A thermoplastic elastomer foamed beads and its preparation method

Abstract

This invention provides thermoplastic elastomer foamed beads and their preparation method, belonging to the field of polymer foaming technology. The invention involves mixing thermoplastic elastomer beads with a CO2-loving surfactant to obtain a mixture; the CO2-loving surfactant is a surfactant containing -F and -OH groups, and its mass is 2-10% of the mass of the thermoplastic elastomer; supercritical CO2 is used as a foaming agent, and the mixture is subjected to anhydrous foaming treatment at 140-160°C to obtain the thermoplastic elastomer foamed beads. The thermoplastic elastomer foamed beads prepared by the method of this invention are in a dispersed state with no adhesion between particles, resulting in a high yield.

Description

Technical Field

[0001] This invention relates to the field of polymer foaming technology, and in particular to a thermoplastic elastomer foamed bead and its preparation method. Background Technology

[0002] Lightweight materials are a key focus of current new materials development. Supercritical CO2 foaming for preparing lightweight polymer materials is a green and environmentally friendly lightweight technology that has attracted widespread attention from researchers. Supercritical CO2 foaming processes can be categorized into autoclave foaming, compression molding foaming, injection molding foaming, and extrusion foaming. Among these, autoclave foaming can produce microporous polymer foam beads with high expansion ratios (low density), dense and uniform pores, and high closed-cell ratios. Furthermore, through molding, these polymer foam beads can be fused together into various complex irregular-shaped products. In addition, autoclave foaming allows for the flexible production of different types and series of polymer foam materials using the same equipment, making it currently the only foaming technology capable of producing microporous, low-density foam products as well as diverse and complex irregular-shaped foam components.

[0003] Currently, traditional autoclaving foaming processes are carried out in high-pressure stirred tanks. Although this process uses supercritical CO2 as a green foaming agent, it generally requires water as a suspension medium to achieve polymer particle dispersion and accurate temperature control. Furthermore, dispersants, flocculants, and other additives need to be added to the water to ensure effective bead dispersion. Subsequent steps include filtration, washing, and drying. This process not only generates wastewater but also involves complex procedures, high energy consumption, and may cause degradation of easily hydrolyzable polymer foam beads. Conversely, if supercritical CO2 anhydrous foaming technology is used, the prepared polymer foam beads exhibit particle adhesion, resulting in poor dispersion and a low yield. Summary of the Invention

[0004] The purpose of this invention is to provide a thermoplastic elastomer foamed bead and its preparation method. The thermoplastic elastomer foamed beads prepared by the method of this invention are in a dispersed state with no adhesion between the particles, resulting in a high yield.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing thermoplastic elastomer foamed beads, comprising the following steps:

[0007] Thermoplastic elastomer beads are mixed with a CO2-loving surfactant to obtain a mixture; the CO2-loving surfactant is a surfactant containing -F and -OH, and the mass of the CO2-loving surfactant is 2 to 10% of the mass of the thermoplastic elastomer;

[0008] Supercritical CO2 was used as a foaming agent, and the mixture was subjected to anhydrous foaming treatment at 140–160°C to obtain the thermoplastic elastomer foamed beads.

[0009] Preferably, the CO2-loving surfactant is a fluorinated organic acid.

[0010] Preferably, the fluorinated organic acid has 2 to 18 carbon atoms, and the fluorinated organic acid is a substitution product in which fluorine partially or completely replaces the hydrogen atoms on the carbon atoms of the organic acid.

[0011] Preferably, the fluorinated organic acid includes one or more of trifluoroacetic acid, heptafluorobutyric acid, perfluorooctanoic acid, perfluorododecanic acid, perfluorohexadecanoic acid, and perfluorooctadecanic acid.

[0012] Preferably, the thermoplastic elastomer beads are made of one or more of thermoplastic polyurethane, thermoplastic polyester, thermoplastic polyamide, and thermoplastic polyolefin.

[0013] Preferably, the density of the thermoplastic elastomer beads is 1.00–1.20 g / cm³. 3 .

[0014] Preferably, the conditions for the anhydrous foaming treatment include: a supercritical CO2 saturation pressure of 14–16 MPa, a supercritical CO2 saturation time of 5–15 min, and a pressure relief rate ≥200 MPa / s after the supercritical CO2 saturation is completed.

[0015] Preferably, the anhydrous foaming process includes: placing the mixture in an autoclave, purging the autoclave with CO2 to remove air, heating the autoclave to 140-160°C, introducing CO2 into the autoclave to make the CO2 supercritical, saturating the mixture with the obtained supercritical CO2, and then depressurizing the autoclave.

[0016] The present invention provides thermoplastic elastomer foamed beads prepared by the preparation method described above, wherein the thermoplastic elastomer foamed beads are in a granular dispersion state.

[0017] Preferably, the expansion ratio of the thermoplastic elastomer foam beads is 14 to 35.

[0018] This invention provides a method for preparing thermoplastic elastomer foamed beads, comprising the following steps: mixing thermoplastic elastomer beads with a CO2-loving surfactant to obtain a mixture; the CO2-loving surfactant is a surfactant containing -F and -OH, and the mass of the CO2-loving surfactant is 2-10% of the mass of the thermoplastic elastomer; using supercritical CO2 as a foaming agent, the mixture is subjected to anhydrous foaming treatment at 140-160℃ to obtain the thermoplastic elastomer foamed beads. This invention uses a surfactant containing -F and -OH, which enables the dispersion of thermoplastic elastomer particles during supercritical CO2 anhydrous foaming, improving the yield of thermoplastic elastomer foamed beads. The supercritical CO2 anhydrous foaming process used in this invention does not require additional power. Compared with traditional batch foaming, it does not require water as a dispersion medium, nor does it require the addition of dispersants, flocculants, etc. Subsequent filtration, washing, and drying steps are unnecessary, reducing energy consumption, shortening the process flow, and improving production efficiency. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the process for preparing thermoplastic elastomer foam beads in an embodiment of the present invention;

[0020] Figure 2 A photograph of the thermoplastic elastomer foamed beads prepared in Example 1;

[0021] Figure 3 A photograph of the thermoplastic elastomer foamed beads prepared in Example 2;

[0022] Figure 4 A photograph of the thermoplastic elastomer foamed beads prepared in Example 3;

[0023] Figure 5 A photograph of the thermoplastic elastomer foamed beads prepared in Example 4;

[0024] Figure 6 A photograph of the thermoplastic elastomer foamed beads prepared in Example 5;

[0025] Figure 7 A photograph of the thermoplastic elastomer foamed beads prepared in Example 6;

[0026] Figure 8 A photograph of the thermoplastic elastomer foamed beads prepared for Comparative Example 1;

[0027] Figure 9 A photograph of the thermoplastic elastomer foamed beads prepared for Comparative Example 2;

[0028] Figure 10 A photograph of the thermoplastic elastomer foamed beads prepared for Comparative Example 3;

[0029] Figure 11 A photograph of the thermoplastic elastomer foamed beads prepared in Comparative Example 4;

[0030] Figure 12 A photograph of the thermoplastic elastomer foamed beads prepared for Comparative Example 5;

[0031] Figure 13 A photograph of the thermoplastic elastomer foamed beads prepared for Comparative Example 6;

[0032] Figure 14 A photograph of the thermoplastic elastomer foamed beads prepared for Comparative Example 7;

[0033] Figure 15 A photograph of the thermoplastic elastomer foamed beads prepared for Comparative Example 8;

[0034] Figure 16 A photograph of the thermoplastic elastomer foamed beads prepared for Comparative Example 9;

[0035] Figure 17 This is a cross-sectional electron microscope image of the thermoplastic elastomer foamed beads prepared in Example 1;

[0036] Figure 18 This is a cross-sectional electron microscope image of the thermoplastic elastomer foamed beads prepared in Example 2. Detailed Implementation

[0037] This invention provides a method for preparing thermoplastic elastomer foamed beads, comprising the following steps:

[0038] Thermoplastic elastomer beads are mixed with a CO2-loving surfactant to obtain a mixture; the CO2-loving surfactant is a surfactant containing -F and -OH, and the mass of the CO2-loving surfactant is 2 to 10% of the mass of the thermoplastic elastomer;

[0039] Supercritical CO2 was used as a foaming agent, and the mixture was subjected to anhydrous foaming treatment at 140–160°C to obtain the thermoplastic elastomer foamed beads.

[0040] Traditional autoclaving processes for preparing polymer foam beads typically require water as a dispersion medium to ensure effective dispersion. However, this method is complex, generates wastewater, and may degrade easily hydrolyzed polymer beads. Supercritical CO2 anhydrous foaming technology can solve these problems. However, current reports indicate that this technology requires high-pressure CO2 gas circulating within an autoclave to induce a jetting motion in the polymer particles, thereby improving heat and mass transfer efficiency. However, this requires a high-pressure pump for CO2 gas circulation, resulting in high energy consumption and cost. Furthermore, this technology can lead to particle adhesion during foaming, affecting dispersion and reducing yield. This invention utilizes surfactants containing -F and -OH to achieve dispersion of thermoplastic elastomer particles during supercritical CO2 anhydrous foaming, thereby improving the yield of thermoplastic elastomer foamed beads. Furthermore, the preparation of thermoplastic elastomer foamed beads can be achieved using conventional equipment, eliminating the need for high-energy-consuming equipment such as high-pressure pumps. The method of this invention is described in detail below.

[0041] In this invention, unless otherwise specified, all raw materials used are commercially available products well known to those skilled in the art or prepared using methods well known to those skilled in the art.

[0042] This invention mixes thermoplastic elastomer beads with a CO2-loving surfactant to obtain a mixture. In one embodiment, the mass of the CO2-loving surfactant is 2-10% of the mass of the thermoplastic elastomer, specifically 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. Controlling the mass of the CO2-loving surfactant within this range helps to achieve good dispersion of the thermoplastic elastomer foam beads, avoids adhesion between particles, and provides a good foaming effect. If the amount is too small, it will not improve the adhesion of the foam beads; if the amount is too large, the CO2-loving surfactant will severely agglomerate on the polymer matrix surface, failing to improve the adhesion of the foam beads and affecting the surface morphology of the foam beads.

[0043] In this invention, the CO2-loving surfactant is a surfactant containing -F and -OH. As one embodiment of this invention, the CO2-loving surfactant can be a fluorinated organic acid, wherein the number of carbon atoms in the fluorinated organic acid can be 2 to 18, specifically 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or 18; the fluorinated organic acid is a substitution product in which fluorine partially or completely replaces the hydrogen atom on the carbon atom of the organic acid, for example, the number of -F atoms in the fluorinated organic acid can be 1 to 35. As one embodiment of this invention, the fluorinated organic acid can include one or more of trifluoroacetic acid, heptafluorobutyric acid, perfluorooctanoic acid, perfluorododecanic acid, perfluorohexadecanoic acid, and perfluorooctadecanic acid, specifically trifluoroacetic acid, heptafluorobutyric acid, perfluorooctanoic acid (PFOA), perfluorododecanic acid, perfluorohexadecanoic acid, or perfluorooctadecanic acid. The surfactants containing -F and -OH in this invention are beneficial for the thermoplastic elastomer foam beads to have a good dispersion effect, avoid the adhesion between particles, and have a good foaming effect. If surfactants without -F and -OH are used, or surfactants containing only -F or only -OH are used, they do not improve the adhesion of foam beads and may even affect the foaming performance of the polymer.

[0044] In one embodiment of the present invention, the material of the thermoplastic elastomer beads may include one or more of thermoplastic polyurethane (TPU), thermoplastic polyester (TPEE), thermoplastic polyamide (TPAE), and thermoplastic polyolefin, specifically thermoplastic polyurethane, thermoplastic polyester, thermoplastic polyamide, or thermoplastic polyolefin; the thermoplastic polyurethane may specifically be polyester-type thermoplastic polyurethane or polyether-type thermoplastic polyurethane. In one embodiment of the present invention, the density of the thermoplastic elastomer beads may be 1.00–1.20 g / cm³. 3 Specifically, it can be 1.01 g / cm³. 3 1.10 g / cm 3 1.11 g / cm 3 Or 1.15g / cm 3 The particle size of the thermoplastic elastomer beads can be 1-5 mm, specifically 1-4 mm, 3-4 mm, or 2-5 mm. In this embodiment of the invention, the thermoplastic elastomer beads used are specifically thermoplastic polyurethane beads, thermoplastic polyester beads, or thermoplastic polyamide beads; the thermoplastic polyurethane beads can be of type 1180A (purchased from BASF (China) Co., Ltd.), 9063A (purchased from Wanhua Chemical Group Co., Ltd.), or 9583A (purchased from Wanhua Chemical Group Co., Ltd.); the thermoplastic polyester beads can be of type 4056 (purchased from Celanese); and the thermoplastic polyamide beads can be of type E40-S3 (purchased from Evonik Industries AG).

[0045] The present invention does not have any particular limitation on the mixing method of the thermoplastic elastomer beads and the CO2-loving surfactant. For example, stirring can be used to mix the two evenly.

[0046] After obtaining the mixture, the present invention uses supercritical CO2 as a foaming agent to perform anhydrous foaming treatment on the mixture at 140-160℃ to obtain the thermoplastic elastomer foamed beads. As one embodiment of the present invention, the conditions for the anhydrous foaming treatment include: a foaming temperature of 140-160℃, specifically 140℃, 145℃, 150℃, 155℃, or 160℃; a supercritical CO2 saturation pressure of 14-16 MPa, specifically 14.5 MPa, 15 MPa, or 15.5 MPa; a supercritical CO2 saturation time of 5-15 min, specifically 8 min, 10 min, or 12 min; and a pressure relief rate ≥200 MPa / s after supercritical CO2 saturation, further ≥300-400 MPa / s. In one embodiment of the present invention, the anhydrous foaming process includes: placing the mixture in an autoclave, introducing CO2 into the autoclave to purge air, then heating the autoclave to 140-160°C (i.e., the foaming temperature), introducing CO2 into the autoclave to make the CO2 supercritical, using the obtained supercritical CO2 to saturate the mixture, then depressurizing the autoclave to remove the supercritical CO2 and generate bubbles to achieve foaming, thereby obtaining the thermoplastic elastomer foamed beads. In this embodiment of the invention, saturation treatment for 5-15 minutes at a foaming temperature of 140-160℃ and a supercritical CO2 saturation pressure of 14-16 MPa is beneficial for achieving good dispersion of the thermoplastic elastomer foam beads, avoiding adhesion between particles, and resulting in good foaming effect. If the foaming temperature is too low, the polymer melt strength is too high, hindering cell growth and leading to a low foaming ratio; if the foaming temperature is too high, the polymer melt strength is too low, unable to support the cells, thus failing to foam, and it does not improve the adhesion of the foam beads. In this embodiment of the invention, the depressurization rate after supercritical CO2 saturation is controlled to be ≥200 MPa / s. Rapid depressurization under this condition is beneficial for achieving suitable nucleation density and cell size in the thermoplastic elastomer foam beads, with a faster depressurization rate resulting in more nucleation and smaller cells.

[0047] This invention does not specifically limit the type of autoclave, as long as it meets the requirements for anhydrous foaming treatment. The method of purging the CO2 is not specifically limited, as long as sufficient air is removed; for example, CO2 can be used for three purgings, and the CO2 supply is stopped after purging. The method of heating the autoclave is not specifically limited, as long as the foaming temperature requirement is met; for example, an oil bath can be used to heat the autoclave. The heating time is based on ensuring the autoclave temperature meets the foaming temperature requirement, for example, 15-20 minutes. In one embodiment of this invention, after heating the autoclave to the foaming temperature, CO2 is introduced into the autoclave through a pressurizing device to bring the CO2 to a supercritical state. This invention does not specifically limit the type of pressurizing device; any pressurizing device well known to those skilled in the art can be used. In one embodiment of this invention, after depressurization, no post-processing is required, and the thermoplastic elastomer foamed beads can be obtained directly.

[0048] This invention provides thermoplastic elastomer foamed beads prepared by the method described above. The thermoplastic elastomer foamed beads are in a dispersed state, meaning there is no adhesion between the particles. In one embodiment of this invention, the foaming ratio of the thermoplastic elastomer foamed beads can be 14–35, more specifically 20–31, and can be 14.04, 14.10, 14.52, 15.13, 17.29, 18.31, 20.15, 22.07, 26.26, or 30.34. In another embodiment of this invention, the pore diameter of the thermoplastic elastomer foamed beads can be 35–50 μm, more specifically 40–45 μm. Furthermore, the thermoplastic elastomer foamed beads prepared by the method of this invention have a more regular morphology, solving the problem of product deformation during the preparation of thermoplastic elastomer beads using supercritical CO2 anhydrous foaming in the prior art.

[0049] Figure 1 This is a schematic diagram of the process for preparing thermoplastic elastomer foam beads in an embodiment of the present invention. The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] Example 1

[0051] Weigh out the thermoplastic elastomer beads (specifically, polyether-type thermoplastic polyurethane beads, TPU, model 1180A, density 1.11 g / cm³). 3The thermoplastic elastomer beads, with a particle size of 3-4 mm, were purchased from BASF (China) Co., Ltd. 5 g of these beads were placed in aluminum foil. 150 mg of a CO2-loving surfactant (specifically perfluorooctanoic acid, PFOA) was weighed, representing 3% of the TPU mass. The PFOA was added to the thermoplastic elastomer beads, stirred until homogeneous, and then placed in an autoclave. The autoclave was connected to a high-pressure pipeline and purged three times with CO2. The autoclave was preheated for 20 minutes at an oil bath temperature of 155°C. Then, CO2 at a pressure of 15 MPa was introduced into the autoclave through a pressurizing device to bring the CO2 to a supercritical state. The thermoplastic elastomer beads were saturated in the autoclave for 10 minutes, followed by rapid depressurization at a rate of 400 MPa / s to obtain the thermoplastic elastomer foamed beads.

[0052] Example 2

[0053] The procedure is the same as in Example 1, except that the mass of the CO2 surfactant is adjusted to be 8% of the mass of the thermoplastic elastomer beads (m2).

[0054] Example 3

[0055] The procedure is the same as in Example 1, except that the CO2-loving surfactant used is heptafluorobutyric acid.

[0056] Example 4

[0057] The procedure is the same as in Example 1, except that the CO2-loving surfactant used is heptafluorobutyric acid and its mass (m2) is 8% of the mass of the thermoplastic elastomer beads.

[0058] Example 5

[0059] The procedure is the same as in Example 1, except that the CO2-loving surfactant used is perfluorododecanoic acid.

[0060] Example 6

[0061] The procedure is the same as in Example 1, except that the CO2-loving surfactant used is perfluorododecanoic acid and its mass (m2) is 8% of the mass of the thermoplastic elastomer beads.

[0062] Example 7

[0063] The procedure is the same as in Example 1, except that the thermoplastic elastomer beads used are thermoplastic polyester beads (TPEE, type 4056, density 1.15 g / cm³). 3 (Particle size 2-5 mm; purchased from Celanese).

[0064] Example 8

[0065] The procedure is the same as in Example 1, except that the thermoplastic elastomer beads used are thermoplastic polyamide beads (TPAE, model E40-S3, density 1.01 g / cm³). 3 The particle size is 1-4 mm; purchased from Evonik Industries.

[0066] Example 9

[0067] The procedure is the same as in Example 1, except that the thermoplastic elastomer beads used are polyester-type thermoplastic polyurethane beads (TPU, model 9063A, density 1.10 g / cm³). 3 The particle size was 2-5 mm; purchased from Wanhua Chemical Group Co., Ltd.

[0068] Example 10

[0069] The procedure is the same as in Example 1, except that the thermoplastic elastomer beads used are polyether-type thermoplastic polyurethane beads (TPU, model 9583A, density 1.10 g / cm³). 3 The particle size was 2-5 mm; purchased from Wanhua Chemical Group Co., Ltd.

[0070] Comparative Example 1

[0071] The procedure is the same as in Example 1, except that the mass of the CO2 surfactant is adjusted to be 1% of the mass of the thermoplastic elastomer beads (m2).

[0072] Comparative Example 2

[0073] The procedure is the same as in Example 1, except that the mass of the CO2 surfactant is adjusted to be 12% of the mass of the thermoplastic elastomer beads.

[0074] Comparative Example 3

[0075] The procedure is the same as in Example 1, except that the foaming temperature is 135°C.

[0076] Comparative Example 4

[0077] The procedure is the same as in Example 1, except that the foaming temperature is 165°C.

[0078] Comparative Example 5

[0079] The procedure is the same as in Example 1, except that the CO2-loving surfactant used is octanoic acid.

[0080] Comparative Example 6

[0081] The procedure is the same as in Example 1, except that the CO2-loving surfactant used is perfluorooctane.

[0082] Comparative Example 7

[0083] The procedure is the same as in Example 1, except that the CO2-loving surfactant used is n-octanol.

[0084] Comparative Example 8

[0085] The procedure is the same as in Example 1, except that the CO2-loving surfactant used is n-octane.

[0086] Comparative Example 9

[0087] Thermoplastic elastomer beads from Example 1 were used as raw materials to prepare thermoplastic elastomer foamed beads according to the method of Example 3 in CN 108359123 A, wherein the foaming temperature was 155°C.

[0088] Test Example 1

[0089] The adhesion of the thermoplastic elastomer foamed beads prepared in Examples 1-10 and Comparative Examples 1-9 was observed. Physical images of some of the thermoplastic elastomer foamed beads prepared in the examples and comparative examples are shown below. Figures 2 to 16 As shown.

[0090] Specifically, Figure 2 This is a photograph of the thermoplastic elastomer foamed beads prepared in Example 1. Figure 3 This is a photograph of the thermoplastic elastomer foamed beads prepared in Example 2. Figure 4 This is a photograph of the thermoplastic elastomer foamed beads prepared in Example 3. Figure 5 This is a photograph of the thermoplastic elastomer foamed beads prepared in Example 4. Figure 6 This is a photograph of the thermoplastic elastomer foamed beads prepared in Example 5. Figure 7 The image shows the actual thermoplastic elastomer foamed beads prepared in Example 6. The results show that the thermoplastic elastomer foamed samples in Examples 1 to 6 did not exhibit adhesion, and the foaming ratio was between 14 and 19, indicating that the surfactant used in Examples 1 to 6 has a good regulating effect on the adhesion behavior of thermoplastic elastomer after foaming under certain foaming conditions.

[0091] Figure 8 This is a photograph of the thermoplastic elastomer foamed beads prepared in Comparative Example 1. Figure 9 This is a photograph of the thermoplastic elastomer foamed beads prepared in Comparative Example 2. Figure 10 The image shows the actual thermoplastic elastomer foamed beads prepared in Comparative Example 3. Figure 11 This is a photograph of the thermoplastic elastomer foamed beads prepared in Comparative Example 4. Figure 12 This is a photograph of the thermoplastic elastomer foamed beads prepared in Comparative Example 5. Figure 13 This is a photograph of the thermoplastic elastomer foamed beads prepared in Comparative Example 6. Figure 14This is a photograph of the thermoplastic elastomer foamed beads prepared in Comparative Example 7. Figure 15 The image shows the actual thermoplastic elastomer foamed beads prepared for Comparative Example 8. The results show that the thermoplastic elastomer foamed samples in Comparative Examples 1-2 and Comparative Examples 4-8 exhibited obvious adhesion, indicating that adding too high or too low a concentration of surfactant, too high a foaming temperature, or adding a surfactant that does not simultaneously contain fluorine and hydroxyl groups cannot effectively regulate the adhesion behavior of the foamed samples and may also affect the foaming performance, resulting in a low foaming ratio. The foaming temperature of Comparative Example 3 was too low. Although the foamed sample did not exhibit adhesion, the low temperature resulted in a low foaming ratio, which could not meet the basic expansion ratio requirements of the foamed sample.

[0092] Figure 16 The image shows the actual thermoplastic elastomer foamed beads prepared in Comparative Example 9. The results show that when the polymer foamed beads were prepared using supercritical CO2 anhydrous foaming technology in Comparative Example 9, no CO2-loving surfactant was used. Instead, high-pressure CO2 gas was circulated in the autoclave to make the polymer particles be in a spraying motion state in the autoclave. However, when using this technology, the polymer particles are prone to sticking together during the foaming process, resulting in a low yield.

[0093] The density of the foamed beads prepared in Examples 1-10 and Comparative Examples 1-9 was measured using a densitometer, and the foaming ratio was calculated. The adhesion of the foamed beads in Examples 1-10 and Comparative Examples 1-9 was also observed. The specific results are shown in Table 1. Table 1 shows that the foamed beads prepared in Examples 1-10 did not exhibit adhesion, and the foaming ratios were all above 14 times. Comparative Example 1 had too little PFOA, which did not improve the adhesion of the foamed beads. Comparative Example 2 had too much PFOA, resulting in severe agglomeration of PFOA on the polymer matrix surface, which did not improve the adhesion of the foamed beads and affected the surface morphology of the foamed beads. Comparative Example 3 had too low a foaming temperature, resulting in high polymer melt strength, which hindered cell growth and led to a low foaming ratio. Comparative Example 4 had too high a foaming temperature, resulting in too low polymer melt strength, which could not support the cells and therefore could not foam, and it did not improve the adhesion of the foamed beads. Comparative Examples 5-8, which used CO2-loving surfactants containing either no fluorine atoms or only hydroxyl groups, did not improve the adhesion of the foamed beads and may even have affected the foaming properties of the polymer. Comparative Example 9 did not use a CO2-loving surfactant; instead, it utilized high-pressure CO2 gas circulating within an autoclave to keep the polymer particles in a jetting motion state, making it easy for the polymer particles to adhere during the foaming process.

[0094] Table 1 shows the foaming ratio and adhesion of the foamed beads prepared in Examples 1-10 and Comparative Examples 1-9.

[0095]

[0096] Test Example 2

[0097] The thermoplastic elastomer foam beads prepared in Examples 1 and 2 were quenched and sampled using liquid nitrogen, and then the cell structure of the samples was measured and analyzed using a scanning electron microscope.

[0098] Figure 17 This is a cross-sectional electron microscope image of the thermoplastic elastomer foamed beads prepared in Example 1. Figure 18 The image shows a cross-sectional electron microscope image of the thermoplastic elastomer foamed beads prepared in Example 2. The results show that the thermoplastic elastomer foamed sample obtained under certain foaming conditions using PFOA as a surfactant has uniform pores, large pore diameter (40-45 μm), and large foaming ratio.

[0099] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing thermoplastic elastomer foamed beads, comprising the following steps: Thermoplastic elastomer beads are mixed with a CO2-affinity surfactant to obtain a mixture; the mass of the CO2-affinity surfactant is 2-10% of the mass of the thermoplastic elastomer; the CO2-affinity surfactant is one or more of perfluorooctanoic acid, heptafluorobutyric acid, and perfluorododecanoic acid; the thermoplastic elastomer beads are made of one or more of thermoplastic polyurethane, thermoplastic polyester, and thermoplastic polyamide. Supercritical CO2 was used as a foaming agent, and the mixture was subjected to anhydrous foaming treatment at 140–160°C to obtain the thermoplastic elastomer foamed beads.

2. The preparation method according to claim 1, characterized in that, The density of the thermoplastic elastomer beads is 1.00–1.20 g / cm³. 3 .

3. The preparation method according to claim 1, characterized in that, The conditions for the anhydrous foaming treatment include: a supercritical CO2 saturation pressure of 14–16 MPa, a supercritical CO2 saturation time of 5–15 min, and a pressure relief rate ≥200 MPa / s after the supercritical CO2 saturation is completed.

4. The preparation method according to claim 1 or 3, characterized in that, The anhydrous foaming process includes: placing the mixture in a high-pressure reactor, purging the reactor with CO2 to remove air, heating the reactor to 140-160°C, introducing CO2 into the reactor to make the CO2 supercritical, saturating the mixture with the obtained supercritical CO2, and then depressurizing the reactor.

5. The thermoplastic elastomer foamed beads prepared by the preparation method according to any one of claims 1 to 4, wherein the thermoplastic elastomer foamed beads are in a particulate dispersion state.

6. The thermoplastic elastomer foamed beads according to claim 5, characterized in that, The foaming ratio of the thermoplastic elastomer foam beads is 14 to 35.

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