JP5713395B2 - Hydrogel cellulose porous membrane - Google Patents

Description

  The present invention relates to a multi-layered hydrogel cellulose porous membrane in which fibrillar cellulose is laminated and a method for producing the same.

  Conventionally, reverse osmosis membranes having fine pores with a pore size of about 0.1 to 1 nm or ultrafiltration membranes with relatively large pores with a pore size of about 1 nm to 100 nm have been used as porous membranes for liquids. . Among them, porous membranes made of organic materials such as polymers are used in many applications because they have a smaller mass per filtration area and higher flexibility than porous membranes made of inorganic materials such as zeolite.

  In general, the smaller the pore size of the porous membrane, the smaller the amount of foreign matter contained in the filtrate. On the other hand, the smaller the pore size, the higher the pressure loss of the porous membrane or the shorter the filtration life. Therefore, in practice, it is desirable to determine the minimum particle size of the foreign matter that needs to be collected and to use a porous membrane having a pore size corresponding to the particle size.

  However, in the case of a porous film made of a polymer, the polymer is polymerized on a porous film having a pore diameter exceeding 50 nm made by utilizing a crack formed by stretching and a gap between polymer crystals, and a porous support. Most of the porous thin films having a pore diameter of less than 1 nm made in this way, and having a pore diameter of about 1 to 50 nm located between them, were very few in terms of practicality. In particular, there were almost no porous membranes capable of collecting 70% or more of particles having a particle size of 5 nm.

  On the other hand, in recent years, since the precision of fine patterns formed on the surface of semiconductors is required on the order of several tens of nanometers, porous membranes for removing relatively large molecules such as agricultural chemicals contained in water are required. Yes. As the pore diameter of the porous membrane, the demand for pore diameters of 1 to 50 nm, particularly 1 to 20 nm, is increasing rapidly.

  Therefore, production of a porous film having a pore diameter of 1 to 50 nm has been attempted by precisely controlling the production conditions of the conventional production method (for example, see Patent Document 1).

  However, since many of them are inorganic films, they lack flexibility. As for membranes made of highly flexible polymers, all of them are 1) excessive pressure loss due to low porosity, 2) insufficient strength, or 3) extremely few millimeters square There is a problem in terms of manufacturing method and filtration performance in practical use such that only a membrane with a very small area can be produced. Further, these porous membranes are likely to be clogged, so that the filtration life is short, and this is also a big problem in practical use.

  As a method of obtaining a highly flexible porous membrane, a method of forming nanofibers into a sheet is known. For example, plants and the like contain nanofibers having a fiber diameter of about several nanometers made by biological activity, and a porous membrane is produced by extracting nanofibers from plants and forming them into sheets. be able to. As a method for extracting nanofiber from a plant, a method of chemically decomposing lignin, hemicellulose, and the like that are bonded to each other and treating them with a grinder or the like can be used (see, for example, Patent Documents 2 to 3). .

  When the nanofibers thus obtained are made into a sheet by a method such as papermaking, the obtained sheet has high flexibility, but there is no change in the fiber diameter in the thickness direction. The hole diameter that can be made does not change in the thickness direction and does not vary in the thickness direction. As a result, the pressure loss increases and the flux decreases.

  Moreover, since the fibers are not firmly bonded to each other simply by making paper, the shape of the hole is unstable. However, if the fibers are bonded together with an adhesive or the like, the gap between the fibers is filled and the flux is lowered. For this reason, it has been difficult to make a high-performance porous membrane with a material obtained from the plant-derived nanofibers.

  Conventionally, regenerated cellulose membranes obtained by coagulating a viscose solution have been used for ultrafiltration membranes and dialysis membranes (see, for example, Patent Documents 4 to 5). However, the fiber diameter of the fibrils constituting the cellulose membrane is at most several hundred nm, and the variation is large. Therefore, it is difficult to make the pore diameter less than 100 nm, and only those having a large variation in pore diameter were obtained. Therefore, it was not possible to obtain a porous material having a small variation in pore diameter in the range of 1 to 50 nm.

Japanese Patent Laying-Open No. 2005-305342 JP 2008-75214 A JP 2010-236109 A JP 59-206007 Japanese Patent Laid-Open No. 2-152531

  An object of the present invention is to provide a method for producing a porous membrane that is excellent in liquid permeability and particle collection ability, has a long filtration life, and is excellent in productivity.

  The present inventors dissolved the raw material cellulose in a solvent, then replaced the solvent with a non-solvent, and reprecipitated the cellulose to obtain fibrillar cellulose (cellulose fibrils) having a diameter of several nm, It was found that by laminating the cellulose fibrils, a porous film having a multilayer structure composed of the cellulose fibrils was obtained, and the present invention was completed.

That is, the gist of the present invention is as follows.
1. It is a hydrogel cellulose porous membrane having a multilayer structure in which cellulose fibrils are laminated and having different pore diameters in the thickness direction, an average fiber diameter of cellulose fibrils in at least one layer of the multilayer structure is less than 100 nm, and a gold nanoparticle having a particle diameter of 5 nm Hydrogel cellulose porous membrane capable of collecting 70% or more of colloid and having a surface of the porous membrane having a large pore size having a passing rate of gold nanocolloid having a particle diameter of 20 nm determined by the following measurement method of 70% or more .
(Measurement method) A gold nanocolloid solution in which a gold nanocolloid with a particle size of 50 nm and a gold nanocolloid with a particle size of 20 nm is mixed so that the number of particles is 1:12 is passed through the porous membrane from the surface with the larger pore size. From the number of particles having a particle size of 50 nm and the number of particles having a particle size of 20 nm in the porous film after passing through, the passing rate is obtained by the following formula.
(Formula) (passage rate) = {1− (number of particles with a particle size of 20 nm ÷ number of particles with a particle size of 50 nm) ÷ 12} × 100%
2. 2. The hydrogel cellulose porous membrane according to item 1 above, wherein the cellulose fibrils are amorphous.
3. 3. The hydrogel cellulose porous membrane according to item 1 or 2, wherein the ratio of the average fiber diameter of cellulose fibrils in the layer constituting the surface of the hydrogel cellulose porous membrane and the layer constituting the back surface is 1.2 to 3.
4). A hydrogel cellulose porous membrane obtained by a method comprising the following steps (1) to (3).
(1) Step of preparing cellulose solution by immersing cellulose in solvent (2) Step of applying cellulose solution prepared in step (1) on support (3) Cellulose solution applied in step (2) 4. Step of depositing cellulose in a non-solvent to precipitate cellulose to obtain a hydrogel cellulose porous membrane 5. The hydrogel cellulose porous membrane according to item 4 above, wherein the concentration of cellulose immersed in the solvent in the step (1) is 0.2 to 20% by mass with respect to the cellulose solution.
6). 6. The hydrogel cellulose porous membrane according to item 4 or 5, wherein in the step (1), the solvent contains i) caustic and ii) urea or thiourea.
7). 7. The hydrogel cellulose porous material according to item 5 or 6, wherein in step (1), the concentration of i) caustic alkali in the solvent is 2 to 20% by mass, and ii) the concentration of urea or thiourea is 4 to 20% by mass. film.
8). 8. The hydrogel cellulose porous membrane according to any one of 4 to 7 above, wherein in the step (3), the non-solvent contains one kind selected from lower alkyl alcohol and water and a mixture thereof.
9. 9. The hydrogel cellulose porous membrane according to any one of 4 to 8 above, wherein in step (3), the non-solvent contains i) caustic and ii) urea or thiourea.
10. 10. The hydrogel cellulose porous membrane according to item 9, wherein in step (3), the concentration of i) caustic and ii) urea or thiourea in the non-solvent is 0.5 to 5% by mass.
11. The manufacturing method of the hydrogel cellulose porous membrane containing the following processes (1)-(3).
(1) Step of preparing cellulose solution by immersing cellulose in solvent (2) Step of applying cellulose solution prepared in step (1) on support (3) Cellulose solution applied in step (2) 11. Step of depositing cellulose in a non-solvent to precipitate cellulose to obtain a hydrogel cellulose porous membrane 12. The production method according to 11 above, wherein in step (1), the concentration of cellulose immersed in the solvent is 0.2 to 20% by mass with respect to the cellulose solution.
13. 13. The production method according to item 11 or 12, wherein in step (1), the solvent contains i) caustic and ii) urea or thiourea.
14 14. In the step (1), the concentration of i) caustic alkali in the solvent is 2 to 20% by mass, and ii) the concentration of urea or thiourea is 4 to 20% by mass, Manufacturing method.
15. 15. The production method according to any one of the above items 11 to 14, wherein in the step (3), the non-solvent contains at least one selected from a lower alkyl alcohol and water.
16. 16. The production method according to any one of the above items 11 to 15, wherein in the step (3), the non-solvent contains i) caustic and ii) urea or thiourea.
17. 17. The production method according to item 16 above, wherein in step (3), the concentration of i) caustic and ii) urea or thiourea in the non-solvent is 0.5 to 5% by mass.

  The hydrogel cellulose porous membrane of the present invention has a multilayer structure in which cellulose fibrils are laminated. Cellulose fibrils have an average fiber diameter of less than 100 nm, little variation in pore diameter, and excellent liquid permeability.

  Moreover, the hydrogel cellulose porous membrane of the present invention can collect 70% or more of gold nanocolloid having a particle size of 5 nm. Such filtration performance is very excellent as a liquid filtration membrane.

  Furthermore, the porous hydrogel cellulose membrane of the present invention has different pore sizes in the thickness direction, and the porous membrane as a whole can collect 70% or more of gold nanocolloid having a particle size of 5 nm. The surface has a feature of allowing 70% or more of a gold nanocolloid having a particle diameter of 20 nm to pass through. Therefore, the pore diameter on one surface of the porous membrane is large and the filtration life is excellent.

  Moreover, since the hydrogel cellulose porous membrane of the present invention is hydrogel-like, it is hydrophilic, has excellent water permeability, and does not require hydrophilic treatment.

FIG. 1 is a photograph of a cross section of the hydrogel cellulose porous membrane obtained in Example 7 observed with a scanning electron microscope (SEM). The photographing magnification was 100,000 times. FIG. 2A is a photograph obtained by observing the glass-side surface of the cellulose porous membrane obtained by freeze-drying the hydrogel cellulose porous membrane obtained in Example 2 with an SEM. The photographing magnification was 100,000 times. FIG. 2B is a photograph of the surface of the non-solvent side of the porous cellulose membrane obtained by freeze-drying the hydrogel cellulose porous membrane obtained in Example 2 observed with an SEM. The photographing magnification was 100,000 times. FIG. 3A is a photograph of the surface on the glass side of the hydrogel cellulose porous membrane obtained in Example 4 observed with an SEM. The photographing magnification was 100,000 times. FIG. 3B is a photograph of the surface of the non-solvent side of the hydrogel cellulose porous membrane obtained in Example 4 observed with an SEM. The photographing magnification was 100,000 times. FIG. 4A is a photograph of the surface on the glass side of the hydrogel cellulose porous membrane obtained with the hydrogel of Example 6 observed with an SEM. The photographing magnification was 100,000 times. FIG. 4B is a photograph of the surface of the non-solvent side of the hydrogel cellulose porous membrane obtained with the hydrogel of Example 6 observed with an SEM. The photographing magnification was 100,000 times.

  As shown in FIG. 1, the hydrogel cellulose porous membrane of the present invention (hereinafter also referred to as the porous membrane of the present invention) has a multilayer structure in which fibrillar cellulose (cellulose fibril) is laminated. By having a multilayer structure in which cellulose fibrils are laminated, holes corresponding to the fiber diameter of cellulose fibrils can be formed.

  The number of cellulose fibrils constituting the multilayer structure is preferably 10 or more, more preferably 20 or more. By setting it as this range, it becomes easy to give a hole diameter gradient in the hole diameter and thickness direction.

  The porous membrane of the present invention is in the form of a hydrogel. In the present invention, the hydrogel refers to a gel in which a network structure is formed by connecting cellulose fibrils, and water is held in the gaps of the network structure. In the present invention, most of the hydrogel is water, and the ratio of water to the total mass of the hydrogel is not particularly limited, but is preferably 80 to 99.8% by mass, and 90 to 99.99. More preferably, it is 5 mass%. By setting it as this range, the strength of the obtained porous membrane is increased and at the same time, the water permeability is excellent.

  At least one layer of the porous membrane of the present invention has an average fiber diameter of cellulose fibrils of less than 100 nm, preferably less than 50 nm, and more preferably less than 25 nm. By setting the average fiber diameter of at least one layer of cellulose fibrils within this range, resistance when the fluid passes is reduced, and liquid permeability is improved, which is preferable.

  The average fiber diameter of the cellulose fibril constituting the porous membrane of the present invention can be measured by observing the porous membrane using an electron microscope, as will be described later in Examples.

  In the porous membrane of the present invention, it is preferable that the fiber diameter of the cellulose fibril constituting each layer is changed in the thickness direction. The ratio of the average fiber diameter of the layer constituting the surface of the hydrogel cellulose porous membrane to the average fiber diameter of the cellulose fibrils in the layer constituting the back surface is preferably 1.2 to 3, preferably 1.5 to 3 It is more preferable that

  By setting the ratio of the average fiber diameter of the cellulose fibrils in the layer constituting the surface of the porous membrane and the layer constituting the back surface of the porous membrane within the above range, the depth filtration can be performed while being a nano-sized pore size filtration membrane. It becomes possible.

  The porous membrane of the present invention collects 70% or more of gold nanocolloid having a particle size of 5 nm. Such filtration performance of the porous membrane of the present invention means having pores having a pore diameter of 1 to 20 nm. That is, the porous membrane of the present invention preferably has a pore diameter of 1 to 20 nm. It is very excellent as a liquid filtration membrane.

  The porous membrane of the present invention has different pore diameters in the thickness direction, and has a large number of pores having a pore diameter of 20 nm or more on the surface of the surface having the larger pore diameter. Therefore, 70% or more of gold nanocolloid having a particle diameter of 20 nm is allowed to pass through the surface of the porous film having a larger pore diameter. That is, the passing rate of the gold nanocolloid having a particle diameter of 20 nm on the surface of the porous membrane having the larger pore diameter is 70% or more, preferably 80% or more, and more preferably 90% or more.

  When the passing rate of the gold nanocolloid having a particle size of 20 nm on the surface of the porous membrane of the present invention having a large pore size is less than 70%, most of the particles are collected on the surface of the porous membrane. Life is shortened. Note that the gold nanocolloid having a particle diameter of 20 nm that has passed through the surface of the porous membrane having the larger pore diameter is trapped in the downstream portion of the surface of the porous membrane having the larger pore diameter, and finally 99%. The above is collected.

  In addition, the collection efficiency and passage rate of the gold nanocolloid by the porous membrane of the present invention are measured by the methods described later in the examples.

  As the cellulose used in the porous membrane of the present invention, cellulose containing an amorphous part is more preferable than so-called crystalline cellulose produced by purifying and extracting from cellulose. This is because the strength of the porous membrane can be improved by using cellulose containing an amorphous part.

  Examples of the cellulose containing an amorphous part include plant cellulose such as wood cellulose and cotton cellulose, microbial-produced cellulose, squirt sac cellulose and derivatives thereof, and mixtures thereof.

  Among these, wood cellulose, cotton cellulose, squirt sac cellulose, and a mixture thereof are particularly preferable because the strength of the resulting porous membrane is increased.

  Further, ashless cellulose obtained by removing mineral salts such as calcium ions from plant cellulose such as pulp is more preferable. Insufficient removal of the mineral salt results in a large amount of undissolved residue when cellulose is later dissolved in a solvent, which may cause pinholes in the porous membrane or during use of the porous membrane. May dissolve in the filtrate and the porous membrane itself may become a source of contamination.

  In the porous membrane of the present invention, various cellulose derivatives can be used as cellulose, and cellulose derivatives obtained by esterifying and / or etherifying a hydroxyl group of cellulose are preferable. The degree of substitution for esterifying and / or etherifying the hydroxyl group of cellulose is preferably 1.0 or less, and more preferably 0.1 to 0.8.

Flux of the porous membrane of the present invention is preferably 20~150L / ^{m 2} / time, and more preferably 30~150L / ^{m 2} / hour. This range is preferable because a high flow rate can be obtained even in a small area while maintaining the required strength. The flux of the porous membrane is measured by the method described later in the examples.

  The thickness of the porous membrane of the present invention is preferably 50 to 1000 μm, and more preferably 100 to 500 μm. This is because, within this range, both flexibility and strength necessary for processing can be obtained.

The porous membrane of the present invention can be produced by a production method including the following steps (1) to (3). In addition, the non-solvent as used in the field of this invention means the solvent which does not melt | dissolve a cellulose.
(1) Step of preparing cellulose solution by immersing cellulose in solvent (2) Step of applying cellulose solution prepared in step (1) on support (3) Cellulose solution applied in step (2) Step of precipitating cellulose by immersing in a non-solvent to obtain a hydrogel cellulose porous membrane Hereinafter, each step will be described in detail.

(1) A step of immersing cellulose in a solvent to prepare a cellulose solution Step (1) is a step of cooling the mixture of cellulose and solvent to dissolve the cellulose in the solvent to obtain a cellulose solution. . Cooling is required for dissolution of cellulose in a solvent, and a homogeneous cellulose solution can be obtained by cooling the mixture of cellulose and solvent to −10 to −200 ° C.

  At this time, the cellulose may be immersed in a solvent and then rapidly cooled, or the cellulose may be immersed in a previously cooled solvent. Once the cellulose is dissolved in the solvent, the cellulose solution state is maintained even when the temperature is returned to room temperature.

  The concentration of cellulose to be immersed in the solvent is preferably 0.2 to 20% by mass and more preferably 0.5 to 10% by mass with respect to the cellulose solution. By setting the amount of cellulose to 0.2% by mass or more, it is possible to improve the strength of the obtained porous film and to prevent the pores from becoming too large. Moreover, by making the amount of cellulose 20% by mass or less, it is possible to suppress the filtration pressure loss of the porous membrane and to prevent the pores from becoming too small.

  Although the solvent is not particularly limited, in order to precipitate the cellulose by substituting the solvent and the non-solvent in the subsequent step, not only the solubility of the cellulose in the solvent but also the non-solvent of the cellulose used in the subsequent step Solvents that are miscible with or that can be converted to non-solvents by chemical reactions such as neutralization are preferred. Furthermore, the solvent which can adjust the substitution rate with a non-solvent or the conversion rate by a chemical reaction is more preferable.

  When the substitution rate of the solvent and the non-solvent is slowed, the cellulose deposition rate is lowered, the pore size of the resulting porous membrane is too large, and the strength of the porous membrane is weakened. In addition, when the substitution rate of the solvent and the non-solvent is increased, the precipitation rate of cellulose becomes excessive, and the cellulose fibrils do not grow to a sufficient diameter, so the resulting porous membrane has a too low porosity, and in some cases There may be no opening at all. For this reason, it is preferable to select the solvent according to the pore diameter and the pore diameter change of the target porous membrane.

  The solvent preferably contains water as a main component and i) caustic and ii) urea or thiourea. Examples of other components include substances having high miscibility with water, such as lower alkyl alcohols (such as methanol and ethanol) and lower ketones (such as acetone).

  i) As caustic, NaOH and LiOH and mixtures thereof are preferable, and LiOH is more preferable. The concentration of i) caustic alkali in the solvent is preferably 2 to 20% by mass, and more preferably 4 to 10% by mass. By setting it as this range, it becomes easy to make the said precipitation rate of the cellulose suitable.

  ii) Of urea or thiourea, urea is preferred. The concentration of ii) urea or thiourea in the solvent is preferably 4 to 20% by mass, and more preferably 6 to 15% by mass. By setting it as this range, it becomes easy to make the said precipitation rate of the cellulose suitable.

  The ratio (mass ratio ii / i) of i) urea or thiourea content to i) caustic alkali in the solvent is preferably 1 to 3, and more preferably 1.5 to 2. By setting it as this range, dissolution of cellulose becomes easier, and it becomes even easier to make the cellulose precipitation rate appropriate.

  In order to increase the strength of the porous membrane, a material for reinforcing the porous membrane may be mixed in advance with the cellulose solution prepared in the step (1). As the material, for example, fibers such as synthetic fibers and natural fibers can be mixed.

  Specific examples of the fibers include ultrafine fibers (for example, fibers having a length of 1 to 10 mm and a diameter of 0.1 to 1 μm) obtained from split fibers made of polyolefin and acrylic, and polyspinds obtained by an electrospinning method. Examples thereof include ultrafine fibers made of lactic acid (fibers having a diameter of 0.1 to 1 μm).

  The viscosity of the cellulose solution is preferably 10 mPa · s or more and 1000 mPa · s or less, and preferably 10 mPa · s or more and 50 mPa · s or less. The viscosity of the cellulose solution can be adjusted mainly by the type of solvent and the amount of cellulose dissolved.

  By setting the viscosity of the cellulose solution to 10 mPa · s or more, an appropriate thickness can be obtained when the cellulose solution is spread on the support in the subsequent step (2).

  Further, by setting the viscosity of the cellulose solution to 1000 mPa · s or less, in the subsequent step (3), the substitution rate of the solvent and the non-solvent in the cellulose solution becomes too slow, so that the cellulose fibril becomes too thick. It is easy to prevent and make the pore diameter less than 20 nm.

  Furthermore, by setting the viscosity of the cellulose solution to 1000 mPa · s or less, in the subsequent step (2), the cellulose solution can be thinly and uniformly applied on the support to obtain a porous film with low pressure loss. Can do.

(2) The process of apply | coating the cellulose solution prepared at the process (1) on a support process (2) is a process of apply | coating the cellulose solution prepared at the process (1) on a support body. The thickness of the layer made of the cellulose solution coated on the support is preferably in the range of 0.05 to 5 mm.

  Examples of the support include a non-porous support and a porous support. Examples of the non-porous support include a glass plate, a polymer sheet, and a metal plate. Examples of the porous support include nonwoven fabrics such as melt blown nonwoven fabrics and spunbond nonwoven fabrics, woven fabrics, wire meshes, and punching plates.

  When a non-porous material such as a glass plate is used as the support, the obtained hydrogel cellulose porous film may be peeled off from the support later. Moreover, when using a porous thing like a nonwoven fabric as a support body, you may use the obtained hydrogel cellulose porous membrane as a composite porous sheet as it is, without peeling from a support body.

  The shape to be coated on the support may be thinly and evenly spread on a flat plate to form a sheet, or may be applied to a porous sheet such as a nonwoven fabric with a fold-like crease, or a hollow fiber. You may apply | coat to the outer surface or inner surface of. In any case, it is preferable to apply uniformly to the support surface. By applying uniformly, the thickness of the porous layer to be produced can be made uniform, and the pore diameter gradient tends to be constant regardless of the location of the support, which is preferable. Examples of the complicated shape of the support include a sheet having a crease-like crease, and a sheet having an uneven pattern on the surface with an embossing roll engraved with a pattern such as a pin shape or a lattice shape.

Specific examples of the method for applying the cellulose solution on the support include the following methods (a) to (c).
(A) A method in which a cellulose solution is spread on a flat film as a support with a glass rod to a uniform thickness.
(B) A method in which a cellulose solution is thinly discharged from a slit of a curtain coater or the like, and thinly spread on a sheet as a support.
(C) A method in which a cellulose solution is spread on a support using centrifugal force by a coating device such as a spin coater.

  In the case of using a porous support, the cellulose solution can be sucked and adhered onto the support by reducing the pressure on the opposite side of the support from the side on which the cellulose solution is applied.

  In addition, when using a support having a complicated shape, the cellulose solution is adjusted to a low viscosity, the support surface or the whole is immersed in the cellulose solution, and then the excess cellulose solution is naturally dropped or subjected to centrifugal force. It may be used and dropped to form a coating film. In this case, the viscosity of the cellulose solution is preferably 0.1 to 10 mPa · s.

  The layer of the cellulose solution coated on the support may be formed into a sheet by thinly and uniformly spreading the cellulose solution on a flat plate, or the cellulose may be formed on a porous sheet such as a non-woven fabric with folds. The solution may be applied or applied to the outer or inner surface of the hollow fiber.

(3) Step of obtaining a hydrogel cellulose porous membrane by immersing the cellulose solution applied in step (2) in a non-solvent to obtain a hydrogel cellulose porous membrane In step (3), the cellulose solution applied on the support is non-coated. By immersing in a solvent and substituting the solvent and the non-solvent in the cellulose solution, the dissolved cellulose is deposited and deposited as regenerated cellulose to obtain a multilayer structure. At this time, the regenerated cellulose becomes low crystalline fibrils (cellulose fibrils), and the cellulose fibrils are connected to form a network structure. Water is retained in the gaps in the network structure to obtain a hydrogel cellulose porous membrane.

  The non-solvent is not particularly limited. For example, water, lower alkyl alcohol (for example, methanol and ethanol), lower alkyl alcohol aqueous solution, lower ketone (for example, acetone), lower fatty acid ester (for example, A dilute aqueous solution of salts (eg, sodium sulfate) can be used.

  Non-solvents may be used alone or in combination. Among these, at least one selected from the group consisting of a lower alkyl alcohol and water is preferable, and a lower alkyl alcohol aqueous solution that is a mixture of water and lower alkyl alcohol is more preferable. The mixing ratio of water and lower alkyl alcohol in the lower alkyl alcohol aqueous solution is not particularly limited.

  In the step (3), the porous membrane obtained has a larger pore size on the side where the cellulose solution coated on the support is in direct contact with the non-solvent, and a smaller pore size on the side in contact with the support. . As a result, the porous membrane of the present invention becomes a porous membrane having different pore diameters in the thickness direction.

  Moreover, since the fiber diameter of the cellulose fibril to refine | purify becomes so small that the speed | rate which substitutes the solvent in a cellulose solution to a non-solvent becomes small, for example, according to the method of the following (a)-(d), a hole diameter and thickness direction The pore diameter gradient can be controlled.

(A) This is a method in which i) caustic and ii) urea or thiourea are mixed in such a ratio that cellulose does not dissolve in the non-solvent used in step (3). By this method, the rate at which cellulose is precipitated can be intentionally reduced. The non-solvent used for this method is not particularly limited.

  For example, when using a method in which a lower alkyl alcohol aqueous solution is used as a non-solvent and i) caustic and ii) urea or thiourea are mixed, the precipitation rate of cellulose can be made appropriate. The concentration of the lower alkyl alcohol in the lower alkyl alcohol aqueous solution is not particularly limited, but is preferably 70 to 100% by mass. By setting it as this range, the precipitation rate of cellulose can be made more appropriate.

  The concentration of i) caustic alkali in the non-solvent is preferably 0.2 to 5% by mass, and more preferably 0.5 to 2% by mass. It is because the precipitation rate of a cellulose becomes more appropriate by setting it as this range.

  The concentration of ii) urea or thiourea in the non-solvent is preferably 0.5 to 5% by mass, more preferably 1 to 3% by mass. It is because the precipitation rate of a cellulose becomes more appropriate by setting it as this range.

  In addition, ii) urea or thiourea / i) caustic (mass ratio) is preferably 1 to 3, and more preferably 1.5 to 2. By setting it as this range, the magnitude | size of a hole diameter gradient becomes easy to take an appropriate value.

(B) In the step (1), a non-solvent is mixed in advance to such an extent that cellulose does not precipitate in the cellulose solution.
The concentration of the non-solvent in the cellulose solution is preferably 0 to 5% by mass, and more preferably 0 to 3% by mass.

(C) In the step (3), several non-solvents having different compositions are prepared, and the cellulose solution is sequentially immersed in them.
Specifically, for example, first, it is immersed in a mixed solution of 90% by mass of methanol, 0.8% by mass of lithium hydroxide, 1.5% by mass of urea, and 7.7% by mass of water. Then, it is immersed in 100% methanol. Thereby, it becomes easy to give a hole diameter gradient in the hole diameter and thickness direction.

(D) In step (3), not only the cellulose solution is simply immersed in the non-solvent, but also the liquid solution is forcibly generated in the non-solvent by stirring with a stirring blade, etc. It is a method of always exposing to a fresh non-solvent.
Specifically, for example, the number of stirring is preferably 10 to 100 rpm.

  The porous membrane of the present invention can be used as a liquid filtration membrane, a drug holding membrane and a surface humidity protective membrane.

  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.

[Used materials]
For sodium hydroxide, lithium hydroxide, and methanol, special grades made by Wako Pure Chemicals were used.

  As the cellulose, Advantech Toyo ashless pulp was used. This cellulose contains amorphous cellulose.

  Three types of gold nanocolloids having a particle size of 5, 20, and 50 nm manufactured by Sigma-Aldrich were used. The particle size of the gold nanocolloid made by Sigma Aldrich used in the present invention represents the average size of the spherical particles, and the manufacturer's display value was used as it was.

  As the support, a glass plate (size 15 cm × 15 cm) was used.

  As the water, ultrapure water having a specific resistance value of 18 MΩ · cm or more manufactured by Millipore ultrapure water production apparatus “DirectQ UV (trade name)” was used.

〔Evaluation method〕
The physical property values of the porous membranes obtained in Examples and Comparative Examples were measured by the following methods.

1) Average fiber diameter The obtained porous membrane was freeze-dried and observed at an magnification of 100,000 times using an electron microscope (JEOL scanning electron microscope JSM). The photograph was subjected to image analysis to determine the diameter of 10 constituent fibers, and the arithmetic average value was taken as the average fiber diameter.

2) Flux The obtained porous membrane was cut to a diameter of 25 mm, set in a filter sheet holder, pressurized with a pressure of 1 MPa, allowed to pass ultrapure water, and the amount of water passed was measured from the discharged liquid amount. It was converted into a numerical value per unit area of the filter sheet to obtain the flux.

3) Particle collection efficiency The obtained porous membrane was cut out to a diameter of 25 mm, set in a filter sheet holder, pressurized with 1 MPa of pressure and allowed to pass through a gold nanocolloid solution having a particle size of 5 nm or 20 nm, before and after filtration. The amount of gold nanocolloid contained in the liquid was measured to obtain the collection efficiency.

  In this example, the surface that was in contact with water in the hydrogelation step with a non-solvent became the surface with the larger pore size, and allowed to pass 70% or more of the gold nanocolloid having a particle size of 20 nm (one of the comparative examples). Part cannot pass).

  In addition, a gold nanocolloid liquid having a particle diameter of 50 nm and a gold nanocolloid having a particle diameter of 20 nm are calculated from the number of particles per volume of the gold nanocolloid so that the number of particles is 1:12, and mixed. The colloidal gold solution is passed from the surface of the porous membrane having the larger pore diameter in the same manner as described above, and the porous membrane after passing is dried, and the magnification is 100,000 times using an electron microscope. The number of particles having a diameter of 50 nm and 20 nm was observed. Since particles having a large diameter of 50 nm are surely collected even on the surface of the porous film having a large pore diameter, the gold nanocolloid having a particle diameter of 20 nm on the surface having the large pore diameter of the porous film is collected. The passage rate of the gold nanocolloid having a particle size of 20 nm on the surface of the porous membrane having the larger pore diameter was determined by the following formula.

(formula)
(Passage rate) = {1− (number of particles with a particle size of 20 nm ÷ number of particles with a particle size of 50 nm) ÷ 12} × 100%

[Example 1]
[Preparation process of raw material liquid]
As shown in Table 1, an aqueous solution in which 8% by mass of lithium hydroxide and 15% by mass of urea were dissolved was used as a solvent for cellulose. 4 parts by weight of cellulose was immersed in 100 parts by weight of the solvent for cellulose, and the liquid was cooled at −15 ° C. for 5 minutes to dissolve the cellulose to obtain a cellulose solution.

[Molding process]
Advantech Toyo's quantitative filter paper 5B was placed on a glass plate, and the end portion was fixed with an adhesive tape. The cellulose solution obtained above was applied on the glass plate to a thickness of 100 μm using a Baker applicator.

[Hydrogelation step with non-solvent]
As shown in Table 1, methanol was used as the non-solvent. Methanol was put in a container up to a depth of 3 cm, and the cellulose solution formed on the glass plate was gently immersed in the glass plate together with the glass plate, and left at room temperature for 15 minutes to convert the cellulose solution into a hydrogel. .

  Next, water was poured into another container to a depth of 10 cm, and the hydrogel was peeled off from the glass plate and immersed. Thereafter, water was exchanged several times to completely remove the alkali remaining in the hydrogel, thereby obtaining a hydrogel cellulose porous membrane. Table 2 shows the physical property values of the obtained hydrogel cellulose porous membrane.

  As shown in Table 2, the obtained hydrogel cellulose porous membrane allows the gold nanocolloid particles having a particle diameter of 20 nm to pass through 78% on the surface of the porous membrane having a larger pore diameter, whereas the gold nanocolloid Since the trapping efficiency reaches 99% or more, the hole diameter was changed in the thickness direction, and it was confirmed that the hole diameter was different in the thickness direction. In addition, this film collected 85% of gold nanocolloid particles having a particle diameter of 5 nm.

[Examples 2 and 3]
As shown in Table 1, a hydrogel cellulose porous membrane was obtained in the same manner as in Example 1 except that the thickness to be applied was 200 and 500 μm in the molding step. Table 2 shows the physical property values of the obtained hydrogel cellulose porous membrane. Moreover, the hydrogel cellulose porous membrane of Example 2 was freeze-dried and the photograph observed with the electron microscope is shown in FIG.

  As shown in FIG. 2, the surface [FIG. 2 (a)] that was in contact with the glass plate in the non-solvent hydrogelation step was more open than the surface that was on the non-solvent side [FIG. 2 (b)]. The size of the perforated holes was slightly large, and the fiber diameter was also large.

[Example 4]
As shown in Table 1, all examples were performed except that a non-solvent mixture of 90% by mass of methanol, 0.8% by mass of lithium hydroxide, 1.5% by mass of urea, and 7.7% by mass of water was used. Hydrogel cellulose porous membrane was obtained by the same method as in No. 2. Table 2 shows the physical property values of the obtained hydrogel cellulose porous membrane.

  As shown in Table 2, the hydrogel cellulose porous membrane obtained in Example 4 had a higher flux than the hydrogel cellulose porous membrane obtained in Example 2, and the particle collection efficiency was also high.

  Further, compared with Example 2, the collection efficiency of gold nanocolloid particles having a particle diameter of 5 nm was not significantly different from Example 2 at 93% and Example 4 at 94%.

  On the other hand, the passing rate of the gold nanocolloid particles having a particle size of 20 nm on the surface of the porous membrane having the larger pore diameter is 92% in Example 4 compared to 80% in Example 2, and the thickness of the pore diameter It was confirmed that the change in the vertical direction was larger.

  Moreover, the photograph which observed this hydrogel with the electron microscope is shown in FIG. As shown in FIG. 3, when compared with Example 2, the surface [FIG. 3 (a)] that was in contact with the glass plate in the non-solvent hydrogelation step was larger than Example 2 [FIG. 2 (a)]. There was no difference. On the other hand, the surface [FIG. 3 (b)] which was on the non-solvent side had a larger hole size and a larger fiber diameter than Example 2 [FIG. 2 (b)].

[Examples 5 to 7]
As shown in Table 1, Example 1 was used except that a non-solvent mixture of 80% by mass, lithium hydroxide 1.6% by mass, urea 3.0% by mass, and water 15.4% by mass was used. A hydrogel cellulose porous membrane was obtained by the same method as ˜3. Table 2 shows the physical property values of the obtained hydrogel cellulose porous membrane.

  As shown in Table 2, the hydrogel cellulose porous membrane obtained in Example 6 had a higher flux than Example 4 and a high particle collection efficiency. Further, compared with Examples 2 and 4, the passing rate of the gold nanocolloid particles having a particle diameter of 20 nm on the surface of the porous membrane having the larger pore diameter is 80% of Example 2 and 92% of Example 4. On the other hand, it was 95% in Example 6, and it was confirmed that the change in the thickness direction of the hole diameter was larger.

  Moreover, the photograph which observed this hydrogel cellulose porous membrane with the electron microscope is shown in FIG. As shown in FIG. 4, as compared with Examples 2 and 4, the surface that was on the non-solvent side [FIG. 4 (a)] had larger holes and fiber diameters. Further, as shown in FIG. 1, when this cross section was observed, it was observed that cellulose was stacked in layers.

Claims (2)

It is a hydrogel cellulose porous membrane having a multilayer structure in which cellulose fibrils are laminated and having different pore sizes in the thickness direction, and an average fiber diameter of cellulose fibrils in at least one layer of the multilayer structure is less than 100 nm, and a layer constituting the surface The ratio of the average fiber diameter of cellulose fibrils in the layer constituting the back surface is 1.2 to 3, the gold nanocolloid having a particle diameter of 5 nm can be collected by 70% or more, and the pore diameter of the porous film is larger. The surface is a hydrogel cellulose porous membrane in which the passing rate of a gold nanocolloid having a particle diameter of 20 nm determined by the following measurement method is 70% or more.
(Measurement method) A gold nanocolloid solution in which a gold nanocolloid with a particle size of 50 nm and a gold nanocolloid with a particle size of 20 nm is mixed so that the number of particles is 1:12 is passed through the porous membrane from the surface with the larger pore size. From the number of particles having a particle size of 50 nm and the number of particles having a particle size of 20 nm in the porous film after passing through, the passing rate is obtained by the following formula.
(Formula) (passage rate) = {1− (number of particles with a particle size of 20 nm ÷ number of particles with a particle size of 50 nm) ÷ 12} × 100%   The hydrogel cellulose porous membrane according to claim 1, wherein the cellulose fibril contains an amorphous substance.

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