Polyurethane elastomer membrane material suitable for low-altitude aircraft rotor blade and preparation method of polyurethane elastomer membrane material

Abstract

The invention discloses a polyurethane elastomer membrane material suitable for a low-altitude aircraft rotor blade and a preparation method of the polyurethane elastomer membrane material, and relates to the technical field of high polymer materials. When the polyurethane elastomer membrane material suitable for the rotor blade of the low-altitude aircraft is prepared, polyester diol, an ultraviolet absorption monomer, dihydroxyl-terminated polydimethylsiloxane and isophorone diisocyanate are polymerized, and chain extension is performed by using N-(4-nitrophenyl) diethanol amine to prepare polyurethane; the preparation method comprises the following steps: carrying out reaction on polyurethane and hydrazine hydrate to prepare modified polyurethane; and uniformly mixing the modified polyurethane, a boric acid ester cross-linking agent, the modified silicon dioxide and N, N-dimethylformamide, and curing to obtain the polyurethane elastomer membrane material suitable for the rotor blade of the low-altitude aircraft. The polyurethane elastomer membrane material suitable for the rotor blade of the low-altitude aircraft, prepared by the invention, has excellent wear resistance, rain erosion resistance, aging resistance and self-repairing performance.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a polyurethane elastomer film material suitable for rotor blades of low-altitude aircraft and its preparation method. Background Technology

[0002] Compared to fixed-wing aircraft, helicopters typically fly at altitudes below 6000m, sometimes even at extremely low altitudes of 15-30m, making them low-altitude, low-speed aircraft. The rotor is a crucial component of a helicopter, providing the primary lift and control force. Early helicopter rotors were mainly made of metals such as aluminum alloys, stainless steel, and titanium alloys. With continuous advancements in materials technology, most helicopter rotors now utilize composite materials such as fiberglass and carbon fiber. Due to their maneuverability and ability to take off and land vertically at any time, helicopters frequently operate in harsh environments such as humid / hot, dry / cold, sand / rain, and marine conditions. During high-speed rotor rotation, sand and rainwater impact the composite material surface with significant force, causing wear and tear. In severe cases, this can lead to fiber breakage or delamination within the composite material, resulting in premature material failure.

[0003] Applying an elastic protective film to helicopter rotors can provide some protection against sand and rain erosion. Polyurethane elastomers are currently the most researched elastic film material and have great application potential in helicopter rotor protection. However, they still suffer from limited protective effect, easy aging, and high replacement frequency. This invention improves upon existing technology by endowing polyurethane elastomer films with excellent wear resistance, rain erosion resistance, aging resistance, and self-healing capabilities, comprehensively enhancing the durability of the protective film and reducing its replacement frequency. Summary of the Invention

[0004] The purpose of this invention is to provide a polyurethane elastomer film material suitable for rotor blades of low-altitude aircraft and its preparation method, so as to solve the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A polyurethane elastomer membrane material suitable for low-altitude aircraft rotor blades is prepared by polymerizing alkenyl fluorene monomer and 9-vinylcarbazole onto the surface of silica to obtain modified silica; reacting polyurethane and hydrazine hydrate to obtain modified polyurethane; and mixing and curing the modified polyurethane, borate ester crosslinking agent, modified silica, and N,N-dimethylformamide uniformly. The alkenyl fluorene monomer is prepared by reacting 9,9-dimethyl-9H-fluorene-2-ol with 3-butyryl chloride; The borate ester crosslinking agent is prepared by reacting 4-formylphenylboronic acid and 3,4-dihydroxybutyraldehyde. The polyurethane is prepared by polymerizing polyester diol, ultraviolet-absorbing monomer, dihydroxy-terminated polydimethylsiloxane and isophorone diisocyanate, and then extending the chain with N-(4-nitrophenyl)diethanolamine. The ultraviolet-absorbing monomer is prepared by reacting ethyl cyanoacetate and 4,4'-dihydroxymethylbenzophenone.

[0006] A method for preparing a polyurethane elastomer film suitable for low-altitude aircraft rotor blades, the method comprising the following preparation steps: (1) Weigh silicon dioxide, alkenyl fluorene monomer, 9-vinylcarbazole and benzoyl peroxide in a mass ratio of 1:(2~3):(2~3):(0.10~0.12); add alkenyl fluorene monomer and 9-vinylcarbazole to toluene in a mass ratio of 8~10 times that of alkenyl fluorene monomer and mix evenly to prepare a reaction solution; mix benzoyl peroxide and toluene in a mass ratio of 1:(6~8) to prepare an initiator solution; mix silicon dioxide, 1 / 4 part of the reaction solution and 1 / 4 part of the initiator solution, and stir the reaction at 70~80℃ and 200~300r / min for 20~30min under nitrogen protection. Add the remaining reaction solution and initiator solution dropwise at a uniform rate within 30min. After the addition is complete, continue stirring the reaction for 10~12h. Filter, wash 3 times with anhydrous ethanol, and dry at 50~60℃ for 13~15h under vacuum to obtain modified silicon dioxide. (2) Add 4-formylphenylboronic acid and 3,4-dihydroxybutyraldehyde in a molar ratio of 1:1 to dichloromethane at a mass ratio of 13 to 15 times that of 4-formylphenylboronic acid, add anhydrous magnesium sulfate at a mass ratio of 0.1 to 0.2 times that of 4-formylphenylboronic acid, stir and react at 50 to 60°C and 300 to 400 r / min for 8 to 9 hours, filter, and dry the filtrate at 40 to 50°C under vacuum for 10 to 12 hours to obtain the borate ester crosslinking agent; (3) Polyester diol, UV-absorbing monomer, dihydroxy-terminated polydimethylsiloxane, dibutyltin dilaurate, and m-xylene are mixed evenly in a mass ratio of 1:(0.4~0.5):(0.5~0.6):(0.01~0.02):(8~10). Under stirring conditions of 200~300 r / min, the temperature is increased to 138~140℃ at a rate of 5℃ / min and stirred under reflux for 2~3 h. The temperature is then reduced to 78~82℃, and isophorone diisocyanate is added at a mass of 2.3~2.5 times that of polyester diol. The reaction is continued to be stirred for 3~4 h. Finally, N-(4-nitrophenyl) is added at a mass of 0.2~0.3 times that of isophorone diisocyanate. Diethanolamine was stirred for 30-40 minutes, and dried at 80-90°C for 13-15 hours under vacuum to obtain polyurethane. Polyurethane, palladium on carbon, and N,N-dimethylformamide were mixed evenly at a mass ratio of 1:(0.05-0.06):(10-12). The mixture was stirred at 200-300 r / min for 20-30 minutes at 90-94°C. The temperature was then lowered to 60-62°C, and 0.7-0.8 times the mass of hydrazine hydrate was added dropwise over 20 minutes. After the addition was complete, the temperature was raised to 90-94°C, and the mixture was stirred for 8-9 hours. The mixture was dried at 70-80°C for 13-15 hours under vacuum to obtain modified polyurethane. (4) Mix the modified polyurethane, borate crosslinking agent, modified silica, and N,N-dimethylformamide in a mass ratio of 1:(0.07~0.08):(0.04~0.05):(2~2.2) until homogeneous. Stir at 55~65℃ and 100~120r / min for 10~12min. Pour into a mold and dry at 70~80℃ for 13~15h under vacuum. After cooling to room temperature, demold to obtain a polyurethane elastomer film material suitable for low-altitude aircraft rotor blades.

[0007] As an optimization, the preparation method of the alkenyl fluorene monomer in step (1) is as follows: 9,9-dimethyl-9H-fluorene-2-ol and 3-butyryl chloride are added to toluene at a molar ratio of 1:1 in 12 to 14 times the mass of 9,9-dimethyl-9H-fluorene-2-ol, and triethylamine is added at a molar ratio of 0.1 to 0.2 times the mass of 9,9-dimethyl-9H-fluorene-2-ol. The mixture is stirred at 40 to 50°C and 300 to 400 r / min for 10 to 12 h. Toluene is removed by rotary evaporation, and the mixture is washed three times with deionized water. Under vacuum conditions, it is dried at 50 to 60°C for 10 to 12 h to obtain the alkenyl fluorene monomer. The reaction mechanism is as follows: .

[0008] As an optimization, the particle size of the silica in step (1) is 1000 mesh.

[0009] As an optimization, the reaction mechanism of the borate ester crosslinking agent in step (2) is as follows: .

[0010] As an optimization, the CAS number of 3,4-dihydroxybutyraldehyde in step (2) is 34764-22-2.

[0011] As an optimization, the preparation method of the ultraviolet absorbing monomer in step (3) is as follows: ammonium acetate and glacial acetic acid are mixed evenly at a molar ratio of 1:3 to prepare a catalyst solution; ethyl cyanoacetate and 4,4'-dihydroxymethylbenzophenone are added to n-heptane at a molar ratio of 1:1, which is 12 to 14 times the mass of ethyl cyanoacetate. Under stirring conditions of 300 to 400 r / min at 50 to 60°C, the catalyst solution, which is 2 to 2.2 times the mass of ethyl cyanoacetate, is added dropwise at a uniform rate over 30 min. After the addition is complete, the mixture is stirred and refluxed at 98 to 100°C for 9 to 10 h, cooled to room temperature, and an equal volume of deionized water at 0 to 4°C is added. The mixture is allowed to stand for 20 to 24 h, filtered, and dried at 50 to 60°C under vacuum for 12 to 14 h to obtain the ultraviolet absorbing monomer. The reaction mechanism is as follows: .

[0012] As an optimization, the CAS number of the 4,4'-dihydroxymethylbenzophenone is 162896-89-1.

[0013] As an optimization, the polyester diol in step (3) is of type PBA1000.

[0014] As an optimization, the molecular weight of the dihydroxy-terminated polydimethylsiloxane in step (3) is 1000.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are: In preparing a polyurethane elastomer membrane suitable for low-altitude aircraft rotor blades, the present invention first reacts 9,9-dimethyl-9H-fluorene-2-ol and 3-butyryl chloride to obtain an alkenyl fluorene monomer; then polymerizes and coats the alkenyl fluorene monomer and 9-vinylcarbazole onto the surface of silica to obtain modified silica. The fluorene and carbazole molecules contain a large number of conjugated π electron structures, which have light conversion properties, can absorb ultraviolet light, and convert ultraviolet light energy into fluorescence, thereby improving the anti-aging properties of the polyurethane elastomer membrane.

[0016] Secondly, 4-formylphenylboronic acid and 3,4-dihydroxybutyraldehyde are reacted to prepare a borate ester crosslinking agent. The aldehyde group on the borate ester crosslinking agent can react with the amino group introduced on the side chain of the modified polyurethane molecule to form a Schiff base reaction, forming a crosslinked network structure. This inhibits the relative slippage between polyurethane molecular chains, making the material less susceptible to tearing by external shear forces, thus improving the wear resistance and rain erosion resistance of the polyurethane elastomer membrane. The borate ester bond on the borate ester crosslinking agent is a dynamic covalent bond. The borate ester bond will decompose when it comes into contact with water, and can be regenerated after the water is removed. This reversible hydrolysis reaction endows the polyurethane elastomer membrane with self-healing ability.

[0017] Secondly, an ultraviolet-absorbing monomer was prepared by performing a brainwave condensation reaction of ethyl cyanoacetate and 4,4'-dihydroxymethylbenzophenone. Polyester diol, ultraviolet-absorbing monomer, dihydroxy-terminated polydimethylsiloxane and isophorone diisocyanate were polymerized and chain extended with N-(4-nitrophenyl)diethanolamine to obtain polyurethane. Octocrylene structure and siloxane structure were introduced into the main chain of polyurethane molecule, and nitro groups were introduced into the side chain. Octocrylene structure belongs to cinnamic acid compound, which can absorb ultraviolet light and release ultraviolet light energy in the form of heat energy, further improving the anti-aging performance of polyurethane elastomer film. The siloxane structure introduced into the polyurethane main chain improves the hydrophobicity of the material. After raindrops hit the material surface, the wetting effect is worse, thereby reducing the contact area and number of water molecules with the material, thus improving the rain erosion resistance.

[0018] Finally, the nitro groups introduced on the side chains of polyurethane molecules are reduced to amino groups by hydrazine hydrate to obtain modified polyurethane. The amino groups introduced on the side chains of the modified polyurethane molecules undergo a Schiff base reaction with the borate ester crosslinking agent to form a crosslinked network structure, which makes the material less susceptible to tearing by external shear forces and improves the wear resistance and rain erosion resistance of the polyurethane elastomer film. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1: A method for preparing a polyurethane elastomer film suitable for low-altitude aircraft rotor blades, the method comprising the following preparation steps: (1) 9,9-dimethyl-9H-fluorene-2-ol and 3-butyryl chloride were added to toluene at a molar ratio of 1:1, which was 12 times the mass of 9,9-dimethyl-9H-fluorene-2-ol. Triethylamine was added at a molar ratio of 0.1 times the mass of 9,9-dimethyl-9H-fluorene-2-ol. The mixture was stirred at 300 r / min for 12 h at 40 °C. Toluene was removed by rotary evaporation. The mixture was washed three times with deionized water and dried at 50 °C for 12 h under vacuum to obtain alkenyl fluorene monomer. Silica, alkenyl fluorene monomer, 9-vinylcarbazole, and benzoyl peroxide were weighed in a mass ratio of 1:2:2:0.10. The alkenyl fluorene monomer was then... Fluorene monomer and 9-vinylcarbazole were added to toluene in an amount equal to 8 times the mass of alkenylfluorene monomer and mixed evenly to prepare a reaction solution. Benzoyl peroxide and toluene were mixed evenly in a mass ratio of 1:6 to prepare an initiator solution. Silica, 1 / 4 part of the reaction solution, and 1 / 4 part of the initiator solution were mixed and stirred at 70°C and 200 r / min for 30 min under nitrogen protection. The remaining reaction solution and initiator solution were added dropwise at a uniform rate over 30 min. After the addition was complete, the reaction was stirred for 12 h. The mixture was filtered, washed three times with anhydrous ethanol, and dried at 50°C for 15 h under vacuum to obtain modified silica. (2) 4-Formylphenylboronic acid and 3,4-dihydroxybutyraldehyde were added to dichloromethane at a molar ratio of 1:1, which was 13 times the mass of 4-formylphenylboronic acid. Anhydrous magnesium sulfate was added at a mass of 0.1 times the mass of 4-formylphenylboronic acid. The mixture was stirred at 50°C and 300 r / min for 9 h. After filtration, the filtrate was dried at 40°C under vacuum for 12 h to obtain the borate ester crosslinking agent. (3) Mix ammonium acetate and glacial acetic acid at a molar ratio of 1:3 to prepare a catalyst solution; add ethyl cyanoacetate and 4,4'-dihydroxymethylbenzophenone at a molar ratio of 1:1 to 12 times the mass of ethyl cyanoacetate in n-heptane, and under stirring conditions of 300 r / min at 50℃, add 2 times the mass of ethyl cyanoacetate catalyst solution dropwise over 30 min. After the addition is complete, stir and reflux at 98℃ for 10 h, cool to room temperature, add an equal volume of 0℃ deionized water to n-heptane, let stand for 20 h, filter, and dry at 50℃ for 14 h under vacuum to obtain the ultraviolet absorbing monomer; mix polyester diol, ultraviolet absorbing monomer, dihydroxy-terminated polydimethylsiloxane, dibutyltin dilaurate, and m-xylene at a mass ratio of 1:0.4:0.5:0.01:8, and stir at 200 r / min. Under stirring conditions, the temperature was increased to 138℃ at a rate of 5℃ / min and stirred under reflux for 3 hours. The temperature was then decreased to 78℃, and isophorone diisocyanate (2.3 times the mass of polyester diol) was added. The reaction was stirred for another 4 hours. N-(4-nitrophenyl)diethanolamine (0.2 times the mass of isophorone diisocyanate) was added, and the reaction was stirred for another 40 minutes. The mixture was then dried at 80℃ for 15 hours under vacuum to obtain polyurethane. Polyurethane, palladium on carbon, and N,N-dimethylformamide were mixed uniformly at a mass ratio of 1:0.05:10. The mixture was stirred at 200 r / min for 30 minutes at 90℃. The temperature was then decreased to 60℃, and hydrazine hydrate (0.7 times the mass of polyurethane) was added dropwise over 20 minutes. After the addition was complete, the temperature was increased to 90℃, and the reaction was stirred for another 9 hours. The mixture was then dried at 70℃ for 15 hours under vacuum to obtain modified polyurethane. (4) The modified polyurethane, borate crosslinking agent, modified silica and N,N-dimethylformamide are mixed evenly in a mass ratio of 1:0.07:0.04:2. The mixture is stirred at 100 r / min for 12 min at 55 °C. The mixture is poured into a mold and dried at 70 °C for 15 h under vacuum. After cooling to room temperature, the mixture is demolded to obtain a polyurethane elastomer film material suitable for rotor blades of low-altitude aircraft.

[0021] Example 2: A method for preparing a polyurethane elastomer film suitable for low-altitude aircraft rotor blades, the method comprising the following preparation steps: (1) 9,9-dimethyl-9H-fluorene-2-ol and 3-butyryl chloride were added to toluene at a molar ratio of 1:1, which was 13 times the mass of 9,9-dimethyl-9H-fluorene-2-ol. Triethylamine was added at a molar ratio of 0.15 times the mass of 9,9-dimethyl-9H-fluorene-2-ol. The mixture was stirred at 350 r / min for 11 h at 45 °C. Toluene was removed by rotary evaporation. The mixture was washed three times with deionized water and dried at 55 °C for 11 h under vacuum to obtain alkenyl fluorene monomer. Silicon dioxide, alkenyl fluorene monomer, 9-vinylcarbazole and benzoyl peroxide were weighed in a mass ratio of 1:2.5:2.5:0.11. Alkenyl fluorene monomer and 9-vinylcarbazole were added to toluene at a mass ratio of 9 times that of alkenyl fluorene monomer and mixed evenly to prepare a reaction solution. Benzoyl peroxide and toluene were mixed evenly at a mass ratio of 1:7 to prepare an initiator solution. Silica, 1 / 4 part of the reaction solution, and 1 / 4 part of the initiator solution were mixed and stirred at 75°C and 250 r / min for 25 min under nitrogen protection. The remaining reaction solution and initiator solution were added dropwise at a uniform rate over 30 min. After the addition was completed, the reaction was stirred for 11 h. The mixture was filtered, washed three times with anhydrous ethanol, and dried at 55°C for 14 h under vacuum to obtain modified silica. (2) 4-Formylphenylboronic acid and 3,4-dihydroxybutyraldehyde were added to dichloromethane at a molar ratio of 1:1, which was 14 times the mass of 4-formylphenylboronic acid. Anhydrous magnesium sulfate was added at a molar ratio of 0.15 times the mass of 4-formylphenylboronic acid. The mixture was stirred at 350 r / min for 8.5 h at 55 °C. After filtration, the filtrate was dried at 45 °C under vacuum for 11 h to obtain the borate ester crosslinking agent. (3) Mix ammonium acetate and glacial acetic acid at a molar ratio of 1:3 to prepare a catalyst solution; add ethyl cyanoacetate and 4,4'-dihydroxymethylbenzophenone at a molar ratio of 1:1 to 13 times the mass of ethyl cyanoacetate in n-heptane, and under stirring conditions of 350 r / min at 55℃, add 2.1 times the mass of ethyl cyanoacetate catalyst solution dropwise at a uniform rate over 30 min. After the addition is complete, stir and reflux at 99℃ for 9.5 h, cool to room temperature, add an equal volume of deionized water at 2℃ to n-heptane, let stand for 22 h, filter, and dry at 55℃ for 13 h under vacuum to obtain the ultraviolet absorbing monomer; mix polyester diol, ultraviolet absorbing monomer, dihydroxy-terminated polydimethylsiloxane, dibutyltin dilaurate, and m-xylene at a mass ratio of 1:0.45:0.55:0.015:9, and stir at 250 r / min. Under stirring conditions, the temperature was increased to 139℃ at a rate of 5℃ / min and stirred under reflux for 2.5h. The temperature was then decreased to 80℃, and isophorone diisocyanate (2.4 times the mass of polyester diol) was added. The reaction was stirred for another 3.5h. N-(4-nitrophenyl)diethanolamine (0.25 times the mass of isophorone diisocyanate) was added and the reaction was stirred for another 35min. The mixture was then dried at 85℃ for 14h under vacuum to obtain polyurethane. Polyurethane, palladium on carbon, and N,N-dimethylformamide were mixed uniformly at a mass ratio of 1:0.055:11. The mixture was stirred at 250r / min for 25min at 92℃. The temperature was then decreased to 61℃, and hydrazine hydrate (0.75 times the mass of polyurethane) was added dropwise over 20min. After the addition was complete, the temperature was increased to 92℃, and the reaction was stirred for another 8.5h. The mixture was then dried at 75℃ for 14h under vacuum to obtain modified polyurethane. (4) The modified polyurethane, borate crosslinking agent, modified silica and N,N-dimethylformamide are mixed evenly in a mass ratio of 1:0.075:0.045:2.1. The mixture is stirred at 110 r / min for 11 min at 60 °C. The mixture is poured into a mold and dried at 75 °C for 14 h under vacuum. After cooling to room temperature, the mixture is demolded to obtain a polyurethane elastomer film material suitable for rotor blades of low-altitude aircraft.

[0022] Example 3: A method for preparing a polyurethane elastomer film suitable for low-altitude aircraft rotor blades, the method comprising the following preparation steps: (1) 9,9-dimethyl-9H-fluorene-2-ol and 3-butyryl chloride were added to toluene at a molar ratio of 1:1 to 14 times the mass of 9,9-dimethyl-9H-fluorene-2-ol, and triethylamine at a molar ratio of 0.2 times the mass of 9,9-dimethyl-9H-fluorene-2-ol was added. The mixture was stirred at 50°C and 400 r / min for 10 h. Toluene was removed by rotary evaporation, and the mixture was washed three times with deionized water. The mixture was dried at 60°C under vacuum for 10 h to obtain alkenyl fluorene monomer. Silica, alkenyl fluorene monomer, 9-vinylcarbazole, and benzoyl peroxide were weighed in a mass ratio of 1:3:3:0.12. The alkenyl fluorene monomer was then... Fluorene monomer and 9-vinylcarbazole were added to toluene at a mass ratio of 10 times that of alkenylfluorene monomer and mixed evenly to prepare a reaction solution. Benzoyl peroxide and toluene were mixed evenly at a mass ratio of 1:8 to prepare an initiator solution. Silica, 1 / 4 part of the reaction solution, and 1 / 4 part of the initiator solution were mixed and stirred at 80°C and 300 r / min for 20 min under nitrogen protection. The remaining reaction solution and initiator solution were added dropwise at a uniform rate over 30 min. After the addition was completed, the reaction was stirred for 10 h. The mixture was filtered, washed three times with anhydrous ethanol, and dried at 60°C for 13 h under vacuum to obtain modified silica. (2) 4-Formylphenylboronic acid and 3,4-dihydroxybutyraldehyde were added to dichloromethane at a molar ratio of 1:1, which was 15 times the mass of 4-formylphenylboronic acid. Anhydrous magnesium sulfate was added at a mass of 0.2 times the mass of 4-formylphenylboronic acid. The mixture was stirred at 60°C and 400 r / min for 8 h. After filtration, the filtrate was dried at 50°C under vacuum for 10 h to obtain the borate ester crosslinking agent. (3) Ammonium acetate and glacial acetic acid were mixed evenly at a molar ratio of 1:3 to prepare a catalyst solution; ethyl cyanoacetate and 4,4'-dihydroxymethylbenzophenone were added to n-heptane at a molar ratio of 1:1, which was 14 times the mass of ethyl cyanoacetate. Under stirring conditions of 60°C and 400 r / min, 2.2 times the mass of ethyl cyanoacetate catalyst solution was added dropwise over 30 min. After the addition was completed, the mixture was stirred and refluxed at 100°C for 9 h, cooled to room temperature, and an equal volume of deionized water at 4°C was added. The mixture was allowed to stand for 24 h, filtered, and dried at 60°C for 12 h under vacuum to obtain the ultraviolet-absorbing monomer; polyester diol, ultraviolet-absorbing monomer, dihydroxy-terminated polydimethylsiloxane, dibutyltin dilaurate, and m-xylene were mixed evenly at a mass ratio of 1:0.5:0.6:0.02:10 and stirred at 300 r / min Under stirring conditions, the temperature was increased to 140℃ at a rate of 5℃ / min and stirred under reflux for 2 hours. The temperature was then decreased to 82℃, and isophorone diisocyanate (2.5 times the mass of polyester diol) was added. The reaction was stirred for another 3 hours. N-(4-nitrophenyl)diethanolamine (0.3 times the mass of isophorone diisocyanate) was added, and the reaction was stirred for another 30 minutes. The mixture was then dried at 90℃ for 13 hours under vacuum to obtain polyurethane. Polyurethane, palladium on carbon, and N,N-dimethylformamide were mixed uniformly at a mass ratio of 1:0.06:12. The mixture was stirred at 300 r / min for 20 minutes at 94℃. The temperature was then decreased to 62℃, and hydrazine hydrate (0.8 times the mass of polyurethane) was added dropwise over 20 minutes. After the addition was complete, the temperature was increased to 94℃, and the reaction was stirred for another 8 hours. The mixture was then dried at 80℃ for 13 hours under vacuum to obtain modified polyurethane. (4) The modified polyurethane, borate crosslinking agent, modified silica and N,N-dimethylformamide are mixed evenly in a mass ratio of 1:0.08:0.05:2.2. The mixture is stirred at 120 r / min for 10 min at 65℃, poured into a mold, dried at 80℃ for 13 h under vacuum, and demolded after cooling to room temperature to obtain a polyurethane elastomer film material suitable for rotor blades of low-altitude aircraft.

[0023] Comparative Example 1: The preparation method of the polyurethane elastomer membrane material suitable for low-altitude aircraft rotor blades in Comparative Example 1 differs from that in Example 2 in that step (1) is omitted, and step (4) is modified as follows: the modified polyurethane, borate ester crosslinking agent, silica, and N,N-dimethylformamide are mixed evenly at a mass ratio of 1:0.075:0.045:2.1, stirred at 110 r / min for 11 min at 60°C, poured into a mold, dried at 75°C for 14 h under vacuum, and demolded after cooling to room temperature to obtain the polyurethane elastomer membrane material suitable for low-altitude aircraft rotor blades. The remaining steps are the same as in Example 2.

[0024] Comparative Example 2: The preparation method of the polyurethane elastomer membrane material suitable for low-altitude aircraft rotor blades in Comparative Example 2 differs from that in Example 2 in that step (2) is omitted, and step (4) is modified as follows: Modified polyurethane, glutaraldehyde, modified silica, and N,N-dimethylformamide are mixed evenly at a mass ratio of 1:0.075:0.045:2.1, stirred at 110 r / min for 11 min at 60°C, poured into a mold, dried at 75°C for 14 h under vacuum, and demolded after cooling to room temperature to obtain the polyurethane elastomer membrane material suitable for low-altitude aircraft rotor blades. The remaining steps are the same as in Example 2.

[0025] Comparative Example 3: The preparation method of the polyurethane elastomer film material suitable for low-altitude aircraft rotor blades in Comparative Example 3 differs from that in Example 2 in that step (2) is omitted, and step (4) is modified as follows: the modified polyurethane, modified silica, and N,N-dimethylformamide are mixed evenly at a mass ratio of 1:0.045:2.1, stirred at 110 r / min for 11 min at 60°C, poured into a mold, dried at 75°C for 14 h under vacuum, and demolded after cooling to room temperature to obtain the polyurethane elastomer film material suitable for low-altitude aircraft rotor blades. The remaining steps are the same as in Example 2.

[0026] Comparative Example 4: The preparation method of the polyurethane elastomer film material suitable for low-altitude aircraft rotor blades in Comparative Example 4 differs from that in Example 2 only in step (3). Step (3) is modified as follows: polyester diol, 1,6-hexanediol, dihydroxy-terminated polydimethylsiloxane, dibutyltin dilaurate, and m-xylene are mixed evenly in a mass ratio of 1:0.45:0.55:0.015:9. Under stirring conditions of 250 r / min, the temperature is increased to 139°C at a rate of 5°C / min and stirred under reflux for 2.5 h. The temperature is then reduced to 80°C, and isophorone diisocyanate with a mass of 2.4 times that of polyester diol is added. The reaction is continued by stirring. After 3.5 hours, N-(4-nitrophenyl)diethanolamine (0.25 times the mass of isophorone diisocyanate) was added, and the reaction was stirred for another 35 minutes. The mixture was then dried at 85°C for 14 hours under vacuum to obtain polyurethane. Polyurethane, palladium on carbon, and N,N-dimethylformamide were mixed uniformly at a mass ratio of 1:0.055:11. The mixture was stirred at 250 rpm for 25 minutes at 92°C, then cooled to 61°C. Hydrazine hydrate (0.75 times the mass of polyurethane) was added dropwise over 20 minutes. After the addition was complete, the temperature was raised to 92°C, and the reaction was stirred for another 8.5 hours. The mixture was then dried at 75°C for 14 hours under vacuum to obtain modified polyurethane. The remaining steps were the same as in Example 2.

[0027] Comparative Example 5: The preparation method of the polyurethane elastomer film material suitable for low-altitude aircraft rotor blades in Comparative Example 5 differs from that in Example 2 only in step (3). Step (3) is modified as follows: Ammonium acetate and glacial acetic acid are mixed evenly at a molar ratio of 1:3 to prepare a catalyst solution; Ethyl cyanoacetate and 4,4'-dihydroxymethylbenzophenone are added to n-heptane at a molar ratio of 1:1, and 2.1 times the mass of ethyl cyanoacetate is added dropwise over 30 minutes under stirring conditions of 350 r / min at 55°C. After the addition is complete, the mixture is stirred and refluxed at 99°C for 9.5 hours, cooled to room temperature, and an equal volume of deionized water at 2°C is added. The mixture is allowed to stand for 22 hours, filtered, and dried at 55°C for 13 hours under vacuum to obtain the ultraviolet-absorbing monomer; Polyester diol, ultraviolet-absorbing monomer, 1,6-hexanediol, dibutyltin dilaurate, and m-xylene are mixed at a mass ratio of 1:0.45: The mixture of 0.55:0.015:9 was thoroughly mixed and heated to 139°C at a rate of 5°C / min under stirring at 250 rpm, and stirred under reflux for 2.5 h. The mixture was then cooled to 80°C, and 2.4 times the mass of isophorone diisocyanate (by weight) was added. The reaction was continued with stirring for 3.5 h. Then, 0.25 times the mass of N-(4-nitrophenyl)diethanolamine (by weight) was added, and the reaction was continued with stirring for 35 min under vacuum. Polyurethane was obtained by drying at 85℃ for 14 hours. Polyurethane, palladium on carbon, and N,N-dimethylformamide were mixed uniformly at a mass ratio of 1:0.055:11, stirred at 92℃ and 250 r / min for 25 minutes, then cooled to 61℃. Hydrazine hydrate (0.75 times the mass of the polyurethane) was added dropwise at a uniform rate over 20 minutes. After the addition was complete, the temperature was raised to 92℃, and the reaction was continued with stirring for 8.5 hours. The mixture was then dried at 75℃ for 14 hours under vacuum to obtain modified polyurethane. The remaining steps were the same as in Example 2.

[0028] Comparative Example 6 The preparation method of the polyurethane elastomer membrane material suitable for low-altitude aircraft rotor blades in Comparative Example 6 differs from that in Example 2 only in step (3). Step (3) is modified as follows: Ammonium acetate and glacial acetic acid are mixed evenly at a molar ratio of 1:3 to prepare a catalyst solution; Ethyl cyanoacetate and 4,4'-dihydroxymethylbenzophenone are added to n-heptane at a molar ratio of 1:1, and 2.1 times the mass of ethyl cyanoacetate is added dropwise over 30 minutes at a stirring rate of 350 r / min at 55°C. After the addition is complete, the mixture is stirred and refluxed at 99°C for 9.5 hours, cooled to room temperature, and an equal volume of deionized water at 2°C is added. The mixture is allowed to stand for 22 hours, filtered, and then subjected to vacuum conditions. The UV-absorbing monomer was obtained by drying at 55℃ for 13 hours. Polyester diol, UV-absorbing monomer, dihydroxy-terminated polydimethylsiloxane, dibutyltin dilaurate, and m-xylene were mixed uniformly in a mass ratio of 1:0.45:0.55:0.015:9. The mixture was stirred at 250 r / min, heated to 139℃ at a rate of 5℃ / min, and refluxed for 2.5 hours. The mixture was then cooled to 80℃, and isophorone diisocyanate (2.4 times its mass) was added. The reaction was continued for 3.5 hours, followed by the addition of N-(4-nitrophenyl)diethanolamine (0.25 times its mass), and the reaction was continued for 35 minutes. The mixture was then dried at 85℃ for 14 hours under vacuum to obtain the modified polyurethane. The remaining steps were the same as in Example 2.

[0029] Test Example 1 Abrasion resistance test Test method: The test standard is based on GB / T 3960-1983. The test is conducted using an M-200 sliding friction and wear testing machine. The sample size is 30 mm × 7 mm × 6 mm. The mass of the sample before and after the wear test is measured, and the wear rate is calculated. The results are shown in Table 1.

[0030] Table 1

[0031] A comparison of the experimental data from Examples 1-3 and Comparative Examples 1-6 in Table 1 reveals that the polyurethane elastomer membrane material prepared by this invention, suitable for rotor blades of low-altitude aircraft, exhibits excellent wear resistance.

[0032] By comparison, the wear rate of Examples 1-3 was less than that of Comparative Example 3, indicating that the borate ester crosslinking agent was prepared by reacting 4-formylphenylboronic acid and 3,4-dihydroxybutyraldehyde. The aldehyde group on the borate ester crosslinking agent can react with the amino group introduced on the side chain of the modified polyurethane molecule to form a Schiff base reaction, thereby forming a crosslinking network structure, inhibiting the relative slippage between polyurethane molecular chains, making the material less susceptible to tearing by external shear forces, and improving the wear resistance of the polyurethane elastomer film.

[0033] By comparison, the wear rate of Examples 1-3 was less than that of Comparative Example 6, indicating that the modified polyurethane was prepared by reducing the nitro group introduced on the side chain of the polyurethane molecule to amino group with hydrazine hydrate. The amino group introduced on the side chain of the modified polyurethane molecule reacted with the borate ester crosslinking agent to form a Schiff base reaction, forming a crosslinked network structure, which made the material less susceptible to tearing by external shear force and improved the wear resistance of the polyurethane elastomer film.

[0034] Test Example 2 Rain erosion resistance test Test method: The test was conducted using a rotating arm test bench in accordance with DNVGL-RP-0171 standard. The raindrop impact angle was 90°, the maximum impact velocity was 160 m / s, the rainfall was 31 ml / h, and the raindrop size was 2.4 mm. The results are shown in Table 2.

[0035] Table 2

[0036] A comparison of the experimental data from Examples 1-3 and Comparative Examples 1-6 in Table 2 reveals that the polyurethane elastomer membrane material prepared by this invention, suitable for low-altitude aircraft rotor blades, exhibits excellent rain erosion resistance.

[0037] By comparison, the rain erosion resistance time of Examples 1-3 is greater than that of Comparative Example 3, indicating that the borate ester crosslinking agent prepared by reacting 4-formylphenylboronic acid and 3,4-dihydroxybutyraldehyde can react with the amino groups introduced on the side chains of the modified polyurethane molecules to form a Schiff base reaction, thereby inhibiting the relative slippage between polyurethane molecular chains, making the material less susceptible to tearing by external shear forces, and improving the rain erosion resistance of the polyurethane elastomer film.

[0038] By comparison, the rain erosion resistance time of Examples 1-3 is greater than that of Comparative Example 5, indicating that the polyurethane was prepared by polymerizing polyester diol, ultraviolet absorbing monomer, dihydroxy-terminated polydimethylsiloxane and isophorone diisocyanate, and then extending the chain with N-(4-nitrophenyl)diethanolamine. The siloxane structure introduced into the polyurethane molecular backbone enhances the hydrophobicity of the material. After raindrops hit the material surface, the wetting effect is worse, thereby reducing the contact area and number of water molecules with the material, and thus improving the rain erosion resistance.

[0039] By comparison, the rain erosion resistance time of Examples 1-3 is greater than that of Comparative Example 6, indicating that the modified polyurethane is prepared by reducing the nitro group introduced on the side chain of the polyurethane molecule to amino group with hydrazine hydrate. The amino group introduced on the side chain of the modified polyurethane molecule undergoes a Schiff base reaction with the borate ester crosslinking agent to form a crosslinked network structure, which makes the material less susceptible to tearing by external shear forces and improves the rain erosion resistance of the polyurethane elastomer film.

[0040] Test Example 3 Testing of self-healing and anti-aging properties According to GB / T1040.1, the examples and comparative examples were cut into standard strips, and their original tensile strength X was tested using a tensile testing machine; Self-healing performance test: A 20mm long tear was cut in the middle of an unstretched standard strip, which was then placed in deionized water and left to stand for 10 minutes. Afterward, it was removed, kept at 70℃ for 12 hours, and then left to stand at room temperature for 12 hours to obtain the repaired strip. Its tensile strength Y was tested using a tensile testing machine. The self-healing rate of the examples and comparative examples before and after repair was calculated as: Self-healing rate = (Y / X) × 100%. The results are shown in Table 3.

[0041] Anti-aging performance test: Unstretched standard specimens were irradiated for 10 days under a 200W UV lamp with a wavelength of 365nm, and their tensile strength Z was tested. The performance degradation rate of the standard specimens before and after UV aging was calculated as (XZ) / X×100%. The results are shown in Table 3.

[0042] Table 3

[0043] A comparison of the experimental data from Examples 1-3 and Comparative Examples 1-6 in Table 2 reveals that the polyurethane elastomer membrane material prepared by this invention, suitable for rotor blades of low-altitude aircraft, has excellent self-healing and anti-aging properties.

[0044] By comparison, the self-healing rates of Examples 1-3 were greater than those of Comparative Examples 2-3, indicating that the borate ester crosslinking agent was prepared by reacting 4-formylphenylboronic acid and 3,4-dihydroxybutyraldehyde. The aldehyde group on the borate ester crosslinking agent can undergo a Schiff base reaction with the amino group introduced on the side chain of the modified polyurethane molecule to form a crosslinked network structure. The borate ester bond on the borate ester crosslinking agent is a dynamic covalent bond. The borate ester bond will decompose when it comes into contact with water. After the water is removed, the borate ester bond can be regenerated. This reversible hydrolysis reaction endows the polyurethane elastomer film with self-healing ability.

[0045] By comparison, the self-healing rates of Examples 1-3 are greater than those of Comparative Example 6 and the Comparative Example. This indicates that the modified polyurethane is prepared by reducing the nitro group introduced on the side chain of the polyurethane molecule to amino group with hydrazine hydrate. The amino group introduced on the side chain of the modified polyurethane molecule undergoes a Schiff base reaction with the borate ester crosslinking agent to form a dynamic crosslinking network structure. When the side chain of the polyurethane does not contain amino group, even if a borate ester crosslinking agent is added, a crosslinking network structure cannot be formed, and the self-healing function cannot be performed.

[0046] By comparison, the performance degradation rate of Examples 1-3 was less than that of Comparative Example 1, indicating that the alkenyl fluorene monomer was prepared by reacting 9,9-dimethyl-9H-fluorene-2-ol and 3-butyryl chloride; and the modified silica was prepared by polymerizing the alkenyl fluorene monomer and 9-vinylcarbazole onto the surface of silica. The fluorene and carbazole molecules contain a large number of conjugated π electron structures, which have light conversion properties. They can absorb ultraviolet light and convert ultraviolet light energy into fluorescence, thereby improving the anti-aging performance of polyurethane elastomer films.

[0047] By comparison, the performance degradation rate of Examples 1-3 was less than that of Comparative Example 4, indicating that the UV-absorbing monomer was prepared by performing a brainwave condensation reaction of ethyl cyanoacetate and 4,4'-dihydroxymethylbenzophenone; polyurethane was prepared by polymerizing polyester diol, UV-absorbing monomer, dihydroxy-terminated polydimethylsiloxane and isophorone diisocyanate, and then chain-extending with N-(4-nitrophenyl)diethanolamine; an octocrylene structure was introduced into the main chain of the polyurethane molecule; the octocrylene structure belongs to the cinnamic acid class of compounds, which can absorb ultraviolet light and release ultraviolet light energy in the form of heat energy, further improving the anti-aging performance of the polyurethane elastomer film.

[0048] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. 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 present invention.

Claims

1. A polyurethane elastomer membrane material suitable for rotor blades of low-altitude aircraft, characterized in that, The polyurethane elastomer membrane material suitable for low-altitude aircraft rotor blades is prepared by polymerizing alkenyl fluorene monomer and 9-vinylcarbazole onto the surface of silica to obtain modified silica; by reacting polyurethane and hydrazine hydrate to obtain modified polyurethane; and by uniformly mixing and curing the modified polyurethane, borate ester crosslinking agent, modified silica, and N,N-dimethylformamide. The alkenyl fluorene monomer is prepared by reacting 9,9-dimethyl-9H-fluorene-2-ol with 3-butyryl chloride; The borate ester crosslinking agent is prepared by reacting 4-formylphenylboronic acid and 3,4-dihydroxybutyraldehyde. The polyurethane is prepared by polymerizing polyester diol, ultraviolet-absorbing monomer, dihydroxy-terminated polydimethylsiloxane and isophorone diisocyanate, and then extending the chain with N-(4-nitrophenyl)diethanolamine. The ultraviolet-absorbing monomer is prepared by reacting ethyl cyanoacetate and 4,4'-dihydroxymethylbenzophenone.

2. A method for preparing a polyurethane elastomer film suitable for low-altitude aircraft rotor blades, characterized in that, The method for preparing the polyurethane elastomer film material suitable for low-altitude aircraft rotor blades includes the following preparation steps: (1) Add alkenylfluorene monomer and 9-vinylcarbazole to toluene and mix evenly to prepare a reaction solution; mix benzoyl peroxide and toluene evenly to prepare an initiator solution; mix silica, 1 / 4 part of the reaction solution and 1 / 4 part of the initiator solution, and react at 70~80℃ for 20~30min under nitrogen protection. Add the remaining reaction solution and initiator solution dropwise at a uniform rate. After the addition is complete, continue stirring and reacting for 10~12h. Filter, wash and dry to obtain modified silica. (2) Add 4-formylphenylboronic acid and 3,4-dihydroxybutyraldehyde to dichloromethane, add anhydrous magnesium sulfate, react at 50~60℃ for 8~9h, filter, and vacuum dry the filtrate for 10~12h to obtain borate ester crosslinking agent; (3) Mix polyester diol, ultraviolet absorbing monomer, dihydroxy-terminated polydimethylsiloxane, dibutyltin dilaurate and m-xylene evenly, heat to 138~140℃ and stir under reflux for 2~3h, cool to 78~82℃, add isophorone diisocyanate, continue stirring and react for 3~4h, add N-(4-nitrophenyl)diethanolamine, continue stirring and react for 30~40min to obtain polyurethane; mix polyurethane, palladium on carbon and N,N-dimethylformamide evenly, stir at 90~94℃ for 20~30min, cool to 60~62℃, add hydrazine hydrate dropwise, after the dropwise addition is complete, heat to 90~94℃ and continue stirring and react for 8~9h to obtain modified polyurethane; (4) Mix the modified polyurethane, borate crosslinking agent, modified silica and N,N-dimethylformamide evenly, stir at 55~65℃ for 10~12min, pour into a mold, vacuum dry for 13~15h, cool to room temperature and demold to obtain a polyurethane elastomer film material suitable for low-altitude aircraft rotor blades.

3. The method for preparing a polyurethane elastomer film material suitable for low-altitude aircraft rotor blades according to claim 2, characterized in that, The preparation method of the alkenyl fluorene monomer in step (1) is as follows: 9,9-dimethyl-9H-fluorene-2-ol and 3-butyryl chloride are added to toluene, triethylamine is added, and the reaction is carried out at 40~50℃ for 10~12h. Toluene is removed by rotary evaporation, washed, and dried to obtain alkenyl fluorene monomer.

4. The method for preparing a polyurethane elastomer film material suitable for low-altitude aircraft rotor blades according to claim 2, characterized in that, The mass ratio of silica, alkenyl fluorene monomer, 9-vinylcarbazole and benzoyl peroxide in step (1) is 1:(2~3):(2~3):(0.10~0.12).

5. The method for preparing a polyurethane elastomer film material suitable for low-altitude aircraft rotor blades according to claim 2, characterized in that, In step (2), the molar ratio of 4-formylphenylboronic acid and 3,4-dihydroxybutyraldehyde is 1:

1.

6. The method for preparing a polyurethane elastomer film material suitable for low-altitude aircraft rotor blades according to claim 2, characterized in that, The method for preparing the ultraviolet-absorbing monomer in step (3) is as follows: Ammonium acetate and glacial acetic acid are mixed evenly to prepare a catalyst solution; Ethyl cyanoacetate and 4,4'-dihydroxymethylbenzophenone are added to n-heptane, and the catalyst solution is added dropwise at a uniform rate under stirring at 50~60℃. After the addition is completed, the mixture is stirred and refluxed at 98~100℃ for 9~10h, cooled to room temperature, deionized water at 0~4℃ is added, the mixture is allowed to stand, filtered, and dried to obtain the ultraviolet-absorbing monomer.

7. The method for preparing a polyurethane elastomer film material suitable for low-altitude aircraft rotor blades according to claim 2, characterized in that, The mass ratio of polyester diol, ultraviolet-absorbing monomer, dihydroxy-terminated polydimethylsiloxane, dibutyltin dilaurate, and m-xylene in step (3) is 1:(0.4~0.5):(0.5~0.6):(0.01~0.02):(8~10).

8. The method for preparing a polyurethane elastomer film material suitable for low-altitude aircraft rotor blades according to claim 2, characterized in that, The mass ratio of the modified polyurethane, borate crosslinking agent, modified silica, and N,N-dimethylformamide in step (4) is 1:(0.07~0.08):(0.04~0.05):(2~2.2).

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