Carbon fiber reinforced polylactic acid composite material and preparation method thereof

Abstract

The invention belongs to the technical field of high polymer materials, and discloses a carbon fiber reinforced polylactic acid composite material and a preparation method thereof, the composite material comprises the following raw materials by weight: polylactic acid, PBAT-g-GMA, modified carbon fiber, modified layered double hydroxide, talcum powder, a lubricant and an antioxidant; the modified carbon fiber is prepared by coating the surface of carbon fiber with a polydopamine layer through auto-polymerization of dopamine, and then carrying out surface catechol, amino-grafted phytic acid and polyhedral oligomeric silsesquioxane through the polydopamine layer; the modified layered double hydroxide is prepared by intercalating chitosan through electrostatic interaction, and then grafting boric acid modified polyphosphazene by utilizing ortho-hydroxyl on a chitosan chain; the polylactic acid is used as a base material, PBAT-g-GMA is added for blending, the brittleness of the polylactic acid is improved, the impact strength of the composite material is improved, the tensile strength, bending strength and rigidity of the composite material are improved through compounding of the modified carbon fibers and the modified layered double hydroxides, and meanwhile the material is endowed with excellent heat resistance and flame retardance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of high polymer materials, and particularly relates to a carbon fiber reinforced polylactic acid composite material and a preparation method thereof. BACKGROUND

[0002] As a kind of aliphatic polyester with wide sources and complete biodegradation, polylactic acid (PLA) has good biocompatibility, mechanical processing property and environmental friendliness, and shows broad application prospects in packaging materials, automobile parts, 3D printing consumables and biomedical devices, etc., and is one of the core materials to replace traditional petroleum-based plastics and relieve white pollution. However, the inherent performance defects of pure PLA seriously limit its large-scale application in high-end scenarios. The tensile strength of pure PLA is only 50-60 MPa, the bending modulus is about 2.3 GPa, and the brittleness is significant, which is difficult to meet the dual requirements of rigidity and toughness for structural parts. The heat resistance is poor, and the heat distortion temperature is only 60-65℃, which is easy to deform in high-temperature processing or use environment, limiting its application in automobile interiors, electronic housings and other fields. The flame retardant performance is weak, and the limiting oxygen index is only 22%-23%, and the vertical burning has no grade. When burning, it is easy to drip and ignite the surrounding combustible materials, which cannot meet the flame retardant safety standards in the fields of building and transportation.

[0003] In the prior art, inorganic reinforcing phases such as carbon fibers and glass fibers are added to improve the mechanical properties and heat resistance of PLA, but the inorganic reinforcing and PLA matrix have poor interfacial compatibility, which is easy to cause debonding, and the reinforcing and toughening effect is limited, and the flame retardant performance of the material cannot be improved. Adding flame-retardant fillers to improve the flame-retardant performance also has poor compatibility with PLA, uneven dispersion, and easy to cause the mechanical properties of the material to decrease. Although the addition of small molecule flame-retardant additives has no effect on the mechanical properties of PLA, small molecules are easy to suffer physical loss such as volatilization and migration, resulting in the decrease of the flame retardancy of the polymer. Therefore, there is an urgent need for a modified polylactic acid material with high strength, high toughness, heat stability and flame retardant effect to meet various application requirements. SUMMARY

[0004] To solve the problems mentioned in the background, the present application provides a carbon fiber reinforced polylactic acid composite material and a preparation method thereof. The present application uses polylactic acid as the matrix material, and adds PBAT-g-GMA blend to improve the brittleness of polylactic acid and improve the impact strength of the composite material. The modified carbon fiber and the modified layered double hydroxide are used in combination to further improve the tensile strength, bending strength and rigidity of the composite material, and at the same time, the material is endowed with excellent heat resistance and flame retardant performance.

[0005] The object of the present application can be achieved by the following technical solutions: A carbon fiber reinforced polylactic acid composite material, comprising the following raw materials by weight: polylactic acid 60-75 parts, PBAT-g-GMA 10-15 parts, modified carbon fiber 8-10 parts, modified layered double hydroxide 6-8 parts, talc 1-2 parts, lubricant 0.5-1.5 parts, antioxidant 0.5-1 part; The modified carbon fiber is a polydopamine layer coated on the surface of the chopped carbon fiber through self-polymerization of dopamine, and a phytic acid and an aminopropyl isobutyl silyl group are grafted on the surface of the polydopamine layer through catechol and amino groups. The modified layered double hydroxide is a chitosan intercalated through electrostatic interaction, and a boronic acid modified polyphosphazene is grafted on the ortho-hydroxyl group on the chitosan chain.

[0006] Preferably, the lubricant is one of calcium stearate, zinc stearate, and ethylene bis-stearamide.

[0007] Preferably, the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.

[0008] Preferably, the preparation method of the modified carbon fiber comprises the following steps: (1) The chopped carbon fiber is added into concentrated nitric acid, and refluxed at 80°C for 4-6 hours. After the reaction is completed, the filtrate is washed with deionized water until it is neutral. The pretreated carbon fiber is obtained by vacuum drying. (2) The hydrochloric acid dopamine is dissolved in a Tris-HCl buffer solution. The pretreated carbon fiber is immersed in the hydrochloric acid dopamine Tris-HCl buffer solution, and magnetically stirred at room temperature for 20-24 hours. After the reaction is completed, the carbon fiber is filtered and washed with deionized water for 3-5 times. The polydopamine coated carbon fiber is obtained by vacuum drying. (2) The phytic acid and the aminopropyl isobutyl silyl group are dissolved in an ethanol / water mixed solution. The polydopamine coated carbon fiber is added into the mixed solution, and reacted at 60°C for 8-12 hours. After filtration, the modified carbon fiber is obtained by washing with deionized water for 3-5 times and vacuum drying.

[0009] Preferably, the ratio of the carbon fiber and the hydrochloric acid dopamine is 1:0.5, and the mass ratio of the polydopamine coated carbon fiber, the phytic acid, and the aminopropyl isobutyl silyl group is 1:0.05:0.03.

[0010] Preferably, the preparation method of the modified layered double hydroxide comprises the following steps: A. The magnesium aluminum double hydroxide is dispersed in deionized water. Under nitrogen protection and stirring, a dilute acetic acid solution of chitosan is slowly added dropwise, and reacted at 60°C for 20-24 hours. After centrifugation, water washing, and freeze drying, the chitosan intercalated magnesium aluminum double hydroxide is obtained. B. The chitosan intercalated magnesium-aluminum double hydroxide is re-dispersed in deionized water, the pH is adjusted to 8-9, and the boric acid modified polyphosphazene is added, and the mixture is reacted at 70℃ for 8-12h. After the reaction is completed, the product is collected by centrifugation, washed with water and ethanol for 3-5 times, and dried under vacuum to obtain the modified layered double hydroxide.

[0011] Preferably, the mass ratio of the magnesium-aluminum double hydroxide, the chitosan and the boric acid modified polyphosphazene is 1:1:0.5-1.

[0012] Preferably, the preparation method of the boric acid modified polyphosphazene comprises the following steps: I. Under a nitrogen atmosphere, mix sulfamic acid, calcium sulfate dihydrate, ammonium chloride, phosphorus pentachloride and 1,2,4-trichlorobenzene, and slowly heat the mixture to 185-195℃ in an oil bath for 2-4h. After the reaction is completed, filter the mixture while hot, slowly add petroleum ether to the filtrate and stir until the precipitate at the bottom is separated out. Remove the supernatant, wash the precipitate with petroleum ether several times until the supernatant is clear, and obtain the purified polydichlorophosphazene; II. Dissolve the polydichlorophosphazene in tetrahydrofuran, and cool the solution to 0-5℃ in an ice water bath. Dissolve 3-amino-1-propanol and triethylamine in tetrahydrofuran, and slowly add the mixed solution of 3-amino-1-propanol and triethylamine to the polydichlorophosphazene solution under vigorous stirring and ice water bath. Slowly warm the mixture to room temperature, continue to stir for 20-24h, remove the precipitate of triethylamine hydrochloride by filtration, and add the filtrate to distilled water to precipitate the product. Filter the product and purify it by repeatedly dissolving and precipitating the solid in a tetrahydrofuran / water system. Finally, dry the product under vacuum to obtain the polyphosphazene derivative; III. Under a nitrogen atmosphere, dissolve the polyphosphazene derivative and 4-carboxyphenylboronic acid in N,N-dimethylformamide, and add N,N'-dicyclohexyl carbodiimide and 4-dimethylamino pyridine. Stir the mixture at room temperature and avoid light for 20-24h. After the reaction is completed, remove the precipitate of N,N'-dicyclohexyl urea by filtration, and dialyze the filtrate with deionized water and methanol for 20-24h. Finally, dry the product under vacuum to obtain the boric acid modified polyphosphazene.

[0013] Preferably, the molar ratio of ammonium chloride and 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 the polyphosphazene derivative, 4-carboxyphenylboronic acid and N,N'-dicyclohexyl carbodiimide is 1:5:4.5.

[0014] A method for preparing a carbon fiber reinforced polylactic acid composite material, comprising the following steps: The polylactic acid, PBAT-g-GMA, modified double hydroxide, talcum powder, antioxidant and lubricant are added from the main feeder to the twin-screw extruder, the screw rotation speed is 200-300 rpm, the temperature of each zone of the extruder is 170 DEG C, 180 DEG C, 190 DEG C, 185 DEG C, 180 DEG C, the modified carbon fiber is added through the side feeder in the downstream of the melting zone, the raw materials are melt blended and then extruded and pelletized, the composite pellets are dried in vacuum at 60 DEG C for 4-6 h, and the carbon fiber reinforced polylactic acid composite material is obtained.

[0015] The beneficial effects of the present application are: The carbon fiber reinforced polylactic acid composite material of the present application uses polylactic acid as the matrix material, provides basic mechanical properties and biodegradability, and adds PBAT-g-GMA blend to improve the brittleness of polylactic acid, improve the impact strength of the composite material, and use modified carbon fiber and modified layered double hydroxide in combination to improve the tensile strength, bending strength and rigidity of the composite material, and at the same time impart excellent heat resistance and flame retardant properties to the material, the GMA groups of PBAT-g-GMA can react with the surface active groups of modified carbon fiber and modified layered double hydroxide, further enhancing the interfacial bonding force, so that the composite material realizes comprehensive performance improvement in the aspects of reinforcement, toughening, heat resistance, flame retardance and the like, meeting the high-end application requirements of automotive interior, 3D printing, medical materials and the like.

[0016] The modified carbon fiber uses original carbon fiber as the matrix, and a composite modification layer is formed on the surface through two-step functionalization modification. A uniform polydopamine layer is formed on the surface of the carbon fiber through dopamine self-polymerization. The layer is rich in o-diphenol groups and amino groups, providing active sites for subsequent grafting reaction. Chemical reactions occur between the o-diphenol groups and amino groups on the surface of the polydopamine layer and the phosphate groups of phytic acid and the amino groups of cage polysilsesquioxane, forming a phytic acid-cage polysilsesquioxane composite grafting layer. Finally, the modified carbon fiber with excellent interfacial bonding force, corrosion resistance and thermal stability is obtained. The polydopamine layer on the surface of the modified carbon fiber is rich in o-diphenol and amino groups, which undergoes epoxy ring-opening reaction with the GMA groups of PBAT-g-GMA. Meanwhile, the phosphate groups of phytic acid form hydrogen bonds with the hydroxyl groups of polylactic acid, and the cage structure of cage polysilsesquioxane enhances the interfacial mechanical engagement, thereby improving the interfacial bonding force between the carbon fiber and the matrix, and realizing efficient stress transfer. The unmodified carbon fiber surface is inert, and only physical contact with the matrix, which is prone to interfacial voids and debonding under stress, resulting in a significant decrease in reinforcement and toughening effect. The carbon fiber itself has high heat resistance, which can form a rigid skeleton in the composite material, inhibit the thermal motion of the polylactic acid molecular chain, and improve the heat distortion temperature. At the same time, in the high-temperature combustion process, the carbon fiber can act as a carbon layer support to enhance the stability of the carbon layer structure formed by the modified layered double hydroxide, reduce the cracking and falling of the carbon layer, and prolong the heat resistance time.

[0017] The modified layered double hydroxide takes magnesium-aluminum layered double hydroxide as a matrix, is modified by intercalation grafting in two steps, and the chitosan molecules are inserted into the interlayer of the magnesium-aluminum layered double hydroxide by electrostatic action, the interlayer spacing is expanded, and active hydroxyl groups are introduced, then the coordination reaction or esterification reaction occurs between the ortho-hydroxyl groups on the chitosan chain and the boric acid groups of the boric acid modified polyphosphazene, the boric acid modified polyphosphazene is grafted to the surface and interlayer of the magnesium-aluminum layered double hydroxide, and an inorganic-organic composite modification layer is formed, and the final product has the layered barrier property of the magnesium-aluminum layered double hydroxide, the biocompatibility of chitosan and the functional characteristics of the boric acid modified polyphosphazene. The layered structure of the modified layered double hydroxide forms a nano barrier during combustion, blocks the transmission of oxygen and heat, and delays the degradation of polylactic acid; the intercalation of chitosan expands the interlayer spacing of the layered double hydroxide, so that the barrier effect is more uniform. The boric acid modified polyphosphazene contains P, B and N flame-retardant elements, and dehydrates to form a dense boron phosphate and boron nitride composite carbon layer at high temperature; at the same time, it releases non-combustible gases such as nitrogen and water vapor, and dilutes the concentration of combustible gases. The layered structure of the modified layered double hydroxide and the carbon layer of the boric acid modified polyphosphazene form a double barrier, delaying the thermal oxidative degradation of the polylactic acid molecular chain; at the same time, the metal ions (Mg 2+ 、Al 3+ ) of the modified layered double hydroxide can catalyze the crosslinking of polylactic acid, and improve the thermal stability.

[0018] In addition, the modified carbon fiber and the modified layered double hydroxide also have a synergistic reinforcing effect on the mechanical properties, heat resistance and flame retardant properties, the modified carbon fiber provides rigid support, the modified layered double hydroxide fills the voids of the matrix, and at the same time, the surface active groups (such as the amino group of CF and the boric acid group of LDH) of the two occur coordination, forming a three-dimensional network structure of fibers, fillers and matrix, reducing stress concentration. The skeleton support of the modified carbon fiber and the layered barrier of the modified layered double hydroxide are combined to achieve the superposition of heat resistance. The modified layered double hydroxide forms a dense carbon layer, the modified carbon fiber enhances the strength of the carbon layer, avoids the carbon layer from falling off during combustion, and synergistically improves the flame retardant effect.

[0019] Of course, it is not necessary for any product embodying the present application to achieve all of the above-listed advantages. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the scope of the present application.

[0021] Embodiment 1

[0022] A modified carbon fiber, the modified carbon fiber is coated with a polydopamine layer on the surface of a chopped carbon fiber through self-polymerization of dopamine, and then a catechol and amino group grafted phytic acid and cage polysilsesquioxane on the surface of the polydopamine layer, and a preparation method thereof comprises the following steps: (1) 5.0 g of chopped carbon fiber is added into 100 mL of concentrated nitric acid, and refluxed at 80°C for 5 h. After the reaction is completed, the filtrate is washed with deionized water until it is neutral. Vacuum drying is performed to obtain pretreated carbon fiber; (2) 2.5 g of dopamine hydrochloride is dissolved in 500 mL of Tris-HCl buffer solution. The pretreated carbon fiber is immersed in the dopamine hydrochloride Tris-HCl buffer solution, and is subjected to magnetic stirring at room temperature for 24 h. After the reaction is completed, the carbon fiber is filtered and washed with deionized water for 3-5 times. Vacuum drying is performed to obtain polydopamine-coated carbon fiber; (2) 0.5 g of phytic acid and 0.3 g of aminopropyl isobutyl silsesquioxane are dissolved in 500 mL of an ethanol / water (volume ratio 1:1) mixed solution. 10.0 g of the polydopamine-coated carbon fiber is added into the mixed solution, and is reacted at 60°C for 10 h. After filtration, the carbon fiber is washed with deionized water for 3-5 times. Vacuum drying is performed to obtain modified carbon fiber.

[0023] Example 2

[0024] A borate-modified polyphosphazene, the borate-modified polyphosphazene is a polydichlorophosphazene which is synthesized into a polyphosphazene containing a hydroxyl group through substitution by aminopropanol, and is capped with boric acid to obtain a functionalized modified polyphosphazene, and a preparation method thereof comprises the following steps: I. 0.15 g of sulfamic acid, 0.15 g of calcium sulfate dehydrate, 7.7 g of ammonium chloride, 30 g of phosphorus pentachloride, and 22 mL of 1,2,4-trichlorobenzene are mixed under a nitrogen atmosphere. The oil bath is slowly heated to 190°C and reacted for 3 h. After the reaction is completed, hot filtration is performed. The filtrate is slowly added into 100 mL of petroleum ether and stirred until the bottom precipitate is separated out. The supernatant is removed, and the precipitate is washed with petroleum ether several times until the supernatant is clear. A purified polydichlorophosphazene is obtained; II. 3.0 g of the polydichlorophosphazene is dissolved in 30 mL of tetrahydrofuran, and is cooled to 0-5°C in an ice water bath. 20 g of 3-amino-1-propanol and 35 mL of triethylamine are dissolved in 20 mL of tetrahydrofuran. Under vigorous stirring and ice water bath, the 3-amino-1-propanol and triethylamine mixed solution is slowly added into the polydichlorophosphazene solution. The temperature is slowly increased to room temperature, and the stirring is continued for 24 h. The triethylamine hydrochloride precipitate is removed by filtration. The filtrate is added into distilled water to precipitate the product. The product is filtered and purified by repeatedly dissolving and precipitating in a tetrahydrofuran / water system. Finally, vacuum drying is performed to obtain a polyphosphazene derivative. III. 2.0 g of polyphosphazene derivative and 8 g of 4-carboxyphenylboronic acid were dissolved in 30 mL of N,N-dimethylformamide under a nitrogen atmosphere, 7.5 g of N,N'-dicyclohexylcarbodiimide and 0.25 g of 4-dimethylaminopyridine were added, and the reaction was stirred at room temperature in the dark for 24 h. After the reaction was completed, N,N'-dicyclohexylurea precipitate was removed by suction filtration, the filtrate was dialyzed against deionized water and methanol for 24 h, respectively, the solvent was rotary evaporated, and finally the product was dried in vacuum to obtain the boronic acid-modified polyphosphazene.

[0025] A modified layered double hydroxide, the modified layered double hydroxide being a chitosan intercalated by electrostatic interaction and a boronic acid-modified polyphosphazene grafted on the ortho-hydroxyl groups of the chitosan chains, and a preparation method of the modified layered double hydroxide, the preparation method comprising the following steps: A. Magnesium-aluminum double hydroxide was dispersed in deionized water, and a dilute acetic acid solution of chitosan was slowly added dropwise under nitrogen protection and stirring, and the reaction was carried out at 60°C for 24 h. After centrifugation, water washing and freeze drying, chitosan intercalated magnesium-aluminum double hydroxide was obtained. B. The chitosan intercalated magnesium-aluminum double hydroxide was re-dispersed in deionized water, the pH was adjusted to 8-9, and the boronic acid-modified polyphosphazene was added. 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 for 3-5 times, and dried in vacuum to obtain the modified layered double hydroxide.

[0026] Example 3

[0027] A carbon fiber reinforced polylactic acid composite material, comprising the following raw materials in parts by weight: polylactic acid 60 parts, PBAT-g-GMA 15 parts, modified carbon fiber 8 parts, modified layered double hydroxide 8 parts, talc 1 part, calcium stearate 1.5 parts, antioxidant 1010 0.25 parts, antioxidant 168 0.25 parts; the modified carbon fiber is prepared in Example 1, and the modified layered double hydroxide is prepared in Example 2.

[0028] The preparation method of the above-mentioned carbon fiber reinforced polylactic acid composite material comprises the following steps: polylactic acid, PBAT-g-GMA, modified double hydroxide, talc, antioxidant 1010, antioxidant 168 and calcium stearate are added from the main feeder into a twin-screw extruder, the screw rotation speed is 200 rpm, the temperature of each zone of the extruder is 170°C, 180°C, 190°C, 185°C and 180°C, modified carbon fiber is added through a feeder in the downstream of the melt zone, and the raw materials are melt blended and then extruded and pelletized. The composite pellets are dried in vacuum at 60°C for 6 h to obtain the carbon fiber reinforced polylactic acid composite material.

[0029] Example 4

[0030] A carbon fiber reinforced polylactic acid composite material, comprising the following raw materials by weight: polylactic acid 75 parts, PBAT-g-GMA 10 parts, modified carbon fiber 10 parts, modified layered double hydroxide 6 parts, talcum powder 2 parts, zinc stearate 0.5 parts, antioxidant 1010 0.5 parts, antioxidant 168 0.5 parts; the modified carbon fiber is prepared in Example 1, and the modified layered double hydroxide is prepared in Example 2.

[0031] The preparation method of the above-mentioned carbon fiber reinforced polylactic acid composite material comprises the following steps: polylactic acid, PBAT-g-GMA, modified double hydroxide, talcum powder, antioxidant 1010, antioxidant 168 and zinc stearate are added from the main feeder to the double screw extruder, the screw rotation speed is 300 rpm, the temperature of each zone of the extruder is 170℃, 180℃, 190℃, 185℃, 180℃, the modified carbon fiber is added through the measuring feeder in the downstream of the melting zone, and the raw materials are melt blended and then extruded and granulated, the composite granules are vacuum dried at 60℃ for 4h, and the carbon fiber reinforced polylactic acid composite material is obtained.

[0032] Example 5

[0033] A carbon fiber reinforced polylactic acid composite material, comprising the following raw materials by weight: polylactic acid 68 parts, PBAT-g-GMA 12 parts, modified carbon fiber 9 parts, modified layered double hydroxide 7 parts, talcum powder 1.5 parts, ethylene bis-stearamide 1.0 part, antioxidant 1010 0.4 parts, antioxidant 168 0.4 parts; the modified carbon fiber is prepared in Example 1, and the modified layered double hydroxide is prepared in Example 2.

[0034] The preparation method of the above-mentioned carbon fiber reinforced polylactic acid composite material comprises the following steps: polylactic acid, PBAT-g-GMA, modified double hydroxide, talcum powder, antioxidant 1010, antioxidant 168 and ethylene bis-stearamide are added from the main feeder to the double screw extruder, the screw rotation speed is 250 rpm, the temperature of each zone of the extruder is 170℃, 180℃, 190℃, 185℃, 180℃, the modified carbon fiber is added through the measuring feeder in the downstream of the melting zone, and the raw materials are melt blended and then extruded and granulated, the composite granules are vacuum dried at 60℃ for 5h, and the carbon fiber reinforced polylactic acid composite material is obtained.

[0035] Comparative Example 1

[0036] A carbon fiber reinforced polylactic acid composite material, comprising the following raw materials by weight: polylactic acid 68 parts, PBAT-g-GMA 12 parts, modified layered double hydroxide 7 parts, talcum powder 1.5 parts, ethylene bis-stearamide 1.0 part, antioxidant 1010 0.4 parts, antioxidant 168 0.4 parts; the modified layered double hydroxide is prepared in Example 2.

[0037] The preparation method of the carbon fiber reinforced polylactic acid composite material comprises the following steps: poly lactic acid, PBAT-g-GMA, modified double hydroxide, talcum powder, antioxidant 1010, antioxidant 168 and ethylene bis stearamide are added from the main feeder to the double screw extruder, the screw rotation speed is 250 rpm, the temperature of each zone of the extruder is 170℃, 180℃, 190℃, 185℃, 180℃, the raw materials are melt blended and then extruded and granulated, and the composite granules are vacuum dried at 60℃ for 5h to obtain the carbon fiber reinforced polylactic acid composite material.

[0038] Comparative example 2

[0039] A carbon fiber reinforced polylactic acid composite material comprises the following raw materials by weight: 68 parts of polylactic acid, 12 parts of PBAT-g-GMA, 9 parts of modified carbon fiber, 7 parts of modified layered double hydroxide, 1.5 parts of talcum powder, 1.0 part of ethylene bis stearamide, 0.4 part of antioxidant 1010, and 0.4 part of antioxidant 168; the modified carbon fiber is prepared according to the preparation method of example 1.

[0040] The preparation method of the carbon fiber reinforced polylactic acid composite material comprises the following steps: poly lactic acid, PBAT-g-GMA, talcum powder, antioxidant 1010, antioxidant 168 and ethylene bis stearamide are added from the main feeder to the double screw extruder, the screw rotation speed is 250 rpm, the temperature of each zone of the extruder is 170℃, 180℃, 190℃, 185℃, 180℃, modified carbon fiber is added through the measuring feeder in the downstream of the melting zone, the raw materials are melt blended and then extruded and granulated, and the composite granules are vacuum dried at 60℃ for 5h to obtain the carbon fiber reinforced polylactic acid composite material.

[0041] Comparative example 3

[0042] A carbon fiber reinforced polylactic acid composite material comprises the following raw materials by weight: 68 parts of polylactic acid, 12 parts of PBAT-g-GMA, 9 parts of carbon fiber, 1.5 parts of talcum powder, 1.0 part of ethylene bis stearamide, 0.4 part of antioxidant 1010, and 0.4 part of antioxidant 168.

[0043] The preparation method of the carbon fiber reinforced polylactic acid composite material comprises the following steps: poly lactic acid, PBAT-g-GMA, talcum powder, antioxidant 1010, antioxidant 168 and ethylene bis stearamide are added from the main feeder to the double screw extruder, the screw rotation speed is 250 rpm, the temperature of each zone of the extruder is 170℃, 180℃, 190℃, 185℃, 180℃, carbon fiber is added through the measuring feeder in the downstream of the melting zone, the raw materials are melt blended and then extruded and granulated, and the composite granules are vacuum dried at 60℃ for 5h to obtain the carbon fiber reinforced polylactic acid composite material.

[0044] Performance detection

[0045] The carbon fiber reinforced polylactic acid materials prepared in Example 5 and Comparative Examples 1-3 were made into standard injection molding samples. Compared with Example 5, Comparative Example 1 lacked modified carbon fibers, Comparative Example 2 lacked modified layered double hydroxides, and Comparative Example 3 replaced the modified carbon fibers with an equal amount of unmodified carbon fibers. The samples were placed in a constant temperature and humidity (23°C, 50% RH) environment for at least 24 hours before testing, and then the following performance tests were conducted: (1) Mechanical property test The tensile property test was carried out in accordance with GB / T1040.2-2006 standard. The sample was made into an I-shaped dumbbell sample (length 150 mm, narrow neck width 10 mm, thickness 4 mm), speed: 5 mm / min, and the tensile strength (MPa) was recorded. The bending property test was carried out in accordance with GB / T9341-2008. The sample was made into an 80 mm x 10 mm x 4 mm standard sample, speed: 2 mm / min, span: 64 mm, and the bending modulus (MPa) was recorded. The impact property test was carried out in accordance with GB / T1843-2008. The sample was made into an 80 mm x 10 mm x 4 mm standard sample, notch depth 2 mm, using a simply supported beam notch impact, pendulum energy 4 J, and the notched impact strength (kJ / m 2 ) was recorded. (2) Heat resistance test The heat distortion temperature test was carried out in accordance with GB / T1634.2-2019. The sample was made into an 80 mm x 10 mm x 4 mm standard sample, load: 1.80 MPa, heating rate: 120°C / h, and the heat distortion temperature HDT (°C) was recorded. The thermal gravimetric analysis was carried out in accordance with GB / T27761-2011. The powder sample (10 mg) was taken, nitrogen atmosphere, heating rate 10°C / min, temperature range 30-600°C, and the 5% thermal weight loss temperature (T5%) and 800°C carbon residue rate were recorded. (3) Flame retardant property test The vertical burning test was carried out in accordance with GB / T2408-2021. The sample was made into a 125 mm x 13 mm x 3.2 mm standard sample, and the UL-94 grade (V-0, V-1, V-2 or no grade) was determined according to the burning behavior. The limiting oxygen index test was carried out in accordance with GB / T2406.2-2009. The sample was made into an 80 mm x 10 mm x 4 mm sample, tested at 23°C, and the minimum oxygen concentration (LOI, %) that could support the continuous combustion of the material was recorded.

[0046] The data obtained are shown in Table 1 below.

[0047] Table 1 Performance test results of carbon fiber reinforced polylactic acid materials

[0048] From the data in Table 1, it can be seen that the tensile strength and bending strength of Comparative Example 1 decrease more obviously compared with Example 5, proving that the modified carbon fiber is the core reinforcing phase, and the surface polydopamine, phytic acid, and POSS composite layer forms chemical bonding with the GMA groups of PBAT-g-GMA, improves the interfacial compatibility, and effectively transmits stress. The tensile strength of unmodified carbon fiber in Comparative Example 3 is only 98 MPa, which is lower than that of Example 5, because the surface of the unmodified carbon fiber is inert, and the interfacial bonding with the matrix is weak, resulting in poor reinforcing effect due to stress concentration. Comparative Example 2 lacks modified layered double hydroxide, and the tensile strength and bending modulus are between Example 5 and Comparative Example 3, slightly decreased, indicating that the modified layered double hydroxide can also further improve the rigidity through the layered structure of the synergistic bearing, and the effect is better than that of the unmodified carbon fiber.

[0049] The notched impact strength of the material in Example 5 is the highest, PBAT-g-GMA provides the basic toughening phase, the strong interface of the modified carbon fiber ensures that the stress can be transmitted to the fiber and the matrix, rather than directly leading to interfacial debonding, and the dynamic borate ester bond in the modified layered double hydroxide dissipates a large amount of energy through reversible fracture when impacted, contributing to significant nano-toughening effect. Comparative Example 2 has no modified layered double hydroxide, and the impact strength decreases significantly, proving that the dynamic interfacial toughening mechanism of the modified layered double hydroxide is one of the core factors to improve the toughness, and its effect even exceeds the contribution of the modified carbon fiber (Comparative Example 1). The toughness of Comparative Example 3 is lower than that of Example 5, indicating that the good interface (PDA layer) of the modified carbon fiber not only improves the strength, but also helps to prevent the rapid expansion of cracks at the interface, thereby improving the toughness.

[0050] The thermal deformation temperature of Example 5 is higher than that of the comparative examples, 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, and at the same time, the talc nucleating agent improves the crystallinity, which together improves the heat resistance. Comparative Examples 2 and 3 are both lower than Example 5, verifying the synergistic heat resistance effect of the modified filler. The T5% of Example 5 is higher than that of Comparative Example 1, and the 800°C residual carbon rate is 2.6 times that of Comparative Example 1. The boron acid modified polyphosphazene component of the modified LDH forms a dense carbon layer at high temperature, which blocks the transmission of heat and gas, and the modified carbon fiber can also enhance the stability of the carbon layer. The residual carbon rate of Comparative Example 2 is only 11.5%, and that of Comparative Example 3 is only 9.8%, highlighting the flame-retardant carbonization effect of the modified LDH.

[0051] Example 5 Limiting Oxygen Index 30.2%, reached the level of difficult to burn, vertical burning rating reached V-0 level, no dripping ignition phenomenon, modified layered double hydroxide provides metal oxide physical barrier, catalytic carbonization, heat absorption and cooling, modified carbon fiber phytic acid (P source) catalytic carbonization, POSS (Si source) generates ceramic layer protection, both synergistic, forming a dense, solid, expanded carbon layer, preventing melt dripping; Comparative Example 1 can only reach V-2 level, and the LOI is also lower. Although the modified layered double hydroxide is effective, it lacks the skeleton effect of CF and the P and Si elements brought by the modified carbon fiber, and the flame retardant system is incomplete, and the carbon layer quality is poor. Comparative Example 2 and Comparative Example 3 can only reach V-1 level. This shows that the lack of catalytic carbonization and barrier effect of modified layered double hydroxide, or the lack of P-Si synergistic effect brought by modified carbon fiber, will greatly reduce the flame retardant efficiency, and cannot achieve the highest level of V-0.

[0052] In the description of the present specification, the description referring to the terms "one embodiment", "an example", "a specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0053] The basic principles, main features and advantages of the present application are shown and described above. It should be understood by those skilled in the art that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application.

Claims

1. A carbon fiber reinforced polylactic acid composite, characterized by, The raw materials include the following components by weight: polylactic acid 60-75 parts, PBAT-g-GMA 10-15 parts, modified carbon fiber 8-10 parts, modified layered double hydroxide 6-8 parts, talc 1-2 parts, lubricant 0.5-1.5 parts, and antioxidant 0.5-1 part; The modified carbon fiber is a polydopamine layer coated on the surface of the chopped carbon fiber through self-polymerization of dopamine, and a phytic acid and aminopropyl isobutyl silyl group are grafted on the surface of the polydopamine layer through catechol and amino groups; The modified layered double hydroxide is a chitosan intercalated magnesium aluminum double hydroxide modified by boron acid modified polyphosphazene through electrostatic interaction, and the boron acid modified polyphosphazene is a functionalized modified polyphosphazene synthesized by replacing polydichlorophosphazene with aminopropanol to form a side group containing a hydroxyl group, and then capped with boric acid.

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

3. The carbon fiber reinforced polylactic acid composite material according to claim 1, characterized by, 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 according to claim 1, characterized by, The preparation method of the modified carbon fiber comprises the following steps: (1) The chopped carbon fiber is added to concentrated nitric acid, and refluxed at 80°C for 4-6 hours. After the reaction is completed, the filtrate is washed with deionized water until it is neutral. The pretreated carbon fiber is obtained by vacuum drying. (2) The hydrochloric acid dopamine is dissolved in a Tris-HCl buffer solution. The pretreated carbon fiber is immersed in the hydrochloric acid dopamine Tris-HCl buffer solution, and magnetically stirred at room temperature for 20-24 hours. After the reaction is completed, the carbon fiber is filtered and washed with deionized water for 3-5 times. The polydopamine-coated carbon fiber is obtained by vacuum drying. (2) The phytic acid and aminopropyl isobutyl silyl group are dissolved in an ethanol / water mixed solution. The polydopamine-coated carbon fiber is added to the mixed solution, and reacted at 60°C for 8-12 hours. After filtration, the modified carbon fiber is washed with deionized water for 3-5 times, and vacuum dried.

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

03.

6. The carbon fiber reinforced polylactic acid composite according to claim 1, characterized by, The preparation method of the modified layered double hydroxide comprises the following steps: A. The magnesium aluminum double hydroxide is dispersed in deionized water. Under nitrogen protection and stirring, a dilute acetic acid solution of chitosan is slowly added dropwise, and reacted at 60°C for 20-24 hours. After centrifugation, water washing, and freeze drying, the chitosan intercalated magnesium aluminum double hydroxide is obtained. B. The chitosan intercalated magnesium aluminum double hydroxide is re-dispersed in deionized water, and the pH is adjusted to 8-9. The boron acid modified polyphosphazene is added, and reacted at 70°C for 8-12 hours. After the reaction is completed, the product is collected by centrifugation, washed with water and ethanol for 3-5 times, and vacuum dried to obtain the modified layered double hydroxide.

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

8. The carbon fiber reinforced polylactic acid composite according to claim 6, characterized by The preparation method of the boron acid modified polyphosphazene comprises the following steps: I. Amidosulfonic acid, calcium sulfate dihydrate, ammonium chloride, phosphorus pentachloride and 1,2,4-trichlorobenzene are mixed under nitrogen atmosphere, and the oil bath is slowly heated to 185-195 DEG C for 2-4 h, after the reaction, hot filtration is carried out, the filtrate is slowly added into petroleum ether and stirred until the bottom precipitate is separated, the supernatant is removed, and the precipitate is washed with petroleum ether several times until the supernatant is clear, and the purified polydichlorophosphazene is obtained; II. The polydichlorophosphazene is dissolved in tetrahydrofuran, and cooled to 0-5 DEG C in an ice water bath, 3-amino-1-propanol and triethylamine are dissolved in tetrahydrofuran, and the mixed solution of 3-amino-1-propanol and triethylamine is slowly added into the polydichlorophosphazene solution under vigorous stirring and ice water bath, slowly heated to room temperature, and continuously stirred for 20-24 h, and the triethylamine hydrochloride precipitate is removed by filtration, the filtrate is added into distilled water to precipitate the product, and the solid precipitate is purified by repeatedly dissolving and precipitating in tetrahydrofuran / water system, and finally vacuum dried to obtain the polyphosphazene derivative; III. The polyphosphazene derivative and 4-carboxyphenylboronic acid are dissolved in N,N-dimethylformamide under nitrogen atmosphere, and then N,N'-dicyclohexyl carbodiimide and 4-dimethylaminopyridine are added, and stirred at room temperature for 20-24 h, after the reaction, the N,N'-dicyclohexylurea precipitate is removed by filtration, and the filtrate is dialyzed with deionized water and methanol for 20-24 h, the solvent is rotary evaporated, and finally vacuum dried to obtain the boronic acid modified polyphosphazene.

9. The carbon fiber reinforced polylactic acid composite according to claim 8, characterized in that, The molar ratio of the ammonium chloride and phosphorus pentachloride is 1:1, the molar ratio of the polydichlorophosphazene, 3-amino-1-propanol and triethylamine is 1:10:10.5, and the molar ratio of the polyphosphazene derivative, 4-carboxyphenylboronic acid and N,N'-dicyclohexyl carbodiimide 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, The following steps are included: The polylactic acid, PBAT-g-GMA, modified dihydroxide, talc, antioxidant and lubricant are added from the main feeder into the twin-screw extruder, the screw rotation speed is 200-300 rpm, the temperature of each zone of the extruder is 170 DEG C, 180 DEG C, 190 DEG C, 185 DEG C and 180 DEG C, the modified carbon fiber is added into the downstream of the melt zone through the side feeder, the raw materials are melt blended and then extruded and pelletized, and the composite pellets are vacuum dried at 60 DEG C for 4-6 h to obtain the carbon fiber reinforced polylactic acid composite material.

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