Flame-retardant polyurethane foam plastic and preparation method thereof

Abstract

The invention provides flame-retardant polyurethane foam plastic and a preparation method thereof, and belongs to the technical field of macromolecules, and the preparation method comprises the following steps: S1, preparing modified lignin: modifying lignin by using a copper-chromium-loaded HZSM-5 zeolite catalyst; s2, preparing modified polyether polyol: mixing the modified lignin with polyol, and adding a catalyst for reaction to prepare lignin-based polyether polyol; and S3, preparing the flame-retardant polyurethane foaming plastic: uniformly stirring lignin-based polyether polyol, a flame retardant, a charring agent, triethanolamine, dibutyltin dilaurate, dichlorofluoroethane, nano tungsten carbide and water at room temperature, then adding isocyanate, continuously stirring, pouring into a mold for molding after uniform fusion, and curing to obtain the flame-retardant polyurethane foaming plastic. According to the technical scheme provided by the invention, the aims of improving the physical properties of the polyurethane foam plastic while achieving a good flame-retardant effect are achieved.

Description

Technical Field

[0001] The present invention relates to the field of polymer technology, in particular to flame-retardant polyurethane foam plastic and a preparation method thereof. Background Art

[0002] Polyurethane foam (PUF) is a polymeric foam material formed by the reaction of isocyanate with polyols (polyether or polyester) to form a repeating unit of urethane. This material is then treated with a blowing agent to form a polymer with urethane as the repeating unit. It exhibits excellent physical, mechanical, acoustic, electrical, and chemical resistance properties. Rigid polyurethane foam, in particular, has low thermal conductivity, making it a high-quality thermal insulation material. Due to its excellent physical and chemical properties, and in line with current social demands for energy conservation and emission reduction in buildings, polyurethane foam is widely used in building insulation, as well as furniture, bedding, transportation, and refrigeration. However, when polyether polyols are used as the primary raw material in the preparation of polyurethane foam, improper dosage can easily lead to cracking or foam collapse. Furthermore, polyurethane foam is highly flammable and burns rapidly, releasing large amounts of heat, thick black smoke, and toxic gases such as CO, NO, and HCN. These can easily cause suffocation, poisoning, and death in fires, resulting in serious loss of life and property. Therefore, flame retardants are often added to improve the flame retardancy of polyurethane foam.

[0003] The patent, entitled "A Flame-Retardant Polyurethane Spray Rigid Foam," with authorization announcement number CN104119498B, discloses a flame-retardant polyurethane spray rigid foam, which is polymerized from an isocyanate component and a polyol component, wherein the volume ratio of the isocyanate component to the polyol component is 1:1; the polyol component comprises a polyester polyol, a reactive flame retardant with a hydroxyl group, inorganic particles, and additives; the percentages of the polyol component by weight are as follows: 5-40% polyester polyol, 10-40% reactive flame retardant with a hydroxyl group, 10-20% inorganic particles, and 24- The above technical solution uses a reactive flame retardant containing phosphorus-bromine flame retardant elements and a polyester polyol with a high benzene ring content. Finally, non-combustible inorganic particles with a particle size of less than 500 mesh are added to the isocyanate component or the polyol component. This not only enhances flame retardancy but also adjusts the volume ratio of the two components, achieving a 1:1 volume ratio. This results in a product that meets the requirements of Class B for flame retardant materials in the national standard GB8624-2012, "Classification of Combustion Performance of Building Materials and Products," for flat-plate building materials and products. However, the high amount of flame retardant used in this technical solution 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 above-mentioned prior art. Summary of the Invention

[0005] In view of this, the present invention provides a flame retardant polyurethane foam plastic and a preparation method thereof, which achieves the purpose of achieving good flame retardant effect while improving the physical properties of the polyurethane foam plastic.

[0006] To achieve the above object, the present invention provides a method for preparing a flame retardant polyurethane foam, comprising the following steps: S1. Preparing modified lignin: modifying lignin using a copper-chromium loaded HZSM-5 zeolite catalyst to obtain modified lignin; S2. Preparing a modified polyether polyol: mixing the modified lignin with a polyol, adding a catalyst to react, and obtaining a lignin-based polyether polyol; S3. Preparation of flame-retardant polyurethane foam: Stir lignin-based polyether polyol, flame retardant, carbonizing agent, triethanolamine, dibutyltin dilaurate, monofluorodichloroethane, nano-tungsten carbide and water evenly, then add isocyanate and continue stirring. After being evenly blended, pour into a mold to form, and obtain flame-retardant polyurethane foam after aging.

[0007] The present invention modifies polyether polyol and combines modified lignin with the polyether polyol. Since the modified lignin has an alcohol hydroxyl content, the amount of polyether polyol used can be reduced, avoiding the phenomenon of cracking or bubble collapse of the material due to excessive use of polyether polyol. The lignin-based polyether polyol also increases the density of the polyurethane foam plastic, increases the compression strength, and reduces the thermal conductivity, thereby improving the strength and flame retardancy of the flame-retardant polyurethane foam.

[0008] The present invention adds a flame retardant, a carbonizing agent and nano-tungsten carbide during the preparation process. Nano-tungsten carbide has a high specific surface area and an active surface. During the combustion process of polyurethane, the compounded flame retardant obtained by compounding the flame retardant and the carbonizing agent is catalyzed on the surface of the nano-tungsten carbide, so that the cooling and carbonizing effect of the compounded flame retardant is improved. Nano-tungsten carbide itself has high strength and thermal stability, which can improve the overall structural strength of foam plastics and help enhance the overall thermal stability of polyurethane foam plastics. Expanded graphite forms a carbonized layer during combustion to block heat transfer and inhibit smoke diffusion, but the stability and strength of the carbonized layer are poor. During the combustion and carbonization process, nano-tungsten carbide can use its own strength and thermal stability to improve the quality of the carbonized layer, so that the heat insulation, oxygen isolation and smoke suppression capabilities of the carbonized layer are enhanced, thereby achieving further improvement in the flame retardancy and strength of flame-retardant polyurethane foam plastics.

[0009] Optionally, lignin modification comprises the following steps: The first step is to place the HZSM-5 molecular sieve carrier into a mixed solution containing copper ions and chromium ions, perform ultrasonication, and then perform a hydrothermal reaction after magnetic stirring. The solid phase is separated and reduced under hydrogen to obtain a copper-chromium loaded HZSM-5 zeolite catalyst. Step 2: dissolving lignin in dioxane, adding the copper-chromium loaded HZSM-5 zeolite catalyst, then adding hydrogen peroxide, reacting at a constant temperature, centrifuging to obtain the liquid phase, and separating the liquid phase through a membrane to obtain a solid product as modified lignin.

[0010] During the lignin modification process of the present invention, the two-dimensional pore structure of the HZSM-5 molecular sieve carrier is used to fully load copper ions and complex ions. The hydrothermal properties and shape selectivity of the molecular sieve can produce a copper-chromium-loaded HZSM-5 zeolite catalyst after hydrogen reduction. The copper-chromium-loaded HZSM-5 zeolite catalyst promotes the cleavage of the bond connecting the phenolic hydroxyl group and the benzene ring in the lignin molecule, that is, it has good selectivity for the Caryl-Cα bond in the lignin molecule, which can promote its cleavage, reduce the molecular weight of the lignin, and convert the phenolic hydroxyl group into alcoholic hydroxyl group, thereby increasing the alcoholic hydroxyl group content. The increase in alcoholic hydroxyl group increases the reaction activity of the lignin, thereby ensuring that the subsequent mixing and catalysis with the polyol completes the reaction, and a lignin-based polyether polyol with excellent performance can be efficiently obtained.

[0011] Optionally, the mixed solution in the first step is a mixed solution of copper nitrate and chromium nitrate, wherein the molar ratio of copper ions to chromium ions is 1:1.

[0012] The present invention uses a molar ratio of copper ions to chromium ions of 1:1, which has a better effect on the catalyst formed after the molecular sieve carrier is loaded. A higher or lower ratio of copper ions to chromium ions will affect the effect of the formed catalyst.

[0013] Optionally, in the first step, the mass ratio of the HZSM-5 molecular sieve carrier to the volume of the mixed solution is 1:1.5~2, and the ratio unit is g / ml; in the second step, the mass ratio of lignin to the copper-chromium loaded HZSM-5 zeolite catalyst is 4~5:1.

[0014] When the ratio of the mass of the molecular sieve used in the present invention to the mixed solution is too high, the molecular sieve carrier has a low loading rate of copper and chromium ions. When the ratio is too low, excessive copper and chromium ions remain, increasing the cost.

[0015] 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 temperature of the reduction is 650~680℃, and the time is 3~5h.

[0016] Optionally, in the first step, the solid phase is ground before reduction and then calcined at 560-600° C. for 4-6 hours.

[0017] In the present invention, the solid phase is ground and calcined before reduction, so as to increase the contact area with hydrogen during reduction and to perform preheating.

[0018] Optionally, the lignin dissolution temperature in the second step is 50~60°C; the constant temperature is 70~80°C, and the time is 30~50min; the centrifugal speed is 6000~10000rpm, and the time is 10~20min; the membrane separation uses a reverse osmosis membrane, and the pressure range is 5~10bar.

[0019] Optionally, the catalyst in S2 is a methanesulfonic acid catalyst, and the mass ratio of the 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° C. for 0.5-1 hour, and then the pH value is adjusted to 7.0 with sodium hydroxide.

[0020] Optionally, the flame retardant polyurethane foam plastic includes 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 carbonizing agent, 8-12 parts of nano-tungsten carbide, 3-5 parts of triethanolamine, 1-3 parts of dibutyltin dilaurate, 40-50 parts of monofluorodichloroethane, 430-470 parts of isocyanate and 5-10 parts of water, wherein the flame retardant is one of dimethyl methylphosphonate and tris(1-chloro-2-propyl) phosphate, and the carbonizing agent is one of expandable graphite, montmorillonite and polysiloxane.

[0021] In order to achieve the above object, the present invention also provides a flame retardant polyurethane foam plastic prepared by the above method for preparing the flame retardant polyurethane foam plastic.

[0022] The flame-retardant polyurethane foam plastic obtained by the invention improves the flame-retardant property and at the same time improves the physical properties of the material such as tensile strength, density, compression strength, thermal conductivity and the like.

[0023] The above technical solution of the present invention includes at least the following beneficial effects: The present invention introduces an oxidatively modified lignin-based polyether polyol into the flame-retardant polyurethane foam formulation, increasing the polyurethane foam density, reducing side effects, and improving the strength and flame retardancy of the polyurethane foam. The addition of nano-tungsten carbide during combustion enhances the cooling and charring effect of the flame retardant and charring agent, improving the thermal and oxygen-insulating properties of the char layer and ultimately enhancing the flame retardancy, strength, and toughness of the polyurethane foam. DETAILED DESCRIPTION

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of the present invention.

[0025] Example 1 30 kg HZSM-5 molecular sieve carrier and 55 L of a mixed solution of copper nitrate and chromium nitrate (the molar ratio of copper ion to chromium ion is 1:1) were added to 1200 L of deionized water, mixed evenly, and then ultrasonicated for 70 minutes. The above solution was placed on a magnetic stirrer and stirred at 1000 rpm for 9 hours, then transferred to a hydrothermal reactor, and the reactor was placed at 105°C for reaction for 11 hours. The reactor was cooled, and the mixed solution was filtered to obtain a solid product. After grinding, it was placed in a muffle furnace and calcined at 580°C for 5 hours, and then placed in a tubular furnace and reduced at 660°C for 4 hours under a H2 atmosphere. After grinding, it 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, placed in a reactor equipped with a reflux condenser, stirred and heated to 55°C. After the lignin was completely dissolved, 35 kg of copper-chromium-loaded HZSM-5 zeolite catalyst was added, followed by 180 kg of H2O2. The mixture was reacted at a constant temperature of 75°C for 40 minutes. After the reaction was completed, the solid catalyst was separated by centrifugation at 8000 rpm for 15 minutes. The remaining solution was separated and the solvent was removed using a reverse osmosis membrane at a pressure of 7 bar. The obtained solid product was dried at 75°C for 18 hours to obtain modified lignin.

[0026] The polyol comprises PEG-400 and glycerol. 300 kg of PEG-400 solution and 800 kg of glycerol solution are added to a reactor. 40 kg of modified lignin is then added to the mixed solution, followed by 4.5 kg of potassium sulfonic acid catalyst. The reaction is carried out in an apparatus equipped with a stirrer, thermometer, and reflux condenser, with continuous stirring at 150°C for 40 minutes. After the reaction is completed, the solution is cooled to room temperature, and the pH is adjusted to 7.0 with sodium hydroxide to produce the lignin-based polyol.

[0027] The method adopts a one-step foaming preparation process, wherein 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 are added into a reactor and rapidly stirred at room temperature, 450 parts of isocyanate are then added and stirred continuously, and after being evenly blended, the mixture is poured into a mold for molding, and the flame-retardant polyurethane foam plastic is obtained after aging for a period of time.

[0028] Example 2 30 kg HZSM-5 molecular sieve carrier and 45 L of a mixed solution of copper nitrate and chromium nitrate (the molar ratio of copper ion to chromium ion is 1:1) were added to 100 L of deionized water, mixed evenly, and then ultrasonicated for 1 hour. The above solution was placed on a magnetic stirrer and stirred at 1200 rpm for 8 hours, then transferred to a hydrothermal reactor, and the reactor was placed at 100°C for reaction for 12 hours. The reactor was cooled, and the mixed solution was filtered to obtain a solid product. After grinding, it was placed in a muffle furnace and calcined at 560°C for 6 hours, and then placed in a tubular furnace and reduced at 650°C for 5 hours under a H2 atmosphere. After grinding, it was vacuum dried to obtain a copper-chromium loaded HZSM-5 zeolite catalyst. 140 kg of lignin was mixed with 2500 kg of dioxane, placed in a reactor equipped with a reflux condenser, stirred and heated to 50°C. After the lignin was completely dissolved, 35 kg of copper-chromium-loaded HZSM-5 zeolite catalyst was added, followed by 150 kg of H2O2. The mixture was reacted at a constant temperature of 70°C for 30 minutes. After the reaction was completed, the mixture was centrifuged at 6000 rpm for 20 minutes to separate the solid catalyst. The remaining solution was subjected to a reverse osmosis membrane to remove the solvent at a pressure of 5 bar. The obtained solid product was dried at 70°C for 15 hours to obtain the modified lignin.

[0029] The polyols include PEG-400 and glycerol. 200 kg of PEG-400 solution and 800 kg of glycerol solution were added to a reactor. 35 kg of modified lignin was added to the mixed solution, followed by 4 kg of methanesulfonic acid catalyst. The reaction was carried out in an apparatus equipped with a stirrer, thermometer, and reflux condenser, with continuous stirring at 140°C for 60 minutes. After the reaction was completed, the solution was cooled to room temperature, and the pH was adjusted to 7.0 with sodium hydroxide to produce a lignin-based polyether polyol.

[0030] The method adopts a one-step foaming preparation process, wherein 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 are added into a reactor and rapidly stirred at room temperature, 430 parts of isocyanate are then added and stirred continuously, and after being evenly blended, the mixture is poured into a mold for molding, and the flame-retardant polyurethane foam plastic is obtained after aging for a period of time.

[0031] Example 3 30 kg of HZSM-5 molecular sieve carrier and 60 L of a mixed solution of copper nitrate and chromium nitrate (the molar ratio of copper ion to chromium ion is 1:1) were added to 130 L of deionized water, mixed evenly, and then ultrasonicated for 1.5 hours. The above solution was placed on a magnetic stirrer and stirred at 800 rpm for 10 hours, then transferred to a hydrothermal reactor, and the reactor was placed at 110°C for reaction for 10 hours. The reactor was cooled, and the mixed solution was filtered to obtain a solid product. After grinding, it was placed in a muffle furnace and calcined at 600°C for 4 hours, and then placed in a tubular furnace and reduced at 680°C for 3 hours under a H2 atmosphere. After grinding, it was vacuum dried to obtain a copper-chromium loaded HZSM-5 zeolite catalyst. 175 kg of lignin was mixed with 2900 kg of dioxane, placed in a reactor equipped with a reflux condenser, stirred and heated to 60°C. After the lignin was completely dissolved, 35 kg of copper-chromium-loaded HZSM-5 zeolite catalyst was added, followed by 200 kg of H2O2. The mixture was reacted at a constant temperature of 80°C for 50 minutes. After the reaction was completed, the solid catalyst was separated by centrifugation at a speed of 10,000 rpm for 10 minutes. The solvent was removed from the remaining solution using a reverse osmosis membrane at a pressure of 10 bar. The resulting solid product was dried at 80°C for 15 hours to obtain modified lignin.

[0032] The polyol comprises PEG-400 and glycerol. 300 kg of PEG-400 solution and 900 kg of glycerol solution are added to a reactor. 45 kg of modified lignin is then added to the mixed solution, followed by 5 kg of potassium sulfonic acid catalyst. The reaction is carried out in an apparatus equipped with a stirrer, thermometer, and reflux condenser, with continuous stirring at 160°C for 30 minutes. After the reaction is completed, the solution is cooled to room temperature, and the pH is adjusted to 7.0 with sodium hydroxide to produce the lignin-based polyol.

[0033] A one-step foaming preparation process is adopted, 230 parts of lignin-based polyether polyol, 60 parts of tris(1-chloro-2-propyl) phosphate, 20 parts of montmorillonite, 10 parts of nano-tungsten carbide, 5 parts of triethanolamine, 2 parts of dibutyltin dilaurate, 40 parts of monofluorodichloroethane, and 5 parts of water are added into a reactor and quickly stirred at room temperature, 470 parts of isocyanate are added and continued to be stirred, and after being evenly blended, the mixture is poured into a mold for molding, and after aging for a period of time, a flame-retardant polyurethane foam plastic is obtained.

[0034] Example 4 The only difference from Example 1 is that the mass ratio of polyol: modified lignin: methanesulfonic acid catalyst is 1000:45:4.5, wherein the polyol includes 300 kg of PEG-400 solution and 700 kg of glycerol solution. The remaining raw materials and steps are the same as those in Example 1.

[0035] Example 5 The only difference from Example 2 is that the hydrothermal reaction temperature is 108° C., the hydrothermal reaction time is 11 h, the reduction temperature is 670° C., and the reduction time is 3.5 h. The remaining raw materials and steps are the same as those in Example 2.

[0036] Example 6 The flame-retardant polyurethane foam differed from Example 3 only in that it included the following raw materials in parts by weight: 236 parts of lignin-based polyether polyol, 65 parts of tris(1-chloro-2-propyl) phosphate, 18 parts of montmorillonite, 11 parts of nano-tungsten carbide, 3 parts of triethanolamine, 1 part of dibutyltin dilaurate, 42 parts of monofluorodichloroethane, 460 parts of isocyanate, and 6 parts of water. The remaining raw materials and steps were the same as those in Example 3.

[0037] Comparative Example 1 Compared with Example 1, the only difference is that lignin-based polyether polyol is not used, that is, polyether polyol is used instead of lignin-based polyether polyol, and the other raw materials and steps are the same as those in Example 1.

[0038] Comparative Example 2 Compared with Example 1, the only difference is that the copper-chromium loaded HZSM-5 zeolite catalyst is not used to modify the lignin, that is, lignin is used instead of modified lignin to prepare lignin-based polyether polyol. The other raw materials and steps are the same as those in Example 1.

[0039] Comparative Example 3 Compared with Example 1, the only difference is that nano tungsten carbide is not used, and the remaining raw materials and steps are consistent with Example 1.

[0040] Comparative Example 4 Compared with Example 1, the only difference is that no carbon-forming agent is used, and the remaining raw materials and steps are the same as those of Example 1.

[0041] Relevant performance tests were performed on the flame retardant polyurethane foams prepared in Examples 1 to 6 and Comparative Examples 1 to 4.

[0042] The flame retardant performance test method is derived from the national standard GB / T 20284-2006 Single-unit combustion test for building materials or products. The performance requirements are derived from the national standard GB 8624-2012 Classification of combustion performance of building materials and products: combustion growth rate index ≤ 120W / s; lateral flame spread does not reach the edge of the long wing of the specimen; total heat release in 600s ≤ 7.5MJ. The flame retardant performance test results are shown in Table 1.

[0043] Table 1 Flame retardant properties of polyurethane foams prepared in Examples 1 to 6 and Comparative Examples 1 to 4

[0044] As shown in Table 1, the flame retardant properties of the polyurethane foams prepared in Examples 1 to 6 are significantly higher than those of the polyurethane foams prepared in Comparative Examples 1 to 4, and meet the requirements of the national standard GB 8624-2012.

[0045] Combined with the data in Table 1, it can be seen from the comparison between Example 1 and Comparative Examples 1 to 4 that lignin-based polyether polyol, modification of lignin, use of nano-tungsten carbide and use of carbonizing agent respectively have an impact on the flame retardant properties. According to the performance indicators of the combustion growth rate index, flame lateral spread length and total heat release of 600S of Comparative Examples 3 and 4 compared with Example 1, there are significant differences. It can be seen that nano-tungsten carbide and carbonizing agent have a greater impact on the flame retardant properties; combined with the performance indicators of Comparative Examples 1 to 4 compared with Example 1, it can be seen that the main factors affecting the flame retardant properties of the prepared polyurethane foam plastic are the use of nano-tungsten carbide and the use of carbonizing agent. The use of lignin-based polyether polyol and modification of lignin also have a certain effect on the flame retardant properties of the prepared polyurethane foam plastic, but it is less than the effect of using nano-tungsten carbide and the use of carbonizing agent.

[0046] The physical performance test methods and requirements are derived from the national standard GB / T 20219-2015 Spray rigid polyurethane foam for thermal insulation, which requires: apparent core density ≥ 45kg / m 3 ; Compression strength ≥ 200kPa; Initial thermal conductivity ≤ 0.030; Aging thermal conductivity ≤ 0.034; Tensile strength ≥ 200kPa; Physical property test results are shown in Table 2.

[0047] Table 2 Physical properties of polyurethane foams prepared in Examples 1 to 6 and Comparative Examples 1 to 4

[0048] As can be seen from Table 2, the physical properties of the polyurethane foam plastics prepared in Examples 1 to 6 are significantly higher than those of the polyurethane foam plastics prepared in Comparative Examples 1 to 4, and meet the requirements of the national standard GB / T 20219-2015.

[0049] Combined with the data in Table 2, it can be seen from the comparison between Example 1 and Comparative Examples 1 to 4 that the lignin-based polyether polyol and the modification of lignin have an impact on the physical properties of the prepared polyurethane foam plastics. The apparent core density, compressive strength and tensile strength performance in Comparative Examples 1 and 2 are several times different from those in Example 1. It can be seen that the use of lignin-based polyether polyol and the modification of lignin have a greater impact on the apparent core density, compressive strength and tensile strength; there is also a gap in the thermal conductivity index between Comparative Examples 1 and 2 and Example 1. It can be seen that lignin-based polyether polyol and the modification of lignin also have a certain effect on the thermal conductivity. By comparing the performance indicators of Comparative Examples 1 to 4 with those of Example 1, it can be seen that the factors affecting the apparent core density, compressive strength and tensile strength of the prepared polyurethane foam plastics are mainly the use of lignin-based polyether polyols and the modification of lignin, while nano-tungsten carbide and the use of carbonizing agents have a greater influence on the thermal conductivity of the prepared polyurethane foam plastics, and also have a certain influence on the apparent core density, compressive strength, tensile strength and thermal conductivity.

[0050] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a flame retardant polyurethane foam, characterized in that: The following steps are involved: S1. Preparing modified lignin: modifying lignin using a copper-chromium loaded HZSM-5 zeolite catalyst to obtain modified lignin; S2. Preparing a modified polyether polyol: mixing the modified lignin with a polyol, adding a catalyst to react, and obtaining a lignin-based polyether polyol; S3. Preparation of flame-retardant polyurethane foam: Stir lignin-based polyether polyol, flame retardant, carbonizing agent, triethanolamine, dibutyltin dilaurate, monofluorodichloroethane, nano-tungsten carbide and water evenly, then add isocyanate and continue stirring. After being evenly blended, pour into a mold to form, and obtain flame-retardant polyurethane foam after aging.

2. The method for preparing the flame retardant polyurethane foam according to claim 1, wherein: Modification of lignin includes the following steps: The first step is to place the HZSM-5 molecular sieve carrier into a mixed solution containing copper ions and chromium ions, perform ultrasonication, and then perform a hydrothermal reaction after magnetic stirring. The solid phase is separated and reduced under hydrogen to obtain a copper-chromium loaded HZSM-5 zeolite catalyst. Step 2: dissolving lignin in dioxane, adding the copper-chromium loaded HZSM-5 zeolite catalyst, then adding hydrogen peroxide, reacting at a constant temperature, centrifuging to obtain the liquid phase, and separating the liquid phase through a membrane to obtain a solid product as modified lignin.

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

1.

4. The method for preparing the flame retardant polyurethane foam according to claim 2, characterized in that: In the first step, the mass ratio of the HZSM-5 molecular sieve carrier to the volume of the mixed solution is 1:1.5-2, and the ratio unit is 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 the flame retardant polyurethane foam according to claim 2, characterized in that: The ultrasonic time in the first step is 1 to 1.5 hours; the magnetic stirring speed is 800 to 1200 rpm and the time is 8 to 10 hours; the temperature of the hydrothermal reaction is 100 to 110° C. and the time is 10 to 12 hours; the temperature of the reduction is 650 to 680° C. and the time is 3 to 5 hours.

6. The method for preparing the 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° C. for 4-6 hours.

7. The method for preparing the flame retardant polyurethane foam according to claim 2, wherein: The lignin dissolution temperature in the second step is 50-60°C; the constant temperature is 70-80°C, and the time is 30-50 minutes; the centrifugal speed is 6000-10000 rpm, and the time is 10-20 minutes; the membrane separation uses a reverse osmosis membrane, and the pressure range is 5-10 bar.

8. The method for preparing the 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 the polyol: modified lignin: catalyst is 1000-1200: 35-45: 4-5. After the catalyst is added to S2, the reaction is carried out at a temperature of 140-160° C. for 0.5-1 hour, and then the pH value is adjusted to 7.0 with sodium hydroxide.

9. The method for preparing the flame retardant polyurethane foam according to claim 1, wherein: The flame-retardant polyurethane foam plastic 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 carbonizing agent, 8-12 parts of nano-tungsten carbide, 3-5 parts of triethanolamine, 1-3 parts of dibutyltin dilaurate, 40-50 parts of monofluorodichloroethane, 430-470 parts of isocyanate and 5-10 parts of water, wherein the flame retardant is one of dimethyl methylphosphonate and tris(1-chloro-2-propyl) phosphate, and the carbonizing agent is one of expandable graphite, montmorillonite and polysiloxane.

10. A flame retardant polyurethane foam plastic prepared by the method for preparing a flame retardant polyurethane foam plastic according to any one of claims 1 to 9.

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