Transparent, tough and antibacterial polyurethane as well as preparation method and application thereof

Abstract

The invention discloses transparent, tough and antibacterial polyurethane and a preparation method and application thereof.The preparation method comprises the following steps that 1, after polycaprolactone diol and polyethylene glycol are dried and dewatered, the temperature is increased to the temperature above the melting point of the polycaprolactone diol and the polyethylene glycol under the protective atmosphere, and the polycaprolactone diol and the polyethylene glycol are melted and fully mixed; step 2, adding diisocyanate into the mixture obtained in the step 1, and fully reacting to obtain an isocyanate-terminated prepolymer; and step 3, adding a solvent into the prepolymer obtained in the step 2, dropwise adding a catechin compound solution, and after full reaction, volatilizing the solvent to obtain the required polyurethane. The polyurethane material obtained by the invention is high in bioavailability, has antioxidant, antibacterial and anti-inflammatory effects, is excellent in mechanical property, and is suitable for the field of food packaging.

Description

Technical Field

[0001] The present invention relates to the technical field of polyurethanes, and particularly relates to a polyurethane with both transparency, toughness and antibacterial properties, a preparation method and an application thereof. Background Art

[0002] Polyurethane is a block polymer synthesized from polyisocyanates and hydroxyl compounds, and is widely used in fields such as coatings, adhesives, elastomers, and foam materials due to its excellent wear resistance, tear resistance, and resilience. However, due to the single functionality of polyurethane, it cannot meet the diverse usage requirements of existing food packaging materials, which limits its development in the field of food packaging.

[0003] In existing technologies that use polyurethane and catechins together, for example: CN115677414A sprays a polyphenol-based biopolyurethane coating solution formed by catechin compounds and isocyanates, and an alkylamine solution onto the surface of urea particles respectively to coat the urea particles to form a coated slow-release fertilizer; CN112210099A prepares a photochromic polyurethane film using diisocyanate, catechin compounds, tannic acid, crosslinking agents, etc. However, currently reported methods are all applying catechin compounds as antibacterial coatings, drug-loaded nanoparticles, bioactive additives, antioxidants, etc. in polyurethane. In the above methods, the bioavailability of catechin compounds is low, and the ideal antioxidant and antibacterial and anti-inflammatory effects cannot be exerted, and it is not suitable for application in the field of food packaging. Summary of the Invention

[0004] The present invention provides a polyurethane with both transparency, toughness and antibacterial properties, a preparation method and an application thereof for the problems existing in the prior art.

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

[0006] A polyurethane with both transparency, toughness and antibacterial properties has the following structure:

[0007]

[0008] In the formula: U is a diisocyanate residue, (R1) x is a polycaprolactone diol residue, (R2) y is a polyethylene glycol residue, EGCG is a catechin compound residue, x is any integer from 10 to 100, and y is any integer from 10 to 200.

[0009] Further, the polycaprolactone diol residue is obtained by polymerization reaction of ε-caprolactone monomers, and the number average molecular weight is 1 to 10 kg / mol.

[0010] Furthermore, the diisocyanate residue is formed by the reaction of diisocyanate and diol soft segment, and the diisocyanate is one or two or more of 4,4'-dimethylmethane diisocyanate, 1,6-hexamethylene diisocyanate, L-lysine diisocyanate and isophorone diisocyanate.

[0011] Furthermore, the number average molecular weight of the polyethylene glycol residue is 0.5 to 8 kg / mol.

[0012] Furthermore, the catechin compound is one of the following structures:

[0013]

[0014] A method for preparing transparent, tough and antibacterial polyurethane comprises the following steps:

[0015] Step 1: After drying and removing water from polycaprolactone diol and polyethylene glycol, the mixture is heated to above the melting point under a protective atmosphere to be melted and fully mixed;

[0016] Step 2: adding diisocyanate to the mixture obtained in step 1, and obtaining an isocyanate-terminated prepolymer after sufficient reaction;

[0017] Step 3: Add a solvent to the prepolymer obtained in step 2, then dropwise add the catechin compound solution, and after sufficient reaction, evaporate the solvent to obtain the desired polyurethane.

[0018] Furthermore, in step 1, the mass ratio of polycaprolactone diol to polyethylene glycol is 1:0.1-1:10; the molar ratio of the terminal hydroxyl group of the diol, the isocyanate in the diisocyanate, and the hydroxyl group in the catechin compound is 0.5:1:0.5-1:4:3.

[0019] Furthermore, the reaction temperature in step 2 and step 3 is 80-100°C.

[0020] Furthermore, the concentration of the catechin compound solution in step 3 is 0.1-2.0 g / mL.

[0021] An application of transparent, tough and antibacterial polyurethane, wherein the polyurethane is prepared into a polyurethane film and used as a food packaging material.

[0022] The beneficial effects of the present invention are:

[0023] (1) The present invention uses catechin compounds as chain extenders to introduce them into the main chain structure of polyurethane. On the one hand, it improves the bioavailability of catechin compounds and endows the polyurethane material with antibacterial, anti-inflammatory, and antioxidant effects. On the other hand, the hardness, toughness, and strength of the polyurethane material can be adjusted by adjusting the introduction amount of catechin compounds, making it have excellent mechanical properties.

[0024] (2) The present invention uses polycaprolactone diol and polyethylene glycol as the double soft segments of polyurethane, which can not only regulate the hardness and mechanical properties of polyurethane, but also customize the water vapor barrier performance, waterproof performance, stability, service life, etc. of polyurethane according to the hydrophilic-hydrophobic difference and degradation rate difference between polycaprolactone and polyethylene glycol to meet the usage requirements of different food packaging materials. More importantly, as water molecules or bioenzyme molecules enter the material interior, the main chain of polyurethane breaks, gradually releasing catechin compounds with antibacterial, anti-inflammatory, antioxidant and other effects, endowing it with self-cleaning performance and extending its service life. Description of the Drawings

[0025] Figure 1 It is a schematic diagram of the transparency of the polyurethane film obtained in Examples 3-5 of the present invention.

[0026] Figure 2 It is a schematic diagram of the transmittance of the polyurethane film obtained in Examples 3-5 of the present invention.

[0027] Figure 3 It is the test result of the mechanical properties of the polyurethane film obtained in Examples 1-5 and Comparative Example 1 of the present invention. Detailed Embodiments

[0028] The present invention will be further described below with reference to the drawings and specific embodiments.

[0029] A polyurethane with both transparency, toughness and antibacterial properties has the following structure:

[0030]

[0031] In the formula: U is a diisocyanate residue, (R1) x is a polycaprolactone diol residue, (R2) y is a polyethylene glycol residue, EGCG is a catechin compound residue, x is any integer from 10 to 100, and y is any integer from 10 to 200.

[0032] The polycaprolactone diol residue is obtained by the polymerization reaction of ε-caprolactone monomers, and the number average molecular weight is 1 to 10 kg / mol. The diisocyanate residue is formed by the reaction of diisocyanate with the soft segment of diol. The diisocyanate is one or more of 4,4'-dimethylmethane diisocyanate, 1,6-hexamethylene diisocyanate, L-lysine diisocyanate, and isophorone diisocyanate.

[0033] The number average molecular weight of the polyethylene glycol residue is 0.5 to 8 kg / mol.

[0034] The catechin compounds are one of the following structures:

[0035]

[0036] A preparation method of a polyurethane with both transparency, toughness and antibacterial properties, comprising the following steps:

[0037] Step 1: After drying and removing water from polycaprolactone diol and polyethylene glycol, heat them to above their melting points in a protective atmosphere and mix them thoroughly in a molten state; the mass ratio of polycaprolactone diol to polyethylene glycol is 1:0.1 to 1:10.

[0038] Step 2: Add diisocyanate to the mixture obtained in Step 1, and react fully to obtain an isocyanate-terminated prepolymer; the molar ratio of the terminal hydroxyl groups of the diol, the isocyanate groups in the diisocyanate, and the hydroxyl groups in the catechin compounds is 0.5:1:0.5 to 1:4:3, and the reaction temperature is 80 to 100 °C.

[0039] Step 3: Add a solvent to the prepolymer obtained in Step 2, and then dropwise add a catechin compound solution. After reacting fully, volatilize the solvent to obtain the required polyurethane. The concentration of the catechin compound solution is 0.1 to 2.0 g / mL, and the reaction temperature is 80 to 100 °C.

[0040] The reaction process is carried out in a protective atmosphere.

[0041] Usually, the polyurethane is used as a food packaging film material. The polyurethane solution obtained in Step 3 is placed in a preheated mold, and the solvent is volatilized at a constant temperature to obtain the required polyurethane film.

[0042] Example 1

[0043] A preparation method of a polyurethane with both transparency, toughness and antibacterial properties, comprising the following steps:

[0044] Step 1: Add polycaprolactone diol with a number average molecular weight of 3 kg / mol and polyethylene glycol with a number average molecular weight of 3.35 kg / mol to a fully dried reactor, wherein the mass ratio of polycaprolactone diol to polyethylene glycol is 25:5.

[0045] Under constant temperature and vacuum conditions, dehydrate and dry for more than 3 hours. After the dehydration is completed, under nitrogen protection, gradually heat up to above the melting point of the soft segment, and fully melt and stir the two soft segments in the reaction flask to mix them evenly.

[0046] Step 2: Under nitrogen protection, slowly add 1,6 - hexamethylene diisocyanate to the mixture obtained in Step 1, where the molar ratio of the terminal hydroxyl groups of the diol to 1,6 - hexamethylene diisocyanate is 1:2. After reacting in an 80°C oil bath for 1 hour, an isocyanate - terminated prepolymer is obtained.

[0047] Step 3: Under nitrogen protection, slowly add DMF solvent to the reaction system in Step 2 to reduce the viscosity of the system. After fully stirring for 1 hour, a dilute solution of the isocyanate - terminated prepolymer is obtained. Then, slowly dropwise add the DMF solution of EGCG to the above - mentioned dilute solution, where the molar ratio of the terminal hydroxyl groups of the diol to the hydroxyl groups in EGCG is 1:1, and the concentration of EGCG is 0.2 g / mL. Maintain the condition at 80°C and react fully for 4 hours to obtain a polyurethane solution.

[0048] Pour the polyurethane solution obtained in this example into a pre - heated polytetrafluoroethylene mold, volatilize at 80°C for 72 hours, and dry at room temperature in a vacuum oven for 12 hours to obtain a polyurethane film with both transparency, toughness, and antibacterial properties.

[0049] Example 2

[0050] A preparation method of a polyurethane with both transparency, toughness, and antibacterial properties, comprising the following steps:

[0051] Step 1: Add polycaprolactone diol with a number - average molecular weight of 3 kg / mol and polyethylene glycol with a number - average molecular weight of 3.35 kg / mol to a fully dried reactor, where the mass ratio of polycaprolactone diol to polyethylene glycol is 20:10.

[0052] Under constant temperature and vacuum conditions, dehydrate and dry for more than 3 hours. After the dehydration is completed, under nitrogen protection, gradually heat up to above the melting point of the soft segment, and fully melt and stir the two soft segments in the reaction flask to mix them evenly.

[0053] Step 2: Under nitrogen protection, slowly add 1,6 - hexamethylene diisocyanate to the mixture obtained in Step 1, where the molar ratio of the terminal hydroxyl groups of the diol to 1,6 - hexamethylene diisocyanate is 1:2. After reacting in an 80°C oil bath for 1 hour, an isocyanate - terminated prepolymer is obtained.

[0054] Step 3: Under nitrogen protection, slowly add DMF solvent to the reaction system in Step 2 to reduce the viscosity of the system. After stirring thoroughly for 1 h, a dilute solution of the isocyanate-terminated prepolymer is obtained. Then, slowly add a DMF solution of EGCG to the above dilute solution, where the molar ratio of the terminal hydroxyl groups of the diol to the hydroxyl groups in EGCG is 1:1, and the concentration of EGCG is 0.2 g / mL. Maintain at 80 °C and react thoroughly for 4 h to obtain a polyurethane solution.

[0055] Pour the polyurethane solution obtained in this example into a preheated polytetrafluoroethylene mold, volatilize at 80 °C for 72 h, and dry at room temperature in a vacuum oven for 12 h to obtain a polyurethane film with both transparency, toughness and antibacterial properties.

[0056] Example 3

[0057] A preparation method of a polyurethane with both transparency, toughness and antibacterial properties, comprising the following steps:

[0058] Step 1: Add polycaprolactone diol with a number-average molecular weight of 3 kg / mol and polyethylene glycol with a number-average molecular weight of 3.35 kg / mol to a thoroughly dried reactor, where the mass ratio of polycaprolactone diol to polyethylene glycol is 15:15.

[0059] Under constant temperature and vacuum conditions, thoroughly remove water and dry for more than 3 h. After the water removal is completed, under nitrogen protection, gradually raise the temperature above the melting point of the soft segment, and fully melt and stir the two soft segments in the reaction flask to mix them evenly.

[0060] Step 2: Under nitrogen protection, slowly add 1,6-hexamethylene diisocyanate to the mixture obtained in Step 1, where the molar ratio of the terminal hydroxyl groups of the diol to 1,6-hexamethylene diisocyanate is 1:2. React in an 80 °C oil bath for 1 h to obtain an isocyanate-terminated prepolymer.

[0061] Step 3: Under nitrogen protection, slowly add DMF solvent to the reaction system in Step 2 to reduce the viscosity of the system. After stirring thoroughly for 1 h, a dilute solution of the isocyanate-terminated prepolymer is obtained. Then, slowly add a DMF solution of EGCG to the above dilute solution, where the molar ratio of the terminal hydroxyl groups of the diol to the hydroxyl groups in EGCG is 1:1, and the concentration of EGCG is 0.2 g / mL. Maintain at 80 °C and react thoroughly for 4 h to obtain a polyurethane solution.

[0062] Pour the polyurethane solution obtained in this example into a preheated polytetrafluoroethylene mold, volatilize at 80 °C for 72 h, and dry at room temperature in a vacuum oven for 12 h to obtain a polyurethane film with both transparency, toughness and antibacterial properties.

[0063] Example 4

[0064] A preparation method of a polyurethane with both transparency, toughness and antibacterial properties, comprising the following steps:

[0065] Step 1: Add polycaprolactone diol with a number-average molecular weight of 3 kg / mol and polyethylene glycol with a number-average molecular weight of 3.35 kg / mol into a fully dried reactor, wherein the mass ratio of polycaprolactone diol to polyethylene glycol is 10:20.

[0066] Under constant temperature and vacuum conditions, carry out sufficient dehydration and drying for more than 3 h. After the dehydration is completed, under nitrogen protection, gradually raise the temperature to above the melting point of the soft segment, and fully melt and stir the two soft segments in the reaction flask to mix them evenly.

[0067] Step 2: Under nitrogen protection, slowly add 1,6-hexamethylene diisocyanate to the mixture obtained in Step 1, wherein the molar ratio of the terminal hydroxyl group of the diol to 1,6-hexamethylene diisocyanate is 1:2. After reacting in an 80°C oil bath for 1 h, an isocyanate-terminated prepolymer is obtained.

[0068] Step 3: Under nitrogen protection, slowly add DMF solvent to the reaction system in Step 2 to reduce the viscosity of the system. After stirring thoroughly for 1 h, an isocyanate-terminated prepolymer dilute solution is obtained. Then slowly dropwise add the DMF solution of EGCG to the above dilute solution, wherein the molar ratio of the terminal hydroxyl group of the diol to the hydroxyl group in EGCG is 1:1, and the concentration of EGCG is 0.2 g / mL. Keep reacting at 80°C for 4 h to obtain a polyurethane solution.

[0069] Pour the polyurethane solution obtained in this example into a preheated polytetrafluoroethylene mold, volatilize at 80°C for 72 h, and dry at room temperature in a vacuum oven for 12 h to obtain a polyurethane film with both transparency, toughness and antibacterial properties.

[0070] Example 5

[0071] A preparation method of a polyurethane with both transparency, toughness and antibacterial properties, comprising the following steps:

[0072] Step 1: Add polycaprolactone diol with a number-average molecular weight of 3 kg / mol and polyethylene glycol with a number-average molecular weight of 3.35 kg / mol into a fully dried reactor, wherein the mass ratio of polycaprolactone diol to polyethylene glycol is 5:25.

[0073] Under constant temperature and vacuum conditions, carry out sufficient dehydration and drying for more than 3 h. After the dehydration is completed, under nitrogen protection, gradually raise the temperature to above the melting point of the soft segment, and fully melt and stir the two soft segments in the reaction flask to mix them evenly.

[0074] Step 2: Under nitrogen protection, 1,6 - hexamethylene diisocyanate was slowly added to the mixture obtained in Step 1, where the molar ratio of the terminal hydroxyl groups of the diol to 1,6 - hexamethylene diisocyanate was 1:2. After reacting in an 80 °C oil bath for 1 h, an isocyanate - terminated prepolymer was obtained.

[0075] Step 3: Under nitrogen protection, DMF solvent was slowly added to the reaction system of Step 2 to reduce the viscosity of the system. After stirring well for 1 h, a dilute solution of the isocyanate - terminated prepolymer was obtained. Then, a DMF solution of EGCG was slowly added dropwise to the above - mentioned dilute solution, where the molar ratio of the terminal hydroxyl groups of the diol to the hydroxyl groups in EGCG was 1:1, and the concentration of EGCG was 0.2 g / mL. Under the condition of maintaining 80 °C, after reacting fully for 4 h, a polyurethane solution was obtained.

[0076] The polyurethane solution obtained in this example was poured into a pre - heated polytetrafluoroethylene mold. After volatilizing at 80 °C for 72 h and drying at room temperature in a vacuum oven for 12 h, a polyurethane film with both transparency, toughness and antibacterial properties was obtained.

[0077] To illustrate the properties of the polyurethane obtained in the present invention, the following tests were used to conduct static tensile tests, hardness tests and transmittance (transparency) tests on the obtained polyurethane samples. The specific test methods are as follows:

[0078] Static tensile test: Tensile specimens of 75×4×5 mm were cut from different sample films using a dumbbell - shaped cutter. Tensile property tests were carried out using an electronic universal testing machine (Gotech AI - 7000 - M) according to the method of GB / T 1040.3 - 2006. The tensile rate was 10 mm / min, and the room temperature was 25 °C; the sensor was 200 N for mechanical property tests. At least 3 parallel tests were carried out on each polyurethane film sample, and the average value was taken.

[0079] Hardness test: The hardness of the samples was tested using a Shore A durometer according to the national standard GB / 531 - 1999 "Test Method for Indentation Hardness of Rubber Pocket Hardness Tester". The set parameters were as follows: the test temperature was 25 °C, and at least 5 parallel determinations were carried out on each sample, and the median value was taken as the final test result.

[0080] Transmittance test: Rectangular strips of 50×20 mm were cut from the polyurethane film using scissors, and the transmittance was tested using an ultraviolet - visible absorption spectrometer (UV - 3600Plus Spectrophotometer). The scanning wavelength range was 200 - 700 nm, and the room temperature was 25 °C.

[0081] Transparency (Transparency value)= - logT 600 / d

[0082] T600 is the transmittance of the polyurethane film at 600 nm, and d is the thickness of the polyurethane film in mm.

[0083] Among them, Figure 1 is the picture taken of the polyurethane film samples obtained in Examples 3-5 of the present invention under natural light. The patterns and words under the film are clearly visible, indicating that the polyurethane has excellent transparency.

[0084] The ultraviolet-visible absorption spectrum was used to quantitatively test the transmittance of the samples in Examples 3-5. From Figure 2 it can be seen that the transmittance of the polyurethane film samples is above 80%. According to the above calculation formula, the transparency of the polyurethane film is between 0.8638 and 0.8072 (Table 1), and it shows an obvious ultraviolet blocking effect (especially UVB: 280-320 nm). This is because the EGCG structure contains unsaturated chromophores such as benzene rings, ketone groups, and conjugated carbonyl groups. These groups will absorb visible light, reduce the emissivity, and achieve the effect of ultraviolet blocking and filtering.

[0085] The specific transparency data is shown in Table 1:

[0086] Table 1. Transparency results of polyurethane films in Examples 3-5

[0087]

[0088] Furthermore, in order to compare and illustrate the influence of different mass ratios of the two soft segments on the mechanical properties of the polyurethane film, Comparative Example 1 (without adding polyethylene glycol soft segment at all, and other preparation steps are the same) was also synthesized according to the same preparation method. It can be seen from the mechanical property results of Examples 1-5 ( Figure 3 and Table 2) that under the condition that other synthesis conditions are the same, by adjusting the different mass ratios of the two soft segments, polyurethane film materials with excellent mechanical properties can be obtained. Their elongation at break is greater than 1000%, and the breaking stress is between 6.98 and 21.80 MPa. Thus, it can be seen that by adjusting conditions such as the different mass ratios of the two soft segments, the hard-soft segment ratio, and the molecular chain length of the soft segment, the mechanical properties of the polyurethane film material can be customized and adjusted to meet the use requirements of different packaging materials. As the addition amount of the polyethylene glycol soft segment increases, the strength and hardness of the polyurethane film gradually decrease, and the yield stress of the polyurethane film also gradually decreases, and the material properties gradually transform into an elastomer without yield. Thus, it can be explained that by adjusting the different mass ratios of the two soft segments, the transformation from a plastic material to an elastomer material can also be achieved, which expands the application field of polyurethane materials to a certain extent.

[0089] Table 2. Mechanical properties of polyurethane films in Examples 1-5

[0090]

[0091] Example 6

[0092] A preparation method of a polyurethane with both transparency, toughness and antibacterial properties, comprising the following steps:

[0093] Step 1: Add polycaprolactone diol with a number average molecular weight of 7 kg / mol and polyethylene glycol with a number average molecular weight of 2 kg / mol into a fully dried reactor, wherein the mass ratio of polycaprolactone diol to polyethylene glycol is 8:1.

[0094] Under constant temperature and vacuum conditions, dehydrate and dry for more than 3 h. After the water removal is completed, under nitrogen protection, gradually heat up to above the soft segment melting point, and fully melt and stir the two soft segments in the reaction flask to mix them evenly.

[0095] Step 2: Slowly add 1,6 - hexamethylene diisocyanate to the mixture obtained in Step 1 under nitrogen protection, wherein the molar ratio of the terminal hydroxyl groups of the diol to 1,6 - hexamethylene diisocyanate is 1:4. After reacting in an 80 °C oil bath for 1 h, an isocyanate - terminated prepolymer is obtained.

[0096] Step 3: Slowly add DMF solvent to the reaction system in Step 2 under nitrogen protection to reduce the viscosity of the system. After fully stirring for 1 h, a dilute solution of the isocyanate - terminated prepolymer is obtained. Then slowly dropwise add a DMF solution of EGC to the above dilute solution, wherein the molar ratio of the terminal hydroxyl groups of the diol to the hydroxyl groups in EGC is 1:3, and the concentration of EGC is 1.5 g / mL. Keep reacting at 80 °C for 4 h to obtain a polyurethane solution.

[0097] Pour the polyurethane solution obtained in this example into a pre - heated polytetrafluoro mold, volatilize at 80 °C for 72 h, and dry at room temperature in a vacuum oven for 12 h to obtain a polyurethane film with both transparency, toughness and antibacterial properties.

[0098] Example 7

[0099] A preparation method of a polyurethane with both transparency, toughness and antibacterial properties, comprising the following steps:

[0100] Step 1: Add polycaprolactone diol with a number average molecular weight of 1 kg / mol and polyethylene glycol with a number average molecular weight of 6 kg / mol into a fully dried reactor, wherein the mass ratio of polycaprolactone diol to polyethylene glycol is 1:9.

[0101] Under constant temperature and vacuum conditions, dehydrate and dry for more than 3 h. After the water removal is completed, under nitrogen protection, gradually heat up to above the soft segment melting point, and fully melt and stir the two soft segments in the reaction flask to mix them evenly.

[0102] Step 2: Under nitrogen protection, isophorone diisocyanate was slowly added to the mixture obtained in Step 1, where the molar ratio of the terminal hydroxyl groups of the diol to isophorone diisocyanate was 1:3. After reacting in an 80 °C oil bath for 1 h, an isocyanate-terminated prepolymer was obtained.

[0103] Step 3: Under nitrogen protection, ultradry DMSO solvent was slowly added to the reaction system of Step 2 to reduce the viscosity of the system. After stirring well for 1 h, a dilute solution of the isocyanate-terminated prepolymer was obtained. Then, a DMF solution of EC was slowly added dropwise to the above dilute solution, where the molar ratio of the terminal hydroxyl groups of the diol to the hydroxyl groups in EC was 1:2, and the concentration of EC was 1.8 g / mL. Under the condition of maintaining 80 °C, after reacting fully for 4 h, a polyurethane solution was obtained.

[0104] The polyurethane solution obtained in this example was poured into a preheated polytetrafluoro mold. After volatilizing at 90 °C for 48 h and drying at room temperature in a vacuum oven for 12 h, a polyurethane film with both transparency, toughness and antibacterial properties was obtained.

[0105] Example 8

[0106] A preparation method of a polyurethane with both transparency, toughness and antibacterial properties, comprising the following steps:

[0107] Step 1: Polycaprolactone diol with a number average molecular weight of 5 kg / mol and polyethylene glycol with a number average molecular weight of 3 kg / mol were added to a fully dried reactor, where the mass ratio of polycaprolactone diol to polyethylene glycol was 2:3.

[0108] Under constant temperature and vacuum conditions, water was removed and dried for more than 3 h. After the water removal was completed, under nitrogen protection, the temperature was gradually raised above the melting point of the soft segment, and the two soft segments in the reaction flask were fully melted and stirred and mixed evenly.

[0109] Step 2: Under nitrogen protection, L-lysine diisocyanate was slowly added to the mixture obtained in Step 1, where the molar ratio of the terminal hydroxyl groups of the diol to L-lysine diisocyanate was 1:2. After reacting in an 80 °C oil bath for 1 h, an isocyanate-terminated prepolymer was obtained.

[0110] Step 3: Under nitrogen protection, DMF solvent was slowly added to the reaction system of Step 2 to reduce the viscosity of the system. After stirring well for 1 h, a dilute solution of the isocyanate-terminated prepolymer was obtained. Then, a DMF solution of GC was slowly added dropwise to the above dilute solution, where the molar ratio of the terminal hydroxyl groups of the diol to the hydroxyl groups in GC was 1:1, and the concentration of GC was 0.1 g / mL. Under the condition of maintaining 80 °C, after reacting fully for 4 h, a polyurethane solution was obtained.

[0111] Pour the polyurethane solution obtained in this example into a preheated polytetrafluoroethylene mold, volatilize it at 80 °C for 72 h, and then dry it at room temperature in a vacuum oven for 12 h to obtain a polyurethane film that is both transparent, tough and antibacterial.

[0112] Example 9

[0113] A preparation method of polyurethane that is both transparent, tough and antibacterial, comprising the following steps:

[0114] Step 1: Add polycaprolactone diol with a number average molecular weight of 3 kg / mol and polyethylene glycol with a number average molecular weight of 8 kg / mol to a fully dried reactor, wherein the mass ratio of polycaprolactone diol to polyethylene glycol is 2:3.

[0115] Under constant temperature and vacuum conditions, dehydrate and dry for more than 3 h. After the dehydration is completed, under nitrogen protection, gradually heat up to above the melting point of the soft segment, and fully melt and stir the two soft segments in the reaction flask to mix them evenly.

[0116] Step 2: Slowly add 4,4'-dimethylmethane diisocyanate to the mixture obtained in Step 1 under nitrogen protection, wherein the molar ratio of the terminal hydroxyl group of the diol to 4,4'-dimethylmethane diisocyanate is 1:2.5. React in an 80 °C oil bath for 1 h to obtain an isocyanate-terminated prepolymer.

[0117] Step 3: Slowly add DMF solvent to the reaction system in Step 2 under nitrogen protection to reduce the viscosity of the system. After stirring well for 1 h, obtain a dilute solution of the isocyanate-terminated prepolymer. Then slowly dropwise add the DMF solution of C to the above dilute solution, wherein the molar ratio of the terminal hydroxyl group of the diol to the hydroxyl group in C is 1:1.5, and the concentration of C is 1.6 g / mL. Keep reacting at 80 °C for 4 h to obtain a polyurethane solution.

[0118] Pour the polyurethane solution obtained in this example into a preheated polytetrafluoroethylene mold, volatilize it at 80 °C for 72 h, and then dry it at room temperature in a vacuum oven for 12 h to obtain a polyurethane film that is both transparent, tough and antibacterial.

[0119] Example 10

[0120] A preparation method of polyurethane that is both transparent, tough and antibacterial, comprising the following steps:

[0121] Step 1: Add polycaprolactone diol with a number average molecular weight of 9 kg / mol and polyethylene glycol with a number average molecular weight of 6 kg / mol to a fully dried reactor, wherein the mass ratio of polycaprolactone diol to polyethylene glycol is 2:1.

[0122] Under constant temperature and vacuum conditions, dehydrate and dry for more than 3 hours. After the dehydration is completed, under nitrogen protection, gradually heat up to above the melting point of the soft segment, and fully melt and stir the two soft segments in the reaction flask to mix them evenly.

[0123] Step 2: Under nitrogen protection, slowly add 4,4'-dimethylmethane diisocyanate to the mixture obtained in Step 1, where the molar ratio of the terminal hydroxyl groups of the diol to 4,4'-dimethylmethane diisocyanate is 1:1.9. React in an 80°C oil bath for 1 hour to obtain an isocyanate-terminated prepolymer.

[0124] Step 3: Under nitrogen protection, slowly add DMF solvent to the reaction system in Step 2 to reduce the viscosity of the system. After stirring thoroughly for 1 hour, obtain a dilute solution of the isocyanate-terminated prepolymer. Then slowly dropwise add the DMF solution of GCG to the above dilute solution, where the molar ratio of the terminal hydroxyl groups of the diol to the hydroxyl groups in GCG is 1:0.9, and the concentration of GCG is 0.2 g / mL. Keep reacting at 80°C for 4 hours to obtain a polyurethane solution.

[0125] Pour the polyurethane solution obtained in this example into a preheated polytetrafluoroethylene mold, volatilize at 80°C for 72 hours, and dry at room temperature in a vacuum oven for 12 hours to obtain a polyurethane film with both transparency, toughness and antibacterial properties.

[0126] The present invention relates to a polyurethane modified by catechin compounds. Catechin compounds are used as chain extenders and introduced into the main chain structure of the polyurethane. On the one hand, it improves the bioavailability of catechin compounds and endows the polyurethane material with antibacterial, anti-inflammatory, and antioxidant effects. On the other hand, when catechin compounds are introduced into the main chain structure of the polyurethane as chain extenders, they react with isocyanates to form the hard segment part of the polyurethane. The content of the hard segment directly affects the physical and chemical properties of the polyurethane. Therefore, the hardness, toughness, and strength of the polyurethane film can be adjusted by changing the amount of catechin compounds introduced to meet the usage requirements of food packaging. More importantly, the catechin compound structure contains multiple hydroxyl reaction sites, which react with isocyanates to form the hard segment part of the polyurethane. There are intramolecular / intermolecular hydrogen bond interactions between the hard segments. The multiple hydroxyl reaction sites make the formed intramolecular / intermolecular hydrogen bond interactions more compact and the intermolecular force greater, endowing the material with more excellent mechanical properties. In addition, the catechin compound structure also contains unsaturated chromophores such as benzene rings, keto groups, and conjugated carbonyl groups. These groups absorb visible light and reduce the emissivity, thus achieving the effect of ultraviolet blocking and filtering. Using polycaprolactone diol and polyethylene glycol as the double soft segments of the polyurethane can not only freely adjust the hardness, mechanical properties, etc. of the polyurethane film material, but also customize and regulate the water vapor barrier performance, waterproof performance, structural stability, service life, etc. of the polyurethane film by utilizing the hydrophilic-hydrophobic differences and degradation rate differences between the polycaprolactone diol soft segment and the polyethylene glycol soft segment to meet the usage requirements of different food packaging materials. More importantly, when the polyurethane material is in use, as water molecules or bioenzyme molecules enter the material interior, the main chain of the polyurethane breaks, gradually releasing catechin compounds with antibacterial, anti-inflammatory, antioxidant, and other effects, preventing the packaging material from being contaminated by microorganisms during use and shortening the service life, endowing the film material with self-cleaning characteristics, and thus extending the service life.

Claims

1. A polyurethane having both transparency, toughness and antibacterial properties, characterized in that: The structure is as follows: Wherein: U is a diisocyanate residue, (R1) x is a polycaprolactone diol residue, (R2) y is a polyethylene glycol residue, EGCG is a catechin compound residue, x is an arbitrary integer from 10 to 100, and y is an arbitrary integer from 10 to 200.

2. The transparent, tough and antibacterial polyurethane according to claim 1, characterized in that: The polycaprolactone diol residue is obtained by polymerization of ε-caprolactone monomers, and has a number average molecular weight of 1 to 10 kg / mol.

3. The transparent, tough and antibacterial polyurethane according to claim 1, characterized in that: The diisocyanate residue is formed by the reaction of diisocyanate and diol soft segment, and the diisocyanate is one or two or more of 4,4'-dimethylmethane diisocyanate, 1,6-hexamethylene diisocyanate, L-lysine diisocyanate and isophorone diisocyanate.

4. The transparent, tough and antibacterial polyurethane according to claim 1, characterized in that: The number average molecular weight of the polyethylene glycol residue is 0.5 to 8 kg / mol.

5. The transparent, tough and antibacterial polyurethane according to claim 1, characterized in that: The catechin compound is one of the following structures:

6. The method for preparing a transparent, tough and antibacterial polyurethane according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1: After drying and removing water from polycaprolactone diol and polyethylene glycol, the mixture is heated to above the melting point under a protective atmosphere to be melted and fully mixed; Step 2: adding diisocyanate to the mixture obtained in step 1, and obtaining an isocyanate-terminated prepolymer after sufficient reaction; Step 3: Add a solvent to the prepolymer obtained in step 2, then dropwise add the catechin compound solution, and after sufficient reaction, evaporate the solvent to obtain the desired polyurethane.

7. The method for preparing a transparent, tough and antibacterial polyurethane according to claim 6, characterized in that: In the step 1, the mass ratio of polycaprolactone diol to polyethylene glycol is 1:0.1-1:10; the molar ratio of the terminal hydroxyl group of the diol, the isocyanate in the diisocyanate, and the hydroxyl group in the catechin compound is 0.5:1:0.5-1:4:

3.

8. The method for preparing a transparent, tough and antibacterial polyurethane according to claim 6, characterized in that: The reaction temperature in step 2 and step 3 is 80-100°C.

9. The method for preparing a transparent, tough and antibacterial polyurethane according to claim 6, characterized in that: The concentration of the catechin compound solution in step 3 is 0.1-2.0 g / mL.

10. The use of transparent, tough and antibacterial polyurethane as claimed in any one of claims 1 to 5, characterized in that: The polyurethane is prepared into a polyurethane film and used as a food packaging material.

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