Method for dissolving all components of plant biomass raw material and application thereof

Abstract

The invention discloses a method for efficiently dissolving all components of a plant biomass raw material. According to the method, a eutecticevaporate solvent system is adopted to carry out mild soaking treatment on a plant biomass raw material, and a homogeneous plant biomass all-component solution is finally formed by combining the dissolution synergistic coupling effect of a metal salt solution. All-component one-pot efficient dissolution of cellulose, hemicellulose and lignin in the plant biomass raw materials can be achieved, the dissolution efficiency reaches up to 100%, the dissolution process is mild, energy consumption is low, and the method has industrial application prospects; the prepared plant biomass all-component solution can be used as a material construction platform for preparing a series of plant biomass gel, films, fiber materials and the like with excellent performance, and can be used in the fields of sewage treatment, bio-based packaging, spinning, energy collection, 3D printing and the like.

Description

Technical Field

[0001] The present invention belongs to the field of biomass refining, and particularly relates to a method for efficiently dissolving all components of plant biomass raw materials in a deep eutectic solvent system. Background Art

[0002] Plant biomass raw materials, mainly composed of cellulose, hemicellulose, and lignin, are renewable and widely sourced biopolymers and are considered ideal substitutes for petroleum-based chemicals and materials. Through technologies such as dissolution and regeneration, chemical modification, catalytic degradation, and bioconversion, plant biomass raw materials can be selectively used to produce biomass energy, chemicals, and materials, and have become a top priority for developing a circular economy in the context of carbon reduction. Using green and sustainable solvents to dissolve plant biomass raw materials is one of the important ways to achieve their high-value utilization.

[0003] The main barrier to the dissolution of plant biomass raw materials is the highly ordered supramolecular structure formed by the original physical hierarchical structure in the plant cell wall, the naturally occurring lignin-carbohydrate bonds (LCC bonds), and the hydrogen bond network. Among them, the original physical hierarchical structure of the plant cell wall is a natural protective barrier for LCC bonds and the hydrogen bond network. It is precisely the original physical hierarchical structure, LCC bonds, hydrogen bond network in the plant cell wall, and the synergistic effect among the three that make the three components (cellulose, hemicellulose, and lignin) in natural plant biomass raw materials tightly connected and not easily dissolved. In particular, the dissolution of all components of large-sized plant biomass raw materials has not been reported yet. Although various dissolution methods for powdered plant biomass raw materials have been reported, there are still problems such as high dissolution temperature (above 150 °C), high energy consumption, and cumbersome steps. At the same time, due to high temperature and excessive mechanical treatment, the structures of the three components (cellulose, hemicellulose, and lignin) in plant biomass raw materials are damaged and degraded, thereby limiting their subsequent construction of high-performance materials and high-value applications.

[0004] Therefore, it is particularly important to construct a solvent system for all components of plant biomass raw materials with low energy consumption, simple process, strong universality, high dissolution efficiency, and low degradation degree for improving the quality and efficiency of plant biomass raw materials. The present invention innovatively utilizes the unique advantages of deep eutectic solvents - breaking the complex LCC chemical connections between components, partially dissolving the amorphous components (hemicellulose and lignin), and increasing the accessibility of cellulose fiber hydroxyl groups - to destroy part of the original physical hierarchical structure of the cell wall, realizing the swelling of plant biomass raw materials and the construction of molecular channels in the plant cell wall, significantly increasing the interaction sites between the metal salt solution and plant biomass; and combining with the dissolution characteristics of the metal salt solution to efficiently break the natural hydrogen bond network barrier of plant biomass. Finally, the two work together to improve the overall dissolution efficiency of all components of plant biomass.

[0005] Thus, the following are formed: (1) The deep eutectic solvent destroys the physical hierarchical structure of plant biomass, dissociates LCC, swells the plant biomass raw material, and dissolves lignin, and provides a channel for the subsequent penetration of metal salts; (2) The metal salt solution penetrates into the interior of the plant biomass to break the natural hydrogen bond network barrier; the two cooperate with each other and promote each other to continuously destroy the physical hierarchical structure of the plant biomass, dissociate LCC, and break the natural hydrogen bond network structure, and finally realize the efficient total component dissolution of large-size plant biomass raw materials.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] Object of the Invention: Aiming at the problems existing in the prior art of plant biomass dissolution, the present invention provides a method for total component dissolution of plant biomass raw materials at room temperature quickly and efficiently. This method uses a deep eutectic solvent to gently soak the plant biomass, and then cooperates with a metal salt solution at room temperature for synergistic treatment to achieve the total component dissolution of the plant biomass. The soaking treatment of the deep eutectic solvent on the plant biomass promotes the dissolution of lignin and hemicellulose on the surface of cellulose, destroys the natural physical structure and LCC bonds of the plant biomass, broadens the distance between cellulose fibers, and increases the content of hydrophilic hydroxyl groups in lignin, which opens up channels and interaction sites for the subsequent penetration, swelling, and dissolution of the metal salt solution.

[0008] The purpose of this part is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Simplifications or omissions may be made in this part, as well as in the abstract and title of the present application, to avoid obscuring the purpose of this part, the abstract, and the title, and such simplifications or omissions shall not be used to limit the scope of the present invention.

[0009] In view of the above and / or problems existing in the prior art, the present invention is proposed.

[0010] One object of the present invention is to provide a method for total component dissolution of plant biomass raw materials, comprising the following steps:

[0011] S1. Soak the plant biomass raw material in a deep eutectic solvent to obtain a plant biomass raw material / deep eutectic solvent mixture;

[0012] S2. Add a metal salt solvent to the mixture obtained in step S1, and quickly stir and mix evenly at room temperature to obtain a homogeneous plant biomass total component solution.

[0013] Further, the plant biomass raw material is a softwood, hardwood, bamboo, hemp, cotton or gramineous raw material.

[0014] Further, the plant biomass raw material has a length of 10 - 50 mm, a width of 10 - 50 mm, and a thickness of 1 - 5 mm.

[0015] Further, in step S1, the hydrogen bond acceptor in the deep eutectic solvent is any one or a combination of aluminum chloride, calcium chloride, iron chloride, lithium chloride, manganese chloride, zinc chloride, zinc bromide, ammonium chloride, potassium carbonate, benzyltrimethylammonium chloride, acetylcholine chloride, and choline chloride, preferably choline chloride, zinc chloride, iron chloride, lithium chloride, and calcium chloride. The hydrogen bond donor is any one or a combination of lactic acid, acetic acid, formic acid, propionic acid, methoxyacetic acid, glyoxylic acid, and pyruvic acid.

[0016] Further, in step S1, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor in the deep eutectic solvent is 1:1 - 1:20, and the preferred molar ratio is 1:4 - 1:15.

[0017] Further, in step S1, the mass ratio of the plant biomass raw material to the deep eutectic solvent is 1:1 - 1:20; the preferred mass ratio is 1:1 - 1:15.

[0018] Further, in step S1, the soaking treatment temperature is 25 - 130°C; the soaking time is 0.1 - 10 h; the preferred soaking treatment temperature is 50 - 120°C; the soaking time is 0.5 - 4 h.

[0019] Further, the soaking treatment in step S1 causes the covalent bonds between lignin β-O-4 and between lignin and hemicellulose to break, transferring the lignin and hemicellulose on the cellulose surface, thereby greatly improving the penetration efficiency of the deep eutectic solvent. In addition, the breakage of the β-O-4 bond in lignin increases the content of hydrophilic hydroxyl groups in lignin, improving the compatibility of lignin in the metal salt solution.

[0020] Further, the soaking treatment in step S1 modifies the cellulose surface, breaking the hydrogen bonds between cellulose fibrils and increasing the distance between cellulose fibrils.

[0021] Further, in the metal salt solution in step S2, the molar ratio of the metal salt to water is 1:1 - 1:9.

[0022] Further, the mass ratio of the metal salt solution to the deep eutectic solvent is 1:1 - 20:1, and the preferred mass ratio is 5:1 - 15:1.

[0023] Further, the viscosity of the plant biomass whole-component solution is 1.6 - 578.5 Pa·s; the mass fraction of the plant biomass whole-component solution is 0.01 - 10 wt%.

[0024] Furthermore, the recovery rate of the plant biomass obtained after the regeneration of the plant biomass whole-component solution is 60-87%, the recovery rate of cellulose in the regenerated plant biomass is 90-99%, and the recovery rate of lignin in the regenerated plant biomass is 90-99%.

[0025] Another object of the present invention is to provide the application of the plant biomass whole-component solution obtained by the method as described above, and to prepare plant biomass gels, plant biomass films, plant biomass fibers, and plant biomass 3D printing materials from the modified plant biomass whole-component solution.

[0026] Furthermore, the cellulose content in the obtained plant biomass gels, films, fibers, and plant biomass 3D printing materials is 31-94%, and the lignin content is 6-69%.

[0027] Furthermore, the compressive strength of the obtained plant biomass gel is 30-549 KPa.

[0028] Furthermore, the tensile stress of the obtained plant biomass film is 72-230 MPa, the tensile strain is 9-480%, and the water swelling rate is 11.1-48.7%.

[0029] Furthermore, the strength of the obtained plant biomass fiber is 118-253 MPa.

[0030] Compared with the prior art, the beneficial effects of the present invention include:

[0031] The present invention uses a deep eutectic solvent to soak plant biomass to form a swollen cell wall structure, and then combines a metal salt solution to achieve the efficient dissolution of large-sized plant biomass in "one pot" at room temperature. This dissolution process is mild, with little degradation, and the efficiency is as high as 100%. Moreover, the cellulose and lignin in the regenerated plant biomass material can be simultaneously regenerated and recovered with a recovery rate close to 100%. The present invention has the characteristics of environmental friendliness, strong universality, high dissolution ability, mild conditions, low energy consumption, economy and environmental protection. The plant biomass materials prepared according to the present invention have excellent mechanical properties and can be used in fields such as water purification, sustainable packaging, textiles, and 3D printing, providing a broad application prospect for the high-value utilization of dissolved plant biomass. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts. Among them:

[0033] Figure 1are the polarized light microscope images of different raw materials and their different dissolution times and the digital photos of the solutions;

[0034] Figure 2 are the XRD patterns before and after wood regeneration;

[0035] Figure 3 are the solid yields, component contents, cellulose recovery rates and lignin recovery rates before and after wood regeneration;

[0036] Figure 4 are the photos of the solution viscosity after wood dissolution and the viscosity curves with different solid contents;

[0037] Figure 5 are the regenerated wood hydrogels, films and their mechanical properties;

[0038] Figure 6 are the regenerated wood aerogels and their heat insulation properties;

[0039] Figure 7 are the regenerated wood fibers and their mechanical properties and the regenerated wood 3D printing materials;

[0040] Figure 8 are the polarized light microscope photos of wood chips after soaking, washing to remove the deep eutectic solvent and dissolving in the metal salt solution for different times. Detailed implementation manners

[0041] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings, technical process steps, specific implementation conditions and materials in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0042] The raw materials used in the present invention can be derived from coniferous wood, broad-leaved wood, bamboo, hemp, cotton or gramineous raw materials, etc. In the following embodiments, wood is used as the raw material to illustrate the present invention.

[0043] Unless otherwise specified, the raw materials used in the embodiments are all commercially purchased.

[0044] Example 1

[0045] 1) Select the hydrogen bond acceptor zinc chloride and the hydrogen bond donor lactic acid to prepare a deep eutectic solvent in a molar ratio of 1:20. Mix zinc chloride and water evenly in a molar ratio of 1:5 to form a metal salt solvent. Mix poplar chips (length 20 mm, width 20 mm, thickness 2 mm), moso bamboo chips (length 20 mm, width 10 mm, thickness 2 mm), hemp (length 30 mm, width 10 mm, thickness 1 mm), rice straw (length 10 mm, width 10 mm, thickness 1 mm), and cotton with the deep eutectic solvent in a mass ratio of 1:10 respectively and mix well. After soaking at 120 °C for 1 h, add a metal salt solution with a mass 6 times that of the deep eutectic solvent, and stir at 500 rpm in one pot at room temperature to obtain a plant biomass solution.

[0046] 2) It can be seen from the observation of the cell wall thickness by SEM that the swelling degree of the cell wall is 14.9 - 31.2%. The dissolution process of the plant biomass was monitored by a polarized light microscope, as Figure 1 shown. Due to the anisotropy of the raw materials, there is an obvious birefringence phenomenon under the polarized light microscope. After adding the metal salt solution to the soaked cell wall, the birefringence phenomenon of the plant biomass disappeared after 0.5 - 3 h, indicating that the plant biomass was completely dissolved. The viscosity of the solution was 21.9 - 32.6 Pa·s, and the concentration was 1 wt%.

[0047] 3) Using distilled water as an antisolvent, slowly drip the plant biomass whole-component solution into distilled water for regeneration. After filtration and washing until neutral, dry to obtain regenerated plant biomass, and the recovery rate is 63 - 98%. Observe the regeneration morphology of the plant biomass by a JSM-7600F scanning electron microscope. The network formed by the regenerated plant biomass gradually changes from micrometers to nanometers, which further confirms the dissolution of wood. Determine the crystal structure of the regenerated plant biomass by a Bruker D8 ADVANCE X-ray diffractometer. The crystal structure of cellulose in the regenerated plant biomass is transformed into cellulose II type. Through chemical composition analysis, the cellulose retention rate in the regenerated plant biomass is 91.7 - 98.02%, and the lignin retention rate is 94.2 - 97.3%.

[0048] 4) The effects of different types of raw materials on the swelling and dissolution of plant biomass were investigated respectively. Due to the differences in the structures and properties of the biomass raw materials themselves, the swelling degree of the cell wall and the dissolution time are different. As shown in the following table, it can be seen that the deep eutectic solvent and the metal salt solution can dissolve various large-size plant biomass raw materials, among which the dissolution time of bamboo is the longest, which is related to the multi-layer cell wall of bamboo.

[0049] Type Degree of cell wall swelling (%) Dissolution time (h) Viscosity of solution (Pa·s) Hardwood - Poplar 15.79 1.7 29.7 Bamboo 14.9 3 27.8 Hemp 19.4 1.3 32.6 Straw 17.8 1.2 21.9 Cotton 31.2 0.5 25.2

[0050] Example 2

[0051] 1) Select hydrogen bond acceptor zinc chloride and hydrogen bond donor lactic acid in a molar ratio of 1:20 to form a low eutectic solvent. Mix zinc chloride and water in a molar ratio of 1:5 to form a metal salt solvent. Thoroughly mix Masson pine chips (length 20mm, width 20mm, thickness 2mm) with a low eutectic solvent in a mass ratio of 1:10, soak at 120°C for 1h, add a metal salt solution 6 times the mass of the low eutectic solvent, and stir at 500rpm in a pot at room temperature to obtain a Masson pine chip solution.

[0052] 2) The thickness of the cell wall was observed by SEM, and the swelling degree of the cell wall was 15.96%. The dissolution process of the Masson pine wood chips was monitored by polarizing microscopy. Due to the anisotropy of the raw material, there is an obvious birefringence phenomenon under the polarizing microscope. After adding the metal salt solution to the cell wall after immersion, the birefringence phenomenon of the plant biomass disappeared after 2.1 hours, indicating that the Masson pine wood chips were completely dissolved. The viscosity of the solution was 30.6 Pa·s and the concentration was 1wt%.

[0053] 3) Using distilled water as an anti-solvent, the plant biomass solution was slowly added to the distilled water for regeneration, filtered and washed to neutrality, and then dried to obtain regenerated wood with a recovery rate of 78%. The morphology of plant biomass regeneration was observed by a JSM-7600F scanning electron microscope. The network formed by the regenerated wood gradually changed from a micron network to a nano network, which further confirmed the dissolution of the wood. The crystal structure of the regenerated plant biomass was determined by a Bruker D8 ADVANCE X-ray diffractometer. Figure 2 As shown, natural wood has obvious cellulose type I diffraction peaks at 2θ = 15.5° and 2θ = 22.5°. In contrast, in regenerated Masson pine wood, cellulose has strong diffraction peaks at 2θ = 12.06° and 2θ = 19.95°, indicating that the crystalline structure of cellulose is transformed into cellulose type II. The cellulose retention rate in the regenerated plant biomass was tested by chemical composition analysis to be 96.02% and the lignin retention rate was 94.37%. Compared with Masson pine, the dissolution time of poplar wood is shorter at 1.7h. Therefore, poplar wood was selected as the plant biomass raw material for further experiments in subsequent embodiments.

[0054] Example 3

[0055] 1) Select hydrogen bond acceptor zinc chloride and hydrogen bond donor lactic acid in a molar ratio of 1:20 to form a low eutectic solvent. Mix zinc chloride and water in a molar ratio of 1:5 to form a metal salt solvent. Fully mix poplar wood chips (length 20mm, width 20mm, thickness 1-5mm) in a low eutectic solvent in a mass ratio of 1:10, soak at 120°C for 1h, add a metal salt solution 6 times the mass of the low eutectic solvent, and stir at 500rpm in a pot at room temperature to obtain a wood full component solution.

[0056] 2) The thickness of the cell wall was observed by SEM, and the swelling degree of the cell wall was 13.94-15.96%. The dissolution process of the wood was monitored by polarizing microscope. Due to the anisotropy of wood, it has obvious birefringence under polarizing microscope. After adding metal salt solution to the cell wall of plant biomass after immersion, the birefringence of wood disappeared after 1-4.5 hours, indicating that the wood was completely dissolved. The viscosity of the solution of all wood components is 23.4-29.1Pa·s, and the concentration is 1wt%.

[0057] 3) Using distilled water as an anti-solvent, slowly drop the solution of all wood components into the distilled water, regenerate, filter and wash until neutral, and then dry to obtain regenerated wood with a recovery rate of 68-79%. The regenerated morphology of the wood was observed by a JSM-7600F scanning electron microscope. The network formed by the regenerated wood gradually changed from a micron network to a nano network, which further confirmed the dissolution of the wood. The crystal structure of the regenerated wood was determined by a Bruker D8 ADVANCE X-ray diffractometer. The crystalline structure of cellulose in the regenerated wood was transformed into cellulose II type. The cellulose retention rate in the regenerated wood was 96.1-98.7%, and the lignin retention rate was 92.6-98.9%. Among them, Figure 3 As shown, the regeneration rate of poplar wood chips with a length of 20 mm, a width of 20 mm, and a thickness of 2 mm was 68.96%. Through chemical composition analysis, the cellulose content increased from 41.29% to 60.19%, the lignin content increased from 25.01% to 31.20%, the cellulose retention rate was 98.14%, and the lignin retention rate was 98.06%.

[0058] 4) The effects of different wood chip thicknesses on their dissolution were studied separately. As shown in the following table, it can be seen that as the thickness of the wood chips increases, the penetration of the low eutectic solvent into the wood chips slows down, and the β-O-4 bonds in the cell walls cannot be effectively broken, resulting in a decrease in the swelling of the cell walls and a slowing down of the efficiency of the metal salt solution in breaking the hydrogen bonds in cellulose, thereby prolonging the dissolution time.

[0059] Thickness of wood chip (mm) Degree of cell wall swelling (%) Dissolution time (h) Viscosity of solution (Pa·s) 1 15.96 1 29.1 2 15.85 1.5 28.8 3 15.26 1.8 27.3 4 14.38 3.2 25.1 5 13.94 4.5 23.4

[0060] Example 4

[0061] 1) Select hydrogen bond acceptor zinc chloride and hydrogen bond donor lactic acid in a molar ratio of 1:20 to form a low eutectic solvent. Mix zinc chloride and water in a molar ratio of 1:5 to form a metal salt solvent. Fully mix poplar wood chips (length 10-50mm, width 10-50mm, thickness 2mm) in a low eutectic solvent in a mass ratio of 1:10, soak at 120°C for 1h, add a metal salt solution 6 times the mass of the low eutectic solvent, and stir at 500rpm in a pot at room temperature to obtain a wood full component solution.

[0062] 2) The thickness of the cell wall was observed by SEM, and the swelling degree of the cell wall was 14.46-15.90%. The dissolution process of the wood was monitored by polarizing microscope. Due to the anisotropy of the wood, it has obvious birefringence under the polarizing microscope. After adding the metal salt solution to the cell wall of the soaked wood, the birefringence of the wood disappeared after 1.2-2.8 hours, indicating that the wood was completely dissolved. The viscosity of the solution of all wood components is 26.4-28.2 Pa·s, and the concentration is 1wt%.

[0063] 3) Using distilled water as an anti-solvent, the solution of all wood components was slowly added dropwise to the distilled water for regeneration. After washing to neutrality, the regenerated wood was dried with a recovery rate of 61-87%. The morphology of wood regeneration was observed by a JSM-7600F scanning electron microscope. The network formed by the regenerated wood gradually changed from a micron network to a nano network, which further confirmed the dissolution of the wood. The crystal structure of the regenerated wood was determined by a Bruker D8 ADVANCE X-ray diffractometer. The crystal structure of cellulose in the regenerated wood was transformed into cellulose II type. The cellulose retention rate in the regenerated wood was tested by chemical composition analysis to be 97.21-98.9%, and the lignin retention rate was 93.6-97.8%.

[0064] 4) The effects of different wood chip lengths and widths on the dissolution of the wood chips were studied separately. As shown in the following table, it can be seen that as the size of the wood chips increases, the dissolution time gradually becomes longer due to the limited penetration of the low eutectic solvent into the wood chips.

[0065] Size of wood chip (mm) Degree of cell wall swelling (%) Dissolution time (h) Viscosity of solution (Pa·s) 50×10×2 15.90 1.2 27.8 40×20×2 15.86 1.5 28.2 20×30×2 15.00 2.3 26.7 20×50×2 14.46 2.8 26.4

[0066] Example 5

[0067] 1) Select hydrogen bond acceptors including aluminum chloride, ferric chloride, lithium chloride, manganese chloride, zinc bromide, calcium chloride, choline chloride, choline bromide, zinc chloride, tetramethylammonium chloride, tetramethylammonium bromide, benzyltrimethylammonium chloride and hydrogen bond donor lactic acid, and configure them into a low eutectic solvent in a molar ratio of 1:20. Mix zinc chloride and water in a molar ratio of 1:5 to form a metal salt solvent. Mix poplar wood chips (length 20mm, width 20mm, thickness 2mm) in a low eutectic solvent in a mass ratio of 1:10, soak at 120℃ for 1h, add a metal salt solution 6 times the mass of the low eutectic solvent, and stir at 500rpm in a pot at room temperature to obtain a wood full component solution.

[0068] 2) The thickness of the cell wall was observed by SEM, and the swelling degree of the cell wall was 12.31-16.86%. The dissolution process of the wood was monitored by polarizing microscope. Due to the anisotropy of wood, it has obvious birefringence under polarizing microscope. After adding metal salt solution to the cell wall of plant biomass after immersion, the birefringence of wood disappeared after 1.5-8h, indicating that the wood was completely dissolved. The viscosity of the solution of all wood components is 25.4-30.2Pa·s, and the concentration is 1wt%.

[0069] 3) Using distilled water as an anti-solvent, slowly drop the wood component solution into distilled water for regeneration, filtration and washing until neutral, and then drying to obtain regenerated wood with a recovery rate of 60-88%. The morphology of the regenerated wood was observed by a JSM-7600F scanning electron microscope. Figure 4 As shown. The network formed by the regenerated wood gradually changes from a micron to a nano-network, which further confirms the dissolution of the wood. The crystal structure of the regenerated wood was determined by a Bruker D8 ADVANCE X-ray diffractometer. The crystal structure of cellulose in the regenerated wood changed to cellulose II type. The cellulose retention rate in the regenerated wood was tested by chemical composition analysis to be 97-99%, and the lignin retention rate was 90-95%.

[0070] 4) The effects of different hydrogen bond acceptors on the dissolution of wood chips were studied separately. As shown in the following table, it can be seen that the hydrogen bond acceptor zinc chloride system has the maximum cell wall swelling degree of 16.86%, and the shortest dissolution time of wood chips in metal salt solution is 1.5h.

[0071] Hydrogen bond acceptor Degree of cell wall swelling (%) Dissolution time (h) Viscosity of solution (Pa·s) Benzyltrimethylammonium chloride 15.47 7.6 25.4 Tetramethylammonium chloride 16.35 5.1 26.9 Tetramethylammonium bromide 16.28 6.7 28.1 Choline chloride 14.42 8 29.4 Calcium chloride 12.31 4.8 30.2 Iron(III) chloride 13.99 3.2 28.6 Zinc chloride 16.86 1.5 28.4 Zinc bromide 14.28 1.7 28.5 Manganese(II) chloride 13.16 3.6 28.2 Aluminium chloride 14.30 3 27.9 Lithium chloride 15.10 2 28.3 Zinc chloride + Choline chloride 12.28 3.5 24.6 Zinc chloride + Calcium chloride 14.79 2.9 26.8 Zinc chloride + Aluminium chloride 15.23 1.4 27.6 Zinc chloride + Lithium chloride 15.87 1.8 26.4

[0072] Example 6

[0073] 1) Select hydrogen bond donors including lactic acid, acetic acid, formic acid, propionic acid, methoxyacetic acid, glyoxylic acid, pyruvic acid and hydrogen bond acceptor zinc chloride, and configure them into a low eutectic solvent at a molar ratio of 20:1. Mix zinc chloride and water at a molar ratio of 1:5 to form a metal salt solvent. Mix poplar wood chips (length 20mm, width 20mm, thickness 2mm) in a low eutectic solvent at a mass ratio of 1:10, soak at 120°C for 1h, add a metal salt solution 6 times the mass of the low eutectic solvent, and stir at 500rpm in a pot at room temperature to obtain a wood full component solution.

[0074] 2) The thickness of the cell wall was observed by SEM, and the swelling degree of the cell wall was 12.18-15.36%. The dissolution process of the wood was monitored by polarizing microscope. Due to the anisotropy of the wood, it has obvious birefringence under the polarizing microscope. After adding the metal salt solution to the cell wall of the plant biomass after immersion, the birefringence of the wood disappeared after 1.5-2.8 hours, indicating that the wood was completely dissolved. The viscosity of the solution of all wood components is 23.5-28.4 Pa·s, and the concentration is 1wt%.

[0075] 3) Using distilled water as an anti-solvent, slowly drop the solution of all wood components into distilled water, regenerate, filter and wash until neutral, and then dry to obtain regenerated wood with a recovery rate of 61-87%. The morphology of wood regeneration was observed by a JSM-7600F scanning electron microscope. The network formed by the regenerated wood gradually changed from a micron network to a nano network, which further confirmed the dissolution of the wood. The crystal structure of the regenerated wood was determined by a Bruker D8 ADVANCE X-ray diffractometer. The crystal structure of cellulose in the regenerated wood was transformed into cellulose II type. The cellulose retention rate in the regenerated wood was tested by chemical composition analysis to be 90.3-99%, and the lignin retention rate was 91.3-98%.

[0076] 4) The effects of different hydrogen bond donors on the dissolution of poplar wood chips were studied separately. As shown in the following table, it can be seen that the hydrogen bond donor lactic acid system has the maximum cell wall swelling degree of 15.36%, the shortest dissolution time of wood chips in metal salt solution is 1.5h, and the viscosity of the solution is the highest.

[0077]

[0078] Example 7

[0079] 1) Select hydrogen bond acceptor zinc chloride and hydrogen bond donor lactic acid in a molar ratio of 1:20 to form a low eutectic solvent. Mix zinc chloride and water in a molar ratio of 1:5 to form a metal salt solvent. Fully mix poplar wood chips (length 20mm, width 20mm, thickness 2mm) in a low eutectic solvent in a mass ratio of 1:10, soak at 120°C for 0.5-4h, add a metal salt solution 6 times the mass of the low eutectic solvent, and stir at 500rpm in a pot at room temperature to obtain a wood full component solution.

[0080] 2) The thickness of the cell wall was observed by SEM, and the swelling degree of the cell wall was 6.23-15.68%. The dissolution process of the wood was monitored by polarizing microscope. Due to the anisotropy of wood, it has obvious birefringence under polarizing microscope. After adding metal salt solution to the cell wall of plant biomass after immersion, the birefringence of wood disappeared after 0.9-4.9h, indicating that the wood was completely dissolved. The viscosity of the solution of all wood components is 22.9-28.6Pa·s, and the concentration is 1wt%.

[0081] 3) Using distilled water as an anti-solvent, slowly drop the solution of all wood components into distilled water for regeneration, filter and wash until neutral, and dry to obtain regenerated wood with a recovery rate of 62-75%. The morphology of wood regeneration was observed by JSM-7600F scanning electron microscope. The network formed by the regenerated wood gradually changed from micron to nano network, which further confirmed the dissolution of the wood. The crystal structure of the regenerated wood was determined by Bruker D8 ADVANCE X-ray diffractometer. The crystal structure of cellulose in the regenerated wood was transformed into cellulose II type. The cellulose retention rate in the regenerated wood was tested by chemical composition analysis to be 90-98.4%, and the lignin retention rate was 90-95.1%.

[0082] 4) As the soaking time increases, the β-O-4 bond of the lignin in the wood is fully broken, and the wood cell wall absorbs more low eutectic solvents, causing the cell wall to be completely opened, thereby promoting the penetration of the metal salt solution into the cell wall to completely break the hydrogen bonds between the cellulose, and finally forming a solution of all wood components. As shown in the following table, the effects of different soaking times on the dissolution of wood chips are studied separately. It can be seen that after the zinc chloride-lactic acid system soaks the cell wall at 120°C for 1 hour, the swelling degree of the cell wall tends to be stable, indicating that the cell wall is completely opened and meets the conditions for the metal salt solution to penetrate into the cell wall; therefore, the optimal soaking time is 1 hour.

[0083]

[0084] Example 8

[0085] 1) Select hydrogen bond acceptor zinc chloride and hydrogen bond donor lactic acid in a molar ratio of 1:20 to form a low eutectic solvent. Mix zinc chloride and water in a molar ratio of 1:5 to form a metal salt solvent. Fully mix poplar wood chips (length 20mm, width 20mm, thickness 2mm) in a low eutectic solvent in a mass ratio of 1:10, soak at 50-120℃ for 1h, add a metal salt solution 6 times the mass of the low eutectic solvent, and stir at 500rpm in a pot at room temperature to obtain a wood full component solution.

[0086] 2) The thickness of the cell wall was observed by SEM, and the swelling degree of the cell wall was 14.02-15.68%. The dissolution process of the wood was monitored by polarizing microscope. Due to the anisotropy of wood, it has obvious birefringence under polarizing microscope. After adding metal salt solution to the cell wall of plant biomass after immersion, the birefringence of wood disappeared after 1.5-2.4h, indicating that the wood was completely dissolved. The viscosity of the solution of all wood components is 20.3-28.9Pa·s, and the concentration is 1wt%.

[0087] 3) Using distilled water as an anti-solvent, the solution of all wood components was slowly added dropwise to the distilled water for regeneration. After filtering and washing to neutrality, the regenerated wood was dried with a recovery rate of 61-74%. The morphology of wood regeneration was observed by a JSM-7600F scanning electron microscope. The network formed by the regenerated wood gradually changed from a micron network to a nano network, which further confirmed the dissolution of the wood. The crystal structure of the regenerated wood was determined by a Bruker D8 ADVANCE X-ray diffractometer. The crystal structure of cellulose in the regenerated wood was transformed into cellulose II type. The cellulose retention rate in the regenerated wood was tested by chemical composition analysis to be 97.8-99.1%, and the lignin retention rate was 93.1-95.6%.

[0088] 4) The effects of different soaking temperatures on the dissolution of wood chips were studied separately. As shown in the following table, it can be seen that with the extension of soaking time, the dissolution time of wood chips gradually accelerated, and the viscosity of the solution increased from 20.3 Pa·s to 28.9 Pa·s at 120°C. Therefore, the optimal soaking temperature is 120°C.

[0089] Soaking temperature (°C) Degree of cell wall swelling (%) Dissolution time (h) Viscosity of solution (Pa·s) 50 14.02 2.4 20.3 70 14.71 2.2 21.7 90 15.23 1.9 23.4 110 15.47 1.6 26.8 120 15.68 1.5 28.9

[0090] Example 9

[0091] 1) Select zinc chloride as the hydrogen bond acceptor and lactic acid as the hydrogen bond donor to prepare a deep eutectic solvent in a molar ratio of 1:20. Mix zinc chloride and water evenly in a molar ratio of 1:5 to form a metal salt solvent. Mix poplar wood chips (20 mm in length, 20 mm in width, and 2 mm in thickness) with the deep eutectic solvent in a mass ratio of 1:1 - 1:15, soak them at 120 °C for 1 h, then add a metal salt solution with a mass 6 times that of the deep eutectic solvent, and stir at 500 rpm in one pot at room temperature to obtain a wood whole-component solution.

[0092] 2) It can be seen from the observation of the cell wall thickness by SEM that the swelling degree of the cell wall is 12.40 - 15.98%. The dissolution process of wood is monitored by a polarized light microscope. Due to the anisotropy of wood, there is an obvious birefringence phenomenon under the polarized light microscope. In the cell wall of the soaked plant biomass, after adding the metal salt solution, the birefringence phenomenon of the wood disappears after 1.6 - 4.7 h, indicating that the wood is completely dissolved. As Figure 4 shown, the viscosity of the wood whole-component solution is 1.6 - 578.5 Pa·s. The concentration of the plant biomass solution is 1 - 10 wt%.

[0093] 3) Use distilled water as the antisolvent, slowly drip the wood whole-component solution into distilled water for regeneration, filter and wash it until neutral, and then dry it to obtain regenerated wood with a recovery rate of 60 - 79%. Observe the morphology of the regenerated wood by a JSM-7600F scanning electron microscope. The network formed by the regenerated wood gradually changes from micrometers to nanometers, which further confirms the dissolution of wood. Determine the crystal structure of the regenerated wood by a Bruker D8 ADVANCE X-ray diffractometer. The crystal structure of cellulose in the regenerated wood is transformed into cellulose II type. Through chemical composition analysis, the cellulose retention rate in the regenerated wood is 98.3 - 99.2%, and the lignin retention rate is 92.6 - 99%.

[0094] 4) Respectively study the influence of the mass ratio of wood chips to the deep eutectic solvent during soaking on the dissolution of the wood chips. As shown in the following table, it can be seen that when the mass ratio of wood chips to the deep eutectic solvent is 1:1, the wood chips are completely dissolved after 4.7 h. This is mainly because at a high mass ratio, the ability of the deep eutectic solvent to cleave the β-O-4 bonds in the wood chips decreases, resulting in a reduced opening degree of the swollen wood cell wall, and slowing down the efficiency of the metal salt solution to penetrate the cell wall and break the hydrogen bonds between cellulose, thus leading to a long dissolution time.

[0095]

[0096] Example 10

[0097] 1) Select hydrogen bond acceptor zinc chloride and hydrogen bond donor lactic acid in a molar ratio of 1:20 to form a low eutectic solvent. Mix zinc chloride and water in a molar ratio of 1:5 to form a metal salt solvent. Fully mix poplar wood chips (length 20mm, width 20mm, thickness 2mm) in a low eutectic solvent in a mass ratio of 1:10, soak at 120°C for 1h, add metal salt solution, wherein the mass ratio of metal salt solution to low eutectic solvent is 1:1-20:1, and stir at 500rpm in a pot at room temperature to obtain a wood full component solution.

[0098] 2) The thickness of the cell wall was observed by SEM, and the swelling degree of the cell wall was 15.40%. The dissolution process of the wood was monitored by polarizing microscope. Due to the anisotropy of the wood, it has obvious birefringence under the polarizing microscope. After adding the metal salt solution to the cell wall after immersion, the birefringence of the wood disappeared after 1.5-8.7 hours, indicating that the wood was completely dissolved. The viscosity of the solution of all wood components was 24.32-29.20 Pa·s, and the concentration was 1wt%.

[0099] 3) Using distilled water as an anti-solvent, slowly drop the solution of all wood components into distilled water for regeneration, filter and wash until neutral, and dry to obtain regenerated wood with a recovery rate of 65-80%. The morphology of wood regeneration was observed by JSM-7600F scanning electron microscope. The network formed by the regenerated wood gradually changed from micron to nano network, which further confirmed the dissolution of the wood. The crystal structure of the regenerated wood was determined by Bruker D8 ADVANCE X-ray diffractometer. The crystal structure of cellulose in the regenerated wood was transformed into cellulose II type. The cellulose retention rate in the regenerated wood was tested by chemical composition analysis to be 97.1-98.6%, and the lignin retention rate was 91.3-95.4%.

[0100] 4) The effect of the mass ratio of the low eutectic solvent to the metal salt solution on the dissolution of the wood chips was studied separately. As shown in the following table, it can be seen that when the mass ratio of the low eutectic solvent to the metal salt solution is 1:6, the dissolution time of the wood chips is as short as 1.5h. This is mainly because the low eutectic solvent can effectively break the β-O-4 bonds in lignin, but cannot effectively break the hydrogen bonds in the crystalline structure of cellulose, and the metal salt solution has the ability to penetrate into the cellulose crystalline structure to destroy the hydrogen bonds of cellulose. Therefore, at a low ratio of the metal salt solution to the low eutectic solvent, the limited hydrogen bonds in the cellulose crystalline structure can be destroyed, resulting in a longer dissolution time. However, at an excessively high ratio of the metal salt solution to the low eutectic solvent, due to the reduced lactic acid content in the system, it is not enough to promote the metal salt solution to destroy the hydrogen bonds in cellulose at room temperature, resulting in a longer dissolution time. This also shows that during the wood dissolution process, the low eutectic solvent and the metal salt solution work together to achieve the dissolution of all wood components.

[0101]

[0102] Example 11

[0103] 1) Select zinc chloride as a hydrogen bond acceptor and lactic acid as a hydrogen bond donor to prepare a deep eutectic solvent in a molar ratio of 1:20. Mix zinc chloride and water evenly in a molar ratio of 1:1 - 1:9 to form a metal salt solvent. Mix poplar wood chips (20 mm in length, 20 mm in width, and 2 mm in thickness) in the deep eutectic solvent in a mass ratio of 1:10. After soaking at 120 °C for 1 h, add a metal salt solution with a mass 6 times that of the deep eutectic solvent, and stir at 500 rpm in one pot at room temperature to obtain a wood whole-component solution.

[0104] 2) It can be seen from the observation of the cell wall thickness by SEM that the swelling degree of the cell wall is 15.38%. The dissolution process of wood is monitored by a polarized light microscope. Due to the anisotropy of wood, there is an obvious birefringence phenomenon under the polarized light microscope. In the soaked cell wall, after adding the metal salt solution, the birefringence phenomenon disappears in wood after 1.5 - 4.8 h, indicating that the wood is completely dissolved. The viscosity of the wood whole-component solution is 22.43 - 30.34 Pa·s, and the concentration is 1 wt%.

[0105] 3) Use distilled water as an antisolvent, slowly drip the wood whole-component solution into distilled water for regeneration, filter and wash until neutral, and then dry to obtain regenerated wood, with a recovery rate of 63 - 81%. Observe the morphology of wood regeneration by a JSM-7600F scanning electron microscope. The network formed by the regenerated wood gradually changes from micrometers to nanometers, which further confirms the dissolution of wood. Determine the crystal structure of the regenerated wood by a Bruker D8 ADVANCE X-ray diffractometer. The crystal structure of cellulose in the regenerated wood changes to cellulose type II. Test the cellulose retention rate in the regenerated wood to be 97.1 - 98.6% and the lignin retention rate to be 91.3 - 95.4% by chemical composition analysis.

[0106] 4) Study the influence of the molar ratio (n / n) of the metal salt to the aqueous solution on the dissolution of wood chips respectively. An appropriate water content in the metal salt can promote the dissolution of plant biomass, while when the water content is too high, the metal salt is oversaturated with water, reducing its interaction with plant biomass and resulting in an extended dissolution time. As shown in the following table, it can be seen that when the molar ratio (n / n) of the metal salt to the aqueous solution is 1:5, the shortest dissolution time of the wood chips is 1.5 h.

[0107] Metal salt : Water (n / n) Degree of cell wall swelling (%) Dissolution time (h) Viscosity of solution (Pa·s) 1:1 15.38 3.6 22.43 1:3 15.38 3.2 22.75 1:5 15.38 1.5 23.58 1:7 15.38 2.3 28.19 1:9 15.38 4.8 30.34

[0108] Example 12

[0109] 1) Select hydrogen bond acceptor zinc chloride and hydrogen bond donor lactic acid in a molar ratio of 1:1-1:20 to form a low eutectic solvent. Mix zinc chloride and water in a molar ratio of 1:5 to form a metal salt solvent. Fully mix poplar wood chips (length 20mm, width 20mm, thickness 1mm) in a low eutectic solvent in a mass ratio of 1:10, soak at 120°C for 1h, add a metal salt solution 6 times the mass of the low eutectic solvent, and stir at 500rpm in a pot at room temperature to obtain a wood full component solution.

[0110] 2) The thickness of the cell wall was observed by SEM, and the swelling degree of the cell wall was 13.72-15.78%. The dissolution process of the wood was monitored by polarizing microscope. Due to the anisotropy of the wood, it has obvious birefringence under the polarizing microscope. After adding the metal salt solution to the cell wall after immersion, the birefringence of the wood disappeared after 1.6-2.7 hours, indicating that the wood was completely dissolved. The viscosity of the solution of all wood components is 20.2-29.1 Pa·s, and the concentration is 1wt%.

[0111] 3) Using distilled water as an anti-solvent, slowly drop the solution of all wood components into distilled water for regeneration, filter and wash until neutral, and dry to obtain regenerated wood with a recovery rate of 67-79%. The morphology of wood regeneration was observed by JSM-7600F scanning electron microscope. The network formed by the regenerated wood gradually changed from micron to nano network, which further confirmed the dissolution of the wood. The crystal structure of the regenerated wood was determined by Bruker D8 ADVANCE X-ray diffractometer. The crystal structure of cellulose in the regenerated wood was transformed into cellulose II type. The cellulose retention rate in the regenerated wood was tested by chemical composition analysis to be 94.7-99.3%, and the lignin retention rate was 90.3-99.1%.

[0112] 4) The effect of the molar ratio (n / n) of hydrogen bond acceptor zinc chloride to hydrogen bond donor lactic acid on the dissolution of wood chips was studied separately. When the lactic acid content in zinc chloride is too low, the high viscosity of the low eutectic solvent will limit its diffusion into the cell wall, thereby prolonging the dissolution time of all components of plant biomass. As shown in the following table, it can be seen that when the molar ratio of hydrogen bond acceptor zinc chloride to hydrogen bond donor lactic acid is 1:20, the shortest dissolution time of wood chips is 1.6h.

[0113]

[0114] Example 13

[0115] 1) Select zinc chloride as the hydrogen bond acceptor and lactic acid as the hydrogen bond donor to prepare a deep eutectic solvent at a molar ratio of 1:20. Mix aluminum chloride, iron chloride, lithium chloride, lithium bromide, manganese chloride, zinc bromide, zinc chloride and water evenly at a molar ratio of 0.1:1:5 to form a metal salt solvent. Mix poplar wood chips (20 mm in length, 20 mm in width and 1 mm in thickness) with the deep eutectic solvent at a mass ratio of 1:10. After soaking at 120 °C for 1 h, add a metal salt solution with a mass 6 times that of the deep eutectic solvent, and stir at 500 rpm in one pot at room temperature to obtain a wood whole-component solution.

[0116] 2) It can be seen from the observation of the cell wall thickness by SEM that the swelling degree of the cell wall is 14.92%. The dissolution process of wood is monitored by a polarized light microscope. Due to the anisotropy of wood, there is an obvious birefringence phenomenon under the polarized light microscope. In the soaked cell wall, after adding the metal salt solution, the birefringence phenomenon of the wood disappears after about 1.3 h, indicating that the wood is completely dissolved. The viscosity of the wood whole-component solution is 25.7 - 29.9 Pa·s, and the concentration is 1 wt%.

[0117] 3) Use distilled water as the antisolvent, slowly drop the wood whole-component solution into distilled water for regeneration, filter and wash until neutral, and then dry to obtain regenerated wood, with a recovery rate of 61 - 81%. Observe the morphology of wood regeneration by a JSM-7600F scanning electron microscope. The network formed by the regenerated wood gradually changes from micrometer to nanometer network, which further confirms the dissolution of wood. Determine the crystal structure of the regenerated wood by a Bruker D8 ADVANCE X-ray diffractometer. The crystal structure of cellulose in the regenerated wood changes to cellulose II type. Through chemical composition analysis, the cellulose retention rate in the regenerated wood is 93.1 - 97.6%, and the lignin retention rate is 91.3 - 98.8%.

[0118] 4) It is found that the dissolution time of wood is shorter than that of zinc chloride metal salt solution (the complete dissolution time is 1.6 h) by compounding two metal salt solutions to dissolve wood, indicating that the compounding of two metal salts is beneficial to breaking the hydrogen bonds between cellulose in wood, and the introduction of the second salt can promote the diffusion of cellulose chains, resulting in a shorter dissolution time of wood.

[0119]

[0120] Example 14

[0121] A method for preparing wood gel

[0122] A hydrogen bond acceptor zinc chloride and a hydrogen bond donor lactic acid were selected to form a low eutectic solvent in a molar ratio of 1:20. Zinc chloride and water were mixed evenly in a molar ratio of 1:5 to form a metal salt solvent. Poplar wood chips (length 20 mm, width 20 mm, thickness 2 mm) were fully mixed in a low eutectic solvent in a mass ratio of 1:1-1:15, soaked at 120°C for 1 hour, and then a metal salt solution 6 times the mass of the low eutectic solvent was added. Stirred in a pot at 500 rpm at room temperature to obtain a wood full component solution with a mass fraction of 1wt%-10wt%.

[0123] The 5 wt % wood component solution was centrifugally degassed and placed in a cylindrical mold to form a wood gel after 12 h in an isopropanol atmosphere. The wood gel was placed in distilled water to replace the solvent for 12 h, and the aqueous solution was replaced every 3 h to obtain a wood hydrogel. Figure 5 a. The wood gel was cut into a cylindrical shape with a diameter of 36 mm and a height of 5 mm, and the mechanical properties were characterized using a TRAPPEZIUM X-type tensile tester. The compressive strength of the gel formed by a 5wt% wood component solution concentration was 549 KPa. As shown in the following table: The compressive strength of the wood gel prepared by the wood component solution of different concentrations of wood gel is 30-549 KPa, and the compressive strain is 2-11%. The strength of the wood gel is closely related to the concentration of the wood solution and the internal pore structure.

[0124] Total wood components solution (wt%) Compressive strength (MPa) Compressive strain (%) 1 30 2 5 549 14 8 478 13 10 404 11

[0125] Embodiment 15

[0126] A method for preparing wood film

[0127] A hydrogen bond acceptor zinc chloride and a hydrogen bond donor lactic acid were selected to form a low eutectic solvent in a molar ratio of 1:20. Zinc chloride and water were mixed evenly in a molar ratio of 1:5 to form a metal salt solvent. Poplar wood chips (length 20 mm, width 20 mm, thickness 2 mm) were fully mixed in a low eutectic solvent in a mass ratio of 1:1-1:15, soaked at 120°C for 1 hour, and then a metal salt solution 6 times the mass of the low eutectic solvent was added. Stirred in a pot at 500 rpm at room temperature to obtain a wood full component solution with a mass fraction of 1wt%-10wt%.

[0128] The above-mentioned 5wt% wood component solution was centrifuged and degassed, then cast into a square mold and placed in an isopropanol atmosphere for 12 hours to form a wood gel. The wood gel was placed in distilled water to replace the solvent for 12 hours, and the aqueous solution was replaced every 3 hours to obtain a wood gel. The wood gel was placed at room temperature and dried for 24 hours to obtain a regenerated wood film. Figure 5As shown in Fig. b, this method can prepare large-sized wood films. Specimens with a width of 5 mm and a length of 15 mm were cut from wood films prepared with lignin whole-component solutions of different concentrations, and their mechanical properties were characterized using a TRAPPEZIUM X type tensile tester, as shown in the following table: the stress and strain of the wood films were 72 - 204 MPa respectively, and the tensile strain was 9 - 62%. The swelling degree of the wood films was 11.1 - 48.7% after soaking in water for 24 h. As Figure 5 shown in Fig. c, the tensile stress of the wood film prepared with a 5 wt% wood solution was 204 MPa, Figure 5 and Fig. d shows that a 0.17 g film can easily lift a 500 g weight, and its mechanical properties are significantly better than those of the wood films prepared by wood dissolution reported in the literature.

[0129]

[0130] Example 16

[0131] A preparation method of wood aerogel

[0132] Select zinc chloride as the hydrogen bond acceptor and lactic acid as the hydrogen bond donor to prepare a deep eutectic solvent in a molar ratio of 1:20. Mix zinc chloride and water evenly in a molar ratio of 1:5 to form a metal salt solvent. Mix poplar wood chips (with a length of 20 mm, a width of 20 mm, and a thickness of 2 mm) with the deep eutectic solvent in a mass ratio of 1:2.8, soak them at 120 °C for 1 h, then add a metal salt solution with a mass 6 times that of the deep eutectic solvent, and stir at 500 rpm in one pot at room temperature to obtain a wood whole-component solution with a mass fraction of 5 wt%.

[0133] After centrifugally defoaming the above-mentioned wood whole-component solution with a concentration of 5 wt%, place it in a cylindrical mold, and form a wood gel after 12 h in an isopropanol atmosphere. Place the wood gel in distilled water to replace the solvent for 12 h, and change the aqueous solution every 3 h to obtain a wood gel. After freeze-drying the wood gel to remove moisture, a cylindrical regenerated wood aerogel with a diameter of 36 mm and a height of 5 mm is obtained, as Figure 6 shown.

[0134] Use an infrared thermal imager to characterize the heat insulation of the regenerated wood aerogel. Under extreme conditions of 120 °C, the upper surface temperature of the wood aerogel is maintained at 50 °C, and under extreme conditions of -196 °C, the upper surface temperature of the wood aerogel is maintained at 25 °C.

[0135] Example 17

[0136] A preparation method of wood fibers

[0137] Select the hydrogen bond acceptor zinc chloride and the hydrogen bond donor lactic acid to prepare a deep eutectic solvent in a molar ratio of 1:20. Mix zinc chloride and water evenly in a molar ratio of 1:5 to form a metal salt solvent. Mix poplar wood chips (length 20 mm, width 20 mm, thickness 2 mm) with the deep eutectic solvent in a mass ratio of 1:1 - 1:15, soak them at 120 °C for 1 h, then add a metal salt solution with a mass 6 times that of the deep eutectic solvent, and stir at 500 rpm in one pot at room temperature to obtain a wood whole-component solution with a mass fraction of 1 wt% - 10 wt%.

[0138] Centrifuge and defoam the above wood whole-component solution with a concentration of 5 wt% and place it in a syringe, extrude it into an isopropyl alcohol solution at a rate of 100 mm / min for regeneration, and dry it to obtain wood fibers with a diameter of 0.4 mm, as Figure 7 shown in Figure 7 a. As shown in

[0139] Example 18

[0140] Select the hydrogen bond acceptor zinc chloride and the hydrogen bond donor lactic acid to prepare a deep eutectic solvent in a molar ratio of 1:20. Mix zinc chloride and water evenly in a molar ratio of 1:5 to form a metal salt solvent. Mix poplar wood chips (length 20 mm, width 20 mm, thickness 2 mm) with the deep eutectic solvent in a mass ratio of 1:1.8, soak them at 120 °C for 1 h, then add a metal salt solution with a mass 6 times that of the deep eutectic solvent, and stir at 500 rpm in one pot at room temperature to obtain a wood whole-component solution with a mass fraction of 8 wt%.

[0141] Centrifuge and defoam the above wood whole-component solution with a concentration of 8 wt% and use it as 3D printing ink, extrude it at a rate of 10 mm / min to prepare wood 3D printing materials, as Figure 7 shown in

[0142] Comparative Example 1

[0143] Prepare a zinc chloride / lactic acid deep eutectic solvent with a molar ratio of 1:20. Then, take 5 g of poplar wood chips (20 mm in length, 20 mm in width, and 2 mm in thickness) and mix them evenly with the zinc chloride / lactic acid deep eutectic solvent at a mass ratio of 1:10 (g / g). After soaking at 120 °C for 1 h, the wood did not dissolve and the viscosity of the solution remained almost unchanged. This is because the deep eutectic solvent is difficult to directly penetrate into the crystalline region of cellulose. Thus, it can be seen that the zinc chloride / lactic acid deep eutectic solvent alone cannot achieve the complete dissolution of plant biomass.

[0144] Comparative Example 2

[0145] Prepare an aqueous zinc chloride solution with a molar ratio of 1:5. Then, take 5 g of poplar wood chips (20 mm in length, 20 mm in width, and 2 mm in thickness) and mix them with the metal salt solution at a mass ratio of 1:10 (g / g). After dissolving at 25 °C for 3 h, it was found that the wood did not dissolve and the viscosity of the solution remained almost unchanged. This is because the hydrophobic lignin in the cell wall hinders the interaction between the metal salt solution and cellulose. Thus, it can be seen that the metal salt solution alone cannot achieve the complete dissolution of plant biomass.

[0146] Comparative Example 3

[0147] Prepare a zinc chloride / lactic acid deep eutectic solvent with a molar ratio of 1:20 and an aqueous metal salt solution of zinc chloride with a molar ratio of 1:5. Then, take 5 g of poplar wood chips (20 mm in length, 20 mm in width, and 2 mm in thickness) and mix them evenly with the zinc chloride / lactic acid deep eutectic solvent at a mass ratio of 1:10 (g / g). After soaking at 120 °C for 1 h, wash them with distilled water until neutral, dry them at room temperature, and then add the metal salt solution. Stir at 500 rpm at room temperature for 8 h, and it was found that the wood did not dissolve and the viscosity of the solution did not increase. As Figure 8 shown, after the wood is removed from the deep eutectic solvent, due to the anisotropy of the wood, the birefringence phenomenon is more obvious. After adding the metal salt solution and stirring for 8 h, there are still undissolved wood particles, and the birefringence phenomenon of the wood has not completely disappeared, indicating that the washed wood cannot dissolve in the metal salt solution.

[0148] Compared with the washed wood, the wood containing the deep eutectic solvent completely dissolved within 2 hours. However, the washed wood did not completely dissolve after being treated under the same conditions for 8 hours. This is because with the washing of distilled water, the interaction between the deep eutectic solvent system and lignin was disrupted. Hydrophobic lignin aggregated and regenerated on the surface of cellulose and wrapped around cellulose, forming a hydrophobic shell layer, which hindered the penetration of dissolution. On the other hand, with the removal of the solvent, the solvent channel structure established by the deep eutectic solvent collapsed and densified to form hydrogen bonds again, thus hindering the interaction between the hydrophilic metal salt solution and cellulose, resulting in the non-dissolution of the wood. It can be seen that the zinc chloride / lactic acid deep eutectic solvent not only established the solvent channel for the metal salt solution, exposing more cellulose interaction sites with the metal salt solution, but also improved the dissolution ability of the whole system for lignin and promoted the dissolution of cellulose.

[0149] Comparative Example 4

[0150] Prepare a zinc chloride / lactic acid deep eutectic solvent with a molar ratio of 1:20 and a zinc chloride aqueous metal salt solution with a molar ratio of 1:5, and mix them according to a mass ratio of the deep eutectic solvent to the metal salt solution of 1:6 to obtain a mixed solution. Then, take 5 g of poplar wood chips (length 20 mm, width 20 mm, thickness 2 mm) and add them to the above mixed solution. At room temperature, stir at 500 rpm for 24 h, and it was found that the wood did not dissolve and the viscosity of the solution did not increase. This is because the zinc chloride / lactic acid deep eutectic solvent cannot break the LCC bonds in the cell wall and the β-O-4 structure of lignin at room temperature, and cannot form an open cell wall structure, hindering the penetration of the metal salt solution into the cell wall to interact with cellulose, resulting in the non-dissolution of the wood. Comparing the dissolution time, it was found that the wood after soaking completely dissolved within 2 hours and the viscosity of the solution increased. It can be seen that zinc chloride / lactic acid broke some of the LCC bonds and the β-O-4 structure of lignin during the soaking stage, thereby increasing the hydrophilic hydroxyl groups of lignin and improving the interaction between lignin and the metal salt solution, laying a foundation for the complete dissolution of wood components; secondly, the breakage of the β-O-4 structure of lignin promoted the penetration of zinc chloride / lactic acid into the cell wall to widen the distance between cellulose, providing a channel for the metal salt solution to quickly penetrate into the interior of the cell wall to interact with cellulose; after adding the metal salt solution, the metal salt solution can quickly penetrate into the cell wall to interact with cellulose and break its hydrogen bonds, finally forming a complete wood component solution.

[0151] Comparative Example 5

[0152] Prepare a zinc chloride / lactic acid deep eutectic solvent with a molar ratio of 1:20 and a zinc chloride-aqueous solution metal salt solution with a molar ratio of 1:5. Then, take 5 g of poplar wood chips (20 mm in length, 20 mm in width, and 2 mm in thickness) and mix them evenly with the zinc chloride / lactic acid deep eutectic solvent at a mass ratio of 1:10 (g / g). After soaking at 130 °C for 1 h, add a zinc chloride solution with a mass six times that of the deep eutectic solvent. Stir at 500 rpm at room temperature for 3 h, and it is found that the wood completely dissolves and the viscosity of the solution increases to 14.32 Pa·s.

[0153] Comparing the viscosities of the whole-component wood solutions in Example 8 and Comparative Example 5, the viscosity of the whole-component wood solution formed after soaking at 120 °C is 2.02 times that of the solution soaked at 130 °C. This is because zinc chloride / lactic acid breaks some chemical bonds in the wood cell wall (such as the LCC and the β-O-4 structure in lignin) at 130 °C, resulting in a high degree of swelling of the cell wall and cellulose degradation, leading to a decrease in the viscosity of the whole-component wood solution.

Claims

1. A method for dissolving all components of plant biomass raw materials, characterized in that: The following steps are involved: S1. Soaking the plant biomass raw material in a deep eutectic solvent to obtain a plant biomass raw material / deep eutectic solvent mixed solution; S2, adding a metal salt solvent to the mixed solution described in step S1, and rapidly stirring and mixing at room temperature to obtain a homogeneous plant biomass full component solution; In step S1, the plant biomass raw material is coniferous wood, hardwood, bamboo, hemp, cotton or grass raw material, and the plant biomass raw material has a length of 10-50 mm, a width of 10-50 mm, and a thickness of 1-5 mm.

2. A method for dissolving all components of plant biomass raw materials as claimed in claim 1, characterized in that : In the step S1, the low eutectic solvent hydrogen bond acceptor includes any one of aluminum chloride, ferric chloride, lithium chloride, manganese chloride, zinc bromide, choline chloride, choline bromide, zinc chloride, tetramethylammonium chloride, tetramethylammonium bromide, and benzyltrimethylammonium chloride, or a combination of two or more thereof; the hydrogen bond donor includes any one of lactic acid, acetic acid, formic acid, propionic acid, methoxyacetic acid, glyoxylic acid, and pyruvic acid, or a combination of two or more thereof; in the step S2, the metal salt solvent includes a mixed solvent of one or two of aluminum chloride, ferric chloride, lithium chloride, lithium bromide, manganese chloride, zinc chloride, and zinc bromide and water.

3. A method for dissolving all components of plant biomass raw materials as claimed in claim 2, characterized in that : The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor in the low eutectic solvent in step S1 is 1:1-1:20; the mass ratio of the metal salt to water in the metal salt solvent in step S2 is 1:1-1:

9.

4. A method for dissolving all components of plant biomass raw materials as claimed in claim 2, characterized in that : The soaking treatment time in S1 is 0.5-4h, the soaking temperature is 50-120°C, and the mass ratio of plant biomass to low eutectic solvent is 1:1-1:

15.

5. A method for dissolving all components of plant biomass raw materials as claimed in claim 2, characterized in that : The mass ratio of the metal salt solution to the low eutectic solvent in S2 is 1:1-20:

1.

6. A method for dissolving all components of a plant biomass raw material as claimed in any one of claims 1 to 5, characterized in that :The viscosity of the plant biomass full component solution is 1.6-578.5 Pa·s; the mass fraction of the plant biomass full component solution is 0.01-10wt%.

7. A method for dissolving all components of a plant biomass raw material as claimed in any one of claims 1 to 5, characterized in that The plant biomass recovery rate obtained after the plant biomass full component solution is regenerated is 60-87%, the cellulose recovery rate in the regenerated plant biomass is 90-99%, and the lignin recovery rate in the regenerated plant biomass is 90-99%.

8. Use of the plant biomass full component solution obtained by the method according to any one of claims 1 to 7, characterized in that : The modified plant biomass full component solution is used to prepare plant biomass gel, plant biomass film, plant biomass fiber, and plant biomass 3D printing material.

9. The use according to claim 8, characterized in that The obtained plant biomass gel, film, fiber, and plant biomass 3D printing material have a cellulose content of 31-94% and a lignin content of 6-69%.

10. The use according to claim 8, characterized in that : The compressive strength of the obtained plant biomass gel is 30-549KPa; the tensile stress of the obtained plant biomass film is 72-230MPa, the tensile strain is 9-480%, and the water swelling rate is 11.1-48.7%; the strength of the obtained plant biomass fiber is 118-253MPa.

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