CN115960387A

CN115960387A - Composite foam and preparation method thereof

Info

Publication number: CN115960387A
Application number: CN202310088187.4A
Authority: CN
Inventors: 侯豪情; 程楚云; 胡昭宇; 邓磊; 曾书婷
Original assignee: Jiangxi Normal University
Current assignee: Jiangxi Normal University
Priority date: 2023-02-09
Filing date: 2023-02-09
Publication date: 2023-04-14

Abstract

The application belongs to the technical field of polymer composite materials, and discloses a composite foam and a preparation method thereof. The preparation method of the composite foam is simple in process and easy in material acquisition, the cost for preparing the polyimide composite foam can be greatly reduced, and the composite foam prepared by the method can have multiple structures and has more excellent heat resistance and compression resilience.

Description

Composite foam and preparation method thereof

Technical Field

The application relates to the technical field of polymer composite materials, in particular to a composite foam and a preparation method thereof.

Background

With the development of science and technology, polymer sponges or foams are applied in more and more fields, such as national defense and military industry, aerospace and navigation, microelectronics and the like. In order to provide a wider range of excellent properties to polymer sponges or foams, sponges or foams made of a combination of various polymer materials are preferred. Polyimide is a high polymer material with excellent high and low temperature resistance, self-extinguishing property, chemical stability and insulating property, so that the polyimide is also a preferred material for preparing sponge or foam. However, the existing process method for preparing the composite sponge or foam by using the polyimide has the disadvantages of complex process, high cost and poor industrial applicability. Therefore, how to reduce the process flow of the polyimide composite foam and reduce the preparation cost becomes a key problem.

Disclosure of Invention

The composite foam and the preparation method thereof are simple in process steps and low in cost, and the prepared composite foam is excellent in performance.

In order to realize the purpose of the application, the following technical scheme is provided:

in a first aspect, the present application provides a method of preparing a syntactic foam, comprising the steps of:

s01, adding a monomer I and a monomer II into a solvent I to obtain a polyamic acid solution I;

s02, adding a solvent II into the polyamic acid solution I to obtain a polyamic acid solution II;

s03, adding a dehydrating agent into the polyamic acid solution II, and soaking the open-cell foam in the dehydrating agent;

and S04, taking out the soaked open-cell foam, cleaning and drying to obtain the composite foam.

According to the application, a polyamic acid solution I is provided, the polyamic acid solution I is diluted by adding a solvent II to obtain a polyamic acid solution II suitable for being soaked in open-cell foam, a dehydrating agent is added into the polyamic acid solution II to enable the polyamic acid solution to be subjected to chemical imidization, the open-cell foam is soaked in the solution, and polyimide fibers subjected to imidization can be connected inside the open-cell foam to obtain the composite foam. The composite foam obtained by the method has simple preparation process, and saves the manufacturing cost of the composite foam; and the mechanical property and the thermal property of the composite foam prepared by the preparation method are greatly improved under the action of the polyimide fiber.

Preferably, the mass fraction of the polyamic acid solution I is 8 to 10 percent, and the intrinsic viscosity is 0.5 to 4dL/g. The intrinsic viscosity can reflect the polymerization degree of the polyamic acid, and the higher the intrinsic viscosity, the higher the polymerization degree of the polyamic acid, the longer the single molecule of the polyamic acid, and the greater the strength of the polyimide fiber obtained after imidization. The polyamide acid solution has high molecular polymerization degree, and when the mass fraction of the solution is 8-10%, the intrinsic viscosity is high, so that a good foundation is laid for subsequent experimental steps.

Preferably, the mass fraction of the polyamic acid solution II is 1% to 4%, and the absolute viscosity is 0.3 pas to 5 pas. When the mass fraction of polyamic acid solution II is within this range, not only can the fluidity be ensured, but also a larger amount of polyamic acid can be provided per unit volume for chemical imidization. The absolute viscosity of the polyamic acid solution II can be the fluidity of the reaction solution. When the absolute viscosity of the polyamic acid solution II is lower than the lower limit of the range, the fluidity of the polyamic acid solution II is too good, and polymer molecules are not easy to stay on the surface of the open-cell foam and are connected with the open-cell foam to form composite foam in the imidization process of the polyamic acid solution II; when the absolute viscosity of the polyamic acid solution II is higher than the upper limit of the range, the polyamic acid solution II has too poor fluidity, the polyamic acid solution II is liable to take a viscous state, the open-cell foam is not easily immersed in the first solution, and the polyamic acid solution II does not sufficiently fill the holes in the open-cell foam, resulting in failure to form a uniform composite foam.

Preferably, the dehydrating agent is at least one of acetic anhydride, propionic anhydride and trifluoroacetic anhydride. The dehydrating agent has the function of promoting the polyamic acid solution to remove the ring closure of water molecules to form polyimide.

Preferably, the molar ratio of the dehydrating agent to the polyamic acid solution II is 3. When the molar weight of the dehydrating agent is lower than the lower limit of the range, the content of the dehydrating agent is too low, which may cause incomplete chemical imidization and failure to form complete polyimide fibers on open-cell foams; when the molar amount of the dehydrating solvent is higher than the upper limit of the range, the content of the dehydrating solvent is too large, and unnecessary waste is liable to occur.

Preferably, the open-cell foam is a melamine foam or an EVA foam.

Preferably, the open-cell foam has a pore size of 50 μm to 500. Mu.m. When the pore diameter of the open-cell foam is lower than the lower limit of the range, the pore diameter is too small, and the polyimide fibers are easy to be stacked too densely, so that a compact structure is easy to form inside the composite foam, and the composite foam is lack of resilience performance; when the pore diameter of the open-cell foam is higher than the upper limit of the range, the pore diameter is too large, the polyimide fibers are sparsely stacked, and the adhesion between adjacent fibers is not firm enough, so that the composite foam structure is easy to loosen.

Preferably, the soaking time of the open-cell foam is 5-12 h, and the soaking temperature is 10-40 ℃. The soaking time should be the time period after the open-cell foam is soaked in the polyamic acid solution II and waits for the chemical imine generated in the polyamic acid solution II. The soaking temperature should be the internal temperature of the polyamic acid solution II at the time of soaking.

Preferably, the method further comprises pretreating the open-cell foam with a surfactant before soaking the open-cell foam in the polyamic acid solution. The method aims to increase more active sites on the open-cell foam and increase the attachment probability of the polyimide fibers on the open-cell foam, thereby improving the compounding degree of the polyimide fibers and the foam.

In a second aspect, the present application also provides a syntactic foam produced by the production method according to any one of the first aspects. The composite foam is composed of open-cell foam and imidized polyimide fibers, namely the imidized polyimide fibers are distributed in the open-cell foam and are fixedly connected with the open-cell foam, wherein the diameter of the imidized polyimide fibers is 200nm-800nm.

The beneficial effect that this application gained does: the preparation method of the composite foam is simple in process, the materials are easy to obtain, the cost for preparing the polyimide composite foam can be greatly reduced, and the composite foam prepared by the method can have multiple structures and has more excellent heat resistance and compression resilience.

Drawings

FIG. 1 is a flow diagram of one embodiment of a process for preparing a syntactic foam;

FIG. 2 is an SEM representation of the resulting syntactic foam.

Detailed Description

The idea and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments and the accompanying drawings to fully understand the objects, aspects and effects of the present invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The present application aims to provide a syntactic foam and a method of preparing the same. The preparation method can obtain the polyimide composite foam by soaking the open-cell foam into a polyamic acid solution subjected to chemical imidization and controlling the concentration of the polyamic acid solution and the reaction time of the chemical imidization. The preparation method of the composite foam has the advantages of simple process and easy material acquisition, and can greatly reduce the cost for preparing the polyimide composite foam. The composite foam prepared by the method has multiple structures and has more excellent heat resistance and compression resilience.

Fig. 1 is a method for preparing a syntactic foam provided herein, comprising the steps of:

in the step S01, the monomer I, the monomer II and the solvent I are added into a reaction kettle to obtain a polyimide solution I with the intrinsic viscosity W. Specifically, the polyamic acid solution I may be polymerized from a monomer I and a monomer II in a solvent I. The purpose of this step is to provide a suitable polyamic acid solution, which has a higher intrinsic viscosity, i.e., a higher molecular polymerization degree, and the greater the strength of the polyimide fiber obtained from imidization of the polyamic acid solution. When the intrinsic viscosity of the polyamic acid solution is less than the lower limit of the range, the polymer polymerization degree is low, and the polyimide obtained after imidization is in the form of particles, and a composite foam filled with polyimide fibers cannot be obtained. The intrinsic viscosity of the polyimide solution I may be 1.2dL/g, 1.5dL/g, 1.8dL/g, 2.1dL/g, 2.4dL/g, 2.6dL/g, 2.9dL/g, 3.3dL/g, 3.6dL/g, 4dL/g.

In one embodiment, monomer I may be a diamine monomer including at least one of 3,3' -diaminodiphenyl ether, 4' -diaminodiphenyl ether, 1, 3-bis (4-aminophenoxy) benzene, 4' -diaminodiphenyl sulfide, p-phenylenediamine, m-phenylenediamine, 3' -diaminodiphenyl sulfoxide, and 4,4' -diaminodiphenyl sulfoxide.

In one embodiment, monomer II may be a dianhydride monomer including pyromellitic dianhydride, 2,3,6, 7-naphthalene tetracarboxylic dianhydride, 3', 4' -biphenyl tetracarboxylic dianhydride, 1,2,5, 6-naphthalene tetracarboxylic dianhydride, 2', 3' -biphenyl tetracarboxylic dianhydride, 3',4,4' -benzophenone tetracarboxylic dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 1-bis (3, 4-dicarboxyphenyl) ethane dianhydride, 1-bis (2, 3-dicarboxyphenyl) ethane dianhydride, bis (2, 3-dicarboxyphenyl) methane dianhydride, bis (3, 4-dicarboxyphenyl) ethane dianhydride, 4' -oxydiphthalic anhydride, diphenyl sulfide dianhydride, bisphenol A dianhydride, and 3,3',4,4' -diphenyl sulfone tetracarboxylic dianhydride.

It is to be understood that the above-mentioned reactive monomers are only examples of some of the monomers that can be used to prepare the polyamic acid, and other monomers can be used to prepare the polyamic acid in other embodiments without limitation.

In one embodiment, solvent I may be a polar organic solvent including a combination of one or more of N, N-dimethylformamide, N-methylpyrrolidone, dimethylsulfoxide, N-dimethylacetamide; preferably, the polar organic solvent is at least one selected from the group consisting of N-methylpyrrolidone, dimethylsulfoxide, and N, N-dimethylacetamide; more preferably, the polar organic solvent is at least one selected from the group consisting of N-methylpyrrolidone and N, N-dimethylacetamide; most preferably, the polar organic solvent is N, N-dimethylacetamide.

In step S02, the solvent II is added to the polyimide solution I and stirred to obtain a polyimide solution II. In particular, the purpose of this step is to dilute the polyamic acid solution I. Because the fluidity of the polyamic acid solution is improved, the open-cell foam can be completely immersed in the polyimide solution.

In one embodiment, the solvent II may be a polar organic solvent including at least one of N, N-dimethylformamide, N-methylpyrrolidone, dimethylsulfoxide, N-dimethylacetamide; in other embodiments, the solvent II may also be a non-polar organic solvent including at least one of tetrahydrofuran, acetone, ethanol.

In step S03, a dehydrating agent is added to polyamic acid solution II, and the open-cell foam is immersed in polyamic acid solution II. Specifically, in the present embodiment, the dehydrating agent may include at least one of acetic anhydride, propionic anhydride, and trifluoroacetic anhydride. The polyamic acid can be dehydrated and imidized to form polyimide under the action of a dehydrating agent at a specific temperature and time. Compared with the dehydration imidization promoted by the polyamic acid at high temperature, the method can avoid the damage of the high temperature to the open-cell foam by the dehydrating agent, reduce the use of electric energy and heat energy in the preparation process and achieve the purposes of energy conservation and emission reduction.

And the specific implementation manner of this step can be that open-cell foam is placed in a container or a mold in advance, and then polyamic acid solution II added with dehydrating agent is poured on the open-cell foam, and the polyamic acid solution II should submerge the open-cell foam. So that when the polyamic acid solution II is poured, the polyamic acid solution II can flow into the open-cell foam under the action of gravity and fill all the open cells of the open-cell foam. This step may also be such that the polyamic acid solution II to which the dehydrating agent is added is poured first into a container or a mold, and then the open-cell foam is sunk into the polyamic acid solution II, and in order to prevent the open-cell foam from floating on the polyamic acid solution II, the open-cell foam may be sunk into the polyamic acid solution II by pressing with a tool.

And step S04, taking out the open-cell foam, cleaning and drying to obtain the composite foam. Specifically, the open-cell foam may be removed from the solution after a period of soaking. It is understood that the soaking time is a time for the polyamic acid solution II to be completely imidized to form polyimide by the action of the dehydrating agent. And the solution should be a mixed solution of polyimide and solvent, and the open-cell foam is compounded with polyimide fibers. When the soaking time is lower than the lower limit of the range, the chemical imidization time is not long enough, and enough polyimide fibers cannot be formed on the open-cell foam, so that the thermal property and the mechanical property of the composite foam are poor; when the soaking time is higher than the upper limit of the range, the solvent in the polyamic acid solution II easily causes a corrosive influence on the open-cell foam during the soaking time. Preferably, the soaking time is 5h.

In one embodiment, the removed foam may be rinsed with deionized water to remove the solvent from the foam. And in order to ensure that the solvent in the foam is completely removed, the residual solvent can be replaced from the foam by repeatedly soaking the foam in deionized water. In other embodiments, residual solvent may also be displaced from the foam by soaking in ethanol. After the foam is cleaned, the cleaned foam can be put into a vacuum oven for drying treatment, so as to remove residual deionized water or ethanol in the foam. And the drying temperature can be between 80 and 120 ℃, and the composite foam can be obtained after drying.

In one embodiment, the mass fraction of the polyamic acid solution I in step S01 is 8% to 10%. The mass fraction of the polyamic acid solution I is the percentage of the monomer I and the monomer II in the solvent I after polymerization, and can be understood as the content of the reactant provided. When the content of the reactant is within this range, the reaction probability after collision between molecules is large, and a polyamic acid solution having a high intrinsic viscosity can be obtained. When the mass fraction of the polyamic acid solution I is lower than the lower limit of the range, the monomer I and the monomer II are less in input amount, the intermolecular collision probability is lower, and a solution with high intrinsic viscosity is not easy to obtain; when the mass fraction of the polyamic acid solution I is higher than the upper limit of the range, the amounts of the monomer I and the monomer II to be charged are large, and the polyamic acid solution obtained in the reaction kettle has poor fluidity and is not easy to extract and further process.

In one embodiment, the absolute viscosity of polyamic acid solution II provided in step S02 is from 0.3 pas to 5 pas. Specifically, the absolute viscosity of the polyamic acid solution II may be the fluidity of the reaction solution. When the absolute viscosity of the polyamic acid solution II is lower than the lower limit of the range, the fluidity of the polyamic acid solution II is too good, and polymer molecules are not easy to stay on the surface of open-cell foam in the imidization process of the polyamic acid solution II to be connected with the open-cell foam to form composite foam; when the absolute viscosity of the polyamic acid solution II is higher than the upper limit of the range, the fluidity of the polyamic acid solution II is too poor, the polyamic acid solution II is easily viscous, the open-cell foam is not easily immersed in the first solution, and the polyamic acid solution II does not sufficiently fill the holes in the open-cell foam, resulting in failure to form a uniform composite foam. The absolute viscosity of the polyamic acid solution II can be 0.6pa · s, 0.8pa · s, 1pa · s, 1.5pa · s, 2pa · s, 2.5pa · s, 3pa · s, 3.6pa · s, 4pa · s, 4.8pa · s.

In one embodiment, the mass fraction of polyamic acid solution II in step S02 is 1% to 4%. When the content of the reactant is within this range, the content of the polyamic acid in the solution is appropriate, and a large amount of the polyamic acid can be provided per unit volume for chemical imidization while the fluidity is maintained. When the mass fraction of the polyamic acid solution II is lower than the lower limit of the range, the content of polyamic acid in unit volume is low, and relatively abundant polyimide fibers cannot be obtained in the open-cell foam, resulting in low performance of the composite foam; when the mass fraction of the polyamic acid solution II is higher than the upper limit of the range, the content of polyamic acid in unit volume is higher, the number of polyimide fibers filled in the open-cell foam is larger, the open-cell foam is more densely filled, and the composite foam having the resilience performance cannot be obtained.

In one embodiment, the dehydrating agent in step S03 is at least one of acetic anhydride, propionic anhydride and trifluoroacetic anhydride, and the molar amount of the dehydrating agent is 3 to 10 times that of the polyamic acid. Specifically, the dehydrating agent functions to promote the polyamic acid solution to remove the ring closure of water molecules to form polyimide, and the molar amount of the dehydrating agent should be higher than that of the polyamic acid. It is understood that when the molar amount of the dehydrating agent is less than the lower limit of the range, the content of the dehydrating agent is too small, which may result in incomplete chemical imidization and failure to form complete polyimide fibers on open-cell foams; when the molar amount of the dehydrating solvent is more than the upper limit of the range, the content of the dehydrating solvent is too large, which tends to cause unnecessary waste. Preferably, the molar amount of the dehydrating agent is 5 times the molar amount of the polyamic acid.

In one embodiment, the soaking temperature in step S03 is 10 ℃ to 40 ℃, wherein the soaking temperature should be the internal temperature of the polyamic acid solution II at the time of soaking. When the soaking temperature is lower than the lower limit of the range, the internal temperature of the polyamic acid solution II is too low, the chemical imidization speed is reduced, the manufacturing time of the syntactic foam is too long, and the increase of the process cost is easily caused; when the soaking temperature is higher than the upper limit of the range, the internal temperature of the polyamic acid solution II is too high, and the polyamic acid is easy to be subjected to ring opening at high temperature, so that the molecular weight of the polyimide is insufficient, the strength of the formed polyimide fiber is poor, and the thermal property and the mechanical property of the composite foam are reduced. Preferably, the soaking temperature is 25 ℃.

In one embodiment, the soaking environment in step S03 is an inert gas atmosphere, wherein the soaking environment should be the gas environment of the polyamic acid solution II. The inert gas comprises at least one of argon, helium, nitrogen and neon. It will be appreciated that the immersion environment selected should be an inert gas atmosphere that is free of water and oxygen. To ensure that water molecules and oxygen in the environment do not affect the polyamic acid solution II during the long-term soaking. Preferably, the soaking environment is a nitrogen atmosphere.

In one embodiment, the open-cell foam in step S03 is a melamine foam or an EVA foam.

In one embodiment, the pore size of the open-cell foam in step S03 is 50 μm to 500 μm, wherein the pore size of the open-cell foam should be approximately the pore size of the open-cell foam, and the pore size of each open cell is not the same size. When the pore diameter of the open-cell foam is lower than the lower limit of the range, the pore diameter is too small, and the polyimide fibers are easy to be stacked too densely, so that a compact structure is easy to form inside the composite foam, and the composite foam is lack of resilience performance; when the pore diameter of the open-cell foam is higher than the upper limit of the range, the pore diameter is too large, the polyimide fibers are sparsely stacked, and the adhesion between adjacent fibers is not firm enough, so that the composite foam structure is easy to loosen.

In one embodiment, the open-cell foam provided prior to step S03 can be pretreated with a surfactant. The method aims to increase more active sites on the open-cell foam and increase the attachment probability of the polyimide fibers on the open-cell foam, thereby improving the compounding degree of the polyimide fibers and the foam.

In a second aspect, the present application further provides a syntactic foam prepared by the method for preparing a syntactic foam according to the above embodiment, wherein the syntactic foam is composed of an open-cell foam and imidized polyimide fibers, i.e., the imidized polyimide fibers are distributed in the open-cell foam and are fixedly connected with the open-cell foam.

The technical solution of the present invention will be described in detail below with reference to specific examples. Furthermore, the following specific examples are to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever, and that all insubstantial modifications and variations of the invention, including those skilled in the art, which fall within the scope of the appended claims, are intended to be embraced therein.

Example 1

The embodiment provides a preparation method of a composite foam, in particular to a melamine-polyimide composite foam, which comprises the following steps:

s01, adding 10.814g of monomer p-phenylenediamine, 29.42g of monomer 3,3', 4' -biphenyl tetracarboxylic dianhydride and 362g of solvent N, N-dimethylformamide into a reaction kettle for reaction to obtain a polyamic acid solution a1 with the intrinsic viscosity of 1.5dL/g, wherein the concentration of the polyamic acid solution a1 is 10%;

s02, adding 70g of solvent N, N-dimethylformamide into 30g of polyamic acid solution a1, and stirring to obtain polyamic acid solution b1, wherein the absolute viscosity of the polyamic acid solution b1 is 0.6pa · S;

s03, adding 0.5mol of acetic anhydride into the polyamic acid solution b1, fully stirring until the acetic anhydride and the polyamic acid solution are fused with each other, and then soaking melamine foam into the polyamic acid solution b 1;

s04, standing the polyamide acid solution b1 in a nitrogen atmosphere at 25 ℃, taking out the melamine foam from the solution after 5 hours, imidizing the polyamide acid solution b1 under the action of acetic anhydride to form polyimide fibers, and accommodating the polyimide fibers in the melamine foam and connecting the polyimide fibers with the melamine foam; and (3) cleaning the open-cell foam with deionized water, and drying in an oven at 120 ℃ for 60 minutes to obtain the melamine-polyimide composite foam.

FIG. 1 is a schematic view of the scanning electron microscope of the obtained melamine-polyimide composite foam, wherein the obtained polyimide fibers are connected with the melamine foam, the fiber diameter is uniform, and a large pore space is reserved in the composite foam.

In this example, the melamine foam used had a size of 200 μm.

In this example, the resulting melamine-polyimide composite foam had a 5% thermal decomposition temperature of 420 ℃, a compressive strength of 52KPa when it was first compressed to 50% of the total volume, and a compressive strength of 49KPa after it was cyclically compressed 100 times to 50% of the total volume. See table 1 for details.

Example 2

s01, adding 20.02g of monomer 4,4' -diaminodiphenyl ether, 29.42g of 3,3', 4' -biphenyl tetracarboxylic dianhydride and 445g of solvent N, N-dimethylformamide into a reaction kettle for reaction to obtain a polyamic acid solution a1 with the intrinsic viscosity of 1.7dL/g, wherein the concentration of the polyamic acid solution a1 is 10%;

s02, adding 70g of solvent N, N-dimethylformamide into 30g of polyamic acid solution a1, and stirring to obtain polyamic acid solution b1, wherein the absolute viscosity of the polyamic acid solution b1 is 0.83pa · S;

In this example, the melamine foam used was the same as in example 1. The resulting melamine-polyimide composite foam had a 5% thermal decomposition temperature of 393 ℃ and a compressive strength of 40KPa when it was first compressed to 50% of the total volume, and a compressive strength of 38KPa after it was compressed 100 times in a cycle to 50% of the total volume. See table 1 for details.

Example 3

s01, adding 10.814g of monomer p-phenylenediamine, 21.812g of pyromellitic dianhydride and 294g of N, N-dimethylformamide into a reaction kettle for reaction to obtain a polyamic acid solution a1 with the intrinsic viscosity of 1.6dL/g, wherein the concentration of the polyamic acid solution a1 is 10%;

s02, adding 70g of N, N-dimethylformamide serving as a solvent into 30g of the polyamic acid solution a1, and stirring to obtain a polyamic acid solution b1, wherein the absolute viscosity of the polyamic acid solution b1 is 0.75pa · S;

In this example, the melamine foam used was the same as in example 1. The resulting melamine-polyimide composite foam had a 5% thermal decomposition temperature of 435 ℃, a compressive strength of 58KPa when it was first compressed to 50% of the total volume, and a compressive strength of 55KPa after it was cyclically compressed 100 times to 50% of the total volume. See table 1 for details.

Example 4

s03, adding 0.8mol of acetic anhydride into the polyamic acid solution b1, fully stirring until the acetic anhydride and the polyamic acid solution are fused with each other, and then soaking melamine foam into the polyamic acid solution b 1;

In this example, the melamine foam used was the same as in example 1. The resulting melamine-polyimide composite foam had a 5% thermal decomposition temperature of 419 ℃, a compressive strength of 52KPa when it was first compressed to 50% of the total volume, and a compressive strength of 48KPa after it was compressed 100 times in a cycle to 50% of the total volume. See table 1 for details.

Example 5

s04, standing the polyamide acid solution b1 in a nitrogen atmosphere at 25 ℃, taking out the melamine foam from the solution after 8 hours, imidizing the polyamide acid solution b1 under the action of acetic anhydride to form polyimide fibers, and accommodating the polyimide fibers in the melamine foam and connecting the polyimide fibers with the melamine foam; and (3) cleaning the open-cell foam with deionized water, and drying in an oven at 120 ℃ for 60 minutes to obtain the melamine-polyimide composite foam.

In this example, the melamine foam used was the same as in example 1. The resulting melamine-polyimide composite foam had a 5% thermal decomposition temperature of 424 ℃, a compressive strength of 55KPa when it was first compressed to 50% of the total volume, and a compressive strength of 53KPa after it was cyclically compressed 100 times to 50% of the total volume. See table 1 for details.

Example 6

s04, standing the polyamic acid solution b1 in a nitrogen atmosphere at 25 ℃, taking out melamine foam from the solution after 5 hours, imidizing the polyamic acid solution b1 under the action of acetic anhydride to form polyimide fibers, and accommodating the polyimide fibers in the melamine foam and connecting the polyimide fibers with the melamine foam; and (3) cleaning the open-cell foam with deionized water, and drying in an oven at 120 ℃ for 60 minutes to obtain the melamine-polyimide composite foam.

In this example, the melamine foam size used was 400 μm. The resulting melamine-polyimide composite foam had a 5% thermal decomposition temperature of 418 ℃, a compressive strength of 45KPa when it was first compressed to 50% of the total volume, and a compressive strength of 42KPa after it was cyclically compressed 100 times to 50% of the total volume. See table 1 for details.

Example 7

The embodiment provides a preparation method of a composite foam, in particular to an EVA-polyimide composite foam, which comprises the following steps:

s03, adding 0.5mol of acetic anhydride into the polyamic acid solution b1, fully stirring until the acetic anhydride and the polyamic acid solution are mutually fused, and then soaking EVA foam into the polyamic acid solution b 1;

s04, standing the polyamic acid solution b1 in a nitrogen atmosphere at 25 ℃, taking the EVA foam out of the solution after 5 hours, imidizing the polyamic acid solution b1 under the action of acetic anhydride to form polyimide fibers, and accommodating the polyimide fibers in the EVA foam and connecting the polyimide fibers with the EVA foam; and (3) cleaning the open-cell foam with deionized water, and drying in an oven at 120 ℃ for 60 minutes to obtain the EVA-polyimide composite foam.

In this example, the EVA foam size used was substantially the same as the melamine foam size in example 1. The obtained polyurethane-polyimide composite foam has a 5% thermal decomposition temperature of 483 ℃, a compressive strength of 114KPa when the polyurethane-polyimide composite foam is firstly compressed to 50% of the total volume, and a compressive strength of 107KPa after the polyurethane-polyimide composite foam is circularly compressed for 100 times to 50% of the total volume. See table 1 for details.

Comparative example 1

This comparative example provides a method for preparing a syntactic foam, in particular a melamine-polyimide syntactic foam, which differs from example 1 only in that step S01 is replaced by: 10.814g of monomer p-phenylenediamine, 27.95g of 3,3', 4' -biphenyl tetracarboxylic dianhydride and 349g of solvent N, N-dimethylformamide are added into a reaction kettle to react to obtain a polyamic acid solution a2 with the intrinsic viscosity of 0.2dL/g, wherein the concentration of the polyamic acid solution a2 is 10%.

In this comparative example, the resulting melamine-polyimide composite foam had a 5% thermal decomposition temperature of 403 ℃, a compressive strength of 38KPa when first compressed to 50% of the total volume, and a compressive strength of 27KPa after cyclic compression 100 times to 50% of the total volume. It can be seen that the performance degradation after multiple compressions is significant after use of solutions having intrinsic viscosities below the ranges provided herein. This is because the polyimide fiber formed has poor strength and the polyimide structure is very likely to collapse after many times of compression. See table 1 for details.

Comparative example 2

This comparative example provides a method for preparing a syntactic foam, specifically a melamine-polyimide syntactic foam, which differs from example 1 only in that step S02 is replaced with: 0.2mol of acetic anhydride was added to the polyamic acid solution b 1.

In this comparative example, the melamine-polyimide composite foam obtained had a 5% thermal decomposition temperature of 423 ℃, a compressive strength of 44KPa when first compressed to 50% of the total volume, and a compressive strength of 34KPa after cyclic compression 100 times to 50% of the total volume. It can be seen that the performance degradation after multiple compressions is significant compared to the above examples because insufficient dehydrating agent is added, resulting in insufficient formation of polyimide fibers in the syntactic foam. See table 1 for details.

Comparative example 3

This comparative example provides a method of preparing a syntactic foam, specifically a melamine-polyimide syntactic foam, which differs from example 1 only in that step S04 is replaced with: the polyamic acid solution b1 was left to stand at 25 ℃ in a nitrogen atmosphere, and after 3 hours, the melamine foam was taken out of the solution.

In this comparative example, the resulting melamine-polyimide composite foam had a 5% thermal decomposition temperature of 424 ℃ and a compressive strength of 45KPa when it was first compressed to 50% of the total volume and 33KPa after it was compressed 100 times in a cycle to 50% of the total volume. It can be seen that the performance degradation after multiple compressions is significant compared to the above examples because of insufficient soak time, resulting in insufficient formation of polyimide fibers in the syntactic foam. See table 1 for details.

TABLE 1

The above description is only a preferred embodiment of the present invention, and the present invention is not limited to the above embodiment, and the present invention shall fall within the protection scope of the present invention as long as the technical effects of the present invention are achieved by the same means. The invention is capable of other modifications and variations in its technical solution and/or its implementation, within the scope of protection of the invention.

Claims

1. A method for preparing a syntactic foam, comprising the steps of:

and S04, taking out the open-cell foam, cleaning and drying to obtain the composite foam.

2. The method according to claim 1, wherein the mass fraction of the polyamic acid solution I is 8% to 10%, and the intrinsic viscosity is 0.5dL/g to 4dL/g.

3. The production method according to claim 1, wherein the mass fraction of the polyamic acid solution II is 1% to 4%, and the absolute viscosity is 0.3pa · s to 5pa · s.

4. The method according to claim 1, wherein the dehydrating agent is at least one of acetic anhydride, propionic anhydride, and trifluoroacetic anhydride.

5. The production method according to claim 1, wherein the molar ratio of the dehydrating agent to polyamic acid solution II in step S03 is 3.

6. The method of claim 1, wherein the open-cell foam is a melamine foam or an EVA foam.

7. The method according to claim 6, wherein the pore size of the open-cell foam is 50 μm to 500 μm.

8. The method of claim 7, wherein the open-cell foam is soaked for a time of 5h to 12h at a temperature of 10 ℃ to 40 ℃.

9. The method of claim 1, wherein the step S03 further comprises pretreating the open-cell foam with a surfactant before soaking the open-cell foam.

10. A composite foam produced by the production method according to any one of claims 1 to 9.