Method for preparing fiber spinning solution by low-temperature dissolutionTechnical Field
The invention belongs to the technical field of fiber preparation, and particularly relates to a method for preparing fiber spinning solution by low-temperature dissolution.
Background
Cellulose is a natural polymer with the greatest reserves and the greatest distribution on the earth, and is an inexhaustible renewable resource in nature. Cellulose fibers have advantages of high strength, good dyeing properties, good spinning performance, wide industrial applications, and the like, and thus, the market demand for cellulose fibers has been continuously increasing worldwide in recent years.
The Lyocell fiber is a cellulose fiber which is prepared from renewable resources such as cotton linters, trees, bamboos and the like as raw materials, NMMO as a solvent and through dry-jet wet spinning, has various excellent performances of natural fibers and synthetic fibers, and is environment-friendly in 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. Thus, there has been a continuing increase in the worldwide market demand for Lyocell fibers in recent years.
The existing preparation methods of Lyocell fiber spinning solution mainly comprise an indirect dissolution method (wet method and dry method) and a direct dissolution method.
Indirect dissolution method: the NMMO aqueous solution with medium and low concentration is mixed with cellulose pulp, after the mixture is fully swelled, the excessive water is removed by reduced pressure distillation to complete dissolution in a dissolution zone, the cellulose cannot be dissolved by the NMMO aqueous solution with medium and low concentration, and the excessive water is favorable for the sufficient swelling of cellulose molecules in a solvent, so that uniform slurry is easy to form. The indirect dissolution method can be classified into wet method and dry method. The wet method is to mix pulp with water for pulping, squeeze pulp solution for removing water, crush, mix with NMMO, and swell in a storage tank to fully combine NMMO with cellulose to form cellulose pulp porridge. When wet pulp and NMMO solution are mixed in wet process, NMMO concentration is about 80% -84%, after swelling is completed, the pulp porridge is conveyed into a reaction kettle (such as a film evaporator) to be dissolved, so as to form spinning solution, and the spinning solution is conveyed to a spinning machine to complete spinning. In the dry method, pulp is directly mixed with NMMO solution in the form of pulp plate without processing such as mixing and crushing with water, and compared with the wet method, the hydraulic pulp crushing and squeezing procedures are omitted. The concentration of NMMO solution required for dry pulp mixing is between 75% and 80%. After swelling, the gruel is conveyed into a reaction kettle (such as a film evaporator) for dissolution to form spinning solution, and the spinning solution is conveyed to a spinning machine for spinning. The prior dry method mainly adopts NMMO (75% -80%) with medium and high concentration to stir and swell at 80-85 ℃, the NMMO is completely swelled, the NMMO is added into a vacuum stirring reaction kettle, and water is evaporated for 2-3 hours at 95-105 ℃ under stirring and vacuum to a dissolution zone to prepare transparent and uniform colloid. However, this method has the following disadvantages: ① The swelling temperature is higher and the energy consumption is high. ② The swelling temperature is high, primary dissolution is easy to occur, a gel layer is formed on the surface of cellulose to prevent the solvent from continuously penetrating and diffusing into the cellulose, and the prepared glue solution possibly contains a part of insoluble white cores. ③ The vacuum evaporation temperature is higher, the energy consumption is high, cellulose, PG, NMMO and the like are easy to thermally degrade, the reaction time is longer, the quality performance quality of the subsequent glue solution and the finished product silk is reduced, and the burden of the anion-cation resin recovered by the subsequent solvent is increased along with the deepening of the color of the colloid solution. ④ The NMMO solution is easy to crystallize and solidify by simply and directly reducing the swelling temperature, and the osmotic swelling speed is slow, and the swelling effect is poor.
Still others have used NMMO solids in the laboratory to prepare colloids with 1-3% cellulose content by direct addition to ethanol solutions, which have the following disadvantages: ① NMMO solid preparation cost is too high; ② NMMO solid has a darker color, which adversely affects the quality of the subsequent finished yarn, and increases the burden of anion-cation exchange resin in a solvent recovery workshop; ③ The added ethanol has too much content, the cost is increased, and potential safety hazards exist in the actual production of the ethanol with too high content: ④ The prepared colloidal cellulose has the content of 1-3 percent and is too low to be applied to actual production.
Direct dissolution method: directly mixing high-concentration NMMO solution with dissolving capacity with crushed cellulose pulp under proper conditions, and directly completing dissolution without swelling. The method does not need to remove water in the dissolution process, simplifies the process, but because cellulose is dissolved when contacted with a high-concentration NMMO solution, solvent molecules possibly not permeate into the cellulose, the surface is primarily dissolved, a gel group is easily formed, the solvent is prevented from continuously permeating and diffusing into the cellulose, and the prepared glue solution possibly contains a part of insoluble white core. In order to overcome the disadvantages of the direct dissolution method, the following solutions are mainly available at present: ① Crushing cellulose raw materials into particle flocks with extremely small particle sizes; ② The supercooled liquid of NMMO/water solvent is used, the dissolving capacity of the solvent is reduced or lost at low temperature, and after cellulose is fully swelled, the dissolution is completed at the temperature rise. However, the cost is high because the raw materials are crushed into flocks, potential safety hazards are easy to generate when the flocks are used as raw materials in workshops, if larger particles are used as raw materials, the dissolution is ensured to be complete, and the flocks are destroyed by using a large rotating speed or strong mechanical force, so that the physical and chemical properties of the cellulose are influenced; physically preparing supercooled liquid of high-concentration NMMO/water solvent, which can be realized only by short-time temperature dip, has high technical requirement and high cost, and is unsuitable for workshop production; the chemical method is used for preparing supercooled liquid of high-concentration NMMO/water solvent, which is characterized in that polyvinyl alcohol is required to be added, the alcohol has higher molecular weight, white solid is required to be dissolved, heating and stirring are required, the viscosity is higher, the penetration of NMMO during pulp premixing is reduced to a certain extent, the solubility of cellulose in NMMO solution is reduced, after the polyvinyl alcohol is added, molecular chains are more, intermolecular entanglement is easy to generate, the polyvinyl alcohol is not easy to wash out in the spinning process, the hygroscopicity of fibers is improved, the moisture absorption and expansion ratio of the fibers is improved, the abrasion in the fabric dyeing and finishing process is caused, the dimensional stability of the fabric is influenced, moreover, the boiling point of the polyvinyl alcohol (PVC) is higher, the recovery of the solvent is not beneficial to seven-effect evaporation recovery, after the polyvinyl alcohol (PVC) is added, the polyvinyl alcohol is swelled and dissolved to prepare colloid through a double-screw extruder, the single double-screw extruder is limited in productivity, and a plurality of double-screw extruders are required, and the equipment cost is higher.
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 dope by low-temperature dissolution.
The invention provides a method for preparing a fiber spinning solution by low-temperature dissolution, which comprises the following steps:
S1) mixing one or more of a low-molecular-weight alcohol solvent, a low-molecular-weight ether solvent and a polymer with a high-concentration NMMO solution to obtain a mixed solution; the polymer comprises one or more of hydroxyl, carboxyl and amino groups;
S2) mixing the mixed solution with crushed pulp for swelling, and then heating to 75 ℃ or more for dissolution to obtain a fiber spinning solution; the swelling temperature is less than or equal to 55 ℃.
Preferably, the mass of one or more of the low molecular weight alcohol solvent, the low molecular weight ether solvent and the polymer is 0.1-18% of the mass of the mixed solution.
Preferably, the mass concentration of the high-concentration NMMO solution is 82% -87%; the mass concentration of NMMO in the mixed solution is more than or equal to 72%.
Preferably, the low molecular weight alcohol solvent is selected from one or more of ethanol, ethylene glycol, glycerol and isopropanol; the low molecular weight ether solvent is selected from one or more of diethyl ether, butyl ether and ethylene glycol diethyl ether; the polymer is selected from one or more of polyvinyl alcohol, polyethylene glycol and dimeric alcohol.
Preferably, the crushed pulp is granular pulp and/or hand-torn bulk pulp.
Preferably, the mass of the crushed pulp is 9-19% of the total mass of the crushed pulp and the mixed solution.
Preferably, the swelling temperature is 50-55 ℃; the swelling time is 15-60 min.
Preferably, the dissolution temperature is 75-98 ℃; the dissolution time is 1 to 1.5 hours.
Preferably, the swelling and dissolving are performed under stirring conditions; the stirring speed is 60-300 rpm.
Preferably, the dissolution is performed under vacuum conditions; the vacuum degree of the vacuum condition is-0.098 MPa.
The invention provides a method for preparing a fiber spinning solution by low-temperature dissolution, which comprises the following steps: s1) mixing one or more of a low-molecular-weight alcohol solvent, a low-molecular-weight ether solvent and a polymer with a high-concentration NMMO solution to obtain a mixed solution; the polymer comprises one or more of hydroxyl, carboxyl and amino groups; s2) mixing the mixed solution with crushed pulp for swelling, and then heating to 75 ℃ or more for dissolution to obtain a fiber spinning solution; the swelling temperature is less than or equal to 55 ℃. Compared with the prior art, the invention swells at low temperature, is not easy to form primary dissolution, is favorable for full permeation and diffusion of NMMO solution, and has more complete swelling, and simultaneously, the added organic matters can increase the permeability of the solution to cellulose, thereby further increasing the swelling effect; in addition, the added organic matters can be removed through heating or vacuum heating, the dissolution area is reached in a short time, the dissolution temperature is reduced through vacuum heating, the thermal degradation of cellulose is greatly reduced while the energy consumption cost is saved, and the mechanical property strength of the cellulose is further improved.
Detailed Description
The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention provides a method for preparing a fiber spinning solution by low-temperature dissolution, which comprises the following steps: s1) mixing one or more of a low-molecular-weight alcohol solvent, a low-molecular-weight ether solvent and a polymer with a high-concentration NMMO solution to obtain a mixed solution; the polymer comprises one or more of hydroxyl, carboxyl and amino groups; s2) mixing the mixed solution with crushed pulp for swelling, and then heating to 75 ℃ or more for dissolution to obtain a fiber spinning solution; the swelling temperature is less than or equal to 55 ℃.
The source of all the raw materials is not particularly limited, and the raw materials are commercially available.
Mixing one or more of low-molecular-weight alcohol solvents, low-molecular-weight ether solvents and polymers with a high-concentration NMMO solution to obtain a mixed solution; the low molecular weight alcohol solvent is a low molecular weight alcohol solvent well known to those skilled in the art, and is not particularly limited, and one or more of ethanol, ethylene glycol, glycerol and isopropanol are preferable in the present invention; the low molecular weight ether solvent is a low molecular weight ether solvent well known to those skilled in the art, and is not particularly limited, and one or more of diethyl ether, butyl ether and ethylene glycol diethyl ether are preferable in the present invention; the polymer is a polymer containing hydroxyl groups, which is well known to those skilled in the art, and is not particularly limited, and one or more of polyvinyl alcohol, polyethylene glycol and dimer alcohol are preferable in the present invention; the molecular weight of the polyvinyl alcohol is preferably 2.5-3.5 ten thousand; the molecular weight of the polyethylene glycol is preferably 1000-5000, and the molecular weight of the dimeric alcohol is preferably 537; the mass of one or more of the low molecular weight alcohol solvent, the low molecular weight ether solvent and the polymer is preferably 0.1 to 18 percent, more preferably 0.1 to 15 percent, still more preferably 0.1 to 10 percent, still more preferably 0.1 to 5 percent, still more preferably 0.1 to 3 percent, and most preferably 0.1 to 2 percent of the mass of the mixed solution; the mass concentration of the high-concentration NMMO solution is preferably 82-87%, preferably 82.8-85%, and more preferably 82.8-84.5%; the mass concentration of NMMO in the mixed solution is preferably more than or equal to 72%; when the boiling point of the low molecular weight alcohol solvent, the low molecular weight ether solvent and the polymer is higher than 110 ℃, the mass concentration of NMMO in the mixed solution is preferably 80% or more, more preferably 83% or more.
Mixing the mixed solution with crushed pulp for swelling; the pulp is preferably hardwood dissolving pulp and/or needle wood dissolving pulp (but not limited to), more preferably sulfate-process hardwood dissolving pulp and/or needle She Muya sulfate-process dissolving pulp; the content of α -cellulose in the pulp is preferably 90% or more, more preferably 95% or more; the pulp has an intrinsic viscosity of preferably 400 to 480ml/g, more preferably 420 to 460ml/g, still more preferably 440ml/g; the Fe content in the pulp is preferably less than 5ppm; the water content of the pulp is preferably 5-10%, more preferably 6-8%, and even more preferably 7%; in the invention, pulp is not required to be beaten into flocks or ultrafine particles, larger particles or large pulp plates are added to be capable of being permeated and swelled completely, transparent uniform colloid is obtained by heating and dissolving, so that the crushed pulp is preferably granular pulp and/or hand-torn large pulp in the invention; the mass of the crushed pulp is preferably 9-19% of the total mass of the pulp and the mixed solution, more preferably 10-15%, and even more preferably 12-14%; in the present invention, a stabilizer is preferably further added; the type of the stabilizer is not particularly limited as long as it is a stabilizer well known to those skilled in the art, and Propyl Gallate (PG) is preferable in the present invention; the mass of the stabilizer is preferably 0.5-10%, more preferably 2-8%, even more preferably 4-6%, and most preferably 4.6% of the mass of the crushed pulp; the swelling temperature is less than or equal to 55 ℃, preferably 25-55 ℃; in the present invention, the swelling temperature is more preferably 50 to 55 ℃ in view of the swelling speed and effect; the low temperature causes the medium-high concentration NMMO solution to lose the dissolving capability of cellulose or greatly weaken the dissolving capability, so that cellulose particles only swell in the high concentration NMMO solution at low temperature or hardly dissolve in a short time, and the penetration completely prevents gel layers formed on the surface of cellulose from preventing the further penetration of NMMO; however, the lower the swelling temperature is, the better, the lower the temperature is, the lower the energy requirement is, but the temperature is too low, the swelling permeation speed is too slow, the energy consumption and the swelling speed can be both ensured by selecting the verified temperature, the lower the swelling speed is, but the addition of one or more of low molecular weight alcohol solvents, low molecular weight ether solvents and polymers can increase the permeability of the solution to cellulose, and the swelling effect is increased; the swelling is preferably carried out under stirring; the stirring is preferably low-speed stirring; the rotation speed of the stirring is preferably 60-300 rpm; the swelling time is preferably 15 to 60 minutes, more preferably 20 to 50 minutes, still more preferably 30 to 40 minutes.
After the fiber spinning solution is fully swelled, heating to 75 ℃ or above for dissolution to obtain the fiber spinning solution; the new process of adding the low boiling point additive changes the evaporated moisture into the evaporated low boiling point organic solvent, and the transparent colloid with good uniform state can be prepared without vacuumizing, thereby greatly saving energy consumption; the gel can be heated and dissolved under vacuum condition, and can simultaneously and rapidly evaporate low molecular weight organic matters and defoam, so that transparent and uniform gel can be obtained in a short time; the vacuum degree of the vacuum condition is preferably-0.098 MPa; the new process of adding high boiling point additive, after swelling, heating to 75 deg.c or above to dissolve, and obtaining transparent and homogeneous fiber spinning liquid without evaporating water; the dissolving temperature is preferably 75-98 ℃, more preferably 85-98 ℃, and still more preferably 90-95 ℃; the dissolving time is preferably 1 to 1.5 hours; the dissolution is preferably carried out under stirring; the stirring is preferably low-speed stirring; the rotational speed of the stirring is preferably 60 to 300rpm. The swelling and dissolving temperature is lower, the energy consumption cost can be greatly saved, the thermal degradation of cellulose is greatly reduced, the mechanical property strength of cellulose and the like are obviously improved, the color of a colloid solvent is obviously lightened, and the burden of anion-cation resin recovered by a subsequent solvent is greatly reduced.
The invention swells at low temperature, is not easy to form primary dissolution, is favorable for full permeation and diffusion of NMMO solution, has more complete swelling, and simultaneously can increase the permeability of the solution to cellulose by the added organic matters, thereby further increasing the swelling effect; in addition, the added organic matters can be removed through heating or vacuum heating, the dissolution area is reached in a short time, the dissolution temperature is reduced through vacuum heating, the thermal degradation of cellulose is greatly reduced while the energy consumption cost is saved, and the mechanical property strength of the cellulose is further improved.
To further illustrate the present invention, the following provides a detailed description of a method for preparing a fiber dope by low temperature dissolution, in conjunction with examples.
The reagents used in the examples below are all commercially available; the paddle type number used in the examples is BSC 430-Brazilian slurry polymerization degree 430.
The tests obtained in the examples were carried out according to the following methods:
1. zero cut viscosity of the colloid: detecting zero-cut viscosity at 85 ℃ by adopting a Hark rheometer;
2. The polymerization degree of the colloid is that after the colloid is washed and dried, the colloid is ground into powder, and after the cuprammonium solution is dissolved, the polymer of the fiber in the colloid is measured by using a Ubbelohde viscometer;
3. Chromaticity of the colloid: adding 10g colloid into 500g water, soaking completely, and testing chromaticity by ultraviolet selective absorbance at 400 nm.
Example 1
Raw materials: BSC430 was a large hand-pulled pulp board 7.471g, propyl Gallate (PG) 0.348g, a 84.5% NMMO solution 49g, and a 1g diethyl ether mixed solution.
The novel process comprises the following steps: adding 0.348g of PGA and 7.471g of a large-sized torn pulp plate into a mixed solution of 50gNMMO and diethyl ether, stirring and premixing for about 30min at about 50 ℃ at 500rpm, and then heating to 95 ℃ for reaction for 1.5h to prepare the uniform transparent colloid.
Traditional direct dissolution method: adding 7.471g of PG0.348g and crushed pulp board flock of a crusher into 84.5% NMMO solution which is heated and melted by 50gNMMO, heating to 110 ℃, regulating the rotating speed to about 500rpm, and reacting for 2.5 hours to prepare uniform transparent colloid.
The physical and chemical properties of the colloid obtained in example 1 were measured, and the results are shown in table 1.
Table 1 example 1 colloid performance test data
| Traditional direct dissolution method | New technological process |
| Temperature of the dissolved colloid/. Degree.C | 110 | 95 |
| Time/h of colloid preparation | 2 | 1 |
| Number of bright spots under microscope (undissolved complete fiber) | 1 | 1 |
| Cellulose content% | 13.2 | 13.2 |
| Zero shear viscosity at 85 DEG C | 16000 | 22500 |
| Degree of polymerization of colloid | 378 | 410 |
| Chromaticity of colloid | 725 | 250 |
Example 2
Raw materials: BSC430 was a large hand-pulled pulp board 7.471g, PG 0.348g, a mixed solution of 82.8% NMMO solution 49.95g+0.05g polyethylene glycol.
The new process direct dissolution preparation method comprises the following steps: PG and a large size pulp plate which is torn by hands are added into 50g of mixed solution of NMMO and polyethylene glycol, the mixture is stirred and premixed for 30min at about 50 ℃ at 300rpm, and then the mixture is heated to 95 ℃ for reaction for 1.5h, thus obtaining the uniform transparent colloid.
Traditional direct dissolution method: adding 7.471g of PG0.348g and crushed pulp board flock of a crusher into 84.5% NMMO solution which is heated and melted by 50gNMMO, heating to 110 ℃, regulating the rotating speed to about 500rpm, and reacting for 2.5 hours to prepare uniform transparent colloid.
The physical and chemical properties of the colloid obtained in example 2 were measured, and the results are shown in table 1.
Table 2 example 2 colloid performance test data
| Traditional direct dissolution method | New technological process |
| Temperature of the dissolved colloid/. Degree.C | 110 | 95 |
| Time/h of colloid preparation | 2 | 1 |
| Number of bright spots under microscope (undissolved complete fiber) | 1 | 1 |
| Cellulose content% | 13.2 | 13.2 |
| Zero shear viscosity at 85 DEG C | 16000 | 22518 |
| Degree of polymerization of colloid | 378 | 411 |
| Chromaticity of colloid | 725 | 252 |
Compared with the traditional method, the new method for preparing the colloid by low-temperature swelling greatly reduces energy consumption, reduces fiber degradation, improves zero-shear viscosity, and reduces chromaticity of the colloid and coagulation bath.