A method for preparing a superhydrophobic high-energy-absorbing thermoplastic polymer foam

Abstract

The present application relates to the technical field of organic polymer materials, in particular to a preparation method of super-hydrophobic high-energy-absorbing thermoplastic polymer foam. The present application provides a preparation method of a dual-functional foam with high strength / high energy absorption and super-hydrophobicity / self-cleaning. By using a gas foaming technology, anisotropic cells are introduced into the polymer material by composite constraint. The unique deformation mode of the anisotropic cells, i.e. progressive buckling and reciprocating twisting under compression or impact, endows the cells with super-energy-absorbing characteristics. Meanwhile, the introduction of barb structures on the surface of the polymer realizes the super-hydrophobicity / self-cleaning function of the polymer foam surface, and finally a polymer foam with dual functions of high strength / high energy absorption and super-hydrophobicity / self-cleaning is obtained. The method is simple and feasible, low in cost, good in environmental protection and repeatability, and can be produced on a large scale. The obtained thermoplastic polymer material, such as polypropylene foam, has excellent performance and is of great significance for the safety protection field.

Description

Technical Field

[0001] This invention relates to the field of organic polymer materials technology, specifically to a method for preparing superhydrophobic, high-energy-absorbing thermoplastic polymer foam. Background Technology

[0002] With the increasing frequency of vehicle accidents and collisions in motion, materials with high energy absorption capacity have become particularly important. Anisotropic polymer foams have become a research hotspot in the field of safety protection due to their high unidirectional modulus and buckling-based strain mechanism, which have extremely strong buffering and energy absorption properties. In addition, foam materials with superhydrophobic surfaces can be applied to antifouling, anti-icing, self-cleaning, oil-water separation and other applications.

[0003] Currently, anisotropic polymer foams are mostly prepared using unidirectional freezing or ice template methods. Anisotropic polymer foams prepared by supercritical fluid foaming generally have an aspect ratio of less than 4, resulting in limited improvement in energy absorption and other functionalities. Common methods for preparing superhydrophobic polymer foams mostly use commercial foams, imparting superhydrophobic properties to them through secondary surface modification, grafting, coating, and etching. However, this method suffers from problems such as complex processes, high manufacturing costs, low durability, difficulty in large-scale production, and secondary pollution. Therefore, developing lightweight polymer materials with both high energy absorption and superhydrophobic properties through green preparation remains a significant challenge.

[0004] In view of this, the present invention proposes a method for preparing superhydrophobic high-energy-absorbing thermoplastic polymer foam. By utilizing unique supercritical fluid foaming technology and simple composite constraint technology, anisotropic polymer foam with a "barbed" structure on the surface is designed, realizing the control of energy absorption and hydrophobic characteristics of high-performance functionalized polymer foam materials, which is of great significance to the field of safety protection. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing superhydrophobic high-energy-absorbing thermoplastic polymer foam, in order to solve the problems of limited improvement in energy absorption function of polymer foam prepared by existing methods, and the fact that existing processes are complex, have high manufacturing costs, low durability, are difficult to scale up, and cause secondary pollution in terms of hydrophobic properties.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a superhydrophobic, high-energy-absorbing thermoplastic polymer foam, comprising the following steps:

[0007] S1. Preparation of a sandwich structure of surface constraint material / thermoplastic polymer / surface constraint material;

[0008] S2. The surface constraint material / thermoplastic polymer / surface constraint material sandwich structure prepared in S1 is anisotropically foamed to obtain super energy-absorbing foam with cell orientation along the foam expansion direction;

[0009] S3. By peeling off the surface constraint material from the S2 super-energy-absorbing foam surface, a thermoplastic polymer foam with a superhydrophobic surface structure and high energy absorption can be obtained.

[0010] Furthermore, in S1, the surface constraint material is in the form of a wire mesh with a pore size of 2500-3500 mesh, and the material includes high-temperature resistant plastics, copper, iron, and stainless steel.

[0011] Furthermore, in S1, the thermoplastic polymer includes polypropylene, acrylic resin, epoxy resin, polyethylene, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polymethyl methacrylate, polyamide, polycarbonate, polyacrylonitrile, and polyethylene terephthalate.

[0012] Furthermore, in S1, the preparation of the surface constraint material / thermoplastic polymer / surface constraint material sandwich structure includes the following steps:

[0013] S11. Pre-treat the surface constraint material;

[0014] S12. Lay out surface constraint material, thermoplastic polymer, and surface constraint material sequentially on the plane;

[0015] S13. In the viscous flow state of the thermoplastic polymer, the surface restraint material is partially or completely embedded in the thermoplastic polymer, and then cooled to obtain a sandwich structure of surface restraint material / thermoplastic polymer / surface restraint material.

[0016] Furthermore, in S11, the surface constraint material is pretreated by using a cleaning agent and ultrasonic cleaning. The ultrasonic cleaning time is 5-30 minutes, and the material is dried in a vacuum oven after ultrasonic cleaning.

[0017] Furthermore, in S13, the thermoplastic polymer is heated to a viscous state using a vacuum hot press, resulting in a surface constraint material / thermoplastic polymer / surface constraint material sandwich structure with a diameter of 25 mm and a thickness of 2 mm.

[0018] Furthermore, in step S2, the anisotropic foaming of the surface constraint material / thermoplastic polymer / surface constraint material sandwich structure includes the following steps:

[0019] S21. Assemble the surface constraint material / thermoplastic polymer / surface constraint material sandwich structure with the mold. The horizontal cross-section of the mold is consistent with the horizontal cross-section of the sandwich structure. The upper and lower ends of the mold are encapsulated with nickel foam. Then, place the assembled mold into a high-pressure reactor.

[0020] S22. In a high-pressure reactor, foaming gas is injected from bottom to top into the mold to foam the surface constraint material / thermoplastic polymer / surface constraint material sandwich structure, thereby obtaining super energy-absorbing foam with cell orientation along the mold direction.

[0021] Furthermore, in S22, the foaming gas includes carbon dioxide, nitrogen, air, helium, argon, petroleum ether, methane, ethane, propane, butane, pentane, hexane, heptane, n-pentane, n-hexane, n-heptane, dichloromethane, and trichlorofluoromethane.

[0022] Furthermore, when the foaming gas is carbon dioxide, the temperature of the high-pressure reactor is controlled at 149°C, 12 MPa of carbon dioxide gas is injected and maintained at pressure for 2 hours, and then the pressure is released to atmospheric pressure at a rate of 3 MPa / s to complete the foaming process.

[0023] Furthermore, in S3, the superhydrophobic surface structure is barbed.

[0024] The beneficial effects of this invention are:

[0025] 1. This invention utilizes unique supercritical fluid foaming technology and simple composite constraint technology to design anisotropic polymer foams with a "barbed" structure on the surface, thereby achieving the control of energy absorption and hydrophobic characteristics of high-performance functionalized polymer foam materials;

[0026] 2. The method of this invention is simple, feasible, low-cost, environmentally friendly, and highly repeatable, and can be mass-produced. The resulting thermoplastic polymer material, such as polypropylene foam, has the properties of "high strength / high energy absorption" and "superhydrophobic / self-cleaning", and can be applied to helmets, surfboards, cushioning pads, life rafts, car bumpers and other fields, which is of great significance for safety protection. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the polymer foam foaming and molding process of the present invention;

[0028] Figure 2 The images shown are: (a) a schematic diagram of the polypropylene foam obtained in Example 1 of the present invention; (b) an electron microscope image of the oriented pores; (c) an electron microscope image of the pores perpendicular to the oriented direction; (d) an electron microscope image of the surface of the polypropylene foam of the present invention (the inset shows an enlarged view of the water contact angle and the "barb" structure); and (e) an electron microscope image of the surface pores.

[0029] Figure 3 This is a schematic diagram of the progressive folding and buckling behavior of anisotropic cells during the compression process of the thermoplastic polymer foam of the present invention and the morphology of the wrinkled foam wall after compression.

[0030] Figure 4 This is a schematic diagram of the orientation foaming principle under composite constraints in Embodiment 1 of the present invention; wherein, (a) the axial expansion of CO2 gas under the bubble collision effect; and (b) the gradient stress balance and microstructure replication principle under the radial constraint of the surface template.

[0031] Figure 5 This is a schematic diagram illustrating the formation and hydrophobic mechanism of the bristle-like microstructure of the thermoplastic polymer foam of the present invention;

[0032] Figure 6 This is a schematic diagram showing the water contact angle and sliding angle at different positions on the surface of the polypropylene foam obtained in Example 1 of the present invention;

[0033] Figure 7 This is a schematic diagram of the hydrodynamic adhesion test in Embodiment 1 of the present invention, wherein (a) is a water droplet adhesion test perpendicular to the surface of polypropylene foam; and (b) a water droplet rolls on the surface of polypropylene foam.

[0034] Figure 8 This is a test chart of the compression performance of polypropylene foam in Example 1 of the present invention; wherein, (a) the compression stress-strain curves of the polypropylene foam of the present invention in the orientation direction and perpendicular to the orientation direction; (b) the maximum stress curves of the polypropylene foam of the present invention and conventional foam in the compression cycle; (c) the energy absorption bar charts of the polypropylene foam of the present invention and conventional foam.

[0035] Figure 9 This is a graph showing the relationship between the impact force and buffering time of polypropylene foam in Embodiment 1 of the present invention; wherein, (a) is a line graph; and (b) is a bar graph.

[0036] Figure 10 These are comparison images of actual objects against the buffer of Embodiment 1 of the present invention; wherein, (a) the polypropylene foam of the present invention can prevent eggs from breaking when falling; (b) eggs break when falling with traditional foam;

[0037] Figure 11 This is a comparison diagram of the buffer used as a support for the actual object in Embodiment 1 of the present invention; wherein, (a) the polypropylene foam of the present invention can prevent the glass from being cracked by a falling ball; (b) the traditional foam glass is cracked by a falling ball.

[0038] Figure 12 This is a diagram illustrating the self-cleaning process of polypropylene foam contaminated with sand at an 11° tilt angle, as described in Example 1 of this invention. Detailed Implementation

[0039] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0040] The process of the method of the present invention is as follows:

[0041] like Figure 1 As shown, the prepared sandwich structure is placed in a mold, with nickel foam used to encapsulate the upper and lower ends of the mold. Then, supercritical CO2 is used to foam the nickel foam from bottom to top, thus obtaining a super energy-absorbing foam with the cell oriented along the mold direction. Then, the surface constraint screen in the sandwich structure is removed, so that a "barbed" superhydrophobic structure is formed on the surface of the super energy-absorbing foam.

[0042] The principle of this invention is as follows:

[0043] 1. Formation mechanism of oriented pores and "barbs" surface structure

[0044] like Figure 4 As shown, in the composite constrained foaming method of the present invention, the foaming mold provides circumferential constraint. Under the constraint, the circumferential stress is transmitted inward to offset the circumferential expansion pressure during gas expansion, thus allowing the foaming gas to expand only from the upper and lower surfaces of the mold opening. This results in unidirectional oriented growth of the foaming material and the formation of anisotropic foam. However, during the unidirectional expansion of the foam, the friction of the mold causes the foam to grow in a "bun-shaped" pattern, forming defects such as a bulge at the top and a pit at the bottom. By simultaneously employing a sandwich structure with radial template constraint on the material surface, the radial stress imbalance during the unidirectional expansion of the foam can be effectively balanced, allowing the foam to grow stably in a unidirectional direction during the foaming process. In addition, the surface constraint template not only eliminates the solid skin structure of traditional foams but also forms a unique "barbed" surface structure on the surface of the foaming material after demolding. Figure 2 Figure ac shows a schematic diagram of the foam structure of the present invention, as well as microscopic images of the internal structure parallel to and perpendicular to the orientation direction of the foam cells. Figure 2 The image shows the "barb" microstructure formed on the foam surface of this invention and the test results of its water contact angle.

[0045] 2. Energy absorption mechanism

[0046] This invention designs an anisotropic cell structure. When the oriented cells are subjected to pressure or impact loads along their growth direction, the cell walls buckle due to the alignment of the cell orientation with the load direction. This "micro-inertial effect" gives the anisotropic foam higher rate sensitivity, transient modulus, and energy dissipation. (Traditional spherical or polygonal cell structures exhibit cell wall bending under pressure or impact, with response rates and energy dissipation far lower than buckling-based response behaviors.) Figure 3As shown, when the strain increases further, the oriented pores undergo progressive folding deformation. This unique deformation process propagates the pressure wave forward, absorbing a large amount of energy. As the strain continues to increase, more pores buckle, creating multiple waves. The pore walls undergo reciprocating torsional deformation and return to their initial positions, subsequently forming wrinkles on the porous walls. These wrinkled structures further enhance the pore wall strength, giving the material stronger energy absorption properties.

[0047] Furthermore, the energy absorption properties of the thermoplastic polymer foam of the present invention can be controlled by the degree of cell orientation; it can also be enhanced by adding fillers such as graphene, carbon fiber, and carbon nanotubes.

[0048] 3. Hydrophobic mechanism

[0049] like Figure 5-7 As shown, after the screen is peeled off, due to the viscoelastic contraction of the thermoplastic polymer and the effect of gravity, the tips of the bristles bend inward to form a "barb"-like structure, which is essentially a double concave structure. This special surface structure has a negative local texture angle, which keeps the liquid profile in a suspended contact state. Under this state, a high liquid-gas interfacial tension is generated, with a water contact angle of about 163° and a roll-off angle as low as 1°. This results in an unprecedented super-repulsion of water on the surface, giving it super hydrophobicity.

[0050] Example 1

[0051] Using wire mesh, polypropylene thermoplastic polymer, and carbon dioxide gas for foaming, a polypropylene foam with superhydrophobicity and high energy absorption is prepared by the method of this invention. The steps are as follows:

[0052] S1. Select an iron wire mesh with a mesh size of 3500 mesh. Clean it by ultrasonic cleaning for 30 minutes under cleaning agent conditions. After cleaning, vacuum dry it for later use.

[0053] S2. Lay the cleaned sieve on a circular flat plate, then lay a layer of polypropylene, the thickness of which is about 2mm, and then lay another layer of sieve.

[0054] S3. Transfer the above-laid material to a vacuum hot press, heat the polypropylene to a viscous state, and embed the screen into the polypropylene. Then cool it to obtain a sandwich structure of screen / polypropylene / screen.

[0055] S4. Place the above-mentioned screen / polypropylene / screen in the mold, and then place it in the high-pressure reactor for foaming. During the process, the temperature is controlled at 149°C, 12MPa carbon dioxide gas is injected and the pressure is maintained for 2 hours, and then the pressure is released to atmospheric pressure at a rate of 3MPa / s to complete the foaming.

[0056] S5. Quickly peel off the screen embedded in the surface of the above material to obtain polypropylene foam with superhydrophobicity and high energy absorption.

[0057] The properties of the polypropylene foam obtained by this method were investigated.

[0058] like Figure 2 As shown in Figures 6-7, it can be seen that the polypropylene foam obtained by the method of the present invention has anisotropic pores with good morphology and high energy absorption. The surface of the polypropylene foam has a "barbed" hydrophobic structure, with a water contact angle of about 163° and a roll-off angle as low as 1°, exhibiting super hydrophobicity.

[0059] The composite constrained polypropylene foam of this invention is compared with traditional foams, circumferentially constrained foams, and radially constrained foams, as follows: Figure 8-9 As shown, the axial compressive strength of the polypropylene foam of this invention is 156 times its radial strength, and the maximum stress after 5 compression cycles (>1.2 MPa) is still much higher than that of traditional foam. The energy absorption value of the polypropylene foam of this invention (approximately 54 MJ / m³) is also significantly higher. -3 The impact force of the polypropylene foam of this invention is 1350% that of traditional foam; the impact force of the polypropylene foam of this invention is only 312N, while that of traditional foam is greater than 1000N, and the buffering time of the polypropylene foam of this invention is about 2.2 times that of traditional foam.

[0060] like Figure 10-11 As shown, the polypropylene foam of the present invention has good cushioning and energy absorption properties, and at the same time... Figure 12 As shown, the polypropylene foam of the present invention has good self-cleaning properties.

[0061] In summary, the present invention develops a thermoplastic polymer foam with a highly oriented porous internal structure and a "barbed" surface structure through a composite constrained unidirectional foaming method. Unlike ordinary bending deformation mechanisms, the buckling response mechanism based on the oriented cell walls leads to a significant increase in the compressive strength of the foam material and a special progressive folding deformation mechanism, resulting in high energy dissipation upon impact. The surface of the foam exhibits a dual-entropy structure, with water droplets in a suspended contact state on the surface, which gives the foam significant superhydrophobicity, with a water contact angle as high as approximately 163°. Given the unique dual-functional properties of the foam, it will be highly desirable in applications requiring energy absorption and self-cleaning.

[0062] This invention is not limited to the preferred embodiments described above. Anyone can derive other forms of products under the guidance of this invention. However, regardless of any changes made in their shape or structure, any technical solution that is the same as or similar to this application falls within the protection scope of this invention.

Claims

1. A method of making a superhydrophobic high-energy-absorbing thermoplastic polymer foam, characterized in that, Includes the following steps: S1. Preparation of a sandwich structure of surface constraint material / thermoplastic polymer / surface constraint material; The surface restraint material is in the form of a wire mesh with a pore size of 2500-3500 mesh, and the materials include high-temperature resistant plastics, copper, iron and / or stainless steel; Thermoplastic polymers include polypropylene, acrylic resin, epoxy resin, polyethylene, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polymethyl methacrylate, polyamide, polycarbonate, polyacrylonitrile, or polyethylene terephthalate. The preparation of the surface constraint material / thermoplastic polymer / surface constraint material sandwich structure includes the following steps: S11. Pre-treat the surface constraint material; S12. Lay out surface constraint material, thermoplastic polymer, and surface constraint material sequentially on the plane; S13. In the viscous flow state of the thermoplastic polymer, the surface restraint material is partially or completely embedded in the thermoplastic polymer, and then cooled to obtain a sandwich structure of surface restraint material / thermoplastic polymer / surface restraint material. S2. The surface constraint material / thermoplastic polymer / surface constraint material sandwich structure prepared in S1 is anisotropically foamed to obtain super energy-absorbing foam with cell orientation along the foam expansion direction; Anisotropic foaming of a surface-constrained material / thermoplastic polymer / surface-constrained material sandwich structure includes the following steps: S21. Assemble the surface constraint material / thermoplastic polymer / surface constraint material sandwich structure with the mold. The horizontal cross-section of the mold is consistent with the horizontal cross-section of the sandwich structure. The upper and lower ends of the mold are encapsulated with nickel foam. Then, place the assembled mold into a high-pressure reactor. S22. In a high-pressure reactor, foaming gas is injected from bottom to top into the mold to foam the sandwich structure of surface constraint material / thermoplastic polymer / surface constraint material, thereby obtaining super energy-absorbing foam with cell orientation along the mold direction. S3. By peeling off the surface constraint material from the S2 super-energy-absorbing foam surface, a thermoplastic polymer foam with a superhydrophobic surface structure and high energy absorption can be obtained. The superhydrophobic surface structure is barbed.

2. The method for preparing a superhydrophobic, high-energy-absorbing thermoplastic polymer foam according to claim 1, characterized in that: In step S11, the surface constraint material is pretreated by using a cleaning agent and ultrasonic cleaning. The ultrasonic cleaning time is 5-30 minutes. After ultrasonic cleaning, it is dried in a vacuum oven.

3. The method for preparing a superhydrophobic, high-energy-absorbing thermoplastic polymer foam according to claim 1, characterized in that: In S13, the thermoplastic polymer is heated to a viscous flow state using a vacuum hot press, resulting in a surface constraint material / thermoplastic polymer / surface constraint material sandwich structure with a diameter of 25 mm and a thickness of 2 mm.

4. The method for preparing a superhydrophobic, high-energy-absorbing thermoplastic polymer foam according to claim 1, characterized in that, In S22, the foaming gas includes carbon dioxide, nitrogen, air, helium, argon, petroleum ether, methane, ethane, propane, butane, pentane, hexane, heptane, n-pentane, n-hexane, n-heptane, dichloromethane, and / or trichlorofluoromethane.

5. The method for preparing a superhydrophobic, high-energy-absorbing thermoplastic polymer foam according to claim 4, characterized in that: When the foaming gas is carbon dioxide, the temperature of the high-pressure reactor is controlled at 149°C, 12 MPa of carbon dioxide gas is injected and the pressure is maintained for 2 hours, and then the pressure is released to atmospheric pressure at a rate of 3 MPa / s to complete the foaming process.

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