Hollow spherical particle

Abstract

Provided is a hollow spherical particle that can be prepared with superior safety and greater ease. A hollow spherical particle according to the present invention is a self-organizing body of lignin, wherein the content of the lignin in a β-O-4 ether structure is 50% or greater, and the solubility with respect to 60 to 80% ethanol at 25°C is 2 w / v% or greater.

Description

hollow spherical particles

[0001] The present invention relates to hollow spherical particles and the like.

[0002] Hollow spherical particles such as microcapsules and nanocapsules are used in a wide range of industries, including pesticides, detergents, fabric softeners, fragrances, cosmetics, pharmaceuticals, latent heat storage materials (PCMs), textiles, paints, and functional chemicals. Encapsulating a wide range of molecules, including pharmaceuticals, within capsules is an important means of controlling the timing, efficacy, properties, dispersibility, compatibility, weather resistance, and responsiveness to external stimuli of the molecules. Most of the base materials for microparticles are derived from petroleum, which raises concerns about environmental loads and endocrine disrupting chemicals. Microparticles are difficult to recover after being released into the environment, and they are one of the sources of microplastics in soil, rivers, and oceans.

[0003] There have been reports of nanoparticles using modified industrial lignin instead of petroleum-derived polymers (Non-Patent Document 1), but there are safety concerns because organic solvents that are harmful to living organisms are used in the manufacturing process.

[0004] M. Lievonen et al. A simple process for lignin nanoparticle preparation, Green Chem. 2016,18, 1416-1422 (https: / / pubs.rsc.org / en / content / articlelanding / 2016 / gc / c5gc01436k)

[0005] An object of the present invention is to provide hollow spherical particles that are safer and can be prepared more easily.

[0006] In view of the above-mentioned problems, the present inventors have conducted extensive research and have found that the above-mentioned problems can be solved by hollow spherical particles that are self-assembled bodies of lignin, wherein the lignin has a β-O-4 ether structure content of 50% or more and a solubility in 60-80% ethanol at 25°C of 2 w / v% or more. Based on this finding, the present inventors have conducted further research and have completed the present invention. Specifically, the present invention encompasses the following aspects.

[0007] Item 1. Hollow spherical particles that are self-assembled bodies of lignin, wherein the lignin has a β-O-4 ether structure content of 50% or more and a solubility of 2 w / v% or more in 60 to 80% ethanol at 25°C.

[0008] Item 2. The hollow spherical particles according to Item 1, wherein the lignin has a number average molecular weight (Mn) of 0.7 to 9 kDa or a weight average molecular weight (Mw) of 1 to 10 kDa.

[0009] Item 3. The hollow spherical particles according to Item 1 or 2, having a number average particle size of 100 μm or less.

[0010] Item 4. The hollow spherical particles according to any one of Items 1 to 3, which have a number average particle size of 50 nm or more.

[0011] Item 5. The hollow spherical particles according to any one of Items 1 to 4, which have a lumen ratio of 60% or more.

[0012] Item 6. The hollow spherical particle according to any one of Items 1 to 5, having a film thickness of 1 nm to 4000 nm.

[0013] Item 7. The hollow spherical particles according to any one of Items 1 to 6, which contain an active ingredient.

[0014] Item 8. The hollow spherical particles according to Item 7, wherein the active ingredient is at least one selected from the group consisting of pigments, agricultural chemicals, fertilizers, pharmaceuticals, cosmetic ingredients, fragrances, fluorescent agents, paints, proteins, nucleic acids, lipids, hormones, sugars, glycosides, surfactants, adhesives, vitamins, coenzymes, minerals, cells, organelles, low-molecular-weight compounds, high-molecular-weight compounds, metal complexes, liposomes, and hydrogels.

[0015] Item 9. The hollow spherical particles according to any one of Items 1 to 8, which contain a liquid, gas, or solid (one of which is a metal) enclosed therein.

[0016] Item 10. The hollow spherical particles according to Item 9, for use as a heat insulating material, a compatibilizer, a catalyst, or a sensitizer.

[0017] Item 11. The hollow spherical particles according to any one of Items 1 to 10, wherein the lignin has a sulfur atom content of 0.15% or less.

[0018] Item 12. The hollow spherical particles according to any one of Items 1 to 11, wherein the content of non-natural condensed structures in the lignin is 1% or less.

[0019] Item 13. The hollow spherical particles according to any one of Items 1 to 12, wherein the lignin has a ratio of phenolic hydroxyl groups to alcoholic hydroxyl groups of 0.8 or less.

[0020] Item 14. The hollow spherical particle according to any one of Items 1 to 13, which exhibits long wavelength fluorescence.

[0021] Item 15. The hollow spherical particle according to Item 14, wherein the long-wavelength fluorescence is fluorescence of 450 nm or longer.

[0022] Item 16. An ultraviolet absorber containing the hollow spherical particles according to any one of items 1 to 15.

[0023] Item 17. A light resistance imparting agent containing the hollow spherical particles according to any one of items 1 to 15.

[0024] Item 18. An anti-Stokes fluorescent agent containing the hollow spherical particles according to any one of items 1 to 15.

[0025] According to the present invention, hollow spherical particles can be provided which are more biocompatible, biodegradable, non-toxic and amphiphilic and can be more easily prepared.

[0026] This figure shows a flowchart of the M-APA method. This figure shows a flowchart of the A-APA method. This figure shows the microwave irradiation conditions, power, temperature, and pressure profiles, and specifications for the Biotage Initiator+ 60 microwave synthesizer, with a stirring speed of 600 rpm, cooling on, and absorption on high. This figure shows a 2D NMR spectrum of a low-denaturation, high-purity, ether-rich lignin. This figure shows the analysis results of lignin isolated by the M-APA method using eucalyptus as the starting material (microwave treatment at 50°C for 10 minutes, acetic acid-peracetic acid 1% condition). This figure shows the partial chemical structure of the inter-lignin bond and the covalent bond between lignin and hemicellulose. This figure shows a 2D NMR spectrum (a-d) of a lignin-hemicellulose copolymer, with enlarged views of the inter-unit bond and sugar regions (a'-d'). Lignin-hemicellulose copolymers isolated by the M-APA method from hardwood (a, b) and softwood (c, d) were analyzed. Circles in the figure indicate LC bonds (ether and ester types). Synchro-scan fluorescence spectrum in the near-infrared wavelength region of bagasse (sugarcane)-derived APA lignin. Synchro-scan measurement was performed to detect a constant Stokes shift, i.e., fluorescence wavelengths Em 80, 90, 150, 160, and 170 nm longer than the excitation wavelength Ex (scanning the excitation wavelength). 3D fluorescence spectrum in the near-infrared wavelength region of red pine APA lignin. APA lignin obtained by treating red pine wood flour with the M-APA method (microwave at 50°C for 10 min using acetic acid and 0.2 M hydrogen peroxide) was measured in an 80% acetonitrile aqueous solution (concentration: 0.1 wt%). This graph shows a comparison of the synchro-scan fluorescence spectra of reagent lignin (Tokyo Kasei TCI alkaline lignin, blue line) and lignin (APA lignin, red line). Fluorescence longer than the excitation wavelength (plus 90 nm) was detected (scanning the excitation wavelength). Lignin (APA lignin) exhibits characteristic fluorescence in the long wavelength region. The figures show the synchro anti-fluorescence spectra of a lignin solid thin film and a lignin-polysaccharide copolymer solid thin film. The excitation wavelength was scanned to selectively detect anti-Stokes shifted fluorescence shorter than the excitation wavelength, as shown in the anti-fluorescence spectra (af) and the control (g).The anti-Stokes shift is the excitation wavelength minus 50 nm, and minus 40 nm for spectrum (b). Comparing spectra (b) and (d) and (e) and (f) reveals that the anti-fluorescence intensity is higher when peracetic acid is used as the oxidizing agent than when hydrogen peroxide is used. Comparing spectra (b) and (c) reveals that the anti-fluorescence intensity of APA lignin is higher than that of lignin polysaccharide copolymer. The UV absorption spectra of lignin and lignin-hemicellulose copolymer are shown. The vertical axis represents absorbance, and the horizontal axis represents wavelength (nm). For an explanation of the legend, see Table 8. A bright-field image of hollow spherical particles obtained in Example 1 is shown. A fluorescent image of hollow spherical particles obtained in Example 2 is shown.

[0027] In this specification, the expressions "contain" and "comprise" include the concepts of "contain," "comprise," "consist essentially of," and "consist only of."

[0028] In one aspect, the present invention relates to hollow spherical particles that are self-assembled bodies of lignin (sometimes referred to herein as "lignin of the present invention"), wherein the lignin has a β-O-4 ether structure content of 50% or more and a solubility of 2 w / v% or more in 60-80% ethanol at 25°C (sometimes referred to herein as "hollow spherical particles of the present invention"). This is described below.

[0029] 1. Lignin Isolation Method The lignin of the present invention can be obtained by a method for isolating lignin from plant biomass (sometimes referred to herein as the "isolation method of the present invention"), which includes the step (A) of contacting plant biomass with a solution containing an organic acid and a peracid. This method is described below.

[0030] The isolation method of the present invention includes step (A), and therefore can produce high-quality (low-condensation) lignin with a high content of β-O-4 ether structures among all the bond types between monolignols.

[0031] The plant biomass is not particularly limited as long as it contains lignin, and examples thereof include the plant itself and mechanically processed products of the plant.

[0032] Examples of plant bodies include coniferous trees, hardwoods, and non-woody materials. Specific examples include cedar, pine, spruce, larch, black pine, Abies sachalinensis, Himekomatsu, yew, Japanese yew, spruce, Japanese spruce, Japanese spruce, Japanese yew, Japanese bead, fir, Japanese yew, Douglas fir, spruce, yellow cedar, Japanese cypress, Douglas fir, Sitka spruce, Radiata pine, eastern spruce, eastern white pine, western larch, western fir, and western Examples of suitable woods include conifers such as hemlock and tamarack; hardwoods such as asbestos, American black cherry, yellow poplar, walnut, birch, zelkova, sycamore, silver cherry, ash, teak, Chinese elm, Chinese maple, oak, beech, hard maple, hickory, pecan, white ash, white oak, white birch, red oak, acacia, and eucalyptus; and non-woody materials such as rice, sugarcane, wheat, corn, pineapple, oil palm, kenaf, cotton, alfalfa, timothy, bamboo, bamboo grass, and sugar beet.

[0033] Examples of mechanically processed products of plants include logs, timber, boards, solid wood, wood materials, laminated lumber, laminated veneer lumber, plywood, wood boards, particle boards, fiber boards, wood chips, particulate wood (chips, particles, wood flour, etc.), fibrous wood, compressed materials, crushed materials, etc.

[0034] From the viewpoint of improving the yield, the plant biomass is preferably wood flour. The volume average particle diameter of the wood flour is, for example, 500 μm or less, preferably 200 μm or less, more preferably 100 μm or less, even more preferably 50 μm or less, and even more preferably 20 μm or less. The lower limit of the average particle diameter is not particularly limited and can be, for example, 1 μm, 2 μm, or 5 μm. By using wood flour with a relatively small particle size, a high yield can be achieved without performing the alkali treatment described below.

[0035] Wood flour can be obtained by pulverizing plant biomass. The pulverization can be carried out according to or in accordance with a known method, for example, using various mills (e.g., ball mills, mixer mills, etc.).

[0036] From the viewpoint of improving yield, the plant biomass is preferably an alkali-treated product of a plant body or a mechanically processed product thereof. According to the present invention, by using the alkali-treated product, the target product can be efficiently obtained without pulverization (even in the case of a relatively small specific surface area, such as wood chips). The alkali-treated product can be obtained by alkali-treating a plant body or a mechanically processed product thereof. The alkali treatment loosens the plant cell wall structure (reducing intermolecular interactions and cleaving hydrogen bonds) and cleaves intramolecular ester bonds, thereby improving yield. This allows high yields to be achieved without physical pulverization of the plant biomass, or even with only a small degree of pulverization, thereby reducing process costs. Furthermore, the yield can be improved by 1.2 to 2 times. Furthermore, the crystallinity of the cellulose fibers obtained through this alkali treatment is good.

[0037] Specifically, the alkali treatment is preferably, for example, (X) a step of contacting a plant body or a mechanically processed product thereof with an alkaline solution.

[0038] The alkaline solution is not particularly limited as long as it is an alkaline solution to the extent that the above-mentioned purpose can be achieved. For example, the alkaline solution may be a solution with a pH of 12 to 15. The pH of the solution is preferably 13 to 14. Furthermore, the alkaline solution may be, for example, a solution containing 0.3 to 2 mass % (preferably 0.7 to 1.5 mass %) of an alkali metal hydroxide (e.g., sodium hydroxide, potassium hydroxide, etc.).

[0039] The amount of alkaline solution used is not particularly limited as long as it is an amount sufficient to achieve the above-mentioned purpose. The amount of alkaline solution used may be, for example, 3 to 20 mL, preferably 5 to 12 mL, per 1 g of plant body or mechanically processed product thereof.

[0040] The manner in which the plant body or a mechanically processed product thereof is brought into contact with the alkaline solution is not particularly limited, but from the standpoint of treatment efficiency and the like, it is preferable to immerse the plant body or a mechanically processed product thereof in the alkaline solution.

[0041] The temperature of the alkaline solution is not particularly limited as long as it is a temperature that can achieve the above-mentioned object. The temperature of the alkaline solution can be, for example, 20 to 150°C, preferably 50 to 120°C, and more preferably 80 to 120°C. When heating, methods include internal heating using microwave heating and external heating using an oil bath or the like, with internal heating using microwave heating being preferred.

[0042] The treatment time in step (X) is not particularly limited as long as it is long enough to achieve the above-mentioned object, and is, for example, 5 to 120 minutes, preferably 15 to 60 minutes.

[0043] After step (X), the soluble portion and the insoluble portion are separated, and the insoluble portion can be subjected to step (A) as an alkali-treated product of the plant body or a mechanically processed product thereof.

[0044] The plant biomass may be one type alone or a combination of two or more types.

[0045] The solution containing an organic acid and a peracid (organic acid-peracid solution) is a solution that contains an organic acid and a peracid and is capable of extracting and solubilizing at least one selected from the group consisting of lignin, hemicellulose, and a lignin-polysaccharide complex, and is not particularly limited thereto.

[0046] The organic acid is not particularly limited, and examples thereof include acetic acid, formic acid, glyoxylic acid, maleic acid, propionic acid, folic acid, isobutyric acid, valeric acid, isovaleric acid, pyruvic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, ketoglutaric acid, adipic acid, lactic acid, tartaric acid, fumaric acid, oxaloacetic acid, malic acid, isocitric acid, citric acid, benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, hemimellitic acid, trimellitic acid, trimesic acid, mellophanic acid, prenitic acid, pyromellitic acid, mellitic acid, methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, camphorsulfonic acid, p-toluenesulfinic acid, and benzenesulfinic acid. Of these, preferred are acetic acid, formic acid, glyoxylic acid, 3-oxopropanoic acid, 2-methyl-3-oxopropanoic acid, etc., more preferred are acetic acid, formic acid, glyoxylic acid, etc., and particularly preferred is acetic acid.

[0047] The organic acid may be one kind alone or two or more kinds in combination.

[0048] The peracid is not particularly limited as long as it is an acid having a hydroperoxide group (—O—OH), and examples thereof include organic peroxoacids such as percarboxylic acids, persulfuric acid, percarbonic acid, perphosphoric acid, and hypoperhalogen acids. Examples of percarboxylic acids include peracetic acid, performic acid, perbenzoic acid, and metachloroperbenzoic acid, and examples of hypoperhalogen acids include hypoperchloric acid, hypoperbromic acid, and hypoperiodic acid. In addition to the above, examples of peracids include hydrogen peroxide, lithium peroxide, sodium peroxide, potassium peroxide, sodium percarbonate, urea peroxide, sodium perborate, tert-butyl hydroperoxide, cumene hydroperoxide, di-tert-butyl peroxide, dimethyldioxirane, acetone peroxide, methyl ethyl ketone peroxide, and hexamethylene triperoxide diamine. Among these, preferred are organic peroxoacids, hydrogen peroxide, sodium percarbonate, urea peroxide, sodium perborate, etc., more preferred are percarboxylic acids (particularly peracetic acid), hydrogen peroxide, etc., and particularly preferred is hydroperoxy acid.

[0049] The peracid may be one kind alone or two or more kinds in combination.

[0050] The content of the organic acid in the organic acid-peracid solution is, for example, 5 to 30 mol / L, preferably 8 to 25 mol / L, and more preferably 10 to 20 mol / L. The content of the organic acid in the organic acid-peracid solution is preferably 3 to 10 g, more preferably 4 to 8 g, and even more preferably 5 to 7 g per 1 g of plant biomass to be contacted with the organic acid-peracid solution.

[0051] The content of peracid in the organic acid-peracid solution is, for example, 0.05 to 3 mol / L, preferably 0.08 to 2.5 mol / L, and more preferably 0.1 to 2 mol / L. The content of peracid in the organic acid-peracid solution is preferably 0.03 to 0.1 g, more preferably 0.04 to 0.08 g, and even more preferably 0.05 to 0.07 g per 1 g of plant biomass to be contacted with the organic acid-peracid solution.

[0052] The manner in which the plant biomass is brought into contact with the organic acid-peracid solution is not particularly limited, but from the viewpoint of treatment efficiency and the like, it is preferable to immerse the plant biomass in the organic acid-peracid solution.

[0053] The temperature of the organic acid-peracid solution is not particularly limited, as long as it is a temperature that can selectively extract and solubilize lignin units. The temperature of the organic acid-peracid solution is, for example, 15 to 90°C (preferably 40 to 90°C). By using this temperature, it is possible to obtain high-quality (low-condensation) lignin with a high content of β-O-4 ether structures among all bond types between monolignols. For example, when the starting material is woody biomass, performing step (A) with an organic acid-peracid solution at, for example, 90°C or less (preferably 40 to 90°C, more preferably 40 to 70°C, and even more preferably 40 to 60°C) can easily produce lignin units selectively. For example, when the starting material is herbaceous biomass, performing step (A) with an organic acid-peracid solution at, for example, 60°C or less (preferably 15 to 60°C) can easily produce lignin units selectively. When heating is performed, examples of the method include internal heating using microwaves and external heating using an oil bath, but internal heating using microwaves is preferred. Rapid internal heating using microwaves enables efficient pretreatment in a short time.

[0054] The treatment time in step (A) is not particularly limited as long as it is long enough to achieve the above-mentioned object, and is, for example, 1 to 60 minutes, preferably 1 to 30 minutes, and more preferably 5 to 20 minutes.

[0055] In step (A), it is preferable to perform microwave treatment while the biomass is immersed in the solution. This improves the lignin yield. The microwave treatment conditions can be set appropriately, but for example, a commercially available microwave synthesis device can be used to perform the treatment while stirring the solution. The microwave treatment time can be, for example, 1 to 30 minutes, and is preferably about 10 minutes. When microwave treatment is performed in the isolation method of the present invention, irradiation for a relatively short period of time is sufficient, so it can easily be constructed as a batch system or a continuous system.

[0056] In step (A), it is preferable to irradiate the plant biomass with microwaves or ultrasound, from the viewpoint of promoting penetration of the solution into the pores inside the plant cell walls and improving the yield. The irradiation time is the same as above.

[0057] After step (A), a separation solvent is added as needed, and the soluble and insoluble portions are then separated. The method for separating the soluble and insoluble portions is not particularly limited, and methods such as decantation, spin-down, and filtration can be used. Lignin is isolated using separation solvents such as dioxane, ethanol, acetone, acetonitrile, DMSO, DMF, NMI, various alcohols such as ethyl acetate, methanol, and butanol, acetic acid, water, and mixtures of these. From the perspectives of extraction efficiency, selectivity, and environmental impact, organic solvents such as acetone, ethanol, and acetonitrile, as well as 10-20% v / v water-mixed organic solvents, are preferred.

[0058] The soluble portion obtained in step (A) contains lignin. Therefore, the soluble portion can be obtained as lignin either directly or after undergoing other treatments as necessary.

[0059] Other examples of treatments include the following: After step (A), if necessary, the water can be removed by evaporation and / or freeze-drying to obtain the target product as a dry powder. If desalting is required, the concentrated solution may be extracted with alcohol, acetone, or the like, and the solvent may be distilled off. This allows the target product to be obtained as a dry powder.

[0060] According to the present invention, a new plant biomass pretreatment method can be provided as a new paper pulp production process that requires low energy and does not produce hazardous waste liquid, and is a low-temperature, mild process that produces cleanly delignified polysaccharides and therefore produces fewer inhibitors in the recovered material that are problematic for ethanol fermentation.

[0061] 2. Lignin According to the isolation method of the present invention, it is possible to obtain lignin having at least the following characteristics: a β-O-4 ether structure content of 50% or more and a solubility of 2 w / v% or more in 60-80% ethanol at 25°C.

[0062] In one aspect, the present invention relates to lignin having a β-O-4 ether structure content of 50% or more and a solubility of 2 w / v% or more in 60 to 80% ethanol at 25°C, or lignin obtainable by the isolation method of the present invention.

[0063] The term "lignin" used in the present invention refers to lignin isolated from biomass (including natural lignin). Natural lignin has a wide variety of bonding modes. Representative bonding modes of natural lignin include the following:

[0064]

[0065] The above is called a β-O-4 bond.

[0066]

[0067] The above is called a resinol (β-β) bond.

[0068]

[0069] The above is called a phenylcoumaran (β-5) bond.

[0070]

[0071] The above is called a 5-5 bond.

[0072]

[0073] The above is called dibenzodioxin (DBDO 5-5 / 4-O-β) binding.

[0074]

[0075] The above is called a 4-O-5 bond.

[0076]

[0077] The above is called β-1 bond.

[0078]

[0079] The above is called spirodienone binding.

[0080] In natural lignin, the content of β-O-4 ether structures is the highest among all bond types between monolignols, although this varies depending on the plant species. For example, in coniferous trees, the content is said to be 40-60%. In broad-leaved trees, such as eucalyptus, the content is said to be around 45%.

[0081] The lignin of the present invention has a β-O-4 ether structure content of 50% or more, preferably 60% or more, more preferably 65 to 85%, and even more preferably 70 to 80% of all bond types between monolignols.

[0082] The lignin of the present invention preferably has a β-O-4 ether structure content (%) of all bond types between monolignols, where x% is the lignin content in the raw biomass. The upper limit is preferably 2x%.

[0083] The content of β-O-4 ether structures among all the linkages between monolignols in lignin was measured as follows. Samples were dissolved in deuterated dimethyl sulfoxide (DMSO-d6) to a concentration of 1-10 wt% and NMR spectra were acquired using a Bruker Avance III 600 MHz NMR instrument equipped with a cryogenic probe. The content of β-O-4 ether structures was estimated from the signal volume in the heteronuclear single-quantum correlation spectroscopy (HSQC) spectrum. The quantitative values ​​obtained using the 2D NMR method were corrected according to the literature (H. Okamura, H. Nishimura, T. Nagata, T. Kigawa, T. Watanabe, and M. Katahira, "Accurate and molecular-size-tolerant NMR quantitation of diverse components in solution," Scientific Reports, 6, 21742. 2016).

[0084] The lignin of the present invention is characterized by its solubility in 60-80% ethanol at 25°C of 2 w / v% or more. Therefore, by using the lignin of the present invention, hollow spherical particles (described below) can be easily obtained without using solvents that are harmful to living organisms, and highly stable hollow spherical particles can be obtained. The solubility is preferably 4 w / v% or more, more preferably 5 w / v% or more, even more preferably 6 w / v% or more, and even more preferably 7 w / v% or more.

[0085] The solubility is measured as follows: The sample is stirred and dissolved in 25°C ethanol, and then separated into an ethanol-soluble portion and an ethanol-insoluble portion by solid-liquid separation. A 25°C aqueous ethanol solution (1 / 1 ethanol / water) is added to the ethanol-insoluble portion, which is stirred to dissolve, yielding an ethanol-soluble portion. The ethanol-soluble portion is mixed with the ethanol-soluble portion to obtain a sample solution. The amount of ethanol solution added is adjusted so that the ethanol concentration of the sample solution is in the range of 60-80%. In the process of obtaining the soluble portion, the sample is dispersed and solubilized, if necessary, using an ultrasonic cleaner for 3 min at 28 kHz. The maximum sample concentration at which the sample solution becomes visually transparent is defined as the "solubility in 60-80% ethanol at 25°C."

[0086] The lignin of the present invention preferably has a constituent ratio of biphenyl-type lignin, which has a condensed structure, of 5% or less.

[0087] The lignin of the present invention preferably has a number average molecular weight (Mn) of 0.7 to 9 kDa, more preferably 1 to 5 kDa, and even more preferably 1.5 to 4 kDa.

[0088] The lignin of the present invention preferably has a weight average molecular weight (Mw) of 1 to 10 kDa, more preferably 1.5 to 8 kDa, and even more preferably 2 to 6 kDa.

[0089] In this invention, the number-average molecular weight (Mn) and weight-average molecular weight (Mw) of lignin are specifically measured as follows. The molecular weight of lignin can be determined by size exclusion chromatography (SEC), also known as gel permeation chromatography (GPC). The sample is dissolved in a solution of acetic anhydride and a base (e.g., pyridine) and reacted for 3-6 hours to obtain an acetylated product. This is then dissolved in tetrahydrofuran (THF) at a concentration of 2.0 mg / mL and separated by high-performance liquid chromatography. A Tosoh HZ-M column (150 mm x 4.6 mm id, 4 μm, three columns connected in series) is used. Analysis is performed by injecting 10 μL of sample, using tetrahydrofuran (THF) as the mobile phase at a column temperature of 40°C and a flow rate of 0.35 mL / min. A mass calibration curve (calibration curve) is prepared using standard polystyrene, Tosoh PStQuickC (molecular weights (MW) of 2,110,000, 427,000, 37,900, and 5,970), pinoresinol (MW 352), and vanillin (MW 152), to determine the Mw and Mn of the sample.

[0090] The lignin of the present invention preferably has a polydispersity (Mw / Mn) of 2.5 or less, more preferably 2 or less.

[0091] Unlike industrial lignins that use sulfur-containing components (sodium sulfide, sodium sulfate, sulfite, etc.), the lignin of the present invention can be prepared without using these components. Therefore, in one embodiment, the lignin of the present invention does not contain sulfur atoms or has a sulfur atom content of 0.15% or less (preferably 0.05% or less). The lignin of the present invention may contain trace amounts of sulfur atoms derived from sulfur-containing amino acids, sulfur components in the atmosphere, etc.

[0092] The presence or absence and content of sulfur atoms can be determined and measured by elemental analysis using an X-ray fluorescence analyzer, SEM-EDX, XAFS, or the like.

[0093] The lignin of the present invention can be prepared under conditions that make it difficult to form unnatural condensation structures or unnatural addition structures. Therefore, in one embodiment of the present invention, the content of unnatural condensation structures in the lignin of the present invention is 1% or less.

[0094] Non-natural condensed structures are structures in which the secondary and / or primary hydroxyl groups of lignin molecules are condensed with other molecules, and are newly generated during the lignin isolation process. Non-natural adduct structures are structures in which lignin molecules are adducted with low-molecular-weight decomposition products produced by decomposition and / or solvents and / or compounds (acids, bases, alcohols, organic acids, carboxylic acids, aldehydes, amino acids, etc.) used in the isolation process. These structures are newly generated during the lignin isolation process. Non-natural condensed structures and non-natural adduct structures are generated during the pretreatment, conversion, or lignin isolation process of plant biomass, and are easily generated under harsh conditions such as those involving strong acids or strong bases, high temperatures (150°C or higher), and / or long periods (1 hour or longer), and / or high pressures (1 atmosphere or higher). They can also be generated by chemical and mechanochemical reactions under physical milling conditions such as those in ball mills and bead mills. The condensed structure restricts the degree of freedom of lignin oligomers in solvents, which is a factor that reduces molecular dispersibility, self-organization, and microparticle formation ability. The lignin used in the present invention has a significantly low content of condensed structures, which allows it to more effectively achieve its characteristics and advantages of excellent dispersibility, water affinity, self-organization, hydrogen bond formation ability, microparticle formation ability, and hollow spherical capsule formation ability, as well as the presence of hydroxyl groups that serve as base points for various derivatizations and functionalizations of microparticles. Examples of non-natural condensed structures include the following structure: and the aforementioned 5-5 bond structure and 4-O-5 bond structure.

[0095]

[0096] [In the formula, R1 and / or R2 represent an alkyl group, -O-RX (RX represents an organic group (e.g., another structural portion in lignin (e.g., a benzene ring))), or a hydroxyl group (excluding the case where both R1 and R2 are hydroxyl groups).]

[0097] The content of the non-natural condensed structure and the non-natural additional structure can be measured according to the method of Reference Test Example 1-6-2 described later, and can be calculated as the ratio per 100 lignin aromatic rings.

[0098] The lignin of the present invention can be prepared under conditions that make it difficult to generate phenolic hydroxyl groups. Therefore, in one embodiment of the present invention, the ratio of phenolic hydroxyl groups to alcoholic hydroxyl groups in the lignin of the present invention is 0.8 or less (preferably 0.6 or less, more preferably 0.5 or less, even more preferably 0.4 or less, even more preferably 0.3 or less, and particularly preferably 0.2 or less). For the same reason, in one embodiment of the present invention, the ratio of phenolic hydroxyl groups to the total hydroxyl groups in the lignin of the present invention is 30% or less (desirably 20% or less). A smaller number of phenolic hydroxyl groups indicates an aromatic polymer with fewer branches. By satisfying the above range, particle formability and self-assembly properties are further improved.

[0099] The hydroxyl groups can be determined in accordance with Reference Test Example 5 described below.

[0100] 3. Hollow Spherical Particles The hollow spherical particles of the present invention are not particularly limited as long as they are a self-assembled product of the lignin of the present invention and have a hollow spherical shape. Self-assembly occurs easily, and the conditions for self-assembly can be appropriately set. For example, hollow spherical particles can be formed by self-assembly in an aqueous solution in which the lignin of the present invention is dispersed.

[0101] Specifically, hollow spherical particles can be formed by gradually adding water to a sample dissolved in an organic solvent (such as alcohol) to induce self-assembly. Although the final water content is approximately 95%, once capsules are formed, they are stable in water. Alternatively, capsules can be formed by dissolving the sample in alcohol-containing water and allowing it to evaporate naturally. This method results in highly uniform capsules on the submicron order.

[0102] Conventional lignin (commercially available industrial lignin) does not exhibit dispersibility or solubility in hydrophilic solvents such as ethanol or water-mixed solvents. However, the lignin of the present invention exhibits dispersibility and solubility in hydrophilic solvents and water-mixed solvents. Therefore, by using the lignin of the present invention, hollow spherical particles that are safer for living organisms can be obtained.

[0103] The hollow spherical particles of the present invention contain hollow portions, and the number of hollow portions is not particularly limited. The hollow spherical particles of the present invention can be mononuclear particles having one hollow portion, or polynuclear particles having multiple hollow portions.

[0104] The lignin self-assembled body of the present invention exhibits fluorescence in the long wavelength region. Specifically, it exhibits fluorescence in the wavelength region of 400 to 700 nm. Furthermore, in the lignin self-assembled body of the present invention, fluorescence that is significantly shifted to shorter wavelengths than the excitation wavelength, known as anti-Stokes fluorescence, is observed. Anti-Stokes fluorescence is exhibited even when the excitation light source is a weaker light source, such as a xenon lamp, which is weaker than conventional strong laser light sources. Therefore, the hollow spherical particles of the present invention can be used as anti-Stokes fluorescent agents. In this case, for example, the hollow spherical particles of the present invention can be used as anti-Stokes fluorescent paints, inks, identification agents, and up-conversion / wavelength conversion molecular materials.

[0105] The hollow spherical particles of the present invention are stably dispersed in an aqueous solution, and furthermore, can maintain the above-mentioned fluorescence even after drying into a solid state.

[0106] The hollow spherical particles of the present invention have a number average particle diameter of, for example, 100 μm or less. In a preferred embodiment of the present invention, the hollow spherical particles of the present invention have a number average particle diameter of, for example, 0.7 μm or more. The number average particle diameter is preferably 50 nm to 100 μm, more preferably 0.7 to 70 μm, even more preferably 1 to 50 μm, still more preferably 1 to 40 μm, and particularly preferably 1 to 30 μm.

[0107] The hollow spherical particles of the present invention can have a high lumen ratio. The lumen ratio of the hollow spherical particles of the present invention is, for example, 60% or more, preferably 70% or more, more preferably 75% or more, and even more preferably 80% or more. The lumen ratio is measured according to the method described in Example 1.

[0108] In one embodiment of the present invention, the hollow spherical particles of the present invention preferably have a certain film thickness. The film thickness of the hollow spherical particles of the present invention is preferably 1 to 4,000 nm, more preferably 10 to 4,000 nm, even more preferably 50 to 2,000 nm, and even more preferably 100 to 1,000 nm. The film thickness is measured according to the method described in Example 1.

[0109] The hollow spherical particles of the present invention can be used, for example, as a substance delivery carrier by incorporating an active ingredient into the hollow portion. This can also impart properties such as solubility resistance, compatibility, and light resistance to the active ingredient. A wide range of active ingredients can be selected, including pesticides, fertilizers, pharmaceuticals, cosmetic ingredients, fragrances, fluorescent agents, paints (e.g., vanillin, limonene, menthol, etc.), proteins, nucleic acids, lipids, hormones, sugars, glycosides, surfactants, adhesives, vitamins, coenzymes, minerals, cells, organelles, low-molecular-weight compounds (e.g., signaling substances such as pheromones; nitrogen-containing compounds such as alkaloids, monoterpenes, and sesquiterpenes; isoprenoids such as terpenoids; phenylpropanoids, etc.), polymeric compounds, metal complexes, liposomes, and hydrogels.

[0110] Specifically, the hollow spherical particles of the present invention can be used as drug carriers (for DDS applications). More specifically, they can be used as organic capsules as drug carriers. Because they are natural products and are expected to be biocompatible, they are useful as drug carriers.

[0111] Specifically, the hollow spherical particles of the present invention can also be used as UV-absorbing capsules to impart light resistance to encapsulated compounds. Because the absorption range includes UV-A, they are useful as UV-absorbing materials for use in skin care products such as sunscreens. This UV-absorbing effect is presumably due to intermolecular interactions such as π-π stacking of aromatic lignin.

[0112] The hollow spherical particles of the present invention can contain a liquid, a gas, or a solid (such as a metal) and can be used, for example, as a heat insulator, a compatibilizer, a catalyst, or a sensitizer.

[0113] The form in which the active ingredients, solids, etc. are present is not particularly limited as long as they are in contact with and held by the hollow spherical particles, for example, they may be present in the hollow portion of the hollow spherical particles, held by or attached to a constituent component (lignin) of the hollow spherical particles, or held by or attached to the outer surface of the hollow spherical particles.

[0114] The hollow spherical particles of the present invention exhibit long-wavelength fluorescence, which is due to the formation of conjugated intermolecular and intrapolymer associations (so-called J-aggregates) caused by the self-organization of lignin. Long-wavelength fluorescence, preferably 450 nm or longer, more preferably 480 nm or longer, and even more preferably 500 to 600 nm (specifically, for example, Ex 515 nm / Em 535 nm), and large Stokes shift fluorescence of 100 nm or longer (for example, Ex 410 nm / Em 670 nm) are observed due to exciplex formation.

[0115] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0116] Reference Test Example 1. Isolation of lignin, lignin-polysaccharide complex, hemicellulose, cellulose-hemicellulose complex, and cellulose Lignin, lignin-polysaccharide complex, hemicellulose, cellulose-hemicellulose complex, and cellulose were isolated from biomass using the M-APA method, the A-APA method, or a method for examining their conditions, and the yield and physical properties of the isolated products were measured. The isolation method of the present invention is a production method that enables highly efficient isolation of soluble lignin, lignin-polysaccharide complex, hemicellulose, cellulose-hemicellulose complex, and cellulose from natural polymers in biomass, and includes a step (A) of contacting plant biomass with a solution containing an organic acid and a peracid. Specifically, the method was carried out as follows.

[0117] Reference Test Example 1-1. Preparation of finely pulverized wood flour Fine powder (finely pulverized wood flour) with a volume average particle size of 10 μm (1-100 μm) was prepared from wood flour of broad-leaved trees (eucalyptus or beech), coniferous trees (red pine, cedar, or cypress), or herbaceous plants (bagasse (sugar cane) or bamboo) using a ball mill or bead mill method.

[0118] An example of a preparation method using a ball mill is shown below. A planetary ball mill (P-6, Fritsch) was used. 2 g of wood flour and 100 g of 3 mm diameter zirconia beads were placed in an 80 cc agate container and sealed in a twin overpot. After evacuating the overpot for 20 minutes, inert nitrogen gas was injected. One cycle consisted of 1 minute of milling followed by a 1 minute 20 second pause, and the milling was carried out for 180 cycles at 550 rpm (a total of 3 hours). These conditions allowed for the production of finely powdered wood flour while suppressing oxidation and heat-induced degradation during milling.

[0119] Reference Test Example 1-2. Preparation of wood flour In two pots, left and right, of a mixer mill (MM301, manufactured by Retsch), 1 g each of wood flour or wood chips (10 mm x 10 mm x 1 mm) from a broadleaf tree (eucalyptus or beech), a conifer (red pine, cedar, or cypress), or a herbaceous plant (bagasse (sugar cane) or bamboo) was placed and ground for a grinding time of 5 minutes at a frequency of 1 / 15 seconds, yielding a powder (wood flour) with a volume average particle size of 0.1 mm.

[0120] Reference Test Example 1-3. Milling-Acid-Peracid Method (M-APA Method) The starting material was the finely ground wood flour (average particle size 10 μm) obtained in Reference Test Example 1-1. 2 g of finely ground wood flour and 10 mL of an acetic acid-peracetic acid solution (composition: 17.4 M acetic acid (99%), 0.14 M peracetic acid (slightly less than 1%), 0.01 M hydrogen peroxide, and trace amounts of water) were placed in an initiator vial and microwaved for 10 min using a Biotage Initiator+ 60 microwave synthesizer at 50°C, initial power 400 W, and stirring speed 600 rpm. After microwave treatment, the soluble fraction was separated by adding 10 mL of separation solvent (acetone) and spinning down (RCF 8000 xg, 5 min). The insoluble fraction was extracted with 10 mL of separation solvent (acetone) and washed three times, and then combined with the soluble fraction. This soluble lignin is called acid peroxyacid lignin (APA lignin).

[0121] The insoluble fraction was subjected to the second extraction procedure, but the microwave heating conditions were changed to 140°C. The soluble fraction was identified as lignin-hemicellulose copolymer. The insoluble fraction was obtained as a cellulose-based copolymer.

[0122] <Reference Test Example 1-4. A-APA Method (Alkali-Acid-PerAcid Method)> The wood flour (average particle size 0.1 mm) obtained in Reference Test Example 1-2 was used as the starting material. A 0.25 M sodium hydroxide solution was prepared (1N diluted 4 times). 2.4 mL of 0.25 M sodium hydroxide solution was added to 0.3 g of wood flour, and microwave extraction (100°C, 30 min) was performed. The required amount of alkali is approximately 1 mmol of NaOH per 1 g of wood flour.

[0123] After microwave treatment, the soluble and insoluble fractions can be easily separated by decantation, spin-down, or filtration. An additional three rounds of acetone (separation solvent) extraction were performed and combined with the soluble fraction. The insoluble fraction was extracted using the same extraction method as the M-APA method in Reference Test Example 1-3 to obtain soluble lignin: acid peroxide lignin (APA lignin) and lignin-hemicellulose copolymer. The insoluble fraction was composed primarily of cellulose.

[0124] <Reference Test Example 1-5. Conditions> Studies were conducted using other organic acids (formic acid, glyoxylic acid) instead of acetic acid. Furthermore, studies were conducted using other peracids (hydrogen peroxide) instead of peracetic acid. When other peracids (hydrogen peroxide) were used, the composition was 12M acetic acid, and the hydrogen peroxide concentration was the concentration shown in the table below.

[0125] The contact temperature between plant biomass or insoluble matter and organic acid + peracid was varied from room temperature to 180°C. In addition, the heating method used was an external heating method using an oil bath, instead of an internal heating method using microwaves.

[0126] <Reference Test Example 1-6. Analysis and Measurement Methods> Lignin, lignin-polysaccharide complexes, and cellulose were analyzed and measured by the following methods.

[0127] <Reference Test Example 1-6-1. Molecular Weight (Mn, Mw, and Polydispersity) Measurement Method> Molecular weight was determined by size exclusion chromatography (SEC), also known as gel permeation chromatography (GPC). The sample was dissolved in a solution of acetic anhydride and a base (e.g., pyridine) and reacted for 3-6 hours to obtain the acetylated product. This was dissolved in tetrahydrofuran (THF) at a concentration of 2.0 mg / mL and separated by high-performance liquid chromatography (Shimadzu Corporation, high-pressure gradient SEC analysis system). A Tosoh HZ-M column (150 mm x 4.6 mm id, 4 μm, three columns connected in series) was used. Analysis was performed by injecting 10 μL of sample, at a column temperature of 40°C, using tetrahydrofuran (THF) as the mobile phase at a flow rate of 0.35 mL / min. Mass calibration curves were constructed using standard polystyrene, Tosoh PStQuickC (molecular weights (MW) of 2,110,000, 427,000, 37,900, and 5,970), pinoresinol (MW 352), and vanillin (MW 152), to determine the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the samples. Polydispersity was calculated as Mw / Mn.

[0128] <Reference Test Example 1-6-2. Calculation Method for the Composition Ratio of Molecular Bonding Units> Samples were dissolved in deuterated dimethyl sulfoxide (DMSO-d6) to a concentration of 1-10 wt%, and NMR spectra were acquired using a Bruker Avance III 600 MHz NMR instrument equipped with a cryogenic probe. The composition ratio of lignin interunit bonding units was calculated from the signal volume in the HSQC (heteronuclear single-quantum correlation spectroscopy) spectrum. The composition ratio was calculated as the ratio per 100 lignin aromatic rings. The content of ether-type bonding units was estimated from the sum of the integrals of the C-H correlation signals at the β-position (δH / δC = 4.0 ± 0.2 ppm / 85.6 ± 1.2 ppm region, δH / δC = 4.3 ± 0.2 ppm / 83.0 ± 0.7 ppm region). Quantitation in the two-dimensional NMR method was performed by correcting using the TAF method described in the literature (H. Okamura, H. Nishimura, T. Nagata, T. Kigawa, T. Watanabe and M. Katahira, Accurate and molecular-size-tolerant NMR quantitation of diverse components in solution, Scientific Reports, 6, 21742. 2016), to calculate accurate content.

[0129] <Reference Test Example 1-6-3. Method for calculating the composition ratio of lignin and polysaccharide> The sum of the integral values ​​of the C-H correlation signals at the anomeric position (1st position) of the polysaccharide was calculated by the NMR method described above, and after correction by the TAF method, the ratio was calculated as a ratio per 100 lignin aromatic rings.

[0130] <Reference Test Example 1-6-4. Method for calculating the composition ratio of lignin-polysaccharide copolymerization points> As described above, the sum of the integral values ​​of the C-H correlation signals (LC ether, δH / δC = 4.50 ± 0.15 ppm / 80.1 ± 1 ppm region) and (LC ester, δH / δC = 5.88 ± 0.15 ppm / 74.0 ± 1.5 ppm region) derived from LC α ether and LC α ester bond units was calculated using 2D HSQC NMR. After correction using the TAF method, the ratio was calculated as a ratio per 100 lignin aromatic rings. Note that although the A-APA method hydrolyzes some of the ester bonds by alkali treatment, it is also possible to obtain LC α ester-type lignin-hemicellulose copolymers.

[0131] <Reference Test Example 1-6-5. Method for calculating yield from raw biomass> Each obtained component was checked using a pH meter or pH test paper or peracid test paper (potassium iodide starch paper), and then neutralized and peracid quenched as necessary. Neutralization was performed by adding 1N HCl or 1N NaOH in small amounts. Peracid quenching was performed by adding 1M aqueous sodium sulfite solution dropwise. The organic solvent was removed using an evaporator. A dry powder was then obtained by freeze-drying. If salts were generated by neutralization, the concentrated solution after organic solvent removal was re-extracted with a separation solvent (acetone) for desalting. The solvent was then removed again using an evaporator, and a dry powder was obtained by freeze-drying. Each obtained component was weighed, and the yield per raw biomass was calculated.

[0132] <Results> The molecular structure, molecular weight, and yield of the obtained polymer are desirable under the following conditions. The results are shown in Tables 1 to 7.

[0133] Table 1 shows the peracid conditions in the two-stage microwave extraction reaction of the M-APA method and the yields of each polymeric lignocellulose component (weight %, raw material biomass ratio, raw material is eucalyptus).

[0134]

[0135] Table 2 shows the yields (wt %, ratio to raw material biomass) of each polymeric lignocellulose component of various biomass in the A-APA method two-stage microwave extraction reaction.

[0136]

[0137] Table 3 shows the peracid conditions in the two-stage microwave extraction reaction of the M-APA method and the molecular weights of each component of high molecular weight lignocellulose (acetylated GPC analysis values).

[0138]

[0139] Table 4 shows the yields (wt %, ratio to raw material biomass) of each polymeric lignocellulose component of various biomass in the two-stage microwave extraction reaction of the M-APA method.

[0140]

[0141] Solvent: Acetic acid (containing 1% peracetic acid, 0.14 mol / L) Microwave extraction conditions: 50°C, 10 min (first stage) to obtain APA lignin soluble fraction, 140°C, 10 min (second stage) to obtain lignin hemicellulose copolymer Table 5 shows the yields (wt%, ratio of raw biomass) of each polymeric lignocellulose component of various biomass in the A-APA method one-stage microwave extraction reaction.

[0142]

[0143] Table 6 shows the molecular weights (acetylated GPC analysis values) of each component of high molecular weight lignocellulose obtained from various biomass materials by the A-APA method.

[0144]

[0145] As a result of examining the conditions, it was found that when the starting material is woody biomass, a contact temperature of 40 to 90°C with organic acid and peracid is suitable for obtaining soluble lignin, and a contact temperature of 100 to 160°C is suitable for obtaining lignin-hemicellulose copolymer.Furthermore, as a result of examining the conditions, it was found that when the starting material is herbaceous biomass, a contact temperature of room temperature to 60°C is suitable for obtaining soluble lignin, and a contact temperature of 70 to 150°C is suitable for obtaining lignin-hemicellulose copolymer.

[0146] As a result of examining the conditions, it was found that the heating time by microwave irradiation is 5-30 min, and preferably 10 min. The net irradiation time is short. See Figure 2 for the microwave profile, temperature, and pressure data.

[0147] As a result of examining the conditions, it was found that microwave heating had higher yield and selectivity than external heating under conditions of low temperature, short time, and low energy input. In other words, the microwave effects of local heating, internal heating, electron transfer, and drug penetration promotion were confirmed.

[0148] As a result of examining the conditions, lignin could be isolated using all of the organic acids, acetic acid, formic acid, and glyoxylic acid, but acetic acid was the most suitable from the standpoints of yield, purity, and industrial application.

[0149] The NMR results for Reference Test Examples 1-6-2 and 1-6-3 are shown in Figure 3. Figure 3 shows the analysis results for lignin isolated by the M-APA method (microwave treatment at 50°C for 10 minutes, acetic acid-peracetic acid 1% conditions) using eucalyptus as the starting material. The proportion of lignocellulose interunit bonds was quantified using TAF-NMR, revealing that 99% of the signals were derived from lignin and 1% from polysaccharides (hemicellulose). The breakdown of lignin interunit bonds was 81% ether-type β-O-4, 5% β-5, 11% β-β, 1% dibenzodioxocine, and 1% other. See Figure 4 for partial chemical structures of lignin interunit bonds and lignin-hemicellulose covalent bonds.

[0150] The NMR results for Reference Test Example 1-6-4 are shown in Figure 5. Figure 5 shows the analysis results for lignin-hemicellulose copolymers isolated by the M-APA method (microwave treatment at 50°C for 10 minutes, acetic acid-peracetic acid 1%) using each plant as the starting material. LC bonds (ether and ester types), indicated by circles in the figure, are the main branched structures present in proportions equal to or greater than the β-5 and β-β bonds, which are the main interunit bonds of lignin. The isolated lignin-hemicellulose copolymers are characterized by the presence of LCα-ester type bonds in particular.

[0151] Reference Test Example 2. Solubility Measurement The solubility of lignin and lignin-hemicellulose copolymers obtained by the method of Reference Test Example 1 or a method similar thereto was measured in 60-80% ethanol at 25°C. Details of the measured samples are shown in Table 7. The abbreviations in Table 7 are as follows: PA: Peracetic acid (peracetic acid), HP: Hydrogen Peroxide. 50: MW50 ACTN, microwave-treated at 50°C, high-quality polymeric lignin. 140: MW50-MW140 ACTN, residue after microwave-treated at 50°C, second-stage treatment at 140°C, lignin-hemicellulose copolymer. A50: Acetic acid-peracetic acid system, HP PA 1% AA, Mw50 ACN, microwave-treated at 50°C, high-quality polymeric lignin. H50: Acetic acid-hydrogen peroxide system, HP 1M hydrogen peroxide, Mw50 ACN, microwave-treated at 50°C, high-quality polymeric lignin.

[0152]

[0153] The solubility was measured as follows. The sample was dissolved in 25°C ethanol by stirring, and then separated into ethanol-soluble and ethanol-insoluble portions by solid-liquid separation. A 25°C aqueous ethanol solution (1 / 1 ethanol / water) was added to the ethanol-insoluble portion and stirred to dissolve, obtaining an aqueous ethanol-soluble portion. The aqueous ethanol-soluble portion was mixed with the ethanol-soluble portion to obtain a sample solution. The amount of aqueous ethanol added was adjusted so that the ethanol concentration of the sample solution was in the range of 60-80%. In the process of obtaining the soluble portion, dispersion and solubilization were performed using an ultrasonic cleaner at 28 kHz for 3 min, as needed. The maximum sample concentration at which the sample solution became visually transparent was defined as the "solubility in 60-80% ethanol at 25°C."

[0154] The results are shown in Table 8. It was found that the lignin and lignin-hemicellulose copolymer obtained by the method of the present invention exhibited good ethanol solubility.

[0155]

[0156] Reference Test Example 3. Preparation and analysis of self-assembled bodies Self-assembled bodies were prepared using lignin isolated by the M-APA method (microwave treatment at 50°C for 10 minutes, acetic acid-peracetic acid 1% or acetic acid-0.2M hydrogen peroxide conditions) using eucalyptus or bamboo as the starting material, or lignin-polysaccharide copolymer isolated by the M-APA method (microwave treatment at 140°C for 10 minutes, acetic acid-peracetic acid 1% or acetic acid-0.2M hydrogen peroxide conditions) using eucalyptus as the starting material. Specifically, the procedure was as follows.

[0157] A DMSO solution with a sample concentration of 1-2 wt% was prepared and diluted to 0.01-0.02 wt% with a mixture (1:1 or 2:1) of a separating solvent (acetonitrile or ethanol) and water (or buffer solution). 0.1-0.2 mL of the sample solution was applied to a glass slide or cover glass, and the solvent was evaporated under atmospheric pressure to obtain a thin film of self-assembled aggregates. Even under the above conditions, a high-concentration self-assembled aggregate was obtained by adding an equal volume of water (or buffer solution) to a DMSO solution with a sample concentration of 1 wt% and applying it.

[0158] Next, the optical properties of the obtained self-assembled bodies (lignin solid thin films or lignin-polysaccharide copolymer solid thin films) and a comparison object (lignin obtained by the APA method (APA lignin)) were analyzed. Specifically, the optical properties were analyzed as follows.

[0159] The following was used for the measurements.

[0160] Ultraviolet-visible absorption spectrum: UV-2700 (Shimadzu Corporation) Fluorescence spectrum: Spectrofluorometer RF-6000 (Shimadzu Corporation) Fluorescence microscope measurement: All-in-one fluorescence microscope BZ-X810 (Keyence Corporation) Analysis was performed using the analysis software provided with each device.

[0161] UV-visible absorption spectrum: black quartz cell for spectroscopic measurement (optical path length: 10 mm), fluorescence measurement: fully transparent synthetic quartz cell (optical path length: 10 mm) and Starna triangular quartz cell SF3 were used. For solid samples, a solid measurement unit was used, and the sample was applied to a cover glass and sandwiched between quartz plates for measurement.

[0162] The 3D fluorescence spectrum was measured at an excitation wavelength of 310-800 nm with a data interval of 5 nm, an emission wavelength of 350-900 nm with a data interval of 1 nm, a scan speed of 12,000 nm / min, and a UV cut filter U310 attached to the excitation side to reduce the effects of scattered light and multi-order light. The bandwidth was 5 nm on the excitation side and 15 nm on the emission side, and the sensitivity was set to Low.

[0163] Synchroscan spectroscopy is a scanning mode in which the excitation and fluorescence spectrometers of a spectrofluorometer are scanned simultaneously, with a fixed wavelength interval between them. Measurements were performed by varying the wavelength interval between the excitation and fluorescence light in the range of -90 nm to 260 nm. When the wavelength interval is negative, fluorescence with shorter wavelengths than the excitation light is detected. In this case, fluorescence due to the anti-Stokes shift can be selectively detected. The scan was set to cover the fluorescence wavelength range of 350-800 nm, with a data interval of 0.1 nm, a scan speed of 600 nm / min, a bandwidth of 15 nm on the excitation side and 20 nm on the emission side, and a sensitivity setting of Low.

[0164] The UV-visible absorption spectrum was measured using a double monochromator UV-2700. A wavelength scan (200-900 nm) was performed.

[0165] The results are shown in Figures 6 to 9. Figure 9 shows that the lignin self-assembled body exhibits anti-Stokes fluorescence.

[0166] Reference Test Example 4. Measurement of UV Absorbency The UV absorbency was measured for the lignin and lignin-hemicellulose copolymer used in Reference Test Example 2. Specifically, the sample was dissolved in ethanol to a concentration of 0.005 w / v %, and the UV absorption spectrum of the resulting solution (transparent) was measured using a spectrophotometer (Shimadzu Corporation, UV-2700) (optical path length 1 cm, quartz cell).

[0167] The results are shown in Figure 10. It was found that the lignin and lignin-hemicellulose copolymer obtained by the method of the present invention exhibit good ultraviolet absorption properties.

[0168] Example 1. Preparation of hollow spherical particles 1 Hollow spherical particles, which are self-assembled bodies, were prepared using the lignin used in Reference Test Example 2 as a sample. Specifically, this was done as follows.

[0169] (1) 20 mg of lignin sample (dry powder) was dissolved in 1.0 mL of DMSO to prepare a 2% w / v lignin solution.

[0170] (2) 0.1 mL of 2% w / v lignin stock solution was added to 0.9 mL of 80% v / v ethanol solution and stirred until uniform.

[0171] (3) The solution was diluted by gradually adding 3 mL of water dropwise while stirring. The dilution ratio was variable, and the formation of hollow spherical particles began at organic solvent concentrations of 40% or less, and a stable dispersion was observed at concentrations of 5-30%.

[0172] Alternatively, hollow spherical particles were obtained by a method employing the following step (4) instead of the above step (3).

[0173] (4) While stirring, 1 mL of an alcohol-water solvent was gradually added dropwise. The alcohol-water solvent used was a 30% ethanol solution or a 10% n-butanol solution. The solution surface was then gently sprayed with nitrogen gas, air-dried to evaporate, or the solvent was distilled off under reduced pressure. Hollow spherical particles began to form at organic solvent concentrations of 40% or less, and a stable dispersion was observed at concentrations between 5% and 30%.

[0174] A bright-field image of the obtained hollow spherical particles is shown in Figure 11. Relatively large particles (diameter of 5 µm or more) and relatively small particles (diameter of less than 5 µm) were confirmed.

[0175] In addition, the particle diameter and membrane thickness of one relatively large particle were measured, and the volume occupied by the hollow spherical particle lumen (lumen ratio) was calculated. Specifically, fluorescence observation was performed using a Keyence BZ-X810 all-in-one fluorescence microscope with a 100x objective lens in sectioning mode, and the particle diameter and membrane thickness were measured from the resulting image data using Keyence analysis software. The lumen ratio (unit: %) was calculated using the formula: lumen ratio = (volume of the lumen portion of the hollow spherical particle (excluding the membrane portion) / total volume of the hollow spherical particle) × 100. The particle diameter was 21.1 μm, the membrane thickness was 635 nm, and the lumen ratio was 83%.

[0176] Example 2 Preparation of hollow spherical particles encapsulating a drug 1 Hollow spherical particles encapsulating a drug were prepared using the lignin used in Reference Test Example 2 as a sample. Specifically, the procedure was as follows.

[0177] A 0.2% w / v lignin solution (in 80% ethanol) was mixed with 1.0 mL of a 0.1% w / v near-infrared fluorescent dye DiR (DiIC18(7)) solution in 80% ethanol while stirring. Water or an alcohol-water solvent was added dropwise while stirring, and the organic solvent concentration was reduced as in Example 1 to form hollow spherical particles.

[0178] The image observed under a fluorescence microscope is shown in Figure 12. Particles exhibiting near-infrared fluorescence originating from the encapsulated dye were observed.

[0179] Example 3. Preparation of hollow spherical particles 2 Hollow spherical particles were prepared using the lignin used in Reference Test Example 2 as a sample. Specifically, the procedure was as follows.

[0180] A 2.5 wt% solution of eucalyptus-derived lignin (30% ethanol) was prepared and stirred to form a homogeneous solution. This was used as the stock solution. 200 μL of 50% organic solvent (ethanol, 1-propanol, allyl alcohol, 2-propanol, or 1-butanol) was gradually added to 100 μL of the stock solution while stirring to form a homogeneous solution. 1.7 mL of water was gradually added while stirring to form a homogeneous solution. The resulting solution (final concentration: 0.125 wt% organic solvent, 5% (including 0.015% ethanol)) was subjected to DLS nanoparticle measurement. DLS measurements were performed using a multi-analyte nanoparticle size measurement system (Otsuka Electronics nanoSAQLA) with 2 mL of sample placed in a disposable spectroscopic cell. Particle size measurements were performed using dynamic light scattering. Each measurement was performed three times, and the average was calculated. The measurement temperature was 25°C, and the solvent refractive index was 1.33.

[0181] The results are shown in Table 9.

[0182]

[0183] In addition, the same tests as above were conducted using lignins derived from other tree species (Japanese red pine, Japanese cypress, Japanese cedar, beech, and bamboo) (lignins obtained by the same method as in Reference Test Example 2), and similar results were obtained for the average particle size and polydispersity index.

[0184] Reference Test Example 5. Determination of hydroxyl groups The lignin used in Reference Test Example 2 was used as a sample to determine the amount of hydroxyl groups. Comparative Examples 1 and 2 were also cited from the literature to show the quantitative values ​​of hydroxyl groups.

[0185] The solvent used in this analysis was a mixture of dehydrated pyridine and CDCl3 (volume ratio 1.6 / 1). The standard derivatization procedure was as follows: 20 mg of sample was dissolved in 400 μL of solvent. 100 μL (5.3 μmol) of N-hydroxy-1,8-naphthalimide solution (concentration 11.4 mg / mL) was added as an internal standard, and 100 μL of Tris(2,4-pentanedionato)-chromium(III) [Cr(acac)3] (solution concentration 5 mg / mL) was added as a relaxation reagent. While stirring in the dark, 100 μL of 2-chloro-4,4,5,5-tetramethly-1,3,2-dioxaphospholane (TMDP) was added and the mixture was stirred at room temperature for 3 hours.

[0186] 31P NMR measurements of derivatized samples were performed using a JEOL 400 MHz NMR spectrometer. The hydroxyl groups were quantified based on the peak integrals of the resulting 31P NMR spectra. Typically, the peaks at 140.3-144.5 ppm (syringyl-OH, condensed OH), 138.3-140.5 ppm (guaiacyl-OH), and 137.0-138.5 ppm (p-hydrolyphenyl-OH) were assigned to phenolic hydroxyl groups, the peaks at 145.0-150.0 ppm to alcoholic hydroxyl groups, and the peaks at 133.6-136.0 ppm to carboxylic hydroxyl groups. The integrals of the alcoholic hydroxyl groups relative to the sum of the integrals of these peaks and the integrals of the phenolic hydroxyl groups relative to the alcoholic hydroxyl groups were calculated.

[0187] The results are shown in Table 10.

[0188]

[0189] The data for Comparative Example 1 was created from Table 1. Functional Groups Contents of EHL and Its Three Fractions Based on the 31P NMR Spectra Results in the reference paper (T. Pang et al., Lignin Fractionation for Reduced Heterogeneity in Self-Assembly Nanosizing: Toward Targeted Preparation of Uniform Lignin Nanoparticles with Small Size, ACS Sustainable Chem. Eng. 2020, 8, 24, 9174-9183 (https: / / pubs.acs.org / doi / 10.1021 / acssuschemeng.0c02967)).

[0190] The data for Comparative Example 2 are based on the reference (JF Araneda et al., Analysis of lignins using 31 P benchtop NMR spectroscopy: quantitative assessment of substructures and comparison to high-field NMR, Can. J. Chem. 2022, 100, 799-808 (http: / / dx.doi.org / 10.1139 / cjc-2022-0041), Table 2, 162 MHz (HF) 31 P NMR analysis data was cited. However, the peak at 144.5-140.3 ppm is expressed as "syringyl OH + condensed phenolic OH." In the case of softwood, syringyl OH is not included, so only condensed phenolic OH is shown.

Claims

1. The hollow spherical particles are self-assembled bodies of lignin, the lignin having a β-O-4 ether structure content of 50% or more and a solubility in 60-80% ethanol at 25°C of 2 w / v% or more.

2. 2. The hollow spherical particle according to claim 1, wherein the number average molecular weight (Mn) of the lignin is 0.7 to 9 kDa, or the weight average molecular weight (Mw) of the lignin is 1 to 10 kDa.

3. 2. The hollow spherical particles according to claim 1, having a number average particle size of 100 μm or less.

4. 2. The hollow spherical particle according to claim 1, having a number average particle size of 50 nm or more.

5. 2. The hollow spherical particle according to claim 1, having a lumen ratio of 60% or more.

6. 2. The hollow spherical particle according to claim 1, having a film thickness of 1 nm to 4000 nm.

7. The hollow spherical particle according to any one of claims 1 to 6, which contains an active ingredient.

8. 8. The hollow spherical particle according to claim 7, wherein the active ingredient is at least one selected from the group consisting of dyes, pesticides, fertilizers, medicines, cosmetic ingredients, fragrances, fluorescent agents, paints, proteins, nucleic acids, lipids, hormones, sugars, glycosides, surfactants, adhesives, vitamins, coenzymes, minerals, cells, organelles, low molecular weight compounds, high molecular weight compounds, metal complexes, liposomes, and hydrogels.

9. 7. The hollow spherical particle according to claim 1, which contains a liquid, a gas, or a solid (one of which is a metal).

10. 10. The hollow spherical particle of claim 9 for use as a thermal insulator, compatibilizer, catalyst, or sensitizer.

11. The hollow spherical particle according to any one of claims 1 to 6, wherein the lignin has a sulfur atom content of 0.15% or less.

12. The hollow spherical particle according to any one of claims 1 to 6, wherein the content of non-natural condensed structures of the lignin is 1% or less.

13. 7. The hollow spherical particle according to claim 1, wherein the ratio of phenolic hydroxyl groups to alcoholic hydroxyl groups of the lignin is 0.8 or less.

14. The hollow spherical particle according to any one of claims 1 to 6, which exhibits long wavelength fluorescence.

15. The hollow spherical particle according to claim 14, wherein the long wavelength fluorescence is fluorescence of 450 nm or longer.

16. An ultraviolet absorber comprising the hollow spherical particles according to any one of claims 1 to 6.

17. A light resistance imparting agent comprising the hollow spherical particles according to any one of claims 1 to 6.

18. An anti-Stokes fluorescent agent comprising the hollow spherical particle according to any one of claims 1 to 6.