JPS6042285B2 - Method for producing permselective cellulose acetate hollow fibers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing cellulose acetate hollow fibers, and more specifically, the present invention relates to a method for producing cellulose acetate hollow fibers, and more specifically, cellulose acetate hollow fibers having good fluid separation properties, a perfectly circular cross-sectional shape, and excellent strength. This invention relates to a method for manufacturing cellulose acetate hollow fibers.

In recent years, the use of selectively permeable membranes has been actively investigated in fields such as seawater desalination, wastewater treatment, artificial storage, gas separation, and recovery of useful components in the food industry.

Hollow fibrous membranes, which are a type of separation membrane used in this field, can increase the membrane area per unit space, making it possible to increase space efficiency and requiring less reinforcing material than flat membranes. It has various advantages such as not requiring the use of a different support, and its development is becoming more and more popular. Hollow fibers made of cellulose acetate, which have been developed so far, are being recognized as useful in the above fields. There are disadvantages such as poor strength, which tends to cause trouble during the separation process, and insufficient strength, which can cause breakage during use.The emergence of cellulose acetate hollow fibers that do not have these disadvantages has been awaited.

Therefore, the present inventors are currently conducting studies with the aim of obtaining cellulose acetate hollow fibers that do not have the above-mentioned drawbacks.
It has been discovered that the strength of cellulose acetate hollow fibers can be improved by stretching the hollow fibers after spinning, but with this method, the hollow fibers become flattened during the stretching process. It was not possible to obtain the desired hollow fiber.

Therefore, as a result of further study, we found that when cellulose acetate hollow fibers are produced by a wet method, they can be easily drawn by using a solution of fatty acid ester as a core material, and the above-mentioned method can be easily drawn without causing the cross-section of the hollow fibers to become flat. The present invention was completed by discovering that it is possible to produce cellulose acetate hollow fibers that can achieve the objectives. The gist of the present invention is to extrude a stock solution of cellulose acetate dissolved in a water-soluble organic solvent with a boiling point of 100'C or higher through an annular slit in the outer tube of a spinneret with a double tube structure, and to A method for producing cellulose acetate hollow fibers, which comprises introducing an ester-based liquid as a core material into an aqueous coagulation bath to coagulate the hollow fibers, and then washing and stretching the hollow fibers in hot water. .

The cellulose acetate used in carrying out the present invention may be any cellulose acetate having an acetylation degree of 45 to 60%.

In addition, the solvent used to dissolve cellulose acetate must be an organic solvent with a boiling point of 100°C or higher, and if this solvent is not water-soluble, the wall structure of the hollow fibers during coagulation must be This is not preferable because it is difficult to control.

In addition, when the boiling point of this solvent is 100°C or less, a thin dense layer may be formed on the outside of the wall of the hollow fiber during spinning, which is the reason for the ultraviolet application and dialysis aimed at in the present invention. This is not preferable because it becomes difficult to make hollow fibers for use. Specific examples of water-soluble organic solvents having a boiling point of 100°C or higher include dimethylformamide, dimethylsulfoxide, dimethylacetamide, dioxane, and the like. In addition, the diameter of the pores formed in the obtained hollow fiber wall membrane is made uniform, and the pores are uniformly distributed in the wall membrane, and the dialysis properties of the hollow fibers are improved.
It improves the ultrapolar characteristics and prevents the formation of macro voids, thereby reducing the mag. In order to prevent troubles such as damage caused by roboids, it is preferable to add a non-solvent, especially water, to the organic solvent solution of cellulose acetate.

When such a non-solvent, especially water, is added, the viscosity of the cellulose acetate solution increases, forming a hollow shape. The permeability of the coagulated liquid into the wall membrane during solidification of the stock solution is now controlled extremely efficiently, and the diameter of the pores formed in the wall membrane is uniform, eliminating undesirable phenomena such as the formation of macrohoids. It almost never happens. Furthermore, since the pores can be distributed extremely uniformly in the wall membrane, the ultrafiltration and dialysis characteristics can also be extremely good. The amount of this non-solvent to be added is preferably 1 to 1% by weight relative to the water-soluble organic solvent to cellulose acetate.If the amount added is less than 1% by weight, no effect will be obtained; If it exceeds 1% by weight, it is not preferable because it causes disadvantageous phenomena such as a decrease in the solubility of cellulose acetate in solvents. The fatty acid ester used as the core material in carrying out the present invention is a fatty acid ester having a total carbon number of 4 to 30, such as methyl oleate, methyl laurate, oleyl oleate, sorbitan oleate, isooctyl stearate. ester, isopropyl stearate, isopropyl myristate, monomethyl azelate, dimethyl azelate, dodecyl acetate, decyl propionate, and the like.

These core materials are slower than water-based coagulants, various alcohols, polyethylene oxides, various hydrocarbons, carbon disulfide, carbon tetrachloride, etc. that have traditionally been used as coagulants in wet spinning of cellulose acetate. Because it has a solidifying effect, there are no problems such as deformation of the yarn due to pulsation near the spinneret or destruction of the hollow part during hollow fiber extrusion. As a result, it is possible to apply a high draft during spinning, and compared to conventional methods, the precision of the spinneret with a special double-tube structure used during spinning is not required to be very precise, and it is possible to By determining only the discharge rate and draft rate, it is possible to easily produce hollow fibers with a desired diameter and uniform wall thickness. The inner surface of the resulting hollow fiber wall membrane can also have excellent smoothness, which improves the characteristics of the hollow fiber.The coagulation bath used in carrying out the present invention improves the stability of spinning. In order to ensure that the bath composition is always constant and the separation characteristics of the obtained hollow fibers to be constant, the water-soluble organic solvent of the cellulose acetate mentioned above is contained in an amount of 5 to 6%. It is preferable to use an aqueous coagulation bath.

In order to produce cellulose acetate hollow fibers by the method of the present invention, the above organic solvent solution of cellulose acetate is discharged from an outer tube with a double tube structure, and a fatty acid ester liquid is injected as a core material from a double inner tube. At the same time as extruding it from the spinneret,
It is necessary to take the hollow stock solution formed in this way under a high draft. It is essential.

At this time, when carrying out the pure wet method, a method using a coagulation bath with relatively low coagulation ability in the high draft process and then a coagulation bath with high coagulation ability can also be used, but it is most preferable to use a coagulation bath with a high coagulation ability. A method that can control the uniformity of the wall film is to introduce the hollow stock solution discharged from the spinneret into air or inert gas, apply a high draft, and then introduce it into the coagulation bath. When carrying out this method, when a solvent with a low boiling point is used as a solvent for cellulose acetate, the solvent evaporates from the hollow stock solution while it travels through the air, and a thin dense layer is formed on the outer wall of the hollow fibers. However, in the present invention, an organic solvent with a boiling point of 100°C or higher is used as the solvent for cellulose acetate, so such inconveniences are extremely unlikely to occur. . In particular, by performing spinning while keeping the temperature of the organic solvent solution of cellulose acetate at 80°C or lower, the volatilization of the solvent during the gas flow from the hollow stock solution can be prevented.
Since it can be reduced to zero, it is possible to prevent the formation of a dense layer on the outer layer of the hollow fiber wall membrane, and it is possible to obtain hollow fibers with excellent ultraviolet permeability and water permeability. In order to produce hollow fibers by the method of the present invention, it is necessary to wash and draw the hollow fibers containing the core material produced by the method described above in hot water.

The hot water used is hot water of 50 to 100°C, and the stretching ratio is preferably in the range of 1.05 to 2.0 times. If the temperature of the hot water used is lower than 50'C, it will not be possible to improve the cleaning effect of the hollow fibers, and furthermore, the hollow fibers will not be able to be stretched. This is undesirable because it causes undesirable phenomena such as breakage and damage. In addition, the stretching ratio must be 1.05 or more, and if the stretching ratio is less than 1.05, it is impossible to obtain hollow fibers with good strength, and the hollow fibers may have irregularities in shape. On the other hand, if the stretching ratio exceeds 2 times, yarn breakage and pinholes may occur, which is not preferable. Therefore, in the present invention, the stretching ratio is set to 1.05 to 2. By stretching the fibers within the range, strength is imparted to the obtained hollow fibers, and the shape is stabilized, and furthermore, the dialysis performance can be controlled by stretching. As specified in the present invention, the drawing of hollow fibers capable of producing the above-mentioned favorable effects was made possible for the first time by using a fatty acid ester as a core material during the production of hollow fibers. This was completely impossible using the conventional hollow fiber manufacturing method that uses an aqueous coagulant as a core material.

The most important feature of the core material used in the present invention is that it is incompatible with an aqueous coagulation bath, and the provision of a high draft during spinning and the stretching in hot water are the most important features of the core material used in the present invention. This was made possible by using a core material. The core material can be easily removed from the hollow fibers obtained as described above by drying with hot air if necessary after forming the hollow fibers, and then washing with methanol, ethanol, etc. can.

The fibers obtained by the method of the present invention have good ultraviolet permeability and dialysis ability, uniformity of the thickness of the hollow fiber wall membrane, uniformity of the pore size of the pores in the wall membrane, and pore distribution. It is extremely good in terms of uniformity, etc., and its manufacturing method has various advantages, such as being easier to manufacture using a simpler device than conventional methods. The present invention will be explained in more detail with reference to Examples below.

Example 1 25 parts of cellulose acetate with a degree of acetylation of 53% was dissolved in 64 parts of dimethylacetamide and w parts of water at 855C and defoamed to obtain a spinning stock solution.

This spinning stock solution was kept at 45°C, and the inner diameter of the double tube outer tube part was 6Tf.
rIn1 inner tube outer diameter 47077! Using a spinning nozzle with the same inner diameter of 1TnJn, the spinning dope was fed into the annular slit of the outer tube of the spinning nozzle at a rate of 4.5 me/min, and dodecyl acetate was fed as a core agent into the inner tube of the spinning nozzle at a rate of 5.6 me/min. The hollow stock solution that passed through the nozzle surface was injected at a rate of 4.5c7n into the air under high draft.
After being allowed to fall, it was introduced into a coagulation bath consisting of a 30% dimethylacetamide aqueous solution kept at 20°C to coagulate it, rolled up at a speed of 80r11/min, and thoroughly washed with water, resulting in a dry strength of 0.25g/min. d1 wet strength 0.13
It was g/d. When this hollow fiber was stretched 1 times in hot water at 80°C, the dry strength of this fiber was 0.5 g/d.
It was confirmed that the wet strength was 0.24 g/d, and the strength was approximately doubled by stretching. When dialysis was performed using the hollow fibers before and after stretching, it was confirmed that ultrafiltration hollow fibers were obtained that sufficiently permeated urea and creatinine but did not permeate albumin at all, but without stretching. While there were some parts of the fibers where damage occurred even if a small amount was applied, no such disadvantages were observed with the drawn fibers.

In addition, the water permeation rate is 3.5×10-2 (Cc/d-Min●
ATM). Example 2 25 parts of cellulose acetate with a degree of acetylation of 55% was dissolved in 67.5 parts of dimethylacetamide and 7.5 parts of water at 80° C., and the solution was degassed and filtered to obtain a spinning stock solution.

This spinning dope was adjusted to 50'C, and using the spinneret used in Example 1, 2.8 me/Mjn was applied to the annular slit of the outer tube.
Isopropyl myristate as a core material was supplied to the inner tube at a ratio of 3.5me/Mjn to form a hollow stock solution, which was allowed to fall 6cm in the air, followed by 40% dimethylacetamide kept at 15°C. It was introduced into a coagulation bath consisting of an aqueous solution and coagulated, and rolled up at a speed of 30r11/min. While continuing to wash in hot water at 80°C, 1. Four types of hollow fibers were prepared by stretching at 1.1 times, 1.3 times, and 1.times., and their properties were investigated and the results are shown in Table 1. The dry strength of the hollow fibers without stretching was low, the handleability was poor, and the cross-sectional shape was highly uneven.

As a result of observing the inner surfaces of the above four types of hollow fibers using an electron microscope, it was found that the inner surfaces were extremely smooth, and the dialysis performance was confirmed in Example 1.
Similar results were obtained.

Example 3 24 parts of cellulose acetate with a degree of acetylation of 55% was dissolved in 7(2) dimethyl sulfoxide and 6 parts of water at 80°C, and the solution was heated to 50°C after being degassed. Similar outer tube inner diameter 3? , inner tube outer diameter 1.5T! $L1 same inner diameter 0.
Using a 5WgfL double tube structure nozzle, dimethyl azelate as a core material was injected from the inner tube at a rate of 4.0rT1'/Min from the annular slit at a rate of 5.0rT1'/Mjn, and the air was After dropping .8cm,
It was introduced into a 25% dimethyl sulfoxide aqueous solution maintained at 25°C and coagulated at a rate of 50111/min, and then poured into hot water at 70°C for 1. After extensive stretching, it was immersed in a 3% glycerin aqueous solution for 5 minutes at 50°C.
Dry with hot air.

Claims (1)

[Scope of Claims] 1. A stock solution of cellulose acetate dissolved in a water-soluble organic solvent containing 1 to 10% by weight of water and having a boiling point of 100°C or higher is extruded through an annular slit in the outer tube of a double tube structure, and A method for producing cellulose acetate hollow fibers, which comprises extruding a fatty acid ester liquid while injecting it as a core material through a pipe, leading it to an aqueous coagulation bath to coagulate it, and then washing and stretching it in hot water. 2. The method for producing hollow fibers according to claim 1, characterized in that the hollow stock solution extruded from the spinneret surface is once passed through air or an inert gas and then introduced into an aqueous coagulation bath.