Preparation method and application of a bio-based aqueous polyurethane aerogel

Abstract

The application belongs to the technical field of polyurethane aerogel materials, and relates to a preparation method and application of a bio-based waterborne polyurethane aerogel, and the preparation method comprises the following steps: performing Aza-Michael addition reaction on amino-modified sodium alginate and waterborne polyurethane terminated with polyethylene glycol methacrylate, and then performing freeze-drying to obtain the bio-based waterborne polyurethane aerogel; the prepared bio-based waterborne polyurethane aergel can be used as a heat insulation material, an oil stain cleaning material or a biomedical stent. Compared with the prior art, the application improves the problem of poor compatibility of polysaccharides and polyurethane in a traditional mixing method, and endows the aerogel with good biodegradability, mechanical properties, thermal insulation, flame retardancy and self-repairing property, and is expected to provide a new material selection for solving problems in the fields of energy, environment and medical treatment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polyurethane aerogel materials, and relates to a preparation method and application of a bio-based waterborne polyurethane aerogel. BACKGROUND

[0002] Polyurethane aerogels have attracted much attention due to their low density, excellent thermal insulation performance and mechanical strength. These unique properties make them ideal candidates for a variety of applications, such as building insulation materials, oil spill cleanup materials and biomedical scaffolds. However, the main raw materials for traditional synthetic polyurethane (polyols and isocyanates) are derived from petroleum, which poses resource depletion and environmental problems. Bio-based polyurethane is considered a sustainable alternative, and current research focuses on replacing polyols with biomass-derived alternatives such as vegetable oil and lignin. However, polyurethanes made from vegetable oil often exhibit poor mechanical properties, flammability and poor solvent resistance, while lignin still faces challenges due to difficulties in separation, poor uniformity, aggregation, structural steric hindrance and low reactivity.

[0003] Currently, it is common to introduce biomass such as cellulose, starch and tannic acid into the polyurethane matrix by physical mixing to improve its overall performance, but due to the lack of chemical bond formation, the compatibility and stability are poor. In contrast, the integration of biomass and polyurethane matrix through covalent bonds can achieve molecular level integration, thereby enhancing interfacial adhesion and mechanical properties.

[0004] Sodium alginate is a natural polysaccharide that is abundant, biodegradable, non-toxic and has intrinsic flame retardancy, so it is considered an ideal additive for modified polyurethane. However, due to the strong polarity of sodium alginate, it often separates from non-polar polyurethane, so achieving compatibility and uniform dispersion of the two has always been a great challenge. SUMMARY

[0005] The purpose of the present application is to provide a preparation method and application of a bio-based waterborne polyurethane aerogel, which forms a covalent carbon-nitrogen bond through the reaction of amide-modified sodium alginate and methacrylate-terminated polyurethane, to solve the problem of poor compatibility and poor comprehensive performance of biomass and polyurethane in the prior art.

[0006] The purpose of the present application can be achieved by the following technical solutions:

[0007] Dynamic covalent bonds, due to their reversibility, endow materials with unique advantages such as self-repairing, recyclability, and adaptability, playing a key role in improving the sustainability and functionality of polyurethanes. In the field of polyurethanes, dynamic covalent bonds play an important role in enhancing the sustainability and functionality of materials. By introducing dynamic covalent bonds into the polymer network, polyurethanes can exhibit unique properties such as easy repairability in response to damage, controllable degradation, and the ability to adapt to environmental changes. In addition, dynamic covalent bonds can adjust material properties, including mechanical strength, flexibility, and degradation kinetics, to meet specific application requirements. Among the many covalent bond construction strategies, the Aza-Michael addition reaction is considered an effective dynamic covalent bond construction strategy due to its mild reaction conditions, good selectivity, reversibility, high efficiency, and wide applicability. The present invention is based on the Aza-Michael addition reaction of amide-modified sodium alginate and methacrylate-terminated polyurethane to form a covalent carbon-nitrogen bond, in order to solve the problem of poor compatibility and poor comprehensive performance of biomass and polyurethane in the prior art.

[0008] The first aspect of the present invention provides a method for preparing a bio-based aqueous polyurethane aerogel, comprising: subjecting amide-modified sodium alginate and polyethylene glycol methacrylate-terminated aqueous polyurethane to Aza-Michael addition reaction, and freeze-drying to obtain a bio-based aqueous polyurethane aerogel.

[0009] Further, the method for preparing the amide-modified sodium alginate comprises: using sodium alginate and melamine as raw materials, subjecting to amide reaction, dialysis, and freeze-drying to obtain.

[0010] Further, in the amide reaction, the reaction temperature is 75-80℃, and the reaction time is 12-24h.

[0011] Further, the mass ratio of the sodium alginate to the melamine is 1:(1-10).

[0012] Further, the amide substitution degree of the amide-modified sodium alginate is 0.2-0.6.

[0013] Further, before the amide reaction, 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide are used to activate the sodium alginate.

[0014] Further, the mass ratio of the sodium alginate, 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride, and N-hydroxysuccinimide is 10:(4.5-5.5):(1-2); in the activation, the activation temperature is 55-60℃, and the activation time is 1-2h.

[0015] Further, the sodium alginate has a molecular weight of 50,000-400,000 g / mol.

[0016] Further, the polyethylene glycol methacrylate-terminated aqueous polyurethane has a molecular weight of 200-2,000 g / mol.

[0017] Further, the method for preparing the polyethylene glycol methacrylate-terminated aqueous polyurethane comprises the following steps:

[0018] 1) reacting polycaprolactone diol, bis-hydroxymethyl propionic acid, lysine diisocyanate, dibutyl tin dilaurate (catalyst) to obtain an isocyanate-terminated polyurethane intermediate;

[0019] 2) reacting the isocyanate-terminated polyurethane intermediate with polyethylene glycol methacrylate to obtain.

[0020] Further, in step 1), the mass ratio of the polycaprolactone diol, bis-hydroxymethyl propionic acid, lysine diisocyanate, and dibutyl tin dilaurate is 100:(5-6):(20-30):(0.5-1.5).

[0021] Further, the polycaprolactone diol has a molecular weight of 1,000-5,000 g / mol.

[0022] Further, in step 1), the reaction temperature is 80-85°C, and the reaction time is 3-4 h.

[0023] Further, in step 2), the amount of the polyethylene glycol methacrylate added is 75-80 g / 100 g of the polycaprolactone diol.

[0024] In the reaction, the reaction temperature is 50-55°C, and the reaction time is 4-6 h.

[0025] Further, the feeding ratio of the amidated modified sodium alginate and the polyethylene glycol methacrylate is (0.1-10) g:(1-100) g.

[0026] Further, in the reaction system of the Aza-Michael addition reaction, the content of the amidated modified sodium alginate is 1-10 wt.%.

[0027] Further, in the Aza-Michael addition reaction, the pH of the reaction system is 8-11.

[0028] Further, in the Aza-Michael addition reaction, lithium chloride is used as a pH regulator, a catalyst, and a moisture absorbent.

[0029] Further, in the Aza-Michael addition reaction, the reaction temperature is 50-90 DEG C, and the reaction time is 8-24 hours.

[0030] The second aspect of the application provides a use of a bio-based aqueous polyurethane aerogel, the bio-based aqueous polyurethane aerogel has a compression strength of 0.15-0.98 MPa, a thermal decomposition temperature of 410-480 DEG C, and a thermal conductivity coefficient of 0.021 W / m / K-0.029 W / m / K, and can be used in thermal insulation materials (for example, building insulation materials), oil spill cleaning materials or biomedical stents.

[0031] Compared with the prior art, the application has the following characteristics:

[0032] 1) The sodium alginate can form a covalent bond with the polyurethane through the Aza-Michael addition reaction, realize the integration at the molecular level, effectively improve the compatibility of the two, and the introduction of the dynamic covalent Aza-Michael bond endows the material with excellent self-repairing, recyclable and other characteristics, and improves the adaptability and sustainability of the material.

[0033] 2) The aerogel obtained in the application not only has the advantages of low density, high porosity and the like, but also has good biodegradability, mechanical properties, thermal insulation, flame retardancy and self-repairing performance; meanwhile, by regulating the degree of substitution of the sodium alginate, the mechanical properties, flame retardancy, degradation efficiency and self-repairing performance of the prepared sodium alginate / polyurethane composite aerogel can be effectively regulated.

[0034] In summary, the sodium alginate-based polyurethane aerogel preparation method based on the Aza-Michael addition reaction can effectively solve the problems in the prior art, prepare a novel bio-based polyurethane aerogel material with excellent performance, and has important theoretical significance and application value. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The flowchart and comprehensive performance chart of the amidated sodium alginate / polyurethane composite aerogel prepared in Example 3.

[0036] Figure 2 The scanning electron microscope chart of the amidated sodium alginate / polyurethane composite aerogel prepared in Example 3. DETAILED DESCRIPTION

[0037] The application will be described in detail below in combination with the drawings and specific examples. The present embodiment is implemented on the premise of the technical solution of the application, and detailed implementation modes and specific operation processes are given, but the protection scope of the application is not limited to the following examples.

[0038] In the following examples, unless otherwise specified, the raw reagents or processing techniques are indicated as conventional commercially available products or conventional processing techniques in the art.

[0039] Example 1: Preparation of amidated sodium alginate with different substitution degree

[0040] Sodium alginate 10 g was dissolved in 1000 ml deionized water, and the pH was adjusted to 5. 4.98 g of 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and 1.52 g of N-hydroxysuccinimide were dissolved in 50 ml pure water, respectively, and added dropwise to the above solution, and stirred at 55°C for 1 hour. Then 20 g, 30 g, and 40 g of small molecule amine-based reagent melamine were added, respectively, and reacted at 75°C for 12 hours to prepare a series of amidated sodium alginate with different substitution degrees. After the reaction was completed, the solution was slowly dropped into hot methanol at 60°C for precipitation, and repeated three times to remove unreacted substances. The precipitate was redissolved in ultrapure water, dialyzed for one week to remove residual salts and impurities, and finally freeze-dried to obtain amidated sodium alginate powder with different substitution degrees.

[0041] Example 2: Synthesis of polyethylene glycol methacrylate-terminated polyurethane

[0042] Poly-caprolactone diol 100.0 g with a molecular weight of about 2000 and 5.4 g of bis-hydroxymethyl propionic acid were vacuum dried overnight, 25 g of lysine diisocyanate and 1 g of dibutyl tin dilaurate were added, and reacted at 80°C for 3 hours to obtain an isocyanate-terminated polyurethane intermediate. After cooling to 50°C, 75 g of polyethylene glycol methacrylate was added, and the reaction was continued for 4 hours. An appropriate amount of acetone was added to reduce the viscosity, and the temperature was cooled to room temperature. 4.1 g of triethylamine was added dropwise and neutralized for 1 hour. Finally, acetone was removed by rotary evaporation to obtain a polyethylene glycol methacrylate-terminated polyurethane aqueous dispersion with a solid content of 30%. By adjusting the amount of water, a polyethylene glycol methacrylate-terminated polyurethane aqueous dispersion with a solid content of 10%-30% was obtained.

[0043] Example 3: Preparation of amidated sodium alginate / polyurethane composite aerogel with different substitution degrees

[0044] At 40°C, the amidated sodium alginate with different substitution degrees prepared in Example 1 was dissolved in water, respectively, and the pH was adjusted to 9 with lithium chloride to prepare a 2wt% aqueous solution. The polyethylene glycol methacrylate-terminated polyurethane aqueous dispersion with a solid content of 10%-30% prepared in Example 2 was added, and an Aza-Michael addition reaction occurred under alkaline conditions at 60°C for 24 hours. The substitution degree and amount of sodium alginate, and the solid content and amount of polyethylene glycol methacrylate-terminated polyurethane aqueous dispersion are listed in Table 1. After the reaction was completed, the freeze-drying was performed to obtain a series of amidated sodium alginate / polyurethane aerogels with different substitution degrees and different densities.

[0045] The aerogel sample prepared by reacting 2wt% of amidated sodium alginate with a substitution degree of 0.4 and a polyethylene glycol methacrylate capped polyurethane aqueous dispersion with a solid content of 20wt% was brittle fractured in liquid nitrogen, and a 0.1mm x 0.1mm x 0.1mm aerogel sample was taken for scanning electron microscope observation of the morphology, as shown in FIG. 1. It can be observed that the filamentous sodium alginate forms a three-dimensional crosslinked network structure with the polyurethane matrix. Figure 2

[0046] Table 1

[0047]

[0048] Preparation of pure polyurethane aerogel

[0049] The polyethylene glycol methacrylate capped polyurethane aqueous dispersion with a solid content of 30% prepared in Example 2 was diluted by adding ultrapure water to obtain polyethylene glycol methacrylate capped polyurethane aqueous dispersions with solid contents of 25%, 20%, 15% and 10%. Pure polyurethane aerogels with different densities were obtained by freeze-drying.

[0050] Non-crosslinked amidated sodium alginate / polyurethane aerogel

[0051] The amidated sodium alginate with a substitution degree of 0.4 prepared in Example 1 was dissolved in water at 40°C and adjusted to pH 9 with lithium chloride to prepare a 2wt% aqueous solution. The polyethylene glycol methacrylate capped polyurethane aqueous dispersion with a solid content of 20% prepared in Example 2 was added, and the mixture was stirred at room temperature for 10min at pH 9. The physically mixed amidated sodium alginate / polyurethane aerogel was obtained by freeze-drying. The non-crosslinked amidated sodium alginate / polyurethane aerogel had a density of 0.08g / cm 3 , a compressive strength of 0.16MPa and a thermal conductivity of 0.026W / m / K.

[0052] Application Example 1

[0053] This example was used to characterize the compressive properties of the materials prepared in Example 3 and Comparative Examples 1-2. The characterization method included compression testing using a Texture Analyzer (model TA.XT plus) with a loading rate of 0.5mm / s, an aerogel sample height of 10mm, a diameter of 14mm and a compression strain of 20%. The stress-strain values during compression were recorded. The compression test results are shown in Table 2.

[0054] ​The test results show that the compressive strength of the sodium alginate / polyurethane aerogel in the application is 0.15-0.98 MPa, which is comparable to other bio-based polyurethane aerogels (such as cellulose / polyurethane aerogel), and exceeds the compressive strength (0.2 MPa) of polyurethane aerogel prepared from agricultural waste.

[0055] Application Example 2:

[0056] This example is used to characterize the self-healing performance of the materials prepared in Example 3 and Comparative Examples 1-2, and the characterization method includes damage-repair and compression test.

[0057] Test method: Prepare aerogel samples of the same size (height 10 mm, diameter 14 mm), and apply a cut of about 3 mm in diameter and 2 mm in depth on the sample to simulate damage. Then, heat the damaged sample at 60℃ for 5h to promote self-healing. After self-healing is completed, the sample is subjected to compression test as in Application Example 1, and compared with the undamaged sample to systematically evaluate its self-healing ability.

[0058] The self-healing test results show that the initial compressive strength of the sodium alginate / polyurethane aerogel with a density of 0.09 g / cm 3 is 0.58 MPa, and the compressive strength after self-healing is 0.48 MPa.

[0059] The above test results show that the sodium alginate / polyurethane aerogel in the application also has excellent self-healing performance, thanks to the reversibility of Aza-Michael addition reaction. Quantitative analysis shows that the healed aerogel can recover up to 82% of the original compressive strength.

[0060] Application Example 3:

[0061] This example is used to characterize the thermal insulation performance of the materials prepared in Example 3 and Comparative Examples 1-2, and the characterization method includes thermal conductivity test and thermal decomposition temperature test.

[0062] Thermal conductivity test method: According to ISO 22007-2b standard, a thermal conductivity analyzer (TPS2500S, sensor model 5465) is used for testing at room temperature 25℃, and the optimization parameters for measurement are: heating power is set to 5mW, and duration is 5 seconds. Each sample is tested 5 times to ensure the reliability of the data, and the results are averaged.

[0063] Thermal decomposition temperature test method: According to ASTM E1131 standard, a thermal gravimetric analyzer (TA, Q500 type) is used to heat the sample in nitrogen at a heating rate of 10℃ / min, and the mass change of the material is recorded, and the temperature at the maximum decomposition rate is defined as the thermal decomposition temperature. The thermal insulation test results are shown in Table 2.

[0064] The test results show that the thermal conductivity of the pure polyurethane aerogel in the application is 0.03 W / m / K, the thermal conductivity of the uncrosslinked sodium alginate / polyurethane aerogel is 0.026 W / m / K, and the thermal conductivity of the crosslinked sodium alginate / polyurethane composite aerogel is 0.022 W / m / K, which is significantly lower than that of traditional polyurethane aerogel and other common thermal insulation materials, such as aramid nanofiber aerogel (0.031 W / m / K), silica aerogel (0.026 W / m / K), and ceramic composite silica aerogel (0.042 W / m / K), indicating that it has potential advantages in thermal insulation applications. The thermal decomposition temperature of the pure polyurethane aerogel in the application is 330℃, the thermal decomposition temperature of the uncrosslinked sodium alginate / polyurethane composite aerogel is 400℃, and the thermal decomposition temperature of the crosslinked sodium alginate / polyurethane composite aerogel is 450℃, which is significantly higher than that of common thermal insulation materials such as urea-formaldehyde foam (317℃) and phenolic foam (400℃).

[0065] Application Example 4:

[0066] This example is used to characterize the combustion performance of the materials prepared in Example 1 and Comparative Examples 1-2. The characterization method includes: limiting oxygen index test.

[0067] Test method: JF-3 type oxygen index tester is used for testing. The sample size is 150mm×10mm×10mm, and according to ASTM D2863-19 standard, the sample needs to be conditioned in an environment with temperature of 23±2℃ and relative humidity of 50±5% for 24 hours before testing. Record the minimum oxygen concentration required for the sample to burn 50mm, and repeat the test five times to take the average value.

[0068] The combustion test results are shown in Table 2. The limiting oxygen index of pure polyurethane aerogel is 17.1%, the limiting oxygen index of uncrosslinked sodium alginate / polyurethane aerogel is 25.8%, and the limiting oxygen index of crosslinked sodium alginate / polyurethane composite aerogel is 28.5%.

[0069] The combustion test shows that the limiting oxygen index value of the sodium alginate / polyurethane composite material in the application is higher, which exceeds that of palm-based polyurethane composite material (22.1%), and is comparable to some polyurethane composite materials with added flame retardant (26.1%), further indicating its application prospect as a potential bio-based flame retardant material.

[0070] Table 2

[0071]

[0072] In summary, the sodium alginate / polyurethane composite aerogel exhibits significantly excellent performance compared with traditional polyurethane aerogel, specifically, lower density (0.02-0.22 g / cm 3 ), higher compressive strength (0.15-0.98 MPa), higher decomposition temperature (410-480℃), lower thermal conductivity (0.021-0.029 W / m / K) and more excellent self-repair efficiency (80-95%), while the compressive strength of traditional polyurethane aerogel is only 0.15 MPa, the decomposition temperature is 330℃, and the thermal conductivity is 0.031 W / m / K. In addition, by adjusting the amidation degree of substitution of sodium alginate, the self-repair, recyclable, biodegradable and flame-retardant properties of the composite aerogel can be effectively regulated. Therefore, the bio-based waterborne polyurethane aerogel provided by the present application has broad application prospects in many fields, and is expected to provide new material options for solving problems in the fields of energy, environment, medical treatment and the like.

[0073] The above description of the embodiments is to facilitate the understanding and use of the present application by those skilled in the art. Those skilled in the art can easily make various modifications to the embodiments and apply the general principles described herein to other embodiments without having to go through creative labor. Therefore, the present application is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art according to the disclosure of the present application without departing from the scope of the present application should be within the scope of protection of the present application.

Claims

1. A method for the preparation of a bio-based aqueous polyurethane aerogel, characterized in that, The application relates to a bio-based waterborne polyurethane aerogel, a preparation method thereof and an application thereof. The preparation method of the amidated modified sodium alginate comprises the following steps: taking sodium alginate and melamine as raw materials, carrying out an amidation reaction, dialysis, and freeze-drying to obtain the amidated modified sodium alginate. In the amidation reaction, the reaction temperature is 75-80 DEG C, and the reaction time is 12-24 h; the mass ratio of the sodium alginate to the melamine is 1:(1-10).

2. The method of preparing a bio-based aqueous polyurethane aerogel according to claim 1, characterized in that, Before the amidation reaction, the sodium alginate is activated by using 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide.

3. The method of preparing a bio-based aqueous polyurethane aerogel according to claim 1, characterized in that, The mass ratio of the sodium alginate, the 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and the N-hydroxysuccinimide is 10:(4.5-5.5):(1-2); in the activation, the activation temperature is 55-60 DEG C, and the activation time is 1-2 h.

4. The method of preparing a bio-based aqueous polyurethane aerogel according to claim 3, characterized in that, The preparation method of the polyethylene glycol methacrylate-terminated waterborne polyurethane comprises the following steps:

5. The method of preparing a bio-based aqueous polyurethane aerogel according to claim 1, characterized in that, 1) reacting polycaprolactone diol, bis-hydroxymethyl propionic acid, lysine diisocyanate and dibutyl tin dilaurate to obtain an isocyanate-terminated polyurethane intermediate; 2) reacting the isocyanate-terminated polyurethane intermediate with polyethylene glycol methacrylate to obtain the polyethylene glycol methacrylate-terminated waterborne polyurethane. In step 1), the mass ratio of the polycaprolactone diol, the bis-hydroxymethyl propionic acid, the lysine diisocyanate and the dibutyl tin dilaurate is 100:(5-6):(20-30):(0.5-1.5); 6. The method of preparing a bio-based aqueous polyurethane aerogel according to claim 5, characterized in that, In the reaction, the reaction temperature is 80-85 DEG C, and the reaction time is 3-4 h. In step 2), the adding amount of the polyethylene glycol methacrylate is 75-80 g / 100 g polycaprolactone diol; 7. The method of preparing a bio-based aqueous polyurethane aerogel according to claim 5, characterized in that, In the reaction, the reaction temperature is 50-55 DEG C, and the reaction time is 4-6 h. The feeding ratio of the amidated modified sodium alginate to the polyethylene glycol methacrylate-terminated waterborne polyurethane is (0.1-10) g:(1-100) g; 8. The method of producing a bio-based aqueous polyurethane aerogel according to claim 1, characterized in that, In the Aza-Michael addition reaction, the reaction temperature is 50-90 DEG C, and the reaction time is 8-24 h. The bio-based waterborne polyurethane aerogel can be used as a heat insulation material or a biomedical stent.

9. Use of a bio-based hydrophilic polyurethane aerogel prepared according to the method of any one of claims 1 to 8, characterized in that, ​

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