JPS6160165B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a regenerated cellulose hollow fiber membrane used for diaphragm separation such as dialysis and ultrafiltration. BACKGROUND ART Conventionally, regenerated cellulose flat membranes, so-called viscose cellophane membranes, and copper ammonium chloride membrane membranes have been used for diaphragm separation in dialysis and the like. On the other hand, hollow fiber membranes, which can be filled into unit containers, have a large membrane area, and do not require a membrane support, have been put to practical use in diaphragm separation technology. An object of the present invention is to provide regenerated cellulose hollow fibers with excellent performance, shape and mechanical properties. Cellulose is known to have a hydrophilic chemical structure in its molecular chains, to have an affinity for water and water-soluble solutes, and to have excellent mechanical strength due to its hard molecular chains and crystallinity. Therefore, by using cellulose as a material and imparting a porous and dense membrane structure, a membrane with excellent water or solute permeability and strength can be obtained, which can then be further formed into a hollow fiber membrane with good roundness. If so, it is expected that the above-mentioned advantages can be utilized as a practical form. Regarding cellulose molding methods, the viscose method, ammonium copper method, and saponification method are known. The present inventors previously developed a method for producing cellulose hollow fibers with good roundness and high hollowness by saponification method in
It was disclosed in JP-A No. 46921 and JP-A-50-70611. In the former invention, a mixture containing cellulose diacetate and a plasticizer is melt-spun to form hollow fibers, and the hollow fibers contain 0.25 to 10% by weight of caustic soda and/or caustic potash and contain 65 to 65% by weight of caustic potassium.
This is a method for producing regenerated cellulose hollow fibers, which is treated with an aqueous solution heated to 100°C to substantially deacetylate it. In addition, the latter invention provides that the hollow fibers are treated with 65
This is a method for producing regenerated cellulose hollow fibers which is heated to ~98°C and immersed in a liquid medium that is a non-solvent for cellulose acetate. The thin film wall of the hollow fiber produced in this way is
It was found that it has a pore-dense membrane structure, a substantially cellulose-type crystal structure, and good semipermeability. As a result of further intensive research by the present inventors, a mixture containing cellulose acetate and a plasticizer was melt-spun to form hollow fibers, and the hollow fibers were placed in a heated non-solvent liquid medium. Hollows manufactured by immersion and heat treatment, then substantially deacetylated with an alkaline aqueous solution heated to a high temperature of about 80°C, followed by immersion treatment in a glycerin aqueous solution and drying heat treatment with a hot air dryer, etc. It has become clear that threads with specific properties can be practically advantageously used in dialysis operations for removing specific components from fluid mixtures by diffusion, or in water pressurization ultraviolet operations. That is, the present invention provides cellulose hollow fibers which have been further heat-treated after saponifying and regenerating cellulose acetate, wherein the hollow fiber membranes constituting the hollow fibers include (a) cellulose-type crystals with a crystallinity of 40 to 70%; (b) has a porosity of 40 to 70% by volume, (c) has a wet strength elongation ratio of 0.75 to 1.30, and (d) has a urea permeability coefficient of 0.02 to 0.04 cm/ min,
and (e) a water permeability coefficient of 1.5×10 ^-9 to 2.2×10 ^-9 cc・cm/
It is a regenerated cellulose hollow fiber characterized by cm ² ·S · cmHg. Here, the porosity is expressed by the following formula. Porosity (%) = (1-cellulose volume/hollow fiber membrane volume when swollen) x 100 The wet strength elongation ratio is expressed by the following formula. Wet strength elongation ratio = Wet strength (g/denier) / Wet elongation (%) × 100 The hollow fiber of the present invention has an inner diameter of 30 to 3000 μ and an outer diameter of 40 to
Particularly preferred are those having a diameter of 4000μ and a hollowness ratio of 40 to 70%. Here, the hollow ratio is expressed by the following formula. Hollowness ratio (%) = (inner diameter/outer diameter) ² × 100 It is a well-known fact that regenerated cellulose crystallizes in the cellulose form in rayon, cellophane, etc., but in the membrane of the present invention, the degree of crystallinity is further improved. is important. The higher the degree of crystallinity, the stronger the strength;
In addition, in the porous and dense membrane structure (see FIG. 1 of the attached drawings), there is an advantage that the amorphous portion is further reduced, and as a result, the proportion of pores is increased. It has been found that when the degree of crystallinity is less than 40%, the membrane is not sufficiently densified, and therefore the proportion of pores is small, making it impossible to obtain the desired permeation performance. In addition, cellulose is generally 70%
There is no crystallization for crystallinity exceeding . In order to provide a hollow fiber that can achieve excellent mechanical properties and permeation performance without any reservations, which is the object of the present invention, the crystallinity of the membrane needs to be in the range of 40 to 70%. A particularly preferred range of crystallinity is 50-65%. The degree of crystallinity was measured using X-ray diffraction on a room-temperature dried sample of a regenerated cellulose membrane using the method of Nelson et al. [MLNelson and RTO'Connor, Journal of Applied Polymer Science (J.Appl. Polym. Sci.) 8 , 1325 (1964)]. In other words, the crystallinity (%) is defined as the height I002 of the 002 plane diffraction peak (2θ = 21.7°) of cellulose type crystals and the amorphous background ground (2θ = 16.0°).
It was calculated from the height Iam using the following formula. Crystallinity (%) = I002-Iam/I002×10
0 The pores of hollow fiber membranes substantially contribute to the permeation of water and solutes. Its pore size is 20 to 100 Å, which allows vitamin _B12 to pass through, while proteins do not leak out.
It seems that. Further, the larger the porosity, that is, the ratio of pores to the entire membrane, the higher the substance permeability, and if the porosity is less than 40%, the desired permeation performance cannot be obtained. On the other hand, from the viewpoint of membrane strength and dimensional stability, it is required that the porosity not exceed 70%. Therefore, the hollow fiber membrane of the present invention has a porosity of 40 to 70%, preferably 50 to 65%. The net volume of cellulose is calculated from its mass (measured as denier, which is the weight per 9000 m for yarn) and specific gravity. The volume of the hollow fiber membrane when swollen can be calculated by measuring the cross-sectional dimension of the hollow fiber using a microscope. Since the membrane of the present invention is used in a wet state, it must have particularly excellent strength, pressure resistance, and dimensional stability in that state. FIG. 2 of the accompanying drawings shows the stretching curve of the hollow fiber membrane of the present invention. The slope of this curve greatly contributes to the pressure resistance and dimensional stability of the membrane〓〓〓〓
This is known. That is, since the slope at 0% elongation is the rigidity modulus, the larger the slope, the better the pressure resistance and dimensional stability, and the smaller the elongation, the better dimensional stability. The present inventor has expressed the slope as a ratio of breaking strength to elongation, and has completed a hollow fiber membrane with excellent mechanical properties by regulating the strength to always have a constant ratio to elongation. . If this strength-elongation ratio is less than 0.7, the pressure resistance and dimensional stability of the hollow fiber membrane will be poor, while if it exceeds 1.30, the hollow fiber membrane will be hard and the desired performance will not be obtained. Therefore, the strength-elongation ratio needs to be in the range of 0.75 to 1.30. On the other hand, when looking at the hollow fiber membrane of the present invention from the perspective of the microstructure of cellulose, it has a high degree of crystallinity and has large crystal micelles with a porous, loosely packed structure. This is also the reason why the membrane of the present invention exhibits low elongation compared to its strength. In order to exhibit such excellent performance and physical properties, the regenerated cellulose hollow fiber membrane of the present invention is a membrane shaped to have crystallinity, porosity, and wet strength/elongation ratio within the above ranges from the structural standpoint. It is. The membrane of the present invention can be treated with an aqueous glycerin solution to maintain its porous, loose and dense membrane structure, thereby preserving its performance and allowing it to be put to practical use. That is, the glycerin treatment makes it possible to dry the hollow fiber membrane, which is then assembled into a diaphragm separator by filling it into a diaphragm separation container and molding resin at the end. Various types of diaphragm separation containers using hollow fibers are known, but the present inventors have proposed a fluid separation method in which hollow fibers cross and overlap each other in Japanese Patent Application Laid-open Nos. 50-81972 and 50-85584. disclosed the device. The effects of the present invention are that mechanical properties, dimensional stability, roundness, and material permeation performance are excellent. The film of the present invention has high crystallinity and wet breaking strength.
Strong at 0.2-0.4g/de. In addition, the elongation is 0.75 to 1.30 in wet strength/elongation ratio, and it has excellent dimensional stability. Further, the modulus of rigidity is Young's modulus of 9 to 10 Kg/mm ² , and the theoretical membrane breakdown pressure is as high as 6 to 9 Kg/cm ² . The roundness of hollow fibers is determined by the manufacturing conditions, but in addition, excellent mechanical properties are effective in stabilizing the hollow fibers, resulting in good roundness of the hollow fibers in the final product. Regarding the permeability of the membrane, in the porous membrane structure, solutes permeate by concentration diffusion through the pores and sparse areas, and water permeates under pressure. The membrane of the present invention has a diffusion permeation of urea of 0.02 to 0.04 cm/min and a pressure permeation of water of 1.5×10 ^-9 to 2.2×10 ^-9 cc・cm/cm ²
It has excellent S cmHg and can be used especially in dialysis equipment for artificial kidneys. The above-mentioned urea permeability coefficient was measured by a single-pass clearance method for a hemodialyzer, and calculated using the following formula. K _u ; Urea permeability coefficient (cm/mm) Q _B ; Flow rate of urea aqueous solution on dialyzer blood side 200
(ml/mm) Q _D ; Water flow rate on dialyzer dialysate side 500 (ml/mm)
min) A: Effective membrane area of dialyzer (cm ² ) DA _u ; Dialysis of urea of dialyzer (ml/min) However, the urea concentration of the urea aqueous solution is 0.01wt%,
The measurement temperature was 37°C. Example 1 A mixture obtained by adding and mixing 40 parts of polyethylene glycol (molecular weight approximately 400) to 100 parts of cellulose diacetate was melt-spun to give an outer diameter of 340μ and an inner diameter.
A hollow fiber with a cross section of 250 μm was made into a nearly perfect circle. The hollow fibers were treated with hot water at 75°C and then treated with 2.4 ml of caustic soda.
% aqueous solution at 80°C, followed by treatment with a glycerin aqueous solution to deposit 50% glycerin per dry weight of the hollow fiber,
Further, when dry heat treatment was performed at 90°C for 5 minutes using a hot air circulation type heat treatment machine, a regenerated cellulose hollow fiber membrane with an outer diameter of 330 μm and an inner diameter of 250 μm was obtained, which had excellent physical properties and performance. 〓〓〓〓

[Table] The above table also includes examples of crystallization and porosity outside the scope of the present invention. It can be seen that these comparative examples have inferior performance. Example 2 Various plasticizers shown in Table 2 were added and mixed to 100 parts of cellulose diacetate, and the mixture was melt-spun to obtain hollow fibers. A saponification treatment was performed for 1.5 minutes in the same manner as in Example 1, and a glycerin treatment and dry heat treatment were further performed in the same manner as in Example 1 to obtain a regenerated cellulose hollow fiber membrane. The membrane of the present invention showed excellent physical properties and performance. On the other hand, comparative examples with strength-elongation ratios outside the range had low performance and poor circularity.

[Table] 〓〓〓〓

【table】 [Brief explanation of the drawing]

FIG. 1 of the accompanying drawings shows a schematic structural diagram of the regenerated cellulose hollow fiber membrane of the present invention, and FIG. 2 shows a drawing curve diagram. In addition, each number in FIG. 2 indicates the sample number of the example, and A indicates the scope of the present invention. 〓〓〓〓

Claims (1)

[Scope of Claims] 1. A cellulose hollow fiber which has been further heat-treated after saponifying and regenerating cellulose acetate, wherein the hollow fiber membrane constituting the hollow fiber comprises (a) cellulose-type crystals with a crystallinity of 40 to 70%; (b) has a porosity of 40 to 70% by volume, (c) has a wet strength elongation ratio of 0.75 to 1.30, and (d) has a urea permeability coefficient of 0.02 to 0.04 cm. /min, and (e) water permeability coefficient of 1.5×10 ^-9 to 2.2×10 ^-9 cc・cm/
A regenerated cellulose hollow fiber characterized by ^cm2・S・cmHg.