Cotton linter pulp bleaching agent and bleaching method

Abstract

The invention provides a cotton linter pulp bleaching agent, a preparation method and a bleaching method. The cotton linter pulp bleaching agent comprises a hydrogen bond acceptor and a hydrogen bond donor, the hydrogen bond acceptor is squaramide, and the hydrogen bond donor is a carboxyl-containing organic matter. The cotton linter pulp bleaching agent provided by the invention is good in stability and good in bleaching effect, and does not excessively consume water resources.

Description

Technical Field

[0001] The present invention relates to the field of bleaching, and particularly to a bleaching agent for cotton linters pulp, a preparation method and a bleaching method thereof. Background Art

[0002] Refined cotton is a kind of cotton cellulose base material produced by cooking and bleaching cotton linters, a by-product of cotton.

[0003] In the existing bleaching process of refined cotton, chlorine dioxide is often used for chlorine bleaching. By oxidizing the lignin in cotton linters and eliminating or reducing the chromogenic groups of lignin, the whiteness of refined cotton is increased. However, chlorine dioxide has poor stability, poor bleaching effect, and increases water resource consumption during use, resulting in waste. Summary of the Invention

[0004] In view of this, the present invention provides a bleaching agent for cotton linters pulp, a preparation method and a bleaching method thereof to solve the problems of poor stability of the bleaching agent, poor bleaching effect and waste of water resources in the prior art.

[0005] To achieve the above object, according to one aspect of the present invention, a bleaching agent for cotton linters pulp is provided. The bleaching agent for cotton linters pulp includes a hydrogen bond acceptor and a hydrogen bond donor, wherein the hydrogen bond acceptor is squaramide and the hydrogen bond donor is a carboxyl-containing organic compound.

[0006] As an implementation manner, the carboxyl-containing organic compound is any one of C1-C6 carboxylic acids or C2-C4 hydroxy acids.

[0007] As an implementation manner, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 0.5:1 - 1:30.

[0008] According to one aspect of the present invention, a preparation method of a bleaching agent for cotton linters pulp is provided. The preparation method mixes squaramide and a carboxyl-containing organic compound and heats them, and the heating temperature is 10 - 70°C.

[0009] According to one aspect of the present invention, a bleaching method for cotton linters pulp is provided. The bleaching method for cotton linters pulp includes: S1. Soaking cotton linters in the bleaching agent to obtain a mixed pulp and performing heat treatment for the first bleaching, and the bleaching agent is the bleaching agent described in any of the above implementation manners; S2. Filtering the mixed pulp to obtain wet cotton linters, adjusting the pH of the wet cotton linters to 7 - 9 for the second bleaching; S3. After the reaction ends, washing with water and drying to end the bleaching process.

[0010] As an implementation manner, the mass ratio of the cotton linters to the bleaching agent is 1:10 - 1:60.

[0011] As an implementation manner, the mass ratio of the cotton linters to the bleaching agent is 1:25 - 1:50.

[0012] As an implementation manner, in the above S1, the heat treatment is heating, and the heating temperature is 10 - 70 °C.

[0013] As an implementation manner, in the above S1, the heat treatment is heating, and the heating temperature is 40 - 60 °C.

[0014] As an implementation manner, the time of the first bleaching in the above S1 is 2 - 24 h, and / or the time of the second bleaching in S2 is 0.5 - 4 h.

[0015] As an implementation manner, both the first bleaching in the above S1 and the second bleaching in S2 include stirring, and the stirring frequency is 5 min / time - 10 min / time.

[0016] As an implementation manner, in the above S3, the number of water washing times is 1 - 3 times.

[0017] As an implementation manner, in the above S3, the drying method is drying by baking, the baking temperature is 50 - 80 °C, and the baking time is 0.5 - 4 h.

[0018] In the technical solution of the present invention, formamide is used as a hydrogen bond acceptor, and the carboxyl - containing organic matter is used as a hydrogen bond donor. The hydrogen bond acceptor and the hydrogen bond donor together form a deep eutectic solvent, which is used as a bleaching agent for cotton linter pulp. The formation of the deep eutectic solvent system is based on hydrogen bonds, so the components inside the system stably exist and do not react. The cellulose and lignin in cotton linter are mainly connected by hydrogen bonds and van der Waals forces. On the one hand, formamide can combine with the phenolic hydroxyl groups in lignin in the form of hydrogen bonds, thereby effectively extracting the lignin in cotton linter, performing the first bleaching on cotton linter, and increasing the whiteness of cotton linter. At the same time, formamide has a planar rigid structure. Inserting between lignin and cellulose can effectively weaken the van der Waals forces between the two, and extract the lignin. The extracted lignin has a high purity and can be industrially produced. On the other hand, formamide is soluble in water at room temperature and can be washed off with water. Further, in the cotton linter pulp bleaching method of the present invention, the pH of the wet cotton linter is adjusted to 7 - 9 to destroy the hydrogen bond network in the deep eutectic solvent system, and the second bleaching is carried out under weak alkaline conditions. Since lignin contains acidic phenolic hydroxyl groups, the amino group in formamide reacts with the phenolic hydroxyl groups in lignin during the second bleaching process, causing the lignin to fall off from the surface of cellulose, which is beneficial to further removing the lignin in cotton linter pulp and increasing the whiteness of cotton linter.

[0019] In summary, the cotton linter pulp bleaching agent provided by the present invention has good stability, good bleaching effect and does not excessively consume water resources. Description of the Drawings

[0020] The accompanying drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof are used to explain the present invention and do not unduly limit the present invention.

[0021] In the drawings: Figure 1 It is a schematic structural diagram of squaramide.

[0022] Figure 2 It is a schematic structural diagram of three main units in lignin. Detailed implementation manners

[0023] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0024] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those with ordinary skills in the field to which the present invention pertains.

[0025] As analyzed in the background art of the present invention, in the prior art, chlorine dioxide bleaching agents have problems such as poor stability, poor bleaching effect, and increased water resource consumption during use, resulting in waste. To solve the above problems, the present invention provides a cotton linter pulp bleaching agent, a preparation method, and a bleaching method to solve the problems of poor stability of the bleaching agent, poor bleaching effect, and waste of water resources in the prior art.

[0026] In one embodiment of the present invention, a cotton linter pulp bleaching agent is provided. The cotton linter pulp bleaching agent includes a hydrogen bond acceptor and a hydrogen bond donor, wherein the hydrogen bond acceptor is squaramide and the hydrogen bond donor is a carboxyl-containing organic compound.

[0027] The molecular formula of squaramide is C4H4N2O2, and the CAS number is 5231-89-0. The structure of squaramide is as Figure 1 shown. Squaramide has a planar rigid structure. The conjugation of sp 2 hybridized carbon atoms of the cyclobutene skeleton with the carbonyl group and the amino group forms a stable planar structure. The lone pair electrons of the nitrogen atom participate in π conjugation, enhancing the molecular stability. The two amino groups in squaramide can provide 4 N-H bonds as hydrogen bond donors (each amino group contains 2 H atoms), and the two carbonyl oxygen atoms in squaramide act as hydrogen bond acceptors and can accept multiple hydrogen bonds simultaneously. This property gives squaramide an advantage in molecular recognition and can be used to bind and remove lignin in cotton linter. The structure of three main units in lignin is as Figure 2 shown, and the lignin structural unit contains phenolic hydroxyl groups.

[0028] Specifically, in the technical solution of the present invention, formamide is used as a hydrogen bond acceptor, and the carboxyl-containing organic compound is used as a hydrogen bond donor. The hydrogen bond acceptor and the hydrogen bond donor together form a deep eutectic solvent, which is used as a bleaching agent for cotton linter pulp. The formation of the deep eutectic solvent system is based on hydrogen bonds, so the components within the system exist stably and do not react. The cellulose and lignin in cotton linter are mainly connected by hydrogen bonds and van der Waals forces. On the one hand, formamide can combine with the phenolic hydroxyl group in lignin in the form of hydrogen bonds, thereby effectively extracting the lignin in cotton linter, performing the first bleaching on cotton linter, and increasing the whiteness of cotton linter. At the same time, formamide has a planar rigid structure. Inserting between lignin and cellulose can effectively weaken the van der Waals forces between the two, and extract the lignin. The extracted lignin has high purity and can be industrially produced. On the other hand, formamide is soluble in water at room temperature and can be washed away with water. Further, in the method for bleaching cotton linter pulp of the present invention, the pH of wet cotton linter is adjusted to 7-9 to destroy the hydrogen bond network in the deep eutectic solvent system, and the second bleaching is carried out under weak alkaline conditions. Since lignin contains acidic phenolic hydroxyl groups, the amino group in formamide reacts with the phenolic hydroxyl group in lignin during the second bleaching process, causing the lignin to fall off from the surface of cellulose, which is beneficial to further removing the lignin in cotton linter pulp and increasing the whiteness of cotton linter.

[0029] In summary, the bleaching agent for cotton linter pulp provided by the present invention has good stability, good bleaching effect and does not consume excessive water resources.

[0030] In one embodiment of the present invention, the carboxyl-containing organic compound is any one of C1-C6 carboxylic acids or C2-C4 hydroxy acids.

[0031] Specifically, the C1-C6 carboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, and caproic acid, and the C2-C4 hydroxy acids include glycolic acid, lactic acid, and malic acid. The carboxyl-containing organic compound acts as a hydrogen bond donor to provide H atoms, and forms a deep eutectic solvent system with formamide through hydrogen bonds. The formation of the deep eutectic solvent system is based on hydrogen bonds, so the components within the system do not react. Selecting the type of hydrogen bond donor helps to increase the electron cloud density of formamide, enhance the binding of formamide to lignin, and increase the whiteness of cotton linter. At the same time, avoid using hydrogen bond donors with too strong corrosiveness, so as to prevent the cellulose structure in the target product, refined cotton, from being damaged, resulting in a decline in the comprehensive performance of refined cotton.

[0032] In an embodiment of the present invention, the molar ratio of the above hydrogen bond acceptor to the hydrogen bond donor is 0.5:1 - 1:30. On the one hand, controlling the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor can ensure the formation of the eutectic solvent system. On the other hand, it can enhance the binding ability between the squaramide in the eutectic solvent system and lignin. If the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor used exceeds this range, it will be difficult to ensure the binding ability between squaramide and lignin in the system, and thus ensure the bleaching effect of the bleaching agent.

[0033] In an embodiment of the present invention, a preparation method of a cotton linter pulp bleaching agent is provided. In this preparation method, squaramide and a carboxyl-containing organic substance are mixed and heated, and the heating temperature is 10 - 70 °C. Specifically, stirring and heating contribute to the formation of the eutectic solvent system.

[0034] In an embodiment of the present invention, a cotton linter pulp bleaching method includes: S1. Soaking the cotton linter in the bleaching agent to obtain a mixed pulp and performing heat treatment for the first bleaching. The bleaching agent is the bleaching agent described in any of the foregoing embodiments; S2. Filtering the mixed pulp to obtain wet cotton linter, adjusting the pH of the wet cotton linter to 7 - 9 for the second bleaching; S3. After the reaction ends, washing with water and drying to end the bleaching process.

[0035] Amide can combine with the phenolic hydroxyl group in lignin in the form of hydrogen bonds, thereby effectively extracting the lignin in cotton linter, performing the first bleaching on the cotton linter, and increasing the whiteness of the cotton linter. At the same time, squaramide has a planar rigid structure. Inserting between lignin and cellulose can effectively weaken the van der Waals force between the two, and extract the lignin. The extracted lignin has a high purity and can be industrially produced. On the other hand, squaramide is soluble in water at room temperature and can be washed away with water. Further, in the cotton linter pulp bleaching method of the present invention, adjusting the pH of the wet cotton linter to 7 - 9 can break the hydrogen bond network in the eutectic solvent system, remove the carboxyl-containing organic substance in the eutectic solvent system, and perform the second bleaching under weak alkaline conditions (using strong alkali will cause the intrinsic viscosity of the refined cotton to decrease and damage part of the cellulose structure). Since lignin contains acidic phenolic hydroxyl groups, during the second bleaching process, the amino group in squaramide reacts with the phenolic hydroxyl group in lignin, causing the lignin to fall off from the surface of cellulose, which is beneficial to further removing the lignin in the cotton linter pulp, increasing the whiteness of the cotton linter, and at the same time retaining the complete structure of cellulose.

[0036] In an embodiment of the present invention, the mass ratio of the above cotton linter to the bleaching agent is 1:10 - 1:60.

[0037] In an embodiment of the present invention, the mass ratio of the above cotton linter to the bleaching agent is 1:25 - 1:50.

[0038] Specifically, controlling the mass ratio of the above-mentioned cotton linter and bleaching agent can not only ensure the bleaching performance but also effectively improve the bleaching efficiency.

[0039] In an embodiment of the present invention, in the above S1, the heat treatment is heating, and the heating temperature is 10 - 70 °C.

[0040] In an embodiment of the present invention, in the above S1, the heat treatment is heating, and the heating temperature is 40 - 60 °C.

[0041] Specifically, controlling the temperature in the first bleaching helps to accelerate the combination of formamide and lignin in cotton linter and improve the bleaching efficiency. Among them, the above heating temperature can be any point value within the range of 10 - 70 °C, such as 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, etc., which will not be elaborated here. The preferred heating temperature is any point value within the range of 40 - 60 °C. At the same time, it should be noted that the temperature should not be too low to avoid the precipitation of formamide in crystal form, so that formamide cannot combine with lignin in cotton linter in a liquid state and cannot play a bleaching role.

[0042] In an embodiment of the present invention, in the above S1, the time of the first bleaching is 2 - 24 h, and / or the time of the second bleaching in S2 is 0.5 - 4 h. Specifically, a sufficient bleaching time can enable lignin to be removed from cotton linter as much as possible to ensure the bleaching effect.

[0043] In an embodiment of the present invention, in the above S3, the number of water washing times is 1 - 3 times. Formamide is soluble in water, and it can be removed by washing with water.

[0044] In an embodiment of the present invention, in the above S3, the drying method is drying by baking, the baking temperature is 50 - 80 °C, and the baking time is 0.5 - 4 h.

[0045] The following further describes the present invention in detail with specific embodiments. These embodiments should not be construed as limiting the scope of the present invention claimed. In addition, in the following embodiments, unless otherwise specified, the reagents and equipment used are commercially available. If the specific treatment conditions and treatment methods are not clearly described in the following embodiments, the conditions and methods known in the art can be used for treatment. Example 1

[0046] S1. Mix 10 g of cotton linter and 150 g of bleaching agent in a mass ratio of 1:15 to obtain a mixed slurry, carry out the first bleaching and stir under the condition of constant temperature at 40 °C. The time of the first bleaching is 8 h. Among them, the molar ratio of formamide and propionic acid in the bleaching agent is 1:10, and it is obtained by heating at 40 °C for 5 min; S2. Use a filtering device to filter out most of the bleaching agent until no liquid flows down within 10 s. Take out the wet cotton linters, add a sodium bicarbonate solution with a mass concentration of 1% to the cotton linters, adjust the pH of the cotton linter solution to 7.5, and perform the second bleaching for 1 h. S3. Wash twice with water, put it in an oven for drying, the drying temperature is 55 °C, and the drying time is 2 h. Example 2

[0047] The difference from Example 1 is that in S1, the molar ratio of formamide to pyruvic acid is 1:5. Example 3

[0048] The difference from Example 1 is that in S1, pyruvic acid in the bleaching agent is replaced by acetic acid. Example 4

[0049] The difference from Example 1 is that in S2, the pH of the cotton linter solution is adjusted to 9.

[0050] Comparative Example 1 The difference from Example 1 is that in S2, use a filtering device to filter out most of the bleaching agent until no liquid flows down within 10 s. After taking out the wet cotton linters, directly perform S3.

[0051] Comparative Example 2 The difference from Example 1 is that in S2, add a sodium hydroxide solution with a mass concentration of 10% to adjust the pH of the cotton linter solution to 12.

[0052] Perform whiteness measurement, intrinsic viscosity measurement, and α-cellulose content measurement on the refined cotton (cotton linter bleaching product) obtained in Example 1, Example 3, and Comparative Examples 1-2. The measurement methods of whiteness, intrinsic viscosity, and α-cellulose content are all carried out according to "GBT-9107-2023". Among them, whiteness is one of the important physical indicators reflecting the quality of refined cotton. Viscosity reflects the length and integrity of cellulose molecular chains in refined cotton. The higher the degree of polymerization, the more complete the structure, and the higher the quality of refined cotton. A high α-cellulose content indicates less impurities in refined cotton and the cellulose structure is not damaged, so the quality of refined cotton is high.

[0053] The specific test results are shown in Table 1.

[0054] Table 1

[0055] According to the test results in Table 1, in the present invention, squaramide is used as a hydrogen bond acceptor and an organic compound containing a carboxyl group is formulated into a deep eutectic solvent as a bleaching agent to bleach unbleached cotton linters. The whiteness of the refined cotton obtained is above 84, the intrinsic viscosity is above 1600, and the α-cellulose content is above 98.8%. The performance of the refined cotton obtained is excellent.

[0056] The test results show that the bleaching agent of the present invention can not only effectively remove the lignin combined with cellulose, and the whiteness of the refined cotton is high. From the values of the intrinsic viscosity and the α-cellulose content, the structure of the cellulose molecules in the refined cotton is complete. The bleaching agent has little damage to cellulose and few impurities, and the quality of the refined cotton is high.

[0057] It further shows that the cotton linter pulp bleaching agent provided by the present invention has good stability, good bleaching effect and will not excessively consume water resources.

[0058] The above are only the preferred embodiments of the present disclosure and are not intended to limit the present disclosure. For those skilled in the art, the present disclosure can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure shall be included within the protection scope of the present disclosure.

Claims

1. A cotton linter pulp bleaching agent, characterized in that, It includes a hydrogen bond acceptor and a hydrogen bond donor, wherein the hydrogen bond acceptor is squaramide and the hydrogen bond donor is a carboxyl-containing organic compound.

2. The cotton linter pulp bleaching agent according to claim 1, characterized in that, The carboxyl-containing organic compound is any one of C1-C6 carboxylic acids or C2-C4 hydroxy acids.

3. The cotton linter pulp bleaching agent according to claim 1, wherein The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 0.5:1 - 1:

30.

4. A preparation method of a cotton linter pulp bleaching agent, characterized in that, Mix the squaramide and the carboxyl-containing organic compound and heat them, with the heating temperature being 10 - 70°C.

5. A bleaching method for cotton linter pulp, characterized in that, It includes the following steps: S1. Immerse cotton linters in a bleaching agent to obtain a mixed pulp and conduct heat treatment, and perform the first bleaching. The bleaching agent is the bleaching agent described in any one of claims 1 - 4; S2. Filter the mixed pulp to obtain wet cotton linters, adjust the pH of the wet cotton linters to 7 - 9, and perform the second bleaching; S3. After the reaction ends, wash with water and dry to finish the bleaching process.

6. The bleaching method of cotton linter pulp according to claim 5, characterized in that The mass ratio of the cotton linters to the bleaching agent is 1:10 - 1:

60.

7. The bleaching method of cotton linters pulp according to claim 5, characterized in that, In S1, the heat treatment is heating, and the heating temperature is 10 - 70°C.

8. The bleaching method of cotton linters pulp according to claim 5, characterized in that, In S1, the time for the first bleaching is 2 - 24 h, and / or in S2, the time for the second bleaching is 0.5 - 4 h.

9. The bleaching method of cotton linter pulp according to claim 5, characterized in that In S3, the number of times of washing with water is 1 - 3 times.

10. The bleaching method of cotton linter pulp according to claim 5, characterized in that, In S3, the drying method is drying by baking, the baking temperature is 50 - 80°C, and the baking time is 0.5 - 4 h.

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