An alkali-resistant lignin monodisperse colloidal sphere, its preparation method and application

Abstract

This invention discloses an alkali-resistant lignin monodisperse colloidal sphere, its preparation method, and its applications. The invention involves adding industrial lignin to an acetone-water mixture, precipitating different fractions of lignin step-by-step by adding water dropwise, then dissolving the target fraction of lignin again in the acetone-water mixture. After adding water dropwise, allowing the mixture to stand, removing the acetone, and finally adding a crosslinking agent to crosslink and solidify the mixture, a dispersion of alkali-resistant lignin monodisperse colloidal spheres is prepared. These alkali-resistant lignin colloidal spheres retain their complete and uniform morphology and color even after being immersed in organic solvents such as ethanol and acetone at pH 11 and 14 for 7 days. The preparation process parameters of this invention are well-defined and highly reproducible. The resulting colloidal spheres exhibit excellent alkali resistance and resistance to organic solvents, effectively broadening the application fields of lignin-based structural materials.

Description

Technical Field

[0001] This invention belongs to the field of lignin preparation technology, specifically relating to a lignin monodisperse colloidal sphere that is resistant to alkali and organic solvents, its preparation method, and its application. Background Technology

[0002] Lignin, as the most abundant aromatic polymer in nature, possesses amphiphilicity, UV resistance, and photothermal effects due to its unique phenylpropane structure and various functional groups, making it highly promising in energy conversion, functional materials development, and the pharmaceutical field. However, lignin's complex and highly disordered three-dimensional network structure and high aggregation characteristics increase the difficulty of its utilization, leading to insufficient high-value utilization. Controlling the aggregation morphology of lignin through structural regulation to develop new materials is an important way to realize the high-value utilization of lignin. Lignin colloidal spheres are a high-value nanomaterial with excellent performance in drug delivery, fragrance sustained release, and photothermal coatings. Their preparation process involves antisolvent self-assembly technology, transforming the originally disordered lignin molecules into ordered nanoparticle aggregates. However, due to the high heterogeneity of intermolecular forces in lignin, the colloidal spheres formed during self-assembly have uneven particle size and poor tunability. By reducing the heterogeneity of lignin through fractionation, ultrafiltration, and modification, colloidal spheres with uniform and tunable size can be obtained. Although the heterogeneity of lignin has been effectively improved, the stability of homogeneous lignin colloidal spheres remains a core challenge to be overcome. Patent CN115155539B utilizes a hydrothermal method to prepare magnetic lignin-phenolic nanospheres from phenols, lignin, and hexamethylenetetramine. Stable covalent bonds are formed through high-temperature curing. The prepared colloidal nanospheres maintain good morphology in an alkaline environment at pH 11, but further increases in alkalinity lead to dissolution of the colloidal spheres. Researchers developed a lignin-epoxy hybrid method to prepare lignin colloidal spheres that can withstand pH 12 alkaline solutions by co-assembling lignin and crosslinking agents into spheres and then curing them (ACS Nano 2021, 15, 4811-4823). However, these spheres cannot withstand even higher alkaline environments. Currently, lignin colloidal spheres prepared by either hydrothermal high-temperature curing or crosslinking agent doping curing cannot maintain spherical stability in highly alkaline environments (pH 14). Furthermore, the curing process leads to the destruction of the sphere's morphology and a decrease in size uniformity, which severely limits the application of lignin colloidal spheres as functional materials in various fields and scenarios. Summary of the Invention

[0003] To address the problems of poor alkali resistance and uneven size distribution of lignin colloidal spheres in the prior art, the primary objective of this invention is to provide a method for preparing alkali-resistant monodisperse lignin colloidal spheres.

[0004] Another object of the present invention is to provide an alkali-resistant monodisperse lignin colloidal ball prepared by the above preparation method.

[0005] The alkali-resistant monodisperse lignin colloid spheres of this invention have a PDI value of 0.03 to 0.08 and a particle size of 100 to 1200 nm.

[0006] Another object of the present invention is to provide the application of the above-mentioned highly alkali-resistant lignin monodisperse colloidal sphere.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing alkali-resistant lignin monodisperse colloidal spheres, comprising the following steps:

[0009] (1) Dissolve lignin fully in a mixed solvent of acetone and water in a volume ratio of 70:30 to 60:40. After removing the insoluble part, add water dropwise to the solution to allow the lignin fractions of different fractions in the system to precipitate and separate step by step. Collect the lignin fractions precipitated in the stage of acetone and water in a volume ratio of 60:40 to 40:60.

[0010] (2) Dissolve the lignin fraction collected in step (1) in a mixed solvent of acetone and water in a volume ratio of 70:30 to 65:35, add water dropwise, let stand, remove acetone, add crosslinking agent to carry out crosslinking and curing reaction to obtain alkali-resistant lignin monodisperse colloidal sphere dispersion, and centrifuge the dispersion to obtain alkali-resistant lignin monodisperse colloidal spheres.

[0011] The alkali-resistant lignin monodisperse colloidal spheres of this invention are made by dispersing lignin in an acetone-water solvent. By continuously adding water to change the water content of the solution system, different fractions of lignin are precipitated, thus solving the problem of large polarity differences between lignin molecules and obtaining lignin fractions with uniform polarity. The target lignin fraction is then dissolved in an acetone-water solvent, and water is added dropwise to induce phase separation. After removing the acetone by rotary evaporation, a cross-linking agent is added, and finally, solidification is performed, resulting in a stable cross-linked structure between the lignin colloidal spheres and the cross-linking agent, which is then dispersed in water. Furthermore, the solvent for dissolving lignin must be an acetone-water solvent; other solvents (tetrahydrofuran or γ-valerolactone) will cause the colloidal spheres to perforate and fail to form a spherical shape. The method of adding water to induce phase separation must be dropwise; if directly mixed with water, the colloidal particles are prone to local aggregation, making it impossible to obtain monodisperse lignin colloidal spheres.

[0012] The collected graded lignin must be lignin precipitated during the grading process in step (1) with a system moisture content in the range of 40–60 vol.% to ensure that the prepared lignin monodisperse colloidal spheres achieve a PDI < 0.1. If the moisture content is less than 40 vol.%, the lignin will not be able to form spheres; if the moisture content is greater than 60 vol.%, it will cause differences in the size of the colloidal spheres. Both of these moisture contents are unfavorable for obtaining monodisperse lignin colloidal spheres and ultimately affect the preparation of lignin-based photonic materials.

[0013] In step (1), the volume ratio of acetone to water in the mixed solvent is 70:30 to 60:40. The volume ratio of acetone to water can be 70:30, 69:31, 68:32, 67:33, 66:34, 65:35, 64:36, 63:37, 62:38, 61:39, or 60:40. Any other specific value within this range can be selected, and it is not convenient to elaborate on them here.

[0014] Preferably, the mass ratio of the mixed solvent in step (1), in which the volume ratio of lignin to acetone and water is 70:30 to 60:40, is 5:(43 to 48) (e.g., 5:43, 5:44, 5:45, 5:46, 5:47, 5:48, etc.). Any other specific value within this range can be selected, and it is not convenient to elaborate on them here.

[0015] Preferably, the rate at which water is added in step (1) is 2.5 to 12.5 mL / min (e.g., 2.5 mL / min, 3 mL / min, 3.5 mL / min, 4 mL / min, 4.5 mL / min, 5 mL / min, 5.5 mL / min, 6 mL / min, 6.5 mL / min, 7 mL / min, 7.5 mL / min, 8 mL / min, 8.5 mL / min, 9 mL / min, 9.5 mL / min, 10 mL / min, 10.5 mL / min, 11 mL / min, 11.5 mL / min, 12 mL / min, 12.5 mL / min, etc.). Any other specific value within this range can be selected, and it is not convenient to elaborate on them here.

[0016] Preferably, the lignin in step (1) includes at least one of alkali lignin and enzymatically hydrolyzed lignin.

[0017] Preferably, the removal of insoluble parts and separation in step (1) are carried out by centrifugation, with a centrifugation speed of 8000-10000 rpm and a time of 5-10 min.

[0018] Preferably, the lignin fractions collected in step (1) need to be dried at 40–70°C.

[0019] In step (2), the volume ratio of acetone to water in the mixed solvent is 70:30 to 65:35. The volume ratio of acetone to water can be 70:30, 69:31, 68:32, 67:33, 66:34, or 65:35. Any other specific value within this range can be selected, which will not be elaborated here.

[0020] Preferably, in step (2), if there is an insoluble portion of the lignin fraction in a mixed solvent of acetone and water in a volume ratio of 70:30 to 65:35, the insoluble portion must be removed first before water is added.

[0021] Preferably, the concentration of the lignin fraction in step (2) in a mixed solvent of acetone and water in a volume ratio of 70:30 to 65:35 is 1.0 to 1.5 g / L (e.g., 1.0 g / L, 1.1 g / L, 1.2 g / L, 1.3 g / L, 1.4 g / L, 1.5 g / L, etc.). Any other specific point value within this range can be selected, which will not be elaborated here.

[0022] Preferably, the rate at which water is added in step (2) is 2.5 to 12.5 mL / min (e.g., 2.5 mL / min, 3 mL / min, 3.5 mL / min, 4 mL / min, 4.5 mL / min, 5 mL / min, 5.5 mL / min, 6 mL / min, 6.5 mL / min, 7 mL / min, 7.5 mL / min, 8 mL / min, 8.5 mL / min, 9 mL / min, 9.5 mL / min, 10 mL / min, 10.5 mL / min, 11 mL / min, 11.5 mL / min, 12 mL / min, 12.5 mL / min, etc.). Any other specific value within this range can be selected, and it is not convenient to elaborate on them here.

[0023] Preferably, after adding water in step (2), the volume ratio of acetone to water in the system is 30:70.

[0024] Preferably, the settling time in step (2) is 15 to 45 minutes (e.g., 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, etc.). Any other specific point value within the above range can be selected, which will not be elaborated here.

[0025] Preferably, the method for removing acetone in step (2) includes rotary evaporation.

[0026] More preferably, the temperature of the rotary evaporation is 45-47℃ (e.g., 45℃, 46℃, 47℃, etc.), and the time of the rotary evaporation is 4-10min (e.g., 4min, 5min, 6min, 7min, 8min, 9min, 10min, etc.). Any other specific point value within the above range can be selected, which will not be elaborated here.

[0027] Preferably, the crosslinking agent in step (2) includes bisphenol A diglycidyl ether.

[0028] Preferably, the mass ratio of the crosslinking agent to lignin in step (2) is 2.33:1 to 4:1 (e.g., 2.33:1, 2.5:1, 3:1, 3.5:1, 4:1, etc.). Any other specific value within this range can be selected, which will not be elaborated here.

[0029] Preferably, the temperature of the crosslinking curing reaction in step (2) is 100-105℃ (e.g., 100℃, 101℃, 102℃, 103℃, 104℃, 105℃, etc.), and the curing time is 3.5-4h (e.g., 3.5h, 3.6h, 3.7h, 3.8h, 3.9h, 4h, etc.). Any other specific point value within this range can be selected, and it is inconvenient to elaborate on them here.

[0030] Secondly, the present invention provides an alkali-resistant lignin monodisperse colloidal sphere obtained by the above preparation method.

[0031] The alkali-resistant lignin monodisperse colloidal spheres have a PDI < 0.1 and an average particle size of 50–1000 nm.

[0032] In the above preparation method, when the concentration of lignin fraction in the mixed solvent of acetone and water in the volume ratio of 70:30 to 65:35 in step (2) is 1.0 to 1.5 g / L, and the rate of water addition is 5 to 12.5 mL / min, the obtained lignin monodisperse colloidal spheres are lignin colloidal sphere structural color materials with a PDI < 0.1 and an average particle size < 350 nm, which can be used as structural color materials in the field of structural color.

[0033] Thirdly, the present invention provides the application of the above-mentioned alkali-resistant lignin monodisperse colloidal sphere.

[0034] This invention allows for the control of the average particle size of lignin monodisperse colloidal spheres within the range of 100–1000 nm by adjusting the concentration of lignin and the rate of water addition. Specifically, a higher lignin concentration results in a larger average particle size, while a faster water addition rate results in a smaller average particle size. By controlling the lignin concentration and the water addition rate within a specific concentration range, lignin monodisperse colloidal spheres of a specific particle size can be obtained.

[0035] This invention allows for the regulation of the alkali resistance and organic solvent resistance of lignin monodisperse colloidal spheres by adjusting the content of the crosslinking agent. Specifically, a higher crosslinking agent content results in better alkali resistance of the lignin monodisperse colloidal spheres, while a mass ratio of crosslinking agent to lignin ≥ 2.33:1 does not significantly alter the alkali resistance.

[0036] This invention can control the average particle size of lignin monodisperse colloidal spheres to below 350 nm by adjusting the concentration of lignin and the rate of water addition, thereby preparing lignin-based photonic materials that can be used as structural colors.

[0037] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0038] 1. This invention uses abundant and inexpensive industrial lignin directly as raw material, employs a single solvent, and is simple to operate. The method for preparing alkali-resistant lignin monodisperse colloidal spheres provided by this invention controls the alkali resistance of the lignin colloidal spheres by adjusting the content of the crosslinking agent. This allows the prepared lignin monodisperse colloidal spheres to have an extremely narrow size distribution and excellent alkali resistance and resistance to organic solvents, with a PDI range of 0.01 to 0.10.

[0039] 2. By controlling the initial concentration of lignin and the rate of water addition, the particle size of the prepared lignin monodisperse colloidal spheres can be precisely controlled within the range of 50–1000 nm, which is beneficial for industrial production.

[0040] 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

[0041] Figure 1 The images show SEM images of the lignin monodisperse colloidal spheres prepared in Comparative Examples 1-3 of this invention.

[0042] Figure 2 The images shown are SEM images of the alkali-resistant lignin monodisperse colloidal spheres prepared in Examples 1-3 of this invention.

[0043] Figure 3The images show SEM images of the alkali-resistant lignin monodisperse colloidal spheres prepared in Examples 1, 4 and 5 of this invention.

[0044] Figure 4 The images are SEM images of the alkali-resistant lignin monodisperse colloidal spheres prepared in Examples 6-9 of this invention (corresponding to Examples 6-9 from left to right).

[0045] Figure 5 This is a SEM image of the lignin colloidal spheres prepared in Comparative Example 10 of this invention.

[0046] Figure 6 Images and SEM images of the alkali-resistant lignin monodisperse colloidal spheres prepared in Examples 1 and 3 of this invention after immersion in an alkaline solution at pH 12.

[0047] Figure 7 Images and SEM images of the lignin colloidal spheres prepared in Comparative Examples 1 and 9 of this invention after soaking in an alkaline solution at pH 12.

[0048] Figure 8 Images and SEM images of the alkali-resistant lignin monodisperse colloidal spheres prepared in Examples 1 and 3 of this invention after being soaked in acetone solvent.

[0049] Figure 9 Images and SEM images of the lignin colloidal spheres prepared in Comparative Examples 1 and 9 of this invention after being soaked in acetone solvent.

[0050] Figure 10 Images and SEM images of the alkali-resistant lignin monodisperse colloidal spheres prepared in Example 1 of this invention, immersed in alkaline solutions at pH 13 and 14 and acetone aqueous solvent (acetone-water volume ratio of 70:30).

[0051] Figure 11 Images and SEM images of the alkali-resistant lignin monodisperse colloidal spheres prepared in Examples 1-3 of this invention after immersion in an alkaline solution at pH 14.

[0052] Figure 12 Images and SEM images of the alkali-resistant lignin monodisperse colloidal spheres prepared in Examples 1, 4 and 5 of this invention after immersion in an alkaline solution at pH 14.

[0053] Figure 13 Images and SEM images of the lignin colloidal spheres prepared in Comparative Examples 1-3 of this invention after soaking in an alkaline solution at pH 14.

[0054] Figure 14 Images and SEM images of the lignin colloidal spheres prepared in Comparative Examples 4-6 of this invention after soaking in an alkaline solution at pH 14.

[0055] Figure 15Images and SEM images of the lignin colloidal spheres prepared in Comparative Example 9 of this invention after soaking in an alkaline solution at pH 14.

[0056] Figure 16 Images and SEM images of the lignin colloidal spheres prepared in Comparative Examples 7 and 8 of this invention after soaking in an alkaline solution at pH 14.

[0057] Figure 17 Images and SEM images of the lignin colloidal spheres prepared in Comparative Example 10 of this invention after soaking in an alkaline solution at pH 14.

[0058] Figure 18 Images and SEM images of the lignin colloidal spheres prepared in Comparative Example 11 of this invention after soaking in an alkaline solution at pH 14.

[0059] Figure 19 The particle size distribution and zeta potential diagrams of the lignin colloidal spheres prepared in Examples 1 and 3 and Comparative Example 9 of this invention are shown.

[0060] Figure 20 The particle size distribution diagrams are for the lignin monodisperse colloidal spheres prepared in Examples 6-9 of this invention (corresponding to Examples 6-9 from top to bottom).

[0061] Figure 21 The lignin-based structural colors obtained by centrifuging the lignin monodisperse colloidal spheres prepared in Examples 6-9 of this invention are shown in the figures (from left to right, corresponding to Examples 6-9).

[0062] Figure 22 This is a schematic diagram of the preparation process of the present invention. Detailed Implementation

[0063] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0064] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available products.

[0065] Example 1

[0066] A method for preparing alkali-resistant lignin monodisperse colloidal spheres specifically includes the following steps:

[0067] S1. Weigh 5g of enzymatically hydrolyzed lignin and place it in a 100mL beaker. Add 45g of acetone-water solution (acetone to water volume ratio of 70:30) and dissolve it completely. Stir at 500rpm for 1h. Add this mixture to a 50mL centrifuge tube and centrifuge at 10000rpm for 6min to obtain the first supernatant.

[0068] The first supernatant was filtered through a 0.22 μm pore size filter membrane. 42 mL of the filtered first supernatant was transferred to a 100 mL beaker using a pipette, and then 7 mL of water was added dropwise at a rate of 2.5 mL / min. The resulting mixture had a acetone to water volume ratio of 60:40. After standing for 2 hours, the mixture was centrifuged at 10,000 rpm for 6 minutes to obtain the precipitate and the second supernatant. The precipitate was dried in a 60℃ oven, and the resulting solid was designated as lignin W40.

[0069] The second supernatant was filtered through a 0.22 μm pore size membrane. 40 mL of the filtered second supernatant was then transferred using a pipette, and 8 mL of water was added dropwise at a rate of 2.5 mL / min. The resulting mixture had a 50:50 volume ratio of acetone to water. After standing for 2 hours, the mixture was centrifuged at 10,000 rpm for 6 minutes to obtain the precipitate and the third supernatant. The precipitate was dried in a 60℃ oven, and the resulting solid was designated as lignin W50.

[0070] The third supernatant was filtered through a 0.22 μm pore size membrane. 42 mL of the filtered third supernatant was then pipetted into it, and 4.67 mL of water was added dropwise at a rate of 2.5 mL / min. The resulting mixture had a 45:55 volume ratio of acetone to water. After standing for 2 hours, the mixture was centrifuged at 10,000 rpm for 6 minutes to obtain the precipitate and the fourth supernatant. The precipitate was dried in a 60℃ oven, and the resulting solid was designated as lignin W55.

[0071] The fourth supernatant was filtered through a 0.22 μm pore size membrane. 40 mL of this supernatant was then transferred using a pipette, and 5 mL of water was added dropwise at a rate of 2.5 mL / min. The resulting mixture had a 40:60 volume ratio of acetone to water. After standing for 2 hours, the mixture was centrifuged at 10,000 rpm for 6 minutes to obtain the precipitate and the fifth supernatant. The precipitate was dried in a 60℃ oven, and the resulting solid was designated as lignin W60.

[0072] The fifth supernatant was filtered through a 0.22 μm pore size membrane. 40 mL of the filtered fifth supernatant was transferred using a pipette, and 14 mL of water was added dropwise at a rate of 2.5 mL / min. The resulting mixture had an acetone to water volume ratio of 30:70. After standing for 2 hours, the mixture was centrifuged at 10,000 rpm for 6 minutes, and the precipitate was retained. The precipitate was dried in a 60℃ oven, and the resulting solid was designated as lignin W70.

[0073] S2. Weigh 5 mg of lignin W50 obtained in S1 and place it in a 100 mL beaker. Add 5 mL of acetone aqueous solvent (acetone to water volume ratio of 70:30) and dissolve it completely. Stir at 500 rpm for 1 h. Filter the mixed solution using a 0.22 μm pore size filter membrane. Add 6.67 mL of water dropwise to the mixed solution at a rate of 2.5 mL / min. After standing for 30 min, remove the acetone using a rotary evaporator at 45 °C. Add 11.67 mg of crosslinking agent (bisphenol A diglycidyl ether) and cure in an oil bath at 105 °C for 4 h to obtain an alkali-resistant lignin monodisperse colloidal sphere dispersion.

[0074] Example 2

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

[0076] In S2, the mass of the crosslinking agent is 15 mg.

[0077] Example 3

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

[0079] In S2, the mass of the crosslinking agent is 20 mg.

[0080] Example 4

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

[0082] The lignin used in S2 is the lignin W55 from step S1.

[0083] Example 5

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

[0085] The lignin used in S2 is the lignin W60 from step S1.

[0086] Example 6

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

[0088] The water in S2 is added at a rate of 12.5 mL / min.

[0089] Example 7

[0090] A method for preparing monodisperse lignin colloidal spheres differs from that in Example 1 in that:

[0091] The water in S2 is added at a rate of 10 mL / min.

[0092] Example 8

[0093] A method for preparing monodisperse lignin colloidal spheres differs from that in Example 1 in that:

[0094] In S2, 7.5 mg of lignin W50 was weighed, 17.5 mg of crosslinking agent was added, and the water was added at a rate of 7.5 mL / min.

[0095] Example 9

[0096] A method for preparing monodisperse lignin colloidal spheres differs from that in Example 2 in that:

[0097] In S2, the mass of lignin W50 is 7.5 mg, the mass of crosslinking agent added is 17.5 mg, and the water is added at a rate of 5 mL / min.

[0098] Comparative Example 1

[0099] A method for preparing monodisperse lignin colloidal spheres differs from that in Example 1 in that:

[0100] The lignin used in S2 is the lignin W50 from step S1, and it is cured without adding a crosslinking agent. That is, in S2, acetone is removed by a rotary evaporator at 45°C to obtain a lignin dispersion.

[0101] Comparative Example 2

[0102] A method for preparing monodisperse lignin colloidal spheres differs from that in Example 1 in that:

[0103] The lignin used in S2 is the lignin W55 from step S1, and it is cured without adding a crosslinking agent. That is, in S2, acetone is removed by a rotary evaporator at 45°C to obtain a lignin dispersion.

[0104] Comparative Example 3

[0105] A method for preparing monodisperse lignin colloidal spheres differs from that in Example 1 in that:

[0106] The lignin used in S2 is the lignin W60 from step S1, and it is cured without adding a crosslinking agent. That is, in S2, acetone is removed by rotary evaporator at 45°C to obtain a lignin colloidal sphere dispersion.

[0107] Comparative Example 4

[0108] A method for preparing lignin colloidal spheres differs from that in Example 1 in that:

[0109] Step S1 is omitted, meaning the lignin is not graded; step S2 is performed directly using enzymatic hydrolysis of the lignin to prepare a lignin colloidal sphere dispersion.

[0110] Comparative Example 5

[0111] A method for preparing lignin colloidal spheres differs from that in Example 1 in that:

[0112] S2 uses lignin of grade S1, which is W40.

[0113] Comparative Example 6

[0114] A method for preparing lignin colloidal spheres differs from that in Example 1 in that:

[0115] S2 uses lignin of grade S1, which is W70.

[0116] Comparative Example 7

[0117] A method for preparing lignin colloidal spheres differs from that in Example 1 in that:

[0118] The solvent used in S2 is tetrahydrofuran-water (THF to water volume ratio of 70:30).

[0119] Comparative Example 8

[0120] A method for preparing lignin colloidal spheres differs from that in Example 1 in that:

[0121] The solvent used in S2 is γ-valerolactone-water (the volume ratio of γ-valerolactone to water is 70:30).

[0122] Comparative Example 9

[0123] A method for preparing lignin colloidal spheres differs from that in Example 1 in that:

[0124] The amount of cross-linking agent added in S2 is 7.50 mg.

[0125] Comparative Example 10

[0126] A method for preparing lignin colloidal spheres differs from that in Example 1 in that:

[0127] The crosslinking agent used in S2 is polyethylene glycol diglycidyl ether (Mn 500) (PEGDE).

[0128] Comparative Example 11

[0129] A method for preparing lignin colloidal spheres differs from that in Example 1 in that:

[0130] In S2, a crosslinking agent is added one step before water is added, and no further crosslinking agent is added after rotary evaporation for curing.

[0131] Performance testing

[0132] 1. Microstructure analysis:

[0133] like Figure 1 The image shows SEM images of the lignin monodisperse colloidal spheres prepared in Comparative Examples 1-3. As can be seen from the images, the colloidal spheres are of uniform size.

[0134] like Figure 2 The image shows SEM images of the alkali-resistant lignin monodisperse colloidal spheres prepared in Examples 1-3. As can be seen from the images, the lignin colloidal spheres maintain low monodispersity within a mass ratio of bisphenol A diglycidyl ether to lignin ranging from 2.33:1 to 4:1.

[0135] like Figure 3 The image shows SEM images of the alkali-resistant lignin monodisperse colloidal spheres prepared in Examples 1, 4, and 5. As can be seen from the images, the colloidal spheres prepared with a lignin fraction of W50-60 exhibit high uniformity.

[0136] like Figure 4 The image shows SEM images of the alkali-resistant lignin monodisperse colloidal spheres prepared in Examples 6-9. As can be seen from the images, the initial lignin concentration and water addition rate are important factors affecting the size of the lignin colloidal spheres.

[0137] like Figure 5 The image shown is a SEM image of the lignin colloidal spheres prepared in Comparative Example 10. The image shows that the introduction of the crosslinking agent polyethylene glycol diglycidyl ether significantly increased the polydispersity index of the lignin colloidal spheres.

[0138] 2. Alkali resistance and organic solvent resistance test:

[0139] The method for testing the alkali resistance and organic solvent resistance of the present invention is as follows: After centrifuging the colloidal ball dispersion prepared in the examples or comparative examples at 10,000 rpm for 6 min, the supernatant is removed, and the resulting colloidal balls are directly added to the alkali solution or organic solvent for the corresponding test.

[0140] like Figure 6 The images show photographs and SEM images of the lignin colloidal spheres prepared in Examples 1 and 3, respectively, after being immersed in an alkaline solution at pH 12 and left to stand for 7 days. The images show that the colloidal spheres with crosslinking agent to lignin mass ratios of 2.33:1 and 4:1 wt% were not affected by the alkaline solution and maintained their intact spherical shape.

[0141] like Figure 7The images show photographs and SEM images of the lignin colloidal spheres prepared in Comparative Examples 1 and 9, respectively, after being immersed in an alkaline solution at pH 12 and left to stand for 7 days. The images show that most of the colloidal spheres could no longer maintain their spherical shape and were dispersed in the alkaline solution.

[0142] like Figure 8 The images show photographs and SEM images of the lignin colloidal spheres prepared in Examples 1 and 3, respectively, after being immersed in acetone solvent and left to stand for 7 days. The images show that the colloidal spheres with a crosslinking agent to lignin mass ratio of 2.33:1 and 4:1 still maintain a complete spherical structure and good dispersibility.

[0143] like Figure 9 The images show photographs and SEM images of the lignin colloidal spheres prepared in Comparative Examples 1 and 9 after immersion in acetone solvent and standing for 7 days. The images show that the colloidal spheres with a crosslinking agent to lignin mass ratio of 1.5:1 are still unstable, exhibiting a significant increase in dispersibility.

[0144] like Figure 10 The images show photographs and SEM images of the lignin colloidal spheres prepared in Example 1 after being immersed in pH 13, 14, and acetone-water (acetone-water volume ratio 70:30) for 7 days. The images show that the colloidal spheres with a crosslinking agent to lignin mass ratio of 2.33:1 exhibit good stability and maintain their spherical shape in highly alkaline solvents and organic solvent environments.

[0145] like Figure 11 The images show photographs and SEM images of the lignin colloidal spheres prepared in Examples 1-3, after being immersed in an alkaline solution at pH 14 and left to stand for 7 days. The images show that the colloidal spheres with a crosslinking agent to lignin mass ratio of 2.33:1 to 4:1 remain stable in strongly alkaline solutions, exhibiting excellent resistance to dissolution.

[0146] like Figure 12 The images show photographs and SEM images of the lignin colloidal spheres prepared in Examples 1, 4, and 5, after being immersed in an alkaline solution at pH 14 for 7 days. The images show that the cross-linked colloidal spheres prepared from lignin fractions W50, W55, and W60 are all resistant to dissolution by the strongly alkaline solution, and a highly stable cross-linked structure is formed inside the spheres.

[0147] like Figure 13 The images show photographs and SEM images of the lignin colloidal spheres prepared in Comparative Examples 1-3 after being immersed in an alkaline solution at pH 14 for 7 days. The images show that the lignin colloidal spheres without cross-linking agent curing do not possess the ability to resist alkaline solutions.

[0148] like Figure 14The images show photographs and SEM images of the lignin colloidal spheres prepared in Comparative Examples 4-6 after soaking in an alkaline solution at pH 14 for 7 days. The images show that although the original lignin and the lignin fractions W40 and W70 have some alkali resistance due to the introduction of cross-linking agents, their heterogeneity results in highly dispersed colloidal spheres that are not even spherical.

[0149] like Figure 15 The images show photographs and SEM images of the lignin colloidal spheres prepared in Comparative Example 9 after immersion in an alkaline solution at pH 14 for 7 days. The images show that the lignin colloidal spheres prepared with insufficient crosslinking agent exhibit instability and redispersibility in the strong alkaline solution.

[0150] like Figure 16 The image shows photographs and SEM images of the lignin colloidal spheres prepared in Comparative Examples 7 and 8 after being immersed in an alkaline solution at pH 14 for 7 days. The images show that the lignin colloidal spheres prepared with tetrahydrofuran-water and γ-valerol-water solvents exhibited perforation. This is essentially due to the difference in solvent concentrations inside and outside the sphere, which easily creates a pressure difference. The internal solvent is rich in organic phase, and to reach equilibrium, it needs to diffuse into the external system rich in aqueous phase. However, the solvents tetrahydrofuran and γ-valerol diffuse very quickly, leading to perforation.

[0151] like Figure 17 The images show photographs and SEM images of the lignin colloidal spheres prepared in Comparative Example 10 after being immersed in an alkaline solution at pH 14 for 7 days. The images show that adding the crosslinking agent polyethylene glycol diglycidyl ether does not stabilize the lignin colloidal spheres in a strongly alkaline solution.

[0152] like Figure 18 The images show photographs and SEM images of the lignin colloidal spheres prepared in Comparative Example 11 after immersion in an alkaline solution at pH 14 for 7 days. The images show that adding a cross-linking agent before lignin self-assembly disrupts the sphere formation process, increasing dispersibility without improving alkali resistance.

[0153] 3. Particle size analysis:

[0154] like Figure 19 The figure shows the particle size distribution of the lignin colloidal spheres prepared in Examples 1, 3, and Comparative Example 9. As can be seen from the figure, the PDI of the samples is much less than 0.1, meeting the standard for monodispersity index. The absolute values ​​of the zeta potentials of the samples are all between 35 mV and 45 mV, indicating that they are relatively stable in the aqueous phase.

[0155] like Figure 20 The figure shows the particle size distribution of the lignin monodisperse colloidal spheres prepared in Examples 6-9. As can be seen from the figure, the PDI of the samples is all much less than 0.1, meeting the requirements for monodispersity.

[0156] 4. Preparation method of lignin-based structural color materials:

[0157] Photonic lignin can be obtained by centrifuging the aqueous solution of lignin monodisperse colloidal spheres prepared in Examples 6-9 at 10000 rpm for 30 min.

[0158] like Figure 21 As shown, the lignin photonic lignin prepared from monodisperse lignin colloidal spheres in Examples 6-9 are presented sequentially. The figures demonstrate that the lignin photonic colloidal spheres exhibit a bright structural color.

[0159] Figure 22 This is a schematic diagram of the preparation process of the present invention.

[0160] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing alkali-resistant lignin monodisperse colloidal spheres, characterized in that, Includes the following steps: (1) Dissolve lignin fully in a mixed solvent of acetone and water in a volume ratio of 70:30 to 60:

40. After removing the insoluble part, add water dropwise to the solution to allow the lignin fractions of different fractions in the system to precipitate and separate step by step. Collect the lignin fractions precipitated in the stage of acetone and water in a volume ratio of 50:50 to 40:

60. (2) Dissolve the lignin fraction collected in step (1) in a mixed solvent of acetone and water in a volume ratio of 70:30 to 65:35, add water dropwise, let stand, remove acetone, add crosslinking agent to carry out crosslinking and curing reaction to obtain alkali-resistant lignin monodisperse colloidal sphere dispersion, and centrifuge the dispersion to obtain alkali-resistant lignin monodisperse colloidal spheres. The mass ratio of the mixed solvent of lignin, acetone and water in step (1) is 5:(43-48) with a volume ratio of 70:30 to 60:

40. The rate at which water is added in step (1) is 2.5–12.5 mL / min; The rate at which water is added in step (2) is 2.5–12.5 mL / min; The concentration of the lignin fraction in step (2) in a mixed solvent of acetone and water in a volume ratio of 70:30 to 65:35 is 1.0 to 1.5 g / L; The crosslinking agent in step (2) includes bisphenol A diglycidyl ether; The mass ratio of the crosslinking agent to lignin in step (2) is 2.33:1 to 4:

1.

2. The method for preparing alkali-resistant lignin monodisperse colloidal spheres according to claim 1, characterized in that, After adding water in step (2), the volume ratio of acetone to water in the system is 30:

70.

3. The method for preparing an alkali-resistant lignin monodisperse colloidal sphere according to claim 1, characterized in that, The temperature of the cross-linking curing reaction in step (2) is 100-105℃, and the curing time is 3.5-4 h.

4. The method for preparing alkali-resistant lignin monodisperse colloidal spheres according to claim 1, characterized in that, The lignin in step (1) includes at least one of alkali lignin or enzymatically hydrolyzed lignin; And / or, the settling time in step (2) is 15 to 45 minutes.

5. The method for preparing alkali-resistant lignin monodisperse colloidal spheres according to claim 1, characterized in that, In step (1), the removal of insoluble parts and separation are both carried out by centrifugation, with a centrifugation speed of 8000-10000 rpm and a time of 5-10 min. And / or, the method of removing acetone in step (2) includes rotary evaporation; The rotary evaporation temperature is 45–47 °C, and the time is 4–10 min; And / or, if there is an insoluble portion in the lignin fraction described in step (2) in a mixed solvent of acetone and water in a volume ratio of 70:30 to 65:35, the insoluble portion must be removed first before water is added.

6. An alkali-resistant lignin monodisperse colloidal sphere prepared by the preparation method according to any one of claims 1 to 5.

7. The application of the alkali-resistant lignin monodisperse colloidal spheres as described in claim 6 as a lignin-based photonic material with structural color.

Images