Porous PTFE material with low heat conductivity coefficient and preparation method thereof

Abstract

The invention discloses a porous PTFE material with a low heat conductivity coefficient and a preparation method thereof. The preparation method comprises the following steps: mixing polytetrafluoroethylene, a cross-linking agent and polyphenyl ether, melting and granulating to obtain modified PTFE particles; the method comprises the following steps: mixing a pore-foaming agent with urea through a boiling granulation process to obtain modified pore-foaming agent particles; and uniformly mixing the modified PTFE particles and the modified pore-foaming agent particles, sintering and molding, and dissolving out the pore-foaming agent to obtain the porous PTFE material with the low heat conductivity coefficient. The heat conductivity coefficient of the porous PTFE material prepared by the method is less than 0.2 W / (K * m), the porosity is greater than 30%, and the compression strength is greater than 5 MPa.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer compounds, and in particular relates to a porous PTFE material with low thermal conductivity and a preparation method thereof. Background Art

[0002] Traditional thermal insulation materials are fiber felt or inorganic refractory materials, among which common materials are PVC, glass fiber or other inorganic materials. These materials have the disadvantages of insufficient temperature resistance or too high density and unsatisfactory thermal insulation effect.

[0003] Polytetrafluoroethylene is a chain polymer material with a thermal conductivity far lower than that of inorganic materials. It is also resistant to chemical corrosion, self-cleaning, and has a long-term use temperature of more than 260°C. It is particularly suitable for thermal insulation applications. The porous PTFE tubes currently on the market are mainly used in the filtration industry. After testing, their thermal conductivity is about 0.35W / (K*m) and their porosity is less than 20%, which cannot meet the thermal insulation requirements. Summary of the invention

[0004] The object of the present invention is to provide a porous PTFE material with low thermal conductivity and high porosity.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution of the present invention is: A porous PTFE material with low thermal conductivity, the preparation method of which comprises the following steps: (1) Mixing polytetrafluoroethylene, a cross-linking agent and polyphenylene ether and then melt-granulating to obtain modified PTFE particles; (2) mixing the porogen and urea through a boiling granulation process to obtain modified porogen particles; (3) The modified PTFE particles and the modified porogen particles are mixed and then sintered to obtain the porous PTFE material with low thermal conductivity after the porogen is dissolved out.

[0006] The present invention uses urea to perform surface treatment on the porogen so that the modified porogen particles can be evenly dispersed after being mixed with the modified PTFE particles; in addition, during the sintering process, not only the modified PTFE particles are partially melted to form a porous structure, but also the urea undergoes thermal polymerization, and the formed carbon nitride also has a porous structure, which effectively increases the porosity of the material. The purpose of using polyphenylene ether to modify PTFE is to enhance the high temperature resistance of the modified PTFE particles, on the one hand, to make the melting temperature of the modified PTFE compatible with the thermal polymerization temperature of urea, and on the other hand, to effectively reduce the thermal conductivity of the material, thus killing two birds with one stone.

[0007] The thermal conductivity of the porous PTFE material prepared by the method is less than 0.2W / (K*m), the porosity is greater than 30%, and the compression strength is greater than 5 MPa.

[0008] Preferably, in step (1) of the above preparation method, the cross-linking agent comprises di-tert-butyl peroxide.

[0009] Preferably, in step (1) of the above preparation method, the mass ratio of polytetrafluoroethylene, crosslinking agent and polyphenylene ether is 100:(2-5):(20-40).

[0010] Preferably, in step (1) of the above preparation method, the melting temperature is 330-360°C.

[0011] Preferably, in step (1) of the above preparation method, the particle size of the modified PTFE particles is between 30-50 μm; and the particle size of the modified porogen particles in step (2) is between 20-40 μm. Appropriate particle size is also very helpful in improving the porosity of the material.

[0012] Preferably, in step (2) of the above preparation method, the porogen comprises calcium phosphate or calcium carbonate.

[0013] Preferably, in step (3) of the above preparation method, the mass ratio of the modified PTFE particles to the modified porogen particles is 10:(4-6).

[0014] Preferably, in step (3) of the above preparation method, sintering is performed at 450-480° C. for 1.0-1.5 h.

[0015] Preferably, in step (3) of the above preparation method, dilute hydrochloric acid is used to dissolve the porogen.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention uses urea to treat the surface of the porogen so that the modified porogen particles can be evenly dispersed after being mixed with the modified PTFE particles; in addition, during the sintering process, not only the modified PTFE particles partially melt together to form a porous structure, but also the urea undergoes thermal polymerization, and the formed carbon nitride also has a porous structure, which effectively increases the porosity of the material. The purpose of using polyphenylene ether to modify PTFE is to enhance the high temperature resistance of the modified PTFE particles. On the one hand, the melting temperature of the modified PTFE is adapted to the thermal polymerization temperature of urea, and on the other hand, the thermal conductivity of the material can be effectively reduced, killing two birds with one stone.

[0017] (2) The thermal conductivity of the porous PTFE material prepared by the above method is less than 0.2W / (K*m), the porosity is greater than 30%, and the compressive strength is greater than 5 MPa. DETAILED DESCRIPTION

[0018] The technical scheme of the present invention is further described in detail with reference to the following embodiments.

[0019] Example 1 The present embodiment provides a porous PTFE material with low thermal conductivity, and the preparation method thereof comprises the following steps: (1) Mixing polytetrafluoroethylene, a cross-linking agent and polyphenylene ether and then melt-granulating to obtain modified PTFE particles; Specifically, polytetrafluoroethylene, a crosslinking agent and polyphenylene ether are uniformly mixed in a mass ratio of 100:2:20, and then melted at 330° C. and granulated in a granulator, and finally the granules are sieved to obtain modified PTFE particles with a particle size between 30 and 50 μm for use; (2) mixing the porogen and urea through a boiling granulation process to obtain modified porogen particles; Specifically, in the boiling granulator, urea is deposited on the surface of calcium phosphate (porogen) powder in a vaporized state. After the surface modification is completed, it can be screened and the modified porogen particles with a particle size between 20-40 μm are taken for use; (3) The modified PTFE particles and the modified porogen particles are mixed and then sintered to form a porous PTFE material with low thermal conductivity of this embodiment is obtained after the porogen is dissolved; Specifically, the modified PTFE particles and the modified porogen particles are mixed in a mass ratio of 10:4, put into a mold for pressing and sent into a sintering furnace, the temperature of the sintering furnace is raised from room temperature to 480°C and then sintered for 1.0 h; after cooling, the sintered product is taken out and immersed in dilute hydrochloric acid for 48 h, and then taken out, washed with clean water and dried; finally, the sintered product is reheated to 300°C and then placed in a shaping mold for cooling and shaping, thereby obtaining the porous PTFE material of this embodiment, specifically a porous PTFE insulation tube (model 200*170*300).

[0020] Example 2 The present embodiment provides a porous PTFE material with low thermal conductivity, and the preparation method thereof comprises the following steps: (1) Mixing polytetrafluoroethylene, a cross-linking agent and polyphenylene ether and then melt-granulating to obtain modified PTFE particles; Specifically, polytetrafluoroethylene, a crosslinking agent and polyphenylene ether are uniformly mixed in a mass ratio of 100:4:30, and then melted at 350° C. and granulated in a granulator, and finally the granules are sieved to obtain modified PTFE particles with a particle size between 30 and 50 μm for later use; (2) mixing the porogen and urea through a boiling granulation process to obtain modified porogen particles; Specifically, in the boiling granulator, urea is deposited on the surface of calcium phosphate (porogen) powder in a vaporized state. After the surface modification is completed, it can be screened and the modified porogen particles with a particle size between 20-40 μm are taken for use; (3) The modified PTFE particles and the modified porogen particles are mixed and then sintered to form a porous PTFE material with low thermal conductivity of this embodiment is obtained after the porogen is dissolved; Specifically, the modified PTFE particles and the modified porogen particles are mixed in a mass ratio of 10:5, put into a mold for pressing and sent into a sintering furnace, the temperature of the sintering furnace is raised from room temperature to 470°C and then sintered for 1.2 hours; after cooling, the sintered product is immersed in dilute hydrochloric acid for 48 hours, and then taken out, washed with clean water and dried; finally, the sintered product is reheated to 300°C and then placed in a shaping mold for cooling and shaping, thereby obtaining the porous PTFE material of this embodiment, specifically a porous PTFE insulation tube (model 200*170*300).

[0021] Example 3 The present embodiment provides a porous PTFE material with low thermal conductivity, and the preparation method thereof comprises the following steps: (1) Mixing polytetrafluoroethylene, a cross-linking agent and polyphenylene ether and then melt-granulating to obtain modified PTFE particles; Specifically, polytetrafluoroethylene, a crosslinking agent and polyphenylene ether are uniformly mixed in a mass ratio of 100:5:40, and then melted at 36° C. and granulated in a granulator, and finally the granules are sieved to obtain modified PTFE particles with a particle size between 30 and 50 μm for use; (2) mixing the porogen and urea through a boiling granulation process to obtain modified porogen particles; Specifically, in the boiling granulator, urea is deposited on the surface of calcium phosphate (porogen) powder in a vaporized state. After the surface modification is completed, it can be screened and the modified porogen particles with a particle size between 20-40 μm are taken for use; (3) The modified PTFE particles and the modified porogen particles are mixed and then sintered to form a porous PTFE material with low thermal conductivity of this embodiment is obtained after the porogen is dissolved; Specifically, the modified PTFE particles and the modified porogen particles are mixed in a mass ratio of 10:6, put into a mold for pressing and sent into a sintering furnace, the temperature of the sintering furnace is raised from room temperature to 450°C and then sintered for 1.5 hours; after cooling, the sintered product is immersed in dilute hydrochloric acid for 48 hours, and then taken out, washed with clean water and dried; finally, the sintered product is reheated to 300°C and then placed in a shaping mold for cooling and shaping, thereby obtaining the porous PTFE material of this embodiment, specifically a porous PTFE insulation tube (model 200*170*300).

[0022] Comparative Example 1 This comparative example is a porous PTFE material, and its preparation method is basically the same as that of Example 2, except that: the particle size of the modified PTFE particles in step (1) is 50-80 μm.

[0023] Comparative Example 2 This comparative example is a porous PTFE material, and its preparation method is basically the same as that of Example 2, except that: the particle size of the modified PTFE particles in step (1) is 20-30 μm.

[0024] The properties of the porous PTFE materials prepared in Examples 1-3 and Comparative Examples 1-2 were tested, and the results are shown in Table 1.

[0025] Table 1 It can be seen from Table 1 that the thermal conductivity of the porous PTFE materials prepared in the present invention is less than 0.2W / (K*m), the porosity is greater than 30%, and the compressive strength is greater than 5 MPa; this indicates that the porous PTFE material of the present invention has good thermal insulation performance and excellent high temperature resistance, can be used for a long time at about 400°C, and has good application prospects in the field of oil drilling.

Claims

1. A method for preparing a porous PTFE material with low thermal conductivity, characterized in that: The following steps are involved: (1) Mixing polytetrafluoroethylene, a cross-linking agent and polyphenylene ether and then melt-granulating to obtain modified PTFE particles; (2) mixing the porogen and urea through a boiling granulation process to obtain modified porogen particles; (3) The modified PTFE particles and the modified porogen particles are mixed and then sintered to obtain the porous PTFE material with low thermal conductivity after the porogen is dissolved out.

2. The preparation method according to claim 1, characterized in that In step (1), the cross-linking agent includes di-tert-butyl peroxide.

3. The preparation method according to claim 1, characterized in that: In step (1), the mass ratio of polytetrafluoroethylene, crosslinking agent and polyphenylene ether is 100:(2-5):(20-40); Melts at 330-360°C.

4. The preparation method according to claim 1, characterized in that: In step (1), the particle size of the modified PTFE particles is between 30-50 μm.

5. The preparation method according to claim 1, characterized in that: In step (2), the porogen includes calcium phosphate or calcium carbonate.

6. The preparation method according to claim 1, characterized in that: In step (3), the particle size of the modified porogen particles is between 20-40 μm.

7. The preparation method according to claim 1, characterized in that: In step (3), the mass ratio of modified PTFE particles to modified porogen particles is 10:(4-6).

8. The preparation method according to claim 1, characterized in that: In step (3), sintering is performed at 450-480°C for 1.0-1.5h.

9. The preparation method according to claim 1, characterized in that: In step (3), dilute hydrochloric acid is used to dissolve the porogen.

10. A porous PTFE material with low thermal conductivity, characterized in that: The method is prepared according to any one of claims 1 to 9.

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