Polyurethane-imide electrospun membranes and methods of making the same

Abstract

This invention relates to polyurethane-imide electrospun films and their preparation methods. The polyurethane-imide electrospun film has a porous structure formed by three-dimensional cross-linking and entanglement of polyurethane-imide nanofibers, wherein the polyurethane-imide molecular chain contains soft segments of polyester diol and hard segments of imide rings. The method includes the following steps: S1: preparing a preparative solution containing a polyimide prepolymer; S2: reacting the preparative solution with a polyester diol to obtain a polyurethane-imide solution; S3: adding a mixed solvent to the polyurethane-imide solution to obtain a spinning solution, and performing electrospinning to obtain polyurethane-imide fibers; S4: heat-treating the polyurethane-imide fibers to obtain a polyurethane-imide intermediate film; S5: hot-pressing the intermediate film to obtain the final polyurethane-imide electrospun film. The polyurethane-imide electrospun film of this invention possesses both high flexibility and high heat resistance.

Description

Technical Field

[0001] This invention relates to the field of polymer materials, specifically to a polyurethane imide (PUI) electrospun film and its preparation method. Background Technology

[0002] In recent years, the application of electrospun membranes (hereinafter referred to as electrospun membranes) in the field of functional textiles has received widespread attention. Polyurethane (PU), as a commonly used textile material, has good flexibility, abrasion resistance, and moisture absorption, and is widely used in the production of various textiles. However, traditional polyurethane electrospun membranes suffer from problems such as insufficient heat resistance and easy softening and deformation (for example, the heat resistance temperature of pure polyurethane electrospun membranes is usually below 120℃), which limits their application range in the field of functional textiles. To solve the problem of insufficient heat resistance of polyurethane electrospun membranes, researchers have tried various methods, such as adding nanofillers and introducing heterocyclic structures. However, these methods often have some limitations, such as the difficulty in uniformly dispersing nanofillers, complex processes, and high costs.

[0003] Furthermore, polyimide (PI), as an engineering polymer material with excellent heat resistance, is widely used in aerospace, microelectronics, and other fields due to its superior electrical insulation, heat resistance, and chemical resistance. However, although polyimide has excellent heat resistance, its flexibility is poor (for example, the elongation at break of pure polyimide fiber membranes is typically less than 50%), making it difficult to meet the flexibility requirements of textiles.

[0004] Therefore, developing a novel polymer material that possesses both good flexibility and excellent heat resistance has become a current research hotspot. Furthermore, this material also needs to have good processability and cost-effectiveness to meet the application requirements in fields such as textiles and industrial high-temperature filtration. Summary of the Invention

[0005] Technical issues To address the shortcomings of existing technologies, the primary objective of this invention is to provide a polyurethane-imide electrospun film that simultaneously possesses high flexibility and high heat resistance.

[0006] The second objective of this invention is to provide a method for preparing polyurethane imide electrospun films, which has the advantages of relatively simple process and low cost.

[0007] Technical solution According to one aspect of the present invention, a polyurethane-imide electrospun membrane is provided, wherein the polyurethane-imide electrospun membrane has a porous structure formed by three-dimensional cross-linking and entanglement of polyurethane-imide nanofibers. The molecular chain of the polyurethane imide contains a polyester diol soft segment and an imide ring hard segment.

[0008] In one embodiment, in the molecular chain of the polyurethane imide, the polyester diol soft segments and the imide ring hard segments are arranged alternately, and, The molar ratio of the polyester diol soft segment to the imide ring hard segment is 4:6 to 8:2.

[0009] In one embodiment, the polyurethane-imide electrospun film has a tensile strength of 11 MPa or higher, an elongation at break of 150% or higher, and a heat resistance temperature of 300°C or higher.

[0010] According to another aspect of the present invention, a method for preparing a polyurethane imide electrospun film is provided, the method comprising the following steps: S1: A preparative solution containing an NCO-terminated polyimide prepolymer and a first high-boiling-point polar solvent; S2: The prepared solution is mixed with polyester diol and a second high-boiling-point polar solvent and subjected to a polymerization reaction to obtain a polyurethane imide solution; S3: A mixed solvent of a volatile non-solvent and a third high-boiling-point polar solvent is added to the polyurethane imide solution to obtain a spinning solution, and The spinning solution was electrospinned to obtain polyurethane imide fibers; S4: The polyurethane imide fiber is heat-treated to remove residual solvent and obtain a polyurethane imide intermediate film. S5: The polyurethane imide intermediate film is hot-pressed to obtain the final polyurethane imide electrospun film.

[0011] In one implementation, in step S1, The dianhydride and diisocyanate are dissolved in the first high-boiling-point polar solvent, then added to the reaction apparatus. The mixture is then heated to 100-150°C and stirred for 1-2 hours to obtain the prepared solution. The molar ratio of the dianhydride to the diisocyanate is 1:(2.05-2.35). The solid content of the preparative solution is 30-50 wt%. The dianhydride is selected from one or more of diphenyl ether dianhydride (ODPA), biphenyl dianhydride (BPDA), triphenyl diether dianhydride (HQPDA), benzophenone dianhydride (BTDA), bisphenol A dianhydride (BPADA), and diphenyl sulfide dianhydride (TDPA). The diisocyanate is selected from one or more of diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI). The first high-boiling-point polar solvent is one or more selected from N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc).

[0012] In one implementation, in step S2, First, the polyester diol is dissolved in the second high-boiling-point polar solvent, then added to the preparative solution and mixed, thereby carrying out the polymerization reaction; The polyester diol is selected from one or more of polyethylene adipate diol (PEA), polybutylene adipate diol (PBA), and polycaprolactone diol (PCL). The second high-boiling-point polar solvent is one or more selected from N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc). The reaction temperature is 60-90℃. The reaction time is 2-4 hours. The molar ratio of the polyester diol to the polyimide prepolymer is 4:6 to 8:2. In the polyurethane imide solution, the concentration of the polyurethane imide is 30-40 wt%.

[0013] In one implementation, in step S3 The mass ratio of the volatile non-solvent to the third high-boiling-point polar solvent is 2:8 to 4:6. The volatile non-solvent is one or more selected from acetone, ethanol, methanol, isopropanol, n-propanol, n-butanol, ethyl acetate, and propyl acetate. The third high-boiling-point polar solvent is one or more selected from N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc). In the spinning solution, the concentration of the polyurethane imide is 10-25 wt%. In the electrospinning process, the voltage is 15-30 kV. The distance between the nozzle and the receiving plate is 15-20 cm. The injection rate of the spinning solution is 1.0-2.5 mL / h.

[0014] In one embodiment, in step S4, the heat treatment is carried out at 80-150°C for 1-2 hours.

[0015] In one embodiment, in step S5, the hot pressing is performed at 100-110°C for 20-40 minutes.

[0016] Beneficial effects Compared with existing technologies, this invention provides a novel polyurethane-imide electrospun membrane. By integrating a flexible and spinnable polyester diol soft segment with a rigid and heat-resistant imide ring hard segment, the two components work synergistically within the molecular chain. This not only maintains the flexibility and spinnability of the polyester diol but also provides excellent mechanical strength and heat resistance. Furthermore, the electrospun membrane simultaneously exhibits excellent tensile strength, elongation at break, and heat resistance, achieving a combined advantage of flexibility and heat resistance that cannot be provided by either polyurethane or polyimide materials alone. The polyurethane-imide electrospun membrane of this invention can be widely used in functional textiles, industrial high-temperature filtration, and other fields, demonstrating a broad range of applications.

[0017] Furthermore, compared with traditional methods for preparing polyimide, the preparation method of the present invention does not require high-temperature imidization treatment (which usually requires above 300°C) throughout the entire process, and the maximum process temperature can be reduced to below 150°C, which greatly reduces production energy consumption and operational difficulty. The process is simple and easy to industrialize.

[0018] Furthermore, the preparation method of this invention can effectively ensure the uniformity and stability of the polyurethane imide fiber structure, and the porosity and thickness of the obtained polyurethane imide electrospun fiber membrane can be adjusted and controlled as needed. Moreover, by optimizing the solvent system, electrospinning parameters, and heat treatment process parameters, this invention can further improve the uniformity, heat resistance, and flexibility of polyurethane imide fibers, thereby meeting the application needs of different fields. Attached Figure Description

[0019] Figure 1 This is a scanning electron microscope (SEM) image of the polyurethane imide intermediate film prepared in step S4 of Example 1 of the present invention.

[0020] Figure 2 This is a scanning electron microscope (SEM) image of the polyurethane imide electrospun film prepared in step S5 of Example 1 of the present invention. Detailed Implementation

[0021] The invention will now be described in detail with reference to the accompanying drawings.

[0022] Unless otherwise defined, all terms used herein, including technical or scientific terms, shall be interpreted as having the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Therefore, unless explicitly defined, terms such as those defined in common dictionaries should not be interpreted in an ideal or overly formal sense.

[0023] When the conditions and methods for measuring the performance or parameter described in this specification are not specifically described, the performance or parameter may be measured using the measurement conditions and methods commonly used by those skilled in the art.

[0024] Unless otherwise stated, "%" as used in this document refers to weight.

[0025] Polyurethane imide electrospun film According to one aspect of the present invention, a polyurethane-imide electrospun membrane is provided, which can be prepared by the following method, wherein the polyurethane-imide electrospun membrane has a porous structure formed by three-dimensional cross-linking and entanglement of polyurethane-imide nanofibers, and the molecular chain of polyurethane-imide contains polyester diol soft segments and imide ring hard segments.

[0026] In the molecular chain of polyurethane imide, polyester diol soft segments and imide ring hard segments are arranged alternately, and the molar ratio of the polyester diol soft segments to the imide ring hard segments can be from 4:6 to 8:2, specifically from 5:5 to 6:4. Furthermore, the polyester diol soft segments and imide ring hard segments can be linked by urethane groups.

[0027] The soft segments of polyester diol provide good flexibility, while the hard segments of imide rings provide excellent heat resistance. Furthermore, the combination of the two does not significantly reduce their individual properties, but rather achieves a good balance between flexibility and heat resistance, resulting in a polyurethane-imide electrospun film that simultaneously possesses high flexibility and high heat resistance.

[0028] The polyurethane-imide electrospun film of the present invention can have a single-layer structure, wherein the average diameter of the polyurethane-imide nanofibers can be 200-900 nm, preferably 200-400 nm.

[0029] The flexibility of polyurethane imide electrospun films can be characterized by tensile strength and elongation at break.

[0030] The tensile strength of the polyurethane-imide electrospun film of the present invention can be above 11 MPa, for example, 11-20 MPa. The tensile strength can be measured according to GB / T 13773-2008 "Determination of Tensile Properties of Nonwoven Fabrics".

[0031] The elongation at break of the polyurethane-imide electrospun film of the present invention can be 150% or more, for example, 150%-200%. The elongation at break can be measured according to GB / T 13773-2008 "Determination of tensile properties of nonwoven fabrics".

[0032] The heat resistance of polyurethane-imide electrospun films can be characterized by heat resistance temperature.

[0033] The heat resistance temperature of the polyurethane imide electrospun film of the present invention can be above 300°C, for example, 300°C-400°C.

[0034] The heat resistance temperature is the 5% thermogravimetric temperature (T5%) determined by thermogravimetric analysis (TGA). Thermogravimetric analysis can be performed using a TA Instruments Q500 thermogravimetric analyzer under a nitrogen atmosphere, with a heating rate of 10 °C / min.

[0035] Method for preparing polyurethane-based electrospun films According to another aspect of the present invention, a method for preparing a polyurethane imide electrospun film is provided, the method comprising the following steps: S1: A preparative solution containing an NCO-terminated polyimide prepolymer and a first high-boiling-point polar solvent; S2: The prepared solution is mixed with polyester diol and a second high-boiling-point polar solvent and subjected to a polymerization reaction to obtain a polyurethane imide solution; S3: A mixed solvent of a volatile non-solvent and a third high-boiling-point polar solvent is added to the polyurethane imide solution to obtain a spinning solution, and The spinning solution was electrospinned to obtain polyurethane imide fibers; S4: The polyurethane imide fiber is heat-treated to remove residual solvent and obtain a polyurethane imide intermediate film. S5: The polyurethane imide intermediate film is hot-pressed to obtain the final polyurethane imide electrospun film.

[0036] The following section will provide a detailed explanation of each step.

[0037] Step S1: Prepare the preliminary solution A preparative solution containing NCO (isocyanate group, -N=C=O)-terminated polyimide (PI) prepolymer and a first high-boiling-point polar solvent can be prepared by conventional processes.

[0038] Compared to polyurethane (PU) prepolymers, the present invention allows for more advantageous subsequent electrospinning by using polyimide (PI) prepolymers.

[0039] In one embodiment, dianhydride and diisocyanate in a molar ratio of 1:(2.05-2.35) are added to a first high-boiling-point polar solvent, then poured into a three-necked flask equipped with a mechanical stirrer, thermometer and nitrogen protection device, heated to 100-150°C, stirred for 1-2 hours, and then cooled to 60-90°C (for polymerization reaction in step S2 below) to obtain the preparative solution containing NCO-terminated (i.e., NCO-terminated) polyimide prepolymer as the reaction product.

[0040] There are no particular restrictions on dianhydrides, diisocyanates, and the first high-boiling polar solvents; any commonly used materials in the field can be used.

[0041] The dianhydride is a compound containing two carboxylic anhydride groups and is a conventional component used in the preparation of polyurethane prepolymers. The dianhydride can be one or more selected from diphenyl ether dianhydride (ODPA), biphenyl dianhydride (BPDA), triphenyl diether dianhydride (HQPDA), benzophenone dianhydride (BTDA), bisphenol A dianhydride (BPADA), and diphenyl sulfide dianhydride (TDPA).

[0042] The diisocyanate is a compound containing two NCO groups and is a conventional component used in the preparation of polyurethane prepolymers. The diisocyanate may be one or more selected from diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI).

[0043] The high-boiling-point polar solvent is a polar solvent with a boiling point above 100°C (especially above 150°C). The first high-boiling-point polar solvent may be one or more selected from N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc).

[0044] The molar ratio of dianhydride to diisocyanate as a raw material component is typically 1:(2.05-2.35), for example 1:(2.1-2.2), so that the resulting polyimide prepolymer retains NCO groups at the ends of the polyimide molecular chains, thereby forming an NCO-terminated structure, which facilitates the introduction of flexible structural units (polyester diol soft segments) in subsequent reactions.

[0045] The amounts of dianhydride and diisocyanate are adjusted relative to the weight of the first high-boiling-point polar solvent (the total weight of the two corresponds to the weight of the resulting polyimide prepolymer) so that the solid content of the polyimide prepolymer in the preparative solution can be 30-50 wt%.

[0046] Step S2: Prepare polyurethane imide solution The prepared solution is mixed with polyester diol and a second high-boiling-point polar solvent and subjected to a polymerization reaction to obtain a polyurethane imide solution.

[0047] In one embodiment, firstly, the polyester diol is dissolved in a second high-boiling-point polar solvent to obtain a polyester diol solution. Then, the polyester diol solution is added to the preparative solution under stirring conditions, and the temperature of the resulting mixture is controlled at 60-90°C, causing the NCO groups in the polyimide prepolymer in the preparative solution to react with the polyester diol, thereby introducing flexible polyester diol soft segments into the polyimide molecular chain to obtain polyurethane imide.

[0048] There are no particular restrictions on the type of material used for polyester diols and the second high-boiling-point polar solvent; any commonly used materials in this field can be used.

[0049] For example, the polyester diol may be one or more selected from polyethylene adipate diol (PEA), polybutylene adipate diol (PBA), and polycaprolactone diol (PCL).

[0050] The second high-boiling-point polar solvent may be one or more selected from N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc).

[0051] The reaction temperature can be 60-90℃. If the temperature is too low, the reaction rate will decrease significantly, or the reaction may be incomplete, resulting in problems such as low strength and poor performance. If the temperature is too high, side reactions are likely to occur, such as the formation of branched cross-linked structures like urethane or biuret, which leads to a sharp increase in the viscosity of the system and gelation.

[0052] The reaction time can be 2-4 hours to ensure that the reaction proceeds fully.

[0053] The molar ratio of polyester diol to polyimide prepolymer can be from 4:6 to 8:2 to control the molar ratio of soft and hard segments in the resulting polyurethane imide molecular chain.

[0054] In addition, the amount of the second high-boiling-point polar solvent is adjusted so that the concentration of polyurethane imide (whose weight corresponds to the weight of the polyimide prepolymer and polyester diol used as raw materials) in the polyurethane imide solution can be 30-40 wt%.

[0055] Through the above reaction, a polyester diol soft segment (a flexible structural unit) is introduced into the polyimide molecular chain of the polyimide prepolymer, thereby obtaining a polyurethane imide containing a polyester diol soft segment and an imide ring hard segment.

[0056] The polyurethane imide solution can be cooled to room temperature (15-25°C) for the following spinning steps.

[0057] Step S3: Electrospinning A mixed solvent of a volatile non-solvent and a third high-boiling-point polar solvent is added to the polyurethane imide solution to obtain a spinning solution, and The spinning solution is electrospun to obtain polyurethane imide fibers.

[0058] In one embodiment, at room temperature (15-25°C), a mixture of a volatile non-solvent and a third high-boiling-point polar solvent (mass ratio of 2:8 to 4:6) is added to the polyurethane imide solution obtained in step S2. The total amount of the volatile non-solvent and the third high-boiling-point polar solvent is adjusted such that the concentration of polyurethane imide, based on the total weight of the resulting mixture, can be 10-25 wt%. The mixture is allowed to stand overnight to obtain a uniform and transparent spinning solution.

[0059] Volatile nonsolvents refer to organic solvents that do not have good solubility for polyurethane imides but are miscible with high-boiling-point polar solvents. They are used to control the viscosity, evaporation rate, and phase separation behavior of spinning solutions. By adding volatile nonsolvents, the phase behavior of polyurethane imide systems can be induced and controlled, resulting in a stable electrospinning window.

[0060] The volatile non-solvent may be one or more selected from acetone, ethanol, methanol, isopropanol, n-propanol, n-butanol, ethyl acetate, and propyl acetate. Preferably, the volatile non-solvent may be one or more selected from acetone, ethanol, and isopropanol.

[0061] The first, second, and third high-boiling-point polar solvents mentioned above may be the same or different from each other. For example, the third high-boiling-point polar solvent may be one or more selected from N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc).

[0062] In one embodiment, the spinning solution is transferred to the syringe of an electrospinning device, spinning parameters are set, electrospinning is performed, and polyurethane imide fibers are collected on a receiving plate.

[0063] Electrospinning is a simple and effective technique for producing nanoscale fibers. It involves causing a statically charged polymer solution to flow and deform in an electrostatic field, solidifying upon solvent evaporation to form a fibrous material. Electrospinning allows for the simple and efficient preparation of continuous nanofibers.

[0064] Electrospinning can be performed using conventional processes. Specifically, the spinning solution can be loaded into the syringe of the electrospinning equipment, with a stainless steel needle with an inner diameter of 0.4-0.6 mm used as the nozzle.

[0065] In the electrospinning process, the voltage can be 15-30 kV, the distance between the nozzle and the receiving plate can be 15-20 cm, and the injection rate of the spinning solution can be 1.0-2.5 mL / h. The spinning time can be determined by allowing the layered polyurethane imide fibers to reach the target thickness.

[0066] In the electrospinning process, the spinning solution is sprayed out by an electrostatic field, causing the solvent to evaporate rapidly. The nanofibers are stretched and shaped in the air to form continuous nanofibers, which are then deposited on the receiving device, ultimately forming layered, uniform, and dense polyurethane imide fibers.

[0067] Step S4: Heat treatment to remove residual solvent The polyurethane imide fiber is heat-treated to remove residual solvent, resulting in a polyurethane imide intermediate film.

[0068] Residual solvents (i.e., residual volatile non-solvents and first, second, and third high-boiling-point polar solvents) in polyurethane-imide fibers can be removed by heat treatment, further stabilizing the fiber structure. This heat treatment can be performed using conventional processes (e.g., vacuum drying).

[0069] The temperature and time of heat treatment can be determined through conventional selection. For example, heat treatment can be carried out at 80-150°C for 1-2 hours.

[0070] Step S5: Hot pressing The polyurethane imide intermediate film is hot-pressed to obtain the final polyurethane imide electrospun film.

[0071] In one embodiment, the polyurethane imide intermediate film can be placed between two flat silicone pads and then placed in an oven for hot pressing at 100-110°C for 20-40 minutes to moderately bond the polyurethane imide fibers together and further stabilize the fiber structure.

[0072] The hot-pressing temperature can be 100-110℃, which can effectively further remove the solvent remaining in the electrospinning process, while avoiding the degradation of the polymer structure or the deterioration of its performance under high temperature conditions. If the temperature is too low, the residual solvent will be difficult to remove completely, resulting in insufficient structural stability of the electrospun film; if the temperature is too high, the soft segments of the polyester diol are prone to thermal relaxation or even local degradation, which will lead to excessive fiber adhesion or destruction of the pore structure, which is not conducive to maintaining the performance of the electrospun film.

[0073] The hot-pressing time can be 20-40 minutes, preferably 25-35 minutes. If the time is too short, the residual solvent will be difficult to remove completely, resulting in insufficient structural stability of the electrospun film; if the time is too long, the soft segments of the polyester diol are prone to excessive thermal relaxation, which will cause changes in fiber morphology or damage to the pore structure, which is not conducive to maintaining the performance of the electrospun film.

[0074] The length, width, and thickness of the electrospun membrane are not particularly limited and can be determined as needed. For example, the length can be 50-200 m, the width can be 90-150 cm, and the thickness is typically 30-60 μm, preferably 40-50 μm. In one embodiment, the areal density of the electrospun membrane is 10 g / m³. 2 At that time, the thickness can be 45 μm.

[0075] In the electrospun film, the average diameter of the polyurethane imide nanofibers can be 200-900 nm, preferably 200-400 nm.

[0076] Example The present invention will be described in detail below with reference to embodiments to specifically describe the invention. However, the embodiments of the present invention can be modified into various other forms, and the scope of the invention should not be construed as limited to the embodiments described below. Embodiments of the present invention are provided to describe the invention more completely to those skilled in the art.

[0077] Unless otherwise specified, the experimental methods described in the following examples are generally conventional conditions in the art or conditions recommended by the manufacturer; the raw materials and equipment used, unless otherwise specified, are all commercially available from the conventional market.

[0078] The areal density of the polyurethane imide electrospun film of the present invention can be measured according to the national standard GB / T 24218.1-2009 "Textiles - Test methods for nonwoven fabrics - Part 1: Determination of mass per unit area".

[0079] The following is based on the same basis weight (i.e., areal density, 10 g / m³). 2 Thin films of the prepared examples and comparative examples were prepared, and their flexibility and heat resistance were compared.

[0080] Example 1 (Preparation of polyurethane-imide electrospun film) Polyurethane imide electrospun films are prepared by a method including the following steps.

[0081] Step S1: Prepare the preliminary solution 31.0 g (100 mmol) diphenyl ether dianhydride (ODPA) and 52.5 g (210 mmol) 4,4'-diphenylmethane diisocyanate (MDI) were dissolved in 100.0 g N,N-dimethylacetamide (DMAc). The resulting mixture was poured into a 1000 mL three-necked flask equipped with a mechanical stirrer, thermometer, and nitrogen protection device. The mixture was heated to 120 °C and stirred for 1 hour. Then it was cooled to 80 °C to obtain a preparative solution containing NCO-terminated polyimide prepolymer with a solid content of approximately 45.4%.

[0082] Step S2: Prepare polyurethane imide solution 300.0 g (150 mmol) of polyethylene adipate diol (PEA, number average molecular weight 2000) was dissolved in 500.0 g of N,N-dimethylacetamide (DMAc) to obtain a polyester diol solution.

[0083] Then, the polyester diol solution was added to the above-mentioned preparative solution under stirring conditions, and the temperature of the resulting mixture was controlled at 80°C. The mixture was stirred for 4 hours to allow the polyethylene adipate diol and the polyimide prepolymer (molar ratio of 6:4) to react further. The mixture was then cooled to room temperature (20°C) to obtain a polyurethane imide solution (concentration of approximately 39.0 wt%, wherein the molar ratio of the polyester diol soft segment to the imide ring hard segment is 4:6), which is a pale yellow viscous liquid.

[0084] Step S3: Electrospinning At room temperature (20°C), a mixed solvent of ethanol and N,N-dimethylacetamide (DMAc) (mass ratio 3:7, total 1573.2g) was added to the polyurethane imide solution to make the mass concentration of polyurethane imide about 15wt%. The solution was left to stand overnight to obtain a uniform and transparent spinning solution.

[0085] The above spinning solution was transferred to the syringe of the electrospinning equipment, and the spinning parameters were set as follows: voltage of 15kV, distance between the needle and the receiving plate of 15cm, injection rate of 1.2mL / h, and spinning time of 10h. Polyurethane imide fibers were collected on the receiving plate.

[0086] Step S4: Heat treatment to remove residual solvent The above-mentioned polyurethane imide fibers were placed in a vacuum drying oven and dried under vacuum at 80°C for 2 hours to remove residual solvent, thereby obtaining a polyurethane imide intermediate film.

[0087] Step S5: Hot pressing The obtained polyurethane imide intermediate film was placed between two flat silicone pads and placed in an oven. It was then hot-pressed at 100°C for 30 minutes to obtain the final polyurethane imide electrospun film.

[0088] Example 2 (using different types of dianhydride monomers) Polyurethane imide electrospun films were prepared using the same method as in Example 1, except that biphenyl dianhydride (BPDA) was used as the dianhydride monomer in step S1.

[0089] Example 3 (Changing the molar ratio of polyester diol to polyimide prepolymer) Polyurethane-imide electrospun films were prepared using the same method as in Example 1, except that in step S2, 200.0 g (100 mmol) of polyethylene adipate diol (PEA, number average molecular weight 2000) was used, so that the molar ratio of polyester diol to polyimide prepolymer was 5:5.

[0090] Example 4 (using different types of polyester diols) Polyurethane imide electrospun films were prepared using the same method as in Example 1, except that in step S2, the same molar amount (i.e., 150 mmol) of polycaprolactone diol (PCL, number average molecular weight 2000) was used as the polyester diol instead of polyethylene adipate diol (PEA).

[0091] Comparative Example 1 (Pure Polyurethane Electrospun Film) Pure polyurethane electrospun films were prepared using a method similar to that in Example 1, wherein the resulting polymer molecular chains do not contain imide ring hard segments. The method includes the following steps: Step S1 (omitted) Step S1 of Example 1 is omitted.

[0092] Step S2: Prepare polyurethane solution Add 500.0g of polyester polyurethane (Wanhua, WHT-1490IV) to a 1000mL three-necked flask equipped with a mechanical stirrer, thermometer and nitrogen protection device, add 600.0g of N,N-dimethylacetamide, and stir rapidly at room temperature (20℃) for 3h to obtain a polyurethane solution.

[0093] Steps S3-S5 The steps S3-S5 are basically the same as in Example 1, except that the total weight of the mixed solvent of ethanol and N,N-dimethylacetamide (DMAc) is changed so that the mass concentration of polyurethane in the spinning solution is also about 15 wt%. Pure polyurethane electrospun film is thus obtained.

[0094] Comparative Example 2 (Pure Polyimide Electrospun Film) Referring to Example 1, a pure polyimide electrospun film was prepared by the following steps, wherein the molecular chain of the obtained polymer does not contain polyester diol soft segments.

[0095] Step S1: Prepare the preliminary solution 31.0 g (100 mmol) of diphenyl ether dianhydride (ODPA) and 20.0 g (100 mmol) of 4,4'-diaminodiphenyl ether (ODA) were added to 100.0 g of N,N-dimethylacetamide and reacted at room temperature (20 °C) for 12 hours to obtain a polyamic acid solution.

[0096] Step S2 (omitted) Step S2 of Example 1 is omitted.

[0097] Step S3: Electrospinning The procedure is essentially the same as step S3 in Example 1, except that the total weight of the mixed solvent of ethanol and N,N-dimethylacetamide (DMAc) is changed so that the mass concentration of polyamic acid in the spinning solution is also approximately 15 wt%. Polyamic acid fibers are obtained.

[0098] Steps S4-S5 (omitted) Steps S4-S5 of Example 1 are omitted.

[0099] Step S6: Thermal imidization treatment The polyamic acid fiber was subjected to thermal imidization treatment at 300°C for 1 hour to obtain a pure polyimide electrospun film.

[0100] Experiment 1: Morphological observation using scanning electron microscopy (SEM) The morphology of the polyurethane-imide intermediate film and the polyurethane-imide electrospun film prepared by steps S4 and S5 of Example 1 were observed using a scanning electron microscope (TESCAN, model VEGA3) according to GB / T36422-2018 (Determination of Microstructure and Diameter of Chemical Fibers by Scanning Electron Microscopy). The results are as follows. Figure 1 As shown.

[0101] from Figure 1 As can be seen, the polyurethane imide intermediate film is formed by the random stacking of continuous fibers with a diameter in the range of 400-800nm, forming a three-dimensional porous network. The fibers are loose and there are a large number of interconnected pores.

[0102] from Figure 2As can be seen, the polyurethane-imide electrospun membrane has a three-dimensional network structure formed by multiple fibers interconnected through molten nodes. This indicates that by performing hot pressing in step S5, the fibers are moltenly bonded together at the contact nodes, transforming the fiber membrane from a loosely stacked fiber structure into a felt-like material with good structural stability.

[0103] Experiment Example 2: Measurement of Flexibility and Heat Resistance The flexibility and heat resistance of the products of each embodiment and comparative example were measured.

[0104] The flexibility was characterized by tensile strength and elongation at break. Specifically, the tensile strength and elongation at break of the products of the examples and comparative examples were measured using a universal testing machine (Shenzhen Xin Sansi Materials Testing Co., Ltd., CMT4204) according to GB / T 13773-2008 "Determination of tensile properties of nonwoven fabrics".

[0105] The heat resistance was characterized by a heat resistance temperature, which was expressed as the 5% thermogravimetric temperature (T5%) determined by thermogravimetric analysis (TGA). The TGA was performed using a TA Instruments Q500 thermogravimetric analyzer with a heating rate of 10 °C / min under a nitrogen atmosphere.

[0106] In addition, the highest temperatures during the preparation processes of each embodiment and comparative example were summarized.

[0107] The results of the above measurements and summaries are shown in Table 1 below.

[0108] Table 1

[0109] As can be seen from Table 1, the tensile strength of the polyurethane imide electrospun films obtained in Examples 1-4 of the present invention is all above 11 MPa, the elongation at break is all above 150%, the heat resistance temperature (T5%) is all above 300℃, and the highest preparation temperature is only 120℃, which fully meets the technical requirements.

[0110] Furthermore, compared with Comparative Example 1 (pure polyurethane electrospun film), the heat resistance temperature (T5%) of the polyurethane imide electrospun film of Example 1 is increased by about 90°C, and the heat resistance is significantly improved. Compared with Comparative Example 2 (pure polyimide fiber membrane), the polyurethane-imide electrospun membrane of Example 1 has an elongation at break of about 4 times, significantly improved flexibility, and the maximum temperature during preparation is reduced from 300°C to 120°C, which significantly saves on process costs.

[0111] The above results demonstrate that by introducing the soft segment of polyester diol and the hard segment of imide ring into the same polymer molecular chain, it is possible to achieve a combination of advantages in both heat resistance and flexibility, which cannot be provided by single polyurethane or single polyimide materials.

[0112] The above examples are merely illustrative to aid in understanding the method and core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims.

Claims

1. A polyurethane-imide electrospun membrane, wherein the polyurethane-imide electrospun membrane has a porous structure formed by three-dimensional cross-linking and entanglement of polyurethane-imide nanofibers. The molecular chain of the polyurethane imide contains a polyester diol soft segment and an imide ring hard segment.

2. The polyurethane-imide electrospun film according to claim 1, wherein in the molecular chain of the polyurethane-imide, the soft segments of the polyester diol and the hard segments of the imide ring are arranged alternately, and, The molar ratio of the polyester diol soft segment to the imide ring hard segment is 4:6 to 8:

2.

3. The polyurethane-imide electrospun film according to claim 1, wherein the polyurethane-imide electrospun film has a tensile strength of 11 MPa or higher, an elongation at break of 150% or higher, and a heat resistance temperature of 300°C or higher.

4. A method for preparing a polyurethane-imide electrospun film, the method comprising the following steps: S1: Prepare a solution containing an NCO-terminated polyimide prepolymer and a first high-boiling-point polar solvent; S2: The prepared solution is mixed with polyester diol and a second high-boiling-point polar solvent and subjected to a polymerization reaction to obtain a polyurethane imide solution; S3: A mixed solvent of a volatile non-solvent and a third high-boiling-point polar solvent is added to the polyurethane imide solution to obtain a spinning solution, and The spinning solution was electrospinned to obtain polyurethane imide fibers; S4: The polyurethane imide fiber is heat-treated to remove residual solvent and obtain a polyurethane imide intermediate film. S5: The polyurethane imide intermediate film is hot-pressed to obtain the final polyurethane imide electrospun film.

5. The method according to claim 4, wherein in step S1, The dianhydride and diisocyanate are dissolved in the first high-boiling-point polar solvent, then added to the reaction apparatus. The mixture is then heated to 100-150°C and stirred for 1-2 hours to obtain the prepared solution. The molar ratio of the dianhydride to the diisocyanate is 1:(2.05-2.35). The solid content of the preparative solution is 30-50 wt%. The dianhydride is selected from one or more of diphenyl ether dianhydride (ODPA), biphenyl dianhydride (BPDA), triphenyl diether dianhydride (HQPDA), benzophenone dianhydride (BTDA), bisphenol A dianhydride (BPADA), and diphenyl sulfide dianhydride (TDPA). The diisocyanate is selected from one or more of diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI). The first high-boiling-point polar solvent is one or more selected from N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc).

6. The method according to claim 4, wherein in step S2, First, the polyester diol is dissolved in the second high-boiling-point polar solvent, then added to the preparative solution and mixed, thereby carrying out the polymerization reaction; The polyester diol is selected from one or more of polyethylene adipate diol (PEA), polybutylene adipate diol (PBA), and polycaprolactone diol (PCL). The second high-boiling-point polar solvent is one or more selected from N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc). The reaction temperature is 60-90℃. The reaction time is 2-4 hours. The molar ratio of the polyester diol to the polyimide prepolymer is 4:6 to 8:

2. In the polyurethane imide solution, the concentration of the polyurethane imide is 30-40 wt%.

7. The method according to claim 4, wherein in step S3, The mass ratio of the volatile non-solvent to the third high-boiling-point polar solvent is 2:8 to 4:

6. The volatile non-solvent is one or more selected from acetone, ethanol, methanol, isopropanol, n-propanol, n-butanol, ethyl acetate, and propyl acetate. The third high-boiling-point polar solvent is one or more selected from N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc). In the spinning solution, the concentration of the polyurethane imide is 10-25 wt%. In the electrospinning process, the voltage is 15-30 kV. The distance between the nozzle and the receiving plate is 15-20 cm. The injection rate of the spinning solution is 1.0-2.5 mL / h.

8. The method according to claim 4, wherein in step S4, the heat treatment is performed at 80-150°C for 1-2 hours.

9. The method according to claim 4, wherein in step S5, the hot pressing is performed at 100-110°C for 20-40 minutes.

Images