Bio-based aqueous polyurethane emulsion, its preparation method and application

Abstract

The present invention discloses a bio-based aqueous polyurethane emulsion, its preparation method and application. It is prepared from a system composed of the following components in parts by weight: 100 to 120 parts of polytetramethylene ether glycol, 10 to 30 parts of 1,5-pentanediisocyanate, 10 to 40 parts of isophorone diisocyanate, 6 to 9 parts of hydrophilic chain extender, 0.4 to 3.5 parts of small molecule chain extender, 2.5 to 4 parts of amine chain extender, 0.5 to 1.5 parts of catalyst, and 5 to 6.5 parts of neutralizer. The prepared bio-based aqueous polyurethane emulsion has uniform droplet size, improves the stability of the bio-based aqueous polyurethane emulsion, and solves the problem of difficult emulsification caused by the high flexibility and regular chain segment structure of 1,5-pentanediisocyanate. Moreover, the bio-based aqueous polyurethane emulsion has good thermal stability and tensile strength after curing into a film, and can be used as a coating or adhesive in the leather or textile fields.

Description

Technical Field

[0001] The present invention relates to the technical field of aqueous polyurethane, and particularly relates to a bio-based aqueous polyurethane emulsion, a preparation method thereof, and an application thereof. Background Art

[0002] In the prior art, most of the polyols and isocyanates used in the production of polyurethanes are derived from petroleum resources. With the depletion of petroleum resources and the popularization of the ecological concept of green development, the disadvantages of traditional petroleum-based chemical materials have become increasingly prominent. Therefore, it is urgent to develop new green and environmentally friendly materials.

[0003] 1,5-Pentane diisocyanate (PDI) is a green material prepared from biomass such as corn straw, and has advantages such as high toughness and high carbon content, and is applied to industrial coatings, automobiles, printing and dyeing, military, aviation and other fields. However, in the prior art, the aqueous polyurethane emulsion developed based on PDI has poor stability, and the tensile strength of the cured aqueous polyurethane film is relatively low. Therefore, it has practical value to develop a bio-based aqueous polyurethane material with excellent mechanical properties. Summary of the Invention

[0004] The first object of the present invention is to provide a bio-based aqueous polyurethane emulsion to solve at least one of the above technical problems.

[0005] The second object of the present invention is to provide a preparation method of a bio-based aqueous polyurethane emulsion to solve at least one of the above technical problems.

[0006] The third object of the present invention is to provide an application of the bio-based aqueous polyurethane emulsion prepared by the above method.

[0007] According to the first aspect of the present invention, there is provided a bio-based aqueous polyurethane emulsion, which is prepared from a system formed by the following components in parts by weight: 100-120 parts of polytrimethylene ether glycol (PO3G), 10-30 parts of 1,5-pentane diisocyanate (PDI), 10-40 parts of isophorone diisocyanate (IPDI), 6-9 parts of hydrophilic chain extender, 0.4-3.5 parts of small molecule chain extender, 0.5-1.5 parts of catalyst, 5-6.5 parts of neutralizer, and 2.5-4 parts of amine chain extender.

[0008] The bio-based aqueous polyurethane emulsion of the present invention uses 1,5-pentamethylene diisocyanate and isophorone diisocyanate together as the hard segments of the bio-based aqueous polyurethane. The prepared bio-based aqueous polyurethane emulsion has higher emulsion stability. Compared with other aqueous polyurethanes, the bio-based aqueous polyurethane emulsion of the present invention has good tensile strength and thermal stability when cured into a film. At the same time, the use of a variety of bio-based materials reduces the use of petroleum resources, making it green and environmentally friendly.

[0009] In some embodiments, the molar ratio of 1,5-pentamethylene diisocyanate to isophorone diisocyanate is 1:(0.3 - 5). By adjusting the molar ratio of PDI to IPDI, a bio-based aqueous polyurethane emulsion with small particle size and high emulsion stability can be obtained.

[0010] In some embodiments, the number-average molecular weight of polytetramethylene ether glycol can be 1900 - 2100.

[0011] In some embodiments, the hydrophilic chain extender can be at least one of 2,2-dimethylolpropionic acid (DMPA), 2,2-dimethylolbutyric acid, bisphenol acid, or tartaric acid.

[0012] In some embodiments, the small molecule chain extender can be at least one of ethylene glycol, 1,3-propanediol (TMP), 1,4-butanediol (BDO), 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, isosorbide, or mannitol.

[0013] In some embodiments, the catalyst is at least one of organic bismuth or bismuth neodecanoate.

[0014] In some embodiments, the neutralizing agent is any one of triethylamine, sodium hydroxide, potassium hydroxide, ammonia water, dimethylaminoethanol, or triethanolamine.

[0015] In some embodiments, the amine chain extender can be at least one of isophorone diamine, ethylenediamine, or diethylenediamine.

[0016] According to the second aspect of the present invention, a method for preparing a bio-based aqueous polyurethane emulsion is provided. The preparation method includes the following steps:

[0017] S1. Add polytetramethylene ether glycol into a reactor and conduct a vacuum dehydration reaction on the polytetramethylene ether glycol in a nitrogen atmosphere. Then cool down to 60°C - 70°C, add isophorone diisocyanate and 1,5-pentane diisocyanate into the reactor, and carry out an isothermal reaction at 75 - 85°C for 1.5 - 3 h. Cool down to 55°C - 65°C, then add a hydrophilic chain extender, a small molecule chain extender and a catalyst into the reactor, and carry out an isothermal reaction at 75°C - 85°C for 1 - 5 h. Then add an organic solvent, and cool down to 50 - 55°C to obtain a bio-based polyurethane prepolymer;

[0018] S2. Add a neutralizing agent to neutralize the bio-based polyurethane prepolymer, add deionized water, conduct a first dispersion treatment, then add an amine chain extender and conduct a second dispersion treatment, and remove the organic solvent under vacuum at 40 - 55°C to obtain the product.

[0019] In the preparation method of the bio-based aqueous polyurethane emulsion of the present invention, two diisocyanates, 1,5-pentane diisocyanate and isophorone diisocyanate, are jointly added into the reaction system to form a prepolymer. The emulsifying property of isophorone diisocyanate is utilized to drive 1,5-pentane diisocyanate to participate in the emulsification reaction, improving the problem that it is difficult to emulsify 1,5-pentane diisocyanate due to its high toughness and regular chain segment structure, thereby improving the stability of the bio-based aqueous polyurethane emulsion.

[0020] In some embodiments, the catalyst can be at least one of organic bismuth or bismuth neodecanoate. The purpose of adding the catalyst is to accelerate the reaction rate of the isothermal reaction, ensure that the remaining isophorone diisocyanate monomer after step S1 can react completely with the system, and enable the hydrophilic chain extender to extend onto the bio-based polyurethane prepolymer.

[0021] In some embodiments, the organic solvent can be any one of acetone or methyl ethyl ketone. An organic solvent is added to the reaction system after the isothermal reaction to adjust the viscosity of the reaction system.

[0022] In some embodiments, in step S1, the treatment method of vacuum dehydration can be to conduct vacuum dehydration for 1 - 2 h under the conditions of a temperature of 100 - 120°C and a vacuum degree greater than 0.085 MPa.

[0023] In some embodiments, in step S1, after adding isophorone diisocyanate and 1,5-pentane diisocyanate into the reactor, the isothermal reaction is controlled at a temperature of 75 - 85°C to avoid the reaction system getting out of control and causing a polymerization explosion due to the difference in reaction activity between 1,5-pentane diisocyanate and isophorone diisocyanate.

[0024] In some embodiments, in step S2, the neutralization reaction time can be 8 - 12 min.

[0025] In some embodiments, in step S2, the method of the first dispersion treatment may be to process in a high-speed disperser at a rotation speed of 1800 - 2200 r / min for 4 - 6 min.

[0026] In some embodiments, in step S2, the method of the second dispersion treatment may be to react in a high-speed disperser at a rotation speed of 900 - 1100 r / min for 0.8 - 1.2 h.

[0027] According to the third aspect of the present invention, there is provided the application of the bio-based aqueous polyurethane emulsion in coatings and adhesives. Specifically, it can be used as a coating or an adhesive in the leather or textile field.

[0028] The beneficial effects of the present invention include:

[0029] (1) The bio-based aqueous polyurethane emulsion prepared by the present invention using isophorone diisocyanate and 1,5-pentane diisocyanate as raw materials has uniform emulsion droplet size, improves the problem of difficult emulsification caused by the high flexibility and regular chain segment structure of 1,5-pentane diisocyanate, and improves the stability of the bio-based aqueous polyurethane emulsion;

[0030] (2) The bio-based aqueous polyurethane emulsion of the present invention uses polytrimethylene glycol and 1,5-pentane diisocyanate as raw materials, reduces the use of non-renewable petroleum resources, is green and environmentally friendly, and the cured film obtained by curing the aqueous polyurethane emulsion has good tensile strength and thermal stability. Description of the Drawings

[0031] Figure 1 It is the infrared spectrum diagram of the bio-based aqueous polyurethane emulsions prepared in Examples 1 - 4 of the present invention and the bio-based PDI aqueous polyurethane emulsion prepared in Comparative Example 1;

[0032] Figure 2 It is the infrared spectrum comparison diagram of the bio-based aqueous polyurethane emulsions prepared in Examples 1 - 2 of the present invention and the bio-based PDI aqueous polyurethane emulsion prepared in Comparative Example 1;

[0033] Figure 3 It is the particle size curve diagram of the aqueous polyurethane emulsions prepared in Examples 1 - 4 and Comparative Example 1 of the present invention;

[0034] Figure 4 It is the stress-strain curve of the cured film of the aqueous polyurethane emulsions prepared in Examples 1 - 4 and Comparative Example 1 of the present invention;

[0035] Figure 5 It is the TGA curve of the cured film formed by curing the bio-based aqueous polyurethane emulsions prepared in Examples 1 and 2 of the present invention;

[0036] Figure 6 The DTG curve of the cured film after the bio-based aqueous polyurethane emulsion prepared in Examples 1 and 2 of the present invention is cured into a film. Detailed implementation manners

[0037] The present invention will be further described in detail below with reference to the accompanying drawings, but the implementation manners of the present invention are not limited thereto. The raw materials and reagents involved in the following examples are all commercially available.

[0038] Example 1

[0039] This example provides a preparation method of a bio-based aqueous polyurethane emulsion, including the following steps:

[0040] In a nitrogen atmosphere, 110 parts of PO3G (number average molecular weight of 2000) are added to a reaction kettle. Under the conditions of a temperature of 120 °C and a vacuum degree greater than 0.085 MPa, the dehydration reaction is carried out for 2 h, and then the temperature is lowered to 65 °C. 20 parts of PDI and 12 parts of IPDI (n(PDI) / n(IPDI) = 2.5) are added to the reaction kettle, and after reacting at a constant temperature of 85 °C for 2 h, the temperature is lowered to 60 °C. 8.1 parts of DMPA, 0.4 parts of TMP, and 1 part of bismuth neodecanoate are added, and then the temperature is raised to 75 °C and the reaction is carried out at a constant temperature for 5 h. Acetone is added, and the temperature is lowered to 50 °C. Then 6.3 parts of triethylamine are added to the reaction kettle for a neutralization reaction for 10 min, and then 200 g of deionized water is added. After high-speed dispersion at a speed of 2000 r / min for 5 min, 2.8 parts of diethylenediamine are added, and then low-speed dispersion is carried out at a speed of 1000 r / min for 1 h. After the emulsification reaction is completed, acetone is removed at 45 °C to obtain the product.

[0041] The product obtained in Example 1 was subjected to infrared detection, and the infrared spectrum is as Figure 1 shown. From Figure 1 it can be seen that the characteristic absorption peak of the product at 2270 cm -1 disappears (-N = C = O), indicating that the isocyanate group of PDI reacts completely with the hydroxyl group of PO3G. The absorption peaks appearing at 3340 cm -1 and 1532 cm -1 are the stretching vibration and bending vibration of N-H respectively. The absorption peak appearing at 1720 cm -1 is attributed to the stretching vibration of C = O in the carbonyl group, which is the result of hydrogen bonding and dipole-dipole interaction. The peak at 1100 cm -1 belongs to the stretching vibration peak of C-O-C in the ester group. The spectral bands near 2930 cm -1 and 1369 cm -1 correspond to the antisymmetric stretching and bending vibrations of C-H of -CH3. The spectral bands at 2864 cm -1 and 1464 cm -1The absorption peaks at [specific positions] are respectively attributed to the symmetric stretching vibration and bending vibration of the methylene (-CH2-) group. The above data indicate the successful synthesis of the bio-based aqueous polyurethane emulsion.

[0042] Example 2

[0043] This example provides a preparation method of a bio-based aqueous polyurethane emulsion, which includes the following steps:

[0044] Add 110 parts of PO3G (number average molecular weight is 2000) into the reaction kettle under a nitrogen atmosphere. Under the conditions of a temperature of 115 °C and a vacuum degree greater than 0.085 MPa, carry out a dehydration reaction under reduced pressure for 2 h, then cool down to 65 °C. Add 14 parts of PDI and 20 parts of IPDI (n(PDI) / n(IPDI) = 1.0) into the reaction kettle. After reacting at a constant temperature of 85 °C for 2 h, cool down to 60 °C, add 8 parts of DMPA, 0.4 part of TMP and 0.5 part of bismuth neodecanoate, then raise the temperature to 85 °C and react at a constant temperature for 4 h. Add acetone, cool down to 50 °C, then add 5.3 parts of triethylamine into the reaction kettle for a neutralization reaction for 10 min, then add 200 g of deionized water, disperse at a high speed of 2000 r / min for 5 min, then add 3 parts of diethylenediamine, and then disperse at a low speed of 1000 r / min for 1 h. After completing the emulsification reaction, remove acetone at 45 °C to obtain the product.

[0045] The product obtained in Example 2 was subjected to infrared detection, and the infrared spectrum is as Figure 1 shown. It can be seen from Figure 1 that its characteristic peaks are consistent with those in Example 1, which also indicates the successful synthesis of the bio-based aqueous polyurethane emulsion.

[0046] Example 3

[0047] This example provides a preparation method of a bio-based aqueous polyurethane emulsion, which includes the following steps:

[0048] Add 110 parts of PO3G (number-average molecular weight of 2000) into a reaction kettle under a nitrogen atmosphere. Under the conditions of a temperature of 115 °C and a vacuum degree greater than 0.085 MPa, carry out a dehydration reaction under reduced pressure for 1 - 2 h, cool down to 65 °C, add 14 parts of PDI and 28 parts of IPDI (n(PDI) / n(IPDI) = 0.72) into the reaction kettle, keep the temperature constant at 78 °C for 2 h and then cool down to 60 °C, add 8.4 parts of DMPA, 3 parts of BDO and 0.5 part of bismuth neodecanoate, then raise the temperature to 85 °C, keep the temperature constant for 4 h, add acetone, cool down to 50 °C, then add 6.1 parts of triethylamine into the reaction kettle for a neutralization reaction for 10 min, add 200 g of deionized water, disperse at a high speed of 2000 r / min for 5 min and then add 4 parts of diethylenediamine, and then disperse at a low speed of 1000 r / min for 1 h. After completing the emulsification reaction, remove acetone at 45 °C to obtain the product.

[0049] The product obtained in Example 3 was subjected to infrared detection, and the infrared spectrum is as Figure 1 shown. From Figure 1 it can be seen that its characteristic peaks are consistent with those in Example 1, which also indicates the successful synthesis of the bio-based aqueous polyurethane emulsion.

[0050] Example 4

[0051] This example provides a preparation method of a bio-based aqueous polyurethane emulsion, including the following steps:

[0052] Add 110 parts of PO3G (number-average molecular weight of 2000) into a reaction kettle under a nitrogen atmosphere. Under the conditions of a temperature of 120 °C and a vacuum degree greater than 0.085 MPa, carry out a dehydration reaction under reduced pressure for 2 h, cool down to 65 °C, add 10 parts of PDI and 40 parts of IPDI (n(PDI) / n(IPDI) = 0.3) into the reaction kettle, keep the temperature constant at 78 °C for 2 h and then cool down to 60 °C, add 8 parts of DMPA, 3 parts of BDO and 1.5 parts of bismuth neodecanoate, then raise the temperature to 75 °C, keep the temperature constant for 5 h, add acetone, cool down to 50 °C, then add 6.1 parts of triethylamine into the reaction kettle for a neutralization reaction for 10 min, add 200 g of deionized water, disperse at a high speed of 2000 r / min for 5 min and then add 4 parts of diethylenediamine, and then disperse at a low speed of 1000 r / min for 1 h. After completing the emulsification reaction, remove acetone at 45 °C to obtain the product.

[0053] The product obtained in Example 4 was subjected to infrared detection, and the infrared spectrum is as Figure 1 shown. From Figure 1 it can be seen that its characteristic peaks are consistent with those in Example 1, which also indicates the successful synthesis of the bio-based aqueous polyurethane emulsion.

[0054] Comparative Example 1

[0055] This comparative example provides a method for preparing a bio-based PDI aqueous polyurethane emulsion, which includes the following steps:

[0056] In a nitrogen atmosphere, 110 parts of PO3G (number average molecular weight of 2000) are added to a reaction kettle. Under the conditions of a temperature of 115 °C and a vacuum degree greater than 0.085 MPa, dehydration reaction is carried out under reduced pressure for 2 h. After cooling to 65 °C, 36 parts of PDI are added to the reaction kettle, and a constant temperature reaction is carried out at 78 °C for 2 h. Then, 6.6 parts of DMPA, 3 parts of BDO, and 0.5 part of bismuth neodecanoate are added, and the temperature is raised to 85 °C for a constant temperature reaction of 4 h. Acetone is added, and after cooling to 50 °C, 4.8 parts of triethylamine are added to the reaction kettle for a neutralization reaction for 10 min. Then, 200 g of deionized water is added, and high-speed dispersion is carried out at a rotation speed of 2000 r / min for 5 min, and then 4 parts of diethylenediamine are added. Subsequently, low-speed dispersion is carried out at a rotation speed of 1000 r / min for 1 h. After the emulsification reaction is completed, acetone is removed at 45 °C to obtain the product.

[0057] The product obtained in Comparative Example 1 was subjected to infrared detection, and the infrared spectrum is as Figure 1 and Figure 2 shown. It can be seen from Figure 1 that its characteristic peaks are consistent with those of Example 1, which also indicates the successful synthesis of the bio-based PDI aqueous polyurethane emulsion. The infrared spectra of the products of Example 1, Example 2, and Comparative Example 1 were compared ( Figure 2 ). It can be seen from Figure 2 that compared with Example 1 and Example 2, the absorbance of the characteristic absorption peak caused by the N-H stretching vibration at 3340 cm -1 and the characteristic absorption peak caused by the symmetric stretching vibration of methylene at 2864 cm -1 of the infrared spectrum curve of Comparative Example 1 is significantly reduced. This is because the high crystallinity of PDI and the regular structure arrangement result in the restriction of the vibration mode of the product of Comparative Example 1 compared with the products of the examples, thus leading to the reduction of the absorbance of the characteristic absorption peak.

[0058] Experimental Example 1

[0059] In this experimental example, the particle size distribution and Zeta potential of the bio-based aqueous polyurethane emulsions prepared in Examples 1 to 4 and the bio-based PDI aqueous polyurethane emulsion prepared in Comparative Example 1 were detected. The particle size distribution results are as Figure 3 shown, and the values of the Zeta potential are shown in Table 1. It can be seen from Figure 3It can be seen that for the bio-based PDI aqueous polyurethane emulsion prepared in Comparative Example 1, due to the relatively large proportion of PDI, it is difficult to emulsify the emulsion, so the particle size distribution is relatively wide. At the same time, due to the strong flexibility of PDI, the intensity of its particle size curve is relatively low. Compared with the bio-based PDI aqueous polyurethane emulsion of Comparative Example 1, the intensity of the particle size curve of the bio-based aqueous polyurethane emulsions prepared in Examples 1 to 4 increases, and the particle size distribution becomes narrower, indicating that the droplet size of the bio-based aqueous polyurethane emulsion prepared by the preparation method of the present invention is more uniform, thereby enhancing the stability of the interfacial film and contributing to improving the emulsion stability. With the addition of a small amount of IPDI, the emulsion particle sizes of Examples 1 and 2 are smaller than that of Comparative Example 1, indicating that combining the rigidity of IPDI with the flexibility of PDI can provide emulsion stability. As the proportion of IPDI in the ratio of IPDI and PDI increases, the particle size of the bio-based aqueous polyurethane emulsion increases. Among them, the particle sizes of the bio-based aqueous polyurethane emulsions prepared in Examples 3 and 4 are larger than that of Comparative Example 1, indicating that the particle size of the bio-based aqueous polyurethane emulsion is affected by the molar ratio of IPDI to PDI. Due to the rigid cycloaliphatic structure of isophorone diisocyanate increasing the spatial volume of the molecular chain, the smaller the molar ratio of PDI to IPDI, the larger the particle size of the emulsion. As can be seen from Table 1, the absolute values of the Zeta potential of the bio-based aqueous polyurethane emulsions prepared in Examples 1 to 4 are all greater than 50, indicating that the bio-based aqueous polyurethane emulsion prepared by using isophorone diisocyanate and 1,5-pentane diisocyanate as raw materials together has more excellent stability than the bio-based PDI aqueous polyurethane emulsion prepared by using 1,5-pentane diisocyanate as the raw material alone. In addition, the polydispersity index of the bio-based aqueous polyurethane emulsions prepared in Examples 1 to 4 is less than 0.3, indicating that they have good dispersibility.

[0060] Table 1 Zeta potential and polydispersity index of bio-based aqueous polyurethane emulsions

[0061] Sample Zeta potential (mV) Polydispersity index Example 1 62±1.74 0.144±0.002 Example 2 57.8±2.34 0.147±0.004 Example 3 56±2.68 0.142±0.002 Example 4 52.3±2.24 0.248±0.004 Comparative Example 1 33.3±0.71 0.299±0.003

[0062] Experimental Example 2

[0063] Weigh 10 g of the bio-based aqueous polyurethane emulsions prepared in Examples 1 to 4 and the bio-based PDI aqueous polyurethane emulsion prepared in Comparative Example 1 and place them in a petri dish. Dry the petri dish at room temperature for 24 h, and then place the petri dish in an electrothermal constant temperature forced air drying oven at 60 °C for 12 h to obtain a cured film.

[0064] In this experimental example, the cured films obtained in the above steps were subjected to tensile property tests, and the results are as Figure 4 and shown in Table 2. From Figure 4As can be seen from Table 2, the tensile strength of the cured film of biobased PDI aqueous polyurethane in Comparative Example 1 is the lowest and the elongation at break is the highest, with the elongation at break being 1145%. This is because PDI has high flexibility and a highly regular chain segment structure, resulting in high crystallinity and difficulty in emulsification, making the cured film of biobased PDI aqueous polyurethane have high flexibility. Compared with the cured film of Comparative Example 1, the tensile strength of the cured films of Examples 1 to 4 is significantly improved. Among them, the tensile strength of the biobased aqueous polyurethane cured film with a molar ratio of isophorone diisocyanate to 1,5-pentane diisocyanate of 1:1 is greatly increased from 0.06 MPa to 0.73 MPa, indicating that the addition of isophorone diisocyanate can improve the tensile strength of the biobased aqueous polyurethane cured film. With the continuous increase in the content of isophorone diisocyanate, the tensile strength of its cured film continuously increases and the elongation at break continuously decreases. This is because the rigid structure of isophorone diisocyanate can endow the cured film with stronger tensile strength. By controlling the molar ratio of 1,5-pentane diisocyanate and isophorone diisocyanate, a biobased aqueous polyurethane cured film with the required tensile properties can be formulated.

[0065] Mechanical properties of the cured film in Table 2

[0066] Sample Tensile strength (MPa) Elongation at break (%) Example 1 0.4 819 Example 2 0.73 657 Example 3 0.8 532 Example 4 0.98 496 Comparative Example 1 0.06 1145

[0067] Experimental Example 3

[0068] In this experimental example, a TG 209F1 Libra type thermogravimetric analyzer was used. In a nitrogen atmosphere with a flow rate of 20 mL·min -1 and a heating rate of 10 °C·min -1 , the test temperature range was 25 °C to 800 °C, and the thermal stability analysis of the cured films obtained by curing the biobased aqueous polyurethane emulsions prepared in Example 1 and Example 2 was carried out. The results are as shown in Figure 5 and Figure 6 . As can be seen from Figure 5 and Figure 6It can be seen that the thermal degradation of the cured film is roughly divided into two stages. The first stage is the degradation of the hard segment, and the second stage is the degradation of the soft segment. The maximum decomposition temperature of Example 1 is about 411 °C, and that of Example 2 is about 395 °C, indicating that the cured film has good thermal stability. Among them, the degradation temperature of the first stage and the second stage of Example 1 are both higher than those of Example 2. This is because IPDI is an alicyclic isocyanate and PDI is an aliphatic isocyanate. PDI has higher regularity, resulting in a higher maximum decomposition temperature of Example 1. In addition, in this temperature range, the char residue rates of the cured films of the bio-based aqueous polyurethane emulsions of Example 1 and Example 2 are measured to be 2.44% and 0.79% respectively. The above results show that the selection of the molar ratio of IPDI to PDI has a certain influence on the thermal stability of the bio-based aqueous polyurethane emulsion.

[0069] Therefore, compared with the prior art, the beneficial effects of the present invention are as follows: Isophorone diisocyanate and 1,5-pentane diisocyanate are used together as diisocyanates to react with polytrimethylene glycol to prepare a bio-based aqueous polyurethane emulsion. The emulsion droplets of this emulsion are relatively uniform in size, and the emulsion has good stability. Moreover, it solves the problem of difficult emulsification of PDI during the preparation of 1,5-pentane diisocyanate aqueous polyurethane emulsion. At the same time, the present invention reduces the use of petroleum resources as raw materials, which is green and environmentally friendly. In addition, the cured film formed by curing the bio-based aqueous polyurethane emulsion of the present invention has good tensile properties and thermal stability.

[0070] The above are only some embodiments of the present invention. For those of ordinary skill in the art, without departing from the creative concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

**1. A bio-based waterborne polyurethane emulsion, characterized in that it is prepared from a system comprising the following components in parts by weight: 100–120 parts of Polytrimethylene Ether Glycol, 10–30 parts of 1,5-pentamethylene diisocyanate, 10–40 parts of isophorone diisocyanate, 6–9 parts of a hydrophilic chain extender, 0.4–3.5 parts of a small molecule chain extender, 2.5–4 parts of an amine chain extender, 0.5–1.5 parts of a catalyst, and 5–6.5 parts of a neutralizing agent; the hydrophilic chain extender is at least one of 2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid, diphenolic acid, or tartaric acid; the small molecule chain extender is at least one of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, isosorbide, or mannitol; the amine chain extender is at least one of isophorone diamine, ethylenediamine, or diethylenediamine.****2. The bio-based waterborne polyurethane emulsion according to claim 1, characterized in that the Polytrimethylene Ether Glycol has a number-average molecular weight of 1900–2100.****3. The bio-based waterborne polyurethane emulsion according to claim 1 or 2, characterized in that the catalyst is an organic bismuth catalyst.****4. The bio-based waterborne polyurethane emulsion according to claim 3, characterized in that the neutralizing agent is any one of triethylamine, sodium hydroxide, potassium hydroxide, ammonia water, dimethylaminoethanol, or triethanolamine.****5. A method for preparing the bio-based waterborne polyurethane emulsion according to any one of claims 1–4, characterized in that the preparation method comprises the following steps:****S1. adding Polytrimethylene Ether Glycol to a reactor and subjecting it to a vacuum dehydration reaction under a nitrogen atmosphere, then cooling to 60°C–70°C, adding isophorone diisocyanate and 1,5-pentamethylene diisocyanate to the reactor, reacting at a constant temperature of 75–85°C for 1.5–3 h, cooling to 55°C–65°C, then adding the hydrophilic chain extender, the small molecule chain extender, and the catalyst to the reactor, reacting at a constant temperature of 75°C–85°C for 1–5 h, then adding an organic solvent, cooling to 50–55°C, to obtain a bio-based polyurethane prepolymer;****S2. adding the neutralizing agent to the bio-based polyurethane prepolymer for neutralization, adding deionized water, performing a first dispersion treatment, then adding the amine chain extender and performing a second dispersion treatment, and removing the organic solvent under vacuum at 40–55°C, to obtain the emulsion;****wherein the organic solvent is either acetone or methyl ethyl ketone.****6. The method for preparing the bio-based waterborne polyurethane emulsion according to claim 5, characterized in that in step S1, the vacuum dehydration treatment is carried out at a temperature of 100–120°C and a vacuum degree greater than 0.085 MPa for 1–2 h.****7. The method for preparing the bio-based waterborne polyurethane emulsion according to claim 5, characterized in that in step S2, the neutralization reaction time is 8–12 min; the first dispersion treatment is carried out in a high-speed disperser at a rotational speed of 1800–2200 r / min for 4–6 min; the second dispersion treatment is carried out in a high-speed disperser at a rotational speed of 900–1100 r / min for 0.8–1.2 h.****8. Use of the bio-based waterborne polyurethane emulsion according to any one of claims 1–4 in the field of coatings or adhesives.**

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