High expansion temperature expandable graphite and method of making same

Abstract

The application relates to the field of graphite processing, and particularly discloses expandable graphite with high expansion temperature and a preparation method thereof. The preparation method of the expandable graphite with high expansion temperature comprises the following steps: uniformly mixing graphite and an intercalation agent to prepare a mixture; adding hydrogen peroxide into the mixture to prepare a reactant through mixing reaction; performing solid-liquid separation on the reactant, washing the reactant with water for 1-5 times, and obtaining a separated product; performing alkali washing on the separated product to obtain an alkali washed product; adding a metal compound into the alkali washed product, mixing and loading the metal compound for 10-120 minutes to obtain a loaded product, the adding amount of the metal compound is 0.1-10% of the mass of the graphite; performing solid-liquid separation on the loaded product to obtain a solid-liquid separated product; and drying the solid-liquid separated product to prepare the expandable graphite with high expansion temperature. The expandable graphite with high expansion temperature prepared by the application has the advantages of high expansion temperature and large expansion ratio.

Description

Technical Field

[0001] This application relates to the field of graphite processing technology, and more specifically, to a high expansion temperature expandable graphite and a method for preparing the same. Background Technology

[0002] Expandable graphite is a graphite interlayer compound produced under liquid-phase reaction conditions using inorganic acids such as sulfuric acid, phosphoric acid, and nitric acid, or organic acids such as formic acid, acetic acid, and oxalic acid as intercalating agents, and potassium permanganate and hydrogen peroxide as oxidants. When expanded graphite is heated, the substances intercalated into the graphite interlayers pyrolyze, vaporize, and escape, expanding and destroying the original graphite sheet structure, increasing disorder, forming a network-like porous structure, and changing the graphite morphology from scaly to worm-like.

[0003] Expandable graphite, due to its excellent expandability, produces products with properties such as high temperature resistance, radiation protection, heat insulation, lubrication, plasticity, chemical stability, and flexibility. It is widely used in sealing materials, fire-retardant materials (such as fire rings and fire strips), petroleum absorption, battery materials, graphite sheets, and antistatic materials. The initial expansion temperature is an important indicator of expandable graphite; specifically, it refers to the temperature at which the volume of the expandable graphite material increases by 10%. When expanding graphite is applied to plastic fire-retardant materials, a higher initial expansion temperature is required.

[0004] In the prior art, Chinese invention patent application CN96122217.4 discloses a method for manufacturing sulfur-free expandable graphite, which involves immersing natural flake graphite in a mixture of 65-98% nitric acid and organic acid, then adding an oxidant to carry out an oxidation reaction, adding a reducing agent to decolorize, and centrifuging to remove acid and drying to obtain sulfur-free expandable graphite.

[0005] The initial expansion temperature of this expandable graphite is 150℃, while the melt processing temperature of plastics is usually higher than 180℃. Therefore, when expandable graphite is used in fields such as flame retardant plastics, there is a problem of premature expansion of the expandable graphite during the hot melt processing. In response to the aforementioned related technologies, the inventors discovered that current applications of expandable graphite in the field of flame retardant plastics may result in premature expansion, leading to a decrease in the flame retardant effect of the plastic flame retardant material. Summary of the Invention

[0006] To increase the initial expansion temperature of expandable graphite, this application provides an expandable graphite with a high initial expansion temperature and a method for preparing the same.

[0007] In a first aspect, this application provides a method for preparing expandable graphite with a high expansion temperature, employing the following technical solution: A method for preparing expandable graphite with high expansion temperature includes the following steps: A mixture is prepared by uniformly mixing graphite and intercalating agent at a mass ratio of 1:2-8. Add hydrogen peroxide to the mixture and react for 10-120 min to obtain the reactant. The reaction temperature is 0-80℃ and the amount of hydrogen peroxide added is 5-15% of the graphite mass. The reactants were subjected to solid-liquid separation and washed with water 1-5 times, each time for 5 min-12 h, to obtain the separated product. The separated material was washed with alkali 0-3 times, each time for 5 min-8 h, to obtain the alkali washed material. A metal compound is added to the alkaline wash, and the mixture is loaded for 10-120 min to obtain the loaded material. The load was subjected to solid-liquid separation to obtain a solid-liquid separator; The solid-liquid separation is dried to obtain expandable graphite with a high expansion temperature.

[0008] By adopting the above technical solution, graphite and intercalating agent are mixed. The intercalating agent is inserted into the interlayer in the form of molecules or ions. The addition of hydrogen peroxide can further increase the interlayer spacing of graphite sheets, promote more intercalating agent to enter the interlayer of graphite sheets and diffuse into the deep layers of graphite sheets. Water washing removes unstable intercalating agent. Within a certain temperature range, the material as a whole can remain unexpanded. During alkaline washing, alkaline substances can neutralize the edges of graphite sheets or unstable intercalating agents, reduce the total amount of intercalating agent, thereby reducing the total amount of gas generated by decomposition at the specific temperature, and thus controlling the degree of volume expansion. Graphite that has undergone intercalation, oxidation, and water and alkali washing is mixed with metal compounds. The metal compounds are then loaded onto the graphite and filled between the graphite flakes. These metal compounds have high heat resistance and fill the gaps between the graphite layers, sealing the flake material. When heated, they can seal the interlayer material of expandable graphite, preventing carbon dioxide and sulfur dioxide from rapidly escaping from the edges of the flake graphite, thereby improving the initial expansion temperature and thermal stability of expandable graphite. Moreover, the metal compounds loaded between the graphite flakes also act as heat insulation and heat absorption, thus improving the initial expansion temperature and preventing the escape of carbon dioxide and sulfur dioxide from expandable graphite at low temperatures, further enhancing the expansion temperature and thermal stability of expandable graphite.

[0009] By adopting the above technical solution, compounds containing iron or magnesium, manganese, and calcium are loaded onto graphite.

[0010] Optionally, the loading of the metal compound is 2-5% of the graphite mass.

[0011] By adopting the above technical solution, 2-5% by weight of metal compound in graphite can enable expandable graphite to have a higher expansion temperature and expansion ratio.

[0012] Optionally, the solid-liquid separator may be pretreated as follows before drying: the solid-liquid separator may be dispersed in water or an organic solvent, subjected to gentle boiling for 2-30 minutes, with a solid-liquid ratio of 1:1-20, and then subjected to solid-liquid separation.

[0013] By adopting the above technical solution, graphite loaded with metal compounds is subjected to micro-boiling treatment. During micro-boiling treatment, the boiling of water or organic solvent changes the structure of the edge of the flake graphite, increases the resistance to the escape of carbon dioxide and sulfur dioxide, and improves the expansion temperature and stability.

[0014] Optionally, the method of micro-boiling treatment using organic solvents further includes the following steps: dispersing the solid-liquid separation in an organic solvent, adding silica aerogel and polyvinyl alcohol, micro-boiling treatment for 2-30 min, the mass ratio of solid-liquid separation, organic solvent, silica aerogel and polyvinyl alcohol being 1:1-20:0.08-0.12:0.01-0.04, filtering, mixing the filtered product with a dopamine solution with a concentration of 2-4 g / L at a solid-liquid ratio of 1:3-5, stirring at 60-70℃ for 20-24 h, and performing solid-liquid separation.

[0015] By employing the above technical solution, a solid-liquid separator containing metal compounds is mixed with an organic solvent, and silica aerogel and polyvinyl alcohol are added. Silica aerogel nanoparticles exhibit uneven dispersion in the solution, easily leading to an uneven network structure in the aerogel material. Using polyvinyl alcohol as a dispersant not only improves the dispersibility of silica aerogel but also increases the adhesion of silica to the solid-liquid separator, thereby forming a nanoparticle layer on the separator. This nanoparticle layer has a heat-insulating effect and can block the escape of carbon dioxide and sulfur dioxide, increasing the expansion temperature. The filter material with the nanoparticle layer on its surface is mixed with a dopamine solution. Dopamine self-polymerizes, forming polydopamine on the filter material, which helps to block heat transfer, reducing the heating temperature of expandable graphite and thus improving its expansion temperature. Furthermore, polydopamine can form hydrogen bonds with plastics, improving the compatibility between expandable graphite and plastics and preventing a decrease in the mechanical properties of plastics after the addition of expandable graphite.

[0016] Optionally, the metal compound is selected from at least one of iron-containing metal compounds, manganese-containing metal compounds, calcium-containing metal compounds, and magnesium-containing metal compounds.

[0017] Preferably, the metal compounds containing the above metals have high heat resistance, can seal graphite flakes, and improve the expansion temperature of graphite.

[0018] Optionally, the iron-containing metal compound is selected from at least one of ferric sulfate, ferrous sulfate, ferrous ammonium sulfate, and ferric chloride; The manganese-containing metal compound is manganese sulfate; The calcium-containing metal compound is selected from at least one of calcium sulfate, calcium carbonate, calcium hydroxide, and calcium pyrophosphate; The magnesium-containing metal compound is selected from at least one of magnesium sulfate, magnesium oxide, and magnesium hydroxide.

[0019] By adopting the above technical solution, metal compounds containing iron or calcium, magnesium, manganese, etc. have good heat insulation and heat absorption effects. After being filled between graphite sheets, they can improve the expansion temperature of expandable graphite.

[0020] Optionally, the metal compound is an iron-containing metal compound and a magnesium-containing metal compound, wherein the mass ratio of the iron-containing metal compound to the magnesium-containing metal compound is 1:0.8-1.2.

[0021] Optionally, the metal compound is an iron-containing metal compound, which includes ferrous ammonium sulfate and ferric chloride in a mass ratio of 1:0.5-1.

[0022] Optionally, the metal compound includes an iron-containing metal compound, a magnesium-containing metal compound, and a manganese-containing metal compound in a mass ratio of 1:0.8-1.2:0.4-0.8, wherein the iron-containing metal compound is ferrous ammonium sulfate, the magnesium-containing metal compound is magnesium sulfate, and the manganese-containing metal compound is manganese sulfate.

[0023] Optionally, the graphite has a purity of 89.99-99.99% and a mesh size of 30-300 mesh.

[0024] By adopting the above technical solution, the particle size of graphite affects the ease with which intercalating agents and hydrogen peroxide enter the graphite interlayer. If the particle size is too large, the chemical substances in the graphite interlayer will have difficulty diffusing to the depths. If the particle size is too small, the graphite edge reaction will be significant, which is not conducive to the formation of intercalating compounds.

[0025] Optionally, the organic solvent is selected from at least one of C1-C8 alcohols, C1-C8 ketones, C1-C8 ethers, chloroform, xylene, petroleum ether, ethyl acetate, and benzene.

[0026] By adopting the above technical solution, the organic solvent is used to treat the edges of the graphite sheets in a slightly boiling state, thereby improving the expansion temperature and expansion ratio.

[0027] Optionally, the intercalating agent is concentrated sulfuric acid or a mixture of concentrated sulfuric acid and phosphoric acid.

[0028] By adopting the above technical solution, substances such as concentrated sulfuric acid and phosphoric acid can be used as intercalating agents to insert between graphite sheets, increase the interlayer spacing, and avoid the formation of edge compounds; hydrogen peroxide has strong oxidizing properties and can fully open the graphite sheets.

[0029] Optionally, the concentrated sulfuric acid has a mass concentration of 75-105%, and the hydrogen peroxide has a mass concentration of 20-50%.

[0030] By adopting the above technical solution and using hydrogen peroxide of this concentration, the graphite layers can be fully opened, preventing over-oxidation or under-oxidation. Concentrated sulfuric acid of this concentration can quickly penetrate into the graphite layers as an intercalating agent.

[0031] Secondly, this application provides a method for preparing expandable graphite with a high expansion temperature, using the following technical solution: A high expansion temperature expandable graphite is prepared by the aforementioned method for preparing high expansion temperature expandable graphite.

[0032] By adopting the above technical solution, metal compounds are loaded onto graphite sheets to seal the graphite sheet material, and organic solutions or water are used to perform micro-boiling treatment to improve the edge structure of the graphite sheets and increase the expansion temperature and thermal stability of expandable graphite.

[0033] In summary, this application has the following beneficial effects: 1. Since the expandable graphite in this application is made by loading metal compounds containing iron, magnesium, manganese and calcium onto graphite, the metal compounds containing iron, magnesium, manganese and calcium are filled between the graphite layers to seal the layers and prevent carbon dioxide and sulfur dioxide from escaping from the interlayer. In addition, the metal compounds containing iron, magnesium, manganese and calcium can also play a role in heat insulation and heat absorption, which can increase the expansion temperature of expandable graphite.

[0034] 2. In this application, graphite with iron or magnesium, manganese and calcium metal compounds loaded on its surface is preferably subjected to micro-boiling treatment, which can change the structure of the edge of the flake graphite, thereby increasing the resistance to the escape of carbon dioxide and sulfur dioxide from the interlayer, and further improving the expansion temperature of expandable graphite.

[0035] 3. In this application, silica aerogel and polyvinyl alcohol are preferably added during the micro-boiling treatment, and dopamine solution is added to form a heat-insulating nanoparticle layer on graphite containing metal compounds. Then, dopamine self-polymerization is used to form a polydopamine layer, which blocks heat transfer into the graphite, further improves the expansion temperature of expandable graphite, and improves the compatibility of expandable graphite with flame-retardant plastics, thereby improving the mechanical strength of flame-retardant plastics.

[0036] 4. The expandable graphite prepared by the method of this application has an initial expansion temperature greater than 250°C, which is 30-70°C higher than that of unloaded expandable graphite, and the expansion ratio is greater than 200 times. This high-initiation-temperature expandable graphite can be applied in the field of flame retardancy, especially for flame retardant applications of polymer materials such as plastics and rubber. Detailed Implementation Example

[0037] Example 1: A method for preparing expandable graphite with high expansion temperature, comprising the following steps: (1) Graphite and intercalating agent with a mass ratio of 1:2 are put into a reaction vessel and mixed evenly to obtain a mixture. The intercalating agent is concentrated sulfuric acid with a mass concentration of 105% and the graphite has a purity of 99.99% and a mesh size of 30. (2) Add hydrogen peroxide with a mass concentration of 20% to the mixture obtained in step (1), mix and react for 10 min at a reaction temperature of 80℃ to obtain the reactant. The amount of hydrogen peroxide added is 15% of the mass of graphite. (3) The reactants obtained in step (2) are separated into solid and liquid by filtration, and washed with water 5 times for 5 minutes each time to obtain the separated product; (4) Wash the separated alkaline solution obtained in step (3) three times, each time for 20 minutes, to obtain alkaline washed product. The alkaline washing solution is sodium hydroxide with a mass concentration of 10%. (5) Add 2% by weight of graphite metal compound to the alkaline washing material obtained in step (4), mix and load for 10 min at room temperature to obtain the loading material. The metal compound is an iron-containing metal compound, and the iron-containing metal compound is ferric sulfate. The content of ferric sulfate is 3% by weight of graphite. (6) The loading obtained in step (5) is separated into solid and liquid by filtration to obtain solid-liquid separation; (7) Disperse the solid-liquid mixture in water at a solid-liquid ratio of 1:20, perform a micro-boiling treatment for 120 min at a micro-boiling temperature of 100°C, and then perform solid-liquid separation by filtration. (8) The product obtained in step (7) is dried to obtain expandable graphite with high expansion temperature. The drying temperature is 65℃ and the drying time is 3h.

[0038] Example 2: A method for preparing expandable graphite with high expansion temperature, comprising the following steps: (1) Graphite and intercalating agent with a mass ratio of 1:8 are put into a reaction vessel and mixed evenly to obtain a mixture. The intercalating agent is concentrated sulfuric acid with a mass concentration of 75% and the graphite has a mesh size of 300. (2) Add hydrogen peroxide with a mass concentration of 50% to the mixture obtained in step (1), mix and react for 80 min at a reaction temperature of 30°C to obtain the reactant. The amount of hydrogen peroxide added is 10% of the mass of graphite. (3) The reactants obtained in step (2) are separated into solid and liquid by filtration, and washed with water twice for 3 hours each time to obtain the separated product; (4) Wash the separated product obtained in step (3) twice with alkali for 3 hours each time to obtain the alkali washed product. The alkali washing solution is sodium hydroxide with a mass concentration of 70%. (5) Add 2% by weight of graphite-containing metal compound to the alkaline washing material obtained in step (4), mix and load for 50 min at room temperature to obtain the loaded material, the iron-containing metal compound being ferrous sulfate; (6) The loading obtained in step (5) is separated into solid and liquid by filtration to obtain solid-liquid separation; (7) Disperse the solid-liquid separation in water at a solid-liquid ratio of 1:15, perform a micro-boiling treatment for 60 minutes at a micro-boiling temperature of 100°C, and then perform solid-liquid separation by filtration. (8) The product obtained in step (7) is dried to obtain expandable graphite with high expansion temperature. The drying temperature is 55℃ and the drying time is 4h.

[0039] Example 3: A method for preparing expandable graphite with high expansion temperature, comprising the following steps: (1) Graphite and intercalating agent with a mass ratio of 1:3 are put into a reaction vessel and mixed evenly to obtain a mixture. The intercalating agent is concentrated sulfuric acid with a mass concentration of 98% and the graphite has a mesh size of 50. (2) Add hydrogen peroxide with a mass concentration of 50% to the mixture obtained in step (1), mix and react for 30 min at a reaction temperature of 50°C to obtain the reactant. The amount of hydrogen peroxide added is 5% of the mass of graphite. (3) The reactants obtained in step (2) are separated into solid and liquid by filtration, and washed with water 3 times for 1 hour each time to obtain the separated product; (4) Wash the separated product obtained in step (3) with alkali once for 1 hour each time to obtain the alkali washed product. The alkali washing solution is sodium hydroxide with a mass concentration of 10%. (5) Add 2% by weight of iron-containing metal compound to the alkaline washing material obtained in step (4), mix and load for 1 hour at room temperature to obtain the loaded material, the iron-containing metal compound being ferrous ammonium sulfate. (6) The loading obtained in step (5) is separated into solid and liquid by filtration to obtain solid-liquid separation; (7) Disperse the obtained solid-liquid mixture in water at a solid-liquid ratio of 1:10, and boil it for 10 minutes at a boiling temperature of 100°C. Then, separate the solid and liquid by filtration. (8) The product obtained in step (7) is dried to obtain expandable graphite with high expansion temperature. The drying temperature is 60℃ and the drying time is 3.5h.

[0040] Example 4: A method for preparing expandable graphite with high expansion temperature, the difference from Example 3 is that the metal compound is a manganese-containing metal compound, and the manganese-containing metal compound is manganese sulfate.

[0041] Example 5: A method for preparing expandable graphite with high expansion temperature, which differs from Example 3 in that the metal compound is a calcium-containing metal compound, and the calcium-containing metal compound is calcium sulfate.

[0042] Example 6: A method for preparing expandable graphite with high expansion temperature, which differs from Example 3 in that the metal compound is a calcium-containing metal compound, and the calcium-containing metal compound is calcium carbonate.

[0043] Example 7: A method for preparing expandable graphite with high expansion temperature, which differs from Example 3 in that the metal compound is a calcium-containing metal compound, and the calcium-containing metal compound is calcium hydroxide.

[0044] Example 8: A method for preparing expandable graphite with high expansion temperature, which differs from Example 3 in that the metal compound is a calcium-containing metal compound, and the calcium-containing metal compound is calcium pyrophosphate.

[0045] Example 9: A method for preparing expandable graphite with high expansion temperature, the difference from Example 3 is that the metal compound is a magnesium-containing metal compound, and the magnesium-containing metal compound is magnesium sulfate.

[0046] Example 10: A method for preparing expandable graphite with high expansion temperature, which differs from Example 3 in that the metal compound is a magnesium-containing metal compound, and the magnesium-containing metal compound is magnesium hydroxide.

[0047] Example 11: A method for preparing expandable graphite with high expansion temperature, the difference from Example 3 is that the amount of ferrous ammonium sulfate added is 5% of the graphite mass.

[0048] Example 12: A method for preparing expandable graphite with high expansion temperature, which differs from Example 3 in that the amount of ferrous ammonium sulfate added is 0.5% of the graphite mass.

[0049] Example 13: A method for preparing expandable graphite with high expansion temperature, which differs from Example 3 in that alkali washing is not performed.

[0050] Example 14: A method for preparing expandable graphite with high expansion temperature, which differs from Example 3 in that the micro-boiling treatment is not performed.

[0051] Example 15: A method for preparing expandable graphite with high expansion temperature, the difference from Example 3 is that the amount of ferrous ammonium sulfate added is 10% of the graphite mass.

[0052] Example 16: A method for preparing expandable graphite with high expansion temperature, the difference from Example 3 is that the intercalating agent is concentrated sulfuric acid with a mass concentration of 80%.

[0053] Example 17: A method for preparing expandable graphite with high expansion temperature, which differs from Example 3 in that the intercalating agent is a mixture of phosphoric acid and concentrated sulfuric acid with a mass concentration of 80%, and the mass ratio of phosphoric acid to concentrated sulfuric acid in the mixture is 1:9.

[0054] Example 18: A method for preparing expandable graphite with high expansion temperature, which differs from Example 3 in that the metal compound is an iron-containing metal compound and a magnesium-containing metal compound, the iron-containing metal compound is ferrous ammonium sulfate, the magnesium-containing metal compound is magnesium sulfate, and the mass ratio of ferrous ammonium sulfate to magnesium sulfate is 1:1.

[0055] Example 19: A method for preparing expandable graphite with high expansion temperature, which differs from Example 3 in that the iron-containing metal compound is ferrous ammonium sulfate and ferric chloride in a mass ratio of 1:1.

[0056] Example 20: A method for preparing expandable graphite with high expansion temperature, which differs from Example 3 in that the metal compound includes an iron-containing metal compound, a magnesium-containing metal compound, and a manganese-containing metal compound in a mass ratio of 1:1:0.5. The iron-containing metal compound is ferrous ammonium sulfate, the magnesium-containing metal compound is magnesium sulfate, and the manganese-containing metal compound is manganese sulfate.

[0057] Example 21: A method for preparing expandable graphite with high expansion temperature, which differs from Example 3 in that, in step (7), the solid-liquid separation is dispersed in an organic solvent for micro-boiling treatment, and the organic solvent is an ethanol solution.

[0058] Example 22: A method for preparing expandable graphite with high expansion temperature, the difference from Example 21 is that step (7) is specifically as follows: 1 kg of solid-liquid separation was dispersed in an ethanol solution, and silica aerogel and polyvinyl alcohol were added. The mixture was then subjected to a gentle boiling treatment for 10 min. The mass ratio of solid-liquid separation, ethanol solution, silica, and aerogel was 1:10:0.12:0.04, and the gentle boiling treatment temperature was 98℃. The mixture was then filtered, and the filtered product was mixed with a 2 g / L dopamine solution at a mass ratio of 1:3. The mixture was stirred at 60℃ for 24 h to achieve solid-liquid separation.

[0059] Example 23: A method for preparing expandable graphite with high expansion temperature, which differs from Example 21 in that step (7) is as follows: 1 kg of solid-liquid separation is dispersed in an ethanol solution, silica aerogel and polyvinyl alcohol are added, and the mixture is subjected to a gentle boiling treatment for 10 min. The mass ratio of solid-liquid separation, ethanol solution, silica and aerogel is 1:20:0.08:0.01, the gentle boiling treatment temperature is 98℃, the mixture is filtered, and the filtered product is mixed with a dopamine solution with a concentration of 4 g / L at a mass ratio of 1:5. The mixture is stirred at 70℃ for 20 h, and the solid and liquid are separated.

[0060] Example 24: A method for preparing expandable graphite with high expansion temperature, which differs from Example 24 in that dopamine solution is not added.

[0061] Example 25: A method for preparing expandable graphite with high expansion temperature, which differs from Example 24 in that silica aerogel and polyvinyl alcohol are not added.

[0062] Example 26: A method for preparing high expansion temperature expandable graphite, which differs from Example 24 in that polyvinyl alcohol is not added.

[0063] Comparative Example Comparative Example 1: A method for preparing expandable graphite with high expansion temperature, comprising the following steps: (1) Graphite and intercalating agent with a mass ratio of 1:3 are put into a reaction vessel and mixed evenly to obtain a mixture. The intercalating agent is concentrated sulfuric acid with a mass concentration of 80% and the graphite has a mesh size of 50. (2) Add hydrogen peroxide with a mass concentration of 50% to the mixture obtained in step (1), mix and react for 30 min at a reaction temperature of 50°C to obtain the reactant. The amount of hydrogen peroxide added is 5% of the mass of graphite. (3) The reactants obtained in step (2) are separated into solid and liquid by filtration, and washed with water 3 times for 1 hour each time to obtain the separated product; (4) The separated product obtained in step (3) is separated into solid and liquid by filtration to obtain the solid-liquid separated product; (5) The obtained solid-liquid separation material was dried to obtain expandable graphite with high expansion temperature. The drying temperature was 60℃ and the drying time was 3.5h.

[0064] Comparative Example 2: A method for preparing expandable graphite with high expansion temperature, comprising the following steps: (1) Graphite and intercalating agent with a mass ratio of 1:3 are put into a reaction vessel and mixed evenly to obtain a mixture. The intercalating agent is concentrated sulfuric acid with a mass concentration of 80% and the graphite has a mesh size of 50. (2) Add hydrogen peroxide with a mass concentration of 50% to the mixture obtained in step (1), mix and react for 30 min at a reaction temperature of 50°C to obtain the reactant. The amount of hydrogen peroxide added is 5% of the mass of graphite. (3) The reactants obtained in step (2) are separated into solid and liquid by filtration, and washed with water 3 times for 1 hour each time to obtain the separated product; (4) Wash the separated product obtained in step (3) with alkali once for 1 hour each time to obtain the alkali washed product. The alkali washing solution is sodium hydroxide with a mass concentration of 70%. (5) The precipitate obtained in step (3) is separated into solid and liquid by filtration to obtain a solid-liquid precipitate; (6) The obtained solid-liquid separation product is dried to obtain expandable graphite with high expansion temperature. The drying temperature is 60℃ and the drying time is 3.5h.

[0065] Comparative Example 3: A method for preparing expandable graphite with high expansion temperature, comprising the following steps: (1) Graphite and intercalating agent with a mass ratio of 1:3 are put into a reaction vessel and mixed evenly to obtain a mixture. The intercalating agent is concentrated sulfuric acid with a mass concentration of 80% and the graphite has a mesh size of 50. (2) Add hydrogen peroxide with a mass concentration of 50% to the mixture obtained in step (1), mix and react for 30 min at a reaction temperature of 50°C to obtain the reactant. The amount of hydrogen peroxide added is 5% of the mass of graphite. (3) The reactants obtained in step (2) are separated into solid and liquid by filtration, and washed with water 3 times for 1 hour each time to obtain the separated product; (4) Wash the separated product obtained in step (3) with alkali once for 1 hour each time to obtain the alkali washed product. The alkali washing solution is sodium hydroxide with a mass concentration of 70%. (5) The precipitate obtained in step (3) is separated into solid and liquid by filtration to obtain a solid-liquid precipitate; (6) Disperse the obtained solid-liquid separation material into water with a solid-liquid ratio of 1:20, and perform micro-boiling treatment for 10 min at a micro-boiling temperature of 100℃. Then, perform solid-liquid separation by filtration. (7) The product obtained in step (7) is dried to obtain expandable graphite with high expansion temperature. The drying temperature is 60℃ and the drying time is 3.5h.

[0066] Comparative Example 4: A method for preparing expandable graphite with high expansion temperature, which differs from Example 3 in that the amount of ferrous sulfate added is 15% of the graphite mass.

[0067] Comparative Example 5: A method for manufacturing sulfur-free expandable graphite, comprising the following steps: 11 grams of 65% nitric acid and 15% acetic anhydride were slowly mixed to prepare a mixture of nitric acid and acetic anhydride. Then, 10 grams of graphite were added to the mixture and stirred until homogeneous. Next, 3 grams of potassium permanganate were added and the mixture was stirred continuously at 5°C for 30 minutes. After the reaction was completed, 20 grams of water were added to the prepared acidic graphite and the mixture was stirred continuously for 60 minutes. Then, 3 grams of oxalic acid were added and the mixture was stirred continuously for 20 minutes to decolorize the graphite. The decolorized acidic graphite was centrifuged to remove acid, then rinsed with water until the pH reached 7. After centrifugation, the graphite was dried at 60°C until the water content was 1% of the graphite weight.

[0068] Performance testing I. High expansion temperature expandable graphite was prepared according to the methods in the examples and comparative examples, and its performance was tested according to the following methods. The test results are recorded in Table 1.

[0069] 1. Expansion Temperature: Set the test temperature, put 1g of expandable graphite into a 10mL test tube, keep the temperature constant for 10min, take out the test tube and read the temperature. If the volume of expandable graphite increases by 3 or more, it is considered to have expanded. If it increases by 0-2, a higher expansion temperature can be measured.

[0070] 2. Expansion ratio: Take 1g of expandable graphite and place it in a quartz beaker that has been heated in a muffle furnace at 1000℃ for 5min until it stops expanding. Immediately remove the beaker and read the volume of the expanded sample (read the average value of the corresponding scales of the highest and lowest points on the top surface).

[0071] 3. pH value: Accurately weigh 1.000g of sample and place it in a 100mL beaker. Use a graduated cylinder to take 50mL of distilled water and pour it into the beaker. Stir for 10min, filter, and then use a pH meter to measure the pH value of the filtrate.

[0072] 4. Fixed Carbon Content: An indirect carbon determination method (i.e., combustion method) is used. This involves measuring the volatile matter and ash content of the sample, then subtracting them from the total amount; the difference is the fixed carbon content. The sample is placed in a nitrogen stream and burned at high temperature, causing the volatile substances to decompose and escape; this loss on ignition is the volatile matter. The residue obtained after the sample has been burned at high temperature until all graphite and volatiles have escaped is the ash content.

[0073] Table 1 As shown in Table 1, loading iron, manganese, calcium, or magnesium metal compounds onto the surface, between, or in the gaps of graphite flakes can increase the swelling temperature, with expansion ratios all exceeding 200 times, fixed carbon content exceeding 93%, pH value exceeding 4, and good product flowability. Loading iron and magnesium metal compounds significantly increases the swelling temperature. Furthermore, comparing the data from Examples 3 and 13 shows that after alkali washing in Example 3, the swelling temperature decreased by 10°C, but the pH value of the product increased. Comparing the data from Examples 3 and 14 shows that after micro-boiling treatment in Example 3, the swelling temperature increased by 10°C, and the pH value of the product further increased. Comparing the data from Examples 3, 11, 12, and 15 shows that with increasing iron-containing metal compound loading, the swelling temperature gradually increases, but the expansion ratio decreases, and the pH value decreases.

[0074] In Example 16, concentrated sulfuric acid with a concentration of 80% was used as an intercalating agent. Compared with Example 3, the concentration of concentrated sulfuric acid was reduced, the amount of intercalation was reduced, and the expansion ratio was reduced.

[0075] In Example 17, a mixture of phosphoric acid and 80% concentrated sulfuric acid was used as an intercalating agent, and the mass ratio of phosphoric acid to concentrated sulfuric acid was 1:9. Compared with Example 3, the expansion temperature was slightly increased and the expansion ratio was decreased.

[0076] In Examples 18-20, the use of complex metal compounds resulted in higher expansion temperatures and expansion ratios.

[0077] In Comparative Example 1, no metal compound was loaded onto the graphite. The expandable graphite produced by intercalation, oxidation, and washing only had a good expansion effect, but the expansion temperature was low.

[0078] In Comparative Example 2, after graphite was intercalated, oxidized, and washed with water, it was then subjected to alkaline washing. Compared with Comparative Example 1, its expansion temperature decreased, its expansion ratio decreased, and its pH value increased.

[0079] Compared with Example 3, in Comparative Example 3, graphite was subjected to intercalation, oxidation, water washing and alkali washing, followed by solid-liquid separation and dispersion in water, and then subjected to micro-boiling treatment. No iron-containing metal compounds were added. Although the expansion temperature in Comparative Example 3 was higher than that in Comparative Example 1 and Comparative Example 2, the expansion ratio was lower.

[0080] Compared with Example 3, Comparative Example 4 showed an increase in the amount of iron-containing compound added. Although the expansion temperature was increased, the expansion ratio and carbon content were significantly reduced.

[0081] In summary, the effects of Examples 1-15, especially Examples 3, 10 and 13, compared with the comparative examples, have yielded better experimental results, indicating that this application can produce expandable graphite with high expansion temperature.

[0082] Compared with Example 21, Examples 22 and 23 added dopamine solution before micro-boiling treatment with organic solvent, and used silica aerogel and polyvinyl alcohol during micro-boiling treatment. Compared with Example 21, the expansion temperature of expandable graphite in Examples 22 and 23 increased, but the expansion ratio decreased.

[0083] Compared with Example 21, Example 24 did not use dopamine solution. The expansion temperature of the expandable graphite prepared in Example 24 decreased, indicating that the dopamine solution can improve the expansion strength of expandable graphite after forming polydopamine.

[0084] Compared with Example 21, Examples 25 and 26 did not include silica aerogel and polyvinyl alcohol, while Example 26 did not include polyvinyl alcohol. The expansion temperature of the expandable graphite prepared in Example 25 decreased significantly, and the expansion ratio of Example 26 decreased significantly. This indicates that silica aerogel and polyvinyl alcohol can improve the expansion temperature and expansion ratio of expandable graphite.

[0085] 2. The expandable graphite prepared in Examples 3-5, 9 and 21-26 was mixed with polyethylene at a mass ratio of 1:9. The mixture was then hot-pressed on a flat vulcanizing agent (ZG-80T, manufactured in Dongguan, China) at 200°C for 10 minutes. Then, it was cold-pressed into sheets at room temperature under a pressure of 17 MPa for 10 minutes. The performance of the sheets was then tested according to the following method. The test results are recorded in Table 2. The polyethylene without the addition of expandable graphite was used as the blank group.

[0086] 1. Limiting Oxygen Index: The LOI value is measured on a 120mm×6.5mm×3.2mm sheet using a JF-4 instrument, in accordance with ASTM D2863-77.

[0087] 2. Mechanical properties: Tested in accordance with GB / T1040.2-2006 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics", with a tensile speed of 50 mm / min.

[0088] Table 2 As can be seen from the data in Table 2, in Examples 3-5, 9, and 18-20, different metal compounds were used to prepare expandable graphite, which, when added to polyethylene, increased the flame retardant effect of polyethylene compared to the blank group, but its mechanical strength was weakened. In Examples 22 and 23, the expandable graphite prepared and added to polyethylene improved the flame retardant coefficient of polyethylene compared to Example 21, and its mechanical strength was stronger than that of Example 21, indicating that the compatibility between expandable graphite treated with dopamine and other components and polyethylene was improved. In Example 24, no dopamine solution was added. Table 2 shows that after the expandable graphite prepared in Example 24 was added to polyethylene, the mechanical strength of polyethylene decreased compared to Example 21. The mechanical strength of the polyethylene samples obtained in Examples 25 and 26 also decreased, and the oxygen index decreased.

[0089] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing expandable graphite with high expansion temperature, characterized in that, Includes the following steps: A mixture is prepared by uniformly mixing graphite and intercalating agent at a mass ratio of 1:2-8. Add hydrogen peroxide to the mixture and react for 10-120 minutes to obtain the reactant. The reaction temperature is 0-80℃, and the amount of hydrogen peroxide added is 5-15% of the graphite mass. The reactants were subjected to solid-liquid separation and washed with water 1-5 times, each time for 5 min-12 h, to obtain the separated product. The separated material was washed with alkali 0-3 times, each time for 5 min-8 h, to obtain the alkali washed material. A metal compound is added to the alkaline washed material, and the mixture is loaded for 10-120 min to obtain a loaded material. The amount of metal compound added is 2-5% of the graphite mass. The load was subjected to solid-liquid separation to obtain a solid-liquid separator; The solid-liquid separation is dried to obtain expandable graphite with a high expansion temperature. Before drying, the solid-liquid separator is pretreated as follows: the solid-liquid separator is dispersed in water or an organic solvent and subjected to a gentle boiling treatment for 2-30 minutes, with a solid-liquid ratio of 1:1-20. The method of using an organic solvent for gentle boiling treatment further includes the following steps: the solid-liquid separator is dispersed in an organic solvent, silica aerogel and polyvinyl alcohol are added, and the mixture is subjected to a gentle boiling treatment for 2-30 minutes, with a mass ratio of solid-liquid separator, organic solvent, silica aerogel and polyvinyl alcohol of 1:1-20:0.08-0.12:0.01-0.

04. The mixture is then filtered, and the filtered product is mixed with a dopamine solution with a concentration of 2-4 g / L at a solid-liquid ratio of 1:3-5. The mixture is stirred at 60-70°C for 20-24 hours to achieve solid-liquid separation. The metal compound is selected from at least one of iron-containing metal compounds, manganese-containing metal compounds, calcium-containing metal compounds, and magnesium-containing metal compounds; The iron-containing metal compound is selected from at least one of ferric sulfate, ferrous sulfate, ferrous ammonium sulfate, and ferric chloride; The manganese-containing metal compound is manganese sulfate; The calcium-containing metal compound is selected from at least one of calcium sulfate, calcium carbonate, calcium hydroxide, and calcium pyrophosphate; The magnesium-containing metal compound is selected from at least one of magnesium sulfate, magnesium oxide, and magnesium hydroxide.

2. The method for preparing high expansion temperature expandable graphite according to claim 1, characterized in that, The graphite has a purity of 89.99-99.99% and a mesh size of 30-300 mesh.

3. The method for preparing high expansion temperature expandable graphite according to claim 1, characterized in that, The organic solvent is selected from at least one of C1-C8 alcohols, C1-C8 ketones, C1-C8 ethers, chloroform, xylene, petroleum ether, ethyl acetate, and benzene.

4. The method for preparing high expansion temperature expandable graphite according to claim 1, characterized in that, The intercalating agent is concentrated sulfuric acid or a mixture of concentrated sulfuric acid and phosphoric acid.

5. A high expansion temperature expandable graphite, characterized in that, It is prepared by the method for preparing high expansion temperature expandable graphite according to any one of claims 1-4.

Images