Preparation method of polymer material with concentric microstructure

Abstract

The invention discloses a preparation method of a polymer material with a concentric microstructure, and the preparation method comprises the following steps: placing a mold filled with a polymer raw material in a freezing environment, so that a temperature gradient which is vertical to the mold wall and points to the center of the mold is generated in the polymer raw material, controlling the freezing rate of the polymer raw material, generating concentrically arranged ice crystals in the polymer raw material, and removing the ice crystals to obtain the polymer material with the concentric microstructure, the polymer raw materials comprise a polymer and water. According to the preparation method provided by the invention, the polymer material with the concentric microstructure can be prepared, the requirement of a required freezing environment on equipment is low, the success rate is high, and batch and large-scale production is easy to realize; and the prepared polymer material has excellent response to compression load, the manufacturing cost of the polymer material containing the microstructure is reduced, and the application scene of the polymer material containing the microstructure is expanded.

Description

Technical Field

[0001] The present invention belongs to the technical field of engineering materials, and particularly relates to a preparation method of a polymer material with a concentric microstructure. Background Art

[0002] The microstructure of a material refers to the arrangement and organizational structure of tiny units such as atoms, molecules, crystals or molecular clusters, and molecular chains inside the material, which are the structural characteristics of the material at the microscale, usually in the micron to nanometer range. The microstructure can affect many physical and chemical properties of the material, such as density, stiffness, strength, toughness, electrical conductivity, thermal conductivity, hydrophilicity or hydrophobicity, etc. In research and engineering, due to the particularity of the application scenarios of many materials, it is necessary to artificially create different microstructures in the materials to change the properties of the materials. Among many related technologies, the method of generating a microstructure with ice crystals has become a popular option due to its simple principle and environmental friendliness.

[0003] In the field of ceramic materials, the freeze-casting method of generating a microstructure with ice crystals is used to prepare porous ceramics to reduce the density of ceramics without losing mechanical properties; in the field of metal materials, the freeze-casting method is used to prepare aluminum alloy materials to improve their specific surface area and mechanical properties; in the field of polymer materials, the ice-template method is widely used in the preparation of different porous hydrogels and aerogels, endowing conventional polymer materials with advanced physical and chemical properties.

[0004] However, at present, in the preparation process of high-performance materials with microstructures, there are still technical defects such as difficult to control the microstructure, single type of microstructure, and high cost of large-scale sample preparation. Summary of the Invention

[0005] In order to overcome at least one of the above-mentioned problems existing in the prior art, one of the purposes of the present invention is to provide a preparation method of a polymer material with a concentric microstructure, which can obtain a polymer material with a high-performance concentric microstructure.

[0006] Another purpose of the present invention is to provide a polymer material with a concentric microstructure obtained by the above preparation method.

[0007] Another purpose of the present invention is to provide a strengthening method of the above polymer material with a concentric microstructure.

[0008] In order to achieve the above purposes, the technical solutions adopted by the present invention are as follows:

[0009] The first aspect of the present invention provides a method for preparing a polymer material with a concentric microstructure, comprising the following steps: placing a mold containing a polymer raw material in a freezing environment to generate a temperature gradient perpendicular to the mold wall and pointing towards the center of the mold inside the polymer raw material, controlling the freezing rate of the polymer raw material to generate concentrically arranged ice crystals in the polymer raw material, and removing the ice crystals to obtain the polymer material with a concentric microstructure; the polymer raw material includes a polymer and water.

[0010] Preferably, the method for controlling the freezing rate includes at least one of the following methods: regulating the temperature of the freezing environment, regulating the heat transfer medium in the freezing environment, and regulating the thermal resistance of the mold.

[0011] Preferably, the method for controlling the freezing rate is: using a constant-temperature gas as the heat transfer medium and controlling the freezing rate by adjusting the temperature of the constant-temperature gas.

[0012] Preferably, the constant-temperature gas is constant-temperature air.

[0013] In some embodiments of the present invention, the temperature of the constant-temperature gas is -50 to -10 °C; for example, it can be -50 °C, -40 °C, -30 °C, -25 °C, -20 °C, -15 °C, -10 °C.

[0014] Preferably, the freezing environment is a constant-temperature environment; more preferably, the freezing environment is a constant-temperature environment within the range of -50 to -10 °C; for example, it can be -50 °C, -40 °C, -30 °C, -25 °C, -20 °C, -15 °C, -10 °C.

[0015] Preferably, the mold is a low-thermal-resistance mold.

[0016] In the present invention, the mold material is required to be a low-thermal-resistance material. Using a low-thermal-resistance material for the mold can reduce the uncontrollability of the temperature gradient during the freezing process caused by processing defects of the mold (such as uneven thickness or density), which is beneficial to forming a more continuous concentric microstructure.

[0017] Preferably, the material of the mold includes a metal material, a polymer material, or a combination thereof; more preferably, the material of the mold is selected from metal materials. In some embodiments of the present invention, the material of the mold is selected from aluminum.

[0018] Preferably, the wall thickness of the mold is in the range of 10 to 1000 μm; more preferably in the range of 15 to 300 μm; even more preferably in the range of 20 to 50 μm; for example, it can be 20 μm, 30 μm, 40 μm, 50 μm.

[0019] The mold made of a metal material has a relatively low thermal resistance, and a thin-wall mold with a thin wall thickness (e.g., within the range of 10 to 1000 μm) is also beneficial for achieving a relatively low thermal resistance. Using the above mold can play a role in heat homogenization, making the temperature distribution inside the mold more uniform.

[0020] In some embodiments of the present invention, the shape of the mold includes a cylindrical shape or a triangular prism shape.

[0021] Taking a cross-section along the long axis direction of the mold, the arrangement shape of the pores in the cross-section presents a concentric shape determined by the outer shape of the mold. For example, in a cylindrical mold, the pores in the cross-section are arranged in concentric circles, and in a triangular prism-shaped mold, the pores in the cross-section are arranged in concentric triangles.

[0022] Preferably, the intermolecular force of the polymer includes a hydrogen bond.

[0023] The hydrogen bond is a relatively strong intermolecular force existing between the polymer molecules. The existence of a relatively strong intermolecular force is more conducive to forming a concentric microstructure.

[0024] Preferably, the concentration of the polymer in the polymer raw material is 1 to 10 w / v%; more preferably 2 to 8 w / v%; even more preferably 4 to 6 w / v%.

[0025] Preferably, the polymer includes at least one of polyvinyl alcohol, chitosan, silk fibroin, collagen, sodium alginate, or methyl cellulose. In some embodiments of the present invention, the polymer is selected from polyvinyl alcohol (PVA).

[0026] Preferably, the method for removing the ice crystals includes a precipitation method, a freeze-drying method, or a combination thereof.

[0027] In some embodiments of the present invention, the precipitation method is to place the material containing ice crystals in a sodium citrate solution for treatment to remove the ice crystals. In some specific embodiments of the present invention, the concentration of the sodium citrate solution is 1 to 2 mol / L.

[0028] The precipitation method of the present invention utilizes the hydrophilic and hydrophobic relationships of the raw materials in different media. By placing the frozen raw materials in a certain salt solution / high-concentration chemical, the polymer molecules precipitate out to form a stronger polymer network. Thereafter, the melting of the ice crystals will not damage the internal microstructure of the material.

[0029] In some embodiments of the present invention, the cold trap temperature used in the freeze-drying method is -90 to -50 °C, for example, it can be -80 °C; the freeze-drying time is 24 to 72 hours, for example, it can be 48 hours.

[0030] In some embodiments of the present invention, after removing the ice crystals by the freeze-drying method, the steps of heating and soaking are further included; in some specific embodiments of the present invention, the temperature of the heating is 90-110 °C, for example, it can be 100 °C; the time of the heating is 80-100 minutes, for example, it can be 90 minutes; the soaking can be carried out with water.

[0031] The freeze-drying method of the present invention utilizes the characteristic that water molecules cannot be transformed into a liquid state under a low-temperature and low-pressure environment, and sublimates the ice crystals in the frozen raw materials into water vapor and extracts them through a freeze-dryer. Subsequent treatment processes such as heating and soaking in solvents such as water will not damage the internal microstructure of the material.

[0032] The second aspect of the present invention provides a polymer material with a concentric microstructure prepared by the preparation method as described in the first aspect of the present invention.

[0033] The third aspect of the present invention provides a strengthening method for a polymer material with a concentric microstructure as described in the second aspect of the present invention, including the following steps: applying pressure continuously or intermittently to the polymer material along the tangent of the outer contour of the polymer material, so that the polymer material deforms, thereby realizing the strengthening of the polymer material.

[0034] The strengthening method provided in the present invention can effectively strengthen the mechanical properties of the material without damaging the concentric microstructure, and the strengthening process is simple and easy to implement.

[0035] In the present invention, by applying pressure, strengthening can be achieved by means such as increasing the material density, improving the crystal structure or eliminating internal defects.

[0036] Preferably, in the strengthening method, while applying pressure, at least one of the methods of translating the material, rotating the material, translating the pressure source, and rotating the pressure source is adopted to adapt to materials with different shapes.

[0037] Through the above various different strengthening methods, the strengthening process can be adapted to materials with different shapes.

[0038] Preferably, the pressure source for applying pressure continuously or intermittently increases the pressure to further strengthen the material when the original pressure cannot effectively cause the material to deform.

[0039] Preferably, during the process of applying pressure, the temperature of the polymer material is changed to change the mechanical response of the polymer material during the strengthening process, so that the material is easy to deform. In particular, by changing the temperature of the polymer material, the crystallinity of specific materials (such as polyvinyl alcohol) can also be increased to achieve a better strengthening effect.

[0040] The beneficial effects of the present invention are as follows: The preparation method provided in the present invention can prepare polymer materials with a concentric microstructure. The required freezing environment has low requirements for equipment and a high success rate, and it is easy to achieve batch and large-scale production. Moreover, the prepared polymer materials have excellent responses to compressive loads, reducing the manufacturing cost of polymer materials with microstructures, expanding their application scenarios, and enhancing their commercial value.

[0041] Specifically, compared with the prior art, the present invention has the following advantages:

[0042] 1. Based on the existing freeze-casting technology, the preparation method of the present invention makes the growth of ice crystals parallel to the cold source by changing the freezing conditions, and the ice front migrates towards the warmer side in the center. Further, by changing the freezing environment and the characteristics of the mold, a stable temperature gradient pointing to the center of the mold shape is generated. Combining the effects produced by changing the freezing conditions above, a concentric arrangement of ice crystals is generated and further a concentric microstructure is generated in the material.

[0043] 2. Through experimental verification, under compressive loads, the concentric microstructure prepared by the present invention has better mechanical properties than the existing typical microstructures in various evaluation systems, and has stronger application potential and a wider application range.

[0044] 3. Compared with the existing freeze-casting technology, the preparation method provided by the present invention requires lower mold manufacturing difficulty and cost, and the required freezing environment has lower requirements for the performance of freezing equipment, thereby further reducing the cost and being more easily mass-produced and large-scale produced.

[0045] 4. Through experimental verification, the material strengthening method provided by the present invention is not easy to damage the concentric microstructure, and can achieve the strengthening of mechanical properties in various evaluation systems, further enhancing its application potential and expanding its application range. Description of the Drawings

[0046] Figure 1 It is a cross-sectional picture of the polymer material of Preparation Example 2 of the present invention after removing ice crystals.

[0047] Figure 2 It is SEM images of different positions on the cross-section of the polymer material of Preparation Example 2 in a dry state after removing ice crystals.

[0048] Figure 3 It is confocal laser microscope images of different positions on the cross-section of the polymer material of Preparation Example 2 in a swollen state after removing ice crystals.

[0049] Figure 4 It is a cross-sectional picture of the polymer material of Comparative Example 1 after removing ice crystals.

[0050] Figure 5 To prepare SEM images of different positions on the cross-section of the polymer material of Comparative Example 1 after removing ice crystals.

[0051] Figure 6 To prepare the cross-section SEM image of the polymer material of Example 3 after removing ice crystals.

[0052] Figure 7 To strengthen the comparison chart of the compression modulus and the compression stress at 90% strain of Example 1, Preparation Example 2, and Comparative Examples 1 - 2.

[0053] Figure 8 To prepare the comparison chart of the compression effects of Preparation Example 2 and Comparative Example 2.

[0054] Figure 9 This is a comparison chart of the mechanical properties of the polymer hydrogel material prepared in the embodiments of the present invention and the unidirectionally frozen hydrogel in the prior art. Detailed Description of the Invention

[0055] The content of the present invention will be further described in detail through specific embodiments below. It should also be understood that the following embodiments are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the principles described in the present invention fall within the protection scope of the present invention. The specific process parameters and the like in the following examples are also only an example within a suitable range, that is, those skilled in the art can adjust the actual parameters according to the description in this article, rather than being limited to the specific data in the following examples. The raw materials, reagents, or devices used in the following examples and comparative examples can be obtained from conventional commercial channels or can be obtained by existing known methods without special instructions.

[0056] In some embodiments of the present invention, a method for preparing a polymer material with a concentric microstructure is provided, including a raw material preparation method, a method for generating concentrically arranged ice crystals, and a method for fixing the microstructure; the specific steps are as follows:

[0057] First, the raw material preparation method includes: melting or dispersing the raw materials in water and making their physical and chemical properties meet the requirements of subsequent processes; taking a certain amount of polyvinyl alcohol powder or particles and mixing them with water as an example, using a magnetic stirrer with a heating function to stir at room temperature first to fully disperse and swell the polymer, and after dispersion, heating the solution to the dissolution temperature of polyvinyl alcohol and continuously stirring to dissolve it evenly in water. After dissolution, the polyvinyl alcohol aqueous solution is placed in a room temperature environment and left to stand and cool.

[0058] Secondly, the method for generating concentrically arranged ice crystals includes: the mechanism for controlling the arrangement and growth direction of ice crystals, the freezing mold and freezing environment requirements that match this mechanism; the control mechanism is that the ice crystals are frozen at a low freezing rate under the condition that there is a strong interaction force between raw material molecules, the growth of the ice crystals is parallel to the cold source, and the ice front migrates towards the warmer side in the center; the freezing mold is a low thermal resistance mold that does not disrupt the direction of the temperature gradient, usually made of metal foil or polymer film; the freezing environment is a constant temperature environment, and the temperature is relatively high to meet the freezing rate threshold requirements for different polymers to generate concentric ice crystals; specifically, the method for controlling the freezing rate is: using constant temperature air as the heat transfer medium, since the heat transfer coefficient between air and the thin-walled metal foil mold is low and very uniform in an environment without external disturbances, the actual freezing rate can be stably regulated by controlling the air temperature, and the freezing rate increases as the temperature decreases.

[0059] Finally, the methods for fixing the microstructure are mainly divided into two categories: drying methods and precipitation methods. The drying method is usually preferably the freeze-drying method in which ice crystals are sublimated under a low-temperature and low-pressure environment; the precipitation method usually refers to the method of putting the frozen polymer into other chemicals to further crosslink the polymer and strengthen the microstructure.

[0060] In some other embodiments of the present invention, a method for strengthening a polymer material with a concentric microstructure is also provided. The specific steps are: according to the shape of the material, perpendicular to the tangent of the outer contour of the material, continuously or intermittently applying pressure to the material to cause the material to deform so as to increase the material density or improve the crystal structure or eliminate internal defects.

[0061] In some specific embodiments of the present invention, in the strengthening method, the temperature of the material can be controlled to change the mechanical response of the material, making it easier for the material to deform, and for specific materials such as polyvinyl alcohol, its crystallinity can also be increased.

[0062] In some specific embodiments of the present invention, in the strengthening method, the process can be adapted to materials with different shapes by methods such as translating the material, rotating the material, translating the pressure source, and rotating the pressure source.

[0063] In some specific embodiments of the present invention, in the strengthening method, the pressure source can continuously or intermittently increase the magnitude of the pressure to further strengthen the material after the original pressure cannot effectively cause the material to deform.

[0064] The present invention will be further described below in conjunction with more specific examples and comparative examples.

[0065] Preparation Example 1

[0066] This example provides a preparation process for a polymer material with a concentric microstructure, including a raw material preparation method, a method for generating concentrically arranged ice crystals, and a method for fixing the microstructure. The method includes the following steps in a typical embodiment of preparing a polyvinyl alcohol hydrogel:

[0067] Step 1: Prepare an aqueous solution of polyvinyl alcohol from solid polyvinyl alcohol

[0068] Weigh 5 g of polyvinyl alcohol powder, add it to 100 mL of deionized water, and stir at room temperature for 2 hours using a magnetic stirrer with a heating function to fully disperse and swell the polyvinyl alcohol. Then heat the mixed system to 100 °C and continue stirring for 2 hours to fully dissolve the solid polyvinyl alcohol in water. After the solution is clear without solid particles, turn off heating and stirring, and let it cool naturally to room temperature to obtain an aqueous solution of polyvinyl alcohol with a concentration of 5 w / v%.

[0069] Step 2: Prepare a freezing mold using aluminum foil

[0070] Take aluminum foil with a nominal thickness of 20 μm, wrap it around a cylindrical object with the required diameter twice, cut off the excess aluminum foil, and fix it into a cylindrical shape using aluminum tape. Seal one side of the cylinder with aluminum foil and fix it with aluminum tape. Roll the cylindrical object to fully press the aluminum tape at the seam, and then remove the cylindrical object to obtain the freezing mold.

[0071] Step 3: Freeze the aqueous solution of polyvinyl alcohol to generate concentric ice crystals

[0072] Pour the aqueous solution of polyvinyl alcohol into the freezing mold, and repeat it several times as needed. Place the mold containing the solution in a constant temperature environment of -20 °C for freezing. During the freezing process, use constant temperature air (-20 °C) as the heat transfer medium to control the material to have an appropriate freezing rate.

[0073] Step 4: Remove the concentric ice crystals and fix the concentric microstructure

[0074] Immerse the frozen aqueous solution of polyvinyl alcohol in a 1.5 M sodium citrate solution to precipitate the polyvinyl alcohol until its state no longer changes. Take out the material and immerse it in deionized water to remove the residual sodium citrate solution to obtain a polymer material with a concentric microstructure.

[0075] Preparation Example 2

[0076] This example provides a preparation process of a polymer material with a concentric microstructure. The difference from Preparation Example 1 is that in Step 4 of this example: the frozen polyvinyl alcohol aqueous solution is freeze-dried for 48 hours using a freeze dryer with a cold trap temperature of -80°C, and repeated several times depending on the drying situation until completely dry. The completely dry polyvinyl alcohol material is heated to 100°C and kept warm for 90 minutes, then allowed to cool naturally. The material is taken out and soaked in deionized water until completely swollen to obtain a polymer material with a concentric microstructure; Steps 1 to 3 are the same as those in Preparation Example 1.

[0077] Preparation Example 3

[0078] This example provides a preparation process of a polymer material with a concentric microstructure. The difference from Preparation Example 2 is that in Step 1 of this example, the concentration of the polyvinyl alcohol aqueous solution is 2 w / v%; Steps 2 to 4 are the same as those in Preparation Example 2.

[0079] Preparation Comparative Example 1

[0080] This example provides a preparation process of a polymer material with a radial microstructure. The difference from Preparation Example 2 is that in Step 3 of this example: the polyvinyl alcohol aqueous solution is poured into a freezing mold, and can be repeated several times as needed. The mold containing the solution is placed in a constant temperature environment of -80°C for freezing; Steps 1, 2, and 4 are the same as those in Preparation Example 2.

[0081] Preparation Comparative Example 2

[0082] This example provides a preparation process of a polymer material with a honeycomb microstructure. This microstructure is prepared by a unidirectional freezing method. For the specific preparation process, refer to the literature: X. Liang, G. Chen, S. Lin, J. Zhang, L. Wang, P. Zhang, Z. Wang, Z. Wang, Y. Lan, Q. Ge, J. Liu, Anisotropically Fatigue-Resistant Hydrogels. Adv. Mater. 2021, 33, 2102011. (DOI: 10.1002 / adma.202102011)

[0083] Preparation Comparative Example 3

[0084] This example provides a preparation process of a polymer material with a random microstructure, which is achieved by repeated freezing and thawing. The specific preparation process reference: X. Liang, G. Chen, S. Lin, J. Zhang, L. Wang, P. Zhang, Z. Wang, Z. Wang, Y. Lan, Q. Ge, J. Liu, Anisotropically Fatigue-Resistant Hydrogels. Adv. Mater. 2021, 33, 2102011. (DOI: 10.1002 / adma.202102011)

[0085] Strengthening Example 1

[0086] This example provides a method for strengthening a polymer material having a concentric microstructure, and the specific steps are as follows:

[0087] Take the polymer material prepared in Preparation Example 2 (not soaked), and use a polyimide heating film to heat the polymer material to 100°C, so that it can produce greater deformation in the subsequent process and improve the crystallinity. Then, while continuing to heat and maintain the temperature, use a cylinder to generate pressure, perpendicular to the tangent of the material's outer contour, and continuously compress the cylindrical polyvinyl alcohol material in a dry state to increase the material density; and during the processing, use an electric linear guide to drive the cylinder to perform translational motion, drive the polyvinyl alcohol material to rotate, switch the compressed area on the material, and uniformly strengthen different positions of the material. In addition, the cylinder pressure gradually increases, so that the polyvinyl alcohol with increased density is further deformed and strengthened, so that the polyvinyl alcohol hydrogel containing concentric microstructures has adjustable mechanical properties. The dried polymer that has undergone the above-mentioned processing process is soaked in deionized water until it swells to obtain a strengthened polymer material.

[0088] Strengthening comparative example 1

[0089] This example provides a method for strengthening a polymer material. The specific steps are the same as those of Strengthening Example 1, except that the polymer material is replaced with the polymer material having a honeycomb microstructure obtained in Preparation Comparative Example 2.

[0090] Strengthening comparative example 2

[0091] This example provides a method for strengthening a polymer material. The specific steps are the same as those of Strengthening Example 1, except that the polymer material is replaced by the polymer material with a random microstructure obtained in Preparation Comparative Example 3.

[0092] Performance Testing

[0093] (1) The dried polymer materials after removing ice crystals in Preparation Examples 2 - 3 and Preparation Comparative Example 1 (the products before soaking in deionized water in Step 4), and the polymer hydrogel materials (the products after soaking in deionized water in Step 4) were each cut along the radial direction to obtain cross-sections, which were characterized using a scanning electron microscope (SEM) and a confocal laser microscope.

[0094] Figure 1 This is a cross-sectional picture of the polymer material of Preparation Example 2 of the present invention after removing ice crystals, where A - E respectively correspond to Figures 2 - 3 the picture shooting positions in. Figure 2 These are SEM images of different positions on the cross-section of the polymer material of Preparation Example 2 in the dry state after removing ice crystals, where A - E respectively correspond to Figure 1 the marked positions in. Figure 3 These are confocal laser microscope images of different positions on the cross-section of the polymer material of Preparation Example 2 in the swollen state after removing ice crystals, where A - E respectively correspond to Figure 1 the marked positions in. It can be seen from Figures 1 - 3 that by using the method in Preparation Example 2, especially the specific freezing method in Step 3, it is possible to ensure that the material has an appropriate freezing rate, thereby generating a concentric microstructure; and through the specific ice crystal removal method in Step 4, it is possible to ensure that the concentric structure is not damaged, obtaining a dry or water-containing polymer material with a concentric microstructure.

[0095] Figure 4 This is a cross-sectional picture of the polymer material of Preparation Comparative Example 1 after removing ice crystals, where A - C respectively correspond to Figure 5 the picture shooting positions in. Figure 5 These are SEM images of different positions on the cross-section of the polymer material of Preparation Comparative Example 1 after removing ice crystals, where A - C respectively correspond to Figure 4 the marked positions in, and D corresponds to the marked position in C. It can be seen from Figure 4 that the polymer material of Preparation Comparative Example 1 does not exhibit a concentric microstructure. This is because the freezing rate is too fast in an environment of -80°C, resulting in the appearance of Figures 4 - 5 the structure in, and thus unable to form a concentric microstructure. In addition, if the mold is soaked in a low-temperature liquid or in direct contact with a low-temperature solid, it may lead to too high a heat conduction efficiency, and even if the environment is stable at -20°C, it may still cause the freezing speed to be too fast. Moreover, modern temperature-controlled refrigeration equipment such as refrigerators mostly uses PID closed-loop control, and there is inevitably a problem of overshoot, which will cause unstable temperature changes. While Preparation Examples 1 - 2 of the present invention use air as the heat transfer medium while adopting a relatively high freezing temperature, it can ensure that even when the ambient temperature fluctuates below the set value, the freezing rate of the polymer is still within a reasonable range, with small rate fluctuations, high fault tolerance, and not easily exceeding the threshold.

[0096] Figure 6 To prepare the cross-sectional SEM images of the polymer material in Example 3 after removing ice crystals, where A and B are SEM images at different positions on the cross-section. From Figure 6 It can be seen that concentric materials can also be generated using different polymer concentrations, but different polymer concentrations will affect the gaps between the concentric structures. Due to the decrease in solute content, the voids formed by ice crystals will increase, resulting in an increase in the width of each morphology in the concentric structure. If the concentration is too low, continuous materials cannot be formed.

[0097] (2) Mechanical property testing: Test the mechanical properties of each example and comparative example, including compressive modulus, compressive stress, and compressive strain.

[0098] Figure 7 It is a comparison chart of the compressive modulus and compressive stress at 90% strain for Reinforced Example 1, Preparation Example 2, Reinforced Comparative Examples 1-2. Among them, the concentric microstructure refers to the material obtained in Reinforced Example 1, the concentric microstructure (unreinforced) refers to the material obtained in Preparation Example 2, the honeycomb microstructure refers to the material obtained in Reinforced Comparative Example 1, and the random porous microstructure refers to the material obtained in Reinforced Comparative Example 2. It can be seen from the figure that compared with the honeycomb microstructure and random porous microstructure, the concentric microstructure of the present invention has better mechanical properties under compressive load and can be comparable to other microstructures after reinforcement even without reinforcement.

[0099] Figure 8 It is a comparison chart of the compression effects of Preparation Example 2 and Preparation Comparative Example 2. Among them, A is the honeycomb microstructure obtained in Preparation Comparative Example 2, and B is the concentric microstructure obtained in Preparation Example 2. Both are unreinforced materials. Under the same test conditions, after compression and release, the concentric microstructure material of Preparation Example 2 did not show fragmentation; while after compression and release of the honeycomb microstructure of Preparation Comparative Example 2, fragmentation occurred at the center of the sample. It can be seen that compared with other microstructures such as the honeycomb microstructure, the concentric microstructure has better compression resistance to fragmentation.

[0100] In addition, the mechanical properties of the polymer material prepared by the present invention were also compared with those of the unidirectionally frozen hydrogel in the prior art. Figure 9 It is a comparison chart of the mechanical properties of the polymer hydrogel material prepared in the examples of the present invention and the unidirectionally frozen hydrogel in the prior art. Among them, the concentric microstructure PVA hydrogel refers to the polymer materials prepared in Preparation Example 2 and Reinforced Example 1 of the present invention, and [1] - [8] respectively represent the unidirectionally frozen hydrogels in the prior art, and the specific information is shown in Table 1.

[0101] Table 1 Figure 9 Using the unidirectionally frozen hydrogel of the prior art

[0102]

[0103]

[0104] From Figure 9 As can be seen from Table 1, the concentric microstructures prepared in the embodiments of the present invention have higher compressive stress under the same compressive strain, and their preparation process is simple and easy to implement.

[0105] As can be seen from the above embodiments, based on the existing freeze-casting technology, the preparation method in the embodiments of the present invention makes the growth of ice crystals parallel to the cold source by changing the freezing conditions, and the ice front migrates towards the warmer side in the center. Further, by changing the freezing environment and the characteristics of the mold, a stable temperature gradient pointing to the center of the mold shape is generated. Combining the effects produced by the above-mentioned change of freezing conditions, a concentric ice crystal arrangement is generated and a concentric microstructure is further generated in the material. Moreover, through experimental verification, under the action of compressive load, the concentric microstructures prepared in the embodiments of the present invention have better mechanical properties than the existing typical microstructures in various evaluation systems, and have stronger application potential and a wider application range.

[0106] Compared with the existing freeze-casting technology, the preparation method provided in the embodiments of the present invention requires lower mold manufacturing difficulty and lower cost, and the required freezing environment has lower requirements for the performance of freezing equipment, thus further reducing the cost and being more suitable for batch and large-scale production.

[0107] In addition, through experimental verification, the material strengthening method provided in the embodiments of the present invention is not easy to damage the concentric microstructure, and can achieve the strengthening of mechanical properties in various evaluation systems, further enhancing its application potential and expanding its application range.

[0108] In summary, the preparation method provided in the present invention can prepare polymer materials with concentric microstructures. The required freezing environment has low requirements for equipment, high success rate, and is easy to achieve batch and large-scale production; and the prepared polymer materials have excellent response to compressive load, reduce the manufacturing cost of polymer materials containing microstructures, expand their application scenarios, and enhance their commercial value.

Claims

1. A method for preparing a polymer material with a concentric microstructure, characterized in that, It includes the following steps: placing a mold filled with a polymer raw material in a freezing environment to generate a temperature gradient perpendicular to the mold wall and pointing towards the center of the mold inside the polymer raw material, controlling the freezing rate of the polymer raw material to generate concentrically arranged ice crystals in the polymer raw material, and removing the ice crystals to obtain the polymer material with a concentric microstructure; the polymer raw material includes a polymer and water.

2. The preparation method according to claim 1, characterized in that, The method for controlling the freezing rate includes at least one of the following methods: regulating the temperature of the freezing environment, regulating the heat transfer medium in the freezing environment, and regulating the thermal resistance of the mold.

3. The preparation method according to claim 1 or 2, characterized in that, The method for controlling the freezing rate is: using a constant-temperature gas as the heat transfer medium and controlling the freezing rate by adjusting the temperature of the constant-temperature gas.

4. The preparation method according to claim 1, wherein The material of the mold includes a metal material, a polymer material, or a combination thereof; and / or, the wall thickness of the mold is in the range of 10 - 1000 μm.

5. The preparation method according to claim 1, wherein, The intermolecular force of the polymer includes hydrogen bonds; and / or, the concentration of the polymer in the polymer raw material is 1 - 10 w / v%.

6. The preparation method according to claim 1, characterized in that The polymer includes at least one of polyvinyl alcohol, chitosan, silk fibroin, collagen, sodium alginate, or methyl cellulose.

7. The preparation method according to claim 1, characterized in that, The method for removing the ice crystals includes a precipitation method, a freeze-drying method, or a combination thereof.

8. A polymer material with a concentric microstructure prepared by the preparation method according to any one of claims 1 - 7.

9. A method for strengthening a polymer material having a concentric microstructure as described in claim 8, characterized in that, It includes the following steps: Continuously or intermittently applying pressure to the polymer material along the tangent of the outer contour of the polymer material to cause deformation of the polymer material, thereby realizing the strengthening of the polymer material.

10. The strengthening method according to claim 9, wherein, In the strengthening method, while applying pressure, at least one of the methods of translating the material, rotating the material, translating the pressure source, or rotating the pressure source is adopted to adapt to materials with different shapes; and / or, the pressure source applying pressure continuously or intermittently increases the pressure to further strengthen the material when the original pressure cannot effectively cause deformation of the material; and / or, during the process of applying pressure, changing the temperature of the polymer material to change the mechanical response of the polymer material during the strengthening process and making the material prone to deformation.

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