JPS5825765B2 - polyvinyl alcohol - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production of polyvinyl alcohol (hereinafter abbreviated as PVA)-based hollow fibers having excellent permeability and mechanical properties.

More specifically, a hollow fiber made of a PVA-based polymer is cross-linked using a polyvalent aldehyde having two or more aldehyde groups in the molecule in the presence of a reaction medium, and then subjected to hot water treatment. Dry hollow fibers with excellent permeability to water, gas, etc., and excellent mechanical properties are obtained by replacing the water with an organic solvent that is miscible with water and then drying the hollow fibers. Relating to a method of manufacturing.

In recent years, remarkable progress has been made in the use of selectively permeable membranes in separation operations.

Some of these membrane separation technologies have already been put into practical use, for example, in areas such as seawater desalination and blood processing using artificial kidneys, but depending on the application, the membranes currently in use may be permeable or have other properties. It is difficult to say that it is necessarily satisfactory in all respects in terms of its nature.

To date, membrane materials used in membrane separation techniques have mainly been made of cellulose or its derivatives.

However, many other materials have been considered for permselective membranes, and one of them, PVA, has been used as an aldehyde cross-linked membrane (L).
Eininger et al., Trans-A
SAI O1022゜1964), a radiation-crosslinked membrane in the presence of the polyfunctional monomer allyl methacrylate (M
, 0dianeta1. , Trans, ASAIO14
5, 1968: Bruce S, Bernstei
n9J-Polymer Sci-Part A, 3
3405, 1965), polyvinyl alcohol-chitosan blend membrane (Susumu Yoshiyuki et al., 20th Polymer Research Conference), polyvinyl alcohol graft copolymer membrane (Yoji Imai et al., Artificial Organs 2 147.1973), etc. It has been done.

However, in these cases, or rather, in general, when a strong hydrophilic substance like PVA is used as a membrane material, the more permeable it is, the less cold it remains, making it unsuitable for use as a membrane material. The conventional situation has been that materials with sufficient strength have insufficient transparency.

This is true not only when the permselective membrane is used in the form of a flat membrane, but also when it is used in the form of a hollow fiber, which is more advantageous in terms of strength. Therefore, to date, practical use of PVA-based permselective membrane materials in the form of flat or hollow fibers has not been realized.

Furthermore, conventional PVA-based membrane materials that have excellent permeability are usually kept in a wet state, and if they are heated or dried at room temperature, their permeability decreases, and in some cases, the membrane materials stick to each other and tear. It had the disadvantage of being prone to pinholes.

A method of attaching a plasticizer, a surfactant, etc. and drying has also been proposed, but this method is not preferred, especially when used for hemodialysis, because the plasticizer etc. are eluted during rewetting.

The present inventors have conducted extensive research into a method for obtaining dry PVA-based hollow fibers that have excellent permeability and mechanical properties and can be used for medical purposes such as hemodialysis without any washing treatment such as washing with water. As a result of overlapping, 2
A polyvalent aldehyde having more than 10 aldehyde groups, a periodate ion, or a tetravalent cerium ion is dissolved together with an acid in a suitable reaction medium such as water or dimethyl sulfoxide, and a hollow made of a PVA-based polymer is formed in this medium. By dipping the fibers, crosslinking is created in the hollow fibers,
Furthermore, the hollow fibers are treated with hot water, and the wet hollow fibers are further solvent-substituted with an appropriate solvent, and then dried.
The present invention was completely defeated by finding a method for obtaining hollow fibers in a dry state that have a high equilibrium water content, excellent permeation performance for solutes, water, etc., and excellent mechanical strength.

The PVA-based polymers used to produce the hollow fibers to be treated in the method of the present invention include completely saponified and partially saponified homopolymers of vinyl esters, as well as ethylene with a concentration not exceeding 50 moles φ; Included are vinyl alcohol polymers containing vinyl monomer units such as vinylpyrrolidone, acrylonitrile, and vinyl chloride.

The PVA-based polymer hollow fibers used in the present invention are made using the above-mentioned PVA-based polymer, for example, in the following manner.

A wet molding method is used in which a solution or stock solution of the PVA composition is spun into a separate liquid phase or coagulation bath and coagulated.

In this case, the spinning nozzle is usually an annular nozzle, but
Even without using an annular nozzle, a hollow product can be obtained by appropriately adjusting the composition of the spinning dope and the coagulation bath.

The composition of the stock solution in the wet molding method is usually PV to 100 parts of water.
It contains 5 to 30 parts of A, and in some cases, 01 to 3 parts of boric acid may be added.

The coagulation bath is an aqueous solution of caustic soda, caustic soda and mirabilite, or only mirabilite, and the total solute concentration is 200 to 500.
9/l, preferably 300 to 40 (J9/l).

Since the inner diameter, outer diameter, and wall thickness of hollow fibers are closely related to permeability and pressure resistance, if the film forming conditions are freely changed within the above ranges and the spinning nozzle system, spinning speed, etc. are appropriately set, It is possible to obtain hollow fibers with inner diameter, outer diameter, and wall thickness that have performance according to the purpose.

As another method, a so-called dry or melt molding method in which a stock solution is spun into a gas phase is also possible, but a wet molding method is the most excellent in terms of permeation performance and surface smoothness.

Even when hollow fibers are produced by the L/displacement method described above, suitable additives may be added to the spinning dope for the purpose of improving permeation performance.

Such additives have an average molecular weight of 400 to 400.
0. Polyalkylene glycol (hereinafter abbreviated as PAG) having an oxygen:carbon ratio of 3 or less carbon atoms per 1 atom of oxygen is preferable, and the addition ratio is 100% of the PVA-based polymer.
3 to 200 parts by weight are chosen.

The PVA-based hollow fibers produced as described above are essentially soluble in water.

Therefore, it was found that if left as is, the membrane shape would deteriorate over time when processing aqueous solutions (blood, protein solutions, etc.), especially high-temperature aqueous solutions.

This is not only inconvenient for work, but also undesirable from a safety standpoint when used for artificial dialysis.

Therefore, we have repeatedly investigated methods for crosslinking and insolubilizing PVA-based hollow fibers, but it has become clear that some of the known crosslinking methods have the following drawbacks.

That is, the method of crosslinking and insolubilizing PVA is (a) a method of crosslinking by intermolecular acetalization reaction with dialdehyde;
(2) A method of crosslinking by high temperature heating in the presence of an acidic substance, (C) A method using boric acid, titanate ester, vanadium ion, etc., and (d) A method using radiation irradiation.

Among these methods, method (b) results in a decrease in water content and permeability of substances, method (c) results in easy removal in the pH range where crosslinking points exist, and method (d) results in efficient crosslinking. There are drawbacks such as the need for deaeration in order to proceed.

However, in addition to the fact that (a) has fewer drawbacks as described above, in the present invention, by further subjecting such acetal crosslinked hollow fibers to a step of hot water treatment, the permeation performance of the hollow fibers can be significantly improved. The cross-linked hollow fibers obtained through such treatment steps have virtually no soluble portions, so
It is extremely effective as a dialysis membrane for artificial kidneys.

In the method of the present invention, in order to obtain hollow fibers with excellent permeability and mechanical properties, crosslinking treatment is an important process, and polyvalent aldehydes having two or more aldehyde groups in the molecule A specific method for crosslinking and insolubilizing PVA-based hollow fibers is as follows: (1) Periodate ions or tetravalent cerium ions are present in the reaction medium to
A method of simultaneously performing the production of VA dialdehyde and the crosslinking reaction of PVA with the compound, and ([1] PVA dialdehyde previously produced by the method (i) or other existing low-molecular polyhydric aldehydes) There are two methods: (i) in terms of reaction efficiency;
Method (11) is preferred from the viewpoint of ease of washing and removing unreacted substances.

Further, when crosslinking and insolubilizing, care must be taken in selecting the reaction medium.

It is desirable to use a reaction medium in which the crosslinking reagent used is completely dissolved and the PVA hollow fibers are appropriately swollen.

For example, when using periodate ion or tetravalent cerium ion, glutaraldehyde, and PVA dialdehyde (obtained by oxidative decomposition of PVA with periodate ion or tetravalent cerium ion, etc.), add water or some salt. Depending on the crosslinking agent, an organic solvent such as dimethyl sulfoxide may be used.

The crosslinking reaction can be carried out by dissolving the above-mentioned crosslinking agent in water or a suitable solvent, adding a small amount of sulfuric acid, hydrochloric acid, etc., and immersing the PVA hollow fibers therein.

The crosslinking reaction rate depends on the crosslinking agent concentration, acid concentration, reaction temperature, and bath ratio.

The bath ratio is usually about 1:100, in which case the crosslinking agent concentration is 0.001 to 1.0 wt, and the acid concentration is 0.001 to 20 wt.
Polymer, reaction temperature is 30-60°C 1 reaction time is 30 minutes-5
The time is appropriate.

Hollow fibers cross-linked in this way are given hot water resistance, but as is, they have a low water content and are free from solutes and
Neither gas permeability nor permeability can be said to be sufficient.

As a result of intensive research into ways to improve the permeation performance while maintaining the strength of hollow fibers, we discovered that hot water treatment is the most effective method.

That is, it has been found that by immersing the hollow fibers subjected to the above-mentioned crosslinking treatment in hot water for an appropriate period of time, hollow fibers with high water content, excellent permeation performance, and high strength can be obtained.

The hot water treatment conditions at this time are preferably at least 70°C, preferably at least 90°C, for at least 5 minutes, and preferably at least 30 minutes.

This hot water treatment can improve water permeability by more than 10 times compared to untreated hollow fibers.

Although the reason for this is not clear, it is presumed that the hot water treatment reduces the crystalline region of the PVA polymer.

Furthermore, not only PVA but also membrane materials made of hydrophilic polymers in general, when dried by normal methods such as air-drying, heating, or drying from a wet state, water permeability and solute permeability decrease, and even if re-wetted, membrane materials deteriorate. It is difficult to completely restore the permeability to the level before drying.

The reason for this differs depending on the material, and is thought to be due to densification of the membrane surface layer, destruction of the porous structure, crystallization, etc. that progress during drying.

Under these circumstances, in the present invention, h obtained through the steps of crosslinking treatment and subsequent hot water treatment as described above
The above-mentioned problems were successfully solved by a method in which the PVA-based hollow fibers were further replaced with an appropriate water-miscible organic solvent to replace the water contained in the membrane of the hollow fibers, and then dried. .

That is, the water, which is a plasticizer, is removed from the PVA-based wet hollow fiber, which is a polymer gel, by appropriate solvent replacement, and then the organic solvent is removed while maintaining a state in which molecular motion is suppressed below the second-order transition humidity of the polymer. As a result, hollow fibers having a loose structure even after drying can be obtained, and the phenomenon of hollow fibers sticking together can also be avoided.

Therefore, when re-wetted, the water permeability and solute permeability are at the same level as before drying, and since a low-molecular organic solvent is used, there is no residue and it is possible to obtain clean hollow fibers with no eluates.

To be more specific, the purpose of solvent replacement in the present invention is (1) to remove water from the hollow fibers (ii)! There are two ways to fix the membrane structure with a high water content formed by the water treatment authority using a solvent, and according to the method of the present invention, the above (i) and (ii) can be fully achieved with one type of organic solvent. However, there is no problem even if operations (i) and (ii) are performed in two steps.

For the purpose of (:), it is necessary to have good miscibility with water, and in order to achieve (ii), it is generally desirable to have a suitable coagulating effect on PVA gel.

As an organic solvent that simultaneously satisfies (i) and (ii),
Examples include lower aliphatic alcohols, lower ketones, and mixtures thereof with water.

On the other hand, aliphatic alcohols having 5 or more carbon atoms, higher ketones, and ethers have difficulty in mutual solubility with water, and cannot be used alone.

Sulfoxides generally mix well with water, but P
It does not coagulate VA.

Polyhydric alcohols such as glycol and glycerin are not suitable for producing dry hollow fibers because their evaporation rate is significantly lower than that of monohydric alcohols such as methyl alcohol.

Further, aromatic alcohols such as phenol and benzyl alcohol are not miscible with water and are highly toxic, so they cannot be used particularly when dry hollow fibers are used for medical purposes.

From the above, what can be used alone as a water replacement solvent for PVA-based hollow fibers can be mixed with water in any proportion and
Characteristic of exerting a coagulating effect on A-based polymers7)
- Preferred are lower aliphatic alcohols such as methyl alcohol, ethyl alcohol, flobyl alcohol, methyl alcohol, lower ketones such as acetone and methyl ethyl ketone, and mixtures thereof with water.

Among the lower aliphatic alcohols and lower ketones, PV
Since there is a hierarchy in coagulation ability of A-based polymers, it is necessary to appropriately select them or adjust the mixing ratio with water depending on the properties of the PVA-based hollow fibers to be subjected to solvent replacement treatment.

As an example, when a water-containing PVA hollow fiber is replaced with the above-mentioned organic solvent, some shrinkage occurs along with coagulation.

The coagulation effect of the organic solvent is strong, and if this contraction is too rapid, the hollow fibers will be distorted, causing the hollow portion to not maintain its perfect circle.

On the other hand, if the coagulation power is insufficient, the membrane structure changes during drying, and the permeation performance before drying may not be able to be reproduced even after rewetting.

If disadvantages in the process are recognized, it is possible to perform solvent replacement in two stages. In such a case, the water is replaced in the first stage, and the membrane structure of the PVA hollow fiber is replaced in the second stage. A method of fixing is adopted.

It is preferable that the solvent replacement is normally carried out at a temperature in the range of -20°C to room temperature.

Further, it is desirable that the solvent treatment time be sufficiently long.

Drying of the PVA-based hollow fiber subjected to solvent substitution as described above is accomplished by air drying or vacuum drying at room temperature or under heating at a temperature 1 m below the glass transition temperature of the fiber.

Further, in the present invention, the PVA hollow fibers to be subjected to solvent replacement have a moisture content adjusted within the range of 10 to 500% by weight (based on the PVA polymer).

Above 1. As described in detail, the hollow fibers obtained by the present invention have good biocompatibility because of their high water content, and have high strength because they have been crosslinked.

Furthermore, hot water treatment has the effect of extracting the soluble portion and making it virtually insoluble in water, and this effect is extremely effective from a safety standpoint, especially for medical applications such as artificial kidney dialysis. It is.

Further, according to the present invention, since hollow fibers with excellent permeation performance can be obtained in a dry state, they are easy to transport and store, and gas sterilization can be used to disinfect and sterilize the device, which has the advantage of being ready for immediate use.

On the other hand, conventional artificial kidney dialysis equipment using hollow fibers requires pre-washing treatment to remove formalin for sterilization and plasticizers contained in the hollow fibers, and cannot be used immediately; Naturally, this is undesirable in the medical field, which must respond to emergencies.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples.

Example 1 7 kg of polyvinyl alcohol with an average degree of polymerization of 2400 and a degree of saponification of 999, 2.4 kg of polyethylene glycol with a molecular weight of 2000, 160 g of boric acid, and 501 g of acetic acid
of water to obtain a homogeneous solution with a pH of 4.7.

This spinning stock solution was spun into an alkaline coagulation bath through an annular nozzle to form hollow fibers, and then sodium periodate 59/l,
Immersed in a treatment bath containing 150 g/l of sulfuric acid at 50°C for 1 hour, further treated in 95°C hot water for 3 hours, washed with water, and immersed in methyl alcohol at 50'C for 3 hours to remove water in the hollow fibers. After that, it was taken out and dried under reduced pressure at room temperature to have an outer diameter of 260. , dry hollow fibers having flexibility and a film thickness of 30 μm were obtained.

In addition, for comparison, dry hollow fibers were prepared by drying under reduced pressure after hot water treatment without solvent replacement treatment. There was a significant decrease in permeation performance.

** Table 1 shows the measurement results of water permeability and compressive strength of the obtained hollow fibers.

All measured values are in a wet state.

Example 2 Average degree of polymerization 1700. 8 kg of polyvinyl alcohol with saponification degree of 98.5%, boric acid 200.9. 50g of acetic acid
1 was dissolved in water to obtain a homogeneous solution.

This spinning stock solution was spun into an alkaline coagulation bath through a nozzle to form hollow fibers, and then glutaraldehyde was added at 0.59/l.
, sulfuric acid 59/I! , 40°C in a treatment bath of 509/l of Glauber's salt,
Soaked for 5 hours, further treated with hot water at 100°C for 1 hour, washed with flo'c methyl alcohol for 30 minutes, immersed in butyl alcohol at 20°C for 1 hour to replace the solvent, then taken out and dried under reduced pressure at room temperature. , dry hollow fibers with excellent permeability and mechanical properties were obtained.

Example 3 Polyvinyl alcohol with an average degree of polymerization of 1700 and saponification degree of 96.6, 9kliJ1, polyethylene glycol 3k with a molecular weight of 1000, and boric acid 16051. 50g of acetic acid
1 in water to prepare a spinning stock solution with a pH of 4.8.

This spinning stock solution is spun into an alkaline coagulation bath through an annular nozzle to form hollow fibers, and then 4g of glutaraldehyde is added.
/ls Hydrochloric acid 39/l immersion at 50℃ for 2 hours to insolubilize crosslinking, further hot water treatment at 100℃ for 1 hour to extract the soluble portion, washed with water 7i, and -20℃ methanol for 1 hour. The fibers were immersed to perform low-humidity solvent replacement, air-dried at 20°C for 5 hours, and then dried under reduced pressure at 30°C to obtain dry hollow fibers with a water absorption rate of 320φ and excellent solute permeability.

Claims (1)

[Claims] 1 Wet hollow fibers obtained by crosslinking hollow fibers made of polyvinyl alcohol polymers using a polyvalent aldehyde having two or more aldehyde groups in the molecule in the presence of a reaction medium, and then treating with hot water. A method for producing dry polyvinyl alcohol-based hollow fibers, which comprises further treating the fibers with a water-miscible organic solvent and then drying them.