KR101297366B1 - Preparation method of silk composition for electrospinning with improved production rate - Google Patents

Abstract

The present invention relates to a method for producing an electrospun silk composition applicable to biotechnology materials and the like, and in particular, a method for producing an electrospun silk composition, characterized in that to perform the refining process of the silk under optimized conditions and It relates to a silk composition, silk nanofibers and the like produced.
If electrospinning is made to include sericin in the silk spinning stock solution, it is possible to remarkably improve the electrospinning speed while making a silk fiber assembly similar to the existing one, and has an excellent effect of increasing the cutting strength of the manufactured silk fiber assembly. .

Description

Preparation method of electrospun silk composition for improving the electrospinning speed {PREPARATION METHOD OF SILK COMPOSITION FOR ELECTROSPINNING WITH IMPROVED PRODUCTION RATE}

The present invention relates to a method for producing a silk composition to significantly improve the electrospinning speed of silk, and more particularly to a method for producing an electrospun silk composition comprising the step of performing a refining process in an optimized range. .

Silk has been widely used as the best garment material in human history for thousands of years due to its excellent strength and luster. However, the silk apparel industry, which has flourished widely in developed countries, has labor-intensive characteristics for sleep and rituals. As a result, the apparel industry using silk has been transferred to developing countries in the late stage due to the deterioration of competitiveness due to high labor costs. Silk countries including Japan and Korea have been making efforts to apply silk as a high value-added functional food and biotechnology material, rather than applying it as a garment material, to maintain and develop their domestic sleep industry. Based on the excellent biocompatibility, blood compatibility, cell adhesion and proliferation, silk has been actively researched worldwide for medical materials such as support for tissue engineering, artificial skin, anti-intestinal adhesion, and tympanic membrane. .

On the other hand, there is a need to manufacture the nanofiber aggregate in order to apply the silk to the biotechnology materials, the production method that is widely used for this is the electrospinning method. Electrospinning, unlike conventional melt spinning or solution spinning, which manufactures fibers using pressure, it is possible to form the fibers using electrical force. That is, in electrospinning, by connecting a high voltage to the radiation source solution and applying a voltage of 0 V or the opposite charge at a time when the radiation source solution is separated, the radiation source solution moves due to the difference in voltage, and the solvent evaporates in the air during the movement. When the molten liquid cools and reaches the collecting plate, the fiber is formed.

Fibers produced by this electrospinning method have a porous web in which fibers having a diameter of several nanometers to several micrometers are entangled. It is easy to proliferate by attaching cells by using the characteristics of the porous formation, so the nanoweb manufactured by electrospinning method is applied to medical materials such as support for tissue engineering, artificial skin, wound dressing, intestinal attachment agent, and tympanic membrane. It is possible.

Regenerated silk, which is made of new types of silk such as fibers, films, powders, and solutions by dissolving natural silk, is called regenerated silk. Various attempts have been made to produce silk nanowebs using electrospinning and to apply them as biotechnology materials. come. However, in the prior art, sericin is removed from silk to produce silk fibroin nanoweb by electrospinning targeting silk fibroin. In this case, the electrospinning rate is very low, the nanoweb productivity is very low, the mass production is difficult or the manufacturing cost is very high when industrializing the silk nanoweb.

Therefore, even when the electrospinning method is applied, it is possible to realize an improved electrospinning speed so that industrialized mass production is possible, and research on the development of a manufacturing process of a regenerated silk composition that can achieve excellent mechanical properties, etc., in the final silk nanoweb manufacturing is necessary. It is a reality.

The present invention is to provide a method for preparing a composition of silk and a silk composition prepared therefrom that can improve the electrospinning speed of silk so that the productivity of silk nanofibers can be greatly enhanced.

The present invention also provides a method for producing silk nanofibers using the composition and silk nanofibers prepared therefrom.

The present invention provides a method for producing an electrospun silk composition comprising the step of refining the silk so that the degumming index (DI, Degumming Index) represented by the following formula 1 is 0.375 to 0.988.

[Equation 1]

Wherein,

The annual deterioration rate coefficient (DI) is a coefficient representing a deterioration rate unit value per 1% of sericin content in silk before refining,

W ₁ is the dry weight of silk (g) before refining,

W ₂ is the dry weight of silk (g) after scouring,

S ₁ is the sericin content (%) of silk before refining.

The present invention also provides an electrospun silk composition prepared through the above method.

The present invention also provides a method for producing silk nanofibers comprising the step of electrospinning after dissolving the composition in an electrospinning solvent.

The present invention also provides silk nanofibers prepared from the composition.

Hereinafter, the electrospun silk composition, the silk nanofibers prepared therefrom, and a method of manufacturing the same according to specific embodiments of the present invention will be described in detail. It will be apparent to those skilled in the art, however, that this is not intended to limit the scope of the invention, which is set forth as an example of the invention, and that various modifications may be made to the embodiments within the scope of the invention.

In addition, throughout this specification, "comprising" or "containing ", unless specifically stated, refers to including any and all components (or components) Can not be interpreted as excluding.

The inventors of the present invention, in the process of producing a silk composition and nanofibers using the same, when the regenerated silk composition is produced by performing the refining step in an optimized range in the regeneration process of silk silk nanofibers with a significantly improved electrospinning rate The manufacturing process can significantly improve the productivity, it was confirmed that the excellent mechanical properties can be given to the silk nanofibers produced to complete the present invention.

According to one embodiment of the invention, there is provided an electrospun silk composition, characterized in that it contains sericin. The electrospinning silk composition of the present invention is based on 100 parts by weight of the total composition,

On the other hand, according to another embodiment of the invention, a method for producing the silk composition is provided. The method of preparing the electrospun silk composition may include performing a refining process of the silk so that the deterioration rate coefficient (DI) represented by the following Formula 1 is 0.375 to 0.988, preferably 0.475 to 0.985.

[Equation 1]

In the formula, the annual decay rate coefficient (DI) is a coefficient representing the decay rate unit value per 1% of the sericin content contained in the silk before refining, W ₁ is the dry weight of the silk before refining (g), and W ₂ is the silk after refining Is the dry weight of (g) and S ₁ is the sericin content (%) of silk before refining. In the formula 1, the sericin content S ₁ of the silk before refining may be 20% to 35% as described above.

In the method for producing an electrospun silk composition according to the present invention, when the deterioration rate coefficient is less than 0.375, the content of sericin remaining in the regenerated silk is increased, so that the entanglement is loosened due to many entanglements of the silk molecular chains, thereby reducing the fiberization. As a result, the rate of electrospinning decreases. In addition, if the annual ratio exceeds 0.988, the content of sericin remaining in the regenerated silk is too low, so that the entanglement between the silk molecular chain is too small to increase the spinning speed, the spinning stock solution is not fibrous, the spinning stock drops and the spinning speed is lowered Causes problems.

In general, silk is a representative natural fiber material obtained from silkworms, and silkworm cocoons, silk yarns obtained by making silkworm cocoons, and the like are representative examples. These natural silks are made up of a mixture of two different polymers that surround two silk fibroin layers. Natural silk, i.e. silk before refining, comprises about 65% to 80% by weight of fibroin, and sericin accounts for 20% to 35% by weight of the total weight of the silk.

Among these, sericin is a gum-like substance, which has been regarded as an impurity in conventional silk processing, and has generally been used as a silk composition mainly by removing sericin through degumming and fibroin only. In fact, the removal of sericin greatly increases the gloss, which is an advantage of silk, and thus has shown a great advantage when applying silk to clothing. In addition, until recently, it has been reported that sericin does not cause an inflammatory response in vivo and has a wound healing effect (Journal of Bioscience and Bioengineering, vol 107, 556-561, 2009). There has been concern that it may cause a reaction. Accordingly, it is true that the application of silk as a biotechnology material has been mainly limited to fibroin.

For this reason, even in the case of application research on silk as a biotechnology material, sericin was removed from silk and only silk fibroin was used, and technology development using silk fibroin from which sericin was removed even when manufacturing silk fiber aggregates by electrospinning was performed. This has been done.

However, in the production of silk nanofiber aggregates irrespective of gloss, the removal of sericin, which is about 25% by weight from silk, which is a relatively expensive raw material, is one factor for the cost increase of the final product. Above all, the present invention has been completed by discovering that the electrospinning speed of the silk spinning solution is greatly increased when the sericin is included in a predetermined optimized range without completely removing sericin.

As described above, in the present invention, the refining process of the natural silk is characterized in that the deterioration rate coefficient represented by the formula (1) is 0.375 to 0.988.

In addition, in such a refining process, the aging rate (D) of the silk represented by the following Formula 2 may be performed to be 2.4% to 25.7%, preferably 13.5% to 25.6%.

[Equation 2]

In the formula, W ₁ is the dry weight of silk (g) before refining, and W ₂ is the dry weight (g) of silk after refining. In this case, the annual range of the silk is based on the sericin content range of general natural silk, for example, based on natural silk containing 26% sericin.

As described above with respect to the annual aging rate coefficient of the present invention, the aging rate of the silk in the refining process may be performed in the optimum range as described above for the excellent radioactivity and spinning speed when applied to the electrospinning process.

In particular, the sericin content in the silk composition of the present invention can be adjusted to the optimum range through various refining processes during regenerated silk processing. As such, the removal of sericin from the silk is called degumming, and the refining of the silk is possible in various ways. For example, it is possible to adjust the degree of removal of sericin by treating with boiling water of 100 ℃ or more without adding a separate refining agent, or by treating at high temperature using various types of aqueous soap solution to control the degree of sericin removal.

In the method for preparing an electrospun silk composition according to the present invention, the refining process may be performed using a refining agent including at least one selected from the group consisting of an aqueous soap solution, an aqueous alkali solution, an acidic aqueous solution, an aqueous enzyme solution, and an aqueous amine solution. Can be. The soap here is Tallow Oliver oil, Coconut oil, Caster oil, Arachis oil, Cotton seed oil, Cry Chrysalis oil, Sodium Laurate, Sodium Myristate, Sodium Stearate, Sodium Arachidate, Sodium Oleate, Sodium Rishi Nooleate (Sodium Ricinoleate), and a variety. Furthermore, it is also possible to refine | purify in alkaline aqueous solution or acidic aqueous solution, and the refining method using an enzyme can also be applied. The alkaline aqueous solution may be used sodium hydroxide, sodium carbonate, calcium carbonate, sodium silicate, sodium phosphate, sodium bicarbonate, borax, ammonia, etc. The acidic aqueous solution is lactic acid, tartaric acid, citric acid, oxalic acid, malonic acid, succinic acid, acetic acid , Chloroacetic acid, dichloroacetic acid, trichloroacetic acid, and the like, and the enzyme may be used trypsin, papain, and the like. In addition, refining using amine chemicals (methyl amine, ethyl amine, etc.) is also applicable.

The bath ratio of the silk to the degumming bath including the refining agent is greater than 1: 5 w / v (g / ml) or 1: 5 to 1: 100 w / v (g / ml, Silk weight / refining bath volume), preferably 1:10 w / v (g / ml) or more. When the bath ratio of the silk is less than 1: 5 w / v (g / ml), the scouring solution is not sufficiently immersed in the silk may not be effectively removed sericin. However, in terms of effective refining process and process cost reduction compared to refining drugs, the bath ratio of the silk to the degumming bath is 1: 100 w / v (g / ml) or less, preferably 1:50. w / v (g / ml) or less.

In addition, the refining process may be carried out under conditions of 70 to 120 ℃, preferably 100 to 110 ℃ In this case, the refining time may be carried out in about 0.1 to 3 hours, preferably 0.5 to 2 hours. When the temperature of the refining process is less than 70 ℃, refining does not occur sufficiently or the process time can be increased by greatly increasing the refining time. In addition, when the temperature of the refining process exceeds 120 ℃, the molecular chain of the silk may occur in the refining process, or the silk may be injured.

The method for producing the electrospun silk composition according to the present invention may further include dissolving the refined silk after performing the refining process and dialysis it. In particular, after the refining process is performed, the refined silk is dissolved in the aqueous metal salt solution, and the thus obtained silk aqueous solution may be dialyzed with water. In this case, the metal salt aqueous solution may be an alcohol mixed aqueous solution further comprising an alcohol component. The metal salt may be any salt compound containing an alkali metal, an alkaline earth metal, a transition metal, or the like, as long as it is a neutral salt compound which does not have acidity or alkalinity when dissolved in water. In particular, the metal salt may be one or more of calcium chloride, calcium nitrate, lithium bromide (LiBr), lithium thiocyanate (LiSCN), magnesium nitrate, zinc nitrate, zinc chloride, and mixtures thereof.

The dissolution process may use a molar ratio of metal salt to solvent in an aqueous metal salt solution of 1 to 2: 10 to 20, and in addition, when using an alcohol, a molar ratio of metal salt to water to alcohol of 1 to 2: 8 to 16: 2 To 4 may be used. In addition, the metal salt aqueous solution may dissolve the silk for 3 to 60 minutes at 70 to 100 ℃ temperature, preferably at 80 to 90 ℃ temperature, may be dissolved for 20 to 40 minutes. In the above process, if the dissolution temperature is less than 70 ℃ may be difficult to dissolve the silk, if it exceeds 85 ℃ may be broken the silk molecular chain is large, resulting in a decrease in physical properties. In addition, when the dissolution time is less than 3 minutes, dissolution of silk may not occur completely or may be uneven. When the dissolution time exceeds 60 minutes, the physical properties may be reduced by cutting the silk molecular chain.

In addition, the dialysis step is a process for removing calcium chloride and ethanol used for dissolution. As described above, after dissolving the refined silk in an aqueous metal salt solution, the solution is placed in a cellulose dialysis membrane (molecular weight cutoff 12,000 to 14,000), and dialyzed in flowing distilled water for three days or longer to remove calcium chloride and ethanol. Can be obtained.

On the other hand, according to another embodiment of the invention, there is provided an electrospinning silk composition prepared through the process as described above. In particular, the electrospun silk composition of the present invention is characterized in that it contains sericin in the optimum range through the refining process.

The electrospun silk composition of the present invention may contain 0.3 to 18.0 parts by weight of sericin, preferably 0.35 to 16.5 parts by weight, based on 100 parts by weight of the total composition. If the sericin content is less than 0.3 parts by weight based on the total amount of the composition, the viscosity becomes low, so that the entanglement between the silk molecules is not sufficient, making the fiber difficult, and increasing the spinning feed solution to increase the spinning speed, the spinning feed solution dripping into drops May occur, and as a result, the electrospinning speed may be lowered. In addition, when the sericin content exceeds 18.0 parts by weight, the viscosity is too high, the silk molecular chain entanglement is excessive, the entanglement is released by the electrical force is prevented from being fiberized, the supply amount of the spinning solution to increase the electrospinning rate Increasing may result in no fiberization and consequently lower spinning speed.

The silk composition of the present invention may have a viscosity of 550 to 1,500 cps, preferably 600 to 1,400 cps, as measured by dissolving in formic acid at a concentration of 18% (w / w) at 25 ° C. When the viscosity of the composition is less than 550 cps, even if the viscosity of the spinning stock solution is too low to increase the supply amount of the spinning stock solution to increase the electrospinning speed, the spinning stock solution is not spun up due to insufficient entanglement between the silk molecular chains. This can cause problems. Accordingly, when the viscosity of the composition is less than 550 cps, it may be difficult to improve the low electrospinning rate. In addition, when the viscosity of the silk composition exceeds 1,500 cps, the entanglement between the silk molecular chains is excessive and it is difficult to entangle the fibers due to entanglement by electrical force, and as a result, it may be difficult to improve the electrospinning rate.

In addition, the silk composition is dissolved in formic acid at a concentration of 17.5% (w / w) at 25 ℃ measured electrical conductivity is 1.70 mS / cm or more or 1.70 to 6.55 mS / cm, preferably 1.75 mS / cm or more Can be. The electrical conductivity of the silk composition may be 1.75 mS / cm or more in terms of increasing the rate of fiberization more effectively by electrical force as the spinning stock solution in the electrospinning process.

When the silk composition of the present invention is applied to the electrospinning, as the amount of charge in the spinning stock solution increases and decreases, the speed of the spinning stock solution is increased by electric force, but by optimizing the viscosity range of the spinning stock solution more effectively. It can improve the electrospinning speed.

The rate of electrospinning is determined by the amount supplied to the spinneret. If the amount of spinneret feed is less than the amount of fiberization and exhaustion in the spinneret, the spinneret of the spinneret dries up and no fiber is produced. If the amount of supplied is large, it is difficult to produce a desired fiber assembly due to the phenomenon that the spinning stock solution dripping without spinning. The amount of spinning stock solution that is fibrinated and exhausted in the electrospinning sphere is closely related to the viscosity of the spinning stock solution.

Although silk fibroin has a higher molecular weight than silk sericin, it is characterized by low viscosity due to the low degree of entanglement between molecules in the preparation of the spinning solution. As a result, due to the low viscosity, the amount of the radioactive raw material that determines the electrospinning rate during electrospinning is 0.2 ~ 0.3 ml / hour, which is very small. On the other hand, when the silk sericin is not removed and the silk sericin is partially removed under different refining conditions, the viscosity of the spinning stock solution is greatly increased to increase the viscosity of the spinning stock solution, resulting in smooth electrospinning. There is a significant improvement.

Since the silk sericin spinning stock solution has a higher viscosity than the fibroin spinning stock solution, the viscosity increases as the sericin content increases in the silk spinning stock solution, and the electrospinning speed of the silk spinning stock solution is related to the sericin content. Therefore, for high electrospinning speed, the content of sericin relative to the total weight of the silk may be included as 0.3 to 18.0 parts by weight as described above.

On the other hand, according to another embodiment of the invention, there is provided a method for producing silk nanofibers using the composition. The method for producing the silk nanofibers may include the step of electrospinning after dissolving the silk composition containing sericin in the optimum range as described above in an electrospinning solvent.

In general, in the processing of regenerated silk, the wet spinning method is a process in which fiberization occurs by spinning a high concentration of a polymer solution (spinning solution) into a nonsolvent coagulation bath, and the spinning speed and the properties of the produced fiber solidify the spinning solution in the coagulation bath. Factors such as force, solidification rate, mass transfer rate between solvent and coagulation bath, viscosity of spinning stock solution, and take-up speed of spinning machine. On the other hand, electrospinning is the principle of spinning the polymer solution with an electric force, and the solvent is volatilized in the air to make the polymer fibrous. The wet spinning method is mainly based on the viscosity, conductivity, and composition of the spinning solution. In the electrospinning method, the factors that determine the spinning speed and the properties of the fabrics have different principles.

Accordingly, the regenerated silk produced by the conventional wet spinning method is mainly made of a filament form, and in order to use it in a web state, it is cut again, a nonwoven fabric manufacturing process is performed, and a web form silk is produced, and process efficiency is deteriorated. However, in the case of the electrospinning method as in the present invention, it is possible to produce silk in the form of a web immediately while spinning, which can be said to be a method of producing silk webs having a simpler and more efficient efficiency than a conventional wet spinning method. In addition, while the wet spinning method has a good solvent / coagulation bath pair is possible to manufacture the fiber, the electrospinning method requires only a good electrospinning solvent, there is an advantage that the web manufacturing using the electrospinning method is more convenient.

The electrospinning process may be performed at a maximum spinning speed of 0.85 ml / hour or more or 0.85 to 5.0 ml / hour, preferably 0.9 ml / hour or more, more preferably 0.95 ml / hour or more. .

The maximum spinning speed of the electrospinning process may be performed at 0.85 ml / hour or more in terms of enabling industrialized mass production during regenerated silk processing.

In the present invention, the term "electrospinning solvent" refers to a solvent that can be applied to electrospinning on the premise that the silk composition containing sericin must be dissolved. According to a specific example of the present invention, it can be confirmed that formic acid or formic acid aqueous solution satisfies all of the above requirements. In addition, one or more alcohol solvents such as water and hexafluroisopropanol may be used.

The electrospinning device which can be usually used in the electrospinning process of the present invention is not particularly limited. However, in consideration of the diameter of the nanofibers, the thickness of the nanofibers may be appropriately selected, an electrospinning apparatus capable of applying a high voltage (for example, 5 to 50 kV) generally used may be widely used. As an example of the electrospinning apparatus, as shown in FIG. 1, a high voltage generator 101, a fiber collector collecting plate 102, an electrospinning hole 103, a spinneret, and a syringe 105 are shown in FIG. 1. And an apparatus including a syringe pump (104).

According to the production method of the present invention, by adjusting the concentration of the silk composition solution, the type of electrospinning apparatus used and the conditions during the electrospinning, it can be produced by adjusting the diameter of the silk nanofibers. At this time, the average diameter of the silk nanofibers according to the present invention can be appropriately adjusted within the range of 200 to 2,500 nm, preferably 500 nm or more, more preferably 800 nm or more.

According to an embodiment of the present invention, the concentration of the silk composition is preferably 5% (w / w) to 25% (w / w), and 15% (w / w) relative to the electrospinning solution containing the silk composition. w) to 19% are more preferable. When the concentration is 5% or less, the viscosity is too low, electrospinning is difficult, when the concentration is more than 25%, the viscosity is too high or the regeneration silk is not dissolved, it is difficult to manufacture the spinning stock solution. Further, the given voltage is preferably carried out in the range of 5 to 35 kV, more preferably 15 to 25 kV. If the voltage is lower than 5 kV, there is a problem that no electrospinning occurs, and if the voltage is higher than 35 kV, fiber formation may be reduced by the electrospinning.

In the electrospinning apparatus as shown in FIG. 1, the shortest distance between the electrospinning hole 103 and the collecting plate 102 may be arranged at 5 to 30 cm, or preferably at 5 to 15 cm. . If the shortest distance between the electrospinning hole 103 and the collecting plate 102 is less than 5 cm, the fiber may not be formed due to the lack of sufficient time for the solvent to volatilize. The electrical force for the reduction may cause a problem that the electrospinning does not proceed efficiently. However, the concentration of the silk composition solution, the voltage and the distance between the spinneret and the collecting plate may be determined in consideration of the type of electrospinning apparatus, the required physical properties, the shape of the final fiber composite.

On the other hand, according to another embodiment of the invention, there is provided silk nanofibers prepared from the composition.

The average diameter of the silk nanofibers may be 200 to 2,500 nm, preferably 1,000 nm or more, more preferably 2,100 nm or more. In addition, the breaking strength of the silk nanofibers may be 8,000 KPa or more or 8,000 to 20,000 KPa, preferably 9,000 KPa or more, and more preferably 9,500 KPa or more. The elongation at break of the silk nanofibers may be at least 3.0% or at least 3.0% to 15%, preferably at least 3.2%, more preferably at least 3.5%.

In addition, the silk nanofibers may be to form a fiber assembly having a structure intertwined with each other in the form of a nonwoven fabric.

Silk nanofibers of the present invention can be used for tissue engineering scaffolds, artificial skin, enteroprotective agents, artificial tympanic membranes, wound dressings, biosensors and the like.

In the present invention, matters other than those described above can be added or subtracted as required, and therefore, the present invention is not particularly limited thereto.

According to the present invention, when the silk composition is prepared by a regeneration process in which the silk refining process is optimized, the electrospinning speed of the silk spinning stock solution can be greatly increased, and the manufacturing cost of the manufactured nanofiber aggregates can be reduced. An excellent effect of increasing the cutting strength of the produced silk fiber assembly can be obtained.

1 is a photograph of an electrospinning apparatus used for electrospinning according to an embodiment of the present invention.
Figure 2 is an electron micrograph of the silk fibers immediately after refining the cocoon according to Comparative Example 1 of the present invention (annual rate 26%, 1,000 times magnification).
3 is an electron micrograph of silk fibers immediately after refining silkworm cocoons according to Comparative Example 2 of the present invention (annual ratio 28%, 1,000 times magnification).
4 is an electron micrograph of silk fibers immediately after refining according to Example 5 of the present invention (12% annual rate, 1,000 times magnification).
5 is a photograph of a regenerated silk fiber assembly obtained by electrospinning the silk composition according to Example 2 of the present invention (1,000 times magnification).

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the scope of the present invention is not limited to the following examples.

Example  1 to Example  5

Using a silkworm cocoon having a sericin content of 26% as a silk material as a test material, a refining process was performed under the conditions as shown in Table 1 below to prepare a regenerated silk composition having optimized sericin content.

First, sodium oleate (sodium oleate) and sodium carbonate as a refining agent to dissolve in water to the content as shown in Table 1 to prepare a refining bath, and then heated to boiling temperature, put the cocoon of the sericin content of 26% 0.5 The refining process was carried out for ˜1 hour.

The sericin of the silk was partially removed through the refining process, washed with water and dried. Subsequently, the silk after refining was treated with a calcium chloride: water: ethanol mixed solvent (molar ratio 1: 8: 2) at a bath ratio of 1:20 at 85 ° C. for 30 minutes to dissolve the silk. After dissolution, the dialysis membrane (MWCO = 12,000 ~ 14,000) Dialysis was carried out in distilled water for 5 days using to remove calcium chloride and ethanol to obtain a regenerated silk aqueous solution. This was dried and ground to obtain regenerated silk powders as an electrospun silk composition in which the sericin content was finally optimized.

At this time, the refining process was carried out by adjusting the refining conditions so that the deduction rate coefficient (DI) represented by the following formula 1 and the deduction rate (%) represented by the following formula 2 as shown in Table 1 below.

[Equation 1]

[Equation 2]

In the formula, the annual decay rate coefficient (DI) is a coefficient representing the decay rate unit value per 1% of the sericin content contained in the silk before refining, W ₁ is the dry weight of the silk before refining (g), and W ₂ is the silk after refining Is the dry weight of (g) and S ₁ is the sericin content (%) of silk before refining. At this time, the dry weight before and after refining was measured using a moisture meter (XM60, Precisa, Switzerland).

Meanwhile, in order to measure the sericin content of silk before scouring, ie, the sericin content in silk cocoon, the sericin content (%) contained in silkworm cocoon previously used by electron microscopic analysis through the scouring process was measured. can do. For example, when only sericin was removed to the extent that fibroin was not injured through excessive refining through electron microscopic analysis, the sericin content of silk silk cocoon was confirmed through the annual altitude (D,%).

Comparative example  1 to Comparative example  4

Except for changing the refining process conditions and the like as shown in Table 1, an electrospun silk composition was prepared in the same manner as in Example 1.

The main process conditions for preparing the electrospun silk composition according to Examples 1 to 5 and Comparative Examples 1 to 4 are as shown in Table 1 below.

division Oleic acid
salt
(%) Carbonic acid
salt
(%) Refining
time
(h) Refining
Temperature
(℃) Silk before refining
Sericin Content (S ₁ , wt%) Refining silk
dry
weight
(W ₁ , g) After refining silk
dry
weight
(W ₂ , g) Annual deduction factor
(DI) Annual rate
(D,%) Example 1 0.2 0.14 One 100 26 40 29.72 0.988 25.7 Example 2 0.1 0.07 One 100 26 40 29.76 0.985 25.6 Example 3 0.024 0.02 One 100 26 40 32.20 0.750 19.5 Example 4 0.012 0.01 One 100 26 40 34.00 0.577 15 Example 5 0 0 One 100 26 40 35.20 0.462 12 Comparative Example 1 0.4 0.27 One 100 26 40 29.60 1,000 26 Comparative Example 2 0.6 0.4 2 100 26 40 28.80 1.077 28 Comparative Example 3 0.3 0.2 One 100 26 40 29.68 0.992 25.8 Comparative Example 4 0 0 0.5 100 26 40 36.32 0.354 9.2

As the content of refining sodium oleate and sodium carbonate, and refining time increases, the annual decrement rate and the annual decay rate result is increased. As shown in Figure 2, the silkworm cocoon used in Examples 1-5 and Comparative Examples 1-4 was confirmed that all the sericin is removed when the annualization rate is 26%, from which the sericin content of the cocoon used in this example is 26 % Was confirmed at the same time. On the other hand, in the case of Comparative Example 2 in which the annual reduction rate was excessively refined to 28%, as shown in FIG. On the other hand, when the annual reduction rate is less than 26%, for example, as shown in FIG. 4, in Example 5 having an annual reduction rate of 12.0%, fibroin was not damaged and sericin was confirmed to remain. From this, it was confirmed that the sericin content and the decay rate can be adjusted by adjusting the amount of the refiner and the refining time, and it was confirmed that the sericin content originally present in the cocoon can be determined by electron microscopy.

Evaluation of physical properties of the electrospun silk compositions prepared according to Examples 1 to 5 and Comparative Examples 1 to 4 was carried out in the following manner, and the measured physical properties are shown in Table 2 below.

a) silk  Sericin Content in the Composition

Based on the aging rate (D,%) for the refining process as described above and the sericin content (S ₁ ,%) of the silk cocoon as the first raw material, the electrospun silk composition obtained through the refining process according to the following formula (3) Sericin content of (S ₂ ,%) was measured.

[Equation 3]

In the formula, D is the annual reduction rate (%) according to the formula 2, S1 is the sericin content (%) of the silk before refining.

b) silk  Viscosity of the composition

Viscosity on the formic acid solution of the electrospun silk composition was measured using a Brookfield viscometer (RVDV-I Prime, Brook field, USA). Four spindles were used at 20 rpm at 25 ° C., and the viscosity value was measured by measuring 18% (w / w) regenerated silk formic acid solution.

c) silk  Electrical conductivity of the composition

The electrical conductivity of the electrospun silk composition on the formic acid solution was prepared using a 17.5% (w / w) regenerated silk formic acid solution and measured using an electroconductor (HI8633N, HANNA, Romania).

division Sericin Content (S ₂ , wt%) Viscosity (cps) Electrical Conductivity (mS / cm) Example 1 0.4 605 1.76 Example 2 0.5 695 1.87 Example 3 8.1 940 2.08 Example 4 12.9 1,160 3.96 Example 5 15.9 1,380 5.57 Comparative Example 1 0 420 1.58 Comparative Example 2 0 180 1.57 Comparative Example 3 0.25 515 1.68 Comparative Example 4 18.5 1,550 7.04

As shown in Table 2, the silk composition of Examples 1 to 5 performed by optimizing the refining process according to the present invention showed that the viscosity and the electrical conductivity of the silk spinning stock solution increased simultaneously with increasing sericin content. However, in the case of Comparative Example 1 and Comparative Example 2 having a sericin content of 0%, it can be seen that the drops significantly to 420 cps and 180 cps, respectively. In particular, it can be seen that the comparative example 2 having the annual reduction coefficient (DI) of 1.077 and the annual reduction ratio (D) of 28% due to excessive refining shows a viscosity that is at least two times lower than that of the comparative example 1. This can be said to be the result of injury caused by fibroin molecular chain cleavage due to excessive refining. On the other hand, in Comparative Example 4, in which the annual reduction coefficient (DI) is 0.354 and the annual reduction ratio (D) is 9.2%, the sericin content is increased to 18.5%, and the viscosity of the silk composition is excessively increased to 1,550 cps. Can be.

Manufacturing example  1 to 5 and Comparative Manufacturing Example  1-4

By using the electrospun silk composition prepared according to Examples 1 to 5 and Comparative Examples 1 to 4 and electrospinning in the following manner, the silk nano of Preparation Examples 1 to 5 and Comparative Preparation Examples 1 to 4 Fibers were prepared.

First, a 19% (w / w) regenerated silk formic acid solution obtained by dissolving the silk composition in 98% formic acid was used as a regenerated silk spinning stock solution, and electrospinning was performed using a syringe needle having a 22 gauge as an electrospinning tool. At this time, the electrospinning apparatus is composed of a high voltage generator 101, a fiber assembly collecting plate 102, an electrospinning hole 103, a syringe 105, and a syringe pump 104, as shown in FIG. A device was used, and the voltage was 20 kV, and the distance between the electrospinning sphere and the collecting plate was fixed at 19 cm to perform electrospinning, thereby preparing a fiber assembly of nonwoven fabric of regenerated silk nanofibers. In addition, the electrospinning rate control was performed by adjusting the flow rate (ml / hr) for delivering the spinning stock solution in the syringe to the electrospinning mouth using a syringe pump.

Evaluation of physical properties and manufacturing process efficiency of the silk nanofibers of Preparation Examples 1 to 5 and Comparative Preparation Examples 1 to 4 was performed by the following method, and measured physical properties are shown in Table 3 below.

i) maximum spinning speed

The maximum possible rate of electrospinning was determined by visual observation and microscopic observation. First, the electrospinning pattern was observed while controlling the flow rate of delivering the spinning solution from the syringe pump to the electrospinning hole while electrospinning the silk spinning solution. If the flow rate is too low, the taylor cones required for fiber formation are not formed at the spinneret, and thus, the fiber is not manufactured. If the flow rate is too high, the spinning solution is not spun and the spinning stock solution splashes or flows to the bottom. Therefore, there exists a flow range that makes a stable electrospinning pattern. The maximum possible electrospinning speed was first determined visually through the largest flow rate in this flow range, and electron microscopic analysis was used to determine whether silk fibers produced at the maximum electrospinning speed were properly formed. In addition to visual observation, in electron microscopic analysis, the value of the electrospinning speed for which the nanofiber web was well prepared was determined as the maximum possible electrospinning speed.

ii A) fiber average diameter

Electron microscopy analysis was first performed by coating the regenerated silk nanoweb with gold foil and then using an electron scanning microscope (S-570, Hitachi, Japan). The average diameter of the electrospun fibers was obtained by averaging the diameters of 50 fibers using a photograph taken with an electron scanning microscope.

iii Manufactured silk  Of the web Cutting strength  And Elongation

The cutting elongation of regenerated silk nanowebs prepared by electrospinning was measured by means of a tensile tester (Minimat, Rheometric scientific, USA) at a temperature of 20 ° C and 65% relative humidity, and measured as 10 average values. Was measured at a rate of 10 mm / min.

division Sericin Content
(S ₂ , wt%) Max Radiation Speed
(ml / hour) Average fiber diameter
(nm) Silk web
Cutting strength
(KPa) Silk web
Truncation
(%) Preparation Example 1 0.4 One 831 9,557 4.03 Production Example 2 0.5 1.2 1,108 10,385 5.01 Production Example 3 8.1 1.5 2,161 10,021 4.15 Production Example 4 12.9 1.2 1,640 10,013 3.92 Production Example 5 15.9 One 1,240 8,718 3.61 Comparative Preparation Example 1 0 0.3 524 8,174 4.02 Comparative Production Example 2 0 0.2 258 3,258 3.40 Comparative Production Example 3 0.25 0.6 743 9,037 3.82 Comparative Production Example 4 18.5 0.4 1,032 7,567 3.68

In addition, an electron micrograph of the silk web prepared by the electrospinning method using the silk composition of Preparation Example 2 is shown in FIG. As can be seen with the naked eye in Figure 5, the nanofibers having a uniform thickness had a structure in which they are entangled with each other in the form of a nonwoven fabric.

As shown in Table 3, in the case of Preparation Examples 1 to 5 using the silk composition of Examples 1 to 5 prepared by optimizing the refining process according to the present invention, the markedly improved maximum spinning speed and excellent elongation properties of the silk web It has been found that can be implemented. On the other hand, in the case of Comparative Preparation Examples 1 to 4 using the silk composition of Comparative Examples 1 to 4 to remove sericin or remain in excess in the conventional manner, it was confirmed that the maximum spinning speed and mechanical properties of the silk web were significantly decreased. It became. In particular, in Comparative Preparation Example 2 in which refining proceeded excessively (annual decay rate of 28%), the electrospinning speed was low, and the strength and elongation of the web was very low when the silk web was produced by electrospinning.

On the other hand, in the production examples 1 to 5 using the silk composition of Examples 1 to 5 prepared by optimizing the refining process according to the present invention, the fiber is formed well during the electrospinning, the annual reduction coefficient (DI) is 0.354 In Comparative Preparation Example 4, in which the sericin content was increased to 18.5%, the electrospinning properties were significantly decreased, such as the fibers sticking together during the electrospinning. In addition, when the silk fibroin of Comparative Example 1, which was subjected to the refining process according to the conventional method, was applied as a spinning stock solution, the maximum spinnable speed was 0.3 ml / hour, which is 0.5 to 5.0 ml / hour which is the electrospinning rate of conventional synthetic fiber polymers. It is lower than that. However, when the silk composition of Example 1 containing 0.4% of sericin was applied to the spinning stock solution during electrospinning to optimize the refining process according to the present invention, the maximum spinning speed is 1.0 ml / hour, after which the sericin content is It can be seen that the maximum spinning rate of silk spinning stock increases with increasing.

Moreover, the silk composition of Example 3 having a sericin content of 8.1% prepared according to Example 3 showed a 5 times increase as compared to the silk composition of Comparative Example 1 prepared by the conventional method with a maximum spinning speed of 1.5 ml / hour. . However, after that, even if the sericin content was increased, the spinnable rate gradually decreased, and in Example 5, where the sericin content was increased to 15.9%, the maximum spinnable rate was 1.0 ml / hour. Therefore, by using the silk compositions of Examples 1 to 5 prepared by optimizing the refining process according to the present invention, it is possible to smoothly produce excellent radioactive regenerated silk fiber webs with improved maximum spinnable speed even when electrospinning is applied. have.

In addition, the average fiber diameter constituting the fiber assembly prepared using the silk composition of Comparative Example 1, which was subjected to the refining process according to the conventional method as the spinning stock solution, was 524 nm, but was prepared by optimizing the refining process according to the present invention. It can be seen that the average fiber diameter in the case of using the silk composition of Example 3 increases to 2,161 nm. In addition, compared to the case of regenerated silk fibroin from which sericin was removed (Comparative Example 1), in the case of regenerated silk having a sericin content of 0.4% to 15.9% according to the present invention (Examples 1 to 5), silk web obtained by electrospinning It can be seen that the breaking strength of the (fiber aggregate) was significantly improved from 20% to 25%.

Claims (26)

Method for producing an electrospun silk composition comprising the step of refining the silk so that the annual reduction coefficient (DI) represented by the following formula 1 is 0.375 to 0.988:
[Equation 1]

Wherein,
The annual deterioration rate coefficient (DI) is a coefficient representing a deterioration rate unit value per 1% of sericin content in silk before refining,
W ₁ is the dry weight of silk (g) before refining,
W ₂ is the dry weight of silk (g) after scouring,
S ₁ is the sericin content of silk before refining (%). The method of claim 1,
The sericin content (S ₁ ) of the silk before refining in the formula 1 is 20 to 35% by weight of the method for producing an electrospun silk composition. The method of claim 1,
The refining process is a method for producing an electrospun silk composition to be carried out so that the annual rate of silk is 2.4% to 25.7%. The method of claim 1,
The refining process is a method for producing an electrospun silk composition using a refining agent comprising at least one selected from the group consisting of aqueous soap solution, aqueous alkali solution, acidic aqueous solution, aqueous enzyme solution, and aqueous amine solution. 5. The method of claim 4,
A method for producing an electrospun silk composition in which the bath ratio of the silk to the degumming bath including the refining agent is 1: 5 w / v (g / ml) or more. The method of claim 1,
The refining process is a method for producing an electrospun silk composition carried out at 70 to 120 ℃ with a refining time of 0.1 to 3 hours. The method of claim 1,
After dissolving the refined silk in the aqueous metal salt solution after performing the refining process, the method of producing an electrospun silk composition further comprising dialysis of the aqueous silk solution with water. The method of claim 7, wherein
The dissolution process is a method for producing an electrospun silk composition is carried out for 3 to 60 minutes at a temperature of 70 to 100 ℃. The method of claim 7, wherein
The metal salt in the dissolution step is a method for producing an electrospun silk composition of at least one selected from the group consisting of calcium chloride, calcium nitrate, lithium bromide (LiBr), lithium thiocyanate (LiSCN), magnesium nitrate, zinc nitrate, and zinc chloride. . The method of claim 7, wherein
The dialysis process is a method for producing an electrospun silk composition is carried out using a cellulose dialysis membrane of molecular weight cutoff 12,000 to 14,000. Electrospun silk composition prepared by the method according to claim 1. 12. The method of claim 11,
Electrospinning silk composition comprising sericin 0.3 to 18.0 parts by weight based on 100 parts by weight of the total composition. 12. The method of claim 11,
The electrospinning silk composition having an electrical conductivity of 1.85 to 7.04 mS / cm. 12. The method of claim 11,
Electrospinning silk composition having a viscosity of 420 to 1,550 cps. A method for producing silk nanofibers comprising the step of electrospinning after dissolving the silk composition according to claim 11 in an electrospinning solvent. 16. The method of claim 15,
The electrospinning process is a method for producing silk nanofibers, the maximum spinning speed is performed at 0.85 ml / hour or more. 16. The method of claim 15,
The electrospinning solvent is a method for producing silk nanofibers is formic acid or formic acid aqueous solution. 16. The method of claim 15,
Method of producing a silk nanofiber dissolving the silk composition at a concentration of 5% to 25% by weight of the electrospinning solvent. 16. The method of claim 15,
The electrospinning process is performed using an electrospinning apparatus including a high voltage generator 101, a fiber aggregate collecting plate 102, an electrospinning hole 103, a syringe 105, and a syringe pump 104. Method of making fibers. 16. The method of claim 15,
The electrospinning process is a method for producing silk nanofibers performed under the condition of voltage 5 to 35 kV. 16. The method of claim 15,
The electrospinning process is a method for producing silk nanofibers under the condition that the shortest distance between the electrospinning sphere and the collecting plate is 5 to 30 cm. Silk nanofibers made from the composition according to claim 11. The method of claim 22,
Silk nanofibers having an average diameter of the fiber 200 to 2,500 nm. The method of claim 22,
Silk nanofibers having a breaking strength of at least 8,000 KPa. The method of claim 22,
Silk nanofibers, wherein the fiber has an elongation at break of 3.0% or more. The method of claim 22,
Silk nanofibers having a form of intertwined fiber aggregates.

Images