Takashi Iwatsubo

PERVAPORATION OF ETHANOL/WATER THROUGH A POLY (VINYL ALCOHOL)/CYCLODEXTRIN(PVA/CD) MEMBRANE

Abstract A poly(vinyl alcohol)/cyclodextrin (PVA/CD) membrane was utilized in the pervaporation of ethanol/water mixtures. The membrane was prepared by casting an aqueous solution of PVA and β-cyclodextrin oligomer. The CD oligomer was successfully immobilized in the membrane by the crosslinking of PVA with glutaraldehyde for 1 h. The content of CD was up to 33%. The effect of CD on the pervaporation performances of water/ethanol was investigated by measurements of the sorption equilibrium and the calculations of the diffusion coefficient of the permeants in the membrane. The addition of CD increased the water selectivity of the pervaporation of water/ethanol, especially at lower (

Development of polyion complex membranes based on cellulose acetate modified by oxygen plasma treatment for pervaporation

Abstract Cellulose acetate (CA) membrane was modified with ultra-thin polyion complex (PIC) layers, and the pervaporation performance for water–ethanol mixture was investigated. Introduction of oxygen-containing anionic groups onto the surface of the CA membrane was attempted by the oxygen plasma treatment, and was confirmed by the electron spectroscopy for chemical analysis (ESCA). The formation of an ultra-thin PIC layer on the membrane surface by dipping of the plasma-treated membrane into an aqueous solution of polyallylamine (PALA) as the polycation was confirmed by the measurement of the attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectra of the membrane. The results of the pervaporation of water–ethanol mixture showed that the PIC layer increased the selectivity of the CA membrane. The considerable increase in the selectivity was not accompanied by any large decrease in the water flux. Furthermore, it was observed that the applied energy for plasma treatment strongly affected the permeate flux and the selectivity of the CA/PIC membrane. Further improvement in the selectivity of the membrane was attained by the formation of multilayer PIC using polyacrylic acid (PAA) as the polyanion.

Pervaporation membranes for ethanol-water mixture prepared by plasma polymerization of fluorocarbons. II. Perfluoropropane membranes☆

Abstract Pervaporation membranes for ethanol-water binary mixtures were prepared by plasma polymerization of perfluoropropane (PFP). The plasma-polymerized thin films were deposited onto porous polysulfone (PS) filters as substrates with an average pore size from 0.1 to 0.45 μm. By adding argon carrier to PFP system, fluorine/carbon elemental ratios (F/C) of the produced membranes evaluated by X-ray photoelectron spectroscopy (XPS), showed a maximum value, then slightly decreased at higher partial pressure of Ar. This tendency was recognized more clearly by comparing the summation of −CF3 and −CF2-peak area percentages based on a whole C18 peak area. As a measure of hydrophobicity, this value is more intelligible than the direct F/C ratio. The influence of substrate pore-size, plasma-treatment time and hydrophobicity of the membranes on the separation capability were studied. The ethanol-separation coefficient, (αEtOH), of PFP membranes increased slightly with decrease of the average pore-size of the substrates, but treatment time did not apparently affect the αEtOH. We classified the prepared membranes into two classes, i.e. the membranes showing higher and lower permeation fluxes than 0.5 kg/m2-hr. The αEtOH was more evidently observed to increase with membrane hydrophobicity for the former class of PFP membranes. We suggest that, at least, three separation schemes might be necessary to understand the correlations found in each group.

Relationship between permselectivity and permeability in pervaporation of water/alcohol mixture

Abstract The evaporation mechanism of a water/alcohol mixture with a polymeric membrane was investigated. Flory-Huggins thermodynamics was adopted to introduce the selective dissolution factor, R . It was shown that the value of R of a water permselective membrane increases as permeability decreases, and that it has no upper limit. For an ethanol permselective membrane, R has a maximum value at a certain value of the swelling ratio. Making some assumptions for R , a semi-quantitative relationship between permselectivity and permeability, J , was derived for a water permselective membrane and examined experimentally. When the swelling ratio is changed, it can be said that selectivity is proportional to J 1− ( 1 s ) depending on s , the molecular volume ratio of water to alcohol.

Formation of Hydroxyapatite Skeletal Materials from Hydrogel Matrices via Artificial Biomineralization.

Several kinds of hydrogels were prepared as mimics for the collagen/acidic protein hydrogel employed as the polymer matrix for mineralization in natural bone formation. The hydrogels prepared as mineralization matrices were employed for synthesizing artificial bones. The artificial bone made from a network of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) prepared by heating (PVA/PAA-h-network) exhibited mechanical properties comparable with those of fish scales. To elucidate the formation mechanism of the artificial bone, we synthesized four further kinds of matrix. Artificial bones were obtained from both a PVA/PAA network prepared by repeated freezing and thawing (PVA/PAA-ft-network) and a chitosan/PAA network, in which hydrogen bonding exists between the two constituent polymers, similar to that observed in a natural collagen/acidic protein network. The artificial bone made from the chitosan/PAA network was confirmed to be formed by the phase transformation of a cartilaginous precursor by a process similar to the transformation of cartilaginous tissue to natural bone. In addition, skeletal phase material, i.e., a homogeneous solid phase of hydroxyapatite/polymers, was formed in the cartilaginous phase, i.e., the hypercomplex gel. The skeletal phase grew thicker at the expense of the cartilaginous phase until it formed the entirety of the composite. Artificial bones were also obtained from a gelatin/PAA network and a poly[N-(2-hydroxyethyl)acrylamide]-co-(acrylic acid) network. These experimental results suggested that the coexistence of proton donor and proton acceptor functions in the hydrogel is a key factor for bone formation. The hydroxyapatite content of our artificial bones was almost conterminous with those of natural bones.

Preparation of a cyclophane-bonded stationary phase and its application to separation of naphthalene derivatives

A cyclophane (CP44)-bonded silica gel stationary phase was prepared and elution behaviour of hydrophobic solutes was investigated in the reversed-phase mode. Aromatic compounds were retained on the stationary phases more strongly than the corresponding alicyclic compounds, as was expected by the complex-forming ability of the cyclophane. The stationary phases also showed isomer-selective separation for monomethyl- and dimethylnaphthalenes. The isomers having methyl groups at the α-position were eluted prior to those having methyl groups at the β-position, i.e., the retention order for methylnaphthalene was, α<β and that for dimethylnaphthalene, α,α<α,β<β,β. Moreover, some dimethylnaphthalene isomers which cannot be separated on ordinary reversed-phase stationary phases were separated finely on this stationary phase. The separation mechanism is discussed on the basis of the structure of the cyclophane-involved complex.

MEASUREMENT OF LIQUID COMPOSITION CHANGE INSIDE POLYMER GELS SHRINKING IN LIQUID MIXTURE

Polymer gels begin to shrink after being transferred from good solvent to mixed solvent that contains poor solvent for the polymer. The shrinking rate becomes so slow that no volume change of the gel can be observed if the concentration of poor solvent is high [1]. At this stage, several spatial patterns are periodically generated within the gel. This phenomenon has been attributed to spinodal decomposition of the gel system. At the early stage of decomposition, the concentration fluctuation of polymer chains begins to increase. Polymer-rich domains and solvent-rich domains grow inside the gel until the macromolecular motion of polymer chains in dense domains (polymer-rich domains) is almost frozen because the glass transition temperature of polymer exceeds the experimental temperature. The volume change of a gel in a single solvent is well described by the cooperative diffusion of polymer network in the solvent [2]. For the gel in a binary mixed solvent, another diffusion should be taken into account: the diffusion of solvent. Moreover, these two diffusions affect each other; generally, there are cross terms in diffusion equations [3]. Thus, a diffusion equation contains several parameters that depend on not only the concentration of each solvent, but also the anisotropic elongation of polymer chains. Therefore, the volume change

Simple thermodynamics of macroscopic phase separation in shrinking gels

The shrinking process induced in spherical gels by an abrupt change in temperature has been investigated qualitatively. The phase diagram of the gel system has been found to be helpful in classifying a variety of shrinking processes. When the solvent quality is lowered within the region between the volume transition and coexistence temperatures, the local swelling ratio of the inner portion, which is divided by a moving interface from the outer shrunk phase, declines in the course of the shrinking process. On the contrary, the local swelling ratio of the inner portion of the shrinking gel is enlarged when the solvent quality is lowered into the region between the coexistence and spinodal temperatures. In this latter case, owing to large local swelling of the inner portion in the vicinity of the interface, spherical symmetry will imply mechanical instability. This instability will be the origin of transient spatial patterns on the surfaces of shrinking gels.