CN114016141B

CN114016141B - Method for preparing fiber spinning solution by direct dissolution method

Info

Publication number: CN114016141B
Application number: CN202111501573.9A
Authority: CN
Inventors: 刘斌; 康宁; 戴家琛
Original assignee: Saideli Changzhou Fiber Co ltd
Current assignee: Saideli Changzhou Fiber Co ltd
Priority date: 2021-12-09
Filing date: 2021-12-09
Publication date: 2023-03-21
Anticipated expiration: 2041-12-09
Also published as: CN114016141A

Abstract

The invention provides a method for preparing a fiber spinning solution by a direct dissolution method. Compared with the prior art, the method adopts the direct mixing pretreatment of the low-concentration NMMO and the pulp, the molecular kinetic energy of the NMMO is lower at low temperature and low concentration, and the damage to the cellulose hydrogen bonds is small, so that the solution can not damage the hydrogen bonds between the cellulose after entering the cellulose amorphous region in the pulp and can not damage the hydrogen bonds of the crystalline region, thereby not causing the occurrence of the initial dissolution phenomenon and further avoiding the possibility of the occurrence of white cores; then, in the squeezing process, the NMMO solution continuously enters the cellulose through the action of external force, the continuous swelling effect is kept, the NMMO solution in cellulose molecules is fully dissolved, and the NMMO solution can be directly and fully dissolved in the high-concentration NMMO solution, so that the fiber spinning solution with high quality is obtained; moreover, the preparation method provided by the invention is simple, does not need special equipment and has low energy consumption.

Description

Method for preparing fiber spinning solution by direct dissolution method

Technical Field

The invention belongs to the technical field of fiber preparation, and particularly relates to a method for preparing a fiber spinning solution by a direct dissolving method.

Background

Cellulose is a natural high polymer with the largest reserve and the widest distribution on the earth, and is an inexhaustible renewable resource in the nature. Since cellulose fibers have advantages such as high strength, good dyeability, good spinning performance, and wide industrial applications, the market demand for cellulose fibers has been increasing worldwide in recent years.

The Lyocell fiber is prepared by using renewable resources such as cotton linters, trees, bamboos and the like as raw materials and NMMO as a solvent through dry-jet wet spinning, has a plurality of excellent performances of natural fiber and synthetic fiber, and is a green and environment-friendly cellulose fiber in the production process.

The Lyocell fiber has the advantages of high strength, good dyeing property, good spinning performance, wide industrial application and the like, and compared with viscose fiber, the Lyocell fiber has more outstanding performance, short process flow and green and pollution-free production process. Therefore, the worldwide market demand for Lyocell fibers has continued to increase in recent years.

At present, the preparation of Lyocell fiber spinning solution is mainly divided into a wet method route and a dry method route. The wet process route is that pulp and water are mixed to a certain concentration, then the mixture is squeezed to obtain a material with a certain dryness, then the material is crushed, 80 to 84 percent of NMMO, PG and other materials are added for premixing, and finally the mixture enters a reaction kettle to prepare a spinning solution; the dry process route is that pulp is firstly crushed, then 75-80% NMMO solution is added for premixing, and finally the mixture enters a reaction kettle to prepare spinning solution. However, both the dry process and the wet process require a dissolution process in a reaction kettle, and in the process, vacuum pumping is required to improve the concentration of NMMO, so that a large amount of energy consumption is required, and the equipment is expensive, fine and limited in capacity. In addition, in the existing dry swelling process, large pulp is directly mixed with concentrated NMMO, the mixing time is long, and the initial dissolution is easy to occur (swelling refers to a physical phenomenon that a high molecular compound expands along with the volume in the process of absorbing liquid; in the application, refers to the state that NMMO solution permeates into the pulp fibril molecules or the interior of the fibril molecules); in addition, the problem that the hydrogen bonds between cellulose molecules are destroyed and the hydrogen bonds are generated between the NMMO and the cellulose molecules in the NMMO swelling process due to the high temperature and the high concentration of the NMMO in the swelling process also exists, and the initial dissolution is also generated. The initial dissolution phenomenon can cause insufficient swelling, generate 'white core' particles which can not be completely dissolved, and influence the quality of glue solution. The pulp used in the current dry process therefore requires a comminution treatment, which, although improving the dissolving effect of the pulp with concentrated NMMO to some extent, also increases the production costs and the risk of dust flash.

Disclosure of Invention

In view of the above, the technical problem to be solved by the present invention is to provide a method for preparing a fiber spinning solution by a direct dissolution method, which does not need to be vacuumized during the dissolution process and has a good swelling effect.

The invention provides a method for preparing fiber spinning solution by a direct dissolution method, which comprises the following steps:

s1) mixing pulp with an NMMO solution with the mass concentration of 72-76% for swelling to obtain a mixed material;

s2) squeezing the mixed material to obtain a squeezed material;

s3) crushing the squeezed material to obtain a crushed material;

and S4) mixing and dissolving the crushed material and an NMMO solution with the mass concentration of 81-85% to obtain a fiber spinning solution.

Preferably, the material crushed in step S4) is mixed with 81-85% NMMO solution by mass concentration under normal pressure to dissolve.

Preferably, the temperature of mixing and swelling in the step S1) is 40-45 ℃; the mixing swelling time is 10-30 min.

Preferably, the mass concentration of the pulp in the mixed material is 4-5%.

Preferably, the temperature of the pressing in the step S2) is 40 to 65 ℃.

Preferably, the pulp is pressed in the step S2) until the dryness of the pulp is 35 to 45 percent.

Preferably, the crushing temperature in the step S3) is 40-50 ℃; the crushed grain diameter is 3-6 mm.

Preferably, the dissolving temperature in the step S4) is 90-110 ℃; the dissolving time is 20-60 min.

Preferably, the mass ratio of the crushed material to the NMMO solution with the mass concentration of 81-85% is 1: (2-3).

Preferably, the NMMO solution obtained after pressing in step S2) is used for mixing with pulp in step S1).

The invention provides a method for preparing fiber spinning solution by a direct dissolution method, which comprises the following steps: s1) mixing pulp with an NMMO solution with the mass concentration of 72-76% for swelling to obtain a mixed material; s2) squeezing the mixed material to obtain a squeezed material; s3) crushing the squeezed material to obtain a crushed material; and S4) mixing and dissolving the crushed material and an NMMO solution with the mass concentration of 81-85% to obtain a fiber spinning solution. Compared with the prior art, the method adopts the direct mixing pretreatment of the low-concentration NMMO and the pulp, the molecular kinetic energy of the NMMO is lower at low temperature and low concentration, and the damage to the cellulose hydrogen bonds is small, so that the solution can not damage the hydrogen bonds between the cellulose after entering the cellulose amorphous region in the pulp and can not damage the hydrogen bonds of the crystalline region, thereby not causing the occurrence of the initial dissolution phenomenon and further avoiding the possibility of the occurrence of white cores; then, in the squeezing process, the NMMO solution continuously enters the cellulose through the action of external force, the continuous swelling effect is kept, the NMMO solution in cellulose molecules is fully dissolved, and then the cellulose can be directly and fully dissolved in the high-concentration NMMO solution, so that in the dissolving process, the cellulose can be fully dissolved through the action of external force shearing without vacuumizing, and the high-quality fiber spinning solution is obtained; moreover, the preparation method provided by the invention is simple, does not need special equipment and has low energy consumption.

Drawings

FIG. 1 is a microscopic view of a cellulose dope obtained in example 1 of the present invention;

FIG. 2 is a microscopic image of the cellulose dope obtained in example 2 of the present invention;

FIG. 3 is a microscopic view of a cellulose dope obtained in example 3 of the present invention;

FIG. 4 is a microscopic image of the cellulose dope obtained in example 4 of the present invention;

FIG. 5 is a microscopic view of the cellulose dope obtained in comparative example 1 of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.

The invention provides a method for preparing fiber spinning solution by a direct dissolution method, which comprises the following steps: s1) mixing pulp with an NMMO solution with the mass concentration of 72-76% for swelling to obtain a mixed material; s2) squeezing the mixed material to obtain a squeezed material; s3) crushing the squeezed material to obtain a crushed material; and S4) mixing and dissolving the crushed material and an NMMO solution with the mass concentration of 81-85% to obtain a fiber spinning solution.

Mixing pulp with an NMMO solution with the mass concentration of 72-76% for swelling to obtain a mixed material; the pulp is preferably hardwood dissolving pulp and/or softwood dissolving pulp (but not limited to), more preferably kraft hardwood dissolving pulp and/or softwood sulfite dissolving pulp; the content of α -cellulose in the pulp is preferably 90% or more, more preferably 95% or more; the intrinsic viscosity of the pulp is preferably 400-480 ml/g, more preferably 420-460 ml/g, and even more preferably 440ml/g; the content of Fe in the pulp is preferably less than 5ppm; the water content of the pulp is preferably 5-10%, more preferably 6-8%, and still more preferably 7%; the mass concentration of the NMMO solution is preferably 72-75%, more preferably 72-74%, and still more preferably 72-73%; the mixing swelling temperature is preferably 40-45 ℃; the mixing swelling time is preferably 10-30 min; the mass concentration of the pulp in the mixed material is preferably 4-5%, more preferably 4.2-4.8%, still more preferably 4.4-4.6%, and most preferably 4.5-4.6%. The method adopts the low-concentration NMMO solution to swell the pulp on the premise of realizing no cellulose dissolution at a lower temperature, so that the fiber is filled with the NMMO solution, and a good basis is provided for subsequent dissolution; the invention adopts the low-concentration NMMO solution to swell the pulp, so that the mixed material can not generate the white core phenomenon, because after a large amount of low-concentration and low-temperature NMMO solution is mixed with the pulp, the NMMO solution can not damage hydrogen bonds among cellulose after entering a non-crystallization area of the cellulose in the pulp, especially can not damage the hydrogen bonds of the crystallization area, because NMMO molecules have lower molecular kinetic energy at lower temperature and lower concentration, the damage to the hydrogen bonds of the cellulose is small, the phenomenon of primary dissolution can not be caused, and the possibility of the occurrence of the white core is avoided.

Squeezing the mixed material to obtain a squeezed material; the squeezing temperature is preferably 40-65 ℃; the pressing is preferably carried out until the dryness of the pulp is 35 to 45 percent, more preferably 38 to 42 percent, and still more preferably 39 to 40 percent; the preparation of subsequent glue solution is influenced by the pressing dryness, because the more the pressing dryness is, the higher the cellulose content in the subsequent glue solution is, and the subsequent composition is influenced; the NMMO solution obtained after pressing is used for mixing with the pulp in the step S1) so as to realize recycling. The NMMO solution can continuously enter the interior of the fiber through external force action through squeezing, the swelling effect is continuously kept, and meanwhile, the good cleanliness of the NMMO solution is kept through low-temperature control in the squeezing process, so that the problem that the quality of the NMMO solution is reduced due to the fact that cellulose is dissolved in the NMMO solution is avoided, the viscosity of the squeezed NMMO solution is not obviously different from that of the NMMO solution used in the swelling process, and therefore the solution after squeezing can be recycled.

Crushing the squeezed material to obtain a crushed material; the crushing temperature is preferably 40-50 ℃; the crushed particle size is preferably 3 to 6mm.

Mixing the crushed material with an NMMO solution with the mass concentration of 81-85% for dissolving; in the invention, the fiber spinning solution is obtained by mixing and dissolving under normal pressure preferably; the dissolution can be carried out in a reaction kettle, such as a double-screw extruder, a thin film evaporator or other reaction vessels; the dissolution is preferably carried out under stirring; the rotation speed of the stirring is preferably 50-100 rpm, more preferably 50-80 rpm, even more preferably 60-70 rpm, and most preferably 60-68 rpm; the dissolving temperature is preferably 90-110 ℃, and more preferably 100-110 ℃; the mass ratio of the crushed material to the NMMO solution with the mass concentration of 81-85% is preferably 1: (2 to 3), more preferably 1: (2.2 to 2.8), more preferably 1: (2.3 to 2.6), most preferably 1: (2.3-2.5); in the embodiment provided by the invention, the mass ratio of the crushed material to the NMMO solution with the mass concentration of 81-85% is specifically 1:2.48, 1:2.35 or 1:2.43; the mass concentration of the fiber in the cellulose spinning solution is preferably 11.5-12.5%. Because the crushed material is in a sufficient swelling state, the material can be directly mixed with high-concentration NMMO, and the concentration of the NMMO can be improved without vacuumizing or dewatering under the condition of meeting the dissolving proportion of three phases of water, cellulose and NMMO, and only the temperature is required to be increased to the dissolving temperature.

According to the invention, the low-concentration NMMO and the pulp are directly mixed for pretreatment, the molecular kinetic energy of the NMMO is low at low temperature and low concentration, and the damage to the cellulose hydrogen bonds is small, so that the solution can not damage the hydrogen bonds between the cellulose and the hydrogen bonds in the crystallization area after entering the cellulose amorphous area in the pulp, and the initial dissolution phenomenon can not be caused, and the possibility of the occurrence of white cores can be avoided; then, in the squeezing process, the NMMO solution continuously enters the cellulose through the action of external force, the continuous swelling effect is kept, the NMMO solution in cellulose molecules is fully dissolved, and the cellulose can be directly and fully dissolved in the high-concentration NMMO solution, namely, the cellulose can be dissolved only through the action of external force shearing without vacuumizing in the dissolving process, and the high-quality fiber spinning solution is obtained; moreover, the preparation method provided by the invention is simple, does not need special equipment and has low energy consumption.

To further illustrate the present invention, the following examples are provided to describe the method of preparing a fiber dope by a direct solution method.

The reagents used in the following examples are all commercially available; the pulp used in the examples is sulfate broadleaf wood dissolving pulp (alpha-cellulose content 95%, pulp intrinsic viscosity 440ml/g, fe content 3ppm; water content of the pulp 7%); NMMO is a 50% strength solution of NMMO from Indonesian APL (72% or higher by solvent seven-effect evaporation system); the autoclave definitions used in the examples: has the temperature control capability (80-120 ℃); the stirring mode has strong shearing effect; the stirring form can be double-screw extrusion or scraper stirring, but is not limited to the double-screw extrusion or the scraper stirring; the materials are crushed into particles with smaller particle size in the stirring process; during the stirring process, the water evaporation can be carried out in a vacuum control mode, and the water evaporation can be carried out according to production requirements without vacuumizing.

Example 1

1.1 mixing and stirring 0.1kg of pulp and 2.22kg of NMMO solution with the mass concentration of 72% for 30min at 40 ℃ to obtain a mixed material with 4.5% pulp concentration, namely the pulp porridge.

1.2 squeezing the porridge obtained in the step 1.1 at the squeezing temperature of 50 ℃ to obtain a squeezed material with the dryness of 40%.

1.3 crushing the squeezed material obtained in 1.2 at 50 ℃ to obtain a crushed material with a particle size of 6mm.

1.4 dissolving 0.25kg of the crushed material obtained in 1.3 and 0.62kg of 81% NMMO solution in mass concentration in a screw extruder, wherein the temperature of the screw extruder is 100 ℃, and the rotating speed is 60rpm; the dissolving time is 25min, and the fiber spinning solution is obtained.

Example 2

2.1 mixing 0.2kg pulp with 4.15kg NMMO solution with mass concentration of 73% at 40 deg.C, stirring for 30min to obtain mixed material of 4.6% pulp concentration, i.e. pulp porridge.

2.2 squeezing the porridge obtained in the step 2.1 at the temperature of 50 ℃ to obtain a squeezed material with the dryness of 39%.

2.3 crushing the squeezed material obtained in 2.2 at 50 ℃ to obtain a crushed material with a particle size of 6mm.

2.4 dissolving 0.51kg of the crushed material obtained in 2.3 and 1.20kg of 81% NMMO solution in mass concentration in a screw extruder, wherein the temperature of the screw extruder is 110 ℃, and the rotating speed is 60rpm; the dissolving time is 30min, and the fiber spinning solution is obtained.

Example 3

3.1 mixing 0.3kg pulp with 6.22kg NMMO solution with mass concentration of 73% at 40 deg.C, stirring for 40min to obtain mixed material of 4.6% pulp concentration, i.e. pulp porridge.

3.2 squeezing the porridge obtained in the step 3.1 at the squeezing temperature of 50 ℃ to obtain a squeezed material with the dryness of 40%.

3.3 crushing the squeezed material obtained in 3.2 at 50 ℃ to obtain a crushed material with the particle size of 6mm.

3.4 mixing 0.75kg of the crushed material obtained in 3.3 with 1.82kg of NMMO solution with the mass concentration of 81%, and stirring and dissolving in a thin film evaporator at the temperature of 110 ℃ and the rotation speed of 68rpm; the dissolving time is 40min, and the fiber spinning solution is obtained under normal pressure.

Example 4

Compared with the embodiment 3, the difference of the embodiment is that the vacuum degree in the film evaporator is-0.094 MPa for dissolution.

Comparative example 1

The difference from example 3 is that 0.5kg of dry pulp was directly mixed with 3.2kg of 84.2% NMMO solution and then placed in a thin film evaporator to be dissolved by stirring, thereby obtaining a cellulose spinning solution.

Rheological data and cellulose content detection were performed on the cellulose spinning dope obtained in examples 1 to 4 and comparative example 1, and the results are shown in table 1.

TABLE 1 rheological Properties of cellulose dope and results of cellulose content measurements

From the above data it can be seen that five different examples and comparative examples can produce spin dope solutions.

The five cellulose spinning glue solutions are characterized by two characterization methods:

the method comprises the following steps: macroscopically detecting whether undissolved particles exist in the cellulose spinning solution, wherein the detection tool is an Olympus partial microscope, and the observation results are shown in figures 1 to 5. Wherein FIG. 1 is a microscopic view of the cellulose dope obtained in example 1, FIG. 2 is a microscopic view of the cellulose dope obtained in example 2, FIG. 3 is a microscopic view of the cellulose dope obtained in example 3, FIG. 4 is a microscopic view of the cellulose dope obtained in example 4, and FIG. 5 is a microscopic view of the cellulose dope obtained in comparative example 1.

Macroscopic observation of the photomicrographs of FIGS. 1 to 5 shows that the dissolution effects of examples 1 to 4 are close, the glue solution has a uniform shape, and undissolved cellulose particles are hardly seen; however, comparative example 1 had a small amount of undissolved fiber particles and the state of dissolution was poor.

The second method comprises the following steps: the dissolution properties of the cellulose dope obtained in examples 1 to 4 and comparative example 1 were analyzed by a method of detecting particle size in cellulose spinning dope by HELOS laser particle size diffractometer, and the results are shown in table 2.

TABLE 2 analysis results of dissolution Properties of cellulose stock solutions

The following data can be obtained: the particle size distribution of the cellulose stock solution obtained in example 1,2,3,4 is basically the same, the content of particles larger than 40 μm in comparative example 1 is much larger than that of other examples, and the maximum particle diameter is also significantly higher than that of other examples, indicating that the dissolution effect is poor.

Claims

1. A method for preparing a fiber spinning solution by a direct dissolution method is characterized by comprising the following steps:

s1) mixing pulp with an NMMO solution with the mass concentration of 72-76% for swelling to obtain a mixed material; the temperature of mixing and swelling is 40-45 ℃; the mass concentration of the pulp in the mixed material is 4-5%;

s2) squeezing the mixed material to obtain a squeezed material; the squeezing temperature is 40-65 ℃; squeezing the mixed material until the dryness of the pulp is 35 to 45 percent;

s3) crushing the squeezed material to obtain a crushed material;

and S4) mixing and dissolving the crushed material and an NMMO solution with the mass concentration of 81-85% under normal pressure to obtain a fiber spinning solution.

2. The method according to claim 1, wherein the mixing swelling time in step S1) is 10 to 30min.

3. The method as claimed in claim 1, wherein the temperature for pulverization in the step S3) is 40 ℃ to 50 ℃; the crushed particle size is 3-6 mm.

4. The method according to claim 1, wherein the temperature for dissolving in the step S4) is 90-110 ℃; the dissolving time is 20-60 min.

5. The method according to claim 1, wherein the mass ratio of the crushed material to the NMMO solution with the mass concentration of 81-85% is 1: (2-3).

6. The method according to claim 1, characterized in that the NMMO solution obtained after pressing in step S2) is used in step S1) for mixing with pulp.