JP2018119035A - Method for producing silk nanofiber, composite material, and silk nanofiber film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently producing silk nanofibers made up of uniformly fine silk, in order to effectively utilize the silk.SOLUTION: A method for producing silk nanofibers includes crushing a silk dispersed fluid of 8.0-11 in pH, to crush silk in the dispersion fluid.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing silk nanofibers, a composite material, and a film using silk nanofibers.

  Silk is a natural material rich in fiber, and has been used conventionally as a raw material for silk fabrics, and in recent years as a material for cosmetics and health foods. It is also being studied as a material for artificial blood vessels, artificial skin, and contact lenses.

  In addition, for the purpose of developing composite materials such as silk-derived green composites and biocompatible materials in the medical field, active research is being conducted to obtain silk that is uniformly refined (nanofiberized) at the nano level. Yes. However, since silk forms a structure similar to biopolymers such as cellulose, chitin, and chitosan, it is difficult to make finer.

  In addition, research on methods for dissolving silk and producing it by the electrospinning method is also in progress (for example, see Patent Documents 1 and 2). However, these methods do not sufficiently refine the silk.

Japanese Patent No. 5186671 Japanese Patent No. 5470569

  Silk has limited available applications due to its strong crystal structure. For effective utilization of silk, it is essential to develop a highly efficient and continuous refinement method for silk, which is a crystalline biopolymer. In view of the above problems, an object of the present invention is to efficiently and sufficiently convert silk into nanofibers.

According to one aspect of the present invention, the production of silk nanofibers includes pulverizing silk dispersion fluid (hereinafter referred to as dispersion fluid) having a pH of 8.0 to 11 to pulverize silk in the dispersion fluid. A method is provided.
According to this configuration, silk can be efficiently and sufficiently made into nanofibers.

  According to another aspect of the present invention, the pulverization treatment is performed by ejecting the dispersion fluid to collide with the collision hard body, or ejecting the dispersion fluid to cause two or more dispersion fluids to collide with each other. Including.

According to this configuration, silk can be made into nanofibers more efficiently and sufficiently.
According to another aspect of the present invention, the dispersion fluid has an injection pressure of 100 to 245 MPa and an injection speed of 440 to 700 m / s.
According to this configuration, silk can be made into nanofibers more efficiently and sufficiently.
According to another aspect of the invention, the dispersion fluid is ejected from an orifice nozzle having an inner diameter of 0.1 to 0.8 mm.
According to such a configuration, pressure energy can be converted into injection velocity energy.

According to another aspect of the present invention, carbonate is dissolved in the dispersion fluid.
Carbonate acts on sericin and fibroin constituting silk, and fibrous fibroin can be taken out of sericin by a water jet.
According to such a configuration, the dispersion fluid can be made alkaline at low cost and easily with an easily available reagent.

According to another aspect of the invention, the alkali metal hydroxide, sodium tetraborate decahydrate, or a mixture thereof is dissolved in the dispersion fluid.
These salts act on sericin and fibroin constituting silk, and fibroin can be extracted from sericin by a water jet. Moreover, the action with respect to sericin and fibroin is more suitable.
According to such a configuration, the dispersion fluid can be made alkaline at low cost and easily with an easily available reagent.

According to another aspect of the invention, phosphate is dissolved in the dispersion fluid.
Phosphate acts on sericin and fibroin constituting silk, and fibroin can be extracted from sericin by a water jet. Moreover, the action with respect to sericin and fibroin is more suitable.
According to such a configuration, the dispersion fluid can be made alkaline at low cost and simply by using an easily available reagent.

  According to another aspect of the present invention, the silk nanofibers have an average diameter of 10 to 100 nm. According to such a configuration, the silk nanofibers are sufficiently made into nanofibers.

  According to another aspect of the present invention, a composite material including the silk nanofiber is provided.

  According to another aspect of the present invention, a silk nanofiber film comprising the above-described silk nanofiber is provided.

  By using this technology, it becomes possible to efficiently make silk nanofibers. The obtained silk nanofibers can be applied to the development of biocompatible materials in the medical field by utilizing properties such as antibacterial properties, wound healing properties, and biodegradability.

Dispersion of silk processed in a single injection chamber. The schematic diagram which shows schematic structure of the single injection chamber of the micronization apparatus used for this invention. The schematic diagram which shows schematic structure of the circuit of a miniaturization apparatus. The expanded partial sectional view of the internal structure of the check valve of the conventional miniaturization apparatus. The expanded sectional view of the internal structure of the check valve of the improved miniaturization apparatus. (A), (B) The expanded sectional view of the conventional raw material tank. The expanded sectional view of the improved raw material tank. Photo of field emission scanning electron microscope of silk nanofiber. Silk film photo.

  Embodiments of the present invention will be described in detail below.

  Silk (also referred to as “raw material” or “silk”) means a polymer derived from silkworms (rabbit, wild silk), in particular, a polymer that is hardly soluble in water. Arbitrary forms, such as a fibrous form and a granular form, can be used, and a commercially available raw material may be used. When high-pressure jetting is applied to the dispersion fluid using a micronizer, the silk is unwound and thins while maintaining the length of the fiber, but the fiber can be reduced by changing the processing conditions such as jetting pressure and the number of treatments. It is also possible to reduce the molecular weight.

  A silk dispersion fluid (hereinafter referred to as a dispersion fluid) is obtained by dispersing silk in a solvent. The solvent is preferably water and optionally an alkaline reagent can be added. Conventionally, a mortar (disc mill) or an electrospinning method has been used to make silk nanofibers, but the production efficiency is low and there is a problem in the uniformity of refinement. According to the method for producing silk nanofibers of the present invention, it is possible to produce silk nanofibers only by shifting the pH of the dispersion fluid used for nanofiber formation to the alkali side without using any catalyst or harmful chemicals. A suitable dispersion fluid can be obtained. Therefore, the method for producing silk nanofibers of the present invention is a technology for silk opening and nanofiberization with a low environmental load.

The dispersion fluid has a high fluidity when the silk concentration is low, but the viscosity increases as the silk becomes finer, and becomes a property close to a paste when the silk concentration increases. The higher the concentration of silk in the dispersion fluid, the higher the processing efficiency of making silk nanofibers, but this is preferable, but the viscosity of the dispersion fluid becomes too high due to the fine fibers at the nano level, and the dispersion fluid becomes pasty. Then, high pressure injection becomes difficult.
The concentration of silk in the dispersion fluid may be, for example, about 1 to 20% by mass, preferably about 5 to 20% by mass, more preferably about 10 to 20% by mass, and further preferably about 11 to 20% by mass. .

  Nanofiber means that the width of the fiber is nano-sized. For example, when the silk is unwound by the manufacturing method of the present invention to form one minimum unit fiber, the silk has a diameter of about 10 to 50 nm. The diameter (width) of silk (raw material) or silk nanofiber can be measured by a field emission scanning electron microscope (FE-SEM, hereinafter referred to as electron microscope) photograph. In such a fiber, even though the length is not nano-sized, the diameter (width) is nano-sized, and thus described as nanofiber.

The manufacturing method of the silk nanofiber of this invention includes grind | pulverizing the dispersion fluid of pH 8.0-11, and grind | pulverizing the silk in a dispersion fluid. Examples of the pulverization treatment include jetting a dispersion fluid and causing it to collide with the collision hard body, and jetting the dispersion fluid and causing two or more dispersion fluids to collide with each other.
When pulverizing with a pulverizer, a known pulverizer such as a grinder, a ball mill, a bead mill, an attritor, or a homogenizer can be used. It can be understood by those skilled in the art that silk nanofibers can be obtained by appropriately changing the pulverization time, pulverization speed, etc. of the pulverizer.
When the dispersion fluid is jetted to pulverize the silk in the dispersion fluid, preferably the dispersion fluid is jetted from one or more nozzles, and the dispersion fluid discharged from the nozzles collides with the collision hard body. Alternatively, the silk is pulverized and refined by colliding with a dispersed fluid discharged from another nozzle.
The injection pressure and the injection speed are not limited, but preferably the injection pressure is 100 to 245 MP.
a, The injection speed is 440 to 700 m / s.
The average fiber diameter (average diameter) of the silk nanofibers obtained by the above production method is preferably 10 to 100 nm, more preferably 10 to 40 nm, and most preferably 15 to 25 nm.
In one embodiment, the average diameter of the silk nanofiber is preferably 100 nm or less, more preferably 80 nm or less, still more preferably 60 nm or less, particularly 40 nm or less.

  In the present invention, since the average diameter of silk nanofibers is very thin, a transparent or translucent dispersion fluid can be obtained by visual observation when dispersed in water. From the silk nanofibers thus obtained, a composite material or a transparent or translucent film can be obtained.

  As composite materials, silk nanofibers are used as fillers, and polyolefin resins, vinyl resins, polyamide resins, and other resins are used as a matrix in which fillers are dispersed; by combining silk nanofibers with resinous substrates Composite material obtained as transparent film or transparent resin; composite material of silk nanofiber and polymer such as phenol resin, polyethylene glycol, polyethylene terephthalate and polyvinyl alcohol capable of forming hydrogen bond; silk nanofiber and poly Composite material with biodegradable resin such as lactic acid, polybutylene succinate, polycaprolactone; Composite material with silk nanofiber made hydrophobic by chemical modification and hydrophobic resin such as acrylic resin; Silk nanofiber and cellulose nano Fiber And the like are; composite material.

  The silk nanofiber film can be produced by pouring a silk nanofiber produced using a micronizer or a dispersion fluid containing the silk nanofiber into a container such as a petri dish and drying. There is no restriction | limiting in particular in the method of film-forming, A film can be produced by drying silk nanofiber after operations, such as a film applicator generally used for film production, and suction filtration. Drying can be performed by heating or room temperature drying.

  The transparency of the film can be adjusted according to the degree of micronization (nanofiber) using a micronizer. According to the physical principle that an object having a size of 1/10 or less with respect to a visible light wavelength (400 to 800 nm) does not cause light scattering, a silk nanofiber film refined with a uniform width of 20 nm is very High transparency. A similar film can be produced for silk nanofibers refined using a miniaturization apparatus.

  FIG. 1 is a photograph of the state of each dispersed fluid after centrifugation (15,000 rpm). Silk that has not been subjected to water jet treatment (treatment of high-pressure jetting of a dispersed fluid) settles without the need for centrifugation (the container on the left side of FIG. 1), whereas the single jet chamber 10 shown in FIG. 2 is used. It can be seen that the silk treated with the water jet is uniformly dispersed (forms an opaque gel) in the dispersion fluid even after centrifugation (15,000 rpm) (the container on the right side of FIG. 1).

  Since silk nanofibers have a large fiber length / fiber width (aspect ratio), they can be easily molded into a film or sheet in which nanofibers are intertwined while maintaining strength, and can be suitably used as various materials. . A film using silk nanofibers is characterized by a very narrow fiber width and high transparency. A plate-like body having a thickness of 0.2 mm or more is referred to as a sheet, and a plate-like body having a thickness of less than 0.2 mm is referred to as a film.

The present inventors have succeeded in developing a new miniaturization technology specialized in biomass based on the water jet technology. Moreover, it discovered that silk was fully refined | miniaturized by disperse | distributing silk in an alkaline solvent. The details of the method for producing silk nanofibers by high-pressure jetting of the dispersion fluid, the obtained silk nanofibers, and the miniaturization apparatus used for carrying out the method will be described below.
When the silk nanofiber gel in the container on the right side of FIG. 1 is cast into a petri dish and then dried, a transparent or translucent film formed from the silk nanofiber is obtained.

A film made of silk nanofiber is synonymous with transparent paper. In principle, the transparency of paper is to reduce the frequency of light refraction (scattering) in the paper layer (between fibers) and reduce opacity. General high quality paper contains about 50% of air in its volume, and there are many fine voids between the fibers. For this reason, the light is complicatedly refracted at the infinite number of interfaces between the two, so that the paper appears white and opaque. Since the wavelength of visible light is 400 to 800 nm, an object sufficiently smaller than that (1/10 or less) can be regarded as causing no light scattering.
Therefore, in order to make the paper transparent, not only the fibers are made thinner than the visible light wavelength (1/10 or less), but also the gaps between the fibers must be made sufficiently thinner than the visible light wavelength.

  The process of forming nanofibers using a miniaturization apparatus will be described with reference to FIG. In the present invention, silk nanofibers are generated by jetting a dispersed fluid at a high pressure from a nozzle using a micronizer using a water jet developed by Sugino Machine Co., Ltd., the applicant.

  FIG. 2 is a schematic diagram showing a schematic configuration of the single injection chamber 10 of the miniaturization apparatus used in the present invention. The single injection chamber 10 includes a dispersion fluid pressurization unit 11, an orifice nozzle 12 provided on the downstream side of the dispersion fluid pressurization unit 11, an impact enhancement region 14 provided on the downstream side of the orifice nozzle 12, and collision enhancement. A collision hard body 15 provided on the downstream side of the region 14 and a recovery channel 16 are provided.

  The dispersion fluid is pressurized to an ultrahigh pressure of 100 to 245 MPa by the dispersion fluid pressurizing unit 11 and sprayed from the fine orifice nozzle 12 at a high pressure to obtain silk nanofibers.

The alkali reagent added to the dispersion fluid is not particularly limited, and examples thereof include carbonates, alkali metal hydroxides, sodium tetraborate decahydrate, phosphates, and mixtures thereof.
Examples of the carbonate include alkali metal carbonates such as sodium carbonate, sodium hydrogen carbonate, and potassium carbonate.
Examples of the alkali metal hydroxide include sodium hydroxide and potassium hydroxide.
Examples of the phosphate include sodium phosphate (for example, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate), potassium phosphate (for example, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, triphosphate phosphate). Potassium), sodium pyrophosphate, potassium pyrophosphate, alkali metal phosphates such as sodium metaphosphate, and the like. These phosphates can be used alone or in combination. Sodium carbonate, sodium hydroxide, potassium hydroxide, or a mixture thereof is particularly preferable from the viewpoint of influence on fibroin which is a component of silk. The addition of alkali simplifies silk opening and fiberization, and can increase its efficiency. Further, in order to keep the pH of the electrolytic solution in a specific range, it is preferable to use an alkaline solvent containing such an alkaline reagent and expected to have a buffer effect as a solvent for dispersing silk.

  Moreover, the dispersion fluid is preferably only mixed with silk at room temperature, and can enter the process of producing silk nanofibers without adding a pre-process such as heating. Furthermore, the silk in the dispersion fluid is not soluble and precipitates in a short time. For this reason, silk nanofibers can be obtained without being solubilized by carrying out a refining treatment with a refining device after timely stirring.

The discharge flow from the orifice nozzle 12 is a high-speed jet of 440 to 700 m / s, but a high shear force is generated in the orifice 13 accelerated to that speed. The orifice nozzle 12 is provided with one orifice 13, and single injection refers to injection through one orifice 13. The diameter of the orifice 13 in the orifice nozzle 12 is preferably 0.1 to 0.8 mm, preferably 0.4 mm. Since the diameter of the orifice nozzle 12 used here is extremely thin, preferably 0.4 mm, almost 100% of the pressure energy can be converted into the velocity energy of the injection. That is, the orifice 13 has a narrow gap of 0.1 to 0.8 mm and an ultrahigh speed of 440 to 700 m / s, and is filled with components for obtaining a high shearing force.

[Shearing force] = [Viscosity of dispersion fluid] × [Speed] / [Gap]

  Further, in a high-speed jet flow (high pressure injection state) of 440 to 700 m / s, cavitation bubbles are generated, and strong impact force is generated by the disappearance of the bubbles. By providing the impact enhancement region 14 after the orifice nozzle 12, cavitation can be efficiently generated.

  The miniaturization apparatus includes a ceramic hard body as the collision hard body 15 as a structural jet receiver. In order to further reduce the crystallinity, a region where the jet pressure is increased and the jet velocity is high is used, and the collision force against the collision hard body 15 is also used for pulverization. In other words, the operation of high-pressure jetting the dispersion fluid that has been jetted by high pressure and collided with the collision hard body 15 from the nozzle 12 toward the collision hard body 15 is necessary times (number of passes), for example, about 1 to 50 times. Preferably about 1 to 40 times, more preferably about 1 to 30 times, still more preferably about 1 to 20 times, and particularly preferably about 1 to 10 times. When the silk collides with the collision-use hard body 15, the fibers are entangled, the fiber diameter is reduced, and the nano size is reduced. The collision hard body 15 can be assumed to have a ball shape, a flat plate shape, or the like.

Next, the circuit 1 of the miniaturization apparatus will be described with reference to FIG. In FIG. 3, a portion surrounded by a dotted-line square corresponds to the single injection chamber 10 of FIG.
In the circuit 1 of the miniaturization apparatus, the raw material tank 2 contains a dispersion fluid 3. A sealing lid 2 a is disposed on the upper part of the raw material tank 2. A liquid supply pump 4 is provided integrally with the raw material tank 2 below the raw material tank 2.

The dispersion fluid 3 from the raw material tank 2 is stirred and mixed by the propeller 2b in the raw material tank 2 supplied with power from the motor, and sent to the single injection chamber 10 through the liquid supply pipe 5. A check valve 6 is provided in the middle of the liquid supply pipe 5 from the raw material tank 2 to the raw material tank 2. The liquid supply pipe 5 is connected to the pressure booster 7 in the check valve 6, and the pressure booster 7 further includes a hydraulic pressure generation / control unit. The dispersion fluid 3 as a raw material is pressurized by the pressure intensifier 7 under the control of the hydraulic pressure generation / control unit 8 before entering the orifice nozzle 12 of the single injection chamber 10.
The circuit 1 in FIG. 3 corresponds to a dispersion fluid having a high concentration (high viscosity). Since the shearing viscosity of the raw material also affects the cutting force, silk can be made into nanofibers more effectively by using a high-concentration circuit. In the past, silk nanofibers have been limited to processing at a silk concentration of 2% by mass, but each unit in the circuit 1 of the miniaturization apparatus has the following improvements, resulting in a concentration of 10-20%. % High-concentration (high viscosity) silk can be made into nanofibers.

By increasing the inner diameter of the liquid supply pipe 5 for supplying the dispersion fluid 3 to the pressure intensifier 7 (high pressure pump) to 40 to 50 mm and further integrating the raw material tank 2 and the liquid supply pump 4, the conventional dispersion fluid 3 The pressure loss due to the piping that has occurred at the time of the suction can be eliminated, and the dispersion fluid 3 having a high concentration (high viscosity) can be supplied to the pressure intensifier 7. There is the following relationship between pressure loss, pipe inner diameter, pipe length, and raw material viscosity.

[Pressure loss] ∝ [Pipe length] x [Raw material viscosity] / ([Pipe inner diameter] to the fourth power)

  Normally, an air-type diaphragm pump capable of a shut-off operation is used as a feed pump for a pressure booster 7 type high-pressure pump of 100 MPa or more. However, since the air pressure is 0.5 MPa of general factory air, the pushing force is It is limited to 0.5 MPa. When the deadline operation can be performed and a high concentration (high viscosity) silk is supplied to the intensifier 7 at an indentation pressure of 0.5 MPa, the above pressure loss reduction is effective.

  Since the check valve 6 (check valve) existing in the middle of supplying to the pressure booster 7 also has a high pressure sealing property, the general check valve 6 has a structure with a large pressure loss. Simplifies the pressure loss.

  More specifically, as shown in FIG. 4, the conventional check valve 6 includes a ball-shaped ball valve 21 held in the ball holder 20 and a spring 22 attached to the ball holder 20 at one end. The ball valve 21 is urged by the end and is received by the valve seat 23 on the side opposite to the spring 22. However, in the conventional check valve 6, the ball valve 21 is pressed by the spring 22 in order to emphasize sealing performance. . Therefore, the dispersion fluid 3 having a high concentration and containing the fibrous substance becomes a resistance when passing through the passage in the spring 22 and cannot be supplied sufficiently. In the figure, the dispersion fluid 3 is supplied from the direction of the arrow 25A, enters the check valve 6, and is discharged from the check valve 6 in the direction of the arrow 25B.

  Therefore, in the present application, as shown in FIG. 5, the pressing spring 22 of the ball valve 21 is excluded, and the pressing force is determined by the pressure of the dispersion fluid 3 itself. In addition, in order to improve the sealing performance only by the pressure of the fluid itself, the material of the sealing sheet 24 used for sealing the slurry is a resin and rubber which are more flexible than conventional resins, with more emphasis on sealing performance. The material has been changed to an intermediate strength material. The sealing property improves with flexibility. That is, when the dispersion fluid 3 becomes highly viscous, it is rather difficult for leakage to occur and the sealing performance tends to be improved. The improved sealing sheet 24 having the conventional hardness is used for a slurry having high abrasiveness, but the material used this time is biomass, and since the abrasiveness is not high, the sealing sheet formed from a soft material is used. Even the sheet 24 has sufficient wear resistance.

  Next, as shown in FIGS. 6A and 6B, in the configuration of the conventional raw material tank 2, the high viscosity slurry of 10-20% by mass causes crosslinking in the raw material tank 2, The rat hole 3a is formed at the suction port. In this case, since air is mixed into the pressure intensifier 7, a pressure increase failure is caused in the high pressure pump. By stirring with the propeller 2b or impact on the wall surface of the raw material tank 2, it is impossible to flatten the high concentration (high viscosity) dispersion fluid 3 below the raw material tank 2 and send it to the suction port.

  Therefore, as shown in FIG. 7, the raw material tank 2 is sealed with a sealing lid 2a, the sealing lid 2a is sealed so as not to leak to the outside, and the dispersion fluid 3 is sent into the raw material tank 2. At the outlet of the raw material tank 2, since the dispersion fluid is sucked by the feed pump 4, the dispersion fluid 3 in the raw material tank 2 is always kept at a constant amount. By maintaining this state, it is possible to inject a high concentration (high viscosity) dispersed fluid multiple times. In the raw material tank 2, the propeller 2b is rotated for mixing.

As described above, the cavitation effect using the water jet technology and the optimization of the effect of miniaturizing the hard body and silk by colliding with each other, and the treatment of dispersed fluid with high concentration and high viscosity are supported. By combining with a miniaturization apparatus equipped with the above-described circuit, it is possible to increase the shearing effect of silk and continuously produce a large amount of silk nanofibers refined with a uniform width. The obtained silk nanofiber can be observed using an electron microscope.
In the present invention, instead of using the collision hard body 15, or in addition to using the collision hard body 15, the water jet treatment was performed.

1. Production of Silk Nanofiber and Measurement of Viscosity of Dispersion Fluid Regarding the dispersion fluid subjected to the water jet treatment in Examples 1 to 3 and Comparative Examples 1 and 2, the viscosity of each dispersion fluid was measured with a viscometer.
In the water jet treatment of the example, the dispersion fluid was pressurized to a high pressure of 100 to 245 MPa and sprayed at a high pressure from one (single) orifice nozzle having a diameter of 0.4 mm to obtain nanofibers. In addition, the sprayed dispersed fluid was made to collide with a ball-shaped ceramic hard body.
For adjusting the pH of the dispersion fluids of Examples 1 to 3 and Comparative Examples 1 and 2, in Example 1, a mixture of sodium carbonate and sodium bicarbonate, in Example 2, sodium tetraborate decahydrate, Example In No. 3, a mixture of potassium dihydrogen phosphate and disodium hydrogen phosphate was used.

Example 1
The viscosity of the dispersion fluid subjected to water jet treatment with the hydrogen ion concentration (pH) of water as a solvent being 11 was measured with a B-type viscometer. The measurement conditions were a spindle rotation speed of 100 rpm, a sample amount of 8% of a dispersed fluid of 2% by mass, a measurement temperature of 25 ° C., and the result 10 minutes after the start of measurement was read.

(Example 2)
The viscosity of the dispersion fluid subjected to water jet treatment with the hydrogen ion concentration (pH) of water as a solvent set to 9.2 was measured with a B-type viscometer. The measurement conditions were a spindle rotation speed of 100 rpm, a sample amount of 8 ml, a measurement temperature of 25 ° C., and the results were read 10 minutes after the start of measurement.

(Example 3)
The viscosity of the dispersion fluid subjected to water jet treatment with the hydrogen ion concentration (pH) of water as a solvent at 8.0 was measured with a B-type viscometer. The measurement conditions were a spindle rotation speed of 100 rpm, a sample amount of 8 ml, a measurement temperature of 25 ° C., and the results were read 10 minutes after the start of measurement.

(Comparative Example 1)
The viscosity of the dispersion fluid subjected to water jet treatment with a hydrogen ion concentration (pH) of water as a solvent being 7.5 was measured with a B-type viscometer. The measurement conditions were a spindle rotation speed of 100 rpm, a sample amount of 8 ml, a measurement temperature of 25 ° C., and the results were read 10 minutes after the start of measurement.

(Comparative Example 2)
The viscosity of the dispersion fluid subjected to water jet treatment with the hydrogen ion concentration (pH) of water as a solvent being 6.9 was measured with a B-type viscometer. Measurement condition is spindle rotation speed 100 rp
m, the sample amount was 8 ml, the measurement temperature was 25 ° C., and the result 10 minutes after the start of the measurement was read.

  As shown in Table 1, an increase in viscosity was confirmed by shifting the hydrogen ion concentration (pH) of water as a solvent to the alkali side.

2. Observation and average diameter measurement of silk nanofibers by electron microscope

Each of the water jet-treated dispersion fluids of Examples 1 to 3 and Comparative Examples 1 and 2 was replaced with t-butanol and freeze-dried. Vapor deposition of a mixture of platinum and palladium was performed on the dried sample with a film thickness of about 3 nanometers. The silk nanofibers obtained from the dispersion fluids of Examples 1 to 3 and Comparative Examples 1 and 2 were observed using an electron microscope, JSMOL JSM-6700, under an accelerating voltage of 2.0 kV. . FIG. 8 shows an FE-SEM photograph of silk nanofiberized by the water jet treatment of Example 2.
In the observation of silk nanofibers with an electron microscope, the dispersion fluid in the vicinity of neutrality in Comparative Examples 1 and 2 is only refined. The shape was confirmed.
Moreover, silk nanofibers in the dispersion fluids of Examples 1 to 3 and Comparative Examples 1 and 2 were observed under the electron microscope, and the average diameter was measured. The results are shown in Table 1. The average diameter of the silk nanofibers of Examples 1 to 3 was as small as 100 mn or less, and the average diameter of the silk nanofibers of Comparative Examples 1 and 2 was found to be much larger than that of Examples 1 to 3.

3. Next, we made a silk nanofiber film and verified it.

  Silk nanofibers produced using a micronizer were poured into a petri dish (cast), cast as thin as possible, and then dried at 50 ° C. with a dryer to obtain a silk nanofiber film. Fig. 9 is a photograph of a film produced from the silk nanofibers of Example 2 ("transparent film in front of paper written as" Silk Nano Fiber "). As shown in Table 1, the silk nanofibers of Examples 1 to 3 were used. The film produced from the fiber was transparent, but the silk nanofiber of Comparative Example 1 could not be produced because the silk was only refined and had no viscosity.

  According to the present invention, silk can be made into nanofibers using a finer apparatus using a water jet as a core technology, thereby enabling a wide range of effective utilization of silk.

  Silk nanofibers have a very smooth feel, and can be expected to have a moisturizing action, skin care action, antibacterial action, and promoting metabolism. Therefore, it can be used for cosmetics (sunscreen agents), organic EL, liquid crystal substrates and the like that make use of optical properties obtained by making silk nanofibers.

  Moreover, by separating the hydroxyl group of silk with various functional groups, separation / filter materials having different characteristics and functions can be produced. Furthermore, by controlling the diameter of the silk nanofiber, the size of the gap can be changed, and a filter that makes use of the nano-order gap generated between the silk fibers can be manufactured.

In addition, since silk is a cationic polymer, it has a power to retain pharmaceuticals and is known to exhibit sustained release as a pharmaceutical carrier. When the medicine taken is absorbed into the body, it is sent to the liver to be detoxified, and the rest goes into the blood, travels around the body, reaches the affected area, and becomes effective. Therefore, the medicine to be taken is administered in anticipation of the amount detoxified in the liver. If silk nanofibers are used as a pharmaceutical carrier, sustained drug efficacy can be increased by gradually releasing the drug, and side effects can be reduced by showing effects in a small amount.

  In addition, the development of contact lenses using silk as a raw material is currently under investigation. In this case, the amide solvent is removed with a special coagulation solution after the gel is dissolved and gelled with an amide solvent in the same manner as the production of sutures. It is assumed that a transparent lens is obtained by drying. In other words, the contact lens is obtained by dissolving the raw material in an amide solvent to obtain a transparent and viscous dope, then removing the amide solvent with a special coagulation liquid and drying to obtain a transparent lens. If used, a special amide solvent is not required, and a lens-shaped transparent molded body can be produced by only drying. Silk nanofibers can be formed into a lens shape simply by giving a thickness and drying, so that they can be used not only as contact lenses but also as biomass-derived optical / transparent materials.

  Examples of synthetic polymer resins used when silk nanofibers are used as fillers include polycondensation resins such as polyolefin resins, vinyl resins, and polyamide resins. A new functional transparent film or resin can be synthesized by compounding with a transparent substrate (resin) such as epoxy having a refractive index equal to that of silk. In particular, silk nanofibers can change strength or surface characteristics by being combined with a polymer such as phenol resin capable of forming hydrogen bonds, polyethylene glycol, polyethylene terephthalate, and polyvinyl alcohol.

  Silk nanofibers can improve properties such as strength and heat resistance of these resins by combining with biodegradable resins such as polylactic acid, polybutylene succinate and polycaprolactone.

  By surface modification (chemical modification) of silk nanofibers, resins with properties other than the above, for example, silk nanofibers are acetylated to give hydrophobic properties, so that they can be combined with hydrophobic resins such as acrylic resins. Is also possible.

  Silk also has a highly reactive amino group and hydroxyl group in the molecule, so it is a natural polymer material that can be variously modified. Silk is known to adsorb many substances such as proteins and metals. Silk nanofibers are suitable as adsorbents because of their increased specific surface area, and the films that can be dried are porous films with voids controlled at the nano level. It can be used as a carrier for immobilizing a biocatalyst, a carrier for chromatography such as separation and purification, or a cell culture substrate.

  Further, since silk exhibits antibacterial and deodorant properties, the antibacterial and deodorant effects can be imparted to these products by blending the silk nanofibers of the present invention into fibers such as clothing, daily necessities, and interiors.

  Conventionally, transparent resin films have been used for envelope window materials. However, resin films are a contraindicated product that prevents recycling, and recently, recyclable paper materials such as glassine paper and coated paper impregnated with aqueous wax. It is moving to. Such a movement is similar not only in the envelope window material but also in various packaging material fields. In order to replace the conventional transparent film with a recyclable paper material, attention is focused on the transparent paper. Since the film using silk nanofibers is derived from 100% biomass, it can be used as a recyclable envelope window material, coated paper, high-quality paper, and various packaging materials.

  Furthermore, by combining silk and nanofibers of cellulose, which is an anionic polymer, the effect of reinforcing electrostatic attraction by electric charge is expected, and it is possible to create stronger nanofibers. The most important factor involved in the strength of paper is the bond strength between fibers, which is determined by hydrogen bonding between the hydroxyl groups of cellulose. In order to increase the strength of the paper, it is only necessary to increase the hydrogen bonds. In addition to the above properties, silk has a chemical structure similar to cellulose and is linear, so it has a high affinity with cellulose and is used as a paper strength enhancer and as an ink-jet ink receptor. -It must be solubilized by chemical modification such as hydroxylation. Since the silk nanofibers of the present invention are already uniformly dispersed in water, there is no need for chemical modification, and ink jet printing paper and the like can be enhanced by simply applying or blending them.

  The silk nanofiber of the present invention can be carbonized by high-temperature treatment in the absence of oxygen (in an inert gas atmosphere such as nitrogen or argon). That is, it is possible to produce biomass-derived silk nanocarbon fibers. Porous carbon containing a large amount of small pores at the nano level is used as a deodorizing agent, decoloring agent, or filter for water purification, and the silk nano carbonized fiber produced by carbonizing the silk nano fiber of the present invention is also such Can be used for fields. Porous carbon not only captures odor and dirt molecules in its small pores, but it can also capture ions (charged atoms and molecules) with the help of electricity. Since the captured charge can be taken out, a large-capacity capacitor (capacitor) has been developed using this. Since such a capacitor can be used as an auxiliary power source for a fuel cell vehicle and a storage for storing surplus power at night, it has attracted much attention in recent years. Since the capacitance of the electric double layer capacitor is determined by the amount of charge stored in the electric double layer, the larger the surface area of the electrode, the larger the capacitance can be obtained, so activated carbon having high conductivity and specific surface area. Is used as an electrode material. The silk nanocarbon fiber produced by carbonizing the silk nanofiber of the present invention is a mesoporous activated carbon having a high specific surface area and controlled pores at the nano level, so that the electrostatic capacity of an electric double layer capacitor and the like is drastically increased. Can be used as an electrode material.

  It goes without saying that the present invention can be modified as appropriate without departing from the spirit of the present invention.

  3 ... Dispersing fluid, 12 ... Orifice nozzle, 15 ... Hard body for collision.

Claims (10)

  A method for producing silk nanofibers, comprising pulverizing a silk dispersion fluid having a pH of 8.0 to 11 and pulverizing the silk in the dispersion fluid.   The said crushing process includes injecting the said dispersion fluid and making it collide with the hard body for collision, or injecting the said dispersion fluid and making two or more silk dispersion fluids collide. The manufacturing method of the silk nanofiber as described in any one of.   The method for producing silk nanofiber according to claim 2, wherein the dispersion fluid has a spray pressure of 100 to 245 MPa and a spray speed of 440 to 700 m / s.   The method for producing silk nanofiber according to claim 2 or 3, wherein the dispersion fluid is ejected from an orifice nozzle having an inner diameter of 0.1 to 0.8 mm.   The method for producing silk nanofiber according to any one of claims 1 to 4, wherein carbonate is dissolved in the dispersion fluid.   The method for producing silk nanofiber according to any one of claims 1 to 4, wherein an alkali metal hydroxide, sodium tetraborate decahydrate, or a mixture thereof is dissolved in the dispersion fluid.   The method for producing silk nanofiber according to claim 1, wherein phosphate is dissolved in the dispersion fluid.   The average diameter of silk nanofiber is 10-100 nm, The manufacturing method of the silk nanofiber in any one of Claims 1-7.   The composite material containing the silk nanofiber in any one of Claims 1-8.   The silk nanofiber film containing the silk nanofiber in any one of Claims 1-8.