阅读说明：本技术 一种微纳米木质素纤维素及其制备方法和用途 (Micro-nano lignin cellulose and preparation method and application thereof ) 是由 王鹏辉 张安 唐地源 张金柱 刘顶 于 2018-05-30 设计创作，主要内容包括：本发明涉及一种微纳米木质素纤维素的制备方法,所述方法包括如下步骤：(1)将含有木质素的纤维素原料分散在50℃以上的水溶液中,得到原料分散液；(2)将步骤(1)得到的原料分散液通过机械预处理进行剥离、磨碎,得到预处理产物；(3)利用高压均质机对步骤(2)得到的预处理产物进行高压均质,得到所述微纳米木质素纤维素的分散液。可选地,除去所述微纳米木质素纤维素的分散液的溶剂得到微纳米木质素纤维素。本发明能够将含有木质素的纤维素原料直接剥离得到微纳米木质素纤维素,木质素的存在改善了纳米纤维素的亲水亲油性能,赋予了微纳米木质素纤维素与其他材料的相容性,尤其是与疏水性材料的相容性。(the invention relates to a preparation method of micro-nano lignocellulose, which comprises the following steps: (1) dispersing a cellulose raw material containing lignin in an aqueous solution at a temperature of 50 ℃ or higher to obtain a raw material dispersion liquid; (2) stripping and grinding the raw material dispersion liquid obtained in the step (1) through mechanical pretreatment to obtain a pretreatment product; (3) and (3) carrying out high-pressure homogenization on the pretreatment product obtained in the step (2) by using a high-pressure homogenizer to obtain the micro-nano lignocellulose dispersion liquid. Optionally, removing the solvent of the micro-nano lignocellulose dispersion to obtain the micro-nano lignocellulose. According to the invention, the cellulose raw material containing lignin can be directly peeled to obtain the micro-nano lignocellulose, the existence of the lignin improves the hydrophilic and lipophilic properties of the nano cellulose, and the micro-nano lignocellulose is endowed with compatibility with other materials, especially compatibility with hydrophobic materials.)

1. a preparation method of micro-nano lignocellulose is characterized by comprising the following steps:

(1) Dispersing a cellulose raw material containing lignin in an aqueous solution at a temperature of 50 ℃ or higher to obtain a raw material dispersion liquid;

(2) stripping and grinding the raw material dispersion liquid obtained in the step (1) through mechanical pretreatment to obtain a pretreatment product;

(3) Carrying out high-pressure homogenization on the pretreatment product obtained in the step (2) by using a high-pressure homogenizer to obtain a micro-nano lignocellulose dispersion liquid;

optionally, removing the solvent of the micro-nano lignocellulose dispersion to obtain the micro-nano lignocellulose.

2. The method according to claim 1, wherein the temperature of the aqueous solution in step (1) is 70 ℃ or higher, preferably the temperature of the aqueous solution is 70 to 80 ℃ or lower, more preferably 70 to 75 ℃.

3. The method according to claim 1, wherein the concentration of the cellulose raw material containing lignin in the raw material dispersion is 0.08 to 18 wt%, preferably 5 to 8 wt%.

4. The method according to any one of claims 1 to 3, wherein the cellulose raw material containing lignin is a residue obtained by completely or partially extracting hemicellulose from a plant raw material;

Preferably, the plant material comprises any 1 or a combination of at least 2 of forest, crop and agricultural and forestry waste;

Preferably, the lignin-containing cellulosic feedstock comprises any 1 or a combination of at least 2 of furfural residues, xylose residues, unbleached wood pulp, unbleached straw pulp, branches, bark, wood shavings, roots, sawdust, straw agricultural waste;

Preferably, the lignin-containing cellulose raw material contains 10-30 wt% of lignin and more than 65% of cellulose;

Preferably, the cellulosic feedstock containing lignin further contains hemicellulose;

Preferably, the cellulose raw material containing lignin contains less than or equal to 10 wt% of hemicellulose.

5. a method according to any one of claims 1 to 4, wherein the mechanical pre-treatment comprises any one or a combination of at least two of ball milling, disc milling or sand milling, further preferably sand milling;

preferably, the number of cycles of the mechanical pretreatment is greater than or equal to 1;

Preferably, when sanding is adopted, the circulation frequency of the sanding machine is 1-3 times, and the diameter of the obtained sanding product is 180-800 nm; the cycle number of the sand mill is more than or equal to 5, and the diameter of the obtained sand-milled product is 80-180 nm;

Preferably, when the disc mill and/or the ball mill are adopted, the circulation times are more than or equal to 12 times;

preferably, when the raw material dispersion obtained in step (1) is peeled and ground by mechanical pretreatment, the temperature of the raw material dispersion is kept at 70 to 80 ℃.

6. The method of any one of claims 1 to 5, wherein the high pressure homogenization is carried out at a pressure of 55 to 170MPa, preferably 70 to 80 MPa;

Preferably, the circulation time of the high-pressure homogenization is 3-7 times;

Preferably, the temperature is kept at 70-80 ℃ in the high-pressure homogenizing process.

7. the preparation method of any one of claims 1 to 6, wherein the method for removing the solvent from the micro-nano lignocellulose dispersion to obtain the micro-nano lignocellulose comprises any 1 or at least 2 of filtration, centrifugation and drying;

Preferably, the method for removing the solvent of the micro-nano lignocellulose dispersion solution to obtain the micro-nano lignocellulose comprises the steps of filtering and separating or centrifuging, and drying filter residues to obtain the micro-nano lignocellulose;

Preferably, the drying comprises any 1 or a combination of at least 2 of spray drying, freeze drying and supercritical drying.

8. The micro-nano lignocellulose as claimed in any one of claims 1 to 7, wherein the micro-nano lignocellulose contains lignin linked to cellulose by chemical bonds.

9. The micro-nano lignocellulose according to claim 8, wherein the micro-nano lignocellulose has a lignin content of 13-37 wt%, preferably 25-28%;

Preferably, the diameter of the micro-nano lignocellulose is 20-800 nm, and the length-diameter ratio is more than or equal to 50; preferably, the diameter of the micro-nano lignocellulose is 20-200 nm, and the length-diameter ratio is more than or equal to 200.

10. use of the micro-nano lignocellulose according to claim 8 or 9, in the preparation of textile materials, medical materials, high performance auxiliaries, adsorption materials, food packaging materials or composite materials.

Technical Field

The invention belongs to the field of preparation of nano materials, and particularly relates to micro-nano lignocellulose as well as a preparation method and application thereof.

background

With the continuous development of social economy, non-renewable resources such as petroleum, coal and the like are increasingly deficient, the problems of environmental pollution and the like are increasingly prominent, and the application of renewable resources in various fields is more and more emphasized. Plant fiber raw materials are the most important biomass resources on the earth, and the efficient comprehensive utilization of the plant fiber raw materials plays an extremely important role in the whole biomass industry. Plant fibers are mainly composed of cellulose, lignin and hemicellulose. Cellulose is a widely available and renewable resource on earth. The nano-cellulose prepared from natural cellulose not only has huge specific surface area, high hydrophilicity, high Young modulus, high strength, good biodegradability and biocompatibility, stable chemical properties, but also has huge chemical modification potential, and shows huge application prospects in the fields of papermaking, adsorption materials, battery diaphragms, high-performance composite materials and the like.

Lignin is the second most abundant renewable resource in the world, mainly existing between cellulose fibers, and plays a role in resisting pressure by forming a cross-woven net to harden cell walls. The lignin can be used as a dispersant, an adsorbent, an enhancer and the like, and has extremely wide utilization value.

Common methods for preparing nano-cellulose include chemical, mechanical, biological and artificial synthesis methods. The mechanical method for preparing the nano-cellulose has small influence on the environment and simple steps, and is a preparation method suitable for large-scale commercial production. Because the hard lignin is interwoven in the middle of the cellulose, the nanocellulose cannot be prepared by direct mechanical stripping, and no method for preparing the nanocellulose with high lignin content exists in the existing method for preparing the nanocellulose. In the prior art, the plant fiber is still required to be pretreated by acid, alkali or organic solvent to remove lignin and hemicellulose, and then is mechanically stripped, so that the steps are complex, and the acid, alkali or organic solvent used in the pretreatment process still causes certain pollution to the environment.

CN101949103A discloses a preparation method of micro-nano cellulose, which utilizes plant straws to directly prepare, but still uses delignification reagents to carry out delignification treatment; CN103194027A discloses a preparation method of a nanocellulose/lignin light-blocking film, which obtains a nanocellulose material with high lignin content, but the preparation process is complex and complicated because the nanocellulose is subjected to cellulose nanocrystallization treatment after the lignin is removed and extracted and then the lignin is mixed with the nanocellulose; CN104693464A discloses a method for preparing a lignin nanocellulose-reinforced polylactic acid composite membrane, which adopts a sulfuric acid hydrolysis-high pressure homogenization method to prepare lignin nanocellulose, and sulfuric acid is used in the process, so that the environment is greatly influenced.

The field needs to develop an environment-friendly and efficient preparation method, does not need delignification pretreatment, and can prepare the micro-nano cellulose with high lignin content.

Disclosure of Invention

The invention aims to provide a preparation method of micro-nano lignocellulose, which comprises the following steps:

(1) dispersing a cellulose raw material containing lignin in an aqueous solution at a temperature of 50 ℃ or higher to obtain a raw material dispersion liquid;

(2) Stripping and grinding the raw material dispersion liquid obtained in the step (1) through mechanical pretreatment to obtain a pretreatment product;

(3) And (3) carrying out high-pressure homogenization on the pretreatment product obtained in the step (2) by using a high-pressure homogenizer to obtain the micro-nano lignocellulose dispersion liquid.

optionally, removing the solvent of the micro-nano lignocellulose dispersion to obtain the micro-nano lignocellulose.

According to the method, the lignin-containing cellulose raw material is not required to be delignified, and only the lignin-containing cellulose raw material is required to be dispersed in an aqueous solution with the temperature of more than 50 ℃, so that the lignin contained in the lignin is softened, the hydrogen bond effect between the lignin of the raw material is weakened, and the pi-pi conjugation effect of a benzene ring in a lignin structure is weakened, so that the hardness of the lignin is reduced, the bonding effect of the lignin on the cellulose is damaged, and the lignin-containing cellulose raw material can be peeled off by combining subsequent mechanical pretreatment and high-pressure homogenization, so that the micro-nano cellulose with high lignin content, namely the micro-nano lignin cellulose, is obtained.

if the temperature of the aqueous solution in the step (1) is lower than 50 ℃, the hardness of the lignin is high, the interaction between the lignin and the cellulose are difficult to weaken, and the subsequent treatment of the raw material is difficult.

Preferably, the temperature of the aqueous solution in the step (1) is not less than 70 ℃ (e.g., 72 ℃, 76 ℃, 78 ℃, 85 ℃, 88 ℃, 92 ℃, etc.), preferably the temperature of the aqueous solution is not more than the boiling point of the aqueous solution, more preferably 70 to 80 ℃, and particularly preferably 70 to 75 ℃.

if the temperature of the aqueous solution is too high (such as higher than 90 ℃), the chemical structure of lignin itself can be damaged, so that lignin is dissociated from cellulose, and the content of lignin in the micro-nano lignocellulose is reduced.

it should be understood by those skilled in the art that the aqueous solution with a temperature higher than 90 ℃ does not mean that the aqueous solution with a temperature higher than 90 ℃ cannot be used in the present invention, but when the temperature of the aqueous solution is higher than 90 ℃, the lignin content in the prepared micro-nano lignocellulose is reduced. When the lignin content in the cellulose raw material containing lignin is 38%, and when the temperature of the aqueous solution is higher than 90 ℃, the lignin content in the prepared micro-nano lignocellulose is about 10-15 wt%; when the temperature of the aqueous solution is 50-90 ℃, the lignin content in the prepared micro-nano lignin cellulose is 13-37 wt%; when the temperature of the aqueous solution is 60-80 ℃, the lignin content in the prepared micro-nano lignin cellulose is 20-37 wt%.

Preferably, the concentration of the lignin-containing cellulosic feedstock in the feedstock dispersion is 0.08 to 18 wt%, such as 0.1 wt%, 0.4 wt%, 0.8 wt%, 1.5 wt%, 2.8 wt%, 6 wt%, 8 wt%, 11 wt%, 14 wt%, 17 wt%, etc., preferably 5 to 8 wt%.

Preferably, the cellulose raw material containing lignin is residue after hemicellulose is completely extracted or hemicellulose is partially extracted from plant raw materials.

Preferably, the plant material comprises any 1 or a combination of at least 2 of forest, crop, and agricultural and forestry waste.

Preferably, the cellulosic feedstock containing lignin comprises any 1 or combination of at least 2 of furfural residue, xylose residue, unbleached wood pulp, unbleached grass pulp, branches, bark, wood shavings, roots, sawdust, agricultural waste of straw.

Preferably, the lignin-containing cellulose raw material has a lignin content of 10 to 30 wt%, for example, 12 wt%, 15 wt%, 17 wt%, 20 wt%, 23 wt%, 25 wt%, 28 wt%, etc., and a cellulose content of 65% or more.

preferably, the cellulosic feedstock containing lignin also contains hemicellulose.

Preferably, the cellulosic feedstock containing lignin has a hemicellulose content of 10 wt% or less, such as 9 wt%, 8 wt%, 7 wt%, 6 wt%, 5 wt%, 4 wt%, 3 wt%, 2 wt%, 1 wt%, etc.

Preferably, the mechanical pretreatment comprises any one of ball milling, disc milling or sand milling or a combination of at least two thereof, and further preferably sand milling.

Preferably, the number of cycles of the mechanical pre-treatment is equal to or greater than 1, such as 2, 3, 4, 5, 6, 7, 8, 9, 12, 14, etc.

Preferably, when sanding is adopted, the circulation frequency of the sanding machine is 1-3 times, and the diameter of the obtained sanding product is 180-800 nm; the cycle number of the sand mill is more than or equal to 5, and the diameter of the obtained sand-milled product is 80-180 nm.

Preferably, when using disk milling and/or ball milling, the number of cycles is equal to or greater than 12, such as 13, 14, 15, 16, 17, 18, etc.

Preferably, when the raw material dispersion obtained in step (1) is peeled and ground by mechanical pretreatment, the temperature of the raw material dispersion is maintained at 70 to 80 ℃, for example, 70 ℃, 72 ℃, 75 ℃, 77 ℃, 78 ℃, 79 ℃ or the like.

During the mechanical pretreatment, the temperature of the raw material dispersion liquid is kept, so that lignin can be softened while being mechanically stripped, and the yield of the micro-nano lignocellulose is improved.

Preferably, the high-pressure homogenization pressure is 55 to 170MPa, such as 60MPa, 65MPa, 70MPa, 75MPa, 80MPa, 85MPa, 90MPa, 110MPa, 120MPa, 140MPa, 145MPa, 150MPa, 155MPa, 160MPa, 165MPa, and the like, preferably 70 to 80 MPa.

preferably, the number of cycles of the high-pressure homogenization is 3 to 7, such as 4, 5, 6 or 7.

Preferably, the temperature is maintained at 70-80 ℃ during the high-pressure homogenization, such as 70 ℃, 72 ℃, 75 ℃, 77 ℃, 78 ℃, 79 ℃ and the like.

The lignin can be softened while being mechanically stripped by keeping the temperature of the raw material dispersion liquid in the high-pressure homogenizing process, so that the yield of the micro-nano lignocellulose is improved.

Preferably, the method for removing the solvent of the micro-nano lignocellulose dispersion liquid to obtain the micro-nano lignocellulose comprises any 1 or at least 2 of filtration, centrifugation and drying.

Preferably, the method for removing the solvent of the micro-nano lignocellulose dispersion solution to obtain the micro-nano lignocellulose comprises the steps of filtering and separating or centrifuging, and drying filter residues to obtain the micro-nano lignocellulose.

Preferably, the drying comprises any 1 or a combination of at least 2 of spray drying, freeze drying and supercritical drying.

The second purpose of the invention is to provide the micro-nano lignocellulose which contains lignin connected with cellulose through chemical bonds.

in the invention, most of lignin (more than about 80%) in the micro-nano lignocellulose is combined with the cellulose in a covalent bond form, and the phenomenon that the lignin cannot form firm interaction with the nanocellulose due to the fact that only van der Waals force or hydrogen bond action exists in a product generated by physically mixing the cellulose and the lignin in the prior art is avoided, so that the application performance of the micro-nano lignocellulose is reduced.

Chemical bonds can be interpreted as a general term for "strong interaction forces between two or more adjacent atoms (or ions) within a pure molecule or within a crystal". The force that binds ions or atoms is known as a chemical bond. The chemical bonds include three types of ionic bonds, covalent bonds, and metallic bonds, excluding hydrogen bonds.

In the micro-nano lignocellulose, the combination mode of lignin and the nano cellulose necessarily comprises chemical bonds (such as covalent bonds), and can also comprise hydrogen bonds, van der waals force and the like.

Preferably, the content of lignin in the micro-nano lignocellulose is 13-37 wt%, for example, 15%, 18%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 30%, 32%, or 35%, and preferably 25-28%.

Preferably, the diameter of the micro-nano lignocellulose is 20-800 nm, such as 25nm, 30nm, 50nm, 80nm, 100nm, 120nm, 140nm, 160nm, 180nm, 200nm, 250nm, 300nm, 400nm, 450nm, 500nm, 600nm, 650nm, 700nm or 750, etc., the length-diameter ratio is more than or equal to 50, preferably, the diameter of the micro-nano lignocellulose is 20-200 nm, such as 25nm, 30nm, 50nm, 80nm, 100nm, 120nm, 140nm, 160nm or 180nm, etc., and the length-diameter ratio is more than or equal to 200.

The third purpose of the invention is to provide the application of the micro-nano lignocellulose which is used for preparing textile materials, medical materials, high-performance auxiliaries, adsorbing materials, food packaging materials or composite materials.

Compared with the prior art, the invention has the following beneficial effects:

(1) According to the invention, the cellulose raw material containing lignin is dispersed in an aqueous solution with the temperature of more than 50 ℃, and mechanical pretreatment and high-pressure homogenization are combined, so that the cellulose raw material containing lignin can be directly peeled off to obtain the micro-nano lignocellulose which contains lignin connected with cellulose through a covalent bond; due to the existence of lignin, the hydrophilic and lipophilic properties of the nano-cellulose are improved, and the micro-nano lignin cellulose is endowed with compatibility with other materials, especially with hydrophobic materials;

(2) the invention selects the aqueous solution with the temperature of more than 50 ℃ to soften lignin, weaken the hydrogen bond action of lignin and cellulose, reduce the hardness of lignin and destroy the bonding action of lignin to cellulose, so that the method makes it possible to directly prepare the micro-nano lignocellulose from high-lignin cellulose raw materials (such as agricultural waste raw materials);

(3) The micro-nano lignocellulose is prepared by adopting mechanical stripping and high-pressure homogenization, the aqueous solution can be recycled, various strong acids, strong bases and organic solvents are avoided, and the environment is protected and pollution is avoided; the production efficiency is high, the continuity is strong, the cost is low, the product fineness is high, and the product fineness can be adjusted by adding or subtracting grinding media.

(3) The raw material dispersion liquid is pretreated by mechanical pretreatment before the high-pressure homogenizer, so that the blockage of the high-pressure homogenizer in the crushing process can be avoided, and the abrasion is reduced.

Detailed Description

The technical solution of the present invention is further explained by the following embodiments.

It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

In the present invention, the contents of lignin, cellulose and hemicellulose in furfural residue, xylose residue, unbleached wood pulp, unbleached straw pulp, agricultural waste of straw and the like obtained after extracting hemicellulose or part of hemicellulose from plant raw materials are similar, so the micro-nano lignocellulose is prepared by taking xylose residue as an example in the following examples.