A method for preparing high-quality bamboo dissolving pulp by slurry screening and eutectic solvent treatment

Abstract

The application discloses a method for preparing high-quality bamboo dissolving pulp by pulp screening and eutectic solvent treatment, and belongs to the technical field of papermaking industry. The technical problems of the traditional method for preparing high-purity dissolving pulp, such as the high content of impurities in non-wood bamboo dissolving pulp, low purity and reaction performance of the pulp, strong resistance of fibers in heterogeneous reaction, uneven distribution of reaction reagents and uneven reaction are solved. Through the synergistic treatment of pulp screening and eutectic solvent, the purity and reaction performance of the dissolving pulp are simultaneously efficiently improved at a shorter reaction time and a lower treatment temperature. The screening of the pulp by the screening instrument with different mesh screens can remove the small component impurities which preferentially react, and the reaction of the long fiber fraction pulp and the reagent is strengthened, so that the problems of strong resistance of fibers in the traditional heterogeneous reaction, uneven distribution of reaction reagents, poor reaction uniformity and low reaction efficiency are overcome, and the purposes of reducing the reaction energy consumption and improving the quality of the dissolving pulp are achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of papermaking industry, and particularly relates to a method for preparing high-quality bamboo dissolving pulp by pulp screening and eutectic solvent treatment. BACKGROUND

[0002] Dissolving pulp is a raw material for producing ordinary cellulose products (90-95% of alpha-cellulose). The raw materials for manufacturing dissolving pulp mainly include cotton linters, wood and bamboo, etc. In recent years, due to the cotton-grain conflict and the fluctuation of cotton prices, the market share of cotton is only about 10%. Compared with wood, China has advantages in the yield and reserves of bamboo, and bamboo has the characteristics of multiple species, fast growth and relatively high cellulose content. Therefore, using bamboo raw materials to prepare dissolving pulp can not only alleviate the demand for wood or cotton and linen fiber raw materials, but also promote the development of the bamboo industry in China. However, bamboo contains a large number of non-cellulose impurities such as parenchyma cells, stone cells and epidermal cells, and the ash content and hemicellulose content in the non-cellulose impurities are high. The existence of the above non-cellulose impurities will lead to the decrease of the purity and reaction performance of bamboo dissolving pulp, and it is difficult to meet the requirements of high-quality dissolving pulp. In addition, the size of the non-cellulose impurities is small, and the specific surface area is large. During the alkalization and yellowing stages, a large amount of reaction reagents will be preferentially adsorbed, which will reduce the degree of alkalization and yellowing of the fiber cells, and seriously affect the production and quality of the dissolving pulp. Therefore, it is still challenging to use bamboo pulp and other non-wood fiber raw materials to prepare high-quality dissolving pulp.

[0003] In order to prepare dissolving pulp with high purity and high reaction performance, chemical methods (such as alkali extraction and acid treatment) or biological methods (enzyme treatment) are often used to improve the purity or reaction performance of the pulp. However, most of the methods cannot consider both the purity and reaction performance of the dissolving pulp. The traditional alkali extraction method has obvious dissolving effect on hemicellulose. Although the purification effect is significant, high-concentration alkali extraction will cause the transformation of the crystal structure of cellulose, resulting in the decrease of the reaction performance of the dissolving pulp. Although the cellulase method has obvious effect on the viscosity reduction and reaction performance improvement of the dissolving pulp, it cannot effectively dissolve hemicellulose. The hemicellulase can improve the purity of the dissolving pulp, but has little effect on the improvement of the reaction performance of the dissolving pulp. In addition, the biological enzyme method has a long reaction time and high reaction requirements (enzymes are sensitive to temperature, pH, etc. and are easy to lose activity), resulting in relatively high production cost. Inorganic acid treatment can consider both the reaction performance and purification of the dissolving pulp, but the purification effect is poor, and high treatment temperature and long reaction time are required.

[0004] The above method has the problems of poor reaction uniformity in heterogeneous reaction and the two parameters of purity and reaction performance cannot be considered simultaneously. Because of the complex structure of the fiber raw material, ordinary chemical reagents and biological enzymes show certain "stubbornness", which greatly reduces the reaction efficiency of the pulp and the reagent. Especially when bamboo is used as the raw material for dissolving pulp, the fine components (heterocellulose) in the bamboo have "priority to react" due to their loose structure and large specific surface area, which are more easily adsorbed by the reagent and react, resulting in a decrease in the reaction rate of long fibers and poor reaction effect. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a method for preparing high-quality bamboo dissolving pulp by pulp screening and low eutectic solvent treatment, which solves the technical problems of high impurity content of non-wood bamboo dissolving pulp, the traditional method cannot consider the purity and reaction performance of bamboo dissolving pulp at the same time, and the fiber is strong in stubbornness in heterogeneous reaction, the reaction reagent is not evenly distributed, and the reaction is not uniform.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] The present application discloses a method for preparing high-quality bamboo dissolving pulp by pulp screening and low eutectic solvent treatment, comprising the following steps:

[0008] S1: After the bamboo dissolving pulp is dispersed, a pulp suspension is obtained; the pulp suspension is injected into a screening instrument containing different mesh screens for screening, and after each screening, the pulp suspension that does not pass is named as the retained pulp, and the pulp suspension that passes is named as the passed pulp;

[0009] The retained pulps of all the target mesh screens are mixed to obtain long fiber fraction pulp; the pulps passing through the target mesh screens are mixed to obtain short fiber fraction pulp; the long fiber fraction pulp and the short fiber fraction pulp are concentrated and dispersed respectively to obtain long fiber fraction pulp blocks and short fiber fraction pulp blocks;

[0010] S2: The long fiber fraction pulp blocks are mixed with the low eutectic solvent for reaction to obtain reacted pulp, and the reacted pulp is washed, concentrated and dispersed, and air-dried to obtain high-quality bamboo dissolving pulp.

[0011] Further, in S1, the bamboo dissolving pulp is obtained by pre-hydrolysis kraft or cold alkali extraction, the alpha-cellulose content of the bamboo dissolving pulp is 85% to 92%, the viscosity is 600 to 850 mL / g, and the Fock reaction performance is less than 50%; when the pulp suspension is screened by the screening instrument, the mass of the bamboo dissolving pulp for each screening is not less than 10 g; the mass concentration of the pulp suspension is 0.5% to 2%.

[0012] Further, in S1, the screening instrument is a Paul screening instrument; the mesh number of different screening plates of the screening instrument is 16 mesh, 30 mesh, 50 mesh, 100 mesh and 200 mesh in turn; and the target mesh number is 100 mesh.

[0013] Further, after the pulp suspension is sequentially screened by the screening instrument with the screening plates of 16 mesh, 30 mesh, 50 mesh, 100 mesh and 200 mesh, all the retained pulp not passing through the 100 mesh screening plate is mixed to obtain long fiber fraction pulp, and the yield of the long fiber fraction pulp is 80%-95%; and the yield of the short fiber fraction pulp is 5%-20%.

[0014] Further, in S1, when screening, the screening time is 15 min-30 min, and the screening water flow rate is 8 L / min-13 L / min.

[0015] Further, in S2, the preparation method of the deep eutectic solvent is that: after a hydrogen bond acceptor and a hydrogen bond donor are mixed, heating and stirring are performed until a transparent and clear liquid is formed to obtain the deep eutectic solvent.

[0016] Further, the hydrogen bond acceptor is choline chloride; the hydrogen bond donor is oxalic acid, lactic acid, formic acid or acetic acid; when the hydrogen bond donor is oxalic acid, formic acid or acetic acid, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is (1:1)-(1:3); and when the hydrogen bond donor is lactic acid, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is (1:5)-(1:10).

[0017] Further, in S2, before the long fiber fraction pulp is mixed with the deep eutectic solvent, the deep eutectic solvent needs to be pretreated, and the pretreatment process is that: the deep eutectic solvent is heated to 40-60 DEG C by using a water bath.

[0018] Further, in S2, the reaction time is 15-30 min; the dosage ratio of the long fiber fraction pulp to the deep eutectic solvent is (1:5)-(1:15); and the mass concentration of the pulp after concentration and dispersion is 20%-25%, and the mass concentration after air drying is 90%-97%.

[0019] Further, in S2, the pulp after reaction is washed to be neutral, and the washing liquid obtained can be concentrated and purified by using a rotary evaporation method to recover the deep eutectic solvent after reaction.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] The application discloses a method for preparing high-quality bamboo dissolving pulp by pulp screening and eutectic solvent treatment, which can efficiently improve the purity and reaction performance of the dissolving pulp at a shorter reaction time and lower treatment temperature. The screening of the pulp by a screening instrument with different mesh screens can remove small component impurities which preferentially react, avoid their invalid adsorption and reaction with reagents, and strengthen the reaction of long-fiber fraction pulp and reagents, thereby overcoming the problems of strong fiber resistance, uneven distribution of reaction reagents, poor reaction uniformity and low reaction efficiency in traditional heterogeneous reactions, so as to shorten the reaction time and reduce the reaction energy consumption. The method can improve the purity of the bamboo dissolving pulp, efficiently reduce the viscosity of the dissolving pulp and improve the reaction performance, thereby preparing high-purity dissolving pulp with high reaction performance, and has a wide application prospect.

[0022] Further, after washing the pulp, the obtained washing liquid can be reused, and the eutectic solvent after reaction can be recycled, which has the advantages of environmental protection, saving and low cost. DETAILED DESCRIPTION

[0023] To enable those skilled in the art to understand the features and effects of the present application, the following is a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific words used herein have their usual meanings understood by those skilled in the art of the present application, and in case of conflict, the definition in the specification shall prevail.

[0024] Theories or mechanisms described and disclosed herein, whether correct or wrong, should not limit the scope of the present application in any way, i.e., the content of the present application can be implemented without being limited by any specific theory or mechanism.

[0025] In this paper, all features defined in the form of numerical range or percentage range, such as numerical value, quantity, content and concentration, are for the sake of brevity and convenience. Therefore, the description of numerical range or percentage range should be considered to have covered and specifically disclosed all possible sub-ranges and individual numerical values (including integers and fractions) within the range.

[0026] In this paper, unless otherwise specified, "comprising", "including", "containing", "having" or similar terms cover the meaning of "consisting of" and "consisting essentially of", for example, "A comprising a" covers the meaning of "A comprising a and other" and "A comprising only a".

[0027] Herein, all possible combinations of various technical features in various embodiments or examples are not described in order to make the description concise. Therefore, as long as there is no contradiction in the combination of the technical features, each technical feature in various embodiments or examples can be combined arbitrarily, and all possible combinations shall be considered as the scope described in the specification.

[0028] The application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the application and not used to limit the scope of the application. Furthermore, it should be understood that those skilled in the art can make various modifications or changes to the application after reading the content taught by the application, and these equivalent forms also fall within the scope defined by the claims attached hereto.

[0029] The following examples use the instruments and equipment that are conventional in the art. The experimental methods in the following examples, unless otherwise specified, are generally carried out according to conventional conditions, or according to the conditions recommended by the manufacturer. Various raw materials are used in the following examples, unless otherwise specified, and conventional commercially available products are used, which are conventional specifications in the art. In the specification of the application and the following examples, unless otherwise specified, "%" means weight percent, "parts" means weight parts, and the ratio means weight ratio.

[0030] Example 1

[0031] A method for preparing high-quality bamboo dissolving pulp by slurry screening and eutectic solvent treatment, comprising the following steps:

[0032] 10 g of bamboo dissolving pulp prepared by cold alkali extraction method was soaked in deionized water for 4 h, and the pulp was dispersed by a fiber defibrator to form a pulp suspension with a concentration of 0.5%, the α-cellulose content of the bamboo dissolving pulp was 85% to 92%, the viscosity was 600 to 850 mL / g, and the Fock reaction performance was less than 50%; the pulp suspension was injected into a Paller screen instrument containing different mesh screens (16, 30, 50, 100, 200 mesh), and was screened in a ladder-like manner, the mass of the dissolving pulp for each screening was not less than 10 g, and after screening, the pulp suspension that did not pass was named as the retained (R) pulp, and the pulp suspension that passed was named as the passed (P) pulp; six groups of pulp were obtained according to the retained (R) and passed (P) conditions, namely R16, R30, R50, R100, R200 and P200; all the retained pulps that did not pass the 100 mesh screen were mixed, i.e. R16, R30, R50 and R100 were mixed to obtain long fiber fraction pulp, and all the retained pulps that passed the 100 mesh screen were mixed, i.e. R200 and P200 fibers were uniformly mixed to obtain short fiber fraction pulp, the long fiber fraction pulp and the short fiber fraction pulp were concentrated to keep the mass concentration at 24%, and were dispersed into pulp blocks with a size of less than 5 mm x 5 mm and stored in polyethylene self-sealing bags for water balance for standby use.

[0033] Choline chloride and formic acid were stirred and heated at 60℃ according to a molar ratio of 1:2 until a transparent and clear liquid was formed, obtaining a deep eutectic solvent, 15g of the deep eutectic solvent was preheated to 50℃ in a thermostatic water bath, then 1g of long fiber fraction pulp was mixed with the deep eutectic solvent in a ziplock bag and reacted uniformly, the reaction time was 30min, the solid-liquid ratio of the reaction was 1:15, and the ziplock bag was kneaded every 5min during the reaction, obtaining the reacted pulp, the reacted pulp was washed to neutral, concentrated to a mass concentration of 22%, and dispersed into pulp blocks smaller than 5mmx5mm, air-dried to a mass concentration of 93%, obtaining high-quality bamboo dissolving pulp; the washing liquid was recovered, concentrated and purified for reuse.

[0034] Table 1 shows the performance comparison between the original pulp prepared in Example 1, the long fiber obtained by separate screening, the high-quality bamboo dissolving pulp obtained by screening and deep eutectic solvent treatment, and the bamboo dissolving pulp treated by deep eutectic solvent alone.

[0035] Table 1 Performance comparison between different pulps in Example 1

[0036]

[0037] Example 2

[0038] A method for preparing high-quality bamboo dissolving pulp by pulp screening and deep eutectic solvent treatment, comprising the following steps:

[0039] 10g of bamboo dissolving pulp prepared by cold alkali extraction method was soaked in deionized water for 4h, and the pulp was dispersed into a 1.0% concentration pulp suspension by a fiber defibrator, the pulp suspension was injected into a Paul screener containing different mesh screens (16, 30, 50, 100, 200 mesh), and the pulp was screened in a ladder-like manner, the pulp suspension that did not pass through the screen was named as the retained (R) pulp, and the pulp suspension that passed through the screen was named as the passed (P) pulp; six groups of pulp were obtained according to the retained (R) and passed (P) pulp, namely R16, R30, R50, R100, R200 and P200; all the retained pulp that did not pass through the 100 mesh screen was mixed, i.e. R16, R30, R50 and R100 were mixed to obtain long fiber fraction pulp, and all the retained pulp that passed through the 100 mesh screen was mixed, i.e. R200 and P200 fibers were uniformly mixed to obtain short fiber fraction pulp, the long fiber fraction pulp and the short fiber fraction pulp were concentrated to a mass concentration of 24% and dispersed into pulp blocks smaller than 5mmx5mm for storage in a polyethylene ziplock bag for water balance;

[0040] Choline chloride and acetic acid were stirred and heated at 60℃ in a 1:3 molar ratio until a transparent and clear liquid was formed, obtaining a deep eutectic solvent. 15 g of the deep eutectic solvent was preheated to 50℃ in a thermostatic water bath, and then 1 g of long fiber fraction pulp was mixed with the deep eutectic solvent in a self-sealing bag for uniform reaction. The reaction time was 20 min, the solid-liquid ratio was 1:10, and the self-sealing bag was kneaded every 5 min during the reaction. The reacted pulp was washed to neutral, concentrated to a mass concentration of 21%, and dispersed into pulp blocks smaller than 5 mm x 5 mm, and air-dried to a mass concentration of 95%, obtaining high-quality bamboo dissolving pulp; the washing liquid was recovered, concentrated and purified for reuse.

[0041] Table 2 shows the performance comparison between the original pulp prepared in Example 2, the long fiber obtained by separate screening, the high-quality bamboo dissolving pulp obtained by screening and deep eutectic solvent treatment, and the bamboo dissolving pulp treated by deep eutectic solvent alone.

[0042] Table 2 Performance comparison between different pulps in Example 2

[0043]

[0044] Example 3

[0045] A method for preparing high-quality bamboo dissolving pulp by pulp screening and deep eutectic solvent treatment, comprising the following steps:

[0046] 10 g of bamboo dissolving pulp prepared by cold alkali extraction method was soaked in deionized water for 4 h, and the pulp was dispersed into a 1.5% concentration pulp suspension by a fiber defibrator. The pulp suspension was injected into a Paul screen instrument containing different mesh screens (16, 30, 50, 100, 200 mesh), and was screened in a ladder-like manner. The pulp suspension that did not pass through the screen was named as the retained (R) pulp, and the pulp suspension that passed through the screen was named as the passed (P) pulp. Six groups of pulp were obtained according to the retained (R) and passed (P) pulp, namely R16, R30, R50, R100, R200 and P200. The retained pulp that did not pass through the 100 mesh screen was mixed, i.e. R16, R30, R50 and R100 were mixed to obtain long fiber fraction pulp. The retained pulp that passed through the 100 mesh screen was mixed, i.e. R200 and P200 fibers were uniformly mixed to obtain short fiber fraction pulp. The long fiber fraction pulp and the short fiber fraction pulp were concentrated to a mass concentration of 23%, and were dispersed into pulp blocks smaller than 5 mm x 5 mm and stored in a polyethylene self-sealing bag for water balance;

[0047] Choline chloride and oxalic acid were stirred and heated at 60℃ according to a 1:1 molar ratio until a transparent and clear liquid was formed, obtaining a deep eutectic solvent, 15 g of the deep eutectic solvent was preheated to 50℃ in a thermostatic water bath, then 1 g of long fiber fraction pulp was mixed with the deep eutectic solvent in a self-sealing bag for uniform reaction, the reaction time was 15 min, the solid-liquid ratio of the reaction was 1:15, and the self-sealing bag was kneaded every 5 min during the reaction, obtaining the reacted pulp, the reacted pulp was washed to neutral, concentrated to a mass concentration of 21%, and dispersed into pulp blocks smaller than 5 mm x 5 mm, air-dried to a mass concentration of 94%, obtaining high-quality bamboo dissolving pulp; the washing liquid was recovered, concentrated and purified for reuse.

[0048] Table 3 shows the performance comparison between the original pulp prepared in Example 3, the long fiber obtained by separate screening, the high-quality bamboo dissolving pulp obtained by screening and deep eutectic solvent treatment, and the bamboo dissolving pulp treated by deep eutectic solvent alone.

[0049]

[0050] Example 4

[0051] A method for preparing high-quality bamboo dissolving pulp by pulp screening and deep eutectic solvent treatment, comprising the following steps:

[0052] 10 g of bamboo dissolving pulp prepared by cold alkali extraction method was soaked in deionized water for 4 h, and the pulp was dispersed into a 2.0% concentration pulp suspension by a fiber defibrator, then the pulp suspension was injected into a Paul screen instrument containing different mesh screens (16, 30, 50, 100, 200 mesh), and the screening was carried out in a ladder-like manner, the pulp suspension that did not pass was named as the retention (R) pulp, and the pulp suspension that passed was named as the pass (P) pulp; six groups of pulp were obtained according to the retention (R) and pass (P) conditions, i.e. R16, R30, R50, R100, R200 and P200; all the retention pulps that did not pass through the 100 mesh screen were mixed, i.e. R16, R30, R50 and R100 were mixed to obtain long fiber fraction pulp, and all the retention pulps that passed through the 100 mesh screen were mixed, i.e. R200 and P200 fibers were uniformly mixed to obtain short fiber fraction pulp, the long fiber fraction pulp and the short fiber fraction pulp were concentrated to a mass concentration of 23% and dispersed into pulp blocks smaller than 5 mm x 5 mm for storage in a polyethylene self-sealing bag for water balance;

[0053] Choline chloride and lactic acid were stirred and heated at 60°C until a clear liquid was formed, obtaining a deep eutectic solvent. 10 g of the deep eutectic solvent was preheated to 50°C in a thermostatic water bath, then 1 g of long fiber fraction pulp was mixed with the deep eutectic solvent in a ziplock bag and reacted uniformly, the reaction time was 30 min, the solid-liquid ratio of the reaction was 1:10, and the ziplock bag was kneaded every 5 min during the reaction. The reacted pulp was washed to neutral, concentrated to a mass concentration of 22%, and dispersed into pulp blocks smaller than 5 mm x 5 mm, and air-dried to a mass concentration of 95%, obtaining high-quality bamboo dissolving pulp; the washing liquid was recovered, concentrated and purified for reuse.

[0054] Table 4 shows the performance comparison between the original pulp prepared in Example 4, the long fiber obtained by separate screening, the high-quality bamboo dissolving pulp obtained by screening and deep eutectic solvent treatment, and the bamboo dissolving pulp treated by deep eutectic solvent alone. Table 4 Performance comparison between different pulps in Example 4

[0055]

[0056]

[0057] Example 5

[0058] A method for preparing high-quality bamboo dissolving pulp by pulp screening and deep eutectic solvent treatment, comprising the following steps:

[0059] 10 g of pre-hydrolyzed kraft bamboo dissolving pulp was soaked in deionized water for 4 h, and the pulp was dispersed into a 1.5% concentration pulp suspension by a fiber defibrator. The pulp suspension was injected into a Paul screen instrument containing different mesh screens (16, 30, 50, 100, 200 mesh), and the pulp suspension was screened in a stepwise manner. After screening, the pulp suspension that did not pass was named as the retention (R) pulp, and the pulp suspension that passed was named as the pass (P) pulp. According to the retention (R) and pass (P) conditions, six groups of pulp were obtained, namely R16, R30, R50, R100, R200 and P200. All the retention pulps that did not pass through the 100 mesh screen were mixed, i.e. R16, R30, R50 and R100 were mixed to obtain long fiber fraction pulp. All the retention pulps that passed through the 100 mesh screen were mixed, i.e. R200 and P200 fibers were uniformly mixed to obtain short fiber fraction pulp. The long fiber fraction pulp and the short fiber fraction pulp were concentrated to a mass concentration of 22%, and dispersed into pulp blocks smaller than 5 mm x 5 mm and stored in polyethylene ziplock bags for water balance.

[0060] Choline chloride and oxalic acid were stirred and heated at 60℃ according to a 1:1 molar ratio until a transparent and clear liquid was formed, obtaining a deep eutectic solvent, 15g of the deep eutectic solvent was preheated to 40℃ in a thermostatic water bath, then 1g of long fiber fraction pulp was mixed with the deep eutectic solvent in a self-sealing bag for uniform reaction, the reaction time was 20min, the solid-liquid ratio of the reaction was 1:10, and the self-sealing bag was kneaded every 5min during the reaction, obtaining the reacted pulp, the reacted pulp was washed to neutral, concentrated to a mass concentration of 22%, and dispersed into pulp blocks smaller than 5mmx5mm, air-dried to a mass concentration of 95%, obtaining high-quality bamboo dissolving pulp; the washing liquid was recovered, concentrated and purified for reuse

[0061] Table 5 shows the performance comparison between the original pulp prepared in Example 5, the long fiber obtained by separate screening, the high-quality bamboo dissolving pulp obtained by screening and deep eutectic solvent treatment, and the bamboo dissolving pulp treated by deep eutectic solvent alone.

[0062] Table 5 Performance comparison between different pulps in Example 5

[0063]

[0064] Example 6

[0065] A method for preparing high-quality bamboo dissolving pulp by pulp screening and deep eutectic solvent treatment, comprising the following steps:

[0066] 10g of bamboo dissolving pulp prepared by cold alkali extraction method was soaked in deionized water for 4h, and the pulp was dispersed into a 2.0% concentration pulp suspension by a fiber defibrator, the pulp suspension was injected into a Paul screener containing different mesh screens (16, 30, 50, 100, 200 mesh), and the screening was carried out in a stepwise and downward flow, the pulp suspension that did not pass through was named as the retention (R) pulp, and the pulp suspension that passed through was named as the pass (P) pulp; six groups of pulp were obtained according to the retention (R) and pass (P) conditions, i.e. R16, R30, R50, R100, R200 and P200; all the retention pulps that did not pass through the 100 mesh screen were mixed, i.e. R16, R30, R50 and R100 were mixed to obtain long fiber fraction pulp, and all the retention pulps that passed through the 100 mesh screen were mixed, i.e. R200 and P200 fibers were uniformly mixed to obtain short fiber fraction pulp, the long fiber fraction pulp and the short fiber fraction pulp were concentrated to a mass concentration of 24% and dispersed into pulp blocks smaller than 5mmx5mm for storage in a polyethylene self-sealing bag for water balance;

[0067] Choline chloride and lactic acid are stirred and heated at 60℃ according to a molar ratio of 1:5 until a transparent and clear liquid is formed, obtaining a deep eutectic solvent, 15g of the deep eutectic solvent is preheated to 50℃ in a thermostatic water bath, then 1g of long fiber fraction pulp is mixed with the deep eutectic solvent in a ziplock bag and uniformly reacted, the reaction time is 30min, the solid-liquid ratio of the reaction is 1:10, and the ziplock bag is kneaded every 5min during the reaction, obtaining the reacted pulp, the reacted pulp is washed to neutral, concentrated to a mass concentration of 22% and dispersed into pulp blocks smaller than 5mmx5mm, air dried to a mass concentration of 94%, obtaining high-quality bamboo dissolving pulp; the washing liquid is recovered, concentrated and purified for reuse.

[0068] Table 6 shows the performance comparison between the original pulp prepared in Example 6, the long fiber obtained by separate screening, the high-quality bamboo dissolving pulp obtained by screening and deep eutectic solvent treatment, and the bamboo dissolving pulp treated by deep eutectic solvent alone.

[0069] Table 6 shows the performance comparison between the original pulp prepared in Example 6, the long fiber obtained by separate screening, the high-quality bamboo dissolving pulp obtained by screening and deep eutectic solvent treatment, and the bamboo dissolving pulp treated by deep eutectic solvent alone.

[0070]

[0071] Specifically, in other specific embodiments of the present application, other non-wood raw materials such as cotton, hemp, reed, and grass that can be used to prepare dissolving pulp can also be used to achieve the improvement of the reaction performance of the dissolving pulp.

[0072] As can be seen from the data in the table, screening can group fibers with different structures and properties, and has a certain purification effect on the long fiber fraction. During the subsequent reaction of the long fiber fraction with the deep eutectic solvent, the availability and utilization of the long fiber fraction to the deep eutectic solvent are improved by eliminating the ineffective wrapping and adsorption of loose small components to the solvent. During the reaction with the deep eutectic solvent, the quality of the long fiber fraction is further improved (purity, viscosity, and reaction performance). Compared with the reaction of the un-screened original pulp with the deep eutectic solvent, the reaction efficiency of the long fiber fraction with the deep eutectic solvent is more uniform and efficient, and the quality of the final dissolving pulp product is more excellent.

[0073] The above content only illustrates the technical idea of the present application and cannot limit the protection scope of the present application. Any modification made according to the technical idea of the present application on the basis of the technical solution falls within the protection scope of the claims of the present application.

Claims

1. A method for preparing high-quality bamboo dissolving pulp by slurry screening and eutectic solvent treatment, characterized in that, Includes the following steps: S1: After dispersing the bamboo dissolving pulp, a pulp suspension is obtained; The slurry suspension is injected into a sieving instrument containing sieves of different mesh sizes for sieving. After each sieving, the slurry suspension that does not pass through is named the retained slurry, and the slurry suspension that passes through is named the passed slurry. All the retained pulp that did not pass through the target mesh pulp slab was mixed to obtain long fiber grade pulp; all the pulp that passed through the target mesh pulp slab was mixed to obtain short fiber grade pulp; the long fiber grade pulp and the short fiber pulp were concentrated and dispersed respectively to obtain long fiber grade pulp blocks and short fiber grade pulp blocks. S2: The long fiber grade pulp block is mixed with a low eutectic solvent to react and obtain the reacted pulp. The reacted pulp is washed, concentrated and dispersed, and air-dried to obtain high-quality bamboo dissolving pulp. In S1, the bamboo dissolving pulp is obtained by pre-hydrolyzing sulfate or cold alkali extraction. The α-cellulose mass fraction of the bamboo dissolving pulp is 85%~92%, the viscosity is 600~850mL / g, and the Fock reactivity is less than 50%. When the pulp suspension is sieved using a sieve, the mass of bamboo dissolving pulp sieved each time is not less than 10g. The mass concentration of the pulp suspension is 0.5%~2%. In S1, the screening instrument is a Paul sieve; the mesh sizes of the different sieve plates configured in the screening instrument are 16 mesh, 30 mesh, 50 mesh, 100 mesh and 200 mesh respectively; the target mesh size is 100 mesh; The slurry suspension is sequentially sieved through sieves with 16-mesh, 30-mesh, 50-mesh, 100-mesh, and 200-mesh sieves. All slurry that fails to pass through the 100-mesh sieve is then mixed to obtain long-fiber grade slurry, with a yield of 80%-95%; the yield of short-fiber grade slurry is 5%-20%. In S2, the method for preparing the eutectic solvent is as follows: after mixing the hydrogen bond acceptor and the hydrogen bond donor, the mixture is heated and stirred until a transparent and clear liquid is formed, thus obtaining the eutectic solvent. The hydrogen bond acceptor is choline chloride; the hydrogen bond donor is oxalic acid, lactic acid, formic acid or acetic acid; when the hydrogen bond donor is oxalic acid, formic acid or acetic acid, the molar ratio of hydrogen bond acceptor to hydrogen bond donor is (1:1) to (1:3); when the hydrogen bond donor is lactic acid, the molar ratio of hydrogen bond acceptor to hydrogen bond donor is (1:5) to (1:10). Before mixing long fiber grade pulp blocks with eutectic solvent, the eutectic solvent needs to be pretreated. The pretreatment process is as follows: the eutectic solvent is heated to 40~60℃ in a water bath. The reaction time is 15-30 min; the ratio of the long fiber grade pulp block to the eutectic solvent is (1:5) to (1:15); the mass concentration of the pulp after the reaction is 20%-25% after concentration and dispersion, and the mass concentration after air drying is 90%-97%.

2. The method for preparing high-quality bamboo dissolving pulp by pulp screening and eutectic solvent treatment according to claim 1, characterized in that, In S1, during screening, the screening time is 15 min to 30 min, and the screening water flow rate is 8 L / min to 13 L / min.

3. The method for preparing high-quality bamboo dissolving pulp by slurry screening and eutectic solvent treatment according to claim 1, characterized in that, In S2, the slurry after the reaction is washed until it is neutral, and the resulting washing liquid is concentrated, purified and recovered by rotary evaporation.

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