A method for recycling polyimide based on dry controllable micro-degradation technology

Abstract

The application discloses a method for recycling polyimide based on a dry controllable micro-degradation technology, and belongs to the field of waste high polymer material recycling and resource utilization. The method first adds a swelling aid and a degradation agent to the polyimide to cause chemical controllable micro-degradation, and then is dried and crushed to obtain polyimide micro-degradation powder; the micro-degradation powder is directly heat imidized to prepare polyimide molding powder, or is added into an organic solvent or a polymer solution to form a dispersion liquid. The obtained polyimide molding powder has excellent thermal stability, the polyimide composite film has similar mechanical properties, thermal stability and dielectric properties to pure polyimide, and recycling of highly insoluble and infusible polyimide can be realized. The process flow of the application is simple, the cost is low, and the application is environment-friendly, which brings great economic and social benefits in solving the problems of environmental pollution and resource waste caused by polyimide offcuts and waste, and provides a brand-new technical scheme for high-value-added recycling of polyimide.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer materials, and particularly relates to a high-efficiency recovery method of polyimide. BACKGROUND

[0002] Polyimide materials are widely used in aerospace, rail transportation and microelectronics industries due to their good mechanical properties, excellent thermal stability, outstanding chemical resistance, strong flame retardant performance and excellent dielectric properties. With the booming development of these industries, the demand for polyimide is also increasing. However, a lot of waste materials will inevitably be produced during the production, slitting and use of polyimide. If only incineration or landfill treatment is used, it will cause waste of resources and environmental pollution. Therefore, from the perspective of environmental protection and development of circular economy, the recycling of polyimide is worth paying attention to.

[0003] At present, the common recovery method of polyimide materials is complete hydrolysis method, that is, polyimide is completely hydrolyzed under strong alkaline conditions to obtain raw monomers for recovery. Although the decomposition rate of waste materials by this method is as high as 100%, the process is complex, the monomer recovery rate is low, the energy consumption and cost of recovery are high, and a large amount of industrial wastewater will be produced to cause secondary pollution. In addition, the recovery methods of polyimide also include melting method, filler method, etc., but the problems of high energy consumption and high cost cannot be avoided, and the equipment requirements are high and the conditions are harsh, which makes it difficult to be applied to industrial practice on a large scale.

[0004] Chinese patent CN 1324789 A proposes to heat and hydrolyze polyimide in an aqueous alkali solution, recover water-insoluble diamine, wash and recrystallize the obtained crude diamine to recover monomer-grade diamine raw material; then treat the filtrate with acid to recover tetracarboxylic acid, wash the tetracarboxylic acid with water to remove salt, and then heat or co-heat with acetic anhydride to obtain monomer-grade tetracarboxylic dianhydride. This method has many steps, long cycle, complex process, and needs to use a large amount of acid and alkali solution, and the monomer recovery rate is low, which is not friendly to the environment and has low product added value.

[0005] Chinese patent CN 109971115 A discloses a physical method for recycling polyimide film, that is, under liquid nitrogen freezing conditions, a variety of pulverizers and high-energy planetary ball mills are used in combination to pulverize the extremely difficult-to-pulverize polyimide film at low temperature and high speed, and polyimide powder with small particle size is obtained. Although the process of this invention is simple and environmentally friendly, the equipment requirements are extremely high, and the extremely low-temperature environment is relatively harsh, which increases the energy consumption and cost.

[0006] In order to realize the high value-added green recycling of polyimide, the polyimide is made to be extremely easy to be crushed and processed in a controllable range by chemical method through chemical micro-degradation embrittlement. Then the powder obtained by micro-degradation is directly heat imidized to obtain polyimide molding powder. The powder can also be added into an organic solvent or a polymer solution to form a dispersion liquid, for example, returned to a polyamide acid precursor solution, and then imidized to obtain a polyimide composite film. The obtained polyimide molding powder has excellent thermal stability, and the obtained polyimide composite film has similar mechanical properties, thermal stability and dielectric properties to pure polyimide, and can realize recycling of highly insoluble and infusible polyimide. SUMMARY

[0007] The present application mainly aims at the problems of high cost, high energy consumption and environmental unfriendliness in the existing polyimide recycling technology, and provides a simple and efficient polyimide recycling method, which aims to solve the problems of resource waste and environmental pollution in the field of polyimide recycling and develop circular economy.

[0008] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0009] A method for recycling polyimide based on dry method controllable micro-degradation technology, wherein the dry method micro-degradation technology is that polyimide waste is reacted with a degradation agent and a swelling aid at 80-350 DEG C and 0.1-5 MPa for 0.5-90 h.

[0010] The method for recycling polyimide based on the dry method controllable micro-degradation technology comprises the following specific steps:

[0011] 1) polyimide waste is reacted with a degradation agent and a swelling aid in a sealed container at 80 DEG C and 5 MPa for 90 h to obtain polyimide micro-degradation products;

[0012] 2) the polyimide micro-degradation products are dried at 60-120 DEG C for 4-12 h and then ground to obtain polyimide micro-degradation powder;

[0013] 3) the polyimide micro-degradation powder is added into an organic solvent and stirred at 0-90 DEG C for 0.1-12 h to obtain a dispersion liquid;

[0014] 4) the dispersion liquid is mixed with a polyamide acid precursor solution at -10-50 DEG C and stirred for 0.1-20 h to form a homogeneous solution;

[0015] 5) the homogeneous solution is cast and dried to obtain a solid film;

[0016] 6) the solid film is heat imidized at 150-350 DEG C to obtain a polyimide composite film.

[0017] The polyimide is selected from one or more of polyimide fiber, polyimide film, polyimide photosensitive material, and polyimide composite material.

[0018] The volume ratio of the degradation agent to the swelling aid is 1:1-50.

[0019] The weight ratio of the polyimide micro-degradation powder to the organic solvent is 1:3-1:40.

[0020] The weight ratio of the polyimide micro-degradation powder to the polyamide acid is 1:8-1:100.

[0021] The degradation agent is selected from one or more of formic acid, acetic acid, hydrochloric acid, triethylamine, tetramethylammonium hydroxide, ammonia, methanol, ethanol, propanol, butanol, ethylene glycol, and deionized water.

[0022] The swelling aid is selected from one or more of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, dimethyl sulfoxide, hexamethylphosphoramide, acetonitrile, 1,3-dimethyl-2-imidazolidinone, and other aprotic polar solvents.

[0023] The present application has the following advantages: Different from the common recycling method of completely hydrolyzing monomer raw materials, the present application provides a method for recycling polyimide based on dry controllable micro-degradation technology, which has a simple process flow, small reagent consumption, no waste liquid generation, high efficiency, low cost, and is friendly to the environment, can solve the environmental pollution and resource waste problems caused by the difficulty in recycling polyimide, and is expected to bring huge economic and social benefits, and can realize high-value recycling of polyimide. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The figures are the physical pictures of the initial polyimide film, polyimide fiber, and polyimide micro-degradation powder, and the scanning electron microscope pictures of the polyimide micro-degradation powder;

[0025] Figure 2 The figures are the FT-IR spectra of the polyimide micro-degradation powder before and after thermal imidization;

[0026] Figure 3 The figures are the thermogravimetric curves of the initial polyimide film and the polyimide molding powder in Example 6;

[0027] Figure 4 The figures are the tensile property diagrams of the pure polyimide film and the polyimide composite film in Examples 3 and 4. DETAILED DESCRIPTION

[0028] In order to make the above objectives, characteristics and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below with specific examples.

[0029] Example 1

[0030] A method for recycling polyimide based on dry controllable micro-degradation technology, comprising the following steps:

[0031] (1) 2.0 g of polyimide film, 0.28 mL of formic acid, 14 mL of tetrahydrofuran are put into a 50 mL pressure reactor, and the polyimide is subjected to chemical controllable micro-degradation at 80°C and 5 MPa for 90 h;

[0032] (2) The polyimide micro-degradation product is dried at 80°C for 4 h and then ground to obtain polyimide micro-degradation powder;

[0033] (3) 1.0 g of the polyimide micro-degradation powder obtained in step (2) is added to 3.0 g of N,N-dimethylformamide, and the mixture is stirred at 25°C for 3 h to obtain a dispersion;

[0034] (4) The dispersion of the polyimide micro-degradation powder is mixed with 28.57 g of a polyamic acid precursor solution with a solid content of 28% at 25°C and stirred for 5 h to form a homogeneous solution;

[0035] (5) The homogeneous solution is cast and the solvent is dried at 60°C for 12 h to obtain a solid film;

[0036] (6) The solid film is subjected to thermal imidization treatment at 300°C for 4 h to obtain a polyimide composite film.

[0037] Example 2

[0038] A method for recycling polyimide based on dry controllable micro-degradation technology, comprising the following steps:

[0039] (1) 0.2 g of polyimide film, 0.19 mL of deionized water, 0.01 mL of acetic acid, 0.2 mL of N,N-dimethylformamide are put into a 10 mL pressure reactor, and the polyimide is subjected to chemical controllable micro-degradation at 350°C and 1 MPa for 0.5 h;

[0040] (2) The polyimide micro-degradation product is vacuum dried at 70°C for 4 h and then ground to obtain polyimide micro-degradation powder;

[0041] (3) 0.1 g of the polyimide micro-degradation powder obtained in step (2) is added to 4.0 g of N,N-dimethylacetamide, and the mixture is stirred at 25°C for 3 h to obtain a dispersion;

[0042] (4) The dispersion solution of the polyimide micro-degradation powder is mixed with 35.71 g of a polyamide acid precursor solution with a solid content of 28% at 25°C for 5 h to form a homogeneous solution;

[0043] (5) The homogeneous solution is cast and placed at 60°C for 12 h to dry the solvent to obtain a solid thin film;

[0044] (6) The solid thin film is subjected to thermal imidization treatment at 300°C for 4 h to obtain a polyimide composite thin film.

[0045] Example 3

[0046] A method for recycling polyimide based on dry controllable micro-degradation technology, comprising the following steps:

[0047] (1) 2.0 g of polyimide film, 0.1 mL of methanol, 0.05 g of tetramethylammonium hydroxide, 0.5 mL of N,N-dimethylacetamide and 0.5 mL of hexamethylphosphoramide are put into a 50 mL pressure reactor, and the polyimide is subjected to chemical controllable micro-degradation at 180°C and 0.5 MPa for 24 h;

[0048] (2) The polyimide micro-degradation product is vacuum dried at 70°C for 5 h and then ground to obtain polyimide micro-degradation powder;

[0049] (3) 0.2 g of the polyimide micro-degradation powder obtained in step (2) is added to 2.32 g of N-methylpyrrolidone, and stirred at 25°C for 3 h to obtain a dispersion solution;

[0050] (4) The dispersion solution of the polyimide micro-degradation powder is mixed with 14.28 g of a polyamide acid precursor solution with a solid content of 28% at 25°C for 5 h to form a homogeneous solution;

[0051] (5) The homogeneous solution is cast and placed at 60°C for 12 h to dry the solvent to obtain a solid thin film;

[0052] (6) The solid thin film is subjected to thermal imidization treatment at 300°C for 4 h to obtain a polyimide composite thin film.

[0053] Example 4

[0054] A method for recycling polyimide based on dry controllable micro-degradation technology, comprising the following steps:

[0055] (1) 500 g of polyimide film, 12.5 mL of deionized water, 7.5 mL of triethylamine, 75 mL of N-methylpyrrolidone and 25 mL of acetonitrile are put into a 10 L pressure reactor, and the polyimide is subjected to chemical controllable micro-degradation at 200°C and 0.8 MPa for 6 h;

[0056] (2) The polyimide micro-degradation product is vacuum dried at 80°C for 12h and then crushed to obtain polyimide micro-degradation powder;

[0057] (3) 2g of the polyimide micro-degradation powder obtained in step (2) is added to 23.2g of dimethyl sulfoxide and stirred at 25°C for 3h to obtain a dispersion;

[0058] (4) The dispersion of the polyimide micro-degradation powder is mixed with 142.8g of a polyamide acid precursor solution with a solid content of 28% at 25°C and stirred for 5h to form a homogeneous solution;

[0059] (5) The homogeneous solution is cast and dried at 60°C for 12h to obtain a solid film;

[0060] (6) The solid film is heat imidized at 300°C for 4h to obtain a polyimide composite film.

[0061] Example 5

[0062] A method for recycling polyimide based on dry controllable micro-degradation technology, comprising the following steps:

[0063] (1) 2.0g of polyimide film, 1.0mL of concentrated hydrochloric acid, and 1.0mL of N-ethyl pyrrolidone are put into a 50mL pressure reactor, and the polyimide is subjected to chemical controllable micro-degradation at 120°C and 1MPa for 15h;

[0064] (2) The polyimide micro-degradation product is vacuum dried at 90°C for 8h and then crushed to obtain polyimide micro-degradation powder;

[0065] (3) The polyimide micro-degradation powder is heat imidized at 300°C for 4h to obtain polyimide molding powder;

[0066] Example 6

[0067] A method for recycling polyimide based on dry controllable micro-degradation technology, comprising the following steps:

[0068] (1) 1kg of polyimide film, 25mL of ethanol, 25mL of propanol, and 300mL of N-methyl pyrrolidone are put into a 20L pressure reactor, and the polyimide is subjected to chemical controllable micro-degradation at 300°C and 0.5MPa for 14h;

[0069] (2) The polyimide micro-degradation product is vacuum dried at 80°C for 5h and then crushed to obtain polyimide micro-degradation powder;

[0070] (3) The polyimide micro-degradation powder is heat imidized at 300°C for 4h to obtain polyimide molding powder;

[0071] Example 7

[0072] A method for recycling polyimide based on dry controllable micro-degradation technology, comprising the following steps:

[0073] (1) 2.0g of polyimide film, 0.1mL of formic acid, 0.05mL of butanol, 0.05mL of deionized water, 0.5mL of N-methyl pyrrolidone and 0.5mL of 1,3-dimethyl-2-imidazolidinone are put into a 50mL pressure reactor, and the polyimide is subjected to chemical controllable micro-degradation at 200°C and 0.5MPa for 10h;

[0074] (2) The polyimide micro-degradation product is dried at 120°C for 8h, and then crushed to obtain polyimide micro-degradation powder;

[0075] (3) The polyimide micro-degradation powder is heat imidized at 300°C for 4h to obtain polyimide molding powder;

[0076] Example 8

[0077] A method for recycling polyimide based on dry controllable micro-degradation technology, comprising the following steps:

[0078] (1) 2.0g of polyimide fiber, 0.25mL of 25% ammonia water, 0.5mL of dimethyl sulfoxide and 0.5mL of N,N-dimethylacetamide are put into a 50mL pressure reactor, and the polyimide is subjected to chemical controllable micro-degradation at 200°C and 0.5MPa for 8h;

[0079] (2) The polyimide micro-degradation product is vacuum dried at 80°C for 8h, and then crushed to obtain polyimide micro-degradation powder;

[0080] (3) The polyimide micro-degradation powder is heat imidized at 300°C for 4h to obtain polyimide molding powder;

[0081] Example 9

[0082] A method for recycling polyimide based on dry controllable micro-degradation technology, comprising the following steps:

[0083] (1) Put 2.0 g of polyimide fiber, 0.5 mL of ethylene glycol, 0.1 mL of triethylamine, 0.5 mL of tetrahydrofuran, 0.25 mL of hexamethylphosphoramide and 0.25 mL of N, N-dimethylacetamide into a 50 mL autoclave, and react at 250℃, 0.8 MPa for 16 h to make the polyimide undergo chemical controllable micro-degradation;

[0084] (2) After vacuum drying the polyimide micro-degradation product at 80℃ for 8 h, crush to obtain polyimide micro-degradation powder;

[0085] (3) After heat imidization treatment of the polyimide micro-degradation powder at 300℃ for 4 h, obtain polyimide molding powder;

[0086] Comparative Example 1

[0087] A preparation method of a pure polyimide solid film, comprising the following steps:

[0088] (1) Cast a synthesized 12 g polyamide acid precursor solution with a solid content of 28%, and dry the solvent at 60℃ for 12 h to obtain a solid film;

[0089] (2) After heat imidization treatment of the solid film at 300℃ for 4 h, obtain a pure polyimide film.

[0090] The samples obtained in Examples 3 and 4 and Comparative Example 1 are respectively subjected to mechanical property, temperature resistance and dielectric property tests, and the results are shown in Table 1.

[0091] Table 1 is the performance test results of the samples obtained in Examples 3 and 4 and Comparative Example 1

[0092] Performance index Example 3 Example 4 Comparative Example 1 Tensile strength (MPa) 29.71 28.45 25.52 Young's modulus (GPa) 3.546 3.748 3.051 Thermal decomposition temperature (°C) 538 543 574 Carbon residue at 1000°C (%) 56.1 56.8 52.6 Dielectric constant (10 MHz) 3.37 3.33 3.42

[0093] By comparing the mechanical properties and temperature resistance of the examples and the comparative example, after adding the polyimide micro-degradation powder, the tensile strength of the obtained polyimide composite film is slightly improved, the Young's modulus is increased, the carbon residue rate of the polyimide composite film at 1000℃ is increased, the thermal decomposition temperature is still above 500℃, and the dielectric constant of the polyimide composite film is almost unchanged compared with the pure polyimide film. It shows that the polyimide composite film maintains the mechanical strength while the high temperature resistance and dielectric properties are still good.

[0094] The above only describes some embodiments of the present application, and does not limit the patent scope of the present application. Any modification, equivalent replacement or direct or indirect use in other related technical fields based on the content of the present application shall be included in the protection scope of the present application.

Claims

1. A method for recycling polyimide based on a dry controllable micro-degradation technology, characterized in that: The dry micro-degradation technique is that the polyimide waste is reacted with a degradation agent and a swelling aid at 80-350 DEG C, 0.1-5 MPa for 0.5-90 h; the specific steps include: 1) the polyimide waste is reacted with a degradation agent and a swelling aid at 80-350 DEG C, 0.1-5 MPa for 0.5-90 h to obtain a polyimide micro-degradation product; 2) the polyimide micro-degradation product is dried at 60-120 DEG C for 4-12 h and then ground to obtain a polyimide micro-degradation powder; 3) the polyimide micro-degradation powder is added to an organic solvent and stirred at 0-90 DEG C for 0.1-12 h to obtain a dispersion; 4) the dispersion is mixed with a polyamide acid precursor solution at -10-50 DEG C and stirred for 0.1-20 h to form a homogeneous solution; 5) the homogeneous solution is cast and dried to obtain a solid film; 6) the solid film is subjected to thermal imidization treatment at 150-350 DEG C to obtain a polyimide composite film; 7) the polyimide micro-degradation powder is subjected to thermal imidization treatment at 150-350 DEG C to obtain a polyimide molding powder.

2. The method for recycling polyimide by dry controllable micro-degradation technology according to claim 1, characterized in that, The polyimide is selected from one or more of polyimide fibers, polyimide films, polyimide photosensitive materials and polyimide composites.

3. The method for recycling polyimide by dry controllable micro-degradation technology according to claim 1, characterized in that, The volume ratio of the degradation agent to the swelling aid is 1:1-50.

4. The method for recycling polyimide by dry controllable micro-degradation technology according to claim 1, characterized in that, The molar ratio of the degradation agent to the polyimide repeating unit is 1:0.1-40.

5. The method for recycling polyimide by dry controllable micro-degradation technology according to claim 1, characterized in that, The weight ratio of the polyimide micro-degradation powder to the organic solvent is 1:3-1:

40.

6. The method for recycling polyimide by dry controllable micro-degradation technology according to claim 1, characterized in that, The weight ratio of the polyimide micro-degradation powder to the polyamide acid is 1:8-1:

100.

7. The method for recycling polyimide using dry-process controlled micro-degradation technology according to claim 1, characterized in that, The degradation agent is selected from one or more of formic acid, acetic acid, hydrochloric acid, triethylamine, tetramethylammonium hydroxide, ammonia, methanol, ethanol, propanol, butanol, ethylene glycol and deionized water.

8. The method for recycling polyimide using dry-process controlled micro-degradation technology according to claim 1, characterized in that, The swelling aid is selected from one or more of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, dimethyl sulfoxide, hexamethylphosphoramide, acetonitrile and 1,3-dimethyl-2-imidazolidinone.

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