A method for preparing lignin-containing cellulose nanospheres

Abstract

The present application provides a preparation method of lignin-containing cellulose nanospheres, comprising the following steps: (1) crushing lignocellulosic biomass raw materials to a particle size of 20-100 mesh to obtain crushed lignocellulosic biomass; (2) mixing the crushed lignocellulosic biomass obtained in step (1) with a ternary eutectic solvent at a mass ratio of 1:10-1:20, stirring and reacting at a temperature of 80-160°C for 4-10 hours; (3) adding a mixture of organic solvent and water to step (2) to terminate the reaction, standing and cooling to room temperature, and then separating the cellulose-rich precipitate; (4) washing the precipitate obtained in step (3) to neutral, mixing with water at a mass ratio of 1:100-1:200, and then repeatedly passing through high-pressure homogenization for several times to obtain lignin-containing nanocellulose spheres. The present application fully combines the pretreatment methods of eutectic solvent and high-pressure homogenization, and has the advantages of mild conditions, simple operation, low cost, small pollution and stable product performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanocellulose preparation, and particularly relates to a preparation method of lignin-containing cellulose nanospheres. BACKGROUND

[0002] Nanocellulose with spherical morphology and size in the nanometer range, referred to as cellulose nanospheres (CNS), is a new type of nanocellulose. The shape of nanoparticles will significantly affect their performance in many applications. Spherical polymer nanoparticles have many outstanding advantages and are recognized in a wide range of applications in the biomedical field such as drug delivery, disease detection and diagnosis. CNS is mainly separated from natural cellulose through a top-down method, including chemical hydrolysis, mechanical dispersion and enzymatic hydrolysis, which are usually time-consuming, consume a large amount of toxic solvents, and face the problem of difficult industrialization.

[0003] Using lignin-containing raw materials can not only reduce the amount of chemicals and energy consumption, but also increase the yield and reduce the cost, thereby producing lignin-containing nanofibers. Recently, deep eutectic solvents (DES) as green solvents have gradually attracted widespread attention. Mild reaction conditions, high purity and good uniformity are the characteristics of deep eutectic solvent pretreatment. In addition, compared with traditional ionic solvents, deep eutectic solvents are low in price, environmentally friendly, easy to prepare and recyclable, which greatly promotes their application in biorefining. In the prior art, deep eutectic solvent pretreatment can only obtain lignin-containing cellulose nanofibrils (LCNF). For example, CN116356596A uses amino acid-based deep eutectic solvents to prepare LCNF. CN113502675A uses sugarcane residue, rice straw and other straw as raw materials, and preliminarily prepares a film material using the obtained LCNF. CN115722198A uses a deep eutectic system with a hydrogen bond acceptor of choline chloride and a hydrogen bond donor of a polyhydric alcohol to prepare LCNF. However, the preparation method of lignin-containing cellulose nanospheres (LCNS) has never been reported. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the prior art and provide a preparation method of lignin-containing cellulose nanospheres. The preparation method of the present application uses a ternary deep eutectic solvent system to separate lignocellulose biomass, and homogenizes the obtained lignin-containing cellulose residue to obtain lignin-containing nanocellulose spheres with uniform size.

[0005] In one aspect, the present application provides a method for preparing lignin-containing cellulose nanospheres, comprising the following steps:

[0006] (1) grinding lignocellulosic biomass raw material to a particle size of 20-100 mesh, preferably 40-60 mesh, to obtain ground lignocellulosic biomass;

[0007] (2) mixing the ground lignocellulosic biomass obtained in step (1) with a ternary eutectic solvent at a mass ratio of 1:10-1:20, stirring and reacting at a temperature of 80-160°C for 4-10 hours;

[0008] (3) adding a mixture of organic solvent and water to step (2) to terminate the reaction, allowing to cool to room temperature, and then separating the precipitate rich in cellulose;

[0009] (4) washing the precipitate obtained in step (3) to neutral, mixing with water at a mass ratio of 1:100-1:200, and after several cycles of high-pressure homogenization, obtaining lignin-containing nanocellulose spheres.

[0010] In a specific embodiment, in step (1), the lignocellulosic biomass raw material can include wood and non-wood, specifically, the wood can include broadleaf wood and / or coniferous wood; the non-wood can include crop straw, corn cob, pith and its residue after chemical extraction, grass, bamboo, cotton, cotton stalk. In particular, the broadleaf wood can include eucalyptus, birch or poplar, the coniferous wood can include larch, pine or spruce; the crop straw can be from wheat, corn, rice straw or sorghum.

[0011] In a specific embodiment, in step (2), the ternary eutectic solvent can be a mixture in a molten state formed by choline chloride as a hydrogen bond acceptor and a polyacid and a polyol as hydrogen bond donors. In a specific embodiment, the polyacid can refer to a bioacid containing multiple carboxyl groups, examples of which include but are not limited to citric acid, malic acid, or a combination thereof. In a specific embodiment, the polyol can refer to an alcohol containing multiple hydroxyl groups, examples of which include but are not limited to 1,4-butanediol, ethylene glycol, glycerol, or a combination thereof. In a specific embodiment, the molar ratio of choline chloride, polyacid, polyol can be 3:1:(2-4), preferably 3:1:2. In a specific embodiment, the ternary eutectic solvent can be obtained by mixing (e.g., at 90°C under 500 rpm) choline chloride, polyacid, polyol and stirring until a clear transparent solution is formed.

[0012] In a specific embodiment, in step (2), the temperature condition can be 120-160°C.

[0013] In the specific embodiment, in step (2), the reaction time can be 6-10 hours.

[0014] In the specific embodiment, in step (3), the volume ratio of the organic solvent to water (e.g., deionized water) can be 10:1-6:1.

[0015] In the specific embodiment, in step (3), the organic solvent can be a solvent that is miscible with the deep eutectic solvent and can dissolve lignin, examples of which include but are not limited to ethanol, acetone, etc., or a combination thereof.

[0016] In the specific embodiment, in step (4), the precipitate is washed to neutral using water (e.g., deionized water).

[0017] In the specific embodiment, in step (4), the homogenization times can be 10-50 times.

[0018] In the specific embodiment, in step (4), the homogenization is performed several times (e.g., 10 times) at a pressure of 1000 bar.

[0019] In the specific embodiment, in step (3) and step (4), the water can be deionized water.

[0020] In the specific embodiment, the size of the lignin-containing nanocellulose spheres obtained by the present application is 100-300 nm, preferably 150-250 nm, and more preferably about 200 nm.

[0021] Advantages

[0022] The present application uses lignocellulosic biomass as raw material, and uses a deep eutectic solvent to pretreat the lignocellulosic biomass raw material, and then performs several times of high-pressure homogenization to obtain cellulose nanospheres containing lignin.

[0023] Specifically, compared with the prior art, the present application has the following advantages and benefits:

[0024] (1) The present application uses a ternary deep eutectic solvent to separate lignocellulosic biomass, which is an environmentally friendly, low-cost, and recyclable new solvent.

[0025] (2) The nanocellulose spheres prepared by the present application have low production cost, simple preparation process, and are more universal and popular than traditional methods. In addition, the size is uniform, and the suspension is stable. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The scanning electron microscope image of the sample after homogenization is a comparative example.

[0027] Figure 2Figure 1 is a graph of the AFM scanning electron microscope of the sample after homogenization.

[0028] Figure 3 Figure 2 is a graph of the AFM scanning electron microscope (a) and SEM scanning electron microscope (b) of the sample of Example 1.

[0029] Figure 4 Figure 3 is a graph of the stability experiment sample of the sample of Example 1 after 90 days of standing.

[0030] Figure 5 Figure 4 is a graph of the SEM scanning electron microscope of the sample of Example 2. DETAILED DESCRIPTION

[0031] The present application will be described in more detail by way of examples. Before describing the present application, it should be understood that the terms used in the specification and the appended claims are not to be interpreted as limiting the present application to the commonly and dictionary meanings and concepts, but are to be interpreted in a manner allowing the inventors to best use the terms in accordance with a principle applied by allowing inventors to define the terms, based on a meaning and concept corresponding to a technical level of the present application. Accordingly, the description herein is merely an example of a preferred embodiment and is not intended to limit the scope of the present application and it should be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of the present application.

[0032] Terminology

[0033] In the present application, DES refers to deep eutectic solvent.

[0034] The following examples are merely set forth to illustrate examples of the present application and should not be construed as limiting the scope of the present application in any way as would be appreciated by one skilled in the art.

[0035] The instruments used in the following examples include: apv 2000 homogenizer, Germany, SU8010 cold field emission scanning electron microscope, Japan, atomic microscope (BRUKER MULTIMODE 8), and polarizing microscope (LEICA DM2500), unless otherwise specified, the reagents or other instruments and equipment used in the following examples are commercially available products.

[0036] Comparative Example

[0037] Formulation of biological acid deep eutectic solvent (DES): choline chloride as a hydrogen bond acceptor and citric acid as a hydrogen bond donor were mixed in a molar ratio of 3:1 at 90°C under stirring at 500 rpm for 3 hours to form a clear and transparent solution to obtain the DES.

[0038] Poplar was crushed to 40-60 mesh, then added to DES according to the mass ratio of 1:20, after stirring at 120℃ for 4 hours, mixed solution of acetone and deionized water with volume ratio of 10:1 was added, and the precipitate containing cellulose was separated after cooling to room temperature.

[0039] The obtained precipitate was washed to neutral with deionized water, then the precipitate and deionized water were dispersed in deionized water according to the mass ratio of 1:200, and the cellulose suspension was obtained after homogenization under the pressure of 1000 bar for 10 times. Figure 1 As shown in Figure 2 , the residue after homogenization showed rough morphology and failed to form nanocellulose balls.

[0040] Example 1

[0041] Biological acid-based deep eutectic solvent (DES) was prepared: choline chloride as a hydrogen bond acceptor and citric acid and 1,4-butanediol as a hydrogen bond donor were stirred at 90℃ for 3 hours under the condition of 500 rpm to form a clear and transparent solution, and DES was obtained.

[0042] Poplar was crushed to 40-60 mesh, then added to DES according to the mass ratio of 1:20, after stirring at 120℃ for 4 hours, mixed solution of acetone and deionized water with volume ratio of 10:1 was added, and the precipitate containing cellulose was separated after cooling to room temperature.

[0043] The obtained precipitate was washed to neutral with deionized water, then the precipitate and deionized water were dispersed in deionized water according to the mass ratio of 1:200, and the cellulose suspension was obtained after homogenization under the pressure of 1000 bar for 10 times.

[0044] Atomic force microscope (AFM) and scanning electron microscope (SEM) were used to observe the morphology of nanocellulose balls, and the results are shown in Figure 2 As shown in Figure 3 , the nanocellulose balls showed uniform size, about 200 nm.

[0045] The changes of the sample of Example 2 after standing for 90 days are shown in Figure 4 As shown in Figure 4 , the low-concentration LCNS suspension prepared from biomass raw materials of the present application is not prone to agglomeration and stratification under long-time standing, and can be stored and used for a long time, and its zeta potential value is-16.22 mV.

[0046] It can be seen that the obtained nanocellulose spheres suspension containing lignin is stable for a long time, and the size of the nanocellulose spheres is about 200 nm.

[0047] Example 2

[0048] Preparation of bio-acid deep eutectic solvent (DES): Choline chloride as a hydrogen bond acceptor and citric acid and ethylene glycol as a hydrogen bond donor were mixed in a molar ratio of 3:1:2 at 90°C under stirring at 500 rpm for 3 hours to form a clear and transparent solution to obtain the deep eutectic solvent DES.

[0049] Poplar was crushed to 40-60 mesh, then added to the DES in a mass ratio of 1:20, and stirred at a temperature of 120°C for 6 hours, then a mixture of acetone and deionized water in a volume ratio of 10:1 was added, and the temperature was lowered to room temperature after standing, and the precipitate containing cellulose was separated.

[0050] The obtained precipitate was washed with deionized water until neutral, then the precipitate and deionized water were dispersed in deionized water in a mass ratio of 1:200, and homogenized under a pressure of 1000 bar for 10 cycles to obtain a nanocellulose spheres suspension containing lignin.

[0051] The nanocellulose spheres suspension containing lignin was tested using the same test method as in Example 1, and similar results were obtained, as shown in Figure 5

[0052] The above examples are only used to illustrate the technical solutions of the present application and not to limit it; the description presented herein is only for preferred embodiments for the purpose of illustration, and is not intended to limit the scope of the present application, so it should be understood that the specific embodiments of the present application can be modified or some technical features can be replaced equivalently without deviating from the spirit and scope of the present application, which should be covered in the technical solution range claimed by the present application.​

Claims

1. A method for preparing lignin-containing cellulose nanospheres, comprising the following steps: (1) crushing lignocellulosic biomass raw material to a particle size of 20-100 mesh to obtain crushed lignocellulosic biomass; (2) mixing the crushed lignocellulosic biomass obtained in step (1) with a ternary eutectic solvent at a mass ratio of 1:10-1:20, stirring and reacting at a temperature of 80-160℃ for 4-10 hours, wherein the ternary eutectic solvent is a mixed solution in a molten state formed by choline chloride as a hydrogen bond acceptor and a polyacid and a polyol as hydrogen bond donors, the polyacid is one or both of citric acid and malic acid, the polyol is one or more of 1,4-butanediol, ethylene glycol and glycerol, and the molar ratio of choline chloride, polyacid and polyol is 3:1:(2-4); (3) adding a mixture of an organic solvent and water to step (2) to terminate the reaction, allowing to cool to room temperature, and then separating the precipitate rich in cellulose; (4) washing the precipitate obtained in step (3) to neutral, mixing with water at a mass ratio of 1:100-1:200, and then obtaining lignin-containing nanocellulose spheres after several cycles of high-pressure homogenization. In step (1), the lignocellulosic biomass raw material is crushed to a particle size of 40-60 mesh to obtain crushed lignocellulosic biomass. In step (1), the lignocellulosic biomass raw material is selected from wood and non-wood. The wood is selected from broadleaf wood or coniferous wood; the non-wood is selected from crop straw, corn cob, pith and residues after chemical extraction, grass, bamboo, cotton and cotton stalks. The broadleaf wood is selected from eucalyptus, birch or poplar, and the coniferous wood is selected from larch, masson pine or spruce; the crop straw is from wheat, corn, rice straw or sorghum.

2. The production method according to claim 1, wherein, The molar ratio of choline chloride, polyacid and polyol is 3:1:

2.

3. The production method according to claim 1, wherein, The ternary eutectic solvent is obtained by mixing choline chloride, polyacid and polyol and stirring until a clear and transparent solution is formed.

4. The production method according to claim 3, wherein In step (2), the temperature condition is 120-160℃, and / or the reaction time is 6-10 hours.

5. The production method according to claim 4, wherein, In step (3), the volume ratio of the organic solvent to water is 10:1-6:1, and the organic solvent is selected from ethanol, acetone or a combination thereof.

6. The production method according to claim 1, wherein In step (4), the high-pressure homogenization is performed at a pressure of 1000 bar for 10-50 times.

7. The production method according to claim 1, wherein The size of the lignin-containing nanocellulose spheres is 100-300 nm.

8. The method of any one of claims 1-7, wherein, The size of the lignin-containing nanocellulose spheres is 150-250 nm. The size of the lignin-containing nanocellulose spheres is 200 nm. ​ 9. The method of any one of claims 1-7, wherein, ​ ​ ​ 10. The method of any one of claims 1-7, wherein, ​ 11. The method of any one of claims 1-7, wherein, ​ 12. The method of any one of claims 1-7, wherein, ​ 13. The method of any one of claims 1-7, wherein, ​

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