A carboxymethylcellulose fiber filament bundle and a continuous production method thereof

Abstract

The application discloses a kind of carboxymethyl cellulose fiber filament bundle and its continuous preparation method, belong to the field of polymer biomaterials.The preparation method includes: cellulose fiber filament bundle is continuously pulled under microtension control, in turn through pretreatment, alkalization, carboxymethylation, pickling, multistage countercurrent elution and drying procedure, obtain carboxymethyl cellulose fiber filament bundle;Pretreatment is to contact long filament bundle with the pretreatment liquid containing penetration enhancer and alkali and react;Alkalization is to react long filament bundle with alkalization liquid at 40-75 DEG C for 3-15 min;Carboxymethylation is to react long filament bundle with etherification liquid by multistage spraying mode at 40-75 DEG C for 3-15 min.The application realizes the full continuous quick production of carboxymethyl cellulose fiber filament bundle, product substitution degree is controllable, dry state breaking strength retention rate is high, effectively avoids fiber entanglement and mechanical damage, production efficiency is high, product quality is stable.

Description

Technical Field

[0001] This application relates to the field of polymer biomedical materials, and more specifically, to a carboxymethyl cellulose fiber bundle and a continuous preparation method thereof. Background Technology

[0002] Carboxymethyl cellulose (CMC) is an important ionic cellulose ether. The hydrophilic carboxymethyl groups (-CH2COOH) introduced into its molecular chain endow cellulose with excellent hygroscopicity, thickening properties, film-forming ability, and gelation ability. When cellulose exists in fibrous form and is modified by carboxymethylation, the modified product, carboxymethyl cellulose fiber, combines the specific surface area advantage of fiber with the functional properties of carboxymethyl groups. When CMC fiber is used as a medical dressing, it can quickly absorb wound exudate and form a soft hydrogel in situ. This not only provides an ideal moist environment for wound healing but also effectively avoids secondary adhesive damage when changing dressings. Therefore, it has become an ideal base material for high-end medical dressings, hemostatic materials, and functional hygiene products.

[0003] The preparation of CMC fibers is essentially a multiphase chemical reaction process of cellulose. Its core steps include: alkalization to disrupt the highly crystalline structure of cellulose, generating highly reactive alkali cellulose; and etherification of the alkali cellulose with an etherifying agent, grafting carboxymethyl groups onto the hydroxyl groups of the cellulose molecular chain to achieve functional modification. This process is accompanied by complex physical structural changes and side reactions: alkalization can lead to excessive fiber swelling and a decrease in mechanical strength; etherification and subsequent neutralization processes generate a large amount of byproduct salts (such as sodium chloride and sodium glycolate), which must be thoroughly removed to ensure product purity.

[0004] Traditional CMC products are mostly in powder form and are widely used in food, pharmaceuticals, and daily chemicals. Their production process is relatively mature, typically involving a reaction vessel under stirring. However, this process and equipment cannot be directly used for the preparation of CMC fibers. Cellulose fibers have an extremely high aspect ratio; under the shearing action of the stirring paddle, the wet fibers will quickly become entangled in the paddle and the inner wall of the vessel. This prevents the reaction medium from penetrating evenly, hinders mass transfer, and causes equipment malfunctions and production interruptions.

[0005] Existing technologies have undergone a series of improvements in the preparation of CMC fibers. For example, Chinese patent CN116695438B discloses a method for preparing hydrophilic carboxymethyl cellulose long fibers, which uses lyocell long fibers as raw materials and prepares CMC fibers through steps such as alkalization, adsorption microspheres, etherification, and post-treatment. This method introduces microsphere adsorbents to assist in desalination, which improves the fiber's breaking strength to a certain extent. However, this process is essentially a static intermittent soaking process, where the filament bundle is statically soaked in the reaction tank, and the reaction mass transfer depends on natural diffusion, which has obvious drawbacks: ① long reaction time and low production efficiency; ② static soaking leads to uneven distribution of the reaction reagent inside and outside the fiber bundle, resulting in poor uniformity of substitution; ③ although microsphere adsorbents are used, the by-product salt still needs to be removed by subsequent long-term elution, resulting in poor process continuity.

[0006] Another technical approach uses short fibers as raw materials and conducts a stirred reaction in a reactor. Chinese patent CN114478809B discloses a method for preparing carboxymethyl cellulose fibers. This technology uses short fibers as raw materials and conducts alkalization, etherification, and post-treatment in a reactor. This process uses a rotating reactor to carry out the modification reaction, which largely solves the problem of roller entanglement. The improvement of the reactor structure improves the fiber's own entanglement, filament hanging, and clumping. However, this method is a single-reactor production of short fibers, with fixed specifications and limited production capacity.

[0007] Another type of technology uses a chemical modification production device for long filament fibers to achieve continuous traction modification of long filaments. Chinese patent CN201110237231.0 discloses that the production device sequence includes a filament toss finishing machine, a hydrolysis reactor, a first press, a first washing tank, a second press, an acid washing tank, a third press, a second washing tank, a fourth press, a dryer, and a packaging machine. The hydrolysis reactor consists of a hydrolysis tank and a reciprocating frame for the filaments placed in the hydrolysis tank. The reciprocating frame for the filaments is a rectangular frame structure, including upper and lower rows of guide rollers, with at least 10 guide rollers in each row, and the upper row having one more guide roller than the lower row. Although this device achieves continuous production of cellulose long filaments, it still uses intermittent process parameters, which has problems such as long alkalization time, large space requirements, and the tendency for the reducing end groups of cellulose macromolecular chains to fall off and the degree of polymerization to decrease under the action of high temperature and high alkali for a long time, which has a significant impact on fiber strength.

[0008] Unlike the batch process of traditional reactors, where the next process only begins after the previous one is completed, allowing for individual control of a single process at any given time, making it easy to regulate the timing of critical processes like alkalization and etherification, the continuous production of carboxymethyl cellulose fibers using a continuous traction method for cellulose fiber bundles presents challenges. Because it's a continuous process, the reaction time for each step is limited (otherwise, the space required would be too large), and the coordination and linkage between steps are crucial. If the next step proceeds before the previous one is fully reacted, the final product will be substandard, with low substitution and failure to gel. Alkaliization and etherification occur in strong alkaline and acidic environments; prolonged reaction times, vigorous reactions, or conventional traction forces can cause significant mechanical damage to the cellulose fibers, leading to plastic deformation, fibrillation, and even breakage.

[0009] It is evident that existing static intermittent processes suffer from problems such as low process efficiency, poor uniformity, and fiber entanglement, making it impossible to achieve efficient, continuous, and minimally damaging industrial production. Existing continuous traction processes are immature and struggle to balance mechanical properties and the degree of carboxymethyl substitution within a limited reaction time, resulting in a failure to balance functionality and strength. Summary of the Invention

[0010] To address the shortcomings of existing technologies, this invention provides a method for the continuous preparation of carboxymethyl cellulose fiber filament bundles. This method uses filament bundles instead of short fibers as the reaction substrate, and achieves uniform etherification through pretreatment to promote penetration and assist fiber alkalization, multi-stage spraying for uniform etherification, and multi-stage countercurrent gradient elution for efficient desalination. While achieving continuous and rapid production, it maximizes the preservation of the fiber's inherent strength, offering advantages such as high efficiency, uniformity, and stable quality.

[0011] To achieve the above objectives, the technical solution of the present invention is as follows:

[0012] The first aspect of the present invention provides a continuous preparation method for carboxymethyl cellulose fiber filament bundles, characterized in that the cellulose fiber filament bundles are continuously drawn under micro-tension control and sequentially pass through the following steps: pretreatment, alkalization, carboxymethylation, acid washing, multi-stage countercurrent elution and drying to obtain carboxymethyl cellulose fiber filament bundles; The method is a fully continuous production process, and the micro-tension refers to the tensile tension experienced by the cellulose fiber filament bundle being less than 10% of its dry breaking strength; The pretreatment process includes the following steps: introducing a bundle of cellulose fiber filaments into a pretreatment tank and reacting it with a pretreatment solution for 1-5 minutes. The pretreatment solution includes: 0.1-2 wt% penetration enhancer, 1-15 wt% alkali, and water as the remainder. The alkalization process includes the following steps: the pretreated cellulose fiber filament bundle is introduced into the alkalization tank after passing through the pressure roller, and reacts with the alkalization solution. The reaction temperature is 40-75℃ and the reaction time is 3-15min. The alkalization solution includes: 10-40wt% alkali, 20-50wt% alcohol, and the balance being water. The carboxymethylation process includes the following steps: the alkalized cellulose fiber filament bundle is introduced into the etherification reactor after passing through the pressure roller, and reacted with the etherification liquid at 40-75℃ through a multi-stage spraying method for 3-15 minutes. The etherification liquid consists of: 15-40wt% etherifying agent, 0.5-15wt% alkali, 10-50wt% alcohol, and water as the balance.

[0013] In some embodiments of the present invention, the micro-tension is controlled by an active tension regulating roller group between each process unit.

[0014] In some embodiments of the present invention, the specific tension value can be adjusted according to the total fineness of the filament bundle. Preferably, the absolute value of the micro-tension is 0.05 - 0.30 cN / dtex to avoid plastic deformation or breakage of the fibers.

[0015] In some embodiments of the present invention, the penetration enhancer used in the pretreatment step is selected from one or more of the following: sodium isooctanol polyoxyethylene ether phosphate (OEP-70), isooctanol polyoxyethylene ether phosphate (AEP), ethoxylated octanol (OE-35), isooctanol ammonium sulfate (HA-08), alkyl polyglucoside (JFC-G), and alkyl aryl alkoxylated derivatives (JFC-14).

[0016] In some embodiments of the present invention, the reaction time for the pretreatment is 2-4 minutes.

[0017] In some embodiments of the present invention, the alkalization reaction time is 5-10 min.

[0018] In some embodiments of the present invention, the reaction time for carboxymethylation is 5-10 min.

[0019] In some embodiments of the present invention, in the alkalization process, the mass ratio of the cellulose fiber bundle to the alkalization solution is 1:(5-25).

[0020] In some embodiments of the present invention, the mass ratio of cellulose to etherification liquid in the carboxymethylation process is 1:(5-25).

[0021] In some embodiments of the present invention, the alkali in the pretreatment step is one or more of sodium hydroxide and potassium hydroxide.

[0022] In some embodiments of the present invention, in the alkalization process, the alkali is one or more of sodium hydroxide and potassium hydroxide; and the alcohol is one or more of ethanol, isopropanol, and methanol.

[0023] In some embodiments of the present invention, in the carboxymethylation process, the etherifying agent is one or more of chloroacetic acid and sodium chloroacetate.

[0024] In some embodiments of the present invention, in the carboxymethylation process, the alkali is one or more of sodium hydroxide and potassium hydroxide.

[0025] In some embodiments of the present invention, in the carboxymethylation process, the alcohol is one or more of ethanol, isopropanol, and methanol.

[0026] In some embodiments of the present invention, the multi-stage countercurrent elution process includes the following steps: the acid-washed cellulose fiber filament bundle is introduced into a countercurrent elution device containing 1-5 stages of elution units in series after passing through a pressure roller; the filament bundle passes through each stage of elution unit in sequence; the elution liquid flows countercurrently to the filament bundle; and the filament bundle is washed with an alcohol-water solution of gradient concentration; wherein the last stage of elution liquid contains a surfactant, and this stage is a elution unit that must be activated.

[0027] In some embodiments of the present invention, the total time for multi-stage countercurrent elution is 1-30 min, preferably 5-15 min.

[0028] In some embodiments of the present invention, the eluent is an ethanol-water mixture with a concentration that increases in a gradient along the direction of the filament bundle's advance. Specifically, the alcohol concentration of the first-stage eluent is 50-65%, the alcohol concentrations of the second, third, and fourth-stage eluents are independently 65-80%, and the alcohol concentration of the fifth-stage eluent is 80-95%. The last-stage eluent contains 0.1-3 wt% of a surfactant, which is one or more of anionic and nonionic surfactants.

[0029] Preferably, the anionic surfactant is sodium dodecyl sulfate or sodium dodecylbenzene sulfonate; the nonionic surfactant is one or more of alkylphenol polyoxyethylene ether, Tween series, or Span series.

[0030] In some embodiments of the present invention, the pickling process includes the following steps: the carboxymethylated cellulose fiber filament bundle is introduced into the pickling tank after passing through a pressure roller, and is immersed in the pickling solution at 25-40°C for 1-15 minutes. The pickling solution includes: 0.1-15 wt% acid, 20-70 wt% alcohol, and the balance being water.

[0031] Preferably, the acid used in the pickling is one or more of acetic acid, hydrochloric acid, or citric acid; the alcohol is one or more of ethanol, isopropanol, and methanol; and the pickling time is 5-10 minutes.

[0032] In some embodiments of the present invention, the drying process includes the following steps: the washed cellulose fiber filament bundle is introduced into the drying equipment after passing through the pressure roller, and dried at 45-80℃ for 3-30 minutes to obtain carboxymethyl cellulose fiber filament bundle.

[0033] Preferably, the drying time is 5-20 minutes.

[0034] In some embodiments of the present invention, the cellulose fiber filament bundle is a lyocell filament bundle or a viscose filament bundle, with a single filament fineness of 1.0-3.0 dtex and a total fineness of 10-180 ktex.

[0035] A second aspect of the present invention provides a carboxymethyl cellulose fiber filament bundle prepared by the above method, wherein the degree of carboxymethyl substitution of the carboxymethyl cellulose fiber filament bundle is 0.10-0.42, and the dry breaking strength retention rate is ≥ 80%; the retention rate is calculated based on the dry breaking strength of unmodified cellulose fiber filament bundles of the same specification.

[0036] Preferably, the degree of carboxymethyl substitution is 0.15-0.35; and the dry breaking strength retention rate of carboxymethyl cellulose fiber filament bundles is ≥ 85%.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows: The continuous preparation method of carboxymethyl cellulose fiber filament bundles of the present invention first pre-activates the fiber fibrils through a pretreatment process to promote penetration, enabling the alcohol-alkali-water ternary system in the subsequent alkalization process to fully penetrate and activate the fiber crystalline region within a very short time of 3-15 minutes at 40-75°C. This synergistic mechanism of pre-opening-rapid penetration-short activation effectively suppresses the defects in the core-sheath structure caused by excessive alkaliing of the sheath layer and insufficient alkaliing of the core layer due to the high surface tension and slow penetration of the alkali solution in traditional processes. It is precisely based on this uniform alkaliing effect that the multi-stage sprayed etherifying agent can quickly and uniformly enter the fiber interior to complete the substitution reaction without the assistance of physical stirring, driven by the concentration difference. This provides a decisive prerequisite for achieving both a high degree of substitution (≥0.10) and a high strength retention rate (≥80%) in the carboxymethyl cellulose fiber filament bundles.

[0038] The specific preparation method of this application has the following advantages: (1) Pioneering a continuous and rapid production mode for filament bundles: This technology realizes the fully continuous production of carboxymethyl cellulose fiber from raw filament bundles to finished filament bundles, completely abandoning the traditional batch reactor process. The continuous operation of the production line eliminates a large amount of auxiliary time such as loading and unloading, centrifugation and dehydration, significantly improving production efficiency compared to the reactor process, significantly improving product batch stability, and strictly controlling the reaction time of each process to achieve continuous and rapid production.

[0039] (2) It perfectly avoids fiber entanglement and mechanical damage: it runs continuously in the form of long filament bundles under micro-tension / low tension, completely avoiding the shearing and cutting of fibers and the problem of entanglement on rollers caused by stirring. The dry breaking strength retention rate of the product is as high as 80% or more.

[0040] (3) A highly efficient and mild purification system was constructed: the multi-stage countercurrent gradient elution technology uses the concentration difference as the mass transfer driving force, and the washing efficiency is significantly improved compared with single-stage soaking. The surfactants (Tween, Span, etc.) introduced in the last stage simultaneously complete the fiber surface modification under mild conditions, giving the filament bundle excellent bundle-forming and spinnability, and avoiding the secondary damage to the fiber caused by traditional high-temperature finishing.

[0041] (4) Excellent product performance and broad application prospects: The carboxymethyl cellulose fiber filament bundles prepared by this invention have a controllable degree of substitution of 0.10-0.42, a dry strength retention rate of ≥80%, and excellent spinnability. They can be directly used for subsequent textile processing such as drawing, crimping, cutting, and hydroentangling. High-end medical dressings and functional textiles made from them are superior to products prepared by traditional methods in terms of liquid absorption rate, wet gel strength, and dressing softness, and have broad prospects for clinical application and industrial promotion.

[0042] This invention relates to the reaction mechanism of carboxymethyl modification. The hydroxyl groups (-OH) on the cellulose molecular chain generate more nucleophilic alkoxide anions (-O) under the action of a base. - ), and then reacted with chloroacetic acid ions (ClCH2COOH) - A nucleophilic substitution reaction occurs, producing carboxymethyl cellulose. Taking the reaction of sodium hydroxide and sodium chloroacetate as an example, the main reaction equations are as follows: (1) Alkalization reaction: Cell-OH + NaOH → Cell-O Na + +H2O (2) Carboxymethylation reaction: Cell-O Na + +ClCH2COONa→Cell-OCH2COONa+NaCl Pretreatment aims to initially swell the fibers, open the microporous structure of the amorphous regions, and simultaneously reduce surface tension using a penetration enhancer, laying the foundation for the rapid and uniform penetration of the subsequent alkali solution into the fiber interior. This step avoids excessive swelling of the surface layer and insufficient reaction of the inner layer caused by direct contact of the high-concentration alkali solution with the fiber.

[0043] Alkalization is a key activation step in carboxymethylation. Sodium hydroxide reacts with the hydroxyl groups of cellulose to generate alkali cellulose, while breaking the intermolecular and intramolecular hydrogen bonds of cellulose, reducing crystallinity, and greatly improving the accessibility of the reaction reagents. The introduction of alcohol can inhibit excessive swelling of the fiber, maintain the fiber morphology, and promote the penetration of alkali solution into the fiber bundle and the gaps between monofilaments, thus achieving rapid and uniform alkalization.

[0044] In the etherification reactor, alkali cellulose undergoes a Williamson etherification reaction with chloroacetate. The multi-stage spray design ensures full and uniform contact between the etherification solution and the filament bundle, avoiding localized concentration unevenness caused by static soaking. The presence of alcohol in the reaction system acts as both a solvent and suppresses the hydrolysis side reaction of chloroacetate, thereby improving the etherification efficiency.

[0045] The pickling step serves the following purposes: ① Reaction termination and pH control: neutralizes residual free alkali inside and on the surface of the fiber, terminates the etherification reaction, and prevents over-substitution; ② Optimization of product morphology and performance: by controlling the concentration and time of the pickling solution, some sodium carboxymethyl salt (-CH2COONa) is converted into carboxylic acid form (-CH2COOH), which is one of the key means to regulate the performance of the final product. The ratio of carboxylic acid to sodium carboxylate directly affects the swelling behavior and mechanical properties of the fiber, thus providing a flexible product design window to adapt to different application scenarios (such as high liquid absorption or high gel strength).

[0046] By utilizing the properties of byproduct salts such as sodium chloride, which have high solubility in low-concentration alcohols but low solubility in high-concentration alcohols, a concentration gradient is constructed. The filament bundle flows counter-currently with the elution solution, maintaining maximum mass transfer driving force to achieve efficient desalination. The surfactant introduced in the final elution solution is adsorbed onto the fiber surface, significantly reducing the dynamic and static friction coefficients of the fiber and giving the filament bundle excellent bundle-like properties, soft hand feel, and spinnability. Attached Figure Description

[0047] The accompanying drawings, which form part of this application, are used to provide a further understanding of the application and to make other features, objects, and advantages of the application more apparent. The illustrative embodiments and descriptions of this application are used to explain the application and do not constitute an undue limitation of the application. In the drawings: Figure 1 This is a process flow diagram of this application; Figure 2 Infrared characteristic spectra of lyocell fiber filament bundles and carboxymethyl cellulose fibers; Figure 2 (a) is the infrared characteristic spectrum of the raw material used in Example 1 of this application—lyocell fiber filament bundle; Figure 2 (b) is the infrared characteristic spectrum of the carboxymethyl cellulose fiber bundle prepared in Example 1 of this application. Detailed Implementation

[0048] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0049] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0050] All concentrations mentioned in the following examples and comparative examples are by weight.

[0051] Example 1 A continuous preparation method for carboxymethyl cellulose fiber filament bundles is as follows: Pretreatment: Lyocell filament bundles with a total fineness of 120 ktex were selected and continuously drawn through a pretreatment tank at a speed of 8 m / min and a tensile tension of 0.10 cN / dtex. The pretreatment solution, by mass fraction, was an aqueous solution containing 0.5% alkyl polyglucoside (JFC-G) and 8% sodium hydroxide, at a temperature of 45℃ for 2 minutes. After exiting the tank, excess liquid was removed by a pair of light pressure rollers, resulting in a fiber liquid content of 100%-150%.

[0052] Next, the filament bundle is continuously drawn through the following processes at the same traction speed and tensile tension: Alkalization: The pretreated filament bundle is introduced into the alkalization tank. The composition of the alkalization solution by mass fraction is: sodium hydroxide 25%, ethanol 35%, water 40%, temperature 55℃. The filament bundle runs in the tank for 6 minutes to complete the alkalization. The mass ratio of cellulose to alkalization solution is 1:12.

[0053] Carboxymethylation: After alkalization, the filament bundle enters a closed etherification reactor through a pressure roller. Inside the reactor, etherification liquid is evenly sprayed onto both the top and bottom surfaces of the filament bundle through multiple sets of nozzles. The composition of the etherification liquid by mass percentage is: sodium chloroacetate 28%, sodium hydroxide 2%, ethanol 42%, and water 28%. The temperature inside the reactor is maintained at 60℃, the reaction time is 8 minutes, and the mass ratio of cellulose to etherification liquid is 1:10.

[0054] Pickling: The carboxymethylated filament bundle is introduced into the pickling tank after passing through the pressure roller. The pickling solution is an aqueous solution containing 5% glacial acetic acid and 60% ethanol by mass fraction, the temperature is 30℃, and the soaking time is 3min.

[0055] Multi-stage countercurrent elution: After pickling, the filament bundle is introduced into a five-stage countercurrent elution unit connected in series after passing through pressure rollers. The filament bundle passes through the first to fifth elution units sequentially. The eluent is an ethanol-water mixture that flows countercurrently to the filament bundle, with its concentration increasing gradually in the direction of the filament bundle's movement: by mass fraction, the first-stage eluent has an alcohol concentration of 55%, the second, third, and fourth-stage eluents all have an alcohol concentration of 75%, and the fifth-stage eluent is an ethanol-water solution with a 90% alcohol concentration containing 1% Tween-80. The washing temperature is 35℃, the total washing time for the filament bundle is 10 minutes, and the residence time for each stage is evenly distributed.

[0056] Drying: The washed filament bundles are introduced into a hot air drying oven through pressure rollers. The drying temperature is 60℃ and the drying time is 12 minutes. The finished carboxymethyl cellulose fiber filament bundles are then wound up.

[0057] Example 2 A continuous preparation method for carboxymethyl cellulose fiber tows differs from Example 1 in that: In the alkalization process, the composition of the alkalization solution by mass fraction is: sodium hydroxide 30%, isopropanol 40%, water 30%, temperature 60℃, reaction time 4min; In the carboxymethylation process, the composition of the etherification solution by mass fraction is: chloroacetic acid 24%, sodium hydroxide 8%, ethanol 38%, water 30%, reaction temperature 65℃, reaction time 6min; In the pickling process, the pickling solution is a 50% ethanol aqueous solution containing 2% hydrochloric acid and 4% citric acid, and the soaking time is 5 minutes. In the multi-stage countercurrent elution process, the surfactant in the last stage eluent is a compound system of 0.5% Span-80 and 0.5% Tween-80 by mass fraction.

[0058] Example 3 A continuous preparation method for carboxymethyl cellulose fiber tows differs from Example 1 in that: The raw material is a viscose filament bundle with a total fineness of 150 ktex; In the pretreatment process, the penetration enhancer in the pretreatment solution is 0.3% isooctanol polyoxyethylene ether phosphate (AEP), and the alkali is potassium hydroxide with a concentration of 10%. The reaction time in the alkalization process is 5 minutes; In the carboxymethylation process, the composition of the etherification solution by mass fraction is: sodium chloroacetate 35%, sodium hydroxide 2%, ethanol 33%, water 30%, reaction temperature 65℃, reaction time 10min; In the pickling process, the pickling solution is a 40% ethanol aqueous solution containing 8% acetic acid, and the soaking time is 4 minutes. The surfactant in the final eluent is 0.8% sodium dodecylbenzenesulfonate.

[0059] Comparative Example 1: Static Immersion Process for Long Filament Tow A method for preparing carboxymethyl cellulose long fibers with good hydrophilicity, referring to the method in Example 1 of patent CN116695438B, is as follows: Lyocell filament bundles of the same specifications as those used in Example 1 of this application were selected. 10g of the filament bundle was added to 72g of alkaline solution (38g sodium hydroxide, 200g anhydrous ethanol, 50g deionized water) and completely immersed at 40°C for 50min. After draining the alkaline solution, 0.3g of microsphere adsorbent and 55g of deionized water were added, and the bundle was immersed at 35°C for 1.5h. After draining the microsphere adsorbent and deionized water, 5.3g of etherification solution (20g chloroacetic acid, 11g anhydrous ethanol) and 60g of deionized water were added, and the bundle was immersed at 60°C for 45min. After draining the etherification solution, the bundle was eluted twice with 85% ethanol. Finally, 7g of salt absorbent, 100g of deionized water, and 30g of anhydrous ethanol were added, and the bundle was immersed at 25°C for 50min. After draining, the bundle was dried at 55°C. The entire process was an intermittent operation.

[0060] Comparative Example 2: Short Fiber Mixing Process A method for preparing carboxymethyl cellulose fiber, referring to the method in CN114478809B, the specific process is as follows: The same Lyocell filament bundles of the same specifications used in Embodiment 1 of this application were cut into 38 m lengths. mShort fibers were used. 500g of short fibers were added to a reaction vessel, and an alkalization solution (same as in Example 1 of CN114478809B, i.e., anhydrous ethanol + water + sodium hydroxide, wherein the ratio of anhydrous ethanol to water is 58:1.5; the ratio of lyocell filament bundle to solvent [anhydrous ethanol + water] is 12.5:59.5; the amount of sodium hydroxide added is 16% of the lyocell filament bundle) was added. The vessel was rotated, and alkalization was carried out at 55°C for 60 minutes. After alkalization, the alkalization solution was drained, and an etherification solution (same as in Example 1 of CN114478809B, i.e., monochloroacetic acid + anhydrous ethanol + hexadecyltrimethylammonium bromide, wherein the amount of monochloroacetic acid added is 28% of the lyocell filament bundle; the amount of anhydrous ethanol added is 16% of the lyocell filament bundle; the amount of hexadecyltrimethylammonium bromide added is 0.025‰ of the lyocell filament bundle) was added. The temperature was raised to 60°C, and the vessel was rotated for 60 minutes. After the reaction was completed, the etherified liquid was discharged, and the crude carboxymethyl cellulose fiber was washed three times with a 90% ethanol solution, and then dried in a dryer at 65°C for 3 hours. Observation revealed that the fibers exhibited a certain degree of agglomeration during the reaction.

[0061] Comparative Example 3 A continuous preparation method for carboxymethyl cellulose fiber filament bundles differs from Example 1 in that it does not include a pretreatment step.

[0062] Comparative Example 4 A continuous preparation method for carboxymethyl cellulose fiber filament bundles differs from Example 1 in that no penetration enhancer is added in the pretreatment process.

[0063] Comparative Example 5 A continuous preparation method for carboxymethyl cellulose fiber tows differs from Example 1 in that the reaction time, temperature, and alkali concentration in the alkalization process are different, as detailed below: Alkalization: The pretreated filament bundle is introduced into the alkalization tank. The composition of the alkalization solution by mass percentage is: sodium hydroxide 18%, ethanol 35%, water 47%, temperature 35℃. The filament bundle runs in the tank for 15 minutes to complete the alkalization. The mass ratio of cellulose to alkalization solution is 1:12.

[0064] Comparative Example 6 A continuous preparation method for carboxymethyl cellulose fiber tows differs from Example 1 in that the reaction time, temperature, and alkali concentration in the alkalization process are different, as detailed below: Alkalization: The pretreated filament bundle is introduced into the alkalization tank. The composition of the alkalization solution by mass percentage is: sodium hydroxide 45%, ethanol 25%, water 30%, temperature 80℃. The filament bundle is alkalized in the tank for 3 minutes. The mass ratio of cellulose to alkalization solution is 1:12.

[0065] Under these process parameters, an alkaline white precipitate easily forms in the solution system, affecting the reaction efficiency. The prepared carboxymethyl cellulose fiber bundles are noticeably yellow and brittle to the touch, which may be due to damage or degradation of the fiber raw materials caused by high temperature and high concentration of alkaline solution.

[0066] Comparative Example 7 A continuous preparation method for carboxymethyl cellulose fiber tows differs from Example 1 in that the reaction time, temperature, and chloroacetic acid concentration in the carboxymethylation process are different, as detailed below: Carboxymethylation: After alkalization, the filament bundle enters a closed etherification reactor through a pressure roller. Inside the reactor, etherification liquid is evenly sprayed onto both the top and bottom surfaces of the filament bundle through multiple sets of nozzles. The composition of the etherification liquid by mass percentage is: sodium chloroacetate 12%, sodium hydroxide 2%, ethanol 42%, and water 44%. The temperature inside the reactor is maintained at 35 ℃, the reaction time is 15 min, and the mass ratio of cellulose to etherification liquid is 1:10.

[0067] Comparative Example 8 A continuous preparation method for carboxymethyl cellulose fiber tows differs from Example 1 in that the reaction time, temperature, and chloroacetic acid concentration in the carboxymethylation process are different, as detailed below: Carboxymethylation: After alkalization, the filament bundle enters a closed etherification reactor through a pressure roller. Inside the reactor, etherification liquid is evenly sprayed onto both the top and bottom surfaces of the filament bundle through multiple sets of nozzles. The composition of the etherification liquid by mass percentage is: sodium chloroacetate 42%, sodium hydroxide 2%, ethanol 22%, and water 34%. The temperature inside the reactor is maintained at 80 ℃, the reaction time is 3 min, and the mass ratio of cellulose to etherification liquid is 1:10.

[0068] Under these process parameters, the carboxymethyl cellulose fiber bundles turned noticeably yellow and became brittle, possibly due to damage or degradation of the fiber raw materials caused by the high-concentration reaction medium under high temperature conditions.

[0069] Comparative Example 9 A continuous preparation method for carboxymethyl cellulose fiber filament bundles differs from Example 1 in that: after alkalization, the filament bundles are directly fed into the etherification reactor for carboxymethylation reaction without passing through pressure rollers, as detailed below: Carboxymethylation: The alkalized filament bundles are directly fed into a closed etherification reactor. Inside the reactor, etherification liquid is sprayed evenly onto both the top and bottom surfaces of the filament bundles through multiple sets of nozzles. The composition of the etherification liquid by mass percentage is: sodium chloroacetate 28%, sodium hydroxide 2%, ethanol 42%, and water 28%. The temperature inside the reactor is maintained at 60℃, the reaction time is 8 minutes, and the mass ratio of cellulose to etherification liquid is 1:10.

[0070] Comparative Example 10 A continuous preparation method for carboxymethyl cellulose fiber bundles, differing from Example 1 in that: no alkali is added to the etherification solution during the carboxymethylation process, as detailed below: Carboxymethylation: After alkalization, the filament bundle enters a closed etherification reactor through a pressure roller. Inside the reactor, etherification liquid is evenly sprayed onto both the top and bottom surfaces of the filament bundle through multiple sets of nozzles. The composition of the etherification liquid by mass percentage is: sodium chloroacetate 28%, ethanol 42%, and water 30%. The temperature inside the reactor is maintained at 60℃, the reaction time is 8 minutes, and the mass ratio of cellulose to etherification liquid is 1:10.

[0071] Comparative Example 11 A continuous preparation method for carboxymethyl cellulose fiber filament bundles differs from Example 2 in that: during the carboxymethylation process, the contact between the reaction solution and the filament bundle fibers is changed from spraying the etherification solution to contacting the fibers in an etherification tank, consistent with the alkalization process, as detailed below: Carboxymethylation: After alkalization, the filament bundles are fed into a closed etherification reactor through a pressure roller. An etherification tank is set up in the reactor. The filament bundles are introduced into the etherification tank for reaction. The composition of the etherification solution by mass percentage is: chloroacetic acid 24%, sodium hydroxide 8%, ethanol 38%, and water 30%. The temperature in the reactor is maintained at 65℃, the reaction time is 6 minutes, and the mass ratio of cellulose to etherification solution is 1:10.

[0072] Comparative Example 12 A continuous preparation method for carboxymethyl cellulose fiber filament bundles differs from Example 1 in that the tensile tension of the lyocell filament bundles is 0.45 cN / dtex throughout the process.

[0073] Experimental Example 1 The degree of substitution and gel properties of the carboxymethyl cellulose fiber bundles prepared in Examples 1-3 and Comparative Examples 1-12 were tested. Test solution A was prepared according to section 3.2 of YY / T 0471.1-2004, and the test results are shown in Table 1.

[0074] Table 1. Results of substitution degree and gel properties test of carboxymethyl cellulose fibers in the examples and comparative examples.

[0075] As shown in Table 1, the carboxymethyl cellulose fibers of Examples 1-3 of this invention have a degree of substitution of 0.27-0.41, a liquid absorption rate of more than 24 times, and good gel properties. The key lies in the synergistic effect of multiple processes: the pretreatment stage promotes penetration and pre-activates the fiber fibrils, so that the alkalization stage adopts rapid high-temperature alkalization at 40-75℃ for 3-15 minutes, combined with an alcohol concentration of 20-50%, which can fully activate the cellulose and avoid excessive swelling; the etherification stage adopts a multi-stage spraying method to ensure continuous replenishment of new etherification liquid and overcome the diffusion dead zone of static soaking; at the same time, the liquid carry-over rate can be precisely controlled by the pressure roller after alkalization, so that the concentration of the subsequent etherification agent is not excessively diluted.

[0076] Comparative Example 5 reduced the alkalization temperature to 35℃, adjusted the time to 15 min, and reduced the sodium hydroxide concentration to 18%, resulting in insufficient activation and failure to form a gel in test solution A. Comparative Example 7 reduced the etherifying agent to 12%, lowered the temperature to 35℃, and adjusted the time to 15 min, but still failed to form a gel in test solution A, indicating that the etherification driving force was lower than the reaction activation energy. Comparative Example 9 eliminated the pressure roller after alkalization, causing the filament bundle to carry a large amount of alkali solution into the etherification section, diluting the effective concentration of sodium chloroacetate, reducing the reaction efficiency, and resulting in failure to form a gel in test solution A.

[0077] Comparative Example 11 replaced the multi-stage spraying of the present invention with immersion tank etherification. The reaction solution could only contact the surface layer of the filament bundles. The internal monofilaments, lacking forced convection, could not obtain sufficient etherifying agent, leading to a decrease in the effective reaction concentration. Simultaneously, the continuously introduced fiber filament bundles caused a sustained decrease in the etherifying agent concentration in the etherification solution. Furthermore, this reaction system involved acids, alkalis, alcohols, and various byproducts. The fiber filament bundles exhibited different affinities for different solvents or solutes, making it difficult to quantitatively replenish the etherification solution, ultimately resulting in the failure to form a gel in test solution A. This demonstrates that the spray etherification method used in Examples 1-3 of this application for carboxymethylation modification has extremely strong process adaptability and feasibility.

[0078] Comparative Example 12 had a relatively high tension parameter, which caused the cellulose molecular chains to be highly oriented along the direction of force, forming more hydrogen bonds and increasing crystallinity. The structure became dense, which hindered the penetration and diffusion of alkalizing agents and etherifying agents into the fiber interior. As a result, most hydroxyl groups could not contact the reaction reagents, the overall average degree of substitution was significantly lower, and gelation was basically not formed.

[0079] Experimental Example 2 The mechanical properties of the carboxymethyl cellulose fiber bundles prepared in Examples 1-3 and Comparative Examples 1-12 were tested, and the test results are shown in Table 2.

[0080] Table 2. Results of mechanical property tests on carboxymethyl cellulose fiber tows

[0081] As shown in Table 2, the strength advantage of this invention stems from the dual control of chemical and physical damage to the fibers. Chemically: alkalization is controlled at 40-75℃ / 3-15min, and etherification is controlled at 40-75℃ / 3-15min. The reaction time is extremely short and the temperature is mild, suppressing alkaline degradation and acidic hydrolysis of cellulose to a low level. Physically: the filament bundles operate continuously under micro-tension, completely avoiding the physical cutting and entanglement damage to the fiber filament bundles caused by stirring, shearing, and winding rollers.

[0082] In Comparative Example 1, the filament bundle was statically immersed in the reaction solution for an extended period (50 min for alkalization and 45 min for etherification). The reagents relied solely on natural diffusion, resulting in extremely uneven reactions between the inner and outer layers. Furthermore, the prolonged exposure of the fibers to a high-concentration alkaline environment induced alkaline degradation. Combined with the mechanical friction caused by repeated loading and unloading during intermittent operation, the fiber strength was significantly damaged. In Comparative Example 2, the filament bundle was cut and stirred in the reaction vessel, essentially resulting in prolonged contact with the alkaline and etherification solutions. Simultaneously, the fiber mechanical properties were more significantly damaged due to the effects of stirring shearing and fiber entanglement. Therefore, compared to static immersion and stirring shearing, the technology of this invention has a process advantage in preserving the fiber mechanical properties.

[0083] The absence or defects in the pretreatment process also have significant consequences. In Comparative Example 3, pretreatment was completely omitted, and the alkali solution directly contacted the fiber surface, causing instantaneous and intense swelling. The surface layer rapidly densified, forming a skin barrier that hindered the uniform penetration of subsequent alkali solution and etherifying agent into the filament bundle, easily leading to uneven reaction and fiber embrittlement. In Comparative Example 4, although pretreatment was retained, the lack of a penetration enhancer resulted in high surface tension and poor wettability of the alkali solution, leading to insufficient reaction inside the filament bundle. Both of these factors reduced fiber strength due to decreased reaction uniformity. This demonstrates that pretreatment and penetration enhancers can ensure the uniformity of the modification of the entire fiber bundle and reduce the decrease in fiber strength caused by the modification process.

[0084] In Comparative Example 6, the alkalization concentration and temperature exceeded the upper limit of this invention (75℃ / 40% NaOH). Under high temperature and high alkali conditions, the reducing end groups of the cellulose macromolecular chains easily detached, resulting in a decrease in the degree of polymerization and thus a significant impact on fiber strength. In Comparative Example 8, the etherification concentration and temperature exceeded the upper limit of this invention (80℃ / 42% NaOH). Under these conditions, the carboxymethylation substitution reaction was too vigorous, and the cellulose glycosidic bonds were easily broken, leading to a significant decrease in the mechanical properties of the fiber. In other words, excessively high parameters such as temperature and concentration can trigger irreversible degradation reactions.

[0085] As shown in Tables 1 and 2, in Comparative Example 9, after alkalization, the pressure roller was removed, and the fiber was saturated with liquid, resulting in a decrease in the effective concentration of the etherifying agent involved in carboxymethylation. In Comparative Example 10, no alkali was added to the etherification solution. Carboxymethylation is a nucleophilic substitution reaction, which requires an alkaline environment. If the reaction system becomes acidic, the highly reactive sodium alkoxide (-ONa) formed by the hydroxyl group (-OH) during alkalization will be replaced by -H.+ The replacement of hydroxyl groups (-OH) leads to the termination of carboxymethylation. In Comparative Example 11, the spraying method was changed to soaking. As continuous production progressed, the concentration of the etherifying agent continued to decrease, and the complex reaction medium made it difficult to achieve quantitative concentration replenishment, resulting in incomplete reaction. In Comparative Example 12, excessive tensile tension caused the fiber molecular chains to be highly oriented along the axial direction and tightened its microstructure, resulting in denser fiber interiors. At the same time, a hydration layer may form on the surface, hindering the effective penetration and diffusion of the reaction solution into the fiber interior, thus affecting reaction efficiency. Due to their respective process defects, the degree of substitution in all four cases was only 0.04-0.12, resulting in poor reaction. The fiber skeleton was almost undamaged due to minimal chemical modification, so the dry strength retention rate was as high as 91.92%-94.30%. This high retention rate was based on the fact that the fiber raw materials were not fully modified.

[0086] Therefore, the key to this invention lies in utilizing pretreatment to promote penetration combined with high-temperature short-time alkalization, achieving a leap in reaction kinetics. This allows for efficient and uniform activation and substitution before significant alkaline hydrolysis of the cellulose β-1,4 glycosidic bonds (temperature <75℃, time <15min). This enables the examples to successfully introduce sufficient carboxymethyl groups (DS≥0.27, gel formation) while maintaining high retention rates (lyocellyl >90%, viscose >80%). This balance between function and strength is a unique technical effect of this invention, achieved through the pretreatment process, alkalization formulation control, precise liquid control by pressure rollers, multi-stage spraying to enhance mass transfer, and the synergistic effect of short-time, mild reactions in two core processes. The absence of any single process or deviation in parameters could lead to insufficient reaction or excessive damage to mechanical properties, thus affecting the further application of carboxymethyl fiber filament bundles. These data systematically demonstrate that the selection of numerical ranges for each process step in this invention has strict technical logic and significant synergistic effects, thereby achieving a balance between function and strength in the continuous production of carboxymethyl fiber filament bundles.

[0087] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A carboxymethyl cellulose fiber filament bundle and its continuous preparation method, characterized in that, Cellulose fiber filament bundles are continuously drawn under micro-tension control and sequentially undergo the following processes: pretreatment, alkalization, carboxymethylation, acid washing, multi-stage countercurrent elution and drying to obtain carboxymethyl cellulose fiber filament bundles. The term "micro-tension" refers to the tensile tension experienced by the cellulose fiber filament bundle being less than 10% of its dry breaking strength. The pretreatment process includes the following steps: introducing a bundle of cellulose fiber filaments into a pretreatment tank and reacting it with a pretreatment solution for 1-5 minutes. The pretreatment solution includes: 0.1-2 wt% penetration enhancer, 1-15 wt% alkali, and water as the remainder. The alkalization process includes the following steps: the pretreated cellulose fiber filament bundle is introduced into the alkalization tank after passing through the pressure roller, and reacts with the alkalization solution. The reaction temperature is 40-75℃ and the reaction time is 3-15min. The alkalization solution includes: 10-40wt% alkali, 20-50wt% alcohol, and the balance being water. The carboxymethylation process includes the following steps: the alkalized cellulose fiber filament bundle is introduced into the etherification reactor after passing through the pressure roller, and reacted with the etherification liquid at 40-75℃ through a multi-stage spraying method for 3-15 minutes. The etherification liquid consists of: 15-40wt% etherifying agent, 0.5-15wt% alkali, 10-50wt% alcohol, and water as the balance.

2. The preparation method according to claim 1, characterized in that, The absolute value of the micro-tension is 0.05 - 0.30 cN / dtex; And / or, the penetration enhancer used in the pretreatment step is selected from one or more of the following: sodium isooctanol polyoxyethylene ether phosphate, isooctanol polyoxyethylene ether phosphate, ethoxylated octanol, isooctanol ammonium sulfate, alkyl polyglucoside, and alkyl aryl alkoxylated derivatives.

3. The preparation method according to claim 1, characterized in that, The reaction time for the pretreatment is 2-4 minutes; And / or, the alkalization reaction time is 5-10 min; And / or, the carboxymethylation reaction time is 5-10 min.

4. The preparation method according to claim 1, characterized in that, In the alkalization process, the mass ratio of the cellulose fiber bundle to the alkalization solution is 1:(5-25). And / or, in the carboxymethylation process, the mass ratio of the cellulose fiber filament bundle to the etherification solution is 1:(5-25).

5. The preparation method according to claim 1, characterized in that, The multi-stage countercurrent elution process includes the following steps: the acid-washed cellulose fiber filament bundle is introduced into a countercurrent elution device containing 1-5 stages of elution units in series after passing through pressure rollers. The filament bundle passes through each stage of elution unit in sequence, the elution liquid flows countercurrently to the filament bundle, and is washed with alcohol-water solutions of gradient concentrations; wherein, the last stage of elution liquid contains a surfactant.

6. The preparation method according to claim 5, characterized in that, The eluent is an ethanol-water mixture, and its concentration increases in a gradient along the direction of the cellulose fiber bundle. Specifically, the alcohol concentration of the first-stage eluent is 50-65%, the alcohol concentration of the second, third, and fourth-stage eluents is 65-80% independently, and the alcohol concentration of the fifth-stage eluent is 80-95%. The last-stage eluent contains 0.1-3 wt% of a surfactant, which is one or more of anionic or nonionic surfactants.

7. The preparation method according to claim 1, characterized in that, The pickling process includes the following steps: the carboxymethylated cellulose fiber filament bundle is introduced into the pickling tank after passing through the pressure roller, and is immersed in the pickling solution at 25-40℃ for 1-15 minutes. The pickling solution includes: 0.1-15wt% acid, 20-70wt% alcohol, and the balance being water.

8. The preparation method according to claim 1, characterized in that, The drying process includes the following steps: the washed cellulose fiber filament bundles are introduced into the drying equipment after passing through the pressure rollers, and dried at 45-80℃ for 3-30 minutes to obtain carboxymethyl cellulose fiber filament bundles.

9. The preparation method according to claim 1, characterized in that, The cellulose fiber filament bundles are lyocell fiber filament bundles or viscose fiber filament bundles, with a single filament fineness of 1.0-3.0 dtex and a total fineness of 10-180 ktex.

10. A carboxymethyl cellulose fiber tow prepared by the preparation method according to any one of claims 1-9, characterized in that, The degree of carboxymethyl substitution of the carboxymethyl cellulose fiber filament bundle is 0.10-0.42, and the dry breaking strength retention rate is ≥80%.

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