Preparation of microcellular foamed beads based on recycled polystyrene and method thereof

Abstract

The application discloses a kind of based on recycled polystyrene preparation microporous foamed beads and its preparation method, including steps: 55-95 parts recycled polystyrene, 20-45 parts polystyrene and 0.1-5 parts talc are premixed after melt blending, 1-10 parts supercritical carbon dioxide is injected therein, and the blend is obtained by melt extrusion;The blend continues to blend and extrusion foaming, and the foamed beads are obtained by die face air cooling hot cutting;Foamed beads are saturated in high-pressure gas medium, and it is secondarily expanded by steam heating, and the microporous foamed beads are obtained by cooling, setting and drying.The polystyrene microporous foamed beads of the application take polystyrene recycled material as main body, extrusion foaming is combined with air cooling hot cutting technology, and the expansion ratio of foamed beads can be controlled by secondary foaming, so that the foamed bead material with high closed cell rate, low density and excellent mechanical properties is obtained, and high-value recycling of recycled material is realized.

Description

Technical Field

[0001] This invention relates to the field of polymer recycling technology, specifically to a method for preparing microporous foamed beads based on recycled polystyrene. Background Technology

[0002] Polystyrene is non-toxic, odorless, colorless, and transparent. Its products exhibit extremely high transparency, with a light transmittance exceeding 90%. It also possesses excellent electrical insulation properties, is easy to color, has good processing fluidity, high rigidity, and good chemical corrosion resistance, making it widely used in household appliances, packaging, electrical appliances, and disposable products. Polystyrene can also be formulated into foamed materials with excellent thermal insulation properties, widely used in construction, packaging, cold chain logistics, and safety protection. However, polystyrene and its foamed materials are rigid yet brittle materials, prone to fracture under stress, and difficult to degrade rapidly in the natural environment after use, consuming significant amounts of energy and causing severe environmental pollution. Therefore, enhancing the recycling of polystyrene is of great significance for environmental protection, energy conservation, and contributing to the achievement of carbon neutrality goals.

[0003] Currently, the recycling of polystyrene mainly involves chemical or mechanical methods to convert it into reusable styrene monomers, granules, and foamed boards. For example, Chinese invention patent CN105566670A discloses an aqueous suspension granulation method for preparing gradient flame-retardant expandable polystyrene beads based on waste polystyrene materials and its products. This invention uses suspension granulation of waste polystyrene foam materials to obtain polystyrene beads, which are then foamed with pentane to obtain polystyrene insulation foam boards. However, this technology requires multiple operations, and the addition of pentane increases the storage risks of the foamed beads.

[0004] Alternatively, polystyrene can be decomposed into styrene monomers through chemical degradation, but this consumes a large amount of organic reagents, generates other chemical waste, increases safety and environmental risks, and is detrimental to sustainable development. The aforementioned recycling methods involve chemical processes that consume large amounts of reagents, are complex, and have high risk factors. Suspension granulation and pentane filling further complicate the preparation process and increase the differences in the performance of the foamed beads.

[0005] CN117024889A discloses a modified expandable polystyrene recycled blend GPO-R foam material and its preparation method. The foam material comprises the following raw materials in the indicated mass fractions: 50-65% modified polystyrene, 20-35% recycled modified polystyrene particles, 1-4% nucleating agent, 3-6% pentane, and 2-5% chain extender. This invention utilizes modified expandable polystyrene and recycled polystyrene to recycle waste polystyrene and prepare GPO-R foam material, which to some extent helps achieve low carbon emissions, reduce material costs, and ensure that the performance of the foam material meets requirements. However, the consumption of recycled polystyrene is not large, and modified polystyrene remains the main raw material.

[0006] Therefore, seeking easy-to-implement, safe, efficient, and clean methods for high-value utilization of recycled plastics is both challenging and valuable. Summary of the Invention

[0007] This invention addresses the problem of ineffective recycling methods for polystyrene recycled materials by providing a polystyrene microporous foamed bead material based on polystyrene recycled material. It combines extrusion foaming with air-cooled hot-cutting technology, and controls the expansion ratio of the foamed beads through secondary foaming to obtain foamed bead material with high closed-cell rate, low density and excellent mechanical properties, thereby realizing high-value reuse of recycled materials.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing microporous foamed beads based on recycled polystyrene includes the following steps:

[0010] Step 1: Recycled polystyrene, polystyrene, and talc are premixed and then melt-blended. Supercritical carbon dioxide is injected into the mixture, and the blend is obtained by melt extrusion.

[0011] Step 2: The blend is further blended, extruded and foamed, and then hot-cut by air cooling through a die to obtain foamed beads;

[0012] Step 3: The foamed beads are placed in a high-pressure gas medium for saturation, heated with steam to cause secondary expansion, and then cooled, shaped and dried to obtain the microporous foamed beads.

[0013] The microporous foamed beads, based on a total mass of 100 parts, include 55-95 parts recycled polystyrene, 20-45 parts polystyrene, 0.1-5 parts talc, and 1-10 parts supercritical carbon dioxide.

[0014] Preferably, the microporous foamed beads, based on a total mass of 100 parts, include 55-90 parts recycled polystyrene (rPS), 20-45 parts polystyrene (PS), 0.1-5 parts talc, and 1-10 parts supercritical carbon dioxide.

[0015] Preferably, the amount of recycled polystyrene used is 60-90 parts, and the amount of polystyrene used is 10-40 parts;

[0016] More preferably, the microporous foamed beads, based on a total mass of 100 parts, include 55-80 parts recycled polystyrene, 20-45 parts polystyrene, 0.1-5 parts talc, and 1-10 parts supercritical carbon dioxide.

[0017] The recycled polystyrene is transparent with a yellowish tint and has a density of 0.9-1.5 g / cm³. 3 It has a glass transition temperature of 90-110℃ and is brittle.

[0018] The polystyrene referred to is virgin polystyrene or a modified version of virgin polystyrene, with a density of 0.9-1.2 g / cm³. 3 The melt index is 1-10 / 10min (200℃, 5kg), preferably 1-5 / 10min (200℃, 5kg).

[0019] Recycled polystyrene suffers from problems such as low glass transition temperature, poor foaming performance, and unsatisfactory secondary expansion. In this invention, a small amount of virgin polystyrene is mixed with talc to improve cell nucleation. Through the action of supercritical carbon dioxide, melt blending and extrusion foaming are combined with die-face air-cooling and hot-cutting technology to obtain primary foamed beads. Furthermore, the expansion ratio of the foamed beads can be controlled and adjusted through secondary foaming technology to obtain foamed bead materials with high closed-cell rate, low density, and excellent mechanical properties, thus realizing high-value reuse of recycled materials.

[0020] Preferably, the talc powder is 0.5-5 parts by weight, and more preferably 1.0-3.0 parts by weight to obtain a more uniform distribution of pores and a higher nucleation density and a lower foam density.

[0021] Preferably, the supercritical carbon dioxide content is 2-8 parts by mass, and more preferably 3.0-6.0 parts by mass to obtain a higher expansion ratio and a more stable foaming process window;

[0022] Preferably, the supercritical carbon dioxide injection pressure in step 1 is 15-20 MPa to ensure the smooth progress of the foaming process and avoid the phenomenon that high pressure causes cell rupture and low pressure makes it difficult for the polymer to foam.

[0023] Preferably, in step 1, the melt extrusion temperature is 160-220℃, the rotation speed is 25-40 r / min, and the pressure is 7-18 MPa. To ensure that the polymer is completely melted and thoroughly mixed with the injected supercritical fluid, preferably, the temperature is 175-200℃, the rotation speed is 30-35 r / min, and the pressure is 8-12 MPa.

[0024] Preferably, in step 2, the blending temperature is 140-180℃, the rotation speed is 3-30 r / min, and the pressure is 7-18 MPa. To avoid the phenomenon that the polymer viscosity is too low at high temperatures, making it difficult to maintain cell stability, and that it is difficult to extrude and foam at low temperatures, preferably, the temperature is 155-170℃, the rotation speed is 30-35 r / min, and the pressure is 8-12 MPa.

[0025] Preferably, the cutting speed of the die surface air-cooled hot cutting in step 2 is 50-3000 r / min, more preferably, it is 600-1600 r / min.

[0026] Preferably, step 2 is carried out in a second extrusion unit connected to the first extrusion unit in step 1, and extrusion foaming is carried out in a static mixer downstream of the second extrusion unit;

[0027] Preferably, the temperature of the static mixer is 140-180℃, and the die pressure is 7-20MPa. Under this temperature and pressure, the stress state of the polymer melt and gas mixture is more stable, the discharge speed at the die is uniform, and the volume of the foamed beads obtained is similar. Preferably, the temperature is 155.0-170.0℃, and the pressure is 8.0-15.0MPa.

[0028] The specified pressure and temperature ensure smooth foaming and yield foamed beads with high expansion ratio and closed-cell ratio, guaranteeing low density and good bead adhesion after steam molding. Preferably, the expansion ratio of the foamed beads in step 2 is 15-25, and the closed-cell ratio is 80-95%.

[0029] Preferably, in step 3, the saturation pressure of the high-pressure gas medium is 0.1-1.5 bar, the temperature is 0-40°C, and the gas medium includes one or more of air, carbon dioxide, and nitrogen.

[0030] Preferably, in step 3, the steam temperature is 80-100℃ and the steam pressure is 0.3-1.5 bar. Excessive temperature in this step will cause the foamed beads to collapse and shrink, while excessively low temperature will hinder secondary foaming. More preferably, in step 3, the steam temperature is 60-100℃.

[0031] The present invention also provides microporous foamed beads prepared from recycled polystyrene according to the preparation method, characterized in that the expansion ratio of the microporous foamed beads is 25-60 and the closed-cell ratio is 75-90%.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] This invention utilizes a simple, easy-to-operate, and highly integrated extrusion foaming technology to directly convert and utilize recycled polystyrene materials, directly preparing high-value-added foamed beads from post-consumer recycled materials. The prepared foamed beads exhibit controllable expansion ratios and high closed-cell ratios, facilitating full expansion during steam molding and ensuring sufficient contact between the beads. This increases the surface area for molecular chain diffusion between adjacent beads, improves adhesion, and yields foamed bead materials with high closed-cell ratios, low density, and excellent mechanical properties, achieving high-value reuse of recycled materials. The recycled foamed bead materials can be applied in packaging, cold chain transportation, building insulation, home appliances, and traffic safety protection. Attached Figure Description

[0034] Figure 1 This is an optical morphology image of the microporous foamed beads prepared in Example 1.

[0035] Figure 2 This is an electron microscope image of the internal pore structure of the microporous foam prepared in Example 1.

[0036] Figure 3 This is an electron microscope image of the surface microstructure of the microporous foamed beads prepared in Example 1.

[0037] Figure 4 This is an electron microscope image of the internal pore structure of the microporous foamed beads in Example 4.

[0038] Figure 5 This is an electron microscope image of the internal pore structure of the microporous foamed beads in Comparative Example 2. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0040] The raw materials used in the following specific embodiments were all purchased from the market. The recycled polystyrene was provided by Qingdao Hailuyuan Recycling Technology Co., Ltd. It is pale yellow, has a certain degree of transparency, and has a glass transition temperature (T). g The temperature was 100.6℃. General-purpose polystyrene (PS: PG 383, unprocessed) was purchased from Zhenjiang Qimei Chemical Co., Ltd., with a density of 1.04 g·cm³. -3 The melt index is 2.7cm. 3 / 10min (200℃ / 5kg). Talc powder (3000 mesh) was purchased from Changzhou Changjiang Talc Powder Factory. Carbon dioxide (CO2, purity 99.8%) was used as a physical foaming agent.

[0041] Examples 1-3 and Comparative Example 1

[0042] The mass proportions of the above-mentioned raw materials are shown in Table 1. The preparation of post-consumer recycled polystyrene foam beads using the above-mentioned raw materials in this embodiment includes the following steps:

[0043] Step 1: Mix rPS, PS and talc powder evenly according to the mass ratio; inject supercritical carbon dioxide into the first single-screw extruder at a speed of 4.0 mL / min and an injection pressure of 18.0 MPa. Set the temperature of the first single-screw mixing unit to 175℃, 190℃, 200℃, 200℃, 200℃, 200℃, 200℃, 200℃, the rotation speed to 35 r / min, and the pressure to 10.0 MPa.

[0044] Step 2: Connect the second single-screw extruder. Set the temperature of the second single-screw mixing unit to 160℃, 160℃, 160℃, 160℃, 160℃, 160℃, with a rotation speed of 7 r / min and a pressure of 9.0 MPa. The temperature of the static mixer is 160℃. The outlet end of the second extruder is a circular extruder die with four 1.2 mm diameter orifices. The pressure is 9.0 MPa, and the rotating cutter, which is in close contact with the die, rotates at 1000 r / min. After extrusion and pelletizing, foamed beads are obtained. These foamed particles are carried away from the cutter by the air force of the blower, blown out of the air-cooling chamber, collected, sieved, bagged, and cured to obtain foamed beads with the appearance of [image missing]. Figure 1 As shown, the internal pore structure is as follows Figure 2 As shown, the foamed beads have uniformly distributed pores with similar sizes. Figure 3 The microscopic surface morphology of the foamed beads shows that their surface is dense and without pores, ensuring that the foamed beads have a high closed-cell rate.

[0045] Table 1. Ingredients and foaming bead parameters for Examples 1-3 and Comparative Example 1

[0046]

[0047] As shown in Table 1, the closed-cell rate of foamed beads prepared directly from recycled polystyrene is only 70%, and there are also problems such as low expansion ratio. After adding 10 parts of virgin polystyrene, the expansion ratio and closed-cell rate can be improved by the above method, and its secondary expansion capacity is also improved.

[0048] Although the closed-cell rate of polystyrene foam beads in the mixed system after one foaming can reach more than 80%, its expansion ratio is still low, making it difficult to further reduce its density and thus achieve a further improvement in thermal insulation performance. Therefore, it is necessary to perform secondary foaming to further optimize its density and performance.

[0049] Examples 4-8

[0050] Examples 4-8 and Comparative Example 2 differ from Example 1 in that the expansion ratio and closed-cell ratio of the foamed beads are controlled by a secondary foaming technique. The foamed beads from Example 1 are used for secondary foaming, as detailed in Table 2. The specific steps are as follows:

[0051] The foamed beads from Example 1 were used for secondary foaming to control the expansion ratio of the prepared foamed beads. The specific steps are as follows: (1) The post-consumer recycled polystyrene extruded foamed beads were saturated in air medium at a saturation pressure of 1.0 bar, a temperature of room temperature, and a saturation time of 5.0 h. (2) The saturated foamed beads from (1) were transported to a foamed bead pre-foaming machine through a feeding system, and steam was introduced to heat them and cause secondary expansion at a temperature of 80.0-105.0 °C. The expansion ratio and closed-cell rate of the foamed beads after secondary expansion are shown in Table 2.

[0052] Table 2 shows the steam pressure conditions, expansion ratio, and closed-cell ratio of the foamed beads during secondary foaming in Examples 5-8 and Comparative Example 2.

[0053] Example 4 80.0 0.50 27.0 95.0 Example 5 85.0 0.60 34.5 92.0 Example 6 90.0 0.70 42.3 87.3 Example 7 95.0 0.90 51.6 84.2 Example 8 100.0 1.00 60.0 80.2 Comparative Example 2 105.0 1.20 45.0 55.0

[0054] The internal microstructure of the microporous foamed beads after secondary foaming in Example 4 is as follows: Figure 4 The pores are noticeably larger. Figure 5 The image shows an electron microscope (EM) image of the internal pore structure of the microporous foamed beads in Comparative Example 2. As shown in Table 2, below the glass transition temperature, the expansion ratio of the foamed beads gradually increases with the gradual increase of the secondary expansion temperature, while the closed-cell ratio decreases. When the secondary expansion temperature is 100℃, the expansion ratio reaches 60, and the closed-cell ratio is 80%. When the temperature is 105℃, because the temperature exceeds the glass transition temperature of the system, the foamed beads exhibit pore collapse, resulting in a low expansion ratio and a significant decrease in the closed-cell ratio.

[0055] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing microporous foamed beads based on recycled polystyrene, characterized in that, Including the following steps: Step 1: Recycled polystyrene, polystyrene, and talc are premixed and then melt-blended. Supercritical carbon dioxide is injected into the mixture, and the blend is obtained by melt extrusion. Step 2: The blend is further blended, extruded and foamed, and then hot-cut by air cooling through a die to obtain foamed beads; Step 3: The foamed beads are placed in a high-pressure gas medium for saturation, heated with steam to cause secondary expansion, and then cooled, shaped and dried to obtain the microporous foamed beads; the steam temperature in step 3 is 60-100℃ and the steam pressure is 0.3-1.5 bar. The microporous foamed beads, based on a total mass of 100 parts, include 55-95 parts recycled polystyrene, 20-45 parts polystyrene, 0.1-5 parts talc, and 1-10 parts supercritical carbon dioxide.

2. The method for preparing microporous foamed beads based on recycled polystyrene according to claim 1, characterized in that, In step 1, the supercritical carbon dioxide injection pressure is 15-20 MPa.

3. The method for preparing microporous foamed beads based on recycled polystyrene according to claim 1, characterized in that, In step 1, the melt extrusion temperature is 160-220℃, the screw speed is 25-40 r / min, and the pressure is 7-18 MPa.

4. The method for preparing microporous foamed beads based on recycled polystyrene according to claim 1, characterized in that, In step 2, the mixing temperature is 140-180℃, the screw speed is 3-30 r / min, and the pressure is 7-18 MPa.

5. The method for preparing microporous foamed beads based on recycled polystyrene according to claim 1, characterized in that, Step 2 is carried out in a second extrusion unit connected to the first extrusion unit in step 1, and extrusion foaming is carried out in a static mixer downstream of the second extrusion unit; The temperature of the static mixer is 140-180℃, and the die pressure is 7-20 MPa.

6. The method for preparing microporous foamed beads based on recycled polystyrene according to claim 1, characterized in that, The expansion ratio of the foamed beads in step 2 is 15-25, and the closed-cell ratio is 80-95%.

7. The method for preparing microporous foamed beads based on recycled polystyrene according to claim 1, characterized in that, In step 3, the saturation pressure of the high-pressure gas medium is 0.1-1.5 bar, and the temperature is 0-40℃. The gas medium includes one or more of air, carbon dioxide, and nitrogen.

8. The microporous foamed beads prepared from recycled polystyrene according to any one of claims 1-7, characterized in that, The initial expansion ratio of the microporous foamed beads is 15-25, and the closed-cell ratio is 80-95%; after secondary foaming by heating with steam, the expansion ratio is 25-60, and the closed-cell ratio is 80-95%.

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