Method for preparing PA6 / 56 bio-based copolyamide fiber through melt direct spinning

Abstract

The invention discloses a method for preparing a PA6 / 56 bio-based copolyamide fiber through melt direct spinning, which comprises the following steps: mixing raw materials containing a caprolactam solution, a PA56 salt solution and a molecular weight regulator, preheating, carrying out prepolymerization reaction and polycondensation reaction to obtain a PA6 / 56 copolymer melt, and carrying out devolatilization to obtain a PA6 / 56 devolatilization melt; and carrying out melt spinning on the PA6 / 56 devolatilization melt to obtain the PA6 / 56 bio-based copolyamide fiber. According to the invention, bio-based 1, 5-pentamethylene diamine is adopted as a raw material of PA56, preheating and pre-polycondensation are firstly carried out after configuration, then polycondensation is carried out to further increase the number-average molecular weight of a nylon 6 prepolymer, and the obtained copolymer melt is in a molten state. Low polymers of the copolymer are removed through the devolatilization reactor, liquid phase extraction of PA6 / 56 is achieved, the extractable matter content of the obtained copolymer melt is smaller than or equal to 2 wt%, the technological process is simplified, and the production cycle, the equipment investment cost and the production energy consumption are greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of composite fiber preparation technology, specifically to a method for preparing PA6 / 56 bio-based copolyamide fibers by melt direct spinning. Background Technology

[0002] Polyamide 6 (PA6) fibers are widely used in textiles and other fields due to their advantages such as light weight, high strength, moisture absorption, and ease of dyeing. Traditional polyamide production processes use petroleum as raw material, involving condensation polymerization of diacid / diamine monomers and ring-opening polymerization of amino acid / lactam monomers, which suffers from high energy consumption and carbon emissions. The development, application, and replacement of traditional petroleum-based materials by bio-based environmentally friendly raw materials have become current research hotspots.

[0003] Bio-based polyamides are produced from renewable resources through bio-fermentation of raw materials such as glucose or cellulose, or by pyrolysis of vegetable oils (including castor oil, oleic acid, and linoleic acid). These bio-based polyamide monomers are then further polycondensed to obtain the final bio-based polyamide. PA56 is a novel bio-based polyamide material with excellent hygroscopicity, resilience, and dyeability, and is widely used in the apparel and textile industries. Compared to traditional petroleum-based nylon, PA56 suffers from lower heat distortion temperature, crystallinity, and mechanical properties, and its production cost is easily affected by fluctuations in the supply and demand of bio-based raw materials, resulting in higher production costs that limit its application and industrialization. However, by copolymerizing PA56 with other highly crystalline, high-strength polyamide materials (such as PA6) to form bio-based copolyamides, these performance defects can be overcome through adjustments to the formulation and structure.

[0004] Applications of PA6 / 5X copolymer fibers, especially in the textile industry, are rarely reported. Furthermore, the polymerization process of PA6 / 56 generates low-molecular-weight polymers (oligomers), primarily because the polymerization of PA6 is an equilibrium reaction, producing approximately 10% monomers and oligomers. These oligomers cannot be spun into fibers, and the large amount of small molecules entering the spinning process not only severely impacts the spinning process but also represents a significant waste of raw materials. Currently, the melt spinning process of chip spinning is commonly used to produce PA6 / 56 copolyamide fibers. This involves first polymerizing the PA6 / 56 copolymer, then extruding, pelletizing, extracting, and drying the resulting chips. These chips are then melt-spun by screw extrusion, metered by a metering pump, and finally spun into fibers.

[0005] For example, CN115449069A discloses "a copolyamide resin, copolyamide fiber and its preparation method," which involves polymerizing a polyamide 56 salt solution with a caprolactam aqueous solution, mixing the polymerized product with water, extracting, and filtering to obtain the copolyamide resin. The resin is then melted and spun to obtain the copolyamide fiber, which exhibits excellent softness, mechanical properties, hygroscopicity, and dyeing properties. CN108250433A discloses a PA6-56 copolymer material and its preparation method, which uses caprolactam as the main component and copolymerizes it with PA56 monomer pentanediamine adipate to obtain the PA6-56 copolymer material. After pelleting, hot water extraction, and drying, the resulting material is sliced. This material not only possesses the advantages of PA6, such as high strength, wear resistance, and acid and alkali resistance, but also exhibits better hygroscopicity and dyeability.

[0006] CN118007276A discloses "a bio-based polyamide carpet yarn and its preparation method," which obtains polyamide 6 / 56 copolymer particles through the reaction of bio-based polyamide 56 salt and caprolactam. After washing and drying, the PA6 / 56 copolyamide carpet yarn obtained by screw extrusion melt spinning exhibits good performance indicators. However, this process requires prior pelleting, extraction, and drying to obtain chips, followed by melt spinning to obtain PA6 / 56 copolyamide fibers. This results in high equipment investment costs, complex processes, long raw material turnover cycles, and high water and energy consumption, hindering its promotion and industrialization. Therefore, developing a new process for direct spinning of bio-based PA56 copolymerized with traditional polyamide 6 is an urgent problem to be solved. Summary of the Invention

[0007] This invention addresses the problem in the existing technology that PA6 / 56 copolyamide fiber preparation process cannot be directly spun from the melt due to the high extractable content. It provides a method for preparing copolyamide fibers by direct melting of PA56 salt and caprolactam after polymerization. This method can effectively control the extractable content and melt viscosity in the copolyamide melt, while improving the strength, dyeing performance, and product quality stability of the copolyamide fibers.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing PA6 / 56 bio-based copolyamide fibers by melt spinning includes the following steps: S1, mix raw materials containing caprolactam and water to obtain a caprolactam solution; mix raw materials containing 1,5-pentanediamine, adipic acid and water to obtain a PA56 salt solution; S2 involves mixing raw materials containing caprolactam solution, PA56 salt solution, and molecular weight regulator, preheating them, and then obtaining PA6 / 56 copolymer melt through prepolymerization and polycondensation reactions, followed by devolatilization to obtain PA6 / 56 devolatilized melt. S3, PA6 / 56 devolatilized melt is transported to the spinning assembly via a booster pump, melt filter, metering pump, and spinning box to obtain fiber through melt spinning. The fiber is then cooled, oiled, drawn, and wound to obtain PA6 / 56 bio-based copolyamide fiber.

[0009] This invention uses bio-based 1,5-pentanediamine as the raw material for PA56. After preparation, it undergoes preheating and pre-condensation, followed by condensation to further increase the number-average molecular weight of the nylon 6 prepolymer, resulting in a molten copolymer melt. The copolymer is then passed through a devolatilization reactor to remove oligomers, achieving liquid-phase extraction of PA6 / 56, ensuring the extractable content of the obtained copolymer melt is ≤2wt%. The resulting melt is then transported to a spinning assembly, where it is cooled, oiled, drawn, and wound to obtain PA6 / 56 copolymer fibers. This invention simplifies the process, significantly reducing production cycle time, equipment investment costs, and energy consumption. The resulting copolymer fibers offer complementary advantages, maintaining moisture-wicking properties close to PA56 while providing better softness, dyeability, mechanical properties, and elasticity due to copolymerization modification. Garments made from these fibers are more comfortable than those made from pure PA6 or pure PET (polyester) and can be widely used in sportswear, underwear, and other fabric applications.

[0010] Preferably, the PA6 / 56 devolatilized melt has a relative viscosity of 2.5-3.5, a number-average molecular weight of 30,000-100,000, and an extractable content of ≤2%.

[0011] Preferably, the raw materials in S2 also include additives, including one or more of antioxidants and matting agents; the added mass of the additives is 0.1 to 4.0 wt% of the total mass of caprolactam and pentanediamine adipate.

[0012] Preferably, the antioxidant comprises one or more of N,N'-bis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hexanediamine, DNP (N,N-di(β-naphthyl)-p-phenylenediamine), tris(2,4-di-tert-butylphenyl) phosphite, and AddWorks® TFB117, and the amount of antioxidant added is 0.1-1.5% of the total mass of caprolactam and pentanediamine adipate. Preferably, the matting agent is titanium dioxide, and the amount of titanium dioxide added is 0.2-2.0% of the total mass of caprolactam and pentanediamine adipate. Preferably, the mass of water added to the caprolactam solution is 1-5 wt% of the caprolactam. Preferably, the molar ratio of 1,5-pentanediamine to adipic acid is (1-1.2):1; wherein the mass concentration of polyamide 56 salt in the PA56 salt solution is 20-80%. Preferably, the mixing temperature is 75-120℃ and the mixing time is 1-10h.

[0013] Preferably, nitrogen gas is continuously purged into the stirred tank for mixing and protection.

[0014] The molar ratio of polyamide 56 salt to caprolactam in PA56 salt solution in S2 is (50:50) to (90:10); Preferably, the molecular weight regulator includes acetic acid and HOOC(CH2). z COOH, terephthalic acid, phthalic acid, aromatic amines, hindered amines (such as 4-amino-2,2,6,6-tetramethylpiperidine), and diamines; the diamines include H2N(CH2). z One or more of NH2, p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, and decanediamine, wherein z is 2 to 10; the amount added is 0.1-0.8% of the total mass of caprolactam and pentanediamine adipate.

[0015] Preferably, the preheating temperature in S2 is 140-200℃, and the preheating time is 1-5h; Preferably, the preheater is a combination of one or more of the following: tubular, stirred tank, and coil type preheaters. This preheater can fully mix caprolactam and pentamethylene adipate salt evenly, and through temperature control, prevent flash evaporation of the slurry when it enters the prepolymerization kettle due to excessive kettle temperature.

[0016] Preferably, the prepolymerization reaction temperature is 210-270℃, and the prepolymerization time is 0.5-2.5 MPa for 5-15 hours. The product obtained by the prepolymerization reaction has a relative viscosity of 1.3-1.8 and an extractable content of 9.0-15.5 wt%.

[0017] Preferably, the prepolymer reactor is equipped with a packed tower at the top to separate the high-temperature caprolactam-containing vapor into gas and liquid components. The monomer is returned to the prepolymer reactor, and the water vapor is condensed and sent to the packed tower to cool the high-temperature caprolactam vapor for reuse. A stirrer is installed in the middle of the prepolymer reactor to mix the pentamethylenediamine adipate salt with the ring-opened linear monomer and oligomers evenly and ensure a thorough reaction.

[0018] Preferably, the polycondensation reaction temperature is 230-290℃, the pressure inside the reactor is controlled at -0.9 to 0.3 bar, and the polycondensation time is controlled at 6 to 20 h; the resulting PA6 / 56 copolymer melt has a relative viscosity of 1.8 to 2.2 and an extractable content of 7.0 to 10.5 wt%.

[0019] Preferably, the top of the polycondensation tower is equipped with a bubble cap tower, which absorbs and refluxes the caprolactam monomers entrained in the high-temperature gas during the vacuuming process on the tower plate, thereby reducing material loss.

[0020] Preferably, the heat medium in the middle tube jacket of the polycondensation tower supplies heat to the polycondensation tower and then directly supplies heat to the preheater. Since heat is released during the polycondensation process, the temperature drop of the heat medium after passing through the middle tube of the polycondensation tower is relatively low, which is sufficient to provide heating for the preheater and can reduce the energy consumption of the heat medium.

[0021] Preferably, the devolatilization temperature in S2 is 250-290℃, the absolute pressure is 0.05-20kPa, and the devolatilization time is 0.5-3.0h; the resulting PA6 / 56 copolymer melt has a relative viscosity of 2.2-3.0 and an extractable content of 0.5-2.5wt%.

[0022] Preferably, the reactor used for devolatilization includes one or more of the following: thin film devolatilizer, falling film evaporator, stirred evaporator, drop strip type, screw extrusion type, co-rotating disk type devolatilizer, and paddle type devolatilizer; the devolatilization level is one of single-stage, two-stage, or three-stage.

[0023] As a preferred option, the level gauge used in the devolatilization reactor is a bubble-type differential pressure level gauge. The nitrogen gas entering from the high-pressure side can act as a desorption aid, removing high-melting-point dimers and oligomers during the vacuuming process, thereby reducing the content of extractables in the melt. The nitrogen gas flow rate is 40 mL / min.

[0024] As a preferred option, the PA6 / 56 devolatilization melt conveying temperature in S3 is 240-260℃, and the melt filter element is 1-10μm. By regulating the melt cooler to reduce the melt temperature after devolatilization and lowering the melt conveying temperature, the occurrence of reverse reaction can be effectively slowed down, the stability of melt viscosity can be maintained, and the formation of low molecular weight substances and gels can be reduced, thereby ensuring melt quality and spinnability.

[0025] Preferably, the spinneret type of the spinning assembly includes one of the following: circular, trilobal, flat, dumbbell-shaped, triangular, and rhomboid. Preferably, the melt conveying temperature is 240-250℃, the melt spinning speed is controlled at 3000-5500m / min, and the spinning temperature is controlled at 250-290℃; cooling is achieved by side blowing or ring blowing; wherein the side blowing air temperature is 16-19℃, the side blowing air velocity is 0.3-0.7m / s, the side blowing air humidity is 55-85%, and the height of the windless zone is 30-50mm.

[0026] Copolymer fibers such as undrawn yarn (UDY), fully drawn yarn (FDY), pre-oriented yarn (POY), and highly oriented yarn (HOY) are prepared according to requirements.

[0027] Preferably, the PA6 / 56 bio-based copolyamide fiber prepared by the method of the present invention has a breaking strength of ≥3.8cN / dtex, a moisture regain of ≥4.5%, a dyeing uniformity (grey card) of ≥4.0 grade, and a washing fastness of ≥4.0 grade.

[0028] Compared with the prior art, the present invention has the following beneficial effects: (1) The raw material for the production of the bio-based copolyamide fiber of the present invention, 1,5-pentanediamine, is produced by a biological method of fermentation or enzyme conversion, and is a green material.

[0029] (2) Currently, the common domestic and international technology for producing copolyamide fibers is the chip spinning process. The method of this invention can achieve direct spinning after the polymerization of PA56 salt solution and caprolactam, without the need to first produce chips. It eliminates intermediate processes such as extraction (crystallization), drying, conveying, and screw extrusion melting, simplifying the process and shortening the production cycle by about 2 / 3. Water consumption, energy consumption, and waste emissions are reduced, equipment investment and land occupation are reduced, and product manufacturing costs are lowered.

[0030] (3) This invention has excellent process controllability. By adding a packed tower to the prepolymerization reactor, high-temperature steam carrying caprolactam is separated into gas and liquid phases. The monomer is returned to the prepolymerization reactor, and the water is discharged. By controlling the drainage volume, the ring-opening reaction rate can be controlled. The agitator in the middle can make the adipate pentanediamine salt mixed evenly with the ring-opened linear monomer and oligomer, and react fully. In addition, by adjusting the vacuum conditions of polycondensation, such as reducing the vacuum degree, part of the polycondensation is placed in the devolatilization reactor, which slows down the liquid phase thickening process in the polycondensation reactor. The overall viscosity of the melt in the polycondensation reactor is low, the fluidity is good, and the residence time is long. This is conducive to the polycondensation reaction and full chain exchange between the ring-opened caprolactam molecules and the amino and carboxyl groups in PA56 salt. This increases the molecular weight while avoiding melt rupture and wall adhesion caused by a large amount of devolatilization and excessive molecular weight growth, which makes spinning difficult.

[0031] (4) The present invention adds a bubble cap tower to the polycondensation reactor, which absorbs and refluxes the caprolactam monomer entrained in the high-temperature gas during the vacuuming process on the tower plate and returns it to the polycondensation tower to continue the reaction, thereby reducing material loss. In combination with the exothermic characteristics of the polycondensation reaction, the heat medium in the middle tube jacket of the polycondensation tower supplies heat to the polycondensation tower and then directly supplies heat to the preheater, thereby reducing energy consumption.

[0032] (5) The bio-based copolyamide melt obtained by process control in this invention has the advantages of wide melting point range and moderate viscosity. The resulting copolyamide fiber has good high shrinkage performance, softness performance, mechanical properties, moisture absorption performance and good dyeing performance, and has good wearing performance. It can be widely used in the textile field.

[0033] This invention utilizes the existing mature PA6 polymerization and processing industrial chain, making it easier to achieve industrialized production and large-scale application, and accelerating the replacement of traditional materials with bio-based materials. Attached Figure Description

[0034] Figure 1 The image shows the GPC test spectrum of the devolatilized melt in Example 1.

[0035] Figure 2 The image shows the finished PA6 / 56 copolyamide fiber filament prepared in Example 1.

[0036] Figure 3 The image shows the cross-sectional morphology of the PA6 / 56 copolyamide fiber prepared in Example 1 under an optical microscope. Detailed Implementation

[0037] 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.

[0038] The raw materials used in the following specific embodiments were all purchased from the market, and the testing methods for the performance parameters involved in the following specific embodiments are as follows: (1) Relative viscosity The Ubbelohde viscometer method using concentrated sulfuric acid: Accurately weigh 0.25 ± 0.0002 g of dried polyamide 56 chips or its short fiber sample, add 50 mL of concentrated sulfuric acid (96 wt%) to dissolve, and measure and record the flow time t0 of the concentrated sulfuric acid and the flow time t of the polyamide sample solution in a 25℃ constant temperature water bath. Viscosity calculation formula: Relative viscosity = t / t0; t—solution flow time; t0—solvent flow time.

[0039] (2) Content of 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 the extract was cooled, it 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: The content of extractable substances in hot water is expressed as ω1, where ω1 is the extractable 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).

[0045] (3) Linear density The linear density test method can refer to GB / T14343-2008 Test Method for Linear Density of Chemical Fiber Filaments; a YG086 yarn length measuring instrument was used, with a yarn frame circumference of (1.000±0.002) m. The length and mass of each sample were collected separately. The length was obtained by multiplying the yarn frame length by the number of turns. After the sample was calibrated in standard atmosphere, it was weighed to an accuracy of 1 mg. Each sample was tested 10 times, and the average value was calculated.

[0046] (4) Fracture strength, elongation at break, and modulus The determination of breaking strength and elongation at break can refer to GB / T14344-2008 Test Method for Tensile Properties of Chemical Fibers; apply a pretension of 0.05±0.005cN / dtex, a holding distance of 500mm, a tensile speed of 500mm / min, and the modulus = breaking strength corresponding to 1% elongation at break × 100.

[0047] (5) Boiling water shrinkage rate The boiling water shrinkage rate test method refers to GB / T 6505-2017 "Test Method for Heat Shrinkage Rate of Chemical Fiber Filaments (After Treatment)". For the fiber sample to be tested, use a length measuring instrument to accurately wind a strand of yarn with a specified number of turns and circumference, ensuring it is in a relaxed state without tension. Suspend the strand with a specified pre-tension weight (selected according to fiber linear density) at the lower end. After 30 seconds, accurately measure and record the original length of the strand. Immerse the relaxed strand in boiling water at 100℃, ensuring it is completely submerged but not in contact with the container wall. The treatment time is strictly controlled to 30 minutes. Remove the strand, cool it in room temperature water, then gently absorb excess water and air dry naturally at room temperature or dry at low temperature to avoid affecting the test results. Apply the same pre-tension as in the first step to the dried strand again and measure its final length. The boiling water shrinkage rate can be calculated using the following formula: Boiling water shrinkage rate = (Original length - Treated length) / Original length × 100%.

[0048] (6) Moisture regain The moisture regain test method follows GB / T 6503-2017 "Test Method for Moisture Regain of Chemical Fibers". Weigh approximately 50g of sample and record the mass before drying. Dry at 105±3℃ to constant weight (weigh every 10 minutes, with a difference ≤0.05%), and weigh the mass directly inside the drying chamber. The moisture regain can be calculated using the following formula: Moisture regain R = (mass before drying - mass after drying) / mass after drying × 100%.

[0049] (7) Color fastness to soap washing The test method for color fastness to washing with soap is in accordance with GB / T 3921-2008 "Textiles - Tests for Color Fastness - Color Fastness to Washing with Soap". A 100mm × 40mm sample is taken and sewn together with a multi-fiber lining of the same size or two single-fiber linings along one short side. The combined sample, a specified number of steel balls, and preheated soap solution are placed in a stainless steel container at a liquor ratio of 50:1 and incubated at 95℃ for 30 minutes. After removal, the sample is first rinsed twice with grade III water, then rinsed thoroughly with running water and the excess water is squeezed out. Under standard light, the color change of the sample and the staining grade of the lining (grades 1-5, with grade 5 being the best) are assessed using the GB / T 250 (color change) and GB / T 251 (staining) gray scales.

[0050] (8) Staining uniformity The dyeing uniformity test method refers to FZ / T-50008-2015 "Test for Dyeing Uniformity of Nylon Filament". Take 5g / L of neutral soap powder, dissolve it in a small amount of water at 60℃ to make a soap solution, and at a liquor ratio of 1:25, immerse the garter belt in the soap solution. Heat to 90℃ for 20 minutes to remove oil. Wash with soft water at 85℃ until neutral, then dehydrate and prepare for dyeing. At a liquor ratio of 1:20, add water, 1% neutral ash, and 1% leveling agent O to the dyeing machine. Dye the degreased garter belt in the dye bath at 98℃ for 30 minutes. Drain the waste liquid, cool, remove the garter belt, wash with water, dehydrate, and dry at 40℃. Place the dyed garter belt on a color judgment frame or color judgment board, with the fabric surface at a 45° angle to the incident light, the observation direction approximately perpendicular to the indicator surface, and the observation distance 30-40cm. The test garter belts were laid flat and slowly moved horizontally. The depth, lightness, spots, stripes, bands, and textures of the garter belts were observed segment by segment. The color difference between the darkest and lightest parts of the garter belts was pressed down with the frame provided by GB / T 250 and compared with the gray sample card. The grade was visually evaluated.

[0051] Example 1 Step 1: At a temperature of 80℃, 100kg of caprolactam and deionized water are mixed in proportion and stirred for 30min under mechanical stirring (100r / min); wherein the mass of deionized water added is 5wt% relative to caprolactam, to obtain caprolactam slurry; Step 2: At a temperature of 85℃, 1124 kg of 1,5-pentanediamine, 1461.4 kg of adipic acid (molar ratio of 1,5-pentanediamine to adipic acid is 1.1:1) and 1108 kg of demineralized water were mixed and stirred for 2 hours under mechanical stirring (50 r / min) to obtain a 70% bio-based PA56 salt solution. Step 3: The PA56 salt solution, caprolactam solution, acetic acid, and antioxidant are delivered by metering pumps, mixed by a static mixer, and then delivered to the preheater. The caprolactam flow rate is 11.3 kg / h, the PA56 salt flow rate is 23.0 kg / h, the acetic acid addition is 0.14 kg / h, and the antioxidant addition is 0.17 kg / h.

[0052] Step 4: The mixture is stirred in a preheater for 2 hours at a pre-reaction temperature of 150°C, a stirring speed of 80 r / min, and a preheater pressure of 10 bar.

[0053] Step 5: The preheated material is pumped to the prepolymer reactor through a gear pump. The prepolymer temperature is controlled at 220℃, the prepolymer pressure is controlled at 5 bar, and the residence time is 6 hours to obtain the prepolymer. The relative viscosity of the prepolymer is 1.6, and the extractable content is 12.3%.

[0054] Step 6: The prepolymer is transported to a polycondensation reactor for polycondensation reaction. The pressure of the polycondensation reaction is controlled at absolute pressure of 50 kPa, the reaction temperature is 260℃, and the residence time is 10h to obtain a bio-based PA6 / 56 copolymer melt with a relative viscosity of 1.9 and an extractable content of 7.6%.

[0055] Step 7: The bio-based PA6 / 56 copolymer melt is pumped to the devolatilization reactor via a melt gear pump, and further devolatilization is performed using a disc devolatilizer. 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 39315, a relative viscosity of 2.56, and an extractable content of 1.4%. Its GPC spectrum is shown below. Figure 1 As shown.

[0056] Step 8: The devolatilized PA6 / 56 copolymer is transported to the spinning box via a melt cooler, a melt booster pump, and a metering pump. The conveying temperature is adjusted to 245°C by the melt cooler.

[0057] Step 9: Using a circular spinneret, the fibers are extruded, cooled, oiled, drawn, and wound through the spinning assembly. The spinneret specifications are Φ75*Φ0.25*0.65*48F. The spinning temperature is 280℃, the side-blowing air velocity is 0.45m / s, the side-blowing air temperature is 17℃, the side-blowing air humidity is 60%, the hot roller temperature is 170℃, and the spinning speed is 4200m / min. This yields bio-based PA6 / 56-FDY copolyamide fiber. (See attached image.) Figure 2 As shown, the cross-sectional morphology under a fiber optic microscope is as follows: Figure 3 As shown.

[0058] Example 2 Step 1: At a temperature of 80℃, 100kg of caprolactam and deionized water are mixed in proportion and stirred for 30min under mechanical stirring (100r / min); wherein the mass of deionized water added is 3wt% relative to caprolactam, to obtain caprolactam slurry; Step 2: At a temperature of 85℃, 1124 kg of 1,5-pentanediamine, 1461.4 kg of adipic acid (molar ratio of 1,5-pentanediamine to adipic acid is 1.1:1) and 1108 kg of demined water were mixed and stirred for 2 hours under mechanical stirring (50 r / min) to obtain a 70% bio-based PA56 salt solution. Step 3: The PA56 salt solution, caprolactam solution, acetic acid, and antioxidant are delivered by metering pumps, mixed by a static mixer, and then delivered to the preheater. The caprolactam flow rate is 11.3 kg / h, the PA56 salt flow rate is 53.7 kg / h, the acetic acid addition is 0.26 kg / h, and the antioxidant addition is 0.33 kg / h.

[0059] Step 4: The mixture is stirred in a preheater for 2 hours at a pre-reaction temperature of 160℃, a stirring speed of 80r / min, and a preheater pressure of 8bar.

[0060] Step 5: The preheated material is pumped to the prepolymer reactor through a gear pump. The prepolymer temperature is controlled at 220℃, the prepolymer pressure is controlled at 5 bar, and the residence time is 8 hours to obtain the prepolymer. The relative viscosity of the prepolymer is 1.7, and the extractable content is 11.0%.

[0061] Step 6: The product obtained from the prepolymerization is transported to the polycondensation reactor for polycondensation reaction. The pressure of the polycondensation reaction is controlled at absolute pressure of 40 kPa, the reaction temperature is 265°C, and the residence time is 10 h to obtain a bio-based PA6 / 56 copolymer melt with a relative viscosity of 2.0 and an extractable content of 6.8%.

[0062] Step 7: The bio-based PA6 / 56 copolymer melt is pumped to the devolatilization reactor via a melt gear pump, and further devolatilization is performed using a falling film evaporator; the devolatilization temperature is maintained at 270℃, the devolatilization lasts for 60 minutes, and the process pressure is below 100 Pa; the resulting devolatilized melt has a molecular weight of 38145, a relative viscosity of 2.53, and an extractable content of 1.5%. Step 8: The devolatilized PA6 / 56 copolymer product is transported to the spinning box via a melt cooler, a melt booster pump, and a metering pump. The conveying temperature is adjusted to 250°C by the melt cooler.

[0063] Step 9: Using a circular spinneret, the spinning process involves extrusion, cooling, oiling, drawing, and winding. The spinneret specifications are Φ75*Φ0.25*0.65*48F. The spinning temperature is 280℃, the side-blowing air velocity is 0.43m / s, the side-blowing air temperature is 17℃, the side-blowing air humidity is 60%, the hot roller temperature is 170℃, and the spinning speed is 4200m / min, thus obtaining bio-based PA6 / 56-FDY copolyamide fiber.

[0064] Example 3 Step 1: At a temperature of 80℃, 100kg of caprolactam and deionized water are mixed in proportion and stirred for 30min under mechanical stirring (100r / min); wherein the mass of deionized water added is 2wt% relative to caprolactam, to obtain caprolactam slurry; Step 2: At a temperature of 85℃, 1226.2 kg of 1,5-pentanediamine, 1461.4 kg of adipic acid (molar ratio of 1,5-pentanediamine to adipic acid is 1.2:1) and 1108 kg of demined water were mixed and stirred for 2 hours under mechanical stirring (50 r / min) to obtain a 70% bio-based PA56 salt solution. Step 3: The PA56 salt solution, caprolactam solution, acetic acid, and antioxidant are delivered by metering pumps, mixed by a static mixer, and then delivered to the preheater. The caprolactam flow rate is 11.3 kg / h, the PA56 salt flow rate is 92.1 kg / h, the acetic acid addition is 0.42 kg / h, and the antioxidant addition is 0.52 kg / h.

[0065] Step 4: The mixture is stirred in a preheater for 2 hours at a pre-reaction temperature of 170°C, a stirring speed of 60 r / min, and a preheater pressure of 8 bar.

[0066] Step 5: The preheated material is pumped to the prepolymer reactor through a gear pump. The prepolymer temperature is controlled at 240℃, the prepolymer pressure is controlled at 6 bar, and the residence time is 8 hours to obtain the prepolymer. The relative viscosity of the prepolymer is 1.6, and the extractable content is 10.2%.

[0067] Step 6: The product obtained from the prepolymerization is transported to the polycondensation reactor for polycondensation reaction. The pressure of the polycondensation reaction is controlled at absolute pressure of 40 kPa, the reaction temperature is 270°C, and the residence time is 10 h to obtain a bio-based PA6 / 56 copolymer melt with a relative viscosity of 2.1 and an extractable content of 6.1%.

[0068] Step 7: The bio-based PA6 / 56 copolymer melt is transported to the devolatilization reactor via a melt gear pump and further devolatilization is carried out using a screw devolatilizer; the devolatilization temperature is maintained at 280℃, the devolatilization lasts for 60 minutes, and the process pressure is below 100Pa; the resulting devolatilized melt has a molecular weight of 37246, a relative viscosity of 2.52, and an extractable content of 0.9wt%.

[0069] Step 8: The devolatilized PA6 / 56 copolymer product is transported to the spinning box via a melt cooler, a melt booster pump, and a metering pump. The conveying temperature is adjusted to 248°C by the melt cooler.

[0070] Step 9: Using a circular spinneret, the spinning process involves extrusion, cooling, oiling, drawing, and winding. The spinneret specifications are Φ75*Φ0.25*0.65*48F. The spinning temperature is 280℃, the side-blowing air velocity is 0.45m / s, the side-blowing air temperature is 17℃, the side-blowing air humidity is 60%, the hot roller temperature is 170℃, and the spinning speed is 4200m / min, thus obtaining bio-based PA6 / 56-FDY copolyamide fiber.

[0071] Example 4 Step 1: At a temperature of 80℃, 100kg of caprolactam and deionized water are mixed in proportion and stirred for 30min under mechanical stirring (100r / min); wherein the mass of deionized water added is 3wt% relative to caprolactam, to obtain caprolactam slurry; Step 2: At a temperature of 85℃, 1226.2 kg of 1,5-pentanediamine, 1461.4 kg of adipic acid (molar ratio of 1,5-pentanediamine to adipic acid is 1.2:1) and 1108 kg of demined water were mixed and stirred for 2 hours under mechanical stirring (50 r / min) to obtain a 70% bio-based PA56 salt solution. Step 3: The PA56 salt solution, caprolactam solution, acetic acid, and antioxidant are delivered by metering pumps, mixed by a static mixer, and then delivered to the preheater. The caprolactam flow rate is 11.3 kg / h, the PA56 salt flow rate is 207.3 kg / h, the acetic acid addition is 0.87 kg / h, and the antioxidant addition is 1.09 kg / h.

[0072] Step 4: The mixture is stirred in a preheater for 2 hours at a pre-reaction temperature of 180°C, a stirring speed of 60 r / min, and a preheater pressure of 8 bar.

[0073] Step 5: The preheated material is pumped to the prepolymer reactor through a gear pump. The prepolymer temperature is controlled at 245℃, the prepolymer pressure is controlled at 8 bar, and the residence time is 8 hours to obtain the prepolymer. The relative viscosity of the prepolymer is 1.6, and the extractable content is 9.4%.

[0074] Step 6: The product obtained from the prepolymerization is transported to the polycondensation reactor for polycondensation reaction. The pressure of the polycondensation reaction is controlled at absolute pressure of 30 kPa, the reaction temperature is 275°C, and the residence time is 10 h to obtain a bio-based PA6 / 56 copolymer melt with a relative viscosity of 2.2 and an extractable content of 5.2%.

[0075] Step 7: The bio-based PA6 / 56 copolymer melt is transported to the devolatilization reactor via a melt gear pump and further devolatilization is carried out using a falling film devolatilizer; the devolatilization temperature is maintained at 280℃, the devolatilization lasts for 60 minutes, and the process pressure is below 100Pa; the resulting devolatilized melt has a molecular weight of 36273, a relative viscosity of 2.50, and an extractable content of 0.8wt%.

[0076] Step 8: The devolatilized PA6 / 56 copolymer is transported to the spinning box via a melt cooler, a melt booster pump, and a metering pump. The conveying temperature is adjusted to 245°C by the melt cooler.

[0077] Step 9: Using a circular spinneret, the spinning process involves extrusion, cooling, oiling, drawing, and winding. The spinneret specifications are Φ75*Φ0.25*0.65*48F. The spinning temperature is 290℃, the side-blowing air velocity is 0.48m / s, the side-blowing air temperature is 17℃, the side-blowing air humidity is 60%, the hot roller temperature is 170℃, and the spinning speed is 4200m / min, thus obtaining bio-based PA6 / 56-FDY copolyamide fiber.

[0078] Comparative Example 1 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); wherein, relative to caprolactam, the mass of deionized water added was 2.0 wt%, and the mass 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.

[0079] Step 5: The preheated material is pumped to the prepolymer reactor through a gear pump. The prepolymer temperature is controlled at 245℃, the prepolymer pressure is controlled at 1.5 bar, and the residence time is 4 hours to obtain the prepolymer. The relative viscosity of the prepolymer is 1.6, and the extractable content is 13.2%.

[0080] Step 6: The product obtained from the prepolymerization is transported to the 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 with a relative viscosity of 1.9 and an extractable content of 8.1%.

[0081] Step 7: 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 2.58, and an extractable content of 0.8 wt%.

[0082] Step 8: The devolatilized PA6 / 56 copolymer is transported to the spinning box via a melt cooler, a melt booster pump, and a metering pump. The conveying temperature is adjusted to 245°C by the melt cooler.

[0083] Step 9: Using a circular spinneret, the spinning process involves extrusion, cooling, oiling, drawing, and winding. The spinneret specifications are Φ75*Φ0.25*0.65*48F. The spinning temperature is 265℃, the side-blowing air velocity is 0.45m / s, the side-blowing air temperature is 17℃, the side-blowing air humidity is 60%, the hot roller temperature is 170℃, and the spinning speed is 4200m / min, thus obtaining bio-based PA6-FDY copolyamide fiber.

[0084] Comparative Example 2 Step 1: At a temperature of 85℃, 1021.2 kg of 1,5-pentanediamine, 1461.4 kg of adipic acid (molar ratio of 1,5-pentanediamine to adipic acid is 1:1) and 2300 kg of demineralized water were mixed and stirred for 2 hours under mechanical stirring (50 r / min) to obtain a 50% bio-based PA56 salt solution. Step 3: The PA56 salt solution, acetic acid, and antioxidant are delivered by metering pump, mixed by static mixer, and then delivered to preheater. The PA56 salt flow rate is 207.3 kg / h, the terephthalic acid addition is 0.83 kg / h, and the antioxidant addition is 1.04 kg / h.

[0085] Step 4: The mixture is stirred in a preheater for 2 hours at a pre-reaction temperature of 160°C, a stirring speed of 60 r / min, and a preheater pressure of 10 bar.

[0086] Step 5: The preheated material is pumped to the prepolymer reactor through a gear pump. The prepolymer temperature is controlled at 245℃, the prepolymer pressure is controlled at 3 bar, and the residence time is 8 hours to obtain the prepolymer with a relative viscosity of 1.5.

[0087] Step 6: The product obtained from the prepolymerization is transported to a polycondensation reactor for polycondensation reaction. The pressure of the polycondensation reaction is controlled at absolute pressure of 30 kPa, the reaction temperature is 280℃, and the residence time is 10 h to obtain a bio-based PA56 copolymer melt with a relative viscosity of 2.1.

[0088] Step 7: The bio-based PA56 copolymer melt is transported to the devolatilization reactor via a melt gear pump, and two-stage devolatilization is carried out using a stirred evaporator and a rotating packed bed. The temperature of the first-stage devolatilization is maintained at 270℃, the devolatilization lasts for 30 minutes, and the process pressure is below 2 kPa. The temperature of the second-stage devolatilization is maintained at 290℃, the devolatilization lasts for 40 minutes, and the process pressure is below 100 Pa. The resulting devolatilized melt has a molecular weight of 31297, a relative viscosity of 2.47, and an extractable content of 1.0 wt%.

[0089] Step 8: The devolatilized PA6 / 56 copolymer product is transported to the spinning box via a melt cooler, a melt booster pump, and a metering pump. The conveying temperature is adjusted to 260°C by the melt cooler.

[0090] Step 9: Using a circular spinneret, the spinning process involves extrusion, cooling, oiling, drawing, and winding. The spinneret specifications are Φ75*Φ0.25*0.65*48F. The spinning temperature is 260℃, the side-blowing air velocity is 0.40m / s, the side-blowing air temperature is 17℃, the side-blowing air humidity is 60%, the hot roller temperature is 170℃, and the spinning speed is 4200m / min, thus obtaining bio-based PA56-FDY copolyamide fiber.

[0091] Comparative Example 3 Step 1: At a temperature of 80℃, 100kg of caprolactam and deionized water are mixed in proportion and stirred for 30min under mechanical stirring (100r / min); wherein the mass of deionized water added is 3wt% relative to caprolactam, to obtain caprolactam slurry; Step 2: At a temperature of 85℃, 1124 kg of 1,5-pentanediamine, 1461.4 kg of adipic acid (molar ratio of 1,5-pentanediamine to adipic acid is 1.1:1) and 1108 kg of demined water were mixed and stirred for 2 hours under mechanical stirring (50 r / min) to obtain a 70% bio-based PA56 salt solution. Step 3: The PA56 salt solution, caprolactam solution, acetic acid, and antioxidant are delivered by metering pumps, mixed by a static mixer, and then delivered to the preheater. The caprolactam flow rate is 11.3 kg / h, the PA56 salt flow rate is 53.7 kg / h, the acetic acid addition is 0.26 kg / h, and the antioxidant addition is 0.33 kg / h.

[0092] Step 4: The mixture is stirred in a preheater for 2 hours at a pre-reaction temperature of 160℃, a stirring speed of 80r / min, and a preheater pressure of 8bar.

[0093] Step 5: The preheated material is pumped to the prepolymer reactor through a gear pump. The prepolymer temperature is controlled at 220℃, the prepolymer pressure is controlled at 5 bar, and the residence time is 8 hours to obtain the prepolymer. The relative viscosity of the prepolymer is 1.7, and the extractable content is 11.0%.

[0094] Step 6: The product obtained from the prepolymerization is transported to the polycondensation reactor for polycondensation reaction. The pressure of the polycondensation reaction is controlled at absolute pressure of 40 kPa, the reaction temperature is 270°C, and the residence time is 16 h to obtain bio-based PA6 melt with a relative viscosity of 2.4 and an extractable content of 8.1%.

[0095] Step 7: The polycondensation melt is transported to a pelletizer through a melt pipeline, pelletized, extracted with 98℃ hot water for 12 hours, and vacuum dried at 80℃ for 8 hours to obtain PA6 / 56 copolyamide chips.

[0096] Step 8: Add the extracted and dried PA6 / 56 copolyamide chips into the hopper, and then melt-extrude them through a screw extruder. The screw extruder includes 5 heating zones with temperatures of 255℃, 260℃, 265℃, 275℃, and 280℃ respectively. The screw speed is 80 r / min.

[0097] Step 9: The copolyamide melt is transported to the spinning box through the melt pipeline. After being accurately metered by the metering pump, it is injected into the spinning assembly. The melt transport temperature is 260℃.

[0098] Step 10: Using a circular spinneret, the spinning process involves extrusion, cooling, oiling, drawing, and winding. The spinneret specifications are Φ75*Φ0.25*0.65*48F. The spinning temperature is 270℃, the side-blowing air velocity is 0.45m / s, the side-blowing air temperature is 17℃, the side-blowing air humidity is 60%, the hot roller temperature is 170℃, and the spinning speed is 4200m / min, thus obtaining bio-based PA6 / 56-FDY copolyamide fiber.

[0099] The spinning melts and polyamide fibers obtained in Examples 1-4 and Comparative Examples 1-3 were subjected to performance testing, and the test results are shown in Table 1.

[0100] Table 1. Properties of spinning melt and polyamide fiber in the examples and comparative examples.

[0101] As shown by the indicators of the various examples and comparative examples, the fiber breaking strength, breaking elongation, and dyeing uniformity obtained in the examples are significantly better than those in the comparative examples. The performance of the bio-based PA6 / 56 copolyamide fiber obtained by melt spinning is better than that of single PA6 or PA56 fibers. This is because the addition of bio-based PA56 disrupts the regularity of the PA6 chain, reduces the number of hydrogen bonds in the copolymer, and forms cavities inside the polymer. This increases the mobility of the chain segments and disrupts the regularity of the PA6 molecular chain and its hydrogen bond network, effectively improving the melt flowability of PA6. This allows PA6 to achieve better flowability at the same temperature, thereby improving the melt processing performance. On the other hand, the introduction of highly crystalline PA6 improves the regularity of the chain, enabling the copolymer to form a more stable structure with a higher melting point. The thermal and mechanical properties of the copolymer are further improved, ultimately resulting in copolyamide fibers with good mechanical properties, moisture absorption properties, and good dyeing properties.

[0102] As can be seen from the data in Example 2 and Comparative Example 3, the PA6 / 56 melt copolymerized using the same method produces fibers with higher breaking strength, elongation at break, and better dyeing uniformity after being spun by a booster pump following melt devolatilization and then remelted and extruded. Furthermore, direct melt spinning significantly simplifies the process, greatly reducing production cycle time and energy consumption. The existing mature PA6 polymerization and processing industrial chain can be utilized, making industrial-scale production and large-scale application easier to achieve, accelerating the replacement of traditional materials with bio-based materials.

[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 / 56 bio-based copolyamide fibers by melt direct spinning, characterized in that, Including the following steps: S1, mix raw materials containing caprolactam and water to obtain a caprolactam solution; mix raw materials containing 1,5-pentanediamine, adipic acid and water to obtain a PA56 salt solution; S2 involves mixing raw materials containing caprolactam solution, PA56 salt solution, and molecular weight regulator, preheating them, and then obtaining PA6 / 56 copolymer melt through prepolymerization and polycondensation reactions, followed by devolatilization to obtain PA6 / 56 devolatilized melt. S3, PA6 / 56 devolatilized melt is transported to the spinning assembly via a booster pump, melt filter, metering pump, and spinning box to obtain fiber through melt spinning. The fiber is then cooled, oiled, drawn, and wound to obtain PA6 / 56 bio-based copolyamide fiber.

2. The method for preparing PA6 / 56 bio-based copolyamide fibers by melt spinning according to claim 1, characterized in that, The PA6 / 56 devolatilized melt has a relative viscosity of 2.5-3.5, a number-average molecular weight of 30,000-100,000, and an extractable content of ≤2%.

3. The method for preparing PA6 / 56 bio-based copolyamide fibers by melt spinning according to claim 1, characterized in that, The raw materials in S2 also include additives, including one or more of antioxidants and matting agents; the added mass of the additives is 0.1 to 4.0 wt% of the total mass of caprolactam and pentanediamine adipate.

4. The method for preparing PA6 / 56 bio-based copolyamide fibers by melt spinning according to claim 1, characterized in that, The mass of water added to the caprolactam solution is 1-5 wt% of the caprolactam mass. The molar ratio of 1,5-pentanediamine to adipic acid is (1-1.2):1; wherein the mass concentration of polyamide 56 salt in the PA56 salt solution is 20-80%. The mixing temperature is 75-120℃, and the mixing time is 1-10h.

5. The method for preparing PA6 / 56 bio-based copolyamide fibers by melt spinning according to claim 1, characterized in that, The molar ratio of polyamide 56 salt to caprolactam in PA56 salt solution in S2 is (50:50) to (90:10); The molecular weight regulators include acetic acid and HOOC(CH2). z COOH, terephthalic acid, phthalic acid, aromatic amines, hindered amines, and diamines; the diamines include H2N(CH2). z One or more of NH2, p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, and decanediamine, wherein z is 2 to 10; the amount added is 0.1-0.8% of the total mass of caprolactam and pentanediamine adipate.

6. The method for preparing PA6 / 56 bio-based copolyamide fibers by melt spinning according to claim 1, characterized in that, The preheating temperature in S2 is 140-200℃, and the preheating time is 1-5 hours. The preheater employs one or more combinations of tubular, stirred tank, and coil preheating equipment; the prepolymerization reaction temperature is 210-270℃, and the prepolymerization time is 5-15 h under the conditions of 0.5-2.5 MPa pressure inside the tank; the product obtained from the prepolymerization reaction has a relative viscosity of 1.3-1.8, and the extractable content is 9.0-15.5 wt%.

7. The method for preparing PA6 / 56 bio-based copolyamide fibers by melt spinning according to claim 1, characterized in that, The polycondensation reaction temperature is 230-290℃, the pressure inside the reactor is controlled at -0.9 to 0.3 bar, and the polycondensation time is controlled at 6 to 20 h; the obtained PA6 / 56 copolymer melt has a relative viscosity of 1.8 to 2.2 and an extractable content of 5.0 to 10.5 wt%.

8. The method for preparing PA6 / 56 bio-based copolyamide fibers by melt spinning according to claim 1, characterized in that, The devolatilization temperature in S2 is 250-290℃, the absolute pressure is 0.05-20kPa, and the devolatilization time is 0.5-3.0h. The reactors used for devolatilization include 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 is one of single-stage, two-stage, or three-stage.

9. The method for preparing PA6 / 56 bio-based copolyamide fibers by melt spinning according to claim 1, characterized in that, In S3, the PA6 / 56 devolatilized melt conveying temperature is 250-270℃, and the melt filter element is 1-10μm.

10. The method for preparing PA6 / 56 bio-based copolyamide fibers by melt spinning according to claim 1, characterized in that, The spinneret type of the spinning assembly includes one of the following: round, trilobal, flat, dumbbell, triangular, and rhomboid. The melt spinning speed is controlled at 3000-5500 m / min, and the spinning temperature is controlled at 250-290℃; cooling is achieved by side blowing or ring blowing; the side blowing air temperature is 16-19℃, the side blowing air velocity is 0.3-0.7 m / s, the side blowing air humidity is 55-85%, and the height of the windless zone is 30-50 mm.

Images