An environmentally friendly calcium-zinc composite PVC heat stabilizer and its preparation method

Abstract

This invention relates to the field of polymer material additives, and discloses an environmentally friendly calcium-zinc composite PVC heat stabilizer and its preparation method. The heat stabilizer is a multi-level core-shell structure particle composed of three parts: (a) a functionalized hydrotalcite core intercalated with β-diketone and polyol; (b) a calcium / zinc metal soap inner shell chemically bonded to the core surface via a silane coupling agent; and (c) a lanthanum-organic complex outer shell coating the outermost layer containing unsaturated double bonds. The preparation method includes: preparing the functionalized core, grafting a silane coupling agent, in-situ co-precipitation to generate the inner shell, and solvent evaporation to coat the outer shell. This invention ensures the integrity of the composite particle structure and the synergistic effect of each component by constructing a stable chemical connection between the core and shell. Through intercalation and final chemical grafting, the migration and precipitation problems of the additives are fundamentally solved.

Description

Technical Field

[0001] This invention relates to the field of polymer material additives technology, specifically to an environmentally friendly calcium-zinc composite PVC heat stabilizer and its preparation method. Background Technology

[0002] Polyvinyl chloride (PVC) is one of the most widely used thermoplastics in the world due to its excellent overall performance and cost advantages. However, the unstable tertiary chlorine and allyl chlorine atoms in the PVC molecular structure make it extremely sensitive to heat and shear stress during processing and use. It is highly susceptible to autocatalytic degradation by dehydrochlorination (HCl), leading to discoloration, a sharp decline in mechanical properties, and ultimately rendering the material unusable. Therefore, heat stabilizers must be added to PVC formulations to inhibit its thermal degradation during processing.

[0003] Traditionally, lead and cadmium salt heat stabilizers have been widely used due to their excellent thermal stabilization efficiency and low cost. However, heavy metals such as lead and cadmium have significant biotoxicity and environmental persistence, and their use has been subject to increasingly stringent regulations worldwide. Against this backdrop, environmentally friendly heat stabilizers, represented by calcium / zinc (Ca / Zn) systems, have become the main alternative to lead / cadmium-based systems due to their low toxicity and environmentally friendly characteristics.

[0004] However, existing environmentally friendly calcium / zinc composite heat stabilizers still have inherent technological limitations. Currently, the mainstream preparation method for these composite stabilizers is physical blending, which involves simple mechanical mixing of calcium stearate, zinc stearate, hydrotalcite, and various organic auxiliary stabilizers such as β-diketones and polyols. The product obtained in this way is essentially a physical mixture of components, lacking structural cohesion and functional integration. This makes it difficult to fully realize the synergistic effect between components, thus affecting the overall stabilization efficiency.

[0005] The lack of this synergistic effect also makes it difficult to effectively address a key technical challenge in the Ca / Zn system—the "zinc burn" phenomenon. During the stabilization process, zinc chloride (ZnCl2), formed by the reaction of zinc stearate and HCl, is a strong Lewis acid that catalyzes more severe degradation of PVC, causing the product to suddenly turn black and become completely ineffective within a short period. Although the organic auxiliary stabilizers added to the formulation are intended to neutralize ZnCl2, their release and timing of action are difficult to control precisely in physical blending systems, thus limiting their actual effectiveness in inhibiting "zinc burn." Furthermore, these small-molecule organic additives have poor compatibility with the PVC matrix and are prone to migrating and precipitating from the product to the surface during processing and long-term use. This not only contaminates processing equipment and affects the appearance and surface properties of the product but also causes stabilizer loss, thereby weakening the long-term thermal stability of the material.

[0006] Therefore, this invention proposes an environmentally friendly calcium-zinc composite PVC heat stabilizer and its preparation method to overcome the shortcomings of the prior art. Summary of the Invention

[0007] The technical problem to be solved by this invention is that, in the process of replacing the lead / cadmium-based system containing toxic heavy metals with an environmentally friendly calcium / zinc-based system, the existing calcium / zinc composite PVC heat stabilizers are usually prepared by physical blending, which leads to poor synergistic effect of each component, easy to cause "zinc burning" phenomenon, insufficient long-term thermal stability, and easy migration and precipitation of small molecule additives.

[0008] To address the aforementioned technical problems, this invention provides a structurally stable and functionally synergistic environmentally friendly calcium-zinc composite PVC heat stabilizer and its preparation method. The technical solution of this invention is based on low-toxicity calcium, zinc, magnesium, aluminum, and lanthanide elements, fundamentally avoiding the use of heavy metals such as lead, cadmium, and barium, which are subject to strict environmental regulations.

[0009] The first aspect of this invention provides an environmentally friendly calcium-zinc composite PVC heat stabilizer.

[0010] The heat stabilizer is a multi-level core-shell structured particle, composed of the following components:

[0011] (a) 15-30 wt% functionalized hydrotalcite core;

[0012] (b) 55-80 wt% calcium / zinc metal soap inner shell;

[0013] (c) 5-15 wt% of lanthanum-organic complex shell containing unsaturated double bonds;

[0014] The total mass percentage of components (a), (b), and (c) is 100%.

[0015] In the above structure, the functionalized hydrotalcite core is based on magnesium aluminum hydrotalcite, with β-diketone compounds and polyols intercalated between its layered structure. This intercalation structure immobilizes small molecule organic auxiliaries in the inorganic matrix.

[0016] This structure has dual technical advantages:

[0017] Firstly, during the processing and use of PVC, the controlled release of HCl can be achieved through the absorption of HCl by the hydrotalcite, which can be used to neutralize newly generated ZnCl2.

[0018] Secondly, because the additives are physically confined between layers, their migration to the surface of PVC products or processing equipment is inhibited, thus reducing the risk of environmental exposure.

[0019] The inner shell is chemically bonded to the surface of the functionalized hydrotalcite core via a silane coupling agent. One end of the silane coupling agent (preferably γ-aminopropyltriethoxysilane, APTES) forms stable Si-O-Al or Si-O-Mg covalent bonds with the hydroxyl groups on the hydrotalcite surface via a hydrolysis-condensation reaction; the exposed amino functional group (-NH2) at the other end serves as a chemical anchor point for the in-situ generation of the inner shell. This chemical anchoring is not a simple physical adsorption, but is achieved through the following well-defined chemical and physicochemical mechanisms:

[0020] First, in step (c), when the system is heated to 90°C and stearic acid is added, the amino functional group (-NH2) grafted onto the nucleus surface, acting as a Lewis base, undergoes an acid-base neutralization reaction with the carboxyl group of stearic acid (R-COOH), which is a Brønsted acid. This reaction forms a chemically bonded surface ammonium salt (i.e., nucleus-Si-(CH2)3-NH3) on the surface of the nucleus particle. + -OOC-R). This step firmly "pre-locates" or "captures" stearic acid molecules on the surface of the core, forming a layer of high local concentration of stearate anions.

[0021] Secondly, when a mixed suspension containing calcium hydroxide and zinc oxide is added dropwise to the system, this high-concentration stearate anion layer pre-anchored on the core surface becomes a metal ion (CaO). 2+ and Zn 2+ These are the preferred nucleation sites for ion exchange and precipitation reactions. Compared to stearic acid molecules that are freely dispersed in solution, metal ions preferentially react with these fixed stearate ions, thus ensuring that the formation and deposition of calcium stearate and zinc stearate occur closely around the surface of the nuclei, rather than as random and uncontrolled precipitation in solution.

[0022] Furthermore, regarding zinc ions (Zn 2+ In addition to the amino group, there is a secondary coordination anchoring effect. The nitrogen atom on the amino functional group contains a lone pair of electrons, which can interact with Zn, which acts as a Lewis acid. 2+ The ions form stable coordination bonds, generating zinc-amine complexes. This coordination further enhances the adhesion of zinc species to the core surface, guiding zinc stearate to be deposited more tightly at the core-shell interface.

[0023] In summary, the amino functional group constitutes a true "chemical anchor" through a triple synergistic mechanism of acid-base interaction, preferential nucleation, and coordination bonding. This ensures that the inner shell of the calcium / zinc metal soap grows tightly around and is firmly bonded to the functionalized core, rather than being a simple physical coating. This stable core-shell chemical connection is the foundation for ensuring the integrity of this multi-level structure under the high shear forces of PVC processing, thereby enabling it to exert its programmed synergistic stabilizing effect.

[0024] The outer shell layer covers the inner shell layer. The lanthanum-organic complex in this outer shell layer is a key component for the long-term thermal stability of PVC, and its mechanism of action is as follows: First, during thermal processing, the carboxylate anion of the organic acid lanthanum in the complex acts as a nucleophile, replacing the unstable allyl chloride or tertiary chloride atoms on the PVC molecular chain through a nucleophilic substitution reaction. This reaction forms an ester structure on the PVC backbone with a thermal stability far higher than the original C-Cl bond, thus inhibiting the initiation of the deHCl degradation reaction from the source. Second, the byproduct lanthanum chloride (LaCl3) generated in this process does not possess catalytic activity for PVC degradation. This is fundamentally different from zinc chloride (ZnCl2) generated in the traditional calcium / zinc stabilization system. The fundamental reason lies in the difference in Lewis acidity of the metal cations. ZnCl2 is a strong Lewis acid that can coordinate with chlorine atoms on the PVC chain, polarizing and weakening the C-Cl bond, thereby violently catalyzing the subsequent deHCl reaction and initiating the "zinc burning" phenomenon. In contrast, lanthanum chloride (LaCl3) is a very weak Lewis acid. This is because the lanthanum ion (LaCl3)... 3+ It has significant differences from zinc ions (Zn) 2+ Physicochemical properties of )

[0025] La 3+ Its ionic radius (approximately 10³ pm) is much larger than that of Zn. 2+ Its ionic radius (approximately 74 pm) is significantly lower than that of Zn. 2+ This greatly weakens its ability to polarize C-Cl bonds;

[0026] According to the hard-soft acid-base theory, La 3+ It is a typical "hard acid" and has almost no coordination tendency with chlorine atoms on the PVC chain, which is a "soft base" or "border base".

[0027] Therefore, even if LaCl3 is generated in the system, it remains essentially chemically inert and will not catalyze the degradation of PVC, allowing the lanthanum component to safely and efficiently exert its stabilizing effect. Furthermore, the phosphite component in the outer shell acts as an auxiliary stabilizer, decomposing hydroperoxides that may be generated during processing and improving the initial color of the material.

[0028] Meanwhile, the unsaturated double bonds in the outer shell provide reactive sites that can react with free radicals on the PVC macromolecular chain during processing, thereby fixing the entire stabilizer particle onto the PVC matrix through chemical grafting. Chemical grafting fundamentally prevents the migration of the stabilizer as a whole or any of its components.

[0029] In summary, the heat stabilizer provided by this invention has all its functional components immobilized through intercalation, chemical bonding, or final matrix grafting, solving the problem of easy precipitation of additives in traditional environmentally friendly stabilizers. Simultaneously, its programmed synergistic stabilization mechanism improves stabilization efficiency, allowing for a reduction in its addition amount in PVC formulations while achieving the same stabilization effect, thereby saving resources.

[0030] In some embodiments, the silane coupling agent is an aminosilane coupling agent, specifically γ-aminopropyltriethoxysilane.

[0031] In some embodiments, the β-diketone compound in the functionalized hydrotalcite core is stearoylbenzoylmethane, and the polyol is pentaerythritol.

[0032] In some embodiments, the molar ratio of calcium stearate to zinc stearate in the inner shell of the calcium / zinc metal soap is 1:1 to 4:1.

[0033] In some embodiments, the lanthanum-organic complex shell containing unsaturated double bonds is a complex prepared by reacting lanthanum trichloride, triphenyl phosphite, and oleic acid.

[0034] A second aspect of this invention provides a method for preparing the environmentally friendly calcium-zinc composite PVC heat stabilizer.

[0035] The method includes the following steps:

[0036] (a) Preparation of functionalized sustained-release core: β-diketone compounds and polyols are introduced into the interlayer of magnesium aluminum hydrotalcite matrix through liquid-phase intercalation reaction to obtain functionalized sustained-release core;

[0037] (b) Grafting silane coupling agent: A silane coupling agent is grafted onto the surface of the functionalized sustained-release core through a chemical reaction to form a chemical anchor point;

[0038] (c) In-situ generation of inner shell layer: On the surface of the core grafted with silane coupling agent, a metal soap inner shell layer composed of calcium stearate and zinc stearate is generated by in-situ co-precipitation method;

[0039] (d) Coating the outer shell: The lanthanum-organic complex containing unsaturated double bonds, which was prepared in advance, is coated on the surface of the inner shell by solvent evaporation to obtain the final product.

[0040] This preparation method constructs composite particles with a defined hierarchical structure and chemical connections through ordered chemical steps, ensuring the orderly spatial arrangement of each functional component, which is the basis for achieving the aforementioned technical effects.

[0041] In some embodiments, the silane coupling agent in step (b) is γ-aminopropyltriethoxysilane, and the grafting reaction is carried out under reflux in anhydrous ethanol.

[0042] In some embodiments, step (c) of the in-situ coprecipitation method includes: dispersing the core grafted with silane coupling agent in an aqueous medium, adding stearic acid, and then adding a mixed suspension containing calcium hydroxide and zinc oxide dropwise, controlling the pH of the reaction system to 8.0-10.0 for the reaction.

[0043] In some embodiments, in step (d), the lanthanum-organic complex containing unsaturated double bonds is prepared by heating and stirring lanthanum trichloride, triphenyl phosphite and oleic acid in an organic solvent to form a complex solution.

[0044] In some embodiments, the solvent evaporation method in step (d) is specifically spray drying or rotary evaporation.

[0045] When the solvent evaporation method is spray drying, the suspension containing particles with adsorbed complexes is fed into the atomizer of the spray dryer by a peristaltic pump for atomization. The specific process parameters include: the inlet temperature is set to 120-160℃, the outlet temperature is controlled at 70-90℃, and the feed rate of the suspension is adjusted according to the outlet temperature to maintain stability.

[0046] In some implementations, the feed rate of the suspension is 5-15 mL / min.

[0047] When the solvent evaporation method is rotary evaporation, the suspension containing particles with adsorbed complexes is placed in the rotating flask of the rotary evaporator. The specific process parameters include: placing the rotating flask in a constant temperature water bath or oil bath at 50-70°C, evacuating the system pressure to a vacuum range of -0.08MPa to -0.095MPa, and rotating it at a speed of 50-150rpm until the solvent is completely evaporated.

[0048] This invention provides an environmentally friendly calcium-zinc composite PVC heat stabilizer and its preparation method, which has the following beneficial effects:

[0049] 1. This invention establishes a stable chemical bond between the functionalized hydrotalcite core and the metal soap inner shell by using a silane coupling agent. Compared with traditional physical coating or blending, the chemical bond ensures that the multi-level core-shell structure is not destroyed under the high shear force of PVC processing, and guarantees the spatial order of each functional component. This structural stability is the basis for realizing programmed synergy, enabling the stable components at the outer, middle and inner levels to play their roles at the appropriate time and place, thereby significantly improving the overall thermal stability efficiency.

[0050] 2. The outer shell layer of this invention uses a lanthanum-organic complex with no catalytic degradation activity to replace the unstable chlorine on the PVC molecular chain, providing excellent long-term thermal stability. At the same time, β-diketones and polyols, which are used to inhibit zinc burning, are pre-intercalated and immobilized in the hydrotalcite core, achieving controlled slow release. This combination of dual mechanisms not only ensures the performance of the material at high temperatures for a long time, but also effectively neutralizes the zinc chloride generated in the early stage, fundamentally inhibiting the occurrence of catastrophic zinc burning.

[0051] 3. This invention immobilizes all functional components through two mechanisms. First, small molecule additives such as β-diketones are confined between the inorganic layers of hydrotalcite through intercalation. Second, an organic acid containing unsaturated double bonds is introduced into the outer shell layer. These unsaturated double bonds can undergo a chemical grafting reaction with the PVC matrix during processing, permanently anchoring the entire stabilizer particle in the polymer matrix. This chemical anchoring method prevents the migration and precipitation of any component, ensuring the surface quality and long-term safety of PVC products.

[0052] 4. All components of this invention are based on low-toxicity elements such as calcium, zinc, magnesium, aluminum, and lanthanum, and are completely free of toxic heavy metals such as lead and cadmium, complying with environmental regulations. The zero migration and zero precipitation of additives achieved through structural design further reduces the product's environmental impact throughout its lifecycle. Furthermore, due to its highly efficient synergistic stabilization mechanism, this invention requires a lower addition amount than traditional blended stabilizers to achieve the same stabilizing effect, saving resources and reducing costs. Detailed Implementation

[0053] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0055] Polyvinyl chloride resin (PVC): SG-5 type, CAS No.: 9002-86-2.

[0056] Dioctyl phthalate (DOP): Industrial grade, CAS No.: 117-81-7.

[0057] Stearic acid: Industrial grade, CAS No.: 57-11-4.

[0058] Magnesium nitrate (hexahydrate): analytical grade, Mg(NO3)2·6H2O, CAS No.: 13446-18-9.

[0059] Aluminum nitrate (nonahydrate): analytical grade, Al(NO3)3·9H2O, CAS No.: 7784-27-2.

[0060] Sodium hydroxide: analytical grade, NaOH, CAS No.: 1310-73-2.

[0061] Sodium carbonate: analytical grade, Na2CO3, CAS No.: 497-19-8.

[0062] Stearoylbenzoylmethane (SBM): Industrial grade, CAS No.: 79583-49-8.

[0063] Pentaerythritol: Industrial grade, CAS No.: 115-77-5.

[0064] Anhydrous ethanol: analytical grade, CAS No.: 64-17-5.

[0065] γ-aminopropyltriethoxysilane (APTES): Industrial grade, CAS No.: 919-30-2.

[0066] Calcium hydroxide: Industrial grade, Ca(OH)2, CAS No.: 1305-62-0.

[0067] Zinc oxide: Industrial grade, ZnO, CAS No.: 1314-13-2.

[0068] Lanthanum trichloride (anhydrous): analytical grade, LaCl3, CAS No.: 10099-58-8.

[0069] Triphenyl phosphite (TPP): Industrial grade, CAS No.: 101-02-0.

[0070] Oleic acid: Industrial grade, CAS No.: 112-80-1.

[0071] Toluene: analytical grade, CAS No.: 108-88-3.

[0072] Example:

[0073] This embodiment provides a method for preparing an environmentally friendly calcium-zinc composite PVC heat stabilizer.

[0074] Step (a): Preparation of functionalized sustained-release core

[0075] Dissolve 76.95 g (0.3 mol) magnesium nitrate (hexahydrate) and 37.51 g (0.1 mol) aluminum nitrate (nonahydrate) in 500 mL of deionized water, and label this solution A. Dissolve 24.0 g (0.6 mol) sodium hydroxide and 10.6 g (0.1 mol) sodium carbonate in 250 mL of deionized water, and label this solution B.

[0076] Under vigorous stirring, solutions A and B were simultaneously added dropwise to a reactor containing 100 mL of deionized water. During the addition, the pH of the reaction system was maintained between 9.5 and 10.5 by adjusting the dropping rate of solution B. After the addition was complete, the resulting slurry was stirred and aged at 80°C for 4 hours.

[0077] After the reaction was completed, the product was filtered, washed with deionized water until neutral, and then dried in an oven at 80°C for 12 hours to obtain a white powdery magnesium aluminum hydrotalcite matrix.

[0078] Take 50.0 g of the magnesium aluminum hydrotalcite matrix prepared above and disperse it in 500 mL of anhydrous ethanol. Add 12.6 g of stearoylbenzoylmethane (SBM) and 5.0 g of pentaerythritol to the suspension and reflux the mixture at 70 °C for 24 hours.

[0079] After the reaction was completed, the product was filtered, washed three times with anhydrous ethanol to remove the organic matter adsorbed on the surface, and then dried in a vacuum oven at 60°C for 12 hours to obtain the functionalized sustained-release nucleus powder, denoted as nucleus-A.

[0080] Step (b): Grafting of silane coupling agent

[0081] Place all the nucleus-A powder obtained in step (a) into a 500 mL three-necked flask, add 300 mL of toluene, and sonicate for 15 minutes to make it uniform. Slowly add 3.5 g of γ-aminopropyltriethoxysilane (APTES) to the suspension. After the addition is complete, heat to 110 °C and reflux for 6 hours under nitrogen protection.

[0082] After the reaction was completed, the product was naturally cooled to room temperature, filtered, washed several times with toluene and anhydrous ethanol, and then dried in a vacuum oven at 80°C for 12 hours to obtain a nucleus powder grafted with APTES, denoted as nucleus-B.

[0083] Step (c): In-situ generation of chemically anchored inner shell

[0084] Disperse all the nucleus-B powder obtained in step (b) in 1000 mL of deionized water, add 120.0 g of stearic acid, heat to 90 °C and stir at 500 rpm to form a uniform emulsion. In another container, disperse 16.4 g of calcium hydroxide and 8.1 g of zinc oxide in 200 mL of deionized water to form a mixed suspension. Use a peristaltic pump to slowly add the mixed suspension to the above emulsion at a dropping rate of about 2 mL / min. During the dropping process, maintain the reaction temperature at 90 °C and the pH value of the reaction system at about 9.0.

[0085] After the addition was complete, the reaction was continued at a constant temperature for 2 hours. After the reaction was completed, the product was filtered, washed five times with hot water at 90°C, and then dried in an oven at 105°C for 24 hours to obtain particles coated with an inner shell, denoted as particle-C.

[0086] Step (d): Coating of the graftable outer shell layer (using spray drying method)

[0087] In a separate reactor, 9.8 g of anhydrous lanthanum trichloride and 12.4 g of triphenyl phosphite (TPP) were added to 200 mL of toluene, stirred, and heated to 80 °C. 11.3 g of oleic acid was slowly added dropwise, and the reaction was continued at the same temperature for 4 hours after the addition was complete, to obtain a pale yellow lanthanum-organic complex solution.

[0088] All particles-C obtained in step (c) were added to the above lanthanum-organic complex solution, and the mixture was stirred and adsorbed at 80°C for 2 hours to form a uniform suspension.

[0089] The suspension is continuously fed into a spray drying tower via a peristaltic pump for drying. The spray drying process parameters are set as follows: inlet temperature 150℃, outlet temperature 80℃, and the feed rate is adjusted according to the outlet temperature feedback to maintain stability. The white powder product collected at the bottom of the cyclone separator is the final environmentally friendly calcium-zinc composite PVC heat stabilizer.

[0090] Comparative example:

[0091] Comparative Example 1: Compared with Example 1, the difference is that the stepwise preparation method of Example 1 is not used. Instead, the chemical components constituting the final product of Example 1 (including magnesium aluminum hydrotalcite, stearoylbenzoylmethane, pentaerythritol, calcium stearate, zinc stearate, and the pre-prepared lanthanum-organic complex) are directly physically blended in a high-speed mixer in the same mass proportions as the final product of Example 1 to obtain a powdered heat stabilizer.

[0092] Comparative Example 2: Compared with Example 1, the difference is that the grafting process of adding γ-aminopropyltriethoxysilane (APTES) in step (b) is omitted, and the functionalized sustained-release core powder obtained in step (a) is directly used in the reaction of generating the inner shell in situ in step (c). All other aspects are the same.

[0093] Comparative Example 3: Compared with Example 1, the difference is that in step (d) when preparing the lanthanum-organic complex, an equimolar amount of stearic acid was used instead of oleic acid, and the resulting outer shell complex did not contain unsaturated double bonds, while all other aspects were the same.

[0094] Test example:

[0095] Preparation of PVC test samples

[0096] Unless otherwise stated, all test cases were prepared using the following formulation and process for PVC test samples.

[0097] Formulation: 100 parts polyvinyl chloride resin (PVC, SG-5 type); 50 parts dioctyl phthalate (DOP); 0.5 parts stearic acid; 2.0 parts heat stabilizer. The heat stabilizer was selected from the samples prepared in Example 1 and Comparative Examples 1-3, respectively.

[0098] Preparation process: First, place 100 parts of PVC resin and 2.0 parts of heat stabilizer powder into the pot of a high-speed mixer and stir at low speed (about 400 rpm) for 2 minutes to initially disperse the stabilizer; then, add 50 parts of DOP and 0.5 parts of stearic acid, increase the speed to 800 rpm, and use the frictional heat between the materials to raise the temperature to 90°C, and keep it at this temperature for 10 minutes to obtain a uniformly dispersed dry mix.

[0099] The mixed materials are transferred to a two-roll plasticizer for plasticizing. The roller surface temperature is preset and controlled at 175±2℃, and the roller gap is set to 0.8mm. Material is added between the rollers, and once the material is completely plasticized and coats one of the rollers, a timer is started. During the 5 minutes of plasticizing, the polymer sheet is cut off from the roller every 30 seconds with a scraper, folded in half, and then fed back into the rollers to ensure material uniformity. After plasticizing, the flat PVC sheet is removed and allowed to cool at room temperature for later use.

[0100] Test Example 1: Dynamic Thermal Stability Evaluation (Congo Red Method)

[0101] Experimental Procedure: Accurately weigh 2.0 ± 0.01 g of the PVC plasticized sheet prepared in step 1 above, cut it into thin strips, and place them at the bottom of a standard hard glass test tube (18 mm × 180 mm). Fold a standard Congo red test paper in half and suspend it inside the mouth of the test tube, with the lower end of the test paper about 20 mm from the mouth, ensuring it does not contact the test tube wall. Vertically immerse the test tube containing the sample into a preheated constant-temperature glycerol bath at 180 ± 1 °C, ensuring the sample is completely submerged below the glycerol surface.

[0102] Timing begins when the test tube is immersed in the oil bath, and the color change of the Congo red test paper is continuously observed. Timing stops when the last trace of red on the test paper completely disappears and the entire surface turns a uniform blue. This time point is the dynamic thermal stability time of PVC. Each sample is tested three times, and the final result is the arithmetic mean. Specific data are shown in Table 1.

[0103] Table 1: Results of Dynamic Thermal Stability Test

[0104] sample Dynamic thermal stability time (minutes) Example 1 102 Comparative Example 1 43 Comparative Example 2 68 Comparative Example 3 95

[0105] Test Example 2: Static Thermal Stability and Initial Hue Evaluation

[0106] Experimental steps:

[0107] A benchtop spectrophotometer was used to measure colorimetry under D65 standard light source and 10° observer viewing angle conditions. Before measurement, the instrument was calibrated using the standard white board provided with it.

[0108] Initial hue evaluation: Take each freshly prepared PVC sheet from step 1 and fold it into four layers to ensure opacity during measurement. Measure at three different locations for each sample, record the L*, a, and b values ​​in the CIELAB color space, and calculate the average value. L represents luminance (100 for pure white, 0 for pure black), and b represents yellow-blue tint (positive values ​​for yellow, negative values ​​for blue).

[0109] Static thermal stability evaluation: The above PVC sheet was cut into 20mm×20mm strips and suspended with metal clips on the sample rack in a preheated forced ventilation constant temperature oven at 180±2℃, ensuring that the strips did not come into contact with each other. Starting from the time the strips were placed in the oven, one corresponding strip was taken out of the oven every 30 minutes. After the strips cooled to room temperature under standard conditions, their L* and b* values ​​were measured immediately using the same method as the initial hue evaluation. The specific data are shown in Table 2.

[0110] Table 2: Changes in chromaticity values ​​(L, b) during static thermal stability testing

[0111]

[0112] Test Example 3: Evaluation of Processing Precipitation Performance

[0113] Experimental Procedure: Take 200g of the PVC dry mix prepared in step 1 and conduct a continuous plasticizing test on a two-roll mill. The roller temperature is set to 180±2℃, and the roller gap is 1.0mm. Continuously plasticize the material on the rollers for 30 minutes. After plasticizing, stop heating and roller rotation, and allow the rollers to cool completely to room temperature.

[0114] Evaluation method:

[0115] Method 1 (Visual Observation): Under standard lighting conditions, carefully observe the metal surfaces of the two rollers that came into contact with the material, record whether there are any visible precipitates attached, and describe the morphology (such as powder, film, wax or oil) and distribution of the precipitates.

[0116] Method 2 (wiping method): Take a clean, dry standard white cotton cloth of 5cm×5cm, and wipe it back and forth along the axial direction for a distance of 10cm with a constant pressing force of about 10N in the area on the roller surface that has been in contact with the material. Observe and record the contamination of the cotton cloth. See Table 3 for specific data.

[0117] Table 3: Results of Processing Precipitation Performance Tests

[0118] sample Roller surface observation Condition after wiping with cotton cloth Example 1 The surface is smooth and free of visible exudates. The cotton cloth was kept basically clean. Comparative Example 1 There is a distinct yellow powdery precipitate. The cotton cloth was severely stained and turned yellow. Comparative Example 2 There is a slight white, thin film-like precipitate. The cotton fabric has slight white stains. Comparative Example 3 A small amount of white waxy precipitate was found. The cotton fabric contains a small amount of visible white waxy substance.

[0119] The comprehensive test results in Tables 1, 2, and 3 show that the heat stabilizer prepared in Example 1 imparts comprehensive performance to PVC materials. It has the longest dynamic heat stability time, the highest initial whiteness (highest L value, lowest b value), and the strongest color retention ability during long-term static heat aging (slowest decrease in L value, slowest increase in b value). Furthermore, no precipitates are observed during long-term simulated processing. The multi-level core-shell structure with complete chemical bonding designed in this invention enables the functional components to work synergistically with the highest efficiency, thereby providing excellent initial hue and long-lasting heat stability protection.

[0120] The comparison between Example 1 and Comparative Examples 1 and 2 highlights the decisive role of ordered chemical structures over physical blends and structures without chemical bonds. The physical blend of Comparative Example 1 performed poorly in all tests, indicating that simple mechanical mixing cannot achieve effective synergistic effects, and the free migration of small molecule auxiliaries led to severe processing precipitation. Comparative Example 2, lacking the chemical bond of a silane coupling agent, exhibited unstable structure under thermal and shear stress, resulting in significantly lower stability and anti-precipitation performance compared to Example 1. This confirms that chemical bonding at the core-shell interface is a key technical feature for maintaining structural integrity and achieving stable performance.

[0121] The comparison between Example 1 and Comparative Example 3 isolates and verifies the technical effect of the graftable shell layer. Although the performance of Comparative Example 3 is superior to that of Comparative Examples 1 and 2, it is still inferior to Example 1 in terms of long-term thermal stability and processing exudation. Although the shell layer of Comparative Example 3 can provide a stabilizing effect, it cannot form a chemical bond with the PVC matrix. Under long-term heat and shear, it or its components may still migrate in small amounts. In contrast, the shell layer of Example 1 chemically grafts with the PVC matrix through unsaturated double bonds, anchoring the entire stabilizer particle in the polymer and fundamentally preventing migration. Therefore, it exhibits more durable thermal stability protection and cleaner processing performance.

Claims

1. An environmentally friendly calcium-zinc composite PVC heat stabilizer, characterized in that, The heat stabilizer is a multi-level core-shell structured particle, composed of the following components: 15-30wt% functionalized hydrotalcite core, wherein the core is based on magnesium aluminum hydrotalcite, and β-diketone compounds and polyols are intercalated between its layers; 55-80wt% calcium / zinc metal soap inner shell; 5-15 wt% lanthanum-organic complex shell containing unsaturated double bonds; The inner shell is chemically bonded to the surface of the functionalized hydrotalcite core via a silane coupling agent. The outer shell layer covers the inner shell layer; the lanthanum-organic complex outer shell layer containing unsaturated double bonds is a complex prepared by reacting lanthanum trichloride, triphenyl phosphite and oleic acid.

2. The environmentally friendly calcium-zinc composite PVC heat stabilizer according to claim 1, characterized in that, The silane coupling agent is an aminosilane coupling agent, specifically γ-aminopropyltriethoxysilane.

3. The environmentally friendly calcium-zinc composite PVC heat stabilizer according to claim 1, characterized in that, In the functionalized hydrotalcite core, the β-diketone compound is stearoylbenzoylmethane, and the polyol is pentaerythritol.

4. The environmentally friendly calcium-zinc composite PVC heat stabilizer according to claim 1, characterized in that, In the inner shell of the calcium / zinc metal soap, the molar ratio of calcium stearate to zinc stearate is 1:1 to 4:

1.

5. A method for preparing an environmentally friendly calcium-zinc composite PVC heat stabilizer according to any one of claims 1-4, characterized in that, Includes the following steps: Preparation of functionalized sustained-release cores: β-diketone compounds and polyols were introduced into the interlayer of a magnesium aluminum hydrotalcite matrix via a liquid-phase intercalation reaction to obtain a functionalized sustained-release core. Grafted silane coupling agent: The silane coupling agent is grafted onto the surface of the functionalized sustained-release core through a chemical reaction to form a chemical anchor point; In-situ generation of inner shell: On the core surface grafted with silane coupling agent, a metal soap inner shell layer composed of calcium stearate and zinc stearate is generated by in-situ co-precipitation. Outer shell layer: The lanthanum-organic complex containing unsaturated double bonds, prepared in advance, is coated onto the surface of the inner shell layer by solvent evaporation.

6. The preparation method of an environmentally friendly calcium-zinc composite PVC heat stabilizer according to claim 5, characterized in that, The silane coupling agent is γ-aminopropyltriethoxysilane, and its grafting reaction is carried out under reflux in anhydrous ethanol.

7. The preparation method of an environmentally friendly calcium-zinc composite PVC heat stabilizer according to claim 5, characterized in that, The in-situ coprecipitation method includes: dispersing the nucleus grafted with silane coupling agent in an aqueous medium, adding stearic acid, and then adding a mixed suspension containing calcium hydroxide and zinc oxide dropwise, controlling the pH of the reaction system to be 8.0-10.0 for the reaction.

8. The preparation method of an environmentally friendly calcium-zinc composite PVC heat stabilizer according to claim 5, characterized in that, The lanthanum-organic complex containing unsaturated double bonds is prepared by heating and stirring lanthanum trichloride, triphenyl phosphite and oleic acid in an organic solvent to form a complex solution.

9. The preparation method of an environmentally friendly calcium-zinc composite PVC heat stabilizer according to claim 5, characterized in that, include: Solvent evaporation methods specifically include spray drying or rotary evaporation.

Images