JPS621403A - Cuprammonium cellulose porous membrane with good dimensional stability - Google Patents

Abstract

PURPOSE:To provide a cuprammonium cellulose membrane having a good dimensional stability when wet, super mechanical disposition and super filtration performance by limiting such characteristics within a specific range as average molecular weight, in-plane orientation of molecular chain, dynamic modulus, average hole diameter, in-plane porosity and hole density. CONSTITUTION:To improve the brittleness, the average molecular weight of cellulose molecule is set over 5X10<4>. Cuprammonium cellulose with less protein molecule adsorbed is used. The average hole diameter should be 0.02-10mum, and the in-plane porosity of one plate is over 30% or the hole density per 1cm<2> of in-plane is 6X10<5>-3X10<7>pcs./D. All this setting increases filtration speed and filtration capacity. Also the in-plane orientation of cellulose molecular chain is limited within 60-80%, which lessens the transformation by swelling. The thermal stability of porous membrane is increased, provided the peak temperature in mechanical loss tangent - thermal curve measured at the frequency 110Hz is over 250 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a copper ammonium cellulose porous membrane with good dimensional stability.

Cocote, copper ammonium cellulose means regenerated cellulose that has been regenerated from cellulose cupric ammonium solution.

The copper ammonium cellulose porous membrane of the present invention is useful for separating and removing and concentrating target components in liquid or gas mixtures containing water, and is particularly used in biological fields and food fermentation fields.

[Conventional technology]

Membrane separation technology is attracting attention among materials separation and purification technologies. Polymer membranes are used in a wide range of fields by taking advantage of the characteristics of the membrane separation process, such as not requiring temperature changes associated with membrane separation, which is different from distillation, requiring little energy for separation, and having a compact process. has been done. For example, fields such as dairy farming, fisheries, livestock farming, food processing, pharmaceuticals, chemical industry, textile dyeing processing, steel, machinery, surface treatment, water treatment, and atomic crab industry. Fields where membrane separation systems may become central in the future include (a) fields that require concentration purification and recovery at low temperatures (food and biochemical industries);
(o) Fields that require sterility and dust-free conditions (pharmaceuticals and therapeutic institutions, electronic industry), (c) Concentration and recovery of trace amounts of expensive substances (
(nuclear power, heavy metal field), (2) special small quantity separation field (medical field), and (e) energy-intensive separation field (distillation alternative). As membranes used in these fields, there is an increasing need for hydrophilic membranes that have large pores, good dimensional stability when wet, and are easy to handle.

A porous membrane made of cellulose, which is a typical example of a hydrophilic polymer, has an average pore diameter of 1001 (0.01μfn).
) The following porous membranes for artificial kidneys are known. This porous membrane has small pore diameter and low porosity (10% or less).
Therefore, it can hardly be used for ultrafiltration or microfiltration. On the other hand, a regenerated cellulose porous membrane has been obtained by saponifying a cellulose derivative membrane such as cellulose acetate or cellulose nitrate with an aqueous alkaline 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 a starting material, the molecular weight of the cellulose molecules after regeneration is low, being 3.5×10′ or less. In a conventional regenerated cellulose porous membrane having pores in such a pore size range, the molecular weight of cellulose molecules is 4.0×10′ or less. Therefore, the mechanical properties (strength in %) of the porous membrane in a dry state are extremely low and brittle. For example, the average porosity of a porous membrane is Pr
If P (expressed as a percentage), the elastic modulus is approximately 102 (10
0-PrP)'dyn/In''. The tensile strength at break is approximately proportional to the modulus of elasticity, which is approximately 1/10. The strength in a wet state with water is even lower than in a dry state. Therefore, conventional regenerated cellulose porous membranes obtained from cellulose derivatives may be damaged during handling.

In addition, the above-mentioned method for producing a regenerated cellulose porous membrane that regenerates cellulose derivatives requires a long manufacturing process;
It also has the disadvantage of being expensive.

Furthermore, when the regenerated cellulose porous membrane is swollen in water, it swells and deforms. As a result, the flow of the fluid to be filtered is disturbed, causing clogging and stagnation.

[Problem that the invention seeks to solve]

The purpose of the present invention is to overcome the drawbacks of the conventional regenerated cellulose porous membrane as described above, to have particularly good dimensional stability when wet, excellent mechanical properties and filtration performance, and to be able to be produced industrially and advantageously. To provide a copper ammonium cellulose porous membrane.

[Means for solving problems]

The copper ammonium cellulose porous membrane according to the present invention has an average molecular weight of cellulose molecules of 5 x 10' or more, and an in-plane orientation degree of cellulose molecular chains constituting the porous membrane of 60% to 80%.
The dynamic elastic modulus at 30°C at a measurement frequency of 110Hz is 3.
．． Ox 108 (100-PrP) dyV/6n" or more (Prp is the average porosity expressed as a percentage), the porous film has an average pore diameter of 0.02 to 10 μm, and has in-plane pores on at least one surface. The porosity (Pr) is 30% or more, or the pore density per 1c1n2 in the plane is 6X10
It is characterized by being 5 pieces/D or more and 3×10 7 pieces/D or less.

The first feature of the copper ammonium cellulose porous membrane of the present invention is that the membrane is composed of cellulose molecules having an average molecular weight of 5 x 10' 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. It is observed that the influence of the average molecular weight on the physical properties of the film tends to become saturated as the average molecular weight increases. For example, if the average molecular weight is 5X1
30 at a measurement frequency of 110Hz if it is greater than 0'
Dynamic modulus of elasticity td 3.0xlO8 (100-PrP
) dyn 702 or more. Therefore, as long as the average molecular landscape is 5.0×10' or more, it is acceptable from the point of view of practical ease of handling. From the viewpoint of ease of manufacturing the porous membrane, the average molecular weight is desirably 3×10 5 or less.

That is, one of the characteristics of the copper ammonium cellulose porous membrane of the present invention is that it has sufficient mechanical properties even in a dry state without a swelling agent such as glycerin.

Furthermore, as a result of studying the adsorption properties between proteins and polymeric materials, ammonium ammonium cellulose is a hydrophilic material, so it has the characteristic that it adsorbs very little protein compared to other polymeric materials. Therefore, the copper ammonium cellulose porous membrane of the present invention can be effectively used in the field of precision filtration related to water treatment and biological systems.

The second feature of the copper ammonium cellulose porous membrane of the present invention is that the average pore diameter is 0.02 to 10 μm, and the in-plane porosity of at least one surface is 30 μm or more, or
Hole density per unit 2 is 6 x 105/D or more, 3 x 1
07 pieces/D or less. When the in-plane porosity is 30% or more, the filtration rate of the porous membrane increases significantly, and the filtration capacity also increases. Theoretically, the filtration rate is proportional to the average porosity in terms of volume and inversely proportional to the membrane thickness, and the filtration capacity is also approximately proportional to the average porosity. When the in-plane porosity increases to 30 inches or more, both the filtration rate and the filtration capacity increase as the in-plane porosity increases. If the in-plane porosity is 30 inches or more,
The thicker both the in-plane porosity and the average porosity, the better. Desirably, the average porosity should be 55% or more. However, from the viewpoint of ease of handling the porous membrane and mechanical properties of the porous membrane, the average porosity is preferably 90% or less. The fluid to be filtered is filtered from the front surface to the back surface of the porous membrane.

When comparing the filtration rates of various membrane combinations with the same average pore size on the surface and the same average porosity, if the pore size on the back side is larger than the pore size on the front side, the filtration rate and filtration capacity are also large. The average pore diameter defined by electron microscopy in the cross-sectional direction of the membrane generally changes depending on the position in the thickness direction of the membrane.

Similarly, the in-plane porosity also changes. The in-plane porosity is generally smaller than the average porosity. In particular, the in-plane porosity in the center of the membrane is important in that it controls the filtration rate, and if the porosity is 30 or more, the filtration rate is high.

Moreover, the average hole radius means an arch defined by equation (1). Porous membrane 1crI! The hole radius per 2 is rxr
If the pore density existing at +dr is expressed as N(r)dr, then (
N(r) is a pore diameter distribution function), and the average pore diameter arch is given by equation (1). The average pore diameter in the present invention is defined as 25.

The ultrafiltration rate per pore is proportional to the fourth power of the pores, and is also proportional to the constant porosity. Therefore, in order to increase only the filtration rate, the larger i is, the better. However, in relation to the particle size of the target separation target,
Naturally, the maximum pore diameter is determined. The region where the characteristics as a hydrophilic screen filter are fully exhibited is an average pore diameter (ie, two bows) of 20 μm or less. Furthermore, if the average pore diameter is less than 0.02 μm, the particles to be separated by the membrane generally have an increased number of particles that are not spherical, and the characteristics of the porous membrane of the present invention cannot be utilized. As will be described later, the main purpose of the porous membrane of the present invention is to separate and remove and concentrate target components in liquid or gas mixtures containing water as separation targets, and to filter at high speed. With the goal. Naturally, as the average pore diameter becomes smaller, the filtration rate decreases significantly.

Generally, the thinner the porous membrane is, the better, but for ease of handling and to avoid the presence of pinholes,
Generally, it has a thickness of μm or more. Average pore size is 0
In the case of holes smaller than 102 μm, the probability of existence of holes that are not through holes (non-through holes) increases.

In other words, the performance as a filtration membrane is lower than that expected for through holes. In order to avoid the presence of non-through holes, the average pore diameter must be 0.02 μm or more. 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 greatest feature of the copper ammonium cellulose porous membrane of the present invention is that the degree of in-plane orientation of the cellulose molecular chains constituting the porous membrane is 60 to 8.
This is a point within the range of 0q6. The present inventors investigated the relationship between the degree of in-plane orientation of cellulose molecular chains and the dimensional stability of the porous membrane during wet conditions. As a result, we found that when the degree of in-plane orientation is less than 60 degrees, the porous membrane deforms due to swelling. elongation) is large. Further, when the degree of in-plane orientation exceeds 80%, swelling (elongation) deformation in the film thickness direction and contraction deformation in the film plane direction occur.

Therefore, in order to prevent deformation of the cellulose porous membrane due to swelling and blockage on the porous membrane surface, the degree of in-plane orientation of the cellulose molecular chains constituting the porous membrane must be between 60 and 80%. be.

Furthermore, in the mechanical loss tangent - δ -temperature curve at a measurement frequency of 110 Hz, the peak temperature T'ma is 25
If the temperature is 0° C. or higher, the thermal stability of the porous membrane increases, and the heat resistance in an organic solvent increases.

The copper ammonium cellulose porous MFi of the present invention can be manufactured as follows. For example, JP-A-58-89625, JP-A-59-45333, JP-A-59-45334 and JP-A-5
According to the method described in No. 9-199728, the cellulose was removed from the copper ammonia solution, left in an acetone vapor atmosphere, regenerated with an aqueous sulfuric acid solution, washed with water, and then the porous membrane was treated with acetone to replace the moisture with acetone. do.

Then, the porous membrane of the present invention is obtained by fixing the membrane in a biaxial stretching machine and drying it in a 5 to 20% stretched state.

A specific example of the method for manufacturing the porous membrane of the present invention is as follows. A 10% (by weight) cellulose cuprammonium solution was cast onto a glass plate using a 500 μm thick applicator in the usual manner, immediately placed in an acetone vapor atmosphere at 35°C, and left for 60 minutes to form a film. at 20℃, 2
% sulfuric acid aqueous solution, then washed with water, and then immersed in 1 ft 20 cm of acetone to replace the moisture in the membrane with acetone, and then fixed the membrane in a biaxial stretching machine, and Dry in a 10% stretched state.

〔Effect of the invention〕

The copper ammonium cellulose porous membrane of the present invention has excellent dimensional stability when wet, as well as mechanical properties such as strength, filtration performance, and heat resistance.

Separation targets for which the porous membrane of the present invention can be used include:
Liquids containing water can be used to separate and remove target components in gas mixtures, and therefore, this porous membrane can be used, for example, to
Part B for artificial kidneys is useful as a porous membrane for artificial liver, artificial pancreas, plasma separation, microorganism separation, and cyst culture. Although it can be used in almost all other fields in which ultrafiltration membranes can be used, the porous membrane of the present invention, which is hydrophilic and has excellent mechanical properties and is strong, can be used in bio-related fields (medicine, biochemical industry) and food fermentation fields. Particularly suitable.

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 [η) (Ill/I) measured in cupric ammonia solution (20'tl:)? By substituting the formula (2), the average molecular weight (viscosity average molecular weight) Mv is calculated.

Horse = [7] x 3.2 A pulse height analyzer is used for the counting section, and 3°k
The X-ray generator was operated at V and 80 mA, and α-rays (wavelength λ = 1.542
) is measured using the symmetric transmission method.

The porous membranes were stacked front and back and bundled in parallel, and fixed to a fiber sample measuring device (rotating sample stand) manufactured by Rigaku Denki I so that the X-rays were incident parallel to the membrane surface. Scanning speed 1°/
min, chart speed 1o/min.

Time constant 1 second, /Epergence slit A
0. When the receiving slit is 0.3 tram and the scattering slit is 0, the diffraction angle 2θ is 4°~
The X-ray diffraction intensity curve is measured in a range of 35°.

Copper ammonium cellulose porous film c, cellulose n crystal m, 2θ = 12° (reflection from (101) plane), 20' (
(reflection from (xoT) plane), 381 diffraction at 22° (reflection from (002) plane).

To determine the in-plane orientation of the (002) plane, xme is incident parallel to the plane of the laminated film. A co9niometer is set at 2θ=21.5°, and an X-ray diffraction intensity curve in an azimuthal direction of 180° from the meridian through the equator line and back to the meridian is measured using the symmetrical transmission method. The scanning speed at this time is 4
°/min, the chart speed is 10/min, the time constant is 1 second, the collimator is 2/min, and the receiving slit is 1.9/min in height and 3.5 days in width. The half-width H is read from the obtained diffraction intensity curve in the azimuthal direction, and is substituted into equation (3) to calculate the degree of in-plane orientation.

In-plane orientation degree (work = ((180-H)/180) cutting 0
0 (3) <Average pore radius ζ, in-plane porosity Pr, pore density N> A JEOL JSM-U3 type scanning electron microscope is used to take electron micrographs of the front and back surfaces.

At this time, the imaging magnification is made as large as possible so that the enlargement magnification is 3 times or less. The pore size distribution function N (r) is calculated from the photograph using a known method, and is expressed as formula (1) in the text. In other words, the pore size distribution is determined and a scanning electron micrograph of the 90-degree area is taken to an appropriate size, for example, 20 m x 20 m.
crn) and draw 20 test lines (straight lines) at equal intervals on the resulting photograph. Each straight line crosses a number of holes.

The length of the straight line where the pore internal pressure exists when it crosses the pores on the front or back surface of the porous membrane is measured, and the frequency distribution function is determined. 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, the pore density calculated by equation (5) is This is defined as the pore density 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, stereology (
For example, N(r) is determined by the method of Norio Suwa, Quantitative Morphology, Goiwa Shoten). In-plane porosity P, is ・N
It is calculated using equation (4) using (r).

Average porosity Prρ> A planar porous membrane is cut out into a circular shape with a diameter of 47 days, and the porous membrane is dried in a vacuum to a moisture content f of 0.596 or less.

If the thickness of the porous membrane after drying is d (i, weight 6wG), the average porosity Prρ is given by equation (6) <Tm1x
and dynamic elastic modulus〉 A strip-shaped sample with a width of 1cm and a length of 5crn was cut out from the porous membrane, and the Toyo? - Rheo Pipelon (Rh) made by Ludwin
ao Vibron) DDV-Inc W,
Measurement frequency 110Hz, average heating rate 1 under dry air
Measure the −δ-temperature curve and the dynamic modulus-temperature curve at 0° C./min. According to the obtained curve, the peak temperature position T'm of sea δ
Read the dynamic elastic modulus at a temperature of 30°C.

Wet Sea Linkage> The obtained porous membrane is left at a temperature of 20° C. and a humidity of 65% for 16 hours or more. After that, porous at width 10, length 106
The porous membrane was cut into a size of n and immersed in pure water at t-25°C. After 30 minutes, the width and length of the wet porous membrane are measured. The wet sea linkage is given by equation (7).

〔Example〕

The present invention will be specifically described below with reference to Examples.

<Example> Cellulose linter (average molecular weight 2.3 x 10) was dissolved in a copper ammonia solution prepared by a known method at a concentration of VcB, then 12% acetone was added to the solution, and after stirring, the solution was dissolved in air at 30°C. 500μ on a glass plate in the usual way.
Cast with m applicator.

Immediately, the cast product was placed in an acetone vapor atmosphere at 20°C with a concentration of 70% of the saturated vapor pressure, and after being left for 100 minutes, it was immersed in an aqueous solution of di-sulfuric acid at 20°C for 15 minutes for regeneration.
After that, the hindlimb membrane was washed with water, immersed in acetone at t-20°C for 15 minutes to replace the moisture in the membrane with acetone, and then fixed in a biaxial stretching machine and vacuumed after being stretched by 10%. Dry. The average molecular weight of the obtained porous membrane was 5
．． 7X10, the in-plane orientation degree of the (002) plane is 6813
The dynamic elastic modulus at 0°C is 1.3 x 10 d7n /y
B”, average pore diameter is 1.1μm, average porosity is 66cm, pore density is 4.1X10, and 'rmax is 260℃
It is. In addition, the wet sea linkage in the vertical direction when wet was +5 qb, and the horizontal wet sea linkage was +6 qb.

Comparative Example A moderately porous cellulose acetate membrane obtained by a known method (US Pat. No. 3,883,626) was saponified at 30°C using an aqueous solution of pi (12.0) sodium hydroxide to obtain a regenerated porous cellulose membrane. Table 1 shows its microstructural characteristics and various physical property values.

Table 1 Note that the average molecular weight of cellulose molecules constituting the porous membranes obtained with sample numbers 1-1 to 1-3 is 1.5X10 to 2.
0x10 distribution.

The porous membrane obtained by regenerating the cellulose derivative has a low average pore diameter, a dynamic elastic modulus lower than that of the porous membrane of the present invention, and a low Tm1. 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. In addition, the wet sea linkage is -10%
It can be seen that the elongation during contraction is large.

Claims (1)

[Scope of Claims] 1. The average molecular weight of cellulose molecules is 5×10^4 or more, and the degree of in-plane orientation of cellulose molecular chains constituting the porous membrane is 6.
It is within the range of 0% to 80%, and the dynamic elastic modulus at 30°C at a measurement frequency of 110Hz is 3.0 × 10^8 (100
-Prρ) dyn/cm^2 or more (Prρ is the average porosity expressed as a percentage), and the average pore diameter (D) in the porous membrane is 0.
．． 02 to 10 μm, and the in-plane porosity (Pr) of at least one surface is 30% or more, or the pore density per 1 cm^2 in the plane is 6 x 10^5 pieces/D or more, 3
A copper ammonium cellulose porous membrane having good dimensional stability when wet, characterized in that the number is 10^7 pieces/D (the unit of D is μm) or less. 2. The average porosity (Prρ) of the porous membrane is 55% or more, 90
% or less, and the in-plane porosity (P
The copper ammonium cellulose porous membrane according to claim 1, wherein r) is 30% or more. 3. Mechanical loss tangent ta at measurement frequency 110Hz
The copper ammonium cellulose porous membrane according to claim 1 or 2, wherein the peak temperature T_m_a_x of n^δ is 250°C or higher.