A polystyrene composite foam material and its preparation method

Abstract

This invention relates to the field of polystyrene foaming technology, and discloses a polystyrene composite foaming material and its preparation method. This invention achieves efficient foaming by utilizing hollow metal-organic framework nanoparticles in polystyrene to form high-density and uniform nucleation sites. The hollow structure of the metal-organic framework nanoparticles significantly enhances its CO2 adsorption capacity, making it easier for CO2 to accumulate at the nucleation sites. Ultimately, the polystyrene foaming material prepared by this invention has characteristics such as high pore density, small pore size, uniform pore structure, and excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of polystyrene foaming technology, and in particular to a polystyrene composite foaming material and its preparation method. Background Technology

[0002] Polystyrene (PS) foam is a high-performance foam material with properties such as light weight, thermal insulation, shock absorption, and ease of molding. It is widely used in building sound and heat insulation layers, packaging materials, and containers. However, there are some technical challenges in preparing high-performance PS foam using supercritical carbon dioxide (CO2). For example, CO2 has low solubility and a high diffusion coefficient in PS melt, resulting in a high expansion ratio and low cell density in the prepared PS foam, which in turn affects its performance.

[0003] In the molding process of foamed materials, bubble nucleation plays a crucial role. The number and distribution of bubble nuclei determine the number and distribution of cells in the foamed material. To increase the number of bubble nucleation points, researchers, based on classical nucleation theory, explored the effect of adding nucleating agents on the nucleation mechanism of foamed plastics, and found that the addition of nucleating agents can significantly increase the number of bubble nuclei.

[0004] In existing technologies, to address the foaming problem of polystyrene, Chinese patent application CN 111393759 A discloses a supercritical fluid-based polystyrene foam material and its preparation method. This patent proposes to improve the absorption capacity of supercritical CO2 by adding appropriate amounts of thermoplastic elastomer materials, bio-based porous carbon, and cellulose nanocrystals to polystyrene, resulting in a higher pore density and smaller pore size. However, this method requires the addition of multiple substances and strict control of their proportions, making the process complex, and the foaming effect is still unsatisfactory, failing to meet the needs of many related fields.

[0005] Metal-organic framework (MOF) nanoparticles are formed by linking one or more metal ions with organic compounds. They possess crystalline and porous structures, exhibiting characteristics such as large internal surface area, high porosity, and small crystal size. MOF nanoparticles have broad application prospects in biomedicine, catalysis, gas storage and separation, and sensing. Summary of the Invention

[0006] To address the aforementioned technical problems in polystyrene foaming, this invention provides a polystyrene composite foam material and its preparation method. This invention utilizes hollow metal-organic framework nanoparticles to form foaming nucleation sites in polystyrene. Specifically, by setting the metal-organic framework nanoparticles in a hollow form and uniformly distributing them within the polystyrene, the resulting foamed polystyrene material exhibits excellent properties such as high pore density, small pore size, and uniform pore structure.

[0007] The specific technical solution of this invention is as follows:

[0008] On one hand, the present invention provides a method for preparing a polystyrene composite foam material, comprising the following steps:

[0009] Step S1: Provide a hollow metal-organic framework nanoparticle;

[0010] Step S2: Mix hollow metal-organic framework nanoparticles with polystyrene, and mold them to obtain a blended board.

[0011] Step S3: Place the co-blended board in a supercritical CO2 fluid environment for foaming.

[0012] This invention utilizes hollow metal-organic framework nanoparticles to form foaming nucleation sites in polystyrene, resulting in a foamed polystyrene material with excellent properties such as high pore density, small pore size, and uniform pore structure distribution. The principle is as follows:

[0013] (a) Hollow metal-organic framework nanoparticles have small particle size, which can form multiple small nucleation sites in polystyrene, and their distribution can be changed by adjusting the mixing method to form a high-density uniform nucleation site.

[0014] (b) The hollow structure of the hollow metal-organic framework nanoparticles can effectively increase the adsorption of CO2 by the nucleation sites during the foaming process, adsorb more CO2, and make it easier for CO2 to accumulate at the nucleation sites to form bubbles.

[0015] As a preferred embodiment of the method described above, in step S1, the hollow metal-organic framework nanoparticles are hollow ZIF-8 nanoparticles.

[0016] Specifically, this invention provides a method for preparing hollow ZIF-8 nanoparticles, comprising the following steps:

[0017] (1) Preparation of ZIF-67 nanoparticles: Cobalt nitrate hexahydrate and 2-methylimidazole were dissolved in solvent and stirred to form nuclei to obtain ZIF-67 nanoparticles;

[0018] (2) Surface coating with ZIF-8 material layer: ZIF-67 nanoparticles are dissolved in a solvent, ultrasonically treated, and then zinc nitrate hexahydrate and 2-methylimidazole are added and stirred to coat the surface of ZIF-67 nanoparticles with a ZIF-8 material layer.

[0019] (3) Removal of the core ZIF-67: The product obtained in step (2) is subjected to hydrothermal reaction to remove the core ZIF-67 material and obtain hollow ZIF-8 nanoparticles.

[0020] As a preferred embodiment of the method described above, in step S3, the pressure of the environment is 8~14MPa.

[0021] As a preferred embodiment of the method described above, in step S3, the foaming temperature is 90~110℃.

[0022] As a preferred embodiment of the method described above, in step S3, before the foaming process, a pre-nucleation step of CO2 is performed on the hollow metal-organic framework nanoparticles to promote uniform nucleation and improve the stability of the foam pores.

[0023] Further preferably, the pre-nucleation step is as follows: placing the blend plate in a supercritical CO2 fluid environment with a pressure of 8~14MPa and a temperature of 140~160℃ for 0.8~2 hours.

[0024] As a preferred embodiment of the method described above, in step S2, the mass percentage of the hollow metal-organic framework nanoparticles in the blended plate is 0.5-2.0%.

[0025] As a preferred embodiment of the method described above, in step S2, the mixing is melt blending, used to form uniform metal-organic framework nanoparticle foaming nucleation sites in polystyrene. This step is crucial for forming high-density, uniform cells.

[0026] Further preferably, the blending temperature is 190~210℃, the blending speed is 50~70rpm, and the blending time is 5~10min.

[0027] On the other hand, the present invention provides a polystyrene composite foam material, which is prepared by the above-described method.

[0028] Compared with the prior art, the present invention has the following technical effects:

[0029] (1) This invention utilizes hollow metal-organic framework nanoparticles to form foaming nucleation sites in polystyrene. The small-particle-size hollow metal-organic framework nanoparticles form high-density and uniform nucleation sites. The hollow structure increases the adsorption of CO2, making it easier for CO2 to accumulate at the nucleation sites, thus obtaining a polystyrene foam material with high pore density, small pore size and uniformly distributed pore structure.

[0030] (2) This invention uses hollow metal-organic framework nanoparticles as foaming nucleating agents, which is simple to prepare and suitable for large-scale industrial production. Under the condition of low filler addition, the prepared polystyrene foam material has the characteristics of uniform cell structure, small cell size and high cell density, and has good prospects for industrial application. Attached Figure Description

[0031] Figure 1 Comparison of SEM, TEM and XRD images of hollow metal-organic framework nanoparticles HZIF-8 and metal-organic framework nanoparticles ZIF-8;

[0032] Figure 2 A comparison chart of CO2 solubility of PS, PS / HZIF-8, and PS / ZIF-8;

[0033] Figure 3 These are scanning electron microscope (SEM) images of the brittle fracture surfaces of the foamed materials prepared in Examples 1-3;

[0034] Figure 4 Scanning electron microscope (SEM) images of the brittle fracture surfaces of the foamed materials prepared in Examples 2, 4, and 5;

[0035] Figure 5 Scanning electron microscope (SEM) images of the brittle fracture surfaces of the foamed materials prepared in Examples 2, 6, and 7;

[0036] Figure 6 Scanning electron microscope (SEM) images of the brittle fracture surfaces of the foamed material samples prepared in Example 2, Comparative Examples 1 and 2;

[0037] Figure 7 The graph shows the compression performance of the foamed materials prepared in Example 2, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0038] The present invention will be further described below with reference to embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0039] In this invention, the performance testing method for foamed materials is as follows:

[0040] The foamed material sample was frozen in liquid nitrogen for 2 hours and then subjected to brittle fracture. The cross-section of the foamed sample was sputter-coated with gold and then the cell morphology was observed using a scanning electron microscope (SEM).

[0041] Import the above SEM image using ImageJ (Image J, USA) image analysis software and calculate the cell size D. The calculation formula is as follows:

[0042] Where n is the number of bubbles in the analyzed SEM image, and D i The diameter of the i-th bubble in the SEM image, calculated according to the scale.

[0043] Calculate the expansion ratio (φ) of the sample:

[0044]

[0045] Where, ρ s and ρ f The densities are before and after foaming, respectively, measured using Archimedes' water displacement method according to ASTM standard D792.

[0046] The formula for calculating the bubble density N is as follows:

[0047]

[0048] Where n is the number of cells in the SEM image, and A is the area of ​​the image.

[0049] Example 1

[0050] Step S1: Provide hollow metal-organic framework nanoparticles (HZIF-8), as follows:

[0051] First, ZIF-67 nanoparticles were prepared: 1.08 g (0.0037 mol) of Co(NO3)·6H2O and 2.4375 g (0.0297 mol) of 2-Methylimidazole were weighed and dissolved separately in 75 mL of methanol. After complete dissolution, the two solutions were mixed and stirred for 10 minutes and allowed to stand for 24 hours. The resulting solution was centrifuged at 8000 rpm for 3 minutes, and the supernatant was discarded. The precipitate was washed with 15 mL of methanol, centrifuged at 6000 rpm for 3 minutes, and the upper methanol layer was discarded. This process was repeated three times. The precipitate was dried in a vacuum oven at 60 °C for 12 hours to obtain metal-organic framework nanoparticles ZIF-67.

[0052] Then, a ZIF-8 material layer was coated onto the surface of ZIF-67 nanoparticles: 100 mg (0.00045 mol) of ZIF-67, 0.372 mg (0.00125 mol) of Zn(NO3)·6H2O, and 0.1026 mg (0.00125 mol) of 2-Methylimidazole were weighed. ZIF-67 was dissolved in 60 mL of methanol, and after complete dissolution, Zn(NO3)·6H2O and 2-Methylimidazole were added, and the mixture was stirred for 1.5 hours.

[0053] Finally, the ZIF-67 core was removed: the mixed solution was poured into a hydrothermal reactor and reacted in a 100°C oven for 24 hours. The resulting solution was centrifuged at 8000 rpm for 3 minutes, and the supernatant was discarded. The precipitate was washed with 15 mL of methanol, centrifuged at 6000 rpm for 3 minutes, and the methanol was discarded. This process was repeated three times. The precipitate was dried in a 60°C vacuum oven for 12 hours to prepare HZIF-8.

[0054] Step S2: The hollow metal-organic framework nanoparticles are mixed with polystyrene and molded to obtain a blend board. The operation is as follows:

[0055] 49.75g of polystyrene and 0.25g of metal-organic framework nanoparticles HZIF-8 were melt-blended. The mixture was then added to a Hacker torque rheometer for blending at 195℃ and 60rpm for 8 minutes. The resulting product was then molded at 195℃ using a tablet press to obtain a 20mm × 10mm × 2mm blend sheet as a sample.

[0056] Step S3: Perform supercritical CO2 foaming treatment on the board sample, as follows:

[0057] The sheet material sample was placed in a high-pressure reactor. The reactor was then closed, and low-pressure CO2 was introduced into the reactor. The reactor was purged for 1 minute to replace the air. The high-pressure reactor was then placed in a 150°C oil bath, and CO2 was introduced into the reactor using a high-pressure pump to a pressure of 13.8 MPa. The mixture was then soaked for 1 hour. The oil bath was then cooled to 100°C at a rate of 5°C / min, and held at 100°C for 10 minutes to obtain the polystyrene foam material. The cross-sectional SEM image of the polystyrene microporous foam material prepared in this embodiment is shown below. Figure 3 (a).

[0058] Example 2

[0059] The main difference between this embodiment and Example 1 is that in step S2, 49.5g of polystyrene and 0.5g of metal-organic framework nanoparticles HZIF-8 are melt-blended. Everything else is the same as in Example 1.

[0060] The cross-sectional SEM image of the polystyrene microporous foam material prepared in this embodiment is shown below. Figure 3 or Figure 4 (b), or Figure 5 (c), or see Figure 6 (a). The compressibility of the polystyrene microporous foam material prepared in this embodiment is shown in [reference needed]. Figure 7 .

[0061] Example 3

[0062] The main difference between this embodiment and Example 1 is that in step S2, 49.0g of polystyrene and 1.0g of metal-organic framework nanoparticles HZIF-8 are melt-blended. Everything else is the same as in Example 1.

[0063] The cross-sectional SEM image of the polystyrene microporous foam material prepared in this embodiment is shown below. Figure 3 (c).

[0064] Example 4

[0065] The main difference between this embodiment and Embodiment 2 is that in step S3, the temperature is lowered to 90°C and then maintained at 90°C. Everything else is the same as in Embodiment 2.

[0066] The cross-sectional SEM image of the polystyrene microporous foam material prepared in this embodiment is shown below. Figure 4 (a).

[0067] Example 5

[0068] The main difference between this embodiment and Embodiment 2 is that in step S3, the temperature is lowered to 110°C and then maintained at 110°C. Everything else is the same as in Embodiment 2.

[0069] The cross-sectional SEM image of the polystyrene microporous foam material prepared in this embodiment is shown below. Figure 4 (c).

[0070] Example 6

[0071] The main difference between this embodiment and Embodiment 2 is that in step S3, the pressure in the autoclave is increased to 8 MPa, and foaming is carried out at 8 MPa. Everything else is the same as in Embodiment 2.

[0072] The cross-sectional SEM image of the polystyrene microporous foam material prepared in this embodiment is shown below. Figure 5 (a).

[0073] Example 7

[0074] The main difference between this embodiment and Embodiment 2 is that in step S3, the pressure in the autoclave is increased to 11 MPa, and foaming is carried out at 11 MPa. Everything else is the same as in Embodiment 2.

[0075] The cross-sectional SEM image of the polystyrene microporous foam material prepared in this embodiment is shown below. Figure 5 (b).

[0076] Comparative Example 1

[0077] The main difference between this comparative example and Example 2 is that hollow metal-organic framework nanoparticles HZIF-8 are not added. The preparation method of this comparative example is as follows:

[0078] 50g of polystyrene was molded into a 20mm×10mm×2mm sheet sample using a tablet press at 195℃. The sheet sample was placed in a high-pressure reactor, the reactor was closed, and low-pressure CO2 was introduced into the reactor for 1 minute to purge and replace the air. The high-pressure reactor was then placed in a 150℃ oil bath, and CO2 was introduced into the reactor to 13.8MPa using a high-pressure pump for 1 hour of soaking. The oil bath was then cooled to 100℃ at a rate of 5℃ / min, and held at 100℃ for 10 minutes to obtain the polystyrene foam material. The cross-sectional SEM image of the polystyrene foam material prepared in this comparative example is shown below. Figure 6 (b).

[0079] Comparative Example 2

[0080] The main difference between this comparative example and Example 2 is that, in step S1, metal-organic framework nanoparticles ZIF-8 are provided. The other steps are the same as in Example 2.

[0081] The steps S1 of this comparative example are as follows:

[0082] Weigh 2 g (0.0067 mol) of Zn(NO3)·6H2O and 2 g (0.0244 mol) of 2-Methylimidazole. Dissolve each in 50 mL of methanol. After complete dissolution, mix the two solutions and sonicate for 1 hour. Centrifuge the resulting solution at 8000 rpm for 3 minutes and discard the supernatant. Wash the precipitate with 15 mL of methanol, centrifuge at 6000 rpm for 3 minutes, and discard the upper methanol layer. Repeat this process three times. Dry the precipitate in a vacuum oven at 60 °C for 12 hours to obtain metal-organic framework nanoparticles ZIF-8.

[0083] The cross-sectional SEM image of the polystyrene foam material prepared in this comparative example is shown below. Figure 6 (c).

[0084] Performance Characterization

[0085] (1) The foamed materials prepared in the examples and comparative examples were tested for cell density, cell size and expansion ratio. The results are shown in Table 1.

[0086] <![CDATA[Cell density (cells / cm 3 )]]> Cell size (μm) Expansion ratio Example 1 <![CDATA[9.2×10 8 ]]> 10.6 3.6 Example 2 <![CDATA[1.4×10 9 ]]> 8.6 3.3 Example 3 <![CDATA[5.3×10 8 ]]> 11.6 2.0 Example 4 <![CDATA[1.6×10 9 ]]> 6.6 1.7 Example 5 <![CDATA[1.3×10 9 ]]> 9.1 4.1 Example 6 <![CDATA[1.3×10 8 ]]> 13.7 3.5 Example 7 <![CDATA[6.4×10 8 ]]> 10.3 3.0 Comparative Example 1 <![CDATA[7.1×10 6 ]]> 52.4 4.9 Comparative Example 2 <![CDATA[5.6×10 8 ]]> 16.9 2.4

[0087] As shown in Table 1:

[0088] As can be seen from the data in Examples 1-7, the present invention utilizes hollow metal-organic framework nanoparticles to form foaming nucleation sites in polystyrene. The smaller particle size of the metal-organic framework nanoparticles forms a high density of uniform nucleation sites in polystyrene. Furthermore, the metal-organic framework nanoparticles are configured with a hollow structure. Through the hollow structure, the adsorption of CO2 by the nucleation sites of the metal-organic framework nanoparticles during the foaming process is effectively increased, allowing for the adsorption of more CO2 and making it easier for CO2 to accumulate at the sites of the metal-organic framework nanoparticles. Thus, a polystyrene foam material with excellent properties of high pore density and small pore size can be obtained.

[0089] The difference between Examples 1, 2, and 3 lies in the amount of hollow metal-organic framework nanoparticles HZIF-8 added. Characterization data from Examples 1-3 demonstrate the effect of the amount of HZIF-8 added on this foaming method. (See Table 1 and...) Figure 3 It is known that the foaming effect does not improve linearly with the increase of the addition amount. When the addition amount is too high, the mixing uniformity of HZIF-8 decreases, which leads to a decrease in cell performance. In Example 2, when the mass ratio of metal-organic framework nanoparticles in the mixed board is 1%, the foamed material obtained has the most uniform cell structure, the highest cell density, and the smallest cell size.

[0090] The difference between Examples 2, 4, and 5 lies in the foaming temperature. The characterization data of Examples 2, 4, and 5 show the effect of foaming temperature on this foaming method. From 110°C to 90°C, as the temperature decreases, the cell diameter becomes smaller and the cell density increases slightly, but the expansion ratio decreases significantly, which does not meet the purpose of weight reduction and increased production. Therefore, the foaming effect is best at a foaming temperature of 100°C, as shown in the characterization data of Example 2.

[0091] The difference between Examples 2, 6, and 7 lies in the pressure of the foaming environment. The characterization data of Examples 2, 6, and 7 can show the influence of foaming pressure on this foaming method. (See Table 1 and...) Figure 5 It can be seen that when the foaming pressure in Example 2 is 13.8 MPa, the foamed material obtained has the most uniform cell structure, the highest cell density, and the smallest cell size.

[0092] Comparative analysis of Comparative Examples 1 and 2 with Example 2 shows that Comparative Example 1, which did not include metal-organic framework nanoparticles, and Comparative Example 2, which did not configure the metal-organic framework nanoparticles as hollow structures, both resulted in a significant reduction in cell density. The addition of hollow ZIF-8 greatly reduced the cell size and increased the cell density by up to three orders of magnitude.

[0093] Further, Figure 1The images show a comparison of SEM, TEM, and XRD patterns of the hollow metal-organic framework nanoparticles HZIF-8 in Example 2 and the metal-organic framework nanoparticles ZIF-8 in Comparative Example 2. In Figure (a), the image is a SEM image of ZIF-8; in Figure (b), the image is a TEM image of ZIF-8; in Figure (c), the image is a SEM image of HZIF-8; in Figure (d), the image is a TEM image of HZIF-8; and in Figure (e), the powder XRD patterns of HZIF-8, ZIF-8, and the standard card ZIF-8. As can be seen from Figure (e), the patterns of HZIF-8 and ZIF-8 have the same diffraction peaks as the pattern of the standard card ZIF-8, indicating that the three have the same crystal structure and belong to the same substance. The SEM and TEM images of HZIF-8 show that the HZIF-8 prepared in Example 2 has a hollow structure. Figure 2 The graph shows a comparison of the CO2 solubility of PS prepared in Comparative Example 1, PS / HZIF-8 prepared in Example 2, and PS / ZIF-8 prepared in Comparative Example 2. It can be seen that the addition of HZIF-8 can enable the material to better adsorb and dissolve CO2. Figure 7 The graphs show the compression properties of the foamed materials obtained in Example 2, Comparative Examples 1 and 2. Figure 7 The excellent compressive properties of the PS / HZIF-8 foam material prepared in Example 2 are shown. A comparison of Comparative Examples 1 and 2 with Example 2 demonstrates the advantages of this invention in promoting polystyrene foaming using hollow metal-organic framework nanoparticles.

[0094] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0095] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a polystyrene composite foam material, characterized in that: Includes the following steps: Step S1: Provide a hollow metal-organic framework nanoparticle; Step S2: Mix hollow metal-organic framework nanoparticles with polystyrene, and mold them to obtain a blended board. Step S3: Place the blended sheet in a supercritical CO2 fluid environment for foaming.

2. The method for preparing a polystyrene composite foam material as described in claim 1, characterized in that: In step S1, the hollow metal-organic framework nanoparticles are hollow ZIF-8 nanoparticles.

3. The method for preparing a polystyrene composite foam material as described in claim 2, characterized in that: The preparation method of hollow ZIF-8 nanoparticles includes the following steps: (1) Preparation of ZIF-67 nanoparticles: Cobalt nitrate hexahydrate and 2-methylimidazole were dissolved in solvent and stirred to form nuclei to obtain ZIF-67 nanoparticles; (2) Surface coating with ZIF-8 material layer: ZIF-67 nanoparticles are dissolved in a solvent, ultrasonically treated, and then zinc nitrate hexahydrate and 2-methylimidazole are added. Stirring is performed to coat the surface of ZIF-67 nanoparticles with a ZIF-8 material layer. (3) Removal of the core ZIF-67: The product obtained in step (2) is subjected to a hydrothermal reaction to remove the core ZIF-67 material, resulting in hollow ZIF-8 nanoparticles.

4. The method for preparing a polystyrene composite foam material as described in claim 1, characterized in that: In step S3, the pressure of the environment is 8~14 MPa.

5. The method for preparing a polystyrene composite foam material as described in claim 4, characterized in that: In step S3, the foaming temperature is 90~110℃.

6. A method for preparing a polystyrene composite foam material as described in claim 1 or 5, characterized in that: In step S3, before the foaming process, a pre-nucleation step of CO2 in the hollow metal-organic framework nanoparticles is performed.

7. The method for preparing a polystyrene composite foam material as described in claim 6, characterized in that: The pre-nucleation step involves placing the blend plate in a supercritical CO2 fluid environment at a pressure of 8-14 MPa and a temperature of 140-160°C for 0.8-2 hours.

8. The method for preparing a polystyrene composite foam material as described in claim 1, characterized in that: In step S2, the hollow metal-organic framework nanoparticles account for 0.5% to 2.0% of the mass of the blended plate.

9. The method for preparing a polystyrene composite foam material as described in claim 1, characterized in that: In step S2, the mixing is a melt blending, used to form uniform metal-organic framework nanoparticle foaming nucleation sites in polystyrene.

10. A polystyrene composite foam material, characterized in that: It is prepared by the method according to any one of claims 1 to 9.

Images