Method for preparing carbon nanotube/polymer composite

Abstract

Provided is a method for preparing a carbon nanotube/polymer composite material, including: coating a nano-silicon oxide film on the surface of a porous polymer by vacuum coating; depositing a metal catalyst nano-film on the nano-silicon oxide film by vacuum sputtering; growing a carbon nanotube array in situ on the surface of the porous polymer by plasma enhanced chemical vapor deposition to obtain a carbon nanotube/polymer porous material; and impregnating the carbon nanotube/polymer porous material with a polymer and curing to obtain the carbon nanotube/polymer composite material. By using a heat-resistant polymer having a high heat-resistant temperature and a PECVD technique, a carbon nanotube array directly grows in situ on the surface of a polymer at a low temperature, which thereby overcomes the defects of the composites previously prepared, in which carbon nanotubes are difficult to be homogeneously dispersed and the interfacial bonding force in the composites is weak.

Claims

1. A method for preparing a carbon nanotube/polymer composite material, comprising the steps of: step 1, subjecting a polymer monomer solution to electrostatic spinning or freeze-drying to obtaina porous polymer; step 2, coating a nano-silicon oxide film on a surface of the porous polymer by vacuum coating; step 3, depositing a metal catalyst nano-film on the nano-silicon oxide film by vacuum sputtering, wherein the thickness of the nano-silicon oxide film is 5˜50 nm, and the thickness of the metal catalyst nano-film is 1˜10 nm; and step 4, growing a carbon nanotube array in situ on a surface of the metal catalyst nano-film on the porous polymer by plasma enhanced chemical vapor deposition to obtain a carbon nanotube/polymer porous material; wherein the growing of the carbon nanotube array in situ is carried out under conditions of: a temperature of 200-450° C. and under a pressure of 5˜20 Pa, H.sub.2 as a carrier gas, a plasma power of 10˜500 W and a radio-frequency signal frequency set at 13.56 MHz.

2. The method according to claim 1, wherein the porous polymer is selected from the group consisting of polyimide, phenolic resin, epoxy resin, polybenzimidazole and polyamide, or a thereof.

3. The method according to claim 1, wherein the metal catalyst nano-film is selected from the group consisting of nickel, iron and cobalt, or a mixture thereof.

4. The method according to claim 1, wherein the growing of the carbon nanotube array in situ is carried out under the following conditions: H.sub.2 as a carrier gas, acetylene or methane as a carbon source, and a growing duration of 5˜60 min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic illustration of steps of a preparation method of the present invention;

(2) FIG. 2 is a scanning electron micrograph of a porous polyimide prepared in the present invention;

(3) FIG. 3 is a scanning electron micrograph of a catalyst-supported polyimide prepared in the present invention;

(4) FIG. 4 is a scanning electron micrograph of a composite with in situ grown carbon nanotubes prepared in the present invention; and

(5) FIG. 5 is a scanning electron micrograph of an enclosed composite prepared in the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

(6) The present invention provides a preparation method of a carbon nanotube/polymer composite material, comprising the steps of:

(7) coating a nano-silicon oxide film on the surface of a porous polymer by vacuum coating;

(8) depositing a metal catalyst nano-film on the nano-silicon oxide film by vacuum sputtering;

(9) growing a carbon nanotube array in situ on the surface of the porous polymer by plasma enhanced chemical vapor deposition to obtain a carbon nanotube/polymer porous material; and

(10) impregnating the carbon nanotube/polymer porous material with a polymer and curing to obtain the carbon nanotube/polymer composite material.

(11) The polymer of the polymer is selected from the group consisting of polyimide, phenolic resin, epoxy resin, polybenzimidazole and polyamide, or a mixture thereof.

(12) The above porous polymer is preferably prepared by:

(13) subjecting a polymer monomer solution to electrostatic spinning or freeze-drying to obtain the porous polymer.

(14) The solvent for the polymer monomer solution can be selected according to the type of the polymer, and is preferably dimethyl acetamide (DMAC) or N-methyl pyrrolidone (NMP).

(15) When the polymerization and curing of the polymer are difficult, a curing agent and/or an accelerator can be added into the solution of the polymer, and the type of the curing agent and accelerator can be applicable ones which are well known to those skilled in the art.

(16) The polymer monomer solution preferably has a solid content of 10%˜30%.

(17) Then, a porous polymer fibrous mat can be prepared by an electrostatic spinning technique; or alternatively, a porous polymer material can be obtained using a freeze-drying technique in which a prepared polymer slurry is freeze-dried in liquid nitrogen, removed for the solvent therefrom and finally curing, either of which is used as a skeletal structure of the composite.

(18) Thereafter, a layer of silicon oxide film with a nano-scaled thickness, referred to as a nano-silicon oxide film, is coated on the surface of the porous polymer by a vacuum coating technique, which serves as a substrate for growing carbon nanotubes. The silicon oxide film is supported on the surface of the polymer and the pores thereof.

(19) The nano-silicon oxide film preferably has a thickness of 5˜50 nm.

(20) Next, a layer of metal catalyst nano-film with a nano-scaled thickness, referred to as a metal catalyst nano-film, is sputtered and deposited on the nano-silicon oxide film by vacuum sputtering, which serves as a catalyst for growing a carbon nanotube array.

(21) The metal catalyst nano-film is preferably of one or more of metals such as nickel, iron, and cobalt.

(22) The metal catalyst nano-film preferably has a thickness of 1˜10 nm.

(23) Subsequently, a carbon nanotube array is grown in situ on the surface of the metal catalyst nano-film by a plasma enhanced chemical vapor deposition (PECVD) process, to obtain a carbon nanotube/polymer porous composite.

(24) Specifically, a metal catalyst-supported porous polymer is placed into a PECVD furnace, and vacuum is applied thereto to form a negative pressure within the furnace tube such that the pressure is preferably 5˜20 Pa. Then, H.sub.2 is introduced as a carrier gas, preferably at a flow rate of 10˜100 sccm. Preferably, when the temperature is raised up to 200˜450° C., a radio-frequency plasma emitter is turned on, preferably with the radio-frequency power set at 10˜500 W and the radio-frequency signal frequency set at 13.56 MHz. Preferably, after treatment under the H.sub.2 plasma environment for 5˜30 min, ethyne or methane is introduced as a carbon source for growing carbon nanotubes, preferably at a flow rate of 10˜80 sccm, during which different flow rate ratios between H.sub.2 and the ethyne or methane are adjusted, with the growth time being preferably 5-60 min. After the reaction is completed, the plasma emitter is turned off, and the resultant is cooled to room temperature along with the furnace under the H.sub.2 atmosphere environment.

(25) The above temperature is lower than the maximum service temperature of the polymer, and thus the polymer does not undergo high temperature pyrolysis.

(26) Finally, the grown carbon nanotube/polymer porous composite is impregnated with corresponding monomers for the polymer with the aid of vacuum, and then subjected to polymerization and curing processes to immobilize the carbon nanotubes and fill the pores such that the pores between the carbon nanotubes are enclosed, and by several impregnation and curing processes above, a dense carbon nanotube/polymer composite material is obtained.

(27) Unlike the composites prepared by a blending process which is currently generally used, a microscopically ordered composite prepared by growing a carbon nanotube array in situ on the surface of a polymer in the present invention can realize directional and high-efficiency thermal conduction and mechanical enhancement, which creates a novel method for preparing an ordered carbon/polymer composite. Using a heat-resistant polymer having a high heat-resistant temperature and a PECVD technique, a carbon nanotube array can be grown at a low temperature such that the carbon nanotubes are directly grown in situ on the surface of a polymer to prepare a composite, which thereby overcomes the defects that in the composites previously prepared, carbon nanotubes are difficult to be uniformly dispersed and the interfacial bonding force in the composites is poor, creating a novel technique utilizing an ordered composite structure to improve the directional thermal conduction and strength properties of the composite.

(28) Hereinafter, the preparation method of a carbon nanotube/polymer composite material of the present invention will be described in detail in combination with examples in order to further illustrate the present invention.

EXAMPLE 1

(29) (1) 3,3,4,4-biphenyltetracarboxylic dianhydride (BPDA) and 4,4′-oxydianiline (ODA) were weighed in a molar ratio of 1:1, dissolved in dimethyl acetamide (DMAC), and reacted at 0° C. for 5 hours. Then, 1,3,5-triaminophenoxy benzene (TAB) was added thereto to perform chemical crosslinking, to obtain a polyamic acid (PAA) stock solution with a solid content of 15%. Subsequently, a fibrous mat of an oligomer was prepared by an electrostatic spinning technique, and finally subjected to imidization at 350° C. to obtain a porous polyimide fibrous mat. A scanning electron micrograph of the porous polyimide is shown in FIG. 2.

(30) (2) The prepared porous polyimide material was coated on its surface with a layer of silicon oxide film having a thickness of 10 nm by a vacuum coating technique. Then, a layer of nickel (or iron, cobalt) thin film having a thickness of 2 nm was sputtered on the polyimide by vacuum sputtering, which was used as a catalyst for growing carbon nanotubes. A scanning electron micrograph of the prepared catalyst-supported polyimide material is shown in FIG. 3.

(31) (3) The catalyst-supported porous polyimide was placed into a PECVD furnace, and vacuum was applied thereto such that the pressure in the furnace tube was 5˜20 Pa. Then, H.sub.2 was introduced as a carrier gas at a flow rate of 100 sccm. When the temperature was raised up to 300° C., a radio-frequency plasma emitter was turned on, with the radio-frequency power set at 200 W and the radio-frequency signal frequency set at 13.56 MHz. After treatment under the H.sub.2 plasma environment for 30 min, ethyne was introduced at a flow rate of 20 sccm as a carbon source for growing carbon nanotubes, to grow carbon nanotubes for a period of 15 min. After the reaction was completed, the plasma emitter was turned off, and the resultant was cooled to room temperature along with the furnace under the H.sub.2 atmosphere environment, to obtain a polyimide with a grown array of carbon nanotubes. A scanning electron micrograph of the above composite with in situ grown carbon nanotubes is shown in FIG. 4.

(32) (4) The porous composite with grown carbon nanotubes was impregnated with a polyamic acid solution and subjected to thermal imidization at 350° C. Such an operation was repeated several times and thus the composite was densified, to finally obtain a dense carbon nanotube/polyimide composite. A scanning electron micrograph of the enclosed composite is shown in FIG. 5.

(33) The resulting carbon nanotube/polyimide composite had a mass fraction of carbon nanotubes of 6.5 wt %, had excellent mechanical properties and thermal conductivity, and had a tensile breaking strength of up to 410 MPa, a tensile modulus of 3.2 GPa and a coefficient of thermal conductivity of 13 W/mK.

EXAMPLE 2

(34) (1) 3,3,4,4-biphenyltetracarboxylic dianhydride (BPDA) and 4,4′-oxydianiline (ODA) were weighed in a molar ratio of 1:1, dissolved in dimethyl acetamide (DMAC), and reacted at 0° C. for 5 hours. Then, 1,3,5-triaminophenoxy benzene (TAB) was added thereto to perform chemical crosslinking, to obtain a polyamic acid (PAA) stock solution with a solid content of 15%. Subsequently, using a freeze-drying technique, the prepared gel was freeze-dried in liquid nitrogen, removed for the solvent therefrom using the freeze-drying technique, and finally subjected to imidization at 350° C. to obtain a porous polyimide material.

(35) (2) The prepared porous polyimide material was coated on its surface with a layer of silicon oxide film having a thickness of 20 nm by a vacuum coating technique. Then, a layer of nickel (or iron, cobalt) thin film having a thickness of 10 nm was sputtered on the polyimide by vacuum sputtering, which was used as a catalyst for growing carbon nanotubes.

(36) (3) The catalyst-supported porous polyimide was placed into a PECVD furnace, and vacuum was applied thereto such that the pressure in the furnace tube was 5˜20 Pa. Then, H.sub.2 was introduced as a carrier gas at a flow rate of 50 sccm. When the temperature was raised up to 450° C., a radio-frequency plasma emitter was turned on, with the radio-frequency power set at 100 W and the radio-frequency signal frequency set at 13.56 MHz. After treatment under the H.sub.2 plasma environment for 30 min, ethyne was introduced at a flow rate of 50 sccm as a carbon source for growing carbon nanotubes, to grow carbon nanotubes for a period of 30 min. After the reaction was completed, the plasma emitter was turned off, and the resultant was cooled to room temperature along with the furnace under the H.sub.2 atmosphere environment.

(37) (4) The porous composite with grown carbon nanotubes was impregnated with a polyamic acid solution and subjected to thermal imidization at 350° C. Such an operation was repeated several times and thus the composite was densified, to finally obtain a dense carbon nanotube/polyimide composite.

(38) The resulting carbon nanotube/polyimide composite had a mass fraction of carbon nanotubes of 8.2 wt %, had excellent mechanical properties and thermal conductivity, and had a tensile breaking strength of up to 479 MPa, a tensile modulus of 4.13 GPa and a coefficient of thermal conductivity of 17.3 W/mK.

EXAMPLE 3

(39) (1) An epoxy resin (E-03, having an epoxide number of 0.00˜0.04) was dissolved in 1-methoxy-2-propanol (MP) at room temperature, and stirred for 30 min to allow sufficient dissolution of the epoxy resin, to formulate an epoxy resin solution at a concentration of 30%. Then, a fibrous mat of the epoxy resin was prepared by an electrostatic spinning technique.

(40) (2) The prepared porous epoxy resin material was coated on its surface with a layer of silicon oxide film having a thickness of 10 nm by a vacuum coating technique. Then, a layer of nickel (or iron, cobalt) thin film having a thickness of 10 nm was sputtered on the epoxy resin by vacuum sputtering, which was used as a catalyst for growing carbon nanotubes.

(41) (3) The catalyst-supported porous epoxy resin was placed into a PECVD furnace, and vacuum was applied thereto such that the pressure in the furnace tube was 5-20 Pa. Then, H.sub.2 was introduced as a carrier gas at a flow rate of 100 sccm. When the temperature was raised up to 200° C., a radio-frequency plasma emitter was turned on, with the radio-frequency power set at 300 W and the radio-frequency signal frequency set at 13.56 MHz. After treatment under the H.sub.2 plasma environment for 10 min, ethyne was introduced at a flow rate of 10 sccm as a carbon source for growing carbon nanotubes, to grow carbon nanotubes for a period of 20 min. After the reaction was completed, the plasma emitter was turned off, and the resultant was cooled to room temperature along with the furnace under the H.sub.2 atmosphere environment.

(42) (4) The porous composite with grown carbon nanotubes was impregnated with an epoxy resin solution and cured in a vacuum oven at 100° C. Such an operation was repeated several times and thus the composite was densified, to finally obtain a dense carbon nanotube/epoxy resin composite.

(43) The resulting carbon nanotube/epoxy resin composite had a mass fraction of carbon nanotubes of 5.5 wt %, had excellent mechanical properties and thermal conductivity, and had a tensile breaking strength of up to 32.2 MPa, a tensile modulus of 3.1 GPa and a coefficient of thermal conductivity of 9.8 W/mK.

EXAMPLE 4

(44) (1) An epoxy resin (E-03, having an epoxide number of 0.00˜0.04) was dissolved in 1-methoxy-2-propanol (MP) at room temperature, and stirred for 30 min to allow sufficient dissolution of the epoxy resin, to formulate an epoxy resin solution at a concentration of 20%. Then, a fibrous mat of the epoxy resin was prepared by an electrostatic spinning technique.

(45) (2) The prepared porous epoxy resin material was coated on its surface with a layer of silicon oxide film having a thickness of 10 nm by a vacuum coating technique. Then, a layer of nickel (or iron, cobalt) thin film having a thickness of 5 nm was sputtered on the epoxy resin by vacuum sputtering, which was used as a catalyst for growing carbon nanotubes.

(46) (3) The catalyst-supported porous epoxy resin was placed into a PECVD furnace, and vacuum was applied thereto such that the pressure in the furnace tube was 5˜20 Pa. Then, H.sub.2 was introduced as a carrier gas at a flow rate of 100 sccm. When the temperature was raised up to 150° C., a radio-frequency plasma emitter was turned on, with the radio-frequency power set at 300 W and the radio-frequency signal frequency set at 13.56 MHz. After treatment under the H.sub.2 plasma environment for 10 min, ethyne was introduced at a flow rate of 20 sccm as a carbon source for growing carbon nanotubes, to grow carbon nanotubes for a period of 30 min. After the reaction was completed, the plasma emitter was turned off, and the resultant was cooled to room temperature along with the furnace under the H.sub.2 atmosphere environment.

(47) (4) The porous composite with grown carbon nanotubes was impregnated with an epoxy resin solution and cured in a vacuum oven at 100° C. Such an operation was repeated several times and thus the composite was densified, to finally obtain a dense carbon nanotube/epoxy resin composite.

(48) The resulting carbon nanotube/epoxy resin composite had a mass fraction of carbon nanotubes of 6.2 wt %, had excellent mechanical properties and thermal conductivity, and had a tensile breaking strength of up to 35.1 MPa, a tensile modulus of 3.5 GPa and a coefficient of thermal conductivity of 10.2 W/mK.

EXAMPLE 5

(49) (1) A phenolic resin and polyvinyl butyral (PVB) were dissolved in ethanol in which a mass ratio of the phenolic resin, PVB, and ethanol was 40:0.5:55.5, and stirred for 2 hours to be mixed homogeneously, to obtain a phenolic resin solution. Subsequently, an as-spun fibrous mat of the phenolic resin was prepared by an electrostatic spinning technique, which was finally cured at 180° C. to obtain a porous fibrous mat of the phenolic resin.

(50) (2) The prepared porous phenolic resin material was coated on its surface with a layer of silicon oxide film having a thickness of 20 nm by a vacuum coating technique. Then, a layer of nickel (or iron, cobalt) thin film having a thickness of 2 nm was sputtered on the phenolic resin by vacuum sputtering, which was used as a catalyst for growing carbon nanotubes.

(51) (3) The catalyst-supported porous phenolic resin was placed into a PECVD furnace, and vacuum was applied thereto such that the pressure in the furnace tube was 5˜20 Pa. Then, H.sub.2 was introduced as a carrier gas at a flow rate of 10 sccm. When the temperature was raised up to 200° C., a radio-frequency plasma emitter was turned on, with the radio-frequency power set at 500 W and the radio-frequency signal frequency set at 13.56 MHz. After treatment under the H.sub.2 plasma environment for 30 min, ethyne was introduced at a flow rate of 20 sccm as a carbon source for growing carbon nanotubes, to grow carbon nanotubes for a period of 60 min. After the reaction was completed, the plasma emitter was turned off, and the resultant was cooled to room temperature along with the furnace under the H.sub.2 atmosphere environment.

(52) (4) The porous material with grown carbon nanotubes was impregnated with a phenolic resin solution and cured at 180° C. Such an operation was repeated several times and thus the composite was densified, to finally obtain a dense carbon nanotube/phenolic resin composite.

(53) The resulting carbon nanotube/phenolic resin composite had a mass fraction of carbon nanotubes of 8.1 wt %, had excellent mechanical properties and thermal conductivity, and had a tensile breaking strength of up to 235.1 MPa, a tensile modulus of 7.5 GPa and a coefficient of thermal conductivity of 19.8 W/mK.

EXAMPLE 6

(54) (1) A phenolic resin and polyvinyl butyral (PVB) were dissolved in ethanol in which a mass ratio of the phenolic resin, PVB, and ethanol was 40:0.5:55.5, and stirred for 2 hours to be mixed homogeneously, to obtain a phenolic resin solution. Subsequently, an as-spun fibrous mat of the phenolic resin was prepared by an electrostatic spinning technique, which was finally cured at 180° C. to obtain a porous fibrous mat of the phenolic resin.

(55) (2) The prepared porous phenolic resin material was coated on its surface with a layer of silicon oxide film having a thickness of 50 nm by a vacuum coating technique. Then, a layer of nickel (or iron, cobalt) thin film having a thickness of 1 nm was sputtered on the phenolic resin by vacuum sputtering, which was used as a catalyst for growing carbon nanotubes.

(56) (3) The catalyst-supported porous phenolic resin was placed into a PECVD furnace, and vacuum was applied thereto such that the pressure in the furnace tube was 5˜20 Pa. Then, H.sub.2 was introduced as a carrier gas at a flow rate of 10 sccm. When the temperature was raised up to 150° C., a radio-frequency plasma emitter was turned on, with the radio-frequency power set at 300 W and the radio-frequency signal frequency set at 13.56 MHz. After treatment under the H.sub.2 plasma environment for 30 min, ethyne was introduced at a flow rate of 20 sccm as a carbon source for growing carbon nanotubes, to grow carbon nanotubes for a period of 30 min. After the reaction was completed, the plasma emitter was turned off, and the resultant was cooled to room temperature along with the furnace under the H.sub.2 atmosphere environment.

(57) (4) The porous material with grown carbon nanotubes was impregnated with a phenolic resin solution and cured at 180° C. Such an operation was repeated several times and thus the composite was densified, to finally obtain a dense carbon nanotube/phenolic resin composite.

(58) The resulting carbon nanotube/phenolic resin composite had a mass fraction of carbon nanotubes of 7.2 wt %, had excellent mechanical properties and thermal conductivity, and had a tensile breaking strength of up to 185.8 MPa, a tensile modulus of 6.1 GPa and a coefficient of thermal conductivity of 18.2 W/mK.

(59) As can be seen from the above examples, a carbon nanotube/polymer composite material is prepared in the present invention, which has excellent mechanical properties and thermal conductivity.

(60) The foregoing description of the examples is provided merely to help understanding the method of the present invention and the core idea thereof. It should be pointed out that those skilled in the art can also make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.