Polyurethane porous material and method for producing the same

Abstract

This invention discloses a polyurethane-based porous material and its preparation method. The material possesses a three-dimensional interconnected pore structure with tunable porosity, ranging from 25% to 80%. The preparation method is based on the principle of humidity-induced phase separation. Water vapor permeates and diffuses into the solution, causing phase separation. The enriched phase solidifies to form a continuous polymer framework, while the depleted phase, after drying to evaporate excess solvent, forms pores, ultimately resulting in a porous structure. The preparation method includes: dissolving a polyurethane-based polymer in a solvent system to obtain a homogeneous solution; placing the homogeneous solution in a constant temperature and humidity environment to contact it with water vapor and induce phase separation; and then drying to remove residual solvent, thereby obtaining the polyurethane-based porous material. This invention not only overcomes the shortcomings of traditional chemical foaming processes, such as complexity and the tendency to leave contaminants, but also enables the formation of a highly interconnected and tunable porous structure, showing broad application prospects in the fields of high-performance polymer porous membranes and medical implants.

Description

Technical Field

[0001] This invention belongs to the technical field of polyurethane porous materials, specifically relating to a polyurethane porous material based on the principle of humidity-induced phase separation and its preparation method. Background Technology

[0002] Polyurethane is a class of polymeric materials containing repeating urethane groups (-NHCOO-) in its main chain, typically polymerized from polyols, isocyanates, and chain extenders. Its molecular structure features alternating soft and hard segments. The soft segments, composed of polyols, impart excellent toughness and elasticity; the hard segments, composed of isocyanates and chain extenders, provide strength and thermal stability. Preparing polyurethane materials into porous materials with numerous micron-sized pores not only results in good biocompatibility but also endows them with low density, high specific surface area, and excellent buffering and energy absorption properties. This makes porous polyurethane materials show broad application prospects in fields such as biomedical materials (tissue engineering scaffolds), high-precision filtration materials, and sound-absorbing materials.

[0003] Currently, the preparation processes for polyurethane porous materials are mainly divided into two categories: chemical methods and physical methods. Chemical methods include chemical foaming agent decomposition and reaction byproduct gas methods, which primarily rely on activating chemical reactions to generate gas within the material to form pores. These methods are mature and suitable for mass production, but they are prone to chemical residues and have relatively large pore sizes, making it difficult to achieve precise control of the porous structure. Physical methods include supercritical fluid foaming, which involves dissolving a supercritical fluid (commonly CO2) under high pressure and then rapidly releasing the gas through rapid heating or depressurization, thereby producing porous materials. This method overcomes the disadvantages of chemical foaming, such as difficulty in producing fine pore structures and the tendency to generate chemical residues, but it is highly dependent on high-pressure precision equipment, and the development of process parameters is difficult. Moreover, porous materials produced by chemical or physical foaming methods often have pores that are approximately spherical or ellipsoidal and are mostly closed-cell, lacking sufficient pore permeability and three-dimensional connectivity. In recent years, 3D printing technology has also been used to directly construct three-dimensional porous structures through fused deposition modeling and photopolymerization. While this method can achieve precise control and directional arrangement of pores, the connectivity of three-dimensional pores is limited, and the complex network topology of the internal channels is difficult to achieve through low-cost mass production.

[0004] Therefore, developing a molding process for polyurethane porous materials that is simple and efficient, leaves no chemical residue, has a controllable pore structure, and can generate a three-dimensional interconnected pore structure has significant scientific and practical value. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to provide a polyurethane-based porous material and its preparation method. This method is based on the principle of humidity-induced phase separation, has a simple preparation process, can control the pore structure, is free from chemical pollution, and can ultimately produce a porous material with three-dimensional interconnected pores.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A polyurethane-based porous material has a three-dimensional interconnected pore structure with a porosity of 25% to 80% and an adjustable pore structure.

[0007] A method for preparing a polyurethane-based porous material includes the following steps: Step (1): Dissolve the polyurethane polymer in a solvent system to obtain a homogeneous solution; Step (2): The homogeneous solution is placed in a constant temperature and humidity environment. The diffusion of water vapor molecules in the solution and the evaporation of solvent occur together, which will induce the formation of a synergistic continuous structure of enriched and depleted phases. As the phase separation process proceeds, the polymer molecular chains in the enriched phase will physically entangle and crystallize, eventually solidifying and forming a continuous polymer skeleton structure. Subsequently, the depleted phase is removed by drying, i.e., the residual solvent is evaporated and removed to form pores, thus obtaining a polyurethane porous material. In particular, the preparation method described in this invention does not use chemical foaming agents or liquid coagulation baths.

[0008] Specifically, the polyurethane polymer is selected from polycarbonate polyurethane, polyether polyurethane, polyester polyurethane, and polyurea polyurethane, preferably polycarbonate polyurethane.

[0009] Preferably, the solvent system in step (1) includes at least one amphiphilic solvent (a solvent that is miscible with water and capable of dissolving polyurethane polymers), and the amphiphilic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, and 1,4-dioxane.

[0010] Preferably, the solvent system in step (1) may further include an auxiliary solvent (a solvent that is poorly miscible or immiscible with water but capable of dissolving polyurethane polymers), and the auxiliary solvent is selected from one or more of dichloromethane, chloroform, 1,2-dichloroethane and cyclopentanone.

[0011] Preferably, the components of the homogeneous solution in step (1) are: 10-20 parts of polyurethane polymer and 80-90 parts of solvent system (wherein the mass ratio of auxiliary solvent to amphiphilic solvent is 0-3.5:1).

[0012] Preferably, the specific implementation steps for dissolving the polyurethane polymer in the solvent system in step (1) are as follows: using a water bath for heating and stirring, setting the temperature to 50-70℃, the stirring speed to 20-150 r / min, and the stirring time to 3-5 h, so that the polyurethane polymer is completely dissolved and a homogeneous solution is obtained.

[0013] Preferably, in step (2), the homogeneous solution is placed in a constant temperature and humidity environment. Specifically, the homogeneous solution is poured into a mold or coated on the surface of a carrier and then placed in a constant temperature and humidity environment for phase separation molding.

[0014] Preferably, the temperature and humidity environment in step (2) is set within the range of: temperature 10-35℃, relative humidity 55%RH-90%RH; the exposure time of the homogeneous solution in the temperature and humidity environment is 6-24 h.

[0015] Preferably, after phase separation in step (2), the method for drying to remove residual solvent is vacuum drying, reduced pressure drying, room temperature evaporation drying, or a combination thereof.

[0016] This invention is based on the principle of humidity-induced phase separation. Polyurethane polymers are dissolved in a solvent system containing an amphiphilic solvent to form a homogeneous solution. Since the amphiphilic solvent can effectively dissolve polyurethane polymers and is miscible with water, when this homogeneous solution is exposed to a water vapor-filled environment, water molecules diffuse into the solution, causing phase separation and forming a polymer-enriched phase and a polymer-depleted phase. Because the diffusion of water vapor molecules in the solution occurs simultaneously with the evaporation of the organic solvent, a synergistic continuous structure between the enriched and depleted phases is induced. As the phase separation process proceeds, the polymer molecular chains in the enriched phase undergo physical entanglement and crystallization, eventually solidifying to form a continuous polymer framework structure, while the depleted phase forms pores after the residual solvent is evaporated. Finally, after the water and organic solvent have completely evaporated, a polyurethane porous material with a three-dimensional interconnected pore structure is formed.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: In the first aspect, the polyurethane porous material of the present invention has a wide porosity range (25% to 80%) and a three-dimensional interconnected pore structure, which can meet the requirements of high-performance medical implants (such as biodegradable polymer porous membranes and hemodialysis membranes) for high porosity, high connectivity and adjustable pore size of porous materials.

[0018] Secondly, this invention employs a humidity-induced phase separation process, using water as a non-solvent to induce phase separation and forming a porous structure through the phase separation process. The preparation method does not use chemical foaming agents or liquid coagulation baths. The preparation process is simple, cost-controllable, and produces no chemical pollution.

[0019] Thirdly, the present invention provides a method for preparing polyurethane-based porous materials, which can control the porosity of the porous structure and optimize the mechanical properties of the material by adjusting the ratio of the polyurethane polymer to the solvent system and the temperature and humidity environment set during the phase separation process. Specifically, when the content of the amphiphilic solvent is higher, the humidity is higher, and the temperature is lower, the porosity of the polyurethane-based porous material is higher, and its elastic modulus and fracture toughness are lower. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the preparation process of a polyurethane porous material according to the present invention.

[0021] Figure 2 This is a scanning electron microscope image of the polyurethane porous material in Embodiment 1 of the present invention.

[0022] Figure 3 This is a scanning electron microscope image of the polyurethane porous material in Embodiment 2 of the present invention.

[0023] Figure 4 This is a scanning electron microscope image of the polyurethane porous material in Embodiment 3 of the present invention.

[0024] Figure 5 This is a scanning electron microscope image of the polyurethane porous material in Embodiment 4 of the present invention.

[0025] Figure 6 This is a scanning electron microscope image of the polyurethane porous material in Embodiment 5 of the present invention.

[0026] Figure 7 This is a scanning electron microscope image of the polyurethane porous material in Embodiment 6 of the present invention. Detailed Implementation

[0027] The present invention will be further explained and described below with reference to specific accompanying drawings and embodiments. However, it should be noted that these examples are only for illustrating the present invention and do not limit the scope of protection of the present invention.

[0028] Example 1 like Figure 1 As shown, in this embodiment, 10 g of polycarbonate polyurethane (PCU) particles were used as the polyurethane polymer raw material and mixed with 90 g of N,N-dimethylformamide (an amphiphilic solvent). The mixture was heated and stirred in a water bath at 58°C for 3 hours until the particles were completely dissolved, at a rotation speed of 150 r / min. A clear and homogeneous solution was obtained. 10 g of the solution was poured into a 140 mm × 90 mm × 6 mm metal mold frame and placed in a constant temperature and humidity incubator at 26°C and 70% RH. The mold frame was left to stand for 12 hours to allow the solution to fully contact the water vapor, thus obtaining a polyurethane porous material.

[0029] The scanning electron microscope (SEM) image of the polyurethane porous material in this embodiment is shown below. Figure 2 As shown. By Figure 2 It can be seen that the polyurethane porous material prepared based on the principle of humidity-induced phase separation has a uniformly distributed three-dimensional interconnected pore structure. The apparent density and true density of the porous material in Example 1 were tested using the density method, and its porosity was estimated to be 73.04%.

[0030] Example 2 Example 2 differs from Example 1 only in the composition of the solvent system; all other operations remain unchanged. The specific operations are as follows: 10 g of polycarbonate polyurethane (PCU) particles were selected as the polyurethane polymer raw material and mixed with 20 g of N,N-dimethylformamide (an amphiphilic solvent) and 70 g of dichloromethane (an auxiliary solvent). The mixture was heated and stirred in a water bath at 58°C and 150 r / min for 3 hours to obtain a transparent, clear, homogeneous solution. 10 g of the solution was poured into a 140 mm × 90 mm × 6 mm metal mold frame and placed in a constant temperature and humidity incubator at 26°C and 70% RH. The mold was allowed to stand for 12 hours to allow the solution to fully contact water vapor, resulting in a polyurethane porous material.

[0031] The scanning electron microscope (SEM) image of the polyurethane porous material in this embodiment is shown below. Figure 3 As shown. By Figure 3 It can be seen that the polyurethane porous material prepared based on the principle of humidity-induced phase separation has a uniformly distributed three-dimensional interconnected pore structure. The apparent density and true density of the porous material in Example 2 were tested using the density method, and its porosity was estimated to be 56.12%.

[0032] Example 3 Compared with Example 2, Example 3 only changed the constant temperature and humidity environment set during phase separation; all other operations remained unchanged. The specific operation was as follows: 10 g of polycarbonate polyurethane (PCU) particles were selected as the polyurethane polymer raw material and mixed with 20 g of N,N-dimethylformamide (amphiphilic solvent) and 70 g of dichloromethane (auxiliary solvent). The mixture was heated and stirred in a water bath at 58°C and 150 r / min for 3 h to obtain a transparent, clear, homogeneous solution. 10 g of the solution was poured into a 140 mm × 90 mm × 6 mm metal mold frame and placed in a constant temperature and humidity incubator at 30°C and 70% RH. The mold was allowed to stand for 12 h to allow the solution to fully contact water vapor, resulting in a polyurethane porous material.

[0033] The scanning electron microscope (SEM) image of the polyurethane porous material in this embodiment is shown below. Figure 4 As shown. By Figure 4It can be seen that the polyurethane porous material prepared based on the principle of humidity-induced phase separation has a uniformly distributed three-dimensional interconnected pore structure. The apparent density and true density of the porous material in Example 3 were tested using the density method, and its porosity was estimated to be 47.28%.

[0034] Example 4 10 g of polycarbonate polyurethane (PCU) particles were selected as the raw material for polyurethane polymers and mixed with 20 g of N,N-dimethylformamide (the first amphiphilic solvent) and 70 g of N,N-dimethylacetamide (the second amphiphilic solvent). The mixture was heated and stirred in a water bath at 60°C at a speed of 150 r / min for 3 h to obtain a transparent, clear, homogeneous solution. 5 g of the solution was poured into a 140 mm × 90 mm × 6 mm metal mold frame and placed in a constant temperature and humidity incubator at 30°C and 60% RH. The mold frame was left to stand for 12 h to allow the solution to fully contact the water vapor, thus obtaining a porous polyurethane material.

[0035] The scanning electron microscope (SEM) image of the polyurethane porous material in this embodiment is shown below. Figure 5 As shown. By Figure 5 It can be seen that the polyurethane porous material prepared based on the principle of humidity-induced phase separation has a uniformly distributed three-dimensional interconnected pore structure. The apparent density and true density of the porous material in Example 4 were tested using the density method, and its porosity was estimated to be 40%.

[0036] Example 5 Compared to Example 4, Example 5 changed the constant temperature and humidity environment set for the phase separation process, while keeping the other operations unchanged. The specific operation is as follows: 10 g of polycarbonate polyurethane (PCU) particles were selected as the polyurethane polymer raw material and mixed with 20 g of N,N-dimethylformamide (the first amphiphilic solvent) and 70 g of N,N-dimethylacetamide (the second amphiphilic solvent). The mixture was heated and stirred in a water bath at 60°C and 150 r / min for 3 h to obtain a transparent, clear, homogeneous solution. 10 g of the solution was poured into a 140 mm × 90 mm × 6 mm metal mold frame and placed in a constant temperature and humidity incubator at 30°C and 55% RH. The mold was allowed to stand for 12 h to allow the solution to fully contact water vapor, resulting in a polyurethane porous material.

[0037] The scanning electron microscope (SEM) image of the polyurethane porous material in this embodiment is shown below. Figure 6 As shown. By Figure 6It can be seen that the polyurethane porous material prepared based on the principle of humidity-induced phase separation has a relatively obvious pore structure. The apparent density and true density of the porous material in Example 5 were tested using the density method, and its porosity was estimated to be 25.95%.

[0038] Based on the mechanical property test data (Table 1), compared with Example 2, Example 1 showed an increase in amphiphilic solvent content, leading to increased porosity in the porous material and a decrease in elastic modulus and fracture toughness. Example 3, compared with Example 2, increased the temperature of the isothermal and humidity-controlled environment during phase separation, resulting in a decrease in relative water vapor content, reduced porosity, and consequently increased elastic modulus and fracture toughness. Example 5, compared with Example 4, showed a decrease in humidity of the isothermal and humidity-controlled environment during phase separation, resulting in smaller porosity and increased elastic modulus and fracture toughness. Therefore, Examples 1-5 demonstrate that the polyurethane-based porous material preparation method of the present invention can control material porosity and optimize mechanical properties by adjusting the ratio of polyurethane polymer to organic solvent and changing the isothermal and humidity-controlled environment during phase separation.

[0039] Table 1 Mechanical properties of different polyurethane porous materials Example Porosity Elastic modulus (MPa) Fracture toughness (KJ / m2) Example 1 73.04% 1.18 12.30 Example 2 56.12% 1.91 15.98 Example 3 47.28% 3.79 17.91 Example 4 40.00% 4.33 22.95 Example 5 25.95% 6.82 40.10 Example 6 Example 6 differs from Example 1 only in that the polyurethane polymer raw material was replaced with polyether polyurethane (PEU) instead of polycarbonate polyurethane (PCU), while all other operations remained unchanged. The specific operation is as follows: 10 g of polyether polyurethane (PEU) particles were selected as the polyurethane polymer raw material and mixed with 90 g of N,N-dimethylformamide (an amphiphilic solvent). The mixture was heated and stirred in a water bath at 58°C at a speed of 150 r / min for 3 h, resulting in a clear and homogeneous solution. 10 g of the solution was poured into a 140 mm × 90 mm × 6 mm metal mold frame and placed in a constant temperature and humidity incubator at 26°C and 70% RH. The mold was allowed to stand for 12 h to allow the solution to fully contact water vapor, thus obtaining a polyurethane porous material.

[0040] The scanning electron microscope (SEM) image of the polyurethane porous material in this embodiment is shown below. Figure 7 As shown. By Figure 7 It can be seen that the polyurethane porous material prepared based on the principle of humidity-induced phase separation also has a uniformly distributed interconnected pore structure. The apparent density and true density of the porous material in Example 6 were tested using the density method, and its porosity was estimated to be 78.94%.

[0041] Example 7 20 g of polyester-type polyurethane particles were selected as the polyurethane polymer raw material and mixed with 60 g of dimethyl sulfoxide (an amphiphilic solvent) and 20 g of chloroform (an auxiliary solvent). The mixture was heated and stirred in a water bath at 55°C at a speed of 20 r / min for 5 h to obtain a transparent, clear, homogeneous solution. 10 g of the solution was poured into a 140 mm × 90 mm × 6 mm metal mold frame and placed in a constant temperature and humidity incubator at 10°C and 55% RH. The mold was allowed to stand for 24 h to allow sufficient contact with water vapor, resulting in phase separation induced by the water vapor and the formation of a porous structure. Finally, the residual solvent was removed by drying to obtain the porous polyurethane material.

[0042] Example 8 Ten g of polyurea-type polyurethane (PUU) particles were selected as the polyurethane polymer raw material and mixed with 40 g of N-methylpyrrolidone (an amphiphilic solvent) and 50 g of cyclopentanone (an auxiliary solvent). The mixture was heated and stirred in a water bath at 60°C at a speed of 150 r / min for 3 h to completely dissolve the particles, resulting in a transparent, clear, and homogeneous solution. Ten g of the solution was poured into a 140 mm × 90 mm × 6 mm metal mold frame and placed in a constant temperature and humidity incubator at 30°C and 90% RH. The mold was allowed to stand for 12 h to allow sufficient contact with water vapor, resulting in phase separation under the induction of water vapor and the formation of a porous structure. Finally, the residual solvent was removed by drying to obtain the porous polyurethane material.

[0043] Example 9 Ten g of polyether polyurethane (PEU) particles were selected as the raw material for polyurethane polymers and mixed with 60 g of tetrahydrofuran (the first type of amphiphilic solvent) and 30 g of 1,4-dioxane (the second type of amphiphilic solvent). The mixture was heated and stirred in a water bath at 60°C at a speed of 100 r / min for 4 h to obtain a transparent, clear, and homogeneous solution. Ten g of the solution was poured into a 140 mm × 90 mm × 6 mm metal mold frame and placed in a constant temperature and humidity incubator at 35°C and 65% RH. The mold was allowed to stand for 6 h to allow the solution to fully contact water vapor, resulting in phase separation under the induction of water vapor and the formation of a porous structure. Finally, the residual solvent was removed by drying to obtain the porous polyurethane material.

[0044] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A polyurethane-based porous material, characterized in that, The polyurethane-based porous material has a three-dimensional interconnected pore structure with a porosity of 25% to 80%, and has an adjustable pore structure.

2. The method for preparing a polyurethane porous material according to claim 1, characterized in that, Includes the following steps: Step (1): Dissolve the polyurethane polymer in a solvent system to obtain a homogeneous solution; Step (2): The homogeneous solution is placed in a constant temperature and humidity environment, so that water vapor in the air comes into contact with the homogeneous solution and induces phase separation. The diffusion of water vapor molecules in the solution and the evaporation of solvent occur simultaneously, which will induce the formation of a synergistic continuous structure of enriched and depleted phases. As the phase separation process proceeds, the polymer molecular chains in the enriched phase will undergo physical entanglement and crystallization, and finally solidify to form a continuous polymer skeleton structure. Subsequently, the depleted phase is removed by drying treatment, that is, the residual solvent is evaporated and removed to form pores, and polyurethane porous materials are obtained. The solvent system includes at least one amphiphilic solvent that is miscible with water and capable of dissolving polyurethane polymers; the solvent system may also optionally include an auxiliary solvent that is poorly miscible with or immiscible with water, but capable of dissolving polyurethane polymers. The porosity of porous materials can be controlled by adjusting the ratio of polyurethane polymers to solvent systems and by setting the temperature and humidity during phase separation. The preparation process does not use liquid coagulation baths or chemical foaming agents.

3. The preparation method according to claim 2, characterized in that, The polyurethane polymer is selected from one of polycarbonate polyurethane, polyether polyurethane, polyester polyurethane, and polyurea polyurethane.

4. The preparation method according to claim 2, characterized in that, The amphiphilic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, and 1,4-dioxane.

5. The preparation method according to claim 2, characterized in that, The auxiliary solvent is selected from one or more of dichloromethane, chloroform, 1,2-dichloroethane, and cyclopentanone.

6. The preparation method according to claim 2, characterized in that, The homogeneous solution comprises, by weight, 10-20 parts of polyurethane polymer and 80-90 parts of solvent system, wherein the mass ratio of auxiliary solvent to amphiphilic solvent is 0-3.5:

1.

7. The preparation method according to claim 2, characterized in that, In step (1), the conditions for obtaining a homogeneous solution are: heating in a water bath at 50-70°C, stirring at a speed of 20-150 r / min, and stirring for 3-5 h, so that the polyurethane polymer is completely dissolved.

8. The preparation method according to claim 2, characterized in that, The temperature and humidity environment in step (2) is set within the range of: temperature 10-35℃, relative humidity 55%RH-90%RH; the exposure time of the homogeneous solution in the temperature and humidity environment is 6-24 h.

9. The preparation method according to claim 2, characterized in that, In step (2), the drying process to remove residual solvent can be vacuum drying, reduced pressure drying, room temperature evaporation drying, or a combination thereof.

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