CN110105756B - High-toughness high-thermal-conductivity PBONF-based composite film and preparation method thereof - Google Patents
High-toughness high-thermal-conductivity PBONF-based composite film and preparation method thereof Download PDFInfo
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Abstract
The invention provides a high-toughness high-heat-conductivity PBONF-based composite film and a preparation method thereof, belonging to the technical field of heat-conducting composite materials. The high-toughness high-thermal-conductivity PBONF-based composite film provided by the invention comprises PBONF and a thermal-conductivity nano material; the PBONF forms a three-dimensional net structure, and the heat-conducting nano material is positioned in the three-dimensional net structure; the PBONF has a bifurcated geometry. The high-toughness high-heat-conductivity PBONF-based composite film provided by the invention has the advantages of low density, high toughness, high heat conductivity and the like, can replace the existing aluminum alloy for aviation, reduces the weight of an aerospace aircraft, and simultaneously provides higher heat dissipation efficiency and excellent structural reliability.
Description
Technical Field
The invention relates to the technical field of heat-conducting composite materials, in particular to a high-toughness high-heat-conducting PBONF-based composite film and a preparation method thereof.
Background
With the rapid development of high-power electronic equipment of military, automobiles and aerospace aircrafts towards miniaturization, integration and high speed, a large amount of heat is accumulated in the operation process of the electronic equipment, and if the heat is not dissipated in time, the service life of an electronic device is easy to be reduced, and even the electronic device is caused to lose efficacy. Therefore, the development of light-weight, high-toughness and high-thermal-conductivity materials is of great significance for improving the thermal management of next-generation high-power electronic devices.
At present, the most widely used heat dissipation materials are metals, especially aluminum alloys, because among various metals and their alloy materials, aluminum alloys have better toughness and higher thermal conductivity, for example, 7075 type aluminum alloy for avionics heat dissipation has a tensile toughness of 81.2MJ/m3The thermal conductivity is 130W/mK, but the density of the 7075 type aluminum alloy is higher and is 2.8g/cm3Therefore, other lightweight, high toughness properties are soughtThe high heat conduction composite material has important significance in replacing aluminum alloy.
Some nanomaterials, such as Graphene Nanoplatelets (GNS), Carbon Nanotubes (CNTs), Boron Nitride Nanoplatelets (BNNS), or Boron Nitride Nanotubes (BNNT), have ultra-high thermal conductivity and low density, but these pure nanomaterial films have low toughness, and thus are difficult to replace aluminum alloys for next-generation electronic devices.
In order to replace aluminum alloy with the nano material for the next generation of electronic devices, some workers introduce polymers into the nano material films to prepare polymer matrix composite materials, and the mechanical properties of the polymer matrix composite materials are improved. However, the introduced polymer wraps the heat-conducting nano material, so that phonon transmission between the nano materials is blocked, and the heat-conducting property of the composite material is reduced sharply.
Recently, some studies have further reported that a thermally conductive nanomaterial and high-strength cellulose nanofibers are mixed and filtered into a composite film. Because the cellulose nano-fiber only partially isolates the heat-conducting nano-material, the heat conductivity of the composite films is improved and is superior to that of the polymer-based composite material. However, the thermal conductivity, especially the toughness, of these cellulose nanofiber-based composite films is still far lower than that of aviation aluminum alloy materials.
Therefore, based on the heat-conducting nano material, designing and preparing the composite film capable of replacing the aluminum alloy is still a great challenge.
Disclosure of Invention
The invention aims to provide a high-toughness high-heat-conduction PBONF (poly-p-phenylene benzobisoxazole) based composite film and a preparation method thereof.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a high-toughness high-heat-conductivity PBONF-based composite film, which comprises PBONF and a heat-conducting nano material; the PBONF forms a three-dimensional net structure, and the heat-conducting nano material is positioned in the three-dimensional net structure; the PBONF has a bifurcated geometry.
Preferably, the mass of the heat-conducting nano material is 30-90% of that of the PBONF-based composite film; the heat conduction nanometer material is one or more of graphene nanometer sheets, carbon nanometer tubes, boron nitride nanometer sheets and boron nitride nanometer tubes.
Preferably, the diameter of the PBONF is 5-20 nm.
The invention provides a preparation method of the high-toughness high-heat-conductivity PBONF-based composite film, which comprises the following steps:
(1) mixing methanesulfonic acid, trifluoroacetic acid and poly-p-phenylene benzobisoxazole micron fibers, and adding sodium salt to obtain a dispersion liquid of the sodium salt and PBONF;
(2) mixing methanesulfonic acid, trifluoroacetic acid and a heat-conducting nano material to obtain a dispersion liquid of the heat-conducting nano material;
(3) uniformly mixing the dispersion liquid of the sodium salt and the PBONF in the step (1) with the dispersion liquid of the heat-conducting nano material in the step (2), pouring the uniformly mixed dispersion liquid into a mold, sealing the mold by using a film, and standing to form gel;
(4) carrying out solvent exchange on the gel obtained in the step (3) and water, and drying to obtain a high-toughness high-heat-conductivity PBONF-based composite film;
the step (1) and the step (2) have no chronological order.
Preferably, the diameter of the poly-p-phenylene benzobisoxazole micron fiber in the step (1) is 5-15 μm.
Preferably, the sodium salt in step (1) is one or more of sodium phosphate, sodium sulfate and sodium acetate.
Preferably, the mass ratio of the methanesulfonic acid to the trifluoroacetic acid in the step (1) is 1: 0.6-1.6; the mass ratio of the total mass of the methanesulfonic acid and the trifluoroacetic acid to the mass of the poly (p-phenylene benzobisoxazole) microfiber and the sodium salt is 1: 0.009-0.015: 0.06-0.11.
Preferably, the mass ratio of the methanesulfonic acid to the trifluoroacetic acid in the step (2) is 1: 0.6-1.6; the mass ratio of the total mass of the methanesulfonic acid and the trifluoroacetic acid to the heat conducting nano material is 1: 0.002-0.017.
Preferably, the mass ratio of the dispersion liquid of the sodium salt and the PBONF to the dispersion liquid of the heat-conducting nano material in the step (3) is 1: 1-3.
Preferably, the standing time in the step (3) is 4-24 hours, and the temperature is 0-25 ℃.
The invention provides a high-toughness high-heat-conductivity PBONF-based composite film, which comprises PBONF and a heat-conducting nano material; the PBONF forms a three-dimensional net structure, and the heat-conducting nano material is positioned in the three-dimensional net structure; the PBONF has a bifurcated geometry. The PBONF of the invention forms a three-dimensional net structure, the heat-conducting nano material is positioned in the three-dimensional net structure, when the composite film is stretched, the heat-conducting nano material slides together with the inhomogeneous PBONF network and releases the hidden length of the PBONF network, wherein pi-pi acting force between the PBONF is damaged (sacrificial bond), the elongation and orientation of the PBONF network can cause local deformation and hardening of the composite film, and due to the high interconnectivity of the PBONF network and the multifunctional crosslinking of the heat-conducting nano material (a plurality of PBONFs crosslinked by one heat-conducting nano material), the local hardening continuously causes the strong elongation and orientation of the adjacent PBONF network, so the PBONF network is diffused to a large amount of materials, and finally, the heat-conducting nano material and the PBONF are pulled out to generate large breaking strain and ultrahigh toughness; in addition, PBONF replaces partial heat conduction nanometer materials, so that the obtained composite film has the characteristic of light weight; PBONF has higher thermal conductivity than other fibers, and the three-dimensional network structure of PBONF does not completely isolate the heat-conducting nano material, so that the obtained composite film has good thermal conductivity.
The results of the examples show that the density of the high-toughness high-thermal-conductivity PBONF-based composite film provided by the invention is low and is 1.3-1.8 g/cm3In the range of significantly lower than that of aluminum alloy (2.8 g/cm)3) (ii) a The PBONF-based composite film has good tensile toughness of 10-100 MJ/m3In the range of near-aviation 7075 type aluminum alloys (81.2 MJ/m)3) (ii) a The PBONF-based composite film has high thermal conductivity which is within the range of 30-300W/mK and partially exceeds the aviation 7075 type aluminum alloy (130W/mK). The PBONF-based composite filmThe aluminum alloy can replace the existing aluminum alloy for aviation, reduce the weight of an aerospace aircraft, and provide higher heat dissipation efficiency and excellent structural reliability.
Drawings
FIG. 1 is a GNS/PBONF hydrogel of example 1 of the present invention;
FIG. 2 is a GNS/PBONF composite film of example 1 of the present invention;
FIGS. 3 to 4 are SEM images of the GNS/PBONF hydrogel of example 1 after freeze-drying;
FIG. 5 is an SEM image of the GNS/PBONF composite film of example 1;
FIG. 6 shows a CNT/PBONF hydrogel of example 4 of the present invention;
FIG. 7 is a CNT/PBONF composite film of example 4 of the present invention;
FIG. 8 is a BNNS/PBONF hydrogel in example 5 of the present invention;
FIG. 9 is a BNNS/PBONF composite film of example 5 of the invention.
Detailed Description
The invention provides a high-toughness high-heat-conductivity PBONF-based composite film, which comprises PBONF and a heat-conducting nano material; the PBONF forms a three-dimensional net structure, and the heat-conducting nano material is positioned in the three-dimensional net structure; the PBONF has a bifurcated geometry.
In the present invention, the diameter of the PBONF is preferably 5 to 20nm, and more preferably 9 to 18 nm.
In the present invention, the heat conductive nanomaterial is preferably one or more of graphene nanoplates, carbon nanotubes, boron nitride nanoplates, and boron nitride nanotubes. The invention has no special requirement on the size specification of the heat-conducting nano material, and the size specification which is well known by the technical personnel in the field can be adopted. In the invention, the mass of the heat-conducting nano material is preferably 30-90% of that of the PBONF-based composite film, more preferably 40-70%, and most preferably 40%. In the invention, when the heat-conducting nano material is CNT and the mass of the CNT is 40 percent of that of the PBONF-based composite film, the tensile toughness of the obtained PBONF-based composite film is as high as 72MJ/m3Thermal conductanceThe rate is 165W/mK, and the density is as low as 1.4g/cm3Can completely replace the aviation 7075 type aluminum alloy. When the GNS is selected as the heat-conducting nano material, and the mass of the GNS is 40-60% of that of the PBONF-based composite film, the specific toughness (the toughness after the density is divided) and the specific thermal conductivity of the obtained PBONF-based composite film are both equivalent to those of 7075 type aluminum alloy. Specifically, the method comprises the following steps: the specific thermal conductivity of the 7075 type aluminum alloy was 46.4Wm-1K-1cm3g-1Specific toughness of 29J g-1(ii) a When the GNS content is 40 percent, the specific thermal conductivity is 59.3Wm-1K-1cm3g-1Specific toughness of 28.8J g-1(ii) a When the content of GNS is 50 percent, the specific thermal conductivity is 63.7W m-1K-1cm3g-1Specific toughness of 29.4J g-1(ii) a When the content of GNS is 60 percent, the specific thermal conductivity is 80.6W m-1K- 1cm3g-1Specific toughness of 22.5J g-1。
The thickness of the PBONF-based composite film has no special requirement, and can be adjusted according to the application requirement. In a specific embodiment of the invention, the thickness of the PBONF-based composite film is 15-35 μm.
The PBONF in the high-toughness high-heat-conductivity PBONF-based composite film forms a three-dimensional net structure, the heat-conducting nano material is positioned in the three-dimensional net structure, and due to the fact that the PBONF has a branched geometrical shape, when the composite film is stretched, the heat-conducting nano material slides together with the non-uniform PBONF network and releases hidden lengths of the PBONF network, wherein pi-pi acting force between the PBONFs is damaged (a sacrificial bond), the partial deformation and hardening of the composite film can be caused by the extension and orientation of the PBONF network, and due to the high interconnectivity of the PBONF network and the multifunctional crosslinking of the heat-conducting nano material (a plurality of PBONFs crosslinked by one heat-conducting nano material), the partial hardening continuously causes the strong extension and orientation of adjacent PBONF networks, so that the PBONF networks are diffused to a large number of materials, and finally, the heat-conducting nano material and the PBONF are pulled out to; in addition, PBONF replaces partial heat conduction nanometer materials, so that the obtained composite film has the characteristic of light weight; PBONF has higher thermal conductivity than other fibers, and the three-dimensional network structure of PBONF does not completely isolate the heat-conducting nano material, so that the obtained composite film has good thermal conductivity.
The invention also provides a preparation method of the high-toughness high-thermal-conductivity PBONF-based composite film, which comprises the following steps:
(1) mixing methanesulfonic acid, trifluoroacetic acid and poly-p-phenylene benzobisoxazole micron fibers, and adding sodium salt to obtain a dispersion liquid of the sodium salt and PBONF;
(2) mixing methanesulfonic acid, trifluoroacetic acid and a heat-conducting nano material to obtain a dispersion liquid of the heat-conducting nano material;
(3) uniformly mixing the dispersion liquid of the sodium salt and the PBONF in the step (1) with the dispersion liquid of the heat-conducting nano material in the step (2), pouring the uniformly mixed dispersion liquid into a mold, sealing the mold by using a film, and standing to form gel;
(4) carrying out solvent exchange on the gel obtained in the step (3) and water, and drying to obtain a high-toughness high-heat-conductivity PBONF-based composite film;
the step (1) and the step (2) have no chronological order.
The invention mixes methanesulfonic acid, trifluoroacetic acid and poly-p-phenylene benzo dioxazole micron fiber, and adds sodium salt to obtain the dispersion liquid of sodium salt and PBONF.
According to the invention, preferably, the methanesulfonic acid and the trifluoroacetic acid are mixed to obtain an acidic mixed solution, and then the acidic mixed solution is mixed with the poly-p-phenylene benzobisoxazole micron fiber. In the invention, the mass ratio of the methanesulfonic acid to the trifluoroacetic acid is preferably 1: 0.6-1.6; the mass concentration of the methanesulfonic acid is preferably more than or equal to 99.0%; the mass concentration of the trifluoroacetic acid is preferably > 99.5%. In the invention, the diameter of the poly-p-phenylene benzobisoxazole micron fiber is preferably 5-15 μm, and more preferably 10-13 μm. The invention has no special requirements on the mixing mode of the methanesulfonic acid and the trifluoroacetic acid, and the methanesulfonic acid and the trifluoroacetic acid can be uniformly mixed. In the present invention, the mixing of the acidic mixed solution and the poly-p-phenylene benzobisoxazole micro-fibers is preferably stirring mixing. After mixing the methanesulfonic acid, the trifluoroacetic acid and the poly-p-phenylene benzobisoxazole micron fibers, the invention preferably continuously stirs for 6-24 h. The present invention does not require any particular speed of agitation, as is well known to those skilled in the art. According to the invention, methanesulfonic acid, trifluoroacetic acid and poly-p-phenylene benzobisoxazole micro-fibers are mixed, the acid mixed solution peels the micro-fibers into nano-fibers, a bifurcation structure is formed, and meanwhile, a three-dimensional network structure of PBONF is formed.
In the present invention, the sodium salt is preferably one or more of sodium phosphate, sodium sulfate and sodium acetate. In the invention, the mass ratio of the total mass of the methanesulfonic acid and the trifluoroacetic acid to the mass of the poly-p-phenylene benzobisoxazole microfiber and the sodium salt is preferably 1: 0.009-0.015: 0.06-0.11, and more preferably 1: 0.01-0.013: 0.07-0.10. In the present invention, the addition of the sodium salt can increase the ionic strength of the fiber dispersion, suppress its electrostatic repulsion, and promote its pi-pi interaction and gelation in the subsequent step. Because the addition of the sodium salt is not beneficial to stripping the poly (p-phenylene-benzobisoxazole) micro fibers into the nano fibers by the acid mixed solution, the acid solution and the poly (p-phenylene-benzobisoxazole) micro fibers need to be mixed firstly to form uniform dispersion liquid, and then the sodium salt is added.
According to the invention, methanesulfonic acid, trifluoroacetic acid and the heat-conducting nano material are mixed to obtain the dispersion liquid of the heat-conducting nano material.
According to the invention, preferably, the methanesulfonic acid and the trifluoroacetic acid are mixed to obtain an acidic mixed solution, and then the acidic mixed solution is mixed with the heat-conducting nano material. The mixing mode of the methanesulfonic acid and the trifluoroacetic acid is not particularly required in the invention, and the mixing mode known by the person skilled in the art can be adopted. In the invention, the mixing of the acidic mixed solution and the heat-conducting nano material is preferably ultrasonic mixing; the power of ultrasonic mixing is preferably 200-400W, and the time of ultrasonic mixing is preferably 2-4 h. In the invention, the type of the heat conduction material corresponds to the type of the heat conduction nanometer material in the high-toughness high-heat-conduction PBONF-based composite film in the technical scheme.
In the invention, the mass ratio of the methanesulfonic acid to the trifluoroacetic acid is preferably 1: 0.6-1.6; the mass ratio of the total mass of the methanesulfonic acid and the trifluoroacetic acid to the heat conducting nano material is preferably 1: 0.002-0.017, and more preferably 1: 0.005-0.013.
After the dispersion liquid of the sodium salt and the PBONF and the dispersion liquid of the heat-conducting nano material are obtained, the dispersion liquid of the sodium salt and the PBONF and the dispersion liquid of the heat-conducting nano material are uniformly mixed, the uniformly mixed dispersion liquid is poured into a mold, the mold is sealed by a film, and gel is formed after standing.
In the invention, the mass ratio of the dispersion liquid of the sodium salt and the PBONF to the dispersion liquid of the heat-conducting nano material is preferably 1: 1-3, and more preferably 1: 1.5-2.5.
The invention pours the evenly mixed dispersion into a mould, the mixed solution is spread in the mould, and then the mould is sealed by a film. The invention has no special requirements on the shape and specification of the mould, and the mould for preparing the film is well known to those skilled in the art. The invention preferably uses a flat bottom die to facilitate obtaining a film with uniform thickness. The invention has no special requirements on the material of the film, and can not react with the mixed solution of two kinds of dispersion liquid. The invention seals the mould by using the film, which is beneficial to preventing the solvent from evaporating and can avoid the gelation of the dispersed mixed solution accelerated by the moisture in the air. When water in the air enters the dispersion mixture, gelation is accelerated, which is not favorable for forming gel with regular external shape.
In the invention, the standing time is preferably 4-24 h, and more preferably 6-20 h; the temperature of the standing is preferably 0 to 25 ℃, and more preferably 5 to 20 ℃. In the standing process, the mixed solution is gelatinized under the action of the sodium salt to form gel with a regular external shape.
After the gel is obtained, the gel and water are subjected to solvent exchange, and the high-toughness high-thermal-conductivity PBONF-based composite film is obtained after drying.
The present invention preferably removes the film from the mold, immerses the gel in water, and then solvent exchanges with water. The present invention does not require any particular embodiment of the solvent exchange, and may be carried out by solvent exchange methods well known to those skilled in the art. The invention has no special requirement on the frequency of the solvent exchange, and can completely exchange the acid liquor in the gel. In a specific embodiment of the invention, the number of solvent exchanges is preferably 4. The invention carries out solvent exchange, and replaces acid liquor in the gel with water to form hydrogel, thereby being beneficial to the subsequent evaporation of the solvent to form a film. The invention dries the hydrogel to obtain the high-toughness high-heat-conductivity PBONF-based composite film. In the invention, the drying temperature is preferably 20-40 ℃, and the drying time is preferably 40-120 h. In the present invention, the dry atmosphere is preferably an air atmosphere. The heat-conducting nano materials are stacked layer by layer in the drying process, and form a layered structure with the fiber network.
The high-toughness and high-thermal-conductivity PBONF-based composite film and the preparation method thereof provided by the present invention are described in detail with reference to the following examples, which should not be construed as limiting the scope of the present invention.
Example 1
GNS/PBONF composite film
(1) Weighing 0.216g of commercial poly (p-phenylene benzobisoxazole) micron fibers, adding the commercial poly (p-phenylene benzobisoxazole) micron fibers into a mixed acid of 7m L methanesulfonic acid and 7m L trifluoroacetic acid, mechanically stirring for 8 hours, and then adding 1.5g of sodium sulfate to form a PBONF dispersion liquid containing the sodium sulfate;
(2) weighing 0.216g of GNS, adding into a mixed acid of 11m L methanesulfonic acid and 11m L trifluoroacetic acid, and carrying out ultrasonic treatment for 3h under the power of 400W to form a uniform GNS dispersion liquid;
(3) mixing the sodium sulfate-containing PBONF dispersion liquid prepared in the step (1) and the GNS dispersion liquid prepared in the step (2), mechanically stirring for 2 hours at the rotating speed of 1000rpm, pouring into a flat-bottom plastic dish with the diameter of 5.5 cm, covering a layer of preservative film on the plastic dish, standing at 5 ℃ for 8 hours, and converting into gel;
(4) soaking the gel in the step (3) in distilled water, diffusing trifluoroacetic acid, methanesulfonic acid and sodium sulfate in the gel into water, diffusing the water into the gel, soaking for 4h, changing the water, and circulating for 4 times to obtain the GNS/PBONF hydrogel (shown in figure 1);
(5) subjecting the mixture obtained in the step (4)The GNS/PBONF hydrogel is dried for 100h at 25 ℃ in the air to obtain a PBONF-based composite film (shown in figure 2) with the GNS mass fraction of 50 percent, the film thickness of 26 mu m and the tensile toughness of 45.5MJ/m3The thermal conductivity is 98.7W/mK, and the density is 1.55g/cm3。
After the GNS/PBONF hydrogel obtained in the step (4) of example 1 is freeze-dried, the GNS/PBONF hydrogel is observed by a scanning electron microscope, and as shown in fig. 3, the GNS are uniformly distributed in the three-dimensional PBONF network, as shown in fig. 3. Further scale-up observations were made on the GNS/PBONF hydrogel after freeze-drying, and the results are shown in figure 4. Figure 4 shows that the PBONF network adheres tightly to the GNS surface.
The scanning electron microscope observation of the composite film finally obtained in example 1 shows that the composite film has a distinct ordered layered structure, as shown in fig. 5.
Example 2
Unlike example 1, the mass fraction of GNS was 40%; the thickness of the PBONF-based composite film is 24 mu m, and the tensile toughness is 42.4MJ/m3The thermal conductivity is 87.2W/mK, and the density is 1.47g/cm3。
Example 3
Different from the embodiment 1, the weight percentage of the GNS is 60 percent; the thickness of the PBONF-based composite film is 30 mu m, and the tensile toughness of the PBONF-based composite film is 34.4MJ/m3The thermal conductivity is 123.4W/mK, and the density is 1.53g/cm3。
Example 4
CNT/PBONF composite film
(1) Weighing 0.216g of commercial poly (p-phenylene benzobisoxazole) micron fibers, adding the commercial poly (p-phenylene benzobisoxazole) micron fibers into a mixed acid of 4m L methanesulfonic acid and 6m L trifluoroacetic acid, mechanically stirring for 8 hours, and then adding 1.5g of sodium phosphate to form a sodium phosphate-containing PBONF dispersion;
(2) weighing CNT0.144g, adding into a mixed acid of 10.4m L methanesulfonic acid and 15.6m L trifluoroacetic acid, and performing ultrasonic treatment for 2 hours under the power of 400W to form a uniform CNT dispersion liquid;
(3) mixing the sodium phosphate-containing PBONF dispersion liquid prepared in the step (1) and the CNT dispersion liquid prepared in the step (2), mechanically stirring for 2 hours at the rotating speed of 1000rpm, pouring into a flat-bottom plastic dish with the diameter of 9 cm, covering a layer of preservative film on the plastic dish, standing at 20 ℃ for 24 hours, and converting into gel;
(4) soaking the gel in the step (3) in distilled water, diffusing trifluoroacetic acid, methanesulfonic acid and sodium phosphate in the gel into water, diffusing the water into the gel, changing the water after soaking for 4 hours, and circulating for 4 times to obtain the CNT/PBONF hydrogel (shown in figure 6);
(5) drying the CNT/PBONF hydrogel obtained in the step (4) in the air at 40 ℃ for 48h to obtain a PBONF-based composite film (shown in figure 7) with the CNT mass fraction of 40 percent, wherein the film thickness is 22 mu m, and the tensile toughness is 72.0MJ/m3The thermal conductivity is 165W/mK, and the density is 1.4g/cm3。
Example 5
BNNS/PBONF composite film
(1) Weighing 0.216g of commercial poly (p-phenylene benzobisoxazole) micron fibers, adding the commercial poly (p-phenylene benzobisoxazole) micron fibers into a mixed acid of 6m L methanesulfonic acid and 4m L trifluoroacetic acid, mechanically stirring for 24 hours, and then adding 1.5g of sodium acetate to form a PBONF dispersion liquid containing the sodium acetate;
(2) weighing 0.504g of BNNS, adding the BNNS into a mixed acid of 15.6m L methanesulfonic acid and 10.4m L trifluoroacetic acid, and carrying out ultrasonic treatment for 4h under the power of 400W to form a uniform BNNS dispersion liquid;
(3) mixing the PBONF dispersion liquid containing sodium acetate prepared in the step (1) and the BNNS dispersion liquid prepared in the step (2), mechanically stirring for 3 hours at the rotating speed of 2000rpm, pouring into a flat-bottom plastic dish with the diameter of 9 cm, covering a layer of preservative film on the plastic dish, standing for 4 hours at 0 ℃ and converting into gel;
(4) soaking the gel in the step (3) in distilled water, diffusing trifluoroacetic acid, methanesulfonic acid and sodium acetate in the gel into water, diffusing the water into the gel, changing the water after soaking for 4 hours, and circulating for 4 times to obtain BNNS/PBONF hydrogel (shown in figure 8);
(5) drying the BNNS/PBONF hydrogel obtained in the step (4) in the air at 40 ℃ for 48h to obtain a PBONF-based composite film (shown in figure 9) with BNNS mass fraction of 70 percent, the film thickness of 35 mu m and the tensile toughness of 23.4MJ/m3The thermal conductivity is 35W/mK, and the density is 1.65g/cm3。
Example 6
BNNT/PBONF composite film
(1) Weighing 0.216g of commercial poly (p-phenylene benzobisoxazole) micron fibers, adding the commercial poly (p-phenylene benzobisoxazole) micron fibers into a mixed acid of 5m L methanesulfonic acid and 5m L trifluoroacetic acid, mechanically stirring for 48 hours, and then adding 1.5g of sodium sulfate to form a PBONF dispersion liquid containing the sodium sulfate;
(2) weighing 0.093g of BNNT, adding into a mixed acid of 13m L methanesulfonic acid and 13m L trifluoroacetic acid, and carrying out ultrasonic treatment for 2h under 400W power to form a uniform BNNT dispersion liquid;
(3) mixing the sodium sulfate-containing PBONF dispersion liquid prepared in the step (1) and the BNNT dispersion liquid prepared in the step (2), mechanically stirring for 2 hours at the rotating speed of 2000rpm, pouring into a flat-bottom plastic dish with the diameter of 5.5 cm, covering a layer of preservative film on the plastic dish, standing at 10 ℃ for 12 hours, and converting into gel;
(4) soaking the gel in the step (3) in distilled water, diffusing trifluoroacetic acid, methanesulfonic acid and sodium sulfate in the gel into water, diffusing the water into the gel, soaking for 4h, changing the water, and circulating for 4 times to obtain BNNT/PBONF hydrogel;
(5) drying the BNNT/PBONF hydrogel in the step (4) at 40 ℃ for 48h in the air to obtain a PBONF-based composite film with the BNNT mass fraction of 30%, wherein the film thickness is 28 mu m, and the tensile toughness is 38MJ/m3The thermal conductivity is 58W/mK, and the density is 1.3g/cm3。
In examples 1 to 6, the tensile test was conducted on an Shimadzu AGS-X electronic universal tester, and the dimensions of the sample bar were: the length is 45mm, the width is 2mm, and the stretching speed is 1 mm/min.
The thermal conductivity was measured by measuring the in-plane thermal diffusivity of the composite material by laser flash at 25 ℃ using L FA467(NETZSCH, Germany) and then calculating the thermal conductivity according to formula 1:
K＝α·Cprho formula 1
In the formula 1, α and rho are respectively the thermal diffusion coefficient and the density of the nano composite material, rho is calculated by a weighing method, CpIs the specific heat capacity and is measured using a differential scanning calorimeter.
The embodiments can show that the high-toughness high-thermal-conductivity PBONF-based composite film and the preparation method thereof provided by the invention have the advantages of low density, high toughness, high thermal conductivity and the like, can replace the existing aluminum alloy for aviation, reduce the weight of an aerospace aircraft, and provide higher heat dissipation efficiency and excellent structural reliability.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (8)
1. The high-toughness high-thermal-conductivity PBONF-based composite film is characterized by comprising PBONF and a thermal-conductivity nano material; the PBONF forms a three-dimensional net structure, and the heat-conducting nano material is positioned in the three-dimensional net structure; the PBONF has a bifurcated geometry; the heat-conducting nano material is a graphene nano sheet, and the PBONF-based composite film has an obvious ordered layered structure; the mass of the heat-conducting nano material is 40-60% of that of the PBONF-based composite film;
the preparation method of the high-toughness high-thermal-conductivity PBONF-based composite film comprises the following steps:
(1) mixing methanesulfonic acid, trifluoroacetic acid and poly-p-phenylene benzobisoxazole micron fibers, and adding sodium salt to obtain a dispersion liquid of the sodium salt and PBONF; the sodium salt is one or more of sodium phosphate, sodium sulfate and sodium acetate;
(2) mixing methanesulfonic acid, trifluoroacetic acid and a heat-conducting nano material to obtain a dispersion liquid of the heat-conducting nano material;
(3) uniformly mixing the dispersion liquid of the sodium salt and the PBONF in the step (1) with the dispersion liquid of the heat-conducting nano material in the step (2), pouring the uniformly mixed dispersion liquid into a mold, sealing the mold by using a film, and standing to form gel;
(4) carrying out solvent exchange on the gel obtained in the step (3) and water, and drying to obtain a high-toughness high-heat-conductivity PBONF-based composite film; the drying atmosphere is air atmosphere, the drying temperature is 20-40 ℃, and the drying time is 40-120 h;
the step (1) and the step (2) have no chronological order.
2. The high-toughness high-thermal-conductivity PBONF-based composite film according to claim 1, wherein the diameter of the PBONF is 5-20 nm.
3. The preparation method of the high-toughness high-thermal-conductivity PBONF-based composite film as claimed in any one of claims 1 to 2, characterized by comprising the following steps:
(1) mixing methanesulfonic acid, trifluoroacetic acid and poly-p-phenylene benzobisoxazole micron fibers, and adding sodium salt to obtain a dispersion liquid of the sodium salt and PBONF; the sodium salt is one or more of sodium phosphate, sodium sulfate and sodium acetate;
(2) mixing methanesulfonic acid, trifluoroacetic acid and a heat-conducting nano material to obtain a dispersion liquid of the heat-conducting nano material;
(3) uniformly mixing the dispersion liquid of the sodium salt and the PBONF in the step (1) with the dispersion liquid of the heat-conducting nano material in the step (2), pouring the uniformly mixed dispersion liquid into a mold, sealing the mold by using a film, and standing to form gel;
(4) carrying out solvent exchange on the gel obtained in the step (3) and water, and drying to obtain a high-toughness high-heat-conductivity PBONF-based composite film; the drying atmosphere is air atmosphere, the drying temperature is 20-40 ℃, and the drying time is 40-120 h;
the step (1) and the step (2) have no chronological order.
4. The preparation method according to claim 3, wherein the diameter of the poly-p-phenylene benzobisoxazole micro-fibers in the step (1) is 5 to 15 μm.
5. The preparation method according to claim 3, wherein the mass ratio of the methanesulfonic acid to the trifluoroacetic acid in the step (1) is 1:0.6 to 1.6; the mass ratio of the total mass of the methanesulfonic acid and the trifluoroacetic acid to the mass of the poly (p-phenylene benzobisoxazole) microfiber and the sodium salt is 1: 0.009-0.015: 0.06-0.11.
6. The preparation method according to claim 3, wherein the mass ratio of the methanesulfonic acid to the trifluoroacetic acid in the step (2) is 1:0.6 to 1.6; the mass ratio of the total mass of the methanesulfonic acid and the trifluoroacetic acid to the heat conducting nano material is 1: 0.002-0.017.
7. The preparation method according to claim 3, wherein the mass ratio of the dispersion of the sodium salt and the PBONF to the dispersion of the heat-conducting nano material in the step (3) is 1: 1-3.
8. The preparation method according to claim 3, wherein the standing time in the step (3) is 4-24 h, and the temperature is 0-25 ℃.
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