Hydrophilic chain extender and its preparation method and application, high-toughness recyclable preservative type bio-based waterborne polyurethane

Abstract

The application discloses a hydrophilic chain extender, a preparation method thereof, a high-toughness recyclable anti-corrosion bio-based waterborne polyurethane and a preparation method thereof. The preparation method of the hydrophilic chain extender comprises the following steps: reacting serinol with succinic anhydride at 50-70 DEG C for 3-4 h. The preparation method uses bio-based serinol and succinic anhydride as raw materials, is simple and green, does not use heavy metal catalysts, and is suitable for industrial continuous production. The hydrophilic chain extender prepared by the preparation method has high-activity primary hydroxyl groups, carboxyl groups and amide bonds, can control the microphase structure of the waterborne polyurethane, and can be used for preparing the high-toughness recyclable anti-corrosion bio-based waterborne polyurethane. The obtained bio-based waterborne polyurethane realizes the performance synergy of high strength, high toughness, self-repair and the like.

Description

Technical Field

[0001] This invention belongs to the field of waterborne polymer materials technology, specifically relating to hydrophilic chain extenders and their preparation methods and applications, and high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane. Background Technology

[0002] Traditional polyurethane (PU) is widely used in coatings, adhesives, sealants, elastomers, foams, automotive, and construction industries due to its broad physical, chemical, mechanical properties and durability. Waterborne polyurethane (WPU), using water as the dispersion medium, has great development potential due to its advantages such as low volatile organic compound (VOC) content, high environmental safety, and convenient construction. Currently, bio-based waterborne polyurethane (WPU) has attracted widespread attention from researchers due to its advantages of sustainability, durability, and low toxicity, aligning with the trend of green development. However, the current preparation of commercial WPU still heavily relies on petroleum-based products, which restricts its green upgrading process. As a core component of the waterborne polyurethane system, the hydrophilic chain extender directly determines the dispersion effect of polyurethane in water, thus having a key impact on the mechanical properties, stability, and functional characteristics of the final product. In the preparation of anionic waterborne polyurethane, the hydrophilic chain extender is the most important type of internal emulsifier, with dimethylolpropionic acid (DMPA) and dimethylolbutyric acid (DMBA) being the most widely used traditional hydrophilic chain extenders. However, DMPA and DMBA have melting points of 189-191℃ and 108-115℃, respectively, exhibiting inherent drawbacks of high melting points and low solubility. They are difficult to melt at conventional temperatures used in the preparation of waterborne polyurethanes and are prone to heterogeneous reactions during polymerization. Researchers often promote the reaction by increasing the reaction temperature and extending the reaction time. This approach not only increases process complexity and cost but also affects the storage stability of the emulsion. Currently, most research methods still face problems such as cumbersome raw material pretreatment procedures, high-temperature reaction conditions, long reaction times, and complex processes, posing certain difficulties for practical industrial applications. Existing bio-based hydrophilic chain extenders mostly focus on improving emulsification performance, lacking control over their structure and failing to achieve synergistic effects of multiple properties such as toughness, corrosion resistance, recyclability, and self-assembly.

[0003] Therefore, the development of novel bio-based hydrophilic chain extenders and waterborne polyurethanes has broad application prospects. Summary of the Invention

[0004] The first objective of this invention is to provide a hydrophilic chain extender and its preparation method, by simultaneously introducing amide and carboxyl functional groups into the hydrophilic chain extender through molecular design and synthesis, thereby constructing an ideal monomer for a novel internal emulsifier with both reactivity and hydrophilicity. The second objective of this invention is to provide a high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane containing the above-mentioned hydrophilic chain extender and its preparation method, by introducing amide functional groups into the polyurethane structure to achieve a synergistic effect of toughness, corrosion resistance, and recyclability.

[0005] According to a first aspect of the present invention, a method for preparing a hydrophilic chain extender is provided, comprising the following steps: reacting serine alcohol with succinic anhydride at 50-70°C for 3-4 hours to obtain the desired product; the molar ratio of serine alcohol to succinic anhydride is 1:1 to 1:1.15. Preferably, the molar ratio of serine alcohol to succinic anhydride is 1:1.

[0006] This invention provides a novel method for preparing a hydrophilic chain extender containing both amide and carboxyl active groups. Serine alcohol and succinic anhydride are used as reactants, and they undergo a ring-opening reaction at 50-70°C. The product containing both amide and carboxyl active groups is prepared by the ring-opening of succinic anhydride by the amino group of serine alcohol.

[0007] In some implementations, the reaction temperature is 60°C.

[0008] In some embodiments, the hydrophilic chain extender has the following structural formula: .

[0009] In some embodiments, serine is bio-based serine, and succinic anhydride is bio-based succinic anhydride.

[0010] Serine alcohol is an amino-substituted derivative of glycerol. Specifically, bio-based serine alcohol can be obtained by converting glycerol into serine alcohol through microbial fermentation or by purchasing it. Bio-based succinic anhydride can be obtained by purchasing it or by preparing it from bio-based succinic acid. As a natural amino acid derivative, serine alcohol has multiple reactive sites, including amino groups, and can undergo a ring-opening reaction with succinic anhydride to introduce a hydrophilic carboxyl group in one step. It is an ideal monomer for constructing novel hydrophilic chain extenders for the synthesis of biopolyurethanes that combine reactivity and hydrophilicity.

[0011] According to a second aspect of the present invention, a hydrophilic chain extender prepared by the above-described preparation method is provided.

[0012] The hydrophilic chain extender of this invention uses bio-based serine alcohol and bio-based succinic anhydride as raw materials, which can effectively reduce dependence on fossil resources. Through molecular design and synthesis, a product containing two highly active primary hydroxyl groups, a carboxyl group and an amide bond can be used as a hydrophilic chain extender to synthesize bio-based waterborne polyurethane. Specifically, the primary hydroxyl and carboxyl groups of the hydrophilic chain extender react with the -NCO of the polyurethane prepolymer to achieve the chain extension effect.

[0013] According to a third aspect of the invention, the use of a hydrophilic chain extender in the preparation of bio-based waterborne polyurethane is provided.

[0014] The hydrophilic chain extender of the present invention contains two hydroxyl groups and one carboxyl group. It is liquid at room temperature and has a low melting point. It is easily melted at the temperature (80~90℃) for preparing waterborne polyurethane. When the hydrophilic chain extender of the present invention is used to prepare bio-based waterborne polyurethane, it solves the technical problem that hydrophilic chain extenders are difficult to melt at the conventional temperature for preparing waterborne polyurethane and are prone to heterogeneous reactions, compared with the inherent defects of common hydrophilic chain extenders (such as DMPA and DMBA) in the prior art, which have high melting points and low solubility. Moreover, the resulting emulsion has good storage stability.

[0015] In some embodiments, the bio-based waterborne polyurethane is a high-toughness, recyclable bio-based waterborne polyurethane.

[0016] According to a fourth aspect of the invention, a mixture comprising, by weight, the following raw materials: 10-14 parts of bio-based polyether polyol, 4.6-5.5 parts of diisocyanate, 0.05-0.2 parts of organometallic catalyst, 0.9-1.8 parts of hydrophilic chain extender, 0.55-1.09 parts of neutralizer, 0.2-0.6 parts of post-chain extender, 4-20 parts of organic solvent, and 40-80 parts of water.

[0017] Preferably, the raw materials, by weight, include: 10 parts of bio-based polyether polyol, 4.6 parts of diisocyanate, 0.05-0.2 parts of organometallic catalyst, 0.9-1.8 parts of hydrophilic chain extender, 0.55-1.09 parts of neutralizer, 0.2 parts of post-chain extender, 4-20 parts of organic solvent, and 60 parts of water. Preferably, the organic solvent is 10-12 parts.

[0018] The high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane of the present invention includes a hydrophilic chain extender (SSA) prepared from bio-based raw materials. This not only effectively reduces dependence on fossil resources, but also improves the dispersion stability, toughness, strength, corrosion resistance, and self-healing properties of the waterborne polyurethane through structural regulation via multiple hydrogen bonds.

[0019] In some embodiments, the organometallic catalyst is selected from at least one of organotin, organobismuth, and organozinc.

[0020] In some embodiments, the bio-based polyether polyol is polytrimethylene ether diol (PO3G), the diisocyanate is selected from at least one of isophorone diisocyanate (IPDI) and pentamethylene diisocyanate (PDI, also known as 1,5-pentanediisocyanate); the chain extender is a diamine chain extender; the organic solvent is acetone or dimethylacetamide (DMAC), and the neutralizing agent is triethylamine (TEA).

[0021] In some embodiments, the organotin is dibutyltin dilaurate (DBTDL); the diamine chain extender is selected from at least one of ethylenediamine (EDA) and isophorone diamine (IPDA).

[0022] It should be noted that this invention studies the performance improvement of bio-based waterborne polyurethane with PO3G as the soft segment by SSA. The bio-based polyether polyol and diisocyanate used are only one embodiment. SSA can also be added to other bio-based waterborne polyurethanes as a hydrophilic chain extender.

[0023] In some embodiments, the amount of hydrophilic chain extender used is 0.9% to 1.8% of the total mass of bio-based polyether polyol, diisocyanate, organometallic catalyst and hydrophilic chain extender.

[0024] In some embodiments, the molar ratio of neutralizing agent to hydrophilic chain extender is 1:1.

[0025] In some embodiments, the molar ratio of bio-based polyether polyol to diisocyanate is (1~1.4):(4.1~8.6).

[0026] In other embodiments, the molar ratio of bio-based polyether polyol to diisocyanate is 1:4.1.

[0027] In some embodiments, the molar ratio of diisocyanate to hydrophilic chain extender is (4.1~8.6):(0.97~1.9).

[0028] In other embodiments, the molar ratio of diisocyanate to hydrophilic chain extender is 4.1:(0.97~1.9).

[0029] In some embodiments, the molar ratio of diisocyanate to chain extender is (4.1~8.6):(0.06~0.09).

[0030] In other embodiments, the molar ratio of diisocyanate to chain extender is 4.1:0.06.

[0031] According to a fifth aspect of the present invention, a method for preparing the above-described high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane is provided, comprising the following steps: S1. Mix bio-based polyether polyol, diisocyanate, organometallic catalyst and organic solvent, and react at 80~90℃ for 2~4 h to obtain prepolymer; S2. Add a hydrophilic chain extender to the prepolymer and react for 3-4 hours. S3. Cool the product from step S2 to 25~30℃, add a neutralizing agent to the product from step S2, then add water, emulsify for 15~30 min, then add a chain extender, and emulsify for 1~1.5 h. S4. Remove the organic solvent by rotary evaporation to obtain the final product.

[0032] In some implementations, emulsification is performed by stirring at 600-1000 rpm.

[0033] The beneficial effects of this invention are as follows: (1) The hydrophilic chain extender of the present invention uses bio-based serine alcohol and succinic anhydride as raw materials, which is green and environmentally friendly; and the preparation method is simple and can be applied to actual industrial production. The hydrophilic chain extender prepared by this method has highly active primary hydroxyl groups, carboxyl groups and amide bonds, and can be used as a hydrophilic chain extender to regulate the microphase structure of waterborne polyurethane.

[0034] (2) The high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane of this invention uses a hydrophilic chain extender obtained from the reaction of serine alcohol and succinic anhydride as a raw material, successfully introducing amide functional groups. The strong hydrogen bonds formed by these functional groups can enhance the mechanical strength and thermal stability of the polyurethane. This hydrophilic chain extender, together with ethylenediamine, constructs multiple dynamic hydrogen bonds and drives hard segment self-assembly, inducing ordered nanophase separation, thereby achieving self-reinforcement and dynamic recyclability of the polyurethane, providing a new structural design strategy for improving overall performance. The high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane, after curing into a film, achieves a toughness of 148.04 MJ. m -3 The crosslinking density is as high as 35580 mol. m -3 It exhibits excellent thermal stability and corrosion resistance (99.97%). This is due to the reversible properties of the dynamic reversible hydrogen bonds and urea self-assembly structure. The material can be recycled in a closed loop through hot pressing and solvent methods, and can achieve rapid self-repair with the assistance of ethanol. Attached Figure Description

[0035] Figure 1 The synthesis route of SSA in Example 1; Figure 2 (a) is the FT-IR chromatogram of SSA, serine alcohol and succinic anhydride in Example 1; Figure 2 (b) is the 1H NMR spectrum of SSA, serine alcohol and succinic anhydride in Example 1; Figure 2 (c) FT-IR images of bio-based waterborne polyurethanes from Examples 2-5; Figure 2 (d) shows the UV-Vis transmittance curves of the bio-based waterborne polyurethane films of Examples 2-5. Figure 3 Particle size distribution of high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane in Examples 2-5; Figure 4 The stress-strain curves of the high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane films of Examples 2-5 are shown. Figure 5 The toughness properties of the high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane films used in Examples 2-5 are shown in the diagram. Figure 6 (a) shows the cyclic tensile test results of the high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane film of Example 2; Figure 6 (b) shows the cyclic tensile test results of the high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane film of Example 3; Figure 6 (c) shows the cyclic tensile test results of the high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane film of Example 4. Figure 6 (d) shows the cyclic tensile test results of the high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane film of Example 5. Figure 6 (e) is the loading-unloading curve of the high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane film of Example 2; Figure 6 (f) is the loading-unloading curve of the high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane film of Example 3; Figure 6 (g) is the loading-unloading curve of the high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane film of Example 4; Figure 6 (h) is the loading-unloading curve of the high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane film of Example 5; Figure 7 (a) TGA curves of the high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane films of Examples 2-5; Figure 7 (b) DTG curves of the high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane films of Examples 2-5; Figure 7 (c) DMA diagrams of the high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane films of Examples 2-5; Figure 7 (d) shows the XRD patterns of the high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane films of Examples 2-5. Figure 8 This image shows the result of a high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane film after hot pressing and dissolution treatment. Figure 9 (a) Tafel curves of the high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane films of Examples 2-5; Figure 9 (b) is the Nyquist plot of the high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane film of Example 2; Figure 9 (c) Nyquist plots of the high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane films of Examples 3-5; Figure 9 (d) is the Bode impedance diagram of the high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane film of Example 3 after immersion for 7 days. Figure 10 Microscopic images of the high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane films of Examples 2-5. Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the accompanying drawings, but the embodiments of the present invention are not limited thereto. The raw materials and reagents involved in the following embodiments are all commercially available.

[0037] Example 1 This embodiment provides a method for preparing a hydrophilic chain extender (SSA), including the following steps: The product is obtained by reacting 0.054 mol of bio-based serine alcohol with 0.054 mol of bio-based succinic anhydride at 60℃ for 3-4 hours.

[0038] The synthesis route of SSA in this invention is as follows: Figure 1 As shown, by Figure 1 It is known that the amino group of serine reacts with the carboxyl hydroxyl group after ring opening of succinic anhydride to give SSA containing both an amide bond and a carboxyl group. The resulting SSA is a liquid product at room temperature.

[0039] SSA, serine alcohol (SER), and succinic anhydride (SA) were characterized by FT-IR and 1H NMR spectroscopy, respectively. The results are as follows: Figure 2 (a) and Figure 2 As shown in (b). From Figure 2 (a) It can be seen that 3421 cm -1 The broad peak at 1726 cm⁻¹ is the stretching vibration peak of -OH. -1 The characteristic absorption peak of the carboxyl group (C=O) is located at 1621 cm⁻¹. -1 With 1541 cm -1 The peaks at points I and II are characteristic absorption peaks of amide I and amide II, respectively, confirming that serine alcohol and succinic anhydride successfully underwent a ring-opening reaction and introduced amide bonds and carboxyl hydrophilic groups.

[0040] Figure 2 (b) shows the 1H NMR spectra of SSA, serine, and succinic anhydride. 1 ¹H NMR (500 MHz, Chloroform-d) δ 3.22–2.64 (m, 5H), 2.27–1.94 (m, 4H), indicating successful product formation.

[0041] Example 2 This embodiment provides a method for preparing a high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane, comprising the following steps: Ten parts of bio-based polytrimethylene ether glycol (PO3G with 0.01 mol of -OH), 4.6 parts of IPDI (IPDI with 0.041 mol of -NCO), 0.05 parts of organobismuth 8108, and 10 parts of acetone were mixed and reacted at 80-90°C for 2 hours. Then, 0.9 parts of SSA prepared in Example 1 (SSA with 0.0098 mol of -OH) were added, and the reaction was continued for 3 hours to obtain a prepolymer. The prepolymer was cooled to 30°C, and 0.55 parts of triethylamine (equal in molar mass to SSA) were added for neutralization. Then, 60 parts of deionized water were added, and the mixture was emulsified at 600 rpm for 15 minutes. An aqueous solution of EDA (0.2 parts of EDA with 0.0067 mol of -OH) was added, and the emulsification reaction was continued for 1 hour. The acetone was removed by rotary evaporation to obtain the final product.

[0042] The resulting high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane is designated as PO3G-0.9%WPU.

[0043] It should be noted that the number-average molecular weight of PO3G used in the embodiments of this application is 2000. The aqueous solution of EDA is prepared by dissolving 0.2 parts of EDA in a small amount of water, or 0.2 parts of EDA can be added directly. It should also be noted that the catalytic effect can also be achieved by replacing organobismuth 8108 with other commercially available organobismuths, organotin, or organozinc.

[0044] Example 3 This embodiment provides a method for preparing a high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane, comprising the following steps: 10 parts of PO3G (0.01 mol of -OH in PO3G), 4.6 parts of IPDI (0.041 mol of -NCO in IPDI), 0.05 parts of organobismuth 8108, and 12 parts of acetone were mixed and reacted at 80-90℃ for 2 hours. Then, 1.2 parts of SSA prepared in Example 1 (0.0129 mol of -OH in SSA) were added, and the reaction was continued for 3 hours to obtain a prepolymer. The prepolymer was cooled to 30℃, and 0.73 parts of triethylamine (equal to the molar mass of SSA) were added for neutralization. 60 parts of deionized water were added, and the mixture was emulsified at 600 rpm for 15 minutes. An aqueous solution of EDA (0.2 parts of EDA, 0.067 mol of -OH in EDA) was added, and the reaction was continued for 1 hour. The acetone was removed by rotary evaporation to obtain the final product.

[0045] The resulting high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane is designated as PO3G-1.2%WPU.

[0046] Example 4 This embodiment provides a method for preparing a high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane, comprising the following steps: 10 parts of PO3G (0.01 mol of -OH in PO3G), 4.6 parts of IPDI (0.041 mol of -NCO in IPDI), 0.05 parts of organobismubyl, and 12 parts of acetone were mixed and reacted at 80-90℃ for 2 hours. Then, 1.5 parts of SSA prepared in Example 1 (0.0162 mol of -OH in SSA) were added, and the reaction was continued for 3 hours to obtain a prepolymer. The prepolymer was cooled to 30℃, and 0.91 parts of triethylamine (equal to the molar mass of SSA) were added for neutralization. 60 parts of deionized water were added, and the mixture was emulsified at 600-1000 rpm for 15 minutes. An aqueous solution of EDA (0.2 parts of EDA, 0.067 mol of -OH in EDA) was added, and the reaction was continued for 1 hour. The acetone was removed by rotary evaporation to obtain the final product.

[0047] The resulting high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane is designated as PO3G-1.5%WPU.

[0048] Example 5 This embodiment provides a method for preparing a high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane, comprising the following steps: 10 parts of PO3G (0.01 mol of -OH in PO3G), 4.6 parts of IPDI (0.041 mol of -NCO in IPDI), 0.05 parts of organobismuth 8108, and 12 parts of acetone were mixed and reacted at 80-90℃ for 2 hours. Then, 1.8 parts of SSA prepared in Example 1 (0.0194 mol of -OH in SSA) were added, and the reaction was continued for 3 hours to obtain a prepolymer. The prepolymer was cooled to 30℃, and triethylamine (1.09 parts) of the same molar mass as SSA was added for neutralization. 60 parts of deionized water were added, and the mixture was emulsified at 600 rpm for 15 minutes. An aqueous solution of EDA (0.2 parts of EDA, 0.0067 mol of -OH in EDA) was added, and the reaction was continued for 1 hour. The acetone was removed by rotary evaporation to obtain the final product.

[0049] The resulting high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane is designated as PO3G-1.8%WPU.

[0050] The high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethanes prepared in Examples 2-5 were characterized by FT-IR, and the results are as follows: Figure 2 As shown in (c), it can be seen that 2270 cm -1 The characteristic absorption peak of isocyanate (-NCO) completely disappeared, indicating that the -NCO reaction was complete. (3330 cm⁻¹) -1The peak value for the stretching vibration of NH is 1723 cm⁻¹. -1 The peak at 2953 cm⁻¹ represents the stretching vibration of the C=O bond in the carbamate ester bond. -1 With 2872 cm -1 The peak at 1100 cm⁻¹ represents the stretching vibrations of -CH₃ and -CH₂-. -1 The peak at 1541 cm⁻¹ is a characteristic absorption peak of the polyether segment COC, confirming the successful introduction of the PO3G soft segment into the WPU molecular structure; -1 The peak at this point is a characteristic absorption peak of the amide II band, indicating that the amide bond in the SSA has been successfully integrated into the WPU backbone.

[0051] The high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane prepared in Examples 2-5 was cured into a film to obtain a high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane film (WPU film). Its optical transparency was studied, and the UV-Vis transmittance curve of the film is shown below. Figure 2 As shown in (d), all WPU films exhibit low transmittance in the 200–300 nm ultraviolet region, demonstrating certain ultraviolet shielding performance. In the 450–800 nm visible light region, the light transmittance exceeds 80%, with the WPU films of Examples 3–5 achieving visible light transmittance exceeding 85%, indicating excellent visible light transparency. SSA has minimal impact on the optical properties of the films because all WPUs are amorphous polymers, and the SSA is uniformly dispersed in the system, without forming obvious phase separation or crystalline regions, thus avoiding light scattering and ensuring good transparency.

[0052] The film preparation process involves pouring a high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane emulsion into a polytetrafluoroethylene mold, allowing it to air dry at room temperature for 24 hours, and then drying it in a 70℃ oven for 24 hours to form the film.

[0053] The high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane emulsions prepared in Examples 2-5 will be subjected to multiple tests below.

[0054] 1. Emulsion stability analysis Particle size, zeta potential, and stability of emulsions are key indicators for the practical application of WPU. The particle size distribution and zeta potential of the high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane emulsions prepared in Examples 2-5 were tested using a laser particle size analyzer (Zetasizer Nano ZSE).

[0055] Table 1 shows the particle size and potential test results of the high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane (WPU) emulsions from different embodiments. As can be seen from the table, all WPU emulsions showed no precipitation, phase separation, or stratification after centrifugation at 3000 r / min for 15 min, indicating that the storage stability of the emulsions exceeded 6 months, demonstrating excellent storage stability. With the increase of SSA content, the average particle size of all WPU emulsions showed a continuous decreasing trend, decreasing from 201.0 nm to 61.15 nm. This is because with the increase of SSA content, the content of carboxyl hydrophilic groups in the molecule increases, resulting in more carboxylate ions generated after neutralization by TEA, significantly enhancing the hydrophilicity of the prepolymer, and forming finer latex particles with a more uniform particle size distribution during water dispersion.

[0056] With increasing SSA content, the absolute value of the Zeta potential of the WPU emulsion showed a trend of increasing and then slightly decreasing. The absolute value of the Zeta potential of all WPU emulsions was greater than 35 mV, indicating that the prepared WPU emulsions possess excellent storage stability. Combined with the particle size variation, it can be seen that the introduction of SSA can effectively improve the stability of WPU emulsions by controlling the content of hydrophilic groups and the surface charge of the particles, confirming the universality of SSA as a hydrophilic chain extender.

[0057] Table 1. Test results of particle size and potential of WPU

[0058] 2. Mechanical property analysis The high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane prepared in Examples 2-5 was cured into a film (denoted as WPU film), and its mechanical properties were analyzed. The results are as follows: Figure 4 , Figure 5 As shown in Table 2.

[0059] Figure 4 The stress-strain curves of the high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane films prepared in Examples 2-5 are shown. Figure 5The graph shows the toughness properties of the high-toughness, recyclable, corrosion-resistant bio-based waterborne polyurethane films prepared in Examples 2-5. As can be seen from the graph, as the SSA content in the polyurethane system increases from 0.9% to 1.5%, the tensile strength of the resulting WPU film increases significantly from 5.08 MPa to 23.28 MPa, while the elongation at break remains above 1500%. This is attributed to the polar hydroxyl and carboxyl groups introduced by SSA, which can form more hydrogen bonds, increasing the crosslinking density of the system and strengthening the interaction forces between molecular chains, effectively improving the material's resistance to external deformation. When the SSA content further increases to 1.8%, the tensile strength of the WPU film decreases to 13.58 MPa, while the elongation at break increases to 1809.58%. This is because the excessive hydrophilicity of the WPU film leads to excessive phase separation. Toughness, as a comprehensive indicator of a material's energy absorption and resistance to fracture, corresponds to the area under the stress-strain curve. Figure 5 It can be seen that the toughness of WPU film first increases and then decreases with increasing SSA content. This is attributed to the fact that moderate cross-linking and hydrogen bonding provide the molecular chains with sufficient load-bearing capacity and slip space, and the synergistic enhancement of tensile strength and toughness of WPU film is achieved through the selection of SSA content. When the SSA content further increases, the significant decrease in strength dominates the decrease in energy absorption capacity, thereby reducing toughness.

[0060] Table 2 Mechanical properties of WPU film

[0061] Cyclic tensile and cyclic loading-unloading experiments were conducted on WPU films of different embodiments. The WPU films were cyclically stretched 5 times using an electronic universal testing machine (UTM5504, Shenzhen Sansi Zongheng Technology Co., Ltd.). The obtained curves were used to characterize the fatigue resistance and recoverability of WPU materials.

[0062] All WPU films were subjected to 5 cycles at 100% strain, and their curves are shown below. Figure 6 As shown in (a)~(d), it can be clearly observed from the figures that when each WPU film enters the second stretching stage, it exhibits a decrease in σ and a softening of the curve, which is a typical Mullins effect. Figure 6 Figures (e) to (h) show the load-unload curves of each WPU film. It can be observed that all samples reached approximately 300% strain during the first loading, and no fracture or sudden drop in strain occurred in the subsequent 5 cycles. The strain can be basically recovered after unloading, indicating that the material has good fatigue resistance and elastic recovery ability, and is reusable, making it suitable for applications requiring repeated deformation.

[0063] 3. Thermal stability analysis Thermogravimetric analysis (TGA) is used to assess the thermal stability of polymer materials. T5 represents the temperature at which a mass loss of 5 wt% occurs. 50 This indicates the temperature corresponding to a 50 wt% mass loss percentage. T max These are the temperatures at which the maximum mass loss rate occurs; these three indicators are typically parameters of a material's thermal stability. The TGA curves for various high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane films are shown below. Figure 7 As shown in (a), the DTG curve is as follows: Figure 7 As shown in (b), the dynamic thermomechanical analysis (DMA) test results are as follows: Figure 7 As shown in (c).

[0064] from Figure 7 As shown in (a)~(b), the thermal degradation of WPU film occurs in two stages. The first stage is the degradation of urethane bonds at 200-320℃, which can be attributed to the decomposition of urethane bonds, forming isocyanates, alcohols, primary and secondary amines, olefins, and the loss of carbon dioxide from urethane bonds. The second stage occurs at 320-500℃, corresponding to the further breakage of aliphatic chains and the degradation of byproducts. The maximum thermal decomposition temperature of WPU film gradually increases with the increase of SSA content. This is because the amide bonds introduced by SSA have high thermal stability, and the strong hydrogen bond network formed by the amide bonds can inhibit the thermal motion of molecular chains and delay the thermal degradation process. Although excessive SSA will lead to a decrease in molecular weight and a slight decrease in the initial thermal weight loss temperature of the material, the synergistic effect of amide bonds and hydrogen bonds will significantly improve the thermal stability of the material, causing the maximum thermal degradation temperature and the 50% thermal weight loss temperature to continue to rise. TGA results show that the thermal decomposition temperature of the material is significantly increased, and the maximum thermal degradation temperature can reach 423.2℃, proving that the introduction of SSA improves heat resistance. DMA test results (see Table 3 and...) Figure 7 (c) indicates that the prepared WPU has good low-temperature stability, and with the increase of SSA content, υ e The increase in SSA content demonstrates that the amide bonds and multiple hydrogen bonds introduced by SSA enhance the crosslinking density. With further increases in SSA content, υ e The decrease is due to excessive SSA inducing local phase separation, which disrupts the uniformity of the crosslinked network. XRD test results are as follows: Figure 7 As shown in (d), the range is 2θ = 5° - 60°. The XRD curves of all WPU films are similar. All WPU samples have a broad diffraction peak at 2θ = 20° without sharp peaks, indicating that the prepared WPU is an amorphous polymer.

[0065] Table 3 Dynamic mechanical properties and crosslinking density of WPU film

[0066] 4. Recyclability test To investigate the recyclability of WPU film, two recycling methods were used: hot-pressing recycling and ethanol-assisted recycling. The WPU film was cut into pieces and directly hot-pressed at 130℃ for 10 minutes. Figure 8 It was observed that the shredded WPU film formed a new film after hot pressing, indicating that the material has excellent hot-pressing recyclability. Simultaneously, the WPU film was placed in anhydrous ethanol and recycled at 50°C for 4 hours, from... Figure 8 It can be observed that the film can be completely dissolved, demonstrating the material's excellent solvent recovery performance. During the ethanol solvent recovery process, the polar solvent can penetrate into the interior of the WPU film, causing the film to dissolve and reform, providing a feasible path for the recycling of WPU materials.

[0067] 5. Corrosion resistance test Test Method: Tafel Analysis Tafel analysis of the CWPU coating was performed using a Chenhua Chi660E (China) electrochemical workstation. A high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane emulsion was coated onto a tinplate surface and immersed in a 3% sodium chloride solution for 3 hours to obtain Tafel curves. Icorr(0) and Icorr(i) represent the corrosion current values ​​of the blank sample (tinplate sheet) and the coated sample, respectively. IE(%) was calculated according to equation (I): , formula (I).

[0068] Polarization curve (Tafel curve) as follows Figure 9 As shown in (a), the figure reveals that among all WPU films, PO3G-1.5%WPU exhibits the best corrosion resistance (IE) at 99.97%, and all systems demonstrate superior corrosion resistance compared to the bare tin. Figure 9 (b) and Figure 9 (c) It can be seen that with the increase of SSA content, the IE of the coating first increases and then decreases. This is attributed to the fact that the introduction of an appropriate amount of SSA improves the crosslinking density and compactness of the coating, while excessive addition leads to an increase in the hydrophilicity of the coating, thereby reducing its anti-corrosion performance. The Bode impedance diagram of PO3G-1.2%WPU after immersion in a 3% sodium chloride solution for 7 days is shown in the figure. Figure 9 (d) It can be observed that the system still maintains high impedance after being impregnated for many days, indicating that the material has excellent anti-corrosion properties.

[0069] 5. Self-healing performance test To investigate the effect of SSA content on the self-healing properties of high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane films, ethanol-assisted self-healing tests were conducted on waterborne polyurethane films containing PO3G-0.9%WPU, PO3G-1.2%WPU, PO3G-1.5%WPU, and PO3G-1.8%WPU. The experiment involved creating essentially identical scratches on the film surface with a blade. After spraying anhydrous ethanol onto the scratched areas, the scratch healing patterns were observed in situ using an optical microscope at 5 min, 10 min, and 15 min. Microscopic images are shown below. Figure 10 As shown. By Figure 10 It was found that the self-healing effects of waterborne polyurethane films modified with different SSA contents varied significantly. The PO3G-1.2%WPU sample exhibited the best self-healing performance; after 5 minutes of ethanol treatment, the scratches narrowed significantly, leaving only very shallow traces after 10 minutes, and the scratch interface completely fused at 15 minutes, achieving defect-free complete repair. The repair effect of the PO3G-1.5%WPU sample was further weakened, with significant scratch shrinkage only appearing after 10 minutes, and slight scratch traces still remaining at 15 minutes. This change is closely related to the structural characteristics of SSA and the internal network structure of the polyurethane matrix. SSA molecules contain abundant hydroxyl and carboxyl active groups, which can construct a large number of dynamic reversible hydrogen bond networks in the polyurethane system, providing core sites for material self-healing. Polar small-molecule ethanol can penetrate into the film interior, causing swelling and plasticizing effects on the polyurethane segments, weakening the physical constraints between molecular chains, promoting the recombination of broken hydrogen bonds and segment migration, thereby achieving scratch repair. When the amount of SSA added is low, the hydrogen bond density in the system is moderate, the degree of cross-linking of polyurethane molecular chains is low and the degree of freedom of movement is high. With the assistance of ethanol, the chain segments can quickly migrate to the scratch interface and reconstruct the hydrogen bond network, exhibiting excellent rapid self-healing properties.

[0070] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a hydrophilic chain extender, characterized in that, Includes the following steps: The product is obtained by reacting serine alcohol with succinic anhydride at 50-70℃ for 3-4 hours. The molar ratio of serine to succinic anhydride is 1:1 to 1:1.

15.

2. The method for preparing the hydrophilic chain extender according to claim 1, characterized in that, Serine alcohol is a bio-based serine alcohol, and succinic anhydride is a bio-based succinic anhydride.

3. A hydrophilic chain extender, characterized in that, It is prepared by the method for preparing the hydrophilic chain extender according to claim 1 or 2.

4. The application of the hydrophilic chain extender according to claim 3 in the preparation of bio-based waterborne polyurethane.

5. A high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane, characterized in that: The product comprises, by weight, the following raw materials: 10-14 parts of bio-based polyether polyol, 4.6-5.5 parts of diisocyanate, 0.05-0.2 parts of organometallic catalyst, 0.9-1.8 parts of the hydrophilic chain extender as described in claim 3, 0.55-1.09 parts of neutralizer, 0.2-0.6 parts of post-chain extender, 4-20 parts of organic solvent, and 40-80 parts of water.

6. The high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane according to claim 5, characterized in that, The product comprises, by weight, the following raw materials: 10 parts of bio-based polyether polyol, 4.6 parts of diisocyanate, 0.05-0.2 parts of organometallic catalyst, 0.9-1.8 parts of the hydrophilic chain extender as described in claim 3, 0.55-1.09 parts of neutralizer, 0.2 parts of post-chain extender, 4-20 parts of organic solvent and 60 parts of water.

7. The high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane according to claim 5 or 6, characterized in that, The molar ratio of neutralizing agent to hydrophilic chain extender is 1:1; the molar ratio of bio-based polyether polyol to diisocyanate is (1~1.4):(4.1~8.6); the molar ratio of diisocyanate to hydrophilic chain extender is (4.1~8.6):(0.97~1.9); the molar ratio of diisocyanate to post-chain extender is (4.1~8.6):(0.06~0.09).

8. The high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane according to claim 5 or 6, characterized in that, The bio-based polyether polyol is polytrimethylene ether glycol; the diisocyanate is selected from at least one of isophorone diisocyanate and pentamethylene diisocyanate; the chain extender is a diamine chain extender; the organic solvent is selected from at least one of acetone and dimethylacetamide; the neutralizing agent is triethylamine; and the organometallic catalyst is selected from at least one of organotin, organobismuth, and organozinc.

9. The high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane according to claim 8, characterized in that, The diamine chain extender is selected from at least one of ethylenediamine and isophorone diamine; the organotin is dibutyltin dilaurate.

10. The method for preparing the high-toughness, recyclable, corrosion-resistant, bio-based waterborne polyurethane according to any one of claims 5 to 9, characterized in that, Includes the following steps: S1. Mix bio-based polyether polyol, diisocyanate, organometallic catalyst and organic solvent, and react at 80~90℃ for 2~4 h to obtain prepolymer; S2. Add a hydrophilic chain extender to the prepolymer and react for 3-4 hours. S3. Cool the product from step S2 to 25~30℃, add a neutralizing agent to the product from step S2, then add water, emulsify for 15~30 min, then add a chain extender, and emulsify for 1~1.5 h. S4. Remove the organic solvent by rotary evaporation to obtain the final product.

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