A halogen-free flame-retardant polypropylene material and its preparation method

Abstract

This invention discloses a halogen-free flame-retardant polypropylene material and its preparation method, comprising 60-80 parts of polypropylene (PP), 4-8 parts of toughening agent, 15-25 parts of halogen-free flame retardant, 1-1.5 parts of antioxidant, 2-3 parts of light stabilizer, and 5-10 parts of modified graphene oxide flame retardant synergist. The modified graphene oxide flame retardant synergist is prepared by "nucleophilic substitution acyl chloride-nucleophilic substitution amidation-electrostatic interaction" using graphene oxide (GO), anhydrous sulfoxide, an amine compound H2N-R-NH2 containing at least two terminal primary amino groups, and molybdate. The -R- group is a divalent organic group used to connect the amide bond to the terminal primary amino group. The modified graphene oxide flame retardant synergist includes at least one amide bond -CONH-R-N- connected to the terminal primary amino group. The halogen-free flame-retardant polypropylene material provided by this invention exhibits excellent flame retardant properties while also improving its impact resistance and anti-dripping effect, and is safe and environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of wire and cable materials, specifically to a halogen-free flame-retardant polypropylene material and its preparation method. Background Technology

[0002] Polypropylene (PP) cable protection pipes, as an indispensable basic component in modern power and communication systems, play a crucial role in protecting internal cables from mechanical damage, chemical corrosion, and external environmental influences. However, standard polypropylene resin itself is highly flammable, has a low limiting oxygen index, and melts and drips during combustion, easily causing secondary flame spread and major fire accidents. Therefore, polypropylene materials used in cable protection pipes must possess excellent flame-retardant properties to meet increasingly stringent fire safety standards. Furthermore, given that cable conduits are often laid in enclosed spaces, underground, or densely populated areas, they must not release large amounts of toxic or corrosive fumes during combustion, which imposes a mandatory requirement for halogen-free flame-retardant systems. Early flame-retardant technologies mainly relied on halogenated flame retardants (such as bromine-based and chlorine-based flame retardants). Although these flame retardants have high flame retardancy efficiency, require low dosage, and have little impact on the mechanical properties of the matrix, they generate a large amount of toxic hydrogen halide gas and dense smoke when burning, causing "secondary disasters" that seriously threaten personnel safety and corrode precision equipment. Therefore, it is essential to develop a new type of halogen-free flame-retardant polypropylene material that possesses halogen-free high flame retardancy, excellent impact resistance, and physical and mechanical properties. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the present invention proposes a halogen-free flame-retardant polypropylene material and its preparation method, aiming to solve the problems of poor flame retardancy, poor physical and mechanical properties, and poor impact resistance of current PP materials.

[0004] To achieve the above objectives, this invention proposes a halogen-free flame-retardant polypropylene material. The raw materials of the halogen-free flame-retardant polypropylene material, by weight, include 60-80 parts of polypropylene (PP), 4-8 parts of toughening agent, 15-25 parts of halogen-free flame retardant, 1-1.5 parts of antioxidant, 2-3 parts of light stabilizer, and 5-10 parts of modified graphene oxide flame retardant synergist. The modified graphene oxide flame retardant synergist is prepared by "nucleophilic substitution acyl chloride-nucleophilic substitution amidation-electrostatic interaction" from graphene oxide (GO), anhydrous sulfoxide, an amine compound H2N-R-NH2 containing at least two terminal primary amino groups, and molybdate. The -R- is a divalent organic group used to connect the amide bond to the terminal primary amino group. The modified graphene oxide flame retardant synergist includes at least one amide bond -CONH-RN- connected to the terminal primary amino group.

[0005] Optionally, the graphene oxide is prepared by a modified Hummers method, and the prepared graphene oxide has a carboxyl content of 10%-20%.

[0006] Optionally, in the amine compound H2N-R-NH2 containing at least two terminal primary amino groups, the -R- is a divalent organic group used to connect the amide bond to the primary amino group, and the -R- group is at least one of a straight-chain alkyl group, a polyether segment, a polyamine segment containing a secondary amine structure, an aromatic structure, a branched structure, and a cyclic structure.

[0007] Optionally, the straight-chain alkyl group is -CH2-CH2-, -(CH2)3-, -(CH2)4-, -(CH2)6-, -(CH2)8-, or -(CH2). 10 At least one of the following: -; the polyether-containing segment is -(CH2-CH2-O). 2-5 At least one of - and -CH2-CH(CH3)-O-; the polyamine segment containing the secondary amine structure is at least one of DETA backbone, TETA backbone, TEPA backbone, PEPA backbone, and BAPA backbone; the aromatic structure is at least one of phenylene, benzyl, biaryl ether, and naphthalene ring structure; the branched structure is at least one of branched propyl, tertiary carbon, and neopentyl type structure; the cyclic structure is -C6H 10 - At least one of the isophorone structure and piperazine structure.

[0008] Optionally, the molybdate dissolves into a molybdate anion, and the molybdate is at least one of monomeric molybdate molybdate, polymolybdate molybdate, and heteropolymolybdate molybdate.

[0009] Optionally, the monomeric molybdate molybdate is at least one selected from sodium molybdate (Na2MoO4·2H2O), potassium molybdate (K2MoO4), ammonium molybdate ((NH4)2MoO4), lithium molybdate (Li2MoO4), and cesium molybdate (Cs2MoO4); the polymolybdate molybdate is at least one selected from ammonium hexamolybdate, sodium hexamolybdate, ammonium heptamolybdate, sodium heptamolybdate, potassium heptamolybdate, ammonium octamolybdate, and sodium octamolybdate; the heteropolymolybdate molybdate is phosphomolybdic acid (H3PMo). 12 O 40 ·xH2O), ammonium phosphomolybdate ((NH4)3PMo 12 O 40 Sodium phosphomolybdate (Na3PMo) 12 O 40 ) and sodium molybdate (Na4SiMo) 12 O 40 At least one of the following.

[0010] Optionally, the modified graphene oxide flame retardant synergist structure includes at least one... , Where x is the number of molybdenum atoms in one molecule of molybdate, and y is the number of oxygen atoms in one molecule of molybdate.

[0011] Optionally, the preparation method of the modified graphene oxide flame retardant synergist includes the following steps: (1) Graphene oxide was dispersed in anhydrous thionyl chloride, and dimethylformamide (DMF) was added as a catalyst. The mixture was refluxed and centrifuged to obtain GO-COCl. (2) Disperse GO-COCl in an anhydrous organic solvent, add an amine compound H2N-R-NH2 containing at least two terminal primary amino groups, and react under nitrogen protection to obtain amidated GO; (3) Disperse amidated GO in deionized water or acidic buffer solution with a pH of 3-6, and sonicate to form a uniform dispersion to obtain a protonated and positively charged amidated GO dispersion. (4) Dissolve molybdate in an acidic water / low alcohol system buffer solution of the same pH, and slowly add it dropwise to a protonated positively charged amidated GO dispersion. The reaction is carried out by electrostatic interaction. After stirring, centrifugation, washing, and freeze drying, the modified graphene oxide flame retardant synergist is obtained.

[0012] Optionally, the anhydrous organic solvent is at least one of alcohols, aromatic hydrocarbons, aliphatic hydrocarbons, alicyclic hydrocarbons, ethers, and ketones, and the acidic water / lower alcohol system buffer is a mixed solution of H2O and at least one lower saturated monohydric alcohol.

[0013] Optionally, the raw materials for the halogen-free flame-retardant polypropylene material, by weight, include: Polypropylene (PP) 60-80 parts 4-8 parts toughening agent 15-25 parts of halogen-free flame retardant Antioxidant 1-1.5 parts, 2-3 parts light stabilizer 6-9 parts of modified graphene oxide flame retardant synergist.

[0014] Optionally, the polypropylene is copolymer polypropylene with a melt index (230℃, 2.16kg) of 3-50g / 10min.

[0015] Optionally, the toughening agent is at least one of ethylene-butene copolymer, ethylene-octene copolymer, ultra-high molecular weight polyethylene, and nano-silicon.

[0016] Optionally, the halogen-free flame retardant is at least one of ammonium polyphosphate, piperazine pyrophosphate, melamine polyphosphate, melamine cyanurate, aluminum hypophosphite, divinyl aluminum hypophosphite, and zinc borate.

[0017] Optionally, the antioxidant is at least one of 1010 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]), 1076, 168 (tris[2,4-di-tert-butylphenyl]phosphite), and 626.

[0018] Optionally, the light stabilizer is at least one of non-alkaline HALS, low-alkaline HALS, high molecular weight HALS, Tinuvin 326, Tinuvin NOR 371, and 329.

[0019] This invention provides a method for preparing a halogen-free flame-retardant polypropylene material, comprising the following steps: A modified graphene oxide flame retardant synergist was prepared by using graphene oxide (GO), anhydrous thionyl chloride, an amine compound H2N-R-NH2 containing at least two terminal primary amino groups, and molybdate. Polypropylene, toughening agent, halogen-free flame retardant, antioxidant, light stabilizer and modified graphene oxide flame retardant synergist are mixed evenly, and then subjected to intensive mixing, extrusion and granulation to obtain granules. The granules are then dried to obtain the halogen-free flame retardant polypropylene material as described above.

[0020] In this invention, the halogen-free flame-retardant polypropylene material comprises polypropylene (PP), toughening agent, antioxidant, light stabilizer, halogen-free flame retardant, and modified graphene oxide flame retardant synergist. The modified graphene oxide flame retardant synergist is prepared from graphene oxide (GO), anhydrous sulfoxide, an amine compound H2N-R-NH2 containing at least two terminal primary amino groups, and molybdate. Anhydrous sulfoxide reacts with the carboxyl groups on the surface of graphene oxide to obtain nucleophilically substituted acyl-chlorinated graphene oxide GO-COCl. The acyl-chlorinated graphene oxide GO-COCl and the amine compound form stable amide bonds through a substitution reaction. The molybdate ions of the molybdate and the amidated graphene oxide are attracted and firmly adsorbed by strong Coulomb electrostatic attraction, thus preparing the modified graphene oxide flame retardant synergist. Ultimately, this achieves efficient, environmentally friendly, and high-performance flame retardant protection, significantly improving the flame retardant properties of the material. In the halogen-free flame-retardant polypropylene material system proposed in this invention, modified graphene oxide flame retardant synergist enhances the flame-retardant properties of polypropylene. During combustion, graphene oxide forms a dense char layer, preventing heat propagation and reducing the flame spread rate. It isolates oxygen and can rapidly weaken the fire source by absorbing heat, further enhancing the self-extinguishing property of polypropylene. Simultaneously, it improves the thermal stability and high-temperature resistance of polypropylene. The structure of graphene oxide allows polypropylene to maintain structural stability, reducing the risk of thermal degradation and molecular chain breakage, significantly extending the service life of polypropylene materials and ensuring their long-term stability at high temperatures. Furthermore, the two-dimensional structure of graphene oxide itself provides enhanced mechanical support, effectively improving the rigidity and strength of polypropylene materials. The halogen-free flame-retardant polypropylene material provided by this invention possesses excellent flame-retardant and mechanical properties, as well as good processing performance and impact resistance. Moreover, the halogen-free flame-retardant polypropylene material proposed in this invention does not contain halogens, making it safe and environmentally friendly. Attached Figure Description

[0021] Figure 1 This is a molecular structure diagram of the modified graphene oxide flame retardant synergist in one embodiment of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0023] Unless otherwise specified, all technical and scientific terms used herein have their usual meaning within the field to which the subject matter is claimed.

[0024] Polypropylene (PP) cable protection pipes, as an indispensable basic component in modern power and communication systems, play a crucial role in protecting internal cables from mechanical damage, chemical corrosion, and external environmental influences. However, standard polypropylene resin itself is highly flammable, has a low limiting oxygen index, and melts and drips during combustion, easily causing secondary flame spread and major fire accidents. Therefore, polypropylene materials used in cable protection pipes must possess excellent flame-retardant properties to meet increasingly stringent fire safety standards. Furthermore, given that cable conduits are often laid in enclosed spaces, underground, or densely populated areas, they must not release large amounts of toxic or corrosive fumes during combustion, which imposes a mandatory requirement for halogen-free flame-retardant systems. Early flame-retardant technologies mainly relied on halogenated flame retardants (such as bromine-based and chlorine-based flame retardants). Although these flame retardants have high flame retardancy efficiency, require low dosage, and have little impact on the mechanical properties of the matrix, they generate a large amount of toxic hydrogen halide gas and dense smoke when burning, causing "secondary disasters" that seriously threaten personnel safety and corrode precision equipment. Therefore, it is essential to develop a new type of halogen-free flame-retardant polypropylene material that possesses halogen-free high flame retardancy, excellent impact resistance, and physical and mechanical properties.

[0025] To address the aforementioned problems, the first aspect of this invention provides a halogen-free flame-retardant polypropylene material. The raw materials of the halogen-free flame-retardant polypropylene material, by weight, include 60-80 parts of polypropylene (PP), 4-8 parts of toughening agent, 15-25 parts of halogen-free flame retardant, 1-1.5 parts of antioxidant, 2-3 parts of light stabilizer, and 5-10 parts of modified graphene oxide flame retardant synergist. The modified graphene oxide flame retardant synergist is prepared by "nucleophilic substitution acyl chloride-nucleophilic substitution amidation-electrostatic interaction" from graphene oxide (GO), anhydrous sulfoxide, an amine compound H2N-R-NH2 containing at least two terminal primary amino groups, and molybdate. The -R- is a divalent organic group used to connect the amide bond to the terminal primary amino group. The modified graphene oxide flame retardant synergist includes at least one amide bond -CONH-RN- connected to the terminal primary amino group.

[0026] Understandably, in halogen-free flame-retardant polypropylene materials, PP is present in any number of parts between 60 and 80 (e.g., 60, 65, 70, 75, 80, etc.); toughening agent is present in any number of parts between 4 and 8 (e.g., 4, 5, 6, 7, 8, etc.); halogen-free flame retardant is present in any number of parts between 15 and 25 (e.g., 15, 18, 21, 23, 25, etc.); antioxidant is present in any number of parts between 1 and 1.5 (e.g., 1, 1.2, 1.4, 1.5, etc.); light stabilizer is present in any number of parts between 2 and 3 (e.g., 2, 2.2, 2.4, 2.6, 2.8, 3, etc.); and modified graphene oxide flame retardant synergist is present in any number of parts between 5 and 10 (e.g., 5, 6, 7, 8, 9, 10, etc.).

[0027] Understandably, the modified graphene oxide flame retardant synergist is prepared from graphene oxide (GO), anhydrous sulfoxide, an amine compound H2N-R-NH2 containing at least two terminal primary amino groups, and molybdate. The surface of graphene oxide has carboxyl, hydroxyl, and epoxy groups. Anhydrous sulfoxide reacts with the carboxyl groups on the graphene oxide surface to obtain nucleophilically substituted acyl-chlorinated graphene oxide GO-COCl, significantly improving the surface reactivity of graphene oxide. This transforms the subsequent amidation reaction from physical adsorption to substitution. The acyl-chlorinated graphene oxide GO-COCl and the amine compound form stable amide bonds through substitution. These amide bonds provide very stable covalent connections, allowing the graphene oxide to firmly adhere to the substrate and resist peeling. Furthermore, the substitution reaction constructs a high-density nitrogen-containing functional group on the graphene oxide surface, resulting in a more complete reaction, more controllable amino group introduction sites, and higher efficiency. This increases the nitrogen content in the modified graphene oxide flame retardant synergist. Simultaneously, the formed amide bonds are strong covalent bonds with excellent thermal stability. With strong qualitative and hydrolysis resistance and resistance to desorption during processing or use, it can effectively improve the density and stability of functional groups on the surface of graphene oxide. Molybdate reduces heat and combustible gas release by promoting char formation, increasing residual char, and forming a dense char layer, thereby reducing smoke generated during material combustion and improving the flame retardant properties of the material. Based on electrostatic interaction, molybdate ions and amidated graphene oxide attract each other and are firmly adsorbed by strong Coulomb electrostatic attraction, thus preparing a modified graphene oxide flame retardant synergist. This avoids the problems of easy migration and poor dispersibility of molybdate in traditional physical mixing, allowing molybdate ions to be evenly distributed on the material surface. Through chemical bonding, graphene oxide and molybdate produce a "nano-synergistic effect", which can significantly improve the limiting oxygen index of polyolefin materials at extremely low addition levels and achieve the V-0 rating of UL-94. It can also significantly reduce the heat release rate, total heat release, and smoke generation during combustion, achieving the goal of high-efficiency flame retardancy. The flame retardant mechanism of the modified graphene oxide flame retardant synergist is specifically reflected in the synergy of catalytic char formation and char layer enhancement. Molybdates can efficiently catalyze dehydration, crosslinking, and aromatization reactions of polymer molecular chains within the polymer thermal decomposition temperature range, significantly improving the solid-phase char formation rate. Graphene oxide itself can serve as a char formation template and can be reduced at high temperatures. Its sheet-like structure can act as physical crosslinking points and a nanoframework, permeating the amorphous carbon catalyzed by molybdates. The combination of the two forms a stable carbon layer structure—graphene oxide acts as the framework, providing support and strength; the catalyzed amorphous carbon fills the space between them. This carbon layer is denser, more continuous, stronger, and has better thermal stability, effectively isolating heat and gas transfer. The graphene oxide nanosheets uniformly dispersed in the matrix migrate to the polymer surface during combustion, forming an insulating layer that effectively delays the escape of internal combustible gases and the penetration of external oxygen, and blocks the inward transfer of heat. Some molybdenum compounds may capture highly reactive H+ in the gas phase.﹢ and OH - Free radicals interrupt the chain reaction of combustion. At the same time, the inert gas released by the decomposition of molybdate can dilute the concentration of combustible gas. Molybdenum compounds are recognized as highly efficient smoke suppressants. On the one hand, they catalyze oxidation, promoting the conversion of soot precursors into CO and CO2, reducing soot generation. On the other hand, the dense carbon layer physically blocks the release of internal soot particles, thereby achieving dual smoke suppression in both the gas phase and condensed phase, and completely eliminating the risk of secondary ignition caused by the melting and dripping of polyolefins. The two-dimensional nanosheet structure of graphene oxide, after being well dispersed in the matrix, can serve as a natural nano-reinforcement. Under the premise of obtaining the same flame retardant rating, it can better maintain the tensile strength, toughness and other mechanical properties of the matrix material than the traditional high-filler flame retardant system. Moreover, the modified graphene oxide flame retardant synergist is halogen-free, meets environmental protection requirements, has good compatibility with the polymer matrix, is not easy to migrate and precipitate, has excellent processing fluidity, and is easy to implement in production. The modified graphene oxide flame retardant synergist of this invention produces multiple synergistic effects at the nanoscale, ultimately achieving efficient, environmentally friendly and comprehensive flame retardant protection.

[0028] Halogen-free flame-retardant polypropylene materials include polypropylene (PP), toughening agents, antioxidants, light stabilizers, halogen-free flame retardants, and modified graphene oxide flame retardant synergists. The modified graphene oxide flame retardant synergist is prepared from graphene oxide (GO), anhydrous sulfoxide, an amine compound H2N-R-NH2 containing at least two terminal primary amino groups, and molybdate. Anhydrous sulfoxide reacts with the carboxyl groups on the surface of graphene oxide to obtain nucleophilically substituted acyl-chlorinated graphene oxide GO-COCl. The acyl-chlorinated graphene oxide GO-COCl forms stable amide bonds with the amine compound through a substitution reaction. The molybdate ions of the molybdate and the amidated graphene oxide are attracted and firmly adsorbed by strong Coulomb electrostatic attraction, thus preparing the modified graphene oxide flame retardant synergist. Ultimately, this achieves efficient, environmentally friendly, and comprehensive flame-retardant protection, significantly improving the flame-retardant performance of the material. In the halogen-free flame-retardant polypropylene material system proposed in this invention, modified graphene oxide flame retardant synergist enhances the flame-retardant properties of polypropylene. During combustion, graphene oxide forms a dense char layer, preventing heat propagation and reducing the flame spread rate. It isolates oxygen and can rapidly weaken the fire source by absorbing heat, further enhancing the self-extinguishing property of polypropylene. Simultaneously, it improves the thermal stability and high-temperature resistance of polypropylene. The structure of graphene oxide allows polypropylene to maintain structural stability, reducing the risk of thermal degradation and molecular chain breakage, significantly extending the service life of polypropylene materials and ensuring their long-term stability at high temperatures. Furthermore, the two-dimensional structure of graphene oxide itself provides enhanced mechanical support, effectively improving the rigidity and strength of polypropylene materials. The halogen-free flame-retardant polypropylene material provided by this invention possesses excellent flame-retardant and mechanical properties, as well as good processing performance and impact resistance. Moreover, the halogen-free flame-retardant polypropylene material proposed in this invention does not contain halogens, making it safe and environmentally friendly.

[0029] Furthermore, graphene oxide was prepared by a modified Hummers method, and the prepared graphene oxide contained 10%-20% carboxyl groups.

[0030] Graphene oxide (GO) can be prepared using the Hummers process. The traditional Hummers process involves oxidizing graphite with strong oxidants such as concentrated sulfuric acid or potassium permanganate, a classic chemical method for preparing GO. By modifying the Hummers process, increasing the proportion and concentration of potassium permanganate or sodium nitrate, and extending the oxidation time during the high-temperature reaction stage, the carboxyl group content in GO can be increased to 10%-20%. Understandably, more carboxyl groups mean that more sites on the graphene oxide surface can be converted to -COCl, thereby enabling the grafting of amine compounds to achieve amidation, resulting in higher functionalization efficiency and improved carboxyl group electrochemical properties. Negatively charged GO generates stronger electrostatic repulsion, making GO more stable in aqueous solutions, less prone to aggregation, and improving the dispersibility of graphene oxide. On the other hand, excessive oxidation produces more carboxyl groups, which often severely damages the SP² lattice structure of graphene oxide. A large number of carboxyl groups enhance the electrostatic repulsion and hydration between GO sheets, hindering their orderly stacking, resulting in a porous and loose film with significantly reduced mechanical properties. Therefore, a carboxyl group content of 10%-20% in graphene oxide is necessary for its stable dispersion in water and polar solvents, ensuring good adsorption of positively charged molecules and preventing severe damage to the graphene oxide structure itself.

[0031] In some embodiments, graphite, potassium persulfate (K2S2O8), and phosphorus pentoxide (P2O5) are weighed and slowly added to concentrated sulfuric acid, reacting at 80°C for 4-6 hours. After the reaction, the mixture is cooled, washed, and dried to obtain pre-oxidized graphite. Low-temperature reaction: Pre-oxidized graphite is mixed with concentrated sulfuric acid in an ice-water bath, and potassium permanganate (KMnO4) is slowly added in batches under vigorous stirring. The system temperature must be strictly controlled below 20°C, and stirring is typically performed at this temperature for 0.5-2 hours. Medium-temperature reaction: The ice bath is removed, and the system temperature is raised to 35-40°C, continuing the stirring reaction for 0.5-4 hours. High-temperature reaction: A large amount of deionized water is slowly added under stirring. After adding water, the temperature is raised to 90-98°C, and the reaction is maintained for 15-60 minutes. Subsequently, hydrogen peroxide (H2O2) is slowly added dropwise until the solution color changes from dark brown to bright yellow. Acid washing: The product is washed with dilute hydrochloric acid (approximately 5%) to remove residual metal ions (such as Mn²⁺). + Washing: Wash repeatedly with a large amount of deionized water by centrifugation or vacuum filtration until the pH of the supernatant is close to neutral. Drying: Dry the final product in a vacuum oven at 40-60℃ to obtain graphene oxide solid with a carboxyl content of 10%-20%.

[0032] The carboxyl content was determined using NaHCO3 (pH=6.4) (standardized method of IEC TS 62607-6-13:2020). After the GO sample reacted with excess NaHCO3, the remaining alkali was back-titrated with hydrochloric acid, and the difference yielded a carboxyl content of 10%-20% on the graphene oxide surface.

[0033] After the amidation reaction, the amidated GO was characterized by infrared absorption spectroscopy. The infrared spectrum showed an amide I band (approximately 1650 cm⁻¹). - ¹, C=O stretching vibration) and amide II band (approximately 1550 cm) - ¹, NH bending and CN stretching coupling), while the original carboxyl group's C=O peak (approximately 1720 cm⁻¹) - ¹) It may weaken or disappear.

[0034] Zeta potentials were measured by dispersing amidated GO in buffer solutions of different pH values. Under acidic conditions (pH < 5, corresponding to acetate-sodium acetate buffer adjustment), the primary amine group (-NH2) was protonated to –NH3. + Its Zeta potential is positive, indicating that the primary amine group has been successfully protonated and its surface is positively charged, which helps to improve the electrostatic stability of colloids or nanoparticles in solution.

[0035] In some embodiments, the carboxyl content in graphene oxide is preferably 15%-20%.

[0036] Furthermore, in the amine compound H2N-R-NH2 containing at least two terminal primary amino groups, -R- is a divalent organic group used to connect the amide bond and the primary amino group, and the -R- group is at least one of the following: straight-chain alkyl, polyether segment, polyamine segment containing a secondary amine structure, aromatic structure, branched structure, and cyclic structure.

[0037] In this embodiment, at least two amine compounds with terminal primary amino groups, H2N-R-NH2, are combined with GO through a substitution reaction. The modified graphene oxide flame retardant synergist includes at least one amide bond -CONH-RN- linked to a terminal primary amino group. -R- is a divalent organic group and is the core structural unit connecting the amide bond and the primary amino group. The -R- group can regulate the affinity between the amide bond and the primary amino group. Its structural polarity determines the interfacial compatibility, dispersion stability and reactivity of graphene oxide. A suitable -R- group can promote char formation during combustion and improve flame retardant synergy. Branched or large-volume -R- groups can provide steric hindrance, hinder π-π interactions and prevent GO sheets from re-stacking.

[0038] In some embodiments, the -R- group is preferably a straight-chain alkyl group.

[0039] Furthermore, the straight-chain alkyl group is -CH2-CH2-, -(CH2)3-, -(CH2)4-, -(CH2)6-, -(CH2)8-, and -(CH2). 10 At least one of the following; containing a polyether segment of -(CH2-CH2-O). 2-5 At least one of - and -CH2-CH(CH3)-O-; the polyamine segment containing the secondary amine structure is at least one of the DETA backbone, TETA backbone, TEPA backbone, PEPA backbone, and BAPA backbone; the aromatic structure is at least one of phenylene, benzyl, biaryl ether, and naphthalene ring structure; the branched structure is at least one of branched propyl, tertiary carbon, and neopentyl type structure; the cyclic structure is -C6H 10 - At least one of the isophorone structure and piperazine structure.

[0040] In this embodiment, the linear alkyl group exhibits good compatibility with the polymer matrix. Its long chain can increase steric hindrance, prevent graphene oxide agglomeration, improve GO dispersibility, and enhance the interfacial bonding force between the filler and the matrix. Furthermore, the alkyl chain can promote char formation at high temperatures, improving the flame retardant performance of the modified graphene oxide flame retardant synergist. The polyether-containing segments are flexible, increasing the degree of freedom of molecular motion and participating in the formation of cross-linking networks. This imparts better flexibility and processability to the modified GO, allowing the modified graphene oxide flame retardant synergist to form a uniform dispersion in the resin matrix, preventing phase separation and improving the mechanical properties of the material. The aromatic structure has high rigidity and thermal stability; the aromatic rings are not easily decomposed at high temperatures, delaying GO structural damage and allowing for the formation of... The stable char layer forms a dense char layer during combustion to block heat transfer. It has π-π interactions with the sp² structure on the GO surface, enhancing interfacial bonding and improving the mechanical properties of the material. The branched structure has multiple branch ends that can retain primary amines, increasing reaction sites and the number of amide bonds, thereby increasing the amount of binding with molybdate and improving the flame retardant performance of the modified graphene oxide flame retardant synergist. The cyclic structure has high thermal stability and can participate in char formation during combustion. The piperazine ring decomposes at high temperatures to produce non-combustible gases, diluting oxygen and combustible gases. The nitrogen-containing heterocycles can release inert gases such as nitrogen at high temperatures, realizing the flame retardant mechanism of char layer formation + gas phase flame retardancy, thus improving the flame retardant performance of the modified graphene oxide flame retardant synergist.

[0041] In some embodiments, the straight-chain alkyl group is preferably -CH2-CH2-.

[0042] In some embodiments, the aromatic structure is preferably phenylene.

[0043] In some embodiments, the amine compound H2N-R-NH2 containing at least two terminal primary amino groups is preferably ethylenediamine.

[0044] In some embodiments, the amine compound H2N-R-NH2 containing at least two terminal primary amino groups is preferably hexamethylenediamine.

[0045] In some embodiments, the amine compound H2N-R-NH2 containing at least two terminal primary amino groups is preferably polyetheramine D-230.

[0046] In some embodiments, the amine compound H2N-R-NH2 containing at least two terminal primary amino groups is preferably diethylenetriamine.

[0047] In some embodiments, the amine compound H2N-R-NH2 containing at least two terminal primary amino groups is preferably p-phenylenediamine.

[0048] In some embodiments, the amine compound H2N-R-NH2 containing at least two terminal primary amino groups is preferably 1,4-bis(3-aminopropyl)piperazine.

[0049] Furthermore, after dissolution, the molybdate forms a molybdate anion, and the molybdate is at least one of monomeric molybdate molybdate, polymolybdate molybdate, and heteropolymolybdate molybdate.

[0050] Molybdate, after dissolution, becomes a molybdate anion, which can combine with amidated graphene oxide (GO) through electrostatic interactions, achieving mild and spontaneous assembly. This "anchors" inorganic flame retardant elements to the high specific surface area of ​​GO. Molybdate is a highly efficient smoke suppressant; during combustion, GO sheets form a dense char layer, effectively isolating heat and oxygen and inhibiting the release of smoke. Molybdate can significantly reduce the generation of toxic fumes. The combination of the two through electrostatic interactions requires no additional substances, thus improving the flame retardant effect of the modified graphene oxide flame retardant synergist.

[0051] In some embodiments, molybdate is preferably monomeric molybdate molybdate.

[0052] Further, the monomeric molybdate molybdate is at least one of sodium molybdate (Na2MoO4·2H2O), potassium molybdate (K2MoO4), ammonium molybdate ((NH4)2MoO4), lithium molybdate (Li2MoO4), and cesium molybdate (Cs2MoO4); the polymolybdate molybdate is at least one of ammonium hexamolybdate, sodium hexamolybdate, ammonium heptamolybdate, sodium heptamolybdate, potassium heptamolybdate, ammonium octamolybdate, and sodium octamolybdate; and the heteropolymolybdate molybdate is phosphomolybdic acid (H3PMo). 12 O 40 ·xH2O), ammonium phosphomolybdate ((NH4)3PMo 12 O 40 Sodium phosphomolybdate (Na3PMo) 12 O 40 ) and sodium molybdate (Na4SiMo) 12 O 40At least one of the following.

[0053] In this embodiment, the monomeric molybdate molybdate has a small molecular size, high charge density, and simple structure. It is highly soluble in water and readily binds tightly to the amino groups on the GO surface to achieve strong electrostatic adsorption, making it difficult to detach. Furthermore, the preparation process is simple and convenient. The polymolybdate molybdate contains multiple Mo atoms, resulting in high molybdenum loading efficiency in a single anion. This allows for higher molybdenum loading with less material. It may decompose at high temperatures, providing more transient catalytic sites and promoting rapid char formation. The heteropolymolybdate molybdate introduces secondary elements such as P and N into the simple molybdate structure, enabling synergistic flame retardancy of multiple elements such as Mo / P / N. It has a stable structure and redox properties, significantly inhibiting the toxic fumes generated by polymer combustion and improving flame retardant efficiency.

[0054] In some embodiments, the monomeric molybdate molybdate is preferably sodium molybdate.

[0055] In some embodiments, polymolybdate molybdate is preferably ammonium hexamolybdate.

[0056] In some embodiments, heteropolymolybdate molybdate is preferably phosphomolybdic acid.

[0057] Furthermore, the modified graphene oxide flame retardant synergist structure includes at least one... , Where x is the number of molybdenum atoms in one molecule of molybdate, and y is the number of oxygen atoms in one molecule of molybdate.

[0058] In this embodiment, the modified graphene oxide flame retardant synergist structure includes at least one structure in which protonated amidated graphene oxide and molybdate anion are mutually adsorbed through electrostatic interaction. The modified graphene oxide flame retardant synergist is thus prepared, achieving a "nano-synergistic effect" between graphene oxide and molybdate, allowing molybdate ions to be uniformly distributed on the material surface, and working together with the two-dimensional nanosheet structure of graphene oxide to improve the flame retardant effect.

[0059] In some embodiments, when the monomeric molybdate molybdate is preferably sodium molybdate, x is 1 and y is 4.

[0060] Furthermore, a method for preparing the modified graphene oxide flame retardant synergist as described above includes the following steps: (1) Graphene oxide was dispersed in anhydrous thionyl chloride, and dimethylformamide (DMF) was added as a catalyst. The mixture was refluxed and centrifuged to obtain GO-COCl. (2) Disperse GO-COCl in an anhydrous organic solvent, add an amine compound H2N-R-NH2 containing at least two terminal primary amino groups, and react under nitrogen protection to obtain amidated GO; (3) Disperse amidated GO in deionized water or acidic buffer solution with a pH of 3-6, and sonicate to form a uniform dispersion to obtain a protonated and positively charged amidated GO dispersion. (4) Dissolve molybdate in an acidic water / low alcohol system buffer solution of the same pH, and slowly add it dropwise to a protonated positively charged amidated GO dispersion. The reaction is carried out by electrostatic interaction. After stirring, centrifugation, washing, and freeze drying, the modified graphene oxide flame retardant synergist is obtained.

[0061] In some embodiments, the acidic buffer solution is preferably an acetate-sodium acetate buffer solution with a pH of 4.

[0062] Furthermore, the anhydrous organic solvent is at least one of alcohols, aromatic hydrocarbons, aliphatic hydrocarbons, alicyclic hydrocarbons, ethers, and ketones, and the acidic water / lower alcohol system buffer is a mixed solution of H2O and at least one lower saturated monohydric alcohol.

[0063] Anhydrous organic solvents possess excellent solubility and stability, avoiding interference from water in chemical reactions and improving reaction efficiency and selectivity. The acidic water / lower alcohol buffer system enables controllable, uniform, and stable electrostatic self-assembly between molybdate anions and positively charged amidated graphene oxide. At pH 3-6, negatively charged molybdate ions can be stably obtained. The acidic water / lower alcohol buffer system can resist local pH fluctuations that may be caused by the addition of amidated graphene oxide, always maintaining the optimal reaction conditions of pH 3-6 and avoiding problems caused by pH changes.

[0064] In some embodiments, the anhydrous organic solvent is preferably anhydrous tetrahydrofuran.

[0065] In some embodiments, the pH of the acidic water / lower alcohol system buffer is preferably pH=4.

[0066] In some embodiments, the acidic water / lower alcohol system buffer is a mixed solution of H2O and methanol.

[0067] Furthermore, the raw materials of the halogen-free flame-retardant polypropylene material, by weight, include: 60-80 parts of polypropylene (PP), 4-8 parts of toughening agent, 15-25 parts of halogen-free flame retardant, 1-1.5 parts of antioxidant, 2-3 parts of light stabilizer, and 6-9 parts of modified graphene oxide flame retardant synergist.

[0068] Increasing the amount of modified graphene oxide flame retardant synergist can further improve the mechanical and flame retardant properties of halogen-free flame retardant thermoplastic polyolefin materials.

[0069] Furthermore, the polypropylene is a copolymer polypropylene with a melt index (230℃, 2.16kg) of 3-50g / 10min.

[0070] Polypropylene has high tensile strength and rigidity, strong resistance to chemical corrosion, and good bending and tensile strength, giving it a significant advantage in applications requiring high strength.

[0071] In some embodiments, the polypropylene is preferably homopolymer polypropylene with a melt index (230°C, 2.16 kg) of 45 g / 10 min.

[0072] Furthermore, the toughening agent is at least one of ethylene-butene copolymer, ethylene-octene copolymer, ultra-high molecular weight polyethylene, and nano-silicon.

[0073] Toughening agents in polypropylene systems can improve the impact toughness of polypropylene materials, significantly improve the impact resistance of polypropylene, and reduce brittleness. Especially in low-temperature environments, they can significantly improve impact strength. Their molecular chains are flexible and can well wet the components, allowing the components to be more evenly dispersed and reducing agglomeration.

[0074] In some embodiments, the toughening agent is preferably an ethylene-octene copolymer.

[0075] Furthermore, the halogen-free flame retardant is at least one of ammonium polyphosphate, piperazine pyrophosphate, melamine polyphosphate, melamine cyanurate, aluminum hypophosphite, divinyl aluminum hypophosphite, and zinc borate.

[0076] Phosphorus-based flame retardants function in the condensed phase, catalyzing the dehydration of polymers into char, forming a dense char layer with heat and oxygen insulation properties, thus effectively inhibiting combustion. Ammonium polyphosphate, as a halogen-free flame retardant, has significant advantages in halogen-free flame retardancy and environmental friendliness, and can effectively improve the flame retardant performance of materials by catalytic carbonization and the formation of a protective layer. During combustion, ammonium polyphosphate decomposes and releases acidic substances, which can promote the charring reaction on the material surface, forming a stable char layer that effectively isolates the oxygen supply. Simultaneously, it also reduces smoke production and the release of toxic gases.

[0077] In some embodiments, the halogen-free flame retardant is preferably ammonium polyphosphate.

[0078] Further, the antioxidant is at least one of 1010 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]), 1076, 168 (tris[2,4-di-tert-butylphenyl]phosphite), and 626.

[0079] Antioxidants effectively reduce the oxidation rate of materials during processing and use by capturing free radicals, decomposing peroxides, and complexing metal ions. This slows down or prevents oxidation or auto-oxidation processes, protects plastic products from oxidation, and extends their service life.

[0080] In some embodiments, the antioxidant is preferably antioxidant 1010.

[0081] Furthermore, the light stabilizer is at least one of non-alkaline HALS, low-alkaline HALS, high molecular weight HALS, Tinuvin 326, Tinuvin NOR 371, and 329.

[0082] Light stabilizers prevent photodegradation caused by ultraviolet (UV) radiation, delaying fading, embrittlement, and cracking, and improving the weather resistance and service life of materials. Through UV absorption, free radical capture, and antioxidant functions, they make materials more stable when exposed to sunlight. By absorbing or scattering UV radiation, they reduce the penetration of UV rays and their damage to the molecular structure of materials, thereby preventing material aging and fading. They improve the photoaging performance of polymer materials under light conditions, especially under the action of ultraviolet (UV) radiation, by protecting the molecular structure of materials and reducing or delaying the degradation process.

[0083] In some embodiments, the light stabilizer is preferably Tinuvin NOR 371.

[0084] To address the aforementioned issues, this invention also proposes a method for preparing halogen-free flame-retardant polypropylene materials, comprising the following steps: preparing a modified graphene oxide flame-retardant synergist using graphene oxide (GO), anhydrous sulfoxide, an amine compound H2N-R-NH2 containing at least two terminal primary amino groups, and molybdate. Polypropylene, toughening agent, halogen-free flame retardant, antioxidant, light stabilizer and modified graphene oxide flame retardant synergist are mixed evenly, and then subjected to intensive mixing, extrusion and granulation to obtain granules. The granules are then dried to obtain the halogen-free flame retardant polypropylene material as described above.

[0085] In some embodiments, mixing is performed in an internal mixer.

[0086] In some embodiments, the mixing is carried out in a twin-screw extruder.

[0087] In some embodiments, the temperature of the twin-screw extruder is 160°C in zone 1, 160°C in zone 2, 170°C in zone 3, 170°C in zone 4, 170°C in zone 5, 180°C in zone 6, 190°C in zone 7, and 190°C in zone 8, and the rotation speed is 150 rpm.

[0088] The following specific embodiments and data explain the content of the present invention.

[0089] Information on the raw materials involved in the specific implementation method is shown in Table 1: Table 1 Information on raw materials for the examples and comparative examples Information on the raw materials involved in the specific implementation method is shown in Table 1:

[0090] Example 1: 10.0 g of graphene oxide (GO) with a carboxyl content of 10%-20% was dispersed in 500 mL of anhydrous thionyl chloride (SOCl2), and 5.0 mL of anhydrous DMF was added as a catalyst. The reaction was carried out under nitrogen protection and reflux at 75±5 °C. After centrifugation, the mixture was washed with anhydrous THF and dried under vacuum at 40 °C to obtain GO-COCl. All of the GO-COCl was added to 200 mL of anhydrous THF and ultrasonically dispersed. Then, 150 mL of ethylenediamine (EDA) was slowly added, and the reaction was carried out under nitrogen protection and reflux. After centrifugation, the mixture was washed twice with anhydrous ethanol and three times with deionized water, and dried under vacuum at 45 °C to obtain amidated GO. 9.0 g of amidated GO was dispersed in 1800 mL of pH 10 ... In a 4.5 mL acetate-sodium acetate buffer solution, the GO was ultrasonically dispersed for 45 minutes to obtain a positively charged amidated GO dispersion. Separately, 12.0 g of sodium molybdate dihydrate (Na2MoO4·2H2O) was dissolved in 60 mL of deionized water, and then 60 mL of methanol was added to prepare a 120 mL water / methanol (1:1) sodium molybdate solution. This solution was slowly added dropwise to the above positively charged GO dispersion at room temperature (dropping rate of about 5-6 mL / min). After the addition was complete, the mixture was stirred for 3 hours. The reaction product was centrifuged, washed three times with deionized water, washed twice with anhydrous ethanol, and finally freeze-dried to obtain modified graphene oxide flame retardant synergist 1. 60 parts PP, 4 parts toughening agent, 15 parts halogen-free flame retardant, 5 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free high flame retardant and impact-resistant polypropylene material is obtained.

[0091] Example 2: The preparation method is the same as in Example 1, except that: 73 parts PP, 6 parts toughening agent, 23 parts halogen-free flame retardant, 9 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80°C, a halogen-free high flame retardant and impact-resistant polypropylene material was obtained.

[0092] Example 3: The preparation method is the same as in Example 1, except that: 80 parts PP, 5 parts toughening agent, 18 parts halogen-free flame retardant, 6 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free high flame retardant and impact-resistant polypropylene material is obtained.

[0093] Example 4: The preparation method is the same as in Example 1, except that: 65 parts PP, 8 parts toughening agent, 25 parts halogen-free flame retardant, 10 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer were mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free high flame retardant and impact-resistant polypropylene material was obtained.

[0094] Example 5: The preparation method is the same as in Example 1, except that: 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80°C, a halogen-free high flame retardant and impact-resistant polypropylene material was obtained.

[0095] Example 6: The preparation method is the same as in Example 1, except that; Lithium molybdate was used to prepare modified graphene oxide flame retardant synergist 2. 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free high flame retardant and impact-resistant polypropylene material is obtained.

[0096] Example 7: The preparation method is the same as in Example 1, except that; The molybdate is ammonium hexamolybdate, which was used to prepare a modified graphene oxide flame retardant synergist 3; 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80°C, a halogen-free high flame retardant and impact-resistant polypropylene material was obtained.

[0097] Example 8: The preparation method is the same as in Example 1, except that; The molybdate is sodium octamolate, and modified graphene oxide flame retardant synergist 4 is prepared. 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80°C, a halogen-free high flame retardant and impact-resistant polypropylene material was obtained.

[0098] Example 9: The preparation method is the same as in Example 1, except that; Molybdate is phosphomolybdic acid, and modified graphene oxide flame retardant synergist 5 was prepared; 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer were mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free high flame retardant and impact-resistant polypropylene material was obtained.

[0099] Example 10: The preparation method is the same as in Example 1, except that; The molybdate is sodium phosphomolybdate, which was used to prepare modified graphene oxide flame retardant synergist 6; 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free high flame retardant and impact-resistant polypropylene material is obtained.

[0100] Example 11: The preparation method is the same as in Example 1, except that; H2N-R-NH2, an amine compound containing at least two terminal primary amino groups, is hexamethylenediamine, which was used to prepare modified graphene oxide flame retardant synergist 7. 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80°C, a halogen-free high flame retardant and impact-resistant polypropylene material was obtained.

[0101] Example 12: The preparation method is the same as in Example 1, except that; An amine compound containing at least two terminal primary amino groups, H2N-R-NH2, is a polyether amine D-230, which was used to prepare a modified graphene oxide flame retardant synergist 8. 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free high flame retardant and impact-resistant polypropylene material is obtained.

[0102] Example 13: The preparation method is the same as in Example 1, except that; An amine compound containing at least two terminal primary amino groups, H2N-R-NH2, is diethylenetriamine, which was used to prepare a modified graphene oxide flame retardant synergist 9. 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80°C, a halogen-free high flame retardant and impact-resistant polypropylene material was obtained.

[0103] Example 14: The preparation method is the same as in Example 1, except that; H2N-R-NH2, an amine compound containing at least two terminal primary amino groups, is p-phenylenediamine, and modified graphene oxide flame retardant synergist 10 was prepared. 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free high flame retardant and impact-resistant polypropylene material is obtained.

[0104] Example 15: The preparation method is the same as in Example 1, except that; An amine compound containing at least two terminal primary amino groups, H2N-R-NH2, is 1,4-bis(3-aminopropyl)piperazine, which was used to prepare a modified graphene oxide flame retardant synergist 11. 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80°C, a halogen-free high flame retardant and impact-resistant polypropylene material was obtained.

[0105] Comparative Example 1: The preparation method is the same as in Example 1, except that: 50 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free flame retardant polypropylene material is obtained.

[0106] Comparative Example 2: The preparation method is the same as in Example 1, except that: 90 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free flame retardant polypropylene material is obtained.

[0107] Comparative Example 3: The preparation method is the same as in Example 1, except that: 70 parts PP, 2 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free flame retardant polypropylene material is obtained.

[0108] Comparative Example 4: The preparation method is the same as in Example 1, except that: 70 parts PP, 10 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free flame retardant polypropylene material is obtained.

[0109] Comparative Example 5: The preparation method is the same as in Example 1, except that: 70 parts PP, 7 parts toughening agent, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free flame retardant polypropylene material is obtained.

[0110] Comparative Example 6: The preparation method is the same as in Example 1, except that: 70 parts PP, 7 parts toughening agent, 10 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free flame retardant polypropylene material is obtained.

[0111] Comparative Example 7: The preparation method is the same as in Example 1, except that: 70 parts PP, 7 parts toughening agent, 35 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free flame retardant polypropylene material is obtained.

[0112] Comparative Example 8: 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180°C to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80°C, a halogen-free flame retardant polypropylene material is obtained.

[0113] Comparative Example 9: The preparation method is the same as in Example 1, except that: 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 2 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free flame retardant polypropylene material is obtained.

[0114] Comparative Example 10: The preparation method is the same as in Example 1, except that: 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 15 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free flame retardant polypropylene material is obtained.

[0115] Comparative Example 11: Graphene oxide with a carboxyl content of 10%-20% was added to dimethylformamide, and after sonication, ethylenediamine, an amine compound containing at least two terminal primary amino groups, was added. The mixture was then subjected to a condensation reaction at 160°C in an autoclave to obtain nitrided graphene (N-GO). Graphene oxide (N-GO) was added to deionized water, and after sonication, sodium molybdate was added. The mixture was stirred, centrifuged, and washed to obtain modified graphene oxide flame retardant synergist 12. 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free flame retardant polypropylene material is obtained.

[0116] Comparative Example 12: Graphene oxide with a carboxyl content of 10%-20% was subjected to a substitution reaction and an acyl chloride reaction with anhydrous thionyl chloride to convert the carboxyl groups on the surface of graphene oxide into more active acyl chloride groups, resulting in GO-COCl. GO-COCl was then reacted with sodium molybdate, and the mixture was stirred, centrifuged, and washed to obtain modified graphene oxide flame retardant synergist 13. 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free flame retardant polypropylene material is obtained.

[0117] Comparative Example 13: Graphene oxide with a carboxyl content of 10%-20% is subjected to a substitution reaction and an acyl chloride reaction with anhydrous thionyl chloride to convert the carboxyl groups on the surface of graphene oxide into more reactive acyl chloride groups, resulting in GO-COCl. GO-COCl is then subjected to a substitution reaction and an amidation reaction with ethylenediamine, an amine compound containing at least two terminal primary amino groups, to obtain amidated GO. The amidated GO is then ultrasonicated and washed to obtain modified graphene oxide flame retardant synergist 14. 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist 14, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free flame retardant polypropylene material is obtained.

[0118] Comparative Example 14: Graphene oxide with a carboxyl content of 10%-20% was subjected to a substitution reaction and an acyl chloride reaction with anhydrous thionyl chloride to convert the carboxyl groups on the surface of graphene oxide into more reactive acyl chloride groups, resulting in GO-COCl. GO-COCl was then subjected to a substitution reaction and an amidation reaction with n-butylamine to obtain amidated GO. The amidated GO was dispersed in an acetate-sodium acetate buffer solution, and an aqueous / methanol solution of sodium molybdate was slowly added dropwise to the amidated GO dispersion to carry out the reaction. After stirring, centrifugation, washing, and freeze-drying, modified graphene oxide flame retardant synergist 15 was obtained. 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free flame retardant polypropylene material is obtained.

[0119] Comparative Example 15: Commercially available graphene oxide was added to dimethylformamide, and after sonication, ethylenediamine, an amine compound containing at least two terminal primary amino groups, was added. The mixture was then subjected to a condensation reaction in an autoclave at 160°C to obtain nitrided graphene (N-GO). The nitrided graphene (N-GO) was added to deionized water, and after sonication, sodium molybdate was added. The mixture was stirred, centrifuged, and washed to obtain modified graphene oxide flame retardant synergist 16. 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts modified graphene oxide flame retardant synergist 16, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free flame retardant polypropylene material is obtained.

[0120] Comparative Example 16: 70 parts PP, 7 parts toughening agent, 20 parts halogen-free flame retardant, 8 parts organic montmorillonite, 1 part antioxidant, and 3 parts light stabilizer are mixed evenly and granulated by twin-screw extrusion at 180℃ to obtain a halogen-free flame retardant polypropylene material preform. After drying at 80℃, a halogen-free flame retardant polypropylene material is obtained.

[0121] Table 2 summarizes the components and key preparation variables of Examples 1-15 and Comparative Examples 1-16.

[0122] Table 2 shows the components of Examples 1-15 and Comparative Examples 1-16 of the present invention.

[0123]

[0124] Samples of the aforementioned cable materials were prepared and subjected to tests for tensile strength, elongation at break, limiting oxygen index, UL94 rating, vertical burning drip test, and impact strength. The test methods and standards are as follows: 1. Tensile properties: Tested according to GB / T 1040-2006 standard.

[0125] 2. Limiting oxygen index: Tested according to GB / T 2406-2009 standard.

[0126] 3. UL94 rating: Tested according to UL94-2013 standard.

[0127] 4. Impact strength: Tested according to GB / T 1843-2008 standard.

[0128] The test results are recorded in Table 3 below.

[0129] Table 3 Performance test table of Examples 1-15 and Comparative Examples 1-16 of the present invention

[0130] As can be seen from the test results above, the halogen-free flame-retardant polypropylene material prepared by this invention has excellent flame-retardant and mechanical properties. The flame-retardant rating of the halogen-free flame-retardant polypropylene materials prepared in Examples 1-15 is V0, the limiting oxygen index is greater than 28.5, the tensile strength of Examples 1-15 is 22.5MPa-25MPa, the elongation at break is 88%-152%, and the impact strength is 412-485J / m. Furthermore, no dripping phenomenon occurred during the combustion process in Examples 1-15. The halogen-free flame-retardant polypropylene material prepared by this invention has excellent flame-retardant and physical-mechanical properties, and can prevent the burning material from dripping during the combustion process. The halogen-free flame-retardant polypropylene material prepared by this invention does not contain halogens, thus meeting the requirements of environmental protection and safety.

[0131] In Examples 1-5, the modified graphene oxide flame retardant synergist 1 of the present invention was added, and the added halogen-free flame retardant was ammonium polyphosphate. The flame retardant ratings of Examples 1-5 were all V0, with limiting oxygen indexes of 28.5-33, exhibiting excellent flame retardancy, high flame retardant efficiency, and superior mechanical properties. The combined action of ammonium polyphosphate and the modified graphene oxide flame retardant synergist can improve the flame retardancy of the prepared halogen-free flame-retardant polypropylene material.

[0132] Example 6 added modified graphene oxide flame retardant synergist 2; Example 7 added modified graphene oxide flame retardant synergist 3, in which the molybdate ion is hexamolybdate and the number of molybdenum atoms is greater than that in Examples 1-6; Example 8 added modified graphene oxide flame retardant synergist 4, in which the molybdate ion is octamolybdate and the number of molybdenum atoms is greater than that in Examples 1-7; Example 9 added modified graphene oxide flame retardant synergist 5, which is phosphomolybdic acid, with a greater number of molybdenum atoms than that in Examples 1-8, and also includes phosphorus; Example 10 added modified graphene oxide flame retardant synergist 6, which is sodium phosphomolybdate, with the same number of molybdenum atoms as in Example 9. Example 11 added modified graphene oxide flame retardant synergist 7, which utilizes hexamethylenediamine as an intermediate linking graphene oxide and molybdate. The hexamethylenediamine in modified graphene oxide flame retardant synergist 7 has a longer chain segment than the ethylenediamine in modified graphene oxide flame retardant synergist 2 in Example 6. Example 12 added modified graphene oxide flame retardant synergist 8, which contains at least two terminal primary amino groups of an amine compound called polyetheramine D-230. The main chain of polyetheramine D-230 has multiple repeating propylene oxide units and has a longer chain segment than the hexamethylenediamine in Example 11. Example 13 added modified graphene oxide flame retardant synergist 9, which contains at least two terminal primary amino groups of an amine compound called diethylenetriamine. The diethylenetriamine contains 2 With one primary amino group and one secondary amino group, it has more binding sites. In Example 14, modified graphene oxide flame retardant synergist 10 was added. Modified graphene oxide flame retardant synergist 10 contains at least two terminal primary amino groups of the amine compound p-phenylenediamine, which has an aromatic structure. During combustion, the benzene ring is rich in carbon elements. Its high carbon content forms a dense char layer during combustion. This char layer can effectively isolate the transfer of heat and oxygen, thereby inhibiting the further spread of combustion and improving flame retardancy. In Example 15, modified graphene oxide flame retardant synergist 11 was added. Modified graphene oxide flame retardant synergist 11 contains at least two terminal primary amino groups of the amine compound 1,4-bis(3-aminopropyl)piperazine. Its structure is based on the piperazine ring, with a 3-aminopropyl (-CH2CH2CH2NH2) substituent attached to the nitrogen atoms at the 1 and 4 positions. When used together with ammonium polyphosphate as a flame retardant, it can improve the flame retardancy of the material. The impact strength of Examples 1-15 is 412-485 J / m, indicating that the halogen-free flame-retardant polypropylene materials prepared with modified graphene oxide flame retardant synergist have excellent impact resistance and reliability, providing assurance for use in harsh environments. Furthermore, the experimental data of Examples 1-15 show that the halogen-free flame-retardant polypropylene materials prepared in Examples 1-15 have excellent flame retardancy.

[0133] Comparative Example 1 reduced the amount of PP added in this invention, while Comparative Example 2 increased the amount of PP added. The amounts of PP added in Comparative Examples 1 and 2 are outside the range proposed in this invention. Experimental data shows that when the amount of matrix resin in the formulation is too low, the tensile strength and elongation at break of Comparative Example 1 decrease, resulting in poor mechanical properties. In Comparative Example 2, the UL94 rating is V2, and dripping occurred during combustion, igniting cotton. This is because the excessive amount of matrix material reduced the proportion of the added flame retardant system in the overall formulation, failing to build a sufficient char layer to prevent material dripping and thus failing to achieve good flame retardant performance. Furthermore, Comparative Example 2 has a tensile strength of 26 MPa, indicating a more robust internal structure that is more prone to brittle fracture and poor mechanical properties.

[0134] Comparative Example 3 reduced the amount of toughening agent used in this invention, while Comparative Example 4 increased the amount of toughening agent used in this invention. The amounts of toughening agent added in Comparative Examples 3 and 4 are all outside the range proposed in this invention. Experimental data shows that Comparative Example 3 exhibits an elongation at break of 45%, indicating poor mechanical properties.

[0135] No magnesium hydroxide was added in Comparative Example 5, no ammonium polyphosphate flame retardant was added in Comparative Example 6, 10 parts of ammonium polyphosphate were added in Comparative Example 7, and 35 parts of ammonium polyphosphate were added in Comparative Example 8. The amount of inorganic flame retardant added in Comparative Examples 5-8 was not within the range of 15-25 parts proposed in this invention. As can be seen from the experimental data, the flame retardant performance of Comparative Examples 5-7 was poor, and a large amount of dripping occurred during the combustion process. The amount of inorganic flame retardant added in Comparative Example 8 was too large. The tensile strength of Comparative Example 8 was 21.5 MPa and the elongation at break was 80%, resulting in poor mechanical properties.

[0136] Comparative Example 8 did not contain any modified graphene oxide flame retardant synergist, Comparative Example 9 contained 2 parts of modified graphene oxide flame retardant synergist, and Comparative Example 10 contained 15 parts of modified graphene oxide flame retardant synergist. The number of parts of modified graphene oxide flame retardant synergist added in Comparative Examples 9-11 was outside the range of 5-10 parts proposed in this invention. The experimental data showed that the flame retardant rating of Comparative Example 8 was V2, indicating poor flame retardant performance. The flame retardant rating of Comparative Example 9 was also V2, indicating that the flame retardant performance did not meet the standard. Comparative Example 10 had good flame retardant performance, but due to the excessive amount of modified graphene oxide flame retardant synergist added, the mechanical properties of the prepared halogen-free flame retardant polypropylene material were affected, resulting in a tensile strength of 22 MPa and an elongation at break of 65% for Comparative Example 10, indicating poor mechanical properties.

[0137] Comparative Example 11 has a flame retardant rating of V1 and exhibits dripping during combustion. The modified graphene oxide flame retardant synergist 12 added to Comparative Example 11 is directly produced by the condensation reaction of amine compounds and graphene oxide. Example 11 utilizes anhydrous thionyl chloride to chlorinate the carboxyl groups on the surface of graphene oxide, then reacts the acyl-chlorinated GO with amine compounds to obtain amidated GO. Protonated amidated GO reacts with molybdate anions. Conventional GO surface carboxyl groups have low nucleophilic activity; after conversion to acyl chloride groups, the chlorine atom in the acyl chloride group is an excellent leaving group, and the carbonyl carbon has a stronger positive charge, allowing the amino group in ethylenediamine to react at room temperature without a catalyst. Under certain conditions, it rapidly undergoes nucleophilic attack to form stable amide bonds. This process has a short reaction time, high yield, and does not require high pressure or high temperature conditions, with mild reaction conditions. On the other hand, the preparation method of first acylation and then amidation has a stable reaction route and a well-defined product structure. It can avoid multi-point crosslinking between ethylenediamine and graphene oxide, or the simultaneous reaction of the amino groups at both ends of ethylenediamine to form interlayer bridges, thereby causing solution precipitation problems. Compared with the modified graphene oxide flame retardant synergist 12 of Comparative Example 11, the modified graphene oxide flame retardant synergist 1 prepared by nucleophilic substitution reaction in Example 11 has more sites that can be linked to molybdate, resulting in better flame retardant effect.

[0138] Comparative Example 12 has a flame retardancy rating of V2 and exhibits dripping during combustion. The modified graphene oxide flame retardant synergist 13 added to Comparative Example 12 did not contain any amine compounds during its preparation, thus not forming amide bonds. Furthermore, the modified graphene oxide flame retardant synergist 13 obtained after reacting with molybdate anions still contains chlorine. Comparative Example 12 produces chloric acid gas during combustion, failing to meet the halogen-free environmental protection requirements and being environmentally unfriendly. The modified graphene oxide flame retardant synergist 14 added to Comparative Example 13 does not contain molybdate, meaning it only consists of amidated GO. Therefore, Comparative Example 13 has a flame retardancy rating of V1, indicating reduced flame retardant performance. The modified graphene oxide flame retardant synergist 14 added to Comparative Example 14... In the preparation of flame retardant synergist 15, a nucleophilic substitution reaction was carried out between n-butylamine and acyl GO chloride. n-butylamine contains only one terminal primary amine group and cannot bind to molybdate anions, resulting in poor flame retardant performance of Comparative Example 15. The flame retardant rating of Comparative Example 15 is V1, and dripping occurs during combustion. In Comparative Example 15, modified graphene oxide flame retardant synergist 16 was prepared using commercially available GO. The carboxyl content on the surface of commercially available GO is 5%-8%, which is lower than the 10%-20% carboxyl content of GO in this invention. In the same preparation method, the binding sites of modified graphene oxide flame retardant synergist 16 with molybdate anions are significantly lower than the binding sites of modified graphene oxide flame retardant synergist 1 in Example 11, resulting in poor flame retardant effect. In Comparative Example 15, 6 parts of organic montmorillonite were added to replace the modified graphene oxide flame retardant synergist of the present invention, forming a flame retardant system together with the inorganic flame retardant. The experimental data showed that the flame retardant rating of Comparative Example 15 was V2, which was insufficient. Compared with Example 11, the flame retardant rating of Example 11 was V0, and no dripping phenomenon occurred. This indicates that organic montmorillonite cannot form an excellent flame retardant system with the inorganic flame retardant. That is, adding the same amount of organic montmorillonite flame retardant cannot achieve the flame retardant effect of the modified graphene oxide flame retardant synergist proposed in this invention.

[0139] Therefore, this invention verifies that the flame retardancy of halogen-free flame-retardant polypropylene materials is improved by modifying graphene oxide flame retardant synergists, giving them excellent physical and mechanical properties and excellent anti-dripping effect during combustion. They are also safe and environmentally friendly, have extremely high industrial value, and can be widely used and promoted.

[0140] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A halogen-free flame-retardant polypropylene material, characterized in that, The raw materials of the halogen-free flame-retardant polypropylene material, by weight, include: Polypropylene (PP) 60-80 parts 4-8 parts toughening agent 15-25 parts of halogen-free flame retardant Antioxidant 1-1.5 parts, 2-3 parts light stabilizer 5-10 parts of modified graphene oxide flame retardant synergist. The modified graphene oxide flame retardant synergist is prepared by "nucleophilic substitution acyl chloride-nucleophilic substitution amidation-electrostatic interaction" from graphene oxide (GO), anhydrous thionyl chloride, an amine compound H2N-R-NH2 containing at least two terminal primary amino groups, and molybdate. The -R- is a divalent organic group used to connect the amide bond to the terminal primary amino group. The modified graphene oxide flame retardant synergist includes at least one amide bond -CONH-RN- connected to the terminal primary amino group.

2. The halogen-free flame-retardant polypropylene material as described in claim 1, characterized in that, The graphene oxide was prepared by a modified Hummers method, and the carboxyl content in the prepared graphene oxide was 10%-20%.

3. The halogen-free flame-retardant polypropylene material as described in claim 1, characterized in that, In the amine compound H2N-R-NH2 containing at least two terminal primary amino groups, the -R- is a divalent organic group used to connect the amide bond to the primary amino group, and the -R- group is at least one of a straight-chain alkyl group, a polyether segment, a polyamine segment containing a secondary amine structure, an aromatic structure, a branched structure, and a cyclic structure.

4. The halogen-free flame-retardant polypropylene material as described in claim 3, characterized in that, The straight-chain alkyl group is -CH2-CH2-, -(CH2)3-, -(CH2)4-, -(CH2)6-, -(CH2)8-, or -(CH2). 10 At least one of the following: -; the polyether-containing segment is -(CH2-CH2-O). 2-5 At least one of - and -CH2-CH(CH3)-O-; the polyamine segment containing the secondary amine structure is at least one of DETA backbone, TETA backbone, TEPA backbone, PEPA backbone, and BAPA backbone; the aromatic structure is at least one of phenylene, benzyl, biaryl ether, and naphthalene ring structure; the branched structure is at least one of branched propyl, tertiary carbon, and neopentyl type structure; the cyclic structure is -C6H 10 - At least one of the isophorone structure and piperazine structure.

5. The halogen-free flame-retardant polypropylene material as described in claim 1, characterized in that, The molybdate dissolves to form a molybdate anion, and the molybdate is at least one of monomeric molybdate molybdate, polymolybdate molybdate, and heteropolymolybdate molybdate.

6. The halogen-free flame-retardant polypropylene material as described in claim 5, characterized in that, The monomeric molybdate molybdate is at least one selected from sodium molybdate (Na2MoO4·2H2O), potassium molybdate (K2MoO4), ammonium molybdate ((NH4)2MoO4), lithium molybdate (Li2MoO4), and cesium molybdate (Cs2MoO4); the polymolybdate molybdate is at least one selected from ammonium hexamolybdate, sodium hexamolybdate, ammonium heptamolybdate, sodium heptamolybdate, potassium heptamolybdate, ammonium octamolybdate, and sodium octamolybdate; the heteropolymolybdate molybdate is phosphomolybdic acid (H3PMo). 12 O 40 ·xH2O), ammonium phosphomolybdate ((NH4)3PMo 12 O 40 Sodium phosphomolybdate (Na3PMo) 12 O 40 ) and sodium molybdate (Na4SiMo) 12 O 40 At least one of the following.

7. The halogen-free flame-retardant polypropylene material as described in claim 1, characterized in that, The modified graphene oxide flame retardant synergist structure includes at least one [structure not specified in the original text]. ， Where x is the number of molybdenum atoms in one molecule of molybdate, and y is the number of oxygen atoms in one molecule of molybdate.

8. The halogen-free flame-retardant polypropylene material as described in claim 1, characterized in that, The preparation method of the modified graphene oxide flame retardant synergist includes the following steps: (1) Graphene oxide was dispersed in anhydrous thionyl chloride, and dimethylformamide (DMF) was added as a catalyst. The mixture was refluxed and centrifuged to obtain GO-COCl. (2) Disperse GO-COCl in an anhydrous organic solvent, add an amine compound H2N-R-NH2 containing at least two terminal primary amino groups, and react under nitrogen protection to obtain amidated GO; (3) Disperse amidated GO in deionized water or acidic buffer solution with a pH of 3-6, and sonicate to form a uniform dispersion to obtain a protonated and positively charged amidated GO dispersion. (4) Dissolve molybdate in an acidic water / low alcohol system buffer solution of the same pH, and slowly add it dropwise to a protonated positively charged amidated GO dispersion. The reaction is carried out by electrostatic interaction. After stirring, centrifugation, washing, and freeze drying, the modified graphene oxide flame retardant synergist is obtained.

9. The halogen-free flame-retardant polypropylene material as described in claim 1, characterized in that, The anhydrous organic solvent is at least one of alcohols, aromatic hydrocarbons, aliphatic hydrocarbons, alicyclic hydrocarbons, ethers, and ketones, and the acidic water / lower alcohol system buffer is a mixed solution of H2O and at least one lower saturated monohydric alcohol.

10. The halogen-free flame-retardant polypropylene material as described in claim 1, characterized in that, The raw materials of the halogen-free flame-retardant polypropylene material, by weight, include: Polypropylene (PP) 60-80 parts 4-8 parts toughening agent 15-25 parts of halogen-free flame retardant Antioxidant 1-1.5 parts, 2-3 parts light stabilizer 6-9 parts of modified graphene oxide flame retardant synergist.

11. The halogen-free flame-retardant polypropylene material as described in claim 1, characterized in that, The polypropylene is a copolymer polypropylene with a melt index (230℃, 2.16kg) of 3-50g / 10min.

12. The halogen-free flame-retardant polypropylene material as described in claim 1, characterized in that, The toughening agent is at least one of ethylene-butene copolymer, ethylene-octene copolymer, ultra-high molecular weight polyethylene, and nano-silicon.

13. The halogen-free flame-retardant polypropylene material as described in claim 1, characterized in that, The halogen-free flame retardant is at least one of ammonium polyphosphate, piperazine pyrophosphate, melamine polyphosphate, melamine cyanurate, aluminum hypophosphite, divinyl aluminum hypophosphite, and zinc borate.

14. The halogen-free flame-retardant polypropylene material as described in claim 1, characterized in that, The antioxidant is at least one of 1010 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]), 1076, 168 (tris[2,4-di-tert-butylphenyl]phosphite), and 626.

15. The halogen-free flame-retardant polypropylene material as described in claim 1, characterized in that, The light stabilizer is at least one of non-alkaline HALS, low-alkaline HALS, high molecular weight HALS, Tinuvin 326, Tinuvin NOR 371, and 329.

16. A method for preparing the halogen-free flame-retardant polypropylene material as described in claim 1, characterized in that, Includes the following steps: A modified graphene oxide flame retardant synergist was prepared by using graphene oxide (GO), anhydrous thionyl chloride, an amine compound H2N-R-NH2 containing at least two terminal primary amino groups, and molybdate. Polypropylene, toughening agent, halogen-free flame retardant, antioxidant, light stabilizer and modified graphene oxide flame retardant synergist are mixed evenly, and then subjected to intensive mixing, extrusion and granulation to obtain granules. The granules are then dried to obtain the halogen-free flame retardant polypropylene material as described in claims 1-15.

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