A method for preparing a transparent polyurethane material with flame retardancy, high strength and recyclability

Abstract

This invention discloses a method for preparing a transparent polyurethane material with flame retardancy, high strength, and recyclability. The transparent polyurethane material is prepared by compounding isocyanate as the hard segment, polyether polyol as the soft segment, with 1,3-bis(2-hydroxyethoxy)benzene and a substituted flame retardant. The preparation method of this invention is simple and easy to control. The tensile strength of the prepared transparent polyurethane material can reach up to 41 MPa, meeting commercial application requirements. Its limiting oxygen index can reach 29, and its UL-94 rating reaches V-0, exhibiting excellent flame retardant properties. Furthermore, this polyurethane material is recyclable and can be reused simply by hot pressing, greatly reducing its application cost. It can be widely used in industries such as cables, pipes, and films.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite materials and relates to a method for preparing a transparent polyurethane material with flame retardancy, high strength and recyclability. Background Technology

[0002] Polyurethane is a polymer material formed by the condensation reaction of polyols and polyisocyanates. It comes in various types, with thermoplastic polyurethane elastomers being the most widely used. Thermoplastic polyurethane elastomers are block copolymers composed of soft and hard segments, combining excellent properties such as high elasticity, low-temperature resistance, corrosion resistance, and wear resistance. These materials are widely used in electronic equipment, transportation, and architectural decoration. However, due to its inherent structure, pure polyurethane contains a large amount of carbon and hydrogen in its soft segments (polyol portion). When heated, it easily breaks down and decomposes, reacting violently with oxygen in the air to burn and release a large amount of heat. Furthermore, it lacks both condensed-phase and gas-phase flame-retardant capabilities, meaning that once ignited, combustion is unstoppable. This deficiency often limits its practical applications and poses potential hazards to life and property, making the improvement of its safety particularly urgent. In terms of flame-retardant modification, halogenated flame retardants were once widely used due to their high efficiency, but because they release large amounts of corrosive and toxic gases during combustion, they are gradually becoming unsuitable for today's green and environmentally friendly development requirements and are thus being phased out. Therefore, improving the flame retardancy of polyurethane materials has become an important research direction.

[0003] To meet increasingly stringent safety and environmental requirements, the flame-retardant upgrade of polyurethane materials is crucial. Among numerous halogen-free flame-retardant solutions, nitrogen-phosphorus flame-retardant systems, which combine high-efficiency smoke suppression performance with low environmental impact, are becoming an important direction for polyurethane flame-retardant modification, providing reliable support for its safe application in various scenarios. Furthermore, in many cutting-edge applications, polyurethane materials need to withstand extremely harsh mechanical environments, thus placing extremely high demands on their comprehensive mechanical properties. They not only need excellent elasticity and flexibility to cope with repeated deformation and impact, but also outstanding tensile strength, tear strength, and abrasion resistance to ensure structural integrity and resistance to damage under long-term dynamic loads. This stringent balance of high strength, high toughness, and durability drives continuous innovation in polyurethane, from molecular structure design to composite reinforcement technology.

[0004] Based on this, the present invention aims to provide a flame-retardant, high-strength, recyclable transparent polyurethane material. The prepared polyurethane material has excellent flame-retardant properties and can be applied in complex mechanical environments. It is recyclable, which reduces the cost of use, and can be applied to a variety of industries. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention aims to provide a method for preparing a transparent polyurethane material with flame retardancy, high strength, and recyclability. This transparent polyurethane material is prepared by compounding isocyanate as the hard segment, polyether polyol as the soft segment, with 1,3-bis(2-hydroxyethoxy)benzene and a substituted flame retardant. The preparation method of this invention is simple and easy to control. The tensile strength of the prepared transparent polyurethane material can reach up to 41 MPa, meeting commercial application requirements. Its limiting oxygen index can reach 29, and its UL-94 rating reaches V-0, exhibiting excellent flame retardant properties. Furthermore, this polyurethane material is recyclable, requiring only hot pressing for repeated use, greatly reducing its application cost. It can be widely used in industries such as cables, pipes, and films.

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

[0007] A method for preparing a transparent polyurethane material with flame retardancy, high strength, and recyclability, comprising the following steps in sequence:

[0008] S1. Preparation of alternative flame retardants

[0009] 50 mL of tetrahydrofuran solution was added to a single-necked flask under ice bath conditions at 0 °C. After the temperature stabilized, tris(3-aminophenyl)phosphine oxide and triethylamine were added and stirred until completely dissolved. Diphenylphosphine chloride was slowly added dropwise to the mixture and the reaction was stirred for 6-12 h. The reaction system was quenched with water, and 100 mL of ethyl acetate and 50 mL of water were added for extraction. The obtained organic phase was dried with 10 g of anhydrous sodium sulfate, filtered and evaporated under reduced pressure, and then purified by column chromatography to obtain the substituted flame retardant (TTPO).

[0010] S2. Preparation of transparent polyurethane materials with flame retardancy, high strength, and recyclability.

[0011] Isocyanate and polyether polyol were added to a three-necked flask at 80°C and stirred at 240-300 r / min for 1.5-2 h to obtain a polyurethane prepolymer. Then, the system temperature was lowered to 60-65°C, and the substituted flame retardant obtained in step S1, 1,3-bis(2-hydroxyethoxy)benzene and 1,4-butanediol were dispersed in N,N-dimethylformamide. After stirring evenly, the mixture was added to the prepolymer and stirred for 30-60 s. The resulting reactant was then poured into a polytetrafluoroethylene mold and vacuum cured in an oven at 80°C for 36 h to obtain a transparent polyurethane material with flame retardancy, high strength and recyclability.

[0012] As a limitation of the present invention, in step S1, the molar ratio between tris(3-aminophenyl)phosphine oxide, triethylamine, and diphenylphosphine chloride is 1:3:3.

[0013] As another limitation of the present invention, in step S1, the dropping rate of the diphenylphosphine chloride is 0.2-0.4 mL / min.

[0014] In this invention, the dropping rate of diphenylphosphine chloride affects the reaction yield. When the dropping rate of diphenylphosphine chloride is 0.2-0.4 mL / min, the overall reaction process is not easily affected, and the yield is easy to reach the theoretical value. However, when the dropping rate is greater than 0.2-0.4 mL / min, the reaction rate will be too fast, and the reaction is prone to generating by-products. When the dropping rate is less than 0.2-0.4 mL / min, the reaction time will be too long, the efficiency will be low, and it will not be conducive to actual production.

[0015] As a third limitation of the present invention, in step S2, the isocyanate is diphenylmethane diisocyanate.

[0016] As a fourth limitation of the present invention, in step S2, the polyether polyol is polytetrahydrofuran ether with a weight-average molecular weight of 1000-3000.

[0017] As a fifth limitation of the present invention, in step S2, the molar ratio of the isocyanate to the polyether polyol is 2:1.

[0018] As a sixth limitation of the present invention, in step S2, the molar ratio between the substituted flame retardant and 1,3-bis(2-hydroxyethoxy)benzene, 1,4-butanediol and N,N-dimethylformamide is (1-3):2:8:26.

[0019] In this invention, the molar ratio between the substituted flame retardant and 1,3-bis(2-hydroxyethoxy)benzene, 1,4-butanediol, and N,N-dimethylformamide affects the mechanical properties of polyurethane. When the molar ratio is within this range, the polyurethane structural network is arranged in an orderly manner, and the polyurethane material can achieve maximum stress and strain. If the molar ratio is greater than this range, there are too many rigid extended chain structures in the polyurethane, which are prone to agglomeration and crystallization, resulting in increased stress and drastically reduced strain. If the molar ratio is less than this range, there are too many plastic structures in the polyurethane, and the molecular chain entanglement increases, resulting in increased strain and reduced stress.

[0020] As a seventh limitation of the present invention, in step S2, the molar ratio of the isocyanate to the substituted flame retardant is 20:(1-3).

[0021] In this invention, the molar ratio of isocyanate to substituted flame retardant affects the flame retardant properties of polyurethane. When the molar ratio is within this range, the flame retardant effect of polyurethane is the best, the limiting oxygen index reaches the highest level, and the dripping phenomenon basically disappears. If the molar ratio is greater than this range, there are too many flame retardant molecules in the polyurethane network, and the polyurethane network is easily destroyed, which leads to the easy occurrence of dripping phenomenon when polyurethane burns. If the molar ratio is less than this range, the molar amount of flame retardant in polyurethane is insufficient, which leads to the inability to obtain the best flame retardant effect.

[0022] As a final limitation of the present invention, the structural formula of the substituted flame retardant prepared in step S1 is:

[0023] .

[0024] The above-mentioned technical solution of this invention, as a whole, involves interconnected and mutually influential steps that collectively determine the morphological characteristics and performance of the product. The polyurethane material prepared by this invention achieves high-efficiency flame retardancy using only a substituted flame retardant. It exhibits two main flame retardant mechanisms: specifically, the flame retardant possesses a nitrogen-phosphorus synergistic flame retardant mechanism. From the perspective of the condensed phase, during combustion, the flame retardant decomposes before the polyurethane to form phosphates, metaphosphates, and pyrophosphates. These substances, after formation, synergistically interact with the carbon layer produced by the polyurethane decomposition, repairing the broken carbon layer to form a uniform and dense structure. This isolates heat transfer and blocks contact between oxygen and polyurethane, thereby preventing further combustion of the polyurethane. From the perspective of the gas phase, the phosphorus-containing free radicals produced by the decomposition of the flame retardant can capture free radicals in the air, and the decomposition of nitrogen elements produces non-combustible gases such as N2 and NH3, which dilute the oxygen concentration around the flame, also achieving a certain flame retardant effect. The synergistic effect of the gas phase and the condensed phase contributes to the flame retardant effect. Furthermore, this flame retardant features a dual-layer phosphorus-based flame retardant effect. The decomposition of the flame retardant occurs in two parts: upon heating, the outer phosphorus-based ligands first break down, releasing phosphorus-containing free radicals and generating phosphorus-containing inorganic salts to repair the carbon layer, thus providing a primary flame retardant effect. When the temperature exceeds a certain level, the central phosphorus-containing portion also decomposes, providing a secondary flame retardant effect. Compared to conventional phosphorus-based flame retardants, which can only release phosphorus-containing free radicals within a narrow temperature range of approximately 50°C, the flame retardant with a dual-layer phosphorus-based flame retardant system developed in this invention can continuously release phosphorus-containing free radicals within a wider temperature range of 180-280°C (nearly 100°C), providing a stronger dilution effect on oxygen and other combustion-supporting gases, as well as combustible gases generated during material combustion. Simultaneously, it continuously generates phosphate substances within this wide temperature range, more effectively repairing the carbon layer formed during combustion, increasing the graphitization degree of the carbon layer, slowing down heat transfer, and isolating oxygen. These two mechanisms of action give polyurethane materials excellent flame retardant properties.

[0025] The polyurethane material prepared by this invention possesses high mechanical strength, high flame retardancy, recyclability, and transparency. This is inseparable from the combined effect of the substituted flame retardant TTPO and 1,3-bis(2-hydroxyethoxy)benzene, which work together to enhance mechanical properties. Structurally, both have benzene ring structures. The benzene ring at the molecular center provides rigidity and planarity, effectively restricting chain segment movement and improving the material's modulus and thermal stability when introduced into the polyurethane chain. For 1,3-bis(2-hydroxyethoxy)benzene, the primary hydroxyl group has extremely high reactivity with the isocyanate group, enabling rapid integration into the polyurethane chain segment. The two terminal hydroxyl groups are connected to the benzene ring through flexible ethoxy groups, effectively rearranging and straightening the long and flexible molecular chain segments of polyurethane. This improves the originally disordered chain structure, effectively enhancing the mechanical properties of polyurethane without sacrificing its flexibility, thus providing mechanical reinforcement. Furthermore, for substituted flame retardants, their molecular size matches the gaps in the polyurethane chain segments. When added to the polyurethane chain segments, the size mismatch does not affect the polyurethane chain network itself. Their symmetrical rigid benzene rings promote the orderly arrangement of the polyurethane network, strengthen the π-π stacking and hydrogen bond density between hard segments, thereby reinforcing the hard phase structure and significantly improving modulus, strength, and hardness. Moreover, the rigid aromatic structure enhances the cohesive energy of the hard segments, promotes microphase separation between hard and soft segments, and forms clearer hard segment microregions as physical crosslinking points, thus simultaneously improving strength and toughness. Both complement each other, reinforcing the polyurethane network without damaging the chain segments, improving network integrity, resisting plastic deformation, and increasing tensile strength and creep resistance. In summary, 1,3-bis(2-hydroxyethoxy)benzene directly reacts and integrates into the polyurethane chain segments, while the substituted flame retardant exists as a reinforcing phase in the network gaps. The combined effect of these two internal and external factors contributes to the excellent mechanical properties of polyurethane. Without the segmental integration effect of 1,3-bis(2-hydroxyethoxy)benzene or the interstitial reinforcement effect of the substituted flame retardant, polyurethane cannot achieve the above mechanical properties.

[0026] The above technical solution has the following advantages or beneficial effects:

[0027] 1. The transparent polyurethane material prepared by this invention has high tensile strength, excellent flame retardant properties, low droplet generation, high transparency, and recyclability, and has a wide range of applications.

[0028] 2. The preparation method of this invention is simple, easy to operate, has a short preparation cycle and low cost, and is suitable for large-scale industrial production.

[0029] 3. The transparent polyurethane material prepared by this invention can achieve a tensile strength of up to 41 MPa, a limiting oxygen index of 29, and a UL-94 rating of V-0, exhibiting excellent flame retardant properties.

[0030] This invention is applicable to the preparation of transparent polyurethane materials with flame retardancy, high strength and recyclability.

[0031] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0032] Figure 1 The structure characterization diagram of the substituted flame retardant prepared in step S1 of Example 2 of the present invention is shown in the figure, wherein: (a) is the proton nuclear magnetic resonance spectrum, and (b) is the Fourier transform infrared spectrum of the substituted flame retardant, tris(3-aminophenyl)phosphine oxide and diphenylphosphine chloride.

[0033] Figure 2 The Fourier transform infrared (FTIR) spectra of the polyurethane materials prepared in Examples 1-4 and Comparative Examples 1-6 of this invention are shown, where (a) is the FTIR spectra of Examples 1-4 and Comparative Example 1, and (b) is the FTIR spectra of Comparative Examples 2-6.

[0034] Figure 3 The flame retardant properties of the polyurethane materials prepared in Examples 1-4 and Comparative Examples 1-6 of this invention are characterized by: (a) Limiting oxygen index test charts of Examples 1-4 and Comparative Examples 1-6; (b) and (c) Vertical burning test charts of Examples 1-4 and Comparative Examples 1-6, respectively; and (d) Evaluation charts of limiting oxygen index and vertical burning test of Examples 1-4 and Comparative Examples 1-6.

[0035] Figure 4 The mechanical properties of the transparent polyurethane materials prepared in Examples 1-4 and Comparative Examples 1-6 of this invention are shown in the diagram.

[0036] Figure 5 The images show the ultraviolet transmittance of the transparent polyurethane materials prepared in Examples 1-4 and Comparative Examples 1-6 of this invention.

[0037] Figure 6 The images show the carbon layer after combustion of the transparent polyurethane material prepared in Example 2 and the pure polyurethane material prepared in Comparative Example 1, respectively. (a1) and (a2) are the carbon layer images of the pure polyurethane prepared in Comparative Example 1 after combustion at 50 μm and 2 μm, respectively. (b1) and (b2) are the carbon layer images of the polyurethane material prepared in Example 2 after combustion at 50 μm and 2 μm, respectively.

[0038] Figure 7 The diagram shows the recyclability of the transparent polyurethane material prepared in Example 2 of this invention, where (a) is a recycling flowchart and (b) is a mechanical property diagram. Detailed Implementation

[0039] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0040] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified. Example 1

[0041] This embodiment prepares a transparent polyurethane material with flame retardancy, high strength, and recyclability. The preparation process and steps are as follows:

[0042] S1. Preparation of alternative flame retardants

[0043] 50 mL of tetrahydrofuran solution was added to a single-necked flask under ice bath conditions at 0 °C. After the temperature stabilized, 2 mol of tris(3-aminophenyl)phosphine oxide and 6 mol of triethylamine were added and stirred until completely dissolved. 6 mol of diphenylphosphine chloride (dropping rate of diphenylphosphine chloride was 0.2 mL / min) was slowly added dropwise to the reaction mixture. The reaction was stirred for 6 h, and the reaction system was quenched with water. 100 mL of ethyl acetate and 50 mL of water were added for extraction. The obtained organic phase was dried with 10 g of anhydrous sodium sulfate, filtered, and evaporated under reduced pressure. The purified phase was then purified by column chromatography to obtain the substituted flame retardant (TTPO).

[0044] S2. Preparation of transparent polyurethane materials with flame retardancy, high strength, and recyclability.

[0045] At 80°C, 20 mmol of diphenylmethane diisocyanate and 10 mmol of polytetrahydrofuran ether (with a weight average molecular weight of 1000) were added to a three-necked flask that had been treated with anhydrous and oxygen-free conditions, and stirred at 240 r / min for 1.5 h to obtain a polyurethane prepolymer. Then, the system temperature was lowered to 60°C, and 1 mmol of the substituted flame retardant prepared in step S1, 2 mmol of 1,3-bis(2-hydroxyethoxy)benzene and 8 mmol of 1,4-butanediol were dispersed together in 2 mL of N,N-dimethylformamide. After stirring evenly, the N,N-dimethylformamide was added to the prepolymer and stirred for 30 s. The resulting reactant was poured into a polytetrafluoroethylene mold and vacuum-cured in an oven at 80°C for 36 h to obtain a transparent polyurethane material with flame retardancy, high strength and recyclability. Example 2

[0046] This embodiment prepares a transparent polyurethane material with flame retardancy, high strength, and recyclability. The preparation process and steps are as follows:

[0047] S1. Preparation of alternative flame retardants

[0048] 50 mL of tetrahydrofuran solution was added to a single-necked flask under ice bath conditions at 0 °C. After the temperature stabilized, 2 mol of tris(3-aminophenyl)phosphine oxide and 6 mol of triethylamine were added and stirred until completely dissolved. 6 mol of diphenylphosphine chloride (dropping rate of diphenylphosphine chloride was 0.3 mL / min) was slowly added dropwise to the reaction mixture. The mixture was stirred for 10 h, and the reaction system was quenched with water. 100 mL of ethyl acetate and 50 mL of water were added for extraction. The obtained organic phase was dried with 10 g of anhydrous sodium sulfate, filtered, and evaporated under reduced pressure. The purified phase was then purified by column chromatography to obtain the substituted flame retardant (TTPO).

[0049] S2. Preparation of transparent polyurethane materials with flame retardancy, high strength, and recyclability.

[0050] At 80°C, 20 mmol of diphenylmethane diisocyanate and 10 mmol of polytetrahydrofuran ether (with a weight average molecular weight of 2000) were added to a three-necked flask that had been treated with anhydrous and oxygen-free conditions, and stirred at 260 r / min for 1.7 h to obtain a polyurethane prepolymer. Then, the system temperature was lowered to 63°C, and 2 mmol of the substituted flame retardant prepared in step S1, 2 mmol of 1,3-bis(2-hydroxyethoxy)benzene and 8 mmol of 1,4-butanediol were dispersed together in 2 mL of N,N-dimethylformamide. After stirring evenly, the mixture was added to the prepolymer and stirred for 50 s. The resulting reactant was poured into a polytetrafluoroethylene mold and vacuum-cured in an oven at 80°C for 36 h to obtain a transparent polyurethane material with flame retardancy, high strength and recyclability. Example 3

[0051] This embodiment prepares a transparent polyurethane material with flame retardancy, high strength, and recyclability. The preparation process and steps are as follows:

[0052] S1. Preparation of alternative flame retardants

[0053] 50 mL of tetrahydrofuran solution was added to a single-necked flask under ice bath conditions at 0 °C. After the temperature stabilized, 2 mol of tris(3-aminophenyl)phosphine oxide and 6 mol of triethylamine were added and stirred until completely dissolved. 6 mol of diphenylphosphine chloride (dropping rate of diphenylphosphine chloride was 0.4 mL / min) was slowly added dropwise to the reaction mixture. The reaction was stirred for 12 h, and the reaction system was quenched with water. 100 mL of ethyl acetate and 50 mL of water were added for extraction. The obtained organic phase was dried with 10 g of anhydrous sodium sulfate, filtered, and evaporated under reduced pressure. The purified phase was then purified by column chromatography to obtain the substituted flame retardant (TTPO).

[0054] S2. Preparation of transparent polyurethane materials with flame retardancy, high strength, and recyclability.

[0055] At 80°C, 20 mmol of diphenylmethane diisocyanate and 10 mmol of polytetrahydrofuran ether (with a weight average molecular weight of 3000) were added to a three-necked flask that had been treated with anhydrous and oxygen-free conditions, and stirred at 300 r / min for 2 h to obtain a polyurethane prepolymer. Then, the system temperature was lowered to 65°C, and 2 mmol of the substituted flame retardant prepared in step S1, 2 mmol of 1,3-bis(2-hydroxyethoxy)benzene and 8 mmol of 1,4-butanediol were dispersed together in 2 mL of N,N-dimethylformamide. After stirring evenly, the mixture was added to the prepolymer and stirred for 60 s. The resulting reactant was poured into a polytetrafluoroethylene mold and vacuum-cured in an oven at 80°C for 36 h to obtain a transparent polyurethane material with flame retardancy, high strength and recyclability. Example 4

[0056] This embodiment prepares a transparent polyurethane material with flame retardancy, high strength, and recyclability. The preparation process and steps are as follows:

[0057] S1. Preparation of alternative flame retardants

[0058] 50 mL of tetrahydrofuran solution was added to a single-necked flask under ice bath conditions at 0 °C. After the temperature stabilized, 2 mol of tris(3-aminophenyl)phosphine oxide and 6 mol of triethylamine were added and stirred until completely dissolved. 6 mol of diphenylphosphine chloride (dropping rate of diphenylphosphine chloride was 0.3 mL / min) was slowly added dropwise to the reaction mixture. The reaction was stirred for 6 h, and the reaction system was quenched with water. 100 mL of ethyl acetate and 50 mL of water were added for extraction. The obtained organic phase was dried with 10 g of anhydrous sodium sulfate, filtered, and evaporated under reduced pressure. The purified phase was then purified by column chromatography to obtain the substituted flame retardant (TTPO).

[0059] S2. Preparation of transparent polyurethane materials with flame retardancy, high strength, and recyclability.

[0060] At 80°C, 20 mmol of diphenylmethane diisocyanate and 10 mmol of polytetrahydrofuran ether (with a weight average molecular weight of 1000) were added to a three-necked flask that had been treated with anhydrous and oxygen-free conditions, and stirred at 240 r / min for 2 h to obtain a polyurethane prepolymer. Then, the system temperature was lowered to 60°C, and 3 mmol of the substituted flame retardant prepared in step S1, 2 mmol of 1,3-bis(2-hydroxyethoxy)benzene and 8 mmol of 1,4-butanediol were dispersed together in 2 mL of N,N-dimethylformamide. After stirring evenly, the mixture was added to the prepolymer and stirred for 40 s. The resulting reactant was poured into a polytetrafluoroethylene mold and vacuum-cured in an oven at 80°C for 36 h to obtain a transparent polyurethane material with flame retardancy, high strength and recyclability. Comparative Example

[0061] To investigate the effects of different parameters and raw materials on the performance of the product of this invention, the following comparative experiments were conducted. Different polyurethane materials were prepared in the following comparative examples:

[0062] Comparative Example 1

[0063] This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 2, except that in step S2, no substituted flame retardant and 1,3-bis(2-hydroxyethoxy)benzene are added, and 8 mmol of 1,4-butanediol is replaced with 10 mmol of 1,4-butanediol.

[0064] Comparative Example 2

[0065] This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 2, except that no substituted flame retardant is added in step S2.

[0066] Comparative Example 3

[0067] This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 2, except that in step S2, 1,3-bis(2-hydroxyethoxy)benzene is not added, and 8 mmol of 1,4-butanediol is replaced with 10 mmol of 1,4-butanediol.

[0068] Comparative Example 4

[0069] This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 2, except that in step S1, the dropping rate of diphenylphosphine chloride is 0.1 mL / min.

[0070] Comparative Example 5

[0071] This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 2, except that in step S1, the stirring speed of the polyurethane prepolymer is 330 r / min.

[0072] Comparative Example 6

[0073] This comparative example prepares a polyurethane material. The preparation process is similar to that of Example 2, except that in step S2, the molar amounts of diphenylmethane diisocyanate, polytetrahydrofuran ether, substituted flame retardant, 1,3-bis(2-hydroxyethoxy)benzene and 1,4-butanediol added are 20 mmol, 10 mmol, 2 mmol, 4 mmol and 6 mmol, respectively.

[0074] Performance testing

[0075] The polyurethane materials prepared in Examples 1-4 and Comparative Examples 1-6 of this invention were subjected to a series of tests, as detailed below:

[0076] like Figure 1 The diagram shows the structural characterization of TTPO prepared in step S1 of Example 2 of this invention. (a) is the 1H NMR spectrum, showing that the chemical shift at 7.81-7.50 ppm belongs to the H on the benzene ring, while the peak at 8.15 ppm belongs to the H of the imine bond formed after the amino group on tris(3-aminophenyl)phosphine oxide is substituted. This indicates that the substituted flame retardant was successfully synthesized. (b) shows the Fourier transform infrared (FTIR) spectra of the substituted flame retardant, tris(3-aminophenyl)phosphine oxide, and diphenylphosphine chloride. The diphenylphosphine chloride... -1 1438 -1 1231 -1 and 616 cm -1 The peaks at 3321 cm⁻¹ are attributed to the stretching vibrations of CH, P-Ph, P=O, and P-Cl, respectively. The peak at 3321 cm⁻¹ is attributed to these vibrations. -1 The absorption peak at 1035 cm⁻¹ belongs to NH₃. However, by comparing the Fourier transform infrared spectra of NH₃ and P-Cl, the absorption peaks of both NH₃ and P-Cl have disappeared, while the peak at 1035 cm⁻¹ remains. -1 A new PN peak was generated at the point, thus proving the successful synthesis of the substituted flame retardant.

[0077] like Figure 2 The figures show the Fourier transform infrared spectra of the polyurethane materials prepared in Examples 1-4 and Comparative Examples 1-6 of this invention. From the perspective of polyurethane structural synthesis, the 2260 cm⁻¹ region in the samples... -1The disappearance of the nearby -NCO absorption peak indicates that the -NCO groups in the isocyanate have completely reacted with the -OH groups in the polyether polyol. Due to the influence of NH, the characteristic CO absorption peak in polyurethane shifted to a lower wavelength of 1728 cm⁻¹. -1 The stretching vibration peaks of saturated CH2 and CH are shown at 2939 cm⁻¹. -1 2925 cm -1 2859 cm -1 Location. A depth of 1221 cm can be observed in Examples 1-4. -1 (P=O) and 1034 cm -1 (PN) and 3344 cm -1 At (NH), with 1221 cm -1 (P=O) and 1034 cm -1 The characteristic peaks at (PN) are the most prominent, and the appearance of these characteristic peaks indicates that the prepared substituted flame retardant is uniformly doped into the polyurethane material.

[0078] like Figure 3 Figure 1 shows the flame retardant properties of the polyurethane materials prepared in Examples 1-4 and Comparative Examples 1-6 of this invention. Figure 3 (a) is a limiting oxygen index (LOI) test graph for the polyurethane materials prepared in Examples 1-4 and Comparative Examples 1-6. It is clearly shown in the graph that the polyurethanes prepared in Comparative Examples 1 and 2 without the addition of phosphorus-based flame retardants cannot self-extinguish or even completely burn, exhibiting low LIO values. In contrast, the polyurethanes prepared in Examples 1-4 can rapidly self-extinguish even under high LIO environments, indicating that the polyurethane materials prepared in this invention possess excellent flame retardant properties. Furthermore, the combustion characteristics and dripping phenomena of the polyurethane materials prepared in this invention are significantly improved. Figure 3 (b) and Figure 3 (c) The digital photograph of the vertical burning test shows that Comparative Examples 1 and 2 burned violently in the vertical burning test, producing a large number of molten droplets. These droplets ignited the absorbent cotton below, and even after manual extinguishing, a second ignition still ignited the absorbent cotton, and the entire sample burned away. After adding the substituted flame retardant, as the addition ratio increased, a significant reduction in molten droplets was observed; only one droplet was produced every 3-4 seconds, and the produced droplets self-extinguished in mid-air and could not ignite the absorbent cotton. The UL-94 flame retardant rating improved from no rating to V-0. Figure 3 As can be seen in (d), the introduction of the substituted flame retardant significantly improves the flame retardancy compared to pure polyurethane. The high-efficiency flame retardant performance of polyurethane materials is mainly due to the dual synergistic flame retardant effect of the prepared substituted flame retardant, thus achieving a better flame retardant effect.

[0079] like Figure 4 The figures show the mechanical property test diagrams of the polyurethane materials prepared in Examples 1-4 and Comparative Examples 1-6 of this invention. The tensile strengths of the polyurethane materials prepared in Examples 1-4 are 38.7 MPa, 41 MPa, 39.1 MPa, and 37.9 MPa, respectively, which are significantly greater than those of the polyurethane materials prepared in Comparative Examples 1-6. Furthermore, the mechanical strain of the polyurethane materials prepared in Examples 1-4 is also greater than that of the polyurethane materials in the comparative examples. Example 2 achieved the best tensile strength and mechanical strain. This is because 1,3-bis(2-hydroxyethoxy)benzene, through its unique structure combining a rigid aromatic core with a flexible ether chain, integrates as a reinforcing unit into the polyurethane network. Its rigid benzene ring skeleton directly increases the tensile modulus and flexural modulus of the material; the flexible segments of the ether bonds can absorb some of the energy brought by impact and tension, maintaining the flexibility of the material, protecting it from excessive damage, and enhancing the elongation at break and impact strength. In addition, the addition of 1,3-bis(2-hydroxyethoxy)benzene also brings hydrogen bonding and promotes microphase separation. TTPO occupies an intersegmental position within the polyurethane network. Due to its small molecular size, its quantitative addition does not affect the structure of the polyurethane network; on the contrary, it can act as a reinforcing agent to enhance the mechanical properties of the polyurethane material. However, when the proportion is mismatched, excessive flame retardant molecules can negatively impact the expansion of the polyurethane network, leading to a decrease in its mechanical properties.

[0080] like Figure 5 The figures show the UV transmittance of the transparent polyurethane materials prepared in Examples 1-4 and Comparative Examples 1-6 of this invention. As can be seen from the figures, the transmittance of the polyurethane materials prepared in Examples 1-4 is consistently above 83%, while the transmittance of the polyurethane material prepared in Example 2 reaches 87%. The transmittance of the polyurethane materials prepared in Comparative Examples 1-6 fluctuates between 68-78%, showing a significant difference compared to the polyurethane materials prepared in the examples. Since excessive amounts of 1,3-bis(2-hydroxyethoxy)benzene in the polyurethane can crystallize upon temperature reduction after preparation, the addition of TTPO allows for interleaved interaction within the polyurethane network. This prevents 1,3-bis(2-hydroxyethoxy)benzene from simultaneously integrating into the polyurethane network in adjacent regions, providing a degree of dilution. The combined use of TTPO and TTPO prevents crystallization, thus maintaining the high transparency of the polyurethane material.

[0081] like Figure 6 The images show scanning electron microscope (SEM) characterizations of the carbon layers after combustion of the polyurethane material prepared in Example 2 and the pure polyurethane material prepared in Comparative Example 1. Figure 6 (a1) and Figure 6As can be seen in (a2), the carbon layer produced after the combustion of pure polyurethane in Comparative Example 1 shows many voids at 50 μm, and is uneven and brittle overall. At 2 μm, it exhibits many tiny particles, indicating poor carbon quality. The carbon layer cannot effectively isolate flammable gases; it also cannot effectively isolate heat, thus having no significance for the flame retardancy of polyurethane. Figure 6 (b1) and Figure 6 (b2) shows that after the addition of the substitute flame retardant, the phosphate, metaphosphate, pyrophosphate and other substances produced by the decomposition of the flame retardant are coated on the surface of the polyurethane matrix, repairing the broken parts of the carbon layer, thereby making the carbon layer uniform and dense, achieving the effect of physically blocking the air and combustible gases and blocking heat transfer, thus achieving the flame retardant effect.

[0082] like Figure 7 The diagram shows the recyclability test results of the polyurethane material prepared in Example 2 of this invention. First, the prepared polyurethane material was sheared to break it into non-uniform polyurethane particles. Then, the particles were hot-pressed and reshaped [e.g.]. Figure 7 [As shown in (a)], the sample was hot-pressed at 120°C and 5 MPa for 1 h, then gradually cooled to 25°C. The cooled sample was held at this temperature for 24 h to achieve structural stability. During this process, the reintegration of the polyurethane was clearly observed. Afterward, the dumbbell-shaped test sample was recut and tensile tests were performed. Figure 7 (b) It can be seen that the original polyurethane sample and the remolded and recycled polyurethane sample are almost identical in mechanical properties, with no major damage, indicating that the polyurethane still maintains good mechanical properties after recycling and has good recyclability.

[0083] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a transparent polyurethane material with flame retardancy, high strength, and recyclability, characterized in that, Follow these steps in sequence: S1. Preparation of alternative flame retardants 50 mL of tetrahydrofuran solution was added to a single-necked flask under ice bath conditions at 0 °C. After the temperature stabilized, tris(3-aminophenyl)phosphine oxide and triethylamine were added and stirred until completely dissolved. Diphenylphosphine chloride was slowly added dropwise to the mixture and the reaction was stirred for 6-12 h. The reaction system was quenched with water, and ethyl acetate and water were added for extraction. The obtained organic phase was dried with anhydrous sodium sulfate, filtered and evaporated under reduced pressure, and then purified by column chromatography to obtain the substituted flame retardant. The molar ratio of tri(3-aminophenyl)phosphine oxide to triethylamine and diphenylphosphine chloride is 1:3:3; The dropping rate of the diphenylphosphine chloride is 0.2-0.4 mL / min; S2. Preparation of transparent polyurethane materials with flame retardancy, high strength, and recyclability. Isocyanate and polyether polyol were added to a three-necked flask at 80°C and stirred at 240-300 r / min for 1.5-2 h to obtain a polyurethane prepolymer. Then, the system temperature was lowered to 60-65°C, and the substituted flame retardant obtained in step S1, 1,3-bis(2-hydroxyethoxy)benzene and 1,4-butanediol were dispersed together in N,N-dimethylformamide. After stirring evenly, the mixture was added to the prepolymer and stirred for 30-60 s. The resulting reaction mixture was then poured into a polytetrafluoroethylene mold and vacuum cured in an oven at 80°C for 36 h to obtain a transparent polyurethane material with flame retardancy, high strength and recyclability. The isocyanate is diphenylmethane diisocyanate; The molar ratio of the substituted flame retardant to 1,3-bis(2-hydroxyethoxy)benzene, 1,4-butanediol, and N,N-dimethylformamide is (1-3):2:8:26; The molar ratio of the isocyanate to the substituted flame retardant is 20:(1-3).

2. The method for preparing a transparent polyurethane material with flame retardancy, high strength, and recyclability according to claim 1, characterized in that, In step S2, the polyether polyol is polytetrahydrofuran ether with a weight-average molecular weight of 1000-3000.

3. The method for preparing a transparent polyurethane material with flame retardancy, high strength, and recyclability according to claim 1, characterized in that, In step S2, the molar ratio of isocyanate to polyether polyol is 2:

1.

4. A method for preparing a transparent polyurethane material with flame retardancy, high strength, and recyclability according to any one of claims 1-3, characterized in that, In step S1, the structural formula of the substituted flame retardant prepared is: 。

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