Carbon fiber flame-retardant composite plastic and preparation method thereof

Abstract

The invention discloses a carbon fiber flame-retardant composite plastic and a preparation method thereof, and belongs to the technical field of composite plastic preparation, the carbon fiber flame-retardant composite plastic comprises: 50-80% of a polymer matrix, the polymer matrix is a mixture of a main resin and a flexibilizer, the main resin is at least one of polyamide 6, polyamide 66, polybutylene terephthalate or polycarbonate, and the flexibilizer is at least one of a flexibilizer and an antioxidant. The flexibilizer is a maleic anhydride grafted polyolefin elastomer, and the content of the flexibilizer accounts for 5-15% of the total mass of the polymer matrix; and 15%-40% of surface modified carbon fibers. A synergistic modification layer of a nitrogen-phosphorus intumescent flame retardant and a two-dimensional nano material is constructed on the surface of the carbon fiber through a chemical grafting technology, nano-scale dispersion and firm loading of flame-retardant components are achieved, the composite material can rapidly form a compact and stable intumescent carbon layer during combustion, the limit oxygen index is increased and passes the UL-94V-0 grade, and the flame-retardant performance of the composite material is improved. The problems of low flame retardant efficiency and poor durability caused by non-uniform dispersion and easy migration of a traditional physical blending flame retardant are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite plastic preparation, more particularly to a carbon fiber flame-retardant composite plastic and a preparation method thereof. BACKGROUND

[0002] With the increasing demand for lightweight, high-strength and high-safety materials in the fields of electronic appliances, transportation, aerospace, etc., carbon fiber reinforced composite plastics have attracted widespread attention due to their excellent mechanical properties and lightweight characteristics. However, carbon fibers themselves do not have flame-retardant properties. Traditional methods usually add flame retardants through physical blending to achieve the flame-retardant function of the material. However, this method faces problems such as uneven dispersion of flame retardants, poor interfacial compatibility with the matrix, easy migration and precipitation, etc. in practical applications, resulting in low flame-retardant efficiency and decreased mechanical properties, which is difficult to meet the comprehensive requirements of high-performance composite materials.

[0003] In the prior art, carbon fiber reinforced flame-retardant composite plastics mostly use the method of directly blending flame retardants, which can improve the flame-retardant properties to some extent, but often at the expense of the mechanical strength and thermal stability of the material. For example, the ordinary physical blending system has problems such as weak interfacial bonding between the flame retardant and the fiber and the matrix, easy loss of the flame-retardant component during processing or use, etc., resulting in poor flame-retardant durability and insufficient synergistic effect. In addition, the conventional flame-retardant system is difficult to form a dense and stable intumescent carbon layer in the early stage of fire, limiting its application in high-temperature and high-load environments.

[0004] Therefore, the present application designs a carbon fiber flame-retardant composite plastic and a preparation method thereof to solve the above problems. SUMMARY

[0005] The present application aims to provide a carbon fiber flame-retardant composite plastic and a preparation method thereof to solve the problems raised in the background.

[0006] Technical solution: A carbon fiber flame-retardant composite plastic, comprising: 50%-80% of a polymer matrix, which is a mixture of a main resin and a toughening agent, wherein the main resin is at least one of polyamide 6, polyamide 66, polybutylene terephthalate or polycarbonate, and the toughening agent is a maleic anhydride grafted polyolefin elastomer, the content of which accounts for 5%-15% of the total mass of the polymer matrix; 15%-40% of surface modified carbon fibers, which are composed of a carbon fiber body and a modification layer firmly loaded on the surface thereof by chemical grafting, the carbon fiber body is polyacrylonitrile-based carbon fiber, the form of which is chopped fiber or continuous fiber bundle with a length of 3-6 mm, the modification layer contains nitrogen-phosphorus intumescent flame retardant and two-dimensional nanomaterial MXene, and the chemical grafting is connected by a covalent bond formed by a silane coupling agent; 5%-15% of a synergistic flame retardant, the synergistic flame retardant being at least one of aluminum hypophosphite, coated aluminum hypophosphite or a metal antimony compound; 0.5%-2% of a processing aid, the processing aid including at least two of an antioxidant, a lubricant and a light stabilizer; The sum of the mass percentages of the above components is 100%.

[0007] Preferably, the nitrogen-phosphorus intumescent flame retardant is compounded by a charring agent, an acid source and a gas source, with a mass ratio of (1-3):(2-4):(1-2), the charring agent being pentaerythritol or tri-pentaerythritol, the acid source being type II ammonium polyphosphate with a polymerization degree of not less than 500, and the gas source being one of melamine, dicyandiamide or an adduct (MPP) of ammonium polyphosphate and melamine.

[0008] Preferably, the two-dimensional nanomaterial MXene is a nanosheet obtained by etching a MAX phase (M represents metal, X represents carbon or nitrogen) with a mixed solution of hydrofluoric acid or lithium fluoride and hydrochloric acid. ) and then peeling off. The nanosheet is obtained by etching a MAX phase (M represents metal, X represents carbon or nitrogen) with a mixed solution of hydrofluoric acid or lithium fluoride and hydrochloric acid. , wherein represents a surface functional group, including at least one of -OH, -O or -F, and the loading amount of the MXene on the surface-modified carbon fiber is 5%-15% of the mass of the carbon fiber body.

[0009] Preferably, the synergistic flame retardant is microspherical coated aluminum hypophosphite with an average particle size D50 of 2-10 μm, the toughening agent is maleic anhydride grafted ethylene-octene copolymer (POE-g-MAH) or maleic anhydride grafted ternary ethylene-propylene rubber (EPDM-g-MAH), and the lubricant is at least one of pentaerythritol stearate, ethylene bis-stearamide or silicone masterbatch.

[0010] A preparation method of a carbon fiber flame-retardant composite plastic, comprising the following steps: S1, preparing surface-modified carbon fiber, specifically: S1.1, surface activation treatment: placing carbon fiber in a nitric acid solution with a concentration of 60-68 wt%, refluxing at 80-100 ℃ for 1-3 hours, washing to neutral after treatment and drying to obtain activated carbon fiber rich in carboxyl active functional groups on the surface; S1.2, preparing a mixed solution: dispersing nitrogen-phosphorus intumescent flame retardant and two-dimensional nanomaterial MXene in deionized water, treating with ultrasonic waves with a power of 500-1000 W for 20-60 minutes to form a uniform mixed dispersion, wherein the mass ratio of the nitrogen-phosphorus intumescent flame retardant to MXene is (5:1) to (10:1); S1.3, chemical grafting: the activated carbon fiber is immersed in the mixed dispersion liquid, 1%-3% of silane coupling agent is added to the total mass of the mixed dispersion liquid, and mechanical stirring is carried out in a constant-temperature water bath at 60-80°C for 2-4 hours; S1.4, post-treatment: after the reaction is completed, the carbon fiber is taken out, washed with deionized water, and dried in a vacuum drying box at 80-100°C for 6-12 hours to obtain the surface-modified carbon fiber; S2, melt blending and granulation, specifically: S2.1, pre-mixing: the polymer matrix, the surface-modified carbon fiber obtained in step S1, the synergistic flame retardant, and the processing aid are placed in a high-speed mixer and mixed at a speed of 800-1500 rpm for 5-15 minutes to obtain a premix, wherein the amounts of the components satisfy that the polymer matrix accounts for 50%-80%, the surface-modified carbon fiber accounts for 15%-40%, the synergistic flame retardant accounts for 5%-15%, and the processing aid accounts for 0.5%-2% in the final composite plastic, and the sum of the mass percentages of the components is 100%; S2.2, melt blending and granulation: the premix is fed into a twin-screw extruder, and after melt blending, extrusion, water tank cooling, air drying, and granulation, the masterbatch of the carbon fiber flame-retardant composite plastic is obtained, wherein the length-diameter ratio of the screw of the twin-screw extruder is not less than 40:1.

[0011] Preferably, the silane coupling agent in step S1.3 is γ-aminopropyl triethoxysilane (KH-550).

[0012] Preferably, in step S1.2, the solid content of the mixed dispersion liquid is 5%-10%.

[0013] Preferably, in step S2.2, the temperature of each section of the twin-screw extruder from the feeding port to the die head is set to a range of 240-290°C, and the screw rotation speed is 200-400 rpm.

[0014] Preferably, in step S2.2, the screw configuration of the twin-screw extruder comprises at least two groups of reverse kneading blocks, and a vacuum exhaust port is located after the reverse kneading blocks.

[0015] Preferably, after step S2.2, the following steps are further included: S3, drying and forming, specifically: S3.1, the obtained masterbatch is air-dried at 100-120°C for 2-4 hours, and then processed into standard test samples or final products by an injection molding machine.

[0016] Compared with the prior art, the advantages of the present application are: 1. This invention constructs a synergistic modification layer of nitrogen-phosphorus intumescent flame retardant and two-dimensional nanomaterial (MXene) on the surface of carbon fiber through chemical grafting technology. This achieves nanoscale dispersion and firm loading of flame retardant components, enabling the composite material to rapidly form a dense and stable intumescent char layer during combustion. This improves the limiting oxygen index (≥30%) and meets the UL-94V-0 rating, solving the problems of uneven dispersion and easy migration of traditional physically blended flame retardants, which lead to low flame retardant efficiency and poor durability.

[0017] 2. This invention, through the strong interfacial bonding between surface-modified carbon fibers and the polymer matrix, and the synergistic effect of toughening agents, endows the material with excellent flame retardant properties while maintaining high mechanical strength (tensile strength ≥ 110 MPa) and good impact toughness (cantilever beam impact strength ≥ 7.8 kJ / m). 2 This overcomes the shortcomings of conventional flame-retardant composite materials, which suffer from poor interfacial compatibility and significant decrease in mechanical properties due to the introduction of flame retardants.

[0018] 3. This invention significantly improves the thermal stability and high-temperature char rate (≥22% at 700℃) of the material by synergistic char formation of two-dimensional nanomaterials (MXene) and nitrogen-phosphorus intumescent flame retardant system at the fiber-matrix interface. At the same time, the chemical grafting process enhances the interfacial compatibility and processing stability of each component, achieving a highly efficient synergy of flame retardant performance, mechanical properties and thermal stability, providing a lightweight flame retardant material solution with better overall performance for the high-end equipment field. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of a carbon fiber flame-retardant composite plastic and its preparation method proposed in this invention. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example Example 1 Material composition (based on 100% total mass): Polymer matrix 68% (of which the main resin is polyamide 6PA6, accounting for 90% of the polymer matrix mass; toughening agent is POE-g-MAH, accounting for 10% of the polymer matrix mass); Surface-modified carbon fiber 20% (the carbon fiber body is polyacrylonitrile-based 4mm short-cut fiber, and the modification layer contains 12% of nitrogen-phosphorus intumescent flame retardant (APP:PER:MEL=3:2:1) and 8% of MXene); Synergistic flame retardant 10% (microsphere-coated aluminum hypophosphite, D50=5μm); Processing aids 2% (antioxidant 10100.5%, EBS 1.0%, light stabilizer 7700.5%).

[0022] Preparation method: I. Preparation of surface-modified carbon fibers: 1. Surface activation treatment: Polyacrylonitrile-based short-cut carbon fibers are immersed in a 65wt% nitric acid solution and refluxed at 90℃ for 2 hours. After treatment, they are washed with deionized water until neutral and dried in a vacuum drying oven at 100℃ for 8 hours to obtain activated carbon fibers.

[0023] 2. Preparation of the mixture: Disperse the nitrogen-phosphorus intumescent flame retardant and MXene in deionized water according to the above ratio, control the solid content to 8%, and sonicate at 800W power for 40 minutes to form a uniform mixed dispersion.

[0024] 3. Chemical grafting: Immerse activated carbon fibers in a mixed dispersion, add 2% of the total mass of the dispersion of silane coupling agent KH-550, and react with mechanical stirring in a 70℃ constant temperature water bath for 3 hours.

[0025] 4. Post-treatment: After the reaction is complete, the carbon fiber is taken out, washed thoroughly with deionized water, and dried in a vacuum drying oven at 90℃ for 10 hours to obtain surface-modified carbon fiber.

[0026] II. Melt blending and granulation: 5. Premixing: Weigh each component according to the above proportions, place them in a high-speed mixer, and mix at 1000 rpm for 10 minutes to obtain the premix.

[0027] 6. Melt Blending and Granulation: The premixed material is fed into a twin-screw extruder. The screw length-to-diameter ratio is 40:1, and the temperatures from the feed port to the die head are set to 240℃, 255℃, 265℃, 270℃, and 265℃ (die head), respectively. The screw speed is 300 rpm. The melt-extruded material is cooled in a water bath, air-dried, and then granulated to obtain composite plastic masterbatch.

[0028] 7. Drying and molding: The masterbatch is dried in a forced-air dryer at 110℃ for 3 hours, and then processed into standard test specimens by injection molding machine.

[0029] Example 2 Material composition (based on 100% total mass): Polymer matrix 58% (of which the main resin is polycarbonate PC, accounting for 92% of the polymer matrix mass; toughening agent is EPDM-g-MAH, accounting for 8% of the polymer matrix mass); Surface-modified carbon fiber 30% (the carbon fiber body is a continuous polyacrylonitrile fiber bundle, and the modification layer contains 15% nitrogen-phosphorus intumescent flame retardant and 12% MXene); Synergistic flame retardant 10% (aluminum hypophosphite and antimony trioxide compounded, mass ratio 4:1); Processing aids 2% (antioxidant 1681.0%, silicone masterbatch 0.6%, light stabilizer 2920.4%).

[0030] Preparation method: I. Preparation of surface-modified carbon fibers: 1. Surface activation treatment: The polyacrylonitrile-based continuous fiber bundle was immersed in a 65wt% nitric acid solution and refluxed at 90℃ for 2.5 hours. After treatment, it was washed with deionized water until neutral and dried in a vacuum drying oven at 100℃ for 8 hours to obtain activated carbon fibers with carboxyl active functional groups on the surface.

[0031] 2. Preparation of the mixture: Nitrogen-phosphorus intumescent flame retardant and two-dimensional nanomaterial MXene are dispersed in deionized water, and the solid content of the mixture is controlled at 7%. The mixture is ultrasonically treated at 1000W for 30 minutes to form a uniform mixture.

[0032] 3. Chemical grafting: The activated carbon fibers are immersed in the mixed dispersion, and 2% of the total mass of the mixed dispersion is added as silane coupling agent γ-aminopropyltriethoxysilane (KH-550). The mixture is then mechanically stirred in a 70°C constant temperature water bath for 3 hours.

[0033] 4. Post-processing: After the reaction is complete, the carbon fiber is removed, thoroughly washed with deionized water, and dried in a vacuum drying oven at 90°C for 10 hours to obtain the surface-modified carbon fiber.

[0034] II. Melt blending and granulation: 5. Premixing: The polymer matrix (PC and EPDM-g-MAH), the surface-modified carbon fiber obtained in step S1, the synergistic flame retardant (aluminum hypophosphite and antimony trioxide) and the processing aids (antioxidant 168, silicone masterbatch, light stabilizer 292) are placed in a high-speed mixer and mixed at 1000 rpm for 10 minutes to obtain the premix.

[0035] 6. Melt blending and granulation: The premixed material is fed into a twin-screw extruder, and after melt blending, extrusion, water cooling, air drying, and pelletizing, the masterbatch of the carbon fiber flame-retardant composite plastic is obtained. The twin-screw extruder has a screw length-to-diameter ratio of 40:1, and the temperature settings for each section from the feed port to the die head are 250℃, 265℃, 275℃, 280℃, and 275℃ (die head), respectively. The screw speed is 350 rpm.

[0036] 7. Drying and molding: The obtained masterbatch is dried in a forced-air dryer at 110℃ for 3 hours, and then processed into standard test strips by injection molding machine.

[0037] Example 3 Material composition (based on 100% total mass): 70% polymer matrix (of which the main resin is polybutylene terephthalate (PBT), accounting for 88% of the polymer matrix mass; toughening agent is POE-g-MAH, accounting for 12% of the polymer matrix mass); 15% surface-modified carbon fiber (the carbon fiber body is 3mm short-cut polyacrylonitrile fiber, and the modification layer contains 10% nitrogen-phosphorus intumescent flame retardant and 8% MXene); 13% synergistic flame retardant (coated aluminum hypophosphite, D50=8μm); 2% processing aids (0.7% antioxidant 1076, 0.8% PETS, 0.5% light stabilizer 622).

[0038] Preparation method: I. Preparation of surface-modified carbon fibers: 1. Surface activation treatment: Polyacrylonitrile-based short-cut carbon fibers are immersed in a 65wt% nitric acid solution and refluxed at 90℃ for 2 hours. After treatment, they are washed with deionized water until neutral and dried in a vacuum drying oven at 100℃ for 8 hours to obtain activated carbon fibers with carboxyl active functional groups on the surface.

[0039] 2. Preparation of the mixture: Nitrogen-phosphorus intumescent flame retardant and two-dimensional nanomaterial MXene are dispersed in deionized water at a mass ratio of 9:1. The solid content of the mixture is controlled at 6%. The mixture is ultrasonically treated at 800W for 40 minutes to form a uniform mixture.

[0040] 3. Chemical grafting: The activated carbon fibers are immersed in the mixed dispersion, and 2% of the total mass of the mixed dispersion is added as silane coupling agent γ-aminopropyltriethoxysilane (KH-550). The mixture is then mechanically stirred in a 65°C constant temperature water bath for 3.5 hours.

[0041] 4. Post-processing: After the reaction is complete, the carbon fiber is removed, thoroughly washed with deionized water, and dried in a vacuum drying oven at 90°C for 10 hours to obtain the surface-modified carbon fiber.

[0042] II. Melt blending and granulation: 5. Premixing: The polymer matrix (PBT and POE-g-MAH), the surface-modified carbon fiber obtained in step S1, the synergistic flame retardant (coated aluminum hypophosphite) and processing aids (antioxidant 1076, PETS, light stabilizer 622) are placed in a high-speed mixer and mixed at 1000 rpm for 10 minutes to obtain the premix.

[0043] 6. Melt blending and granulation: The premixed material is fed into a twin-screw extruder, and after melt blending, extrusion, water cooling, air drying, and pelletizing, the masterbatch of the carbon fiber flame-retardant composite plastic is obtained. The twin-screw extruder has a screw length-to-diameter ratio of 40:1, and the temperature settings for each section from the feed port to the die head are 235℃, 250℃, 260℃, 265℃, and 260℃ (die head), respectively. The screw speed is 280 rpm.

[0044] 7. Drying and molding: The obtained masterbatch is dried in a forced-air dryer at 110℃ for 3 hours, and then processed into standard test strips by injection molding machine.

[0045] Example 4 Material composition (based on 100% of total mass): 50% polymer matrix (of which the main resin is polyamide 66PA66, accounting for 90% of the polymer matrix mass; toughening agent is POE-g-MAH, accounting for 10% of the polymer matrix mass); 40% surface-modified carbon fiber (the carbon fiber body is 6mm short-cut polyacrylonitrile fiber, and the modification layer contains 18% nitrogen-phosphorus intumescent flame retardant and 15% MXene); 8% synergistic flame retardant (microsphere-coated aluminum hypophosphite, D50=3μm); 2% processing aids (0.5% antioxidant 1010, 0.5% antioxidant 168, 1.0% EBS).

[0046] Preparation method: I. Preparation of surface-modified carbon fibers: 1. Surface activation treatment: Polyacrylonitrile-based chopped carbon fibers were immersed in a 68wt% nitric acid solution and refluxed at 95°C for 1.5 hours. After treatment, they were washed with deionized water until neutral and dried in a vacuum drying oven at 100°C for 8 hours to obtain activated carbon fibers with surface rich in carboxyl active functional groups.

[0047] 2. Preparation of the mixture: Nitrogen-phosphorus intumescent flame retardant and two-dimensional nanomaterial MXene are dispersed in deionized water, and the solid content of the mixture is controlled at 9%. The mixture is ultrasonically treated at 600W for 50 minutes to form a uniform mixture.

[0048] 3. Chemical grafting: The activated carbon fibers are immersed in the mixed dispersion, and 2% of the total mass of the mixed dispersion is added as silane coupling agent γ-aminopropyltriethoxysilane (KH-550). The mixture is then mechanically stirred in a 70°C constant temperature water bath for 3 hours.

[0049] 4. Post-processing: After the reaction is complete, the carbon fiber is removed, thoroughly washed with deionized water, and dried in a vacuum drying oven at 90°C for 10 hours to obtain the surface-modified carbon fiber.

[0050] II. Melt blending and granulation: 5. Premixing: The polymer matrix (PA66 and POE-g-MAH), the surface-modified carbon fiber obtained in step S1, the synergistic flame retardant (microsphere-coated aluminum hypophosphite) and the processing aids (antioxidant 1010, antioxidant 168, EBS) are placed in a high-speed mixer and mixed at 1000 rpm for 10 minutes to obtain the premix.

[0051] 6. Melt blending and granulation: The premixed material is fed into a twin-screw extruder, and after melt blending, extrusion, water cooling, air drying, and pelletizing, the masterbatch of the carbon fiber flame-retardant composite plastic is obtained. The twin-screw extruder has a screw length-to-diameter ratio of 40:1, and the temperature settings for each section from the feed port to the die head are 255℃, 270℃, 280℃, 285℃, and 280℃ (die head), respectively. The screw speed is 320 rpm.

[0052] 7. Drying and molding: The obtained masterbatch is dried in a forced-air dryer at 110℃ for 3 hours, and then processed into standard test strips by injection molding machine.

[0053] Comparative Example 1 (Conventional Physical Blend Flame Retardant System) Material composition (by total mass): 68% polymer matrix (main resin is PA6, no toughening agent added); 20% carbon fiber (ordinary polyacrylonitrile-based 4mm short chopped fiber, without any surface modification); 10% synergistic flame retardant (ordinary APP and antimony trioxide compound, mass ratio 3:1); 2% processing aids (2.0% lubricant EBS).

[0054] Preparation method: Premix: The polymer matrix (PA6), ordinary carbon fiber, synergistic flame retardant (ordinary APP and antimony trioxide) and processing aid (EBS) are placed in a high-speed mixer and mixed at 1000 rpm for 10 minutes to obtain a premix (Comparative Example 1 does not have a carbon fiber surface modification step).

[0055] Melt blending and granulation: The premixed material is fed into a twin-screw extruder, melt blended, extruded, cooled in a water bath, air-dried, and then granulated to obtain composite plastic masterbatch. The twin-screw extruder has a screw length-to-diameter ratio of 40:1, and the temperature settings for each section from the feed port to the die head are 240℃, 255℃, 265℃, 270℃, and 265℃ (die head), respectively. The screw speed is 300 rpm.

[0056] Drying and molding: The obtained masterbatch was dried in a forced-air dryer at 110°C for 3 hours, and then processed into standard test specimens by an injection molding machine.

[0057] Comparative Example 2 (without MXene and chemical grafting modification) Material composition (based on 100% of total mass): 68% polymer matrix (of which the main resin is PA6, accounting for 90% of the polymer matrix mass; the toughening agent is POE-g-MAH, accounting for 10% of the polymer matrix mass); 20% carbon fiber and flame retardant (a physical mixture of ordinary short-cut carbon fiber and nitrogen-phosphorus intumescent flame retardant in the same amount as in Example 1, the carbon fiber was not surface activated or chemically grafted, and no MXene was added); 10% synergistic flame retardant (microsphere-coated aluminum hypophosphite); 2% processing aids (same type and amount as in Example 1).

[0058] Preparation method: Premixing: The polymer matrix (PA6 and POE-g-MAH), ordinary short-cut carbon fibers, nitrogen-phosphorus intumescent flame retardant, synergistic flame retardant (microsphere-coated aluminum hypophosphite), and processing aids (antioxidant 1010, EBS, light stabilizer 770) were all placed in a high-speed mixer and mixed at 1000 rpm for 10 minutes to obtain a premix (comparative example 2 omitted the preparation step S1 of surface-modified carbon fibers, and all components were physically mixed in one step). Melt blending and granulation: The premixed material is fed into a twin-screw extruder, melt blended, extruded, cooled in a water bath, air-dried, and then granulated to obtain composite plastic masterbatch. The twin-screw extruder has a screw length-to-diameter ratio of 40:1, and the temperature settings for each section from the feed port to the die head are 240℃, 255℃, 265℃, 270℃, and 265℃ (die head), respectively. The screw speed is 300 rpm.

[0059] Drying and molding: The obtained masterbatch was dried in a forced-air dryer at 110°C for 3 hours, and then processed into standard test specimens by an injection molding machine.

[0060] I. Experimental Objective Comprehensive evaluation of the performance of the present invention: The flame retardant properties, mechanical properties and thermal stability of the carbon fiber flame retardant composite plastics prepared in Examples 1-4 were evaluated, thereby proving the inventiveness and effectiveness of the present invention.

[0061] Verification of the superiority of the technical approach: By comparing with Comparative Example 1 (conventional physical blending) and Comparative Example 2 (without MXene and chemical grafting), it is confirmed that: The key role of surface-modified carbon fibers (including chemically grafted layers of MXene and nitrogen-phosphorus flame retardants) in improving the overall performance of materials.

[0062] Chemical grafting processes offer advantages over simple physical mixing in improving interfacial bonding and flame retardant efficiency.

[0063] II. Experimental Samples Test group: Example 1, Example 2, Example 3, Example 4.

[0064] Control group: Comparative Example 1 (conventional physical blending), Comparative Example 2 (without MXene and chemical grafting).

[0065] III. Experimental Methods, Procedures and Standards 1. Limiting Oxygen Index Test Test standard: ASTM D2863 Testing equipment: Oxygen index meter Sample specifications: length 80-150mm, width 6.5mm±0.5mm, thickness 3.0mm±0.5mm.

[0066] Test steps: (1) Fix the sample vertically in the fixture inside the combustion tube, so that its top end is at least 100 mm below the top of the combustion tube.

[0067] (2) Adjust the gas supply system so that the oxygen / nitrogen mixed gas flow enters the combustion chamber at a specified flow rate (usually 4±1cm / s).

[0068] (3) Ignite the sample from the top with an igniter.

[0069] (4) The test is conducted using the lifting method. If the burning time of the sample exceeds 3 minutes or the burning length exceeds 50 mm, the oxygen concentration is reduced; otherwise, the oxygen concentration is increased.

[0070] (5) According to the calculation method specified in the standard, determine the minimum oxygen concentration required for the material to burn continuously for at least 3 minutes or for a burning length of 50 mm, which is the LOI value.

[0071] 2. Vertical Burning Test Test standard: ASTM D3801 (UL-94).

[0072] Test equipment: Vertical combustion tester.

[0073] Sample specifications: length 125mm±5mm, width 13.0mm±0.5mm, thickness standard thickness (e.g. 1.6mm, 3.2mm).

[0074] Test steps: (1) Clamp the upper end of the sample so that its longitudinal axis is perpendicular.

[0075] (2) Place dry degreased cotton at the bottom of the sample.

[0076] (3) Apply a Bunsen burner (blue flame height 20 mm) to the center of the lower end of the sample for the first time, and remove it after 10 seconds.

[0077] (4) Record the afterflame burning time (t1) of the sample.

[0078] (5) After the residual flame of the sample is extinguished (or 30 seconds after the first ignition), immediately apply the flame again for 10 seconds.

[0079] (6) Record the second afterflame burning time (t2) and the afterglow burning time.

[0080] (7) Observe and record whether any burning material drips and ignites the absorbent cotton.

[0081] (8) Determine the UL-94 rating (V-0, V-1, V-2 or NR) of the material based on the total time t1+t2, whether it drips and ignites, and other criteria.

[0082] 3. Tensile property test Test standard: ASTM D638.

[0083] Testing equipment: Universal testing machine.

[0084] Sample specifications: Type I dumbbell-shaped sample.

[0085] Test steps: (1) Measure the width and thickness of the narrow parallel part of the sample, accurate to 0.01 mm.

[0086] (2). The specimen is symmetrically clamped in the fixture of the testing machine and the extensometer is set up.

[0087] (3) Start the testing machine and stretch it at the specified speed (e.g., 5 mm / min or 50 mm / min, depending on the material) until the specimen breaks.

[0088] (4) Record the stress-strain curve.

[0089] (5) Calculate and report the tensile strength (maximum stress), elongation at break and tensile modulus from the curve.

[0090] 4. Bending performance test Test standard: ASTM D790.

[0091] Testing equipment: Universal testing machine (equipped with a three-point bending device).

[0092] Sample specifications: length 80mm+, width 10.0mm±0.5mm, thickness 4.0mm±0.5mm.

[0093] Test steps: (1) Measure the width and thickness of the midpoint of the sample.

[0094] (2). Set the span (usually 16 times the thickness).

[0095] (3) Place the sample on the two supports with the indenter at the midpoint of the sample.

[0096] (4) Apply the load at a specified strain rate (calculated by formula, which is related to the span and specimen thickness).

[0097] (5) Record the load-deflection curve until the specified strain is reached or the specimen breaks.

[0098] (6) Calculate and report the bending strength and bending modulus.

[0099] 5. Cantilever beam impact strength test Test standard: ASTM D256 (Method A).

[0100] Testing equipment: Cantilever beam impact testing machine.

[0101] Sample specifications: length 63.5mm±2.0mm, width 12.7mm±0.2mm, thickness standard thickness (e.g. 3.2mm, 6.4mm), and a standard V-shaped notch on one side.

[0102] Test steps: (1) Measure the remaining thickness at the notch of the sample.

[0103] (2). Fix the sample horizontally in the fixture with the notch facing away from the impact blade.

[0104] (3) Release the pendulum and let it impact the specimen.

[0105] (4) Record the angle at which the pendulum bounces after impact, or directly read the energy absorbed by the sample during fracture from the energy scale.

[0106] (5) Divide the absorbed energy by the remaining thickness at the notch of the specimen to obtain the impact strength (kJ / m). 2 (or J / m).

[0107] 6. Thermogravimetric analysis Test standard: ASTM E1131.

[0108] Test equipment: thermogravimetric analyzer.

[0109] Sample specifications: Powder or small flake samples, weighing approximately 5-15 mg.

[0110] Test steps: (1) Place the sample in a platinum or alumina crucible for TGA.

[0111] (2) In a specific atmosphere (usually nitrogen, used to assess thermal stability; or air, used to assess thermal oxidative stability), heat from room temperature to the target temperature (e.g., 800°C) at a constant heating rate (e.g., 10°C / min or 20°C / min).

[0112] (3) Record the sample mass change curve with temperature or time in real time.

[0113] (4) Analyze and report the initial decomposition temperature (e.g., the temperature at which 5% weight loss occurs, Td5%), the temperature at which the maximum decomposition rate is reached, and the char residue at a specific high temperature (e.g., 700°C) from the TGA curve.

[0114] 7. Observation using a scanning electron microscope Test equipment: Scanning electron microscope.

[0115] Sample preparation: Select fracture surface samples after impact testing.

[0116] Fix the sample with the cross-section facing upwards on the sample stage.

[0117] Non-conductive plastic samples are sputter-coated with gold to enhance their conductivity and prevent charge accumulation.

[0118] Test steps: (1) Place the sample stage into the SEM sample chamber and evacuate it.

[0119] (2) Select appropriate acceleration voltage (e.g., 5-15kV) and working distance.

[0120] (3) Observe the fracture morphology of the sample at different magnifications, focusing on: The interfacial bonding between carbon fibers and the polymer matrix (whether they are pulled out smoothly or encapsulated by resin), fiber dispersion, and fracture characteristics (whether they are ductile or brittle fractures).

[0121] IV. Experimental Results and Analysis The experimental results are shown in Table 1. Table 1 ; V. Conclusion Through the above systematic performance testing and comparative analysis, it can be fully demonstrated that: 1. This invention uses surface chemical grafting technology to firmly load nitrogen-phosphorus intumescent flame retardant and two-dimensional nanomaterial MXene onto the surface of carbon fiber, successfully constructing a multifunctional fiber that integrates reinforcement, flame retardancy, and char formation.

[0122] 2. This design enables the targeted and efficient utilization of flame retardants and produces a significant synergistic effect with co-active flame retardants and polymer matrix, enabling the material to achieve high levels of flame retardant performance and thermal stability while maintaining excellent mechanical properties.

[0123] 3. The technical approach of this invention is significantly superior to the traditional physical blending process, and has outstanding creativity and application value.

[0124] 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 preferred examples and are not intended to limit 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 present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A carbon fiber flame-retardant composite plastic, characterized in that, include: The polymer matrix comprises 50%-80%, wherein the polymer matrix is ​​a mixture of a main resin and a toughening agent, wherein the main resin is at least one of polyamide 6, polyamide 66, polybutylene terephthalate, or polycarbonate, and the toughening agent is a maleic anhydride-grafted polyolefin elastomer, the content of which accounts for 5%-15% of the total mass of the polymer matrix; The surface-modified carbon fiber comprises 15%-40%, which consists of a carbon fiber body and a modification layer firmly loaded on its surface by chemical grafting. The carbon fiber body is polyacrylonitrile-based carbon fiber, which is in the form of short chopped fibers or continuous fiber bundles with a length of 3-6 mm. The modification layer contains a nitrogen-phosphorus intumescent flame retardant and two-dimensional nanomaterial MXene. The chemical grafting is connected by covalent bonds formed by a silane coupling agent. The synergistic flame retardant is 5%-15%, wherein the synergistic flame retardant is at least one of aluminum hypophosphite, coated aluminum hypophosphite, or a metallic antimony compound. Processing aids of 0.5%-2%, wherein the processing aids include at least two of antioxidants, lubricants and light stabilizers; The sum of the mass percentages of the above components is 100%.

2. The carbon fiber flame-retardant composite plastic according to claim 1, characterized in that, The nitrogen-phosphorus intumescent flame retardant is composed of a charring agent, an acid source, and a gas source in a mass ratio of (1-3):(2-4):(1-2). The charring agent is pentaerythritol or tripentaerythritol, the acid source is type II ammonium polyphosphate with a degree of polymerization of not less than 500, and the gas source is melamine, dicyandiamide, or an adduct of ammonium polyphosphate and melamine (MPP).

3. The carbon fiber flame-retardant composite plastic according to claim 1, characterized in that, The two-dimensional nanomaterial MXene is etched by etching the MAX phase using a mixture of hydrofluoric acid or lithium fluoride and hydrochloric acid. After peeling, the resulting product Nanosheets, in which The surface functional group includes at least one of -OH, -O or -F, and the loading of MXene on the surface-modified carbon fiber is 5%-15% of the carbon fiber bulk mass.

4. The carbon fiber flame-retardant composite plastic according to claim 1, characterized in that, The synergistic flame retardant is microsphere-coated aluminum hypophosphite with an average particle size D50 of 2-10 μm; the toughening agent is maleic anhydride-grafted ethylene-octene copolymer (POE-g-MAH) or maleic anhydride-grafted ethylene propylene diene monomer (EPDM-g-MAH); and the lubricant is at least one of pentaerythritol stearate, ethylene bis-stearamide, or silicone masterbatch.

5. A method for preparing a carbon fiber flame-retardant composite plastic, characterized in that, Includes the following steps: S1. Preparation of surface-modified carbon fibers, specifically: S1.1 Surface activation treatment: The carbon fiber is placed in a 60-68wt% nitric acid solution and refluxed at 80-100℃ for 1-3 hours. After treatment, it is washed until neutral and dried to obtain activated carbon fiber with a surface rich in carboxyl active functional groups. S1.2 Preparation of the mixture: The nitrogen-phosphorus intumescent flame retardant and the two-dimensional nanomaterial MXene are dispersed in deionized water and treated with ultrasonic waves at a power of 500-1000W for 20-60 minutes to form a uniform mixed dispersion, wherein the mass ratio of the nitrogen-phosphorus intumescent flame retardant to MXene is (5:1) to (10:1). S1.3 Chemical grafting: Immerse the activated carbon fibers in the mixed dispersion, add 1%-3% of the total mass of the mixed dispersion as silane coupling agent, and mechanically stir the reaction in a constant temperature water bath at 60-80℃ for 2-4 hours. S1.4 Post-treatment: After the reaction is complete, the carbon fiber is taken out, washed thoroughly with deionized water, and dried in a vacuum drying oven at 80-100℃ for 6-12 hours to obtain the surface-modified carbon fiber. S2, melt blending and granulation, specifically: S2.1 Premixing: The polymer matrix, the surface-modified carbon fibers obtained in step S1, the synergistic flame retardant, and the processing aids are placed in a high-speed mixer and mixed at 800-1500 rpm for 5-15 minutes to obtain a premix. The amount of each component added is such that the polymer matrix accounts for 50%-80%, the surface-modified carbon fibers account for 15%-40%, the synergistic flame retardant accounts for 5%-15%, and the processing aids account for 0.5%-2% in the final composite plastic, and the sum of the mass percentages of each component is 100%. S2.2 Melt Blending and Granulation: The premixed material is fed into a twin-screw extruder, and after melt blending, extrusion, water cooling, air drying, and pelletizing, the masterbatch of the carbon fiber flame-retardant composite plastic is obtained, wherein the length-to-diameter ratio of the screw of the twin-screw extruder is not less than 40:

1.

6. The method for preparing a carbon fiber flame-retardant composite plastic according to claim 5, characterized in that, The silane coupling agent in step S1.3 is γ-aminopropyltriethoxysilane (KH-550).

7. The method for preparing a carbon fiber flame-retardant composite plastic according to claim 5, characterized in that, In step S1.2, the solid content of the mixed dispersion is 5%-10%.

8. The method for preparing a carbon fiber flame-retardant composite plastic according to claim 5, characterized in that, In step S2.2, the temperature setting range of each section of the twin-screw extruder from the feed port to the die head is 240-290℃, and the screw speed is 200-400rpm.

9. The method for preparing a carbon fiber flame-retardant composite plastic according to claim 5, characterized in that, In step S2.2, the screw configuration of the twin-screw extruder includes at least two sets of reverse kneading blocks, and the vacuum exhaust port is located after the reverse kneading blocks.

10. The method for preparing a carbon fiber flame-retardant composite plastic according to claim 5, characterized in that, The process after step S2.2 also includes: S3. Drying and molding, specifically: S3.1 The obtained masterbatch is dried in a forced-air dryer at 100-120℃ for 2-4 hours, and then processed into standard test strips or final products by injection molding machine.

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