Method for producing collagen fibers, collagen fibers and applications

Abstract

A method for producing collagen fibers, collagen fibers, and applications are disclosed. The method for producing collagen fibers includes (1) a step of producing a spinning dope, in which a collagen raw material is immersed in a dissolving solution having a pH of 3.5 to 5.5 to dissolve it, and then the pH is adjusted to 9.9 to 12.5 to form a spinning dope, and (2) a step of producing a primary fiber, in which the spinning dope is placed in a coagulation bath having a pH of 4.4 to 6.8 to coagulate and spin the dope to form a primary fiber. A salting-out environment for collagen is formed by multiple pH adjustments, and collagen fibers having spinnability are obtained by wet spinning.

Description

Technical Field

[0001] This application relates to the technical field of new materials, and more specifically, to a method for manufacturing collagen fibers, collagen fibers, and applications.

Background Art

[0002] Collagen is a type of protein composed of α-amino acids, mainly present in animal skin, bones, teeth, tendons, ligaments, and blood vessels, and is an important constituent and functional substance of connective tissue.

[0003] The tropocollagen molecule, which is the basic structural unit of collagen, has a diameter of about 115 nm, a length of about 280 - 300 nm, and a relative molecular weight of about 30 kDa. Collagen has a triple helical structure of three rod-shaped structures, consisting of three α-chain polypeptides, and each collagen chain has a left-handed helical structure. The three polypeptide chains further mesh with each other through hydrogen bonds to form a very stable right-handed helical structure with a molecular structure. There are acting forces such as ionic bonds, hydrogen bonds, van der Waals forces, and hydrophobic bonds due to non-polar groups between the unique rod-shaped helical structure of collagen and the collagen peptide chains.

[0004] Collagen molecules can self-organize into a supramolecular form, and this self-organization is formed by five triple helical collagen molecules arranged in a stagger pattern at one-quarter intervals, and is highly oriented to have a D-periodic banded space, with each D-period being about 67 nm. Telopeptides consist of a non-helical region with a length of about 20 amino acid residues, play an important role in the formation of fibrils, and form mature collagen molecules through cross-linking.

[0005] Fibril-forming collagens include types I, II, III, V, and XI collagens. These collagens are characterized by self-organizing into highly oriented supramolecular aggregates with a typical ultrastructure of a fibril array arranged in a stagger pattern at one-quarter intervals with a diameter of 25 nm to 400 nm. Type I collagen is the most abundant and well-studied collagen.

[0006] Most type I collagen exhibits a cross-linked structure in animal tendons, skin, ligaments, and corneas and exists in the form of highly cross-linked fibers. Therefore, they cross each other to form a network structure, and this type of collagen is basically insoluble in water.

[0007] In the wet spinning process, after the spinning solution is dissolved, defoamed, and filtered, it is extruded from the spinning holes and directly put into a coagulation bath, where it is stretched, washed with water, dried, and wound up for forming. However, wet spinning has high requirements for the performance of the spinning dope, and the quality of the spinning dope is also a necessary condition for obtaining the raw yarn. If the breaking strength of the raw yarn of the spinning dope after passing through processes such as spinning, coagulation, and drafting is less than 1.99 cN / dtex, basically, there is no spinnability.

Summary of the Invention

Problems to be Solved by the Invention

[0008] In order to manufacture collagen fibers with spinnability and realize the industrial production of collagen fibers, the present application provides a method for manufacturing collagen fibers, collagen fibers, and applications.

Means for Solving the Problems

[0009] In a first aspect, the present application provides a method for manufacturing collagen fibers using the following technical means.

[0010] The method for manufacturing collagen fibers includes (1) A step of manufacturing a spinning dope, immersing a collagen raw material in a dissolving solution with a pH of 3.5 to 5.5, dissolving it, and then adjusting the pH to 9.9 to 12.5 to form a spinning dope; and (2) A step of manufacturing primary fibers, putting the spinning dope into a coagulation bath with a pH of 4.4 to 6.8 to coagulate and spin to form primary fibers.

[0011] By using the above technical means, after dissolving the collagen raw material in an acidic dissolution solution and then adjusting the acidic dissolution solution to be basic, the acid-base solution reacts to form a salt, providing a salting-out environment for collagen. Furthermore, when the basic spinning dope enters the acidic coagulation bath, the acid-base solution reacts again to form a salt, providing a salting-out environment for collagen, rapidly precipitating collagen from the spinning dope, solidifying it, and forming primary fibers. After undergoing post-treatments such as general wet drafting, dry drafting, and heat setting, collagen fibers with a raw yarn breaking strength greater than 1.99 cN / dtex can be obtained, that is, collagen fibers with spinnability can be obtained.

[0012] The isoelectric point of collagen is such that the pH of the coagulation bath is within the range of 4.4 to 6.8. The isoelectric point is the pH at which the net charge on the surface of collagen becomes zero. Therefore, when the spinning dope enters the coagulation bath with a pH equal to the isoelectric point of collagen, the solubility of collagen is the lowest, and collagen is more likely to aggregate and precipitate, thereby promoting salting out and rapidly solidifying into fibers.

[0013] Therefore, in the present application, through the cooperation of the pH of the dissolution solution, the pH of the spinning dope, and the pH of the coagulation bath, collagen is salted out and rapidly solidified into collagen fibers with spinnability. In addition, in the present application, there is no need to add a toxic cross-linking agent, the reaction rate is faster, and it is suitable for continuous production.

[0014] Preferably, the coagulation bath contains, by weight percentage, 8 - 12% of a protein solidifying agent, 36 - 47% of a dehydrating agent, and 0.8 - 3% of a pH adjusting agent.

[0015] By using the above technical means, the protein solidifying agent can solidify collagen. The dehydrating agent can further improve the salting-out effect. On the one hand, it competes with protein and water molecules, destroying the water film on the surface of protein colloid particles. On the other hand, it neutralizes a large amount of charges on protein particles, accumulating protein particles in water and precipitating them. The pH adjusting agent adjusts the pH of the coagulation bath to the isoelectric point of collagen, making collagen more likely to aggregate and precipitate.

[0016] Preferably, the coagulation bath contains, by weight percentage, 8-12% of a protein solidifying agent, 36-47% of a dehydrating agent, 0.8-3% of a pH adjusting agent, and 1.2-5% of a zinc salt.

[0017] By using the above technical means, when the dehydrating agent is a sodium salt or a potassium salt, the dispersion of the spinning dope in the coagulation bath is too fast, so the rigidity of the primary fiber is too large, the subsequent fiber becomes brittle, which is disadvantageous for the spinnability. Adding a zinc salt can relieve the rapid dispersion of sodium and potassium ions and improve the tensile performance of the fiber.

[0018] Preferably, the dehydrating agent is a strong electrolyte salt.

[0019] By using the above technical means, since the strong electrolyte salt can be completely ionized in water, it can compete sufficiently with collagen and water to more easily precipitate and deposit collagen in water.

[0020] Preferably, the dehydrating agent is one or a mixture of multiple kinds of sodium salts, potassium salts, and ammonium salts.

[0021] By using the above technical means, sodium salts, potassium salts, and ammonium salts are easily available and convenient for industrial production.

[0022] Preferably, the sodium salt is one or a mixture of multiple kinds of sodium sulfate, sodium chloride, and sodium nitrate.

[0023] Preferably, the potassium salt is one or a mixture of multiple kinds of potassium sulfate, potassium chloride, and potassium nitrate.

[0024] Preferably, the ammonium salt is one or a mixture of multiple kinds of ammonium sulfate, ammonium chloride, and ammonium nitrate.

[0025] Preferably, the pH adjuster is a strong acid.

[0026] By using the above technical means, since a strong acid easily forms a salt with the basic spinning dope, the salt concentration of the coagulation bath is improved, and collagen precipitates more easily as the salt concentration increases.

[0027] Preferably, the pH adjuster is one or a mixture of more than one of sulfuric acid, hydrochloric acid, and nitric acid.

[0028] Preferably, the zinc salt is one or a mixture of more than one of zinc sulfate, zinc chloride, and zinc nitrate.

[0029] Preferably, the dissolving solution contains protease and water, and the mass ratio of the protease to water is (0.2 - 0.5):(6 - 10).

[0030] By using the above technical means, the existence form of collagen is a reticular cross-linked structure, and the telopeptide of collagen can be selectively cleaved by the enzyme preparation in the dissolving solution without acting on the helical segment, thereby ensuring that the triple helical structure of collagen is not destroyed, enabling collagen to be dissolved, and achieving the purpose of extracting collagen.

[0031] Preferably, the mass ratio of the collagen raw material, protease, and water is (1 - 2):(0.2 - 0.5):(6 - 10).

[0032] Preferably, the protease is one or a mixture of more than one of pepsin, trypsin, and papain.

[0033] Preferably, the dissolving solution adjusts the pH with a weak acid.

[0034] By using the above technical means, the weak acid is relatively mild, improves the stability of the dissolving solution, and reduces the influence on collagen activity.

[0035] Preferably, the weak acid is a carboxylic acid.

[0036] By using the above technical means, carboxylic acid is likely to form a hydrogen bond with collagen, has little influence on collagen activity, and when adjusting the pH of the spinning dope, carboxylic acid reacts with a base to form a salt and water, and the increase in salt concentration further helps collagen to salting out into the yarn.

[0037] Preferably, the mass ratio of the collagen raw material, protease, and water is (1 - 2):(0.2 - 0.5):(6 - 10).

[0038] Preferably, in step (1), the pH of the spinning dope is adjusted with a strong base.

[0039] By using the above technical means, the strong base in the spinning dope reacts with the strong acid in the coagulation bath to form a neutral salt, providing a salting - out environment for collagen as a strong electrolyte, quickly precipitating collagen from the spinning dope, forming fibers, and achieving and improving the spinnability of collagen fibers.

[0040] Preferably, the collagen raw material is produced by a method of immersing a tropocollagen raw material in a sodium carbonate solution.

[0041] By using the above technical means, after immersing the tropocollagen raw material in a sodium carbonate solution, the collagen in the tropocollagen raw material can be activated and decolorized, facilitating the extraction of collagen by subsequent enzymatic hydrolysis.

[0042] Preferably, the tropocollagen raw material is derived from one or a mixture of multiple kinds of animal tendons, skins, and ligaments.

[0043] Preferably, in step (2), the primary fiber is put into a coagulation bath tank and subjected to negative drafting with a spinning speed: off - bath speed of (1 - 1.5):(0.5 - 0.9).

[0044] By using the above technical means, since the crystallinity of collagen spinning is high and the collagen fiber is brittle, the breaking strength of the primary fiber and the collagen fiber can be improved according to the above negative draft ratio, and the thread breakage can be reduced.

[0045] In a second aspect, the present application provides a collagen fiber using the following technical means.

[0046] The collagen fiber is produced by the method for producing the above collagen fiber.

[0047] By using the above technical means, the collagen fiber produced by the production method of the present application has a raw yarn breaking strength greater than 1.99 cN / dtex and has spinnability.

[0048] In a third aspect, the present application provides an application of a collagen fiber using the following technical means.

[0049] As an application of the above collagen fiber, in the field of non-woven fabrics, for example, it is used in face masks, sanitary napkins, diapers, side seals, etc. In the field of spinning, for example, it is used in underwear, socks, shorts, clothing fabrics, bedding products, etc. The collagen fiber is more suitable for the spinning production of protein fibers than general vegetable proteins, has excellent moisture retention, has good affinity with the human skin, is comfortable to wear, and is suitable for the development of products such as bedding products, shirts, knitted inners, socks, etc. In the medical field, for example, it is used in band-aids, bandages, wound dressing materials, etc., and has good penetration prevention effect and recovery promotion function. In the food field, for example, it is used in food preservatives, freshness-keeping bags for fruits, etc., and can also be used in artificial leather. In the paper industry, it mainly forms composite products with plant fibers in the form of fibers to improve the strength, water absorbency, air permeability, density, whiteness, etc. of the paper. It is used in composite materials and nanomaterials. In addition to being mixed with other polymer materials for spinning, the collagen fiber has excellent film-forming performance.

Advantages of the Invention

[0050] From the above, the present application has the following beneficial effects.

[0051] 1. By adjusting the pH of the dissolution solution, the pH of the spinning dope, and the pH of the coagulation bath, the present application provides a salting-out environment for collagen and rapidly solidifies collagen into collagen fibers with spinnability.

[0052] 2. By acid enzymatic hydrolysis, the present application extracts collagen from tropocollagen raw materials and, in combination with pH adjustment, can obtain a spinning dope without using a cross-linking agent, and can be adapted to continuous production and industrial production.

[0053] 3. The collagen fibers produced by the present application are widely used and highly plastic.

Mode for Carrying Out the Invention

[0054] Hereinafter, the present application will be described in more detail with reference to examples.

[0055] All raw materials used in the present application can be obtained commercially. The dissolution solution contains one or a mixture of more than one of pepsin, trypsin, and papain. In the examples of the present application, pepsin is taken as an example for explanation, and the CAS number of pepsin is 9001-75-6. The chrome tanning agent is purchased from Jiangsu Bohong Chemical Co., Ltd., and the chromium content of Cr2O3 is (25 ± 1)%. The tropocollagen raw material is derived from one or a mixture of more than one of animal tendons, skins, and ligaments. In the examples of the present application, cowhide is taken as an example for explanation. Acetic acid is used as the carboxylic acid.

[0056] (Example) (Examples 1 to 11) As shown in Table 1, the main difference between Examples 1 to 11 is that the pH of the dissolution solution, the pH of the spinning dope, and the pH of the coagulation bath are different.

[0057] Hereinafter, Example 1 will be described as an example.

[0058] The manufacturing method of the collagen fiber according to Example 1 includes the following steps (1) to (3).

[0059] (1) Manufacture of the spinning dope Take 100 g of cowhide, immerse it in 1000 mL of a sodium carbonate solution with a concentration of 1 mg / mL for 2 h. After taking it out, rinse it with distilled water and dry it. Then adjust the pH of the solution to 4.5 with acetic acid, keep the solution at 34 °C, put the cowhide into the solution and dissolve it sufficiently. Specifically, the solution is a pepsin solution, and the mass ratio of pepsin to deionized water is 0.2:10. More specifically, the mass ratio of the input of cowhide, pepsin, and deionized water is 1:0.2:10. Specifically, it is 100 g of cowhide, 20 g of pepsin, and 1000 g of deionized water. Furthermore, adjust the pH to 10.9 using sodium hydroxide to form a basic spinning dope, and control the temperature of the spinning dope at 35 °C.

[0060] Note that the pH of the spinning dope may also be adjusted with other strong bases. The temperature of the above solution may be maintained at the active adaptation temperature of pepsin. Specifically, it may be 29 - 34 °C, and the temperature of the spinning dope may be 32 - 35 °C.

[0061] The mass ratio of the input of cowhide, pepsin, and deionized water may be (1 - 2):(0.2 - 0.5):(6 - 10).

[0062] (2) Manufacture of the primary fiber Put the spinning dope into a coagulation bath with a pH of 5.9 through a wet spinning metering pump with an inlet pressure of 0.1 MPa and an outlet pressure of 1 MPa, a candle filter, a gooseneck pipe, and a spinneret having a spinning hole with a diameter of 0.1 mm, and coagulate and spin it at 20 meters per minute to form a primary fiber. Put the primary fiber into the coagulation bath tank and perform negative drafting with a spinning speed: leaving bath speed of 1:0.7.

[0063] The coagulation bath contains substances of 10% tannic acid, 42% sodium sulfate, 1% sulfuric acid, and 47% water by weight percentage.

[0064] The installation and parameters of the wet spinning metering pump, candle filter, gooseneck pipe, and spinneret can all be generally adjusted by those skilled in the art according to the actual production situation. For example, the inlet pressure of the wet spinning metering pump is 0.08 - 0.11 MPa, the outlet pressure is 0.9 - 1.3 MPa, the diameter of the spinning holes is 0.05 - 0.12 mm, and the length of the hole channels is 0.1 - 0.25 mm. The description is omitted here.

[0065] (3) Manufacture of collagen fibers The primary fibers are subjected to post - treatments such as wet drawing, dry drawing, and heat setting to obtain collagen fibers. Similarly, operations such as wet drawing, dry drawing, and heat setting can all be generally adjusted by those skilled in the art according to the actual production situation, and the description is omitted here.

[0066] Table 1 pH table of the reaction solutions in Examples 1 - 7 [Table 1]

[0067] (Examples 11 - 16) The differences between Examples 11 - 16 and Example 7 are that the compounding ratios of the coagulation bath are different, specifically shown in Table 2.

[0068] Table 2 Compounding ratio table of the coagulation bath in Examples 8 - 13 [Table 2]

[0069] (Examples 17 - 18) The differences between Examples 17 - 19 and Example 15 are that the compounding ratios of the coagulation bath are different and the coagulation bath further contains zinc salt. Here, taking zinc sulfate as an example of the zinc salt, it is specifically shown in Table 3.

[0070] Table 3 Compounding ratio table of the coagulation bath in Examples 14 - 16

Table 3

[0071] (Examples 20 - 24) The difference between Examples 20 - 24 and Example 18 is that the raw materials of the coagulation bath are different, specifically shown in Table 4.

[0072] Table 4 Raw material table of the coagulation bath for Examples 17 - 20

Table 4

[0073] (Example 24) The difference between Example 24 and Example 18 is that the primary fiber is put into the coagulation bath tank, and minus draft is carried out with the spinning speed: the speed of leaving the bath being 1:0.5.

[0074] (Example 25) The difference between Example 22 and Example 18 is that the primary fiber is put into the coagulation bath tank, and minus draft is carried out with the spinning speed: the speed of leaving the bath being 1.5:0.9.

[0075] (Comparative Example) (Comparative Example 1) The difference from Example 2 is that the pH of the dissolution solution is 6.5.

[0076] (Comparative Example 2) The difference from Example 2 is that the pH of the coagulation bath is 8.5.

[0077] (Comparative Example 3) The difference from Example 2 is that the pH of the spinning dope is 8.5.

[0078] Performance detection test According to the method described in GB / T 14463-2008 "Viscose Staple Fiber", the fineness dtex, dry breaking strength cN / dtex, wet breaking strength cN / dtex, coefficient of variation of dry breaking strength %, dry breaking elongation %, staple fiber length mm, ultra-long fiber rate %, double-length fiber mg / 100g, residual sulfur content mg / 100g, and conditioned moisture regain % of Examples 1 to 21 were measured respectively, and the dry breaking strength cN / dtex of Comparative Examples 1 to 3 was measured. The measurement results are shown in Table 5 below.

[0079] Table 5 Performance Detection Results

Table 5

[0080] According to Table 5, when comparing Examples 1 to 25 with Comparative Examples 1 to 3, it can be seen that the selection and cooperation of the respective pH values of the pH of the dissolving solution, the pH of the spinning dope, and the pH of the coagulation bath have a great influence on the produced collagen fibers. Examples 1 to 25 can all produce collagen fibers with a dry breaking strength greater than 1.99 cN / dtex, and since the dry breaking strength of all of them is greater than 2.27, the collagen fibers produced in this application have completely spinnability.

[0081] Also, as described in GB / T 14463-2008 "Viscose Staple Fiber", the collagen fibers produced in this application can achieve excellent product indicators and have great market prospects. The measured collagen fibers of Comparative Examples 1 to 3 all have a dry breaking strength of less than 1.99 cN / dtex and do not have spinnability.

[0082] Next, as can be seen from Examples 1 to 7, the differences in the pH of the dissolution solution, the pH of the spinning dope, and the pH of the coagulation bath affect the performance of the produced collagen fibers. In Examples 1 to 6, the greater the differences in the pH of the dissolution solution, the pH of the spinning dope, and the pH of the coagulation bath, the greater the dry breaking strength of the produced collagen fibers. Also, when comparing Examples 1 to 6 with Example 7, it can be seen that the pH of the coagulation bath has a great influence on the strength performance of the dry breaking strength of the collagen fibers. When the pH of the coagulation bath is within the isoelectric point range of collagen, it can be seen that the dry breaking strength of the produced collagen fibers is more excellent.

[0083] Furthermore, when comparing Examples 7 to 10, it can be seen that when the pH of the dissolution solution is 5.5, the pH of the spinning dope is 11.2, and the pH of the coagulation bath is 6.8, the dry breaking strength of the produced collagen fibers is the most excellent.

[0084] Next, from Examples 6 and 8 to 13, it can be seen that using the blending ratio range of the coagulation bath of the present application, that is, the ratio of the protein solidifying agent, the dehydrating agent, the pH adjusting agent, and water, does not have a great influence on the performance of the collagen fibers, but it can be seen that the performance of the collagen fibers produced in Example 12 is the most excellent.

[0085] Next, from Examples 12 and 14 to 16, it can be seen that adding zinc salt affects the performance of the collagen fibers. Specifically, when the dehydrating agent is a sodium salt or a potassium salt, the dispersion in the coagulation bath of the spinning dope is too fast, so the rigidity of the primary fiber is too large, and the subsequent fibers become brittle, which is disadvantageous for the spinnability. Adding zinc salt can relieve the rapid dispersion of sodium and potassium ions and improve the tensile performance of the fibers. Also, the performance of the collagen fibers produced at the blending ratio of Example 15 is the most excellent.

[0086] Next, from Examples 17 to 20, it can be seen that different raw materials in the coagulation bath do not have a great influence on the obtained collagen fibers. This shows that the production of the present application has convenience in the selection of raw materials and is convenient for industrial production.

[0087] Next, from Example 15, Example 21, and Example 22, it can be seen that using the negative draft parameters of the present application does not significantly affect the obtained collagen fibers, and preferably, the spinning speed: the leaving bath speed is negatively drafted at 1:0.7.

[0088] (Application Example) The collagen fibers produced in Example 15 of the present application are used in the field of non-woven fabrics, for example, in face masks, sanitary napkins, diapers, side seals, etc. In the field of spinning, for example, it is used in underwear, socks, shorts, clothing fabrics, bedding supplies, etc. Collagen fibers are more suitable for the spinning production of protein fibers compared to general vegetable proteins, have excellent moisture retention, have good affinity with the human skin, are comfortable to wear, and are suitable for the development of products such as bedding supplies, shirts, knitted inners, socks, etc. In the medical field, for example, it is used in band-aids, bandages, wound dressing materials, etc., and has good anti-permeation and recovery-promoting functions. In the food field, for example, it is used in food preservatives, freshness-keeping bags for fruits, etc., and can also be used in artificial leather. In the paper industry, it mainly forms composite products with plant fibers in the form of fibers to improve the strength, water absorption, air permeability, density, whiteness, etc. of the paper. It is used in composite materials and nanomaterials. In addition to being mixed with other polymer materials for spinning, collagen fibers have excellent film-forming performance.

[0089] When the collagen fibers of the present application are used in the above fields, the weaving method is the same as that of materials such as polyester fibers known to those skilled in the art.

[0090] This specific embodiment is merely an explanation of the present application and does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. (1) A step of manufacturing a spinning dope, comprising: immersing cowhide in a dissolving solution having a pH of 3.5 to 5.5 to dissolve it, and then adjusting the pH to 9.9 to 12.5 to form a spinning dope; and (2) A step of manufacturing primary fibers, comprising: putting the spinning dope into a coagulation bath having a pH of 4.4 to 6.8 to coagulate and spin, thereby forming primary fibers, wherein the dissolving solution contains protease and water, and the mass ratio of the cowhide, the protease, and the water is (1 to 2):(0.2 to 0.5):(6 to 10); the coagulation bath contains, by weight percentage, 8 to 12% of a protein solidifying agent, 36 to 47% of a dehydrating agent, and 0.8 to 3% of a pH adjusting agent; the protein solidifying agent is a tannic acid agent or a chrome tanning agent; the dehydrating agent is a strong electrolyte salt; the pH adjusting agent is one or a mixture of more than one of sulfuric acid, hydrochloric acid, and nitric acid, characterized in that it is a method for manufacturing collagen fibers.

2. The coagulation bath further contains 1.2 to 5% of a zinc salt, characterized in that it is the manufacturing method according to Claim 1.

3. the dehydrating agent is one or a mixture of more than one of sodium salts, potassium salts, and ammonium salts, the sodium salt is one or a mixture of more than one of sodium sulfate, sodium chloride, and sodium nitrate; the potassium salt is one or a mixture of more than one of potassium sulfate, potassium chloride, and potassium nitrate; the ammonium salt is one or a mixture of more than one of ammonium sulfate, ammonium chloride, and ammonium nitrate, characterized in that it is the manufacturing method according to Claim 1.

4. the zinc salt is one or a mixture of more than one of zinc sulfate, zinc chloride, and zinc nitrate, characterized in that it is the manufacturing method according to Claim 2.

5. the protease is one or a mixture of more than one of pepsin, trypsin, and papain, characterized in that it is the manufacturing method according to Claim 1.

6. In step (1), the pH of the spinning dope is adjusted with a strong base, characterized in that it is the manufacturing method according to Claim 1.

7. The cowhide is manufactured by a method of immersing cowhide in a sodium carbonate solution, characterized in that it is the manufacturing method according to Claim 1.

8. In step (2), the primary fibers are put into a coagulation bath tank, and minus drafting is performed with a spinning speed: leaving bath speed of (1 to 1.5):(0.5 to 0.9). The manufacturing method according to claim 1, characterized in that...

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