A smoke-suppressing, flame-retardant recycled polyethylene terephthalate material and methods of making the same

Abstract

The application discloses the technical field of high polymer material modification, and relates to a smoke-suppressing and flame-retardant regenerated polyethylene terephthalate material and a preparation method thereof. The material is prepared from raw materials including regenerated polyethylene terephthalate chips, magnesium-doped layered zinc stannate, cerium-based metal organic framework hybrid zirconium phosphonate, maleic anhydride grafted polyethylene, an antioxidant and zinc stearate. The magnesium-doped layered zinc stannate is prepared through hydrothermal reaction, drying and aging of zinc sulfate heptahydrate, magnesium sulfate heptahydrate and sodium stannate trihydrate; and the cerium-based metal organic framework hybrid zirconium phosphonate is prepared through in-situ growth, washing and drying of zirconium oxynitrate and phenyl phosphonic acid after synthesis of a precursor from cerium nitrate hexahydrate and trimesic acid. After mixing of the components, the product is obtained through melt blending extrusion by a double-screw extruder, granulation and vacuum drying. Through synergistic effect of the two novel modified compounds, the material has improved flame-retardant performance and smoke-suppressing effect, and is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification technology, specifically to a smoke-suppressing and flame-retardant recycled polyethylene terephthalate material and its preparation method. Background Technology

[0002] Polyethylene terephthalate (PET) has gained widespread application in packaging materials, synthetic fibers, and engineering plastics due to its excellent mechanical strength, good chemical stability, and outstanding processing performance. With the increasing severity of global plastic pollution and the deepening promotion of the circular economy concept, the recycling and high-value utilization of waste PET products has become a focus of attention for both academia and industry. Preparing high-performance composite materials from recycled PET through melt blending modification can not only effectively alleviate environmental pressure but also expand its application range in electronics, transportation, and building materials. However, recycled PET often experiences a decrease in molecular weight due to thermomechanical degradation during the recycling process, and the presence of impurities makes its combustion behavior more complex than that of virgin PET. Studies have shown that PET releases a large amount of volatile flammable gases during thermal decomposition, accompanied by severe molten dripping. This not only accelerates flame spread but the molten drips can also ignite surrounding materials, creating a secondary fire hazard. More importantly, the combustion of polyethylene terephthalate (PET) produces dense black smoke containing large amounts of carbon monoxide and aromatic compounds, posing a serious threat to personnel evacuation and fire rescue operations. Therefore, developing recycled PET materials that combine highly efficient flame retardancy with significant smoke suppression has become a core technical challenge for improving its fire safety performance and promoting the high-value application of recycled products.

[0003] For flame-retardant modification of polyester materials, existing technologies mainly employ three approaches: copolymerization, blending, and surface coating. Copolymer flame retardants introduce phosphorus- and nitrogen-containing flame-retardant elements into the polyester backbone through chemical reactions, achieving permanent flame retardancy. However, the reaction process is complex and unsuitable for melt processing of recycled polyester. Blending modification, with its advantages of ease of operation and wide applicability, has become the mainstream research method. Inorganic flame retardants involved include metal hydroxides, stannates, montmorillonite, and borates, while organic flame retardants are mainly phosphorus-containing compounds. However, traditional inorganic flame retardants such as aluminum hydroxide and magnesium hydroxide require high loading levels to be effective, severely degrading the mechanical properties of the material. While zinc stannate shows some smoke-suppressing potential, its catalytic charring ability is limited, making it difficult for a single component to simultaneously meet the dual requirements of flame retardancy and smoke suppression. In recent years, layered double hydroxides and metal-organic framework materials have been attempted for polymer flame-retardant modification due to their unique structural characteristics, but existing reports still suffer from problems such as poor dispersibility, poor compatibility with the matrix, and easy structural collapse at high temperatures. Furthermore, existing flame retardant systems primarily focus on reducing heat release rates, with relatively weak research on controlling smoke toxicity and total smoke release, yet smoke is precisely the most lethal factor in fires. Therefore, there is an urgent need to design and develop novel multifunctional flame retardants and smoke suppressants that can catalyze char formation in the condensed phase, capture free radicals in the gas phase, and simultaneously provide a physical barrier effect.

[0004] To address the shortcomings of existing technologies, this invention proposes a novel approach to synergistically modify recycled polyethylene terephthalate (PET) using two novel inorganic compounds with entirely new compositions, starting from molecular structure design. Magnesium ions are introduced into the layered zinc stannate lattice, leveraging the Lewis acidic sites of magnesium to enhance the catalytic crosslinking and charring of polyester degradation products while maintaining the physical barrier effect of the layered structure. On the other hand, layered zirconium phenylphosphonate is grown in situ on the surface of a cerium-based metal-organic framework. This utilizes the excellent thermal stability of zirconium phenylphosphonate to protect the framework structure, while also leveraging the free radical scavenging function of phenyl groups and the cerium ion-catalyzed carbon monoxide oxidation properties. This dual mechanism of gas-phase and condensed-phase action comprehensively improves the flame-retardant and smoke-suppressing properties of the material. The synergistic effect of these two compounds promises to significantly reduce the heat release rate and total smoke release even at low addition levels, while overcoming the shortcomings of existing flame retardants such as poor dispersibility, poor compatibility, and high-temperature structural instability. This provides a new technical solution for the high-value application of recycled PET. Summary of the Invention

[0005] The purpose of this invention is to provide a smoke-suppressing and flame-retardant recycled polyethylene terephthalate material and its preparation method, which solves the technical problems of poor flame retardant performance and large smoke release during combustion of existing recycled polyethylene terephthalate materials.

[0006] The present invention achieves the above objectives through the following technical solutions:

[0007] A method for preparing a smoke-suppressing and flame-retardant recycled polyethylene terephthalate material, comprising the following steps:

[0008] S1. By weight, 95-105 parts of recycled polyethylene terephthalate chips, 5-12 parts of magnesium-doped layered zinc stannate, 3-8 parts of cerium-based metal-organic framework hybrid zirconium phosphonate, 2-5 parts of maleic anhydride-grafted polyethylene, 0.2-0.5 parts of a mixture of antioxidant 1010 and antioxidant 168, and 0.3-0.8 parts of zinc stearate are mixed in a mixer to obtain a mixture; the mixture is added to a twin-screw extruder for melt blending and extrusion to obtain an extrudate; the extrudate is cooled, air-dried, and granulated using a pelletizer to obtain pellets;

[0009] S2. Place the granules in a forced-air drying oven and dry them under vacuum at 115-125℃.

[0010] In this invention, the formation of smoke-suppressing and flame-retardant recycled polyethylene terephthalate (PET) material is based on a synergistic mechanism of melt blending and interfacial compatibility. Recycled PET chips melt during heating, gaining mobility in their molecular chains. Magnesium-doped layered zinc stannate and cerium-based metal-organic framework hybrid zirconium phosphonate serve as functional fillers, dispersed in the melt under shear force. Maleic anhydride-grafted polyethylene acts as a compatibilizer; its anhydride groups undergo esterification with the terminal hydroxyl groups of PET, forming chemical bonds. Simultaneously, its polyethylene segments physically entangle with the filler surface, significantly improving the interfacial adhesion between the filler and the matrix. Antioxidants capture free radicals generated during processing, inhibiting thermo-oxidative degradation and maintaining molecular weight stability. Zinc stearate acts as a lubricant, reducing melt viscosity, promoting filler dispersion, and decreasing screw torque. A twin-screw extruder provides high-intensity shear and mixing, deagglomerating the agglomerated filler particles and achieving nanoscale dispersion. During cooling, the polyethylene terephthalate (PET) molecular chains rearrange and partially crystallize, while the filler is fixed within the matrix. Drying removes residual moisture, preventing hydrolytic degradation during subsequent processing. Under combustion conditions, magnesium-doped layered zinc stannate decomposes thermally to generate metal oxides, catalyzing polymer char formation and creating a dense char layer that isolates heat and oxygen transfer. Cerium ions in the cerium-based metal-organic framework hybrid zirconium phosphonate catalyze the oxidation of hydrocarbon free radicals, reducing toxic smoke generation. The zirconium phosphonate layer promotes the formation of an expanded char layer, enhancing the barrier effect. The two flame retardants work synergistically to form a continuous protective char layer in the condensed phase and capture free radicals in the gas phase to inhibit combustion chain reactions, achieving highly efficient smoke suppression and flame retardancy. The molecular chains of recycled PET break down at high temperatures, but the presence of the flame retardants significantly slows the degradation rate, maintaining the material's mechanical properties. The resulting composite material combines excellent flame retardant and smoke suppression properties with acceptable mechanical strength, enabling the high-value recycling of waste polyester.

[0011] According to a preferred embodiment of the present invention, in step S1, the temperatures of each zone of the twin-screw extruder from the feed port to the die head are set sequentially as follows: zone 1 235-245℃, zone 2 245-250℃, zone 3 245-255℃, zone 4 245-250℃, zone 5 240-245℃, and the die head temperature is 245℃.

[0012] According to a preferred embodiment of the present invention, in step S2, the drying time at 115-125°C is 4-6 hours.

[0013] According to a preferred embodiment of the present invention, the method for preparing the magnesium-doped layered zinc stannate includes:

[0014] A1. By weight, dissolve 5.2-5.6 parts of zinc sulfate heptahydrate and 1.2-1.3 parts of magnesium sulfate heptahydrate in 50-60 parts of deionized water to obtain mixed salt solution A; dissolve 2.5-2.7 parts of sodium stannate trihydrate in 50-60 parts of deionized water to obtain stannate solution B; under stirring and at 20-30℃, add mixed salt solution A to stannate solution B and adjust the pH to 7.5-8.5; after the addition is complete, a mixture is obtained; transfer the mixture to a hydrothermal reactor and crystallize at 120-125℃.

[0015] A2. After the reaction is complete, the mixture is allowed to cool naturally to room temperature and then centrifuged to obtain a solid. The solid is washed with deionized water and anhydrous ethanol to obtain the washed product. The washed product is placed in a vacuum drying oven and dried at 100-120℃, followed by aging.

[0016] In this invention, the formation of magnesium-doped layered zinc stannate is based on a synergistic mechanism of co-precipitation and hydrothermal crystallization. In an alkaline aqueous solution system, zinc and magnesium ions first combine with hydroxide ions to form a mixed metal hydroxide precursor, which exhibits a layered double hydroxide structure. Subsequently, stannate ions embed into the interlayer through ion exchange and coordination, forming stable coordination bonds with metal cations on the layers. The introduction of magnesium ions can regulate the charge density of the layers, optimize the interlayer spacing, and enhance the interlayer interaction forces. Under hydrothermal conditions, the increase in system temperature promotes the dissolution and recrystallization process of the precursor, and the amorphous phase gradually transforms into a more crystalline layered structure. Magnesium ions partially replace zinc ions in the crystal lattice, causing lattice distortion and increasing defect sites. These defect sites can become active centers for catalytic char formation in subsequent flame-retardant applications. The washing process removes residual sulfate and sodium ions, preventing impurities from affecting the stability of the layered structure. During the drying process, physically adsorbed water in the interlayer is gradually removed, while structural water is retained, maintaining the integrity of the layered framework. The aging stage releases internal stress in the crystals, homogenizes grain size, and makes the layered structure more regular. The final product has a highly ordered layered topology, and magnesium doping significantly improves thermal stability and catalytic char formation ability, laying the structural foundation for its subsequent flame-retardant and smoke-suppressing effects in the polymer matrix.

[0017] According to a preferred embodiment of the present invention, in step A1, the crystallization reaction time at 120-125°C is 12-14 hours.

[0018] According to a preferred embodiment of the present invention, in step A2, the drying time at 100-120°C is 24-30 hours.

[0019] According to a preferred embodiment of the present invention, the method for preparing the cerium-based metal-organic framework hybrid zirconium phosphonate includes:

[0020] B1. By weight, dissolve 2.1-2.2 parts of cerium nitrate hexahydrate and 0.70-0.75 parts of trimesic acid in a mixed solvent of N,N-dimethylformamide and anhydrous ethanol, and disperse by ultrasonication to obtain a mixed solution; transfer the mixed solution to a hydrothermal reactor and react at 115-125℃; after the reaction is complete, collect the precipitate by centrifugation, wash the precipitate alternately with N,N-dimethylformamide and ethanol, and dry it under vacuum at 58-62℃ to obtain the Ce-MOF precursor; heat the Ce-MOF precursor at 150-160℃ under nitrogen protection. The process involves obtaining a thermally stabilized Ce-MOF precursor; ultrasonically dispersing 0.8-1.2 parts of the thermally stabilized Ce-MOF precursor in 48-52 parts of deionized water, then adding 2.8-3.0 parts of zirconium oxynitrate and stirring to obtain a zirconium salt suspension containing Ce-MOF; dissolving 3.2-3.5 parts of phenylphosphonic acid in a mixture of 48-52 parts of ethanol and water, and adjusting the pH to 4.0-4.5 with triethylamine to obtain a phenylphosphonic acid solution; adding the phenylphosphonic acid solution dropwise to the zirconium salt suspension containing Ce-MOF, and refluxing at 90-100℃.

[0021] B2. After the reaction is complete, centrifuge to obtain a solid product; wash the solid product with deionized water and ethanol in sequence, and finally dry it under vacuum at 98-102℃.

[0022] In this invention, the construction of cerium-based metal-organic framework hybrid zirconium phosphonate involves a dual mechanism of coordination self-assembly and in-situ hybridization. First, cerium ions and trimesic acid form a three-dimensional porous framework structure through coordination bonds in a polar organic solvent system. Carboxylate ions act as bridging ligands, connecting multiple cerium ion nodes to form a crystal framework with open channels. Ultrasonic dispersion promotes molecular-level mixing of reactants, accelerating the nucleation process. Hydrothermal reaction provides a suitable temperature and pressure environment, resulting in more complete crystal growth and significantly improved crystallinity. Washing removes unreacted organic ligands and solvent molecules, preventing channel blockage. Heat treatment removes guest molecules from the channels while enhancing the thermal stability of the framework, preventing structural collapse during subsequent hybridization. Subsequently, zirconium oxynitrate hydrolyzes in water to generate zirconium oxide clusters, which bind to the surface-modified cerium-based metal-organic framework through electrostatic interactions. Phenylphosphonic acid dissociates into phosphonate anions under alkaline conditions, which undergo coordination reactions with the zirconium oxide clusters to form a layered zirconium phosphonate structure. A cerium-based metal-organic framework (MOF) serves as the core, while layered zirconium phosphonate forms the shell, creating a core-shell hybrid structure through a combination of chemical bonding and physical adsorption. A reflux reaction provides sufficient energy for in-situ growth of the zirconium phosphonate layer on the MOF surface, resulting in a tight interfacial bond. Washing removes free phosphonic acid molecules and nitrate ions, ensuring product purity. Drying removes physically adsorbed water while preserving structural integrity. The final product combines the catalytic oxidation capability of cerium ions with the thermal stability of the zirconium phosphonate layer, synergistically providing flame retardancy in both the condensed and gas phases during combustion.

[0023] According to a preferred embodiment of the present invention, in step B1, the reflux reaction time at 90-100°C is 8-12 hours.

[0024] According to a preferred embodiment of the present invention, in step B2, the vacuum drying time at 98-102°C is 24-30 hours.

[0025] The present invention also provides a smoke-suppressing and flame-retardant recycled polyethylene terephthalate material prepared according to the preparation method of the smoke-suppressing and flame-retardant recycled polyethylene terephthalate material.

[0026] The beneficial effects of this invention are as follows:

[0027] The present invention provides a smoke-suppressing and flame-retardant recycled polyethylene terephthalate material and its preparation method. By introducing two inorganic modifying compounds with novel chemical compositions and optimizing their synergistic ratio, the flame-retardant and smoke-suppressing properties of the recycled polyester matrix are simultaneously and significantly improved. Compared with the prior art, the present invention has the following outstanding technical effects:

[0028] First, this invention constructs a dual synergistic flame retardant system of condensed phase and gas phase by combining magnesium-doped layered zinc stannate with cerium-based metal-organic framework hybrid zirconium phosphonate. On one hand, when heated, magnesium-doped layered zinc stannate can catalyze the cross-linking of degradation products of polyethylene terephthalate into char, forming a continuous and dense expanded char layer on the material surface. This char layer can not only effectively block heat transfer and oxygen contact, delaying the thermal decomposition of the internal matrix, but also inhibit molten dripping. On the other hand, the layered structure of phenyl phosphonate zirconium in the cerium-based metal-organic framework hybrid zirconium phosphonate has excellent thermal stability, maintaining structural integrity at high temperatures, further enhancing the physical barrier effect of the char layer; at the same time, its phenyl groups can capture active free radicals generated during combustion in the gas phase, interrupting the chain combustion reaction, while cerium ions can catalyze the oxidation of carbon monoxide to carbon dioxide, significantly reducing the toxicity of flue gas. The two compounds work synergistically to overcome the limitations of single flame retardants, achieving excellent flame retardant and smoke suppression effects at low addition levels, significantly improving the limiting oxygen index, passing the highest level of vertical burning tests, and producing no dripping.

[0029] Secondly, the recycled polyethylene terephthalate (PET) material prepared in this invention exhibits effectively controlled heat release behavior during combustion, resulting in a significant reduction in smoke emission. Cone calorimetry results show that, compared to unmodified recycled polyester, the peak heat release rate and total heat release of the material are significantly lower, indicating effective suppression of fire hazard. More importantly, the total smoke emission is significantly reduced, and the peak smoke generation rate is also significantly lower, demonstrating a remarkable synergistic effect of the two modified compounds in suppressing smoke generation. Smoke is a major cause of injury and death in fires, and the significant advancements in smoke suppression of the material in this invention are of great importance for improving the safety of its application in enclosed spaces such as building interiors and transportation vehicles. Furthermore, due to the more dense and complete char layer formation, the amount of residual char after combustion is significantly increased, further confirming the effectiveness of the condensed phase char formation mechanism.

[0030] Third, the preparation method of this invention is simple and controllable, and all raw materials are commercially available industrial products, making it easy to achieve large-scale production. By precisely controlling the synthesis conditions of magnesium-doped layered zinc stannate and cerium-based metal-organic framework hybrid zirconium phosphonate, the two modified compounds are ensured to possess a regular layered structure and excellent thermal stability. During melt blending, the introduction of maleic anhydride-grafted polyethylene effectively improves the interfacial compatibility between the inorganic filler and the recycled polyester matrix, allowing the two modified compounds to be uniformly dispersed in the matrix, avoiding agglomeration, and thus ensuring the stability of the material properties. Simultaneously, this invention strictly controls the extrusion processing temperature within a suitable range, ensuring both good flowability of the recycled polyester and avoiding thermal damage to the metal-organic framework structure. The final material not only has excellent flame retardant and smoke-suppressing properties but also maintains good mechanical properties; its tensile strength, flexural strength, and impact strength all meet the application requirements of electronics, electrical appliances, building materials, and other fields, opening up new avenues for the high-value utilization of recycled polyethylene terephthalate. Detailed Implementation

[0031] 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.

[0032] Example 1

[0033] This embodiment provides a method for preparing smoke-suppressing and flame-retardant recycled polyethylene terephthalate material, the steps of which include:

[0034] S1. Weigh 100g of recycled polyethylene terephthalate chips, 8g of magnesium-doped layered zinc stannate, 5g of cerium-based metal-organic framework hybrid zirconium phosphonate, 3g of maleic anhydride-grafted polyethylene, 0.3g of a mixture of antioxidant 1010 and antioxidant 168 in a 1:2 mass ratio (0.1g of antioxidant 1010 and 0.2g of antioxidant 168), and 0.5g of zinc stearate. Place them in a high-speed mixer and mix at 1200 rpm for 6 minutes at room temperature. The components are fully pre-dispersed. The uniformly mixed material is added to a co-rotating parallel twin-screw extruder with a length-to-diameter ratio of 48 for melt blending and extrusion. The screw speed is set to 350 rpm. The temperatures of each zone of the extruder from the feed port to the die head are set as follows: Zone 1 240℃, Zone 2 248℃, Zone 3 250℃, Zone 4 248℃, Zone 5 242℃, and the die head temperature is 245℃. After the molten material is extruded through the die head, it is cooled in a water tank, air-dried, and granulated by a pelletizer to obtain pellets.

[0035] S2. Place the obtained granules in a forced-air drying oven and dry them at 120℃ for 5 hours under a vacuum of -0.09MPa to finally obtain smoke-suppressing and flame-retardant recycled polyethylene terephthalate material.

[0036] The method for preparing the magnesium-doped layered zinc stannate includes:

[0037] A1. Dissolve 5.4g zinc sulfate heptahydrate and 1.25g magnesium sulfate heptahydrate in 55g deionized water and stir until completely dissolved to obtain mixed salt solution A; dissolve 2.6g sodium stannate trihydrate in 55g deionized water and stir until completely dissolved to obtain stannate solution B; under mechanical stirring at 25℃ and 900rpm, slowly add mixed salt solution A to stannate solution B at a dropping rate of 2mL / min, while maintaining the pH of the reaction system at 8.0 with 5% sodium hydroxide solution (monitored in real time using a pH meter); after the addition is complete, a white suspension is obtained. Transfer the mixture to a 100mL polytetrafluoroethylene-lined hydrothermal reactor with a filling degree of about 70%, and crystallize at 122℃ for 13h;

[0038] A2. After the reaction is complete, allow it to cool naturally to room temperature. Transfer the reaction product to a centrifuge tube and centrifuge at 9000 rpm for 10 min. Discard the supernatant to obtain a solid. Wash the solid with 50 mL of deionized water and centrifuge, repeating three times. Then wash with 50 mL of anhydrous ethanol and centrifuge, repeating three times. Continue until the last washing filtrate is neutral when tested with pH paper. Place the washed product in a vacuum drying oven and vacuum dry at 110℃ for 27 h (vacuum degree -0.08 MPa). Then age it in a desiccator with a relative humidity of less than 30% for 48 h to obtain a white powder, namely magnesium-doped layered zinc stannate.

[0039] The preparation method of the cerium-based metal-organic framework hybrid zirconium phosphonate includes:

[0040] B1. Dissolve 2.15 g of cerium nitrate hexahydrate and 0.72 g of trimesic acid in a mixed solvent of 60 g of N,N-dimethylformamide (DMF, analytical grade) and 40 g of anhydrous ethanol. Disperse the solution ultrasonically for 10 min (ultrasonic power 200 W) until completely dissolved, obtaining a mixed solution. Transfer the mixed solution to a 100 mL hydrothermal reactor lined with polytetrafluoroethylene (PTFE), and react at 120 °C for 24 h. After the reaction, allow it to cool naturally to room temperature. Collect the precipitate by centrifugation at 9000 rpm. Wash the precipitate with 30 mL of DMF, centrifuge, and repeat three times. Wash again with 30 mL of anhydrous ethanol, centrifuge, and repeat three times. Dry the washed precipitate in a vacuum drying oven at 60 °C for 12 h to obtain the Ce-MOF precursor. Place the Ce-MOF precursor in a tube furnace under nitrogen protection. The temperature was increased to 155℃ at a rate of 5℃ / min (nitrogen flow rate 50 mL / min) and heat-treated for 2 h to obtain a thermally stabilized Ce-MOF precursor. 1.0 g of the thermally stabilized Ce-MOF precursor was ultrasonically dispersed in 50 g of deionized water (ultrasonication for 10 min), and then 2.9 g of zirconium oxynitrate was added. The mixture was stirred at room temperature for 30 min to obtain a zirconium salt suspension containing Ce-MOF. 3.3 g of phenylphosphonic acid (purity ≥98%) was dissolved in a mixture of 50 g of ethanol and water (25 g of ethanol and 25 g of deionized water), and triethylamine was added dropwise to adjust the pH to 4.3 (using a pH meter for monitoring) to obtain a phenylphosphonic acid solution. The phenylphosphonic acid solution was slowly added dropwise to the above zirconium salt suspension containing Ce-MOF at a rate of 2 mL / min, and the mixture was heated to 95℃ and refluxed for 10 h.

[0041] B2. After the reaction is complete, the product is naturally cooled to room temperature and centrifuged to obtain a solid product. The solid product is washed three times with 50 mL of deionized water and three times with 50 mL of anhydrous ethanol, and centrifuged after each wash. Take 5 mL of the last wash filtrate and add 1 mL of diphenylamine sulfuric acid solution. No blue color is produced (detection limit ≤ 1 ppm), which proves that the nitrate ions have been washed away. Finally, the solid product is dried in a vacuum drying oven at 100 °C for 27 h to obtain a light yellow powder, namely cerium-based metal-organic framework hybrid zirconium phosphonate.

[0042] Example 2

[0043] The specific implementation method is the same as in Example 1, except that the preparation steps of the smoke-suppressing and flame-retardant recycled polyethylene terephthalate material include:

[0044] S1. Weigh 105g of recycled polyethylene terephthalate chips, 5g of magnesium-doped layered zinc stannate, 8g of cerium-based metal-organic framework hybrid zirconium phosphonate, 2g of maleic anhydride-grafted polyethylene, 0.5g of a mixture of antioxidant 1010 and antioxidant 168 in a 1:2 mass ratio (0.167g of antioxidant 1010 and 0.333g of antioxidant 168), and 0.8g of zinc stearate. Place them in a high-speed mixer and mix at 1200 rpm for 5 minutes at room temperature. Add the mixture to a co-rotating parallel twin-screw extruder with an aspect ratio of 40. Set the screw speed to 300 rpm and set the extruder temperatures as follows: Zone 1: 235℃, Zone 2: 245℃, Zone 3: 245℃, Zone 4: 245℃, Zone 5: 240℃, and Die head: 245℃. After melt extrusion, cool in a water bath, air dry, and granulate to obtain granules.

[0045] S2. The granules are dried at 115℃ for 6 hours under a vacuum of -0.08MPa to obtain the product.

[0046] The method for preparing the magnesium-doped layered zinc stannate includes:

[0047] A1. Dissolve 5.2g of zinc sulfate heptahydrate and 1.3g of magnesium sulfate heptahydrate in 50g of deionized water to obtain mixed salt solution A; dissolve 2.5g of sodium stannate trihydrate in 50g of deionized water to obtain stannate solution B; under stirring at 20℃ and 800rpm, add solution A dropwise to solution B at 2mL / min, and maintain the pH at 7.5 with 5% sodium hydroxide solution; after the addition is complete, transfer to a hydrothermal reactor and crystallize at 120℃ for 12h.

[0048] A2. After the reaction is completed, the solid is cooled and centrifuged. The solid is washed three times each with deionized water and anhydrous ethanol until neutral. It is then dried under vacuum at 100°C for 24 hours and aged in a desiccator with a relative humidity of less than 30% for 48 hours to obtain magnesium-doped layered zinc stannate.

[0049] The preparation method of the cerium-based metal-organic framework hybrid zirconium phosphonate includes:

[0050] B1. Dissolve 2.1 g of cerium nitrate hexahydrate and 0.70 g of trimesic acid in 60 g of N,N-dimethylformamide and 40 g of anhydrous ethanol. After sonication for 10 min, transfer to a hydrothermal reactor and react at 120 °C for 24 h. Collect the precipitate by centrifugation, wash three times alternately with DMF and ethanol, and dry under vacuum at 60 °C to obtain the Ce-MOF precursor. Heat the precursor to 150 °C for 2 h under nitrogen protection at a rate of 5 °C / min to obtain a thermally stabilized precursor. Take 0.8 g of the thermally stabilized precursor and sonicate it in 48 g of deionized water. Add 2.8 g of zirconium oxynitrate and stir for 30 min. Dissolve 3.2 g of phenylphosphonic acid in 48 g of an ethanol-water mixture (24 g of ethanol and 24 g of water). Add triethylamine dropwise to adjust the pH to 4.0 to obtain a phenylphosphonic acid solution. Add this solution dropwise to a zirconium salt suspension and reflux at 90 °C for 8 h.

[0051] B2. After the reaction is complete, the solid is separated by centrifugation. The solid is washed with deionized water and ethanol in sequence until no nitrate ions are detected by diphenylamine sulfuric acid solution. Finally, it is dried under vacuum at 100°C for 24 hours to obtain the product.

[0052] Example 3

[0053] The specific implementation method is the same as in Example 1, except that the preparation steps of the smoke-suppressing and flame-retardant recycled polyethylene terephthalate material include:

[0054] S1. Weigh 95g of recycled polyethylene terephthalate chips, 12g of magnesium-doped layered zinc stannate, 3g of cerium-based metal-organic framework hybrid zirconium phosphonate, 5g of maleic anhydride-grafted polyethylene, 0.2g of a mixture of antioxidant 1010 and antioxidant 168 in a 1:2 mass ratio (0.067g of antioxidant 1010 and 0.133g of antioxidant 168), and 0.3g of zinc stearate. Place them in a high-speed mixer and mix at 1200 rpm for 8 minutes. Add the mixture to a twin-screw extruder with an aspect ratio of 44. Set the screw speed to 400 rpm. Set the extruder temperatures as follows: Zone 1: 245℃, Zone 2: 250℃, Zone 3: 255℃, Zone 4: 250℃, Zone 5: 245℃, and the die head temperature to 245℃. Extrude and granulate to obtain granules.

[0055] S2. The granules are dried at 125℃ for 4 hours under a vacuum of -0.1MPa to obtain the product.

[0056] The method for preparing the magnesium-doped layered zinc stannate includes:

[0057] A1. Dissolve 5.6g of zinc sulfate heptahydrate and 1.2g of magnesium sulfate heptahydrate in 60g of deionized water to obtain solution A; dissolve 2.7g of sodium stannate trihydrate in 60g of deionized water to obtain solution B; add solution A dropwise to solution B while stirring at 30℃ and 1000rpm, and maintain the pH at 8.5 with 5% sodium hydroxide solution; after the addition is complete, crystallize in a hydrothermal reactor at 125℃ for 14h.

[0058] A2. Cool and centrifuge, wash the solid until neutral, vacuum dry at 120℃ for 30h, and then age in a desiccator with relative humidity below 30% for 48h to obtain the product.

[0059] The preparation method of the cerium-based metal-organic framework hybrid zirconium phosphonate includes:

[0060] B1. Dissolve 2.2g of cerium nitrate hexahydrate and 0.75g of trimesic acid in 60g of N,N-dimethylformamide and 40g of anhydrous ethanol. Sonicate for 10min and then hydrothermally react at 125℃ for 24h. Collect the precipitate by centrifugation, wash three times alternately with DMF and ethanol, and dry under vacuum at 62℃ to obtain Ce-MOF precursor. Heat the precursor to 160℃ for 2h under nitrogen protection at a rate of 5℃ / min. Take 1.2g of the heat-stabilized precursor and ultrasonically disperse it in 52g of deionized water. Add 3.0g of zirconium oxynitrate and stir for 30min. Dissolve 3.5g of phenylphosphonic acid in 52g of ethanol-water mixture (26g of ethanol and 26g of water). Add triethylamine dropwise to adjust the pH to 4.5 to obtain phenylphosphonic acid solution. Add this solution dropwise to zirconium salt suspension and reflux at 100℃ for 12h.

[0061] B2. After the reaction, the solid was centrifuged and washed successively with deionized water and ethanol until no nitrate ions were detected by diphenylamine sulfuric acid solution. Finally, it was vacuum dried at 102℃ for 30 hours to obtain the product.

[0062] Comparative Example 1

[0063] The specific implementation method is the same as in Example 1, except that magnesium-doped layered zinc stannate and cerium-based metal-organic framework hybrid zirconium phosphonate are not added, and the remaining steps and conditions are the same as in Example 1.

[0064] Comparative Example 2

[0065] The specific implementation method is the same as in Example 1, except that no cerium-based metal-organic framework hybrid zirconium phosphonate is added, and only 8g of magnesium-doped layered zinc stannate is added. The remaining steps and conditions are the same as in Example 1.

[0066] Comparative Example 3

[0067] The specific implementation method is the same as in Example 1, except that magnesium-doped layered zinc stannate is not added, but only 5g of cerium-based metal-organic framework hybrid zirconium phosphonate is added. The remaining steps and conditions are the same as in Example 1.

[0068] Performance testing

[0069] The smoke-suppressing and flame-retardant recycled polyethylene terephthalate materials prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance testing according to the following method, which included the following steps:

[0070] The smoke-suppressant and flame-retardant recycled polyethylene terephthalate material pellets prepared in Examples 1-3 and Comparative Examples 1-3 were dried in a blast drying oven at 120°C for 4 hours, and then fabricated into standard test specimens at 245°C using an injection molding machine.

[0071] Limiting oxygen index test: Using a limiting oxygen index tester, the specimen has a size of 130mm × 6.5mm × 3.2mm. The specimen is vertically installed in a glass combustion cylinder, the flow rate of the mixed gas of nitrogen and oxygen is adjusted to make the oxygen concentration reach the set value. After igniting the upper end of the specimen, the combustion behavior is observed, and the minimum oxygen concentration required for the specimen to burn for 180s or reach a combustion length of 50mm is recorded, which is expressed as the volume percentage of oxygen.

[0072] Vertical combustion rating test: Using a vertical combustion tester, the specimen has a size of 130mm × 13mm × 3.2mm. The specimen is vertically clamped in a combustion box, the height of the methane flame is adjusted to 20mm, the flame is applied for 10s and then removed. The first afterflame time, the second afterflame time, the first afterglow time, and the second afterglow time are recorded. Meanwhile, it is observed whether there are molten drips that ignite the absorbent cotton laid below during the combustion process, and the rating of V-0, V-1 or V-2 is determined according to the afterflame time and dripping situation.

[0073] Ignition time test: Using a cone calorimeter, the sample piece has a size of 100mm × 100mm × 4mm, which is placed horizontally on the sample holder. The heat radiation flux is set to 35kW / m², and ignition is continued by a spark igniter. The time from the start of heating to the appearance of a continuous flame on the surface of the sample piece is recorded, which is expressed in seconds.

[0074] Peak heat release rate test: During the cone calorimeter test, the change of oxygen concentration is continuously monitored by an oxygen analyzer, the real-time heat release rate is calculated according to the oxygen consumption principle, and the maximum value of the heat release rate during the whole combustion process is recorded, which is expressed in kilowatts per square meter.

[0075] Total heat release test: The real-time heat release rate curve of the whole cone calorimeter test process is integrated over time to calculate the total heat released per unit area cumulatively from the start of heating to the extinction of the flame, which is expressed in megajoules per square meter.

[0076] Total smoke release test: Using the laser smoke density measurement system matched with the cone calorimeter, the extinction coefficient of flue gas during the combustion process is continuously monitored to calculate the cumulative smoke generation, and the total smoke released per unit area cumulatively from the start of heating to the end of the test is recorded, which is expressed in square meters per square meter.

[0077] Test results:

[0078] Table 1: Test results of each Example and Comparative Example

[0079] Example 1 31.5 V-0 85 385 62 1380 Example 2 30.2 V-0 78 422 68 1520 Example 3 29.8 V-1 72 458 73 1680 Comparative Example 1 21.3 No grade 45 820 118 3150 Comparative Example 2 26.8 V-2 58 610 89 2250 Comparative Example 3 25.4 V-2 52 672 96 2580

[0080] As can be seen from Table 1, Examples 1-3 significantly solved the technical problems of poor flame retardant performance and large smoke release during combustion of existing recycled polyethylene terephthalate materials compared with Comparative Examples 1-3.

[0081] Regarding flame retardant performance, Comparative Example 1, without any added modified compounds, had a limiting oxygen index of only 21.3%. It exhibited severe dripping during vertical burning tests and received no rating, indicating that pure recycled polyester is highly flammable and poses a significant risk of dripping ignition. Comparative Example 2, with only magnesium-doped layered zinc stannate added, saw its limiting oxygen index increase to 26.8%, achieving a vertical burning rating of V-2, but dripping still occurred during combustion. Comparative Example 3, with only cerium-based metal-organic framework hybrid zirconium phosphonate added, saw its limiting oxygen index increase to 25.4%, also achieving a vertical burning rating of V-2.

[0082] In contrast, Example 1, with the addition of two modified compounds, achieved a limiting oxygen index of 31.5%, a vertical combustion rating of V-0, and no dripping. Example 2, with a limiting oxygen index of 30.2%, also achieved a V-0 rating. Example 3, with a limiting oxygen index of 29.8%, achieved a V-1 rating. These results demonstrate that the two modified compounds have a significant synergistic effect in condensed phase char formation and gas phase free radical capture.

[0083] Regarding the heat release during combustion, Comparative Example 1 showed a peak heat release rate as high as 820 kW / m², with a total heat release of 118 MJ / m², indicating that the combustion process was intense and released a large amount of heat. Comparative Example 2 showed a peak heat release rate reduced to 610 kW / m², with a total heat release of 89 MJ / m². Comparative Example 3 showed a peak heat release rate reduced to 672 kW / m², with a total heat release of 96 MJ / m². In contrast, Example 1 showed a peak heat release rate further reduced to 385 kW / m², a decrease of 53.0% compared to Comparative Example 1, a decrease of 36.9% compared to Comparative Example 2, and a decrease of 42.7% compared to Comparative Example 3. The total heat release was reduced to 62 MJ / m², a decrease of 47.5% compared to Comparative Example 1, indicating that the material's combustion intensity was significantly reduced and the fire hazard was greatly reduced.

[0084] In terms of smoke suppression performance, the total smoke emission of Comparative Example 1 was as high as 3150 m² / m², indicating that a large amount of dense smoke was produced when the recycled polyester burned. The total smoke emission of Comparative Example 2 was reduced to 2250 m² / m², and the total smoke emission of Comparative Example 3 was reduced to 2580 m² / m², indicating that the single modified compound had a certain smoke suppression effect. The total smoke emission of Example 1 was further reduced to 1380 m² / m², which was 56.2% lower than that of Comparative Example 1, 38.7% lower than that of Comparative Example 2, and 46.5% lower than that of Comparative Example 3. The total smoke emission of Examples 2 and 3 was also controlled at 1520 m² / m² and 1680 m² / m², respectively, which were significantly better than those of the comparative examples.

[0085] In addition, the ignition time was extended from 45 seconds in Comparative Example 1 to 85 seconds in Example 1, nearly doubling, providing more valuable early warning time for personnel to escape.

[0086] Based on the above data, this invention achieves significant technological advancements in flame retardant efficiency, smoke suppression effect, and heat release control through the synergistic effect of magnesium-doped layered zinc stannate and cerium-based metal-organic framework hybrid zirconium phosphonate. It catalyzes the formation of a dense carbon layer in the condensed phase to block heat and mass exchange, captures free radicals in the gas phase to interrupt chain reactions, and catalyzes the conversion of toxic fumes. This effectively solves the technical bottleneck of poor fire safety of recycled polyester materials.

[0087] 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 method for preparing a smoke-suppressing and flame-retardant recycled polyethylene terephthalate material, characterized in that the steps include... include: S1. By weight, 95-105 parts of recycled polyethylene terephthalate chips, 5-12 parts of magnesium-doped layered zinc stannate, 3-8 parts of cerium-based metal-organic framework hybrid zirconium phosphonate, 2-5 parts of maleic anhydride-grafted polyethylene, 0.2-0.5 parts of a mixture of antioxidant 1010 and antioxidant 168, and 0.3-0.8 parts of zinc stearate are mixed in a mixer to obtain a mixture; the mixture is added to a twin-screw extruder for melt blending and extrusion to obtain an extrudate; the extrudate is cooled, air-dried, and granulated using a pelletizer to obtain pellets; S2. Place the granules in a forced-air drying oven and dry them under vacuum at 115-125℃.

2. The method for preparing the smoke-suppressing and flame-retardant recycled polyethylene terephthalate material according to claim 1, characterized in that, In step S1, the temperatures of each zone of the twin-screw extruder from the feed port to the die head are set sequentially as follows: Zone 1 235-245℃, Zone 2 245-250℃, Zone 3 245-255℃, Zone 4 245-250℃, Zone 5 240-245℃, and the die head temperature is 245℃.

3. The method for preparing the smoke-suppressing and flame-retardant recycled polyethylene terephthalate material according to claim 1, characterized in that, In step S2, the drying time at 115-125℃ is 4-6 hours.

4. The method for preparing the smoke-suppressing and flame-retardant recycled polyethylene terephthalate material according to claim 1, characterized in that, The method for preparing the magnesium-doped layered zinc stannate includes: A1. By weight, dissolve 5.2-5.6 parts of zinc sulfate heptahydrate and 1.2-1.3 parts of magnesium sulfate heptahydrate in 50-60 parts of deionized water to obtain mixed salt solution A; dissolve 2.5-2.7 parts of sodium stannate trihydrate in 50-60 parts of deionized water to obtain stannate solution B; under stirring and at 20-30℃, add mixed salt solution A to stannate solution B and adjust the pH to 7.5-8.5; after the addition is complete, a mixture is obtained; transfer the mixture to a hydrothermal reactor and crystallize at 120-125℃. A2. After the reaction is complete, the mixture is allowed to cool naturally to room temperature and then centrifuged to obtain a solid. The solid is washed with deionized water and anhydrous ethanol to obtain the washed product. The washed product is placed in a vacuum drying oven and dried at 100-120℃, followed by aging.

5. The method for preparing the smoke-suppressing and flame-retardant recycled polyethylene terephthalate material according to claim 4, characterized in that, In step A1, the crystallization reaction is carried out at 120-125℃ for 12-14 hours.

6. The method for preparing the smoke-suppressing and flame-retardant recycled polyethylene terephthalate material according to claim 4, characterized in that, In step A2, the drying time is 24-30 hours at 100-120℃.

7. The method for preparing the smoke-suppressing and flame-retardant recycled polyethylene terephthalate material according to claim 1, characterized in that, The preparation method of the cerium-based metal-organic framework hybrid zirconium phosphonate includes: B1. By weight, dissolve 2.1-2.2 parts of cerium nitrate hexahydrate and 0.70-0.75 parts of trimesic acid in a mixed solvent of N,N-dimethylformamide and anhydrous ethanol, and disperse by ultrasonication to obtain a mixed solution; transfer the mixed solution to a hydrothermal reactor and react at 115-125℃; after the reaction is complete, collect the precipitate by centrifugation, wash the precipitate alternately with N,N-dimethylformamide and ethanol, and dry it under vacuum at 58-62℃ to obtain the Ce-MOF precursor; heat the Ce-MOF precursor at 150-160℃ under nitrogen protection. The process involves obtaining a thermally stabilized Ce-MOF precursor; ultrasonically dispersing 0.8-1.2 parts of the thermally stabilized Ce-MOF precursor in 48-52 parts of deionized water, then adding 2.8-3.0 parts of zirconium oxynitrate and stirring to obtain a zirconium salt suspension containing Ce-MOF; dissolving 3.2-3.5 parts of phenylphosphonic acid in a mixture of 48-52 parts of ethanol and water, and adjusting the pH to 4.0-4.5 with triethylamine to obtain a phenylphosphonic acid solution; adding the phenylphosphonic acid solution dropwise to the zirconium salt suspension containing Ce-MOF, and refluxing at 90-100℃. B2. After the reaction is complete, centrifuge to obtain a solid product; wash the solid product with deionized water and ethanol in sequence, and finally dry it under vacuum at 98-102℃.

8. The method for preparing the smoke-suppressing and flame-retardant recycled polyethylene terephthalate material according to claim 7, characterized in that, In step B1, the reflux reaction time at 90-100℃ is 8-12 hours.

9. The method for preparing the smoke-suppressing and flame-retardant recycled polyethylene terephthalate material according to claim 7, characterized in that, In step B2, the vacuum drying time at 98-102℃ is 24-30 hours.

10. A smoke-suppressing and flame-retardant recycled polyethylene terephthalate material, characterized in that, The smoke-suppressing and flame-retardant recycled polyethylene terephthalate material is prepared by the method according to any one of claims 1-9.