Rare earth flame retardant heat stabilizer for PVC sheet, PVC sheet and preparation method thereof

Abstract

The present invention discloses a rare earth flame retardant heat stabilizer for PVC sheets, PVC sheets and preparation methods thereof. The heat stabilizer has sodium phytate-modified magnesium aluminum lanthanum rare earth hydrotalcite as a main component, has both thermal stability and flame retardant functions, and is supplemented with industrial inorganic solid wastes such as fly ash and rare earth smelting waste as inorganic fillers to form a synergistic effect, thereby improving the overall thermal stability and flame retardant properties of the composite system. The prepared rare earth flame retardant heat stabilizer can be efficiently applied to the preparation of PVC sheets, giving the sheets good thermal stability, flame retardancy and mechanical properties, meeting the safety and performance requirements of interior decoration, building materials and floor coverings. At the same time, the preparation of environmentally friendly PVC sheets is conducive to the resource recycling and comprehensive utilization of industrial solid waste, effectively alleviating the current problems of land occupation and environmental pollution caused by solid waste stockpiling.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer material processing aids and solid waste resource utilization, and in particular to a rare earth flame retardant heat stabilizer for PVC sheets, the PVC sheets and a preparation method thereof. Background Art

[0002] PVC is a cost-effective, general-purpose thermoplastic with excellent mechanical properties, good molding and processing capabilities, and a wide range of application adaptability. It is widely used in interior decoration, architectural decoration, floor coverings, and other fields. However, PVC is prone to thermal degradation during processing and use, releasing large amounts of hydrogen chloride gas, which in turn causes molecular chain breakage, darkening of color, and a decrease in mechanical properties, seriously affecting the performance and lifespan of the product. Furthermore, during combustion, PVC releases toxic and harmful gases such as dioxins, posing a serious threat to the environment and human health. Therefore, the development of PVC products with both excellent thermal stability and flame retardancy has become an important research direction in the fields of material modification and environmental protection technology.

[0003] While traditional lead salt heat stabilizers offer excellent stability and low cost, they contain toxic heavy metals, making them difficult to meet current green and environmentally friendly development needs. Organotin heat stabilizers, while highly efficient and environmentally friendly, are expensive, limiting their application in large-scale production. Calcium-zinc heat stabilizers, a relatively ideal non-toxic alternative, offer advantages in inhibiting PVC degradation. However, their high zinc ion content can lead to "zinc burn," which not only affects the product's color but also weakens its mechanical properties.

[0004] In recent years, layered double hydroxides (LDHs) have garnered widespread attention as novel, non-toxic, and environmentally friendly thermal stabilizers in PVC thermal stabilization systems. Their excellent ion exchange capacity and sustained HCl release not only slow degradation but also partially inhibit the "zinc burn" effect. Rare earth elements, with their unique electronic structures and chemical properties, further broaden the functional scope of PVC stabilizers. Introducing the rare earth element La into the LDHs structure enhances its thermal stability and hydrogen chloride adsorption capacity, significantly improving the thermal stability of PVC products during processing and use. More importantly, rare earth elements possess a certain degree of flame retardancy, which can significantly improve the flame retardancy of PVC materials and enhance the safety of the products.

[0005] On the other hand, with the acceleration of industrialization, large quantities of general industrial solid waste, such as fly ash, steel slag, smelting waste, and rare earth tailings, are accumulating. If not effectively treated and reutilized, these wastes will severely impact the ecological environment and lead to a waste of land resources. Fly ash, rich in silicon-aluminum oxides, has a certain ability to absorb hydrogen chloride, making it a suitable inorganic filler for PVC to improve its thermal stability. Steel slag and rare earth smelting waste contain a variety of beneficial metal oxides, particularly rare earth oxides, which offer potential advantages in improving mechanical properties, thermal stability, and flame retardancy. In recent years, the synergistic use of solid wastes such as fly ash with traditional lead salt heat stabilizers and calcium-zinc composite stabilizers has improved PVC processing stability, but this has raised concerns about lead toxicity and "zinc burn." Therefore, there is an urgent need to develop a new, non-toxic, efficient, and flame-retardant additive system that combines flame retardancy with thermal stability. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention modifies the surface of magnesium-aluminum-lanthanum rare earth hydrotalcites (Mg-Al-La-LDHs) by introducing sodium phytate, which has a high phosphorus content. As a green polyphosphate flame retardant, sodium phytate contains a large number of phosphorus-oxygen bonds, which can produce phosphorus-containing free radicals such as PO· and HPO· during thermal decomposition. These radicals promote carbonization of the polymer surface, inhibit heat and oxygen transfer, and effectively inhibit flame propagation. The modified Mg-Al-La-LDHs not only improve their dispersibility and interfacial bonding properties in PVC but also significantly enhance the flame retardancy and thermal stability of PVC composites by synergistically releasing rare earth ions and phosphorus-based free radicals. The present invention constructs a composite rare earth flame retardant and heat stabilizer system based on modified magnesium-aluminum-lanthanum hydrotalcite and supplemented with industrial solid wastes such as fly ash and rare earth waste residue. This system, applied in the preparation of PVC sheets, not only enables the green manufacturing of high-performance PVC products but also effectively promotes the resource-based, high-value utilization of general industrial solid wastes. This system aligns with the strategic needs of green, low-carbon, and circular development, and possesses significant technological innovation and application promotion value.

[0007] One of the purposes of the present invention is to provide a rare earth flame retardant heat stabilizer for PVC sheets.

[0008] A second object of the present invention is to provide a PVC sheet prepared from the rare earth flame retardant heat stabilizer.

[0009] A third object of the present invention is to provide a method for preparing the PVC sheet.

[0010] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0011] In a first aspect, the present invention provides a rare earth flame retardant heat stabilizer for PVC sheets, comprising the following components in parts by mass: 3 to 8 parts of sodium phytate-modified magnesium aluminum lanthanum rare earth hydrotalcite; 0.5 to 1.5 parts of calcium stearate; 0.5 to 1.5 parts of zinc stearate; and 10 to 30 parts of inorganic solid waste filler.

[0012] In some embodiments, the method for preparing the sodium phytate-modified magnesium aluminum lanthanum rare earth hydrotalcite comprises the following steps:

[0013] Step S1, dissolving magnesium nitrate, aluminum nitrate and lanthanum nitrate in deionized water to prepare a mixed metal salt solution A;

[0014] Step S2, dissolving sodium bicarbonate and sodium hydroxide in deionized water to prepare a mixed alkali solution precipitant B;

[0015] Step S3, under stirring conditions, solution A and precipitant B are simultaneously added dropwise to the reactor, and the reaction temperature and pH value are controlled to reach the set value. After the addition is completed, the temperature is kept constant and the reaction is aged;

[0016] Step S4, filtering the precipitate generated in step S3, washing it to neutrality, drying it, and grinding the dried product to obtain magnesium aluminum lanthanum rare earth hydrotalcite powder;

[0017] Step S5: adding magnesium aluminum lanthanum rare earth hydrotalcite powder to a water-ethanol mixture and ultrasonically dispersing the mixture, then adding sodium phytate and stirring, centrifuging and washing, and drying to obtain sodium phytate-modified magnesium aluminum lanthanum rare earth hydrotalcite powder.

[0018] Preferably, in step S1, magnesium nitrate, aluminum nitrate and lanthanum nitrate are added according to a molar ratio of magnesium ion: aluminum ion: lanthanum ion of (10-20): (2-5): (0.5-3), more preferably a molar ratio of 15:4:1;

[0019] Preferably, the molar ratio of sodium bicarbonate to sodium hydroxide in step S2 is 1:1 to 1:4, more preferably 1:2;

[0020] Preferably, the reaction temperature in step S3 is 60-90°C, more preferably 70°C; the pH value is 10-11;

[0021] Preferably, the heat preservation and aging time in step S3 is 8 to 24 hours, more preferably 12 hours;

[0022] Preferably, the volume ratio of water to ethanol in the water-ethanol mixture in step S5 is 1:1 to 2:1;

[0023] Preferably, the ultrasonic dispersion time in step S5 is 1 to 2 hours, more preferably 1 hour;

[0024] Preferably, in step S5, the mass ratio of magnesium aluminum lanthanum rare earth hydrotalcite powder to sodium phytate is 1:1 to 2:1;

[0025] Preferably, the stirring temperature in step S5 is 60-80° C., more preferably 65° C.; the stirring time is 1-3 hours, more preferably 2 hours;

[0026] Preferably, the drying temperature in step S5 is 60-80°C.

[0027] The mass fractions of the sodium phytate-modified magnesium aluminum lanthanum rare earth hydrotalcite are, for example, 3, 4, 5, 6, 7, or 8 parts.

[0028] The mass fraction of the calcium stearate is, for example, 0.5, 0.6, 0.8, 1, 1.2, 1.3, 1.4, or 1.5 parts.

[0029] The mass fraction of the zinc stearate is, for example, 0.5, 0.6, 0.8, 1, 1.2, 1.3, 1.4, or 1.5 parts.

[0030] In some embodiments, the inorganic solid waste filler is one or more of fly ash, steel slag, rare earth tailings and rare earth smelting waste slag, and more preferably the inorganic solid waste filler is fly ash or rare earth smelting waste slag.

[0031] The mass fractions of the inorganic solid waste filler are, for example, 10, 15, 20, 25, or 30 parts.

[0032] The preparation method of the rare earth flame retardant heat stabilizer for PVC sheets can be: weigh the components according to the above mass ratio, mix them in a high-speed mixer for 10 minutes, and then obtain the required environmentally friendly composite rare earth heat stabilizer for PVC containing solid waste inorganic filler.

[0033] In a second aspect, the present invention provides a PVC sheet, which is made by mixing the above-mentioned rare earth flame retardant heat stabilizer with PVC powder, DOP, ACR, and PE wax, and then plasticizing and molding.

[0034] Specifically, the PVC sheet includes the following raw materials in parts by mass: 100 parts of PVC powder; 3 to 8 parts of sodium phytate-modified magnesium aluminum lanthanum rare earth hydrotalcite; 0.5 to 1.5 parts of calcium stearate; 0.5 to 1.5 parts of zinc stearate; 10 to 30 parts of inorganic solid waste filler; 10 to 30 parts of di(2-ethylhexyl) phthalate (DOP); 1 to 3 parts of acrylic acid ester copolymer (ACR); and 0.2 to 1 part of polyethylene wax (PE wax).

[0035] In a third aspect, the present invention provides a method for preparing the above-mentioned PVC sheet, comprising the following steps:

[0036] Step 1: Weigh PVC powder, the rare earth flame retardant heat stabilizer, DOP, ACR, and PE wax in proportion, place them in a high-speed mixer, and mix for 5 to 10 minutes to obtain a uniform mixture;

[0037] Step 2: The uniform mixture obtained in step 1 is fed into a double-roll mill for pre-plasticization at a temperature of 150-180°C. The plasticized material is removed after mixing for 5-10 minutes.

[0038] Step 3: Place the plasticized material obtained in step 2 into a mold and send it into a flat-plate vulcanizer for high-temperature molding at a temperature of 160-185°C, a pressure of 10-15 MPa, and a hot pressing time of 5-10 minutes;

[0039] Step 4: cooling and demoulding to obtain the PVC sheet.

[0040] Beneficial effects:

[0041] This invention uses sodium phytate-modified magnesium-aluminum-lanthanum rare earth hydrotalcite as the primary thermal stabilizer, with zinc stearate and calcium stearate added as synergistic thermal stabilizers. The hydrotalcite effectively suppresses "zinc burn" and improves the thermal stability of PVC during processing. Modification with sodium phytate further enhances the flame retardancy of the hydrotalcite. Using inorganic industrial solid wastes such as fly ash, steel slag, rare earth tailings, and rare earth smelting waste as fillers not only improves the mechanical properties of PVC products but also utilizes their active ingredients (such as silicon-aluminum oxide and rare earths) to absorb hydrogen chloride gas generated by PVC degradation, hindering degradation and improving the thermal stability of PVC products. Furthermore, the composite rare earth thermal stabilizer enhances the flame retardancy of PVC sheets by enhancing their flame retardancy. The use of composite rare earth thermal stabilizers containing inorganic industrial solid waste fillers to produce environmentally friendly PVC sheets facilitates the resource recycling and comprehensive utilization of industrial solid waste, alleviating the land occupation and environmental pollution caused by solid waste accumulation.

[0042] The PVC sheet produced by this invention not only has excellent thermal stability and flame retardancy, but also possesses good mechanical properties, making it widely applicable in interior decoration, building materials, floor coverings, and other fields. This invention provides a new high-value-added, efficient resource recycling path for industrial inorganic solid waste, with significant environmental and economic benefits.

[0043] The present invention has been described in detail above, but the above embodiments are merely illustrative in nature and are not intended to limit the present invention. In addition, the present invention is not limited by any theory described in the above prior art or invention summary or the following examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a scanning electron microscope image of the sodium phytate-modified magnesium aluminum lanthanum rare earth hydrotalcite obtained in the preparation example of the present invention;

[0045] Figure 2 This is a photo of the PVC sheet obtained in Example 1 of the present invention;

[0046] Figure 3 This is a photo of the PVC sheet obtained in Example 2 of the present invention. DETAILED DESCRIPTION

[0047] The present invention will be further described below with reference to the examples. It should be noted that the following examples are provided for illustrative purposes only and do not constitute a limitation on the scope of protection claimed in the present invention.

[0048] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, and methods in the art.

[0049] PVC resin was SG-3 from Baotou Sea Level Polymer Industry Co., Ltd.;

[0050] The fly ash comes from a thermal power plant in Baotou;

[0051] The rare earth smelting waste slag comes from a rare earth extraction plant in Baotou;

[0052] Calcium stearate (Aladdin), zinc stearate (Aladdin), DOP (Aladdin, AR), ACR (Shandong Ruifeng Polymer Materials Co., Ltd.), and PE wax (Wuhan Xindongyi Chemical Co., Ltd.) were all commercially available.

[0053] Preparation Example Preparation of Sodium Phytate Modified Magnesium Aluminum Lanthanum Rare Earth Hydrotalcite

[0054] Weigh magnesium nitrate (30 mmol), aluminum nitrate (8 mmol), and lanthanum nitrate (2 mmol) at a molar ratio of 15:4:1 for magnesium ion:aluminum ion:lanthanum ion. Dissolve them in deionized water and stir until completely dissolved to obtain a clear mixed metal salt solution A. Separately, prepare a mixed alkali solution B with 60 mmol of sodium carbonate and 120 mmol of sodium hydroxide at a molar ratio of 1:2 as a precipitant.

[0055] Solution A and B were added dropwise simultaneously to a thermostatic reactor at 70°C, with a stirring rate of 500 rpm. The pH was maintained between 10 and 11 during the addition. After the addition was complete, the reaction was allowed to age for 12 hours.

[0056] The generated precipitate was filtered, washed with deionized water until neutral, dried at 80° C. for 12 hours, and finally ground through a 100-mesh sieve to obtain white magnesium-aluminum-lanthanum rare earth hydrotalcite powder.

[0057] Next, the hydrotalcite powder was added to a water-ethanol mixture prepared in a volume ratio of 1:1, and ultrasonically dispersed at room temperature for 1 hour. After adding an appropriate amount of sodium phytate according to the mass ratio of magnesium aluminum lanthanum rare earth hydrotalcite powder and sodium phytate of 3:2, the mixture was reacted at 65°C with magnetic stirring for 2 hours. After the reaction, the product was centrifuged and washed with deionized water and ethanol in turn, and dried at 80°C to obtain sodium phytate-modified magnesium aluminum lanthanum rare earth hydrotalcite powder (morphology see Figure 1 ).

[0058] Example 1

[0059] Based on 100 parts of PVC by mass, the ingredients are prepared according to the following contents:

[0060] 100 parts of PVC resin, 5 parts of sodium phytate-modified magnesium aluminum lanthanum rare earth hydrotalcite obtained in the preparation example, 1 part of calcium stearate, 1 part of zinc stearate, 20 parts of fly ash, 20 parts of DOP, 2 parts of ACR, and 0.5 parts of PE wax.

[0061] After mixing the ingredients according to the ingredients, place them in a high-speed mixer and mix them at room temperature for 8 minutes to obtain a uniform mixture. Then send the mixture to a double-roll mill and mix it at 160°C for 7 minutes to form a plasticized material. Then, in a flat vulcanizer, hot press it at 170°C and a pressure of 12 MPa for 8 minutes. After cooling, demoulding is carried out to obtain an environmentally friendly PVC sheet containing solid waste inorganic fillers ( Figure 2 shown).

[0062] Example 2

[0063] Based on 100 parts of PVC by mass, the ingredients are prepared according to the following contents:

[0064] 100 parts of PVC resin, 5 parts of sodium phytate-modified magnesium aluminum lanthanum rare earth hydrotalcite obtained in the preparation example, 1 part of calcium stearate, 1 part of zinc stearate, 30 parts of rare earth smelting waste slag, 30 parts of DOP, 3 parts of ACR, and 1 part of PE wax.

[0065] After mixing the ingredients according to the ingredients, place them in a high-speed mixer and mix them at room temperature for 8 minutes to obtain a uniform mixture. Then send the mixture to a double-roll mill and mix it at 160°C for 7 minutes to form a plasticized material. Then, in a flat vulcanizer, hot press it at 170°C and a pressure of 12 MPa for 8 minutes. After cooling, demoulding is carried out to obtain an environmentally friendly PVC sheet containing solid waste inorganic fillers ( Figure 3 shown).

[0066] Comparative Example 1

[0067] The only difference from Example 1 is that the amount of fly ash added is 0 parts. Plasticizing and molding are performed according to the method of Example 1 to obtain the PVC sheet of Comparative Example 1 without fly ash inorganic filler.

[0068] Comparative Example 2

[0069] The only difference from Example 2 is that the amount of rare earth smelting waste slag added is 0. Plasticizing and molding are performed according to the method of Example 2 to obtain the PVC sheet of Comparative Example 2 without the rare earth smelting waste slag inorganic filler.

[0070] Comparative Example 3

[0071] The difference from Example 1 is that the sodium phytate-modified magnesium aluminum lanthanum rare earth hydrotalcite is replaced by an equal amount of magnesium aluminum lanthanum rare earth hydrotalcite.

[0072] Comparative Example 4

[0073] The difference from Example 1 is that the PVC raw materials are:

[0074] 100 parts of PVC resin, 2 parts of sodium phytate, 3 parts of magnesium aluminum lanthanum rare earth hydrotalcite, 1 part of calcium stearate, 1 part of zinc stearate, 20 parts of fly ash, 20 parts of DOP, 2 parts of ACR, and 0.5 parts of PE wax.

[0075] Performance Testing

[0076] 1.1 Thermal stability test

[0077] The thermal stability time was tested using the Congo red method in accordance with the national standard GB / T 2917.1-2002: 5 g of the PVC sheets prepared in Examples 1-2 and Comparative Examples 1-4 were ground and dispersed, respectively, and placed in a test tube. Congo red test paper was then placed in the test tube. The test tube was fixed in an oil bath at 180±1°C, with the oil level level with the sample surface. The time it took for the Congo red test paper to turn blue was recorded, which was the thermal stability time of the sample.

[0078] The performance test results are shown in Table 1.

[0079] Table 1 Thermal stability time data of PVC sheets prepared in Examples 1-2 and Comparative Examples 1-4

[0080]

[0081] Result analysis: By comparing the thermal stability time data of Examples 1-2 and Comparative Examples 1-4, it can be seen that the present invention uses inorganic solid wastes such as fly ash and rare earth smelting waste slag as fillers, and the Congo red test color change time is long, which shows that it has good long-term stability. This shows that adding inorganic solid wastes such as fly ash and rare earth smelting waste slag to the modified hydrotalcite thermal stability system is beneficial to improving the thermal stability of PVC products.

[0082] The thermal stability time in Comparative Example 3 was 45 minutes, significantly shorter than that in Example 1 (66 minutes). This indicates that replacing the sodium phytate-modified magnesium-aluminum-lanthanum rare earth hydrotalcite with unmodified magnesium-aluminum-lanthanum rare earth hydrotalcite reduced the thermal stability of the material. This may be due to the poor dispersibility of the unmodified hydrotalcite in the PVC system and its slow neutralization reaction with HCl at high temperatures. This prevents the timely absorption of HCl during the thermal degradation of the PVC, reducing the thermal stability.

[0083] The thermal stability time of Comparative Example 4 was 38 minutes, a significant decrease compared to Example 1 (66 minutes vs. 38 minutes). This indicates that the thermal stability of the physical mixture of sodium phytate and magnesium-aluminum-lanthanum-rare-earth hydrotalcite in the PVC system was less than expected. This may be because the physical blend of sodium phytate and magnesium-aluminum-lanthanum-rare-earth hydrotalcite does not form a good synergistic interface. However, the composite system obtained through chemical modification in the present invention is more compatible with the PVC matrix and effectively neutralizes degradation products, significantly improving thermal stability.

[0084] In summary, the formula and preparation method shown in Examples 1-2 can significantly improve the thermal stability of PVC. In particular, the sodium phytate-modified magnesium aluminum lanthanum rare earth hydrotalcite and inorganic solid waste (fly ash or rare earth smelting waste) work together to exert a significant synergistic effect in inhibiting the thermal decomposition of PVC and prolonging the thermal stability time.

[0085] 1.2 Mechanical properties test

[0086] Mechanical properties were tested according to GB / T 1040.2-2006. The PVC sheets prepared in Examples 1-2 and Comparative Examples 1-4 were cut into test specimens meeting national standard dimensions using a standard dumbbell cutter. Mechanical properties, such as tensile strength and elongation at break, were measured using an electronic universal testing machine under standard testing conditions to evaluate the mechanical properties of the PVC sheets.

[0087] Table 2 Mechanical properties of PVC sheets prepared in Examples 1-2 and Comparative Examples 1-4

[0088]

[0089] Results Analysis: As shown in Table 2, the environmentally friendly PVC sheets prepared in Examples 1 and 2 significantly outperformed those in Comparative Examples 1-4 in terms of tensile strength and elongation at break. Specifically, Example 2 achieved the best performance, with a tensile strength of 22.1 MPa and an elongation at break of 182%. This performance was primarily attributed to the excellent dispersibility and interfacial bonding of the rare earth smelting waste slag within the PVC matrix, significantly improving the composite's stress transfer efficiency. Example 1 also exhibited excellent performance, with a tensile strength of 21.3 MPa and an elongation at break of 175%, attributed to the filler effect of fly ash and its synergistic effect with the modified hydrotalcite. In contrast, Comparative Examples 1 and 2, which did not add fly ash or rare earth smelting waste, had poor interface structures and more pores, resulting in tensile strengths of only 17.5 MPa and 18.3 MPa, and elongations at break of 148% and 152%, respectively, significantly lower than those in the Examples. Comparative Example 3 had a tensile strength of 18.0 MPa and an elongation at break of 150%, lower than in Example 1. This was because the hydrotalcite was not modified with sodium phytate, resulting in poor dispersibility and interfacial bonding in the PVC, making it difficult to enhance overall performance. Comparative Example 4 had a tensile strength of 17.2 MPa and an elongation at break of only 145%, the lowest. This was because the physical mixing of sodium phytate and hydrotalcite lacked the synergistic effect of a chemically modified system, making it difficult to effectively improve interfacial bonding and resulting in a significant decrease in mechanical properties. Overall, the synergistic compounding of sodium phytate-modified magnesium-aluminum-lanthanum rare earth hydrotalcite with fly ash and rare earth smelting waste helped improve the mechanical properties of the PVC sheet, demonstrating the significant advantages of the environmentally friendly PVC sheet formulation of the present invention.

[0090] 1.3 Flame retardant performance test

[0091] To evaluate the flame retardancy of the environmentally friendly PVC sheets of the present invention, samples were tested for limiting oxygen index (LOI) according to the national standard GB / T 2406.2-2009, and their flame retardancy ratings were assessed according to the UL-94 vertical burning test standard. PVC sheets prepared in Example 1, Example 2, and Comparative Examples 1-4 were cut to standard sizes and tested. The test results are shown in Table 3.

[0092] Table 3 Mechanical properties of PVC sheets prepared in Examples 1-2 and Comparative Examples 1-4

[0093]

[0094] Results Analysis: Table 3 shows that the PVC sheets prepared in Examples 1 and 2 exhibit significantly superior flame retardancy to Comparative Examples 1-4. Specifically, the Limiting Oxygen Index (LOI) of Example 2 reached 30.1%, while that of Example 1 reached 28.8%, both significantly higher than those of Comparative Examples 1 (26.1%), 2 (26.8%), 3 (25.9%), and 4 (26.5%). According to the GB / T 2406.2-2009 standard, materials with an oxygen index greater than 28% are classified as relatively flame-retardant, demonstrating the excellent flame suppression properties of the materials in the Examples. This is further confirmed by the UL-94 vertical combustion test results. Both Examples 1 and 2 achieved a UL-94 V-0 rating, demonstrating self-extinguishing within 10 seconds after the ignition source is removed and no dripping igniting cotton, demonstrating excellent flame retardant safety. Comparative Examples 1-4, on the other hand, only achieved a V-1 rating. Despite exhibiting no dripping, their extinguishing time after combustion was prolonged, significantly inferior to the flame retardant properties of the Examples.

[0095] From the analysis of the formula, Examples 1 and 2 use a synergistic system of sodium phytate-modified magnesium aluminum lanthanum rare earth hydrotalcite and fly ash or rare earth smelting waste slag, which can improve the dispersibility, interfacial bonding and carbonization of the system, thereby effectively suppressing the spread of combustion during the flame retardant process. However, due to the lack of sodium phytate modification, the dispersibility of the hydrotalcite in Comparative Example 3 is poor, resulting in the lowest LOI value of only 25.9%; although Comparative Example 4 contains sodium phytate and magnesium aluminum lanthanum rare earth hydrotalcite, the two are only physically mixed, lacking synergistic effect, and the LOI value does not exceed 27%. In summary, the synergistic effect of the flame retardant and solid waste inorganic filler in Examples 1 and 2 is significant, greatly improving the flame retardant properties of the PVC sheet, fully demonstrating the superiority of the formula of the present invention.

[0096] In summary, the sodium phytate-modified magnesium-aluminum-lanthanum hydrotalcite used in this example, along with inorganic solid waste fillers such as fly ash and rare earth smelting slag, exhibit a synergistic flame retardant effect. On the one hand, these inorganic materials improve the thermal stability of the material and inhibit its thermal decomposition rate; on the other hand, their inherent charring ability and high heat capacity help prevent flame spread and dripping.

[0097] The above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced with equivalents, without departing from the spirit and substance of the claims of the present invention; and such modifications or replacements remain within the scope of the claims of the present invention.

Claims

1. A rare earth flame retardant heat stabilizer for PVC sheet, characterized in that: The invention comprises the following components in parts by mass: 3 to 8 parts of sodium phytate-modified magnesium aluminum lanthanum rare earth hydrotalcite; 0.5 to 1.5 parts of calcium stearate; 0.5 to 1.5 parts of zinc stearate; and 10 to 30 parts of inorganic solid waste filler. The inorganic solid waste filler is one or both of fly ash and rare earth smelting waste slag; The preparation method of the sodium phytate-modified magnesium aluminum lanthanum rare earth hydrotalcite comprises the following steps: Step S1, dissolving magnesium nitrate, aluminum nitrate and lanthanum nitrate in deionized water to prepare a mixed metal salt solution A; Step S2, dissolving sodium bicarbonate and sodium hydroxide in deionized water to prepare a mixed alkali solution precipitant B; Step S3, under stirring conditions, solution A and precipitant B are simultaneously added dropwise to the reactor, and the reaction temperature and pH value are controlled to reach the set value. After the addition is completed, the temperature is kept constant and the reaction is aged; Step S4, filtering the precipitate generated in step S3, washing it to neutrality, drying it, and grinding the dried product to obtain magnesium aluminum lanthanum rare earth hydrotalcite powder; Step S5, adding magnesium aluminum lanthanum rare earth hydrotalcite powder to a water-ethanol mixture and ultrasonically dispersing it, then adding sodium phytate and stirring, centrifuging and washing, and drying to obtain sodium phytate-modified magnesium aluminum lanthanum rare earth hydrotalcite powder; In step S1, magnesium nitrate, aluminum nitrate and lanthanum nitrate are added according to the molar ratio of magnesium ion: aluminum ion: lanthanum ion (10-20): (2-5): (0.5-3).

2. The rare earth flame retardant heat stabilizer for PVC sheet according to claim 1, characterized in that: The molar ratio of sodium bicarbonate to sodium hydroxide in step S2 is 1:1 to 1:

4.

3. The rare earth flame retardant heat stabilizer for PVC sheet according to claim 1, characterized in that: In step S3, the reaction temperature is 60-90° C. and the pH value is 10-11; The heat preservation and aging time in step S3 is 8 to 24 hours.

4. The rare earth flame retardant heat stabilizer for PVC sheet according to claim 1, characterized in that: The ultrasonic dispersion time in step S5 is 1 to 2 hours; In step S5, the mass ratio of magnesium aluminum lanthanum rare earth hydrotalcite powder to sodium phytate is 1:1 to 2:1; In step S5, the stirring temperature is 60-80° C., and the stirring time is 1-3 hours.

5. A PVC sheet, characterized in that: The method is prepared by mixing the rare earth flame retardant heat stabilizer for the PVC sheet material as claimed in any one of claims 1 to 4 with PVC powder, DOP, ACR and PE wax, and then performing plasticizing and molding.

6. The PVC sheet according to claim 5, characterized in that: The PVC sheet comprises the following raw materials in parts by mass: 100 parts of PVC powder; 3-8 parts of sodium phytate-modified magnesium aluminum lanthanum rare earth hydrotalcite; 0.5-1.5 parts of calcium stearate; 0.5-1.5 parts of zinc stearate; 10-30 parts of inorganic solid waste filler; 10-30 parts of DOP; 1-3 parts of ACR; and 0.2-1 part of PE wax.

7. A method for preparing a PVC sheet according to claim 5 or 6, characterized in that: The following steps are involved: Step 1: Weigh PVC powder, the rare earth flame retardant heat stabilizer, DOP, ACR, and PE wax in proportion, place them in a high-speed mixer, and mix for 5 to 10 minutes to obtain a uniform mixture; Step 2: The uniform mixture obtained in step 1 is fed into a double-roll mill for pre-plasticization at a temperature of 150-180°C. The plasticized material is removed after mixing for 5-10 minutes. Step 3: Place the plasticized material obtained in step 2 into a mold and send it into a flat-plate vulcanizer for high-temperature molding at a temperature of 160-185°C, a pressure of 10-15 MPa, and a hot pressing time of 5-10 minutes; Step 4: cooling and demoulding to obtain the PVC sheet.

Images