NANOFIBER STRUCTURE CONSTITUTED OF POLYHYDROXYALKANOIC ACID, AND NON-WOVEN FABRIC

Abstract

The biodegradability of a nanofiber film (a nanofiber structure) produced in example 1 by microorganisms or the like when the nanofiber film is allowed to leave in soil is examined. FIG. 4(a) shows a photograph of the nanofiber film immediately after the nanofiber film is placed in soil. FIG. 4(b) shows a photograph of the nanofiber film (a) that is allowed to leave as it for 12 days. As is obvious from the comparison between these photographs, a polyhydroxyalkanoic acid nanofiber film can be degraded in soil remarkably rapidly. Therefore, PHA can be produced from a plant-derived resource occurring in nature, can be degraded by microorganisms in soil to return to nature, and can be used as a resource material which can overcome the disadvantages of the conventional PP non-woven fabrics (e.g., the generation of CO.sub.2 upon incineration) and which can be used permanently, thereby enabling the production of a novel non-woven fabric.

Claims

1. A nanofiber structure formed of polyhydroxyalkanoic acid.

2. The nanofiber structure according to claim 1, wherein the polyhydroxyalkanoic acid includes polyhydroxybutylate as a main component.

3. The nanofiber structure according to claim 1, wherein the nanofiber structure has a fiber diameter of 1 m or less.

4. The nanofiber structure according to claim 1, wherein the nanofiber structure is degraded by microorganisms in soil in a natural environment.

5. The nanofiber structure according to claim 1, wherein the nanofiber structure has a porosity of 50% or more.

6. The nanofiber structure according to claim 1, wherein the nanofiber structure has water repellency, and a contact angle of pure water to a surface of the nanofiber structure is 100 or more.

7. The nanofiber structure according to claim 1, wherein the nanofiber structure has oil absorbency.

8. The nanofiber structure according to claim 1, wherein the nanofiber structure has organic solvent absorbency.

9. The nanofiber structure according to claim 1, wherein the surface of the nanofiber structure has hydrophilicity by surface modification by a plasma treatment, a corona discharge, electron beam irradiation, or laser irradiation, or the like.

10. The nanofiber structure according to claim 1, further comprising an adsorbent material.

11. The nanofiber structure according to claim 1, wherein the nanofiber structure is partially fused to have a film shape.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0032] FIG. 1 is a conceptual diagram representing a basic configuration of an electrospray deposition device.

[0033] FIG. 2 is a SEM photograph of a nanofiber structure manufactured in Example 1 as a material.

[0034] FIG. 3 is an electron microscope photograph (SEM photograph) of a PHA nanofiber structure shown in FIG. 2.

[0035] FIG. 4 is a drawing representing biodegradability of a nanofiber film of Example 1.

[0036] FIG. 5 is a drawing representing water repellency of the nanofiber film of Example 1.

[0037] FIG. 6 is a drawing representing oil-water separability and oil absorbency of the nanofiber film of Example 1.

[0038] FIG. 7 is a drawing representing organic solvent absorbency of the nanofiber film of Example 1.

[0039] FIG. 8 is an electron microscope photograph (SEM photograph) of a nanofiber film (nanofiber structure) which is partially fused to have a film shape.

[0040] FIG. 9 is an electron microscope photograph (SEM photograph) of a nanofiber film including fine particles as an adsorbent material.

DESCRIPTION OF EMBODIMENTS

[0041] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0042] A polyhydroxyalkanoic acid used in an exemplary embodiment of the present invention is a sample prepared by microbial culture and purification method, the patentee of which is University of Science-Malaysia to which one of the inventors of the present application belongs. Nanofiber may be manufactured from the sample by an electrospray deposition (ESD) method, a melt blown method, or other method of manufacturing nanofiber, however, an ESD method or a melt blown method is preferred.

<Electrospray Deposition Method>

[0043] Before the embodiments of the present invention are described, the principle of an electrospray deposition method (ESD method) used in the embodiment of the present invention and an electrospray deposition device (ESD: electrospray device) allowing the electrospray deposition method to be carried out will be described.

<Electrospray Deposition Device>

[0044] FIG. 1 is a conceptual diagram representing a basic configuration of an electrospray deposition device. As shown in the drawing, a container (CNT) contains a sample solution (SL). The sample solution (SL) is, for example, an organic polymer solution, a polymer solution, or the like. In the present embodiment, the sample solution is a polyhydroxyalkanoic acid solution, that is, a polyhydroxyalkanoic acid solution.

[0045] Although the ESD method is a very complicated physical phenomenon and all of the processes are not explained, the ESD method is generally considered as being the following phenomenon. The sample solution is contained in a thin capillary shaped nozzle (NZL), and voltage of thousands to tens of thousands of volts is applied to a target substrate (TS) (counter electrode) opposing thereto. At a capillary tip, a strong electric field occurs by an electric field concentration effect, and microdroplets with charge on a liquid surface gather to form a cone (also called Taylor cone). In addition, the sample solution from the tip destroys surface tension to become a jet. The jet is strongly charged and becomes spray by a repulsion of electrostatic force (coulomb explosion). The droplets formed by spray are very small so that the solvent is evaporated and dried within a short time to become fine nanoparticles or nanofiber. Of course, the solvent may be deposited in a wet state which is not evaporated or dried. The charged fine nanoparticles or nanofiber having a small diameter is pulled to the target substrate (TS) functioning as a counter electrode by electrostatic force. A pattern to be deposited may be controlled by an insulator mask or an auxiliary electrode (not shown). The sample is not limited to a solution, and a dispersion solution is fine.

[0046] In addition, preferably, the sample solution in the container (CNT) applies extrusion pressure toward the nozzle (NZL) by an air pressure syringe pump, plunger, or the like (ejection means, not shown). The extrusion pressure is imparted by for example, a stepping motor and a screw feed mechanism (not shown). The sample solution (SL) to which the extrusion pressure is applied has increased internal pressure in the container (CNT) so as to be discharged from the tip of nozzle (NZL). As described above, by installing an adjustment mechanism (the stepping motor and the screw feed mechanism) adjusting the speed of ejecting the sample solution, it is possible to adjust the ejection speed appropriately.

[0047] The nozzle (NZL) is made of metal, and positive voltage is supplied from a high voltage power supply (HPS) through a conductor wire (WL). The negative side of the high voltage power supply (HPS) is connected to the target substrate (TS) (substrate to be a counter electrode). By applying voltage from the high voltage power supply (HPS), positive voltage is applied via the nozzle (NZL) to the sample solution (SL) so that the solution is positively charged. The polarity of the voltage applied to the sample solution (SL) may be negative.

[0048] In addition, when the nanofiber structure is manufactured, it is preferred that non-woven fabric is placed on the target substrate (TS), and the nanofiber structure is deposited on the non-woven fabric. In addition, various conditions such as voltage level, concentration of the sample solution, the kind of polyhydroxyalkanoic acid as a sample, the kind of solvent, and the like are adjusted to manufacture the nanofiber structure.

[0049] The sprayed material becomes fiber or droplets, and repeats division during scattering by repulsion due to charging to form nanofiber or nanoparticles. Since the sprayed material has a large surface area in a nano size, when the sprayed material comes into contact with the substrate, it is in an almost dried state. The shape or size may be changed depending on the spray conditions, and for example, when a polymer solution is used, thick nanofiber is formed with a high molecular weight and a high concentration, and thin nanofiber or nanoparticles are formed with a low molecular weight and a low concentration. Besides, various conditions such as voltage or a distance between the nozzle and the substrate and ambient temperature or humidity have an influence thereon. In the present embodiment, various kinds of solvent-soluble polyhydroxyalkanoic acid are used as a sample to manufacture nanofiber under various conditions, and confirmation of water repellency, air permeability, hydrophilicity, and the like were carried out by the method described in the Example. As the electrospray deposition device, another type of ESD device as well as the above-described device can be used. In particular, for mass production, a method using air current described in Japanese Patent No. 5491189, developed by the applicants, is preferred.

[0050] In addition, during mass production, a non-woven manufacturing device using a melt blown method is also preferred, in addition to the ESD device.

<Example 1> Nanofiberization by ESD Method

[0051] FIG. 2 is a photograph of a polyhydroxyalkanoic acid nanofiber film (PHA nanofiber structure) manufactured by an ESD device of FIG. 1. As a sample solution, a chloroform solution including 10% by weight of polyhydroxyalkanoic acid (PHA) was used. In the manufacturing process, an ESD device (ES-4000, manufactured by HUENS Co., LTD.) was used to spray the solution at voltage of 50 kV and a flow rate of 10 l/min. A thickness of nanofiber film shown in the drawing was 20 m. This nanofiber film is very thin, is a free-standing film in spite of the small fiber diameter, may be deposited on other non-woven fabric or film or incorporated into another member or instrument, and is very useful.

[0052] FIG. 3 is an electron microscope photograph (SEM photograph) of the PHA nanofiber structure shown in FIG. 2. The magnification of the photograph is 1000 times. In addition, an average diameter of the nanofiber was about 1 m. As shown in the drawing, it is observed that a porous film in which fiber is entangled in a mesh-like pattern is formed, which has high porosity and forms a light structure. The PHA nanofiber structure may be used as a filter using the porous property. The nanofiber diameter, porosity, density, and the like are varied by changing various solution compositions or spray conditions according to the purpose, and are controllable.

<Example 2> Biodegradability

[0053] FIG. 4 is a drawing representing biodegradability of the nanofiber film of Example 1. The biodegradability of the nanofiber film (nanofiber structure) obtained in Example 1 by microorganisms and the like was studied by leaving the nanofiber film in soil. FIG. 4(a) is a photograph immediately after placing the nanofiber film in soil. FIG. 4(b) is a photograph after leaving the nanofiber film in FIG. 4(a) for 12 days as it is. As seen from the comparison of these photographs, the polyhydroxyalkanoic acid nanofiber film degrades quite rapidly in soil. As such, since PHA can be produced by microbial fermentation from a plant raw material of nature, and degraded by microorganisms in soil to be returned to nature, the nanofiber film may be used as a resource which does not increase gas causing global warming and may be permanently used.

<Example 3> Water Repellency

[0054] FIG. 5 is a drawing representing water repellency of the nanofiber film of Example 1. FIG. 5 is a photograph immediately after adding pure water dropwise by a pipette on the nanofiber film obtained in Example 1. The dropped pure water (WD) remained on the film as a droplet, as shown in the photograph. As a result of visually measuring the contact angle, a value of 87.5-130.5 was obtained by measurement with 10 droplets, and the average was 113.7. The nanofiber film had water repellency.

<Example 4> Oil-Water Separability and Oil Absorbency

[0055] FIG. 6 is a drawing representing oil-water separability and oil absorbency of the nanofiber film of Example 1. The nanofiber film obtained in Example 1 was added to a container having a methylene blue solution and salad oil therein by pouring it from the above. FIG. 6(a) is a photograph before the nanofiber film was added to the container. The aqueous methylene blue solution and salad oil are mixed in a separated state. FIG. 6(b) is a photograph 1 minute after the nanofiber film was added to the container. As shown in FIG. 6(b), it is observed that the nanofiber film floated on the aqueous methylene blue solution so that only the salad oil (OL) remained in the nanofiber film. FIG. 6(c) is a photograph 10 minutes after the nanofiber film was added. As shown in the photograph of FIG. 6(c), it is observed that the nanofiber film absorbed only the salad oil within 10 minutes, and absorbed all of the salad oil in the film, at the end. In addition, the nanofiber film did not absorb the aqueous methylene blue solution at all. That is, it was found that polyhydroxyalkanoic acid nanofiber film has a function of separating water and oil simultaneously with a function of selectively absorbing only oil.

<Example 5> Organic Solvent Absorbency

[0056] FIG. 7 is a drawing representing organic solvent absorbency of the nanofiber film of Example 1. FIG. 7(a) is a photograph before the nanofiber film obtained in Example 1 was added to the container having an aqueous methylene blue solution (MB) and hexane (HX). Here, the aqueous methylene blue solution (MB) and hexane (HX) were separated into two layers. FIG. 7(b) is a photograph 10 minutes after the nanofiber film was added to the container. As shown in the photograph of the drawing, it is observed that hexane (HX) was all absorbed in the nanofiber film within 10 minutes. Since the amount of the aqueous methylene blue solution (MB) was not changed, it was found that the nanofiber film selectively absorbed only hexane of the organic solvent and did not absorb water. That is, it was found that the nanofiber film represents excellent organic solvent absorbency.

<Example 6> Nanofiber Film (Nanofiber Structure) Partially Having a Film Shape

[0057] FIG. 8 is an electron microscope photograph (SEM photograph) of the nanofiber film (nanofiber structure) in which the nanofiber film is partially fused to have a film shape. As shown in the drawing, it is observed that there is a film shape in the front side and a nanofiber film in the inside. This film shaped part is useful for improving strength of the film itself.

<Example 7> Adsorbent Material-Containing Nanofiber Film

[0058] FIG. 9 is an electron microscope photograph (SEM photograph) of the nanofiber film including fine particles as an adsorbent material. As shown in the drawing, it is observed that activated carbon fine particles AC1 and AC2 as the adsorbent material are entangled with the nanofiber FBR1 and FBR2 and maintained. In addition, the activated carbon fine particles may be in the nanofiber or on the surface of the nanofiber. The adsorbent material effectively absorbs the components dissolved in the organic solvent (impurities or components to be separated) passing between the nanofiber films. As an adsorbent, for example, activated carbon, zeolite, or the like can be selected depending on the use.

[0059] Finally, the advantages of the nanofiber film (nanofiber structure and the like) according to each Example of the present invention are indicated. Biodegradable polyhydroxyalkanoic acid (PHA) which is a raw material of the nanofiber film can be produced using a plant component of nature as a raw material. It is possible to suppress an increase in carbon dioxide gas by using the biodegradable polyhydroxyalkanoic acid to manufacture the nanofiber structure and widely use it for a non-woven fabric.

[0060] The polypropylene non-woven fabric which is the conventional product is flexible and strong and has good adhesion with other materials, and thus, has been used for various uses. In particular, the polypropylene non-woven fabric has been used as an oil adsorbent material since the polypropylene non-woven fabric absorbs oil. It was found by an experiment that the polyhydroxyalkanoic acid or polyhydroxybutyric acid which is a material of the nanofiber structure according to an exemplary embodiment of the present invention absorbs an organic solvent and toxic organic compounds soluble in the solvent as well as oil.

[0061] For example, when ocean, river, lake, groundwater, or the like contaminated with an organic solvent and an organic compound dissolved in the organic solvent was passed through the nanofiber structure according to an exemplary embodiment of the present invention, using these characteristics, contaminated goods can be filtered and absorbed to make clean water.

[0062] As described above, the nanofiber structure (nanofiber film) according to the present invention is expected to be used for various purposes mainly as a non-woven fabric.

REFERENCE SIGNS LIST

[0063] CNT: Container [0064] HPS: High voltage power supply [0065] NZL: Nozzle [0066] SL: Sample solution [0067] TS: Target substrate [0068] ESD: Electrospray deposition device [0069] WL: Wire