Preparation method of environment-friendly polyurethane flame-retardant material

Abstract

The present application relates to the technical field of environment-friendly flame-retardant polyurethane preparation, in particular to a preparation method of environment-friendly polyurethane flame-retardant material, modified nano-SiO2, foam stabilizer, water, amine catalyst and gel catalyst are added to a composite system of lignin-based polyol and polyether polyol, modified intumescent flame retardant microcapsules are added after uniform stirring to obtain component A; polymeric isocyanate is mixed and stirred with component A, injection molding foaming is carried out, and demolding and curing are carried out to obtain polyurethane flame-retardant material; during the foaming and curing of the polyurethane, the modified intumescent flame retardant microcapsules form a gradient distribution in the surface layer region of the polyurethane material; by modifying the nano-SiO2, it is preferentially distributed in the cell wall region during the cell formation process, the overflow of CO2 is delayed, the aromatic structure in the lignin-based polyol participates in the carbonization reaction, the graphitization degree and thermal stability of the carbon layer are improved, and the three-phase synergy realizes the multiple flame-retardant functions of gas phase dilution, solid phase barrier and carbon layer enhancement.

Description

Technical Field

[0001] This invention relates to the field of environmentally friendly flame-retardant polyurethane preparation technology, specifically to a method for preparing environmentally friendly polyurethane flame-retardant materials. Background Technology

[0002] Environmentally friendly flame-retardant polyurethane is a polymer material that combines environmental friendliness with flame-retardant properties. It uses polyols and isocyanates as the main reactants, and introduces halogen-free, low-toxicity, low-volatile organic compound (VOC) and renewable raw material components into the system, thereby achieving a synergistic improvement in both environmental friendliness and fire safety. Due to its excellent mechanical properties, processing performance, and designability, polyurethane materials are widely used in building insulation, fireproof partitions, furniture upholstery, automotive interiors, and electronic packaging. Rigid polyurethane foam, in particular, has become an important material in the field of building energy-saving insulation due to its low thermal conductivity and high closed-cell ratio.

[0003] However, in traditional polyurethane systems, polyols mainly include polyether polyols and polyester polyols, whose raw material sources primarily rely on petrochemical products, resulting in non-renewable nature and high carbon emissions. With increasing environmental protection requirements, bio-based polyols are gradually being introduced to partially replace traditional polyol systems. Bio-based polyols are typically derived from renewable biomass resources such as castor oil, soybean oil, cashew nut shells, and lignin. They can absorb carbon dioxide during plant growth, thus significantly reducing the material's carbon footprint over its life cycle. Among these, lignin-based polyols, due to their aromatic structures, not only provide a renewable carbon source but also promote char formation during combustion, thus showing good application potential in the field of flame-retardant polyurethanes.

[0004] Intumescent flame retardants are widely used in the flame-retardant modification of polyurethanes due to their characteristics such as being halogen-free, producing low smoke, and forming a char layer during combustion. However, traditional intumescent flame retardants are usually introduced into the polyurethane system through physical blending, and are mainly in a random dispersion state during foaming and curing. Since the surface and cell walls of polyurethane materials are usually important areas for heat transfer, oxygen diffusion, and combustion reactions, and traditional uniformly distributed flame retardants are mostly present inside the material, they cannot fully play their role in blocking heat transfer and inhibiting the release of combustible components in the early stages of combustion, resulting in low utilization efficiency of some flame-retardant components.

[0005] Furthermore, polyurethane systems often use water as a chemical foaming agent. Water reacts with isocyanate to generate carbon dioxide gas, forming a closed-cell structure. This closed-cell structure reduces the material's thermal conductivity and improves its thermal insulation performance. Simultaneously, carbon dioxide, as a non-flammable gas, can dilute the oxygen concentration and combustible pyrolysis products during combustion, thus inhibiting flame propagation to some extent.

[0006] However, carbon dioxide molecules have a high diffusion coefficient and easily migrate outward through the cell walls, causing changes in the internal gas composition of the foam and a gradual decrease in the gas-phase assisted flame retardant effect. Improving the structural stability of the cell walls and synergistically optimizing the distribution of flame-retardant components within the cell structure has become an important direction for enhancing the long-term performance of environmentally friendly flame-retardant polyurethane materials. Therefore, how to reduce the proportion of petroleum-based raw materials used while increasing the effective utilization rate of flame-retardant components in polyurethane materials and enhancing the stability of the cell structure is a problem that needs to be solved in the development of environmentally friendly flame-retardant polyurethane materials. Based on this, this invention provides a method for preparing an environmentally friendly polyurethane flame-retardant material. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for preparing an environmentally friendly polyurethane flame-retardant material, comprising the following steps: S1. By weight, take 20 parts of a composite polyol, add 1-5 parts of modified nano-SiO2, and disperse at high speed of 1200-2000 rpm for 8-15 min to form a modified nano-SiO2 pre-dispersion system; take another 80 parts of a composite polyol, add the modified nano-SiO2 pre-dispersion system to the composite polyol, stir at 800-1200 rpm for 5-10 min, and sequentially add 1.5-3 parts of foam stabilizer, 1.5-3.5 parts of water, 0.3-1 parts of amine catalyst, and 0.05-0.3 parts of gel catalyst. After each raw material is added, stir evenly before adding the next raw material. After all raw materials are added, continue stirring for 5-10 min. Finally, add 15-25 parts of modified intumescent flame-retardant microcapsules, stir at 1000 rpm for 30-90 s, and degas under vacuum at -0.08 MPa for 3-5 min to obtain component A.

[0008] The composite polyol is a compound system of polyether polyol and lignin-based polyol, with a total amount of 100 parts by weight, 20-35 parts by weight of lignin-based polyol, and the remainder being polyether polyol.

[0009] S2. Take 90-130 parts by weight of polymeric isocyanate as component B; mix component A and component B, stir at high speed, inject into mold for foaming and molding, demold and cure at 50-60℃ for 12-24h to obtain polyurethane flame retardant material.

[0010] The modified intumescent flame retardant microcapsule comprises an intumescent flame retardant core encapsulated by a polyurethane shell covering the core and a silicon-oxygen structure loaded on the surface of the polyurethane shell.

[0011] Preferably, the preparation process of the composite polyol is as follows: 20-35 parts of lignin-based polyol are mixed with 65-80 parts of polyether polyol, and stirred at 300-500 rpm for 10-20 minutes at 40-50°C until the lignin-based polyol is fully dispersed to obtain the composite polyol.

[0012] Preferably, the foam stabilizer is an organosilicon foam stabilizer; the amine catalyst is selected from one or more of triethylenediamine and pentamethyldiethylenetriamine; and the gel catalyst is selected from one or more of stannous octoate and bismuth-based catalysts.

[0013] Preferably, the polyether polyol is selected from rigid foam polyether polyols with a hydroxyl value of 300-500 mg KOH / g; the lignin-based polyol has a hydroxyl value of 200-400 mg KOH / g.

[0014] Preferably, the intumescent flame retardant is selected from one or more of ammonium polyphosphate (APP), melamine polyphosphate (MPP), and piperazine polyphosphate (PAPP).

[0015] Preferably, the preparation process of modified intumescent flame retardant microcapsules is as follows: 25-40 parts by weight of intumescent flame retardant are dispersed in 100 parts of deionized water and stirred at high speed to form a uniform suspension; a polyol mixture is slowly added to the suspension and stirred evenly; toluene diisocyanate (TDI) is slowly added dropwise and stirred at 50-70°C for 2-4 hours to obtain a microcapsule slurry; a silane coupling agent hydrolysate is added to the microcapsule slurry for surface modification; after centrifugation, washing, and drying, modified intumescent flame retardant microcapsules are obtained.

[0016] The polyurethane-organosilicon composite shell includes polyether segments and is loaded with siloxane structures. The siloxane structures are formed by the hydrolysis and condensation of silane coupling agents and are used to regulate the interfacial interaction between the microcapsules and the continuous polyurethane phase.

[0017] Preferably, the modified intumescent flame retardant microcapsules are enriched in the near-surface layer along the thickness direction of the polyurethane material; the modified silica is enriched in the cell wall region.

[0018] Preferably, the polyol mixture includes polyethylene glycol (PEG-400), polypropylene glycol (PPG-1000), and pentaerythritol (PER); the mass ratio of the intumescent flame retardant, polyethylene glycol, polypropylene glycol, and pentaerythritol is 1:(0.15-0.3):(0.08-0.2):(0.02-0.06).

[0019] Preferably, the mass ratio of the intumescent flame retardant, toluene diisocyanate (TDI), and silane coupling agent is 1:(0.4-0.6):(0.01-0.05); the silane coupling agent hydrolysate is prepared by dissolving the silane coupling agent in an ethanol-water mixed solvent, and the mass fraction of the silane coupling agent is 1%-5%.

[0020] Preferably, 1-5 parts of nano-SiO2 are added to an ethanol-water mixed solvent and ultrasonically dispersed to obtain a dispersion. 3%-10% of the mass of nano-SiO2 is added to the dispersion as a silane coupling agent. The mixture is stirred at 50-70℃ for 3-5 hours, filtered, washed, and dried to obtain modified nano-SiO2. The silane coupling agent is selected from one or more of KH-560, KH-550, or isocyanate-based silanes.

[0021] Preferably, the modified nano-SiO2 particles have a diameter of 20–80 nm, and the modified intumescent flame retardant microcapsules have a diameter of 0.8–3 μm.

[0022] This invention has at least one of the following technical effects: By regulating the surface and interfacial properties of intumescent flame retardant microcapsules, it enables a gradient distribution in the surface region of the polyurethane material during the foaming and curing process. Simultaneously, by modifying nano-SiO2, it preferentially distributes itself in the cell wall region during cell formation, delaying CO2 leakage, thereby forming a multi-scale flame-retardant and heat-insulating system combining a surface flame-retardant reinforcement structure and an internal inorganic cell wall reinforcement structure. Furthermore, the aromatic structure in the lignin-based polyol participates in the char formation reaction, improving the graphitization degree and thermal stability of the char layer. Additionally, the lignin-based polyol partially replaces the polyether polyol, enhancing the environmental performance of the polyurethane material. Attached Figure Description

[0023] Figure 1 Here is a SEM-EDS line scan image of the cross-section of the polyurethane flame-retardant material prepared in Example 1;

[0024] Figure 2 The image shows a SEM-EDS line scan of the cross-section of the polyurethane flame-retardant material prepared in Comparative Example 5. Detailed Implementation

[0025] The present invention will now be described in detail through specific embodiments. However, these illustrative embodiments are for purposes and uses only to illustrate the invention and do not constitute any limitation on the actual scope of protection of the invention, nor are they intended to limit the scope of protection of the invention to these embodiments. All equivalent transformations or simple substitutions made based on the substantive content of this application should fall within the scope of protection of this application. For parameter ranges not mentioned, intermediate values ​​are selected. Furthermore, for mass percentages or weight percentages not explicitly stated or mentioned, they generally refer to the final concentration after addition.

[0026] The singular forms “for,” “or,” “a,” “any,” and “the” used in this application are intended to include the plural forms unless the context clearly indicates otherwise.

[0027] The modified intumescent flame retardant microcapsules exhibit a gradient distribution from the surface to the interior along the thickness direction of the polyurethane material. Preliminary analysis suggests that their formation process is mainly influenced by the surface interface properties of the modified intumescent flame retardant microcapsules, the evolution of the gas-liquid interface during the foaming process, and the polyurethane foaming and curing process.

[0028] The silica-oxygen structure loaded on the surface of the modified intumescent flame retardant microcapsules is formed by the hydrolysis and condensation of KH-560. This structure results in a significantly lower interfacial free energy on the microcapsule surface compared to unmodified intumescent flame retardant particles. In the initial stages of the polyurethane reaction, the system viscosity is low, and the polyurethane shell exhibits good structural compatibility with the polyurethane matrix, enabling the microcapsules to maintain low interfacial migration resistance during the initial foaming phase.

[0029] During polyurethane foaming, water reacts with isocyanate to generate CO2, and bubble nucleation, growth, and pore structure formation gradually occur within the system. As the gas-liquid interface continuously forms, the modified intumescent flame retardant microcapsules are redistributed within the continuous phase due to factors such as particle-liquid interfacial interactions, gas-liquid interfacial adsorption, and changes in system viscosity. Microcapsule particles with certain interfacial activity are more likely to accumulate in the pore-forming region and near-surface area of ​​the material. As the polyurethane crosslinking reaction proceeds, the system viscosity rapidly increases, and the positions of the microcapsules are gradually fixed, resulting in a gradient distribution structure of flame-retardant components that gradually changes from the interior of the material to the near-surface region. Due to the time window limitations of the polyurethane foaming and gelation process, microcapsules do not migrate extensively to the outermost surface of the material and precipitate; instead, they are mainly stably distributed in the near-surface and pore interface regions.

[0030] After surface modification with KH-560, the epoxy groups on the surface of nano-SiO2 can chemically bond with isocyanate groups, making it easier for nano-SiO2 to be adsorbed and fixed in the gas-liquid interface region during the formation of cell walls. Based on the geometric characteristics of the cell walls being composed of a very thin polyurethane film, nano-SiO2, with its high specific surface area, can form localized enrichment within the limited cell wall space, constructing an organic-inorganic composite cell wall structure. This composite wall can improve the structural stability of the cell wall, increase the tortuosity of the gas molecule diffusion path, and reduce the rate of outward diffusion of gases such as CO2 in the closed-cell structure, thereby helping to maintain the stability of the gas composition inside the cell.

[0031] The aromatic structures in lignin-based polyols can improve the rigidity of polyurethane networks and promote the formation of aromatic char layers during combustion, thereby enhancing the continuity and thermal stability of the char residue. Simultaneously, lignin-based polyols partially replace traditional petroleum-based polyether polyols, reducing the proportion of petroleum-based raw materials used and improving the environmental friendliness of polyurethane materials.

[0032] The above structure forms a multi-scale synergistic flame-retardant effect during combustion: the modified intumescent flame-retardant microcapsules enriched in the near-surface and cell interface regions release flame-retardant active components during heating and promote the formation of an expanded char layer, forming a continuous barrier layer on the material surface to reduce heat transfer and oxygen diffusion; the modified nano-SiO2 distributed in the cell wall region forms an inorganic barrier layer, delaying the outward diffusion of CO2 and enhancing the structural stability of the char layer; the aromatic structure in the lignin polyol promotes the formation of the char layer during combustion, providing a certain flame-retardant enhancement effect for the polyurethane material and playing an auxiliary flame-retardant role; the three-phase synergy achieves multiple flame-retardant functions of gas phase dilution, solid phase barrier, and char layer enhancement, and the modified intumescent flame-retardant microcapsules enriched in the near-surface region of the polyurethane material can have a higher effective utilization rate.

[0033] Example

[0034] Example 1

[0035] Five parts of nano-SiO2 with a particle size of 20-80 nm were added to an ethanol-water mixed solvent and ultrasonically dispersed for 30 min to obtain a dispersion. 0.2 parts of KH-560 were added to the dispersion, and the mixture was stirred at 60 °C for 4 h. After filtration, washing, and drying, modified nano-SiO2 was obtained.

[0036] 35 parts of ammonium polyphosphate were dispersed in 100 parts of deionized water and stirred at high speed to form a uniform suspension. 8 parts of PEG-400, 5 parts of PPG-1000, and 1.4 parts of PER were mixed to prepare a polyol mixture. The polyol mixture was slowly added to the suspension and stirred at 500 rpm for 30 min to fully wet the APP surface. After stirring, 17.5 parts of toluene diisocyanate were slowly added dropwise, and the mixture was stirred at 600 rpm for 3 h at 60 °C to obtain a microcapsule slurry. Silane coupling agent hydrolysate was added to the microcapsule slurry for surface modification. After centrifugation at 8000 rpm for 10 min, the microcapsules were washed twice with deionized water and once with anhydrous ethanol, and dried at 50 °C for 24 h to obtain modified intumescent flame retardant microcapsules.

[0037] The silane coupling agent hydrolysate is prepared by dissolving 1 part KH-560 and 0.5 parts KH-570 in an ethanol-water mixed solvent (45 parts anhydrous ethanol and 5 parts deionized water), and the mass fraction of silane coupling agent in the silane coupling agent hydrolysate is about 3%.

[0038] Take 28 parts of lignin-based polyol and 72 parts of polyether polyol, mix them, and stir at 400 rpm for 15 min at 45℃ until the lignin-based polyol is fully dispersed to obtain 100 parts of composite polyol; take 20 parts of composite polyol, add 3 parts of modified nano-SiO2, and disperse at 1600 rpm for 10 min to form a modified nano-SiO2 pre-dispersion system; add the modified nano-SiO2 pre-dispersion system to the remaining 80 parts of composite polyol, stir at 1000 rpm for 10 min, and add 2 parts of organosilicon foam stabilizer, 2.5 parts of water, 0.6 parts of triethylenediamine and 0.2 parts of bismuth-based catalyst in sequence. After each raw material is added, stir evenly before adding the next raw material. After all raw materials are added, continue stirring for 5-10 min. Finally, add 20 parts of modified intumescent flame retardant microcapsules, stir at 1000 rpm for 1 min, and degas under vacuum at -0.08 MPa for 5 min to obtain component A.

[0039] Take 110 parts of polymeric isocyanate as component B, mix component A and component B, stir at high speed, inject into mold for foaming and molding, demold and cure at 50°C for 24 hours to obtain polyurethane flame retardant material.

[0040] Example 2

[0041] The difference from Example 1 is that the amount of lignin-based polyol is 20 parts and the amount of polyether polyol is 80 parts, while the remaining steps are the same as in Example 1.

[0042] Example 3

[0043] The difference from Example 1 is that the number of lignin-based polyols is 35 parts and the number of polyether polyols is 65 parts, while the remaining steps are the same as in Example 1.

[0044] Example 4

[0045] The difference from Example 1 is that the amount of modified nano-SiO2 added is 5 parts, and the rest of the steps are the same as in Example 1.

[0046] Example 5

[0047] The difference from Example 1 is that the number of parts of the modified intumescent flame retardant microcapsules is 15, and the remaining steps are the same as in Example 1.

[0048] Example 6

[0049] The difference from Example 1 is that the number of parts of the modified intumescent flame retardant microcapsules is 25, and the remaining steps are the same as in Example 1.

[0050] Example 7

[0051] The difference from Example 1 is that the intumescent flame retardant used is melamine polyphosphate, and the remaining steps are the same as in Example 1.

[0052] Example 8

[0053] The difference from Example 1 is that the amine catalyst used is pentamethyldiethylenetriamine, the gel catalyst is stannous octoate, and the remaining steps are the same as in Example 1.

[0054] Comparative Example

[0055] Comparative Example 1

[0056] The difference from Example 1 is that no lignin polyol is added, but the rest of the steps are the same as in Example 1.

[0057] Comparative Example 2

[0058] The difference from Example 1 is that the nano-SiO2 is not modified, and the remaining steps are the same as in Example 1.

[0059] Comparative Example 3

[0060] The difference from Example 1 is that no modified nano-SiO2 is added, while the rest of the steps are the same as in Example 1.

[0061] Comparative Example 4

[0062] The difference from Example 1 is that the number of parts of the modified expandable microcapsules is 10, and the remaining steps are the same as in Example 1.

[0063] Comparative Example 5

[0064] The difference from Example 1 is that the microcapsules do not undergo surface modification, while the remaining steps are the same as in Example 1.

[0065] Comparative Example 6

[0066] The difference from Example 1 is that no modified expanded microcapsules and modified nano-SiO2 are added, while the remaining steps are the same as in Example 1.

[0067] Performance testing

[0068] The polyurethane materials prepared in Example 1 and Comparative Example 5 were subjected to SEM-EDS analysis, as follows: The cross-sectional morphology of the polyurethane materials prepared in Example 1 and Comparative Example 5 was observed using a scanning electron microscope, and elemental line scanning analysis was performed using energy-dispersive X-ray spectroscopy (EDS). See details below. Figure 1 and Figure 2 .

[0069] The following performance tests were performed on the polyurethane flame-retardant materials prepared in Examples 1-8 and Comparative Examples 1-6.

[0070] Apparent density: The apparent density of the polyurethane flame retardant materials prepared in Examples 1-8 and Comparative Examples 1-6 were tested according to the method of GB / T 6343-2009 "Determination of Apparent Density of Foamed Plastics and Rubber".

[0071] Closed-cell ratio: According to GB / T 10799-2008 "Determination of open-cell and closed-cell volume percentage of rigid foamed plastics", the closed-cell ratios of the polyurethane flame-retardant materials prepared in Example 1, Comparative Example 3, and Comparative Example 6 were tested respectively.

[0072] Thermal conductivity: The initial thermal conductivity of the polyurethane flame retardant materials prepared in Example 1, Comparative Example 3 and Comparative Example 6 was tested according to GB / T 10294-2008 "Determination of steady-state thermal resistance and related properties of thermal insulation materials by protective hot plate method". Then, the polyurethane was aged at 70°C for 14 days, and the thermal conductivity after aging was tested using the same method. The change rate of thermal conductivity was calculated as follows: thermal conductivity change rate = (thermal conductivity after aging - initial thermal conductivity) / initial thermal conductivity × 100%.

[0073] Limiting Oxygen Index (LOI): The limiting oxygen index of the polyurethane flame retardant materials prepared in Examples 1-8 and Comparative Examples 1-6 was tested according to GB / T 2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test".

[0074] UL-94 Vertical Burning Rating: The vertical burning rating of the polyurethane flame retardant materials prepared in Examples 1-8 and Comparative Examples 1-6 was tested according to GB / T 2408-2008 "Determination of Burning Performance of Plastics - Horizontal and Vertical Methods".

[0075] Cone calorimetry: Cone calorimetry was performed on the polyurethane flame retardant material samples prepared in Example 1, Comparative Examples 1, 3, 5 and 6 in accordance with GB / T 16172-2007 "Test Method for Heat Release Rate of Building Materials" to detect the peak heat release rate (pHRR), total heat release (THR), smoke release rate (SPR), total smoke release (TSP) and ignition time (TTI).

[0076] Table 1 Performance test results of Examples 1-8 and Comparative Examples 1-6

[0077]

[0078] Table 2. Cone calorimetry results for Example 1, Comparative Examples 1, 3, 5, and 6.

[0079]

[0080] Table 1 shows that the polyurethane flame-retardant material prepared in Example 1, while maintaining a reasonable apparent density, exhibits a high closed-cell ratio, low thermal conductivity, and a low rate of change in thermal conductivity after aging. This indicates that the participation of modified nano-SiO2 in the construction of the cell wall structure is beneficial to improving the stability of the cell structure and enhancing the long-term thermal insulation performance of the material. The limiting oxygen index and vertical burning rating of Example 1 are superior to those of the comparative examples, indicating a synergistic flame-retardant effect among the modified intumescent flame-retardant microcapsules, modified nano-SiO2, and lignin-based polyols.

[0081] As shown in Table 2, the ignition time of Example 1 was prolonged, while the peak heat release rate, total heat release, and smoke release-related indicators decreased, indicating that Example 1 could more effectively suppress heat and smoke release during combustion. Combined with... Figure 1 and Figure 2 It can be seen that in Example 1, the P element exhibits a gradient distribution that decreases from the near-surface layer to the interior, while in Comparative Example 5, the gradient distribution of the P element is not obvious. This indicates that the surface modification of the microcapsule is beneficial for the enrichment of flame retardants in the near-surface region, thereby improving the effective utilization rate of flame retardants in the early stage of combustion.

[0082] The above results demonstrate and describe the basic principles and main features of this application, as well as its advantages.

[0083] Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the equivalents of the appended claims.

Claims

1. A method for preparing an environmentally friendly polyurethane flame-retardant material, characterized in that, Includes the following steps: S1. By weight, take 20 parts of composite polyol, add 1-5 parts of modified nano-SiO2, and disperse at high speed to form a modified nano-SiO2 pre-dispersion system; take another 80 parts of composite polyol, add the modified nano-SiO2 pre-dispersion system to the composite polyol, stir evenly, and then add 1.5-3 parts of foam stabilizer, 1.5-3.5 parts of water, 0.3-1 parts of amine catalyst and 0.05-0.3 parts of gel catalyst in sequence. Stir evenly after each raw material is added before adding the next raw material. Finally, add 15-25 parts of modified intumescent flame retardant microcapsules, stir evenly, and degas under vacuum to obtain component A; The composite polyol is a compound system of polyether polyol and lignin-based polyol, with a total amount of 100 parts by weight, 20-35 parts by weight of lignin-based polyol, and the remainder being polyether polyol. S2. Take 90-130 parts by weight of polymeric isocyanate as component B; mix component A and component B, stir at high speed, inject into mold for foaming and molding, demold and cure at 50-60℃ for 12-24h to obtain polyurethane flame retardant material. The modified intumescent flame retardant microcapsule comprises an intumescent flame retardant core encapsulated by a polyurethane shell covering the core and a silicon-oxygen structure loaded on the surface of the polyurethane shell.

2. The method for preparing an environmentally friendly polyurethane flame-retardant material according to claim 1, characterized in that: The preparation process of the composite polyol is as follows: 20-35 parts of lignin-based polyol are mixed with 65-80 parts of polyether polyol, and stirred at 300-500 rpm for 10-20 minutes at 40-50℃ until the lignin-based polyol is fully dispersed to obtain the composite polyol.

3. The method for preparing an environmentally friendly polyurethane flame-retardant material according to claim 1, characterized in that: The foam stabilizer is an organosilicon foam stabilizer; the amine catalyst is selected from one or more of triethylenediamine and pentamethyldiethylenetriamine; the gel catalyst is selected from one or more of stannous octoate and bismuth-based catalysts.

4. The method for preparing an environmentally friendly polyurethane flame-retardant material according to claim 1, characterized in that: For rigid foam, polyether polyols with a hydroxyl value of 300-500 mg KOH / g are selected; for lignin-based polyols, the hydroxyl value is 200-400 mg KOH / g.

5. The method for preparing an environmentally friendly polyurethane flame-retardant material according to claim 1, characterized in that: The intumescent flame retardant is selected from one or more of ammonium polyphosphate, melamine polyphosphate, and piperazine polyphosphate.

6. The method for preparing an environmentally friendly polyurethane flame-retardant material according to claim 5, characterized in that: The preparation process of modified intumescent flame retardant microcapsules is as follows: 25-40 parts by weight of intumescent flame retardant are dispersed in 100 parts of deionized water and stirred at high speed to form a uniform suspension; a polyol mixture is slowly added to the suspension and stirred evenly; toluene diisocyanate is slowly added dropwise and stirred at 50-70℃ for 2-4 hours to obtain a microcapsule slurry; a silane coupling agent hydrolysate is added to the microcapsule slurry for surface modification; after centrifugation, washing, and drying, modified intumescent flame retardant microcapsules are obtained. The polyurethane-silicone composite shell includes polyether segments and is loaded with a silicon-oxygen structure, which is formed by the hydrolytic condensation of a silane coupling agent.

7. The method for preparing an environmentally friendly polyurethane flame-retardant material according to claim 6, characterized in that: The polyol mixture includes polyethylene glycol, polypropylene glycol, and pentaerythritol; the mass ratio of the intumescent flame retardant, polyethylene glycol, polypropylene glycol, and pentaerythritol is 1:(0.15-0.3):(0.08-0.2):(0.02-0.06).

8. The method for preparing an environmentally friendly polyurethane flame-retardant material according to claim 6, characterized in that: The mass ratio of the intumescent flame retardant, toluene diisocyanate, and silane coupling agent is 1:(0.4-0.6):(0.01-0.05); the silane coupling agent hydrolysate is prepared by dissolving the silane coupling agent in an ethanol-water mixed solvent, and the mass fraction of the silane coupling agent is 1%-5%.

9. The method for preparing an environmentally friendly polyurethane flame-retardant material according to claim 1, characterized in that: The preparation process of modified nano-SiO2 is as follows: 1-5 parts of nano-SiO2 are added to an ethanol-water mixed solvent and ultrasonically dispersed to obtain a dispersion. 3%-10% of the mass of nano-SiO2 silane coupling agent is added to the dispersion, and the mixture is stirred at 50-70℃ for 3-5 hours. After filtration, washing, and drying, modified nano-SiO2 is obtained. The silane coupling agent is selected from one or more of KH-560, KH-550, or isocyanate-based silanes.

10. The method for preparing an environmentally friendly polyurethane flame-retardant material according to claim 1, characterized in that: The modified nano-SiO2 particles have a diameter of 20–80 nm, and the modified intumescent flame retardant microcapsules have a diameter of 0.8–3 μm.

Images