Perfluorodioxolane Polymers for Gas Separation Membrane Applications

Since the discovery of polytetrafluoroethylene (PTFE) in 1938, fluorinated polymers have drawn attention in the chemical and pharmaceutical field, as well as in optical and microelectronics applications. The reasons for this attention are their high thermal and oxidative stability, excellent chemical resistance, superior electrical insulating ability, and optical transmission properties. Despite their unprecedented combination of desirable attributes, PTFE and copolymers of tetrafluoroethylene (TFE) with hexafluoropropylene and perfluoropropylvinylether are crystalline and exhibit poor solubility in solvents, which makes their processability very challenging. Since the 1980s, several classes of solvent-soluble amorphous perfluorinated polymers showing even better optical and gas transport properties were developed and commercialized. Amorphous perfluoropolymers exhibit, however, moderate selectivity in gas and liquid separations. Recently, we have synthesized various new perfluorodioxolane polymers which are amorphous, soluble, chemically and thermally stable, while exhibiting much enhanced selectivity. In this article, we review state-of-the-art and recent progress in these perfluorodioxolane polymers for gas separation membrane applications.

Study of Thermal and Oxidative Stability of Cottonseed Biodiesel

Biodiesel is a renewable fuel with excellent lubricity and biodegradability. However, its use may be compromised by factors that change its characteristics and occur during production, transportation and/or storage. Some of them are associated with biodiesel stability and can affect vehicle performance. The objective of this work was to analyze the main causes of cottonseed oil biodiesel instability due to the storage process, determining some physicochemical properties as kinematic viscosity, acidity index, refractive index, electrical conductivity as well as ester content, mass of precipitate formed and pH. The acidity and kinematic viscosity of biodiesel from cottonseed oil increase with storage time. The latter suggests the occurrence of a partial oxidation of biodiesel with formation of products that increase its viscosity. Gas chromatography results showed that even after thermo-oxidative treatment, biodiesel samples maintained the minimum ester content required by the ANP (Brazilian National Agency of Petroleum, Natural Gas and Biofuels) and unsaturated bonds tends to be preferentially oxidized over other carbon-carbon bonds. There was no significant influence of light exposure (storage in amber and transparent vials) on the ester content, refractive index and mass of precipitate formed. On the other hand, the latter was influenced by the heating time.

The Effect of Dopant Type on The Morphology and Electrical Properties of Hollow Polyester Fabric

Intrinsically conducting polymers (ICPs) have been intensively the subject of research since these polymers have superlative electrical and thermophysical properties. Due to the low hydrogen content and aromatic structure, they show perfect chemical, thermal, and oxidative stability and are practically insoluble in all common solvents. Also these polymers are latently electrical conducting materials, especially when doped. Polypyrole (PPy) is a very promising conducting polymer. It can be in easy way processes and has many interesting electrical properties. Also ıt is chemically and thermally stable. Like many other fully aromatic polymers, PPy is an electrical insulator, however, when oxidized it becomes an electrical conductor.The conductivity of PPy strongly consists in the preparation technique, and on the polymer additives and can be increased by about two orders of magnitude. In this study, electrically conductive hollow fabrics were prepared via ın situ chemical polymerization method and scanning electron microscopy (SEM) and electrical properties of conductive hollow fabrics were invesigated.