Flame-retardant polypropylene foamed plastic and preparation method thereof

Abstract

The invention discloses flame-retardant polypropylene foamed plastic and a preparation method thereof, and relates to the technical field of thermal insulation materials. The preparation method of the flame-retardant polypropylene foamed plastic comprises the following steps: adding polypropylene and a functional additive into a charging barrel of an extruder according to the raw material ratio, and carrying out melt blending, extrusion and granulation to obtain microparticles; the microparticles, deionized water and a dispersing agent are added into a high-pressure reaction kettle, a physical foaming agent is introduced, heat preservation and pressure maintaining treatment is conducted, pressure relief, cooling and drying are conducted, and foamed beads are obtained; the foamed beads are subjected to water vapor molding and annealing shaping, and the flame-retardant polypropylene foamed plastic is obtained. The polypropylene foamed plastic prepared by the invention has the characteristics of flame retardance and excellent mechanical properties.

Description

Technical Field

[0001] The invention relates to the technical field of thermal insulation materials, and in particular to a flame-retardant polypropylene foam plastic and a preparation method thereof. Background Art

[0002] With the rapid development of fresh food e-commerce and the increasing awareness of consumers about food safety, the proportion of short-distance distribution transportation of fresh food products in cold chain logistics has increased significantly, and multi-temperature zone insulation boxes have become efficient equipment for the same-box distribution of goods of different types and different storage temperatures. Polymer foam materials are gas / solid two-phase composite materials with polymer as continuous phase and bubbles as dispersed phase. The bubbles dispersed in the polymer matrix can significantly change the morphology and structure of the polymer, making it have the advantages of light weight, low thermal conductivity, and good thermal insulation. There are many types of polymer foam materials, which can be roughly divided into three categories according to the matrix resin: polyurethane soft and hard foams, polystyrene foams and polyolefin foams. In recent years, with the continuous exploration of foaming technology, foamed polypropylene materials have attracted widespread attention for their excellent performance. The foamed spherical particles obtained by foaming foamed polypropylene microparticles are used for secondary expansion in the mold cavity of the molding equipment and make them adhere to each other, and can be used to prepare products with complex shapes. Compared with other foam materials, expanded polypropylene bead products have the following advantages: (1) Polypropylene has better rigidity than polyethylene and better impact resistance than polystyrene. The mechanical strength of the foamed material is at the highest level among plastic foamed materials. It has a medium degree of compressive resistance and excellent resilience. (2) Polypropylene has a high load deformation temperature and can usually withstand high temperatures of 130°C. (3) Compared with the chlorofluorocarbons used in the processing of polystyrene foam and the isocyanates residual in polyurethane foam, expanded polypropylene beads prepared using foaming agents such as carbon dioxide are non-toxic, harmless and environmentally friendly materials. (4) The polypropylene material molecular chain contains side methyl groups, which are more susceptible to β-degradation, which is conducive to the degradation of the material in nature.

[0003] The foaming process of expanded polypropylene beads is divided into intermittent kettle foaming, continuous extrusion foaming, compression molding and injection molding foaming. The intermittent kettle method and continuous extrusion method are generally used to prepare expanded polypropylene beads. The foaming mechanism of the kettle method is the principle of supersaturated gas. First, a polymer / gas homogeneous saturation state is formed, which triggers the growth of a large number of gas nuclei. The gas dissolved in the polypropylene melt quickly diffuses to the nucleation point, and the bubbles undergo a process of expansion to cooling and shaping, and finally form foamed beads. The intermittent kettle method has a low processing temperature and no screw shearing effect, which can maintain a high melt strength and make it easier to achieve high-ratio and high-closed-cell foaming. However, since polypropylene is a highly crystalline polymer, its softening point is close to its melting point, and its melt viscosity is very sensitive to temperature changes. When polypropylene is heated to its melting temperature, as the processing temperature increases, the viscosity of the polypropylene resin drops sharply, causing the melt surface tension to be too low, and the gas decomposed by the foaming agent is difficult to remain in the melt and cannot form bubbles. In addition, the heat capacity of polypropylene resin is large, and a large amount of heat needs to be released when the resin changes from a molten state to a crystalline state, which also reduces the melt strength of polypropylene. After foaming, the bubbles are easily destroyed, and the gas escapes, causing the bubble collapse and the decrease in bubble stability. Summary of the invention

[0004] The purpose of the present invention is to provide a flame retardant polypropylene foam plastic and a preparation method thereof, so as to solve the following technical problems: Due to the limitations of the existing physical and chemical properties of polypropylene resins, the melt surface tension is difficult to control during the polypropylene foaming process, and the melt is difficult to form bubbles; and the polypropylene resin that forms bubbles releases a large amount of heat when it changes from a molten state to a crystalline state, resulting in a decrease in melt strength and the destruction of already formed bubbles.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A method for preparing a flame retardant polypropylene foam plastic comprises the following steps: S1: According to the raw material ratio, high melt strength polypropylene and functional additives are added into the extruder barrel for melt blending, extrusion and granulation to obtain microgranules; S2: adding microparticles, deionized water and dispersant into a high-pressure reactor, introducing a physical foaming agent, performing heat and pressure preservation treatment, rapidly releasing pressure, cooling and drying to obtain foamed beads; S3: molding the foamed beads by steam molding and annealing to obtain a flame-retardant polypropylene foam plastic; The preparation method of the functional additive comprises the following steps: A1: Add deionized water, anhydrous ethanol and aminopropyl triethoxysilane into a reaction kettle and disperse them evenly, add nano-silicon dioxide, control the temperature at 40-50°C, keep the temperature for reaction for 1-3 hours, wash and dry to obtain modified silicon dioxide; A2: In a nitrogen atmosphere, modified silica, deionized water, formaldehyde solution and phosphorous acid are added into a reaction kettle and dispersed evenly. The temperature is controlled at 60-70°C, and the reaction is kept warm for 6-12 hours. The mixture is centrifuged, washed and dried to obtain a functional additive.

[0006] Preferably, the addition ratio of deionized water, anhydrous ethanol, aminopropyltriethoxysilane and nano-silicon dioxide in A1 is 1 mL: 4-9 mL: 1 g: 1-5 g.

[0007] Preferably, the formaldehyde solution in A2 is a 20-40% w / v methanol aqueous solution; the addition ratio of modified silica, deionized water, 20-40% w / v formaldehyde solution, and phosphorous acid is 1 g: 100-200 mL: 7.5-15 mL: 10-15 g.

[0008] Preferably, the preparation method of high melt strength polypropylene comprises the following steps: in a nitrogen atmosphere, adding polypropylene, xylene and benzoyl peroxide into a high-pressure reactor, mixing styrene and glycidyl methacrylate evenly and adding them into the reactor, controlling the temperature at 120-130° C., and keeping the temperature for 3-6 hours to obtain high melt strength polypropylene.

[0009] Preferably, the addition ratio of polypropylene, xylene, styrene, benzoyl peroxide and glycidyl methacrylate is 1 g: 2-20 mL: 0.001-0.01 g: 0.03-0.06 g: 0.03-0.06 g.

[0010] Preferably, the temperature of the barrel mixing section of the extruder in S1 is 180-210° C.; the temperature of the extrusion die of the extruder is 100-150° C.; and the pressure of the extrusion die of the extruder is 10-25 MPa.

[0011] Preferably, the addition ratio of high melt strength polypropylene to functional additives in S1 is 100:2-5.

[0012] Preferably, the specific steps of the heat preservation and pressure treatment in S2 are: controlling the temperature at 130-140°C and the pressure at 1.5-2.5MPa, and treating for 0.5-1h; and the pressure relief rate of the rapid pressure relief is 70-90MPa / s.

[0013] Preferably, the dispersion medium in S2 is deionized water; the physical foaming agent is carbon dioxide and / or nitrogen; the dispersant is at least one of sodium dodecylbenzene sulfonate, calcium stearate, sodium benzene sulfonate, vinyl bisstearamide and stearic acid monoglyceride; the addition ratio of the microparticles: dispersion medium: dispersant is 100g: 100-200mL: 0.01-0.1g; the density of the foamed beads is 0.015-0.045g / cm 3 .

[0014] A flame retardant polypropylene foam plastic is made by any of the above preparation methods.

[0015] Beneficial effects of the present invention: (1) The present application first uses an aminosilane coupling agent to perform organic amino modification on the surface of nano-silica to obtain modified silica; and uses nano-silica to react with formaldehyde and phosphorous acid in an aqueous phase to produce a Mannich reaction to obtain a functional additive. The present application also uses polypropylene as a matrix, styrene and glycidyl methacrylate as grafting monomers to obtain high melt strength polypropylene through grafting polymerization. The present application uses the high melt strength polypropylene as a raw material, adds a functional additive, and prepares microparticles. In the process of preparing microparticles, the epoxy groups grafted on the molecular chain of high melt strength polypropylene and the phosphate groups grafted on the surface of the functional additive undergo a ring-opening reaction to graft silica onto the high melt strength polypropylene to obtain microparticles.

[0016] The present application utilizes a reactor method to place microparticles into a reactor, add a dispersion medium and a physical foaming agent for use, raise the temperature to increase the pressure in the reactor, maintain the pressure at the foaming temperature for a period of time, and form a supersaturated system by causing thermodynamic instability through rapid pressure relief. During the reaction, the polypropylene resin separates from the water vapor and the physical foaming agent, and the bubbles begin to nucleate and grow in large quantities. After stabilization, they are cooled and shaped to form foamed beads. The dispersion medium added in the preparation process of the foamed beads of the present application forms water vapor in a high temperature and high pressure environment, effectively reducing the pressure required for the reaction. The foamed bead preparation method of the present application has simple process conditions that are easy to control, a high foaming ratio, and a good pore structure, and can be subjected to secondary foaming.

[0017] (2) The functional additives prepared in this application are grafted with high melt strength polypropylene through chemical bonds and are evenly dispersed in the melt to form hot spots, effectively reducing the viscosity and surface tension of local areas, so that when the foaming agent decomposes, it is easy to adsorb gas to form bubble nuclei. At the same time, it accelerates the cooling rate of polypropylene, prevents excessive bubble growth, and makes the pore structure of the growing bubbles uniform and dense, effectively avoiding the formation of large bubbles and pore merging during the foaming process due to silica agglomeration. Moreover, with the addition of the functional additives of this application, polypropylene is effectively endowed with good flame retardant properties and mechanical properties. The flame-retardant polypropylene foam plastic prepared in this application has dense pores, uniform pore size distribution, closed-cell structure and a density of 0.015-0.045g / cm 3 The foamed beads can be widely used in the fields of thermal insulation tableware, product shock-absorbing packaging, etc. DETAILED DESCRIPTION

[0018] The following will be described clearly and completely in conjunction with the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] Example 1 The preparation method of the functional additive comprises the following steps: A1: Add 10 mL of deionized water, 40 mL of anhydrous ethanol, and 10 g of aminopropyltriethoxysilane into a reaction kettle and disperse them evenly, add 20 g of nano-silicon dioxide, control the temperature to 40°C, keep the temperature for 1 hour, wash and dry to obtain modified silicon dioxide; A2: In a nitrogen atmosphere, 10 g of modified silica, 1000 mL of deionized water, 75 mL of 40% w / v formaldehyde aqueous solution, and 100 g of phosphorous acid were added into a reactor and dispersed evenly. The temperature was controlled at 60°C, and the reaction was kept warm for 6 hours. The functional additive was obtained by centrifugation, washing, and drying.

[0020] Example 2 The preparation method of the functional additive comprises the following steps: A1: Add 10 mL of deionized water, 70 mL of anhydrous ethanol, and 10 g of aminopropyltriethoxysilane into a reaction kettle and disperse them evenly, add 20 g of nano-silicon dioxide, control the temperature to 45°C, keep the temperature for 2 hours, wash, and dry to obtain modified silicon dioxide; A2: In a nitrogen atmosphere, 10 g of modified silica, 1500 mL of deionized water, 110 mL of 40% w / v formaldehyde aqueous solution, and 120 g of phosphorous acid were added into a reactor and dispersed evenly. The temperature was controlled at 65°C, and the reaction was kept warm for 9 hours. The mixture was centrifuged, washed, and dried to obtain a functional additive.

[0021] Example 3 The preparation method of the functional additive comprises the following steps: A1: Add 10 mL of deionized water, 90 mL of anhydrous ethanol, and 10 g of aminopropyltriethoxysilane into a reaction kettle and disperse them evenly, add 20 g of nano-silicon dioxide, control the temperature to 50°C, keep the temperature for 3 hours, wash and dry to obtain modified silicon dioxide; A2: In a nitrogen atmosphere, 10 g of modified silica, 2000 mL of deionized water, 150 mL of 40% w / v formaldehyde aqueous solution, and 150 g of phosphorous acid were added into a reactor and dispersed evenly. The temperature was controlled at 70°C, and the reaction was kept warm for 12 h. The functional additive was obtained by centrifugation, washing, and drying.

[0022] Example 4 The method for preparing high melt strength polypropylene comprises the following steps: In a nitrogen atmosphere, 1 g of polypropylene particles T30s, 10 mL of xylene, and 0.005 g of benzoyl peroxide were added to a high-pressure reactor, and 0.04 g of styrene and 0.05 g of glycidyl methacrylate were mixed evenly and added to the reactor. The temperature was controlled at 120°C and the reaction was kept warm for 6 hours to obtain high melt strength polypropylene.

[0023] Example 5 A method for preparing a flame retardant polypropylene foam plastic comprises the following steps: S1: According to the raw material ratio, 100g of the high melt strength polypropylene prepared in Example 4 and 5g of the functional additive prepared in Example 1 were added to the barrel of a twin-screw blending extruder for melt blending. The temperature of the barrel mixing section was 210°C, the temperature of the extrusion die of the extruder was 130°C, and the pressure of the extrusion die was 15MPa. Extrusion and underwater pelletizing were performed to obtain micro-particles with a length of 1mm and a diameter of 0.8mm. S2: 100 g of microparticles, 100 mL of deionized water, and 0.1 g of calcium stearate were added to a high-pressure reactor, and a physical foaming agent was introduced. The temperature was controlled at 130° C. and the pressure was 2.3 MPa. The reaction was continued for 0.5 h. The pressure release rate was 77 MPa / s for rapid pressure release, cooling, and drying to obtain foamed beads. S3: The foamed beads are molded by steam molding. Under a steam pressure of 0.4 MPa, the beads undergo secondary expansion and adhere to each other, and are annealed and shaped to obtain a flame-retardant polypropylene foam plastic.

[0024] Example 6 A method for preparing a flame retardant polypropylene foam plastic comprises the following steps: S1: According to the raw material ratio, 100g of the high melt strength polypropylene prepared in Example 4 and 5g of the functional additive prepared in Example 2 were added to the barrel of a twin-screw blending extruder for melt blending. The temperature of the barrel mixing section was 210°C, the temperature of the extruder extrusion die was 130°C, and the pressure of the extrusion die was 15MPa. Extrusion and underwater pelletizing were performed to obtain micro-particles with a length of 1mm and a diameter of 0.8mm. S2: 100 g of microparticles, 100 mL of deionized water, and 0.1 g of calcium stearate were added to a high-pressure reactor, and a physical foaming agent was introduced. The temperature was controlled at 130° C. and the pressure was 2.3 MPa. The reaction was continued for 0.5 h. The pressure release rate was 77 MPa / s for rapid pressure release, cooling, and drying to obtain foamed beads. S3: The foamed beads are molded by steam molding. Under a steam pressure of 0.4 MPa, the beads undergo secondary expansion and adhere to each other, and are annealed and shaped to obtain a flame-retardant polypropylene foam plastic.

[0025] Example 7 A method for preparing a flame retardant polypropylene foam plastic comprises the following steps: S1: According to the raw material ratio, 100g of the high melt strength polypropylene prepared in Example 4 and 5g of the functional additive prepared in Example 3 were added to the barrel of a twin-screw blending extruder for melt blending. The temperature of the barrel mixing section was 210°C, the temperature of the extrusion die of the extruder was 130°C, and the pressure of the extrusion die was 15MPa. Extrusion and underwater pelletizing were performed to obtain micro-particles with a length of 1mm and a diameter of 0.8mm. S2: 100 g of microparticles, 100 mL of deionized water, and 0.1 g of calcium stearate were added to a high-pressure reactor, and a physical foaming agent was introduced. The temperature was controlled at 130° C. and the pressure was 2.3 MPa. The reaction was continued for 0.5 h. The pressure release rate was 77 MPa / s for rapid pressure release, cooling, and drying to obtain foamed beads. S3: The foamed beads are molded by steam molding. Under a steam pressure of 0.4 MPa, the beads undergo secondary expansion and adhere to each other, and are annealed and shaped to obtain a flame-retardant polypropylene foam plastic.

[0026] Comparative Example 1 The preparation method of the functional additive comprises the following steps: A1: Add 10 mL of deionized water, 70 mL of anhydrous ethanol, and 10 g of aminopropyltriethoxysilane into a reaction kettle and disperse them evenly. Add 20 g of nano-silicon dioxide, control the temperature to 45°C, keep the reaction warm for 2 hours, wash, and dry to obtain a functional additive.

[0027] Comparative Example 2 The preparation method of high melt strength polypropylene comprises the following steps: In a nitrogen atmosphere, 1 g of polypropylene particles T30s, 10 mL of xylene, and 0.005 g of benzoyl peroxide were added to a high-pressure reactor, and 0.04 g of styrene was added to the reactor. The temperature was controlled at 120° C. and the reaction was kept warm for 6 hours to obtain high melt strength polypropylene.

[0028] Comparative Example 3 A method for preparing a flame retardant polypropylene foam plastic comprises the following steps: S1: According to the raw material ratio, 100g of high melt strength polypropylene prepared in Example 4 and 5g of the functional additive prepared in Comparative Example 1 were added to the barrel of a twin-screw blending extruder for melt blending. The temperature of the barrel mixing section was 210°C, the temperature of the extrusion die of the extruder was 130°C, and the pressure of the extrusion die was 15MPa. Extrusion and underwater pelletization were performed to obtain micro-particles with a length of 1mm and a diameter of 0.8mm. S2: 100 g of microparticles, 100 mL of deionized water, and 0.1 g of calcium stearate were added to a high-pressure reactor, and a physical foaming agent was introduced. The temperature was controlled at 130° C. and the pressure was 2.3 MPa. The reaction was continued for 0.5 h. The pressure release rate was 77 MPa / s for rapid pressure release, cooling, and drying to obtain foamed beads. S3: The foamed beads are molded by steam molding. Under a steam pressure of 0.4 MPa, the beads undergo secondary expansion and adhere to each other, and are annealed and shaped to obtain a flame-retardant polypropylene foam plastic.

[0029] Comparative Example 4 A method for preparing a flame retardant polypropylene foam plastic comprises the following steps: S1: According to the raw material ratio, 100g of high melt strength polypropylene prepared in Comparative Example 2 and 5g of the functional additive prepared in Example 2 were added to the barrel of a twin-screw blending extruder for melt blending. The temperature of the barrel mixing section was 210°C, the temperature of the extruder extrusion die was 130°C, and the pressure of the extrusion die was 15MPa. Extrusion and underwater pelletizing were performed to obtain micro-particles with a length of 1mm and a diameter of 0.8mm. S2: 100 g of microparticles, 100 mL of deionized water, and 0.1 g of calcium stearate were added to a high-pressure reactor, and a physical foaming agent was introduced. The temperature was controlled at 130° C. and the pressure was 2.3 MPa. The reaction was continued for 0.5 h. The pressure release rate was 77 MPa / s for rapid pressure release, cooling, and drying to obtain foamed beads. S3: The foamed beads are molded by steam molding. Under a steam pressure of 0.4 MPa, the beads undergo secondary expansion and adhere to each other, and are annealed and shaped to obtain a flame-retardant polypropylene foam plastic.

[0030] Comparative Example 5 A method for preparing a flame retardant polypropylene foam plastic comprises the following steps: S1: According to the raw material ratio, 100g of high melt strength polypropylene prepared in Comparative Example 2 and 5g of the functional additive prepared in Comparative Example 1 were added to the barrel of a twin-screw blending extruder for melt blending. The temperature of the barrel mixing section was 210°C, the temperature of the extrusion die of the extruder was 130°C, and the pressure of the extrusion die was 15MPa. Extrusion and underwater pelletizing were performed to obtain micro-particles with a length of 1mm and a diameter of 0.8mm. S2: 100 g of microparticles, 100 mL of deionized water, and 0.1 g of calcium stearate were added to a high-pressure reactor, and a physical foaming agent was introduced. The temperature was controlled at 130° C. and the pressure was 2.3 MPa. The reaction was continued for 0.5 h. The pressure release rate was 77 MPa / s for rapid pressure release, cooling, and drying to obtain foamed beads. S3: The foamed beads are molded by steam molding. Under a steam pressure of 0.4 MPa, the beads undergo secondary expansion and adhere to each other, and are annealed and shaped to obtain a flame-retardant polypropylene foam plastic.

[0031] Performance Testing (1) Density: The density of the material is calculated using the drainage method. The test steps are as follows: Take a volume not less than 1cm 3For a sample, accurately weigh the mass m with an electronic balance, fill a measuring cylinder with a certain amount of distilled water, immerse the sample in the distilled water, calculate the density based on the mass change before and after immersion, and calculate the apparent density ρ of the sample according to the following formula: ρ = (mρ 水 ) / Δm Where, ρ-sample density, g / cm 3 ρ 水 - Density of distilled water, g / cm 3 ; m-sample mass, g; Δm-increased mass of the sample when immersed in water, g; the test results are shown in Table 1; (2) Water absorption: Test according to GB / T 8810-2005 and calculate the water absorption σ according to the following formula: σ=[(m1-m0) / V0]×100% Wherein, σ-water absorption rate,%; m0-mass of sample before water absorption,g; m1-mass of sample before water absorption,g; V0-initial volume of sample,cm 3 ; The test results are shown in Table 1; (3) Foaming ratio: It is expressed as the ratio of the density of dense plastic to the surface density of foamed plastic of the same material, that is, the density ratio of unfoamed products to foamed products; η=ρ / ρ f Where, η is the expansion ratio; ρ is the average density of the unfoamed product, g / cm 3 ρ f -Apparent density of foamed products, g / cm 3 ; The test results are shown in Table 1; (4) Limiting oxygen index (LOI): tested according to GB / T 2406-2008 "Plastic combustion performance test method oxygen index method", the lowest oxygen index when the material just maintains combustion in a mixture of oxygen and nitrogen, expressed as volume percentage, sample size: 100mm×100mm×100mm, test results are shown in Table 3; Table 1: Statistical table of performance test data of Examples 5-7 and Comparative Examples 3-5 As shown in Table 1, the foamed plastic prepared by adding the functional additives prepared in the present application to the resin has good flame retardant properties, and the polypropylene is grafted with styrene and glycidyl methacrylate to give the material excellent high melt strength performance, so that the resin has a high foaming ratio and good pore structure during the foaming process. The high melt strength polypropylene prepared in the present application and the functional additives work synergistically, so that the silicon dioxide and the polypropylene are grafted through molecular links. During the foaming process of the polypropylene, the silicon dioxide plays a role in the nucleation of bubbles and their massive growth, and after stabilization, they are cooled and shaped to form foamed beads.

[0032] (4) Tensile strength and elongation at break: tested in accordance with GB / T 6344-2008 “Determination of tensile strength and elongation at break of flexible foam polymer materials”. The test results are shown in Table 2. (5) Impact strength: tested according to GB / T 1043-2008 “Rigid Plastics Simply Supported Beam Impact Test Method”. The test results are shown in Table 2. (6) Bending strength: tested according to GB / T 9341-2008 “Test method for bending properties of plastics”. The test results are shown in Table 2. Table 2: Statistical table of mechanical properties test data of Examples 5-7 and Comparative Examples 3-5 As shown in Table 2, the functional additive prepared in this application is organically modified based on nano-silicon dioxide, and the functional additive is added to high melt strength polypropylene to give the material excellent impact resistance. Moreover, the silicon dioxide undergoes a ring-opening reaction with the epoxy group of high melt strength polypropylene through the surface phosphate group, and the silicon dioxide is organically cross-linked with the polypropylene through the molecular chain, effectively improving the flexibility and mechanical properties of the polypropylene. The flame-retardant polypropylene foam plastic prepared in this application has good impact resistance and bending properties, and the materials such as the incubator prepared with the plastic foam in this application have good mechanical properties during use.

[0033] The above is a detailed description of an embodiment of the present invention, but the content is only a preferred embodiment of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A method for preparing a flame retardant polypropylene foam plastic, characterized in that: The steps include: S1: According to the raw material ratio, high melt strength polypropylene and functional additives are added into the extruder barrel for melt blending, extrusion and granulation to obtain microgranules; S2: adding microparticles, dispersion medium and dispersant into a high-pressure reactor, introducing a physical foaming agent, heat-maintaining and pressure-maintaining treatment, rapid pressure relief, cooling and drying to obtain foamed beads; S3: molding the foamed beads by steam molding and annealing to obtain a flame retardant polypropylene foam plastic; The preparation method of the functional additive comprises the following steps: A1: Add deionized water, anhydrous ethanol and aminopropyl triethoxysilane into a reaction kettle and disperse them evenly, add nano-silicon dioxide, control the temperature at 40-50°C, keep the temperature for reaction for 1-3 hours, wash and dry to obtain modified silicon dioxide; A2: In a nitrogen atmosphere, modified silica, deionized water, formaldehyde solution and phosphorous acid are added into a reaction kettle and dispersed evenly. The temperature is controlled at 60-70°C, and the reaction is kept warm for 6-12 hours. The mixture is centrifuged, washed and dried to obtain a functional additive.

2. The method for preparing a flame retardant polypropylene foam plastic according to claim 1, characterized in that: The addition ratio of deionized water, anhydrous ethanol, aminopropyl triethoxysilane and nano-silicon dioxide in A1 is 1 mL: 4-9 mL: 1 g: 1-5 g.

3. The method for preparing a flame retardant polypropylene foam plastic according to claim 1, characterized in that: The formaldehyde solution in A2 is a 20-40% w / v methanol aqueous solution; the addition ratio of modified silica, deionized water, 20-40% w / v formaldehyde solution, and phosphorous acid is 1 g: 100-200 mL: 7.5-15 mL: 10-15 g.

4. The method for preparing a flame retardant polypropylene foam plastic according to claim 1, characterized in that: The preparation method of high melt strength polypropylene comprises the following steps: in a nitrogen atmosphere, adding polypropylene, xylene and benzoyl peroxide into a high pressure reactor, mixing styrene and glycidyl methacrylate evenly and adding them into the reactor, controlling the temperature at 120-130° C., and keeping the temperature for reaction for 3-6 hours to obtain high melt strength polypropylene.

5. The method for preparing a flame retardant polypropylene foam plastic according to claim 4, characterized in that: The addition ratio of polypropylene, xylene, styrene, benzoyl peroxide, and glycidyl methacrylate is 1 g: 2-20 mL: 0.001-0.01 g: 0.03-0.06 g: 0.03-0.06 g.

6. The method for preparing a flame retardant polypropylene foam plastic according to claim 1, characterized in that: The temperature of the barrel mixing section of the extruder in S1 is 180-210°C; the temperature of the extrusion die of the extruder is 100-150°C; and the pressure of the extrusion die of the extruder is 10-25MPa.

7. The method for preparing a flame retardant polypropylene foam plastic according to claim 1, characterized in that: The addition ratio of high melt strength polypropylene and functional additives in S1 is 100g:2-5g.

8. The method for preparing a flame retardant polypropylene foam plastic according to claim 1, characterized in that: The specific steps of the heat preservation and pressure treatment in S2 are: controlling the temperature at 130-140°C and the pressure at 1.5-2.5MPa for 0.5-1h; the pressure relief rate of the rapid pressure relief is 70-90MPa / s.

9. The method for preparing a flame retardant polypropylene foam plastic according to claim 1, characterized in that: In S2, the dispersion medium is deionized water; the physical foaming agent is carbon dioxide and / or nitrogen; the dispersant is at least one of sodium dodecylbenzene sulfonate, calcium stearate, sodium benzene sulfonate, vinyl bisstearamide and stearic acid monoglyceride; the addition ratio of the microparticles: dispersion medium: dispersant is 100g: 100-200mL: 0.01-0.1g; the density of the foamed beads is 0.015-0.045g / cm 3 .

10. A flame retardant polypropylene foam plastic, characterized in that: Prepared by the preparation method described in any one of claims 1 to 9.

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