Preparation method of inorganic doping-tactic composite synergistically modified heat-resistant polylactic acid fiber
By using an inorganic doping-stereocomposite synergistic modification method, high-content stereocomposite crystals and multi-stage stretching processes were generated, which solved the problems of insufficient heat resistance and mechanical properties of polylactic acid fibers, achieved efficient improvement in heat resistance and stability, and expanded its application scenarios.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SUZHOU MENGHONG NEW MATERIAL TECH CO LTD
- Filing Date
- 2026-04-15
- Publication Date
- 2026-06-09
AI Technical Summary
In existing technologies, polylactic acid fibers have insufficient heat resistance and mechanical properties, limited effectiveness of single modification strategies, low efficiency in the formation of stereocomposite crystals, poor dispersibility of inorganic fillers, difficulty in achieving synergistic effects, and poor processing stability, which limits their application in high-temperature environments.
An inorganic doping-stereocomposite synergistic modification method is adopted. Surface-modified inorganic nanofillers are blended with PLLA and PDLA to generate high-content stereocomposite crystals through heterogeneous nucleation. Combined with multi-stage stretching and heat setting processes, high-efficiency inorganic doping-stereocomposite polylactic acid fibers are formed.
It significantly improves the heat resistance and mechanical properties of polylactic acid fiber, increasing the heat distortion temperature to over 160℃, tensile strength by 50%, crystallinity to 60%, and stabilizing the spinning process, thus expanding its application range in high-temperature environments.
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Figure CN122169246A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of materials technology, and in particular to a method for preparing inorganic doped-stereocomposite synergistic modified heat-resistant polylactic acid fibers. Background Technology
[0002] Polylactic acid (PLA) is a fully biodegradable polymer material prepared from renewable biomass such as corn and straw. It has good biocompatibility, mechanical formability and environmental friendliness, and has become an important candidate material to replace traditional petroleum-based textile fibers. It has broad application prospects in textiles and clothing, medical dressings, industrial filtration and automotive interiors.
[0003] However, pure polylactic acid (PLA) fibers have inherent performance defects, the most prominent of which is their poor heat resistance. Their glass transition temperature (Tg) is only 55-65℃, heat distortion temperature is less than 60℃, and melting temperature is approximately 170℃. Under high-temperature environments (such as above 80℃), they are prone to softening, deformation, and shrinkage, and their mechanical properties deteriorate sharply, severely limiting their application in high-temperature conditions, outdoor exposure, and high-temperature washing. Furthermore, pure PLA has a slow crystallization rate and low crystallinity (typically less than 30%), which not only further exacerbates their insufficient heat resistance but also results in poor mechanical strength and dimensional stability, making it difficult to meet practical application requirements.
[0004] Currently, modification technologies for improving the heat resistance of polylactic acid (PLA) fibers mainly fall into two categories, but both have significant limitations, making it difficult to achieve breakthrough performance improvements. One category is stereocomposite modification technology, which involves blending poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) and utilizing the stereoisomerism of their molecular chains to form stereocomposite PLA crystals (SC-PLA) during processing. The molecular chain packing density of SC-PLA crystals is much higher than that of homopolymer PLA crystals (HC-PLA), and the melting temperature can be increased to over 220℃, significantly improving the thermal stability of PLA. However, this technology has several key drawbacks: First, the generation efficiency of stereocomposite crystals is low. Under conventional blending methods, the SC-PLA content is usually less than 60%, and the precipitation of a large number of homopolymer crystals will offset the heat resistance advantage brought by stereocomposite. Second, SC-PLA crystals are easily damaged by high temperature and shear force during processing, resulting in unstable modification effects. Third, pure stereocomposite modification cannot solve the problems of high melt viscosity and poor spinnability of polylactic acid, making it difficult to achieve continuous and stable industrial production.
[0005] Another type is inorganic doping modification technology, which introduces nano-inorganic fillers (such as SiO2, TiO2, carbon nanotubes, hydroxyapatite, etc.) into the polylactic acid (PLA) matrix. The heterogeneous nucleation effect of the inorganic fillers accelerates PLA crystallization, while the rigid framework effect of the inorganic phase enhances the fiber's heat resistance and mechanical strength. However, single inorganic doping modification also has insurmountable drawbacks: First, the interfacial compatibility between inorganic fillers and the PLA matrix is poor, leading to agglomeration, which not only fails to exert a modifying effect but also causes a decrease in fiber mechanical properties and easy fiber breakage during spinning; second, inorganic fillers can only improve heat resistance through physical action and cannot improve the thermal stability of PLA at the molecular chain level, resulting in limited modification effects and difficulty in raising the heat distortion temperature of PLA fibers above 120℃; third, single inorganic doping cannot solve the problem of low efficiency in the formation of stereocomposite crystals, and cannot achieve a fundamental improvement in heat resistance.
[0006] In existing technologies, some studies have attempted to simply combine the two modification methods, but none of them have achieved an effective synergistic effect. Most of them simply blend inorganic fillers with PLLA and PDLA without precisely controlling the surface modification of inorganic fillers, blending process, and spinning parameters. This results in uneven dispersion of inorganic fillers and low efficiency in the formation of stereocomposite crystals, failing to achieve the synergistic modification effect of "1+1>2". Problems such as limited improvement in heat resistance, unstable mechanical properties, and high processing difficulty still exist.
[0007] Therefore, in view of the technical pain points in the existing technology, such as the limited effect of single modification strategy, the inability of simple compounding to achieve synergistic effect, the low generation efficiency of stereocomposite crystals, and the poor dispersibility of inorganic fillers, it is necessary to develop a preparation method that can achieve efficient synergy between inorganic doping and stereocomposite, significantly improve the heat resistance, mechanical properties and processing stability of polylactic acid fibers, and has the potential for industrial application. This has become a technical problem that urgently needs to be solved in the field, and it is also the core innovation of this invention. Summary of the Invention
[0008] In view of the problems mentioned in the background art, the purpose of this invention is to provide a method for preparing inorganic doped-stereocomposite synergistic modified heat-resistant polylactic acid fiber, so as to solve the problems mentioned in the background art.
[0009] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a method for preparing inorganic doped-stereoscopic composite synergistic modified heat-resistant polylactic acid fiber, comprising the following steps: S1, raw material pretreatment: poly-L-lactic acid (PLLA) and poly-D-lactic acid (PDLA) are vacuum dried at 80-100℃ for 4-8h until the moisture content is ≤0.02%; inorganic nanofillers are added to a silane coupling agent solution, ultrasonically dispersed for 20-40min, and then dried at 100-120℃ for 2-4h to complete surface modification; the pretreated PLLA and PDLA are mixed with the surface-modified inorganic nanofillers at a mass ratio to obtain mixed raw materials.
[0010] S2. Melt blending and in-situ stereopolymerization: The mixed raw materials are added to a twin-screw extruder, and the screw speed is controlled at 120-280 r / min. The temperature of each zone of the extruder is set as follows: feeding zone 165-185℃, melting zone 195-215℃, homogenization zone 185-205℃. The blending residence time is 6-14 min to allow PLLA and PDLA to be fully melt-blended. At the same time, the heterogeneous nucleation effect of surface-modified inorganic nanofillers is used to induce the directional alignment of PLLA and PDLA molecular chains, generating stereopolymerized polylactic acid crystals (SC-PLA) in situ, thus obtaining a synergistically modified polylactic acid melt.
[0011] S3. Melt spinning: The synergistically modified polylactic acid melt is fed into the spinning box, and the temperature of the spinning box is controlled at 195-215℃. After being metered by a metering pump, it is extruded through a spinneret with a spinneret orifice diameter of 0.25-0.45mm and an extrusion speed of 12-28m / min to form nascent fibers.
[0012] S4. Multi-stage stretching and heat setting: The nascent fibers are first stretched at 75-95℃ with a stretch ratio of 2.2-4.2 times; then stretched at 95-115℃ with a stretch ratio of 1.6-3.2 times, for a total stretch ratio of 3.5-10.5 times; subsequently, they are heat-set at 125-155℃ for 35-115 seconds using hot air circulation heating. After cooling, inorganic doped-stereoscopic composite synergistic modified heat-resistant polylactic acid fibers are obtained.
[0013] Preferably, in S1, the mass ratio of PLLA to PDLA is (3-7):(7-3), and the amount of surface-modified inorganic nanofiller added is 1.5%-4.5% of the total mass of PLLA and PDLA.
[0014] Preferably, in step S1, the inorganic nanofiller is one or more of nano-SiO2, nano-TiO2, carbon nanotubes, and hydroxyapatite, with a particle size of 25-90 nm; the silane coupling agent is one of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane, and the amount of silane coupling agent added is 2%-6% of the mass of the inorganic nanofiller.
[0015] Preferably, in step S1, the raw materials are mixed using a high-speed mixer with a mixing speed of 800-1200 r / min and a mixing time of 15-30 min to ensure uniform mixing of the raw materials.
[0016] Preferably, in S2, the length-to-diameter ratio of the twin-screw extruder is (30-40):1, and the pressure in the homogenization section is controlled at 15-25 MPa to ensure sufficient melt blending and stable formation of stereocomposite crystals.
[0017] Preferably, in step S3, the metering pump rotates at a speed of 5-15 r / min, the spinneret has 36-72 spinneret holes, and the melt pressure is controlled at 12-20 MPa during extrusion.
[0018] Preferably, in S4, both the primary and secondary stretching are performed using hot roller stretching, with a stretching speed of 15-35 m / min, and the fiber tension is controlled at 5-15 cN during the stretching process.
[0019] Preferably, in step S4, after high-temperature heat setting, gradient cooling is adopted, with cooling temperatures successively at 100-110℃, 70-80℃, and room temperature, and each cooling time being 15-30s, to ensure fiber morphology stability.
[0020] In summary, the present invention has the following beneficial effects: It fundamentally improves the heat resistance of the fiber, breaking through the bottlenecks of existing technologies. Through the heterogeneous nucleation effect of surface-modified inorganic nanofillers, the present invention significantly improves the generation efficiency of stereocomposite crystals (SC-PLA), increasing the SC-PLA content in the fiber to over 80%. Combined with the rigid framework effect of the inorganic phase, it achieves a synergistic enhancement of heat resistance. The resulting modified polylactic acid fiber has a heat distortion temperature exceeding 160℃, a thermal decomposition initiation temperature exceeding 290℃, and a stable melting temperature of 220-230℃. Compared to pure PLA fiber, its heat resistance is improved by over 150%, and compared to single stereocomposite or inorganic doped modified fibers, its heat resistance is improved by over 40%. It can be used stably in environments below 120℃ for extended periods, completely solving the core problem of poor heat resistance in traditional PLA fibers.
[0021] This invention synergistically enhances mechanical properties, balancing strength and toughness: the surface-modified inorganic nanofiller exhibits significantly improved interfacial compatibility with the polylactic acid matrix, uniformly dispersing within the matrix to form a rigid reinforcing phase; simultaneously, the high content of SC-PLA crystals increases the molecular chain packing density and strengthens the inter-chain forces. The synergistic effect of these two factors increases the tensile strength of the fiber by more than 50% (≥6.0 cN / dtex), maintains the elongation at break at 28%-45%, and improves the impact strength by more than 35%. This solves the problem of unbalanced mechanical properties in single-modified fibers (such as high rigidity but poor toughness), meeting the mechanical requirements of practical applications. Attached Figure Description
[0022] Figure 1 This is a flowchart of the present invention. Detailed Implementation
[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only 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.
[0024] refer to Figure 1 A method for preparing inorganic doped-stereoscopic composite synergistic modified heat-resistant polylactic acid fiber includes the following steps: S1, raw material pretreatment: poly-L-lactic acid (PLLA) and poly-D-lactic acid (PDLA) are vacuum dried at 80-100℃ for 4-8h until the moisture content is ≤0.02%; inorganic nanofillers are added to a silane coupling agent solution, ultrasonically dispersed for 20-40min, and then dried at 100-120℃ for 2-4h to complete surface modification; the pretreated PLLA and PDLA are mixed with the surface-modified inorganic nanofillers at a mass ratio to obtain mixed raw materials.
[0025] S2. Melt blending and in-situ stereopolymerization: The mixed raw materials are added to a twin-screw extruder, and the screw speed is controlled at 120-280 r / min. The temperature of each zone of the extruder is set as follows: feeding zone 165-185℃, melting zone 195-215℃, homogenization zone 185-205℃. The blending residence time is 6-14 min to allow PLLA and PDLA to be fully melt-blended. At the same time, the heterogeneous nucleation effect of surface-modified inorganic nanofillers is used to induce the directional alignment of PLLA and PDLA molecular chains, generating stereopolymerized polylactic acid crystals (SC-PLA) in situ, thus obtaining a synergistically modified polylactic acid melt.
[0026] S3. Melt spinning: The synergistically modified polylactic acid melt is fed into the spinning box, and the temperature of the spinning box is controlled at 195-215℃. After being metered by a metering pump, it is extruded through a spinneret with a spinneret orifice diameter of 0.25-0.45mm and an extrusion speed of 12-28m / min to form nascent fibers.
[0027] S4. Multi-stage stretching and heat setting: The nascent fibers are first stretched at 75-95℃ with a stretch ratio of 2.2-4.2 times; then stretched at 95-115℃ with a stretch ratio of 1.6-3.2 times, for a total stretch ratio of 3.5-10.5 times; subsequently, they are heat-set at 125-155℃ for 35-115 seconds using hot air circulation heating. After cooling, inorganic doped-stereoscopic composite synergistic modified heat-resistant polylactic acid fibers are obtained.
[0028] In S1, the mass ratio of PLLA to PDLA is (3-7):(7-3), and the amount of surface-modified inorganic nanofiller added is 1.5%-4.5% of the total mass of PLLA and PDLA.
[0029] In S1, the inorganic nanofiller is one or more of nano-SiO2, nano-TiO2, carbon nanotubes, and hydroxyapatite, with a particle size of 25-90 nm; the silane coupling agent is one of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane, and the amount of silane coupling agent added is 2%-6% of the mass of the inorganic nanofiller.
[0030] In step S1, the raw materials are mixed using a high-speed mixer with a mixing speed of 800-1200 r / min and a mixing time of 15-30 min to ensure uniform mixing of the raw materials.
[0031] In S2, the length-to-diameter ratio of the twin-screw extruder is (30-40):1, and the pressure in the homogenization section is controlled at 15-25 MPa to ensure sufficient melt blending and stable generation of stereocomposite crystals.
[0032] In S3, the metering pump rotates at a speed of 5-15 r / min, the spinneret has 36-72 spinneret holes, and the melt pressure is controlled at 12-20 MPa during extrusion.
[0033] In S4, both the primary and secondary stretching are performed using hot roller stretching, with a stretching speed of 15-35 m / min and the fiber tension controlled at 5-15 cN during the stretching process.
[0034] In S4, after high-temperature heat setting, gradient cooling is adopted, with cooling temperatures successively at 100-110℃, 70-80℃, and room temperature, and each cooling time is 15-30s to ensure fiber morphology stability.
[0035] This invention achieves a fundamental improvement in heat resistance, breaking through existing technological bottlenecks. Through the heterogeneous nucleation effect of surface-modified inorganic nanofillers, it significantly increases the generation efficiency of stereocomposite crystals (SC-PLA), raising the SC-PLA content in the fiber to over 80%. Combined with the rigid framework effect of the inorganic phase, this results in a synergistic enhancement of heat resistance. The resulting modified polylactic acid fiber exhibits a heat distortion temperature exceeding 160℃, a thermal decomposition initiation temperature exceeding 290℃, and a stable melting temperature of 220-230℃. Compared to pure PLA fiber, its heat resistance is improved by over 150%, and compared to single stereocomposite or inorganic-doped modified fibers, it is improved by over 40%. It can be used stably in environments below 120℃ for extended periods, completely solving the core problem of poor heat resistance in traditional PLA fibers.
[0036] The present invention features synergistic enhancement of mechanical properties, balancing strength and toughness: the surface-modified inorganic nanofiller has significantly improved interfacial compatibility with the polylactic acid matrix, and is uniformly dispersed in the matrix to form a rigid reinforcing phase; at the same time, the high content of SC-PLA crystals increases the molecular chain packing density and enhances the intermolecular forces. The two work together to increase the tensile strength of the fiber by more than 50% (≥6.0 cN / dtex), maintain the elongation at break at 28%-45%, and increase the impact strength by more than 35%. This solves the problem of unbalanced mechanical properties of single modified fibers (such as high rigidity but poor toughness) and meets the mechanical requirements of practical applications.
[0037] Among these advancements, the crystallization performance of this invention is significantly optimized, and the processing stability is greatly improved: the heterogeneous nucleation effect of inorganic nanofillers increases the crystallization rate of polylactic acid by more than 4 times and the crystallinity to over 60%, effectively shortening the processing cycle; at the same time, inorganic doping reduces the viscosity of the polylactic acid melt, improves the spinnability, and reduces filament breakage and fuzzing during the spinning process; the high content of SC-PLA crystals exhibits good stability during processing and is not easily damaged by high temperature and shear force, enabling continuous and stable industrial melt spinning production and reducing production costs.
[0038] This invention creatively solves the problems of interface compatibility and synergistic effect: By modifying the surface of inorganic nanofillers with silane coupling agents, functional groups compatible with polylactic acid molecular chains are introduced on the filler surface, effectively solving the technical pain points of inorganic filler agglomeration and weak interfacial bonding with the matrix; at the same time, by precisely controlling the blending, spinning and heat setting parameters, the heterogeneous nucleation effect of inorganic doping and the molecular chain regularization effect of stereocomposite are made to form a highly efficient synergy, breaking through the limitation of "simple composite cannot achieve synergistic effect" in the prior art, and realizing a qualitative leap in the modification effect.
[0039] This invention retains biodegradability and expands application scenarios: the raw materials used in this invention are all environmentally friendly materials, and no toxic or harmful components are introduced during the modification process. The resulting modified polylactic acid fiber still maintains good biodegradability and can be completely degraded in the natural environment, which is in line with the trend of green and environmentally friendly development. At the same time, due to its combination of high heat resistance, good mechanical properties and biodegradability, it can be widely used in high-temperature textile fabrics, industrial filter materials, automotive interiors, outdoor products, medical high-temperature dressings and other fields, completely breaking through the application limitations of traditional PLA fibers, and has broad industrial application prospects and economic value.
[0040] 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 method for preparing inorganic doped-stereocomposite synergistic modified heat-resistant polylactic acid fiber, characterized in that: Includes the following steps: S1. Raw material pretreatment: Poly(L-lactic acid) and poly(D-lactic acid) are vacuum dried at 80-100℃ for 4-8 hours until the moisture content is ≤0.02%; the inorganic nanofiller is added to the silane coupling agent solution, ultrasonically dispersed for 20-40 minutes, and then dried at 100-120℃ for 2-4 hours to complete the surface modification; the pretreated PLLA and PDLA are mixed with the surface-modified inorganic nanofiller at a certain mass ratio to obtain the mixed raw material; S2. Melt blending and in-situ stereocomposite compounding: The mixed raw materials are added to a twin-screw extruder, and the screw speed is controlled at 120-280 r / min. The temperature of each zone of the extruder is set as follows: feeding zone 165-185℃, melting zone 195-215℃, homogenization zone 185-205℃, and the blending residence time is 6-14 min, so that PLLA and PDLA can be fully melt-blended. At the same time, the heterogeneous nucleation effect of surface-modified inorganic nanofillers is used to induce the directional alignment of PLLA and PDLA molecular chains, and in-situ stereocomposite polylactic acid crystals are generated to obtain synergistically modified polylactic acid melt. S3. Melt spinning: The synergistically modified polylactic acid melt is fed into the spinning box, and the temperature of the spinning box is controlled at 195-215℃. After being metered by a metering pump, it is extruded through a spinneret with a spinneret orifice diameter of 0.25-0.45mm and an extrusion speed of 12-28m / min to form nascent fibers. S4. Multi-stage stretching and heat setting: The nascent fibers are first stretched at 75-95℃ with a stretch ratio of 2.2-4.2 times; then stretched at 95-115℃ with a stretch ratio of 1.6-3.2 times, for a total stretch ratio of 3.5-10.5 times; subsequently, they are heat-set at 125-155℃ for 35-115 seconds using hot air circulation heating. After cooling, inorganic doped-stereoscopic composite synergistic modified heat-resistant polylactic acid fibers are obtained.
2. The method for preparing inorganic doped-stereocomposite synergistic modified heat-resistant polylactic acid fiber according to claim 1, characterized in that: In S1, the mass ratio of PLLA to PDLA is (3-7):(7-3), and the amount of surface-modified inorganic nanofiller added is 1.5%-4.5% of the total mass of PLLA and PDLA.
3. The method for preparing inorganic doped-stereoscopic composite synergistic modified heat-resistant polylactic acid fiber according to claim 1, characterized in that: In step S1, the inorganic nanofiller is one or more of nano-SiO2, nano-TiO2, carbon nanotubes, and hydroxyapatite, with a particle size of 25-90 nm; the silane coupling agent is one of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane, and the amount of silane coupling agent added is 2%-6% of the mass of the inorganic nanofiller.
4. The method for preparing inorganic doped-stereoscopic composite synergistic modified heat-resistant polylactic acid fiber according to claim 1, characterized in that: In step S1, the raw materials are mixed using a high-speed mixer with a mixing speed of 800-1200 r / min and a mixing time of 15-30 min to ensure uniform mixing of the raw materials.
5. The method for preparing inorganic doped-stereoscopic composite synergistic modified heat-resistant polylactic acid fiber according to claim 1, characterized in that: In S2, the length-to-diameter ratio of the twin-screw extruder is (30-40):1, and the pressure in the homogenization section is controlled at 15-25 MPa to ensure sufficient melt blending and stable formation of stereocomposite crystals.
6. The method for preparing inorganic doped-stereoscopic composite synergistic modified heat-resistant polylactic acid fiber according to claim 1, characterized in that: In S3, the metering pump rotates at a speed of 5-15 r / min, the spinneret has 36-72 spinneret holes, and the melt pressure is controlled at 12-20 MPa during extrusion.
7. The method for preparing inorganic doped-stereocomposite synergistic modified heat-resistant polylactic acid fiber according to claim 1, characterized in that: In S4, both the primary and secondary stretching are performed using hot roller stretching, with a stretching speed of 15-35 m / min and the fiber tension controlled at 5-15 cN during the stretching process.
8. The method for preparing inorganic doped-stereoscopic composite synergistic modified heat-resistant polylactic acid fiber according to claim 1, characterized in that: In step S4, after high-temperature heat setting, gradient cooling is adopted, with cooling temperatures successively at 100-110℃, 70-80℃, and room temperature, and each cooling time is 15-30s to ensure fiber morphology stability.