JP2012075995A - Nanofiber-reinforced protein porous film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filtration film having high liquid passing property and high film strength, and a method for manufacturing the filtration film.SOLUTION: A porous film contains cationic polymer nanofiber with an average fiber diameter of 100 nm or less, and protein, wherein the protein is crosslinked.

Description

  The present invention relates to a protein porous membrane reinforced with nanofibers and a method for producing the same.

  Conventionally, many filtration membranes for water purification have been developed, such as an ultrafiltration membrane capable of removing particles having a particle diameter of 2 to 100 nm and a microfiltration membrane capable of removing particles of 100 to 1000 nm. In general, the water quality of the filtrate of the filtration membrane is better as the pore size of the filtration membrane is smaller.

  However, if the pore size of the filtration membrane is small, it is necessary to apply high pressure to allow the filtration membrane to flow at a constant flow rate, which increases equipment costs and running costs, and incorporates power to apply filtration pressure. For this reason, there is a problem that the apparatus is enlarged.

  As means for solving these problems, a method of obtaining a self-supporting thin film of pure protein by thinning a protein such as ferritin to a thickness of 10 nm to 10 μm and cross-linking each other is disclosed (for example, see Patent Document 1). .

The thin film described in Patent Document 1 has a high Young's modulus of 4 GPa or more, and has a high liquid permeability of a flow rate of 5000 L · m ⁻² · h ⁻¹ under a pressure of 90 kPa when the thickness is 60 nm. Therefore, there is no need to apply high pressure.

JP 2009-131725 A

  However, the thin film of Patent Document 1 has a film strength that is not so high, and the use of the thin film may be limited particularly in applications where pressure is applied.

  Moreover, when manufacturing the thin film of patent document 1, it is necessary to make the metal hydroxide nanostrand by keeping the dilute liquid of a certain kind of metal nitrate or hydrochloride at neutral or weak basic pH. For this reason, there are drawbacks such as limiting the production rate by using the dilute solution and inability to purify the membrane if pH adjustment is inappropriate.

  Accordingly, an object of the present invention is to provide a filtration membrane having high liquid permeability and high membrane strength and a method for producing the same.

  As a result of searching for various substances from the above viewpoints, the present inventors have reinforced the protein membrane using polymer nanofibers having a large amount of cationic charges on the surface, particularly chitin nanofibers. As a result, the present invention has been completed.

  That is, the present invention relates to the following.

1. A porous membrane comprising a cationic polymer nanofiber having an average fiber diameter of 100 nm or less and a protein, wherein the protein is crosslinked.
2. 2. The porous membrane according to item 1, wherein the cationic polymer nanofiber is a polysaccharide nanofiber and the protein is a globular protein.
3. 3. The porous membrane according to item 2, wherein the polysaccharide nanofiber is chitin nanofiber and the globular protein is ferritin.
4). 4. The porous membrane according to any one of items 1 to 3, wherein the cationic polymer nanofiber and the protein are crosslinked.
5. 5. The porous membrane according to any one of 1 to 4 above, wherein the mass ratio of the cationic polymer nanofiber to the protein is 1: 9 to 9: 1.
6). 6. The porous membrane according to any one of items 1 to 5, which is a material for a separation membrane.
7). The manufacturing method of the porous film containing the cationic polymer nanofiber with an average fiber diameter of 100 nm or less and protein including the following processes (1)-(3).
(1) Adsorption step of stirring a mixed suspension of cationic polymer nanofibers and proteins having an average fiber diameter of 100 nm or less and adsorbing the protein to the cationic polymer nanofibers (2) The mixed suspension 7. Filtering step of filtering on a porous support (3) Crosslinking step of cross-linking proteins in the filtered product filtered on the porous support 8. The production method according to item 7, wherein in step (3), the cationic polymer nanofiber and the protein are further crosslinked.

  Since the porous membrane of the present invention has high liquid permeability and high membrane strength, it is excellent as a filtration membrane for water and the like.

It is a schematic diagram of the porous film of this invention. It is a scanning electron microscope (SEM) photograph of the surface of the film | membrane (Example 1) which mixed and crosslinked chitin nanofiber and ferritin. The magnification is 10,000 times. It is a transmission electron microscope (TEM) photograph in a state where ferritin is adsorbed to chitin nanofibers. Black grains are ferritin. The magnification is 50,000 times.

  Hereinafter, the present invention will be specifically described.

  The porous membrane of the present invention contains a cationic polymer nanofiber having an average fiber diameter of 100 nm or less and a protein, and the protein is crosslinked.

(Cationic polymer nanofiber)
The cationic polymer nanofiber used in the present invention has an average fiber diameter of 100 nm or less, preferably 50 nm or less, and more preferably 20 nm or less. Moreover, it is preferable that it is 5 nm or more. The average fiber diameter of the cationic polymer nanofiber can be measured by an electron microscope by the method described later in Examples.

  By making the average fiber diameter of the cationic polymer nanofibers 100 nm or less, it becomes easy to form a homogeneous and dense film. Moreover, by setting it as 5 nm or more, a cationic polymer nanofiber can be obtained cheaply and easily.

  The cationic polymer nanofiber is not particularly limited as long as it has a cationic charge on the surface and does not interfere with the effect of the present invention. Among the fibers, those hardly soluble or insoluble in water are more preferable.

  Examples of the polysaccharide nanofiber include chitin nanofiber, chitosan nanofiber, and cellulose nanofiber chemically modified with a cation. Moreover, it is more preferable if it is a polysaccharide nanofiber which can be crosslinked with a protein using a crosslinking agent or the like. These polysaccharide nanofibers may be used alone or in combination of two or more.

  If the amount of cationic charge on the surface of the cationic polymer nanofiber is low, the cationic polymer nanofiber and protein are sufficient because they aggregate without being uniformly dispersed in water or the protein adsorption is insufficient. Difficult to be mixed. Accordingly, chitin nanofibers are particularly preferred because of the extremely high amount of cationic charge on the surface among the polysaccharide nanofibers. In addition, chitin nanofibers are also included in large amounts in shells such as crabs and shrimps, and thus have the advantage of being easy to prepare.

  Chitin includes alpha chitin produced by crabs and beta chitin produced by squid. Beta chitin is different from alpha chitin in that it is more soluble in formic acid and the like, but both can be used as long as the effects of the present invention are not impaired. In general, alpha chitin is preferred in terms of strength and chemical resistance.

  As chitin nanofibers, chitin nanofibers obtained by the method described later can be preferably used, and modified chitin nanofibers with a further increased cationic charge amount can be more preferably used.

(Method for producing cationic polymer nanofiber)
The method for producing the cationic polymer nanofiber is not particularly limited. Cationic polymer nanofibers can be extracted from living organisms containing them, and polymers obtained by synthesis or semi-synthesis can be processed into nanofibers.

  When processing synthetic or semi-synthetic polymers into nanofibers, cationic polymers can be used, or non-cationic polymers can be used to cationize after processing into nanofibers. May be used.

  Examples of the method for producing the cationic polymer nanofiber include a method of obtaining chitin nanofiber from a living organism.

  Chitin is a biopolymer contained in shells of crustaceans such as crabs and shrimps, and has a diameter of about 10 nm and a length of several mm. Chitin is a strong three-dimensional structure like a crustacean shell because it binds strongly and complexly with protein and minerals as binding components in vivo.

  Crustacean shells are milled, mixed with alkali, thoroughly stirred and washed, as listed in Biomacromolecules 2009, 10, 1584-1588, then mixed with acid and stirred well, By washing, protein and mineral salts such as calcium carbonate are removed, and a pure chitin nanofiber suspension can be obtained.

Specific examples of the method for obtaining chitin nanofibers include a method including the following steps (i) and (ii).
(I) A chitin dispersion in which chitin powder is dispersed is prepared. The chitin dispersion can be prepared by mixing with water so that the concentration of chitin powder is 1% by mass and the concentration of acetic acid is 0.5% by mass. As the chitin powder, not only purified α-chitin powder sold as a reagent but also chitin powder produced from natural crab shells may be used.

  Specific examples of the method for producing chitin powder from natural crab shells include the following methods. First, the crab shell is pulverized with a grinder, and the crushed crab shell is refluxed in a 5 mass% aqueous potassium hydroxide solution for 6 hours. The aqueous potassium hydroxide solution is separated into a filtrate and a filtered product, and the filtered product is washed with pure water and immersed in an aqueous 7% by mass hydrochloric acid solution for 2 days. The aqueous hydrochloric acid solution is separated into a filtrate and a filtered product, and the filtered product is washed with pure water and refluxed in a 5% by mass aqueous potassium hydroxide solution for 2 days. The aqueous potassium hydroxide solution is separated into a filtrate and a filtered product, the filtered product is washed with pure water, and the filtered product is immersed in a 1.7% by mass sodium hypochlorite aqueous solution at 80 ° C. for 6 hours. The obtained suspension is filtered into a filtrate and a filtered product, and the filtered product is washed with pure water and dried to obtain chitin powder from natural crab shells. The filtered product refers to an insoluble material obtained after filtering.

(Ii) After stirring the chitin dispersion obtained in step (i), chitin nanofibers can be obtained by grinding and defibrating chitin. The temperature during stirring is preferably room temperature to 40 ° C. Chitin can be defibrated using a commercially available stone mill grinder (for example, Supermass colloider, manufactured by Masuko Sangyo). The grinding wheel is preferably rotated at 1000 to 1500 rpm during grinding, and the number of grinding is preferably 1 to 3 times. The temperature during grinding is preferably room temperature to 60 ° C.

  In addition, there is a method in which chitin, chitosan or the like is dissolved in a suitable solvent to form a fiber by electrospinning. Nanofibers made by this method can also be used in the present invention. However, when the electrospinning method is used, the fiber strength is low, and it is difficult to reduce the fiber diameter to 100 nm or less, or mass production is difficult. Is excellent.

(protein)
The protein used in the present invention is preferably a globular protein. By using globular protein, it becomes easy to make a homogeneous film. In addition, globular proteins tend to be regularly packed when they are filtered out in the subsequent process due to their geometric structure, and a certain gap is formed between the filled proteins, and the gap is formed after cross-linking of proteins. Since it functions as a pore of the porous film, it is excellent as a porous film. The globular protein has a shape close to a sphere and is dispersed in a colloidal form in water.

  The protein size is preferably 2 to 200 nm in diameter, and more preferably 5 to 100 nm in diameter.

  By setting the diameter of the protein to 2 nm or more, a sufficient gap between the proteins can be secured when crosslinked, and the liquid permeability can be improved.

  In addition, by setting the protein diameter to 200 nm or less, it becomes easy to form a porous membrane later, and further, when crosslinked, the gap between proteins is prevented from becoming too wide, and a porous membrane excellent in particle collection performance is obtained. Obtainable.

  In addition, the protein is preferably a hydrophilic protein having the ability to uniformly disperse in water. By uniformly dispersing in water, when a film is formed later, the possibility of an extremely large lump is reduced, and a porous film having a uniform thickness over the area can be obtained.

  However, even non-hydrophilic proteins can be used as long as they can be dispersed almost uniformly in water by adding an appropriate dispersant or the like.

  In addition, an anionic protein is preferable because a protein that is easily adsorbed to the cationic polymer nanofiber is preferable.

  Examples of the protein used in the present invention include anionic proteins such as ferritin, apoferritin, cytochrome c, myoglobin, and glucose oxidase. Among them, ferritin is preferable because it is abundant in the living body and can obtain a large amount of globular proteins having a uniform size in diameter at low cost.

  In addition, even if it is not a protein existing in nature, a protein semi-synthesized using an existing protein or amino acid or a protein synthesized by a genetically modified organism can be used as long as it has the above characteristics.

  A protein may be used by 1 type and may be used in combination of 2 or more type.

(Porous membrane)
As shown in FIG. 1, the porous membrane of the present invention preferably has a structure in which cationic polymer nanofibers and proteins are mixed in a substantially homogeneous state and are crosslinked with each other. Here, the term “cross-linking” refers to cross-linking between proteins and cross-linking between cationic polymer nanofibers and protein, and may include cross-linking between cationic polymer nanofibers.

  Although the membrane strength of a thin film in which only protein is crosslinked does not generally exceed the crosslinking strength between proteins, the porous membrane of the present invention contains cationic polymer nanofibers in addition to protein, so the strength of the fiber When added, the film strength is high.

  The membrane strength of the porous membrane of the present invention is not particularly limited, but when alpha chitin nanofiber is used for the cationic polymer nanofiber and ferritin is used for the protein, it is preferably 50 kPa or more. The film strength can be measured by the method described later in Examples.

  The mixing ratio of the cationic polymer nanofiber and the protein in the porous membrane of the present invention is preferably 1: 9 to 9: 1 by mass ratio, more preferably 2: 8 to 8: 2.

  By setting the mixing ratio of the cationic polymer nanofibers to be equal to or higher than the lower limit, the strength of the obtained porous film is improved and can be used for various applications. In addition, it becomes easy to make the thickness of the membrane uniform when forming a porous membrane, and it is possible to prevent pinholes and cracks from being generated in the membrane and to make the filtration performance uniform.

  By setting the mixing ratio of the cationic polymer nanofibers to the upper limit or less, it becomes easy to form the membrane densely, it becomes easy to make the pores small and the crosslinking is sufficient, and the strength of the membrane is improved. be able to.

  In addition, it is also possible to add an arbitrary component to the mixed suspension of the cationic polymer nanofiber and the protein as long as the effect of the present invention is not hindered. Examples of the optional component include another nanofiber, a dye, a surfactant, and a pH adjuster for further increasing the film strength.

  In the case of adding a surfactant and a pH adjuster such as those that have the effect of reducing the protein adsorptive power of the cationic polymer nanofiber, it is necessary to sufficiently adjust the addition amount.

  The content of the optional component in the porous membrane of the present invention is usually preferably 50% by mass or less, and more preferably 10% by mass or less. For example, when a dye is used as an optional component, an effect of improving the appearance of the porous film can be expected.

  The optimum film thickness range of the porous membrane of the present invention varies depending on the types of cationic polymer nanofibers and proteins used, and the mixing ratio thereof. In general, it is preferably larger than the cationic polymer nanofiber used, larger than twice the diameter or thickness of the protein used, and smaller than 100 times the diameter or thickness of the protein used.

  For example, since chitin nanofibers collected from crab shells have a fiber diameter of about 10 nm and ferritin has a diameter of about 12 nm, the thickness is preferably in the range of 24-1200 nm as long as the porous film is a mixture of both.

  By setting the film thickness of the porous film to the above lower limit or more, the structure of the gap between proteins can be prevented from becoming indefinite, stable filtration performance can be obtained, and film formation is easy. Moreover, the pressure loss of a film | membrane can be suppressed and liquid permeability can be improved by making the film thickness of a porous film below the said upper limit.

  In addition, the lower limit value and the upper limit value of the film thickness are only for porous membranes containing cationic polymer nanofibers and proteins.

  The porous film of the present invention can be laminated with an appropriate support, for example, another film or molded body having a coarse mesh, as long as the effects of the present invention are not hindered. It is safe to exceed the upper limit of this range.

  The porosity of the porous membrane of the present invention is not particularly limited, but when alpha chitin nanofibers are used for the cationic polymer nanofibers and ferritin is used for the proteins, it is preferably 40 to 98%, It is preferable that it is 60 to 90%.

(Production method)
The porous film of the present invention is obtained by a production method including the following steps (1) to (3).
(1) Adsorption step of stirring a mixed suspension of cationic polymer nanofibers and proteins having an average fiber diameter of 100 nm or less and adsorbing the protein to the cationic polymer nanofibers (2) The mixed suspension Filtering step of filtering on a porous support (3) Crosslinking step of cross-linking proteins in the filtered product filtered on the porous support Hereinafter, each step will be described separately.

(1) Adsorption step of stirring a mixed suspension of cationic polymer nanofibers having an average fiber diameter of 100 nm or less and protein, and adsorbing the protein to the cationic polymer nanofiber In step (1), first, a cation A cationic polymer nanofiber suspension is prepared by suspending the cationic polymer nanofiber in water. The content of the cationic polymer nanofiber in the suspension of the cationic polymer nanofiber is preferably 0.001 to 1% by mass, and more preferably 0.003 to 5% by mass.

  By setting the concentration to 1% by mass or less, it is possible to prevent the influence of a slight liquid amount error from increasing and to easily form a uniform film. In addition, by setting the concentration to 0.001% by mass or more, it is possible to suppress the amount of liquid to be filtered and to eliminate waste in processes such as time and materials.

  Next, a protein suspension is prepared by suspending the protein in water. The protein concentration in the protein suspension is preferably 0.001 to 5% by mass, and more preferably 0.005 to 1% by mass.

  Furthermore, the cationic polymer nanofiber suspension and the protein suspension are mixed and sufficiently stirred. The mixing ratio of the cationic polymer nanofiber suspension and the protein suspension is adjusted to be within the range of the mixing ratio of the cationic polymer nanofiber and the protein described above.

  Stirring is continued until the protein is sufficiently adsorbed to the cationic polymer nanofibers. Whether or not the cationic polymer nanofiber and the protein are adsorbed can be confirmed with a transmission electron microscope or the like.

  The stirring time depends on the combination of cationic polymer nanofiber and protein, but when alpha chitin nanofiber is used for cationic polymer nanofiber and ferritin is used for protein, 15 minutes or more is appropriate. It is.

  The upper limit of the stirring time is not particularly specified, and when alpha chitin nanofibers are used for the cationic polymer nanofibers and ferritin is used for the proteins, the difference between the mixing time and the time immediately after mixing is almost 30 days. It has been confirmed that this is not possible. When the stirring is stopped, the cationic polymer nanofibers adsorbed with the protein may precipitate, but can be used without problems if stirred again.

  The stirring speed is usually preferably 50 to 500 rpm, and more preferably 200 to 400 rpm. Moreover, it is preferable that the temperature at the time of stirring shall be 5-40 degreeC.

(2) Filtering step of filtering mixed suspension on porous support In step (2), the mixed suspension of cationic polymer nanofibers and protein is filtered on the porous support. . The porous support used in the step (2) can be used as it is as a support for a porous membrane later, or can be used as a self-supporting membrane by peeling the porous membrane from the porous support, depending on the purpose. Should be considered.

  When the porous film is peeled off from the porous support later, the porous support preferably has a smooth surface. For example, as the porous support, a polycarbonate membrane having a cylindrical hole in the film is preferable.

  Even when the porous film is not peeled off from the porous support later, it is preferable that the surface of the porous support is smooth in order to form a uniform porous film.

  In the case where the porous membrane is not peeled off from the porous support later, a material that can crosslink with at least one of the cationic polymer nanofiber and the protein is more preferable because unexpected peeling during use is reduced. Examples of the material capable of crosslinking with at least one of the cationic polymer nanofiber and the protein include a thin film made of chitin nanofiber alone, a woven fabric of a fiber containing a protein such as silk, a nonwoven fabric, and paper.

  The porosity of the porous support is not particularly defined, but is preferably 2 to 90%, more preferably 5 to 80% with respect to the effective filtration area. By setting the open area ratio to 90% or less, the contact points with the cationic polymer nanofibers and the protein can be sufficiently secured, the crosslinking is sufficient, and the strength of the porous support is improved. Can do. Moreover, liquid permeability becomes favorable by the said aperture ratio being 2% or more.

  Further, the pore size of the porous support is not particularly limited, but when alpha chitin nanofiber is used for the cationic polymer nanofiber and ferritin is used for the protein, it may be 0.05 to 1.0 μm. Preferably, it is 0.1-0.45 micrometer. By setting the pore diameter to 0.05 μm or more, the filtration time of the mixed suspension of cationic polymer nanofibers and protein can be shortened. By setting the pore diameter to 0.45 μm or less, the cationic polymer nanofibers are sufficiently collected.

(3) Crosslinking step of cross-linking proteins in the filtered product separated on the porous support In the step (3), proteins in the filtered product filtered on the porous support are cross-linked. While cross-linking proteins, it is preferable to cross-link cationic polymer nanofibers and proteins. This is because the film strength of the porous film can be further improved. Moreover, you may bridge | crosslink with cationic polymer nanofibers.

  Proteins can be cross-linked using a cross-linking agent. As the cross-linking agent, a cross-linking agent that cross-links only proteins can be used, but it is more preferable to use a cross-linking agent capable of cross-linking cationic polymer nanofibers and also cationic polymer nanofibers and proteins. .

  Examples of the crosslinking agent include glutaraldehyde, which is a bifunctional crosslinking agent, various imide esters, N-hydroxysuccinimide esters, and carbodiimides. Examples of the imide esters include succinic acid imide esters. Examples of carbodiimides include dicyclohexyl carbodiimide. Although depending on the type of the crosslinking agent, it is preferable to use an aqueous solution of 0.5 to 25% by mass as the crosslinking agent.

  The crosslinking conditions vary depending on the cationic polymer nanofiber used, the type of protein, and the like, and are not particularly limited. Specifically, for example, when alpha chitin nanofiber is used for the cationic polymer nanofiber, ferritin is used for the protein, and glutaraldehyde is used as the crosslinking agent, the concentration is 1 to 10 mass as the crosslinking agent. % Aqueous glutaraldehyde solution is preferably used. The aqueous glutaraldehyde solution can be cross-linked by pouring gently onto the filtered product separated in step (2) and leaving it for 30 minutes to 2 hours. Moreover, it is preferable that the temperature at the time of bridge | crosslinking shall be 5-40 degreeC.

  In addition to the method using a crosslinking agent, for example, thermal crosslinking and gamma ray crosslinking can also be used. If this cross-linking is sufficient, the strength of the membrane will not be lowered, the pore structure of the porous membrane can be maintained, and it can be used favorably as a porous membrane.

  According to the porous film of the present invention, particles having a particle diameter of 1.5 to 20 nm can be collected with high collection efficiency.

  Such a porous membrane of the present invention is most effective when used as a filtration membrane for water. However, the application is not limited thereto, and it can be used as a filter membrane for organic solvents or gases, and a reaction catalyst support.

  Hereinafter, the present invention will be described in more detail with reference to examples and the like, but the scope of the present invention is not limited by these descriptions.

<Materials used>
A 50 mg / mL horse spleen ferritin solution and a gold nanocolloid aqueous solution were purchased from Sigma-Aldrich Japan. The chitin used was purified α-chitin from Nacalai Tesque. Other chemicals purchased from Wako Pure Chemical Industries were used.
As pure water and ultrapure water, purified water produced using “DirectQ UV” (trade name) manufactured by Millipore was used. Ultrapure water has a water quality with a specific resistance value of 18 MΩ · cm or more, and pure water has a specific resistance value of 0.5 MΩ · cm or more and less than 18 MΩ · cm.

<Method for evaluating physical properties>
The physical property values of the porous films obtained in Examples and Comparative Examples were measured by the following methods.

1) Mixing ratio of cationic polymer nanofibers and protein The amount of cationic polymer nanofibers in the suspension is determined by separating the primary suspension into a filtrate and a filtered product, and drying the resulting filtered product. And obtained from the mass. And the quantity of the cationic polymer nanofiber in a porous membrane was calculated | required as that the used material was all contained in the porous membrane.

  The amount of protein contained in the filtrate of the porous membrane production process was determined from the absorbance of light having a wavelength of 520 nm obtained by preparing a calibration curve in advance and using an ultraviolet-visible absorption spectrum apparatus. The amount of protein in the porous membrane was determined to be equal to the amount of protein used minus the amount of protein contained in the filtrate of the porous membrane production process.

  And {amount of protein in porous membrane ÷ (amount of protein in porous membrane + amount of cationic polymer nanofiber)} × 100% was defined as a protein ratio.

2) Particle collection efficiency A gold nanocolloid solution having a particle diameter of 10 nm is passed through the obtained membrane, and the liquid concentration before and after the filtration is obtained from the absorbance of light having a wavelength of 520 nm obtained using an ultraviolet-visible absorption spectrum apparatus. {1- (concentration after filtration) ÷ (concentration before filtration)} × 100% was defined as the particle collection efficiency.

3) Water permeability test The membrane was attached to a stainless syringe holder KS-25 manufactured by Advantech Toyo without peeling from the porous support, and this was attached to a Toyo Seiki strograph, and the membrane surface was ultrapure water at a pressure of 0.03 MPa. The pressure was increased and the flow rate of the water coming out was determined.

  Further, in the same manner, the flow rate of water for the KS-25 alone without the membrane was separately obtained, and the value obtained by subtracting the flow rate of the KS-25 alone from the flow rate when the membrane was attached was taken as the membrane flow rate. The values were converted per unit area and unit time, and the sizes were compared.

4) Membrane strength test The obtained porous membrane was carefully peeled from the porous support, the end of a plastic tube having an inner diameter of 5 mm and an outer diameter of 7 mm was closed with the porous membrane, and the inner diameter was 7 mm and the outer diameter was Was connected to another 10 mm plastic tube, and then ultrapure water was carefully poured into a plastic tube having an inner diameter of 7 mm and an outer diameter of 10 mm.

  Further, a plastic tube having an inner diameter of 7 mm and an outer diameter of 10 mm is gradually pressurized with nitrogen gas, the pressure at the time when the membrane is broken is read, and the pressure at which the membrane is broken is obtained from the total of the pressure and the height of the water column, The size was compared.

<Example 1>
[Manufacture of raw material liquid]
Dry chitin powder (product code 07946-62) derived from crab shell manufactured by Nacalai Tesque was used as a raw material for the cationic polymer nanofiber, and ferritin was used as a protein.

  20 g of chitin powder was dispersed in 2 liters of pure water, and 10 g of acetic acid was further added, followed by stirring for 1 hour. The obtained dispersion was pulverized with a stone mill (“Supermass colloider” (trade name) manufactured by Masuko Sangyo), and chitin nanofiber primary suspension was obtained by defibrating the chitin in the dispersion. . In addition, the rotation speed of the grindstone at the time of defibration was set to 1500 rpm.

  The chitin after defibration was observed with a field emission electron microscope, and the diameters of 50 fibers selected at random were determined, and it was found that the minimum and maximum fiber diameters were in the range of 10 to 20 nm. It was. It was also found to be a uniform and high aspect ratio nanofiber. The primary suspension was diluted with pure water to obtain a chitin nanofiber diluted suspension having a chitin concentration of 0.05 mg / mL.

  1 mL of an aqueous ferritin solution adjusted to a concentration of 5 mg / mL was added to 50 mL of the diluted chitin nanofiber suspension, and stirred sufficiently to obtain a porous membrane raw material liquid. The mixing ratio of chitin and ferritin was calculated from each dry mass contained in the liquid.

[Porous membrane production]
A porous polycarbonate membrane having a pore diameter of 0.2 μm (a polycarbonate type membrane filter manufactured by Advantech Toyo Co., Ltd.) was used as the porous support. 3 mL of the porous membrane raw material solution was passed through a porous support having an effective filtration area of 9.6 cm ² , and the filtered product was immersed in an aqueous glutaraldehyde solution having a concentration of 10% by mass together with the porous support for 1 hour at room temperature (25 ° C.). The mixture was cross-linked by allowing to stand to obtain a mixed porous membrane of chitin nanofibers and ferritin. Table 1 shows the physical property values of the obtained porous film.

<Example 2>
In the porous membrane production process, all the membranes were formed in the same manner as in Example 1 except that the porous membrane material solution was changed from 3 mL to 6 mL. Table 1 shows the physical property values of the obtained porous film.

<Example 3>
In the manufacturing process of the porous membrane raw material liquid, all the films were formed in the same manner as in Example 1 except that the concentration of the ferritin aqueous solution was changed from 5 mg / mL to 10 mg / mL. In this method, some ferritin that flowed out to the filtrate side without being collected in the polycarbonate porous flat membrane was observed in the porous membrane production process, but the membrane itself could be produced without any problem. Table 1 shows the physical property values of the obtained porous film.

<Example 4>
Films were formed in the same manner as in Example 1 except that the concentration of the chitin nanofiber diluted suspension was changed from 0.005% by mass to 0.001% by mass in the manufacturing process of the porous membrane raw material liquid. Table 1 shows the physical property values of the obtained porous film.

<Comparative Example 1>
Film formation was attempted in the same manner as in Example 1 except that 50 mL of ultrapure water was used instead of 50 mL of the suspension having a chitin concentration of 0.005% by mass. However, ferritin was not filtered off on the polycarbonate porous flat membrane at all, and all flowed out as a filtrate, and it was not possible to form a membrane.

<Comparative example 2>
Instead of chitin nanofibers, film formation was attempted in the same manner as in Example 1 except that nanofibers made of purified cellulose ("Theolas (registered trademark)" PH101 manufactured by Asahi Kasei Chemicals Corporation) were used. However, nanofibers made of purified cellulose were filtered out on the polycarbonate porous membrane, and ferritin was not filtered out but flowed out to the filtrate side, and it was not possible to form a membrane in which ferritin was crosslinked. .

<Comparative Example 3>
Film formation was attempted in the same manner as in Example 1 except that ultrapure water was used instead of the ferritin aqueous solution. The chitin filtered off on the polycarbonate porous membrane was in the form of a sheet. Table 1 shows the physical property values of the obtained porous film.

<Comparative example 4>
Example 1 except that cadmium hydroxide nanofibers obtained by mixing an aqueous solution of cadmium chloride with a concentration of 4 mmol / L and an aqueous solution of 2-aminoethanol with a concentration of 0.6 mmol / L were used instead of chitin nanofibers. A film was formed by the same method. After film formation, the cadmium hydroxide nanofibers were removed by washing with 10 ml of diluted hydrochloric acid having a concentration of 0.01 mol / L. The physical properties of the obtained film are shown in Table 1.

<Comparative Example 5>
Film formation was attempted in the same manner as in Example 1 except that the step of immersing in a 10% strength by weight glutaraldehyde aqueous solution and omitting it for 1 hour was omitted. However, the filtered product was simply a lump of fibrous material. Therefore, even if an attempt was made to peel off the filtered product from the porous support for the film strength test, no film was formed and it was impossible to peel off as a self-supporting film.
From the above results, it was determined that the protein was cross-linked by forming a film in the examples and comparative examples.

  As shown in Table 1, Examples 1-4 which are porous membranes of the present invention show a high flow rate and membrane strength, and show a trapping effect of 65% or more for gold nanocolloid with a particle diameter of 10 nm, It was found that it can be used as a filtration membrane for the particles.

  From the results of Example 1 and Example 2, it was found that the membrane strength was improved by increasing the amount of nanofibers in the porous membrane. Moreover, from the results of Example 1 and Example 3, it was found that the membrane strength was improved by increasing the protein content ratio in the porous membrane.

  Furthermore, from the results of Example 4, it was found that even when the amount of nanofibers and protein in the porous film was reduced and the film thickness of the porous film was reduced, a particle capturing effect of a certain level or more was obtained.

  On the other hand, Comparative Example 3 in which cationic polymer nanofibers were formed using ultrapure water instead of protein hardly collects gold nanocolloids having a particle diameter of 10 nm, and is hardly used as a filtration membrane for the particles. It was not effective.

  In Comparative Example 4 using cadmium hydroxide nanofibers instead of cationic polymer nanofibers, the particle collection efficiency and water permeability were almost the same as in Example 1, but the film strength was greatly inferior. .

11 Cationic polymer nanofiber 12 Protein

Claims (8)

  A porous membrane comprising a cationic polymer nanofiber having an average fiber diameter of 100 nm or less and a protein, wherein the protein is crosslinked.   The porous membrane according to claim 1, wherein the cationic polymer nanofiber is a polysaccharide nanofiber, and the protein is a globular protein.   The porous membrane according to claim 2, wherein the polysaccharide nanofiber is chitin nanofiber and the globular protein is ferritin.   The porous membrane according to any one of claims 1 to 3, wherein the cationic polymer nanofiber and the protein are crosslinked.   The porous membrane according to any one of claims 1 to 4, wherein a mass ratio of the cationic polymer nanofiber to the protein is 1: 9 to 9: 1.   The porous membrane according to any one of claims 1 to 5, wherein the porous membrane is a material for a separation membrane. The manufacturing method of the porous film containing the cationic polymer nanofiber with an average fiber diameter of 100 nm or less and protein including the following processes (1)-(3).
(1) Adsorption step of stirring a mixed suspension of cationic polymer nanofibers and proteins having an average fiber diameter of 100 nm or less and adsorbing the protein to the cationic polymer nanofibers (2) The mixed suspension Filtering step of filtering on a porous support (3) Crosslinking step of cross-linking proteins in the filtered product filtered on the porous support   The production method according to claim 7, wherein in step (3), the cationic polymer nanofiber and the protein are further crosslinked.