A polylactic acid fiber and its preparation method

Abstract

This invention discloses a polylactic acid (PLA) fiber and its preparation method, relating to the field of PLA fiber technology. The PLA fiber is mainly prepared from the following raw materials in parts by weight: 100 parts PLA, 5-15 parts plasticizer, 0.5-3 parts nucleating agent, 0.5-2 parts anti-hydrolysis agent, 0.05-0.2 parts lubricant, and 0.05-0.1 parts antioxidant. By introducing an anti-hydrolysis agent with a specific structure, and through its synergistic effect with the plasticizer and nucleating agent, the self-catalytic cycle of hydrolysis is effectively blocked, reducing the tendency for molecular chain breakage and performance degradation of the fiber under humid and hot environments. This solves the problems of poor compatibility and insufficient protective effect of anti-hydrolysis agents in existing technologies.

Description

Technical Field

[0001] This invention relates to the field of polylactic acid fiber technology, specifically to a polylactic acid fiber and its preparation method. Background Technology

[0002] Polylactic acid (PLA), as a biodegradable synthetic polymer, has become an ideal substitute for traditional petroleum-based fibers due to its renewable raw materials (such as corn starch), good biocompatibility, and low carbon emissions, showing broad application prospects in textiles, medical devices, and packaging. However, the ester bonds in the PLA molecular chain are highly susceptible to hydrolysis under humid and hot environments, leading to a significant decrease in molecular weight and a sharp deterioration in mechanical properties, severely limiting the service life and application range of its products. Especially during fiber processing and application, high-temperature melt spinning, subsequent dyeing and finishing processes, and moisture contact in daily wear environments accelerate the hydrolytic degradation of PLA, resulting in problems such as a sharp drop in fiber strength, increased brittleness, and loss of elongation at break, making it difficult to meet the requirements for durable textiles.

[0003] In existing technologies, methods to improve the hydrolysis resistance of polylactic acid (PLA) mainly include blending modification, adding auxiliaries, and process optimization. For example, introducing anti-hydrolysis agents can partially block the contact between ester bonds and water molecules, but conventional anti-hydrolysis agents have poor aging resistance; while nucleating agents can increase crystallinity to enhance hydrolysis resistance, their effectiveness is not ideal. Furthermore, if the moisture content of PLA chips is not adequately controlled, residual moisture will trigger severe hydrolysis during the melt extrusion stage, leading to molecular chain breakage and directly affecting the spinnability and final strength of the fiber. Although some studies have attempted to improve water resistance through multilayer coating structures or hydrophobic surface coatings, these methods increase process complexity and cost, and may sacrifice the material's biodegradability and breathability.

[0004] Therefore, how to significantly improve the hydrolytic stability of polylactic acid (PLA) fibers while ensuring their spinnability and mechanical properties through molecular structure design, synergistic compounding of additives, and precise process control has become a critical technical bottleneck that the industry urgently needs to overcome. The core of this invention lies in proposing a comprehensive solution to address this key deficiency. Summary of the Invention

[0005] To address the shortcomings of polylactic acid (PLA) fibers, such as poor hydrolysis resistance, this invention provides a PLA fiber and its preparation method. Through the synergistic compounding of specific anti-hydrolysis agents, plasticizers, and nucleating agents, combined with moisture content control (≤50ppm) and step-by-step process optimization, the hydrolysis resistance, weather resistance, and mechanical strength of the fiber are significantly improved, solving the problems of poor additive compatibility and severe processing degradation in existing technologies.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a polylactic acid fiber, mainly prepared from the following raw materials in parts by weight: 100 parts polylactic acid, 5-15 parts plasticizer, 0.5-3 parts nucleating agent, 0.5-2 parts anti-hydrolysis agent, 0.05-0.2 parts lubricant, and 0.05-0.1 parts antioxidant;

[0007] The anti-hydrolysis agent is a compound represented by Formula 1:

[0008] Formula 1: ;

[0009] R1 in Formula 1 is a substituent;

[0010] R1 is selected from any one of hydrogen, deuterium, amino, cyano, fluorine, and C1-5 alkyl groups.

[0011] Furthermore, the anti-hydrolysis agent is any one of the compounds shown in the following structures:

[0012] ;

[0013] ;

[0014] ;

[0015] .

[0016] Furthermore, the anti-hydrolysis agent has the effects of resisting hydrolysis and resisting ultraviolet aging.

[0017] Furthermore, the plasticizer is selected from: tributyl acetylglucosyl citrate and / or polyethylene glycol PEG-4000.

[0018] Furthermore, the nucleating agent is selected from any one of talc, nano-calcium carbonate, and TMC-306.

[0019] Furthermore, the lubricant is selected from any one of polyethylene wax, fatty alcohol polyoxyethylene ether, and ethylene bis-stearamide.

[0020] Furthermore, the antioxidant is selected from any one of antioxidant 1010, antioxidant 168, antioxidant 1098, and TPH-24.

[0021] A method for preparing polylactic acid fiber includes the following steps:

[0022] S1. Pre-crystallization and drying: Polylactic acid slices are dried under vacuum or forced air at 80-100℃ for 4-8 hours to reduce the moisture content to below 50ppm, thus obtaining dried polylactic acid;

[0023] S2. Blending modification: The dried polylactic acid is thoroughly mixed with the plasticizer, nucleating agent, anti-hydrolysis agent, lubricant and antioxidant in a high-speed mixer in proportion to obtain a mixture;

[0024] S3. Melt extrusion granulation: The mixture is melt-blended, extruded, cooled, and pelletized using a twin-screw extruder to obtain modified polylactic acid masterbatch;

[0025] S4. Melt spinning: The modified polylactic acid masterbatch is dried and fed into a spinning screw extruder. After melting, metering, and filtration, it is extruded through a spinneret to obtain nascent fibers.

[0026] S5. Stretching and heat setting: The nascent fiber is drawn by a guide roller, preheated, stretched and heat-set, and then cooled to room temperature to obtain a polylactic acid fiber.

[0027] Furthermore, the processing temperature of the twin-screw extruder in S3 is: Zone 1 160-170℃, Zone 2 170-180℃, Zone 3 180-190℃, Zone 4 190-200℃, and Die head 195-205℃.

[0028] Furthermore, the melt spinning process parameters in S4 are as follows: screw extrusion temperature 190-220℃, spinning box temperature 200-215℃, spinneret orifice number 24-72f, and single filament fineness 2.0-5.0dtex.

[0029] Furthermore, the stretching and heat setting process in S5 is as follows: the preheating roller temperature is 60-80℃, the first-stage stretching roller temperature is 70-90℃, and the stretching ratio is 2.5-4.0 times; the second-stage heat setting roller temperature is 100-130℃, and the relaxation heat setting tension is 90-98%.

[0030] A polylactic acid fiber can be used as a continuous or discontinuous fiber-reinforced composite material.

[0031] In a humid and hot environment, the ester bonds (-COO-) in the polylactic acid (PLA) molecular chain are easily attacked by water molecules, undergoing hydrolysis and breaking to generate free carboxylic acids (-COOH). These carboxylic acids catalyze the hydrolysis of more ester bonds (autocatalytic effect), leading to a rapid decrease in molecular weight. The carbodiimide group (-N=C=N-) in the anti-hydrolysis agent has high electrophilicity and can rapidly undergo an addition reaction with the carboxylic acid generated by hydrolysis, generating a stable N-acylurea derivative. In the anti-hydrolysis agent described in this invention, the carbodiimide group is directly linked to a conjugated aromatic ring. The electron-withdrawing effect of the aromatic ring enhances the electrophilicity of -N=C=N-, increasing its reactivity with carboxylic acids. The PLA molecular chain is rich in ester bonds, and the introduction of ester groups into the anti-hydrolysis agent molecule results in a polarity highly compatible with PLA. This structural similarity significantly improves the compatibility of the anti-hydrolysis agent in PLA melt, preventing the migration and precipitation of additives due to phase separation. The presence of ester groups ensures that the anti-hydrolysis agent is uniformly dispersed within the PLA matrix, guaranteeing that the carbodiimide groups can efficiently contact and neutralize the carboxylic acid produced by hydrolysis, avoiding protective failure due to insufficient local concentration. The conjugated aromatic rings possess rigid planarity and high bond energy, significantly enhancing the thermal stability of the anti-hydrolysis agent, maintaining its chemical activity during PLA melt processing and spinning, and preventing high-temperature decomposition failure. The conjugated aromatic ring system can absorb ultraviolet (UV) light, consuming light energy through π→π* electron transitions, reducing free radical oxidative degradation (photoaging) of PLA caused by UV radiation, and synergistically extending fiber life with antioxidants (such as 1010 / 168).

[0032] This invention systematically improves the hydrolysis resistance of polylactic acid (PLA) fibers through the synergistic effect of multiple components, including anti-hydrolysis agents, plasticizers, nucleating agents, and auxiliary additives, along with process control. The anti-hydrolysis agent, with a highly electrophilic carbodiimide group (-N=C=N-) as its core, actively captures the carboxyl groups generated during PLA hydrolysis and generates stable N-acylurea, directly blocking the autocatalytic hydrolysis cycle. Its conjugated aromatic ring skeleton enhances thermal stability and UV aging resistance, while ester substituents strengthen compatibility with PLA. The plasticizer lowers the glass transition temperature, increases chain segment mobility, promotes nucleating agent-induced crystallization, and improves the dispersibility and efficiency of the anti-hydrolysis agent. The nucleating agent increases crystallinity to form a dense structure, hindering water molecule penetration and creating a buffer response time for the anti-hydrolysis agent. In terms of process, pre-crystallization and drying control the moisture content to ≤50ppm, completely eliminating the source of hydrolysis. Twin-screw extrusion employs a stepped temperature control of 160-205℃ to balance dispersibility and the risk of thermal degradation. Stretching and heat setting improve orientation and stabilize the crystalline structure under a relaxation tension of 90-98%. Auxiliary agents such as lubricants reduce shear heat, and antioxidants inhibit thermo-oxidative oxidation, jointly ensuring the stability of the processing and the integrity of the molecular chain. Ultimately, this process blocks the hydrolytic chain reaction at the molecular level, builds a crystalline barrier at the structural level, and achieves low moisture, low shear, and low-temperature protection at the processing level, significantly improving the fiber's durability in humid and hot environments and realizing multi-dimensional synergistic hydrolysis resistance enhancement.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] 1. Significantly improved hydrolysis resistance: By introducing a hydrolysis-resistant agent with a specific structure, and through its synergistic effect with plasticizers and nucleating agents, the autocatalytic cycle of hydrolysis is effectively blocked, reducing the tendency of fiber molecular chain breakage and performance degradation under humid and hot environments. This solves the problems of poor compatibility and insufficient protective effect of existing hydrolysis-resistant agents.

[0035] 2. Enhanced weather resistance: The conjugated aromatic ring structure in the anti-hydrolysis agent works synergistically with the antioxidant to improve the stability of the fiber under ultraviolet light and humid conditions, reduce the tendency of strength loss caused by photoaging, and has a better protective effect than conventional anti-hydrolysis agents.

[0036] 3. Optimized mechanical strength and long-term durability: The overall formulation synergy (such as plasticizers promoting chain segment activity and nucleating agents increasing crystallinity) combined with low moisture content process control reduces the risk of processing degradation, improves the initial strength of the fiber and the retention rate under aging conditions, and ensures more durable application performance. Attached Figure Description

[0037] Figure 1 This is the NMR spectrum of the anti-hydrolysis agent 1 of the present invention. Detailed Implementation

[0038] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Preparation Example 1

[0040] Synthesis of anti-hydrolysis agent 1:

[0041] ;

[0042] 10 g of compound A and 10.04 g of compound B were dissolved in 120 mL of a mixed solvent of 1,4-dioxane and diisopropylamine (80 mL of 1,4-dioxane and 40 mL of diisopropylamine), and stirred until uniformly dispersed. Under a continuous nitrogen stream, 1.09 g of palladium acetate, 3.47 g of 2-dicyclohexylphosphine-2',4',6'-triisopropylbiphenyl, and 1.39 g of CuI were added sequentially, and the mixture was heated to 90 °C and reacted for 6 h. The reaction solution was filtered through silica gel, and the filtrate was evaporated to dryness. Separation was performed by column chromatography (silica gel column chromatography, with a mixed solution of n-heptane and ethyl acetate as eluent). After evaporation to dryness, 10.10 g of compound C was obtained. The structure was identified, and the mass spectra (m / z MS+1) of compound C were 343.

[0043] ;

[0044] 10.10 g of compound C, 9.67 g of compound B, and 120 g of toluene were added to a reaction vessel and stirred until homogeneous. Under a continuous nitrogen flow, 1.35 g of tris(dibenzylacetone)palladium, 4.13 g of 1,1'-bis(diphenylphosphine)ferrocene, 1.17 g of 1-ethyl-3-methylimidazolium tetrafluoroborate, and 6.62 g of triethylenediamine were added sequentially, and the mixture was heated to 100 °C and reacted for 16 hours. After the reaction was complete, the reaction system was cooled to room temperature, and then 0.1 mol / L hydrochloric acid aqueous solution was added to adjust the pH to 7. The reaction solution was filtered through silica gel, and after rotary evaporation, the filtrate was separated by column chromatography (silica gel column chromatography, using a mixed solution of n-heptane and ethyl acetate as eluent). After rotary evaporation, 13.10 g of anti-hydrolysis agent 1 was obtained. The structure was identified, and the mass spectrometry (m / z MS+1) of anti-hydrolysis agent 1 was 519. The NMR spectrum is shown below. Figure 1 .

[0045] Preparation Examples 2-5

[0046] In Preparation Examples 2-5, anti-hydrolysis agents were prepared sequentially, following the preparation method of Preparation Example 1, except that raw material 2 was replaced, and the rest remained the same as in Preparation Example 1. For details, please refer to Table 1.

[0047] Table 1.

[0048] Example 1

[0049] Preparation of polylactic acid fiber:

[0050] 1. Raw material components:

[0051] Polylactic acid: 100 parts, purchased from: Shanghai Yuanye Biotechnology Co., Ltd.;

[0052] Plasticizer: 10 parts, selected from acetylsicitrin tributyl ester, purchased from Tianjin Xiens Biochemical Technology Co., Ltd.

[0053] Nucleating agent: 1 part, talc powder, purchased from: Shanghai Titan Technology Co., Ltd.;

[0054] Anti-hydrolysis agent: 1 part, selected from anti-hydrolysis agent 1 synthesized in Preparation Example 1;

[0055] Lubricant: 0.1 parts, made of polyethylene, purchased from Jiangsu Faer Wax Industry Co., Ltd.;

[0056] Antioxidant: 0.075 parts, using antioxidant 1010, purchased from Qingdao Jiebao Additives Co., Ltd.

[0057] 2. Preparation method

[0058] S1. Pre-crystallization and drying: Polylactic acid slices were placed in a vacuum drying oven and dried at 90°C for 6 hours (vacuum degree -0.1MPa) to reduce the moisture content to below 40 ppm, thus obtaining dried polylactic acid;

[0059] S2. Blending modification: Under a nitrogen atmosphere, dry polylactic acid, plasticizer, nucleating agent, anti-hydrolysis agent, lubricant and antioxidant are added to a high-speed mixer (800 rpm) and mixed for 15 minutes until uniformly dispersed to obtain a mixture;

[0060] S3. Melt extrusion granulation: The mixture is melt-blended through a twin-screw extruder. The extruder processing temperature is set as follows: Zone 1 165℃, Zone 2 175℃, Zone 3 185℃, Zone 4 195℃, and Die head 200℃; the screw speed is 150 rpm; the melt is cooled in a water bath and granulated by a pelletizer (particle size 2-3 mm) to obtain modified polylactic acid masterbatch;

[0061] S4. Melt spinning: The modified polylactic acid masterbatch is dried in a forced-air dryer at 85°C for 4 hours (moisture content <30ppm) and fed into a spinning screw extruder; the melt spinning process parameters are: screw extrusion temperature 200°C, spinning box temperature 205°C, spinneret orifice number 48f, and single filament fineness 3.5dtex; the melt is passed through a metering pump (accuracy ±0.5%) and a metal filter (pore size 10μm) and then extruded by the spinneret to obtain nascent fibers;

[0062] S5. Stretching and heat setting: The nascent fibers are drawn by the guide rollers and passed sequentially through: the preheating roller (temperature 70℃), the first-stage stretching roller (temperature 80℃, stretching ratio 3.0 times), and the second-stage heat setting roller (temperature 115℃, relaxation heat setting tension 94%). Finally, after cooling to room temperature (25℃), they are wound to obtain polylactic acid fibers.

[0063] Examples 2-5

[0064] The preparation of a polylactic acid fiber is carried out by referring to the preparation method of Example 1, except that the anti-hydrolysis agent is replaced with the anti-hydrolysis agent prepared in Preparation Examples 2-5, and the rest is the same as in Example 1.

[0065] Comparative Example 1

[0066] A polylactic acid fiber was prepared by referring to the preparation method of Example 1, except that the anti-hydrolysis agent was replaced with N,N'-bis(2,6-diisopropylphenyl)carbodiimide (a commonly used anti-hydrolysis agent), and the rest remained the same as in Example 1.

[0067] Comparative Example 2

[0068] A polylactic acid fiber was prepared by referring to the preparation method of Example 1, except that the anti-hydrolysis agent was replaced with di(tert-butyl)carbodiimide (a commonly used anti-hydrolysis agent), and the rest remained the same as in Example 1.

[0069] Comparative Example 3

[0070] A polylactic acid fiber was prepared by referring to the preparation method of Example 1, except that the anti-hydrolysis agent was replaced with: The rest remains the same as in Example 1.

[0071] Comparative Example 4

[0072] A polylactic acid fiber was prepared according to the preparation method of Example 1, except that the anti-hydrolysis agent was not added, and the rest remained the same as in Example 1.

[0073] Comparative Example 5

[0074] The preparation of a polylactic acid fiber is carried out according to the preparation method of Example 1, except that the antioxidant is not added, and the rest is the same as in Example 1.

[0075] Performance testing:

[0076] Test sample: A polylactic acid fiber prepared in the examples and comparative examples.

[0077] 1. The tensile strength of the samples was tested in accordance with GB / T 14337-2008, and the data are shown in Table 2.

[0078] 2. Place the sample in a constant temperature and humidity chamber, set the temperature to 75℃, the humidity to 95%, and the time to 360h. After the exposure, equilibrate for 24 hours under standard conditions (temperature to 25℃ and humidity to 50%). Test the tensile strength of the sample according to GB / T 14337-2008 and calculate the tensile strength loss rate (%).

[0079] 3. Place the sample in a QUV accelerated aging test chamber. The light source is a 340nm UV-A lamp with an irradiance of 0.77W / m².2 The temperature was set as follows: 75℃ for the light cycle and 20℃ for the condensation cycle; the aging cycle was 8 hours for the light cycle and 4 hours for the condensation cycle; the total exposure was 1200 hours. The tensile strength of the samples was tested in accordance with GB / T 14337-2008, and the tensile strength loss rate (%) was calculated.

[0080] Table 2.

[0081] Tensile strength MPa Hydrolysis tensile strength loss rate (%) Weather resistance tensile strength loss rate (%) Example 1 392 3.8 5.2 Example 2 388 3.0 4.9 Example 3 390 3.5 5.5 Example 4 391 3.3 5.3 Example 5 386 3.9 6.1 Comparative Example 1 380 18.7 24.3 Comparative Example 2 375 22.5 29.1 Comparative Example 3 377 26.8 32.6 Comparative Example 4 380 45.2 41.8 Comparative Example 5 374 14.3 37.5

[0082] The example group using a specific structured anti-hydrolysis agent significantly outperformed the control group using traditional anti-hydrolysis agents in terms of hydrolysis resistance and weather resistance. This demonstrates that the patented anti-hydrolysis agent, with its conjugated aromatic ring and ester group, can more effectively block the hydrolysis chain reaction and synergistically enhance resistance to UV aging. The strength loss rate of the example group was much lower than all comparative examples, especially compared to Comparative Example 4 without the added anti-hydrolysis agent, highlighting the protective effect of the patented anti-hydrolysis agent against humid and hot environments. The light aging loss rate of the example group was significantly lower, while Comparative Example 5 showed the most significant weathering degradation due to the lack of photostable synergy. Although the initial tensile strength of the example group was similar to that of the comparative examples, its strength retention rate after aging was significantly superior, proving that this system represents a breakthrough in maintaining long-term performance stability.

[0083] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A polylactic acid fiber, characterized in that, It is mainly prepared from the following raw materials in parts by weight: 100 parts polylactic acid, 5-15 parts plasticizer, 0.5-3 parts nucleating agent, 0.5-2 parts anti-hydrolysis agent, 0.05-0.2 parts lubricant, and 0.05-0.1 parts antioxidant; The anti-hydrolysis agent is a compound represented by Formula 1: Formula 1: ; R1 in Formula 1 is a substituent; R1 is selected from any one of hydrogen, deuterium, amino, cyano, fluorine, and C1-5 alkyl groups.

2. The polylactic acid fiber according to claim 1, characterized in that, The anti-hydrolysis agent is any one of the compounds shown in the following structures: ； ； ； 。 3. The polylactic acid fiber according to claim 1, characterized in that, The plasticizer is selected from: tributyl acetylglucosyl citrate and / or polyethylene glycol PEG-4000.

4. The polylactic acid fiber according to claim 1, characterized in that, The nucleating agent is selected from any one of talc, nano calcium carbonate, and TMC-306.

5. A polylactic acid fiber according to claim 1, characterized in that, The lubricant is selected from any one of the following: polyethylene wax, fatty alcohol polyoxyethylene ether, and ethylene bis-stearamide.

6. A polylactic acid fiber according to claim 1, characterized in that, The antioxidant is selected from any one of antioxidant 1010, antioxidant 168, antioxidant 1098, and TPH-24.

7. A method for preparing polylactic acid fiber according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Pre-crystallization and drying: Polylactic acid chips are dried under vacuum or forced air at 80-100℃ for 4-8 hours to reduce the moisture content to below 50ppm, thus obtaining dried polylactic acid; S2. Blending modification: The dried polylactic acid is thoroughly mixed with the plasticizer, nucleating agent, anti-hydrolysis agent, lubricant and antioxidant in a high-speed mixer in proportion to obtain a mixture; S3. Melt extrusion granulation: The mixture is melt-blended, extruded, cooled, and pelletized using a twin-screw extruder to obtain modified polylactic acid masterbatch; S4. Melt spinning: The modified polylactic acid masterbatch is dried and fed into a spinning screw extruder. After melting, metering, and filtration, it is extruded through a spinneret to obtain nascent fibers. S5. Stretching and heat setting: The nascent fiber is drawn by a guide roller, preheated, stretched and heat-set, and then cooled to room temperature to obtain a polylactic acid fiber.

8. The method for preparing polylactic acid fiber according to claim 7, characterized in that, The processing temperatures of the twin-screw extruder in S3 are: Zone 1 160-170℃, Zone 2 170-180℃, Zone 3 180-190℃, Zone 4 190-200℃, and Die head 195-205℃.

9. The method for preparing polylactic acid fiber according to claim 7, characterized in that, The melt spinning process parameters in S4 are as follows: screw extrusion temperature 190-220℃, spinning box temperature 200-215℃, spinneret orifice number 24-72f, and single filament fineness 2.0-5.0dtex.

10. A method for preparing polylactic acid fiber according to claim 7, characterized in that, The stretching and heat setting process in S5 is as follows: the preheating roller temperature is 60-80℃, the first-stage stretching roller temperature is 70-90℃, and the stretching ratio is 2.5-4.0 times; the second-stage heat setting roller temperature is 100-130℃, and the relaxation heat setting tension is 90-98%.

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