CN113388148A - Preparation method of supercritical carbon dioxide assisted heat-conducting composite material - Google Patents

Preparation method of supercritical carbon dioxide assisted heat-conducting composite material Download PDF

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CN113388148A
CN113388148A CN202110634485.XA CN202110634485A CN113388148A CN 113388148 A CN113388148 A CN 113388148A CN 202110634485 A CN202110634485 A CN 202110634485A CN 113388148 A CN113388148 A CN 113388148A
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carbon dioxide
supercritical carbon
heat
conducting
composite material
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CN113388148B (en
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卢翔
瞿金平
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Huazhong University of Science and Technology
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Abstract

The invention belongs to the field of polymer chemistry, and particularly relates to a preparation method of a supercritical carbon dioxide assisted heat-conducting composite material. The invention comprises the following steps: (1) mixing a thermoplastic high polymer material, a compatibilizer and a heat-conducting filler to obtain a polymer melt; (2) injecting supercritical carbon dioxide into the polymer melt and infiltrating into the heat-conducting filler; (3) the supercritical carbon dioxide is vaporized to form carbon dioxide gas through pressure relief, and the heat-conducting filler is uniformly dispersed in the polymer melt through the explosion effect of the carbon dioxide gas. According to the invention, the flow rate is accurately controlled by the metering pump, and the supercritical carbon dioxide is injected into the extruder from different injection ports to be mixed with the polymer melt, so that the supercritical carbon dioxide has the effects of promoting the stripping, intercalation and dispersion of the heat-conducting filler, and the interface interaction between the polymer molecular chain and the heat-conducting filler is enhanced, thereby constructing a three-dimensional heat-conducting passage, reducing the interface thermal resistance and improving the thermal conductivity of the composite material.

Description

Preparation method of supercritical carbon dioxide assisted heat-conducting composite material
Technical Field
The invention belongs to the field of polymer chemistry, and particularly relates to a preparation method of a supercritical carbon dioxide assisted heat-conducting composite material.
Background
With the development of modern electronic components toward integration, miniaturization and intellectualization, the heat dissipation problem of electronic devices becomes a bottleneck that hinders the development of the microelectronic field. How to timely discharge the heat generated by electronic components has become an important research topic in the field of microelectronic product system assembly. High polymer materials such as polyolefin, polyester and the like are widely applied due to the advantages of easy molding and processing, good insulating property and the like, but due to low thermal conductivity, the high polymer materials are difficult to meet the heat dissipation requirement when being used alone in certain fields. At present, two methods are mainly used for improving the heat-conducting property of a high-molecular material, one method is an intrinsic method, and the heat-conducting property is improved by changing the molecular chain or the molecular chain distribution of a polymer to obtain different structures; the other is a filling method, in which a thermally conductive composite is made by adding a highly thermally conductive filler to a polymer matrix. Due to the complex process and the high processing difficulty of the intrinsic method, the filled heat-conducting composite material appears in the public field of vision more. However, for the filled type heat conductive polymer composite material, the dispersion state of the heat conductive filler in the resin matrix is the key to determine the heat conductive performance.
Although the solution blending can obtain a good heat-conducting filler dispersing effect, a large amount of organic solvent is needed to cause environmental pollution, and the composite material is not easy to continuously prepare and is difficult to popularize and apply on a large scale. The melt blending does not need to use organic solvent, and has the advantages of simple operation, short production period, continuous batch production and the like, thereby being widely applied. And the common melt blending is difficult to strip, intercalate and disperse the heat-conducting filler efficiently, so that the heat conductivity of the composite material is not obviously improved. Researchers often need to carry out organic modification treatment on the heat-conducting filler to improve the dispersion effect or increase the filling amount of the heat-conducting filler, so that not only the preparation process is complicated, but also the production cost is increased, and the popularization and the application are difficult.
Supercritical fluid (SCF) is a fluid having a temperature and pressure above its Critical point, and is commonly used to produce supercritical fluids such as carbon dioxide, ammonia, ethylene, propane, propylene, water, etc. When an object is in a supercritical state, the properties of gas phase and liquid phase are very similar, so that the two phases cannot be clearly separated, and the object is called a supercritical fluid. CN100493885C discloses a supercritical fluid assisted high polymer material extrusion molding machine, which is further provided with a supercritical carbon dioxide fluid conveying device, wherein the supercritical carbon dioxide fluid conveying device is communicated with a charging barrel through at least one gas injection port, so as to convey supercritical fluid to the charging barrel. The comparative document 1 discloses a supercritical carbon dioxide-assisted polymer extrusion method, but simply discloses lowering the viscosity, avoiding high shear action on a high-viscosity polymer material, and sufficiently plasticizing the material, does not disclose preparation of a heat conductive composite material, further does not disclose interaction of a heat conductive filler and carbon dioxide, does not disclose efficient dispersion of the heat conductive filler, and leaves room for improvement.
CN104262516A discloses a method for preparing a graphene/fluoropolymer composite material in situ by using a supercritical fluid, in which a fluoropolymer monomer is dissolved in a supercritical fluid, the supercritical fluid and the polymer monomer are used to intercalate graphite simultaneously, the supercritical fluid is used as a polymerization medium to initiate a polymerization reaction to generate a fluoropolymer, thereby promoting the significant expansion of the graphite interlayer distance, and the intercalated graphite is finally rapidly exfoliated layer by layer in the rapid pressure relief process of the supercritical pressure, so as to prepare the fluoropolymer conductive and heat conductive composite material with good graphene dispersion. Although the technical scheme uses the supercritical fluid, the technical scheme is not applied to a high polymer melt, and there is still room for improvement.
In summary, the prior art is still lack of a preparation method of a supercritical carbon dioxide assisted heat-conducting composite material capable of efficiently dispersing heat-conducting fillers.
Disclosure of Invention
Addressing the above deficiencies or needs in the artThe invention provides a method for preparing a carbon dioxide catalyst by using supercritical carbon dioxide (scCO)2) The method for preparing the high-thermal-conductivity polymer composite material by auxiliary melt blending extrusion enables the thermal-conductivity fillers such as expanded graphite, boron nitride and the like to be well stripped, intercalated and dispersed in a polymer matrix in situ, and aims to enhance the interface interaction between polymer molecular chains and the thermal-conductivity fillers, thereby constructing a three-dimensional thermal-conductivity passage, reducing the interface thermal resistance and improving the thermal conductivity of the composite material.
In order to achieve the above object, according to one aspect of the present invention, there is provided a method for preparing a supercritical carbon dioxide assisted heat conductive composite, comprising the steps of:
(1) mixing a thermoplastic high polymer material, a compatibilizer and a heat-conducting filler to obtain a polymer melt;
(2) setting the pressure of the supercritical carbon dioxide to exceed the pressure of the polymer melt, and injecting the supercritical carbon dioxide into the polymer melt and infiltrating into the heat-conducting filler;
(3) the supercritical carbon dioxide is vaporized to form carbon dioxide gas through pressure relief, and the heat-conducting filler is uniformly dispersed in the polymer melt through the explosion effect of the carbon dioxide gas, so that the heat-conducting composite material can be obtained.
The compatibilizer is used for promoting the heat-conducting filler to be dissolved by the polymer melt, and after the supercritical carbon dioxide enters the polymer melt, the whole system is in a liquid state, so that the heat-conducting filler can be internally dissolved, and the dispersion of the heat-conducting filler is promoted.
Preferably, step (2) and step (3) are repeated several times, preferably 3 or more times, for one combination.
Preferably, the thermoplastic polymer material is polyolefin or polyester, the compatibilizer is a maleic anhydride graft copolymer or a glycidyl methacrylate graft copolymer, and the heat-conducting filler is expanded graphite or boron nitride.
Preferably, the mass ratio of the total injection amount of the supercritical carbon dioxide to the addition amount of the polymer melt is (2-40): 100; the mass ratio of the heat-conducting filler to the thermoplastic polymer material is (5-40): 100.
Preferably, the mixing in the step (1) is realized by a supercritical carbon dioxide-assisted melt blending extrusion device, the supercritical carbon dioxide-assisted melt blending extrusion device comprises a twin-screw extruder, a supercritical carbon dioxide injection device and a vacuum exhaust pump, the twin-screw extruder is sequentially provided with a feeding section, an injection section and an exhaust section along the movement direction of the thermoplastic polymer material, the feeding section is provided with a feeding port, the injection section is connected with the supercritical carbon dioxide injection device through the supercritical carbon dioxide injection port, and the exhaust section is connected with the vacuum exhaust pump through the vacuum exhaust port.
Preferably, the injection section and the exhaust section are repeatedly provided in plural for one combination.
Preferably, the injection section is provided with a metering pump. The metering pump can monitor the flow of carbon dioxide entering the polymer melt in real time and is a high-pressure metering pump.
Preferably, in step (2), the pressure of the supercritical carbon dioxide is made to exceed the pressure of the polymer melt in the injection section by adjusting the feeding amount, the screw rotation speed and the extruder barrel temperature.
Preferably, the screw length-diameter ratio of the double-screw extruder is (35-48):1, the screw rotating speed of the extruder is 200-.
According to another aspect of the invention, the heat-conducting composite material prepared by the preparation method of the supercritical carbon dioxide assisted heat-conducting composite material is provided.
The invention has the following beneficial effects:
(1) the invention mixes the thermoplastic material, the interface compatibilizer and the heat-conducting filler in advance and then adds the scCO2Mixing and extruding in an auxiliary melt blending extrusion device, and accurately controlling the flow rate of the scCO by means of a metering pump2Injecting the mixture into an extruder from different injection ports to be mixed with polymer melt, and mixing the polymer melt with the SCCO2Has the effects of promoting the stripping, intercalation and dispersion of the heat-conducting filler and enhancing the interface interaction between polymer molecular chains and the heat-conducting filler, thereby constructing the three-dimensional heat-conducting fillerThe thermal path is opened, the interface thermal resistance is reduced, and the thermal conductivity of the composite material is improved.
(2) According to the invention, the pressure of the supercritical carbon dioxide exceeds the pressure of the polymer melt in the injection section by adjusting the feeding amount, the feeding saturation, the screw rotating speed, the screw combination and the temperature of the extruder barrel, and the injection amount is analyzed by the metering pump, so that the controllability degree is high.
(3) The preparation method is simple to operate, is easy for large-scale production, and does not need any pretreatment on the heat-conducting filler.
Drawings
FIG. 1 is a schematic structural diagram of a supercritical carbon dioxide-assisted melt blending extrusion device;
wherein: a feeding port 1, a first supercritical carbon dioxide injection port 2, a second supercritical carbon dioxide injection port 3, a third supercritical carbon dioxide injection port 4, a first vacuum exhaust port 5, a second vacuum exhaust port 6, a third vacuum exhaust port 7, a twin-screw extruder 8, a first supercritical carbon dioxide injection device 9, a second supercritical carbon dioxide injection device 10, a third supercritical carbon dioxide injection device 11, a first vacuum pump 12, a second vacuum pump 13, and a third vacuum pump 14.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Examples
The structural schematic diagram of the supercritical carbon dioxide auxiliary melt blending extrusion equipment of the invention is shown in fig. 1, and comprises a double screw extruder 8, a supercritical carbon dioxide injection device and a vacuum exhaust pump, wherein the double screw extruder is sequentially provided with a feeding section, an injection section and an exhaust section along the movement direction of a thermoplastic polymer material, the feeding section is provided with a feeding port 1, the embodiment is provided with three supercritical carbon dioxide injection devices comprising a first supercritical carbon dioxide injection device 9, a second supercritical carbon dioxide injection device 10 and a third supercritical carbon dioxide injection device 11, three vacuum pumps and a vacuum exhaust pump are correspondingly arranged, a first vacuum pump 12, a second vacuum pump 13 and a third vacuum pump 14,
the injection section is connected with the first supercritical carbon dioxide injection device 9 through a first supercritical carbon dioxide injection port 2, is connected with the second supercritical carbon dioxide injection device 10 through a first supercritical carbon dioxide injection port 3, is connected with the first supercritical carbon dioxide injection device B3 through a third supercritical carbon dioxide injection port 4, the exhaust section is connected with the first vacuum pump 12 through the first vacuum exhaust port 5, is connected with the second vacuum pump 13 through the first vacuum exhaust port 6, and is connected with the first vacuum pump C3 through the third vacuum exhaust port 7.
The following are specific preparation examples.
Example 1
(1) Premixing Polypropylene (PP), polypropylene grafted maleic anhydride (PP-g-MAH) and Expanded Graphite (EG) powder according to a mass ratio of 90:5:5, and adding the premixed materials into an extruder from a feeding port for melt mixing;
(2) setting the rotation speed of a screw of the extruder to be 200r/min, setting the temperature of a machine barrel to be 200 ℃, and accurately controlling the flow rate of the scCO by means of a metering pump2First scCO from extruder at a flow rate of 1L/h2The sprue is injected into the PP melt. Under the mixing action of a screw, scCO2Quickly permeate into the EG layers, enlarge the interlayer spacing of EG, and play a role in plasticizing PP molecular chains;
(3)scCO2the pressure relief and vaporization at the first vacuum vent produce a strong blasting effect and form CO2And pumping the mixture out of an exhaust port by a vacuum pump, and finally extruding the mixture at an outlet of an extruder to prepare the PP/EG composite material with the EG being stripped, intercalated and dispersed well.
Example 2
The difference between this example and example 1 is that PP, PP-g-MAH and EG powders were premixed at a mass ratio of 85:5:10 and added from the feed portAdding into an extruder for melting and mixing, and accurately controlling the flow rate by a metering pump to obtain scCO2First scCO from extruder2The sprue is injected into the PP melt.
Example 3
This example differs from example 1 in that the PP, PP-g-MAH and EG powders were premixed at a mass ratio of 75:5:20 and fed into an extruder from a feed port to be melt-kneaded, and scCO was fed into the extruder with the flow rate precisely controlled by a metering pump2First scCO from extruder2The sprue is injected into the PP melt.
Example 4
This example differs from example 1 in that the PP, PP-g-MAH and EG powders were premixed at a mass ratio of 75:5:20 and fed into an extruder from a feed port to be melt-kneaded, and scCO was fed into the extruder with the flow rate precisely controlled by a metering pump2First and second scCOs were simultaneously extruded from the extruder at a flow rate of 1L/h2The sprue is injected into the PP melt.
Example 5
This example differs from example 1 in that the PP, PP-g-MAH and EG powders were premixed at a mass ratio of 75:5:20 and fed into an extruder from a feed port to be melt-kneaded, and scCO was fed into the extruder with the flow rate precisely controlled by a metering pump2First, second and third scCOs were simultaneously extruded from the extruder at a flow rate of 1L/h2The sprue is injected into the PP melt.
Example 6
This example differs from example 1 in that PP and PP-g-MAH and Boron Nitride (BN) powders were premixed at a mass ratio of 75:5:20 and fed from a feed port into an extruder for melt-kneading, and scCO was fed with a flow rate precisely controlled by a metering pump2First scCO from the extruder at a flow rate of 1L/h simultaneously2The sprue is injected into the PP melt.
Example 7
This example differs from example 1 in that polylactic acid (PLA), butyl acrylate-glycidyl methacrylate (BA-GMA) and EG powder were premixed in a mass ratio of 75:5:20 and then fed from a feed port into an extruder for melt-kneading, and scCO was fed into the extruder with the flow rate accurately controlled by a metering pump2Extruding at a flow rate of 1L/hFirst scCO of machine2The sprue is injected into the PLA melt.
Example 8
This example differs from example 1 in that polylactic acid (PLA), butyl acrylate-glycidyl methacrylate (BA-GMA) and EG powder were premixed in a mass ratio of 75:5:20 and then fed from a feed port into an extruder for melt-kneading, and scCO was fed into the extruder with the flow rate accurately controlled by a metering pump2First and second scCOs were simultaneously extruded from the extruder at a flow rate of 1L/h2The sprue is injected into the PLA melt.
Example 9
This example differs from example 1 in that polylactic acid (PLA), butyl acrylate-glycidyl methacrylate (BA-GMA) and EG powder were premixed in a mass ratio of 75:5:20 and then fed from a feed port into an extruder for melt-kneading, and scCO was fed into the extruder with the flow rate accurately controlled by a metering pump2First, second and third scCOs were simultaneously extruded from the extruder at a flow rate of 1L/h2The sprue is injected into the PLA melt.
Comparative example 1
This example is different from example 1 in that PP, PP-g-MAH and EG powders were premixed at a mass ratio of 90:5:5, and then fed into an extruder from a feed port to be melt-kneaded, and extruded at the outlet of the extruder to prepare a PP/EG composite material.
Comparative example 2
This example is different from example 1 in that PP, PP-g-MAH and EG powders were premixed at a mass ratio of 85:5:10, and then fed into an extruder from a feed port to be melt-kneaded, and extruded at the outlet of the extruder to prepare a PP/EG composite material.
Comparative example 3
This example is different from example 1 in that PP, PP-g-MAH and EG powders were premixed at a mass ratio of 75:5:20, and then fed into an extruder from a feed port to be melt-kneaded, and extruded at the outlet of the extruder to prepare a PP/EG composite material.
Comparative example 4
This example is different from example 1 in that PP/EG composite material was prepared by premixing PP, PP-g-MAH and BN powders at a mass ratio of 75:5:20, feeding the premixed powders into an extruder through a feed port, melt-kneading the kneaded materials, and extruding the kneaded materials at an outlet of the extruder.
Comparative example 5
The difference between the embodiment and the embodiment 1 is that PLA, BA-g-MAH and EG powder are premixed according to the mass ratio of 75:5:20, then added into an extruder from a feeding port for melt mixing, and extruded at the outlet of the extruder to prepare the PLA/EG composite material.
Test examples
The thermal conductivity values of examples 1 to 9 and comparative examples 1 to 5 were measured, and the results are shown in Table 1.
TABLE 1
Figure BDA0003104912270000081
As can be seen from Table 1, the thermal conductivity of the composite material gradually increased with the content of the thermally conductive filler, and examples 1 to 3 (scCO) were compared with comparative examples 1 to 3 (conventional melt blending)2Auxiliary melt blending) has larger thermal conductivity improvement range of the prepared composite material; by comparative example 3 (conventional melt blending) and examples 3-5 (scCO)2Auxiliary melt blending), and comparative example 5 (conventional melt blending) and examples 7-9 (scCO)2Assisted melt blending), it can be found that scCO2The higher the auxiliary degree is, the larger the thermal conductivity improvement amplitude of the obtained composite material is; in addition, by comparative example 4 and example 6, the scCO2The auxiliary melt blending may be adapted to facilitate dispersion of the different thermally conductive fillers.
Comparing the properties of the composites prepared in examples 1-9 and comparative examples 1-5 in summary, it can be seen that the scCO is a mixture of2The auxiliary melt blending extrusion technology obviously promotes the stripping, intercalation and dispersion of the heat-conducting filler, and enhances the interaction between polymer molecular chains and the heat-conducting filler, thereby improving the heat conductivity of the composite material.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. A preparation method of a supercritical carbon dioxide assisted heat-conducting composite material is characterized by comprising the following steps:
(1) mixing a thermoplastic high polymer material, a compatibilizer and a heat-conducting filler to obtain a polymer melt;
(2) setting the pressure of the supercritical carbon dioxide to exceed the pressure of the polymer melt, and injecting the supercritical carbon dioxide into the polymer melt and infiltrating into the heat-conducting filler;
(3) the supercritical carbon dioxide is vaporized to form carbon dioxide gas through pressure relief, and the heat-conducting filler is uniformly dispersed in the polymer melt through the explosion effect of the carbon dioxide gas, so that the heat-conducting composite material can be obtained.
2. The method according to claim 1, wherein the steps (2) and (3) are repeated several times, preferably 3 times or more, for one combination.
3. The preparation method according to claim 1 or 2, wherein the thermoplastic polymer material is polyolefin or polyester, the compatibilizer is maleic anhydride graft copolymer or glycidyl methacrylate graft copolymer, and the thermally conductive filler is expanded graphite or boron nitride.
4. The preparation method according to claim 3, wherein the mass ratio of the total injection amount of the supercritical carbon dioxide to the addition amount of the polymer melt is (2-40): 100; the mass ratio of the heat-conducting filler to the thermoplastic high polymer material is (5-40): 100.
5. The preparation method according to claim 1, wherein the mixing in the step (1) is realized by a supercritical carbon dioxide-assisted melt-blending extrusion device, the supercritical carbon dioxide-assisted melt-blending extrusion device comprises a twin-screw extruder, a supercritical carbon dioxide injection device and a vacuum exhaust pump, the twin-screw extruder is provided with a feeding section, an injection section and an exhaust section in sequence along the movement direction of the thermoplastic polymer material, the feeding section is provided with a feeding port, the injection section is connected with the supercritical carbon dioxide injection device through the supercritical carbon dioxide injection port, and the exhaust section is connected with the vacuum exhaust pump through the vacuum exhaust port.
6. The production method according to claim 5, wherein the injection section and the exhaust section are provided in plural in one combination repeatedly.
7. A method as claimed in claim 5, characterized in that the injection section is provided with a metering pump.
8. The method according to claim 5, wherein in the step (2), the pressure of the supercritical carbon dioxide is made to exceed the pressure of the polymer melt in the injection section by adjusting the feeding amount, the screw rotation speed and the extruder barrel temperature.
9. The preparation method according to claim 5, wherein the screw length-diameter ratio of the twin-screw extruder is (35-48) 1, the screw rotation speed of the extruder is 200-500r/min, and the barrel temperature is 150-300 ℃.
10. The heat-conducting composite material prepared by the preparation method of the supercritical carbon dioxide assisted heat-conducting composite material according to any one of claims 1 to 9.
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