Polyimide aerogel for 3D printing and preparation method and application thereof

Abstract

The invention belongs to the technical field of aerogel, and particularly relates to polyimide aerogel for 3D printing as well as a preparation method and application of the polyimide aerogel. According to the preparation method disclosed by the invention, the polyaniline with a curved surface structure is prepared by taking ice micro powder as a synthesis template of an aniline monomer, and the polyaniline / polyimide composite aerogel is prepared by adopting a polyamide acid in-situ compounding method. The polyaniline with the curved surface structure is a three-dimensional conductive unit, and when the polyaniline is dispersed in a polyimide matrix, the curved surface structures can be in contact with one another, so that an efficient three-dimensional conductive network is constructed in the composite material. The curved surface structure has a relatively large specific surface area, so that a relatively large contact area is formed between polyaniline and a polyimide matrix, stress is favorably transferred from the matrix to a filler, the polyaniline with the curved surface structure is favorably prevented from being agglomerated in the matrix, the polyaniline is more uniformly distributed, and the flexibility of the polyimide aerogel is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aerogels, and particularly relates to a polyimide aerogel for 3D printing and a preparation method and application thereof. BACKGROUND

[0002] 3D printing materials are the material basis of 3D printing technology, directly affecting the performance and potential applications of printed objects. The consumables used in 3D printing include plastics, ceramics, metals, biological and other composite materials. Each consumable has its unique characteristics, such as strength, flexibility, heat resistance and biocompatibility. Engineering plastics used for 3D printing are divided into thermoplastic and thermosetting. Thermoplastic engineering plastics do not undergo chemical bonding during 3D printing, and can be recycled, melted and reused. Common materials include ultra-high molecular weight polyethylene, polyformaldehyde and polyurethane.

[0003] Polyurethane is a high-performance polymer material commonly used in 3D printing, with excellent mechanical properties, wear resistance, excellent flexibility and elasticity, as well as corrosion resistance and chemical resistance. Polyurethane has high strength and toughness, and is suitable for the manufacture of various engineering and functional components. Polyurethane materials are divided into rigid and elastic types, with different hardness and elastic modulus. Rigid polyurethane materials are commonly used to manufacture structural parts and engineering parts, while elastic polyurethane materials are suitable for manufacturing elastic parts and cushioning materials. Polyurethane materials can be processed through different 3D printing technologies, including traditional injection molding processes. It is commonly used to manufacture footwear, clothing, electronic products, household goods, automotive parts, spacecraft components, medical devices, etc.

[0004] Polyurethane is a multi-segment copolymer, which is polymerized by polyglycol and diisocyanate with diamine or diol as a chain extender, resulting in a linear polymer composed of soft segments (polyol) and hard segments (rigid diisocyanate part combined with chain extender). The elastic properties of the material are caused by the intermolecular interaction between urethane groups and the hard segment domains as physical cross-linking components. By adjusting the ratio of hard and soft segments, molecular weight and chemical functional groups, polyurethane materials with special functions can be prepared.

[0005] Currently, the development direction of 3D printing polyurethane materials mainly focuses on optimizing material performance (mechanical properties, wear resistance, chemical resistance), developing multifunctional materials with self-repairing, intelligent sensing and flame retardant properties, improving sustainability and environmental friendliness, realizing flexible, fast and economical customized production applications and large-scale printing applications, etc. to meet the growing market demand and application demand. However, there is still a lack of research on the antistatic performance of 3D printing polyurethane materials. The existing technology mostly uses various conductive polymer fillers to solve the technical problem of poor antistatic performance of polyurethane. However, the interfacial adhesion between the conductive polymer filler and polyurethane is low, and it is difficult to directly print by blending. The existing technology uses different templates to prepare conductive polymers with special morphology to solve the compatibility problem. Among them, ice template is a kind of green and environmentally friendly technology widely used in recent years. For example, CN118681506A, CN105597622A, CN103191019A, CN106860403A, CN119701808A and other patent technologies disclose the preparation of ice template and the preparation of corresponding biomaterials, but there is no report on the preparation of conductive materials using ice template in the existing technology. SUMMARY

[0006] The purpose of the present application is to provide a kind of 3D printing polyimide aerogel and its preparation method and application, the polyimide aerogel prepared has the advantages of high strength, strong chemical stability, good compatibility, used as the conductive, reinforcing filler of thermoplastic polyurethane, can greatly increase the mechanical properties and antistatic ability of thermoplastic polyurethane.

[0007] To achieve the above purpose, the technical scheme adopted by the present application is as follows: A preparation method of a 3D printing polyimide aerogel, comprising the following steps: (1) under ice-salt bath conditions, aniline monomer and ice powder are added to deionized water while stirring to obtain a monomer mixture solution; (2) under stirring conditions of not less than 400 rpm, the initiator is added to the monomer mixture solution in batches, and after the addition is completed, the stirring reaction is continued, and after the post-treatment, a curved polyaniline is obtained; wherein the first addition of initiator accounts for 10-20 wt% of the total initiator, and after 0.5-1 h of reaction, the remaining initiator is continuously added; (3) polyamide acid powder, organic base and curved polyaniline are added to deionized water and stirred uniformly; a polyamide acid hydrogel is obtained by sol-gel; (4) the polyamide acid hydrogel is freeze-dried and thermal imidized to obtain a 3D printing polyimide aerogel.

[0008] Polyaniline is composed of two parts of oxidized units and reduced units, with the characteristics of low cost, easy preparation, stable chemical properties, high electrical conductivity, excellent magnetic properties and unique optical properties, which makes it widely used in the field of high polymers. Because of the existence of flexible amino groups on both sides of the benzene ring of polyaniline, its excellent performance of easy processing is different from other conductive polymers. By changing the reaction conditions and synthesis process, the electrical properties of polyaniline can be controlled more ideally. Moreover, polyaniline has many advantages, such as wide and cheap raw material sources, mild synthesis conditions, safety and environmental protection, good oxidation resistance in natural environment, adjustable electrical conductivity, ideal film forming effect and so on. However, because of the rigid structure in the molecule, the application of polyaniline as a conductive filler is limited to some extent; in addition, it has the characteristics of neither dissolving nor melting, which greatly limits the practical application of conductive polyaniline high polymer. Therefore, combining conductive high polymer with other ordinary high polymer which is easy to be shaped and processed to prepare functional high polymer with special purpose according to the actual application needs has become the main way to broaden the application field of polyaniline conductive high polymer.

[0009] In the previous work, nylon was used as the aerogel matrix material of curved polyaniline. Although the cost is low, nylon is mostly aliphatic polyamide, and the methylene segment between the amide bonds is flexible, with low melting point and thermal decomposition temperature. When the composite material filled with nylon aerogel is processed or used in a high temperature environment, the nylon aerogel filler itself will soften, resulting in a decrease in its reinforcing effect and possibly becoming a defect in the material. The molecular backbone of polyimide-based aerogel is composed of aromatic rings and imide rings, with high bond energy and extremely stable structure, so it does not melt or decompose at high temperatures, continuing to provide effective support and reinforcement for the matrix. Moreover, the rigidity of the polyimide molecular chain and the strong intermolecular force make its skeleton very strong, so even with very low density, it can form a well-supported porous network, thus having higher compression and tensile modulus and strength, which can meet the stress requirements in the 3D printing process of polyurethane materials, prevent the aerogel structure from collapsing under stress, and maintain the stability of the aerogel morphology. In addition, the polyimide aerogel itself has a low thermal expansion coefficient, and adding it to the polyurethane matrix of 3D printing can significantly reduce the overall thermal expansion coefficient of the composite material, making its size change less with temperature. This is crucial for high-precision original parts of 3D printing. Due to its own strong aromatic molecular skeleton, the nano-porous skeleton of polyimide aerogel has extremely high rigidity and strength. As a filler, it can more effectively transfer the load from the matrix to itself, thereby significantly improving the modulus (rigidity) and strength of the composite material. At the same time, its reinforcing effect is better than that of nylon aerogel when the same amount is added. When combined with polyurethane materials, the porous structure of polyimide aerogel provides a large specific surface area, forming a large interfacial area, and producing strong interfacial bonding force through physical anchoring and chemical bonding. This strong interface is the premise of effective reinforcement.

[0010] Moreover, as a kind of special engineering plastics, the imide ring in the molecular chain of polyimide endows the polyimide material with excellent chemical resistance and high mechanical properties, and both of them have nitrogen-containing functional groups, so they have good compatibility and can be used as the matrix of polyaniline conductive molecules to prepare conductive fillers for polyurethane. Moreover, during the blending process, the carboxyl groups in the polyamide acid also act as a proton acid to a certain extent, which dopes the generated polyaniline and converts it into the conductive emeraldine salt form, thereby improving its conductivity.

[0011] In previous work (CN120818176A, CN120865604A), the inventors also prepared polyaniline microspheres with core-shell structure by in-situ polymerization in a polyamide solution using inorganic solid or hollow nanoparticles as templates. However, the above process requires additional addition of inorganic nanoparticles as templates, and the above process needs to be carried out in a polyamide solution, which has a complex in-situ polymerization preparation process, harsh reaction conditions, and is difficult to promote in the market. More importantly, due to the limitation of solution viscosity, there are a large number of unreacted aniline monomers in the product, which not only does not meet the development needs of green chemistry, but also affects the improvement of the mechanical properties of aerogels and 3D printing products.

[0012] In order to solve the problem of additional addition of non-conductive templates in the preparation process of special morphology polyaniline, the present application uses ice micro-powder as the synthesis template of aniline monomer to prepare polyaniline with curved surface structure, which has the characteristics of high efficiency, compatibility, light weight and stability.

[0013] Ice template method is a very widely used material preparation technology. The present application combines ice crystal template method with freeze-drying method to adjust the microstructure of polyimide aerogel containing polyaniline, and prepare a polyimide-based aerogel conductive polymer material with multi-level structure.

[0014] The preparation of the antistatic material is key to the requirement of good compatibility between the conductive filler and the matrix to achieve uniform dispersion, and then through simple mechanical stirring, ultrasonic dispersion and other methods can be achieved, without complex equipment or process, suitable for large-scale production. The polyaniline constructed by the inventor in the polyamide matrix is a zero-dimensional spherical particle. Due to its containing inorganic particles, the specific gravity is large, and it is difficult to distribute in the polyamide matrix, and it is not easy to build a conductive path, and a large proportion needs to be added to realize the antistatic performance; and the presence of inorganic nanoparticles also affects the pore structure of the polyamide aerogel, which is not conducive to the construction of high-porosity aerogel materials. By using the curved surface structure of polyaniline as a conductive filler, efficient and stable combination of conductivity and inherent excellent performance of polyimide (such as flexibility, strength) is realized. The curved surface structure of polyaniline itself is a three-dimensional conductive unit. When they are dispersed in the polyimide matrix, these curved surfaces can be in contact with each other or form a "tunnel effect" through a very thin insulating layer, thereby building an efficient three-dimensional conductive network in the composite material. Compared with planar polyaniline, the amount of curved surface polyaniline required to achieve the same conductivity is less, which means a lower "percolation threshold", and a small amount of addition is crucial to maintaining the original mechanical properties of the polyimide aerogel. Moreover, compared with fibrous or irregular particles, the curved surface polyaniline has a lower stress concentration effect. The curved surface morphology is easier to disperse in the polyimide molecular chain, reducing the hindrance to polymer chain segment movement, improving the flexibility of the polyimide aerogel, and effectively avoiding the brittleness of traditional conductive fillers at high content. In addition, the curved surface structure has a large specific surface area, which means that the polyaniline has a larger contact area with the polyimide matrix. A larger contact area can produce stronger interfacial interactions, not only helping to transfer stress from the matrix to the filler, to some extent, to improve the mechanical strength of the material, but also helping to prevent the curved surface polyaniline from agglomerating in the matrix, making it more evenly distributed, thereby ensuring the stability of the conductive network.

[0015] Further, the ice micropowder particle size in step (1) is not particularly limited, and micrometer-level particles can be used. Further, the micropowder can be in a spherical structure with an average particle size of 100 nm-50 μm. The ice micropowder preparation process is not particularly limited, and a common spray freezing or freeze grinding process in the prior art can be used for preparation. Using ice micropowder nanoparticles as a template for aniline monomers, arc-shaped polyaniline can be prepared. The inventors analyzed that, as a solid substance of water, the nucleation of ice particles is limited. However, under the action of strong stirring, the solvent flow rate is fast, and there is a certain rate difference between the movement of the solvent and the solid ice particles. Moreover, during stirring, the ice particles have a revolution behavior around the center and a rotation behavior around themselves. There is a large rate difference between the macroscopic revolution behavior and the microscopic rotation behavior of the ice micropowder, and the shear effect caused by the speed difference leads to uneven adhesion of aniline. Moreover, due to the volume change of water after crystallization, a large number of micro-cracks exist on the surface of the ice micropowder, which is beneficial to the adhesion of aniline. With the stirring, more aniline monomers are gradually polymerized with the aniline preferentially adhered as the core, and the curved surface structure of polyaniline is formed on the surface of the ice micropowder. With the progress of the polymerization reaction, the curved surface structure of polyaniline gradually increases, and when the curved surface structure of polyaniline grows to a certain arc, the area of the curved surface structure of polyaniline is too large, the interaction force with the ice micropowder decreases, and the solvent impact force gradually increases, and under the action of the ice micropowder self-rotation centrifugal force, the curved surface structure of polyaniline falls off from the surface of the ice micropowder, forming an arc-shaped polyaniline. It is worth mentioning that the nucleation of ice micropowder mainly occurs in the initial stage of the reaction. At a low temperature, the ice micropowder dissolves slowly, and the initial curved surface structure is quickly formed due to the fast initial polymerization rate. The initial reaction process should control the temperature of the reaction system to prevent the ice particles from dissolving too early due to a too high temperature (the reaction system is controlled by an ice-salt bath in the present application). In the middle and late stages of the reaction, the curved arc structure has been formed on the surface of the ice micropowder, and the subsequent reaction temperature is not strictly limited. Even if the initial curved surface structure falls off, the aniline monomers can continue to polymerize on the basis of the curved arc structure to promote the formation of the curved arc structure. In particular, in order to improve the regularity of the hollow arc-shaped polyaniline, the reaction system can be maintained below 0 ℃ during the polymerization process. Specifically, the ice-salt bath reaction system is used in the present application. Using ice micropowder as a template, the curved surface polyaniline is synthesized by a one-step method, without the complicated steps of template preparation and removal, and the process flow is simple.

[0016] Further, the aniline monomers and deionized water in step (1) and the initiator in step (2) are pre-cooled. The pre-cooling temperature is -10-0 ℃. The pre-cooling process can cool the solution system to prevent the ice template structure from being damaged. During the pre-cooling process, stirring can be performed to prevent ice formation. The polyaniline preparation process uses an ice-salt bath system, which can control the reaction temperature to be lower than 0 ℃. Specifically, the temperature can be -20-0 ℃, and further, the temperature can be controlled to be (-10)-(-1 ℃) or (-6)-(-1 ℃).

[0017] Further, the mass ratio of the ice micro powder to the aniline monomer in step (1) is 5-20:1. Specifically, it can be 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1. In particular, it can be 8-15:1. An appropriate amount of ice micro powder can fully play a nucleation role, preventing excessive ice micro powder from causing disturbance to the solution, which is not conducive to the dispersion, adhesion and polymerization process of the aniline monomer.

[0018] Further, the mass ratio of the aniline monomer to deionized water in step (1) is (0.1-2):100. Further, it can be (0.5-1):100. The addition of a large amount of deionized water can improve the stability of the ice micro powder and promote the formation of a curved surface structure.

[0019] Further, the stirring rate in step (1) is not particularly limited, and in particular, it can be 400-600 rpm. Further, the stirring rate is 500-600 rpm. Stirring can promote the dispersion of components and facilitate the full combination of the ice micro powder and the aniline monomer.

[0020] Further, in step (1), the aniline monomer is first added and mixed uniformly, and then the ice micro powder is added, and the mixing of the ice micro powder and the aniline monomer is promoted by stirring.

[0021] Further, the stirring rate in step (2) is 400-700 rpm. The initiator is one or more of ammonium persulfate, potassium persulfate and ferric chloride. The mass ratio of the initiator to the aniline monomer is (2-4):1. In particular, ferric chloride with a doping effect is selected. The conductivity of polyaniline can be greatly improved after Lewis acid doping. Specifically, an aqueous solution of ferric chloride can be added dropwise, and the mass / volume ratio of ferric chloride to water in the aqueous solution of ferric chloride can be (0.01-0.5):1. In particular, it can be 0.1:1.

[0022] Further, the step (2) is divided into two batches of dropping, specifically, the first batch of initiator is 12-18wt% of the total initiator, and after 0.6-0.8h, the remaining initiator is continuously dropped until the dropping is completed. The dropping rate is not particularly limited, and each batch can be uniformly dropped. Further, the first batch of initiator is 13-18wt% of the total initiator; further, 14-15wt%. In order to minimize the influence of temperature change on the ice micro powder, the first batch of initiator is quickly dropped after the completion of step (1). The dropping rate of the first batch of initiator is the same as that of the second batch of initiator, and the total dropping time is 10-30min. By dropping the initiator in batches, the polymerization process of aniline monomer can be reasonably controlled. After the first batch of initiator is dropped, a small amount of initiator can control the polymerization rate of aniline monomer, which is beneficial to the attachment of aniline monomer on the surface of ice particles to fully play the nucleation role. Moreover, after the first batch of initiator is dropped, the aniline monomer quickly polymerizes on the surface of the ice micro powder, promotes the formation of the initial curved surface morphology of polyaniline, and prevents the continuous dropping of the initiator from causing random polymerization of aniline. On the one hand, the preliminary formation of the curved structure can eliminate the influence of the possible melting of the ice micro powder during the reaction process, and promote the formation of the curved structure; on the other hand, the segmented addition of the initiator and the segmented polymerization can reduce the influence of the polar substance on the solution system, and improve the stability of the ice micro powder.

[0023] Further, the total time of the stirring reaction in step (2), i.e. the time from the start of dropping the initiator to the completion of the reaction, is 10-20h. After the reaction is completed, the ice micro powder is dissolved at room temperature. The post-treatment is a filtration, washing, and drying process at room temperature. Specifically, the washing can be deionized water washing, and the drying can be performed in a vacuum oven.

[0024] Further, the polyamide acid powder in step (3) is prepared by copolymerization of dianhydride monomers and diamine monomers to form a polyamide acid solution, which is then dropped into deionized water to precipitate. Since polyamide acid has poor stability, it is best to be prepared as needed. Specifically, the dianhydride monomers and diamine monomers can be used as raw materials to prepare in an organic solvent. Mixing the polyamide acid powder and the curved polyaniline again in a solvent can play a role of secondary doping for the polyaniline. Secondary doping can promote the unfolding of the polyaniline main chain, enhance the interaction of carriers, and further improve the conductivity and mechanical properties of the polyaniline.

[0025] The types of dianhydride monomers, diamine monomers, and organic solvents are not particularly limited, and those commonly used in the art can be used. Specifically, the molar ratio of dianhydride monomers to diamine monomers is (0.95-1.05):(0.95-1.05). Specifically, a variety of dianhydride monomers or diamine monomers can be used for copolymerization to improve the processing performance of polyimide.

[0026] For example, the dianhydride monomer can be at least one of pyromellitic dianhydride (PMDA), oxydiphthalic anhydride (ODPA), 3,3',4,4'-diphenyltetracarboxylic dianhydride (s-BPDA), 2,3,3',4'-diphenyltetracarboxylic dianhydride (a-BPDA), diphenyl sulfone-3,4,3',4'-tetracarboxylic dianhydride (DSDA), bis(3,4-dicarboxyphenyl)sulfide dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,3,3',4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), bis(3,4-dicarboxyphenyl)methane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, p-phenylene bis(trimellitic monoester anhydride), p-biphenylene bis(trimellitic monoester anhydride), m-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, p-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, 1,3-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, 2,2-bis〔(3,4-dicarboxyphenoxy)phenyl〕propane dianhydride (BPADA), 2,3,6,7-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, and 4,4'- (2,2-hexafluoroisopropylidene)diphthalic dianhydride.

[0027] The diamine monomer can be at least one of p-phenylenediamine (PPD), m-phenylenediamine, 3,3'-dimethylbenzidine, 2,2'-dimethylbenzidine, 2,4-diaminotoluene, 2,6-diaminotoluene, 3,5-diaminobenzoic acid (DABA), 4,4'-oxydianiline (ODA), 3,4'-oxydianiline, 4,4'-methylenedianiline, 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-dicarboxy-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetramethyl-4,4'-diaminodiphenylmethane, bis(4-aminophenyl) sulfide, 4,4'-diaminobenzanilide, 3,3'-dimethoxybenzidine, 2,2'-dimethoxybenzidine, 3,3'-diaminophenyl ether, 3,4'-diaminophenyl ether, 4,4'-diaminophenyl ether, 3,3'-diaminophenyl sulfide, 3,4'-diaminophenyl sulfide, 4,4'-diaminophenyl sulfide, 3,3'-diaminophenyl sulfone, 3,4'-diaminophenyl sulfone, 4,4'-diaminophenyl sulfone, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,3'-diamino-4,4'-dichlorobenzophenone, 3,3'-diamino-4,4'-dimethoxybenzophenone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 2,2-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 2,2-bis(3-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 2,2-bis(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 3,3'-diaminophenyl sulfoxide, 3,4'-diaminophenyl sulfoxide, 4,4'-diaminophenyl sulfoxide, 1,3-bis(3-aminophenyl)benzene, 1,3-bis(4-aminophenyl)benzene, 1,4-bis(3-aminophenyl)benzene, 1,4-bis(4-aminophenyl)benzene, 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,4-bis(3-aminophenoxy)benzene (TPE-Q), 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene, 3,3'-diamino-4-(4-phenylphenoxy)benzophenone, 3,3'-diamino-4,4'-bis(4-phenylphenoxy)benzophenone, and the like.

[0028] The organic solvent can be one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide, N-methyl-pyrrolidone (NMP), gamma-butyrolactone (GBL).

[0029] Further, the organic base in step (3) is one or more of triethylamine, tripropylamine, diethylenetriamine, and triethylenetetramine; and the mass ratio of the organic base to the polyamic acid powder is (0.1-1):1.

[0030] Further, the mass ratio of the polyamide acid powder to the deionized water in step (3) is 1-10 wt.%, in particular, 5 wt.%.

[0031] Further, the mass ratio of the curved surface polyaniline to the polyamide acid powder in step (3) is (0.1-1):1.

[0032] Further, the thermal imidization temperature in step (4) is 150-230℃, and the time is 3-10 h.

[0033] In another aspect, the present application also provides a polyimide aerogel for 3D printing prepared by the above method. The polyimide resin is used as the aerogel base resin, which has good compatibility with polyaniline because both of them contain nitrogen-containing groups. More importantly, the polyimide solution is easy to freeze-dry, which promotes the formation of aerogel.

[0034] In another aspect, the present application also provides the application of the polyimide aerogel for 3D printing and the 3D printing polyurethane material enhanced by using the same. In particular, the polyimide aerogel for 3D printing is used in the light-curing molding technology, selective laser sintering technology, fused deposition technology, or layer manufacturing technology in the 3D printing technology. Specifically, the 3D printing polyurethane material comprises a polyurethane resin material and a polyimide aerogel for 3D printing. Further, the light-curing molding technology or the fused deposition technology can be used. In particular, the fused deposition technology is used to prepare the polyurethane material. In the fused deposition technology, the printing temperature is not particularly limited, which is generally between 190-220℃, and can be adjusted according to the production process. Further, the 3D printing polyurethane material can further comprise various reinforcing fillers, flow modifiers, lubricants, antioxidants, ultraviolet light-resistant agents, hydrolysis-resistant agents, colorants, and other auxiliaries. In particular, the type of reinforcing fillers is not particularly limited, which can comprise particulate, fibrous, and flaky structure fillers. It should be noted that the types of raw materials used in the present application are not particularly limited, which can be prepared by using conventional processes in the art, or can be commercially available. For example, the thermoplastic polyurethane can be selected from common Wanhua Q / 0600, etc.

[0035] Beneficial Effects: To address the issue of requiring additional non-conductive templates during the preparation of polyaniline with special morphologies, this invention utilizes ice micron powder as a synthetic template for aniline monomers to prepare polyaniline with curved structures; and uses polyimide as the matrix resin to prepare polyimide aerogels for 3D printing. The curved polyaniline surfaces can contact each other or form a "tunneling effect" through a very thin insulating layer, thereby constructing a highly efficient three-dimensional conductive network in the composite material. Furthermore, the curved polyaniline structure exhibits a lower stress concentration effect compared to fibrous or irregular particles. While imparting conductivity to the composite material, it does not significantly increase the composite's density. This not only facilitates stress transfer from the matrix to the filler, improving the material's mechanical strength to some extent, but also helps prevent polyaniline agglomeration in the matrix, resulting in a more uniform distribution, thus ensuring the stability of the conductive network and improving the mechanical properties of the composite material. Attached Figure Description

[0036] Figure 1 Scanning electron microscope image of the curved polyaniline prepared in Example 10; Figure 2 Scanning electron microscope image of polyaniline prepared for Comparative Example 1. Detailed Implementation

[0037] In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the specific embodiments of the present invention will be described in further detail below with reference to specific examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0038] The performance testing method for the polyimide aerogels for 3D printing prepared in the following examples and comparative examples is as follows: Under the same conditions, the effect of the polyimide aerogels for 3D printing prepared in Examples 1-10 and Comparative Examples 1-2 on the performance of 3D printed polyurethane products is tested.

[0039] Specifically, the 3D printing polyurethane material comprises 100 parts thermoplastic polyurethane, 15 parts 3D printing polyimide aerogel, and 3 parts zinc stearate. The 3D printing polyurethane material is printed into specimens, and the elongation at break of the specimens is tested according to GB / T528-2009 "Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber," and its conductivity is tested using a conductivity meter.

[0040] Example 1 A method for preparing polyimide aerogel for 3D printing includes the following steps: (1) under the ice-salt bath condition, pre-cooled aniline monomer and ice micro-powder were added into deionized water in sequence at a stirring speed of 400 rpm to obtain a monomer mixed solution; the particle size of the ice micro-powder was 15 μm; the mass ratio of the ice micro-powder to the aniline monomer was 5:1; the mass ratio of the aniline monomer to the deionized water was 0.3:100; (2) under the stirring condition at 400 rpm, pre-cooled aqueous ferric chloride initiator was added into the monomer mixed solution in batches, after the addition was completed, stirring reaction was continued, and then the product was filtered, washed and dried to obtain a curved surface polyaniline; the mass ratio of the initiator to the aniline monomer was 2.5:1; the adding in batches was that the initiator was added in two batches at a constant speed, specifically, 11 wt% of the total initiator was added in the first batch, after 0.5 h of reaction, the remaining initiator was continuously added until the addition was completed, and the total time of the two additions was 17 min; the total time of the stirring reaction was 15 h; (3) diamine monomer was dispersed in an organic solvent N,N-dimethylacetamide, then dianhydride monomer was added, and a polyamide acid solution was obtained after 9 h of reaction at 25℃; the polyamide acid solution was dropped into water for precipitation, and then the product was filtered to obtain a polyamide acid powder; the diamine monomer was composed of 4,4'-oxydianiline and 4,4'-diaminodiphenylmethane at a molar ratio of 3:1, the dianhydride monomer was composed of 3,3',4,4'-biphenyltetracarboxylic dianhydride and pyromellitic dianhydride at a molar ratio of 1:1, the molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the diamine monomer and the dianhydride monomer to the organic solvent was 5 wt%; The polyamide acid powder, an organic base triethylamine and the curved surface polyaniline were added into deionized water and stirred uniformly; a polyamide acid hydrogel was obtained after sol-gel; the mass ratio of the curved surface polyaniline to the polyamide acid powder was 0.4:1; the mass ratio of the organic base to the polyamide acid powder was 0.3:1; and the mass ratio of the polyamide acid powder to the deionized water was 2 wt%; (4) the polyamide acid hydrogel was freeze-dried, and then thermal imidization was performed under the conditions of 150℃ / 1 h, 200℃ / 2 h and 230℃ / 2 h to obtain a polyimide aerogel for 3D printing; the polyimide aerogel was used as a conductive reinforcing filler of thermoplastic polyurethane, and the elongation at break of the product was 585% and the electrical conductivity was 33.43×10 -4 S / cm.

[0041] Example 2 A preparation method of a polyimide aerogel for 3D printing, comprising the following steps: (1) under the ice-salt bath condition, pre-cooled aniline monomer and ice micro-powder were added into deionized water in sequence at a stirring speed of 600 rpm to obtain a monomer mixed solution; the particle size of the ice micro-powder was 800 nm; the mass ratio of the ice micro-powder to the aniline monomer was 17:1; the mass ratio of the aniline monomer to the deionized water was 0.5:100. (2) under the condition of 700 rpm stirring, the pre-cooled initiator aqueous solution of ferric chloride was added into the monomer mixed solution in batches, after the addition was completed, the stirring reaction was continued, and then the product was obtained by filtering, washing and drying at room temperature; the mass ratio of the initiator to aniline monomer was 3.3:1; the adding in batches was that the initiator was added in two batches at a constant speed, specifically, 18wt% of the total initiator was added in the first batch, after 1h of reaction, the remaining initiator was continuously added until the addition was completed, and the total time of the two additions was 26min; the total time of the stirring reaction was 10h; (3) the diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, then the dianhydride monomer was added, and a polyamic acid solution was obtained after 7h of reaction at 30℃; the obtained polyamic acid solution was dropped into water for precipitation, and then the polyamic acid powder was obtained by filtering; wherein the diamine monomer was composed of 4,4'-diamino diphenyl ether and 4,4'-diamino diphenyl sulfone with a molar ratio of 2:1, the dianhydride monomer was composed of 3,3',4,4'-biphenyl tetracarboxylic dianhydride and 3,3',4,4'-benzophenone tetracarboxylic dianhydride with a molar ratio of 2:1, the molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 7wt%; The polyamic acid powder, the organic base triethylamine and the curved surface polyaniline were added into deionized water and stirred uniformly; a polyamic acid hydrogel was obtained by sol-gel; the mass ratio of the curved surface polyaniline to the polyamic acid powder was 0.8:1; the mass ratio of the organic base to the polyamic acid powder was 0.7:1; and the mass ratio of the polyamic acid powder to the deionized water was 3.5wt%; (4) the polyamic acid hydrogel was freeze-dried, and then thermal imidization was performed under the conditions of 150℃ / 1h, 200℃ / 2h and 230℃ / 2h, and thus a polyimide aerogel for 3D printing was obtained; the polyimide aerogel was used as a conductive reinforcing filler of thermoplastic polyurethane, and the elongation at break of the thermoplastic polyurethane was 568% and the electrical conductivity was 38.32×10 -4 S / cm.

[0042] Example 3 A preparation method of a polyimide aerogel for 3D printing, comprising the following steps: (1) under the condition of an ice-salt bath, aniline monomer and ice micro-powder were added into deionized water in sequence under the stirring speed of 550 rpm, and a monomer mixed solution was obtained; the particle size of the ice micro-powder was 4μm; the mass ratio of the ice micro-powder to aniline monomer was 20:1; and the mass ratio of aniline monomer to deionized water was 0.5:100; (2) under the condition of 500 rpm stirring, the pre-cooled initiator aqueous solution of ferric chloride was added into the monomer mixed solution in batches, after the addition was completed, the stirring reaction was continued, and then the product was obtained by filtering, washing and drying at room temperature; the mass ratio of the initiator to aniline monomer was 3:1; the adding in batches was that the initiator was added in two batches at a constant speed, specifically, 15wt% of the total initiator was added in the first batch, after 0.7h of reaction, the remaining initiator was continuously added until the addition was completed, and the total time of the two additions was 20min; the total time of the stirring reaction was 13h; (3) the diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, then the dianhydride monomer was added, and a polyamic acid solution was obtained after 8h of reaction at 27℃; the obtained polyamic acid solution was dropped into water for precipitation, and then the polyamic acid powder was obtained by filtering; wherein the diamine monomer was composed of 4,4'-diaminodiphenyl methane and 3,3'-diaminobenzophenone with a molar ratio of 1:2, the dianhydride monomer was composed of 3,3',4,4'-benzophenonetetracarboxylic dianhydride and oxybisphthalic anhydride with a molar ratio of 1:1, the molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 6wt%; The polyamic acid powder, the organic base triethylamine and the curved surface polyaniline were added into deionized water and stirred uniformly; a polyamic acid hydrogel was obtained by sol-gel; the mass ratio of the curved surface polyaniline to the polyamic acid powder was 0.7:1; the mass ratio of the organic base to the polyamic acid powder was 0.5:1; and the mass ratio of the polyamic acid powder to the deionized water was 3wt%; (4) the polyamic acid hydrogel was freeze-dried, and then heat imidization was performed under the conditions of 150℃ / 1h, 200℃ / 2h and 230℃ / 2h, and thus a polyimide aerogel for 3D printing was obtained; the polyimide aerogel was used as a conductive reinforcing filler of thermoplastic polyurethane, and the elongation at break of the thermoplastic polyurethane was 572% and the electrical conductivity was 36.24×10 -4 S / cm.

[0043] Example 4 A preparation method of a polyimide aerogel for 3D printing, comprising the following steps: (1) under the condition of an ice-salt bath, aniline monomer and ice micro-powder were added into deionized water in sequence under the stirring speed of 400 rpm, and a monomer mixed solution was obtained; the particle size of the ice micro-powder was 4μm; the mass ratio of the ice micro-powder to the aniline monomer was 16:1; and the mass ratio of the aniline monomer to the deionized water was 0.35:100; (2) under the condition of 650 rpm stirring, the pre-cooled initiator aqueous solution of ferric chloride was added into the monomer mixed solution in batches, after the addition was completed, the stirring reaction was continued, and then the product was obtained by filtering, washing and drying at room temperature; the mass ratio of the initiator to aniline monomer was 2.6:1; the adding in batches was that the initiator was added in two batches at a constant speed, specifically, 12wt% of the total initiator was added in the first batch, after 0.8h of reaction, the remaining initiator was continuously added until the addition was completed, and the total time of the two additions was 25min; the total time of the stirring reaction was 10h; (3) the diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, then the dianhydride monomer was added, and a polyamic acid solution was obtained after 9h of reaction at 30℃; the obtained polyamic acid solution was dropped into water for precipitation, and then the polyamic acid powder was obtained by filtering; wherein the diamine monomer was composed of 4,4'-oxydianiline and 3,3'-diaminophenyl ether with a molar ratio of 1:1, the dianhydride monomer was composed of 3,3',4,4'-biphenyl tetracarboxylic dianhydride and oxybisphthalic anhydride with a molar ratio of 2:1, the molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 5wt%; The polyamic acid powder, the organic base triethylamine and the curved surface polyaniline were added into deionized water and stirred uniformly; a polyamic acid hydrogel was obtained by sol-gel; the mass ratio of the curved surface polyaniline to the polyamic acid powder was 0.75:1; the mass ratio of the organic base to the polyamic acid powder was 0.65:1; and the mass ratio of the polyamic acid powder to the deionized water was 2wt%; (4) the polyamic acid hydrogel was freeze-dried, and then heat imidized under the conditions of 150℃ / 1h, 200℃ / 2h and 230℃ / 2h, to obtain a polyimide aerogel for 3D printing; the polyimide aerogel was used as a conductive reinforcing filler of thermoplastic polyurethane, and the elongation at break of the thermoplastic polyurethane was 577% and the electrical conductivity was 37.69×10 -4 S / cm.

[0044] Example 5 A preparation method of a polyimide aerogel for 3D printing, comprising the following steps: (1) under the condition of an ice-salt bath, aniline monomer and ice micro-powder were added into deionized water in sequence under the stirring speed of 550 rpm to obtain a monomer mixed solution; the particle size of the ice micro-powder was 4μm; the mass ratio of the ice micro-powder to aniline monomer was 12:1; and the mass ratio of aniline monomer to deionized water was 0.5:100; (2) under the condition of 500 rpm stirring, the pre-cooled initiator aqueous solution of ferric chloride was added into the monomer mixed solution in batches, after the addition was completed, the stirring reaction was continued, and then the product was obtained by filtering, washing and drying at room temperature; the mass ratio of the initiator to aniline monomer was 3:1; the adding in batches was that the initiator was added in two batches at a constant speed, specifically, 10wt% of the total initiator was added in the first batch, after 0.7h of reaction, the remaining initiator was continuously added until the addition was completed, and the total time of the two additions was 20min; the total time of the stirring reaction was 13h; (3) the diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, then the dianhydride monomer was added, and a polyamic acid solution was obtained after 8h of reaction at 27℃; the obtained polyamic acid solution was dropped into water for precipitation, and then the polyamic acid powder was obtained by filtering; wherein the diamine monomer was composed of 4,4'-diaminodiphenyl methane and 3,3'-diaminobenzophenone with a molar ratio of 1:2, the dianhydride monomer was composed of 3,3',4,4'-benzophenonetetracarboxylic dianhydride and oxybisphthalic anhydride with a molar ratio of 1:1, the molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 6wt%; The polyamic acid powder, the organic base triethylamine and the curved surface polyaniline were added into deionized water and stirred uniformly; a polyamic acid hydrogel was obtained by sol-gel; the mass ratio of the curved surface polyaniline to the polyamic acid powder was 0.7:1; the mass ratio of the organic base to the polyamic acid powder was 0.5:1; and the mass ratio of the polyamic acid powder to the deionized water was 3wt%; (4) the polyamic acid hydrogel was freeze-dried, and then heat imidized under the conditions of 150℃ / 1h, 200℃ / 2h and 230℃ / 2h, to obtain a polyimide aerogel for 3D printing; the polyimide aerogel was used as a conductive reinforcing filler of thermoplastic polyurethane, and the elongation at break of the thermoplastic polyurethane was 583% and the electrical conductivity was 36.86×10 -4 S / cm.

[0045] Example 6 A preparation method of a polyimide aerogel for 3D printing, comprising the following steps: (1) under the condition of an ice-salt bath, aniline monomer and ice micro-powder were added into deionized water in sequence under the stirring speed of 450 rpm to obtain a monomer mixed solution; the particle size of the ice micro-powder was 15μm; the mass ratio of the ice micro-powder to the aniline monomer was 8.5:1; and the mass ratio of the aniline monomer to the deionized water was 0.35:100; (2) under the condition of 450 rpm stirring, the pre-cooled initiator aqueous solution of ferric chloride was added into the monomer mixed solution in batches, after the addition was completed, the stirring reaction was continued, and then the product was obtained by filtering, washing and drying at room temperature; the mass ratio of the initiator to aniline monomer was 2.8:1; the adding in batches was that the initiator was added in two batches at a constant speed, specifically, 13wt% of the total initiator was added in the first batch, after 0.6h of reaction, the remaining initiator was continuously added until the addition was completed, and the total time of the two additions was 19min; the total time of the stirring reaction was 11.5h; (3) the diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, then the dianhydride monomer was added, and a polyamic acid solution was obtained after 7.5h of reaction at 26℃; the obtained polyamic acid solution was dropped into water for precipitation, and then the polyamic acid powder was obtained by filtering; wherein the diamine monomer was composed of 4,4'-diaminodiphenyl sulfone and 3,3'-diaminophenyl ether with a molar ratio of 1.5:1, the dianhydride monomer was composed of pyromellitic dianhydride and oxybisphthalic anhydride with a molar ratio of 2:1, the molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 5.5wt%; The polyamic acid powder, the organic base triethylamine and the curved surface polyaniline were added into deionized water and stirred uniformly; a polyamic acid hydrogel was obtained by sol-gel; the mass ratio of the curved surface polyaniline to the polyamic acid powder was 0.45:1; the mass ratio of the organic base to the polyamic acid powder was 0.4:1; and the mass ratio of the polyamic acid powder to the deionized water was 2.5wt%; (4) the polyamic acid hydrogel was freeze-dried, and then heat imidization was performed under the conditions of 150℃ / 1h, 200℃ / 2h and 230℃ / 2h, and thus a polyimide aerogel for 3D printing was obtained; the polyimide aerogel was used as a conductive reinforcing filler of thermoplastic polyurethane, and the elongation at break of the thermoplastic polyurethane was 587% and the electrical conductivity was 34.36×10 -4 S / cm.

[0046] Example 7 A preparation method of a polyimide aerogel for 3D printing, comprising the following steps: (1) under the condition of an ice-salt bath, aniline monomer and ice micro-powder were added into deionized water in sequence under the stirring speed of 550 rpm, and a monomer mixed solution was obtained; the particle size of the ice micro-powder was 4μm; the mass ratio of the ice micro-powder to aniline monomer was 12:1; and the mass ratio of aniline monomer to deionized water was 0.5:100; (2) under the condition of 500 rpm stirring, the pre-cooled initiator aqueous solution of ferric chloride was added into the monomer mixed solution in batches, after the addition was completed, the stirring reaction was continued, and then the product was obtained by filtering, washing and drying at room temperature; the mass ratio of the initiator to aniline monomer was 3:1; the adding in batches was that the initiator was added in two batches at a constant speed, specifically, 20wt% of the total initiator was added in the first batch, after 0.7h of reaction, the remaining initiator was continuously added until the addition was completed, and the total time of the two additions was 20min; the total time of the stirring reaction was 13h; (3) the diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, then the dianhydride monomer was added, and a polyamic acid solution was obtained after 8h of reaction at 27℃; the obtained polyamic acid solution was dropped into water for precipitation, and then the polyamic acid powder was obtained by filtering; wherein the diamine monomer was composed of 4,4'-diaminodiphenyl methane and 3,3'-diaminobenzophenone with a molar ratio of 1:2, the dianhydride monomer was composed of 3,3',4,4'-benzophenonetetracarboxylic dianhydride and oxybisphthalic anhydride with a molar ratio of 1:1, the molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 6wt%; The polyamic acid powder, the organic base triethylamine and the curved surface polyaniline were added into deionized water and stirred uniformly; a polyamic acid hydrogel was obtained by sol-gel; the mass ratio of the curved surface polyaniline to the polyamic acid powder was 0.7:1; the mass ratio of the organic base to the polyamic acid powder was 0.5:1; and the mass ratio of the polyamic acid powder to the deionized water was 3wt%; (4) the polyamic acid hydrogel was freeze-dried, and then heat imidized under the conditions of 150℃ / 1h, 200℃ / 2h and 230℃ / 2h, to obtain a polyimide aerogel for 3D printing; the polyimide aerogel was used as a conductive reinforcing filler of thermoplastic polyurethane, and the elongation at break of the thermoplastic polyurethane was 579% and the electrical conductivity was 37.31×10 -4 S / cm.

[0047] Example 8 A preparation method of a polyimide aerogel for 3D printing, comprising the following steps: (1) under the condition of an ice-salt bath, aniline monomer and ice micro-powder were added into deionized water in sequence under the stirring speed of 550 rpm to obtain a monomer mixed solution; the particle size of the ice micro-powder was 15μm; the mass ratio of the ice micro-powder to the aniline monomer was 14:1; and the mass ratio of the aniline monomer to the deionized water was 0.45:100; (2) under the condition of 600 rpm stirring, the pre-cooled initiator aqueous solution of ferric chloride was added into the monomer mixed solution in batches, after the addition was completed, the stirring reaction was continued, and then the product was obtained by filtering, washing and drying at room temperature; the mass ratio of the initiator to aniline monomer was 3:1; the adding in batches was that the initiator was added in two batches at a constant speed, specifically, 16wt% of the total initiator was added in the first batch, after 0.8h of reaction, the remaining initiator was continuously added until the addition was completed, and the total time of the two additions was 23min; the total time of the stirring reaction was 13.5h; (3) the diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, then the dianhydride monomer was added, and a polyamic acid solution was obtained after 8.5h of reaction at 28℃; the obtained polyamic acid solution was dropped into water for precipitation, and then the polyamic acid powder was obtained by filtering; wherein the diamine monomer was composed of 4,4'-diaminodiphenyl methane and 3,3'-diamino diphenyl ether with a molar ratio of 1:1, the dianhydride monomer was composed of pyromellitic dianhydride and 3,3',4,4'-benzophenone tetracarboxylic dianhydride with a molar ratio of 1:2, the molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 6wt%; The polyamic acid powder, the organic base triethylamine and the curved surface polyaniline were added into deionized water and stirred uniformly; a polyamic acid hydrogel was obtained by sol-gel; the mass ratio of the curved surface polyaniline to the polyamic acid powder was 0.65:1; the mass ratio of the organic base to the polyamic acid powder was 0.6:1; and the mass ratio of the polyamic acid powder to the deionized water was 3wt%; (4) the polyamic acid hydrogel was freeze-dried, and then heat imidization was performed under the conditions of 150℃ / 1h, 200℃ / 2h and 230℃ / 2h, and thus a polyimide aerogel for 3D printing was obtained; the polyimide aerogel was used as a conductive reinforcing filler of thermoplastic polyurethane, and the elongation at break of the thermoplastic polyurethane was 577% and the electrical conductivity was 36.54×10 -4 S / cm.

[0048] Example 9 A preparation method of a polyimide aerogel for 3D printing, comprising the following steps: (1) under the condition of an ice-salt bath, aniline monomer and ice micro-powder were added into deionized water in sequence under the stirring speed of 500 rpm, and a monomer mixed solution was obtained; the particle size of the ice micro-powder was 4μm; the mass ratio of the ice micro-powder to the aniline monomer was 15:1; and the mass ratio of the aniline monomer to the deionized water was 0.45:100; (2) under the condition of 650 rpm stirring, the pre-cooled initiator aqueous solution of ferric chloride was added into the monomer mixed solution in batches, after the addition was completed, the stirring reaction was continued, and then the product was obtained by filtering, washing and drying at room temperature; the mass ratio of the initiator to aniline monomer was 2.9:1; the adding in batches was that the initiator was added in two batches at a constant speed, specifically, 16wt% of the total initiator was added in the first batch, after 0.7h of reaction, the remaining initiator was continuously added until the addition was completed, and the total time of the two additions was 20min; the total time of the stirring reaction was 12.5h; (3) the diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, then the dianhydride monomer was added, and a polyamic acid solution was obtained after 8h of reaction at 27℃; the obtained polyamic acid solution was dropped into water for precipitation, and then the polyamic acid powder was obtained by filtering; wherein the diamine monomer was composed of 3,3'-diaminobenzophenone and 3,3'-diamino diphenyl ether with a molar ratio of 1:2.5, the dianhydride monomer was composed of 3,3',4,4'-biphenyl tetracarboxylic dianhydride and oxybisphthalic anhydride with a molar ratio of 1:1, the molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 5.5wt%; The polyamic acid powder, the organic base triethylamine and the curved surface polyaniline were added into deionized water and stirred uniformly; a polyamic acid hydrogel was obtained by sol-gel; the mass ratio of the curved surface polyaniline to the polyamic acid powder was 0.55:1; the mass ratio of the organic base to the polyamic acid powder was 0.55:1; and the mass ratio of the polyamic acid powder to the deionized water was 2.8wt%; (4) the polyamic acid hydrogel was freeze-dried, and then heat imidization was performed under the conditions of 150℃ / 1h, 200℃ / 2h and 230℃ / 2h, and thus a polyimide aerogel for 3D printing was obtained; the polyimide aerogel was used as a conductive reinforcing filler of thermoplastic polyurethane, and the elongation at break of the thermoplastic polyurethane was 571% and the electrical conductivity was 36.67×10 -4 S / cm.

[0049] Example 10 A preparation method of a polyimide aerogel for 3D printing, comprising the following steps: (1) under the condition of an ice-salt bath, aniline monomer and ice micro-powder were added into deionized water in sequence under the stirring speed of 550 rpm, and a monomer mixed solution was obtained; the particle size of the ice micro-powder was 4μm; the mass ratio of the ice micro-powder to aniline monomer was 12:1; and the mass ratio of aniline monomer to deionized water was 0.5:100; (2) under the condition of 500 rpm stirring, the pre-cooled initiator aqueous solution of ferric chloride was added into the monomer mixed solution in batches, after the addition was completed, the stirring reaction was continued, and then the product was obtained by filtering, washing and drying at room temperature; the mass ratio of the initiator to aniline monomer was 3:1; the adding in batches was that the initiator was added in two batches at a constant speed, specifically, 15wt% of the total initiator was added in the first batch, after 0.7h of reaction, the remaining initiator was continuously added until the addition was completed, and the total time of the two additions was 20min; the total time of the stirring reaction was 13h; (3) the diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, then the dianhydride monomer was added, and a polyamic acid solution was obtained after 8h of reaction at 27℃; the obtained polyamic acid solution was dropped into water for precipitation, and then the polyamic acid powder was obtained by filtering; wherein the diamine monomer was composed of 4,4'-diaminodiphenyl methane and 3,3'-diaminobenzophenone with a molar ratio of 1:2, the dianhydride monomer was composed of 3,3',4,4'-benzophenonetetracarboxylic dianhydride and oxybisphthalic anhydride with a molar ratio of 1:1, the molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 6wt%; The polyamic acid powder, the organic base triethylamine and the curved surface polyaniline were added into deionized water and stirred uniformly; a polyamic acid hydrogel was obtained by sol-gel; the mass ratio of the curved surface polyaniline to the polyamic acid powder was 0.7:1; the mass ratio of the organic base to the polyamic acid powder was 0.5:1; and the mass ratio of the polyamic acid powder to the deionized water was 3wt%; (4) the polyamic acid hydrogel was freeze-dried, and then heat imidized under the conditions of 150℃ / 1h, 200℃ / 2h and 230℃ / 2h, to obtain a polyimide aerogel for 3D printing; the polyimide aerogel was used as a conductive reinforcing filler of thermoplastic polyurethane, and the elongation at break of the thermoplastic polyurethane was 593% and the electrical conductivity was 38.27×10 -4 S / cm.

[0050] Comparative Example 1 A preparation method of a polyimide aerogel for 3D printing, comprising the following steps: (1) under the condition of an ice-salt bath, aniline monomer and ice micro-powder were added into deionized water in sequence under the stirring speed of 550 rpm to obtain a monomer mixed solution; the particle size of the ice micro-powder was 4μm; the mass ratio of the ice micro-powder to aniline monomer was 12:1; and the mass ratio of aniline monomer to deionized water was 0.5:100; (2) under the condition of 500 rpm stirring, continuously drop the pre-cooled initiator aqueous solution of ferric chloride into the monomer mixed solution, after the dropping is completed, continue to stir and react, filter, wash at room temperature, and after drying, polyaniline is obtained; the mass ratio of the initiator to aniline monomer is 3:1; the total dropping time is 20 min; the total time of the stirring reaction is 13 h; (3) disperse the diamine monomer in the organic solvent N,N-dimethylacetamide, then add the dianhydride monomer, and obtain a polyamic acid solution after 8 h of reaction at 27℃; drop the obtained polyamic acid solution into water for precipitation, filter, and obtain a polyamic acid powder; wherein the diamine monomer is composed of 4,4'-diaminodiphenyl methane and 3,3'-diaminobenzophenone with a molar ratio of 1:2, the dianhydride monomer is composed of 3,3',4,4'-benzophenonetetracarboxylic dianhydride and oxybisphthalic anhydride with a molar ratio of 1:1, the molar ratio of the diamine monomer to the dianhydride monomer is 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent is 6wt%; add the polyamic acid powder, the organic base triethylamine, and the polyaniline into deionized water, and stir uniformly; obtain a polyamic acid hydrogel through sol-gel; the mass ratio of the polyaniline to the polyamic acid powder is 0.7:1; the mass ratio of the organic base to the polyamic acid powder is 0.5:1; and the mass ratio of the polyamic acid powder to the deionized water is 3wt%; (4) freeze dry the polyamic acid hydrogel, and perform thermal imidization under the conditions of 150℃ / 1h, 200℃ / 2h, and 230℃ / 2h, and obtain a polyimide aerogel for 3D printing. As a conductive reinforcing filler of thermoplastic polyurethane, the elongation at break is 538%, and the electrical conductivity is 2.49×10 -4 S / cm.

[0051] Comparative Example 2 A preparation method of a polyimide aerogel for 3D printing, comprising the following steps: (1) under the condition of an ice-salt bath, add pre-cooled aniline monomer and ice micro-powder into deionized water at a stirring speed of 550 rpm to obtain a monomer mixed solution; the particle size of the ice micro-powder is 4μm; the mass ratio of the ice micro-powder to the aniline monomer is 12:1; and the mass ratio of the aniline monomer to the deionized water is 0.5:100; (2) under the condition of 200 rpm stirring, the pre-cooled initiator aqueous solution of ferric chloride was added into the monomer mixed solution in batches, after the addition was completed, the stirring reaction was continued, and the product was obtained after filtration, washing and drying at room temperature; the mass ratio of the initiator to aniline monomer was 3:1; the adding in batches was that the initiator was added in two batches at a constant speed, specifically, 15wt% of the total initiator was added in the first batch, after 0.7h of reaction, the remaining initiator was continuously added until the addition was completed, and the total time of the two additions was 20min; the total time of the stirring reaction was 13h; (3) the diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, then the dianhydride monomer was added, and a polyamide acid solution was obtained after 8h of reaction at 27℃; the obtained polyamide acid solution was dropped into water for precipitation, and the polyamide acid powder was obtained after filtration; wherein the diamine monomer was composed of 4,4'-diaminodiphenyl methane and 3,3'-diaminobenzophenone with a molar ratio of 1:2, the dianhydride monomer was composed of 3,3',4,4'-benzophenonetetracarboxylic dianhydride and oxybisphthalic anhydride with a molar ratio of 1:1, the molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 6wt%; The polyamide acid powder, organic base triethylamine and polyaniline were added into deionized water and stirred uniformly; a polyamide acid hydrogel was obtained after sol-gel; the mass ratio of polyaniline to polyamide acid powder was 0.7:1; the mass ratio of organic base to polyamide acid powder was 0.5:1; the mass ratio of polyamide acid powder to deionized water was 3wt%; (4) the polyamide acid hydrogel was freeze-dried, and thermal imidization was carried out under the conditions of 150℃ / 1h, 200℃ / 2h and 230℃ / 2h, and a polyimide aerogel for 3D printing was obtained. When the polyimide aerogel was used as a conductive reinforcing filler of thermoplastic polyurethane, the elongation at break was 547% and the electrical conductivity was 4.13×10 -4 S / cm.

[0052] Figure 1 The scanning electron microscope image of the curved polyaniline prepared in Example 10. As can be seen from the figure, the polyaniline has a clear arc structure, the existence of the arc structure is conducive to the dispersion of the stress and promotes the stability of the polyaniline morphology; and the arc structure is also conducive to the full infiltration of the polyimide resin solution, and the polyimide resin filled in the hollow interior enhances the bonding force of the polyaniline and the matrix resin.

[0053] Figure 2 The scanning electron microscope image of the polyaniline prepared in Comparative Example 1, which presents an obvious agglomerated block structure. This is because the initiator is added continuously at one time, which is not conducive to the formation of the initial curved structure, and the polymerization reaction rate is too fast, the aniline monomer cannot be combined to the surface of the ice powder in time and the polymerization reaction occurs, so that the curved structure cannot be formed.

[0054] It can be seen from the mechanical data and conductive data of the various embodiments and comparative examples that the efficient combination of electrical conductivity and the inherent excellent performance of polyimide (such as flexibility and strength) is achieved by adding polyaniline with a curved structure. The polyaniline with a curved structure is a three-dimensional conductive unit itself, thereby constructing an efficient three-dimensional conductive network in the composite material. The curved morphology is more easily dispersed in the polyimide molecular chain, reducing the hindrance to the movement of the polymer chain segment, improving the flexibility of the polyimide aerogel, and effectively avoiding the disadvantage that the traditional conductive filler will make the composite material brittle at a high content. In addition, the curved structure has a large specific surface area, which means that there is a larger contact area between polyaniline and the polyimide matrix. The larger contact area can produce stronger interfacial interactions, not only helping to transfer stress from the matrix to the filler, to some extent, to improve the mechanical strength of the material, but also helping to prevent the curved structure polyaniline from agglomerating in the matrix, making it more uniformly distributed, thereby ensuring the stability of the conductive network.

[0055] Specifically, compared with Example 10, the initiator in Comparative Example 1 is continuously added, on the one hand, the polymerization reaction rate is too fast, and the aniline monomer cannot be combined with the surface of the ice micro powder in time and polymerization reaction occurs; on the other hand, too much initiator will cause the generated polyaniline to cause self-nucleation effect, resulting in the appearance of accumulation structure, which is not conducive to the improvement of electrical conductivity and mechanical properties. The stirring rate in Comparative Example 2 is too low during polymerization, which is not conducive to the heterogeneous nucleation effect of the ice micro powder, and cannot effectively construct the conductive, reinforcing, and dispersed network, resulting in a decrease in the electrical conductivity and elongation at break of the 3D printing material.

[0056] The above is only a preferred embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent flow transformation made by using the content of the specification and drawings of the present application, or directly or indirectly applied to other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for preparing polyimide aerogel for 3D printing, characterized in that, Includes the following steps: (1) Under ice-salt bath conditions, aniline monomer and ice powder were added to deionized water while stirring to obtain a monomer mixed solution; (2) Under stirring conditions of not less than 400 rpm, the initiator is added dropwise to the monomer mixture solution in batches. After the addition is completed, the reaction is stirred and the reaction is continued. After post-treatment, curved polyaniline is obtained. The initiator added for the first time accounts for 10-20 wt% of the total initiator. After the reaction is carried out for 0.5-1 h, the remaining initiator is added dropwise. (3) Add polyamic acid powder, organic base and curved polyaniline to deionized water and stir evenly; obtain polyamic acid hydrogel by sol-gelation; (4) Freeze-dry the polyamic acid hydrogel and heat imidize it to obtain polyimide aerogel for 3D printing.

2. The method for preparing a polyimide aerogel for 3D printing as described in claim 1, characterized in that, In step (1), the mass ratio of ice micro powder to aniline monomer is 5-20:1, and in step (2), the stirring speed is 400-700 rpm.

3. The method for preparing a polyimide aerogel for 3D printing as described in claim 1, characterized in that, In step (3), the polyamic acid powder is prepared by copolymerizing dianhydride monomer and diamine monomer to form a polyamic acid solution, which is then precipitated by dripping into deionized water.

4. The method for preparing a polyimide aerogel for 3D printing as described in claim 3, characterized in that, The dianhydride monomer is selected from pyromellitic dianhydride, oxydiphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, diphenyl sulfone-3,4,3',4'-tetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)sulfide dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,3,3',4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, and p-phenylene bis(p-phenylene)sulfide. The dianhydride is selected from at least one of the following: benzotriphenyl dianhydride, p-triphenyl bis(triphenyl dianhydride), meta-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, p-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, 1,3-bis(3,4-dicarboxyphenoxy)phenyl dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)phenyl dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, and 4,4'-(2,2-hexafluoroisopropylidene)diphthalic dianhydride.

5. The method for preparing a polyimide aerogel for 3D printing as described in claim 3, characterized in that, The diamine monomer is selected from p-phenylenediamine, m-phenylenediamine, 3,3'-dimethylbenzidine, 2,2'-dimethylbenzidine, 2,4-diaminotoluene, 2,6-diaminotoluene, 3,5-diaminobenzoic acid, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-dicarboxy-4,4 '-Diaminodiphenylmethane, 3,3',5,5'-Tetramethyl-4,4'-Diaminodiphenylmethane, bis(4-aminophenyl)sulfide, 4,4'-diaminobenzoylaniline, 3,3'-dimethoxybenzidine, 2,2'-dimethoxybenzidine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3 '-Diaminobenzophenone, 4,4'-Diaminobenzophenone, 3,3'-Diamino-4,4'-Dichlorobenzophenone, 3,3'-Diamino-4,4'-Dimethoxybenzophenone, 3,3'-Diaminodiphenylmethane, 3,4'-Diaminodiphenylmethane, 4,4'-Diaminodiphenylmethane, 2,2-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 2,2-bis(3-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 2,2-bis(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 3,3'-Diamino At least one of the following: diphenyl sulfoxide, 3,4'-diaminodiphenyl sulfoxide, 4,4'-diaminodiphenyl sulfoxide, 1,3-bis(3-aminophenyl)benzene, 1,3-bis(4-aminophenyl)benzene, 1,4-bis(3-aminophenyl)benzene, 1,4-bis(4-aminophenyl)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene, 3,3'-diamino-4-(4-phenyl)phenoxybenzophenone, and 3,3'-diamino-4,4'-bis(4-phenylphenoxy)benzophenone.

6. The method for preparing a polyimide aerogel for 3D printing as described in claim 1, characterized in that, The organic base in step (3) is one or more of triethylamine, tripropylamine, diethylenetriamine, and triethylenetetramine.

7. The method for preparing a polyimide aerogel for 3D printing as described in claim 1, characterized in that, In step (3), the mass ratio of organic base to polyamic acid powder is (0.1-1):

1.

8. A polyimide aerogel for 3D printing, characterized in that, It is prepared by the method for preparing a polyimide aerogel for 3D printing according to any one of claims 1-7.

9. An application of the polyimide aerogel for 3D printing as described in claim 8, characterized in that, The polyimide aerogel for 3D printing is used in photopolymerization, selective laser sintering, fused deposition modeling, or layered solid manufacturing technologies in 3D printing.

10. A 3D printing polyurethane material, characterized in that, It comprises a polyurethane resin material and a polyimide aerogel for 3D printing; the polyimide aerogel for 3D printing is the polyimide aerogel for 3D printing as described in claim 8.

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