CN112876759A - Method for preparing high-heat-dissipation polymer material by using hyperbranched polyethylene as auxiliary agent through ball milling method - Google Patents
Method for preparing high-heat-dissipation polymer material by using hyperbranched polyethylene as auxiliary agent through ball milling method Download PDFInfo
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- C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
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Abstract
The invention discloses a method for preparing a heat-dissipating polymer material by using hyperbranched polyethylene as an auxiliary agent through a ball milling method, which comprises the following steps: (1) mixing a certain amount of natural graphite and hyperbranched polyethylene in a certain organic solvent, and removing the solvent after fully and uniformly mixing to form a first mixture; (2) mixing and stirring the first mixture and high-density polyethylene, then putting the mixture into a ball milling tank to form a second mixture, and carrying out ball milling treatment, wherein in the ball milling process, under the assistance of hyperbranched polyethylene, natural graphite is stripped into few-layer graphene and is adhered to the surface of the high-density polyethylene, so that a ball milling product is obtained; the high-density polyethylene is granular and porous on the surface; (3) and taking out the ball-milled product, and hot-pressing into a sheet to obtain the heat-dissipating polymer material. The method is simple, easy to operate, low in price, mild in preparation conditions, environment-friendly and capable of efficiently and continuously producing the high-heat-dissipation polymer material in a large scale.
Description
Technical Field
The application relates to the field of preparation of heat dissipation polymers, in particular to a method for preparing a high heat dissipation polymer material.
Background
The polymer material has the advantages of good corrosion resistance, low price, light weight, easy processing and forming and the like, can be widely applied to the fields of chemical industry, energy, electronic device heat dissipation, electronic information, electrical engineering, aerospace and the like, and shows wide application prospect.
The thermal conductivity and electrical conductivity of polymer materials are far from the same as those of metal materials. Therefore, the application of the polymer material in many aspects is limited to a certain extent. But the problem is effectively solved by adding different high-thermal-conductivity fillers (such as graphite, nano graphite sheets, copper powder, carbon nano tubes and the like) to blend and modify the high polymer material. Since the formation of the heat-conducting network and the magnitude of the interface thermal resistance are key factors influencing the heat-conducting performance of the filled polymer, the precise control of the types of the added fillers and the amount of the fillers becomes important in the process of researching the high-molecular materials. Since the discovery of graphene, graphene has been widely used in materials science due to its excellent thermal conductivity, electrical conductivity, and good mechanical properties. The addition of the graphene effectively improves the heat-conducting property, the electric conductivity and the dielectric property of the polymer. Graphene is used as a modified filler and added into a polymer for modification, and the method is an effective means for preparing the high-performance heat-conducting composite material.
Disclosure of Invention
The application aims to provide a method for preparing a high-heat-dissipation polymer material by using hyperbranched polyethylene as an auxiliary agent through a ball milling method, and the method has the advantages of simplicity, easiness in operation, low price, mild preparation conditions, environmental friendliness and capability of efficiently and continuously producing a large amount of high-polymer materials with good heat dissipation performance.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for preparing a heat-dissipating polymer material by using hyperbranched polyethylene as an auxiliary agent through a ball milling method comprises the following steps:
(1) mixing a certain amount of natural graphite and hyperbranched polyethylene (HBPE) in a certain organic solvent, and removing the solvent after fully and uniformly mixing to form a first mixture;
(2) mixing and stirring the first mixture and High Density Polyethylene (HDPE), then putting the mixture into a ball milling tank to form a second mixture, carrying out ball milling treatment, and stripping natural graphite into few-layer graphene with the aid of HBPE in the ball milling process and adhering the graphene to the surface of the high density polyethylene to obtain a ball milling product; the high-density polyethylene is granular and porous on the surface;
(3) taking out the ball-milled product, and hot-pressing into a sheet to obtain a heat-dissipating polymer material;
wherein, the total mass of the natural graphite, the hyperbranched polyethylene and the high-density polyethylene is 100%, the mass percentage of the high-density polyethylene is 1-90%, and the mass ratio of the natural graphite to the hyperbranched polyethylene is 1-20: 1.
the invention is characterized in that the natural graphite and HDPE are used as main bodies, and under the action of ball milling and the auxiliary stripping of hyperbranched polyethylene, the few-layer graphene is generated. Graphene adheres to the surface of HDPE and is embedded into pores on the surface of HDPE, and the graphene modifies the heat dissipation performance of HDPE with good heat conduction performance. After hot press forming, the graphene forms a three-dimensional heat conduction network in the HDPE base, and rapid conduction can be realized through network heat built between the graphene.
In the above technical solution, the hyperbranched polyethylene (HBPE) has two functions, the first: due to the specific dendritic structure of the HBPE surface, when the HBPE is in contact with graphite, CH-pi and pi-pi effects can be generated, and graphene can be stripped under the action of external force; secondly, the method comprises the following steps: the compatibility of HBPE and HDPE is very good, when the HBPE is stripped from graphene and is adhered to the surface of the graphene under the action of CH-pi and pi-pi, the force is so strong that the HBPE cannot be separated from the graphene under the action of external force. At this time, the graphene adhered with the HBPE is adhered to the surface of the HDPE along with the HBPE to form a wrapping layer similar to a core-shell structure.
In the above technical solution, HDPE has two functions as a substrate, one of which is: the friction force borne by the graphite can be increased, so that the yield of the graphene is higher; the second step is as follows: because HBPE can be well dissolved with HDPE, the effect of capturing graphene can be achieved, and therefore the positive effect on the product recovery rate is achieved. The heat dissipation of HDPE embedded in HDPE with more graphene adhered will be significantly improved.
In the present invention, the heat dissipation performance of the final polymer material is also greatly affected by the state of the high density polyethylene. Because the HDPE of selection is porous graininess, and its surface has a lot of pores, and these pores can fully contact with natural graphite, increase the shearing force and the extrusion force that natural graphite received, and the graphite alkene that produces can get into in the gap on HDPE surface and the adhesion on the HDPE surface under the effect of ball-milling power for graphite alkene productivity is higher, and graphite alkene productivity height can form more perfect three-dimensional heat conduction network in the HDPE base, and the heat conduction effect is better. Preferably, the particle size of the high density polyethylene is 30-200 mesh and the surface pore size is 10-200nm, and most preferably, the particle size of the high density polyethylene is 80 mesh and the surface pore size is 50-100 nm.
According to the invention, due to the positive effects of the HBPE and the HDPE, the heat dissipation performance of the final ball-milled product can be influenced by the addition amount of the HBPE and the HDPE, and meanwhile, the heat dissipation performance of the final ball-milled product can be influenced by the difference of the addition amount of the natural graphite serving as a raw material for producing graphene. Preferably, the mass percentage of the high-density polyethylene is 10-90%, and the mass ratio of the natural graphite to the hyperbranched polyethylene is 5-20: 1; more preferably, the mass percentage of the high-density polyethylene is 40-80%, and the mass ratio of the natural graphite to the hyperbranched polyethylene is 5-15: 1; most preferably, the mass percentage of the high-density polyethylene is 64.9%, and the mass ratio of the natural graphite to the hyperbranched polyethylene is 12: 1. the ball-milled product obtained in the method has good heat dissipation performance.
In step (1) of the present invention, the purpose of mixing and sufficiently stirring a certain amount of natural graphite and hyperbranched polyethylene (HBPE) in a certain amount of an organic solvent is to allow the HBPE to sufficiently and uniformly adhere to the surface of the natural graphite (first mixture). The organic solvent is preferably an organic solvent with good solubility for the HBPE, the organic solvent comprises a plurality of organic solvents such as chloroform, tetrahydrofuran, dichloromethane, petroleum ether and diethyl ether, the particularly preferred organic solvent is at least one of chloroform, dichloromethane and tetrahydrofuran, the HBPE has the best solubility in the organic solvents, so that the branched chain of the HBPE can be completely unfolded, the HBPE can be in contact with natural graphite and better adhered to the surface of the natural graphite, more graphene can be obtained and adhered and embedded into the surface of the HDPE and gaps on the surface of the HDPE, and the heat dissipation polymer material with better heat dissipation performance can be obtained.
Preferably, the step (1) may be performed by dissolving the hyperbranched polyethylene in the organic solvent and then mixing the hyperbranched polyethylene solution with the natural graphite.
Preferably, in the step (1), the natural graphite and the HBPE are uniformly mixed in the organic solvent by stirring, the stirring time is 0.1-12 h, and the stirring speed is 50-500 rad/min. In the embodiment, the stirring can enable the HBPE to have more chances to contact with the natural graphite, the HBPE can have CH-pi action or pi-pi action after contacting with the natural graphite, more HBPE is adhered to the surface of the natural graphite, more graphene is generated, more graphene is adhered to and embedded into the surface of the HDPE and gaps on the surface of the HDPE, and therefore the heat dissipation polymer material with better heat dissipation performance is obtained.
Preferably, in the step (1), the solvent is removed by one or a combination of the following ways: rotary steaming, (cold air or hot air) blowing, and vacuum drying.
In the step (2), in the ball milling process, the ball milling balls are divided into three types, namely large, medium and small, and are added into the second mixture according to a certain proportion, the different proportions of the three balls can also affect the heat dissipation performance of the final polymer, and the preferable proportions of the large, medium and small are as follows: 1-10: 5-20: 15-40.
In the step (2), the heat dissipation performance of the final polymer is also greatly influenced by different ball milling treatment time, and the preferred ball milling treatment time is 4-96 hours, and more preferably 24-60 hours.
In the step (3), the conditions for hot pressing into the tablet are as follows: the hot pressing temperature is 180-210 ℃, the hot pressing pressure is 13-20MPa, the hot pressing process comprises preheating for 3-8 min, air bleeding for 3-6 times, pressing for 5-15 min, and cooling for 2-6 min. If the temperature is too low during hot pressing to form the sheet, the polymer cannot completely reach a molten state, and graphene on the surface and in gaps cannot form a three-dimensional heat-conducting network. Meanwhile, if the temperature is too high, the polymer begins to decompose, and the temperature is too high, which may cause the aggregation of graphene, so that the heat dissipation performance of the polymer material is reduced.
Compared with the prior art, the invention has the beneficial effects that: the method is simple, easy to operate, low in price, mild in preparation conditions, environment-friendly and capable of efficiently and continuously producing the high-heat-dissipation polymer material in a large scale. The graphene prepared by the ball milling method has the characteristics of few lamella and few defects, and the prepared heat dissipation polymer has good heat dissipation performance.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments of the present application will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and that those skilled in the art can also obtain other related drawings based on the drawings without inventive efforts.
FIG. 1: HBPE assists stripping graphene schematic diagram.
FIG. 2: the technical process of the embodiment of preparing the high heat dissipation polymer material by using the hyperbranched polyethylene as the auxiliary agent through the ball milling method.
FIG. 3: a heat conduction schematic diagram of a high heat dissipation polymer material is prepared by using hyperbranched polyethylene as an auxiliary agent through a ball milling method.
FIG. 4: scanning electron micrographs of HDPE used in example 1 at different magnifications.
Fig. 5 and 6: scanning electron micrographs at different magnifications of the ball-milled product prepared in example 1.
FIG. 7: transmission electron micrograph of graphene in the ball milled product prepared in example 1.
FIG. 8: electron diffraction pattern, sheet thickness, and lateral dimension pattern of 100 sheets of graphene in the ball-milled product prepared in example 1.
FIG. 9: HDPE samples used in example 1 and comparative examples 1-2 are shown.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
In the present invention, the high density polyethylene can be selected from various kinds, and for example, the high density polyethylene produced by macro-liter plasticization, which is in the form of granules and has a porous structure, can be selected, wherein the high density polyethylene comprises one or at least two of 40 meshes, 60 meshes, 80 meshes and 100 meshes.
In the present invention, natural graphite can be selected from a wide variety of materials. One or more of natural flaky graphite with the purity of 99.5 percent produced by Sigma Aldrich company in the United states, natural flaky graphite with the purity of 75 to 99.9 percent produced by Nanguo graphite mining plants in Lexi, Qingdao, and natural flaky graphite with the purity of 80 to 99.98 percent produced by Yichanbei graphite New Material company can be exemplarily selected.
In the invention, the hyperbranched polyethylene has various selected types, illustratively, the hyperbranched polyethylene can be obtained by catalyzing ethylene by adopting a Pd-diimine catalyst and adopting a one-step chain removal copolymerization mechanism, and the specific preparation process comprises the following steps:
under the protection of nitrogen, adding ethylene gas into a reaction vessel, ensuring that no oxygen or water exists in the reaction vessel, ensuring that the whole reaction vessel is filled with the ethylene gas, using an anhydrous solvent as a solvent, controlling the temperature to be 5-35 ℃, then adding a Pd-diimine catalyst dissolved in the anhydrous solvent, stirring and reacting for 6-72 hours under the conditions of the temperature of 5-35 ℃ and the ethylene pressure of 0.01-0.8 MPa, pouring the obtained product into acidified methanol after the polymerization is finished to terminate the polymerization, and separating and purifying the obtained polymerization reaction mixture to obtain the hyperbranched polyethylene.
Optionally, the anhydrous grade solvent comprises at least one selected from the group consisting of anhydrous dichloromethane, anhydrous chloroform, or anhydrous chlorobenzene; optionally, the dosage of the Pd-diimine catalyst and the total volume of the anhydrous solvent are 0.5-10.0 g/L; optionally, the Pd-diimine catalyst is an acetonitrile group Pd-diimine catalyst
Or hexatomic ring Pd-diimine catalyst containing carbomethoxy.
The above-mentioned separation and purification of the polymerization reaction mixture can be carried out according to the following steps:
(a) removing the solvent from the polymerization reaction mixture;
(b) dissolving the obtained product in tetrahydrofuran, adding acetone to precipitate the product, removing supernatant liquid to obtain a polymerization product again; repeating the process for 2-3 times;
(c) dissolving the obtained product in tetrahydrofuran again, adding a small amount of hydrochloric acid and hydrogen peroxide (for example, 5-10 drops of each), stirring for 1-5 hours to dissolve a small amount of Pd particles contained in the product, and then adding methanol or acetone to precipitate the product;
(d) and (3) carrying out vacuum drying on the obtained product at the temperature of 50-80 ℃ for 24-48 h to obtain the hyperbranched polyethylene.
The features and properties of the present application are described in further detail below with reference to examples.
Example 0: synthesis of HBPE
In this embodiment, the hyperbranched polyethylene may be obtained by catalyzing ethylene with a Pd-diimine catalyst and using a one-step "chain removal" copolymerization mechanism, and the specific preparation process includes the following steps:
under the protection of nitrogen, adding ethylene gas into a reaction vessel, ensuring that no oxygen or water exists in the reaction vessel, ensuring that the whole reaction vessel is filled with the ethylene gas, using an anhydrous solvent as a solvent, controlling the temperature to be 5-35 ℃, then adding a Pd-diimine catalyst dissolved in the anhydrous solvent, stirring and reacting for 6-72 hours under the conditions of the temperature of 5-35 ℃ and the ethylene pressure of 0.01-0.8 MPa, pouring the obtained product into acidified methanol after the polymerization is finished to terminate the polymerization, and separating and purifying the obtained polymerization reaction mixture to obtain the hyperbranched polyethylene.
Optionally, the anhydrous grade solvent comprises at least one selected from the group consisting of anhydrous dichloromethane, anhydrous chloroform, or anhydrous chlorobenzene; optionally, the dosage of the Pd-diimine catalyst and the total volume of the anhydrous solvent are 0.5-10.0 g/L; optionally, the Pd-diimine catalyst is an acetonitrile Pd-diimine catalyst or a hexatomic ring Pd-diimine catalyst containing a carbomethoxy group.
The above-mentioned separation and purification of the polymerization reaction mixture can be carried out according to the following steps:
(a) removing the solvent from the polymerization reaction mixture;
(b) dissolving the obtained product in tetrahydrofuran, adding acetone to precipitate the product, removing supernatant liquid to obtain a polymerization product again; repeating the process for 2-3 times;
(c) dissolving the obtained product in tetrahydrofuran again, adding a small amount of hydrochloric acid and hydrogen peroxide (for example, 5-10 drops of each), stirring for 1-5 hours to dissolve a small amount of Pd particles contained in the product, and then adding methanol or acetone to precipitate the product;
(d) and (3) carrying out vacuum drying on the obtained product at the temperature of 50-80 ℃ for 24-48 h to obtain the hyperbranched polyethylene.
In this embodiment, different types and different addition amounts of the high-density polyethylene, and different addition amounts of the hyperbranched polyethylene and the natural graphite all affect the heat dissipation performance of the final polymer.
The features and properties of the present application are described in further detail below with reference to examples.
Example 1, comparative example 1 and comparative example 2
1. Preparation of samples
(1) Embodiment 1 provides a method for stripping graphene by using hyperbranched polyethylene as an auxiliary agent, which comprises the following steps:
the first step is as follows: 5g of natural graphite (manufacturer: Sigma Aldrich, USA, specification of 99.5%, other examples and comparative examples are not specifically described, and the natural graphite is also used) is weighed at normal temperature.
The second step is that: 0.416g of hyperbranched polyethylene (1: 12 by mass ratio to graphite) was weighed out and dissolved in 15ml of chloroform.
The third step: the HBPE solution and natural graphite were mixed and placed in a beaker, and 35ml chloroform was added
The fourth step: and stirring the mixed solution of the natural graphite and the HBPE at the stirring speed of 300rad/min for 30 min.
The fifth step: the solvent in the mixed solution was removed using a blower, and after the solvent was volatilized, the remaining solid was vacuum-dried in a vacuum oven for 8 hours to completely remove the organic solvent chloroform.
And a sixth step: the dried mixture was transferred to a ball mill jar and 10g of HDPE (manufactured by Dow DGDB-3485, U.S.A., having a particle size of 80 mesh and a morphology with surface porosity of 50-100nm, and other examples and comparisons such as those not specifically mentioned were also used) was added.
The seventh step: and (3) adding three large, medium and small ball milling beads into the ball milling tank, wherein the ratio of the large, medium and small ball milling beads is 4:7: 20.
Eighth step: ball milling is carried out at the speed of 400rad/min, and the ball milling time is 48 h.
The ninth step: taking out the ball-milled product for hot pressing treatment. Hot pressing at 200 deg.C under 15Mp for 5min, degassing for 5 times each time for one second, pressing for 8min, cooling at 50-60 deg.C, and taking out hot pressed tablet with thickness of 1mm and diameter of 12.7 mm.
(2) Comparative example 1 provides a method for preparing a high heat dissipation polymer material by using a ball milling method with hyperbranched polyethylene as an auxiliary agent, the preparation method is substantially the same as that of example 1, and the details are not repeated herein, except that:
the HDPE used in this example was manufactured in the form of the rutabaga petrochemical, model DMDA-8008H, and the HDPE was in the form of powder with no pores on the surface, thereby obtaining a ball-milled product.
(3) Comparative example 2 provides a method for preparing a high heat dissipation polymer material by using a ball milling method with hyperbranched polyethylene as an auxiliary agent, the preparation method is substantially the same as that of example 1, and the details are not repeated herein, except that:
the HDPE used in this example was in pellet form, and the manufacturer was china, model number DMDA-8008, the pellet granulation method was extrusion granulation, and the pellets were uniform in particle size, consistent in color, and free of voids on the surface, thereby obtaining a ball-milled product.
2. Characterization and testing
Testing the heat dissipation performance of the ball-milled polymer
(1) Before testing, in order to make experimental data more convincing, the ball-milled products of example 1, comparative example 1 and comparative example 2 need to be hot-pressed into a sheet and tested for density and thermal diffusivity, according to a calculation formula of thermal conductivity, wherein a is the thermal diffusivity, ρ is the density of the material, and c is the specific heat capacity of the material, the thermal conductivity of the material can be calculated according to the three parameters, and then the heat dissipation of the material is verified. The method can accurately calculate the thermal conductivity of the material.
(2) SEM analysis
SEM analysis of 20KV VEGA3-TESCAN type SEM produced by Jack electron
Sample preparation, namely taking about 1mg of sample powder to disperse on conductive gel, and blowing off redundant powder by using an ear washing ball.
(3) Heat conductivity coefficient tester
The thermal conductivity tester is manufactured by TA of America
The sample is circular, the diameter is 12.7mm, and the maximum thickness is 10 mm.
(4) Graphene structural performance testing
In order to test the structural properties of graphene in the ball-milled product, the ball-milled product obtained in the eighth step of example 1 was added to 50mL of chloroform to be sufficiently dissolved and stirred for 30min, and subjected to ultrasonic treatment at a power of 80Hz for 1 h. Taking out the ultrasonic product, centrifuging for 45min at 4000rad/min, taking out the HDPE floating on the upper layer by using a medicine spoon, and taking 70% of the supernatant. The supernatant was placed on medical gauze, which was wetted with chloroform in advance and had a thickness of 9 layers, to filter out excess HDPE particles, thereby obtaining a graphene solution.
(ii) high resolution TEM analysis
The high-resolution TEM analysis was carried out by using a 300kV JEM-100CXII type high-resolution transmission electron microscope manufactured by Japan Electron.
Preparing a sample: taking 15ml of centrifuged supernatant, dropping a proper amount of suspension on the surface of a copper mesh, and testing after the solvent is evaporated to dryness, wherein the result is shown in fig. 7 and 8, and the graphene has the characteristics of less defects and less sheets.
3. Comparison and analysis of test results
The difference between example 1, comparative example 1 and comparative example 2 is the kind of HDPE used, and it is found through testing that the thermal conductivity of comparative example 1 and comparative example 2 is not as high as that of example 1. The reason for this is that in example 1, the surface of HDPE is porous during the ball milling process, which results in that the extrusion force and the shearing force received by graphite are larger, and more few-layer graphene is produced, thereby realizing the production of a high-heat-dissipation polymer material. The surfaces of comparative examples 1 and 2 are smoother than those of examples, so that the graphite cannot be subjected to enough extrusion force and shearing force to exfoliate the graphene and capture the exfoliated graphene, and more graphite is still bulk graphite after ball milling, and the sheets are thicker and even have graphite which is not exfoliated, so that the heat conductivity of comparative examples 1 and 2 is lower than that of example 1. Table 1 shows the thermal conductivity of the materials under different processes.
TABLE 1
Example 1, comparative example 3
1. Preparation of samples
Comparative example 3 provides a method for preparing a high heat dissipation polymer material by using a ball milling method with hyperbranched polyethylene as an auxiliary agent, the preparation method is substantially the same as that of example 1, and the details are not repeated herein, except that:
in comparative example 3, no HDPE was added during the ball milling, and the ball milled product obtained in the eighth step was mixed with 10g of HDPE and stirred uniformly, followed by hot press molding under the conditions of the ninth step, thereby obtaining a high heat dissipation polymer material.
2. Characterization and testing
Testing the heat dissipation performance of the ball-milled polymer
Same as example 1, comparative examples 1 and 2
3. Comparison and analysis of test results
The difference between example 1 and comparative example 3 is whether or not HDPE was added, and the thermal conductivity of example 1 was found to be significantly higher than that of comparative example 3 by measuring the respective thermal conductivities. The reasons for this are as follows: in comparative example 3, the extrusion force and the shearing force received by the natural graphite during the ball milling process without adding HDPE are not as large as 1, so that the amount of generated graphene is far less than that of example 1; the second step is as follows: the graphene in comparative example 3 is not adhered or embedded on the surface of HDPE, so that the material of comparative example 3 is not uniform and it is difficult to form a three-dimensional network after hot pressing. The specific data are shown in Table 2.
TABLE 2
Example 1, comparative example 4 and comparative example 5
1. Preparation of samples
(1) Comparative examples 4 and 5 provide a method for preparing a high heat dissipation polymer material by using a hyperbranched polyethylene as an auxiliary agent through a ball milling method, the preparation method is substantially the same as that of example 1, and the description is omitted, except that:
the proportion of HDPE in example 1 is 64.9%, and a high heat dissipation polymer material is obtained.
The HDPE content in comparative example 4 is 90%, and a high heat dissipation polymer material is obtained.
The HDPE content in comparative example 5 was 10%, and a high heat-dissipating polymer material was obtained.
The feeding amount of the natural graphite and the HBPE is kept unchanged.
2. Characterization and testing
Testing the heat dissipation performance of the ball-milled polymer
Same as example 1, comparative examples 1 and 2
3. Comparison and analysis of test results
Example 1, comparative example 4, and comparative example 5 differ in the amount of HDPE added, and the highest thermal conductivity was found in example 5 when the thermal conductivity was measured by ball milling and hot pressing into sheets. The reason for this is that the amount of natural graphite in comparative example 4 is relatively small, and although there is enough HDPE to provide more shear force, the relatively small amount of graphite has less chance of each HDPE particle being able to contact with graphite, the contact chance is small, and even though graphene can be formed, it is difficult to form a three-dimensional heat conducting network during the reshaping process, and example 5 has the best heat conducting effect, but the yield of graphene is the lowest, and is not increased much compared with example 1, and the mechanical properties are poor enough to meet the actual requirements because the amount of added graphite is increased, so the product in example 1 is the best choice. The specific data are shown in Table 3.
TABLE 3
Example 1, comparative example 6 and comparative example 7
1. Preparation of samples
(1) Comparative examples 6 and 7 provide a method for preparing a high heat dissipation polymer material by using a hyperbranched polyethylene as an auxiliary agent through a ball milling method, the preparation method is substantially the same as that of example 1, and the description is omitted, except that:
the HBPE in the embodiment 1 is 1/12 with the quality of natural graphite, so that the high-heat-dissipation polymer material is obtained.
In comparative example 6, HBPE was 1/5 of natural graphite quality, and a high heat dissipating polymer material was obtained.
In comparative example 7, HBPE was 1/20 of natural graphite quality, and a high heat dissipating polymer material was obtained.
The feeding amount of the natural graphite and the HDPE is kept unchanged.
2. Characterization and testing
Testing the heat dissipation performance of the ball-milled polymer
Same as example 1, comparative examples 1 and 2
3. Comparison and analysis of test results
The difference between example 1, comparative example 6 and comparative example 7 is that the amount of HBPE added is different, and the material in example 1 has the highest thermal conductivity as tested. The reason is that when the amount of HBPE is small, the HBPE is not sufficiently adhered to the surface of graphite, and the acting force between graphene layers and layers is insufficient; when the amount of the polymer is large, the treated graphite is easy to agglomerate, a strong acting force is generated, the contact between the ball-milling beads and the graphite is not facilitated, the graphene with more lamellae is difficult to adhere or inlay on the surface of HDPE (high-density polyethylene), and a three-dimensional heat conduction network is difficult to form in the re-forming process, if the addition amount of HBPE in comparative example 6 is too high or the content of the polymer is increased, the heat conduction capability of the material is reduced, and meanwhile, the efficiency of preparing the graphene by using the HBPE with high content can be reduced. The product of example 1 has the highest thermal conductivity as a result. As shown in table 4.
TABLE 4
Example 1, comparative example 8 and comparative example 9
1. Preparation of samples
(1) Comparative examples 8 and 9 provide a method for stripping graphene with hyperbranched polyethylene as an auxiliary agent, the preparation method is substantially the same as that of example 1, and the details are not repeated here, except that:
the ball milling time in example 1 was 48 hours, and a high heat dissipation polymer material was obtained.
In comparative example 8, the ball milling time was 24 hours, and thus a high heat dissipation polymer material was obtained.
In comparative example 9, the ball milling time was 60 hours, and a high heat dissipation polymer material was obtained.
2. Characterization and testing
Testing the heat dissipation performance of the ball-milled polymer
Same as example 1, comparative examples 1 and 2
3. Comparison and analysis of test results
The difference between the example 1, the comparative example 8 and the comparative example 9 is that the ball milling time is different, the test shows that the material in the example 1 has the highest thermal conductivity, the preparation efficiency is obviously increased along with the increase of the ball milling time, but the stripping efficiency difference between 48h and 60h is not large, probably because the product is mainly concentrated on the surface of the ball milling beads and HDPE particles, the attached amount has a certain limit, and meanwhile, when the stripped multilayer thicker graphene falls to the bottom of a tank to be contacted with a large number of graphite sheets, agglomeration is easy to occur again due to the CH-pi action of HBPE on the graphene, and the agglomeration and stripping reach a certain balance after a certain time. When the ball milling time is increased from 24h to 48h, the increase of the graphene concentration is not obvious, and the increase of the ball milling time can reduce the transverse size of the graphene, so that the reasonable ball milling time is helpful for maintaining the transverse size of the graphene, and further improving the performance of the graphene in all aspects. The specific data are shown in Table 5.
TABLE 5
Example 1, comparative example 10, and comparative example 11
1. Preparation of samples
(1) Comparative examples 10 and 11 provide methods for stripping graphene with hyperbranched polyethylene as an auxiliary agent, and the preparation methods are substantially the same as those of example 1, and are not repeated herein, except that:
in example 1, hot pressing temperature is 200 ℃, hot pressing pressure is 15Mp, preheating time is 5min, air is discharged for 5 times and one second each time, full pressure is 8min, cooling is carried out for 50min to about 60 ℃, and hot pressed tablets are taken out, wherein the thickness of the hot pressed tablets is 1mm, and the diameter of the hot pressed tablets is 12.7 mm. Thereby obtaining the high heat dissipation polymer material.
In comparative example 10, hot pressing temperature was 130 ℃, hot pressing pressure was 15Mp, preheating time was 5min, 5 times of air release was performed for one second each, total pressure was 8min, and cooling was performed for 50min to about 60 ℃, and hot pressed tablets were taken out, the thickness of the hot pressed tablets was 1mm, and the diameter was 12.7 mm. Thereby obtaining the high heat dissipation polymer material.
In comparative example 11, hot pressing temperature was 250 deg.C, hot pressing pressure was 15Mp, preheating time was 5min, degassing was performed 5 times for one second each, total pressure was 8min, and cooling was performed for 50min to 60 deg.C or so, and hot-pressed tablets were taken out, the thickness of the hot-pressed tablets being 1mm, and the diameter thereof being 12.7 mm. Thereby obtaining the high heat dissipation polymer material.
2. Characterization and testing
Testing the heat dissipation performance of the ball-milled polymer
Same as example 1, comparative examples 1 and 2
3. Comparison and analysis of test results
The difference among the example 1, the comparative example 10 and the comparative example 11 is that the temperature of hot pressing is different, and the test shows that the thermal conductivity of the example 1 is the best. The reason for this is that in comparative example 10, the hot-pressing temperature is low, the polymer cannot reach a completely molten state, many polymer particles still remain inside the hot-pressing sheet, and the large particles affect the graphene to form a three-dimensional heat-conducting network, thereby affecting the heat-conducting performance of the material. In comparative example 11, the polymer reaches the viscous flow temperature, no large polymer blocks remain in the pressed sheet, but the temperature is too high, so that the stripped graphene is easy to agglomerate, and the thermal conductivity of the agglomerated graphene is much lower than that of the few-layer graphene, so that the temperature is too high and the thermal performance is not good.
TABLE 6
In summary, the method of the embodiment of the application is simple, easy to operate, low in price, mild in preparation conditions, environment-friendly and capable of efficiently and continuously producing the heat dissipation material in a large scale.
The above description is only an example of the present application and is not intended to limit the scope of the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Claims (10)
1. A method for preparing a heat-dissipating polymer material by using hyperbranched polyethylene as an auxiliary agent through a ball milling method comprises the following steps:
(1) mixing a certain amount of natural graphite and hyperbranched polyethylene in a certain organic solvent, and removing the solvent after fully and uniformly mixing to form a first mixture;
(2) mixing and stirring the first mixture and high-density polyethylene, then putting the mixture into a ball milling tank to form a second mixture, and carrying out ball milling treatment, wherein in the ball milling process, under the assistance of hyperbranched polyethylene, natural graphite is stripped into few-layer graphene and is adhered to the surface of the high-density polyethylene, so that a ball milling product is obtained; the high-density polyethylene is granular and porous on the surface;
(3) taking out the ball-milled product, and hot-pressing into a sheet to obtain a heat-dissipating polymer material;
wherein, the total mass of the natural graphite, the hyperbranched polyethylene and the high-density polyethylene is 100%, the mass percentage of the high-density polyethylene is 1-90%, and the mass ratio of the natural graphite to the hyperbranched polyethylene is 1-20: 1.
2. the method of claim 1, wherein: the particle diameter of the high-density polyethylene is 30-200 meshes, and the surface aperture is 10-200 nm.
3. The method of claim 1, wherein: the particle diameter of the high-density polyethylene is 80 meshes, and the surface aperture is 50-100 nm.
4. A method according to any one of claims 1 to 3, wherein: the mass percentage of the high-density polyethylene is 10-90%, and the mass ratio of the natural graphite to the hyperbranched polyethylene is 5-20: 1.
5. the method of claim 4, wherein: the mass percentage of the high-density polyethylene is 40-80%, and the mass ratio of the natural graphite to the hyperbranched polyethylene is 5-15: 1.
6. the method of claim 4, wherein: the mass percentage of the high-density polyethylene is 64.9%, and the mass ratio of the natural graphite to the hyperbranched polyethylene is 12: 1.
7. the method of claim 1, wherein: in the step (1), the organic solvent is an organic solvent having good solubility for HBPE, and the preferred organic solvent is at least one of chloroform, dichloromethane and tetrahydrofuran.
8. The method of claim 1, wherein: the specific operation of the step (1) is as follows: firstly, dissolving hyperbranched polyethylene in an organic solvent, and then uniformly mixing natural graphite and the hyperbranched polyethylene in the organic solvent by stirring, wherein the stirring time is 0.1-12 h, and the stirring speed is 50-500 rad/min.
9. The method of claim 1, wherein: in the step (2), in the ball milling process, the ball milling balls are divided into three types, namely large, medium and small, and the ratio of large, medium and small is as follows: 1-10: 5-20: 15-40; the ball milling treatment time is 4-96 h, and more preferably 24-60 h.
10. The method of claim 1, wherein: in the step (3), the conditions of hot pressing into the tablet are as follows: the hot pressing temperature is 180-210 ℃, the hot pressing pressure is 13-20MPa, the hot pressing process comprises preheating for 3-8 min, air bleeding for 3-6 times, pressing for 5-15 min, and cooling for 2-6 min.
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