Zbynek Pientka

Gas permeabilities of polymers with indan groups in the main chain.: 2: Polyimides

Abstract Permeability coefficients and ideal selectivities for H2, CO2, O2, and N2 were determined for two series of polyimides with indan groups in the main chain. The bulkiness of the indan group was varied by replacing methyl groups at the indan ring system by bulky cyclohexyl groups. The effects of the linking group in the dianhydride part of the polymer repeating unit could be explained on the basis of bulkiness and flexibility. However, the introduction of two cyclohexyl substituents at the indan group to increase the bulkiness of this structural element had no uniform effect on permeability coefficients and selectivities. Positive or negative effects were observed, depending on the linking group in the dianhydride moiety. This was tentatively attributed to the conformational flexibility of the cyclohexyl rings, which can result in different sterical requirements.

Gas permeabilities of polymers with indan groups in the main chain.: 1: Poly(ether ketone)s

Abstract The gas permeabilities for hydrogen, carbon dioxide, oxygen and nitrogen of a series of poly(ether ketone)s containing indan groups were determined. The effects of structural variations on permeability coefficients and selectivities for the gas pairs H 2 /N 2 , CO 2 /N 2 , O 2 /N 2 , H 2 /O 2 , CO 2 /O 2 and H 2 /CO 2 are discussed. Based on the results, it is suggested that gas permeation and hence selectivity in these polymers is controlled by a specific chain segment, which consists of a sequence of flexibly linked phenyl rings. These segments are connected by the bulky and immobile indan groups.

Ultrafiltration and microfiltration membranes in latex purification by diafiltration with suction

Operation conditions of diafiltration with suction in purification of poly(glycidyl) methacrylate latex from sodium tetraborate and emulsifier were studied in a batch process using ultrafiltration blend polysulfone/poly(vinylpyrrolidone) and microfiltration Synpor® membranes. Intensity of permeate suction was controlled by changing the pumping rate at fixed cross-sections of the inlet tubes in both the retentate and permeate lines. An optimum value of flow rate was determined for each membrane type to ensure the best purification efficiency. Operating at this flow rate prevented not only undesirable dilution of the latex with osmotic water but also ensured the highest membrane permeability to solutes without cake formation on the membrane surface. It was shown that 92% degree of latex purification could be obtained by 8-h suction diafiltration with Synpor membrane having the pore entrance sizes close to nanoparticle dimensions. The possibility of complete purification of GMA nanoparticles from impurities using the hybrid membrane process combining dialysis followed by suction diafiltration with microporous membranes, and ultrafiltration with an appropriate membrane is discussed.

Effect of POSS™ functionality on morphology of thin hybrid chitosan films

—Organic-inorganic hybrid films based on chitosan (Chi) and hydrophilic polyhedral oligomeric silsesquioxanes (POSS™) were prepared by alkaline precipitation of the dried blends. The effect of the POSS type and concentration on morphology and permeability of Chi/POSS hybrid films were evaluated by IR spectroscopy, solid phase NMR, SEM and AFM and by diffusion transport of low-molecular-weight electrolytes. In mechanically stable hybrid films, contents of octakis{[3-(2,3- dihydroxypropoxy)propyl]dimethylsilyl}-POSS™ (DL-POSS), octakis(trimethylammonium)-POSS™ (TMA-POSS) and octaammonium-POSS™ (OA-POSS) range between 0.625 and 2.5 mol% (in relation to amount of the deacetylated chitosan amino groups). The large POSS molecules (approx. 2–3 nm) influenced the packing the chitosan chains on a nanoscale due to multiple intermolecular bonds and changed the heterogeneity of hybrid films. The electrolyte (HCl, NaCl and NaOH) transport through the films depended on the POSS type, its content, and the preparation method. With increasing POSS content, the permeabilities tended to increase across the hybrid films with the crosslinker (ethyleneglycol diglycidyl ether, 75 mol%), which was added into a precursor film before its drying and alkaline treatment. In contrast, the electrolyte penetration usually decreased through the films cross-linked after their drying and alkaline precipitation. The dependence of the diffusion permeability of Chi/POSS hybrid films on their morphology is discussed.

Map of gas and vapor permeability in polymer blends

Abstract A novel method for measuring local permeabilities of gas or vapor in polymers was proposed and developed. The method utilizes a thin reactive layer of potassium prepared on one side of the examined polymer film. Molecules of an appropriate gas (oxygen, water vapor) diffusing through the film corrode the reactive layer to various extent at various places, proportionally to the amount of the gas passed. A “permeation map” is created which can be visualized with optical microscopy. Compatibilized polystyrene/polypropylene blend was examined with this method. The permeability map pattern obtained was in accord with the morphology of that system. The lateral resolution attained was approximately 2 μm.

Improved Hydrogen Separation Using Hybrid Membrane Composed of Nanodiamonds and P84 Copolyimide

Membrane gas separation is a prospective technology for hydrogen separation from various refinery and petrochemical process streams. To improve efficiency of gas separation, a novel hybrid membrane consisting of nanodiamonds and P84 copolyimide is developed. The particularities of the hybrid membrane structure, physicochemical, and gas transport properties were studied by comparison with that of pure P84 membrane. The gas permeability of H2, CO2, and CH4 through the hybrid membrane is lower than through the unmodified membrane, whereas ideal selectivity in separation of H2/CO2, H2/CH4, and CO2/CH4 gas pairs is higher for the hybrid membrane. Correlation analysis of diffusion and solubility coefficients confirms the reliability of the gas permeability results. The position of P84/ND membrane is among the most selective membranes on the Robeson diagram for H2/CH4 gas pair.