A hemp fiber degumming method based on ternary eutectic solvent

Abstract

This invention belongs to the field of hemp fiber degumming technology, specifically relating to a hemp fiber degumming method based on a ternary eutectic solvent. The method includes: pre-impregnation for impurity removal, degumming treatment, solid-liquid separation and solvent recovery, and fine processing. The resulting hemp fiber semi-finished product is then dehydrated, oiled, and dried to obtain a refined hemp finished product. This invention uses a ternary eutectic solvent composed of an alkanolamine / betaine / polyol as the degumming medium. This system can efficiently and selectively remove non-cellulose components such as pectin, hemicellulose, and lignin from hemp fibers, ensuring complete fiber separation while significantly inhibiting cellulose degradation, thereby guaranteeing the mechanical properties and spinnability of the refined hemp finished product. Furthermore, the ternary eutectic solvent is non-toxic, harmless, and recyclable, reducing wastewater and waste gas treatment costs and environmental impact. This invention has significant advantages such as good degumming effect, high fiber quality, environmental friendliness, and high production efficiency, with broad industrial application prospects and high promotional value.

Description

Technical Field

[0001] This invention belongs to the field of hemp fiber degumming technology, specifically relating to a hemp fiber degumming method based on a ternary eutectic solvent. Background Technology

[0002] Fiber kenaf, ramie, flax, hemp, and jute are all important bast fiber plants, possessing characteristics such as rapid growth, high yield, high strength, moisture absorption and wicking, and resistance to mildew and abrasion. They are widely used in bast textiles, packaging materials, green composite materials, and industrial textiles. With the popularization of green manufacturing concepts, the market demand for bast fibers continues to rise. Degumming is a key step in bast fiber processing, aiming to remove pectin, hemicellulose, lignin, and waxy substances that encapsulate cellulose fibers to obtain cellulose fibers that meet the requirements of spinning. The degumming effect directly affects the smoothness of subsequent spinning and weaving, as well as the performance and quality of the final product. Among them, kenaf has a lignin content of 15% to 20%, far higher than ramie and flax, and its gum composition is more complex, making degumming the most difficult. Other bast fiber varieties, such as jute and hemp, also contain high levels of lignin or hemicellulose, and similarly face the challenge of degumming.

[0003] Currently, the mainstream process for degumming bast fibers is still the traditional alkaline boiling method. Although this method is mature and easy to control, it has obvious drawbacks: First, the large amounts of acids, alkalis, and auxiliaries result in high-concentration, high-COD, and strongly acidic / alkaline wastewater, leading to high treatment costs, easy water and soil pollution, and violating the requirements of green production. Second, strong alkalis can irreversibly damage cellulose, making the fibers brittle and reducing their strength, making it difficult to meet the fineness and flexibility requirements of high-end textiles. Third, the process is lengthy (5-8 hours in total), energy-intensive, and has low production efficiency. These problems are particularly prominent in kenaf, jute, and hemp, which have high lignin content.

[0004] While biological degumming (using microorganisms or enzymes) and physical degumming (ultrasound, microwave, steam flash explosion) offer some improvements in environmental friendliness, each has its own shortcomings: biological methods are easily affected by factors such as microbial activity, temperature, and humidity, resulting in poor degumming stability and a long cycle (>12 hours), and are not effective for high-lignin kenaf; physical methods can only peel off the surface gum and cannot achieve complete separation of fiber and gum, requiring combination with chemical methods, and also involve large equipment investments.

[0005] To address the aforementioned environmental and quality challenges, eutectic solvents (DES) have become a research hotspot in the field of hemp degumming due to their readily available raw materials, simple synthesis, non-toxicity, biodegradability, non-volatile nature, and selective dissolution of pectins. Existing patents (such as CN110284200A) have reported the use of binary DES, such as choline chloride / amide or polyols, for degumming ramie and flax, achieving some progress in emission reduction and fiber protection. Patent CN116463732A discloses a method for improving the degumming effect of DES on hemp / flax loose fibers using cysteine; however, the additional introduction of cysteine ​​increases the complexity and cost of the degumming system. Furthermore, cysteine ​​may undergo oxidation or side reactions under prolonged heating, affecting degumming stability and solvent reusability. The system's thermal stability and cycling performance are limited, and no substantial improvement has been observed in the synergistic removal of pectin and hemicellulose.

[0006] Studies have shown that existing DES technology still has significant shortcomings, especially for raw hemp with high lignin content (such as kenaf and jute): First, binary DES has limited ability to remove complex gums, often resulting in high residual gum rates after a single treatment, making it difficult to achieve the required standard in one step; second, degumming is incomplete, often requiring alkali boiling to obtain qualified dried hemp, failing to truly simplify the process and reduce pollution; third, the viscosity and solubility of the binary system have a narrow adjustable range, easily leading to uneven wetting and gum residue, resulting in fluctuations in fiber quality and making it unsuitable for large-scale production. Furthermore, existing DES degumming research focuses primarily on ramie and flax, lacking specialized processes for high-lignin hemp varieties such as kenaf, jute, and hemp, and even more so, a universal degumming technology applicable to all types of hemp fibers.

[0007] Patent CN113322525A discloses a method for one-step degumming and extraction of refined ramie fibers based on a eutectic solvent. However, the eutectic solvent system of this technology is a binary system (such as choline chloride / urea or polyol), which has limited ability to synergistically dissolve lignin and hemicellulose. In particular, it is difficult to efficiently remove the high content of lignin in ramie varieties such as kenaf and jute, resulting in a high residual gum rate. Furthermore, it still relies on long-term cooking at high temperatures.

[0008] In summary, there is an urgent need to develop a green and efficient degumming technology that not only suits the characteristics of high-lignin hemp varieties but can also be applied to other hemp species such as ramie, flax, hemp, and jute. This technology would reduce chemical consumption and wastewater discharge, improve degumming efficiency and product quality, and meet the requirements of continuous industrial production. This has significant practical and economic implications for promoting the green and high-quality development of the hemp fiber industry. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a method for degumming hemp fibers based on a ternary eutectic solvent. This method is applicable to a variety of bast fibers including but not limited to kenaf, ramie, flax, hemp, and jute. It has high degumming efficiency, minimal fiber damage, is environmentally friendly, and allows for solvent recycling.

[0010] The technical solution adopted is as follows: A method for degumming hemp fibers based on a ternary eutectic solvent includes the following steps: S1. Pre-soaking to remove impurities: Place the raw hemp basts in an soaking tank and immerse them in warm water for pre-soaking to remove impurities; after completion, remove the raw hemp, drain the water, and set aside. S2. Degumming treatment: (1) Preparation of ternary eutectic solvent degumming solution: Betaine compounds are selected as hydrogen bond acceptors, and polyol compounds and alkanolamine compounds are selected as hydrogen bond donors; among them, the molecular structure of alkanolamine compounds contains both amino and hydroxyl groups, and has the dual function of hydrogen bond donor and hydrogen bond acceptor, forming complementary hydrogen bond interactions with polyols or betaine; the above three components are mixed in a certain molar ratio and added to the mixing tank, heated and stirred until the system is a transparent and homogeneous liquid without precipitation and layering, and the degumming solution is obtained for later use; (2) Loading and boiling: Place the pre-soaked and impurity-removed raw hemp into the boiling kettle, open the liquid inlet valve, and inject the degumming liquid until the hemp bast is completely submerged; (3) Heating and degumming: The degumming liquid in the boiling kettle is heated and stirred at the same time for continuous boiling; after boiling is completed, the liquid outlet valve is opened, and the liquid in the boiling kettle is removed by squeezing or centrifugation and then recycled. After emptying, the liquid outlet valve is closed. (4) Spray rinsing: Open the water inlet valve and repeatedly spray and rinse the degummed hemp fibers to obtain hemp fiber semi-finished products; S3. Solid-liquid separation and solvent recovery: After degumming is completed, the liquid recovered in step (3) is used directly for the next batch of degumming after solid-liquid separation by a 100-300 mesh filter or a plate and frame filter press. S4. Fine processing: The hemp fiber semi-finished product in step S3 is dehydrated, and then oiled and dried in sequence. The dried fiber is combed by an opening machine to remove short fibers and impurities, and uniformly dispersed fine hemp fiber is obtained.

[0011] Preferably, the hemp fiber is one or more of kenaf fiber, ramie fiber, flax fiber, hemp fiber, and jute fiber.

[0012] Preferably, in step S1, the water temperature used for pre-soaking and impurity removal is 40-60°C, and the immersion time is 10-30 minutes.

[0013] Preferably, in step S1, the polyol compound is selected from any one of ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, and butanediol; the alkanolamine compound is selected from at least one of monoethanolamine, diethanolamine, triethanolamine, isopropanolamine, or diethanolmonoisopropanolamine; and the betaine compound is selected from any one of anhydrous betaine, alkylamidopropyl betaine, or sulfobetaine.

[0014] Preferably, in step S2, the molar ratio of alkanolamine, betaine and polyol compound is 1:2 to 12:1 to 3; and the preparation temperature of the degumming solution in the mixing tank is 60 to 80°C.

[0015] Preferably, in step S2, during the loading and boiling process, the mass ratio of raw hemp bast to the ternary eutectic solvent degumming solution is 1:15-30.

[0016] Preferably, in step S2, during the degumming process, the temperature is raised to 130-150°C and continuously boiled for 2-3 hours.

[0017] Preferably, in step S2, the spray rinsing uses warm water with a temperature of 40-60°C until the rinsing solution is colorless and the pH is neutral.

[0018] Preferably, in step S3, after the filter is recycled 3 to 5 times, water is added to dilute the colloid and precipitate it. Then, the eutectic solvent is purified by distillation to achieve solvent recycling.

[0019] Preferably, in step S4, the dehydration time is 15-20 min; the oiling time is 10-20 min; and the drying time is 60-90 min.

[0020] Compared with the prior art, the hemp fiber degumming process provided by the present invention has the following beneficial effects: High degumming efficiency with minimal fiber damage: Utilizing a ternary eutectic solvent system composed of alkanolamine / betaine / polyol, the alkaline environment provided by the alkanolamine and the hydroxyl network provided by the polyol synergistically break the ester and ether bonds between pectin, hemicellulose, and lignin. Compared to binary eutectic solvents, this method achieves highly efficient degumming under relatively mild conditions (130–150°C, 2–3 hours), while avoiding excessive hydrolysis of cellulose molecular chains by strong acids and alkalis, reducing residual gum content while preserving fiber breaking strength.

[0021] Environmentally friendly and solvent recyclable: This ternary eutectic solvent is designable and has low volatility. After degumming, it can be recovered through simple extrusion and filtration. The recovered solvent can be directly reused 3-5 times without significant reduction in degumming effect. Compared with traditional alkaline degumming, it eliminates highly polluting and toxic chemical reagents such as caustic soda and sodium sulfite, achieving near-zero discharge of degumming wastewater.

[0022] The refined hemp has uniform quality and good spinnability: Through a multi-stage combination of pre-impregnation and impurity removal, ternary solvent synergistic degumming and fine processing, the glue and impurities on the surface of hemp fibers can be effectively removed. The whiteness, softness and splitting uniformity of refined hemp fibers are significantly improved, which is beneficial to subsequent spinning processing.

[0023] The process is highly adaptable and easy to industrialize: This invention does not require special high-pressure equipment, and conventional boiling kettles can meet the production requirements; the degumming liquid can be prepared in batches through a mixing tank, and the solid-liquid separation and solvent recovery equipment are all common equipment in the textile industry, with low modification costs and easy to promote and apply in existing kenaf degumming production lines.

[0024] The technical features of the present invention are explained and described in detail below: First, the hemp bast bark is immersed in warm water at 40–60°C for 10–30 minutes. During this process, mud, dust, and some water-soluble impurities on the surface of the bast bark are effectively removed. Simultaneously, under the influence of warm water, water molecules gradually penetrate into the interior of the bast bark, breaking the intramolecular and intermolecular hydrogen bonds of cellulose molecules. The bonds between the gum complexes (pectin, hemicellulose, and lignin) are gradually weakened under the polar protonation effect of water molecules, ultimately making the originally dense structure of the bast bark looser. This creates favorable mass transfer and reaction conditions for the subsequent ternary eutectic solvent degumming process.

[0025] The subsequent ternary eutectic solvent (DES) degumming process plays a decisive role in the final production of refined sesame hemp and is also the key technical point of this invention.

[0026] After the aforementioned warm water softening process, the internal structure of the hemp bast has become loose, allowing DES molecules to penetrate more easily into the bast. This invention employs betaine compounds as the primary hydrogen bond acceptors and polyols and alkanolamines as hydrogen bond donors. The alkanolamines form complementary hydrogen bonds with the polyols or betaine, constructing a unique ternary eutectic solvent system. This system strongly competes with the hydrogen bond networks of non-cellulose components such as pectin, hemicellulose, and lignin in the hemp bast: the zwitterionic betaine ions and the dense hydroxyl groups of the polyols in the DES can form stronger hydrogen bonds with the hydroxyl and carboxyl groups of non-cellulose components, thus "stealing" and disrupting the original intramolecular and intermolecular hydrogen bonds of the non-cellulose components. Simultaneously, the weakly alkaline environment (pH approximately 9-11) provided by alkanolamines (such as monoethanolamine) can catalyze the cleavage of ester bonds between pectin and cellulose, ether bonds between hemicellulose and lignin (especially the β-O-4 bonds in lignin), and ester bonds within lignin. Under the aforementioned dual effects, the internal structure of hemp bast becomes further porous, and some pectin, hemicellulose, and lignin degrade and dissolve in DES, detaching from the fiber matrix.

[0027] It is particularly noteworthy that the ternary system of alkanolamine / betaine / polyol selected in this invention exhibits a significant synergistic effect compared to conventional binary DES (such as choline chloride / urea): betaine provides strong polarity and hydrogen bond binding sites, while its surface activity endows the system with excellent permeability; the polyol reduces the system viscosity and increases the hydrogen bond density, promoting mass transfer; and the alkanolamine combines the functions of hydrogen bond donor, hydrogen bond acceptor, and weak base catalysis. When the three are mixed in a specific molar ratio (1:2–12:1–3), a stable and homogeneous eutectic solvent system can be formed at 60–80°C, and it remains thermally stable at a degumming temperature of 130–150°C. This ternary DES can simultaneously and efficiently remove pectin, hemicellulose, and lignin. Cellulose, due to the extremely stable intramolecular and intermolecular hydrogen bonds (the hydrogen bond energy in the crystalline region is much higher than that of non-cellulose components), is not easily damaged under these mild conditions, thus achieving the invention's objective of "selective degumming and cellulose protection." The hemp fibers processed by the process of this invention have low residual glue content and high breaking strength.

[0028] This invention utilizes a ternary eutectic solvent degumming process based on alkanolamine / betaine / polyol, which maximizes the removal of non-cellulose components, allowing hemp fibers to be fully separated into single fibers or bundles, while minimizing cellulose degradation and preserving the strength, softness, and spinnability of refined and dried hemp. More importantly, the ternary DES system used in this degumming solution is non-toxic, harmless, and free of volatile organic solvents, and can be recovered through simple extrusion and filtration. The recovered DES can be directly reused 3-5 times without significant attenuation of degumming effect; when gum accumulates, dilution with water causes precipitation, followed by distillation and dehydration for regeneration. This characteristic significantly reduces the high COD wastewater and chemical reagent consumption generated by traditional alkaline degumming methods, substantially lowering environmental treatment costs.

[0029] In this degumming process, warm water pre-impregnation and ternary DES degumming are organically combined and inseparable. Only after the dense structure inside the bast of the kenaf is loosened through pre-impregnation and impurity removal can DES molecules fully penetrate and exert their hydrogen bond competition and catalytic hydrolysis effects. Conversely, if the pre-impregnation and impurity removal step is omitted, the mud and some gum adhering to the surface of the kenaf will hinder the contact between DES and the fiber, resulting in uneven degumming and increasing the impurity load during DES circulation. Therefore, pre-impregnation and DES degumming constitute a complete process chain that is interconnected and mutually reinforcing.

[0030] In the technical solution of this invention, particularly after ternary DES degumming treatment involving alkanolamines (such as monoethanolamine and triethanolamine), the gum and natural pigments in the hemp fibers are effectively removed, significantly improving fiber whiteness. Furthermore, no additional bleaching process is required, avoiding secondary damage to the fibers from bleaching agents (such as sodium hypochlorite and hydrogen peroxide) and the discharge of chlorine-containing wastewater. Simultaneously, the DES-treated fibers have a smooth surface, increased splitting degree, and a lower short fiber rate after opening and combing, which is more beneficial for subsequent spinning processing.

[0031] The degumming mechanism of hemp fibers based on the ternary eutectic solvent of alkanolamine / betaine / polyol in this invention is as follows: By competitively disrupting the intermolecular forces of non-cellulose components through hydrogen bonding, and combining this with the weak base catalytic cleavage of ester and ether bonds by alkanolamines, this method has broad applicability. Although different bast fibers (rock kenaf, ramie, flax, hemp, jute, etc.) differ in cellulose content, lignin content, pectin content, and fiber fineness, the chemical nature of their gum complexes (all consisting of pectin, hemicellulose, and lignin linked by ester and ether bonds) is the same. Based on the teachings of this invention, those skilled in the art can achieve ideal degumming results by simply optimizing the degumming temperature (adjusted within the range of 130–150°C), time (adjusted within 2–3 hours), or material-to-liquid ratio (adjusted within the range of 1:15–30) for different bast fibers, without requiring any inventive effort. Therefore, the scope of protection of this invention should not be limited to rock kenaf, but should cover all bast fibers of bast fibers.

[0032] In summary, this invention achieves efficient, environmentally friendly, and high-quality degumming of hemp fibers through a technical route of pre-soaking in warm water to remove impurities, combined with ternary eutectic solvent for synergistic degumming and solvent recycling. The various steps work together to form a complete technical solution that is distinct from existing technologies. Attached Figure Description

[0033] Figure 1 An electron microscope image of the dried hemp fibers produced in Example 2 of this invention.

[0034] Figure 2 An electron microscope image of the ramie refined dried hemp produced in Example 3 of this invention. Detailed Implementation

[0035] The accompanying drawings are for illustrative purposes only. The invention will now be described in detail with reference to embodiments. Unless otherwise specified, the raw materials, reagents, and equipment used in this invention are all commercially available products conventional in the art.

[0036] Raw material description: The raw kenaf was produced in Kashgar, Xinjiang, and the raw ramie was produced in Dazhou, Sichuan. 400 kg of raw kenaf was divided into two equal portions, which were used in Example 1 and Example 2, respectively; 600 kg of raw ramie was divided into three equal portions, which were used in Example 3, Comparative Example 1, and Comparative Example 2, respectively.

[0037] Example 1 A method for degumming hemp fibers based on a ternary eutectic solvent includes the following steps: The first step is pre-soaking to remove impurities. Place the kenaf bast in an impregnation tank and immerse it in 40℃ warm water for 10 minutes for pre-soaking to remove impurities; after completion, remove the raw kenaf, drain the water, and set aside.

[0038] The second step is degumming. (1) Preparation of ternary eutectic solvent degumming solution: Diethanolamine, alkylamidopropyl betaine and butanediol are mixed in a ratio of 1:2:1 and added to a mixing tank. The mixture is heated and stirred at 60°C until it becomes a transparent and homogeneous liquid without precipitation or stratification. The degumming solution is then obtained and ready for use.

[0039] (2) Loading and boiling: Place the pre-soaked and impurity-removed kenaf into the boiling kettle, open the liquid inlet valve, and inject the degumming liquid until it is completely submerged. The mass ratio of kenaf bast to degumming liquid is 1:15.

[0040] (3) Heating and degumming: Heat the degumming liquid in the boiling kettle to 130°C while slowly stirring the liquid and boiling continuously for 2 hours. After boiling is completed, open the liquid outlet valve and remove the liquid in the boiling kettle by squeezing or centrifugation for recycling. After emptying, close the liquid outlet valve.

[0041] (4) Spray rinsing: Open the water inlet valve and use warm water to repeatedly spray and rinse the degummed hemp fibers until the rinsing solution is colorless and the pH is neutral, thus obtaining the hemp fiber semi-finished product.

[0042] The third step is solid-liquid separation and solvent recovery. After degumming is completed, the liquid recovered in step (3) is separated into solid and liquid by a 100-mesh filter or a plate and frame filter press and then directly used for the next batch of degumming, and the cycle is repeated 5 times. Fourth step, meticulous processing The above-mentioned hemp fiber semi-finished product was dehydrated (15 min), and then oiled (10 min) and dried (60 min) in sequence. The dried fiber was combed by an opening machine to remove short fibers and impurities, and uniformly dispersed fine hemp fiber was obtained.

[0043] The product inspection and testing results are shown in Table 1.

[0044] Example 2 A method for degumming hemp fibers based on a ternary eutectic solvent includes the following steps: The first step is pre-soaking to remove impurities. Place the kenaf bast in an impregnation tank and immerse it in 60℃ warm water for 30 minutes for pre-soaking to remove impurities; after completion, remove the raw kenaf, drain the water, and set aside.

[0045] The second step is degumming. (1) Preparation of ternary eutectic solvent degumming solution: Monoethanolamine, anhydrous betaine and ethylene glycol are mixed in a ratio of 1:4:0.8 and added to a mixing tank. The mixture is heated and stirred at 80°C until it becomes a transparent and homogeneous liquid without precipitation or stratification. The degumming solution is then obtained and is ready for use.

[0046] (2) Loading and boiling: Place the pre-soaked and impurity-removed kenaf into the boiling kettle, open the liquid inlet valve, and inject the degumming liquid until it is completely submerged. The mass ratio of kenaf bast to degumming liquid is 1:30.

[0047] (3) Heating and degumming: Heat the degumming liquid in the boiling kettle to 150°C while slowly stirring the liquid and boiling continuously for 3 hours. After boiling is completed, open the liquid outlet valve and remove the liquid in the boiling kettle by squeezing or centrifugation for recycling. After emptying, close the liquid outlet valve.

[0048] (4) Spray rinsing: Open the water inlet valve and use warm water to repeatedly spray and rinse the degummed hemp fibers until the rinsing solution is colorless and the pH is neutral, thus obtaining the hemp fiber semi-finished product.

[0049] The third step is solid-liquid separation and solvent recovery. After degumming is completed, the liquid recovered in step (3) is used directly for the next batch of degumming after solid-liquid separation by a 200-mesh filter or a plate and frame filter press, and is recycled 4 times. Fourth step, meticulous processing The above-mentioned hemp fiber semi-finished product was dehydrated (20 min), and then oiled (20 min) and dried (90 min) in sequence. The dried fiber was combed by an opening machine to remove short fibers and impurities, and uniformly dispersed fine hemp fiber was obtained.

[0050] The product inspection and testing results are shown in Table 1.

[0051] Example 3 A method for degumming hemp fibers based on a ternary eutectic solvent includes the following steps: The first step is pre-soaking to remove impurities. Place the ramie bast fibers in an impregnation tank and immerse them in 60℃ warm water for 30 minutes for pre-soaking to remove impurities; after completion, remove the raw ramie fibers, drain the water, and set aside.

[0052] The second step is degumming. (1) Preparation of ternary eutectic solvent degumming solution: Monoethanolamine, anhydrous betaine and ethylene glycol are mixed in a ratio of 1:4:1 and added to a mixing tank. The mixture is heated and stirred at 80°C until it becomes a transparent and homogeneous liquid without precipitation or stratification. The degumming solution is then obtained and ready for use.

[0053] (2) Loading and boiling: Place the pre-soaked and impurity-removed ramie into the boiling kettle, open the liquid inlet valve, and inject the degumming liquid until it is completely submerged. The mass ratio of ramie bast to degumming liquid is 1:30.

[0054] (3) Heating and degumming: Heat the degumming liquid in the boiling kettle to 150°C while slowly stirring the liquid and boiling continuously for 3 hours. After boiling is completed, open the liquid outlet valve and remove the liquid in the boiling kettle by squeezing or centrifugation for recycling. After emptying, close the liquid outlet valve.

[0055] (4) Spray rinsing: Open the water inlet valve and use warm water to repeatedly spray and rinse the degummed hemp fibers until the rinsing solution is colorless and the pH is neutral, thus obtaining the hemp fiber semi-finished product.

[0056] The third step is solid-liquid separation and solvent recovery. After degumming is completed, the liquid recovered in step (3) is separated into solid and liquid by a 300-mesh filter or a plate and frame filter press and then used directly for the next batch of degumming, and the cycle is repeated 3 times. Fourth step, meticulous processing The above-mentioned hemp fiber semi-finished product was dehydrated (20 min), and then oiled (20 min) and dried (90 min) in sequence. The dried fiber was combed by an opening machine to remove short fibers and impurities, and uniformly dispersed fine hemp fiber was obtained.

[0057] The product inspection and testing results are shown in Table 1.

[0058] Comparative Example 1: Ramie refined hemp was produced using existing traditional technology.

[0059] Process flow: Pre-soak raw ramie (1% sulfuric acid, 1h) → Wash (20min) → First boil (1% sodium hydroxide, 1h) → Wash (20min) → Second boil (1% sodium hydroxide, 3% sodium silicate, 3% urea, 3% hydrogen peroxide, 3% sodium tripolyphosphate, 2% sodium sulfite, 1h) → Wash (20min) → Dehydration (20min) → Oiling (20min) → Drying (1h) → Refined ramie.

[0060] This comparative example cannot achieve the recycling of the degumming liquid (the number of cycles is 0).

[0061] The product inspection and testing results are shown in Table 1.

[0062] Comparative Example 2: Alkylamine / polyol binary DES system.

[0063] Ramie was degummed using a binary eutectic solvent system of alkanolamine / polyol, and compared with the ternary system of this invention.

[0064] The first step is pre-soaking to remove impurities. Same as Example 3.

[0065] The second step is degumming. (1) Preparation of degumming solution of binary eutectic solvent: Mix monoethanolamine and ethylene glycol in a 1:1 ratio and add to the mixing tank. Heat and stir at 80°C until the system is a transparent and homogeneous liquid without precipitation and layering. The degumming solution is then obtained and ready for use.

[0066] (2) Loading and boiling: Same as in Example 3.

[0067] (3) Heating to degumme: Same as in Example 3.

[0068] (4) Spray rinsing: Same as in Example 3.

[0069] The third step is solid-liquid separation and solvent recovery. Same as Example 3, repeated 3 times.

[0070] Fourth step, meticulous processing Same as Example 3.

[0071] The product inspection and testing results are shown in Table 1.

[0072] The test results of Examples 1-3 and Comparative Examples 1-2 are shown in Table 1.

[0073] Table 1. Comparison of test results between Examples 1-3 and Comparative Examples 1-2 As shown in Table 1, a comparison of the test results of Examples 1-3 and Comparative Examples 1-2 reveals the following: Degumming efficiency and fiber protection: The ternary DES process in Examples 2 and 3 is significantly superior to the binary DES process in Comparative Example 2 (comparison of residual gum content, where kenaf, due to its high lignin content, is more difficult to degumme and has a higher residual gum content than ramie), and far superior to the traditional alkali boiling method in terms of fiber strength protection (comparison of breaking strength). Although the residual gum content of Comparative Example 1 is slightly lower than that of this invention, its fiber strength loss is severe, and it generates a large amount of highly polluting wastewater. The comparison between Examples 1 and 2 demonstrates that the overall fiber quality can be improved through the optimization of process parameters.

[0074] Process simplicity: The traditional "two-step" alkaline degumming process requires two alkaline boilings and two water washings, which is a lengthy process; while the degumming process of this invention only requires one DES boiling, and the degumming waste liquid can be recycled and reused, which greatly reduces the amount of wastewater discharged and shortens the total processing time.

[0075] Whiteness Improvement: This invention uses a DES system containing alkanolamine components. The whiteness of the resulting ramie refined dry ramie (48 for the first time in Example 3, 52 after cycling) meets the national standard (≤55), and no additional bleaching process is required, thus avoiding secondary damage to the fibers by bleaching agents and the discharge of chlorine-containing wastewater.

[0076] Solvent recycling: The ternary DES of this invention can be stably recycled 3 to 5 times with good degumming effect, while the residual glue rate of the binary DES in Comparative Example 2 increases significantly after recycling, indicating that the ternary system has better stability.

[0077] In summary, the hemp fiber degumming process based on a ternary eutectic solvent of alkanolamine / betaine / polyol provided by this invention can achieve efficient degumming under mild conditions, protect fiber strength, significantly reduce pollution emissions, and realize solvent recycling. It is a green, efficient degumming method applicable to a variety of hemp fibers.

[0078] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for degumming hemp fibers based on a ternary eutectic solvent, characterized in that, Includes the following steps: S1. Pre-soaking to remove impurities: Place the raw hemp basts in an soaking tank and immerse them in warm water for pre-soaking to remove impurities; after completion, remove the raw hemp, drain the water, and set aside. S2. Degumming treatment: (1) Preparation of ternary eutectic solvent degumming solution: After mixing betaine compounds, polyol compounds and alkanolamine compounds, add them to the mixing tank, heat and stir until the system is a transparent and homogeneous liquid without precipitation and layering, and the degumming solution is obtained and ready for use; (2) Loading and boiling: Place the pre-soaked and impurity-removed raw hemp into the boiling kettle, open the liquid inlet valve, and inject the degumming liquid until the hemp bast is completely submerged; (3) Heating and degumming: The degumming liquid in the boiling kettle is heated and stirred at the same time for continuous boiling; after boiling is completed, the liquid outlet valve is opened, and the liquid in the boiling kettle is removed by squeezing or centrifugation and then recycled. After emptying, the liquid outlet valve is closed. (4) Spray rinsing: Open the water inlet valve and repeatedly spray and rinse the degummed hemp fibers to obtain hemp fiber semi-finished products; S3. Solid-liquid separation and solvent recovery: After degumming is completed, the liquid recovered in step (3) is used directly for the next batch of degumming after solid-liquid separation by a 100-300 mesh filter or a plate and frame filter press. S4. Fine processing: The hemp fiber semi-finished product in step S3 is dehydrated, and then oiled and dried in sequence. The dried fiber is combed by an opening machine to remove short fibers and impurities, and uniformly dispersed fine hemp fiber is obtained.

2. The method for degumming hemp fibers based on a ternary eutectic solvent according to claim 1, characterized in that, The hemp fiber is one or more of the following: kenaf fiber, ramie fiber, flax fiber, hemp fiber, and jute fiber.

3. The method for degumming hemp fibers based on a ternary eutectic solvent according to claim 1, characterized in that, In step S1, the water temperature used for pre-soaking and impurity removal is 40-60℃, and the immersion time is 10-30 minutes.

4. The method for degumming hemp fibers based on a ternary eutectic solvent according to claim 1, characterized in that, In step S1, the polyol compound is selected from any one of ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, and butanediol; the alkanolamine compound is selected from at least one of monoethanolamine, diethanolamine, triethanolamine, isopropanolamine, or diethanolmonoisopropanolamine; and the betaine compound is selected from any one of anhydrous betaine, alkylamidopropyl betaine, or sulfobetaine.

5. The method for degumming hemp fibers based on a ternary eutectic solvent according to claim 4, characterized in that, In step S2, the molar ratio of alkanolamine, betaine and polyol compounds is 1:2 to 12:1 to 3; the preparation temperature of the degumming solution in the mixing tank is 60 to 80°C.

6. The method for degumming hemp fibers based on a ternary eutectic solvent according to claim 1, characterized in that, In step S2, during the loading and boiling process, the mass ratio of raw hemp bast to the ternary eutectic solvent degumming solution is 1:15-30.

7. The method for degumming hemp fibers based on a ternary eutectic solvent according to claim 1, characterized in that, In step S2, during the degumming process, the temperature is raised to 130-150°C and continuously boiled for 2-3 hours.

8. The method for degumming hemp fibers based on a ternary eutectic solvent according to claim 1, characterized in that, In step S2, warm water is used for spray rinsing, with a water temperature of 40-60℃, until the rinsing solution is colorless and the pH is neutral.

9. The method for degumming hemp fibers based on a ternary eutectic solvent according to claim 1, characterized in that, In step S3, after the filter is recycled 3 to 5 times, water is added to dilute the colloid and precipitate it. Then, the eutectic solvent is purified by distillation to achieve solvent recycling.

10. The method for degumming hemp fibers based on a ternary eutectic solvent according to claim 1, characterized in that, In step S4, the dehydration time is 15-20 min; the oiling time is 10-20 min; and the drying time is 60-90 min.

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