Hydrotalcite sodium alginate carbon material and application thereof in modification of polytetrafluoroethylene granulation material

Abstract

The invention provides a hydrotalcite sodium alginate carbon material and application thereof in modification of a polytetrafluoroethylene granulation material. The hydrotalcite and the sodium alginate are compounded, the performance of the carbon material is optimized through the synergistic effect, porosity can be introduced through the layered structure of the hydrotalcite, the sodium alginate provides a sufficient carbon source, and finally the composite carbon material with the larger specific surface area and the better conductivity is obtained. And the mechanical property of the granulated material can be obviously improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of carbon material preparation, and relates to a hydrotalcite-sodium alginate carbon material and application thereof in modification of polytetrafluoroethylene granules. BACKGROUND

[0002] Granular polytetrafluoroethylene is a physical form of polytetrafluoroethylene (PTFE) and has the characteristics of small friction coefficient, wide temperature resistance range, strong corrosion resistance, high dielectric property and non-stickiness. In industrial applications, granular PTFE is processed into a shape through dry or wet granulation process. The wet granulation process uses an organic liquid and a surfactant to improve the apparent density and flowability of the granules. In order to improve the low mechanical strength and poor wear resistance of the granules, filling modification (such as adding bronze powder and carbon fiber), blending modification (such as compounding with polyether ether ketone) and surface treatment (plasma modification and laser treatment) are often used. In view of the above problems, the application develops a carbon material for modifying polytetrafluoroethylene granules.

[0003] Carbon material is a functional material system formed by taking carbon element as a matrix, and has both basic theoretical value and engineering practical significance in the field of forestry. Hydrotalcite and sodium alginate can both be used as raw materials to prepare carbon materials.

[0004] Hydrotalcite is a kind of layered inorganic compound composed of positively charged metal hydroxide layers (such as Mg-Al and Zn-Al layers) and interlayer anions (such as CO3 2- , NO3 - , or organic anions). By introducing organic anions (such as dodecyl sulfate and phthalate) into the interlayer or loading organic carbon sources through surface modification, the organic components will be converted into carbon skeleton during high-temperature carbonization (600-1000℃, inert atmosphere), and the inorganic metal layer can be used as a template to control the morphology (such as porous structure) of the carbon material. First, the hydrotalcite is "organically modified" (carbon source is introduced), and then carbonized and acid washed (to remove inorganic metal residues) to obtain pure carbon material. Sodium alginate is extracted from natural polysaccharides (brown algae) and has a molecular chain containing a large number of carboxyl and hydroxyl groups. It is a typical natural organic carbon source and contains a high proportion of carbon elements (about 40%-45%) without the need for additional introduction of organic carbon sources. It is easily soluble in water and can be formed into a solution (such as gel, fiber and microspheres). After carbonization, the macro / micro structure of the precursor can be retained.

[0005] After searching, no report has been found on the preparation of carbon material by compounding hydrotalcite and sodium alginate for modifying polytetrafluoroethylene granules. SUMMARY

[0006] In view of the above problems, the application provides a hydrotalcite sodium alginate carbon material and application thereof in modification of polytetrafluoroethylene granules.

[0007] The technical scheme of the application is as follows: a preparation method of a hydrotalcite sodium alginate carbon material, characterized by, (1) mixing hydrotalcite and sodium alginate uniformly and calcining in a tube furnace, wherein the calcining conditions are as follows: inert gas is introduced, the temperature is raised to 90-110 DEG C at a rate of 0.8-1.2 DEG C / min from room temperature, then the temperature is raised to 450-550 DEG C at a rate of 8-12 DEG C / min, and the temperature is kept for 20-40 min, and then the temperature is cooled to room temperature; (2) mixing the calcined sample and potassium hydroxide solid in deionized water at a mass ratio of 1:3.5-4.5, then drying and heating and activating in a tube furnace: the temperature is raised to 90-110 DEG C at a rate of 0.8-1.2 DEG C / min from room temperature under the protection of inert gas, then the temperature is raised to 750-850 DEG C at a rate of 8-12 DEG C / min, the temperature is kept for 0.5-1.5 h, and then the temperature is cooled to room temperature; after cleaning with hydrochloric acid solution, washing with deionized water until neutral and drying, the carbon material is obtained.

[0008] Further, the mass ratio of the hydrotalcite and the sodium alginate is 2-4:1.

[0009] Further, the drying is carried out at 100-110 DEG C in an oven for 10-15 h.

[0010] Further, the inert gas is N2.

[0011] The application also provides application of the above carbon material in modification of polytetrafluoroethylene granules.

[0012] The application also provides a method for modifying polytetrafluoroethylene granules by using the above carbon material, characterized by: air flow crushing of polytetrafluoroethylene fine powder, so that the particle size of the carbon material is close to that of the polytetrafluoroethylene; mixing the carbon material and the crushed polytetrafluoroethylene uniformly; adding an organic solvent to the mixed master batch, fully mixing by mechanical stirring, so that the polytetrafluoroethylene can wetly wrap the carbon material, drying the obtained wet granules to fully remove the solvent, and obtaining the polytetrafluoroethylene granules filled with the carbon material.

[0013] Further, the addition amount of the carbon material in the polytetrafluoroethylene is 0.1-25%, preferably 0.1-10%.

[0014] Further, the mixed organic solvent is: 15% anhydrous acetone + 85% anhydrous alcohol by mass ratio.

[0015] Further, by screening classification, large particles and powder in the particles are removed. According to market requirements, the finished product meeting the particle size process is taken, and this method can control the particle size of the granulated material finished product to be between 260 microns and 700 microns.

[0016] Technical effects of the present application: both hydrotalcite and sodium alginate can be used as raw materials to prepare carbon materials. Due to the composition and structural characteristics, they can play the roles of carbon source, template or structure regulator in the preparation process. The present application combines hydrotalcite and sodium alginate, optimizes the performance of carbon materials through synergistic effect, introduces porosity through the layered structure of hydrotalcite, and provides sufficient carbon source through sodium alginate. Ultimately, a composite carbon material with larger specific surface area and better conductivity is obtained, which further expands its application in the fields of catalysis, energy storage, etc. When used for modifying polytetrafluoroethylene granules, the mechanical properties of the granules can be significantly improved. DETAILED DESCRIPTION

[0017] The effects are illustrated below in combination with examples.

[0018] Preparation of Mg-Al-LDH: 128 g of Mg(NO3)2·H2O and 93.6 g of Al(NO3)3·9H2O were dissolved in distilled water to form a transparent salt solution, and 66 g of NaOH and 53.2 g of Na2CO3 were dissolved in distilled water to form a transparent alkali solution. The above two solutions were added dropwise into a 500 mL beaker containing distilled water heated at 60℃, and the dropping speed was controlled to maintain the pH of the system at about 9-10, and stirred for 10 h. After the reaction was completed, the white precipitate was taken out, washed with distilled water until neutral, and dried in an oven at 80℃. The precipitate was ground into powder and sieved through a 100 mesh sieve to obtain Mg-Al-LDH.

[0019] Example 1: 6 g of Mg-Al-LDH powder was mixed with 2 g of sodium alginate in a porcelain boat, and calcined in a tube furnace. The calcination conditions were as follows: N2 was introduced, the temperature was raised to 100℃ at a rate of 1℃ / min, then the temperature was raised to 500℃ at a rate of 10℃ / min, and the temperature was maintained for 30 min, and then the temperature was cooled to room temperature.

[0020] The calcined sample was taken out and weighed, then the calcined sample was mixed with potassium hydroxide solid in a mass ratio of 1:4 in 60 ml of deionized water, then dried in an oven at 105°C for 12h, after drying, it was heated and activated in a tube furnace, under nitrogen protection, from room temperature to 100°C at a rate of 1°C / min, then to 800°C at a rate of 10°C / min, and kept for 1h, then cooled to room temperature, finally the activated carbon material was washed with 200ml of 0.1M hydrochloric acid solution, then washed with deionized water until neutral and dried at 105°C for 24h, obtaining a carbon material with a specific surface area of 650g / m 2 , and a conductivity of 60S / m; (the specific surface area of the carbon material prepared by the same method from pure hydrotalcite is 200g / m 2 , and a conductivity of 0.1S / m; the specific surface area of the carbon material prepared by the same method from pure sodium alginate is 250g / m 2 , and a conductivity of 10S / m).

[0021] Example 2: 7g of Mg-Al-LDH powder was weighed and mixed with 3g of sodium alginate in a porcelain boat, and the rest was the same as in Example 1.

[0022] Example 3: The calcined sample was mixed with potassium hydroxide solid in a mass ratio of 1:4.2 in 60 ml of deionized water, and the rest was the same as in Example 1.

[0023] Test Example 1: Modification of PTFE granules The method of pretreating PTFE fine powder is air flow crushing, using an air flow crushing device, the PTFE is frozen in a refrigerator at -15°C for 12h, and the crushing speed is controlled at 20kg / hour. The experimental data show that after 2 crushing, the particle size can reach D 50 about 3 microns, and further crushing cannot significantly reduce the particle size. It is necessary to reduce the size difference between PTFE fine powder and carbon material as much as possible, similar to mixing rice with small rice.

[0024] The specific gravity of the carbon material prepared in the above Example 1 is about 2.1g / cm 3 (20°C environment), and the specific gravity of the crushed PTFE is 2.2g / cm 3 (20°C environment), and the specific gravities of the two are close, so that uniform mixing is possible.

[0025] Mixing formula: 0.1-25% (preferably 0.1-10%) of carbon material is added by weight. When mixing, a small sample mixing mode is used first, and then mixed multiple times. The purpose of this process is to mix more uniformly. The mixed masterbatch cannot be stored for a long time to prevent the two materials from settling and separating. The granulation process solves this problem.

[0026] The mixed master batch is added with a mixed solvent (15% anhydrous acetone + 85% anhydrous alcohol), and mechanical stirring is performed to fully mix, so as to realize the wet wrapping effect of polytetrafluoroethylene on the carbon material.

[0027] The wet granular form obtained is placed in an oven and dried at 80-100°C for 6h to fully discharge the mixed solvent, so as to obtain the carbon material-filled polytetrafluoroethylene granular material finished product. Large particles and powder in the granular material are removed by screening classification. According to market requirements, the finished product meeting the particle size process is taken, and this method can control the particle size of the granular material finished product to be between 260 microns and 700 microns.

[0028] The detection report (measurement method: ASTM D4745) of the modified polytetrafluoroethylene granular material with 10%, 15% and 25% carbon material addition amount (weight ratio) is shown in Table 1. As can be seen from Table 1, with the increase of the amount of carbon material, the tensile strength, elongation and loose density are reduced, and other indicators are not greatly affected. Compared with the unmodified high-purity polytetrafluoroethylene granular material, the mechanical properties of the polytetrafluoroethylene are improved.

[0029] Table 1 Detection report of modified polytetrafluoroethylene granular material with different carbon material addition amounts

[0030] The advantages of the finally modified granular material are: convenient for long-time transportation and storage; the wrapped granules are not easy to break, so that the mixing is more uniform; the force transmission performance of the granular material under pressure is better than that of the powder material, and the density is more uniform; the flowability of the granular material is better than that of the powder, and automatic production can be realized in thin-walled or special-shaped products.

Claims

1. A method for preparing a hydrotalcite sodium alginate carbon material, characterized in that, (1) mixing hydrotalcite and sodium alginate uniformly and placing in a tube furnace for calcination, the calcination conditions being: passing inert gas, heating at a rate of 0.8-1.2 ℃ / min from room temperature to 90-110 ℃, then heating at a rate of 8-12 ℃ / min to 450-550 ℃, maintaining for 20-40 min, then cooling to room temperature; (2) mixing the calcined sample with potassium hydroxide solid in a mass ratio of 1:3.5-4.5 in deionized water, then drying and placing in a tube furnace for heating and activation: heating at a rate of 0.8-1.2 ℃ / min from room temperature to 90-110 ℃ under inert gas protection, then heating at a rate of 8-12 ℃ / min to 750-850 ℃, maintaining for 0.5-1.5 h, then cooling to room temperature; after washing with hydrochloric acid solution, washing with deionized water until neutral and drying, a carbon material is obtained. The mass ratio of the hydrotalcite and sodium alginate is 2-4:

1. The drying is drying in an oven at 100-110 ℃ for 10-15 h.

2. The production method according to claim 1, wherein The inert gas is N2.

3. The production method according to claim 1, wherein 5. The carbon material prepared by the preparation method of any one of claims 1-4.

4. The production method according to claim 1, wherein 6. The use of the carbon material of claim 5 in modifying polytetrafluoroethylene granules. The polytetrafluoroethylene fine powder is air flow crushed to make the particle size of the carbon material close to that of the polytetrafluoroethylene; the carbon material is mixed uniformly with the crushed polytetrafluoroethylene; the mixed master batch is added to a mixed organic solvent, and after mechanical stirring and full mixing, the polytetrafluoroethylene realizes the effect of wet wrapping the carbon material, the obtained wet granular form is dried to fully discharge the solvent, and a polytetrafluoroethylene granule filled with carbon material is obtained. The addition amount of the carbon material in the polytetrafluoroethylene is 0.1-25%.

7. The method of modifying polytetrafluoroethylene pellets with the carbon material of claim 5, characterized by, The mixed organic solvent is: 15% anhydrous acetone + 85% anhydrous alcohol by mass ratio.

8. The method of claim 7 wherein, ​ 9. The method of claim 8 wherein, ​

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