A method for preparing high-density flame-retardant gypsum-based fiberboard

Abstract

The present invention relates to the field of building materials technology, specifically a method for preparing a high-density, flame-retardant gypsum-based fiberboard. The method comprises the following steps: Step 1: aminating alkaline lignin and then grafting DOPO; Step 2: carboxylating wood fibers and then grafting 4-(6-amino-3-pyridyl)piperazine-1-tert-butyl carboxylate; Step 3: preparing a modified wood fiber liquid using polysiloxane and the modified wood fibers; Step 4: preparing a gypsum fiber slurry, forming a slab, and applying pressure, maintaining the pressure, maintaining the slab, and drying the slab to obtain a high-density, flame-retardant gypsum-based fiberboard. The high-density, flame-retardant gypsum-based fiberboard comprises the following components, by weight: 45-65 parts of gypsum powder, 110-130 parts of deionized water, 0.05-0.07 parts of a retarder, 8-15 parts of modified lignin, and 20-30 parts of the modified wood fiber liquid.

Description

Technical Field

[0001] The invention relates to the technical field of building materials, in particular to a method for preparing a high-density flame-retardant gypsum-based fiberboard. Background Art

[0002] With the continuous advancement of urban modernization and the rapid growth of housing construction, gypsum-based fiberboard has partially replaced cement board materials as a building material due to its superior comfort and strength. Gypsum-based fiberboard can be used in drywall, partition boards, and wainscoting. Its ease of handling and resistance to damage have led to its increasing use in the construction industry. However, gypsum-based fiberboard's fire resistance and flame retardancy are inferior to those of cement-steel boards, and its flame retardancy is relatively poor. Furthermore, the majority of existing fiberboard products suffer from insufficient overall density, resulting in poor strength and significantly limiting its widespread use in construction.

[0003] In summary, the present invention will prepare a high-density flame-retardant gypsum-based fiberboard, which is of great significance. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing a high-density flame-retardant gypsum-based fiberboard to solve the problems raised in the above background technology.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] Step 1: alkaline lignin is subjected to amination treatment and then grafted with DOPO to obtain modified lignin;

[0007] Step 2: Carboxylating the wood fiber and then grafting it with tert-butyl 4-(6-amino-3-pyridyl)piperazine-1-carboxylate to obtain modified wood fiber;

[0008] Step 3: Dimethylpolysiloxane, sodium methylsiliconate, and tert-butyl 4-(6-amino-3-pyridyl)piperazine-1-carboxylate are mixed evenly, and then modified wood fiber is added and stirred evenly to obtain a modified wood fiber liquid;

[0009] Step 4: Gypsum powder, deionized water, and retarder are mixed and stirred evenly to obtain gypsum slurry; modified lignin and modified wood fiber liquid are then added, and the mixture is continued to be mixed and stirred to obtain gypsum fiber slurry; the gypsum fiber slurry is formed into a slab, and finally pressurized, maintained, maintained, and dried to obtain a high-density flame-retardant gypsum-based fiberboard.

[0010] Furthermore, the preparation method of the modified lignin is as follows: (1) adding alkaline lignin to deionized water under mechanical stirring, adding 5-15wt% sodium hydroxide solution to adjust the pH value to 8-10, adjusting the temperature to 40-60°C, and dissolving the alkaline lignin; (2) heating the reaction solution to 70-100°C, adding sodium dodecylbenzenesulfonate and formaldehyde, mechanically stirring for 30-60 minutes, then adding dodecylamine, continuing to stir and react for 3-6 hours, terminating the reaction, and allowing it to cool naturally to room temperature to obtain an aminated lignin solution; (3) mixing DOPO and formaldehyde to obtain a mixed solution, adjusting the temperature of the aminated lignin solution to 50-70°C, and dropping the mixed solution into the aminated lignin solution under stirring. After reacting for 6-12 hours, terminating the reaction, allowing it to cool naturally to room temperature, and adding hydrochloric acid solution to adjust the pH value to 6.5-7.2 to obtain modified lignin.

[0011] Furthermore, the mass ratio of the raw materials alkaline lignin, sodium dodecylbenzenesulfonate, formaldehyde and dodecylamine in the aminated lignin solution is 1:(0.003-0.01):(0.1-0.3):(0.1-0.3).

[0012] Furthermore, the mass ratio of the raw materials DOPO and formaldehyde in the mixed solution is (7-8):1.

[0013] Furthermore, the preparation method of the modified wood fiber is as follows: (1) placing the wood fiber in a mixed acid solution and ultrasonically treating it for 2 to 10 hours, filtering, washing, and drying to obtain carboxylated wood fiber; (2) dissolving tert-butyl 4-(6-amino-3-pyridyl)piperazine-1-carboxylate in N,N-diisopropylethylamine to prepare a uniform solution A with a concentration of 0.025 to 0.035 mol / L, then adding the carboxylated wood fiber to N,N-diisopropylethylamine, and ultrasonically dispersing it for 30 to 60 minutes to obtain a suspension B; (3) adding 4-pyrrolidinopyridine to the suspension B, heating it to 90 to 110° C., stirring it at a speed of 200 to 400 r / min, adding solution A while stirring, keeping the temperature constant, stirring for 12 to 24 hours, terminating the reaction, waiting for it to naturally cool to room temperature, filtering, washing, and drying to obtain modified wood fiber.

[0014] Furthermore, the mixed acid solution is prepared by mixing 98 wt % concentrated sulfuric acid and 35 wt % nitric acid in a ratio of 1:1.

[0015] Furthermore, the mass ratio of the tert-butyl 4-(6-amino-3-pyridyl)piperazine-1-carboxylate and the carboxylated wood fiber is (1-2):1; and the amount of the added 4-pyrrolidinopyridine is 2-5% of the mass of the carboxylated wood fiber.

[0016] Furthermore, the mass ratio of dimethylpolysiloxane, sodium methylsiliconate, tert-butyl 4-(6-amino-3-pyridyl)piperazine-1-carboxylate and modified wood fiber in the modified wood fiber liquid is (2-5):1:(60-80):(30-60).

[0017] Furthermore, the high-density flame-retardant gypsum-based fiberboard includes the following components: by weight: 45-65 parts of gypsum powder, 110-130 parts of deionized water, 0.05-0.07 parts of retarder, 8-15 parts of modified lignin, and 20-30 parts of modified wood fiber liquid.

[0018] Furthermore, the pressurizing pressure is 2-3.5 MPa, and the pressurizing time is 30-60 minutes; the holding pressure is 1-2 MPa, and the holding time is 12-24 hours; the maintenance temperature is 50-70°C, the maintenance humidity is 80-90%, and the maintenance time is 3-7 days; the drying temperature is 65-80°C, and the drying time is 12-24 hours.

[0019] Compared with the prior art, the present invention has the following beneficial effects: the present invention modifies alkaline lignin and grafts DOPO on its surface, further promoting the flame retardant properties of the alkaline lignin, and then using it as an additive to improve the flame retardant properties of the fiberboard; at the same time, the present invention improves the wood fiber to have good dispersion, thereby enhancing the density of the fiberboard, and also introduces a large number of flame retardant groups, thereby improving the flame retardant properties of the fiberboard;

[0020] (1) Alkaline lignin has a rich structure of aromatic rings and aromatic hydroxyl groups, and can be used as an additive to improve the strength of gypsum fiberboard. In addition, after pyrolysis, it generates a dense carbon layer, which can prevent the diffusion of oxygen and heat. Therefore, it can also be used as an efficient flame retardant additive. In order to further improve the density and flame retardancy of gypsum-based fiberboard, the alkaline lignin was treated with amination to introduce amino groups on its surface, and then reacted with DOPO for grafting, introducing nitrogen and phosphorus elements, which synergistically formed a carbon layer after pyrolysis to achieve a better flame retardant effect.

[0021] (2) Due to the poor dispersibility of wood fiber, in the scheme, the wood fiber is first treated with carboxylation to introduce carboxyl groups on its surface, and then reacted with 4-(6-amino-3-pyridyl)piperazine-1-carboxylic acid tert-butyl ester for grafting, which not only improves the dispersibility, but also introduces amide groups, pyridine groups, etc., which can improve heat resistance and improve flame retardancy to a certain extent; the modified wood fiber is mixed with 4-(6-amino-3-pyridyl)piperazine-1-carboxylic acid tert-butyl ester, dimethyl polysiloxane, and sodium methyl siliconate to prepare a modified wood fiber liquid, among which 4-(6-amino-3-pyridyl)piperazine-1-carboxylic acid tert-butyl ester can further promote the dispersibility of the modified wood fiber, and dimethyl polysiloxane has good flexibility and high temperature resistance, and can adapt to the temperature changes during the pressurization, pressure holding, maintenance, and drying of the fiberboard, which greatly guarantees the quality of the fiberboard and makes it have better performance. Sodium methyl siliconate works together with dimethyl polysiloxane to enhance the flame retardancy. DETAILED DESCRIPTION

[0022] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0023] In the following examples, the purity of alkaline lignin is 99%, CAS number: 8068-05-1, item number: L3308880 (Shanghai Aladdin Biochemical Technology Co., Ltd.), the purity of sodium hydroxide is 99% (Henan Tianfu Chemical Co., Ltd.), the purity of sodium dodecylbenzenesulfonate is 98% (Dusi Tiande Biotechnology Co., Ltd.), the purity of formaldehyde, dodecylamine, and DOPO is 97%, item number: S46419 (Shanghai Yuanye Biotechnology Co., Ltd.), wood fiber model HP54-60 (Dongguan Jinshixiang Plastic Raw Materials Co., Ltd.), sulfuric acid purity is 98wt% (Nanjing Reagent Co., Ltd.), nitric acid concentration is 35wt% (Nanjing Reagent Co., Ltd.), the purity of tert-butyl 4-(6-amino-3-pyridyl)piperazine-1-carboxylate is 98%, CAS number: 571188-59-5, article number: T161525 (Shanghai Aladdin Biochemical Technology Co., Ltd.), the purity of N,N-diisopropylethylamine is 99.5%, CAS number: 7087-68-5 (Kunshan Huierzhong Chemical Co., Ltd.), the purity of 4-pyrrolidinopyridine is 99%, CAS number: 2456-87-7 (Hebei Zhentian Food Additive Co., Ltd.), the purity of dimethylpolysiloxane is 99%, article number: T22990 (Shanghai Yuanye Biotechnology Co., Ltd.), the purity of sodium methylsiliconate is 99% (Wuhan Jixin Yibang Biotechnology Co., Ltd.), the purity of gypsum powder is 100% (Tai'an Jiangzhou Biotechnology Co., Ltd.), and the retarder model is YLD-HNJ01 (Shandong Yonglida New Materials Technology Co., Ltd.).

[0024] Example 1: A method for preparing a high-density flame-retardant gypsum-based fiberboard:

[0025] Step 1: Preparation method of modified lignin: (1) Under mechanical stirring, 20 parts of alkaline lignin are added to sufficient deionized water, 10 wt% sodium hydroxide solution is added to adjust the pH value to 10, and the temperature is adjusted to 50°C to dissolve the alkaline lignin; (2) The reaction solution is heated to 90°C, 0.16 parts of sodium dodecylbenzenesulfonate and 4 parts of formaldehyde are added, and mechanical stirring is carried out for 60 minutes. Then 4 parts of dodecylamine are added, and the stirring reaction is continued for 5 hours. The reaction is terminated and the mixture is allowed to cool naturally to room temperature to obtain an aminated lignin solution; (3) 7.3 parts of DOPO and 1 part of formaldehyde are mixed to obtain a mixed solution, the temperature of the aminated lignin solution is adjusted to 55°C, and the mixed solution is dropped into the aminated lignin solution under stirring. After the reaction is allowed to react for 10 hours, the reaction is terminated and the mixture is allowed to cool naturally to room temperature. Hydrochloric acid solution is added to adjust the pH value to 7.0, and the modified lignin is obtained by filtration;

[0026] Step 2: The preparation method of modified wood fiber is as follows: (1) 30 parts of wood fiber are added to a mixed acid solution and ultrasonically treated for 5 hours, and then filtered, washed, and dried to obtain carboxylated wood fiber; (2) 8 parts of 4-(6-amino-3-pyridyl)piperazine-1-carboxylic acid tert-butyl ester are dissolved in N,N-diisopropylethylamine to prepare a solution A with a concentration of 0.03 mol / L, and then 5 parts of carboxylated wood fiber are added to an equal amount of N,N-diisopropylethylamine, and ultrasonically dispersed for 60 minutes to obtain a suspension B; (3) 0.18 parts of 4-pyrrolidinopyridine are added to the suspension B, the temperature is raised to 100°C, and the suspension is stirred at a speed of 300 r / min. Solution A is added while stirring, the temperature is kept constant, and the suspension is stirred for 24 hours. The reaction is terminated, and the suspension is naturally cooled to room temperature, filtered, washed, and dried to obtain modified wood fiber;

[0027] Step 3: Evenly mix 1 part of dimethylpolysiloxane, 0.3 parts of sodium methylsiliconate, and 20 parts of tert-butyl 4-(6-amino-3-pyridyl)piperazine-1-carboxylate, then add 16 parts of modified wood fiber and continue stirring to obtain a modified wood fiber liquid;

[0028] Step 4: Gypsum powder, deionized water, and retarder are mixed and stirred uniformly to obtain gypsum slurry; modified lignin and modified wood fiber liquid are then added, and the mixture is continued to be mixed and stirred to obtain gypsum fiber slurry; the gypsum fiber slurry is formed into a 9 mm thick slab, which is then pressurized at a pressure of 3 MPa for 60 minutes to press it together, and then maintained at a pressure of 2 MPa for 24 hours, and then maintained at 65°C and 80% humidity for 7 days. Finally, it is dried at 65°C for 24 hours to obtain a high-density flame-retardant gypsum-based fiberboard;

[0029] The gypsum fiber slurry includes the following components, calculated in parts by weight: 55 parts of gypsum powder, 120 parts of deionized water, 0.05 parts of retarder, 12 parts of modified lignin, and 28 parts of modified wood fiber liquid.

[0030] Example 2: A method for preparing a high-density flame-retardant gypsum-based fiberboard:

[0031] Step 1: Preparation method of modified lignin: (1) Under mechanical stirring, add 20 parts of alkaline lignin to sufficient deionized water, add 5wt% sodium hydroxide solution to adjust the pH value to 8, adjust the temperature to 40°C, and dissolve the alkaline lignin; (2) Heat the reaction solution to 70°C, add 0.06 parts of sodium dodecylbenzenesulfonate and 2 parts of formaldehyde, mechanically stir for 30 minutes, then add 2 parts of dodecylamine, continue stirring and react for 3 hours, terminate the reaction, and wait for it to cool naturally to room temperature to obtain an aminated lignin solution; (3) Mix 7 parts of DOPO and 1 part of formaldehyde to obtain a mixed solution, adjust the temperature of the aminated lignin solution to 55°C, and drop the mixed solution into the aminated lignin solution under stirring. After reacting for 6 hours, terminate the reaction, wait for it to cool naturally to room temperature, add hydrochloric acid solution to adjust the pH value to 7.0, and filter to obtain modified lignin;

[0032] Step 2: The preparation method of modified wood fiber is as follows: (1) 30 parts of wood fiber are added to a mixed acid solution and ultrasonically treated for 2 hours, and then filtered, washed, and dried to obtain carboxylated wood fiber; (2) 5 parts of 4-(6-amino-3-pyridyl)piperazine-1-carboxylic acid tert-butyl ester are dissolved in N,N-diisopropylethylamine to prepare a solution A with a concentration of 0.025 mol / L, and then 5 parts of carboxylated wood fiber are added to an equal amount of N,N-diisopropylethylamine, and ultrasonically dispersed for 30 minutes to obtain a suspension B; (3) 0.1 parts of 4-pyrrolidinopyridine are added to the suspension B, the temperature is raised to 90°C, and the suspension is stirred at a speed of 200 r / min. While stirring, solution A is added, the temperature is kept constant, and the suspension is stirred for 12 hours. The reaction is terminated, and the suspension is naturally cooled to room temperature, filtered, washed, and dried to obtain modified wood fiber;

[0033] Step 3: Evenly mix 1 part of dimethylpolysiloxane, 0.5 part of sodium methylsiliconate, and 30 parts of tert-butyl 4-(6-amino-3-pyridyl)piperazine-1-carboxylate, then add 15 parts of modified wood fiber and continue stirring to obtain a modified wood fiber liquid;

[0034] Step 4: Gypsum powder, deionized water, and retarder are mixed and stirred uniformly to obtain gypsum slurry; modified lignin and modified wood fiber liquid are then added, and the mixture is continued to be mixed and stirred to obtain gypsum fiber slurry; the gypsum fiber slurry is formed into a 9 mm thick slab, which is then pressurized at a pressure of 2 MPa for 30 minutes to press it together, and then maintained at a pressure of 1 MPa for 12 hours, and then maintained at 50°C and 90% humidity for 3 days, and finally dried at 65°C for 12 hours to obtain a high-density flame-retardant gypsum-based fiberboard;

[0035] The gypsum fiber slurry includes the following components, calculated in parts by weight: 55 parts of gypsum powder, 120 parts of deionized water, 0.05 parts of retarder, 12 parts of modified lignin, and 28 parts of modified wood fiber liquid.

[0036] Example 3: A method for preparing a high-density flame-retardant gypsum-based fiberboard:

[0037] Step 1: Preparation method of modified lignin: (1) Under mechanical stirring, 20 parts of alkaline lignin are added to sufficient deionized water, 15wt% sodium hydroxide solution is added to adjust the pH value to 10, and the temperature is adjusted to 60°C to dissolve the alkaline lignin; (2) The reaction solution is heated to 90°C, 0.2 parts of sodium dodecylbenzenesulfonate and 6 parts of formaldehyde are added, and mechanical stirring is carried out for 60 minutes. Then 6 parts of dodecylamine are added, and the stirring reaction is continued for 6 hours. The reaction is terminated and the mixture is allowed to cool naturally to room temperature to obtain an aminated lignin solution; (3) 8 parts of DOPO and 1 part of formaldehyde are mixed to obtain a mixed solution, the temperature of the aminated lignin solution is adjusted to 70°C, and the mixed solution is dropped into the aminated lignin solution under stirring. After the reaction is allowed to react for 12 hours, the reaction is terminated and the mixture is allowed to cool naturally to room temperature. Hydrochloric acid solution is added to adjust the pH value to 7.0, and the modified lignin is obtained by filtration;

[0038] Step 2: The preparation method of modified wood fiber is as follows: (1) 30 parts of wood fiber are added to a mixed acid solution and ultrasonically treated for 10 hours, and then filtered, washed, and dried to obtain carboxylated wood fiber; (2) 10 parts of 4-(6-amino-3-pyridyl)piperazine-1-carboxylic acid tert-butyl ester are dissolved in N,N-diisopropylethylamine to prepare a solution A with a concentration of 0.035 mol / L, and then 5 parts of carboxylated wood fiber are added to an equal amount of N,N-diisopropylethylamine, and ultrasonically dispersed for 60 minutes to obtain a suspension B; (3) 0.25 parts of 4-pyrrolidinopyridine are added to the suspension B, the temperature is raised to 110°C, and the suspension is stirred at a speed of 400 r / min. Solution A is added while stirring, the temperature is kept constant, and the suspension is stirred for 24 hours. The reaction is terminated, and the suspension is naturally cooled to room temperature, filtered, washed, and dried to obtain modified wood fiber;

[0039] Step 3: Evenly mix 1 part of dimethylpolysiloxane, 0.2 parts of sodium methylsiliconate, and 16 parts of tert-butyl 4-(6-amino-3-pyridyl)piperazine-1-carboxylate, then add 12 parts of modified wood fiber and continue stirring to obtain a modified wood fiber liquid;

[0040] Step 4: Gypsum powder, deionized water, and retarder are mixed and stirred uniformly to obtain gypsum slurry; modified lignin and modified wood fiber liquid are then added, and the mixture is continued to be mixed and stirred to obtain gypsum fiber slurry; the gypsum fiber slurry is formed into a 9 mm thick slab, which is then pressurized at a pressure of 3.5 MPa for 60 minutes to press it together, and then maintained at a pressure of 2 MPa for 24 hours, and then maintained at 70°C and 80% humidity for 7 days, and finally dried at 80°C for 24 hours to obtain a high-density flame-retardant gypsum-based fiberboard;

[0041] The gypsum fiber slurry includes the following components, calculated in parts by weight: 55 parts of gypsum powder, 120 parts of deionized water, 0.05 parts of retarder, 12 parts of modified lignin, and 28 parts of modified wood fiber liquid.

[0042] Comparative Example 1: The gypsum fiber slurry comprises the following components, calculated in parts by weight: 55 parts of gypsum powder, 120 parts of deionized water, 0.05 parts of retarder, 8 parts of modified lignin, and 20 parts of modified wood fiber liquid; other components are the same as in Example 1;

[0043] Comparative Example 2: The gypsum fiber slurry comprises the following components, calculated in parts by weight: 55 parts of gypsum powder, 120 parts of deionized water, 0.05 parts of retarder, 15 parts of modified lignin, and 30 parts of modified wood fiber liquid; other components are the same as in Example 1;

[0044] Comparative Example 3: The alkaline lignin was not modified; the gypsum fiber slurry included the following components, calculated in parts by weight: 55 parts of gypsum powder, 120 parts of deionized water, 0.05 parts of retarder, 12 parts of alkaline lignin, and 28 parts of modified wood fiber liquid; other components were the same as in Example 1;

[0045] Comparative Example 4: No modification treatment was performed on the wood fiber;

[0046] Step 3: Evenly mix 1 part of dimethylpolysiloxane, 0.3 parts of sodium methylsiliconate, and 20 parts of tert-butyl 4-(6-amino-3-pyridyl)piperazine-1-carboxylate, then add 16 parts of wood fiber and continue stirring to obtain a wood fiber liquid;

[0047] The gypsum fiber slurry comprises the following components, calculated in parts by weight: 55 parts of gypsum powder, 120 parts of deionized water, 0.05 parts of retarder, 12 parts of modified lignin, and 28 parts of wood fiber liquid; other components are the same as those in Example 1;

[0048] Comparative Example 5: No dimethylpolysiloxane or sodium methylsiliconate was added to the modified wood fiber liquid; other conditions were the same as those in Example 1;

[0049] Step 3: 20 parts of tert-butyl 4-(6-amino-3-pyridyl)piperazine-1-carboxylate and 16 parts of modified wood fiber are mixed and stirred uniformly to obtain a modified wood fiber liquid.

[0050] Performance Testing: The high-density flame-retardant gypsum-based fiberboards prepared in Examples 1 to 3 and Comparative Examples 1 to 5 were subjected to flame retardancy testing and internal bonding strength testing. According to LY / T 1598-2011, an AG-10TA microcomputer-controlled electronic universal mechanical testing machine was used at a loading speed of 2 mm / s to test the internal bonding strength of the gypsum-based fiberboards. A JF-3 oxygen index meter was used to test the limiting oxygen index of the gypsum-based fiberboards. The data obtained are shown in the following table:

[0051] Examples Internal bonding strength (MPa) Limiting oxygen index (%) Example 1 1.46 34 Example 2 1.26 30 Example 3 1.38 33 Comparative Example 1 1.22 31 Comparative Example 2 1.31 32 Comparative Example 3 1.12 29 Comparative Example 4 1.06 32 Comparative Example 5 1.18 31

[0052] Result analysis: From the data in the above table, it can be seen from the comparative example and comparative examples 3 to 5 that, in the scheme, modifying the alkaline lignin and wood fiber and adding flexible polysilane can effectively improve the flame retardant properties and density of the fiberboard; finally, the fiberboard prepared by the present invention has good internal bonding strength and flame retardant properties, the fiberboard is of good quality, and can adapt to more uses.

[0053] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-density flame-retardant gypsum-based fiberboard, characterized by: The following steps are involved: Step 1: alkaline lignin is aminated and then grafted with DOPO to obtain modified lignin; Step 2: Carboxylating the wood fiber and then grafting it with tert-butyl 4-(6-amino-3-pyridyl)piperazine-1-carboxylate to obtain modified wood fiber; Step 3: Dimethylpolysiloxane, sodium methylsiliconate, and tert-butyl 4-(6-amino-3-pyridyl)piperazine-1-carboxylate are mixed evenly, and then modified wood fiber is added and stirred evenly to obtain a modified wood fiber liquid; Step 4: Gypsum powder, deionized water, and retarder are mixed and stirred uniformly to obtain gypsum slurry; modified lignin and modified wood fiber liquid are then added and continued to mix and stir to obtain gypsum fiber slurry; the gypsum fiber slurry is formed into a slab, and finally pressurized, maintained, maintained, and dried to obtain a high-density flame-retardant gypsum-based fiberboard; The preparation method of the modified lignin is: (1) Add alkaline lignin to deionized water, stir and mix, add 5-15 wt% sodium hydroxide solution to adjust the pH value to 8-10, and adjust the temperature to 40-60 ° C to dissolve the alkaline lignin; (2) The reaction solution was heated to 70-100°C, sodium dodecylbenzenesulfonate and formaldehyde were added, and mechanical stirring was performed for 30-60 min. Then, dodecylamine was added and the stirring reaction was continued for 3-6 h. The reaction was terminated and allowed to cool naturally to room temperature to obtain an aminated lignin solution. (3) DOPO and formaldehyde are mixed to obtain a mixed solution, the temperature of the aminated lignin solution is adjusted to 50-70°C, and the mixed solution is dropped into the aminated lignin solution under stirring. After the reaction is completed for 6-12 hours, the reaction is terminated and the solution is cooled to room temperature naturally. Hydrochloric acid solution is added to adjust the pH value to 6.5-7.2 to obtain modified lignin; The preparation method of the modified wood fiber is: (1) The wood fiber is placed in a mixed acid solution and ultrasonically treated for 2 to 10 hours, and then filtered, washed, and dried to obtain carboxylated wood fiber; (2) Dissolve tert-butyl 4-(6-amino-3-pyridyl)piperazine-1-carboxylate in N,N-diisopropylethylamine to prepare a solution A with a concentration of 0.025-0.035 mol / L. Then, add the carboxylated wood fiber to the N,N-diisopropylethylamine and disperse it by ultrasonication for 30-60 min to obtain a suspension B. (3) Add 4-pyrrolidinopyridine to suspension B, heat it to 90-110°C, stir it at a speed of 200-400 r / min, add solution A while stirring, keep the temperature constant, mechanically stir for 12-24 hours, terminate the reaction, wait for it to cool naturally to room temperature, filter, wash, and dry to obtain modified wood fiber; The high-density flame-retardant gypsum-based fiberboard comprises the following components: by weight: 45-65 parts of gypsum powder, 110-130 parts of deionized water, 0.05-0.07 parts of retarder, 8-15 parts of modified lignin, and 20-30 parts of modified wood fiber liquid.

2. The method for preparing a high-density flame-retardant gypsum-based fiberboard according to claim 1, characterized in that: The mass ratio of the raw materials alkaline lignin, sodium dodecylbenzenesulfonate, formaldehyde, and dodecylamine in the aminated lignin solution is 1:(0.003~0.01):(0.1~0.3):(0.1~0.3); the mass ratio of the raw materials DOPO and formaldehyde in the mixed solution is (7~8):

1.

3. The method for preparing a high-density flame-retardant gypsum-based fiberboard according to claim 1, characterized in that: The mixed acid solution is prepared by mixing 98wt% concentrated sulfuric acid and 35wt% nitric acid in a ratio of 1:1; the mass ratio of tert-butyl 4-(6-amino-3-pyridyl)piperazine-1-carboxylate and carboxylated wood fiber is (1-2):1; and the amount of 4-pyrrolidinopyridine added is 2-5% of the mass of the carboxylated wood fiber.

4. The method for preparing a high-density flame-retardant gypsum-based fiberboard according to claim 1, characterized in that: In the step 3, the mass ratio of dimethylpolysiloxane, sodium methylsiliconate, tert-butyl 4-(6-amino-3-pyridyl)piperazine-1-carboxylate, and modified wood fiber is (2-5):1:(60-80):(30-60).

5. The method for preparing a high-density flame-retardant gypsum-based fiberboard according to claim 1, characterized in that: The pressurizing pressure is 2~3.5MPa, and the pressurizing time is 30~60min; the holding pressure is 1~2MPa, and the holding time is 12~24h; the maintenance temperature is 50~70℃, the maintenance humidity is 80~90%, and the maintenance time is 3~7 days; the drying temperature is 65~80℃, and the drying time is 12~24h.

6. A high-density flame-retardant gypsum-based fiberboard prepared by the method for preparing a high-density flame-retardant gypsum-based fiberboard according to any one of claims 1 to 5.