Method and solvent for promoting dissolution of cellulose and application of solvent in preparation of high-strength regenerated cellulose fiber

Abstract

The invention belongs to the technical field of cellulose dissolution, and particularly relates to a method and a solvent for promoting cellulose dissolution and application of the solvent in preparation of high-strength regenerated cellulose fibers. The invention finds for the first time that when a common solvent system of silicon dioxide and cellulose is subjected to ball-milling mixing, the obtained solvent composition not only improves the solubility of the cellulose, but also can obtain a stable spinning solution after dissolving the cellulose, and improves the strength of the regenerated cellulose fiber prepared from the solvent composition.

Description

Technical Field

[0001] The invention belongs to the technical field of cellulose dissolution, and particularly relates to a method and solvent for promoting cellulose dissolution and application thereof in preparing high-strength regenerated cellulose fibers. Background Art

[0002] In recent years, biomass resources have garnered widespread attention due to their advantages, including reduced carbon emissions, environmental friendliness, energy conservation and emission reduction, and renewable raw materials. Cellulose is the world's most abundant natural polymer, derived from a wide range of sources, including cotton, wood, and straw. As an environmentally friendly material, it boasts advantages such as low cost, renewability, biodegradability, and good biocompatibility. Cellulose can be dissolved and regenerated to produce regenerated cellulose materials in various forms, including fibers, films, and microbeads. These materials are widely used in the textile, packaging, and biomedical industries, offering promise as a sustainable alternative to plastics.

[0003] It is known that cellulose has a multi-layered structure. The inability of cellulose to melt makes it difficult to process cellulose through heat treatment. At the same time, the hydrogen bond network inside and outside the molecule and the highly ordered crystal structure make cellulose insoluble in water and conventional organic solvents. Therefore, finding efficient cellulose solvents and promoting the effective utilization of cellulose are currently a major focus of cellulose research.

[0004] Over the past few decades, many cellulose solvent systems have been developed, as described below. Representative examples include inorganic acids, N,N-dimethylacetamide / lithium chloride (DMAc / LiCl), N-methylmorpholine-N-oxide monohydrate (NMMO·H2O), deep eutectic solvents (DES), and ionic liquids (ILs). Among them, regenerated cellulose fibers produced using N-methylmorpholine-N-oxide monohydrate as a raw material, namely Lyocell fibers, have achieved rapid industrial development. However, all of the above solvent systems have various disadvantages, such as high cost, high energy consumption, and high toxicity.

[0005] Chinese patent 200310111566.3 discloses a solvent composition for dissolving cellulose - sodium hydroxide / urea aqueous solution. The solvent system is green and efficient, and the alkali and urea used in the system are low-cost, showing the industrial prospects of cellulose solution processing. However, the solvent system has defects such as harsh dissolution conditions, low solubility, poor spinning solution stability, high coagulation bath cost, and low finished fiber strength. To address this defect, the existing technology (Cellulose (2021) 28: 1267–1281) often adds zinc oxide to the alkali / urea / water low-temperature dissolution system. Although this method can improve the solubility of cellulose in the solvent and the stability of the cellulose solution, zinc oxide is toxic and will cause pollution to the environment (Comparative Biochemistry and Physiology, Part C 273 (2023) 109720), and fails to significantly improve the performance of regenerated fibers and cannot meet industrial requirements.

[0006] From the above analysis, it can be seen that there is an urgent need to develop a new solvent composition in the alkali / urea / water low-temperature dissolution system. On the one hand, it can improve the solubility of cellulose in dissolution, maintain the green and efficient nature of the alkali-urea dissolution system, and reduce its coagulation bath cost; on the other hand, it can also significantly improve the strength of regenerated cellulose fibers. This is of great significance for further promoting the efficient dissolution and industrial production of cellulose.

[0007] Silica is widely present in nature and is widely used in environmental, rubber, catalytic, and biomedical applications due to its superior stability, reinforcement, and thickening properties. Previous studies have demonstrated excellent results in improving the flame retardancy, water resistance, and mechanical strength of cellulose-based composites. However, no studies have examined its effectiveness in improving the solubility of alkali / urea systems or reducing coagulation bath costs. Summary of the Invention

[0008] To address these deficiencies, the present invention provides a method for promoting cellulose dissolution, a solvent composition, and its use in producing high-strength regenerated cellulose fibers. This solvent not only increases cellulose solubility but also produces a stable spinning solution after dissolving the cellulose. It also improves the strength of the regenerated cellulose fibers produced therefrom (the solubility of 10W molecular weight cellulose can be increased by 60.1%, while the breaking strength of the regenerated fiber at maximum solubility is increased from 270.2 MPa to 547.6 MPa, and the elongation is increased from 12.8% to 19.1%), making it easy to industrialize.

[0009] The technical solution of the present invention:

[0010] In a first aspect, the present invention provides a method for increasing the solubility of cellulose, comprising adding hydrophilic silica to a solvent for dissolving cellulose.

[0011] Furthermore, the solvent is an alkali / urea / water mixed system.

[0012] Furthermore, the alkali / urea / water mixed system contains 5-16% by mass of alkali and 10-20% by mass of urea.

[0013] Furthermore, the base is an inorganic base.

[0014] Furthermore, the inorganic base includes but is not limited to lithium hydroxide and sodium hydroxide.

[0015] Furthermore, the amount of hydrophilic silica added is 0.2-1.25% by mass of the solvent.

[0016] Furthermore, the particle size of the hydrophilic silica is 10 to 40 nm.

[0017] In a second aspect, the present invention provides a solvent for dissolving cellulose, wherein the solvent is an alkali / urea / water mixed system containing hydrophilic silica.

[0018] Furthermore, the mass percentage of hydrophilic silica in the solvent is 0.2-1.25%, the mass percentage of alkali is 5-16%, and the mass percentage of urea is 10-20%.

[0019] Furthermore, the base is an inorganic base.

[0020] Furthermore, the inorganic base includes lithium hydroxide and sodium hydroxide.

[0021] Furthermore, the particle size of the hydrophilic silica is 10 to 40 nm.

[0022] In a third aspect, the present invention provides a method for preparing a solvent for dissolving cellulose as described herein, comprising mixing hydrophilic silica, alkali, urea and water in a desired mass fraction, and then ball milling to obtain the solvent.

[0023] Further, the ball milling includes ball milling at 100 to 580 rpm for 10 to 60 minutes;

[0024] Furthermore, the solvent is stored below 0°C for future use.

[0025] Without being bound by theory, it is believed that ball milling can overcome the problem of silica particles existing in the form of large aggregates in solution due to the nano-agglomeration effect. Compared with simple mechanical stirring, the strong shear and collision effects of high-energy ball milling can destroy the aggregates, making the silica more evenly and stably dispersed in the solvent, thereby promoting the dissolution of cellulose.

[0026] In a fourth aspect, the present invention provides a method for preparing high-strength regenerated cellulose fiber, comprising the following steps:

[0027] (1) preparing a solvent for dissolving cellulose as described herein: mixing a desired mass fraction of hydrophilic silica, an alkali, urea, and water, and ball milling the mixture to obtain the solvent;

[0028] (2) dispersing cellulose pulp in the solvent and stirring to dissolve the cellulose pulp to obtain a cellulose solution;

[0029] (3) The cellulose solution obtained in step (2) is wet-spinned to produce regenerated cellulose fibers.

[0030] Furthermore, the solvent prepared in step (1) is stored below 0°C for future use.

[0031] Furthermore, the molecular weight of the cellulose pulp in step (2) is less than 15W.

[0032] Furthermore, the dissolution in step (2) is carried out at 0-5°C.

[0033] Furthermore, step (2) further comprises centrifuging after stirring and dissolving to obtain a completely transparent cellulose solution in the upper layer.

[0034] Furthermore, the wet spinning in step (3) uses a phytic acid aqueous solution or a sulfuric acid / sodium sulfate aqueous solution as a coagulation bath.

[0035] Furthermore, step (3) also includes washing and drying the regenerated cellulose fibers obtained by wet spinning.

[0036] In a fifth aspect, the present invention provides a high-strength regenerated cellulose fiber produced by the method for producing high-strength regenerated cellulose fiber described herein.

[0037] Advantageous Effects of the Invention

[0038] (1) The dissolution system adopted in the cellulose dissolution method of the present invention is a mixed system of silicon dioxide, inorganic alkali (lithium hydroxide, sodium hydroxide), and urea. Compared with the previous technology of adding zinc oxide, it has the advantages of being green, environmentally friendly, and low cost, and is conducive to industrial production.

[0039] (2) Compared with the conventional technique of adding zinc oxide, the dissolution method of the present invention can significantly improve the solubility of the cellulose solution. The dissolution method of the present invention can increase the solubility of cellulose by 60.1%.

[0040] (3) The rheological properties of the cellulose solution obtained by the dissolution method of the present invention are improved, and the solution viscosity increases from 5 Pa.s to 10-20 Pa.s. The slight increase in viscosity is beneficial to the formation and stretching of the fiber in the subsequent wet spinning.

[0041] (4) The cellulose solution obtained by the dissolution method of the present invention can be used as a stable spinning solution for wet spinning to prepare regenerated cellulose fibers.

[0042] (5) The strength of the regenerated cellulose fiber prepared by wet spinning the cellulose solution obtained by the dissolution method of the present invention is significantly improved, such as the breaking strength is increased from 270.2 MPa to 547.6 MPa, and the elongation is increased from 12.8% to 19.1%. By using a low-cost sulfuric acid / sodium sulfate coagulation bath, the breaking strength of the silica / sodium hydroxide / urea regenerated cellulose fiber can reach 404 MPa and the elongation at break can reach 21%.

[0043] (6) When the cellulose solution obtained by the dissolution method of the present invention is used for wet spinning, the range of choices for the coagulation bath is wider, and the cost of the coagulation solution can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. A person of ordinary skill in the art can derive other relevant drawings based on these drawings without inventive effort.

[0045] Figure 1 Schematic diagram of the mechanism of the present invention.

[0046] Figure 2 This is a polarizing microscope image of the cellulose solution obtained by high-speed stirring of cellulose in Example 1 of the present invention.

[0047] Figure 3 This is a polarizing microscope image of the cellulose solution obtained by high-speed stirring of cellulose in Example 2 of the present invention.

[0048] Figure 4 This is a photograph of the regenerated cellulose fiber obtained in Example 14 of the present invention.

[0049] Figure 5 It is the solubility of cellulose in the solvent obtained in Examples 1-9 of the present invention.

[0050] Figure 6It is the solubility of cellulose in the solvent obtained in Examples 10-12 of the present invention.

[0051] Figure 7 It is the gel temperature of the cellulose solution obtained in Examples 1-3 of the present invention.

[0052] Figure 8 These are the stress-strain curves of the regenerated cellulose fibers obtained in Examples 13-18 of the present invention.

[0053] Figure 9 These are the stress-strain curves of the regenerated cellulose fibers obtained in Examples 19-25 of the present invention. DETAILED DESCRIPTION

[0054] The present invention screened a variety of fillers and finally found that when silica is ball-milled with an alkali / urea system (which is a commonly used solvent system for cellulose), a solvent system can be produced that can both improve the solubility of cellulose and obtain a stable spinning solution, and can also improve the strength of the regenerated cellulose fiber prepared therefrom.

[0055] Without being bound by theory, it is believed that the mechanism of the present invention includes (as shown in the accompanying Figure 1 shown):

[0056] (1) Silanol bonds combine with cellulose hydroxyl groups to form new hydrogen bonds, destroying the original hydrogen bond network and promoting cellulose dissolution;

[0057] (2) Silica converts the free water in the system into bound water, allowing the solvent to well infiltrate the cellulose and promote the dissolution of cellulose;

[0058] (3) Silica can accumulate around cellulose to prevent dissolved cellulose molecules from reaggregating.

[0059] The present invention is further described below with reference to specific examples, which, however, are not intended to limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0060] Example 1

[0061] 100g of 8wt% lithium hydroxide / 15wt% urea mixed aqueous solution was ground by ball milling (580rpm, 20min) and pre-cooled to below 0℃ to prepare a cellulose solvent. Then, 5g of cellulose pulp (molecular weight 10W) was dispersed in the cellulose solvent, stirred thoroughly in an ice water bath (5℃) for 4min, and centrifuged (8000rpm) for 5min to obtain a completely transparent cellulose solution on the upper layer. No obvious undissolved cellulose microfibrils were found under a polarizing microscope. Figure 2The cellulose solution was neutralized with 2 mol / L sulfuric acid, and the precipitate was washed three times with ethanol and water respectively, dried under vacuum and then weighed. The solubility of cellulose in the solvent was measured to be 3.48 wt%.

[0062] Example 2

[0063] 100 g of a mixed aqueous solution of 0.25 wt% 12 nm hydrophilic fumed silica / 8 wt% lithium hydroxide / 15 wt% urea was ball milled (580 rpm, 20 min) and pre-cooled to below 0°C to prepare a cellulose solvent. Then, 6 g of cellulose pulp (molecular weight 10W) was dispersed in the cellulose solvent, stirred thoroughly in an ice-water bath (5°C) for 4 min, and centrifuged (8000 rpm) for 5 min to obtain a completely transparent upper layer of cellulose solution. No obvious undissolved cellulose microfibrils were found under a polarizing microscope. Figure 3 The cellulose solution was neutralized with 2 mol / L sulfuric acid, and the precipitate was washed three times with ethanol and water respectively, dried under vacuum and then weighed. The solubility of cellulose in the solvent was measured to be 5.28 wt%.

[0064] Example 3

[0065] Other conditions were the same as those in Example 2, except that the mass fraction of silicon dioxide was 0.5 wt%, 0.75 wt%, 1 wt%, and 1.25 wt%. The concentrations of the prepared viscous cellulose solutions were 5.34 wt%, 5.51 wt%, 5.57 wt%, 5.40 wt%, and 5.57 wt%.

[0066] Example 4

[0067] A cellulose solvent was prepared by ball milling 100g of a 0.25wt% 30nm hydrophilic fumed silica / 8wt% lithium hydroxide / 15wt% urea aqueous solution (580rpm, 20min) and pre-cooling to below 0°C. Six grams of cellulose pulp (molecular weight 10W) was then dispersed in the cellulose solvent, stirred thoroughly in an ice-water bath (5°C) for 4min, and centrifuged (8000rpm) for 5min to obtain a completely transparent upper layer of cellulose solution. This cellulose solution was neutralized with 2mol / L sulfuric acid, and the precipitate was washed three times with ethanol and water, respectively, dried under vacuum, and weighed. The solubility of cellulose in the solvent was measured to be 5.20wt%.

[0068] Example 5

[0069] Other conditions were the same as those in Example 4, except that the mass fraction of silicon dioxide was 0.5 wt%, 0.75 wt%, 1 wt%, and 1.25 wt%. The concentrations of the prepared viscous cellulose solutions were 5.32 wt%, 5.54 wt%, 5.49 wt%, and 5.19 wt%.

[0070] Example 6

[0071] A cellulose solvent was prepared by ball milling 100g of a 0.25wt% 15nm hydrophilic silica / 8wt% lithium hydroxide / 15wt% urea aqueous solution (580rpm, 20min) and pre-cooling to below 0°C. Six grams of cellulose pulp (molecular weight 10W) was then dispersed in the cellulose solvent, stirred thoroughly in an ice-water bath (5°C) for 4min, and centrifuged (8000rpm) for 5min to obtain a completely transparent upper layer of cellulose solution. This cellulose solution was neutralized with 2mol / L sulfuric acid, and the precipitate was washed three times with ethanol and then water, dried under vacuum, and weighed. The solubility of cellulose in the solvent was measured to be 5.12wt%.

[0072] Example 7

[0073] Other conditions were the same as those in Example 6, except that the mass fraction of silicon dioxide was 0.5 wt%, 0.75 wt%, 1 wt%, and 1.25 wt%. The concentrations of the prepared viscous cellulose solutions were 5.12 wt%, 5.16 wt%, 5.21 wt%, 5.22 wt%, and 4.43 wt%.

[0074] Example 8

[0075] A cellulose solvent was prepared by ball milling 100g of a 0.25wt% 30nm hydrophilic silica / 8wt% lithium hydroxide / 15wt% urea aqueous solution (580rpm, 20min) and pre-cooling to below 0°C. Six grams of cellulose pulp (molecular weight 10W) was then dispersed in the cellulose solvent, stirred thoroughly in an ice-water bath (5°C) for 4min, and centrifuged (8000rpm) for 5min to obtain a completely transparent upper layer of cellulose solution. This cellulose solution was neutralized with 2mol / L sulfuric acid, and the precipitate was washed three times with ethanol and water, respectively, dried under vacuum, and weighed. The solubility of cellulose in the solvent was measured to be 4.79wt%.

[0076] Example 9

[0077] Other conditions were the same as those in Example 8, except that the mass fraction of silicon dioxide was 0.5 wt%, 0.75 wt%, 1 wt%, and 1.25 wt%. The concentrations of the prepared viscous cellulose solutions were 5.16 wt%, 5.41 wt%, 5.49 wt%, and 5.15 wt%.

[0078] Example 10

[0079] A cellulose solvent was prepared by ball milling 100g of a 7wt% sodium hydroxide / 12wt% urea aqueous solution (580rpm, 20min) and pre-cooling to below 0°C. Four grams of cellulose pulp (molecular weight 10W) was then dispersed in the cellulose solvent, stirred thoroughly in an ice-water bath (5°C) for 4min, and centrifuged (8000rpm) for 5min to obtain a clear upper cellulose solution. Observation under a polarizing microscope revealed no obvious undissolved cellulose microfibrils. The cellulose solution was neutralized with 2mol / L sulfuric acid, and the precipitate was washed three times with ethanol and water, respectively, dried under vacuum, and weighed. The solubility of the cellulose in the solvent was determined to be 3.1wt%.

[0080] Example 11

[0081] A cellulose solvent was prepared by ball milling 100g of a 0.2wt% 12nm hydrophilic fumed silica / 7wt% sodium hydroxide / 12wt% urea aqueous solution (580rpm, 20min) and pre-cooling to below 0°C. Then, 5g of cellulose pulp (molecular weight 10W) was dispersed in the cellulose solvent, stirred thoroughly in an ice-water bath (5°C) for 4min, and centrifuged (8000rpm) for 5min to obtain a completely transparent upper layer of cellulose solution. This cellulose solution was neutralized with 2mol / L sulfuric acid, and the precipitate was washed three times with ethanol and water, respectively, dried under vacuum, and weighed. The solubility of cellulose in the solvent was measured to be 3.4wt%.

[0082] Example 12

[0083] Other conditions were the same as those in Example 11, except that the mass fraction of silicon dioxide was 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, and 0.7wt%, and the concentrations of the prepared viscous cellulose solutions were 3.9wt%, 4.5wt%, 4.2wt%, 4.0wt%, and 3.8wt%.

[0084] The concentrations of the cellulose solutions obtained in Examples 1-9 are summarized in the attached table. Figure 5 shown.

[0085] The concentrations of the cellulose solutions obtained in Examples 10-12 are summarized in the attached table. Figure 6 shown.

[0086] The gel temperatures of the cellulose solutions obtained in Examples 1-3 are summarized in the attached figure. Figure 7 shown.

[0087] By the attached Figure 5 、 6It is clear that cellulose solubility increases initially and then decreases with increasing silica mass fraction. When the solvent composition is 1 wt% 12 nm fumed silica, 8 wt% lithium hydroxide, and 15 wt% urea, the solubility of 10 W cellulose reaches a maximum of 5.57 wt%. At this point, the gel point of the solution remains unchanged. This is likely because the hydroxyl groups on the silica surface can form hydrogen bonds with those on the cellulose chains, disrupting the hydrogen bond network between cellulose molecules to a certain extent and making them easier to separate. Furthermore, silica, with its large surface area and surface activity, acts as a steric hindrance between cellulose chains, preventing them from reaggregating and improving their dispersion in the solution, thereby promoting dissolution. Furthermore, silica can convert free water in the system into bound water, which helps maintain the stability of the new hydrogen bond network. However, when the silica content reaches a certain level, the silica forms large aggregates, resulting in a decrease in surface area and a weakened interaction with cellulose, leading to a decrease in cellulose solubility. In addition, fumed silica has a strong ability to promote the dissolution of cellulose. This is because the surface of fumed silica contains a large number of hydroxyl groups, which are highly active. The number of hydroxyl groups on the surface of ordinary silica is relatively small, and due to its dense structure, some hydroxyl groups may be wrapped inside and difficult to participate in the reaction, resulting in lower activity than fumed silica.

[0088] By the attached Figure 7 It can be clearly seen that when a small amount of silica is added, the gel point of the cellulose solution can still be maintained above 33°C at maximum solubility. It is speculated that this is because silica has a large specific surface area and surface activity, which can act as a steric hindrance between cellulose molecular chains, preventing the cellulose molecular chains from re-aggregating, making the cellulose molecules better dispersed in the solution, thereby promoting dissolution. At the same time, silica can consume free water in the system, and the reduction of free water is conducive to maintaining the stability of the new hydrogen bond network. However, excessive silica will cause the solution viscosity to increase rapidly, restricting the movement of molecular chains, and thus reducing the stability of the solution.

[0089] Next, the application practice of preparing regenerated cellulose fiber from cellulose solution was carried out.

[0090] Example 13

[0091] 3.48 g of cellulose pulp was dispersed in the corresponding solvent described in Example 1. A 15 wt% aqueous phytic acid solution was used as a coagulation bath. Regenerated cellulose fibers were prepared using a simple spinning machine at room temperature. The fibers were rinsed with water and air-dried. An electronic tensile tester determined the fibers to have a breaking strength of 270.2 MPa and an elongation at break of 12.8%.

[0092] Example 14

[0093] 5.28g of cellulose pulp was dispersed in the corresponding solvent in Example 2, and a 15wt% phytic acid aqueous solution was used as a coagulation bath. Regenerated cellulose fibers were prepared using a simple spinning machine at room temperature, rinsed with water, and naturally dried. Figure 4 The breaking strength measured by an electronic tensile testing machine is 401.4 MPa and the breaking elongation is 25.7%.

[0094] Example 15

[0095] 5.34 g of cellulose pulp was dispersed in the solvent described in Example 2, except that the silica fraction was 0.5 wt%. A 15 wt% aqueous phytic acid solution was used as the coagulation bath. Regenerated cellulose fibers were prepared using a simple spinning machine at room temperature. The fibers were rinsed with water and air-dried. An electronic tensile testing machine revealed a breaking strength of 547.6 MPa and an elongation at break of 18.7%.

[0096] Example 16

[0097] 5.51 g of cellulose pulp was dispersed in the solvent described in Example 2, except that the silica fraction was 0.75 wt%. A 15 wt% aqueous phytic acid solution was used as the coagulation bath. Regenerated cellulose fibers were prepared using a simple spinning machine at room temperature. The fibers were rinsed with water and air-dried. An electronic tensile testing machine revealed a breaking strength of 410.6 MPa and an elongation at break of 13.8%.

[0098] Example 17

[0099] 5.57 g of cellulose pulp was dispersed in the solvent described in Example 2, except that the silica fraction was 1 wt %. A 15 wt % aqueous phytic acid solution was used as the coagulation bath. Regenerated cellulose fibers were prepared using a simple spinning machine at room temperature. The fibers were rinsed with water and air-dried. An electronic tensile testing machine revealed a breaking strength of 353.1 MPa and an elongation at break of 13.8%.

[0100] Example 18

[0101] 5.40 g of cellulose pulp was dispersed in the solvent described in Example 2, except that the silica fraction was 1.25 wt%. A 15 wt% aqueous phytic acid solution was used as the coagulation bath. Regenerated cellulose fibers were prepared using a simple spinning machine at room temperature. The fibers were rinsed with water and air-dried. An electronic tensile testing machine revealed a breaking strength of 293.1 MPa and an elongation at break of 12.6%.

[0102] Example 19

[0103] 3.1g of cellulose pulp was dispersed in the corresponding solvent described in Example 10 and coagulated using a 10wt% sulfuric acid / 12wt% sodium sulfate aqueous solution at room temperature using a simple spinning machine to produce regenerated cellulose fibers. The fibers were then rinsed with water and air-dried. An electronic tensile tester revealed a breaking strength of 313.7 MPa and an elongation at break of 12.4%.

[0104] Example 20

[0105] 3.4 g of cellulose pulp was dispersed in the corresponding solvent described in Example 11 and coagulated in a 10 wt% sulfuric acid / 12 wt% sodium sulfate aqueous solution at room temperature using a simple spinning machine to produce regenerated cellulose fibers. The fibers were then rinsed with water and air-dried. An electronic tensile tester revealed a breaking strength of 365.6 MPa and an elongation at break of 15.5%.

[0106] Example 21

[0107] 3.9 g of cellulose pulp was dispersed in the solvent described in Example 11, except that the silica fraction was 0.3 wt%. A 10 wt% sulfuric acid / 12 wt% sodium sulfate aqueous solution was used as the coagulation bath. Regenerated cellulose fibers were prepared using a simple spinning machine at room temperature. The fibers were then rinsed with water and air-dried. An electronic tensile tester revealed a breaking strength of 370.9 MPa and an elongation at break of 16.0%.

[0108] Example 22

[0109] 4.5 g of cellulose pulp was dispersed in the solvent described in Example 11, except that the silica fraction was 0.4 wt%. A 10 wt% sulfuric acid / 12 wt% sodium sulfate aqueous solution was used as the coagulation bath. Regenerated cellulose fibers were prepared using a simple spinning machine at room temperature. The fibers were then rinsed with water and air-dried. An electronic tensile tester revealed a breaking strength of 404.0 MPa and an elongation at break of 20.3%.

[0110] Example 23

[0111] 4.2 g of cellulose pulp was dispersed in the solvent described in Example 11, except that the silica fraction was 0.5 wt%. A 10 wt% sulfuric acid / 12 wt% sodium sulfate aqueous solution was used as the coagulation bath. Regenerated cellulose fibers were prepared using a simple spinning machine at room temperature. The fibers were then rinsed with water and air-dried. An electronic tensile tester revealed a breaking strength of 296.6 MPa and an elongation at break of 12.3%.

[0112] Example 24

[0113] 4.0 g of cellulose pulp was dispersed in the solvent described in Example 11, except that the silica fraction was 0.6 wt %. A 10 wt % sulfuric acid / 12 wt % sodium sulfate aqueous solution was used as the coagulation bath. Regenerated cellulose fibers were prepared using a simple spinning machine at room temperature. The fibers were then rinsed with water and air-dried. An electronic tensile tester revealed a breaking strength of 324.3 MPa and an elongation at break of 15.4%.

[0114] Example 25

[0115] 3.8 g of cellulose pulp was dispersed in the solvent described in Example 11, except that the silica fraction was 0.7 wt%. A 10 wt% sulfuric acid / 12 wt% sodium sulfate aqueous solution was used as the coagulation bath. Regenerated cellulose fibers were prepared using a simple spinning machine at room temperature. The fibers were then rinsed with water and air-dried. An electronic tensile tester revealed a breaking strength of 309.1 MPa and an elongation at break of 13.0%.

[0116] The strength of the regenerated cellulose fibers obtained in Examples 13-18 is summarized in the attached figure. Figure 8 shown.

[0117] The strength of the regenerated cellulose fibers obtained in Examples 19-25 is summarized in the attached figure. Figure 9 shown.

[0118] By the attached Figure 8 、 9 It can be clearly seen that silica has an improving effect on the strength of regenerated cellulose fibers. When the solvent composition ratio is: 0.5wt% 12nm fumed silica, 8wt% lithium hydroxide, and 15wt% urea, and the coagulation bath is 15wt% phytic acid, the regenerated fiber strength can reach up to 547.6Mpa. This may be because silica has a high hardness and modulus. When a small amount of silica can be evenly dispersed in the regenerated cellulose fibers, it can withstand part of the externally applied load and reduce the stress borne by the cellulose matrix, thereby improving the overall strength and stiffness of the fibers. At the same time, silica is tightly bound to the cellulose molecular chains through hydrogen bonds, which can limit the movement of cellulose molecular segments. When the fibers are subjected to external forces, the relative sliding between the molecular chains is reduced, so that the fibers can better resist deformation and enhance the mechanical properties of the fibers. However, when silica is excessive, it is difficult to disperse evenly in the regenerated cellulose fibers, and agglomeration occurs. The agglomerates form stress concentration points inside the fibers, resulting in reduced fiber strength.

[0119] Next, the effect of ball milling on the gelation temperature of cellulose solution was studied.

[0120] Example 26

[0121] A 100g solution of 0.75wt% 30nm hydrophilic fumed silica / 8wt% lithium hydroxide / 15wt% urea was stirred magnetically for 30 minutes and pre-cooled to below 0°C to prepare a cellulose solvent. 5.54g of cellulose pulp (molecular weight 9W) was then dispersed in the cellulose solvent and thoroughly stirred in an ice-water bath (5°C) for 4 minutes. The mixture was centrifuged (8000 rpm) for 5 minutes. The cellulose solution remained unchanged compared to before centrifugation. The cellulose solution was poured out, and no micelles were found at the bottom of the centrifuge tube. Rheological testing of the resulting cellulose solution revealed a gel temperature of 23.44°C.

[0122] Example 27

[0123] 100 g of a mixed aqueous solution of 0.75 wt % 30 nm hydrophilic fumed silica / 8 wt % lithium hydroxide / 15 wt % urea was ball milled for 10 min, with other conditions being the same as those in Comparative Example 1, to prepare a cellulose solution having a gel temperature of 26.89° C.

[0124] Example 28

[0125] 100 g of a mixed aqueous solution of 0.75 wt % 30 nm hydrophilic fumed silica / 8 wt % lithium hydroxide / 15 wt % urea was ball milled for 20 min. Other conditions were the same as those in Comparative Example 1, and the obtained cellulose solution had a gel temperature of 34.07° C.

[0126] Example 29

[0127] 100 g of a mixed aqueous solution of 0.75 wt % 30 nm hydrophilic fumed silica / 8 wt % lithium hydroxide / 15 wt % urea was ball milled for 25 min. Other conditions were the same as those in Comparative Example 1, and the obtained cellulose solution had a gel temperature of 32.59° C.

[0128] From the comparison of Examples 26-29, it can be seen that when the same raw materials are used but the ball milling method is not adopted, although the obtained solvent system can improve the solubility, the solution obtained by dissolving the cellulose is not stable enough as a spinning solution.

[0129] It should be noted that the preferred embodiments of the present invention are given in the specification and drawings of the present invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described in this specification. These embodiments are not intended to be additional limitations on the content of the present invention. The purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive. In addition, the above-mentioned technical features can be combined with each other to form various embodiments not listed above, which are all considered to be within the scope of the description of the present invention. Furthermore, it is obvious to those skilled in the art that improvements or changes can be made based on the above description, and all such improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for improving the solubility of cellulose, characterized in that: The method comprises adding hydrophilic silica to a solvent for dissolving cellulose.

2. The method according to claim 1, characterized in that The solvent is an alkali / urea / water mixed system; Furthermore, the alkali / urea / water mixed system comprises 5-16% by mass of alkali and 10-20% by mass of urea; Further, the base is an inorganic base; Furthermore, the inorganic base includes lithium hydroxide and sodium hydroxide.

3. The method according to claim 1, characterized in that The amount of hydrophilic silica added is 0.2 to 1.25% by mass of the solvent; Furthermore, the particle size of the hydrophilic silica is 10 to 40 nm.

4. A solvent for dissolving cellulose, characterized in that The solvent is an alkali / urea / water mixed system containing hydrophilic silica.

5. The solvent according to claim 4, characterized in that The mass percentage of hydrophilic silica in the solvent is 0.2-1.25%, the mass percentage of alkali is 5-16%, and the mass percentage of urea is 10-20%; Further, the base is an inorganic base; Furthermore, the inorganic base includes lithium hydroxide and sodium hydroxide; Furthermore, the particle size of the hydrophilic silica is 10 to 40 nm.

6. A method for preparing a solvent for dissolving cellulose according to claim 4 or 5, characterized in that: The method comprises the steps of mixing hydrophilic silicon dioxide, alkali, urea and water, and then ball milling the mixture to obtain the solvent.

7. The preparation method according to claim 6, characterized in that The ball milling comprises ball milling at 100 to 580 rpm for 10 to 60 minutes; Furthermore, the solvent is stored below 0°C for future use.

8. A method for preparing high-strength regenerated cellulose fiber, characterized in that: The following steps are involved: (1) preparing a solvent for dissolving cellulose according to claim 6 or 7; (2) dispersing cellulose pulp in the solvent and stirring to dissolve the cellulose pulp to obtain a cellulose solution; (3) The cellulose solution obtained in step (2) is wet-spinned to produce regenerated cellulose fibers.

9. The preparation method according to claim 8, characterized in that The molecular weight of the cellulose pulp in step (2) is less than 15W. Furthermore, the dissolving in step (2) is carried out at 0-5°C; Furthermore, the wet spinning in step (3) uses a phytic acid aqueous solution, a phytic acid / sulfuric acid aqueous solution or a sulfuric acid / sodium sulfate aqueous solution as a coagulation bath.

10. A high-strength regenerated cellulose fiber produced by the preparation method according to claim 8 or 9.

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