Bio-based hydrophilic chain extender as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to a bio-based hydrophilic chain extender as well as a preparation method and application thereof. According to the invention, malic acid and allyl glycidyl ether are used as main raw materials to prepare the bio-based hydrophilic chain extender. Then, polyol, diisocyanate, a bio-based hydrophilic chain extender and a chain extender solution are used as main raw materials, and the bio-based waterborne polyurethane dispersion is prepared. A waterborne polyurethane material prepared from the bio-based hydrophilic chain extender disclosed by the invention has the potential of further UV curing cross-linking or functional modification while maintaining excellent basic performance. The bio-based hydrophilic chain extender is a bio-based raw material and replaces a petroleum-based hydrophilic chain extender, the bio-based content of waterborne polyurethane is remarkably increased, and the environment-friendly trend is better met.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a bio-based hydrophilic chain extender, its preparation method, and its application. Background Technology

[0002] With increasing global awareness of environmental protection and sustainable development, green and environmentally friendly practices have become a transformation trend in the polymer materials industry. Waterborne polyurethane, using water as the dispersion medium, boasts advantages such as low volatile organic compound content, safety and non-toxicity, adjustable performance, and strong adhesion. It is gradually replacing traditional solvent-based polyurethane and is widely used in coatings, adhesives, leather finishing, and inks. However, its performance is highly dependent on the introduced hydrophilic groups. Currently, the most commonly used hydrophilic chain extenders in the preparation of anionic waterborne polyurethane are dimethylolpropionic acid (DMPA) and dimethylolbutyric acid (DMBA). DMPA has a melting point as high as 189-191℃, and DMBA has a melting point of 108-115℃, both far exceeding the conventional reaction temperature for polyurethane synthesis (usually 60-90℃). DMPA and DMBA have inherent drawbacks of high melting point and low solubility, making them difficult to melt at the conventional temperatures for preparing waterborne polyurethane and prone to heterogeneous reactions during polymerization. To ensure the emulsion melts and participates uniformly in the reaction, researchers often promote the reaction by increasing the reaction temperature, extending the reaction time, or adding large amounts of organic solvents such as N-methylpyrrolidone for dissolution. This approach not only increases process complexity, cost, and environmental pollution, but also exacerbates energy consumption, increases the risk of side reactions, and results in a wider particle size distribution in the emulsion, thus affecting its storage stability. Therefore, developing a novel hydrophilic chain extender that is liquid at conventional reaction temperatures, easy to process, and exhibits excellent performance is of great significance for simplifying the preparation process of waterborne polyurethanes, reducing energy consumption and costs, and improving product performance. Summary of the Invention

[0003] The first objective of this invention is to provide a method for preparing a bio-based hydrophilic chain extender; the second objective of this invention is to provide a bio-based hydrophilic chain extender obtained by the method; and the third objective of this invention is to provide the application of the bio-based hydrophilic chain extender.

[0004] According to a first aspect of the present invention, a method for preparing a bio-based hydrophilic chain extender is provided, comprising the following steps: Malic acid, catalyst, and allyl glycidyl ether are mixed and reacted at 100-120℃ for 2-3 hours to obtain the product.

[0005] This invention utilizes a ring-opening reaction between the carboxyl group in malic acid and the epoxy group in allyl glycidyl ether. While consuming one carboxyl group, a new hydroxyl group is formed through epoxy ring-opening, ultimately yielding a bio-based hydrophilic chain extender (AGMA). During the consumption of the epoxy group in allyl glycidyl ether, the allyl double bond is retained in the AGMA molecule. Subsequently, when AGMA participates in polyurethane chain extension as a functional monomer, the double bond is simultaneously incorporated into the polyurethane backbone. Therefore, AGMA contains a carboxyl group, providing hydrophilicity; a hydroxyl group, participating in polyurethane chain extension; and an allyl double bond, providing modification sites. Thus, AGMA possesses a triple function of hydrophilicity, chain extension, and modifiability. This invention integrates hydrophilic groups, hydroxyl chain extension sites, and allyl double bonds into the same AGMA molecule, and then uses AGMA as a functional monomer in the polyurethane reaction. This avoids random reactions of functional groups, resulting in a more controllable reaction process, fewer byproducts, a narrower molecular weight distribution of the product, and higher molecular structural regularity.

[0006] In some embodiments, the catalyst is at least one selected from p-toluenesulfonic acid, triphenylphosphine, dibutyltin dilaurate, and triethylamine, and the amount used is 0.03%-0.2% of the sum of the mass of malic acid and allyl glycidyl ether.

[0007] In some embodiments, the mass ratio of allyl glycidyl ether to malic acid is (10-50):(10-60).

[0008] According to a second aspect of the present invention, a bio-based hydrophilic chain extender prepared by the above-described preparation method is provided.

[0009] According to a third aspect of the present invention, the application of the above-described bio-based hydrophilic chain extender in the preparation of bio-based waterborne polyurethane is provided.

[0010] According to a fourth aspect of the present invention, a method for preparing a bio-based aqueous polyurethane dispersion is provided, comprising the following steps: The polyol and diisocyanate are reacted at 60-90℃ for 2-3 hours, then the above-mentioned bio-based hydrophilic chain extender is added, and the reaction is carried out at 60-80℃ for 2-4 hours. After that, the temperature is lowered to below 50℃, solvent is added for dilution, and then a neutralizing agent is added for neutralization for 20-40 minutes. Then water is added for emulsification for 5-15 minutes, and then the chain extender solution is added for chain extension reaction. Emulsification is continued for 0.5-2 hours to obtain the final product.

[0011] In some embodiments, the polyol is at least one of polycarbonate diol, cashew nut shell oil polyol, castor oil, and palm oil polyol.

[0012] In some embodiments, the diisocyanate is at least one selected from isophorone diisocyanate, dicyclohexylmethane diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, and L-lysine diisocyanate.

[0013] In some embodiments, the solvent is at least one of acetone, 2-butanone, and N,N-dimethylacetamide.

[0014] In some embodiments, the neutralizing agent is at least one of triethylamine, dimethylethanolamine, aminoethylpiperazine, and ammonia.

[0015] In some embodiments, the chain extender solution is obtained by mixing a chain extender and water, wherein the chain extender is at least one of piperazine, ethylenediamine, isophorone diamine, and diethylenetriamine, and the mass ratio of the chain extender to water is 1:(3-6).

[0016] In some embodiments, the raw materials used, by mass parts, are: 5-30 parts of polyol, 2-6 parts of diisocyanate, 1-4 parts of bio-based hydrophilic chain extender, 10-40 parts of solvent, 0.8-3.6 parts of neutralizer, 35-60 parts of water, and 0.1-0.8 parts of chain extender solution.

[0017] According to a fifth aspect of the present invention, a bio-based aqueous polyurethane dispersion prepared by the above-described preparation method is provided.

[0018] According to a sixth aspect of the present invention, the above-described bio-based aqueous polyurethane dispersion is provided for use in the preparation of coatings, adhesives, leather finishing, inks, flexible sensors, wearable electronic products, biomedical products, smart packaging, and triboelectric nanogenerators.

[0019] The beneficial effects of this invention include: (1) This invention fully utilizes the bio-based properties of malic acid and the dual reactivity of allyl glycidyl ether to achieve the liquefaction of the hydrophilic chain extender, simplifying the production process of waterborne polyurethane and reducing energy consumption and dependence on auxiliary solvents. Waterborne polyurethane materials prepared using the bio-based hydrophilic chain extender of this invention retain excellent basic properties and possess the potential for further UV curing, crosslinking, or functional modification. Simultaneously, the natural properties of malic acid endow the bio-based hydrophilic chain extender with good biocompatibility potential, aligning with the development trend of green materials. The bio-based hydrophilic chain extender of this invention is a bio-based raw material, replacing petroleum-based hydrophilic chain extenders, significantly increasing the bio-based content of waterborne polyurethane, and better conforming to the green and environmentally friendly trend. This invention has practical application value for reducing the polymer materials industry's dependence on petroleum-based raw materials, reducing environmental pollution, and developing high-performance green chemicals.

[0020] (2) The bio-based hydrophilic chain extender of the present invention is in a liquid state at room temperature and can be dispersed without the addition of additional solvents, resulting in higher reaction efficiency and reduced VOC emissions. This alleviates the problems of poor solubility and uneven dispersion of traditional solid hydrophilic chain extenders, enabling a mild, homogeneous, and highly efficient reaction. Furthermore, the bio-based hydrophilic chain extender of the present invention retains the carbon-carbon double bonds of the raw material allyl glycidyl ether and the active groups such as hydroxyl and ester groups generated during the reaction. Therefore, the bio-based hydrophilic chain extender of the present invention not only has the functions of hydrophilic chain extension and internal emulsification, but also allows the carbon-carbon double bonds to crosslink with other monomers containing double bonds under initiator or UV irradiation, providing a structural basis for the subsequent preparation of high-performance materials such as UV-curable coatings. The uniform distribution of double bonds also imparts a more uniform crosslinking network to the coating film. The bio-based hydrophilic chain extender of the present invention can be widely used in traditional fields such as coatings, inks, and adhesives, and also shows excellent application prospects in cutting-edge fields such as green materials, UV-curable coatings, and biomedical polymer materials. Attached Figure Description

[0021] Figure 1 Fourier transform infrared spectra of allyl glycidyl ether (AGE), malic acid (MAL), and AGMA from Example 1.

[0022] Figure 2 The Fourier transform infrared spectra of the bio-based aqueous polyurethane dispersions of Examples 5-9 are shown.

[0023] Figure 3 The results are the storage stability test results of the bio-based aqueous polyurethane dispersions of Examples 5-9.

[0024] Figure 4 The fluorescence spectra of the bio-based aqueous polyurethane dispersions of Examples 5-9 are shown.

[0025] Figure 5 The mechanical properties of the films obtained from the bio-based aqueous polyurethane dispersions in Examples 5-9 are shown in the test results.

[0026] Figure 6 The results show the thermal stability test results of the films obtained from the bio-based waterborne polyurethane dispersions in Examples 5-9.

[0027] Figure 7 The results are the UV transmittance test results of the films obtained from the bio-based aqueous polyurethane dispersions in Examples 5-9.

[0028] Figure 8 The results are the water contact angle test results of the films obtained by the bio-based waterborne polyurethane dispersion system in Examples 5-9. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to embodiments. It is worth noting that the following embodiments are only for better explaining the content of the present invention and do not limit the scope of protection of the present invention. Process steps not disclosed in the embodiments are prior art. Unless otherwise specified, all raw materials are commercially available.

[0030] Example 1 The preparation method of the bio-based hydrophilic chain extender in this embodiment includes the following steps: 30g of allyl glycidyl ether was mixed with 33.6g of malic acid and 0.0636g of triethylamine and reacted at 110℃ for 2.5h to obtain a bio-based hydrophilic chain extender (hereinafter referred to as AGMA).

[0031] The Fourier transform infrared spectra of allyl glycidyl ether (AGE), malic acid (MAL), and AGMA in this embodiment are as follows: Figure 1 As shown. From Figure 1 It can be seen that in the initial stage of the reaction, 910 cm -1 The absorption peak appearing nearby corresponds to the characteristic vibrational peak of the epoxy group in allyl glycidyl ether, 1710 cm⁻¹. -1 The absorption peak at 910 cm⁻¹ corresponds to the stretching vibration of the carboxylic acid carbonyl group in malic acid; as the reaction continues, the peak at 910 cm⁻¹... -1 The characteristic peak of the epoxy group gradually weakens until it disappears completely, 1710 cm⁻¹ -1 The intensity of the C=O peak of the carboxylic acid at this point decreases, and it reaches approximately 1720-1730 cm⁻¹. -1 An absorption peak appears in the range, which is attributed to the C=O stretching vibration of the ester group (-COO-). This change indicates that the carboxyl group of malic acid underwent a ring-opening esterification reaction with the epoxy group of allyl glycidyl ether. Furthermore, at 3450 cm⁻¹... -1 The presence of a broad and strong characteristic absorption peak of hydroxyl (-OH) further confirms that the reaction produced the target product containing hydroxyl groups, a bio-based hydrophilic chain extender (AGMA).

[0032] Example 2 The preparation method of the bio-based hydrophilic chain extender in this embodiment includes the following steps: 10g of allyl glycidyl ether was mixed with 11.5g of malic acid and 0.00645g of dibutyltin dilaurate and reacted at 100℃ for 2h to obtain the bio-based hydrophilic chain extender (AGMA).

[0033] Fourier transform infrared spectroscopy was performed on the raw materials and products of Example 2. The results were similar to those of Example 1, and will not be repeated here to save space.

[0034] Example 3 The preparation method of the bio-based hydrophilic chain extender in this embodiment includes the following steps: 50g of allyl glycidyl ether was mixed with 58.75g of malic acid and 0.2175g of p-toluenesulfonic acid and reacted at 120℃ for 3h to obtain the bio-based hydrophilic chain extender (AGMA).

[0035] Fourier transform infrared spectroscopy was performed on the raw materials and products of Example 3. The results were similar to those of Example 1, and will not be repeated here to save space.

[0036] Example 4 The preparation method of the bio-based hydrophilic chain extender in this embodiment includes the following steps: 20g of allyl glycidyl ether was mixed with 23.6g of malic acid and 0.0645g of triphenylphosphine and reacted at 115℃ for 2.5h to obtain the bio-based hydrophilic chain extender (AGMA).

[0037] Fourier transform infrared spectroscopy was performed on the raw materials and products of Example 4. The results were similar to those of Example 1, and will not be repeated here to save space.

[0038] Example 5 The preparation method of the bio-based aqueous polyurethane dispersion in this embodiment includes the following steps: In a 250 mL reactor equipped with a stirrer, 10 g of polycarbonate diol (molecular weight 2000) was added, and the mixture was evacuated at 110 °C for 1 h. Then, the temperature was lowered to 85 °C, and 4.6 g of isophorone diisocyanate was added. The mixture was reacted at 85 °C for 2.5 h, then the temperature was lowered to 75 °C, and 1.2 g of the bio-based hydrophilic chain extender (AGMA) prepared in Example 1 was added. The mixture was reacted at 75 °C for 3 h, then the temperature was lowered to 45 °C, and 30 g of 2-butanone was added for dilution. Then, 0.8 g of triethylamine was added for neutralization for 30 min. Then, 56 g of deionized water was added and emulsified at 1000 rpm for 10 min. Then, 0.2 g of a chain extender solution obtained by mixing diethylenetriamine and water in a mass ratio of 1:3 was added to carry out the chain extension reaction. The emulsification was continued for 1 h to obtain the bio-based aqueous polyurethane dispersion.

[0039] Example 6 The preparation method of the bio-based aqueous polyurethane dispersion in this embodiment is basically the same as that in Example 5, except that the amount of AGMA added in this embodiment is 1.6g.

[0040] Example 7 The preparation method of the bio-based aqueous polyurethane dispersion in this embodiment is basically the same as that in Example 5, except that the amount of AGMA added in this embodiment is 2.0g.

[0041] Example 8 The preparation method of the bio-based aqueous polyurethane dispersion in this embodiment is basically the same as that in Example 5, except that the amount of AGMA added in this embodiment is 2.4g.

[0042] Example 9 The preparation method of the bio-based aqueous polyurethane dispersion in this embodiment is basically the same as that in Example 5, except that the amount of AGMA added in this embodiment is 2.8g.

[0043] Example 10 The preparation method of the bio-based aqueous polyurethane dispersion in this embodiment includes the following steps: In a 250 mL reactor equipped with a stirrer, 10 g of cashew nut shell oil polyol (purchased from Jining Mobei Chemical Co., Ltd., product model FX-9001LV) was added. The mixture was evacuated at 110°C for 1 hour, then cooled to 85°C. 5 g of toluene diisocyanate was added, and the mixture was reacted at 80°C for 2.5 hours. The mixture was then cooled to 75°C, and 2 g of the bio-based hydrophilic chain extender (AGMA) prepared in Example 2 was added. The mixture was reacted at 75°C for 3 hours, then cooled to 45°C. 30 g of 2-butanone was added for dilution, followed by 1.2 g of triethylamine for neutralization for 30 minutes. Then, 50 g of deionized water was added, and the mixture was emulsified at 1000 rpm for 10 minutes. Finally, 0.2 g of a chain extender solution obtained by mixing diethylenetriamine and water in a mass ratio of 1:4 was added to carry out the chain extension reaction. The mixture was further emulsified for 1 hour to obtain the bio-based waterborne polyurethane dispersion.

[0044] Example 11 The preparation method of the bio-based aqueous polyurethane dispersion in this embodiment includes the following steps: In a 250 mL reactor equipped with a stirrer, 10 g of castor oil was added, and the mixture was evacuated at 110 °C for 1 h. Then, the temperature was lowered to 85 °C, and 4.6 g of dicyclohexylmethane diisocyanate was added. The mixture was reacted at 90 °C for 3 h, and then the temperature was lowered to 75 °C. 2 g of the bio-based hydrophilic chain extender (AGMA) prepared in Example 3 was added, and the mixture was reacted at 75 °C for 3 h. Then, the temperature was lowered to 45 °C, and 30 g of acetone was added for dilution. Then, 1.46 g of dimethylethanolamine was added for neutralization for 30 min. Then, 50 g of deionized water was added and emulsified at 1000 rpm for 10 min. Then, 0.3 g of a chain extender solution obtained by mixing piperazine and water in a mass ratio of 1:5 was added to carry out the chain extension reaction. The emulsification was continued for 1 h to obtain the bio-based aqueous polyurethane dispersion.

[0045] Example 12 The preparation method of the bio-based aqueous polyurethane dispersion in this embodiment includes the following steps: In a 250 mL reactor equipped with a stirrer, 10 g of palm oil polyol (purchased from Shandong Moore Chemical Co., Ltd., hydroxyl value approximately 250 mgKOH / g) was added. The mixture was evacuated at 110°C for 1 h, then cooled to 85°C. 6 g of L-lysine diisocyanate was added, and the mixture was reacted at 90°C for 2.5 h. The mixture was then cooled to 75°C, and 2 g of the bio-based hydrophilic chain extender (AGMA) prepared in Example 4 was added. The mixture was reacted at 75°C for 3 h, then cooled to 45°C. 30 g of 2-butanone was added for dilution, followed by 1.3 g of aminoethylpiperazine for neutralization for 30 min. Then, 55 g of deionized water was added, and the mixture was emulsified at 1000 rpm for 10 min. Finally, 0.46 g of a chain extender solution obtained by mixing ethylenediamine and water in a 1:6 mass ratio was added for chain extension reaction. The mixture was further emulsified for 1 h to obtain the bio-based waterborne polyurethane dispersion.

[0046] The Fourier transform infrared spectra of the bio-based aqueous polyurethane dispersions in Examples 5-9 are as follows: Figure 2 As shown. From Figure 2 It can be seen that the product is at 2240 cm⁻¹ -1 The characteristic absorption peak of NCO near 3340 cm⁻¹ disappears. -1 and 1532 cm -1 The absorption peaks appearing at 1740 cm⁻¹ are the stretching and bending vibrations of NH₃, respectively. -1 A C=O stretching vibration peak appears at 1230 cm⁻¹. -1 The nearby peaks belong to the CO peaks of polyols, while the COC tensile vibrations of the polyether segment are located at 1101-944 cm⁻¹. -1 The area is at 2930cm. -1 and 1369 cm -1 The nearby spectral band corresponds to the CH antisymmetric stretching and bending vibrations of -CH3. At 2864 cm⁻¹ -1 and 1464cm -1 The absorption peaks at the specified locations are attributed to the symmetric stretching and bending vibrations of the methylene (-CH2) group, respectively. This analysis indicates the successful synthesis of the bio-based aqueous polyurethane dispersion.

[0047] Fourier transform infrared spectroscopy was performed on the bio-based waterborne polyurethane dispersions of Examples 10-12. The results were similar to those of Examples 5-9, and will not be repeated here for the sake of brevity.

[0048] In order to verify the performance of the bio-based aqueous polyurethane dispersion of the present invention, the performance of the bio-based aqueous polyurethane dispersion prepared in Examples 5-9 and the film obtained from the above-mentioned bio-based aqueous polyurethane dispersion were tested.

[0049] 1. Preparation of the adhesive film Weigh approximately 10g of the bio-based aqueous polyurethane dispersions prepared in Examples 5-9, place them in a petri dish, dry them at room temperature for 8 hours, and then dry them in an electric heating drying oven at 70°C for 12 hours to obtain a film.

[0050] 2. Storage stability test Centrifugal stability test: Take an appropriate amount of bio-based aqueous polyurethane dispersion and centrifuge it at 3000 r / min for 15 min using a high-speed centrifuge. If no obvious phase separation, precipitation or stratification occurs in the emulsion, it indicates that its storage stability is good.

[0051] Particle size analysis: The particle size distribution and zeta potential of the bio-based aqueous polyurethane dispersion were tested using a laser particle size analyzer.

[0052] The storage stability test results of the bio-based waterborne polyurethane dispersion are shown in Table 1 and Figure 3 As shown.

[0053] Table 1. Storage stability test results of bio-based waterborne polyurethane dispersions

[0054] Figure 3 Table 1 shows that as the AGMA content increases, the particle size of the bio-based waterborne polyurethane dispersion gradually decreases, and the Zeta potential is greater than -35 mV, indicating that the bio-based waterborne polyurethane dispersion prepared in this invention has good storage stability.

[0055] 3. Fluorescence spectroscopy test Test method: The emission behavior of the bio-based waterborne polyurethane dispersion in the 400-800 nm scanning range at an excitation wavelength of 365 nm was measured using an FS5 fluorescence spectrometer from Edinburgh Instruments Ltd., UK.

[0056] The fluorescence spectrum of the bio-based aqueous polyurethane dispersion is shown below. Figure 4 As shown. Figure 4The results show that, under different amounts of bio-based hydrophilic chain extender (AGMA), the fluorescence emission peaks of all bio-based aqueous polyurethane dispersion samples are concentrated in the 450-500 nm range. This is mainly because the C=O and NH groups of the urethane and amide bonds in the aqueous polyurethane undergo n-π* electronic transitions through aggregation and assembly with the carboxyl and hydroxyl groups introduced by AGMA, which is a cluster luminescence behavior characteristic of systems without traditional chromophores. The fluorescence intensity is initially enhanced and then weakened by the AGMA content. The bio-based aqueous polyurethane dispersion in Example 5 has the weakest fluorescence intensity because the AGMA content is low, resulting in insufficient density of polar groups that can form effective luminescent clusters in the system, leading to the weakest fluorescence intensity. As the AGMA content increases, the fluorescence intensity of Example 8 is the highest. This is because the carboxyl and hydroxyl groups provided by AGMA form clusters with a moderate number and uniform dispersion with the polar groups of the aqueous polyurethane itself. This structure can maximally restrict intramolecular movement, enhance orbital overlap, and optimize the radiative transition channels. When the AGMA content is further increased, the fluorescence intensity of Example 9 decreases. This is because excessive hydrophilic AGMA may destroy the original microphase separation structure of waterborne polyurethane, resulting in an excessively large hydrophilic cluster region or macrophase separation, which triggers the aggregation fluorescence quenching effect, destroys the electronic orbital overlap structure of the cluster compound, and thus reduces the fluorescence emission efficiency.

[0057] 4. Mechanical performance testing Test method: The tensile properties of the film were tested using a UTM 4204 universal testing machine manufactured by Shenzhen Sansi.

[0058] The mechanical property test results of the adhesive film are as follows: Figure 5 As shown. By Figure 5 It can be seen that as the AGMA content increases, the mechanical properties of the films obtained by the bio-based aqueous polyurethane dispersions in Examples 5-7 gradually improve. However, as the AGMA content continues to increase, the mechanical properties of the films obtained by the bio-based aqueous polyurethane dispersions in Examples 8-9 gradually decrease, while the elongation at break gradually increases. This is because when the AGMA content is low, its carboxyl groups enhance the film's density, and the hydroxyl and allyl double bonds moderately increase the crosslinking density, resulting in a significant improvement in the film's mechanical properties. Conversely, when the AGMA content is too high, the excess hydrophilic carboxyl groups disrupt the density of the hydrophobic network of the film. Simultaneously, the excessively high crosslinking density and the steric hindrance of the allyl double bonds negate the synergistic effect of the flexible structure, leading to a decrease in the film's mechanical properties. Furthermore, AGMA molecules introduce flexible structural units such as aliphatic carbon chains of malic acid and ester bonds generated by ring-opening reactions into the polyurethane system, enhancing the rotational ability of the molecular chains. Simultaneously, the dynamic hydrogen bond network formed by the hydroxyl groups in AGMA can release the molecular chain movement space under stress, synergistically improving the film's flexibility, thus increasing the elongation at break of the film.

[0059] 5. Thermal stability test Test method: The thermal stability of the film was tested using a thermogravimetric analyzer in a nitrogen atmosphere with a flow rate of 20 mL / min and a heating rate of 10℃ / min. The test temperature range was 35-600℃.

[0060] The thermal stability test results of the film are as follows Figure 6 As shown. By Figure 6 It can be seen that the decomposition of the films obtained by the bio-based aqueous polyurethane dispersion in Examples 5-9 is divided into three stages: decomposition of a small amount of solvent, decomposition of hard segments, and decomposition of soft segments. The decomposition is basically completed at 500°C.

[0061] 6. Ultraviolet transmittance test Test method: The transmittance of the film was measured using a UV-2600i (Shimadzu Advanced Scientific Corporation, Japan) in the wavelength range of 200-800 nm.

[0062] The UV transmittance test results of the film are as follows: Figure 7 As shown. By Figure 7 It is known that in the UVC band of 200-280 nm, the transmittance of all films is 0%, which can completely block ultraviolet light in this band. Therefore, they can be used as protective materials for disinfection and sterilization equipment. In the UVB and UVA sun protection band of 280-400 nm, the film obtained by the bio-based waterborne polyurethane dispersion in Example 5 exhibits the best ultraviolet blocking performance, with a transmittance of about 15% at 300 nm (UVB) and about 50% at 400 nm, which can effectively reduce the risk of sunburn and photoaging. In the visible light region of 550-800 nm, the transmittance of all films is above 80%, among which the transmittance of the films obtained by the bio-based waterborne polyurethane dispersion in Examples 6-9 is above 90%, with good transparency. Overall, the film obtained by the bio-based waterborne polyurethane dispersion in Example 5 has strong UV blocking properties and is suitable for protective applications such as sunscreen coatings; the films obtained by the bio-based waterborne polyurethane dispersion in Examples 6-9 have excellent transparency, providing a potential application basis for transparent packaging, optical device protection and other scenarios.

[0063] 7. Water contact angle test Test method: The water contact angle of the film surface was tested using a contact angle measuring instrument according to the national standard GB / T 30693-2014. Three measurements were taken, and the average value was used as the test result.

[0064] The water contact angle test results of the film are as follows Figure 8 As shown. By Figure 8It can be seen that the water contact angle of the film obtained by the bio-based aqueous polyurethane dispersion in Example 5 is approximately 95°. With the increase of AGMA content, the water contact angle of the film obtained by the bio-based aqueous polyurethane dispersion in Example 6 decreases to approximately 78°. The water contact angle of the film obtained by the bio-based aqueous polyurethane dispersion in Example 7 increases again. With further increases in AGMA content and hydrophilic group content, the water contact angle of the films obtained by the bio-based aqueous polyurethane dispersion in Examples 8-9 gradually decreases again. This is because AGMA, as a hydrophilic chain extender, theoretically enhances hydrophilicity, thereby reducing the contact angle. However, AGMA also promotes the increase of crosslinking density in the aqueous polyurethane, and the dense crosslinking network offsets some of the effect of the hydrophilic groups. Therefore, the contact angle does not continuously decrease with the increase of AGMA content.

[0065] The above descriptions are merely some specific embodiments of the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the inventive concept of the present invention, and all such modifications and improvements fall within the scope of protection of the present invention.

Claims

1. A method for preparing a bio-based hydrophilic chain extender, characterized in that, Includes the following steps: Malic acid, catalyst, and allyl glycidyl ether are mixed and reacted at 100-120℃ for 2-3 hours to obtain the product.

2. The preparation method according to claim 1, characterized in that, The catalyst is at least one of p-toluenesulfonic acid, triphenylphosphine, dibutyltin dilaurate, and triethylamine, and its amount is 0.03%-0.2% of the sum of the mass of malic acid and allyl glycidyl ether.

3. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of the allyl glycidyl ether to malic acid is (10-50):(10-60).

4. The bio-based hydrophilic chain extender prepared by the preparation method according to any one of claims 1-3.

5. The application of the bio-based hydrophilic chain extender according to claim 4 in the preparation of bio-based waterborne polyurethane.

6. A method for preparing a bio-based aqueous polyurethane dispersion, characterized in that, Includes the following steps: The polyol and diisocyanate are reacted at 60-90℃ for 2-3 hours, then the bio-based hydrophilic chain extender described in claim 4 is added, and the reaction is carried out at 60-80℃ for 2-4 hours. After that, the temperature is lowered to below 50℃, a solvent is added for dilution, and then a neutralizing agent is added for neutralization for 20-40 minutes. Then water is added for emulsification for 5-15 minutes, and then the chain extender solution is added for chain extension reaction. Emulsification is continued for 0.5-2 hours to obtain the final product.

7. The preparation method according to claim 6, characterized in that, The polyol is at least one of polycarbonate diol, cashew nut shell oil polyol, castor oil, and palm oil polyol; The diisocyanate is at least one of isophorone diisocyanate, dicyclohexylmethane diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, and L-lysine diisocyanate; The solvent is at least one of acetone, 2-butanone, and N,N-dimethylacetamide; The neutralizing agent is at least one of triethylamine, dimethylethanolamine, aminoethylpiperazine, and ammonia. The chain extender solution is obtained by mixing a chain extender and water, wherein the chain extender is at least one of piperazine, ethylenediamine, isophorone diamine, and diethylenetriamine, and the mass ratio of the chain extender to water is 1:(3-6).

8. The preparation method according to claim 6 or 7, characterized in that, The raw materials used, by mass, are: 5-30 parts of polyol, 2-6 parts of diisocyanate, 1-4 parts of bio-based hydrophilic chain extender, 10-40 parts of solvent, 0.8-3.6 parts of neutralizer, 35-60 parts of water, and 0.1-0.8 parts of chain extender solution.

9. A bio-based aqueous polyurethane dispersion prepared by the preparation method according to any one of claims 6-8.

10. The application of the bio-based aqueous polyurethane dispersion of claim 9 in the preparation of coatings, adhesives, leather finishing, inks, flexible sensors, wearable electronic products, biomedical products, smart packaging, and triboelectric nanogenerators.

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