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

Abstract

The present application belongs to the technical field of aerogel, and particularly relates to a kind of polyimide aerogel for 3D printing and its preparation method and application. The present application uses ice micro powder as the synthetic template of aniline monomer, prepares polyphenylamine with curved surface structure, and uses polyamide acid in-situ composite method to prepare polyphenylamine / polyimide composite aerogel. The polyphenylamine with curved surface structure is a three-dimensional conductive unit itself, when they are dispersed in polyimide matrix, these curved surface structures can contact with each other, thereby constructing efficient three-dimensional conductive network in the composite material. And the curved surface structure has larger specific surface area, so that polyphenylamine has larger contact area with polyimide matrix, which not only helps stress transfer from matrix to filler, but also helps to prevent the curved surface structure polyphenylamine from agglomerating in the matrix, so that it is more uniformly distributed, and the flexibility of 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 the polyurethane is low, and it is difficult to directly print by blending. The existing technology uses different templates to prepare special morphology of conductive polymer 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:

[0008] A preparation method of a 3D printing polyimide aerogel, comprising the following steps:

[0009] (1) under ice-salt bath conditions, aniline monomer and ice powder are added to deionized water while stirring to obtain a monomer mixture solution;

[0010] (2) under stirring conditions of not less than 400 rpm, an initiator is added to the monomer mixture solution in batches, and after the addition is completed, the stirring reaction is continued, and after 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;

[0011] (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;

[0012] (4) the polyamide acid hydrogel is freeze-dried and thermal imidized to obtain a 3D printing polyimide aerogel.

[0013] 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 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, and its electrical properties can be ideally controlled by changing the reaction conditions and synthesis process. 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, and ideal film forming effect. 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 polymer. Therefore, combining conductive polymers with other ordinary polymers that are easy to be molded and processed to prepare functional polymers with special purposes according to the actual application needs has become the main way to broaden the application field of polyaniline conductive polymers.

[0014] In the previous work, the inventors used nylon 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 a 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 to the matrix. Moreover, the rigidity of the polyimide molecular chain and the strong intermolecular forces make the skeleton very strong, and even at a 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 3D printed polyurethane matrix 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 amount of addition, its reinforcing effect is better than that of nylon aerogel. 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 a prerequisite for effective reinforcement.

[0015] Moreover, as a kind of special engineering plastic, the imide ring in the molecular chain of polyimide imparts excellent chemical resistance and high mechanical properties to the polyimide material. Both polyimide and polyurethane have nitrogen-containing functional groups, and they have good compatibility, so they can be used as a matrix for preparing conductive fillers for polyurethane. Moreover, during the blending process, the carboxyl groups in the polyamide acid also act as a proton acid to some extent, doping the generated polyaniline and converting it into the conductive emeraldine salt form, thereby improving its conductivity.

[0016] In previous work (CN120818176A, CN120865604A), the inventors also used inorganic solid or hollow nanoparticles as templates to prepare polyaniline microspheres with core-shell structure by in-situ polymerization in a polyaniline solution, however, the above process needs to add inorganic nanoparticles as templates, and the above process needs to be carried out in a polyaniline solution, the in-situ polymerization preparation process is complex, the reaction conditions are harsh, and it is difficult to popularize in the market. More importantly, due to the limitation of solution viscosity, a large amount of unreacted aniline monomer small molecules exist 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 aerogel and 3D printing products.

[0017] In order to solve the problem of additional addition of non-conductive templates in the preparation process of special morphology polyaniline, the ice micro-powder is used as the synthesis template of aniline monomer to prepare the polyaniline with curved surface structure, which has the characteristics of high efficiency, compatibility, light weight and stability.

[0018] The ice template method is a very widely used material preparation technology. The ice crystal template method is combined with the freeze-drying method to adjust the microstructure of the polyaniline-containing polyimide aerogel, and a polyaniline-based aerogel conductive polymer material with a multi-level structure is prepared.

[0019] 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.

[0020] 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.

[0021] 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 ℃).

[0022] Furthermore, the mass ratio of ice micropowder to 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, or 15:1. In particular, it can be 8-15:1. An appropriate amount of ice micropowder can fully exert its nucleation effect, preventing excessive ice micropowder from causing disturbance in the solution, which is detrimental to the dispersion, adhesion, and polymerization process of aniline monomer.

[0023] Furthermore, in step (1), the mass ratio of aniline monomer to deionized water is (0.1-2):100. Alternatively, it can be (0.5-1):100. The addition of a large amount of deionized water can improve the stability of the ice micron powder and promote the formation of curved structures.

[0024] Furthermore, the stirring rate in step (1) is not particularly limited, but can be 400-600 rpm. More specifically, the stirring rate is 500-600 rpm. Stirring promotes the dispersion of the components and facilitates the full binding of the ice micro powder with the aniline monomer.

[0025] Furthermore, in step (1), aniline monomer is added first and mixed evenly, and then ice powder is added. The mixing of ice powder and aniline monomer is promoted by stirring.

[0026] Furthermore, 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, which has a doping effect, is selected. Lewis acid doping can greatly improve the conductivity of polyaniline. Specifically, it can be added dropwise in the form of an aqueous solution of ferric chloride, 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.

[0027] Furthermore, the batch addition mentioned in step (2) involves adding the initiator in two batches. Specifically, the initial addition of initiator accounts for 12-18 wt% of the total initiator. After reacting for 0.6-0.8 hours, the remaining initiator is added until the addition is complete. There is no particular limitation on the dropping rate, and each batch can be added at a uniform rate. Further, the initial addition of initiator accounts for 13-18 wt% of the total initiator; even further, it is 14-15 wt%. In order to minimize the impact of temperature changes on ice micropowder, after the addition of materials in step (1), the first batch of initiator is added quickly. 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 10-30 minutes. By adding the initiator in batches, the polymerization process of aniline monomer can be reasonably controlled. After the initial addition of 12-18 wt% initiator, after reacting for a period of time, a small amount of initiator can control the polymerization rate of aniline monomer, which is conducive to the aniline monomer adhering to the surface of ice particles and fully exerting the nucleation effect. Furthermore, after the first batch of initiator is added, the aniline monomer quickly polymerizes on the surface of the ice micro powder after a period of reaction, promoting the formation of the initial curved surface morphology of polyaniline and preventing random polymerization of aniline caused by continuous addition of initiator. On the one hand, the initially formed curved surface structure can eliminate the influence of morphological changes caused by melting during the reaction of ice micro powder, promoting the formation of the curved surface structure; on the other hand, the batch addition and segmented polymerization of the initiator can reduce the influence of polar substances on the solution system and improve the stability of ice micro powder.

[0028] Furthermore, the total reaction time described in step (2), i.e., the time from the initial addition of the initiator to the completion of the reaction, is 10-20 hours. After the reaction is complete, the mixture can be brought back to room temperature, and the ice powder will dissolve. The post-treatment involves filtration, washing, and drying at room temperature. Specifically, washing can be done with deionized water, and drying can be carried out in a vacuum oven.

[0029] Furthermore, the polyamic acid powder mentioned in step (3) is prepared by copolymerizing dianhydride monomers and diamine monomers to form a polyamic acid solution, which is then precipitated by dropping it into deionized water. Since polyamic acid has poor stability, it is best to prepare it immediately before use. Specifically, it can be prepared using dianhydride monomers and diamine monomers as raw materials in an organic solvent. Mixing the polyamic acid powder and curved polyaniline again in the solvent can perform a secondary doping effect on the polyaniline. Secondary doping can promote the unfolding of the polyaniline backbone, enhance the interaction of charge carriers, and further improve the conductivity and mechanical properties of polyaniline.

[0030] There are no particular limitations on the type of dianhydride monomer, diamine monomer, or organic solvent; any commonly used in the field may be used. Specifically, the molar ratio of dianhydride monomer to diamine monomer is (0.95-1.05):(0.95-1.05). In particular, multiple dianhydride monomers or diamine monomers can be used for copolymerization to improve the processing properties of polyimide.

[0031] For example, dianhydride monomers can be pyromellitic dianhydride (PMDA), oxydiphthalic anhydride (ODPA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA), 2,3,3',4'-biphenyltetracarboxylic 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-di... The following are at least one of the following: (carboxyphenyl)propane dianhydride, p-phenylenebis(triphenyltriacrylic acid monoester anhydride), p-biphenylenebis(triphenyltriacrylic acid monoester anhydride), m-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 (BPADA), 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, and 4,4'-(2,2-hexafluoroisopropylidene)diphthalic dianhydride.

[0032] The diamine monomer can be p-phenylenediamine (PPD), m-phenylenediamine, 3,3'-dimethylbenzidine, 2,2'-dimethylbenzidine, 2,4-diaminotoluene, 2,6-diaminotoluene, 3,5-diaminobenzoic acid (DABA), 4,4'-diaminodiphenyl ether (ODA), 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane (methylenediamine), 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'-Diaminodiphenyl sulfoxide, At least one of 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 (TPE-R), 1,4-bis(3-aminophenoxy)benzene (TPE-Q), 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene, 3,3'-diamino-4-(4-phenyl)phenoxybenzophenone, 3,3'-diamino-4,4'-bis(4-phenylphenoxy)benzophenone, etc.

[0033] The organic solvent may be one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide, N-methylpyrrolidone (NMP), and γ-butyrolactone (GBL).

[0034] Furthermore, in step (3), the organic base is one or more of triethylamine, tripropylamine, diethylenetriamine, and triethylenetetramine; the mass ratio of the organic base to the polyamic acid powder is (0.1-1):1.

[0035] Furthermore, in step (3), the mass ratio of polyamic acid powder to deionized water is 1-10 wt%. In particular, it can be 5 wt%.

[0036] Furthermore, in step (3), the mass ratio of curved polyaniline to polyamic acid powder is (0.1-1):1.

[0037] Furthermore, in step (4), the thermal imidization temperature is 150℃-230℃ and the time is 3-10h.

[0038] On the other hand, the present invention also provides a polyimide aerogel for 3D printing prepared by the above method. Using polyimide resin as the aerogel matrix resin, both it and polyaniline contain nitrogen-containing groups, resulting in good compatibility. More importantly, the polyimide solution is easily freeze-dried, promoting aerogel formation.

[0039] On the other hand, the present invention also provides an application of polyimide aerogel for 3D printing and a 3D printing polyurethane material reinforced with it. Specifically, the polyimide aerogel for 3D printing is used in photopolymerization, selective laser sintering, fused deposition modeling (FDM), or layered solid fabrication techniques in 3D printing technology. Specifically, the 3D printing polyurethane material comprises polyurethane resin material and polyimide aerogel for 3D printing. Further, photopolymerization or FDM techniques can be used. Specifically, the polyurethane material is prepared using FDM. The printing temperature in FDM is not particularly limited, generally between 190-220°C, and can be adjusted according to the production process. Furthermore, the 3D printing polyurethane material may also contain various reinforcing fillers, flow modifiers, lubricants, antioxidants, UV stabilizers, hydrolysis inhibitors, colorants, and other additives. Specifically, the type of reinforcing filler is not particularly limited and may include granular, fibrous, or sheet-like fillers. It should be noted that the types of raw materials used in this invention are not particularly limited; they can be prepared using conventional processes in the art or commercially available. For example, the thermoplastic polyurethane used can be common materials such as Wanhua Q / 0600.

[0040] 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

[0041] Figure 1 Scanning electron microscope image of the curved polyaniline prepared in Example 10;

[0042] Figure 2 Scanning electron microscope image of polyaniline prepared for Comparative Example 1. Detailed Implementation

[0043] 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.

[0044] 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.

[0045] 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.

[0046] Example 1

[0047] A method for preparing polyimide aerogel for 3D printing includes the following steps:

[0048] (1) Under ice-salt bath conditions, the pre-cooled aniline monomer and ice powder were added to deionized water at a stirring speed of 400 rpm to obtain a monomer mixed solution; the ice powder had a particle size of 15 μm; the mass ratio of ice powder to aniline monomer was 5:1; the mass ratio of aniline monomer to deionized water was 0.3:100.

[0049] (2) Under stirring at 400 rpm, the pre-cooled ferric chloride aqueous solution of the initiator was added dropwise to the monomer mixture in batches. After the addition was completed, the reaction was stirred and the mixture was filtered, washed and dried at room temperature to obtain curved polyaniline. The mass ratio of the initiator to the aniline monomer was 2.5:1. The batch addition was to add the initiator in two batches at a uniform rate. Specifically, the first batch was 11 wt% of the total initiator mass. After reacting for 0.5 h, the remaining initiator was added dropwise until the addition was completed. The total time for the two additions was 17 min. The total time for the stirring reaction was 15 h.

[0050] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 25°C for 9 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenyl ether and 4,4'-diaminodiphenylmethane in a molar ratio of 3:1, and the dianhydride monomer was composed of 3,3',4,4'-biphenyltetracarboxylic dianhydride and pyromellitic dianhydride in 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 mass of the organic solvent was 5 wt%.

[0051] Polyamic acid powder, triethylamine (an organic base), and curved polyaniline were added to deionized water and stirred until homogeneous. A polyamic acid hydrogel was obtained through sol-gelation. The mass ratio of curved polyaniline to polyamic acid powder was 0.4:1; the mass ratio of organic base to polyamic acid powder was 0.3:1; and the mass ratio of polyamic acid powder to deionized water was 2 wt%.

[0052] (4) The polyamic acid hydrogel was freeze-dried and then thermally imidized at 150℃ / 1h, 200℃ / 2h, and 230℃ / 2h to obtain polyimide aerogel for 3D printing. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 585%, and its electrical conductivity was 33.43×10⁻⁶. -4 S / cm.

[0053] Example 2

[0054] A method for preparing polyimide aerogel for 3D printing includes the following steps:

[0055] (1) Under ice-salt bath conditions, the pre-cooled aniline monomer and ice powder were added to deionized water at a stirring speed of 600 rpm to obtain a monomer mixed solution; the ice powder had a particle size of 800 nm; the mass ratio of ice powder to aniline monomer was 17:1; the mass ratio of aniline monomer to deionized water was 0.5:100.

[0056] (2) Under stirring at 700 rpm, the pre-cooled ferric chloride aqueous solution of the initiator was added dropwise to the monomer mixture in batches. After the addition was completed, the reaction was stirred and the mixture was filtered, washed and dried at room temperature to obtain curved polyaniline. The mass ratio of the initiator to the aniline monomer was 3.3:1. The batch addition was to add the initiator in two batches at a uniform rate. Specifically, the first batch was 18 wt% of the total initiator mass. After reacting for 1 hour, the remaining initiator was added dropwise until the addition was completed. The total time for the two additions was 26 minutes. The total time for the stirring reaction was 10 hours.

[0057] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 30°C for 7 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl sulfone in a molar ratio of 2:1. The dianhydride monomer was composed of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 3,3',4,4'-benzophenonetetracarboxylic dianhydride in a molar ratio of 2:1. The molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02. The mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 7 wt%.

[0058] Polyamic acid powder, triethylamine (an organic base), and curved polyaniline were added to deionized water and stirred until homogeneous. A polyamic acid hydrogel was obtained through sol-gelation. The mass ratio of curved polyaniline to polyamic acid powder was 0.8:1; the mass ratio of organic base to polyamic acid powder was 0.7:1; and the mass ratio of polyamic acid powder to deionized water was 3.5 wt%.

[0059] (4) The polyamic acid hydrogel was freeze-dried and then thermally imidized at 150℃ / 1h, 200℃ / 2h, and 230℃ / 2h to obtain polyimide aerogel for 3D printing. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 568%, and its electrical conductivity was 38.32×10⁻⁶. -4 S / cm.

[0060] Example 3

[0061] A method for preparing polyimide aerogel for 3D printing includes the following steps:

[0062] (1) Under ice-salt bath conditions, the pre-cooled aniline monomer and ice powder were added to deionized water at a stirring speed of 550 rpm to obtain a monomer mixed solution; the ice powder had a particle size of 4 μm; the mass ratio of ice powder to aniline monomer was 20:1; the mass ratio of aniline monomer to deionized water was 0.5:100.

[0063] (2) Under stirring at 500 rpm, the pre-cooled ferric chloride aqueous solution of the initiator was added dropwise to the monomer mixture in batches. After the addition was completed, the reaction was stirred and the mixture was filtered, washed and dried at room temperature to obtain curved polyaniline. The mass ratio of the initiator to the aniline monomer was 3:1. The batch addition was to add the initiator in two batches at a uniform rate. Specifically, the first batch was 15 wt% of the total initiator mass. After reacting for 0.7 h, the remaining initiator was added dropwise until the addition was completed. The total time for the two additions was 20 min. The total time for the stirring reaction was 13 h.

[0064] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 27°C for 8 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenylmethane and 3,3'-diaminobenzophenone in a molar ratio of 1:2. The dianhydride monomer was composed of 3,3',4,4'-benzophenone tetracarboxylic dianhydride and oxydiphthalic anhydride in a molar ratio of 1:1. The molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02. The mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 6 wt%.

[0065] Polyamic acid powder, triethylamine (an organic base), and curved polyaniline were added to deionized water and stirred until homogeneous. A polyamic acid hydrogel was obtained through sol-gelation. The mass ratio of curved polyaniline to polyamic acid powder was 0.7:1; the mass ratio of organic base to polyamic acid powder was 0.5:1; and the mass ratio of polyamic acid powder to deionized water was 3 wt%.

[0066] (4) The polyamic acid hydrogel was freeze-dried and then thermally imidized at 150℃ / 1h, 200℃ / 2h, and 230℃ / 2h to obtain polyimide aerogel for 3D printing. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 572%, and its electrical conductivity was 36.24×10⁻⁶. -4 S / cm.

[0067] Example 4

[0068] A method for preparing polyimide aerogel for 3D printing includes the following steps:

[0069] (1) Under ice-salt bath conditions, the pre-cooled aniline monomer and ice powder were added to deionized water at a stirring speed of 400 rpm to obtain a monomer mixed solution; the ice powder had a particle size of 4 μm; the mass ratio of ice powder to aniline monomer was 16:1; and the mass ratio of aniline monomer to deionized water was 0.35:100.

[0070] (2) Under stirring at 650 rpm, the pre-cooled ferric chloride aqueous solution of the initiator was added dropwise to the monomer mixture in batches. After the addition was completed, the reaction was stirred and the mixture was filtered, washed and dried at room temperature to obtain curved polyaniline. The mass ratio of the initiator to the aniline monomer was 2.6:1. The batch addition was to add the initiator in two batches at a uniform rate. Specifically, the first batch was 12 wt% of the total initiator mass. After reacting for 0.8 h, the remaining initiator was added dropwise until the addition was completed. The total time for the two additions was 25 min. The total time for the stirring reaction was 10 h.

[0071] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 30°C for 9 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenyl ether and 3,3'-diaminodiphenyl ether in a molar ratio of 1:1, and the dianhydride monomer was composed of 3,3',4,4'-biphenyltetracarboxylic dianhydride and oxydiphthalic anhydride in 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 wt%.

[0072] Polyamic acid powder, triethylamine (an organic base), and curved polyaniline were added to deionized water and stirred until homogeneous. A polyamic acid hydrogel was obtained through sol-gelation. The mass ratio of curved polyaniline to polyamic acid powder was 0.75:1; the mass ratio of organic base to polyamic acid powder was 0.65:1; and the mass ratio of polyamic acid powder to deionized water was 2 wt%.

[0073] (4) The polyamic acid hydrogel was freeze-dried and then thermally imidized at 150℃ / 1h, 200℃ / 2h, and 230℃ / 2h to obtain polyimide aerogel for 3D printing. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 577%, and its electrical conductivity was 37.69×10⁻⁶. -4 S / cm.

[0074] Example 5

[0075] A method for preparing polyimide aerogel for 3D printing includes the following steps:

[0076] (1) Under ice-salt bath conditions, the pre-cooled aniline monomer and ice powder were added to deionized water at a stirring speed of 550 rpm to obtain a monomer mixed solution; the ice powder had a particle size of 4 μm; the mass ratio of ice powder to aniline monomer was 12:1; the mass ratio of aniline monomer to deionized water was 0.5:100.

[0077] (2) Under stirring at 500 rpm, the pre-cooled ferric chloride aqueous solution of the initiator was added dropwise to the monomer mixture in batches. After the addition was completed, the reaction was stirred and the mixture was filtered, washed and dried at room temperature to obtain curved polyaniline. The mass ratio of the initiator to the aniline monomer was 3:1. The batch addition was to add the initiator in two batches at a uniform rate. Specifically, the first batch was 10 wt% of the total initiator mass. After reacting for 0.7 h, the remaining initiator was added dropwise until the addition was completed. The total time for the two additions was 20 min. The total time for the stirring reaction was 13 h.

[0078] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 27°C for 8 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenylmethane and 3,3'-diaminobenzophenone in a molar ratio of 1:2. The dianhydride monomer was composed of 3,3',4,4'-benzophenone tetracarboxylic dianhydride and oxydiphthalic anhydride in a molar ratio of 1:1. The molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02. The mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 6 wt%.

[0079] Polyamic acid powder, triethylamine (an organic base), and curved polyaniline were added to deionized water and stirred until homogeneous. A polyamic acid hydrogel was obtained through sol-gelation. The mass ratio of curved polyaniline to polyamic acid powder was 0.7:1; the mass ratio of organic base to polyamic acid powder was 0.5:1; and the mass ratio of polyamic acid powder to deionized water was 3 wt%.

[0080] (4) The polyamic acid hydrogel was freeze-dried and then thermally imidized at 150℃ / 1h, 200℃ / 2h, and 230℃ / 2h to obtain polyimide aerogel for 3D printing. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 583%, and its electrical conductivity was 36.86×10⁻⁶. -4 S / cm.

[0081] Example 6

[0082] A method for preparing polyimide aerogel for 3D printing includes the following steps:

[0083] (1) Under ice-salt bath conditions, the pre-cooled aniline monomer and ice powder were added to deionized water at a stirring speed of 450 rpm to obtain a monomer mixed solution; the ice powder had a particle size of 15 μm; the mass ratio of ice powder to aniline monomer was 8.5:1; and the mass ratio of aniline monomer to deionized water was 0.35:100.

[0084] (2) Under stirring at 450 rpm, the pre-cooled ferric chloride aqueous solution of the initiator was added dropwise to the monomer mixture in batches. After the addition was completed, the reaction was stirred and the mixture was filtered, washed and dried at room temperature to obtain curved polyaniline. The mass ratio of the initiator to the aniline monomer was 2.8:1. The batch addition was to add the initiator in two batches at a uniform rate. Specifically, the first batch was 13 wt% of the total initiator mass. After reacting for 0.6 h, the remaining initiator was added dropwise until the addition was completed. The total time for the two additions was 19 min. The total time for the stirring reaction was 11.5 h.

[0085] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 26°C for 7.5 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenyl sulfone and 3,3'-diaminodiphenyl ether in a molar ratio of 1.5:1, and the dianhydride monomer was composed of pyromellitic dianhydride and oxydiphthalic anhydride in 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 5.5 wt%.

[0086] Polyamic acid powder, triethylamine (an organic base), and curved polyaniline were added to deionized water and stirred until homogeneous. A polyamic acid hydrogel was obtained through sol-gelation. The mass ratio of curved polyaniline to polyamic acid powder was 0.45:1; the mass ratio of organic base to polyamic acid powder was 0.4:1; and the mass ratio of polyamic acid powder to deionized water was 2.5 wt%.

[0087] (4) The polyamic acid hydrogel was freeze-dried and then thermally imidized at 150℃ / 1h, 200℃ / 2h, and 230℃ / 2h to obtain polyimide aerogel for 3D printing. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 587%, and its electrical conductivity was 34.36×10⁻⁶. -4 S / cm.

[0088] Example 7

[0089] A method for preparing polyimide aerogel for 3D printing includes the following steps:

[0090] (1) Under ice-salt bath conditions, the pre-cooled aniline monomer and ice powder were added to deionized water at a stirring speed of 550 rpm to obtain a monomer mixed solution; the ice powder had a particle size of 4 μm; the mass ratio of ice powder to aniline monomer was 12:1; the mass ratio of aniline monomer to deionized water was 0.5:100.

[0091] (2) Under stirring at 500 rpm, the pre-cooled ferric chloride aqueous solution of the initiator was added dropwise to the monomer mixture in batches. After the addition was completed, the reaction was stirred and the mixture was filtered, washed and dried at room temperature to obtain curved polyaniline. The mass ratio of the initiator to the aniline monomer was 3:1. The batch addition was to add the initiator in two batches at a uniform rate. Specifically, the first batch was 20 wt% of the total initiator mass. After reacting for 0.7 h, the remaining initiator was added dropwise until the addition was completed. The total time for the two additions was 20 min. The total time for the stirring reaction was 13 h.

[0092] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 27°C for 8 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenylmethane and 3,3'-diaminobenzophenone in a molar ratio of 1:2. The dianhydride monomer was composed of 3,3',4,4'-benzophenone tetracarboxylic dianhydride and oxydiphthalic anhydride in a molar ratio of 1:1. The molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02. The mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 6 wt%.

[0093] Polyamic acid powder, triethylamine (an organic base), and curved polyaniline were added to deionized water and stirred until homogeneous. A polyamic acid hydrogel was obtained through sol-gelation. The mass ratio of curved polyaniline to polyamic acid powder was 0.7:1; the mass ratio of organic base to polyamic acid powder was 0.5:1; and the mass ratio of polyamic acid powder to deionized water was 3 wt%.

[0094] (4) The polyamic acid hydrogel was freeze-dried and then thermally imidized at 150℃ / 1h, 200℃ / 2h, and 230℃ / 2h to obtain polyimide aerogel for 3D printing. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 579%, and its electrical conductivity was 37.31×10⁻⁶. -4 S / cm.

[0095] Example 8

[0096] A method for preparing polyimide aerogel for 3D printing includes the following steps:

[0097] (1) Under ice-salt bath conditions, the pre-cooled aniline monomer and ice powder were added to deionized water at a stirring speed of 550 rpm to obtain a monomer mixed solution; the ice powder had a particle size of 15 μm; the mass ratio of ice powder to aniline monomer was 14:1; the mass ratio of aniline monomer to deionized water was 0.45:100.

[0098] (2) Under stirring at 600 rpm, the pre-cooled ferric chloride aqueous solution of the initiator was added dropwise to the monomer mixture in batches. After the addition was completed, the reaction was stirred and the mixture was filtered, washed and dried at room temperature to obtain curved polyaniline. The mass ratio of the initiator to the aniline monomer was 3:1. The batch addition was to add the initiator in two batches at a uniform rate. Specifically, the first batch was 16 wt% of the total initiator mass. After reacting for 0.8 h, the remaining initiator was added dropwise until the addition was completed. The total time for the two additions was 23 min. The total time for the stirring reaction was 13.5 h.

[0099] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 28°C for 8.5 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenylmethane and 3,3'-diaminodiphenyl ether in a molar ratio of 1:1, and the dianhydride monomer was composed of pyromellitic dianhydride and 3,3',4,4'-benzophenone tetracarboxylic dianhydride in 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 6 wt%.

[0100] Polyamic acid powder, triethylamine (an organic base), and curved polyaniline were added to deionized water and stirred until homogeneous. A polyamic acid hydrogel was obtained through sol-gelation. The mass ratio of curved polyaniline to polyamic acid powder was 0.65:1; the mass ratio of organic base to polyamic acid powder was 0.6:1; and the mass ratio of polyamic acid powder to deionized water was 3 wt%.

[0101] (4) The polyamic acid hydrogel was freeze-dried and then thermally imidized at 150℃ / 1h, 200℃ / 2h, and 230℃ / 2h to obtain polyimide aerogel for 3D printing. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 577%, and its electrical conductivity was 36.54×10⁻⁶. -4 S / cm.

[0102] Example 9

[0103] A method for preparing polyimide aerogel for 3D printing includes the following steps:

[0104] (1) Under ice-salt bath conditions, the pre-cooled aniline monomer and ice powder were added to deionized water at a stirring speed of 500 rpm to obtain a monomer mixed solution; the ice powder had a particle size of 4 μm; the mass ratio of ice powder to aniline monomer was 15:1; the mass ratio of aniline monomer to deionized water was 0.45:100.

[0105] (2) Under stirring at 650 rpm, the pre-cooled ferric chloride aqueous solution of the initiator was added dropwise to the monomer mixture in batches. After the addition was completed, the reaction was stirred and the mixture was filtered, washed and dried at room temperature to obtain curved polyaniline. The mass ratio of the initiator to the aniline monomer was 2.9:1. The batch addition was to add the initiator in two batches at a uniform rate. Specifically, the first batch was 16 wt% of the total initiator mass. After reacting for 0.7 h, the remaining initiator was added dropwise until the addition was completed. The total time for the two additions was 20 min. The total time for the stirring reaction was 12.5 h.

[0106] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 27°C for 8 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 3,3'-diaminobenzophenone and 3,3'-diaminodiphenyl ether in a molar ratio of 1:2.5, and the dianhydride monomer was composed of 3,3',4,4'-biphenyltetracarboxylic dianhydride and oxydiphthalic anhydride in 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 5.5 wt%.

[0107] Polyamic acid powder, triethylamine (an organic base), and curved polyaniline were added to deionized water and stirred until homogeneous. A polyamic acid hydrogel was obtained through sol-gelation. The mass ratio of curved polyaniline to polyamic acid powder was 0.55:1; the mass ratio of organic base to polyamic acid powder was 0.55:1; and the mass ratio of polyamic acid powder to deionized water was 2.8 wt%.

[0108] (4) The polyamic acid hydrogel was freeze-dried and then thermally imidized at 150℃ / 1h, 200℃ / 2h, and 230℃ / 2h to obtain polyimide aerogel for 3D printing. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 571%, and its electrical conductivity was 36.67×10⁻⁶. -4 S / cm.

[0109] Example 10

[0110] A method for preparing polyimide aerogel for 3D printing includes the following steps:

[0111] (1) Under ice-salt bath conditions, the pre-cooled aniline monomer and ice powder were added to deionized water at a stirring speed of 550 rpm to obtain a monomer mixed solution; the ice powder had a particle size of 4 μm; the mass ratio of ice powder to aniline monomer was 12:1; the mass ratio of aniline monomer to deionized water was 0.5:100.

[0112] (2) Under stirring at 500 rpm, the pre-cooled ferric chloride aqueous solution of the initiator was added dropwise to the monomer mixture in batches. After the addition was completed, the reaction was stirred and the mixture was filtered, washed and dried at room temperature to obtain curved polyaniline. The mass ratio of the initiator to the aniline monomer was 3:1. The batch addition was to add the initiator in two batches at a uniform rate. Specifically, the first batch was 15 wt% of the total initiator mass. After reacting for 0.7 h, the remaining initiator was added dropwise until the addition was completed. The total time for the two additions was 20 min. The total time for the stirring reaction was 13 h.

[0113] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 27°C for 8 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenylmethane and 3,3'-diaminobenzophenone in a molar ratio of 1:2. The dianhydride monomer was composed of 3,3',4,4'-benzophenone tetracarboxylic dianhydride and oxydiphthalic anhydride in a molar ratio of 1:1. The molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02. The mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 6 wt%.

[0114] Polyamic acid powder, triethylamine (an organic base), and curved polyaniline were added to deionized water and stirred until homogeneous. A polyamic acid hydrogel was obtained through sol-gelation. The mass ratio of curved polyaniline to polyamic acid powder was 0.7:1; the mass ratio of organic base to polyamic acid powder was 0.5:1; and the mass ratio of polyamic acid powder to deionized water was 3 wt%.

[0115] (4) The polyamic acid hydrogel was freeze-dried and then thermally imidized at 150℃ / 1h, 200℃ / 2h, and 230℃ / 2h to obtain polyimide aerogel for 3D printing. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 593%, and its electrical conductivity was 38.27×10⁻⁶. -4 S / cm.

[0116] Comparative Example 1

[0117] A method for preparing polyimide aerogel for 3D printing includes the following steps:

[0118] (1) Under ice-salt bath conditions, the pre-cooled aniline monomer and ice powder were added to deionized water at a stirring speed of 550 rpm to obtain a monomer mixed solution; the ice powder had a particle size of 4 μm; the mass ratio of ice powder to aniline monomer was 12:1; the mass ratio of aniline monomer to deionized water was 0.5:100.

[0119] (2) Under stirring at 500 rpm, the pre-cooled ferric chloride aqueous solution of the initiator was continuously added dropwise to the monomer mixture solution. After the addition was completed, the reaction was stirred and reacted. The mixture was filtered, washed, and dried at room temperature to obtain polyaniline. The mass ratio of the initiator to the aniline monomer was 3:1. The total addition time was 20 min. The total reaction time was 13 h.

[0120] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 27°C for 8 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenylmethane and 3,3'-diaminobenzophenone in a molar ratio of 1:2. The dianhydride monomer was composed of 3,3',4,4'-benzophenone tetracarboxylic dianhydride and oxydiphthalic anhydride in a molar ratio of 1:1. The molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02. The mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 6 wt%.

[0121] Polyamic acid powder, triethylamine (an organic base), and polyaniline were added to deionized water and stirred until homogeneous. A polyamic acid hydrogel was obtained through sol-gelation. The mass ratio of polyaniline to polyamic acid powder was 0.7:1; the mass ratio of organic base to polyamic acid powder was 0.5:1; and the mass ratio of polyamic acid powder to deionized water was 3 wt%.

[0122] (4) The polyamic acid hydrogel was freeze-dried and then thermally imidized at 150℃ / 1h, 200℃ / 2h, and 230℃ / 2h to obtain polyimide aerogel for 3D printing. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 538%, and its electrical conductivity was 2.49×10⁻⁶. -4 S / cm.

[0123] Comparative Example 2

[0124] A method for preparing polyimide aerogel for 3D printing includes the following steps:

[0125] (1) Under ice-salt bath conditions, the pre-cooled aniline monomer and ice powder were added to deionized water at a stirring speed of 550 rpm to obtain a monomer mixed solution; the ice powder had a particle size of 4 μm; the mass ratio of ice powder to aniline monomer was 12:1; the mass ratio of aniline monomer to deionized water was 0.5:100.

[0126] (2) Under stirring at 200 rpm, the pre-cooled ferric chloride aqueous solution of the initiator was added dropwise to the monomer mixture in batches. After the addition was completed, the reaction was stirred and the mixture was filtered, washed and dried at room temperature to obtain polyaniline. The mass ratio of the initiator to the aniline monomer was 3:1. The batch addition was to add the initiator in two batches at a uniform rate. Specifically, the first batch was 15 wt% of the total initiator mass. After reacting for 0.7 h, the remaining initiator was added dropwise until the addition was completed. The total time for the two additions was 20 min. The total time for the stirring reaction was 13 h.

[0127] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 27°C for 8 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenylmethane and 3,3'-diaminobenzophenone in a molar ratio of 1:2. The dianhydride monomer was composed of 3,3',4,4'-benzophenone tetracarboxylic dianhydride and oxydiphthalic anhydride in a molar ratio of 1:1. The molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02. The mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 6 wt%.

[0128] Polyamic acid powder, triethylamine (an organic base), and polyaniline were added to deionized water and stirred until homogeneous. A polyamic acid hydrogel was obtained through sol-gelation. The mass ratio of polyaniline to polyamic acid powder was 0.7:1; the mass ratio of organic base to polyamic acid powder was 0.5:1; and the mass ratio of polyamic acid powder to deionized water was 3 wt%.

[0129] (4) The polyamic acid hydrogel was freeze-dried and then thermally imidized at 150℃ / 1h, 200℃ / 2h, and 230℃ / 2h to obtain polyimide aerogel for 3D printing. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 547%, and its electrical conductivity was 4.13×10⁻⁶. -4 S / cm.

[0130] Figure 1The image shows a scanning electron microscope (SEM) image of the curved polyaniline prepared in Example 10. As can be seen from the image, the polyaniline exhibits a distinct arc-shaped structure. This arc-shaped structure helps to disperse the stress and promotes the stability of the polyaniline's morphology. Furthermore, the arc-shaped structure also facilitates thorough wetting with the polyimide resin solution, and the polyimide resin injected into the hollow interior enhances the bonding force between the polyaniline and the matrix resin.

[0131] Figure 2 The scanning electron microscope image of polyaniline prepared for Comparative Example 1 shows a clearly aggregated blocky structure. This is because the initiator is added continuously in one drop, which is not conducive to the formation of the initial curved structure. Moreover, the polymerization rate is too fast, and the aniline monomers do not have time to bind to the surface of the ice micro powder before the polymerization reaction occurs, thus failing to form a curved structure.

[0132] Combining the mechanical and electrical data from various embodiments and comparative examples, it can be seen that by adding polyaniline with a curved structure, a highly efficient combination of conductivity and the inherent excellent properties of polyimide (such as flexibility and strength) is achieved. The curved polyaniline itself is a three-dimensional conductive unit, thus constructing a highly efficient three-dimensional conductive network in the composite material. The curved shape makes it easier to disperse within the polyimide molecular chains, reducing resistance to polymer chain movement, improving the flexibility of the polyimide aerogel, and effectively avoiding the disadvantage of traditional conductive fillers causing the composite material to become brittle at high contents. Furthermore, the curved structure has a larger specific surface area, which means a larger contact area between the polyaniline and the polyimide matrix. A larger contact area can generate stronger interfacial interactions, which not only helps to transfer stress from the matrix to the filler, improving the mechanical strength of the material to a certain extent, but also helps to prevent the curved polyaniline from agglomerating in the matrix, making its distribution more uniform, thereby ensuring the stability of the conductive network.

[0133] Specifically, compared to Example 10, the initiator in Comparative Example 1 was added continuously. On the one hand, the polymerization rate was too fast, and the aniline monomer did not have enough time to bind to the surface of the ice micropowder before the polymerization reaction occurred. On the other hand, too much initiator caused the generated polyaniline to undergo a self-nucleation effect, resulting in a stacked structure that could not form a curved morphology, which was detrimental to improving conductivity and mechanical properties. In Comparative Example 2, the stirring rate during the polymerization reaction was too low, which was not conducive to the heterogeneous nucleation effect of the ice micropowder, and it was impossible to effectively build a conductive, reinforcing, and dispersed network, resulting in a decrease in the electrical conductivity and elongation at break of the 3D printing material.

[0134] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

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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