Lyocell fiber, its production method and use in the production of nonwovens

Abstract

The application discloses lyocell fiber, a production method thereof and application thereof in preparation of non-woven fabric, and belongs to the technical field of lyocell fiber production. The production method comprises the following steps: mixing cellulose raw materials with NMMO solvent, and dissolving by heating to form a spinning stock solution; spinning the spinning stock solution through a spinning assembly, and cooling the spun yarn through accurate and cooperative combination of specific conditions to form nascent fibers; the spinning temperature is 100-110 DEG C; and the nascent fibers are subjected to stretching treatment to obtain high-performance lyocell fibers. The lyocell fiber of the embodiment has obviously improved breaking strength, can be widely applied to the fields of medical health, filtering materials, personal care and the like, and is beneficial to application.

Description

Technical Field

[0001] This invention belongs to the field of lyocell fiber production technology, and relates to a lyocell fiber, its production method, and its application in the preparation of nonwoven fabrics. Background Technology

[0002] Lyocell fiber, as a solvent-based cellulose fiber, uses N-methylmorpholine oxide (NMMO) as a solvent, making it non-toxic, harmless, renewable, and environmentally friendly. Currently, the global lyocell fiber market focuses on textile applications, while in the nonwoven fabric field, especially in high-end applications such as medical and health care and filtration materials, the research and development of specialized fibers is still in its early stages.

[0003] Existing production processes for nonwoven-specific lyocell fibers often fail to meet the strength and other performance requirements of nonwoven fabrics used in medical and hygiene, filtration, and other fields. With the widespread application of nonwoven fabrics in medical and hygiene, personal care, and industrial filtration, the performance requirements for the fibers used are becoming increasingly stringent. Traditional lyocell fiber production processes are primarily geared towards the textile industry, resulting in fibers that fall short of the strength and other performance requirements for nonwoven-specific fibers. Currently, research and production of nonwoven-specific lyocell fibers are still in their developmental stages. Summary of the Invention

[0004] This invention aims to provide a lyocell fiber, its production method, and its application in the preparation of nonwoven fabrics. The lyocell fiber produced by this invention has high strength and low production cost, and can be applied to nonwoven fabrics and other fields.

[0005] This invention provides a method for producing lyocell fiber, comprising the following steps:

[0006] Cellulose raw materials are mixed with NMMO solvent and dissolved by heating to form a spinning solution;

[0007] The spinning solution is spun through a spinning assembly, and the resulting filaments are cooled to form nascent fibers. The spinning temperature is 100~110℃, the cooling medium temperature is 18~25℃, and the cooling medium flow rate is 8-12m / s. The nascent fibers are then stretched to obtain lyocell fibers.

[0008] In some embodiments, the degree of polymerization of the cellulose feedstock is 950-1200.

[0009] In some embodiments, the cellulose raw material is pulverized and sieved to remove impurities before being mixed with the NMMO solvent.

[0010] In some embodiments, the heating and dissolving temperature is 80~90°C, and the heating and dissolving is carried out under a pressure of 0.5~0.8MPa.

[0011] In some embodiments, the spinning assembly includes a spinneret having a plurality of uniform circular spinneret holes with a diameter of 0.04-0.06 mm.

[0012] In some embodiments, the spinning pressure is 0.5~1MPa; the stretching ratio of the stretching treatment is 1.5~2.

[0013] In some embodiments, the production method further includes: coating the stretched fiber surface with a moisture-absorbing agent or subjecting it to plasma treatment to obtain finished lyocell fiber;

[0014] The production method further includes: recovering and purifying the NMMO solvent used in the formation of nascent fibers.

[0015] In some embodiments, the tensile strength of the lyocell fiber is 3.3~4 cN / dtex.

[0016] This invention provides the use of lyocell fibers obtained by the production method described above in the preparation of medical and health nonwoven fabrics, nonwoven filter materials or personal care nonwoven fabrics.

[0017] This invention first mixes cellulose raw materials with NMMO, dissolves them by heating to form a spinning solution, then spins and cools under specific process conditions to form nascent fibers, which are then stretched to obtain lyocell fibers. By synergistically optimizing production process parameters, this invention significantly improves the strength and uniformity of the produced lyocell fibers, better meeting the application needs of nonwoven fabrics in various fields. Compared with lyocell fibers produced by traditional processes, the fiber breaking strength of this invention is increased by 10%-20%, while reducing production costs. The lyocell fibers produced by this invention can be widely used in nonwoven fabric fields such as medical and health care, filtration materials, and personal care, expanding the application range of lyocell fibers and improving the market competitiveness of the products. Detailed Implementation

[0018] The technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0019] Traditional lyocell fiber production processes have the following limitations: First, to meet the demands of textile yarns, they employ relatively low draw ratios, typically 1.2-1.5 times, resulting in fiber breaking strength generally below 3.2 cN / dtex, which is insufficient for high-strength nonwoven fabrics. Second, they require a wide range of polymerization degrees (600-900) for the raw material cellulose pulp, and a wide window for dissolution and spinning process parameters, leading to poor uniformity of fiber fineness. This results in uneven basis weight and large strength fluctuations in the produced nonwoven fabrics. Tex is a commonly used unit of fiber fineness in the textile industry; it refers to the mass of 1000 meters of fiber per kilogram, and is typically used to indicate finer fibers.

[0020] Finally, post-processing typically involves only simple oiling, failing to effectively modify the nonwoven fabrics to meet the high absorbency and hydrophilicity requirements of applications such as medical and hygiene products and filtration materials. Currently, some manufacturers are attempting to produce nonwoven-specific lyocell fibers through localized adjustments, but with limited success.

[0021] This invention provides a method for producing lyocell fiber, comprising the following steps:

[0022] Cellulose raw materials are mixed with NMMO solvent and dissolved by heating to form a spinning solution;

[0023] The spinning solution is spun through a spinning assembly, and the resulting filaments are cooled to form nascent fibers. The spinning temperature is 100~110℃, the cooling medium temperature is 18~25℃, and the cooling medium flow rate is 8-12m / s.

[0024] The nascent fibers are stretched to obtain lyocell fibers.

[0025] The production method of this invention can effectively improve the strength and other properties of lyocell fibers, making it suitable for nonwoven fabric processing and other fields.

[0026] This invention first prepares raw materials, including selecting cellulose raw materials of specific quality (in pulp form, the conventional raw material form for lyocell fiber production), and pre-treating them (generally crushing and sieving) to remove impurities primarily through physical means. This invention uses cellulose raw materials with a high degree of polymerization, which can be commercially available products. The degree of polymerization of the cellulose raw material is preferably 950-1200, and more preferably 1000-1200; then, it undergoes crushing and sieving pre-treatment. After pre-treatment, the moisture content of the cellulose raw material is preferably controlled at 8%-12% (too high a moisture content will affect the dissolution efficiency of the NMMO solvent, while too low a moisture content will easily lead to excessive dust generation during the raw material crushing process); the ash content is less than or equal to 0.15%, as excessive ash content can easily introduce impurities and affect the uniformity of the spinning solution.

[0027] In this embodiment of the invention, pretreated cellulose raw materials are mixed with NMMO solvent in a certain proportion and dissolved under specific temperature and pressure conditions to form a uniform spinning solution.

[0028] In embodiments of the present invention, the mass ratio of the cellulose raw material to the NMMO solvent can be 1:3 to 5, for example, 1:3, 1:3.2, or 1:3.5. The resulting mixture is preferably subjected to a cellulose macromolecule dissolution process at 80-90°C and 0.5-0.8 MPa for 3-5 hours. The precisely controlled dissolution process in these embodiments ensures the high uniformity and absence of gel particles in the spinning solution; simultaneously, the simple composition of the spinning solution facilitates subsequent spinning and solvent recovery, thus reducing production costs.

[0029] After obtaining the spinning solution, this embodiment of the invention employs a wet spinning assembly for spinning. The spinning assembly mainly includes equipment for adjusting spinning temperature and pressure, and a spinneret, wherein the spinneret has multiple uniform circular spinneret holes. In this embodiment, the spinning temperature is 100~110℃, and the spinning pressure is 0.5~1MPa; the orifice diameter of the spinneret is preferably 0.04-0.06mm. This embodiment of the invention adjusts parameters such as spinning temperature, pressure, and spinneret orifice diameter to primarily control the fineness and uniformity of the fibers. A smaller spinneret orifice diameter (0.04-0.06mm), combined with stable spinning pressure and temperature, helps ensure the consistency of the initial conditions and fineness of each monofilament. The spinning speed can be controlled at 30-50m / min, matching the spinneret orifice diameter and cooling medium flow rate to ensure fiber uniformity.

[0030] In addition to employing the aforementioned higher spinning temperature, this invention also incorporates a forced and efficient filament cooling process. The cooling process typically involves heat exchange between the ejected filaments and a cool air medium. In this invention, the cooling medium temperature is 18-25°C (e.g., 18°C, 20°C, 22°C, 25°C), and the cooling medium flow rate is 8-12 m / s (e.g., 8 m / s, 10 m / s, 12 m / s). The cooling medium is usually dry, clean air, which is low-cost and easily scalable for continuous production. The air humidity must be controlled to be less than or equal to 30% to avoid affecting fiber formation. This invention synergistically optimizes the optimal medium range of temperature and flow rate of the cooling medium, which is beneficial for improving the fiber's crystalline structure and increasing fiber strength. Simultaneously, the controlled cooling conditions avoid differences in the fiber sheath and crystalline structure caused by uneven cooling, ensuring the uniformity of the fiber structure from the source of formation.

[0031] In the embodiments of this invention, the aforementioned spinning temperature ensures that the spinning solution has good rheological properties, facilitating high-ratio stretching. The subsequent efficient cooling rapidly "freezes" the fiber morphology, forming a more complete and uniform crystalline structure, providing a structural basis for subsequent high-ratio stretching (1.5-2.0 times). Simply increasing the spinning temperature or simply decreasing the cooling temperature can easily lead to solvent decomposition, spinning solution instability, increased breakage rate, or the formation of an excessively thick sheath, making the fiber brittle and hard. This process uses dry spinning, eliminating the need for a coagulation bath; the cooling process after spinning is completed through an air medium, directly achieving fiber solidification and shaping.

[0032] In this invention, the nascent fibers formed by spinning are stretched, with a stretching ratio preferably of 1.5 to 2, to further improve fiber strength. The fiber stretching ratio typically refers to the ratio of the length of the nascent fiber after spinning to its original length after the stretching process. This invention primarily combines medium-temperature cooling and high-stretching in a specific synergistic combination, simultaneously addressing issues related to strength, uniformity, and moisture absorption.

[0033] Subsequently, in a preferred embodiment of the invention, a layer of desiccant is coated onto the surface of the stretched fiber to ultimately obtain lyocell fiber. The optimized processes described above in this embodiment of the invention create a microstructure in the fiber that facilitates the adhesion and penetration of the desiccant, thereby improving the durability of the moisture-absorbing function. This embodiment of the invention employs a special surface coating process (using a coating process with strong adhesion to the fiber to apply the desiccant), which improves the fiber's moisture absorption and abrasion resistance.

[0034] In some embodiments, the surface coating process is an integrated "push-dry" process, including: an effective component mass fraction of 8%-15% for the desiccant, a push-dry temperature of 40-60℃, a push-dry pressure of 0.2-0.3MPa, and a roll-off rate of 60%-70%; and a drying temperature of 80-100℃ for 3-5 minutes to ensure uniform adhesion and curing of the desiccant. Alternatively, plasma treatment can be used to replace desiccant coating. The plasma treatment process may include: an argon atmosphere, a power of 300-500W, and a treatment time of 1-3 minutes, used to improve the hydrophilicity of the fibers.

[0035] More preferably, the hygroscopic agent described in this embodiment of the invention is an aqueous solution of PEG-400 (polyethylene glycol) and AEO-7 (fatty alcohol polyoxyethylene ether, abbreviated as AEO) in a mass ratio of 3:1. This hygroscopic agent is applied in aqueous solution form, with a mass fraction of 8%-15%, preferably 10%-12%. The hygroscopic agent selected in this specific embodiment of the invention contains certain hydrophilic groups, which can firmly bind to the surface of lyocell fibers through hydrogen bonding, forming a hydrophilic film on the fiber surface, significantly improving the fiber's water absorption and water molecule diffusion ability, while not affecting the fiber's breaking strength. For example, after coating with the hygroscopic agent, the fiber's moisture absorption rate can be increased to 10-13%, the adhesion strength ≥4 (wash resistance ≥20 times), and the fiber breaking strength remains at 3.3-4 cN / dtex. If the hydrophilic agent is applied by padding, the functional layer adhesion is weak, the durability is poor, and it may affect subsequent processing of the nonwoven fabric. Compared with lyocell fibers produced by traditional processes, the moisture absorption rate of the fibers in this embodiment of the invention can be increased by 5%-10%, which is more conducive to the application of lyocell fibers in the preparation of nonwoven products with high moisture absorption requirements.

[0036] In an embodiment of the present invention, the lyocell fiber has a circular cross-section, a breaking strength of 3.3~4 cN / dtex, further 3.5-4.0 cN / dtex, a fiber fineness of 1.5~1.8 dtex, and a water absorption rate of 10~13%.

[0037] This invention primarily achieves consistent control over the crystalline structure of nascent fibers through a precise and coordinated combination of spinning temperature, cooling medium temperature, and flow rate. This combination overcomes the technical bias of using cooling conditions only as an auxiliary means in conventional lyocell fiber production, significantly improving the fiber's breaking strength (to 3.3~4 cN / dtex). The embodiments of this invention innovatively solve problems related to strength, fineness uniformity, and hygroscopicity through a synergistic optimization of parameter systems across each step, and the systematic synergy of "medium-temperature spinning - medium-low temperature forced cooling - high-ratio stretching" in the overall production scheme. Furthermore, the production process of these embodiments improves the stability of the production process, reduces product quality fluctuations, and lowers the defect rate by precisely controlling the parameters of each production stage.

[0038] Furthermore, the production method described in this embodiment of the invention further includes: recovering and purifying the NMMO solvent during the formation of nascent fibers. The optimized solvent recovery process in this embodiment of the invention can improve the solvent recovery rate and reduce solvent consumption costs; simultaneously, improved production stability also reduces raw material waste, further lowering production costs. In some embodiments, the solvent recovery employs a combined "evaporation-distillation" process, specifically:

[0039] NMMO is recovered from spinning cooling waste liquid at an evaporation temperature of 120-140℃ and a pressure of 0.05-0.1MPa, with an evaporation efficiency of ≥95%. The evaporated NMMO solvent is purified by a distillation column at a distillation temperature of 160-180℃, with a purity of over 99.5%, and is recycled back to the dissolution process.

[0040] This invention provides the application of lyocell fibers obtained by the production method described above as raw materials in the preparation of nonwoven fabrics; the preparation processes of nonwoven fabrics include: spunbonding, meltblowing, needle punching, hydroentangling, thermal bonding, etc. The raw materials for preparing nonwoven fabrics in the embodiments of this invention include the obtained lyocell fibers, and the nonwoven products are prepared through wet processes, dry processes, etc.

[0041] The lyocell fiber obtained by this invention has high strength and good uniformity, which can meet the needs of high-end nonwoven products (such as medical and health products, personal care products, and filter materials). It can be called nonwoven-specific lyocell fiber, which has a wide range of applications and high market competitiveness.

[0042] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention. The substances used in these embodiments are commercially available.

[0043] Example 1

[0044] Raw material preparation: Cellulose raw material (pulp) with a degree of polymerization of 1000 is selected and pretreated by crushing and screening. After pretreatment, the moisture content of the cellulose raw material is 9%-10% and the ash content is 0.15%.

[0045] Dissolution: The pretreated cellulose raw material is mixed with NMMO solvent at a mass ratio of 1:3 and dissolved at 80℃ and 0.5MPa for 4 hours to form a spinning solution.

[0046] Spinning: The spinning temperature is 100℃, the spinning pressure is 0.8MPa, the spinneret orifice diameter is 0.05mm, and the spinning speed is controlled at 40m / min. The cooling medium (dry, clean air, humidity ≤30%) has a temperature of 21-25℃ and a flow rate of 8-9m / s.

[0047] Post-treatment: The nascent spun fibers are stretched 1.5 times, then coated with a moisture-absorbing agent (an aqueous solution of PEG-400 and AEO-7 in a 3:1 mass ratio, with an effective component mass fraction of 10%). Specific process: The moisture-absorbing agent is applied during padding at 40-60℃ and 0.2-0.3MPa, with a roll-off rate of 60%-70%. Afterward, the fibers are dried at 80-100℃ for 3-5 minutes. The resulting nonwoven lyocell fiber has a fineness of 1.5 dtex, a breaking strength of 3.5 cN / dtex, and a moisture absorption rate of 12%.

[0048] Testing methods: The breaking strength (GB / T 14337), moisture absorption rate (GB / T 6503), and fineness (GB / T 14335) are all tested using the national standard methods (the same applies to the following examples); the fineness uniformity is reflected by the coefficient of variation (CV). The fineness CV of the fibers produced by this process is ≤3% (the traditional process usually has ≥5%).

[0049] Example 2

[0050] Raw material preparation: Cellulose raw material with a degree of polymerization of 1200 is selected and pretreated. After pretreatment, the moisture content of the cellulose raw material is 9%-10%; the ash content is equal to 0.15%.

[0051] Dissolution: The pretreated cellulose raw material is mixed with NMMO solvent at a mass ratio of 1:3.5 and dissolved at 85℃ and 0.6MPa for 3.5 hours to form a spinning solution.

[0052] Spinning: Spinning temperature 105℃, pressure 0.9MPa, spinneret orifice diameter 0.06mm, spinning speed controlled at 40m / min. Cooling medium (dry, clean air, humidity ≤30%) temperature 18-20℃, flow rate 10-12m / s.

[0053] Post-treatment: The stretching ratio is 2 times, and the surface treatment adopts plasma treatment process, including: argon atmosphere, power 300-500W, treatment time 1-3 minutes.

[0054] The obtained lyocell fiber was tested and found to have a fineness of 1.8 dtex, a breaking strength of 3.8 cN / dtex, and a moisture absorption rate of 13%.

[0055] Example 3

[0056] Raw material preparation: Pretreatment of cellulose raw material with a degree of polymerization of 1100. After pretreatment, the moisture content of the cellulose raw material is 9%-10%; the ash content is equal to 0.15%.

[0057] Dissolution: The pretreated cellulose raw material is mixed with NMMO solvent at a mass ratio of 1:3.2 and dissolved at 90℃ and 0.7MPa for 4.5 hours to form a spinning solution.

[0058] Spinning: Spinning temperature 110℃, pressure 1.0MPa, spinneret orifice diameter 0.04mm, cooling medium temperature 18-20℃, flow rate 8-9m / s.

[0059] Post-treatment: The stretching ratio is 1.8 times, and the surface is coated with a desiccant (same as in Example 1). Specific process: impregnation with the desiccant (8%-15% by mass of effective ingredient) at a temperature of 40-60℃, a rolling pressure of 0.2-0.3MPa, and a roll-off rate of 60%-70%; followed by drying at a temperature of 80-100℃ for 3-5 minutes.

[0060] The obtained lyocell fiber was tested and found to have a fineness of 1.6 dtex, a breaking strength of 4.0 cN / dtex, and a moisture absorption rate of 11%.

[0061] Fineness uniformity is reflected by the coefficient of variation (CV). The fineness CV of the fibers produced by the process in the above embodiments of this application is ≤3% (compared to ≥5% in conventional processes). Due to the synergistic effect of process parameters such as spinning temperature, cooling medium temperature and flow rate, and stretching ratio, the resulting fiber products unexpectedly have high strength and good moisture absorption, and the production method is simple, efficient, and low-cost.

[0062] Comparative Example 1

[0063] Process: Cellulose pulp with a degree of polymerization of 800 is mixed with NMMO at a mass ratio of 1:2.9 and dissolved at 75°C and atmospheric pressure for 3 hours. The resulting spinning solution is then spun at 95°C and atmospheric pressure with a spinneret orifice diameter of 0.10 mm, and cooled naturally by still air at room temperature. The nascent fibers are stretched 1.3 times and treated with conventional spinning oil to obtain lyocell fiber products.

[0064] Product performance: The fiber fineness is 2.0±0.3 dtex, the breaking strength is 3.0 cN / dtex, and the moisture absorption rate is 9%. Compared with this application, its fiber strength is lower, the fineness is uneven, and the moisture absorption is generally lower.

[0065] Comparative Example 2

[0066] Process: Based on Comparative Example 1, the spinning temperature was increased to 115℃ while the cooling air temperature was reduced to 10℃ in an attempt to improve the strength.

[0067] Production Process and Results: Numerous fiber breaks and fuzz occurred during spinning, accompanied by a noticeable charring odor from the solvent, making continuous and stable production impossible and hindering control of production efficiency and costs. While the small amount of collected fibers showed a slight increase in strength (approximately 3.2 cN / dtex), their brittleness increased significantly, rendering them unsuitable for further processing. Stable production using a comparative process range was not feasible; precise coordination is essential to achieve the production of high-performance lyocell fiber products.

[0068] As can be seen from the above embodiments, the present invention studies the precise and synergistically optimized production process, such as optimal range (18-25℃, 8-12m / s) cooling, high-ratio stretching, and application methods for high-performance fiber products. This can improve the strength (strength 3.5-4.0cN / dtex), uniformity, and moisture absorption properties of lyocell fibers, resulting in good production stability, reduced production costs, and better meeting the product needs of nonwoven fabrics in different fields. This enhances the market competitiveness of the products and is of great significance.

[0069] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for producing lyocell fiber, characterized in that, Includes the following steps: Cellulose raw materials are mixed with NMMO solvent and dissolved by heating to form a spinning solution; The spinning solution is spun through a spinning assembly, and the resulting filaments are cooled to form nascent fibers. The spinning temperature is 100~110℃, the cooling medium temperature is 18~25℃, and the cooling medium flow rate is 8-12m / s. The nascent fibers are then stretched to obtain lyocell fibers.

2. The production method according to claim 1, characterized in that, The degree of polymerization of the cellulose raw material is 950-1200.

3. The production method according to claim 1, characterized in that, The heating and dissolving temperature is 80~90℃, and the heating and dissolving is carried out under a pressure of 0.5~0.8MPa.

4. The production method according to any one of claims 1-3, characterized in that, The spinning assembly includes a spinneret with a plurality of uniform circular spinneret holes, the diameter of which is 0.04-0.06 mm.

5. The production method according to claim 4, characterized in that, The spinning pressure is 0.5~1MPa; the stretching ratio of the stretching treatment is 1.5~2.

6. The production method according to any one of claims 1-3, characterized in that, The production method further includes coating the surface of the stretched fiber with a moisture absorbent or subjecting it to plasma treatment to obtain finished Lyocell fiber.

7. The production method according to claim 6, characterized in that, The stretched fibers are coated with a moisture absorbent through a pad-drying process. The moisture absorbent is a mixture of polyethylene glycol and fatty alcohol polyoxyethylene ether.

8. The production method according to any one of claims 1-3, characterized in that, The production method further includes: recovering and purifying the NMMO solvent used in the formation of nascent fibers.

9. Lyocell fiber obtained by the production method according to any one of claims 1-7, characterized in that, The tensile strength of the lyocell fiber is 3.3~4 cN / dtex.

10. The use of lyocell fibers obtained by the production method according to any one of claims 1-7 in the preparation of medical and health nonwoven fabrics, nonwoven filter materials or personal care nonwoven fabrics.