A polymer foam having a bimodal cell structure and a method of making the same

Abstract

The application discloses a polymer foam with a bimodal cell structure, which is mainly composed of a nucleating agent and an elastomer, the nucleating agent is one of gallium, mercury, indium, tin, copper, iron, calcium, magnesium, barium, nickel, cobalt, lead and bismuth, and the elastomer is at least one of thermoplastic polyurethane, ethylene vinyl acetate, thermoplastic polyester elastomer, polyether block polyamide, styrene-ethylene-butylene-styrene block copolymer, ethylene octene copolymer, ethylene propylene terpolymer, natural rubber, silicone rubber and nitrile rubber, the average particle size of the nucleating agent is 1-500 mu m, and the content of the nucleating agent is not more than 15 vol%. By controlling the particle size and content of the nucleating agent, the pore size of the polymer foam can be controlled, different application requirements can be met, and the application range is wide. The application further discloses a preparation method of the polymer foam with the bimodal cell structure, and the process is simple and suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of polymer foam technology, specifically to a polymer foam with a bimodal cell structure and its preparation method. Background Technology

[0002] Bimodal cell structure polymer foam is a type of foam material with a bimodal pore size distribution. Due to its unique microstructure, it has found wide application in industrial fields. Compared with traditional foam materials with a uniform cell structure, bimodal cell structure polymer microfoam exhibits superior physical and mechanical properties through the formation of a dual structure combining macropores and micropores within the material. Macropores help reduce material weight and improve energy absorption, while micropores enhance structural strength and thermal insulation performance. By optimizing the pore size distribution, bimodal cell structure foam can significantly improve its mechanical strength and durability while maintaining lightweight properties. Furthermore, this bimodal cell structure also enables the foam material to exhibit better energy absorption and cushioning performance under dynamic impact loads. Therefore, bimodal cell structure foam has become an ideal choice for applications requiring high-performance and multifunctional materials.

[0003] Currently, the main methods for preparing polymer foams with bimodal porous structures are physical foaming and chemical foaming. Physical foaming first achieves dissolution equilibrium of the gas within the polymer, then rapidly depressurizes or heats the system to create thermodynamic instability, thus transitioning from a homogeneous to a multiphase phase and inducing nucleation and pore growth. Finally, the polymer forms a porous structure. This includes rapid depressurization foaming and temperature-increasing foaming. Chemical foaming is similar to physical foaming, both reducing the solubility of the gas in the polymer, followed by bubble nucleation and pore growth. However, the gas source in chemical foaming is obtained through chemical reactions between different reagents. However, current preparation methods often employ multi-step processes to prepare polymer foams with bimodal porous structures, resulting in complex processes and low production efficiency, which limits the large-scale application of polymer foams with bimodal porous structures.

[0004] CN105385024A discloses a bimodal polypropylene foam and its preparation method. The bimodal polypropylene foam is composed of porous inorganic particles and a matrix resin, possessing large pores with an average diameter of 15μm-50μm and small pores with an average diameter of 1μm-10μm. The porous inorganic particles are one or more of activated carbon, porous alumina, porous silica gel, molecular sieves, and porous silica. However, the resulting polypropylene foam exhibits little difference in pore size, being quite similar and failing to meet the requirements for different pore sizes.

[0005] CN114702720A discloses a polybutene foam, its preparation method, preform, and application. The preparation method includes the following steps: (1) annealing the polybutene resin to obtain the preform; the annealing method includes supercritical CO2 annealing or room temperature and pressure annealing; supercritical CO2 annealing includes: in the presence of supercritical CO2, the polybutene resin is kept at a constant temperature and pressure, and then depressurized to obtain the preform; the depressurization rate is 0.1-1 MPa / min; room temperature and pressure annealing includes: melting the polybutene resin and cooling it at room temperature and pressure to obtain the preform; (2) in the presence of supercritical CO2, the preform is kept at a constant temperature and pressure, and then depressurized to obtain the preform; wherein, the depressurization rate is 5-300 MPa / s. However, the polybutene resin needs to be annealed first, which is a complex process. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a polymer foam with a bimodal pore structure. This polymer foam incorporates a nucleating agent that has poor compatibility with elastomers. By controlling the average particle size, content, and distribution of the nucleating agent, the bimodal pore structure can be directionally designed.

[0007] A polymer foam with a bimodal pore structure, the main raw materials of which are composed of a nucleating agent and an elastomer. The nucleating agent is one element, metal oxide, or alloy formed by multiple elements selected from gallium, mercury, indium, tin, copper, iron, calcium, magnesium, barium, nickel, cobalt, lead, and bismuth. The elastomer is at least one selected from thermoplastic polyurethane, ethylene vinyl acetate, thermoplastic polyester elastomer, polyether block polyamide, styrene-ethylene-butene-styrene block copolymer, ethylene octene copolymer, ethylene propylene diene monomer (EPDM) rubber, natural rubber, silicone rubber, and nitrile rubber. The average particle size of the nucleating agent is 1-500 μm, and the content of the nucleating agent does not exceed 15 vol.

[0008] In this invention, a nucleating agent is dispersed in an elastomer, and after blending and foaming, a polymer foam with a bimodal pore structure is obtained. For nucleating agents with smooth surfaces, due to the poor compatibility between the nucleating agent and the elastomer, a distinct interface exists between them. The presence of this interface significantly reduces the Gibbs free energy barrier that needs to be overcome for bubble nucleation. For nucleating agents with uneven surfaces and many irregular structures, microvoids exist on the surface of the nucleating agent particles. These microvoids, as well as areas with weaker bonds at the solid solution interface, are more likely to generate bubbles.

[0009] During physical or chemical foaming, bubble nucleation preferentially occurs on the surface of the nucleating agent, resulting in heterogeneous nucleation at the nucleating agent sites. The presence of heterogeneous nucleation sites does not preclude homogeneous nucleation; homogeneous nucleation can also occur in regions far from the influence of heterogeneous nucleation sites. Bubbles formed by heterogeneous nucleation at the nucleating agent sites are larger than those formed by homogeneous nucleation, growing into large pores, while bubbles formed by homogeneous nucleation in the matrix grow into small pores, resulting in a polymer foam with a bimodal pore structure after foaming.

[0010] In this invention, homogeneous and heterogeneous nucleation can occur simultaneously after the nucleating agent and elastomer are co-mixed. By adjusting the proportion of the nucleating agent in the elastomer, the size of the bimodal pores can be directionally designed. As the proportion of the nucleating agent increases, the pore sizes in the resulting polymer foam gradually become closer, forming a polymer foam with a uniform pore structure. Therefore, when the proportion of the nucleating agent does not exceed 15%, the internal pore structure of the resulting polymer foam exhibits a clear coexistence of large and small pores.

[0011] Preferably, the nucleating agent is a gallium indium tin alloy, the elastomer is thermoplastic polyurethane, and the content of the nucleating agent does not exceed 10 vol%.

[0012] In a preferred embodiment, gallium indium tin alloy (GaInT) is dispersed in thermoplastic polyurethane as a nucleating agent. Due to the poor compatibility between the two, during physical or chemical foaming, bubble nucleation preferentially occurs on the surface of the GaInT surface, resulting in heterogeneous nucleation at the GaInT sites. When the GaInT proportion does not exceed 10 vol%, the resulting polymer foam exhibits a clear distinction between large and small pore sizes, displaying a distinct bimodal pore structure.

[0013] Preferably, the nucleating agent is copper, the elastomer is thermoplastic polyurethane, the average particle size of the nucleating agent is 1-100 μm, and the content of the nucleating agent does not exceed 10 vol%.

[0014] Preferably, in the polymer foam with bimodal cell structure, the pore size of the large pores is between 40-1000 μm, the pore size of the small pores is between 1-100 μm, and the proportion of large pores is 5-90%.

[0015] The present invention also provides a method for preparing polymer foam with bimodal cell structure, which prepares polymer foam with bimodal cell structure through one-step foaming. The process is simple and suitable for large-scale production.

[0016] A method for preparing a polymer foam with a bimodal pore structure includes the following steps:

[0017] (1) The composite material is obtained by uniformly mixing the elastomer and the nucleating agent;

[0018] (2) The composite material obtained in step (1) is used to prepare a polymer foam with a bimodal cell structure by physical foaming or chemical foaming.

[0019] Preferably, the physical foaming method is a heating foaming method or a rapid depressurization foaming method.

[0020] More preferably, the heating foaming method involves saturating the composite material obtained in step (1) at room temperature in a high-pressure fluid, immersing it in heated glycerol, and then cooling and shaping it to obtain a polymer foam with a bimodal pore structure.

[0021] In a preferred embodiment, at room temperature, the composite material after blending the elastomer and nucleating agent is saturated and then immersed in heated glycerol. As the temperature rises rapidly, the entire system quickly becomes a supersaturated system. The gas dissolved in the composite material concentrates and nucleates, and the gas molecules begin to gradually diffuse toward the nucleus, causing the cells to grow and resulting in a polymer foam with a bimodal cell structure.

[0022] More preferably, the glycerin temperature is 100-160℃, and the soaking time is 5-30s.

[0023] The temperature and soaking time of glycerol are the foaming temperature and foaming time of polymer foam, respectively. When the foaming temperature increases and the foaming time is extended, the surface tension of the elastomer decreases, and the cells are easier to grow. Therefore, the pore size in the foam increases, the foaming ratio increases, and the density of the polymer foam decreases.

[0024] More preferably, the rapid depressurization method involves saturating the composite material obtained in step (1) in a high-pressure fluid, and after saturation, rapidly depressurizing and cooling to obtain a polymer foam with a bimodal pore structure.

[0025] More preferably, the saturation temperature is 120-160℃, the saturation pressure is 10-16MPa, and the saturation time is 0.5-1h.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) In this invention, metals, metal oxides or alloys are introduced as nucleating agents. Due to the compatibility difference between the nucleating agent and the elastomer, homogeneous nucleation and heterogeneous nucleation can occur simultaneously. After foaming, a polymer foam with a bimodal cell structure can be obtained.

[0028] (2) In this invention, the pore size of polymer foam can be controlled by controlling the particle size and content of the nucleating agent, so as to meet different application needs and have a wide range of applications;

[0029] (3) The method used in this invention is the conventional physical foaming method and chemical foaming method, both of which require only one foaming step to prepare polymer foam with bimodal cell structure. The process is simple and suitable for large-scale production. Attached Figure Description

[0030] Figure 1 This is a scanning electron microscope (SEM) image of the polymer foam with a bimodal pore structure obtained in Example 1.

[0031] Figure 2 This is a cell size distribution diagram of the polymer foam with a bimodal cell structure obtained in Example 1.

[0032] Figure 3 This is an SEM image of the polymer foam with a bimodal pore structure obtained in Example 2.

[0033] Figure 4 This is a SEM image of the polymer foam with a bimodal pore structure obtained in Example 3.

[0034] Figure 5 This is an SEM image of the polymer foam with a bimodal pore structure obtained in Example 4.

[0035] Figure 6 This is a SEM image of the polymer foam with a bimodal pore structure obtained in Example 5.

[0036] Figure 7 This is a SEM image of the polymer foam with a bimodal pore structure obtained in Example 6.

[0037] Figure 8 This is an SEM image of the polymer foam with a bimodal pore structure obtained in Example 7.

[0038] Figure 9 This is a SEM image of the polymer foam with a bimodal pore structure obtained in Example 8.

[0039] Figure 10 The image shows the SEM image of the polymer foam obtained in Comparative Example 1. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited to the following embodiments.

[0041] All raw materials used in this invention are commercially available.

[0042] Example 1

[0043] (1) A thermoplastic polyurethane solution was obtained by dissolving 35.7984 g of thermoplastic polyurethane (BASF, grade 1190A) in 100.24 mL of dimethylacetamide. 0.32 mL of gallium indium tin alloy (Ga68.5In21.5Sn10) with an average particle size of 17 μm was mixed thoroughly with the thermoplastic polyurethane solution. The mixture was poured into a mold, and the dimethylacetamide solution was removed by vacuum to obtain a thermoplastic polyurethane / gallium indium tin alloy composite material with a thickness of 1.1 mm, wherein the content of gallium indium tin alloy was 1 vol%.

[0044] (2) The thermoplastic polyurethane / gallium indium tin alloy composite material obtained in step (1) was placed in an autoclave for saturation treatment at a saturation pressure of 4 MPa, a saturation temperature of 23°C, and a saturation time of 48 h. The saturated sample was then immersed in glycerol at 150°C for 25 s, and rapidly water-cooled to solidify the foam cells, resulting in a polymer foam with a bimodal foam structure. The scanning electron microscope (SEM) image of the polymer foam is shown below. Figure 1 As shown.

[0045] like Figure 1 As shown, the internal pore structure of polymer foam exhibits a coexistence of large and small pores.

[0046] Figure 2 The image shows the cell size distribution of the polymer foam with a bimodal cell structure obtained in Example 1. Figure 2 As shown, the polymer foam obtained in Example 1 has a bimodal cell structure, with the average cell size of the large cells being 99.36 μm and the average cell size of the small cells being 11.53 μm, of which the large cells account for 49%.

[0047] Example 2

[0048] The preparation process was the same as in Example 1, except that the content of gallium indium tin alloy was 5 vol%. The resulting polymer foam with a bimodal pore structure was shown in the scanning electron microscope (SEM) image below. Figure 2 As shown. The polymer foam obtained in Example 2 has a bimodal cell structure, with an average cell size of 87.35 μm for large cells and an average cell size of 14.82 μm for small cells, of which large cells account for 75%.

[0049] Example 3

[0050] The preparation process was the same as in Example 1, except that the saturated sample was immersed in glycerol at 150°C for 8 seconds. The resulting polymer foam with a bimodal pore structure was shown in the scanning electron microscope (SEM) image below. Figure 3 As shown. The polymer foam obtained in Example 3 has a bimodal cell structure, with an average cell size of 61.73 μm for large cells and an average cell size of 12.12 μm for small cells, of which large cells account for 49%.

[0051] Example 4

[0052] The preparation process was the same as in Example 1, except that the saturated sample was immersed in glycerol at 130°C for 25 seconds. The resulting polymer foam with a bimodal pore structure was shown in the scanning electron microscope (SEM) image below. Figure 4 As shown. The polymer foam obtained in Example 4 has a bimodal cell structure, with an average cell size of 58.13 μm for large cells and an average cell size of 12.32 μm for small cells, of which large cells account for 46%.

[0053] Example 5

[0054] (1) 20g of thermoplastic polyurethane and 3.2220g of copper powder with an average particle size of 40μm were mixed evenly in an internal mixer. The mixed material was then pressed into a thermoplastic polyurethane / copper composite material with a thickness of 1.1mm, wherein the copper content was 2vol%.

[0055] (2) The thermoplastic polyurethane / copper composite material obtained in step (1) was placed in an autoclave for saturation treatment at a saturation pressure of 4 MPa, a saturation temperature of 23°C, and a saturation time of 48 h. The saturated sample was then immersed in glycerol at 150°C for 25 s, and rapidly water-cooled to solidify the foam cells, resulting in a polymer foam with a bimodal foam structure. The scanning electron microscope (SEM) image of the polymer foam is shown below. Figure 5 As shown. The polymer foam obtained in Example 5 has a bimodal cell structure, with an average cell size of 98.15 μm for large cells and 35.62 μm for small cells, of which large cells account for 60%.

[0056] Example 6

[0057] (1) A thermoplastic polyurethane solution was obtained by dissolving 35.7984 g of thermoplastic polyurethane in 100.24 mL of dimethylacetamide. 0.32 mL of gallium indium tin alloy (Ga68.5In21.5Sn10) with an average particle size of 17 μm was mixed evenly with the thermoplastic polyurethane solution, poured into a mold, and the dimethylacetamide solution was removed by vacuum to obtain a thermoplastic polyurethane / gallium indium tin alloy composite material with a thickness of 1.1 mm, wherein the content of gallium indium tin alloy was 1 vol%.

[0058] (2) The thermoplastic polyurethane / gallium indium tin alloy composite material obtained in step (1) was placed in an autoclave for saturation treatment. The saturation pressure was 12 MPa, the saturation temperature was 140 °C, and the saturation time was 30 min. The saturated sample was rapidly depressurized within 2 s, and after cooling and shaping, a polymer foam with a bimodal pore structure was obtained. The scanning electron microscope (SEM) image of the obtained polymer foam with a bimodal pore structure is shown below. Figure 6As shown. The polymer foam obtained in Example 6 has a bimodal cell structure, with an average cell size of 56.36 μm for large cells and an average cell size of 11.29 μm for small cells, of which large cells account for 9%.

[0059] Example 7

[0060] The preparation process was the same as in Example 6, except that the content of gallium indium tin alloy was 5 vol%. The resulting polymer foam with a bimodal pore structure was shown in the scanning electron microscope (SEM) image below. Figure 7 As shown. The polymer foam obtained in Example 7 has a bimodal cell structure, with an average cell size of 45.52 μm for large cells and 6.67 μm for small cells, of which large cells account for 35%.

[0061] Example 8

[0062] The preparation process was the same as in Example 6, except that the content of gallium indium tin alloy was 10 vol%. The resulting polymer foam with a bimodal pore structure was shown in the scanning electron microscope (SEM) image below. Figure 8 As shown. The polymer foam obtained in Example 8 has a bimodal cell structure, with an average cell size of 54.60 μm for large cells and an average cell size of 12.60 μm for small cells, of which large cells account for 68%.

[0063] Comparative Example 1

[0064] The preparation process is the same as in Example 1, except that no nucleating agent is added.

[0065] (1) Dissolve 10g of thermoplastic polyurethane in 28mL of dimethylacetamide to obtain a thermoplastic polyurethane solution. Pour the thermoplastic polyurethane solution into a mold, remove the dimethylacetamide solution by vacuuming, and obtain a thermoplastic polyurethane material with a thickness of 1.1mm.

[0066] (2) The thermoplastic polyurethane / gallium indium tin alloy composite material obtained in step (1) was placed in an autoclave for saturation treatment at a saturation pressure of 4 MPa, a saturation temperature of 23 °C, and a saturation time of 48 h. The saturated sample was then immersed in glycerol at 150 °C for 25 s, and after cooling and setting, polymer foam was obtained. The scanning electron microscope (SEM) image of the polymer foam is shown below. Figure 9 As shown.

[0067] Figure 9 The image shows a scanning electron microscope (SEM) image of the polymer foam obtained in Comparative Example 1. Since no nucleating agent was added, the polymer foam prepared by the heating foaming method exhibits a uniform single-peak cell structure with an average cell size of 24.58 μm.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A polymer foam with a bimodal cell structure, mainly composed of a nucleating agent and an elastomer, characterized in that, The nucleating agent is an alloy formed from one or more elements selected from gallium, mercury, indium, tin, copper, iron, calcium, magnesium, barium, nickel, cobalt, lead, and bismuth; the elastomer is at least one selected from thermoplastic polyurethane, ethylene vinyl acetate, thermoplastic polyester elastomer, polyether block polyamide, styrene-ethylene-butene-styrene block copolymer, ethylene octene copolymer, ethylene propylene diene monomer (EPDM) rubber, natural rubber, silicone rubber, and nitrile rubber; the average particle size of the nucleating agent is 1-500 μm, and the content of the nucleating agent does not exceed 15 vol%. In the polymer foam with bimodal pore structure, the pore size of the large pores is 40-1000 μm, the pore size of the small pores is 1-100 μm, and the proportion of the large pores is 5-90%.

2. The polymer foam with a bimodal cell structure according to claim 1, characterized in that, The nucleating agent is a gallium indium tin alloy, the elastomer is a thermoplastic polyurethane, and the content of the nucleating agent does not exceed 10 vol.

3. The polymer foam with a bimodal cell structure according to claim 1, characterized in that, The nucleating agent is copper, the elastomer is thermoplastic polyurethane, the average particle size of the nucleating agent is 1-100 μm, and the content of the nucleating agent does not exceed 10 vol.

4. The method for preparing polymer foam with a bimodal pore structure according to any one of claims 1-3, characterized in that, Includes the following steps: (1) The elastomer and nucleating agent are mixed evenly to obtain a composite material; (2) The composite material obtained in step (1) is used to prepare a polymer foam with a bimodal cell structure by physical foaming.

5. The method for preparing polymer foam according to claim 4, characterized in that, The physical foaming method mentioned is either the heating foaming method or the rapid depressurization foaming method.

6. The method for preparing polymer foam according to claim 5, characterized in that, The steps of the heating foaming method are as follows: the composite material obtained in step (1) is subjected to room temperature saturation treatment in a high-pressure fluid, then immersed in heated glycerol, and cooled and shaped to obtain a polymer foam with a bimodal pore structure.

7. The method for preparing polymer foam according to claim 6, characterized in that, The glycerin temperature is 100-160℃, and the soaking time is 5-30 seconds.

8. The method for preparing polymer foam according to claim 5, characterized in that, The rapid depressurization method involves saturating the composite material obtained in step (1) in a high-pressure fluid, and after saturation, rapidly depressurizing and cooling to obtain a polymer foam with a bimodal pore structure.

9. The method for preparing polymer foam with a bimodal pore structure according to claim 8, characterized in that, The saturation temperature is 120-160℃, the saturation pressure is 10-16 MPa, and the saturation time is 0.5-1 h.

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