A method and device for preparing polyimide aerogel

Abstract

The present invention proposes a method for preparing a polyimide aerogel and a preparation device thereof, which relate to the field of aerogel materials, and include the following steps: adding BPDA dianhydride and ODA diamine to triethylamine to prepare a water-soluble polyamic acid salt solution and precipitate particles; placing the water-soluble polyamic acid salt solution in a mold, and adding aramid composite material, crosslinking agent, dehydrating agent, and softener to the mold; realizing crosslinking of macromolecular substances under low temperature freezing, and forming a polyamic acid wet gel through a sol-gel process; drying the polyamic acid wet gel; thermal imidization to obtain a polyimide aerogel; and taking out the polyimide aerogel. The method for preparing a polyimide aerogel and a preparation device thereof provided by the present invention improve the production process, so that the produced polyimide aerogel has a smaller pore size and a more regular appearance, is easier to demold, and ensures the stability of its performance.

Description

Technical Field

[0001] The invention belongs to the field of aerogel materials, and particularly relates to a preparation method and a preparation device of a polyimide aerogel. Background Art

[0002] Aerogel is a highly dispersed solid nanomaterial composed of colloidal particles or polymer molecules that are aggregated into a nanoporous network structure, and the nanopores are filled with a gaseous dispersion medium. Aerogel has the characteristics of low density, high specific surface area, low thermal conductivity and low acoustic impedance. Polyimide aerogel is a kind of organic aerogel. Compared with pure inorganic aerogel, it has good mechanical properties and flexibility, and low thermal conductivity. The film made of it has good flexibility, can be bent and folded, and has very broad application prospects in folding spacecraft, spacecraft thermal control systems, space suits, military tents, etc.

[0003] Polyimide aerogels can be divided into two types: linear and cross-linked. Linear polyimide aerogels tend to shrink significantly during supercritical drying, making them unsuitable for industrial production. However, cross-linked polyimide aerogels, in principle, can form a three-dimensional network structure due to the introduction of cross-linking agents that allow polyimide polymer chains to be combined through covalent bonds, which can reduce the density and thermal conductivity of the sample while improving its thermal and mechanical properties.

[0004] However, the pore size of the polyimide (PI) aerogel currently produced is relatively large, and the pore size distribution is not uniform. During the mold freezing forming process, it is easy to encounter problems such as demolding difficulties and irregular molding. Strong demolding can also cause damage to the polyimide (PI) aerogel. This solution aims to solve this technical problem. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing a polyimide aerogel and a preparation device thereof, which solves the technical problem of how to simultaneously control the pore size of the aerogel and demolding. By improving the production process, the produced polyimide aerogel has a smaller pore size and a more regular appearance, is easier to demold, and ensures the stability of its performance.

[0006] A method for preparing a polyimide aerogel specifically comprises the following steps:

[0007] Step S1: adding BPDA dianhydride and ODA diamine to triethylamine to prepare a water-soluble polyamic acid salt solution and precipitate particles;

[0008] Step S2: placing a water-soluble polyamic acid salt solution in an inner mold, and adding an aramid composite material, a cross-linking agent, a dehydrating agent, a softener, a graphene material and glycerol into the inner mold to fix the shape; meanwhile, the inner mold is arranged inside the outer mold with a distance between the two;

[0009] Under low temperature freezing, the cross-linking of macromolecular substances is achieved, and a polyamic acid wet gel is formed through a sol-gel process;

[0010] Step S3: drying the polyamide acid wet gel in step S2 to prepare a polyamide aerogel;

[0011] Step S4: thermally imidizing the polyamide aerogel in step S3 by heating to obtain a polyimide aerogel;

[0012] Step S5: taking out the polyimide aerogel.

[0013] In the step S1 and step S2, the amount of each raw material used, by mass percentage, is 10% to 20% of BPDA dianhydride, 15% to 25% of ODA diamine, 30% to 45% of triethylamine, 5% to 10% of aramid composite material, 1% to 2% of cross-linking agent, 1% to 2% of dehydrating agent, 1% to 2% of softening agent, 5% to 10% of graphene material, and 2% to 10% of propylene glycol.

[0014] In step S2, before the water-soluble polyamic acid salt solution is placed in the inner mold, an oil film with a thickness of 0.1-0.3 cm is first laid in the inner mold, and the oil film is cryogenically frozen to form a frozen layer, in which the solution is wrapped.

[0015] In the step S2, before the oil film is laid in the inner mold, air is introduced into the oil film in advance so that the oil film is filled with small bubbles.

[0016] In the step S5, the inner mold and the outer mold are placed in a closed space, and when the prepared polyimide aerogel needs to be taken out, the closed space is vacuumed.

[0017] In the step S2, the outer mold is connected to an electric heating wire, and the electric heating wire is connected to a power source.

[0018] The type of the oil film is any one of vegetable oil, animal oil, mineral oil and essential oil.

[0019] A preparation device for polyimide aerogel comprises a closed box, a fixed cover and a movable cover are arranged at the top of the closed box, a cooling and freezing device is arranged inside the closed box, an outer mold is arranged inside the closed box, an inner mold is arranged inside the outer mold, a spacing is arranged between the inner side surface of the outer mold and the outer side surface of the inner mold, a plurality of liquid inlet holes are arranged at the upper end of the inner mold, liquid oil is arranged inside the spacing, a lifting piston is arranged inside the inner mold, the bottom end of the inner mold is connected to one end of a connecting pipe, and the other end of the connecting pipe extends to the outside; the closed box is connected to an air suction and jetting assembly;

[0020] The outer mold is also connected to the electric heating component.

[0021] The air suction and injection assembly includes a vacuum pump connected to the closed box, a suction pipe connected to the vacuum pump at one end, an air blowing pipe connected to the suction pipe at one end, a second valve arranged on the suction pipe, and a first valve arranged on the air blowing pipe, the other end of the air blowing pipe passes through the fixed cover and is connected to one end of a thin tube, and the other end of the thin tube extends below the oil level in the gap.

[0022] The electric heating component comprises two electric heating wires, one end of which is connected to the outer mold, and a power source connected to the two electric heating wires.

[0023] The beneficial effects of the present invention are as follows:

[0024] (1) Adding propylene glycol and graphene has the following technical effects:

[0025] First, the addition of propylene glycol makes the aerogel network structure finer, the skeleton particles finer, and the pores smaller, evenly distributed and dense. The pore size distribution is tested by BET adsorption instrument, which produces excellent technical effects.

[0026] Second, it is combined with graphene to form an electrorheological fluid. The microscopic morphology of the particles in the liquid presents a parachute structure, which is beneficial to improve the anti-sedimentation performance of the colloidal solution and avoid excessive aggregation of the sol;

[0027] Third, adding graphene can also help form a dense solution with good dispersion performance, which is helpful for optimizing the formulation process, and also indirectly improves the anti-corrosion and mechanical properties of polyimide aerogel;

[0028] (2) An oil film is provided on the inner side and bottom surface of the mold and is frozen to form a frozen oil film layer. On the one hand, when the polyimide (PI) aerogel is formed and demolded, it is easier. At this time, the temperature is raised to melt the oil film layer, and the polyimide aerogel can be easily separated from the mold. On the other hand, although the addition of graphene can produce good effects, it also increases the interfacial adhesion between the polyimide aerogel and other materials. Therefore, the frozen oil film layer can be provided to further avoid the phenomenon that the polyimide aerogel is difficult to separate from the mold.

[0029] In addition, polyimide aerogel has a high water absorption rate. If the water absorption rate is too high, the aerogel will be destroyed and lose its use value. Therefore, the use of oil film helps to reduce the water absorption rate of polyimide aerogel, which plays an important role in maintaining its performance, extending its service life and expanding its application field.

[0030] Finally, glycerol is not soluble in the oil film, that is, the two do not wet each other, so the addition of glycerol also helps to separate the polyimide aerogel and the oil film more easily;

[0031] (3) Setting a heating wire on the mold can achieve the following technical effects:

[0032] First, it helps to achieve thermal imidization of aerogels;

[0033] The second is to melt the frozen oil film layer and dry the polyimide aerogel in a closed box;

[0034] Third, since there are many bubbles in the oil film, heating the oil film causes the bubbles to burst, making it easier to separate the polyimide aerogel from the oil film.

[0035] (4) An air suction and jetting assembly is provided, which has the following technical effects:

[0036] First, the liquid oil between the outer mold and the inner mold is sprayed into the liquid oil through a capillary tube, so that more tiny bubbles are generated in the liquid oil. When the temperature is reduced and frozen, the bubbles are preserved in the oil film.

[0037] The second step is to close valve one, open valve two, close the movable cover, and evacuate the closed box, which is helpful for the rupture of bubbles in the oil film on the one hand, and helps the lifting mold to rise on the other hand, so as to eject the formed polyimide aerogel, thereby facilitating the removal of the polyimide aerogel;

[0038] (5) The relationship between the pore size of aerogel and the ease of demolding is contradictory. The smaller the pore size of aerogel, the more difficult it is to demold, and the larger the pore size of aerogel, the easier it is to demold. In the process of preparing polyimide aerogel, this scheme combines oil film, propylene glycol and graphene. The three are combined and cooperate with each other, and the technical problems of controlling the pore size of aerogel and demolding are solved at the same time, so that the produced polyimide aerogel has a smaller pore size and a more regular appearance, and demolding is easier. The addition of aramid composite material forms a reinforcing base for polyimide aerogel, avoiding damage to the polyimide aerogel during demolding. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The external structure of the preparation device in the present invention is shown in FIG. Figure 1 .

[0040] Figure 2 The external structure of the preparation device in the present invention is shown in FIG. Figure 2 .

[0041] Figure 3 It is a schematic diagram of the internal structure of the preparation device in the present invention.

[0042] Figure 4 It is a schematic diagram of the structure of the outer mold and the inner mold in the present invention.

[0043] Figure 5 It is the front view of the internal and external molds of the present invention.

[0044] Figure 6 This is the original fracture SEM morphology image without adding aramid composite material, graphene material and glycerol in the present invention.

[0045] Figure 7 This is the SEM morphology of the fracture surface of Example 1 in the present invention.

[0046] Figure 8 Schematic diagram of mechanical property comparison between Example 1 of the present invention and the original fracture morphology.

[0047] Among them, the figures are marked as: 1. closed box; 2. movable cover; 3. heating wire; 4. fixed cover; 5. blowing pipe; 51. capillary tube; 6. valve one; 7. valve two; 8. suction pipe; 9. vacuum pump; 10. rotating plate; 11. connecting pipe; 12. outer mold; 121. supporting leg; 122. bottom shell; 13. inner mold; 14. liquid inlet hole; 15. lifting piston. DETAILED DESCRIPTION

[0048] In order to more clearly illustrate the technical features of this solution, this solution is described below through specific implementation methods.

[0049] See also Figure 6-Figure 8, a method for preparing a polyimide aerogel, specifically comprising the following steps:

[0050] Step S1: adding BPDA dianhydride and ODA diamine to triethylamine to prepare a water-soluble polyamic acid salt solution and precipitate particles;

[0051] Step S2: placing a water-soluble polyamic acid salt solution in the inner mold 13, and adding an aramid composite material, a cross-linking agent, a dehydrating agent, a softener, a graphene material and glycerol into the inner mold 13 to fix the shape; at the same time, the inner mold 13 is arranged inside the outer mold 12, with a distance between the two;

[0052] Under low temperature freezing, the cross-linking of macromolecular substances is achieved, and a polyamic acid wet gel is formed through a sol-gel process;

[0053] Step S3: drying the polyamide acid wet gel in step S2 to prepare a polyamide aerogel;

[0054] Step S4: thermally imidizing the polyamide aerogel in step S3 by heating to obtain a polyimide aerogel;

[0055] Step S5: taking out the polyimide aerogel.

[0056] In the step S1 and step S2, the amount of each raw material used, by mass percentage, is 10% to 20% of BPDA dianhydride, 15% to 25% of ODA diamine, 30% to 45% of triethylamine, 5% to 10% of aramid composite material, 1% to 2% of cross-linking agent, 1% to 2% of dehydrating agent, 1% to 2% of softening agent, 5% to 10% of graphene material, and 2% to 10% of propylene glycol.

[0057] In step S2, before the water-soluble polyamic acid salt solution is placed in the inner mold 13, an oil film with a thickness of 0.1-0.3 cm is first laid in the inner mold 13, and the oil film is cryogenically frozen to form a frozen layer, in which the solution is wrapped.

[0058] In the step S2, before the oil film is laid in the inner mold 13, air is introduced into the oil film in advance so that the oil film is filled with small bubbles.

[0059] In step S5, the inner mold 13 and the outer mold 12 are placed in a closed space, and when the prepared polyimide aerogel needs to be taken out, the closed space is vacuumed.

[0060] In the step S2, the outer mold 12 is connected to an electric heating wire, and the electric heating wire is connected to a power source.

[0061] The type of the oil film is any one of vegetable oil, animal oil, mineral oil and essential oil.

[0062] Example 1

[0063] In this embodiment 1, the amount of each raw material selected by mass percentage is 15% BPDA dianhydride, 20% ODA diamine, 40% triethylamine, 6% aramid composite material, 1% cross-linking agent, 1% dehydrating agent, 12% softener, 6% graphene material, and 8% propylene glycol.

[0064] In step S2, the mold is frozen in liquid nitrogen at a temperature of -50°C for 1.5 hours and then heated and dried.

[0065] During drying, supercritical carbon dioxide drying was performed at a heating temperature of 200°C and a pressure of 7.0 MPa, and the pressure was maintained for 1.2 hours.

[0066] The temperature range of thermal imidization is 205-220° C., preferably, the thermal imidization temperature is 210° C., and the vacuum pressure is 2.0 Pa-7.0 KPa, preferably 3.0 KPa.

[0067] In this scheme, only to illustrate that good technical effects are achieved after adding aramid composite materials, graphene materials and propylene glycol, Example 1 is used to compare the existing original fracture morphology, and other embodiments are not listed. The mechanical properties of the two are compared. It can be seen that the pore size of the polyimide aerogel in this scheme is significantly reduced, the original fracture morphology is 2-6μm, and the pore size in this scheme is 1.0-2.5um; the compressive strength is also significantly improved, which is due to the addition of aramid composite materials as a reinforcing base.

[0068] Example 2

[0069] See also Figure 1-Figure 5 , a preparation device of polyimide aerogel, comprising a closed box 1, a fixed cover 4 and a movable cover 2 are arranged at the top of the closed box 1, and a cooling and freezing device is arranged inside, an outer mold 12 is arranged inside the closed box 1, an inner mold 13 is arranged inside the outer mold 12, a spacing is arranged between the inner side surface of the outer mold 12 and the outer side surface of the inner mold 13, a plurality of liquid inlet holes 14 are arranged at the upper end of the inner mold 13, liquid oil is arranged inside the spacing, a lifting piston 15 is arranged inside the inner mold 13, the bottom end of the inner mold 13 is connected with one end of a connecting pipe 11, and the other end of the connecting pipe 11 extends to the outside; the closed box 1 is connected to an air suction and jetting assembly;

[0070] The outer mold 12 is also connected to an electric heating assembly.

[0071] More preferably, a rotatable rotating piece 10 is provided on the outer side of the closed box 1 for limiting and blocking one end of the movable cover 2 .

[0072] More preferably, a supporting leg 121 is provided at the bottom end of the outer mold.

[0073] More preferably, a plurality of bottom holes are provided at the bottom end of the outer mold 12, the bottom holes are connected with the inner bottom end of the inner mold 13, a bottom shell 122 is provided on the outer side of the bottom holes to seal the bottom holes, the connecting tube 11 is connected with the bottom shell 122, and under the pressure difference between the inside and the outside, the air enters the connecting tube 11 and the bottom shell 122 and passes through the bottom holes, acting on the lifting piston 15, pushing the lifting piston 15 to rise.

[0074] It should be noted that the bottom end of the inner mold 13 is fixedly and closedly connected to the inner bottom surface of the outer mold 12 .

[0075] The air suction and injection assembly includes a vacuum pump 9 connected to the closed box 1, a suction pipe 8 connected to the vacuum pump 9 at one end, an air blowing pipe 5 connected to the suction pipe 8 at one end, a valve 2 7 arranged on the suction pipe 8, and a valve 1 6 arranged on the air blowing pipe 5. The other end of the air blowing pipe 5 passes through the fixed cover 4 and is connected to one end of a thin tube 51. The other end of the thin tube 51 extends below the oil level in the gap.

[0076] The electric heating component includes two electric heating wires 3 , one end of which is connected to the outer mold 12 , and a power source connected to the two electric heating wires 3 .

[0077] Preferably, the electric heating component may also use other types of heaters, as long as they can achieve a heating effect, without any specific restrictions.

[0078] The specific working process of Example 2 of the present invention is as follows:

[0079] Add liquid oil between the outer mold 12 and the inner mold 13, start the air suction and jet assembly, start the valve 1 6, close the valve 2 7, and under the action of the vacuum pump 9, spray air into the air blowing pipe 5. At this time, the movable cover 2 is opened to facilitate the balance of air pressure inside and outside the closed box 1. The gas enters the liquid oil through the capillary 51, and more bubbles are generated in the liquid oil.

[0080] The liquid oil gradually rises above the liquid inlet hole 14 and enters the inner mold 13 through the liquid inlet hole 14. The inner side and bottom surfaces of the inner mold 13 are manually coated with an oil film layer, and the cooling and freezing device is started and frozen to form a frozen oil film layer. After cooling and freezing, the bubbles are preserved in the oil film.

[0081] A water-soluble polyamic acid salt solution is prepared and placed in a mold, and an aramid composite material, a cross-linking agent and a dehydrating agent, a graphene material and glycerol are added to the mold to fix the shape and form a polyamic acid wet gel;

[0082] The polyamide acid wet gel is dried to prepare the polyamide aerogel;

[0083] The polyimide aerogel is obtained by thermal imidization of the polyamide aerogel by heating;

[0084] A softener is added to the obtained polyimide aerogel, and finally the polyimide aerogel is taken out.

[0085] When the polyimide (PI) aerogel is formed and demolded, the power supply is started to make the electric heating wire 3 work, the temperature is increased to melt the oil film layer, and at the same time, the vacuum pump 9 is turned on, the valve 1 6 is closed, and the valve 2 7 is opened to suck the air in the closed box 1. At this time, under the negative pressure of the closed box 1, the lifting piston 15 rises and drives the aerogel above to rise, so that people can easily separate the polyimide aerogel from the mold;

[0086] The electric heating wire 3 is arranged on the mold to help achieve thermal imidization of the aerogel; the frozen oil film layer is melted, and the polyimide aerogel is dried in the closed box 1;

[0087] During the ascending process of the lifting piston 15, since there are many bubbles in the oil film, after the oil film is heated, the bubbles are broken under negative pressure, making it easier to separate the polyimide aerogel from the oil film.

[0088] Close valve 1 6, open valve 2 7, close the movable cover 2, and evacuate the closed box 1. This will help to rupture the bubbles in the oil film on the one hand, and help to lift the lifting mold to eject the formed polyimide aerogel on the other hand, thereby facilitating the removal of the polyimide aerogel.

[0089] Technical features not described in the present invention can be achieved through or by adopting existing technologies and will not be described in detail here. Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by ordinary technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A method for preparing a polyimide aerogel, characterized in that: The specific steps include: Step S1: adding BPDA dianhydride and ODA diamine to triethylamine to prepare a water-soluble polyamic acid salt solution and precipitate particles; Step S2: placing a water-soluble polyamic acid salt solution in an inner mold (13), and adding an aramid composite material, a cross-linking agent, a dehydrating agent, a softener, a graphene material and glycerol into the inner mold (13) to fix the shape; at the same time, the inner mold (13) is arranged inside the outer mold (12) with a distance between the two; Under low temperature freezing, the cross-linking of macromolecular substances is achieved, and a polyamic acid wet gel is formed through a sol-gel process; Before placing the water-soluble polyamic acid salt solution in the inner mold (13), a layer of oil film is first laid in the inner mold (13), the thickness of the oil film is 0.1-0.3 cm, and the oil film is cryogenically frozen to form a frozen layer, and the solution is located in the frozen layer package; Before the oil film is laid in the inner mold (13), air is introduced into the oil film in advance so that the oil film is filled with small bubbles; The outer mold (12) is connected to an electric heating wire, and the electric heating wire is connected to a power source; Step S3: drying the polyamide acid wet gel in step S2 to prepare a polyamide aerogel; Step S4: thermally imidizing the polyamide aerogel in step S3 by heating to obtain a polyimide aerogel; Step S5: taking out the polyimide aerogel; The inner mold (13) and the outer mold (12) are placed in a closed space, and when the prepared polyimide aerogel needs to be taken out, the closed space is vacuumed.

2. The method for preparing a polyimide aerogel according to claim 1, characterized in that: In the step S1 and step S2, the amount of each raw material used is, by mass percentage, 10% to 20% of BPDA dianhydride, 15% to 25% of ODA diamine, 30% to 45% of triethylamine, 5% to 10% of aramid composite material, 1% to 2% of cross-linking agent, 1% to 2% of dehydrating agent, 1% to 2% of softener, 5% to 10% of graphene material, and 2% to 10% of glycerol.

3. The method for preparing the polyimide aerogel according to claim 1, characterized in that: The type of the oil film is any one of vegetable oil, animal oil, mineral oil and essential oil.

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