JPH0246608B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a regenerated cellulose porous membrane having an average pore diameter of 0.01 to 20 μm and an in-plane porosity of at least one surface of 30% or more. More specifically, it is a regenerated cellulose porous membrane in which the average molecular weight of cellulose molecules is 5 × 10 ⁴ or more, the crystalline region is substantially composed of cellulose and/or -2 crystals, and the porous membrane surface has a (101) plane. The degree of orientation (hereinafter referred to as degree of orientation) is 40% or less, and the measurement frequency is 110.
The dynamic elastic modulus at 30℃ at Hz is 1.5×10 ⁸ (100−
Prρ) dyn/cm ² or more (Pr is porosity in percentage),
The porous membrane has an average pore diameter of 0.01 to 20 μm,
and the in-plane porosity of at least one surface is 30% or more, or the number of pores per ¹ cm2 in the plane is 6
The present invention relates to a regenerated cellulose porous membrane characterized in that the number of cells is ×10 ⁵ /D to 3 × 10 ⁷ /D. Membrane separation technology is attracting attention among materials separation and purification technologies. Unlike distillation, polymer membranes are used in a wide range of fields, taking advantage of the characteristics of the membrane separation process: no temperature change is required for separation, little energy is required for separation, and the process is compact. ing. For example, dairy farming,
These include fisheries, livestock, food processing, pharmaceuticals, chemical industry, textile dyeing, steel, machinery, surface treatment, water treatment, and nuclear power industry. Fields in which membrane separation systems may become central in the future include low-temperature concentration,
Fields that require purification and recovery (food, biochemical industry), fields that require sterility and dust-free (pharmaceutical and therapeutic institutions, electronic industry), concentration and recovery of trace amounts of expensive substances (nuclear power, heavy metal fields), Possible fields include special small-volume separation field (medical field) and energy-intensive separation field (distillation alternative). As membranes used in these fields, there is an increasing need for hydrophilic membranes with large pores and easy handling. A porous membrane composed of cellulose, which is a typical example of a hydrophilic polymer, has an average pore diameter of 100 Å (0.01 μ
m) The following porous membranes for artificial kidneys are known. A typical example of this type of membrane is a cuprammonium cellulose membrane. The average molecular weight of cellulose constituting this membrane is 5 x ¹⁰⁴ , the crystalline region is substantially cellulose, the dynamic elastic modulus is ^about 5 x ¹⁰¹⁰ dyn/cm2, and the mechanical loss tangent tanδ-temperature curve The peak temperature Tmax at is about 200°C. Porosity Pr is approximately 10
%, and the average pore diameter is too small to be evaluated using the method of the present invention, and cannot be observed using an electron microscope. Furthermore, the degree of orientation of the (101) plane is approximately 50%. Furthermore, a regenerated cellulose porous membrane has been obtained by saponifying a cellulose derivative membrane such as cellulose acetate or cellulose nitrate with an alkaline aqueous solution. The average pore diameter of the porous membrane obtained by such a method is in the range of 0.01 to 2 μm, and since a cellulose derivative is used as the starting material, the molecular weight of the cellulose molecules after regeneration is 3.5×10 ⁴ or less. The molecular weight of cellulose molecules in conventional regenerated cellulose porous membranes having pores in such a pore size range is 4.0×10 ⁴ or less. For example, the average molecular weight of a regenerated cellulose porous membrane obtained by saponifying cellulose acetate is 2×10 ⁴ . The crystalline region is a cellulose type crystal, the degree of orientation of the (101) plane is approximately 60%, and the porosity is 70%.
%, and the dynamic elastic modulus is as low as 3×10 ⁶ dyn/cm ² .
Further, the peak temperature Tmax in the mechanical loss tangent tan δ-temperature curve is about 200°C. Therefore, the mechanical properties (especially strength) of the porous membrane in a dry state are extremely low and brittle. For example, the porosity of a porous membrane is
If Prρ (expressed as a percentage), the elastic modulus is approximately 10 ²
(100−Prρ) ³ dyn/ ^cm2 . The tensile breaking strength is approximately proportional to the elastic modulus, and is approximately 1/10 of the elastic modulus. Conventional regenerated cellulose porous membranes obtained from cellulose derivatives may break during handling because their strength in a wet state with water is even lower than in a dry state. The first feature of the regenerated cellulose porous membrane of the present invention is that the membrane is composed of cellulose molecules having an average molecular weight of 5×10 ⁴ or more. Regenerated cellulose porous membranes are brittle in dry conditions. As the molecular weight increases, the strength of the porous membrane increases and its brittleness is improved. Therefore, handling of the porous membrane becomes easier and damage to the porous membrane is reduced. The higher the average molecular weight of cellulose, the lower the breakage rate when compared at the same porosity. The influence of the average molecular weight on the film properties tends to become saturated as the average molecular weight increases. Therefore,
An average molecular weight of 5.0×10 ⁴ or more is acceptable in terms of practical ease of handling. From the viewpoint of ease of producing a porous membrane, the average molecular weight is desirably 3×10 ⁵ or less. A second feature of the present invention is that the crystalline region is composed of cellulose, cellulose-2 crystals, or a mixture of both. The fact that the crystalline region is composed of cellulose or -2 crystals or a mixture of both means that the inside of the crystalline region is substantially composed of cellulose molecules, and as in cellulose derivatives, the hydroxyl groups in the cellulose molecules are not connected to other groups. means that it is not replaced. Cellulose or -2 crystals are chemically and thermally stable. The greatest feature of the present invention is that in cellulose and -2 crystals, the degree of orientation of the (101) plane to the porous membrane surface is 40% or less. In conventionally known regenerated cellulose membranes, the normal direction of the (101) plane is perpendicular to the membrane surface. To express the extent to which this normal line is oriented in a direction perpendicular to the film surface, it is possible to use the X-ray diffraction intensity obtained by making X-rays incident parallel to the film surface. The degree of orientation of the (101) plane to the membrane surface obtained by the measurement method described below is 50% or more in known regenerated cellulose membranes. The orientation of the (101) plane to the porous membrane plane is a parameter that indicates the degree of orientation of the normal line of the (101) plane of cellulose or -2 crystal in the direction perpendicular to the membrane plane, and it can be measured by X-ray diffraction method. be measured. Specifically, this will be described later as a measurement of the degree of crystal orientation of the (101) plane.
Since the (101) plane is a plane perpendicular to hydrogen bonding, if the degree of crystal orientation of this plane to the porous membrane surface becomes 40% or less,
This results in a porous film with high tensile fracture strength. For example, the tensile fracture strength of a film with a degree of crystal orientation of 40% or less is 1.5×
10 ⁶ (100−Prρ)dyn/cm ² or more. On the other hand, as the degree of crystal orientation decreases, the bursting strength of the porous membrane decreases. However, the degree of crystal orientation is 40
% or less at a measurement frequency of 110Hz.
The dynamic elastic modulus at 30℃ is 1.5×10 ⁸ (100−Prρ) dyn/cm ²
If it is above, almost no decrease in bursting strength is observed. For example, average pore diameter 1-2 μm, porosity 61-71,
Table 1 shows the tensile fracture strength and burst strength of the porous membrane when the dynamic elastic modulus was varied while the degree of crystal orientation was constant within the range of 25 to 35%.

[Table] * Comparative example This feature of orientation appears in swelling deformation when the porous membrane is immersed in water or an organic solvent. That is, as the degree of orientation of the (101) plane increases, the swelling in the film thickness direction becomes larger when the film is swollen with water compared to the other two directions, whereas in the present invention, the film swells in almost the same direction. Another feature of the present invention is that the average pore diameter is from 0.01 to
2.0 μm, and the in-plane porosity of at least one surface is 30% or more, or the number of pores per 1 cm ² in the plane is 6 × 10 ⁵ /D to 3 × 10 ⁷ /D. At the point. When the in-plane porosity is 30% or more, the overspeed using a porous membrane increases significantly, and the overcapacity also increases. Theoretically, the overspeed is proportional to the volumetric porosity (hereinafter, this porosity is simply referred to as porosity), and the overcapacity is also approximately proportional to the porosity. When the porosity is 30% or more, both overspeed and overcapacity increase as the in-plane porosity increases, and as long as the in-plane porosity is 30% or more, the larger the better. Desirably, the in-plane porosity should be 55% or more. However, the ease of handling porous membranes,
Due to the mechanical properties of the porous membrane, the in-plane porosity is 90%
The following are desirable. The permeated liquid is passed from the front surface to the back surface of the porous membrane. When comparing the overspeed of various membrane combinations with the same average pore size on the surface and the same porosity, if the pore size on the back side is larger than the pore size on the front side, the overspeed and overcapacity will also be large. The external shape of the porous membrane includes a flat membrane, a tube shape, and a hollow fiber shape. Further, the average pore radius means ₃ defined by equation (1).
If the number of pores with a pore radius of r to r+dr per 1 ^cm2 of porous membrane is expressed as N(r)dr (N(r) is the pore size distribution function), the average pore radius ₃ is given by equation (1). .
The average pore diameter in the present invention is defined as 2 ₃ . ₃ = ∫ ^∞ / ₀ r ³ N (r) dr / ∫ ^∞ / ₀ r ² N (r) dr (1) The ultimate overspeed per hole is approximately proportional to the fourth power of ₃ , and the proportional to the rate. Therefore,
To increase only the overspeed, the larger ₃ is, the better. However, the maximum pore size is naturally determined in relation to the target particle size to be separated. The region where the characteristics as a hydrophilic screen filter are fully exhibited is an average pore diameter (ie, 2 ₃ ) of 20 μm or less. Also, the average pore size
When the diameter is 0.01 μm or less, the particles to be separated by the membrane are generally non-spherical, and the characteristics of the porous membrane of the present invention cannot be utilized. As described later,
The object to be separated using the porous membrane of the present invention is to separate and remove and concentrate a target component in a liquid or gas mixture containing water, and to perform the separation at a high rate. Naturally, as the average pore diameter becomes smaller, the overspeed decreases significantly. In addition, the thickness of the porous membrane is normally the thinner the better, but for ease of handling and to prevent pinholes from forming, a thickness of 5 μm is recommended.
It is common to have a thickness greater than or equal to that. The average pore size is
In the case of pores of 0.01 μm or less, the probability of the existence of non-through holes (non-through holes) increases, so that the performance as a membrane becomes lower than that expected for through holes. In order to avoid the mixture of non-penetrating holes, the average pore diameter is
Must be 0.01μm or more. As the average pore diameter increases, the thickness of the porous membrane can be increased to prevent pinholes from being included. However, since overspeed is inversely proportional to film thickness,
It is desirable that the film be thinner. Because of these contradictory tendencies, the optimum range of film thickness is closely related to the manufacturing method of the porous film. Furthermore, in the mechanical loss tangent tanδ-temperature curve at a measurement frequency of 110Hz, the peak temperature Tmax
When the temperature is 250°C or higher, the thermal stability of the porous membrane increases, and the heat resistance in organic solvents increases. The porous membrane of the present invention can be used for separation and removal of target components in liquid or gas mixtures containing water, for example, membranes for artificial kidneys, artificial livers, and artificial pancreases. Although it can be used in almost all other fields in which ultrafiltration membranes can be used, this strong porous membrane with excellent hydrophilic properties and mechanical properties is suitable for bio-related fields (medicine, biochemical industry).
Or it is particularly suitable for the food fermentation field. In the present invention, for example, a solution obtained by adding 10% by weight of acetone to a 10% (by weight) cellulose cupric ammonia solution is cast onto a glass plate in the usual manner using an applicator having a thickness of 500 μm. Immediately 35℃
After leaving the membrane in an acetone vapor atmosphere for 60 minutes, the resulting membrane was immersed in a 2% sulfuric acid aqueous solution at 20℃
It can then be obtained by washing with water, then immersing the membrane in acetone at 20°C to replace the moisture in the membrane with acetone, and drying. Note that the film composed of cellulose-2 crystals can be obtained by immersing the film in liquid ammonia for 10 seconds and then removing the ammonia at 20°C. The thermal stability of the membrane obtained is significantly increased. Prior to Examples, methods for measuring various physical property values used in the detailed description of the invention are shown below. <Average Molecular Weight> The average molecular weight (viscosity average molecular weight) Mv is calculated by substituting the intrinsic viscosity number [η] (ml/g) measured in a cupric ammonia solution (20° C.) into equation (2). Mv=[η]×3.2×10 ³ (2) <Identification of cellulose and -2 crystals, degree of crystal orientation> Rigaku Corporation X-ray generator (RU-200PL) and goniometer (SG-9R)), counter tube Using a scintillation counter and a pulse height analyzer for the counting section, the X-ray generator was operated at 30 KV and 800 mA, and the X-ray diffraction intensity was measured using Cu-Kα rays (wavelength λ = 1.5418 Å) made monochromatic with a nickel filter. Measure. In the case of determining the crystal structure, X-rays are incident perpendicularly to the film surface, or in the case of hollow fibers, perpendicularly to the fiber axis. Scanning speed 1°/
min, chart speed 10mm/min, time constant 1sec, divergence slit 1/2°, receiving slit 0.3mm, scattering slit 1/2°, and the diffraction angle 2θ is in the range of 4° to 35°.
Measure the linear diffraction intensity. Cellulose crystal has 2θ=12゜{reflection from (101) plane}, 20.2゜{reflection from (101) plane}, 21゜{(00
2)
It is characterized by three types of diffraction: reflection from a surface.
Furthermore, cellulose-2 crystals are characterized by two types of diffraction: 2θ=12° {reflection from the (101) plane} and 20° {reflection from the (101) plane}. To measure the degree of crystal orientation of the (101) plane, if the sample is a flat film, X-rays are incident parallel to the film surface. In the case of hollow fibers, the hollow fibers are compressed into a planar shape to eliminate hollow voids and deform into the appearance of two laminated membranes. X-rays are made incident parallel to the plane of the laminated film. The goniometer is set at 2θ = 12°, and the azimuth direction is scanned from +30° to -30° using the symmetrical transmission method, and the diffraction intensity in the azimuthal direction is recorded. Furthermore, the diffraction intensity in the azimuth directions of +180° and -180° is recorded. The scanning speed at this time is
4°/min, the chart speed is 10mm/min, the time constant is 1sec, the collimator is 2mmφ, and the receiving slit is 1.9mm long and 35mm wide.
The degree of crystal orientation is determined from the obtained diffraction intensity curve in the azimuthal direction. First, take the average value of the X-ray diffraction intensities obtained at ±180°, and draw a horizontal line to use it as the baseline. Drop a perpendicular line from the top of the peak to the baseline and find the midpoint of its height. A horizontal line passing through the midpoint is drawn, the distance between the two intersections of this and the diffraction intensity curve is measured, and this value is converted into an angle (°), and the value is defined as the orientation angle H (°). The degree of crystal orientation is given by equation (3). Crystal orientation degree (%) = {(180-H)/180}×100 (3) When the crystal is non-oriented, H is 180 and the crystal orientation degree is 0%. <Porosity Prρ> A planar porous membrane is cut into a circular shape of 47 mmφ, and the porous membrane is dried in vacuum to reduce the moisture content to 0.5% or less. The thickness of the porous membrane after drying is d (cm), the weight is W
(g), the porosity Prρ (%) is given by equation (4). Prρ (%) = (1-17.34×d/1.50×W)×100 (4) In the case of hollow fibers, the inner diameter of the hollow fiber is D ₂ (cm), the outer diameter is D ₁ (cm), and the When the length is l (cm) and the weight is W (g), Prρ is given by equation (5). Prρ (%) = {1-W/6.0×π( ^D2 / ₁ - ^D2 / ₂ )l}×100(5
) <Average pore radius ₃ , in-plane porosity Pr, and number of pores N> For the scanning electron microscope, JSM-U3 manufactured by JEOL Ltd.
Using the mold, take electron micrographs of the front and back sides.
The pore size distribution function N(r) is calculated from the photograph by a known method and substituted into equation (1) in the text. That is, a scanning electron micrograph of the area where the pore size distribution is to be determined is enlarged and printed to an appropriate size (for example, 20 cm x 20 cm), and 20 test lines (straight lines) are drawn at equal intervals on the resulting photograph. Each straight line crosses a number of holes. Measure the length of the straight line that exists within the pores when crossing the pores on the front or back surface of the porous membrane,
Find this frequency distribution function. If it is difficult to determine whether the pores are on the membrane surface (on the back side), all pores observed on the photograph are considered to be pores on the membrane surface, and in this case, N 1/3 is defined as the number of holes in the present invention. Further, the in-plane porosity at this time is defined as twice Pr calculated by equation (6). Using this frequency distribution function, for example, by the method of stereology (for example, Norio Suwa, Quantitative Morphology, Iwanami Shoten), N(r)
Establish. The in-plane porosity Pr is calculated by equation (6) using N(r). Further, the number of holes N is given by equation (7). Pr(%)=π∫r ² N(r)dr×100 (6) N=∫ ^∞ ₀ N(r)dr (7) <tan-δ-temperature curve, dynamic elastic modulus> Width 1mm, length A 5 cm strip sample was cut out from the porous membrane, and a Reo Vibron manufactured by Toyo Baldwin was used.
Using a DDV-c model, the tan δ-temperature curve and dynamic elastic modulus are measured at a measurement frequency of 110 Hz, under dry air, and an average heating rate of 10° C./min. Measured tanδ−
Read the peak temperature Tmax (℃) of tan δ from the temperature curve. Example 1 Cellulose linter (average molecular weight 2.3×10 ⁵ ) was dissolved in a copper ammonia solution prepared by a known method at a concentration of 10% by weight, then 12% acetone was added to the solution, stirred, and then heated at 30°C. Cast with a 500 μm applicator on a glass plate in the usual manner in air. Immediately, the cast product was placed in an acetone vapor atmosphere at 20°C with a velocity of 70% of the saturated vapor pressure, and after being left for 120 minutes, the obtained film was placed in a 2% by weight sulfuric acid aqueous solution at 20°C.
Regenerate by soaking for 15 minutes, then rinse with water, and then remove the membrane.
Immerse it in acetone at 20℃ for 15 minutes to replace the moisture in the membrane with acetone, dry it by sandwiching it between paper sheets, and reduce the thickness.
A porous membrane of 50 μm was obtained. Its microstructural features and various physical property values are as follows. The average molecular weight is
5.7×10 ⁴ , (101) plane orientation degree is 28%, measurement frequency
The dynamic elastic modulus at 30℃ at 110Hz is 9.1×10 ⁹ dyn/
cm ² , average pore diameter is about 1 μm, in-plane porosity is 65%, number of pores is 4.0×10 ⁷ , and Tmax is 264°C. In addition,
An electron micrograph of the front surface of this porous membrane is shown in FIG. 1, and an electron micrograph of the back surface is shown in FIG. Comparative Example 1 Various cellulose acetate porous membranes obtained by a known method (USP 3883626) were saponified at 30°C using a caustic soda aqueous solution of pH 12.0 to obtain regenerated cellulose porous membranes. Table 2 shows its microstructural characteristics and various physical property values.

【table】

[Table] The average molecular weight of the cellulose molecules constituting the porous membranes obtained with sample numbers 1-1 to 1-4 is 1.5.
Distributed between ×10 ⁴ and 2.0 × 10 ⁴ . The porous membrane obtained by regenerating cellulose derivatives has a low average pore diameter, a dynamic elastic modulus that is 1/3 or less of that of the present invention, and a low Tmax. It can be seen that due to these factors, the strength and heat resistance of the porous membrane are significantly inferior to those of the porous membrane of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a scanning electron micrograph of the front surface of the product of the present invention, and FIG. 2 is a scanning electron micrograph of the back surface of the same.

Claims (1)

[Scope of Claims] 1. The average molecular weight of cellulose molecules is 5 × 10 ⁴ or more, and the crystalline region is substantially cellulose or -2 crystals, or a mixture of both,
The degree of crystal orientation of the (101) plane to the porous membrane surface is 40% or less,
Dynamic elastic modulus at 30℃ at measurement frequency 110Hz is 1.5
×10 ⁸ (100−Prρ) dyn/cm ² or more (Prρ is porosity expressed as a percentage), average pore diameter (Dμm) in porous membrane
is 0.01 to 20 μm, and the in-plane porosity of at least one surface is 30% or more, or the number of pores per 1 cm ² in the plane is 6 × 10 ⁵ /D or more, and 3 ×
A regenerated cellulose porous membrane characterized in that the number of cells is 10 ⁷ /D or less. 2 The in-plane porosity of at least one surface of the porous membrane is
The regenerated cellulose porous membrane according to claim 1, wherein the regenerated cellulose porous membrane is 55% or more and 90% or less. 3 Mechanical loss tangent at measurement frequency 110Hz
The regenerated cellulose porous membrane according to claim 1 or 2, wherein the tan δ peak temperature Tmax is 250°C or higher.