CA1140713A - Process for producing a cellulose acetate- type permselective membrane having very high water permeability and protein retention - Google Patents
Process for producing a cellulose acetate- type permselective membrane having very high water permeability and protein retentionInfo
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- CA1140713A CA1140713A CA000342455A CA342455A CA1140713A CA 1140713 A CA1140713 A CA 1140713A CA 000342455 A CA000342455 A CA 000342455A CA 342455 A CA342455 A CA 342455A CA 1140713 A CA1140713 A CA 1140713A
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Abstract
ABSTRACT OF THE DISCLOSURE
.
A process for producing a cellulose acetate-type permselective membrane having very high water-permeability and protein retention, which comprises casting a dope comprising (a) 1 part by weight of cellu-lose acetate, and (b) 2 to 20 parts by weight of a mixed solvent composed of (i) dimethylsulfoxide and (ii) at least one water-soluble organic compound selected from the group consisting of monohydric alcohols having 2 to 5 carbon atoms, dihydric alcohols of the formula HO (RO)n H wherein R is an alkylene group having 2 or 3 carbon atoms and n is an integer of 1 to 16, and carboxy-lic acids having 1 or 2 carbon atoms, the weight ratio of said water-soluble organic compound to dimethylsulfoxide being not more than l; and solidifying the resulting raw membrane with a coagulating solution.
.
A process for producing a cellulose acetate-type permselective membrane having very high water-permeability and protein retention, which comprises casting a dope comprising (a) 1 part by weight of cellu-lose acetate, and (b) 2 to 20 parts by weight of a mixed solvent composed of (i) dimethylsulfoxide and (ii) at least one water-soluble organic compound selected from the group consisting of monohydric alcohols having 2 to 5 carbon atoms, dihydric alcohols of the formula HO (RO)n H wherein R is an alkylene group having 2 or 3 carbon atoms and n is an integer of 1 to 16, and carboxy-lic acids having 1 or 2 carbon atoms, the weight ratio of said water-soluble organic compound to dimethylsulfoxide being not more than l; and solidifying the resulting raw membrane with a coagulating solution.
Description
PROCESS FOR PRODUCING A C~LLULOS~ AC~TATE-TYPE
PERMS~LECTIVE MEMBRA~ HAVING V~RY HJGH WATER
P~RMEABILITY AND PROT~IN RETENTION
This in~ention relates to the production o~
cellulose acetate-type permselective membranes, and more specifically -to a process for producing a perm~
selective membrane comprising a base of cellulose acetate and having very high water-permeability and protein-retention which is particularly suitable as hemofilters for artificial kidneys.
Some permselective membranes compr~sing a base of cellulose acetate have been suggested in the past.
The m~st typical example is a cellulose acetate perm-selective membrane called to Loeb-type membrane disclosed in U. S. Patents ~,133,132 and 3,133,137. The Loeb-type permselective membrane ~as developed in order to separate water from saline solutions. It is produced by dissolv-ing a film-forming cellulose acetate and an a~ueous solution of perchloric acid in an organic solvent, casting the solution to form a membrane having a sub-stantially uniform thickness, evaporating a part of tha solvent ~or a certain period of time, and then ~ippi~g the cast membrane in water to remove the perchlorate salt.
As an improvement o~ the Loeb-type membrane 9 Manjikian et al. added a water-soluble additive compound such as urea, glyoxal, H202, dimethylfo~mamide ~Dr~F)~
dimethylsulfoxide ~D~SO) and acetic acid to a cellulose acetate casting solution~ and examined the effect of '`'~
~3L4~)7~3 the additive compounds on ~he properties of the resulting membrane. (Proc. First International Symp. on Water Desalination Washington D. C. ~Pub. U. S. Dept. Interior, 0. S. W.) 2, 159 (1965)).
The Loeb-type and Manjikian-type membranes are reverse osmosis membranes for the separation of water from saline solutions. They have a salt rejection of about 9~/0, but their water ultrafiltration rate (to be sometimes abbreviated "UFR") is at most 2 ml/m2~hr m~g.
Accordingly, these types of membranes cannot be applied to hemofilters for arti~icial kidneys which are the main use contemplated by the present invention.
Various permselective membranes of varying water UFR and/or varying retentions of solutes have been suggested recently by modifying the composition of a cellulose ester-containing film-forming dope. For example, ~. Kunst et al. disclosed in Journal of Applied Polymer Science, 18, 8423 (1974) membranes having a water UFR of 10 to 60 ml/m2 hr.mmHg and a sodium chloride retention of ~ to 50~. U. S, Patent No, 3,494,780 discloses a process for producing a permselective membrane which comprises incorporating a polyhydric alcohol wllich is a non-plasticizer for a cellulose ester in a plasticized cellulose ester, melting the mixture and forming it into a film, and leaching the resulting film with a solvent which is a nonsolvent for the ester and is capable of dissolving the plasticizer and the polyhydric alcohol, thereby to remove -the plasticizer and the polyhydric alcohol. It is shown in the Patent that the water-permeability of the resulting film is 5 to 8 times as high as tha-t of a comm~rcially available re~enerated cellulose dialysis tube (water UFR=1.5 - 2 ml/m2ohr-mn~Ig).
U. S. Patent 4,147,622 discloses a process for producing an asymmetric permselec-tive cellulose acetate membrane having a skin layer on at least one surface thereof,which comprises casting a mi~ed solution 7~3 consisting of 12 to 20~ of cellulose triacetate, at least 40~ of acetone, a solvent (e.g., dioxane or dimethylsulEoxide) for the cellulose triace-tate and a swelling agent (e.g., formamide) for the cellulose -triacetate.
United States Patent 4,035,459 discloses cellulose acetate membrane in the form of hollow fibers having an outside surface formed by a dry phase-inversion method and an inside surface formed by a wet phase-inversion method, the space between the two surfaces being of asymmetrical structure.
These conventional cellulose ester-type permselective memberances are based on the technique of producing reverse osmosis membranes, and are sometimes directed to the separation of low-molecular-weight materials such as sodium chloride. Their ultrafiltration rate is low. In other words, they res-tric-t the permeation and diffusion of low-molecular-weight ma-terials, and are undesirable in removing low-molecular-weight -to medium-molecular-weight ma-terials such as waste matter of the blood by filtration and diffusion, as in artifical kidneys.
~he present inventor extensively considered this problem, and found that the properties !especially porosity and water content) of the celluloses ester and their performances (the water ultra-filtration rate; the retentions of low molecular-weight, medium-molecular-weight and high-molecular-weight materials) can be selected within wide ranges by using dimethylsulfoxide as a main film-forming solvent. On further investigations, it has now been found that by incorporating a certain additive in a film-forming solution containing dimethylsulfoxide, a permselective membrane having superior processability and performances and being applicable to a broad range of utility can be obtained.
Thus~ according to this invention, -there can be provided , a cellulose acetate-type permselective membrane having a high water ultra~iltration rate and a high retention of high-molecular-weight materials under a low operating pressure.
T~e present inventor also ~ound that by using a mixture of a water-soluble organic compound such as alcohols and dimethylsulfoxide as a solvent for ~ilm formation from cellulose acetate, the water flux of -the membrane increases double and a high retention of proteins can be maintained. This ef~ect can be applied to a novel permselective membrane for ultrafiltration composed mainly of cellulose acetate (to be referred to as "cellulose acetate-type"), and a process for preparation thereof. This led to the accomplishment of the present invention.
It is an object o~ this invention -to provide a process for producing a permselective membrane comp-rising cellulose acetate as a base which has very high water-permeability and protein retention.
Another object o~ this invention is to provide a process for producing a permselective membrane comprising cellulose acetate as a base which h~s very high water permeability and protein retention under low operating pressures and which is suitable as hemofilters for artificial kidneys.
Still another object of this invention is to provide a permselective membrane produced by such a process.
Other objects and advantages of this invention will become more apparent from the following description.
According to this invention~ there is provided a process ~or producing a cellulose acetate-type permselective membrane having very high water-permea-bility and protein retention which comprises casting a cellulose acetate-containing dope consisting of (a) 1 part by weight of cellulose acetate, and (b~ 2 to 20 parts by weight of a mixed solvent ~10`~3 composed of (i) dimethylsulfoxide and (ii) at least one water-soluble organic compound selected from the group consisting of monohydric alcohols having 2 to 5 carbon atoms, dihydric alcohols of the formula H0tR0~ H wherein R is an alkylene group having 2 or 3 carbon atoms and n is an integer of l to 16, and carboxylic acids having l or 2 carbon atoms, the weight ratio of said water-soluble organic compound to dimethylsulfoxide being not more than l; solidifying the resulting raw membrane with a coagulating solution which comprises non-solvent for the cellulose acetate.
The cellulose acetate used as a material for the membrane in accordance with this invention may be any of those film-forming cellulose acetates which have been used heretofore in the field of ultrafiltration and reverse osmosis.
Specific examples include cellulose diacetate having an average acetyl con-tent of about 35% to about 41%, cellulose triacetate having an average acetyl content of about 41% to about 45%, and mixtures of these. A material composed mainly of cellulose diacetate is preferred.
The term "material composed mainly of cellulose diacetate", as used herein, means not only cellulose diacetate alone, but also a mixture of cellulose diacetate and cellulose triacetate with a cellulose triacetate content of at most 30% by weight, preferably not more than 10% by weight, based on the to-tal weight of the cellulose acetates.
The most characteristic feature of the process of this invention is that as a solvent for preparing a cellulose acetate-containing dope by dissolv-ing cellulose acetate, there is used a mixture co~prising: (i) dimethylsul-foxide (sometimes abbreviated "DMS0"), and ~ii) at least one water-soluble organic compound selected from the group consisting of monohydric alcohols having 2 to 5 carbon atoms, dihydric alcohols of the formula T-10-~R ~ ~T wherein R is an alkylene group having
PERMS~LECTIVE MEMBRA~ HAVING V~RY HJGH WATER
P~RMEABILITY AND PROT~IN RETENTION
This in~ention relates to the production o~
cellulose acetate-type permselective membranes, and more specifically -to a process for producing a perm~
selective membrane comprising a base of cellulose acetate and having very high water-permeability and protein-retention which is particularly suitable as hemofilters for artificial kidneys.
Some permselective membranes compr~sing a base of cellulose acetate have been suggested in the past.
The m~st typical example is a cellulose acetate perm-selective membrane called to Loeb-type membrane disclosed in U. S. Patents ~,133,132 and 3,133,137. The Loeb-type permselective membrane ~as developed in order to separate water from saline solutions. It is produced by dissolv-ing a film-forming cellulose acetate and an a~ueous solution of perchloric acid in an organic solvent, casting the solution to form a membrane having a sub-stantially uniform thickness, evaporating a part of tha solvent ~or a certain period of time, and then ~ippi~g the cast membrane in water to remove the perchlorate salt.
As an improvement o~ the Loeb-type membrane 9 Manjikian et al. added a water-soluble additive compound such as urea, glyoxal, H202, dimethylfo~mamide ~Dr~F)~
dimethylsulfoxide ~D~SO) and acetic acid to a cellulose acetate casting solution~ and examined the effect of '`'~
~3L4~)7~3 the additive compounds on ~he properties of the resulting membrane. (Proc. First International Symp. on Water Desalination Washington D. C. ~Pub. U. S. Dept. Interior, 0. S. W.) 2, 159 (1965)).
The Loeb-type and Manjikian-type membranes are reverse osmosis membranes for the separation of water from saline solutions. They have a salt rejection of about 9~/0, but their water ultrafiltration rate (to be sometimes abbreviated "UFR") is at most 2 ml/m2~hr m~g.
Accordingly, these types of membranes cannot be applied to hemofilters for arti~icial kidneys which are the main use contemplated by the present invention.
Various permselective membranes of varying water UFR and/or varying retentions of solutes have been suggested recently by modifying the composition of a cellulose ester-containing film-forming dope. For example, ~. Kunst et al. disclosed in Journal of Applied Polymer Science, 18, 8423 (1974) membranes having a water UFR of 10 to 60 ml/m2 hr.mmHg and a sodium chloride retention of ~ to 50~. U. S, Patent No, 3,494,780 discloses a process for producing a permselective membrane which comprises incorporating a polyhydric alcohol wllich is a non-plasticizer for a cellulose ester in a plasticized cellulose ester, melting the mixture and forming it into a film, and leaching the resulting film with a solvent which is a nonsolvent for the ester and is capable of dissolving the plasticizer and the polyhydric alcohol, thereby to remove -the plasticizer and the polyhydric alcohol. It is shown in the Patent that the water-permeability of the resulting film is 5 to 8 times as high as tha-t of a comm~rcially available re~enerated cellulose dialysis tube (water UFR=1.5 - 2 ml/m2ohr-mn~Ig).
U. S. Patent 4,147,622 discloses a process for producing an asymmetric permselec-tive cellulose acetate membrane having a skin layer on at least one surface thereof,which comprises casting a mi~ed solution 7~3 consisting of 12 to 20~ of cellulose triacetate, at least 40~ of acetone, a solvent (e.g., dioxane or dimethylsulEoxide) for the cellulose triace-tate and a swelling agent (e.g., formamide) for the cellulose -triacetate.
United States Patent 4,035,459 discloses cellulose acetate membrane in the form of hollow fibers having an outside surface formed by a dry phase-inversion method and an inside surface formed by a wet phase-inversion method, the space between the two surfaces being of asymmetrical structure.
These conventional cellulose ester-type permselective memberances are based on the technique of producing reverse osmosis membranes, and are sometimes directed to the separation of low-molecular-weight materials such as sodium chloride. Their ultrafiltration rate is low. In other words, they res-tric-t the permeation and diffusion of low-molecular-weight ma-terials, and are undesirable in removing low-molecular-weight -to medium-molecular-weight ma-terials such as waste matter of the blood by filtration and diffusion, as in artifical kidneys.
~he present inventor extensively considered this problem, and found that the properties !especially porosity and water content) of the celluloses ester and their performances (the water ultra-filtration rate; the retentions of low molecular-weight, medium-molecular-weight and high-molecular-weight materials) can be selected within wide ranges by using dimethylsulfoxide as a main film-forming solvent. On further investigations, it has now been found that by incorporating a certain additive in a film-forming solution containing dimethylsulfoxide, a permselective membrane having superior processability and performances and being applicable to a broad range of utility can be obtained.
Thus~ according to this invention, -there can be provided , a cellulose acetate-type permselective membrane having a high water ultra~iltration rate and a high retention of high-molecular-weight materials under a low operating pressure.
T~e present inventor also ~ound that by using a mixture of a water-soluble organic compound such as alcohols and dimethylsulfoxide as a solvent for ~ilm formation from cellulose acetate, the water flux of -the membrane increases double and a high retention of proteins can be maintained. This ef~ect can be applied to a novel permselective membrane for ultrafiltration composed mainly of cellulose acetate (to be referred to as "cellulose acetate-type"), and a process for preparation thereof. This led to the accomplishment of the present invention.
It is an object o~ this invention -to provide a process for producing a permselective membrane comp-rising cellulose acetate as a base which has very high water-permeability and protein retention.
Another object o~ this invention is to provide a process for producing a permselective membrane comprising cellulose acetate as a base which h~s very high water permeability and protein retention under low operating pressures and which is suitable as hemofilters for artificial kidneys.
Still another object of this invention is to provide a permselective membrane produced by such a process.
Other objects and advantages of this invention will become more apparent from the following description.
According to this invention~ there is provided a process ~or producing a cellulose acetate-type permselective membrane having very high water-permea-bility and protein retention which comprises casting a cellulose acetate-containing dope consisting of (a) 1 part by weight of cellulose acetate, and (b~ 2 to 20 parts by weight of a mixed solvent ~10`~3 composed of (i) dimethylsulfoxide and (ii) at least one water-soluble organic compound selected from the group consisting of monohydric alcohols having 2 to 5 carbon atoms, dihydric alcohols of the formula H0tR0~ H wherein R is an alkylene group having 2 or 3 carbon atoms and n is an integer of l to 16, and carboxylic acids having l or 2 carbon atoms, the weight ratio of said water-soluble organic compound to dimethylsulfoxide being not more than l; solidifying the resulting raw membrane with a coagulating solution which comprises non-solvent for the cellulose acetate.
The cellulose acetate used as a material for the membrane in accordance with this invention may be any of those film-forming cellulose acetates which have been used heretofore in the field of ultrafiltration and reverse osmosis.
Specific examples include cellulose diacetate having an average acetyl con-tent of about 35% to about 41%, cellulose triacetate having an average acetyl content of about 41% to about 45%, and mixtures of these. A material composed mainly of cellulose diacetate is preferred.
The term "material composed mainly of cellulose diacetate", as used herein, means not only cellulose diacetate alone, but also a mixture of cellulose diacetate and cellulose triacetate with a cellulose triacetate content of at most 30% by weight, preferably not more than 10% by weight, based on the to-tal weight of the cellulose acetates.
The most characteristic feature of the process of this invention is that as a solvent for preparing a cellulose acetate-containing dope by dissolv-ing cellulose acetate, there is used a mixture co~prising: (i) dimethylsul-foxide (sometimes abbreviated "DMS0"), and ~ii) at least one water-soluble organic compound selected from the group consisting of monohydric alcohols having 2 to 5 carbon atoms, dihydric alcohols of the formula T-10-~R ~ ~T wherein R is an alkylene group having
2 or 3 carbon atoms and n is an integer of 1 to 16 and carboxylic acids having 1 or 2 carbon a-toms.
The use of the above-specified mixed solven-t has made it possible to provide very easily a cellulose acetate-type permselective membrane having very high water permeability and protein retention by a casting method The water-soluble organic compounds used in tha mixed solvent are described below in more detail.
(a) Monohydric alcohols having 2 -to 5 carbon atoms These are linear or branched saturated or unsaturated aliphatic monohydric alcohols having 2 to 5 carbon atoms such as lower alkanols (e.g., ethyl alcohol, n- or iso-propyl alcohol, n-, iso-, sec- or tert-butyl alcohol, n-pentyl alcohol, and iso-amyl alcohol)S and alkenols such as allyl alcohol and butenyl alcohol. Of these, lower alkanols having 2 to 4 carbon atoms such as ethyl alcohol, propyl alcohol and butyl alcohol, and allyl alcohol are preferred.
~thyl alcohol and tert-butyl alcohol are most preferred (b) Dihydric alcohols of the formula H0 -~R ~ 1ll (I) In formula (I), the C2-C3 alkylene group R
may be linear or branched, and includes -CH2C~2-, -CH2Cl~2C~2-, and -CTI~C1l3)CIT2 , and n is an integer of from 1 to 1~, preferably from 1 to 10. If n is at least two, the two or more groups R may be different ~rom each other. ~xamples of such dihydric alcohols are ethylene glycol~ diethylene glycol, tr~ethylene glycol, tetraethylene glycol, polyethylene glycol having an average molecular weight of 400 (n=about 9)~ poly-ethylene glycol having an average molecular weight of 600 ~n=about 13), propylene glycol, dipropylene glycol, and 1,3-propanediol. Of these, ethylene glycol, diethylene glycol, polyethylene glycol having an average molecular weight of 400 and propylene glycol are pre-ferred. Diethylene glycol and polyethylene glycolhaving an average molecular weight of 400 are most preferred.
(c) Carboxylic acids having 1 or 2 carbon atoms These carboxylic acids include formic acid and acetic acid, the former being especially preferred.
The above water-soluble organic compounds may be used singly, or as a combination of two or more.
The especially preferred water-soluble organic compounds in this invention are ethyl alcohol and tert-butyl alcohol.
The weight ratio of the water-soluble organic compouncl to DMS0 is important. The water-soluble organic compound is mixed in a weight ratio to DMS0 of not more than 1 (water-soluble organic compound/DMS0 ~- 1).
If this weight ratio is more than 1, various inconve-niences will be caused. For example, the solubility of cellulose acetate in DMS0 is reduced9 and DMS0 does not function as a solvent, or the resulting dope becomes extremely viscous and undergoes gellation.
The preferred weight ratio of the water-soluble organic compound to DMS0 in the mixed solvent is from 0.05 to 0.7. rne optimum range differs depend-ing upon the water-soluble organic compound to be mixed, The optimum mixing ratios of typical water-soluble organic compounds to DMS0 are listed in Table 1 below.
~1~0~
Table 1 Water-soluble__~e~ m~ound Optimum weight ratio of the water-soluble organic com~ound to DMSO
~ . . . ~ . . . . . ..
E-t~lyl alcohol 0.23 - 0.45 Isopropyl alcohol 0.10 - 0.3~
ter-t-Butyl alcohol 0.40 - 1.00 iso-Amyl alcohol 0.60 - 1.00 Allyl alcohol 0.05 - 0~10 Ethylene glycol 0.05 - 0.3~
~iethylene glycol 0.05 - 0.14 Polyethylene glycol (molecular weig~t 400) 0.05 - 0.14 Propylene glycol 0.05 - 0.21 Formic acid 0,05 - 0.23 Acet~c acid 0.23 - 0.45 The present invention does not exclude the use of a dope whicIl contains a third component in addition to cellulose acetate and the mixed solvent. Such a third component may be incorporated as required in an amount which does not substantially affect the present invention.
~xamples of the third component are water-soluble inorga-nic compounds such as magnesium perchlorate, magnesium chloride, lithium chloride, lithium bromide, lithium nitrate, calcium chloride, and calcium nitrate, and water-soluble polymeric compounds such as polyethylene glycol (molecular weight more than 800), polyvinyl alcohol, and polyvinyl pyrrolidone.
The amounts of such an additive to be incorpo-rated in the mixed solvent is not critical, but can be ~aried widely according to its type and the purpose of addition. ~Tenerally, the amount is not more than 25~
based on the -total weight of DMSO and the water-soluble organic compound, preferably not more than 10~ in order to make use of the proper-ties of the mixture of the water-soluble organic compound and DMSO.
According to this invention~ the cellulose acetate is dissol~ed in the mixed solvent -to prepare a dope containing cellulose acetate, The cellulose acetate 0~3 may be mixed with the water-soluble organic compound or DMSO a~ter it is dissolvecl or dispersed in ~MSO or the water-soluble organic compound. Or the cellulose acetate may be dissolved directly in the mixed solvent of DMSO and the water-soluble organic compound.
In any case, the amoun-t of the mixed solvent is generally 2 to 20 parts by weight, preferably 2.2 to 14 parts by weight, more preferably 2.3 to 8 parts by weight, per part by weight of the cellulose acetateO
m e water permeability of -the mei~brane in accordance with this invention varies between 5 and 2000 ml/m2-hr-mm~Ig when 2 to 20 parts by weight of the mixed solvent is added to 1 part by weight of cellulose acetate. For use as an ultra-filtration membrane, the membrc~ne of this invention preferably has a water permeability of at least 10 ml/m2 hr-m1~lg. From the standpoint of -the strength of the membrane 3 the amount of the mixed solvent is preferably not more than 10 parts by weight. A water permeability of not more than 1000 ml/m2-hr-mm~Ig can be obtained. If a film is fo~med on the surface of a porous support in order to increase the strength of the membrane, a memb-rane ha~ing a water flux of at least 1000 ml/m2-hr mmHg can be obtained. In view of the self-supporting property of the membrane, the amount of the mixed solvent is preferably 2.3 to 8 parts by weight.
~ ne role of the water-soluble organic compound in the mixed solvent is to increase the water permea-bility of the membrane tremendously, and to adjust its properties finally. Specifically, it has the following functions.
(1) Adjustment of the viscosity of the film-forming dope:-The viscosity is decreased by adding a mono hydric alcohol because the dope will become highlyviscous when the dimethylsulfoxide~cellulose ace-tate ratio is small. I~rnen this ratio is high and the dope is ~14~37~3 of low viscosity, a dihydric alcohol is added to raise the viscosity of the dope. In short, the viscosity of the dope is adjusted to the one which permits easy film formation by a wet method. At a film forming temperature (generally in the range of 0 to 80C), the viscosity of the dope is adjusted to 10 to 100,000 poises, preferably 100 -to 30,000 poises, more preferably 300 -to 3,000 poises.
(2) Adjustment of the performances of the membrane:-Since a membrane having a relatively rough structure is formed from the dope containing the water-soluble organic compound in accordance witll this invention, the membrane has an increased water permea-bilîty and a reduced reten-tion of solutes of low -to medium molecular weights. Since the performance of the membrane varies greatly depending upon other film-forming conditions, especially by a coagulating solution, it is necessary to consider performances of membranes and the film-forming conditions comprehensively.
(~) Adjustment of the properties of the membrane:-Since the additives to the dope and the com-position of the dope affect the proper-ties, especially strength and elongation, of the membrane, the conditions should be prescribed wi-th regard to the performances of the membrane.
The resulting dope containing cellulose acetate should desirably have a ~iscosity of generally 10 to 1007000 poises, preferably 100 to 30,000 poises, more preferably 300 to 3,000 poises at the -temperature of film casting, usually at 25C.
The cellulose acetate-con-taining dope so prepared ca~ be formed into permselective membranes in the form of flat film, tube, capillary or hollow filamen-ts by a known we-t-method film forming technique 9 for example the method disclosed in Peter R. Keller, "Membrane Technology and Industrial Separation Techniques"
~ ,~
~4lJ~:13 published in Park Ridge, Mew Jersey, U. S. A. by Noyes Data Corporation, pages 3-163, 1976~ The desired permselective membrane can be formed by casting the cellulose acetate-con-taining dope prepared as above to form a raw membrane of a predetermined shape, and solidifying the raw membrane with a coagulating solution.
More specifically, a permselec-tive membrane in the form of a flat film can be producecl by forming the dope prepared as above into a film by a device such as a slit die or doctor knife, casting it on a moving or non-mo~ing flat casting surface while controlling its thickness, optionally allowing tlle cast raw membrane to stand or op-tionally evaporating some amount of the solvent, and then treating the raw membrane with a coagulat.ing solution. The standing conditions such as the atmosphere~ temperature, humidity and -time are not as critical as in reverse osmosis membranes~ but can be varied wiclely. Generally, a temperature of 0 to 60C, preferably 10 to 40C, and a relative humidity of 30 to 90% are selected. ~le standing time may be within 30 minu-tes because the volatility of DMS0 is low.
Generally, it is about 30 seconds. In an extreme case, the sta~ding time may be zero by directly extruding the dope into a coagulating solution.
In the formation of a tubular permselective membrane, the cellulose acetate-containing dope is formed into a tubular wet raw membrane in a customary manner using an annular slit or a mandrel within a tubular support, and treating it in the same way as in the production of the flat ~ilm type membrane~
In the production of a permselective membrane in the form of capillaries or hollow fibers, the dope is wet-sp~m into capillaries or hollow fibers by using an annular nozzle (double tube or tube-in-orifice
The use of the above-specified mixed solven-t has made it possible to provide very easily a cellulose acetate-type permselective membrane having very high water permeability and protein retention by a casting method The water-soluble organic compounds used in tha mixed solvent are described below in more detail.
(a) Monohydric alcohols having 2 -to 5 carbon atoms These are linear or branched saturated or unsaturated aliphatic monohydric alcohols having 2 to 5 carbon atoms such as lower alkanols (e.g., ethyl alcohol, n- or iso-propyl alcohol, n-, iso-, sec- or tert-butyl alcohol, n-pentyl alcohol, and iso-amyl alcohol)S and alkenols such as allyl alcohol and butenyl alcohol. Of these, lower alkanols having 2 to 4 carbon atoms such as ethyl alcohol, propyl alcohol and butyl alcohol, and allyl alcohol are preferred.
~thyl alcohol and tert-butyl alcohol are most preferred (b) Dihydric alcohols of the formula H0 -~R ~ 1ll (I) In formula (I), the C2-C3 alkylene group R
may be linear or branched, and includes -CH2C~2-, -CH2Cl~2C~2-, and -CTI~C1l3)CIT2 , and n is an integer of from 1 to 1~, preferably from 1 to 10. If n is at least two, the two or more groups R may be different ~rom each other. ~xamples of such dihydric alcohols are ethylene glycol~ diethylene glycol, tr~ethylene glycol, tetraethylene glycol, polyethylene glycol having an average molecular weight of 400 (n=about 9)~ poly-ethylene glycol having an average molecular weight of 600 ~n=about 13), propylene glycol, dipropylene glycol, and 1,3-propanediol. Of these, ethylene glycol, diethylene glycol, polyethylene glycol having an average molecular weight of 400 and propylene glycol are pre-ferred. Diethylene glycol and polyethylene glycolhaving an average molecular weight of 400 are most preferred.
(c) Carboxylic acids having 1 or 2 carbon atoms These carboxylic acids include formic acid and acetic acid, the former being especially preferred.
The above water-soluble organic compounds may be used singly, or as a combination of two or more.
The especially preferred water-soluble organic compounds in this invention are ethyl alcohol and tert-butyl alcohol.
The weight ratio of the water-soluble organic compouncl to DMS0 is important. The water-soluble organic compound is mixed in a weight ratio to DMS0 of not more than 1 (water-soluble organic compound/DMS0 ~- 1).
If this weight ratio is more than 1, various inconve-niences will be caused. For example, the solubility of cellulose acetate in DMS0 is reduced9 and DMS0 does not function as a solvent, or the resulting dope becomes extremely viscous and undergoes gellation.
The preferred weight ratio of the water-soluble organic compound to DMS0 in the mixed solvent is from 0.05 to 0.7. rne optimum range differs depend-ing upon the water-soluble organic compound to be mixed, The optimum mixing ratios of typical water-soluble organic compounds to DMS0 are listed in Table 1 below.
~1~0~
Table 1 Water-soluble__~e~ m~ound Optimum weight ratio of the water-soluble organic com~ound to DMSO
~ . . . ~ . . . . . ..
E-t~lyl alcohol 0.23 - 0.45 Isopropyl alcohol 0.10 - 0.3~
ter-t-Butyl alcohol 0.40 - 1.00 iso-Amyl alcohol 0.60 - 1.00 Allyl alcohol 0.05 - 0~10 Ethylene glycol 0.05 - 0.3~
~iethylene glycol 0.05 - 0.14 Polyethylene glycol (molecular weig~t 400) 0.05 - 0.14 Propylene glycol 0.05 - 0.21 Formic acid 0,05 - 0.23 Acet~c acid 0.23 - 0.45 The present invention does not exclude the use of a dope whicIl contains a third component in addition to cellulose acetate and the mixed solvent. Such a third component may be incorporated as required in an amount which does not substantially affect the present invention.
~xamples of the third component are water-soluble inorga-nic compounds such as magnesium perchlorate, magnesium chloride, lithium chloride, lithium bromide, lithium nitrate, calcium chloride, and calcium nitrate, and water-soluble polymeric compounds such as polyethylene glycol (molecular weight more than 800), polyvinyl alcohol, and polyvinyl pyrrolidone.
The amounts of such an additive to be incorpo-rated in the mixed solvent is not critical, but can be ~aried widely according to its type and the purpose of addition. ~Tenerally, the amount is not more than 25~
based on the -total weight of DMSO and the water-soluble organic compound, preferably not more than 10~ in order to make use of the proper-ties of the mixture of the water-soluble organic compound and DMSO.
According to this invention~ the cellulose acetate is dissol~ed in the mixed solvent -to prepare a dope containing cellulose acetate, The cellulose acetate 0~3 may be mixed with the water-soluble organic compound or DMSO a~ter it is dissolvecl or dispersed in ~MSO or the water-soluble organic compound. Or the cellulose acetate may be dissolved directly in the mixed solvent of DMSO and the water-soluble organic compound.
In any case, the amoun-t of the mixed solvent is generally 2 to 20 parts by weight, preferably 2.2 to 14 parts by weight, more preferably 2.3 to 8 parts by weight, per part by weight of the cellulose acetateO
m e water permeability of -the mei~brane in accordance with this invention varies between 5 and 2000 ml/m2-hr-mm~Ig when 2 to 20 parts by weight of the mixed solvent is added to 1 part by weight of cellulose acetate. For use as an ultra-filtration membrane, the membrc~ne of this invention preferably has a water permeability of at least 10 ml/m2 hr-m1~lg. From the standpoint of -the strength of the membrane 3 the amount of the mixed solvent is preferably not more than 10 parts by weight. A water permeability of not more than 1000 ml/m2-hr-mm~Ig can be obtained. If a film is fo~med on the surface of a porous support in order to increase the strength of the membrane, a memb-rane ha~ing a water flux of at least 1000 ml/m2-hr mmHg can be obtained. In view of the self-supporting property of the membrane, the amount of the mixed solvent is preferably 2.3 to 8 parts by weight.
~ ne role of the water-soluble organic compound in the mixed solvent is to increase the water permea-bility of the membrane tremendously, and to adjust its properties finally. Specifically, it has the following functions.
(1) Adjustment of the viscosity of the film-forming dope:-The viscosity is decreased by adding a mono hydric alcohol because the dope will become highlyviscous when the dimethylsulfoxide~cellulose ace-tate ratio is small. I~rnen this ratio is high and the dope is ~14~37~3 of low viscosity, a dihydric alcohol is added to raise the viscosity of the dope. In short, the viscosity of the dope is adjusted to the one which permits easy film formation by a wet method. At a film forming temperature (generally in the range of 0 to 80C), the viscosity of the dope is adjusted to 10 to 100,000 poises, preferably 100 -to 30,000 poises, more preferably 300 -to 3,000 poises.
(2) Adjustment of the performances of the membrane:-Since a membrane having a relatively rough structure is formed from the dope containing the water-soluble organic compound in accordance witll this invention, the membrane has an increased water permea-bilîty and a reduced reten-tion of solutes of low -to medium molecular weights. Since the performance of the membrane varies greatly depending upon other film-forming conditions, especially by a coagulating solution, it is necessary to consider performances of membranes and the film-forming conditions comprehensively.
(~) Adjustment of the properties of the membrane:-Since the additives to the dope and the com-position of the dope affect the proper-ties, especially strength and elongation, of the membrane, the conditions should be prescribed wi-th regard to the performances of the membrane.
The resulting dope containing cellulose acetate should desirably have a ~iscosity of generally 10 to 1007000 poises, preferably 100 to 30,000 poises, more preferably 300 to 3,000 poises at the -temperature of film casting, usually at 25C.
The cellulose acetate-con-taining dope so prepared ca~ be formed into permselective membranes in the form of flat film, tube, capillary or hollow filamen-ts by a known we-t-method film forming technique 9 for example the method disclosed in Peter R. Keller, "Membrane Technology and Industrial Separation Techniques"
~ ,~
~4lJ~:13 published in Park Ridge, Mew Jersey, U. S. A. by Noyes Data Corporation, pages 3-163, 1976~ The desired permselective membrane can be formed by casting the cellulose acetate-con-taining dope prepared as above to form a raw membrane of a predetermined shape, and solidifying the raw membrane with a coagulating solution.
More specifically, a permselec-tive membrane in the form of a flat film can be producecl by forming the dope prepared as above into a film by a device such as a slit die or doctor knife, casting it on a moving or non-mo~ing flat casting surface while controlling its thickness, optionally allowing tlle cast raw membrane to stand or op-tionally evaporating some amount of the solvent, and then treating the raw membrane with a coagulat.ing solution. The standing conditions such as the atmosphere~ temperature, humidity and -time are not as critical as in reverse osmosis membranes~ but can be varied wiclely. Generally, a temperature of 0 to 60C, preferably 10 to 40C, and a relative humidity of 30 to 90% are selected. ~le standing time may be within 30 minu-tes because the volatility of DMS0 is low.
Generally, it is about 30 seconds. In an extreme case, the sta~ding time may be zero by directly extruding the dope into a coagulating solution.
In the formation of a tubular permselective membrane, the cellulose acetate-containing dope is formed into a tubular wet raw membrane in a customary manner using an annular slit or a mandrel within a tubular support, and treating it in the same way as in the production of the flat ~ilm type membrane~
In the production of a permselective membrane in the form of capillaries or hollow fibers, the dope is wet-sp~m into capillaries or hollow fibers by using an annular nozzle (double tube or tube-in-orifice
3~ structure) or a se~nentec'~ arc nozzle.
The cast wet raw material can generally have a thickness of about 5 to about 1000 microns9 preferably L4(;~713 about 10 to 500 microns, Coagulation of the raw membrane cas-t in the form of a film, tube, capillary or hollow ~ibers can be performed by dipping i-t in a coagulating solution, or contacting it intimately with a coagulatin~ solution by spraying or other means, in Q customary manner.
The coagulating solution is composed of a liquid which does not substantially dissol~e cellulose acetate and is miscible with the mixed solvent used in the preparation of -the film-forming dope (i.e., a nonsolvent for -the cellulose acetate). The coagulating solution has the functio~ of solidifying cellulose acetate by diffusing or extracting the DMS0 and the water-sol~lble organic compound from -the cast raw membrane. The coagulating solution having such a function includes water, alcohols, and ethers. ~xamples of the alcohols are methyl alcohol, ethyl alcohol, and propyl alcohol, and examples of the ethers are acrylic ethers such as methyl ether and ethyl ether. The water, alcohols and ethers can be used as a coagulating solution either alone or as a mixture of two or more.
For reference, the coagulating abilities and film-forming ability of typical coagulating solutions are shown in Table 2.
Table 2 Ability of nonsolvents to coagulate the cellulose acetate dope (~1) ,.. _ . . - _ _ . ~. . . . _ \ Cellulose Cellulose diacetate Cellulose triacetate \ esters (*2) (*3) \ . ._ __ _ ~ . ~
\ Rate Appea- Streng- P~ate Appea- Stren-Non- \ rance of th of rance of gth of solvent \ the mem- the mem- the mem- the (Volume \ brane brane brane mem-ratio~ ~ _ ~ _ .... . ~ . brane Water l~igh Montrans- Medium ~igh Nontrans ~ediu~
paren-t parent htiog Methyl alcollol ~edium 1~ T~igh Mmdi- ll Low ~thyl alcohol n It 1~ ~1 ,l Mediu~
~thyl ether Very _ _ Low Semi- Mediu~
low trans- to parent high ~ethyl alcohol Nontrans~ High Medi- Montrans- Low (elt/ly) ether ~qedium parent um parent Ethyl alcohol/ n n n ,l Semi- ~-ligh ether ether . trans-(1/1) parent ~ . . _ ~ _ __ , ~ , (*1): 1 part by weight of cellulo~ ;e estc r and 10 parts by weight o~ dimethylsulfoxide (*2): ~ type made by Teijin Limited (*3 ) CTA-432 ~ a product of East.man Rodak Co.
Additives for controlling the balance between the rate o~ diffusing or extracting DMSO and the water-soluble organic compound ~rom the cast raw membrane and the speed o~ coagulating the cellulose acetate may be added to the coagulating solution~ ~xamples of such additives include salts SUCll as sodium acetate, sodium sulfate~ .sodium chloride, soclium carbonate, calcium chloride and zinc chloride, alkal.ies such as sodium hyclroxicle, potassium hydroxide, sodium methylate and ammoniwn hydroxide, and acids such as hydrochloric acid, sul~uric acid, nitric acid and acetic acid.
Alternatively, the rate o~ coagulating the cast raw membrane may be inhibited by adding tl~e same DMSO and/or water~soluble organic compound as used in the preparation of the ~ilm~forming dope.
The temperature of the coagulating solution and the -time during whiclh ~-he coagulating solution makes contact with the cast raw membrane can be deter-mined wit'1in a broad range by considering the composition and propor~ion o~ the mixed solvent used in dope prepara-tion and the composition of the coagulating solution.
The temperature is generally room temperature, and the contact:in~ tirne is about 0.1 to 10 minutes.
A raw membrane in the form of capillary or hollow fibers may be prepared by discharging the dope through an outside tube o~ a double tube nozzle and the aforesaid coagulating solution, the mixed solvent used in dope formation, DMSO, t~e aforesaid water-soluble organic compound, and other liquid or gas through an inside tube. ~len the coagulating solution is to be discharged ~rom the inside tube, film formation and the coagulation treatment can be performed simultaneously.
The coagulated membrane 9 as re~uiredJ may be subjected to scouring trea-tments such as washing with water or bleaching, or further to physical treatments such as stretching or heat-treatmen~t.
The performances and/or mechanical properties of the resulting membrane may be improved by chemically treating (e.g., saponifyjng) ity modifying (e.g.~
grafting, or ionizing) it 9 or by physically -treating (e.g., crosslinking by radiation) it. ~hese chemical and physical treatments or modification can be performed by methods known per sep ~or example, those described in Robert ~. Kesting~ "Synthetic Polymeric Membranes"
published by McGraw~ 300k Company~ ~!ew York, U S. A. 9 pages 55-~26~ 1971.
~he storage stability of the membrane can be ~ P
31:14~ 3 increased by treating it Wit7L~ glycerol or a surface-active agent, and the trea-ted membrane can be stored in the dried state.
~he process of the present invention described above has the commercial advantage that permselective membranes o~ high performances to be described below can be produced safely under normal temperature and pressure condi-tions from a ~ilm-fo~ning solution (dope) of a relatively simple composi-tion Since DMS0 and the water-soluble organic compounds used in the prepara-tion of tl~e film-forming dope are water soluble, they can be substantially completely removed in the coagula-ting a1ld washing steps, alld do not remain substantially in the resulting membranes. Thus, -the membranes provided by this invention are useful in the fields of manufactur-ing medical instruments i~ld appliances, medicines, and foodstuffs ~nong the advantages of the permselective membranes of this invention are (i) they have a very high water flux, or a high water ultrafiltration rate, (ii) they have a very high protein re-tention~
and (iii) there is scarcely any decrease .in the ultrafiltration rate o~ water in the ultrafiltration of medi~molecular-weig?.~t materials and proteins, especially albumin.
~1e permselective membranes provided. by this invention generally have (A) a porosity in the range of 40 to 95~, especially 60 to 90~o, (~) a water permeability of 5 to 2000 ml/m hr~mmT-lg, especially 10 to 1000 ml/m2 hr mmi.1g, ar~d (C) a protein retention in the range of 80 to 10~', especially 90 to 100,~".
In the present specification and the appended claims, t:he "porosity" re~ers to a value calcula-ted by ~ 3 -the following equation.
Volume of the material for Porosity (%) = l _ the membrane x lO0 .. ~l) Volume of the ~ membrane ,, The volume of tlle ~aterial for the membrane is obtained by dividing the weight of the membrane material by the density of the membrane m~terial, and the volume of the membrane is a value obtained by multiplying the uni-t area by the thickness of the membrane.
The porosity corresponds to the water content (52 to 87S'~) of a wet membrane composed of cellulose diaceta-te (specific gravity 1.34) and water (specific gravity l.0), and for con~enience, the water content can be used in lieu thereof.
Water-permeability is expressed by water flux per unit pressure (mm~Jg), and as is customarily used in the fleld of medical treatment, its unit is (ml/m2 hr-mm~g). ~1e operating pressure is usually 0 to lO00 mmHg, and the water flu~ is measured at one or more points withi~ the range of 200 to 600 mrn~g.
Retention of solute is expressed by the following equation.
Retention (%) S~ x lO0 .............. (2) wherein ~0 is the average concentration of a solute in the feed 9 and S is the concentration of the solute in the filtrate that has permeated the membrane.
The permselectivity of the membrane in accord~lce with this invention varies according to the molecular weight of the solute) and the membrane has . J
7~3 the following retention.
The re-tention of low-molecular-~eight materials (with a molecular weigh-t of about lOO)such as sodium chloride (with a molecular weight of 58.5) and urea (with a molecular weight of 60) is as low as 0 -to 10~, preferably substantially 0. The retention of medium-molecular-weight materials (with a molecular weight of about 1000) such as polyetlQylene glycol 7~1000 (with a molecular weight of 1000) or vitamin B12 (wi-th a molecular weight of 1355) can be prescribed according to the purpose of-using the membrane if t,he membrane has a low water permeability o~, say, 5 to 10 ml/m2 hr m~lg~.
For example, when it is desired to recover valuable materials having a molecular weight of 1000, the reten-tion can be preset at more than 90/n. l~ en it isdesired to obtain a fraction with a molecular weight of 1000, -the retention can be preset at 50S~. Within a water per~eability range of 10 to 1000 ml/m2 hr mml{g, the retention of medium-molecular-weight materials is preset a-t not more than 10% so as to remove medium-molecular-weight material,s into -the fil-trate as in hemofi~ters for artificial kiclneys.
Tlle retention of high-molecular weight substances (with a molecular weight of more ~han 10000) such as ribonuclease (with a molecular weight of 13000), bovine serum albumin (wi th a molecular weight of 46000) and garnma-globulin (with a molecular weight of 160000) is 80 to 100%j preferably 90 to 100,S, more preferably 95 to 10~. In preparations from blood or hemofilters for artificial kidneys, tl-le freedom from leakage of blood proteins is preferred.
The permselective membranes provided by this invention generally have a thickness of 5 to 500 microns, preferably 10 to 300 microns.
Because of these performances, the membranes in accorclance with this inven-tion can be principal materials for ultrafilters and dialyzers, and find a wide 1~40~13 range of applications in industrial and medical treat-ment ~ields. For example, they are suitable for recovery, purification7 concentration, etc. of valuable materials in foodstuffs and pharmaceutical in~ustries, and permit production of preparations from naturally occurring substances, blood, etc. and of sterilized water or pyrogen-free water~ In the field of medical trea~nent, these membranes can be used for the filtration or dialysis of the blood (artificial kidneys) or for the removal of hazardous materials from body fluids ~artificial liver).
m e permselective membralles provided by this invention have very high water-permeability as described hereinabove, and there~ore, a sufficient water flux can be acllieved at low pressures and low- and medium-molecular weight waste materials can be removed from the blood. Furthermore, they scarcely permit permea-tion of proteins which are valuable to the human body Accordingly, the membrane in accordance with this invention is very suitable as a hemofilter for artifi-cial l~id~eys. In using the membrane in accordance with this inverl-tion as a hemofilter for artificial kidneys, it is necessary to mold i-t into a membrane in the ~orm of flat film or hollow filaments, and to build a filter out of the resulting membrane. GenerallyJ the membrane is dipped in glycerol and dried, and is placed in a container so as to define a blood compartment and a filtrate compartment therein. Preferred methods of sterilization involve using an ethylene oxide gas or radiaoacti~e ~-rays. IIeat sterilization is preferred because -the membrane is -toxin-free without an~ residue o~ etl~ylene oxide, but tlle water permeabili-ty of -the membrane tends to decrease to less than about 1/3.
~lowever~ such a membrane is still fully usable.
In usin~ the permselective membrane in accordance with this invention in the aforesaid applica-tions, the membrane can-take various forms suitable for the res~ective uses, such as a flat membrane, spiral ~embrane, tubular, capillary and hollow filaments. I-t can be used in the form of a composi-te material on a porous support such as a woven knitted or nonwoven fabric or paper. ~uch a composite material can be produced by bonding tl~e membrane produced as above to the aforesaid support, or by directly casting the aforesaid cellulose acetate-containing dope or~o the aforesaid support and treating lt with a coagulating solution as described hereinabove.
Tlle membrane providecl by this invention may also be used as a support ~or a composite membrane for reverse osmosis with an ultrathin film laminated thereto.
T~e following exam~les illustrate the present invention more specifically.
~xample 1 A dope was prepared from 1 part by weight of cellulose diacetate (T-l type~ a product of Teijin Limited), 3 parts by weight of dimethylsulfoxide and 1 part by weight of ethyl alcohol. The dope was cast on a glass plate by a doctor knife having a thickness of 150 microns, and allowed to stand for 30 seconds in an atmosphere kept at room temperature. Tlle glass plate having the dope cast thereon was dipped for 10 ~ninutes in cold water to coagulate the cast membrane. A permselective membrane having an average thickness of 74 ~icrons was obtained.
I'he water permeability (ultrafiltration rate uFr~ ) of the resulting membrane ~7ith regar~ to pure water, and its solute retention and water flux in an aqueous solution of bovine serum albumin (molecular weight 4~hOO09 0.1,~6~ were measured. The porosity of the membrane was also measured. ~he results are shown in Table 3. The urea reten-tion of this membrane was ~,6, and its ~itamin ~12 retentiQn was l~o.
~o --Table 3 ~_. ~ . , . . .
~xample Thickness U~ 2 ~~ovine serum albumin Porosity of the (ml/m ~ . _ membrane hr~mmM~) Water flux ~etention ~o/~
(microns) (ml/m2-hr mmHg) (~!) . _ . ___ ....... ....... _ . ~ _ _ ....... ~ . __ UFR was measured by the followi~g procedure.
The per-nselective membrane was held by an in-line filter holder having a diameter of 47 mm made by Millipore Co.. A transparent tube having an inside diameter o~ 5 mm and a length of ~00 mm was connected to the top end of the holder. Pure water was filled into this -tube, and pressurized with a nitrogen gas to a pressure of 200 -to 600 m~-Tg. ~he amount of pure water decreased per unit time was measured.
The water flux and reten-tion of the a~ueous solution of bovine serum albumin were measured by using an ultrafiltration device (MC-2Q type, a product of ~ioen-gineering Co.). The membrane was fixed to the device, and pure water or an aqueous solution of bovine serum albumin was filled, and pressurized with nitrogen gas usually -to 200 to 600 ~rg. The water flux per unit time (ml/m2~hr), and the water permeability (ml/m2-hr mmllg) was calculated. On the other hand, the retention was calculated from the concentration of the solute ~bovine serum albumin).
Com~arative Pxam~le 1 A dope was prepared from 1 part by weight of cellulose diacetate and 4 parts by weight of di~et'nyl-sulfoxide, and a membrane was prepared from it in the same way as in ~xample 1. T}le performances of the membrane were measured i~l the same way as in Example 1.
Table 4 below shows the averages of the measured values on six samples and standard deviations. These samples .
~a~7~.3 had a porosity of 7~ to 79D~.
Table 4 Compara- Membrane ~ R (ml/ 'ovine ~-r~r aD ~i. , tive thickness m hr~ _ _ .
~xample (microns) mm~lg) ¦ml/m2 hr~ netention mml-lg ) (~ ~
_ . __ ~ _ _ , 1 97 + 1l 102 + 1~ 9~ + 10 _ _ , Comparative Examples ? to_l6 Various clopes were prepared from 1 par-t by weight o~ cellulose diacetate and 4 parts by weight of a mixed solvent composed o.~ dimethylsulfoxide and an organic compound selectecl from acetone, t.riethyl phosphate and dimethylacetamide (t~le organic compounds outside the scope of the i~vention). Films were prepared from these dopes t and their properties were measured in the same way as in ~xample 1. ~he resul-ts are shown in Table 5. As is seen from Table 5, the water permeability abruptly clecreased with an increase in the amount of the organic compound. This shows that the above organic compounds are undesirable as additives for the mixed solvent.
-~6~b C~ ----~d ~,e~ ,, __~
C) ~ ~, ~i U~
~ ~ ~ o o ~ ~ ~
~ _ _ ~ a~
~ ~ ~ ~ ~ ~1 N _ _ _ ~ O O ~ ~
~ ~; ~ ~D ~
~ ~0 ___ _ u~ ,~ L~
r l +~ 1lO N Lt~
,~:2 ~ O O ~1 N
~ _ _ . h ~1 ~ a3 O ~1 O r X ~ r--l r-l _ ~0 __ , N ~j 0O r-l ~1 ~ r-l ~ O O~ u~ ~ O
(I~ ~ _ _ h ~rl o L~
Q. PO O ~1 N ;i`
cC ~ _ .~
h ~1 U~
~o ~
~ u~ ~u~
O M t~ ~-1 ~ o t~ N O
. ~. ~ ~ ~ . _ .
In each run, a dope was prepared from 1 part by weigllt of cellulose diacetate and 4 parts by weight of a mixed solvent composed of dimethylsulfoxide and each of the monohydric alcohols shown in Table 6 in -the amounts indicated. A membrane was formed from the dope, and its properties were measured, in the same way as in ~xample 1. The resul-ts are shown in Table 6. All of the membranes obtained showed superior performances.
~able 6 -~ . _~ ~
~xam- Monohydric alcohol Tllick- UFR 2 Bovlne ser~ Poro- , ple ~ ness (ml/m albumin __ sity I~pe ~nount o~ the hr.
(parts mern~ mn~lg) Water tieOtnn- (~) by brane , weight) r~ S) m~-hr (~0) . .. _ ~) . . - .. .
2 iso-Propyl 0.5 6~ 173 165 96 7o I lco~lol _ _ _ __, _ _ _ _._ .
3 ¦ ert-Rutyl 1.5 6~ 175 168 97 71 - . . _ ._ ~ . . _ ~ __ .
The cast wet raw material can generally have a thickness of about 5 to about 1000 microns9 preferably L4(;~713 about 10 to 500 microns, Coagulation of the raw membrane cas-t in the form of a film, tube, capillary or hollow ~ibers can be performed by dipping i-t in a coagulating solution, or contacting it intimately with a coagulatin~ solution by spraying or other means, in Q customary manner.
The coagulating solution is composed of a liquid which does not substantially dissol~e cellulose acetate and is miscible with the mixed solvent used in the preparation of -the film-forming dope (i.e., a nonsolvent for -the cellulose acetate). The coagulating solution has the functio~ of solidifying cellulose acetate by diffusing or extracting the DMS0 and the water-sol~lble organic compound from -the cast raw membrane. The coagulating solution having such a function includes water, alcohols, and ethers. ~xamples of the alcohols are methyl alcohol, ethyl alcohol, and propyl alcohol, and examples of the ethers are acrylic ethers such as methyl ether and ethyl ether. The water, alcohols and ethers can be used as a coagulating solution either alone or as a mixture of two or more.
For reference, the coagulating abilities and film-forming ability of typical coagulating solutions are shown in Table 2.
Table 2 Ability of nonsolvents to coagulate the cellulose acetate dope (~1) ,.. _ . . - _ _ . ~. . . . _ \ Cellulose Cellulose diacetate Cellulose triacetate \ esters (*2) (*3) \ . ._ __ _ ~ . ~
\ Rate Appea- Streng- P~ate Appea- Stren-Non- \ rance of th of rance of gth of solvent \ the mem- the mem- the mem- the (Volume \ brane brane brane mem-ratio~ ~ _ ~ _ .... . ~ . brane Water l~igh Montrans- Medium ~igh Nontrans ~ediu~
paren-t parent htiog Methyl alcollol ~edium 1~ T~igh Mmdi- ll Low ~thyl alcohol n It 1~ ~1 ,l Mediu~
~thyl ether Very _ _ Low Semi- Mediu~
low trans- to parent high ~ethyl alcohol Nontrans~ High Medi- Montrans- Low (elt/ly) ether ~qedium parent um parent Ethyl alcohol/ n n n ,l Semi- ~-ligh ether ether . trans-(1/1) parent ~ . . _ ~ _ __ , ~ , (*1): 1 part by weight of cellulo~ ;e estc r and 10 parts by weight o~ dimethylsulfoxide (*2): ~ type made by Teijin Limited (*3 ) CTA-432 ~ a product of East.man Rodak Co.
Additives for controlling the balance between the rate o~ diffusing or extracting DMSO and the water-soluble organic compound ~rom the cast raw membrane and the speed o~ coagulating the cellulose acetate may be added to the coagulating solution~ ~xamples of such additives include salts SUCll as sodium acetate, sodium sulfate~ .sodium chloride, soclium carbonate, calcium chloride and zinc chloride, alkal.ies such as sodium hyclroxicle, potassium hydroxide, sodium methylate and ammoniwn hydroxide, and acids such as hydrochloric acid, sul~uric acid, nitric acid and acetic acid.
Alternatively, the rate o~ coagulating the cast raw membrane may be inhibited by adding tl~e same DMSO and/or water~soluble organic compound as used in the preparation of the ~ilm~forming dope.
The temperature of the coagulating solution and the -time during whiclh ~-he coagulating solution makes contact with the cast raw membrane can be deter-mined wit'1in a broad range by considering the composition and propor~ion o~ the mixed solvent used in dope prepara-tion and the composition of the coagulating solution.
The temperature is generally room temperature, and the contact:in~ tirne is about 0.1 to 10 minutes.
A raw membrane in the form of capillary or hollow fibers may be prepared by discharging the dope through an outside tube o~ a double tube nozzle and the aforesaid coagulating solution, the mixed solvent used in dope formation, DMSO, t~e aforesaid water-soluble organic compound, and other liquid or gas through an inside tube. ~len the coagulating solution is to be discharged ~rom the inside tube, film formation and the coagulation treatment can be performed simultaneously.
The coagulated membrane 9 as re~uiredJ may be subjected to scouring trea-tments such as washing with water or bleaching, or further to physical treatments such as stretching or heat-treatmen~t.
The performances and/or mechanical properties of the resulting membrane may be improved by chemically treating (e.g., saponifyjng) ity modifying (e.g.~
grafting, or ionizing) it 9 or by physically -treating (e.g., crosslinking by radiation) it. ~hese chemical and physical treatments or modification can be performed by methods known per sep ~or example, those described in Robert ~. Kesting~ "Synthetic Polymeric Membranes"
published by McGraw~ 300k Company~ ~!ew York, U S. A. 9 pages 55-~26~ 1971.
~he storage stability of the membrane can be ~ P
31:14~ 3 increased by treating it Wit7L~ glycerol or a surface-active agent, and the trea-ted membrane can be stored in the dried state.
~he process of the present invention described above has the commercial advantage that permselective membranes o~ high performances to be described below can be produced safely under normal temperature and pressure condi-tions from a ~ilm-fo~ning solution (dope) of a relatively simple composi-tion Since DMS0 and the water-soluble organic compounds used in the prepara-tion of tl~e film-forming dope are water soluble, they can be substantially completely removed in the coagula-ting a1ld washing steps, alld do not remain substantially in the resulting membranes. Thus, -the membranes provided by this invention are useful in the fields of manufactur-ing medical instruments i~ld appliances, medicines, and foodstuffs ~nong the advantages of the permselective membranes of this invention are (i) they have a very high water flux, or a high water ultrafiltration rate, (ii) they have a very high protein re-tention~
and (iii) there is scarcely any decrease .in the ultrafiltration rate o~ water in the ultrafiltration of medi~molecular-weig?.~t materials and proteins, especially albumin.
~1e permselective membranes provided. by this invention generally have (A) a porosity in the range of 40 to 95~, especially 60 to 90~o, (~) a water permeability of 5 to 2000 ml/m hr~mmT-lg, especially 10 to 1000 ml/m2 hr mmi.1g, ar~d (C) a protein retention in the range of 80 to 10~', especially 90 to 100,~".
In the present specification and the appended claims, t:he "porosity" re~ers to a value calcula-ted by ~ 3 -the following equation.
Volume of the material for Porosity (%) = l _ the membrane x lO0 .. ~l) Volume of the ~ membrane ,, The volume of tlle ~aterial for the membrane is obtained by dividing the weight of the membrane material by the density of the membrane m~terial, and the volume of the membrane is a value obtained by multiplying the uni-t area by the thickness of the membrane.
The porosity corresponds to the water content (52 to 87S'~) of a wet membrane composed of cellulose diaceta-te (specific gravity 1.34) and water (specific gravity l.0), and for con~enience, the water content can be used in lieu thereof.
Water-permeability is expressed by water flux per unit pressure (mm~Jg), and as is customarily used in the fleld of medical treatment, its unit is (ml/m2 hr-mm~g). ~1e operating pressure is usually 0 to lO00 mmHg, and the water flu~ is measured at one or more points withi~ the range of 200 to 600 mrn~g.
Retention of solute is expressed by the following equation.
Retention (%) S~ x lO0 .............. (2) wherein ~0 is the average concentration of a solute in the feed 9 and S is the concentration of the solute in the filtrate that has permeated the membrane.
The permselectivity of the membrane in accord~lce with this invention varies according to the molecular weight of the solute) and the membrane has . J
7~3 the following retention.
The re-tention of low-molecular-~eight materials (with a molecular weigh-t of about lOO)such as sodium chloride (with a molecular weight of 58.5) and urea (with a molecular weight of 60) is as low as 0 -to 10~, preferably substantially 0. The retention of medium-molecular-weight materials (with a molecular weight of about 1000) such as polyetlQylene glycol 7~1000 (with a molecular weight of 1000) or vitamin B12 (wi-th a molecular weight of 1355) can be prescribed according to the purpose of-using the membrane if t,he membrane has a low water permeability o~, say, 5 to 10 ml/m2 hr m~lg~.
For example, when it is desired to recover valuable materials having a molecular weight of 1000, the reten-tion can be preset at more than 90/n. l~ en it isdesired to obtain a fraction with a molecular weight of 1000, -the retention can be preset at 50S~. Within a water per~eability range of 10 to 1000 ml/m2 hr mml{g, the retention of medium-molecular-weight materials is preset a-t not more than 10% so as to remove medium-molecular-weight material,s into -the fil-trate as in hemofi~ters for artificial kiclneys.
Tlle retention of high-molecular weight substances (with a molecular weight of more ~han 10000) such as ribonuclease (with a molecular weight of 13000), bovine serum albumin (wi th a molecular weight of 46000) and garnma-globulin (with a molecular weight of 160000) is 80 to 100%j preferably 90 to 100,S, more preferably 95 to 10~. In preparations from blood or hemofilters for artificial kidneys, tl-le freedom from leakage of blood proteins is preferred.
The permselective membranes provided by this invention generally have a thickness of 5 to 500 microns, preferably 10 to 300 microns.
Because of these performances, the membranes in accorclance with this inven-tion can be principal materials for ultrafilters and dialyzers, and find a wide 1~40~13 range of applications in industrial and medical treat-ment ~ields. For example, they are suitable for recovery, purification7 concentration, etc. of valuable materials in foodstuffs and pharmaceutical in~ustries, and permit production of preparations from naturally occurring substances, blood, etc. and of sterilized water or pyrogen-free water~ In the field of medical trea~nent, these membranes can be used for the filtration or dialysis of the blood (artificial kidneys) or for the removal of hazardous materials from body fluids ~artificial liver).
m e permselective membralles provided by this invention have very high water-permeability as described hereinabove, and there~ore, a sufficient water flux can be acllieved at low pressures and low- and medium-molecular weight waste materials can be removed from the blood. Furthermore, they scarcely permit permea-tion of proteins which are valuable to the human body Accordingly, the membrane in accordance with this invention is very suitable as a hemofilter for artifi-cial l~id~eys. In using the membrane in accordance with this inverl-tion as a hemofilter for artificial kidneys, it is necessary to mold i-t into a membrane in the ~orm of flat film or hollow filaments, and to build a filter out of the resulting membrane. GenerallyJ the membrane is dipped in glycerol and dried, and is placed in a container so as to define a blood compartment and a filtrate compartment therein. Preferred methods of sterilization involve using an ethylene oxide gas or radiaoacti~e ~-rays. IIeat sterilization is preferred because -the membrane is -toxin-free without an~ residue o~ etl~ylene oxide, but tlle water permeabili-ty of -the membrane tends to decrease to less than about 1/3.
~lowever~ such a membrane is still fully usable.
In usin~ the permselective membrane in accordance with this invention in the aforesaid applica-tions, the membrane can-take various forms suitable for the res~ective uses, such as a flat membrane, spiral ~embrane, tubular, capillary and hollow filaments. I-t can be used in the form of a composi-te material on a porous support such as a woven knitted or nonwoven fabric or paper. ~uch a composite material can be produced by bonding tl~e membrane produced as above to the aforesaid support, or by directly casting the aforesaid cellulose acetate-containing dope or~o the aforesaid support and treating lt with a coagulating solution as described hereinabove.
Tlle membrane providecl by this invention may also be used as a support ~or a composite membrane for reverse osmosis with an ultrathin film laminated thereto.
T~e following exam~les illustrate the present invention more specifically.
~xample 1 A dope was prepared from 1 part by weight of cellulose diacetate (T-l type~ a product of Teijin Limited), 3 parts by weight of dimethylsulfoxide and 1 part by weight of ethyl alcohol. The dope was cast on a glass plate by a doctor knife having a thickness of 150 microns, and allowed to stand for 30 seconds in an atmosphere kept at room temperature. Tlle glass plate having the dope cast thereon was dipped for 10 ~ninutes in cold water to coagulate the cast membrane. A permselective membrane having an average thickness of 74 ~icrons was obtained.
I'he water permeability (ultrafiltration rate uFr~ ) of the resulting membrane ~7ith regar~ to pure water, and its solute retention and water flux in an aqueous solution of bovine serum albumin (molecular weight 4~hOO09 0.1,~6~ were measured. The porosity of the membrane was also measured. ~he results are shown in Table 3. The urea reten-tion of this membrane was ~,6, and its ~itamin ~12 retentiQn was l~o.
~o --Table 3 ~_. ~ . , . . .
~xample Thickness U~ 2 ~~ovine serum albumin Porosity of the (ml/m ~ . _ membrane hr~mmM~) Water flux ~etention ~o/~
(microns) (ml/m2-hr mmHg) (~!) . _ . ___ ....... ....... _ . ~ _ _ ....... ~ . __ UFR was measured by the followi~g procedure.
The per-nselective membrane was held by an in-line filter holder having a diameter of 47 mm made by Millipore Co.. A transparent tube having an inside diameter o~ 5 mm and a length of ~00 mm was connected to the top end of the holder. Pure water was filled into this -tube, and pressurized with a nitrogen gas to a pressure of 200 -to 600 m~-Tg. ~he amount of pure water decreased per unit time was measured.
The water flux and reten-tion of the a~ueous solution of bovine serum albumin were measured by using an ultrafiltration device (MC-2Q type, a product of ~ioen-gineering Co.). The membrane was fixed to the device, and pure water or an aqueous solution of bovine serum albumin was filled, and pressurized with nitrogen gas usually -to 200 to 600 ~rg. The water flux per unit time (ml/m2~hr), and the water permeability (ml/m2-hr mmllg) was calculated. On the other hand, the retention was calculated from the concentration of the solute ~bovine serum albumin).
Com~arative Pxam~le 1 A dope was prepared from 1 part by weight of cellulose diacetate and 4 parts by weight of di~et'nyl-sulfoxide, and a membrane was prepared from it in the same way as in ~xample 1. T}le performances of the membrane were measured i~l the same way as in Example 1.
Table 4 below shows the averages of the measured values on six samples and standard deviations. These samples .
~a~7~.3 had a porosity of 7~ to 79D~.
Table 4 Compara- Membrane ~ R (ml/ 'ovine ~-r~r aD ~i. , tive thickness m hr~ _ _ .
~xample (microns) mm~lg) ¦ml/m2 hr~ netention mml-lg ) (~ ~
_ . __ ~ _ _ , 1 97 + 1l 102 + 1~ 9~ + 10 _ _ , Comparative Examples ? to_l6 Various clopes were prepared from 1 par-t by weight o~ cellulose diacetate and 4 parts by weight of a mixed solvent composed o.~ dimethylsulfoxide and an organic compound selectecl from acetone, t.riethyl phosphate and dimethylacetamide (t~le organic compounds outside the scope of the i~vention). Films were prepared from these dopes t and their properties were measured in the same way as in ~xample 1. ~he resul-ts are shown in Table 5. As is seen from Table 5, the water permeability abruptly clecreased with an increase in the amount of the organic compound. This shows that the above organic compounds are undesirable as additives for the mixed solvent.
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In each run, a dope was prepared from 1 part by weigllt of cellulose diacetate and 4 parts by weight of a mixed solvent composed of dimethylsulfoxide and each of the monohydric alcohols shown in Table 6 in -the amounts indicated. A membrane was formed from the dope, and its properties were measured, in the same way as in ~xample 1. The resul-ts are shown in Table 6. All of the membranes obtained showed superior performances.
~able 6 -~ . _~ ~
~xam- Monohydric alcohol Tllick- UFR 2 Bovlne ser~ Poro- , ple ~ ness (ml/m albumin __ sity I~pe ~nount o~ the hr.
(parts mern~ mn~lg) Water tieOtnn- (~) by brane , weight) r~ S) m~-hr (~0) . .. _ ~) . . - .. .
2 iso-Propyl 0.5 6~ 173 165 96 7o I lco~lol _ _ _ __, _ _ _ _._ .
3 ¦ ert-Rutyl 1.5 6~ 175 168 97 71 - . . _ ._ ~ . . _ ~ __ .
4 tert-Butyl2.0 ~,3 494 459 95 75 ~ ... ___ __ _ ~ .. .. .~ , _ , alcogol 2.0 ~4 123 117 9~74 ,, _, ~ . ~ _ . . , ~
6 Qllyl alcohol 0.25 62 143 1~8 9868 Com~arative ~xamples 17 to ~0 . .
Dopes were prepared from 1 part by weight of cellulose diacetate 9 3 parts by weight of dimethyl-sulfoxide, and 1 part by weight of phenol or clihydric alcohols other -than those specified in this invention.
Membranes were formed from the dopes in the same way as in ~xam~le 1, and their water fluxes were measured. ~he resul-~s are shown below.
- 2~ -Table 7 ~ . . ____ ~xample Alcohol UFR (ml/m2-hr mm~1g) __ ~ . ..
17 Methyl aloohol 64 1~. Cyolohexyl alcohol 23 19 Benzyl alcohol less than 0.1 Phenol 25 _~, _ Dopes were prepared from 1 part by weight of cellulose diacetate and 4 parts by weigh-t of a mixture of dimet!~ylsulfoxi~e and each o~ the dihydric alcohols show~ i~ Table ~ in the amo~mts indicated. Membranes were forlned ~rom the dopes, and their properties were measured, in the same way as in ~,xample 1. The results are sl~o~ in Table 8. These membranes had a high strength and were easy to handle.
The membrane of ~xample 14 had a wet tensile strength of 0.74 kg/mm2 and an elongation of 43~. In contrast, the membrane of Comparative ~xample 1 had a wet strength of 0.51 kg/mm2 and a break elongation of 36SS.
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~ 3 A dope was prepared from 1 part by weight of cellulose diacetate, 3.5 parts by weight of dimethyl-sulfoxide and 0.5 part by weight of butanediol-1,3 ~Comparative ~xample 21) or polyethylene glycol 1000 (Comparative ~xample 22), and a membrane was produced from the dope and tested in the same way as in Example 1.
The membrane of Comparative ~xample 21 had a water ~lux of 53 ml/m2~hr-m~L~Tg, and the membrane of Comparative Example 22 had a water permeability of 92 ml/m2-hr mmllg.
_xamples 16 to_l8 and Com~ara-tive ~xamples 23 to 25 A dope was prepared from 1 part by weight of cellulose diacetate ànd 4 parts by weight of a mixture of dime-thylsulfoxide and each of the carboxylic acids shown in Table 9 in the amoun-ts indicated. A membrane was produced from the dope and tested in the same way as in Example 1. The results are shown in Table 9. It is seen from the results obtained that membranes obtained by using formic acid or acetic acid as the water-soluble organic compound showed excellent resul-ts, whereas the use of propionic acid and n-butyric acid led to drastical-ly reduced water fluxes.
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_ 19 and Comparative Fxalnple 26 A dope was prepared from 1 part by weight of cellulose diacetate, 2.2 parts by weight of dimethyl-sulfoxide and 0.8 part by weight of tert-butyl alcohol, and a membrane was produced from the dope in the same way as in ~xample 1 (~xample 19). .or comparison, a membrane was produced from a dope composed of 1 part by weight of cellulose diacetate and 3 parts by weight of dimethylsulfoxide (Comparative ~xamples 26). The properties o~ these membranes are shown in Table 10.
Tab . _ , _ . ~ _ . __ .
Thickness UFR ~ovine serum albumin Porosity membrane (ml/m2 hr- Water ~lux Retention (%~
(microns) (ml/m2-hr- (~) __. . . . ._ ._ .... .. .
~xample 19 ~ 35 31 99 6 . ~ . __ ~ ., - _ _ . . __ .
Compara-tive 62 29 26 99 65 Example __________ _ _ ~ - ~ _ Fxamples 20 and ~ a-tive ~xample 27 Dopes were prepared from 1 part by weight of cellulose diacetate and 6 parts by weight o~ a mixture of dimetl1ylsulfoxide and each of the alcohols sho~m in Table 11 in the amounts indicated. Membranes were prepared from the dopes and tested in t'ne same way as in ~xample 1. The results are sho~n in Table 11. It is seen from the results that the membranes of t~is inven-tion showed superior performances. In particular, the membrane obtained by using diethylene glycol as one component o~ t~le mixed solvent had about twice as high UFR as the membrane obtained by using dimethylsulfoxide alone as a solvent (Comparative ~ample 27~, and moreover, its mechanical strength was improved.
.
7~3 The membrane of ~xample 21 had a wet strength of 0.33 kg/mm2 and a break elongation of 24~. The membrane of Comparative I~`xample 27 had a wet strength of 0.29 kg/mm2 and a break elongation of 16S~.
Table 11 ~ . _ , . , . . _ ,.
~xample Alcohol Thickness UFR 2 Bovine serum Poro-(Ex ) or _ ~... ., ~ of t:~le (ml/m albumin sity tompara- Type ~myrtts (microns) mrn.~lg) Water Reten-(C~`x.) weight) (m21/r. (%) m~Yg) . ., _ . . ~ _ __ . .
Ex. 20 Eth~rl 1. 5 51 ?63 771 96 69 alco'lol ~x. 21 lene~,ly_ 0.4 ~0 426 413 97 90 glycol CE~. 27 None 0 60 253 249 97 74 . ~ _ . ......... __ . . . .~ _ ,.. _ xsmples 22 to 24 and Com~arative ~xamples 2~ to ~0 Dopes were prepared from 1 part by weight of cellulose diacetate and the amounts shown in Table 12 of dimethylsulfoxide and diethylene glycol.
~ach of the dopes was cast on the surface of a porous polyest.er filament material (non-woven fabric; basis weight 1~5 g/m2) by a doctor knife to a thickness o~
200 microns, and dipped in cold water for 15 minutes to coagulate it. The properties of the resulting membranes were measured in the same way as in ~xample 1. Tlle results are shown in Table 12. The thicknesses and porosities of the membranes could not be measured because tlQe membrane and the nonwoven material were united with each otherO
Table 12 ._ . _ _ . . . _ ~
Example Mixed solvent U~R Bovine serum albumin (Ex,~ or (p~rts by weight) (~1/ 2-h _ __ Compara- ~ ~ ~- tTm~ r- Water flux Retention tive Dimethyl Diethy- "Imlg~ (ml/m2~hr~ (%) (C~x.) sul~oxide glyceol mm~lg) _ . _ .. . ._ . _ __ ~ , _ .
Ex. 22 9 1 765 743 97 Ex. 23 13.5 1.5 1102 1090 95 Ex. 24 18 2 1~57 1360 81 CEx. 28 10 0 451 447 97 CEx. 29 15 0 896 871 93 C~x. 30 20 0 1290 1250 82 .~ ,~____ ., _ __ . _ __ ~xamples 25 and ~ F.x~nple 31 Dopes were prepared from 1 par-t by weight of cellulose -triacetate (CI'A-432, a product of Eastman Kodak Co.) and 6 parts o~ a mix-ture of dimethylsulfoxide and tertbutyl alcohol in t'ne amounts shown in Table 13.
Membranes were produced from the dopes and tested in the same way as in xample 1. It is seen from Table 13 that the membranes obtained by using tert-butyl alcohol as one component of the mixecl solvent had superior wa-ter fluxes~ and tert-butyl alcohol as one component of the mixed solvent aided in the dissolving of cellulose triacetate and could give a membrane having high uniformity.
'1'~`~
~xam le Amount of Thick- _ ~ Bovine serum albv- Poro-~~Fx.~ or tert-butyl ness of (~l/m2~ min sity Compara- alcohol the hr~ ___________ ,---____ tive (parts by mem- mmTIg) Water flux Reten~ (%) ~xample wei~nt) brane (ml/m2-hr. tion (CEx.) (omnsC) mmllg) _ ~ ___ ~ _~
~x. 2~ 0~4 126 ~31 316 98 88 Fx. 26 0.7 139 41X 398 98 89 C~. 31 _ 56 9~ 97 99 73 . . ___ __ __ ~ _ ~L~4~37~3 A dope was prepared from 0.5 part by weight of cellulose diacetate, 0.5 part by weight of cellulose triacetate, 4.5 parts by weight of dimethylsulfoxide and 1.5 parts by weight of ethyl alcohol. A membrane was preparecl ~rom the dope and tested in the same way as in ~xample 1.
For comparison, a dope was prepared in the same way as above except that 6 parts by weight of only dimethylsulfoxide was added as the solvent (Comparative ~xample 32). Tlle results are shown in Table 14.
Table 14 _ __ _ . , . ._ Tllickness f UF1~2 Porosity (~) the membrane (ml/m hr mmHg) (microns) .,. ~ . .. _._ ~xample Compara-tive 58 125 73 3m2Ple . . _ _ xamples 28 to 33 A dope composed of 1 part by weight of cellulose acetate, 3.75 parts by weight of dimetllylsulfoxide and 0.25 parts by weight of diethylene glycol was cast on a glass plate in the same way as in Example 1. The membrane formed on the glass plate was dipped in each of the coagulating solutions sho~n in Table 15 at 25C for 20 minutes to coagulate it. The solidified membrane was washed wit~ water, an~ tes-ted for its water flux. The results are shown in Table 14.
T_ble_lL!
~ _ _ , __. _, _ _ .
~xample Coagulating solution Thickness of UFR (ml/m2 (volw~e ratio) the membrane hr-mmHg) (microns) , .___ , _ . . . _ ._ ....... , 28 Methyl alcohol 125 158 29 Ethyl alcohol 118 149 Methyl alcohol:water (1.1) 124 181 31 ~thyl alcohol:water (1 ~1 ) 110 1~9 32 Methyl alcohol:ethyl etl~er (1:1) 105 127 ~thyl alcohol.ethyl _~ __ ether (1:1) 96 118 ~xample 34 The same flat membrane as obtained in ~xample 1 was saponified in a 2% aqueous solution of sodium hydroxicle at 80C for 3 minutes to form a cellulose membrane, then treated wi-t'n glycerol, and driecl. ~he dried memhrane obtained had a water UFR of 31 ml/mZ hr nn~Ig.
~xample 35 An outer support -tube was made out of a non-woven tape, and its inside was coated with the dope preparecl in ~xample 7 using a mandrel. The coated tube was dipped in water to coagulate the coa-ting, followed by washing wi-th water and treating with glycerol to form a tubular dry membrane having a diameter of 6 mm. The tubular dry membrane had a water I~R of 89 ml/m2 hr mml-Tg, and a bovine serum albumin retention of 98,~ It is seen tllat the resulting tubular membrane is useful for the co~centration of high-molechlar-weight material.
A spinning dope prepared from 1 part by weight of cellulose diacetate, 2.5 parts by weigl~t of ~L4~)~13 dimethylsulfoxide and 0.5 part by weigh-t of tert~butyl aicohol was filtered and defoamed. It was then extruded from an outside tube of a double-tube nozzle, and an 80~ aqueous solution of dirnethylsulfoxide was ex-truded from its inner tube. The extrudate was passefl through -the air, and then dipped in cold water -to coagulate it.
The filaments were washed with water ancl treated with glycerol, dried, and taken up at a rate of 10 meters/
min. flollow fibers llaving an outside diameter of 250 microns, an inside diameter of 200 microns and a cross-sectional shape near a true circle were obtained. ~o thousand such hollow fibers were bundled, and both ends of the bundle were embedded in urethane resin partition walls to build an ultrafiltration device. T~le perfor mance of the ultrafiltration device was tested in the following manner.
An ultrafil-tration test was performed at a pressure of 200 mrnE~g while circulating a test aqueous solution through the device at a rate of 200 ml/min.
~he ultrafiltration device showed a UF~ of 1~.1 ml/rn2-hr-l~T-lg, a vitamin B12 retention of 3~, and a bovine ~erum albumin retention of 100%.
For comparison, the spinning dope was prepared in the same way as above except that tert-butyl alcohol was not added. It was dlfficult to filter and defoam the dope because it had a high viscosity.
Example 37 and 38 A solution consisting of 1 part by weight of cellulose diacetate~ 3 parts by weight of dime-thyl sulfoxide and 1 part by weig~t of ethyl alcohol was filterecl and defoamed, and extruded from an outer tube of a double tube nozzle. Sirnultaneously, polyethylene glycol 400 (molecular weight 400) was extruded from its inner tubeO ~le extrudate was passed through the air9 and dipped in water to coagulate it. The extrudate was thereafter treated in the same way as in Example 36 to form hollow fibrous membrane (~xample 37).
1~4()~3 -- ~4 --T~ollow fibers (Æxample 38) were obtained in the same way as in ~xample 36 excep-t that a water metannol mixture (lol) was used instead of cold water as a coagulating solution in the above procedur~, The properties of the membranes are shown in Table 16, ~able 15 __ ~ _ ~ , ~xample Spinning Filament size (microns) I~T~
speed ____________ ______________ 2 (m/min.) Outside Inside~ml/m) hr dia~e ter diameter -_ _ ~ , _ . , 3~15 3~0 260 129 ___A__..... ......__ ~ ~ _ ,xa,,m~2 Three thousand hollow fiber membranes having an available length of 75 cm obtained in ~xample 37 were bundled9 and a hemofilter for artificial kic~eys having a membrane area of 0.35 m2 was built. This hemofilter was small-sized with blood priming volume of only 30 ml. From the superior properties of the membrane used, a wa-ter flux of 40 ml/hr-~mmHg was achieve~.
As a model blood, an aqueous solution contain-ing 0.5~'~ of serum albumin and 0.1j~ of gamma-globulin was used, and a filtration tes-t was performed at a pressure of 200 and 600 mQTI~. ~T\lo leakage of proteins was seen, and the total ~A!ater flux of the dialyzer was 16 and 10 ml/hr-mmT~g. ~is result shows that the perm-selective membrane provided by the present invention can be sufficiently used as a hemofilter (for artificial kidnsys), Tlle safety of the present filter was tested by the methods shown in "~valuation of Membfanes for T~emodialyzers") r~Tational Insti-tute of FIealth, U. S, A.
~JII-I 74-605,and "~valuation of llemodialyzers"9 ibid., NI~ 74-103~ ~le 9tll ~evised ~dition of Japan Pharmacopoeia, ~3L4(~ 3 and Draft. of Japan S-tandards for Ar-tificial l~idneys.
The present hemofilter was found to be acceptable in any of toxic and hemolytic p.roperties, an eluate test?
an acute toxicity test, and a hemolysis test.
6 Qllyl alcohol 0.25 62 143 1~8 9868 Com~arative ~xamples 17 to ~0 . .
Dopes were prepared from 1 part by weight of cellulose diacetate 9 3 parts by weight of dimethyl-sulfoxide, and 1 part by weight of phenol or clihydric alcohols other -than those specified in this invention.
Membranes were formed from the dopes in the same way as in ~xam~le 1, and their water fluxes were measured. ~he resul-~s are shown below.
- 2~ -Table 7 ~ . . ____ ~xample Alcohol UFR (ml/m2-hr mm~1g) __ ~ . ..
17 Methyl aloohol 64 1~. Cyolohexyl alcohol 23 19 Benzyl alcohol less than 0.1 Phenol 25 _~, _ Dopes were prepared from 1 part by weight of cellulose diacetate and 4 parts by weigh-t of a mixture of dimet!~ylsulfoxi~e and each o~ the dihydric alcohols show~ i~ Table ~ in the amo~mts indicated. Membranes were forlned ~rom the dopes, and their properties were measured, in the same way as in ~,xample 1. The results are sl~o~ in Table 8. These membranes had a high strength and were easy to handle.
The membrane of ~xample 14 had a wet tensile strength of 0.74 kg/mm2 and an elongation of 43~. In contrast, the membrane of Comparative ~xample 1 had a wet strength of 0.51 kg/mm2 and a break elongation of 36SS.
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~ 3 A dope was prepared from 1 part by weight of cellulose diacetate, 3.5 parts by weight of dimethyl-sulfoxide and 0.5 part by weight of butanediol-1,3 ~Comparative ~xample 21) or polyethylene glycol 1000 (Comparative ~xample 22), and a membrane was produced from the dope and tested in the same way as in Example 1.
The membrane of Comparative ~xample 21 had a water ~lux of 53 ml/m2~hr-m~L~Tg, and the membrane of Comparative Example 22 had a water permeability of 92 ml/m2-hr mmllg.
_xamples 16 to_l8 and Com~ara-tive ~xamples 23 to 25 A dope was prepared from 1 part by weight of cellulose diacetate ànd 4 parts by weight of a mixture of dime-thylsulfoxide and each of the carboxylic acids shown in Table 9 in the amoun-ts indicated. A membrane was produced from the dope and tested in the same way as in Example 1. The results are shown in Table 9. It is seen from the results obtained that membranes obtained by using formic acid or acetic acid as the water-soluble organic compound showed excellent resul-ts, whereas the use of propionic acid and n-butyric acid led to drastical-ly reduced water fluxes.
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_ 19 and Comparative Fxalnple 26 A dope was prepared from 1 part by weight of cellulose diacetate, 2.2 parts by weight of dimethyl-sulfoxide and 0.8 part by weight of tert-butyl alcohol, and a membrane was produced from the dope in the same way as in ~xample 1 (~xample 19). .or comparison, a membrane was produced from a dope composed of 1 part by weight of cellulose diacetate and 3 parts by weight of dimethylsulfoxide (Comparative ~xamples 26). The properties o~ these membranes are shown in Table 10.
Tab . _ , _ . ~ _ . __ .
Thickness UFR ~ovine serum albumin Porosity membrane (ml/m2 hr- Water ~lux Retention (%~
(microns) (ml/m2-hr- (~) __. . . . ._ ._ .... .. .
~xample 19 ~ 35 31 99 6 . ~ . __ ~ ., - _ _ . . __ .
Compara-tive 62 29 26 99 65 Example __________ _ _ ~ - ~ _ Fxamples 20 and ~ a-tive ~xample 27 Dopes were prepared from 1 part by weight of cellulose diacetate and 6 parts by weight o~ a mixture of dimetl1ylsulfoxide and each of the alcohols sho~m in Table 11 in the amounts indicated. Membranes were prepared from the dopes and tested in t'ne same way as in ~xample 1. The results are sho~n in Table 11. It is seen from the results that the membranes of t~is inven-tion showed superior performances. In particular, the membrane obtained by using diethylene glycol as one component o~ t~le mixed solvent had about twice as high UFR as the membrane obtained by using dimethylsulfoxide alone as a solvent (Comparative ~ample 27~, and moreover, its mechanical strength was improved.
.
7~3 The membrane of ~xample 21 had a wet strength of 0.33 kg/mm2 and a break elongation of 24~. The membrane of Comparative I~`xample 27 had a wet strength of 0.29 kg/mm2 and a break elongation of 16S~.
Table 11 ~ . _ , . , . . _ ,.
~xample Alcohol Thickness UFR 2 Bovine serum Poro-(Ex ) or _ ~... ., ~ of t:~le (ml/m albumin sity tompara- Type ~myrtts (microns) mrn.~lg) Water Reten-(C~`x.) weight) (m21/r. (%) m~Yg) . ., _ . . ~ _ __ . .
Ex. 20 Eth~rl 1. 5 51 ?63 771 96 69 alco'lol ~x. 21 lene~,ly_ 0.4 ~0 426 413 97 90 glycol CE~. 27 None 0 60 253 249 97 74 . ~ _ . ......... __ . . . .~ _ ,.. _ xsmples 22 to 24 and Com~arative ~xamples 2~ to ~0 Dopes were prepared from 1 part by weight of cellulose diacetate and the amounts shown in Table 12 of dimethylsulfoxide and diethylene glycol.
~ach of the dopes was cast on the surface of a porous polyest.er filament material (non-woven fabric; basis weight 1~5 g/m2) by a doctor knife to a thickness o~
200 microns, and dipped in cold water for 15 minutes to coagulate it. The properties of the resulting membranes were measured in the same way as in ~xample 1. Tlle results are shown in Table 12. The thicknesses and porosities of the membranes could not be measured because tlQe membrane and the nonwoven material were united with each otherO
Table 12 ._ . _ _ . . . _ ~
Example Mixed solvent U~R Bovine serum albumin (Ex,~ or (p~rts by weight) (~1/ 2-h _ __ Compara- ~ ~ ~- tTm~ r- Water flux Retention tive Dimethyl Diethy- "Imlg~ (ml/m2~hr~ (%) (C~x.) sul~oxide glyceol mm~lg) _ . _ .. . ._ . _ __ ~ , _ .
Ex. 22 9 1 765 743 97 Ex. 23 13.5 1.5 1102 1090 95 Ex. 24 18 2 1~57 1360 81 CEx. 28 10 0 451 447 97 CEx. 29 15 0 896 871 93 C~x. 30 20 0 1290 1250 82 .~ ,~____ ., _ __ . _ __ ~xamples 25 and ~ F.x~nple 31 Dopes were prepared from 1 par-t by weight of cellulose -triacetate (CI'A-432, a product of Eastman Kodak Co.) and 6 parts o~ a mix-ture of dimethylsulfoxide and tertbutyl alcohol in t'ne amounts shown in Table 13.
Membranes were produced from the dopes and tested in the same way as in xample 1. It is seen from Table 13 that the membranes obtained by using tert-butyl alcohol as one component of the mixecl solvent had superior wa-ter fluxes~ and tert-butyl alcohol as one component of the mixed solvent aided in the dissolving of cellulose triacetate and could give a membrane having high uniformity.
'1'~`~
~xam le Amount of Thick- _ ~ Bovine serum albv- Poro-~~Fx.~ or tert-butyl ness of (~l/m2~ min sity Compara- alcohol the hr~ ___________ ,---____ tive (parts by mem- mmTIg) Water flux Reten~ (%) ~xample wei~nt) brane (ml/m2-hr. tion (CEx.) (omnsC) mmllg) _ ~ ___ ~ _~
~x. 2~ 0~4 126 ~31 316 98 88 Fx. 26 0.7 139 41X 398 98 89 C~. 31 _ 56 9~ 97 99 73 . . ___ __ __ ~ _ ~L~4~37~3 A dope was prepared from 0.5 part by weight of cellulose diacetate, 0.5 part by weight of cellulose triacetate, 4.5 parts by weight of dimethylsulfoxide and 1.5 parts by weight of ethyl alcohol. A membrane was preparecl ~rom the dope and tested in the same way as in ~xample 1.
For comparison, a dope was prepared in the same way as above except that 6 parts by weight of only dimethylsulfoxide was added as the solvent (Comparative ~xample 32). Tlle results are shown in Table 14.
Table 14 _ __ _ . , . ._ Tllickness f UF1~2 Porosity (~) the membrane (ml/m hr mmHg) (microns) .,. ~ . .. _._ ~xample Compara-tive 58 125 73 3m2Ple . . _ _ xamples 28 to 33 A dope composed of 1 part by weight of cellulose acetate, 3.75 parts by weight of dimetllylsulfoxide and 0.25 parts by weight of diethylene glycol was cast on a glass plate in the same way as in Example 1. The membrane formed on the glass plate was dipped in each of the coagulating solutions sho~n in Table 15 at 25C for 20 minutes to coagulate it. The solidified membrane was washed wit~ water, an~ tes-ted for its water flux. The results are shown in Table 14.
T_ble_lL!
~ _ _ , __. _, _ _ .
~xample Coagulating solution Thickness of UFR (ml/m2 (volw~e ratio) the membrane hr-mmHg) (microns) , .___ , _ . . . _ ._ ....... , 28 Methyl alcohol 125 158 29 Ethyl alcohol 118 149 Methyl alcohol:water (1.1) 124 181 31 ~thyl alcohol:water (1 ~1 ) 110 1~9 32 Methyl alcohol:ethyl etl~er (1:1) 105 127 ~thyl alcohol.ethyl _~ __ ether (1:1) 96 118 ~xample 34 The same flat membrane as obtained in ~xample 1 was saponified in a 2% aqueous solution of sodium hydroxicle at 80C for 3 minutes to form a cellulose membrane, then treated wi-t'n glycerol, and driecl. ~he dried memhrane obtained had a water UFR of 31 ml/mZ hr nn~Ig.
~xample 35 An outer support -tube was made out of a non-woven tape, and its inside was coated with the dope preparecl in ~xample 7 using a mandrel. The coated tube was dipped in water to coagulate the coa-ting, followed by washing wi-th water and treating with glycerol to form a tubular dry membrane having a diameter of 6 mm. The tubular dry membrane had a water I~R of 89 ml/m2 hr mml-Tg, and a bovine serum albumin retention of 98,~ It is seen tllat the resulting tubular membrane is useful for the co~centration of high-molechlar-weight material.
A spinning dope prepared from 1 part by weight of cellulose diacetate, 2.5 parts by weigl~t of ~L4~)~13 dimethylsulfoxide and 0.5 part by weigh-t of tert~butyl aicohol was filtered and defoamed. It was then extruded from an outside tube of a double-tube nozzle, and an 80~ aqueous solution of dirnethylsulfoxide was ex-truded from its inner tube. The extrudate was passefl through -the air, and then dipped in cold water -to coagulate it.
The filaments were washed with water ancl treated with glycerol, dried, and taken up at a rate of 10 meters/
min. flollow fibers llaving an outside diameter of 250 microns, an inside diameter of 200 microns and a cross-sectional shape near a true circle were obtained. ~o thousand such hollow fibers were bundled, and both ends of the bundle were embedded in urethane resin partition walls to build an ultrafiltration device. T~le perfor mance of the ultrafiltration device was tested in the following manner.
An ultrafil-tration test was performed at a pressure of 200 mrnE~g while circulating a test aqueous solution through the device at a rate of 200 ml/min.
~he ultrafiltration device showed a UF~ of 1~.1 ml/rn2-hr-l~T-lg, a vitamin B12 retention of 3~, and a bovine ~erum albumin retention of 100%.
For comparison, the spinning dope was prepared in the same way as above except that tert-butyl alcohol was not added. It was dlfficult to filter and defoam the dope because it had a high viscosity.
Example 37 and 38 A solution consisting of 1 part by weight of cellulose diacetate~ 3 parts by weight of dime-thyl sulfoxide and 1 part by weig~t of ethyl alcohol was filterecl and defoamed, and extruded from an outer tube of a double tube nozzle. Sirnultaneously, polyethylene glycol 400 (molecular weight 400) was extruded from its inner tubeO ~le extrudate was passed through the air9 and dipped in water to coagulate it. The extrudate was thereafter treated in the same way as in Example 36 to form hollow fibrous membrane (~xample 37).
1~4()~3 -- ~4 --T~ollow fibers (Æxample 38) were obtained in the same way as in ~xample 36 excep-t that a water metannol mixture (lol) was used instead of cold water as a coagulating solution in the above procedur~, The properties of the membranes are shown in Table 16, ~able 15 __ ~ _ ~ , ~xample Spinning Filament size (microns) I~T~
speed ____________ ______________ 2 (m/min.) Outside Inside~ml/m) hr dia~e ter diameter -_ _ ~ , _ . , 3~15 3~0 260 129 ___A__..... ......__ ~ ~ _ ,xa,,m~2 Three thousand hollow fiber membranes having an available length of 75 cm obtained in ~xample 37 were bundled9 and a hemofilter for artificial kic~eys having a membrane area of 0.35 m2 was built. This hemofilter was small-sized with blood priming volume of only 30 ml. From the superior properties of the membrane used, a wa-ter flux of 40 ml/hr-~mmHg was achieve~.
As a model blood, an aqueous solution contain-ing 0.5~'~ of serum albumin and 0.1j~ of gamma-globulin was used, and a filtration tes-t was performed at a pressure of 200 and 600 mQTI~. ~T\lo leakage of proteins was seen, and the total ~A!ater flux of the dialyzer was 16 and 10 ml/hr-mmT~g. ~is result shows that the perm-selective membrane provided by the present invention can be sufficiently used as a hemofilter (for artificial kidnsys), Tlle safety of the present filter was tested by the methods shown in "~valuation of Membfanes for T~emodialyzers") r~Tational Insti-tute of FIealth, U. S, A.
~JII-I 74-605,and "~valuation of llemodialyzers"9 ibid., NI~ 74-103~ ~le 9tll ~evised ~dition of Japan Pharmacopoeia, ~3L4(~ 3 and Draft. of Japan S-tandards for Ar-tificial l~idneys.
The present hemofilter was found to be acceptable in any of toxic and hemolytic p.roperties, an eluate test?
an acute toxicity test, and a hemolysis test.
Claims (15)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for producing a cellulose acetate-type permselective membrane having very high water-permeability and protein retention, which comprises casting a dope comprising: (a) 1 part by weight of cellulose acetate, and (b) 2 to 20 parts by weight of a mixed solvent composed of (i) dimethylsul-foxide and (ii) at least one water-soluble organic compound selected from the group consisting of monohydric alcohols having 2 to 5 carbon atoms, dihydric alcohols of the formula H wherein R is an alkylene group having 2 or 3 carbon atoms and n is an integer of 1 to 16, and carboxylic acids having 1 or 2 carbon atoms, the weight ratio of said water-soluble organic compound to dimethylsulfoxide being not more than 1; and solidifying the resulting raw mem-brane with a coagulating solution which comprises a non-solvent for the cellu-lose acetate.
2. The process of claim 1 wherein said monohydric alcohol is selected from the group consisting of ethyl alcohol, propyl alcohol, butyl alcohol and allyl alcohol.
3. The process of claim 1 wherein said dihydric alcohol is selected from the group consisting of ethylene glycol, diethylene glycol, polyethylene glycol having an average molecular weight of 400 and propylene glycol.
4. The process of claim 1 wherein said water-soluble organic compound is selected from the group consisting of ethyl alcohol and tert-butyl alcohol.
5. The process of claim 1 wherein said dope consists of 1 part by weight of (a) cellulose acetate and 2.3 to 8 parts by weight of (b) mixed solvent.
6. The process of claim 1 wherein said cellulose acetate is selected from the group consisting of cellulose diacetate, cellulose triacetate and a mixture thereof.
7. The process of claim 6 wherein the major portion of said cellulose acetate is cellulose diacetate.
8. The process of claim 1 wherein the weight ratio of said water-soluble organic compound to dimethylsulfoxide in said mixed solvent is from 0.05 to 0.7.
9. The process of claim 1 wherein said coagulating agent comprises a non-solvent for the cellulose acetate.
10. The process of claim 9 wherein said nonsolvent is at least one member of the group consisting of water, alcohols and ethers.
11. The process of claim 1 wherein said membrane is in the form of a film, tube, capillary or hollow filament.
12. A cellulose acetate-type permselective membrane having very high water-permeability and protein retention, which membrane is obtained by casting a dope comprising: (a) 1 part by weight of cellulose acetate, and (b) 2 to 20 parts by weight of a mixed solvent composed of (i) dimethylsulfoxide and (ii) at least one water-soluble organic compound selected from the group con-sisting of monohydric alcohols having 2 to 5 carbon atoms, dihydric alcohols of the formula H wherein R is an alkylene group having 2 or 3 carbon atoms and n is an integer of 1 to 16, and carboxylic acids having 1 or 2 carbon atoms, the weight ratio of said water-soluble organic compound to dimethylsulfoxide being not more than 1; and solidifying the resulting raw membrane with a coagulating solution which comprises a nonsolvent for the cellulose acetate.
13. The membrane of claim 12 which has (A) a porosity of 40 to 95%, (B) a water-permeability of 5 to 2000 ml/m .hr.mmHg, and (C) a protein reten-tion of 80 to 100%.
14. The membrane of claim 12 which has (A) a porosity of 60 to 90%, (B) a water-permeability of 10 to 1000 ml/m2.hr.mmHg, and (C) a protein reten-tion of 90 to 100%.
15. A hemofilter for artificial kidneys which includes a membrane as claimed in claim 12, 13 or 14.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000342455A CA1140713A (en) | 1979-12-21 | 1979-12-21 | Process for producing a cellulose acetate- type permselective membrane having very high water permeability and protein retention |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000342455A CA1140713A (en) | 1979-12-21 | 1979-12-21 | Process for producing a cellulose acetate- type permselective membrane having very high water permeability and protein retention |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1140713A true CA1140713A (en) | 1983-02-08 |
Family
ID=4115879
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000342455A Expired CA1140713A (en) | 1979-12-21 | 1979-12-21 | Process for producing a cellulose acetate- type permselective membrane having very high water permeability and protein retention |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1140713A (en) |
-
1979
- 1979-12-21 CA CA000342455A patent/CA1140713A/en not_active Expired
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