JPS5889628A - Regenerated cellulose porous membrane - Google Patents

Abstract

PURPOSE:To obtain titled membrane both surfaces of which have circular pores, suitable for membrane separation systems such as artificial kidney, ultrafiltration membrane, etc., comprising high-molecular weight cellulose having arystalline region consisting of cellulose II and/or cellulose III-2. CONSTITUTION:A soluton prepared by adding 7wt% of a 30% sodium silicate aqueous solution to a, e.g., 10wt% cuprammonium solution of cellulose having an average molecular weight >=50,000 is cast on a glass plate and allowed to stand in air for 16hrs. The resulting membrane is then immersed in a 2% sulfuric acid aqueous solution at 20 deg.C followed by washing, and further immersing in acetone at 20 deg.C to substitute the acetone for the water in said membrane, then drying to obtain the objective membrane both surfaces of which have circular pores. The characteristics of the final membrane are as follows: crystalline region: consisting of cellulose II and/or III-2; average pore size D: 0.01-20mum; the pore size ratio of the face to the back: 1/3-1/10; porosity of at least one surface: 30-90%, or the pore number/cm<2>: 6X10<5>-3X10<7>.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a regenerated cellulose porous membrane having circular pores with an average pore diameter of 0.01 to 2011 m.

More specifically, the average molecular weight of cellulose molecules is 5
104 or more, and the crystalline region is substantially cellulose ■
Alternatively, in a regenerated cellulose porous membrane composed of cellulose lll-2 & 4 or crystals containing both,
Both the front and back surfaces have circular pores, and the average pore diameter of the wire pores is 0.01 to 20 μm, and the porosity is 50 to 90, or the number of pores per Ia in the plane. is 6X10
The present invention relates to a regenerated cellulose porous membrane characterized in that the number of cells is 1/l) or more and 3X1G'/D or less. Here, the regenerated cellulose porous membrane means one that can be expressed by a Xa diffraction pattern of 6, cellulose 3, cellulose 1[-2, or a mixture of both, which will be described later.

'Among the separation and purification technologies for substances, membrane separation technology is attracting attention. Polymer membranes are used in a wide range of fields, taking advantage of the characteristics of the membrane separation process, such as not requiring temperature changes associated with membrane separation unlike distillation, requiring little energy for separation, and having a compact process. ing.

For example, dairy farming, aquatic and livestock farming, food processing, pharmaceuticals, chemical industry, textile dyeing processing, steel, machinery, surface treatment, water treatment, and atomic crab industry. Fields in which membrane separation systems may become central in the future include: ■ Fields that require concentration, purification, and recovery at low temperatures (food, biochemical industries), ■ Fields that require sterility and dust-free operation (pharmaceuticals, etc.) Possible applications include: ■concentration and recovery of trace amounts of expensive substances (nuclear energy and heavy metal fields), ■special small quantity separation field (medical field), and ■energy-intensive fields (alternative to distillation). As membranes used in these fields, there is an increasing need for hydrophilic membranes with large pores that are easy to handle.

As a porous membrane composed of cellulose, which is a typical example of a wood-loving polymer, a porous membrane for artificial kidneys having an average pore diameter of 1ooX (0.01 μm) or less is known. 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,
The molecular weight of the Celsys needle after regeneration #i is 5.5×10′ or less. Therefore, the mechanical properties (strong f in %) of the porous membrane in a dry state are extremely low and brittle. For example, if the porosity of the porous membrane is t-Pr, the strength is n108 (1-Pr)
dyn/cd. Conventional regenerated cellulose membranes obtained from cellulose derivatives may break during handling because their strength in the wet state with water is even lower than in the dry state.

The first feature of the regenerated cellulose porous membrane of the present invention is that the linear 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,
Fragility is improved.

Handling of the rolled 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 with the same porosity. It is recognized that the influence of the average molecular weight on the film properties tends to become saturated as the average molecular weight becomes larger. Therefore, if the average molecular weight is #i5×104 or more, the porous membrane is suitable for practical ease of handling.
f): From the viewpoint of ease of m, an average molecular weight of less than ti5×101i is desirable.

The second feature of the present invention is that the crystalline region is composed of cellulose (2), cellulose [[-2, or a mixture of both. The fact that the crystalline region is composed of cellulose ■ or cellulose l[-2 crystals or a mixture of both means that the inside of the crystalline region is essentially composed of cellulose molecules, and the water in the cellulose molecules, such as in cellulose derivatives, is It means that the brewing group is not substituted with other groups. Cellulose ■ or cellulose [j
-2 or a crystal containing both is chemically and thermally stable.

The greatest feature of the present invention is that the regenerated cellulose porous membrane has circular pores on both the front and back surfaces, and the average pore diameter is 0.01 to
20μm, in-plane porosity of at least one surface is 30~
9096, or the number of holes per 1 d in the plane is 6 x 101/D or more and 3 x 10 mm/D or less. Here, the circular hole refers to the outer IPI (2E
The radius is rm and the center is the same as IIPet
39 radius trn means a hole with ra/rm of 0.5 or more. Although the pore shape of a porous membrane is not necessarily constant within the membrane, a porous membrane with circular pores is defined as having a probability of existence of pores satisfying r+a/rm≧0.5 of 80 or more.0 yen The shaped pores have excellent filtration performance by backwashing (cleaning the porous membrane surface by applying a cleaning solution in a direction opposite to the filtration direction). Further, when the in-plane porosity containing the circular shape becomes 30 or more, the filtration rate II' using the linear membrane increases significantly, and the filtration capacity also increases.

Theoretically, the filtration rate is proportional to the porosity, and the filtration capacity is also approximately proportional to the porosity.In a membrane containing 0 circular pores, when the 9 porosity becomes 3096 or more, the porosity increases. As long as the accompanying filtration rate and V overcapacity both increase and the porosity is 50% or more, the larger the better. However, from the viewpoint of ease of handling the porous membrane and mechanical properties of the porous membrane, a porosity of 90 or less is desirable. The liquid to be filtered flows Fj! from the surface of the porous membrane to the back surface. be done. When comparing various membrane combinations with the same average pore diameter on the surface and the same porosity, the filtration speed and filtration capacity were higher when the pore diameter on the back surface was larger than the pore diameter on the surface. .

Another feature of the product of the present invention is that the pore diameter ratio between the front and back surfaces is 115 or less and 1710 or more. When the surface directly in contact with the fluid to be filtered is the front surface, the filtration speed f is influenced not only by the average pore diameter and porosity of the front surface but also by the pore diameter of the back surface. As the surface pore size increases, the filtration rate increases. In addition, the backwashability of the membrane after filtration increases as the pore size ratio between the front and back surfaces is decreased. However, when the pore size ratio is 1/Is or less, almost no increase in backwashing performance is observed even if the pore size ratio is further lowered. Therefore, the pore size ratio is 1/1LTf
It is sufficient if it is 1/10 or more. If it is 1/10 or less, the number of pores on the membrane surface will decrease significantly, and the filtration rate fFi will decrease when compared with the same pore diameter.

The external shape of the porous membrane includes flat membranes, tubes, and hollow fibers. Moreover, the average pore radius means rstl defined by formula 111. Therefore, the average pore diameter as used in the present invention is defined as 273.

If the pore radius of 1 cdfi of porous membrane is r - r 10d r, then the number of pores t N (rld r ) is expressed as (N
(rl is the pore size distribution function), average pore radius ma5ti (given by equation 11).

The holes of the present invention are substantially circular holes, so that
The porous membrane of the present invention has the properties of a screen type filter. In other words, particles with a diameter larger than the diameter of the circumscribed circle touching the pores cannot absolutely pass through the pores. Laminated materials of fibrous or fine powder materials can be used as filter media, but these conventional filtration media , the shape of the pores is not constant, and depending on the rounding transient conditions (pressure, filtration rate) K, some particles may emit V, while others may not.In other words, a certain particle of interest may be captured by the pores. However, the average pore radius σS) shown in equation 111 cannot be obtained with these laminates.Therefore, the porous membrane of the present invention has the same porosity as that of a screen-type filter. The ultrafiltration rate of the membrane, which has pores, is approximately 7
It is proportional to the fourth power of s and also proportional to the porosity. Therefore, in order to increase only the overspeeding stations, the larger i is, the better. However, the maximum pore size is naturally determined in relation to the target particle size to be separated.

The area where the characteristics of a hydrophilic screen filter are fully demonstrated is 2 as the average pore diameter (2r).
It is 0 μm or less. (9) When the average pore diameter is 0.01 μm or less, the particles that can be separated by the eardrum are generally spherical and the surface area increases, and the characteristics of the circular pores of the present invention cannot be utilized. The object of the present invention is to use a porous membrane to separate and remove a target component in a liquid or gas mixture containing water as an object of good separation, and to do so at a high speed. Naturally, when the average pore size becomes small, the filtration rate decreases significantly. Further, although the thickness of the porous membrane is usually as thin as possible, it is generally 5 μm or more thick for ease of handling and to avoid the presence of pinholes. In the case of pores with an average pore diameter of 0.017 vm or less,
The probability of existence of non-through holes (non-through holes) increases, and the performance as a so-called membrane becomes lower than that expected for through holes.

The ninth step is to avoid the mixture of non-penetrating pores, and the average pore diameter is 0.01 μm.
It has to be more than that. By increasing the thickness of the porous membrane as the average pore diameter increases, the inclusion of pinholes can be prevented. However, since the filtration rate is inversely proportional to the membrane thickness, it is desirable that the membrane be thinner. Because of these contradictory tendencies, the optimal range of film thickness is closely related to the manufacturing method of the porous film.

The larger the porosity is, the more desirable it is; #) However, as the porosity increases, the mechanical properties of the porous membrane deteriorate. When the porosity becomes 30 hiss or more, the linearity of through-holes increases rapidly, and when the porosity exceeds 70, there are almost only through-holes.

We investigated the filtration characteristics of many regenerated cellulose porous membranes with the same σ average pore size and porosity, and found that even if ultrafiltration is performed at a pressure of less than 1 g (d pressure difference 160), cellulose crystals If the (101) plane in is averagely good looking with respect to the porous membrane surface, selective filtration of water is better if the plane is oriented parallel to the porous membrane surface. However, the amount of change in film thickness when immersed in water is greater when the film is oriented as described above than when it is not. The reason for this is unknown, but when the hydroxyl groups stand upright on the membrane surface (that is, when the (101) plane is arranged parallel to the porous membrane surface), water is selectively adsorbed, and the amorphous region of the membrane This is thought to be because it easily retains water inside. Such water selective permselectivity appears significantly when the degree of orientation of the (101) plane on the porous membrane is 60 or more.

Furthermore, in the mechanical loss tangent tanJ at K11l constant frequency v1110 ug and the temperature curve, the peak temperature Tm*
When x is 200C or more and 250C or less, the thermal stability of the porous membrane increases, and the post-treatment (t
There is little deterioration in physical properties after M resin processing and solvent treatment. Tmax
If Tmax is below 200C, it becomes thermally unstable and the silt filtration rate is significantly reduced by hot water treatment.If Tmax is above 250C, not only the selective filtration of water decreases, but also the physical properties after post-treatment of the porous membrane deteriorate. The deterioration is significant, and it becomes particularly brittle when processed with resin.

To increase the thermal stability and dimensional stability of the present invention,
The (101) plane microcrystal must have a major defect of 25A or more and a crystal perfection of 0.15 or less! ! There is.

However, swelling of the porous membrane when wet with water is unavoidable, and this swelling can be reduced by liquid bathing, resin processing, etc. Depending on the purpose, the porous membrane of the present invention may be post-treated by any of these methods.

The porous membrane of the present invention can be used to separate and remove target components from liquid or gas mixtures containing water, and for example, membranes for artificial kidneys, artificial livers, and artificial pancreases. Although it can be used in almost all fields in which it can be used as an ultra-fine membrane, this porous membrane, which is hydrophilic and has excellent mechanical properties, is particularly suitable for bio-related fields (medicine, biochemical industry) and food fermentation fields.

The product of the present invention can be prepared by adding an aqueous solution of sodium silicate (sodium silicate concentration f 3 o
A solution mixed with 7 layers of
It can be obtained by immersing the wire membrane in a sulfuric acid aqueous solution and washing with water, then immersing the wire membrane in 20C acetone, replacing the water in the membrane with acetone, and drying. .

Prior to Examples, methods for measuring various physical property values used in the detailed description of the invention are shown below.

average molecular weight> Intrinsic viscosity number ['! By substituting IF/- into 121, the average molecular weight (viscosity average molecular weight) My is calculated.

My - (II) X S, 2 X 10S (
21 Cellulose ■ and Cellulose [[-2 Identification of crystals, size of microcrystals, degree of crystal perfection, degree of crystal orientation] Rigaku Hxli1 generation [1 (RU-200PL) and goniometer (8G-9R), counter % 30KV using a scintillation counter and a Ka wave height analyzer in the counting section.
, the X-ray generator was operated at 80 mA, monochromated with a nickel filter, and alpha rays (wavelength λg 1,5
418 K) and X! 1. Measure the diffraction intensity.

Crystal structure (W1 constant, microcrystal size, crystal perfection #
In the case of j constant, xII is incident in the direction perpendicular to the film plane, and in the case of hollow fibers, xII is incident in the direction perpendicular to the fiber axis.

Scanning speed IC/min, chart speed 10a/min,
Time constant 1 second, divergence slit 4
, receiving slit 0.5 x 11, scattering slit 4, and the diffraction angle 2φ is in the range of 46 to 35'' to measure the X-ray diffraction intensity.

Cellulose ■Crystals are 2#, 12" (reflection from (101) plane), 20.f (reflection from (1oe) plane)
, 21' (reflection from the (002) plane). Cellulose [1-2 crystals are characterized by two diffraction patterns, 20 is about 12'' and 2f. To determine the size of microcrystals, for example, use the method "Polymer X-ray Diffraction" by E. Alexander. Kagaku Doujin Publishing, Chapter 7 Scheler
The formula (8ch@rr@r) is used.

Connect between 20-t and 55'' with [11]. Draw a base lIK perpendicular line from the top of the 0 diffraction peak as the base line, find the midpoint between the peak and the base edge, and draw a horizontal line passing through the midpoint. It is drawn between the diffraction intensity curves, the distance from the shoulder of the peak is determined, it is doubled, and this value is converted into radians to determine the line width.Furthermore, the line width is corrected using the following formula.

The line width determined above, b, is the line width measured using a silicone single crystal. The size of the microcrystals is AC8 (
3) Given by Eq.

A C8(lx+-λ/β-c-a'm 11
131λ is the wavelength of X-rays 1,5418X
It is.

The crystal perfection of cellulose IBM crystal is defined by the formula (41).

Here, Hl means (101) plane has 4 reflections and (002)
C%'b is the minimum value of X@diffraction during surface reflection and is (
The maximum diffraction intensity of 101) surface reflection, Hl, is the maximum diffraction intensity of (002) surface reflection. A value of 10 is the highest crystal perfection.

lowest when .

To measure the degree of crystal orientation of the (101) plane, when the sample is a flat film, xlII is incident parallel to the orientation. In the case of hollow fibers, the hollow fibers are compressed into a flat shape, and the hollow voids are transformed into an apparent state of two laminated films. KX@ is incident parallel to the plane of the laminated film. 2#-
Set the i-niometer at 12°. The azimuthal direction is scanned from -50° to +50° using the symmetrical transmission method, and the diffraction intensity in the azimuthal direction is recorded. Furthermore -1800 and +1800
Record the same-sex strength in the azimuthal direction. The scanning speed at this time was 47 minutes, and the chart speed was 1o m15)%
-16- Time consciousness is 1 second, collimator ij 2 M
φ, receiving slit aJ1m1.9, l114
It is 3.5 cranes wide. The resulting azimuthal diffraction! jlf
The orientation Hco is determined from the lll line. First, the average value of the diffraction intensities obtained at ±180@ is taken, and a horizontal line is drawn to define it as a baseline. Drop a bell from the top of the peak to the baseline and find the midpoint of its height. Draw a horizontal line passing through the midpoint, measure the distance between the two intersections of this and the diffraction intensity curve, convert this value to the angle white, and set the value to the orientation angle H (1).

The crystal orientation Hco is given by equation 151.

Co(11-((180-H)7180)X100
When the 151 crystal is unoriented, H is 180" and C
O is O.

Porosity PT A planar porous membrane is cut into a circular shape of 47tiφ, and the eardrum is dried in a vacuum to reduce the moisture content to OoS@ or less. When the thickness of the porous membrane after drying is d ((to)) and the weight is w (rl), the 9-porosity Pr (expressed as %) is given by formula (61).

In the case of hollow fibers, the inner diameter of the middle 9 fibers is p, (m), the outer diameter is
(-), hollow fiber length tt (ml), weight tW (f
), Pr is given by equation (71).

Average pore radius r1 and number of pores> Electron micrographs of the front and back surfaces are taken using a scanning electron microscope. From the photograph, the pore size distribution amount II N
Calculate (r) and substitute it into Equation 11I in the main text.

Also, hole l per 1a11! N Fi (given by formula 81.

N,,=/N(rld r
(81) Enlarge and print a scanning electron micrograph of the area where you want to find the pore size distribution to an appropriate size, for example 20m x 20m, and draw test lines (straight lines) at equal intervals on the resulting photo.
Draw 20 lines. Each straight line crosses a number of holes. The length of the straight line existing in the hole when it crosses the hole is measured, and this frequency linear distribution function l1lVt is determined. Using this frequency distribution function, one stereology (for example, Norio Suiwa,
Quantitative morphology.

(Iwanami Shoten) method to determine the N old. The in-plane porosity Pr is N
(Calculated using equation (9) using rl.

/Pr(11-π'f r"N(rld r
100 (9) (tan δ - temperature curve) A strip-shaped sample with a width of 1 W and a length of 5 scratches was cut out from the porous membrane, and a strip sample with a width of 1 W and a length of 5 scratches was cut out from the porous membrane.
A V-■e type was used, and the measurement frequency was 110 Hz.

Measured under dry air at an average heating rate of 10 C/-.

The peak temperature fTmax (r) of LatlB is read from the measured nine tan δ-temperature curves.

Example 1 Cellulose linters (average molecular weight 2jxlo") were added to a solution of copper ammonia prepared by a known method, with a concentration of 816.9"
After dissolving the rice cake at a concentration of 10%, an aqueous solution of sodium silicate (silicate soda concentration: 30%) was mixed into the solution, and after stirring, the mixture was cast onto a glass plate to a thickness of 50 μm. 9 of 20C
After being left in air for 14 hours, the resulting membrane is immersed in a 20C aqueous dithiosulfuric acid solution for 20 minutes, and then washed with water. After washing 2
The membrane was immersed in acetone at 0C, water in the membrane was replaced with acetone, and the membrane was sandwiched between filter papers and dried to obtain a porous membrane with a thickness of 10 μm. Table 1 shows the relationship between its microstructural features and various physical property values.

Ultrafiltration experiments were conducted using the membranes listed in Table 1.

Water permeability coefficient FiO, 07m/formula 1 fat Hg #1 is more than 3 times that of a regenerated cellulose porous membrane with the same porosity of 9. In addition, compared to conventional regenerated cellulose (molecular weight 3.5 x 104), the strength of this porous material is 10
It was more than 0 times. An electron micrograph of the front surface of the back of the wood is shown in FIG. 2, and an electron micrograph of the back surface is shown in FIG.

Table 1 Note that the average molecular weights of the cellulose molecules constituting the nine-porous membranes obtained with sample numbers 1-1 to 1-3 are all 5.5 to 6.
．． It is within the range of OX104.

Example 2 Cellulose linter (average molecular weight 2.5 x 101.
) was dissolved in a cupric ammonia solution prepared by a known method at a concentration of 9%, and then an aqueous solution of sodium silicate (with a concentration of 3.5, 11,1511% silicate) was mixed into the solution, and the four types were mixed. Polyethylene glycol and isopropyl alcohol (t-1011 L) were added to each of the liquids, stirred, cast in the same manner as in Example 1, solidified and regenerated, washed with water, and dried to form a second liquid.
A porous membrane shown in the table was obtained.

Samples N2-1.2-2.2-5 and 2-10.2-1
In No. 1.2-12, the pore diameter on the membrane surface was 0.01 μm or less, and almost no pores were observed under an electron microscope. Therefore, the permeability coefficient is extremely low, and the permeability coefficient of water under the same conditions as in Example 1 is 1X101, m/formula, scratch, and crane Hg.
It is as follows. In sample 2-6, the pore size ratio is less than 1710, and the water permeability coefficient is 2X 10'' m/equation...Hg, which is the same as that of sample y with the same porosity and average pore diameter.
2-sttr<, the transmission coefficient is about 1/2. Compared to sample N2-8, sample No. 2-9 has a tensile fracture strength (strength) of about 30%, and the rate of increase in overspeed due to backwashing is also 59, which is 77 for sample No. 111i112-8. %K
<Remarkably low compared to other countries.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing circular holes, FIG. 2 is a scanning electron micrograph of the front surface of the membrane of the present invention, and FIG. 5 is a scanning electron micrograph of the back surface.

Claims (1)

[Claims] Regenerated cellulose having an average molecular weight of 11+ cellulose molecules of 5 x 104 or more, and a crystalline region consisting essentially of cellulose, cellulose, l[-2, or a mixture of both. The cellulose porous membrane has circular pores on both the front and back surfaces of the eardrum, with an average pore diameter of 0 μm.
is 0.01 to 20g, and the pore size ratio between the front and back surfaces is 1/3 to 1/1.
0, and the in-plane porosity of at least one m is 50~?
091, or the number of pores per 1 d in the t4I image is 4X101/D or more and 5X10'/D or less. (21 Cellulose ■ Regenerated cell consisting only of crystals 4-
The regenerated cellulose porous membrane according to claim 1, wherein the degree of orientation of (1o1)lii with respect to the porous membrane surface is 60 or more. (3) The regenerated cellulose porous membrane according to claim 1 or 2, wherein the polydynamic loss peak temperature Tmax at a measurement frequency of 110 Hz is 200 to 250 c. (4) Claim 83 in which the size of the microcrystal of the (101) plane is 25λ or more and the crystal perfection is 0.15 or less
The regenerated cellulose porous membrane described in m.