Short fiber spinning methods and short fibers

Abstract

This invention provides a method for spinning short fibers, comprising: wet spinning a fiber stream obtained from a solution containing natural polymers and passing it through at least one coagulation bath; the nascent fibers are then bundled, stretched, sheared, washed, oiled, and dried to obtain short fibers; the solution containing natural polymers contains metal hydroxides and auxiliaries, the auxiliaries being selected from at least one of urea, zinc oxide, and thiourea; bicarbonate or bisulfite or a combination of bicarbonate and carbonate or a combination of bisulfite and sulfite is used as a coagulation bath component, employing a low-cost, green, efficient, non-toxic, harmless, and inexpensive inorganic salt solution, free of strong acids and organic solvents, to prepare short fibers with a circular cross-section and excellent mechanical properties, and the short fibers have a smooth, soft, and lustrous surface.

Description

Technical Field

[0001] This invention relates to the field of natural polymer spinning technology, specifically to a short fiber spinning method and short fibers. Background Technology

[0002] Viscose technology, with a history of over 100 years, remains the most widely used technology for manufacturing regenerated cellulose fibers and films [Fink HP, Ganster J, Lehmann A. Progress in cellulose shaping: 20 years of industrial case studies at Fraunhofer IAP[J]. Cellulose, 2014, 21: 31-51.]. In 2021, the global production capacity of viscose staple fiber was approximately 7.5 million tons, with China accounting for over 70% of the world's total output. However, the viscose system's production process involves multiple stages, including impregnation, pressing, aging, sulfonation, and post-dissolution, resulting in a long and complex process. The preparation process utilizes large amounts of hazardous chemicals such as carbon disulfide, leading to significant pollution, low efficiency, and high energy consumption. Therefore, developing green manufacturing technologies for regenerated cellulose materials has become an inevitable requirement and direction for the high-quality development of the global cellulose fiber and film industry. Further research is needed on key technologies for NMMO-specific pulp, solvents, crosslinking agents, and improving the large-scale production of NMMO fibers. Simultaneously, research is being conducted on green manufacturing technologies for cellulose fibers and other materials using low-temperature alkali / urea methods and ionic liquid methods.

[0003] The alkali / urea / water system is green, non-toxic, inexpensive and efficient. It can be used to dissolve cellulose raw materials from various plant sources and prepare high-strength regenerated cellulose functional materials in different forms, such as membranes, hydrogels, filaments, microspheres, etc. [Tu H, Zhu M, Duan B, et al. Recent progress in high-strength and robust regenerated cellulose materials[J]. Advanced Materials, 2021, 33(28): 2000682. Pang B, Jiang G, Zhou J, et al. Molecular-scale design of cellulose-based functional materials for flexible electronic devices[J]. Advanced Electronic Materials, 2021, 7(2): 2000944.]. However, due to the rapid formation of high-strength nanofiber structures by commonly used strong acid coagulation baths, it is difficult to form them. Mild weak acid systems such as acetic acid and phytic acid are conducive to the formation of high-strength nanostructures, but the cost is high [32. Zhu K, Qiu C, Lu A, et al. Mechanically strong multifilament fibers spun from cellulose solution via inducing formation of nanofibers[J].ACS SustainableChemistry&Engineering,2018,6(4):5314-5321.]. The above strong or weak acids react with alkali / urea to form mixed solutions of various salts, which are not easy to separate, making it difficult to recycle and reuse the salts. This directly increases the difficulty and cost of salt separation and recovery as well as waste treatment. Physical coagulation and solvent recovery can be achieved using hot water and its salt solution (CN101921402A, CN102443869A) or organic solvent solution (CN110129923A). However, this method results in slow coagulation speed, low product performance, and high alkali residue in the fibers, requiring subsequent alkali removal processes and hindering industrial production. Therefore, there is an urgent need to develop a mild and low-cost post-coagulation treatment method using an alkali / urea green system. Summary of the Invention

[0004] To address the problems of poor product performance and high costs associated with the recovery and processing of coagulated bath salts in existing technologies, this invention provides a short fiber spinning method and the short fiber itself. Using the spinning method described in this invention, a low-cost, green, efficient, non-toxic, harmless, and inexpensive inorganic salt solution is employed. This solution is free of strong acids and organic solvents, enabling the production of short fibers with a circular cross-section and excellent mechanical properties. Furthermore, the short fibers have a smooth, soft, and lustrous surface. The entire production process is simple: the nascent fibers undergo bundling, stretching, shearing, washing, oiling, and drying, eliminating the need for lengthy refining and desulfurization processes. This results in high efficiency, low energy consumption, and significant water savings.

[0005] The first aspect of the present invention provides a method for spinning short fibers, the method comprising: wet spinning a fiber stream obtained by a solution containing natural polymers through at least one coagulation bath to form a nascent fiber; the nascent fiber being bundled, stretched, sheared, washed, oiled, and dried to obtain short fibers; wherein the solution containing natural polymers contains a metal hydroxide and an auxiliary agent, the auxiliary agent being selected from at least one of urea, zinc oxide, and thiourea;

[0006] The coagulation bath is a first coagulation bath, which contains bicarbonate or bisulfite; the mass concentration of bicarbonate or bisulfite is 0.5-30 wt% respectively; or

[0007] The coagulation bath is a second coagulation bath, which contains bicarbonate and carbonate, or bisulfite and sulfite; wherein the mass concentration of bicarbonate or bisulfite is 0.5-30 wt% and the mass concentration of carbonate or sulfite is 0.5-30 wt%.

[0008] A second aspect of the present invention provides a short fiber prepared by the spinning method described in the present invention.

[0009] Compared with the prior art, the short fiber spinning method of the present invention uses bicarbonate or bisulfite or a combination of bicarbonate and carbonate or a combination of bisulfite and sulfite as coagulation bath components to provide a mild coagulation solution. This is beneficial for the uniform coagulation and shaping of the fiber filaments formed by the natural polymer solution of the present invention. In this process, the fiber filaments have not yet fully formed the intermolecular hydrogen bond network of cellulose, which is conducive to full solidification and stretching in the coagulation bath and subsequent stretching. After shearing, washing, oiling and drying, short fibers with a circular cross section and excellent performance (strength up to 2.7 cN / dtex) are obtained. The fiber surface is smooth, the fiber is soft and shiny, the cross section is dense and the structure is uniform, and there is no obvious core-sheath structure.

[0010] In the coagulation bath described in this invention, the main components of the salt solution are weakly alkaline bicarbonate or bisulfite. This salt reacts with metal hydroxides. The accumulation of urea and / or thiourea as additives in the coagulation bath is beneficial to improving product performance. When the additive is a metal salt (e.g., zinc oxide), a corresponding precipitate is generated in the coagulation bath, which can be filtered out without affecting the regeneration of weakly acidic bicarbonate or bisulfite. It is regenerated into bicarbonate or bisulfite through carbon dioxide or sulfation. Therefore, urea and / or thiourea can be recycled. Furthermore, bicarbonate, carbonate, bisulfite, and sulfite are easily separated and recovered, making the consumption of chemical materials comparable to or even lower than that of adhesive processes. This solves the problem of recycling and processing high-concentration salts, reduces production difficulty and costs, and has broad application prospects. Attached Figure Description

[0011] Figure 1 The image is a scanning electron microscope (SEM) image of the short fiber prepared in Example 1.

[0012] Figure 2 The image is a scanning electron microscope (SEM) image of the short fiber prepared in Example 1.

[0013] Figure 3 The image is a scanning electron microscope (SEM) image of the short fiber prepared for Comparative Example 1.

[0014] Figure 4 The image shows a scanning electron microscope (SEM) image of the short fiber prepared for Comparative Example 1. Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] The first aspect of the present invention provides a method for spinning short fibers, the method comprising: wet spinning a fiber stream obtained by a solution containing natural polymers through at least one coagulation bath to form a nascent fiber; the nascent fiber being bundled, stretched, sheared, washed, oiled, and dried to obtain short fibers; wherein the solution containing natural polymers contains a metal hydroxide and an auxiliary agent, the auxiliary agent being selected from at least one of urea, zinc oxide, and thiourea;

[0017] The coagulation bath is a first coagulation bath, which contains bicarbonate or bisulfite; the mass concentration of bicarbonate or bisulfite is 0.5-30 wt% respectively; or

[0018] The coagulation bath is a second coagulation bath, which contains bicarbonate and carbonate, or bisulfite and sulfite; wherein the mass concentration of bicarbonate or bisulfite is 0.5-30 wt% and the mass concentration of carbonate or sulfite is 0.5-30 wt%.

[0019] In this invention, bicarbonate, bisulfite, a combination of bicarbonate and carbonate, or a combination of bisulfite and sulfite are used as components of the coagulation bath to provide a mild coagulation solution. This facilitates the uniform coagulation and shaping of the fiber filaments formed by the natural polymer solution described in this invention. During this process, the fiber filaments have not yet fully formed an intermolecular hydrogen bond network of cellulose molecules, which is beneficial for sufficient solidification and stretching in the coagulation bath and subsequent stretching. After shearing, washing, oiling, and drying, short fibers with a circular cross-section and excellent performance are obtained. Furthermore, the fiber surface is smooth, the fiber is soft and lustrous, the cross-section is dense, the structure is uniform, and there is no obvious core-sheath structure.

[0020] According to a preferred embodiment of the present invention, the bicarbonate, carbonate, bisulfite and sulfite are each selected from at least one of lithium salt, sodium salt, potassium salt, rubidium salt, cesium salt and ammonium salt.

[0021] In this invention, there are no particular limitations on the molding conditions. According to a preferred embodiment of the invention, the molding conditions include a temperature of 10-80°C, preferably 20-40°C.

[0022] In this invention, the additives urea and / or thiourea accumulate in the coagulation bath to improve the performance of the product. According to a preferred embodiment of the invention, the coagulation bath also contains urea and / or thiourea, preferably, the mass concentration of urea and / or thiourea is 0.4-60 wt%.

[0023] According to a preferred embodiment of the present invention, the mass concentration of the natural polymer material in the solution containing the natural polymer is 5wt%-9wt%; preferably, the degree of polymerization of the natural polymer material is 200-800.

[0024] According to a preferred embodiment of the present invention, the mass concentration of the auxiliary agent in the solution containing natural polymers is 0.01wt%-15wt%.

[0025] According to a preferred embodiment of the present invention, the mass concentration of the metal hydroxide is 2wt%-15wt%, preferably 5wt%-12wt%.

[0026] In this invention, there is no particular limitation on the material of the natural polymer. Conventional natural polymer materials in the art can be used in this invention. According to a preferred embodiment of the invention, the natural polymer material is selected from at least one of cellulose, chitin, chitosan and sodium alginate, preferably cellulose and / or chitin.

[0027] According to a preferred embodiment of the present invention, the metal hydroxide is selected from at least one of sodium hydroxide, potassium hydroxide and lithium hydroxide.

[0028] In this invention, the fiber stream passes through at least one coagulation bath, for example, it can be coagulated and formed through one, two, three, or four coagulation baths. According to a preferred embodiment of this invention, the fiber stream passes through two coagulation baths, which is beneficial to improving the performance of the fiber.

[0029] According to a preferred embodiment of the present invention, in the first coagulation bath, when the coagulation bath is a first coagulation bath, the mass concentration of bicarbonate or bisulfite is 0.5-30 wt%; when the coagulation bath is a second coagulation bath, the mass concentration of bicarbonate or bisulfite is 0.5-30 wt% respectively; and the mass concentration of carbonate or sulfite is 0.5-30 wt% respectively.

[0030] According to a preferred embodiment of the present invention, in the second coagulation bath, when the coagulation bath is the first coagulation bath, the mass concentration of bicarbonate or bisulfite is 5-15 wt%; when the coagulation bath is the second coagulation bath, the mass concentration of bicarbonate or bisulfite is 5-15 wt%; and the mass concentration of carbonate or sulfite is 1-10 wt%.

[0031] According to a preferred embodiment of the present invention, in the first coagulation bath, when the coagulation bath is a first coagulation bath, the mass concentration of bicarbonate or bisulfite is 8-20 wt% each; when the coagulation bath is a second coagulation bath, the mass concentration of bicarbonate or bisulfite is 8-20 wt% each, and the mass concentration of carbonate or sulfite is 2-6 wt% each.

[0032] According to a preferred embodiment of the present invention, in the first coagulation bath, the coagulation bath is a second coagulation bath, wherein the mass concentration of bicarbonate or bisulfite is 8-15 wt% each; the mass concentration of carbonate or sulfite is 2-6 wt% each; and the mass concentration of urea and / or thiourea is 20-40 wt%.

[0033] In this invention, bundle drawing is used to collect nascent fibers and improve fiber orientation. During this stage, the orientation is controlled at 0-60%, and the draw rate of bundle drawing is 0% to 60%.

[0034] In this invention, shearing is used to obtain fibers with different thickness-to-length ratios as needed, typically 38-40 mm in length.

[0035] In this invention, there are no particular limitations on the washing conditions; it is sufficient to wash away the salt.

[0036] In this invention, oiling is used to improve softness; for example, silicone oil can be applied to the nascent fibers obtained after washing.

[0037] In this invention, there are no particular limitations on the drying conditions. Preferably, the drying conditions include a temperature of 80-130°C and a time of 1-5 hours.

[0038] In this invention, the dried short fibers are packaged, preferably with a package weight of 80-200 kg / bag.

[0039] A second aspect of the present invention provides a short fiber prepared by the short fiber spinning method described in the present invention.

[0040] In this invention, short fibers, also known as cut fibers, refer to fiber segments cut into certain lengths from spun filaments. Based on their thickness-to-length ratio, they can be classified into cotton-type short fibers (commonly known as "artificial cotton"), wool-type short fibers (commonly known as "artificial wool"), and medium-length short fibers (abbreviated as "medium-short fibers"). They can be spun purely on cotton or wool spinning machines, or blended with cotton, wool, or other fibers.

[0041] The present invention will be further illustrated by the following embodiments, but these embodiments in no way limit the scope of the present invention.

[0042] In the following examples, the density, dry elongation, and average strength of the regenerated fiber staple fiber were tested according to the viscose staple fiber standard (GB / T 14463-2022).

[0043] Example 1

[0044] (1) Dissolve cellulose with a DP of 400 in a sodium hydroxide / urea / water system (mass ratio of 7:12:81), and filter and degas to obtain a solution containing 7.5 wt% cellulose;

[0045] (2) The solution in step (1) is subjected to wet spinning to obtain a fiber stream. The fiber stream is passed through a coagulation bath containing 14 wt% sodium bicarbonate and 2 wt% sodium carbonate (the temperature of the coagulation bath is 50°C) to obtain nascent fibers.

[0046] (3) The nascent fibers are sequentially bundled and stretched at a stretch rate of 20%, then cut to a length of 40 mm, washed with hot water at 65°C, oiled (with silicone oil), and dried at 110°C to obtain regenerated cellulose short fibers. The regenerated cellulose short fibers have a linear density of 133 dtex, a dry elongation of 14.1%, and an average strength of 1.8 cN / dtex.

[0047] The short fiber scanning electron microscope (SEM) image is shown below. Figure 1 , Figure 2 As shown, the short fiber has a circular cross-section, a smooth surface, a dense cross-section, a uniform structure, and no obvious skin-core structure.

[0048] Example 2

[0049] (1) Dissolve cellulose with a DP of 250 in a sodium hydroxide / urea / water system (mass ratio of 7:5:87) and degas to obtain a solution containing 8 wt% cellulose;

[0050] (2) The solution in step (1) is subjected to wet spinning to obtain a fiber stream. The fiber stream is passed through a coagulation bath containing 15 wt% sodium bisulfite and 15 wt% sodium sulfite (the temperature of the coagulation bath is 20°C) to obtain nascent fibers.

[0051] (3) The nascent fibers are sequentially bundled and stretched at a stretch rate of 30%, then cut to a length of 40 mm, washed with hot water at 65°C, oiled (with silicone oil), and dried at 130°C to obtain regenerated cellulose short fibers. The regenerated cellulose short fibers have a linear density of 133 dtex, a dry elongation of 15.6%, and an average strength of 1.9 cN / dtex.

[0052] Example 3

[0053] The method of Preparation Example 1 is the same, except that in step (2), the composition of the coagulation bath is: 9 wt% sodium bicarbonate, 2 wt% sodium carbonate, and 20 wt% urea (the temperature of the coagulation bath is 20 °C); the other conditions are the same as those of Preparation Example 1.

[0054] The regenerated fiber has a short fiber linear density of 133 dtex, a dry elongation of 15.6%, and an average strength of 2.3 cN / dtex.

[0055] Example 4

[0056] (1) Chitin with a DP of 250 was dissolved in a potassium hydroxide / urea / water system (mass ratio of 12.7:5.7:81.6) and degassed to obtain a solution containing 7wt% chitin;

[0057] (2) The solution in step (1) is subjected to wet spinning to obtain a fiber stream. The fiber stream is passed through a coagulation bath containing 20 wt% potassium bicarbonate, 15 wt% potassium carbonate and 30 wt% urea (the temperature of the coagulation bath is 10°C) to obtain nascent fibers.

[0058] (3) The nascent fibers are sequentially bundled and stretched at a stretch rate of 30%, then cut to a length of 40 mm, washed with hot water at 65°C, oiled (with silicone oil), and dried at 110°C to obtain regenerated chitin short fibers. The regenerated chitin short fibers have a linear density of 133 dtex, a dry elongation of 14.3%, and an average strength of 1.9 cN / dtex.

[0059] Example 5

[0060] (1) Dissolve cellulose with a DP of 400 in a sodium hydroxide / urea / water system (mass ratio of 7:12:81) and degas to obtain a solution containing 7.5 wt% cellulose;

[0061] (2) The solution in step (1) is wet-spun to obtain a fiber stream. The fiber stream passes through a first coagulation bath (containing 9 wt% sodium bicarbonate and 2 wt% sodium carbonate). The temperature of the coagulation bath is 20°C, and 20% positive drawing is performed.

[0062] Then it goes through a second coagulation bath (containing 5 wt% sodium bicarbonate and 2 wt% sodium carbonate), the temperature of the coagulation bath is 50°C, and it is subjected to 30% positive stretching;

[0063] (3) The nascent fibers are sequentially bundled and stretched with a stretching rate of 50%, then cut into 40mm lengths, washed with hot water at 65℃, oiled (silicone oil), and dried at 110℃ to obtain regenerated cellulose short fibers.

[0064] The regenerated cellulose short fibers have a linear density of 133 dtex, a dry elongation of 16.0%, and an average strength of 2.5 cN / dtex.

[0065] Example 6

[0066] (1) Dissolve cellulose with a DP of 400 in a sodium hydroxide / urea / water system (mass ratio of 7:12:81) and degas to obtain a solution containing 7.5 wt% cellulose;

[0067] (2) The solution in step (1) is subjected to wet spinning to obtain a fiber stream. The fiber stream passes through the first coagulation bath (sodium bicarbonate 9wt%, sodium carbonate 2wt%, urea 20wt%), and the temperature of the coagulation bath is 20℃.

[0068] Then it passes through a second coagulation bath (containing 5 wt% sodium bicarbonate and 2 wt% sodium carbonate), the temperature of which is 50°C.

[0069] (3) The nascent fibers are washed with hot water at 65°C, oiled (with silicone oil), and dried at 110°C to obtain regenerated cellulose short fibers.

[0070] The regenerated cellulose short fibers have a linear density of 133 dtex, a dry elongation of 16.2%, and an average strength of 2.7 cN / dtex.

[0071] Example 7

[0072] The method of Preparation Example 1 is the same, except that in step (2), the composition of the coagulation bath is: 16 wt% sodium bicarbonate (the temperature of the coagulation bath is 60 °C); the other conditions are the same as those of Preparation Example 1.

[0073] The regenerated cellulose short fibers have a linear density of 133 dtex, a dry elongation of 14.2%, and an average strength of 1.8 cN / dtex.

[0074] Example 8

[0075] (1) Dissolve cellulose with a DP of 400 in a sodium hydroxide / urea / water system (mass ratio of 7:12:81) and degas to obtain a solution containing 7.5 wt% cellulose;

[0076] (2) The solution in step (1) is wet-spun to obtain a fiber stream. The fiber stream passes through the first coagulation bath (containing 7 wt% sodium bicarbonate and 1 wt% sodium carbonate). The temperature of the coagulation bath is 20°C, and 20% positive drawing is performed.

[0077] Then it goes through a second coagulation bath (containing 5 wt% sodium bicarbonate and 2 wt% sodium carbonate), the temperature of the coagulation bath is 50°C, and it is subjected to 30% positive stretching;

[0078] (3) The nascent fibers are sequentially bundled and stretched with a stretching rate of 50%, then cut into 40mm lengths, washed with hot water at 65℃, oiled (silicone oil), and dried at 110℃ to obtain regenerated cellulose short fibers.

[0079] The regenerated cellulose short fibers have a linear density of 133 dtex, a dry elongation of 15.7%, and an average strength of 2.0 cN / dtex.

[0080] Comparative Example 1

[0081] The method is the same as in Example 1, except that the coagulation bath is a sulfuric acid coagulation bath system (specifically composed of 110 g / L sulfuric acid and 150 g / L sodium sulfate), and the other conditions are the same as in Example 1.

[0082] The regenerated fiber has a short fiber linear density of 133 dtex, a dry elongation of 8.1%, and an average strength of 1.6 cN / dtex.

[0083] The regenerated short fiber scanning electron microscope (SEM) image is shown below. Figure 3 , Figure 4 As shown, the short fiber has an irregular cross-section, numerous surface wrinkles, and a large number of irregular pores, exhibiting a distinct skin-core structure.

[0084] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for spinning short fibers, characterized in that, The method is as follows: Fiber streams obtained by wet spinning a solution containing natural polymers are formed through two coagulation baths; the nascent fibers are then bundled, stretched, sheared, washed, oiled, and dried to obtain short fibers; the solution containing natural polymers contains metal hydroxides and auxiliaries, the auxiliaries being selected from urea and / or thiourea; the natural polymer material is selected from at least one of cellulose, chitin, chitosan, and sodium alginate; in the solution containing natural polymers, the mass concentration of the natural polymer material is 5wt%-9wt%; the mass concentration of the auxiliaries is 0.01wt%-15wt%; and the mass concentration of the metal hydroxide is 2wt%-15wt%. The coagulation bath is a first coagulation bath, which contains bicarbonate or bisulfite; or The coagulation bath is a second coagulation bath, which contains bicarbonate and carbonate, or bisulfite and sulfite. In the first coagulation bath, which is the second coagulation bath, the mass concentration of bicarbonate or bisulfite is 8-15 wt% each; the mass concentration of carbonate or sulfite is 2-6 wt% each; and the mass concentration of urea and / or thiourea is 20-40 wt%. In the second coagulation bath, when the coagulation bath is the first coagulation bath, the mass concentration of bicarbonate or bisulfite is 5-15 wt%. When the coagulation bath is the second coagulation bath, the mass concentration of bicarbonate or bisulfite is 5-15 wt%; the mass concentration of carbonate or sulfite is 1-10 wt%.

2. The spinning method according to claim 1, wherein, Bicarbonate, carbonate, bisulfite, and sulfite are each selected from at least one of lithium, sodium, potassium, rubidium, cesium, and ammonium salts; and / or Molding conditions include a temperature of 10-80℃.

3. The spinning method according to claim 2, wherein, Molding conditions include a temperature of 20-40℃.

4. The spinning method according to claim 1 or 2, wherein, The degree of polymerization of the natural polymer material is 200-800.

5. The spinning method according to any one of claims 1-3, wherein, The metal hydroxide is selected from at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

6. The spinning method according to any one of claims 1-3, wherein, The draw ratio of bundled drawing is 0% to 60%.

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