Polyethylene composite material with enhanced thermal conductivity and preparation method and application thereof

Abstract

The invention discloses a polyethylene composite material with enhanced thermal conductivity and a preparation method and application thereof, and the preparation method comprises the following steps: adding boron nitride into a sodium hydroxide solution, heating to boiling, and then refluxing and stirring to obtain modified boron nitride; the preparation method comprises the following steps: mixing a coupling agent, distilled water and ethanol, hydrolyzing to obtain hydrolysate, mixing the hydrolysate with aluminum oxide, and carrying out surface modification treatment on the aluminum oxide to obtain modified aluminum oxide; mixing high-density polyethylene, a silane cross-linking agent, the modified boron nitride and the modified aluminum oxide through a double-roller open mill to obtain a mixed rubber sheet; and carrying out secondary vulcanization treatment on the mixed rubber sheet to obtain the polyethylene composite material with enhanced thermal conductivity. The aluminum oxide and the boron nitride are modified, and the modified aluminum oxide and the modified boron nitride are compounded into the polyethylene material under the action of the silane crosslinking agent to obtain the polyethylene composite material with insulativity and excellent thermal conductivity, and the polyethylene composite material can effectively reduce the working temperature of a cable when being applied to a submarine cable sheath material.

Description

Technical Field

[0001] The present invention relates to the field of composite material preparation, and particularly to a polyethylene composite material with enhanced thermal conductivity, its preparation method and application. Background Art

[0002] Polyethylene is one of the widely used cable materials, which has the advantages of corrosion resistance and good insulation, but has a low thermal conductivity. Cables are prone to heat generation during power transmission. Due to the increase in temperature, the resistance of the conductor increases, resulting in an increase in power transmission loss. Therefore, it is of great significance to improve the thermal conductivity of the cable insulation layer or sheath layer.

[0003] In the prior art, for polymers applied to cable insulation layers and sheath layers, the method to improve their thermal conductivity is to fill thermal conductive fillers. The thermally conductive polyethylene composite material is not only simple to manufacture and low in cost, but also can give full play to the advantageous properties of polyethylene to a certain extent. Since polyethylene materials are widely used in insulation fields such as electronic packaging, aerospace, and electrical equipment, there is a high demand for the insulation performance of the fillers. Therefore, it is of great significance to research and develop a polyethylene composite material with both insulation performance and high thermal conductivity. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the present invention provides a polyethylene composite material with enhanced thermal conductivity, its preparation method and application. Alumina and boron nitride are modified, and the modified alumina and modified boron nitride are compounded into the polyethylene material under the action of a silane cross-linking agent to obtain a polyethylene composite material with both insulation and excellent thermal conductivity. When applied to the sheath material of submarine cables, it can effectively conduct the heat generated during the operation of the cables, reduce heat accumulation, and thus lower the working temperature of the cables.

[0005] To solve the above technical problems, on the one hand, the present invention provides a preparation method for a polyethylene composite material with enhanced thermal conductivity, which includes the following steps:

[0006] S1. Add boron nitride to sodium hydroxide solution, heat to boiling and then reflux and stir to obtain modified boron nitride;

[0007] S2. Mix a coupling agent, distilled water and ethanol to hydrolyze to obtain a hydrolysis solution, mix the hydrolysis solution with alumina, and perform surface modification treatment on the alumina to obtain modified alumina;

[0008] S3. Mix high-density polyethylene, a silane cross-linking agent, modified boron nitride, and modified alumina through a two-roll mill to obtain a mixed rubber sheet;

[0009] S4. Perform secondary vulcanization treatment on the mixed rubber sheet to obtain the polyethylene composite material with enhanced thermal conductivity.

[0010] In the present invention, boron nitride is subjected to alkali treatment with sodium hydroxide to obtain alkali-treated hexagonal boron nitride (h-BN), and alumina is surface-modified with a hydrolyzed coupling agent to obtain modified alumina. The modified alumina is spherical, and the modified boron nitride is flaky. The modified boron nitride and modified alumina are blended with polyethylene to form a more effective heat conduction network. The alumina fills the gaps between the particles, and the flaky structure of boron nitride can form a heat conduction path over a larger range.

[0011] Since polyethylene is usually non-polar and the surface of alumina is polar, the interfacial compatibility between the two is poor, resulting in the inability to form a good bond between the filler and the matrix, and the small contact area leads to an increase in the interfacial thermal resistance. By surface-modifying the alumina, the compatibility between the two is improved. At the same time, the surface energy of unmodified alumina is relatively high, and it is easy to agglomerate and difficult to be uniformly dispersed in the polyethylene matrix. The surface modification improves the uniformity of dispersion.

[0012] The modified boron nitride and modified alumina are blended with polyethylene, and the intermolecular interaction is stronger. The crystal structure after blending is denser, improving the thermal conductivity and mechanical properties of the material.

[0013] Further, after S1, it also includes: washing the modified boron nitride with distilled water until neutral, and then performing vacuum drying treatment at a temperature of 85 - 95 °C.

[0014] Further, in S2, the hydrolysis temperature is 25 - 35 °C, and the time is 1 - 2 h.

[0015] Further, in S2, the temperature of the surface modification treatment is 90 - 100 °C.

[0016] Further, in S3, the mass ratio of high-density polyethylene, silane cross-linking agent, modified boron nitride, and modified alumina is 100:(2 - 5):(10 - 50):(10 - 50).

[0017] Further, in S3, in the two-roll mill, the distance between the two rolls is 0.8 - 2 mm, and the roll temperature is 160 - 165 °C.

[0018] Further, in S4, the secondary vulcanization treatment is specifically: placing the mixed rubber sheet in a mold, performing the first pre-vulcanization on a flat vulcanizer, and then placing it in an air aging box for the second vulcanization.

[0019] Further, the temperature of the first pre-vulcanization is 175 - 200 °C, the vulcanization time is 5 - 10 min, and the vulcanization pressure is 8 - 12 MPa;

[0020] And / or, the temperature of the second vulcanization is 210 - 220 °C, the vulcanization time is 100 - 120 min, and the vulcanization pressure is 8 - 12 MPa.

[0021] The second aspect of the present invention provides a polyethylene composite material with enhanced thermal conductivity obtained by the preparation method described in the first aspect.

[0022] The third aspect of the present invention provides the application of the polyethylene composite material described in the second aspect in submarine cable sheath materials.

[0023] Beneficial effects of the present invention:

[0024] In the present invention, boron nitride is alkali-treated with sodium hydroxide to obtain alkali-treated hexagonal boron nitride (h-BN), and alumina is surface-modified with a hydrolyzed coupling agent to obtain modified alumina. The flaky modified boron nitride and spherical modified alumina are blended with polyethylene. The compatibility between the filler and the matrix is good, the contact area is small, a more effective thermal conduction network is formed, the interfacial thermal resistance is reduced, and the thermal conductivity is improved.

[0025] In the present invention, by surface-modifying alumina, the surface energy is reduced, avoiding the problem that alumina is prone to agglomeration and difficult to be uniformly dispersed in the polyethylene matrix, and the uniformity of the filler dispersion in the matrix is improved through surface modification.

[0026] In the present invention, modified boron nitride and modified alumina are blended with polyethylene, the intermolecular interaction is stronger, and the crystal structure after blending is denser, improving the thermal conductivity and mechanical properties of the material. Specific embodiments

[0027] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

[0028] The embodiments of the present invention provide a preparation method for a polyethylene composite material with enhanced thermal conductivity, including the following steps:

[0029] S1. Add boron nitride to a sodium hydroxide solution, heat to boiling and then reflux and stir to obtain modified boron nitride;

[0030] S2. Mix a coupling agent, distilled water and ethanol for hydrolysis to obtain a hydrolysis solution, mix the hydrolysis solution with alumina, and perform surface modification treatment on the alumina to obtain modified alumina;

[0031] S3. Knead high-density polyethylene, a silane cross-linking agent, modified boron nitride, and modified alumina through a two-roll mill to obtain a kneaded film;

[0032] S4. Perform secondary vulcanization treatment on the kneaded film to obtain the polyethylene composite material with enhanced thermal conductivity.

[0033] In this embodiment, boron nitride is alkali-treated with sodium hydroxide to obtain alkali-treated hexagonal boron nitride (h-BN), and alumina is surface-modified with a hydrolyzed coupling agent to obtain modified alumina. The modified alumina is spherical, and the modified boron nitride is flaky. The modified boron nitride and modified alumina are blended with polyethylene to form a more effective heat conduction network. The alumina fills the gaps between the particles, and the flaky structure of boron nitride can form a heat conduction path over a larger range. Since polyethylene is usually non-polar and the surface of alumina is polar, the interfacial compatibility between the two is poor, resulting in poor bonding between the filler and the matrix, and the small contact area leads to an increase in interfacial thermal resistance. By surface-modifying alumina, the compatibility between the two is improved. At the same time, the surface energy of unmodified alumina is relatively high, making it prone to agglomeration and difficult to disperse uniformly in the polyethylene matrix. Surface modification improves the uniformity of dispersion. The modified boron nitride and modified alumina are blended with polyethylene, with stronger intermolecular interactions, and the crystal structure after blending is denser, improving the thermal conductivity and mechanical properties of the material.

[0034] As a preferred embodiment, after S1, it further includes: washing the modified boron nitride with distilled water until neutral, and then performing vacuum drying treatment at a temperature of 85 - 95°C.

[0035] As a preferred embodiment, in S2, the hydrolysis temperature is 25 - 35°C, the time is 1 - 2 h, and the surface modification treatment temperature is 90 - 100°C.

[0036] As a preferred embodiment, in S3, the mass ratio of high-density polyethylene, silane cross-linking agent, modified boron nitride, and modified alumina is 100:(2 - 5):(10 - 50):(10 - 50); in the two-roll mill, the distance between the two rolls is 0.8 - 2 mm, and the roll temperature is 160 - 165°C.

[0037] As a preferred embodiment, in S4, the secondary vulcanization treatment is specifically: placing the kneaded rubber sheet in a mold, performing the first pre-vulcanization on a flat vulcanizer at a temperature of 175 - 200°C, a vulcanization time of 5 - 10 min, and a vulcanization pressure of 8 - 12 MPa, and then placing it in an air aging oven for the second vulcanization at a temperature of 210 - 220°C, a vulcanization time of 100 - 120 min, and a vulcanization pressure of 8 - 12 MPa.

[0038] Another embodiment provides a polyethylene composite material with enhanced thermal conductivity prepared by the preparation method described in the above embodiment.

[0039] Another embodiment provides the application of the polyethylene composite material described in the above embodiment in submarine cable sheath materials.

[0040] Example 1

[0041] This embodiment provides a method for preparing a polyethylene composite material with enhanced thermal conductivity, which includes the following steps:

[0042] (1) Place boron nitride in a three-necked flask, then add sodium hydroxide solution to the three-necked flask. Heat the mixture to boiling and reflux and stir for 1 h to obtain alkali-treated h-BN powder. Then wash the alkali-treated h-BN powder with distilled water until neutral and place it in a vacuum drying oven at 90 °C for drying for later use;

[0043] (2) Pour distilled water, silane coupling agent and absolute ethanol into a three-necked flask respectively, hydrolyze them in a water bath at 30 °C for 1 h, add the hydrolyzate to a high-speed mixer containing alumina, and perform surface modification on alumina at 100 °C to obtain modified alumina;

[0044] (3) By weight, add high-density polyethylene (50 parts), silane cross-linking agent KH550 (1 part), modified boron nitride (10 parts), and modified alumina (15 parts) to a two-roll mill for the first mixing. The roll temperature is 165 °C, the roll gap is 1.2 mm, and mix for 3 min;

[0045] (4) Add high-density polyethylene (50 parts), silane cross-linking agent KH550 (0.5 part), modified boron nitride (10 parts), and modified alumina (15 parts) for the second mixing. The roll temperature is 165 °C, the roll gap is 1.2 mm, and mix for 3 min to obtain a mixed rubber;

[0046] (5) Place the mixed rubber on a two-roll mill with a roll temperature of 160 °C and plasticize it until it completely wraps around the roll, take off the sheet to make a mixed rubber, and let it stand for 24 h;

[0047] (6) Remill the standing mixed rubber on a two-roll mill until the mixed rubber wraps around the roll, then add silane cross-linking agent KH550 (1 part), and adjust the roll gap to make a mixed rubber sheet with a thickness of 2 mm;

[0048] (7) Place the mixed rubber sheet into a mold and perform primary pre-vulcanization on a flat vulcanizer. The vulcanization temperature is 200 °C, the vulcanization time is 5 min, and the vulcanization pressure is 10 MPa;

[0049] (8) Place it in a hot air aging oven for secondary vulcanization. The vulcanization temperature is 220 °C, the vulcanization time is 120 min, and the vulcanization pressure is 10 MPa. After cooling, obtain the finished polyethylene composite material.

[0050] Example 2

[0051] This embodiment provides a method for preparing a polyethylene composite material with enhanced thermal conductivity. The difference from Example 1 is that:

[0052] Step (3): By weight, add high-density polyethylene (50 parts), silane cross-linking agent KH550 (1 part), modified boron nitride (5 parts), and modified alumina (5 parts) to a two-roll mill for the first mixing. The roll temperature is 165°C, the roll gap is 1.2 mm, and the mixing is carried out for 3 min;

[0053] Step (4): Add high-density polyethylene (50 parts), silane cross-linking agent KH550 (0.5 part), modified boron nitride (5 parts), and modified alumina (5 parts) for the second mixing. The roll temperature is 165°C, the roll gap is 1.2 mm, and the mixing is carried out for 3 min to obtain a mixed rubber;

[0054] Keep other steps and parameters unchanged to obtain the finished polyethylene composite.

[0055] Example 3

[0056] This example provides a method for preparing a polyethylene composite with enhanced thermal conductivity. The difference from Example 1 is as follows:

[0057] Step (3): By weight, add high-density polyethylene (50 parts), silane cross-linking agent KH550 (1 part), modified boron nitride (15 parts), and modified alumina (15 parts) to a two-roll mill for the first mixing. The roll temperature is 165°C, the roll gap is 1.2 mm, and the mixing is carried out for 3 min;

[0058] Step (4): Add high-density polyethylene (50 parts), silane cross-linking agent KH550 (0.5 part), modified boron nitride (15 parts), and modified alumina (15 parts) for the second mixing. The roll temperature is 165°C, the roll gap is 1.2 mm, and the mixing is carried out for 3 min to obtain a mixed rubber;

[0059] Keep other steps and parameters unchanged to obtain the finished polyethylene composite.

[0060] Example 4

[0061] This example provides a method for preparing a polyethylene composite with enhanced thermal conductivity. The difference from Example 1 is as follows:

[0062] Step (3): By weight, add high-density polyethylene (50 parts), silane cross-linking agent KH550 (1 part), modified boron nitride (25 parts), and modified alumina (25 parts) to a two-roll mill for the first mixing. The roll temperature is 165°C, the roll gap is 1.2 mm, and the mixing is carried out for 3 min;

[0063] Step (4): Add high-density polyethylene (50 parts), silane cross-linking agent KH550 (0.5 part), modified boron nitride (25 parts), and modified alumina (25 parts) for the second mixing. The roll temperature is 165°C, the roll gap is 1.2 mm, and the mixing is carried out for 3 min to obtain a mixed rubber;

[0064] Keep other steps and parameters unchanged to obtain the finished polyethylene composite material.

[0065] Comparative Example 1

[0066] This comparative example provides a method for preparing a polyethylene composite material, which is different from Example 3 in that: no silane crosslinking agent is added in steps (3), (4), and (6), and other steps and parameters remain unchanged to obtain the finished polyethylene composite material.

[0067] Comparative Example 2

[0068] This comparative example provides a method for preparing a polyethylene composite material, which is different from Example 3 in that: no modified boron nitride and modified alumina are added in steps (3) and (4), and other steps and parameters remain unchanged to obtain the finished polyethylene composite material.

[0069] The thermal conductivity and hardness of the polyethylene composite materials obtained in Examples 1-4 and Comparative Examples 1-2 were tested, and the results are shown in Table 1.

[0070] Table 1

[0071] Group Thermal Conductivity (W / (m·K)) Hardness (MPa) Example 1 1.427 146 Example 2 1.053 109 Example 3 2.559 153 Example 4 1.241 124 Comparative Example 1 0.974 74 Comparative Example 2 0.463 88

[0072] As can be seen from Table 1, compared with Example 1, Example 2 reduced the amounts of modified boron nitride and modified alumina, and the thermal conductivity and hardness of the composite material decreased; compared with Example 1, Example 3 increased the amounts of modified boron nitride and modified alumina and maintained a 1:1 ratio, which increased the thermal conductivity and hardness of the composite material. When the addition ratios of the two fillers are the same, it is easier to achieve uniform dispersion and avoid the agglomeration phenomenon caused by excessive single filler. Uniform dispersion helps to form a more uniform thermal conduction network. The uniformly dispersed fillers can reduce the interfacial thermal resistance between the fillers and the matrix and improve the heat conduction efficiency; compared with Example 3, Example 4 increased the amounts of modified boron nitride and modified alumina while keeping the manufacturing process the same. It can be found from the test data that the thermal conductivity and hardness of the composite material decreased. Due to the excessive amount of thermal conductive fillers, it hindered the formation of a uniform thermal conduction network and reduced the thermal conductivity instead.

[0073] Compared with Example 3, Comparative Example 1 lacked a silane crosslinking agent, which reduced the intermolecular interaction between the fillers and the matrix, and the thermal conductivity and hardness of the composite material decreased; compared with Example 3, Comparative Example 1 lacked modified alumina and modified boron nitride, and the thermal conductivity and hardness of the material decreased significantly.

[0074] The present invention has been described in detail in connection with specific embodiments and exemplary examples. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications or improvements can be made to the technical solutions and their implementation manners of the present invention, and all of these fall within the scope of the present invention. The protection scope of the present invention shall be subject to the appended claims.

Claims

1. A method for preparing a polyethylene composite material with enhanced thermal conductivity, characterized in that: The steps include: S1, adding boron nitride to a sodium hydroxide solution, heating to boiling and then refluxing with stirring to obtain modified boron nitride; S2, hydrolyzing a coupling agent, distilled water and ethanol to obtain a hydrolyzate, mixing the hydrolyzate with alumina, and performing surface modification on the alumina to obtain modified alumina; S3, mixing high-density polyethylene, silane crosslinking agent, modified boron nitride and modified aluminum oxide through a double-roll mill to obtain a mixed film; S4, performing secondary vulcanization treatment on the mixed rubber sheet to obtain the polyethylene composite material with enhanced thermal conductivity.

2. The method for preparing a polyethylene composite material with enhanced thermal conductivity according to claim 1, characterized in that: After S1, the modified boron nitride is washed with distilled water until it becomes neutral, and then vacuum dried at a temperature of 85-95°C.

3. The method for preparing a polyethylene composite material with enhanced thermal conductivity according to claim 1, characterized in that: In S2, the hydrolysis temperature is 25-35°C and the time is 1-2h.

4. The method for preparing a polyethylene composite material with enhanced thermal conductivity according to claim 1, characterized in that: In S2, the temperature of the surface modification treatment is 90-100°C.

5. The method for preparing a polyethylene composite material with enhanced thermal conductivity according to claim 1, characterized in that: In S3, the mass ratio of the high-density polyethylene, the silane crosslinking agent, the modified boron nitride, and the modified alumina is 100:(2-5):(10-50):(10-50).

6. The method for preparing a polyethylene composite material with enhanced thermal conductivity according to claim 1, characterized in that: In S3, in the twin-roll mill, the distance between the twin rolls is 0.8-2 mm, and the roll temperature is 160-165°C.

7. The method for preparing a polyethylene composite material with enhanced thermal conductivity according to claim 1, characterized in that: In S4, the secondary vulcanization treatment specifically includes: placing the mixed rubber sheet in a mold, performing a first pre-vulcanization on a flat vulcanizer, and then placing it in an air aging box for a second vulcanization.

8. The method for preparing a polyethylene composite material with enhanced thermal conductivity according to claim 7, characterized in that: The first pre-vulcanization temperature is 175-200°C, the vulcanization time is 5-10min, and the vulcanization pressure is 8-12MPa; And / or, the temperature of the second vulcanization is 210-220° C., the vulcanization time is 100-120 min, and the vulcanization pressure is 8-12 MPa.

9. A polyethylene composite material with enhanced thermal conductivity prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the polyethylene composite material according to claim 9 in submarine cable sheath materials.