CN111234297B

CN111234297B - 3D printing polyimide aerogel and preparation method thereof

Info

Publication number: CN111234297B
Application number: CN202010024259.5A
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: 2021-11-02
Anticipated expiration: 2040-01-10
Also published as: CN111234297A

Abstract

The invention relates to a 3D printing polyimide aerogel and a preparation method thereof, wherein the polyimide aerogel is obtained by printing a set structure from a polyamic acid solution through a 3D printer, freezing, solidifying and forming by assisting a cold plate, and then deeply freezing, freeze-drying and thermal imidization. This preparation is through the accurate effectual 3D structure that founds of 3D printing technique, and cold drawing aided forming makes polyamide acid solution can be good keep 3D print structure, and then obtains the polyimide aerogel that has specific structure, and this synthetic process is simple and easy, the environmental protection, and easy operation is a green preparation method.

Description

3D printing polyimide aerogel and preparation method thereof

Technical Field

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

Background

The 3D printing technology is a novel die-free forming technology. The technology prepares simple three-dimensional periodic structures and complex three-dimensional structures containing spans (without support) or having large height-width ratios in a layer-by-layer overlapping mode by means of computer aided design and precision machinery. Currently, 3D printing technology based on extrusion principles has led to extensive research in advanced material manufacturing due to low cost, large scale, high efficiency, and programmable geometry and programmable fine structure. However, the Fused Deposition Modeling (FDM) has high requirements for printing materials, typically thermosetting plastics or resins, and the feeding manner is typically wire or tube, and this high requirement limits the further application of 3D printing technology. At present, a 3D printer based on ink direct writing technology (DIW) can be obtained by assembling a computer, a dispenser, an air compressor and a 3D printing platform in a laboratory. The application of the 3D printing technology in the fields of hydrogel, aerogel and the like can be widened. A prerequisite for using DIW-based 3D printing technology is that the ink must meet certain rheological properties. The ink is required to be a non-Newtonian fluid and to have a rheological behavior of shear thinning so as to be capable of smoothly extruding out a needle. And the ink is required to have good moldability, specifically: under high shear strain, the loss modulus must be higher than the storage modulus to show fluid properties, and under low shear strain, the storage modulus must be higher than the loss modulus to show gel properties, so that the ink can recover the gel properties after extruding the needle to well maintain the 3D printing structure.

Due to the characteristics of excellent high temperature resistance, high strength, high modulus, irradiation resistance and the like, the polyimide aerogel can be widely applied to the fields of extreme environments, space exploration, aerospace equipment and the like. The precursor polyamic acid is a macromolecule formed by condensation polymerization of diamine and dicarboxylic anhydride, a solution formed by water-soluble polyamic acid has rheological property of shear thinning, so that a needle can be smoothly extruded, but under low shear strain, the solution generally shows fluid property that loss modulus is higher than storage modulus, so that the solution has stronger fluidity after being extruded, and a 3D printing structure cannot be maintained before printing is completed, so that the solution collapses, and the application of a 3D printing technology in the field of polyimide aerogel is limited.

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 invention has the following defects: firstly, because silica aerogel powder is brittle, the silica aerogel powder is used as a rheology modifier to blend with polyamic acid, and the finally obtained polyimide aerogel is impure and heterogeneous aerogel, and the mechanical properties of the polyimide aerogel can be greatly influenced. Second, the chemical imidization used in the present invention requires the use of toxic substances such as acetic anhydride and pyridine, which is likely to cause environmental pollution. Third, the supercritical drying used in this invention often requires a solvent exchange step, which is lengthy, requires bulky equipment and is costly.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a 3D printing polyimide aerogel and a preparation method thereof, wherein the used printing ink is polyamic acid sol, the polyamic acid is formed by an auxiliary freezing and curing technology, and an additional curing agent or rheological modifier (such as silicon dioxide aerogel powder) is not required to be added to support a 3D printing structure, so that the mechanical property and the like of the aerogel are not influenced, and the formed pure polyimide aerogel has high strength, high modulus and higher fracture strain. In addition, the invention uses the freeze drying technology and the thermal imidization method to form the aerogel with a network pore structure inside, and the whole process has low cost, is simple, convenient, green and environment-friendly. Therefore, the invention can design and prepare polyimide aerogel with various fine structures by the aid of a 3D printing technology for freeze-assisted solidification molding, and the heteromorphic polyimide aerogel has potential application value.

The 3D printing polyimide aerogel is obtained by performing 3D printing on a set structure by using a polyamide acid sol, performing freeze curing molding, and then performing deep freezing, freeze drying and thermal imidization by using liquid nitrogen.

The invention discloses a preparation method of 3D printing polyimide aerogel, which comprises the following steps:

(1) 3D printing is carried out on the polyamic acid sol, and freezing forming is carried out to obtain freezing and solidifying polyamic acid with a structure;

(2) and carrying out deep freezing on the polyamic acid in a liquid nitrogen atmosphere, carrying out freeze drying on the frozen polyamic acid to obtain a polyamic acid aerogel, and then carrying out thermal imidization to obtain the 3D printing 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 specifically: dissolving water-soluble polyamic acid in deionized water, adding triethylamine, and stirring until the polyamic acid is completely dissolved to obtain polyamic acid sol; wherein the stirring time is 6-12 h.

The water-soluble polyamic acid is specifically prepared by the following method:

(a) 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 3-6h, adding a cosolvent triethylamine, and continuously reacting for 2-5h to finally prepare a polyamic acid solution;

(b) 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.

The monomer diamine in the step (a) comprises one or two of 4, 4' -diaminodiphenyl ether and p-phenylenediamine; the binary anhydride monomer comprises one or more of pyromellitic dianhydride, diphenyl ether tetracarboxylic dianhydride and biphenyl tetracarboxylic dianhydride; the polar solvent comprises one or more of N, N-dimethylacetamide, N-methylpyrrolidone and dimethylformamide.

The solid content of the polyamide acid sol in the step (1) is 4-12%.

The step (1) is specifically as follows: and transferring the polyamic acid sol solution into a needle cylinder, removing bubbles, printing a set structure by using a 3D printer provided with a cold plate, and performing freeze forming by using an auxiliary cold plate.

The diameter of the needle head of the needle cylinder is 0.1 mm-2 mm; the defoaming time is 2min-10 min; the temperature of the cold plate is-45 to-15 ℃.

The 3D printing speed in the step (1) is 1mm s^-1～12mm s^-1(ii) a The printing air pressure is 100 kPa-700 kPa.

The 3D printing setting structure in the step (1) comprises one of a fiber structure, a spider-web structure, a cylinder structure, a honeycomb structure, a three-dimensional frame structure, a cube structure, a chair-shaped structure, a hollow frame structure and 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.

In the invention, in order to keep the printing structure of the polyamic acid well, the polyamic acid is cured and molded in the printing process, wherein the freezing and curing method is most convenient and effective and cannot influence the performance of the final polyimide aerogel due to the introduction of a rheological modifier or other curing agents and the like. Therefore, further, the steps (1) and (2) are specifically: the cold drawing that will connect in the refrigeration circulator is fixed to the platform that 3D printed, can regulate and control the cold drawing temperature through the refrigeration circulator, polyamic acid prints the deposit on the cold drawing through 3D, freeze the shaping by the cold drawing to it, print superimposed in-process successive layer freezing solidification at the successive layer, make its good 3D that keeps print the structure, the polyamic acid that will freeze the shaping is arranged in the liquid nitrogen atmosphere and is carried out deep freezing, the polyamic acid that will freeze the reality is through freeze-drying, obtain the polyimide aerogel that has specific structure after the thermal imidization.

The invention provides a 3D printing polyimide aerogel prepared by the method.

The invention provides a 3D printing device adopted by the method, which comprises a cold plate connected with a refrigeration cycle machine, wherein the cold plate is fixed on a platform for 3D printing, and the temperature of the cold plate can be regulated and controlled through the refrigeration cycle machine.

The invention provides an application of the 3D printing polyimide aerogel.

The polyimide aerogel with various special shapes has potential application value and can be used as parts of aircrafts such as automobiles, aerospace and the like. Such as heat insulating materials, photothermal conversion substrates, sensing substrates, and the like.

The method of the invention can also be applied to the preparation of other aerogels.

Advantageous effects

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

(2) The experimental conception is ingenious: the water-soluble polyamic acid is used as the printing ink, has the characteristic of non-Newtonian fluid which is thinned by shearing, can smoothly extrude a needle head, and assists in freezing, curing and forming to enable the polyamic acid to well keep a 3D printing structure. Therefore, the polyimide aerogel with various fine structures can be designed and prepared through 3D printing, and can be used as parts of aircrafts such as automobiles and aerospace.

(3) The polyamic acid solution can accurately and effectively construct a 3D structure through a 3D printing technology, the 3D printing structure can be well maintained through an auxiliary freezing and curing molding technology, and the molded polyamic acid is subjected to deep freezing, freeze drying and imidization processes to form a polyimide aerogel product with a structure.

(4) Chinese patent CN107936685A has prepared a polyimide ink that can supply 3D to print through molecular structure design, adds silicon dioxide aerogel powder in polyamic acid, forms polyimide/silicon dioxide aerogel powder mixed gel through chemical imidization, plays the effect of supporting the 3D structure with the help of silicon dioxide, carries out supercritical drying after 3D prints and obtains polyimide aerogel. The difference between the invention and Chinese patent CN104355302A is that: 1. the ink used in the invention is polyamic acid sol, and the polyamic acid is formed by an auxiliary freezing and curing technology without an additional curing agent or a rheology modifier (such as silicon dioxide), so that the mechanical properties of the aerogel and the like are not influenced, and the formed pure polyimide aerogel has high strength, high modulus and higher fracture strain and has the same mechanical properties as the polyimide aerogel formed by a casting mould. (see FIG. 4). 2. The invention uses the freeze drying technology, the formed aerogel has a network pore structure 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 design and prepare polyimide aerogel with various fine structures by the aid of a 3D printing technology for freeze-assisted solidification molding, and the heteromorphic polyimide aerogel has potential application value.

Drawings

FIG. 1 shows three stages of preparation of a polyimide aerogel according to example 1; the device comprises a cold plate, a polyamide acid, a liquid nitrogen gas source and a liquid nitrogen gas source, wherein (a) is a 3D printer device connected with the cold plate, the polyamide acid is extruded by a needle head and then deposited on the cold plate for solidification and forming, (b) is completely frozen in the liquid nitrogen gas source, and (c) is polyimide aerogel with a honeycomb structure;

FIG. 2 is an SEM electron micrograph of a three-dimensional frame polyimide aerogel prepared in example 1; wherein (a) is the top layer surface morphology of the aerogel, (b) is the bottom two-layer side morphology of the aerogel, and (c) is the internal morphology of the bottom layer crosscut of the aerogel;

FIG. 3 is an optical photograph of the three-dimensional frame polyimide aerogel prepared in examples 1 to 3;

FIG. 4 is a graph showing the mechanical properties of the polyimide aerogel bars prepared in example 4 and comparative example 1;

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 3D printing device who adopts is including connecting in the cold drawing of refrigeration circulator, the cold drawing is fixed to the platform of 3D printing, provides the condensate through the refrigeration circulator, and the condensate gets into the cold drawing from the import to in flowing out to the refrigeration circulator from the export, form circulation backward flow with stable temperature. The cold plate temperature may be further regulated by regulating the condensate temperature by a refrigeration cycle machine (see fig. 1 a).

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) 1g of polyamic acid dry filament is taken and dissolved in 12.5mL of deionized water, 0.5g of triethylamine is added, and then magnetons are placed on a stirring table to be stirred for 12 hours, so that the polyamic acid sol with the solid content of 8% is obtained and is marked as PAA 8.

(3) Filling the polyamide acid sol into a syringe with a needle head of 0.6mm, and placing the syringe in a bubble remover to remove bubbles for 3min till no bubbles exist. The shape of the hand-held box of the programmer is designed, the shape path of the three-dimensional frame structure is led into the 3D printer, the air compressor provides power, and the printing speed is set to be 4mm s^-1Printing air pressure to set 250kPa, extruding a polyamide acid gel out of a needle head, depositing the polyamide acid gel on a cold plate, freezing, curing and forming, controlling the temperature of the cold plate through a connected freezing circulating machine, setting the temperature to be-30 ℃, and obtaining frozen and cured polyamide acid with a three-dimensional frame structure after printing, wherein the frozen and cured polyamide acid is marked as PAA-8.

(4) And (3) placing the solidified and molded polyamic acid in a liquid nitrogen atmosphere for 3h for deep freezing, then placing the polyamic acid in a freeze dryer at the temperature of-40 ℃ for drying for 48h, removing ice crystals by sublimation, and leaving a network pore structure (shown in figure 2c) in the polyamic acid aerogel, and performing thermal imidization on the obtained polyamic acid aerogel for 2h at the temperature of 300 ℃ to obtain the polyimide aerogel with a three-dimensional frame structure, wherein the polyimide aerogel is marked as PI-8.

Example 2

The amount of deionized water in example 1 was changed to 16.6mL, a polyamic acid solution with a solid content of 6% was prepared, and the frozen and solidified polyamic acid with a three-dimensional frame structure obtained by cold plate assisted 3D printing was designated as PAA-6. The obtained polyimide aerogel having a three-dimensional frame structure was denoted by PI-6, and the rest was the same as in example 1.

Example 3

The amount of deionized water in example 1 was changed to 10mL, a polyamic acid solution with a solid content of 10% was prepared, and the frozen and solidified polyamic acid with a three-dimensional frame structure obtained by cold plate assisted 3D printing was designated as PAA-10. The obtained polyimide aerogel having a three-dimensional frame structure was denoted by PI-10, and the rest was the same as in example 1.

Example 4

The shape path in example 1 was changed to the shape path of a type I standard spline in the ASTM D638-2003 tensile test method, and the rest was the same as in example 1. The specific test method comprises the following steps: an electronic universal testing machine with a model number of UTM17335, produced by Shenzhen Sansi longitudinal and transverse science and technology Limited is adopted. The test temperature is 23 +/-2 ℃, the humidity is 50 +/-5%, the test mode is a plate tensile test, the maximum tensile force is 50N, and the tensile speed is 5 mm/min. The aerogel test bars tested were of the type I standard bar size, and had a total length of 165mm, a narrow portion length of 67mm, a total width of 19mm, a narrow portion width of 13mm, and an internal fillet radius of 76mm (see FIG. 4 for test results in which the mechanical properties of the Cast (Cast) and 3D printed (3D printing) aerogel test bars, respectively, were tested).

Comparative example 1

The polyamic acid sol obtained in example 1 was poured into a mold of a type I standard bar in a custom-made ASTM D638-2003 tensile test method, and directly placed in a liquid nitrogen atmosphere for 3 hours for freezing, all of which were the same as in example. And obtaining the polyimide aerogel in a standard sample strip shape. The specific test method was the same as in example 4.

Comparative example 2

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

As shown in fig. 1: the polyamic acid solution can well maintain a 3D printing structure with the aid of cold plate freezing and curing molding. As can be seen from fig. a and b, the polyamic acid well maintains the 3D printed structure, and as can be seen from fig. c, the polyimide aerogel obtained by freeze-drying and thermal imidization of the freeze-molded polyamic acid maintains a good honeycomb structure.

As shown in fig. 2: the regularity and the self-supporting property of the 3D printing polyimide aerogel structure are shown in a figure a, and the structure takes on a regular nine-grid shape. As can be seen from fig. b, the polyimide aerogel fibers of the bottom two layers can bridge each other, thereby supporting the 3D printed structure. And as can be seen from the graph c, the inside of the polyimide aerogel presents the pore structure of the aerogel.

As shown in fig. 3: polyimide aerogels with different solid contents have different formability. The polyamic acid with a solid content of 6% has low viscosity and modulus, and therefore, blocking and collapse occur after printing, and the 3D printed structure cannot be well maintained. Only when the solid content reaches more than 8%, the polyamic acid can maintain the 3D printed structure. However, when the solid content is too high to reach 10%, the resultant polyimide aerogel may show significant shrinkage. Thus 8% solids polyamic acid is the best printing ink. When the solid content of the polyamic acid is 8%, the polyamic acid solution has high viscosity and modulus and small shrinkage rate, so that the polyamic acid solution can be used as ink for 3D printing, and a cold plate freezing and curing molding auxiliary 3D printing technology is used for constructing a 3D structure. The formed polyamic acid can well keep a 3D printing structure after being deeply frozen in a liquid nitrogen atmosphere, and then is subjected to freeze drying and thermal imidization to form the polyimide aerogel with a specific structure.

As shown in fig. 4, the 3D printed (3D printing) polyimide aerogel has a fracture strength of 4.7MPa, a high modulus of 74.4MPa, and a fracture strain of 12.5%, which is equivalent to the mechanical properties of the mold-formed (Cast) polyimide aerogel.

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. The 3D printing polyimide aerogel is characterized in that the aerogel is obtained by performing 3D printing on a polyamide acid sol, then performing freeze curing molding, and then performing liquid nitrogen freezing, freeze drying and thermal imidization; the polyamic acid sol specifically comprises: dissolving water-soluble polyamic acid in deionized water, adding triethylamine, and stirring until the polyamic acid is completely dissolved to obtain polyamic acid sol; wherein the stirring time is 6-12 h; the solid content of the polyamic acid sol is 8-12%.

2. A method of preparing the 3D printed polyimide aerogel of claim 1, comprising:

(1) 3D printing is carried out on the polyamic acid sol, and the polyamic acid is obtained after freezing and forming;

(2) freezing above-mentioned polyamic acid in liquid nitrogen atmosphere, freeze-drying again obtains the polyamic acid aerogel, then carries out the thermal imidization, obtains 3D and prints polyimide aerogel.

3. The preparation method according to claim 2, wherein the step (1) is specifically: and transferring the polyamic acid sol solution into a needle cylinder, removing bubbles, printing a set structure by using a 3D printer provided with a cold plate, and performing freeze forming by using an auxiliary cold plate.

4. The method according to claim 3, wherein the needle of the cylinder has a diameter of 0.1mm to 2 mm; the defoaming time is 2min-10 min; the temperature of the cold plate is-45 to-15 ℃.

5. The production method according to claim 2, wherein the 3D printing speed in the step (1) is 1mm s^-1～12 mm s^-1(ii) a The printing air pressure is 100 kPa-700 kPa.

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

7. A 3D printed polyimide aerogel prepared by the method of claim 2.

8. Use of the 3D printed polyimide aerogel according to claim 1 in parts of automobiles, aerospace vehicles.