Vegetable oil-based polyhydric alcohol, preparation method thereof and application of vegetable oil-based polyhydric alcohol in polyurethane foam

Abstract

The invention relates to vegetable oil-based polyhydric alcohol, a preparation method thereof and application of the vegetable oil-based polyhydric alcohol in polyurethane foam, and belongs to the technical field of polyurethane materials. The method comprises the following steps: firstly, reacting amine and phenolic compounds with paraformaldehyde in a solvent to generate a benzoxazine intermediate, and then reacting the benzoxazine intermediate with epoxidized vegetable oil to prepare the vegetable oil-based polyol with a side chain containing a benzoxazine ring. The polyol is blended with assistants such as isocyanate, a foaming agent and the like, and after curing, the polyurethane foam can be prepared. Due to the introduction of the benzoxazine ring, the foam has excellent flame retardant property while obtaining good mechanical properties, the limit oxygen index can reach 21% or above, and the HB-1 flame retardant grade can be reached. Besides, the structure can catalyze the dynamic exchange of ester bonds and carbamate bonds under mild conditions, so that the waste foam can be converted into the adhesive with adhesive property through chemical recovery without adding a catalyst, and the cyclic utilization of the material is realized.

Description

Technical Field

[0001] This invention belongs to the field of polyurethane materials technology, specifically relating to a vegetable oil-based polyol, its preparation method, and its application in polyurethane foam. Background Technology

[0002] Polyurethane foam plays a crucial role in numerous fields, including automotive protection, precision instrument packaging, building insulation, and home furnishings, due to its excellent compressive strength, energy absorption, and lightweight properties. However, its traditional production heavily relies on non-renewable petroleum-based raw materials, facing challenges to resource sustainability and resulting in a high carbon footprint. More seriously, conventional polyurethane foam is highly flammable, releasing large amounts of toxic fumes during combustion, posing a significant threat to life and property safety. This severely limits its application in scenarios with stringent flame-retardant requirements, such as vehicle interiors, electrical equipment, and public places. Therefore, developing polyurethane foam materials that combine flame-retardant properties with environmental friendliness has become a pressing challenge for the industry. Furthermore, the highly cross-linked three-dimensional network structure of polyurethane foam, especially the widely used thermosetting polyurethane, while providing excellent dimensional stability and mechanical strength, also leads to serious challenges in its disposal. Waste polyurethane foam is difficult to degrade, and traditional landfill or incineration methods not only waste resources but also cause environmental pollution. Promoting the circular economy of polyurethane materials and achieving efficient recycling and high-value reuse is an important research direction under the current concepts of green chemistry and sustainable development. To address these challenges, the industry has begun exploring feasible pathways to replace petroleum-based feedstocks with renewable vegetable oils and is committed to designing recyclable polymer structures at the molecular level. For example, existing research has shown that phenolic compounds can be directly grafted onto vegetable oil molecules via Friedel-Crafts alkylation to prepare vegetable oil-based polyphenols. These polyphenols, upon reaction with isocyanates, form a dynamic phenol-carbamate crosslinking network. This design based on dynamic covalent bonds allows the resulting polyurethane foam to be crushed and remolded under specific hot-pressing conditions, achieving physical reprocessing and shape reshaping, providing a new approach for the recycling of polyurethane materials. However, the function of such materials is relatively limited; their dynamic behavior primarily serves physical reprocessing and does not simultaneously impart excellent inherent flame-retardant properties, making it difficult to meet the combined requirements of flame retardancy and safety. Other studies focus on introducing functional elements into vegetable oil-based polyols through chemical modification to improve foam performance. For example, using phosphoric acid as a ring-opening agent to epoxidized vegetable oils can produce phosphorus-containing vegetable oil-based polyols. The introduction of phosphorus gives the resulting polyurethane foam a certain flame-retardant potential. The focus of this technology is on using environmentally friendly processes and element doping to enhance the material's environmental properties and potential functionality. However, this method primarily addresses the issues of raw material recyclability and green foaming processes. The obtained flame-retardant properties are often based on the principle of additive flame retardants, and it also fails to address the chemical recycling mechanism after material use, thus failing to solve the fundamental degradation and resource recycling challenges of thermosetting polyurethane waste.In summary, while existing technologies have made progress in the recyclability of polyurethane raw materials, physical reprocessing, or specific functional modification, there is still a lack of a solution that can integrate multiple core functions—especially efficient flame retardant properties and intrinsic chemical recycling capabilities under mild conditions—at the molecular structure level. Summary of the Invention

[0003] Technical Problem Solved: To address the aforementioned problems in existing technologies, this invention provides a vegetable oil-based polyol and a method for preparing functionalized polyurethane foam using it. This method aims to introduce flame-retardant and catalytically cycling functional groups into the vegetable oil-based polyol through innovative molecular design. This results in polyurethane foam that possesses excellent intrinsic flame-retardant properties and can achieve self-driven chemical recycling and reprocessing under mild conditions, ultimately achieving a balance between high material safety, recyclability, and raw material renewability.

[0004] Technical Solution: A method for preparing a vegetable oil-based polyol, comprising the following steps: a) mixing an amine compound, a phenolic compound, and paraformaldehyde in a first solvent and reacting at 90-110 °C for 4-8 hours to obtain an intermediate containing a benzoxazine structure, wherein the first solvent is anhydrous ethanol or ethyl acetate; wherein, based on the molar amount of the amine compound, the molar amount of the phenolic compound is 1.0-1.05 times, and the molar amount of the paraformaldehyde is 1.0-1.5 times; b) mixing the intermediate obtained in step a) with a catalyst and epoxidized vegetable oil, and reacting at 110-130 °C for 8-12 hours, and after the reaction, post-processing to obtain the vegetable oil-based polyol; wherein, based on the molar amount of the phenolic compound in step a), the molar amount of the epoxy groups in the epoxidized vegetable oil is 1.0-1.2 times.

[0005] In step a), the amine compound is selected from at least one of ethanolamine, furfurylamine, 2-furan ethylamine, 2-cyclohexylethylamine or 2-benzyl-1-ethylamine; the phenolic compound is selected from at least one of salicylic acid, p-hydroxybenzoic acid, o-hydroxybenzoic acid, ferulic acid or caffeic acid.

[0006] In step b), the catalyst is selected from at least one of cyclohexylamine, 4-dimethylaminopyridine or 1,8-diazabicyclo[5.4.0]undec-7-ene; the epoxidized vegetable oil is selected from at least one of castor oil glycidyl ether, epoxidized soybean oil, epoxidized rapeseed oil or epoxidized sunflower oil.

[0007] A plant oil-based polyol is prepared by the above-described method.

[0008] A method for preparing polyurethane foam includes the following steps: mixing vegetable oil-based polyol, isocyanate and additives, foaming and curing; wherein the additives include foaming agents and surfactants.

[0009] By weight, the raw materials used include: 100 parts of vegetable oil-based polyol, 60-120 parts of isocyanate, 3-4 parts of surfactant, and 2-10 parts of foaming agent.

[0010] The isocyanate is selected from at least one of MDI-100, HDI trimer, PM-200 or MDI-50; the foaming agent is at least one of water or cyclopentane; and the surfactant is at least one of AK158, DC-193 or L-633.

[0011] A polyurethane foam is prepared by the above method.

[0012] The above-mentioned plant oil-based polyols are used in the preparation of polyurethane materials.

[0013] The above-mentioned polyurethane foam is used as an adhesive or glue.

[0014] Beneficial Effects: This invention utilizes widely available, inexpensive, and environmentally friendly vegetable oils as raw materials. Through a simple synthesis process, a benzoxazine ring structure is successfully introduced into the molecular side chain, achieving synergistic integration of flame retardancy and recyclability in a single molecular system. This benzoxazine ring structure not only spontaneously triggers a highly efficient fire-retardant mechanism upon heating, endowing polyurethane foam with excellent inherent flame retardant properties, significantly improving its limiting oxygen index to HB-1 flame retardancy rating; simultaneously, this structure can also act as a built-in catalyst under mild conditions, promoting the dynamic exchange reaction between ester and urethane bonds in the system without the need for additional catalysts. This enables efficient chemical recycling and reprocessing of polyurethane foam, and the resulting recycled adhesive maintains considerable shear strength on different substrates. Experiments show that the polyurethane foam prepared using the polyol described in this invention successfully unifies flame retardancy and recyclability—two key properties that are often difficult to achieve simultaneously—within a single material system while maintaining good compressive strength and suitable density. This not only significantly improves the safety and lifecycle sustainability of the material but also provides a technical solution for developing resource-saving, environmentally friendly, high-performance functionalized polyurethane materials. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the castor oil-based polyol in Example 1 of the present invention.

[0016] Figure 2 The infrared spectrum of the castor oil-based polyol in Example 1 of this invention is shown.

[0017] Figure 3This is the 1H NMR spectrum of the castor oil-based polyol in Example 1 of the present invention.

[0018] Figure 4 This refers to the recycling of castor oil-based polyurethane foam in Example 1 of the present invention.

[0019] Figure 5 The shear strength of the adhesive after repeated recycling in Example 1 of this invention. Detailed Implementation

[0020] The present invention will be further described below with reference to specific embodiments: Example 1

[0021] (1) Furfurylamine (19.74 g), salicylic acid (27.66 g), and paraformaldehyde (6.06 g) were mixed in ethyl acetate and refluxed at 100 °C for 6 h. Then, castor oil glycidyl ether (100 g) and 1,8-diazabicyclo[5.4.0]undec-7-ene (1 g) were added, and the mixture was heated to 130 °C and reacted for another 8 h. After the reaction was complete, the mixture was extracted 3-5 times with deionized water, dried over anhydrous magnesium sulfate, filtered to obtain the organic phase, and ethyl acetate was removed by vacuum rotary evaporation to obtain castor oil-based polyol (see technical route for details). Figure 1 For the structural identification of polyols, infrared spectroscopy (IR spectroscopy) is used. Figure 2 The display showed a -OH peak (3280 cm⁻¹). -1 ), COC peak (1294 cm) -1 CNC peak (1131 cm) -1 ) and the characteristic peak of the oxazine ring (945 cm⁻¹) -1 ); 1 H NMR spectrum ( Figure 3 In the sample, the proton peaks of -CH2- and -CH- linked by epoxy groups (2.77 ppm and 2.62 ppm) disappeared, and a -OH peak signal was observed at 4.43 ppm. These results collectively confirm the successful synthesis of castor oil-based polyols.

[0022] (2) According to the formula in Table 1, the synthesized castor oil-based polyol, polyether 4110 polyol and additives were thoroughly mixed according to different ratios of vegetable oil-based polyol and polyether 4110 polyol. Then, it was mixed with isocyanate and stirred for 15 s at a speed of 1800 r / min. Then, it was poured into a mold and cured at room temperature for 24 h to obtain polyurethane foam, labeled as SPU-1, SPU-2, SPU-3, SPU-4 and SPU-5. The obtained castor oil-based polyurethane foam was crushed into 50-200 mesh powder using a multi-functional pulverizer; then, 1 g of powder was dissolved in 15 mL of N,N-dimethylformamide, heated to 140 ℃ and held for 1.5 h to obtain adhesive. Figure 4 As shown, they are labeled as SPUF-1, SPUF-2, SPUF-3, SPUF-4, and SPUF-5, respectively.

[0023] Testing revealed that the polyurethane foam produced in this embodiment has a compressive strength of 0.8-1.4 MPa and a density of 80-110 kg / m³. 3 When the mass fraction of castor oil polyol in the system exceeds 30%, the flame retardant performance of the foam can reach HB-1 level (measured according to ASTM D 63577 standard), with a limiting oxygen index of 21%-23%. Furthermore, the adhesive obtained after solvent recovery maintains a shear strength of 1–5 MPa on various substrates (such as iron, aluminum, copper, wood, glass, and polytetrafluoroethylene). Notably, this adhesive can be dissolved in N,N-dimethylformamide and recycled more than 5 times while maintaining a shear strength of 1–5 MPa.

[0024] Table 1. Formulations for preparing polyurethane foam using different proportions of vegetable oil-based polyols in Example 1 (all by parts by weight).

[0025] Comparative Example 1 The procedure is the same as step (2) in Example 1, but without the addition of castor oil-based polyols. Polyurethane foam is synthesized using only polyether 4110 following the same steps and proportions. However, this type of polyurethane foam requires a reaction at 140 °C for 3 days to obtain a viscous mixture.

[0026] Testing showed that the polyurethane foam prepared in Comparative Example 1 had a compressive strength of 0.5-0.9 MPa and a density of 70-100 kg / m³. 3 The foam did not exhibit flame-retardant properties, with a limiting oxygen index of 18-20%. Furthermore, the mixture obtained after solvent recovery did not possess adhesive properties. Example 2

[0027] (1) Furfurylamine (39.48 g), salicylic acid (55.32 g), and paraformaldehyde (12.12 g) were mixed in ethyl acetate and refluxed at 100 °C for 6 h. Then, epoxidized soybean oil (100 g) and 1,8-diazabicyclo[5.4.0]undec-7-ene (2 g) were added, and the mixture was heated to 130 °C and reacted for another 8 h. After the reaction was completed, the mixture was extracted with deionized water 3-5 times, dried with anhydrous magnesium sulfate, filtered to obtain the organic phase, and the ethyl acetate was removed by vacuum rotary evaporation to obtain soybean oil-based polyol.

[0028] (2) Referring to the formula in Table 1, the synthesized soybean oil-based polyol, phthalic anhydride polyol and additives were thoroughly mixed according to different ratios of vegetable oil-based polyol and phthalic anhydride polyol. Then, it was mixed with isocyanate and stirred for 15 s at a speed of 1800 r / min. The mixture was then poured into a mold and cured at room temperature for 24 h to obtain polyurethane foam. The obtained soybean oil-based polyurethane foam was crushed into 50-200 mesh powder using a multi-functional pulverizer. Then, 1 g of powder was dissolved in 15 mL of N,N-dimethylformamide, heated to 140 ℃ and maintained for 1.5 h to obtain adhesive.

[0029] Testing revealed that the polyurethane foam produced in this embodiment has a compressive strength of 0.7–1.5 MPa and a density of 70–110 kg / m³. 3 When the mass fraction of soybean oil polyol in the system exceeds 30%, the flame retardant performance of the foam can reach HB-1 level (measured according to ASTM D 63577 standard), with a limiting oxygen index of 20%-23%. Furthermore, the adhesive obtained after solvent recovery maintains a shear strength of 1.5-5 MPa on various substrates (such as iron, aluminum, copper, wood, glass, and polytetrafluoroethylene). Notably, this adhesive can be dissolved in N,N-dimethylformamide and recycled more than 5 times while maintaining a shear strength of 1.5-5 MPa.

[0030] Comparative Example 2 The process is the same as step (2) in Example 2, but without the addition of soybean oil-based polyols; polyurethane foam is synthesized using only phthalic anhydride following the same steps and proportions. However, this type of polyurethane foam requires a reaction at 140°C for one day to obtain a viscous mixture.

[0031] Testing revealed that the polyurethane foam prepared in Comparative Example 1 had a compressive strength of 0.5-0.9 MPa and a density of 70-100 kg / m³. The foam did not exhibit flame-retardant properties, and its limiting oxygen index was 18-20%. Furthermore, the mixture obtained after solvent recovery did not possess adhesive properties. Example 3

[0032] (1) Furfurylamine (19.74 g), ferulic acid (38.84 g), and paraformaldehyde (6.06 g) were mixed in ethyl acetate and refluxed at 100 °C for 6 h. Then castor oil glycidyl ether (100 g) and 1,8-diazabicyclo[5.4.0]undec-7-ene (1 g) were added, and the mixture was heated to 130 °C and reacted for another 8 h. After the reaction was completed, the mixture was extracted with deionized water 3-5 times, dried with anhydrous magnesium sulfate, filtered to obtain the organic phase, and ethyl acetate was removed by vacuum rotary evaporation to obtain castor oil-based polyol.

[0033] (2) Referring to the formulation in Table 1, the synthesized castor oil-based polyol, polyether 4110 polyol, and additives were thoroughly mixed according to different ratios of vegetable oil-based polyol and polyether 4110 polyol. Then, it was mixed with isocyanate and stirred for 10 s at a speed of 1800 r / min. The mixture was then poured into a mold and cured at room temperature for 24 h to obtain polyurethane foam. The obtained castor oil-based polyurethane foam was crushed into 50-200 mesh powder using a multi-functional pulverizer. 1 g of the powder was then dissolved in 15 mL of N,N-dimethylformamide, heated to 140 ℃ and maintained for 1.5 h to obtain the adhesive.

[0034] Testing revealed that the polyurethane foam produced in this embodiment has a compressive strength of 0.8-1.6 MPa and a density of 80-110 kg / m³. 3 When the mass fraction of castor oil polyol in the system exceeds 30%, the flame retardant performance of the foam can reach HB-1 level (measured according to ASTM D 63577 standard), with a limiting oxygen index of 21%-24%. Furthermore, the adhesive obtained after solvent recovery maintains a shear strength of 1-6 MPa on various substrates (such as iron, aluminum, copper, wood, glass, and polytetrafluoroethylene). Notably, this adhesive can be dissolved in N,N-dimethylformamide and recycled more than 5 times while maintaining a shear strength of 1-6 MPa. Example 4

[0035] (1) Furfurylamine (39.48 g), ferulic acid (77.68 g), and paraformaldehyde (12.12 g) were mixed in ethyl acetate and refluxed at 100 °C for 6 h. Then, epoxidized soybean oil (100 g) and 1,8-diazabicyclo[5.4.0]undec-7-ene (2 g) were added, and the mixture was heated to 130 °C and reacted for another 8 h. After the reaction was completed, the mixture was extracted with deionized water 3-5 times, dried with anhydrous magnesium sulfate, filtered to obtain the organic phase, and ethyl acetate was removed by vacuum rotary evaporation to obtain soybean oil-based polyol.

[0036] (2) Referring to the formula in Table 1, the synthesized soybean oil-based polyol, polyether 4110 polyol and additives were thoroughly mixed according to different ratios of vegetable oil-based polyol and polyether 4110 polyol. Then, it was mixed with isocyanate and stirred for 10 s at a speed of 1800 r / min, and then poured into a mold and cured at room temperature for 24 h to obtain polyurethane foam. The obtained soybean oil-based polyurethane foam was crushed into 50-200 mesh powder using a multi-functional pulverizer; then 1 g of powder was dissolved in 15 mL of N,N-dimethylformamide, heated to 140 ℃ and held for 1.5 h to obtain adhesive.

[0037] Testing revealed that the polyurethane foam produced in this embodiment has a compressive strength of 1.0-1.5 MPa and a density of 70-110 kg / m³. 3 When the mass fraction of soybean oil polyol in the system exceeds 30%, the flame retardant performance of the foam can reach HB-1 level (measured according to ASTM D 63577 standard), with a limiting oxygen index of 21%-24%. Furthermore, the adhesive obtained after solvent recovery maintains a shear strength of 1.5-6 MPa on various substrates (such as iron, aluminum, copper, wood, glass, and polytetrafluoroethylene). Notably, this adhesive can be dissolved in N,N-dimethylformamide and recycled more than 5 times while maintaining a shear strength of 1.5-6 MPa. Example 5

[0038] (1) 2-Furfurylamide (22.14 g), salicylic acid (27.66 g), and paraformaldehyde (6.06 g) were mixed in ethyl acetate and refluxed at 100 °C for 6 h. Then castor oil glycidyl ether (100 g) and 1,8-diazabicyclo[5.4.0]undec-7-ene (1 g) were added, and the mixture was heated to 130 °C and reacted for another 8 h. After the reaction was completed, the mixture was extracted 3-5 times with deionized water, dried with anhydrous magnesium sulfate, filtered to obtain the organic phase, and ethyl acetate was removed by vacuum rotary evaporation to obtain castor oil-based polyol.

[0039] (2) Referring to the formulation in Table 1, the synthesized castor oil-based polyol, polyether 4110 polyol, and additives were thoroughly mixed according to different ratios of vegetable oil-based polyol and polyether 4110 polyol. Then, it was mixed with isocyanate and stirred for 10 s at a speed of 1800 r / min. The mixture was then poured into a mold and cured at room temperature for 24 h to obtain polyurethane foam. The obtained castor oil-based polyurethane foam was crushed into 50-200 mesh powder using a multi-functional pulverizer. 1 g of the powder was then dissolved in 15 mL of N,N-dimethylformamide, heated to 140 ℃ and maintained for 1.5 h to obtain the adhesive.

[0040] Testing revealed that the polyurethane foam produced in this embodiment has a compressive strength of 0.6-1.2 MPa and a density of 80-110 kg / m³. 3 When the mass fraction of castor oil polyol in the system exceeds 30%, the flame retardant performance of the foam can reach HB-1 level (measured according to ASTM D 63577 standard), with a limiting oxygen index of 21%-22%. Furthermore, the adhesive obtained after solvent recovery maintains a shear strength of 1-4 MPa on various substrates (such as iron, aluminum, copper, wood, glass, and polytetrafluoroethylene). Notably, this adhesive can be dissolved in N,N-dimethylformamide and recycled more than 5 times while maintaining a shear strength of 1-4 MPa. Example 6

[0041] (1) 2-Furfural ethylamine (44.28 g), salicylic acid (55.32 g), and paraformaldehyde (12.12 g) were mixed in ethyl acetate and refluxed at 100 °C for 6 h. Then, epoxidized soybean oil (100 g) and 1,8-diazabicyclo[5.4.0]undec-7-ene (2 g) were added, and the mixture was heated to 130 °C and reacted for another 8 h. After the reaction was completed, the mixture was extracted 3-5 times with deionized water, dried with anhydrous magnesium sulfate, filtered to obtain the organic phase, and the ethyl acetate was removed by vacuum rotary evaporation to obtain soybean oil-based polyol.

[0042] (2) Referring to the formula in Table 1, the synthesized soybean oil-based polyol, polyether 4110 polyol and additives were thoroughly mixed according to different ratios of vegetable oil-based polyol and polyether 4110 polyol. Then, it was mixed with isocyanate and stirred for 10 s at a speed of 1800 r / min, and then poured into a mold and cured at room temperature for 24 h to obtain polyurethane foam. The obtained soybean oil-based polyurethane foam was crushed into 50-200 mesh powder using a multi-functional pulverizer; then 1 g of powder was dissolved in 15 mL of N,N-dimethylformamide, heated to 140 ℃ and held for 1.5 h to obtain adhesive.

[0043] Testing revealed that the polyurethane foam produced in this embodiment has a compressive strength of 0.6-1.2 MPa and a density of 80-110 kg / m³. 3 When the mass fraction of soybean oil polyol in the system exceeds 30%, the flame retardant performance of the foam can reach HB-1 level (measured according to ASTM D 63577 standard), with a limiting oxygen index of 21%-22%. Furthermore, the adhesive obtained after solvent recovery maintains a shear strength of 1-6 MPa on various substrates (such as iron, aluminum, copper, wood, glass, and polytetrafluoroethylene). Notably, this adhesive can be dissolved in N,N-dimethylformamide and recycled more than 5 times while maintaining a shear strength of 1-6 MPa. Example 7

[0044] (1) 2-Furfural ethylamine (44.28 g), salicylic acid (55.32 g), and paraformaldehyde (12.12 g) were mixed in ethyl acetate and refluxed at 100 °C for 6 hours. Then, epoxidized rapeseed oil (100 g) and 1,8-diazabicyclo[5.4.0]undec-7-ene (2 g) were added, and the mixture was heated to 130 °C and reacted for another 8 hours. After the reaction was completed, the mixture was extracted 3–5 times with deionized water, dried with anhydrous magnesium sulfate, filtered to obtain the organic phase, and the ethyl acetate was removed by vacuum rotary evaporation to obtain rapeseed oil-based polyol.

[0045] (2) Referring to the formulation in Table 1, the synthesized rapeseed oil-based polyol, polyether 4110 polyol, and additives were thoroughly mixed according to different ratios of vegetable oil-based polyol and polyether 4110 polyol. Then, it was mixed with isocyanate and stirred for 10 s at a speed of 1800 r / min. The mixture was then poured into a mold and cured at room temperature for 24 h to obtain polyurethane foam. The obtained rapeseed oil-based polyurethane foam was crushed into 50–200 mesh powder using a multi-functional pulverizer. 1 g of the powder was then dissolved in 15 mL of N,N-dimethylformamide, heated to 140 ℃ and maintained for 1.5 h to obtain the adhesive.

[0046] Testing revealed that the polyurethane foam produced in this embodiment has a compressive strength of 0.6-1.3 MPa and a density of 80-110 kg / m³. 3 When the mass fraction of rapeseed oil polyol in the system exceeds 30%, the flame retardant performance of the foam can reach HB-1 level (measured according to ASTM D 63577 standard), with a limiting oxygen index of 21%-23%. Furthermore, the adhesive obtained after solvent recovery maintains a shear strength of 1-6 MPa on various substrates (such as iron, aluminum, copper, wood, glass, and polytetrafluoroethylene). Notably, this adhesive can be dissolved in N,N-dimethylformamide and recycled more than 5 times while maintaining a shear strength of 1-6 MPa. Example 8

[0047] (1) Furfurylamine (19.74 g), p-hydroxybenzoic acid (27.62 g), and paraformaldehyde (6.06 g) were mixed in ethyl acetate and refluxed at 100 °C for 6 hours. Then castor oil glycidyl ether (100 g) and 1,8-diazabicyclo[5.4.0]undec-7-ene (1 g) were added, and the mixture was heated to 130 °C and reacted for another 8 hours. After the reaction was completed, the mixture was extracted 3–5 times with deionized water, dried with anhydrous magnesium sulfate, filtered to obtain the organic phase, and ethyl acetate was removed by vacuum rotary evaporation to obtain castor oil-based polyol.

[0048] (2) Referring to the formulation in Table 1, the synthesized castor oil-based polyol, polyether 4110 polyol, and additives were thoroughly mixed according to different ratios of vegetable oil-based polyol and polyether 4110 polyol. Then, it was mixed with isocyanate and stirred for 15 s at a speed of 1800 r / min. The mixture was then poured into a mold and cured at room temperature for 24 h to obtain polyurethane foam. The obtained castor oil-based polyurethane foam was crushed into 50–200 mesh powder using a multi-functional pulverizer. 1 g of the powder was then dissolved in 15 mL of N,N-dimethylformamide, heated to 140 ℃ and maintained for 1.5 h to obtain the adhesive.

[0049] Testing revealed that the polyurethane foam produced in this embodiment has a compressive strength of 0.8–1.4 MPa and a density of 80–110 kg / m³. 3 When the mass fraction of castor oil polyol in the system exceeds 30%, the flame retardant performance of the foam can reach HB-1 level (measured according to ASTM D 63577 standard), with a limiting oxygen index of 21%–23%. Furthermore, the adhesive obtained after solvent recovery maintains a shear strength of 1–5 MPa on various substrates (such as iron, aluminum, copper, wood, glass, and polytetrafluoroethylene). Notably, this adhesive can be dissolved in N,N-dimethylformamide and recycled more than 5 times while maintaining a shear strength of 1–6 MPa.

[0050] By comparing Examples 1-8 and Comparative Examples 1-2, it can be seen that the polyurethane foam obtained by the technical solution of the present invention not only has excellent mechanical properties and flame retardant properties, but can also be self-driven to achieve upgrading and recycling.

Claims

1. A method for preparing a vegetable oil-based polyol, characterized in that, Includes the following steps: a) An amine compound, a phenolic compound, and paraformaldehyde are mixed in a first solvent and reacted at 90-110 °C for 4-8 hours to obtain an intermediate containing a benzoxazine structure. The first solvent is anhydrous ethanol or ethyl acetate. The molar amount of the phenolic compound is 1.0-1.05 times that of the amine compound, and the molar amount of the paraformaldehyde is 1.0-1.5 times that of the amine compound. b) The intermediate obtained in step a) is mixed with a catalyst and epoxidized vegetable oil and reacted at 110-130 °C for 8-12 hours. After the reaction, post-treatment is performed to obtain the vegetable oil-based polyol. The molar amount of the epoxy groups in the epoxidized vegetable oil is 1.0-1.2 times that of the phenolic compound in step a).

2. The preparation method according to claim 1, characterized in that, In step a), the amine compound is selected from at least one of ethanolamine, furfurylamine, 2-furan ethylamine, 2-cyclohexylethylamine or 2-benzyl-1-ethylamine; the phenolic compound is selected from at least one of salicylic acid, p-hydroxybenzoic acid, o-hydroxybenzoic acid, ferulic acid or caffeic acid.

3. The preparation method according to claim 1, characterized in that, In step b), the catalyst is selected from at least one of cyclohexylamine, 4-dimethylaminopyridine or 1,8-diazabicyclo[5.4.0]undec-7-ene; the epoxidized vegetable oil is selected from at least one of castor oil glycidyl ether, epoxidized soybean oil, epoxidized rapeseed oil or epoxidized sunflower oil.

4. A plant oil-based polyol, characterized in that, It is prepared by the preparation method described in any one of claims 1-3.

5. A method for preparing polyurethane foam, characterized in that, The process includes the following steps: mixing the vegetable oil-based polyol, isocyanate, and additives as described in claim 4, foaming, and curing; the additives include foaming agents and surfactants.

6. The preparation method according to claim 5, characterized in that, By weight, the raw materials used include: 100 parts of the plant oil-based polyol, 60-120 parts of isocyanate, 3-4 parts of surfactant, and 2-10 parts of foaming agent.

7. The preparation method according to claim 6, characterized in that, The isocyanate is selected from at least one of MDI-100, HDI trimer, PM-200 or MDI-50; the foaming agent is at least one of water or cyclopentane; and the surfactant is at least one of AK158, DC-193 or L-633.

8. A polyurethane foam, characterized in that, The polyurethane foam is prepared by the method described in any one of claims 5-7.

9. The application of the vegetable oil-based polyol according to claim 4 in the preparation of polyurethane materials.

10. The use of the polyurethane foam of claim 8 as an adhesive or glue.

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