A bio-based polyurethane flame-retardant protective material and its application in safety helmets

Abstract

This invention discloses a bio-based polyurethane flame-retardant protective material and its application in safety helmets, belonging to the technical field of safety helmet materials. The bio-based polyurethane flame-retardant protective material of this invention comprises the following components by weight: 95-110 parts of modified bio-based PN flame-retardant polyester diol, 10-20 parts of chain extender, 0.8-1.5 parts of surfactant, 2-6 parts of water-based foaming agent, 60-90 parts of diisocyanate, 0.1-0.5 parts of organotin catalyst, and 0.2-0.5 parts of organic amine catalyst. The modified bio-based PN flame-retardant polyester diol is obtained by grafting PN flame-retardant components melamine, diethyl phenyl phosphate, and benzotriazole onto a bio-based castor oil matrix. The bio-based polyurethane flame-retardant protective material provided by this invention has excellent flame-retardant properties and impact resistance, and can be used in the manufacture of safety helmets.

Description

Technical Field

[0001] This invention relates to the field of safety helmet materials technology, specifically to a bio-based polyurethane flame-retardant protective material and its application in safety helmets. Background Technology

[0002] In high-risk work environments such as petrochemicals, metallurgy, and firefighting, where there are risks of open flames, high temperatures, or molten material splashes, safety helmets are essential protective equipment to protect workers' heads and prevent secondary injuries. Most safety helmets contain rigid polyurethane foam, a polymer material obtained by repeatedly linking long-chain polyols and polyisocyanates through urethane segments. It possesses excellent and adjustable mechanical properties, is lightweight, and its porous elasticity provides good impact resistance. Traditional polyurethane foam mainly relies on petroleum raw materials, but with increasingly scarce petroleum resources, biomass-based polyurethane foam has emerged. However, rigid polyurethane foam is rich in elements such as C, H, and O, making it highly flammable; its porous structure also provides airflow channels, further promoting combustion and causing more serious fire accidents. Therefore, it is necessary to develop biomass-based polyurethane materials with fire-resistant and flame-retardant properties.

[0003] Researchers typically add flame retardants containing elements such as nitrogen, phosphorus, and boron to polyurethane foam as additives, which significantly improves its flame retardant properties. However, the flame retardant properties are closely related to the amount added. Increasing the amount added can effectively improve the flame retardancy, but its incompatibility with polyurethane can also cause it to precipitate, making the polyurethane material brittle and unsuitable for use in safety helmets. At the same time, the flame retardant components can also migrate and be lost during the use of the material, thus losing their flame retardant properties. Summary of the Invention

[0004] To overcome the shortcomings of the existing technology, this invention provides a bio-based polyurethane flame-retardant protective material and its application in safety helmets. The bio-based polyurethane flame-retardant protective material is a rigid polyurethane foam prepared by the combined action of modified bio-based PN flame-retardant polyester glycol, chain extender, surfactant, water-based foaming agent, diisocyanate, organotin catalyst, and organoamine catalyst. Castor oil, as a bio-based component, is environmentally friendly. Modified bio-based PN flame-retardant polyester glycol is prepared by grafting N and P-containing flame-retardant molecular structures of melamine, diethyl phenyl phosphate, and benzotriazole onto bio-based castor oil. The combustion of the phosphate groups decomposes a viscous semi-solid substance that coats the polyurethane surface and promotes dehydration and carbonization of the polyurethane, preventing oxygen penetration and heat transfer. Simultaneously, the nitrogen-containing groups decompose upon heating, releasing flammable gases such as nitrogen, nitrogen oxides, and water vapor, which not only dilutes the oxygen concentration but also removes energy. The PN synergistic effect improves the flame-retardant properties of the polyurethane. Furthermore, since the flame-retardant groups are grafted into the polyurethane chain, the loss of flame-retardant components is less likely.

[0005] The purpose of this invention is to provide a bio-based polyurethane flame-retardant protective material and its application in safety helmets.

[0006] This invention is achieved through the following technical solution:

[0007] A bio-based polyurethane flame-retardant protective material, comprising, by weight, the following components: 95-110 parts of modified bio-based PN flame-retardant polyester diol, 10-20 parts of chain extender, 0.8-1.5 parts of surfactant, 2-6 parts of water-based foaming agent, 60-90 parts of diisocyanate, 0.1-0.5 parts of organotin catalyst, and 0.2-0.5 parts of organic amine catalyst; wherein the modified bio-based PN flame-retardant polyester diol has a structure as shown in Formula 1:

[0008] Formula 1.

[0009] In one specific embodiment, the chain extender is one of ethylene glycol, propylene glycol, and butanediol;

[0010] In one specific embodiment, the surfactant is an organosilicon foam stabilizer AK8805;

[0011] In one specific embodiment, the diisocyanate is 4,4'-methylenebis(phenyl isocyanate);

[0012] In one specific embodiment, the organotin catalyst is dibutyltin dilaurate;

[0013] In one specific embodiment, the organic amine catalyst is triethylenediamine;

[0014] In one specific embodiment, the modified bio-based PN flame-retardant polyester diol is prepared in-house, and the preparation steps are as follows:

[0015] S1. Under a nitrogen atmosphere, melamine, 5-bromo-1H-benzotriazole, an inorganic base, and the ligand Ruphos were dissolved in toluene; Pd2(dba)3 was added as a catalyst, the temperature was raised to 100-110 °C, and the reaction was stopped after stirring for 18-24 hours; the product A was obtained by cooling, column chromatography purification, concentration, and drying.

[0016] S2. Under a nitrogen atmosphere, product A, diethyl 4-chlorophenyl phosphate, base and ligand Xphos were dissolved in toluene; Pd(OAc)2 was added as a catalyst, the temperature was raised to 100-110 °C, and the reaction was stirred for 24-36 hours; the product B was obtained by cooling, column chromatography purification, concentration and drying.

[0017] S3. Under a nitrogen atmosphere, product B, 4-bromobenzoic acid, inorganic base and ligand Ruphos were dissolved in toluene; Pd2(dba)3 was added as a catalyst, the temperature was raised to 95-115 °C, the reaction was stirred for 20-24 hours, and the product C was obtained by cooling, column chromatography purification, concentration and drying.

[0018] S4. Dissolve product C in anhydrous dichloromethane, heat to 0 °C in an ice bath, and add organic base and di-tert-butyl dicarbonate in sequence; heat to room temperature and stir for 10-16 h; wash the reaction solution with 1M HCl, concentrate and dry the organic phase to obtain product D;

[0019] S5. Dissolve product D in anhydrous dichloromethane, heat to 0 °C in an ice bath, add oxalyl chloride dropwise, followed by 1-2 drops of DMF; heat to room temperature and stir the reaction for 1-3 h; concentrate the reaction solution and dry to obtain crude product E;

[0020] S6. Dissolve product E in anhydrous dichloromethane, heat to 0 °C in an ice bath, add triethylamine; then slowly add trimethylsilyl trifluoromethanesulfonate and stir for 0.5-2 hours; add saturated NaHCO3 solution, concentrate the organic phase, purify by column chromatography, concentrate, and dry to obtain product F;

[0021] S7. Dissolve bio-based polyol castor oil in anhydrous dichloromethane, heat to 0 °C in an ice bath, add triethylamine; then add F solution dissolved in a small amount of dichloromethane dropwise, react at room temperature for 1-4 hours; add 1M HCl to wash the reaction solution and saturated NaHCO3 solution in sequence, take the organic phase to concentrate, separate and purify to obtain modified bio-based PN flame retardant diol;

[0022] S8. Esterification and Polycondensation

[0023] The modified bio-based PN flame-retardant polyester glycol was dissolved in anhydrous dichloromethane, cooled to 0 °C in an ice bath, and triethylamine was added. Then, malonyl chloride solution dissolved in a small amount of dichloromethane was added dropwise, and the mixture was stirred at room temperature for 4-10 hours. The reaction solution was washed with 1M HCl and saturated NaHCO3 solution until neutral. The organic phase was concentrated and cold methanol was added dropwise to precipitate the polymer. The mixture was filtered and dried to obtain modified bio-based PN flame-retardant polyester glycol with a hydroxyl value of 28.05-56.1 mg KOH / g.

[0024] In one specific embodiment, in step S1, the amount of 5-bromo-1H-benzotriazole is 0.95-1 times the molar amount of melamine; the inorganic base is potassium phosphate or cesium carbonate, and the amount is 3-5 times the molar amount of melamine; the amount of the ligand Ruphos is 0.1 wt% of melamine.

[0025] In one specific embodiment, in step S2, the amount of diethyl 4-chlorophenyl phosphate is 0.95-1 times the molar amount of A; the base is potassium tert-butoxide or sodium tert-butoxide, and the amount is 3-5 times the molar amount of A; the amount of ligand Xphos is 0.1 wt% of A.

[0026] In one specific embodiment, in step S3, the amount of 4-bromobenzoic acid is 0.95-1 times the molar amount of B; the inorganic base is cesium carbonate, and the amount is 3-5 times the molar amount of B; the amount of the ligand Ruphos is 0.1 wt% of B.

[0027] In one specific embodiment, in step S4, the organic base is triethylamine or 4-dimethylaminopyridine, and the amount used is 4.5-5 times the molar amount of C; the amount of ditert-butyl dicarbonate is 4.1-4.5 times the molar amount of C.

[0028] In one specific embodiment, in step S5, the amount of oxalyl chloride used is 1.3-1.5 times the molar amount of D;

[0029] In one specific embodiment, in step S6, the amount of triethylamine used is 5-7 times the molar amount of E; the amount of trimethylsilyl trifluoromethanesulfonate used is 4.1-4.5 times the molar amount of E.

[0030] In one specific embodiment, in step S7, the amount of triethylamine used is 1.5-2 times the molar amount of bio-based polyol castor oil; the amount of F used is 0.95-1 times the molar amount of bio-based polyol castor oil.

[0031] In one specific embodiment, in step S8, the amount of modified bio-based PN flame-retardant diol is 2.01-2.3 times the molar amount of malonyl chloride; the amount of triethylamine is 2.5-3 times the molar amount of malonyl chloride; and the number-average molecular weight of the modified bio-based flame-retardant polyester diol is 2000-4000.

[0032] Another object of the present invention is to protect the application of the aforementioned bio-based polyurethane flame-retardant protective material in safety helmets.

[0033] The present invention also discloses a method for preparing a bio-based polyurethane flame-retardant protective material, comprising the following steps: pouring modified bio-based PN flame-retardant polyester glycol, chain extender, surfactant, and water foaming agent into a container, stirring at low speed (300-500 rpm) for 5-10 minutes; adding a catalyst and stirring for 2-3 minutes; then adding diisocyanate and stirring at high speed for 8-15 seconds; quickly pouring the mixture into a mold preheated to 40-50 ℃ for foaming for 10-15 minutes and then curing and demolding; and finally curing at 80 ℃ for 8-10 hours to obtain the bio-based polyurethane flame-retardant protective material.

[0034] Beneficial effects

[0035] This invention provides a bio-based polyurethane flame-retardant protective material and its application in safety helmets. The bio-based polyurethane flame-retardant protective material is a rigid polyurethane foam prepared by the combined action of modified bio-based PN flame-retardant polyester glycol, chain extender, surfactant, water-based foaming agent, diisocyanate, organotin catalyst, and organoamine catalyst. Castor oil, as a bio-based component, is environmentally friendly. Modified bio-based PN flame-retardant polyol is prepared by grafting N and P-containing flame-retardant molecular structures of melamine, diethyl phenyl phosphate, and benzotriazole onto bio-based castor oil. The combustion of the phosphate groups decomposes a viscous semi-solid substance that coats the polyurethane surface and promotes dehydration and carbonization of the polyurethane, preventing oxygen penetration and heat transfer. Simultaneously, the nitrogen-containing groups decompose upon heating, releasing flammable gases such as nitrogen, nitrogen oxides, and water vapor, which not only dilutes the oxygen concentration but also removes energy during decomposition. The synergistic effect of PN endows polyurethane with excellent flame retardant properties and low smoke density, which effectively protects the safety of workers. Moreover, the flame retardant groups are grafted into the polyurethane chain, which makes it difficult for the flame retardant components to be lost, ensuring the long-term usability of the material. The bio-based polyurethane flame retardant protective material prepared by this invention has the advantages of being environmentally friendly, impact-resistant, having high energy absorption, and being flame retardant, and is particularly suitable for use as the inner protective layer of safety helmets. Attached Figure Description

[0036] Figure 1 Synthetic pathway for bio-based polyurethane flame-retardant protective materials;

[0037] Figure 2 The 1H NMR spectrum of intermediate product F;

[0038] Figure 3 Infrared spectra of castor oil, modified bio-based PN flame-retardant polyester glycol, and flame-retardant polyurethane; Detailed Implementation

[0039] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0040] Unless otherwise specified, the experimental methods used in the embodiments are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0041] The raw materials used in the examples and comparative examples are described below:

[0042] Melamine: Product number M766808, purchased from Shanghai Bid Pharmaceutical Technology Co., Ltd.;

[0043] 5-Bromo-1H-benzotriazole: 98%, product number B857816, purchased from Shanghai Bid Pharmaceutical Technology Co., Ltd.;

[0044] Diethyl 4-chlorophenyl phosphate: 98%, product number A021341, purchased from Shanghai Anaiji Chemical Co., Ltd.;

[0045] 4-Bromobenzoic acid: 97%, product number A010083, purchased from Shanghai Anaiji Chemical Co., Ltd.;

[0046] Malonyl chloride: 98%, product number W810324, purchased from Shanghai Anaiji Chemical Co., Ltd.;

[0047] Tris(dibenzylacetone)dipalladium(0) (Pd2(dba)3): 98%, product number BD21135, purchased from Shanghai Bid Pharmaceutical Technology Co., Ltd.;

[0048] 2-Dicyclohexylphosphine-2',6'-diisopropoxy-1,1'-biphenyl (Ruphos): 97%, catalog number BD74362, purchased from Shanghai Bid Pharmaceutical Technology Co., Ltd.;

[0049] Palladium acetate (Pd(OAc)2): Product number P815382, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0050] 2-Dicyclohexylphosphine-2,4,6-triisopropylbiphenyl (XPhos): 97%, product number D806579, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0051] Triethylamine (TEA): 99%, product number T818772, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0052] Di-tert-butyl dicarbonate ((Boc)2O): 98%, product number D806924, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0053] Oxaloyl chloride ((COCl)2): 98%, product number O815154, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0054] Trimethylsilyl trifluoromethanesulfonate (TMSOTf): 98%, product number T819078, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0055] Diisocyanate: 4,4'-methylenebis(phenyl isocyanate) (MDI), 98%, product number M813280, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0056] Chain extender: Butanediol, 98%, product number B802727, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.;

[0057] Organotin catalyst: Dibutyltin dilaurate (DBTDL), 95%, product number D806313, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0058] Organic amine catalyst: Triethylenediamine (A33), industrial grade, American Gas Company;

[0059] Surfactant: Organosilicon foam stabilizer (AK8805), industrial grade, Nanjing Meiside Chemical Co., Ltd.;

[0060] Modified bio-based PN flame-retardant diol: self-made, preparation steps are as follows:

[0061] S1. Under a nitrogen atmosphere, melamine (1 equivalent), 5-bromo-1H-benzotriazole (0.95 equivalent), cesium carbonate (4 equivalent), and ligand Ruphos (0.1 wt%) were dissolved in toluene and bubbled for 30 minutes. Catalyst Pd2(dba)3 was added, and the mixture was bubbled for another 10 minutes. The temperature was raised to 100 °C, and the reaction was stirred for 24 hours until the reaction was complete. The reaction mixture was cooled to room temperature, purified by column chromatography, the solution was concentrated, and dried to obtain product A.

[0062] S2. Under a nitrogen atmosphere, product A (1 equivalent), diethyl 4-chlorophenyl phosphate (0.95 equivalent), sodium tert-butoxide (3 equivalent), and ligand Xphos (0.1 wt%) were dissolved in toluene and bubbled for 30 minutes. Catalyst Pd(OAc)2 was added and bubbled for another 10 minutes. The temperature was raised to 110 °C, and the reaction was stirred for 24 hours until the reaction was complete. The reaction mixture was cooled to room temperature, purified by column chromatography, concentrated, and dried to obtain product B.

[0063] S3. Under a nitrogen atmosphere, product B (1 equivalent), 4-bromobenzoic acid (0.95 equivalent), cesium carbonate (4 equivalent), and ligand Ruphos (0.1 wt%) were dissolved in toluene and bubbled for 30 minutes. Catalyst Pd2(dba)3 was added, and the mixture was bubbled for another 10 minutes. The temperature was raised to 100 °C, and the reaction was stirred for 24 hours until the reaction was complete. The reaction mixture was cooled to room temperature, purified by column chromatography, the solution was concentrated, and dried to obtain product C.

[0064] S4. Dissolve product C (1 equivalent) in anhydrous dichloromethane, heat to 0 °C in an ice bath, and add triethylamine (4.5 equivalent) and di-tert-butyl dicarbonate (4.2 equivalent) in sequence. Slowly raise the temperature to room temperature and stir the reaction. Monitor the reaction by TLC until the starting material C disappears (8 h). Wash the reaction solution with 1M HCl, take the organic phase, concentrate and dry to obtain product D.

[0065] S5. Dissolve product D (1 equivalent) in anhydrous dichloromethane, heat to 0 °C in an ice bath, add oxaloyl chloride (1.3 equivalent) dropwise, followed by 1-2 drops of DMF; slowly raise to room temperature and stir for 3 h to complete the reaction; concentrate the reaction solution and dry to obtain crude product E;

[0066] S6. Dissolve product E (1 equivalent) in anhydrous dichloromethane, heat to 0 °C in an ice bath, add triethylamine (5-7 equivalents) and stir for 5 minutes; then slowly add trimethylsilyl trifluoromethanesulfonate (TMSOTf, 4.3 equivalents) and stir for 1.5 hours until the reaction is complete; add saturated NaHCO3 solution, concentrate the organic phase, purify by column chromatography, concentrate the solution, and dry to obtain product F;

[0067] S7. Dissolve bio-based polyol castor oil (1 equivalent) in anhydrous dichloromethane, heat to 0 °C in an ice bath, slowly add triethylamine (1.8 equivalent) and stir for 10 minutes; then add F solution (0.95 equivalent) dissolved in a small amount of dichloromethane dropwise, heat to room temperature and stir for 3 hours to complete the reaction; add 1M HCl to wash the reaction solution and saturated NaHCO3 solution in sequence, take the organic phase, concentrate, separate and purify to obtain modified bio-based PN flame retardant diol.

[0068] Modified bio-based PN flame-retardant polyester glycol: self-made, preparation steps are as follows:

[0069] Modified bio-based PN flame-retardant polyester glycol (2.1 equivalents) was dissolved in anhydrous dichloromethane, cooled to 0 °C in an ice bath, and triethylamine (2.5 equivalents) was slowly added and stirred for 10 minutes. Then, malonyl chloride solution (1 equivalent) dissolved in a small amount of dichloromethane was added dropwise, and the mixture was heated to room temperature and stirred for 8 hours until the reaction was complete. The reaction solution was washed with 1M HCl and saturated NaHCO3 solution until neutral. The organic phase was concentrated and cold methanol was added dropwise to precipitate the polymer. The product was filtered and dried to obtain modified bio-based PN flame-retardant polyester glycol with a hydroxyl value of 44.88 mg KOH / g and a number average molecular weight of 2500.

[0070] Modified bio-based P flame-retardant polyester glycol: self-made, the preparation method is the same as that for bio-based PN flame-retardant polyester glycol, the difference is that 4-chlorophenyl phosphate containing the P flame-retardant component is grafted onto castor oil to obtain a modified bio-based P flame-retardant polyester glycol with a hydroxyl value of 32.06 mgKOH / g and a number-average molecular weight of 3500.

[0071] Bio-based polyester glycol: prepared in-house, using the same method as bio-based PN flame retardant glycol, except that no flame retardant component was modified on castor oil, resulting in a bio-based polyester glycol with a hydroxyl value of 28.05 mg KOH / g and a number-average molecular weight of 4000.

[0072] It should be noted that the term "equivalent" used in this invention refers to "molar equivalent".

[0073] Unless otherwise specified, all components and raw materials used in the embodiments and comparative examples of this invention are commercially available, and the same type of components and raw materials are used in each parallel experiment.

[0074] Examples and Comparative Examples

[0075] A bio-based polyurethane flame-retardant protective material, the weight parts of which are shown in Table 1, is prepared by the following method:

[0076] Add the modified bio-based PN flame-retardant polyester glycol, chain extender, surfactant, and water-based foaming agent to a container and mix at low speed (300-500 rpm) for 5-10 minutes. Add the catalyst and stir for 2-3 minutes. Then add the diisocyanate and stir at high speed for 8-15 seconds. Quickly pour the mixture into a mold preheated to 40-50 ℃, foam for 10-15 minutes, and then solidify and demold. Finally, cure at 80 ℃ for 8-10 hours to obtain the bio-based polyurethane flame-retardant protective material.

[0077] Table 1. Bio-based polyurethane flame-retardant protective materials (parts by weight)

[0078]

[0079] The bio-based polyurethane flame-retardant protective material prepared in the examples and comparative examples was subjected to the following performance tests, and the results are shown in the figure and table 2, respectively.

[0080] 1. Infrared Spectroscopy: Modified bio-based PN flame-retardant polyester glycol and bio-based polyurethane flame-retardant protective material were mixed with potassium bromide at a ratio of 1:50 to prepare tablets. An Avatar 380 spectrometer was used for this test. Before testing, a blank background was scanned, followed by the placement of the tablet sample for testing. The scanning range was 500-4000 cm⁻¹. -1 The result is as follows Figure 1 As shown.

[0081] 2. Compressive Strength: The compressive strength of the bio-based polyurethane flame-retardant protective material was tested using a universal testing machine. The test was conducted according to the method specified in GB / T 8813-2008 "Determination of Compressive Properties of Rigid Foamed Plastics". Polyurethane samples were cut into 10cm*10cm*10cm strips, and the universal testing machine was used at a testing rate of 5 mm / min. The average value of the test results was taken.

[0082] 3. Impact resistance (peak force): Using a drop hammer impact tester and in accordance with ISO 6603 standard, polyurethane was cut into sample strips of 5 cm*5 cm*2 cm, the impact energy was set to 15 J, and the maximum impact force that the sample strip could withstand was recorded.

[0083] 4. Oxygen Index Test (LOI): According to the test method of GB / T 2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test", polyurethane was cut into 10 cm*1 cm*1 cm sample strips for testing.

[0084] 5. Vertical Burning Test: Following the test method in GB / T2408-2008 standard "Determination of Burning Performance of Plastics - Horizontal and Vertical Methods", polyurethane was cut into sample strips measuring 12.5 cm * 1.3 cm * 1 cm for testing. The bottom of the sample strip was placed 1 cm directly above the center of the flame. After igniting the sample strip for 10 seconds, the flame was immediately removed, and the afterflame extinguishing time t1 was recorded. The operation was repeated, and the extinguishing time t2 was recorded twice. Each sample was tested 5 times.

[0085] 6. UL-94 Vertical Burning Rating Judgment Criteria: The UL-94 rating is determined based on the ratio of t1 to t2. V-0: Single sample strip (t1 / t2) ≤ 10 s, all sample strips t1+t2 ≤ 50 s, indicating that the sample was not completely burned and the molten droplets did not ignite the cotton; V-1: Single sample strip (t1 / t2) ≤ 30 s, all sample strips t1+t2 ≤ 250 s, indicating that the sample was not completely burned and the molten droplets did not ignite the cotton; V-2: Single sample strip (t1 / t2) ≤ 30 s, all samples t1+t2 ≤ 250 s, indicating that the sample was not completely burned and the molten droplets ignited the cotton.

[0086] 7. Smoke Density Test (Dm): According to GB / T8323.2-2008 "Plastics Smoke Generation Part 2: Test Method for Determination of Smoke Density by Single Chamber Method", polyurethane sample strips of 7.5 cm * 7.5 cm * 0.1 cm were cut for the experiment. An NBS smoke density test chamber was used, placed below a radiation cone, with a thermal radiation power set to 25 kW / m². 2 The chamber temperature was 35℃, the test lasted 25 minutes, and the results were recorded.

[0087] Table 2 Performance test results of bio-based polyurethane flame-retardant protective materials

[0088]

[0089] From the appendix Figure 2 The 1H NMR spectrum shows that the integral number is consistent with the number of hydrogen atoms in the molecule, and the shifts of each hydrogen atom in the spectrum are consistent with their chemical environment, indicating that the intermediate product F was successfully synthesized.

[0090] From the appendix Figure 3 It can be seen that the peak occurs at 3490 cm. -1 The stretching vibrations in the vicinity are attributed to -OH, with peak values ​​occurring at 2980–2850 cm⁻¹. -1The stretching vibrations attributed to CH peak at 1161 cm⁻¹. -1 The stretching vibrations attributable to the ester COC in the vicinity are located at 1675–1500 cm⁻¹. -1 The signal peak at 3382 cm⁻¹ belongs to the C=C vibration. In the flame-retardant polydiol spectrum, the peak at 3382 cm⁻¹ is... -1 A new peak appears nearby; this is the CN absorption peak, located at 1675-1500 cm⁻¹. -1 The range includes absorption signals belonging to the secondary amines -NH- and benzotriazoles -N=N-; among which 1239 cm⁻¹ -1 The characteristic peak of phosphate ester -P=O is 903 cm⁻¹. -1 The characteristic peak of -POC is 1215 cm⁻¹. -1 This represents the stretching vibration of -NN- in benzotriazole, and the para-substituted benzene can also be observed at 830 cm⁻¹. -1 The presence of a unique signal indicates the successful incorporation of flame-retardant components melamine, diethyl phenyl phosphate, and benzotriazole into bio-based castor oil. In the flame-retardant polyurethane spectrum, the -OH signal disappears, while a signal is observed at 3400-3300 cm⁻¹. -1 A broad peak appears at 2270-2250 cm⁻¹, which is the stretching vibration peak of -NHCOO and NH in the original flame-retardant polydiol. -1 No asymmetric vibration peaks belonging to -NCO in isocyanate MDI were observed nearby, while characteristic signals of flame-retardant polyol were also present, indicating that flame-retardant polyol and MDI reacted to prepare flame-retardant polyurethane.

[0091] As can be seen from Table 2, compared with Comparative Examples 1 and 2, the modified bio-based PN flame-retardant polyurethane prepared by introducing melamine, diethyl phenyl phosphate and benzotriazole into the bio-based castor oil structure has the advantages of improving the crosslinking density of polyurethane and having a stable three-dimensional crosslinking network, which greatly improves the mechanical strength of polyurethane foam. At the same time, the flexible long chain structure of castor oil allows it to retain a certain degree of elasticity, and has the advantages of good impact resistance and high energy absorption.

[0092] On the other hand, when polyurethane foam burns, the phosphate ester groups decompose and coat the polyurethane surface with a viscous semi-solid substance, while also promoting dehydration and carbonization, thus preventing oxygen penetration and heat transfer. Simultaneously, the nitrogen-containing melamine and benzotriazole flame-retardant groups decompose upon heating, releasing flammable gases such as nitrogen, nitrogen oxides, and water vapor. This not only dilutes the oxygen concentration but also removes energy during the decomposition process. This synergistic effect of PN (phosphorus and benzotriazole) results in a shorter burning time and lower smoke density for the polyurethane, exhibiting excellent flame-retardant properties. Conversely, when only phosphorus (P) flame-retardant groups are present, the flame retardancy of the polyurethane decreases significantly, demonstrating the superiority of the PN synergistic flame-retardant effect.

[0093] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A bio-based polyurethane flame-retardant protective material, wherein the bio-based polyurethane flame-retardant protective material comprises, by weight, the following components: 95-110 parts of modified bio-based PN flame-retardant polyester diol, 10-20 parts of chain extender, 0.8-1.5 parts of surfactant, 2-6 parts of water-blowing agent, 60-90 parts of diisocyanate, 0.1-0.5 parts of organotin catalyst, and 0.2-0.5 parts of organic amine catalyst; the preparation steps of the modified bio-based PN flame-retardant polyester diol are as follows: S1. Under a nitrogen atmosphere, melamine, 5-bromo-1H-benzotriazole, an inorganic base, and the ligand Ruphos are dissolved in toluene; Pd2(dba)3 is added as a catalyst, the temperature is raised to 100-110 °C, and the reaction is stirred for 18-24 hours; the product A is obtained by cooling, column chromatography purification, concentration, and drying; the amount of 5-bromo-1H-benzotriazole is 0.95-1 times the molar amount of melamine. S2. Under a nitrogen atmosphere, product A, diethyl 4-chlorophenyl phosphate, base, and ligand Xphos are dissolved in toluene; Pd(OAc)2 is added as a catalyst, the temperature is raised to 100-110 °C, and the reaction is stirred for 24-36 hours; the product B is obtained by cooling, column chromatography purification, concentration, and drying; the amount of diethyl 4-chlorophenyl phosphate used is 0.95-1 times the molar amount of A. S3. Under a nitrogen atmosphere, product B, 4-bromobenzoic acid, an inorganic base, and ligand Ruphos are dissolved in toluene; Pd2(dba)3 is added as a catalyst, the temperature is raised to 95-115 °C, the reaction is stirred for 20-24 hours, cooled, purified by column chromatography, concentrated, and dried to obtain product C; the amount of 4-bromobenzoic acid used is 0.95-1 times the molar amount of B; S4. Dissolve product C in anhydrous dichloromethane, place in an ice bath, and add organic base and di-tert-butyl dicarbonate sequentially; raise to room temperature and stir for 10-16 h; wash the reaction solution with 1M HCl, concentrate and dry the organic phase to obtain product D; S5. Dissolve product D in anhydrous dichloromethane, place in an ice bath, add oxaloyl chloride dropwise, followed by 1-2 drops of DMF; raise to room temperature and stir the reaction for 1-3 h; concentrate the reaction solution and dry to obtain crude product E; S6. Dissolve product E in anhydrous dichloromethane, place in an ice bath, add triethylamine; then slowly add trimethylsilyl trifluoromethanesulfonate and stir for 0.5-2 hours; add saturated NaHCO3 solution, concentrate the organic phase, purify by column chromatography, concentrate, and dry to obtain product F; S7. Dissolve castor oil in anhydrous dichloromethane, place in an ice bath, add triethylamine; then add F solution dissolved in a small amount of dichloromethane dropwise, react at room temperature for 1-4 hours; add HCl to wash the reaction solution and saturated NaHCO3 solution in sequence, take the organic phase to concentrate, separate and purify to obtain modified bio-based PN flame retardant diol; S8. Esterification and Polycondensation The modified bio-based PN flame-retardant diol was dissolved in anhydrous dichloromethane in an ice bath. Triethylamine was added, followed by the dropwise addition of malonyl chloride solution dissolved in a small amount of dichloromethane. The mixture was stirred at room temperature for 4-10 hours. The reaction solution was washed with HCl and saturated NaHCO3 solution until neutral. The organic phase was concentrated and cold methanol was added dropwise to precipitate the polymer. The mixture was filtered and dried to obtain a modified bio-based PN flame-retardant polyester diol with a hydroxyl value of 28.05-56.1 mg KOH / g. The amount of the modified bio-based PN flame-retardant diol was 2.01-2.3 times the molar amount of malonyl chloride.

2. The bio-based polyurethane flame-retardant protective material as described in claim 1, characterized in that, The chain extender is one of ethylene glycol, propylene glycol, and butanediol; the surfactant is an organosilicon foam stabilizer; the diisocyanate is 4,4'-methylenebis(phenyl isocyanate); the organotin catalyst is dibutyltin dilaurate; and the organoamine catalyst is triethylenediamine.

3. The bio-based polyurethane flame-retardant protective material as described in claim 1, characterized in that, In step S1, the inorganic base is potassium phosphate or cesium carbonate, and the amount used is 3-5 times the molar amount of melamine; the amount of the ligand Ruphos is 0.1 wt% of melamine.

4. The bio-based polyurethane flame-retardant protective material as described in claim 1, characterized in that, In step S2, the base is potassium tert-butoxide or sodium tert-butoxide, and the amount used is 3-5 times the molar amount of A; the amount of the ligand Xphos is 0.1 wt% of A.

5. The bio-based polyurethane flame-retardant protective material as described in claim 1, characterized in that, The inorganic base is cesium carbonate, and the amount used is 3-5 times the molar amount of B; the amount of the ligand Ruphos is 0.1 wt% of B.

6. The bio-based polyurethane flame-retardant protective material as described in claim 1, characterized in that, In step S4, the organic base is triethylamine or 4-dimethylaminopyridine, and the amount used is 4.5-5 times the molar amount of C; the amount of di-tert-butyl dicarbonate is 4.1-4.5 times the molar amount of C; in step S5, the amount of oxaloyl chloride is 1.3-1.5 times the molar amount of D; in step S6, the amount of triethylamine is 5-7 times the molar amount of E; and the amount of trimethylsilyl trifluoromethanesulfonate is 4.1-4.5 times the molar amount of E.

7. The bio-based polyurethane flame-retardant protective material according to claim 1, wherein in step S8, the amount of triethylamine is 2.5-3 times the molar amount of malonyl chloride; and the number-average molecular weight of the modified bio-based PN flame-retardant polyester diol is 2000-4000.

8. The application of the bio-based polyurethane flame-retardant protective material as described in any one of claims 1-7 in safety helmets.

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