Method for preparing super-hydrophobic high-energy-absorbing thermoplastic polymer foam

Abstract

A method for preparing a bifunctional foam featuring "high strength / high energy absorption" and "super-hydrophobicity / self-cleaning", relating to the technical field of organic polymer materials. By means of a gas foaming technology, composite constraint is used to introduce anisotropic foam cells into a polymer material, and the anisotropic foam cells endow the polymer material with super energy absorption characteristics by means of unique deformation of progressive buckling and reciprocating distortion under compression or impact; and a "barbed" structure is introduced onto the surface of the polymer, achieving the super-hydrophobic / self-cleaning function on the surface of the polymer foam, and finally obtaining a bifunctional polymer foam featuring "high strength / high energy absorption" and "super-hydrophobicity / self-cleaning". The method is simple, feasible, and environmentally friendly, has low cost and good reproducibility, and can achieve large-scale production. The resulting thermoplastic polymer material, such as a polypropylene foam, has excellent performance and important significance in the field of safety protection.

Description

Preparation method of super-hydrophobic high-energy-absorbing thermoplastic polymer foam

[0001] The present application claims priority to the Chinese patent application No. 202410631284.8, filed on May 21, 2025, and entitled "Preparation method of super-hydrophobic high-energy-absorbing thermoplastic polymer foam", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] 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. BACKGROUND

[0003] Under the background of increasing frequency of vehicle accidents and collisions in sports, materials with high energy absorption capacity become particularly important. Anisotropic polymer foam has become a research hotspot in the field of safety protection due to its high unidirectional modulus and buckling-based strain mechanism, which has extremely strong buffering and energy-absorbing performance. In addition, foam materials with super-hydrophobic properties on the surface can be applied to antifouling, anti-icing, self-cleaning, and oil-water separation applications.

[0004] Currently, anisotropic polymer foam is mostly prepared by unidirectional freezing or ice template method. The aspect ratio of the cells of anisotropic polymer foam prepared by supercritical fluid foaming method is generally less than 4, and the energy absorption and other functions are limited. Common methods for preparing super-hydrophobic polymer foam mostly use commercial foam as raw material, and super-hydrophobic properties are given to the commercial foam by secondary surface modification grafting, coating, etching, and other methods. However, this method has the problems of complex process, high manufacturing cost, low durability, difficulty in large-scale production, and secondary pollution.

[0005] Therefore, it is still a great challenge to develop green preparation of lightweight polymer materials with high energy absorption characteristics and super-hydrophobic properties.

[0006] SUMMARY

[0007] The purpose of the present application is to provide a preparation method of super-hydrophobic high-energy-absorbing thermoplastic polymer foam, to solve the problem that the energy absorption function of the polymer foam prepared by the existing method is limited, and at the same time, the existing process is complex, the manufacturing cost is high, the durability is low, it is difficult to mass-produce, and there is secondary pollution.

[0008] To achieve the above-mentioned purpose, the present application adopts the following technical solution: a preparation method of super-hydrophobic high-energy-absorbing thermoplastic polymer foam, comprising the following steps:

[0009] S1, preparation of a sandwich structure of surface constraint material / thermoplastic polymer / surface constraint material;

[0010] S2, anisotropic foaming the surface-restricted material / thermoplastic polymer / surface-restricted material sandwich structure to obtain a super-absorbing energy foam with oriented cells along the direction of foam expansion;

[0011] S3, peeling the surface-restricted material on the surface of the super-absorbing energy foam to obtain the super-hydrophobic high-absorbing energy thermoplastic polymer foam.

[0012] Preferably, the preparation of the surface-restricted material / thermoplastic polymer / surface-restricted material sandwich structure comprises the following steps:

[0013] S11, pre-treating the surface-restricted material to obtain a pre-treated surface-restricted material;

[0014] S12, sequentially laying the pre-treated surface-restricted material, the thermoplastic polymer and the pre-treated surface-restricted material on a plane;

[0015] S13, embedding the surface-restricted material partially or entirely into the thermoplastic polymer in the viscous flow state of the thermoplastic polymer, and cooling to obtain the surface-restricted material / thermoplastic polymer / surface-restricted material sandwich structure.

[0016] Preferably, the surface-restricted material is in the form of a wire mesh with a pore size of 2500-3500 mesh and a material including high-temperature-resistant plastic, copper, iron or stainless steel.

[0017] Preferably, the thermoplastic polymer includes polypropylene, acrylic resin, epoxy resin, polyethylene, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polymethyl methacrylate, polyamide, polycarbonate, polyacrylonitrile or polyethylene terephthalate.

[0018] Preferably, the pre-treatment is sequentially ultrasonic cleaning with a cleaning agent and drying with a vacuum oven.

[0019] The ultrasonic cleaning time is 5-30 min.

[0020] Preferably, the viscous flow state of the thermoplastic polymer is obtained by heating the thermoplastic polymer with a vacuum hot press.

[0021] The diameter of the surface-restricted material / thermoplastic polymer / surface-restricted material sandwich structure is 25 mm and the thickness is 2 mm.

[0022] Preferably, S2 comprises the following steps:

[0023] S21, assemble the surface constraint material / thermoplastic polymer / surface constraint material sandwich structure with a mold, the horizontal section of the mold is consistent with the horizontal section of the surface constraint material / thermoplastic polymer / surface constraint material sandwich structure, and the upper and lower ends of the mold are packaged with foamed nickel, and then the assembled mold is placed in a high-pressure reaction kettle;

[0024] S22, foaming the surface constraint material / thermoplastic polymer / surface constraint material sandwich structure in the mold from bottom to top by injecting a foaming gas to obtain a super energy-absorbing foam with oriented cells along the foaming direction.

[0025] Preferably, the foaming gas includes supercritical carbon dioxide, nitrogen, air, helium, argon, petroleum ether, methane, ethane, propane, butane, pentane, hexane, heptane, n-pentane, n-hexane, n-heptane, dichloromethane or trichlorofluoromethane.

[0026] Preferably, when the foaming gas is supercritical carbon dioxide, the foaming process is as follows: the temperature of the high-pressure reaction kettle is controlled at 149 DEG C, 12 MPa carbon dioxide gas is injected and pressure is maintained for 2 h, and then pressure is released to normal pressure at a rate of 3 MPa / s.

[0027] Preferably, the energy-absorbing property of the super-hydrophobic high-energy-absorbing thermoplastic polymer foam is enhanced by adding graphene, carbon fiber or carbon nanotube.

[0028] The application also provides a super-hydrophobic high-energy-absorbing thermoplastic polymer foam prepared by the preparation method.

[0029] The application has the following beneficial effects:

[0030] 1. The application realizes the energy-absorbing and hydrophobicity regulation of high-performance functional polymer foam material by using unique supercritical fluid foaming technology and simple composite constraint technology to design an anisotropic polymer foam with a "barb" structure on the surface.

[0031] 2. 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 the properties of "high strength / high energy absorption" and "super-hydrophobicity / self-cleaning", and can be applied to the fields of helmets, surfboards, cushion pads, life rafts and automobile bumpers, and has important significance for safety protection. BRIEF DESCRIPTION OF DRAWINGS

[0032] Fig. 1 is a schematic diagram of the foaming and molding process of the polymer foam of the application;

[0033] Fig. 2 is a schematic diagram of the polypropylene foam obtained in Example 1 of the application.

[0034] Figure 3 is an electron micrograph of the oriented cells of the polypropylene foam of Example 1 of the present application;

[0035] Figure 4 is an electron micrograph of the cells perpendicular to the oriented direction of the polypropylene foam of Example 1 of the present application;

[0036] Figure 5 is an electron micrograph of the surface of the polypropylene foam of Example 1 of the present application (inset is a magnified view of the water contact angle and "barb" structure);

[0037] Figure 6 is an electron micrograph of the surface cells of the polypropylene foam of Example 1 of the present application;

[0038] Figure 7 is a schematic representation of the progressive folding buckling behavior of anisotropic cells during compression of a thermoplastic polymer foam and the corrugated cell wall morphology of the foam after compression;

[0039] Figure 8 is a simulation analysis of the deformation of anisotropic cells during compression of a thermoplastic polymer foam;

[0040] Figure 9 is a schematic representation of the oriented foaming principle under complex constraints of Example 1 of the present application - axial expansion of CO2 gas under cell collision effect;

[0041] Figure 10 is a schematic representation of the oriented foaming principle under complex constraints of Example 1 of the present application - gradient stress balance and microstructure replication principle under radial constraint of the surface template;

[0042] Figure 11 is a schematic representation of the formation of bristle-like microstructure of a thermoplastic polymer foam of the present application;

[0043] Figure 12 is a schematic representation of the hydrophobic mechanism of a thermoplastic polymer foam of the present application;

[0044] Figure 13 is a schematic representation of the water contact angle and sliding angle at different locations on the surface of the polypropylene foam of Example 1 of the present application;

[0045] Figure 14 is a water droplet adhesion test perpendicular to the surface of the polypropylene foam of Example 1 of the present application;

[0046] Figure 15 is a schematic representation of a water droplet rolling on the surface of the polypropylene foam of Example 1 of the present application;

[0047] Figure 16 is a compression stress-strain curve of the oriented direction and perpendicular to the oriented direction of the polypropylene foam of Example 1 of the present application;

[0048] Figure 17 is a maximum stress curve of the polypropylene foam and conventional foam of Example 1 of the present application; and Figure 18 is an energy absorption bar chart of the polypropylene foam and conventional foam of Example 1 of the present application;

[0049] Figure 19 is a line graph of the impact force-buffering time relationship of the polypropylene foam and conventional foam of Example 1 of the present application;

[0050] Figure 20 is a column chart of the traditional foam impact-force-buffering time relationship of the polypropylene foam of Example 1 of the present application;

[0051] Figure 21 is a comparison chart of the buffering of the real object of Example 1 of the present application, the polypropylene foam of the present application can prevent the falling eggs from breaking;

[0052] Figure 22 is a comparison chart of the buffering of the real object of Example 1 of the present application, the polypropylene foam of the present application can prevent the glass from being cracked by the falling ball, the traditional foam glass is cracked by the falling ball;

[0053] Figure 23 is a chart of the self-cleaning process of the polypropylene foam of Example 1 of the present application contaminated by sand at an 11° inclination angle. DETAILED DESCRIPTION

[0054] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application.

[0055] The flow of the method of the present application is as follows:

[0056] As shown in Figure 1, the prepared sandwich structure is placed in a mold, wherein the upper and lower ends of the mold are encapsulated by foam nickel, and then the supercritical CO2 is used to foam from bottom to top through the foam nickel, so that the super energy-absorbing foam with oriented cells along the direction of the mold is obtained, and then the surface constraint screen in the sandwich structure is removed, so that the "barb" shaped super-hydrophobic structure is formed on the surface of the super energy-absorbing foam.

[0057] The principle of the present application is as follows:

[0058] 1. Formation mechanism of oriented cells and "barb" surface structure

[0059] As shown in FIGS. 9-10, in the composite constraint foaming method of the present application, the foaming mold provides a circumferential constraint, and the circumferential stress under the constraint is conducted inward to offset the circumferential expansion pressure when the gas expands, so that the foaming gas can only expand from the upper and lower surfaces of the mold opening, thus leading to the unidirectional oriented growth of the foaming material and the formation of an anisotropic foam. However, during the unidirectional expansion of the foam, the friction of the mold can cause the foam to grow in a "steamed bun type", forming a defect of a top protrusion and a bottom pit. By synchronously using a radial template constraint in the sandwich structure on the surface of the material, the radial stress imbalance during the unidirectional expansion of the foam can be effectively balanced, so that the foam can stably grow in a unidirectional manner during the foaming process. In addition, the surface constraint template can not only eliminate the solid skin structure of the traditional foam, but also form a unique "barb" surface structure on the surface of the foaming material after demolding. FIGS. 2-4 show the schematic diagram of the foam structure of the present application and the microstructure photos of the internal parallel and perpendicular to the orientation direction of the cells. FIGS. 5-6 show the "barb" microstructure formed on the surface of the foam of the present application and the water contact angle test results thereof.

[0060] 2. Energy absorption mechanism

[0061] The present application designs an anisotropic cell structure. When the oriented cells are subjected to pressure or impact load along the growth direction thereof, the cell walls will produce buckling deformation due to the consistency of the cell orientation direction and the load direction. This "micro-inertia effect" makes the anisotropic foam have higher rate sensitivity and transient modulus and energy dissipation. (The traditional spherical or polygonal cell structure foam shows bending of the cell walls when subjected to pressure or impact, and the response rate and energy dissipation are much lower than the buckling-based response behavior). As shown in FIG. 7, when the strain further increases, the oriented cells undergo progressive folding deformation. The pressure wave is transmitted forward through this unique deformation process, which can absorb a large amount of energy; as the strain continues to increase, more cells are buckled, multiple waves appear, the cell walls produce reciprocating torsional deformation, and return to the initial position, and then wrinkles are formed on the porous walls, which can further enhance the strength of the cell walls and endow the material with stronger energy absorption performance.

[0062] In addition, the energy absorption of the thermoplastic polymer foam of the present application can be controlled by the degree of cell orientation; and can also be enhanced by adding fillers such as graphene, carbon fiber, carbon nanotube, etc.

[0063] 3. Hydrophobic mechanism

[0064] As shown in Figures 11-15, after the stripping of the screen, the bristle-like tips bend inward due to the viscoelastic shrinkage of the thermoplastic polymer and the effect of gravity to form a "barb" 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 hanging contact state, in which a high liquid-gas interfacial tension is generated. The water contact angle is about 163°, and the roll-off angle is as low as 1°, which leads to an unprecedented super-repellence of the surface to water and a super-hydrophobicity.

[0065] Example 1

[0066] The polypropylene foam with super-hydrophobicity and high energy absorption is prepared by selecting a wire screen, a polypropylene thermoplastic polymer, and using carbon dioxide gas for foaming, and using the method of the present application, and the steps are as follows:

[0067] S1, a wire screen is selected, the aperture of the screen is 3500 meshes, and the screen is cleaned under the condition of a cleaning agent for 30 min under ultrasonic cleaning, and the cleaned screen is vacuum dried for standby use;

[0068] S2, the cleaned screen is laid on a circular flat plate, and then a layer of polypropylene is laid, the thickness of the polypropylene layer is about 2 mm, and then a layer of screen is laid again;

[0069] S3, the above-mentioned laid material is transferred to a vacuum hot press, the polypropylene is heated to a viscous flow state, and the screen is embedded into the polypropylene, and then cooled to obtain a sandwich structure of screen / polypropylene / screen;

[0070] S4, the above-mentioned screen / polypropylene / screen is placed in a mold, and then placed in a high-pressure reaction kettle for foaming, the temperature is controlled at 149°C during the process, 12 MPa of carbon dioxide gas is injected and pressure is maintained for 2 h, and then the pressure is released to normal pressure at a rate of 3 MPa / s, that is, the foaming is completed;

[0071] S5, the screen embedded on the surface of the above-mentioned material is quickly stripped, and the polypropylene foam with super-hydrophobicity and high energy absorption is obtained.

[0072] The performance of the polypropylene foam obtained by the method is explored.

[0073] As shown in Figures 2-6 and 13-15, it can be seen that the polypropylene foam obtained by the method of the present application has anisotropic cells and good morphology, has a very high energy absorption, and has a "barb" hydrophobic structure on the surface of the polypropylene foam, wherein the water contact angle is about 163°, the roll-off angle is as low as 1°, and has a super-hydrophobicity.

[0074] As shown in Figs. 16-20, the axial compression strength of the polypropylene foam of the present application is 156 times the radial strength, and the maximum stress (>1.2 MPa) after 5 cycles of compression is still much higher than that of conventional foams. The energy absorption value (about 54 MJ·m -3 ) of the polypropylene foam of the present application is 1350% of that of conventional foams; the impact force of the polypropylene foam of the present application is only 312 N, while that of conventional foams is greater than 1000 N, and the cushioning time of the polypropylene foam of the present application is about 2.2 times that of conventional foams.

[0075] As shown in Figs. 21-22, the polypropylene foam of the present application has good cushioning and energy absorption performance, and as shown in Fig. 23, the polypropylene foam of the present application has good self-cleaning performance.

[0076] In summary, the method of the present application develops thermoplastic polymer foams with highly oriented porous structures inside and "barb" structures on the surface by composite constraint unidirectional foaming method; unlike ordinary bending deformation mechanism, the buckling response mechanism based on oriented cell walls leads to a significant increase in the compression strength of the foams of the present application, and the foams have a special progressive folding deformation mechanism, thereby leading to high energy dissipation during impact; the surface of the foams of the present application presents a double-entry structure, and water droplets are in a pendant contact state on the double-entry structure surface, which makes the foams have significant superhydrophobicity, with a water contact angle of about 163°. Given the unique dual-functionality of the foams of the present application, they will be very popular in applications requiring energy absorption and self-cleaning.

[0077] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered within the scope of protection of the present application.

Claims

1. A method of making a superhydrophobic high-energy-absorbing thermoplastic polymer foam, characterized in that, The method comprises the following steps: S1, preparation of a surface constraint material / thermoplastic polymer / surface constraint material sandwich structure; S2, anisotropic foaming of the surface constraint material / thermoplastic polymer / surface constraint material sandwich structure to obtain a super-absorbing energy foam with oriented cells along the foam expansion direction; S3, peeling off the surface constraint material on the surface of the super-hydrophobic high-energy-absorbing thermoplastic polymer foam to obtain the super-hydrophobic high-energy-absorbing thermoplastic polymer foam.

2. The production method according to claim 1, characterized by, The preparation of the surface constraint material / thermoplastic polymer / surface constraint material sandwich structure comprises the following steps: S11, pretreatment of the surface constraint material to obtain a pretreated surface constraint material; S12, sequentially laying the pretreated surface constraint material, the thermoplastic polymer and the pretreated surface constraint material on a plane; S13, embedding the surface constraint material partially or entirely into the thermoplastic polymer in the viscous flow state of the thermoplastic polymer, and cooling to obtain the surface constraint material / thermoplastic polymer / surface constraint material sandwich structure.

3. The production method according to claim 1 or 2, characterized by, The surface constraint material is in the form of a wire mesh with a pore size of 2500-3500 mesh and a material including high-temperature-resistant plastic, copper, iron or stainless steel.

4. The production method according to claim 1 or 2, characterized by, The thermoplastic polymer includes polypropylene, acrylic resin, epoxy resin, polyethylene, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polymethyl methacrylate, polyamide, polycarbonate, polyacrylonitrile or polyethylene terephthalate.

5. The preparation method according to claim 2, characterized in that, The pretreatment is ultrasonic cleaning with a cleaning agent and drying with a vacuum oven. The ultrasonic cleaning time is 5-30 min.

6. The preparation method according to claim 2, characterized in that, The viscous flow state of the thermoplastic polymer is obtained by heating the thermoplastic polymer with a vacuum hot press. The diameter of the surface constraint material / thermoplastic polymer / surface constraint material sandwich structure is 25 mm, and the thickness is 2 mm.

7. The preparation method according to claim 1, characterized in that, The S2 comprises the following steps: S21, assembling the surface constraint material / thermoplastic polymer / surface constraint material sandwich structure with a mold, the horizontal section of the mold is consistent with the horizontal section of the surface constraint material / thermoplastic polymer / surface constraint material sandwich structure, and the upper and lower ends of the mold are encapsulated with foam nickel, and then the assembled mold is put into a high-pressure reaction kettle; S22, foaming the surface constraint material / thermoplastic polymer / surface constraint material sandwich structure in the mold from bottom to top by injecting a foaming gas to obtain the super-absorbing energy foam with oriented cells along the foam expansion direction.

8. The preparation method according to claim 7, characterized in that, The foaming gas includes supercritical carbon dioxide, nitrogen, air, helium, argon, petroleum ether, methane, ethane, propane, butane, pentane, hexane, heptane, n-pentane, n-hexane, n-heptane, dichloromethane or trichlorofluoromethane.

9. The production method according to claim 8, characterized by, When the foaming gas is supercritical carbon dioxide, the foaming process is as follows: controlling the temperature of the high-pressure reaction kettle to be 149℃, injecting 12 MPa carbon dioxide gas and keeping pressure for 2 h, and then releasing pressure to normal pressure at a rate of 3 MPa / s.

10. The preparation method according to claim 9, wherein the energy-absorbing property of the super-hydrophobic high-energy-absorbing thermoplastic polymer foam is enhanced by adding graphene, carbon fiber or carbon nanotube.

10. The superhydrophobic high-energy-absorbing thermoplastic polymer foam prepared by the method of any one of claims 1 to 9, characterized in that, The superhydrophobic surface structure of the superhydrophobic high-energy-absorbing thermoplastic polymer foam is in the shape of "barbs". The superhydrophobic surface structure of the superhydrophobic high-energy-absorbing thermoplastic polymer foam is in the shape of "barbs".

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