Flame-retardant polyurethane foams and methods for making the same

Abstract

The application provides a kind of flame-retardant polyurethane foam and its preparation method, belong to high molecular technical field, including the following steps: S1, preparation modified lignin: lignin is modified with copper-chromium loaded HZSM-5 zeolite catalyst;S2, preparation modified polyether polyol: modified lignin is mixed with polyol, catalyst is added to react, lignin-based polyether polyol is prepared;S3, preparation flame-retardant polyurethane foam: lignin-based polyether polyol, flame retardant, char-forming agent, triethanolamine, dibutyltin dilaurate, monofluorodichloroethane, nano tungsten carbide, water are stirred uniformly at room temperature, then isocyanate is added to continue stirring, after uniform fusion, pour into mold forming, after curing, obtain flame-retardant polyurethane foam.The technical scheme provided by the application realizes the purpose of improving the physical properties of polyurethane foam while achieving good flame-retardant effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high polymer technology, in particular to a flame-retardant polyurethane foam and a preparation method thereof. BACKGROUND

[0002] Polyurethane foam (PUF) is a polymer foam material formed by the reaction of isocyanate and polyol (polyether or polyester type) to form a repeating unit of urethane, under the action of a foaming agent. It has excellent physical and mechanical properties, acoustic properties, electrical properties and chemical resistance, especially rigid polyurethane foam, which has low thermal conductivity and is a high-quality thermal insulation material. Due to its excellent physical and chemical properties, as well as the current social form of building energy saving and emission reduction requirements, polyurethane foam is widely used in building insulation fields, and is also widely used in furniture, bedding, transportation, refrigeration and other fields. However, when polyether polyol is used as the main raw material to prepare polyurethane foam, improper use can cause the prepared material to crack or collapse. At the same time, polyurethane foam has high flammability, burns quickly, and releases a large amount of heat and thick black smoke, as well as CO, NO, HCN and other toxic gases, which can easily cause suffocation, poisoning and death in a fire, causing serious loss of life and property. Therefore, flame retardants are usually added to improve the flame retardant properties of polyurethane foam.

[0003] A patent with the name of a flame-retardant polyurethane spray hard foam plastic and the authorization announcement number CN104119498B discloses a flame-retardant polyurethane spray hard foam plastic, which is polymerized from an isocyanate component and a polyol component, and the volume ratio of the isocyanate component to the polyol component is 1:1. The polyol component is composed of a polyester polyol, a hydroxyl-containing reactive flame retardant, inorganic microparticles and an auxiliary agent. The percentages of the above components in the total weight of the polyol component are as follows: 5-40% of the polyester polyol, 10-40% of the hydroxyl-containing reactive flame retardant, 10-20% of the inorganic microparticles, and 24-50% of the auxiliary agent. The above technical solution uses a reactive flame retardant containing phosphorus and bromine flame-retardant elements and a polyester polyol with a high benzene ring content. Finally, incombustible inorganic microparticles with a particle size of less than 500 mesh are added to the isocyanate component or the polyol component, which not only increases the flame-retardant performance, but also adjusts the volume ratio of the two components, so that the mixing ratio of the two components is 1:1. The flame-retardant polyurethane foam can meet the requirements of the B-level difficult-to-burn material in the combustion performance grade and classification criterion for flat building materials and products in the national standard GB8624-2012 “Combustion Performance Classification of Building Materials and Products”. However, the use amount of the flame retardant in the above technical solution is large, which affects the physical properties of the polyurethane foam.

[0004] Therefore, it is necessary to provide a flame-retardant polyurethane foam and a preparation method thereof to solve the problems existing in the prior art. SUMMARY

[0005] Therefore, the present application provides a kind of flame-retardant polyurethane foam and its preparation method, realize the purpose of good flame-retardant effect while improving the physical properties of polyurethane foam.

[0006] To achieve the above object, the present application provides a kind of preparation method of flame-retardant polyurethane foam, comprising the following steps:

[0007] S1, preparation of modified lignin: lignin is modified by using copper-chromium loaded HZSM-5 zeolite catalyst, to obtain modified lignin;

[0008] S2, preparation of modified polyether polyol: modified lignin is mixed with polyol, and catalyst is added to react, to obtain lignin-based polyether polyol;

[0009] S3, preparation of flame-retardant polyurethane foam: lignin-based polyether polyol, flame retardant, char-forming agent, triethanolamine, dibutyltin dilaurate, monofluorodichloroethane, nano tungsten carbide and water are stirred uniformly, then isocyanate is added and continues to stir, after uniform fusion, pour into mold forming, after curing to obtain flame-retardant polyurethane foam.

[0010] The present application is modified by polyether polyol, modified lignin is combined with polyether polyol, because modified lignin has alcohol hydroxyl content, the amount of polyether polyol can be reduced, to avoid the phenomenon of material cracking or bubble collapse due to excessive use of polyether polyol, lignin-based polyether polyol also increases the density of polyurethane foam, increases the compressive strength, reduces the thermal conductivity, improves the strength and flame retardancy of flame-retardant polyurethane foam.

[0011] The present application adds flame retardant, carbonization agent and nano tungsten carbide in the preparation process. Nano tungsten carbide has high specific surface area and active surface. In the process of polyurethane combustion, the complex flame retardant obtained by compounding the flame retardant and the carbonization agent is catalyzed on the surface of nano tungsten carbide, so that the cooling and carbonization effect of the complex flame retardant is improved. Nano tungsten carbide itself has high strength and thermal stability, which can improve the overall structural strength of the foam plastic and enhance the overall thermal stability of the polyurethane foam. When expanded graphite burns, it forms a carbonized layer to block heat transfer and inhibit smoke diffusion. However, the stability and strength of the carbonized layer are poor. Nano tungsten carbide can improve the quality of the carbonized layer by using its strength and thermal stability during carbonization, so as to enhance the heat insulation and oxygen insulation capacity of the carbonized layer, thereby further improving the flame retardancy and strength of the flame-retardant polyurethane foam.

[0012] Optionally, the lignin modification comprises the following steps:

[0013] The first step is to take the HZSM-5 molecular sieve carrier into a mixed solution containing copper ions and chromium ions, ultrasonic, magnetic stirring, hydrothermal reaction, separation of solid phase, reduction under hydrogen, and the copper-chromium loaded HZSM-5 zeolite catalyst is obtained;

[0014] The second step is to dissolve the lignin in dioxane, add the copper-chromium loaded HZSM-5 zeolite catalyst, then add hydrogen peroxide, constant temperature reaction, centrifugal liquid phase, and the solid product is modified lignin by membrane separation.

[0015] In the modification process of lignin, the two-dimensional pore structure of the HZSM-5 molecular sieve carrier is used to fully load the copper ions and chromium ions, and the hydrothermal performance and shape selection of the molecular sieve can obtain the copper-chromium loaded HZSM-5 zeolite catalyst after hydrogen reduction, and the copper-chromium loaded HZSM-5 zeolite catalyst is used to promote the bond between the phenolic hydroxyl group and the benzene ring in the lignin molecule, that is, the Caryl-Cα bond in the lignin molecule has good selectivity, which can promote the bond to break, reduce the molecular weight of the lignin, and convert the phenolic hydroxyl group into an alcoholic hydroxyl group, so that the content of the alcoholic hydroxyl group is increased. The increase of the alcoholic hydroxyl group improves the reaction activity of the lignin, and then the subsequent mixing and catalysis with the polyol are carried out, so that the reaction is complete and the lignin-based polyether polyol with excellent performance can be efficiently obtained.

[0016] Optionally, the mixed solution in the first step is a mixed solution of copper nitrate and chromium nitrate, and the molar ratio of copper ions to chromium ions is 1:1.

[0017] The catalyst formed after the molecular sieve carrier is loaded with copper ions and chromium ions with a molar ratio of 1:1 has better effect. When the ratio of copper ions to chromium ions is higher or lower, the effect of the formed catalyst will be affected.

[0018] Optionally, the mass ratio of the HZSM-5 molecular sieve carrier to the mixed solution in the first step is 1:1.5-2, and the ratio unit is g / ml; and the mass ratio of the lignin to the copper-chromium loaded HZSM-5 zeolite catalyst in the second step is 4-5:1.

[0019] When the ratio of the mass of the molecular sieve to the mixed solution used in the application is too high, the loading rate of copper and chromium ions on the molecular sieve carrier is low, and when the ratio is too low, too much copper and chromium ions are left, which increases the cost.

[0020] Optionally, the ultrasonic time in the first step is 1-1.5h; the speed of the magnetic stirring is 800-1200rpm, and the time is 8-10h; the temperature of the hydrothermal reaction is 100-110℃, and the time is 10-12h; the reduction temperature is 650-680℃, and the time is 3-5h.

[0021] Optionally, the solid phase in the first step is ground before reduction, and then calcined at 560-600 DEG C for 4-6h.

[0022] In the present application, the solid phase is ground and calcined before reduction, which facilitates the increase of contact area with hydrogen during reduction and preheating.

[0023] Optionally, the lignin dissolution temperature in the second step is 50-60 DEG C; the temperature of the constant temperature is 70-80 DEG C, and the time is 30-50 min; the centrifugal speed is 6000-10000 rpm, and the time is 10-20 min; the membrane separation uses reverse osmosis membrane, and the pressure range is 5-10 bar.

[0024] Optionally, the catalyst in S2 is methanesulfonic acid catalyst, and the mass ratio of the polyol, modified lignin and catalyst is 1000-1200: 35-45: 4-5; after adding the catalyst in S2, the reaction is carried out at a temperature of 140-160 DEG C for 0.5-1h, and then the pH value is adjusted to 7.0 by sodium hydroxide.

[0025] Optionally, the flame-retardant polyurethane foam plastic comprises the following raw materials in parts by weight: lignin-based polyether polyol 230-240 parts, flame retardant 60-80 parts, char-forming agent 10-20 parts, nano tungsten carbide 8-12 parts, triethanolamine 3-5 parts, dibutyltin dilaurate 1-3 parts, monofluorodichloroethane 40-50 parts, isocyanate 430-470 parts and water 5-10 parts, the flame retardant is one of dimethyl methylphosphonate and tris (1-chloro-2-propyl) phosphate, and the char-forming agent is one of expandable graphite, montmorillonite and polysiloxane.

[0026] In order to achieve the above-mentioned purpose, the present application also provides a flame-retardant polyurethane foam plastic prepared by the preparation method of the flame-retardant polyurethane foam plastic.

[0027] The flame-retardant polyurethane foam plastic obtained by the present application improves the flame-retardant property, and improves the tensile strength, density, compressive strength, thermal conductivity and other physical properties of the material.

[0028] The above technical scheme of the present application at least has the following beneficial effects:

[0029] The present application introduces lignin-based polyether polyol modified by oxidation into the formula of flame-retardant polyurethane foam plastic, which improves the foaming density of polyurethane, reduces the occurrence of side effects, and improves the strength and flame retardancy of polyurethane foam. The addition of nano tungsten carbide in the combustion process improves the cooling and carbonization effect of the flame retardant and carbonization agent, improves the heat insulation and oxygen insulation performance of the carbon layer, and improves the flame retardancy and strength and toughness of polyurethane foam plastic. DETAILED DESCRIPTION

[0030] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the described embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present application.

[0031] Embodiment 1

[0032] 30 Kg of HZSM-5 molecular sieve carrier and 55 L of a mixed solution of copper nitrate and chromium nitrate (molar ratio of copper ions to chromium ions is 1:1) were added into 1200 L of deionized water, mixed uniformly, and then ultrasonically treated for 70 min. The above solution was stirred at 1000 rpm on a magnetic stirrer for 9 h, and then transferred into a hydrothermal reaction kettle. The reaction kettle was placed in a 105℃ environment for 11 h of reaction. The reaction kettle was cooled, and the mixed solution was filtered to obtain a solid product. After grinding, the solid product was placed in a muffle furnace and calcined at 580℃ for 5 h. Then, the solid product was placed in a tube furnace and reduced at 660℃ in a H2 atmosphere for 4 h. After grinding, the solid product was vacuum dried to obtain a copper-chromium-loaded HZSM-5 zeolite catalyst. 157.5 Kg of lignin was mixed with 2800 Kg of dioxane, and then placed in a reaction kettle equipped with a reflux condenser device. The mixture was stirred and heated to 55℃. After the lignin was completely dissolved, 35 Kg of the copper-chromium-loaded HZSM-5 zeolite catalyst was added, followed by the addition of 180 Kg of H2O2. The mixture was reacted at a constant temperature of 75℃ for 40 min. After the reaction was completed, the solid catalyst was separated by centrifugation at a speed of 8000 rpm for 15 min. The remaining solution was separated by using a reverse osmosis membrane under a pressure of 7 bar to remove the solvent. The obtained solid product was dried at 75℃ for 18 h to obtain modified lignin.

[0033] Polyols include PEG-400 and glycerol. 300 Kg of a PEG-400 solution and 800 Kg of a glycerol solution were added into a reaction kettle. 40 Kg of the modified lignin was added into the above mixed solution, followed by the addition of 4.5 Kg of a potassium sulfonic acid catalyst. The reaction was carried out on a device equipped with a stirrer, a thermometer and a reflux condenser tube. The mixture was continuously stirred and reacted at a constant temperature of 150℃ for 40 min. After the reaction was completed, the mixture was cooled to room temperature. The pH value of the solution was adjusted to 7.0 by using sodium hydroxide to obtain lignin-based polyols.

[0034] A one-step foaming method was used to prepare the process, taking 235 parts of lignin-based polyether polyol, 70 parts of dimethyl methylphosphonate, 15 parts of polysiloxane, 12 parts of nano tungsten carbide, 5 parts of triethanolamine, 3 parts of dibutyltin dilaurate, 45 parts of monofluorodichloroethane, and 7 parts of water into the reaction kettle, stirring quickly and uniformly at room temperature, then adding isocyanate 450 parts for continuous stirring, after uniform fusion, pour into the mold for molding, after a period of curing to obtain flame-retardant polyurethane foam plastic.

[0035] Example 2

[0036] HZSM-5 molecular sieve carrier 30Kg and 45L copper nitrate, chromium nitrate mixed solution (molar ratio of copper ion to chromium ion is 1:1) were added to 100L deionized water and mixed uniformly, then ultrasonic for 1h, the above solution was placed on the magnetic stirrer for 1200rpm stirring for 8h, then into the hydrothermal reaction kettle, the reaction kettle was placed at 100℃ for 12h, the reaction kettle was cooled, the mixed solution was filtered, the solid product was obtained, ground and put into the muffle furnace at 560℃ for 6h, then placed in the tube furnace at 650℃ under H2 atmosphere for 5h, ground and vacuum dried to obtain copper and chromium loaded HZSM-5 zeolite catalyst. 140Kg of lignin was mixed with 2500Kg of dioxane, placed in a reaction kettle equipped with reflux condensing equipment, stirred and heated to 50℃, then 35Kg of copper and chromium loaded HZSM-5 zeolite catalyst was added, followed by the addition of 150Kg of H2O2, and the reaction was carried out at 70℃ for 30min. After the reaction, the solid catalyst was separated by centrifugation at 6000rpm for 20min. The remaining solution was treated by reverse osmosis membrane under a pressure of 5bar to remove the solvent. The obtained solid product was dried at 70℃ for 15h to obtain modified lignin.

[0037] The polyol includes PEG-400 and glycerol, taking 200Kg of PEG-400 solution and 800Kg of glycerol solution into the reaction kettle, adding 35Kg of modified lignin to the above mixed solution, and then adding 4Kg of methanesulfonic acid catalyst. The reaction was carried out in a device equipped with a stirrer, a thermometer and a reflux condenser, and the stirring was continued and the reaction was carried out at 140℃ for 60min. After the reaction, the solution was cooled to room temperature, and the pH value of the solution was adjusted to 7.0 with sodium hydroxide to obtain lignin-based polyether polyol.

[0038] A one-step foaming method was used to prepare the process, taking 240 parts of lignin-based polyether polyol, 80 parts of dimethyl methylphosphonate, 10 parts of expandable graphite, 8 parts of nano tungsten carbide, 3 parts of triethanolamine, 1 part of dibutyltin dilaurate, 50 parts of monofluorodichloroethane, and 10 parts of water into the reaction kettle, stirring quickly and uniformly at room temperature, then adding isocyanate 430 parts for continuous stirring, after uniform fusion, pour into the mold for molding, after a period of curing to obtain flame-retardant polyurethane foam plastic.

[0039] Example 3

[0040] Put 30 Kg HZSM-5 molecular sieve carrier and 60 L copper nitrate, chromium nitrate mixed solution (molar ratio of copper ion to chromium ion is 1:1) into 130 L deionized water, mix uniformly, and then ultrasonic for 1.5 h. Put the above solution on a magnetic stirrer and stir at 800 rpm for 10 h, and then transfer into a hydrothermal reaction kettle. Put the reaction kettle at 110℃ for 10 h. Cool the reaction kettle, and then filter the mixed solution to obtain a solid product. Grind the solid product, put it into a muffle furnace, and calcine at 600℃ for 4 h. Then put it into a tube furnace and reduce at 680℃ under H2 atmosphere for 3 h. Grind the product, and then vacuum dry to obtain a copper-chromium loaded HZSM-5 zeolite catalyst. Mix 175 Kg of lignin with 2900 Kg of dioxane, and then put them into a reaction kettle equipped with a reflux condenser device. Start stirring and heating to 60℃. When the lignin is completely dissolved, add 35 Kg of the copper-chromium loaded HZSM-5 zeolite catalyst, and then add 200 Kg of H2O2. React at 80℃ for 50 min. After the reaction is completed, centrifuge at 10000 rpm for 10 min to separate the solid catalyst. Use a reverse osmosis membrane to remove the solvent from the remaining solution under a pressure of 10 bar. Dry the obtained solid product at 80℃ for 15 h to obtain modified lignin.

[0041] The polyol includes PEG-400 solution 300 Kg and glycerol solution 900 Kg. Put 45 Kg of modified lignin into the above mixed solution, and then add 5 Kg of potassium sulfonic acid catalyst. React in a device equipped with a stirrer, a thermometer, and a reflux condenser under continuous stirring and at 160℃ for 30 min. After the reaction is completed, cool to room temperature, and then adjust the pH value of the solution to 7.0 with sodium hydroxide to obtain lignin-based polyol.

[0042] Use one-step foaming process to prepare the process. Take lignin-based polyether polyol 230 parts, tris (1-chloro-2-propyl) phosphate 60 parts, montmorillonite 20 parts, nano tungsten carbide 10 parts, triethanolamine 5 parts, dibutyltin dilaurate 2 parts, monofluorodichloroethane 40 parts, and water 5 parts, and then add them into a reaction kettle and stir uniformly at room temperature. Then add isocyanate 470 parts and continue to stir. After the mixture is uniformly melted, pour it into a mold to form. After a certain period of aging, obtain flame-retardant polyurethane foam plastic.

[0043] Example 4

[0044] The difference from Example 1 is only the mass ratio of polyol: modified lignin: methanesulfonic acid catalyst, which is 1000:45:4.5. The polyol includes PEG-400 solution 300 Kg and glycerol solution 700 Kg. The remaining raw materials and steps are consistent with Example 1.

[0045] Example 5

[0046] The difference from Example 2 is only that the temperature of hydrothermal reaction is 108℃, the time of hydrothermal reaction is 11h, and the temperature of reduction is 670℃, and the time of reduction is 3.5h. The rest of raw materials and steps are consistent with Example 2.

[0047] Example 6

[0048] The difference from Example 3 is only that the flame-retardant polyurethane foam includes the following raw materials in parts by weight: lignin-based polyether polyol 236 parts, tris (1-chloro-2-propyl) phosphate 65 parts, montmorillonite 18 parts, nano tungsten carbide 11 parts, triethanolamine 3 parts, dibutyltin dilaurate 1 part, monofluorodichloroethane 42 parts, isocyanate 460 parts, and water 6 parts. The rest of raw materials and steps are consistent with Example 3.

[0049] Comparative Example 1

[0050] Compared with Example 1, the difference is only that lignin-based polyether polyol is not used, i.e. polyether polyol is used instead of lignin-based polyether polyol, and the rest of raw materials and steps are consistent with Example 1.

[0051] Comparative Example 2

[0052] Compared with Example 1, the difference is only that lignin is not modified by using copper-chromium-loaded HZSM-5 zeolite catalyst, i.e. lignin is used instead of modified lignin to prepare lignin-based polyether polyol, and the rest of raw materials and steps are consistent with Example 1.

[0053] Comparative Example 3

[0054] Compared with Example 1, the difference is only that nano tungsten carbide is not used, and the rest of raw materials and steps are consistent with Example 1.

[0055] Comparative Example 4

[0056] Compared with Example 1, the difference is only that char-forming agent is not used, and the rest of raw materials and steps are consistent with Example 1.

[0057] The flame-retardant polyurethane foams prepared in Examples 1-6 and Comparative Examples 1-4 are tested for relevant performance.

[0058] The flame-retardant performance testing method is derived from the national standard GB / T 20284-2006 Single Burning Test for Building Materials or Products, and the performance requirement is derived from the national standard GB 8624-2012 Classification of Building Materials and Products by Burning Performance: the burning growth rate index is ≤120 W / S; the flame transverse spread does not reach the long wing edge of the sample; the total heat release in 600s is ≤7.5 MJ, and the flame-retardant performance test results are shown in Table 1.

[0059] Table 1: Results of flame retardant properties of polyurethane foams prepared in Examples 1-6 and Comparative Examples 1-4

[0060]

[0061] As can be seen from Table 1, the flame retardant properties of the polyurethane foams prepared in Examples 1-6 are significantly higher than those of the polyurethane foams prepared in Comparative Examples 1-4, and meet the requirements of the national standard GB 8624-2012.

[0062] Combining the data in Table 1, it can be seen from the comparison of Example 1 with Comparative Examples 1-4 that the lignin-based polyether polyol, modification of lignin, use of nano-tungsten carbide, and use of a char-forming agent all have an effect on the flame retardant properties. According to the significant differences in the performance indicators of the burn growth rate index, flame lateral spread length, and total heat release at 600S between Comparative Examples 3 and 4 and Example 1, it can be seen that nano-tungsten carbide and the char-forming agent have a greater effect on the flame retardant properties. Combining the performance indicators of Comparative Examples 1-4 and Example 1, it can be seen that the main factors affecting the flame retardant properties of the prepared polyurethane foams are the use of nano-tungsten carbide and the use of a char-forming agent. The use of a lignin-based polyether polyol and modification of lignin also have some effect on the flame retardant properties of the prepared polyurethane foams, but less than the effect of using nano-tungsten carbide and using a char-forming agent.

[0063] The physical property testing method and requirements are derived from the national standard GB / T 20219-2015 Spray-Applied Rigid Polyurethane Foam for Thermal Insulation, with the requirements being: apparent core density ≥ 45 kg / m 3 ; compressive strength ≥ 200 kPa; initial thermal conductivity ≤ 0.030; aged thermal conductivity ≤ 0.034; tensile strength ≥ 200 kPa; and the physical property test results are shown in Table 2.

[0064] Table 2: Results of physical properties of polyurethane foams prepared in Examples 1-6 and Comparative Examples 1-4

[0065]

[0066] As can be seen from Table 2, the physical properties of the polyurethane foams prepared in Examples 1-6 are significantly higher than those of the polyurethane foams prepared in Comparative Examples 1-4, and meet the requirements of the national standard GB / T 20219-2015.

[0067] Compared with the data in Table 2, it can be seen from Example 1 and Comparative Examples 1-4 that the lignin-based polyether polyol and the modification of lignin have an effect on the physical properties of the polyurethane foam prepared. Comparative Examples 1 and 2 have a fold difference in apparent core density, compressive strength and tensile strength compared with Example 1, indicating that the use of lignin-based polyether polyol and the modification of lignin have a greater effect on the apparent core density, compressive strength and tensile strength. Comparative Examples 1 and 2 also have a difference in the thermal conductivity index compared with Example 1, indicating that the lignin-based polyether polyol and the modification of lignin have a certain effect on the thermal conductivity. Compared with the performance indicators of Comparative Examples 1-4 and Example 1, it can be seen that the main factors affecting the apparent core density, compressive strength and tensile strength of the polyurethane foam prepared are the use of lignin-based polyether polyol and the modification of lignin, while the nano-tungsten carbide and the use of carbonization agent have a greater effect on the thermal conductivity of the polyurethane foam prepared, and also have a certain effect on the apparent core density, compressive strength, tensile strength and thermal conductivity.

[0068] The above is the preferred embodiment of the present application. It should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which should also be considered within the scope of protection of the present application.

Claims

1. A method for preparing flame-retardant polyurethane foam, characterized in that, Includes the following steps: S1. Preparation of modified lignin: lignin is modified by using HZSM-5 zeolite catalyst loaded with copper and chromium to obtain modified lignin; S2. Preparation of modified polyether polyol: Mix modified lignin with polyol, add catalyst to react, and obtain lignin-based polyether polyol. S3. Preparation of flame-retardant polyurethane foam: The lignin-based polyether polyol, flame retardant, flame retardant compounding agent, triethanolamine, dibutyltin dilaurate, dichlorofluoroethane, nano tungsten carbide and water are stirred evenly, then isocyanate is added and stirring is continued. After being evenly mixed, it is poured into a mold to be shaped and cured to obtain flame-retardant polyurethane foam. The flame retardant compound is one of expandable graphite, montmorillonite, and polysiloxane.

2. The method for preparing flame-retardant polyurethane foam according to claim 1, characterized in that, Modification of lignin includes the following steps: Step 1: Take HZSM-5 molecular sieve support and put it into a mixed solution containing copper ions and chromium ions and sonicate it. After magnetic stirring, carry out hydrothermal reaction, separate the solid phase, and reduce it under hydrogen to obtain HZSM-5 zeolite catalyst loaded with copper and chromium. Step 2: Dissolve lignin in dioxane, add the above-mentioned copper-chromium-loaded HZSM-5 zeolite catalyst, then add hydrogen peroxide, react at a constant temperature, centrifuge to collect the liquid phase, and separate the liquid phase through a membrane to obtain the solid product, which is modified lignin.

3. The method for preparing flame-retardant polyurethane foam according to claim 2, characterized in that, The mixed solution in the first step is a mixture of copper nitrate and chromium nitrate, wherein the molar ratio of copper ions to chromium ions is 1:

1.

4. The method for preparing flame-retardant polyurethane foam according to claim 2, characterized in that, In the first step, the mass ratio of the HZSM-5 molecular sieve support to the volume of the mixed solution is 1:1.5~2, with the ratio unit being g / ml; in the second step, the mass ratio of lignin to the copper-chromium-loaded HZSM-5 zeolite catalyst is 4~5:

1.

5. The method for preparing flame-retardant polyurethane foam according to claim 2, characterized in that, The ultrasonic treatment time in the first step is 1~1.5h; the magnetic stirring speed is 800~1200rpm and the time is 8~10h; the hydrothermal reaction temperature is 100~110℃ and the time is 10~12h; the reduction temperature is 650~680℃ and the time is 3~5h.

6. The method for preparing flame-retardant polyurethane foam according to claim 2, characterized in that, In the first step, the solid phase is ground before reduction and then calcined at 560~600℃ for 4~6 hours.

7. The method for preparing flame-retardant polyurethane foam according to claim 2, characterized in that, The second step involves dissolving lignin at a temperature of 50-60°C; maintaining a constant temperature of 70-80°C for 30-50 minutes; centrifuging at 6000-10000 rpm for 10-20 minutes; and using a reverse osmosis membrane for membrane separation at a pressure range of 5-10 bar.

8. The method for preparing flame-retardant polyurethane foam according to claim 1, characterized in that, The catalyst in S2 is a methanesulfonic acid catalyst, and the mass ratio of polyol: modified lignin: catalyst is 1000~1200:35~45:4~5; After adding the catalyst to S2, the reaction is carried out at a temperature of 140~160℃ for 0.5~1h, and then the pH value is adjusted to 7.0 with sodium hydroxide.

9. The method for preparing flame-retardant polyurethane foam according to claim 1, characterized in that, Flame-retardant polyurethane foam comprises the following raw materials in parts by weight: 230-240 parts of lignin-based polyether polyol, 60-80 parts of flame retardant, 10-20 parts of flame retardant compounding agent, 8-12 parts of nano-tungsten carbide, 3-5 parts of triethanolamine, 1-3 parts of dibutyltin dilaurate, 40-50 parts of dichlorofluoroethane, 430-470 parts of isocyanate, and 5-10 parts of water. The flame retardant is one of dimethyl methylphosphonate and tris(1-chloro-2-propyl) phosphate, and the flame retardant compounding agent is one of expandable graphite, montmorillonite, and polysiloxane.

10. A flame-retardant polyurethane foam prepared by a method according to any one of claims 1-9.

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