High-strength PVC foam and preparation method thereof

Abstract

The invention relates to the technical field of plastics, and particularly discloses high-strength PVC foam and a preparation method thereof. The high-strength PVC foam comprises the following raw materials in parts by weight: 100 parts of SG-5 PVC resin, 15-18 parts of maleic anhydride grafted polyvinyl chloride coated magnesium citrate, 4-5 parts of a calcium-zinc stabilizer, 8-10 parts of a plasticizer and 5-6 parts of butadiene styrene rubber. The maleic anhydride grafted polyvinyl chloride coated magnesium citrate salt is prepared from maleic anhydride grafted polyvinyl chloride and magnesium citrate salt by adopting a melt blending method. According to the preparation method, the strength of the prepared PVC foam is improved by improving the dispersity of the magnesium citrate salt in a PVC matrix.

Description

Technical Field

[0001] This application relates to the field of plastics technology, and more specifically, to a high-strength PVC foam and a method for preparing the same. Background Technology

[0002] Foam, also known as porous plastic, is a type of plastic. It is a composite polymer material with a large number of interconnected or non-interconnected gas micropores dispersed within a solid plastic, resulting in a significant reduction in apparent density. Due to its unique structure, foam plastics possess unique properties, combining the porosity of foam with the characteristics of the matrix resin. This gives them advantages such as light weight, high specific strength, ability to absorb impact loads, and good thermal insulation. Compared to ordinary plastics, the presence of numerous gas micropores and low density allows for the production of lighter products by saving raw materials. This achieves weight reduction without compromising material performance, resulting in high cost-effectiveness. Therefore, foam is widely used in industry, agriculture, construction, daily necessities, and packaging and transportation.

[0003] PVC is one of the world's five major general-purpose resins, and my country currently ranks first globally in PVC production capacity, output, and consumption. PVC foam, as a functional material processed through a special foaming process, is gradually gaining attention. Using PVC resin as its main base material, it undergoes physical foaming, chemical foaming, or a combination of both composite foaming processes to create a large number of uniformly distributed cell structures within the material. This cell structure enables PVC foam to achieve lightweighting. However, because the chlorine atoms in the PVC resin structure are highly reactive, PVC easily releases HCl under heating conditions. When a large amount of HCl is released, the mechanical properties of PVC decrease significantly, resulting in a shorter service life.

[0004] Patent application CN113462098A discloses a high-strength PVC foam and its preparation method, comprising a PVC resin mixture, isocyanate, polyether polyol, diglycidyl 4,5-epoxycyclohexane-1,2-dicarboxylate, foaming agent, antioxidant, ultraviolet absorber, acrylonitrile-butadiene-styrene copolymer, and filler; the filler consists of potassium titanate whiskers, calcium sulfate whiskers, polyvinyl alcohol, and hollow microspheres. In this patent application, the potassium titanate whiskers and calcium sulfate whiskers are modified only by the silane coupling agent KH550, while the PVC matrix has a chlorinated hydrocarbon structure, resulting in a low polarity match between the two; simultaneously, the large difference in interfacial tension between the hydrophilic polyvinyl alcohol and the hydrophobic PVC easily leads to filler agglomeration, reducing the material strength. Summary of the Invention

[0005] To improve the strength of PVC foam, this application provides a high-strength PVC foam and a method for preparing the same.

[0006] In the first aspect, this application provides a high-strength PVC foam, which adopts the following technical solution: A high-strength PVC foam comprises the following raw materials in parts by weight: 100 parts of SG-5 PVC resin, 15-18 parts of maleic anhydride-grafted polyvinyl chloride coated magnesium citrate, 4-5 parts of calcium-zinc stabilizer, 8-10 parts of plasticizer, and 5-6 parts of styrene-butadiene rubber. The maleic anhydride-grafted polyvinyl chloride coated magnesium citrate salt is prepared by melt blending maleic anhydride-grafted polyvinyl chloride with magnesium citrate salt.

[0007] By adopting the above technical solution, maleic anhydride-grafted polyvinyl chloride forms a coating layer on the surface of magnesium citrate. This coating layer contains both polyvinyl chloride segments with the same structure as the PVC matrix and polar maleic anhydride groups. During the coating process, the maleic anhydride groups can undergo esterification or form hydrogen bonds with the hydroxyl groups on the surface of magnesium citrate, forming a stable chemical bond. At the same time, the polyvinyl chloride segments extend outward and entangle with the molecular chains of the subsequent PVC matrix, thus acting as a bridge between magnesium citrate and the PVC matrix, significantly reducing interfacial tension and preventing the aggregation of magnesium citrate.

[0008] In this application, magnesium citrate can serve as both a reinforcing phase and a foaming agent. Its magnesium ions and citrate ions are combined through coordination bonds to form a stable six-membered ring structure, which can act as a rigid node in the PVC matrix to restrict the sliding of molecular chains. The magnesium oxide generated after high-temperature decomposition is dispersed in the cell walls, further strengthening the structure. At the same time, the organic segments of citrate ions decompose to generate gas at the PVC processing temperature. Because the new substance is uniformly dispersed, the gas release is more controllable, avoiding the uneven cell structure caused by the local aggregation of traditional foaming agents.

[0009] Therefore, this application improves the dispersibility of maleic anhydride-grafted polyvinyl chloride coated magnesium citrate salt in the PVC foam system, thereby increasing the strength of the PVC foam.

[0010] Preferably, the preparation method of maleic anhydride-grafted polyvinyl chloride coated magnesium citrate is as follows: maleic anhydride-grafted polyvinyl chloride and magnesium citrate are added to a twin-screw mixer and mixed at 130-140°C and 300-400 rpm for 30-40 minutes. After cooling to room temperature, the mixture is pulverized to obtain maleic anhydride-grafted polyvinyl chloride coated magnesium citrate. The amount of maleic anhydride-grafted polyvinyl chloride added is 6%-8% of the mass of magnesium citrate.

[0011] By adopting the above technical solution, maleic anhydride-grafted polyvinyl chloride (PVC) melts and spreads evenly on the surface of magnesium citrate salt through shear force. At the same time, one end of the maleic anhydride-grafted PVC is covalently bonded to magnesium citrate salt, and the other end is molecularly wrapped and anchored to the PVC matrix, constructing a continuous stress transmission channel. Maleic anhydride and the hydroxyl groups on the surface of magnesium citrate salt undergo esterification reaction to form covalent bonds, while chlorinated PVC is tightly bonded to the PVC matrix through molecular chain entanglement, van der Waals forces, and dipole interactions, improving the compatibility between magnesium citrate salt and PVC matrix and increasing the strength of PVC foam.

[0012] Preferably, when the maleic anhydride-grafted polyvinyl chloride and magnesium citrate are mixed, epoxidized soybean oil is also added, and the amount of epoxidized soybean oil added is 1%-1.5% of the mass of magnesium citrate.

[0013] By adopting the above technical solution, epoxidized soybean oil utilizes the epoxy groups in its molecular structure to chemically react with the hydroxyl groups on the surface of magnesium citrate salt and the anhydride groups in maleic anhydride-grafted polyvinyl chloride, thereby enhancing interfacial bonding and improving compatibility. At the same time, epoxidized soybean oil can also act as a plasticizer, reducing the viscosity of the system, improving processing performance, and absorbing hydrogen chloride produced during the decomposition of polyvinyl chloride resin, playing an auxiliary stabilizing role and improving the strength of the material.

[0014] Preferably, the method for preparing the magnesium citrate salt includes the following steps: (1) Add magnesium hydroxide to deionized water and ultrasonically disperse to form a suspension; add anhydrous citric acid to deionized water and stir until completely dissolved to obtain a citric acid solution; (2) Add the suspension dropwise into the citric acid solution and stir for 1-2 hours at 50°C and pH 5.8-6.8. (3) After the reaction is complete, the sample is filtered, washed and dried to obtain magnesium citrate. The molar ratio of anhydrous citric acid to magnesium hydroxide is 2:(3-3.5).

[0015] By adopting the above technical solution, the method for preparing magnesium citrate salt in this application adjusts the raw material ratio and reaction parameters to make the product decomposition temperature suitable for PVC extrusion foaming process. The product has uniform particle size, high purity, and good reinforcement and foaming properties. The process is stable and easy to operate, making it suitable for industrial production.

[0016] Preferably, in step (3), the drying process adopts a step-by-step drying method, specifically: in the first stage, drying is carried out for 1.5-2.5 hours at a temperature of 55-65℃ and a vacuum of -0.085 to -0.095 MPa; in the second stage, drying is carried out for 1.5-2.5 hours at a temperature of 75-85℃ and a vacuum of -0.085 to -0.095 MPa.

[0017] By adopting the above technical solution and using a step-by-step drying method, free water is first removed at low temperature, and then crystal water is removed at medium temperature. Combined with a vacuum environment and precise temperature control, magnesium citrate can be prevented from decomposing prematurely at high temperature, effectively reducing its water content and ensuring that it has a suitable average particle size. This ensures that the product decomposition temperature is suitable for PVC extrusion foaming process.

[0018] Preferably, in step (3), the magnesium citrate is further subjected to hydroxyl activation treatment, specifically by subjecting the magnesium citrate to low-temperature plasma treatment at a power of 100-120W for 60-90s.

[0019] By adopting the above technical solution, after low-temperature plasma treatment, the hydroxyl density of citrate increases, the number of binding sites between magnesium citrate and maleic anhydride-grafted polyvinyl chloride increases, the interfacial bonding energy between the two is improved, and the compatibility between magnesium citrate and PVC matrix is ​​further improved.

[0020] Preferably, during the low-temperature plasma treatment, a mixture of oxygen and water vapor with a volume ratio of (3-4):1 is used as the gas atmosphere.

[0021] By adopting the above technical solution, water vapor can provide sufficient hydrogen elements, which decompose into hydroxyl radicals in the plasma environment. These radicals react with the metal oxide sites on the surface of magnesium citrate salt to generate stable surface hydroxyl groups, thereby increasing the hydroxyl density. At the same time, the introduction of water vapor can weaken the strong oxidizing effect of pure oxygen, avoid structural damage caused by excessive surface oxidation, and the generated hydroxyl groups are more likely to react chemically with the anhydride groups of maleic anhydride-grafted polyvinyl chloride, thereby strengthening the interfacial bonding.

[0022] Preferably, the method for preparing maleic anhydride-grafted polyvinyl chloride includes the following steps: S1, mix the following raw materials in parts by weight evenly to obtain a mixture: 100 parts PVC resin, 5-8 parts maleic anhydride, 0.4-0.6 parts di-tert-butyl peroxide, 1.5 parts ACR-401 and 0.3 parts antioxidant 1010; S2, the mixture is added to a twin-screw extruder, extruded, granulated and dried to obtain maleic anhydride-grafted polyvinyl chloride; wherein the temperature of the extruder feeding section is 80-100℃, the temperature of the compression section is 130-150℃, the temperature of the reaction section is 160-170℃, the temperature of the homogenization section is 150-160℃ and the temperature of the die head is 140-150℃.

[0023] By adopting the above technical solution, the effective grafting of maleic anhydride and PVC is achieved by using a melt grafting process. The MAH group in the product can form a strong interaction with the hydroxyl group on the surface of magnesium citrate, while the PVC backbone can be perfectly compatible with the PVC matrix, thereby improving the dispersibility and interfacial bonding of magnesium citrate in the PVC matrix.

[0024] Preferably, in S1, the raw material further includes 2-3 parts by weight of styrene.

[0025] By adopting the above technical solution, on the one hand, the copolymerization activity of styrene and maleic anhydride is higher than that of maleic anhydride homopolymerization, which inhibits the homopolymerization of maleic anhydride itself and reduces the residue of free maleic anhydride; on the other hand, the synergistic effect of styrene and maleic anhydride can provide more grafting sites for PVC molecular chains, improve the grafting rate, improve the uniformity of the distribution of grafted chains in the PVC matrix, reduce the risk of crosslinking caused by local aggregation of maleic anhydride, and ultimately improve the compatibility of maleic anhydride-grafted PVC with the PVC matrix and magnesium citrate.

[0026] Secondly, this application provides a method for preparing high-strength PVC foam, employing the following technical solution: A method for preparing high-strength PVC foam includes the following steps: According to the compounding ratio, SG-5 PVC resin, calcium zinc stabilizer, and plasticizer are mixed in sequence, then styrene-butadiene rubber is added, and then maleic anhydride-grafted polyvinyl chloride-coated magnesium citrate salt is added and mixed evenly to obtain a premix. The premixed material is extruded and granulated to obtain foaming masterbatch; High-strength PVC foam is obtained by molding and foaming the foaming masterbatch.

[0027] In summary, this application has the following beneficial effects: 1. This application uses a melt blending method to coat maleic anhydride-grafted polyvinyl chloride (PVC) onto the surface of magnesium citrate. The maleic anhydride groups can undergo esterification or form hydrogen bonds with the hydroxyl groups on the surface of magnesium citrate, forming a stable chemical bond. At the same time, its PVC chain segments extend outward and entangle with the molecular chains of the subsequent PVC matrix, thus acting as a bridge between magnesium citrate and PVC matrix. This significantly reduces interfacial tension, prevents magnesium citrate from agglomerating, improves its dispersibility in the matrix, and thereby improves the strength of the produced PVC foam.

[0028] 2. This application improves the hydroxyl density of magnesium citrate by subjecting it to low-temperature plasma treatment, thereby increasing the number of binding sites between magnesium citrate and maleic anhydride-grafted polyvinyl chloride, enhancing the interfacial bonding energy between the two, and further improving the compatibility between magnesium citrate and the PVC matrix.

[0029] 3. In this application, epoxidized soybean oil is added when preparing magnesium citrate salt coated with maleic anhydride-grafted polyvinyl chloride. The epoxy groups in the molecular structure of the epoxidized soybean oil react chemically with the hydroxyl groups on the surface of magnesium citrate salt and the anhydride groups in maleic anhydride-grafted polyvinyl chloride, thereby enhancing the interfacial bonding force and improving compatibility. Detailed Implementation

[0030] The present application will be further described in detail below with reference to the embodiments.

[0031] Unless otherwise specified, the raw materials used in the preparation examples, embodiments, and comparative examples of this application are all commercially available.

[0032] Preparation Examples 1-13: Maleic anhydride-grafted polyvinyl chloride coated magnesium citrate Preparation Example 1 This preparation example discloses a method for preparing maleic anhydride-grafted polyvinyl chloride coated magnesium citrate, specifically including the following steps: Preparation of magnesium citrate: 10 kg of anhydrous citric acid was added to 50 L of deionized water and stirred until completely dissolved to obtain a citric acid solution. 4.53 kg of magnesium hydroxide powder was added to 18 L of deionized water and sonicated at 400 W for 15 min to obtain a suspension. The citric acid solution was added to a three-necked flask, and the suspension was added dropwise at 400 r / min and heated to 50 °C. During the dropwise addition, the pH of the system was maintained at 6.5-7.5 by controlling the dropwise rate of the suspension. After the dropwise addition was completed, the mixture was kept at the same temperature and stirred for 2 h to obtain a mixture. The reaction was considered complete when phenolphthalein indicator was added to the supernatant and no red color appeared. After the reaction was completed, the mixture was cooled to room temperature, and the solid product was separated by vacuum filtration. The filter cake was repeatedly washed with deionized water until the washing liquid was neutral. The cleaned filter cake was placed in a vacuum drying oven and dried at 60 °C for 6 h to obtain a powder. The powder was pulverized to an average particle size of 3 μm using an air jet mill to obtain magnesium citrate. Preparation of maleic anhydride-grafted polyvinyl chloride: 10 kg of suspension PVC resin with an average degree of polymerization of 1000, 500 g of maleic anhydride, 40 g of di-tert-butyl peroxide, 150 g of ACR-401 and 30 g of antioxidant 1010 were mixed evenly to obtain a mixture; the mixture was added to a twin-screw extruder, and the feeding section temperature was 80-100℃, the compression section temperature was 130-150℃, the reaction section temperature was 160-170℃, the homogenization section temperature was 150-160℃, the die head temperature was 140-150℃, and the screw speed was 200 rpm to obtain an extrudate; the extrudate was water-cooled and shaped, then granulated by a granulator, and the granules were dried in an 80℃ forced-air drying oven for 4 hours, pulverized and passed through an 80-mesh sieve to obtain maleic anhydride-grafted polyvinyl chloride; Preparation of maleic anhydride-grafted polyvinyl chloride coated magnesium citrate: 600g of maleic anhydride-grafted polyvinyl chloride and 10kg of magnesium citrate were added to a twin-screw mixer. The temperature was set to 130-140℃ and the mixture was stirred at 300rpm for 40min to obtain the product. After cooling the product to room temperature, it was pulverized and passed through a 200-mesh sieve to obtain maleic anhydride-grafted polyvinyl chloride coated magnesium citrate.

[0033] Preparation Example 2 This preparation example is basically the same as preparation example 1, except that: Preparation of magnesium citrate: 10 kg of anhydrous citric acid was added to 50 L of deionized water and stirred until completely dissolved to obtain a citric acid solution; 5.29 kg of magnesium hydroxide powder was added to 20 L of deionized water and sonicated at 400 W for 15 min to obtain a suspension; the citric acid solution was added to a three-necked flask, and the suspension was added dropwise at 400 r / min and heated to 50 °C. During the dropwise addition, the pH of the system was maintained at 6.5-7.5 by controlling the dropwise rate of the suspension; after the dropwise addition was completed, the mixture was kept at the same temperature and stirred for 2 h to obtain a mixture. The reaction was considered complete when phenolphthalein indicator was added to the supernatant and no red color appeared; after the reaction was completed, the mixture was cooled to room temperature, and the solid product was separated by vacuum filtration. The filter cake was repeatedly washed with deionized water until the washing liquid was neutral; the cleaned filter cake was placed in a vacuum drying oven and dried at 60 °C for 6 h to obtain a powder; the powder was pulverized by an air jet mill to an average particle size of 3 μm to obtain magnesium citrate.

[0034] Preparation Example 3 This preparation example is basically the same as preparation example 1, except that: Preparation of magnesium citrate: 10 kg of anhydrous citric acid was added to 50 L of deionized water and stirred until completely dissolved to obtain a citric acid solution; 4.53 kg of magnesium hydroxide powder was added to 20 L of deionized water and sonicated at 400 W for 15 min to obtain a suspension; the citric acid solution was added to a three-necked flask, and the suspension was added dropwise at 400 r / min and heated to 50 °C. During the dropwise addition, the pH of the system was maintained stable at 6.5-7.5 by controlling the dropping rate of the suspension; after the dropwise addition was completed, the mixture was kept at this temperature and stirred for 2 h to obtain the final product. The reaction was completed when phenolphthalein indicator was added to the supernatant of the mixture and the mixture did not turn red. After the reaction, the mixture was cooled to room temperature and the solid product was separated by vacuum filtration. The filter cake was repeatedly washed with deionized water until the washing liquid was neutral. The cleaned filter cake was placed in a vacuum drying oven and dried for 2 hours at 60°C and -0.09 MPa, and then dried for 2 hours at 80°C and -0.09 MPa to obtain powder. The powder was then pulverized to an average particle size of 3 μm using an air jet mill to obtain magnesium citrate.

[0035] Preparation Example 4 This preparation example is basically the same as preparation example 1, except that: Preparation of magnesium citrate: 10 kg of anhydrous citric acid was added to 50 L of deionized water and stirred until completely dissolved to obtain a citric acid solution; 4.53 kg of magnesium hydroxide powder was added to 20 L of deionized water and sonicated at 400 W for 15 min to obtain a suspension; the citric acid solution was added to a three-necked flask, and the suspension was added dropwise at 400 r / min and heated to 50 °C. During the dropwise addition, the pH of the system was maintained at 6.5-7.5 by controlling the dropping rate of the suspension; after the dropwise addition was completed, the mixture was kept at the same temperature and stirred for 2 h to obtain a mixed solution. The reaction was considered complete when phenolphthalein indicator was added to the supernatant and no red color appeared. After the reaction, the mixture was cooled to room temperature, and the solid product was separated by vacuum filtration. The filter cake was repeatedly washed with deionized water until the washing liquid was neutral. The cleaned filter cake was placed in a vacuum drying oven and dried for 2 hours at 60℃ and -0.09MPa, and then dried for 2 hours at 80℃ and -0.09MPa to obtain powder. The powder was pulverized to an average particle size of 3μm by an air jet mill to obtain magnesium citrate. The obtained magnesium citrate was placed in a low-temperature plasma treatment instrument and treated for 90 seconds at 100W power under an oxygen atmosphere to obtain hydroxyl-activated magnesium citrate.

[0036] Preparation Example 5 This preparation example is basically the same as preparation example 1, except that: Preparation of magnesium citrate: 10 kg of anhydrous citric acid was added to 50 L of deionized water and stirred until completely dissolved to obtain a citric acid solution. 4.53 kg of magnesium hydroxide powder was added to 20 L of deionized water and sonicated at 400 W for 15 min to obtain a suspension. The citric acid solution was added to a three-necked flask, and the suspension was added dropwise at 400 r / min and heated to 50 °C. During the addition, the pH of the system was maintained stable at 6.5-7.5 by controlling the dropping rate of the suspension. After the addition was complete, the mixture was kept at this temperature and stirred for 2 h to obtain a mixed solution. The reaction was considered complete when phenolphthalein indicator was added to the supernatant and no red color appeared. The mixture was cooled to room temperature, and the solid product was separated by vacuum filtration. The filter cake was repeatedly washed with deionized water until the washing liquid was neutral. The cleaned filter cake was placed in a vacuum drying oven and dried for 2 hours at 60°C and -0.09 MPa, and then dried for 2 hours at 80°C and -0.09 MPa to obtain powder. The powder was pulverized to an average particle size of 3 μm by an air jet mill to obtain magnesium citrate. The obtained magnesium citrate was placed in a low-temperature plasma treatment instrument and treated for 90 seconds in an oxygen and water vapor atmosphere with a volume ratio of 3:1 at 100W to obtain hydroxyl-activated magnesium citrate.

[0037] Preparation Example 6 This preparation example is basically the same as preparation example 1, except that: Preparation of magnesium citrate: 10 kg of anhydrous citric acid was added to 50 L of deionized water and stirred until completely dissolved to obtain a citric acid solution. 4.53 kg of magnesium hydroxide powder was added to 20 L of deionized water and sonicated at 400 W for 15 min to obtain a suspension. The citric acid solution was added to a three-necked flask, and the suspension was added dropwise at 400 r / min and heated to 50 °C. During the addition, the pH of the system was maintained stable at 6.5-7.5 by controlling the dropping rate of the suspension. After the addition was complete, the mixture was kept at this temperature and stirred for 2 h to obtain a mixed solution. The reaction was considered complete when phenolphthalein indicator was added to the supernatant and no red color appeared. The mixture was cooled to room temperature, and the solid product was separated by vacuum filtration. The filter cake was repeatedly washed with deionized water until the washing liquid was neutral. The cleaned filter cake was placed in a vacuum drying oven and dried for 2 hours at 60°C and -0.09 MPa, and then dried for 2 hours at 80°C and -0.09 MPa to obtain powder. The powder was pulverized to an average particle size of 3 μm by an air jet mill to obtain magnesium citrate. The obtained magnesium citrate was placed in a low-temperature plasma treatment instrument and treated for 60 seconds in an oxygen and water vapor atmosphere with a volume ratio of 4:1 at 120W to obtain hydroxyl-activated magnesium citrate.

[0038] Preparation Example 7 This preparation example is basically the same as preparation example 1, except that: Preparation of maleic anhydride-grafted polyvinyl chloride: 10 kg of suspension PVC resin with an average degree of polymerization of 1000, 800 g of maleic anhydride, 60 g of di-tert-butyl peroxide, 150 g of ACR-401 and 30 g of antioxidant 1010 were mixed evenly to obtain a mixture. The mixture was added to a twin-screw extruder, and the feeding section temperature was 80-100℃, the compression section temperature was 130-150℃, the reaction section temperature was 160-170℃, the homogenization section temperature was 150-160℃, the die head temperature was 140-150℃, and the screw speed was 500 rpm to obtain an extrudate. After water cooling and shaping, the extrudate was granulated by a granulator, and then the granules were dried in an 80℃ forced-air drying oven for 4 hours. After pulverization and passing through an 80-mesh sieve, maleic anhydride-grafted polyvinyl chloride was obtained.

[0039] Preparation Example 8 This preparation example is basically the same as preparation example 1, except that: Preparation of maleic anhydride-grafted polyvinyl chloride: 10 kg of suspension PVC resin with an average degree of polymerization of 1000, 800 g of maleic anhydride, 60 g of di-tert-butyl peroxide, 150 g of ACR-401, 30 g of antioxidant 1010 and 200 g of styrene were mixed evenly to obtain a mixture. The mixture was added to a twin-screw extruder, and the feeding section temperature was 80-100℃, the compression section temperature was 130-150℃, the reaction section temperature was 160-170℃, the homogenization section temperature was 150-160℃, the die head temperature was 140-150℃, and the screw speed was 500 rpm to obtain an extrudate. After water cooling and shaping, the extrudate was granulated by a granulator, and then the granules were dried in an 80℃ forced-air drying oven for 4 hours. After pulverization and passing through an 80-mesh sieve, maleic anhydride-grafted polyvinyl chloride was obtained.

[0040] Preparation Example 9 This preparation example is basically the same as preparation example 1, except that: Preparation of maleic anhydride-grafted polyvinyl chloride: 10 kg of suspension PVC resin with an average degree of polymerization of 1000, 800 g of maleic anhydride, 60 g of di-tert-butyl peroxide, 150 g of ACR-401, 30 g of antioxidant 1010 and 300 g of styrene were mixed evenly to obtain a mixture. The mixture was added to a twin-screw extruder, and the feeding section temperature was 80-100℃, the compression section temperature was 130-150℃, the reaction section temperature was 160-170℃, the homogenization section temperature was 150-160℃, the die head temperature was 140-150℃, and the screw speed was 500 rpm to obtain an extrudate. After water cooling and shaping, the extrudate was granulated by a granulator, and then the granules were dried in an 80℃ forced-air drying oven for 4 hours. After pulverization and passing through an 80-mesh sieve, maleic anhydride-grafted polyvinyl chloride was obtained.

[0041] Preparation Example 10 This preparation example is basically the same as preparation example 1, except that: Preparation of maleic anhydride-grafted polyvinyl chloride coated magnesium citrate: 700g of maleic anhydride-grafted polyvinyl chloride and 10kg of magnesium citrate were added to a twin-screw mixer. The temperature was set to 130-140℃ and the mixture was stirred at 300rpm for 40min to obtain the product. After cooling the product to room temperature, it was pulverized and passed through a 200-mesh sieve to obtain maleic anhydride-grafted polyvinyl chloride coated magnesium citrate.

[0042] Preparation Example 11 This preparation example is basically the same as preparation example 1, except that: Preparation of maleic anhydride-grafted polyvinyl chloride coated magnesium citrate: 800g of maleic anhydride-grafted polyvinyl chloride and 10kg of magnesium citrate were added to a twin-screw mixer. The temperature was set to 130-140℃ and the mixture was stirred at 300rpm for 40min to obtain the product. After cooling the product to room temperature, it was pulverized and passed through a 200-mesh sieve to obtain maleic anhydride-grafted polyvinyl chloride coated magnesium citrate.

[0043] Preparation Example 12 This preparation example is basically the same as preparation example 1, except that: Preparation of maleic anhydride-grafted polyvinyl chloride coated magnesium citrate: 700g of maleic anhydride-grafted polyvinyl chloride and 10kg of magnesium citrate were added to a twin-screw mixer and run at 130℃ and 300rpm for 5min. Then, 100g of epoxidized soybean oil was added through the feed port. The temperature was set at 130-140℃ and the mixture was run at 300rpm for 35min to obtain the product. After cooling the product to room temperature, it was pulverized and passed through a 200-mesh sieve to obtain maleic anhydride-grafted polyvinyl chloride coated magnesium citrate.

[0044] Preparation Example 13 This preparation example is basically the same as preparation example 1, except that: Preparation of maleic anhydride-grafted polyvinyl chloride coated magnesium citrate: 700g of maleic anhydride-grafted polyvinyl chloride and 10kg of magnesium citrate were added to a twin-screw mixer and run at 130℃ and 300rpm for 5min. Then, 150g of epoxidized soybean oil was added through the feed port. The temperature was set at 130-140℃ and the mixture was run at 300rpm for 35min to obtain the product. After cooling the product to room temperature, it was pulverized and passed through a 200-mesh sieve to obtain maleic anhydride-grafted polyvinyl chloride coated magnesium citrate.

[0045] Example 1 This embodiment provides a high-strength PVC foam, comprising 10 kg SG-5 PVC resin, 1.5 kg maleic anhydride-grafted polyvinyl chloride coated magnesium citrate, 0.4 kg calcium-zinc stabilizer, 0.8 kg plasticizer dioctyl phthalate, and 0.5 kg styrene-butadiene rubber; Among them, the maleic anhydride-grafted polyvinyl chloride-coated magnesium citrate salt comes from Preparation Example 1.

[0046] This embodiment also provides a method for preparing the above-mentioned high-strength PVC foam, including the following steps: (1) Add SG-5 PVC resin to a high-speed mixer according to the above ratio, add calcium zinc stabilizer and dioctyl phthalate in sequence (add in 3 parts), stir at 500 rpm for 3 min, add styrene-butadiene rubber, stir at 1200 rpm for 5 min, and control the material temperature below 80℃ during the process; reduce the mixer speed to 800 rpm, slowly add maleic anhydride grafted polyvinyl chloride coated magnesium citrate salt, stir for 8 min to obtain a uniform premix; (2) The above premixed material is fed into a twin-screw extruder. The screw speed is 200 rpm, the vacuum degree is -0.07 MPa, the material stays for 3 minutes, and after extrusion, it is water-cooled and pelletized to obtain foamed masterbatch. The temperature of each section of the twin-screw extruder is set as follows: feeding section 140-150℃, compression section 160-170℃, homogenization section 170-180℃, and die head temperature 165-175℃. (3) Add the foaming masterbatch to the mold of the flat vulcanizing machine. During the preheating stage, maintain the pressure at 160℃ and 5MPa for 3 minutes; quickly reduce the pressure to 0.5MPa and raise the temperature to 175℃ for 5 minutes; transfer the mold to a 25℃ cold water bath and maintain the pressure at 0.5MPa for 10 minutes to obtain the foam product; remove the foam product, remove the flash and burrs, and place it at room temperature for 24 hours; place the product in a 60℃ forced-air drying oven for aging treatment for 8 hours to obtain PVC foam.

[0047] Example 2 This embodiment is basically the same as Embodiment 1, except that this embodiment provides a high-strength PVC foam, including 10 kg SG-5 PVC resin, 1.65 kg maleic anhydride grafted polyvinyl chloride coated magnesium citrate, 0.45 kg calcium zinc stabilizer, 0.9 kg plasticizer dioctyl phthalate and 0.55 kg styrene-butadiene rubber; Among them, the maleic anhydride-grafted polyvinyl chloride-coated magnesium citrate salt comes from Preparation Example 1.

[0048] Example 3 This embodiment is basically the same as Embodiment 1, except that this embodiment provides a high-strength PVC foam, including 10kg SG-5 PVC resin, 1.8kg maleic anhydride-grafted polyvinyl chloride coated magnesium citrate, 0.5kg calcium zinc stabilizer, 1kg plasticizer dioctyl phthalate and 0.6kg styrene-butadiene rubber; Among them, the maleic anhydride-grafted polyvinyl chloride-coated magnesium citrate salt comes from Preparation Example 1.

[0049] Example 4 This embodiment is basically the same as Example 1, except that the maleic anhydride-grafted polyvinyl chloride-coated magnesium citrate salt comes from Preparation Example 2.

[0050] Example 5 This embodiment is basically the same as Example 1, except that the maleic anhydride-grafted polyvinyl chloride-coated magnesium citrate salt comes from Preparation Example 3.

[0051] Example 6 This embodiment is basically the same as Example 1, except that the maleic anhydride-grafted polyvinyl chloride-coated magnesium citrate salt comes from Preparation Example 4.

[0052] Example 7 This embodiment is basically the same as Example 1, except that the maleic anhydride-grafted polyvinyl chloride-coated magnesium citrate salt comes from Preparation Example 5.

[0053] Example 8 This embodiment is basically the same as Example 1, except that the maleic anhydride-grafted polyvinyl chloride-coated magnesium citrate salt comes from Preparation Example 6.

[0054] Example 9 This embodiment is basically the same as Example 1, except that the maleic anhydride-grafted polyvinyl chloride-coated magnesium citrate salt comes from Preparation Example 7.

[0055] Example 10 This embodiment is basically the same as Example 1, except that the maleic anhydride-grafted polyvinyl chloride-coated magnesium citrate salt comes from Preparation Example 8.

[0056] Example 11 This embodiment is basically the same as Example 1, except that the maleic anhydride-grafted polyvinyl chloride-coated magnesium citrate salt comes from Preparation Example 9.

[0057] Example 12 This embodiment is basically the same as Example 1, except that the maleic anhydride-grafted polyvinyl chloride coated magnesium citrate salt comes from Preparation Example 10.

[0058] Example 13 This embodiment is basically the same as Example 1, except that the maleic anhydride-grafted polyvinyl chloride-coated magnesium citrate salt comes from Preparation Example 11.

[0059] Example 14 This embodiment is basically the same as Example 1, except that the maleic anhydride-grafted polyvinyl chloride-coated magnesium citrate salt comes from Preparation Example 12.

[0060] Example 15 This embodiment is basically the same as Example 1, except that the maleic anhydride-grafted polyvinyl chloride-coated magnesium citrate salt comes from Preparation Example 13.

[0061] Comparative Example 1 This comparative example provides a high-strength PVC foam, comprising 10 kg of SG-5 PVC resin, 1.5 kg of modified magnesium citrate, 0.4 kg of calcium-zinc stabilizer, 0.8 kg of plasticizer dioctyl phthalate, and 0.5 kg of styrene-butadiene rubber. The preparation of modified magnesium citrate salt involved the following steps: 10 kg of anhydrous citric acid was added to 50 L of deionized water and stirred until completely dissolved to obtain a citric acid solution; 4.53 kg of magnesium hydroxide powder was added to 18 L of deionized water and sonicated at 400 W for 15 min to obtain a suspension; the citric acid solution was added to a three-necked flask, and the suspension was added dropwise at 400 r / min and heated to 50 °C. During the dropwise addition, the pH of the system was maintained stable at 6.5-7.5 by controlling the dropping rate of the suspension; after the dropwise addition was completed, the mixture was kept at this temperature and stirred for 2 h to obtain a mixed solution. The reaction was considered complete when phenolphthalein indicator was added to the supernatant and the solution did not turn red. After the reaction, the mixture was cooled to room temperature, and the solid product was separated by vacuum filtration. The filter cake was repeatedly washed with deionized water until the washing liquid was neutral. The cleaned filter cake was placed in a vacuum drying oven and dried at 60°C for 6 hours to obtain powder. The powder was pulverized to an average particle size of 3 μm using an air jet mill to obtain magnesium citrate. An ethanol-silane coupling agent KH550 mixed solvent was added to the magnesium citrate, ultrasonically vibrated for 30 minutes, filtered and dried to obtain modified magnesium citrate.

[0062] This comparative example also provides a method for preparing the above-mentioned high-strength PVC foam, comprising the following steps: (1) Add SG-5 PVC resin to a high-speed mixer according to the above ratio, add calcium zinc stabilizer and dioctyl phthalate in sequence (add in 3 parts), stir at 500 rpm for 3 minutes, add styrene-butadiene rubber, stir at 1200 rpm for 5 minutes, and control the material temperature below 80℃ during the process; reduce the mixer speed to 800 rpm, slowly add modified magnesium citrate salt, and stir for 8 minutes to obtain a uniform premix. (2) The above premixed material is fed into a twin-screw extruder. The screw speed is 200 rpm, the vacuum degree is -0.07 MPa, the material stays for 3 minutes, and after extrusion, it is water-cooled and pelletized to obtain foamed masterbatch. The temperature of each section of the twin-screw extruder is set as follows: feeding section 140-150℃, compression section 160-170℃, homogenization section 170-180℃, and die head temperature 165-175℃. (3) Add the foaming masterbatch to the mold of the flat vulcanizing machine. During the preheating stage, maintain the pressure at 160℃ and 5MPa for 3 minutes; quickly reduce the pressure to 0.5MPa and raise the temperature to 175℃ for 5 minutes; transfer the mold to a 25℃ cold water bath and maintain the pressure at 0.5MPa for 10 minutes to obtain the foam product; remove the foam product, remove the flash and burrs, and place it at room temperature for 24 hours; place the product in a 60℃ forced-air drying oven for aging treatment for 8 hours to obtain PVC foam.

[0063] Performance testing Mechanical property testing: The tensile strength, elongation at break and compressive strength of the PVC foams provided in Examples 1-15 and Comparative Example 1 were tested in accordance with the testing standards GB / T 1040.1-2006 and GB / T 8813-2022. The test results are shown in Table 1.

[0064] Density test: The density of the PVC foam provided in Examples 1-15 and Comparative Example 1 was tested in accordance with the testing standard GB / T6343-2009. The test results are shown in Table 1.

[0065] Table 1 Performance test data of high-strength PVC foam in Examples 1-15 and Comparative Example 1

[0066] As can be seen from Example 1 and Comparative Example 1 and Table 1, the addition of maleic anhydride-grafted PVC-coated magnesium citrate salt to the PVC matrix in this application, compared with silane-modified magnesium citrate salt, can further improve the mechanical strength of PVC foam. This is because the maleic anhydride-grafted PVC-coated magnesium citrate salt can form molecular-level entanglement and chemical bonding with the PVC molecular chains. Although the silane coupling agent improves the surface polarity of magnesium citrate salt, the compatibility between the small molecule modified layer and the PVC matrix is ​​limited, and the interfacial bonding strength is weaker than that of the coated type. Therefore, the strength improvement of PVC foam is insufficient.

[0067] Referring to Examples 5-7 and Table 1, it can be seen that by plasma treatment of magnesium citrate, this application can improve its strength density, increase the binding sites of magnesium citrate and maleic anhydride-grafted polyvinyl chloride, and improve the interfacial bonding between the two, thereby further improving the compatibility between magnesium citrate and PVC matrix, and thus further improving the mechanical properties of the PVC foam. At the same time, when the plasma uses a mixed gas atmosphere of oxygen and water vapor, the bonding between magnesium citrate and maleic anhydride-grafted polyvinyl chloride can be further improved.

[0068] Referring to Examples 9-11 and Table 1, it can be seen that this application, by adding an appropriate amount of styrene during the preparation of maleic anhydride-grafted polyvinyl chloride (PVC), utilizes the higher copolymerization activity of styrene and maleic anhydride compared to the homopolymerization of maleic anhydride, thereby inhibiting the homopolymerization of maleic anhydride itself and reducing the residue of free maleic anhydride. Simultaneously, the synergistic effect of styrene and maleic anhydride provides more grafting sites for PVC molecular chains, increasing the grafting rate and improving the uniformity of graft chain distribution in the PVC matrix. This reduces the risk of crosslinking caused by local aggregation of maleic anhydride, ultimately enhancing the compatibility of maleic anhydride-grafted PVC with the PVC matrix and magnesium citrate, further improving the strength of the prepared PVC foam.

[0069] Referring to Examples 12, 14, and 15 and Table 1, it can be seen that this application adds an appropriate amount of epoxidized soybean oil during the preparation of maleic anhydride-grafted polyvinyl chloride coated magnesium citrate. The epoxy groups in the epoxidized soybean oil's molecular structure react chemically with the hydroxyl groups on the surface of magnesium citrate and the anhydride groups in the maleic anhydride-grafted polyvinyl chloride, thereby enhancing the interfacial bonding force and improving compatibility. At the same time, the epoxidized soybean oil can also act as a plasticizer, reducing the viscosity of the system, improving processing performance, and absorbing the hydrogen chloride produced during the decomposition of polyvinyl chloride resin, playing an auxiliary stabilizing role and improving the strength of the material.

[0070] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A high-strength PVC foam, characterized in that, The raw materials include the following parts by weight: 100 parts SG-5 PVC resin, 15-18 parts maleic anhydride-grafted polyvinyl chloride coated magnesium citrate, 4-5 parts calcium-zinc stabilizer, 8-10 parts plasticizer and 5-6 parts styrene-butadiene rubber. The maleic anhydride-grafted polyvinyl chloride coated magnesium citrate salt is prepared by melt blending maleic anhydride-grafted polyvinyl chloride with magnesium citrate salt.

2. The high-strength PVC foam according to claim 1, characterized in that, The preparation method of maleic anhydride-grafted polyvinyl chloride coated magnesium citrate is as follows: maleic anhydride-grafted polyvinyl chloride and magnesium citrate are added to a twin-screw mixer and mixed at 130-140℃ and 300-400rpm for 30-40min. After cooling to room temperature, the mixture is pulverized to obtain maleic anhydride-grafted polyvinyl chloride coated magnesium citrate. The amount of maleic anhydride-grafted polyvinyl chloride added is 6%-8% of the mass of magnesium citrate.

3. The high-strength PVC foam according to claim 2, characterized in that, When maleic anhydride-grafted polyvinyl chloride and magnesium citrate are mixed, epoxidized soybean oil is also added, and the amount of epoxidized soybean oil added is 1%-1.5% of the mass of magnesium citrate.

4. The high-strength PVC foam according to claim 1, characterized in that, The method for preparing the magnesium citrate salt includes the following steps: (1) Add magnesium hydroxide to deionized water and ultrasonically disperse to form a suspension; add anhydrous citric acid to deionized water and stir until completely dissolved to obtain a citric acid solution; (2) Add the suspension dropwise into the citric acid solution and stir for 1-2 hours at 50°C and pH 5.8-6.

8. (3) After the reaction is complete, the sample is filtered, washed and dried to obtain magnesium citrate. The molar ratio of anhydrous citric acid to magnesium hydroxide is 2:(3-3.5).

5. The high-strength PVC foam according to claim 4, characterized in that, In step (3), the drying process adopts a step-by-step drying method, specifically: in the first stage, the drying is carried out at a temperature of 55-65℃ and a vacuum degree of -0.085~-0.095MPa for 1.5-2.5h; in the second stage, the drying is carried out at a temperature of 75-85℃ and a vacuum degree of -0.085~-0.095MPa for 1.5-2.5h.

6. The high-strength PVC foam according to claim 4, characterized in that, In step (3), the magnesium citrate is further subjected to hydroxyl activation treatment, specifically by subjecting the magnesium citrate to low-temperature plasma treatment at 100-120W power for 60-90s.

7. The high-strength PVC foam according to claim 6, characterized in that, During the low-temperature plasma treatment, a mixture of oxygen and water vapor with a volume ratio of (3-4):1 is used as the gas atmosphere.

8. The high-strength PVC foam according to claim 1, characterized in that, The method for preparing maleic anhydride-grafted polyvinyl chloride includes the following steps: S1, mix the following raw materials in parts by weight evenly to obtain a mixture: 100 parts PVC resin, 5-8 parts maleic anhydride, 0.4-0.6 parts di-tert-butyl peroxide, 1.5 parts ACR-401 and 0.3 parts antioxidant 1010; S2, the mixture is added to a twin-screw extruder, extruded, granulated and dried to obtain maleic anhydride-grafted polyvinyl chloride; wherein the temperature of the extruder feeding section is 80-100℃, the temperature of the compression section is 130-150℃, the temperature of the reaction section is 160-170℃, the temperature of the homogenization section is 150-160℃ and the temperature of the die head is 140-150℃.

9. The high-strength PVC foam according to claim 8, characterized in that, In S1, the raw material also includes 2-3 parts by weight of styrene.

10. A method for preparing high-strength PVC foam as described in any one of claims 1-9, characterized in that, Includes the following steps: According to the compounding ratio, SG-5 PVC resin, calcium zinc stabilizer, and plasticizer are mixed in sequence, then styrene-butadiene rubber is added, and then maleic anhydride-grafted polyvinyl chloride-coated magnesium citrate salt is added and mixed evenly to obtain a premix. The premixed material is extruded and granulated to obtain foaming masterbatch; High-strength PVC foam is obtained by molding and foaming the foaming masterbatch.

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