Monodisperse lignin colloidal spheres, and methods of making and using the same

Abstract

The application discloses monodisperse lignin colloidal spheres and a preparation method and application thereof. The preparation method comprises the following steps: S1. lignin is dissolved in a mixed solution of glacial acetic acid and acetylation reagent, and stirring and heating are carried out to obtain a reaction solution containing acetylated lignin; the mass ratio of the lignin to the acetylation reagent is 1:2.2-3.3; S2. the reaction solution containing the acetylated lignin obtained in the step S1 is subjected to removal of excessive acetylation reagent and solvent to obtain acetylated lignin; S3. the acetylated lignin obtained in the step S2 is dissolved in an organic solvent-water mixed solvent, water is added dropwise, and centrifugal treatment is carried out to obtain monodisperse lignin colloidal spheres. The preparation process is simple, the yield of the acetylated lignin product reaches more than 90%, and the monodisperse (PDI<0.1) lignin colloidal spheres with adjustable size can be prepared; when the average particle size of the monodisperse lignin colloidal spheres is regulated to be below 350 nm, the photonic lignin colloidal spheres which can be used as structural color materials can be prepared.

Description

Technical Field

[0001] This invention relates to the field of derivatives of natural polymer compounds, and more specifically, to a monodisperse lignin colloidal sphere, its preparation method, and its application. Background Technology

[0002] Lignin is an abundant, renewable aromatic polymer found in nature. It boasts advantages such as a short regeneration cycle, low cost, and easy availability, making it a potential source for producing high-value-added chemicals and materials. However, lignin has traditionally been considered a low-value waste, often directly burned or discharged as a byproduct, leading to resource waste and environmental pollution. This is because the natural structure and aggregation morphology of lignin molecules are complex, making it difficult to exhibit stable and uniform physicochemical properties on a macroscopic scale, thus hindering its high-value utilization. Therefore, chemically modifying lignin molecules to reduce differences in structure and aggregation morphology, thereby improving the uniformity of its physicochemical properties, is key to achieving high-value utilization of lignin. This has significant economic, environmental, and social benefits for increasing the economic value of renewable resources and reducing environmental pollution.

[0003] Lignin colloidal spheres are a novel type of lignin-based high-value-added material, typically prepared from lignin molecules via antisolvent self-assembly technology. They possess excellent biocompatibility, tunable hydrophilic / hydrophobic properties, UV resistance, and antioxidant properties, exhibiting superior performance in areas such as drug storage and transportation, coatings, pollutant adsorption, and UV protection, demonstrating immense application potential. Most physicochemical properties of colloidal spheres are highly dependent on their size distribution, with significant differences in physicochemical properties between spheres of different sizes. However, industrial lignin has a diverse range of functional groups and molecular structures, resulting in uneven size distribution (typically PDI > 0.5) and poor size tunability in lignin-prepared spheres, hindering industrial applications. Therefore, preparing lignin into size-tunable monodisperse (PDI < 0.1) colloidal spheres is a prerequisite for its widespread application in this field.

[0004] For example, patent document CN103242555B discloses an acetylated lignin amphiphilic polymer nanocolloid and its preparation method. The method involves acetylifying alkali lignin and then adding water to the organic solvent of acetylated lignin, so that the acetylated lignin self-assembles into nanoscale amphiphilic polymer colloidal spheres under the drive of hydrophobic interaction. However, the colloidal spheres prepared by the method cannot yet reach the level of monodispersity. Summary of the Invention

[0005] The primary objective of this invention is to overcome the problems of uneven size distribution and poor dispersibility of colloidal spheres in the prior art, and to provide a method for preparing monodisperse lignin colloidal spheres.

[0006] Another object of the present invention is to provide a monodisperse lignin colloidal sphere prepared by the above-described method for preparing monodisperse lignin colloidal spheres.

[0007] Another objective of this invention is to provide a method for preparing photonic lignin colloidal spheres. Using the above preparation method, photonic lignin colloidal spheres with PDI < 0.1 and average particle size < 350 nm can be obtained.

[0008] Another object of the present invention is to provide a photonic lignin colloidal sphere prepared by the above-described method for preparing photonic lignin colloidal spheres.

[0009] Another object of the present invention is to provide a structural color coating made from the above-mentioned photonic lignin colloidal spheres.

[0010] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0011] A method for preparing monodisperse lignin colloidal spheres includes the following steps:

[0012] S1. Lignin is dissolved in a mixed solution of glacial acetic acid and an acetylation reagent, stirred and heated to obtain a reaction solution containing acetylated lignin; the mass ratio of lignin to acetylation reagent is 1:2.2-3.3.

[0013] S2. Remove excess acetylation reagent and solvent from the reaction solution containing acetylated lignin obtained in step S1 to obtain acetylated lignin;

[0014] S3. Dissolve the acetylated lignin obtained in step S2 in an organic solvent-water mixture, add water dropwise, and centrifuge to obtain monodisperse lignin colloidal spheres;

[0015] Wherein, the concentration of the acetylated lignin in organic solvent-water in S3 is 0.5-4 g / L; and the rate of water addition is 0.5-50 mL / min.

[0016] The monodisperse lignin colloidal spheres of this invention are produced by dispersing lignin in glacial acetic acid to enhance the reactivity of its phenolic and alcoholic hydroxyl groups. Then, it reacts with an acetylation reagent dissolved in glacial acetic acid, causing the phenolic and alcoholic hydroxyl groups to be replaced by hydrophobic acetyl groups. This effectively modifies the polar functional groups of lignin, thus solving the problem of large polarity differences between lignin molecules and reducing these differences, resulting in acetylated lignin with uniform polarity. The acetylated lignin is dissolved in an organic solvent-water mixture, and water is added dropwise to induce phase separation. Finally, centrifugation and sedimentation yield the monodisperse lignin colloidal spheres. Furthermore, the phase separation caused by adding water must be done dropwise; if directly mixed with water, the colloidal particles tend to aggregate locally, making it impossible to obtain monodisperse lignin colloidal spheres.

[0017] The mass ratio of lignin to acetylation reagent must be between 1:2.2 and 3.3 to achieve a PDI < 0.1 in the final monodisperse lignin colloidal spheres. If the mass ratio is less than 1:3.3, the dispersion will be insufficiently uniform; if the mass ratio is greater than 1:2.2, the colloidal particles will be highly aggregated. Neither of these mass ratios is conducive to obtaining monodisperse lignin colloidal spheres and ultimately affects the preparation of photonic lignin.

[0018] Preferably, the concentration of the acetylated lignin in organic solvent-water in S3 is 0.5-2 g / L, and the rate of water addition is 2-30 mL / min.

[0019] Preferably, the lignin in S1 is enzymatically hydrolyzed lignin or alkali lignin.

[0020] Preferably, the heating temperature in S1 is 40-60°C; more preferably, the heating temperature in S1 is 40-50°C.

[0021] Preferably, the heating time in S1 is 2 to 4 hours; more preferably, the heating time in S1 is 2 to 3 hours.

[0022] Preferably, the acetylation reagent in S1 is acetyl bromide or acetyl chloride.

[0023] Preferably, the method for removing excess acetylation reagent and solvent in S2 is to first remove acetyl chloride from the reaction solution containing acetylated lignin by rotary evaporation, and then remove the solvent from the remaining reaction solution by washing with water.

[0024] Preferably, the temperature of the rotary evaporation is 40–60°C.

[0025] Preferably, after removing excess acetylation reagent and solvent, step S2 further includes the drying of acetylated lignin.

[0026] Preferably, the drying temperature is 40–60°C, and the drying time is 12–24 hours.

[0027] Preferably, the organic solvent in S3 is at least one of tetrahydrofuran, acetone, γ-valerolactone, and dioxane.

[0028] Preferably, the volume ratio of organic solvent to water in the organic solvent-water mixed solvent in S3 is 1:0 to 0.25.

[0029] Preferably, the volume ratio of the organic solvent in the water added in step S3 to the organic solvent-water mixture is 3.5 to 35:1.

[0030] Preferably, the centrifugation speed in S3 is 5000-10000 rpm, and the centrifugation time is 10-30 min.

[0031] Preferably, the PDI of the monodisperse lignin colloidal spheres is <0.1.

[0032] This invention allows for the control of the average particle size of monodisperse lignin colloidal spheres within the range of 50–1000 nm by adjusting the concentration of acetylated lignin and the rate of water addition. Specifically, a higher concentration of acetylated lignin results in a larger average particle size, while a faster rate of water addition results in a smaller average particle size. By controlling the concentration of acetylated lignin and the rate of water addition within a specific concentration range, monodisperse lignin colloidal spheres with a specific particle size can be obtained.

[0033] This invention also protects a monodisperse lignin colloidal sphere prepared by the above preparation method.

[0034] Furthermore, the present invention can control the average particle size of monodisperse lignin colloidal spheres to be below 350 nm by adjusting the concentration of acetylated lignin and the rate of water addition, thereby preparing photonic lignin colloidal spheres that can be used as structural color materials.

[0035] This invention also protects a method for preparing photonic lignin colloidal spheres. The photonic lignin colloidal spheres prepared by the above method have a PDI < 0.1 and an average particle size < 350 nm.

[0036] This invention also protects a photonic lignin colloidal sphere prepared using the above-described method for preparing photonic lignin colloidal spheres.

[0037] This invention also protects a structural color coating made from the above-mentioned photonic lignin colloidal spheres.

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] 1. This invention uses abundant and inexpensive industrial lignin directly as raw material, without the need for large amounts of organic solvents. The operation is simple and the entire preparation process is green and environmentally friendly. The method for preparing monodisperse lignin colloidal spheres provided by this invention controls the degree of acetylation by controlling the mass ratio of lignin to acetylation reagent, which can make the obtained monodisperse lignin colloidal spheres have an extremely narrow size distribution, with a PDI range of 0.01 to 0.10.

[0040] 2. By controlling the initial concentration of acetylated lignin and the rate of water addition, the particle size of the monodisperse lignin colloidal spheres can be precisely controlled within the range of 50–1000 nm, and the yield of acetylated lignin products is high (greater than 90%), which is conducive to industrial production.

[0041] 3. The photonic lignin colloidal spheres prepared by this invention have a PDI of less than 0.1 and an average particle size of less than 350 nm, and can be used for the preparation of structural color materials. Attached Figure Description

[0042] Figure 1 Photograph of the lignin structural color coating prepared from the monodisperse lignin colloidal spheres prepared in Example 3 of this invention.

[0043] Figure 2 This is a SEM image of the monodisperse lignin colloidal spheres prepared in Example 3 of the present invention.

[0044] Figure 3 This is a SEM image of the lignin colloidal spheres prepared in Comparative Example 1 of this invention.

[0045] Figure 4 This is a SEM image of the lignin colloidal spheres prepared in Comparative Example 2 of this invention.

[0046] Figure 5 This is a SEM image of the lignin colloidal spheres prepared in Comparative Example 3 of this invention.

[0047] Figure 6 This is a SEM image of the lignin colloidal spheres prepared in Comparative Example 4 of this invention.

[0048] Figure 7 This is a particle size distribution diagram of the monodisperse lignin colloidal spheres prepared in Example 1 of the present invention.

[0049] Figure 8 This is a particle size distribution diagram of the lignin colloidal spheres prepared in Comparative Example 1 of the present invention.

[0050] Figure 9 This is a particle size distribution diagram of the lignin colloidal spheres prepared in Comparative Example 2 of the present invention.

[0051] Figure 10 This is a particle size distribution diagram of the lignin colloidal spheres prepared in Comparative Example 3 of the present invention. Detailed Implementation

[0052] The enzymatically hydrolyzed lignin and alkali lignin used in the following examples and comparative examples were purchased from Shandong Longli Biotechnology Co., Ltd.

[0053] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0054] Example 1

[0055] A method for preparing monodisperse lignin colloidal spheres specifically includes the following steps:

[0056] S1. Place the enzymatically hydrolyzed lignin in a 250 mL round-bottom flask, add 50 mL of a mixed solution of acetyl chloride and glacial acetic acid and dissolve it thoroughly (the amount of acetyl chloride used is 15 mL, and the mass ratio of enzymatically hydrolyzed lignin to acetyl chloride is 1:3.3), seal the flask and react at 40 °C for 2 h to obtain a reaction solution containing acetylated lignin.

[0057] S2. The reaction solution containing acetylated lignin obtained in S1 is subjected to rotary evaporation at 50°C to remove excess acetylation reagent. Then, the remaining reaction solution is added to water and stirred continuously. The solution is filtered and washed with water 2-3 times. The remaining solid is then dried at 60°C for 12 hours to obtain acetylated lignin.

[0058] S3. Weigh 10 mg of the acetylated lignin obtained in S2 and dissolve it completely in 10 mL of a tetrahydrofuran-water mixed solvent, wherein the volume ratio of tetrahydrofuran to water is 8:2. Add 30 mL of water dropwise to the mixed solution at a rate of 3 mL / min, and then centrifuge at 8000 rpm for 10 min to obtain monodisperse lignin colloidal spheres.

[0059] Example 2

[0060] A method for preparing monodisperse lignin colloidal spheres differs from that in Example 1 in that:

[0061] The amount of acetyl chloride used in S1 is 10 mL, and the mass ratio of enzymatically hydrolyzed lignin to acetyl chloride is 1:2.2.

[0062] Example 3

[0063] A method for preparing monodisperse lignin colloidal spheres differs from that in Example 1 in that:

[0064] In S3, 5 mg of acetylated lignin was weighed out, and the water was added at a rate of 2.5 mL / min.

[0065] Example 4

[0066] A method for preparing monodisperse lignin colloidal spheres differs from that in Example 1 in that:

[0067] In S3, 30 mg of acetylated lignin was weighed out, and the water was added at a rate of 30 mL / min.

[0068] Example 5

[0069] A method for preparing monodisperse lignin colloidal spheres differs from that in Example 1 in that:

[0070] In S3, 40 mg of acetylated lignin was weighed out, and the water was added at a rate of 5 mL / min.

[0071] Example 6

[0072] A method for preparing monodisperse lignin colloidal spheres differs from that in Example 1 in that:

[0073] In S3, 40 mg of acetylated lignin was weighed out, and the water was added at a rate of 10 mL / min.

[0074] Example 7

[0075] A method for preparing monodisperse lignin colloidal spheres differs from that in Example 1 in that:

[0076] The lignin used in S1 is alkali lignin, and the water is added at a rate of 5 mL / min.

[0077] Comparative Example 1

[0078] A method for preparing lignin colloidal spheres differs from that in Example 1 in that:

[0079] Steps S1 and S2 are omitted, acetylation is not performed, and step S3 is directly carried out by enzymatic hydrolysis of lignin to prepare lignin colloidal spheres.

[0080] Comparative Example 2

[0081] A method for preparing lignin colloidal spheres differs from that in Example 1 in that:

[0082] The mass ratio of enzymatically hydrolyzed lignin to acetyl chloride in S1 is 1:1.1.

[0083] Comparative Example 3

[0084] A method for preparing lignin colloidal spheres differs from that in Example 1 in that:

[0085] The mass ratio of enzymatically hydrolyzed lignin to acetyl chloride in S1 is 1:4.4.

[0086] Comparative Example 4

[0087] A method for preparing lignin colloidal spheres differs from that in Example 1 in that:

[0088] In S1, the acetylation reaction is changed to an etherification reaction, and the etherification reagent used is allyl glycidyl ether, and the solvent is sodium hydroxide.

[0089] Performance testing

[0090] 1. Preparation method of lignin-based structural color materials:

[0091] Photonic lignin can be obtained by centrifuging an aqueous solution of monodisperse colloidal spheres at 10,000 rpm for 30 min.

[0092] like Figure 1 The image shown is a photograph of the lignin structural color coating prepared from the monodisperse lignin colloidal spheres of Example 3. As can be seen from the image, the photonic lignin colloidal spheres exhibit a bright structural color.

[0093] 2. Microstructure analysis:

[0094] like Figure 2 The image shown is a SEM image of the monodisperse lignin colloidal spheres prepared in Example 3. As can be seen from the image, the colloidal spheres are uniform in size and regular in shape.

[0095] like Figures 3-6 The image shows SEM images of the lignin colloidal spheres prepared in Comparative Examples 1 to 4. It can be seen from the images that the uniformity of the colloidal spheres prepared in Comparative Examples 1 to 4 is poor. Specifically, Comparative Example 1 prepared fewer colloidal spheres, and the colloidal spheres prepared in Comparative Example 4 also exhibited depressions.

[0096] 3. Particle size analysis:

[0097] like Figure 7 The figure shows the particle size distribution of the monodisperse lignin colloidal spheres prepared in Example 1. As can be seen from the figure, the PDI of the colloidal spheres is 0.04, which is much smaller than 0.1, meeting the requirements for monodispersity.

[0098] like Figures 8-10 The figure shows the particle size distribution of the lignin colloidal spheres prepared in Comparative Examples 1 to 3. As can be seen from the figure, the PDI of the colloidal spheres prepared in Comparative Examples 1 to 3 is greater than 0.1, failing to meet the requirement of monodispersity. In particular, the colloidal spheres prepared in Comparative Example 3 exhibit excessive acetylation, resulting in partial high agglomeration and an average particle size greater than 350 nm, all of which are unfavorable for the preparation of structural colors.

[0099] Table 1. Comparison of test performance results between Examples 1-7 and Comparative Examples 1-4

[0100]

[0101]

[0102] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing monodisperse lignin colloidal spheres, characterized in that, Includes the following steps: S1. Lignin is dissolved in a mixed solution of glacial acetic acid and an acetylation reagent, stirred and heated to obtain a reaction solution containing acetylated lignin; the mass ratio of lignin to acetylation reagent is 1:2.2-3.

3. S2. Remove excess acetylation reagent and solvent from the reaction solution containing acetylated lignin obtained in step S1 to obtain acetylated lignin; S3. Dissolve the acetylated lignin obtained in step S2 in an organic solvent-water mixture, add water dropwise, and centrifuge to obtain monodisperse lignin colloidal spheres; Wherein, the concentration of the acetylated lignin in organic solvent-water in S3 is 0.5-4 g / L; and the rate of water addition is 0.5-50 mL / min.

2. The preparation method according to claim 1, characterized in that, The lignin mentioned in S1 is enzymatically hydrolyzed lignin or alkali lignin.

3. The preparation method according to claim 1, characterized in that, The heating temperature described in S1 is 40–60°C.

4. The preparation method according to claim 1, characterized in that, The heating time described in S1 is 2 to 4 hours.

5. The preparation method according to claim 1, characterized in that, The acetylation reagent in S1 is acetyl bromide or acetyl chloride.

6. The preparation method according to claim 1, characterized in that, The organic solvent mentioned in S3 is at least one of tetrahydrofuran, acetone, γ-valerolactone, and dioxane.

7. A monodisperse lignin colloidal sphere, prepared by the preparation method according to any one of claims 1 to 6.

8. A method for preparing photonic lignin colloidal spheres, wherein the photonic lignin colloidal spheres are prepared by any one of the preparation methods described in claims 1 to 6, wherein the PDI of the photonic lignin colloidal spheres is <0.1 and the average particle size is <350 nm.

9. A photonic lignin colloidal sphere, prepared by the method described in claim 8.

10. A structural color coating, prepared from the photonic lignin colloidal spheres of claim 9.

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