Nitrogen-phosphorus-boron flame retardant, flame retardant and melt dripping resistant polyurethane elastomer and preparation method thereof

Abstract

The present invention discloses a nitrogen-phosphorus-boron flame retardant, a flame-retardant and melt-drop resistant polyurethane elastomer and a preparation method thereof, belonging to the technical field of polyurethane elastomers. The preparation method of the nitrogen-phosphorus-boron flame retardant includes: dissolving monoethanolamine borate and furfural in absolute ethanol, introducing nitrogen, and stirring and reacting at 45-55 °C to obtain an intermediate product; mixing a phosphaphenanthrene DOPO solution with the intermediate product and stirring and reacting at 70-80 °C to obtain the nitrogen-phosphorus-boron flame retardant. The modified polyurethane elastomer includes: 70%-80% of polyether diol, 0.5-3% of boron nitride nanocomposite, 16%-22% of toluene-2,4-diisocyanate, 8%-10% of dimethyl toluene diamine, 0.5-1% of ultraviolet light stabilizer and 0.5-3% of nitrogen-phosphorus-boron flame retardant. The nitrogen-phosphorus-boron flame retardant proposed by the present invention improves the flame retardancy, melt-drop resistance and mechanical properties of the polyurethane elastomer.

Description

Technical Field

[0001] The present invention relates to the technical field of polyurethane elastomers, and particularly relates to a nitrogen-phosphorus-boron flame retardant, a flame-retardant and melt-drop resistant polyurethane elastomer, and a preparation method thereof. Background Art

[0002] Thermoplastic polyurethane elastomer (TPU) is an elastomeric material that can be plastified by heating. Its molecular structure is a linear polymer formed by polycondensation of diisocyanate and polyol, and a physical crosslinking network can be formed at the use temperature, so it has good elasticity. Due to its excellent mechanical properties, such as high strength, high elasticity, excellent wear resistance, as well as good oil resistance, aging resistance and other characteristics, TPU has been widely used in industry, life, medical treatment, military and other aspects. Although TPU has many performance advantages and is easy to process, it also has obvious defects, that is, it is flammable and has serious melt dripping. Its limiting oxygen index is only 16% - 18%, and it will burn rapidly when encountering fire, and produce a large amount of melt droplets, accelerating the spread of the fire. Therefore, the flame retardant modification of TPU materials is also very important. Most of the TPU materials on the market currently use flame retardants containing halogen or phosphorus elements. Since halogen will produce a large amount of harmful gases during combustion and cause serious environmental pollution, it has been gradually replaced by phosphorus-based flame retardants. However, conventional phosphorus-based flame retardants cannot solve the problem of melt dripping during the combustion of TPU. Therefore, endowing TPU materials with both flame retardancy and melt-drop resistance characteristics is the focus of current research on TPU flame retardant modification.

[0003] Boron nitride is a crystal composed of nitrogen atoms and boron atoms, and has 4 different crystal structures: hexagonal boron nitride, rhombohedral boron nitride, cubic boron nitride and wurtzite boron nitride. Among them, the structure and properties of hexagonal boron nitride are very similar to those of graphite, and it can be exfoliated into two-dimensional nanosheets, which have strong stiffness and high-temperature lubricity. Research shows that hexagonal boron nitride nanosheets can significantly improve the mechanical properties of polymers, and at the same time can also enhance the flame retardancy of polymers. Therefore, introducing boron nitride nanosheets into TPU is expected to improve its melt-drop resistance. However, when directly applying boron nitride nanosheets to polymers, due to polarity reasons, it is difficult to disperse uniformly in polymers, affecting the full play of its performance. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above technical deficiencies, and provide a nitrogen-phosphorus-boron flame retardant, as well as a flame-retardant and melt-drop resistant polyurethane elastomer and a preparation method thereof, to solve the technical problem of how to simultaneously improve the flame retardancy, melt-drop resistance, and mechanical properties of polyurethane elastomers in the prior art.

[0005] To achieve the above technical purpose, the technical solution of the present invention provides a nitrogen-phosphorus-boron flame retardant, as well as a flame-retardant and melt-drop resistant polyurethane elastomer and a preparation method thereof.

[0006] The preparation method of the nitrogen-phosphorus-boron flame retardant proposed by the present invention includes the following steps:

[0007] Dissolve monoethanolamine borate and furfural in absolute ethanol, introduce nitrogen, and stir and react at 45 - 55 °C to obtain an intermediate product;

[0008] Mix the phosphaphenanthrene DOPO solution with the intermediate product and stir and react at 70 - 80 °C to obtain the nitrogen-phosphorus-boron flame retardant.

[0009] Furthermore, the present invention also proposes a nitrogen-phosphorus-boron flame retardant prepared by the above preparation method.

[0010] Furthermore, in order to cooperate with the new flame retardant to improve the melt dripping resistance of TPU, the present invention also invents a boron nitride nanocomposite.

[0011] The preparation method of the boron nitride nanocomposite includes the following steps: Mix the polydopamine-coated boron nitride nanosheets with a DMF solvent to form a suspension; then add 4,4'-diphenylmethane diisocyanate to the suspension and continue stirring, and then raise the temperature to 50 - 60 °C and add a catalyst to continue the reaction to obtain an isocyanated boron nitride nanocomposite.

[0012] Furthermore, the catalyst is dibutyltin dilaurate; and / or, the reaction time is 10 - 12 h; and / or, the 4,4'-diphenylmethane diisocyanate is added according to the mass ratio of the polydopamine-coated boron nitride nanosheets to the 4,4'-diphenylmethane diisocyanate of (1 - 2):(50 - 60); and / or, the polydopamine-coated boron nitride nanosheets are prepared by the following steps: Stir the boron nitride nanosheets with water to obtain a boron nitride suspension, then add a Tris buffer solution and stir, continue to adjust the pH to 8 - 9, and then add dopamine hydrochloride and continue stirring to obtain the polydopamine-coated boron nitride nanosheets.

[0013] In addition, the present invention also proposes a modified polyurethane elastomer, which includes, by mass percentage, raw materials: 70% - 80% of polyether diol, 0.5 - 3% of the above-mentioned boron nitride nanocomposite, 16% - 22% of toluene-2,4-diisocyanate, 8% - 10% of dimethyl toluene diamine, 0.5 - 1% of ultraviolet light stabilizer, and 0.5 - 3% of nitrogen-phosphorus-boron flame retardant.

[0014] Furthermore, the polyether diol is one or both of polyoxypropylene ether diol and tetrahydrofuran homopolyether diol; and / or, the ultraviolet light stabilizer is 2-(2-hydroxy-3,5-di-tert-amylphenyl)benzotriazole.

[0015] In addition, the present invention also proposes a preparation method of the above-mentioned modified polyurethane elastomer, which includes the following steps:

[0016] S1. Mix boron nitride nanocomposite and polyether diol at 80 - 85 °C, then add toluene - 2,4 - diisocyanate and mix at 45 - 50 °C, and then stir and react at 85 - 90 °C to obtain a modified polyurethane prepolymer;

[0017] S2. Stir and mix the modified polyurethane prepolymer obtained in step S1, dimethylthio - toluene diamine, ultraviolet light stabilizer, and nitrogen - phosphorus - boron flame retardant at 110 - 120 °C, and then cure to obtain the modified polyurethane elastomer.

[0018] Further, in step S2, the curing includes: curing at 100 - 105 °C and keeping warm at 95 - 100 °C after molding to obtain the modified polyurethane elastomer.

[0019] Further, in step S1, the stirring reaction time is 1.5 - 2 h.

[0020] Further, in step S2, the stirring and mixing time is 5 - 10 min.

[0021] Compared with the prior art, the beneficial effects of the present invention include: the high - efficiency flame retardancy of the novel nitrogen - phosphorus - boron flame retardant, that is, an ideal flame retardant effect (UL94 - V0 level) can be achieved when the addition amount is very small (less than 3%), and at the same time, polydopamine - coated boron nitride nanosheets can efficiently graft with 4,4' - diphenylmethane diisocyanate to prepare a highly dispersed boron nitride nanocomposite with isocyanate characteristics, enabling it to participate in the next polymerization and curing process with polyether polyol. This can not only well solve the dispersion problem of boron nitride nanosheets in the polyurethane matrix, but also connect the dispersed nano - boron nitride into the polyurethane elastomer resin molecular chain through chemical bonds, improving the mechanical properties and combustion anti - dripping property of the modified polyurethane elastomer. Description of the Drawings

[0022] Figure 1 is the 1H NMR spectrum of the nitrogen - phosphorus - boron flame retardant prepared by the present invention;

[0023] Figure 2 is the SEM image of the boron nitride nanocomposite prepared in Example 1 of the present invention.

[0024] Figure 3 is the dispersion diagram of hexagonal boron nitride powder in the organic solvent DMF (left figure), and the dispersion diagram of the boron nitride nanocomposite prepared in Example 1 in the organic solvent DMF (right figure). Detailed Embodiments

[0025] This specific embodiment provides a method for preparing a boron nitride nanocomposite, comprising the following steps: mixing polydopamine-coated boron nitride nanosheets with a DMF solvent to form a suspension; then adding 4,4'-diphenylmethane diisocyanate to the suspension and continuing to stir, and then heating to 50-60 °C and adding a catalyst to continue the reaction for 10-12 h to obtain an isocyanated boron nitride nanocomposite; the catalyst is dibutyltin dilaurate; and / or adding the 4,4'-diphenylmethane diisocyanate according to the mass ratio of (1-2):(50-60) of the polydopamine-coated boron nitride nanosheets to the 4,4'-diphenylmethane diisocyanate; and / or the polydopamine-coated boron nitride nanosheets are prepared by the following steps: stirring boron nitride nanosheets with water to obtain a boron nitride suspension, then adding a Tris buffer solution and stirring, continuing to adjust the pH to 8-9, and then adding dopamine hydrochloride and continuing to stir to obtain the polydopamine-coated boron nitride nanosheets;

[0026] The boron nitride nanosheets are prepared by the following steps: mixing hexagonal boron nitride powder with sucrose crystals, performing solid-phase ball milling at a rotation speed of 500 rpm for 10-12 h, ultrasonically stirring the obtained ball-milled boron nitride in water, and then centrifuging and filtering, repeating the above stirring, centrifuging, and filtering steps three times to obtain boron nitride nanosheets, and drying at room temperature for 20-24 h; the particle size of the hexagonal boron nitride is 15-50 μm, and the mass ratio of hexagonal boron nitride to sucrose crystals is 1:(4-5).

[0027] This specific embodiment also provides a boron nitride nanocomposite prepared by the above preparation method.

[0028] This specific embodiment also provides a modified polyurethane elastomer, calculated by mass percentage, the raw materials include: 70%-80% of polyether diol, 0.5-3% of boron nitride nanocomposite, 16%-22% of toluene-2,4-diisocyanate, 8%-10% of dimethyl toluene diamine, 0.5-1% of ultraviolet light stabilizer, and 0.5-3% of nitrogen-phosphorus-boron flame retardant; the polyether diol is one or both of polyoxypropylene ether diol and tetrahydrofuran homopolyether diol; and / or the ultraviolet light stabilizer is 2-(2-hydroxy-3,5-di-tert-amylphenyl) benzotriazole.

[0029] In addition, this specific embodiment also provides a method for preparing a modified polyurethane elastomer, comprising the following steps:

[0030] S1. Mix the boron nitride nanocomposite and polyether diol at 80-85 °C, then add toluene-2,4-diisocyanate and mix at 45-50 °C, and then stir and react at 85-90 °C for 1.5-2 h to obtain a modified polyurethane prepolymer;

[0031] S2. Stir and mix the modified polyurethane prepolymer, dimethylthiotoluenediamine, ultraviolet light stabilizer, and nitrogen-phosphorus-boron flame retardant prepared in step S1 at 110 - 120 °C for 5 - 10 min, then cure at 100 - 105 °C for 1 - 1.5 h. After molding, place it in an oven and keep it at 95 - 100 °C for 24 - 28 h to obtain the modified polyurethane elastomer;

[0032] The nitrogen-phosphorus-boron flame retardant in this specific embodiment is prepared by the following steps:

[0033] Dissolve monoethanolamine borate and furfural in anhydrous ethanol, introduce nitrogen, and stir and react at 45 - 55 °C to obtain an intermediate product;

[0034] Mix the phosphaphenanthrene DOPO solution with the intermediate product and stir and react at 70 - 80 °C to obtain the nitrogen-phosphorus-boron flame retardant.

[0035] Conventional phosphorus-based flame retardants such as ammonium polyphosphate need to have a relatively large addition amount (more than 10% by mass) to achieve an ideal flame retardant effect, and there is smoke during combustion. Generally, although boron-based flame retardants have a certain smoke suppression effect, their resin compatibility is poor and they are easily affected by humidity and temperature. The nitrogen-phosphorus-boron flame retardant MFD synthesized in the present invention combines the advantages of phosphorus-based flame retardants and boron-based flame retardants at the molecular level. The borate structure and the phosphaphenanthrene structure DOPO are combined together through Schiff base chemical bonds, and at the same time, N elements with flame retardant effects are introduced, greatly improving the flame retardant efficiency of the flame retardant, and having good compatibility with the resin. It can achieve an efficient flame retardant and smoke suppression synergistic effect on polyurethane elastomers at a relatively small addition amount (0.5% - 3%).

[0036] By coating the surface of boron nitride nanosheets with polydopamine, a surface-modified boron nitride nanomaterial is obtained. Due to the rich hydroxyl active sites on the surface of polydopamine, compared with unmodified boron nitride, polydopamine-coated boron nitride nanosheets can efficiently graft with 4,4'-diphenylmethane diisocyanate to prepare a highly dispersed boron nitride nanocomposite with isocyanate characteristics, which well solves the dispersion problem of boron nitride nanosheets in the polyurethane matrix. At the same time, polydopamine also has a certain flame retardancy. The polyurethane elastomer prepolymer synthesized from the isocyanated boron nitride nanocomposite, polyether diol, and toluene-2,4-diisocyanate further reacts with dimethylthiotoluenediamine to uniformly embed the nitrogen-phosphorus-boron flame retardant therein, and the prepared polyurethane elastomer has excellent flame retardancy, anti-dripping property, and mechanical properties.

[0037] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] The nitrogen-phosphorus-boron flame retardant (MFD) in the following examples is prepared by the following steps:

[0039] Dissolve 0.05 mol of monoethanolamine borate and 0.05 mol of furfural in 50 ml of anhydrous ethanol respectively, add them to a three-necked flask, introduce nitrogen, and stir and react at 50 °C for 4 h to obtain an intermediate product (MF);

[0040] Add 0.05 mol of phosphaphenanthrene DOPO dissolved in 50 ml of anhydrous ethanol to the above reaction three-necked flask, raise the temperature to 80 °C and stir for 12 h; after the reaction is completed, filter the precipitate, wash it three times with anhydrous ethanol, and dry it in vacuum at 60 °C for 12 h. Finally, a pale yellow solid powder is obtained, which is the nitrogen-phosphorus-boron flame retardant (MFD). The 1H NMR spectrum of the synthesized nitrogen-phosphorus-boron flame retardant MFD is as Figure 1 shown.

[0041] The reaction formula is:

[0042]

[0043] In addition, it should be noted that all commercially available drugs used are of analytical purity. Among them, the molecular weight of polytetrahydrofuran ether glycol is 2000, and the particle size of boron nitride is 15 - 50 μm.

[0044] Example 1

[0045] This example presents a boron nitride nanocomposite, which is prepared by the following steps:

[0046] 1) Mix 4 g of hexagonal boron nitride powder with 16 g of sucrose crystals, perform solid-phase ball milling at 500 rpm for 12 h, ultrasonically stir the obtained ball-milled boron nitride in deionized water, then centrifuge and filter. Repeat the above stirring, centrifuging and filtering steps three times to obtain boron nitride nanosheets, and dry them at room temperature for 24 h;

[0047] 2) Add 1 g of boron nitride nanosheets to 100 mL of deionized water and ultrasonically stir to obtain a boron nitride suspension. Then add 12.5 mL of Tris buffer solution and continue ultrasonic treatment for 30 min; add an appropriate amount of 6 mol / L NaOH solution to adjust the pH of the solution to 8.5. Subsequently, add 1.0 g of dopamine hydrochloride to the above solution system and stir and react at room temperature for 24 h; after the reaction is completed, centrifuge at 5000 rpm for 5 min, wash it with deionized water multiple times until the pH of the centrifuged upper solution becomes neutral. Finally, dry the boron nitride nanosheets coated with dopamine polymer in a vacuum oven at 80 °C for 24 h;

[0048] 3) Add 1 g of dopamine-coated boron nitride nanosheets to 200 mL of DMF as the solvent, and stir ultrasonically to form a suspension. Add 55 g of 4,4'-diphenylmethane diisocyanate to the above suspension and continue stirring. Heat up to 55 °C, add 7 - 8 drops of the catalyst dibutyltin dilaurate, and continue the reaction for 10 h. Filter and remove the solvent by vacuum pumping to obtain the isocyanated boron nitride nanocomposite. From Figure 2 It can be seen that its flaky morphology is still retained. From Figure 3 It can be seen that the boron nitride nanocomposite can be uniformly dispersed in the organic solvent DMF, while the unmodified hexagonal boron nitride powder cannot be dispersed in the organic solvent DMF.

[0049] This example also presents a polyurethane elastomer, which is prepared by the following steps:

[0050] 1) Add 0.5 g of the isocyanated boron nitride nanocomposite prepared in this example to 70 g of polytetrahydrofuran ether glycol, stir and heat up to 80 °C for reaction for 0.5 h, then cool down to 50 °C and add it to 20 g of toluene-2,4-diisocyanate, continue stirring and heat up to 90 °C for reaction for 1.5 h, and remove bubbles by vacuum pumping to obtain a modified polyurethane prepolymer;

[0051] 2) Mix the modified polyurethane prepolymer obtained from the above reaction, 8 g of dimethylthiotoluenediamine, 0.5 g of the ultraviolet light stabilizer 2-(2-hydroxy-3,5-di-tert-amylphenyl)benzotriazole, and 1 g of a nitrogen-phosphorus-boron flame retardant, and then transfer them to a mixer for mixing for 5 min at a mixing temperature of 110 °C; then pour the mixed sample into a mold, react and cure at 100 °C for 1.5 h, and place it in an oven at 100 °C for heat preservation for 24 h to obtain a flame-retardant and anti-melting-drop polyurethane elastomer sample; among them, the mass percentage content of the boron nitride nanocomposite is 0.5%, and the MFD content of the nitrogen-phosphorus-boron flame retardant is 1%.

[0052] Example 2

[0053] This example presents a boron nitride nanocomposite, which is prepared by the following steps:

[0054] 1) Mix 4 g of hexagonal boron nitride powder with 20 g of sucrose crystals, perform solid-phase ball milling at a rotation speed of 500 rpm for 12 h, ultrasonically stir the obtained ball-milled boron nitride in deionized water, and then centrifuge and filter. Repeat the above stirring, centrifuging and filtering steps three times to obtain boron nitride nanosheets, and dry at room temperature for 24 h;

[0055] 2) Add 2 g of boron nitride nanosheets to 200 mL of deionized water, and stir ultrasonically to obtain a boron nitride suspension. Then add 25 mL of Tris buffer solution and continue ultrasonic treatment for 30 min. Then add an appropriate amount of 6 mol / L NaOH solution to adjust the pH of the solution to 8.5. Then add 3 g of dopamine hydrochloride to the above solution system. Stir and react at room temperature for 24 h. After the reaction is completed, centrifuge at 5000 rpm for 5 min, and wash with deionized water multiple times until the pH of the upper layer solution of centrifugation becomes neutral. Finally, dry the boron nitride nanosheets coated with dopamine polymer in a vacuum oven at 80 °C for 24 h.

[0056] 3) Add 2 g of boron nitride nanosheets coated with dopamine polymer to 200 mL of DMF as a solvent, stir ultrasonically to form a suspension, add 100 g of 4,4'-diphenylmethane diisocyanate to the above suspension and continue stirring, heat up to 55 °C, add 14 - 15 drops of catalyst dibutyltin dilaurate, continue the reaction for 12 h, filter, and remove the solvent by vacuum to obtain an isocyanated boron nitride nanocomposite.

[0057] This example also proposes a modified polyurethane elastomer, which is prepared by the following steps:

[0058] 1) Add 1.5 g of the boron nitride nanocomposite prepared in this example to 80 g of polytetrahydrofuran ether glycol, stir and heat up to 80 °C for reaction for 0.5 h, then cool down to 50 °C and add it to 15 g of toluene - 2,4 - diisocyanate, continue stirring and heat up to 90 °C for reaction for 1.5 h, and remove bubbles by vacuum to obtain a modified polyurethane prepolymer;

[0059] 2) Mix the above - obtained modified polyurethane prepolymer, 10 g of dimethylthiotoluenediamine, 0.8 g of ultraviolet light stabilizer 2-(2 - hydroxy - 3,5 - di - tert - amylphenyl) benzotriazole, and 2 g of nitrogen - phosphorus - boron flame retardant, then transfer to a mixer and mix for 5 min at a mixing temperature of 110 °C; then pour the mixed sample into a mold, react and cure at 100 °C for 1.5 h, and after forming, put it into an oven and keep it at 100 °C for 24 h to obtain a flame - retardant and anti - melt - dripping polyurethane elastomer sample. Among them, the mass percentage content of the boron nitride nanocomposite is 1.3%, and the MFD content of the nitrogen - phosphorus - boron flame retardant is 1.8%.

[0060] Example 3

[0061] This example proposes a boron nitride nanocomposite, which is prepared by the following steps:

[0062] 1) Mix 3 g of hexagonal boron nitride powder with 15 g of sucrose crystals, perform solid-phase ball milling at a rotation speed of 500 rpm for 12 h, ultrasonically stir the obtained ball-milled boron nitride in deionized water, then centrifuge and filter. Repeat the above stirring, centrifuging, and filtering steps three times to obtain boron nitride nanosheets, and dry them at room temperature for 24 h;

[0063] 2) Add 2 g of boron nitride nanosheets to 200 mL of deionized water and ultrasonically stir to obtain a boron nitride suspension. Then add 25 mL of Tris buffer solution and continue ultrasonic treatment for 30 min; Add an appropriate amount of 6 mol / L NaOH solution to adjust the solution pH to 8.5; Subsequently, add 3 g of dopamine hydrochloride to the above solution system and stir at room temperature for 24 h; After the reaction, centrifuge at 5000 rpm for 5 min and wash with deionized water multiple times until the pH of the centrifuged upper solution becomes neutral; Finally, dry the boron nitride nanosheets coated with dopamine polymer in a vacuum oven at 80 °C for 24 h;

[0064] 3) Add 2 g of boron nitride nanosheets coated with dopamine polymer to 200 mL of DMF solvent and ultrasonically stir to form a suspension. Add 100 g of 4,4'-diphenylmethane diisocyanate to the above suspension and continue stirring. Heat up to 55 °C, add 14 - 15 drops of the catalyst dibutyltin dilaurate, and continue the reaction for 12 h. Filter and remove the solvent by vacuum to obtain an isocyanated boron nitride nanocomposite.

[0065] This example also proposes a modified polyurethane elastomer, which is prepared by the following steps:

[0066] 1) Add 2 g of the boron nitride nanocomposite prepared in this example to 70 g of polytetrahydrofuran ether glycol, stir and heat up to 80 °C for reaction for 0.5 h, then cool down to 50 °C and add it to 16 g of toluene-2,4-diisocyanate, continue stirring and heat up to 90 °C for reaction for 2 h, and remove bubbles by vacuum to obtain a modified polyurethane prepolymer;

[0067] 2) Mix the above-obtained modified polyurethane prepolymer, 10 g of dimethylthiotoluenediamine, 0.6 g of the ultraviolet light stabilizer 2-(2-hydroxy-3,5-di-tert-amylphenyl)benzotriazole, and 3 g of a novel nitrogen-phosphorus-boron flame retardant, and then transfer them to a mixer for mixing for 5 min, with a mixing temperature of 110 °C; Then pour the mixed sample into a mold and react and cure at 100 °C for 1.5 h. After molding, place it in an oven and keep it at 100 °C for 24 h to obtain a flame-retardant and anti-melting-dripping polyurethane elastomer sample. Among them, the mass percentage content of the boron nitride nanocomposite is 2%, and the MFD content of the nitrogen-phosphorus-boron flame retardant is 3%.

[0068] Comparative example

[0069] The comparative examples used in the experiments were obtained by making changes based on the composition of Example 1. The difference from Example 1 is that the same mass of conventional modified boron nitride and conventional flame retardant APP (ammonium polyphosphate) were used to replace the boron nitride nanocomposite and the nitrogen-phosphorus-boron flame retardant, and other reaction steps and reaction conditions were the same as those in Example 1. Example 1 and Comparative Examples 1-1, 1-2, 1-3, 1-4, 1-5 have the compositions as shown in Table 1 below (mass percentage).

[0070] Table 1 Composition Table of Polyurethane Elastomers in Example 1 and Each Comparative Example

[0071]

[0072] The flame retardancy performance test and mechanical property test were carried out on the examples and comparative examples, and the results are shown in Table 2 below.

[0073] Flame retardancy performance test: Vertical burning (UL94); Limiting oxygen index LOI (IOS4589-2).

[0074] Mechanical property test: Tensile property test (using an electronic universal tensile testing machine, tensile rate 250 mm / min).

[0075] Table 2 Test Performance Table of Polyurethane Elastomers in Examples 1-3 and Each Comparative Example

[0076]

[0077]

[0078] By comparing the data in Table 2, it can be clearly found that the introduction of the boron nitride nanocomposite significantly improves the combustion dripping problem of the polyurethane elastomer, and the flame retardant effect of the flame retardant prepared by the present invention is better than that of the conventional flame retardant ammonium polyphosphate. At the same time, in terms of mechanical properties, the polyurethane elastomer with the addition of the boron nitride nanocomposite is also better than the system with the addition of ammonium polyphosphate or unmodified boron nitride. The reason may be that the modified boron nitride nanoparticles are evenly dispersed between the polyurethane matrixes and have chemical bond binding, which can well exert the nano-enhancement effect and improve the strength of the polyurethane.

[0079] The modified polyurethane elastomer prepared by the present invention not only has excellent flame retardancy performance, but also has good mechanical properties and has good application prospects.

[0080] The specific embodiments of the present invention described above do not constitute a limitation to the protection scope of the present invention. Any other corresponding changes and deformations made according to the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A preparation method of a nitrogen-phosphorus-boron flame retardant, characterized in that It includes the following steps: Dissolve monoethanolamine borate and furfural in absolute ethanol, introduce nitrogen, and stir and react at 45 - 55 °C to obtain an intermediate product; Mix the phosphaphenanthrene DOPO solution with the intermediate product and stir and react at 70 - 80 °C to obtain the nitrogen - phosphorus - boron flame retardant; The structural formula of the intermediate product is as follows: The structural formula of the nitrogen - phosphorus - boron flame retardant is as follows:

2. A nitrogen-phosphorus-boron flame retardant, characterized in that, Prepared by the preparation method described in Claim 1, the structural formula of the nitrogen - phosphorus - boron flame retardant is as follows:

3. A flame-retardant and melt-drip resistant polyurethane elastomer, characterized in that, Prepared by the following steps: S1. Mix the isocyanated boron nitride nanocomposite and polyether diol at 80 - 85 °C, then add toluene - 2,4 - diisocyanate and mix at 45 - 50 °C, and then stir and react at 85 - 90 °C to obtain a modified polyurethane prepolymer; S2. Stir and mix the modified polyurethane prepolymer prepared in step S1, dimethylthiotoluenediamine, ultraviolet light stabilizer, and the nitrogen - phosphorus - boron flame retardant described in Claim 2 at 110 - 120 °C, and then cure to obtain the modified polyurethane elastomer; The preparation method of the isocyanated boron nitride nanocomposite includes the following steps: Mix the polydopamine - coated boron nitride nanosheets with a DMF solvent to form a suspension; then add 4,4'-diphenylmethane diisocyanate to the suspension and continue stirring, and then raise the temperature to 50 - 60 °C and add a catalyst to continue the reaction to obtain the isocyanated boron nitride nanocomposite; The polyether diol is one or both of polyoxypropylene ether diol and tetrahydrofuran homopolyether diol; the ultraviolet light stabilizer is 2-(2 - hydroxy - 3,5 - di - tert - amylphenyl)benzotriazole.

4. The flame-retardant and anti-melting-dripping polyurethane elastomer according to claim 3, wherein, In step S2, the curing includes: curing at 100 - 105 °C, and after molding, keeping warm at 95 - 100 °C to obtain the modified polyurethane elastomer.

5. The flame-retardant and melt-drip resistant polyurethane elastomer according to claim 3, wherein In step S1, the time of the stirring reaction is 1.5 - 2 h.

6. The flame-retardant and melt-drip resistant polyurethane elastomer according to claim 5, characterized in that, In step S2, the time of the stirring and mixing is 5 - 10 min.

7. The flame-retardant and melt-drip resistant polyurethane elastomer according to claim 3, characterized in that, The catalyst is dibutyltin dilaurate; the time of the continued reaction is 10 - 12 h; add the 4,4'-diphenylmethane diisocyanate according to the mass ratio of (1 - 2):(50 - 60) of the polydopamine - coated boron nitride nanosheets to the 4,4'-diphenylmethane diisocyanate; the polydopamine - coated boron nitride nanosheets are prepared by the following steps: Stir the boron nitride nanosheets with water to obtain a boron nitride suspension, then add Tris buffer solution and stir, continue to adjust the pH to 8 - 9, and then add dopamine hydrochloride and continue stirring to obtain the polydopamine - coated boron nitride nanosheets.

Images