Method for breaking PI film through one-step method and method for recycling waste polyimide

Abstract

The invention provides a method for breaking a PI film by a one-step method and a method for recovering waste polyimide, and belongs to the technical field of solid waste recovery. The plasma ball milling technology is creatively adopted, the polyimide film raw material with the width of 5-50 mm and the polyimide coarse powder can be crushed into the micron-sized polyimide micro powder through a one-step method by adjusting ball milling parameters, and recycling of the polyimide film waste and the polyimide coarse powder waste is achieved. The plasma ball milling technology is applied to the high polymer material crushing and refining direction for the first time, the problem that the polyimide film is difficult to crush effectively by the traditional crushing technology (such as a common shear type crusher) is solved, and the method is simple in one-step crushing process, low in cost and environment-friendly; and a brand new thought is provided for crushing and recycling the polyimide waste.

Description

Technical Field

[0001] This invention relates to the field of solid waste recycling technology, and more specifically, to a one-step method for crushing waste polyimide films into micron-sized powder. Background Technology

[0002] Polyimide (PI) is a high-performance specialty engineering plastic. Due to its excellent high-temperature resistance, mechanical properties, electrical insulation, chemical stability, and self-lubricating properties, it exhibits a wide range of applications in various high-tech fields such as electronics, aerospace, automotive, composite materials, sensors, energy, and medical. The production process of polyimide films generates a large amount of waste material annually. Currently, incineration, landfill, and hydrolysis are used to treat PI waste. Incineration and landfill cause environmental pollution and resource waste. Disposing of PI waste through incineration or landfill will lead to serious environmental and economic problems.

[0003] Currently, the main method for treating polyimide film waste through hydrolysis involves treating the film with alkaline and acidic solutions to recover high-purity monomers, which are then reused as raw materials for polyimide synthesis. This type of recycling process suffers from problems such as long processing cycles, multiple stages, high energy consumption, complex processes, and the need for large quantities of alkaline and acidic solutions, resulting in high costs and environmental pollution from the wastewater.

[0004] Polyimide films possess extremely high mechanical strength, with very high tensile strength and modulus. This means that significant mechanical force is required to break them during the pulverization process. Traditional pulverizing equipment (such as ordinary shear pulverizers) struggles to pulverize polyimide films to the micron level. Polyimide films not only have high strength but also good toughness. They deform rather than break directly under external force, making the pulverization process even more difficult. For example, the film may become entangled in the blades or shafts of the equipment during pulverization, leading to equipment malfunction or blockage.

[0005] The particle size of pulverized polyimide films needs to be strictly controlled to meet the requirements of subsequent applications. For example, as fillers used in composite materials, particle sizes typically need to be in the micrometer range. However, due to the toughness and strength of the film, it is difficult to achieve the ideal size through a single pulverization, which may require multiple pulverization and sieving processes, increasing process complexity and cost.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a one-step method for crushing polyimide (PI) films and recycling waste polyimide. This one-step method can crush polyimide film raw materials with a width of 5-50 mm and coarse polyimide powder into micron-sized polyimide powder, enabling the recycling and reuse of waste polyimide films and coarse polyimide powder. The one-step crushing process is simple, low-cost, and environmentally friendly, providing a completely new approach to the crushing and recycling of polyimide waste.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A method for breaking PI films in one step includes the following steps: Step S1, Raw material pretreatment: The PI film is cut into fragments; Step S2, Plasma ball milling: The fragments of the PI film are placed in a ball mill jar and crushed using plasma external field assisted ball milling to obtain PI micron powder.

[0009] Further, in step S1, the PI film is cut into fragments with a width of less than 1 cm and a length of less than 5 cm.

[0010] Furthermore, in step S2, the ball-to-material ratio for ion milling is 10~60:1.

[0011] Furthermore, in step S2, the plasma ball milling discharge intensity is 8.0~10.0 kHz.

[0012] Furthermore, in step S2, the plasma discharge time is 1~8h.

[0013] Furthermore, in step S2, the plasma ball milling is carried out under a protective atmosphere, which is an argon atmosphere, a nitrogen atmosphere, or a vacuum.

[0014] A method for recycling waste polyimide includes the following steps: Step A: Raw material pretreatment; Step B, Plasma ball milling treatment: The pretreated raw material is placed in a ball mill jar and crushed using plasma external field assisted ball milling to obtain PI micron powder; Step C, sieving: The processed PI micron powder is sieved, and the sieved powder is recycled as filler for composite materials.

[0015] Furthermore, the method for pre-treating raw materials in step A is to divide the recycled waste PI film into fragments, or to recycle the waste PI coarse powder.

[0016] Further, in step A, the recycled waste PI film is cut into fragments with a width of less than 1 cm and a length of less than 5 cm.

[0017] Furthermore, in step B, the ball-to-material ratio in the ion mill is 10~60:1.

[0018] Furthermore, in step B, the plasma ball milling discharge intensity is 8.0~10.0 kHz.

[0019] Furthermore, in step B, the plasma discharge time is 1~8h.

[0020] Furthermore, in step B, the plasma ball milling is carried out under a protective atmosphere, which may be an argon atmosphere, a nitrogen atmosphere, or a vacuum.

[0021] Furthermore, in step C, a 30-100 mesh sieve is used for sieving.

[0022] Furthermore, the powder screened off in step C is recycled as filler for the composite material. Large-diameter powder is removed by sieving and is processed simultaneously with the next batch of recycled waste polyimide.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention provides a one-step method for crushing PI films and a method for recycling waste polyimide, which successfully solves the technical problem that mechanical methods cannot quickly and efficiently crush polyimide films into micron-sized powder due to their extremely high mechanical strength and good toughness.

[0024] 2. The one-step method for crushing PI film and recycling waste polyimide of the present invention has the advantages of simple process, good repeatability and suitability for industrial production. It provides a new technical route for the green treatment of polymer recycled materials and has important application value in the fields of electronic materials, composite materials and polymer material recycling.

[0025] 3. The one-step crushing method of PI film of the present invention significantly improves crushing efficiency and reduces particle size: Polyimide film has extremely high mechanical strength and good toughness. Ordinary ball milling is difficult to crush polyimide film to the micron size. Under the same processing conditions, the yield of micron powder obtained by plasma ball milling is 3 times that of other mechanical crushing methods.

[0026] 4. The one-step method for crushing PI film and the method for recycling waste polyimide of the present invention have the following advantages in preparation process: (1) Process integration: micron-sized polyimide powder is prepared in one step by plasma ball milling technology, and the process flow is simple; (2) Strong controllability: the process parameters are adjustable in a wide range, which is suitable for the preparation of polyimide powder with size requirements; (3) Industrialization prospects: low energy consumption, no waste liquid or waste gas is generated, which is suitable for large-scale industrial production.

[0027] 5. The method for recycling waste polyimide according to the present invention can recycle waste polyimide film and waste polyimide coarse powder, and has a wide range of applications. Attached Figure Description

[0028] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 Electron microscopy image (calibrated) of PI micron powder obtained by pulverization in Example 1 of this invention; Figure 2 This is an electron microscope image of PI micron powder obtained by pulverization in Example 1 of the present invention; Figure 3 This is an electron microscope image of PI micron powder obtained by pulverization in Example 2 of the present invention; Figure 4 This is an electron microscope image of PI micron powder obtained by pulverization in Example 3 of the present invention; Figure 5 The image shown is an electron microscope image of PI micron powder obtained by crushing in Comparative Example 1 of this invention. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0031] A one-step method for breaking PI films includes the following steps: Step S1, Raw material pretreatment: The PI film is cut into fragments; Step S2, Plasma ball milling: The fragments of the PI film are placed in a ball mill jar and crushed using plasma external field assisted ball milling to obtain PI micron powder.

[0032] Preferably, in step S1, the PI film is cut into fragments with a width of less than 1 cm and a length of less than 5 cm.

[0033] Preferably, in step S2, the ball-to-material ratio of the plasma ball mill is 10 to 60:1, including but not limited to 10:1, 20:1, 30:1, 40:1, 50:1, and 60:1.

[0034] Preferably, the plasma ball milling discharge intensity in step S2 is 8.0~10.0kHz, including but not limited to 8.0kHz, 8.5kHz, 9.0kHz, 9.5kHz, and 10.0kHz.

[0035] Preferably, the plasma discharge time in step S2 is 1 to 8 hours, including but not limited to 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, and 8 hours.

[0036] Preferably, in step S2, the grinding balls for the plasma ball mill are stainless steel or cemented carbide metal balls.

[0037] Preferably, in step S2, the plasma ball milling is carried out under a protective atmosphere, which is an argon atmosphere, a nitrogen atmosphere, or a vacuum.

[0038] A method for recycling waste polyimide includes the following steps: Step A: Raw material pretreatment; Step B, Plasma ball milling treatment: The pretreated raw material is placed in a ball mill jar and crushed using plasma external field assisted ball milling to obtain PI micron powder; Step C, sieving: The processed PI micron powder is sieved using a 30-100 mesh sieve, and the sieved powder is recycled as a filler for composite materials.

[0039] Preferably, the method for pre-treating raw materials in step A is to divide the recycled waste PI film into fragments or to recycle the waste PI coarse powder.

[0040] Preferably, in step A, the recycled waste PI film is cut into fragments with a width of less than 1 cm and a length of less than 5 cm.

[0041] Preferably, in step B, the ball-to-material ratio of the ion mill is 10 to 60:1, including but not limited to 10:1, 20:1, 30:1, 40:1, 50:1, and 60:1.

[0042] Preferably, the plasma ball milling discharge intensity in step B is 8.0~10.0kHz, including but not limited to 8.0kHz, 8.5kHz, 9.0kHz, 9.5kHz, and 10.0kHz.

[0043] Preferably, the plasma discharge time in step B is 1 to 8 hours, including but not limited to 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, and 8 hours.

[0044] Preferably, in step B, the grinding balls for the plasma ball mill are stainless steel or cemented carbide metal balls.

[0045] Preferably, in step B, the plasma ball milling is carried out under a protective atmosphere, which is an argon atmosphere, a nitrogen atmosphere, or a vacuum.

[0046] Preferably, the powder screened off in step C is recycled as filler for the composite material. Large-diameter powder is removed by sieving. Large-diameter powder refers to a very small amount of powder that cannot pass through the sieve due to incomplete crushing. The large-diameter powder is processed simultaneously with the next batch of new recycled waste polyimide.

[0047] Example 1 A one-step method for breaking PI films includes the following steps: a. Cut the recycled waste PI film into pieces less than 1cm wide and less than 5cm long; b. The material is placed in a ball mill jar and crushed under an argon atmosphere using plasma-assisted ball milling with a ball-to-material ratio of 50:1, a discharge intensity of 10kHz, and a discharge time of 6h to obtain PI micron powder with a particle size range of 4~18μm.

[0048] Example 2 A one-step method for breaking PI films includes the following steps: a. Cut the recycled waste PI film into pieces less than 1cm wide and less than 5cm long; b. The material is placed in a ball mill jar and crushed under an argon atmosphere using plasma-assisted ball milling with a ball-to-material ratio of 50:1, a discharge intensity of 10kHz, and a discharge time of 3h, resulting in PI micron powder with a particle size range of 40~100μm.

[0049] Example 3 A one-step method for breaking PI films includes the following steps: a. Cut the recycled waste PI film into pieces less than 1cm wide and less than 5cm long; b. The material is placed in a ball mill jar and crushed under an argon atmosphere using plasma-assisted ball milling with a ball-to-material ratio of 50:1, a discharge intensity of 10 kHz, and a discharge time of 1 h. The resulting PI micron powder has a particle size range of 50~120 μm.

[0050] Example 4 A one-step method for breaking PI films includes the following steps: a. Cut the recycled waste PI film into pieces less than 1cm wide and less than 5cm long; b. The material is placed in a ball mill jar and crushed under an argon atmosphere using plasma-assisted ball milling with a ball-to-material ratio of 60:1, a discharge intensity of 10 kHz, and a discharge time of 6 h, resulting in PI micron powder with a particle size range of 4~14 μm.

[0051] Example 5 A one-step method for breaking PI films includes the following steps: a. Cut the recycled waste PI film into pieces less than 1cm wide and less than 5cm long; b. The material is placed in a ball mill jar and crushed under an argon atmosphere using plasma-assisted ball milling with a ball-to-material ratio of 50:1, a discharge intensity of 8 kHz, and a discharge time of 6 h, resulting in PI micron powder with a particle size range of 22~44 μm.

[0052] Example 6 A one-step method for breaking PI films includes the following steps: a. Cut the recycled waste PI film into pieces less than 1cm wide and less than 5cm long; b. The material is placed in a ball mill jar and crushed under an argon atmosphere using plasma-assisted ball milling with a ball-to-material ratio of 50:1, a discharge intensity of 9 kHz, and a discharge time of 6 h, resulting in PI micron powder with a particle size range of 18~32 μm.

[0053] Example 7 A one-step method for breaking PI films includes the following steps: a. Cut the recycled waste PI film into pieces less than 1cm wide and less than 5cm long; b. The material is placed in a ball mill jar and crushed under an argon atmosphere using plasma-assisted ball milling with a ball-to-material ratio of 30:1, a discharge intensity of 10kHz, and a discharge time of 6h, resulting in PI micron powder with a particle size range of 28~52μm.

[0054] Example 8 A one-step method for breaking PI films includes the following steps: a. Cut the recycled waste PI film into pieces less than 1cm wide and less than 5cm long; b. The material is placed in a ball mill jar and crushed under an argon atmosphere using plasma-assisted ball milling with a ball-to-material ratio of 10:1, a discharge intensity of 10 kHz, and a discharge time of 6 h. The resulting PI micron powder has a particle size range of 55~120 μm.

[0055] Example 9 A method for recycling waste polyimide includes the following steps: a. Cut the recycled waste PI film into pieces less than 1cm wide and less than 5cm long; b. The material is placed in a ball mill jar and crushed under an argon atmosphere using plasma-assisted ball milling with a ball-to-material ratio of 50:1, a discharge intensity of 10kHz, and a discharge time of 6h to obtain PI micron powder with a particle size range of 4~18μm. c. Screening removes large-particle-size powder, which is then processed simultaneously with the next batch of recycled waste polyimide. The powder that passes through the screen is recycled as filler for composite materials.

[0056] Example 10 A method for recycling waste polyimide includes the following steps: a. Cut the recycled waste PI film into pieces less than 1cm wide and less than 5cm long; b. The material is put into a ball mill jar and crushed under an argon atmosphere by plasma-assisted ball milling with a ball-to-material ratio of 50:1, a discharge intensity of 10kHz, and a discharge time of 3h to obtain PI micron powder with a particle size range of 40~100μm. c. Screening removes large-particle-size powder, which is then processed simultaneously with the next batch of recycled waste polyimide. The powder that passes through the screen is recycled as filler for composite materials.

[0057] Example 11 A method for recycling waste polyimide includes the following steps: a. Cut the recycled waste PI film into pieces less than 1cm wide and less than 5cm long; b. The material is put into a ball milling jar and crushed under an argon atmosphere using plasma-assisted ball milling with a ball-to-material ratio of 50:1, a discharge intensity of 10kHz, and a discharge time of 1h to obtain PI micron powder with a particle size range of 50~120μm. c. Screening removes large-particle-size powder, which is then processed simultaneously with the next batch of recycled waste polyimide. The powder that passes through the screen is recycled as filler for composite materials.

[0058] Example 12 A method for recycling waste polyimide includes the following steps: a. Cut the recycled waste PI film into pieces less than 1cm wide and less than 5cm long; b. The material is placed in a ball mill jar and crushed under an argon atmosphere using plasma-assisted ball milling with a ball-to-material ratio of 60:1, a discharge intensity of 10kHz, and a discharge time of 6h to obtain PI micron powder with a particle size range of 4~14μm. c. Screening removes large-particle-size powder, which is then processed simultaneously with the next batch of recycled waste polyimide. The powder that passes through the screen is recycled as filler for composite materials.

[0059] Example 13 A method for recycling waste polyimide includes the following steps: a. Cut the recycled waste PI film into pieces less than 1cm wide and less than 5cm long; b. The material is placed in a ball mill jar and crushed under an argon atmosphere using plasma-assisted ball milling with a ball-to-material ratio of 50:1, a discharge intensity of 8kHz, and a discharge time of 6h to obtain PI micron powder with a particle size range of 22~44μm. c. Screening removes large-particle-size powder, which is then processed simultaneously with the next batch of recycled waste polyimide. The powder that passes through the screen is recycled as filler for composite materials.

[0060] Example 14 A method for recycling waste polyimide includes the following steps: a. Cut the recycled waste PI film into pieces less than 1cm wide and less than 5cm long; b. The material is placed in a ball mill jar and crushed under an argon atmosphere using plasma-assisted ball milling with a ball-to-material ratio of 50:1, a discharge intensity of 9kHz, and a discharge time of 6h to obtain PI micron powder with a particle size range of 18~32μm. c. Screening removes large-particle-size powder, which is then processed simultaneously with the next batch of recycled waste polyimide. The powder that passes through the screen is recycled as filler for composite materials.

[0061] Example 15 A method for recycling waste polyimide includes the following steps: a. Cut the recycled waste PI film into pieces less than 1cm wide and less than 5cm long; b. The material is placed in a ball mill jar and crushed under an argon atmosphere using plasma-assisted ball milling with a ball-to-material ratio of 30:1, a discharge intensity of 10kHz, and a discharge time of 6h to obtain PI micron powder with a particle size range of 28~52μm. c. Screening removes large-particle-size powder, which is then processed simultaneously with the next batch of recycled waste polyimide. The powder that passes through the screen is recycled as filler for composite materials.

[0062] Example 16 A method for recycling waste polyimide includes the following steps: a. Cut the recycled waste PI film into pieces less than 1cm wide and less than 5cm long; b. The material is placed in a ball mill jar and crushed under an argon atmosphere using plasma-assisted ball milling with a ball-to-material ratio of 10:1, a discharge intensity of 10kHz, and a discharge time of 6h to obtain PI micron powder with a particle size range of 55~120μm. c. Screening removes large-particle-size powder, which is then processed simultaneously with the next batch of recycled waste polyimide. The powder that passes through the screen is recycled as filler for composite materials.

[0063] Example 17 A method for recycling waste polyimide includes the following steps: a. Recycle waste PI coarse powder; b. The material is put into a ball mill jar and crushed under an argon atmosphere using plasma-assisted ball milling with a ball-to-material ratio of 50:1, a discharge intensity of 10kHz, and a discharge time of 6h to obtain PI micron powder with a particle size range of 4~20μm. c. Screening removes large-particle-size powder, which is then processed simultaneously with the next batch of recycled waste polyimide. The powder that passes through the screen is recycled as filler for composite materials.

[0064] Comparative Example 1 A method for breaking PI film includes the following steps: a. Cut the recycled waste PI film into pieces less than 1cm wide and less than 5cm long; b. Place the powder into a ball mill jar and crush it using ball milling under an argon atmosphere. The ball-to-powder ratio is 50:1. No plasma discharge intensity is added to obtain PI micron powder with a particle size range of 200~400μm.

[0065] Comparative Example 2 The difference between this comparative example and Example 1 is that in step b, the material is put into a ball milling jar and crushed under an argon atmosphere using plasma external field assisted ball milling. The ball-to-material ratio is 5:1, and the resulting PI powder has a particle size range of 150~300μm. Comparative Example 3 The difference between this comparative example and Example 1 is that in step b, the powder is put into a ball milling jar and crushed under an argon atmosphere using plasma external field assisted ball milling with a discharge intensity of 5.0 kHz, resulting in PI powder with a particle size range of 80~100 μm. Experimental example: Table 1 shows the crushing process parameters of Examples 1-8, Example 17, and Comparative Examples 1-3, as well as the particle size range of the obtained PI powder.

[0066] Table 1. Crushing process parameters for Examples 1-9, Example 19, and Comparative Examples 1-3, and the resulting PI powder particle size range.

[0067] As shown in Table 1, traditional mechanical ball milling only uses the high-speed impact and shear force of the grinding balls to refine the powder. This method is prone to component agglomeration due to the single energy input and the inability to overcome intermolecular forces. In contrast, plasma ball milling utilizes a synergistic effect of mechanical force and plasma. Through the action of a high-voltage electric field, the atmosphere inside the milling chamber is broken down, generating high-energy electrons, ions, active free radicals, and active groups. These active particles bombard the powder surface, creating numerous active sites and defects, thus reducing the agglomeration energy between particles. Simultaneously, the plasma bombardment of the material surface causes a sudden increase in the temperature of the micro-area electrons. Under the action of thermal stress, the particles are more easily broken down by mechanical force, resulting in more thorough and uniform powder refinement.

[0068] II. Electron micrographs of PI micron powder obtained by pulverizing in Examples 1-3 and Comparative Example 1 are shown below. Figures 1-5 As shown contrast Figure 1 and Figure 5 It is known that while mechanical force alone can refine PI films to the 100-nanometer scale, its refining effect is limited and accompanied by serious negative effects. The cold welding effect caused by intense mechanical impact and friction leads to severe particle agglomeration, transforming the initial sheet-like morphology into larger, irregular blocky particles. The introduction of plasma can disrupt this balance. In plasma ball milling, the refining state of the powder is fundamentally improved. The high-energy particle stream in the plasma continuously bombards the particle surface, significantly suppressing the tendency for cold welding and agglomeration between particles. Ultimately, the PI powder is efficiently broken down to the micrometer scale with good particle dispersion. (Comparison) Figures 1-4 The influence of processing time on the refining effect was investigated in depth. As the plasma ball milling processing time increased, the average particle size of the powder showed a continuous decreasing trend.

Claims

1. A method of breaking PI film in a one-step process, characterized in that, The method comprises the following steps: Step S1, raw material pretreatment: cutting the PI film into pieces; Step S2, plasma ball milling treatment: putting the pieces of the PI film into a ball milling tank, and performing breaking treatment by using plasma external field assisted ball milling to obtain PI micron powder.

2. The method of breaking PI film in one step as claimed in claim 1, wherein, In step S1, the PI film is cut into pieces with a width less than 1 cm and a length less than 5 cm.

3. The method of breaking PI film in one step as claimed in claim 1, wherein, In step S2, the ball-to-material ratio of the plasma ball milling is 10-60:

1.

4. The method of breaking PI films in one step as claimed in claim 1, wherein, In step S2, the discharge intensity of the plasma ball milling is 8.0-10.0 kHz.

5. The method of breaking PI film in one step as claimed in claim 4, wherein, In step S2, the plasma discharge time is 1-8 h.

6. The method of breaking PI film in one step according to any one of claims 1 to 5, characterized in that, In step S2, the plasma ball milling is performed in a protective atmosphere, which is an argon atmosphere, a nitrogen atmosphere or vacuum.

7. A method of recycling waste polyimide, characterized by, The method comprises the following steps: Step A, raw material pretreatment; Step B, plasma ball milling treatment: putting the pretreated raw material into a ball milling tank, and performing breaking treatment by using plasma external field assisted ball milling to obtain PI micron powder; Step C, screening: screening the treated PI micron powder, and recycling the screened powder as filler of a composite material.

8. The method of recycling waste polyimide according to claim 7, wherein In step A, the raw material pretreatment method is: cutting the recycled waste PI film into pieces, or recycling waste PI coarse powder.

9. The method of recovering waste polyimide according to claim 7 or 8, characterized in that, The method comprises at least one of the following technical features: (1) In step A, the recycled waste PI film is cut into pieces with a width less than 1 cm and a length less than 5 cm; (2) In step B, the ball-to-material ratio of the plasma ball milling is 10-60:1; (3) In step B, the discharge intensity of the plasma ball milling is 8.0-10.0 kHz; (4) In step B, the plasma discharge time is 1-8 h; (5) In step B, the plasma ball milling is performed in a protective atmosphere, which is an argon atmosphere, a nitrogen atmosphere or vacuum; (6) In step C, a 30-100 mesh screen is used for screening.

10. The method of recycling waste polyimide according to claim 9, wherein In step C, the screened powder is recycled as filler of a composite material, large particle size powder is removed by screening, and the large particle size powder is processed synchronously with the next batch of recycled waste polyimide.

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