A flame-retardant expandable polystyrene bead and its preparation method

Abstract

This invention provides a flame-retardant expandable polystyrene bead and its preparation method, belonging to the field of polystyrene bead technology. By weight, it is prepared from the following raw materials: 20 parts styrene monomer, 0.20-0.25 parts organic dispersant, 0.05-0.15 parts inorganic dispersant, 0.75-0.85 parts foaming agent, 3.8-4.2 parts hyperbranched core-shell flame retardant, 0.4-0.6 parts initiator, and 90-110 parts water. The hyperbranched core-shell flame retardant is obtained by shell coating and hyperbranching of expanded graphite. Adding the hyperbranched core-shell flame retardant during the polystyrene polymerization process ensures good compatibility between the expanded graphite and the polymer matrix. Simultaneously, after high-temperature expansion, it effectively encapsulates and protects the matrix material. The resulting polystyrene foam material exhibits excellent flame-retardant properties while maintaining high compressive strength.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polystyrene beads, and particularly relates to a flame-retardant expandable polystyrene bead and a preparation method thereof. BACKGROUND

[0002] Expandable polystyrene (EPS) is also known as foamed polystyrene, which is a kind of foam material with low cost and excellent performance, can prevent moisture, heat insulation, sound insulation and vibration reduction, has small thermal conductivity and water absorption, and excellent dielectric performance, and is widely used in the fields of filling packaging of articles and energy-saving and thermal insulation of buildings.

[0003] Expandable polystyrene beads are white bead-shaped particles containing high-volatility and low-boiling-point blowing agents, which are used for foaming and molding to prepare EPS foam materials. EPS foam materials have a large specific surface area and a honeycomb-like cell structure, and are easy to burn at high temperatures, producing toxic gases and molten droplets, which seriously limits their application in many fields. Expanded graphite has expandability and flame-retardant performance. When expanded graphite is introduced into a polymer emulsion, the expanded graphite particles can be uniformly dispersed in the polymer matrix as the polymerization reaction proceeds. Compared with conventional mixing, the combination has higher flame-retardant efficiency. However, the porous structure of expanded graphite expands at high temperatures, and the diffusion and deformation ability is poor, so it is difficult to effectively wrap and protect the foam matrix after expansion, which affects the flame-retardant effect. At the same time, the interface interaction between expanded graphite and polystyrene molecular chains is weak, and stress concentration occurs between expanded graphite and polystyrene matrix when subjected to external force, thereby reducing the compressive strength and affecting the overall mechanical properties of the material. SUMMARY

[0004] To solve the problems in the background art, the application provides a flame-retardant expandable polystyrene bead and a preparation method thereof, so that the prepared foamed polystyrene material has good flame-retardant performance and can maintain high compressive strength.

[0005] To achieve the above-mentioned purpose, the application provides the following technical solutions.

[0006] A flame-retardant expandable polystyrene bead is prepared from the following raw materials by weight parts: 20 parts of styrene monomer, 0.20-0.25 parts of an organic dispersant, 0.05-0.15 parts of an inorganic dispersant, 0.75-0.85 parts of a blowing agent, 3.8-4.2 parts of an ultrabranched core-shell flame retardant, 0.4-0.6 parts of an initiator, and 90-110 parts of water, wherein the ultrabranched core-shell flame retardant is prepared by coating and ultrabranched processing of expanded graphite, and the preparation method of the flame-retardant expandable polystyrene bead comprises the following steps:

[0007] The raw materials are weighed by mass fraction, the styrene monomer, hyperbranched core-shell flame retardant and deionized water are put into the reaction kettle, mixed uniformly, then half of the amount of inorganic dispersant, half of the amount of organic dispersant and initiator are put in, mechanical stirring for 30-60 min, the temperature of the material in the reaction kettle is raised to 80-90℃, and the polymerization reaction is carried out at this temperature for 6-10 hours; the remaining dispersant and foaming agent are added, the reaction kettle is heated to 110-130℃, and kept constant temperature for 3-5h; the material in the reaction kettle is taken out, filtered, dried, and the flame-retardant expandable polystyrene beads are obtained.

[0008] Preferably, the specific preparation method of the hyperbranched core-shell flame retardant comprises the following steps:

[0009] S1. In an oil bath at 50-55℃, 10-15 parts of expanded graphite, 0.2-0.4 parts of stearic acid and 100-200 parts of water are added into the reaction container, stirred uniformly, then 2-3 parts of acrylamide, 2-3 parts of acrylic acid, 1-2 parts of 2-acrylamide-2-methylpropane sulfonic acid, 0.5-1 parts of sodium hydroxide, 0.05-0.1 parts of propylene glycol and 0.03-0.08 parts of pentaerythritol triallyl ether are added, stirred for 30-60 min, heated to 80-90℃ under nitrogen protection, 0.02-0.05 parts of potassium persulfate is added for polymerization reaction for 3-5h, after the reaction is completed, filtration is carried out to obtain the first shell coated material;

[0010] S2. The first shell coated material in step 1 is added into a mixed solution containing 1-3 parts of diethyl methylphosphonate and 80-100 parts of methanol, stirred uniformly, 0.05-0.1 parts of azobisisobutyronitrile, 0.5-1 parts of ethylene glycol dimethacrylate and 1.0-1.5 parts of vinyl acetate are mixed, slowly added into the reaction container, stirred at a speed of 100-300 rpm for 12-18h;

[0011] S3. After the reaction is completed, the heating is stopped and cooled to room temperature, hydrochloric acid is added to adjust the pH to 2-4, the oil bath is heated to 70-80℃, and the reflux reaction is carried out for 8-10h;

[0012] S4. The reaction container is sealed, the pressure in the container is maintained at 1.5-2MPa, heated to 120-140℃, reacted for 6-12h, cooled to room temperature, filtered and dried to obtain the hyperbranched core-shell flame retardant.

[0013] Preferably, the organic dispersant is one or a combination of two or more of hydroxyethyl cellulose, methyl cellulose, sodium methyl cellulose and carboxymethyl cellulose.

[0014] Preferably, the inorganic dispersant is one or a combination of two or more of calcium carbonate, calcium phosphate, talc and magnesium carbonate.

[0015] Preferably, the initiator is one or a combination of two or more of benzoyl peroxide, t-butyl benzene peroxide and dicumyl peroxide.

[0016] Preferably, the blowing agent is one or a combination of two or more of n-pentane, iso-pentane and neopentane.

[0017] Preferably, the expanded graphite has a particle size range of 100-500 mesh.

[0018] The present application has the following beneficial effects:

[0019] 1. The present application provides a flame-retardant expandable polystyrene bead and a preparation method thereof, which has a simple preparation process. The expanded graphite is coated with a shell and subjected to hyperbranched treatment to obtain a hyperbranched core-shell flame retardant. The hyperbranched core-shell flame retardant is added to the polystyrene polymerization process, so that the expanded graphite has good compatibility with the polymer matrix, and can effectively wrap and protect the matrix material after high-temperature expansion. The finally obtained polystyrene foam material has good flame-retardant performance and maintains high compressive strength.

[0020] 2. The hyperbranched core-shell flame retardant provided by the present application has a structure of one core and two shells. The expanded graphite is used as the core, and the shell has a layered cross-linked framework structure and a large number of active functional groups on the surface. The inner shell layer is a structural layer, and the outer shell layer is a hyperbranched cross-linked layer. The inner shell layer has diffusion and deformation capacity at high temperature, effectively wraps and protects the matrix material after expansion, prolongs the plugging time of the flame retardant to the material pores, and improves the flame-retardant effect. The outer shell layer is obtained by surface treatment of the core-shell microspheres, so that the surface cross-linking density of the flame retardant microspheres is greater than the central cross-linking density, which helps to form a stable and perfect structure system and enhance the compressive strength of the material.

[0021] 3. The double-shell structure of the hyperbranched core-shell flame retardant cooperates with each other. The inner shell layer provides basic support, and the outer shell layer is effectively cross-linked. The two cooperate with each other to produce a certain synergistic effect, so that the network structure system of the core-shell microspheres is more dense and stable, and the bonding strength and integrity of the beads during foaming are improved, so that the compressive strength of the finally obtained material is further improved. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The trend chart of the limiting oxygen index and compressive strength of the flame-retardant expandable polystyrene beads in the preparation of polystyrene foam materials in Examples 1-5 and Comparative Examples 1-3 of the present application. DETAILED DESCRIPTION

[0023] The present application is further described below in conjunction with examples.

[0024] The raw materials of the examples and comparative examples of the present application are all ordinary commercial products unless otherwise specified.

[0025] Example 1

[0026] The raw materials were weighed by parts by weight, including 20 parts of styrene monomer, 0.22 parts of organic dispersant hydroxyethyl cellulose, 0.1 parts of inorganic dispersant calcium carbonate, 0.8 parts of foaming agent n-pentane, 4.0 parts of hyperbranched core-shell flame retardant, 0.5 parts of initiator benzoyl peroxide and 100 parts of water. The styrene monomer, hyperbranched core-shell flame retardant and deionized water were put into the reaction kettle, mixed uniformly, and then half of the inorganic dispersant, half of the organic dispersant and the initiator were put in, and mechanically stirred for 45 min. The temperature of the material in the reaction kettle was raised to 85℃, and the polymerization reaction was carried out at this temperature for 8 hours. The remaining dispersant and foaming agent were added, and the reaction kettle was heated to 120℃, and kept constant for 4h. The material in the reaction kettle was taken out, filtered, dried, and the flame-retardant expandable polystyrene beads were obtained.

[0027] The specific preparation method of the hyperbranched core-shell flame retardant includes the following steps:

[0028] S1. In an oil bath at 50℃, 12 parts of expanded graphite with a particle size of 200 mesh, 0.3 parts of stearic acid and 150 parts of water were added into the reaction container, stirred uniformly, then 2.5 parts of acrylamide, 2.5 parts of acrylic acid, 1.5 parts of 2-acrylamide-2-methylpropane sulfonic acid, 0.7 parts of sodium hydroxide, 0.1 parts of propylene glycol and 0.05 parts of pentaerythritol triallyl ether were added, stirred for 30 min, heated to 85℃ under nitrogen protection, and 0.03 parts of potassium persulfate was added for polymerization reaction for 4h. After the reaction was completed, it was filtered to obtain a primary shell coated material;

[0029] S2. The primary shell coated material in step 1 was added to a mixed solution containing 2 parts of diethyl methylphosphonate and 100 parts of methanol, stirred uniformly, and 0.08 parts of azobisisobutyronitrile, 0.8 parts of ethylene glycol dimethacrylate and 1.2 parts of vinyl acetate were mixed, slowly added into the reaction container, and stirred at a speed of 200 rpm for 15h;

[0030] S3. After the reaction was completed, the heating was stopped and cooled to room temperature, hydrochloric acid was added to adjust the pH to 2-4, the oil bath was heated to 75℃, and the reflux reaction was carried out for 10h;

[0031] S4. The reaction container was sealed, the pressure in the container was maintained at 1.5MPa, and the temperature was raised to 130℃, and the reaction was carried out for 10h. After cooling to room temperature, it was filtered and dried to obtain the hyperbranched core-shell flame retardant.

[0032] Example 2

[0033] The raw materials are weighed by parts, including 20 parts of styrene monomer, 0.20 parts of organic dispersant methyl cellulose, 0.05 parts of inorganic dispersant calcium phosphate, 0.75 parts of foaming agent isopentane, 3.8 parts of hyperbranched core-shell flame retardant, 0.4 initiator tert-butyl benzene acid peroxide and 90 parts of water. The styrene monomer, hyperbranched core-shell flame retardant and deionized water are put into the reaction kettle, mixed uniformly, then half of the inorganic dispersant, half of the organic dispersant and the initiator are put in, and the material in the reaction kettle is heated to 80℃, and the polymerization reaction is carried out for 10 hours at this temperature. The remaining dispersant and foaming agent are added, the reaction kettle is heated to 110℃, and kept at this temperature for 5h. The material in the reaction kettle is taken out, filtered and dried to obtain the flame-retardant expandable polystyrene beads.

[0034] The specific preparation method of the hyperbranched core-shell flame retardant includes the following steps:

[0035] S1. In an oil bath at 50℃, 10 parts of expanded graphite with a particle size of 100 mesh, 0.2 parts of stearic acid and 100 parts of water are added into the reaction container, stirred uniformly, then 2 parts of acrylamide, 2 parts of acrylic acid, 1 part of 2-acrylamide-2-methylpropane sulfonic acid, 0.5 parts of sodium hydroxide, 0.05 parts of propylene glycol and 0.03 parts of pentaerythritol triallyl ether are added, stirred for 30 min, heated to 80℃ under nitrogen protection, 0.02 parts of potassium persulfate are added for polymerization reaction for 3h. After the reaction is completed, filtration is carried out to obtain the first shell coated material;

[0036] S2. The first shell coated material in step 1 is added into a mixed solution containing 1 part of diethyl methylphosphonate and 80 parts of methanol, stirred uniformly, 0.05 parts of azobisisobutyronitrile, 0.5 parts of dimethyl acrylate and 1 part of vinyl acetate are mixed, slowly added into the reaction container, stirred at a speed of 100rpm for 12h;

[0037] S3. After the reaction is completed, stop heating and cool to room temperature, add hydrochloric acid to adjust the pH to 2, heat the oil bath to 70℃, and reflux for 10h;

[0038] S4. Seal the reaction container, maintain the pressure in the container at 1.5MPa, heat to 120℃, react for 12h, cool to room temperature, filter and dry to obtain the hyperbranched core-shell flame retardant.

[0039] Example 3

[0040] The raw materials are weighed by parts, including 20 parts of styrene monomer, 0.25 parts of organic dispersant sodium methyl cellulose, 0.15 parts of inorganic dispersant talc, 0.85 parts of foaming agent neopentane, 4.2 parts of hyperbranched core-shell flame retardant, 0.6 parts of initiator dicumyl peroxide and 110 parts of water. The styrene monomer, hyperbranched core-shell flame retardant and deionized water are put into the reaction kettle, mixed uniformly, then half of the inorganic dispersant, half of the organic dispersant and the initiator are put in, and the material in the reaction kettle is heated to 90℃, and the polymerization reaction is carried out at this temperature for 6 hours. The remaining dispersant and foaming agent are added, the reaction kettle is heated to 130℃, and the temperature is kept for 3h. The material in the reaction kettle is taken out, filtered, dried, and the flame-retardant expandable polystyrene beads are obtained.

[0041] The specific preparation method of the hyperbranched core-shell flame retardant includes the following steps:

[0042] S1. In an oil bath at 55℃, 15 parts of expanded graphite with a particle size of 500 mesh, 0.4 parts of stearic acid and 200 parts of water are added into the reaction container, stirred uniformly, then 3 parts of acrylamide, 3 parts of acrylic acid, 2 parts of 2-acrylamide-2-methylpropane sulfonic acid, 1 part of sodium hydroxide, 0.1 part of propylene glycol and 0.08 part of pentaerythritol triallyl ether are added, stirred for 60 min, heated to 90℃ under nitrogen protection, 0.05 part of potassium persulfate is added for polymerization reaction for 5h, after the reaction is completed, filtration is carried out, and the first shell coated material is obtained;

[0043] S2. The first shell coated material in step 1 is added into a mixed solution containing 3 parts of diethyl methylphosphonate and 100 parts of methanol, stirred uniformly, 0.1 part of azobisisobutyronitrile, 1 part of dimethyl acrylate and 1.5 parts of vinyl acetate are mixed, slowly added into the reaction container, stirred at a speed of 300 rpm for 12h;

[0044] S3. After the reaction is completed, the heating is stopped and cooled to room temperature, hydrochloric acid is added to adjust the pH to 4, the oil bath is heated to 80℃, and the reflux reaction is carried out for 8h;

[0045] S4. The reaction container is sealed, the pressure in the container is maintained at 2MPa, heated to 140℃, reacted for 6h, cooled to room temperature, filtered and dried to obtain the hyperbranched core-shell flame retardant.

[0046] Example 4

[0047] The raw materials are weighed by parts, including 20 parts of styrene monomer, 0.20 parts of organic dispersant carboxymethyl cellulose, 0.1 parts of inorganic dispersant magnesium carbonate, 0.85 parts of foaming agent n-pentane, 3.8 parts of hyperbranched core-shell flame retardant, 0.6 parts of initiator tert-butyl benzene acid peroxide and 90 parts of water. The styrene monomer, hyperbranched core-shell flame retardant and deionized water are put into the reaction kettle, mixed uniformly, then half of the inorganic dispersant, half of the organic dispersant and the initiator are put in, and the material in the reaction kettle is heated to 80℃, and the polymerization reaction is carried out at this temperature for 10 hours. The remaining dispersant and foaming agent are added, the reaction kettle is heated to 130℃, and kept at this temperature for 3h. The material in the reaction kettle is taken out, filtered and dried to obtain the flame-retardant expandable polystyrene beads.

[0048] The specific preparation method of the hyperbranched core-shell flame retardant includes the following steps:

[0049] S1. In an oil bath at 55℃, 12 parts of expanded graphite with a particle size of 100 mesh, 0.4 parts of stearic acid and 100 parts of water are added into the reaction container, stirred uniformly, then 2 parts of acrylamide, 2 parts of acrylic acid, 1 part of 2-acrylamide-2-methylpropane sulfonic acid, 1 part of sodium hydroxide, 0.1 part of propylene glycol and 0.03 part of pentaerythritol triallyl ether are added, stirred for 60 min, heated to 80℃ under nitrogen protection, 0.05 parts of potassium persulfate are added for polymerization reaction for 3h, after the reaction is completed, filtration is carried out to obtain the first shell coated material;

[0050] S2. The first shell coated material in step 1 is added into a mixed solution containing 3 parts of diethyl methylphosphonate and 100 parts of methanol, stirred uniformly, 0.05 parts of azobisisobutyronitrile, 1 part of dimethyl acrylate and 1.5 parts of vinyl acetate are mixed, slowly added into the reaction container, stirred at a speed of 300 rpm for 12h;

[0051] S3. After the reaction is completed, the heating is stopped and cooled to room temperature, hydrochloric acid is added to adjust the pH to 2, the oil bath is heated to 75℃, and the reflux reaction is carried out for 8h;

[0052] S4. The reaction container is sealed, the pressure in the container is maintained at 1.5MPa, heated to 120℃, reacted for 12h, cooled to room temperature, filtered and dried to obtain the hyperbranched core-shell flame retardant.

[0053] Example 5

[0054] The raw materials are weighed by parts, including 20 parts of styrene monomer, 0.25 parts of organic dispersant hydroxyethyl cellulose, 0.15 parts of inorganic dispersant calcium carbonate, 0.85 parts of foaming agent isopentane, 4 parts of hyperbranched core-shell flame retardant, 0.4 parts of initiator tert-butyl benzene acid peroxide and 100 parts of water. The styrene monomer, hyperbranched core-shell flame retardant and deionized water are put into the reaction kettle, mixed uniformly, then half of the amount of inorganic dispersant, half of the amount of organic dispersant and initiator are added, and mechanical stirring is carried out for 30 min. The temperature of the material in the reaction kettle is raised to 80℃, and the polymerization reaction is carried out at this temperature for 10 hours. The remaining dispersant and foaming agent are added, and the reaction kettle is heated to 120℃ and kept at this temperature for 4h. The material in the reaction kettle is taken out, filtered and dried to obtain the flame-retardant expandable polystyrene beads.

[0055] The specific preparation method of the hyperbranched core-shell flame retardant includes the following steps:

[0056] S1. In an oil bath at 50℃, 12 parts of expanded graphite with a particle size of 500 mesh, 0.2 parts of stearic acid and 150 parts of water are added into the reaction container, stirred uniformly, then 3 parts of acrylamide, 3 parts of acrylic acid, 1 part of 2-acrylamide-2-methylpropane sulfonic acid, 0.5 parts of sodium hydroxide, 0.05 parts of propylene glycol and 0.05 parts of pentaerythritol triallyl ether are added, stirred for 60 min, heated to 85℃ under nitrogen protection, and 0.05 parts of potassium persulfate is added for polymerization reaction for 4h. After the reaction is completed, filtration is carried out to obtain the first shell coated material;

[0057] S2. The first shell coated material in step 1 is added into a mixed solution containing 3 parts of diethyl methylphosphonate and 80 parts of methanol, stirred uniformly, and 0.1 parts of azobisisobutyronitrile, 0.5 parts of ethylene glycol dimethacrylate and 1 part of vinyl acetate are mixed under nitrogen protection, slowly added into the reaction container, and stirred at a speed of 200 rpm for 12h;

[0058] S3. After the reaction is completed, the heating is stopped and the temperature is cooled to room temperature. Hydrochloric acid is added to adjust the pH to 3. The oil bath is heated to 80℃ and refluxed for 8h;

[0059] S4. The reaction container is sealed, the pressure in the container is maintained at 2MPa, the temperature is raised to 120℃, and the reaction is carried out for 10h. The temperature is cooled to room temperature, filtered and dried to obtain the hyperbranched core-shell flame retardant.

[0060] Comparative Example 1

[0061] The difference between this comparative example and Example 1 is only that the preparation of the hyperbranched core-shell flame retardant does not have an inner shell coating, which includes the following steps:

[0062] S1. In a reaction vessel, 12 parts of expanded graphite with a particle size of 200 mesh, 0.3 parts of stearic acid, and 150 parts of water were added in an oil bath at 50°C, stirred for 30 min, heated to 85°C under nitrogen protection, and 0.03 parts of potassium persulfate was added for polymerization reaction for 4 h. After the reaction was completed, filtration was performed to obtain a primary shell coating material;

[0063] S2. The primary shell coating material in step 1 was added to a mixed solution containing 2 parts of diethyl methylphosphonate and 100 parts of methanol, stirred uniformly, and 0.08 parts of azobisisobutyronitrile, 0.8 parts of ethylene glycol dimethacrylate, and 1.2 parts of vinyl acetate were mixed and slowly added into the reaction vessel under nitrogen protection. The reaction was stirred at a rate of 200 rpm for 15 h;

[0064] S3. After the reaction was completed, heating was stopped and cooled to room temperature, hydrochloric acid was added to adjust the pH to 2-4, the oil bath was warmed to 75°C, and reflux reaction was performed for 10 h;

[0065] S4. The reaction vessel was sealed, the pressure in the vessel was maintained at 1.5 MPa, and the temperature was raised to 130°C. The reaction was performed for 10 h, cooled to room temperature, filtered, and dried to obtain a hyperbranched core-shell flame retardant.

[0066] Comparative Example 2

[0067] The difference between this comparative example and Example 1 is that no outer shell coating was performed in the preparation of the hyperbranched core-shell flame retardant, which specifically includes the following steps:

[0068] S1. In a reaction vessel, 12 parts of expanded graphite with a particle size of 200 mesh, 0.3 parts of stearic acid, and 150 parts of water were added in an oil bath at 50°C, stirred for 30 min, heated to 85°C under nitrogen protection, and 0.03 parts of potassium persulfate was added for polymerization reaction for 4 h. After the reaction was completed, filtration was performed to obtain a primary shell coating material;

[0069] S2. The primary shell coating material in step 1 was added to 100 parts of methanol, stirred uniformly, and stirred at a rate of 200 rpm for 15 h under nitrogen protection;

[0070] S3. After the reaction was completed, heating was stopped and cooled to room temperature, hydrochloric acid was added to adjust the pH to 2-4, the oil bath was warmed to 75°C, and reflux reaction was performed for 10 h;

[0071] S4. The reaction vessel was closed and the pressure in the vessel was maintained at 1.5 MPa. The temperature was raised to 130°C and the reaction was allowed to proceed for 10 h. The reaction mixture was cooled to room temperature, filtered and dried to obtain the hyperbranched core-shell flame retardant.

[0072] Comparative Example 3

[0073] The only difference between this comparative example and Example 1 is that the hyperbranched core-shell flame retardant was replaced by ordinary expanded graphite in the preparation of the flame-retardant expandable polystyrene beads.

[0074] Effectiveness demonstration

[0075] The flame-retardant expandable polystyrene beads obtained in the examples and comparative examples were filled into a mold, the temperature was controlled at 110°C, and the polystyrene foamed material was prepared by mold foaming. The compressive strength of the foamed material was determined according to GB / T 8813-2008 "Hard Foam Plastic Compression Strength Test Method", and the limiting oxygen index was tested according to GB / T 2406.2-2009 "Oxygen Index Method for Determining Combustion Behavior of Plastics". The specific test results are shown in Table 1:

[0076]

[0077] Result analysis

[0078] Examples 1-5 and Comparative Examples 1-3 were analyzed, combined with the data in Table 1 and Figure 1 It can be seen that the polystyrene foamed material prepared from the flame-retardant expandable polystyrene beads provided by the present application has good flame-retardant performance, and at the same time has a high compressive strength. The specific analysis is as follows:

[0079] As can be seen from Comparative Example 1, when the inner shell layer is not coated in the preparation of the hyperbranched core-shell flame retardant, the limiting oxygen index of the polystyrene foamed material prepared is significantly reduced, and the flame-retardant performance is greatly reduced;

[0080] As can be seen from Comparative Example 2, when the outer shell layer is not coated in the preparation of the hyperbranched core-shell flame retardant, the compressive strength of the polystyrene foamed material prepared is significantly reduced, and the mechanical properties are greatly reduced;

[0081] In summary, Comparative Examples 1-3, it can be seen that the inner shell layer of the hyperbranched core-shell flame retardant can improve the flame-retardant performance of the polystyrene foamed material, the outer shell layer can improve the compressive strength of the polystyrene foamed material, and at the same time the inner and outer shell layer structure can cooperate with each other to produce a certain synergistic effect, so that the compressive strength of the foamed material is further improved.

[0082] It should be further noted that any technically feasible combination of the various technical features described in the above embodiments is possible, provided that there is no contradiction, and the present application does not make any further statement on the various possible combinations.

[0083] Furthermore, any combination of the various embodiments of the present application is possible, provided that there is no contradiction, and should be considered as disclosed by the present application.

Claims

1. A flame-retardant expandable polystyrene bead characterized by, Prepared from the following raw materials by weight parts: 20 parts of styrene monomer, 0.20-0.25 parts of organic dispersant, 0.05-0.15 parts of inorganic dispersant, 0.75-0.85 parts of foaming agent, 3.8-4.2 parts of hyperbranched core-shell flame retardant, 0.4-0.6 parts of initiator and 90-110 parts of water, wherein the hyperbranched core-shell flame retardant is prepared by coating the shell with expanded graphite and hyperbranched treatment; The specific preparation method of the hyperbranched core-shell flame retardant includes the following steps: S1. In an oil bath at 50-55℃, 10-15 parts of expanded graphite, 0.2-0.4 parts of stearic acid and 100-200 parts of water are added to the reaction container, stirred uniformly, then 2-3 parts of acrylamide, 2-3 parts of acrylic acid, 1-2 parts of 2-acrylamide-2-methylpropane sulfonic acid, 0.5-1.0 parts of sodium hydroxide, 0.05-0.1 parts of propylene glycol and 0.03-0.08 parts of pentaerythritol triallyl ether are added, stirred for 30-60 min, heated to 80-90℃ under nitrogen protection, 0.02-0.05 parts of potassium persulfate is added for polymerization reaction for 3-5 h, after the reaction is completed, filtration is carried out to obtain a first shell coating material; S2. The first shell coating material in step 1 is added to a mixed solution containing 1-3 parts of diethyl methylphosphonate and 80-100 parts of methanol, stirred uniformly, 0.05-0.1 parts of azobisisobutyronitrile, 0.5-1 parts of ethylene glycol dimethacrylate and 1.0-1.5 parts of vinyl acetate are mixed, slowly added into the reaction container, stirred at a speed of 100-300 rpm for 12-18 h; S3. After the reaction is completed, heating is stopped and cooled to room temperature, hydrochloric acid is added to adjust the pH to 2-4, the oil bath is heated to 70-80℃, and reflux reaction is carried out for 8-10 h; S4. The reaction container is sealed, the pressure in the container is maintained at 1.5-2.0 MPa, heated to 120-140℃ for 6-12 h, cooled to room temperature, filtered, dried to obtain a hyperbranched core-shell flame retardant.

2. The flame retardant expandable polystyrene bead according to claim 1, wherein, The organic dispersant is one or more than two combinations of hydroxyethyl cellulose, methyl cellulose, sodium methyl cellulose and carboxymethyl cellulose.

3. The flame retardant expandable polystyrene bead according to claim 1, wherein, The inorganic dispersant is one or more than two combinations of calcium carbonate, calcium phosphate, talc and magnesium carbonate.

4. The flame retardant expandable polystyrene bead of claim 1, wherein, The initiator is one or more than two combinations of benzoyl peroxide, tert-butyl benzene peroxide and dicumyl peroxide.

5. The flame retardant expandable polystyrene bead of claim 1, wherein, The foaming agent is one or more than two combinations of n-pentane, isopentane and neopentane.

6. The flame retardant expandable polystyrene bead according to claim 1, wherein, The expanded graphite particle size range is 100-500 mesh.

7. A process for the preparation of flame-retardant expandable polystyrene beads, characterized in that, The method for preparing the flame-retardant expandable polystyrene beads of any one of claims 1-6, specifically includes the following steps: The raw materials are weighed, the styrene monomer, hyperbranched core-shell flame retardant and deionized water are put into a reaction kettle, mixed uniformly, then half of the inorganic dispersant, half of the organic dispersant and the initiator are put in, and mechanical stirring is carried out for 30-60 min, the temperature of the materials in the reaction kettle is raised to 80-90 ℃, and the polymerization reaction is carried out at this temperature for 6-10 h, the remaining dispersant and foaming agent are added, the reaction kettle is heated to 110-130 ℃, and the temperature is kept constant for 3-5 h, then the materials in the reaction kettle are taken out, filtered and dried to obtain the flame-retardant expandable polystyrene beads.

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