Ritchie A. Wessling

Oxygen/nitrogen transport in glassy polymers with oxygen-binding pendent groups

Abstract Polymeric membranes exhibit an inverse relation between O2/N2 selectivity and O2 permeability. O2 carriers can be used to cross this selectivity barrier. O2/N2 selectivity was increased by incorporating oxygen-binding cobalt complexes into glassy polymers. The O2 carriers have been incorporated both by blending with the polymer and by attaching to the polymeric backbone as pendent groups. Polymers with O2 carriers as pendent groups showed better O2/N2 selectivities. The improved selectivity results from facilitation of O2 and inhibition of N2 transport. Oxygen selectivity increases with increasing content of the cobalt complex and decreasing O2 partial pressure. The O2 transport in these polymers has been interpreted using the dual-mode model. O2 bound to carrier site diffuses slowly but has very high solubility coefficient. These membranes have a life time problem. O2 selectivity decreases with increasing O2 exposure time. More stable O2 carriers are required to make these membranes commercially viable.

THERMAL AND FLAMMABILITY PROPERTIES OF POLY(P-PHENYLENE-BENZOBISOXAZOLE)

Poly( p-phenylene-benzobisoxazole), PBO, is a member of a family of rigid-rod, lyotropic liquid crystal polymers which can be fabricated into fiber, film and composites. PBO exhibits exceptional ignition resistance, low heat release rate, and very low smoke emission. PBOs fire, smoke, and toxicity (FST) properties are one of the best thermally stable polymers. PBO begins to ther mally decompose at 660 ° C and it has a char yield > 70% at 900 °C. It has LOI of > 56 and UL94 rating of VTM0 for 1 mil thick film. PBO generates almost no smoke, and very little toxic combustion products are generated during fire. PBO is more ignition resistant and has very low heat release (measured by the Cone Calorimeter) compared to other high temperature polymers. Carbon fabric/PBO composites do not ignite even after 15 minutes when exposed to a heat flux of 50 kW/m2. Preliminary results indicate that this carbon fabric/PBO composite meets the Navys most critical fire, smoke, and toxicity requirements for applications inside submarines. PBOs unique combination of thermal, mechanical, and physical properties could provide enabling technology for the next generation of products for interior components of airplanes, ships, off shore structures, and other places where the fire, smoke, toxicity properties of the material and weight are critical.

Water Transport in Ionic Polymers

Hydrophilic polymers such as perfluorinated ionomers with sulfonic acid functional groups have high water permeabilities and good selectivities for water over most gases and organic liquids. Understanding the water transport mechanism in these water plasticized membranes is necessary in order to effectively utilize them for dehydration applications. Water diffusion in these polymers is non-Fickian. Water permeabilities and solubility coefficients are a function of water vapor pressure. A careful analysis is required to arrive at the concentration dependent diffusion coefficients. An approach for calculating thermodynamic diffusion coefficients based on steady state permeabilities and equilibrium sorption measurements is presented in this paper. At very low water vapor pressures, strong ion-water interactions give rise to high solubility coefficients and low diffusion coefficients. At water activities of 0.1 to 0.6, the solubility coefficient decreases and the diffusion coefficient increases with water activity. At very high water activities (≥0.6), the diffusion coefficient appears to attain a limiting value while the solubility coefficient sharply increases. An anomalous thickness effect was also observed. Thickness normalized permeabilities increased with increasing membrane thickness. Several mechanisms were considered.

Cationic Polymer Colloids

Cationic polymer colloids are a diverse group of materials. They have two common features: a particulate morphology in aqueous dispersion and a net positive charge on the dispersed particles. They represent only a small fraction of known polymer colloids (most of which are anionic), and have been of little commercial significance until quite recently (1–6). Accordingly, they have not drawn the attention of many colloid and polymer scientists.