A core-shell structure polyimide@silica nanofiber and a preparation method thereof

Abstract

This invention relates to a core-shell structured polyimide@silica nanofiber and its preparation method. The invention first synthesizes a polyamic acid solution system with excellent compatibility with a silica precursor solution, and then uses coaxial electrospinning technology to spin the nanofiber. By adjusting the spinning process and curing temperature, polyimide@silica nanofibers with a core-shell structure are prepared. Due to the uniform coating of silica in the shell, these nanofibers exhibit excellent temperature resistance, thermal dimensional stability, and antigenic oxygen resistance, making them highly promising and valuable for applications in aerospace, microelectronic devices, flexible printed circuits, lithium battery separators, and electromagnetic shielding.

Description

Technical Field

[0001] This invention belongs to the field of synthesis and preparation of organic-inorganic hybrid materials, and relates to a core-shell structured polyimide@silica nanofiber and its preparation method. Background Technology

[0002] Polyimide and its derivatives are chemically stable, resistant to high and low temperatures, and possess excellent electrical insulation properties, making them widely used in aerospace, microelectronic devices, flexible printed circuits, and protective applications. However, with the development of science and technology, higher demands are being placed on the performance of polyimide materials. Traditional polyimides, which can maintain their main physical properties for short periods at 500℃ and can be used for extended periods at temperatures close to 300℃, can no longer meet the functional applications required by the microelectronics and optoelectronics manufacturing industries. High-temperature resistant polyimides have become a fundamental direction for performance pursuit.

[0003] Taking flexible displays as an example, the process temperature for the transformation from amorphous silicon to polycrystalline silicon in low-temperature polycrystalline silicon technology is as high as 300-500℃, which puts forward higher requirements for the high temperature resistance of flexible substrates. In the coating process of flexible CIGS thin-film solar cells, the thermal stability and thermal expansion coefficient of the thin film will affect the subsequent process flow, so it is necessary to prepare polyimide materials with excellent thermal stability.

[0004] Chinese patent CN201410240773.7 discloses a polyimide@silica composite nanofiber membrane and its preparation method, while Chinese patent CN201810583014.9 discloses a polyimide@silica composite material and its preparation method. These patents, through dip-coating or blending methods, prepare polyimide@silica hybrid fiber membranes with excellent temperature resistance and thermal dimensional stability. However, the dip-coating method makes it difficult to control the thickness of the silica coating, leading to easy coating peeling and reduced porosity of the fiber membrane. Blending to prepare a polyamic acid solution containing a silicon source can, to some extent, affect the mechanical properties of the polyimide material. Summary of the Invention

[0005] This invention provides a polyimide@silica nanofiber with a core-shell structure and uniformly coated with an inorganic silica layer on its surface, and its preparation method. The core-shell structured polyimide@silica nanofiber has the characteristics of high porosity, thermal dimensional stability, low dielectric, high temperature resistance, anti-ionic oxygen, wave absorption, and electromagnetic shielding.

[0006] In a first aspect, the present invention provides a method for preparing core-shell structured polyimide@silica nanofibers, comprising the following steps:

[0007] Step 1: Mix the silicon source with anhydrous ethanol and stir, then add a catalyst and deionized water to carry out a hydrolysis-condensation reaction to obtain a silica hydrolysate. Dissolve PVP in an aprotic solvent to obtain a PVP solution. Then add the hydrolysate to the PVP solution and mix and stir to prepare a silica precursor solution. The PVP accounts for 5% to 15% of the total mass of the precursor solution; the silica hydrolysate accounts for 10% to 45% of the total mass of the precursor solution; and the mass ratio of the silicon source to deionized water is 1:0.01 to 1.

[0008] Step 2: The diamine is dissolved in a mixture of diamine and a non-protic solvent. Then, aromatic dianhydride is added to the diamine solution at a rate of 0.1–1 g / min. After the aromatic dianhydride has been completely added, stirring is continued for 2–6 h to obtain a polyamic acid solution. The mass percentage concentration of the polyamic acid solution is 5%–40%.

[0009] Step 3: Using a silica precursor solution as the shell spinning solution and a polyamic acid solution as the core spinning solution, polyamic acid@PVP / SiO2 hybrid fibers with a polyamic acid core and a PVP / SiO2 shell are prepared by coaxial electrospinning; the volume ratio of the polyamic acid solution to the silica precursor solution is 1:0.3~2.

[0010] Step 4: The above-mentioned polyamic acid@PVP / SiO2 hybrid fibers are cured to thermally imidize the polyamic acid and thermally decompose the PVP to obtain core-shell structured polyimide@silica nanofibers.

[0011] According to a preferred embodiment of the present invention, in the first step, the silicon source is one or more selected from tetramethyl silicate, tetraethyl silicate, tetrapropyl silicate, tetrabutyl silicate, tetraphenyl silicate, silicon tetrachloride, and silicates; the catalyst is one selected from oxalic acid, phosphoric acid, hydrochloric acid, acetic acid, sulfuric acid, and nitric acid; the mass ratio of the silicon source to anhydrous ethanol is 1:0.1~2; and the mass ratio of the silicon source to the catalyst is 1:0.01~1.

[0012] According to a preferred embodiment of the present invention, in the third step, no flocculation occurs when the shell spinning solution and the core spinning solution are directly miscible.

[0013] According to a preferred embodiment of the present invention, in the first step, the aprotic solvent is one of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, and N,N-dimethyl sulfone.

[0014] According to a preferred embodiment of the present invention, the diamine is one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, and 3,4'-diaminophenyl ether; the aromatic dianhydride is one of 4,4′-(hexafluoroisopropene)phthalic anhydride, pyromellitic anhydride, and biphenyltetracarboxylic anhydride; and the molar ratio of the diamine to the aromatic dianhydride is 1:0.5~2.

[0015] According to a preferred embodiment of the present invention, in the third step, the coaxial electrospinning method refers to inputting the skin layer injection rate of 0.1-50 mL / h and the core layer injection rate of 0.1-50 mL / h into the spinneret of the electrospinning equipment under conditions of 15-35℃ and relative humidity of 20-70%, while simultaneously connecting the spinneret to a 10-100 kV high-voltage power supply for electrospinning.

[0016] According to a preferred embodiment of the present invention, in the fourth step, the curing is carried out by heating at a rate of 5±3℃ / min to 250℃-350℃, holding at that temperature for 10-120 min to perform thermal imidization, and then further heating to 350℃-600℃ and holding at the highest temperature for 10-120 min to remove PVP.

[0017] Secondly, the present invention provides a core-shell structured polyimide@silica nanofiber prepared by the above method. More preferably, the core-shell structured polyimide@silica nanofiber refers to a core layer consisting of continuous polyimide filaments, and a shell layer consisting of a uniformly coated, non-porous silica layer, with the silica shell thickness accounting for 34.5%-65.4% of the total fiber diameter; both the core polyimide nanofiber and the shell silica layer remain continuous.

[0018] Thirdly, this invention provides the application of the core-shell structured polyimide@silica nanofibers in the preparation of lithium battery separators, microwave absorbing materials, or electromagnetic shielding materials.

[0019] The preparation method of this invention is simple, and the obtained fiber membrane has the characteristics of high porosity, thermal dimensional stability, low dielectric, high temperature resistance, and antigenic oxygen. After further high-temperature carbonization, flexible carbon@silica nanofibers with a core-shell structure are obtained, which can be used as electromagnetic shielding materials. The preferred high-temperature carbonization method is as follows: the carbonization temperature is increased to 900℃-1100℃ at a heating rate of 5-8℃ / min, and held for 30-240 min.

[0020] Compared with the prior art, the beneficial effects of the present invention include:

[0021] This invention utilizes coaxial electrospinning to prepare core-shell structured polyimide@silica nanofibers. The resulting nanofibers inherit the high-temperature resistance of silica while possessing the excellent flexibility of polyimide. Compared to traditional fiber surface impregnation, where thickness is difficult to control and adhesion is weak, leading to easy detachment, this invention achieves a core-shell structure by adjusting spinning parameters and curing processes. The uniform coating of the polyimide fiber surface with a silica inorganic layer forms a dense silica protective layer, preventing gaseous oxygen atoms from penetrating the protective layer to react with the carbon elements on the polyimide surface, thus enhancing the polyimide's ability to react with atomic oxygen. Furthermore, the microscopic coating of polyimide with silica gives the polyimide fibers excellent temperature resistance, thermal dimensional stability, and high porosity, making them an ideal material for lithium-ion battery separators. Attached Figure Description

[0022] Figure 1 This is a TEM image of the polyimide@silica nanofibers with a core-shell structure in Example 1.

[0023] Figure 2 This is a TEM image of carbon@silica nanofibers with a core-shell structure from Example 1. Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0025] Example 1

[0026] The specific steps for preparing core-shell structured polyimide@silica nanofibers are as follows:

[0027] Step 1: Mix 20 g of tetraethyl orthosilicate with 18 g of anhydrous ethanol and 2 g of deionized water using a magnetic stirrer. While stirring, quickly add 0.2 g of phosphoric acid and stir at room temperature for 10 h to obtain a tetraethyl orthosilicate hydrolysate. Separately, slowly add PVP to DMAc while stirring. After all PVP has been added, continue stirring for 8 h to obtain a PVP solution with a PVP to DMAc mass ratio of 3:17. Finally, add the PVP solution to the tetraethyl orthosilicate hydrolysate and stir for 10 h with a PVP to tetraethyl orthosilicate hydrolysate mass ratio of 2:1. Mix thoroughly to form a precursor solution with excellent compatibility.

[0028] Step 2: Take 2 g of 4,4'-diaminodiphenyl ether and add it to 42.26 mL of N,N-dimethylacetamide. Control the temperature at 20℃ and stir to dissolve. Then add 2.4 g of pyromellitic anhydride to the above solution at 0.12 g / min. After the pyromellitic anhydride has been completely added, continue the reaction for 6 h to obtain a polyamic acid solution with a mass fraction of 8%.

[0029] Step 3: Using the precursor solution as the shell spinning solution and polyamic acid as the core spinning solution, a hybrid fiber membrane is produced by coaxial electrospinning. Electrospinning process parameters: spinning temperature 25℃, relative humidity 40%, shell injection rate 0.7 mL / h, core injection rate 0.6 mL / h, spinning voltage 20 kV, and receiving distance 30 cm.

[0030] Step 4: The above-mentioned fiber membrane is placed in a muffle furnace for thermal imidization in an air atmosphere. The thermal imidization temperature is determined by gradually increasing the temperature from room temperature to 250°C, holding at that temperature for 60 min, then further increasing the temperature to 470°C at a rate of 5°C / min, and holding at the highest temperature for 10 min, to obtain polyimide@silica nanofibers with a core-shell structure. Their morphology is as follows: Figure 1 As shown, from Figure 1 As can be seen, the core-shell structured nanofibers have a polyimide nanofiber core layer uniformly coated with silica. Further, the aforementioned polyimide@silica nanofibers were placed in a tube furnace and carbonized under a nitrogen atmosphere. The carbonization temperature was gradually increased from room temperature to 900℃ at a heating rate of 5℃ / min, and held at the highest temperature for 90 min, resulting in flexible carbon@silica nanofibers with a core-shell structure. Their morphology is as follows. Figure 2 As shown, the fiber structure remains intact after high-temperature carbonization, with silica tightly coating the surface of the carbon fiber. Figure 1 This is a TEM image of the core-shell structured polyimide@silica nanofibers from Example 1. As shown in the image, the core-shell structured polyimide@silica nanofibers consist of a continuous polyimide filament core and a uniformly coated, non-porous silica shell. The silica shell thickness accounts for 34.5%-65.4% of the total fiber diameter; both the core polyimide nanofiber and the silica shell remain continuous. The resulting nanofibers inherit the high-temperature resistance of silica and possess the good flexibility of polyimide. Because the surface of the polyimide fiber is uniformly coated with a silica inorganic layer, a dense silica protective layer is formed, preventing gaseous oxygen atoms from passing through the protective layer to react with the carbon elements on the polyimide surface, thus improving the polyimide's ability to react with atomic oxygen. Furthermore, the microscopic coating of polyimide with silica gives the polyimide fibers excellent temperature resistance, thermal dimensional stability, and high porosity.

[0031] Example 2

[0032] The specific steps for preparing core-shell structured polyimide@silica nanofibers are as follows:

[0033] Step 1: Mix 20 g of tetraethyl orthosilicate with 18 g of anhydrous ethanol and 2 g of deionized water using a magnetic stirrer. While stirring, quickly add 0.2 g of phosphoric acid and stir at room temperature for 10 h to obtain a tetraethyl orthosilicate hydrolysate. Separately, slowly add PVP to DMAc while stirring. After all PVP has been added, continue stirring for 8 h to obtain a PVP solution with a PVP to DMAc mass ratio of 3:17. Finally, add the PVP solution to the tetraethyl orthosilicate hydrolysate and stir for 10 h with a PVP to tetraethyl orthosilicate hydrolysate mass ratio of 2:1. Mix thoroughly to form a precursor solution with excellent compatibility.

[0034] Step 2: Take 2 g of 4,4'-diaminodiphenyl ether and add it to 42.26 mL of N,N-dimethylacetamide. Control the temperature at 20℃ and stir to dissolve. Then add 2.4 g of pyromellitic anhydride to the above solution at 0.12 g / min. After the pyromellitic anhydride is completely added, continue the reaction for 6 h to obtain a polyamic acid solution with a mass fraction of 10%.

[0035] Step 3: Using the precursor solution as the shell spinning solution and polyamic acid as the core spinning solution, a hybrid fiber membrane is produced by coaxial electrospinning. Electrospinning process parameters: spinning temperature 25℃, relative humidity 40%, shell injection rate 0.7 mL / h, core injection rate 0.6 mL / h, spinning voltage 20 kV, and receiving distance 30 cm.

[0036] Step 4: The above-mentioned fiber membrane is placed in a muffle furnace for thermal imidization in an air atmosphere. The thermal imidization temperature is determined by gradually increasing the temperature from room temperature to 250°C, holding at that temperature for 60 min, then further increasing the temperature to 470°C at a rate of 5°C / min, and holding at the highest temperature for 10 min, to obtain polyimide@silica nanofibers with a core-shell structure. Their morphology is as follows: Figure 1 As shown, from Figure 1 As can be seen, the core-shell structured nanofibers have a polyimide nanofiber core layer uniformly coated with silica. Further, the polyimide@silica nanofibers were placed in a tube furnace and carbonized under a nitrogen atmosphere. The carbonization temperature was gradually increased from room temperature to 900°C at a rate of 5°C / min, and held at the highest temperature for 90 min, resulting in flexible carbon@silica nanofibers with a core-shell structure, whose morphology is similar to that of Example 1.

[0037] Example 3

[0038] The specific steps of the preparation method of core-shell structured polyimide@silica nanofibers are as follows:

[0039] Step 1: Mix 20 g of tetraethyl orthosilicate with 18 g of anhydrous ethanol and 2 g of deionized water, and then magnetically stir. While stirring, rapidly add 0.2 g of phosphoric acid. Stir at room temperature for 10 h to obtain a tetraethyl orthosilicate hydrolysate. Separately, slowly add PVP to DMAc while stirring, continuing until all PVP is completely added.

[0040] The mixture was stirred continuously for 8 h to obtain a PVP solution, in which the mass ratio of PVP to DMAc was 3:17. Finally, the PVP solution was added to the tetraethyl orthosilicate hydrolysate and stirred for 10 h, in which the mass ratio of PVP solution to tetraethyl orthosilicate hydrolysate was 2:1. The mixture was stirred evenly to form a precursor solution with excellent compatibility.

[0041] Step 2: Take 2 g of 4,4'-diaminodiphenyl ether and add it to 34.42 mL of N,N-dimethylacetamide. Control the temperature at 20℃ and stir to dissolve. Then add 2.4 g of pyromellitic anhydride to the above solution at 0.12 g / min. After the pyromellitic anhydride is completely added, continue the reaction for 6 h to obtain a polyamic acid solution with a mass fraction of 12%.

[0042] Step 3: Using the precursor solution as the shell spinning solution and polyamic acid as the core spinning solution, a hybrid fiber membrane is produced by coaxial electrospinning. Electrospinning process parameters: spinning temperature 25℃, relative humidity 40%, shell injection rate 0.7 mL / h, core injection rate 0.6 mL / h, spinning voltage 20 kV, and receiving distance 30 cm.

[0043] Step 4: The above-mentioned fiber membrane was placed in a muffle furnace for thermal imidization in an air atmosphere. The thermal imidization temperature was gradually increased from room temperature to 250°C, held for 60 min, then increased to 470°C at a rate of 5°C / min, and held at the highest temperature for 10 min, resulting in polyimide@silica nanofibers with a core-shell structure. The product prepared in this embodiment has a similar core-shell structure to that in Example 1. Further, the above-mentioned polyimide@silica nanofiber membrane was placed in a tube furnace for carbonization in a nitrogen atmosphere. The carbonization temperature was gradually increased from room temperature to 900°C at a rate of 5°C / min, and held at the highest temperature for 90 min, resulting in flexible carbon@silica nanofibers with a core-shell structure, whose morphology is similar to that in Example 1.

[0044] Example 4

[0045] The specific steps of the preparation method of core-shell structured polyimide@silica nanofibers are as follows:

[0046] Step 1: Mix 20 g of tetraethyl orthosilicate with 18 g of anhydrous ethanol and 2 g of deionized water using a magnetic stirrer. While stirring, quickly add 0.2 g of phosphoric acid and stir at room temperature for 10 h to obtain a tetraethyl orthosilicate hydrolysate. Separately, slowly add PVP to DMAc while stirring. After all PVP has been added, continue stirring for 8 h to obtain a PVP solution with a PVP to DMAc mass ratio of 3:17. Finally, add the PVP solution to the tetraethyl orthosilicate hydrolysate and stir for 10 h with a PVP to tetraethyl orthosilicate hydrolysate mass ratio of 2:1. Mix thoroughly to form a precursor solution with excellent compatibility.

[0047] Step 2: Take 2 g of 4,4'-diaminodiphenyl ether and add it to 18.88 mL of N,N-dimethylacetamide. Control the temperature at 20℃ and stir to dissolve. Then add 2.4 g of pyromellitic anhydride to the above solution at 0.12 g / min. After the pyromellitic anhydride is completely added, continue the reaction for 6 h to obtain a polyamic acid solution with a mass fraction of 20%.

[0048] Step 3: Using the precursor solution as the shell spinning solution and polyamic acid as the core spinning solution, a hybrid fiber membrane is produced by coaxial electrospinning. Electrospinning process parameters: spinning temperature 25℃, relative humidity 40%, shell injection rate 0.7 mL / h, core injection rate 0.6 mL / h, spinning voltage 20 kV, and receiving distance 30 cm.

[0049] Step 4: The above-mentioned fiber membrane is placed in a muffle furnace for thermal imidization in an air atmosphere. The thermal imidization temperature is defined as gradually increasing from room temperature to 250°C, holding at that temperature for 60 min, and then continuing to increase the temperature to 470°C at a rate of 5°C / min. The highest temperature is then held for 10 min. Core-shell structured polyimide@silica nanofibers are obtained.

[0050] This demonstrates that a high-concentration silica precursor solution in the shell layer can drive the flow of a low-concentration polyamic acid solution in the core layer. In other words, the viscous stress between the two solutions must be sufficient to overcome the interfacial tension, allowing fibers to form simultaneously both inside and out. Therefore, when the concentration of the polyamic acid solution in the core layer increases, the silica precursor solution in the shell layer cannot drive the flow of the polyamic acid solution, and a complete core-shell structure cannot be formed.

[0051] This invention solves the problem of low-concentration polyamic acid solutions being unable to spin by using coaxial spinning technology. The synthesized polyamic acid solution has excellent compatibility with the silica precursor solution, and will not cause flocculation and blockage of the needle tip during long-term spinning.

[0052] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for preparing a core-shell structured polyimide@silica nanofiber, characterized by, Includes the following steps: Step 1: Mix the silicon source with anhydrous ethanol and stir, then add a catalyst and deionized water to carry out a hydrolysis-condensation reaction to obtain a silica hydrolysate. Dissolve PVP in an aprotic solvent to obtain a PVP solution. Then add the hydrolysate to the PVP solution and mix and stir to prepare a silica precursor solution. The PVP accounts for 5% to 15% of the total mass of the precursor solution; the silica hydrolysate accounts for 10% to 45% of the total mass of the precursor solution; and the mass ratio of the silicon source to deionized water is 1:0.01 to 1. Step 2: The diamine is dissolved in a mixture of diamine and a non-protic solvent. Then, aromatic dianhydride is added to the diamine solution at a rate of 0.1–1 g / min. After the aromatic dianhydride has been completely added, stirring is continued for 2–6 h to obtain a polyamic acid solution. The mass percentage concentration of the polyamic acid solution is 5%–40%. Step 3: Using a silica precursor solution as the shell spinning solution and a polyamic acid solution as the core spinning solution, polyamic acid@PVP / SiO2 hybrid fibers with a polyamic acid core and a PVP / SiO2 shell are prepared by coaxial electrospinning; the volume ratio of the polyamic acid solution to the silica precursor solution is 1:0.3~2. Step 4: The above-mentioned polyamic acid@PVP / SiO2 hybrid fibers are cured to thermally imidize the polyamic acid and thermally decompose the PVP to obtain core-shell structured polyimide@silica nanofibers.

2. The method for preparing core-shell structured polyimide@silica nanofibers according to claim 1, characterized in that, In the first step, the silicon source is one or more of tetramethyl silicate, tetraethyl silicate, tetrapropyl silicate, tetrabutyl silicate, silicon tetrachloride, and silicates; the catalyst is one of oxalic acid, phosphoric acid, hydrochloric acid, acetic acid, sulfuric acid, and nitric acid; the mass ratio of the silicon source to anhydrous ethanol is 1:0.1~2; and the mass ratio of the silicon source to the catalyst is 1:0.001~1. 3.The method for preparing core-shell structured polyimide@silica nanofibers according to claim 1, characterized in that, In the first step, the aprotic solvent is one of N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone. 4.The method for preparing core-shell structured polyimide@silica nanofibers according to claim 1, characterized in that, The diamine is one of 4,4'-diaminodiphenyl ether and p-phenylenediamine; the aromatic dianhydride is one of 4,4′-(hexafluoroisopropene)phthalic anhydride, pyromellitic anhydride, and biphenyltetracarboxylic anhydride; the molar ratio of the diamine to the aromatic dianhydride is 1:0.5~2. 5.The method for preparing core-shell structured polyimide@silica nanofibers according to claim 1, characterized in that, In the third step, the coaxial electrospinning method refers to the process of inputting the shell layer injection rate of 0.1-50 mL / h and the core layer injection rate of 0.1-50 mL / h into the spinneret of the electrospinning equipment under the conditions of 15-35℃ and relative humidity of 20-70%, while simultaneously connecting the spinneret to a 10-100 kV high-voltage power supply for electrospinning. 6.The method for preparing core-shell structured polyimide@silica nanofibers according to claim 1, characterized in that, In the fourth step, curing involves heating to 250℃-350℃ at a rate of 5±3℃ / min, holding at that temperature for 10-120 min to perform thermal imidization, and then further heating to 350℃-600℃ and holding at the highest temperature for 10-120 min to remove PVP.

7. Core-shell structured polyimide@silica nanofibers prepared by the method according to any one of claims 1-6.

8. The core-shell structured polyimide@silica nanofiber according to claim 7, characterized by, The core-shell structured polyimide@silica nanofibers refer to a core layer consisting of continuous polyimide filaments and a shell layer consisting of a uniformly coated, non-porous silica layer, with the silica layer thickness accounting for 34.5%-65.4% of the total fiber diameter; both the core polyimide nanofibers and the silica layer remain continuous.

9. The application of the core-shell structured polyimide@silica nanofibers according to claim 7 in the preparation of lithium battery separators, microwave absorbing materials, or electromagnetic shielding materials.

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