Halogen-free flame-retardant crosslinked polyolefin material and method for producing the same

Abstract

This invention discloses a halogen-free flame-retardant crosslinked polyolefin material and its preparation method, comprising 5-10 parts of polyethylene (PE), 5-15 parts of ethylene-vinyl acetate copolymer (EVA), 8-12 parts of polyolefin elastomer (POE), 50-70 parts of inorganic flame retardant, 2-5 parts of modified graphene oxide flame retardant synergist, and 3-8 parts of compatibilizer. 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- 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 crosslinked polyolefin material provided by this invention exhibits excellent flame retardancy, physical and mechanical properties, and electrical properties; it is safe and environmentally friendly; and its anti-dripping effect is greatly improved.

Description

Technical Field

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

[0002] With increasingly stringent global requirements for fire safety and environmental protection, the wire and cable industry is rapidly developing towards halogen-free, low-smoke, and low-toxicity materials. Polyolefins, due to their excellent electrical properties, processing performance, and cost advantages, have become the preferred material for cable insulation. However, polyolefins are inherently flammable, have a low limiting oxygen index, generate a large amount of heat during combustion, and are prone to molten dripping, which greatly limits their application in high-end, harsh environments. To address these issues, halogen-free flame-retardant systems, especially environmentally friendly flame retardants represented by metal hydroxides such as aluminum hydroxide, magnesium hydroxide, and phosphorus-nitrogen intumescent flame retardants, have become the mainstream in research and application. However, these halogen-free flame-retardant systems still face many severe challenges in the practical application of polyolefin cable materials. Therefore, it is essential to develop a novel halogen-free flame-retardant cross-linked polyolefin material that possesses halogen-free high flame retardancy, anti-dripping effect, high physical and mechanical properties, and excellent electrical properties. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the present invention proposes a halogen-free flame-retardant cross-linked polyolefin material and its preparation method, aiming to solve the problems of poor flame retardancy, poor physical and mechanical properties, and insufficient dripping and electrical properties during combustion of current cross-linked polyolefin materials.

[0004] To achieve the above objectives, the present invention proposes a halogen-free flame-retardant cross-linked polyolefin material, wherein the raw materials of the halogen-free flame-retardant cross-linked polyolefin material, by weight, include... 5-10 parts of polyethylene (PE) 5-15 parts of ethylene-vinyl acetate copolymer (EVA) 8-12 parts of polyolefin elastomer (POE) 50-70 parts of inorganic flame retardant 2-5 parts of modified graphene oxide flame retardant synergist. 3-8 parts compatibilizer 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 of the halogen-free flame-retardant cross-linked polyolefin material include 5-10 parts of polyethylene (PE) by weight. 5-15 parts of ethylene-vinyl acetate copolymer (EVA) 8-12 parts of polyolefin elastomer (POE) 50-70 parts of inorganic flame retardant 3-5 parts of modified graphene oxide flame retardant synergist. 3-8 parts compatibilizer.

[0014] Optionally, the polyethylene is low-density polyethylene, the VA content in the EVA is 25%-30%, and the POE is at least one of ethylene-butene copolymer and ethylene-octene copolymer.

[0015] Optionally, the inorganic flame retardant is composed of magnesium hydroxide and aluminum hydroxide in a 1:1 ratio, wherein the weight ratio of magnesium hydroxide to aluminum hydroxide is (25-35):(25-35).

[0016] Optionally, the raw materials of the halogen-free flame-retardant crosslinked polyolefin material further include at least one of lubricant, antioxidant, coupling agent and sensitizer, wherein the lubricant is 1-2 parts, the antioxidant is 1-2 parts, the coupling agent is 0.5-1 parts, and the sensitizer is 1-3 parts.

[0017] This invention provides a method for preparing a halogen-free flame-retardant crosslinked polyolefin material, comprising the following steps: preparing a modified graphene oxide flame retardant synergist by using graphene oxide (GO), anhydrous sulfoxide, an amine compound H2N-R-NH2 containing at least two terminal primary amino groups, and molybdate. Polyethylene, EVA, POE, compatibilizer, inorganic flame retardant, modified graphene oxide flame retardant synergist and other additives are mixed evenly, and then subjected to intensive mixing, extrusion and granulation to obtain granules; the granules are dried to obtain the halogen-free flame retardant cross-linked polyolefin material as described above.

[0018] Optionally, the raw materials may also include at least one of lubricant, antioxidant, coupling agent and sensitizer.

[0019] In this invention, the halogen-free flame-retardant crosslinked polyolefin material is a resin base composed of polyethylene and EVA, with the addition of POE, compatibilizer, inorganic flame retardant, modified graphene oxide flame retardant synergist, and other additives as the main components of the halogen-free flame-retardant polyolefin irradiated insulating cable material. 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. It is obtained by reacting anhydrous sulfoxide with the carboxyl groups on the surface of graphene oxide to obtain a nucleophilic substituted acyl chloride. GO-COCl, an acyl chloride of graphene oxide, forms stable amide bonds with amine compounds through substitution reactions. The molybdate ions of molybdate attract and adsorb firmly with the amidated graphene oxide through strong Coulomb electrostatic attraction, thus preparing a modified graphene oxide flame retardant synergist. This ultimately achieves efficient, environmentally friendly, and high-performance flame retardant protection. The components work together synergistically to improve the flame retardancy and smoke suppression properties of the cable material, resulting in a halogen-free flame-retardant polyolefin irradiated insulating cable material with excellent physical, mechanical, and electrical properties. Attached Figure Description

[0020] 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

[0021] 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.

[0022] Unless otherwise specified, all technical and scientific terms used herein have their usual meaning within the field to which the subject matter is claimed.

[0023] With increasingly stringent global requirements for fire safety and environmental protection, the wire and cable industry is rapidly developing towards halogen-free, low-smoke, and low-toxicity materials. Polyolefins, due to their excellent electrical properties, processing performance, and cost advantages, have become the preferred material for cable insulation. However, polyolefins are inherently flammable, have a low limiting oxygen index, generate a large amount of heat during combustion, and are prone to molten dripping, which greatly limits their application in high-end, harsh environments. To address these issues, halogen-free flame-retardant systems, especially environmentally friendly flame retardants represented by metal hydroxides such as aluminum hydroxide, magnesium hydroxide, and phosphorus-nitrogen intumescent flame retardants, have become the mainstream in research and application. However, these halogen-free flame-retardant systems still face many severe challenges in the practical application of polyolefin cable materials. Therefore, it is essential to develop a novel halogen-free flame-retardant cross-linked polyolefin material that possesses halogen-free high flame retardancy, anti-dripping effect, high physical and mechanical properties, and excellent electrical properties.

[0024] To address the aforementioned problems, in a first aspect, this invention provides a halogen-free flame-retardant cross-linked polyolefin material, wherein the raw materials of the halogen-free flame-retardant cross-linked polyolefin material, by weight, include 5-10 parts of polyethylene (PE). 5-15 parts of ethylene-vinyl acetate copolymer (EVA) 8-12 parts of polyolefin elastomer (POE) 50-70 parts of inorganic flame retardant 2-5 parts of modified graphene oxide flame retardant synergist. 3-8 parts compatibilizer Among them, 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. -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.

[0025] Understandably, in halogen-free flame-retardant cross-linked polyolefin materials, polyethylene (PE) is any number between 5 and 10 parts (e.g., 5, 6, 7, 8, 9, 10, etc.); EVA resin is any number between 5 and 15 parts (e.g., 5, 7, 10, 12, 15, etc.); POE is any number between 8 and 12 parts (e.g., 8, 9, 10, 11, 12, etc.); inorganic flame retardant is any number between 50 and 70 parts (e.g., 50, 55, 60, 65, 70, etc.); modified graphene oxide flame retardant synergist is any number between 2 and 5 parts (e.g., 2, 3, 4, 5, etc.); and compatibilizer is any number between 3 and 8 parts (e.g., 3, 4, 5, 6, 7, 8, etc.).

[0026] 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 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, exhibiting excellent... With strong thermal stability and resistance to hydrolysis, 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 nanoframeworks, permeating the amorphous carbon catalyzed by molybdates.The combination of these two elements forms a stable carbon layer structure—graphene oxide serves as the framework, providing support and strength; catalytically generated amorphous carbon fills the space within, resulting in a denser, more continuous, stronger, and more thermally stable carbon layer that effectively isolates heat and gas transfer. 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, while also blocking the inward transfer of heat. Some molybdenum compounds may capture highly reactive H+ and OH- free radicals in the gas phase, interrupting the chain reaction of combustion. Simultaneously, the inert gases released from the decomposition of molybdates can dilute the concentration of combustible gases. Molybdenum compounds are recognized as highly effective smoke suppressants, acting as catalytic oxidation to convert soot precursors into CO and CO2, reducing smoke generation. On the one hand, the dense carbon layer physically blocks the release of internal smoke particles, thereby achieving dual smoke suppression in both the gas phase and the 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 level, 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 does not contain halogens, 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.

[0027] Halogen-free flame-retardant crosslinked polyolefin materials are mainly composed of a resin base of polyethylene and EVA, with the addition of POE, compatibilizer, inorganic flame retardant, modified graphene oxide flame retardant synergist, and other additives. 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. It is obtained by reacting anhydrous sulfoxide with the carboxyl groups on the surface of graphene oxide to obtain a nucleophilically substituted acyl chloride oxide. Graphene GO-COCl, an acyl chloride graphene oxide, forms stable amide bonds with amine compounds through substitution reactions; molybdate ions of molybdate attract and adsorb firmly with amidated graphene oxide through strong Coulomb electrostatic attraction, thus preparing a modified graphene oxide flame retardant synergist. Ultimately, this achieves efficient, environmentally friendly, and high-performance flame retardant protection. The components work together synergistically to improve the flame retardancy and smoke suppression properties of cable materials, resulting in halogen-free flame-retardant polyolefin irradiated insulating cable materials with excellent physical, mechanical, and electrical properties.

[0028] Furthermore, graphene oxide was prepared by a modified Hummers method, and the prepared graphene oxide contained 10%-20% carboxyl groups.

[0029] 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.

[0030] 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%.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] In some embodiments, the carboxyl content in graphene oxide is preferably 15%-20%.

[0035] 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.

[0036] 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.

[0037] In some embodiments, the -R- group is preferably a straight-chain alkyl group.

[0038] 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.

[0039] 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.

[0040] In some embodiments, the straight-chain alkyl group is preferably -CH2-CH2-.

[0041] In some embodiments, the aromatic structure is preferably phenylene.

[0042] In some embodiments, the amine compound H2N-R-NH2 containing at least two terminal primary amino groups is preferably ethylenediamine.

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

[0044] In some embodiments, the amine compound H2N-R-NH2 containing at least two terminal primary amino groups is preferably polyetheramine D-230.

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

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

[0047] 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.

[0048] 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.

[0049] 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.

[0050] In some embodiments, molybdate is preferably monomeric molybdate molybdate.

[0051] 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.

[0052] 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.

[0053] In some embodiments, the monomeric molybdate molybdate is preferably sodium molybdate.

[0054] In some embodiments, polymolybdate molybdate is preferably ammonium hexamolybdate.

[0055] In some embodiments, heteropolymolybdate molybdate is preferably phosphomolybdic acid.

[0056] 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.

[0057] 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.

[0058] In some embodiments, when the monomeric molybdate molybdate is preferably sodium molybdate, x is 1 and y is 4.

[0059] Furthermore, a method for preparing the above-mentioned 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.

[0060] In some embodiments, the acidic buffer solution is preferably an acetate-sodium acetate buffer solution with a pH of 4.

[0061] 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.

[0062] 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.

[0063] In some embodiments, the anhydrous organic solvent is preferably anhydrous tetrahydrofuran.

[0064] In some embodiments, the pH of the acidic water / lower alcohol system buffer is preferably pH=4.

[0065] In some embodiments, the acidic water / lower alcohol system buffer is a mixed solution of H2O and methanol.

[0066] Furthermore, the raw materials of the halogen-free flame-retardant crosslinked polyolefin material, by weight, include 5-10 parts of polyethylene (PE), 5-15 parts of ethylene-vinyl acetate copolymer (EVA), 8-12 parts of polyolefin elastomer (POE), 50-70 parts of inorganic flame retardant, 3-5 parts of modified graphene oxide flame retardant synergist, and 3-8 parts of compatibilizer.

[0067] Increasing the amount of modified graphene oxide flame retardant synergist can further improve the mechanical and flame retardant properties of halogen-free flame-retardant cross-linked polyolefin materials.

[0068] Furthermore, the polyethylene is low-density polyethylene, the VA content in the EVA is 25%-30%, and the POE is at least one of ethylene-butene copolymer and ethylene-octene copolymer.

[0069] The core advantages of low-density polyethylene (LDPE) lie in its superior electrical insulation and excellent processing fluidity, ensuring the insulation safety and efficient production of cables. The vinyl acetate (VA) segments in EVA play a crucial role: their polarity significantly enhances compatibility and dispersibility with inorganic flame retardants; simultaneously, they act as highly efficient charring agents, synergistically working with the flame retardant system to construct a denser protective char layer and impart excellent flexibility to the material. Using both VA and flame retardants as the matrix, combined with graphene oxide-molybdate flame retardant synergists, the flame retardancy and smoke suppression properties of the material can be effectively improved.

[0070] In some embodiments, the halogen-free flame-retardant cross-linked polyolefin material polyethylene is preferably linear low-density polyethylene, and the EVA is preferably EVA resin with a VA content of 28%.

[0071] Furthermore, the inorganic flame retardant is composed of magnesium hydroxide and aluminum hydroxide in a 1:1 ratio, wherein the weight ratio of magnesium hydroxide to aluminum hydroxide is (25-35):(25-35).

[0072] The inorganic flame retardant is a 1:1 mixture of magnesium hydroxide and aluminum hydroxide. Its core advantage lies in forming a wide-temperature-range, multi-layered protective system. Aluminum hydroxide decomposes and absorbs heat first at 200-300℃, while magnesium hydroxide decomposes subsequently at 340-490℃, achieving continuous dehydration and heat absorption within the 200-490℃ range. The compound system can balance the material processing temperature and flame retardant protection requirements. The total amount of water vapor released by both is superimposed, which more effectively dilutes the oxygen concentration and forms a more stable water vapor barrier, isolating oxygen from combustibles. Al2O3 and MgO are deposited together to form a denser and more stable heat insulation layer. Under the same flame retardant effect, the compound system has less negative impact on the mechanical properties of the material than a single high-filler system.

[0073] In some embodiments, the weight ratio of magnesium hydroxide to aluminum hydroxide is 30:30.

[0074] Furthermore, the raw materials for halogen-free flame-retardant cross-linked polyolefin materials also include at least one of lubricant, antioxidant, coupling agent and sensitizer, wherein the lubricant is 1-2 parts, the antioxidant is 1-2 parts, the coupling agent is 0.5-1 parts, and the sensitizer is 1-3 parts.

[0075] Lubricants improve the flowability of halogen-free flame-retardant crosslinked polyolefin resins, reduce the coefficient of friction, make the product surface smoother, improve processing efficiency, and also improve the transparency and gloss of plastics. Antioxidants effectively reduce the oxidation rate of materials during processing and use by capturing free radicals, decomposing peroxides, and complexing metal ions, thereby delaying or preventing oxidation or auto-oxidation processes, protecting plastic products from oxidation, and thus extending their service life. Coupling agents can establish chemical bonds between inorganic fillers / reinforcing agents and organic polymer matrices, improving interfacial bonding and filler dispersion. Sensitizers play a decisive role in radiation crosslinking.

[0076] In some embodiments, the lubricant is at least one selected from calcium stearate, magnesium stearate, polyethylene wax, paraffin, and silicone, with silicone being the preferred lubricant.

[0077] In some embodiments, the antioxidant is at least one of bis(octadecyl)hydroxylamine, tris[2,4-di-tert-butylphenyl]phosphite, pentaerythritol tetra(3-lauryl thiopropionate), bis[3-[3-tert-butyl-4-hydroxy-5-tolyl]2,4,8,10-tetraoxaspiro[5,5]undecane-3,9-diylbis(2-methylpropane-2,1-diyl) ester, 1,5,8,12-tetra[4,6-bis(N-1,2,2,6,6-pentamethyl-4-piperidinylamino)-1,3,5-triazin-2-yl]-1,5,8,12-tetraazadodecane and N-salicylamidophthalimide, with bis(octadecyl)hydroxylamine being the preferred antioxidant.

[0078] In some embodiments, the coupling agent is a silane coupling agent, which is at least one of vinyltriethoxysilane, vinyltrimethoxysilane and vinyltri(β-methoxyethoxy)silane, and the coupling agent is preferably vinyltriethoxysilane.

[0079] In some embodiments, the sensitizer is one or more of trimethylolpropane triacrylate and bis(trimethylolpropane)tetraacrylate, preferably trimethylolpropane triacrylate.

[0080] To address the above problems, this invention also proposes a method for preparing a halogen-free flame-retardant cross-linked polyolefin 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. Polyethylene, EVA, POE, compatibilizer, inorganic flame retardant, modified graphene oxide flame retardant synergist and other additives are mixed evenly, and then subjected to intensive mixing, extrusion and granulation to obtain granules; the granules are dried to obtain the halogen-free flame retardant cross-linked polyolefin material as described above.

[0081] In some embodiments, mixing is performed in an internal mixer.

[0082] In some embodiments, the mixing is carried out in a twin-screw extruder.

[0083] In some embodiments, the twin-screw extruder has the following temperature zones: Zone 1: 100°C, Zone 2: 120°C, Zone 3: 130°C, Zone 4: 130°C, Zone 5: 130°C, Zone 6: 130°C, Zone 7: 120°C, Zone 8: 120°C, and the rotation speed: 150 rpm.

[0084] In some embodiments, insulated cables made from irradiated cross-linked polyolefin cable material are irradiated and cross-linked using an 8-Mrad electron beam.

[0085] Furthermore, the raw materials also include at least one of lubricant, antioxidant, coupling agent and sensitizer.

[0086] The following specific embodiments and data explain the content of the present invention.

[0087] 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:

[0088] 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. 5 parts PE, 5 parts EVA, 8 parts POE, 25 parts magnesium hydroxide, 35 parts aluminum hydroxide, 3 parts compatibilizer, 2 parts modified graphene oxide flame retardant synergist, 1.5 parts lubricant, 1.5 parts antioxidant, 1.8 parts coupling agent, and 2 parts sensitizer are mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material is obtained.

[0089] Example 2: The preparation method is the same as in Example 1, except that: Eight parts of PE, 13 parts of EVA, 11 parts of POE, 28 parts of magnesium hydroxide, 28 parts of aluminum hydroxide, 6 parts of compatibilizer, 4 parts of modified graphene oxide flame retardant synergist, 1.5 parts of lubricant, 1.5 parts of antioxidant, 1.8 parts of coupling agent, and 2 parts of sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0090] Example 3: The preparation method is the same as in Example 1, except that: 6 parts PE, 9 parts EVA, 9 parts POE, 28 parts magnesium hydroxide, 28 parts aluminum hydroxide, 5 parts compatibilizer, 3 parts modified graphene oxide flame retardant synergist, 1.5 parts lubricant, 1.5 parts antioxidant, 1.8 parts coupling agent, and 2 parts sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0091] Example 4: The preparation method is the same as in Example 1, except that: 10 parts PE, 15 parts EVA, 12 parts POE, 35 parts magnesium hydroxide, 35 parts aluminum hydroxide, 5 parts compatibilizer, 4 parts modified graphene oxide flame retardant synergist, 1.5 parts lubricant, 1.5 parts antioxidant, 1.8 parts coupling agent, and 2 parts sensitizer are mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material is obtained.

[0092] Example 5: The preparation method is the same as in Example 1, except that: Eight parts of PE, 12 parts of EVA, 10 parts of POE, 30 parts of magnesium hydroxide, 30 parts of aluminum hydroxide, 5 parts of compatibilizer, 4 parts of modified graphene oxide flame retardant synergist, 1.5 parts of lubricant, 1.5 parts of antioxidant, 1.8 parts of coupling agent, and 2 parts of sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0093] 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. Eight parts of PE, 12 parts of EVA, 10 parts of POE, 30 parts of magnesium hydroxide, 30 parts of aluminum hydroxide, 5 parts of compatibilizer, 4 parts of modified graphene oxide flame retardant synergist, 1.5 parts of lubricant, 1.5 parts of antioxidant, 1.8 parts of coupling agent, and 2 parts of sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0094] 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; 8 parts PE, 12 parts EVA, 10 parts POE, 30 parts magnesium hydroxide, 30 parts aluminum hydroxide, 5 parts compatibilizer, 4 parts modified graphene oxide flame retardant synergist, 1.5 parts lubricant, 1.5 parts antioxidant, 1.8 parts coupling agent, and 2 parts sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0095] 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. 8 parts PE, 12 parts EVA, 10 parts POE, 30 parts magnesium hydroxide, 30 parts aluminum hydroxide, 5 parts compatibilizer, 4 parts modified graphene oxide flame retardant synergist, 1.5 parts lubricant, 1.5 parts antioxidant, 1.8 parts coupling agent, and 2 parts sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0096] 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; 8 parts PE, 12 parts EVA, 10 parts POE, 30 parts magnesium hydroxide, 30 parts aluminum hydroxide, 5 parts compatibilizer, 4 parts modified graphene oxide flame retardant synergist, 1.5 parts lubricant, 1.5 parts antioxidant, 1.8 parts coupling agent, and 2 parts sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0097] 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; 8 parts PE, 12 parts EVA, 10 parts POE, 30 parts magnesium hydroxide, 30 parts aluminum hydroxide, 5 parts compatibilizer, 4 parts modified graphene oxide flame retardant synergist, 1.5 parts lubricant, 1.5 parts antioxidant, 1.8 parts coupling agent, and 2 parts sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0098] 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. 8 parts PE, 12 parts EVA, 10 parts POE, 30 parts magnesium hydroxide, 30 parts aluminum hydroxide, 5 parts compatibilizer, 4 parts modified graphene oxide flame retardant synergist, 1.5 parts lubricant, 1.5 parts antioxidant, 1.8 parts coupling agent, and 2 parts sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0099] 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. 8 parts PE, 12 parts EVA, 10 parts POE, 30 parts magnesium hydroxide, 30 parts aluminum hydroxide, 5 parts compatibilizer, 4 parts modified graphene oxide flame retardant synergist, 1.5 parts lubricant, 1.5 parts antioxidant, 1.8 parts coupling agent, and 2 parts sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0100] 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. 8 parts PE, 12 parts EVA, 10 parts POE, 30 parts magnesium hydroxide, 30 parts aluminum hydroxide, 5 parts compatibilizer, 4 parts modified graphene oxide flame retardant synergist, 1.5 parts lubricant, 1.5 parts antioxidant, 1.8 parts coupling agent, and 2 parts sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0101] 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. Eight parts of PE, 12 parts of EVA, 10 parts of POE, 30 parts of magnesium hydroxide, 30 parts of aluminum hydroxide, 5 parts of compatibilizer, 4 parts of modified graphene oxide flame retardant synergist, 1.5 parts of lubricant, 1.5 parts of antioxidant, 1.8 parts of coupling agent, and 2 parts of sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0102] 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. 8 parts PE, 12 parts EVA, 10 parts POE, 30 parts magnesium hydroxide, 30 parts aluminum hydroxide, 5 parts compatibilizer, 4 parts modified graphene oxide flame retardant synergist, 1.5 parts lubricant, 1.5 parts antioxidant, 1.8 parts coupling agent, and 2 parts sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0103] Comparative Example 1: The preparation method is the same as in Example 1, except that: Two parts of PE, two parts of EVA, ten parts of POE, thirty parts of magnesium hydroxide, thirty parts of aluminum hydroxide, five parts of compatibilizer, four parts of modified graphene oxide flame retardant synergist, one part of lubricant, one part of antioxidant, one and eight parts of coupling agent, and two parts of sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0104] Comparative Example 2: The preparation method is the same as in Example 1, except that: 15 parts PE, 20 parts EVA, 10 parts POE, 30 parts magnesium hydroxide, 30 parts aluminum hydroxide, 5 parts compatibilizer, 4 parts modified graphene oxide flame retardant synergist, 1.5 parts lubricant, 1.5 parts antioxidant, 1.8 parts coupling agent, and 2 parts sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0105] Comparative Example 3: The preparation method is the same as in Example 1, except that: Eight parts of PE, 12 parts of EVA, 3 parts of POE, 30 parts of magnesium hydroxide, 30 parts of aluminum hydroxide, 5 parts of compatibilizer, 4 parts of modified graphene oxide flame retardant synergist, 1.5 parts of lubricant, 1.5 parts of antioxidant, 1.8 parts of coupling agent, and 2 parts of sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0106] Comparative Example 4: The preparation method is the same as in Example 1, except that: 8 parts PE, 12 parts EVA, 15 parts POE, 30 parts magnesium hydroxide, 30 parts aluminum hydroxide, 5 parts compatibilizer, 4 parts modified graphene oxide flame retardant synergist, 1.5 parts lubricant, 1.5 parts antioxidant, 1.8 parts coupling agent, and 2 parts sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0107] Comparative Example 5: The preparation method is the same as in Example 1, except that: 8 parts PE, 12 parts EVA, 10 parts POE, 60 parts aluminum hydroxide, 5 parts compatibilizer, 4 parts modified graphene oxide flame retardant synergist, 1.5 parts lubricant, 1.5 parts antioxidant, 1.8 parts coupling agent and 2 parts sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0108] Comparative Example 6: The preparation method is the same as in Example 1, except that: Eight parts of PE, 12 parts of EVA, 10 parts of POE, 60 parts of magnesium hydroxide, 5 parts of compatibilizer, 4 parts of modified graphene oxide flame retardant synergist, 1.5 parts of lubricant, 1.5 parts of antioxidant, 1.8 parts of coupling agent, and 2 parts of sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0109] Comparative Example 7: The preparation method is the same as in Example 1, except that: 8 parts PE, 12 parts EVA, 10 parts POE, 10 parts magnesium hydroxide, 20 parts aluminum hydroxide, 5 parts compatibilizer, 4 parts modified graphene oxide flame retardant synergist, 1.5 parts lubricant, 1.5 parts antioxidant, 1.8 parts coupling agent, and 2 parts sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0110] Comparative Example 8: The preparation method is the same as in Example 1, except that: 8 parts PE, 12 parts EVA, 10 parts POE, 45 parts magnesium hydroxide, 45 parts aluminum hydroxide, 5 parts compatibilizer, 4 parts modified graphene oxide flame retardant synergist, 1.5 parts lubricant, 1.5 parts antioxidant, 1.8 parts coupling agent, and 2 parts sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0111] Comparative Example 9: Eight parts of PE, 12 parts of EVA, 10 parts of POE, 30 parts of magnesium hydroxide, 30 parts of aluminum hydroxide, 5 parts of compatibilizer, 1.5 parts of lubricant, 1.5 parts of antioxidant, 1.8 parts of coupling agent, and 2 parts of sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame-retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame-retardant cross-linked polyolefin material was obtained.

[0112] Comparative Example 10: The preparation method is the same as in Example 1, except that: 8 parts PE, 12 parts EVA, 10 parts POE, 30 parts magnesium hydroxide, 30 parts aluminum hydroxide, 5 parts compatibilizer, 0.5 parts modified graphene oxide flame retardant synergist, 1.5 parts lubricant, 1.5 parts antioxidant, 1.8 parts coupling agent, and 2 parts sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0113] Comparative Example 11: The preparation method is the same as in Example 1, except that: 8 parts PE, 12 parts EVA, 10 parts POE, 30 parts magnesium hydroxide, 30 parts aluminum hydroxide, 5 parts compatibilizer, 8 parts modified graphene oxide flame retardant synergist, 1.5 parts lubricant, 1.5 parts antioxidant, 1.8 parts coupling agent, and 2 parts sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0114] Comparative Example 12: 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. Eight parts of PE, 12 parts of EVA, 10 parts of POE, 30 parts of magnesium hydroxide, 30 parts of aluminum hydroxide, 5 parts of compatibilizer, 4 parts of modified graphene oxide flame retardant synergist, 1.5 parts of lubricant, 1.5 parts of antioxidant, 1.8 parts of coupling agent, and 2 parts of sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0115] Comparative Example 13: 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. Eight parts of PE, 12 parts of EVA, 10 parts of POE, 30 parts of magnesium hydroxide, 30 parts of aluminum hydroxide, 5 parts of compatibilizer, 4 parts of modified graphene oxide flame retardant synergist, 1.5 parts of lubricant, 1.5 parts of antioxidant, 1.8 parts of coupling agent, and 2 parts of sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0116] Comparative Example 14: 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. Eight parts of PE, 12 parts of EVA, 10 parts of POE, 30 parts of magnesium hydroxide, 30 parts of aluminum hydroxide, 5 parts of compatibilizer, 4 parts of modified graphene oxide flame retardant synergist, 1.5 parts of lubricant, 1.5 parts of antioxidant, 1.8 parts of coupling agent, and 2 parts of sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0117] Comparative Example 15: 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. Eight parts of PE, 12 parts of EVA, 10 parts of POE, 30 parts of magnesium hydroxide, 30 parts of aluminum hydroxide, 5 parts of compatibilizer, 4 parts of modified graphene oxide flame retardant synergist, 1.5 parts of lubricant, 1.5 parts of antioxidant, 1.8 parts of coupling agent, and 2 parts of sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0118] Comparative Example 16: 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. Eight parts of PE, 12 parts of EVA, 10 parts of POE, 30 parts of magnesium hydroxide, 30 parts of aluminum hydroxide, 5 parts of compatibilizer, 4 parts of modified graphene oxide flame retardant synergist, 1.5 parts of lubricant, 1.5 parts of antioxidant, 1.8 parts of coupling agent, and 2 parts of sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame retardant cross-linked polyolefin material was obtained.

[0119] Comparative Example 17: Eight parts of PE, 12 parts of EVA, 10 parts of POE, 30 parts of magnesium hydroxide, 30 parts of aluminum hydroxide, 5 parts of compatibilizer, 4 parts of organo-modified montmorillonite, 1.5 parts of lubricant, 1.5 parts of antioxidant, 1.8 parts of coupling agent, and 2 parts of sensitizer were mixed evenly and granulated by twin-screw extrusion at 180°C to obtain halogen-free flame-retardant cross-linked polyolefin material granules. After drying at 80°C, a halogen-free flame-retardant cross-linked polyolefin material was obtained.

[0120] Table 2 summarizes the components and key preparation variables of Examples 1-15 and Comparative Examples 1-17.

[0121] Table 2 summarizes the components and key preparation variables of Examples 1-15 and Comparative Examples 1-17.

[0122] Table 2 shows the components of Examples 1-15 and Comparative Examples 1-17 of the present invention.

[0123]

[0124] According to the requirements of GB / T 32129-2015, the above-mentioned cable material was sampled (including molding and extrusion of 1.5mm). 2 After being cross-linked by 8 Mrad irradiation, the insulated core wires undergo tensile strength, elongation at break, volume resistivity, limiting oxygen index, UL94 rating, smoke density, single-wire vertical burning test, and vertical burning drip test. The test standards are as follows: 1. Tensile properties: Tested according to GB / T 1040-2006 standard.

[0125] 2. Volume resistivity: Tested according to GB / T 31838.2-2019 standard.

[0126] 3. Limiting oxygen index: Tested according to GB / T 2406-2009 standard.

[0127] 4. UL94 rating: Tested according to UL94-2013 standard.

[0128] 5. Smoke density: Tested according to GB / T 8323-2008 standard.

[0129] 6. Single vertical burning: Tested according to GB / T 18380-2008 standard.

[0130] The test results are detailed in Table 3.

[0131] Table 3 Performance test table of Examples 1-15 and Comparative Examples 1-17 of the present invention

[0132] As can be seen from the test results above, the halogen-free flame-retardant cross-linked polyolefin material prepared by this invention has excellent flame-retardant and mechanical properties. The flame-retardant rating of the halogen-free flame-retardant cross-linked polyolefin materials prepared in Examples 1-15 is V0, and the limiting oxygen index is greater than 34.5. The tensile strength of Examples 1-15 is 10.5 MPa-12.5 MPa, and the elongation at break is 130%-180%. Furthermore, no dripping occurred during the combustion process in Examples 1-15, and the smoke density during the combustion process in Examples 1-15 was less than 98, demonstrating a significant smoke suppression effect. The volume resistivity is 1.5-2.3 × 10¹. 4 With an Ω·cm content, the halogen-free flame-retardant cross-linked polyolefin material prepared by this invention exhibits excellent electrical properties and superior flame retardant and physical-mechanical properties. It can prevent the dripping of burning materials during combustion. The halogen-free flame-retardant cross-linked polyolefin material prepared by this invention does not contain halogens, thus meeting environmental protection and safety requirements.

[0133] Examples 1-5 include the modified graphene oxide flame retardant synergist 1 of the present invention. The added inorganic flame retardants are aluminum hydroxide and magnesium hydroxide. The flame retardant ratings of Examples 1-5 are all V0, with limiting oxygen indexes of 34.5-38.5, exhibiting excellent flame retardancy, high flame retardant efficiency, and superior mechanical properties. The combined action of aluminum hydroxide and magnesium hydroxide as inorganic flame retardants with the modified graphene oxide flame retardant synergist can improve the flame retardancy of the prepared halogen-free flame-retardant crosslinked polyolefin material.

[0134] 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 amine and one secondary amine, 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 amines, namely p-phenylenediamine, which has an aromatic structure. During combustion, the benzene ring is rich in carbon elements, and 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 further spread of combustion and improving flame retardancy. In Example 15, modified graphene oxide flame retardant synergist 10 was added. The modified graphene oxide flame retardant synergist 11 was added. The modified graphene oxide flame retardant synergist 11 contains an amine compound with at least two terminal primary amino groups, namely 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 inorganic flame retardants as flame retardants, it can form a dense carbon layer on the material surface and decompose to produce non-combustible gas, thereby improving the flame retardancy of the material.Examples 1-15 showed no cracking in thermal shock tests at 110°C, 130°C, and 150°C, indicating that the halogen-free flame-retardant cross-linked polyolefin materials prepared with modified graphene oxide flame retardant synergists have excellent adaptability and reliability under rapidly changing temperature environments, providing assurance for use in harsh environments. Furthermore, the experimental data from Examples 1-15 demonstrate that the halogen-free flame-retardant cross-linked polyolefin materials prepared in Examples 1-15 possess excellent flame retardancy.

[0135] Comparative Example 1 reduced the amount of PE and EVA added in this invention, while Comparative Example 2 increased the amount of PE and EVA added. The amounts of PE and EVA 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 14 MPa, indicating a more robust internal structure and a greater susceptibility to brittle fracture. The smoke densities of Comparative Examples 1 and 2 are 115-180, indicating poor smoke suppression.

[0136] Comparative Example 3 reduced the amount of POE added in this invention, while Comparative Example 4 increased the amount of POE added. The amounts of POE added in Comparative Examples 3 and 4 are all outside the range proposed in this invention. Experimental data shows that Comparative Example 3 had a smoke density of 110, indicating poor smoke suppression. Comparative Example 4 had a flame retardant rating of V0, but a smoke density of 105, also indicating poor smoke suppression.

[0137] Comparative Example 5 did not contain magnesium hydroxide, Comparative Example 6 did not contain aluminum hydroxide, Comparative Example 7 contained 10 parts magnesium hydroxide and 20 parts aluminum hydroxide, and Comparative Example 8 contained 45 parts magnesium hydroxide and 45 parts aluminum hydroxide. The proportions of inorganic flame retardants added in Comparative Examples 5-8 were all outside the 1:1 and 25-35 parts range proposed in this invention. The experimental data show that Comparative Examples 5-7 had poor flame retardant performance and a large amount of dripping occurred during combustion. The smoke density of the three was 190-210, and a large amount of smoke was produced during combustion, indicating poor flame retardant performance and poor smoke suppression effect. Comparative Example 8 contained too much inorganic flame retardant, and its tensile strength was 9.5 MPa and its elongation at break was 100%, resulting in poor mechanical properties.

[0138] No modified graphene oxide flame retardant synergist was added in Comparative Example 9, 0.5 parts of modified graphene oxide flame retardant synergist were added in Comparative Example 10, and 8 parts of modified graphene oxide flame retardant synergist were added in Comparative Example 11. The number of parts of modified graphene oxide flame retardant synergist added in Comparative Examples 9-11 was outside the range of 2-5 parts proposed in this invention. The experimental data shows that the flame retardant rating of Comparative Example 9 was V1, indicating poor flame retardant performance. The flame retardant rating of Comparative Example 10 was also V1, indicating that the flame retardant performance did not meet the standard. Comparative Example 11 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 cross-linked polyolefin material were affected, resulting in a tensile strength of 10 MPa and an elongation at break of 110% in Comparative Example 11, indicating poor mechanical properties.

[0139] Comparative Example 12 has a flame retardant rating of V1 and exhibits dripping during combustion. The modified graphene oxide flame retardant synergist 12 added to Comparative Example 12 is directly produced by the condensation reaction of amine compounds and graphene oxide. In Example 11, the carboxyl groups on the surface of graphene oxide are chlorinated using anhydrous thionyl chloride, and then the chlorinated GO is reacted with amine compounds to obtain amidated GO. The protonated amidated GO reacts with molybdate anions. Conventional GO surface carboxyl groups have low nucleophilic activity. After converting it 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 the problem of solution precipitation. Compared with the modified graphene oxide flame retardant synergist 12 of Comparative Example 12, 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.

[0140] Comparative Example 13 has a flame retardancy rating of V1 and exhibits dripping during combustion. The modified graphene oxide flame retardant synergist 13 added to Comparative Example 13 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 13 produces chloric acid gas during combustion, failing to meet the halogen-free environmental protection requirements and being environmentally unfriendly. Comparative Example 14, which also has a modified graphene oxide flame retardant synergist 14, does not contain molybdate; it consists only of amidated GO. Comparative Example 14 has a flame retardancy rating of V1, indicating reduced flame retardant performance. Comparative Example 14 also exhibits dripping during combustion. The modified graphene oxide flame retardant synergist 15 added in Example 15 was prepared by nucleophilic substitution reaction between n-butylamine and acyl GO chloride. Since n-butylamine contains only one terminal primary amine group, it cannot bind to molybdate anions, resulting in poor flame retardant performance in Comparative Example 15. Comparative Example 16 had a flame retardant rating of V1 and exhibited dripping during combustion. Comparative Example 16 used commercially available GO to prepare the modified graphene oxide flame retardant synergist 16. The carboxyl content on the surface of commercially available GO was 5%-8%, lower than the 10%-20% carboxyl content of GO in this invention. In the same preparation method, the binding sites of the modified graphene oxide flame retardant synergist 16 with molybdate anions were significantly lower than those in the modified graphene oxide flame retardant synergist 1 in Example 11, resulting in poor flame retardant effect. In Comparative Example 17, 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 17 was V1, 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.

[0141] Therefore, this invention verifies that modifying graphene oxide as a flame retardant synergist improves the flame retardancy of halogen-free flame-retardant cross-linked polyolefin materials, enhances the flame retardant efficiency of the flame retardant, and enables the flame retardant to achieve excellent flame retardant effects with a small amount of addition. The prepared halogen-free flame-retardant cross-linked polyolefin materials have excellent physical and mechanical properties and excellent anti-dripping and smoke-suppressing effects, and meet environmental protection requirements. They have extremely high industrial value and can be widely used and promoted.

[0142] 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 cross-linked polyolefin material, characterized in that, The raw materials of the halogen-free flame-retardant cross-linked polyolefin material, by weight, include: 5-10 parts of polyethylene (PE) 5-15 parts of ethylene-vinyl acetate copolymer (EVA) 8-12 parts of polyolefin elastomer (POE) 50-70 parts of inorganic flame retardant 2-5 parts of modified graphene oxide flame retardant synergist. 3-8 parts compatibilizer 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 cross-linked polyolefin 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 cross-linked polyolefin 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 cross-linked polyolefin 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 cross-linked polyolefin 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 cross-linked polyolefin 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 cross-linked polyolefin 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 cross-linked polyolefin 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 cross-linked polyolefin material as described in claim 8, 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 cross-linked polyolefin material as described in claim 1, characterized in that, The raw materials of the halogen-free flame-retardant cross-linked polyolefin material, by weight, include: 5-10 parts of polyethylene (PE) 5-15 parts of ethylene-vinyl acetate copolymer (EVA) 8-12 parts of polyolefin elastomer (POE) 50-70 parts of inorganic flame retardant 3-5 parts of modified graphene oxide flame retardant synergist. 3-8 parts compatibilizer.

11. The halogen-free flame-retardant cross-linked polyolefin material as described in claim 1, characterized in that, The polyethylene is low-density polyethylene, the VA content in the EVA is 25%-30%, and the POE is at least one of ethylene-butene copolymer and ethylene-octene copolymer.

12. The halogen-free flame-retardant cross-linked polyolefin material as described in claim 1, characterized in that, The inorganic flame retardant is composed of magnesium hydroxide and aluminum hydroxide in a 1:1 ratio, wherein the weight ratio of magnesium hydroxide to aluminum hydroxide is (25-35):(25-35).

13. The halogen-free flame-retardant cross-linked polyolefin material as described in claim 1, characterized in that, The ingredients of the halogen-free flame-retardant polyolefin irradiated insulating cable material also include at least one of lubricant, antioxidant, coupling agent and sensitizer, wherein the lubricant is 1-2 parts, the antioxidant is 1-2 parts, the coupling agent is 0.5-1 parts and the sensitizer is 1-3 parts.

14. A method for preparing a halogen-free flame-retardant cross-linked polyolefin 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. Polyethylene, EVA, POE, compatibilizer, inorganic flame retardant, modified graphene oxide flame retardant synergist and other additives are mixed evenly, and then subjected to intensive mixing, extrusion and granulation to obtain granules; the granules are dried to obtain the halogen-free flame retardant thermoplastic cross-linked polyolefin material as described in claims 1-13.

15. The method for preparing the halogen-free flame-retardant crosslinked polyolefin material as described in claim 14, characterized in that, The raw materials also include at least one of lubricant, antioxidant, coupling agent and sensitizer.

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