A preparation method of non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer

Abstract

The invention discloses a method for preparing a non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer. The polyurethane elastomer is prepared by using isocyanate as a hard segment, poly-1,4-butylene adipate as a soft segment, and compounding with 2-amino-4-hydroxy-6-methylpyrimidine, a phosphorus-based reactive flame retardant and cerium oxide. The preparation method of the invention is simple, the process is easy to control, and the prepared polyurethane elastomer has good tensile strength. In addition, the polyurethane elastomer has a limiting oxygen index of 27.4, which meets the commercial standard of flame-retardant materials and the flame-retardant grade requirement of UL-94 V-0, and has a light transmittance of 0% in the ultraviolet band, which can completely isolate ultraviolet rays and has good antioxidant function. The polyurethane elastomer can be applied to industries such as wires, cables, pipe profiles, films, and general molding.

Description

Technical Field

[0001] The invention belongs to the field of polymer composite materials and relates to a method for preparing a non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer. Background Art

[0002] Polyurethane elastomers (PU) are well-known for their good processability, elasticity and biocompatibility, and have great application prospects in the automotive industry, electrical products, construction engineering and medical equipment. However, the above applications usually require polyurethane elastomers to have excellent flame retardant properties to ensure their fire safety during use. Traditional halogen additives based on bromine, chlorine and fluorine have been used in polyurethane elastomers to achieve flame retardant effects, but due to the increasingly stringent environmental safety requirements in most countries and industries in recent years, this requires the addition of other non-halogens to polyurethane elastomers as flame retardant systems, so it is necessary to develop a halogen-free flame retardant.

[0003] Huntsman Co.'s Chinese patent publication No. CN103492470 discloses a flame retardant polyurethane elastomer composition containing metal oxides, ammonium polyphosphate and its derivative phosphates, and oligomeric phosphate components, and Shin-Etsu Co.'s Chinese patent publication No. CN101993588 discloses a flame retardant polyurethane elastomer composition containing ammonium polyphosphate, melamine phosphate, surface-treated ammonium polyphosphate, pentaerythritol and its derivatives, and an organic siloxane component. Both of the above patents use a physical mixing method to add flame retardants to thermoplastic polyurethane elastomers, but the flame retardant thermoplastic polyurethane elastomer compositions finally prepared generally have the defects of certain mobility of the flame retardant, poor durability, and low mechanical strength.

[0004] Based on this, the present invention aims to provide a polyurethane elastomer with good flame retardant effect. The prepared polyurethane elastomer can be applied to various industries. While having excellent flame retardant effect, it can also maintain high tensile strength and has anti-aging function. Summary of the invention

[0005] In view of the above technical problems, the present invention aims to provide a method for preparing a non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer. The polyurethane elastomer is prepared by using isocyanate as a hard segment and poly(1,4-butylene adipate) as a soft segment, and is composited with 2-amino-4-hydroxy-6-methylpyrimidine, a phosphorus-based reactive flame retardant and cerium oxide. The preparation method of the present invention is simple, the process is easy to control, and the prepared polyurethane elastomer has good tensile strength. In addition, the limiting oxygen index of the polyurethane elastomer reaches 27.4, which meets the commercial standards of flame-retardant materials and the UL-94 V-0 flame retardant grade requirements. The transmittance in the ultraviolet band is 0%, which can completely isolate ultraviolet rays and has good antioxidant function. It can be applied to industries such as wires, cables, pipe profiles, films, and general molding.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing a non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer is carried out in the following steps in sequence:

[0008] S1. Preparation of phosphorus-based reactive flame retardant

[0009] After adding 50 mL of tetrahydrofuran solution to a glass flask, add 2 mol of p-hydroxybenzaldehyde and 2 mol of triethylamine, stir until completely dissolved, slowly drop 1 mol of phenylphosphoryl dichloride into the reaction mixture under 0°C ice bath conditions, stir and react for 3-6 h, quench the reaction mixture with water, add 100 mL of ethyl acetate and 30 mL of water for extraction, dry the obtained organic phase with 5 g of anhydrous sodium sulfate, filter, and evaporate under reduced pressure to obtain a phosphorus-based reactive flame retardant intermediate;

[0010] In the present invention, the glass flask used should be flame-dried under vacuum conditions and flushed with nitrogen several times to prevent water vapor and oxygen in the air from reducing the yield of the reaction when the reaction occurs;

[0011] 1 mol of the phosphorus-based reactive flame retardant intermediate is added to a 2 mol triethylamine ethanol solution (the volume ratio of triethylamine to ethanol is 1:10, and the volume fraction of ethanol is 75%), and then 2 mol of hydroxylamine hydrochloride is added, and the mixture is stirred for reaction for 2-5 h, and 100 mL of ethyl acetate and 30 mL of water are added for extraction, and the obtained organic phase is dried with 5 g of anhydrous sodium sulfate, filtered, and subjected to vacuum rotary evaporation to obtain the phosphorus-based reactive flame retardant;

[0012] S2. Preparation of nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer

[0013] Add polyester and isocyanate into a three-necked flask and stir for 1-1.5 h to obtain a prepolymer, add 2-amino-4-hydroxy-6-methylpyrimidine and cerium oxide into the prepolymer and stir until uniformly dispersed, then dissolve the phosphorus-based reactive flame retardant and 1,4-dihydroxyethoxybenzene prepared in step S1 in a solvent and add them into the prepolymer and stir to react for 30-60 s, then pour the obtained reactant into a polytetrafluoroethylene mold and age it in an oven at 80°C for 24 h to obtain a nitrogen-phosphorus-cerium synergistic flame retardant polyurethane elastomer.

[0014] As a limitation of the preparation method of the present invention, in step S1, the stirring speed is 220-250 rpm.

[0015] As another limitation of the preparation method of the present invention, in step S2, the polyester is poly(1,4-butylene adipate) with a weight average molecular weight of 1000-5000.

[0016] As a third limitation of the preparation method of the present invention, in step S2, the isocyanate is any one of hexamethylene diisocyanate, isophorone diisocyanate, methylcyclohexyl diisocyanate, dicyclohexylmethylene diisocyanate, xylene diisocyanate, 2,2,4-trimethylhexane diisocyanate, and dimer acid diisocyanate.

[0017] As a fourth limitation of the preparation method of the present invention, in step S2, the molar ratio of the polyester to the isocyanate, 2-amino-4-hydroxy-6-methylpyrimidine and cerium oxide is 10:5:0.2:3.

[0018] As a fifth limitation of the preparation method of the present invention, in step S2, the molar ratio of the phosphorus-based reactive flame retardant to 1,4-dihydroxyethoxybenzene and the solvent is 3:7:5.

[0019] As a sixth limitation of the preparation method of the present invention, in step S2, the molar ratio of the polyester to the phosphorus-based reactive flame retardant is 10:3.

[0020] As the seventh limitation of the preparation method of the present invention, in step S2, the solvent is any one of N,N-dimethylformamide, N,N-dimethylacetamide, and acetone.

[0021] As an eighth limitation of the preparation method of the present invention, in step S2, the stirring rate is 300-330 rpm.

[0022] In the present invention, 2-amino-4-hydroxy-6-methylpyrimidine, phosphorus-based reactive flame retardant, and cerium oxide have a synergistic flame retardant effect, as follows:

[0023] The phosphorus-containing reactive flame retardant and the reactive nitrogen ligand 2-amino-4-hydroxy-6-methylpyrimidine are embedded into the polyurethane elastomer through reaction, and nano-cerium oxide is added. The addition of the phosphorus-containing ligand can capture oxygen free radicals in the air and isolate the combustibles from the oxygen free radicals. The 2-amino-4-hydroxy-6-methylpyrimidine can not only increase the cross-linking degree of the polyurethane elastomer, but also the nitrogen released during the pyrolysis process can effectively dilute the oxygen content, thereby increasing the limiting oxygen index of the polyurethane elastomer. In addition, the intervention of nano-cerium oxide can achieve organic-inorganic synergistic flame retardancy without destroying its own mechanical properties.

[0024] The nitride of 2-amino-4-hydroxy-6-methylpyrimidine promotes the phosphorylation reaction of phosphoric acid produced by the phosphorus-based reactive flame retardant, thereby obtaining an ammonium phosphate product, such as ammonium phosphate salt or ester formed by ammonium phosphate. Compared with phosphoric acid esters formed by phosphorus alone, this ester has higher thermal stability, which increases the thermal decomposition temperature of the obtained polyurethane. In addition, unlike the sharp decrease in mechanical properties of the polyurethane caused by directly adding ammonium phosphate salt, the ammonium phosphate salt produced by this post-reaction maintains the flame retardancy of the material itself while also maintaining high mechanical properties of the material, thereby obtaining better flame retardancy and mechanical properties.

[0025] Due to the extremely high thermal stability of cerium oxide as a metal oxide, it will not be destroyed by combustion. The polyurethane network is destroyed during the combustion process. In the process of generating ammonium phosphate synergistically generated by 2-amino-4-hydroxy-6-methylpyrimidine and phosphorus-based reactive flame retardants, cerium oxide is exposed on the surface, so that the ammonium phosphate is coated on the surface of nano cerium oxide to form a unique core-shell flame-retardant nanofiller. Due to the different interlayer structures of phosphates, metaphosphates, and ammonium phosphates formed by combustion, the carbon layers between each layer are not combined but nested. However, when the core-shell flame-retardant nanofiller exists, it will self-assemble with phosphates, metaphosphates, and ammonium phosphates to form stacked interlayer carbon. Compared with ordinary carbon layers, it is equivalent to having multiple protective layers. In addition, unlike ordinary carbon layers that may be impacted by gases to form holes, the multi-layer protection basically isolates the impact of gases, thereby forming a stable and dense carbon layer, and therefore has a better flame retardant effect.

[0026] The above technical solution of the present invention is taken as a whole, and each step is closely related and influences each other, which jointly determine the morphological characteristics and performance of the product.

[0027] The above technical solution has the following advantages or beneficial effects:

[0028] 1. The transmittance of the nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer prepared by the present invention in the ultraviolet band is 0%, achieving full shielding of ultraviolet rays;

[0029] 2. The nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer prepared by the present invention has a limiting oxygen index value of 27.4, and a UL-94 test reaches a V-0 flame retardant grade; and while having good flame retardant properties, it maintains a high tensile strength, which can reach 62.8 MPa;

[0030] 3. The preparation method of the present invention is simple, the process is easy to control, the preparation cycle is short and the cost is low.

[0031] The invention is suitable for preparing nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elasticity.

[0032] The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The figures are scanning electron microscope images of cerium oxide, pure polyurethane elastomer and nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer prepared in Example 1 of the present invention after combustion, wherein: (a) is a scanning electron microscope image of cerium oxide, (b) is a scanning electron microscope image of a carbon layer of pure polyurethane elastomer after combustion, and (c) is a scanning electron microscope image of the non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer prepared in Example 1 of the present invention after combustion;

[0034] Figure 2 The structure characterization diagram of the phosphorus-based reactive flame retardant prepared in Example 1 of the present invention, wherein: (a) is a nuclear magnetic resonance hydrogen spectrum diagram, and (b) is a Fourier transform infrared spectrum diagram;

[0035] Figure 3 This is an infrared spectrum of the nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer prepared in Example 1 of the present invention;

[0036] Figure 4 These are performance characterization diagrams of the nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer prepared in Example 1 of the present invention, wherein: (a) is a LOI test diagram, and (b) is a UL-94 test diagram;

[0037] Figure 5 This is a graph showing the mechanical properties of the nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer prepared in Example 1 of the present invention;

[0038] Figure 6 This is the ultraviolet transmission spectrum of the nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0039] The following embodiments are only some embodiments of the present invention, rather than all embodiments. Therefore, the detailed description in the embodiments of the present invention provided below is not intended to limit the scope of the present invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the protection scope of the present invention.

[0040] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments are all conventional methods in the art unless otherwise specified. Example 1

[0041] This embodiment prepares a non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastic, and the preparation process and steps are as follows:

[0042] S1. Preparation of phosphorus-based reactive flame retardant

[0043] The glass flask was flame dried under vacuum conditions and flushed with nitrogen several times, then 50 mL of tetrahydrofuran solution was added to the glass flask, and then 2 mol of p-hydroxybenzaldehyde and 2 mol of triethylamine were added, and stirred at a stirring rate of 220 rpm until completely dissolved, 1 mol of phenylphosphoryl dichloride was slowly added dropwise to the reaction mixture under 0°C ice bath conditions, and stirred at a stirring rate of 220 rpm for 3 h, the reaction mixture was quenched with water, and 100 mL of ethyl acetate and 30 mL of water were added for extraction, and the obtained organic phase was dried with 5 g of anhydrous sodium sulfate, filtered, and vacuum rotary evaporated to obtain a phosphorus-based reactive flame retardant intermediate;

[0044] 1 mol of the phosphorus-based reactive flame retardant intermediate was added to a 2 mol triethylamine ethanol solution (the volume ratio of triethylamine to ethanol was 1:10, and the volume fraction of ethanol was 75%), and then 2 mol of hydroxylamine hydrochloride was added, and the mixture was stirred at a stirring rate of 220 rpm for 2 h, and 100 mL of ethyl acetate and 30 mL of water were added for extraction. The obtained organic phase was dried with 5 g of anhydrous sodium sulfate, filtered, and evaporated under reduced pressure to obtain the phosphorus-based reactive flame retardant.

[0045] S2. Preparation of nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer

[0046] 10 mol of poly(1,4-butylene adipate) (weight average molecular weight of 1000-5000) and 5 mol of hexamethylene diisocyanate were added to a three-necked flask and stirred at a stirring rate of 300 rpm for 1 h to obtain a prepolymer. 0.2 mol of 2-amino-4-hydroxy-6-methylpyrimidine and 3 mol of cerium oxide were added to the prepolymer and stirred at a stirring rate of 300 rpm until uniformly dispersed. Then, 3 mol of the phosphorus-based reactive flame retardant and 7 mol of 1,4-dihydroxyethoxybenzene prepared in step S1 were dissolved in 5 mol of N,N-dimethylformamide and added to the prepolymer. The mixture was stirred at a stirring rate of 300 rpm for 30 s. The obtained reactant was poured into a polytetrafluoroethylene mold and aged in an oven at 80°C for 24 h to obtain a nitrogen-phosphorus-cerium synergistic flame retardant polyurethane elastomer.

[0047] The nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer prepared in this embodiment has good flame-retardant properties while maintaining high mechanical properties and has anti-aging function. Example 2

[0048] This embodiment prepares a non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastic, and the preparation process and steps are as follows:

[0049] S1. Preparation of phosphorus-based reactive flame retardant

[0050] The glass flask was flame dried under vacuum conditions and flushed with nitrogen several times, then 50 mL of tetrahydrofuran solution was added to the glass flask, and then 2 mol of p-hydroxybenzaldehyde and 2 mol of triethylamine were added, and stirred at a stirring rate of 240 rpm until completely dissolved, 1 mol of phenylphosphoryl dichloride was slowly added dropwise to the reaction mixture under 0°C ice bath conditions, and stirred at a stirring rate of 240 rpm for 5 h, the reaction mixture was quenched with water, and 100 mL of ethyl acetate and 30 mL of water were added for extraction, and the obtained organic phase was dried with 5 g of anhydrous sodium sulfate, filtered, and vacuum rotary evaporated to obtain a phosphorus-based reactive flame retardant intermediate;

[0051] 1 mol of the phosphorus-based reactive flame retardant intermediate was added to a 2 mol triethylamine ethanol solution (the volume ratio of triethylamine to ethanol was 1:10, and the volume fraction of ethanol was 75%), and then 2 mol of hydroxylamine hydrochloride was added, and the mixture was stirred at a stirring rate of 240 rpm for 4 h, and 100 mL of ethyl acetate and 30 mL of water were added for extraction. The obtained organic phase was dried with 5 g of anhydrous sodium sulfate, filtered, and evaporated under reduced pressure to obtain the phosphorus-based reactive flame retardant.

[0052] S2. Preparation of nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer

[0053] 10 mol of poly(1,4-butylene adipate) (weight average molecular weight of 1000-5000) and 5 mol of isophorone diisocyanate were added to a three-necked flask and stirred at a stirring rate of 320 rpm for 1.2 h to obtain a prepolymer, 0.2 mol of 2-amino-4-hydroxy-6-methylpyrimidine and 3 mol of cerium oxide were added to the prepolymer and stirred at a stirring rate of 320 rpm until uniformly dispersed, then 3 mol of the phosphorus-based reactive flame retardant and 7 mol of 1,4-dihydroxyethoxybenzene prepared in step S1 were dissolved with 5 mol of N,N-dimethylacetamide and added to the prepolymer, stirred at a stirring rate of 320 rpm for reaction for 50 s, and then the obtained reactant was poured into a polytetrafluoroethylene mold and aged in an oven at 80°C for 24 h to obtain a nitrogen-phosphorus-cerium synergistic flame retardant polyurethane elastomer.

[0054] The nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer prepared in this embodiment has good flame-retardant properties while maintaining high mechanical properties and has anti-aging function. Example 3

[0055] This embodiment prepares a non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastic, and the preparation process and steps are as follows:

[0056] S1. Preparation of phosphorus-based reactive flame retardant

[0057] The glass flask was flame dried under vacuum conditions and flushed with nitrogen several times, then 50 mL of tetrahydrofuran solution was added to the glass flask, and then 2 mol of p-hydroxybenzaldehyde and 2 mol of triethylamine were added, and stirred at a stirring rate of 250 rpm until completely dissolved, 1 mol of phenylphosphoryl dichloride was slowly added dropwise to the reaction mixture under 0°C ice bath conditions, and stirred at a stirring rate of 250 rpm for 6 h, the reaction mixture was quenched with water, and 100 mL of ethyl acetate and 30 mL of water were added for extraction, and the obtained organic phase was dried with 5 g of anhydrous sodium sulfate, filtered, and vacuum rotary evaporated to obtain a phosphorus-based reactive flame retardant intermediate;

[0058] 1 mol of the phosphorus-based reactive flame retardant intermediate was added to a 2 mol triethylamine ethanol solution (the volume ratio of triethylamine to ethanol was 1:10, and the volume fraction of ethanol was 75%), and then 2 mol of hydroxylamine hydrochloride was added, and the mixture was stirred at a stirring rate of 250 rpm for 5 h, and 100 mL of ethyl acetate and 30 mL of water were added for extraction. The obtained organic phase was dried with 5 g of anhydrous sodium sulfate, filtered, and evaporated under reduced pressure to obtain the phosphorus-based reactive flame retardant.

[0059] S2. Preparation of nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer

[0060] 10 mol of poly(1,4-butylene adipate) (weight average molecular weight of 1000-5000) and 5 mol of dicyclohexylmethylene diisocyanate were added to a three-necked flask and stirred at a stirring rate of 330 rpm for 1.5 h to obtain a prepolymer. 0.2 mol of 2-amino-4-hydroxy-6-methylpyrimidine and 3 mol of cerium oxide were added to the prepolymer and stirred at a stirring rate of 330 rpm until uniformly dispersed. Then, 3 mol of the phosphorus-based reactive flame retardant and 7 mol of 1,4-dihydroxyethoxybenzene prepared in step S1 were dissolved in 5 mol of acetone and added to the prepolymer. The mixture was stirred at a stirring rate of 330 rpm for 60 s. The obtained reactant was then poured into a polytetrafluoroethylene mold and aged in an oven at 80°C for 24 h to obtain a nitrogen-phosphorus-cerium synergistic flame retardant polyurethane elastomer.

[0061] The nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer prepared in this embodiment has good flame-retardant properties while maintaining high mechanical properties and has anti-aging function. Comparative Example

[0062] In order to explore the influence of different substances in the preparation process of the present invention on the performance of the product of the present invention, the following comparative experiments were carried out. Different polyurethane elastomers were prepared in the following comparative examples, as follows: Comparative Example 1

[0063] In this comparative example, a polyurethane elastomer similar to that in Example 1 is prepared, except that in step (2), 2-amino-4-hydroxy-6-methylpyrimidine is not added, and the remaining parameters are the same as those in Example 1. Comparative Example 2

[0064] In this comparative example, a polyurethane elastomer similar to that in Example 1 is prepared, except that cerium oxide is not added in step (2). The other parameters are the same as those in Example 1. Comparative Example 3

[0065] The present comparative example prepares a polyurethane elastomer similar to that of Example 1, except that in step (2), no phosphorus-based reactive flame retardant is added, and the remaining parameters are the same as those of Example 1.

[0066] Performance Testing

[0067] The performance of the polyurethane elastomers prepared in the examples of the present invention and the comparative examples was characterized as follows:

[0068] like Figure 1 are scanning electron microscope images related to Example 1 of the present invention, wherein (a) is a scanning electron microscope image of cerium oxide filler, (b) is a scanning electron microscope image of the carbon layer of pure polyurethane elastomer after combustion, and (c) is a scanning electron microscope image of the nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer prepared in Example 1 of the present invention after combustion; Figure 1 As can be seen in (a), the cerium oxide powder has uniform particle size, good dispersion and high specific surface area, which is not only conducive to the dispersion of nano-cerium oxide powder in the polyurethane network, but also conducive to its better compatibility, and plays a greater role in flame retardancy and UV shielding; Figure 1 As can be seen in (b), the carbon layer of pure polyurethane is thin and has pore defects, which is very easy to collapse. The defects also lead to continuous contact with the combustible gas, resulting in continuous combustion. Figure 1 (c) It can be seen that after adding 2-amino-4-hydroxy-6-methylpyrimidine, phosphorus-based reactive flame retardants and cerium oxide, nitrides and phosphoric acid products promote the formation of ammonium phosphate salts, which are then coated on the surface of cerium oxide to form a core-shell assembled new flame retardant. This newly formed core-shell flame retardant aggregates to form flame-retardant sheets, which are nested and self-assembled with ordinary carbon layers, making the carbon layer dense and thick, thereby physically blocking the combustible gas from the air, thereby achieving a better flame retardant effect.

[0069] like Figure 2 As shown, it is a structural characterization diagram of the phosphorus-based reactive flame retardant (BFPP) prepared in step S1 of Example 1 of the present invention, wherein (a) is a nuclear magnetic resonance hydrogen spectrum of the phosphorus-based reactive flame retardant. It can be seen from the figure that 1H NMR (400MHz, DMSO): δ = 10.00 (s, 2H), 7.94 (s, 2H), 7.63 (s, 2H), 7.46 (s, 4H). From the peak position and the integrated area, it can be obtained that the phosphorus-based reactive flame retardant was successfully prepared; (b) is the Fourier transform infrared spectrum of the phosphorus-based reactive flame retardant. It can be seen from the figure that the main characteristic peaks are PO at 915cm -1 The characteristic peak position of P=O is 1215cm -1 , 1736cm -1 , 3292cm -1 The peak at is the characteristic peak of oxime group. These data indicate that the phosphorus-based reactive flame retardant was successfully synthesized.

[0070] Figure 3 The infrared spectrum of the nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer prepared in Example 1 of the present invention shows that the synthesized phosphorus-based reactive flame retardant and 2-amino-4-hydroxy-6-methylpyrimidine have entered the polyurethane elastomer, wherein the polyurethane elastomer has a peak at 2260 cm -1 The NCO absorption peak near the NH group disappears, indicating that the NCO group reacts fully with the OH group; the NH stretching vibration peak appears at 3327 cm -1 This indicates that 2-amino-4-hydroxy-6-methylpyrimidine was successfully introduced into the polyurethane elastomer, and the saturated CH 2 The tensile vibration peak appears at 2939 -1 ,2924 -1 and 2854 cm -1 At 1222 cm -1 The peak at 1704 cm-1 is attributed to the COC stretching vibration peak of the soft segment, and the characteristic peak of phosphorus-based reactive flame retardants appears at 1704 cm-1. -1 (C=N), 1273 cm -1 (P=O) and 984 cm -1 (P-O) These results indicate that the phosphorus-based reactive flame retardant and 2-amino-4-hydroxy-6-methylpyrimidine are introduced into the polyurethane elastomer molecular chain in the form of chemical bonds.

[0071] like Figure 4 and Figure 5 It can be seen that the nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer prepared in Example 1 has excellent mechanical properties and flame retardant properties. Figure 4 ,from Figure 4As can be seen in (a), compared with pure polyurethane elastomer, the combustion conditions of the polyurethane elastomers prepared in Example 1 and Comparative Examples 1-3 are reduced to varying degrees, and the droplet phenomenon is greatly improved, but the limiting oxygen index LOI of the nitrogen-phosphorus-cerium synergistic flame retardant polyurethane elastomer prepared in Example 1 is increased from 19 to 27.4. Compared with the limiting oxygen index LOI of 25.3, 25.7, and 24.8 of the polyurethane elastomers in Comparative Examples 1-3, the nitrogen-phosphorus-cerium synergistic flame retardant polyurethane elastomer prepared in Example 1 of the present invention has the best flame retardant performance;

[0072] Figure 4 (b) is a vertical combustion test of different polyurethane elastomers. It can be seen that the pure polyurethane elastomer has obvious combustion phenomenon in the vertical combustion test, and the melting drop phenomenon is serious. The dripping droplets ignite the absorbent cotton below, and the secondary ignition not only ignites the absorbent cotton again, but also the sample strip is almost burned out; although the combustion conditions of the polyurethane elastomers prepared in Comparative Examples 1-3 are improved, it can be seen that the ignition time of the polyurethane elastomer prepared in Comparative Example 1 is increased, but after burning for 5 s, the dripping droplets ignite the absorbent cotton below, indicating that although the oxygen index LOI is improved compared with pure polyurethane, the combustion conditions have not been completely improved; the polyurethane elastomer prepared in Comparative Example 2 is ignited for 10 s after the first ignition. Although some liquid droplets fell after 10 s, the absorbent cotton below was not ignited. After the second repeated ignition, it was found that the molten droplets were further intensified, thereby igniting the absorbent cotton below; the polyurethane elastomer prepared in Comparative Example 3 was similar to Comparative Example 1. Although the oxygen index LOI was partially improved, the molten drop problem was not solved, so the flame retardant grade was not improved; the nitrogen-phosphorus-cerium synergistic flame retardant polyurethane elastomer prepared in Example 1 did not produce molten droplets 10 s after the first ignition, and some molten droplets were produced 10 s after the second ignition, but the absorbent cotton below was still not ignited, so the UL-94 flame retardant grade was improved from no grade to V-0 grade. (UL-94 flame retardant rating standard: V-2: After two 10-second combustion tests on the sample, the flame goes out within 60 seconds, and the burning material can fall off; V-1: After two 10-second combustion tests on the sample, the flame goes out within 60 seconds, and no burning material can fall off; V-0: After two 10-second combustion tests on the sample, the flame goes out within 30 seconds, and no burning material can fall off; No rating means that the test sample burns out and cannot extinguish itself.)

[0073] In addition, if Figure 5Compared with pure polyurethane elastomer, the tensile strength of the nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer prepared in Example 1 of the present invention slightly decreases from 69.3 MPa to 62.8 MPa, but still maintains relatively high mechanical properties. It can be seen from the figure that the tensile strengths of the polyurethane elastomers prepared in Comparative Examples 1-3 are 44.8 MPa, 50.9 MPa and 41.3 MPa, respectively. It can be seen that compared with Comparative Examples 1-3, the non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer prepared in Example 1 of the present invention can maintain relatively high mechanical properties while improving flame retardancy.

[0074] Figure 6 It can be seen that compared with pure polyurethane elastomer, the transmittance of the nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer prepared in Example 1 of the present invention is reduced to 0% in both the ultraviolet short-wave band UV-B and the long-wave band UV-A, indicating that it has excellent ultraviolet shielding function and achieves complete ultraviolet band shielding.

[0075] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer, characterized in that: Follow the steps below in order: S1. Preparation of phosphorus-based reactive flame retardant After adding 50 mL of tetrahydrofuran solution to a glass flask, add 2 mol of p-hydroxybenzaldehyde and 2 mol of triethylamine, stir until completely dissolved, slowly drop 1 mol of phenylphosphoryl dichloride into the reaction mixture under 0°C ice bath conditions, stir and react for 3-6 h, quench the reaction mixture with water, add 100 mL of ethyl acetate and 30 mL of water for extraction, dry the obtained organic phase with 5 g of anhydrous sodium sulfate, filter, and evaporate under reduced pressure to obtain a phosphorus-based reactive flame retardant intermediate; 1 mol of the phosphorus-based reactive flame retardant intermediate is added to a 2 mol ethanol solution of triethylamine, and then 2 mol of hydroxylamine hydrochloride is added, and the mixture is stirred for reaction for 2-5 h, and 100 mL of ethyl acetate and 30 mL of water are added for extraction, and the obtained organic phase is dried with 5 g of anhydrous sodium sulfate, filtered, and subjected to reduced pressure rotary evaporation to obtain the phosphorus-based reactive flame retardant; S2. Preparation of nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer Add polyester and isocyanate into a three-necked flask and stir for 1-1.5 h to obtain a prepolymer, add 2-amino-4-hydroxy-6-methylpyrimidine and cerium oxide into the prepolymer and stir until uniformly dispersed, then dissolve the phosphorus-based reactive flame retardant and 1,4-dihydroxyethoxybenzene prepared in step S1 in a solvent and add them into the prepolymer and stir to react for 30-60 s, then pour the obtained reactant into a polytetrafluoroethylene mold and age it in an oven at 80°C for 24 h to obtain a nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer.

2. The method for preparing a non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer according to claim 1, characterized in that: In step S1, the stirring speed is 220-250 rpm.

3. The method for preparing a non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer according to claim 1, characterized in that: In step S2, the polyester is poly(1,4-butylene adipate) with a weight average molecular weight of 1000-5000.

4. The method for preparing a non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer according to claim 1, characterized in that: In step S2, the isocyanate is any one of hexamethylene diisocyanate, isophorone diisocyanate, methylcyclohexyl diisocyanate, dicyclohexylmethylene diisocyanate, xylylene diisocyanate, and dimer acid diisocyanate.

5. The method for preparing a non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer according to claim 1, characterized in that: In step S2, the molar ratio of the polyester to the isocyanate, 2-amino-4-hydroxy-6-methylpyrimidine and cerium oxide is 10:5:0.2:

3.

6. The method for preparing a non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer according to claim 1, characterized in that: In step S2, the molar ratio of the phosphorus-based reactive flame retardant to 1,4-dihydroxyethoxybenzene and the solvent is 3:7:

5.

7. The method for preparing a non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer according to claim 1, characterized in that: In step S2, the molar ratio of the polyester to the phosphorus-based reactive flame retardant is 10:

3.

8. The method for preparing a non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer according to claim 1, characterized in that: In step S2, the solvent is any one of N,N-dimethylformamide, N,N-dimethylacetamide and acetone.

9. The method for preparing a non-additive nitrogen-phosphorus-cerium synergistic flame-retardant polyurethane elastomer according to claim 1, characterized in that: In step S2, the stirring rate is 300-330 rpm.

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