Mof flame-retardant recycled abs composite material and preparation method thereof

Abstract

The application belongs to the technical field of polymer composites, and particularly relates to a MOF flame-retardant recycled ABS composite material and a preparation method thereof; the composite material takes recycled ABS as a matrix, adds a zirconium-lanthanum bimetallic organic framework flame retardant containing a phosphorus ligand and a borosilicon zirconium-based organic-inorganic hybrid flame retardant as core flame-retardant components through co-assembly, and is supplemented with a specific interfacial compatibilizer and a processing aid. The preparation method mainly comprises the following steps: drying and pre-mixing the components, melt blending and extruding granulation through a double-screw extruder in a specific temperature range, and finally injection molding. The method utilizes the synergistic effect of the two flame retardants and the compatibilization effect of the interfacial compatibilizer, improves the flame-retardant performance of the composite material, and effectively maintains the mechanical properties. The application has a simple and efficient process, the obtained composite material has excellent comprehensive performance, and is suitable for large-scale production of recycled ABS products with flame-retardant requirements.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite material technology, specifically relating to a MOF flame-retardant recycled ABS composite material and its preparation method. Background Technology

[0002] Recycled acrylonitrile-butadiene-styrene (ABR) plastics are a key material for achieving a circular economy in plastics, and their high-value utilization is of great significance for environmental protection and resource conservation. However, after multiple processing and uses, the molecular chains of post-consumer recycled ABR plastics may break or cross-link, leading to a certain degree of decline in mechanical properties, especially impact toughness. More importantly, the ABR matrix itself is a flammable material, and the recycling process usually cannot impart flame-retardant properties, which severely limits its application in fields such as electronics, automotive parts, and other areas with strict requirements for flame-retardant safety. Therefore, how to efficiently and environmentally improve the flame-retardant rating of recycled ABR plastics without significantly damaging its original mechanical properties has become a critical technical bottleneck that urgently needs to be overcome in the high-value recycling of this material.

[0003] Currently, research on flame-retardant modification of recycled acrylonitrile-butadiene-styrene mainly draws on the flame-retardant technology of Virgin materials. While traditional halogenated flame retardants are highly efficient, they suffer from problems such as releasing toxic fumes during combustion and being environmentally unfriendly, leading to increasingly stringent regulatory restrictions on their application. Halogen-free flame-retardant systems, such as metal hydroxides and intumescent flame retardants, often require high addition levels to achieve the desired flame-retardant effect. High filler content can easily lead to a sharp increase in the melt viscosity of the composite material, deterioration of processing performance, and serious negative impacts on the material's toughness, strength, and other mechanical properties, resulting in a trade-off. In recent years, metal-organic frameworks (MOFs), as a novel type of porous crystalline material, have shown unique potential in the field of polymer flame retardancy. Their high specific surface area, adjustable pore size, and high thermal stability enable them to promote the formation of a dense char layer in the condensed phase and adsorb free radicals and delay combustion in the gas phase. However, directly applying metal-organic framework nanoparticles to polymer matrices, especially when composited with recycled acrylonitrile-butadiene-styrene, still faces two major challenges: First, metal-organic framework nanoparticles are prone to aggregation due to their extremely high surface energy, making it difficult to achieve uniform nanoscale dispersion in hydrophobic polymer matrices, thus affecting the full realization of flame retardant efficiency; Second, the interfacial compatibility between the inorganic surface of the metal-organic framework and the organic polymer matrix is ​​poor, and the interfacial bonding force is weak, making it easy to become a stress concentration point under stress, thereby aggravating the loss of material mechanical properties.

[0004] To overcome these obstacles, researchers have attempted to modify the surface of metal-organic frameworks (MOFs) or add compatibilizers. Common approaches include pretreating the MOFs with silane coupling agents or introducing reactive compatibilizers such as maleic anhydride-grafted polymers into the blend system. These methods improve dispersibility and interfacial adhesion to some extent. However, these physical coating or simple grafting methods typically only focus on improving compatibility and do not enhance the intrinsic flame-retardant performance of the MOFs themselves at the molecular design level, resulting in limited improvement in flame-retardant efficiency. Furthermore, the complex composition and aging history of recycled acrylonitrile-butadiene-styrene (CRS) matrix make interfacial problems more prominent, and single modification strategies often fail to simultaneously achieve significant improvements in flame-retardant performance and good maintenance of mechanical properties. Therefore, developing a novel multifunctional flame retardant that can generate strong interfacial interactions with the recycled acrylonitrile-butadiene-styrene matrix and possesses highly efficient intrinsic flame-retardant properties, and achieving a balance between flame retardancy and mechanical properties at a lower addition level through a synergistic flame-retardant mechanism, has become an important research direction in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a MOF flame-retardant recycled ABS composite material and its preparation method.

[0006] In a first aspect, the present invention provides a method for preparing MOF flame-retardant recycled ABS composite material, comprising the following steps:

[0007] S1. By weight, 80-92 parts of recycled ABS granules are dried in a forced-air drying oven at 84-86℃; 5-10 parts of zirconium-lanthanum bimetallic organic framework flame retardant co-assembled with phosphorus ligands and 3-8 parts of zirconium borosilicate-based organic-inorganic hybrid flame retardant are dried in a vacuum drying oven at 118-122℃; 3-8 parts of interface compatibilizer are dried at 78-82℃; the dried recycled ABS granules, zirconium-lanthanum bimetallic organic framework flame retardant co-assembled with phosphorus ligands, zirconium borosilicate-based organic-inorganic hybrid flame retardant and interface compatibilizer are added to a mixer with 0.1-0.5 parts of antioxidant 1010 and 0.05-0.2 parts of calcium stearate, and mixed at room temperature to obtain a premix; the premix is ​​fed into a twin-screw extruder to obtain a melt; the melt is extruded, water-cooled, and dried, and then cut by a pelletizer to obtain composite material granules;

[0008] S2. Dry the composite material particles at 84-86℃ and then use an injection molding machine to inject them at an injection temperature of 200-220℃.

[0009] In this invention, the preparation of the MOF flame-retardant recycled ABS composite material is based on an in-situ interfacial compatibilization mechanism through melt blending. When the premixed material is melted at high temperature and under strong shear in an extruder, the active functional groups of the interfacial compatibilizer migrate directionally to the interface between the flame retardant and the plastic matrix: the anhydride groups undergo ring-opening / esterification reactions with the epoxy or hydroxyl groups on the surface of the zirconium borosilicate hybrid particles; the epoxy groups can also react with the hydroxyl groups. Simultaneously, the anhydride or epoxy groups in the interfacial compatibilizer form strong hydrogen bonds with the residual carboxyl groups on the surface of the metal-organic framework through their electronegative oxygen atoms. This chemical bonding and physical entanglement significantly improves the uniformity of filler dispersion and the interfacial bonding strength. During combustion, the metal-organic framework decomposes to release non-combustible gases, diluting oxygen and catalyzing the formation of a dense char layer in the matrix; the zirconium borosilicate hybrid agent melts at high temperature to generate a continuous borosilicate ceramic film, effectively isolating heat and oxygen transfer. Through the synergistic effect of gas-phase dilution cooling and condensed-phase barrier insulation, the flame-retardant performance is significantly improved, while the retention rate of the mechanical properties of the recycled plastic is significantly optimized, providing a green technology path for the high-value recycling of waste plastics.

[0010] According to a preferred embodiment of the present invention, in step S1, the interface compatibilizer is interface compatibilizer SMA800; the temperature of each section of the twin-screw extruder from the feed port to the die is set as follows: 168-172℃, 184-186℃, 198-202℃, 208-212℃, 208-212℃, 204-206℃, wherein the temperature range of the fourth zone and the fifth zone is the same, both being 208-212℃.

[0011] According to a preferred embodiment of the present invention, in step S2, the mold temperature of the injection molding machine is 50-80°C.

[0012] According to a preferred embodiment of the present invention, the method for preparing the zirconium-lanthanum bimetallic organic framework flame retardant co-assembled with phosphorus-containing ligands includes:

[0013] A1. By weight, dissolve 1.0-1.1 parts of zirconium nitrate hexahydrate and 0.22-0.24 parts of lanthanum nitrate hexahydrate together in 38-42 parts of N,N-dimethylformamide, and disperse by ultrasonication to obtain solution A; dissolve 0.32-0.35 parts of trimesic acid and 0.11-0.15 parts of 2-carboxyethylphenylphosphonic acid together in 19-21 parts of N,N-dimethylformamide to obtain solution B; add solution B dropwise to solution A with stirring, then add 4.8-5.2 parts of glacial acetic acid and 1.8-2.2 parts of deionized water to obtain a mixture; transfer the mixture to a reaction vessel and react it solvothermally at 118-122℃ to obtain a reaction mixture;

[0014] A2. The reaction mixture was naturally cooled to room temperature and centrifuged to obtain a solid precipitate. The solid precipitate was washed successively with N,N-dimethylformamide and anhydrous methanol. Finally, it was dried under vacuum at 148-152℃.

[0015] In this invention, the preparation of the zirconium-lanthanum bimetallic organic framework flame retardant co-assembled with phosphorus-containing ligands relies on a solvothermal coordination self-assembly mechanism. Soluble zirconium and lanthanum salts are co-dissolved in a polar aprotic solvent to form a homogeneous metal precursor. Aromatic polycarboxylic acid ligands and phosphorus-containing functional carboxylic acid ligands are dissolved in the same solvent to prepare a ligand solution. The ligand solution is added dropwise to the metal solution under continuous stirring, and an organic acid crystallization regulator and trace amounts of water are introduced to control the nucleation kinetics. The closed system is subjected to programmed temperature rise, where metal ions and carboxylic acid groups construct zirconium-lanthanum-containing metal-oxygen cluster nodes through coordination bonds. The phosphorus-containing ligands act as bridging units embedded in the framework, forming a porous material with high crystallinity, regular nanopores, and a large specific surface area. The product is cooled, separated from the liquid, washed with solvent displacement, and vacuum dried to obtain a white powder. Phosphorus is uniformly distributed in the framework in the form of chemical bonds. When heated, it promotes dehydration and char formation and releases flame-retardant gases. The bimetallic synergy significantly improves thermal stability, and the porous structure effectively adsorbs pyrolysis products, achieving a dual flame-retardant effect of gas-phase dilution and condensed-phase catalytic char formation.

[0016] According to a preferred embodiment of the present invention, in step A1, the solvothermal reaction time at 118-122°C is 36-42 h.

[0017] According to a preferred embodiment of the present invention, in step A2, the vacuum drying time at 148-152°C is 12-14 hours.

[0018] According to a preferred embodiment of the present invention, the preparation method of the zirconium borosilicate-based organic-inorganic hybrid flame retardant includes:

[0019] B1. Dissolve 1.0-1.1 parts by weight of zirconium oxychloride octahydrate in a mixed solvent of 48-52 parts anhydrous ethanol and 9-11 parts deionized water; under nitrogen protection and in an ice-water bath at 0-5℃, add 1.2-1.4 parts of tetraethyl orthosilicate, and reflux at 58-62℃ to obtain zirconium-silica sol; add 0.66-0.73 parts of triethyl borate solution dissolved in 9-11 parts anhydrous ethanol to the zirconium-silica sol, and continue the reaction at 58-62℃ to obtain the reaction solution;

[0020] B2. The reaction solution is dried at 78-82℃ to obtain a dry gel. The dry gel is ground to obtain a powder. The powder is dispersed in 58-62 parts of toluene, and 0.5-0.6 parts of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, 0.05-0.1 parts of glacial acetic acid, and 0.4-0.6 parts of deionized water are added. The mixture is refluxed at 108-112℃ to obtain the reaction product. The reaction product is centrifuged, washed alternately with toluene / ethanol, and dried under vacuum at 98-102℃.

[0021] In this invention, the preparation of the zirconium borosilicate-based organic-inorganic hybrid flame retardant integrates the principles of sol-gel and surface chemical grafting. After zirconium salt is dissolved in an alcohol-water mixture, a silicon source precursor is added dropwise under an inert atmosphere and low-temperature protection. Heating promotes hydrolysis and condensation to form a zirconium-silicon oxide network. Subsequently, a boron source precursor is introduced, and boron is embedded into the inorganic framework through co-condensation to construct a borosilicate-zirconium composite network gel, which is then dried and pulverized to obtain an inorganic powder. The powder is dispersed in an aromatic hydrocarbon solvent, and an epoxy-containing silane coupling agent and an appropriate amount of water are added. Under reflux conditions, the silane first hydrolyzes to generate silanol, which then undergoes a condensation reaction with the hydroxyl groups on the particle surface, covalently grafting the organic epoxy groups onto the inorganic surface. The reaction system is equipped with a water separator to continuously remove byproducts, promoting complete grafting. The product is separated, alternately washed, and dried to obtain an ultrafine powder rich in epoxy functional groups on the surface. The inorganic network imparts high-temperature stability and char-forming catalytic ability, while the surface organic groups significantly enhance chemical compatibility with the polymer matrix, effectively solving the interfacial dispersion problem.

[0022] According to a preferred embodiment of the present invention, in step B1, the reflux reaction time at 58-62°C is 2-4 hours.

[0023] According to a preferred embodiment of the present invention, in step B2, the reflux reaction at 108-112°C is carried out for 12-14 hours.

[0024] In a second aspect, the present invention provides a MOF flame-retardant recycled ABS composite material prepared according to the method for preparing the MOF flame-retardant recycled ABS composite material.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The core effect of this invention lies in achieving extremely efficient and environmentally friendly flame retardant performance. By introducing a zirconium-lanthanum bimetallic organic framework flame retardant co-assembled with phosphorus ligands and a zirconium borosilicate-based organic-inorganic hybrid flame retardant, a triple synergistic flame retardant mechanism of "gas phase-condensed phase-physical barrier" is constructed. The former utilizes its stable porous framework structure to effectively adsorb heat and decomposed combustible gases in the early stage of combustion. At the same time, the zirconium and lanthanum bimetallic centers can catalyze the cross-linking of the polymer matrix into char at high temperatures, while the phosphorus element embedded in the framework releases free radical scavengers in the gas phase, interfering with the combustion chain reaction. The latter forms a dense borosilicate glassy protective layer at high temperatures, firmly covering the substrate surface, isolating oxygen and heat, and enhancing the strength and continuity of the char layer. The two flame retardants work synergistically with a relatively low total addition amount, enabling the composite material to achieve a high flame retardant rating, far exceeding the effect of using traditional single flame retardants or ordinary metal-organic framework materials. Moreover, the entire system is completely halogen-free, which is in line with the development trend of green environmental protection.

[0027] (2) This invention achieves an excellent balance between improving flame retardant performance and maintaining basic mechanical properties, overcoming the industry problem that traditional flame retardant modification often leads to material embrittlement. This effect is attributed to the unique integrated "flame retardant-compatibility" design. The two flame retardants are not simply physical additions; their surfaces or skeletons are designed with abundant polar functional groups or reactive groups. During melt blending, specific interfacial compatibilizers can interact strongly with them, such as forming hydrogen bonds or undergoing grafting reactions, thereby constructing a strong and flexible interfacial layer between the inorganic flame retardant particles and the organic ABS matrix. This interfacial layer can effectively transfer and disperse stress, preventing particles from becoming stress concentration points, and greatly improving the common problem of decreased impact strength caused by the addition of fillers. At the same time, good interfacial bonding also avoids flame retardant agglomeration caused by poor compatibility, ensuring its nanoscale uniform dispersion in the matrix. This not only maximizes the flame retardant efficiency but also further ensures the uniformity and stability of the material's mechanical properties.

[0028] (3) The preparation method involved in this invention has the outstanding advantages of simple process, strong controllability, and easy large-scale production. The synthesis routes of the two key flame retardants are clear, the raw materials used are all commercially available common chemicals, the reaction conditions are mild, the reproducibility is good, and it is suitable for batch preparation. The processing of the composite material is fully compatible with existing plastic industrial production lines and can be completed using conventional drying, premixing, melt extrusion and injection molding processes without the need for special or complex equipment. By precisely controlling the temperature field and shear force of the twin-screw extruder, the effective migration and reaction of the interfacial compatibilizer and the uniform construction of the flame retardant network are ensured. The entire process is stable and efficient, and the resulting composite material particles have good processing fluidity, which is convenient for subsequent molding into various complex shapes of end products. Therefore, this invention not only provides a high-performance composite material formulation, but also provides a complete, feasible and economical technical solution from the preparation of key additives to the molding of end products, which has extremely high practical application value and market promotion potential. Detailed Implementation

[0029] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0030] Example 1

[0031] This embodiment provides a method for preparing MOF flame-retardant recycled ABS composite material, the steps of which include:

[0032] The preparation method of the zirconium-lanthanum bimetallic organic framework flame retardant co-assembled with phosphorus-containing ligands is as follows: First, accurately weigh 1.05 g of zirconium nitrate hexahydrate and 0.23 g of lanthanum nitrate hexahydrate, and transfer them together to a clean 250 mL beaker. Add 40 g of N,N-dimethylformamide solvent to the beaker, and then place the beaker in an ultrasonic cleaner and ultrasonically disperse at room temperature for 10 minutes until the solid is completely dissolved, obtaining a clear and transparent solution A. Next, take another 100 mL beaker, accurately weigh 0.33 g of trimesic acid organic ligand and 0.13 g of 2-carboxyethylphenylphosphonic acid phosphorus-containing ligand, add 20 g of N,N-dimethylformamide to this beaker, and stir on a magnetic stirrer until completely dissolved, obtaining solution B. Under continuous magnetic stirring, use a constant pressure dropping funnel to slowly add solution B dropwise to the 250 mL beaker containing solution A at a rate of about 1 drop per second. This process takes about 30 minutes. After the addition was complete, 5.0 g of glacial acetic acid as a crystallization regulator and 2.0 g of deionized water were added sequentially to the mixed solution, and the mixture was stirred for another 30 minutes to ensure homogeneity. The resulting mixture was then transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene (PTFE), ensuring a tight seal. The autoclave was placed in a temperature-controlled oven, and the temperature was increased to 120 °C at a rate of 5 °C / min, and maintained at this temperature for 36 hours. After the reaction was complete, the oven was turned off, and the autoclave was allowed to cool naturally to room temperature. The autoclave was opened, and all the material was transferred to a 50 mL centrifuge tube. The tube was centrifuged at 9000 rpm for 10 minutes using a high-speed centrifuge, and the supernatant was carefully discarded. 40 g of fresh N,N-dimethylformamide was added to the precipitate, and the mixture was stirred with a glass rod to redisperse the precipitate. The mixture was then centrifuged again at 9000 rpm for 10 minutes. This washing process was repeated three times. Subsequently, the mixture was washed three times with anhydrous methanol in the same manner. The resulting white solid precipitate was transferred to a petri dish and placed in a vacuum drying oven. The oven door was closed, and the vacuum pump was turned on to reduce the internal pressure to below -0.09 MPa. The drying temperature was set to 150°C, and the drying time was 12 hours. After drying, the heating and vacuum were turned off, and the precipitate was allowed to cool before being removed. The dried zirconium-lanthanum bimetallic organic framework flame retardant containing phosphorus ligands was then placed in a desiccator for later use.

[0033] The preparation method of zirconium borosilicate-based organic-inorganic hybrid flame retardant is as follows: First, accurately weigh 1.05 g of zirconium oxychloride octahydrate and place it in a 250 mL three-necked round-bottom flask. Add a mixed solvent of 50 g anhydrous ethanol and 10 g deionized water to the flask and stir at room temperature until the solid is completely dissolved. Place the three-necked flask in an ice-water bath and install a mechanical stirrer on the middle neck of the flask, connect a nitrogen gas delivery tube to one neck, and install a reflux condenser on the other neck. Open the nitrogen cylinder valve and introduce nitrogen gas into the flask at a flow rate of 80 mL / min for protection, continuing for 10 minutes to purge air, and maintain this nitrogen flow rate in the subsequent reaction. Turn on the mechanical stirrer and set the speed to 300 rpm. Under ice-water bath (0 °C) and continuous stirring, slowly add 1.3 g of tetraethyl orthosilicate to the flask using a constant-pressure dropping funnel, the addition process taking about 20 minutes. After the addition was complete, the ice-water bath was removed, and the reaction apparatus was transferred to an oil bath. The temperature was slowly raised to 60°C and reflux was initiated. The reaction was continued at this temperature for 2 hours to obtain a clear and transparent zirconium-silica sol. In another 50 mL beaker, 0.70 g of triethyl borate was dissolved in 10 g of anhydrous ethanol to prepare a solution. With stirring, this solution was slowly added dropwise to the zirconium-silica sol at 60°C through a constant pressure dropping funnel. After the addition was complete, the reaction was continued at 60°C for 3 hours under reflux. After the reaction was completed, the reaction solution was poured into a 250 mL crystallizing dish and placed in a drying oven at 80°C for 6 hours to obtain a brittle dry gel block. The dry gel was ground into a fine powder using an agate mortar. All of this powder was weighed and transferred to a 250 mL three-necked flask, and 60 g of toluene was added to the flask as a dispersion medium. The mixture was ultrasonically dispersed at room temperature for 30 minutes. Subsequently, 0.55 g of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, 0.075 g of glacial acetic acid, and 0.5 g of deionized water were added to the flask. A reflux condenser and water separator were installed on the flask, and the mixture was heated to 110 °C in an oil bath and refluxed at this temperature for 12 hours. After the reaction was complete, the reaction product was transferred to a centrifuge tube and centrifuged at 8000 rpm for 5 minutes, discarding the supernatant. 40 g of toluene was added to the precipitate, and the mixture was dispersed by shaking and centrifuged again; this operation was repeated twice. Subsequently, the product was washed three times with anhydrous ethanol in the same manner. The resulting white solid was placed in a vacuum drying oven and dried at 100 °C and -0.09 MPa for 6 hours to obtain a zirconium borosilicate-based organic-inorganic hybrid flame retardant, which was then stored in a desiccator for later use.

[0034] Preparation of composite materials: First, the raw materials were pretreated. 92g of recycled ABS granules were accurately weighed, spread evenly on a tray, and placed in a forced-air drying oven. The mixture was dried at 85℃ for at least 6 hours to ensure a moisture content below 0.05%. 5g of the zirconium-lanthanum bimetallic organic framework flame retardant and 3g of the zirconium borosilicate-based organic-inorganic hybrid flame retardant, prepared above, were weighed and placed in a vacuum drying oven at 120℃ and -0.09MPa for 8 hours. 3g of the interface compatibilizer SMA800 was weighed and dried in a forced-air drying oven at 80℃ for 4 hours. Then, premixing was performed. All the dried raw materials, along with 0.3g of antioxidant 1010 and 0.1g of calcium stearate, were added to the mixing tank of a high-speed mixer. The tank lid was closed, the mixer was started, and the mixture was stirred at 800rpm for 8 minutes at room temperature to ensure thorough and uniform mixing of all components, resulting in a premix. Finally, melt blending and granulation are performed. The premixed material is fed into a co-rotating parallel twin-screw extruder at a rate of 20 kg / h via the main feeder. The extruder is divided into six zones from the feed port to the die, with temperatures set at 170℃, 185℃, 200℃, 210℃, 210℃, and 205℃ respectively. The screw speed is set to 300 rpm, and vacuum exhaust is activated in the middle section of the extruder, maintaining a vacuum level of -0.08 MPa. After melting, shearing, and mixing within the extruder, the material is extruded from the die into strips. The strip melt is immediately cooled by a cooling water tank, then the surface moisture is dried by a blower, and finally, it is cut into uniformly sized composite material particles by a pelletizer. After drying the obtained composite material particles again in an 85°C forced-air drying oven for 4 hours, they were injection molded into standard test specimens using an injection molding machine under the following conditions: mold temperature 60°C, injection temperature (from barrel to nozzle) 205°C, 215°C, 220°C, injection pressure 80MPa, and holding time 20 seconds.

[0035] Example 2

[0036] The difference between this embodiment and Example 1 lies in the preparation of the zirconium-lanthanum bimetallic organic framework flame retardant co-assembled with phosphorus-containing ligands: First, accurately weigh 1.00 g of zirconium nitrate hexahydrate and 0.22 g of lanthanum nitrate hexahydrate, and dissolve them together in 38 g of N,N-dimethylformamide. Disperse the solutions ultrasonically for 10 minutes at room temperature to obtain a clear and transparent solution A. Next, accurately weigh 0.32 g of trimesic acid and 0.11 g of 2-carboxyethylphenylphosphonic acid, and dissolve them together in 19 g of N,N-dimethylformamide to obtain solution B. Under magnetic stirring, slowly add solution B to solution A using a constant-pressure dropping funnel. After the addition is complete, add 4.8 g of glacial acetic acid and 1.8 g of deionized water to the mixture sequentially, and continue stirring for 30 minutes to ensure homogeneity. Transfer the resulting mixture to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and seal it. The reactor was placed in a temperature-controlled oven and heated to 118°C at a rate of 5°C / min, and maintained at this temperature for 42 hours. After the reaction, the reactor was allowed to cool naturally to room temperature. The reactor was opened, and the material was transferred to centrifuge tubes and centrifuged at 8500 rpm for 10 minutes using a high-speed centrifuge. The supernatant was discarded. 38 g of fresh N,N-dimethylformamide was added to the precipitate, and the mixture was shaken to disperse and then centrifuged again. This washing process was repeated three times. Subsequently, the same washing process was performed three times with anhydrous methanol. The resulting white solid was placed in a vacuum drying oven and dried at 148°C and -0.09 MPa for 14 hours to obtain a white powdery zirconium-lanthanum bimetallic organic framework flame retardant containing phosphorus ligands.

[0037] Preparation of zirconium borosilicate-based organic-inorganic hybrid flame retardant: Accurately weigh 1.00 g of zirconium oxychloride octahydrate and dissolve it in a mixed solvent of 48 g anhydrous ethanol and 9 g deionized water. Place the solution in an ice-water bath, and under nitrogen protection (flow rate 60 mL / min) and mechanical stirring, slowly add 1.2 g of tetraethyl orthosilicate to the solution dropwise. After the addition is complete, transfer the reaction apparatus to an oil bath, heat to 58 °C, and reflux for 4 hours to obtain zirconium-silica sol. Dissolve 0.66 g of triethyl borate in 9 g of anhydrous ethanol and slowly add it to the aforementioned zirconium-silica sol at 58 °C with stirring. Continue refluxing at the same temperature for 3 hours. After the reaction is complete, dry the reaction solution in a 78 °C forced-air drying oven for 6 hours to obtain a dry gel, which, after grinding, yields a light white powder. The powder was dispersed in 58 g of toluene, and 0.50 g of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, 0.05 g of glacial acetic acid, and 0.4 g of deionized water were added. The mixture was refluxed at 108 °C for 14 hours in an apparatus equipped with a water separator. After the reaction, the mixture was centrifuged, and the resulting solid was washed three times alternately with toluene and anhydrous ethanol. Finally, it was vacuum dried at 98 °C for 6 hours to obtain a white powder of zirconium borosilicate-based organic-inorganic hybrid flame retardant.

[0038] Preparation of composite materials: Accurately weigh 80g of recycled ABS granules and dry them in an 84℃ forced-air drying oven for 6 hours. Weigh 10g and 8g of the two flame retardants prepared above, and dry them in a 118℃ vacuum drying oven for 8 hours. Weigh 8g of interface compatibilizer SMA800 and dry it at 78℃ for 4 hours. Add all the dried raw materials, 0.1g of antioxidant 1010, and 0.05g of calcium stearate to a high-speed mixer and mix at 600rpm for 10 minutes at room temperature to obtain a premix. Feed the premix into a twin-screw extruder, setting the temperatures of each section of the extruder to 168℃, 184℃, 198℃, 208℃, 208℃, and 204℃, and the screw speed to 280rpm. The melt is extruded, water-cooled, dried, and then pelletized. After drying the obtained composite material particles at 84°C for 4 hours, they were injection molded into standard test specimens using an injection molding machine at a mold temperature of 50°C and an injection temperature of 200°C.

[0039] Example 3

[0040] The difference between this embodiment and Example 1 lies in the preparation of the zirconium-lanthanum bimetallic organic framework flame retardant co-assembled with phosphorus-containing ligands: 1.10 g of zirconium nitrate hexahydrate and 0.24 g of lanthanum nitrate hexahydrate were accurately weighed and dissolved together in 42 g of N,N-dimethylformamide. The solution was ultrasonically dispersed for 10 minutes at room temperature to obtain solution A. 0.35 g of trimesic acid and 0.15 g of 2-carboxyethylphenylphosphonic acid were accurately weighed and dissolved together in 21 g of N,N-dimethylformamide to obtain solution B. Solution B was slowly added dropwise to solution A under magnetic stirring. Then, 5.2 g of glacial acetic acid and 2.2 g of deionized water were added sequentially to the mixture, and stirring was continued for 30 minutes. The resulting mixture was transferred to a high-pressure reactor and reacted in an oven at 122°C for 36 hours. After the reaction, the mixture was naturally cooled to room temperature, and the product was centrifuged at 9500 rpm. The resulting solid precipitate was washed three times sequentially with N,N-dimethylformamide and anhydrous methanol. Finally, the product was placed in a vacuum drying oven and dried at 152°C for 12 hours to obtain a white powdery zirconium-lanthanum bimetallic organic framework flame retardant containing phosphorus ligands.

[0041] Preparation of zirconium borosilicate-based organic-inorganic hybrid flame retardant: 1.10 g of zirconium oxychloride octahydrate was accurately weighed and dissolved in a mixed solvent of 52 g anhydrous ethanol and 11 g deionized water. Under nitrogen protection (flow rate 100 mL / min) and in an ice-water bath, 1.4 g of tetraethyl orthosilicate was slowly added dropwise to the solution. After the addition was complete, the temperature was raised to 62 °C and refluxed for 2 hours to obtain a zirconium-silica sol. 0.73 g of triethyl borate was dissolved in 11 g of anhydrous ethanol and added to the aforementioned zirconium-silica sol at 62 °C with stirring. The reaction was continued at the same temperature for 3 hours. The reaction solution was dried at 82°C for 6 hours to obtain a dry gel, which was then ground and dispersed in 62 g of toluene. 0.60 g of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, 0.1 g of glacial acetic acid, and 0.6 g of deionized water were added, and the mixture was refluxed at 112°C for 12 hours in an apparatus equipped with a water separator. After the reaction, the mixture was centrifuged, and the resulting solid was washed three times alternately with toluene and anhydrous ethanol. Finally, it was vacuum dried at 102°C for 6 hours to obtain a white powder of zirconium borosilicate-based organic-inorganic hybrid flame retardant.

[0042] Preparation of MOF flame-retardant recycled ABS composite material: 86g of recycled ABS granules were accurately weighed and dried in an 86℃ forced-air drying oven for 6 hours. 7g and 6g of the two flame retardants prepared above were weighed separately and dried in a 122℃ vacuum drying oven for 8 hours. 5g of interface compatibilizer SMA800 was weighed and dried at 82℃ for 4 hours. All the dried raw materials, along with 0.5g of antioxidant 1010 and 0.2g of calcium stearate, were added to a high-speed mixer and mixed at 750rpm for 7 minutes at room temperature to obtain a premix. The premix was fed into a twin-screw extruder, with the extruder temperatures set at 172℃, 186℃, 202℃, 212℃, 212℃, and 206℃, and the screw speed at 320rpm. The melt was extruded, water-cooled, dried, and then pelletized. After drying the obtained composite material particles at 86°C for 4 hours, they were injection molded into standard test specimens using an injection molding machine at a mold temperature of 80°C and an injection temperature of 220°C.

[0043] Comparative Example 1

[0044] The difference between this comparative example and Example 1 is that this comparative example does not add the zirconium-lanthanum bimetallic organic framework flame retardant co-assembled with phosphorus ligands, the zirconium borosilicate-based organic-inorganic hybrid flame retardant, and the interface compatibilizer; otherwise, it is the same as Example 1.

[0045] Comparative Example 2:

[0046] The difference between this comparative example and Example 1 is that this comparative example does not add a zirconium-lanthanum bimetallic organic framework flame retardant co-assembled with phosphorus ligands; otherwise, it is the same as Example 1.

[0047] Comparative Example 3:

[0048] The difference between this comparative example and Example 1 is that this comparative example does not contain a zirconium borosilicate-based organic-inorganic hybrid flame retardant; otherwise, it is the same as Example 1.

[0049] Comparative Example 4

[0050] The difference between this comparative example and Example 1 is that the zinc borate flame retardant in this comparative example is used to replace the zirconium-lanthanum bimetallic organic framework flame retardant and the zirconium borosilicate-based organic-inorganic hybrid flame retardant with the same mass; the rest is the same as in Example 1.

[0051] Comparative Example 5

[0052] The difference between this comparative example and Example 1 is that no interface compatibilizer is added in this comparative example; otherwise, it is the same as Example 1.

[0053] According to relevant national and industry standards, the performance of the MOF flame-retardant recycled ABS composite materials provided in the above embodiments and comparative examples was tested. The test methods are as follows: Performance tests were conducted on all prepared composite material standard specimens. All tests were carried out in a constant temperature and humidity laboratory, with environmental conditions strictly controlled at a temperature of 23°C and a relative humidity of 50%. All specimens were allowed to stand in the above environment for more than 24 hours before testing to achieve humidity equilibrium.

[0054] The limiting oxygen index (LOI) test characterizes the minimum oxygen concentration required for a material to sustain combustion. A dedicated oxygen index meter is used, with test specimens measuring 80 mm in length, 10 mm in width, and 4 mm in thickness. The specimen is vertically mounted in a fixture inside a transparent glass combustion chamber, with the top of the specimen at least 100 mm below the top of the chamber. The chamber is filled with a predetermined mixture of oxygen and nitrogen. Propane is used as fuel, and an igniter ignites the top of the specimen directly above it. The volume percentage of oxygen in the mixture is precisely adjusted and controlled using a rotor flow meter. After each adjustment, a new specimen is tested. The minimum oxygen concentration required for the material to sustain continuous combustion for at least 180 seconds, or for a combustion spread length of 50 mm, is measured and expressed as a volume percentage (%). At least five valid specimens are tested for each formulation group, and the final result is the arithmetic mean.

[0055] The vertical burning rating test evaluates a material's resistance to a small, ignited flame. A vertical burning test chamber was used, with a sample measuring 125 mm in length, 13 mm in width, and 1.6 mm in thickness. The sample was suspended vertically in a metal clamp, its lower end 9.5 mm from the tip of a Bunsen burner nozzle. Using a methane gas source, the Bunsen burner was adjusted to produce a blue flame 20 mm high. The flame was applied to the center of the lower end of the sample for 10 seconds, then immediately removed at least 150 mm, while a stopwatch was started to record the flaming time t1. After the flame on the sample had completely extinguished, the same sample was immediately re-applied with the flame for 10 seconds, and the second flaming time t2 and subsequent flameless incandescence time were recorded. Throughout the test, any burning or flaming droplets were observed and recorded, as well as whether dry, degreased cotton placed 305 mm below was ignited. The flame retardancy rating of the material is comprehensively evaluated based on the sum of t1 and t2 of the five samples, the longest single burning time, and whether it ignites the absorbent cotton, with the highest rating being V-0.

[0056] Notched impact strength testing is used to evaluate the toughness of materials under high-speed impact. A cantilever beam impact testing machine is used, with specimen dimensions of 63.5 mm in length, 12.7 mm in width, and 3.2 mm in thickness. A standard V-shaped notch is prefabricated at the center of the specimen's side surface using machining or injection molding, with a notch depth of 2.5 mm and a notch root radius of 0.25 mm. Before testing, the remaining thickness at the notch of each specimen is accurately measured using vernier calipers. During testing, the specimen is placed horizontally in the testing machine fixture and clamped, ensuring that the notch center is aligned with the support groove and that the notch faces away from the direction of the pendulum impact. The pendulum is released, impacting the back of the notch of the specimen at an impact velocity of 3.5 m / s. The equipment directly reads the impact energy value consumed to break the specimen, in J. This energy value is divided by the remaining net cross-sectional area at the notch of the specimen to obtain the notched impact strength of the material, expressed as kJ / m². The average value is taken from 10 specimens tested in each group.

[0057] Tensile strength and elongation at break tests were performed simultaneously on a universal testing machine to evaluate the tensile mechanical properties of materials. Standard Type I dumbbell-shaped tensile specimens were prepared with a parallel gauge length of 50 mm, a width of 10 mm, and a thickness of 4 mm. Before testing, a non-contact extensometer or markings were directly applied to the gauge length of the specimen. The specimen was secured at both ends to the pneumatic or mechanical clamps of the testing machine, ensuring the longitudinal axis of the specimen was coaxial with the direction of the tensile force. Tension was applied at a constant beam speed of 50 mm / min until the specimen completely broke. The testing machine system acquired load and displacement data in real time and automatically plotted stress-strain curves. The maximum load value during the tensile process was determined from the curve and divided by the original cross-sectional area of ​​the specimen to obtain the tensile strength, expressed in MPa. Simultaneously, the system recorded the absolute elongation of the gauge length at the moment of specimen breakage and calculated its percentage relative to the original gauge length of 50 mm to obtain the elongation at break, expressed as a percentage (%). Five specimens were tested in each group, and the average result was taken.

[0058] The performance test data above are shown in Table 1.

[0059] Table 1 Performance Test Results

[0060] Test Project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Limiting oxygen index (%) 32.1 31.5 33.0 18.2 26.8 27.5 25.5 28.8 Vertical flammability rating V-0 V-0 V-0 No grade V-1 V-1 V-1 V-1 Notched impact strength (kJ / m²) 20.1 19.3 20.8 19.5 18.5 17.9 16.8 18.2 Tensile strength (MPa) 39.5 38.0 40.2 37.7 37.8 37.2 35.2 36.9 Elongation at break (%) 14.8 13.5 15.0 11.2 13.0 11.8 8.5 10.1

[0061] As can be seen from the above, the complete technical solution of the present invention represented by Examples 1-3, through a systematic comparison of Comparative Examples 1-5, clearly and data-drivenly demonstrates that it simultaneously solves the three core technical problems that have long existed in the field of flame-retardant modification of recycled ABS:

[0062] This reverses the traditional dilemma of "performance trade-offs" where adding flame retardants inevitably leads to severe degradation of mechanical properties. This is most evident in Comparative Example 4, where using an equal amount of ordinary zinc borate flame retardant increases the limiting oxygen index to 25.5%, but at the cost of a sharp drop in notched impact strength from 21.5 kJ / m² to 16.8 kJ / m² and elongation at break from 15.2% to 8.5%, reflecting the traditional path of sacrificing toughness for flame retardancy. In contrast, Examples 1-3 significantly increase the limiting oxygen index to over 31.5% and achieve the highest V-0 flame retardancy rating, while restoring the notched impact strength (19.3-20.8 kJ / m²) and tensile strength (38.0-40.2 MPa) to levels close to or even exceeding those of the pure matrix, and maintaining good elongation at break (13.5-15.0%), achieving a synergistic effect of flame retardancy and toughness.

[0063] Overcoming the technical bottleneck of insufficient efficiency of a single flame retardant mechanism, the test results of Comparative Example 2 (a zirconium-lanthanum bimetallic organic framework flame retardant lacking phosphorus-containing ligands) and Comparative Example 3 (a zirconium borosilicate-based organic-inorganic hybrid flame retardant lacking borosilicate) (limiting oxygen indices of 26.8% and 27.5%, respectively, both reaching only V-1 level) directly prove that relying solely on either gas-phase flame retardancy or condensed-phase barrier mechanisms cannot achieve a V-0 level flame retardancy breakthrough. The high flame retardant performance data of Examples 1-3 empirically demonstrate that the multiple synergistic effects of the two newly designed flame retardants in gas-phase dilution of free radicals, catalytic char formation, and the formation of high-temperature ceramic barriers are the key to achieving ultra-high flame retardant efficiency.

[0064] Third, the technical challenge of poor interfacial compatibility leading to performance shortcomings in multiphase composite systems has been overcome. Data from Comparative Example 5 (lacking interfacial compatibilizer) shows that even with two highly efficient flame retardants, the vertical burning rating remains stuck at V-1 due to weak interfacial bonding, and the impact strength (18.2 kJ / m²) is low. However, after introducing an interfacial compatibilizer, all embodiments not only stably reached the V-0 rating, but also achieved significant optimization of mechanical properties. This data verifies the indispensable role of a "strong interface" constructed through specific interface design in fully leveraging the effectiveness of flame retardants and bearing stress.

[0065] In summary, Embodiments 1-3 of this invention, through the organic combination of "dual-effect flame retardant design" and "precise interface compatibilization," have successfully achieved the unification of high flame retardancy (V-0, LOI>31%), high toughness (impact strength retention rate>90%), and high strength (tensile strength retention rate>98%) in recycled ABS matrix, based on the shortcomings of various single technical paths revealed by comparative data. This provides a solution with both high efficiency and high reliability for the high-value and functional recycling of waste plastics.

Claims

1. A method for preparing MOF flame-retardant recycled ABS composite material, characterized in that the steps include... include: S1. By weight, 80-92 parts of recycled ABS granules, 5-10 parts of zirconium-lanthanum bimetallic organic framework flame retardant co-assembled with phosphorus ligands, 3-8 parts of zirconium borosilicate-based organic-inorganic hybrid flame retardant, and 3-8 parts of interface compatibilizer are dried and added to a mixer with 0.1-0.5 parts of antioxidant 1010 and 0.05-0.2 parts of calcium stearate. The mixture is then mixed at room temperature to obtain a premix. The premix is ​​fed into a twin-screw extruder to obtain a melt. The melt is extruded, water-cooled, and dried, and then cut into composite material granules by a pelletizer. S2. Dry the composite material particles and then injection mold them using an injection molding machine; The preparation method of the zirconium borosilicate-based organic-inorganic hybrid flame retardant includes: B1. Dissolve 1.0-1.1 parts by weight of zirconium oxychloride octahydrate in a mixed solvent of 48-52 parts anhydrous ethanol and 9-11 parts deionized water; under nitrogen protection and in an ice-water bath at 0-5℃, add 1.2-1.4 parts of tetraethyl orthosilicate, and reflux at 58-62℃ to obtain zirconium-silica sol; add 0.66-0.73 parts of triethyl borate solution dissolved in 9-11 parts anhydrous ethanol to the zirconium-silica sol, and continue the reaction at 58-62℃ to obtain the reaction solution; B2. The reaction solution is dried at 78-82℃ to obtain a dry gel. The dry gel is ground to obtain a powder. The powder is dispersed in 58-62 parts of toluene, and 0.5-0.6 parts of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, 0.05-0.1 parts of glacial acetic acid, and 0.4-0.6 parts of deionized water are added. The mixture is refluxed at 108-112℃ to obtain the reaction product. The reaction product is centrifuged, washed alternately with toluene / ethanol, and dried under vacuum at 98-102℃.

2. The method for preparing MOF flame-retardant recycled ABS composite material according to claim 1, characterized in that, In step S1, the interface compatibilizer is interface compatibilizer SMA800; the temperature settings of each section of the twin-screw extruder from the feed port to the die are: 168-172℃, 184-186℃, 198-202℃, 208-212℃, 208-212℃, 204-206℃, wherein the temperature range of the fourth and fifth zones is the same, both being 208-212℃.

3. The method for preparing MOF flame-retardant recycled ABS composite material according to claim 1, characterized in that, In step S2, the mold temperature of the injection molding machine is 50-80℃.

4. The method for preparing MOF flame-retardant recycled ABS composite material according to claim 1, characterized in that, The preparation method of the zirconium-lanthanum bimetallic organic framework flame retardant co-assembled with phosphorus-containing ligands includes: A1. By weight, dissolve 1.0-1.1 parts of zirconium nitrate hexahydrate and 0.22-0.24 parts of lanthanum nitrate hexahydrate together in 38-42 parts of N,N-dimethylformamide, and disperse by ultrasonication to obtain solution A; dissolve 0.32-0.35 parts of trimesic acid and 0.11-0.15 parts of 2-carboxyethylphenylphosphonic acid together in 19-21 parts of N,N-dimethylformamide to obtain solution B; add solution B dropwise to solution A with stirring, then add 4.8-5.2 parts of glacial acetic acid and 1.8-2.2 parts of deionized water to obtain a mixture; transfer the mixture to a reaction vessel and react it solvothermally at 118-122℃ to obtain a reaction mixture; A2. The reaction mixture was naturally cooled to room temperature and centrifuged to obtain a solid precipitate. The solid precipitate was washed successively with N,N-dimethylformamide and anhydrous methanol. Finally, it was dried under vacuum at 148-152℃.

5. The method for preparing MOF flame-retardant recycled ABS composite material according to claim 4, characterized in that, In step A1, the solvothermal reaction at 118-122℃ takes 36-42 hours.

6. The method for preparing MOF flame-retardant recycled ABS composite material according to claim 4, characterized in that, In step A2, the vacuum drying time at 148-152℃ is 12-14 hours.

7. The method for preparing MOF flame-retardant recycled ABS composite material according to claim 1, characterized in that, In step B1, the reflux reaction time at 58-62℃ is 2-4 hours.

8. The method for preparing MOF flame-retardant recycled ABS composite material according to claim 1, characterized in that, In step B2, the reflux reaction at 108-112℃ takes 12-14 hours.

9. A MOF flame-retardant recycled ABS composite material, characterized in that, The MOF flame-retardant recycled ABS composite material is prepared by the method according to any one of claims 1-8.