Continuous production of keratin fibers

Abstract

The present disclosure relates to a method for producing keratin fibers, for example, a continuous production method. In some embodiments, the production method described herein may include extruding a keratin solution into a first solution to form a first fiber, stretching the first fiber and oxidizing the first fiber to form a treated fiber, stretching the treated fiber one or more times and oxidizing the treated fiber, and curing the treated fiber to form the keratin fiber. Such a production method may be useful for producing keratin fibers with a high draw ratio.

Description

[Technical Field]

[0001] Indication of federally funded research or development This invention was made with government support under Grant No. 2019-67021-29940, awarded by the U.S. Department of Agriculture, National Food and Agriculture Research Institute. The government has certain rights to this invention.

[0002] Cross-reference of related applications This application claims priority to U.S. Provisional Application No. 62 / 963,968, filed on 21 January 2020, the contents of which are incorporated herein by reference in their entirety.

[0003] This disclosure relates to a continuous method for producing keratin fibers. Such a method may be useful, for example, for producing keratin fibers with high draw ratios. [Background technology]

[0004] Research into the production of high-quality materials using green synthesis technologies is gaining increasing attention [1-3]. At the same time, the production of general-purpose products for everyday use using green and sustainable methods, such as the use of renewable monomers to produce sustainable polyester, is also becoming widespread [4, 5]. However, many of these sustainable polymers are not biodegradable [6]. The long-term accumulation of such materials will inevitably have an impact on the environment and human health. Synthetic polymers have been reported to circulate in the atmosphere and oceans after becoming nanoparticles and microparticles [7]. For example, polymer particles have been found in precipitation in many areas, even in the Arctic [8]. Recently, it has been revealed that plastic particles fall from the sky with the snow in the Arctic. These plastic particles inevitably enter and accumulate in the human body [9]. Recent studies have revealed that synthetic polymer particles may be the cause of various harms to human health, including cancer, chronic diseases, and damage to the reproductive system

[10] . Therefore, developing high-quality products with good biodegradability using waste will also need to be given attention in the future

[11] , especially in the textile sector, which is prone to environmental pollution. Regarding textile fibers, more than 80 million tons of synthetic fibers are produced worldwide every year.

[12] Almost all synthetic fibers are petroleum-based and are not very biodegradable in the environment.

[13] Therefore, it is desirable to find alternatives to petroleum-based fibers.[14, 15] These alternatives need to be sustainable, environmentally responsible, and affordable.

[0005] Although research into the utilization of keratinous waste began several decades ago, few high-quality recycled products have been developed due to damage to the primary structure during extraction and the restoration of the secondary structure during the regeneration of keratin materials. Among recycled keratin products, fibers possess high-quality specifications, including resistance to repeated washing and high toughness. [Overview of the Initiative]

[0006] This specification provides a method for producing keratin fibers. In some embodiments, the method includes: extruding a keratin solution into a first solution to form a first fiber; stretching the first fiber and oxidizing the first fiber to form a treated fiber; stretching the treated fiber and oxidizing the treated fiber one or more times; and curing the treated fiber to form a keratin fiber.

[0007] In some embodiments, the stretch ratio of the keratin fiber is at least about 500%. In some embodiments, the stretch ratio of the keratin fiber is about 800% to about 1000%. In some embodiments, the stretch ratio of the keratin fiber is about 1500%.

[0008] In some embodiments, the diameter of the keratin fiber is approximately 5 micrometers to approximately 30 micrometers. In some embodiments, the diameter of the keratin fiber is approximately 15 micrometers.

[0009] In some embodiments, the keratin fiber contains at least about 70% keratin. In some embodiments, the keratin fiber contains at least about 85% keratin.

[0010] In some embodiments, the tensile strength of the keratin fiber is greater than approximately 0.8 g / denier. In some embodiments, the tensile strength of the keratin fiber is approximately 1 g / denier to approximately 2 g / denier.

[0011] In some embodiments, the strain of the keratin fiber is greater than approximately 5%. In some embodiments, the strain of the keratin fiber is approximately 10% to approximately 30%. In some embodiments, the strain of the keratin fiber is approximately 15%. In some embodiments, the keratin fiber is dried before the strain is measured.

[0012] In some embodiments, the toughness of the keratin fibers is higher than about 15 J / cm 3 More than.

[0013] In some embodiments, the consistency coefficient (K) of the keratin solution is about 2 Pa·s n ~ about 6 Pa·s n Wherein the keratin solution is at about 25 ° C and contains about 18% w / w of keratin in the composition. In some embodiments, the consistency coefficient (K) of the keratin solution is about 4.2 Pa·s n Wherein the keratin solution is at about 25 ° C and contains about 18% w / w of keratin in the composition. In some embodiments, the flow index of the keratin solution is about 0.9 to about 0.94, provided that the keratin solution is at about 25 ° C and contains about 18% w / w of keratin in the composition. In some embodiments, the flow index of the keratin solution is about 0.91, provided that the keratin solution is at about 25 ° C and contains about 18% w / w of keratin in the composition.

[0014] In some embodiments, the keratin solution contains a reducing agent. In some embodiments, the keratin solution contains an electrolyte. In some embodiments, the electrolyte is a sulfate, acetate, chloride, citrate, carbonate, phosphate, or a combination thereof. In some embodiments, the keratin solution contains sodium dodecyl sulfate (SDS). In some embodiments, the keratin solution is prepared from a keratinous material.

[0015] In some embodiments, the manufacturing method further includes preparing the keratin solution. In some embodiments, preparing the keratin solution includes extracting keratin from a keratinous material to form extracted keratin; and dissolving the extracted keratin in an aqueous solution containing a reducing agent to form the keratin solution. In some embodiments, the aqueous solution further contains SDS.

[0016] In some embodiments, the keratinous material includes one or more animal hairs, horns, and feathers. In some embodiments, the hair is sheep's wool, camel hair, alpaca hair, rabbit hair, or a combination thereof. In some embodiments, the feathers are duck feathers, goose feathers, chicken feathers, or a combination thereof.

[0017] In some embodiments, the keratin fibers contain at least 70% disulfide crosslinks compared to the amount of disulfide crosslinks in the keratinous material. In some embodiments, the keratin fibers contain at least 85% of the beta-sheet crystallinity compared to the amount of beta-sheet crystallinity in the keratinous material.

[0018] In some embodiments, the reducing agent comprises a thiol group. In some embodiments, the reducing agent comprises mercaptoethanol, cysteine, dithiothreitol, 1,2-ethanedithiol, 1,3-benzenedithiol, bis(2-mercaptoethyl) ether, ethylene glycol bisthioglycolate, or a combination thereof.

[0019] In some embodiments, the step of extruding the keratin solution into a first solution includes extruding the keratin solution using a spinneret. In some embodiments, the spinneret is provided with a hole, the diameter of which is about 50 micrometers.

[0020] In some embodiments, the first solution comprises sodium sulfate, zinc sulfate, and acetate buffer. In some embodiments, the pH of the first solution is about 2. In some embodiments, the first solution comprises sodium sulfate in an amount of about 15% w / w of the composition, zinc sulfate in an amount of about 5% w / w of the composition, and acetate buffer with a pH of 2.

[0021] In some embodiments, the oxidation step involves exposing the fibers to an oxidizing solution containing an oxidizing agent selected from the group consisting of peroxides, halogen oxoacids or their salts, high-valent metal salts, and combinations thereof. In some embodiments, the peroxide is an alkali metal peroxide, an alkaline earth metal peroxide, or a combination thereof. In some embodiments, the oxidizing agent is sodium periodate. In some embodiments, the oxidizing solution further comprises a buffer. In some embodiments, the oxidizing solution further comprises an acetate buffer. In some embodiments, the pH of the oxidizing solution is about 2. In some embodiments, the temperature of the oxidizing solution is about 35°C.

[0022] In some embodiments, the steps of stretching the treated fibers and oxidizing the treated fibers are repeated twice. In some embodiments, the manufacturing method further includes stretching the treated fibers before curing them.

[0023] In some embodiments, curing the treated fibers involves exposing the treated fibers to a cleaning solution containing a surfactant. In some embodiments, the surfactant is selected from the group consisting of ammonium lauryl sulfate, SDS, sodium laureth sulfate, sodium myreth sulfate, sodium stearate, sodium lauroyl sarcosinate, perfluorononanoate, perfluorooctanoate, (3-[(3-coramidopropyl)dimethylammonio]-1-propanesulfonate), cocamidopropyl hydroxysultaine, cocamidopropyl betaine, phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine, sphingomyelin, cetrimonium bromide (CTAB), cetylpyridinium chloride (CPC), benzalkonium chloride (BAC), benzethonium chloride (BZT), dimethyldioctadecylammonium chloride, dioctadecyldimethylammonium bromide (DODAB), and combinations thereof.

[0024] In some embodiments, the washing solution further comprises an acetate buffer. In some embodiments, the pH of the washing solution is approximately 2. In some embodiments, the temperature of the washing solution is approximately 40°C.

[0025] In some embodiments, curing the treated fibers includes winding the treated fibers and oxidizing the treated fibers.

[0026] In some embodiments, the treated fibers are wound up and exposed to a cleaning solution containing a surfactant before oxidation. In some embodiments, the treated fibers are wound up at a speed of about 15 meters per minute.

[0027] In some embodiments, the keratin fibers are dried at approximately 85°C for approximately 1 hour. In some embodiments, the keratin fibers are annealed at approximately 125°C for approximately 1 hour. In some embodiments, the keratin fibers are annealed after drying.

[0028] In some embodiments, this manufacturing method is a continuous manufacturing method.

[0029] In some embodiments, the manufacturing method further comprises exposing the keratin fibers to a solution containing an oxidized sugar. In some embodiments, the keratin fibers are exposed to the solution containing the oxidized sugar for about 3 to about 25 hours. In some embodiments, the oxidized sugar is sucrose polyaldehyde.

[0030] In some embodiments, the step of exposing the keratin fibers to a solution containing oxidized sugars is performed before exposing the treated fibers to a cleaning solution containing a surfactant.

[0031] This specification also describes keratin fibers produced by any of the manufacturing methods described herein.

[0032] In some embodiments, the term “about” is used herein to mean approximately, around, roughly, or outline. When the term “about” is used with a numerical range, “about” modifies that range by extending the upper and lower boundaries of the stated numerical value. Generally, herein the term “about” is used to change a numerical value by a range of 10% deviation above or below the stated value.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention pertains. Methods and materials for use in the present invention are described herein; other preferred methods and materials known in the art may also be used. The materials, methods, and examples described herein are illustrative and not intended to limit the scope of use. All publications, patent applications, patents, database entries, and other references referenced herein are incorporated in their entirety. In case of any inconsistency, this specification, including its definitions, shall prevail. [Brief explanation of the drawing]

[0034] [Figure 1] This is a diagram of a wet spinning line using stepwise oxidation and drawing. [Figure 2] This is a reduced SDS-PAGE gel containing: Lane 1: standard protein markers; Lane 2: regenerated keratin; Lane 3: chicken feathers. [Figure 3A] This study compares the disulfide bonds in keratin between chicken feathers and spun keratin fibers using Raman spectroscopy. [Figure 3B] This figure shows the recovery rate of disulfide bonds in keratin fibers through controlled disulfide bond formation at various oxidation stages, as measured by HPLC. [Figure 3C]This figure illustrates the effect of controlled disulfide bond formation on the spinnability of keratin fibers. Precise control of disulfide bond formation was achieved using stepwise oxidation and drawing on a continuous spinning line. [Figure 4A] This figure shows the relationship between the recovery rate of disulfide bonds in the fiber and the maximum draw ratio. [Figure 4B] This shows the morphology of spun keratin fibers at the maximum draw ratio (scale bar = 50 μm). [Figure 5] This figure shows the morphological changes of keratin fibers on a continuous spinning line, involving the construction of controlled disulfide bonds. [Figure 6A] This shows a continuous line for keratin fiber production. [Figure 6B] This shows spun keratin fibers. [Figure 7A] This plot shows typical stress-strain curves for barbed and continuously spun keratin fibers. [Figure 7B] This keratin fiber exhibits resistance to high-level twisting. [Figure 8A] This figure shows the XRD spectra of chicken feathers and keratin fibers. [Figure 8B] This figure shows the deconvolution of the 13C NMR spectrum (around 170 ppm) of chicken feathers and keratin fibers. [Modes for carrying out the invention]

[0035] Keratinous waste, particularly poultry feathers, is an abundant, safe, cost-effective, and readily available material that can be used to manufacture fibers.

[16] Of all poultry species, chickens have the largest global consumption.

[17] Global annual chicken consumption is approximately 65 million tons, with 5 million tons of chicken feathers produced afterward.

[18] The potential production of protein fibers from chicken feathers already exceeds the current production of both wool and silk by 2.5 times. Chicken feathers are also rich in protein (keratin), with a high content of 90–92%.

[19] Feather keratin has a linear polymer backbone and an average molecular weight exceeding 10 kDa.

[20] It meets the molecular standards for fiber spinning. Feather keratin is expected to have good tensile properties and water stability, with approximately 7% cysteine ​​acting as crosslinking sites.

[21] Fibers produced from feather keratin are very likely to have a smooth feel, moisture permeability, and heat insulation properties due to their chemical structure being similar to that of wool and silk.

[15]

[0036] The failure of continuous fiber production may be due to the difficulty of extracting keratin from feathers, the inability to completely redissolve keratin, the limited alignment of protein molecular chains, and the inefficient recovery of disulfide crosslinks. For a long time, strong alkaline solutions were used to dissolve and extract keratin

[22] . However, high pH can not only hydrolyze the protein backbone but also reduce the amount of sulfhydryl groups on the keratin [23, 24]. Damage to the protein backbone and reduction of sulfur groups can make it difficult to produce high-quality fibers. Ionic liquids have been used to extract keratin from waste [25, 26]. More recently, ionic liquids have been used to dissolve keratin for spinning. However, the properties of the resulting fibers were not satisfactory

[27] . One reason for these poor mechanical properties is the poor solubility of keratin. Even if the liquid can block ionic interactions and hydrogen bonds, it cannot block disulfide bonds and hydrophobic interactions between keratin molecules. A non-destructive extraction system was developed, which allowed for the regeneration of chicken keratin fibers on a laboratory scale.

[28] However, the spinning of these fibers lacked techniques for efficiently regenerating disulfide bonds and secondary structures. As a result, the spinnability of the keratin fibers was poor. Furthermore, the drawability of the regenerated fibers was severely limited. The linearity of the regenerated fibers was low, which resulted in longer distances between keratin skeletons and reduced the opportunity for the formation of intermolecular disulfide crosslinks. The resulting fibers were large in diameter, low in strength, and poor in flexibility. The tensile strength of the regenerated fibers was only 50% of that of the original chicken feathers, and the strain was only 4%. Moreover, the regenerated keratin fibers did not inherit the good wettability of chicken feathers. Research on the production of fibers from keratinous waste began in the 1940s.

[29] However, few effective production methods were developed to continuously produce high-quality pure keratin regenerated fibers. The fibers should ideally have a stress exceeding 100 MPa and a strain exceeding 10%.To achieve this, most research has focused on either post-crosslinking or the addition of high-performance polymers such as PVA or cellulose into keratin fibers to improve their properties [27, 30-33].

[0037] Accordingly, this application provides keratin fibers and a method for producing said keratin fibers. Such fibers include keratin fibers produced on a continuous line through stepwise oxidation and stretching. As a result of the stepwise oxidation and stretching of the fibers, one or more of the following are possible: the construction of controlled disulfide crosslinks, optimal recovery of the secondary structure, sufficient mechanical properties, and the ability to produce keratin fibers on a large scale. For example, the properties of these recycled keratin fibers can be similar to those of chicken feathers. Furthermore, through the use of safe and inexpensive chemicals and recycling, the continuous production of keratin fibers disclosed herein is sustainable, environmentally responsible, and affordable. The continuous production of keratin fibers through efficient recovery of the secondary structure and disulfide bonds minimizes the use and generation of hazardous substances in this production method and opens up a new window for the utilization of keratinous waste.

[0038] In this specification, “keratin fiber” means a fiber containing at least about 70% keratin. In this specification, the term “fiber” or “fiber” means a unit of material that can be woven into a fabric by spinning into a yarn, or by bonding, or by entangling in various processes including weaving, knitting, braiding, felting, twisting, or webbing, and which is a basic structural element of a textile product.

[0039] In some embodiments, the keratin fibers described herein have at least about 70% keratin. For example, the keratin fibers may have about 70% to about 99%, about 70% to about 95%, about 70% to about 90%, about 70% to about 85%, about 70% to about 80%, about 70% to about 75%, or about 95% to about 99%, about 90% to about 99%, about 85% to about 99%, about 80% to about 99%, about 75% to about 99%, or about 75% to about 95% keratin.

[0040] In some embodiments, a method for producing keratin fibers includes: extruding a keratin solution into a first solution to form first fibers; stretching the first fibers and oxidizing them to form treated fibers; stretching the treated fibers and oxidizing them one or more times; and curing the treated fibers to form keratin fibers. In some embodiments, this production method is a continuous production method.

[0041] The keratin solutions described herein include keratin, for example, extracted keratin. In some embodiments, the keratin solutions further include sodium dodecyl sulfate (SDS) and / or a reducing agent. The reducing agents described herein may include thiol groups, for example, monothiols and dithiols. Non-limiting examples of such reducing agents include mercaptoethanol, cysteine, dithiothreitol, 1,2-ethanedithiol, 1,3-benzenedithiol, bis(2-mercaptoethyl) ether, and ethylene glycol bisthioglycolate. In some embodiments, the keratin solution contains a reducing agent in a concentration of about 0.5% to about 3% w / w of the keratin, for example, about 0.5% to about 2.5% w / w, about 0.5% to about 2% w / w, about 0.5% to about 1.5% w / w, about 0.5% to about 1% w / w, about 2.5% to about 3% w / w, about 2% to about 3% w / w, about 1.5% to about 3% w / w, about 1.5% to about 2.5% w / w, or about 1.75% to about 2.25% w / w of the keratin. In some embodiments, the keratin solution contains a reducing agent in a concentration of about 1.4% w / w, about 1.6% w / w, about 1.8% w / w, about 2% w / w, about 2.2% w / w, about 2.4% w / w, about 2.6% w / w, or about 2.8% w / w of the keratin.

[0042] In some embodiments, the keratin solution contains about 20% to about 35% w / w of extracted keratin, for example, about 20% to about 25% w / w, about 20% to about 30% w / w, about 30% to about 35% w / w, or about 25% to about 35% w / w of extracted keratin. In some embodiments, the keratin solution contains about 25% to about 30% w / w, or about 26% to about 28% w / w of extracted keratin. In some embodiments, the keratin solution contains about 24% w / w, about 25% w / w, about 26% w / w, about 27% w / w, about 28% w / w, about 29% w / w, or about 30% w / w of extracted keratin.

[0043] In some embodiments, the keratin solution contains SDS. In some embodiments, the keratin solution contains SDS in an amount of about 5% to about 15% w / w of the solution, for example, about 5% to about 8% w / w, about 5% to about 10% w / w, about 5% to about 12% w / w, about 12% to about 15% w / w, about 10% to about 15% w / w, about 8% to about 15% w / w, or about 8% to about 12% w / w of the solution. In some embodiments, the keratin solution contains SDS in an amount of about 5% w / w, about 6% w / w, about 7% w / w, about 8% w / w, about 9% w / w, about 10% w / w, about 11% w / w, about 12% w / w, about 13% w / w, about 14% w / w, or about 15% w / w of the solution.

[0044] In some embodiments, the pH of the keratin solution is adjusted to about 7 to about 10, for example, about 7 to about 8, about 7.5 to about 8.5, about 8 to about 9, about 8.5 to about 9.5, or about 9 to about 10. Any buffer suitable for maintaining the desired pH can be used. Non-limiting examples of such buffers include carbonate-bicarbonate buffer, glycine-sodium hydroxide buffer, sodium borate buffer, TRIZMA® buffer (e.g., 2-amino-2-(hydroxymethyl)-1,3-propanediol buffer), and diethanolamine buffer. In some embodiments, the keratin solution comprises a buffer solution of about 0.1 M to about 0.3 M, for example, about 0.1 M to about 0.15 M, about 0.1 M to about 0.2 M, about 0.1 M to about 0.25 M, about 0.25 M to about 0.3 M, about 0.2 M to about 0.3 M, about 0.15 M to about 0.3 M, about 0.15 M to about 0.2 M, about 0.18 M to about 0.22 M, or about 0.2 M to about 0.25 M.

[0045] In some embodiments, the amount of the reducing agent in the keratin solution described herein is optimized such that the keratin is completely dissolved and / or the molecular entanglement is reduced. In some embodiments, the degree of molecular entanglement is indicated by the flow index (n), and n can be determined by measuring the shear stress using a rotational rheometer (see Equation 1). The consistency coefficient (K) of the keratin solution is proportional to the polymer viscosity in the solution, and this can also be determined by measuring the shear stress using a rotational rheometer. Equation 1: τ = Kγ n (where γ is the shear rate (s -1 ) measured in the range of 0 to 1000 s -1 )

[0046] In some embodiments, the flow index of the keratin solution is from about 0.8 to about 0.95, such as from about 0.8 to about 0.82, from about 0.8 to about 0.84, from about 0.8 to about 0.86, from about 0.8 to about 0.88, from about 0.8 to about 0.9, from about 0.8 to about 0.92, from about 0.8 to about 0.94, from about 0.92 to about 0.95, from about 0.9 to about 0.95, from about 0.88 to about 0.95, from about 0.86 to about 0.95, from about 0.84 to about 0.95, from about 0.82 to about 0.95, from about 0.88 to about 0.92, or from about 0.90 to about 0.94. In some embodiments, the flow index of the keratin solution is about 0.88, about 0.89, about 0.9, about 0.91, about 0.92, about 0.93, about 0.94, or about 0.95. In some embodiments, the keratin solution is at about 25 °C and contains about 18% w / w extracted keratin when measuring the shear stress.

[0047] In some embodiments, the consistency coefficient (K) of the keratin solution is from about 2 Pa·s n to about 6 Pa·s n , such as from about 2 Pa·s n to about 6 Pa·s n , from about 3 Pa·s n to about 6 Pa·s n , from about 4 Pa·s n to about 6 Pa·s n , from about 5 Pa·sn ~Approx. 6 Pa·s n Approximately 4 Pa·s n ~Approx. 6 Pa·s n , about 3Pa·s n ~Approx. 6 Pa·s n , about 3Pa·s n ~Approx. 5Pa·s n , about 3.5Pa·s n ~Approx. 5.5Pa·s n , about 3.5Pa·s n ~Approx. 4.5Pa·s n , or approximately 4 Pa·s n ~Approx. 4.5Pa·s n In some embodiments, the keratin solution is at approximately 25°C and contains approximately 18% w / w extracted keratin when measuring shear stress.

[0048] In some embodiments, the manufacturing method described herein further comprises preparing the keratin solution, for example, any of the keratin solutions described herein. In some embodiments, preparing the keratin solution comprises extracting keratin from a keratinous material to form extracted keratin; and dissolving the extracted keratin in an aqueous solution containing a reducing agent, for example, any of the reducing agents described herein, to form the keratin solution.

[0049] In some embodiments, keratin can be extracted from any keratinous material, such as a keratin-containing material. Non-limiting examples of keratinous materials include hair, horns, and feathers. In some embodiments, the keratinous material may be wool, camel hair, alpaca hair, rabbit hair, duck feathers, goose feathers, chicken feathers, or a combination thereof. In some embodiments, the step of extracting keratin from a keratinous material to form extracted keratin includes exposing the keratinous material to an extraction solution. The extraction solution may contain one or more of SDS, urea, and a reducing agent.

[0050] In some embodiments, the extraction solution contains SDS. In some embodiments, the extraction solution contains about 5% to about 15% w / w of the solution, for example, about 5% to about 8% w / w, about 5% to about 10% w / w, about 5% to about 12% w / w, about 12% to about 15% w / w, about 10% to about 15% w / w, about 8% to about 15% w / w, or about 8% to about 12% w / w of SDS. In some embodiments, the extraction solution contains about 5% w / w, about 6% w / w, about 7% w / w, about 8% w / w, about 9% w / w, about 10% w / w, about 11% w / w, about 12% w / w, about 13% w / w, about 14% w / w, or about 15% w / w of SDS.

[0051] In some embodiments, the extraction solution contains about 1 M to about 3 M of urea, for example, about 1 M to about 1.5 M, about 1 M to about 2 M, about 1 M to about 2.5 M, about 2.5 M to about 3 M, about 2 M to about 3 M, about 1.5 M to about 3 M, about 1.5 M to about 2 M, about 1.8 M to about 2.2 M, or about 2 M to about 2.5 M.

[0052] In some embodiments, the extraction solution contains a reducing agent, for example, any of the reducing agents described herein. In some embodiments, the extraction solution contains about 5% to about 15% w / w of the solution, for example, about 5% to about 8% w / w, about 5% to about 10% w / w, about 5% to about 12% w / w, about 12% to about 15% w / w, about 10% to about 15% w / w, about 8% to about 15% w / w, or about 8% to about 12% w / w of the reducing agent. In some embodiments, the extraction solution contains about 5% w / w, about 6% w / w, about 7% w / w, about 8% w / w, about 9% w / w, about 10% w / w, about 11% w / w, about 12% w / w, about 13% w / w, about 14% w / w, or about 15% w / w of the reducing agent. In some embodiments, the reducing agent is cysteine.

[0053] In some embodiments, the pH of the extraction solution is adjusted to be about 9 to about 11.5, for example, about 9 to about 11, about 9 to about 10.5, about 9 to about 10, about 11 to about 11.5, about 10.5 to about 11.5, about 10 to about 11.5, about 9.5 to about 11.5, or about 10 to about 11. In some embodiments, the pH of the extraction solution is adjusted to be about 9, about 9.5, about 10, about 10.5, about 11, or about 11.5.

[0054] In some embodiments, the above step of extracting keratin from a keratinous material to form extracted keratin includes exposing the keratinous material to an extraction solution for a certain period of time. In some embodiments, the above period is about 8 to about 15 hours, for example, about 8 to about 9 hours, about 8 to about 10 hours, about 8 to about 11 hours, about 8 to about 12 hours, about 8 to about 13 hours, about 8 to about 14 hours, about 14 to about 15 hours, about 13 to about 15 hours, about 12 to about 15 hours, about 11 to about 15 hours, about 10 to about 15 hours, about 9 to about 15 hours, about 10 to about 14 hours, or about 11 to about 13 hours. In some embodiments, the above period is about 8 hours, about 9 hours, about 10 hours, about 11 hours, about 12 hours, about 13 hours, about 14 hours, or about 15 hours.

[0055] In some embodiments, the temperature of the extraction solution is maintained at approximately 60°C to approximately 80°C, for example, approximately 60°C to approximately 65°C, approximately 60°C to approximately 70°C, approximately 60°C to approximately 75°C, approximately 75°C to approximately 80°C, approximately 70°C to approximately 80°C, or approximately 65°C to approximately 80°C. In some embodiments, the temperature of the extraction solution is maintained at approximately 65°C, approximately 66°C, approximately 67°C, approximately 68°C, approximately 70°C, approximately 71°C, approximately 72°C, approximately 73°C, approximately 74°C, or approximately 75°C.

[0056] In some embodiments, the step of extracting keratin from a keratinous material to form extracted keratin further includes centrifuging the extract solution containing the keratinous material to form a centrifugal extract solution containing the keratinous material. In some embodiments, the supernatant of the centrifugal extract solution containing the keratinous material is adjusted to an isoelectric point using an optional and appropriate acid (e.g., hydrochloric acid). In some embodiments, sodium sulfate is added to the supernatant of the centrifugal extract solution containing the keratinous material to precipitate the extracted keratin. In some embodiments, the extracted keratin is washed to remove impurities. In some embodiments, the extracted keratin is vacuum-dried.

[0057] The keratin solution described herein can be extruded into a first solution and placed on a spinning line before the step of forming a first fiber. The spinning line may be any and appropriate spinning line, such as a wet spinning line. In some embodiments, the step of extruding the keratin solution into the first solution includes extruding the keratin solution using a spinneret. For example, the keratin solution is extruded into the first solution using a spinneret. In some embodiments, the spinneret has one or more holes, the diameter of which is about 50 micrometers.

[0058] In some embodiments, the first solution contains an electrolyte. Non-limiting examples of suitable electrolytes include sulfates, acetates, chlorides, citrates, carbonates, and phosphates. These electrolytes can be paired with any and appropriate cations. Non-limiting examples of such cations include alkali metals and transition metals, such as lithium, sodium, magnesium, and zinc. Therefore, in some embodiments, the first solution contains lithium sulfate, sodium sulfate, sodium acetate, zinc sulfate, zinc acetate, zinc chloride, sodium carbonate, sodium phosphate, zinc carbonate, or a combination thereof.

[0059] In some embodiments, the first solution contains an amount of electrolyte in the proportion of about 10% to about 30% w / w of the composition, for example, about 10% to about 15% w / w, about 10% to about 20% w / w, about 10% to about 25% w / w, about 25% to about 30% w / w, about 20% to about 30% w / w, about 15% to about 30% w / w, about 15% to about 20% w / w, or about 18% to about 22% w / w of the composition. In some embodiments, the first solution contains an electrolyte in an amount of about 10% w / w, about 12% w / w, about 14% w / w, about 16% w / w, about 18% w / w, about 20% w / w, about 22% w / w, about 24% w / w, about 26% w / w, about 28% w / w, or about 30% w / w of the composition. In some embodiments, the first solution contains 15% w / w of sodium sulfate and 5% w / w of zinc sulfate of the composition.

[0060] In some embodiments, the first solution further comprises a buffer. Any buffer suitable for maintaining a desired pH can be used. Non-limiting examples of such buffers include hydrochloric acid (HCl)-potassium chloride buffer, glycine-HCl buffer, and acetate buffer. In some embodiments, the first solution comprises a buffer at a concentration of about 0.1 M to about 0.3 M, for example, about 0.1 M to about 0.15 M, about 0.1 M to about 0.2 M, about 0.1 M to about 0.25 M, about 0.25 M to about 0.3 M, about 0.2 M to about 0.3 M, about 0.15 M to about 0.3 M, about 0.15 M to about 0.2 M, about 0.18 M to about 0.22 M, or about 0.2 M to about 0.25 M.

[0061] In some embodiments, the pH of the first solution is adjusted to be about 1 to about 4, for example, about 1 to about 1.5, about 1 to about 2, about 1 to about 2.5, about 1 to about 3, about 1 to about 3.5, about 3.5 to about 4, about 3 to about 4, about 2.5 to about 4, about 2 to about 4, about 2 to about 4, about 1.5 to about 4, or about 1.5 to about 2.5. In some embodiments, the pH of the first solution is adjusted to be about 1, about 1.4, about 1.6, about 1.8, about 2, about 2.2, about 2.4, about 2.6, about 3, about 3.5, or about 4.

[0062] In some embodiments, the first solution comprises sodium sulfate, zinc sulfate, and acetate buffer. In some embodiments, the first solution comprises 15% w / w sodium sulfate, 5% w / w zinc sulfate, and acetate buffer.

[0063] After extruding the keratin solution into a first solution to form first fibers, the fibers can be progressively stretched and oxidized to help establish disulfide bonds and a regular structure within the first fibers. In some embodiments, the oxidation step involves exposing the first fibers to an oxidizing solution containing an oxidizing agent selected from the group including peroxides, halogen oxoacids or their salts, high-valent metal salts, or combinations thereof. Non-limiting examples of peroxides include alkali metal peroxides and alkaline earth metal peroxides such as sodium periodate, hydrogen peroxide, chlorites, hypochlorites, and sodium ferrate(VI). In some embodiments, the oxidizing agent is present in an amount of about 2 g / L to about 6 g / L, for example, about 2 g / L to about 2.5 g / L, about 2 g / L to about 3 g / L, about 2 g / L to about 3.5 g / L, about 2 g / L to about 4 g / L, about 2 g / L to about 4.5 g / L, about 2 g / L to about 5 g / L, about 2 g / L to about 5.5 g / L, about 5.5 g / L to about 6 g / L, about 5 g / L to about 6 g / L, about 4.5 g / L to about 6 g / L, about 4 g / L to about 6 g / L, about 3.5 g / L to about 6 g / L, about 3 g / L to about 6 g / L, about 2.5 g / L to about 6 g / L, about 3 g / L to about 5 g / L, or about 3.5 g / L to about 4.5 g / L. In some embodiments, the oxidizing agent is present in amounts of about 2 g / L, about 2.5 g / L, about 3 g / L, about 3.5 g / L, about 4 g / L, about 4.5 g / L, about 5 g / L, about 5.5 g / L, and about 6 g / L.

[0064] In some embodiments, the oxidizing solution further comprises a buffer. In some embodiments, the first solution further comprises a buffer. Any buffer suitable for maintaining a desired pH can be used. Non-limiting examples of such buffers include HCl-potassium chloride buffer, glycine-HCl buffer, citrate buffer, and acetate buffer. In some embodiments, the first solution comprises a buffer at a concentration of about 0.1 M to about 0.3 M, for example, about 0.1 M to about 0.15 M, about 0.1 M to about 0.2 M, about 0.1 M to about 0.25 M, about 0.25 M to about 0.3 M, about 0.2 M to about 0.3 M, about 0.15 M to about 0.3 M, about 0.15 M to about 0.2 M, about 0.18 M to about 0.22 M, or about 0.2 M to about 0.25 M.

[0065] In some embodiments, the pH of the first solution is adjusted to be about 1 to about 4, for example, about 1 to about 1.5, about 1 to about 2, about 1 to about 2.5, about 1 to about 3, about 1 to about 3.5, about 3.5 to about 4, about 3 to about 4, about 2.5 to about 4, about 2 to about 4, about 1.5 to about 4, or about 1.5 to about 2.5. In some embodiments, the pH of the first solution is adjusted to be about 1, about 1.4, about 1.6, about 1.8, about 2, about 2.2, about 2.4, about 2.6, about 3, about 3.5, or about 4.

[0066] In some embodiments, the temperature of the oxidizing solution is about 30 to about 40 degrees Celsius, for example, about 30°C to about 35°C, about 35°C to about 40°C, or about 33°C to about 38°C. In some embodiments, the temperature of the oxidizing solution is about 30°C, about 31°C, about 32°C, about 33°C, about 34°C, about 35°C, about 35°C, about 36°C, about 37°C, about 238°C, about 39°C, or about 40°C.

[0067] In some embodiments, the steps of stretching the treated fibers and oxidizing the treated fibers are repeated two or more times. For example, the steps of stretching the treated fibers and oxidizing the treated fibers are repeated two, three, four, or five times. In some embodiments, the steps of stretching the treated fibers and oxidizing the treated fibers are repeated twice. In some embodiments, the manufacturing method further includes stretching the treated fibers before curing the treated fibers.

[0068] Fiber hardening and strengthening In some embodiments, curing the treated fibers involves exposing the treated fibers to a cleaning solution containing a surfactant. Non-limiting examples of suitable surfactants include ammonium lauryl sulfate, SDS, sodium laureth sulfate, sodium myreth sulfate, sodium stearate, sodium lauroyl sarcosinate, perfluorononanoate, perfluorooctanoate, (3-[(3-coramidopropyl)dimethylammonio]-1-propanesulfonate), cocamidopropyl hydroxysultaine, cocamidopropyl betaine, phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine, sphingomyelin, cetrimonium bromide (CTAB), cetylpyridinium chloride (CPC), benzalkonium chloride (BAC), benzethonium chloride (BZT), dimethyldioctadecylammonium chloride, and dioctadecyldimethylammonium bromide (DODAB). In some embodiments, the surfactant is present in an amount of about 0.2 to about 2 g / L, for example, about 0.2 g / L to about 0.6 g / L, about 0.2 g / L to about 1 g / L, about 0.2 g / L to about 1.4 g / L, about 0.2 g / L to about 1.8 g / L, about 1.6 g / L to about 2 g / L, about 1.2 g / L to about 2 g / L, about 0.8 g / L to about 2 g / L, about 0.4 g / L to about 2 g / L, about 0.5 g / L to about 1.5 g / L, or about 0.8 g / L to about 1.2 g / L.

[0069] In some embodiments, the washing solution further comprises a buffer. Any buffer suitable for maintaining a desired pH can be used. Non-limiting examples of such buffers include HCl-potassium chloride buffer, glycine-HCl buffer, citrate buffer, and acetate buffer. In some embodiments, the washing solution comprises a buffer at a concentration of about 0.05 M to about 0.3 M, for example, about 0.05 M to about 0.1 M, about 0.05 M to about 0.15 M, about 0.05 M to about 0.2 M, about 0.05 M to about 0.25 M, about 0.25 M to about 0.3 M, about 0.2 M to about 0.3 M, about 0.15 M to about 0.3 M, about 0.1 M to about 0.3 M, about 0.15 M to about 0.2 M, about 0.18 M to about 0.22 M, or about 0.2 M to about 0.25 M.

[0070] In some embodiments, the pH of the cleaning solution is adjusted to be about 1 to about 4, for example, about 1 to about 1.5, about 1 to about 2, about 1 to about 2.5, about 1 to about 3, about 1 to about 3.5, about 3.5 to about 4, about 3 to about 4, about 2.5 to about 4, about 2 to about 4, about 1.5 to about 4, or about 1.5 to about 2.5. In some embodiments, the pH of the cleaning solution is adjusted to be about 1, about 1.4, about 1.6, about 1.8, about 2, about 2.2, about 2.4, about 2.6, about 3, about 3.5, or about 4.

[0071] In some embodiments, the cleaning solution is at a temperature of about 35°C to about 45°C, for example, about 35°C to about 40°C, about 40°C to about 45°C, or about 38°C to about 42°C. In some embodiments, the cleaning solution is at a temperature of about 35°C, about 36°C, about 37°C, about 38°C, about 39°C, about 40°C, about 41°C, about 42°C, about 43°C, about 44°C, or about 45°C.

[0072] In some embodiments, curing the treated fibers includes winding the treated fibers and oxidizing the treated fibers.

[0073] In some embodiments, the treated fibers are exposed to a cleaning solution containing a surfactant before the treated fibers are wound up and oxidized. In some embodiments, the treated fibers are wound up at a speed of about 15 meters per minute.

[0074] In some embodiments, the keratin fibers are dried at approximately 85°C for approximately 1 hour. In some embodiments, the keratin fibers are annealed at approximately 125°C for approximately 1 hour. In some embodiments, the keratin fibers are annealed after drying.

[0075] In some embodiments, the manufacturing method further comprises exposing the keratin fibers to a solution containing oxidized sugars. Non-limiting examples of suitable sugars include glucose, sucrose, raffinose, cellobiose, dextran, and alginates. The sugars can be oxidized using any of the oxidizing agents described herein. In some embodiments, the keratin fibers are exposed to the above solution containing oxidized sugars for about 3 to about 25 hours, for example, about 3 to about 5, about 3 to about 10, about 3 to about 15, about 3 to about 25, about 20 to about 25, about 15 to about 25, about 10 to about 25, or about 5 to about 25. In some embodiments, the keratin fibers are exposed to the above solution containing oxidized sugars for about 1 hour, about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, about 10 hours, about 15 hours, or about 20 hours. In some embodiments, the oxidized sugar is sucrose polyaldehyde.

[0076] In some embodiments, the step of exposing the keratin fibers to a solution containing oxidized sugars is performed before exposing the treated fibers to a cleaning solution containing a surfactant.

[0077] Keratin fibers produced using the manufacturing method described herein can have a high draw ratio. The draw ratio is the ratio of the take-up speed to the extrusion speed. In some embodiments, the draw ratio of the keratin fibers can be at least about 500%, for example, at least about 600%, about 700%, about 800%, about 900%, about 1000%, about 1100%, about 1200%, about 1300%, about 1400%, about 1500%, about 1600%, about 1700%, about 1800%, about 1900%, or about 2000%. In some embodiments, the stretch ratio of keratin fibers produced using the manufacturing method described herein is about 500% to about 2500%, for example, about 500% to about 2300%, about 500% to about 2100%, about 500% to about 1900%, about 500% to about 1700%, about 500% to about 1500%, about 500% to about 1300%, about 500% to about 1100%, about It can be 500% to approximately 900%, approximately 500% to approximately 700%, approximately 2300% to approximately 2500%, approximately 2100% to approximately 2500%, approximately 1900% to approximately 2500%, approximately 1700% to approximately 2500%, approximately 1500% to approximately 2500%, approximately 1300% to approximately 2500%, approximately 1100% to approximately 2500%, approximately 900% to approximately 2500%, or approximately 700% to approximately 2500%. In some embodiments, the draw ratio of keratin fibers produced using the manufacturing method described herein can be about 500%, about 600%, about 700%, about 800%, about 900%, about 1000%, about 1100%, about 1200%, about 1300%, about 1500%, about 1600%, about 17000%, about 1800%, about 1900%, about 2000%, about 2100%, about 2200%, about 2300%, about 2400%, or about 2500%.

[0078] In some embodiments, the diameter of the keratin fibers produced using the manufacturing method described herein may be about 5 micrometers to about 30 micrometers, for example, about 5 micrometers to about 25 micrometers, about 5 micrometers to about 20 micrometers, about 5 micrometers to about 15 micrometers, about 5 micrometers to about 10 micrometers, about 25 micrometers to about 30 micrometers, about 20 micrometers to about 30 micrometers, about 15 micrometers to about 30 micrometers, or about 10 micrometers to about 30 micrometers.

[0079] Several methods can be used to evaluate the tensile strength and strain of the fibers described herein. Non-limiting examples of such methods include ASTM standard D-3822 and ISO 5079:1995. In some embodiments, the keratin fibers are equilibrated for 24 hours at 21°C and 65% relative humidity before the above tests. In some embodiments, the gauge length and tensile speed are 1 inch and 18 mm / min, respectively.

[0080] In some embodiments, the tensile strength of keratin fibers produced using the manufacturing method described herein can be at least about 0.8 g / denier, for example, at least about 1 g / denier, about 1.2 g / denier, or about 1.4 g / denier. In some embodiments, the tensile strength of keratin fibers produced as described herein can be about 0.8 g / denier to about 2.5 g / denier, for example, about 0.8 g / denier to about 2.4 g / denier, about 0.8 g / denier to about 2.2 g / denier, about 0.8 g / denier to about 2.0 g / denier, about 0.8 g / denier to about 1.8 g / denier, about 0.8 g / denier to about 1.6 g / denier, about 0.8 g / denier to about 1.4 g / denier, or about 0.8 g / denier. It can be approximately 1.2g / denier, approximately 0.8g / denier to approximately 1g / denier, approximately 2.4g / denier to approximately 2.5g / denier, approximately 2.2g / denier to approximately 2.5g / denier, approximately 2g / denier to approximately 2.5g / denier, approximately 1.8g / denier to approximately 2.5g / denier, approximately 1.6g / denier to approximately 2.5g / denier, approximately 1.4g / denier to approximately 2.5g / denier, approximately 1.2g / denier to approximately 2.5g / denier, or approximately 1g / denier to approximately 2.5g / denier.

[0081] In some embodiments, the strain of the keratin fiber is at least about 5%, for example, at least about 5%, at least about 6%, at least about 7%, or at least about 8%. In some embodiments, the strain of the keratin fiber is about 10% to about 30%, for example, about 10% to about 15%, about 10% to about 20%, about 10% to about 25%, about 25% to about 30%, about 20% to about 30%, or about 15% to about 30%. In some embodiments, the strain of the keratin fiber is 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19%, or about 20%. In some embodiments, the keratin fiber is dried before the strain is measured.

[0082] The toughness of the keratin fibers described herein can be determined by measuring the total area under the stress-strain curve of the keratin fibers. Any method that can obtain the stress-strain curve can be used. In some embodiments, the keratin fibers are equilibrated for 24 hours at 21°C and 65% relative humidity prior to the above test. In some embodiments, the gauge length and tensile speed are 1 inch and 18 mm / min, respectively. In some embodiments, the toughness of the keratin fibers is at least about 15 J / cm². 3 For example, at least about 20 J / cm² 3 , or at least about 25 J / cm² 3 In some embodiments, the toughness of this keratin fiber is approximately 15 J / cm². 3 ~About 30J / cm 3 That is the case.

[0083] The beta-sheet crystallinity of keratin fibers and / or keratinous materials can be measured, for example, using X-ray diffraction. In some embodiments, the keratin fibers contain at least 85% of the beta-sheet crystallinity compared to the amount of beta-sheet crystallinity in the keratinous material.

[0084] Disulfide bonds in keratin fibers and / or keratinous materials can be measured, for example, using Raman spectroscopy. In some embodiments, the keratin fibers contain at least 70% disulfide crosslinks compared to the amount of disulfide crosslinks in the keratinous material.

[0085] This specification also provides keratin fibers produced by any of the manufacturing methods described herein. For example, this specification provides keratin fibers produced by extruding a keratin solution into a first solution to form a first fiber; stretching the first fiber and oxidizing the first fiber to form a treated fiber; stretching the treated fiber and oxidizing the treated fiber one or more times; and curing the treated fiber to form a keratin fiber. In some embodiments, the manufacturing method is a continuous manufacturing method. In some embodiments, this specification provides keratin fibers produced by: extracting keratin from a keratinous material to form extracted keratin; dissolving the extracted keratin in an aqueous solution containing a reducing agent to form a keratin solution; extruding the keratin solution into a first solution to form first fibers; stretching and oxidizing the first fibers to form treated fibers; and curing the treated fibers to form keratin fibers.

[0086] Further details of the embodiments provided herein are, for example, described in References 39 and 40, both of which are incorporated herein by reference in their entirety. [Examples]

[0087] Example 1: Continuous production of keratin fibers from chicken feathers material Chicken feathers were supplied by Featherfiber Corporation, Nixa, MO. Other ACS reagent-grade chemicals, such as sodium dodecyl sulfate (SDS), cysteine, mercaptoethanol, and urea, were purchased from VWR International (Radnor, PA). Chemical reagents used for SDS-PAGE analysis, including LDS sample buffer (4×), NuPAGE MES running buffer (20×), and NuPAGE 4-12% Bis-Tris gel, were purchased from Invitrogen, Inc., Grand Island, NY.

[0088] Extraction of keratin from chicken feathers Keratin extraction from chicken feathers was carried out using aqueous solutions containing various amounts of urea and SDS. To determine the optimal recipe, the viscosity of the supernatant and keratin yield of the extract were measured. Detailed results are shown in Table S1. 10% SDS was selected based on 2M urea and the weight of the feathers. 10% cysteine ​​was used to completely cleave the disulfide bonds in the feathers for optimal keratin dissolution. Following previous studies, the pH of the extract solution was adjusted to 10.5 using a 15% by weight NaOH solution. This extract was held at 70°C for 12 hours. After extraction, the dispersion was centrifuged at 9800 rcf (relative centrifugal force) for 20 minutes to obtain the supernatant, which was then adjusted to its isoelectric point using hydrochloric acid with sodium sulfate to precipitate the internal keratin. The precipitated keratin was further washed to remove other impurities and then vacuum-dried. [Table 1]

[0089] Preparation of keratin spinning solution A spinning stock for continuous pilot-scale spinning was prepared by dissolving 27% extracted keratin and 10% SDS (based on the weight of keratin) in a 0.2 M carbonate-bicarbonate buffer at pH 8. Various amounts of reducing agents (mercaptoethanol) were added to completely dissolve the keratin and to obtain optimal molecular entanglement in solution, aiming for controlled cleavage of disulfide bonds in the keratin molecules.

[0090] To construct disulfide bonds in keratin fibers in a controlled manner, stepwise oxidation and drawing were applied to a continuous wet spinning line (ALEX JAMES AND ASSOC, US). Stepwise oxidation and drawing can help improve spinnability, keratin molecule orientation, degree of crosslinking, and fiber properties. The detailed design is shown in Figure 1. The prepared keratin spinning stock was centrifuged and placed on the spinning line. The keratin solution was extruded through a spinneret with multiple 50 μm diameter pores into a coagulation bath containing 15 wt% sodium sulfate, 5 wt% zinc sulfate, and pH 2 acetate buffer. The fibers were drawn once after exiting the coagulation bath, and then sent to a first oxidation bath. This oxidation bath contained 4 g / L sodium periodate and pH 2 acetate buffer as oxidizing agents. The oxidation temperature was set to 35°C to ensure rapid disulfide bond formation and fine fiber drawability. The fibers were then subjected to multiple stretching and oxidation steps, and subsequently placed in a washing bath. Multiple stretching and oxidation steps help establish a regular structure. The washing bath contained a surfactant at a concentration of 1 g / L and an acetate buffer at pH 2. The temperature was set to 40°C to ensure high washing efficiency. Upon reaching the final winding roller, the fibers were passed through the oxidation bath again to immobilize the regular molecular structure within the keratin fibers. The final fiber recovery rate was 15 meters / minute. The resulting dry fibers were dried in an oven at 8°C for 1 hour, and then annealed at 125°C for approximately 1 hour. Annealing was performed to improve the mechanical properties of the fibers.

[0091] characteristics Rheological properties of spinning solution The shear stress (τ(Pa)) of keratin spinning stock containing various concentrations of reducing agents was measured using a rotational rheometer, R / S Plus (Brookfield, USA), and the consistency coefficient (K(Pa·s)) was calculated based on Equation 1. n The viscosity (K) and fluidity index (n) were determined. K is directly proportional to the polymer viscosity in the solution, and n indicates the degree of molecular entanglement in the solution. A smaller value of n indicates better molecular entanglement. An 18 wt% keratin solution was used to accurately measure the rheological properties. τ=Kγ n formula 1 (In the formula, γ is 0 to 1000 s) -1 Shear rate measured within the range (s -1 )

[0092] Molecular weight of the keratin skeleton Approximately 1 mg of feather and keratin fibers were dissolved in 100 μL of NuPAGE LDS sample buffer (1×) containing excess mercaptoethanol and heated at 70°C for 5 hours. This solution was centrifuged and then loaded. 10 μL of each sample was loaded into individual slots of the gel. Molecular markers from the Spectra Multicolor Low Range Protein Ladder were used. The molecular weights of the protein standard mixture ranged from 4.6 to 42 kDa.

[0093] Mechanical properties Keratin fibers were tempered at 21°C and 65% relative humidity for 24 hours prior to testing. The tensile properties of the keratin fibers were obtained using an Instron (Norwood, MA) tensile testing machine in accordance with ASTM standard D-3822. The gauge length set for the test was 1 inch, and the crosshead speed was 18 mm / min. Denier was used to describe the fineness of the keratin fibers. At least 20 test specimens were used for each test.

[0094] Qualitative measurement of disulfide bonds in keratin using Raman spectroscopy. Feathers and keratin fibers were characterized using a Raman spectrometer (DXR Raman microscope, Thermo, USA). The laser wavelength was set to 532 nm and the output power was 10 mW. The sample collection exposure time was 15 seconds per sample for 15 cycles. To compare disulfide bonds in keratin, a 500 cm² exposure was used. -1 (SS) and 1450cm -1 The ratio of peak areas near (CH) was used.

[0095] Determination of cystine in fibers Fibers collected from each step of the continuous spinning line were washed with distilled water, frozen immediately, and then freeze-dried. The cystine content in the fibers was measured based on the method developed by Campanella et al

[34] . Specifically, the dried fibers were hydrolyzed with 6N HC1 at 110°C for 24 hours to obtain amino acids. Phenyl isothiocyanate was used for quantitative pre-column derivatization of amino acids using an HPLC, UltiMate 3000 series, USA, equipped with a C-18 column (Acclaim 120, 120 Å, 4.6 × 250 mm, 5 μm) and a UV detector set to 254 nm. The flow rate was 1 mL / min, and a ternary gradient was used with 0.7 M sodium acetate (phase A) at pH 6.4, water (phase B), and acetonitrile / water (phase C) in a volume ratio of 8:2. The gradients are shown in Table 1. The total retention time was 30 minutes, plus an additional 10 minutes for column re-equilibrium. [Table 2]

[0096] The inventors used mercaptoethanol as a reducing agent in the spinning solution described above, and therefore, the cystine newly formed on the regenerated fiber could be considered as intramolecular or intermolecular crosslinks. In addition, cystine was formed during fiber stretching. Stretching can increase the degree of linearity of the molecular chains. Therefore, the majority of the cystine originated from intermolecular crosslinks.

[0097] Analysis of secondary structure X-ray diffraction and solid 13 ¹³C NMR studies were performed to analyze the secondary structure of feathers and keratin fibers. X-ray diffraction was obtained using a Rigaku D / Max-B X-ray diffractometer equipped with a Bragg-Blendano focusing optical system, a diffraction beam monochromator, and a conventional copper target X-ray tube (λ=1.54Å) set to 40kV and 30mA at 26°C. Diffraction intensities were recorded at 2θ in the range of 3° to 40° with a scanning speed of 0.05° per second. Crystallinity was calculated using the Gaussian peak approximation with Jade 6.0 software (Materials Data Incorporated: Livermore, CA, USA). 13 The 1C solid-state NMR spectrum was obtained using a triple-resonance (1H / 13C / 15N) magic-angle spinning probe (3.2 mm) equipped on an NMR spectrometer (Bruker, Avance 600, USA).

[0098] statistical analysis A one-way analysis of variance using Scheffe's test with a 95% confidence interval was performed on all obtained data. Statistical analysis was carried out using SAS 9.4 software (Cary, North Carolina) and the PROC GLIMMIX survey procedure.

[0099] Results and Discussion Figure 2 compares the molecular weights of the protein backbone of regenerated keratin and chicken feather-derived protein backbone. These results indicate that damage to the regenerated keratin backbone is minimized. Compared to chicken feather, the content of 21 kDa protein in regenerated keratin was slightly lower than that of chicken feather, but the content of 8 kDa and 12 kDa protein was higher than that of chicken feather. The results in Figure 2 also indicate that regenerated keratin contains a large amount of γ-keratin, which has a molecular weight of 11 kDa

[35] and a high sulfur content. γ-keratin would promote the formation of disulfide bonds during the fiber regeneration process. The above results indicate that the molecular structure in keratin fibers can be optimized through controlled cleavage and construction of disulfide bonds on a continuous production line. As a result, the final properties of the keratin fibers were improved.

[0100] [Table 3] Table 2 shows the effect of various concentrations of reducing agents on the rheological properties of keratin spinning solutions. These results indicate that the degree of disulfide bond cleavage in the spinning solution directly affects the viscosity and entanglement of keratin molecules in the solution. Specifically, as the concentration of the reducing agent in the spinning solution increased, the viscosity of the solution gradually decreased, while the degree of molecular entanglement initially increased and then decreased. Increasing the concentration of the reducing agent led to disulfide bond cleavage. As a result, the viscosity decreased as the molecular weight of keratin gradually decreased. Regarding the degree of molecular entanglement, as the amount of reducing agent increased from 0.5% to 2%, most of the regular structure was unraveled as the disulfide bonds cleaved, improving the solubility of keratin molecules. Therefore, molecular entanglement increased. As the concentration of the reducing agent continued to increase, the molecular weight of keratin decreased further while the solubility remained unchanged. As a result, the degree of molecular entanglement decreased.

[0101] To ensure better spinnability of keratin fibers on a continuous spinning line, it is necessary to partially retain the disulfide bonds in the keratin for the following three advantages: 1) ensuring that the protein still has good solubility, 2) ensuring that the entanglement of protein molecules is in its best state, and 3) maintaining the molecular weight of the protein high enough to rapidly solidify the spinning solution in the coagulation bath. Therefore, a 2% reducing agent was selected to partially cleave the disulfide bonds in the spinning solution.

[0102] Figures 3A-3C show the efficient recovery of disulfide bonds in keratin fibers through controlled disulfide bond formation on a continuous spinning line, and the resulting spinnability of the keratin fibers. These results indicate that the rapid establishment of disulfide crosslinks in continuous spinning is a crucial factor in ensuring good spinnability of keratin fibers. Figure 3A qualitatively compares disulfide bonds in keratin fibers and chicken feathers. These results show that the keratin fibers recovered a high degree of disulfide crosslinking. (Approximately 500 cm) -1 and 1450cm -1The peaks were considered to be SS bonds and CH bonds, respectively. The Raman spectra were normalized by the CH band, which has a relatively large peak area and is unaffected by chemical treatment. The intensity of the SS band in keratin fibers was only slightly lower than that of chicken feathers, indicating a high rate of disulfide crosslinking recovery. Disulfide bonds were quantified using HPLC. Figure 3B shows that less than 10% of the crosslinking in the fibers was recovered by stretching in the coagulation bath. After the initial stretching and introduction of the first oxidation bath, approximately 20% of the disulfide bonds in the fibers were recovered. Further introduction of the oxidation bath with a certain amount of fiber stretching further increased the degree of disulfide bond recovery. By the time the fibers reached the final recovery roller on the spinning line, approximately 70% of the disulfide bonds were recovered, and the degree of crosslinking was approximately 5%. The rapid and high level of recovery of disulfide bonds in this continuous spinning process ensured good spinnability of the fibers. As shown in Figure 3C, the spinnability of this fiber was substantially higher with precise control of disulfide bond construction than with uncontrolled and simply controlled disulfide bond construction. The only oxidation process when disulfide bond construction was uncontrolled was air oxidation. Simple control involved only a single-step oxidation. With controlled disulfide bond construction, the final recovery rate of this fiber could reach 15 m / min, which is 160% of spinning using simple control of disulfide bond construction and 300% of spinning by air oxidation.

[0103] Figure 4A shows that the degree of crosslinking recovery in keratin fibers determined the maximum draw ratio on this continuous spinning line. These results indicate that a high disulfide bond recovery rate was key to a high draw ratio of the fibers. A high draw ratio is useful for producing high-quality fibers. As shown in Figure 4A, when the degree of disulfide bond recovery was less than 10%, the draw ratio of the fibers was only 2x. As the degree of disulfide bond recovery increased, the maximum draw ratio of the fibers could be increased to 10x. Figure 4A also shows that the draw ratio of the fibers on the continuous spinning line had a linear relationship with the degree of disulfide bond recovery. In detail, R 2 The correlation coefficient was 0.98, and the maximum draw ratio was 0.2 × disulfide bond recovery rate + 0.5. Increasing the draw ratio substantially reduced the diameter of the spun fiber. As shown in Figure 4B, the fiber diameter after 10 draws was only 15 μm, which is lower than most natural wool fibers (30 μm) and only slightly larger than silk fibers (10 μm). The fine fibers ensure good feel, breathability, and dyeability. The above results further indicate that the continuous production of high-quality keratin fibers heavily relied on the rapid crosslinking achieved by the controlled construction of disulfide bonds. Without controlled disulfide bond construction, the degree of disulfide bond recovery was less than 20%, resulting in limited fiber draw ratios and subsequent insufficient fiber properties.

[0104] Figure 5 illustrates how a highly regular protein structure is formed in keratin fibers by controlled disulfide bond construction under external stretching force. The distance between protein backbones in the newly solidified fiber can be shortened to some extent due to the presence of limited internal disulfide bonds. This shortening of the distance between protein backbones promotes the formation of intermolecular disulfide bonds during the first oxidation process. Subsequently, the crosslinks formed in the oxidation bath can help improve the extensibility and draw ratio of the fiber. A high draw ratio may contribute to the linearity of molecular chains in the keratin fiber and the shortening of the distance between protein backbones. This further promotes the formation of intermolecular disulfide bonds. Through the controlled cleavage and construction of disulfide bonds, the intermolecular disulfide crosslinks gradually increase, and secondary structure is gradually restored in the keratin fiber. In the recovery step, the final step of continuous spinning, the fiber is oxidized again to fix the regular structure of keratin.

[0105] Restored secondary structure in keratin fibers [Table 4]

[0106] XRD and 13 Data obtained from 1C solid-state NMR. These spectra are shown in Figures 8A and 8B, respectively. In XRD, the secondary structure is analyzed using two peaks: a secondary peak around 9° and a primary peak around 19°. In NMR, the crystal structures of chicken feathers and keratin fibers were analyzed using the chemical shift of the carbonyl group. Typically, deconvolution of the carbonyl group produces two peaks: one at 176 ppm, attributed to the α-helix, and another at 172 ppm, attributed to both the random coil and β-sheet stereostructure.

[0107] Table 3 compares the secondary structure of keratin fibers with that of chicken feathers. These results showed that the recovered beta-sheet secondary structure and the total crystallinity of the keratin fibers were 95% and 80%, respectively. The high crystallinity in the keratin fibers is attributed to a highly regular structure resulting from the rapid and controlled cleavage and construction of disulfide bonds. The reason for the high recovery rate of the beta-sheet is as follows: the controlled construction of disulfides contributed to the high extensibility of the fibers and the improvement of the fiber's draw ratio, resulting in the conversion of some of the alpha-helix structures in the fibers to beta-sheet structures. The reason the crystallinity of the keratin fibers was lower than that of the original chicken feathers is mainly because the disulfide bonds in the chicken feathers could not be fully recovered, resulting in less regular structure in the keratin fibers than in the chicken feathers. Furthermore, slight damage to the keratin skeleton also contributed to the lower crystallinity in the keratin fibers.

[0108] Figure 6A shows that the continuous production of keratin fibers was achieved by the controlled cleavage and construction of disulfide bonds. Figure 6B shows a sample of continuously spun keratin fibers. Figure 7A compares the stress-strain curves of the original feather and the keratin fibers derived from continuous spinning. These results revealed that although the strain of the barbs was approximately 10%, the barbs exhibited a fragile pattern in the curve. However, the keratin fibers underwent a "strain hardening" stage before fracture. This is because chicken feathers have a high degree of crosslinking and a regular molecular structure, which gives strong interactions between intermolecular chains. Therefore, under external force, the molecular segments were unlikely to undergo dislocations. As a result, the fibers fractured before the yield point. In keratin fibers, the interactions between molecular chains were relatively weak, but the majority of the protein backbone was linked by the controlled recovery of disulfide crosslinks. Weak interactions may promote protein chain movement, while long molecular chains may promote increased slip distances between two molecular chains. Under external force, dislocations between molecular segments are likely to occur, resulting in strain hardening. In addition, the keratin fibers described above have undergone high stretch ratios, which leads to a stretched state of molecular chains. Therefore, the degree of molecular entanglement was high. Under external force, the overall orientation of molecular segments in the fiber increased, which likely contributed to strain hardening.

[0109] Keratin fibers exhibited high ductility due to a strain-hardening process. Figure 7B shows that keratin fibers can withstand a high degree of twisting. Two other supplementary videos further demonstrate the high ductility of keratin fibers. The ductility of the fibers was high due to the high toughness of the fibers, which stemmed from the substantial recovery of the secondary protein structure through controlled disulfide bond cleavage and construction during the continuous spinning process.

[0110] [Table 5] Table 4 shows the mechanical properties of fibers with a restored protein secondary structure through controlled cleavage and construction of disulfide bonds in a continuous manufacturing process, comparing their properties with those of other common fibers. These results indicate that the keratin fibers recovered 86% of the original chicken feather's dry stress properties, 64% of its wet stress, 89% of its dry toughness, and 91.55% of its wet toughness. The good properties of the feather were maintained. The keratin fibers with the restored secondary structure were slightly weaker than the barbs due to damage to the protein backbone and a decrease in the degree of disulfide crosslinking. The strain of the keratin fibers was slightly higher than that of the original feather due to easier dislocation of protein segments. Compared to other commonly used fibers, keratin fibers had advantages. For example, the strain and toughness of keratin were substantially higher than those of cotton and linen. Its toughness was close to that of viscose fibers. These results demonstrate that keratin fibers with restored secondary structure from continuous manufacturing meet the standards for practical use.

[0111] [Table 6] Table 5 compares the properties of keratin fibers derived from various regeneration methods. All keratin fibers except those studied were regenerated on a laboratory scale. These results indicate that the recovery of tensile strength was low, even at the highest level of less than 50%, due to the low recovery rate of the secondary structure. The insufficient recovery rate of the secondary structure also resulted in insufficient strain in the regenerated fibers. To improve strain, the incorporation of plasticizers or other polymers into the keratin was developed. As a result, strain improved, but the tensile strength of the fiber was sacrificed. For example, after the incorporation of glycerin, the tensile strength of the regenerated keratin fibers was only 4% of that of the raw material fibers.

[0112] Cost-effective manufacturing with minimal environmental impact Non-toxic chemicals were used in the continuous fiber production by controlled disulfide bond cleavage and construction. Furthermore, the tubs on the spinning line, such as those undergoing coagulation and oxidation, could be reused. Therefore, the emissions from continuous spinning are minimal. The keratin content in the continuously spun fibers is higher than 98%, indicating the complete biodegradability of the fibers. The inventors' method for producing keratin fibers from chicken feathers does not involve toxic chemicals that have adverse effects on the environment. To estimate the potential demand for these recycled keratin fibers, the material consumption and cost in the inventors' method are evaluated as shown in Table S2. [Table 7]

[0113] As shown in Table S2, the total material cost to produce 1 kg of pure keratin fiber is approximately $0.83. Since the inventors cannot obtain the material costs of commercially available protein fibers and compare them to the material costs of recycled keratin fiber, they have used the retail prices of commercially available proteins such as wool and silk. Compared to the bulk prices (metric ton scale) of wool at approximately $7-$30 / kg and silk at approximately $45-$80 / kg, the cost of keratin fiber derived from chicken feathers is at least 91% and 99% lower than the selling price. Considering other costs in large-scale production, the final price of keratin fiber derived from chicken feathers becomes competitive. Assuming that keratin fiber derived from poultry feathers sells for approximately $4 per kg, this is close to the price of some natural cellulose fibers such as linen, but at least $3,000 worth of fiber can be produced from one ton of poultry feathers. If 5 million tons of poultry feathers worldwide could be fully utilized, the market value of recycled keratin fibers would exceed $15 billion.

[0114] Example 2: Chemical crosslinking using oxidized sugars A 5% aqueous solution of sucrose was reacted with sodium periodate at room temperature for 5 hours. The molar ratio of sucrose to periodate was 1:3. The pH of the reaction medium was maintained at 5.5 ± 0.1. After the reaction, a slightly excess amount of barium dichloride was added to completely precipitate the oxidizing agent. This mixture was filtered to obtain a polyaldehyde derivative of sucrose. Spun fibers derived from chicken feathers were immersed in the solution containing sucrose polyaldehyde at room temperature for 5 hours prior to the washing process described above. After washing, the fibers were dried in an oven at 85°C for 1 hour, and then annealed at 125°C for approximately 1 hour. The stress and strain of the resulting fibers were 1.5 ± 0.2 g / denier and 16 ± 2.1%, respectively.

[0115] References 1. Y. Zhang, N. Du, Y. Chen, Y. Lin, J. Jiang, Y. He, Y. Lei and D. Yang, Nanoscale, 2018, 10, 5626-5633. 2. AG Nandgaonkar, Q. Wang, K. Fu, WE Krause, Q. Wei, R. Gorga and LA Lucia, Green Chemistry, 2014, 16, 3195-3201. 3. Y. Li, H. Liu, J. Song, OJ Rojas and JP Hinestroza, ACS applied materials & interfaces, 2011, 3, 2349-2357. 4. M. Rabnawaz, I. Wyman, R. Auras and S. Cheng, Green Chemistry, 2017, 19, 4737-4753. 5. L. Lin, J. Liang, Y. Xu, S. Wang, M. Xiao, L. Sun and Y. Meng, Green Chemistry, 2019, 21, 2469-2477. 6. S. Rajendran, R. Raghunathan, I. Hevus, R. Krishnan, A. Ugrinov, M. P. Sibi, D. C. Webster and J. Sivaguru, Angewandte Chemie International Edition, 2015, 54, 1159-1163. 7. J. Christensen, ‘It is raining plastic’: Scientists find colorful microplastic in rain, cnn.com / 2019 / 08 / 14 / health / plastic-rain-colorado-trnd / index.html). 8. M. Bergmann, S. Mutzel, S. Primpke, M. B. Tekman, J. Trachsel and G. Gerdts, Science Advances, 2019, 5, eaax1157. 9. L. Parker, Nat. Geogr. Mag. Online, 2018. 10. Z. Singh and S. Bhalla, Adv Res Text Eng, 2017, 2, 1012. 11. Z. Yang, A. Kumar, A. W. Apblett and A. M. Moneeb, Green Chemistry, 2017, 19, 757-768. 12. Industrievereinigung-Chemiefaser, Worldwide production volume of chemical and textile fibers from 1975 to 2016 (in 1,000 metric tons), statista-com.libproxy.unl.edu / statistics / 263154 / worldwide-production-volume-of-textile-fibers-since-1975 / (accessed 7 / 7, 2018). 13. N. Reddy and Y. Yang, Green Chemistry, 2005, 7, 190-195. 14. G. Gao, MA Karaaslan, JF Kadla and F. Ko, Green Chemistry, 2014, 16, 3890-3898. 15. B. Mu, H. Xu, W. Li, L. Xu and Y. Yang, Food Hydrocolloids, 2019, 90, 443-451. 16. B. Mu, W. Li, H. Xu, L. Xu and Y. Yang, Journal of Materials Chemistry A, 2018, 6, 10320-10330. 17. F. Allievi, M. Vinnari and J. Luukkanen, Journal of Cleaner Production, 2015, 92, 142-151. 18. L. Gao, H. Hu, X. Sui, C. Chen and Q. Chen, Environmental science & technology, 2014, 48, 6500-6507. 19. N. Reddy, L. Chen, Y. Zhang and Y. Yang, Journal of Cleaner Production, 2014, 65, 561-567. 20. AJ Poole, JS Church and MG Huson, Biomacromolecules, 2008, 10, 1-8. 21. KM ARAI, R. TAKAHASHI, Y. YOKOTE and K. AKAHANE, European journal of biochemistry, 1983, 132, 501-507. 22. C. Tonin, A. Aluigi, C. Vineis, A. Varesano, A. Montarsolo and F. Ferrero, Journal of thermal analysis and calorimetry, 2007, 89, 601-608. 23. K. Ziegler, Journal of Biological Chemistry, 1964, 239, PC2713-PC2714. 24. W. Crewther, L. Dowling, A. Inglis and J. Maclaren, Textile research journal, 1967, 37, 736-745. 25. N. Singh and K. Prasad, Green Chemistry, 2019. 26. S. Zheng, Y. Nie, S. Zhang, X. Zhang and L. Wang, ACS Sustainable Chemistry & Engineering, 2015, 3, 2925-2932. 27. K. Kammiovirta, A.-S. Jaaskelainen, L. Kuutti, U. Holopainen-Mantila, A. Paananen, A. Suurnakki and H. Orelma, RSC Advances, 2016, 6, 88797-88806. 28. H. Xu and Y. Yang, ACS Sustainable Chemistry & Engineering, 2014, 2, 1404-1410. 29. R. Wormell and F. Happey, Nature, 1949, 163, 18. 30. J. G. Rouse and M. E. Van Dyke, Materials, 2010, 3, 999-1014. 31. Y. Li, X. Zhi, J. Lin, X. You and J. Yuan, Materials Science and Engineering: C, 2017, 73, 189-197. 32. NV Patil and AN Netravali, ACS Omega, 2019, 4, 5392-5401. 33. J. Li, Y. Li, L. Li, A. F. Mak, F. Ko and L. Qin, Polymer Degradation and Stability, 2009, 94, 1800-1807. 34. L. Campanella, G. Crescentini and P. Avino, Journal of Chromatography A, 1999, 833, 137-145. 35. T. Posati, D. Giuri, M. Nocchetti, A. Sagnella, M. Gariboldi, C. Ferroni, G. Sotgiu, G. Varchi, R. Zamboni and A. Aluigi, European Polymer Journal, 2018, 105, 177–185. 36. X. Fan, 2008. 37. B. Ma, X. Qiao, X. Hou and Y. Yang, International journal of biological macromolecules, 2016, 89, 614-621. 38. A. Aluigi, C. Vineis, A. Varesano, G. Mazzuchetti, F. Ferrero and C. Tonin, European Polymer Journal, 2008, 44, 2465-2475. 39. Mu, BN, Hassan, F., and Yang, YQ Controlled assembly of secondary keratin structures for continuous and scalable production of tough fibers from chicken feathers. Green Chemistry. 22(5), 1726-1734 (2020). 40. Mi, X., Mu, BN, Li, W., Xu, HL and Yang*, YQ From poultry wastes to quality protein products via restoration of secondary structure with extended disulfide linkages. ACS Sustainable Chemistry & Engineering.ACS Sustainable Chemistry & Engineering. 8(3). 1396-1405 (2020).

[0116] Other embodiments While the present invention has been described in detail, it should be understood that the above description is illustrative and does not limit the scope of the invention as defined by the appended claims. Other aspects, advantages, and modifications are included in the appended claims.

Claims

1. A method for producing keratin fibers, (i) Extruding the keratin solution into the first solution to form the first fiber, (ii) stretching the first fiber and oxidizing the first fiber to form a treated fiber, (iii) stretching the treated fibers once or more times and oxidizing the treated fibers, (iv) Hardening the treated fibers to form the keratin fibers. Includes, A method for producing keratin fibers, wherein the oxidation step includes exposing the fibers to an oxidizing solution containing an oxidizing agent selected from the group consisting of peroxides, halogen oxoacids or their salts, high-valent metal salts, and combinations thereof.

2. The manufacturing method according to claim 1, wherein the stretch ratio of the keratin fiber is 500% to 2000%.

3. The manufacturing method according to claim 1 or 2, wherein the diameter of the keratin fiber is 5 micrometers to 30 micrometers.

4. The manufacturing method according to any one of claims 1 to 3, wherein the keratin fiber contains at least 70% w / w keratin.

5. The manufacturing method according to any one of claims 1 to 4, wherein the strain of the keratin fiber is 5% to 30% in accordance with ASTM standard D-3822 or ISO 5079:1995.

6. The manufacturing method according to any one of claims 1 to 5, wherein the fluidity index of the keratin solution is 0.8 to 0.95, provided that the keratin solution is at 25°C and contains 18% w / w keratin in its composition.

7. The manufacturing method according to any one of claims 1 to 6, wherein the keratin solution comprises a reducing agent, sodium dodecyl sulfate (SDS), or both a reducing agent and sodium dodecyl sulfate (SDS).

8. The manufacturing method according to any one of claims 1 to 7, wherein the keratin solution is prepared from a keratinous material.

9. The manufacturing method according to claim 8, wherein the keratin fiber contains at least 70% disulfide crosslinks compared to the amount of disulfide crosslinks in the keratinous material.

10. The manufacturing method according to claim 8 or 9, wherein the keratin fibers have a beta-sheet crystallinity of at least 85% compared to the amount of beta-sheet crystallinity in the keratinous material.

11. The manufacturing method according to any one of claims 1 to 10, wherein the step of extruding the keratin solution into a first solution includes extruding the keratin solution using a spinneret.

12. The manufacturing method according to any one of claims 1 to 11, wherein the first solution contains an electrolyte.

13. The manufacturing method according to any one of claims 1 to 12, wherein the step of stretching the treated fibers and oxidizing the treated fibers is repeated twice.

14. The manufacturing method according to any one of claims 1 to 13, further comprising stretching the treated fibers before curing the treated fibers.

15. The manufacturing method according to any one of claims 1 to 14, wherein curing the treated fibers comprises exposing the treated fibers to a cleaning solution containing a surfactant.

16. The manufacturing method according to any one of claims 1 to 15, wherein hardening the treated fibers includes winding the treated fibers and oxidizing the treated fibers.

17. A manufacturing method according to any one of claims 1 to 16, which is a continuous manufacturing method.

18. The manufacturing method according to any one of claims 1 to 17, further comprising exposing the keratin fibers to a solution containing oxidized sugar.

Images