Flame-retardant regenerated PA6 electric vehicle battery bracket plastic and preparation method thereof

Abstract

The invention discloses flame-retardant regenerated PA6 electric vehicle battery bracket plastic and a preparation method thereof, and belongs to the technical field of high polymer materials. The raw materials mainly comprise regenerated polyamide, alkali-free chopped glass fibers, a zinc-based metal organic phosphaphenanthrene framework flame retardant, a polydopamine grafted polyphosphonate interfacial compatibilizer, polytetrafluoroethylene, an antioxidant, zinc stearate and silane. The flame retardant is prepared through a solvothermal method, and the interfacial compatibilizer is prepared through a polymerization grafting reaction. In the plastic preparation process, the raw materials are mixed and then melt-blended by a twin-screw extruder, extruded and granulated, and finally subjected to injection molding. The product disclosed by the invention has excellent flame retardance and mechanical strength, is suitable for the battery bracket of the electric vehicle, and is environment-friendly and low in cost.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a flame-retardant recycled PA6 electric vehicle battery bracket plastic and its preparation method. Background Technology

[0002] With the rapid development of the electric vehicle industry, the performance and safety requirements for core components are increasing. As the power source of electric vehicles, the choice of battery bracket material is crucial. It not only needs excellent mechanical strength to support and secure the battery pack and withstand vibrations and impacts during vehicle operation, but also outstanding flame-retardant properties to cope with extreme situations such as potential thermal runaway, ensuring overall vehicle safety. Traditional battery brackets mostly use metal materials or ordinary engineering plastics. The former has disadvantages such as being heavy and prone to corrosion, while the latter often fails to meet stringent requirements in terms of flame retardancy and long-term durability. Therefore, developing a new type of plastic material that combines high strength, high flame retardancy, lightweight, and cost-effectiveness has become an urgent need in the field of electric vehicle materials.

[0003] Currently, the polymer materials used in such structural components are mostly based on engineering plastics such as nylon, reinforced with glass fiber, and supplemented with conventional flame retardants to improve fire resistance. However, existing technologies have significant limitations. On the one hand, many high-efficiency flame retardants are halogen-based systems, which produce large amounts of toxic fumes and corrosive gases during combustion, posing secondary hazards to personal safety and the environment. Halogen-free flame retardants, such as phosphorus-nitrogen products, while addressing environmental issues to some extent, are often added in high quantities, easily causing significant deterioration of the material's mechanical properties, especially impact strength and toughness, affecting the reliability of the components. On the other hand, while directly using recycled nylon materials aligns with the environmentally friendly concept of a circular economy, recycled materials, due to their multiple processing histories, may have broken or degraded molecular chains, resulting in decreased mechanical properties. Furthermore, their interfacial compatibility with various additives is poor, leading to unsatisfactory overall performance of the composite material after simple blending, making it difficult to directly use in high-requirement structural components.

[0004] To overcome the aforementioned technical bottlenecks, the industry urgently needs an innovative material design solution. The ideal solution should be based on environmentally friendly recycled substrates, designing and synthesizing a novel, high-efficiency, low-addition-volume halogen-free flame retardant that imparts excellent flame-retardant properties to the material while maximizing the preservation of the matrix's mechanical properties. Simultaneously, a highly efficient interfacial compatibilizer needs to be developed to improve the bonding force at the multiphase interface between the recycled matrix, flame retardant, and reinforcing fibers, solving the stress defects and performance losses caused by poor compatibility. This will allow for the construction of a stable and efficient multiphase composite material system, ultimately achieving a comprehensive goal of ensuring safety while possessing excellent mechanical properties, environmental friendliness, and economic efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide a flame-retardant recycled PA6 electric vehicle battery bracket plastic and its preparation method, which solves the technical problems of insufficient flame retardancy, poor mechanical properties, and poor interfacial compatibility between recycled plastics and additives in existing electric vehicle battery bracket materials.

[0006] The present invention achieves the above objectives through the following technical solutions: A flame-retardant recycled PA6 electric vehicle battery bracket plastic comprises the following raw materials in parts by weight: Recycled PA6: 55-75 parts by weight; Alkali-free chopped glass fiber: 15-25 parts by weight; Zinc-based metal-organophosphorus phenanthrene framework flame retardant: 4-10 parts by weight; Polydopamine-grafted-polyphosphonate interface compatibilizer: 2-6 parts by weight; Polytetrafluoroethylene: 0.1-0.3 parts by weight; Antioxidant 1098 / Antioxidant 168: 0.3-0.6 parts by weight; Zinc stearate: 0.2-0.5 parts by weight; γ-aminopropyltriethoxysilane: 0.5-1.5 parts by weight; The preparation method of the zinc-based metal-organophosphorus phenanthrene framework flame retardant includes: A1. Dissolving DOPO and terephthalaldehyde in xylene, and reacting at 138-142℃ under nitrogen protection; filtering after cooling, and washing with ethanol to obtain an aldehyde intermediate; then dissolving the aldehyde intermediate in sodium carbonate solution, adding hydrogen peroxide while stirring, and reacting at 58-62℃; subsequently cooling the reaction solution to 20-30℃, adding dilute hydrochloric acid while stirring, adjusting the pH to 2-3, and precipitating a solid. A1. Filter the filter cake, wash it with water until neutral, and finally dry it under vacuum at 70-75℃ to obtain purified DOPO-TA ligand; A2. Dissolve zinc nitrate and DOPO-TA ligand in N,N-dimethylformamide, sonicate to dissolve, transfer to a high-pressure reactor with a polytetrafluoroethylene liner, and solvothermal reaction at 118-122℃; After the reaction is completed, cool naturally to room temperature to precipitate crystals, wash with N,N-dimethylformamide and ethanol, and finally dry under vacuum at 118-122℃.

[0007] In this invention, the raw materials are first collected and sorted. PA6 waste is precisely sorted through manual preliminary selection, flotation separation, and near-infrared spectroscopy separator to ensure the purity of the raw materials is ≥99% and remove metal and other plastic impurities. Then, it is crushed and washed. The raw materials are crushed into 5-10mm fragments using a high-power crusher. After being stirred and washed with 80℃ hot alkaline solution (concentration 5%) for 30 minutes, it is rinsed in two stages of countercurrent and centrifuged to remove water content <15%. Next, it is deeply dried. The material is placed in a dehumidifying dryer and dried at 105℃ for 8 hours until the water content is <0.03%. Finally, it is melt-filtered and granulated. It is melt-plasticized in the temperature range of 240-260℃ using a twin-screw extruder (L / D=40:1). After continuous filtration through a 250-mesh stainless steel filter, it is granulated by underwater cutting, cyclone separation, and vibrating screening (particle size 3×3mm) to obtain recycled PA6 granules.

[0008] In this invention, DOPO, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, is a cyclic organophosphorus compound with a unique phosphaphenanthrene skeleton structure. Due to its excellent thermal stability and high-efficiency flame retardant properties, it plays a crucial role in the field of modern halogen-free flame retardant materials, particularly in high-end engineering plastics and epoxy resins. The core characteristic of the DOPO molecule is that its biphenyl ring structure is bridged by a phosphorus atom and an oxygen atom to form a rigid, large-volume fused ring. This rigid structure endows the molecule with extremely high thermal and chemical stability.

[0009] In this invention, the preparation of a zinc-based metal-organophosphorus phenanthrene framework flame retardant is a precise process involving organic synthesis and coordination chemistry. Its core lies in constructing a stable porous framework structure with zinc ions as the metal center and functionalized molecules derived from organophosphorus phenanthrene as organic ligands. The preparation of this flame retardant begins with the synthesis of key organic ligands. First, under an inert atmosphere, the organophosphorus phenanthrene compound reacts with terephthalaldehyde in a high-temperature inert solvent. This step is a typical nucleophilic addition reaction; the highly reactive phosphorus-hydrogen bonds in the organophosphorus phenanthrene molecule break, and the phosphorus atom launches a nucleophilic attack on the carbon atom on the aldehyde group, generating a hydroxyalkyl intermediate. This intermediate is unstable and rapidly dehydrates to form an aldehyde-based intermediate product containing a carbon-carbon double bond. This step introduces the aldehyde functional group into the organophosphorus phenanthrene molecular framework, laying the foundation for subsequent modification and coordination. Subsequently, this aldehyde intermediate undergoes an oxidation reaction with hydrogen peroxide under alkaline conditions. The aldehyde group is selectively oxidized to a carboxyl group, resulting in a bifunctional organic ligand containing both an electron-rich organophosphorus phenanthrene unit (as an excellent flame-retardant functional group) and a carboxyl functional group (as a strong metal coordination site). The introduction of the carboxyl group is crucial, as it endows the ligand with the ability to form strong coordination bonds with metal ions. After obtaining the purified ligand, it is co-dissolved with a zinc salt in a high-boiling-point polar solvent. In this solution, the carboxyl oxygen atom on the ligand molecule provides a lone pair of electrons, coordinating with zinc ions. Zinc ions have a clear coordination geometry preference, tending to form tetrahedral or octahedral coordination configurations. Under high temperature and pressure solvothermal conditions, molecular thermal motion intensifies, and zinc ions approach multiple ligand molecules, self-assembling through carboxyl bridging or chelation. Each zinc ion can simultaneously coordinate with multiple carboxyl oxygen atoms from different ligands, while multiple carboxyl groups on each ligand molecule can simultaneously connect to multiple zinc ions, thus forming an infinitely extended metal-organic framework with a three-dimensional network structure. Organophosphorus phenanthrene groups are firmly integrated into this rigid framework as large side groups or components. The resulting crystalline material has a microstructure consisting of a porous crystalline network of zinc ion clusters and organic ligands, with the organophosphorus phenanthrene flame-retardant functional groups distributed in a high-density, ordered manner throughout the framework. This structural mechanism determines its high thermal stability, high phosphorus content, and unique flame-retardant mechanism: during combustion, it can both capture gaseous free radicals and promote the formation of a dense char layer, providing a highly efficient barrier protection effect.

[0010] According to a preferred embodiment of the present invention, in step A1, the reaction time is 8-10 hours when the temperature is raised to 138-142°C; and the reaction time is 6-8 hours when the temperature is stirred at 58-62°C.

[0011] According to a preferred embodiment of the present invention, in step A2, the solvothermal reaction time at 118-122°C is 24-30 h.

[0012] According to a preferred embodiment of the present invention, the preparation method of the polydopamine-grafted-polyphosphonate interface compatibilizer includes: B1, dissolving dopamine hydrochloride in Tris-HCl buffer solution with pH=8.4-8.6, stirring and polymerizing at room temperature to obtain a polydopamine solution, centrifuging and washing with water to collect the polydopamine solid, and then dispersing the polydopamine solid in anhydrous N,N-dimethylformamide; adding 2-chloro-2-oxo-1,3,2-dioxophosphazenecyclopentane dropwise to the polydopamine solution, and simultaneously adding triethylamine, reacting under ice bath conditions, and then heating to 48-52°C to continue the reaction; B2, after the reaction is completed, pouring the reaction solution into ice-cold diethyl ether under stirring to precipitate the solid; collecting the solid product by filtration and washing with diethyl ether; finally, vacuum drying the product at 40-50°C.

[0013] In this invention, the synthesis of a polydopamine-grafted-polyphosphonate interfacial compatibilizer is an ingenious design combining biomimetic polymerization and living graft polymerization. Its mechanism aims to create an amphiphilic molecule with both strong adhesion and excellent interfacial compatibility. The first step in this process is the biomimetic synthesis of polydopamine. In a weakly alkaline buffer solution of dopamine hydrochloride, dissolved oxygen acts as an oxidant, initiating the oxidation, cyclization, and self-polymerization reactions of dopamine molecules. The reaction mechanism is similar to the formation pathway of natural melanin: dopamine molecules are first oxidized to dopaquinone, then form indole structures through intramolecular cyclization. These indole intermediates are further oxidized and interconnected through covalent bonds or strong π-π stacking, hydrogen bonds, and other non-covalent forces, ultimately polymerizing into polydopamine nanoparticles with numerous catechol / quinone groups, amino groups, and other active functional groups. Polydopamine is well-known for its catechol structure, which generates extremely strong adhesion through strong interactions with various surfaces, allowing it to firmly attach to surfaces such as recycled polyamide matrices or glass fibers. The second step is the crucial in-situ grafting reaction. The synthesized polydopamine solid is dispersed in an anhydrous organic solvent, followed by the addition of a cyclic phosphonate monomer and an organic base as an acid absorber. This cyclic monomer is a highly reactive compound with its phosphorus atom bonded to a chlorine atom. The chlorine atom acts as a favorable leaving group, facilitating ring-opening polymerization. The reaction is initiated under low-temperature ice-bath conditions to control the reaction rate. The abundant amino groups (primary and secondary amines) on the polydopamine molecular chain act as nucleophilic initiators, attacking the chlorine atom on the phosphorus atom of the cyclic phosphonate monomer, causing it to break. Simultaneously, the amino group forms a phosphorus-nitrogen covalent bond with the phosphorus atom, thereby opening the cyclic structure and initiating ring-opening polymerization. The organic base serves to neutralize the hydrogen chloride byproduct produced in the reaction, preventing its protonation of the amino group and thus terminating the reaction. Once initiated, the reaction proceeds with increasing temperature, and the ring-opening polymerization continues. Multiple amino sites on the polydopamine molecular chain can initiate the growth of multiple polyphosphonate chains, forming comb-like or star-shaped graft copolymers with polydopamine as the core and numerous polyphosphonate chains as arms. Polyphosphonate segments themselves contain phosphorus and possess some flame retardancy, but their more important role lies in the fact that their molecular structure shares similar polarity and chemical compatibility with the polyamide matrix and phosphorus-based flame retardants. Therefore, the resulting interfacial compatibilizer molecule has a unique amphiphilic structure: the polydopamine core on one side can strongly adhere to the surfaces of various materials; the polyphosphonate arm on the other side can intertwine and miscible with the polyamide matrix molecular chains and phosphorus-based flame retardant molecules, forming a strong molecular bridge. This structural mechanism greatly improves the interfacial compatibility and adhesion between the hydrophobic recycled polyamide matrix and the hydrophilic glass fiber and flame retardant particles, which is key to achieving high-performance composite materials.

[0014] According to a preferred embodiment of the present invention, in step B1, the stirring polymerization time is 24-30 h; the reaction time under ice bath conditions is 2-4 h; and the reaction time is continued at 48-52 °C for 18-20 h.

[0015] According to a preferred embodiment of the present invention, in step B2, the vacuum drying time at 40-50°C is 5-8 hours.

[0016] This invention also provides a method for preparing the flame-retardant recycled PA6 electric vehicle battery bracket plastic, comprising the following steps: S1. Vacuum dry the recycled PA6 at 98-102℃; dry the alkali-free chopped glass fiber at 108-112℃; weigh the dried recycled PA6, zinc-based metal-organophosphorus phenanthrene framework flame retardant, polydopamine-grafted-polyphosphonate interface compatibilizer, antioxidant 1098 / antioxidant 168, and zinc stearate and mix them in a high-speed mixer to obtain a premix. S2. The premixed material is added from the main feed port of the twin-screw extruder. The temperature settings of each zone of the screw from the feeding section to the die head are 230℃, 240℃, 250℃, 255℃, 260℃, and 255℃ respectively. The alkali-free chopped glass fiber and polytetrafluoroethylene treated with γ-aminopropyltriethoxysilane are added from the side feed port in the middle section of the melting zone. The melt-blended material is extruded through a die, cooled in a water bath, dried, and pelletized. S3. Finally, after drying the granules at 98-102℃, they are molded using an injection molding machine.

[0017] In this invention, the entire plastic preparation process is a physicochemical process of multi-component melt blending and in-situ composite. Its core mechanism lies in achieving optimal dispersion, distribution, and interfacial bonding of each functional component in the matrix through precise process control, thereby exerting a synergistic effect. Preparation begins with rigorous raw material pretreatment. Vacuum drying of recycled polyamide particles aims to remove trace amounts of moisture. Polyamide is a hygroscopic polymer; moisture can cause hydrolytic degradation during high-temperature processing, leading to molecular chain breakage and severely deteriorating the mechanical properties of the final product. Therefore, deep drying is fundamental to ensuring material performance. Drying of glass fibers also aims to remove surface-adsorbed water, ensuring the interfacial bonding strength between the glass fiber and the polymer. The treatment of glass fibers with silane coupling agents is an important surface chemical modification process. One end of the silane molecule is an easily hydrolyzed alkoxy group, which undergoes a hydrolytic condensation reaction with the hydroxyl groups on the glass fiber surface to form a strong siloxane bond; the other end is an amino group, which is reactive and compatible with the carboxyl or amide bonds at the ends of the polyamide matrix. This coupling agent molecular layer constructs a robust "molecular bridge" between the inorganic glass fiber and the organic polyamide matrix, greatly enhancing interfacial adhesion and preventing interfacial delamination from becoming a weak point in the material. During the melt blending stage, the twin-screw extruder provides intense shear, mixing, and thermal history. The premixed matrix resin, flame retardant, interfacial compatibilizer, and other additives are added from the main feed inlet and begin to melt and plasticize under the conveying and shearing action of the screw. At this point, the polydopamine-grafted-polyphosphonate interfacial compatibilizer begins to play a crucial role. Its polydopamine portion, with its strong adhesive properties, tends to coat the surface of the zinc-based metal-organic framework flame retardant particles and the surface of glass fibers that may not be completely covered by silane. Meanwhile, its polyphosphonate segments dissolve and entangle with the molten polyamide matrix, achieving good compatibility through intermolecular forces. This "bridging" mechanism effectively reduces the interfacial energy between flame retardant particles and the matrix, and between fibers and the matrix, avoiding phase separation and stress concentration points caused by poor compatibility. Simultaneously, it promotes the uniform dispersion of nano / micron-sized flame retardant particles in the matrix, preventing agglomeration, which is crucial for simultaneously achieving excellent mechanical and flame retardant properties. Silane-treated glass fibers and polytetrafluoroethylene (PTFE) are added from the side feed port in the middle of the melting zone. This process design aims to precisely control the retained fiber length and the dispersion morphology of PTFE. Excessive shearing time will excessively damage the fiber length, while adding it too early may cause excessive breakage. Under strong shearing, PTFE fibrillates, forming a tiny fibrous network distributed in the matrix. When the material is impacted, it can effectively induce crazing and shear bands, absorbing a large amount of energy, thereby significantly improving the material's impact resistance and abrasion resistance. The temperature settings of the screw section ensure that the material reaches its optimal plasticization state while avoiding polymer degradation or flame retardant decomposition due to overheating. Ultimately, all components are melted, dispersed, distributed, and kneaded in the extruder to form a homogeneous, multiphase composite material with strong interfacial bonding.During the injection molding stage, the material rapidly fills the mold cavity under high pressure, and the glass fibers are oriented along the flow direction, thus providing higher strength and modulus in a specific direction. Its synergistic flame-retardant mechanism lies in the following: the zinc-based metal-organic framework releases phosphorus free radicals in the early stages of combustion, capturing hydrogen and hydroxyl free radicals in the gas phase and interrupting the chain reaction; in the condensed phase, it promotes the catalytic carbonization of the polyamide matrix and synergizes with phosphorus elements in the interfacial compatibilizer to form a robust and dense expanded char layer. This char layer effectively insulates against heat and oxygen, inhibiting the escape of combustible gases, thereby achieving highly efficient and environmentally friendly halogen-free flame retardancy. In summary, from molecular-level chemical synthesis to macroscopic-level processing, each step contains profound chemical and physical mechanisms. Through ingenious synergistic effects, the various components ultimately create a battery bracket material with excellent comprehensive performance.

[0018] According to a preferred embodiment of the present invention, in step S1, the vacuum drying time at 98-102°C is 12-14 hours; the mixing time in the high-speed mixer is 3-5 minutes.

[0019] According to a preferred embodiment of the present invention, in step S2, the screw speed of the twin-screw extruder is 350-400 rpm; the treatment step of the alkali-free chopped glass fiber treated with γ-aminopropyltriethoxysilane includes: immersing the alkali-free chopped glass fiber in a γ-aminopropyltriethoxysilane ethanol solution, and then drying it at 110-120°C.

[0020] According to a preferred embodiment of the present invention, in step S3, the drying time at 98-102°C is 4-6 hours.

[0021] The beneficial effects of this invention are as follows: The flame-retardant recycled polyamide electric vehicle battery bracket plastic provided by this invention exhibits superior comprehensive technical effects, significantly improving the material's performance in mechanical properties, flame-retardant safety, and environmental friendliness. Firstly, this material system achieves a balance of high strength, high rigidity, and good toughness through innovative component design and synergistic effects. Using recycled polyamide as the matrix not only effectively reduces costs but also endows the product with environmental value; while the addition of alkali-free chopped glass fibers significantly improves the material's mechanical strength and dimensional stability. Crucially, the specially designed polydopamine-grafted polyphosphonate interface compatibilizer has polydopamine segments in its molecular structure that have good affinity with the recycled polyamide matrix, while the polyphosphonate segments can interact with the flame retardant and glass fiber surface, greatly improving the compatibility and adhesion between multiphase interfaces. This strong interfacial bonding effectively avoids stress concentration caused by interfacial defects, ensuring efficient transfer of external forces between components. This results in excellent tensile strength, flexural modulus, and impact toughness of the composite material, fully meeting the stringent structural integrity requirements of battery brackets under complex vehicle operating conditions.

[0022] Secondly, this material has achieved a breakthrough in flame retardant performance. The zinc-based organophosphorus phenanthrene framework flame retardant used is a novel metal-organic framework material carefully prepared via a solvothermal method. This flame retardant effectively captures free radicals in the early stages of combustion, interrupting the combustion chain reaction; in the condensed phase, it promotes the formation of a dense and stable char layer on the material surface. This char layer not only isolates heat and oxygen transfer but also inhibits the escape of combustible gases, thus exerting a highly efficient gas-phase and condensed-phase synergistic flame retardant mechanism. Due to its unique framework structure and high specific surface area, this flame retardant achieves excellent flame retardant ratings with a relatively low addition amount, greatly reducing the negative impact on the mechanical properties of the matrix material, resolving the contradiction between the addition amount and performance retention rate of traditional flame retardants, and ensuring the high safety of the product.

[0023] Finally, the material formulation system is scientifically complete, with each auxiliary component working synergistically to ensure excellent processing stability and long-term durability. The compound use of antioxidants effectively inhibits thermo-oxidative aging of the material during high-temperature processing and subsequent use, extending the product life. The addition of lubricants and silane coupling agents not only improves processing fluidity and reduces equipment wear, but also further strengthens the interfacial bonding between glass fiber and resin. The entire preparation process is rationally designed, ensuring uniform dispersion and good orientation of each component, especially glass fiber and polytetrafluoroethylene, in the matrix through two-stage feeding and precise temperature control and screw shearing. The resulting particles have good processability, and the products obtained after injection molding have a smooth appearance, dense internal structure, and uniform performance. They also possess multiple advantages such as lightweight, low cost, high reliability, and environmental friendliness, making them ideal materials for electric vehicle battery brackets. Detailed Implementation

[0024] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content.

[0025] The following is information on domestic suppliers of key related equipment and materials: The alkali-free chopped glass fiber was purchased from China Jushi Co., Ltd.

[0026] The polytetrafluoroethylene was purchased from Zhonghao Chenguang Chemical Research Institute Co., Ltd.

[0027] The antioxidant 1098 / antioxidant 168 was purchased from BASF (China) Co., Ltd.

[0028] The zinc stearate was purchased from Hangzhou Oil & Fat Chemical Co., Ltd.

[0029] The γ-aminopropyltriethoxysilane was purchased from Nanjing Shuguang Chemical Group Co., Ltd.

[0030] The DOPO was purchased from Anqing Huiyinbi Pharmaceutical Co., Ltd.

[0031] The terephthalaldehyde was purchased from Zhejiang Baikang Chemical Co., Ltd.

[0032] The xylene was purchased from China Petroleum & Chemical Corporation (Sinopec).

[0033] The nitrogen gas was purchased from Hangzhou Oxygen Plant Group Co., Ltd.

[0034] The sodium carbonate solution was purchased from Tianjin Bohua Yongli Chemical Co., Ltd.

[0035] The hydrogen peroxide was purchased from Zhejiang Satellite Petrochemical Co., Ltd.

[0036] The dilute hydrochloric acid was purchased from Shanghai Huayi Group Co., Ltd.

[0037] The zinc nitrate was purchased from Changshu Hongjia Fluorine Technology Co., Ltd.

[0038] The high-pressure reactor was purchased from Senmatsu (China) Investment Co., Ltd.

[0039] The ethanol was purchased from Jilin Fuel Ethanol Co., Ltd.

[0040] The Tris-HCl buffer solution was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0041] The dopamine hydrochloride was purchased from Alfa Essa (China) Chemical Co., Ltd.

[0042] The 2-chloro-2-oxo-1,3,2-dioxophosphoric acid cyclopentane was purchased from Yantai Jiumu Chemical Co., Ltd.

[0043] The triethylamine was purchased from Zhejiang Xinhua Chemical Co., Ltd.

[0044] The diethyl ether was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0045] The high-speed mixer was purchased from Zhangjiagang Yili Machinery Co., Ltd.

[0046] The twin-screw extruder was purchased from Keya Equipment (Shenzhen) Co., Ltd.

[0047] The injection molding machine was purchased from Haitian Plastics Machinery Group Co., Ltd.

[0048] Example 1 Preparation of zinc-based organophosphorus phenanthrene framework flame retardants: 20.6 g DOPO and 6.7 g terephthalaldehyde were dissolved in 150 mL xylene, and the mixture was heated to 140 °C for 9 hours under nitrogen protection. The mixture was cooled to 25 °C, filtered, and washed three times with 100 mL ethanol to obtain an aldehyde intermediate. This intermediate was dissolved in 200 mL of 10% sodium carbonate solution, and 15 mL of 30% hydrogen peroxide was slowly added with stirring. The mixture was stirred at 60 °C for 7 hours. The reaction solution was cooled to 25 °C, and 10% dilute hydrochloric acid was slowly added with stirring to adjust the pH to 2.5, resulting in the precipitation of a white solid. The filter cake was washed with water until neutral and dried under vacuum at 72 °C for 12 hours to obtain the purified DOPO TA ligand. 14.9 g of zinc nitrate and 32.2 g of DOPO TA ligand were dissolved in 300 mL of N,N-dimethylformamide and sonicated for 30 minutes. The solution was then transferred to a 500 mL high-pressure reactor lined with polytetrafluoroethylene and reacted solvothermically at 120 °C for 28 hours. After the reaction, the solution was allowed to cool naturally to 25 °C, and white crystals precipitated. The crystals were washed three times each with N,N-dimethylformamide and ethanol, and finally dried under vacuum at 120 °C for 24 hours to obtain a zinc-based organophosphorus phenanthrene framework flame retardant. Preparation of polydopamine-grafted polyphosphonate interfacial compatibilizer: 20.0 g of dopamine hydrochloride was dissolved in 500 mL of Tris HCl buffer (pH 8.5), and polymerized by stirring at 25 °C for 28 hours to obtain a polydopamine solution. The polydopamine solid was collected after centrifugation and washing with water. Polydopamine solid was dispersed in 300 mL of anhydrous N,N-dimethylformamide. 25.0 g of 2-chloro-2-oxo-1,3,2-dioxophosphazenecyclopentane was slowly added dropwise to the solution, along with 15.0 g of triethylamine. The reaction was carried out in an ice bath for 3 hours, then the temperature was raised to 50 °C and the reaction continued for 19 hours. After the reaction was completed, the reaction solution was poured into 1000 mL of ice-cold diethyl ether with stirring, resulting in the precipitation of a brown solid. The solid product was collected by filtration and washed three times with diethyl ether. Finally, the product was vacuum-dried at 45 °C for 6 hours to obtain a polydopamine-grafted polyphosphonate interfacial compatibilizer. Preparation of flame-retardant recycled PA6 electric vehicle battery bracket plastic: 6500 g of recycled PA6 was vacuum-dried at 100 °C for 13 hours, and 2000 g of alkali-free chopped glass fiber was dried at 110 °C for 6 hours. Weigh out 6500g of dried recycled PA6, 700g of zinc-based organophosphorus phenanthrene framework flame retardant, 400g of polydopamine-grafted polyphosphonate interface compatibilizer, 200g of antioxidant 1098, 200g of antioxidant 168, and 350g of zinc stearate, and mix them in a high-speed mixer for 4 minutes to obtain a premix. Add the premix to the main feed port of a twin-screw extruder. The temperature settings for each zone of the screw, from the feeding section to the die head, are 230℃, 240℃, 250℃, 255℃, 260℃, and 255℃ respectively.2000g of alkali-free chopped glass fiber was impregnated with 100g of a 2.0 wt% γ-aminopropyltriethoxysilane ethanol solution, ensuring uniform wetting. After initial drying at 80℃ for 20 minutes, it was then cured in an oven at 115℃ for 3 hours. After cooling, the resulting alkali-free chopped glass fiber treated with γ-aminopropyltriethoxysilane ethanol solution and 20g of polytetrafluoroethylene were fed into the side feed port in the middle of the melting zone at a screw speed of 380rpm. The melt-blended material was extruded through a die, cooled in a water bath, dried, and pelletized. Finally, the pellets were dried at 100℃ for 5 hours and then injection molded.

[0049] Example 2 The specific implementation method is the same as in Example 1, except that the zinc-based organophosphorus phenanthrene framework flame retardant is prepared as follows: 18.5 g of DOPO and 6.0 g of terephthalaldehyde are dissolved in 130 mL of xylene, and the mixture is heated to 139 °C and reacted for 8 hours under nitrogen protection. After cooling to 26 °C and filtering, the mixture is washed three times with 90 mL of ethanol to obtain an aldehyde intermediate. This intermediate is dissolved in 180 mL of 10% sodium carbonate solution, and 13 mL of 30% hydrogen peroxide is slowly added while stirring. The mixture is stirred at 59 °C for 6 hours. The reaction solution is cooled to 26 °C, and 10% dilute hydrochloric acid is slowly added while stirring to adjust the pH to 2.2, resulting in the precipitation of a white solid. After filtration, the filter cake is washed with water until neutral, and then vacuum dried at 71 °C for 11 hours to obtain the purified DOPO TA ligand. 13.5 g of zinc nitrate and 29.0 g of DOPO TA ligand were dissolved in 270 mL of N,N-dimethylformamide and sonicated for 28 minutes. The solution was then transferred to a 450 mL high-pressure reactor lined with polytetrafluoroethylene and solvothermal reacted at 119 °C for 26 hours. After the reaction, the solution was allowed to cool naturally to 26 °C, and white crystals precipitated. The crystals were washed three times each with N,N-dimethylformamide and ethanol, and finally vacuum dried at 119 °C for 22 hours to obtain a zinc-based organophosphorus phenanthrene framework flame retardant. Preparation of polydopamine-grafted polyphosphonate interfacial compatibilizer: 18.0 g of dopamine hydrochloride was dissolved in 450 mL of Tris HCl buffer (pH 8.4), and polymerized by stirring at 26 °C for 26 hours to obtain a polydopamine solution. The polydopamine solid was collected after centrifugation and washing with water. Polydopamine solid was dispersed in 270 mL of anhydrous N,N-dimethylformamide. 22.5 g of 2-chloro-2-oxo-1,3,2-dioxophosphazenecyclopentane was slowly added dropwise to the solution, along with 13.5 g of triethylamine. The reaction was carried out in an ice bath for 2.5 hours, then the temperature was raised to 49 °C and the reaction continued for 18 hours. After the reaction was completed, the reaction solution was poured into 900 mL of ice-cold diethyl ether with stirring, resulting in the precipitation of a brown solid. The solid product was collected by filtration and washed three times with diethyl ether. Finally, the product was vacuum-dried at 42 °C for 5.5 hours to obtain a polydopamine-grafted polyphosphonate interfacial compatibilizer. Preparation of flame-retardant recycled PA6 electric vehicle battery bracket plastic: 5500 g of recycled PA6 was vacuum-dried at 99 °C for 12 hours, and 1500 g of alkali-free chopped glass fiber was dried at 109 °C for 5 hours. Weigh out 5500g of dried recycled PA6, 400g of zinc-based organophosphorus phenanthrene framework flame retardant, 200g of polydopamine-grafted polyphosphonate interface compatibilizer, 150g of antioxidant 1098, 150g of antioxidant 168, and 200g of zinc stearate, and mix them in a high-speed mixer for 3 minutes to obtain a premix. Add the premix from the main feed port of a twin-screw extruder.1500g of alkali-free chopped glass fiber and 10g of polytetrafluoroethylene, treated with 50g of γ-aminopropyltriethoxysilane ethanol solution, were added from the side feed port in the middle of the melting zone, with the screw speed at 350rpm. Finally, the granules were dried at 99℃ for 4 hours and then molded using an injection molding machine.

[0050] Example 3 The specific implementation method is the same as in Example 1, except that the zinc-based organophosphorus phenanthrene framework flame retardant is prepared as follows: 22.8 g of DOPO and 7.4 g of terephthalaldehyde are dissolved in 170 mL of xylene, and the mixture is heated to 141 °C and reacted for 10 hours under nitrogen protection. The mixture is cooled to 28 °C, filtered, and washed three times with 110 mL of ethanol to obtain an aldehyde intermediate. This intermediate is dissolved in 220 mL of 10% sodium carbonate solution, and 17 mL of 30% hydrogen peroxide is slowly added while stirring. The mixture is stirred at 61 °C for 8 hours. The reaction solution is cooled to 28 °C, and 10% dilute hydrochloric acid is slowly added while stirring to adjust the pH to 2.8, resulting in the precipitation of a white solid. After filtration, the filter cake is washed with water until neutral and dried under vacuum at 74 °C for 13 hours to obtain the purified DOPO TA ligand. 16.3 g of zinc nitrate and 35.4 g of DOPO TA ligand were dissolved in 330 mL of N,N-dimethylformamide and sonicated for 32 minutes. The solution was then transferred to a 550 mL high-pressure reactor lined with polytetrafluoroethylene and reacted solvothermically at 121 °C for 30 hours. After the reaction, the solution was allowed to cool naturally to 28 °C, and white crystals precipitated. The crystals were washed three times each with N,N-dimethylformamide and ethanol, and finally dried under vacuum at 121 °C for 26 hours to obtain a zinc-based organophosphorus phenanthrene framework flame retardant. Preparation of polydopamine-grafted polyphosphonate interfacial compatibilizer: 22.0 g of dopamine hydrochloride was dissolved in 550 mL of Tris HCl buffer (pH=8.6), and polymerized by stirring at 28 °C for 30 hours to obtain a polydopamine solution. The polydopamine solid was collected after centrifugation and washing with water. Polydopamine solid was dispersed in 330 mL of anhydrous N,N-dimethylformamide. 27.5 g of 2-chloro-2-oxo-1,3,2-dioxophosphazenecyclopentane was slowly added dropwise to the solution, along with 16.5 g of triethylamine. The reaction was carried out in an ice bath for 3.5 hours, then the temperature was raised to 51 °C and the reaction continued for 20 hours. After the reaction was completed, the reaction solution was poured into 1100 mL of ice-cold diethyl ether with stirring, resulting in the precipitation of a brown solid. The solid product was collected by filtration and washed three times with diethyl ether. Finally, the product was vacuum-dried at 48 °C for 7.5 hours to obtain a polydopamine-grafted polyphosphonate interface compatibilizer. Preparation of flame-retardant recycled PA6 electric vehicle battery bracket plastic: 7500 g of recycled PA6 was vacuum-dried at 101 °C for 14 hours, and 2500 g of alkali-free chopped glass fiber was dried at 111 °C for 7 hours. Weigh out 500g of dried recycled PA67, 1000g of zinc-based organophosphorus phenanthrene framework flame retardant, 600g of polydopamine-grafted polyphosphonate interface compatibilizer, 300g of antioxidant 1098, 300g of antioxidant 168, and 500g of zinc stearate, and mix them in a high-speed mixer for 5 minutes to obtain a premix. Add the premix from the main feed port of a twin-screw extruder.2500g of alkali-free chopped glass fiber and 30g of polytetrafluoroethylene, treated with 150g of γ-aminopropyltriethoxysilane ethanol solution, were added from the side feed port in the middle of the melting zone, with the screw speed at 400rpm. Finally, the granules were dried at 101℃ for 6 hours and then molded using an injection molding machine.

[0051] Comparative Example 1 The specific implementation method is the same as in Example 1, except that zinc-based organophosphorus phenanthrene framework flame retardant and polydopamine-grafted polyphosphonate interface compatibilizer are not added.

[0052] Comparative Example 2 The specific implementation method is the same as in Example 1, except that no zinc-based organophosphorus phenanthrene framework flame retardant is added.

[0053] Comparative Example 3 The specific implementation method is the same as in Example 1, except that no polydopamine-grafted polyphosphonate interface compatibilizer is added.

[0054] Performance testing The flame-retardant recycled PA6 electric vehicle battery bracket plastics prepared according to Examples 1-3 and Comparative Examples 1-3 were tested as follows: All test samples were conditioned in a standard laboratory environment (temperature 23±2℃, relative humidity 50±5%) for at least 48 hours after injection molding. Tensile properties were tested according to ASTM D638 using a universal testing machine at a tensile speed of 50 mm / min, with type I test specimens, and at least 5 valid specimens were taken as the average value for each test group. Flexural properties were tested according to ASTM D790 using a universal testing machine with a span of 64 mm, a loading speed of 2 mm / min, and test specimen dimensions of 80 mm × 10 mm × 4 mm, with at least 5 valid specimens taken as the average value for each test group. Notched impact strength testing was conducted according to ASTM D256 using a cantilever beam impact testing machine. The notch depth was 2.54 mm, the notch tip radius was 0.25 mm, the pendulum energy was 5.5 J, and the test specimen size was 63.5 mm × 12.7 mm × 4 mm. At least five valid specimens were tested in each group, and the average value was taken. Flame retardancy testing was conducted according to UL-94 vertical burning. The specimen size was 130 mm × 13 mm × 3.2 mm, the Bunsen burner flame height was 20 mm, and the flame application time was 10 seconds. The flaming time (t1 and t2) after the first and second flame extinguishing and whether the absorbent cotton was ignited were recorded. Based on this, a V-0, V-1, V-2, or NR (no rating) rating was assigned. The Limiting Oxygen Index (LOI) test was conducted according to ASTM D2863 using an oxygen index meter. The specimen size was 100 mm × 10 mm × 4 mm. The initial oxygen concentration was based on the estimated result. The LOI was determined by the specimen burning continuously in a nitrogen-oxygen mixed gas flow for 3 minutes or a burning distance of 50 mm. At least three valid specimens were used in each test group, and the average value was taken. The Heat Deflection Temperature (HDT) test was conducted according to ASTM D648 using a load of 1.82 MPa and a heating rate of 2 °C / min. The specimen size was 125 mm × 13 mm × 3.2 mm. The temperature at which the deformation reached 0.25 mm was recorded as the HDT. At least two valid specimens were used in each test group, and the average value was taken.

[0055] Performance test results: Table 1: Performance test results of each embodiment and comparative example ; Based on the comparative analysis of the performance test results of Examples 1-3 and Comparative Examples 1-3 in Table 1 above, it can be clearly concluded that the embodiments of the present invention have successfully solved the three major technical problems of insufficient flame retardancy, poor mechanical properties, and poor interfacial compatibility between recycled plastics and additives in existing electric vehicle battery bracket materials.

[0056] Firstly, regarding flame retardancy, Comparative Example 1 (without any functional additives) had a limiting oxygen index (LOI) of only 19.5% and no UL-94 rating (NR), indicating that the basic recycled PA6 material is highly flammable and cannot meet the safety requirements of the battery holder. While Comparative Example 2 (using only the interface compatibilizer) showed improved flame retardancy (LOI 26.0%, UL-94 V-1), Comparative Example 3 (using only the flame retardant) only achieved UL-94 V-2 and a LOI of 24.5%, demonstrating that the flame retardant effect of either ingredient alone is limited. In contrast, Examples 1-3, which added both additives simultaneously, exhibited superior flame retardant performance, with LOI values ​​exceeding 30% (up to 33.8%) and all meeting the highest flame retardant standard of UL-94 V-0. This indicates that the zinc-based metal-organophosphorus phenanthrene framework flame retardant and the polydopamine-grafted-polyphosphonate interface compatibilizer produced a significant synergistic flame retardant effect, completely solving the key problem of insufficient material flame retardancy.

[0057] Secondly, regarding mechanical properties, the mechanical properties of Comparative Example 1 (tensile strength 78 MPa, flexural strength 105 MPa, notched impact strength 5.0 kJ / m) are as follows: 2 The mechanical properties of the samples were all at a low level, making it difficult to withstand the mechanical load of the battery pack. The mechanical properties of Examples 1-3 were comprehensively and significantly enhanced. The tensile strength (138-152 MPa) and flexural strength (198-218 MPa) were more than doubled compared to Comparative Example 1, and the notched impact strength was also increased by approximately 150%. More importantly, compared to Comparative Example 3, the mechanical properties of the examples were significantly improved due to the presence of the interfacial compatibilizer, even with the addition of an equal amount of flame retardant (e.g., tensile strength of Example 1 145 MPa vs. Comparative Example 3 102 MPa). This directly demonstrates that the interfacial compatibilizer effectively solves the problem of decreased mechanical properties caused by the addition of inorganic fillers by enhancing the interfacial bond between the recycled PA6 matrix, glass fiber, and flame retardant, thus enabling the material to simultaneously possess high strength, high toughness, and high modulus.

[0058] Finally, performance data provides indirect but compelling evidence regarding the resolution of interfacial compatibility issues. Comparative Example 3 (lacking an interfacial compatibilizer) exhibited significantly lower mechanical properties and heat distortion temperature (172°C) compared to examples with the same amount of flame retardant. This indicates that the lack of good interfacial compatibility leads to uneven flame retardant dispersion and weak bonding with the matrix, thus becoming a performance bottleneck. The high-performance balance of Examples 1-3 fully demonstrates that the polydopamine-grafted-polyphosphonate interfacial compatibilizer successfully bridged the recycled PA6 with the non-polar glass fiber and flame retardant particles, improving interfacial compatibility, promoting stress transfer between components, and avoiding interfacial defects. This allows multiple additives to work synergistically, ultimately resulting in a battery holder material with excellent overall performance.

[0059] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A flame-retardant recycled PA6 electric vehicle battery bracket plastic, characterized in that, Including the following parts by weight of raw materials: Recycled PA6: 55-75 parts by weight; Alkali-free chopped glass fiber: 15-25 parts by weight; Zinc-based metal-organophosphorus phenanthrene framework flame retardant: 4-10 parts by weight; Polydopamine-grafted-polyphosphonate interface compatibilizer: 2-6 parts by weight; Polytetrafluoroethylene: 0.1-0.3 parts by weight; Antioxidant 1098 / Antioxidant 168: 0.3-0.6 parts by weight; Zinc stearate: 0.2-0.5 parts by weight; γ-aminopropyltriethoxysilane: 0.5-1.5 parts by weight; The preparation method of the zinc-based metal-organophosphorus phenanthrene framework flame retardant includes: A1. Dissolving DOPO and terephthalaldehyde in xylene, and reacting at 138-142℃ under nitrogen protection; filtering after cooling, and washing with ethanol to obtain an aldehyde intermediate; then dissolving the aldehyde intermediate in sodium carbonate solution, adding hydrogen peroxide while stirring, and reacting at 58-62℃; subsequently cooling the reaction solution to 20-30℃, adding dilute hydrochloric acid while stirring, adjusting the pH to 2-3, and precipitating a solid. A1. Filter the filter cake, wash it with water until neutral, and finally dry it under vacuum at 70-75℃ to obtain purified DOPO-TA ligand; A2. Dissolve zinc nitrate and DOPO-TA ligand in N,N-dimethylformamide, sonicate to dissolve, transfer to a high-pressure reactor with a polytetrafluoroethylene liner, and solvothermal reaction at 118-122℃; After the reaction is completed, cool naturally to room temperature to precipitate crystals, wash with N,N-dimethylformamide and ethanol, and finally dry under vacuum at 118-122℃.

2. The flame-retardant recycled PA6 electric vehicle battery bracket plastic according to claim 1, characterized in that, In step A1, the reaction time is 8-10 hours when the temperature is raised to 138-142℃; the reaction time is 6-8 hours when the temperature is stirred at 58-62℃.

3. The flame-retardant recycled PA6 electric vehicle battery bracket plastic according to claim 1, characterized in that, In step A2, the solvothermal reaction time at 118-122℃ is 24-30h.

4. The flame-retardant recycled PA6 electric vehicle battery bracket plastic according to claim 1, characterized in that, The preparation method of the polydopamine-grafted-polyphosphonate interface compatibilizer includes: B1, dissolving dopamine hydrochloride in Tris-HCl buffer solution with pH=8.4-8.6, stirring and polymerizing at room temperature to obtain a polydopamine solution, centrifuging and washing with water to collect the polydopamine solid, and then dispersing the polydopamine solid in anhydrous N,N-dimethylformamide; adding 2-chloro-2-oxo-1,3,2-dioxophosphazenecyclopentane dropwise to the polydopamine solution, and simultaneously adding triethylamine, reacting under ice bath conditions, and then heating to 48-52℃ to continue the reaction; B2, after the reaction is completed, pouring the reaction solution into ice-cold diethyl ether under stirring to precipitate the solid; collecting the solid product by filtration and washing with diethyl ether; finally, vacuum drying the product at 40-50℃.

5. The flame-retardant recycled PA6 electric vehicle battery bracket plastic according to claim 4, characterized in that, In step B1, the stirring polymerization time is 24-30 h; the reaction time under ice bath conditions is 2-4 h; and the reaction time is continued at 48-52℃ for 18-20 h.

6. The flame-retardant recycled PA6 electric vehicle battery bracket plastic according to claim 4, characterized in that, In step B2, the vacuum drying time at 40-50℃ is 5-8 hours.

7. A method for preparing flame-retardant recycled PA6 electric vehicle battery bracket plastic according to any one of claims 1-6, characterized in that, step include: S1. Vacuum dry the recycled PA6 at 98-102℃; dry the alkali-free chopped glass fiber at 108-112℃; weigh the dried recycled PA6, zinc-based metal-organophosphorus phenanthrene framework flame retardant, polydopamine-grafted-polyphosphonate interface compatibilizer, antioxidant 1098 / antioxidant 168, and zinc stearate and mix them in a high-speed mixer to obtain a premix. S2. The premixed material is added from the main feed port of the twin-screw extruder. The temperature settings of each zone of the screw from the feeding section to the die head are 230℃, 240℃, 250℃, 255℃, 260℃, and 255℃ respectively. The alkali-free chopped glass fiber and polytetrafluoroethylene treated with γ-aminopropyltriethoxysilane are added from the side feed port in the middle section of the melting zone. The melt-blended material is extruded through a die, cooled in a water bath, dried, and pelletized. S3. Finally, after drying the granules at 98-102℃, they are molded using an injection molding machine.

8. The preparation method according to claim 7, characterized in that, In step S1, the vacuum drying time at 98-102℃ is 12-14 hours; the mixing time in the high-speed mixer is 3-5 minutes.

9. The preparation method according to claim 7, characterized in that, In step S2, the screw speed of the twin-screw extruder is 350-400 rpm; the treatment steps of the alkali-free chopped glass fibers treated with γ-aminopropyltriethoxysilane include: immersing the alkali-free chopped glass fibers in a γ-aminopropyltriethoxysilane ethanol solution, and then drying them at 110-120°C.

10. The preparation method according to claim 7, characterized in that, In step S3, the drying time is 4-6 hours at 98-102℃.