A method for preparing large-diameter Lyocell fiber

Abstract

The invention belongs to the technical field of Lyocell fiber preparation, and discloses a preparation method of large-diameter Lyocell fiber, wherein the preparation method is as follows: a cellulose spinning stock solution is metered by a metering pump and then extruded from a large-aperture spinneret for spinning, the filaments pass through an air section and enter a coagulation bath for coagulation, and after being drawn by a nozzle 5 to 6 times, enter a water bath for secondary drawing with a drawing ratio of 1.1 to 1.5, and finally washed with water and dried and heat-set in sequence to obtain a large-diameter Lyocell fiber; the aperture of the large-aperture spinneret is 0.3 to 0.5 mm; the spinning temperature is 80 to 87° C., and the spinning pressure is 2.5 to 4.5 MPa; the coagulation bath is a NMMO aqueous solution with a concentration of 10 to 20 wt%, the coagulation bath temperature is 0 to 15° C., and the coagulation time is 2 to 3 s. The preparation method of large-diameter Lyocell fiber of the invention improves the mechanical properties of the fiber while ensuring the fineness.

Description

Technical Field

[0001] The invention belongs to the technical field of Lyocell fiber preparation, and relates to a method for preparing large-diameter Lyocell fibers. Background Art

[0002] Lyocell fiber, as an innovative fiber material, significantly reflects the concept of green environmental protection in its preparation process compared to traditional viscose fiber. In this process, not only does it avoid the production of toxic and harmful chemicals, but it also relies entirely on 100% pure natural materials. In addition, the environmentally friendly design of the entire manufacturing process makes Lyocell fiber perfectly meet the deep needs of modern consumers for environmental protection. And its solvent recovery rate is as high as 99.5%, which is a truly green fiber.

[0003] In addition to its significant environmental advantages, Lyocell fiber also exhibits performance characteristics that surpass viscose fiber and cotton fiber. It has good hygroscopicity, biodegradability, and excellent strength in both dry and wet states. These characteristics make Lyocell fiber widely used in clothing, home textiles and other fields. In addition, its high strength and high modulus characteristics brought by high crystallinity and high orientation have also attracted the attention of the industry. Related research has involved the development of industrial Lyocell fibers such as carbon fiber precursor and tire cord.

[0004] After decades of in-depth research and development, the preparation principle of Lyocell fiber, spinning process and the relationship between fiber structure and performance have become relatively clear. Especially in the preparation of short fibers, the technology for fineness in the range of 1.3~2.2 dtex is already quite mature. However, with the continuous expansion of the potential application of Lyocell fiber in special fields, such as compression-resistant filling fiber, wigs, concrete reinforcement fiber, etc., the requirements for the diameter of a single fiber are also increasing, usually requiring a diameter of more than 50μm (fineness of more than 40dtex).

[0005] To solve the above problems, the existing technologies mainly change the fiber diameter by adjusting single conditions such as spinning speed, draft ratio, pump supply and spinning solution concentration. However, these methods often ignore the subsequent coagulation and forming process, resulting in unsatisfactory fiber performance. At the same time, although these methods have improved the fiber fineness to a certain extent, the improvement is limited and it is difficult to meet the potential demand of Lyocell fibers in some special fields.

[0006] Reference 1 (Effects of air gap length and spinning speed on the properties of Lyocell fibers [J]. Synthetic Fibers, 1998, 27(6):4. DOI:CNKI:SUN:HCXW.0.1998-06-001.) increased the fiber fineness by reducing the spinning speed, but the fiber fineness was 13.79 dtex and the dry breaking strength was only 2.12 cN / dtex.

[0007] Reference 2 (Effects of pump supply and spinning solution concentration on the cross-sectional shape and properties of Y-shaped Lyocell fibers [J]. Polymer Materials Science and Engineering, 2020, 36(10):6. DOI:10.16865 / j.cnki.1000-7555.2020.0225.) changes the fiber diameter by changing the pump supply. Using conventional spinning parameters, when the stretching speed and nozzle stretching ratio remain unchanged, the pump supply is increased from 14 g / min to 18 g / min, and the fiber fineness increases from 6.25 dtex to 7.08 dtex, but this also leads to a decrease in the dry breaking strength and dry modulus of the fiber.

[0008] Reference 3 (Effect of Spinning Conditions on the Structure and Properties of Bamboo Pulp Fibers Processed by Lyocell Technology [J]. Journal of Textile Research, 2011, 32(1):5. DOI:CNKI:SUN:FZXB.0.2011-01-005.) shows that when the spinning solution concentration is increased from 5.0wt% to 10.0wt%, the fiber fineness only increases from 0.86dtex to 1.89dtex. Although the spinnability and fiber mechanical properties will change accordingly, under the condition of continuous and stable spinning, the strength and elongation of the fiber increase with the increase of spinning solution concentration. However, the fiber fineness of the fiber prepared by this method is limited.

[0009] Reference 4 (Effects of Pump Supply and Spinning Solution Concentration on the Cross-sectional Shape and Properties of Y-shaped Lyocell Fibers [J]. Polymer Materials Science and Engineering, 2020, 36(10):6. DOI:10.16865 / j.cnki.1000-7555.2020.0225.) increased the spinning solution concentration from 11% to 13%, but the fineness of the prepared fiber was only increased from 6.87 dtex to 7.38 dtex, with a limited degree of improvement.

[0010] The patent application with application publication number CN113481615A discloses a method for producing coarse denier lyocell fibers, which uses a lower spinning speed to reduce the nozzle draft ratio. Although the fineness is improved to a certain extent, the fineness of the produced fiber is only 2.67 dtex, and the dry breaking strength is 3.35 cN / dtex, and the degree of improvement is limited.

[0011] In summary, the existing methods are unable to produce large-diameter Lyocell fibers with a fineness greater than 40 dtex and good mechanical properties.

[0012] Therefore, it is of great significance to study an efficient and widely adaptable method for large-scale preparation of large-diameter Lyocell fibers with excellent mechanical properties. Summary of the invention

[0013] The purpose of the present invention is to solve the problems existing in the prior art and provide a method for preparing large-diameter Lyocell fibers.

[0014] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0015] A preparation method of large-diameter Lyocell fiber, wherein a cellulose spinning stock solution is metered by a metering pump and then extruded from a large-aperture spinneret for spinning, the filaments pass through an air section and enter a coagulation bath for coagulation, and then are drawn by a nozzle 5 to 6 times and enter a water bath for secondary drawing with a drawing ratio of 1.1 to 1.5, and finally are washed with water and dried and heat-set in sequence to obtain large-diameter Lyocell fiber;

[0016] The aperture of the large-aperture spinneret is 0.3-0.5 mm; the spinning temperature is 80-87 °C, the spinning pressure is 2.5-4.5 MPa; the extrusion speed is 6-8 m / min; the coagulation bath is a 10-20 wt% NMMO aqueous solution, the coagulation bath temperature is 0-15 °C, and the coagulation time is 2-3 s;

[0017] The fineness of large-diameter Lyocell fiber is 47~55 dtex, the fineness deviation rate is 1.5~1.8%, the dry modulus is ≥135 cN / dtex, the dry breaking strength is ≥3.5 cN / dtex, the wet breaking strength is ≥2.5 cN / dtex, and the dry breaking elongation is ≥5%.

[0018] To prepare large-diameter Lyocell fibers, conventional spinnerets can be used to achieve the required fineness by reducing the nozzle draft, but this will result in poor mechanical properties of the fiber; if the pump supply is increased, the extrusion speed will be too high, the spinning speed will also be very high, and excessive tensile stress will easily cause difficulty in drafting. Conventional fibers can be coagulated in 0.5 to 1 s, while large-diameter Lyocell fibers require a longer coagulation time. Therefore, it is necessary to design a spinneret with a larger aperture to reduce the extrusion speed and thus the spinning speed; in addition, while increasing the spinneret hole, the upper limit of the pump supply can also be increased, allowing more room for fineness design, and the spinning temperature can be appropriately adjusted to balance the spinning pressure. The spinneret of the present invention has a spinneret aperture of 0.3-0.5 mm. After the aperture is enlarged, the extrusion speed is reduced while the pump supply is increased to ensure the fineness, so that the spinning speed is relatively low while ensuring appropriate drafting, and the tensile stress is correspondingly reduced. The drafting multiple can reach 5-6 times, which improves the crystallization and orientation of the fiber. At the same time, the reduction in spinning speed also prolongs the residence time of the filaments in the coagulation bath to 2-3 s, so that the large-diameter fiber is fully coagulated to avoid the formation of a skin-core structure, thereby ensuring the fineness and improving the mechanical properties of the fiber. The increase in the spinneret aperture will lead to an increase in the spinning pressure drop. In order to avoid the increase in the spinning pressure drop caused by the large-aperture spinneret, which leads to poor spinning stability, the present invention designs the spinning temperature to be 80-87°C, and balances the spinning pressure by reducing the spinning temperature to increase the viscosity of the solution. At this temperature, the spinning solution has both high viscosity and good fluidity, thereby maintaining the spinning pressure at 2.5-4.5 MPa.

[0019] In order to ensure the successful preparation of Lyocell fibers with large diameter and excellent mechanical properties, the coagulation bath temperature and concentration of the present invention adopt a lower temperature and lower concentration condition. Conventional Lyocell fibers have a smaller fineness, and the time required to reach diffusion equilibrium in the coagulation bath is shorter, but the time required for the double diffusion of large diameter fibers in the coagulation bath to reach equilibrium is longer. If conventional coagulation bath conditions are used, the double diffusion of the fibers cannot reach diffusion equilibrium, which is not conducive to the crystallization orientation of the fibers. Therefore, it is necessary to appropriately increase the diffusion rate, but too intense diffusion is not conducive to the formation of a high side order, uniform and compact structure. At the same time, too fast solidification of the surface layer will hinder the double diffusion, which is easy to cause an increase in internal defects of the fibers and affect the mechanical properties of the fibers; using lower concentration conditions will increase the double diffusion rate of the filaments, and at the same time appropriately reduce the coagulation bath temperature, the double diffusion of the filaments will be relatively increased and will not be too intense, reducing the difference in the skin-core structure of the fibers, making the coagulation process uniform, and the primary fiber structure compact, which is conducive to the increase of fiber crystallinity and grain size, thereby improving its mechanical properties, while ensuring a certain amount of solvent residue, providing conditions for subsequent secondary drafting.

[0020] In order to further improve the mechanical properties of the fiber, a certain amount of drafting is added in the water bath to increase the stress along the axial direction of the fiber, so that the fiber is further oriented along the axial direction and its mechanical properties are improved. This process route ensures the residence time of the filament in the coagulation bath by designing the spinneret, and at the same time adjusts the spinning temperature to ensure normal spinning pressure, and by changing the coagulation bath conditions, the diffusion speed of the filament is relatively increased while making it coagulate evenly, reducing the difference in the skin-core structure, and ensuring the strength of the fiber. At the same time, the filament is drafted twice, which increases the stress along the axial direction of the filament again, appropriately increases the orientation of the fiber, and further improves the strength of the large-diameter Lyocell fiber. The filament coming out of the coagulation bath enters the subsequent water bath for 1.1~1.5 times of secondary drafting, and the total fiber drafting multiple is 5.5~10.5 times.

[0021] As the preferred technical solution:

[0022] In the method for preparing a large-diameter Lyocell fiber as described above, the aspect ratio of the large-aperture spinneret is 3:1-4:1, and the number of holes is 10-20 holes.

[0023] The preparation method of a large-diameter Lyocell fiber as described above, the specific preparation steps are as follows:

[0024] (1) Mixing cellulose pulp, a 50 wt% NMMO aqueous solution and propyl gallate (PG), dehydrating and dissolving the mixture to obtain a cellulose spinning solution;

[0025] (2) The cellulose spinning stock solution is metered by a metering pump and then extruded from a large-aperture spinneret for spinning;

[0026] (3) After the extruded filaments pass through the air section, they enter a coagulation bath with set temperature and concentration for coagulation treatment;

[0027] (4) The filaments coming out of the coagulation bath enter the water bath for secondary drawing;

[0028] (5) After the secondary drawing, the filaments are washed, dried and heat-set in sequence to produce large-diameter Lyocell fibers.

[0029] In the method for preparing a large-diameter Lyocell fiber as described above, the degree of polymerization of the cellulose pulp in step (1) is 450-820, the content of cellulose pulp in the cellulose spinning solution is 9-13 wt %, and the content of propyl gallate in the cellulose spinning solution is 0.5-1.0 wt %.

[0030] In the method for preparing a large-diameter Lyocell fiber as described above, the pump supply in step (2) is 12.1-15.0 mL / min, the spinning speed is 30-40 m / min, and the spinning speed is determined according to the nozzle draft multiple and the extrusion speed.

[0031] In the method for preparing a large-diameter Lyocell fiber as described above, in step (3), the length of the air segment is 5-10 cm, the blowing speed of the air segment is 2.1-4.0 m / s, and the blowing temperature is 15-20°C. The air segment is slightly lengthened, and the blowing time required for large-diameter coagulation is slightly longer. The blowing time of the filaments in the air segment should be increased. If the height of the air segment is too large, the possibility of fiber spinning and sticking is greater. If the height of the air segment is too small, the fiber coagulation is insufficient and the blowing speed needs to be increased. However, increasing the wind speed will cause fiber deformation, twisting and even breakage, which is not conducive to spinning. Therefore, the air segment length is determined to be 5-10 cm, the blowing speed of the air segment is 2.1-4.0 m / s, and the blowing temperature is 15-20°C.

[0032] In the method for preparing a large-diameter Lyocell fiber as described above, in step (5), the water washing temperature is 20-25°C, the drying and heat setting temperature is 130-150°C, and the drying and heat setting time is 10-20 minutes.

[0033] A method for preparing a large diameter Lyocell fiber as described in any of the above items, wherein the large diameter Lyocell fiber has a regain of 4.58~5.56%, a dry modulus of 135~160 cN / dtex, a dry breaking strength of 3.5~4.0 cN / dtex, a wet breaking strength of 2.5~2.8 cN / dtex, and a dry breaking elongation of 5~10%.

[0034] Beneficial effects:

[0035] The preparation method of a large-diameter Lyocell fiber of the present invention can prepare a large-diameter Lyocell fiber with a fineness of 47-55 dtex and excellent mechanical properties, thereby meeting the potential demand for Lyocell fibers in certain special fields. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0037] In order to ensure that the properties of the materials used in each embodiment and comparative example are fully disclosed, the manufacturers and brands of the materials are indicated, and products of other manufacturers and brands that meet the requirements of the present invention are also feasible.

[0038] The testing methods of the relevant performance indicators in the following embodiments and comparative examples are as follows:

[0039] Fineness deviation rate: The Lyocell fibers prepared in each embodiment and each comparative example were respectively used as samples, and then the fineness deviation rate of the samples was measured according to the “Method A - Mid-Bundle Fiber Weighing Method” in the GB / T 14335-2008 standard.

[0040] Moisture regain: The Lyocell fibers prepared in each embodiment and each comparative example were taken as samples, and then the moisture regain of the samples was measured with reference to GB / T9995-1997 standard; wherein, when the material was dried to constant weight, it was weighed by the outside weighing method. When the difference between two consecutive weighed masses (referring to the mass value directly measured by the weighing instrument) was less than 0.1% of the latter weighed mass, the latter weighed mass was taken.

[0041] Dry breaking strength and dry modulus: The Lyocell fibers prepared in each embodiment and each comparative example were respectively used as samples, and then the dry breaking strength of the samples was tested according to GB / T 14337-2008 standard. The dry modulus (i.e., the ratio of stress to strain) was calculated based on the stress-strain curve obtained when testing the dry breaking strength.

[0042] Wet breaking strength: The Lyocell fibers prepared in each embodiment and each comparative example were respectively used as samples, and then the wet breaking strength of the samples was measured according to GB / T 14337-2008 standard.

[0043] Dry elongation at break: The Lyocell fibers prepared in each embodiment and each comparative example were used as samples, and the dry elongation at break of the samples was measured according to GB / T 14337-2008 standard.

[0044] Example 1

[0045] A method for preparing a large-diameter Lyocell fiber, comprising the following steps:

[0046] (1) Mixing cellulose pulp with a degree of polymerization of 450, a NMMO aqueous solution with a concentration of 50 wt% and propyl gallate, dehydrating and dissolving them to obtain a cellulose spinning solution; wherein the content of propyl gallate in the cellulose spinning solution is 1 wt%, and the content of cellulose pulp is 13 wt%;

[0047] (2) The cellulose spinning stock solution was metered by a metering pump and then extruded from a large-aperture spinneret for spinning; wherein the spinning temperature was 80°C, the spinning pressure was 2.5 MPa, the extrusion speed was 6 m / min, the pump supply was 12.1 mL / min, the spinning speed was 30 m / min, the aperture of the large-aperture spinneret was 0.3 mm, the aspect ratio was 3:1, and the number of holes was 20;

[0048] (3) The filaments extruded in step (2) passed through an air section with a length of 5 cm and then entered into a 0°C, 10 wt% NMMO aqueous solution for coagulation for 2 s; wherein the blowing speed of the air section was 2.1 m / s and the blowing temperature was 15°C;

[0049] (4) After being drawn by the nozzle at a ratio of 5, the filaments coming out of the coagulation bath enter the water bath for secondary drawing at a drawing ratio of 1.1;

[0050] (5) After the secondary drawing, the filaments were washed and dried and heat-set in sequence to obtain large-diameter Lyocell fibers; the washing temperature was 20°C, the drying and heat-setting temperature was 130°C, and the drying and heat-setting time was 20 min.

[0051] The final large-diameter Lyocell fiber has a fineness of 47 dtex, a fineness deviation rate of 1.5%, a regain of 4.6%, a dry modulus of 135 cN / dtex, a dry breaking strength of 3.52 cN / dtex, a wet breaking strength of 2.51 cN / dtex, and a dry breaking elongation of 5%.

[0052] Comparative Example 1

[0053] A method for preparing Lyocell fiber is basically the same as Example 1, except that the aperture of the spinneret used in step (2) is 0.2 mm, the corresponding extrusion speed is 16 m / min, and the spinning speed is 80 m / min.

[0054] The final Lyocell fiber has a dry modulus of 110 cN / dtex, a dry breaking strength of 1.8 cN / dtex, a wet breaking strength of 0.9 cN / dtex, and a dry breaking elongation of 11%.

[0055] By comparing Comparative Example 1 with Example 1, it can be seen that the dry modulus, dry breaking strength and wet breaking strength of the Lyocell fiber prepared in this comparative example are greatly reduced. This is because when the pump supply and the nozzle draft multiple remain unchanged, the diameter of the spinneret hole becomes smaller, the extrusion speed during spinning will be greatly improved, and the spinning speed will also be greatly improved accordingly, which leads to excessive stress on the fiber, easily causing fiber defects, and ultimately causing the mechanical properties of the Lyocell fiber prepared in Comparative Example 1 to be significantly worse at the same fineness.

[0056] Comparative Example 2

[0057] A method for preparing large-diameter Lyocell fibers is basically the same as that of Example 1, except that the spinning temperature in step (2) is 75° C. and the corresponding spinning pressure is 8.5 MPa.

[0058] The final large-diameter Lyocell fiber had a fineness deviation rate of 2.0%, a dry modulus of 128 cN / dtex, a dry breaking strength of 3.0 cN / dtex, and a wet breaking strength of 2.0 cN / dtex.

[0059] By comparing Comparative Example 2 with Example 1, it can be seen that the fineness deviation rate of the large-diameter Lyocell fiber obtained in this comparative example is relatively large, and at the same time, the dry modulus, dry breaking strength and wet breaking strength of the fiber are reduced. This is because when the spinneret aperture is large, if the spinning temperature is low, the spinning pressure will increase, and excessive spinning pressure will cause the cellulose spinning solution to flow unstably in the spinneret aperture, resulting in uneven fiber diameter and surface defects, resulting in a large fineness deviation rate of the obtained large-diameter Lyocell fiber; at the same time, excessive spinning pressure will increase the tensile stress of the fiber during the spinning process, causing the fiber to break during forming, and may even cause excessive stretching or destruction of the molecular chain, affecting the crystallization and orientation of the fiber, and ultimately resulting in a decrease in the mechanical properties of the large-diameter Lyocell fiber.

[0060] Comparative Example 3

[0061] A method for preparing large-diameter Lyocell fibers is basically the same as that of Example 1, except that the spinning temperature in step (2) is 90° C. and the corresponding spinning pressure is 1.1 MPa.

[0062] The large-diameter Lyocell fiber finally obtained has a dry modulus of 125 cN / dtex, a dry breaking strength of 2.8 cN / dtex, and a wet breaking strength of 1.8 cN / dtex.

[0063] By comparing Comparative Example 3 with Example 1, it can be seen that the dry modulus, dry breaking strength and wet breaking strength of the large-diameter Lyocell fiber prepared in this comparative example are reduced. This is because when the spinneret aperture is large, if the spinning temperature is high, the spinning pressure will be too low. On the one hand, it will cause the cellulose spinning solution to flow too slowly in the spinneret aperture, easily causing broken fibers. On the other hand, it will also lead to insufficient orientation and crystallinity of the fiber molecular chains, thereby reducing the dry modulus, dry breaking strength and wet breaking strength of the fiber.

[0064] Comparative Example 4

[0065] A method for preparing large-diameter Lyocell fibers is basically the same as that of Example 1, except that the temperature of the NMMO aqueous solution in step (3) is 18°C.

[0066] The large-diameter Lyocell fiber finally obtained has a dry modulus of 127 cN / dtex, a dry breaking strength of 2.9 cN / dtex, and a wet breaking strength of 1.9 cN / dtex.

[0067] By comparing Comparative Example 4 with Example 1, it can be seen that the dry modulus, dry breaking strength and wet breaking strength of the large-diameter Lyocell fiber prepared in this comparative example are reduced. This is because the double diffusion rate of the large-diameter fiber needs to be relatively increased and not too intense in order to achieve equilibrium in the double diffusion in the coagulation bath. Although the NMMO aqueous solution used in Comparative Example 4 can also increase the double diffusion rate, excessively high temperature will make the double diffusion more intense, which is not conducive to forming a high-order, uniform and compact structure, resulting in the fiber surface solidification too quickly, which hinders the double diffusion and easily causes an increase in internal defects in the fiber, thereby affecting the mechanical properties of the fiber.

[0068] Comparative Example 5

[0069] A method for preparing large-diameter Lyocell fibers is basically the same as in Example 1, except that the concentration of the NMMO aqueous solution in step (3) is 23 wt%.

[0070] The large-diameter Lyocell fiber finally obtained has a dry modulus of 125 cN / dtex, a dry breaking strength of 2.8 cN / dtex, and a wet breaking strength of 1.8 cN / dtex.

[0071] By comparing Comparative Example 5 with Example 1, it can be seen that the dry modulus, dry breaking strength and wet breaking strength of the large-diameter Lyocell fiber prepared in this comparative example are reduced. This is because the double diffusion rate of the large-diameter fiber needs to be relatively increased to achieve equilibrium in the coagulation bath. However, the concentration of the NMMO aqueous solution used in Comparative Example 5 is too high, which leads to a decrease in the double diffusion rate of the filaments, resulting in insufficient coagulation of the filaments in the coagulation bath, which in turn leads to a decrease in the crystallization and orientation of the fiber, thereby reducing the mechanical properties of the final fiber.

[0072] Comparative Example 6

[0073] A method for preparing large-diameter Lyocell fibers is basically the same as that of Example 1, except that in step (4), the filaments emerging from the coagulation bath are not drawn into a water bath for secondary drawing after being drawn by a nozzle, but are directly drawn into step (5).

[0074] The final large-diameter Lyocell fiber has a fineness of 52.5 dtex, a dry modulus of 130 cN / dtex, a dry breaking strength of 3.2 cN / dtex, and a wet breaking strength of 2.2 cN / dtex.

[0075] By comparing Comparative Example 6 with Example 1, it can be seen that the fineness of the large-diameter Lyocell fiber prepared in this comparative example is improved, but its dry modulus, dry breaking strength and wet breaking strength are reduced. This is because when the filaments in Comparative Example 6 are not subjected to subsequent secondary drawing, the axial stretching thereof will be reduced. Although the fineness of the prepared fiber will be increased, the orientation degree of the prepared large-diameter Lyocell fiber will be too low, which will ultimately lead to a decrease in its mechanical properties.

[0076] Comparative Example 7

[0077] A method for preparing large-diameter Lyocell fibers is basically the same as that of Example 1, except that the secondary drawing ratio in step (4) is 1.02.

[0078] The final large-diameter Lyocell fiber has a fineness of 52 dtex, a dry modulus of 133 cN / dtex, a dry breaking strength of 3.4 cN / dtex, and a wet breaking strength of 2.4 cN / dtex.

[0079] By comparing Comparative Example 7 with Example 1, it can be seen that the fineness of the large-diameter Lyocell fiber prepared in this comparative example is improved, but its dry modulus, dry breaking strength and wet breaking strength are reduced. This is because adding a certain amount of stretching in the water bath will increase the stress of the fiber along the axial direction, further orient the fiber along the axial direction, and improve its mechanical properties. However, the secondary stretching multiple in Comparative Example 7 is low, and the fiber is stretched less along the axial direction. Although this will increase the fineness of the large-diameter Lyocell fiber obtained, it will also cause the orientation of the obtained fiber to be too low, which ultimately leads to a decrease in the mechanical properties of the large-diameter Lyocell fiber.

[0080] Comparative Example 8

[0081] A method for preparing large-diameter Lyocell fibers is basically the same as that of Example 1, except that the secondary drawing ratio in step (4) is 1.6.

[0082] The final large-diameter Lyocell fiber has a fineness of 42 dtex, a dry modulus of 118 cN / dtex, a dry breaking strength of 2.6 cN / dtex, and a wet breaking strength of 1.6 cN / dtex.

[0083] By comparing Comparative Example 8 with Example 1, it can be seen that the fineness, dry modulus, dry breaking strength and wet breaking strength of the large-diameter Lyocell fiber prepared in this comparative example are reduced. This is because adding a certain amount of stretching in the water bath will increase the axial stress of the fiber, further orient the fiber in the axial direction, and improve its mechanical properties. However, the secondary stretching in Comparative Example 8 is larger, and the fiber is stretched more in the axial direction, so the fineness of the prepared large-diameter Lyocell fiber is reduced; in addition, excessive axial stress of the fiber will cause an imbalance in the crystallinity and orientation of the fiber, destroying its microstructure, and excessive stretching will also cause defects on the fiber surface and poor spinnability, ultimately leading to a decrease in the mechanical properties of the large-diameter Lyocell fiber.

[0084] Example 2

[0085] A method for preparing a large-diameter Lyocell fiber, comprising the following steps:

[0086] (1) Mixing cellulose pulp with a degree of polymerization of 560, a 50 wt% NMMO aqueous solution and propyl gallate, dehydrating and dissolving them to obtain a cellulose spinning solution; wherein the content of propyl gallate in the cellulose spinning solution is 0.8 wt% and the content of cellulose pulp is 12 wt%;

[0087] (2) The cellulose spinning stock solution was metered by a metering pump and then extruded from a large-aperture spinneret for spinning; wherein the spinning temperature was 84°C, the spinning pressure was 4.5 MPa, the extrusion speed was 7 m / min, the pump supply was 13.5 mL / min, the spinning speed was 35 m / min, the aperture of the large-aperture spinneret was 0.4 mm, the aspect ratio was 4:1, and the number of holes was 15;

[0088] (3) The filaments extruded in step (2) passed through an air section with a length of 8 cm and then entered into a NMMO aqueous solution with a temperature of 9° C. and a concentration of 15 wt % for coagulation for 3 s; wherein the blowing speed of the air section was 4 m / s and the blowing temperature was 20° C.;

[0089] (4) After being drawn by the nozzle 5 times, the filaments coming out of the coagulation bath enter the water bath for secondary drawing with a drawing ratio of 1.5;

[0090] (5) After the secondary drawing, the filaments are washed and dried and heat-set in sequence to obtain large-diameter Lyocell fibers; wherein the washing temperature is 25°C, the drying and heat-setting temperature is 150°C, and the drying and heat-setting time is 10 min.

[0091] The final large-diameter Lyocell fiber has a fineness of 48 dtex, a fineness deviation of 1.6%, a regain of 4.58%, a dry modulus of 140 cN / dtex, a dry breaking strength of 3.6 cN / dtex, a wet breaking strength of 2.6 cN / dtex, and a dry breaking elongation of 6%.

[0092] Example 3

[0093] A method for preparing a large-diameter Lyocell fiber, comprising the following steps:

[0094] (1) Mixing cellulose pulp with a degree of polymerization of 656, a 50 wt% NMMO aqueous solution and propyl gallate, dehydrating and dissolving them to obtain a cellulose spinning solution; wherein the content of propyl gallate in the cellulose spinning solution is 1 wt%, and the content of cellulose pulp is 11 wt%;

[0095] (2) The cellulose spinning stock solution was metered by a metering pump and then extruded from a large-aperture spinneret for spinning; wherein the spinning temperature was 87°C, the spinning pressure was 3.5 MPa, the extrusion speed was 8 m / min, the pump supply was 15 mL / min, the spinning speed was 40 m / min, the aperture of the large-aperture spinneret was 0.5 mm, the aspect ratio was 3:1, and the number of holes was 10;

[0096] (3) After passing the filaments extruded in step (2) through an air section with a length of 10 cm, they were placed in a 15° C., 15 wt% NMMO aqueous solution for coagulation for 2 s; wherein the blowing speed of the air section was 3.2 m / s and the blowing temperature was 18° C.;

[0097] (4) After being drawn by the nozzle at a ratio of 6, the filaments coming out of the coagulation bath enter the water bath for secondary drawing at a drawing ratio of 1.11;

[0098] (5) After the secondary drawing, the filaments were washed and dried and heat-set in sequence to produce large-diameter Lyocell fibers; the washing temperature was 22°C, the drying and heat-setting temperature was 140°C, and the drying and heat-setting time was 15 min.

[0099] The final large-diameter Lyocell fiber has a fineness of 50 dtex, a fineness deviation of 1.7%, a regain of 5.56%, a dry modulus of 160 cN / dtex, a dry breaking strength of 3.8 cN / dtex, a wet breaking strength of 2.8 cN / dtex, and a dry breaking elongation of 9%.

[0100] Example 4

[0101] A method for preparing a large-diameter Lyocell fiber, comprising the following steps:

[0102] (1) Mixing cellulose pulp with a degree of polymerization of 709, a 50 wt% NMMO aqueous solution and propyl gallate, dehydrating and dissolving to obtain a cellulose spinning solution; wherein the content of propyl gallate in the cellulose spinning solution is 0.6 wt% and the content of cellulose pulp is 10 wt%;

[0103] (2) The cellulose spinning stock solution was metered by a metering pump and then extruded from a large-aperture spinneret for spinning; wherein the spinning temperature was 85°C, the spinning pressure was 3.6 MPa, the extrusion speed was 8 m / min, the pump supply was 15 mL / min, the spinning speed was 40 m / min, the aperture of the large-aperture spinneret was 0.35 mm, the aspect ratio was 3.2:1, and the number of holes was 17;

[0104] (3) The filaments extruded in step (2) were passed through an air section with a length of 6 cm, and then placed in a 10° C., 20 wt % NMMO aqueous solution for coagulation for 2 s; wherein the blowing speed of the air section was 3.5 m / s and the blowing temperature was 17° C.;

[0105] (4) After being drawn by the nozzle 5 times, the filaments coming out of the coagulation bath enter the water bath for secondary drawing with a drawing ratio of 1.2;

[0106] (5) After the secondary drawing, the filaments were washed and dried and heat-set in sequence to obtain large-diameter Lyocell fibers; the washing temperature was 23°C, the drying and heat-setting temperature was 135°C, and the drying and heat-setting time was 18 min.

[0107] The final large-diameter Lyocell fiber has a fineness of 47 dtex, a fineness deviation of 1.8%, a regain of 5%, a dry modulus of 136 cN / dtex, a dry breaking strength of 3.55 cN / dtex, a wet breaking strength of 2.5 cN / dtex, and a dry breaking elongation of 8%.

[0108] Example 5

[0109] A method for preparing a large-diameter Lyocell fiber, comprising the following steps:

[0110] (1) Mixing cellulose pulp with a degree of polymerization of 820, a 50 wt% NMMO aqueous solution and propyl gallate, dehydrating and dissolving to obtain a cellulose spinning solution; wherein the content of propyl gallate in the cellulose spinning solution is 0.5 wt% and the content of cellulose pulp is 9 wt%;

[0111] (2) The cellulose spinning stock solution was metered by a metering pump and then extruded from a large-aperture spinneret for spinning; wherein the spinning temperature was 83°C, the spinning pressure was 3.0 MPa, the extrusion speed was 7 m / min, the pump supply was 15 mL / min, the spinning speed was 35 m / min, the aperture of the large-aperture spinneret was 0.5 mm, the aspect ratio was 3:1, and the number of holes was 10;

[0112] (3) The filaments extruded in step (2) were passed through an air section with a length of 7 cm, and then placed in a 15° C., 15 wt% NMMO aqueous solution for coagulation for 3 s; wherein the blowing speed of the air section was 4 m / s and the blowing temperature was 20° C.;

[0113] (4) After being drawn by the nozzle 5 times, the filaments coming out of the coagulation bath enter the water bath for secondary drawing with a drawing ratio of 1.3;

[0114] (5) After the secondary drawing, the filaments were washed and dried and heat-set in sequence to obtain large-diameter Lyocell fibers; the washing temperature was 25°C, the drying and heat-setting temperature was 145°C, and the drying and heat-setting time was 13 min.

[0115] The final large-diameter Lyocell fiber has a fineness of 55 dtex, a fineness deviation of 1.6%, a regain of 5.2%, a dry modulus of 145 cN / dtex, a dry breaking strength of 3.7 cN / dtex, a wet breaking strength of 2.7 cN / dtex, and a dry breaking elongation of 7%.

Claims

1. A method for preparing a large-diameter Lyocell fiber, characterized in that: The cellulose spinning stock solution is metered by a metering pump and extruded from a large-aperture spinneret for spinning. The filaments pass through an air section and enter a coagulation bath for coagulation. After being drawn by a nozzle 5 to 6 times, they enter a water bath for secondary drawing with a drawing ratio of 1.1 to 1.

5. Finally, they are washed, dried, and heat-set in sequence to obtain large-diameter Lyocell fibers. The aperture of the large-aperture spinneret is 0.3-0.5 mm; the spinning temperature is 80-87 °C, the spinning pressure is 2.5-4.5 MPa; the extrusion speed is 6-8 m / min; the coagulation bath is a 10-20 wt% NMMO aqueous solution, the coagulation bath temperature is 0-15 °C, and the coagulation time is 2-3 s; The fineness of large-diameter Lyocell fiber is 47~55 dtex, the fineness deviation rate is 1.5~1.8%, the dry modulus is ≥135cN / dtex, the dry breaking strength is ≥3.5 cN / dtex, the wet breaking strength is ≥2.5 cN / dtex, and the dry breaking elongation is ≥5%.

2. The method for preparing a large-diameter Lyocell fiber according to claim 1, characterized in that: The aspect ratio of the large-aperture spinneret is 3:1~4:1, and the number of holes is 10~20 holes.

3. The method for preparing a large-diameter Lyocell fiber according to claim 1, characterized in that: The specific preparation steps are as follows: (1) Mixing cellulose pulp, a 50 wt% NMMO aqueous solution and propyl gallate and dehydrating and dissolving them to obtain a cellulose spinning solution; (2) The cellulose spinning stock solution is metered by a metering pump and then extruded from a large-aperture spinneret for spinning; (3) After the extruded filaments pass through the air section, they enter a coagulation bath with a set temperature and concentration for coagulation treatment; (4) The filaments coming out of the coagulation bath enter the water bath for secondary drawing; (5) After the secondary drawing, the filaments are washed, dried and heat-set in sequence to produce large-diameter Lyocell fibers.

4. The method for preparing a large-diameter Lyocell fiber according to claim 3, characterized in that: In step (1), the degree of polymerization of the cellulose pulp is 450-820, the content of the cellulose pulp in the cellulose spinning solution is 9-13 wt %, and the content of propyl gallate in the cellulose spinning solution is 0.5-1.0 wt %.

5. The method for preparing a large-diameter Lyocell fiber according to claim 3, characterized in that: In step (2), the pump supply is 12.1-15.0 mL / min, and the spinning speed is 30-40 m / min.

6. The method for preparing a large-diameter Lyocell fiber according to claim 3, characterized in that: In step (3), the length of the air section is 5-10 cm, the blowing speed of the air section is 2.1-4.0 m / s, and the blowing temperature is 15-20°C.

7. The method for preparing a large-diameter Lyocell fiber according to claim 3, characterized in that: In step (5), the water washing temperature is 20-25°C, the drying and heat setting temperature is 130-150°C, and the drying and heat setting time is 10-20 minutes.

8. The method for preparing a large-diameter Lyocell fiber according to any one of claims 1 to 7, characterized in that: The moisture regain of large-diameter Lyocell fibers is 4.58~5.56%, the dry modulus is 135~160 cN / dtex, the dry breaking strength is 3.5~4.0 cN / dtex, the wet breaking strength is 2.5~2.8 cN / dtex, and the dry breaking elongation is 5~10%.