven binder dispersion, poor compatibility between the sheath and core, and poor product quality stability. Therefore, achieving direct melt spinning is a major trend in the development of composite fibers. The key to achieving direct melt spinning of polyester-nylon composite fibers lies in preparing PA6 melt and PBT melt that can be directly spun.

[0006] Currently, in the production process of PA6 fiber, the high fiber tension and the presence of bubbles or impurities can cause monofilament breakage. Therefore, PA6 spinning requires high-quality melts, with the content of hot-water extractables in the melt needing to be below 2 wt%. The conversion rate of caprolactam hydrolysis polymerization is generally around 90%, meaning that approximately 10% of caprolactam monomers and oligomers (also known as hot-water extractables, of which monomers account for about 75% and oligomers about 25%) remain in the polymer. These impurities in the melt significantly affect spinning, especially the caprolactam monomers, whose boiling point is close to the spinning temperature. These monomers easily form bubbles during spinning, leading to melt collapse and volatilization, forming fumes. Therefore, before PA6 spinning, the chips need to undergo extraction treatment. According to FZ / T51004-2011, the hot-water extractable content of PA6 chips should be less than 0.5 wt% (superior grade). Currently, the industry commonly uses continuous hot-water extraction processes to remove monomers and oligomers from PA6 chips, ensuring that the extractable content in the chips is below 0.5 wt%, meeting the requirements for high-speed spinning.

[0007] Methods for producing PA6 fibers through direct melt spinning are rarely mentioned. Chinese patent application CN111424328A discloses a method for direct melt spinning of nylon that includes gas phase extraction and liquid phase extraction. It uses acids as end-capping agents and achieves direct melt spinning of nylon 6 through devolatilization in a thin-film reactor. However, the addition of acids as end-capping agents will significantly reduce the content of terminal amino groups in the melt after devolatilization, resulting in a lower dye uptake rate during subsequent dyeing and a lighter color after dyeing compared to conventional chip spinning.

[0008] Currently, the traditional production process for PBT fibers involves spinning PBT resin chips, specifically through the drying and remelting of the PBT chips. Melt spinning technology for PBT fibers is still under investigation. The main problem lies in the poor thermal stability of PBT, which undergoes significant thermal degradation during high-temperature transport in melt pipes. This results in the melt failing to spin or producing fibers with unsatisfactory mechanical properties once it enters the spinning box, thus limiting the development of PBT melt spinning technology. Summary of the Invention

[0009] This invention addresses the problems of complex processes and insufficient mechanical strength of composite fiber melt direct spinning in existing technologies by providing a method for preparing PA6 / PBT composite fibers through melt direct spinning. This method enables direct spinning after polymerization of polyamide melt and polyester melt, eliminating the need for pre-processing into chips. It produces PA6 / PBT composite fibers with excellent peel resistance and dyeability, and offers advantages such as reduced production energy consumption, smaller footprint, simplified process flow, significantly shortened production cycle, lower equipment investment costs, and stable product quality.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing PA6 / PBT composite fibers by melt spinning includes the following steps: S1, mix raw materials containing caprolactam, end-capping agent, water and catalyst A, and obtain PA6 condensate through ring-opening reaction and condensation reaction, and then devolatilize to obtain PA6 melt; S2, after mixing raw materials containing 1,4-butanediol, terephthalic acid and catalyst B, PBT condensate is obtained by esterification, pre-condensation and condensation reaction, and PBT melt is obtained by liquid phase thickening and segmented temperature control. S3, PA6 melt and PBT melt are respectively fed to the composite spinning assembly for melt direct spinning. The fiber is cooled, oiled, drawn and wound to obtain the PA6 / PBT composite fiber.

[0011] In this invention, raw materials are first prepared in a batching reactor. The prepared raw materials are then transported to a preheater and a ring-opening reactor. After a ring-opening reaction, PA6 prepolymer is obtained. The obtained prepolymer is then transported to a polycondensation reactor to further increase the number-average molecular weight of the PA6 prepolymer. The polycondensation polymer is then passed through a devolatilization reactor to remove oligomers, achieving liquid-phase extraction of PA6, further reducing the monomer content in the melt and improving the fiber mechanical properties. On the other hand, raw materials are prepared in the batching reactor, and the prepared slurry is transported to an esterification reactor. PBT esterification liquid is obtained through negative pressure esterification. The obtained esterification liquid is transported to a pre-polycondensation reactor for polycondensation reaction. The obtained melt is then transported to a final polycondensation reactor for further polycondensation to obtain a melt with a certain molecular weight and viscosity. The final polycondensation low-viscosity melt is thoroughly mixed with a compatibilizer after being transported to a liquid phase thickening reactor. Small molecule by-reactants generated during the reaction are vacuum-extracted, increasing the melt viscosity. Through liquid phase thickening and segmented temperature control of the screw, a PBT melt with viscosity meeting the spinning process (intrinsic viscosity 1.0-1.2 dl / g) is obtained and transported to the composite spinning assembly.

[0012] Two melts are passed through a specific spinning assembly, and after cooling, oiling, drawing, and winding, PA6 / PBT composite fibers are obtained. This invention simplifies the process, significantly reducing production cycle time, equipment investment costs, and energy consumption. The resulting composite fibers achieve complementary advantages, improving properties such as dyeing resistance, peel resistance, mechanical properties, and elasticity, making them widely applicable to footwear and apparel fabrics for leading sportswear brands.

[0013] Preferably, the PA6 melt has a hot water extractable content of ≤2wt%, wherein the monomer content is ≤0.5wt%, the number average molecular weight is 32,000-50,000, and the relative viscosity is 2.4-2.8.

[0014] The content of low molecular weight compounds in the devolatilized PA6 melt can be significantly reduced, which can significantly improve the breaking strength of the composite fiber.

[0015] Preferably, the intrinsic viscosity of the PBT melt obtained in S2 is 1.0-1.2 dl / g. This invention further enhances the viscosity of PBT condensate and compatibilizer through liquid-phase thickening and segmented temperature control. By utilizing the devolatilization of small molecules and the action of the compatibilizer, and by installing an online viscometer at the outlet, the process conditions of the equipment in liquid-phase thickening and segmented temperature control are adjusted and controlled in real time to obtain a PBT melt with a suitable direct-spinning viscosity.

[0016] Preferably, in S1, the amount of water added is 1-5 wt% relative to caprolactam, the amount of end-capping agent added is 0.1-0.9 wt%, and the amount of catalyst added is 0.01-1.5 wt%.

[0017] Preferably, the capping agent is a monoamine and / or a diamine; the monoamine includes aromatic amines, hindered amines (4-amino-2,2,6,6-tetramethylpiperidine), and n-butylamine; the diamine includes H2N(CH2). z NH2, p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, decanediamine, where z = 1~10.

[0018] Preferably, catalyst A comprises nylon 66 salt and NH2(CH2). X One or more of COOH; wherein X is 4-10.

[0019] Preferably, the raw materials in S1 also include one or more additives, such as matting agents, heat stabilizers, antioxidants, etc.; the added mass of a single additive is 0-2 wt% of caprolactam.

[0020] Preferably, the mixing temperature in S1 is 75-120℃, the mixing time is 10-60 min; the ring-opening reaction temperature is 210-270℃, the pressure inside the reactor is controlled at 1.0-6.0 bar, the residence time is controlled at 2-10 h, and the resulting product has a number-average molecular weight of 6000-15000, a relative viscosity of 1.4-2.0, and a hot water extractable content of 9.0-15.0 wt%. Preferably, the polycondensation reaction temperature in S1 is 240-270℃, the pressure inside the reactor is controlled at -1.0-0.5 bar, and the time is 10-18 seconds. The resulting PA6 polycondensate has a number-average molecular weight of 15,000-40,000, a relative viscosity of 2.1-2.3, and a hot water extractable content of 8.0-9.9 wt%. Preferably, the devolatilization temperature in S1 is 250-290℃, the absolute pressure is 0.05-20kPa, and the residence time is controlled at 0.5-2.0h.

[0021] Preferably, the devolatilization reactor used includes one or more of the following: flash evaporator, thin film devolatilizer, falling film evaporator, stirred evaporator, drop bar type, screw extrusion type, co-rotating disc type devolatilizer, paddle type devolatilizer, and rotating packed bed; the devolatilization level of the devolatilization reactor is single-stage, two-stage, or three-stage.

[0022] Preferably, the molar ratio of 1,4-butanediol to terephthalic acid in S2 is 1.0-1.5, and the mass of catalyst added is 6-100 × 10⁻⁶ of the mass of terephthalic acid. -3 wt% Preferably, the catalyst B comprises one or more of tetraisopropyl titanate, tetrabutyl titanate, alkoxyzirconium, antimony acetate, and alkoxytin.

[0023] Preferably, S2 also includes one or more of the following additives: heat stabilizer, flame retardant, antibacterial agent, and UV stabilizer, wherein the mass of the additives is 0.5-10% of the total raw material. Preferably, the esterification reaction in S2 is carried out at a pressure of 40-90 kPa and an esterification temperature of 210-240℃, with the esterification rate controlled to reach ≥98%; the pre-condensation and condensation reaction temperatures in S2 are 220-250℃, the pressure inside the reactor is controlled at 10-40 kPa, and the intrinsic viscosity of the obtained PBT condensate is 0.5-0.7 dl / g.

[0024] As a preferred embodiment, the liquid phase viscosity enhancement and segmented temperature control in S2 specifically include the following steps: The PBT melt is obtained by melt blending the PBT condensate in a segmented temperature-controlled screw devourer with an online addition of a compatibilizer to achieve liquid-phase thickening. Preferably, the segmented temperature-controlled screw devolatilization reactor comprises at least 5 segments, with a temperature of 240-270℃, an absolute pressure of 0.1-10kPa, and a residence time controlled at 0.3-0.5h.

[0025] Preferably, the compatibilizer includes one or more of bisphenol A type epoxy resins E-44, E-54, and EP-0199. The compatibilizer is added to the PBT melt through an online addition system, and disperses more evenly in the PBT melt through strong shear action. The required amount is less than that of traditional methods. The added mass of the compatibilizer is 0.05-0.1% of the PBT condensate.

[0026] Preferably, the screw devolatilization reactor includes one or more of single-screw, twin-screw, and triple-screw reactors, which have high surface renewal rate, short residence time, good small molecule devolatilization effect, and can be controlled in stages. An online viscometer is installed at the outlet, and a melt with suitable viscosity and conveying temperature can be obtained by controlling the screw extrusion speed, vacuum degree, and staged temperature control.

[0027] As a preferred option, the mass percentage of PA6 melt in S3 is 10%-40%, and the mass percentage of PBT melt is 60%-90%.

[0028] Preferably, the conveying temperature in S3 is 250-270℃, and the melt is filtered through a filter with a filter element of 1-10μm. The process parameters for direct spinning of the melt in S3 include: using a spinneret with an outer circular internal gear structure, a side-blowing air velocity of 0.2-0.8m / s, a spinning temperature controlled at 255-290℃, a draw ratio of 1.1-4.0, and a spinning speed controlled at 1500-4000m / min. The use of a spinneret with an outer circular internal gear structure allows for closer contact between the PA6 and PBT melts, stronger interfacial interaction, and improved peel resistance.

[0029] Compared with the prior art, the present invention has the following beneficial effects: (1) In this invention, the content of extractable material in PA6 melt is reduced by combining amine end-capping agent and devolatilization process, while the content of terminal amino group is controlled to improve the binding ability with PBT melt under the action of compatibilizer and ensure the dyeing performance in the downstream. On the other hand, combined with the thickening of PBT, the compatibilizer and PBT melt are efficiently mixed and rapidly thickened by the segmented temperature-controlled screw thickening reactor, the residence time is greatly shortened, and the thickened PBT melt is reduced to a suitable conveying temperature and viscosity by the screw segmented temperature control system, which effectively reduces the degradation of PBT melt and the content of compatibilizer in high temperature conveying, thereby ensuring that the final composite fiber has the advantages of both PA6 and PBT, with a soft hand feel, excellent dyeing performance, strong bonding, good wear resistance and excellent elasticity, and can be widely used in the textile field and other industrial fields.

[0030] (2) The method of the present invention is the first to realize the preparation of PA6 / PBT composite fiber by melt direct spinning, and can effectively control the content of hot water extractables in PA6 melt, especially the monomer content and the thermal degradation of PBT melt. The production energy consumption is greatly reduced. There is no need to make chips first. The intermediate processes such as extraction, drying, conveying, screw extrusion and melting are eliminated. The process is simplified, the production cycle is shortened by about 2 / 3, water consumption, energy consumption and waste discharge are reduced, equipment investment and land occupation are reduced, and product manufacturing costs are reduced. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the process flow for preparing PA6 / PBT composite fibers in Example 1.

[0032] Figure 2 This is a schematic diagram of the spinneret structure with an outer circle and an inner gear shape used in the embodiment.

[0033] Figure 3 This is a GPC diagram of the PA6 melt after devolatilization in Example 5.

[0034] Figure 4 The image shows the surface morphology of the composite fiber obtained by spinning in Example 5 under an optical microscope. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0036] The raw materials used in the following specific embodiments were all purchased from the market, and the methods for testing the performance parameters involved in this invention are as follows: (1) Relative viscosity The concentrated sulfuric acid method using an Ubbelohde viscometer: Accurately weigh 0.25 g (to a depth of 0.1 mg) of the dried sample melt and dry it in an 80°C forced-air drying oven for 1 h; dry the finished product slices in an 80°C vacuum drying oven for 3 h; place them in a 100 mL stoppered ground glass bottle, minimizing moisture absorption. Add sulfuric acid solution using a dispensing device at a ratio of m:v = 1:100 to prepare a sample solution with a concentration of 0.010 g / mL, and stopper the bottle. Heat and stir in a polymer dissolving apparatus at 65°C until the sample is completely dissolved (approximately 90 min), then cool to room temperature. Flow time determination: After shaking the sample well, carefully pour it into the Ubbelohde viscometer, ensuring the liquid level is between the two filling marks.

[0037] Install the viscometer in a constant temperature water bath at (25.00±0.02)℃, ensuring that the viscometer is vertical and the upper bulb is completely immersed in the aqueous solution, and maintain the temperature for 20 min. Measure and record the flow time t0 of concentrated sulfuric acid and the flow time t of the polyamide sample solution.

[0038] Viscosity calculation formula: Relative viscosity = t / t0; where t is the solution flow time; t0 is the solvent flow time.

[0039] (2) Test for hot water extractables Water-soluble oligomers and caprolactam in the sample were extracted in hot water using automatic and intermittent siphon distillation and measured by gravimetric method. The sample was extracted in hot water at ≥97℃, and the content of hot water extractables was calculated by the mass difference of the sample before and after extraction.

[0040] Weigh approximately 15 g of copolymer sample or approximately 10 g of oil-free filament, record the mass m0, and place it in a covered stainless steel porous cylinder. Then, place the covered stainless steel porous cylinder into a 500 mL beaker, add approximately 400 mL of ultrapure water, cover the beaker with two layers of plastic wrap and one layer of aluminum foil, tighten with a rubber band, and place it in a water bath at 97°C or higher for extraction for 16 h.

[0041] After extraction, while still hot, separate the extract from the slides and rinse the slides with a small amount of pure water (make sure to add the rinsing solution back into the extract).

[0042] After separation, the slices were first placed in an 80℃ forced-air drying oven for 3 hours, then separated from the covered stainless steel porous cylinder into a foil bowl. They were then dried in a 100℃ vacuum drying oven to constant weight (weighing began after 12 hours of drying, with weighing every 10 minutes, and the difference between two consecutive weighings not exceeding 0.05% of the last weighing). The slices were then transferred to a desiccator to cool to room temperature for 30-45 minutes, and the mass was recorded as m1, weighed to 0.1 mg. After the sample was poured out, the mass of the foil bowl was recorded as m2, and weighed to 0.1 mg.

[0043] After cooling, the extract was transferred to a 500 mL volumetric flask and diluted to volume, and retained as solution A for monomer and dimer content testing.

[0044] The content of hot water extractables in the sample is calculated using the following formula:

[0045] The content of extractable substances in hot water is expressed as ω1, where ω1 is the extractable substance content in hot water, expressed as a percentage by mass (%). m0 — Mass of the sample, in grams (g); W – Moisture content of the sample; m1 — The mass of the foil bowl and the dried sample, in grams (g). m2 — the mass of the tin foil bowl, expressed in grams (g).

[0046] (3) Monomer and dimer content test The mobile phase is pumped through the injection valve to mix with the sample solution, then flows through the chromatographic column where it undergoes adsorption and separation. Finally, each component is detected and converted into an electrical signal, resulting in a corresponding sample peak on the chromatography workstation. The extract (containing less than 0.05% of the hot-water extractable) or the diluted sample (if the content of the hot-water extractable is not less than 0.05%, it must be diluted to within the standard curve range) is brought to a final volume of 100 mL, thoroughly mixed, and immediately used to prepare the solution for testing caprolactam monomers and cyclic dimers in liquid chromatography. During preparation, 5% trifluoroethanol is added as a solvent to maintain good dissolution. After preparation, the solution is filtered through a 0.45 μm filter into a 1.5 mL chromatographic vial and then analyzed by the liquid chromatograph.

[0047] caprolactam content w in the sample CPL , cyclic dimer content w CD The calculation method for percentage content is as follows: w CPL %=c CPL ×dfi×V÷1000÷1000m×100= c CPL ×dfi×V10000m w CD %=c CD ×dfi×V÷1000÷1000m×100= c CD ×dfi×V10000m In the formula: V—Volume at constant volume, in milliliters (mL); w CPL wCD — These represent the caprolactam content and cyclic dimer content in the sample, respectively, in mass percentage (%). c CPL c CD — These represent the caprolactam concentration and cyclic dimer concentration read from the curve in the liquid phase test, respectively, in milligrams per milliliter (mg / L). dfi—Dilution factor; m — the mass of the sample taken, in grams (g).

[0048] (4) Test of terminal amino content Weigh 0.5 g of the sample to a depth of 0.1 mg and place it in a 100 mL stoppered conical flask. Add 45 mL of phenol solution. Heat under reflux for 50 min on a fat analyzer pre-adjusted to (140±2)℃ (actual temperature 120℃). Remove the sample and cool for 5 min. Add 3 drops of dimethyl yellow-methylene blue as an indicator. Perform chemical titration with 0.02 mol / L hydrochloric acid-ethanol standard titration solution. The endpoint is reached when the sample solution color changes from green to pale purple. Record the volume of hydrochloric acid-ethanol standard titration solution consumed, V1. Perform a blank test simultaneously. Record the volume of hydrochloric acid-ethanol standard titration solution consumed, V0.

[0049] Amino content is expressed as X -NH2 The calculation formula is as follows:

[0050] In the formula, X -NH2 —Amino content of the sample, in millimoles per kilogram (mmol / kg); V1 — The volume of hydrochloric acid-ethanol standard titration solution consumed in titrating the sample, in milliliters (mL). V0 — The volume of hydrochloric acid-ethanol standard titration solution consumed in the titration of the blank solution (solvent), in milliliters (mL); —The concentration of the hydrochloric acid-ethanol standard titration solution, in moles per liter (mol / L). m 样 —Sample mass, in grams (g).

[0051] Example 1 A schematic diagram of the specific process flow for preparing PA6 / PBT composite fibers by melt spinning is shown below. Figure 1As shown, the first step is to mix caprolactam, 1,6-hexanediamine, and deionized water in a certain proportion at a temperature of 80℃, and stir for 30 minutes under mechanical stirring (100 r / min); wherein the amount of deionized water added is 2.2 wt% and the amount of hexanediamine added is 0.3 wt% relative to caprolactam. Step 2: The mixture obtained in Step 1 is heated by a melt pump and a preheater (preheater temperature 140℃), and then transferred to a ring-opening reactor for ring-opening reaction. The ring-opening temperature is controlled at 220℃, the ring-opening pressure is controlled at 1.5 bar, and the ring-opening reaction time is 6 hours. The resulting ring-opening melt has a number-average molecular weight of 6400, a relative viscosity of 1.68, and a hot water extractable content of 13.6 wt%. Step 3: The product obtained from ring-opening is transferred to a polycondensation reactor for reaction. The pressure of the pre-polycondensation reaction is -0.04 MPa, the reaction temperature is 250°C, and the residence time is 13 h. The reaction is terminated when the following conditions are met: the number average molecular weight of the obtained PA6 polycondensate is 21600, the relative viscosity is 1.99, and the extractable content is 8.4 wt%. Step 5: The PA6 condensate is fed to the spinning line, where it undergoes further devolatilization using a disc devolatilizer before the spinning box. The devolatilization temperature is maintained at 260℃, the devolatilization lasts for 2 hours, and the process pressure is below 100 Pa. The resulting devolatilized melt has a molecular weight of 33,100, a relative viscosity of 2.50, a hot water extractable content of 1.4%, and a monomer content of 0.4%. PBT melt preparation is carried out simultaneously, and the preparation method includes the following steps: Step 1: Slurry preparation. 1,4-Butanediol and terephthalic acid are mixed at a molar ratio of 1.2:1 and pulped for 30 minutes to ensure thorough mixing. Simultaneously, tetrabutyl titanate is added as a catalyst, and esterification is carried out under negative pressure. The absolute pressure of the esterification reaction is 60 kPa, the reaction temperature is 220℃, the catalyst dosage is 30 ppm, and the esterification time is 200 minutes. The esterification reaction ends when the amount of water produced reaches 99% of the theoretical output. Step 2: The PBT esterification liquid is pumped to a prepolymerization reactor at a prepolymerization temperature of 235℃, a pressure of 20 kPa, and a residence time of 30 min. The prepolymerized melt is further polymerized in a final polymerization reactor at a final polymerization temperature of 245℃, a pressure of 1 kPa, and a residence time of 80 min. The resulting PBT condensate has an intrinsic viscosity of 0.61 dl / g.

[0052] Step 3: The obtained final polycondensation melt is fed into a twin-screw reactor via a melt pipeline with 0.08 wt% bisphenol A epoxy resin EP-0199 added online for mixing and liquid-phase thickening. The conveying temperature is 240℃, the liquid-phase thickening reaction temperature is 260℃, the absolute pressure is controlled at 100 Pa, and the residence time is 40 min. The resulting thickened PBT melt has an intrinsic viscosity of 1.08 dl / g and an outlet melt temperature of 250℃. The liquid-phase thickened product is then fed into a spinning box.

[0053] Step 4: Mix the obtained PA6 melt and PBT melt in a 20:80 mass ratio, and then... Figure 2 The spinneret with an outer circle and inner gear structure shown is extruded, cooled, oiled, drawn, and wound by a core-sheath composite spinning assembly. The spinning temperature is 260℃, the side blowing speed is 0.4m / s, the draw ratio is 1.25, and the spinning speed is 3000m / min, to obtain composite fibers with PA6 as the core layer and PBT as the sheath layer.

[0054] Example 2 Step 1: At a temperature of 85℃, caprolactam, 1,6-hexanediamine, and deionized water were mixed in a specific ratio and stirred for 30 minutes under mechanical stirring (100 r / min); the amount of deionized water added was 2.0 wt% relative to caprolactam, and the amount of p-phenylenediamine added was 0.4 wt%. Step 2: The mixture obtained in Step 1 is heated by a melt pump and a preheater (preheater temperature 180℃), and then transferred to a ring-opening reactor for ring-opening reaction. The ring-opening temperature is controlled at 230℃, the ring-opening pressure is controlled at 1.5 bar, and the ring-opening reaction time is 5 hours. The resulting ring-opening melt has a number-average molecular weight of 8500, a relative viscosity of 1.70, and a hot water extractable content of 12.8 wt%. Step 3: The product obtained from ring-opening is transferred to a polycondensation reactor for pre-polycondensation reaction. The pressure of the polycondensation reaction is -0.03 MPa, the reaction temperature is 255°C, and the residence time is 13 h. The reaction is terminated when the following conditions are met: the molecular weight of the obtained PA6 polycondensate is 26800, the relative viscosity is 2.02, and the hot water extractable content is 9.4 wt%. Step 4: The PA6 condensate is transported to the spinning line and further devolatilized using a falling film evaporator before the spinning box; the devolatilization temperature is maintained at 270℃, the devolatilization lasts for 30 minutes, and the process pressure is below 100 Pa; the resulting devolatilized melt has a molecular weight of 37100, a relative viscosity of 2.48, an extractable content of 1.2%, and a monomer content of 0.3%.

[0055] PBT melt preparation is carried out simultaneously, and the preparation method is as follows: Step 1: Slurry preparation. 1,4-Butanediol and terephthalic acid were mixed at a molar ratio of 1.1:1 and pulped for 30 minutes to ensure thorough mixing. Simultaneously, tetrabutyl titanate was added as a catalyst, and esterification was carried out under negative pressure. The absolute pressure of the esterification reaction was 50 kPa, the reaction temperature was 225℃, the catalyst dosage was 60 ppm, and the esterification time was 160 minutes. The esterification reaction ended when the amount of water produced reached 99% of the theoretical output. Step 2: The PBT esterification liquid is pumped to a prepolymerization reactor at a prepolymerization temperature of 235℃, a pressure of 10 kPa, and a residence time of 50 min. The prepolymerized melt is then further polymerized in a final polymerization reactor at a final polymerization temperature of 250℃, a pressure of 500 Pa, and a residence time of 60 min. The resulting final polymerized melt has an intrinsic viscosity of 0.68 dl / g.

[0056] Step 3: The resulting final polycondensation melt is fed into a three-screw reactor via a melt pipeline with 0.05 wt% bisphenol A epoxy resin EP-0199 added online for rapid mixing and liquid-phase thickening. The conveying temperature is 240℃, the liquid-phase thickening reaction temperature is 270℃, the absolute pressure is controlled at 200 Pa, and the residence time is 30 min. The resulting thickened melt has an intrinsic viscosity of 1.15 dl / g and an outlet melt temperature of 250℃. The liquid-phase thickened product is then fed into a spinning box.

[0057] Step 4: The PA6 melt and PBT melt obtained above are mixed in a mass ratio of 30:70, and extruded, cooled, oiled, and wound through a core-sheath composite spinning assembly using a spinneret with an outer circle and inner gear structure. The spinning temperature is 265℃, the side blowing speed is 0.45m / s, the draw ratio is 1.2, and the spinning speed is 3000m / min to obtain a composite fiber with PA6 as the core layer and PBT as the sheath layer.

[0058] Example 3 Step 1: At a temperature of 85℃, caprolactam, 1,6-hexanediamine, and deionized water were mixed in a specific ratio and stirred for 30 minutes under mechanical stirring (100 r / min); the amount of deionized water added was 3.5 wt% relative to caprolactam, and the amount of deionized water added was 0.5 wt%. Step 2: The mixture obtained in Step 1 was heated by a melt pump and a preheater (preheater temperature 180℃), and then transferred to a ring-opening reactor for ring-opening reaction. The ring-opening temperature was controlled at 240℃, the ring-opening pressure at 1.5 bar, and the ring-opening reaction time was 4 hours. The resulting ring-opening melt had a number-average molecular weight of 9200, a relative viscosity of 1.72, and a hot water extractable content of 11.6 wt%. Step 3: The product obtained from ring-opening is transferred to a polycondensation reactor for pre-polycondensation reaction. The pressure of the polycondensation reaction is 0.01 MPa, the reaction temperature is 265°C, and the residence time is 13 h. The reaction is terminated when the following conditions are met: the molecular weight of the obtained product is 22400, the relative viscosity is 2.10, and the hot water extractable content is 9.0 wt%. Step 4: The product of the final polycondensation reaction is transported to the spinning line, and further devolatilization is carried out in front of the spinning box using a thin-film evaporator; the devolatilization temperature is maintained at 280℃, the devolatilization lasts for 60 minutes, and the process pressure is below 100 Pa; the resulting devolatilized melt has a molecular weight of 35,500, a relative viscosity of 2.50, a hot water extractable content of 1.1%, and a monomer content of 0.3%.

[0059] PBT melt preparation is carried out simultaneously, and the preparation method is as follows: Step 1: Slurry preparation. 1,4-Butanediol and terephthalic acid were mixed at a molar ratio of 1.05:1 and pulped for 30 minutes to ensure thorough mixing. Simultaneously, tetrabutyl titanate was added as a catalyst, and esterification was carried out under negative pressure. The absolute pressure of the esterification reaction was 50 kPa, the reaction temperature was 225℃, the catalyst dosage was 60 ppm, and the esterification time was 160 minutes. The esterification reaction ended when the amount of water produced reached 99% of the theoretical output. Step 2: The PBT esterification liquid is pumped to the prepolymerization reactor via a melt pump. The prepolymerization temperature is 238℃, the pressure is 1 kPa, and the time is 40 min. The prepolymerized melt is further polymerized in the final polymerization reactor at a final polymerization temperature of 255℃, a pressure of 200 Pa, and a residence time of 50 min. The resulting final polymerized melt has an intrinsic viscosity of 0.70 dl / g.

[0060] Step 3: The resulting final polycondensation melt is fed into a three-screw reactor via a melt pipeline with 0.10 wt% bisphenol A epoxy resin E-44 added online for rapid mixing and liquid-phase thickening. The conveying temperature is 245°C, the liquid-phase thickening reaction temperature is 265°C, the absolute pressure is controlled at 100 Pa, and the residence time is 30 min. The resulting thickened melt has an intrinsic viscosity of 1.19 dl / g and an outlet melt temperature of 245°C. The liquid-phase thickened product is then fed into a spinning box.

[0061] Step 4: The PA6 melt and PBT melt obtained above are mixed in a mass ratio of 35:65, and extruded, cooled, oiled, and wound through a new composite spinning assembly using a spinneret with an outer circle and inner gear structure. The spinning temperature is 258℃, the side blowing speed is 0.38m / s, the draw ratio is 1.25, and the spinning speed is 3500m / min to obtain a composite fiber with PA6 as the core layer and PBT as the sheath layer.

[0062] Example 4 Step 1: At a temperature of 85℃, caprolactam, 4-amino-2,2,6,6-tetramethylpiperidine, and deionized water were mixed in a specific ratio and stirred for 30 minutes under mechanical stirring (100 r / min); wherein the amount of deionized water added was 2.5 wt% relative to caprolactam, and the amount of 4-amino-2,2,6,6-tetramethylpiperidine added was 0.5 wt%. Step 2: The mixture obtained in Step 1 was heated by a melt pump and a preheater (preheater temperature 180℃), and then transferred to a ring-opening reactor for ring-opening reaction. The ring-opening temperature was controlled at 230℃, the ring-opening pressure at 1.5 bar, and the ring-opening reaction time was 5 hours. The resulting ring-opening melt had a number-average molecular weight of 8600, a relative viscosity of 1.67, and a hot water extractable content of 14.6 wt%. Step 3: The product obtained from ring-opening is transferred to a polycondensation reactor for polycondensation reaction. The pressure of the polycondensation reaction is -0.03 MPa, the reaction temperature is 248℃, and the residence time is 14 h. The molecular weight of the obtained product is 27600, the relative viscosity is 2.04, and the hot water extractable content is 8.6 wt%. Step 4: The product of the final polycondensation reaction is transported to the spinning line, and further devolatilization is carried out in front of the spinning box using a screw extruder; the devolatilization temperature is maintained at 285℃, the devolatilization lasts for 15 minutes, and the process pressure is below 100Pa; the resulting devolatilized melt has a molecular weight of 33400, a relative viscosity of 2.45, a hot water extractable content of 1.0%, and a monomer content of 0.25%.

[0063] PBT melt preparation is carried out simultaneously, and the preparation method is as follows: Step 1: Slurry preparation. 1,4-Butanediol and terephthalic acid were mixed at a molar ratio of 1.08:1 and pulped for 30 minutes to ensure thorough mixing. Simultaneously, tetrabutyl titanate was added as a catalyst, and esterification was carried out under negative pressure. The absolute pressure of the esterification reaction was 40 kPa, the reaction temperature was 225℃, the catalyst dosage was 70 ppm, and the esterification time was 150 minutes. The esterification reaction ended when the amount of water produced reached 99% of the theoretical output. Step 2: The PBT esterification liquid is pumped to the prepolymerization reactor via a melt pump. The prepolymerization temperature is 236℃, the pressure is 5 kPa, and the time is 60 min. The prepolymerized melt is further polymerized in the final polymerization reactor at a final polymerization temperature of 260℃, a pressure of 1 kPa, and a residence time of 80 min. The resulting final polymerized melt has an intrinsic viscosity of 0.66 dl / g.

[0064] Step 3: The resulting final polycondensation melt is fed into a twin-screw reactor via a melt pipeline with 0.09 wt% bisphenol A epoxy resin E-44 added online for rapid mixing and liquid-phase thickening. The conveying temperature is 240℃, the liquid-phase thickening reaction temperature is 265℃, the absolute pressure is controlled at 100 Pa, and the residence time is 40 min. The resulting thickened melt has an intrinsic viscosity of 1.08 dl / g and an outlet melt temperature of 245℃. The liquid-phase thickened product is then conveyed to the spinning box.

[0065] Step 4: The PA6 melt and PBT melt obtained above are mixed in a mass ratio of 30:70, and extruded, cooled, oiled and wound through a composite spinning assembly using a spinneret with an outer circle and inner gear structure. The spinning temperature is 260℃, the side blowing wind speed is 0.5m / s, the draw ratio is 1.22 and the spinning speed is 3000m / min to obtain a composite fiber with PA6 as the core layer and PBT as the sheath layer.

[0066] Example 5 Step 1: At a temperature of 85℃, caprolactam, n-butylamine, and deionized water were mixed in proportion and stirred for 30 minutes under mechanical stirring (100 r / min); wherein the amount of deionized water added was 2.0 wt% relative to caprolactam, and the amount of p-phenylenediamine added was 0.4 wt%. Step 2: The mixture obtained in Step 1 was heated by a melt pump and a preheater (preheater temperature 180℃), and then transferred to a ring-opening reactor for ring-opening reaction. The ring-opening temperature was controlled at 230℃, the ring-opening pressure at 1.5 bar, and the ring-opening reaction time was 5 hours. The resulting ring-opening melt had a number-average molecular weight of 7500, a relative viscosity of 1.69, and a hot water extractable content of 13.2 wt%. Step 3: The product obtained from ring-opening is transferred to a polycondensation reactor for polycondensation reaction. The pressure of the polycondensation reaction is -0.01 MPa, the reaction temperature is 250℃, and the residence time is 13.5 h. The molecular weight of the obtained product is 26700, the relative viscosity is 2.14, and the hot water extractable content is 8.8 wt%. Step 4: The product of the polycondensation reaction is transported to the spinning line, where further devolatilization is performed in a stirred evaporator before the spinning box. The devolatilization temperature is maintained at 285℃, the devolatilization lasts for 40 minutes, and the process pressure is below 100 Pa. The resulting devolatilized melt has a molecular weight of 37,000, a relative viscosity of 2.55, a hot water extractable content of 1.0%, and a monomer content of 0.2%. The GPC diagram of the devolatilized PA6 melt is shown below. Figure 3 As shown.

[0067] PBT melt preparation is carried out simultaneously, and the preparation method is as follows: Step 1: Slurry preparation. 1,4-Butanediol and terephthalic acid were mixed at a molar ratio of 1.16:1 and pulped for 30 minutes to ensure thorough mixing. Simultaneously, tetrabutyl titanate was added as a catalyst, and esterification was carried out under negative pressure. The absolute pressure of the esterification reaction was 30 kPa, the reaction temperature was 220℃, the catalyst dosage was 50 ppm, and the esterification time was 190 minutes. The esterification reaction ended when the amount of water produced reached 99% of the theoretical output. Step 2: The PBT esterification liquid is pumped to the polycondensation reactor via a melt pump. The prepolymerization temperature is 235℃, the pressure is 5 kPa, and the time is 80 min. The prepolymerized melt is further polymerized in the final polycondensation reactor at a final polycondensation temperature of 255℃, a pressure of 500 Pa, and a residence time of 50 min. The resulting final polymerized melt has an intrinsic viscosity of 0.69 dl / g.

[0068] Step 3: The resulting final polycondensation melt is fed into a twin-screw reactor via a melt pipeline with 0.09 wt% bisphenol A epoxy resin E-44 added online for rapid mixing and liquid-phase thickening. The conveying temperature is 248°C, the liquid-phase thickening reaction temperature is 258°C, the absolute pressure is controlled at 100 Pa, and the residence time is 45 min. The resulting thickened melt has an intrinsic viscosity of 1.14 dl / g and an outlet melt temperature of 245°C. The liquid-phase thickened product is then fed into a spinning box.

[0069] Step 4: The obtained PA6 melt and PBT melt are mixed in a 40:60 mass ratio, and extruded, cooled, oiled, drawn, and wound using a spinneret with an external cylindrical internal gear structure. The spinning temperature is 264℃, the side-blowing air velocity is 0.55m / s, the draw ratio is 1.2, and the spinning speed is 3000m / min to obtain PA6 / PBT composite fibers. The fiber surface morphology under an optical microscope is as follows. Figure 4 As shown.

[0070] Comparative Example 1 (Direct-spun PA6 monofilament) Step 1: At a temperature of 85℃, caprolactam, terephthalic acid, and deionized water were mixed in a specific ratio and stirred for 30 minutes under mechanical stirring (100 r / min); the amount of deionized water added was 2.0 wt%, and the amount of terephthalic acid added was 0.4 wt%, relative to caprolactam. Step 2: The mixture is stirred in a preheater for 2 hours at a pre-reaction temperature of 150°C, a stirring speed of 60 r / min, and a preheater pressure of 2 bar.

[0071] Step 3: The preheated material is transported to the open-loop reactor via a gear pump. The open-loop temperature is controlled at 245℃, the open-loop pressure is controlled at 1.5 bar, and the residence time is 4 hours.

[0072] Step 4: The product obtained from ring opening is transported to a polycondensation reactor for polycondensation reaction. The pressure of the polycondensation reaction is controlled at absolute pressure of 60 kPa, the reaction temperature is 270 °C, and the residence time is 12 h to obtain PA6 melt.

[0073] Step 5: The PA6 melt is transported to the devolatilization reactor via a melt gear pump and devolatilization is carried out using a stirred evaporator; the devolatilization temperature is maintained at 290℃, the devolatilization lasts for 50 minutes, and the process pressure is below 100 Pa; the resulting devolatilized melt has a molecular weight of 39465, a relative viscosity of 2.47, and a hot water extractable content of 0.8 wt%.

[0074] Step 6: The devolatilized PA product is transported to the spinning box via a melt booster pump and a metering pump at a conveying temperature of 260°C.

[0075] Step 7: Using a circular spinneret, the spinneret is extruded, cooled, oiled, drawn, and wound through the spinning assembly. The spinning temperature is 265℃, the side-blowing air velocity is 0.45m / s, the draw ratio is 1.25, and the spinning speed is 4300m / min to obtain direct-spun PA6 fibers.

[0076] Comparative Example 2 (Direct-spun PA6 monofilament) The only difference between Comparative Example 2 and Comparative Example 1 is that the end-capping agent was changed from terephthalic acid to terephthalic dimethylamine, resulting in a higher content of terminal amino groups in the final melt.

[0077] Step 1: At a temperature of 85℃, caprolactam, terephthalic acid, and deionized water were mixed in a specific ratio and stirred for 30 minutes under mechanical stirring (100 r / min); the amount of deionized water added was 2.0 wt% relative to caprolactam, and the amount of terephthalic acid added was 0.4 wt%. Step 2: The mixture is stirred in a preheater for 2 hours at a pre-reaction temperature of 150°C, a stirring speed of 60 r / min, and a preheater pressure of 2 bar.

[0078] Step 3: The preheated material is transported to the open-loop reactor via a gear pump. The open-loop temperature is controlled at 245℃, the open-loop pressure is controlled at 1.5 bar, and the residence time is 4 hours.

[0079] Step 4: The product obtained from ring opening is transported to a polycondensation reactor for polycondensation reaction. The pressure of the polycondensation reaction is controlled at absolute pressure of 60 kPa, the reaction temperature is 270 °C, and the residence time is 12 h to obtain PA6 melt.

[0080] Step 5: The PA6 melt is transported to the devolatilization reactor via a melt gear pump and devolatilization is carried out using a stirred evaporator; the devolatilization temperature is maintained at 290℃, the devolatilization lasts for 50 minutes, and the process pressure is below 100 Pa; the resulting devolatilized melt has a molecular weight of 37600, a relative viscosity of 2.48, and a hot water extractable content of 0.9 wt%.

[0081] Step 6: The devolatilized PA product is transported to the spinning box via a melt booster pump and a metering pump at a conveying temperature of 260°C.

[0082] Step 7: Using a circular spinneret, the spinneret is extruded, cooled, oiled, drawn, and wound through the spinning assembly. The spinning temperature is 265℃, the side-blowing air velocity is 0.45m / s, the draw ratio is 1.25, and the spinning speed is 4300m / min to obtain direct-spun PA6 fibers.

[0083] Comparative Example 3 (PA6 monofilament spun from chips) After extraction and drying, the commercial PA6 dry chips are melted by screw extrusion, metered and transported by different metering pumps, and then extruded, cooled, oiled and wound by a spinning assembly using a circular spinneret. The spinning temperature is 255℃, the side blowing wind speed is 0.48m / s, the spinning speed is 4500m / min, and the draw ratio is 1.25 to obtain PA6 chip spun fibers.

[0084] Comparative Example 4 (Direct-spun PBT monofilament) Step 1: Pulp preparation. Mix 1,4-butanediol and terephthalic acid at a molar ratio of 1.2:1 and beat for 30 minutes to ensure thorough mixing of the raw materials.

[0085] Step 2: Add tetrabutyl titanate as a catalyst and carry out esterification under negative pressure. The absolute pressure of the esterification reaction is 60 kPa, the reaction temperature is 220℃, the catalyst dosage is 30 ppm, and the esterification time is 200 min. The esterification reaction ends when the amount of water produced reaches 99% of the theoretical output.

[0086] Step 3: The PBT esterification liquid is pumped to the prepolymerization reactor via a melt pump. The prepolymerization temperature is 235℃, the pressure is 20 kPa, and the time is 30 min. The prepolymerized melt is further polymerized in the final polymerization reactor at a final polymerization temperature of 245℃, a pressure of 1 kPa, and a residence time of 80 min. The intrinsic viscosity of the resulting final polymerized melt is 0.63 dl / g.

[0087] Step 4: The resulting final polycondensation melt is pumped to a twin-screw reactor for liquid-phase thickening via a gear pump. The pumping temperature is 240°C, the liquid-phase thickening reaction temperature is 260°C, the absolute pressure is controlled at 100 Pa, and the residence time is 40 min. The resulting thickened melt has an intrinsic viscosity of 1.08 dl / g and an outlet melt temperature of 250°C. The liquid-phase thickened product is then pumped to a spinning box.

[0088] Step 5: The PBT melt obtained above is extruded, cooled, oiled, drawn, and wound through a spinning assembly using a circular spinneret. The spinning temperature is 260℃, the draw ratio is 1.25, the side blowing speed is 0.45m / s, and the spinning speed is 4500m / min to obtain direct-spun PBT fibers.

[0089] Comparative Example 5 (PA6 / PBT chips) After extraction and drying, the commercial PA6 dry chips are melted by screw extrusion; PBT chips are conveyed, crystallized, dried, and melted by screw extrusion. They are then metered and conveyed through their respective pipelines by different metering pumps. They are then extruded, cooled, oiled, and wound through a composite spinning assembly using a spinneret with an outer circle and inner gear structure. The spinning temperature is 265℃, the side blowing wind speed is 0.5m / s, and the spinning speed is 3000m / min, to obtain composite fibers with PA6 as the core layer and PBT as the sheath layer.

[0090] Comparative Example 6 (PBT monofilament spun without increasing viscosity) Step 1: Pulp preparation. Mix 1,4-butanediol and terephthalic acid at a molar ratio of 1.2:1 and beat for 30 minutes to ensure thorough mixing of the raw materials.

[0091] Step 2: Add tetrabutyl titanate as a catalyst and carry out esterification under negative pressure. The absolute pressure of the esterification reaction is 60 kPa, the reaction temperature is 220℃, the catalyst dosage is 30 ppm, and the esterification time is 200 min. The esterification reaction ends when the amount of water produced reaches 99% of the theoretical output.

[0092] Step 3: The PBT esterification liquid is pumped to the prepolymerization reactor via a melt pump. The prepolymerization temperature is 235℃, the pressure is 20 kPa, and the time is 30 min. The prepolymerized melt is further polymerized in the final polymerization reactor at a final polymerization temperature of 245℃, a pressure of 1 kPa, and a residence time of 80 min. The intrinsic viscosity of the resulting final polymerized melt is 0.63 dl / g.

[0093] Step 4: The resulting final polycondensation melt is transported to the spinning box via a melt gear pump.

[0094] Step 5: The PBT melt obtained above is extruded through a spinning assembly using a circular spinneret. However, the filament formation is poor, and stable spinning is not possible.

[0095] Comparative Example 7 (PA6 directly spun without devolatilization) Step 1: At a temperature of 85℃, caprolactam, terephthalic acid, and deionized water were mixed in a specific ratio and stirred for 30 minutes under mechanical stirring (100 r / min); the amount of deionized water added was 2.0 wt%, and the amount of terephthalic acid added was 0.4 wt%, relative to caprolactam. Step 2: The mixture is stirred in a preheater for 2 hours at a pre-reaction temperature of 150°C, a stirring speed of 60 r / min, and a preheater pressure of 2 bar.

[0096] Step 3: The preheated material is transported to the open-loop reactor via a gear pump. The open-loop temperature is controlled at 245℃, the open-loop pressure is controlled at 1.5 bar, and the residence time is 4 hours.

[0097] Step 4: The product obtained from ring opening is transported to a polycondensation reactor for polycondensation reaction. The pressure of the polycondensation reaction is controlled at absolute pressure of 60 kPa, the reaction temperature is 270 °C, and the residence time is 12 h to obtain bio-based PA6 melt.

[0098] Step 5: The PA6 melt is transported through a melt gear pump, then through a melt booster pump and a metering pump to the spinning box, with a transport temperature of 260℃.

[0099] Step 6: Using a circular spinneret, the melt does not form strips after being extruded by the spinning assembly, and there is a lot of smoke at the spinneret, making it impossible to start spinning normally.

[0100] The PA6 / PBT composite fibers and monofilaments obtained in Examples 1-5 and Comparative Examples 1-5 were subjected to performance testing. The testing standards were based on GB / T14344-2008 "Test Method for Tensile Properties of Chemical Fiber Filaments" and GB / T 6505-2008 "Test Method for Heat Shrinkage Rate of Chemical Fiber Filaments". The test results are shown in Table 1.

[0101] Table 1. Fiber performance parameters of different PA6 / PBT composite yarns in the examples.

[0102] As shown in Examples 1-5, the content of low molecular weight compounds in the devolatilized PA6 melt can be significantly reduced after process adjustment. During fiber forming and stretching, these extractable small molecules cannot withstand external forces like macromolecular chains. Their presence disrupts the orderly arrangement and tight packing of fiber macromolecular chains, forming structural defects or "weak links" within the fiber. When the fiber is subjected to tension, stress preferentially concentrates around these defect points. Due to the extremely low strength of these small molecules, they cannot effectively transfer and disperse stress, making the fiber more prone to breakage at these weak points. As the extractant content decreases, the breaking strength of the composite fiber significantly increases. The PA6 / PBT composite fiber obtained in the examples exhibits significantly better breaking strength, breaking elongation, crimp shrinkage, and abrasion resistance than the comparative example, and the composite yarn has a high dyeing rate, uniform dyeing, and no color difference. This invention is suitable for industrial production.

[0103] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0104] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing PA6 / PBT composite fibers by melt direct spinning, characterized in that, Including the following steps: S1, mix raw materials containing caprolactam, end-capping agent, water and catalyst A, and obtain PA6 condensate through ring-opening reaction and condensation reaction, and then devolatilize to obtain PA6 melt; S2, after mixing raw materials containing 1,4-butanediol, terephthalic acid and catalyst B, PBT condensate is obtained by esterification, pre-condensation and condensation reaction, and PBT melt is obtained by liquid phase thickening and segmented temperature control. S3, PA6 melt and PBT melt are respectively fed to the composite spinning assembly for melt direct spinning. The fiber is cooled, oiled, drawn and wound to obtain the PA6 / PBT composite fiber.

2. The method for preparing PA6 / PBT composite fibers by melt spinning according to claim 1, characterized in that, The PA6 melt has a hot water extractable content of ≤2wt%, of which the monomer content is ≤0.5wt%, the molecular weight is 32000-50000, and the relative viscosity is 2.4-2.

8.

3. The method for preparing PA6 / PBT composite fibers by melt direct spinning according to claim 1, characterized in that, The intrinsic viscosity of the PBT melt obtained by S2 is 1.0-1.2 dl / g.

4. The method for preparing PA6 / PBT composite fibers by melt spinning according to claim 1, characterized in that, In S1, the amount of water added relative to caprolactam is 1-5 wt%, the amount of end-capping agent added is 0.1-0.9 wt%, and the amount of catalyst added is 0.01-1.5 wt%.

5. The method for preparing PA6 / PBT composite fibers by melt spinning according to claim 1, characterized in that, The capping agent is a monoamine and / or a diamine; the monoamine includes aromatic amines and hindered amines; the diamine includes H2N(CH2). z NH2, p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, decanediamine, where z = 1~10; Catalyst A comprises nylon 66 salt and NH2(CH2). X One or more of COOH; wherein X is 4-10.

6. The method for preparing PA6 / PBT composite fibers by melt spinning according to claim 1, characterized in that, The mixing temperature in S1 is 75-120℃, and the mixing time is 10-60 min; the ring-opening reaction temperature is 210-270℃, the pressure inside the reactor is controlled at 1.0-6.0 bar, and the residence time is controlled at 2-10 h. The resulting product has a number-average molecular weight of 6000-15000, a relative viscosity of 1.4-2.0, and a hot water extractable content of 9.0-15.0 wt%. The polycondensation reaction in S1 is carried out at a temperature of 240-270℃, with the pressure inside the reactor controlled at -1.0-0.5 bar, for a time of 10-18 hours. The resulting PA6 polycondensate has a number-average molecular weight of 15,000-40,000, a relative viscosity of 2.1-2.3, and a hot water extractable content of 8.0-9.9 wt%. The devolatilization temperature in S1 is 250-290℃, the absolute pressure is 0.05-20kPa, and the residence time is controlled at 0.5-2.0h.

7. The method for preparing PA6 / PBT composite fibers by melt spinning according to claim 1, characterized in that, The molar ratio of 1,4-butanediol to terephthalic acid in S2 is 1.0-1.5, and the mass of catalyst added is 6-100 × 10⁻⁶ times the mass of terephthalic acid. -3 wt% Catalyst B comprises one or more of tetraisopropyl titanate, tetrabutyl titanate, alkoxyzirconium, antimony acetate, and alkoxytin.

8. The method for preparing PA6 / PBT composite fibers by melt spinning according to claim 1, characterized in that, In S2, the esterification reaction pressure is 40-90 kPa, the esterification temperature is 210-240℃, and the esterification rate is controlled to reach ≥98%; the pre-condensation and condensation reaction temperatures in S2 are 220-250℃, the pressure inside the reactor is controlled at 10-40 kPa, and the intrinsic viscosity of the obtained PBT condensate is 0.5-0.7 dl / g.

9. The method for preparing PA6 / PBT composite fibers by melt spinning according to claim 1, characterized in that, The specific steps involved in liquid phase viscosity enhancement and segmented temperature control in S2 are as follows: The PBT melt is obtained by melt blending the PBT condensate in a segmented temperature-controlled screw devourer with an online addition of a compatibilizer to achieve liquid-phase thickening. The segmented temperature-controlled screw devouring reactor comprises at least 5 segments, with a temperature of 240-270℃, an absolute pressure of 0.1-10kPa, and a residence time controlled at 0.3-0.5h; The compatibilizer includes one or more of bisphenol A type epoxy resins E-44, E-54, and EP-0199, and the added mass of the compatibilizer is 0.05-0.1% of the PBT condensate.

10. The method for preparing PA6 / PBT composite fibers by melt spinning according to claim 1, characterized in that, In S3, PA6 melt accounts for 10%-40% of the total mass, and PBT melt accounts for 60%-90% of the total mass. In S3, the conveying temperature is 250-270℃, and the melt is filtered through a filter with a filter element of 1-10μm. The process parameters for direct spinning of the melt in S3 include: using a spinneret with an outer circle and an inner gear structure, a side blowing speed of 0.2-0.8m / s, a spinning temperature controlled at 255-290℃, a draw ratio of 1.1-4.0, and a spinning speed controlled at 1500-4000m / min.

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