Method and system for preparing high-modulus fine denier bamboo fibers

Abstract

The invention relates to a high-modulus fine denier bamboo fiber preparation method and system, and relates to the technical field of biomass fiber preparation. Dissolving treatment; performing micro-gradient solidification; spinning drafting: performing air gap control and multi-stage drafting on the solidified fibers; and water washing post-treatment: carrying out water washing, soft finishing, drying and winding treatment on the fibers. A three-layer coagulating bath structure is innovatively designed and comprises an upper-layer solvent area, a middle-layer transition area and a lower-layer regeneration area. The middle layer CaCl2 delays water molecule permeation through an ion shielding effect, and the lower layer temperature gradient induces molecular chain rearrangement crystallization. And in cooperation with a two-stage drafting process, molecular chain height orientation arrangement is realized. According to the method, the problems of homogeneous phase solidification, fibrillation and fineness limitation in a traditional process are effectively solved, the prepared bamboo fibers have high section roundness, small fineness and high dry modulus, and high-quality fiber raw materials are provided for the high-end textile field.

Description

Technical Field

[0001] This application relates to the field of biomass fiber preparation technology, and in particular to a method and system for preparing high-modulus fine-denier bamboo fiber. Background Technology

[0002] With increasing environmental awareness and the growing acceptance of sustainable development concepts, the application of renewable plant resources, represented by bamboo, in the textile fiber field has received widespread attention. Bamboo fiber, due to its short growth cycle, abundant resources, good biodegradability, and natural antibacterial properties, is considered an ideal alternative to traditional natural fibers such as cotton and linen.

[0003] Currently, industrially produced bamboo fiber mainly employs a wet spinning process. This involves extracting cellulose from bamboo using physical or chemical methods, dissolving it in a specific solvent to form a spinning solution, and then processing it through spinning, coagulation, washing, and drying to produce regenerated fibers. Traditional wet spinning processes typically use NMMO, alkaline solutions, or ionic liquids as solvents, and fiber regeneration is carried out in a single-component coagulation bath. While this process is simple and easy to implement, it faces significant technical bottlenecks in the preparation of fine-denier, high-modulus bamboo fibers.

[0004] The homogeneous coagulation environment used in existing technologies leads to bidirectional instantaneous diffusion between the solvent and coagulant, causing the surface and inner layers of the fiber to solidify simultaneously, forming a loose structure. In this state, the internal microstructure of the fiber is uneven, the surface roughness is high, and the cross-section exhibits an irregular shape, severely affecting the physical and mechanical properties of the fiber. When process parameters are not set properly, regenerated fibers are also prone to "fibrillation," where the solution solidification rate is too fast, causing the molecular chains to not have enough time to align, forming a large number of microfiber bundles and resulting in low strength and low modulus characteristics.

[0005] Furthermore, traditional processes are limited by dissolution concentration and solidification kinetics, making it difficult to achieve efficient fine denier fiber production. When the fineness drops below 1 dtex, the fiber cross-section becomes severely distorted, and the strength and modulus decrease significantly, failing to meet the demands of high-end textiles and functional materials. Simultaneously, the limitations of existing drawing processes also lead to insufficient molecular chain arrangement and an imbalance in the ratio of crystalline to amorphous regions, affecting the overall performance of the fiber.

[0006] Therefore, there is an urgent need to develop a new bamboo fiber preparation technology to solve problems such as homogeneous solidification, fibrillation, and fineness limitations in traditional processes, so as to realize the large-scale production of high-modulus fine denier bamboo fiber and promote the widespread application of bamboo fiber in the high-end textile field. Summary of the Invention

[0007] The purpose of this application is to provide a method and system for preparing high-modulus fine-denier bamboo fiber, which solves the problems of uneven fiber structure, easy fibrillation, and difficulty in achieving efficient fine denier fiber production caused by the homogeneous solidification environment in traditional wet spinning processes.

[0008] In the first aspect, the method for preparing high-modulus fine-denier bamboo fiber provided in this application adopts the following technical solution, including the following steps: S1, bamboo pretreatment: mechanical treatment, chemical treatment and fiber separation of bamboo; S2, Dissolution treatment: Dissolve the pretreated bamboo fiber in NMMO solution and filter it; S3, micro-gradient coagulation: gradient coagulation of solution through a three-layer coagulation bath structure; S4, Spinning Drafting: Air gap control and multi-stage drafting of solidified fibers; S5, post-washing treatment: the fibers are washed, softened, dried and wound.

[0009] Preferably, the bamboo pretreatment includes: Mechanical processing: Peel the bamboo, cut it into sections, and crush it to the specified particle size; Chemical treatment: alkaline treatment, neutralization treatment, and bleaching treatment; Fiber separation: high-speed shear dispersion, homogenization and centrifugal dehydration are performed.

[0010] Preferably, the dissolution process includes: Prepare NMMO solution and add stabilizer; Dissolve according to a specific temperature procedure and time; The solution undergoes pre-filtration and precision filtration.

[0011] Preferably, the stabilizer comprises glycerol and N-propyl gallate, and the dissolution process is carried out under a dual-propeller stirring and vacuum environment.

[0012] Preferably, the micro-gradient solidification is achieved through a three-layer solidification bath structure, comprising: Upper solvent region: a low-temperature region containing a specific concentration of NMMO; Intermediate transition zone: a medium-temperature region containing specific concentrations of NMMO and CaCl2; Lower regeneration zone: a high-temperature zone containing low concentrations of NMMO.

[0013] Preferably, the coagulation bath is provided with partitions and anti-mixing devices between each layer. The partitions are honeycomb-shaped guide plates with a specific porosity, and the anti-mixing devices are PEEK material screens with a specific pore size.

[0014] Preferably, the coagulation bath is equipped with a temperature control system, including an upper cooling system and a lower heating system, wherein the upper layer uses semiconductor refrigeration and the lower layer uses titanium alloy heating coils.

[0015] Preferably, the spinning draw includes: Spinning is performed through spinnerets of a specific diameter; Control the air gap height and environmental parameters; Two-stage drawing is performed, with a total drawing ratio of 1.7-1.9.

[0016] Preferably, the post-washing treatment includes: Multi-stage series washing, with water flow direction opposite to fiber movement direction; Silicone oil emulsion softening finish; Hot air circulation pre-drying and hot roller main drying; Controlling a specific tension during winding.

[0017] Secondly, the system for preparing high-modulus fine-denier bamboo fibers provided in this application adopts the following technical solution: including: Bamboo pretreatment equipment includes a segmenter, a shredder, and a high-speed shear disperser; The dissolving system includes a twin-propeller dissolver and a filtration device; The micro-gradient coagulation device includes a three-layer coagulation bath, partitions, a temperature control system, and an anti-mixing device. The spinning and drawing system includes a spinneret, an air gap control device, and a multi-stage drawing device; The post-washing treatment system includes a multi-stage series washing tank, a softening device, a drying device, and a winding device; The control system is used to monitor and control various process parameters.

[0018] In summary, this application includes at least one of the following beneficial technical effects: 1. This invention solves the problem of homogeneous coagulation in traditional wet spinning by using micro-gradient coagulation technology and a three-layer coagulation bath structure design, achieving uniform coagulation of fibers and making the prepared bamboo fibers have high cross-sectional roundness and low fineness, effectively overcoming the fine denier limit of traditional processes.

[0019] 2. In this invention, CaCl2 is added to the middle coagulation bath to slow down the water molecule permeation rate by utilizing its ion shielding effect. Combined with the design of lower layer temperature gradient-induced crystallization, the fiber fibrillation phenomenon is significantly suppressed, the crystallinity and modulus of the fiber are improved, and the fiber has excellent mechanical properties.

[0020] 3. The partition plate and anti-mixing device design adopted in this invention precisely controls the mixing degree and mass transfer rate of each layer of coagulation bath. Combined with the two-stage drawing process, it achieves a high degree of orientation of molecular chains, improves the strength and modulus of the fiber, and maintains good toughness. Attached Figure Description

[0021] Figure 1 This is a process flow diagram of the high-modulus fine-denier bamboo fiber preparation method provided in the embodiments of the present invention; Figure 2 This is a schematic diagram of the micro-gradient solidification system structure provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the high-modulus fine-denier bamboo fiber preparation system in an embodiment of the present invention; Figure 4 This is a schematic diagram of the bamboo pretreatment device in an embodiment of the present invention; Figure 5 This is a schematic diagram of the solidification bath partition and anti-mixing device in an embodiment of the present invention. Detailed Implementation

[0022] The following is in conjunction with the appendix Figure 1 -Appendix Figure 5 This application will be described in further detail below.

[0023] See attached document Figure 1 Appendix Figure 3 and attached Figure 4 The first aspect of this invention provides a method for preparing high-modulus fine-denier bamboo fiber, comprising the following steps: S1, Bamboo Pretreatment: Mechanical treatment, chemical treatment and fiber separation of bamboo; Bamboo pretreatment is the primary step in preparing high-modulus, fine-denier bamboo fibers, directly affecting subsequent processing and the final fiber performance. This step, through three stages—mechanical treatment, chemical treatment, and fiber separation—transforms the raw bamboo into a fiber raw material suitable for dissolution spinning. Selecting suitable bamboo and performing standardized pretreatment are crucial for ensuring the stability of the preparation process and product quality.

[0024] In this embodiment, the bamboo pretreatment first selects 3-5 year old moso bamboo as raw material, as the bamboo at this stage has a high cellulose content, which is beneficial for obtaining high-quality fiber. The mechanical processing stage begins with the peeling of the bamboo, after which the outer green skin is removed and the bamboo is cut into 5-10 cm long segments. Then, a hammer mill is used to pulverize the cut bamboo segments to a particle size of 10-20 mm. During the pulverizing process, the hammer mill speed is controlled at 2500-3000 rpm to ensure uniform crushing effect.

[0025] The chemical treatment stage employs a multi-step process. First, a primary alkali treatment is performed, where bamboo pulverizer is soaked in a 5-8% NaOH aqueous solution at a ratio of 1:8, maintained at 90-95℃ for 60-90 minutes. This process primarily removes non-cellulose components such as pectin and hemicellulose from the bamboo. After alkali treatment, a 0.5-1% acetic acid solution is used for neutralization, adjusting the pH to 6.5-7.0. A secondary bleaching treatment is then performed using a 3-5% H₂O₂ solution at 60-70℃ for 40-60 minutes to remove pigments and lignin residues from the bamboo fibers. Finally, the treated fibers are washed repeatedly with deionized water until the pH reaches neutral.

[0026] The fiber separation stage first employs high-speed shear dispersion technology, with a rotation speed of no less than 8000 rpm, to fully disperse the aggregated fibers. The dispersion degree of bamboo fibers can be evaluated using the following formula: ; In the formula: This represents the percentage of fiber dispersion. This represents the total theoretical surface area of ​​a single fiber. This represents the actual measured fiber surface area. The dispersed fibers are homogenized by passing them through a 120-200 mesh sieve to ensure uniform fiber length and thickness distribution.

[0027] The treated fibers are then centrifuged to remove water, with the final moisture content controlled within the range of 40-45%. The moisture content is calculated using the following formula: ; In the formula: The percentage is the moisture content. For wet fiber quality; This refers to the oven-dry fiber quality. Appropriate moisture content helps ensure uniform solvent penetration during subsequent dissolution.

[0028] The selection of parameters during bamboo pretreatment is based on a balance between protecting the cellulose structure and effectively removing non-cellulose components. Excessive alkali concentration leads to cellulose degradation, affecting the final fiber strength; insufficient concentration fails to effectively remove non-cellulose components. Temperature and time control during bleaching are equally important for maintaining the integrity of the fiber structure.

[0029] After standardized pretreatment, the bamboo fiber is light beige, soft to the touch, with a fiber length distribution between 0.8 and 2.5 mm, a cellulose content of 88-92%, and an ash content of less than 0.5%, providing a high-quality raw material basis for subsequent dissolution processes.

[0030] S2, Dissolution treatment: Dissolve the pretreated bamboo fiber in NMMO solution and filter it; See attached document Figure 2 After bamboo pretreatment, the resulting fibers need to undergo a dissolution process, a crucial step in converting bamboo fibers into a spinning solution. The quality of the dissolution process directly determines the smoothness of the subsequent spinning process and the final internal structural characteristics of the fibers. This stage mainly involves the preparation of a specific solvent system, precise temperature control during dissolution, and multi-stage filtration to achieve complete dissolution and homogenization of the bamboo fibers, laying the foundation for micro-gradient coagulation.

[0031] In this embodiment, an aqueous solution of N-methylmorpholine-N-oxide (NMMO) was used as the main solvent for the dissolution process. An NMMO aqueous solution with a concentration of 88–92% was selected, as this concentration range effectively balances dissolution efficiency with the risk of cellulose degradation. A combination of stabilizers was added to the solvent system, including 0.8–1.2% glycerol and 0.05–0.1% N-propyl gallate. The former improves the rheological properties of the solution, while the latter acts as an antioxidant to prevent oxidative degradation of cellulose. The mass ratio of bamboo fiber to solvent was controlled within the range of 1:15 to 1:18, a ratio that ensures sufficient dissolution while maintaining a suitable solution viscosity.

[0032] The dissolution process employed a stepwise heating program. The initial temperature was set at 70℃ and maintained for 30 minutes to ensure thorough solvent wetting of the fiber surface. Subsequently, the temperature was increased to 85–95℃ at a constant rate of 1℃ / min; this temperature range represents the optimal temperature window for NMMO dissolution of bamboo fiber. The dissolution apparatus used a twin-propeller stirrer, with the speed controlled between 80 and 120 rpm. The stirring intensity was characterized by the Reynolds number (Re). ; In the formula: The Reynolds number (dimensionless); The density of the solution is expressed in g / cm³. The stirring speed (r / s) is the stirring speed. The diameter of the agitator blades (cm); The dynamic viscosity of the solution is (g / (cm·s)).

[0033] The entire dissolution process was carried out under a vacuum of -0.08 MPa; reducing the oxygen concentration effectively inhibited the oxidative degradation of cellulose. The dissolution time was controlled between 120 and 150 minutes to ensure complete dissolution of the bamboo fiber and the formation of a homogeneous solution. Solubility was assessed using the optical transmittance method, calculated using the following formula: ; In the formula: This represents the percentage of solubility. The transmittance of the solution to be tested; Transmittance of the undissolved suspension; The transmittance of a completely dissolved solution.

[0034] The solution filtration employs a two-stage filtration process. First, a 40–60 μm metal wire mesh is used for pre-filtration to remove undissolved particles and mechanical impurities. Then, a 5–10 μm sintered stainless steel filter element is used for precision filtration to ensure the purity of the spinning solution. The filtration temperature is maintained at 75–80℃, which ensures good solution flowability while preventing degradation caused by excessively high temperatures. The filtration pressure is controlled within the range of 0.3–0.5 MPa; excessive pressure may cause localized degradation, while excessively low pressure will affect filtration efficiency.

[0035] The filtered solution is allowed to stand for 4–6 hours to eliminate internal stress introduced during processing and prevent instability in subsequent spinning processes. Solution viscosity is an important indicator for evaluating its spinning suitability, and it is correlated with temperature through the following equation: ; In the formula: The viscosity of the solution is expressed in Pa·s. , These are constants related to the properties of the solution; This represents the actual temperature (K). Reference temperature (K).

[0036] After dissolution treatment, the bamboo fiber solution is amber-colored and translucent, with a zero-shear viscosity controlled at 80–120 Pa·s at 25°C, and a solid content (cellulose concentration) maintained within the range of 8–12%. This solution possesses ideal spinning properties and can meet the requirements of subsequent micro-gradient coagulation processes.

[0037] S3, micro-gradient coagulation: gradient coagulation of solution through a three-layer coagulation bath structure; See attached document Figure 2 Micro-gradient coagulation is the core technology of this invention, transforming the dissolved bamboo fiber solution into a solid fiber structure. Traditional coagulation baths employ a homogeneous environment, leading to bidirectional instantaneous diffusion of solvent and water molecules, resulting in a loose outer layer and irregular cross-sections. This step innovatively designs a three-layer coagulation bath structure, utilizing concentration gradients, temperature gradients, and ion shielding effects to achieve gradient regeneration and crystallization control of the fibers, solving the three major technical bottlenecks of homogeneous coagulation, fibrillation, and fineness limitations in traditional processes.

[0038] In this embodiment, the micro-gradient coagulation system constructs a three-layer coagulation bath with a clearly defined structural hierarchy. The upper solvent zone uses a 28–32% NMMO aqueous solution, with the temperature controlled within the range of 18–22°C, and the liquid layer height is 30–40 mm. The pH value of this layer is adjusted to 6.0–6.5, and 0.2–0.5% polyethylene glycol (PEG-4000) is added to improve surface lubricity. The upper region is mainly responsible for forming a dense fibrous surface layer to prevent the internal structure from solidifying too quickly. The solution circulation flow rate is maintained at 0.05–0.08 m / s to ensure uniformity of the concentration field.

[0039] The key technique for preparing a 13-17% NMMO solution in the intermediate transition zone is the addition of 4-6% calcium chloride (CaCl2). The intermediate layer temperature is controlled at 25-28℃, and the liquid level is set at 50-60 mm. CaCl2 plays an ion-shielding role in this layer. 2+ It forms coordination complexes with the hydroxyl groups on the cellulose molecular chain, significantly slowing down the water molecule permeation rate. The decrease in the water molecule diffusion coefficient can be estimated using the modified Stokes-Einstein equation: ; In the formula: The diffusion coefficient of water molecules (mm² / s); Boltzmann constant (1.38 × 10⁻⁶) -23 J / K); Absolute temperature (K); The viscosity of the solution is expressed in Pa·s. The effective radius of a water molecule (mm); It is the ion shielding factor (dimensionless, positively correlated with CaCl2 concentration).

[0040] Add 0.01-0.05% of quaternary ammonium salt antibacterial agent to the middle layer to prevent microbial growth. Homogenize and stir every 5-8 minutes, with the speed controlled at 15-20 rpm to prevent uneven local concentration fields.

[0041] In the lower regeneration zone, a 4–6% low-concentration NMMO solution is prepared, and the temperature is raised to 33–37°C, with a liquid layer height of 80–100 mm. A buffer salt (disodium hydrogen phosphate / potassium dihydrogen phosphate) of 0.1–0.3% is added to this layer to maintain pH stability. The temperature gradient in the lower layer induces cellulose molecular chain rearrangement, promoting increased crystallinity. The temperature gradient is calculated using the following formula: ; In the formula: The temperature gradient is expressed in °C / mm. Temperature of the lower layer (°C); Temperature of the upper layer (°C); This represents the total height of the coagulation bath (mm).

[0042] Partitions are installed between the layers of the coagulation bath, and honeycomb baffles made of 316L stainless steel or polyetheretherketone (PEEK) are used. The cell diameter is controlled at 5–8 mm, the porosity is 28–32%, and the thickness is 1.5–2.0 mm. The baffles are installed at a 3–5° angle to the horizontal plane to facilitate natural bubble discharge. The edges are finished with a 0.5–1.0 mm radius rounded transition to avoid scratching the fibers.

[0043] The temperature control system consists of two parts: upper cooling and lower heating. Upper cooling utilizes a semiconductor refrigeration device (TEC module) with a power density of 0.2–0.3 W / cm² and a control accuracy of ±0.5℃. Temperature monitoring uses 3–5 PT100 platinum resistance thermometers, averaging the values, and employs PID closed-loop control with a sampling frequency of 5 seconds per measurement. The control equation is: ; In the formula: To control the output; Temperature deviation; , , These are the proportional, integral, and differential coefficients, respectively.

[0044] The lower heating system uses titanium alloy heating coils with a diameter of 10-12mm, evenly distributed in a serpentine pattern with a spacing of 40-50mm. The heating rate is controlled at 1.8-2.2℃ / min, and the heat transfer medium flow rate is adjusted by an electromagnetic proportional valve (response time <2s). The heat transfer medium can be heat transfer oil or deionized water.

[0045] See attached document Figure 5 The anti-mixing device is made of PEEK engineering plastic with a screen mesh of 1.8–2.2 mm aperture, installed in a staggered pattern, achieving a coverage rate of over 85%. The flow rate is controlled at ≤0.1 m / s and precisely adjusted via a variable frequency pump. A backwashing device is installed, with a cleaning cycle of 30–45 minutes per cycle to prevent clogging of the channels.

[0046] The solidification strengthening during microgradient solidification can be expressed by the following formula: ; In the formula: For solidification strength (dimensionless); This represents the percentage of CaCl2 concentration. The temperature gradient is expressed in °C / mm. The diffusion coefficient of water molecules is denoted as (mm² / s).

[0047] The crystallization kinetics of fibers during solidification follow a modified Avrami equation: ; In the formula: for Crystallinity at time; To achieve the final equilibrium crystallinity; This is the crystallization rate constant (related to temperature and CaCl2 concentration); The Avrami index (typically 1.5–2.5); The crystallization time is denoted as s.

[0048] The fibers formed by the micro-gradient coagulation process have a gradually changing structural gradient from the outside to the inside. The outer layer forms a dense skin, while the interior maintains a moderately porous structure, with the skin-to-core ratio controlled within the range of 1:2.5 to 1:3. The roundness of the fiber cross-section is significantly better than that of traditional processes, providing a good foundation for subsequent drawing processes.

[0049] S4, Spinning Drafting: Air gap control and multi-stage drafting of solidified fibers; After micro-gradient solidification, the wet fibers need to undergo spinning and drawing, a crucial step that determines the final denier and mechanical properties of the fibers. By precisely controlling the spinneret parameters, air gap environment, and multi-stage drawing conditions, the directional alignment and crystalline structure of the fibers are optimized. During spinning and drawing, the molecular chains rearrange and orient, forming highly oriented crystalline regions and less oriented amorphous regions. The synergistic effect of these two processes endows the fibers with excellent physical and mechanical properties. Combined with micro-gradient solidification technology, a well-designed drawing process can further enhance the fiber's denier and modulus.

[0050] In this embodiment, the spinning and drawing process begins with the design of the spinneret system. High-titanium stainless steel or zirconium alloy spinnerets are selected, as both materials possess excellent corrosion resistance and dimensional stability. The spinneret orifice diameter is controlled within the range of 0.04–0.06 mm, and the orifice length-to-diameter ratio is set at 2.0–2.5:1. This ratio ensures stable solution flow while providing a sufficient pressure stability zone. The spinneret orifice is designed with an inlet funnel-shaped structure and an outlet cylindrical structure, effectively reducing inlet resistance and stabilizing the outlet flow field. The spacing between adjacent spinnerets is set at 1.5–2.0 mm to prevent fiber adhesion. The spinneret temperature is maintained at 70–75°C, and the spinning pressure is controlled within the range of 0.4–0.6 MPa.

[0051] The relationship between spinning pressure and flow rate conforms to the Hagen-Poiseuille equation: ; In the formula: Volumetric flow rate (mm³ / s); The spinneret radius (mm); Pressure drop (MPa); The viscosity of the solution is expressed in Pa·s. The length of the spinneret orifice is in mm.

[0052] The air gap control element is located between the spinneret and the coagulation bath surface, with the air gap height adjusted to 5–15 mm. The temperature in this region is controlled at 75–80℃, and the humidity is maintained within the RH range of 65–75%. The air gap environment is crucial for the initial molecular chain orientation; the airflow velocity is set ≤0.2 m / s to prevent airflow disturbances from causing fiber oscillation. The extended flow in the air gap region can be described using the Maxwell model. ; In the formula: Stress (MPa); Viscosity (Pa·s); It represents the elastic modulus (MPa). The strain rate is 1 / s.

[0053] The drafting process employs a two-stage drafting design. In the first drafting zone, the drafting ratio is set at 1.3–1.4, the drafting roller temperature is 30–35℃, the linear speed is controlled at 15–25 m / min, and the tension is maintained at 0.1–0.15 cN / dtex. The primary purpose of the first drafting zone is to achieve initial fiber orientation and prevent excessive stress concentration.

[0054] The second drafting zone has a total draft ratio of 1.7 to 1.9, and the drafting roll temperature is raised to 45 to 50°C. The surface of the drafting roll undergoes precision sandblasting, with a surface roughness Ra controlled at 0.2 to 0.4 μm to enhance the friction between the roll surface and the fibers. The tension in the second zone is controlled at 0.15 to 0.2 cN / dtex, and a twist of 20 to 30 T / m in the S direction is applied to prevent fiber adhesion.

[0055] The deformation behavior during the drawing process is represented by the draw ratio: ; In the formula: The draw ratio (dimensionless); The length of the fiber after stretching (mm); The original fiber length (mm).

[0056] The relationship between molecular chain orientation and draw ratio can be expressed as: ; In the formula: The orientation factor (dimensionless, ranging from 0 to 1); The angle between the molecular chain and the fiber axis (rad); It is the average of the square of the cosine of the included angle.

[0057] Fiber orientation can also be determined by the sound velocity method: ; In the formula: Orientation factor; The velocity of sound in isotropic fibers (m / s); The velocity of sound in the fiber to be tested is denoted as ρ (m / s).

[0058] The relationship between fiber fineness and spinneret diameter and draw ratio can be expressed as: ; In the formula: The final fiber linear density (dtex); The original spinneret linear density (dtex); Total draw ratio (dimensionless); The fiber shrinkage coefficient is 0.85 to 0.95, which depends on the post-processing conditions.

[0059] The effect of stretching temperature on molecular chain motion can be described by the WLF equation: ; In the formula: This is the time-temperature displacement factor; , These are material constants; This is the actual temperature (°C). The glass transition temperature is ℃.

[0060] The stress-strain relationship during the stretching process follows a nonlinear viscoelastic model: ; In the formula: Stress (MPa); Young's modulus (MPa); For strain (dimensionless); is the strain hardening coefficient (dimensionless).

[0061] After two stages of drawing, the fiber cross-sectional shape becomes more regular, the fineness decreases to the range of 0.68–0.85 dtex, the molecular chain orientation degree increases to 78–90%, and the breaking strength reaches 3.7–4.7 cN / dtex. At this point, the fiber already possesses high modulus and fine denier characteristics, but further washing is still required to stabilize the structure and improve the hand feel.

[0062] S5, post-washing treatment: the fibers are washed, softened, dried and wound.

[0063] Although the bamboo fiber has formed a basic structure after spinning and drawing, it still needs to undergo a post-washing treatment to remove residual solvents, stabilize the internal structure, and impart good performance properties. The post-washing treatment is the final step in the entire manufacturing process, including four steps: multi-stage washing, softening finishing, drying, and winding. This process not only removes residual NMMO solvents and CaCl2 from the fiber but also improves the fiber's feel and durability through specific finishing agents. Simultaneously, precisely controlled drying and winding processes stabilize the fiber's internal structure, preventing excessive shrinkage and stress accumulation, thus ensuring the quality of the final product.

[0064] In this embodiment, the washing system is designed with a multi-stage series washing tank structure, containing at least three washing units. The temperature of the first-stage washing tank is controlled at 40–45°C to accelerate solvent dissolution; the temperature of the second-stage washing tank is reduced to 30–35°C; and the third-stage washing tank is at room temperature. The entire system uses deionized water with a conductivity ≤5 μS / cm to prevent secondary contamination of the fibers by metal ions. The liquid-to-fiber ratio is controlled at 1:30–1:40 during the washing process to ensure sufficient space for solvent exchange. The water flow direction is designed to be opposite to the fiber's direction of movement, creating a countercurrent extraction effect and improving solvent removal efficiency.

[0065] The solvent removal rate of water washing follows an exponential decay model: ; In the formula: Let be the solvent removal rate (%) at time t; The theoretical maximum removal rate (%); The removal rate constant is 1 / min; The washing time is in minutes.

[0066] The overall efficiency of a multi-stage washing tank can be calculated using a cascade efficiency equation: ; In the formula: The total removal efficiency; , ... These represent the single-stage removal efficiency of each type of water washing tank.

[0067] The change in solvent concentration in the fiber during the washing process follows Fick's diffusion law: ; In the formula: Solvent concentration (mg / g); Time (s); The diffusion coefficient is (cm² / s). Radial distance (cm).

[0068] The softening finishing process is carried out immediately after washing. A 1.0–2.0% concentration of silicone oil emulsion is prepared as the softener, and the treatment temperature is maintained within the range of 40–45℃. The immersion time is controlled at 30–45 seconds to ensure uniform penetration of the softener. The pH value of the finishing solution is adjusted to 5.5–6.5, which is conducive to the uniform adsorption of the silicone oil emulsion on the fiber surface. The oiling rate, i.e., the percentage of oil adsorbed by the fiber, is controlled within the range of 0.3–0.5%, calculated using the following formula: ; In the formula: Oiling rate (%); The dry weight of the fiber (g) before processing; The dry weight of the fiber after treatment (g).

[0069] After softening, the fibers enter the drying process, employing a two-stage drying technique. The pre-drying stage uses hot air circulation equipment, with the temperature controlled at 50–60℃ for 1–2 minutes, to slowly remove surface moisture from the fibers. The main drying stage uses hot roller drying, raising the temperature to 100–110℃ and maintaining a contact time of 15–20 seconds to rapidly evaporate internal moisture from the fibers. The fiber shrinkage rate (Sh) during the drying process is calculated as follows: ; In the formula: Shrinkage rate (%); The wet fiber length (mm); The length of the fiber after drying (mm).

[0070] The drying process controls the final fiber moisture content to be within the range of 7% to 9%, which is beneficial for maintaining good elasticity and strength. Moisture content is measured using the oven drying method, and the calculation formula is as follows: ; In the formula: Moisture content (%); To test the original mass (g) of the sample; The mass (g) of the sample after it has been oven-dried.

[0071] Winding is the final step. The winding tension is controlled between 0.08 and 0.12 cN / dtex; this range ensures a tight package without excessive fiber stretching. The winding speed is 150–200 m / min; excessive speed may lead to static electricity buildup and fiber scattering. The package density is controlled between 0.55 and 0.65 g / cm³; excessive density can cause inner fiber deformation, while insufficient density affects package stability. The unwinding tension is set between 0.05 and 0.08 cN / dtex to ensure smooth fiber release during subsequent processing.

[0072] The interlayer pressure distribution during the winding process follows the following relationship: ; In the formula: radius Interlayer pressure (MPa); The outer pressure (MPa); The outer diameter of the roll (mm); For any layer radius (mm).

[0073] Finished fiber rolls are packaged in isolated packaging, with the outer layer sealed using waterproof and dustproof materials. The storage environment is controlled at a temperature of 20±2℃ and a relative humidity of 65±5%. The fiber packaging is labeled with the batch number, production date, specifications, and basic performance indicators for easy quality traceability.

[0074] After a complete washing and post-treatment process, the surface smoothness of bamboo fiber is improved, its hand feel is soft, and the residual solvent content is less than 0.01%. The fiber cross-section maintains good roundness (≥85%), and the dry modulus is stable in the range of 20-24 GPa. The final high-modulus fine denier bamboo fiber has a uniform color, appearing as a natural light yellow or milky white, and possesses good spinnability and stable physical and mechanical properties.

[0075] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Identical components are represented by the same reference numerals. Therefore, all equivalent changes made to the structure, shape, and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for preparing high-modulus fine-denier bamboo fiber, characterized in that, Includes the following steps: S1, Bamboo Pretreatment: Mechanical treatment, chemical treatment and fiber separation of bamboo; S2, Dissolution treatment: Dissolve the pretreated bamboo fiber in NMMO solution and filter it; S3, micro-gradient coagulation: gradient coagulation of solution through a three-layer coagulation bath structure; S4, Spinning Drafting: Air gap control and multi-stage drafting of solidified fibers; S5, post-washing treatment: the fibers are washed, softened, dried and wound.

2. The method for preparing high-modulus fine-denier bamboo fiber according to claim 1, characterized in that, The bamboo pretreatment includes: Mechanical processing: Peel the bamboo, cut it into sections, and crush it to the specified particle size; Chemical treatment: alkaline treatment, neutralization treatment, and bleaching treatment; Fiber separation: high-speed shear dispersion, homogenization and centrifugal dehydration are performed.

3. The method for preparing high-modulus fine-denier bamboo fiber according to claim 1, characterized in that, The dissolution process includes: Prepare NMMO solution and add stabilizer; Dissolve according to a specific temperature procedure and time; The solution undergoes pre-filtration and precision filtration.

4. The method for preparing high-modulus fine-denier bamboo fiber according to claim 3, characterized in that, The stabilizer comprises glycerol and N-propyl gallate, and the dissolution process is carried out under a dual-propeller stirring and vacuum environment.

5. The method for preparing high-modulus fine-denier bamboo fiber according to claim 4, characterized in that, The micro-gradient solidification is achieved through a three-layer solidification bath structure, including: Upper solvent region: a low-temperature region containing a specific concentration of NMMO; Intermediate transition zone: a medium-temperature region containing specific concentrations of NMMO and CaCl2; Lower regeneration zone: a high-temperature zone containing low concentrations of NMMO.

6. The method for preparing high-modulus fine-denier bamboo fiber according to claim 5, characterized in that, The coagulation bath is equipped with partitions and anti-mixing devices between each layer. The partitions are honeycomb-shaped guide plates with a specific porosity, and the anti-mixing devices are PEEK material screens with a specific pore size.

7. The method for preparing high-modulus fine-denier bamboo fiber according to claim 5, characterized in that, The coagulation bath is equipped with a temperature control system, including an upper cooling system and a lower heating system. The upper system uses semiconductor refrigeration, and the lower system uses titanium alloy heating coils.

8. The method for preparing high-modulus fine-denier bamboo fiber according to claim 1, characterized in that, The spinning draw includes: Spinning is performed through spinnerets of a specific diameter; Control the air gap height and environmental parameters; Two-stage drawing is performed, with a total drawing ratio of 1.7-1.

9.

9. The method for preparing high-modulus fine-denier bamboo fiber according to claim 1, characterized in that, The post-washing treatment includes: Multi-stage series washing, with water flow direction opposite to fiber movement direction; Silicone oil emulsion softening finish; Hot air circulation pre-drying and hot roller main drying; Controlling a specific tension during winding.

10. A system for preparing high-modulus fine-denier bamboo fibers, applied to the method for preparing high-modulus fine-denier bamboo fibers according to any one of claims 1-9, characterized in that, include: Bamboo pretreatment equipment includes a segmenter, a shredder, and a high-speed shear disperser; The dissolving system includes a twin-propeller dissolver and a filtration device; The micro-gradient coagulation device includes a three-layer coagulation bath, partitions, a temperature control system, and an anti-mixing device. The spinning and drawing system includes a spinneret, an air gap control device, and a multi-stage drawing device; The post-washing treatment system includes a multi-stage series washing tank, a softening device, a drying device, and a winding device; The control system is used to monitor and control various process parameters.

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