阅读说明：本技术 一种石墨烯改性聚酰亚胺复合薄膜的制备方法 (Preparation method of graphene modified polyimide composite film ) 是由 常树全 安恒 鲜莉 杨生胜 卢国庆 张海黔 于 2020-12-31 设计创作，主要内容包括：本发明公开一种石墨烯改性聚酰亚胺复合薄膜的制备方法,该薄膜由改性氧化石墨烯和POSS按照一定比例引入聚酰亚胺基体中,通过多异氰酸酯对氧化石墨烯改性增大层间距,提高了氧化石墨烯在聚酰亚胺基体中的分散性,POSS引入聚酰亚胺薄膜后,薄膜被辐照时会在薄膜表面形成SiO-2保护层,增强薄膜的耐辐照性能,同时以二胺为链接剂与封端酸酐基团进行反应,使聚酰亚胺前驱体之间链接,实现链增长,得到大分子量的聚酰亚胺,进一步改善了薄膜的力学性能。该复合薄膜可应用于航天器外表面,具有优异的耐辐照性能。(The invention discloses a preparation method of a graphene modified polyimide composite film, wherein the film is prepared by introducing modified graphene oxide and POSS (polyhedral oligomeric silsesquioxane) into a polyimide substrate according to a certain proportion, the graphene oxide is modified by polyisocyanate to increase the interlayer spacing, the dispersibility of the graphene oxide in the polyimide substrate is improved, and after the polyimide film is introduced by POSS, SiO (silicon dioxide) is formed on the surface of the film when the film is irradiated 2 The protective layer enhances the irradiation resistance of the film, and simultaneously, diamine is used as a linking agent to react with the end-capped anhydride group to link polyimide precursors and realize chainThe growth of the polyimide can obtain polyimide with large molecular weight, and the mechanical property of the film is further improved. The composite film can be applied to the outer surface of a spacecraft and has excellent radiation resistance.)

1. A preparation method of a graphene modified polyimide composite film is characterized by comprising the following steps:

the method comprises the following steps: preparation of graphene oxide powder by Hummers method

Under the ice bath condition, uniformly mixing graphite, 98% concentrated sulfuric acid and 85% concentrated phosphoric acid, then placing the mixture in an oil bath kettle which is preheated to 50 ℃, starting magnetic stirring, slowly adding potassium permanganate into a reaction system, adding hydrogen peroxide into the reaction system after reacting for 6 hours, enabling the solution to be bright yellow, continuing to react at 50 ℃ for 3 hours, then cooling to room temperature, washing with deionized water, centrifuging, and drying to obtain graphene oxide powder;

step two: preparation of modified graphene oxide powder

Uniformly dispersing the prepared graphene oxide powder in a polar organic solvent to obtain a graphene oxide dispersion liquid, adding a stirrer, transferring to an oil bath pot, adding polyisocyanate, heating to 60 ℃ in a nitrogen atmosphere, reacting for 48 hours, washing, centrifuging and drying to obtain modified graphene oxide powder;

step three: preparation of modified polyimide precursor solution

Uniformly dispersing the obtained powder in a polar organic solvent to obtain a modified graphene oxide dispersion liquid, adding polyhedral oligomeric silsesquioxane (POSS) into the obtained modified graphene oxide dispersion liquid, mechanically stirring for 1h to uniformly mix, introducing nitrogen for protection, adding a diamine monomer, continuously and mechanically stirring under an ice water bath condition, adding an anhydride monomer in an equivalent amount at intervals of 0.5h for three times after 2h, continuously stirring for 6h, adding a small amount of diamine monomer as a linking agent to increase the chain length of polyimide molecules, continuously mechanically stirring for 6h, transferring to a 50 ℃ constant-temperature water bath kettle, and heating and degrading for 30min to obtain a modified polyimide precursor solution;

step four: preparation of modified polyimide film

Uniformly coating the obtained modified polyimide precursor solution on a clean high-temperature-resistant glass plate, placing the glass plate in a vacuum drying oven, removing bubbles in vacuum for 1h under the pressure of 25MPa, then heating to 80-120 ℃ at the heating rate of 2 ℃/min for thermosetting treatment for 8-12 h, transferring a rear sample to a muffle furnace after the thermosetting treatment is finished, heating to 150-350 ℃ at the heating rate of 3 ℃/min for imidization for 6h by adopting a programmed heating treatment mode, naturally cooling to room temperature, placing the sample in deionized water for 2-5 min, and treating a stripping film in the vacuum drying oven at 105 ℃ for 1h to obtain the modified polyimide film.

2. The method of claim 1, wherein: the polar organic solvent includes one or a combination of two or more of N-methylpyrrolidone (NMP), N-Dimethylformamide (DMF), N-dimethylacetamide (DMAc), N-diethylacetamide, N-diethylformamide and Dimethylsulfoxide (DMSO).

3. The method of claim 1, wherein: the polyisocyanate in the second step comprises one or more of toluene diisocyanate, 2, 4-diphenylmethane diisocyanate, 4,4' -diphenylmethane diisocyanate and diphenylmethane diisocyanate, the dianhydride comprises 3,3 ', 4,4' -biphenyl tetracarboxylic dianhydride, 1,2,4, 5-pyromellitic dianhydride, 3 ', 4,4' -benzophenone tetracarboxylic dianhydride, the diamine comprises 4, 4-diaminodiphenyl ether, p-phenylenediamine and 4, 4-diaminodiphenylmethane, and the POSS comprises phenyl-POSS and octamethyl POSS.

4. The method of claim 1, wherein:

in the modified graphene oxide dispersion liquid in the second step, the ratio of the graphene oxide powder, the isocyanate and the polar organic solvent is 10: 80-150: 500, a step of;

in the modified polyimide precursor solution in the third step, the addition amount of the modified graphene oxide is controlled to be 0.1-1 wt% of the solid content of the modified graphene oxide dispersion liquid in the modified graphene oxide dispersion liquid, and the addition amount of POSS is controlled to be 1-5 wt% of the solid content of the modified graphene oxide dispersion liquid in the modified graphene oxide dispersion liquid;

in the step III, the molar ratio of diamine to anhydride is 1.03-1.13: the adding amount of the polar organic solvent is that the solid content of modified graphene oxide powder, POSS, diamine and anhydride in the obtained modified polyimide precursor solution is controlled to be 10-60 wt%;

in the third step, the first addition amount of diamine monomer is 95% of the total mass of diamine, the proportion of the addition amount of anhydride monomer in the total mass of anhydride is 90% of the first addition amount, 8% of the second addition amount and 2% of the third addition amount, and after 6 hours of reaction, the remaining 5% of diamine is added to react with the end-capped anhydride groups, so that polyimide precursors are linked, chain growth is realized, and polyimide precursors with large molecular weight are obtained;

after the modified polyimide precursor solution is uniformly coated on a clean high-temperature-resistant glass plate, the temperature and the time of thermosetting treatment in a vacuum drying oven are respectively 80 ℃ for 8 hours, 100 ℃ and 120 ℃ for 1 hour, after the modified polyimide precursor solution is transferred to a muffle furnace, the temperature and the time of imidization are respectively 150 ℃, 200 ℃, 250 ℃ and 300 ℃ for 1 hour, and the temperature is 0.5 hour at 350 ℃, and the modified polyimide precursor solution is naturally cooled to room temperature and then taken out.

5. The method of claim 1, wherein: treating the polar organic solvent with a 4A molecular sieve for more than three days; the anhydride monomer is treated for 3 hours at 120 ℃ in a vacuum drying oven.

Technical Field

The invention relates to the technical field of film preparation, in particular to a preparation method of a graphene modified polyimide composite film.

Background

The polyimide film has excellent mechanical property and high and low temperature resistance, can resist the high temperature of 400 ℃, can be used for a long time within the temperature range of-260-300 ℃, and also has a series of excellent properties such as chemical corrosion resistance, wear resistance, irradiation resistance, oxidation resistance, good air permeability and the like, so the polyimide film is widely applied to the fields of aerospace industry, automobile industry, microelectronics, nanotechnology, laser, separation membranes, composite materials and the like.

In the field of aerospace, the polyimide film can be applied to the manufacture of parts of an aero-engine, such as a bush, an engine outer duct and the like, can also be applied to the manufacture of aircraft structural materials, an extravehicular thermal control coating of an aerospace vehicle, a solar sail surface and the like, and can also be applied to the manufacture of an aerospace vehicle wiring system (an aviation insulated wire), a flexible printed circuit board (FPC) of an integrated circuit of an aerospace electronic product, an electronic display screen of the aerospace vehicle, a solar cell and the like. However, the surface of the spacecraft is in direct contact with the space environment for a long time, and is affected by various space environment effects such as corrosion of space atomic oxygen, irradiation of ultraviolet rays, irradiation of high-energy electron beams and the like, and the performance of the polyimide film is degraded.

Researchers have made many researches on the improvement of the irradiation resistance and the mechanical property of the polyimide film, and an invention patent with publication number of CN109337365A discloses a composite atomic oxygen resistant polyimide film, in which TSP-POSS is introduced into a polyimide matrix, and a POSS-PI composite material is subjected to atomic oxygen treatmentSiO is formed on the surface when the catalyst is attacked₂And the protective layer enhances the atomic oxygen resistance of the film. The invention patent with publication number CN107082996B discloses a preparation method of a graphene oxide crosslinked polyimide semi-interpenetrating network type composite membrane, which comprises the steps of carrying out amino end capping on polyimide, mixing the polyimide with perfluorinated sulfonic acid resin organic solution and graphene oxide, stirring, drying and cooling to obtain the composite membrane with the semi-interpenetrating network structure, wherein the prepared membrane has excellent mechanical property and thermal stability.

However, both the POSS-PI composite film and the modified GO-PI composite film cannot meet the application requirement of a space vehicle on a long-life radiation-resistant film in a space environment, so that a new method and a new technical route need to be found.

Disclosure of Invention

The invention aims to provide a preparation method of a modified polyimide composite film for solving the technical problems, and the prepared film has excellent irradiation resistance and mechanical property and can be applied to the surface of an aerospace vehicle.

A preparation method of a graphene modified polyimide composite film comprises the following steps:

the method comprises the following steps: preparation of graphene oxide powder by Hummers method

Under the ice bath condition, uniformly mixing graphite, 98% concentrated sulfuric acid and 85% concentrated phosphoric acid, then placing the mixture in an oil bath kettle which is preheated to 50 ℃, starting magnetic stirring, slowly adding potassium permanganate into a reaction system, adding hydrogen peroxide into the reaction system after reacting for 6 hours, enabling the solution to be bright yellow, continuing to react at 50 ℃ for 3 hours, then cooling to room temperature, washing with deionized water, centrifuging, and drying to obtain graphene oxide powder;

step two: preparation of modified graphene oxide powder

Uniformly dispersing the prepared graphene oxide powder in a polar organic solvent to obtain a graphene oxide dispersion liquid, adding a stirrer, transferring to an oil bath pot, adding polyisocyanate, heating to 60 ℃ in a nitrogen atmosphere, reacting for 48 hours, washing, centrifuging and drying to obtain modified graphene oxide powder;

step three: preparation of modified polyimide precursor solution

Uniformly dispersing the obtained powder in a polar organic solvent to obtain a modified graphene oxide dispersion liquid, adding polyhedral oligomeric silsesquioxane (POSS) into the obtained modified graphene oxide dispersion liquid, mechanically stirring for 1h to uniformly mix, introducing nitrogen for protection, adding a diamine monomer, continuously and mechanically stirring under an ice water bath condition, adding an anhydride monomer in an equivalent amount at intervals of 0.5h for three times after 2h, continuously stirring for 6h, adding a small amount of diamine monomer as a linking agent to increase the chain length of polyimide molecules, continuously mechanically stirring for 6h, transferring to a 50 ℃ constant-temperature water bath kettle, and heating and degrading for 30min to obtain a modified polyimide precursor solution;

step four: preparation of modified polyimide film

Uniformly coating the obtained modified polyimide precursor solution on a clean high-temperature-resistant glass plate, placing the glass plate on a vacuum drying oven, removing bubbles in vacuum for 1h under the pressure of 25MPa, then heating to 80-120 ℃ at the heating rate of 2 ℃/min for thermosetting treatment for 8-12 h, transferring a sample to a muffle furnace after the thermosetting treatment is finished, heating to 150-350 ℃ at the heating rate of 3 ℃/min for imidization for 6h by adopting a programmed heating treatment mode, naturally cooling to room temperature, placing the sample in deionized water for 2-5 min, taking a film, and treating for 1h in the vacuum drying oven at 105 ℃ to obtain a modified polyimide film;

the polar organic solvent comprises one or more of N-methylpyrrolidone (NMP), N-Dimethylformamide (DMF), N-dimethylacetamide (DMAc), N-diethylacetamide, N-diethylformamide and dimethyl sulfoxide (DMSO);

the polyisocyanate in the second step comprises one or more of toluene diisocyanate, 2, 4-diphenylmethane diisocyanate, 4,4' -diphenylmethane diisocyanate and diphenylmethane diisocyanate, the dianhydride comprises 3,3 ', 4,4' -biphenyl tetracarboxylic dianhydride, 1,2,4, 5-pyromellitic dianhydride, 3 ', 4,4' -benzophenone tetracarboxylic dianhydride, the diamine comprises 4, 4-diaminodiphenyl ether, p-phenylenediamine and 4, 4-diaminodiphenylmethane, and the POSS comprises phenyl-POSS and octamethyl POSS;

in the modified graphene oxide dispersion liquid in the second step, the ratio of the graphene oxide powder, the isocyanate and the polar organic solvent is 10: 80-150: 500, a step of;

in the modified polyimide precursor solution in the third step, the addition amount of the modified graphene oxide is controlled to be 0.1-1 wt% of the solid content of the modified graphene oxide dispersion liquid in the modified graphene oxide dispersion liquid, and the addition amount of POSS is controlled to be 1-5 wt% of the solid content of the modified graphene oxide dispersion liquid in the modified graphene oxide dispersion liquid;

in the step III, the molar ratio of diamine to anhydride is 1.06-1.16: the adding amount of the polar organic solvent is that the solid content of modified graphene oxide powder, POSS, diamine and anhydride in the obtained modified polyimide precursor solution is controlled to be 10-60 wt%;

in the third step, the first addition amount of diamine monomer is 95% of the total mass of diamine, the proportion of the addition amount of anhydride monomer in the total mass of anhydride is 90% of the first addition amount, 8% of the second addition amount and 2% of the third addition amount, and after 6 hours of reaction, the remaining 5% of diamine is added to react with the end-capped anhydride groups, so that polyimide precursors are linked, chain growth is realized, and polyimide precursors with large molecular weight are obtained;

after the modified polyimide precursor solution in the fourth step is uniformly coated on a clean high-temperature-resistant glass plate, the temperature and the time of thermosetting treatment in a vacuum drying oven are respectively 80 ℃ for 8 hours, 100 ℃ and 120 ℃ for 1 hour, after the solution is transferred to a muffle furnace, the temperature and the time of imidization are respectively 150 ℃, 200 ℃ and 250 ℃ and 300 ℃ for 1 hour, and the temperature is 0.5 hour at 350 ℃, and the solution is naturally cooled to room temperature and then taken out;

treating the polar organic solvent with a 4A molecular sieve for more than three days; treating the anhydride monomer for 3 hours at 120 ℃ in a vacuum drying oven;

the beneficial technical effects of the invention are as follows: the modified polyimide composite film prepared by reasonable proportioning has excellent mechanical property and irradiation resistance, graphene is introduced into a polyimide matrix, the interlayer spacing between the graphene is increased by modifying polyisocyanate, the dispersibility of the graphene in the polyimide matrix is improved, and the mechanical property of the modified polyimide composite film is obviously improvedLifting, introducing POSS (polyhedral oligomeric silsesquioxane), and forming SiO (silicon dioxide) on the surface of the POSS-PI composite film when the POSS-PI composite film is irradiated₂The protective layer enhances the irradiation resistance of the film, and simultaneously, diamine is used as a linking agent to react with the end-capped anhydride groups, so that polyimide precursors are linked, chain growth is realized, polyimide with high molecular weight is obtained, and the mechanical property of the film is further improved.

The modified polyimide composite film has excellent mechanical property, the normal-temperature tensile strength is more than 150MPa, the elastic modulus is more than 2.5GPa, the elongation at break is more than 40 percent, the irradiation resistance is good, and after the high-dose irradiation of 1000kGy, the strength of more than 85 percent can be maintained.

Detailed Description

The present invention is further illustrated by the following examples, which include, but are not limited to, the following examples.

Example one

A preparation method of a graphene modified polyimide composite film comprises the following steps:

the method comprises the following steps: preparation of graphene oxide powder by Hummers method

Under the ice bath condition, 1.5g of graphite, 330g of concentrated sulfuric acid (98%) and 38g of concentrated phosphoric acid (85%) are uniformly mixed, then the mixture is placed in an oil bath kettle which is preheated to 50 ℃, magnetic stirring is started, 9g of potassium permanganate are slowly added into a reaction system, after reaction for 6 hours, 90g of hydrogen peroxide is added into the reaction system until the solution becomes bright yellow, the reaction is continuously carried out for 3 hours at 50 ℃, then the solution is cooled to room temperature, and the solution is washed for 5 times by 1000g of deionized water, centrifuged for 5 minutes each time, and vacuum-dried at 60 ℃ until the weight is constant, so that graphene oxide powder is obtained;

step two: preparation of modified graphene oxide powder

Adding 1.5g of graphene oxide powder into 50g of DMAc, performing ultrasonic dispersion for 30min to obtain a graphene oxide dispersion liquid, adding a stirrer, transferring to an oil bath pot, adding a mixture of 13g of phenyl isocyanate and 4,4-MDI (the mass ratio of the phenyl isocyanate to the 4,4-MDI is 1: 4.5), heating to 60 ℃ in a nitrogen atmosphere, reacting for 48h, washing for 5 times by 500g of deionized water, centrifuging for 5min each time, and performing vacuum drying treatment at 60 ℃ to constant weight to obtain modified graphene oxide powder;

step three: preparation of modified polyimide precursor solution

Adding 0.0525g of modified graphene oxide powder into 42g of DMAc, performing ultrasonic dispersion for 30min to obtain a modified graphene oxide dispersion liquid, and adding 1.0485g of NH₂Adding POSS into the obtained modified graphene oxide dispersion liquid, mechanically stirring for 1 hour to uniformly mix the modified graphene oxide dispersion liquid, introducing nitrogen for protection, adding 3.9948g of ODA, continuously and mechanically stirring under the ice-water bath condition, adding 4.9295g of anhydride monomers (90% for the first time, 5% for the second time and 5% for the third time) at intervals of 0.5 hour after 2 hours, continuously stirring for 6 hours, adding 0.2102g of diamine monomers as a linking agent to increase the chain length of polyimide molecules, continuously and mechanically stirring for 6 hours, transferring to a 50 ℃ constant-temperature water bath kettle, and heating and degrading for 30 minutes to obtain a modified polyimide precursor solution;

step four: preparation of modified polyimide film

Uniformly coating the obtained modified polyimide precursor solution on a clean high-temperature-resistant glass plate by using a coater, placing the glass plate in a vacuum drying box, removing bubbles in vacuum under the pressure of 25MPa for 1h, and then carrying out thermocuring treatment by temperature programming: 80 ℃/8 h; 100 ℃/1 h; 120 ℃/1h, then transferring the sample to a muffle furnace, and carrying out amidation treatment by temperature programming: 150 ℃/1 h; 200 ℃/1 h; 250 ℃/1 h; 300 ℃/1 h; cooling to room temperature naturally at 350 deg.C/0.5 h. Soaking the glass plate in deionized water for 5min, stripping the film, and treating in a vacuum drying oven at 105 ℃ for 1h to obtain a modified polyimide film;

the content of the obtained modified GO is 0.1wt%, NH₂The modified polyimide composite film with 2wt% POSS content has the thickness of 30 μm, the normal-temperature tensile strength of 150MPa, the elastic modulus of 2.55GPa and the elongation at break of 45%, and after the high-dose gamma-ray irradiation of 1000kGy (0.45 kGy/h), the modified polyimide composite film with the POSS content has the normal-temperature tensile strength of 132MPa, the elastic modulus of 2.02GPa and the elongation at break of 30%, and the strength of 80% is maintained.

Example two

A preparation method of a graphene modified polyimide composite film comprises the following steps:

the method comprises the following steps: preparation of graphene oxide powder by Hummers method

Under the ice bath condition, 1.5g of graphite, 330g of concentrated sulfuric acid (98%) and 38g of concentrated phosphoric acid (85%) are uniformly mixed, then the mixture is placed in an oil bath kettle which is preheated to 50 ℃, magnetic stirring is started, 9g of potassium permanganate are slowly added into a reaction system, after reaction for 6 hours, 90g of hydrogen peroxide is added into the reaction system until the solution becomes bright yellow, the reaction is continuously carried out for 3 hours at 50 ℃, then the solution is cooled to room temperature, and the solution is washed for 5 times by 1000g of deionized water, centrifuged for 5 minutes each time, and vacuum-dried at 60 ℃ until the weight is constant, so that graphene oxide powder is obtained;

step two: preparation of modified graphene oxide powder

Adding 1.5g of graphene oxide powder into 50g of DMAc, performing ultrasonic dispersion for 30min to obtain a graphene oxide dispersion liquid, adding a stirrer, transferring to an oil bath pot, adding a mixture of 13g of phenyl isocyanate and 4,4-MDI (the mass ratio of the phenyl isocyanate to the 4,4-MDI is 1: 4.5), heating to 60 ℃ in a nitrogen atmosphere, reacting for 48h, washing for 5 times by 500g of deionized water, centrifuging for 5min each time, and performing vacuum drying treatment at 60 ℃ to constant weight to obtain modified graphene oxide powder;

step three: preparation of modified polyimide precursor solution

Adding 0.1575g of modified graphene oxide powder into 42g of DMAc, performing ultrasonic dispersion for 30min to obtain a modified graphene oxide dispersion liquid, and adding 1.0515g of NH₂Adding POSS into the obtained modified graphene oxide dispersion liquid, mechanically stirring for 1 hour to uniformly mix the modified graphene oxide dispersion liquid, introducing nitrogen for protection, adding 3.9948g of ODA, continuously and mechanically stirring under the ice-water bath condition, adding 4.9295g of anhydride monomers (90% for the first time, 5% for the second time and 5% for the third time) at intervals of 0.5 hour after 2 hours, continuously stirring for 6 hours, adding 0.2102g of diamine monomers as a linking agent to increase the chain length of polyimide molecules, continuously and mechanically stirring for 6 hours, transferring to a 50 ℃ constant-temperature water bath kettle, and heating and degrading for 30 minutes to obtain a modified polyimide precursor solution;

step four: preparation of modified polyimide film

Uniformly coating the obtained modified polyimide precursor solution on a clean high-temperature-resistant glass plate by using a coater, placing the glass plate in a vacuum drying box, removing bubbles in vacuum under the pressure of 25MPa for 1h, and then carrying out thermocuring treatment by temperature programming: 80 ℃/8 h; 100 ℃/1 h; 120 ℃/1h, then transferring the sample to a muffle furnace, and carrying out amidation treatment by temperature programming: 150 ℃/1 h; 200 ℃/1 h; 250 ℃/1 h; 300 ℃/1 h; cooling to room temperature naturally at 350 deg.C/0.5 h. And (3) soaking the glass plate in deionized water for 5min, stripping the film, and treating for 1h at 105 ℃ in a vacuum drying oven to obtain the modified polyimide film.

The content of the obtained modified GO is 0.3wt%, NH₂The modified polyimide composite film with 2wt% POSS content has the thickness of 30 μm, the normal-temperature tensile strength of 168MPa, the elastic modulus of 2.65GPa and the elongation at break of 55%, and after the high-dose gamma-ray irradiation of 1000kGy (0.45 kGy/h), the modified polyimide composite film with the POSS content has the normal-temperature tensile strength of 148MPa, the elastic modulus of 2.15GPa and the elongation at break of 37%, and the strength of 80% is maintained.

EXAMPLE III

A preparation method of a graphene modified polyimide composite film comprises the following steps:

the method comprises the following steps: preparation of graphene oxide powder by Hummers method

Under the ice bath condition, 1.5g of graphite, 330g of concentrated sulfuric acid (98%) and 38g of concentrated phosphoric acid (85%) are uniformly mixed, then the mixture is placed in an oil bath kettle which is preheated to 50 ℃, magnetic stirring is started, 9g of potassium permanganate are slowly added into a reaction system, after reaction for 6 hours, 90g of hydrogen peroxide is added into the reaction system until the solution becomes bright yellow, the reaction is continuously carried out for 3 hours at 50 ℃, then the solution is cooled to room temperature, and the solution is washed for 5 times by 1000g of deionized water, centrifuged for 5 minutes each time, and vacuum-dried at 60 ℃ until the weight is constant, so that graphene oxide powder is obtained;

step two: preparation of modified graphene oxide powder

Adding 1.5g of graphene oxide powder into 50g of DMAc, performing ultrasonic dispersion for 30min to obtain a graphene oxide dispersion liquid, adding a stirrer, transferring to an oil bath pot, adding a mixture of 13g of phenyl isocyanate and 4,4-MDI (the mass ratio of the phenyl isocyanate to the 4,4-MDI is 1: 4.5), heating to 60 ℃ in a nitrogen atmosphere, reacting for 48h, washing for 5 times by 500g of deionized water, centrifuging for 5min each time, and performing vacuum drying treatment at 60 ℃ to constant weight to obtain modified graphene oxide powder;

step three: preparation of modified polyimide precursor solution

0.2632g of modified graphene oxide powder is added into 42g of DMAc, ultrasonic dispersion is carried out for 30min to obtain modified graphene oxide dispersion liquid, 1.0525g of NH is added₂Adding POSS into the obtained modified graphene oxide dispersion liquid, mechanically stirring for 1 hour to uniformly mix the modified graphene oxide dispersion liquid, introducing nitrogen for protection, adding 3.9948g of ODA, continuously and mechanically stirring under the ice-water bath condition, adding 4.9295g of anhydride monomers (90% for the first time, 5% for the second time and 5% for the third time) at intervals of 0.5 hour after 2 hours, continuously stirring for 6 hours, adding 0.2102g of diamine monomers as a linking agent to increase the chain length of polyimide molecules, continuously and mechanically stirring for 6 hours, transferring to a 50 ℃ constant-temperature water bath kettle, and heating and degrading for 30 minutes to obtain a modified polyimide precursor solution;

step four: preparation of modified polyimide film

Uniformly coating the obtained modified polyimide precursor solution on a clean high-temperature-resistant glass plate by using a coater, placing the glass plate in a vacuum drying box, removing bubbles in vacuum under the pressure of 25MPa for 1h, and then carrying out thermocuring treatment by temperature programming: 80 ℃/8 h; 100 ℃/1 h; 120 ℃/1h, then transferring the sample to a muffle furnace, and carrying out amidation treatment by temperature programming: 150 ℃/1 h; 200 ℃/1 h; 250 ℃/1 h; 300 ℃/1 h; cooling to room temperature naturally at 350 deg.C/0.5 h. And (3) soaking the glass plate in deionized water for 5min, stripping the film, and treating for 1h at 105 ℃ in a vacuum drying oven to obtain the modified polyimide film.

The content of the obtained modified GO is 0.5wt%, NH₂The modified polyimide composite film with 2wt% POSS content has the thickness of 30 μm, the normal-temperature tensile strength of 205MPa, the elastic modulus of 2.95GPa and the elongation at break of 62%, and after the high-dose gamma-ray irradiation of 1000kGy (0.45 kGy/h), the modified polyimide composite film with the POSS content has the normal-temperature tensile strength of 178MPa, the elastic modulus of 2.56GPa and the elongation at break of 56%, and the strength of more than 85% is maintained.

Example four

A preparation method of a graphene modified polyimide composite film comprises the following steps:

the method comprises the following steps: preparation of graphene oxide powder by Hummers method

Under the ice bath condition, 1.5g of graphite, 330g of concentrated sulfuric acid (98%) and 38g of concentrated phosphoric acid (85%) are uniformly mixed, then the mixture is placed in an oil bath kettle which is preheated to 50 ℃, magnetic stirring is started, 9g of potassium permanganate are slowly added into a reaction system, after reaction for 6 hours, 90g of hydrogen peroxide is added into the reaction system until the solution becomes bright yellow, the reaction is continuously carried out for 3 hours at 50 ℃, then the solution is cooled to room temperature, and the solution is washed for 5 times by 1000g of deionized water, centrifuged for 5 minutes each time, and vacuum-dried at 60 ℃ until the weight is constant, so that graphene oxide powder is obtained;

step two: preparation of modified graphene oxide powder

Adding 1.5g of graphene oxide powder into 50g of DMAc, performing ultrasonic dispersion for 30min to obtain a graphene oxide dispersion liquid, adding a stirrer, transferring to an oil bath pot, adding a mixture of 13g of phenyl isocyanate and 4,4-MDI (the mass ratio of the phenyl isocyanate to the 4,4-MDI is 1: 4.5), heating to 60 ℃ in a nitrogen atmosphere, reacting for 48h, washing for 5 times by 500g of deionized water, centrifuging for 5min each time, and performing vacuum drying treatment at 60 ℃ to constant weight to obtain modified graphene oxide powder;

step three: preparation of modified polyimide precursor solution

0.3695g of modified graphene oxide powder is added into 42g of DMAc, ultrasonic dispersion is carried out for 30min to obtain modified graphene oxide dispersion liquid, 1.0545g of NH is added₂Adding POSS into the obtained modified graphene oxide dispersion liquid, mechanically stirring for 1 hour to uniformly mix the modified graphene oxide dispersion liquid, introducing nitrogen for protection, adding 3.9948g of ODA, continuously and mechanically stirring under the ice-water bath condition, adding 4.9295g of anhydride monomers (90% for the first time, 5% for the second time and 5% for the third time) at intervals of 0.5 hour after 2 hours, continuously stirring for 6 hours, adding 0.2102g of diamine monomers as a linking agent to increase the chain length of polyimide molecules, continuously and mechanically stirring for 6 hours, transferring to a 50 ℃ constant-temperature water bath kettle, and heating and degrading for 30 minutes to obtain a modified polyimide precursor solution;

step four: preparation of modified polyimide film

Uniformly coating the obtained modified polyimide precursor solution on a clean high-temperature-resistant glass plate by using a coater, placing the glass plate in a vacuum drying box, removing bubbles in vacuum under the pressure of 25MPa for 1h, and then carrying out thermocuring treatment by temperature programming: 80 ℃/8 h; 100 ℃/1 h; 120 ℃/1h, then transferring the sample to a muffle furnace, and carrying out amidation treatment by temperature programming: 150 ℃/1 h; 200 ℃/1 h; 250 ℃/1 h; 300 ℃/1 h; cooling to room temperature naturally at 350 deg.C/0.5 h. And (3) soaking the glass plate in deionized water for 5min, stripping the film, and treating for 1h at 105 ℃ in a vacuum drying oven to obtain the modified polyimide film.

The content of the obtained modified GO is 0.7wt%, NH₂The modified polyimide composite film with 2wt% POSS content has the thickness of 30 μm, the normal-temperature tensile strength of 194MPa, the elastic modulus of 2.65GPa and the elongation at break of 55%, and after the high-dose gamma-ray irradiation of 1000kGy (0.45 kGy/h), the modified polyimide composite film with the normal-temperature tensile strength of 165MPa, the elastic modulus of 2.09GPa and the elongation at break of 40% maintains the strength of 80%.

EXAMPLE five

A preparation method of a graphene modified polyimide composite film comprises the following steps:

the method comprises the following steps: preparing graphene oxide powder by using a Hummers method:

under the ice bath condition, 1.5g of graphite, 330g of concentrated sulfuric acid (98%) and 38g of concentrated phosphoric acid (85%) are uniformly mixed, then the mixture is placed in an oil bath kettle which is preheated to 50 ℃, magnetic stirring is started, 9g of potassium permanganate are slowly added into a reaction system, after reaction for 6 hours, 90g of hydrogen peroxide is added into the reaction system until the solution becomes bright yellow, the reaction is continuously carried out for 3 hours at 50 ℃, then the solution is cooled to room temperature, and the solution is washed for 5 times by 1000g of deionized water, centrifuged for 5 minutes each time, and vacuum-dried at 60 ℃ until the weight is constant, so that graphene oxide powder is obtained;

step two: preparation of modified graphene oxide powder

Adding 1.5g of graphene oxide powder into 50g of DMAc, performing ultrasonic dispersion for 30min to obtain a graphene oxide dispersion liquid, adding a stirrer, transferring to an oil bath pot, adding a mixture of 13g of phenyl isocyanate and 4,4-MDI (the mass ratio of the phenyl isocyanate to the 4,4-MDI is 1: 4.5), heating to 60 ℃ in a nitrogen atmosphere, reacting for 48h, washing for 5 times by 500g of deionized water, centrifuging for 5min each time, and performing vacuum drying treatment at 60 ℃ to constant weight to obtain modified graphene oxide powder;

step three: preparation of modified polyimide precursor solution

0.5295g of modified graphene oxide powder is added into 42g of DMAc, and the modified graphene oxide is obtained by ultrasonic dispersion for 30minDispersion of 1.0595gNH₂Adding POSS into the obtained modified graphene oxide dispersion liquid, mechanically stirring for 1 hour to uniformly mix the modified graphene oxide dispersion liquid, introducing nitrogen for protection, adding 3.9948g of ODA, continuously and mechanically stirring under the ice-water bath condition, adding 4.9295g of anhydride monomers (90% for the first time, 5% for the second time and 5% for the third time) at intervals of 0.5 hour after 2 hours, continuously stirring for 6 hours, adding 0.2102g of diamine monomers as a linking agent to increase the chain length of polyimide molecules, continuously and mechanically stirring for 6 hours, transferring to a 50 ℃ constant-temperature water bath kettle, and heating and degrading for 30 minutes to obtain a modified polyimide precursor solution;

step four: preparation of modified polyimide film

Uniformly coating the obtained modified polyimide precursor solution on a clean high-temperature-resistant glass plate by using a coater, placing the glass plate in a vacuum drying box, removing bubbles in vacuum under the pressure of 25MPa for 1h, and then carrying out thermocuring treatment by temperature programming: 80 ℃/8 h; 100 ℃/1 h; 120 ℃/1h, then transferring the sample to a muffle furnace, and carrying out amidation treatment by temperature programming: 150 ℃/1 h; 200 ℃/1 h; 250 ℃/1 h; 300 ℃/1 h; cooling to room temperature naturally at 350 deg.C/0.5 h. And (3) soaking the glass plate in deionized water for 5min, stripping the film, and treating for 1h at 105 ℃ in a vacuum drying oven to obtain the modified polyimide film.

Obtaining modified GO with a content of 1wt%, NH₂The modified polyimide composite film with 2wt% POSS content has the thickness of 30 μm, the normal-temperature tensile strength of 153MPa, the elastic modulus of 2.12GPa and the elongation at break of 40%, and after the high-dose gamma-ray irradiation of 1000kGy (0.45 kGy/h), the modified polyimide composite film with the POSS content has the normal-temperature tensile strength of 140MPa, the elastic modulus of 1.56GPa and the elongation at break of 30%, and the strength of 80% is maintained.