Preparation method and application of polylactic acid-based composite fiber

Abstract

The application discloses a preparation method and application of polylactic acid-based composite fibers, and relates to the technical field of fiber materials.The preparation method comprises the following steps: preparing polyimide A;extruding and cutting polylactic acid, inorganic fillers, a crosslinking agent and the prepared polyimide A to obtain a master batch;then adding the prepared master batch into a feeding hopper, and obtaining the polylactic acid-based composite fibers through coaxial jet holes.

Description

Technical Field

[0001] This invention relates to the field of fiber materials technology, specifically to a method for preparing polylactic acid-based composite fibers and their applications. Background Technology

[0002] Polylactic acid (PLA), a bio-based polymer material derived from renewable biomass (such as corn starch and sugarcane), possesses excellent biocompatibility and biodegradability. Its products can be completely degraded into carbon dioxide and water through composting or natural processes after use, fundamentally solving the long-term residue problem of plastic waste. Therefore, PLA fibers show broad application prospects and enormous potential to replace traditional petroleum-based plastics in fields such as disposable medical and hygiene products, agricultural nonwoven fabrics, textiles, clothing, and packaging materials.

[0003] However, polylactic acid (PLA) materials have several inherent drawbacks in practical applications. First, the high rigidity of PLA molecular chains restricts the movement of chain segments, leading to significant brittleness. Its notched impact strength at room temperature is low, and its elongation at break is typically less than 10%, severely limiting its application in flexible textiles and impact-resistant products. Second, PLA has a low heat distortion temperature, making its products prone to creep deformation at high temperatures, and its heat resistance is far inferior to traditional engineering plastics. Furthermore, PLA has a narrow melt processing window and insufficient melt strength, making it susceptible to melt fracture or breakage during high-speed spinning, thus limiting its spinning speed and production efficiency.

[0004] In recent years, research on blending high-performance polyimide (PI) with polylactic acid (PLA) to improve its heat resistance and mechanical properties has gradually attracted attention. Polyimide possesses excellent high-temperature resistance, mechanical strength, and chemical stability, which theoretically can effectively compensate for the heat resistance deficiencies of PLA. However, the molecular chains of traditional polyimide are extremely rigid, with melting temperatures typically exceeding 300°C, higher than the decomposition temperature of PLA (approximately 210°C). Furthermore, due to the significant difference in polarity between the hydrophobic aromatic backbone of polyimide and the aliphatic ester chains of PLA, interfacial adhesion is weak, and phase separation is severe, leading to the deterioration of fiber mechanical properties.

[0005] Therefore, developing a polyimide compound with good interfacial compatibility and excellent mechanical properties with polylactic acid is the key to realizing one-step melt molding and high performance of polylactic acid fibers. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing polylactic acid-based composite fibers and their applications, so as to overcome the shortcomings in related technologies.

[0007] According to a first aspect of the present invention, a method for preparing polylactic acid-based composite fibers is provided, the method comprising the following steps: Step 1: Prepare polyimide A; the polyimide A has the structural formula represented by the following formula A-1: R1, R2, R3, and R4 are each independently selected from direct bonds, substituted or unsubstituted C1-C10 alkyl groups, substituted or unsubstituted C2-C10 alkenyl groups, or substituted or unsubstituted C1-C10 alkoxy groups; Ar1 ​​and Ar2 are each independently selected from substituted or unsubstituted C3-30 cycloalkyl groups, substituted or unsubstituted C6-C30 aryl groups, substituted or unsubstituted 3-30 membered heterocyclic groups, or substituted or unsubstituted 5-30 membered heteroaryl groups. Step 2: Polylactic acid, inorganic filler, crosslinking agent and polyimide A prepared in step 1 are extruded and pelletized to obtain masterbatch; Step 3: Add the masterbatch prepared in Step 2 into the feeding funnel, and spin it through the coaxial nozzle to obtain the polylactic acid-based composite fiber.

[0008] In one aspect of this invention, in step 2, the polylactic acid is selected from poly-L-lactic acid, poly-D-lactic acid, or poly-racemic lactic acid.

[0009] In one aspect of this invention, the inorganic filler is selected from at least one of magnesium carbonate, barium carbonate, calcium carbonate, silicon dioxide, aluminum hydroxide, calcium oxide, zinc oxide, montmorillonite, talc, kaolin, and hydroxyapatite. Preferably, the inorganic filler is selected from at least one of calcium carbonate, talc, silicon dioxide, montmorillonite, and kaolin.

[0010] In one aspect of the present invention, the crosslinking agent is selected from at least one of pyromellitic dianhydride, trimellitic anhydride, citric acid, dicumyl peroxide, benzoyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane, aluminum acetylacetonate, polyethylene glycol diglycidyl ether, and trimethylolpropane triacrylate.

[0011] In one aspect of the present invention, the polyimide A has a structural formula represented by the following formula A-2: R1 and R2 are each independently selected from direct bonds, substituted or unsubstituted C1-C5 alkyl groups or substituted or unsubstituted C1-C5 alkoxy groups; Ar1 is selected from substituted or unsubstituted C3-12 cycloalkyl groups or substituted or unsubstituted 3-12 heterocyclic groups; Ar2 is selected from substituted or unsubstituted C6-C18 aryl groups or substituted or unsubstituted 5-18 heteroaryl groups.

[0012] In one aspect of the present invention, the polyimide A has a structural formula represented by the following formula A-3: Wherein, the Ar2 is selected from substituted or unsubstituted C6-C18 aryl groups; the substituents are selected from C1-C5 alkyl, C1-C5 alkoxy, nitro or halogen atoms.

[0013] In one aspect of the present invention, the polyimide A has a structural formula represented by the following formula A-4: In one aspect of the present invention, the polyimide A having the structural formula represented by formula A-4 is prepared by the following steps: Step 1-a: Preparation of bis(methylenetriphenylamine)-4-cyclohexenyl-1,2-dimethyl ester; the bis(methylenetriphenylamine)-4-cyclohexenyl-1,2-dimethyl ester has the following structural formula: Step 2-a: Add organic solvent to the reactor, start stirring and purge with nitrogen for protection; control the internal temperature of the reactor at 5°C; then add p-phenylenediamine to the reactor and stir until completely dissolved; then add bis(methylenetriphenylamine)-4-cyclohexenyl-1,2-dimethyl ester prepared in step 1-a, and continue stirring for 10-20 h; then reflux for 2-5 h to end the reaction. Step 3-a: After the reaction is complete, cool to room temperature; the obtained product is then filtered, washed, dried, and subjected to thermal imidization treatment to obtain the polyimide A.

[0014] In one aspect of the present invention, the bis(methylenetriphenyl trioxide)-4-cyclohexenyl-1,2-dimethyl ester is prepared by the following steps: Step 1-b: Preparation of 4-cyclohexenyl-1,2-diethanol; Lithium aluminum hydride was added to a three-necked flask, and the flask was placed under nitrogen protection and ice bath conditions. Tetrahydrofuran was added dropwise using a constant pressure funnel. Tetrahydrophthalic anhydride was then dissolved in tetrahydrofuran to obtain a solution. The solution was then added dropwise to the three-necked flask using a constant pressure funnel. After the addition was complete, the ice bath was removed, and the mixture was stirred at room temperature for 6-12 hours. After the reaction was completed, deionized water was added dropwise to the three-necked flask until the white precipitate was completely precipitated. After filtration, a yellow oily liquid was obtained, which was then distilled under reduced pressure to obtain a colorless oily liquid of 4-cyclohexenyl-1,2-diethanol. Step 2-b: Preparation of bis(methylenetriphenyl trihydric anhydride)-4-cyclohexenyl-1,2-dimethyl ester: Add trimellitic anhydride chloride, tetrahydrofuran, and pyridine to a three-necked flask, place it under nitrogen protection and ice bath conditions, and then dissolve the 4-cyclohexenyl-1,2-diethanol prepared in step 1-b in tetrahydrofuran to obtain a solution; add the solution dropwise to the three-necked flask using a constant pressure funnel, and then react in an ice bath for 4-8 hours; After the reaction was completed, the filtrate was obtained by suction filtration; the filtrate was concentrated to obtain a pale yellow solid; then recrystallized with chloroform and dried under vacuum to obtain the bis(methylenetribenzoic anhydride)-4-cyclohexenyl-1,2-dimethyl ester.

[0015] In one aspect of this invention, in step 2-a, the organic solvent is selected from N,N-dimethylacetamide.

[0016] In one aspect of this invention, in step 2-a, the mass ratio of bis(methylenetriphenylamine)-4-cyclohexenyl-1,2-dimethyl ester to p-phenylenediamine is selected from (4.3-4.7):1.

[0017] In one aspect of this invention, in step 2-b, the mass ratio of trimellitic anhydride chloride to 4-cyclohexenyl-1,2-diethanol is selected from (3.6-3.9):1.

[0018] In one aspect of the present invention, during the coaxial nozzle spinning process, the nozzle temperature is 185℃-195℃, wherein the temperature of the feed head section is 190℃-195℃ and the temperature of the nozzle outlet section is 185℃-190℃.

[0019] In one aspect of the present invention, during the coaxial nozzle spinning process, the inner ring is filled with nitrogen gas, and the pressure of the outer ring melt is 6-10 MPa.

[0020] In one aspect of this invention, in step 3, the spinning speed is 800-1500 m / min; the draw ratio is 2.5-4.0.

[0021] In one aspect of the present invention, after being spun through coaxial nozzles, the polylactic acid-based composite fiber is cooled and cured by cold air and then wound up to obtain the polylactic acid-based composite fiber.

[0022] According to a second aspect of the present invention, a polylactic acid-based composite fiber is provided, which is prepared by the aforementioned preparation method.

[0023] The technical solutions provided by the embodiments of the present invention may include the following beneficial effects: As can be seen from the above embodiments, the present invention prepares a polyimide compound that has good interfacial compatibility with polylactic acid and uses it as a raw material to prepare high-performance polylactic acid fibers.

[0024] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Detailed Implementation

[0025] Exemplary embodiments will now be described in detail. The embodiments described below are not representative of all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the invention as detailed in the appended claims.

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of this application. The embodiments of this application should not be construed as limiting this application.

[0027] For the sake of brevity, this article only discloses a few specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0028] In this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0029] In this description, unless otherwise stated, "above" and "below" include the stated number.

[0030] Unless otherwise stated, the terminology used in this invention has the common meanings understood by those skilled in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this invention can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this invention).

[0031] The term "about" is used to describe and indicate small variations. When used in conjunction with an event or situation, the term may refer to examples in which the event or situation occurred precisely or in examples in which the event or situation occurred very approximately. For example, when used in conjunction with numerical values, the term may refer to a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format herein. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only numerical values ​​explicitly specified as range limits but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0032] The list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0033] The present invention will be further described below by way of specific embodiments. Unless otherwise specified, all chemical reagents used in the embodiments of the present invention were obtained through conventional commercial means. Unless otherwise specified, all contents mentioned below are mass contents. Unless otherwise specified, it is understood that the experiments were conducted at room temperature.

[0034] Example Example 1:

[0035] Example 1 includes the following steps: 1. Preparation of bis(methylenetriphenylamine)-4-cyclohexenyl-1,2-dimethyl ester: Add 2.85 g of lithium aluminum hydride (LiAlH4, 75 mmol) to a 250 mL three-necked flask, place under nitrogen protection and ice bath conditions, and slowly add 75 mL of tetrahydrofuran dropwise using a constant pressure funnel (the addition is completed within about 75 min); then dissolve 9.45 g of tetrahydrophthalic anhydride (62.1 mmol) in 50 mL of tetrahydrofuran to obtain a solution; slowly add this solution dropwise to the three-necked flask using a constant pressure funnel (the addition is completed within about 60 min), remove the ice bath after the addition is complete, and stir the reaction at room temperature for 8 h; after the reaction is complete, add deionized water dropwise to the three-necked flask until a white precipitate is completely formed, filter to obtain a yellow oily liquid, and distill under reduced pressure to obtain a colorless oily liquid of 4-cyclohexenyl-1,2-diethanol (6.35 g). ¹H NMR (400 MHz): δ 5.50 (s, 2H), 4.86 (s, 2H), 3.53 (s, 4H), 1.92 (s, 4H), 1.58–1.71 (t, 2H). It has the following structural formula: 7.98 g of trimellitic anhydride chloride (38 mmol), 20 mL of tetrahydrofuran, and 3.16 g of pyridine (40 mmol) were added to a 250 mL three-necked flask. The flask was protected with nitrogen and placed in an ice bath. Then, 2.13 g of the prepared 4-cyclohexenyl-1,2-diethanol (15 mmol) was dissolved in 80 mL of tetrahydrofuran to obtain a solution. The solution was added dropwise to the three-necked flask using a constant pressure funnel (the addition was completed within about 60 min), and the reaction was carried out in an ice bath for 6 h. After the reaction was completed, the filtrate was obtained by suction filtration. The filtrate was concentrated to obtain a pale yellow solid. The solid was then recrystallized with chloroform and dried under vacuum to obtain bis(methylenetriphenyl anhydride)-4-cyclohexenyl-1,2-dimethyl ester (2.91 g). 1H NMR (400 MHz): δ 8.21(s,2H),8.06(s,4H),7.75(d,2H),5.65(s,2H),4.32-4.41(m,4H),2.07-2.22(m,4H),1.23(s,2H).

[0036] Repeat the above steps multiple times to prepare sufficient bis(methylenetribenzoic anhydride)-4-cyclohexenyl-1,2-dimethyl ester for the reactions in the following steps.

[0037] 2. Preparation of polyimide A having the structure of formula A-4: 102g of DMAc was added to the reactor, stirring was started and nitrogen gas was introduced for protection; the internal temperature of the reactor was controlled at 5℃; then 5.42g of p-phenylenediamine was added to the reactor and stirred until completely dissolved; then 24.55g of the previously prepared bis(methylenetriphenylamine)-4-cyclohexenyl-1,2-dimethyl ester was added, and the reaction was continued to be stirred for 12h; then the temperature was raised to reflux for 3h and the reaction was stopped; after the reaction was completed, the mixture was cooled to room temperature; the obtained product was filtered, washed, dried and thermally imidized to obtain polyimide A.

[0038] 3. Preparation of the fibers in this embodiment: 45 parts by weight of poly-L-lactic acid, 10 parts by weight of the aforementioned prepared polyimide A, 1 part by weight of nano-silica (hydrophobic, D50 200 nm), 3 parts by weight of talc (1250 mesh), 2 parts by weight of montmorillonite (900 mesh), and 3 parts by weight of crosslinking agent polyethylene glycol diglycidyl ether were mixed evenly in a mixer, and then extruded through an extruder at a feed head temperature of 210℃, a screw speed of 180 r / min, an extrusion pressure of 11 MPa, and a shear rate of 275 s. -1 The masterbatch is obtained by extrusion and pelletizing. The masterbatch is added to the feeding hopper of the single-screw spinning machine. The metering section temperature is set to 190℃-200℃, the bending tube temperature to 185℃-190℃, and the coaxial nozzle temperature to 185℃-195℃. The head section temperature is 190℃-195℃, and the nozzle outlet section temperature is 185℃-190℃. The coaxial nozzle adopts a concentric double-layer sleeve structure. The outer ring gap width is 0.3-0.5mm for the melt to pass through, and the inner hole diameter is 0.5-1.0mm for nitrogen to pass through. The outer ring melt pressure is controlled at 8-10 MPa, and the inner ring nitrogen pressure at 3-4 MPa to ensure stable nitrogen penetration into the melt center to form a core. Spinning is carried out at a spinning temperature of 180℃-185℃, a spinning pressure of 4.2-4.5 MPa, and a spinning speed of approximately 800 m / min. After extrusion from the nozzle, the fiber first enters a 30-50 cm long quenching zone, cooled by cold air perpendicular to the fiber axis at a temperature of 5℃-10℃, a velocity of 3-6 m / s, and a relative humidity controlled below 40%. Subsequently, the fiber enters a 50-100 cm long slow cooling zone with an air temperature of 15℃-20℃ and a velocity of 1-2 m / s, allowing the fiber to cool uniformly to room temperature. After cooling, the fiber is drawn by a guide disc and passes through the cooling zone at a natural draw ratio of 1.2 to 1.5 times; then it is treated by a hot drawing roller at a drawing temperature of 110℃-125℃, a draw ratio of 2.0 to 3.0 times, and a total draw ratio controlled in the range of 2.5 to 4.0 times; finally, it is wound to obtain the polylactic acid-based composite fiber of this embodiment. Example 2:

[0039] Example 2 includes the following steps: 1. Preparation of bis(methylenetriphenylamine)-4-cyclohexenyl-1,2-dimethyl ester: Add 2.85 g of lithium aluminum hydride (LiAlH4, 75 mmol) to a 250 mL three-necked flask, place under nitrogen protection and ice bath conditions, and slowly add 75 mL of tetrahydrofuran dropwise using a constant pressure funnel (the addition is completed within about 75 min); then dissolve 9.45 g of tetrahydrophthalic anhydride (62.1 mmol) in 50 mL of tetrahydrofuran to obtain a solution; slowly add this solution dropwise to the three-necked flask using a constant pressure funnel (the addition is completed within about 60 min), remove the ice bath after the addition is complete, and stir the reaction at room temperature for 8 h; after the reaction is complete, add deionized water dropwise to the three-necked flask until a white precipitate is completely formed, filter to obtain a yellow oily liquid, and distill under reduced pressure to obtain a colorless oily liquid of 4-cyclohexenyl-1,2-diethanol (6.35 g).

[0040] 7.98 g of trimellitic anhydride chloride (38 mmol), 20 mL of tetrahydrofuran, and 3.16 g of pyridine (40 mmol) were added to a 250 mL three-necked flask. The flask was then placed under nitrogen protection and an ice bath. 2.13 g of the prepared 4-cyclohexenyl-1,2-diethanol (15 mmol) was dissolved in 80 mL of tetrahydrofuran to obtain a solution. This solution was added dropwise to the three-necked flask using a constant-pressure funnel (the addition was completed within approximately 60 min), and the reaction was carried out in an ice bath for 6 h. After the reaction was complete, the solution was filtered to obtain a filtrate. The filtrate was concentrated to obtain a pale yellow solid. This solid was then recrystallized from chloroform and dried under vacuum to obtain bis(methylenetriphenyl anhydride)-4-cyclohexenyl-1,2-dimethyl ester (2.91 g). The above steps were repeated multiple times to prepare sufficient bis(methylenetriphenyl anhydride)-4-cyclohexenyl-1,2-dimethyl ester for the reactions in the following steps.

[0041] 2. Preparation of polyimide A having the structure of formula A-4: 102g of DMAc was added to the reactor, stirring was started and nitrogen gas was introduced for protection; the internal temperature of the reactor was controlled at 5℃; then 5.42g of p-phenylenediamine was added to the reactor and stirred until completely dissolved; then 24.55g of the previously prepared bis(methylenetriphenylamine)-4-cyclohexenyl-1,2-dimethyl ester was added, and the reaction was continued to be stirred for 12h; then the temperature was raised to reflux for 3h and the reaction was stopped; after the reaction was completed, the mixture was cooled to room temperature; the obtained product was filtered, washed, dried and thermally imidized to obtain polyimide A.

[0042] 3. Preparation of the fibers in this embodiment: 45 parts by weight of poly-L-lactic acid, 6 parts by weight of the aforementioned prepared polyimide A, 1 part by weight of nano-silica (hydrophobic, D50 200 nm), 3 parts by weight of talc (1250 mesh), 2 parts by weight of montmorillonite (900 mesh), and 3 parts by weight of crosslinking agent polyethylene glycol diglycidyl ether were mixed evenly in a mixer, and then extruded through an extruder at a feed head temperature of 210℃, a screw speed of 180 r / min, an extrusion pressure of 11 MPa, and a shear rate of 275 s. -1 The masterbatch is obtained by extrusion and pelletizing. The masterbatch is added to the feeding hopper of the single-screw spinning machine. The metering section temperature is set to 190℃-200℃, the bending tube temperature to 185℃-190℃, and the coaxial nozzle temperature to 185℃-195℃. The head section temperature is 190℃-195℃, and the nozzle outlet section temperature is 185℃-190℃. The coaxial nozzle adopts a concentric double-layer sleeve structure. The outer ring gap width is 0.3-0.5mm for the melt to pass through, and the inner hole diameter is 0.5-1.0mm for nitrogen to pass through. The outer ring melt pressure is controlled at 8-10 MPa, and the inner ring nitrogen pressure at 3-4 MPa to ensure stable nitrogen penetration into the melt center to form a core. Spinning is carried out at a spinning temperature of 180℃-185℃, a spinning pressure of 4.2-4.5 MPa, and a spinning speed of approximately 800 m / min. After extrusion from the nozzle, the fiber first enters a 30-50 cm long quenching zone, cooled by cold air perpendicular to the fiber axis at a temperature of 5℃-10℃, a velocity of 3-6 m / s, and a relative humidity controlled below 40%. Subsequently, the fiber enters a 50-100 cm long slow cooling zone with an air temperature of 15℃-20℃ and a velocity of 1-2 m / s, allowing the fiber to cool uniformly to room temperature. The cooled fibers are drawn by a guide roller and passed through the cooling zone at a natural draw ratio of 1.2 to 1.5. They are then treated by hot drawing rollers at a drawing temperature of 110℃-125℃, a draw ratio of 2.0 to 3.0, and a total draw ratio controlled within the range of 2.5 to 4.0. Finally, they are wound to obtain the polylactic acid-based composite fiber of this embodiment. The conditions for Example 2 are basically the same as those for Example 1, except that the mass of polyimide A added is different.

[0043] Comparative Example 1: Comparative Example 1 includes the following steps: 1. Preparation of the fibers in this comparative example: 45 parts by weight of poly-L-lactic acid, 10 parts by weight of polyimide KH-320N (purchased from Hubei Fangde New Material Co., Ltd.), 1 part by weight of nano-silica (hydrophobic, D50 of 200nm), 3 parts by weight of talc (1250 mesh), 2 parts by weight of montmorillonite (900 mesh), and 3 parts by weight of crosslinking agent polyethylene glycol diglycidyl ether were mixed evenly in a mixer. The mixture was then extruded through an extruder at a feed head temperature of 210℃, a screw speed of 180 r / min, an extrusion pressure of 11 MPa, and a shear rate of 275 s. -1The masterbatch is obtained by extrusion and pelletizing. The masterbatch is added to the feeding hopper of the single-screw spinning machine. The metering section temperature is set to 190℃-200℃, the bending tube temperature to 185℃-190℃, and the coaxial nozzle temperature to 185℃-195℃. The head section temperature is 190℃-195℃, and the nozzle outlet section temperature is 185℃-190℃. The coaxial nozzle adopts a concentric double-layer sleeve structure. The outer ring gap width is 0.3-0.5mm for the melt to pass through, and the inner hole diameter is 0.5-1.0mm for nitrogen to pass through. The outer ring melt pressure is controlled at 8-10 MPa, and the inner ring nitrogen pressure at 3-4 MPa to ensure stable nitrogen penetration into the melt center to form a core. Spinning is carried out at a spinning temperature of 180℃-185℃, a spinning pressure of 4.2-4.5 MPa, and a spinning speed of approximately 800 m / min. After extrusion from the nozzle, the fiber first enters a 30-50 cm long quenching zone, cooled by cold air perpendicular to the fiber axis at a temperature of 5℃-10℃, a velocity of 3-6 m / s, and a relative humidity controlled below 40%. Subsequently, the fiber enters a 50-100 cm long slow cooling zone with an air temperature of 15℃-20℃ and a velocity of 1-2 m / s, allowing the fiber to cool uniformly to room temperature. The cooled fibers are drawn through a guide roller at a natural draw ratio of 1.2 to 1.5 times in the cooling zone; then they are treated with hot drawing rollers at a drawing temperature of 110°C-125°C, a draw ratio of 2.0 to 3.0 times, and a total draw ratio controlled within the range of 2.5 to 4.0 times; finally, they are wound to obtain the polylactic acid-based composite fiber of this comparative example. The conditions of Comparative Example 1 and Example 1 are basically the same as those of Example 1, except that the polyimide added is a commercially available product.

[0044] Comparative Example 2: Comparative Example 2 includes the following steps: 1. Preparation of the fibers in this comparative example: 45 parts by weight of poly-L-lactic acid, 10 parts by weight of polyimide GCPITM (purchased from Changzhou Guangcheng New Plastics Co., Ltd.), 1 part by weight of nano-silica (hydrophobic, D50 of 200nm), 3 parts by weight of talc (1250 mesh), 2 parts by weight of montmorillonite (900 mesh), and 3 parts by weight of crosslinking agent polyethylene glycol diglycidyl ether were mixed evenly in a mixer. The mixture was then extruded through an extruder at a feed head temperature of 210℃, a screw speed of 180r / min, an extrusion pressure of 11MPa, and a shear rate of 275s. -1The masterbatch is obtained by extrusion and pelletizing. The masterbatch is added to the feeding hopper of the single-screw spinning machine. The metering section temperature is set to 190℃-200℃, the bending tube temperature to 185℃-190℃, and the coaxial nozzle temperature to 185℃-195℃. The head section temperature is 190℃-195℃, and the nozzle outlet section temperature is 185℃-190℃. The coaxial nozzle adopts a concentric double-layer sleeve structure. The outer ring gap width is 0.3-0.5mm for the melt to pass through, and the inner hole diameter is 0.5-1.0mm for nitrogen to pass through. The outer ring melt pressure is controlled at 8-10 MPa, and the inner ring nitrogen pressure at 3-4 MPa to ensure stable nitrogen penetration into the melt center to form a core. Spinning is carried out at a spinning temperature of 180℃-185℃, a spinning pressure of 4.2-4.5 MPa, and a spinning speed of approximately 800 m / min. After extrusion from the nozzle, the fiber first enters a 30-50 cm long quenching zone, cooled by cold air perpendicular to the fiber axis at a temperature of 5℃-10℃, a velocity of 3-6 m / s, and a relative humidity controlled below 40%. Subsequently, the fiber enters a 50-100 cm long slow cooling zone with an air temperature of 15℃-20℃ and a velocity of 1-2 m / s, allowing the fiber to cool uniformly to room temperature. The cooled fibers are drawn through a guide roller at a natural draw ratio of 1.2 to 1.5 times in the cooling zone; then they are treated with hot drawing rollers at a drawing temperature of 110°C-125°C, a draw ratio of 2.0 to 3.0 times, and a total draw ratio controlled within the range of 2.5 to 4.0 times; finally, they are wound to obtain the polylactic acid-based composite fiber of this comparative example. The conditions for Comparative Example 2 and Example 1 are basically the same as those for Example 1, except that the polyimide added is a commercially available product.

[0045] Comparative Example 3: Comparative Example 3 includes the following steps: 1. Preparation of the fibers in this comparative example: 45 parts by weight of poly-L-lactic acid, 10 parts by weight of polyimide YGM200 (purchased from Changchun Gaoqi Polyimide Materials Co., Ltd.), 1 part by weight of nano-silica (hydrophobic, D50 of 200nm), 3 parts by weight of talc (1250 mesh), 2 parts by weight of montmorillonite (900 mesh), and 3 parts by weight of crosslinking agent polyethylene glycol diglycidyl ether were mixed evenly in a mixer. The mixture was then extruded through an extruder at a feed head temperature of 210℃, a screw speed of 180r / min, an extrusion pressure of 11MPa, and a shear rate of 275s. -1The masterbatch is obtained by extrusion and pelletizing. The masterbatch is added to the feeding hopper of the single-screw spinning machine. The metering section temperature is set to 190℃-200℃, the bending tube temperature to 185℃-190℃, and the coaxial nozzle temperature to 185℃-195℃. The head section temperature is 190℃-195℃, and the nozzle outlet section temperature is 185℃-190℃. The coaxial nozzle adopts a concentric double-layer sleeve structure. The outer ring gap width is 0.3-0.5mm for the melt to pass through, and the inner hole diameter is 0.5-1.0mm for nitrogen to pass through. The outer ring melt pressure is controlled at 8-10 MPa, and the inner ring nitrogen pressure at 3-4 MPa to ensure stable nitrogen penetration into the melt center to form a core. Spinning is carried out at a spinning temperature of 180℃-185℃, a spinning pressure of 4.2-4.5 MPa, and a spinning speed of approximately 800 m / min. After extrusion from the nozzle, the fiber first enters a 30-50 cm long quenching zone, cooled by cold air perpendicular to the fiber axis at a temperature of 5℃-10℃, a velocity of 3-6 m / s, and a relative humidity controlled below 40%. Subsequently, the fiber enters a 50-100 cm long slow cooling zone with an air temperature of 15℃-20℃ and a velocity of 1-2 m / s, allowing the fiber to cool uniformly to room temperature. The cooled fibers are drawn through a guide roller at a natural draw ratio of 1.2 to 1.5 times in the cooling zone; then they are treated with hot drawing rollers at a drawing temperature of 110°C-125°C, a draw ratio of 2.0 to 3.0 times, and a total draw ratio controlled within the range of 2.5 to 4.0 times; finally, they are wound to obtain the polylactic acid-based composite fiber of this comparative example. The conditions for Comparative Example 3 and Example 1 are basically the same as those for Example 1, except that the polyimide added is a commercially available product.

[0046] Comparative Example 4: Comparative Example 4 includes the following steps: 1. Preparation of polyimide B having the structure of formula B-1: 102g of DMAc was added to the reactor, stirring was started and nitrogen gas was introduced for protection; the internal temperature of the reactor was controlled at 5℃; then 4.82g of p-phenylenediamine was added to the reactor and stirred until completely dissolved; then 13.16g of 3,3',4,4'-biphenyltetracarboxylic dianhydride was added, and the reaction was continued to be stirred for 12h; then the temperature was raised to reflux for 3h and the reaction was stopped; after the reaction was completed, the mixture was cooled to room temperature; the obtained product was then filtered, washed, dried and thermally imidized to obtain polyimide B.

[0047] 2. Preparation of the fibers in this comparative example: 45 parts by weight of poly-L-lactic acid, 10 parts by weight of the aforementioned prepared polyimide B, 1 part by weight of nano-silica (hydrophobic, D50 200 nm), 3 parts by weight of talc (1250 mesh), 2 parts by weight of montmorillonite (900 mesh), and 3 parts by weight of crosslinking agent polyethylene glycol diglycidyl ether were mixed evenly in a mixer, and then extruded through an extruder at a feed head temperature of 210℃, a screw speed of 180 r / min, an extrusion pressure of 11 MPa, and a shear rate of 275 s. -1 The masterbatch is obtained by extrusion and pelletizing. The masterbatch is added to the feeding hopper of the single-screw spinning machine. The metering section temperature is set to 190℃-200℃, the bending tube temperature to 185℃-190℃, and the coaxial nozzle temperature to 185℃-195℃. The head section temperature is 190℃-195℃, and the nozzle outlet section temperature is 185℃-190℃. The coaxial nozzle adopts a concentric double-layer sleeve structure. The outer ring gap width is 0.3-0.5mm for the melt to pass through, and the inner hole diameter is 0.5-1.0mm for nitrogen to pass through. The outer ring melt pressure is controlled at 8-10 MPa, and the inner ring nitrogen pressure at 3-4 MPa to ensure stable nitrogen penetration into the melt center to form a core. Spinning is carried out at a spinning temperature of 180℃-185℃, a spinning pressure of 4.2-4.5 MPa, and a spinning speed of approximately 800 m / min. After extrusion from the nozzle, the fiber first enters a 30-50 cm long quenching zone, cooled by cold air perpendicular to the fiber axis at a temperature of 5℃-10℃, a velocity of 3-6 m / s, and a relative humidity controlled below 40%. Subsequently, the fiber enters a 50-100 cm long slow cooling zone with an air temperature of 15℃-20℃ and a velocity of 1-2 m / s, allowing the fiber to cool uniformly to room temperature. After cooling, the fibers are drawn by a guide disc and pass through the cooling zone at a natural draw ratio of 1.2 to 1.5. They are then treated by hot drawing rollers at a draw temperature of 110℃-125℃ and a draw ratio of 2.0 to 3.0, with the total draw ratio controlled in the range of 2.5 to 4.0. Finally, the polylactic acid-based composite fibers of this comparative example are obtained by winding.

[0048] Comparative Example 5: 45 parts by weight of poly-L-lactic acid, 1 part by weight of nano-silica (hydrophobic, D50 200nm), 3 parts by weight of talc (1250 mesh), 2 parts by weight of montmorillonite (900 mesh), and 3 parts by weight of crosslinking agent polyethylene glycol diglycidyl ether were mixed evenly in a mixer. The mixture was then extruded through an extruder at a feed head temperature of 210℃, a screw speed of 180 r / min, an extrusion pressure of 11 MPa, and a shear rate of 275 s. -1The masterbatch is obtained by extrusion and pelletizing. The masterbatch is added to the feeding hopper of the single-screw spinning machine. The metering section temperature is set to 190℃-200℃, the bending tube temperature to 185℃-190℃, and the coaxial nozzle temperature to 185℃-195℃. The head section temperature is 190℃-195℃, and the nozzle outlet section temperature is 185℃-190℃. The coaxial nozzle adopts a concentric double-layer sleeve structure. The outer ring gap width is 0.3-0.5mm for the melt to pass through, and the inner hole diameter is 0.5-1.0mm for nitrogen to pass through. The outer ring melt pressure is controlled at 8-10 MPa, and the inner ring nitrogen pressure at 3-4 MPa to ensure stable nitrogen penetration into the melt center to form a core. Spinning is carried out at a spinning temperature of 180℃-185℃, a spinning pressure of 4.2-4.5 MPa, and a spinning speed of approximately 800 m / min. After extrusion from the nozzle, the fiber first enters a 30-50 cm long quenching zone, cooled by cold air perpendicular to the fiber axis at a temperature of 5℃-10℃, a velocity of 3-6 m / s, and a relative humidity controlled below 40%. Subsequently, the fiber enters a 50-100 cm long slow cooling zone with an air temperature of 15℃-20℃ and a velocity of 1-2 m / s, allowing the fiber to cool uniformly to room temperature. After cooling, the fiber is drawn by a guide disc and passes through the cooling zone at a natural draw ratio of 1.2 to 1.5 times; then it is treated by a hot drawing roller at a drawing temperature of 110℃-125℃, a draw ratio of 2.0 to 3.0 times, and a total draw ratio controlled in the range of 2.5 to 4.0 times; finally, it is wound to obtain the polylactic acid-based composite fiber of this embodiment.

[0049] Mechanical property testing: The tensile strength of Examples 1-2 and Comparative Examples 1-5 was tested using GB / T14344-2022 "Test Method for Tensile Properties of Chemical Fiber Filaments", and the results are shown in Table 1. The heat distortion temperature of Examples 1-2 and Comparative Examples 1-5 was tested using GB / T 1634.1-2025 (fiber bundle sample preparation, load 0.45 MPa), and the results are shown in Table 1.

[0050] Table 1 Comparative Examples 1 to 3 used different commercially available polyimides. These materials were all traditional aromatic thermoplastic polyimides or molding grade polyimides, whose molecular backbone consisted of rigid benzene rings and imide rings, and had high melting temperatures. Therefore, during melt blending, these polyimides could not achieve uniform miscibility with polylactic acid at the molecular level, but were dispersed in the polylactic acid matrix as solid particles or micro-regions, forming a phase interface. Due to the significant difference in polarity between the hydrophobic aromatic backbone of polyimide and the aliphatic ester chain of polylactic acid, the interfacial adhesion was weak. Under external force, stress concentration and debonding were easily generated at the interface, resulting in no significant improvement in tensile strength and no significant increase in heat distortion temperature compared with pure polylactic acid.

[0051] Comparative Example 4 used rigid polyimide B obtained by polycondensation of 3,3',4,4'-biphenyltetracarboxylic dianhydride and p-phenylenediamine. This structure does not contain flexible segments or ester groups, and its compatibility with polylactic acid is worse. Its mechanical properties and heat resistance are actually worse than those of pure polylactic acid, proving that rigid polyimide alone may not only fail to enhance the strength of polylactic acid fibers, but may also become a source of structural defects.

[0052] In contrast, the polyimide A prepared in Examples 1-2 of this application incorporates ester groups and cyclohexene flexible segments into its molecular structure, lowering its melt processing temperature and thus making it compatible with polylactic acid. The ester groups in the side chains of polyimide A and the ester groups in the polylactic acid backbone can form dipole-dipole interactions and intermolecular hydrogen bonds, achieving uniform interfacial compatibility. This structural similarity allows polyimide A to be uniformly dispersed in the polylactic acid matrix, forming an effective physical cross-linking network. This improves the fiber's load-bearing capacity through the rigid imide structure and enhances compatibility through the flexible segments.

[0053] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein.

Claims

1. A method for preparing polylactic acid-based composite fibers, characterized in that, The preparation method includes the following steps: Step 1: Prepare polyimide A; the polyimide A has the structural formula represented by the following formula A-1: R1, R2, R3, and R4 are each independently selected from direct bonds, substituted or unsubstituted C1-C10 alkyl groups, substituted or unsubstituted C2-C10 alkenyl groups, or substituted or unsubstituted C1-C10 alkoxy groups; Ar1 ​​and Ar2 are each independently selected from substituted or unsubstituted C3-30 cycloalkyl groups, substituted or unsubstituted C6-C30 aryl groups, substituted or unsubstituted 3-30 membered heterocyclic groups, or substituted or unsubstituted 5-30 membered heteroaryl groups. Step 2: Polylactic acid, inorganic filler, crosslinking agent and polyimide A prepared in step 1 are extruded and pelletized to obtain masterbatch; Step 3: Add the masterbatch prepared in Step 2 into the feeding funnel, and spin it through the coaxial nozzle to obtain the polylactic acid-based composite fiber.

2. The method for preparing polylactic acid-based composite fibers according to claim 1, characterized in that, In step 2, the polylactic acid is selected from poly-L-lactic acid, poly-D-lactic acid, or polyracemic lactic acid; The inorganic filler is selected from at least one of magnesium carbonate, barium carbonate, calcium carbonate, silicon dioxide, aluminum hydroxide, calcium oxide, zinc oxide, montmorillonite, talc, kaolin, and hydroxyapatite. The crosslinking agent is selected from at least one of pyromellitic dianhydride, trimellitic anhydride, citric acid, dicumyl peroxide, benzoyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane, aluminum acetylacetonate, polyethylene glycol diglycidyl ether, and trimethylolpropane triacrylate.

3. The method for preparing polylactic acid-based composite fibers according to claim 1, characterized in that, The polyimide A has the following structural formula represented by formula A-2: R1 and R2 are each independently selected from direct bonds, substituted or unsubstituted C1-C5 alkyl groups or substituted or unsubstituted C1-C5 alkoxy groups; Ar1 is selected from substituted or unsubstituted C3-12 cycloalkyl groups or substituted or unsubstituted 3-12 heterocyclic groups; Ar2 is selected from substituted or unsubstituted C6-C18 aryl groups or substituted or unsubstituted 5-18 heteroaryl groups.

4. The method for preparing polylactic acid-based composite fibers according to claim 3, characterized in that, The polyimide A has the following structural formula represented by formula A-3: Wherein, the Ar2 is selected from substituted or unsubstituted C6-C18 aryl groups; the substituents are selected from C1-C5 alkyl, C1-C5 alkoxy, nitro or halogen atoms.

5. The method for preparing polylactic acid-based composite fibers according to claim 4, characterized in that, The polyimide A has the following structural formula, represented by formula A-4: 。 6. The method for preparing polylactic acid-based composite fibers according to claim 5, characterized in that, The polyimide A having the structural formula represented by formula A-4 is prepared by the following steps: Step 1-a: Preparation of bis(methylenetriphenylamine)-4-cyclohexenyl-1,2-dimethyl ester; the bis(methylenetriphenylamine)-4-cyclohexenyl-1,2-dimethyl ester has the following structural formula: Step 2-a: Add organic solvent to the reactor, start stirring and purge with nitrogen for protection; control the internal temperature of the reactor at 5°C; then add p-phenylenediamine to the reactor and stir until completely dissolved; then add bis(methylenetriphenylamine)-4-cyclohexenyl-1,2-dimethyl ester prepared in step 1-a, and continue stirring for 10-20 h; then reflux for 2-5 h to end the reaction. Step 3-a: After the reaction is complete, cool to room temperature; the obtained product is then filtered, washed, dried, and subjected to thermal imidization treatment to obtain the polyimide A.

7. The method for preparing polylactic acid-based composite fibers according to claim 6, characterized in that, The bis(methylenetriphenyl trihydric anhydride)-4-cyclohexenyl-1,2-dimethyl ester was prepared by the following steps: Step 1-b: Preparation of 4-cyclohexenyl-1,2-diethanol; Lithium aluminum hydride was added to a three-necked flask, and the flask was placed under nitrogen protection and ice bath conditions. Tetrahydrofuran was added dropwise using a constant pressure funnel. Tetrahydrophthalic anhydride was then dissolved in tetrahydrofuran to obtain a solution. The solution was then added dropwise to the three-necked flask using a constant pressure funnel. After the addition was complete, the ice bath was removed, and the mixture was stirred at room temperature for 6-12 hours. After the reaction was completed, deionized water was added dropwise to the three-necked flask until the white precipitate was completely precipitated. After filtration, a yellow oily liquid was obtained, which was then distilled under reduced pressure to obtain a colorless oily liquid of 4-cyclohexenyl-1,2-diethanol. Step 2-b: Preparation of bis(methylenetriphenyl trihydric anhydride)-4-cyclohexenyl-1,2-dimethyl ester: Add trimellitic anhydride chloride, tetrahydrofuran, and pyridine to a three-necked flask, place it under nitrogen protection and ice bath conditions, and then dissolve the 4-cyclohexenyl-1,2-diethanol prepared in step 1-b in tetrahydrofuran to obtain a solution; add the solution dropwise to the three-necked flask using a constant pressure funnel, and then react in an ice bath for 4-8 hours; After the reaction was completed, the filtrate was obtained by suction filtration; the filtrate was concentrated to obtain a pale yellow solid; then recrystallized with chloroform and dried under vacuum to obtain the bis(methylenetribenzoic anhydride)-4-cyclohexenyl-1,2-dimethyl ester.

8. The method for preparing polylactic acid-based composite fibers according to claim 6 or 7, characterized in that, The preparation method satisfies at least one of the following conditions: (1) In step 2-a, the organic solvent is selected from N,N-dimethylacetamide; (2) In step 2-a, the mass ratio of bis(methylenetriphenyl trihydride)-4-cyclohexenyl-1,2-dimethyl ester to p-phenylenediamine is selected from (4.3-4.7):1; (3) In step 2-b, the mass ratio of trimellitic anhydride chloride and 4-cyclohexenyl-1,2-diethanol is selected from (3.6-3.9):

1.

9. The method for preparing polylactic acid-based composite fibers according to claim 1, characterized in that, Step 3 satisfies at least one of the following conditions: (1) During the coaxial nozzle spinning process, the nozzle temperature is 185℃-195℃, of which the temperature of the material head section is 190℃-195℃ and the temperature of the nozzle outlet section is 185℃-190℃. (2) During the spinning process of the coaxial nozzle, the inner ring is filled with nitrogen gas, and the pressure of the outer ring melt is 6-10 MPa; (3) In step 3, the spinning speed is 800-1500 m / min; the draw ratio is 2.5-4.0; (4) After being spun through coaxial nozzles, the polylactic acid-based composite fiber is obtained by cooling and curing with cold air and then being wound up.

10. A polylactic acid-based composite fiber, characterized in that, The polylactic acid-based composite fiber is prepared by the preparation method according to any one of claims 1-9.

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