Preparation method of viscose-based short fiber thermal insulation composite material

Abstract

The present invention uses viscose-based carbon fiber as raw material, chops it and mixes it with auxiliary material A solution, then puts the mixed chopped fibers into a vacuum tube furnace for heating to obtain pretreated carbon fiber, then mixes auxiliary material B solution with the pretreated carbon fiber to obtain mixed carbon fiber, and puts the mixed carbon fiber into an oven for cross-linking and curing to obtain a mixed gel, and finally performs a high-temperature cracking reaction on the mixed gel to finally obtain a short-fiber hard thermal insulation composite material. The viscose-based short-fiber thermal insulation composite material of the present invention has low thermal conductivity, good mechanical properties, and excellent density and high-temperature resistance.

Description

Technical Field

[0001] The present invention relates to the field of thermal insulation materials, in particular to a viscose-based short fiber thermal insulation composite material. Background Art

[0002] Carbon fiber is a new type of fiber material with high strength and high modulus fiber with a carbon content of more than 95%. It is a microcrystalline graphite material obtained by stacking organic fibers such as flaky graphite crystals along the axial direction of the fiber and undergoing carbonization and graphitization treatment. Carbon fiber thermal insulation materials (such as carbon fiber thermal insulation felt) have excellent properties such as low thermal conductivity, low heat capacity, small linear expansion coefficient, constant mechanical strength at high temperature, corrosion resistance, and lightweight. They are widely used in high-temperature vacuum furnaces or inert atmosphere furnaces due to their superior high-temperature resistance, high-temperature thermal insulation performance, easy molding and processing performance, and low impurity content. At present, carbon fiber thermal insulation materials are divided into three categories according to the type of raw materials: polyacrylonitrile (PAN)-based carbon fiber thermal insulation materials, viscose-based carbon fiber thermal insulation materials, and asphalt-based carbon fiber thermal insulation materials. The quality of thermal insulation performance directly affects the operating process and energy consumption of high-temperature equipment. Some studies have reported that viscose-based materials have the best thermal insulation performance. The present invention provides a method for preparing viscose-based short fibers with excellent thermal insulation performance. Summary of the Invention

[0003] The present invention uses viscose-based carbon fiber as raw material, chops it and mixes it with auxiliary material A solution, then puts the mixed chopped fibers into a vacuum tube furnace for heating to obtain pretreated carbon fiber, then mixes auxiliary material B solution with the pretreated carbon fiber to obtain mixed carbon fiber, and puts the mixed carbon fiber into an oven for cross-linking and curing to obtain a mixed gel, and finally performs a high-temperature cracking reaction on the mixed gel to finally obtain a short-fiber hard thermal insulation composite material. The viscose-based short-fiber thermal insulation composite material of the present invention has low thermal conductivity, good mechanical properties, and excellent density and high-temperature resistance.

[0004] A method for preparing a viscose-based short fiber thermal insulation composite material, the method comprising:

[0005] 1) pre-treating the viscose fiber, then placing the treated viscose fiber in a tube furnace, evacuating, heating, introducing water vapor, and keeping the temperature; replacing the introduced water vapor with ammonia, heating, and keeping the temperature; replacing the introduced ammonia with carbon dioxide, keeping the temperature, and then cooling to room temperature to obtain a viscose-based carbon fiber;

[0006] 2) dispersing boric acid, polyvinyl alcohol, and 2,2-dihydroxybiphenyl in an ethanol solvent, and adding ammonia water to adjust the pH value to obtain an auxiliary material A solution;

[0007] 3) chopping the viscose-based carbon fiber obtained in step 1 to obtain short fibers, then mixing the short fibers with the auxiliary material A solution, heating the short fibers, and filtering the short fibers to obtain a solid;

[0008] 4) placing the product of step 3 into a vacuum tube furnace and heat-treating it under nitrogen protection to obtain pretreated carbon fiber;

[0009] 5) dispersing a soluble zirconium salt, oxalic acid, polyvinyl alcohol, and glycerol in deionized water and stirring uniformly to obtain a zirconium sol; dispersing a phenolic resin and polyethyleneimine in ethanol to obtain a phenolic resin mixed solution; and mixing the zirconium sol and the phenolic resin mixed solution to obtain an auxiliary material B solution;

[0010] 6) The pretreated carbon fibers from step 4, the auxiliary material B solution, ethyl orthosilicate, and dimethyldiethoxysilane were mixed evenly, placed in an oven, heated, and cross-linked to obtain a mixed gel;

[0011] 7) placing the mixed gel in a high-temperature furnace under nitrogen protection and heat treatment to obtain a viscose-based short fiber thermal insulation composite material.

[0012] Furthermore, the pretreatment process in step 1 includes soaking the viscose fiber in 90-100° C. water for 0.5-3 hours, drying, and then soaking in 50-70° C. diammonium hydrogen phosphate aqueous solution with a concentration of 3-6 wt% for 0.5-3 hours, and drying.

[0013] Furthermore, in step 1, the treated viscose fiber is placed in a tubular furnace, vacuumed, heated to 600-700°C, and water vapor is introduced at a flow rate of 50-100 ml / min, which is maintained for 1-2 hours; the introduced water vapor is replaced with ammonia, the temperature is raised to 850-900°C, the flow rate of ammonia is 50-100 ml / min, and the temperature is maintained for 2-4 hours; the introduced ammonia is replaced with carbon dioxide, the flow rate of carbon dioxide is 50-100 ml / min, and the temperature is maintained for 0.2-0.5 hours, and then the carbon dioxide is kept introduced and cooled to room temperature to obtain viscose-based carbon fiber.

[0014] Furthermore, in step 2, boric acid, polyvinyl alcohol and 2,2-dihydroxybiphenyl are dispersed in an ethanol solvent in a mass ratio of 1:2-2.5:2-2.5, wherein the mass ratio of boric acid to ethanol is 1:100-150, and ammonia water is added to adjust the pH value to 4-6 to obtain an auxiliary material A solution.

[0015] Furthermore, in step 3, the short fibers are mixed with the auxiliary material A solution in a mass ratio of 1:1.5-3, heated at 70-90° C. for 3-6 hours, and filtered to obtain a solid.

[0016] Furthermore, in step 4, the product of step 3 is placed in a vacuum tube furnace, heated at 100-150° C. for 1-2 hours under nitrogen protection, and then heated to 1000-1200° C. and heat treated for 4-6 hours to obtain pretreated carbon fiber.

[0017] Furthermore, in step 5, zirconium nitrate, oxalic acid, polyvinyl alcohol and glycerol are dispersed in deionized water in a mass ratio of 100:10-15:5-10:5-10, wherein the mass ratio of zirconium nitrate to deionized water is 10-15:100; stirring is performed at 80-90°C to obtain a zirconium sol; phenolic resin and polyethyleneimine are dispersed in ethanol in a mass ratio of 10:1 to obtain a phenolic resin mixed solution, wherein the mass ratio of phenolic resin to ethanol is 3-6:100; the zirconium sol and the phenolic resin mixed solution are mixed in a mass ratio of 1:1.5-2 to obtain an auxiliary material B solution.

[0018] Furthermore, in step 6, the pretreated carbon fiber of step 4, auxiliary material B solution, ethyl orthosilicate, and dimethyldiethoxysilane are evenly mixed in a mass ratio of 100:100-120:5-10:5-10, placed in an oven and heated for 2-6 hours, and cross-linked and cured to obtain a mixed gel.

[0019] Furthermore, in step 7, the mixed gel is placed in a high-temperature furnace, protected by nitrogen, and heated at 800-900° C. for 5-7 hours, and then heated to 2000-2200° C. for 0.5-1 hour to obtain a viscose-based short fiber thermal insulation composite material.

[0020] Furthermore, a viscose-based short fiber thermal insulation composite material is provided, characterized in that the material is prepared using the method described above.

[0021] Beneficial technical effects of the present invention

[0022] The beneficial effects of the present invention compared with the traditional process are:

[0023] 1) By oxidizing viscose fiber at high temperature under water vapor, oxidized groups are generated on the surface of the viscose fiber, thereby improving the efficiency of ammonia gas activating amino groups on its surface at high temperature. Then, the nitrogen-containing groups react with the subsequently added carbon dioxide at high temperature to generate groups containing carbonized nitrogen on the fiber surface. The carbonized nitrogen groups can increase the surface activity of the fiber and at the same time, can also improve the mechanical strength of the fiber;

[0024] 2) Boric acid and polyvinyl alcohol, under the action of 2,2-dihydroxybiphenyl, can form a stable high-temperature protective layer of boron carbide on the surface of the pretreated carbon fiber at high temperature, thereby reducing the degradation rate of the carbon fiber during subsequent high-temperature carbonization, protecting the carbon fiber and providing excellent mechanical properties. In addition, the presence of boron carbide can effectively improve the interfacial bonding state between the fiber and the zirconium dioxide ceramic.

[0025] 3) By mixing zirconium sol, phenolic resin and polyethyleneimine, due to the charge adsorption ability of polyethyleneimine, the carbon fibers can be dispersed more evenly during the dispersion process, thereby improving the dispersion performance of the carbon fibers in the gel and improving the mechanical properties of the material. In addition, the chopped carbon fibers and ceramic powders can increase the packing density of the gel. At the same time, the phenolic resin and polyethyleneimine are cracked into porous carbon during the high-temperature carbonization process, thereby improving the density and strength of the thermal insulation material while improving the thermal insulation performance. DETAILED DESCRIPTION

[0026] The present invention will be described in more detail below through specific examples, but the protection scope of the present invention is not limited to these examples.

[0027] Example 1:

[0028] 1) soaking the viscose fiber in 90° C. water for 3 h, drying, and then soaking it in a 3wt% diammonium hydrogen phosphate aqueous solution at 60° C. for 3 h, drying, and placing the dried product in a tube furnace, evacuating, heating to 600° C., and introducing water vapor at a flow rate of 50 ml / min for 1 h; replacing the introduced water vapor with ammonia, heating to 850° C., and introducing ammonia at a flow rate of 50 ml / min for 2 h; replacing the introduced ammonia with carbon dioxide at a flow rate of 50 ml / min for 0.5 h, and then cooling to room temperature while continuing to introduce carbon dioxide to obtain a viscose-based carbon fiber;

[0029] 2) dispersing boric acid, polyvinyl alcohol, and 2,2-dihydroxybiphenyl in an ethanol solvent at a mass ratio of 1:2:2, wherein the mass ratio of boric acid to ethanol is 1:100, and adding ammonia water to adjust the pH to 4 to obtain an auxiliary material A solution;

[0030] 3) chopping the viscose-based carbon fiber obtained in step 1 to obtain short fibers, then mixing the short fibers with the auxiliary material A solution at a mass ratio of 1:1.5, heating at 70° C. for 3 h, and filtering to obtain a solid;

[0031] 4) placing the product of step 3 into a vacuum tube furnace, heating it at 100° C. for 1 h under nitrogen protection, then raising the temperature to 1000° C. and heat treating it for 4 h to obtain pretreated carbon fiber;

[0032] 5) Dispersing zirconium nitrate, oxalic acid, polyvinyl alcohol, and glycerol in deionized water at a mass ratio of 100:10:5:5, wherein the mass ratio of zirconium nitrate to deionized water is 10:100; stirring uniformly at 80° C. to obtain a zirconium sol; dispersing phenolic resin and polyethyleneimine in ethanol at a mass ratio of 10:1 to obtain a phenolic resin mixed solution, wherein the mass ratio of phenolic resin to ethanol is 3:100; mixing the zirconium sol and the phenolic resin mixed solution at a mass ratio of 1:1.5 to obtain an auxiliary material B solution;

[0033] 6) The pretreated carbon fibers of step 4, the auxiliary material B solution, ethyl orthosilicate, and dimethyldiethoxysilane were mixed uniformly in a mass ratio of 100:100:5:5, and then placed in an oven and heated for 2 hours to crosslink and solidify to obtain a mixed gel;

[0034] 7) The mixed gel was placed in a high-temperature furnace under nitrogen protection, heated at 900° C. for 5 h, and then heated to 2000° C. for 1 h to obtain a viscose-based short fiber thermal insulation composite material.

[0035] Example 2:

[0036] 1) soaking the viscose fiber in 100° C. water for 1 hour, drying, and then soaking it in a 4wt% diammonium hydrogen phosphate aqueous solution at 60° C. for 1 hour, drying, and placing the dried product in a tube furnace, evacuating, heating to 700° C., and introducing water vapor at a flow rate of 100 ml / min for 2 hours; replacing the introduced water vapor with ammonia, heating to 900° C., and introducing ammonia at a flow rate of 100 ml / min for 4 hours; replacing the introduced ammonia with carbon dioxide at a flow rate of 100 ml / min for 0.5 hours, and then cooling to room temperature while continuing to introduce carbon dioxide to obtain a viscose-based carbon fiber;

[0037] 2) dispersing boric acid, polyvinyl alcohol, and 2,2-dihydroxybiphenyl in an ethanol solvent at a mass ratio of 1:2.5:2.5, wherein the mass ratio of boric acid to ethanol is 1:150, and adding ammonia water to adjust the pH to 5 to obtain an auxiliary material A solution;

[0038] 3) chopping the viscose-based carbon fiber obtained in step 1 to obtain short fibers, then mixing the short fibers with the auxiliary material A solution at a mass ratio of 1:3, heating at 90° C. for 3 h, and filtering to obtain a solid;

[0039] 4) placing the product of step 3 into a vacuum tube furnace, heating it at 100° C. for 2 h under nitrogen protection, then raising the temperature to 1200° C. and heat treating it for 4 h to obtain pretreated carbon fiber;

[0040] 5) Dispersing zirconium nitrate, oxalic acid, polyvinyl alcohol, and glycerol in deionized water at a mass ratio of 100:12:7:7, wherein the mass ratio of zirconium nitrate to deionized water is 12:100; stirring uniformly at 90° C. to obtain a zirconium sol; dispersing phenolic resin and polyethyleneimine in ethanol at a mass ratio of 10:1 to obtain a phenolic resin mixed solution, wherein the mass ratio of phenolic resin to ethanol is 4:100; mixing the zirconium sol and the phenolic resin mixed solution at a mass ratio of 1:2 to obtain an auxiliary material B solution;

[0041] 6) The pretreated carbon fibers of step 4, the auxiliary material B solution, ethyl orthosilicate, and dimethyldiethoxysilane were mixed uniformly in a mass ratio of 100:110:6:6, and then placed in an oven and heated for 4 hours to cross-link and solidify to obtain a mixed gel;

[0042] 7) The mixed gel was placed in a high-temperature furnace under nitrogen protection, heated at 800° C. for 7 h, and then heated to 2000° C. for 1 h to obtain a viscose-based short fiber thermal insulation composite material.

[0043] Example 3:

[0044] 1) soaking the viscose fiber in 90° C. water for 3 h, drying, and then soaking it in a 6wt% diammonium hydrogen phosphate aqueous solution at 60° C. for 3 h, drying, and placing the dried product in a tube furnace, evacuating, heating to 650° C., and introducing water vapor at a flow rate of 80 ml / min for 1 h; replacing the introduced water vapor with ammonia, heating to 900° C., and introducing ammonia at a flow rate of 80 ml / min for 2 h; replacing the introduced ammonia with carbon dioxide at a flow rate of 80 ml / min for 0.2 h, and then cooling to room temperature while continuing to introduce carbon dioxide to obtain a viscose-based carbon fiber;

[0045] 2) dispersing boric acid, polyvinyl alcohol, and 2,2-dihydroxybiphenyl in an ethanol solvent at a mass ratio of 1:2.2:2.2, wherein the mass ratio of boric acid to ethanol is 1:120, and adding ammonia water to adjust the pH to 5 to obtain an auxiliary material A solution;

[0046] 3) chopping the viscose-based carbon fiber obtained in step 1 to obtain short fibers, then mixing the short fibers with the auxiliary material A solution at a mass ratio of 1:2, heating at 80° C. for 4 h, and filtering to obtain a solid;

[0047] 4) placing the product of step 3 into a vacuum tube furnace, heating it at 120° C. for 2 h under nitrogen protection, then raising the temperature to 1200° C. and heat treating it for 5 h to obtain pretreated carbon fiber;

[0048] 5) Dispersing zirconium nitrate, oxalic acid, polyvinyl alcohol, and glycerol in deionized water at a mass ratio of 100:14:8:8, wherein the mass ratio of zirconium nitrate to deionized water is 12:100; stirring uniformly at 90° C. to obtain a zirconium sol; dispersing phenolic resin and polyethyleneimine in ethanol at a mass ratio of 10:1 to obtain a phenolic resin mixed solution, wherein the mass ratio of phenolic resin to ethanol is 6:100; mixing the zirconium sol and the phenolic resin mixed solution at a mass ratio of 1:1.6 to obtain an auxiliary material B solution;

[0049] 6) The pretreated carbon fibers of step 4, the auxiliary material B solution, ethyl orthosilicate, and dimethyldiethoxysilane were mixed uniformly in a mass ratio of 100:110:8:8, and then placed in an oven and heated for 6 hours to cross-link and solidify to obtain a mixed gel;

[0050] 7) The mixed gel was placed in a high-temperature furnace under nitrogen protection, heated at 900° C. for 7 h, and then heated to 2000° C. for 0.5 h to obtain a viscose-based short fiber thermal insulation composite material.

[0051] Example 4:

[0052] 1) soaking the viscose fiber in 90° C. water for 1 hour, drying, and then soaking it in a 5wt% diammonium hydrogen phosphate aqueous solution at 60° C. for 2 hours, drying, and placing the dried product in a tube furnace, evacuating, heating to 650° C., and introducing water vapor at a flow rate of 100 ml / min for 1 hour; replacing the introduced water vapor with ammonia, heating to 900° C., and introducing ammonia at a flow rate of 100 ml / min for 2 hours; replacing the introduced ammonia with carbon dioxide at a flow rate of 100 ml / min for 0.2 hours, and then cooling to room temperature while continuing to introduce carbon dioxide to obtain a viscose-based carbon fiber;

[0053] 2) dispersing boric acid, polyvinyl alcohol, and 2,2-dihydroxybiphenyl in an ethanol solvent at a mass ratio of 1:2.5:2.5, wherein the mass ratio of boric acid to ethanol is 1:150, and adding ammonia water to adjust the pH to 6 to obtain an auxiliary material A solution;

[0054] 3) chopping the viscose-based carbon fiber obtained in step 1 to obtain short fibers, then mixing the short fibers with the auxiliary material A solution at a mass ratio of 1:2.5, heating at 90° C. for 5 h, and filtering to obtain a solid;

[0055] 4) placing the product of step 3 into a vacuum tube furnace, heating it at 150° C. for 2 h under nitrogen protection, then raising the temperature to 1200° C. and heat treating it for 5 h to obtain pretreated carbon fiber;

[0056] 5) Dispersing zirconium nitrate, oxalic acid, polyvinyl alcohol, and glycerol in deionized water at a mass ratio of 100:15:10:10, wherein the mass ratio of zirconium nitrate to deionized water is 15:100; stirring uniformly at 90° C. to obtain a zirconium sol; dispersing phenolic resin and polyethyleneimine in ethanol at a mass ratio of 10:1 to obtain a phenolic resin mixed solution, wherein the mass ratio of phenolic resin to ethanol is 6:100; mixing the zirconium sol and the phenolic resin mixed solution at a mass ratio of 1:1.8 to obtain an auxiliary material B solution;

[0057] 6) The pretreated carbon fibers of step 4, the auxiliary material B solution, ethyl orthosilicate, and dimethyldiethoxysilane were mixed uniformly in a mass ratio of 100:120:10:10, and then placed in an oven and heated for 6 hours to crosslink and solidify to obtain a mixed gel;

[0058] 7) Place the mixed gel in a high temperature furnace under nitrogen protection and heat at 900℃ for 7h, then raise the temperature to

[0059] After heating at 2000℃ for 1h, a viscose-based short fiber thermal insulation composite material was obtained.

[0060] Comparative Example 1 (without pretreatment)

[0061] 1) placing the viscose fiber in a tube furnace, evacuating the temperature, heating to 900° C., maintaining the temperature for 2 h, and then cooling the temperature to room temperature to obtain a viscose-based carbon fiber;

[0062] 2) dispersing boric acid, polyvinyl alcohol, and 2,2-dihydroxybiphenyl in an ethanol solvent at a mass ratio of 1:2.2:2.2, wherein the mass ratio of boric acid to ethanol is 1:120, and adding ammonia water to adjust the pH to 5 to obtain an auxiliary material A solution;

[0063] 3) chopping the viscose-based carbon fiber obtained in step 1 to obtain short fibers, then mixing the short fibers with the auxiliary material A solution at a mass ratio of 1:2, heating at 80° C. for 4 h, and filtering to obtain a solid;

[0064] 4) placing the product of step 3 into a vacuum tube furnace, heating it at 120° C. for 2 h under nitrogen protection, then raising the temperature to 1200° C. and heat treating it for 5 h to obtain pretreated carbon fiber;

[0065] 5) Dispersing zirconium nitrate, oxalic acid, polyvinyl alcohol, and glycerol in deionized water at a mass ratio of 100:14:8:8, wherein the mass ratio of zirconium nitrate to deionized water is 12:100; stirring uniformly at 90° C. to obtain a zirconium sol; dispersing phenolic resin and polyethyleneimine in ethanol at a mass ratio of 10:1 to obtain a phenolic resin mixed solution, wherein the mass ratio of phenolic resin to ethanol is 6:100; mixing the zirconium sol and the phenolic resin mixed solution at a mass ratio of 1:1.6 to obtain an auxiliary material B solution;

[0066] 6) The pretreated carbon fibers of step 4, the auxiliary material B solution, ethyl orthosilicate, and dimethyldiethoxysilane were mixed uniformly in a mass ratio of 100:110:8:8, and then placed in an oven and heated for 6 hours to cross-link and solidify to obtain a mixed gel;

[0067] 7) The mixed gel was placed in a high-temperature furnace under nitrogen protection, heated at 900° C. for 7 h, and then heated to 2000° C. for 0.5 h to obtain a viscose-based short fiber thermal insulation composite material.

[0068] Comparative Example 2 (without boron carbide coating)

[0069] 1) soaking the viscose fiber in 90° C. water for 3 h, drying, and then soaking it in a 6wt% diammonium hydrogen phosphate aqueous solution at 60° C. for 3 h, drying, and placing the dried product in a tube furnace, evacuating, heating to 650° C., and introducing water vapor at a flow rate of 80 ml / min for 1 h; replacing the introduced water vapor with ammonia, heating to 900° C., and introducing ammonia at a flow rate of 80 ml / min for 2 h; replacing the introduced ammonia with carbon dioxide at a flow rate of 80 ml / min for 0.2 h, and then cooling to room temperature while continuing to introduce carbon dioxide to obtain a viscose-based carbon fiber;

[0070] 2) chopping the viscose-based carbon fiber obtained in step 1 to obtain short fibers, placing the short fibers in a vacuum tube furnace, heating them at 120° C. for 2 h under nitrogen protection, then heating them to 1200° C. and heat treating them for 5 h to obtain carbon fibers;

[0071] 3) Dispersing zirconium nitrate, oxalic acid, polyvinyl alcohol, and glycerol in deionized water at a mass ratio of 100:14:8:8, wherein the mass ratio of zirconium nitrate to deionized water is 12:100; stirring uniformly at 90° C. to obtain a zirconium sol; dispersing phenolic resin and polyethyleneimine in ethanol at a mass ratio of 10:1 to obtain a phenolic resin mixed solution, wherein the mass ratio of phenolic resin to ethanol is 6:100; mixing the zirconium sol and the phenolic resin mixed solution at a mass ratio of 1:1.6 to obtain an auxiliary material B solution;

[0072] 4) The carbon fiber from step 2, auxiliary material B solution, ethyl orthosilicate, and dimethyldiethoxysilane were mixed uniformly in a mass ratio of 100:110:8:8, and then placed in an oven and heated for 6 hours to cross-link and solidify to obtain a mixed gel;

[0073] 5) The mixed gel was placed in a high-temperature furnace under nitrogen protection, heated at 900° C. for 7 h, and then heated to 2000° C. for 0.5 h to obtain a viscose-based short fiber thermal insulation composite material.

[0074] Comparative Example 3 (auxiliary material A without 2,2-dihydroxybiphenyl)

[0075] 1) soaking the viscose fiber in 90° C. water for 3 h, drying, and then soaking it in a 6wt% diammonium hydrogen phosphate aqueous solution at 60° C. for 3 h, drying, and placing the dried product in a tube furnace, evacuating, heating to 650° C., and introducing water vapor at a flow rate of 80 ml / min for 1 h; replacing the introduced water vapor with ammonia, heating to 900° C., and introducing ammonia at a flow rate of 80 ml / min for 2 h; replacing the introduced ammonia with carbon dioxide at a flow rate of 80 ml / min for 0.2 h, and then cooling to room temperature while continuing to introduce carbon dioxide to obtain a viscose-based carbon fiber;

[0076] 2) dispersing boric acid and polyvinyl alcohol in an ethanol solvent at a mass ratio of 1:2.2, wherein the mass ratio of boric acid to ethanol is 1:120, and adding ammonia water to adjust the pH to 5 to obtain an auxiliary material A solution;

[0077] 3) chopping the viscose-based carbon fiber obtained in step 1 to obtain short fibers, then mixing the short fibers with the auxiliary material A solution at a mass ratio of 1:2, heating at 80° C. for 4 h, and filtering to obtain a solid;

[0078] 4) placing the product of step 3 into a vacuum tube furnace, heating it at 120° C. for 2 h under nitrogen protection, then raising the temperature to 1200° C. and heat treating it for 5 h to obtain pretreated carbon fiber;

[0079] 5) Dispersing zirconium nitrate, oxalic acid, polyvinyl alcohol, and glycerol in deionized water at a mass ratio of 100:14:8:8, wherein the mass ratio of zirconium nitrate to deionized water is 12:100; stirring uniformly at 90° C. to obtain a zirconium sol; dispersing phenolic resin and polyethyleneimine in ethanol at a mass ratio of 10:1 to obtain a phenolic resin mixed solution, wherein the mass ratio of phenolic resin to ethanol is 6:100; mixing the zirconium sol and the phenolic resin mixed solution at a mass ratio of 1:1.6 to obtain an auxiliary material B solution;

[0080] 6) The pretreated carbon fibers of step 4, the auxiliary material B solution, ethyl orthosilicate, and dimethyldiethoxysilane were mixed uniformly in a mass ratio of 100:110:8:8, and then placed in an oven and heated for 6 hours to cross-link and solidify to obtain a mixed gel;

[0081] 7) The mixed gel was placed in a high-temperature furnace under nitrogen protection, heated at 900° C. for 7 h, and then heated to 2000° C. for 0.5 h to obtain a viscose-based short fiber thermal insulation composite material.

[0082] Comparative Example 4 (auxiliary material B without adding polyethyleneimine)

[0083] 1) soaking the viscose fiber in 90° C. water for 3 h, drying, and then soaking it in a 6wt% diammonium hydrogen phosphate aqueous solution at 60° C. for 3 h, drying, and placing the dried product in a tube furnace, evacuating, heating to 650° C., and introducing water vapor at a flow rate of 80 ml / min for 1 h; replacing the introduced water vapor with ammonia, heating to 900° C., and introducing ammonia at a flow rate of 80 ml / min for 2 h; replacing the introduced ammonia with carbon dioxide at a flow rate of 80 ml / min for 0.2 h, and then cooling to room temperature while continuing to introduce carbon dioxide to obtain a viscose-based carbon fiber;

[0084] 2) dispersing boric acid, polyvinyl alcohol, and 2,2-dihydroxybiphenyl in an ethanol solvent at a mass ratio of 1:2.2:2.2, wherein the mass ratio of boric acid to ethanol is 1:120, and adding ammonia water to adjust the pH to 5 to obtain an auxiliary material A solution;

[0085] 3) chopping the viscose-based carbon fiber obtained in step 1 to obtain short fibers, then mixing the short fibers with the auxiliary material A solution at a mass ratio of 1:2, heating at 80° C. for 4 h, and filtering to obtain a solid;

[0086] 4) placing the product of step 3 into a vacuum tube furnace, heating it at 120° C. for 2 h under nitrogen protection, then raising the temperature to 1200° C. and heat treating it for 5 h to obtain pretreated carbon fiber;

[0087] 5) Dispersing zirconium nitrate, oxalic acid, polyvinyl alcohol, and glycerol in deionized water at a mass ratio of 100:14:8:8, wherein the mass ratio of zirconium nitrate to deionized water is 12:100; stirring uniformly at 90° C. to obtain a zirconium sol; dispersing phenolic resin in ethanol to obtain a phenolic resin mixed solution, wherein the mass ratio of phenolic resin to ethanol is 6:100; mixing the zirconium sol and the phenolic resin mixed solution at a mass ratio of 1:1.6 to obtain an auxiliary material B solution;

[0088] 6) The pretreated carbon fibers of step 4, the auxiliary material B solution, ethyl orthosilicate, and dimethyldiethoxysilane were mixed uniformly in a mass ratio of 100:110:8:8, and then placed in an oven and heated for 6 hours to cross-link and solidify to obtain a mixed gel;

[0089] 7) The mixed gel was placed in a high-temperature furnace under nitrogen protection, heated at 900° C. for 7 h, and then heated to 2000° C. for 0.5 h to obtain a viscose-based short fiber thermal insulation composite material.

[0090] Comparative Example 5 (pretreatment without oxidation)

[0091] 1) soaking the viscose fiber in 90° C. water for 3 h, drying, and then soaking in a 6 wt % diammonium hydrogen phosphate aqueous solution at 60° C. for 3 h, drying, placing the dried product in a tube furnace, evacuating, introducing ammonia, heating to 900° C. at a flow rate of 80 ml / min, and maintaining for 2 h; replacing the introduced ammonia with carbon dioxide at a flow rate of 80 ml / min, maintaining for 0.2 h, and then cooling to room temperature while continuing to introduce carbon dioxide to obtain a viscose-based carbon fiber;

[0092] 2) dispersing boric acid, polyvinyl alcohol, and 2,2-dihydroxybiphenyl in an ethanol solvent at a mass ratio of 1:2.2:2.2, wherein the mass ratio of boric acid to ethanol is 1:120, and adding ammonia water to adjust the pH to 5 to obtain an auxiliary material A solution;

[0093] 3) chopping the viscose-based carbon fiber obtained in step 1 to obtain short fibers, then mixing the short fibers with the auxiliary material A solution at a mass ratio of 1:2, heating at 80° C. for 4 h, and filtering to obtain a solid;

[0094] 4) placing the product of step 3 into a vacuum tube furnace, heating it at 120° C. for 2 h under nitrogen protection, then raising the temperature to 1200° C. and heat treating it for 5 h to obtain pretreated carbon fiber;

[0095] 5) Dispersing zirconium nitrate, oxalic acid, polyvinyl alcohol, and glycerol in deionized water at a mass ratio of 100:14:8:8, wherein the mass ratio of zirconium nitrate to deionized water is 12:100; stirring uniformly at 90° C. to obtain a zirconium sol; dispersing phenolic resin and polyethyleneimine in ethanol at a mass ratio of 10:1 to obtain a phenolic resin mixed solution, wherein the mass ratio of phenolic resin to ethanol is 6:100; mixing the zirconium sol and the phenolic resin mixed solution at a mass ratio of 1:1.6 to obtain an auxiliary material B solution;

[0096] 6) The pretreated carbon fibers of step 4, the auxiliary material B solution, ethyl orthosilicate, and dimethyldiethoxysilane were mixed uniformly in a mass ratio of 100:110:8:8, and then placed in an oven and heated for 6 hours to cross-link and solidify to obtain a mixed gel;

[0097] 7) The mixed gel was placed in a high-temperature furnace under nitrogen protection, heated at 900° C. for 7 h, and then heated to 2000° C. for 0.5 h to obtain a viscose-based short fiber thermal insulation composite material.

[0098] Comparative Example 6 (No carbonized nitrogen layer was formed after pretreatment)

[0099] 1) soaking the viscose fiber in 90° C. water for 3 h, drying, and then soaking in a 6 wt % diammonium hydrogen phosphate aqueous solution at 60° C. for 3 h, drying, and placing the dried product in a tube furnace, evacuating, heating to 650° C., and introducing water vapor at a flow rate of 80 ml / min for 1 h; replacing the introduced water vapor with ammonia gas, heating to 900° C. at a flow rate of 80 ml / min for 2 h, and then cooling to room temperature to obtain a viscose-based carbon fiber;

[0100] 2) dispersing boric acid, polyvinyl alcohol, and 2,2-dihydroxybiphenyl in an ethanol solvent at a mass ratio of 1:2.2:2.2, wherein the mass ratio of boric acid to ethanol is 1:120, and adding ammonia water to adjust the pH to 5 to obtain an auxiliary material A solution;

[0101] 3) chopping the viscose-based carbon fiber obtained in step 1 to obtain short fibers, then mixing the short fibers with the auxiliary material A solution at a mass ratio of 1:2, heating at 80° C. for 4 h, and filtering to obtain a solid;

[0102] 4) placing the product of step 3 into a vacuum tube furnace, heating it at 120° C. for 2 h under nitrogen protection, then raising the temperature to 1200° C. and heat treating it for 5 h to obtain pretreated carbon fiber;

[0103] 5) Dispersing zirconium nitrate, oxalic acid, polyvinyl alcohol, and glycerol in deionized water at a mass ratio of 100:14:8:8, wherein the mass ratio of zirconium nitrate to deionized water is 12:100; stirring uniformly at 90° C. to obtain a zirconium sol; dispersing phenolic resin and polyethyleneimine in ethanol at a mass ratio of 10:1 to obtain a phenolic resin mixed solution, wherein the mass ratio of phenolic resin to ethanol is 6:100; mixing the zirconium sol and the phenolic resin mixed solution at a mass ratio of 1:1.6 to obtain an auxiliary material B solution;

[0104] 6) The pretreated carbon fibers of step 4, the auxiliary material B solution, ethyl orthosilicate, and dimethyldiethoxysilane were mixed uniformly in a mass ratio of 100:110:8:8, and then placed in an oven and heated for 6 hours to cross-link and solidify to obtain a mixed gel;

[0105] 7) The mixed gel was placed in a high-temperature furnace under nitrogen protection, heated at 900° C. for 7 h, and then heated to 2000° C. for 0.5 h to obtain a viscose-based short fiber thermal insulation composite material.

[0106] Test data

[0107] In the embodiments and comparative examples of the present invention, the process is adjusted in the comparative examples to demonstrate the influence of various process parameters on product performance. The product prepared by the method of the present invention has good thermal insulation performance and good mechanical strength.

[0108] Thermal conductivity: Place the sample in an intelligent double-plate thermal conductivity tester to test the thermal conductivity of the sample at room temperature.

[0109] Compressive strength: Load the sample at a speed of 10 mm / min. The load when the sample is compressed and deformed by 5% is the failure load and the failure load P1 is recorded.

[0110] Compressive strength calculation formula: A = P1 / S;

[0111] A is the compressive strength of the sample, MPa; P1 is the breaking load of the sample, unit N; S is the compressive area of ​​the sample, unit mm 2 .

[0112] The test results are shown in Table 1 below:

[0113] Table 1

[0114] <![CDATA[Density (g / cm 3 )]]> Thermal conductivity (W / m·K) Compressive strength (MPa) Example 1 0.182 0.136 4.02 Example 2 0.185 0.137 4.10 Example 3 0.191 0.134 4.08 Example 4 0.179 0.135 4.06 Comparative Example 1 0.175 0.105 3.65 Comparative Example 2 0.190 0.192 3.20 Comparative Example 3 0.185 0.176 3.85 Comparative Example 4 0.180 0.180 3.75 Comparative Example 5 0.188 0.186 3.90 Comparative Example 6 0.183 0.195 3.75

[0115] By comparing the embodiments and comparative examples, it can be seen that the mechanical strength and dispersion performance of carbon fibers affect the mechanical properties and thermal insulation performance of the product. The higher the mechanical strength of the fiber and the more uniform the dispersion, the better the compressive performance of the product. Reducing the aggregation of carbon fibers is also beneficial to reducing thermal conductivity, that is, improving thermal insulation performance. Referring to comparative examples 1, 5, and 6, it can be seen that pre-treating the fibers can effectively improve the mechanical strength and dispersion performance of the fibers; and referring to comparative examples 2 and 3, it can be seen that the boron nitride coating of the product and the presence of 2,2-dihydroxybiphenyl in auxiliary material A have a significant effect on the performance of the product. Referring to comparative example 4, it can be seen that in auxiliary material B, polyethyleneimine has an effect on the performance of the product; the product obtained by the present invention is obtained by oxidizing the viscose fiber at high temperature under water vapor to generate oxidized groups on the surface of the viscose fiber, thereby improving the activation efficiency of the amino groups on its surface by ammonia at high temperature, and then the nitrogen-containing groups and the subsequent addition of carbon dioxide at high temperature The carbonized nitrogen groups can improve the surface activity of the fiber and at the same time improve the mechanical strength of the fiber; 2,2-dihydroxybiphenyl can form a stable high-temperature protective layer of boron carbide on the surface of the pretreated carbon fiber at high temperature, thereby reducing the degradation rate of the carbon fiber during subsequent high-temperature carbonization, protecting the carbon fiber and providing excellent mechanical properties, and the presence of boron carbide can also effectively improve the interfacial bonding state of the fiber and the zirconium dioxide ceramic; the charge adsorption capacity of polyethyleneimine can disperse the carbon fiber more evenly during the dispersion process, thereby improving the dispersion performance of the carbon fiber in the gel and improving the mechanical properties of the material, and the chopped carbon fiber and ceramic powder can increase the packing density of the gel, while the phenolic resin and polyethyleneimine are decomposed into porous carbon during the high-temperature carbonization process, thereby improving the density and strength of the thermal insulation material while improving the thermal insulation performance.

[0116] Although the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as limiting the present invention.

Claims

1. A method for preparing a viscose-based short fiber thermal insulation composite material, characterized in that: The method comprises: 1) pretreating the viscose fiber, then placing the treated viscose fiber in a tube furnace, evacuating, heating to 600-700° C., introducing water vapor at a flow rate of 50-100 ml / min, and maintaining for 1-2 hours; replacing the introduced water vapor with ammonia, raising the temperature to 850-900° C., introducing ammonia at a flow rate of 50-100 ml / min, and maintaining for 2-4 hours; replacing the introduced ammonia with carbon dioxide at a flow rate of 50-100 ml / min, and maintaining for 0.2-0.5 hours, and then continuing to introduce carbon dioxide and cooling to room temperature to obtain a viscose-based carbon fiber; 2) dispersing boric acid, polyvinyl alcohol, and 2,2-dihydroxybiphenyl in an ethanol solvent at a mass ratio of 1:2-2.5:2-2.5, wherein the mass ratio of boric acid to ethanol is 1:100-150, and adding ammonia water to adjust the pH to 4-6 to obtain an auxiliary material A solution; 3) chopping the viscose-based carbon fibers obtained in step 1 to obtain short fibers, mixing the short fibers with the auxiliary material A solution at a mass ratio of 1:1.5-3, heating at 70-90° C. for 3-6 hours, and filtering to obtain a solid; 4) placing the product of step 3 into a vacuum tube furnace and heat-treating it under nitrogen protection to obtain pretreated carbon fiber; 5) Dispersing zirconium nitrate, oxalic acid, polyvinyl alcohol, and glycerol in deionized water at a mass ratio of 100:10-15:5-10:5-10, wherein the mass ratio of zirconium nitrate to deionized water is 10-15:100; stirring at 80-90° C. to obtain a zirconium sol; dispersing phenolic resin and polyethyleneimine in ethanol at a mass ratio of 10:1 to obtain a phenolic resin mixed solution, wherein the mass ratio of phenolic resin to ethanol is 3-6:100; mixing the zirconium sol and the phenolic resin mixed solution at a mass ratio of 1:1.5-2 to obtain an auxiliary material B solution; 6) The pretreated carbon fibers from step 4, the auxiliary material B solution, ethyl orthosilicate, and dimethyldiethoxysilane were mixed evenly, placed in an oven, heated, and cross-linked to obtain a mixed gel; 7) placing the mixed gel in a high-temperature furnace under nitrogen protection and heat treatment to obtain a viscose-based short fiber thermal insulation composite material.

2. The method for preparing the viscose-based short fiber thermal insulation composite material according to claim 1, characterized in that: The pretreatment process in step 1 includes soaking the viscose fiber in 90-100° C. water for 0.5-3 hours, drying, then soaking in 50-70° C. diammonium hydrogen phosphate aqueous solution with a concentration of 3-6 wt% for 0.5-3 hours, and drying.

3. The method for preparing the viscose-based short fiber thermal insulation composite material according to claim 1, characterized in that: In the step 4, the product of step 3 is placed in a vacuum tube furnace, heated at 100-150° C. for 1-2 hours under nitrogen protection, and then heated to 1000-1200° C. and heat treated for 4-6 hours to obtain pretreated carbon fiber.

4. The method for preparing the viscose-based short fiber thermal insulation composite material according to claim 1, wherein: In step 6, the pretreated carbon fiber of step 4, auxiliary material B solution, ethyl orthosilicate, and dimethyldiethoxysilane are evenly mixed in a mass ratio of 100:100-120:5-10:5-10, placed in an oven and heated for 2-6 hours to cross-link and solidify to obtain a mixed gel.

5. The method for preparing the viscose-based short fiber thermal insulation composite material according to claim 1, wherein: In step 7, the mixed gel is placed in a high-temperature furnace, protected by nitrogen, and heated at 800-900° C. for 5-7 hours, and then heated to 2000-2200° C. for 0.5-1 hour to obtain a viscose-based short fiber thermal insulation composite material.

6. A viscose-based short fiber thermal insulation composite material, characterized by: The material is prepared by the method according to any one of claims 1 to 5.