High-strength high-transparency bio-based polyurethane film and preparation method thereof

Abstract

This invention belongs to the field of bio-based functional polymer materials, specifically relating to a high-strength, high-transmittance bio-based polyurethane film and its preparation method. The invention utilizes the reaction of malic acid with an aromatic ring diol to obtain a malic acid polyol, which is then polymerized with isocyanate. Chain extension is performed using a small molecule chain extender, and coumarin derivative monomers are used for end-capping to obtain the bio-based polyurethane. The bio-based polyurethane film is then obtained using a casting method and ice bath cooling treatment, exhibiting high transmittance, good mechanical properties, and biodegradability. This invention pertains to bio-based renewable materials and has potential applications in fields such as agricultural mulch films and packaging materials.

Description

Technical Field

[0001] This invention belongs to the field of bio-based functional polymer materials, and specifically relates to a high-strength, high-transmittance bio-based polyurethane film and its preparation method. Background Technology

[0002] Mulching technology, as a low-cost and practical planting technique, is widely used in agricultural planting. This technology can reduce the impact of rain on crops, effectively reduce soil moisture evaporation, maintain suitable soil temperature and humidity, promote crop water absorption and growth, and significantly increase crop yield. Agricultural mulch film is the key material in this technology. In actual use, agricultural mulch film is subject to erosion by wind, sand, and rainwater, therefore requiring high mechanical strength and corrosion resistance. Furthermore, crops need sufficient sunlight for growth, so agricultural mulch film must also have excellent light transmittance. Traditional agricultural mulch film material is polyethylene (PE), which, while having excellent light transmittance, has relatively poor mechanical strength and corrosion resistance.

[0003] Polyurethane materials, due to their designable molecular structure, play an irreplaceable role in fields such as foams, medical devices, adhesives / sealants, coatings, and packaging materials, earning them the reputation of "universal polymer materials." In the field of agricultural mulch films, polyurethane materials show promising application prospects due to their excellent corrosion resistance and mechanical properties. However, like the aforementioned polyethylene materials, traditional polyurethane materials are petroleum-based, with non-renewable raw materials and no biodegradability in natural environments, putting pressure on environmental and resource sustainability. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a high-strength, high-transmittance bio-based polyurethane film and its preparation method.

[0005] The technical solution of the present invention is as follows:

[0006] A method for preparing a high-strength, high-transmittance bio-based polyurethane film includes the following steps:

[0007] (1) Mix malic acid and aromatic ring diol evenly, then add catalyst dissolved in organic solvent, and react at 130-140℃ under N2 protection until the acid value drops to 1mgKOH / g and the reaction is stopped. Then cool to obtain malic acid polyol.

[0008] Preferably, the aromatic ring diol is any one of 1,4-benzenediol, hydroquinone dihydroxyethyl ether, resorcinol dihydroxyethyl ether, or bisphenol A; and the catalyst is any one of dibutyltin dilaurate, tetrabutyl titanate, or zinc acetate.

[0009] The molar ratio of malic acid to aromatic diol is 1:2, and the amount of catalyst used is 0.25-0.5 wt% of malic acid.

[0010] (2) After dehydrating the malic acid polyol, it is mixed with isocyanate and organotin catalyst in an organic solvent and reacted at 75-85℃ for 2h to obtain isocyanate-terminated bio-based polyurethane prepolymer; then the bio-based polyurethane prepolymer is dissolved with a small molecule chain extender in an organic solvent and reacted at 35-45℃ for 1h to obtain isocyanate-terminated bio-based polyurethane.

[0011] Preferably, the isocyanate is any one of isophorone diisocyanate, 2,4-toluene diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, or hexamethylene diisocyanate; and the organotin catalyst is any one of dibutyltin dilaurate or stannous octoate.

[0012] The molar ratio of malic acid polyol to isocyanate is 3:1; the amount of organotin catalyst is 0.25-0.5 wt% of malic acid polyol; the small molecule chain extender is any one of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol or 1,4-cyclohexanediol, wherein the molar ratio of small molecule chain extender to malic acid polyol is 1.5:1.

[0013] (3) After dissolving the coumarin derivative monomer and the bio-based polyurethane prepared in step (2) in an organic solvent, react at 35-45℃ for 1h to obtain the coumarin derivative monomer-terminated bio-based polyurethane; then dissolve it in an organic solvent and pour it into a polytetrafluoroethylene plate, put it in an oven, dry it at 80℃ for 24-48h, and then cool it in an ice bath for 30min to obtain a high-strength, high-transmittance bio-based polyurethane film.

[0014] Preferably, the coumarin derivative monomer is either 7-hydroxycoumarin or 4-methylumbelliferone.

[0015] Preferably, the molar ratio of coumarin derivative monomer to malic acid polyol is 3:1.

[0016] Preferably, the organic solvent in steps (1) to (3) is any one of N,N-dimethylformamide, acetone, ethyl acetate, butyl acetate or dichloromethane.

[0017] The structural formula of the high-strength, high-transmittance bio-based polyurethane film prepared by the above method is shown in Formula I:

[0018]

[0019] Where R1 is Any one of them; R2 is Any one of them; R3 is Any of the following; R4 is Any one of them.

[0020] The beneficial effects of this invention are as follows:

[0021] 1. This invention uses malic acid to react with aromatic ring diols to obtain malic acid polyols, and then uses malic acid polyols with bio-based raw materials such as coumarin derivatives as reactants and end-capping agents to react and obtain bio-based polyurethane films. These bio-based polyurethane films have good mechanical properties and high light transmittance. They are renewable materials derived from bio-based sources, are green and environmentally friendly, and are biodegradable. They can be widely used in industries such as agricultural mulch films and packaging materials.

[0022] 2. The present invention uses a casting molding method and annealing treatment to obtain a bio-based polyurethane film, which can reduce the crystallinity of the material and further enhance the light transmittance of the material. Attached image description:

[0023] Figure 1 The image shows the infrared spectrum of the bio-based polyurethane film from Example 1. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1

[0026] (1) Add 20g of malic acid and 32.84g of 1,4-benzene to a three-necked flask, then add 0.1g of dibutyltin dilaurate dissolved in 2mL of N,N-dimethylformamide. After mixing evenly, heat to 130℃ with nitrogen gas, stir the reaction and continuously monitor the acid value. Stop the reaction when the acid value drops to 1mgKOH / g to confirm that the carboxyl group on the malic acid has reacted completely, and obtain malic acid polyol.

[0027] (2) 10g of malic acid polyol was dehydrated at 100℃ for 3h and then dissolved in 5mL of N,N-dimethylformamide. Diphenylmethane diisocyanate (23.58g) and dibutyltin dilaurate (0.05g) dissolved in 2mL of N,N-dimethylformamide were added. The mixture was reacted at 80℃ for 2h to obtain a viscous isocyanate-terminated bio-based polyurethane prepolymer. Subsequently, 1,4-butanediol (3.87g) dissolved in 3.5mL of N,N-dimethylformamide was added and the mixture was reacted at 45℃ for 1h to obtain a viscous isocyanate-terminated bio-based polyurethane.

[0028] (3) Add bio-based polyurethane to 10 mL of 4-methylumbelliferone (15.29 g) dissolved in N,N-dimethylformamide and react at 40 °C for 1 h to obtain viscous coumarin derivative monomer-terminated bio-based polyurethane; then dissolve it with N,N-dimethylformamide, pour it into a polytetrafluoroethylene plate, dry it in an oven at 80 °C for 48 h, and then cool it in an ice bath for 30 min to obtain a high-strength, high-transmittance bio-based polyurethane film.

[0029] Figure 1 The infrared spectrum of the high-strength, high-transmittance bio-based polyurethane film prepared in this embodiment is shown. As can be seen from the figure, at 2270 cm⁻¹... -1 The disappearance of the characteristic peak of the isocyanate group indicates that the prepolymer reaction is complete; at 3300 cm⁻¹ -1 The characteristic peak of -NH is at 850 cm⁻¹. -1 The peak at 1440 cm⁻¹ is a characteristic peak for the para-disubstituted group of the benzene ring. -1 and 2910cm -1 The characteristic peak of -CH2 is at 1500 cm⁻¹. -1 and 1600cm -1 The characteristic peak of amide is at 1700 cm⁻¹. -1 The peak at this position is a characteristic peak of the carbonyl group. The appearance of the above characteristic peaks indicates the introduction of benzene ring structure and coumarin structure, and a high-strength, high-transmittance bio-based polyurethane film has been successfully synthesized.

[0030] Example 2

[0031] (1) Add 20g of malic acid and 59.11g of hydroquinone dihydroxyethyl ether to a three-necked flask, then add 0.1g of dibutyltin dilaurate dissolved in 2mL of N,N-dimethylformamide. After mixing evenly, heat to 130℃ with nitrogen gas, stir the reaction and continuously monitor the acid value. Stop the reaction when the acid value drops to 1mgKOH / g to confirm that the carboxyl group on the malic acid has reacted completely, and obtain malic acid polyol.

[0032] (2) 10g of malic acid polyol was dehydrated at 100℃ for 3h and then dissolved in 5mL of N,N-dimethylformamide. Diphenylmethane diisocyanate (23.58g) and dibutyltin dilaurate (0.05g) dissolved in 2mL of N,N-dimethylformamide were added. The mixture was reacted at 80℃ for 2h to obtain a viscous isocyanate-terminated bio-based polyurethane prepolymer. Subsequently, 1,4-butanediol (3.87g) dissolved in 3.5mL of N,N-dimethylformamide was added and the mixture was reacted at 45℃ for 1h to obtain a viscous isocyanate-terminated bio-based polyurethane.

[0033] (3) Add bio-based polyurethane to 10 mL of 4-methylumbelliferone (15.29 g) dissolved in N,N-dimethylformamide and react at 40 °C for 1 h to obtain viscous coumarin derivative monomer-terminated bio-based polyurethane; then dissolve it with N,N-dimethylformamide, pour it into a polytetrafluoroethylene plate, dry it in an oven at 80 °C for 48 h, and then cool it in an ice bath for 30 min to obtain a high-strength, high-transmittance bio-based polyurethane film.

[0034] Example 3

[0035] (1) Add 20g of malic acid and 32.84g of 1,4-benzene to a three-necked flask, then add 0.1g of dibutyltin dilaurate dissolved in 2mL of N,N-dimethylformamide. After mixing evenly, heat to 130℃ with nitrogen gas, stir the reaction and continuously monitor the acid value. Stop the reaction when the acid value drops to 1mgKOH / g to confirm that the carboxyl group on the malic acid has reacted completely, and obtain malic acid polyol.

[0036] (2) 10g of malic acid polyol was dehydrated at 100℃ for 3h and then dissolved in 5mL of N,N-dimethylformamide. Diphenylmethane diisocyanate (23.58g) and dibutyltin dilaurate (0.05g) dissolved in 2mL of N,N-dimethylformamide were added. The mixture was reacted at 80℃ for 2h to obtain a viscous isocyanate-terminated bio-based polyurethane prepolymer. Subsequently, 1,4-butanediol (3.87g) dissolved in 3.5mL of N,N-dimethylformamide was added and the mixture was reacted at 45℃ for 1h to obtain a viscous isocyanate-terminated bio-based polyurethane.

[0037] (3) Add bio-based polyurethane to 10 mL of 7-hydroxycoumarin (13.98 g) dissolved in N,N-dimethylformamide and react at 40 °C for 1 h to obtain viscous coumarin derivative monomer-terminated bio-based polyurethane; then dissolve it with N,N-dimethylformamide, pour it into a polytetrafluoroethylene plate, dry it in an oven at 80 °C for 48 h, and then cool it in an ice bath for 30 min to obtain a high-strength, high-transmittance bio-based polyurethane film.

[0038] Example 4

[0039] (1) Add 20g of malic acid and 68.05g of bisphenol A to a three-necked flask, then add 0.1g of dibutyltin dilaurate dissolved in 2mL of N,N-dimethylformamide. After mixing evenly, heat to 130℃ with nitrogen gas, stir the reaction and continuously monitor the acid value. Stop the reaction when the acid value drops to 1mgKOH / g to confirm that the carboxyl group on the malic acid has reacted completely, and obtain malic acid polyol.

[0040] (2) 10g of malic acid polyol was dehydrated at 100℃ for 3h and then dissolved in 5mL of N,N-dimethylformamide. Diphenylmethane diisocyanate (23.58g) and dibutyltin dilaurate (0.05g) dissolved in 2mL of N,N-dimethylformamide were added. The mixture was reacted at 80℃ for 2h to obtain a viscous isocyanate-terminated bio-based polyurethane prepolymer. Subsequently, 1,4-butanediol (3.87g) dissolved in 3.5mL of N,N-dimethylformamide was added and the mixture was reacted at 45℃ for 1h to obtain a viscous isocyanate-terminated bio-based polyurethane.

[0041] (3) Add bio-based polyurethane to 10 mL of 4-methylumbelliferone (15.29 g) dissolved in N,N-dimethylformamide and react at 40 °C for 1 h to obtain viscous coumarin derivative monomer-terminated bio-based polyurethane; then dissolve it with N,N-dimethylformamide, pour it into a polytetrafluoroethylene plate, dry it in an oven at 80 °C for 48 h, and then cool it in an ice bath for 30 min to obtain a high-strength, high-transmittance bio-based polyurethane film.

[0042] Example 5

[0043] (1) Add 20g of malic acid and 32.84g of 1,4-benzene to a three-necked flask, then add 0.1g of dibutyltin dilaurate dissolved in 2mL of N,N-dimethylformamide. After mixing evenly, heat to 130℃ with nitrogen gas, stir the reaction and continuously monitor the acid value. Stop the reaction when the acid value drops to 1mgKOH / g to confirm that the carboxyl group on the malic acid has reacted completely, and obtain malic acid polyol.

[0044] (2) 10g of malic acid polyol was dehydrated at 100℃ for 3h and then dissolved in 5mL of N,N-dimethylformamide. Hexamethylene diisocyanate (15.84g) and dibutyltin dilaurate (0.05g) dissolved in 2mL of N,N-dimethylformamide were added. The mixture was reacted at 80℃ for 2h to obtain a viscous isocyanate-terminated bio-based polyurethane prepolymer. Subsequently, 1,4-butanediol (3.87g) dissolved in 3.5mL of N,N-dimethylformamide was added and the mixture was reacted at 45℃ for 1h to obtain a viscous isocyanate-terminated bio-based polyurethane.

[0045] (3) Add bio-based polyurethane to 10 mL of 4-methylumbelliferone (15.29 g) dissolved in N,N-dimethylformamide and react at 40 °C for 1 h to obtain viscous coumarin derivative monomer-terminated bio-based polyurethane; then dissolve it with N,N-dimethylformamide, pour it into a polytetrafluoroethylene plate, dry it in an oven at 80 °C for 48 h, and then cool it in an ice bath for 30 min to obtain a high-strength, high-transmittance bio-based polyurethane film.

[0046] Example 6

[0047] (1) Add 20g of malic acid and 32.84g of 1,4-benzene to a three-necked flask, then add 0.1g of dibutyltin dilaurate dissolved in 2mL of N,N-dimethylformamide. After mixing evenly, heat to 130℃ with nitrogen gas, stir the reaction and continuously monitor the acid value. Stop the reaction when the acid value drops to 1mgKOH / g to confirm that the carboxyl group on the malic acid has reacted completely, and obtain malic acid polyol.

[0048] (2) 10g of malic acid polyol was dehydrated at 100℃ for 3h and then dissolved in 5mL of N,N-dimethylformamide. Hexamethylene diisocyanate (15.84g) and dibutyltin dilaurate (0.05g) dissolved in 2mL of N,N-dimethylformamide were added. The mixture was reacted at 80℃ for 2h to obtain a viscous isocyanate-terminated bio-based polyurethane prepolymer. Subsequently, 1,4-cyclohexanediol (4.68g) dissolved in 3.5mL of N,N-dimethylformamide was added and the mixture was reacted at 45℃ for 1h to obtain a viscous isocyanate-terminated bio-based polyurethane.

[0049] (3) Add bio-based polyurethane to 10 mL of 4-methylumbelliferone (15.29 g) dissolved in N,N-dimethylformamide and react at 40 °C for 1 h to obtain viscous coumarin derivative monomer-terminated bio-based polyurethane; then dissolve it with N,N-dimethylformamide, pour it into a polytetrafluoroethylene plate, dry it in an oven at 80 °C for 48 h, and then cool it in an ice bath for 30 min to obtain a high-strength, high-transmittance bio-based polyurethane film.

[0050] Example 7

[0051] (1) Add 20g of malic acid and 32.84g of 1,4-benzene to a three-necked flask, then add 0.1g of dibutyltin dilaurate dissolved in 2mL of N,N-dimethylformamide. After mixing evenly, heat to 130℃ with nitrogen gas, stir the reaction and continuously monitor the acid value. Stop the reaction when the acid value drops to 1mgKOH / g to confirm that the carboxyl group on the malic acid has reacted completely, and obtain malic acid polyol.

[0052] (2) 10g of malic acid polyol was dehydrated at 100℃ for 3h and then dissolved in 5mL of N,N-dimethylformamide. Hexamethylene diisocyanate (15.84g) and dibutyltin dilaurate (0.05g) dissolved in 2mL of N,N-dimethylformamide were added. The mixture was reacted at 80℃ for 2h to obtain a viscous isocyanate-terminated bio-based polyurethane prepolymer. Subsequently, 1,3-propanediol (3.11g) dissolved in 3.5mL of N,N-dimethylformamide was added and the mixture was reacted at 45℃ for 1h to obtain a viscous isocyanate-terminated bio-based polyurethane.

[0053] (3) Add bio-based polyurethane to 10 mL of 4-methylumbelliferone (15.29 g) dissolved in N,N-dimethylformamide and react at 40 °C for 1 h to obtain viscous coumarin derivative monomer-terminated bio-based polyurethane; then dissolve it with N,N-dimethylformamide, pour it into a polytetrafluoroethylene plate, dry it in an oven at 80 °C for 48 h, and then cool it in an ice bath for 30 min to obtain a high-strength, high-transmittance bio-based polyurethane film.

[0054] Example 8

[0055] (1) Add 20g of malic acid and 68.05g of bisphenol A to a three-necked flask, then add 0.1g of dibutyltin dilaurate dissolved in 2mL of N,N-dimethylformamide. After mixing evenly, heat to 130℃ with nitrogen gas, stir the reaction and continuously monitor the acid value. Stop the reaction when the acid value drops to 1mgKOH / g to confirm that the carboxyl group on the malic acid has reacted completely, and obtain malic acid polyol.

[0056] (2) 10g of malic acid polyol was dehydrated at 100℃ for 3h and then dissolved in 5mL of N,N-dimethylformamide. Hexamethylene diisocyanate (15.84g) and dibutyltin dilaurate (0.05g) dissolved in 2mL of N,N-dimethylformamide were added. The mixture was reacted at 80℃ for 2h to obtain a viscous isocyanate-terminated bio-based polyurethane prepolymer. Subsequently, 1,4-butanediol (3.87g) dissolved in 3.5mL of N,N-dimethylformamide was added and the mixture was reacted at 45℃ for 1h to obtain a viscous isocyanate-terminated bio-based polyurethane.

[0057] (3) Add bio-based polyurethane to 10 mL of 4-methylumbelliferone (15.29 g) dissolved in N,N-dimethylformamide and react at 40 °C for 1 h to obtain viscous coumarin derivative monomer-terminated bio-based polyurethane; then dissolve it with N,N-dimethylformamide, pour it into a polytetrafluoroethylene plate, dry it in an oven at 80 °C for 48 h, and then cool it in an ice bath for 30 min to obtain a high-strength, high-transmittance bio-based polyurethane film.

[0058] Comparative Example 1

[0059] (1) Add 20g of malic acid and 62.54g of 1,4-butanediol to a three-necked flask, then add 0.1g of dibutyltin dilaurate dissolved in 2mL of N,N-dimethylformamide. After mixing evenly, heat to 130℃ with nitrogen gas, stir the reaction and continuously monitor the acid value. Stop the reaction when the acid value drops to 1mgKOH / g to confirm that the carboxyl group on the malic acid has reacted completely, and obtain malic acid polyol.

[0060] (2) 10g of malic acid polyol was dehydrated at 100℃ for 3h and then dissolved in 5mL of N,N-dimethylformamide. Diphenylmethane diisocyanate (23.58g) and dibutyltin dilaurate (0.05g) dissolved in 2mL of N,N-dimethylformamide were added. The mixture was reacted at 80℃ for 2h to obtain a viscous isocyanate-terminated bio-based polyurethane prepolymer. Subsequently, 1,4-butanediol (3.87g) dissolved in 3.5mL of N,N-dimethylformamide was added and the mixture was reacted at 45℃ for 1h to obtain a viscous isocyanate-terminated bio-based polyurethane.

[0061] (3) Add bio-based polyurethane to 10 mL of 4-methylumbelliferone (15.29 g) dissolved in N,N-dimethylformamide and react at 40 °C for 1 h to obtain viscous coumarin derivative monomer-terminated bio-based polyurethane; then dissolve it with N,N-dimethylformamide, pour it into a polytetrafluoroethylene plate, dry it in an oven at 80 °C for 48 h, and then cool it in an ice bath for 30 min to obtain a high-strength, high-transmittance bio-based polyurethane film.

[0062] Comparative Example 2

[0063] (1) Add 20g of malic acid and 32.84g of 1,4-benzene to a three-necked flask, then add 0.1g of dibutyltin dilaurate dissolved in 2mL of N,N-dimethylformamide. After mixing evenly, heat to 130℃ with nitrogen gas, stir the reaction and continuously monitor the acid value. Stop the reaction when the acid value drops to 1mgKOH / g to confirm that the carboxyl group on the malic acid has reacted completely, and obtain malic acid polyol.

[0064] (2) 10g of malic acid polyol was dehydrated at 100℃ for 3h and then dissolved in 5mL of N,N-dimethylformamide. Diphenylmethane diisocyanate (23.58g) and dibutyltin dilaurate (0.05g) dissolved in 2mL of N,N-dimethylformamide were added. The mixture was reacted at 80℃ for 2h to obtain a viscous isocyanate-terminated bio-based polyurethane prepolymer. Subsequently, 1,4-butanediol (3.87g) dissolved in 3.5mL of N,N-dimethylformamide was added and the mixture was reacted at 45℃ for 1h to obtain a viscous isocyanate-terminated bio-based polyurethane.

[0065] (3) Dissolve the bio-based polyurethane with N,N-dimethylformamide, then pour it into a polytetrafluoroethylene plate, dry it in an oven at 80°C for 48 hours, and then cool it in an ice bath for 30 minutes to obtain a high-strength, high-transmittance bio-based polyurethane film.

[0066] Comparative Example 3

[0067] (1) Dissolve 3.46g of 1,4-diphenylhydroquinone in 5mL of N,N-dimethylformamide, then add diphenylmethane diisocyanate (23.58g) and dibutyltin dilaurate (0.05g) dissolved in 2mL of N,N-dimethylformamide, and react at 80℃ for 2h to obtain a viscous isocyanate-terminated bio-based polyurethane prepolymer; then add 1,4-butanediol (3.87g) dissolved in 3.5mL of N,N-dimethylformamide, and react at 45℃ for 1h to obtain a viscous isocyanate-terminated bio-based polyurethane.

[0068] (2) Add bio-based polyurethane to 10 mL of 4-methylumbelliferone (15.29 g) dissolved in N,N-dimethylformamide and react at 40 °C for 1 h to obtain viscous coumarin derivative monomer-terminated bio-based polyurethane; then dissolve it with N,N-dimethylformamide, pour it into a polytetrafluoroethylene plate, dry it in an oven at 80 °C for 48 h, and then cool it in an ice bath for 30 min to obtain a high-strength, high-transmittance bio-based polyurethane film.

[0069] To verify the optical, mechanical, and biodegradability properties of the bio-based polyurethane film, transmittance testing was conducted according to GB2410-80 "Test Methods for Transparent Plastics - Transmittance and Haze". Mechanical property testing was performed using samples prepared according to ASTM D882 at a testing speed of 500 mm / min. The bio-based polyurethane film was immersed in a standard phosphate solution for 12 weeks, and the mass loss rate was measured to test its biodegradability. The test results for each example and comparative example are shown in Tables 1 and 2.

[0070] Table 1. Test results of light transmittance and mechanical properties of Examples 1-8 and Comparative Examples 1-3.

[0071] transmittance / % Haze / % Tensile strength / MPa Elongation at break / % Example 1 96.2 2.18 15.63 720 Example 2 93.3 3.42 13.61 708 Example 3 94.2 3.06 13.59 715 Example 4 90.6 3.94 14.53 660 Example 5 95.5 6.11 10.88 940 Example 6 95.5 4.99 11.02 910 Example 7 93.3 4.96 10.62 940 Example 8 94.66 4.84 11.02 670 Comparative Example 1 68.2 6.18 6.02 410 Comparative Example 2 76.2 4.78 10.13 520 Comparative Example 3 89.2 4.78 9.67 610

[0072] As shown in Table 1, the light transmittance and mechanical properties of the bio-based polyurethane films prepared in Examples 1-8 are significantly better than those in Comparative Examples 1-3.

[0073] Table 2. Biodegradability test results of Examples 1-8 and Comparative Examples 1-3

[0074] Quality loss rate / % Example 1 36.2 Example 2 34.9 Example 3 34.1 Example 4 30.9 Example 5 32.8 Example 6 33.3 Example 7 31.5 Example 8 36.7 Comparative Example 1 36.1 Comparative Example 2 28.4 Comparative Example 3 0.05

[0075] As can be seen from Table 2, compared with Comparative Example 3, the mass loss rate of Examples 1-8 is all above 30%, indicating that the introduction of malic acid greatly improves the biodegradability of the polyurethane film.

Claims

1. A method for preparing a high-strength, high-transmittance bio-based polyurethane film, characterized in that, Includes the following steps: (1) Mix malic acid and aromatic ring diol evenly, then add catalyst dissolved in organic solvent, and react at 130-140℃ under N2 protection until the acid value drops to 1mg KOH / g and the reaction is stopped. Then cool to obtain malic acid polyol; the aromatic ring diol is any one of 1,4-benzenediol, hydroquinone dihydroxyethyl ether, resorcinol dihydroxyethyl ether or bisphenol A; the molar ratio of malic acid to aromatic ring diol is 1:2; (2) After dehydration treatment of malic acid polyol, it is mixed with isocyanate and organotin catalyst and dissolved in organic solvent. The mixture is reacted at 75-85℃ for 2h to obtain isocyanate-terminated bio-based polyurethane prepolymer. Then, the bio-based polyurethane prepolymer is dissolved with small molecule chain extender in organic solvent and reacted at 35-45℃ for 1h to obtain isocyanate-terminated bio-based polyurethane. The molar ratio of malic acid polyol to isocyanate is 3:1; the molar ratio of small molecule chain extender to malic acid polyol is 1.5:

1. (3) After dissolving the coumarin derivative monomer and the bio-based polyurethane prepared in step (2) in an organic solvent, react at 35-45℃ for 1 h to obtain the coumarin derivative monomer-terminated bio-based polyurethane; then dissolve it in an organic solvent and pour it into a polytetrafluoroethylene plate, put it in an oven, dry it at 80℃ for 24-48 h, and then cool it in an ice bath for 30 min to obtain a high-strength, high-transmittance bio-based polyurethane film; the coumarin derivative monomer is either 7-hydroxycoumarin or 4-methylumbelliferone; the molar ratio of coumarin derivative monomer to malic acid polyol is 3:

1.

2. The method for preparing the high-strength, high-transmittance bio-based polyurethane film according to claim 1, characterized in that, In step (1), the catalyst is any one of dibutyltin dilaurate, tetrabutyl titanate, or zinc acetate.

3. The method for preparing the high-strength, high-transmittance bio-based polyurethane film according to claim 1, characterized in that, In step (1), the amount of catalyst used is 0.25-0.5 wt% of malic acid.

4. The method for preparing the high-strength, high-transmittance bio-based polyurethane film according to claim 1, characterized in that, In step (2), the isocyanate is any one of isophorone diisocyanate, 2,4-toluene diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, or hexamethylene diisocyanate; the organotin catalyst is any one of dibutyltin dilaurate or stannous octoate.

5. The method for preparing the high-strength, high-transmittance bio-based polyurethane film according to claim 1, characterized in that, In step (2), the amount of organotin catalyst used is 0.25-0.5 wt% of malic acid polyol; the small molecule chain extender is any one of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol or 1,4-cyclohexanediol.

6. The method for preparing the high-strength, high-transmittance bio-based polyurethane film according to claim 1, characterized in that, The organic solvent is any one of N,N-dimethylformamide, acetone, ethyl acetate, butyl acetate, or dichloromethane.

7. A high-strength, high-transmittance bio-based polyurethane film prepared by the method according to any one of claims 1-6, characterized in that, The structural formula is shown in Formula I: ， The R1 structure comes from , , or Any one of them; the R2 structure comes from , , , or Any one of them; the R3 structure comes from , , , , or Any of the above; the R4 structure comes from or Any one of them.

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