Studies on syntheses and permeabilities of special polymer membranes: 41. Finger-like cavities in cellulose nitrate membranes from binary organic solvents

The formation of finger-like cavities in asymmetric cellulose nitrate membranes was investigated by changing the composition of binary mixed casting solvent and the evaporation period during the membrane formation process. The nature of the casting mixture, during the solvent evaporation process, was of coacervated droplets with absorbed water molecules from the atmosphere. Changes in the concentration of cellulose nitrate and the dissolution state of the cellulose nitrate molecules in the evaporation loss of the casting solvent, were clearly related to the formation of the finger-like cavity in the back sponge layer in asymmetric cellulose nitrate membranes.     

Studies on syntheses and permeabilities of special polymer membranes. 40. Formation conditions of finger-like cavities of cellulose nitrate membranes

The permeation characteristics for polymer aqueous solution and asymmetric structure of cellulose nitrate membranes, in particular the finger-like cavity in the back sponge layer of these membranes, were investigated by changing the preparation conditions of the membranes— the casting solvent, evaporation period, and gelation medium. The formation of the finger-like cavity was dependent on absorption of a water molecule into the casting mixture from the atmosphere during the solvent evaporation process and the exchange velocity between the casting solvent and the gelation medium. The mechanism and conditions for the formation of a finger-like cavity in cellulose nitrate membranes were discussed.     

Studies on syntheses and permeabilities of special polymer membranes. VI. Permeation characteristics of cellulose nitrate membranes and cellulose membranes

The permeation characteristics of cellulose nitrate membranes and cellulose membranes were investigated using aqueous solutions of poly(ethylene glycol) as feed. To gain cellulose membranes the nitro groups in cellulose nitrate were converted to hydroxyl groups. It was found that cellulose nitrate membranes separate poly(ethylene glycol) 6000 but not any cellulose membrane did separate poly(ethylene glycol) 20 000.     

Studies on syntheses and permeabilities of special polymer membranes: 33. Permeation behaviour of aqueous alcohol solution through cellulose membranes

The permeabilities of various aqueous alcohol solutions through cellulose membranes were investigated by changing the preparation conditions of membranes, the feed concentration, and the feed solute, etc. The permeation rates for aqueous solutions of alcohols, glycols, glycerol, trihydroxyl benzene were greater than for pure water. This permeation phenomenon could be explained by some permeation models considering water cluster, activation of water molecules (second bound water-like) attached weakly to the bound water in cellulose membrane, and the surface of cellulose membrane, and plasticization of cellulose molecules.     

Studies on syntheses and permeabilities of special polymer membranes. IV. Permeation characteristics of improved cellulose nitrate membranes

For the purpose of the application of cellulose nitrate membranes for artificial kidneys, the permeation characteristics and the bursting strength of three types of membranes, which were prepared from a system of cellulose nitrate/methyl alcohol/1,4-dioxane/barium perchlorate (CN-1), from a system of cellulose nitrate/methyl alcohol/formamide (CN-2), and a poly(ethylene terephthalate) cloth coated with the casting solution of CN-2 (CN-3), were investigated under various conditions. It was found that permeabilities of these membranes were influenced significantly by the preparation methods of the membranes and the permeation conditions, and they depended upon the structure of the resulting membranes and the interaction between the polymer in the membrane and the feed. In blood filtrations, the permeation rates of our three types of membranes had about four-fold values than a cuprophane membrane, and moreover no protein was found in the blood filtrate. The bursting strength of the membranes swollen with water was in the order CN-3 > cuprophane > CN-2 > CN-1, and this ratio was calculated to be about 5.9:1.0:0.5:0.3     

Studies on syntheses and permeabilities of special polymer membranes. 22. Ultrafiltration characteristics and membrane structure of cellulose nitrate membranes

The formation mechanism of anisotropic polymer membranes formed by a system of cellulose nitrate (CN)/n-propyl alcohol (n-PrOH)/N,N-dimethyl formamide (DMF) was investigated. The ultrafiltration characteristics and the membrane structure were influenced significantly by the casting solvents (ratio of n-PrOH to DMF) and the evaporation period during the membrane formation process. The finger-like structure in the sponge layer was observed in all systems except that of n-PrOH/DMF = 2/1 and increased with the evaporation period, after 2 min in the system of pure DMF and after 5 min in the system of n-PrOH/DMF = 1/3. The formation mechanism of the anisotropic CN membranes and the ultrafiltration characteristics were discussed in detail.     

Studies on syntheses and permeabilities of special polymer membranes, 32. New preparation method of cellulose membranes

The preparation of cellulose membranes from mixtures of cellulose, nonprotonic polar organic solvents, paraformaldehyde, and basic catalyst was studied. When dimethyl sulfoxide was used as casting solvent, the resulting membrane was the densest. An increase of an additional amount of triethyl amine used as basic catalyst gave denser membranes.     

Studies on syntheses and permeabilities of special polymer membranes.: 15. Permeation characteristics of nylon-12 cellulose acetate blends

The permeation characteristics of nylon-12-cellulose acetate polymer blend membranes in the separation of polymers, poly(vinyl alcohols), from their aqueous solutions were investigated under various conditions. The permeation characteristics were influenced markedly by the ratio of nylon-12-cellulose acetate, the feed concentration, the operating pressure and temperature. It was found that the changes of polymer ratio and the concentration of blended polymer were related to the change of microporous structure of the resulting membranes. When the cellulose acetate content was higher a significant compaction of the membrane occurred under pressure. It was found that there was a concentration polarization of poly(vinyl alcohol) molecules on the membrane surface, whose thickness increased with increase in molecular weight of poly(vinyl alcohol) and in feed concentration. The bursting strength of the polymer blend membranes swollen with water increased considerably as the cellulose acetate content in the blended polymer increased.     

Studies on syntheses and permeabilities of special polymer membranes: 30. Ultrafiltration and dialysis characteristics of cellulose nitrate-poly(vinyl pyrrolidone) polymer blend membranes

The ultrafiltration and dialysis characteristics of the semipermeable polymer blend membranes obtained from cellulose nitrate, poly(vinyl pyrrolidone), and N,N-dimethyl formamide were investigated under various conditions. The water content fraction and the ultrafiltration rate were dependent on the poly(vinyl pyrrolidone) content in the membranes, and the strengths were governed by the cellulose nitrate content in the polymer blend. If the pore radius in the membranes, calculated according to the Hagen-Poiseuilli equation for capillary model, was identical, the water content in each membrane was not identical. It was found that urea molecules broke very weak hydrogen bonds of the bound water in the membrane, but sodium chloride did not, also, the diffusion of urea through the membrane was more rapid than that of sodium chloride. The ratio of the membrane diffusion coefficient to the ultrafiltration rate was explained qualitatively by the capillary model, however, when the bound water in the water content fraction was considered, this ratio showed better agreement with the model.     

Studies on syntheses and permeabilities of special polymer membranes. XIV. Permeation characteristics of modified nylon 12 membranes

The permeation characteristics and the burst strength of nylon 12 membranes treated with heat in various solutions such as aqueous solutions of formic acid, formic acid/formalin, and sodium hydroxide/ formalin were investigated under various conditions. They were significantly influenced by the treatment solution, temperature and time, and the concentration of acid and alkali in the treatment solution. In particular, nylon 12 membranes treated with formic acid/formalin remarkably improved the permeation characteristics and the burst strength. These phenomena were discussed from the standpoint of the effective pore size and pore number in the membrane, and the form and aggregation of polymer molecules forming the membrane.     

Studies on syntheses and permeabilities of special polymer membranes. V. Effect of casting solution composition on permeation characteristics of cellulose acetate membranes in separation of aqueous polymer solutions

The permeation characteristics of cellulose acetate membranes in separation of polymers from their aqueous solutions were investigated by changing the preparation conditions of the membranes, that are the solvent evaporation period and the casting solution composition consisting of a mixture of cellulose acetate (CA), acetone (A), and formamide (FA). The rates of pure water permeability were influenced remarkably by the solvent evaporation period and the casting solution composition. When the solvent evaporation period was short, the rates of pure water permeability increased with a decrease in A/CA, increase in FA/A, and increase in FA/CA in the casting solution. From the experimental results using poly(vinyl alcohol) as poly(ethylene glycol) as feed solute, it was seen that the changes of solvent evaporation period and casting solution composition related to the change of microporous structure of the resulting membranes. The effect of feed concentration and operating pressure on the permeation characteristics were also studied. There was found a concentration polarization of poly(vinyl alcohol) molecules on the surface of the membrane, and a compaction of the membrane occurred under pressure.     

Studies on syntheses and permeabilities of special polymer membranes: 24. Permeation characteristics of poly(vinylidene fluoride) membranes

The permeation characteristics of poly(vinylidene fluoride) membranes were investigated by changing the preparation conditions of the membranes, the composition of the casting solution, membrane thickness, time of heat treatment and temperature, etc.; and by changing the permeation conditions, operating temperature, the feed concentration, and the feed solute, etc. Aqueous solutions of poly(vinyl alcohol) and poly(ethylene glycol) were used as feed. The permeation characteristics were influenced significantly by the change of the above conditions and were dependent on the structure of resulting membrane, the viscosity of feed, the form of polymer molecules in aqueous solution, and the concentration polarization of polymer solute molecules onto the membrane surface. The permeation through very swollen membranes (ca. 85% in water content) followed the viscous flow.     

Studies on syntheses and permeabilities of special polymer membranes. X. Effects of conditions of membrane preparation on permeation characteristics of cellulose acetate membranes in separation of aqueous polymer solutions

The effects of casting solvents, dissolution temperature of casting solution, and pH and temperature of gelation solution, etc. on the permeation characteristics of cellulose acetate membranes in the separation of polymers from their aqueous solutions were investigated, using aqueous solutions of poly(ethylene glycol) and poly(vinyl alcohol) as feed. The permeation characteristics were influenced significantly by the conditions of membrane preparation and of the permeation. It was found that a concentration polarization at the membrane surface occurred with poly(vinyl alcohol) molecules, but it was very small with poly(ethylene glycol). The above results were discussed in detail from points of view of structure of the resulting membranes and the interactions between the solvent, the solute in the feed and the cellulose acetate molecules.     

Studies on syntheses and permeabilities of special polymer membranes. 37. Permeabilities of poly(γ-methyl L-glutamate) membranes

The permeation characteristics of poly(γ-methyl L-glutamate) (PMLG) membranes in the separation of polymers, poly(ethylene glycol) and poly(vinyl alcohol), from their aqueous solutions were influenced by the compaction of membrane swollen with water under pressure. The rate of pure water permeability up to an operating temperature of 70°C was governed by a change in the secondary-structure of PMLG. In addition, the permeabilities of alcohols through PMLG membrane were discussed.     

Studies on syntheses and permeabilities of special polymer membranes. XVI. Permeation and separation characteristics of aqueous polymer solutions for acrylonitrile-styrene copolymer membranes

The permeation and separation characteristics of aqueous polymer solutions using acrylonitrile-styrene copolymer membranes were investigated under various conditions. The membranes obtained from dimethyl sulfoxide solution of acrylonitrile-styrene copolymer have not a sufficient reproducibility and stability of permeation. These lacks were improved by adding ethylene glycol or glycerol to the casting solution and treating the membranes with pressure. The permeation and separation characteristics were influenced significantly by the additional amount of above additives, the heat treatment temperature, and the operating pressure. It was found that the concentration polarization of poly(vinyl alcohol) molecules onto the surface of the acrylonitrile-styrene copolymer membranes is smaller than that onto hydrophilic polymer membranes such as membranes of cellulose acetate, cellulose nitrate, and nylon 12, etc. Moreover, the acrylonitrile-styrene copolymer membranes show better performance for separation and concentrating of aqueous polymer solutions than hydrophilic membranes.     

Studies on syntheses and permeabilities of special polymer membranes: 50. Transport of metal ions against their concentration gradient through water-insoluble poly(styrene sulphonic acid) membrane

Water-insoluble cation exchange membranes were prepared by heat treating membranes made of poly(styrene sulphonic acid) and poly(vinyl alcohol). Transport of metal ions through the above cation exchange membrane against their concentration gradient was investigated under various conditions. The transport in this system, where one side of the membrane in a diaphragm cell was acidic and the other alkaline, was influenced significantly by the initial H⁺ ion concentration on the acidic side. The selectivity of metal ions in diffusive transport depended on the size of their hydrated ions and that in transport against their concentration gradient was due to the affinity between the metal ions and the carrier fixed to the membrane.     

Studies on syntheses and permeabilities of special polymer membranes. 25. Effects of membrane preparation method on structure and permeation characteristics of poly(vinylidene fluoride) membranes

The permeation characteristics and the formation mechanisms of poly(vinylidene fluoride) (PVF₂) membranes were investigated by changing the casting solvent and the exposure period in the preparation conditions of the membranes. Changes of the microporous structure of the resulting membranes with the exposure period are dependent on differences in forming coacervated droplets based on phase separation. Changes of the permeation characteristics and the formation of coacervation by changing the combination of the mixed solvents are related to differences of the form of PVF₂ molecules in the casting solution, to differences of the formation of surface layer with the evaporation of a low and a high boiling point solvent, and to differences of the hygroscopicity of the high boiling point solvent.     

Studies on syntheses and permeabilities of special polymer membranes. 62. Active transport of alkali metal ions through poly(vinyl alcohol) membranes crosslinked with glutaraldehyde

The transport of alkali metal ion through poly(vinyl alcohol) crosslinked with glutaraldehyde without dissociating groups in a diaphragm cell, at one side being an alkaline and at the other an acidic solution, was investigated under various conditions. The active transport fraction of alkali metal ions from the alkaline side to the acidic side was significantly influenced by the degree of crosslinking of the membrane, size of anion species, initial pH on the acidic side, and the electric potential difference across the membrane.     

Studies on syntheses and permeabilities of special polymer membranes, 36. Permeabilities of alcohols through poly(γ-alkyl l-glutamate) membranes

To reveal the permeation mechanism of liquids through polypeptide membranes, the permeation of n-alcohols through poly(γ-alkyl L-glutamate) membranes such as the polymers of methyl, ethyl, and benzyl glutamates was investigated by changing the operating temperature. It was found that there was a significant interaction between the ester groups of the side chain of poly(γ-alkyl L-glutamate) and the alcohol molecule. This interaction affected significantly the permeation rates of alcohols and the separation characteristics of alcohol mixtures.