A method for preparing halogen-free flame-retardant polystyrene beads and expandable polystyrene beads using waste polystyrene.

Abstract

This invention relates to the field of polymer materials technology, and provides a method for preparing halogen-free flame-retardant polystyrene beads and expandable polystyrene beads from waste polystyrene. The invention uses a non-water-soluble composite halogen-free flame retardant and waste polystyrene as raw materials, employing a dissolution-distillation-suspension method to effectively composite the flame retardant and polystyrene, thus preparing halogen-free flame-retardant polystyrene beads. A foaming agent is then added to prepare halogen-free flame-retardant expandable polystyrene beads. The method provided by this invention is simple, energy-saving, emission-reducing, and environmentally friendly. The resulting halogen-free flame-retardant expandable polystyrene beads exhibit excellent flame-retardant properties, solving the "white pollution" problem caused by waste polystyrene and the safety hazards of storing polystyrene as a flammable material. It also reduces resource waste caused by traditional processing methods and the large consumption of petroleum resources in polystyrene production, aligning with the national "dual-carbon" strategic goal and possessing broad prospects.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a method for preparing halogen-free flame-retardant polystyrene beads and expandable polystyrene beads using waste polystyrene. Background Technology

[0002] Polymer materials are widely used in production and daily life, but most polymer materials are flammable, posing a serious fire hazard. Polystyrene foam is widely used in production and daily life, is extremely flammable, and releases toxic gases when burning, seriously endangering the lives of users. Waste polystyrene is extremely difficult to degrade, causing "white pollution." Therefore, the flammability of polystyrene materials and the recycling and reuse of waste polystyrene are urgent problems that need to be solved.

[0003] Chinese patent CN113652075A discloses a halogen-free flame-retardant composite material, its preparation method, and its application. The method involves adding thermoplastic polymers and functional additives to a twin-screw extruder for extrusion, followed by injection molding to obtain the finished product. Chinese patent CN110922691A discloses a halogen-free flame-retardant polystyrene masterbatch and its preparation method. The method involves dry-mixing polystyrene resin, phosphorus-based flame retardant, antioxidant, toughening agent, flame retardant synergist, anti-dripping agent, and lubricant in a high-speed mixer according to a specified ratio. The mixture is then added to a twin-screw extruder for melting, mixing, extrusion, cooling, drying, and granulation to obtain the halogen-free flame-retardant polystyrene masterbatch. In addition, there are reports of preparing halogen-free flame-retardant polystyrene beads through suspension polymerization. This method involves adding flame retardants during the polymerization of styrene monomers. In the literature on the mechanism of suspension polymerization, B. Kichatov et al. explained in "Particle Size Distribution of the Product of Suspension Polymerization" that the stability of the suspension polymerization system is the key to successful polymerization. Introducing flame retardants during suspension polymerization will inevitably affect the stability of the polymerization system, resulting in slowed polymerization or even inhibition of polymerization.

[0004] In summary, existing methods for preparing halogen-free flame-retardant polystyrene composites mainly include copolymerization and blending. Suspension polymerization requires the selection of flame retardants with high compatibility with styrene monomers to minimize negative impacts on the suspension polymerization system, making the selection of flame retardants quite stringent. Copolymerization and blending methods typically require extrusion granulation, which involves harsh reaction conditions, complex process parameters, and the release of toxic and harmful gases during production. Furthermore, the aforementioned patents and literature all utilize virgin polystyrene materials and do not involve the recycling and reuse of waste polystyrene.

[0005] Therefore, there is an urgent need to provide a simple and easy-to-operate method for preparing halogen-free flame-retardant polystyrene beads that can achieve the reuse of waste polystyrene. Summary of the Invention

[0006] In view of this, the present invention provides a method for preparing halogen-free flame-retardant polystyrene beads and expandable polystyrene beads using waste polystyrene. The method provided by the present invention uses waste polystyrene as raw material, and the preparation method is simple and easy to operate, effectively solving the problems of environmental pollution caused by waste polystyrene and the safety hazards posed by polystyrene as a flammable material.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] A method for preparing halogen-free flame-retardant polystyrene beads using waste polystyrene includes the following steps:

[0009] Waste polystyrene, a composite halogen-free flame retardant, a dispersant, water, and an organic solvent are mixed to obtain a mixed solution; the composite halogen-free flame retardant is obtained by combining at least two halogen-free flame retardants; the halogen-free flame retardant is a phosphorus-based flame retardant, a nitrogen-based flame retardant, or a nitrogen-phosphorus-based flame retardant; the halogen-free flame retardant is a non-water-soluble flame retardant.

[0010] Under stirring conditions, the organic solvent in the mixed solution is evaporated to obtain halogen-free flame-retardant polystyrene beads.

[0011] Preferably, the mixture includes:

[0012] Waste polystyrene, composite halogen-free flame retardant and organic solvent are mixed to obtain a premix of composite halogen-free flame retardant and waste polystyrene;

[0013] The dispersant and water are mixed to obtain an aqueous dispersant solution;

[0014] The aqueous dispersant solution is added to the premixed solution of the composite halogen-free flame retardant and waste polystyrene.

[0015] Preferably, the mass ratio of the waste polystyrene to the organic solvent is 1:2 to 10; the mass ratio of the waste polystyrene to the composite halogen-free flame retardant is 100:0.5 to 10.

[0016] The dispersant is a surfactant, or a mixture of a surfactant and a water-soluble dispersant; when the dispersant is a surfactant, the mass fraction of the aqueous dispersant solution is 0.2-4.5%; when the dispersant is a mixture of a surfactant and a water-soluble dispersant, the total mass fraction of the surfactant and the water-soluble dispersant in the aqueous dispersant solution is 0.2-5%, wherein the mass fraction of the water-soluble dispersant is ≤0.5%.

[0017] The volume ratio of the dispersant aqueous solution to the premixed solution of the composite halogen-free flame retardant and waste polystyrene is 2 to 10:1.

[0018] Preferably, the composite halogen-free flame retardant comprises at least two of the following: ammonium polyphosphate, hexaphenoxycyclotriphosphazene, melamine polyphosphate, melamine cyanurate, melamine phytate, tripentaerythritol phosphate, tricresyl phosphate, triphenyl phosphate, triisopropylphenyl phosphate, toluene diphenyl phosphate, and tetraethyl N,N-p-phenylenediamine (2-hydroxy)dibenzylphosphonate.

[0019] The surfactant includes one or more of sulfates, sulfonates, fatty acid salts, sodium lauryl alcohol polyoxyethylene ether sulfate, and terdizoli; the water-soluble dispersant includes one or more of alkyl cellulose, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, and alkylphenol polyoxyethylene ether.

[0020] The organic solvents include dichloromethane, acetone, methyl ethyl ketone, benzene, toluene, xylene, cyclohexane, methyl acetate, ethyl acetate, butyl acetate, limonene, or terpenes.

[0021] Preferably, the distillation includes a first-stage distillation and a second-stage distillation performed sequentially; the temperature of the first-stage distillation is the boiling point of the organic solvent, and the holding time is 1-3 hours; the temperature of the second-stage distillation is 15-30°C above the boiling point of the organic solvent, and the holding time is 0.5-4 hours; the heating rate from room temperature to the temperature of the first-stage distillation is 0.5-2°C / min; the heating rate from the temperature of the first-stage distillation to the temperature of the second-stage distillation is 0.2-0.5°C / min.

[0022] The present invention also provides halogen-free flame-retardant polystyrene beads prepared by the method described above, wherein the particle size of the halogen-free flame-retardant polystyrene beads is 0.5-3 mm.

[0023] This invention also provides a method for preparing halogen-free flame-retardant expandable polystyrene beads, comprising the following steps:

[0024] Under closed conditions, the halogen-free flame-retardant polystyrene beads and surfactant aqueous solution described in the above scheme are mixed and heated to 85-100°C. Then, a physical foaming agent is added and the mixture is stirred at a constant temperature for 4-6 hours. During the stirring process, an inorganic dispersant is added to the system.

[0025] After the constant temperature stirring is completed, the resulting product liquid is cooled and then subjected to solid-liquid separation and drying in sequence to obtain halogen-free flame-retardant expandable polystyrene beads.

[0026] Preferably, the mass fraction of the surfactant aqueous solution is 4-8%; the mass ratio of the halogen-free flame-retardant polystyrene beads to the surfactant aqueous solution is 1:1-4.

[0027] Preferably, the physical blowing agent includes one or more of propane, butane, pentane, hexane, heptane, petroleum ether, Freon 11 or Freon 12; the mass of the physical blowing agent is 6 to 10% of the mass of the halogen-free flame-retardant polystyrene beads.

[0028] The inorganic dispersant includes one or more of calcium phosphate, hydroxycalcium phosphate, calcium carbonate, calcium oxalate, barium sulfate, calcium sulfate, zinc oxide, magnesium hydroxide, aluminum hydroxide, bentonite, kaolin, titanium dioxide, graphite, and mica; the mass of the inorganic dispersant is 0.1% to 8% of the mass of water in the system.

[0029] The present invention also provides halogen-free flame-retardant expandable polystyrene beads prepared by the preparation method described above, wherein the particle size of the halogen-free flame-retardant expandable polystyrene beads is 0.5-3 mm.

[0030] This invention provides a method for preparing halogen-free flame-retardant polystyrene beads from waste polystyrene, comprising the following steps: mixing waste polystyrene, a composite halogen-free flame retardant, a dispersant, water, and an organic solvent to obtain a mixed solution; wherein the composite halogen-free flame retardant is obtained by combining at least two halogen-free flame retardants; wherein the halogen-free flame retardant is a phosphorus-based flame retardant, a nitrogen-based flame retardant, or a nitrogen-phosphorus-based flame retardant; wherein the halogen-free flame retardant is a non-water-soluble flame retardant; and, under stirring conditions, evaporating the organic solvent from the mixed solution to obtain halogen-free flame-retardant polystyrene beads. This invention uses waste polystyrene as raw material and employs a dissolution-distillation-suspension method to prepare halogen-free flame-retardant polystyrene beads. This method enables better composite formation of halogen-free flame retardants and polystyrene, and the preparation process is simple, easy to scale up, and achieves efficient recycling of waste polystyrene. This invention uses halogen-free flame retardants, which are safe and environmentally friendly. Furthermore, the phosphorus-based flame retardants selected in this invention have high compatibility with polystyrene and organic solvents, and are less prone to adhesion during the composite process. They synergistically form an intumescent flame-retardant system with nitrogen-based flame retardants, resulting in a flame-retardant effect superior to that of using a single flame retardant. Moreover, the halogen-free flame retardants selected in this invention are all non-water-soluble flame retardants. By utilizing these non-water-soluble flame retardants to composite with polystyrene in the organic phase, the preparation of halogen-free flame-retardant polystyrene beads is achieved.

[0031] Furthermore, the organic solvent selected in this invention is a low-toxicity solvent, especially dichloromethane, which is non-flammable, non-explosive, low-boiling point, non-toxic and environmentally friendly. The organic solvent used can be recycled after distillation, and the dispersant solution can also be recycled, avoiding the generation of waste liquid, making it more environmentally friendly, and further reducing the preparation cost.

[0032] In summary, this invention simultaneously solves the problem of "white pollution" caused by waste polystyrene and the safety hazards of storing polystyrene as a flammable material. It can also reduce resource waste caused by traditional treatment methods and the large amount of petroleum resources consumed in the production of polystyrene. It is energy-saving, emission-reducing, and environmentally friendly, and is in line with the national "dual carbon" strategic goal.

[0033] The present invention also provides a halogen-free flame-retardant expandable polystyrene bead, which is prepared by using the above-mentioned method to obtain halogen-free flame-retardant polystyrene beads, as well as surfactants and foaming agents. The results of the examples show that the halogen-free flame-retardant expandable polystyrene beads provided by the present invention have excellent flame-retardant effect. Attached Figure Description

[0034] Figure 1 This is a photograph of the halogen-free flame-retardant polystyrene beads prepared in Example 1 of the present invention.

[0035] Figure 2 This is a photograph of the halogen-free flame-retardant polystyrene beads prepared in Example 2 of the present invention.

[0036] Figure 3 This is a photograph of the halogen-free flame-retardant polystyrene beads prepared in Example 3 of the present invention.

[0037] Figure 4 This is a photograph of the halogen-free flame-retardant polystyrene beads prepared in Example 4 of the present invention.

[0038] Figure 5 This is a photograph of the halogen-free flame-retardant polystyrene beads prepared in Example 5 of the present invention.

[0039] Figure 6 This is a photograph of the halogen-free flame-retardant polystyrene beads prepared in Comparative Example 1 of this invention.

[0040] Figure 7 This is a photograph of the halogen-free flame-retardant polystyrene beads prepared in Comparative Example 2 of this invention. Detailed Implementation

[0041] This invention provides a method for preparing halogen-free flame-retardant polystyrene beads using waste polystyrene, comprising the following steps:

[0042] Waste polystyrene, a composite halogen-free flame retardant, a dispersant, water, and an organic solvent are mixed to obtain a mixed solution; the composite halogen-free flame retardant is obtained by combining at least two halogen-free flame retardants; the halogen-free flame retardant is a phosphorus-based flame retardant, a nitrogen-based flame retardant, or a nitrogen-phosphorus-based flame retardant; the halogen-free flame retardant is a non-water-soluble flame retardant.

[0043] Under stirring conditions, the organic solvent in the mixed solution is evaporated to obtain halogen-free flame-retardant polystyrene beads.

[0044] Unless otherwise specified, all raw materials used in this invention are commercially available.

[0045] This invention mixes waste polystyrene, a composite halogen-free flame retardant, a surfactant, water, and an organic solvent to obtain a mixed solution. This invention does not have special requirements for the waste polystyrene; common waste polystyrene products in the art can be used as raw materials, such as shockproof packaging materials for valuable or fragile items and packaging for fast food, provided they are washed and crushed before use. In this invention, the composite halogen-free flame retardant is obtained by combining at least two halogen-free flame retardants; the halogen-free flame retardant is a phosphorus-based flame retardant, a nitrogen-based flame retardant, or a nitrogen-phosphorus-based flame retardant, and the halogen-free flame retardant is a non-water-soluble flame retardant; specifically, the composite halogen-free flame retardant includes ammonium polyphosphate, hexaphenoxycyclotriphosphazene, melamine polyphosphate, melamine cyanurate, melamine phytate, tripentaerythritol phosphate, tricresyl phosphate, triphenyl phosphate, triisopropylphenyl phosphate, toluene diphenyl phosphate, and tetraethyl N,N-p-phenylenediamine (2-hydroxy)dibenzylphosphonate. At least two of the following are preferred, preferably two to three: In a specific embodiment of the present invention, the composite halogen-free flame retardant is preferably a composite of a phosphorus-based flame retardant and a nitrogen-based flame retardant, or a composite of a phosphorus-based, a nitrogen-based, and a nitrogen-phosphorus-based flame retardant, or a composite of a phosphorus-based, a nitrogen-based, and a nitrogen-phosphorus-based flame retardant, more preferably a melamine cyanurate-triphenyl phosphate composite, a melamine polyphosphate-triphenyl phosphate composite, a hexaphenoxycyclotriphosphazene-melamine cyanurate-triphenyl phosphate composite, a high-polyphosphate ammonium-tripentaerythritol phosphate-triphenyl phosphate composite, or a melamine polyphosphate-melamine cyanurate composite. The urate-triphenyl phosphate complex; the mass ratio of melamine cyanurate to triphenyl phosphate in the melamine cyanurate-triphenyl phosphate complex is preferably 1:0.6-1.4, more preferably 1:1; the mass ratio of melamine polyphosphate to triphenyl phosphate in the melamine polyphosphate-triphenyl phosphate complex is preferably 1:0.1-0.3, more preferably 1:0.2; the mass ratio of hexaphenoxycyclotriphosphazene, melamine cyanurate, and triphenyl phosphate complex in the hexaphenoxycyclotriphosphazene-melamine cyanurate-triphenyl phosphate complex is preferably... The mass ratio of ammonium polyphosphate, tripentaerythritol phosphate, and triphenyl phosphate in the ammonium polyphosphate-tripentaerythritol phosphate-triphenyl phosphate composite is preferably 1:0.2-0.4:0.2-0.4, more preferably 3:1:1; the mass ratio of melamine polyphosphate, melamine cyanurate, and triphenyl phosphate in the melamine polyphosphate-melamine cyanurate-triphenyl phosphate composite is preferably 1:0.2-0.4:0.2-0.4, more preferably 3:1:1.

[0046] In this invention, the dispersant is preferably a surfactant, or preferably a mixture of a surfactant and a water-soluble dispersant; the surfactant preferably includes one or more of sulfates, sulfonates, fatty acid salts, sodium fatty alcohol polyoxyethylene ether sulfate, and terdizoli; the water-soluble dispersant preferably includes one or more of alkyl cellulose, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, and alkylphenol polyoxyethylene ether; the sulfate is preferably sodium dodecyl sulfate; the sulfonate is preferably one or more of sodium dodecylbenzenesulfonate, disodium monoisodecyl sulfosuccinate, sodium octyl succinate, sodium methyl isobutyl sulfosuccinate, sodium dicyclohexyl sulfosuccinate, and disodium octadecyl sulfosuccinate; the fatty acid salt is preferably one or more of sodium laurate, sodium myristate, sodium palmitate, and barium laurate; the alkyl cellulose preferably includes one or more of hydroxypropyl cellulose, methylcellulose, methyl hydroxyethyl cellulose, and hydroxyethyl cellulose.

[0047] In this invention, the organic solvent preferably includes dichloromethane, acetone, methyl ethyl ketone, benzene, toluene, xylene, cyclohexane, methyl acetate, ethyl acetate, butyl acetate, limonene, or a terpene, and more preferably dichloromethane.

[0048] In this invention, the mixing preferably includes: mixing waste polystyrene, a composite halogen-free flame retardant, and an organic solvent to obtain a premix of the composite halogen-free flame retardant and waste polystyrene; mixing a dispersant and water to obtain an aqueous dispersant solution; adding the aqueous dispersant solution to the premix of the composite halogen-free flame retardant and waste polystyrene; the mass ratio of the waste polystyrene to the organic solvent is preferably 1:2 to 10, more preferably 1:3 to 8; the mass ratio of the waste polystyrene to the composite halogen-free flame retardant is preferably 100:0.5 to 10, more preferably 100:2 to 7; when the dispersant is a surfactant, the mass fraction of the aqueous dispersant solution is preferably 0.2 to 4.5%, more preferably 0.5 to 3%; when the dispersant is a mixture of a surfactant and a water-soluble dispersant... The total mass fraction of surfactant and water-soluble dispersant in the dispersant aqueous solution is preferably 0.2-5%, wherein the mass fraction of water-soluble dispersant is preferably ≤0.5%, more preferably 0.1-0.4% (the remainder being surfactant); the volume ratio of the dispersant aqueous solution to the premixed solution of the composite halogen-free flame retardant and waste polystyrene is preferably 2-10:1, more preferably 3-8:1; in this invention, it is preferable to first add waste polystyrene and composite halogen-free flame retardant to an organic solvent, and then add the resulting mixture to a three-necked flask and stir continuously for 40 minutes to ensure that the waste polystyrene and composite halogen-free flame retardant are fully mixed; the dispersant aqueous solution is preferably added slowly to the premixed solution of the composite halogen-free flame retardant and waste polystyrene, and the specific addition rate is based on ensuring uniform stirring and dispersion.

[0049] After obtaining the mixed solution, the present invention removes the organic solvent from the mixed solution under stirring conditions to obtain halogen-free flame-retardant polystyrene beads. In the present invention, the stirring speed is preferably 200-400 rpm, more preferably 250-350 rpm. The removal of solvent includes a first-stage distillation and a second-stage distillation performed sequentially. The temperature of the first-stage distillation is preferably the boiling point of the organic solvent, and the holding time is 1-3 hours. The temperature of the second-stage distillation is 15-30°C above the boiling point of the organic solvent, more preferably 20°C, and the holding time is 0.5-4 hours. The heating rate from room temperature to the temperature of the first-stage distillation is preferably 0.5-2°C / min. The heating rate from the temperature of the first-stage distillation to the temperature of the second-stage distillation is preferably 0.2-0.5°C / min. In a specific embodiment of the present invention, when the organic solvent is dichloromethane, the temperature of the first stage distillation is 40°C, and the temperature of the second stage distillation is 60°C. The present invention can ensure the complete removal of organic solvent from the system through two-stage distillation. The present invention removes organic solvent from the system under stirring conditions. In this process, polystyrene first enters the aqueous phase and forms droplets under the shear force of stirring. Under the action of the dispersant, the oil-in-water (O / W) emulsion droplets can be stabilized. Then, the solvent is distilled off to separate the polystyrene particles from the solvent. The flame retardants selected in the present invention are all insoluble in water and are combined with polystyrene during the first stage distillation to form halogen-free flame-retardant polystyrene beads. The distilled liquid is an organic solvent that can be reused.

[0050] After the organic solvent is completely evaporated, the present invention preferably cools down the material before discharge, and then the resulting liquid is filtered, washed and dried in sequence to obtain halogen-free flame-retardant polystyrene beads; the present invention removes moisture and residual dichloromethane in the beads by drying; the filtrate obtained by filtration is a dispersant aqueous solution, and the present invention preferably reuses the dispersant aqueous solution obtained by filtration.

[0051] The present invention also provides halogen-free flame-retardant polystyrene beads prepared by the preparation method described above, wherein the particle size of the halogen-free flame-retardant polystyrene beads is 0.5–3 mm, preferably 1–1.5 mm. In a specific embodiment of the present invention, the halogen-free flame-retardant polystyrene beads are mainly used to prepare halogen-free flame-retardant expandable polystyrene beads, which will be described in detail later.

[0052] This invention also provides a method for preparing halogen-free flame-retardant expandable polystyrene beads, comprising the following steps:

[0053] Under closed conditions, the halogen-free flame-retardant polystyrene beads and surfactant aqueous solution described in the above scheme are mixed and heated to 85-100°C. Then, a physical foaming agent is added and the mixture is stirred at a constant temperature for 4-6 hours. During the stirring process, an inorganic dispersant is added to the system.

[0054] After constant temperature stirring, the resulting product liquid was cooled and then subjected to solid-liquid separation and drying to obtain halogen-free flame-retardant expandable polystyrene beads.

[0055] In this invention, under sealed conditions, the halogen-free flame-retardant polystyrene beads and the surfactant aqueous solution described in the above scheme are mixed and heated to 85-100°C. A physical foaming agent is then added, and the mixture is stirred at a constant temperature for 4-6 hours. During the stirring process, an inorganic dispersant is added to the system. In this invention, the mass fraction of the surfactant aqueous solution is preferably 4-8%, more preferably 5-7%; the mass ratio of the halogen-free flame-retardant polystyrene beads to the surfactant aqueous solution is preferably 1:1-4, more preferably 1:2-3; the types of surfactants that can be selected are preferably the same as those described above, and will not be repeated here. The surfactant acts as a dispersant, preventing the halogen-free flame-retardant polystyrene beads from sticking together during the heating process. In this invention, the physical foaming agent preferably includes one or more of propane, butane, pentane, hexane, heptane, petroleum ether, Freon 11, or Freon 12; the mass of the physical foaming agent is preferably 6-10% of the mass of the halogen-free flame-retardant polystyrene beads, more preferably 8.5-9.5%; the inorganic dispersant preferably includes one or more of calcium phosphate, hydroxycalcium phosphate, calcium carbonate, calcium oxalate, barium sulfate, calcium sulfate, zinc oxide, magnesium hydroxide, aluminum hydroxide, bentonite, kaolin, titanium dioxide, graphite, and mica; the mass of the inorganic dispersant is preferably 0.1-8% of the mass of water in the system (i.e., water introduced during the foaming process), more preferably 2-4%; the addition of an inorganic dispersant with a layered structure in this invention allows the dispersant to adhere to the halogen-free flame-retardant polystyrene beads, allowing the foaming agent to remain on the surface of the halogen-free flame-retardant polystyrene beads, making it easier for the foaming agent to contact the halogen-free flame-retardant polystyrene beads, and at the same time, it can play a dispersing role and prevent particle adhesion.

[0056] In this invention, the sealed conditions are preferably provided by a high-pressure reactor. Preferably, halogen-free flame-retardant polystyrene beads are first added to the high-pressure reactor, followed by an aqueous surfactant solution. Then, under continuous stirring, the temperature is raised to 85–100°C, preferably 90–95°C. A foaming agent is then added through the liquid feed port of the high-pressure reactor, and stirring continues for 4–6 hours, preferably 4.5–5.5 hours. During this continued stirring, an inorganic dispersant is added through the solid feed port of the high-pressure reactor. The inorganic dispersant is preferably added after 0.5–1 hour of constant-temperature stirring, and the feed port of the high-pressure reactor is immediately sealed after addition. In this invention, the stirring speed is preferably 50–300 rpm, and the heating rate to 85–100°C is preferably 0.5–1°C / min.

[0057] After constant-temperature stirring, the resulting product liquid is cooled and then subjected to solid-liquid separation and drying to obtain halogen-free flame-retardant expandable polystyrene beads. Preferably, the cooling device of the high-pressure reaction vessel is opened while stirring to cool to room temperature, and then the material is discharged for solid-liquid separation. The specific drying conditions are not particularly demanding, as long as the moisture in the wet material obtained from the solid-liquid separation is sufficiently removed. After drying, the dried halogen-free flame-retardant expandable polystyrene beads are preferably cooled, sieved, and packaged to obtain finished halogen-free flame-retardant expandable polystyrene beads with a particle size of 0.5–3 mm.

[0058] This invention also provides halogen-free flame-retardant expandable polystyrene beads prepared by the preparation method described above, wherein the particle size of the halogen-free flame-retardant expandable polystyrene beads is 0.5–3 mm, preferably 1–2.5 mm. This invention does not specify the method of use for the halogen-free flame-retardant expandable polystyrene beads. In specific embodiments of this invention, the halogen-free flame-retardant expandable polystyrene beads are preferably foamed and molded into sheets.

[0059] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0060] Example 1

[0061] Take 25g of waste polystyrene, 0.25g of melamine cyanurate, and 0.25g of triphenyl phosphate and dissolve them in 100g of dichloromethane to obtain a premix. Add the premix to a three-necked flask and stir continuously for 40 minutes to ensure thorough mixing of the waste polystyrene and flame retardant. Add 1g of sodium dodecyl sulfate to 100mL of distilled water to obtain an aqueous dispersant solution. Slowly add the aqueous dispersant solution to the three-necked flask and mix it with the premix to obtain a mixed solution.

[0062] The stirring speed was controlled at 380 rpm, and the mixed solution was heated from room temperature to 40°C at a rate of 0.5°C / min and held for 2 hours. Then, the temperature was increased to 60°C at a rate of 0.5°C / min and held for 1 hour to ensure no more dichloromethane was distilled off. The mixture was cooled, discharged, filtered, and washed to obtain spherical beads. These beads were then dried to remove moisture and residual dichloromethane, yielding halogen-free flame-retardant polystyrene beads. The filtrate obtained after filtration was an aqueous solution containing dispersant, which could be reused. The distilled liquid, containing dichloromethane, could also be reused. Figure 1 This is a photograph of the halogen-free flame-retardant polystyrene beads prepared in this embodiment. Figure 1 It can be seen that the halogen-free flame-retardant polystyrene beads prepared by this invention are spherical particles with uniform particle size and good dispersibility.

[0063] The halogen-free flame-retardant polystyrene beads prepared above were added to a reactor. 5g of sodium dodecylbenzenesulfonate was added to 100mL of distilled water to obtain a surfactant aqueous solution. The surfactant aqueous solution was added to the reactor, and the mixture was continuously stirred at a speed of 200rpm. The temperature was increased to 90℃ at a rate of 1℃ / min. 3g of butane was added to the reactor, and the mixture was stirred at a constant temperature for 4 hours. During the process, 3g of calcium hydroxyphosphate was added to the reactor. The feed port of the high-pressure reactor was immediately sealed after the addition of the feed. After the constant temperature stirring was completed, the reactor cooling device was turned on while stirring to cool the mixture to room temperature. Solid-liquid separation was performed (the obtained filtrate is a surfactant aqueous solution, which can be reused) to obtain halogen-free flame-retardant expandable polystyrene spherical beads with a certain humidity. After drying, cooling, sieving, and packaging, the halogen-free flame-retardant expandable polystyrene bead product was obtained.

[0064] The halogen-free flame-retardant expandable polystyrene beads prepared in Example 1 were evenly placed in a mold and heated with steam for 30-50 seconds. After cooling, halogen-free flame-retardant polystyrene foam boards of the same size as the mold were obtained and prepared into boards. Performance tests were conducted according to national standards. The specific testing standards and results are shown in Table 1. The particle size data in Table 1 are the test data of the halogen-free flame-retardant polystyrene beads, and the other data are the test data of the boards prepared from the halogen-free flame-retardant expandable polystyrene beads. The subsequent examples will not be described in detail.

[0065] Table 1. Performance test data of halogen-free flame-retardant expandable polystyrene beads obtained in Example 1.

[0066]

[0067] Example 2

[0068] Take 25g of waste polystyrene, 1.25g of melamine polyphosphate, and 0.25g of triphenyl phosphate, and dissolve them in 100g of dichloromethane to obtain a premix. Add the premix to a three-necked flask and stir continuously for 40 minutes to ensure thorough mixing of the waste polystyrene and flame retardant. Add 2g of sodium dodecylbenzenesulfonate to 100mL of distilled water to obtain an aqueous dispersant solution. Slowly add the aqueous dispersant solution to a glass reactor and mix it with the premix to obtain a mixed solution.

[0069] The stirring speed was controlled at 300 rpm, and the mixed solution was heated from room temperature to 40°C at a rate of 0.5°C / min and held for 2 hours. Then, the temperature was increased to 60°C at a rate of 0.5°C / min and held for 1 hour to ensure no more dichloromethane was distilled off. The mixture was cooled and discharged, filtered, and washed to obtain spherical beads. These beads were then dried to remove moisture and residual dichloromethane, yielding halogen-free flame-retardant polystyrene beads. The filtrate obtained was an aqueous solution containing a dispersant, which could be reused. The distilled liquid, containing dichloromethane, could also be reused. Figure 2 This is a photograph of the halogen-free flame-retardant polystyrene beads prepared in this embodiment.

[0070] The halogen-free flame-retardant polystyrene beads prepared above were added to a reaction vessel. 8g of sodium dodecylbenzenesulfonate was added to 100mL of distilled water to obtain a surfactant solution. The surfactant solution was added to the reaction vessel, and the mixture was continuously stirred at a speed of 160rpm. The temperature was increased to 90℃ at a rate of 1℃ / min. 3g of pentane was added to the reaction vessel, and the mixture was stirred at a constant temperature for 4 hours. During the process, 2g of bentonite was added to the reaction vessel. The feed port of the high-pressure reaction vessel was immediately sealed after the addition of the materials. The cooling device of the reaction vessel was turned on while stirring, and the temperature was lowered to room temperature. Solid-liquid separation was performed (the obtained filtrate is a surfactant solution that can be reused) to obtain halogen-free flame-retardant expandable polystyrene beads with a certain humidity. After drying, cooling, sieving, and packaging, the halogen-free flame-retardant expandable polystyrene bead product was obtained.

[0071] The halogen-free flame-retardant expandable polystyrene spherical beads from Example 2 were evenly placed in a mold, heated with steam for 30–50 seconds, and then cooled to obtain a halogen-free flame-retardant polystyrene foam board of the same size as the mold. The board was then prepared and its performance was tested according to national standards. The specific testing standards and results are shown in Table 2.

[0072] Table 2. Performance test data of halogen-free flame-retardant expandable polystyrene beads obtained in Example 2.

[0073]

[0074] Example 3

[0075] 300g of waste polystyrene, 9g of hexaphenoxycyclotriphosphazene, 3g of melamine cyanurate, and 3g of triphenyl phosphate were dissolved in 1000g of dichloromethane to obtain a premix. The premix was added to a glass reactor and stirred continuously for 40 minutes to ensure thorough mixing of the waste polystyrene and the flame retardant. 15g of sodium fatty alcohol polyoxyethylene ether sulfate was added to 1L of distilled water to obtain an aqueous dispersant solution. The aqueous dispersant solution was slowly added to the glass reactor and mixed with the premix to obtain a mixed solution.

[0076] The stirring speed was controlled at 380 rpm, and the resulting mixed solution was heated from room temperature to 40°C at a rate of 0.5°C / min and held for 2 hours. Then, the temperature was increased to 60°C at a rate of 0.5°C / min and held for 1 hour to ensure no more dichloromethane was distilled off. The mixture was cooled, discharged, filtered, and washed to obtain spherical beads. These beads were then dried to remove moisture and residual dichloromethane, yielding halogen-free flame-retardant polystyrene beads. The filtrate, containing a dispersant, was an aqueous solution that could be reused. The distilled liquid, containing dichloromethane, could also be reused. Figure 3 This is a photograph of the halogen-free flame-retardant polystyrene beads prepared in this embodiment.

[0077] The halogen-free flame-retardant polystyrene beads prepared above were added to a high-pressure reactor. 40g of sodium dodecyl sulfate was added to 500mL of distilled water to obtain a surfactant aqueous solution. This surfactant aqueous solution was then added to the high-pressure reactor, and the mixture was continuously stirred at 260rpm. The temperature was increased to 90℃ at a rate of 1℃ / min. 30g of Freon 11 was added to the high-pressure reactor. After stirring at a constant temperature for 1 hour, 20g of sericite was added through the reactor's feed port. The feed port was immediately closed after the second addition. After the second addition, the mixture was stirred at a constant temperature for 3 hours. The reactor cooling device was then turned on while stirring to lower the temperature to room temperature. Solid-liquid separation was performed (the resulting filtrate was a surfactant aqueous solution, which could be reused), yielding halogen-free flame-retardant expandable polystyrene beads with a certain moisture content. These beads were then dried, cooled, sieved, and packaged to obtain the halogen-free flame-retardant expandable polystyrene bead product.

[0078] The halogen-free flame-retardant expandable polystyrene spherical beads from Example 3 were evenly placed in a mold, heated with steam for 30–50 seconds, and then cooled to obtain a halogen-free flame-retardant polystyrene foam board of the same size as the mold. The board was then prepared and its performance was tested according to national standards. The specific testing standards and results are shown in Table 3.

[0079] Table 3. Performance test data of halogen-free flame-retardant expandable polystyrene beads obtained in Example 3.

[0080]

[0081]

[0082] Example 4

[0083] Dissolve 300g of waste polystyrene, 9g of ammonium polyphosphate, 3g of tripentaerythritol phosphate, and 3g of tricresyl phosphate in 1000g of dichloromethane to obtain a premix. Add the premix to a glass reactor and stir continuously for 40 minutes to ensure thorough mixing of the waste polystyrene and flame retardant. Add 8g of sodium dodecylbenzenesulfonate and 2g of alkylphenol polyoxyethylene ether to 1L of distilled water to obtain an aqueous dispersant solution. Slowly add the aqueous dispersant solution to the glass reactor and mix with the premix to obtain a mixed solution.

[0084] The stirring speed was controlled at 400 rpm, and the mixed solution was heated from room temperature to 40°C at a rate of 0.5°C / min and held for 2 hours. Then, the temperature was increased to 60°C at a rate of 0.5°C / min and held for 1 hour to ensure no more dichloromethane was distilled off. The mixture was cooled and discharged, filtered, and washed to obtain spherical beads. These beads were then dried to remove moisture and residual dichloromethane, yielding halogen-free flame-retardant polystyrene beads. The filtrate obtained was an aqueous solution containing a dispersant, which could be reused. The distilled liquid, containing dichloromethane, could also be reused. Figure 4 This is a photograph of the halogen-free flame-retardant polystyrene beads prepared in this embodiment.

[0085] The halogen-free flame-retardant polystyrene beads prepared above were added to a high-pressure reactor. 25g of sodium dodecylbenzenesulfonate was added to 500mL of distilled water to obtain a surfactant aqueous solution. This surfactant aqueous solution was added to the high-pressure reactor, and the mixture was continuously stirred at 260rpm. The temperature was increased to 90℃ at a rate of 1℃ / min. 30g of butane was added to the high-pressure reactor, and after stirring at a constant temperature for 1 hour, 10g of sericite and 10g of talc were added through the reactor's feed port. The feed port was immediately closed after the second addition. After the second addition, the reactor was stirred at a constant temperature for 3 hours. The reactor cooling device was then turned on while stirring to cool to room temperature. Solid-liquid separation was performed to obtain halogen-free flame-retardant expandable polystyrene beads with a certain moisture content. These beads were then dried, cooled, sieved, and packaged to obtain the halogen-free flame-retardant expandable polystyrene bead product.

[0086] The halogen-free flame-retardant expandable polystyrene beads from Example 4 were evenly placed in a mold, heated with steam for 30–50 seconds, and then cooled to obtain a halogen-free flame-retardant polystyrene foam board of the same size as the mold. The board was then prepared and its performance was tested according to national standards. The specific testing standards and results are shown in Table 4.

[0087] Table 4. Performance test data of halogen-free flame-retardant expandable polystyrene beads obtained in Example 4

[0088]

[0089] Example 5

[0090] Take 3000g of waste polystyrene, 90g of melamine polyphosphate, 30g of melamine cyanurate, and 30g of triphenyl phosphate, and dissolve them in 7500g of dichloromethane to obtain a premix. Add the premix to a glass reactor and stir continuously for 40 minutes to ensure thorough mixing of the waste polystyrene and flame retardant. Add 100g of sodium dodecyl sulfate and 10g of hydroxypropyl cellulose to 5L of distilled water to obtain a dispersant aqueous solution. Slowly add the dispersant aqueous solution to the glass reactor and mix it with the premix to obtain a mixed solution.

[0091] The stirring speed was controlled at 350 rpm, and the mixed solution was heated from room temperature to 40°C at a rate of 0.5°C / min and held for 2 hours. Then, the temperature was increased to 60°C at a rate of 0.5°C / min and held for 1 hour to ensure no more dichloromethane was distilled off. The mixture was cooled, discharged, filtered, and washed to obtain spherical beads. These beads were then dried to remove moisture and residual dichloromethane, yielding halogen-free flame-retardant polystyrene beads. The filtrate, containing a dispersant, was an aqueous solution that could be reused. The distilled liquid, containing dichloromethane, could also be reused. Figure 5 This is a photograph of the halogen-free flame-retardant polystyrene beads prepared in this embodiment.

[0092] The halogen-free flame-retardant polystyrene beads prepared above were added to a high-pressure reactor. 250g of sodium dodecylbenzenesulfonate was added to 5L of distilled water to obtain a surfactant aqueous solution. This surfactant aqueous solution was added to the high-pressure reactor, and the mixture was continuously stirred at 260 rpm. The temperature was increased to 90°C at a rate of 1°C / min. 300g of pentane was added to the high-pressure reactor. After stirring at a constant temperature for 1 hour, 100g of sericite and 100g of calcium hydroxyphosphate were added through the reactor's feed port. The feed port was immediately closed after the second addition. After the second addition, the mixture was stirred at a constant temperature for 3 hours. The reactor cooling device was then turned on while stirring to cool to room temperature. Solid-liquid separation was performed to obtain halogen-free flame-retardant expandable polystyrene beads with a certain moisture content. These beads were then dried, cooled, sieved, and packaged to obtain the halogen-free flame-retardant expandable polystyrene bead product.

[0093] The halogen-free flame-retardant expandable polystyrene beads from Example 5 were evenly placed in a mold, heated with steam for 30–50 seconds, and then cooled to obtain a halogen-free flame-retardant polystyrene foam board of the same size as the mold. The board was then prepared and its performance was tested according to national standards. The specific testing standards and results are shown in Table 5.

[0094] Table 5. Performance test data of halogen-free flame-retardant expandable polystyrene beads obtained in Example 5.

[0095]

[0096] Comparative Example 1 uses a water-soluble flame retardant

[0097] Take 25g of waste polystyrene and 1.5g of water-soluble oligomeric ammonium polyphosphate, dissolve them in 100g of dichloromethane to obtain a premix. Add the premix to a three-necked flask and stir continuously for 40 minutes to ensure thorough mixing of the waste polystyrene and flame retardant. Add 2g of sodium dodecylbenzenesulfonate to 100mL of distilled water to obtain an aqueous dispersant solution. Slowly add the aqueous dispersant solution to a glass reactor and mix it with the premix to obtain a mixed solution.

[0098] The stirring speed was controlled at 300 rpm, and the mixed solution was heated from room temperature to 40°C at a rate of 0.5°C / min and held for 2 hours. Then, the temperature was increased to 60°C at a rate of 0.5°C / min and held for 1 hour to ensure no more dichloromethane was distilled off. The mixture was cooled and discharged, filtered, and washed to obtain spherical beads. These beads were then dried to remove moisture and residual dichloromethane, yielding halogen-free flame-retardant polystyrene beads. The filtrate obtained was an aqueous solution containing a dispersant, which could be reused. The distilled liquid, containing dichloromethane, could also be reused. Figure 6 This is a photograph of the halogen-free flame-retardant polystyrene beads prepared in Comparative Example 1.

[0099] The halogen-free flame-retardant polystyrene beads prepared above were added to a reaction vessel. 8g of sodium dodecylbenzenesulfonate was added to 100mL of distilled water to obtain a surfactant solution. The surfactant solution was added to the reaction vessel, and the mixture was continuously stirred at a speed of 160rpm. The temperature was increased to 90℃ at a rate of 1℃ / min. 3g of pentane was added to the reaction vessel, and the mixture was stirred at a constant temperature for 4 hours. During the process, 2g of bentonite was added to the reaction vessel. The feed port of the high-pressure reaction vessel was immediately sealed after the addition of the materials. The cooling device of the reaction vessel was turned on while stirring, and the temperature was lowered to room temperature. Solid-liquid separation was performed (the obtained filtrate is a surfactant solution that can be reused) to obtain halogen-free flame-retardant expandable polystyrene beads with a certain humidity. After drying, cooling, sieving, and packaging, the halogen-free flame-retardant expandable polystyrene bead product was obtained.

[0100] Halogen-free flame-retardant expandable polystyrene spherical beads from Comparative Example 1 were evenly placed in a mold, heated with steam for 30–50 seconds, and then cooled to obtain halogen-free flame-retardant polystyrene foam boards of the same size as the mold. The boards were then prepared and their performance was tested according to national standards. The specific testing standards and results are shown in Table 6.

[0101] Table 6 shows the performance test data of halogen-free flame-retardant expandable polystyrene beads obtained from Comparative Example 1.

[0102]

[0103]

[0104] Comparative Example 2 uses a single halogen-free flame retardant

[0105] Take 25g of waste polystyrene and 1.5g of melamine polyphosphate, dissolve them in 100g of dichloromethane to obtain a premix. Add the premix to a three-necked flask and stir continuously for 40 minutes to ensure thorough mixing of the waste polystyrene and flame retardant. Add 2g of sodium dodecylbenzenesulfonate to 100mL of distilled water to obtain an aqueous dispersant solution. Slowly add the aqueous dispersant solution to a glass reactor and mix it with the premix to obtain a mixed solution.

[0106] The stirring speed was controlled at 300 rpm, and the mixed solution was heated from room temperature to 40°C at a rate of 0.5°C / min and held for 2 hours. Then, the temperature was increased to 60°C at a rate of 0.5°C / min and held for 1 hour to ensure no more dichloromethane was distilled off. The mixture was cooled and discharged, filtered, and washed to obtain spherical beads. These beads were then dried to remove moisture and residual dichloromethane, yielding halogen-free flame-retardant polystyrene beads. The filtrate obtained was an aqueous solution containing a dispersant, which could be reused. The distilled liquid, containing dichloromethane, could also be reused. Figure 7 This is a photograph of the halogen-free flame-retardant polystyrene beads prepared in Comparative Example 2.

[0107] The halogen-free flame-retardant polystyrene beads prepared above were added to a reaction vessel. 8g of sodium dodecylbenzenesulfonate was added to 100mL of distilled water to obtain a surfactant solution. The surfactant solution was added to the reaction vessel, and the mixture was continuously stirred at a speed of 160rpm. The temperature was increased to 90℃ at a rate of 1℃ / min. 3g of pentane was added to the reaction vessel, and the mixture was stirred at a constant temperature for 4 hours. During the process, 2g of bentonite was added to the reaction vessel. The feed port of the high-pressure reaction vessel was immediately sealed after the addition of the materials. The cooling device of the reaction vessel was turned on while stirring, and the temperature was lowered to room temperature. Solid-liquid separation was performed (the obtained filtrate is a surfactant solution that can be reused) to obtain halogen-free flame-retardant expandable polystyrene beads with a certain humidity. After drying, cooling, sieving, and packaging, the halogen-free flame-retardant expandable polystyrene bead product was obtained.

[0108] The halogen-free flame-retardant expandable polystyrene spherical beads of Comparative Example 2 were evenly placed in a mold, heated with steam for 30-50 seconds, and then cooled to obtain halogen-free flame-retardant polystyrene foam boards of the same size as the mold. The boards were then prepared and their performance was tested according to national standards. The specific testing standards and results are shown in Table 7.

[0109] Table 7 shows the performance test data of halogen-free flame-retardant expandable polystyrene beads obtained from Comparative Example 2.

[0110]

[0111] As can be seen from the results of the examples and comparative examples, the fire rating of the boards prepared in the examples is B1. Comparative Example 1 uses water-soluble ammonium oligophosphate as a flame retardant and the fire rating of the board prepared is B3. The reason may be that the flame retardant is easy to dissolve in the aqueous phase and cannot achieve effective composite with polystyrene. Comparative Example 2 uses a single halogen-free flame retardant and the fire rating of the board prepared is B2.

[0112] The above results demonstrate that this invention prepares halogen-free flame-retardant polystyrene beads using a non-water-soluble composite halogen-free flame retardant and waste polystyrene as raw materials, and then prepares halogen-free flame-retardant expandable polystyrene beads by adding a foaming agent. The resulting product exhibits excellent flame-retardant performance, reaching B1 level. Furthermore, water-soluble flame retardants cannot be compounded with polystyrene using the method of this invention. The flame-retardant performance of the halogen-free flame-retardant expandable polystyrene beads prepared using the composite halogen-free flame retardant is superior to that using a single halogen-free flame retardant. In addition, this invention enables efficient recycling of waste polystyrene, solving the environmental pollution problem caused by waste polystyrene. Simultaneously, the halogen-free flame-retardant expandable polystyrene beads prepared by this invention have good flame retardancy, avoiding safety hazards during polystyrene storage. The preparation method provided by this invention is simple, energy-saving, emission-reducing, and environmentally friendly, with broad application prospects.

[0113] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing halogen-free flame-retardant polystyrene beads using waste polystyrene, characterized in that, Includes the following steps: Waste polystyrene, a composite halogen-free flame retardant, a dispersant, water, and an organic solvent are mixed to obtain a mixed solution; the composite halogen-free flame retardant is obtained by combining at least two halogen-free flame retardants; the halogen-free flame retardant is a phosphorus-based flame retardant, a nitrogen-based flame retardant, or a nitrogen-phosphorus-based flame retardant; the halogen-free flame retardant is a non-water-soluble flame retardant; the composite halogen-free flame retardant is a complex of a phosphorus-based flame retardant and a nitrogen-based flame retardant, or a complex of a phosphorus-based, a nitrogen-based, and a nitrogen-phosphorus-based flame retardant; the mixing includes: mixing waste polystyrene, the composite halogen-free flame retardant, and an organic solvent to obtain a premixed liquid of the composite halogen-free flame retardant and waste polystyrene; The dispersant and water are mixed to obtain an aqueous dispersant solution; the aqueous dispersant solution is added to the premixed solution of the composite halogen-free flame retardant and waste polystyrene; the organic solvent is dichloromethane; Under stirring conditions, the organic solvent in the mixed solution is evaporated to obtain halogen-free flame-retardant polystyrene beads. The evaporation includes a first-stage distillation and a second-stage distillation performed sequentially. The temperature of the first-stage distillation is the boiling point of the organic solvent, and the holding time is 1-3 hours. The temperature of the second-stage distillation is 15-30°C above the boiling point of the organic solvent, and the holding time is 0.5-4 hours. The heating rate from room temperature to the temperature of the first-stage distillation is 0.5-2°C / min. The heating rate from the temperature of the first-stage distillation to the temperature of the second-stage distillation is 0.2-0.5°C / min.

2. The method according to claim 1, characterized in that, The mass ratio of the waste polystyrene to the organic solvent is 1:2~10; the mass ratio of the waste polystyrene to the composite halogen-free flame retardant is 100:0.5~10. The dispersant is a surfactant, or a mixture of a surfactant and a water-soluble dispersant; when the dispersant is a surfactant, the mass fraction of the aqueous dispersant solution is 0.2-4.5%; when the dispersant is a mixture of a surfactant and a water-soluble dispersant, the total mass fraction of the surfactant and the water-soluble dispersant in the aqueous dispersant solution is 0.2-5%, wherein the mass fraction of the water-soluble dispersant is ≤0.5%; the volume ratio of the aqueous dispersant solution to the premixed solution of the composite halogen-free flame retardant and waste polystyrene is 2-10:

1.

3. The method according to claim 2, characterized in that, The composite halogen-free flame retardant includes at least two of the following: ammonium polyphosphate, hexaphenoxycyclotriphosphazene, melamine polyphosphate, melamine cyanurate, melamine phytate, tripentaerythritol phosphate, tricresyl phosphate, triphenyl phosphate, triisopropylphenyl phosphate, toluene diphenyl phosphate, and tetraethyl N,N-p-phenylenediamine (2-hydroxy)dibenzylphosphonate. The surfactant includes one or more of sulfates, sulfonates, and fatty acid salts; the water-soluble dispersant includes one or more of alkyl cellulose, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, and alkylphenol polyoxyethylene ether.

4. The halogen-free flame-retardant polystyrene beads prepared by the method according to any one of claims 1 to 3, characterized in that, The particle size of the halogen-free flame-retardant polystyrene beads is 0.5~3mm.

5. A method for preparing halogen-free flame-retardant expandable polystyrene beads, characterized in that, Includes the following steps: Under closed conditions, the halogen-free flame-retardant polystyrene beads described in claim 4 and the surfactant aqueous solution are mixed and heated to 85~100°C. Then, a physical foaming agent is added and the mixture is stirred at a constant temperature for 4~6 hours. During the constant temperature stirring process, an inorganic dispersant is added to the system. After the constant temperature stirring is completed, the resulting product liquid is cooled and then subjected to solid-liquid separation and drying in sequence to obtain halogen-free flame-retardant expandable polystyrene beads.

6. The preparation method according to claim 5, characterized in that, The mass fraction of the surfactant aqueous solution is 4-8%; the mass ratio of the halogen-free flame-retardant polystyrene beads to the surfactant aqueous solution is 1:1-4.

7. The preparation method according to claim 5, characterized in that, The physical blowing agent includes one or more of propane, butane, pentane, hexane, heptane, petroleum ether, Freon 11, or Freon 12; the mass of the physical blowing agent is 6-10% of the mass of the halogen-free flame-retardant polystyrene beads. The inorganic dispersant includes one or more of calcium phosphate, hydroxycalcium phosphate, calcium carbonate, calcium oxalate, barium sulfate, calcium sulfate, zinc oxide, magnesium hydroxide, aluminum hydroxide, bentonite, kaolin, titanium dioxide, graphite, and mica; the mass of the inorganic dispersant is 0.1-8% of the mass of water in the system.

8. The halogen-free flame-retardant expandable polystyrene beads prepared by the preparation method according to any one of claims 5 to 7, characterized in that, The particle size of the halogen-free flame-retardant expandable polystyrene beads is 0.5~3mm.

Images