Method for producing solubilized keratin aqueous solution and solubilized keratin, solubilized keratin aqueous solution and solubilized keratin, and molded article and composition comprising solubilized keratin

Abstract

In this method for producing a solubilized keratin aqueous solution, keratin fibers and water with a pH of 6-8 are brought into contact with each other in a reactor heated to 135-230°C at a mass ratio of the water to the keratin fibers (water / keratin fibers) of at least 1 but less than 18.

Description

Solubilized keratin aqueous solution, method for producing solubilized keratin, solubilized keratin aqueous solution, solubilized keratin, and molded article and composition containing solubilized keratin

[0001] The present invention relates to a method for producing an aqueous solubilized keratin solution and a solubilized keratin by contacting keratin fibers with water.

[0002] Keratin fibers are proteins that make up the hair, nails, horns, or skin present on the surface of animal bodies. In recent years, it has been reported that solubilized keratin obtained by hydrolyzing keratin fibers can be used as animal feed, fertilizer, cosmetic base material, ecologically friendly surfactant, medical polymer material, etc., and active research is being conducted into producing solubilized keratin from collected wool and feathers. Keratin fibers are a poorly soluble polymeric substance that contains multiple bonds (chemical bonds and hydrogen bonds) including sulfide bonds, so solubilizing them has been extremely complicated.

[0003] As a method for converting keratin fibers into solubilized keratin, a method has been reported in which keratin fibers are brought into contact with an alkaline aqueous solution containing a reducing agent such as thioglycolic acid or a salt thereof at a temperature of 60°C or less to reduce disulfide bonds (-SS-) in the keratin fibers to sulfhydryl groups (-SH) (see, for example, Patent Documents 1 and 3). Also reported is a method in which keratin fibers are reacted with an alkaline aqueous solution at 20 to 120°C to decompose amide bonds and the like (see, for example, Patent Documents 2 and 4).

[0004] Japanese Patent Laid-Open No. 7-126296 Japanese Patent Laid-Open No. 2009-023924 Japanese Patent Laid-Open No. 2008-247925 Japanese Patent Laid-Open No. 2008-280326

[0005] However, the methods of Patent Documents 1 and 3 have problems of coloring and odor due to the use of a reducing agent. Furthermore, the methods of Patent Documents 1 and 3 require further treatment with an oxidizing agent, and the method of Patent Document 2 requires neutralizing the treatment solution and then extracting the keratin decomposition product, which requires complicated steps when obtaining the resulting solubilized keratin. The method of Patent Document 4 requires neutralizing the treatment solution and then desalting using an ion exchange resin. Furthermore, the methods of Patent Documents 2 and 4 require alkaline conditions for decomposition, which requires neutralization when obtaining the keratin, and also have problems of generating a large amount of by-products such as free amino acids.

[0006] The present invention aims to provide a method for producing an aqueous solution of solubilized keratin that does not require complicated operations, has a high yield of solubilized keratin, and suppresses the production of by-products such as free amino acids and free alanine, and a method for producing solubilized keratin.

[0007] The present invention relates to the following items [1] to

[12] : [1] A method for producing a solubilized keratin aqueous solution, comprising contacting keratin fibers with water having a pH of 6 to 8 in a reactor heated to 135 to 230°C, at a mass ratio of the water to the keratin fibers (water / keratin fibers) of 1 or more and less than 18. [2] The method for producing a solubilized keratin aqueous solution according to [1], wherein the keratin fibers are crushed keratin fibers. [3] The method for producing a solubilized keratin aqueous solution according to [1] or [2], wherein the total free amino acid concentration is more than 0% by mass and 0.35% by mass or less, and the free alanine concentration is 0.005 to 0.100% by mass, in 100% by mass of the solubilized keratin aqueous solution. [4] The method for producing a solubilized keratin aqueous solution according to any one of [1] to [3], wherein the total free amino acid concentration is 0.05 to 0.35% by mass and the free alanine concentration is 0.005 to 0.100% by mass in 100% by mass of the solubilized keratin aqueous solution. [5] A method for producing solubilized keratin, comprising removing the solvent from the solubilized keratin aqueous solution obtained by any one of the production methods [1] to [4]. [6] Solubilized keratin, wherein the total free amino acid concentration is more than 0% by mass and not more than 0.35% by mass and the free alanine concentration is 0.005 to 0.100% by mass in 100% by mass of the solubilized keratin. [7] A solubilized keratin aqueous solution comprising the solubilized keratin of [6] and a water solvent. [8] A molded article comprising the solubilized keratin of [6]. [9] The molded article of [8], which is a film.

[10] The solubilized keratin of [6], which has a glass transition temperature of 15 to 85° C.

[11] A composition comprising the solubilized keratin of [6].

[12] A molded article comprising the composition comprising the solubilized keratin of

[11] .

[0008] The method for producing a solubilized keratin aqueous solution and the method for producing solubilized keratin according to the first aspect of the present invention can obtain a solubilized keratin aqueous solution and solubilized keratin without requiring complicated operations, and the yield of solubilized keratin is high and the production of by-products such as free amino acids and free alanine is suppressed. Therefore, the solubilized keratin obtained can form a film with good film-forming properties without the need for operations such as extraction. The solubilized keratin according to the second aspect of the present invention has low concentrations of total free amino acids and free alanine.

[0009] <First Aspect of the Invention> The present invention is a method for producing a solubilized keratin aqueous solution, which comprises contacting keratin fibers with water having a pH of 6 to 8 in a reactor heated to 135 to 230°C, at a mass ratio of the water to the keratin fibers (water / keratin fibers) of 1 or more and less than 18. [Method for producing a solubilized keratin aqueous solution]

[0010] (Keratin Fibers) The "keratin fibers" used in the present invention can be any material containing keratin, such as animal hair, nails, horns, or skin, and animal hair such as chicken, sheep, alpaca, mohair, angora, and cashmere is preferably used, with feathers and wool being particularly preferred. The "keratin fibers" are preferably α-keratin or β-keratin.

[0011] It is preferable to use crushed keratin fibers to increase the surface area when they come into contact with water, and crushed keratin fibers having a fiber length of 1 to 20 mm are preferably used. There are no particular limitations on the crushing method, and known means such as a mill, a cutter, or a hammer can be used. Furthermore, a pretreatment step of washing and drying the keratin fibers may be carried out before step 1.

[0012] (Water) The water used in the present invention is not particularly limited, but purified water, distilled water, etc. can be used. Water with a pH of 6 to 8 is used. By using water that is close to neutral in this way, the amount of by-products such as free amino acids and free alanine can be suppressed. The water preferably does not contain other components, and for example, it is preferable that it does not contain reducing agents such as thioglycolic acid and its salts. Note that, as long as the reaction is not inhibited, it is acceptable for the water to contain a trace amount of salt. The trace amount of salt is less than 1% by mass based on 100% by mass of water.

[0013] (Contact) Contact refers to allowing water to act on keratin fibers for a certain period of time. There are no particular limitations on the method for contacting keratin fibers with water, but it is usually carried out in a sealed state and can be carried out batchwise or continuously, with the batch method being preferred. Preferably, keratin fibers are placed in a pressure-resistant reactor and heated to a predetermined temperature. At this time, the pressure inside the reactor may be adjusted as necessary. Examples of reactors include sealed reactors such as autoclaves and reaction tubes. There are no particular limitations on the heating method, and examples include methods using a heater, a molten salt bath, etc. The contact is preferably carried out in an inert gas.

[0014] (Contacting Conditions) Keratin fibers and water are placed in a reactor and contacted so that the mass ratio of water to keratin fibers (water / keratin fibers) is 1 or more and less than 18, preferably 2 or more and less than 18, and more preferably 5 or more and less than 18. If this mass ratio is less than 1, hydrolysis does not proceed sufficiently, whereas if it is 18 or more, excessive decomposition proceeds, generating a considerable amount of free amino acids.

[0015] Keratin fibers and water are placed in a reactor, and the reactor is heated to 135 to 230° C., preferably 150 to 220° C., and more preferably 180 to 200° C. If the temperature is below 135° C., the reaction proceeds very slowly, while if the temperature exceeds 230° C., excessive decomposition occurs, generating a considerable amount of free amino acids, which affects the quality of the solubilized keratin when it is molded into a molded product.

[0016] The pressure inside the reactor is not particularly limited, and there is no problem as long as it is a pressure at which at least a part of the water is in a liquid state.

[0017] At the above temperature, the liquid water is considered to be subcritical water, which is suitable for hydrolysis of keratin fibers. Subcritical water is water that exists in a liquid state near the critical point and in a temperature and / or pressure range lower than the critical point. Subcritical water can be obtained by pressurizing water at a temperature range above its boiling point.

[0018] The contact time depends on the temperature, but from the viewpoint of productivity, it is preferably from 1 to 180 minutes, more preferably from 1 to 120 minutes, even more preferably from 5 to 90 minutes, and particularly preferably from 15 to 75 minutes.

[0019] A suitable combination of heating temperature and contact time is preferably such that the reactor is heated to 135 to 230°C for a contact time of 30 to 180 minutes, and more preferably such that the reactor is heated to 180 to 200°C for a contact time of 30 to 60 minutes.

[0020] By contacting the keratin fibers with water through the above-described procedure, the keratin fibers are hydrolyzed to form solubilized keratin. The solubilized keratin is obtained as an aqueous solution by the above-described production method.

[0021] If the solubilized keratin aqueous solution contains insoluble matter, it is preferable to separate and remove the solid from the resulting reaction solution to obtain a solubilized keratin aqueous solution that does not contain insoluble matter. The means for separation and removal is not particularly limited as long as it is capable of separating the solid from the liquid, and examples thereof include filtration using a filter and decantation.

[0022] The solubilized keratin aqueous solution preferably has a total free amino acid concentration of more than 0% by mass but not more than 0.35% by mass, and a free alanine concentration of 0.005 to 0.100% by mass, more preferably a total free amino acid concentration of 0.05 to 0.35% by mass and a free alanine concentration of 0.005 to 0.100% by mass, even more preferably a total free amino acid concentration of 0.05 to 0.20% by mass and a free alanine concentration of 0.005 to 0.080% by mass, and particularly preferably a total free amino acid concentration of 0.07 to 0.18% by mass and a free alanine concentration of 0.006 to 0.060% by mass, based on 100% by mass of the solubilized keratin aqueous solution. The total free amino acids refer to all free amino acids generated by hydrolysis of keratin fibers. The free alanine concentration is also defined as above, but free alanine is also included in the total free amino acids. Alanine is an amino acid found in large amounts in keratin, and therefore serves as an indicator of the degree of decomposition specific to keratin. Decomposition of keratin fibers under the above temperature conditions and with water used at approximately neutral pH suppresses excessive decomposition of keratin fibers, and the total free amino acid concentration and free alanine concentration can be kept within the above ranges. Having the total free amino acid concentration and free alanine concentration within the above ranges reduces the inclusion of by-products in molded articles made using the aqueous solution, which tends to improve the quality of the molded articles. The total free amino acid concentration and free alanine concentration can be measured using the methods described in the Examples.

[0023] [Solubilized Keratin] Solubilized keratin can be obtained by removing the solvent from the solubilized keratin aqueous solution obtained by the above-mentioned production method. The method for removing the solvent from the solubilized keratin aqueous solution is not particularly limited, but includes methods such as concentrating under reduced pressure. "Solubilization" refers to the reduction of the molecular weight of keratin and a change in its chemical structure, and refers to the uniform dissolution of keratin in water after contacting keratin fibers with water.

[0024] The yield of solubilized keratin in the solubilized keratin aqueous solution is calculated using the following formula 1: Solubilized keratin yield (mass %) = (dry mass of obtained solubilized keratin aqueous solution (corresponding to the mass of solubilized keratin) / mass of keratin fiber at the time of raw material addition) × 100 (Formula 1) From the viewpoint of productivity, a yield of 50% or more is preferred, and 75% or more is more preferred. According to the present invention, solubilized keratin can be obtained with such a high yield. If the yield is low, separation from the raw material keratin fiber (insoluble matter) is required, which makes the operation complicated. However, according to the present invention, the high yield makes it possible to omit such an operation, and solubilized keratin can be easily obtained.

[0025] The solubilized keratin preferably has a total free amino acid concentration of more than 0% by mass and not more than 0.35% by mass, and a free alanine concentration of 0.005 to 0.100% by mass, more preferably a total free amino acid concentration of 0.05 to 0.35% by mass, and a free alanine concentration of 0.005 to 0.100% by mass, even more preferably a total free amino acid concentration of 0.05 to 0.20% by mass, and a free alanine concentration of 0.005 to 0.080% by mass, and particularly preferably a total free amino acid concentration of 0.07 to 0.18% by mass, and a free alanine concentration of 0.006 to 0.060% by mass, based on 100% by mass of the solubilized keratin.

[0026] The total free amino acid concentration and the free alanine concentration differ between the solubilized keratin aqueous solution and the solubilized keratin, but the preferred concentration ranges in the solubilized keratin aqueous solution and the preferred concentration ranges in the solubilized keratin are the same as described above.

[0027] Solubilized keratin is also excellent from the viewpoint of efficient utilization of resources. Solubilized keratin can be used as a molded product as it is, or can be mixed with other resins to form a solubilized keratin-containing molded product. Furthermore, it can also be used by mixing it with a composition. When the resulting molded product is affected by moisture, such as a non-aqueous molded product (e.g., the molded product swells upon contact with water), it is desirable to use solubilized keratin in solid form. Furthermore, when used as a solid, it may be washed with water or an organic solvent before use.

[0028] [Solubilized Keratin Aqueous Solution or Molded Articles and Compositions Containing Solubilized Keratin] The solubilized keratin aqueous solution and solubilized keratin can be derived into various molded articles and can also be incorporated into compositions. These molded articles and compositions contain solubilized keratin. Examples of molded articles include films and sheets for daily necessities, automobile parts, electrical and electronic parts, etc.; covering films and coating materials for non-aqueous or anaerobic materials, etc. These molded articles may be molded from compositions containing soluble keratin, in which solubilized keratin is incorporated into a resin composition, etc., or from soluble keratin alone. Examples of the composition include hair cosmetics such as shampoo, treatment, hair rinse, hair cream, hair conditioner, hair lotion, hair pack, hair care product, hair restorer, hair color, and permanent wave agent; and cosmetic ingredients to be blended into makeup products such as lotion, milky lotion, facial cleanser, hand cream, shaving foam, after-shave foam, depilatory agent, bath additive, soap, and mascara. Molded articles containing solubilized keratin are useful as molded articles that make effective use of resources and are also environmentally friendly.

[0029] (Method for Producing Molded Articles) There are no particular limitations on the method for producing a molded article containing solubilized keratin. For example, in the case of a film, a known method can be used, such as applying an aqueous solution of solubilized keratin to a substrate and heating the resulting film. The production conditions (temperature, pressure, time, etc.) for the molded article are adjusted appropriately depending on the molding method, but it is desirable to carry out the process at a temperature below approximately 250°C, at which the solubilized keratin does not decompose.

[0030] The glass transition temperature of the solubilized keratin obtained, as measured by the DSC measurement method described in the Examples, is preferably 15 to 85°C, more preferably 15 to 45°C, and even more preferably 15 to 40°C.

[0031] <Second Aspect of the Present Invention> The second aspect of the present invention is solubilized keratin having, in 100% by mass of solubilized keratin, a total free amino acid concentration of more than 0% by mass and not more than 0.35% by mass, and a free alanine concentration of 0.005 to 0.100% by mass, preferably 0.05 to 0.35% by mass and 0.005 to 0.100% by mass. The solubilized keratin more preferably has a total free amino acid concentration of 0.05 to 0.20% by mass and a free alanine concentration of 0.005 to 0.080% by mass, and even more preferably 0.07 to 0.18% by mass and a free alanine concentration of 0.006 to 0.060% by mass. When the content is within the above range, the quality of a molded article made using the aqueous solution tends to be good; more specifically, when the content is below the above range, the molded article becomes brittle, and when the content is above the above range, foreign matter is present in the molded article, impairing its good appearance.

[0032] The solubilized keratin can be obtained by obtaining an aqueous solubilized keratin solution by the production method of the first aspect of the present invention, and then removing the solvent from the obtained aqueous solubilized keratin solution. The solvent removal procedure is the same as in the first aspect of the present invention.

[0033] The solubilized keratin can be converted into a solubilized keratin aqueous solution by adding an aqueous solvent. The aqueous solvent is not particularly limited, but purified water, distilled water, etc. can be used. The aqueous solvent may contain a trace amount of salt. The trace amount of salt is less than 1% by mass in 100% by mass of water.

[0034] The solubilized keratin aqueous solution and the solubilized keratin can be derived into various molded articles and can be incorporated into compositions. These molded articles and compositions contain solubilized keratin. The molded articles and compositions are the same as those exemplified in the first aspect of the present invention, and a preferred example of the molded article is a film.

[0035] The glass transition temperature of the solubilized keratin measured by the DSC measurement method described in the Examples is preferably 15 to 85°C, more preferably 15 to 45°C, and even more preferably 15 to 40°C.

[0036] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0037] <Yield of solubilized keratin> Yield of solubilized keratin (mass%) = (dry mass of obtained solubilized keratin aqueous solution (corresponding to the mass of solubilized keratin) / mass of keratin fiber at the time of raw material preparation) × 100 (Equation 1)

[0038] <Measurement of solubilized keratin aqueous solution and total free amino acid concentration and free alanine concentration of solubilized keratin> The solubilized keratin aqueous solutions obtained in the Examples and Comparative Examples were measured for the total free amino acid concentration and free alanine concentration in the solubilized keratin aqueous solution under the following conditions. Method: High-performance liquid column chromatography Apparatus: Nexera (Shimadzu Corporation) Column: Triart C18 (YMC Corporation) Column temperature: 35°C Flow rate: 0.8 mL / min. Developing solvent: 20 mM phosphate buffer (pH 6.5) and a mixture of acetonitrile / methanol / water (= 45 / 40 / 15 (volume ratio)) were used, varying the ratio. Detection wavelength: Ex. 350 nm, Em. 450 nm → Ex. 266 nm, Em. 305 nm (DSC measurement conditions) Apparatus: TA DSC 25 (manufactured by TA Instruments) Measurement environment: nitrogen atmosphere Flow rate: 400 mL / min Sample weight: 6.0 mg Measurement temperature range: -40°C to 120°C Heating / cooling rate: 10°C / min The solvent was removed from the solubilized keratin aqueous solutions obtained in the Examples and Comparative Examples to obtain solubilized keratin. The total free amino acid concentration and free alanine concentration of the obtained solubilized keratin were measured under the same conditions as above, and it was confirmed that the total free amino acid concentration was greater than 0% by mass and not more than 0.35% by mass, and the free alanine concentration was 0.005 to 0.100% by mass, based on 100% by mass of solubilized keratin.

[0039] [Example 1] Ground feathers (150 mg, length 5 mm) and purified water (1,500 mg, pH 7) were added to a reactor with an internal volume of 8.3 mL (water / keratin fiber = 10 (mass ratio)), and the reactor was placed in a reactor heated to 180°C. The ground feathers and water were contacted at the same temperature for 30 minutes. The resulting solution was then cooled, and the solid and liquid were separated. The yield of solubilized keratin from the separated liquid calculated based on Equation 1 was 51.4 mass%. Furthermore, the total free amino acid concentration of the separated liquid measured by the above method was 0.08 mass%, and the free alanine concentration was 0.009 mass%. The separated liquid can be said to be a solubilized keratin aqueous solution.

[0040] Examples 2 to 6, Comparative Example 1 Aqueous solutions of solubilized keratin were prepared in the same manner as in Example 1, except that the contact temperature and / or contact time was changed. The results are shown in Table 1.

[0041] [Example 7] Aqueous solutions of solubilized keratin were produced in the same manner as in Example 1, except that the mass ratio of water to keratin fibers (water / keratin fibers) and the contact time were changed. The results are shown in Table 1.

[0042] Example 8 Aqueous solutions of solubilized keratin were prepared in the same manner as in Example 1, except that the contact time was changed. The results are shown in Table 1.

[0043] [Example 9] Aqueous solutions of solubilized keratin were produced in the same manner as in Example 1, except that the mass ratio of water to keratin fibers (water / keratin fibers), contact temperature, and contact time were changed. The results are shown in Table 1.

[0044] [Film Production] The liquid (solubilized keratin aqueous solution) separated from the reaction solution obtained in the Examples and Comparative Examples was applied to a release film and cast-molded to produce a film (film precursor) containing solubilized keratin. The film was then heated at 80°C for 20 hours and at 110°C for 30 minutes, and then allowed to cool, yielding a film with a diameter of 3.4 cm and a thickness of 300 μm. The appearance of the obtained film was evaluated visually and the glass transition temperature was measured by DSC measurement using the following method.

[0045] <Film-forming properties (appearance evaluation)> The appearance of the obtained film was visually evaluated and rated according to the following criteria: ×: Localized cloudiness was observed. Δ: Wrinkles and cracks were observed. ◯: Wrinkles and cracks were slightly observed. ⊚: No wrinkles or cracks were observed.

[0046] <Film-formability (glass transition temperature (Tg))> The glass transition temperature of the obtained film was measured by DSC under the following conditions, and evaluated according to the following criteria: 15 to 50°C: particularly good film-formability. 15 to 85°C: good film-formability. Less than 15°C, more than 85°C: poor film-formability.

[0047] (DSC measurement conditions) Apparatus: TA DSC 25 (manufactured by TA Instruments) Measurement environment: under nitrogen atmosphere Flow rate: 400 mL / min Sample weight: 6.0 mg Measurement temperature range: -40°C to 120°C Temperature increase / decrease rate: 10°C / min

[0048]

[0049] The above results demonstrate that the solubilized keratin obtained by the methods of Examples 1 to 9 of the present invention can be induced into good films, and that the solubilized keratin obtained in Examples 4 to 8 in particular can be induced into even better films. The yield of solubilized keratin was also high in Examples 4 to 8. The aqueous solubilized keratin solution of Comparative Example 1 had high concentrations of total free amino acids and free alanine, and the film obtained from that solubilized keratin had poor appearance.

[0050] The aqueous solubilized keratin solution and solubilized keratin obtained by the production method of the present invention can be incorporated into molded articles and compositions.

Claims

1. A method for producing a solubilized keratin aqueous solution, comprising contacting keratin fibers with water having a pH of 6 to 8 in a reactor heated to 135 to 230°C, at a mass ratio of the water to the keratin fibers (water / keratin fibers) of 1 or more and less than 18.

2. The method for producing a solubilized keratin aqueous solution according to claim 1, wherein the keratin fibers are crushed keratin fibers.

3. The method for producing a solubilized keratin aqueous solution according to claim 1, wherein the total free amino acid concentration is greater than 0% by mass and not more than 0.35% by mass, and the free alanine concentration is 0.005 to 0.100% by mass, in 100% by mass of the solubilized keratin aqueous solution.

4. A method for producing a solubilized keratin aqueous solution according to claim 1, wherein the total free amino acid concentration is 0.05 to 0.35% by mass and the free alanine concentration is 0.005 to 0.100% by mass in 100% by mass of the solubilized keratin aqueous solution.

5. A method for producing solubilized keratin, which comprises removing the solvent from the aqueous solubilized keratin solution obtained by the method according to any one of claims 1 to 4.

6. Solubilized keratin in which the total free amino acid concentration is greater than 0% by mass and not more than 0.35% by mass, and the free alanine concentration is 0.005 to 0.100% by mass, based on 100% by mass of the solubilized keratin.

7. An aqueous solubilized keratin solution comprising the solubilized keratin according to claim 6 and a water solvent.

8. A molded article comprising the solubilized keratin of claim 6.

9. The molded article according to claim 8, which is a film.

10. The solubilized keratin according to claim 6, which has a glass transition temperature of 15 to 85°C.

11. A composition comprising the solubilized keratin of claim 6.

12. A molded article containing a composition comprising the solubilized keratin of claim 11.

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