Preparation method of magnesium-aluminum hydrotalcite for enhancing thermal stability of PVC

Abstract

The application relates to the technical field of inorganic functional material preparation, and particularly discloses a preparation method of magnesium-aluminum hydrotalcite for enhancing the thermal stability of PVC, which comprises the following steps: preparing an intercalation agent solution by compounding pentaerythritol monomaleate and L-arginine; complexing soluble salt and citric acid to obtain a complex mixed metal salt solution; mixing the two solutions and performing a co-precipitation reaction under the assistance of pulse ultrasonic; aging and centrifuging to obtain a precursor slurry; adding ethylene glycol and performing microwave hydrothermal crystallization; then, sequentially coating with vinyl silane coupling agent and modified epoxy soybean oil; and finally, filtering, washing, drying, depolymerizing and screening to obtain the product. The application significantly improves the acid absorption efficiency, dispersibility and interface compatibility of the hydrotalcite by means of organic intercalation, multi-metal synergistic doping, pulse ultrasonic assisted co-precipitation, microwave crystallization in an alcohol-water system and composite organic coating, and can comprehensively improve the initial whiteness and long-term thermal stability of PVC products.

Description

Technical Field

[0001] This invention relates to the field of inorganic functional material preparation technology, specifically a method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC. Background Technology

[0002] Polyvinyl chloride (PVC) is widely used in pipes, profiles, wires and cables, films, artificial leather, and medical products due to its advantages such as wide availability of raw materials, good flame retardancy, adjustable mechanical properties, strong processing adaptability, and low cost. However, the PVC molecular chain contains unstable structures such as allyl chloride, tertiary chloride, and branching points, which easily undergo dehydrochlorination reactions under heating, shearing, or oxidizing conditions. The released HCl further catalyzes the continuous degradation of PVC, forming conjugated polyene structures, leading to yellowing, browning, or even blackening of products, accompanied by a decrease in mechanical properties and deterioration of processing fluidity. Therefore, heat stabilizers are usually added during PVC processing to inhibit its thermal degradation.

[0003] Traditional lead- and barium-cadmium heat stabilizers, while offering good stabilization effects, suffer from high toxicity and significant environmental impact, limiting their application. Calcium-zinc heat stabilizers offer advantages in terms of low toxicity and environmental friendliness, but their long-term thermal stability is insufficient when used alone, and zinc salts readily generate zinc chloride at high temperatures, potentially accelerating PVC degradation and causing a "zinc burning" phenomenon. Magnesium-aluminum hydrotalcite, as a layered bimetallic hydroxide, can capture HCl released during PVC degradation through interlayer anion exchange, layer hydroxyl neutralization, and adsorption, making it a crucial inorganic functional material to replace traditional toxic heat stabilizers.

[0004] However, most existing magnesium-aluminum hydrotalcites are prepared using the conventional co-precipitation method. The interlayer anions are typically carbonate, resulting in small interlayer spacing and limited diffusion of HCl into the interlayer, leading to low initial acid absorption efficiency. Simultaneously, the hydrotalcite surface is rich in hydroxyl groups, exhibiting strong hydrophilicity and high surface energy, resulting in poor dispersibility in hydrophobic PVC resin and a tendency to form aggregates. This not only reduces the effective acid absorption area but also affects the transparency and mechanical properties of the finished product. Furthermore, single magnesium-aluminum hydrotalcites primarily rely on their layered structure to absorb HCl, lacking the ability to synergistically regulate initial coloring, free radical thermo-oxidative aging, and interfacial compatibility. While existing organically modified hydrotalcites can improve dispersibility to some extent, most only involve surface coating or simple intercalation, failing to simultaneously achieve the comprehensive effects of rapid acid absorption, long-term stability, zinc burn resistance, and high compatibility.

[0005] Based on the above statements, the present invention provides a method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC. Summary of the Invention

[0006] To address the problems of low interlayer anion exchange efficiency, difficulty in balancing acid absorption capacity and rate, poor dispersibility due to strong surface hydrophilicity, insufficient initial whiteness and long-term thermal stability of magnesium aluminum hydrotalcite heat stabilizers, and easy catalytic degradation of traditional calcium zinc stabilizers in the later stage, this invention provides a method for preparing magnesium aluminum hydrotalcite that enhances the thermal stability of PVC.

[0007] In a first aspect, the present invention provides a method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC, employing the following technical solution: A method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC includes the following steps: S1. Pentaerythritol and maleic anhydride are mixed, added to an organic solvent, stirred and reacted, and subjected to reduced pressure to obtain pentaerythritol monomaleate; pentaerythritol monomaleate is mixed with L-arginine, added to deionized water, stirred evenly, and the pH is adjusted to obtain an intercalating agent solution. S2. Mix soluble magnesium salt, soluble zinc salt, soluble aluminum salt and soluble cerium salt, add to deionized water, stir evenly to obtain a mixed metal salt solution; add citric acid to the mixed metal salt solution, stir to react, and obtain a complexed mixed metal salt solution. S3. Mix the intercalating agent solution and the complexed mixed metal salt solution, adjust the pH, stir the reaction under pulsed ultrasound, continue aging after the reaction is completed, centrifuge and concentrate to obtain the precursor slurry; S4. Add ethylene glycol to the precursor slurry and stir until homogeneous to obtain an alcohol-water co-soluble precursor slurry; subject the alcohol-water co-soluble precursor slurry to microwave hydrothermal crystallization reaction, and cool after the reaction to obtain a hydrotalcite slurry. S5. Add vinyl silane coupling agent to the hydrotalcite slurry and stir to react; then add modified epoxidized soybean oil and stir to react to obtain composite coated hydrotalcite slurry. S6. The composite coated hydrotalcite slurry is filtered, washed, dried, depolymerized and sieved to obtain magnesium aluminum hydrotalcite that enhances the thermal stability of PVC.

[0008] Preferably, the specific operation steps of step S1 are as follows: Pentaerythritol and maleic anhydride were mixed to obtain mixture A. Mixture A was added to an organic solvent at a mass ratio of 1:6-8, and the mixture was stirred at 80-95℃ and 300-500rpm for 3-5 hours. After the reaction was completed, the mixture was subjected to reduced pressure treatment at 60-80℃ and a vacuum degree of -0.08MPa to -0.095MPa for 1-1.5 hours to obtain pentaerythritol monomaleate. Pentaerythritol monomaleate was mixed with L-arginine to obtain mixture B. Mixture B was added to deionized water at a mass ratio of 1:6-10, and the mixture was stirred at 25-40℃ and 300-500rpm for 20-40 minutes. The pH was then adjusted to 9.5-10.5 with a 5-10% sodium hydroxide solution to obtain the intercalating agent solution.

[0009] Preferably, in step S1, the organic solvent is selected from one or more of toluene, xylene, and chloroform; the molar ratio of pentaerythritol to maleic anhydride is 1:1.05-1.15; and the molar ratio of pentaerythritol monomaleate to L-arginine is 2-4:1.

[0010] Preferably, the specific operation steps of step S2 are as follows: Soluble magnesium salt, soluble zinc salt, soluble aluminum salt, and soluble cerium salt are mixed to obtain mixture C. Mixture C is added to deionized water at a mass ratio of 1:6-8, and stirred for 20-40 minutes at 25-35℃ and 300-500 rpm to obtain a mixed metal salt solution. Citric acid is added to the mixed metal salt solution, controlling the Mg²⁺ content in the citric acid to a specific level. + Zn² + Al³ + and Ce³ + The total molar ratio is 0.01-0.03:1. The reaction is continued to be stirred for 20-30 minutes at 25-35℃ and 300-500rpm to obtain a complexed mixed metal salt solution.

[0011] Preferably, in step S2, the Mg²⁺ in the soluble magnesium salt, soluble zinc salt, soluble aluminum salt, and soluble cerium salt is... + Zn² + Al³ + and Ce³ + The molar ratio is 2.5-3.5:0.1-0.3:1:0.06-0.08.

[0012] Preferably, in step S2, the soluble magnesium salt is selected from one or more of magnesium chloride, magnesium nitrate, and magnesium sulfate; the soluble zinc salt is selected from one or more of zinc chloride, zinc nitrate, and zinc acetate; the soluble aluminum salt is selected from one or more of aluminum chloride, aluminum nitrate, and aluminum sulfate; and the soluble cerium salt is selected from one or more of cerium chloride, cerium nitrate, and cerium sulfate.

[0013] Preferably, the specific operation steps of step S3 are as follows: Mix the intercalating agent solution and the complexed mixed metal salt solution at a mass ratio of 1:3-5, adjust the pH to 9.8-10.2 with a 1-2 mol / L sodium hydroxide solution to obtain mixture D. Mixture D is then stirred at room temperature and 400-600 rpm for 40-60 min under pulsed ultrasonic conditions. After the reaction is completed, continue aging, and then concentrate by centrifugation at 20-30℃ and 3000-5000 rpm until the solid content is 5-15% to obtain the precursor slurry.

[0014] Preferably, in step S3, the frequency of the pulsed ultrasound is 20-40kHz, the power is 300-500W, and the pulse mode is 2-4s operation followed by 1-3s interval; the aging temperature is 40-50℃, the aging speed is 400-600rpm, and the aging time is 45-60min.

[0015] Preferably, the specific operation steps of step S4 are as follows: Ethylene glycol is added to the precursor slurry and stirred for 20-30 minutes at 30-40℃ and 400-600 rpm to obtain an alcohol-water co-soluble precursor slurry. The alcohol-water co-soluble precursor slurry is transferred to a microwave hydrothermal reactor for microwave hydrothermal crystallization reaction. After the reaction is completed, it is cooled to 70-80℃ to obtain a hydrotalcite slurry.

[0016] Preferably, in step S4, the volume ratio of the precursor slurry to ethylene glycol is 1-2:1; the temperature of the microwave hydrothermal crystallization reaction is 130-150℃, the microwave power is 500-800W, and the reaction time is 1-2h.

[0017] Preferably, the specific operation steps of step S5 are as follows: Add 1-3% (by dry weight of hydrotalcite) of vinylsilane coupling agent to the hydrotalcite slurry and stir for 20-40 minutes at 70-80℃ and 300-500 rpm to obtain solution A; add 3-5% (by dry weight of hydrotalcite) of modified epoxidized soybean oil to solution A and stir for 45-60 minutes at 70-80℃ and 500-700 rpm to obtain composite coated hydrotalcite slurry.

[0018] Preferably, the vinyl silane coupling agent in step S5 is selected from one or more of vinyltriethoxysilane, vinyltrimethoxysilane, and vinyltri(β-methoxyethoxy)silane.

[0019] Preferably, the method for preparing the modified epoxidized soybean oil in step S5 is as follows: Epoxidized soybean oil, maleic anhydride, and catalyst were mixed and reacted under nitrogen protection to obtain maleic anhydride-grafted epoxidized soybean oil. A polyol modifier was added to the maleic anhydride-grafted epoxidized soybean oil, and the reaction was continued with stirring. After the reaction was completed, the mixture was cooled and subjected to reduced pressure to obtain modified epoxidized soybean oil.

[0020] Preferably, the specific preparation method of the modified epoxidized soybean oil in step S5 is as follows: Epoxidized soybean oil, maleic anhydride, and catalyst were added to a reaction vessel at a mass ratio of 100:5-15:0.3-0.5 and mixed. Under nitrogen protection, the mixture was stirred and reacted at 85-105℃ and 300-500rpm for 2-3 hours to obtain maleic anhydride-grafted epoxidized soybean oil. A polyol modifier, accounting for 3-5% of the mass of the epoxidized soybean oil, was added to the maleic anhydride-grafted epoxidized soybean oil, and the mixture was stirred and reacted at 90-110℃ and 300-500rpm for 1-2 hours. After the reaction was completed, the temperature was lowered to 80-100℃ and the mixture was subjected to reduced pressure treatment at a vacuum degree of -0.08MPa to -0.095MPa for 1-1.5 hours to obtain modified epoxidized soybean oil.

[0021] Preferably, the catalyst is selected from one or more of tetrabutylammonium bromide, triethylamine, and N,N-dimethylbenzylamine.

[0022] Preferably, the polyol modifier is selected from one or more of glycerol, pentaerythritol, and trimethylolpropane.

[0023] Preferably, the specific operation steps of step S6 are as follows: The composite-coated hydrotalcite slurry was filtered through a 200-300 mesh sieve, and the filter cake was collected. The filter cake was washed sequentially with deionized water and anhydrous ethanol until the pH of the washing solution was 7.0-8.0. The washed filter cake was placed in a vacuum drying oven at 60-80℃ and dried for 8-12 hours to obtain the dried material. The dried material was depolymerized by an air jet mill at 1800-2500 rpm for 10-20 minutes, and then sieved through a 200-300 mesh vibrating screen. The undersize material was collected to obtain magnesium aluminum hydrotalcite that enhances the thermal stability of PVC.

[0024] Secondly, the present invention provides a magnesium-aluminum hydrotalcite with enhanced PVC thermal stability prepared by the above-mentioned method.

[0025] Thirdly, the present invention provides an application of the above-mentioned magnesium aluminum hydrotalcite that enhances the thermal stability of PVC in the preparation of PVC heat stabilizers.

[0026] In summary, the present invention has the following beneficial effects: (1) In this invention, pentaerythritol monomaleate and L-arginine are combined as intercalating agents. The guanidinyl functional group of L-arginine provides a fast acid capture site to achieve rapid absorption of HCl. At the same time, the hydroxyl and ester structure in pentaerythritol monomaleate provides a long-term synergistic thermal stability. The synergistic effect of the two solves the problems of low interlayer anion exchange efficiency and difficulty in balancing acid absorption capacity and acid absorption rate in traditional hydrotalcite.

[0027] (2) This invention utilizes zinc ions and cerium ions in the magnesium aluminum hydrotalcite layer to improve the color retention of PVC in the early stage of PVC processing, and utilizes the variable valence characteristics of cerium ions to capture or quench free radicals generated during thermo-oxidative aging, inhibiting the generation of allyl chloride and chain dehydrochlorination reaction, thereby improving the initial whiteness and long-term thermal stability of PVC products, and alleviating the problem of easy late-stage catalytic degradation of traditional calcium zinc stabilization system.

[0028] (3) The present invention uses citric acid to pre-complex zinc ions and cerium ions, so that zinc and cerium ions are slowly released in a complexed state during the co-precipitation process, reducing the risk of uneven doping caused by the difference in precipitation rate between zinc ions, cerium ions and magnesium ions, aluminum ions, which is conducive to achieving uniform doping of zinc ions and cerium ions in the hydrotalcite layer and improving the consistency and stability of product performance.

[0029] (4) The present invention uses pulsed ultrasound-assisted stirring co-precipitation reaction. The cavitation effect and mechanical vibration of pulsed ultrasound promote the uniform mixing of intercalating agent solution and metal salt solution, effectively refine the grain size and inhibit grain agglomeration, and prepare lamellar hydrotalcite with narrow particle size distribution and good dispersibility. This is beneficial to increase its specific surface area and shorten the diffusion path of HCl between layers, thereby improving the acid absorption rate and acid absorption efficiency.

[0030] (5) In the microwave hydrothermal crystallization process, ethylene glycol is introduced as an alcohol-water co-solvent. By adjusting the dielectric environment, viscosity and surface tension of the system, the dispersion state of the precursor during the crystallization process is improved, the nucleation and crystal growth process of hydrotalcite is controlled, and a hydrotalcite product with thinner layers and more uniform structure is prepared. This further shortens the diffusion distance of HCl between layers and improves the overall thermal stability efficiency.

[0031] (6) This invention uses a vinyl silane coupling agent and modified epoxidized soybean oil to construct a composite coating layer. The vinyl silane coupling agent can undergo a condensation reaction with the hydroxyl groups on the surface of hydrotalcite to form a stable anchoring layer. The modified epoxidized soybean oil is further modified by maleic anhydride grafting and polyols, which can introduce ester groups, carboxyl groups and hydroxyl groups as interaction sites to form a flexible organic coating layer outside the silane grafting layer. This composite coating layer can reduce the surface polarity of hydrotalcite, improve its interfacial compatibility and dispersion uniformity with PVC resin, and at the same time, the modified epoxidized soybean oil has the functions of auxiliary thermal stabilization and plasticizing, which is beneficial to improving the mechanical property retention rate of PVC products. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0033] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0034] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available products.

[0035] Among them, the epoxidized soybean oil was purchased from Jiangsu Sanmu Group Co., Ltd., with an epoxy value of ≥6.0%; The calcium-zinc composite heat stabilizer was purchased from Zanyu Technology Group Co., Ltd. The PVC resin was purchased from Cangzhou Julong Chemical Co., Ltd. The PE wax was purchased from Wuhan Jiyesheng Chemical Co., Ltd.

[0036] Examples 1-3 provide a method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC.

[0037] Example 1 A method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC includes the following steps: S1. Pentaerythritol and maleic anhydride were mixed at a molar ratio of 1:1.05 to obtain mixture A. Mixture A was added to toluene at a mass ratio of 1:6, and the mixture was stirred at 80°C and 300 rpm for 3 h. After the reaction was completed, the mixture was subjected to reduced pressure treatment at 60°C and -0.08 MPa for 1 h to obtain pentaerythritol monomaleate. Pentaerythritol monomaleate was mixed with L-arginine at a molar ratio of 2:1 to obtain mixture B. Mixture B was added to deionized water at a mass ratio of 1:6, and the mixture was stirred at 25°C and 300 rpm for 20 min. The pH was then adjusted to 9.5 with a 5% sodium hydroxide solution to obtain the intercalating agent solution. S2, according to Mg² + Zn² + Al³ + and Ce³ + Magnesium chloride, zinc chloride, aluminum chloride, and cerium chloride were mixed in a molar ratio of 2.5:0.1:1:0.06 to obtain mixture C. Mixture C was added to deionized water at a mass ratio of 1:6, and stirred for 20 minutes at 25°C and 300 rpm to obtain a mixed metal salt solution. Citric acid was added to the mixed metal salt solution to control the Mg²⁺ content in the solution. + Zn² + Al³ + and Ce³ + The total molar ratio was 0.01:1. The reaction was continued for 20 min at 25℃ and 300 rpm to obtain a complexed mixed metal salt solution. S3. Mix the intercalating agent solution and the complexed mixed metal salt solution at a mass ratio of 1:3. Adjust the pH to 9.8 with a 1 mol / L sodium hydroxide solution to obtain mixture D. Mixture D is then subjected to pulsed ultrasound (frequency 20 kHz, power 300 W, pulse mode 2 s working, 1 s intermittent) at room temperature and stirred at 400 rpm for 40 min. After the reaction is completed, the mixture is further aged at 40℃ and 400 rpm for 50 min. Then, it is concentrated by centrifugation at 20℃ and 3000 rpm to a solid content of 5% to obtain the precursor slurry. S4. Add ethylene glycol to the precursor slurry at a volume ratio of 1:1, and stir at 30℃ and 400rpm for 20min to obtain an alcohol-water co-soluble precursor slurry; transfer the alcohol-water co-soluble precursor slurry to a microwave hydrothermal reactor, and perform a microwave hydrothermal crystallization reaction at 130℃ and 500W for 1h. After the reaction is completed, cool to 70℃ to obtain a hydrotalcite slurry. S5. Add 1% vinyltriethoxysilane (by dry weight of hydrotalcite) to the hydrotalcite slurry and stir at 70°C and 300 rpm for 20 min to obtain solution A. Add 3% modified epoxidized soybean oil (by dry weight of hydrotalcite) to solution A and stir at 70°C and 500 rpm for 45 min to obtain composite coated hydrotalcite slurry. S6. Filter the composite coated hydrotalcite slurry through a 200-mesh sieve and collect the filter cake. Wash the filter cake sequentially with deionized water and anhydrous ethanol until the pH of the washing solution is 7.0. Place the washed filter cake in a vacuum drying oven at 60℃ and dry for 8 hours to obtain the dried material. Depolymerize the dried material by air jet mill at 1800 rpm for 10 minutes, and then sieve it through a 200-mesh vibrating sieve to collect the undersize material to obtain magnesium aluminum hydrotalcite that enhances the thermal stability of PVC.

[0038] The specific preparation method of the modified epoxidized soybean oil in step S5 is as follows: Epoxidized soybean oil, maleic anhydride, and tetrabutylammonium bromide were added to a reaction vessel at a mass ratio of 100:5:0.3 and mixed. Under nitrogen protection, the mixture was stirred and reacted at 85°C and 300 rpm for 2 hours to obtain maleic anhydride-grafted epoxidized soybean oil. Glycerin at 3% of the mass of the epoxidized soybean oil was added to the maleic anhydride-grafted epoxidized soybean oil, and the mixture was stirred and reacted at 90°C and 300 rpm for 1 hour. After the reaction was completed, the temperature was lowered to 80°C and the mixture was subjected to reduced pressure treatment at a vacuum degree of -0.08 MPa for 1 hour to obtain modified epoxidized soybean oil.

[0039] Example 2 A method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC includes the following steps: S1. Pentaerythritol and maleic anhydride were mixed at a molar ratio of 1:1.1 to obtain mixture A. Mixture A was added to xylene at a mass ratio of 1:6, and the mixture was stirred at 80°C and 300 rpm for 3 h. After the reaction was completed, the mixture was subjected to reduced pressure treatment at 60°C and -0.09 MPa for 1.2 h to obtain pentaerythritol monomaleate. Pentaerythritol monomaleate was mixed with L-arginine at a molar ratio of 3:1 to obtain mixture B. Mixture B was added to deionized water at a mass ratio of 1:8, and the mixture was stirred at 35°C and 400 rpm for 30 min. The pH was then adjusted to 10.0 with a 7.5% sodium hydroxide solution to obtain the intercalating agent solution. S2, according to Mg² + Zn² + Al³ + and Ce³ +Magnesium nitrate, zinc nitrate, aluminum nitrate, and cerium nitrate were mixed in a molar ratio of 3:0.2:1:0.07 to obtain mixture C. Mixture C was added to deionized water at a mass ratio of 1:7, and stirred at 30°C and 400 rpm for 30 minutes to obtain a mixed metal salt solution. Citric acid was added to the mixed metal salt solution to control the Mg²⁺ content in the solution. + Zn² + Al³ + and Ce³ + The total molar ratio was 0.02:1. The reaction was continued at 30℃ and 400rpm for 25min to obtain a complexed mixed metal salt solution. S3. Mix the intercalating agent solution and the complexed mixed metal salt solution at a mass ratio of 1:4. Adjust the pH to 10.0 with a 1.5 mol / L sodium hydroxide solution to obtain mixture D. Mixture D is then subjected to pulsed ultrasound (frequency 30 kHz, power 400 W, pulse mode 3 s working, 2 s intermittent) at room temperature and stirred at 500 rpm for 50 min. After the reaction is completed, the mixture is aged at 45 ℃ and 500 rpm for another 55 min. Finally, it is concentrated by centrifugation at 25 ℃ and 4000 rpm to a solid content of 10% to obtain the precursor slurry. S4. Ethylene glycol is added to the precursor slurry at a volume ratio of 1.5:1, and stirred at 35℃ and 500rpm for 25min to obtain an alcohol-water co-soluble precursor slurry. The alcohol-water co-soluble precursor slurry is transferred to a microwave hydrothermal reactor and subjected to microwave hydrothermal crystallization reaction at 140℃ and 600W for 1.5h. After the reaction is completed, it is cooled to 75℃ to obtain a hydrotalcite slurry. S5. Add 2% vinyltrimethoxysilane (by dry weight of hydrotalcite) to the hydrotalcite slurry and stir at 75°C and 400 rpm for 30 min to obtain solution A. Add 4% modified epoxidized soybean oil (by dry weight of hydrotalcite) to solution A and stir at 75°C and 600 rpm for 50 min to obtain composite coated hydrotalcite slurry. S6. Filter the composite coated hydrotalcite slurry through a 250-mesh sieve and collect the filter cake. Wash the filter cake sequentially with deionized water and anhydrous ethanol until the pH of the washing solution is 7.5. Place the washed filter cake in a vacuum drying oven at 70℃ and dry for 10 hours to obtain the dried material. Depolymerize the dried material by air jet milling at 2200 rpm for 15 minutes, and then sieve it through a 250-mesh vibrating sieve to collect the undersize material, thus obtaining magnesium aluminum hydrotalcite that enhances the thermal stability of PVC.

[0040] The specific preparation method of the modified epoxidized soybean oil in step S5 is as follows: Epoxidized soybean oil, maleic anhydride, and triethylamine were added to a reaction vessel at a mass ratio of 100:10:0.4 and mixed. Under nitrogen protection, the mixture was stirred at 95°C and 400 rpm for 2.5 h to obtain maleic anhydride-grafted epoxidized soybean oil. Pentaerythritol (4% by mass of epoxidized soybean oil) was added to the maleic anhydride-grafted epoxidized soybean oil, and the mixture was stirred at 100°C and 400 rpm for another 1.5 h. After the reaction was completed, the temperature was lowered to 90°C and the mixture was subjected to reduced pressure treatment at a vacuum of -0.09 MPa for 1.2 h to obtain modified epoxidized soybean oil.

[0041] Example 3 A method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC includes the following steps: S1. Pentaerythritol and maleic anhydride were mixed at a molar ratio of 1:1.15 to obtain mixture A. Mixture A was added to chloroform at a mass ratio of 1:8 and stirred at 95°C and 500 rpm for 5 h. After the reaction was completed, the mixture was subjected to reduced pressure treatment at 80°C and -0.095 MPa for 1.5 h to obtain pentaerythritol monomaleate. Pentaerythritol monomaleate was mixed with L-arginine at a molar ratio of 4:1 to obtain mixture B. Mixture B was added to deionized water at a mass ratio of 1:10 and stirred at 40°C and 500 rpm for 40 min. The pH was then adjusted to 10.5 with a 10% sodium hydroxide solution to obtain the intercalating agent solution. S2, according to Mg² + Zn² + Al³ + and Ce³ + The molar ratio of magnesium sulfate, zinc acetate, aluminum sulfate, and cerium sulfate was 3.5:0.3:1:0.08. Mixture C was obtained by mixing these components. Mixture C was then added to deionized water at a mass ratio of 1:8 and stirred at 35°C and 500 rpm for 40 minutes to obtain a mixed metal salt solution. Citric acid was added to the mixed metal salt solution to control the concentration of Mg²⁺ in the solution. + Zn² + Al³ + and Ce³ + The total molar ratio was 0.03:1. The reaction was continued at 35℃ and 500rpm for 30min to obtain a complexed mixed metal salt solution. S3. Mix the intercalating agent solution and the complexed mixed metal salt solution at a mass ratio of 1:5. Adjust the pH to 10.2 with a 2 mol / L sodium hydroxide solution to obtain mixture D. Mixture D is subjected to pulsed ultrasound (frequency 40 kHz, power 500 W, pulse mode 4 s working, 3 s intermittent) at room temperature and stirred at 600 rpm for 60 min. After the reaction is completed, it is aged at 50℃ and 600 rpm for another 60 min. Then it is centrifuged and concentrated at 30℃ and 5000 rpm until the solid content is 15% to obtain the precursor slurry. S4. Add ethylene glycol to the precursor slurry at a volume ratio of 2:1, and stir at 40℃ and 600rpm for 30min to obtain an alcohol-water co-soluble precursor slurry; transfer the alcohol-water co-soluble precursor slurry to a microwave hydrothermal reactor, and perform microwave hydrothermal crystallization reaction at 150℃ and 800W for 2h. After the reaction is completed, cool to 80℃ to obtain a hydrotalcite slurry; S5. Add 3% vinyltris(β-methoxyethoxy)silane (by dry weight of hydrotalcite) to the hydrotalcite slurry and stir at 80°C and 500 rpm for 40 min to obtain solution A; add 5% modified epoxidized soybean oil (by dry weight of hydrotalcite) to solution A and stir at 80°C and 700 rpm for 60 min to obtain composite coated hydrotalcite slurry. S6. Filter the composite coated hydrotalcite slurry through a 300-mesh sieve and collect the filter cake. Wash the filter cake sequentially with deionized water and anhydrous ethanol until the pH of the washing solution is 8.0. Place the washed filter cake in an 80℃ vacuum drying oven and dry for 12 hours to obtain the dried material. Depolymerize the dried material by air jet milling at 2500 rpm for 20 minutes, and then sieve it through a 300-mesh vibrating sieve to collect the undersize material, thus obtaining magnesium aluminum hydrotalcite that enhances the thermal stability of PVC.

[0042] The specific preparation method of the modified epoxidized soybean oil in step S5 is as follows: Epoxidized soybean oil, maleic anhydride, and N,N-dimethylbenzylamine were added to a reaction vessel at a mass ratio of 100:15:0.5 and mixed. Under nitrogen protection, the mixture was stirred and reacted at 105°C and 500 rpm for 3 hours to obtain maleic anhydride-grafted epoxidized soybean oil. Trimethylolpropane (5% by mass of epoxidized soybean oil) was added to the maleic anhydride-grafted epoxidized soybean oil, and the mixture was stirred and reacted at 110°C and 500 rpm for 2 hours. After the reaction was completed, the temperature was lowered to 100°C and subjected to reduced pressure treatment at a vacuum degree of -0.095 MPa for 1.5 hours to obtain modified epoxidized soybean oil.

[0043] Comparative Example 1 This comparative example provides a method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC. The only difference from Example 2 is that in step S1, only pentaerythritol monomaleate is used as a single intercalating agent, and L-arginine is not added for compounding; the other raw material types, amounts and preparation process parameters are completely consistent with Example 2.

[0044] Specifically: S1. Pentaerythritol and maleic anhydride were mixed at a molar ratio of 1:1.1 to obtain mixture A. Mixture A was added to xylene at a mass ratio of 1:6, and the mixture was stirred at 80°C and 300 rpm for 3 h. After the reaction was completed, the mixture was subjected to reduced pressure treatment at 60°C and -0.09 MPa for 1.2 h to obtain pentaerythritol monomaleate. Pentaerythritol monomaleate was added to deionized water at a mass ratio of 1:8, and the mixture was stirred at 35°C and 400 rpm for 30 min. The pH was then adjusted to 10.0 with a 7.5% sodium hydroxide solution to obtain the intercalating agent solution.

[0045] Comparative Example 2 This comparative example provides a method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC. The only difference from Example 2 is that in step S1, only L-arginine is used as an intercalating agent, and pentaerythritol monomaleate is not added for compounding; the other raw material types, amounts and preparation process parameters are completely consistent with Example 2.

[0046] Specifically: S1. Add L-arginine to deionized water at a mass ratio of 1:8 and stir for 30 min at 35℃ and 400 rpm. Then adjust the pH to 10.0 with a 7.5% sodium hydroxide solution to obtain the intercalating agent solution.

[0047] Comparative Example 3 This comparative example provides a method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC. The only difference from Example 2 is that citric acid is not added for complexation in step S2, and a mixed metal salt solution is used for co-precipitation. The other raw material types, amounts, and preparation process parameters are completely consistent with those of Example 2.

[0048] Specifically: S2, according to Mg² + Zn² + Al³ + and Ce³ + Magnesium nitrate, zinc nitrate, aluminum nitrate, and cerium nitrate were mixed in a molar ratio of 3:0.2:1:0.07 to obtain mixture C. Mixture C was added to deionized water in a mass ratio of 1:7 and stirred at 30°C and 400 rpm for 55 min to obtain a mixed metal salt solution.

[0049] Comparative Example 4 This comparative example provides a method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC. The only difference from Example 2 is that pulsed ultrasound is not used in step S3, and only ordinary stirring reaction is performed; the other raw material types, amounts and preparation process parameters are completely consistent with Example 2.

[0050] Specifically: S3. Mix the intercalating agent solution and the complexed mixed metal salt solution at a mass ratio of 1:4. Adjust the pH to 10.0 with a 1.5 mol / L sodium hydroxide solution to obtain mixture D. Stir mixture D at room temperature and 500 rpm for 50 min. After the reaction is complete, continue aging at 45℃ and 500 rpm for 55 min. Then, centrifuge at 25℃ and 4000 rpm to concentrate the mixture to a solid content of 10% to obtain the precursor slurry.

[0051] Comparative Example 5 This comparative example provides a method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC. The only difference from Example 2 is that in step S4, ethylene glycol is replaced with an equal volume of deionized water; the other raw material types, amounts, and preparation process parameters are completely consistent with Example 2.

[0052] Specifically: S4. Add deionized water to the precursor slurry at a volume ratio of 1.5:1, and stir at 35℃ and 500rpm for 25min to obtain an aqueous precursor slurry. Transfer the aqueous precursor slurry to a microwave hydrothermal reactor and perform a microwave hydrothermal crystallization reaction at 140℃ and 600W for 1.5h. After the reaction is completed, cool to 75℃ to obtain a hydrotalcite slurry.

[0053] Comparative Example 6 This comparative example provides a method for preparing magnesium-aluminum hydrotalcite to enhance the thermal stability of PVC. The only difference from Example 2 is that in step S5, only vinyltrimethoxysilane is added for single coating, and modified epoxidized soybean oil is not added for composite coating; the other raw material types, amounts and preparation process parameters are completely consistent with Example 2.

[0054] Specifically: S5. Add 2% vinyltrimethoxysilane by dry weight of hydrotalcite to the hydrotalcite slurry and stir at 75°C and 400 rpm for 30 min to obtain a single-coated hydrotalcite slurry.

[0055] Comparative Example 7 This comparative example provides a method for preparing magnesium-aluminum hydrotalcite to enhance the thermal stability of PVC. The only difference from Example 2 is that in step S5, unmodified epoxidized soybean oil is used to replace the modified epoxidized soybean oil by mass for composite coating; the other raw material types, amounts, and preparation process parameters are completely consistent with Example 2.

[0056] Specifically: S5. Add 2% vinyltrimethoxysilane (by dry weight of hydrotalcite) to the hydrotalcite slurry and stir at 75°C and 400 rpm for 30 min to obtain solution A. Add 4% epoxidized soybean oil (by dry weight of hydrotalcite) to solution A and stir at 75°C and 600 rpm for 50 min to obtain composite coated hydrotalcite slurry.

[0057] Performance testing 1. Detection Object Magnesium aluminum hydrotalcites that enhance the thermal stability of PVC were prepared in Examples 1-3 and Comparative Examples 1-7, respectively, and PVC sheet samples were prepared according to the following unified method before performance testing.

[0058] 2. Preparation of PVC sheet samples By weight, 100 parts of PVC resin (SG-5 type), 2.5 parts of calcium-zinc composite heat stabilizer, 2.0 parts of magnesium-aluminum hydrotalcite to be tested, 5.0 parts of DOP, 0.4 parts of paraffin wax and 0.3 parts of PE wax were added to a high-speed mixer and stirred for 8 minutes at 95℃ and 1000rpm. After cooling to room temperature, a PVC dry mix was obtained. The PVC dry mix was placed in a two-roll mill and mixed at 175℃ for 5 minutes. Then the mixed material was placed in a flat vulcanizing machine and pressed into sheets at 180℃ and 10MPa for 5 minutes to obtain a PVC sheet sample with a thickness of 1.0mm.

[0059] 3. Testing Methods (1) Initial whiteness test The surface color of PVC sheet samples was measured using a colorimeter under the following conditions: temperature 25℃ and relative humidity 50%. Five different locations were selected for measurement on each sample, and the average value was taken as the initial whiteness of the sample.

[0060] (2) Test of heat stability time of Congo red Weigh 0.5g of the shredded PVC sheet sample and place it in a thermal stability test tube. Heat the sample in an oil bath at 180℃. The time it takes for the Congo red test paper to turn from red to blue is taken as the Congo red thermal stability time, in minutes.

[0061] (3) Dynamic thermal stability time test The dynamic thermal stability of PVC sheet samples was tested using a torque rheometer. The test conditions were: test temperature 180℃, rotor speed 60rpm, and loading amount 35g. The time corresponding to the inflection point of thermal degradation characteristics after the torque of the sample reached the lowest value during the test was recorded as the dynamic thermal stability time, in min.

[0062] (4) Oven thermal aging failure time test The PVC sheet samples were placed in a 180℃ forced-air oven for heat aging. The samples were taken out and the color change was observed every 10 minutes. When the surface of the sample showed obvious browning, the corresponding time was recorded as the oven heat aging failure time, in minutes.

[0063] 5. Test Results and Analysis The specific test results are shown in Table 1.

[0064] Table 1 Performance test results of PVC sheet samples

[0065] As shown in Table 1, the magnesium aluminum hydrotalcite prepared in Examples 1-3 of this invention has significantly better initial whiteness, Congo red thermal stability time, dynamic thermal stability time and oven thermal aging failure time in the PVC system than Comparative Examples 1-7, with Example 2 showing the best overall performance.

[0066] Compared with Example 2, Comparative Example 1 used only pentaerythritol monomaleate as a single intercalating agent, and its initial whiteness, Congo red heat stability time and dynamic heat stability time were significantly reduced. This indicates that the dual-effect intercalation system formed by pentaerythritol monomaleate and L-arginine can take into account both the rapid capture and long-term stabilization of HCl, and plays an important role in improving the thermal stability of PVC.

[0067] Compared to Example 2, Comparative Example 2 used only L-arginine as a single intercalating agent, and all its performance indicators were significantly reduced. This indicates that although L-arginine can promote HCl absorption through the interaction of amino and carboxyl groups, it is difficult to form a stable intercalation structure when used alone. The combination of pentaerythritol monomaleate and L-arginine can exert a synergistic effect, improving the thermal stability of the PVC system.

[0068] Compared with Example 2, Comparative Example 3 did not add citric acid to pre-complex zinc and cerium ions during the preparation process, and all its performance indicators showed a significant decrease. This indicates that the citric acid pre-complexation treatment is beneficial to reduce the doping unevenness caused by the difference in precipitation rate of different metal ions, thereby improving the uniformity of zinc and cerium ions in the hydrotalcite layer and the stability of product performance.

[0069] Compared with Example 2, Comparative Example 4 did not use pulsed ultrasound assistance in step S3, but only carried out ordinary stirring reaction. Its Congo red thermal stability time and dynamic thermal stability time were significantly reduced, indicating that pulsed ultrasound can promote micro-mixing of the reaction system and inhibit grain agglomeration, which is beneficial to obtaining a lamellar hydrotalcite structure with better dispersibility and higher acid absorption efficiency.

[0070] Compared with Example 2, Comparative Example 5, which replaced ethylene glycol with deionized water in step S4, showed a decrease in both thermal stability and aging performance. This indicates that the alcohol-water co-solubilized system constructed with ethylene glycol is beneficial for regulating the nucleation and crystal growth process of hydrotalcite, improving the lamellar structure characteristics, and thus enhancing the acid absorption and thermal stability of the PVC system.

[0071] Compared with Example 2, Comparative Example 6 used only vinyltrimethoxysilane for single coating in step S5, and its dynamic thermal stability time and oven thermal aging failure time were both lower than those of Example 2. This shows that it is difficult to simultaneously achieve interfacial compatibility and auxiliary thermal stability by relying solely on silane coating. The composite coating structure is more conducive to improving the dispersion uniformity and thermal stability of hydrotalcite in PVC.

[0072] Compared with Example 2, Comparative Example 7 used unmodified epoxidized soybean oil instead of modified epoxidized soybean oil for composite coating. Although its various performance indicators were better than some of the comparative examples, they were still lower than those of Example 2. This indicates that modified epoxidized soybean oil has more polar interaction sites and stronger interfacial bonding ability than unmodified epoxidized soybean oil, which can further improve the interfacial compatibility between hydrotalcite and PVC resin and improve the thermal stability of PVC products.

[0073] RoHS testing 1. Detection Object The magnesium aluminum hydrotalcite sample with enhanced PVC thermal stability prepared in Example 2 was subjected to RoHS compliance testing.

[0074] 2. Testing Basis According to EU RoHS Directive 2011 / 65 / EU and its amendment Directive EU 2015 / 863, the levels of lead (Pb), cadmium (Cd), mercury (Hg), and hexavalent chromium (Cr) in magnesium aluminum hydrotalcite samples used to enhance the thermal stability of PVC were investigated. 6+ The contents of polybrominated biphenyls (PBBs), polybrominated diphenyl ethers (PBDEs), di-n-butyl phthalate (DBP), butyl benzyl phthalate (BBP), di(2-ethylhexyl) phthalate (DEHP), and diisobutyl phthalate (DIBP) were determined.

[0075] 3. Detection Method Lead (Pb) and cadmium (Cd) were tested using ICP-OES according to the method specified in IEC 62321-5:2013. Mercury (Hg) was tested using ICP-OES according to the method specified in IEC 62321-4:2013+AMD1:2017 CSV. Hexavalent chromium (Cr) 6+ The method specified in IEC 62321-7-2:2017 is adopted, and UV-Vis is used for testing; Polybrominated biphenyls (PBBs), polybrominated diphenyl ethers (PBDEs), DBP, BBP, DEHP and DIBP were detected using GC-MS according to the method specified in IEC 62321-12:2023.

[0076] 4. Test Results The specific test results are shown in Table 2.

[0077] Table 2. RoHS test results of magnesium aluminum hydrotalcite for enhancing the thermal stability of PVC in Example 2.

[0078] The report states that the limits of quantification for Pb, Cd, and Hg are 2 mg / kg, and for Cr... 6+ The limit of quantitation (LOQ) is 8 mg / kg, and the LQ for DBP, BBP, DEHP, and DIBP is 50 mg / kg; "ND" indicates not detected or below the LQ. The test result is "Compliant / Pass".

[0079] 5. Results Analysis As can be seen from the RoHS test results above, the magnesium aluminum hydrotalcite sample for enhancing the thermal stability of PVC prepared in Example 2 was free of lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyls, polybrominated diphenyl ethers, and four restricted phthalates, and the levels were all below the corresponding limits of quantification. This meets the limit requirements of the EU RoHS Directive 2011 / 65 / EU and its amendment directive EU 2015 / 863, indicating that the product prepared by this invention has good environmental compliance and can meet the environmental application requirements in the fields of PVC heat stabilizers and related PVC products.

[0080] The above specific embodiments are merely explanations of the present invention and are not intended to limit the present invention. After reading this specification, those skilled in the art can make modifications to these embodiments without contributing any inventive step, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC, characterized in that, Includes the following steps: S1. Pentaerythritol and maleic anhydride are mixed, added to an organic solvent, stirred and reacted, and subjected to reduced pressure to obtain pentaerythritol monomaleate; pentaerythritol monomaleate is mixed with L-arginine, added to deionized water, stirred evenly, and the pH is adjusted to obtain an intercalating agent solution. S2. Mix soluble magnesium salt, soluble zinc salt, soluble aluminum salt and soluble cerium salt, add to deionized water, stir evenly to obtain a mixed metal salt solution; add citric acid to the mixed metal salt solution, stir to react, and obtain a complexed mixed metal salt solution. S3. Mix the intercalating agent solution and the complexed mixed metal salt solution, adjust the pH, stir the reaction under pulsed ultrasound, continue aging after the reaction is completed, centrifuge and concentrate to obtain the precursor slurry; S4. Add ethylene glycol to the precursor slurry and stir until homogeneous to obtain an alcohol-water co-soluble precursor slurry; subject the alcohol-water co-soluble precursor slurry to microwave hydrothermal crystallization reaction, and cool after the reaction to obtain a hydrotalcite slurry. S5. Add vinyl silane coupling agent to the hydrotalcite slurry and stir to react; then add modified epoxidized soybean oil and stir to react to obtain composite coated hydrotalcite slurry. S6. The composite coated hydrotalcite slurry is filtered, washed, dried, depolymerized and sieved to obtain magnesium aluminum hydrotalcite that enhances the thermal stability of PVC.

2. The method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC according to claim 1, characterized in that, In step S1, the organic solvent is selected from one or more of toluene, xylene, and chloroform; the molar ratio of pentaerythritol to maleic anhydride is 1:1.05-1.15; and the molar ratio of pentaerythritol monomaleate to L-arginine is 2-4:

1.

3. The method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC according to claim 1, characterized in that, In step S2, the Mg²⁺ in the soluble magnesium salt, soluble zinc salt, soluble aluminum salt, and soluble cerium salt + Zn² + Al³ + and Ce³ + The molar ratio is 2.5-3.5:0.1-0.3:1:0.06-0.

08.

4. The method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC according to claim 1, characterized in that, In step S2, the soluble magnesium salt is selected from one or more of magnesium chloride, magnesium nitrate, and magnesium sulfate; the soluble zinc salt is selected from one or more of zinc chloride, zinc nitrate, and zinc acetate; the soluble aluminum salt is selected from one or more of aluminum chloride, aluminum nitrate, and aluminum sulfate; and the soluble cerium salt is selected from one or more of cerium chloride, cerium nitrate, and cerium sulfate.

5. The method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC according to claim 1, characterized in that, In step S3, the frequency of the pulsed ultrasound is 20-40kHz, the power is 300-500W, and the pulse mode is 2-4s operation followed by 1-3s interval; the aging temperature is 40-50℃, the aging speed is 400-600rpm, and the aging time is 45-60min.

6. The method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC according to claim 1, characterized in that, In step S4, the volume ratio of the precursor slurry to ethylene glycol is 1-2:1; the temperature of the microwave hydrothermal crystallization reaction is 130-150℃, the microwave power is 500-800W, and the reaction time is 1-2h.

7. The method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC according to claim 1, characterized in that, In step S5, the vinyl silane coupling agent is selected from one or more of vinyltriethoxysilane, vinyltrimethoxysilane, and vinyltri(β-methoxyethoxy)silane.

8. The method for preparing magnesium aluminum hydrotalcite to enhance the thermal stability of PVC according to claim 1, characterized in that, The preparation method of the modified epoxidized soybean oil in step S5 is as follows: Epoxidized soybean oil, maleic anhydride, and catalyst were mixed and reacted under nitrogen protection to obtain maleic anhydride-grafted epoxidized soybean oil. A polyol modifier was added to the maleic anhydride-grafted epoxidized soybean oil, and the reaction was continued with stirring. After the reaction was completed, the mixture was cooled and subjected to reduced pressure to obtain modified epoxidized soybean oil.

9. A magnesium aluminum hydrotalcite for enhancing the thermal stability of PVC prepared by the method of any one of claims 1-8.

10. The application of the magnesium aluminum hydrotalcite as described in claim 9, which enhances the thermal stability of PVC, in the preparation of a PVC heat stabilizer.

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