A flame-retardant polypropylene foam and its preparation method

Abstract

The present invention discloses a flame-retardant polypropylene foam and a preparation method thereof, relating to the technical field of thermal insulation materials. The preparation method of the flame-retardant polypropylene foam of the present invention comprises the following steps: according to the raw material ratio, polypropylene and functional additives are added into the barrel of an extruder for melt blending, extrusion and granulation to obtain microparticles; the microparticles, deionized water and a dispersant are added into a high-pressure reaction kettle, a physical foaming agent is introduced, and heat preservation and pressure maintaining treatment are carried out, followed by pressure relief, cooling and drying to obtain foamed beads; the foamed beads are molded by steam and annealed to obtain the flame-retardant polypropylene foam; the polypropylene foam prepared in this application has the characteristics of flame retardancy and excellent mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal insulation materials, and particularly relates 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 continuous improvement of consumers' awareness of food safety, the proportion of short-distance distributive transportation of fresh products in cold chain logistics has increased significantly. Multi-temperature zone insulation boxes have become an efficient equipment for co-box distribution of commodities with different types and different storage temperatures. Polymer foaming materials are gas / solid two-phase composite materials with polymers as the continuous phase and bubbles as the 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, good heat insulation, etc. There are many types of polymer foaming materials, which can be generally divided into three categories according to the matrix resin: polyurethane soft and rigid foams, polystyrene foams, and polyolefin foams. In recent years, with the continuous exploration of foaming technology, foamed polypropylene materials have received extensive attention due to their excellent performance. The foamed pellets obtained by foaming foamed polypropylene microparticles are used for secondary expansion in the mold cavity of a molding device and adhered to each other, and can be used to prepare products with complex shapes. Compared with other foam materials, the foamed polypropylene bead products have the following advantages: (1) The rigidity of polypropylene is better than that of polyethylene, and the impact resistance is better than that of polystyrene. The mechanical strength of the foaming material is at the highest level among plastic foaming materials, with medium compressive strength and excellent resilience; (2) Polypropylene has a relatively high load deformation temperature and can usually withstand high temperatures of 130°C; (3) Compared with the chlorofluorocarbon compounds used in the processing of polystyrene foam and the residual isocyanate substances in polyurethane foam, the foamed polypropylene beads prepared using foaming agents such as carbon dioxide are an environmentally friendly material that is non-toxic and harmless; (4) The molecular chain of polypropylene material contains side methyl groups, which are more likely to undergo β degradation, facilitating the degradation of the material in nature.

[0003] The foaming process of polypropylene beads is divided into batch kettle foaming, continuous extrusion foaming, compression molding and injection molding foaming. The batch kettle method and continuous extrusion method are generally used to prepare foamed polypropylene beads. The foaming mechanism of the kettle method is the supersaturated gas principle. First, a polymer / gas homogeneous saturated 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 points, and the pores undergo a process of expansion to cooling and shaping, and finally form foamed beads. The batch kettle method has a lower processing temperature and no screw shearing effect, which can maintain a higher melt strength and is easier to achieve high magnification and high closed cell rate foaming. However, since polypropylene is a highly crystalline polymer, the softening point of polypropylene is close to the melting point, and its melt viscosity is very sensitive to temperature changes. When polypropylene is heated to the melting temperature, with the increase of the processing temperature, the viscosity of the polypropylene resin drops sharply, resulting in too low melt surface tension, and the gas decomposed from the foaming agent is difficult to remain in the melt and cannot form a foam. Moreover, the heat capacity of the polypropylene resin is relatively large, and a large amount of heat needs to be released when the resin changes from the molten state to the crystalline state, which also reduces the melt strength of polypropylene. After foaming, the bubbles are easily damaged, the gas escapes, causing the pores to collapse and the pore stability to decrease. Summary of the Invention

[0004] The purpose of the present invention is to provide a flame-retardant polypropylene foam plastic and its preparation method, and solve the following technical problems:

[0005] Due to the limitations of the physical and chemical properties of existing polypropylene resins, during the foaming process of polypropylene, it is difficult to control the melt surface tension, and it is difficult for the melt to form a foam; and when the polypropylene resin forming the foam changes from the molten state to the crystalline state by releasing heat, a large amount of heat is released, resulting in a decrease in melt strength and the destruction of the already formed bubbles.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A preparation method of a flame-retardant polypropylene foam plastic includes the following steps:

[0008] S1: According to the raw material ratio, add high melt strength polypropylene and functional additives into the barrel of the extruder for melt blending, extrude and granulate to obtain microparticles;

[0009] S2: Add the microparticles, deionized water and dispersant into a high-pressure reaction kettle, introduce a physical foaming agent, perform heat preservation and pressure preservation treatment, quickly release pressure, cool and dry to obtain foamed beads;

[0010] S3: Mold the foamed beads by steam molding and anneal and shape them to obtain a flame-retardant polypropylene foam plastic;

[0011] The preparation method of the functional additive includes the following steps:

[0012] A1: Add deionized water, anhydrous ethanol, and aminopropyltriethoxysilane into a reaction kettle and disperse them evenly. Then add nano-silica. Control the temperature at 40 - 50 °C and keep the reaction for 1 - 3 h. Wash and dry to obtain modified silica;

[0013] A2: In a nitrogen atmosphere, add modified silica, deionized water, formaldehyde solution, and phosphorous acid into a reaction kettle and disperse them evenly. Control the temperature at 60 - 70 °C and keep the reaction for 6 - 12 h. Centrifuge, wash, and dry to obtain a functional additive.

[0014] Preferably, the addition ratio of deionized water, anhydrous ethanol, aminopropyltriethoxysilane, and nano-silica in A1 is 1 mL : 4 - 9 mL : 1 g : 1 - 5 g.

[0015] 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.

[0016] Preferably, the preparation method of high melt strength polypropylene includes the following steps: In a nitrogen atmosphere, add polypropylene, xylene, and benzoyl peroxide into a high-pressure reaction kettle. After mixing styrene and glycidyl methacrylate evenly, add them into the reaction kettle. Control the temperature at 120 - 130 °C and keep the reaction for 3 - 6 h to obtain high melt strength polypropylene.

[0017] 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.

[0018] Preferably, in S1, the temperature of the barrel mixing section of the extruder is 180 - 210 °C; the temperature of the extruder die is 100 - 150 °C; the pressure of the extruder die is 10 - 25 MPa.

[0019] Preferably, the addition ratio of high melt strength polypropylene and the functional additive in S1 is 100 : 2 - 5.

[0020] Preferably, the specific steps of the heat preservation and pressure maintenance treatment in S2 are: Control the temperature at 130 - 140 °C and the pressure at 1.5 - 2.5 MPa, and treat for 0.5 - 1 h; the pressure relief rate of the rapid pressure relief is 70 - 90 MPa / s.

[0021] Preferably, 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 dodecylbenzenesulfonate, calcium stearate, sodium benzenesulfonate, vinyl bisstearamide, and monoglyceryl stearate; the addition ratio of the microparticles:dispersion medium:dispersant is 100 g:100 - 200 mL:0.01 - 0.1 g; the density of the foamed beads is 0.015 - 0.045 g / cm 3 .

[0022] A flame-retardant polypropylene foam is made by the preparation method of any one of the above.

[0023] The beneficial effects of the present invention are as follows:

[0024] (1) First, the surface of nano-silica is organically amino-modified by an amino-silane coupling agent to obtain modified silica; and a functional auxiliary is obtained by the Mannich reaction of nano-silica with formaldehyde and phosphorous acid in an aqueous phase. The present application also uses polypropylene as the matrix, and styrene and glycidyl methacrylate as graft monomers to carry out graft polymerization to obtain high melt strength polypropylene. The present application uses this high melt strength polypropylene as the raw material, adds a functional auxiliary, and prepares microparticles. During the preparation of the microparticles, the epoxy groups grafted on the molecular chain of the high melt strength polypropylene react with the phosphate groups grafted on the surface of the functional auxiliary to graft silica onto the high melt strength polypropylene to obtain microparticles.

[0025] The present application uses the reactor method to put the microparticles into a reactor, add a dispersion medium and a physical foaming agent for combined use, raise the temperature to increase the pressure in the reactor, keep the pressure for a period of time at the foaming temperature, and then form a supersaturated system by rapid pressure relief to cause thermodynamic instability. During the reaction process, the polypropylene resin undergoes phase separation with water vapor and the physical foaming agent, and bubbles begin to nucleate and grow in large numbers. After stabilization, it is cooled and shaped to form foamed beads. The dispersion medium added during the preparation of the foamed beads in the present application forms water vapor in a high-temperature and high-pressure environment, effectively reducing the pressure required for the reaction. The preparation method of the foamed beads in the present application has simple and easy-to-control process conditions, a high foaming ratio, a good cell structure, and can be subjected to secondary foaming.

[0026] (2) The functional additive prepared in this application is grafted with high melt strength polypropylene through chemical bonds and is uniformly dispersed in the melt to form hot spots, effectively reducing the viscosity and surface tension in the local area. Therefore, 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 the bubbles from growing excessively, makes the cell structure of the growing bubbles uniform and dense, and effectively avoids the formation of large cell holes and cell coalescence during the foaming process due to the aggregation of silica. Moreover, with the addition of the functional additive of this application, good flame retardant properties and mechanical properties are effectively imparted to polypropylene. The flame retardant polypropylene foam plastic prepared in this application has dense cells, uniform pore size distribution, a closed cell structure, and a density of 0.015 - 0.045 g / cm 3 of expandable beads, which can be widely used in fields such as heat-insulating tableware and product shock-absorbing packaging. Specific Embodiments

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0028] Example 1 The preparation method of the functional additive includes the following steps:

[0029] A1: Add 10 mL of deionized water, 40 mL of absolute ethanol, and 10 g of aminopropyltriethoxysilane into the reaction kettle and disperse evenly. Then add 20 g of nano-silica, control the temperature at 40 °C, and keep the reaction for 1 h. Wash and dry to obtain modified silica;

[0030] A2: In a nitrogen atmosphere, add 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 into the reaction kettle and disperse evenly. Control the temperature at 60 °C and keep the reaction for 6 h. Centrifuge, wash, and dry to obtain the functional additive.

[0031] Example 2 The preparation method of the functional additive includes the following steps:

[0032] A1: Add 10 mL of deionized water, 70 mL of absolute ethanol, and 10 g of aminopropyltriethoxysilane into the reaction kettle and disperse evenly. Then add 20 g of nano-silica, control the temperature at 45 °C, and keep the reaction for 2 h. Wash and dry to obtain modified silica;

[0033] A2: In a nitrogen atmosphere, 10 g of modified silica, 1500 mL of deionized water, 110 mL of 40% w / v aqueous formaldehyde solution, and 120 g of phosphorous acid were added to a reaction kettle and dispersed evenly. The temperature was controlled at 65 °C, and the reaction was carried out with heat preservation for 9 h. After centrifugation, washing, and drying, a functional additive was obtained.

[0034] Example 3 The preparation method of the functional additive includes the following steps:

[0035] A1: 10 mL of deionized water, 90 mL of absolute ethanol, and 10 g of aminopropyltriethoxysilane were added to a reaction kettle and dispersed evenly. 20 g of nano-silica was added, and the temperature was controlled at 50 °C. The reaction was carried out with heat preservation for 3 h. After washing and drying, modified silica was obtained.

[0036] A2: In a nitrogen atmosphere, 10 g of modified silica, 2000 mL of deionized water, 150 mL of 40% w / v aqueous formaldehyde solution, and 150 g of phosphorous acid were added to a reaction kettle and dispersed evenly. The temperature was controlled at 70 °C, and the reaction was carried out with heat preservation for 12 h. After centrifugation, washing, and drying, a functional additive was obtained.

[0037] Example 4 The preparation method of high melt strength polypropylene includes the following steps:

[0038] In a nitrogen atmosphere, 1 g of polypropylene granules T30s, 10 mL of xylene, and 0.005 g of benzoyl peroxide were added to a high-pressure reaction kettle. After mixing 0.04 g of styrene and 0.05 g of glycidyl methacrylate evenly, they were added to the reaction kettle. The temperature was controlled at 120 °C, and the reaction was carried out with heat preservation for 6 h to obtain high melt strength polypropylene.

[0039] Example 5 The preparation method of a flame-retardant polypropylene foam plastic includes the following steps:

[0040] S1: According to the raw material ratio, 100 g of the high melt strength polypropylene prepared in Example 4 and 5 g of the functional additive prepared in Example 1 were added to the barrel of a twin-screw co-extrusion machine for melt blending. The temperature of the mixing section of the barrel was 210 °C, the temperature of the die of the extruder was 130 °C, and the pressure of the die was 15 MPa. After extrusion and underwater pelletization, micro-particles with a length of 1 mm and a diameter of 0.8 mm were obtained.

[0041] S2: 100 g of micro-particles, 100 mL of deionized water, and 0.1 g of calcium stearate were added to a high-pressure reaction kettle. A physical foaming agent was introduced, and the temperature was controlled at 130 °C and the pressure at 2.3 MPa. After treatment for 0.5 h, rapid pressure relief was carried out at a pressure relief rate of 77 MPa / s, followed by cooling and drying to obtain foamed beads.

[0042] S3: Mold the expanded beads by steam molding. Under a steam pressure of 0.4 MPa, the beads undergo secondary expansion, adhere to each other, and are annealed and shaped to obtain flame-retardant polypropylene foam.

[0043] Example 6 A method for preparing flame-retardant polypropylene foam, comprising the following steps:

[0044] S1: According to the raw material ratio, add 100 g of the high melt strength polypropylene prepared in Example 4 and 5 g of the functional additive prepared in Example 2 into the barrel of a twin-screw co-mixing extruder for melting and co-mixing. The temperature of the mixing section of the barrel is 210 °C, the temperature of the die of the extruder is 130 °C, and the pressure of the die is 15 MPa. Extrude and cut underwater to obtain microparticles with a length of 1 mm and a diameter of 0.8 mm.

[0045] S2: Add 100 g of microparticles, 100 mL of deionized water, and 0.1 g of calcium stearate into a high-pressure reactor, introduce a physical foaming agent, control the temperature at 130 °C and the pressure at 2.3 MPa, process for 0.5 h, and rapidly depressurize at a depressurization rate of 77 MPa / s, cool, and dry to obtain expanded beads.

[0046] S3: Mold the expanded beads by steam molding. Under a steam pressure of 0.4 MPa, the beads undergo secondary expansion, adhere to each other, and are annealed and shaped to obtain flame-retardant polypropylene foam.

[0047] Example 7 A method for preparing flame-retardant polypropylene foam, comprising the following steps:

[0048] S1: According to the raw material ratio, add 100 g of the high melt strength polypropylene prepared in Example 4 and 5 g of the functional additive prepared in Example 3 into the barrel of a twin-screw co-mixing extruder for melting and co-mixing. The temperature of the mixing section of the barrel is 210 °C, the temperature of the die of the extruder is 130 °C, and the pressure of the die is 15 MPa. Extrude and cut underwater to obtain microparticles with a length of 1 mm and a diameter of 0.8 mm.

[0049] S2: Add 100 g of microparticles, 100 mL of deionized water, and 0.1 g of calcium stearate into a high-pressure reactor, introduce a physical foaming agent, control the temperature at 130 °C and the pressure at 2.3 MPa, process for 0.5 h, and rapidly depressurize at a depressurization rate of 77 MPa / s, cool, and dry to obtain expanded beads.

[0050] S3: Mold the expanded beads by steam molding. Under a steam pressure of 0.4 MPa, the beads undergo secondary expansion, adhere to each other, and are annealed and shaped to obtain flame-retardant polypropylene foam.

[0051] Comparative Example 1 The method for preparing the functional additive comprises the following steps:

[0052] A1: Add 10 mL of deionized water, 70 mL of absolute ethanol, and 10 g of aminopropyltriethoxysilane into a reaction kettle and disperse them evenly. Then add 20 g of nano-silica, control the temperature at 45 °C, and keep the reaction for 2 h. After washing and drying, a functional auxiliary agent is obtained.

[0053] Comparative Example 2 The preparation method of high melt strength polypropylene comprises the following steps:

[0054] In a nitrogen atmosphere, add 1 g of polypropylene particles T30s, 10 mL of xylene, and 0.005 g of benzoyl peroxide into a high-pressure reaction kettle. Then add 0.04 g of styrene into the reaction kettle, control the temperature at 120 °C, and keep the reaction for 6 h to obtain high melt strength polypropylene.

[0055] Comparative Example 3 A preparation method of a flame-retardant polypropylene foam plastic comprises the following steps:

[0056] S1: According to the raw material ratio, add 100 g of the high melt strength polypropylene prepared in Example 4 and 5 g of the functional auxiliary agent prepared in Comparative Example 1 into the barrel of a twin-screw co-extrusion machine for melt blending. The temperature of the mixing section of the barrel is 210 °C, the temperature of the die of the extruder is 130 °C, and the pressure of the die is 15 MPa. After extrusion and underwater pelletizing, micro-particles with a length of 1 mm and a diameter of 0.8 mm are obtained;

[0057] S2: Add 100 g of micro-particles, 100 mL of deionized water, and 0.1 g of calcium stearate into a high-pressure reaction kettle, introduce a physical foaming agent, control the temperature at 130 °C and the pressure at 2.3 MPa, process for 0.5 h, and perform rapid pressure relief at a pressure relief rate of 77 MPa / s, then cool and dry to obtain foamed beads;

[0058] S3: Mold the foamed beads by steam. Under a steam pressure of 0.4 MPa, the beads undergo secondary expansion, adhere to each other, and are annealed and shaped to obtain the flame-retardant polypropylene foam plastic.

[0059] Comparative Example 4 A preparation method of a flame-retardant polypropylene foam plastic comprises the following steps:

[0060] S1: According to the raw material ratio, add 100 g of the high melt strength polypropylene prepared in Comparative Example 2 and 5 g of the functional auxiliary agent prepared in Example 2 into the barrel of a twin-screw co-extrusion machine for melt blending. The temperature of the mixing section of the barrel is 210 °C, the temperature of the die of the extruder is 130 °C, and the pressure of the die is 15 MPa. After extrusion and underwater pelletizing, micro-particles with a length of 1 mm and a diameter of 0.8 mm are obtained;

[0061] S2: Add 100 g of micro-particles, 100 mL of deionized water, and 0.1 g of calcium stearate into a high-pressure reactor. Introduce a physical foaming agent, control the temperature at 130 °C and the pressure at 2.3 MPa, process for 0.5 h, and perform rapid pressure relief, cooling, and drying at a pressure relief rate of 77 MPa / s to obtain foamed beads.

[0062] S3: Mold the foamed beads by steam molding. Under a steam pressure of 0.4 MPa, the beads undergo secondary expansion, adhere to each other, and are annealed and shaped to obtain a flame-retardant polypropylene foam plastic.

[0063] Comparative Example 5 A method for preparing a flame-retardant polypropylene foam plastic, comprising the following steps:

[0064] S1: According to the raw material ratio, add 100 g of the high melt strength polypropylene prepared in Comparative Example 2 and 5 g of the functional additive prepared in Comparative Example 1 into the barrel of a twin-screw co-extrusion machine for melt blending. The temperature of the mixing section of the barrel is 210 °C, the temperature of the die of the extruder is 130 °C, and the pressure of the die is 15 MPa. Extrude and cut into underwater pellets to obtain micro-particles with a length of 1 mm and a diameter of 0.8 mm.

[0065] S2: Add 100 g of micro-particles, 100 mL of deionized water, and 0.1 g of calcium stearate into a high-pressure reactor. Introduce a physical foaming agent, control the temperature at 130 °C and the pressure at 2.3 MPa, process for 0.5 h, and perform rapid pressure relief, cooling, and drying at a pressure relief rate of 77 MPa / s to obtain foamed beads.

[0066] S3: Mold the foamed beads by steam molding. Under a steam pressure of 0.4 MPa, the beads undergo secondary expansion, adhere to each other, and are annealed and shaped to obtain a flame-retardant polypropylene foam plastic.

[0067] Performance Testing

[0068] (1) Density: Calculate the density of the material by the drainage method. The test steps are as follows: Take a specimen with a volume of not less than 1 cm 3 , accurately weigh the mass m with an electronic balance, fill a certain amount of distilled water in a graduated cylinder, immerse the specimen in the distilled water, and calculate the density by the change in mass before and after immersion. Calculate the apparent density ρ of the specimen according to the following formula:

[0069] ρ = (mρ 水 ) / Δm

[0070] In the formula, ρ - density of the specimen, g / cm 3 ; ρ 水 - density of distilled water, g / cm 3 ; m - mass of the specimen, g; Δm - increased mass of the specimen when immersed in water, g; The test results are shown in Table 1;

[0071] (2) Water absorption rate: It is detected according to GB / T 8810-2005, and the water absorption rate σ is calculated according to the following formula:

[0072] σ = [(m 1 - m 0 ) / V 0 ] × 100%

[0073] In the formula, σ - water absorption rate, %; m 0 - mass of the specimen before water absorption, g; m 1 - mass of the specimen after water absorption, g; V 0 - initial volume of the specimen, cm 3 ; The test results are shown in Table 1;

[0074] (3) Foaming ratio: It is expressed by the ratio of the density of the dense plastic to the surface density of the foamed plastic of the same material, that is, the density ratio of the unfoamed product to the foamed product;

[0075] η = ρ / ρ f

[0076] In the formula, η - foaming ratio; ρ - average density of the unfoamed product, g / cm 3 ; ρ f - apparent density of the foamed product, g / cm 3 ; The test results are shown in Table 1;

[0077] (4) Limiting oxygen index (LOI): It is detected according to GB / T 2406-2008 "Test Method for Flammability of Plastics - Oxygen Index Method". The lowest oxygen index when the material just maintains combustion in a mixture of oxygen and nitrogen is expressed as a volume percentage. Specimen size: 100 mm × 100 mm × 100 mm. The test results are shown in Table 3;

[0078] Table 1: Statistical Table of Performance Test Data for Examples 5-7 and Comparative Examples 3-5

[0079]

[0080] As can be seen from Table 1, the foam plastics prepared by adding the functional additives prepared in this application to the resin have good flame retardant properties. Moreover, polypropylene is grafted with styrene and glycidyl methacrylate, endowing the material with excellent high melt strength properties, resulting in a high foaming ratio and good cell structure during the foaming process of the resin. And the high melt strength polypropylene prepared in this application and the functional additives act synergistically, enabling silica to graft with polypropylene through molecular linkages. During the foaming process of polypropylene, silica plays a role in the initial nucleation and massive growth of bubbles, and after stabilization, the foamed beads are formed through cooling and shaping.

[0081] (4)Tensile strength and elongation at break: Tested according to GB / T 6344-2008 "Determination of Tensile Strength and Elongation at Break of Flexible Cellular Polymer Materials", and the test results are shown in Table 2;

[0082] (5)Impact strength: Tested according to GB / T 1043-2008 "Test Method for Izod Impact Strength of Rigid Plastics", and the test results are shown in Table 2;

[0083] (6)Flexural strength: Tested according to GB / T 9341-2008 "Plastics - Determination of Flexural Properties", and the test results are shown in Table 2;

[0084] Table 2: Statistical Table of Mechanical Property Test Data of Examples 5-7 and Comparative Examples 3-5

[0085]

[0086] As can be seen from Table 2, the functional additive prepared in this application is organically modified based on nano-silica. Adding the functional additive to high melt strength polypropylene endows the material with excellent impact resistance. Moreover, the silica undergoes a ring-opening reaction with the epoxy groups of high melt strength polypropylene through the surface phosphate groups, and the silica is organically cross-linked with polypropylene through molecular chains, effectively improving the flexibility and mechanical properties of polypropylene. The flame-retardant polypropylene foam plastic prepared in this application has good impact resistance and flexural properties, and materials such as insulation boxes prepared from the plastic foam of this application have good mechanical properties during use.

[0087] The above has described a specific embodiment of the present invention in detail, but the content described is only the preferred embodiment of the present invention and cannot be considered as limiting the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of the present invention application should still fall within the scope covered by the patent 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 addition ratio of high melt strength polypropylene and functional additives is 100g: 2-5g; 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 functional additive is then centrifuged, washed and dried to obtain the functional additive. 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; 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.

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 formaldehyde 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 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.

5. 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.

6. 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 .

7. A flame retardant polypropylene foam plastic, characterized in that: Prepared by the preparation method described in any one of claims 1 to 6.

Images