Lignin sulfonate / titanium dioxide nanoparticles as well as preparation method and application thereof

Abstract

The invention provides sulfonated lignin / titanium dioxide nanoparticles as well as a preparation method and application thereof, and belongs to the technical field of lignin materials. The preparation method comprises the following steps: sequentially mixing formaldehyde and sodium sulfite in a dealkalized lignin alkaline solution, and then sequentially performing dialysis, rotary evaporation and drying to obtain sulfonated dealkalized lignin; mixing the sulfonated dealkalized lignin in water to obtain a sulfonated dealkalized lignin solution; and mixing the tetrabutyl titanate dispersion liquid in the sulfonated dealkalized lignin solution, carrying out a hydrothermal synthesis reaction, and drying the product to obtain the sulfonated lignin / titanium dioxide nanoparticles. The sulfonated dealkalized lignin / titanium dioxide nanoparticles prepared by the method can be used as an anti-ultraviolet agent to improve the weather resistance of waterborne polyurethane, and the result of the method is expected to expand the potential application and optimization strategy of a lignin-based nano composite material.

Description

Technical Field

[0001] The present invention relates to the technical field of lignin materials, and particularly relates to a sulfonated lignin / titanium dioxide nanoparticle, a preparation method thereof, and an application thereof. Background Art

[0002] In most current applications, polyurethane (PU) is highly dependent on organic solvents as solvent formulations. However, due to concerns about the generation of volatile organic compounds (VOCs) and harmful air pollutants, there has been active research on environmentally friendly waterborne polyurethane formulations to eliminate the need for organic solvents. Waterborne polyurethane (WPU) is a new polyurethane system that uses water instead of organic solvents as the dispersion medium, and has the advantages of being pollution-free, safe and reliable, excellent mechanical properties, good compatibility, and easy modification. It is widely used in fields such as coatings, adhesives, and fillers. However, under long-term outdoor use, waterborne polyurethane will undergo ultraviolet aging degradation. In recent decades, due to environmental pollution and the intensification of the greenhouse effect, the earth's ozone layer has been damaged, and the ultraviolet rays reaching the earth's surface have increased sharply, causing certain damage to outdoor polymer materials. Therefore, it is very necessary to research and develop a stable ultraviolet absorber for waterborne polyurethane.

[0003] Metal oxide nanomaterials have excellent ultraviolet absorption properties and stability, and have broad application prospects in the field of ultraviolet resistance of polymer materials. Titanium dioxide (TiO2) is one of them, with excellent stability, non-migration properties, strong tinting strength, covering power, low corrosiveness, and being non-toxic, odorless, non-irritating, and also having the function of sterilization and deodorization. When ultraviolet rays irradiate the surface of titanium dioxide, its nanoparticles will excite electrons to generate free radicals and singlet oxygen, and these reactive oxygen species can decompose ultraviolet rays, causing them to lose energy, thereby preventing ultraviolet rays from damaging the skin. However, there are relatively weak van der Waals forces between the molecules of pure TiO2 nanomaterials. When the nanoparticles are mixed, these forces will cause the particles to attract and aggregate with each other, forming aggregates. In addition, the surface energy of titanium dioxide particles is relatively high, showing serious aggregation behavior, difficult dispersion, and poor interfacial compatibility in polymer materials.

[0004] To overcome this problem, a feasible method is to improve the dispersibility and compatibility of TiO2 in polymer materials by compounding with lignin. Lignin is an amorphous polymer composed of phenylpropane units connected by carbon-carbon bonds and ether bonds, and it is the second largest biomass resource in the plant kingdom after cellulose in terms of reserves. The molecular structure of lignin contains a large number of aromatic structures, which have good absorption of ultraviolet light and can form a synergistic anti-ultraviolet effect with TiO2. In addition, lignin itself has a certain antibacterial effect and can inhibit the growth of bacteria. Sulfonate lignin, introducing sulfonic acid groups (-SO3H) on the basis of maintaining the basic structural units of natural lignin, enhances the dispersing effect on TiO2. For example, Chinese Patent CN 115160666 B discloses a preparation method of sodium lignosulfonate polyurethane / SBR composite modifier, using lignin to improve the anti-ultraviolet aging ability of SBR materials and achieving the effects of water reduction and dispersion by introducing sulfonic acid groups. Chinese Patent CN 113025073 B discloses a preparation method of lignin / titanium dioxide hybrid composite nanomaterials, using lignin to modify the surface of titanium dioxide, which has characteristics such as ultraviolet protection and antioxidant properties, can effectively improve the agglomeration of TiO2, and at the same time utilize the rigid characteristics of inorganic particles to solve the problem of poor reinforcement performance of lignin. However, the above-mentioned existing technologies cannot provide protection in the entire ultraviolet light band.

[0005] Therefore, how to obtain a lignin / titanium dioxide composite material for providing protection in the entire ultraviolet light band is a technical problem that needs to be solved currently. Summary of the Invention

[0006] The purpose of the present invention is to provide a sulfonated lignin / titanium dioxide nanoparticle, its preparation method and application to solve the above-mentioned technical problems.

[0007] To achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0008] The present invention provides a preparation method of sulfonated lignin / titanium dioxide nanoparticles (SDL / TiO2), comprising the following steps:

[0009] 1) Mix formaldehyde (HCHO) and sodium sulfite (Na2SO3) successively in the alkaline solution of delignified lignin, and then perform dialysis, rotary evaporation and drying successively to obtain sulfonated delignified lignin (SDL);

[0010] 2) Mix sulfonated delignified lignin in water to obtain a sulfonated delignified lignin solution;

[0011] 3) Disperse tetrabutyl titanate (TBOT) dispersion in the sulfonated delignified lignin solution, perform hydrothermal synthesis reaction, and dry the product to obtain sulfonated lignin / titanium dioxide nanoparticles.

[0012] Furthermore, the alkali-removed lignin alkali solution is obtained by mixing alkali-removed lignin and sodium hydroxide solution, and the dosage ratio of the alkali-removed lignin to the sodium hydroxide solution is 4-6 g: 100 mL.

[0013] Furthermore, the mass ratio of the formaldehyde, sodium sulfite and alkali-removed lignin is 0.6-1.2: 1.5-3.5: 4-6.

[0014] Furthermore, the pH of the sodium hydroxide solution is 10-12;

[0015] The dialysis is carried out in a dialysis bag with a cut-off molecular weight of 1000 Da for 2-7 days.

[0016] Furthermore, the temperature for mixing the formaldehyde is 70-80 °C, and the mixing time is 2-3 h;

[0017] The temperature for mixing the sodium sulfite is 80-90 °C, and the mixing time is 5-6 h.

[0018] Furthermore, in the step 3), the mass ratio of tetrabutyl titanate in the tetrabutyl titanate dispersion liquid to sulfonated alkali-removed lignin in the sulfonated alkali-removed lignin solution is 3-5: 3-6; the mass content of tetrabutyl titanate in the tetrabutyl titanate dispersion liquid is 18-22%;

[0019] The temperature of the hydrothermal synthesis is 130-170 °C, the time of the hydrothermal synthesis is 8-9 h, and the drying temperature is 40-50 °C.

[0020] The present invention also provides a sulfonated lignin / titanium dioxide nanoparticle.

[0021] The present invention also provides an application of the sulfonated lignin / titanium dioxide nanoparticle as an ultraviolet-resistant agent in a polyurethane material, including the following steps:

[0022] Disperse the sulfonated lignin / titanium dioxide nanoparticle in water to obtain an SDL / TiO2 dispersion liquid;

[0023] Add the SDL / TiO2 dispersion liquid into the aqueous polyurethane, and after shearing, vacuum defoaming and drying in sequence, a sulfonated lignin / titanium dioxide composite polyurethane material is obtained.

[0024] Furthermore, the mass ratio of the sulfonated lignin / titanium dioxide nanoparticle to the aqueous polyurethane is 0.5-5: 100;

[0025] The mass ratio of the sulfonated lignin / titanium dioxide nanoparticle to water is 1.25-12.5: 100.

[0026] Further, the rotation speed of shearing is 300 - 400 r / min, the time of shearing is 15 - 60 min, the temperature of drying is 40 - 60 °C, and the time of drying is 10 - 14 h.

[0027] Advantages of the present invention:

[0028] The present invention mainly sulfonates and modifies lignin and then composites it with TiO2 to prepare SDL / TiO2 nanoparticles, and applies them to waterborne polyurethane to improve the anti-ultraviolet aging ability of waterborne polyurethane. When the addition amount of SDL / TiO2 nanoparticles in the present invention is 1%, the polyurethane composite material obtained has excellent anti-ultraviolet performance on the premise of ensuring a certain transparency. However, too much addition amount will cause their aggregation inside the polyurethane, thus reducing the performance of the polyurethane. The sulfonated delignified lignin / titanium dioxide nanoparticles prepared by the present invention can improve the weather resistance of waterborne polyurethane as an anti-ultraviolet agent. The results of the present invention are expected to expand the potential applications and optimization strategies of lignin-based nanocomposites. Description of the drawings

[0029] Figure 1 It is the preparation flow chart of the sulfonated delignified lignin of the present invention;

[0030] Figure 2 It is the preparation flow chart of the sulfonated lignin / titanium dioxide nanoparticles of the present invention;

[0031] Figure 3 It is the SEM diagram of TiO2 and sulfonated lignin / titanium dioxide of the present invention;

[0032] Figure 4 It is the particle size distribution diagram of TiO2 and sulfonated lignin / titanium dioxide of the present invention;

[0033] Figure 5 It is the diagram of the influence of different proportions of sulfonated lignin / titanium dioxide nanoparticles incorporated into waterborne polyurethane on the spectral properties of the WPU-based composite film of the present invention. Detailed implementation manners

[0034] The present invention provides a preparation method of sulfonated lignin / titanium dioxide nanoparticles, comprising the following steps:

[0035] 1) Mix formaldehyde and sodium sulfite successively in the delignified lignin alkali solution, and then carry out dialysis, rotary evaporation and drying successively to obtain sulfonated delignified lignin;

[0036] 2) Mix the sulfonated delignified lignin in water to obtain a sulfonated delignified lignin solution;

[0037] 3) Mix the tetrabutyl titanate dispersion in the sulfonated delignified lignin solution, conduct a hydrothermal synthesis reaction, and dry the product to obtain sulfonated lignin / titanium dioxide nanoparticles.

[0038] In the present invention, the type of lignin used is delignified lignin (DL). Delignified lignin contains abundant functional groups such as carboxyl and hydroxyl groups. Delignified lignin is produced by the delkalinization of paper-making black liquor and contains abundant sulfonate functional groups in the form of salts. The sulfonate can be converted into -SO3H groups through ion exchange. Compared with conventional alkaline lignin (AL), delignified lignin has a larger molecular weight and a more stable structure.

[0039] In the present invention, the delignified lignin alkaline solution is obtained by mixing delignified lignin and sodium hydroxide solution, and the dosage ratio of delignified lignin to sodium hydroxide solution is 4 - 6 g:100 mL, preferably 4 - 5 g:100 mL, and more preferably 5 g:100 mL.

[0040] In the present invention, the mass ratio of formaldehyde, sodium sulfite, and delignified lignin is 0.6 - 1.2:1.5 - 3.5:4 - 6, preferably 0.8 - 1.0:1.8 - 3.0:4 - 5, and more preferably 1:2.5 - 3:4 - 5.

[0041] In the present invention, the pH of the sodium hydroxide solution is 10 - 12, preferably 11.

[0042] In the present invention, the dialysis is carried out in a dialysis bag with a molecular weight cut-off of 1000 Da for 2 - 7 days, preferably 3 - 6 days, and more preferably 4 - 5 days.

[0043] In the present invention, the temperature for mixing formaldehyde is 70 - 80 °C, preferably 70 - 75 °C, and more preferably 70 - 72 °C; the mixing time is 2 - 3 h, preferably 2 h;

[0044] In the present invention, the temperature for mixing sodium sulfite is 80 - 90 °C, preferably 85 - 90 °C, and more preferably 90 °C; the mixing time is 5 - 6 h, preferably 5 h.

[0045] In the present invention, in step 3), the mass ratio of tetrabutyl titanate in the tetrabutyl titanate dispersion to sulfonated delignified lignin in the sulfonated delignified lignin solution is 3 - 5:3 - 6, preferably 2.5 - 3.5:3.5 - 4.5, and more preferably 3:4; the mass content of tetrabutyl titanate in the tetrabutyl titanate dispersion is 18 - 22%, preferably 19 - 21%, and more preferably 20 - 21%;

[0046] The temperature of the hydrothermal synthesis is 130 - 170 °C, preferably 130 - 150 °C, and more preferably 130 °C; the time of the hydrothermal synthesis is 8 - 9 h, preferably 8 h; the drying temperature is 40 - 50 °C, preferably 50 °C.

[0047] The present invention also provides a sulfonated lignin / titanium dioxide nanoparticle.

[0048] The present invention also provides an application of the sulfonated lignin / titanium dioxide nanoparticle as an ultraviolet resistant agent in a polyurethane material, including the following steps:

[0049] Disperse the sulfonated lignin / titanium dioxide nanoparticle in water to obtain an SDL / TiO₂ dispersion;

[0050] Add the SDL / TiO₂ dispersion to the aqueous polyurethane, and after shearing, vacuum defoaming and drying in sequence, a sulfonated lignin / titanium dioxide composite polyurethane material is obtained.

[0051] In the present invention, the mass ratio of the sulfonated lignin / titanium dioxide nanoparticle to the aqueous polyurethane is 0.5 - 5:100, preferably 1:100;

[0052] The mass ratio of the sulfonated lignin / titanium dioxide nanoparticle to water is 1.25 - 12.5:100, preferably 2.5 - 7.5:100.

[0053] In the present invention, the rotation speed of the shearing is 300 - 400 r / min, preferably 350 r / min; the shearing time is 15 - 60 min, preferably 20 - 50 min, and more preferably 30 - 40 min; the drying temperature is 40 - 60 °C, preferably 45 - 55 °C, and more preferably 50 °C; the drying time is 10 - 14 h, preferably 12 h.

[0054] In the present invention, besides TiO₂, the metal oxide can also be compounded with sulfonated lignin and materials that are prone to agglomeration and have certain ultraviolet shielding properties, such as zinc oxide, iron oxide, cerium dioxide, aluminum trioxide, lead oxide, etc.

[0055] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0056] Example 1

[0057] A preparation method of SDL / TiO₂ nanoparticles:

[0058] Use the raw materials in Table 1:

[0059] Table 1 Raw materials for preparing SDL / TiO₂ nanoparticles

[0060]

[0061] Preparation method:

[0062] 1) Weigh the delignified lignin and place it in 100 mL of an aqueous NaOH solution (containing 0.03 g of sodium hydroxide) with a pH of 10, and stir magnetically at room temperature for 30 min. The sodium hydroxide solution can break the hydrogen bonds and other interactions between lignin molecules, enabling lignin to dissolve and disperse better in the solution, ensuring the uniformity of the reaction system, and allowing the sulfonation reaction to proceed more fully;

[0063] 2) Add formaldehyde to the above liquid and stir at 70 °C for 2 h. Formaldehyde has two active aldehyde groups, which can react with the functional groups in the lignin molecules to form a cross-linked structure between the lignin molecules. This cross-linking effect can increase the molecular weight and intermolecular interaction force of the lignin molecules; then add anhydrous sodium sulfite and stir at 90 °C for 5 h. Anhydrous sodium sulfite provides sulfonic acid groups for this reaction;

[0064] 3) Cool the above liquid to room temperature, then dialyze it in a dialysis bag with a molecular weight cut-off of 1000 Da for 5 d; place the dialyzed liquid in a round-bottom flask, rotary evaporate the solvent, and then dry it in a vacuum drying oven at 50 °C for 48 h to obtain sulfonated delignified lignin;

[0065] 4) Dissolve 3 g of sulfonated delignified lignin in 25 mL of distilled water to prepare an aqueous solution of sulfonated delignified lignin; disperse tetrabutyl titanate in ethanol, then add the aqueous solution of sulfonated delignified lignin, and hydrothermally synthesize at 130 °C for 8 h. After cooling to room temperature, take it out and then dry it in a vacuum drying oven at 50 °C and 0.09 MPa to obtain SDL / TiO2 nanoparticles.

[0066] The particle size analysis test was carried out on the sulfonated lignin / titanium dioxide composite particles obtained in Example 1, and the results are as follows.

[0067] The field emission scanning electron microscope was used to analyze the micro-morphology of titanium dioxide and sulfonated lignin / titanium dioxide composite nanoparticles, and the results are shown in the figure. From Figure 3 (a), it can be seen that the agglomeration of titanium dioxide is relatively serious. After being compounded with sulfonated lignin, Figure 3 (b) the size of the sulfonated lignin / titanium dioxide composite nanoparticles decreases, the particle distribution is uniform, and it shows a regular spherical shape with uniform morphology. It can be inferred from this that well-dispersed sulfonated lignin is beneficial to eliminating the aggregation of TiO2 nanoparticles. The good dispersibility of SL / TiO2 provides a reliable guarantee for subsequent physical blending modification.

[0068] The particle sizes of titanium dioxide and sulfonated lignin / titanium dioxide composite nanoparticles were analyzed using a laser particle size analyzer and DLS, respectively, and the results are as Figure 4 shown. The particle size range of titanium dioxide is mainly from 0.224 to 563.677 μm, while the particle size distribution of sulfonated lignin / titanium dioxide composite nanoparticles is mainly concentrated in the range of 78.820 to 341.995 nm. This is because the addition of sulfonated lignin effectively reduces the specific surface area of titanium dioxide, reduces the agglomeration phenomenon of titanium dioxide, is conducive to the dispersion of sulfonated lignin / titanium dioxide composite nanoparticles in the polyurethane matrix, and improves the ultraviolet shielding effect.

[0069] Example 2

[0070] Preparation of a sulfonated lignin / titanium dioxide composite polyurethane material:

[0071] Using the raw materials in Table 2:

[0072] Table 2 Raw materials for preparing sulfonated lignin / titanium dioxide composite polyurethane materials

[0073] Raw material <![CDATA[SDL / TiO2 nanoparticles]]> Water WPU Mass / g 0.025 2 5

[0074] Preparation method:

[0075] 1) Ultrasonically disperse the SDL / TiO2 nanoparticles obtained in Example 1 in water at room temperature for 30 min to obtain an SDL / TiO2 dispersion;

[0076] 2) Add the SDL / TiO2 dispersion to the WPU, mechanically shear at 400 r / min for 30 min, and then defoam in a vacuum defoamer for 5 min;

[0077] Pour the obtained liquid into a polytetrafluoroethylene mold and place it in a vacuum drying oven to dry at 60 °C and 0.09 MPa for 12 h to obtain a sulfonated lignin / titanium dioxide composite polyurethane film material with excellent performance.

[0078] Example 3

[0079] The preparation method is the same as that of Example 2, except that the raw materials are different. The raw materials are shown in Table 3 below.

[0080] Table 3 Raw materials for preparing sulfonated lignin / titanium dioxide composite polyurethane materials

[0081] Raw material <![CDATA[SDL / TiO2 nanoparticles]]> Water WPU Mass / g 0.05 2 5

[0082] Example 4

[0083] The preparation method is the same as that of Example 2, except that the raw materials are different. The raw materials are shown in Table 4 below.

[0084] Table 4 Raw materials for preparing sulfonated lignin / titanium dioxide composite polyurethane materials

[0085] Raw material <![CDATA[SDL / TiO2 nanoparticles]]> Water WPU Mass / g 0.15 2 5

[0086] Example 5

[0087] The preparation method was the same as that of Example 2, except that the raw materials were different, and the raw materials are shown in Table 5 below.

[0088] Table 5 Raw materials for preparing sulfonated lignin / titanium dioxide composite polyurethane materials

[0089] Raw material <![CDATA[SDL / TiO2 nanoparticles]]> Water WPU Mass / g 0.25 2 5

[0090] The WPU-based composite films obtained in Examples 2 to 5 were analyzed using a UV-visible spectrophotometer, and the results are as Figure 5 shown. Due to the synergistic UV resistance of lignin and titanium dioxide, after modifying the aqueous polyurethane film by adding SDL / TiO2 nanoparticles, the composite film has excellent UV resistance. When 1% of SDL / TiO2 nanoparticles were incorporated, the composite film achieved a UV shielding rate of 99.9% in the full light band while ensuring a transparency of 70%.

[0091] From the above examples, it can be seen that the present invention provides a sulfonated lignin / titanium dioxide nanoparticle, its preparation method and application. The sulfonated delignified lignin / titanium dioxide nanoparticle prepared by the present invention can improve the weather resistance of aqueous polyurethane as an anti-UV agent, and the results of the present invention are expected to expand the potential applications and optimization strategies of lignin-based nanocomposites.

[0092] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of sulfonated lignin / titanium dioxide nanoparticles, characterized in that, It includes the following steps: 1) Mix formaldehyde and sodium sulfite successively in the alkali solution of delignified lignin, and then successively carry out dialysis, rotary evaporation and drying to obtain sulfonated delignified lignin; 2) Mix the sulfonated delignified lignin in water to obtain a sulfonated delignified lignin solution; 3) Mix the tetrabutyl titanate dispersion in the sulfonated delignified lignin solution, carry out a hydrothermal synthesis reaction, and dry the product to obtain sulfonated lignin / titanium dioxide nanoparticles.

2. The preparation method of the sulfonated lignin / titanium dioxide nanoparticles according to claim 1, characterized in that, The alkali solution of delignified lignin is obtained by mixing delignified lignin and sodium hydroxide solution, and the dosage ratio of delignified lignin to sodium hydroxide solution is 4 - 6 g: 100 mL.

3. The preparation method of sulfonated lignin / titanium dioxide nanoparticles according to claim 2, wherein The mass ratio of formaldehyde, sodium sulfite and delignified lignin is 0.6 - 1.2: 1.5 - 3.5: 4 - 6.

4. The preparation method of sulfonated lignin / titanium dioxide nanoparticles according to claim 2, characterized in that, The pH of the sodium hydroxide solution is 10 - 12; The dialysis is carried out in a dialysis bag with a molecular weight cut-off of 1000 Da for 2 - 7 days.

5. The preparation method of the sulfonated lignin / titanium dioxide nanoparticles according to any one of claims 2 to 4, characterized in that, The temperature for mixing formaldehyde is 70 - 80 °C, and the mixing time is 2 - 3 h; The temperature for mixing sodium sulfite is 80 - 90 °C, and the mixing time is 5 - 6 h.

6. The preparation method of the sulfonated lignin / titanium dioxide nanoparticles according to claim 5, characterized in that, In step 3), the mass ratio of tetrabutyl titanate in the tetrabutyl titanate dispersion to sulfonated delignified lignin in the sulfonated delignified lignin solution is 3 - 5: 3 - 6; the mass content of tetrabutyl titanate in the tetrabutyl titanate dispersion is 18 - 22%; The temperature of the hydrothermal synthesis is 130 - 170 °C, the time of the hydrothermal synthesis is 8 - 9 h, and the drying temperature is 40 - 50 °C.

7. Sulfonated lignin / titanium dioxide nanoparticles prepared by the preparation method of the sulfonated lignin / titanium dioxide nanoparticles according to any one of claims 1 - 6.

8. Use of the sulfonated lignin / titanium dioxide nanoparticles according to claim 7 as an anti-ultraviolet agent in polyurethane materials, characterized in that, It includes the following steps: Disperse the sulfonated lignin / titanium dioxide nanoparticles according to claim 7 in water to obtain an SDL / TiO2 dispersion; Add the SDL / TiO2 dispersion to aqueous polyurethane, and successively carry out shearing, vacuum defoaming and drying to obtain a sulfonated lignin / titanium dioxide composite polyurethane material.

9. The application according to claim 8, wherein The mass ratio of the sulfonated lignin / titanium dioxide nanoparticles to aqueous polyurethane is 0.5 - 5: 100; The mass ratio of the sulfonated lignin / titanium dioxide nanoparticles to water is 1.25 - 12.5:

100.

10. The application according to any one of claims 7 to 9, characterized in that, The rotation speed of the shearing is 300 - 400 r / min, the shearing time is 15 - 60 min, the drying temperature is 40 - 60 °C, and the drying time is 10 - 14 h.

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