CN111138710B

CN111138710B - 3D printing fiber reinforced polyimide aerogel and preparation method thereof

Info

Publication number: CN111138710B
Application number: CN202010024268.4A
Authority: CN
Inventors: 樊玮; 元诗佳; 刘天西; 王栋
Original assignee: Donghua University
Current assignee: Donghua University
Priority date: 2020-01-10
Filing date: 2020-01-10
Publication date: 2021-05-11
Anticipated expiration: 2040-01-10
Also published as: CN111138710A

Abstract

The invention relates to a 3D printing fiber reinforced polyimide aerogel and a preparation method thereof, wherein the aerogel is a 3D printing aerogel; wherein the ink components adopted by the 3D printing comprise: polyimide staple fibers, polyamic acid. According to the invention, the 3D structure is accurately and effectively constructed through the 3D printing technology, the polyimide short fibers can play a role of physical enhancement, so that the composite printing ink can well support the 3D printed structure, and further the fiber-reinforced polyimide aerogel with a specific structure is obtained.

Description

3D printing fiber reinforced polyimide aerogel and preparation method thereof

Technical Field

The invention belongs to the field of aerogel materials and preparation methods thereof, and particularly relates to a 3D printing fiber reinforced polyimide aerogel and a preparation method thereof.

Background

3D printing is one of rapid prototyping technologies, materials are overlapped layer by layer through computer control, and finally a three-dimensional model on a computer is changed into a three-dimensional object, so that the method is a leading technology for developing a mass manufacturing mode to a personalized manufacturing mode. Currently, 3D printing technology based on the extrusion principle has led to extensive research in advanced material manufacturing due to its outstanding advantages of simple equipment, low cost and easy operation, as well as programmable geometry and programmable fine structure. At present, most laboratories assemble point gum machine, air compressor machine, 3D print platform and obtain the fashioned 3D printer that can be used to ink direct writing technique (DIW). The printing ink with various components and performances can be prepared according to the requirements by the ink direct writing technology, so that the raw materials can be powder, solution, gel and the like, and the application of the 3D printing technology in the fields of hydrogel and aerogel is widened. Currently, to form using 3D printing technology based on DIW, the ink must satisfy certain rheological properties. First, the ink must be a non-newtonian fluid, exhibiting shear-thinning rheology to ensure that the ink can be smoothly extruded through the needle without clogging. Secondly, the ink needs to have good moldability. The concrete expression is as follows: under high shear stress, the loss modulus of the ink is higher than the storage modulus, so that the fluid property is shown, and the good fluidity of the ink in a needle head can be ensured; under low shear stress, the storage modulus is higher than the loss modulus, and the gel property is shown, so that the ink can support a 3D printing structure after extruding a needle, and the ink has good formability.

Polyimide aerogel has better flexibility compared with inorganic aerogel, and in addition, the rigid structure of polyimide enables the polyimide aerogel to present high mechanical strength, excellent thermal stability and wear resistance, so that the polyimide aerogel has attracted extensive attention as a structural material or a functional material. However, the current methods for forming polyimide aerogel are mainly limited to injection molding and cast film molding, and thus the application thereof is limited. The preparation method of the polyimide aerogel prepared by using the 3D printing technology can be enriched, application objects are widened, and the development of the polyimide aerogel is promoted. But at present, the polyamic acid precursor cannot meet the rheological property required by the 3D printing technology. Although polyamic acid can smoothly extrude a needle and meet the requirement of shear thinning, the moldability is poor. Because polyamic acid generally exhibits a fluid characteristic of a loss modulus greater than a storage modulus under low shear stress, the 3D printed structure cannot be maintained after the needle is extruded and thus collapses. Therefore, the preparation of polyimide aerogel by 3D printing technology requires modification of the rheological properties of polyamic acid.

A common method of modifying the rheological properties of inks today is to add rheology modifiers such as carbomers, F127, nanoclays, etc. to the ink. While rheology modifiers are effective in improving the rheology of the ink, they can, after post-removal, substantially affect the properties of the final printed article, such as reducing the mechanical properties of the printed article, and the like.

Patent CN107936685A has prepared a polyimide/silica aerogel powder printing ink that can supply 3D to print to silica aerogel powder is used for supporting the 3D structure as the rheology modifier, obtains the polyimide aerogel through supercritical drying. The silicon dioxide aerogel powder used in the invention is brittle, and the polyimide aerogel obtained by blending the silicon dioxide aerogel powder with polyamic acid, imidizing and drying is impure and heterogeneous aerogel, and the mechanical property of the polyimide aerogel is reduced. In addition, the chemical imidization used in the invention requires the use of toxic substances such as acetic anhydride and pyridine, which easily causes environmental pollution. And the supercritical drying used usually needs a solvent exchange step, the time is long, and the required equipment is large and high in cost.

Disclosure of Invention

The invention aims to solve the technical problem of providing a 3D printing fiber reinforced polyimide aerogel and a preparation method thereof. Polyimide staple fiber has the characteristic of original polyimide, and with the nature phase-match of final polyimide aerogel, the aerogel that obtains is pure polyimide aerogel, consequently need not to get rid of and can not reduce the performance of polyimide aerogel itself. Compared with other rheology modifiers (such as silicon dioxide aerogel powder), the fiber with large length-diameter ratio has stronger physical supporting effect and can effectively reduce the shrinkage rate of the polyimide aerogel. And the physical enhancement effect can be achieved, and the mechanical property of the polyimide aerogel is improved. The invention takes the polyamic acid of the composite polyimide short fiber as the printing ink, and can accurately and effectively construct the fiber-reinforced polyimide aerogel with a specific structure through the programming design of a computer.

According to the fiber reinforced polyimide aerogel, the aerogel is a 3D printing aerogel; wherein the ink components adopted by the 3D printing comprise: polyimide staple fibers, polyamic acid.

The length of the polyimide short fiber is 200-500 mu m; the polyamic acid is a polyamic acid sol.

The mass ratio of the polyamic acid to the polyimide is 4: 1-1: 2.

The invention discloses a preparation method of a fiber reinforced polyimide aerogel, which comprises the following steps:

(1) adding polyimide short fibers into a polyamide acid sol, uniformly dispersing until the solution is converted into non-flowing viscous slurry, and then printing a set structure by using a 3D printer to obtain the composite ink with the structure;

(2) and (3) freezing the composite printing ink with the structure in a liquid nitrogen atmosphere, freeze-drying the frozen composite printing ink, and performing thermal imidization to obtain the fiber reinforced polyimide aerogel with the structure.

The preferred mode of the above preparation method is as follows:

the polyamic acid sol in the step (1) is as follows: dissolving water-soluble polyamic acid in deionized water, adding triethylamine, and stirring until the polyamic acid is completely dissolved to obtain polyamic acid sol with the solid content of 4-12%; wherein the stirring time is 6-12 h.

The water-soluble polyamic acid specifically comprises: firstly, dissolving a polymerization monomer diamine of polyimide in a polar solvent, adding another dicarboxylic anhydride monomer, carrying out polymerization reaction in an ice-water bath for 3-6 hours, adding a cosolvent triethylamine, and continuously reacting for 2-5 hours to finally prepare a polyamic acid solution; and placing the obtained polyamic acid solution at the height of 0.5-1 m, slowly flowing into deionized ice water, precipitating to obtain filamentous polyamic acid, and freeze-drying the filamentous polyamic acid to obtain the water-soluble polyamic acid dry filament.

Further, the polymeric monomer diamine comprises 4, 4' -diaminodiphenyl ether and p-phenylenediamine; the binary anhydride monomer comprises pyromellitic dianhydride, diphenyl ether tetracarboxylic dianhydride or biphenyl tetracarboxylic dianhydride; the polar solvent includes N, N-dimethylacetamide, N-methylpyrrolidone, or dimethylformamide.

The length of the polyimide short fiber in the step (1) is 200-500 mu m; the mass ratio of the polyamic acid to the polyimide is 4: 1-1: 2; the uniform dispersion is as follows: the refiner disperses evenly for 20-60 min.

The 3D printing in the step (1) is specifically as follows: transferring the mixture into a needle cylinder, removing bubbles by a bubble removing machine, and printing by a 3D printer; wherein the diameter of the needle head of the needle cylinder is 0.1 mm-2 mm; the defoaming time is 5-15 min.

The 3D printing speed in the step (1) is1mm s^-1～12mm s^-1The printing air pressure is 100 kPa-600 kPa.

The 3D printing setting structure in the step (1) comprises: a fiber structure, a spider-web structure, a cylinder structure, a honeycomb structure, a three-dimensional frame structure, a cube structure, a chair-like structure, a hollow frame structure, or a pyramid structure.

The thermal imidization temperature in the step (2) is 200-350 ℃, and the thermal imidization time is 1-3 h.

The freezing time in the liquid nitrogen atmosphere in the step (2) is 30 min-3 h; the temperature of freeze drying is-50 ℃ to-30 ℃, and the time is 24h to 72 h.

The invention provides a fiber reinforced polyimide aerogel prepared by the method.

The invention provides an application of the fiber reinforced polyimide aerogel, which can be used in parts of aircrafts such as automobiles, aerospace and the like, such as heat insulation materials, photothermal conversion matrix materials, sensing matrix materials and the like, and the fiber reinforced method can also be applied in the preparation of other aerogels.

The polyimide short fiber has the original polyimide characteristic and is matched with the property of the final polyimide aerogel, so that the polyimide short fiber is added into the polyamic acid without being removed. The polyimide short fiber is added into the polyamic acid to form solid-liquid blended slurry, so that the rheological property of the ink can be effectively improved. The polyimide short fibers play a role in physical support, so that the 3D printing structure of the composite ink can be well maintained, and collapse cannot occur after extrusion. Meanwhile, due to the structural supporting effect of the polyimide short fibers, the shrinkage rate of the polyimide aerogel can be greatly reduced, and the printing fidelity is improved. And because the polyimide staple fiber can produce the orientation along the syringe needle extrusion direction under the effect that receives the syringe needle shear force, produce the effect of physical enhancement, consequently can improve the mechanical properties of polyimide aerogel.

Advantageous effects

(1) The synthetic process is simple, environment-friendly and simple to operate, and is a green chemical preparation method.

(2) The experimental concept of the invention is ingenious: the polyimide short fiber is adopted to improve the rheological property of the polyamic acid, and the formed solid-liquid mixed paste can well keep a 3D printing structure. And the polyimide staple fibers serve as structural support and physical reinforcement therein. Therefore, the fiber-reinforced polyimide aerogel with various fine structures can be designed and prepared by 3D printing, and can be used as parts of aircrafts such as automobiles and aerospace.

(3) The polyamide acid slurry of the composite polyimide staple fibers can accurately and effectively construct a 3D structure through a 3D printing technology, and the formed composite printing ink is frozen, freeze-dried and imidized to form the fiber-reinforced polyimide aerogel with the structure. Patent CN107936685A has prepared the polyimide ink that can supply 3D to print through molecular structure design, adds silicon dioxide aerogel powder in polyamic acid, through chemical imidization formation polyimide/silicon dioxide aerogel powder mixed gel, plays the effect of supporting the 3D structure with the help of silicon dioxide, carries out supercritical drying after 3D prints and obtains the polyimide aerogel. The difference between the invention and Chinese patent CN104355302A is that: 1. the printing ink used by the invention is polyamide acid slurry of the composite polyimide short fiber, and the polyimide short fiber can be structurally supported, so that the composite printing ink can well keep a 3D printing structure, and meanwhile, the shrinkage rate of the polyimide aerogel can be greatly reduced. And the one-dimensional short fibers are oriented along the extrusion direction, so that the physical enhancement effect can be achieved, and the mechanical property of the polyimide aerogel is improved. 2. The invention uses the freeze-drying technology, the formed aerogel has a network pore structure (see figure 2c) inside, and the whole process is low in cost and simple and convenient. 3. The polyimide aerogel is formed by thermal imidization, and is more green and environment-friendly. Therefore, the invention can be designed and prepared into various fiber reinforced polyimide aerogels with fine structures through 3D printing, and the aerogel has potential application value.

Drawings

FIG. 1 optical photographs of different structures of fiber reinforced polyimide aerogels prepared in example 1; wherein (a) is the light display of the aerogel with the three-dimensional frame structure; (b) aerogel with a hollow frame structure;

FIG. 2 is an SEM electron micrograph of a space-frame fiber-reinforced polyimide aerogel prepared in example 1; wherein (a) is the surface morphology of the top layer of the aerogel, and (b) is the morphology of local single fibers; (c) the appearance of the interior of the polyimide aerogel is shown.

Fig. 3 is a mechanical test of the aerogel fibers prepared in example 1 and comparative example 1.

FIG. 4 is a comparison of the aerogels prepared in example 1(b) and comparative example 1 (a).

Fig. 5 is an SEM electron micrograph of the polyimide aerogel (a) and the polyimide-based carbon aerogel (a-1) prepared in comparative example 2.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims. All the raw materials are purchased from chemical reagents of the national medicine group, and the purity is chemical purity or analytical purity grade without special indication.

The mechanical test adopts an electronic universal tester with the model number UTM17335 produced by Shenzhen Sansi longitudinal and transverse science and technology Limited. The test temperature is 23 +/-2 ℃, the humidity is 50 +/-5%, the test mode is a fiber tensile test, the maximum tensile force is 50N, and the tensile speed is 5 mm/min. The test sample was aerogel fiber with a diameter of 450 μm and a length of 50mm (see FIG. 3 for mechanical test results).

Example 1

(1) N, N-dimethylacetamide is used as a solvent, 4' -diaminodiphenyl ether and pyromellitic dianhydride in equal molar ratio are added to carry out condensation polymerization reaction in an ice-water bath, and polyamic acid with solid content of 15% is prepared. The specific process is as follows: 8.0096g of 4, 4' -diaminodiphenyl ether was dissolved in 95.57g N, N-dimethylacetamide, and 8.86g of pyromellitic anhydride was added thereto, followed by reaction in an ice-water bath for 5 hours. Then, 4.0476g of triethylamine was added, and the reaction was continued for 3 hours to prepare a water-soluble polyamic acid solution having a solid content of 15%. Precipitating the prepared water-soluble polyamic acid by using deionized water, and then washing and freeze-drying to obtain water-soluble polyamic acid dry filaments for later use.

(2) Dissolving 1g of polyamide acid dry filament in 20mL of deionized water, adding 0.5g of triethylamine, placing magnetons on a stirring table, stirring for 12 hours to obtain polyamide acid sol with the solid content of 5%, adding 1g of polyimide short fiber with the length of 300 mu m into the polyamide acid sol, and dispersing for 30 minutes by a homogenizer to obtain the solid-liquid mixed composite ink similar to viscose.

(3) Filling the composite ink into a needle cylinder with a 0.6mm needle head, designing the shape of a hand-held box through a programmer, guiding the shape path of a three-dimensional frame structure into a 3D printer, providing power by an air compressor, and setting the printing speed to be 4mm s^-1Printing air pressure is set to be 200kPa, the composite ink is extruded out of a needle, and after printing is finished, the composite ink with a three-dimensional frame structure is obtained, and the polyimide short fiber is recorded as PAA/PIf-3 because the length of the polyimide short fiber is 300 mu m.

(4) And (3) placing the formed composite ink in a liquid nitrogen atmosphere for 3h for freezing, then placing the frozen composite ink in a freeze dryer at the temperature of-40 ℃ for drying for 48h, and performing thermal imidization on the obtained composite aerogel for 2h at the temperature of 300 ℃ to obtain the fiber-reinforced polyimide aerogel with a three-dimensional frame structure, which is marked as PI/PIf-3.

Example 2

The length of the polyimide staple fibers in example 1 was changed to 200 μm, and the composite ink having a three-dimensional frame structure obtained by 3D printing was designated as PAA/PIf-2. The obtained fiber-reinforced polyimide aerogel having a three-dimensional frame structure was designated as PI/PIf-2, and the rest was the same as in example 1.

Example 3

The length of the polyimide staple fiber in example 1 was changed to 500 μm, and the composite ink having a three-dimensional frame structure obtained by 3D printing was designated as PAA/PIf-5. The obtained fiber-reinforced polyimide aerogel having a three-dimensional frame structure was designated as PI/PIf-5, and the rest was the same as in example 1.

Comparative example 1

The mass of the polyamic acid in example 1 was changed to 2g, and no polyimide staple fiber was added, to obtain a pure PAA solution with a solid content of 10%, which was denoted as PAA, and a polyimide aerogel prepared by cold plate assisted 3D printing was denoted as PI. The rest is the same as in example 1.

Comparative example 2

Polyimide aerogel and polyimide-based carbon aerogel prepared by patent CN107936685A (see fig. 5).

As shown in fig. 1: the composite ink has good formability, and can form fiber-reinforced polyimide aerogel with various structures through 3D printing. And as can be seen from figure a, the aerogel of the frame structure is light in weight and can be placed on the flower buds.

As shown in fig. 2: the 3D printed fiber reinforced polyimide aerogel has an ordered periodic structure. As shown in the figure a, the regular four-grid shape is presented. As can be seen from the graph b, on the local single fiber, the polyimide staple fiber is oriented along the fiber direction, and the surface presents a porous structure. Thus, the polyimide short fibers can support the 3D printed structure and can enhance the mechanical properties of the polyimide aerogel. As can be seen from fig. 2c, the polyimide aerogel presents a network porous structure inside, which is due to the pore structure left after sublimation of the ice crystals during the freeze-drying process.

As shown in fig. 3: the tensile mechanical test is carried out on the single fiber extruded by the 3D printing, so that the mechanical property of the polyimide aerogel of the composite polyimide short fiber is improved, the tensile strength is 63.5MPa, the modulus is 409MPa, and the elongation at break is 20.3%.

As shown in fig. 4, (a) is the polyimide aerogel prepared in comparative example 1, and (b) is the polyimide aerogel prepared in example 1, it can be seen that the shrinkage of the composite polyimide short fiber is greatly reduced from 30% to 19%.

When the polyamic acid is compounded with the polyimide short fiber, the modulus of the polyamic acid is improved and the polyamic acid shows gel characteristics, so that the polyamic acid can be directly used as ink for 3D printing to construct a 3D structure by using a 3D printing technology. After the formed composite printing ink is frozen in a liquid nitrogen atmosphere, the 3D printing structure can be well kept, and the fiber-reinforced polyimide aerogel with a specific structure is formed through freeze drying and thermal imidization processes. The aerogel has small shrinkage and excellent mechanical properties (see figure 3 and figure 4)

As shown in fig. 5, the polyimide aerogel prepared in patent CN107936685A shows a phenomenon of non-uniform fibers (see fig. a), and it can be seen from fig. a-1 that many agglomerated silica powders are distributed on the surface of the carbon aerogel formed by carbonizing the polyimide aerogel, which greatly affects the mechanical properties of the polyimide aerogel.

Claims

1. A fiber reinforced polyimide aerogel, wherein the aerogel is obtained by 3D printing; wherein the ink components employed for 3D printing include: polyimide staple fibers, polyamic acid; wherein the mass ratio of the polyamic acid to the polyimide is 4: 1-1: 2.

2. The aerogel according to claim 1, wherein the polyimide staple fibers are 200 to 500 μm in length; the polyamic acid is a polyamic acid sol.

3. A method of preparing a fiber reinforced polyimide aerogel comprising:

(1) adding polyimide short fibers into a polyamide acid sol, uniformly dispersing, and then performing 3D printing;

(2) and (2) freezing the 3D printing material obtained in the step (1) in a liquid nitrogen atmosphere, and then carrying out freeze drying and thermal imidization to obtain the fiber-reinforced polyimide aerogel.

4. The preparation method according to claim 3, characterized in that the length of the polyimide staple fibers in the step (1) is 200 to 500 μm; the mass ratio of the polyamic acid to the polyimide is 4: 1-1: 2; the uniform dispersion is as follows: the refiner disperses evenly for 20-60 min.

5. The preparation method according to claim 3, wherein the 3D printing in the step (1) is specifically: transferring the mixture into a needle cylinder, removing bubbles by a bubble removing machine, and printing by a 3D printer; wherein the diameter of the needle head of the needle cylinder is 0.1 mm-2 mm; the defoaming time is 5-15 min.

6. The production method according to claim 3, wherein the 3D printing speed in the step (1) is 1mm s^-1～12 mm s^-1The printing air pressure is 100 kPa-600 kPa.

7. The method according to claim 3, wherein the thermal imidization temperature in step (2) is 200 to 350 ℃ and the thermal imidization time is 1 to 3 hours.

8. A fiber reinforced polyimide aerogel prepared by the method of claim 3.

9. Use of the fiber reinforced polyimide aerogel of claim 1 in an aircraft part.