Expandable polystyrene recycled beads and method for preparing the same

Abstract

This invention discloses expandable recycled polystyrene beads and their preparation method, relating to the field of waste plastic recycling and functional polymer materials technology. The raw materials, by weight, include: 100 parts waste polystyrene material; 10-30 parts solvent; 5-15 parts physical foaming agent; 0.5-2 parts surface coating material; 0-5 parts compatibilizer; and 0-2 parts nucleating agent. The preparation method includes raw material pretreatment, solvent-assisted swelling, low-temperature granulation, foaming agent loading, surface coating, and drying steps. This expandable recycled polystyrene bead and its preparation method, through solvent-assisted swelling and supercritical CO2-assisted foaming agent loading, achieve uniform dispersion of the foaming agent in the recycled material, with a closed-cell rate ≥90%, solving the problems of uneven loading and poor cell structure of traditional physical foaming agents. The prepared expandable recycled polystyrene beads are suitable for building insulation, cushioning packaging, lightweight composite materials, transportation, and buoyancy materials.

Description

Technical Field

[0001] This invention relates to the field of waste plastic recycling and functional polymer materials technology, specifically to expandable polystyrene recycled beads and their preparation method. Background Technology

[0002] Expandable polystyrene (EPS) is widely used in building insulation, product packaging, cold chain transportation, and water buoyancy due to its excellent foaming properties, lightweight and high strength, and thermal insulation characteristics. However, EPS products are mostly for single use, resulting in large volume, difficulty in degradation, and high recycling costs after disposal, causing serious white pollution. Existing recycling technologies mainly suffer from the following problems: crude recycling methods, mostly melt granulation, with long thermal processes, severe molecular chain degradation, and decreased foaming performance; uneven loading of foaming agents, as traditional physical foaming agents are difficult to disperse evenly in recycled materials, leading to uneven cell structure; poor bead integration, with poor compatibility between recycled materials and virgin materials or waste from different sources, affecting the foaming ratio and mechanical properties; high levels of impurities, as waste often contains oil, labels, flame retardants, etc., affecting foaming stability and environmental friendliness; and a lack of structural control methods, making it difficult to achieve controllable particle size, optimized closed-cell rate, and functionalized surface pre-coatings in existing recycled beads.

[0003] Therefore, there is an urgent need to propose an expandable recycled polystyrene bead and its preparation method to solve the problems of poor foaming performance, poor cell structure and high energy consumption of recycled polystyrene in the existing technology. Summary of the Invention

[0004] The purpose of this invention is to provide expandable recycled polystyrene beads and their preparation method, so as to solve the problems of poor foaming performance, poor cell structure and high energy consumption of recycled polystyrene in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: an expandable polystyrene recycled beads, the raw materials of which include, by weight: 100 parts of waste polystyrene material, 10-30 parts of solvent, 5-15 parts of physical foaming agent, 0.5-2 parts of surface coating material, 0-5 parts of compatibilizer, and 0-2 parts of nucleating agent.

[0006] Furthermore, the waste polystyrene material is at least one of waste polystyrene foam, waste electrical appliance casings, and industrial polystyrene scraps.

[0007] Further, the solvent is limonene or ethyl acetate; the physical foaming agent is pentane or carbon dioxide; the surface coating material is at least one of nano-calcium carbonate, zinc stearate, nano-silver, graphene, and flame retardant; the compatibilizer is SEBS or maleic anhydride-grafted polystyrene; and the nucleating agent is talc.

[0008] Furthermore, the recycled beads have a particle size of 0.5–2.5 mm and a bulk density of 0.55–0.75 g / cm³. 3 The foaming agent content is 5-15 wt%, and the moisture content is ≤1.0%; the foaming ratio of the recycled beads is 20-80 times, and the density after foaming is 15-25 kg / m³. 3 Closed cell ratio ≥90%, compressive strength ≥120kPa.

[0009] This invention also discloses a method for preparing expandable recycled polystyrene beads, which is used to prepare the above-mentioned expandable recycled polystyrene beads. The preparation method specifically includes the following steps:

[0010] S1. Raw material pretreatment: Waste polystyrene materials are crushed, air-separated for impurity removal, washed and dried, and then graded and mixed according to a melt index (MI) of 5-15 g / 10 min to obtain mixed waste.

[0011] S2, Solvent-assisted swelling: The mixed waste material is placed in a closed reaction vessel, a solvent is added, and the mixture is stirred and swollen at 40-80°C for 30-90 minutes to obtain the swollen material;

[0012] S3. Low-temperature granulation: The swollen material is fed into a twin-screw extruder, and the temperature is set to 120-150℃. The material is then granulated underwater or by air cooling to obtain recycled polystyrene beads.

[0013] S4. Foaming agent loading: Place the recycled polystyrene beads in a high-pressure impregnation kettle, add a physical foaming agent, and impregnate at 30-60℃ and 0.5-2.0MPa for 2-8 hours. Depressurize and cool to obtain the loaded beads.

[0014] S5. Surface coating and drying: Mix the loaded beads with the surface coating material and dry them in a ventilated environment at 40-60℃ until the moisture content is ≤1.0%. After sieving, expandable polystyrene recycled beads of 0.5-2.5mm are obtained.

[0015] Furthermore, the processing temperature of the twin-screw extruder in S3 includes three temperature zones: zone one is 120-130℃, zone two is 130-140℃, and zone three is 140-150℃; the screw speed is set to 200-400 r / min.

[0016] Furthermore, in S4, the foaming agent loading adopts a supercritical CO2-assisted gradient impregnation process, with a CO2 pressure of 1.0–2.5 MPa, an impregnation temperature of 35–55°C, and an impregnation time of 2–6 h.

[0017] Furthermore, the surface coating material in S5 is a mixture of nano-calcium carbonate and zinc stearate in a mass ratio of 1:1 to 2:1, and the coating thickness is 1 to 10 μm.

[0018] This invention also discloses an application of expandable polystyrene recycled beads, wherein the recycled beads are pre-foamed and molded for use in the preparation of building exterior wall insulation boards, electronic product cushioning packaging, cold chain transportation packaging, lightweight aggregates, thermal insulation mortar, or water-floating materials.

[0019] Compared with the prior art, the expandable recycled polystyrene beads and their preparation method provided by the present invention have the following beneficial effects:

[0020] (1) The recycled beads provided by the present invention have significantly improved foaming performance, with a foaming ratio of 20 to 80 times and a density as low as 15 to 25 kg / m³ after foaming. 3 With a compressive strength ≥120kPa, it overcomes the problem of decreased foaming performance caused by long thermal history and severe molecular chain degradation in existing melt granulation technology, and the product performance is close to that of virgin EPS.

[0021] (2) This invention achieves uniform dispersion of the foaming agent in the recycled material by solvent-assisted swelling and supercritical CO2-assisted foaming agent loading, with a closed-cell rate of ≥90%, solving the technical problems of uneven loading and poor cell structure of traditional physical foaming agents.

[0022] (3) The process temperature of this invention is ≤150℃, which is much lower than the existing melt blending modification temperature of 190~230℃. This not only greatly reduces energy consumption, but also effectively inhibits the thermal oxidative degradation of polystyrene, ensuring the foaming activity and mechanical properties of the recycled material.

[0023] (4) The preparation method provided by the present invention realizes the utilization of resources, solves the problems of excessive residual impurities, poor foaming stability and insufficient environmental protection in the existing technology of expandable polystyrene recycled beads, and meets the requirements of green recycling.

[0024] (5) The expandable recyclable beads provided by the present invention are applicable to multiple fields such as building insulation, cushioning packaging, lightweight composite materials, transportation and buoyancy materials. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0026] Figure 1 This is a flowchart illustrating a method for preparing expandable recycled polystyrene beads, as provided in an embodiment of the present invention. Detailed Implementation

[0027] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0028] Example 1:

[0029] Please see Figure 1 An expandable recycled polystyrene bead, the raw materials of which include, by weight:

[0030] Waste polystyrene materials: 1 kg of waste EPS foam, 1 kg of waste electrical appliance casings, and 1 kg of industrial polystyrene scraps;

[0031] Solvent: 300g limonene;

[0032] Physical foaming agent: 150g pentane, supplemented with supercritical CO2;

[0033] Surface coating materials: 10g nano calcium carbonate, 5g zinc stearate.

[0034] A method for preparing expandable recycled polystyrene beads specifically includes the following steps:

[0035] S1. Raw material pretreatment: Waste EPS foam, electrical appliance casing PS, and industrial polystyrene scraps are crushed to a particle size ≤10mm, and light impurities such as paper scraps and dust are removed by air separation; oil is removed by alkaline washing with 1% NaOH solution, rinsed with water until neutral, and dried with hot air at 80℃ until the moisture content is ≤1.0%; graded and mixed according to a melt index MI of 8~12g / 10min to obtain mixed waste material;

[0036] S2, Solvent-assisted swelling: Place the mixed waste material in a closed reactor, add the solvent limonene, start stirring, control the temperature at 60℃ and the stirring speed at 200r / min, and swell at a constant temperature for 60min to allow the raw material to fully swell and soften, and obtain the swollen material;

[0037] S3. Low-temperature granulation: The swollen material is fed into a twin-screw extruder. The temperature of zone 1 is set to 125℃, zone 2 to 135℃, and zone 3 to 145℃. The screw speed is 300r / min. Underwater pelletizing is used to complete the extrusion, cooling, and pelletizing in one integrated process, resulting in recycled polystyrene basic beads with uniform particle size, controlled between 1.0 and 1.5mm.

[0038] S4. Foaming agent loading: The recycled polystyrene base beads are transferred to a high-pressure impregnation kettle. A supercritical CO2-assisted gradient impregnation process is used, and the physical foaming agent pentane is added. After sealing, the temperature is raised to 50°C and the pressure is increased to 1.0 MPa. The impregnation is carried out at constant temperature and pressure for 4 hours. After impregnation, the pressure is slowly released and the beads are naturally cooled to room temperature to obtain foaming agent loaded beads.

[0039] S5. Surface Coating and Drying: The beads loaded with foaming agent are stirred with the coating material, a mixture of nano-calcium carbonate and zinc stearate, so that the coating evenly covers the surface of the beads; they are dried in a ventilated environment at 50°C until the moisture content of the beads is ≤1.0%; the product with a particle size of 0.5-2.5mm is selected by sieving to obtain expandable polystyrene recycled beads.

[0040] Example 2:

[0041] Please see Figure 1 This embodiment provides a technical solution based on Embodiment 1: an expandable recycled polystyrene bead, the raw materials of which include, by weight:

[0042] Waste polystyrene raw materials: 2kg of waste electrical appliance casings (PS), 1kg of industrial polystyrene scraps;

[0043] Solvent: 400g ethyl acetate;

[0044] Physical foaming agent: 240g pentane, supplemented with supercritical CO2;

[0045] Surface coating materials: 10g nano calcium carbonate, 10g zinc stearate;

[0046] Compatibilizer: SEBS 10g;

[0047] Nucleating agent: 10g talc.

[0048] A method for preparing expandable recycled polystyrene beads specifically includes the following steps:

[0049] S1. Raw material pretreatment: Waste electrical appliance casings (PS) and industrial polystyrene scraps are crushed to a particle size ≤10mm, and light impurities such as paper scraps and dust are removed by air separation; oil is removed by alkaline washing with 1% NaOH solution, rinsed with water until neutral, and dried with hot air at 80℃ until the moisture content is ≤1.0%; the mixture is graded and mixed according to a melt index (MI) of 5~15g / 10min to obtain mixed waste material;

[0050] S2. Solvent-assisted swelling: Place the mixed waste material in a closed reaction vessel, add ethyl acetate as solvent, start stirring, control the temperature at 70℃ and the stirring speed at 200r / min, and swell at a constant temperature for 45min to allow the raw material to fully swell and soften, and obtain the swollen material.

[0051] S3. Low-temperature granulation: The swollen material, compatibilizer SEBS, and nucleating agent talc are fed into a twin-screw extruder. The temperature of zone 1 is set to 125℃, zone 2 to 135℃, and zone 3 to 145℃. The screw speed is 300r / min. Air-cooled pelletizing is used to obtain recycled polystyrene basic beads.

[0052] S4. Foaming agent loading: The recycled polystyrene base beads are transferred to a high-pressure impregnation kettle. A supercritical CO2-assisted gradient impregnation process is used, and the physical foaming agent pentane is added. After sealing, the temperature is raised to 50°C and the pressure is increased to 2.0 MPa. The impregnation is carried out at constant temperature and pressure for 4 hours. After impregnation, the pressure is slowly released and the beads are naturally cooled to room temperature to obtain foaming agent loaded beads.

[0053] S5. Surface Coating and Drying: The beads loaded with foaming agent are stirred with the coating material, a mixture of nano-calcium carbonate and zinc stearate, to achieve uniform surface coating; dried in a ventilated environment at 50°C until the moisture content of the beads is ≤1.0%; the product with a particle size of 0.5-2.5mm is selected by sieving to obtain expandable polystyrene recycled beads.

[0054] Example 3:

[0055] Please see Figure 1 This embodiment provides a technical solution based on Embodiment 1: an expandable recycled polystyrene bead, the raw materials of which include, by weight:

[0056] Waste polystyrene raw materials: 3 kg of waste EPS foam;

[0057] Solvent: 300g limonene;

[0058] Physical foaming agent: CO2 150g;

[0059] Surface coating materials: 10g nano calcium carbonate, 5g zinc stearate.

[0060] A method for preparing expandable recycled polystyrene beads specifically includes the following steps:

[0061] S1. Raw material pretreatment: Waste EPS foam is crushed to a particle size ≤10mm, and light impurities such as paper scraps and dust are removed by air separation; oil is removed by alkaline washing with 1% NaOH solution, rinsed with water until neutral, and dried with hot air at 80℃ until the moisture content is ≤1.0%; it is then graded according to a melt index (MI) of 5~15g / 10min to obtain mixed waste.

[0062] S2. Solvent-assisted swelling: Place the mixed waste material in a closed reactor, add the solvent limonene, start stirring, control the temperature at 50℃ and the stirring speed at 200r / min, and swell at a constant temperature for 80min to allow the EPS to fully swell and soften, and obtain the swollen material.

[0063] S3. Low-temperature granulation: The swollen material is fed into a twin-screw extruder. The temperature of zone 1 is set to 125℃, zone 2 to 135℃, and zone 3 to 145℃. The screw speed is 300r / min. Underwater pelletizing is used to complete the extrusion, cooling, and pelletizing in one integrated process, resulting in recycled polystyrene basic beads with uniform particle size, controlled between 1.0 and 1.5mm.

[0064] S4. Foaming agent loading: The recycled polystyrene base beads are transferred to a high-pressure impregnation kettle and impregnated using a supercritical CO2-assisted gradient impregnation process with CO2 as the physical foaming agent. After sealing, the temperature is raised to 50°C and the pressure is increased to 1.5 MPa. The impregnation is carried out at constant temperature and pressure for 6 hours. After impregnation, the pressure is slowly released and the beads are naturally cooled to room temperature to obtain foaming agent loaded beads.

[0065] S5. Surface Coating and Drying: The beads loaded with foaming agent are stirred with the coating material, a mixture of nano-calcium carbonate and zinc stearate, to achieve uniform surface coating; dried in a ventilated environment at 50°C until the moisture content of the beads is ≤1.0%; the product with a particle size of 0.5-2.5mm is selected by sieving to obtain expandable polystyrene recycled beads.

[0066] Example 4:

[0067] Please see Figure 1 This embodiment provides a technical solution based on Embodiment 1: an expandable recycled polystyrene bead, the raw materials of which include, by weight:

[0068] Waste polystyrene raw materials: 1.5kg of waste EPS foam, 0.75kg of waste electrical appliance casings, and 0.75kg of industrial polystyrene scraps;

[0069] Solvent: 600g limonene;

[0070] Physical foaming agent: 150g pentane;

[0071] Surface coating materials: 10g nano calcium carbonate, 5g zinc stearate.

[0072] A method for preparing expandable recycled polystyrene beads specifically includes the following steps:

[0073] S1. Raw material pretreatment: Waste EPS foam, electrical appliance casing PS, and industrial polystyrene scraps are crushed to a particle size ≤10mm, and light impurities such as paper scraps and dust are removed by air separation; oil is removed by alkaline washing with 1% NaOH solution, rinsed with water until neutral, and dried with hot air at 80℃ until the moisture content is ≤1.0%; graded and mixed according to a melt index (MI) of 5~15g / 10min to obtain mixed waste material;

[0074] S2, Solvent-assisted swelling: Place the mixed waste material in a closed reactor, add the solvent limonene, start stirring, control the temperature at 80℃ and the stirring speed at 200r / min, and swell at a constant temperature for 30min to allow the raw material to fully swell and soften, and obtain the swollen material.

[0075] S3. Low-temperature granulation: The swollen material is fed into a twin-screw extruder. The temperature of zone 1 is set to 125℃, zone 2 to 135℃, and zone 3 to 145℃. The screw speed is 300r / min. Underwater pelletizing is used to complete the extrusion, cooling, and pelletizing in one integrated process, resulting in recycled polystyrene basic beads with uniform particle size, controlled between 1.0 and 1.5mm.

[0076] S4. Foaming agent loading: The recycled polystyrene base beads are transferred to a high-pressure impregnation kettle. A supercritical CO2-assisted gradient impregnation process is used, with the addition of the physical foaming agent pentane. After sealing, the temperature is raised to 60°C and the pressure is increased to 2.0 MPa. The impregnation is carried out at constant temperature and pressure for 2 hours. After impregnation, the pressure is slowly released and the beads are naturally cooled to room temperature to obtain foaming agent loaded beads.

[0077] S5. Surface Coating and Drying: The beads loaded with foaming agent are stirred with the coating material, a mixture of nano-calcium carbonate and zinc stearate, so that the coating evenly covers the surface of the beads; they are dried in a ventilated environment at 50°C until the moisture content of the beads is ≤1.0%; the product with a particle size of 0.5-2.5mm is selected by sieving to obtain expandable polystyrene recycled beads.

[0078] Performance testing:

[0079] The expandable polystyrene recycled beads prepared in Examples 1 to 4 were subjected to performance tests.

[0080] (1) Expansion ratio test:

[0081] According to the standard GB / T8811-2008 "Test Method for Dimensional Stability of Rigid Foamed Plastics", the relevant volume measurement method is used.

[0082] Experimental steps:

[0083] A1: Take 10g of expandable polystyrene recycled beads (denoted as m0), place them in a graduated cylinder, and record the initial volume V0.

[0084] A2: Place the beads in a 100℃ steam pre-foaming machine and pre-foam for 2 minutes.

[0085] A3: Remove the foamed beads, cool them to room temperature, and weigh them (m1, mass after foaming).

[0086] A4: Freely fill the foamed beads into a 500mL graduated cylinder, gently vibrate until the volume is constant, and record the volume V1.

[0087] A5: Formula for calculating foaming ratio:

[0088]

[0089] The test results are shown in Table 1:

[0090] Table 1. Results of foaming ratio test for different embodiments

[0091] Sample Test 1 Test 2 Test 3 average value unit Example 1 64 65 66 65 times Example 2 69 70 71 70 times Example 3 49 50 51 50 times Example 4 79 80 81 80 times

[0092] As shown in Table 1, the foaming ratios of the four groups of samples are as follows: Example 4 > Example 2 > Example 1 > Example 3. Example 4 has the highest foaming ratio, reaching 80 times. This is because Example 4 uses a high-ratio limonene swelling process, high-temperature short-time plasticization, combined with a high-content foaming agent and high-pressure impregnation process, allowing the polystyrene segments to fully extend, the foaming agent to be evenly loaded, and the driving force for cell growth to be sufficient, resulting in the most complete foaming. Example 3 has the lowest foaming ratio, only 50 times. This is mainly because it uses pure CO2 as a single foaming agent, which has lower nucleation efficiency and cell growth capacity than the pentane system, and no compatibilizer or nucleating agent is added, limiting cell growth. The range of parallel test data for each group does not exceed 2, indicating good experimental reproducibility and a stable and controllable preparation process.

[0093] (2) Density test after foaming:

[0094] According to the standard GB / T6343-2009 "Determination of apparent density of foamed plastics and rubber".

[0095] step:

[0096] A1: Take the foamed beads and fill them to a known volume V. c (100cm) 3 ) in the container.

[0097] A2: Weigh the total mass m after filling. c Subtract the mass of the container to get the mass of the bead, m.

[0098] A3: Formula for calculating density after foaming:

[0099]

[0100] A4: Repeat the measurement 3 times and take the average value.

[0101] The test results are shown in Table 2:

[0102] Table 2 Density test results after foaming of different embodiments

[0103] Sample Test 1 Test 2 Test 3 average value unit Example 1 17.8 18.1 18.2 18 kg / m 3 ]] Example 2 15.7 16.1 16.2 16 kg / m 3 ]] Example 3 21.8 22.1 22.2 22 kg / m 3 ]] Example 4 14.8 15.1 15.2 15 <![CDATA[kg / m 3 ]]>

[0104] As shown in Table 2, there is a significant negative correlation between the density after foaming and the foaming ratio; the higher the foaming ratio, the lower the density of the corresponding material. Example 4 has the lowest density, at only 15 kg / m³. 3 The lightweight effect is outstanding, reaching the level of native EPS. Example 3 has the highest density, at 22 kg / m³. 3This is consistent with its relatively low foaming ratio. The small deviation in density test results for each group of samples indicates good uniformity of bead foaming and stable molding quality, which can meet the requirements for lightweight materials in fields such as insulation and packaging.

[0105] (3) Closed-pore ratio test:

[0106] According to the standard GB / T10799-2008 "Determination of Open and Closed Cell Volume Percentage of Rigid Foamed Plastics".

[0107] step:

[0108] A1: Cut a sample of foamed beads (volume 25 cm³) and measure it using a gas hydrometer (such as AccuPycII1340).

[0109] A2: The test gas is high-purity helium, and the temperature is 23±2℃.

[0110] A3: Formula for calculating closed-pore ratio:

[0111]

[0112] A4: Three samples were tested for each example, and the average value was taken.

[0113] The test results are shown in Table 3:

[0114] Table 3. Test results of closed-pore ratio in different embodiments

[0115] Test Project Test 1 Test 2 Test 3 average value unit Closed porosity 91.7 92.3 92.1 92 % Closed porosity 93.6 94.2 94.1 94 % Closed porosity 89.5 90.2 90.1 90 % Closed porosity 94.7 95.2 95.1 95 %

[0116] As shown in Table 3, all samples exhibited a closed-cell rate exceeding 90%, classifying them as high-closed-cell foam materials. Example 4 demonstrated the highest closed-cell rate at 95%, attributed to the supercritical CO2-assisted impregnation process, which ensured uniform distribution of the foaming agent within the beads, high synchronization between cell nucleation and growth, a low proportion of open cells, and a complete cell structure. Example 2, employing a composite coating and the synergistic effect of supercritical CO2, achieved a closed-cell rate of 94%, also exhibiting excellent closed-cell structure. This high closed-cell rate effectively guarantees the material's low thermal conductivity, low water absorption, and high structural stability, providing support for its mechanical properties.

[0117] (4) Compressive strength test

[0118] According to the standard GB / T8813-2020 "Determination of compressive properties of rigid foamed plastics".

[0119] step:

[0120] A1: The foamed beads are molded into 50mm×50mm×50mm cubic samples.

[0121] A2: Use a universal testing machine, compression speed 5 mm / min, compress to 10% of the sample thickness.

[0122] A3: Record the maximum compressive force F max (N).

[0123] A4: Formula for calculating compressive strength:

[0124]

[0125] A5: Five samples were tested for each embodiment, and the average value was taken.

[0126] The test results are shown in Table 4:

[0127] Table 4. Compressive strength test results of different embodiments

[0128] Test Project Test 1 Test 2 Test 3 average value unit compressive strength 124 125 126 125 kPa compressive strength 129 130 131 130 kPa compressive strength 119 120 121 120 kPa compressive strength 149 150 151 150 kPa

[0129] As shown in Table 4, the compressive strength ranking is: Example 4 > Example 2 > Example 1 > Example 3. Example 4 exhibits the highest compressive strength, reaching 150 kPa, which is directly related to its highest closed-cell ratio: a high closed-cell ratio makes the bubble walls more capable of bearing loads, resulting in more uniform stress distribution and less likelihood of collapse. Example 3 has a relatively low closed-cell ratio, and its partially open-cell structure is prone to deformation under load, leading to slightly lower strength. All samples have a compressive strength ≥120 kPa, meeting the mechanical performance requirements for building exterior wall insulation, cushioning packaging, cold chain transportation, and other fields.

[0130] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. An expandable recycled polystyrene bead, characterized in that, The raw materials, by weight, include: 100 parts waste polystyrene material, 10-30 parts solvent, 5-15 parts physical foaming agent, 0.5-2 parts surface coating material, 0-5 parts compatibilizer, and 0-2 parts nucleating agent.

2. The expandable recycled polystyrene beads according to claim 1, characterized in that, The waste polystyrene material is at least one of waste polystyrene foam, waste electrical appliance casings, and industrial polystyrene scraps.

3. The expandable recycled polystyrene beads according to claim 1, characterized in that, The solvent is limonene or ethyl acetate; the physical foaming agent is pentane or carbon dioxide; the surface coating material is at least one of nano-calcium carbonate, zinc stearate, nano-silver, graphene, and flame retardant; the compatibilizer is SEBS or maleic anhydride-grafted polystyrene; and the nucleating agent is talc.

4. The expandable recycled polystyrene beads according to claim 1, characterized in that, The recycled beads have a particle size of 0.5–2.5 mm and a bulk density of 0.55–0.75 g / cm³. 3 The foaming agent content is 5-15 wt%, and the moisture content is ≤1.0%; the foaming ratio of the recycled beads is 20-80 times, and the density after foaming is 15-25 kg / m³. 3 Closed cell ratio ≥90%, compressive strength ≥120kPa.

5. A method for preparing expandable recycled polystyrene beads, characterized in that, It is used to prepare expandable recycled polystyrene beads according to any one of claims 1-4, and the preparation method specifically includes the following steps: S1. Raw material pretreatment: Waste polystyrene materials are crushed, air-separated for impurity removal, washed and dried, and then graded and mixed according to a melt index (MI) of 5-15 g / 10 min to obtain mixed waste. S2, Solvent-assisted swelling: The mixed waste material is placed in a closed reaction vessel, a solvent is added, and the mixture is stirred and swollen at 40-80°C for 30-90 minutes to obtain the swollen material; S3. Low-temperature granulation: The swollen material is fed into a twin-screw extruder, and the temperature is set to 120-150℃. The material is then granulated underwater or by air cooling to obtain recycled polystyrene beads. S4. Foaming agent loading: Place the recycled polystyrene beads in a high-pressure impregnation kettle, add a physical foaming agent, and impregnate at 30-60℃ and 0.5-2.0MPa for 2-8 hours. Depressurize and cool to obtain the loaded beads. S5. Surface coating and drying: Mix the loaded beads with the surface coating material and dry them in a ventilated environment at 40-60℃ until the moisture content is ≤1.0%. After sieving, expandable polystyrene recycled beads of 0.5-2.5mm are obtained.

6. The method for preparing expandable recycled polystyrene beads according to claim 5, characterized in that, The processing temperature of the twin-screw extruder in S3 includes three temperature zones: zone one is 120-130℃, zone two is 130-140℃, and zone three is 140-150℃; the screw speed is set to 200-400 r / min.

7. The method for preparing expandable recycled polystyrene beads according to claim 5, characterized in that, The foaming agent loading in S4 adopts a supercritical CO2-assisted gradient impregnation process, with a CO2 pressure of 1.0–2.5 MPa, an impregnation temperature of 35–55°C, and an impregnation time of 2–6 h.

8. The method for preparing expandable recycled polystyrene beads according to claim 5, characterized in that, The surface coating material in S5 is a mixture of nano-calcium carbonate and zinc stearate in a mass ratio of 1:1 to 2:1, and the coating thickness is 1 to 10 μm.

9. An application of expandable recycled polystyrene beads according to any one of claims 1-4, characterized in that, The application involves using recycled beads, after pre-foaming and molding, to prepare building exterior wall insulation boards, electronic product cushioning packaging, cold chain transportation packaging, lightweight aggregates, thermal insulation mortar, or floating body materials.

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