Preparation method of flame-retardant and recyclable polyimide film based on double dynamic bond cross-linking structure

Abstract

The application discloses a preparation method of a flame-retardant and recyclable polyimine film based on a double dynamic bond cross-linking structure, which is prepared by introducing C=N bonds and -S-S- bonds into a bio-based vanillin as a raw material. The Schiff base structure and the disulfide bond structure in the cross-linking structure are reversible under heating conditions, and can be used to realize the post-processing or reprocessing of the cross-linked polymer material. The flexible polyether amine and the rigid diamine diphenyl disulfide are used in combination to control the mechanical properties of the polyimine film. The Schiff base and the disulfide bond double dynamic bond structure enables the polyimine film to have good reprocessing performance, and can be reshaped after being cut and heated at 150 DEG C for 10 minutes. The Schiff base structure can be degraded in hydrochloric acid and tetrahydrofuran solution, and the TFMP can be recycled, so that the polyimine film has good degradation and recycling performance.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, specifically relating to a method for preparing a bio-based polyimide film that is degradable, recyclable, high-temperature resistant, and has excellent flame-retardant properties. Background Technology

[0002] Currently, widely used polymer materials can be broadly classified into two categories: thermoplastics and thermosetting materials. Compared to thermoplastics, thermosetting materials exhibit superior mechanical properties, thermodynamic properties, thermal stability, and solvent resistance, leading to broader application prospects. However, their stable chemically cross-linked network structure makes them difficult to degrade or recycle after curing. Current recycling methods for thermosetting materials primarily involve incineration and landfill, resulting in significant environmental pollution and resource waste. Therefore, developing thermosetting polymer materials with excellent comprehensive properties, along with good degradability, reprocessing capabilities, and recyclability, has become a current research hotspot in polymer materials.

[0003] Furthermore, the global production and use of a large amount of thermosetting polymer materials consumes a significant amount of fossil fuels. This extensive use of fossil resources has also caused serious environmental pollution and climate problems such as global warming. In contrast, bio-based compounds offer diverse, abundant, inexpensive, and renewable raw materials, attracting increasing research interest from researchers both domestically and internationally in recent years. Over the past two decades, numerous studies have been reported on the preparation of thermosetting materials from bio-based raw materials such as vegetable oils, rosin, lignin, itaconic acid, isosorbide, cashew nut shell powder, and vanillin. However, current research on high-performance thermosetting materials, such as bio-based epoxy resins or bio-based benzoxazine materials, primarily focuses on partially replacing petroleum-based raw materials with bio-based materials to reduce their use. Little attention has been paid to addressing the pressing issues of thermosetting materials' difficulty in degradation and recycling. Moreover, currently widely used thermosetting and bio-based materials contain large amounts of C and H elements in their chemical structures, resulting in rapid combustion upon ignition, accompanied by large amounts of dense smoke and molten dripping. Therefore, designing and preparing bio-based polyimide films with excellent mechanical properties, biodegradability, recyclability, and flame retardancy has practical application significance.

[0004] Wang et al. first reported a thermosetting material containing a Schiff base structure (Macromolecules 51, 8001-8012) using vanillin as a bio-based raw material. This material exhibited good mechanical properties, with tensile strengths exceeding 30 MPa. It also demonstrated good thermal stability and flame retardancy, with a residual carbon content exceeding 20% ​​and a LOI as high as 30% at 700℃ in a N2 atmosphere. Building on this, Liu et al. prepared a vanillin-based cyclophosphonitrile polyimide thermosetting material and applied it to carbon fiber to prepare a fully recyclable, flame-retardant, high-performance carbon fiber composite material. Due to the rational combination of cyclophosphonitrile and imide bonds, the gas phase and condensed phase synergistically enhance flame retardancy during combustion, resulting in excellent flame-retardant properties in the composite material. The vanillin-based monomer and carbon fiber in the composite material achieved non-destructive closed-loop recycling under mild conditions, providing a green, environmentally friendly, and sustainable development strategy for designing environmentally friendly high-performance composite materials. However, the above work has several shortcomings, such as poor toughness of the prepared polyimide film, low flame retardant efficiency, long degradation and recycling processes, and stringent reprocessing conditions. Therefore, it is particularly important to design a multifunctional flame-retardant polyimide film that is biodegradable and recyclable under mild conditions. Summary of the Invention

[0005] This invention addresses the shortcomings of current thermosetting materials by providing a method for preparing a bio-based polyimide film and its applications. This film possesses excellent mechanical properties, is biodegradable, recyclable, reprocessable, and exhibits superior flame retardant properties.

[0006] In this invention, based on the presence of aldehyde and phenolic hydroxyl groups in the vanillin molecule, a phosphorus-containing vanillin derivative, tris(4-formyl-2-methoxyphenyl) phosphate (TFMP), was first designed and prepared. TFMP was subsequently reacted with flexible polyetheramine and rigid diaminodiphenyl disulfide to prepare a bio-based polyimide film. The Schiff base structure and disulfide bond structure in its crosslinking structure are both reversible under heating conditions and can be used to achieve post-processing or reprocessing of the crosslinked polymer material. The combination of flexible polyetheramine and rigid diaminodiphenyl disulfide can regulate the mechanical properties of the polyimide film, and the introduction of the rigid diaminodiphenyl disulfide can significantly improve the mechanical strength of the polyimide film. Furthermore, during the combustion of the polyimide film, the Schiff base structure decomposes upon heating, releasing a large amount of non-flammable components, diluting the oxygen concentration, and playing a certain flame-retardant role. The polyimide film decomposes rapidly upon heating into carbon, forming a dense carbon layer on the surface, which acts as a shield, protecting the internal substrate from further combustion. The introduction of phosphorus significantly improves the flame retardant properties of the prepared polymer material, playing a synergistic flame-retardant role in both the gas and condensed phases. The Schiff base and disulfide double dynamic bond structure endow the polyimide film with excellent reprocessing properties; it can be reshaped after being cut and hot-pressed at 150°C for 10 minutes. Furthermore, the Schiff base structure is degradable in hydrochloric acid and tetrahydrofuran solutions, allowing for the recovery of TFMP. The polyimide film exhibits excellent degradation and recycling performance, with a TFMP monomer recovery rate reaching 70%. Therefore, this invention successfully designed and synthesized a multifunctional polyimide film based on the bio-based raw material vanillin, exhibiting good mechanical properties, rapid degradation, efficient recycling, and excellent thermal stability and flame retardant properties.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] The method for preparing the bio-based polyimide film of the present invention includes the following steps:

[0009] Step 1: First, synthesize tris(4-formyl-2-methoxyphenyl) phosphate (TFMP);

[0010] Step 2: Dissolve a certain mass of TFMP in a chloroform solution to obtain solution A, and dissolve a certain amount of flexible polyetheramine and rigid diaminodiphenyl disulfide in a chloroform solution to obtain solution B;

[0011] Step 3: Mix solution A and solution B and stir to disperse evenly. Transfer the mixture into a PTFE mold, dry and shape it at room temperature, and then place it in a forced-air oven to dry. After drying, a pretreated polyimide film is obtained.

[0012] Step 4: The pretreated polyimide film obtained in Step 3 is hot-pressed in a flat vulcanizing machine to obtain the final bio-based polyimide film.

[0013] In step 1, the tris(4-formyl-2-methoxyphenyl) phosphate was prepared by reacting phosphorus oxychloride and vanillin. First, vanillin (45.6 g, 0.3 mol) and triethylamine (30.3 g, 0.3 mol) were mixed and dissolved in 200 mL of ethyl acetate. Phosphorus oxychloride (15.3 g, 0.1 mol) was added dropwise to the above mixed solution in an ice-water bath. After the addition was complete, the mixture was kept at 0-5°C for 30 min in the ice-water bath, and then stirred at 25°C for 24 h. After the reaction was complete, the mixture was poured into 1000 mL of deionized water, cooled to room temperature, and stirred for another 0.5 h. After filtering to remove the solution, a white solid was obtained (yield approximately 95%). The crude product obtained by filtration was recrystallized from ethanol and dried in a vacuum oven at 70°C for 24 h to obtain the final product TFMP.

[0014] In step 2, TFMP is dissolved in chloroform to obtain a 10% (w / w) solution A, and flexible polyetheramine and rigid diaminodiphenyl disulfide are dissolved in chloroform to obtain an amine solution B with a 10% (w / w) amine content. The TFMP contains an aldehyde group, and the molar ratio of the aldehyde group to the amino group in the two diamines is 1:1.

[0015] When preparing polyimide films with different ratios, the molar ratio of flexible polyetheramine and rigid diaminodiphenyl disulfide can be controlled as 1-2:0-2, such as 1:0, 2:1, 1:1, or 1:2.

[0016] In step 2, the flexible polyetheramine is selected from one of D230, D400, and D2000; the rigid diaminodiphenyl disulfide is selected from one of 4,4′-diaminodiphenyl disulfide and 2,2′-diaminodiphenyl disulfide.

[0017] In step 3, the mixed solution obtained by mixing solution A and solution B is stirred at 50°C for 30 seconds and then poured into a mold. The solvent is evaporated at room temperature for 2 hours to set the shape, and then the solvent is dried in an oven at 50°C for another 2 hours to obtain a pretreated polyimide film.

[0018] In step 4, the hot pressing conditions are: hot pressing at 150℃ and 18 MPa for 5 min, of which 1 min is for removing air bubbles and 4 min is for hot pressing.

[0019] The beneficial effects of this invention are reflected in:

[0020] Compared with existing technologies and literature reports, the preparation method and application of a bio-based polyimide film disclosed in this invention have the following advantages:

[0021] (1) The bio-based raw material vanillin is inexpensive and the synthesis process is simple and easy to operate;

[0022] (2) The prepared polyimide film has good mechanical properties and transparency;

[0023] (3) The double dynamic bonds in the structure endow the material with good reprocessing, degradability and recyclability;

[0024] (4) P and N elements play a good synergistic role in flame retardancy, and the prepared polyimide film exhibits excellent thermal stability and flame retardancy.

[0025] (5) The prepared polyimide film has excellent overall performance. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the bio-based polyimide film synthesis process in Example 1.

[0027] Figure 2 Characterization of TFMP synthesis in Example 1. 1H NMR spectroscopy showed that the reaction between vanillin and phosphorus oxychloride had an integrated area ratio of 1:1:2:3. Phosphorus NMR spectroscopy indicated a relatively complete reaction, with only a single peak. Infrared spectroscopy showed a peak at 1700 cm⁻¹. -1 The characteristic peak at 1280 cm⁻¹ belongs to C=O. -1 The characteristic peak at 1025 cm⁻¹ belongs to P=O. -1 The characteristic peak at [location] corresponds to PO. NMR and IR results confirm the successful preparation of TFMP.

[0028] Figure 3 The light transmittance of the prepared film indicates that the material has good light transmittance.

[0029] Figure 4 To prepare a demonstration image of the film after it has been shredded and reprocessed, the film prepared on the surface exhibits good reprocessing properties.

[0030] Figure 5 (a) is a bar chart showing the mechanical properties of the prepared film, indicating that the material has good mechanical properties; (b) is a bar chart showing the mechanical properties of the prepared film after shearing and reprocessing, indicating that the material has good reprocessing performance and less mechanical loss.

[0031] Figure 6 The rapid degradation process of the prepared film in a 1 M HCl: THF = 2:8 (v:v) mixed solution was demonstrated, indicating that the prepared film has the characteristic of rapid degradation.

[0032] Figure 7 The NMR of the TFMP monomer recovered from degradation in a 1 M HCl: THF = 2:8 (v:v) mixed solution for the preparation of the thin film was compared with that of the prepared TFMP monomer.

[0033] Figure 8 (a) is a digital photograph showing the bio-based polyimide prepared in Example 1 achieving a UL-94 test level of V1; (b) is a digital photograph showing the bio-based polyimide prepared in Example 2 achieving a UL-94 test level of V1; (c) is a digital photograph showing the bio-based polyimide prepared in Example 3 achieving a UL-94 test level of V0; and (d) is a digital photograph showing the bio-based polyimide prepared in Example 4 achieving a UL-94 test level of V0.

[0034] Figure 9 (a) is a SEM image of the char residue after testing with UL-94 of the bio-based polyimide prepared in Example 1; (b) is a SEM image of the char residue after testing with UL-94 of the bio-based polyimide prepared in Example 2; (c) is a SEM image of the char residue after testing with UL-94 of the bio-based polyimide prepared in Example 3; and (d) is a SEM image of the char residue after testing with UL-94 of the bio-based polyimide prepared in Example 4. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. The purpose of this description is to illustrate the content of the present invention more specifically and clearly, rather than to limit the scope of protection of the present invention.

[0036] Example 1:

[0037] 1. First, tris(4-formyl-2-methoxyphenyl) phosphate (TFMP) was synthesized. Vanillin (45.6 g, 0.3 mol) and triethylamine (30.3 g mol, 0.3 mol) were dissolved in 200 mL of ethyl acetate. Phosphorus oxychloride (15.3 g, 0.1 mol) was added dropwise to the above mixture in an ice-water bath. After the addition was complete, the mixture was kept at 0-5°C for 30 min in an ice-water bath, and then stirred at 25°C for 24 h. After the reaction was completed, the mixture was poured into 1000 mL of deionized water, cooled to room temperature, and stirred for another 0.5 h. The solution was removed by filtration to obtain a white solid. The crude product obtained by filtration was recrystallized from ethanol and dried in a vacuum oven at 70°C for 24 h to obtain the final product TFMP.

[0038] 2. Dissolve 2g of the above TFMP product in 18g of CHCl3 solution. Then dissolve 1.38g of polyetheramine D230 in 13g of CHCl3 solution. The molar ratio of aldehyde to amino groups is 1:1.

[0039] 3. Mix the two CHCl3 solutions thoroughly, stir at 50°C for 30 seconds, pour into a mold, allow the solvent to evaporate at room temperature for 2 hours to set, and continue drying the solvent in a 50°C oven for 2 hours to obtain the pretreated polyimide film.

[0040] 4. The pretreated polyimide film was hot-pressed at 150℃ and 18 MPa for 5 min, including 1 min to remove air bubbles and 4 min for hot pressing, to obtain the final bio-based polyimide film TFMP-D230-1. Its structure contains a large amount of flexible chain polyetheramine D230. The prepared TFMP-D230-1 exhibits good toughness and can degrade in a short time of 4 min.

[0041] Figure 1 This is a schematic diagram of the bio-based polyimide film prepared in a specific embodiment;

[0042] Figure 2 The TFMP monomer's hydrogen NMR spectrum, carbon NMR spectrum, phosphorus NMR spectrum, and infrared characterization are used in the specific embodiments.

[0043] Figure 3 This is a demonstration of the light transmittance properties of the bio-based polyimide film prepared in a specific embodiment;

[0044] Figure 4 This is a demonstration of the reprocessing properties of the bio-based polyimide film prepared in a specific embodiment;

[0045] Figure 5 The mechanical properties of the bio-based polyimide film prepared in the specific embodiments and its mechanical properties after reprocessing are shown.

[0046] Figure 6 This is a demonstration of the degradation performance of the bio-based polyimide film prepared in a specific embodiment;

[0047] Figure 8 (a) is a digital photograph showing that the bio-based polyimide prepared in Example 1 achieved a UL-94 test level of V1.

[0048] Figure 9 (a) is a SEM image of the carbon slag after testing with the bio-based polyimide UL-94 prepared in Example 1.

[0049] Example 2:

[0050] 1. First, tris(4-formyl-2-methoxyphenyl) phosphate (TFMP) was synthesized.

[0051] 2. Dissolve 2g of the above TFMP product in 20g of CHCl3 solution. Then dissolve 0.92g of polyetheramine D230 and 0.496g of 4,4′-diaminodiphenyl disulfide in 13g of CHCl3 solution. The molar ratio of aldehyde to amino groups is 1:1.

[0052] 3. Mix the two CHCl3 solutions thoroughly, stir at 50°C for 30 seconds, pour into a mold, allow the solvent to evaporate at room temperature for 2 hours to set, and continue drying the solvent in a 50°C oven for 2 hours to obtain the pretreated polyimide film.

[0053] 4. The pretreated polyimide film was hot-pressed at 150℃ and 18 MPa for 5 min, including 1 min for removing air bubbles and 4 min for hot pressing, to obtain the final bio-based polyimide film TFMP-APDS-2. Its structure shows a decrease in the content of flexible chain polyetheramine D230 and an increase in the content of rigid chain segment 4,4′-diaminodiphenyl disulfide. The rigidity of the prepared TFMP-APDS-2 film gradually increases, while its toughness decreases, but it can still degrade in a relatively short time of 7 min.

[0054] Figure 8 (b) is a digital photograph showing that the bio-based polyimide prepared in Example 2 achieved a V1 level in the UL-94 test;

[0055] Figure 9 (b) is a SEM image of the carbon slag after testing with the bio-based polyimide UL-94 prepared in Example 2.

[0056] Example 3:

[0057] 1. First, tris(4-formyl-2-methoxyphenyl) phosphate (TFMP) was synthesized.

[0058] 2. Dissolve 2g of the above TFMP product in 18g of CHCl3 solution. Then dissolve 0.69g of polyetheramine D230 and 0.744g of 4,4′-diaminodiphenyl disulfide in 13g of CHCl3 solution. The molar ratio of aldehyde to amino groups is 1:1.

[0059] 3. Mix the two CHCl3 solutions thoroughly, stir at 50°C for 30 seconds, pour into a mold, allow the solvent to evaporate at room temperature for 2 hours to set, and continue drying the solvent in a 50°C oven for 2 hours to obtain the pretreated polyimide film.

[0060] 4. The pretreated polyimide film was hot-pressed at 150℃ and 18 MPa for 5 min, including 1 min for bubble removal and 4 min for hot pressing, to obtain the final bio-based polyimide film TFMP-APDS-3. In its structure, the content of flexible chain polyetheramine D230 was further reduced, while the content of rigid chain segment 4,4′-diaminodiphenyl disulfide was further increased. The prepared TFMP APDS-3 film showed increased tensile strength but decreased toughness. It exhibited good degradation performance, still degrading in a relatively short time of 7 min.

[0061] Figure 7 Comparison of the 1H NMR spectra of the TFMP monomer after degradation and recycling of the bio-based polyimide film prepared in Example 3 and the prepared TFMP monomer.

[0062] Figure 8Image (c) shows a digital photograph of the bio-based polyimide prepared in Example 3, which achieved a V0 level in the UL-94 test.

[0063] Figure 9 Image (c) is a SEM image of the carbon slag after testing with the bio-based polyimide UL-94 prepared in Example 3.

[0064] Example 4:

[0065] 1. First, tris(4-formyl-2-methoxyphenyl) phosphate (TFMP) was synthesized.

[0066] 2. Dissolve 2g of the above TFMP product in 18g of CHCl3 solution, and then dissolve 0.69g of polyetheramine D230 and 0.744g of 4,4′-diaminodiphenyl disulfide in 13g of CHCl3 solution. The molar ratio of aldehyde to amino groups is 1:1.

[0067] 3. Mix the two CHCl3 solutions thoroughly, stir at 50°C for 30 seconds, pour into a mold, allow the solvent to evaporate at room temperature for 2 hours to set, and continue drying the solvent in a 50°C oven for 2 hours to obtain the pretreated polyimide film.

[0068] 4. The pretreated polyimide film was hot-pressed at 150℃ and 18 MPa for 5 min, including 1 min for bubble removal and 4 min for hot pressing, to obtain the final bio-based polyimide film TFMP-APDS-4. Its structure has a low content of flexible chain polyetheramine D230 and a high content of rigid chain segment 4,4′-diaminodiphenyl disulfide. The prepared TFMP-APDS-4 film exhibits good tensile strength, but its degradation performance remains essentially unchanged, still degrading in a relatively short time of 7 min.

[0069] Figure 8 (d) is a digital photograph showing that the bio-based polyimide prepared in Example 4 achieved a V0 level in the UL-94 test;

[0070] Figure 9 Image d shows a SEM image of the carbon slag after testing with the bio-based polyimide UL-94 prepared in Example 4.

[0071] In addition, the LOI and UL-94 test results of different bio-based polyimide film samples are shown in Table 1.

[0072]

Claims

1. A method for preparing a flame-retardant, recyclable polyimide film based on a dual dynamic bond crosslinking structure, characterized in that... Includes the following steps: Step 1: First, synthesize tris(4-formyl-2-methoxyphenyl) phosphate TFMP; Step 2: Dissolve a certain mass of TFMP in a chloroform solution to obtain solution A, and dissolve a certain amount of flexible polyetheramine and rigid diaminodiphenyl disulfide in a chloroform solution to obtain solution B; Step 3: Mix solution A and solution B and stir to disperse evenly. Transfer the mixture into a PTFE mold, dry and shape it at room temperature, and then place it in a forced-air oven to dry. After drying, a pretreated polyimide film is obtained. Step 4: The pretreated polyimide film obtained in Step 3 is hot-pressed in a flat vulcanizing machine to obtain the final bio-based polyimide film; In step 2, the flexible polyetheramine is selected from one of D230, D400, and D2000; the rigid diaminodiphenyl disulfide is selected from one of 4,4′-diaminodiphenyl disulfide and 2,2′-diaminodiphenyl disulfide.

2. The preparation method according to claim 1, characterized in that: In step 1, the tris(4-formyl-2-methoxyphenyl) phosphate is prepared by reacting phosphorus oxychloride and vanillin.

3. The preparation method according to claim 2, characterized in that: First, vanillin and triethylamine were dissolved in ethyl acetate. Phosphorus oxychloride was added dropwise to the mixture in an ice-water bath. After the addition was complete, the mixture was kept at 0-5°C for 30 min in an ice-water bath, and then stirred at 25°C for 24 h. After the reaction was complete, the mixture was poured into deionized water, cooled to room temperature, and stirred for 0.5 h. The solution was removed by filtration to obtain a white solid. The crude product obtained by filtration was recrystallized from ethanol and dried under vacuum to obtain the final product TFMP.

4. The preparation method according to claim 1, characterized in that: In step 2, the TFMP is dissolved in chloroform to obtain a solution A with a mass percentage of 10%, and the flexible polyetheramine and rigid diaminodiphenyl disulfide are dissolved in chloroform to obtain a solution B with a mass percentage of amines of 10%.

5. The preparation method according to claim 4, characterized in that: The molar ratio of aldehyde groups in TFMP to the total amino groups in flexible polyetheramine and rigid diaminodiphenyl disulfide is 1:

1.

6. The preparation method according to claim 1, characterized in that: In step 3, the mixed solution obtained by mixing solution A and solution B is stirred at 50°C for 30 seconds and then poured into a mold. The solvent is evaporated at room temperature for 2 hours to set the shape, and then the solvent is dried in an oven at 50°C for another 2 hours to obtain a pretreated polyimide film.

7. The preparation method according to claim 1, characterized in that: In step 4, the hot pressing conditions are: hot pressing at 150℃ and 18 MPa for 5 min, of which 1 min is for removing air bubbles and 4 min is for hot pressing.

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