JP3011759B2 - Sericin fine powder and its production method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION <Industrial application field> The present invention relates to a method for recovering or producing sericin fine powder and waste liquid after refining of silk fiber. is there.

Silk fibers have been prized since ancient times for their unique texture, elegant luster, and the like. This silk fiber forms a structure in which the surface of fibroin, which is the essence of silk, is covered with sericin, a glue-like protein, a so-called double structure, and is a special fiber form not found in other fibers Is formed. However, in the state of this raw silk, the unique soft and supple texture that is the original characteristic of silk fiber,
Elegant and dignified gloss and sharp dyeability cannot be exhibited. Since the unique properties of silk are exhibited by the fibers composed of the fibroin, in the processing of silk fibers and silk fabrics, a treatment for dissolving and removing sericin coating around fibroin is performed.

The proportion of sericin contained in the raw silk made from cocoon yarn is quite high at 20 to 30%, and flowing scouring waste liquid containing such a protein component into rivers is not permitted because it poses a great pollution. Is being studied. For example, a coagulation sedimentation method, an excess method, an activated carbon adsorption method and the like can be mentioned, but each has its own problems in practical use,
At present, the treatment of silk smelting waste liquid is mainly performed by biochemical digestion using the activated sludge method. In this case, the pollution control facility is enormous, and the operation cost of the facility is also high.

Sericin, on the other hand, contains a high percentage of serine, an important amino acid as a material for cosmetics and pharmaceuticals, at about 30% by weight. Even today, some of this valuable serine is directly extracted from raw silk. From the current situation obtained by
It is clear that the technology for separating and recovering sericin from the waste liquid of silk scouring is important from the viewpoints of water pollution prevention and resource utilization.

<Prior Art> Conventionally, various methods for separating and recovering sericin as a solid content from this silk scouring waste liquid have been tried. The method comprises partially hydrolyzing and eluted sericin contained in silk fibers by a chemical scouring method or an enzyme scouring method, and then recovering the sericin by the following means.

(1) After adjusting the isoelectric point of sericin to pH 4.5 to 5.0 with an organic acid or an inorganic acid, an inorganic coagulant or an organic coagulant is added to precipitate sericin, which is separated and dried to obtain sericin. Obtain as a powder.

(2) Sericin is precipitated by mixing an aqueous solvent such as methanol, ethanol, dioxane or the like, and then dried separately to obtain sericin as a powder.

Although these methods are useful as such, they have disadvantages in industrialization from the viewpoint of economical recovery (prior attempts have been made to reduce the load on wastewater treatment because of the In addition, the protein sericin is produced as a precipitate, but is very difficult to separate), and at present, it has not been put to practical use.

By the way, as described above, sericin is useful as a serine source, and it is also useful as a polypeptide as a functional-modifying filler such as a synthetic leather, a molded product, and a coating process of a fiber cloth. Although, there are examples of sericin obtained by the method described above dried and pulverized and then obtained as a powder, but the particle size is large or irregular, and depending on the application Since it is difficult to control the moisture content, it is difficult to say that the above-mentioned polypeptide is not always satisfactory for use as a powder by pulverizing the polypeptide. There is also an attempt to pulverize fibroin to obtain a powder, but the application as a powder is difficult due to the large number of large particles of several hundred μm having irregular particle diameters.

Therefore, in order to separate and recover sericin as a solid content from the waste liquid of silk scouring, there are problems in both the physical properties of the recovered sericin and the separation and recovery method.

For the production of fibroin powder, a fibroin solution containing a salt is purified by dialysis and then spray-dried (JP-A-56-40675) or freeze-dried (JP-A-6-40675).
No. 1-180800), a method for obtaining a powdery fibroin peptide is known, but the average particle size of the obtained powder seems to be as large as 10 to 40 μm. There is also disclosed a method in which a coagulable salt is added to a fibroin solution containing a salt to coagulate and precipitate fibroin, followed by drying and pulverization to obtain a particle diameter of 1 to 100 μm (Japanese Patent Laid-Open No. 55-139427). Publication), the resulting powder has a wide particle size distribution and seems to contain large particles.

[Summary of the Invention]

<Summary> The present invention aims to provide a solution to the above points, and aims to achieve this object by providing sericin powder having specific physical properties and treating silk refined waste liquid by a specific method. Is what you do.

That is, sericin fine powder comprising sericin derived from raw silk having a molecular weight in the range of 300 to 50,000 according to the present invention,
It is characterized by an average particle size of 5 μm or less, a narrow particle size distribution range, and a substantially spherical particle shape.

Further, one method for producing sericin fine powder according to the present invention is to subject a silk scouring waste liquid by chemical scouring to an ultra-excess to obtain a sericin solution containing sericin having a molecular weight in the range of 5,000 to 50,000, This is subjected to spray drying while controlling the viscosity to 100 cP or less.

And, another method for producing sericin fine powder according to the present invention is to obtain a sericin solution containing sericin having a molecular weight in the range of 300 to 10,000 by subjecting a silk scouring waste liquid obtained by enzyme scouring to a reverse osmosis membrane, This is subjected to spray drying while controlling the viscosity to 100 cP or less.

Here, "the distribution range of the particle size is narrow" means that
It means that 80% or more exists within 5 μm above and below the average particle size and 1% or less exceeds 25 μm at the maximum. Also, that the `` particle shape is substantially spherical '' refers to a macroscopic sphere and does not mean only a true sphere, and specifically, the ratio of the long axis to the short axis is 2: 1
Up to an ellipse and an individual having no acute-angled portion on the surface of the powder.

<Effects> The sericin fine powder according to the present invention has
It can be advantageously used as the above-mentioned polypeptide.
That is, the sericin fine powder obtained according to the present invention has a small particle size, is spherical, and is uniform in a uniform state. In addition, it has the feature of being able to control moisture, so when it is used as a functional modification filler for synthetic leather, molded products, fiber fabric coating, etc., it is miscible with the base resin. This property is advantageous in terms of improving air bubble incorporation at the time of molding, touch of a coated surface, and the like, and is also useful in use as a humectant for cosmetics and the like.

In particular, in the case of the present invention, sericin is purified in a solution state, so that sericin fine powder can be obtained by a simple method. In addition, the method for producing fine sericin powder according to the present invention can be industrially implemented as a method for economically recovering individual sericin, if this is regarded as a method for treating silk scouring waste liquid. That is, there is a great advantage that the wastewater treatment load such as the wastewater treatment equipment for the wastewater and the operation cost of the equipment can be reduced.

[Specific description of the invention]

<Silk scouring waste liquid> Silk scouring itself is well-known, and accordingly, silk scouring waste liquid (hereinafter referred to as a scouring liquid) to be treated by the present invention is also well-known.

As described above, there are chemical scouring and enzyme scouring as typical examples of silk scouring. The scouring solution to which the present invention is applied may be one obtained by any of these methods. As one of the scouring methods, there is a fermentation scouring method, which is also recognized in the art as a kind of enzyme scouring method, and will be treated as being included in the category of the enzyme scouring method in the present invention.

In the chemical scouring method, an alkali aqueous solution, that is, a 0.5 to 2.5% (weight) aqueous solution of generally sodium carbonate or silicon soda, rarely sodium hydroxide or ammonia, and a surfactant such as Marcel soap are also added to a 0.5 to 2.5% aqueous solution. (weight)
Mix, with a strong alkaline aqueous solution with a pH of 11.5 or more,
Treating the silk at a temperature of 95 ° C. or higher for 3-4 hours. Chemical scouring is currently the most practiced scouring method.

On the other hand, when performing enzyme scouring, silk is treated with a solution in which several ppm to several hundred ppm of protease is dissolved at pH 9 to 10 for 2 to 3 hours. In that case, the enzyme used
Ordinary proteolytic enzymes, pronase obtained from actinomycetes, enzyme vinegar obtained from papain, protease obtained from molds such as Aspergillus niger, protease obtained from bacteria such as Bacillus subtilis, such as subtilisin B, P, N, and Trypsin, chymotrypsin, papain, proline and the like can be mentioned, and these can be used alone or as a mixture of two or more. The amount of the enzyme to be used usually varies depending on the type, purity, reaction conditions and the like of the enzyme, but is usually on the order of several ppm to several hundred ppm. The treatment conditions in this case vary depending on the type and concentration of the enzyme used, but are usually pH 5 to 9, preferably 6 to 8.5, and a temperature of 20 to 50 ° C, preferably 30 to 45 ° C.

Fermentation scouring is also a type of enzyme scouring, but requires a processing time of 24-48 hours due to the low enzyme concentration.

The scouring solution obtained by these methods usually has a sericin concentration of about 0.5% to 2%. Note that sericin in the scouring waste liquid has been depolymerized by the scouring treatment and has a reduced molecular weight compared to when sericin was present as the outer skin of silk. That is, the amide bond of sericin undergoes hydrolysis in the scouring treatment, and is dissolved as a peptide in a colloidal form in the scouring solution. In this case, the molecular weight of the peptide generated by hydrolysis is more correlated with the alkali concentration of the treatment liquid than with the treatment time.

<Treatment of scouring liquid> The present invention is applicable to all these scouring methods,
As described above, sericin fine powder can be finally obtained. However, the sericin concentration / refining process from the refining solution has some differences depending on the refining method employed.

In order to obtain sericin fine powder, it is necessary to concentrate and purify sericin in the obtained scouring liquid. In the case of the present invention, this step can be carried out very simply and with high efficiency by using the ultrafiltration method. It goes without saying that prior to (or after) concentration, excess, adjustment of concentration, sterilization, and other pretreatments can be performed.

When sericin is recovered from a scouring solution obtained by chemical scouring, the molecular weight of sericin is in the range of 300 to 50,000, and it is distributed broadly. In order to obtain it, it is efficient and preferable to carry out concentration and purification using an ultraperm membrane having a molecular weight cut off of around 20,000. In this case, the molecular weight cut off 2
By using a membrane (Table 1) of about 0,000 (molecular weight in terms of polyethylene glycol (PEG)) (an interface between sodium carbonate or silicon soda which is a general scouring aid, rarely sodium hydroxide or ammonia, and Marcel soap etc.) Since the activator is sufficiently smaller than the molecular weight cut-off of the ultra-membranous membrane, it may flow out of the membrane, and the purity of sericin increases as it is concentrated. It is possible to obtain a concentrated solution having a higher purity of sericin than a chemical scouring solution. Further, when high purity is required, purification can be carried out to a desired purity simply as a continuous step by purifying by substitution by adding distilled water after concentration.

In the case of enzymatic scouring, in the step of concentrating and purifying sericin, the protein present in the scouring solution is relatively high from the beginning because the enzyme and the salt are the main components.
A protein concentrate with sufficient purity can be obtained only by concentrating sericin using the ultrafiltration method.

The molecular weight of sericin in the enzymatic scouring bath is generally in the range of 300 to 10,000, and as a specific treatment, it is preferable to use an ultra-perm membrane having a relatively small molecular weight cut-off. It is preferable to use one having a molecular weight of about 10,000. In this case, the molecular weight of the resulting sericin is 5000-10,0
It is in the range of 00. In addition, when desalination alone can be used for purification, desalting and concentration using a reverse osmosis membrane enhances the sericin recovery rate. The molecular weight of sericin obtained in this case is between 300 and 10,000.

Also in the case of fermentation scouring, the method for preparing a sericin concentrate is the same as in enzyme scouring, and it is preferable to use an ultraperm membrane having a relatively small molecular weight cut-off. However, in the case of fermentation scouring, as a treatment before concentration, pore size 0.2μ
It is desirable to remove bacteria by a precision membrane of about m or so.

In the present invention, the ultrafiltration can be performed by simultaneously performing the electrodialysis, which can contribute to performing the ultrafiltration completely or promptly. Therefore, "extreme excess" in the present invention is to be understood as such.

Ultrafiltration is performed using a suitable limiting membrane, such as those shown in Table 1, to achieve a sericin concentration of about 0.5% to 2%.
Concentrate the scouring liquid which was%. Concentration of sericin solution
In terms of concentration, it is preferable to make the concentration as high as possible from the viewpoint of drying efficiency.However, when the purity of the sericin solution increases, the viscosity of the solution increases in proportion to the concentration, and gelation starts. Preferably, the concentration is up to around 10%. In addition, since the sericin is gradually decomposed in the ultrafiltration step, a long-term ultrafiltration leads to a decrease in the yield.

<Pulverization of sericin> There are various methods for pulverizing a sericin solution concentrated by ultrafiltration. For example, 1) freeze drying method, 2) vacuum drying method, 3) spray drying method However, when the particle size of the dried powder is to be controlled, it is desirable to carry out the spray drying method according to the production method of the present invention. In the case of other drying methods, it is difficult to simultaneously control the particle size in the drying step.

In the present invention, as described above, since a pure solution of sericin can be obtained in a solution state, spray drying can be performed as it is.

Regarding the spray drying method, a typical spray method in the case of spray drying a sericin solution is shown in Table 2 below.
There are the following.

It is preferable that this atomized sericin aqueous solution is dried and powdered in an atmosphere of usually 110 to 250 ° C., preferably 150 to 200 ° C. in a short time. When drying is performed at a high temperature of about 250 ° C., the spherical shape is not maintained due to bumping of water droplets. Spray drying conditions can be appropriately selected in order to obtain sericin fine powder having desired performance.

There is no particular limitation on the spray dryer that performs spray drying, and spray dryers of various companies and specifications can be used. However, when spraying a solution having a very high water content, a phenomenon in which sericin adheres to the wall surface due to insufficient drying occurs. Therefore, it is preferable to use a drying chamber having a diameter of 100 cm or more. When a spray dryer having a small drying chamber diameter is used, it is possible to cope with the problem by increasing the drying temperature as high as possible (200 ° C. or higher).

As described above, there are various types of spraying in a spray dryer, but when it is desired to obtain an average particle diameter of about 5 μm or less than 5 μm, a rotary disk atomizer using centrifugal energy is used. It is effective to use a rotary atomizer (generally called a rotary atomizer). The diameter of the atomizer in this case is 10
The diameter is preferably 0 mm or more, and the number of revolutions of the atomizer is preferably 20,000 or more per minute. This is because a fine powder having an average particle size of 5 μm or less can be stably prepared. In principle, in the case of the centrifugal spraying method, it is not possible to make a similar spraying state by increasing the rotation speed with a smaller diameter object than the above large diameter atomizer or at a lower rotation speed with a large diameter atomizer. Yes, but it doesn't seem to happen in reality.

When spray drying is performed, the state of the solution subjected to drying has a great influence on the particle size of the produced particles.

The production method of the present invention has succeeded in elucidating this point and obtaining granular sericin having good particle characteristics. Specifically, when the sericin solution is sprayed, if the sericin solution exceeds about 1%, the viscosity of the solution sharply increases with the start of partial gelation. When supplied to the chamber, a spray-dried product having a small particle size and a uniform particle size distribution cannot be obtained. From this, it is necessary that the sericin solution to be supplied for spray drying has a sericin concentration of 1% or less. On the other hand, when a sericin solution having a concentration of 1% or less is spray-dried. In the first place, a powder with a particle size of about 5 μm is completed, but the air inside the powder shrinks when returning to room temperature after drying in hot air because the powder particles are extremely hollow. And the powder shrinks,
Sericin powder with severe irregularities on the surface. Such sericin powder is not a sericin fine powder comprising substantially spherical particles according to the present invention.

The method for producing sericin fine powder according to the present invention also provides a solution to this point, and controls the temperature of the supply liquid, specifically, heats the supply liquid to reduce the viscosity, or By preventing gelation, it became possible to subject the sericin solution to spray drying at a concentration of around 10%.

That is, since the optimum conditions of the sericin solution as the spray-drying feed solution are governed by the concentration and the temperature, the present invention reduces the viscosity of the sericin solution at a given temperature to 100 cp (centipoise) or less, preferably 60 cp or less. Control achieves this optimal condition. In the case of a sericin solution having a concentration of about 10%, the temperature may be increased to about 60 ° C. or more to reduce the viscosity to 100 cp or less. The viscosity of the sericin solution was measured at a given temperature using a B-type viscometer.

There are many factors that affect the moisture content in spray drying, but the factors that particularly affect the drying temperature and the residence time of the sprayed droplets (powder) in the drying chamber.

When the prepared powder is mixed with another polymer material and used, the range of application is widened if the moisture content is reduced as much as possible.

<Example> The following example is for describing the present invention.
In addition, the measurement in an Example is performed by the following method.

(I) Particle Size Measurement of Peptide The particle size of 1,000 arbitrary particles on a photograph of the powdery sericin peptide obtained by photographing with a scanning electron microscope is measured. Here, the measurement was performed by an SEM manufactured by Hitachi.

(II) Moisture content measurement of peptide Determined by moisture content measurement with a moisture content meter. here,
An arbitrary about 3 g was measured three times using a moisture meter manufactured by Sartorius, and the average value was defined as the moisture rate.

(III) Measurement of Sericin Concentration The concentration of the sericin solution was determined by measuring the absorbance using an ultraviolet spectrophotometer. In this case, the conversion from the absorbance to the concentration was performed by preparing a calibration curve in advance.

(IV) Measurement of molecular weight of peptide The molecular weight was measured by SDS-page electrophoresis or gel permeation.

(V) Viscosity of scouring liquid It was indicated by apparent viscosity by a B-type viscometer at a given temperature.

[Example 1] (Chemical scouring of silk and concentration / purification of sericin solution) Silk scouring was mixed with 1.5% (by weight) aqueous solution of silicon soda and Marcel soap 1.0 (by weight), and a very strong alkaline aqueous solution having a pH of 11.5 or more was used. The treatment was performed at a temperature of 95 ° C. or higher for 3 hours. The sericin concentration here was about 1.0%. The scouring solution obtained here was subjected to an ultrafiltration and concentrated to a sericin concentration of about 10%. A polysulfone-based membrane having a molecular weight cut-off of 20,000 (calculated as PEG) was used as the ultra-supermembrane.

Silicon soda and Marcel soap permeate the membrane because their molecular weights are sufficiently small compared to the molecular weight cut off of the ultra-membranous membrane of 20,000. Therefore, the concentration of sericin is improved at the same time as the concentration, and the concentration step and the purification step are combined by a simple method. Further, when high purity is required, purification can be performed to an arbitrary purity by adding distilled water after concentration and performing purification. Here, reconcentration was performed by adding the same amount of pure water as the concentrated liquid.

About 8% of scouring solution (sericin concentration about 1%)
A sericin solution of a concentration was obtained. At this time, the molecular weight of sericin was distributed between 6,000 and 50,000. Since the molecular weight of sericin after chemical scouring is mainly distributed in the range of 300 to 50,000, it was confirmed that concentration and purification could be performed very efficiently by using the present concentration method.

[Example 1-2] (Oxygen scouring of silk and concentration / purification of sericin solution) Silk scouring was performed in a 10 ppm aqueous solution of enzyme protease at pH 8.0.
Time went on. The enzymes used here were those generally sold for scouring. The sericin concentration obtained here was about 0.5%, and the distribution range of the molecular weight was 300 to 10,000. Thereafter, the resulting sericin solution was applied to a reverse osmosis membrane, and concentrated and desalted to a sericin concentration of about 6%.

[Example 2] (Particle size control) The sericin concentrate prepared in Example 1-1 was spray-dried using a spray drier (manufactured by Okawara Kakoki Co., Ltd.). At this time, spraying was performed by changing the centrifugal force of the centrifugal spray and changing the drying temperature.

The spray dryer used has the following characteristics.

Drying chamber diameter: 1,200 mm or more Atomizer diameter: 120 mm or more Collection device: cyclone + bag filter (recovery rate 95%
Above) The spray drying conditions are as follows.

Sericin solution: about 8% concentration (at 60 ° C to 70 ° C, viscosity 50cp
Atomizer rotation speed: 20,000 rpm Drying temperature: 200 ° C. The experimental results obtained are as follows.

Sericin was obtained as a powder under the condition that the rotation number of the rotary atomizer exceeded 15,000 rpm. Further, it was confirmed that the particle size of sericin produced decreased as the number of rotations increased.

(B) Experimental result 2 (effect of supply liquid temperature) Spray dryer operating conditions Rotation speed: 20,000 rpm Drying temperature: 200 ° C At this time, the viscosity of the supply liquid is 100 cP at a temperature exceeding 50 ° C.
It was below. From this result, it was confirmed that the distribution range of the particle size can be controlled by controlling the viscosity of the supply liquid.

After performing the above tests, the rotational speed of the centrifugal sprayer was
20,000rpm or more, supply liquid temperature 60 ℃ or more, drying temperature 200 ℃
Thus, a fine powder having an average particle size of 5 μm or less was obtained. Here, the most effective method for producing uniform fine powder was temperature control of the supply liquid.

FIG. 1 attached shows a scanning electron micrograph of the obtained sericin fine powder.

The following shows the measurement results of the particle size distribution of the sericin fine powder.

[Comparative Example] Separation of sericin by agglomeration method As a comparative experiment, a method of adding an inorganic acid, which is a conventional general protein separation method, to wastewater after a chemical scouring treatment containing sericin as in Example 1 And the method of adding an organic solvent to separate sericin. Hydrochloric acid was used as the inorganic acid, and methanol was used as the organic solvent.

In the experimental method, the pH of the scouring waste liquid was adjusted to 3.5 with hydrochloric acid, and the sedimentation amount of sericin at that time was traced from the change in the concentration of sericin in the solution. In the case of an organic solvent, the organic solvent was added until a precipitate was formed, and tracking was performed in the same manner.

The results are shown in the table below. When an inorganic acid was added, formation of a precipitate started around the isoelectric point of sericin at pH 3.9, and pH 3.8.
Even when the amount was changed from 3.5 to 3.5, the same amount of precipitate was formed.
The amount of precipitate generated at this time was calculated to be about 60%. On the other hand, when the organic solvent was added, no precipitate was formed even if it was added in an amount of twice or more to the original scouring waste liquid.

An attempt was made to separate the sericin thus obtained, but the filter was found to be too clogged and was not suitable for practical use, and the recovery was abandoned. Therefore, it was not possible to obtain sericin just for spray drying. Thus, an attempt was made to freeze-dry to form a dried form of sericin. However, the obtained powder had a particle size of several μm to several hundred μm, which was non-uniform.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph showing the particle structure of the sericin fine powder obtained in the example.

Continuation of the front page (51) Int.Cl. ⁷ identification code FI C07K 1/34 C07K 1/34 C12P 21/06 C12P 21/06 (58) Field surveyed (Int.Cl. ⁷ , DB name) C08H 1 / 00-1/06 C12P 21/00-21/06 A61K 7/00

Claims (3)

(57) [Claims] 1. Sericin derived from raw silk having a molecular weight in the range of 300 to 50,000, characterized by an average particle size of 5 μm or less, a narrow particle size distribution range, and a substantially spherical particle shape. , Sericin fine powder. 2. A silk scouring waste liquid obtained by chemical scouring is subjected to ultrafiltration to obtain a sericin solution containing sericin having a molecular weight in the range of 5,000 to 50,000, and then controlling the viscosity to 100 cP or less. A method for producing fine sericin powder, which is subjected to spray drying. 3. A silk scouring waste solution obtained by enzymatic scouring is applied to a reverse osmosis membrane to obtain a sericin solution containing sericin having a molecular weight in the range of 300 to 10,000, and then controlled to a viscosity of 100 cP or less. A method for producing fine sericin powder, which is subjected to spray drying.