High-strength straw skin cellulose coarse fiber and preparation method thereof

Abstract

The application discloses high-strength straw skin cellulose coarse fiber and a preparation method thereof. The preparation method comprises the following steps: A, lignin hemicellulose removal of straw skin and peeling of thin skin cells to obtain wet cellulose coarse fiber; and B, room temperature drying and densification of the coarse fiber. The lignin hemicellulose in the straw skin is removed by soaking in a treatment liquid, so that the thin skin cells are peeled off, and wet cellulose coarse fiber which still retains the original directional arrangement of cellulose microfibers is obtained. Room temperature drying densifies the original loose coarse fiber under the action of hydrogen bonds, and high-strength cellulose coarse fiber is obtained. The top-down treatment method is green, efficient, simple in process, high in raw material utilization rate, good in equipment versatility, and convenient for large-scale production. The obtained cellulose coarse fiber has a tensile strength of 0.8-1.5 GPa, a diameter of 50-200 mu m, a length of 1-200 mm, a yield of 20%, is a full biomass, is degradable, and can be applied in large-scale industrialization.

Description

Technical Field

[0001] This invention belongs to the field of materials and process preparation technology, specifically relating to a high-strength straw husk cellulose crude fiber and its preparation method. Background Technology

[0002] Corn and sorghum crop straw, as an important type of agricultural waste biomass, is considered a potential alternative to recalcitrant, high-carbon-emission petrochemical-based plastics, packaging materials, building materials, and fibers due to its low cost, wide availability, and biodegradability. my country is a major corn-producing country, with an annual corn straw production of up to 200 million tons, accounting for approximately 24% of the country's total straw mass. Corn straw consists of leaves (which can be used as animal feed), husks (approximately 30%), and stalks (approximately 15%). In traditional agriculture, corn and other crop straws are mainly used for rural domestic energy and livestock feed, with the remainder mostly returned to the field. This wastes resources and increases methane emissions, making the methane-promoting effect of straw return to the field far outweigh its carbon sequestration effect, thus failing to meet dual carbon goals. High-efficiency and high-value utilization of straw has become a new approach to carbon reduction. Since corn straw contains 40% cellulose, researchers have obtained straw cellulose fibers through physicochemical treatment methods such as steam explosion, alkali treatment, and siloxane treatment. However, since the prepared straw fiber is composed of coarse fiber bundles and thin bark cells, even after adjusting the lignin and hemicellulose content with alkali and siloxane, its tensile strength is only 50-300 MPa, far lower than that of cotton and linen fibers. Therefore, extracting high-strength cellulose coarse fiber from corn, sorghum, and other straws is a huge challenge. Summary of the Invention

[0003] The first objective of this invention is to provide a high-strength straw husk cellulose crude fiber, and the second objective of this invention is to provide a method for preparing high-strength straw husk cellulose crude fiber.

[0004] The first objective of this invention is achieved as follows: It comprises crude cellulose fibers containing cellulose, hemicellulose, and lignin. The lignin content is 1.0%–8.0%, and the hemicellulose and cellulose content is 92%–99%. The biomass crude fibers maintain the microstructure of cellulose microfibers with directional and densely arranged cellulose microfiber bundles from straw husks. The length of the crude cellulose fibers is 1–200 mm, and the diameter is 50–200 µm. The surface of the crude cellulose fibers is free of thin-walled cells. The tensile strength of the crude cellulose fibers is as high as 0.8–1.5 GPa. The yield of the crude cellulose fibers in the original straw husk is 20%, which can produce 12 million tons of straw husk cellulose crude fibers annually, 2.1 times the annual production of cotton lint (approximately 5.6 million tons).

[0005] The second objective of this invention is achieved by including: A: removing lignin and hemicellulose from straw husks and peeling off thin-layer cells; B: drying and densifying crude cellulose fibers at room temperature and normal pressure, specifically including:

[0006] A: Remove lignin and hemicellulose, and peel off the thin-layered cells.

[0007] Straw husks with a moisture content of less than 25% are made into biomass units with a length of 1-200 mm and a width of 1-50 mm. A treatment solution with a concentration of 1-10 mol / L is heated to 25℃-100℃ and the biomass units are treated with the treatment solution for 2-24 hours to remove lignin and hemicellulose, thereby peeling the thin-layer cells from the surface of the fiber bundles. The units are then rinsed with water 3-5 times, and the resulting wet cellulose crude fiber is stored in water for later use.

[0008] B: Densified cellulose crude fiber dried at room temperature and normal pressure

[0009] The wet cellulose crude fiber obtained in step A is removed from the water and dried at room temperature for 1-2 days. Under the action of hydrogen bonds, as the water in the cellulose crude fiber evaporates, the microfibers that make up the crude fiber will shrink and densify. The resulting dry cellulose crude fiber is stored at room temperature and normal pressure for later use.

[0010] This invention employs a treatment solution to remove lignin and hemicellulose from straw husks, and to peel off the thin-walled, macroporous, and weak bark cells, yielding moist crude cellulose fibers. During room temperature and atmospheric pressure drying, under the influence of hydrogen bonding, the microfibers composing the crude cellulose fibers shrink and densify as water evaporates, resulting in high-strength crude cellulose fibers. Water-soluble chemicals such as formic acid, acetic acid, sulfuric acid, sodium hydroxide, sodium carbonate, hydrogen peroxide, peroxyformic acid, or peracetic acid are used as treatment agents; water is used as a solvent. By precisely controlling the treatment time and liquid-to-material ratio, lignin and hemicellulose are removed from the straw husks, and the bark cells are peeled off, forming moist crude cellulose fibers saturated with adsorbed water. The lignin content can be reduced to 1.0%–8.0%, while the original oriented, densely arranged microfiber microstructure is completely preserved. Drying at room temperature and atmospheric pressure, due to the evaporation of water, enhances the hydrogen bonding forces between the microfibers, leading to microfiber densification and successfully obtaining high-strength straw husk cellulose fibers. The processing method described in this invention is green, efficient, simple, has high raw material utilization, and good equipment versatility, making it easy to carry out large-scale production; the resulting crude cellulose fiber has high strength, is entirely biomass, biodegradable, has low carbon emissions, and can be applied on a large scale industrial basis. Attached Figure Description

[0011] Figure 1 The images shown are a camera photograph (a), a scanning electron microscope image (b), and a polarized light photograph (c) of the crude cellulose fiber from corn stalk husk in Example 1.

[0012] Figure 2 The figures (a) and (b) show the cellulose, hemicellulose, and lignin content of the crude cellulose fiber in corn stalk husk in Example 1. Detailed Implementation

[0013] The present invention will be further described below with reference to the accompanying drawings and embodiments, but it should not be limited in any way. Any changes or improvements made based on the teachings of the present invention shall fall within the protection scope of the present invention.

[0014] A high-strength straw husk cellulose crude fiber contains cellulose, hemicellulose, and lignin. The lignin content is 1%~8%, and the hemicellulose and cellulose content is 92%~99%. The cellulose crude fiber maintains the microstructure of cellulose microfibers in which the original cellulose fiber bundles of straw husk are oriented and densely arranged. The length of the cellulose crude fiber is 1~200mm, and the diameter is 50~200µm. The microfibers are oriented and densely arranged through hydrogen bonding interactions. There are no thin-layer cells attached to the surface of the cellulose crude fiber. The tensile strength of the cellulose crude fiber is 0.8~1.5GPa. The yield of the cellulose crude fiber in the original straw husk is 20%, and the annual production of straw husk cellulose crude fiber is 12 million tons, which is 2.1 times that of cotton fiber.

[0015] This material is prepared by the following methods: A) removing lignin and hemicellulose from straw bark and peeling off thin-layered cells; B) drying at room temperature and pressure to densify crude cellulose fibers, specifically including:

[0016] A: Straw bark removes lignin, hemicellulose, and thin skin cells.

[0017] Straw husks with a moisture content of less than 25% are made into biomass units with a length of 1-200 mm and a width of 1-50 mm. A treatment solution with a concentration of 1-10 mol / L is heated to 25℃-100℃ and the biomass units are treated with the treatment solution for 2-24 hours to remove lignin and hemicellulose, thereby peeling the thin-layer cells from the surface of the fiber bundles. The units are then rinsed with water 3-5 times, and the resulting wet cellulose crude fiber is stored in water for later use.

[0018] B: Drying at room temperature and normal pressure

[0019] The wet cellulose crude fiber obtained in step A is removed from the water and dried at room temperature for 1-2 days. Under the action of hydrogen bonds, as the water in the cellulose crude fiber evaporates, the microfibers that make up the crude fiber will shrink and densify. The resulting dry cellulose crude fiber is stored at room temperature and normal pressure for later use.

[0020] In step A, the straw husks are made from corn, sorghum, sugarcane, etc.

[0021] In step A, the bleaching solvent is any one or a combination of formic acid, acetic acid, sulfuric acid, sodium hydroxide, sodium carbonate, hydrogen peroxide, peroxyformic acid, or peracetic acid.

[0022] In step A, before rinsing with water, neutralize with 0.5% sodium hydroxide or sodium carbonate for 5 minutes.

[0023] Example 1

[0024] After the leaves are removed from naturally air-dried corn stalks, the husks are separated using a husk separator, and the corn husks are kept for later use. The corn husks with a moisture content of 10% are processed into 150mm × 50mm samples and placed in a glass beaker (containing formic acid, with a formic acid to hydrogen peroxide molar ratio of 1:1, a concentration of 8 mol / L, and sulfuric acid as a catalyst). The samples are treated at 50℃ for 4 hours, then removed and neutralized with 0.5% sodium hydroxide for 5 minutes, and rinsed three times with water to obtain wet crude cellulose fibers. These wet crude cellulose fibers are dried at room temperature and atmospheric pressure for 2 days to obtain high-strength corn stalk husk cellulose fibers. (See...) Figure 1 .

[0025] Test methods: The methods for determining the content of cellulose, hemicellulose, and lignin, and the morphology of the cellulose skeleton, are respectively found in *Industrial Crops & Products*, Vol. 188, 2022, Article No. 115699, and *Applied Surface Science*, Vol. 328, 2015, starting pages: 453-458. Mechanical strength and light transmittance are as per national standards.

[0026] Test results: The obtained corn stalk husk cellulose crude fiber has a length of 150 mm and a diameter of about 200 µm. It is composed of parallel and densely arranged microfibers with a diameter of about 5 µm. The lignin content is 2%, hemicellulose is 4%, cellulose is 94%, and the tensile strength is 1.4 GPa.

[0027] Example 2

[0028] After the leaves of naturally air-dried sorghum stalks are removed, the sorghum stalk husks are separated using a husk separator, and the sorghum stalk husks are reserved for later use. The sorghum stalk husks with a moisture content of 10% are processed into 200mm × 30mm samples and placed in a glass beaker (containing formic acid, with a formic acid to hydrogen peroxide molar ratio of 1:1 and a concentration of 10mol / L, and sulfuric acid as a catalyst). The samples are treated at 50℃ and atmospheric pressure for 4 hours, then removed and neutralized with 0.5% sodium carbonate for 5 minutes, and rinsed three times with water to obtain wet crude cellulose fibers. These wet crude cellulose fibers are then dried at room temperature and atmospheric pressure for 2 days to obtain high-strength sorghum stalk husk cellulose fibers.

[0029] Test results: The crude cellulose fiber obtained from sorghum straw husk has a length of approximately 200 mm and a diameter of approximately 150 µm. The lignin content is 1.5%, the hemicellulose content is 3.5%, the cellulose content is 95%, and the tensile strength is 1.5 GPa.

[0030] Example 3

[0031] After the leaves of naturally air-dried Job's tears stalks are removed, the husks are separated using a husk separator, and the husks are kept for later use. The Job's tears husks with a moisture content of 10% are processed into 100mm × 20mm samples. These samples are placed in a glass beaker (containing peracetic acid, with a 1:1 molar ratio of acetic acid to hydrogen peroxide, and water added to adjust the concentration to 8 mol / L, with sulfuric acid as a catalyst) and treated at 100℃ for 2 hours. Then, they are removed and neutralized with 0.5% sodium hydroxide for 5 minutes, and rinsed three times with water to obtain wet crude cellulose fibers. These wet crude cellulose fibers are dried at room temperature and atmospheric pressure for 1 day to obtain high-strength Job's tears husk cellulose crude fibers.

[0032] Test results: The crude cellulose fiber obtained from the Job's tears straw peel has a length of approximately 100 mm and a diameter of approximately 180 µm. The lignin content is 1%, the hemicellulose content is 4%, the cellulose content is 95%, and the tensile strength is 1.2 GPa.

[0033] Example 4

[0034] Sugarcane bagasse was separated using a peel-straw separator, and the bagasse peel was set aside. Sugarcane peel with a moisture content of 10% was crushed, sieved, and processed into samples approximately 1 mm in length. These samples were placed in a glass beaker (containing a 1:1 mixture of 5% potassium hydroxide and 30% hydrogen peroxide) and pretreated at 25°C for 12 hours. After washing with water, the samples were removed and set aside. The pretreated biomass samples were placed in a glass beaker (containing peracetic acid, formic acid, and hydrogen peroxide in a 1:1 molar ratio, diluted with water to 1 mol / L, with sulfuric acid as a catalyst) and treated at 25°C under normal pressure for 24 hours. The samples were then removed, neutralized with 0.5% sodium hydroxide for 5 minutes, and rinsed three times with water to obtain wet crude cellulose fibers. These wet crude cellulose fibers were dried at room temperature and normal pressure for one day to obtain high-strength sugarcane stalk peel cellulose fibers.

[0035] Test results: The obtained sugarcane bagasse cellulose crude fiber has a length of about 1 mm, a diameter of about 50 µm, a lignin content of 8%, a hemicellulose content of 8%, a cellulose content of 84%, and a tensile strength of 0.8 GPa.

Claims

1. A method for preparing high-strength straw husk cellulose crude fiber, characterized in that... The process includes the following steps: A: Removing lignin and hemicellulose from the straw husk, and peeling off the thin-layered cells; B: Drying at room temperature and normal pressure to densify the crude cellulose fibers, specifically: A: Remove lignin and hemicellulose from the straw husk, and peel off the thin outer cells. Straw husks with a moisture content of less than 25% are processed into biomass units with a length of 1-200 mm and a width of 1-50 mm. A treatment solution with a concentration of 1-10 mol / L is heated to 25℃-100℃ and the biomass units are treated with the treatment solution for 2-24 hours to remove lignin and hemicellulose, thereby peeling the husk cells from the surface of the fiber bundles. The units are then rinsed with water 3-5 times, and the resulting wet cellulose crude fiber is stored in water for later use. B: Drying at room temperature and normal pressure The wet cellulose crude fiber obtained in step A is taken out of the deionized water and dried at room temperature for 1 to 2 days. Under the action of hydrogen bonding, as the water in the fiber bundle evaporates, the microfibers that make up the crude fiber will shrink and densify. The resulting cellulose crude fiber is stored at room temperature and normal pressure for later use. In step A, the treatment solution is an aqueous solution of any one or more of the following: formic acid, acetic acid, sulfuric acid, sodium hydroxide, sodium carbonate, hydrogen peroxide, peroxyformic acid, or peracetic acid. The tensile strength of the crude cellulose fibers prepared in step B is 0.8–1.5 GPa; The crude cellulose fiber contains cellulose, hemicellulose and lignin, wherein the lignin content is 1.0%~8.0%, the hemicellulose and cellulose content is 92%~99%, wherein the hemicellulose content is 3.5%-8.0% and the cellulose content is 84-95%.

2. The method for preparing high-strength straw husk cellulose crude fiber according to claim 1, characterized in that: In step A, the straw husk is made of corn straw, sorghum straw, Job's tears straw, or sugarcane straw. It has coarse fiber bundles, macroporous thin-walled thin-walled skin cells, and thin-walled skin cells attached around the coarse fiber bundles. It is composed of lignin, hemicellulose, and cellulose.

3. The method for preparing high-strength straw husk cellulose crude fiber according to claim 1, characterized in that: In step A, before rinsing with water, neutralize with 0.5% sodium hydroxide or sodium carbonate for 5 minutes.

4. A high-strength straw husk cellulose crude fiber prepared by the method according to any one of claims 1-3, characterized in that: It includes crude cellulose fibers, which maintain the microstructure of cellulose microfibers that are oriented and densely arranged in the original fiber bundles of straw bark. The crude cellulose fibers have a length of 1~200mm and a diameter of 50~200µm. The microfibers are oriented and densely arranged through hydrogen bond interactions. There are no thin skin cells attached to the surface of the crude cellulose fibers.

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