Carbon fiber reinforced polylactic acid composite and method for manufacturing the same

Abstract

This invention belongs to the field of polymer materials technology and discloses a carbon fiber reinforced polylactic acid composite material and its preparation method. The composite material includes the following raw materials in parts by weight: polylactic acid, PBAT-g-GMA, modified carbon fiber, modified layered double hydroxide, talc, lubricant, and antioxidant. The modified carbon fiber is formed by coating a polydopamine layer on the surface of carbon fiber through the self-polymerization of dopamine, and then grafting catechol, amino-grafted phytic acid, and cage-like polysilsesquioxane onto the surface of the polydopamine layer. The modified layered double hydroxide is formed by intercalating chitosan through electrostatic interaction, and then modifying polyphosphazene with boric acid by grafting ortho-hydroxyl groups on the chitosan chain. This invention uses polylactic acid as the matrix material and adds PBAT-g-GMA blend to improve the brittleness of polylactic acid and enhance the impact strength of the composite material. By combining modified carbon fiber and modified layered double hydroxide, the tensile strength, flexural strength, and rigidity of the composite material are improved, while also endowing the material with excellent heat resistance and flame retardant properties.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a carbon fiber reinforced polylactic acid composite material and its preparation method. Background Technology

[0002] Polylactic acid (PLA), a widely available and fully biodegradable aliphatic polyester, possesses excellent biocompatibility, machinability, and environmental friendliness. It shows broad application prospects in packaging materials, automotive parts, 3D printing consumables, and biomedical devices, making it one of the core materials for replacing traditional petroleum-based plastics and alleviating white pollution. However, the inherent performance defects of pure PLA severely limit its large-scale application in high-end scenarios. Pure PLA has a tensile strength of only 50-60 MPa, a flexural modulus of approximately 2.3 GPa, and is significantly brittle, making it difficult to meet the dual requirements of rigidity and toughness for structural components. It also has poor heat resistance, with a heat distortion temperature of only 60-65℃, making it prone to deformation in high-temperature processing or usage environments, limiting its application in automotive interiors, electronic casings, and other fields. Furthermore, its flame retardant properties are weak, with a limiting oxygen index of only 22%-23%, no vertical burning rating, and it easily drips and ignites surrounding combustibles during combustion, failing to meet the flame retardant safety standards in construction, transportation, and other fields.

[0003] Existing technologies improve the mechanical properties and heat resistance of PLA by adding inorganic reinforcing phases such as carbon fiber and glass fiber. However, the interfacial compatibility between inorganic reinforcements like carbon fiber and the PLA matrix is ​​poor, leading to debonding and limited strengthening and toughening effects, and it cannot improve the material's flame retardant properties. Adding flame-retardant fillers to improve flame retardancy also suffers from poor compatibility with PLA, uneven dispersion, and a tendency to decrease the material's mechanical properties. While adding small-molecule flame-retardant additives does not affect the mechanical properties of PLA, these small molecules are prone to physical losses, such as volatilization and migration, resulting in a decrease in the polymer's flame retardancy. Therefore, there is an urgent need for a modified polylactic acid material with high strength, high toughness, thermal stability, and flame retardant properties to meet various application requirements. Summary of the Invention

[0004] To address the shortcomings mentioned in the background art, the present invention aims to provide a carbon fiber reinforced polylactic acid composite material and its preparation method. The present invention uses polylactic acid as the matrix material and adds PBAT-g-GMA blend to improve the brittleness of polylactic acid and enhance the impact strength of the composite material. By using modified carbon fiber and modified layered double hydroxide in combination, the tensile strength, flexural strength and rigidity of the composite material are further improved, while giving the material excellent heat resistance and flame retardant properties.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A carbon fiber reinforced polylactic acid composite material comprises the following raw materials in parts by weight: 60-75 parts polylactic acid, 10-15 parts PBAT-g-GMA, 8-10 parts modified carbon fiber, 6-8 parts modified layered double hydroxide, 1-2 parts talc, 0.5-1.5 parts lubricant, and 0.5-1 part antioxidant.

[0007] The modified carbon fiber is formed by coating a polydopamine layer on the surface of short-cut carbon fiber through the self-polymerization of dopamine, and then applying catechol, amino-grafted phytic acid and cage-type polysilsesquioxane to the surface of the polydopamine layer.

[0008] The modified layered double hydroxide is obtained by intercalating chitosan through electrostatic interaction, and then using the ortho-hydroxyl groups on the chitosan chain to graft boric acid to modify polyphosphazene. The boric acid modified polyphosphazene is a polyphosphazene with hydroxyl side groups synthesized by replacing polydichlorophosphazene with aminopropanol, and then end-capped with boric acid to obtain functionalized modified polyphosphazene.

[0009] Preferably, the lubricant is one of calcium stearate, zinc stearate, or ethylene bis-stearamide.

[0010] Preferably, the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.

[0011] Preferably, the method for preparing modified carbon fiber includes the following steps:

[0012] (1) Add short-cut carbon fibers to concentrated nitric acid and reflux at 80°C for 4-6 hours. After the reaction is complete, wash with deionized water and the filtrate is neutral. Vacuum dry to obtain pretreated carbon fibers.

[0013] (2) Dissolve dopamine hydrochloride in Tris-HCl buffer, immerse the pretreated carbon fiber in dopamine hydrochloride Tris-HCl buffer, stir magnetically at room temperature for 20-24 h, filter and wash with deionized water 3-5 times after the reaction, and vacuum dry to obtain polydopamine-coated carbon fiber.

[0014] (2) Add phytic acid and aminopropyl isobutylsilsesquioxane to an ethanol / water mixture to dissolve them, add polydopamine-coated carbon fibers to the mixture, react at 60°C for 8-12 hours, filter and wash with deionized water 3-5 times, and vacuum dry to obtain modified carbon fibers.

[0015] Preferably, the ratio of carbon fiber to dopamine hydrochloride is 1:0.5, and the mass ratio of polydopamine-coated carbon fiber, phytic acid, and aminopropyl isobutylsilsesquioxane is 1:0.05:0.03.

[0016] Preferably, the method for preparing the modified layered double hydroxide includes the following steps:

[0017] A. Magnesium aluminum hydroxide was dispersed in deionized water, and under nitrogen protection and stirring, a dilute acetic acid solution of chitosan was slowly added dropwise. The mixture was reacted at 60°C for 20-24 hours, centrifuged, washed with water, and freeze-dried to obtain chitosan-intercalated magnesium aluminum hydroxide.

[0018] B. Redisperse the chitosan-intercalated magnesium aluminum double hydroxide in deionized water, adjust the pH to 8-9, add boric acid-modified polyphosphazene, and react at 70℃ for 8-12 h. After the reaction is complete, collect the product by centrifugation, wash with water and ethanol 3-5 times, and vacuum dry to obtain the modified layered double hydroxide.

[0019] Preferably, the mass ratio of magnesium aluminum hydroxide, chitosan, and boric acid-modified polyphosphazene is 1:1:0.5~1.

[0020] Preferably, the preparation method of boric acid modified polyphosphazene includes the following steps:

[0021] I. Under a nitrogen atmosphere, aminosulfonic acid, calcium sulfate dihydrate, ammonium chloride, phosphorus pentachloride and 1,2,4-trichlorobenzene are mixed and reacted in an oil bath at 185-195°C for 2-4 hours. After the reaction is completed, the mixture is filtered while hot. The filtrate is slowly added to petroleum ether and stirred until a precipitate forms at the bottom. The supernatant is removed, and the precipitate is washed several times with petroleum ether until the supernatant is clear, thus obtaining purified polydichlorophosphazene.

[0022] II. Polydichlorophosphazene was dissolved in tetrahydrofuran and cooled to 0-5°C in an ice-water bath. 3-Amino-1-propanol and triethylamine were dissolved in tetrahydrofuran. Under vigorous stirring and an ice-water bath, the mixed solution of 3-amino-1-propanol and triethylamine was slowly added dropwise to the polydichlorophosphazene solution. The temperature was slowly raised to room temperature, and the reaction was continued with stirring for 20-24 hours. The triethylamine hydrochloride precipitate was removed by filtration. The filtrate was added to distilled water and stirred to precipitate the product. The product was filtered, and the obtained solid precipitate was purified by repeated dissolution-precipitation in a tetrahydrofuran / water system. Finally, the product was dried under vacuum to obtain the polyphosphazene derivative.

[0023] III. Under a nitrogen atmosphere, polyphosphazene derivatives and 4-carboxyphenylboronic acid were dissolved in N,N-dimethylformamide, and then N,N'-dicyclohexylcarbodiimide and 4-dimethylaminopyridine were added. The mixture was stirred at room temperature in the dark for 20-24 hours. After the reaction was completed, the N,N'-dicyclohexylurea precipitate was removed by filtration. The filtrate was dialyzed against deionized water and methanol for 20-24 hours in sequence. The solvent was evaporated by rotary evaporation, and finally the mixture was dried under vacuum to obtain boric acid-modified polyphosphazene.

[0024] Preferably, the molar ratio of ammonium chloride to phosphorus pentachloride is 1:1, the molar ratio of polydichlorophosphazene, 3-amino-1-propanol and triethylamine is 1:10:10.5, and the molar ratio of polyphosphazene derivative, 4-carboxyphenylboronic acid and N,N'-dicyclohexylcarbodiimide is 1:5:4.5.

[0025] A method for preparing carbon fiber reinforced polylactic acid composite material includes the following steps:

[0026] Polylactic acid, PBAT-g-GMA, modified layered double hydroxide, talc, antioxidant, and lubricant are fed into a twin-screw extruder through the main feeder. The screw speed is 200-300 rpm, and the temperatures of each zone of the extruder are 170℃, 180℃, 190℃, 185℃, and 180℃. Modified carbon fiber is added through a side feeder in the downstream of the melting zone. After the raw materials are melt-blended, they are extruded and granulated. The composite granules are vacuum dried at 60℃ for 4-6 hours to obtain carbon fiber reinforced polylactic acid composite material.

[0027] The beneficial effects of this invention are:

[0028] This invention relates to a carbon fiber reinforced polylactic acid (PLA) composite material. PLA serves as the matrix material, providing fundamental mechanical properties and biodegradability. The addition of PBAT-g-GMA blends improves the brittleness of PLA and enhances the impact strength of the composite. Modified carbon fibers and modified layered double hydroxides are used in combination to improve the tensile strength, flexural strength, and rigidity of the composite, while also imparting excellent heat resistance and flame retardancy. The GMA groups in PBAT-g-GMA can react with the surface-active groups of the modified carbon fibers and modified layered double hydroxides, further strengthening the interfacial bonding. This results in a comprehensive improvement in the composite material's performance in multiple areas, including reinforcement, toughening, heat resistance, and flame retardancy, meeting the needs of high-end applications such as automotive interiors, 3D printing, and medical materials.

[0029] This modified carbon fiber uses original carbon fiber as the matrix, and its surface undergoes a two-step functionalization modification to form a composite modified layer. A uniform polydopamine layer, rich in catechol and amino groups, is formed on the carbon fiber surface through dopamine self-polymerization, providing active sites for subsequent grafting reactions. The catechol and amino groups on the polydopamine layer surface react chemically with the phosphate groups of phytic acid and the amino groups of cage-like polysilsesquioxane to form a phytic acid-cage-like polysilsesquioxane composite grafting layer, ultimately yielding modified carbon fiber with excellent interfacial bonding, corrosion resistance, and thermal stability. The polydopamine layer on the modified carbon fiber surface, rich in catechol and amino groups, undergoes an epoxy ring-opening reaction with the GMA groups of PBAT-g-GMA. Simultaneously, the phosphate groups of phytic acid form hydrogen bonds with the hydroxyl groups of polylactic acid, and the cage-like structure of the cage-like polysilsesquioxane enhances interfacial mechanical interlocking. These three elements synergistically improve the interfacial bonding between the carbon fiber and the matrix, achieving efficient stress transfer. Unmodified carbon fibers have an inert surface and only physical contact with the matrix, making them prone to interfacial voids. Under stress, they debond, significantly reducing their reinforcing and toughening effects. Carbon fibers themselves have high heat resistance and can form a rigid skeleton in composite materials, inhibiting the thermal motion of polylactic acid molecular chains and increasing the heat distortion temperature. At the same time, during high-temperature combustion, carbon fibers can act as a carbon layer support, enhancing the structural stability of the carbon layer formed by modified layered double hydroxides, reducing carbon layer cracking and detachment, and extending the thermal barrier time.

[0030] This invention relates to a modified layered double hydroxide matrix based on magnesium-aluminum layered double hydroxide. Through a two-step composite modification process involving intercalation and grafting, chitosan molecules are inserted into the interlayer spaces of the magnesium-aluminum layered double hydroxide via electrostatic interaction, expanding the interlayer spacing and introducing active hydroxyl groups. Then, through coordination or esterification reactions between the ortho-hydroxyl groups on the chitosan chains and the boric acid groups of the boric acid-modified polyphosphazene, the boric acid-modified polyphosphazene is grafted onto the surface and interlayer spaces of the magnesium-aluminum layered double hydroxide, forming an inorganic-organic composite modified layer. The final product combines the layered barrier properties of magnesium-aluminum layered double hydroxide, the biocompatibility of chitosan, and the functional properties of boric acid-modified polyphosphazene. The layered structure of the modified layered double hydroxide forms a nano-barrier during combustion, blocking oxygen and heat transfer and delaying polylactic acid degradation. The chitosan intercalation expands the interlayer spacing of the layered double hydroxide, resulting in a more uniform barrier effect. Boric acid-modified polyphosphazene contains P, B, and N flame-retardant elements. At high temperatures, it undergoes a dehydration and charring reaction, forming a dense composite char layer of boron phosphate and boron nitride. Simultaneously, it releases non-combustible gases such as nitrogen and water vapor, diluting the concentration of combustible gases. The layered structure of the modified layered double hydroxide forms a double barrier with the char layer of the boric acid-modified polyphosphazene, delaying the thermal oxidative degradation of the polylactic acid molecular chains. Furthermore, the metal ions (Mg²⁺, Mg²⁺, and Mg²⁺) in the modified layered double hydroxide... 2+ Al 3+ It can catalyze the cross-linking of polylactic acid, thereby improving thermal stability.

[0031] Furthermore, the modified carbon fiber and modified layered aluminum hydroxide exhibit a synergistic reinforcing effect in terms of mechanical properties, heat resistance, and flame retardancy. The modified carbon fiber provides rigid support, while the modified layered aluminum hydroxide fills the matrix voids. Simultaneously, the surface active groups of both (such as the amino groups of CF and the boric acid groups of LDH) coordinate to form a three-dimensional network structure of fiber, filler, and matrix, reducing stress concentration. The skeletal support of the modified carbon fiber combined with the layered barrier properties of the modified layered aluminum hydroxide achieves a synergistic improvement in heat resistance. The modified layered aluminum hydroxide forms a dense char layer, and the modified carbon fiber enhances the strength of the char layer, preventing char layer detachment during combustion and synergistically improving the flame retardant effect.

[0032] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] A modified carbon fiber, wherein the modified carbon fiber is prepared by coating a polydopamine layer on the surface of short-cut carbon fibers through the self-polymerization of dopamine, and then applying catechol, amino-grafted phytic acid, and cage-like polysilsesquioxane to the surface of the polydopamine layer. The preparation method includes the following steps:

[0036] (1) Add 5.0g of short-cut carbon fiber to 100mL of concentrated nitric acid and reflux at 80℃ for 5h. After the reaction is completed, wash the middle filtrate with deionized water until it is neutral and then vacuum dry to obtain pretreated carbon fiber.

[0037] (2) Dissolve 2.5g of dopamine hydrochloride in 500mL of Tris-HCl buffer, immerse the pretreated carbon fiber in dopamine hydrochloride Tris-HCl buffer, stir magnetically at room temperature for 24h, filter and wash with deionized water 3-5 times after the reaction is completed, and vacuum dry to obtain polydopamine-coated carbon fiber.

[0038] (2) Dissolve 0.5g phytic acid and 0.3g aminopropyl isobutyl silsesquioxane in 500mL of ethanol / water (volume ratio 1:1). Add 10.0g polydopamine-coated carbon fiber to the mixed solution and react at 60℃ for 10h. After filtration, wash with deionized water 3-5 times and vacuum dry to obtain modified carbon fiber.

[0039] Example 2

[0040] A boric acid-modified polyphosphazene is prepared by substituting aminopropanol into a polyphosphazene with hydroxyl-containing side groups, followed by end-capping with boric acid to obtain a functionalized modified polyphosphazene. The preparation method includes the following steps:

[0041] I. Under a nitrogen atmosphere, 0.15 g of aminosulfonic acid, 0.15 g of calcium sulfate dihydrate, 7.7 g of ammonium chloride, 30 g of phosphorus pentachloride, and 22 mL of 1,2,4-trichlorobenzene were mixed and reacted in an oil bath at 190 °C for 3 h. After the reaction was completed, the mixture was filtered while hot. The filtrate was slowly added to 100 mL of petroleum ether and stirred until a precipitate formed at the bottom. The supernatant was removed, and the precipitate was washed several times with petroleum ether until the supernatant was clear, yielding purified polydichlorophosphazene.

[0042] II. Dissolve 3.0 g of polydichlorophosphazene in 30 mL of tetrahydrofuran and cool to 0-5 °C in an ice-water bath. Dissolve 20 g of 3-amino-1-propanol and 35 mL of triethylamine in 20 mL of tetrahydrofuran. Under vigorous stirring and an ice-water bath, slowly add the mixed solution of 3-amino-1-propanol and triethylamine to the polydichlorophosphazene solution. Slowly raise the temperature to room temperature and continue stirring for 24 h. Filter to remove the triethylamine hydrochloride precipitate. Add the filtrate to distilled water and stir to precipitate the product. Filter and purify the solid precipitate by repeated dissolution-precipitation in a tetrahydrofuran / water system. Finally, vacuum dry to obtain the polyphosphazene derivative.

[0043] III. Under a nitrogen atmosphere, 2.0 g of polyphosphazene derivative and 8 g of 4-carboxyphenylboronic acid were dissolved in 30 mL of N,N-dimethylformamide, and then 7.5 g of N,N'-dicyclohexylcarbodiimide and 0.25 g of 4-dimethylaminopyridine were added. The mixture was stirred at room temperature in the dark for 24 h. After the reaction was completed, the N,N'-dicyclohexylurea precipitate was removed by filtration. The filtrate was dialyzed against deionized water and methanol for 24 h, the solvent was evaporated by rotary evaporation, and finally the mixture was dried under vacuum to obtain the boric acid-modified polyphosphazene.

[0044] A modified layered double hydroxide, wherein the modified layered double hydroxide is prepared by electrostatic intercalation of chitosan and grafting of the above-mentioned boric acid-modified polyphosphazene onto the ortho-hydroxyl groups on the chitosan chain. The preparation method of the modified layered double hydroxide includes the following steps:

[0045] A. Magnesium aluminum hydroxide was dispersed in deionized water, and under nitrogen protection and stirring, a dilute acetic acid solution of chitosan was slowly added dropwise. The mixture was reacted at 60°C for 24 hours, centrifuged, washed with water, and freeze-dried to obtain chitosan-intercalated magnesium aluminum hydroxide.

[0046] B. The chitosan-intercalated magnesium aluminum double hydroxide was redispersed in deionized water, the pH was adjusted to 8-9, boric acid-modified polyphosphazene was added, and the reaction was carried out at 70°C for 10 h. After the reaction was completed, the product was collected by centrifugation, washed with water and ethanol 3-5 times, and vacuum dried to obtain the modified layered double hydroxide.

[0047] Example 3

[0048] A carbon fiber reinforced polylactic acid composite material comprises the following raw materials in parts by weight: 60 parts polylactic acid, 15 parts PBAT-g-GMA, 8 parts modified carbon fiber, 8 parts modified layered double hydroxide, 1 part talc, 1.5 parts calcium stearate, 0.25 parts antioxidant 1010, and 0.25 parts antioxidant 168; the modified carbon fiber was prepared in Example 1, and the modified layered double hydroxide was prepared in Example 2.

[0049] The preparation method of the above-mentioned carbon fiber reinforced polylactic acid composite material includes the following steps: polylactic acid, PBAT-g-GMA, modified layered double hydroxide, talc, antioxidant 1010, antioxidant 168 and calcium stearate are added to a twin-screw extruder through the main feeder. The screw speed is 200 rpm. The temperatures of each zone of the extruder are 170℃, 180℃, 190℃, 185℃ and 180℃. Modified carbon fiber is added through a side feeder in the middle and downstream of the melting zone. After the raw materials are melt-blended, they are extruded and granulated. The composite granules are vacuum dried at 60℃ for 6 hours to obtain the carbon fiber reinforced polylactic acid composite material.

[0050] Example 4

[0051] A carbon fiber reinforced polylactic acid composite material comprises the following raw materials in parts by weight: 75 parts polylactic acid, 10 parts PBAT-g-GMA, 10 parts modified carbon fiber, 6 parts modified layered double hydroxide, 2 parts talc, 0.5 parts zinc stearate, 0.5 parts antioxidant 1010, and 0.5 parts antioxidant 168; the modified carbon fiber was prepared in Example 1, and the modified layered double hydroxide was prepared in Example 2.

[0052] The preparation method of the above-mentioned carbon fiber reinforced polylactic acid composite material includes the following steps: polylactic acid, PBAT-g-GMA, modified layered double hydroxide, talc, antioxidant 1010, antioxidant 168 and zinc stearate are added to a twin-screw extruder through the main feeder. The screw speed is 300 rpm. The temperatures of each zone of the extruder are 170℃, 180℃, 190℃, 185℃ and 180℃. Modified carbon fiber is added through a side feeder in the middle and downstream of the melting zone. After the raw materials are melt-blended, they are extruded and granulated. The composite granules are vacuum dried at 60℃ for 4 hours to obtain the carbon fiber reinforced polylactic acid composite material.

[0053] Example 5

[0054] A carbon fiber reinforced polylactic acid composite material comprises the following raw materials in parts by weight: 68 parts polylactic acid, 12 parts PBAT-g-GMA, 9 parts modified carbon fiber, 7 parts modified layered double hydroxide, 1.5 parts talc, 1.0 part ethylene bis-stearamide, 0.4 parts antioxidant 1010, and 0.4 parts antioxidant 168; the modified carbon fiber was prepared in Example 1, and the modified layered double hydroxide was prepared in Example 2.

[0055] The preparation method of the above-mentioned carbon fiber reinforced polylactic acid composite material includes the following steps: polylactic acid, PBAT-g-GMA, modified layered double hydroxide, talc, antioxidant 1010, antioxidant 168 and ethylene bis-stearamide are added to a twin-screw extruder through the main feeder. The screw speed is 250 rpm. The temperatures of each zone of the extruder are 170℃, 180℃, 190℃, 185℃ and 180℃. Modified carbon fiber is added through a side feeder in the middle and downstream of the melting zone. After the raw materials are melt-blended, they are extruded and granulated. The composite granules are vacuum dried at 60℃ for 5 hours to obtain the carbon fiber reinforced polylactic acid composite material.

[0056] Comparative Example 1

[0057] A carbon fiber reinforced polylactic acid composite material comprises the following raw materials in parts by weight: 68 parts polylactic acid, 12 parts PBAT-g-GMA, 7 parts modified layered double hydroxide, 1.5 parts talc, 1.0 part ethylene bis-stearamide, 0.4 parts antioxidant 1010, and 0.4 parts antioxidant 168; the modified layered double hydroxide was prepared in Example 2.

[0058] The preparation method of the above-mentioned carbon fiber reinforced polylactic acid composite material includes the following steps: polylactic acid, PBAT-g-GMA, modified layered double hydroxide, talc, antioxidant 1010, antioxidant 168 and ethylene bis-stearamide are added to a twin-screw extruder from the main feeder. The screw speed is 250 rpm, and the temperatures of each zone of the extruder are 170℃, 180℃, 190℃, 185℃ and 180℃. The raw materials are melt-blended and then extruded and granulated. The composite granules are vacuum dried at 60℃ for 5 hours to obtain the carbon fiber reinforced polylactic acid composite material.

[0059] Comparative Example 2

[0060] A carbon fiber reinforced polylactic acid composite material comprises the following raw materials in parts by weight: 68 parts polylactic acid, 12 parts PBAT-g-GMA, 9 parts modified carbon fiber, 7 parts modified layered double hydroxide, 1.5 parts talc, 1.0 part ethylene bis-stearamide, 0.4 parts antioxidant 1010, and 0.4 parts antioxidant 168; the modified carbon fiber is prepared as in Example 1.

[0061] The preparation method of the above-mentioned carbon fiber reinforced polylactic acid composite material includes the following steps: polylactic acid, PBAT-g-GMA, talc, antioxidant 1010, antioxidant 168 and ethylene bis-stearamide are added to a twin-screw extruder through the main feeder. The screw speed is 250 rpm. The temperatures of each zone of the extruder are 170℃, 180℃, 190℃, 185℃ and 180℃. Modified carbon fiber is added through a side feeder in the middle and downstream of the melting zone. After the raw materials are melt-blended, they are extruded and granulated. The composite granules are vacuum dried at 60℃ for 5 hours to obtain the carbon fiber reinforced polylactic acid composite material.

[0062] Comparative Example 3

[0063] A carbon fiber reinforced polylactic acid composite material comprises the following raw materials in parts by weight: 68 parts polylactic acid, 12 parts PBAT-g-GMA, 9 parts carbon fiber, 1.5 parts talc, 1.0 part ethylene bis-stearamide, 0.4 parts antioxidant 1010, and 0.4 parts antioxidant 168.

[0064] The preparation method of the above-mentioned carbon fiber reinforced polylactic acid composite material includes the following steps: polylactic acid, PBAT-g-GMA, talc, antioxidant 1010, antioxidant 168 and ethylene bis-stearamide are added to a twin-screw extruder through the main feeder. The screw speed is 250 rpm. The temperatures of each zone of the extruder are 170℃, 180℃, 190℃, 185℃ and 180℃. Carbon fiber is added through a side feeder in the middle and downstream of the melting zone. After the raw materials are melted and blended, they are extruded and granulated. The composite granules are vacuum dried at 60℃ for 5 hours to obtain the carbon fiber reinforced polylactic acid composite material.

[0065] Performance testing

[0066] The carbon fiber reinforced polylactic acid materials prepared in Example 5 and Comparative Examples 1-3 were used to make standard injection-molded specimens. Compared with Example 5, Comparative Example 1 lacked modified carbon fiber, Comparative Example 2 lacked modified layered double hydroxide, and Comparative Example 3 replaced the modified carbon fiber with an equal amount of unmodified carbon fiber. Before testing, the specimens were placed in a constant temperature and humidity (23°C, 50%RH) environment for at least 24 hours, and then the following performance tests were performed:

[0067] (1) Mechanical property testing

[0068] Tensile properties were tested according to GB / T1040.2-2006 standard. The sample was prepared as a type I dumbbell specimen (150mm long, 10mm wide at the narrow neck, and 4mm thick). The speed was 5mm / min, and the tensile strength (MPa) was recorded. Bending properties were tested according to GB / T9341-2008 standard. The sample was prepared as an 80mm×10mm×4mm standard specimen. The speed was 2mm / min, the span was 64mm, and the flexural modulus (MPa) was recorded. Impact properties were tested according to GB / T1843-2008 standard. The sample was prepared as an 80mm×10mm×4mm standard specimen with a notch depth of 2mm. A simply supported beam notched impact was performed with a pendulum energy of 4J, and the notched impact strength (kJ / m²) was recorded. 2 );

[0069] (2) Heat resistance test

[0070] Heat distortion temperature was tested according to GB / T1634.2-2019. The sample was made into a standard specimen of 80mm×10mm×4mm, with a load of 1.80MPa and a heating rate of 120℃ / h. The heat distortion temperature HDT (℃) was recorded. Thermogravimetric analysis was performed according to GB / T27761-2011. A powder sample (10mg) was taken, under nitrogen atmosphere, with a heating rate of 10℃ / min and a temperature range of 30~600℃. The 5% thermogravimetric temperature (T5%) and the char rate at 800℃ were recorded.

[0071] (3) Flame retardant performance test

[0072] Vertical burning tests were conducted according to GB / T2408-2021. The samples were prepared as standard specimens of 125mm×13mm×3.2mm. The UL-94 rating (V-0, V-1, V-2 or no rating) was determined based on the burning behavior. Limiting oxygen index tests were conducted according to GB / T2406.2-2009. The samples were prepared as 80mm×10mm×4mm and tested at 23℃. The lowest oxygen concentration (LOI,%) that could support the continuous burning of the material was recorded.

[0073] The obtained data is shown in Table 1 below.

[0074] Table 1. Performance test results of carbon fiber reinforced polylactic acid materials

[0075] Group performance indicators Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Tensile strength (MPa) 125 65 110 98 Flexural modulus (GPa) 9.5 3.8 8.0 7.2 Notched impact strength (kJ / m²) 18.5 15.0 9.5 12.0 Heat distortion temperature (HDT) (°C) 135 75 105 118 5% thermogravimetric temperature (°C) 338.5 312.7 325.4 318.2 Carbon residue rate at 800℃ (%) 18.7 7.2 11.5 9.8 UL-94 rating V-0 V-2 V-1 V-1 Limiting Oxygen Index (LOI) (%) 35.5 25.0 30.5 28.0

[0076] As can be seen from the data in Table 1, compared with Example 5, the tensile strength and flexural strength of Comparative Example 1 decreased significantly, proving that the modified carbon fiber is the core reinforcing phase. Its surface polydopamine, phytic acid, and POSS composite layer form a chemical bond with the GMA groups of PBAT-g-GMA, improving interfacial compatibility and effectively transferring stress. The tensile strength of the unmodified carbon fiber in Comparative Example 3 is only 98 MPa, which is lower than that of Example 5. This is because the surface of the unmodified carbon fiber is inert, and the interfacial bonding with the matrix is ​​weak, resulting in stress concentration and poor reinforcement effect. Comparative Example 2 lacks modified layered double hydroxides, and its tensile strength and flexural modulus are between those of Example 5 and Comparative Example 3, slightly lower. This indicates that the modified layered double hydroxides can further improve rigidity through the synergistic load-bearing of the layered structure, and the effect is better than that of the unmodified carbon fiber.

[0077] In Example 5, the material exhibited the highest notched impact strength. PBAT-g-GMA provided the basic toughening phase, and the strong interface of the modified carbon fiber ensured that stress energy was transferred to the fiber and matrix, rather than directly causing interfacial debonding. The dynamic borate ester bonds in the modified layered double hydroxide dissipated a large amount of energy through reversible fracture during impact, contributing significantly to the nano-toughening effect. In Comparative Example 2, without modified layered double hydroxide, the impact strength decreased significantly, demonstrating that the dynamic interfacial toughening mechanism of the modified layered double hydroxide is one of the core factors in improving toughness, and its effect even exceeds the contribution of modified carbon fiber (Comparative Example 1). The toughness of Comparative Example 3 was lower than that of Example 5, indicating that the good interface (PDA layer) of the modified carbon fiber not only improves strength but also helps prevent rapid crack propagation at the interface, thereby improving toughness.

[0078] Example 5 exhibits a higher heat distortion temperature than the comparative example. The high heat resistance of the modified carbon fiber and the layered barrier effect of the modified LDH inhibit the movement of PLA molecular chains. Simultaneously, the talc nucleating agent enhances crystallinity, collectively improving heat resistance. Comparative examples 2 and 3 show lower temperatures than Example 5, verifying the synergistic heat resistance effect of the modified filler. Example 5 has a higher T5% than comparative example 1, and its char residue at 800℃ is 2.6 times that of comparative example 1. The boric acid-modified polyphosphazene component of the modified LDH forms a dense char layer at high temperatures, blocking heat and gas transfer. The modified carbon fiber also enhances the stability of the char layer. In contrast, the char residue of comparative example 2 is only 11.5%, and that of comparative example 3 is only 9.8%, highlighting the flame-retardant char-forming effect of the modified LDH.

[0079] Example 5 achieved a limiting oxygen index of 30.2%, reaching the flame-retardant level, with a vertical combustion rating of V-0. No dripping ignition was observed. The modified layered double hydroxide provided a physical barrier for the metal oxides, catalyzed char formation, and provided endothermic cooling. Phytic acid (P source) in the modified carbon fiber catalyzed char formation, while POSS (Si source) generated a ceramic protective layer. These two elements worked synergistically to form a dense and robust expanded char layer, preventing melt dripping. Comparative Example 1 only achieved a V-2 rating, with a lower LOI. Although the modified layered double hydroxide was effective, the lack of the skeletal function of CF and the P and Si elements provided by the modified carbon fiber resulted in an incomplete flame-retardant system and poor char layer quality. Comparative Examples 2 and 3 both only achieved a V-1 rating. This indicates that the lack of catalytic char formation and barrier effects from the modified layered double hydroxide, or the lack of the P-Si synergistic effect from the modified carbon fiber, significantly reduces the flame-retardant efficiency, making it impossible to achieve the highest V-0 rating.

[0080] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0081] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A carbon fiber reinforced polylactic acid composite material, characterized in that, The raw materials include the following parts by weight: 60-75 parts polylactic acid, 10-15 parts PBAT-g-GMA, 8-10 parts modified carbon fiber, 6-8 parts modified layered double hydroxide, 1-2 parts talc, 0.5-1.5 parts lubricant, and 0.5-1 part antioxidant. The modified carbon fiber is formed by coating a polydopamine layer on the surface of short-cut carbon fiber through the self-polymerization of dopamine, and then by applying catechol, amino-grafted phytic acid and cage-type polysilsesquioxane to the surface of the polydopamine layer. The modified layered double hydroxide is obtained by electrostatically intercalating chitosan and then grafting boric acid onto the ortho-hydroxyl groups on the chitosan chain to modify polyphosphazene. The boric acid-modified polyphosphazene is obtained by substituting aminopropanol into polyphosphazene with hydroxyl groups on the side groups, and then capping with boric acid to obtain functionalized modified polyphosphazene.

2. The carbon fiber reinforced polylactic acid composite material according to claim 1, characterized in that, The lubricant is one of calcium stearate, zinc stearate, or ethylene bis-stearamide.

3. The carbon fiber reinforced polylactic acid composite material according to claim 1, characterized in that, The antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:

1.

4. The carbon fiber reinforced polylactic acid composite material according to claim 1, characterized in that, The method for preparing the modified carbon fiber includes the following steps: (1) Add short-cut carbon fibers to concentrated nitric acid and reflux at 80°C for 4-6 hours. After the reaction is complete, wash with deionized water and the filtrate is neutral. Vacuum dry to obtain pretreated carbon fibers. (2) Dissolve dopamine hydrochloride in Tris-HCl buffer, immerse the pretreated carbon fiber in dopamine hydrochloride Tris-HCl buffer, stir magnetically at room temperature for 20-24 h, filter and wash with deionized water 3-5 times after the reaction, and vacuum dry to obtain polydopamine-coated carbon fiber. (2) Add phytic acid and aminopropyl isobutylsilsesquioxane to an ethanol / water mixture to dissolve them, add polydopamine-coated carbon fibers to the mixture, react at 60°C for 8-12 hours, filter and wash with deionized water 3-5 times, and vacuum dry to obtain modified carbon fibers.

5. The carbon fiber reinforced polylactic acid composite material according to claim 4, characterized in that, The ratio of carbon fiber to dopamine hydrochloride is 1:0.5, and the mass ratio of polydopamine-coated carbon fiber, phytic acid, and aminopropyl isobutylsilsesquioxane is 1:0.05:0.

03.

6. The carbon fiber reinforced polylactic acid composite material according to claim 1, characterized in that, The method for preparing the modified layered double hydroxide includes the following steps: A. Magnesium aluminum hydroxide was dispersed in deionized water, and under nitrogen protection and stirring, a dilute acetic acid solution of chitosan was slowly added dropwise. The mixture was reacted at 60°C for 20-24 hours, centrifuged, washed with water, and freeze-dried to obtain chitosan-intercalated magnesium aluminum hydroxide. B. The chitosan-intercalated magnesium aluminum double hydroxide was redispersed in deionized water, the pH was adjusted to 8-9, boric acid-modified polyphosphazene was added, and the reaction was carried out at 70°C for 8-12 hours. After the reaction was completed, the product was collected by centrifugation, washed with water and ethanol 3-5 times, and vacuum dried to obtain the modified layered double hydroxide.

7. The carbon fiber reinforced polylactic acid composite material according to claim 6, characterized in that, The mass ratio of the magnesium aluminum double hydroxide, chitosan, and boric acid modified polyphosphazene is 1:1:0.5~1.

8. The carbon fiber reinforced polylactic acid composite material according to claim 6, characterized in that, The preparation method of the boric acid modified polyphosphazene includes the following steps: I. Under a nitrogen atmosphere, aminosulfonic acid, calcium sulfate dihydrate, ammonium chloride, phosphorus pentachloride and 1,2,4-trichlorobenzene are mixed and reacted in an oil bath at 185-195°C for 2-4 hours. After the reaction is completed, the mixture is filtered while hot. The filtrate is slowly added to petroleum ether and stirred until a precipitate forms at the bottom. The supernatant is removed, and the precipitate is washed several times with petroleum ether until the supernatant is clear, thus obtaining purified polydichlorophosphazene. II. Polydichlorophosphazene was dissolved in tetrahydrofuran and cooled to 0-5°C in an ice-water bath. 3-Amino-1-propanol and triethylamine were dissolved in tetrahydrofuran. Under vigorous stirring and an ice-water bath, the mixed solution of 3-amino-1-propanol and triethylamine was slowly added dropwise to the polydichlorophosphazene solution. The temperature was slowly raised to room temperature, and the reaction was continued with stirring for 20-24 hours. The triethylamine hydrochloride precipitate was removed by filtration. The filtrate was added to distilled water and stirred to precipitate the product. The product was filtered, and the obtained solid precipitate was purified by repeated dissolution-precipitation in a tetrahydrofuran / water system. Finally, the product was dried under vacuum to obtain the polyphosphazene derivative. III. Under a nitrogen atmosphere, polyphosphazene derivatives and 4-carboxyphenylboronic acid were dissolved in N,N-dimethylformamide, and then N,N'-dicyclohexylcarbodiimide and 4-dimethylaminopyridine were added. The mixture was stirred at room temperature in the dark for 20-24 hours. After the reaction was completed, the N,N'-dicyclohexylurea precipitate was removed by filtration. The filtrate was dialyzed against deionized water and methanol for 20-24 hours in sequence. The solvent was evaporated by rotary evaporation, and finally the mixture was dried under vacuum to obtain the boric acid-modified polyphosphazene.

9. The carbon fiber reinforced polylactic acid composite material according to claim 8, characterized in that, The molar ratio of ammonium chloride to phosphorus pentachloride is 1:1, the molar ratio of polydichlorophosphazene, 3-amino-1-propanol and triethylamine is 1:10:10.5, and the molar ratio of polyphosphazene derivative, 4-carboxyphenylboronic acid and N,N'-dicyclohexylcarbodiimide is 1:5:4.

5.

10. The method for preparing the carbon fiber reinforced polylactic acid composite material according to any one of claims 1 to 9, characterized in that, Includes the following steps: Polylactic acid, PBAT-g-GMA, modified layered double hydroxide, talc, antioxidant, and lubricant are fed into a twin-screw extruder via the main feeder. The screw speed is 200-300 rpm, and the temperatures of each zone of the extruder are 170℃, 180℃, 190℃, 185℃, and 180℃. Modified carbon fiber is added in the downstream of the melting zone via a side feeder. After the raw materials are melt-blended, they are extruded and granulated. The composite granules are vacuum-dried at 60℃ for 4-6 hours to obtain the carbon fiber reinforced polylactic acid composite material.