Flower-like silver micro-nanoparticles and application thereof in preparation of high-cell-density polymer microporous material

Abstract

The application discloses flower-shaped silver micro-nanoparticles and application of the flower-shaped silver micro-nanoparticles in preparation of polymer microporous materials, and the flower-shaped silver micro-nanoparticles are prepared by the following steps: reacting silver nitrate with a structure directing agent in a solvent, adding a reducing agent into the solution, continuing to react, centrifuging, washing and drying the precipitate to obtain flower-shaped silver powder; adding all the flower-shaped silver powder into a reaction kettle, controlling the humidity of nitrogen atmosphere in the reaction kettle to be 10%-15% and keeping for 30 min, closing the air knob, rapidly injecting a modifier, sealing the reaction kettle, and reacting for 30 min at room temperature to obtain the flower-shaped silver micro-nanoparticles; the flower-shaped silver micro-nanoparticles prepared by the application can be used as a high-efficiency heterogeneous nucleating agent, can significantly improve nucleation efficiency, can reduce cell size, and can make cell density reach 10-11 orders of magnitude and be improved by 1-2 orders of magnitude. The method is simple in operation and easy to control, and is expected to be used in industrialized application of polymer supercritical CO2 foaming and improve economic benefits.

Description

(I) Technical Field

[0001] This invention relates to the field of foaming materials technology, and in particular to a flower-shaped silver micro / nanoparticle and its application in the preparation of high-porosity polymer microporous materials. (II) Background Technology

[0002] Polymer microporous materials are a class of lightweight functional materials with extremely wide applications. In recent decades, with the development of the social economy and the improvement of people's living standards, polymer microporous materials have been widely used in many industries such as construction, decoration, furniture, packaging, and transportation. Currently, polymer microporous materials have become an indispensable part of modern industries such as building insulation materials, furniture upholstery materials, automotive seat cushions, and thermal insulation packaging. The unique properties of polymer microporous materials, such as low density, excellent thermal insulation performance, sound absorption performance, and ease of processing, make them an ideal choice for meeting the needs of energy conservation, emission reduction, and lightweight industrial development. For example, in the field of building decoration, polymer microporous materials can significantly improve the thermal insulation effect of buildings, thereby saving energy; in the automotive industry, using lightweight polymer microporous materials to replace traditional metal materials effectively reduces vehicle weight, enhances maneuverability, and reduces energy consumption; in the packaging field, their thermal and sound insulation effects extend the shelf life of food and significantly reduce losses during transportation. The performance of microporous materials depends on their internal pore structure, especially the porosity, which has a particularly significant impact on performance. Generally, a high porosity leads to a decrease in material density, which is beneficial for improving its thermal insulation performance. Meanwhile, a high porosity also means that the material has more gas phase inside, which easily absorbs and suppresses sound propagation, thereby optimizing the material's sound absorption and insulation performance. Excessively large or uneven pores may cause a decrease in mechanical properties. Therefore, increasing the porosity is one of the important methods to improve the overall performance of microporous materials.

[0003] Supercritical CO2 foaming is widely used in the preparation and production of polymer microporous materials due to its advantages such as being environmentally friendly, low-cost, and offering good controllability of foaming conditions. While the production process of microporous materials using CO2 foaming is becoming increasingly mature, obtaining high-porosity polymer microporous materials under low-pressure foaming conditions remains a challenge. This is mainly because the existence of a nucleation energy barrier limits cell nucleation and growth, making it difficult to obtain a large number of cells per unit volume of polymer during the foaming process. To improve cell nucleation efficiency, traditional foaming processes often employ the addition of heterogeneous nucleating agents or the increase of foaming pressure. However, traditional foaming nucleating agents generally have low nucleation efficiency, and increasing foaming pressure leads to expensive equipment investment, complex process control, and increased production safety risks. Therefore, how to design and develop novel, highly efficient nucleating agents to achieve the preparation of high-porosity polymer microporous materials under low-pressure foaming conditions is a key research topic in the current foaming field. According to classical nucleation theory, compared to homogeneous nucleation, heterogeneous nucleation has a lower nucleation energy barrier, which is beneficial for cell nucleation and growth. In other words, the lower the nucleation energy barrier on the surface of the nucleating agent, the better it is for improving the nucleation efficiency and pore density. Therefore, the development and application of efficient heterogeneous nucleating agents are key to achieving the preparation of high-porosity polymer microporous materials under low-pressure foaming conditions. (III) Summary of the Invention

[0004] The purpose of this invention is to provide a flower-shaped silver micro / nanoparticle as an ultra-efficient heterogeneous nucleating agent and its application in the preparation of polymer microporous materials. This invention uses surface-roughened flower-shaped silver micro / nanoparticles as an efficient heterogeneous nucleating agent, which can prepare polymer microporous materials with high porosity under low-pressure foaming conditions. At the same time, the preparation process is simple and easy to use for molding, which solves the problem in the prior art that the high nucleation energy barrier makes it difficult to obtain a large number of micron-sized pores per unit volume of polymer during the foaming process.

[0005] The technical solution adopted in this invention is:

[0006] This invention provides flower-like silver micro / nanoparticles for use as ultra-efficient heterogeneous nucleating agents. The flower-like silver micro / nanoparticles are prepared according to the following steps: Silver nitrate and a structure-directing agent are reacted in a solvent in an ice-water bath or at room temperature for 5-60 min. After the reaction, a reducing agent is added to the solution, and the reaction continues for another 10-60 min in an ice-water bath or at room temperature. After the reaction, the reaction solution is centrifuged (preferably at 25°C and 8000-10000 rpm for 10 min), and the precipitate is washed sequentially with deionized water and anhydrous ethanol, and then dried (preferably at 40°C). After drying for 12 hours, flower-shaped silver powder was obtained. All the flower-shaped silver powder was added to a reaction vessel. The humidity of the nitrogen atmosphere in the reaction vessel was controlled at 10%-15% and maintained for 30 minutes. Then, the venting knob was turned off, and the modifier was drawn up with a long syringe, inserted into the rubber stopper at the top of the reaction vessel, and injected quickly. The reaction vessel was then sealed and reacted at room temperature for 30 minutes. The lid was then opened to obtain flower-shaped silver micro / nano particles. The structure guiding agent was succinic acid or citric acid; the solvent was deionized water; the reducing agent was ascorbic acid; and the modifier was dichloroethylsilane.

[0007] Preferably, the mass ratio of silver nitrate to structure directing agent is 1:1 to 2.5, more preferably 1:1.2 to 1.3; the volume of solvent used is 50-400 mL / g based on the mass of silver nitrate, more preferably 80-400 mL / g; the mass ratio of silver nitrate to reducing agent is 1:0.5 to 1.5; and the volume of modifier used is 1-5 mL / g based on the mass of silver nitrate, more preferably 4 mL / g.

[0008] This invention also provides an application of the aforementioned flower-like silver micro / nanoparticles in the preparation of high-porosity polymer microporous materials, the application being carried out according to the following steps:

[0009] (1) Flower-shaped silver micro / nano particles and polymer are fed into a twin-screw extruder and mixed at 100-200℃ for 3 minutes to obtain a polymer composite material; the polymer composite material is placed in a mold and held under pressure at 180℃ and 10 MPa for 10 minutes to obtain a polymer composite sheet; the polymer includes polymethyl methacrylate (PMMA), polypropylene (PP), polyurethane (TPU) or (polystyrene) PS.

[0010] (2) Add the polymer composite sheet obtained in step (1) into the reactor, introduce supercritical CO2 fluid as a physical foaming agent until the pressure reaches 6-8 MPa, seal the reactor, and saturate in the reactor for 4-8 hours at room temperature and 6-8 MPa pressure. Then reduce the pressure to 1 MPa within 1 second, and then immerse the polymer composite sheet in a constant temperature water bath at 80-120℃ to foam. Then quench it in an ice bath for 30 minutes to obtain the polymer microporous material.

[0011] Preferably, the mold in step (1) is an open cuboid with dimensions of 4×3×0.05 cm.

[0012] Preferably, in step (1), the mass ratio of flower-shaped silver micro / nanoparticles to polymer is 1:5-15, preferably 1:10.

[0013] Preferably, in step (2), the supercritical CO2 fluid flow rate is 15 m / s.

[0014] Preferably, the foaming time in step (2) is 1-30 seconds.

[0015] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in:

[0016] The flower-like silver micro / nanoparticles prepared in this invention are surface-modified inorganic particles. Their roughened surface provides a large number of nano-void structures, lowering the nucleation energy barrier and providing more nucleation sites. As a highly efficient heterogeneous nucleating agent, the flower-like silver micro / nanoparticles improve the wettability with the substrate polymer, allowing nucleation to occur primarily in the lower-energy nanocavities. This enables them to absorb more physical blowing agents (such as supercritical CO2 fluid), increasing the concentration of the physical blowing agent and thus significantly improving the nucleation efficiency. The addition of the flower-like silver micro / nanoparticles increases the pore density by 5-6 orders of magnitude, reaching a pore density of 10-1. 11 pcs / cm 3 This method also reduces the cell size. It is simple to operate and easy to control, and is expected to be used in the industrial application of polymer supercritical CO2 foaming, thereby improving economic efficiency. (iv) Description of the attached drawings

[0017] Figure 1 This is a SEM image of the flower-shaped silver micro / nanoparticles prepared in Example 1.

[0018] Figure 2 This is a SEM image of the flower-shaped silver micro / nanoparticles prepared in Example 2.

[0019] Figure 3 This is a SEM image of the cross-section of the foamed material prepared in Example 3, at a scale of 10 μm.

[0020] Figure 4 This is a SEM image of the cross-section of the foamed material prepared in Comparative Example 1, scale 100 μm.

[0021] Figure 5 This is a SEM image of the cross-section of the foamed material prepared in Example 4, at a scale of 50 μm.

[0022] Figure 6 This is a SEM image of the cross-section of the foamed material prepared in Comparative Example 2, at a scale of 50 μm.

[0023] Figure 7 This is a SEM image of the cross-section of the foamed material prepared in Example 5, at a scale of 20 μm.

[0024] Figure 8 This is a SEM image of the cross-section of the foamed material prepared in Comparative Example 3, at a scale of 20 μm.

[0025] Figure 9 This is a SEM image of the cross-section of the foamed material prepared in Example 6, at a scale of 50 μm.

[0026] Figure 10 SEM image of the cross-section of the foamed material prepared in Comparative Example 4, scale 50 μm.

[0027] Figure 11 SEM image of the cross-section of the foamed material prepared in Example 7, scale 20 μm. (V) Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto:

[0029] In this invention, unless otherwise specified, all equipment and raw materials are available from the market or commonly used in the industry. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0030] The room temperature described in this invention is 25-30℃.

[0031] The polymers used in the embodiments of this invention are: polymethyl methacrylate (PMMA) with a molecular weight of 80,000-200,000, polypropylene (PP) with a molecular weight of 80,000-150,000, polyurethane (TPU) with a molecular weight of 1,000-3,000, or polystyrene (PS) with a molecular weight of 50,000-300,000.

[0032] Example 1: Flower-shaped silver micro / nanoparticles

[0033] 0.128 g (0.75 mmol) of silver nitrate and 0.148 g (1 mmol) of succinic acid were reacted in 10 mL of deionized water under an ice-water bath for 10 min. After the reaction, 0.176 g (1 mmol) of ascorbic acid was added to the solution, and the reaction was continued under an ice-water bath for 15 min. After the reaction, the reaction solution was centrifuged at 25 °C and 8000 rpm for 10 min. The precipitate was washed successively with deionized water and anhydrous ethanol, and dried at 40 °C for 12 h to obtain flower-shaped silver powder. All the flower-shaped silver powder was added to a reaction vessel. The humidity of the nitrogen atmosphere in the reaction vessel was controlled at 15% and maintained for 30 min. The vent knob was closed, and 0.5 mL of dichloroethylsilane was drawn up with a long syringe, inserted into the rubber stopper at the top of the reaction vessel, and injected quickly. The reaction vessel was sealed and reacted at room temperature for 30 min. The lid was opened to obtain 0.1 g of flower-shaped silver micro / nano particles with a particle size of 2000–3000 nm. SEM image is shown below. Figure 1 As shown.

[0034] Example 2: Flower-shaped silver micro / nanoparticles

[0035] 0.128 g (0.75 mmol) of silver nitrate and 0.168 g (1 mmol) of citric acid were added to 50 mL of deionized water and stirred at room temperature for 5 min. After the reaction was complete, 0.066 g (0.375 mmol) of ascorbic acid was added to the solution, and the reaction was continued at room temperature for 60 min. After the reaction was complete, the reaction solution was centrifuged at 25 °C and 10,000 rpm for 10 min. The precipitate was washed successively with deionized water and anhydrous ethanol, and dried at 40 °C for 12 h to obtain flower-shaped silver powder. All the flower-shaped silver powder was added to a reaction vessel. The humidity of the nitrogen atmosphere in the reaction vessel was controlled at 15% and maintained for 30 min. The vent knob was closed, and 0.5 mL of dichloroethylsilane was drawn up with a long syringe, inserted into the rubber stopper at the top of the reaction vessel, and injected quickly. The reaction vessel was sealed and reacted at room temperature for 30 min. The lid was opened to obtain 0.1 g of flower-shaped silver micro / nano particles with a particle size of 400–500 nm. SEM image is shown below. Figure 2 As shown.

[0036] Example 3: High-porosity polymer microporous materials

[0037] (1) 1g of the flower-shaped silver micro / nanoparticles prepared in Example 1 and 10g of PMMA were fed into a micro twin-screw extruder and mixed at 155°C for 3 minutes to obtain a PMMA composite material. The PMMA composite material was placed in an open rectangular mold with dimensions of 4×3×0.05 cm and held at 180°C and 10 MPa for 10 minutes to obtain a PMMA composite sheet with a thickness of 2 mm.

[0038] (2) The PMMA composite sheet obtained in step (1) was added to a reactor (24×24cm). Supercritical CO2 fluid was introduced at a flow rate of 15m / s as a physical foaming agent until the pressure reached 6MPa. The reactor was sealed and saturated in the reactor at room temperature and 6MPa pressure for 4 hours. Then, the pressure was rapidly reduced to 1MPa within 1 second. Subsequently, the PMMA composite sheet was immersed in a constant temperature water bath at 80℃ for 30s to foam, and then quenched in an ice bath for 30min to obtain a high-porosity polymer microporous material. The cross-sectional SEM image is shown below. Figure 3 As shown.

[0039] from Figure 3 It can be seen that the addition of ultra-efficient heterogeneous nucleating agent, flower-shaped silver micro / nanoparticles, reduces the pore size and increases the pore density of the material, with the pore density being approximately [missing information]. Figure 4 The strength is tens of times greater than that of PMMA composites, attributed to the addition of flower-shaped silver micro / nanoparticles, which enhances the melt strength and reduces the pore size. The highly efficient heterogeneous nucleating agent provides more nucleation sites, resulting in more micropores. Smaller pore size at the same expansion ratio allows the material to absorb more energy, thus exhibiting superior mechanical properties.

[0040] Comparative Example 1

[0041] Omit the step (1) of the flower-shaped silver micro / nanoparticles in Example 3, and perform the same operations as before to obtain the polymer foam material. See the SEM image of the cross-section. Figure 4 As shown.

[0042] Example 4

[0043] In Example 3, PMMA was replaced with PP, and the temperature was changed to 200℃, while other operations remained the same, resulting in a polymer microporous material. The cross-sectional SEM image is shown below. Figure 5 As shown. From Figure 5 It can be seen that, compared to Figure 6 The cell size was significantly reduced, the cell density was significantly increased, and a bimodal cell structure appeared.

[0044] Comparative Example 2

[0045] Step (1) of Example 3, which involved omitting the flower-shaped silver micro / nanoparticles, replaced PMMA with PP, with all other operations remaining the same, yielded a polymer foam material. The cross-sectional SEM image is shown below. Figure 6 As shown.

[0046] Example 5

[0047] In Example 3, PMMA was replaced with PS, and the temperature was changed to 200℃, while other operations remained the same, resulting in a polymer microporous material. The cross-sectional SEM image is shown below. Figure 7 As shown. From Figure 7 It can be seen that, compared to Figure 8The morphology of the bubbles is more uniform.

[0048] Comparative Example 3

[0049] Step (1) of Example 3, which involved omitting the flower-shaped silver micro / nanoparticles, replaced PMMA with PS, with all other operations remaining the same, yielded a polymer foam material. The cross-sectional SEM image is shown below. Figure 8 .

[0050] Example 6

[0051] In Example 3, PMMA was replaced with TPU, the temperature was changed to 100℃, and all other operations remained the same, resulting in a polymer microporous material. The cross-sectional SEM image is shown below. Figure 9 ,from Figure 9 It can be seen that, compared to Figure 10 The cell walls thicken, and the cell size decreases.

[0052] Comparative Example 4

[0053] Step (1) of Example 3, which involves omitting the flower-shaped silver micro / nanoparticles, replaces PMMA with TPU, and performs the same other operations to obtain a polymer foam material. The cross-sectional SEM image is shown below. Figure 10 .

[0054] Example 7

[0055] The flower-shaped silver micro / nanoparticles in Example 3 were replaced with those prepared by the method in Example 2, with all other operations remaining the same, to obtain a polymer microporous material. The cross-sectional SEM image is shown below. Figure 11 As shown.

[0056] Example 8

[0057] Based on the SEM images, the cell diameter, cell density, and porosity of the foamed materials prepared in Examples 3-7 and Comparative Examples 1-4 were calculated using ImageJ software. The results are shown in Table 1 below.

[0058] Table 1. Pore diameter, pore density and porosity of polymer foam materials.

[0059] Cell diameter (μm) <![CDATA[Cell density (cells / cm 3 )]]> Porosity (%) Example 3 2 <![CDATA[2.1x 1011 ]]> 92 Example 4 7 <![CDATA[1.16x10 9 ]]> 89 Example 5 6 <![CDATA[4.39x10 9 ]]> 90 Example 6 9 <![CDATA[1.93x10 11 ]]> 95 Example 7 1 <![CDATA[6.1x10 11 ]]> 91 Comparative Example 1 8 <![CDATA[9.29x10 5 ]]> 78 Comparative Example 2 20 <![CDATA[6.25x10 4 ]]> 80 Comparative Example 3 14 <![CDATA[1.49x10 4 ]]> 76 Comparative Example 4 4 <![CDATA[4.21x10 6 ]]> 83

[0060] As shown in Table 1 above, the difference between the examples and the comparative examples lies in whether or not flower-shaped silver micro / nanoparticles were added. After adding the micro / nanoparticles, the size of the four polymer cell materials decreased, and the cell density increased to 10. 11 pcs / cm 3 This represents an improvement of 5 to 6 orders of magnitude.

[0061] 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.

[0062] 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. The application of flower-shaped silver micro / nanoparticles in the preparation of high-porosity polymer microporous materials, characterized in that, The application is performed according to the following steps: (1) Silver nitrate and the structure-directing agent are reacted in a solvent under ice-water bath or room temperature conditions for 5-60 min. After the reaction is completed, a reducing agent is added to the solution, and the reaction is continued under ice-water bath or room temperature conditions for 10-60 min. After the reaction is completed, the reaction solution is centrifuged, and the precipitate is washed with deionized water and anhydrous ethanol in sequence, and dried to obtain flower-shaped silver powder. All the flower-shaped silver powder is added to the reaction vessel, and the humidity of the nitrogen atmosphere in the reaction vessel is controlled at 10%-15% and maintained for 30 min. Then, the venting knob is turned off, the modifier is quickly injected, and the reaction vessel is closed. The mixture was sealed and reacted at room temperature for 30 minutes. The reactor lid was then opened to obtain flower-shaped silver micro / nano particles. The structure-directing agent was succinic acid or citric acid; the solvent was deionized water; the reducing agent was ascorbic acid; the modifier was dichloroethylsilane; the mass ratio of silver nitrate to the structure-directing agent was 1:1~2.5; the volume of solvent used was 50-400 mL / g based on the mass of silver nitrate; the mass ratio of silver nitrate to the reducing agent was 1:0.5-1.5; and the volume of modifier used was 1-5 mL / g based on the mass of silver nitrate. (2) The flower-shaped silver micro-nano particles and polymer are fed into a twin-screw extruder and mixed at 100-200℃ for 3 minutes to obtain a polymer composite material; the polymer composite material is placed in a mold and held under pressure at 180℃ and 10MPa for 10 minutes to obtain a polymer composite sheet; the mold is an open cuboid with dimensions of 4×3×0.05 cm. (3) Add the polymer composite sheet obtained in step (2) into the reactor, introduce supercritical CO2 fluid as a physical foaming agent until the pressure reaches 6-8 MPa, seal the reactor, and saturate it in the reactor for 4-8 hours at room temperature and 6-8 MPa pressure. Then reduce the pressure to 1 MPa within 1 second, and then immerse the polymer composite sheet in a constant temperature water bath at 80-120°C to foam it. Then quench it in an ice bath for 30 min to obtain a cell density of 10. 11 pcs / cm 3 Polymer microporous materials.

2. The application as described in claim 1, characterized in that, The polymer in step (2) includes polymethyl methacrylate, polypropylene, polyurethane or polystyrene.

3. The application as described in claim 1, characterized in that, Step (2) The mass ratio of flower-shaped silver micro / nanoparticles to polymer is 1:5-15.

4. The application as described in claim 1, characterized in that, Step (3) The supercritical CO2 fluid flow rate is 15 m / s.

5. The application as described in claim 1, characterized in that, Step (3) The foaming time is 1-30 seconds.

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